{"id":69,"slug":"69-sermorelin-ala-2-aib-aminoisobutyric-acid-single-substitution-at-positi","title":"Sermorelin Ala-2 → α-aminoisobutyric acid (Aib) for DPP-IV resistance","status":"DISCARDED","fold_verdict":"DISCARDED","discard_reason":null,"peptide":{"name":"Sermorelin","class":"PERFORMANCE","sequence":"YADAIFTNSYRKVLGQLSARKLLQDIMSR","modified_sequence":"Y-Aib-DAIFTNSYRKVLGQLSARKLLQDIMSR","modification_description":"Ala-2 → Aib (α-aminoisobutyric acid) single substitution at position 2"},"target":{"protein":"Growth hormone-releasing hormone receptor","uniprot_id":"Q02643","chembl_id":"CHEMBL2049","gene_symbol":"GHRHR"},"rationale":{"hypothesis":"We hypothesize that replacing Ala-2 with α-aminoisobutyric acid (Aib) in Sermorelin will block dipeptidyl peptidase-IV (DPP-IV) cleavage of the Tyr1-Ala2 bond, dramatically extending plasma half-life while preserving GHRHR binding. Aib is the canonical DPP-IV-resistant Ala mimetic used successfully in semaglutide and tirzepatide at the analogous position-2 site, and unlike D-Ala (Fold #2 DISCARDED) it retains L-stereochemistry at the backbone interaction face seen by the receptor.","rationale":"DPP-IV cleaves N-terminal X-Ala/Pro dipeptides; Aib's gem-dimethyl Cα prevents cleavage by sterically blocking the catalytic pocket while subtly biasing backbone φ/ψ toward helical geometry, which is the bioactive conformation of GHRH at the GHRHR ECD. Class B GPCR modeling can be unreliable for backbone-staple/non-canonical chemistries on the helical core, but a single Aib at position 2 is on the flexible N-cap (not the staple-prone central helix), making it the safest non-canonical substitution to adjudicate by Boltz-2/Chai-1. This diverges from the last 3 folds (CONFORMATION/disulfide on Humanin, SELECTIVITY/D-aa on TB-500, SELECTIVITY/non-canonical on SS-31) by rotating focus to STABILITY on a different peptide and category.","predicted_outcome":"Boltz-2/Chai-1 should predict an N-terminal segment that retains the canonical extended-to-helical transition seen in GHRH–GHRHR complexes, with Aib-2 occupying the same backbone position as native Ala-2 and the receptor ECD interface preserved (pLDDT > 0.65 at the binding interface).","mechanism_class":null,"biohacker_use":null},"confidence":{"plddt":0.4848611354827881,"ptm":0.46194857358932495,"iptm":0.42002689838409424,"chai_agreement":null,"chai1_gated_decision":"SKIPPED_LOW_CONFIDENCE","binding_probability":null,"binding_pic50":null,"predicted_binding_change":null},"profile":{"aggregation_propensity":0.164,"stability_score":0.319,"bbb_penetration_score":0.05,"half_life_estimate":"moderate-to-long (~1–6 hours)"},"narrative":{"tldr":"Fold №69 tested whether replacing Ala-2 of Sermorelin with α-aminoisobutyric acid (Aib) — the canonical DPP-IV-resistant Ala mimetic used in semaglutide and tirzepatide — could extend plasma half-life while preserving GHRHR binding. The structural prediction returned a pLDDT of 0.48 and ipTM of 0.42, confidence levels too low to adjudicate whether the N-terminal Aib-2 occupies the same binding geometry as native Ala-2. This fold is DISCARDED as a tool-limit failure, not a biological invalidation: the hypothesis remains chemically sound and literature-supported. It joins a consistent pattern of sub-threshold confidence across all seven prior Sermorelin and Tesamorelin folds in this lab.","detailed_analysis":"Sermorelin (YADAIFTNSYRKVLGQLSARKLLQDIMSR) is the shortest GHRH fragment retaining full biological activity at the GHRHR, but its clinical utility is curtailed by a plasma half-life of under 15 minutes. The primary enzymatic culprit is DPP-IV, which cleaves the Tyr1–Ala2 bond to yield the inactive [3-29] fragment — a metabolite confirmed in anti-doping analytical literature and detected in biological matrices under serum protease challenge. This vulnerability is well-established, and the clinical field has already validated N-terminal engineering as the solution: Tesamorelin's trans-3-hexenoic acid N-cap and CJC-1295's DAC conjugation both extend GHRH-class half-life while preserving GHRHR agonism, confirming the receptor's tolerance for position-1/2 modification.\n\nThe Aib substitution strategy proposed here is among the most chemically conservative tools available for solving the DPP-IV problem. α-Aminoisobutyric acid (α-methyl alanine) is an achiral, α,α-disubstituted residue whose gem-dimethyl Cα sterically occludes the DPP-IV catalytic pocket while retaining a pseudo-L backbone orientation. Unlike the D-Ala substitution explored in Fold #2 — which inverts backbone stereochemistry and risks disrupting the receptor interaction geometry — Aib preserves the L-configured backbone face seen by the GHRHR extracellular domain. Furthermore, Aib is a potent helix-inducing residue, meaning it could subtly bias the N-terminal cap toward the α-helical geometry that dominates GHRHR engagement across the mid-peptide and C-terminal segments. The theoretical case for [Aib2]-Sermorelin is therefore stronger than for [D-Ala2]-Sermorelin, making it unfortunate that both folds collide with the same tool-limit ceiling.\n\nThe structural prediction was run on the modified sequence Y-Aib-DAIFTNSYRKVLGQLSARKLLQDIMSR against the GHRHR extracellular domain (UniProt Q02643). The returned pLDDT of 0.48 and ipTM of 0.42 are essentially identical to the values seen across every prior Sermorelin and Tesamorelin fold in this lab: Fold #53 (hexenoyl N-cap, pLDDT 0.49), Fold #42 (lactam staple, pLDDT 0.50), Fold #2 (D-Ala2, pLDDT 0.49), and Fold #60 (Tesamorelin truncation, pLDDT 0.48). The emergence of a consistent ~0.48–0.50 pLDDT floor across structurally diverse modifications on this target is itself informative: it suggests the GHRHR ECD is a genuinely difficult system for current AlphaFold-class predictors, likely because Class B GPCR extracellular domains sample large conformational ensembles and lack sufficient co-complex training data to produce high-confidence complex structures.\n\nThe heuristic peptide profile is unremarkable and consistent with a Sermorelin scaffold: aggregation propensity of 0.164 (low), stability score of 0.319, and a moderate-to-long heuristic half-life estimate (1–6 hours, though this is a sequence-based heuristic and does not model enzymatic cleavage). Notably, the heuristic half-life estimate reflects the Aib2 modification's expected DPP-IV resistance, but cannot be taken as a predicted in vivo half-life — real-world PK would also reflect renal filtration (Sermorelin is ~3,357 Da, near the glomerular filtration threshold) and other protease exposures not captured by these estimates.\n\nThe absence of Chai-1 agreement data and Boltz-2 affinity values means no orthogonal signal is available to rescue the verdict. With a single-run pLDDT below 0.55 and ipTM below 0.50, the model cannot reliably distinguish whether Aib-2 occupies the same backbone position as native Ala-2 or whether the N-terminal cap has shifted off the receptor interface entirely. The single-residue Ala→Aib substitution is too subtle a chemical perturbation to emerge from background noise at this confidence level.\n\nThis result does not disprove the hypothesis. The DPP-IV resistance rationale for Aib at position 2 is validated in incretin pharmacology at the level of marketed drugs (semaglutide, tirzepatide) and is mechanistically sound for the GHRH scaffold. The absence of a GHRHR co-crystal structure with any Aib-containing peptide is a gap in the field, not evidence that such binding cannot occur. The question this fold asked — does Aib-2 preserve GHRHR binding geometry? — simply cannot be answered by current in silico tools at this confidence level.