Capromorelin increases food consumption, body weight, growth hormone, and sustained insulin-like growth factor 1 concentrations when administered to healthy adult Beagle dogs

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.

Detection of capromorelin in urine following oral and dermal routes of administration

Capromorelin is a growth hormone secretagogue. Despite promising results to alleviate muscle-wasting in the elderly, it has not advanced further in human development. Subsequent studies demonstrated capromorelin's ability to increase food intake in animals, leading to approval in the United States and Europe as an appetite stimulant for cats (Elura) and dogs (Entyce). Capromorelin is prohibited in sports due to its ability to stimulate growth hormone production and enhance performance. However, given that its veterinary preparation is formulated as a highly concentrated solution (20 or 30 mg/mL) delivered orally, incidental ingestion or dermal absorption may result in an adverse analytical finding (AAF) by way of direct exposure during oral administration to a pet. An administration study was conducted by either oral or transdermal application of capromorelin solution to mimic the scenario of inadvertent exposure to the drug. Ingestion of 30 μg of capromorelin orally (equivalent to 1 μL of Entyce) resulted in detectable amounts of capromorelin in urine for up to 48 h after administration with a maximum urinary concentration of 7 ng/mL. Importantly, when applied directly to the skin on the hands in larger quantities mimicking a pet administration exposure scenario (30 mg or 1 mL of Entyce), capromorelin was also detected reaching a maximum urinary concentration of 0.7 ng/mL. Athletes and testing authorities should be aware of the risk of an AAF arising due to incidental exposure to veterinary preparations of capromorelin. To our knowledge, before 2022, no positive test for capromorelin had ever been reported.

Comparison of Effects of Capromorelin and Mirtazapine on Appetite in New Zealand White Rabbits (Oryctolagus cuniculus)

Inappetence is a welfare concern in rabbits (Oryctolagus cuniculus), as it can lead to potentially fatal gastrointestinal stasis. In other species, inappetence is commonly treated with appetite stimulants; however, few published studies have evaluated the efficacy of appetite stimulants in rabbits. We performed 2 studies to evaluate the effects of capromorelin and mirtazapine on appetite in New Zealand White (NZW) rabbits. In the first study, healthy rabbits ( n = 9) were evaluated using a randomized crossover design and 9 treatments: capromorelin 4 mg/kg oral (PO) once a day (SID), capromorelin 8 mg/kg PO SID, saline control PO SID, capromorelin 4 mg/kg PO twice a day (BID), capromorelin 8 mg/kg PO BID, saline control PO BID, mirtazapine 0.5 mg/kg transdermal (TD) SID, mirtazapine 1 mg/kg TD SID, and saline control TD SID for 3 d with a 1-wk washout period between treatments. Treatment efficacy was assessed by measuring daily feed intake and fecal output and by weighing rabbits twice a week. Overall, feed intake and fecal output were higher for all treatments as compared with controls, except for fecal output in the capromorelin 4 mg/kg and 8 mg/kg PO SID groups. Feed intake and fecal output were significantly higher with mirtazapine as compared with capromorelin. Body weight and erythema/petechia of the pinnae were greater in the mirtazapine 1 mg/kg TD SID group than in the control group. A second study evaluated rabbits that had undergone surgery (castration, n = 7) and then received one of 3 treatments: capromorelin 8 mg/kg PO BID, mirtazapine 1 mg/kg TD SID, or saline PO BID for 3 d postoperatively. Feed intake and fecal output in the postoperative mirtazapine group were not significantly different from those of the capromorelin and control groups. Due to its superior efficacy as compared with capromorelin in healthy NZW rabbits, we recommend considering mirtazapine as a treatment for inappetence in NZW rabbits.

2022 ISFM Consensus Guidelines on Management of the Inappetent Hospitalised Cat

PRACTICAL RELEVANCE

Inappetence may have many origins and, as a presenting sign or observation in the hospitalised patient, is common in feline practice. Nutritional assessment of every patient is encouraged, to identify the need for, and appropriate type of, intervention indicated. The impact of malnutrition may be significant on the feline patient, perpetuating illness, delaying recovery, slowing wound healing and negatively impacting gut health and immunity. Delayed intervention may result in the cat's deterioration; hence prompt control of contributing factors such as the underlying illness, pain, nausea, ileus and stress is vital to optimise voluntary food intake. Management is multimodal, comprising reduction of stress, medications and assisted nutrition in the form of tube feeding or parenteral nutrition. Use of antiemetic, analgesic, prokinetic and appetite stimulant medications may restore appetite, but placement of feeding tubes should not be delayed. Feeding tubes are generally well tolerated and allow provision of food, water and medication with minimal stress, although clinicians must be aware of complications such as stoma site infections and refeeding syndrome.

