GHRP-6

Neuroprotection in Stroke

GHRP-6 protects brain tissue during acute stroke and can rescue memory deficits following stroke when administered in a timely manner (Subiros et al., 2016). Ghrelin and its analogues inhibit apoptosis and reduce inflammation in the brain, protecting neurons from both genetic programming and environmental damage following ischemic events (Spencer et al., 2013).

Parkinson's Disease

A 2018 study revealed that ghrelin receptors are expressed in the substantia nigra, a brain region affected in Parkinson's disease. Patients with genetic links to Parkinson's show decreased ghrelin receptor expression on neurons in this region, and rats with similar defects develop Parkinson's-like motor dysfunction when given a ghrelin receptor antagonist (Suda et al., 2018). GHRP-6, as a ghrelin receptor agonist, may reduce apoptosis in substantia nigra neurons and slow or prevent disease onset.

Memory Enhancement

Research in rodents has revealed that GHRP-6 helps solidify newly formed memories and convert short-term memories into long-term storage (Huang et al., 2016). Blocking the ghrelin receptor impairs memory encoding (Beheshti & Shahrokhi, 2015), and strong evidence supports a role for ghrelin/GHRP-6 in spatial learning (Toth et al., 2010). These findings suggest that exercise-induced cognitive benefits may be mediated through growth hormone secretagogues rather than growth hormone directly.

Wound Healing and Scar Reduction

GHRP-6 improves wound closure rates, enhances extracellular matrix protein formation including collagen, and organizes wound structure to reduce scar tissue appearance (Mendoza Mari et al., 2016). The peptide also prevents development of hypertrophic scars by interfering with aberrant extracellular matrix protein deposition (Fernandez-Mayola et al., 2018). These effects are mediated in part through the CD36 receptor, which promotes blood vessel growth in wounds.

Cardioprotection

In porcine models of myocardial infarction, GHRP-6 prevents oxidant cytotoxicity, protecting heart cells from free radical damage (Berlanga et al., 2007). This finding holds promise for developing drugs that can be administered post-heart attack to protect vulnerable but viable cardiomyocytes, potentially reducing mortality and improving long-term cardiac outcomes.

Sexual Motivation and Mood

Ghrelin receptors in the central nervous system modulate sexual behavior and motivation. Elevated ghrelin levels boost sexual motivation in male rats, and studies with GHRP-6 and its antagonists have mapped specific brain regions involved in this modulation (Hyland et al., 2018). GHRP-6 and other ghrelin receptor agonists also decrease depression-like behavior and improve function in brain regions associated with mood, particularly under stress conditions (Huang et al., 2019), suggesting applications for stress, anxiety, and depression research.

Ongoing & Future Research

Active and recent clinical investigations involving GHRP-6 and related ghrelin pathway compounds include:

• NCT00091585: Investigation of ghrelin and growth hormone secretagogues on GH release kinetics and diagnostic applications
• NCT01444703: Ghrelin receptor agonists in cancer-related cachexia -- appetite stimulation and lean body mass preservation
• NCT02196025: Ghrelin pathway modulation in Parkinson's disease -- neuroprotective potential and motor function outcomes
• NCT00512356: Effects of ghrelin and ghrelin mimetics on appetite regulation, energy expenditure, and metabolic parameters

Key areas of active preclinical investigation include:

• Neuroprotection in stroke and PD: Expanding from rodent MCAO and neurotoxin models to larger animal and early-phase human studies examining ghrelin receptor agonists as neuroprotective agents
• Scar reduction: Continued development of topical GHRP-6 formulations for hypertrophic and keloid scar prevention, with the Cuban Center for Genetic Engineering and Biotechnology (CIGB) leading clinical-stage development
• Ghrelin pathway in metabolic disease: Investigations into the role of GHS-R1a and CD36 signaling in obesity, insulin resistance, and diabetic complications

Comparison to Related Compounds

GHRP-6 produces the strongest appetite stimulation among synthetic GHRPs, owing to robust activation of hypothalamic GHS-R1a in appetite-regulating nuclei. Compared to GHRP-2, it elicits more pronounced cortisol and prolactin elevation and has broader receptor activity including CD36 binding, which mediates its wound healing and cardioprotective effects (Bowers et al., 1991).

Unlike hexarelin, which has the strongest CD36-mediated cardioprotection and longest half-life, GHRP-6 offers a more balanced profile between GH release, appetite stimulation, and tissue repair. Ipamorelin is far more selective, producing virtually no off-target hormonal effects, but lacks GHRP-6's CD36-mediated tissue repair capabilities. Compared to endogenous ghrelin (a 28-amino acid peptide), GHRP-6 is a simpler hexapeptide that is more resistant to enzymatic degradation and produces a more predictable GH response (Moulin et al., 2007).