\n\nLooking across the full Sermorelin/Tesamorelin campaign in this lab (Folds #2, #42, #50, #53, #60, #69), a clear pattern emerges: no modification to the Sermorelin/Tesamorelin scaffold has achieved an adjudicable structural prediction against the GHRHR ECD. The consistent sub-threshold confidence suggests the limiting factor is the target representation, not the peptide modifications themselves. Future work on this scaffold should prioritize wet-lab approaches — binding assays, DPP-IV stability assays, and ideally cryo-EM or X-ray crystallography of the [Aib2]-Sermorelin/GHRHR complex — over further in silico permutations against this receptor until a better-resolved training structure becomes available.","executive_summary":"Aib-2 Sermorelin: pLDDT 0.48, ipTM 0.42 — tool-limit discard, not biological disproof. GHRHR resists confident prediction across all six lab folds. DPP-IV resistance hypothesis remains chemically sound; wet-lab validation required.","tweet_draft":"DISTILLATION №69 — discarded.\nSermorelin [Aib2]: canonical DPP-IV-resistant substitution (see semaglutide, tirzepatide).\npLDDT 0.48 | ipTM 0.42 — tool-limit failure, not biological disproof.\n6th GHRHR fold, same confidence floor. The question is still open.\nalembic.bio","research_brief_markdown":"# FOLD №69 — Sermorelin [Aib2]: DPP-IV Resistance via α-Aminoisobutyric Acid\n**Verdict: DISCARDED** | Class: PERFORMANCE | Target: GHRHR (Q02643)\n\n---\n\n## TLDR\n\nFold №69 is **DISCARDED** due to a **tool-limit failure**: the structural predictor could not achieve sufficient confidence (pLDDT 0.48, ipTM 0.42) to adjudicate whether replacing Ala-2 of Sermorelin with α-aminoisobutyric acid (Aib) preserves GHRHR binding geometry. This is not a biological invalidation — the DPP-IV resistance hypothesis for [Aib2]-Sermorelin is chemically sound and extrapolated from validated incretin pharmacology. The GHRHR extracellular domain has consistently resisted confident structural prediction across all seven Sermorelin/Tesamorelin folds in this lab, suggesting the bottleneck is the **target representation in current predictors**, not the peptide modifications themselves.\n\n---\n\n## What We Tried\n\nWe hypothesized that substituting the native Ala at position 2 of Sermorelin with α-aminoisobutyric acid (Aib, α-methyl alanine) would block DPP-IV cleavage at the Tyr1–Ala2 bond — the confirmed primary degradation pathway — without disrupting GHRHR binding or activation. The modified sequence, Y-**Aib**-DAIFTNSYRKVLGQLSARKLLQDIMSR, was selected because Aib is the canonical DPP-IV-resistant Ala mimetic at position 2, validated in semaglutide and tirzepatide at the analogous GLP-1 scaffold position.\n\nThe mechanistic case for Aib over the previously tested D-Ala (Fold #2, also DISCARDED) is that Aib's gem-dimethyl Cα provides steric occlusion of DPP-IV's catalytic pocket while maintaining a pseudo-L backbone orientation — retaining the receptor interaction geometry that D-Ala inversion risks disrupting. Aib is also a strong helix-inducing residue, raising the possibility that position-2 substitution could subtly enhance the helical pre-organization of the N-terminal cap, which is the activation domain for GHRHR. This fold was designed as the most conservative, chemically defensible test of DPP-IV resistance on this scaffold.\n\n---\n\n## Why It Was Discarded\n\nThe structural prediction returned:\n- **pLDDT: 0.48** — below the 0.55 threshold required for meaningful interface analysis\n- **ipTM: 0.42** — indicating the model could not confidently resolve the peptide–receptor interface\n- **Chai-1 agreement: not available**\n- **Boltz-2 affinity: not available**\n\nAt this confidence level, the model cannot distinguish whether Aib-2 occupies the same backbone position as native Ala-2 or whether the N-terminal segment has adopted an off-target conformation. The single-residue Ala→Aib substitution — a subtle change adding only two methyl groups at Cα — is chemically too small to emerge from prediction noise when the baseline complex confidence is already sub-threshold.\n\nThis result is consistent with a now well-established pattern across the entire Sermorelin/Tesamorelin campaign in this lab:\n\n| Fold | Modification | pLDDT | Verdict |\n|------|-------------|-------|--------|\n| #2 | Ala-2 → D-Ala | 0.49 | DISCARDED |\n| #42 | Lys21–Asp25 lactam staple | 0.50 | DISCARDED |\n| #50 | Val13/Leu17 hydrocarbon staple (Tesamorelin) | 0.46 | DISCARDED |\n| #53 | trans-3-Hexenoyl N-cap + C-terminal amidation | 0.49 | DISCARDED |\n| #60 | Tesamorelin C-terminal truncation to GHRH(1-29) | 0.48 | DISCARDED |\n| **#69** | **Ala-2 → Aib** | **0.48** | **DISCARDED** |\n\nThe consistency of the ~0.48–0.50 pLDDT floor across structurally diverse modifications — N-terminal caps, staples, stereochemical inversions, truncations, and now Aib substitution — points to a **target-level limitation**: the GHRHR extracellular domain is poorly represented in current AlphaFold-class training data for co-complex prediction, likely reflecting the inherent conformational dynamics of Class B GPCR extracellular domains and the scarcity of high-resolution GHRHR co-crystal structures in the PDB.\n\n---\n\n## What This Doesn't Mean\n\n**DISCARDED is not \"disproved.\"** The DPP-IV resistance hypothesis for [Aib2]-Sermorelin rests on well-established incretin pharmacology: Aib at position 2 is validated across semaglutide, tirzepatide, and related GLP-1-class drugs as the canonical solution to DPP-IV susceptibility. The GHRHR's demonstrated tolerance for N-terminal modification — evidenced by the clinical activity of Tesamorelin (trans-3-hexenoic acid at Tyr1) and CJC-1295 (DAC conjugation) — further supports the plausibility that [Aib2]-Sermorelin could retain agonist activity. The gap in the literature is the absence of any direct SAR study testing Aib at position 2 of any GHRH scaffold, meaning this question is genuinely unanswered rather than answered negatively. Current in silico tools simply lack the resolution to adjudicate a single-residue backbone methylation against a dynamically challenging Class B GPCR extracellular domain. The biological hypothesis remains open.\n\n---\n\n## What Would Answer the Question\n\n- **DPP-IV stability assay (in vitro):** Incubate [Aib2]-Sermorelin and native Sermorelin with purified DPP-IV or pooled human plasma; HPLC/LC-MS quantification of intact peptide vs. [3-29] cleavage product over 0–120 min. This is the most direct, rapid, and low-cost experiment to confirm the primary hypothesis and has precedent in GHRH anti-doping analytical literature (PMID:37688464).\n- **GHRHR binding and cAMP functional assay:** Radioligand displacement or TR-FRET binding assay at GHRHR-expressing cells (e.g., HEK293 overexpression), followed by GH secretion assay in pituitary cell culture (rat primary or GH3 cells) to confirm preserved agonist potency and Emax. Standard pharmacological characterization for GHRH analogues.\n- **Surface plasmon resonance (SPR) or ITC against GHRHR ECD:** Biophysical binding affinity measurement against recombinant GHRHR extracellular domain to directly confirm whether Aib-2 preserves the binding pose — the precise question the structural predictor could not answer.\n- **Cryo-EM or X-ray crystallography of [Aib2]-Sermorelin/GHRHR complex:** Definitive structural answer; would also resolve the broader tool-limit failure seen across all six Sermorelin/Tesamorelin folds and provide a high-quality template for future in silico work on this target. Technically demanding but transformative for the field given the absence of any GHRHR co-crystal structure with a modified GHRH analogue.\n- **Molecular dynamics (MD) simulation with explicit Aib parameters:** Classical MD or free-energy perturbation (FEP) with properly parameterized Aib force-field terms could provide binding free energy estimates not available from AlphaFold-class predictors, which handle non-canonical residue chemistry poorly.\n\n---\n\n## Raw Metrics\n\n| Metric | Value |\n|--------|-------|\n| pLDDT | 0.485 |\n| pTM | 0.462 |\n| ipTM | 0.420 |\n| Chai-1 agreement | Not available |\n| Boltz-2 affinity | Not available |\n| Predicted binding change | Not determinable |\n| Aggregation propensity (heuristic) | 0.164 (low) |\n| Stability score (heuristic) | 0.319 |\n| BBB penetration (heuristic) | 0.05 (negligible) |\n| Half-life estimate (heuristic) | Moderate-to-long (1–6 h) |\n\n*Heuristic peptide profile values are sequence-based estimates only — not wet-lab measurements and not validated for non-canonical residues.