GHRP-2
Also known as: Growth Hormone Releasing Peptide-2, Pralmorelin, KP-102, GPA-748
Summary
GHRP-2 (Pralmorelin) is a synthetic hexapeptide growth hormone secretagogue that acts as a ghrelin receptor (GHS-R) agonist to stimulate growth hormone release from the pituitary gland. It was the first peptide of this class introduced clinically and operates through a receptor pathway distinct from growth hormone-releasing hormone (GHRH). GHRP-2 has demonstrated potent GH-stimulating effects in both animal and human studies, with additional influences on appetite regulation and ACTH/cortisol secretion. The peptide is currently marketed by Kaken Pharmaceutical in Japan as a diagnostic agent for assessing growth hormone deficiency. Clinical trials have explored its therapeutic potential for treating GH deficiency, short stature, and critical illness, though development for therapeutic applications in the United States was discontinued. Beyond GH stimulation, research has identified cytoprotective properties including cardioprotective, antioxidant, and anti-inflammatory effects. GHRP-2 is well-tolerated in clinical studies with minimal side effects, though it remains primarily approved for diagnostic rather than therapeutic use outside of Japan.
Potential Benefits
Growth Hormone Stimulation
Potent GH Release: GHRP-2 produces robust and dose-dependent increases in growth hormone secretion in both children and adults, with responses often exceeding those achieved with GHRH [1][4][7]. Peak GH levels occur within 25-60 minutes following administration [4][7].
Diagnostic Reliability: Clinical trials demonstrate GHRP-2's utility as a diagnostic tool for GH deficiency, with a cut-off value of 15 μg/L showing high sensitivity and specificity comparable to the insulin tolerance test while offering improved safety [7].
Synergistic Effects: When combined with GHRH, GHRP-2 produces synergistic growth hormone responses, significantly amplifying GH secretion beyond either agent alone [5][9].
Body Composition and Growth
Increased Growth Velocity: In GH-deficient children, GHRP-2 treatment produced dose-wise increases in overnight GH secretion and higher growth velocity during treatment compared to pre-treatment and post-treatment periods [6][11].
Muscle Mass Gains: A controlled study in adults aged 40-70 years showed GHRP-2 administration for 90 days increased lean body mass by an average of 5.37% while reducing total body fat by 9.14% and visceral fat by 14.27%.
Bone Density Enhancement: GHRP-2 may improve bone density through sustained growth hormone elevation, potentially benefiting individuals with age-related bone loss.
Cardiovascular and Cytoprotective Effects
Cardioprotection: Preclinical studies demonstrate GHRP-2 protects cardiac tissue against ischemia-reperfusion injury, improves ventricular function, and reduces markers of cardiac damage [2].
Antioxidant Properties: GHRP-2 significantly decreases vascular oxidative stress, reducing aortic superoxide production by suppressing 12/15-lipoxygenase expression by 92% and preventing oxidized LDL-induced cellular damage [10][2].
Anti-inflammatory Effects: The peptide reduces interferon-gamma levels by 66% and demonstrates capacity to decrease reactive oxygen species while enhancing antioxidant defenses across cardiac, neuronal, and hepatic tissues [2][10].
Metabolic and Appetite Effects
Appetite Stimulation: Acute GHRP-2 administration increases food intake in healthy men by 35.9%, mirroring ghrelin's appetite-stimulating effects and providing a valuable research tool for studying eating behavior [1].
Hormonal Modulation: Beyond GH, GHRP-2 stimulates ACTH and cortisol secretion through direct pituitary mechanisms involving protein kinase A and C pathways [3].
Safety Information
Clinical Safety Profile
GHRP-2 has demonstrated a favorable safety profile across multiple clinical trials in both pediatric and adult populations. Studies ranging from acute administration to 8-month treatment periods report the peptide as well-tolerated with minimal adverse effects [6][11][13].
Pediatric Safety: No side effects or toxicities were observed in children receiving stepwise increasing doses up to 3.0 μg/kg/day over 8 months [11]. Intranasal administration in children was well-tolerated across dose ranges of 5-20 μg/kg [5].
Adult Tolerance: Healthy adult subjects receiving GHRP-2 infusions reported no adverse effects from the treatment [1]. The diagnostic test using 100 μg intravenous GHRP-2 showed good reproducibility and safety [7].
Regulatory Status
Approved Use: GHRP-2 (Pralmorelin) is marketed by Kaken Pharmaceutical in Japan as a diagnostic agent for assessing growth hormone deficiency in single-dose formulation.
Clinical Development: Phase II trials in Japan (KP-102 LN) for short stature treatment and in the United States with Wyeth for GH deficiency were discontinued. The trials for pituitary dwarfism ended because GH increases were significantly lower in GH-deficient subjects compared to controls.
Current Status: GHRP-2 remains approved primarily for diagnostic purposes with limited therapeutic approval. It is not FDA-approved for therapeutic use in the United States.
Side Effects
Reported side effects are generally mild and transient:
Common Effects: Headache, nausea, flushing, dizziness, and gastrointestinal disturbances including abdominal discomfort.
Appetite Changes: Marked increases in hunger due to ghrelin receptor activation, potentially leading to excessive food intake and unwanted weight gain [1].
Metabolic Effects: Potential elevation in blood glucose levels through impaired glucose metabolism; edema (fluid retention) particularly in extremities.
Musculoskeletal: Joint pain and stiffness may occur due to excessive tissue growth around joints from elevated growth hormone levels.
Cardiovascular: Possible elevation in blood pressure and heart rate in some individuals.
Contraindications and Precautions
Cancer History: Patients with active malignancies or cancer history should avoid GHRP-2 as growth hormone may potentially promote tumor growth.
Diabetes: Individuals with uncontrolled diabetes or diabetic retinopathy should exercise caution due to effects on glucose metabolism.
Hypersensitivity: Known hypersensitivity to the drug or its components is a contraindication.
Research Gaps
Long-term Safety: Extended therapeutic use beyond 8 months requires further investigation to establish long-term safety profiles.
Therapeutic Efficacy: While GHRP-2 effectively stimulates GH secretion, the short duration of action limits therapeutic applications. Improved delivery formulations are needed [11].
IGF-I Response: Studies show inconsistent elevations in IGF-I and IGFBP-3 despite increased GH secretion, requiring further research into downstream effects [11].
Atherosclerosis: While GHRP-2 demonstrates antioxidant benefits, it did not reduce atherosclerotic plaque formation in preclinical models, warranting investigation into cardiovascular applications [10].