Efficacy of a growth hormone-releasing peptide mimetic in cardiac ischemia/reperfusion injury

Insights on discovery, efficacy, safety and clinical applications of ghrelin receptor agonist capromorelin in veterinary medicine

Growth hormone and insulin like growth factor-1 plays an important role in the regulation of body composition and metabolism. Growth Hormone is released from the pituitary through a specific G-protein coupled receptor (GPCR) called growth hormone secretagogue receptor 1a expressed in the hypothalamus. Ghrelin is a peptide hormone released from the cells in the stomach, which stimulates appetite and food intake in mammals, regulates gut motility, gastric acid secretion, taste sensation, circadian rhythm, learning and memory, oxidative stress, autophagy, glucose metabolism etc. When the release of the endogenous ligand GHSR-1a, i.e., ghrelin is malfunctioned or stopped, external substitutes are administrated to induce the stimulation of growth hormone and appetite. A class of compound known as ghrelin receptor agonists are developed as an external substitute of ghrelin for regulation and stimulation of growth hormone in frailty, for body weight gain, muscle mass gain, prevention of cachexia and for the treatment of chronic fatigue syndromes. Capromorelin [Entyce™ (Aratana Therapeutics, Leawood, KS, USA)] is the only FDA (Food and Drug Administration) approved (May 2016) drug used for stimulating appetite in dogs and was marketed in the fall of 2017. In 2020, USFDA approved Capromorelin [Elura™ (Elanco US Inc.)] for the management of weight loss in chronic kidney disease of cats. This article reviews the discovery of the ghrelin receptor agonist capromorelin, its efficacy, safety, clinical applications and aims to delineate its further scope of use in veterinary practice.

Growth hormone-releasing hormone agonists reduce myocardial infarct scar in swine with subacute ischemic cardiomyopathy

BACKGROUND

Growth hormone-releasing hormone agonists (GHRH-As) stimulate cardiac repair following myocardial infarction (MI) in rats through the activation of the GHRH signaling pathway within the heart. We tested the hypothesis that the administration of GHRH-As prevents ventricular remodeling in a swine subacute MI model.

METHODS AND RESULTS

Twelve female Yorkshire swine (25 to 30 kg) underwent transient occlusion of the left anterior descending coronary artery (MI). Two weeks post MI, swine were randomized to receive injections of either 30 μg/kg GHRH-A (MR-409) (GHRH-A group; n=6) or vehicle (placebo group; n=6). Cardiac magnetic resonance imaging and pressure-volume loops were obtained at multiple time points. Infarct, border, and remote (noninfarcted) zones were assessed for GHRH receptor by immunohistochemistry. Four weeks of GHRH-A treatment resulted in reduced scar mass (GHRH-A: -21.9 ± 6.42%; P=0.02; placebo: 10.9 ± 5.88%; P=0.25; 2-way ANOVA; P=0.003), and scar size (percentage of left ventricular mass) (GHRH-A: -38.38 ± 4.63; P=0.0002; placebo: -14.56 ± 6.92; P=0.16; 2-way ANOVA; P=0.02). This was accompanied by improved diastolic strain. Unlike in rats, this reduced infarct size in swine was not accompanied by improved cardiac function as measured by serial hemodynamic pressure-volume analysis. GHRH receptors were abundant in cardiac tissue, with a greater density in the border zone of the GHRH-A group compared with the placebo group.

CONCLUSIONS

Daily subcutaneous administration of GHRH-A is feasible and safe in a large animal model of subacute ischemic cardiomyopathy. Furthermore, GHRH-A therapy significantly reduced infarct size and improved diastolic strain, suggesting a local activation of the GHRH pathway leading to the reparative process.

The use of gastrointestinal intubation studies for controlled release development

AIMS

This review describes clinical results of gastrointestinal intubation studies of eight controlled release (CR) candidates under development during the 1990s and offers suggestions for determining why, when and how to conduct human intubation studies.

METHODS

Experience with the administration of the following eight compounds to various regions of the gastrointestinal tract is described: CJ-13,610, CP-195,543, CP-331,684, CP-409,092, CP-424,391, azithromycin, sertraline, and trovafloxacin. Also included are human pharmacokinetic studies with prototype CR dosage forms for CJ-13,610 and CP-424,391.

RESULTS

Intubation studies, while appearing invasive, are safe and not unpleasant procedures that have been found to be valuable in the development of CR formulations.

CONCLUSIONS

The following recommendations are made regarding intubation studies: (i) no intubation study is recommended for compounds with high permeability, since these compounds are likely to be well absorbed from the colon; (ii) compounds with moderate permeability may require an intubation study if the dog colon and in silico models predict a marginally acceptable CR concentration-time profile; (iii) use a dose that approximates 1 h of the intended CR delivery rate; (iv) use the smallest volume possible; (v) define and record tubing placement; (vi) use a thermodynamically stable solution or/and suspension.

Dog Colonoscopy Model for Predicting Human Colon Absorption

PURPOSE

This study was conducted to develop and validate a dog colon model that predicts colon permeability in humans.

METHODS

The following compounds were studied: Class 1 highly soluble (HS)/highly permeable (HP): aminophylline, propranolol, CP-409092; Class 2 LS/HP: nifedipine; trovafloxacin, sertraline; Class 3 HS/LP: azithromycin, atenolol, CP-331684, CP-424391; Class 4 LS/LP: CJ-13610. Administration to dogs was made 30 cm cranial to the anal sphincter with a lubricated Schott Model VFS-5 flexible endoscope. The bioavailability of the compound following the colon administration in dogs, relative to the same formulation administered orally (relative bioavailability), was determined.