*\n\n---\n\n*This distillation is an in silico prediction only. It is not medical advice, not a validated discovery, and not a recommendation for synthesis or administration. All predicted properties require experimental validation.*","structural_caption":"The predicted Aib2-sermorelin / GHRHR-ECD complex shows low overall pLDDT (~0.48) and a weak interface score (ipTM 0.42), indicating the model could not confidently place the N-terminal segment of the peptide on the receptor. While the heuristic peptide profile (aggregation 0.164, moderate stability) is unremarkable and consistent with a sermorelin-like scaffold, the structural model itself does not resolve whether Aib-2 preserves the canonical extended-to-helical N-terminal transition characteristic of GHRH–GHRHR engagement. No predicted affinity is available to rescue the verdict. The single-residue Ala→Aib substitution is too subtle to be distinguished from baseline noise at this confidence level.","key_findings_summary":"Sermorelin is a 29-amino acid synthetic analogue of human GHRH (hGHRH 1-29-NH2) representing the shortest fragment retaining full biological activity at the GHRHR. It is well-established as a diagnostic and therapeutic agent for growth hormone deficiency, acting specifically on the anterior pituitary to stimulate endogenous GH secretion (PMID:18031173). Its short plasma half-life — a principal limitation in clinical use — is attributable in large part to rapid N-terminal cleavage by dipeptidyl peptidase-IV (DPP-IV), which cleaves between Tyr1 and Ala2, as well as by other serum proteases. The anti-doping and analytical literature confirms that sermorelin degrades rapidly in biological matrices, producing characteristic N-terminal fragments; a 2023 study (PMID:37688464) directly characterized enzymatic and serum stability of GHRH-related peptides including sermorelin fragments (1-11, 13-20, 22-29), confirming distinct degradation profiles under protease exposure and human blood treatment, consistent with known DPP-IV susceptibility at the Tyr1-Ala2 bond.\n\nThe broader peptide drug field provides strong precedent for the Ala-2 → Aib substitution strategy. α-Aminoisobutyric acid (Aib, α-methyl alanine) is a conformationally constrained, achiral, α,α-disubstituted amino acid that is well-documented to confer resistance to DPP-IV cleavage at position 2 of incretin-class peptides. Its successful deployment at the analogous position in GLP-1 receptor agonists (semaglutide, tirzepatide) and the GHRH analogue tesamorelin — which uses a trans-3-hexenoic acid conjugation and has a modified N-terminus — demonstrates that N-terminal engineering of GHRH-class peptides is both feasible and clinically validated. Tesamorelin (CJC-1295 uses a different DAC linker strategy), reviewed across multiple papers in this set (PMID:41490200, preprints), achieves markedly extended half-life compared to sermorelin through structural modifications, though the precise contribution of position-2 protection versus other modifications varies by analogue.\n\nWith respect to GHRHR binding, the structural literature on GHRH analogues indicates that the N-terminal region (residues 1-5) is critical for receptor activation rather than primary binding affinity per se, with the mid-region and C-terminal helix dominating receptor contact. Aib, being an L-configured backbone mimic that enforces helical conformation (it is a well-known helix-inducing residue), is expected to preserve and potentially enhance the α-helical secondary structure that the receptor's binding cleft recognizes. Unlike D-Ala substitution, which inverts the backbone stereochemistry at position 2 and risks disrupting the interaction geometry with the GHRHR extracellular domain, Aib retains a pseudo-L backbone orientation while adding the gem-dimethyl steric shield that prevents DPP-IV accommodating the substrate. This mechanistic rationale is chemically sound but is not directly tested in the sermorelin literature retrieved here.\n\nThe clinical and gray-market literature (PMID:32257855, preprints 2025/2026) confirms that sermorelin's short half-life is a practical limitation driving use of longer-acting GHRH analogues (tesamorelin, CJC-1295) and combination secretagogue regimens. The regulatory and quality-control literature (DOI:10.20944/preprints202604.1748.v1) notes that sermorelin is among the most widely used gray-market peptides, with significant purity variability, underscoring demand for improved pharmaceutical-grade, longer-acting formulations. Notably, the oncology and inflammatory biology literature in this set (PMID:40244089, PMID:31392398, PMID:32123064, PMID:39456984, PMID:37983492) focuses exclusively on GHRHR antagonists (MIA-602, MIA-690) in disease contexts and does not directly inform the agonist binding pharmacology relevant to sermorelin modifications."},"structured":{"known_activity":null,"known_binders":null,"candidate_variants":null,"domain_annotations":null,"literature_context":{"pubmed":[{"pmid":"18046908","title":"Sermorelin: a better approach to management of adult-onset growth hormone insufficiency?","abstract":"","authors":["Walker Richard F"],"year":2006,"journal":"Clinical interventions in aging"},{"pmid":"41490200","title":"Therapeutic Peptides in Orthopaedics: Applications, Challenges, and Future Directions.","abstract":"Therapeutic peptides are emerging as promising adjuncts in the management of orthopaedic injuries, grounded in their ability to modulate molecular signaling networks central to cellular medicine. By acting on key pathways such as PI3K/Akt, mTOR, MAPK, TGF-β, and AMPK, peptides exert influence over tissue regeneration, inflammation resolution, and neuromuscular recovery. Wound-healing peptides such as BPC-157, TB-500, and GHK-Cu promote angiogenesis, integrin-mediated extracellular matrix remodeling, and fibroblast activation, whereas growth hormone secretagogues like ipamorelin, CJC-1295, tesamorelin, sermorelin, and AOD-9604 activate IGF-1 signaling and satellite cell repair. Recovery-enhancing agents such as epithalon, delta sleep-inducing peptide, and pinealon target circadian and mitochondrial regulators, and neuroactive peptides like selank, semax, and dihexa enhance brain-derived neurotrophic factor and HGF/c-Met pathways critical to neuroplasticity. Although preclinical studies are promising, there is a current lack of clinical trials. This review integrates current mechanistic insights with orthopaedic relevance, emphasizing safety, efficacy, and future directions for responsible integration into musculoskeletal care.","authors":["Rahman Omar F","Lee Steven J","Seeds William A"],"year":2026,"journal":"Journal of the American Academy of Orthopaedic Surgeons. Global research & reviews"},{"pmid":"33842627","title":"A potentially effective drug for patients with recurrent glioma: sermorelin.","abstract":"BACKGROUND: Treatment insensitivity is the main cause of glioma. This study was designed to screen out effective drugs for recurrent gliomas based on the transcriptomics data.\n\nMETHODS: A total of 1,018 glioma patients with transcriptome sequencing data and clinical data were included in this study. There were 325 patients in the discovery cohort, including 229 primary patients and 92 recurrent patients. There were 693 patients in the validation cohort, including 422 primary patients and 271 relapsed patients. Drug Resistant Scores (DRS) of 4,865 drugs of each patient were used for screening. The analysis and drawing in this study were mainly based on R language.\n\nRESULTS: After high-throughput drug screening, we found that recurrent glioma patients were most sensitive to sermorelin. Further analysis revealed that sermorelin was suitable for recurrent patients with high grade, IDH-wildtype and 1p/19q non-codeletion status. GO and KEGG analyses found that sermorelin may inhibit tumor cell proliferation by cell cycle blocking. Moreover, sermorelin was also related to the immune system process and negatively regulated immune checkpoints and M0 macrophages. Lastly, the Kaplan-Meier method showed the patient's benefit from sermorelin was independent of postoperative adjuvant treatment.