CLINICAL CHALLENGES

Cats are vulnerable to malnutrition owing to their unique metabolism and specific nutritional requirements. Moreover, their nature as a species means they are susceptible to stress in the hospital environment, which may result in reduced food intake; previous negative experiences may compound the problem. In particular, an inappropriate clinic environment and/or handling may cause or exacerbate inappetence in hospitalised patients, with negative impacts on recovery. Postponing interventions such as feeding tube placement to await improvement, owing to clinician or caregiver apprehension, may hinder recovery and worsen nutritional deficits.

EVIDENCE BASE

The 2022 ISFM Consensus Guidelines on Management of the Inappetent Hospitalised Cat have been created by a panel of experts brought together by the International Society of Feline Medicine (ISFM). Information is based on the available literature, expert opinion and the panel members' experience.

Capromorelin, a ghrelin receptor agonist, increases feed intake and body weight gain in broiler chickens (Gallus gallus domesticus)

Ghrelin is a hormone that induces orexigenic effects in mammals. However, in avian species, there is scant and conflictive results on the effect of ghrelin on feed intake (FI). Therefore, we evaluated the effect of a ghrelin receptor agonist (capromorelin) on FI, ADG, water intake (WI), animal behavior and concentrations of ghrelin, glucose, growth hormone (GH) and insulin in broiler chickens. One-day-old male broilers were reared as recommended by the industry. At 4 wk of age (experimental day 0; D0), birds were blocked by weight and randomly assigned to 3 treatments in 2 identical trials. Control birds received a vehicle control solution containing 0 mg/kgBW/d of capromorelin. Birds in treatments 2 and 3 received capromorelin at target doses of 6 or 12 mg/kgBW/d of capromorelin (n = 27). FI and WI were measured 3 times a day at 0700 h (Period 1; P1), 1200 h (P2) and 1700 h (P3), while BW was recorded daily. Blood samples were collected on D-1 and D5. Bird behavior (pecking, sitting and standing) was evaluated for 9 h on D2. Data were analyzed using a randomized complete block design with repeated measures over time. Orthogonal polynomial contrasts were used to determine linear and quadratic effects of increasing levels of capromorelin. Polynomial contrasts showed that capromorelin doses linearly increased FI (P = 0.002) and ADG (P = 0.019). There were no treatment, day or treatment x d interactions on glucose, ghrelin and GH concentrations. However, there was a treatment x d interaction (P = 0.041) on insulin concentrations. Concentrations of insulin were higher on D5 for the 0 and 12 mg/kgBW/d treatments as compared with D-1. Polynomial contrasts showed that capromorelin doses linearly increased number of pecks/h (P = 0.018). Per hour FI and WI was higher during P1 (i.e., 0700-1200) as compared to P2 and P3 (P < 0.001). Our observations suggest that capromorelin linearly increases feed intake; thus, the same effect of that reported in mammalian species.

Use of propofol to induce food consumption by anorectic dogs following ovariohysterectomy

OBJECTIVE

To determine whether IV propofol administration at a dose of 2 mg/kg (0.9 mg/lb) could induce food consumption by anorectic female dogs following elective ovariohysterectomy.

ANIMALS

51 healthy female dogs that failed to eat voluntarily when food was offered 6 hours after ovariohysterectomy.

PROCEDURES

In a randomized, blinded, controlled clinical trial, dogs received propofol (2 mg/kg; n = 31) or an equivalent volume of saline (0.9% NaCl) solution (20) IV 6 hours after ovariohysterectomy. Afterward, food was offered to the dogs and food consumption was reassessed. Pain, sedation, and stress were scored before and immediately after treatment.

RESULTS

27 of the 31 (87%) dogs in the propofol group consumed food immediately after administration of the assigned treatment, whereas only 1 of 20 (5%) dogs in the placebo group did. No difference in pain, sedation, or stress scores was identified between the 2 groups. Sedation scores for dogs in the propofol group increased immediately after propofol administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that food consumption following elective surgical procedures can be effectively induced in anorectic female dogs by IV administration of propofol at a dose of 2 mg/kg.

The effect of the ghrelin-receptor agonist capromorelin on glucose metabolism in healthy cats

Somatostatin secretion from islet delta cells is important in maintaining low glycemic variability (GV) by providing negative feedback to beta cells and inhibiting insulin secretion. Capromorelin is a ghrelin-receptor agonist that activates the growth hormone secretagogue receptor on delta cells. We hypothesized that in cats, capromorelin administration will result in decreased GV at the expense of reduced insulin secretion and glucose tolerance. Seven healthy cats were treated with capromorelin from days 1-30. After the first day, fasting blood glucose increased (+13 ± 3 mg/dL, P < 0.0001), insulin decreased (+128 ± 122 ng/dL, P = 0.03), and glucagon was unchanged. Blood glucose was increased throughout an intravenous glucose tolerance test on day 1 with blunting of first-phase insulin response ([FPIR] 4,931 ± 2,597 ng/L/15 min) compared with day -3 (17,437 ± 8,302 ng/L/15 min, P = 0.004). On day 30, FPIR was still blunted (9,993 ± 4,285 ng/L/15 min, P = 0.045), but glucose tolerance returned to baseline. Mean interstitial glucose was increased (+19 ± 6 mg/dL, P = 0.03) on days 2-4 but returned to baseline by days 27-29 (P = 0.3). On days 2-4, GV was increased (SD = 9.7 ± 3.2) compared with baseline (SD = 5.0 ± 1.1, P = 0.02) and returned to baseline on days 27-29 (SD = 6.1 ± 1.1, P = 0.16). In summary, capromorelin caused a decline in insulin secretion and glycemic control and an increase in glucose variability early in the course of treatment, but these effects diminished toward the end of 30 d of treatment.