RESULTS

Except for atenolol, a small hydrophillic molecule, the relative bioavailability from administration to the colon of the dog correlated well with the following compound properties: high solubility and high, passive permeability > high solubility, low permeability > low solubility, high, passive permeability approximately low solubility, low permeability.

CONCLUSION

The dog colon model is proposed as a surrogate for human intubation studies when the controlled release candidate falls in BCS Classes 2 (LS/HP), 3 (HS/LP), and 4 (LS/LP). However, no human intubation or dog colon studies are required for Class 1 (HS/HP), as these compounds are likely to be well absorbed from the colon.

Ghrelin and immunity: a young player in an old field

There is increasing evidence of the coupling of immune status to the metabolic system. The communication between the state of systemic and cellular energy balance to immune compartment is mediated via a complex array of cytokines, hormones and neuropeptides. Ghrelin, a recently described orexigenic peptide hormone, is predominantly produced by the stomach and functions as a positive regulator of the somatotropic axis and a peripheral signal of negative energy balance. Apart from its well-studied metabolic effects, ghrelin also exerts multiple regulatory effects on several other organ systems including the cardiovascular, central nervous and immune systems. Here, we summarize the growing evidence of ghrelin as a significant player in the regulation of inflammation and the immune function and the potential therapeutic targeting of ghrelin or its receptor, the growth hormone secretagogue receptor (GHS-R), in various inflammatory and cachexic disease states.

Privileged structure-based ligands for melanocortin receptors—tetrahydroquinolines, indoles, and aminotetralines

Substitution of the aryl sulfonamide moiety contained in MC4 agonist 1 with bicyclic heterocycles and aminotetralines produced compounds with MC4 activity. The heterocycles represent alternative privileged structures to that contained in 1. Compounds in which the polar group of the privileged structure was displayed in an endocyclic fashion were not as active as the parent agonist 1, while those with an exocyclic polar group afforded activity competitive with 1.

EP 80317, a ligand of the CD36 scavenger receptor, protects apolipoprotein E‐deficient mice from developing atherosclerotic lesions

CD36, a type B scavenger receptor expressed on macrophages, appears to play a major role in fatty streak formation through scavenging oxidatively modified lipoproteins in the arterial wall. We tested the hypothesis that EP 80317, a novel CD36 ligand derived from the growth hormone (GH)-releasing peptide family but devoided of any GH releasing activity, exerts anti-atherosclerotic effects in apolipoprotein E-deficient (apoE-/-) mice fed an atherogenic diet from 6 wk of age. Daily subcutaneous injections of EP 80317 (300 microg/kg) or vehicle were initiated at 6, 10, 12, or 14 wk until death at 18 wk. En face analyses of the entire aortic tree revealed a striking reduction (up to 51%) of lesion areas in EP 80317-treated apoE-/- mice compared with controls. Chronic treatment with EP 80317 (12 wk) is also associated with a 30% decrease in total plasma cholesterol, suggesting potential effects of this drug on cholesterol metabolism at the intestine/hepatic levels. EP 80317 exerts both preventive and curative effects on atherosclerotic lesion progression that were shown to be reversible after cessation of treatment. At the macrophage level, EP 80317 reduced oxidized low density lipoproteins internalization and up-regulated genes involved in cholesterol efflux, including peroxisome proliferator-activated receptor gamma (PPARgamma), liver x receptor alpha (LXRalpha), and the ATP binding cassette (ABC) transporters ABCA1 and ABCG1, supporting a role in regulating peripheral cholesterol trafficking. Importantly, the effects of EP 80317 were shown to be CD36 dependent, inasmuch as no anti-atherosclerotic or hypocholesterolemic effects were observed in apoE/CD36 double-deficient mice. In addition, long-term treatment of apoE/CD36 double-deficient mice with EP 80317 did not modulate the expression of genes of the PPARgamma-LXRalpha-ABC transporters pathway. Our results suggest that EP 80317, as a CD36 ligand, might be a prototype for a novel class of anti-atherosclerotic agents.

Identification of low-level degradants from low dose tablets

A multifaceted approach was successfully used to identify three of four unknown degradants in degraded low dose tablets. Accelerated solvent extraction (ASE) was found to be an invaluable tool in this multifaceted approach. ASE was capable of extracting four individual degradants of an active pharmaceutical component from 10 tablets into 15 mL of solvent with approximately 100% recovery for each degradant. Using ASE instead of manual extraction led to the extraction and isolation of the degradants in 1 day instead of 7 days. One of the degradants was extracted by ASE, isolated by semi-prep HPLC, and identified by LC-MS and NMR spectroscopy. The structures of two of the remaining three degradants were confirmed by synthesis of authentic samples, while the fourth degradant is yet to be identified.

Effects of early treatment with growth hormone on infarct size, survival, and cardiac gene expression after acute myocardial infarction

OBJECTIVE

This study examined the effects of growth hormone (GH) on infarct size, survival, and cardiac gene expression in rats with acute myocardial infarction.

DESIGN

Animals randomly received sc injection of either saline vehicle (n = 98) or GH (2mg/kg/day, n = 105) for 14 days commencing the day of left coronary artery ligation. Infarct size was determined by morphometric analysis at the time of death or at 52 weeks post-surgery. Gene expression was analyzed by real-time RT-PCR after 2-week treatment.

RESULTS

GH decreased infarct size by 18% (P < 0.01) and increased survival by 36% at 52 weeks. GH also significantly reduced cardiac expression of atrial natriuretic factor, beta-myosin heavy chain, alpha-smooth muscle actin, collagen I, collagen III, fibronectin, and pro-inflammatory cytokines.

CONCLUSIONS

Treatment with GH for 2 weeks beginning on the day of myocardial infarction produced beneficial effects that were associated with reductions in cardiac gene expression symptomatic of pathological remodeling.