\n\nCONCLUSIONS: Recurrent glioma patients are sensitive to sermorelin and it makes effect through glioma cells proliferation inhibiting and immune response enhancing.","authors":["Chang Yuanhao","Huang Ruoyu","Zhai You","Huang Lijie","Feng Yuemei","Wang Di","Chai Ruichao","Zhang Wei","Hu Huimin"],"year":2021,"journal":"Annals of translational medicine"},{"pmid":"18031173","title":"Sermorelin: a review of its use in the diagnosis and treatment of children with idiopathic growth hormone deficiency.","abstract":"UNLABELLED: Sermorelin, a 29 amino acid analogue of human growth hormone-releasing hormone (GHRH), is the shortest synthetic peptide with full biological activity of GHRH. Intravenous and subcutaneous sermorelin specifically stimulate growth hormone secretion from the anterior pituitary. Hormone responses to intravenous sermorelin 1 microg/kg bodyweight appear to be a rapid and relatively specific test for the diagnosis of growth hormone deficiency. False positive growth hormone responses are observed in fewer children without growth hormone deficiency after sermorelin than after other provocative tests. Adult data indicate that the combination of intravenous sermorelin and arginine is a more specific test and this merits evaluation in children with growth hormone deficiency. However, normal growth hormone responses to intravenous sermorelin cannot exclude growth hormone deficiency due to a hypothalamic deficit: subnormal growth hormone response to other provocative tests is needed to confirm the presence of disease in these patients. Limited data indicate that once daily subcutaneous sermorelin 30 microg/kg bodyweight given at bedtime is effective in treating some prepubertal children with idiopathic growth hormone deficiency. Significant increases in height velocity were sustained during 12 months' treatment with sermorelin and data in a few children suggest the effect is maintained for 36 months of continued treatment. Sermorelin induced catch-up growth in the majority of growth hormone-deficient children. Slow growing, shorter children with delayed bone and height age appear to have a good response to treatment with sermorelin. The effect of long term treatment with once daily subcutaneous sermorelin 30 microg/kg bodyweight on final adult height is yet to be determined. The effects of the recommended dosage of sermorelin have not been directly compared with those of somatropin. However, increases in height velocity from baseline values with subcutaneous sermorelin 30 microg/kg bodyweight per day, given as continuous infusion or as 3 divided doses, were less than those in children receiving once daily subcutaneous somatropin 30 microg/kg bodyweight. Intravenous single dose and repeated once daily subcutaneous doses of sermorelin are well tolerated. Transient facial flushing and pain at injection site were the most commonly reported adverse events.\n\nCONCLUSIONS: Sermorelin is a well tolerated analogue of GHRH which is suitable for use as a provocative test of growth hormone deficiency when given as a single intravenous 1 microg/kg bodyweight dose in conjunction with conventional tests. Limited data suggest that once daily subcutaneous sermorelin 30 microg/kg bodyweight is effective in promoting growth in some prepubertal children with idiopathic growth hormone deficiency.","authors":["Prakash A","Goa K L"],"year":1999,"journal":"BioDrugs : clinical immunotherapeutics, biopharmaceuticals and gene therapy"},{"pmid":"37688464","title":"In-house standards derived from doping peptides: Enzymatic and serum stability and degradation profile of GHRP and GHRH-related peptides.","abstract":"Matrix effect and sample pretreatment significantly affect the percentage recovery of peptides in biological matrices, affecting the method robustness and accuracy. To counteract this effect, an internal standard (IS) is used; however, in most cases this is not available, which limits the analytical method. It is important to identify short peptides that can be used as ISs in the quantification of peptides in biological matrices. In this study, doping peptides GHRP-4, GHRP-5, GHRP-6, Sermorelin (1-11), Sermorelin (13-20) and Sermorelin (22-29) were synthesized using solid-phase peptide synthesis. Treatment with human blood, trypsin and chymotrypsin was used to determine the stability of the peptides. Products were evaluated using the high-performance liquid chromatography-diode array detector (HPLC-DAD) method. The analytical methodology and sample pretreatment were effective for the analysis of these molecules. A unique profile related to protein binding and enzymatic stability of each peptide was established. GHRP-4, GHRP-6 and Sermorelin (22-29) can be considered as in-house ISs as they were stable to enzyme and blood treatment and can be used for the quantification of peptides in biological samples. Peptides GHRP-6 and Sermorelin (22-29) were used to analyse a dimeric peptide (26 [F] LfcinB (20-30)2 ) in four different matrices to test these peptides as in-house IS.","authors":["González-López Nicolás Mateo","Guerra-Acero-Turizo Luisa María","Blanco-Medina Isabella","Barragán-Cárdenas Andrea Carolina","Ramírez-Celis David Augusto","Martínez-Ramírez Jorge Ariel","Fierro-Medina Ricardo","García-Castañeda Javier Eduardo","Rivera-Monroy Zuly Jenny"],"year":2023,"journal":"Biomedical chromatography : BMC"},{"pmid":"32257855","title":"Beyond the androgen receptor: the role of growth hormone secretagogues in the modern management of body composition in hypogonadal males.","abstract":"Male hypogonadism is an increasingly prevalent clinical condition that affects patients' quality of life and overall health. Obesity and metabolic syndrome can both cause and result from hypogonadism. Although testosterone remains the gold standard for hypogonadism management, its benefits are not always conserved across different populations, especially with regards to changes in body composition. Partially in response to this, growth hormone secretagogues (GHS) have emerged as a potential novel adjunctive therapy for some of the symptoms of hypogonadism, although current data on their clinical efficacy largely remain lacking. The present review examines the existing literature on the use of GHS and explores their potential complementary role in the management of hypogonadal and eugonadal males with metabolic syndrome or subclinical hypogonadism (SH). The GHS that will be discussed include sermorelin, growth hormone-releasing peptides (GHRP)-2, GHRP-6, ibutamoren, and ipamorelin. All are potent GH and IGF-1 stimulators that can significantly improve body composition while ameliorating specific hypogonadal symptoms including fat gain and muscular atrophy. However, a paucity of data examining the clinical effects of these compounds currently limits our understanding of GHS' role in the treatment of men with hypogonadism, but does open opportunities for future investigation.","authors":["Sinha Deepankar K","Balasubramanian Adithya","Tatem Alexander J","Rivera-Mirabal Jorge","Yu Justin","Kovac Jason","Pastuszak Alexander W","Lipshultz Larry I"],"year":2020,"journal":"Translational andrology and urology"},{"pmid":"37806509","title":"Cationic exchange SPE combined with triple quadrupole UHPLC-MS/MS for detection of GHRHs in urine samples.","abstract":"The use of growth hormone-releasing hormones (GHRHs) is prohibited in sports according to the regulations of the World Anti-Doping Agency (WADA). Considering the complexity of urine samples and the low concentrations at which these analytes should be detected, analyzing GHRHs is a challenging task. In most of the studies, GHRHs are analyzed using UHPLC-HRMS with an orbitrap. The present developed and validated method for some GHRHs (tesamorelin, CJC-1295, sermorelin (GRF 1-29), sermorelin (3-29)-NH2, somatorelin) is based on the triple quadrupole UHPLC/MS-MS method with solid phase extraction (SPE) with weak cation exchange and is able to detect concentrations as low as 0.2 ng/mL (LOD), a limit of quantification (LOQ) at 0.6 ng/mL, and linearity across the range of 0.1 ng/mL to 1.2 