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Hexarelin: mechanism of action

Hexarelin is a synthetic growth hormone secretagogue peptide that acts at the GHS-R1a receptor. This page reviews the receptor pharmacology and the tissue-specific mechanisms reported in the preclinical literature, inclu

peptides-pro Editorial

Hexarelin (also written as hexarelin acetate in some catalogue listings; synonyms include His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2) is a synthetic hexapeptide belonging to the growth hormone secretagogue (GHS) class. It is a peptidic agonist of the growth hormone secretagogue receptor type 1a (GHS-R1a), the same receptor family engaged by ghrelin and by other synthetic GHS ligands such as GHRP-2, GHRP-6 and ipamorelin [3]. The evidence block supplied for this page does not provide a sequence, molecular formula or molecular weight, so those identifiers are not stated here.

The mechanistic work reviewed below centres on GHS-R1a agonism and on downstream signalling that converges on apoptotic regulation, with additional literature addressing CD36-related inflammatory signalling and oral permeation behaviour.

Research Studies

Hexarelin and retinal ganglion cell survival after optic nerve transection

Hexarelin was studied as a GHS-R1a agonist with reported anti-apoptotic activity, and its neuroprotective effect was tested on retinal ganglion cell (RGC) survival in the retina after optic nerve transection (ONT) [1]. The work used Golden hamsters aged 8–9 weeks. In a single-dose arm, animals received saline or hexarelin at 25 μg/kg, 50 μg/kg or 100 μg/kg once daily for 5 days after ONT, with assessment at 7 days. In a two-dose arm, saline, 100 μg/kg or 150 μg/kg hexarelin was injected twice daily for 5 days, again with assessment at 7 days. RGC survival was quantified by Tuj1 immunostaining [1]. This is an animal model; the findings describe RGC survival in hamsters and do not establish an effect in humans.

Hexarelin and apoptosis in ischemic acute kidney injury via MDM2/p53

Hexarelin has shown protection against organ injury in ischemia/reperfusion (I/R)-induced injury models, and one study examined its effect on acute kidney injury (AKI) together with the underlying molecular mechanism [2]. The investigators used both in vivo and in vitro experiments. In the I/R-induced AKI model, rats were pretreated with hexarelin at 100 μg/kg/day for 7 days and were sacrificed 24 h after I/R injury; kidney function, histology and apoptosis were then assessed [2]. The reported mechanism is routed through the MDM2/p53 pathway [2]. This is a rat model with in vitro support; the findings describe renal apoptosis in that model and do not establish an effect in humans.

Hexarelin and the GH-IGF-1 axis as a class-level mechanism

Hexarelin is grouped with other growth hormone secretagogues — GHRP-2, GHRP-6 and ipamorelin — as agents intended to modulate the growth hormone–insulin-like growth factor-1 (GH-IGF-1) axis [3]. That review frames these peptides as performance-enhancing drugs marketed as research compounds and notes that they are encountered in clinical practice and in online self-administration protocols [3]. The mechanistic claim at class level is GHS-R1a-mediated modulation of GH-IGF-1 signalling; the review does not report a hexarelin-specific clinical outcome, and no human efficacy claim is made here.

Hexarelin and CD36-related inflammatory signalling in a viral pneumonia model

A study of the hyper-inflammatory response to SARS-CoV-2 infection in K18-hACE2 mice used a cluster of differentiation 36 (CD36) receptor modulator [4]. The paper describes the viral infection driving alveolar macrophages toward an inflammatory phenotype, regulated at least in part through CD36-related signalling [4]. Hexarelin appears in this literature as a CD36-binding peptide ligand, and the CD36 receptor is the mechanistic node under investigation. This is a mouse model of viral pneumonia; the findings describe inflammatory signalling in that model and do not establish an effect in humans.

Hexarelin and intestinal permeation enhancers in the presence of bile salts

All-atom molecular dynamics simulations were used to examine the interaction between two permeability enhancers — sodium caprate and SNAC — and four peptides (octreotide, hexarelin, degarelix and insulin) in the presence of taurocholate, an intestinal bile salt [5]. The enhancers had distinct effects on peptide release depending on their properties, promoting release of hydrophobic peptides while inhibiting release of water-soluble peptides. Lowering peptide concentrations in the simulations reduced peptide–peptide interactions but increased their interactions with other components [5]. This is an in silico study; it describes simulated molecular behaviour and does not establish oral bioavailability in humans.

Hexarelin and MPTP-induced lung injury in mice

A mouse study investigated the protective and therapeutic effects of hexarelin against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced lung injury, evaluating oxidative stress, IL-6-mediated inflammation and Caspase-3-dependent apoptosis [6]. Fifty male Balb/C mice were used [6]. This is an animal model; the findings describe lung injury markers in mice and do not establish an effect in humans.

Hexarelin and GHS-R1a binding in the broader secretagogue literature

Work on alexamorelin, a synthetic peptide and growth hormone secretagogue with potential performance-enhancing properties, describes the class mechanism as mimicking the natural peptide hormone ghrelin by binding to the GHS type 1a receptor (GHS-R1a) [7]. That receptor-level description is the same node at which hexarelin acts [1][3]. This is a reference point for the receptor pharmacology rather than a hexarelin-specific finding.

Comparison of reported hexarelin study models and endpoints

ModelSpecies / systemReported endpointSource
Optic nerve transectionGolden hamster, in vivoRetinal ganglion cell survival (Tuj1 immunostaining)[1]
Ischemia/reperfusion acute kidney injuryRat, in vivo, with in vitro supportKidney function, histology, apoptosis; MDM2/p53 pathway[2]
SARS-CoV-2 infectionK18-hACE2 mouse, in vivoAlveolar macrophage inflammatory phenotype; CD36 signalling[4]
Permeation enhancer interactionAll-atom molecular dynamics, in silicoPeptide release in the presence of taurocholate[5]
MPTP-induced lung injuryBalb/C mouse, in vivoOxidative stress, IL-6 inflammation, Caspase-3 apoptosis[6]

Hexarelin and the limits of the current mechanistic evidence

Across the studies above, the mechanistic picture is built from animal models and in vitro or in silico systems. The retinal work is in hamsters [1]; the kidney work is in rats with in vitro support [2]; the inflammatory signalling work is in mice [4]; the permeation work is a simulation [5]; and the lung injury work is in mice [6]. The class-level review places hexarelin among GHS agents intended to modulate the GH-IGF-1 axis but does not report a hexarelin-specific clinical outcome [3]. No human mechanistic or efficacy data for hexarelin are supplied in the evidence block for this page, and none are claimed here.

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