ng/mL. The present method developed by our doping control laboratory was validated according to WADA technical documents for selectivity, limit of detection (LOD), carryover, reliability of detection, stability and recovery. The results show that the method has adequate recoveries and sensitivity, hence, it can be employed for routine screening in anti-doping laboratories.","authors":["Cristea Cătălina-Diana","Radu Mihai","Toboc Ani","Stan Cristina","David Victor"],"year":2023,"journal":"Analytical biochemistry"},{"pmid":"40244089","title":"Growth Hormone-Releasing Hormone Antagonists Increase Radiosensitivity in Non-Small Cell Lung Cancer Cells.","abstract":"Growth hormone-releasing hormone (GHRH) antagonists exert antitumor functions in different experimental cancers. However, their role in combination with radiotherapy in non-small cell lung cancer (NSCLC) remains unknown. Therefore, we investigated the radiosensitizing effect of GHRH antagonists in NSCLC. A549 and H522 NSCLC cell lines were exposed to ionizing radiation (IR) and GHRH antagonists MIA-602 and MIA-690, either individually or in combination. Cell viability and proliferation were evaluated by MTT, BrdU, flow cytofluorimetry, and clonogenic assays; gene and protein expression, signaling pathways, and apoptosis were analyzed by real-time PCR, Western blot, annexin staining, and caspase-3 assay. GHRH antagonists showed antitumor effects alone and potentiated IR-induced inhibition of cell viability and proliferation. The combination of MIA-690 and IR decreased the expression of GHRH receptor, its oncogenic splice variant 1, and IGF1 mRNA levels. Additionally, cell cycle inhibitors and proapoptotic markers were upregulated, whereas cyclins, oncogenic MYC, and the antiapoptotic protein Bcl-2 were downregulated. Radioresistance was prevented by MIA-690, which also blunted epithelial-mesenchymal transition by enhancing E-cadherin and reducing mesenchymal, oxidative, and proangiogenic effectors. Finally, both MIA-602 and MIA-690 enhanced radiosensitivity in primary human NSCLC cells. These findings highlight the potential of GHRH antagonists as radiosensitizers in NSCLC treatment.","authors":["Gesmundo Iacopo","Pedrolli Francesca","Giglioli Francesca Romana","Jazaj Florian","Granato Giuseppina","Bertoldo Alessia","Bistolfi Federica","Gregorc Vanesa","Sapino Anna","Righi Luisella","Cai Renzhi","Sha Wei","Wangpaichitr Medhi","Papotti Mauro","Ghigo Ezio","Ricardi Umberto","Schally Andrew V","Granata Riccarda"],"year":2025,"journal":"International journal of molecular sciences"},{"pmid":"31392398","title":"Growth Hormone-Releasing Hormone Receptor Antagonist Modulates Lung Inflammation and Fibrosis due to Bleomycin.","abstract":"PURPOSE: Growth hormone-releasing hormone (GHRH) is a 44-amino acid peptide that regulates growth hormone (GH) secretion. We hypothesized that a GHRH receptor (GHRH-R) antagonist, MIA-602, would inhibit bleomycin-induced lung inflammation and/or fibrosis in C57Bl/6J mice.\n\nMETHODS: We tested whether MIA-602 (5 μg or vehicle given subcutaneously [SC] on days 1-21) would decrease lung inflammation (at day 14) and/or fibrosis (at day 28) in mice treated with intraperitoneal (IP) bleomycin (0.8 units on days 1, 3, 7, 10, 14, and 21). Bleomycin resulted in inflammation and fibrosis around airways and vessels evident histologically at days 14 and 28.\n\nRESULTS: Inflammation (histopathologic scores assessed blindly) was visibly less evident in mice treated with MIA-602 for 14 days. After 28 days, lung hydroxyproline (HP) content increased significantly in mice treated with vehicle; in contrast, lung HP did not increase significantly compared to naïve controls in mice treated with GHRH-R antagonist. GHRH-R antagonist increased basal and maximal oxygen consumption of cultured lung fibroblasts. Multiple genes related to chemotaxis, IL-1, chemokines, regulation of inflammation, and extracellular signal-regulated kinases (ERK) were upregulated in lungs of mice treated with bleomycin and MIA-602. MIA-602 also prominently suppressed multiple genes related to the cellular immune response including those for T-cell differentiation, receptor signaling, activation, and cytokine production.\n\nCONCLUSIONS: MIA-602 reduced lung inflammation and fibrosis due to bleomycin. Multiple genes related to immune response and T-cell functions were downregulated, supporting the view that MIA-602 can modulate the cellular immune response to bleomycin lung injury.","authors":["Zhang Chongxu","Cai Renzhi","Lazerson Aaron","Delcroix Gaetan","Wangpaichitr Medhi","Mirsaeidi Mehdi","Griswold Anthony J","Schally Andrew V","Jackson Robert M"],"year":2019,"journal":"Lung"},{"pmid":"32123064","title":"Signaling mechanisms of growth hormone-releasing hormone receptor in LPS-induced acute ocular inflammation.","abstract":"Ocular inflammation is a major cause of visual impairment attributed to dysregulation of the immune system. Previously, we have shown that the receptor for growth-hormone-releasing hormone (GHRH-R) affects multiple inflammatory processes. To clarify the pathological roles of GHRH-R in acute ocular inflammation, we investigated the inflammatory cascades mediated by this receptor. In human ciliary epithelial cells, the NF-κB subunit p65 was phosphorylated in response to stimulation with lipopolysaccharide (LPS), resulting in transcriptional up-regulation of GHRH-R. Bioinformatics analysis and coimmunoprecipitation showed that GHRH-R had a direct interaction with JAK2. JAK2, but not JAK1, JAK3, and TYK2, was elevated in ciliary body and iris after treatment with LPS in a rat model of endotoxin-induced uveitis. This elevation augmented the phosphorylation of STAT3 and production of proinflammatory factors, including IL-6, IL-17A, COX2, and iNOS. In explants of iris and ciliary body, the GHRH-R antagonist, MIA-602, suppressed phosphorylation of STAT3 and attenuated expression of downstream proinflammatory factors after LPS treatment. A similar suppression of STAT3 phosphorylation was observed in human ciliary epithelial cells. In vivo studies showed that blocking of the GHRH-R/JAK2/STAT3 axis with the JAK inhibitor Ruxolitinib alleviated partially the LPS-induced acute ocular inflammation by reducing inflammatory cells and protein leakage in the aqueous humor and by repressing expression of STAT3 target genes in rat ciliary body and iris and in human ciliary epithelial cells. Our findings indicate a functional role of the GHRH-R/JAK2/STAT3-signaling axis in acute anterior uveitis and suggest a therapeutic strategy based on treatment with antagonists targeting this signaling pathway.","authors":["Liang Wei Cheng","Ren Jia Lin","Yu Qiu Xiao","Li Jian","Ng Tsz Kin","Chu Wai Kit","Qin Yong Jie","Chu Kai On","Schally Andrew V","Pang Chi Pui","Chan Sun On"],"year":2020,"journal":"Proceedings of the National Academy of Sciences of the United States of America"},{"pmid":"39456984","title":"Antagonist of Growth Hormone-Releasing Hormone Receptor MIA-690 Suppresses the Growth of Androgen-Independent Prostate Cancers.","abstract":"The development of resistance remains the primary challenge in treating castration-resistant prostate cancer (CRPC). GHRH receptors (GHRH-R), which are coupled to G-proteins (GPCRs), can mediate EGFR transactivation, offering an alternative pathway for tumour survival. This study aimed to evaluate the effects of the GHRH-R antagonist MIA-690, in combination with the EGFR inhibitor Gefitinib, on cell viability, adhesion, gelatinolytic activity, and the cell cycle in advanced prostate cancer PC-3 cells. The findings demonstrate a synergistic effect between MIA-690 and Gefitinib, leading to the inhibition of cell viability, adhesion, and metalloprotease activity. Cell cycle analysis suggests that both compounds induce cell cycle arrest, both individually and in combination. Furthermore, similar effects of the GHRH-R antagonist MIA-690 combined with Gefitinib were observed in PC-3 tumours developed by subcutaneous injection in athymic nude mice 36 days post-inoculation. These results indicate that combined therapy with a GHRH-R antagonist and an EGFR inhibitor exerts a stronger antitumor effect compared to monotherapy by preventing transactivation between EGFR and GHRH-R in CRPC.","authors":["Muñoz-Moreno Laura","Gómez-Calcerrada M Isabel","Arenas M Isabel","Carmena M José","Prieto Juan C","Schally Andrew V","Bajo Ana M"],"year":2024,"journal":"International journal of molecular sciences"},{"pmid":"37983492","title":"Growth hormone-releasing hormone receptor antagonist MIA-602 attenuates cardiopulmonary injury induced by BSL-2 rVSV-SARS-CoV-2 in hACE2 mice.","abstract":"COVID-19 pneumonia causes acute lung injury and acute respiratory distress syndrome (ALI/ARDS) characterized by early pulmonary endothelial and epithelial injuries with altered pulmonary diffusing capacity and obstructive or restrictive physiology. Growth hormone-releasing hormone receptor (GHRH-R) is expressed in the lung and heart. GHRH-R antagonist, MIA-602, has been reported to modulate immune responses to bleomycin lung injury and inflammation in granulomatous sarcoidosis. We hypothesized that MIA-602 would attenuate rVSV-SARS-CoV-2-induced pulmonary dysfunction and heart injury in a BSL-2 mouse model. Male and female K18-hACE2tg mice were inoculated with SARS-CoV-2/USA-WA1/2020, BSL-2-compliant recombinant VSV-eGFP-SARS-CoV-2-Spike (rVSV-SARS-CoV-2), or PBS, and lung viral load, weight loss, histopathology, and gene expression were compared. K18-hACE2tg mice infected with rVSV-SARS-CoV-2 were treated daily with subcutaneous MIA-602 or vehicle and conscious, unrestrained plethysmography performed on days 0, 3, and 5 (n = 7 to 8). Five days after infection mice were killed, and blood and tissues collected for histopathology and protein/gene expression. Both native SARS-CoV-2 and rVSV-SARS-CoV-2 presented similar patterns of weight loss, infectivity (~60%), and histopathologic changes. Daily treatment with MIA-602 conferred weight recovery, reduced lung perivascular inflammation/pneumonia, and decreased lung/heart ICAM-1 expression compared to vehicle. MIA-602 rescued altered respiratory rate, increased expiratory parameters (Te, PEF, EEP), and normalized airflow parameters (Penh and Rpef) compared to vehicle, consistent with decreased airway inflammation. RNASeq followed by protein analysis revealed heightened levels of inflammation and end-stage necroptosis markers, including ZBP1 and pMLKL induced by rVSV-SARS-CoV-2, that were normalized by MIA-602 treatment, consistent with an anti-inflammatory and pro-survival mechanism of action in this preclinical model of COVID-19 pneumonia.","authors":["Condor Capcha Jose M","Kamiar Ali","Robleto Emely","Saad Ali G","Cui Tengjiao","Wong Amanda","Villano Jason","Zhong William","Pekosz Andrew","Medina Edgar","Cai Renzhi","Sha Wei","Ranek Mark J","Webster Keith A","Schally Andrew V","Jackson Robert M","Shehadeh Lina A"],"year":2023,"journal":"Proceedings of the National Academy of Sciences of the United States of America"}],"biorxiv":[{"pmid":"","doi":"10.20944/preprints202604.1748.v1","title":"Evaluation of Research Grade Peptides Marketed Directly to Consumers Reveals Extensive Variability in Purity and Measured Abundance","abstract":"Peptides are a rapidly expanding drug class with a parallel and largely unregulated gray market that sells preparations directly to consumers for self-administration. The use of gray market peptides has grown substantially, with patients self-administering these compounds for purported benefits including accelerated musculoskeletal injury recovery, muscle hypertrophy, fat loss, and athletic performance enhancement. The objective of this study was to evaluate the purity, measured abundance, and endotoxin burden of gray market research peptides using a large, publicly available independent testing dataset, and to compare their cost to compounded and FDA-approved alternatives. A total of 6441 peptide samples across fourteen compounds, including BPC-157, cagrilintide, CJC-1295, GHK-Cu, ipamorelin, PT-141, retatrutide, semaglutide, sermorelin, survodutide, TB-500, tesamorelin, thymosin beta-4, and tirzepatide, were analyzed. Two quality acceptance frameworks were applied: a model that approximated regulatory standards for 503A compounded medications, and a more conservative model that utilized regulatory standards often applied to the production of FDA approved peptide drugs. Between the two models, 41.6% to 71.1% of samples failed to meet basic quality criteria, and measurable endotoxin contamination was present in 15% of samples. Gray market compounds were consistently less expensive than FDA-approved peptides, but there were considerable differences in the cost differential. Compared with gray market preparations, the estimated cost of a clinically relevant treatment course for FDA-approved peptides was 72.8% higher for tirzepatide, and 3850% higher for PT-141. These findings indicate that many peptides used for sports medicine and performance-related purposes fail basic quality benchmarks. Further, consumer-directed third-party testing improves transparency, but captures only a small fraction of the safety profile relevant to patients self-administering injectable peptide preparations.","authors":["Mendias CL","Awan TM."],"year":2026,"journal":"PPR","source":"PPR","preprint":true},{"pmid":"","doi":"10.20944/preprints202512.1011.v3","title":"Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance","abstract":"Peptides are short chains of amino acids with a unique pharmacological niche between small-molecule drugs and large proteins. Their use in sports medicine is rapidly expanding, driven by patient demand for accelerated injury recovery and performance enhancement. While numerous peptide drugs have undergone a rigorous approval process that evaluates both safety and efficacy, a parallel \"gray market\" of unapproved compounds has emerged, operating largely outside regulatory oversight. Our objective is to present the pharmacological mechanisms, safety profiles, and regulatory status of prominent approved and unapproved peptides marketed direct to patients, including AOD-9604 (Anti-Obesity Drug 9604), BPC-157 (Body Protection Compound 157), CJC-1295, FS-344 (Follistatin-344), GHK-Cu (Glycyl-L-histidyl-L-lysine copper), ipamorelin, MOTS-C (Mitochondrial ORF of the 12S rRNA type-c), sermorelin, SS-31 (Elamipretide), tesamorelin (Egrifta), Tβ4 (thymosin beta-4), and TB-500 (thymosin beta-4 fragment). Many unapproved peptides demonstrate favorable tissue repair and metabolic outcomes in animal models, but rigorous human safety data is scarce, and there is potential for serious harm to patients. This narrative review focuses on the utilization of peptides in sports medicine, and alternative treatments that may be considered. We provide a framework to navigate patient discussions about peptides to better facilitate evidence-based practices for musculoskeletal healing and athletic performance. We also discuss the placebo effect as a mediator of peptide efficacy, and how social media amplifies this effect.","authors":["Mendias CL","Awan TM."],"year":2026,"journal":"PPR","source":"PPR","preprint":true},{"pmid":"","doi":"10.20944/preprints202512.1011.v1","title":"Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance","abstract":"Peptides are short chains of amino acids with a unique pharmacological niche between small-molecule drugs and large proteins. Their use in sports medicine is rapidly expanding, driven by patient demand for accelerated injury recovery and performance enhancement. While numerous peptide drugs have undergone a rigorous approval process that evaluates both safety and efficacy, a parallel \"gray market\" of unapproved compounds has emerged, operating largely outside regulatory oversight. Our objective is to present the pharmacological mechanisms, safety profiles, and regulatory status of prominent approved and unapproved peptides marketed direct to patients, including AOD-9604 (Anti-Obesity Drug 9604), BPC-157 (Body Protection Compound 157), CJC-1295, FS-344 (Follistatin-344), GHK-Cu (Glycyl-L-histidyl-L-lysine copper), Ipamorelin, MOTS-C (Mitochondrial ORF of the 12S rRNA type-c), sermorelin, SS-31 (Elamipretide), tesamorelin (Egrifta), and TB-500 (Thymosin Beta-4 fragment). Many unapproved peptides demonstrate favorable tissue repair and metabolic outcomes in animal models, rigorous human safety data is scarce, and there is potential for serious harm. This review focuses on peptide utilization in sports medicine and alternative treatments for specific peptides. We provide a framework to navigate patient discussions about peptides to better facilitate evidence-based practices for musculoskeletal healing and athletic performance. We also discuss the placebo effect as a mediator of peptide efficacy, and how social media amplifies this effect.","authors":["Mendias CL","Awan TM."],"year":2025,"journal":"PPR","source":"PPR","preprint":true}],"preprints":[{"pmid":"","doi":"10.20944/preprints202604.1748.v1","title":"Evaluation of Research Grade Peptides Marketed Directly to Consumers Reveals Extensive Variability in Purity and Measured Abundance","abstract":"Peptides are a rapidly expanding drug class with a parallel and largely unregulated gray market that sells preparations directly to consumers for self-administration. The use of gray market peptides has grown substantially, with patients self-administering these compounds for purported benefits including accelerated musculoskeletal injury recovery, muscle hypertrophy, fat loss, and athletic performance enhancement. The objective of this study was to evaluate the purity, measured abundance, and endotoxin burden of gray market research peptides using a large, publicly available independent testing dataset, and to compare their cost to compounded and FDA-approved alternatives. A total of 6441 peptide samples across fourteen compounds, including BPC-157, cagrilintide, CJC-1295, GHK-Cu, ipamorelin, PT-141, retatrutide, semaglutide, sermorelin, survodutide, TB-500, tesamorelin, thymosin beta-4, and tirzepatide, were analyzed. Two quality acceptance frameworks were applied: a model that approximated regulatory standards for 503A compounded medications, and a more conservative model that utilized regulatory standards often applied to the production of FDA approved peptide drugs. Between the two models, 41.6% to 71.1% of samples failed to meet basic quality criteria, and measurable endotoxin contamination was present in 15% of samples. Gray market compounds were consistently less expensive than FDA-approved peptides, but there were considerable differences in the cost differential. Compared with gray market preparations, the estimated cost of a clinically relevant treatment course for FDA-approved peptides was 72.8% higher for tirzepatide, and 3850% higher for PT-141. These findings indicate that many peptides used for sports medicine and performance-related purposes fail basic quality benchmarks. Further, consumer-directed third-party testing improves transparency, but captures only a small fraction of the safety profile relevant to patients self-administering injectable peptide preparations.","authors":["Mendias CL","Awan TM."],"year":2026,"journal":"PPR","source":"PPR","preprint":true},{"pmid":"","doi":"10.20944/preprints202512.1011.v3","title":"Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance","abstract":"Peptides are short chains of amino acids with a unique pharmacological niche between small-molecule drugs and large proteins. Their use in sports medicine is rapidly expanding, driven by patient demand for accelerated injury recovery and performance enhancement. While numerous peptide drugs have undergone a rigorous approval process that evaluates both safety and efficacy, a parallel \"gray market\" of unapproved compounds has emerged, operating largely outside regulatory oversight. Our objective is to present the pharmacological mechanisms, safety profiles, and regulatory status of prominent approved and unapproved peptides marketed direct to patients, including AOD-9604 (Anti-Obesity Drug 9604), BPC-157 (Body Protection Compound 157), CJC-1295, FS-344 (Follistatin-344), GHK-Cu (Glycyl-L-histidyl-L-lysine copper), ipamorelin, MOTS-C (Mitochondrial ORF of the 12S rRNA type-c), sermorelin, SS-31 (Elamipretide), tesamorelin (Egrifta), Tβ4 (thymosin beta-4), and TB-500 (thymosin beta-4 fragment). Many unapproved peptides demonstrate favorable tissue repair and metabolic outcomes in animal models, but rigorous human safety data is scarce, and there is potential for serious harm to patients. This narrative review focuses on the utilization of peptides in sports medicine, and alternative treatments that may be considered. We provide a framework to navigate patient discussions about peptides to better facilitate evidence-based practices for musculoskeletal healing and athletic performance. We also discuss the placebo effect as a mediator of peptide efficacy, and how social media amplifies this effect.","authors":["Mendias CL","Awan TM."],"year":2026,"journal":"PPR","source":"PPR","preprint":true},{"pmid":"","doi":"10.20944/preprints202512.1011.v1","title":"Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance","abstract":"Peptides are short chains of amino acids with a unique pharmacological niche between small-molecule drugs and large proteins. Their use in sports medicine is rapidly expanding, driven by patient demand for accelerated injury recovery and performance enhancement. While numerous peptide drugs have undergone a rigorous approval process that evaluates both safety and efficacy, a parallel \"gray market\" of unapproved compounds has emerged, operating largely outside regulatory oversight. Our objective is to present the pharmacological mechanisms, safety profiles, and regulatory status of prominent approved and unapproved peptides marketed direct to patients, including AOD-9604 (Anti-Obesity Drug 9604), BPC-157 (Body Protection Compound 157), CJC-1295, FS-344 (Follistatin-344), GHK-Cu (Glycyl-L-histidyl-L-lysine copper), Ipamorelin, MOTS-C (Mitochondrial ORF of the 12S rRNA type-c), sermorelin, SS-31 (Elamipretide), tesamorelin (Egrifta), and TB-500 (Thymosin Beta-4 fragment). Many unapproved peptides demonstrate favorable tissue repair and metabolic outcomes in animal models, rigorous human safety data is scarce, and there is potential for serious harm. This review focuses on peptide utilization in sports medicine and alternative treatments for specific peptides. We provide a framework to navigate patient discussions about peptides to better facilitate evidence-based practices for musculoskeletal healing and athletic performance. We also discuss the placebo effect as a mediator of peptide efficacy, and how social media amplifies this effect.","authors":["Mendias CL","Awan TM."],"year":2025,"journal":"PPR","source":"PPR","preprint":true}],"consensus_view":"The literature consensus is that sermorelin is a short-lived GHRH agonist whose plasma half-life is severely limited by N-terminal proteolytic cleavage, with DPP-IV-mediated Tyr1-Ala2 bond cleavage being the primary enzymatic vulnerability. This is well-established in the peptide pharmacology and anti-doping analytical fields. The consensus further holds that structural modification of the N-terminus — exemplified by tesamorelin (trans-3-hexenoic acid on Tyr1) and CJC-1295 (DAC conjugation) — successfully extends GHRH analogue half-life without abolishing GHRHR agonism. The Aib substitution strategy itself is consensus-validated in incretin pharmacology (semaglutide, tirzepatide) as the canonical DPP-IV-resistant Ala mimetic at position 2. However, there is no published study directly applying Aib at position 2 of sermorelin, meaning the specific claim of preserved GHRHR binding affinity and activation for [Aib2]-sermorelin rests on mechanistic extrapolation rather than direct experimental evidence in the retrieved literature.","knowledge_gaps":"The most critical gap is the absence of any published structure-activity relationship (SAR) study directly testing Aib at position 2 of sermorelin or any other GHRH(1-29) scaffold. While DPP-IV resistance of Aib at position 2 is well-documented for GLP-1-class peptides, the structural requirements of the GHRHR binding pocket at position 2 differ from GLP-1R, and no co-crystal structure or mutagenesis study in the retrieved literature directly addresses tolerance of the gem-dimethyl steric addition at Ala2 by GHRHR. Additionally, the degree to which DPP-IV versus other N-terminal exopeptidases (e.g., dipeptidyl aminopeptidase II, prolyl oligopeptidase) contribute to sermorelin in vivo clearance is not quantitatively resolved in these papers. The relative contribution of renal clearance vs. proteolysis to overall sermorelin PK, and whether Aib2 alone (without additional modifications) provides clinically meaningful half-life extension, also remain unaddressed.","supporting_evidence":"1) DPP-IV cleavage at the Tyr1-Ala2 bond is a confirmed degradation pathway: anti-doping analytical work (PMID:37806509) explicitly distinguishes sermorelin (3-29)-NH2 as a known metabolite, and PMID:37688464 demonstrates rapid N-terminal enzymatic cleavage of sermorelin fragments in biological matrices. 2) Aib is the established canonical solution to DPP-IV susceptibility at position 2, validated at scale in semaglutide and tirzepatide — this is textbook incretin pharmacology even if not extensively reviewed in these specific papers. 3) Aib is a potent helix-inducing residue (stronger than Ala) that would be expected to stabilize or enhance the α-helical conformation of sermorelin's N-terminal region, which is the bioactive recognition element for GHRHR. 4) Retention of L-backbone geometry (pseudo-L orientation due to achiral α,α-disubstitution) avoids the receptor interaction disruption associated with D-Ala, supporting preservation of GHRHR binding. 5) Clinical precedent that N-terminal GHRH modification is tolerated by GHRHR: tesamorelin (N-terminal trans-3-hexenoic acid modification) retains full agonist activity (PMID:41490200, PMID:32257855), demonstrating the receptor's tolerance for position-1/2 modifications.","challenging_evidence":"1) No paper in the retrieved set directly tests Aib2 substitution in any GHRH analogue — all supporting evidence is mechanistic extrapolation from incretin pharmacology and general peptide chemistry, making the potency-preservation claim unverified for GHRHR. 2) The GHRHR binding pharmacophore has distinct structural requirements from GLP-1R; position 2 of GHRH may make specific contacts with the GHRHR extracellular domain or transmembrane bundle that the gem-dimethyl of Aib could sterically disrupt, a possibility not addressed in available literature. 3) The glioma computational study (PMID:33842627) suggests sermorelin may have GHRHR-independent biological activities, implying the receptor binding model may be incomplete. 4) Gray-market purity data (preprint DOI:10.20944/preprints202604.1748.v1) shows high failure rates for sermorelin preparations, suggesting that even the baseline pharmacology of native sermorelin is not well-characterized under real-world conditions — complicating any comparative PK claims. 5) Sermorelin's short half-life may reflect not only DPP-IV cleavage but also rapid renal filtration (MW ~3,357 Da, below the glomerular filtration threshold for small peptides); Aib2 substitution alone would not address renal clearance, potentially limiting the magnitude of half-life extension achievable with this single modification compared to CJC-1295 (albumin binding) or PEGylated analogues."},"caveats":["in silico prediction only — requires wet lab validation","single-run prediction (not ensembled)","predicted properties may not reflect real-world biological behavior","this is research, not medical advice","Aib is a non-canonical residue not natively represented in AlphaFold-class training data — its backbone geometry may be approximated or misrepresented in the structural model","heuristic half-life estimate (1–6 h) is sequence-based and does not model enzymatic cleavage or renal filtration — real PK would differ significantly","GHRHR ECD has returned sub-threshold pLDDT (~0.48–0.50) across six structurally diverse modifications in this lab — confidence floor may be a target-level training data limitation, not a peptide property","Chai-1 agreement and Boltz-2 affinity data were unavailable — no orthogonal signal to supplement the primary prediction"],"works_cited":[{"pmid_or_doi":"18031173","title":"Sermorelin: a review of its use in the diagnosis and treatment of children with idiopathic growth hormone deficiency.","year":1999,"relevance":"Establishes sermorelin as the minimal 29-aa GHRH fragment with full GHRHR agonist activity and documents its clinical half-life and pituitary-specific mechanism, providing the baseline pharmacology that the Ala2→Aib modification aims to improve."},{"pmid_or_doi":"18046908","title":"Sermorelin: a better approach to management of adult-onset growth hormone insufficiency?","year":2006,"relevance":"Reviews sermorelin's therapeutic limitations including short half-life in the context of adult GH deficiency management, directly motivating the need for DPP-IV-resistant analogues."},{"pmid_or_doi":"37688464","title":"In-house standards derived from doping peptides: Enzymatic and serum stability and degradation profile of GHRP and GHRH-related peptides.","year":2023,"relevance":"Directly characterizes serum and enzymatic degradation of sermorelin fragments (1-11, 13-20, 22-29), confirming rapid N-terminal proteolytic cleavage in biological matrices consistent with DPP-IV activity at the Tyr1-Ala2 bond — the exact site targeted by the Aib substitution."},{"pmid_or_doi":"37806509","title":"Cationic exchange SPE combined with triple quadrupole UHPLC-MS/MS for detection of GHRHs in urine samples.","year":2023,"relevance":"Analytically distinguishes native sermorelin (GRF 1-29) from the des-Tyr1 fragment sermorelin (3-29)-NH2, implying DPP-IV cleavage is a recognized in vivo metabolic event for sermorelin surveillance purposes."},{"pmid_or_doi":"41490200","title":"Therapeutic Peptides in Orthopaedics: Applications, Challenges, and Future Directions.","year":2026,"relevance":"Contextualizes sermorelin within the landscape of GHRH secretagogues including longer-acting tesamorelin and CJC-1295, highlighting that half-life extension through structural modification is the key differentiator for clinical utility."},{"pmid_or_doi":"32257855","title":"Beyond the androgen receptor: the role of growth hormone secretagogues in the modern management of body composition in hypogonadal males.","year":2020,"relevance":"Reviews sermorelin's clinical limitations relative to longer-acting GH secretagogues, supporting the translational need for a DPP-IV-resistant sermorelin analogue with extended half-life."},{"pmid_or_doi":"10.20944/preprints202604.1748.v1","title":"Evaluation of Research Grade Peptides Marketed Directly to Consumers Reveals Extensive Variability in Purity and Measured Abundance","year":2026,"relevance":"Demonstrates widespread gray-market use of sermorelin and quality failures, indirectly supporting demand for a more stable, pharmaceutical-grade analogue with predictable pharmacokinetics."},{"pmid_or_doi":"10.20944/preprints202512.1011.v3","title":"Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance","year":2026,"relevance":"Provides comparative pharmacological context for sermorelin vs. tesamorelin and CJC-1295, noting half-life as the critical pharmacokinetic limitation of unmodified sermorelin."},{"pmid_or_doi":"40244089","title":"Growth Hormone-Releasing Hormone Antagonists Increase Radiosensitivity in Non-Small Cell Lung Cancer Cells.","year":2025,"relevance":"Characterizes GHRHR expression and downstream signaling via antagonist probes (MIA-602, MIA-690), providing receptor biology context though not directly relevant to agonist half-life modification."},{"pmid_or_doi":"33842627","title":"A potentially effective drug for patients with recurrent glioma: sermorelin.","year":2021,"relevance":"Reports computational drug-sensitivity findings for sermorelin in glioma; marginally relevant as it suggests GHRHR-independent or off-target activity, which could complicate interpretation of binding-preservation claims for the Aib 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