A Structural Analysis of the FDA Green Book-Approved Veterinary Drugs and Roles in Human Medicine

The FDA Green Book is a list of all drug products that have been approved by the FDA for use in veterinary medicine. The Green Book, as published, lacks structural information corresponding to approved drugs. To address this gap, we have compiled the structural data for all FDA Green Book drugs approved through the end of 2019. Herein we discuss the relevance of this data set to human drugs in the context of structural classes and physicochemical properties. Analysis reveals that physicochemical properties are highly optimized and consistent with a high probability of favorable drug metabolism and pharmacokinetic properties, including good oral bioavailability for most compounds. We provide a detailed analysis of this data set organized on the basis of structure and function. Slightly over half (51%) of vet drugs are also approved in human medicine. Combination drugs are biologics are also discussed.

Anorexia and the Cancer Patient

Appetite influences perceived quality of life for a dog or cat with cancer. Inappetence often is multifactorial, complicating treatment. Cancer-related anorexia/cachexia syndrome is a metabolic, paraneoplastic syndrome characterized by decreased food intake, involuntary weight loss, and loss of fat and muscle. If weight loss/cachexia has an impact on canine and feline cancer patients as in humans, management may improve survival times and quality of life. The challenge is having effective, proved therapies available for clinical use. Recent Food and Drug Administration approvals for appetite stimulation have renewed interest and discussion and has the potential to alter the course of case management.

Capromorelin: a ghrelin receptor agonist and novel therapy for stimulation of appetite in dogs

Ghrelin is a hormone, secreted from cells in the stomach, which is important in the regulation of appetite and food intake in mammals. It exerts its action by binding to a specific G-protein-coupled receptor, the growth hormone secretagogue receptor 1a (GHS-R1a) which is found in areas of the brain associated with the regulation of food intake. Ghrelin causes a release of growth hormone (GH) through binding to GHS-R1a in the hypothalamus and pituitary gland. A class of compounds known as growth hormone secretagogues, or ghrelin receptor agonists, were developed for therapeutic use in humans for the stimulation of GH in the frail elderly, and have subsequently been studied for their effects on increasing appetite and food intake, increasing body weight, building lean muscle mass, and treating cachexia. Subsequent research has shown that ghrelin has anti-inflammatory and immunomodulatory effects. This article reviews the basic physiology of ghrelin and the ghrelin receptor agonists, including the available evidence of these effects in vitro and in vivo in rodent models, humans, dogs and cats. One of these compounds, capromorelin, has been FDA-approved for the stimulation of appetite in dogs (ENTYCE ®). The data available on the safety and effectiveness of capromorelin is reviewed, along with a discussion of the potential clinical applications for ghrelin receptor agonists in both human and veterinary medicine.

A Prospective, Randomized, Masked, Placebo-Controlled Clinical Study of Capromorelin in Dogs with Reduced Appetite

BACKGROUND

Reduced appetite is a common clinical sign in dogs. This study evaluated the effectiveness and safety of capromorelin oral solution, (ENTYCE^® , Aratana Therapeutics, Leawood, KS) a new drug that is a ghrelin receptor agonist, for stimulation of appetite in dogs with reduced appetite.

HYPOTHESIS/OBJECTIVES

Capromorelin will increase appetite, as measured by the owner's evaluation, over 4 days. An additional objective was to evaluate the safety of capromorelin at the labeled dose.

ANIMALS

A total of 244 client-owned dogs reported by owners to be inappetent for at least 2 days were enrolled, with 177 cases in the effectiveness analysis.

METHODS

In this prospective, randomized, masked, placebo-controlled study, dogs were treated daily with capromorelin (3 mg/kg) oral solution (n = 121) or placebo oral solution (n = 56). Owners completed an evaluation of appetite at days 0 and 3 ± 1. Success was defined as improvement in appetite at day 3. Safety was evaluated by physical examination, clinical pathology, and monitoring adverse events and owner observations.

RESULTS

Capromorelin treatment improved appetite compared to placebo (68.6% and 44.6% treatment successes with 95% CI 59.7, 76.3 and 32.2, 57.8, respectively, P = .008). Mean body weight in capromorelin-treated dogs increased compared to placebo-treated dogs (1.8% with 95% CI 1.3, 2.3, and 0.1% with 95% CI 0.9, 1.1, respectively, P < .001). Adverse reactions occurring in >5% of either group were diarrhea and vomiting.

CONCLUSIONS AND CLINICAL IMPORTANCE

Capromorelin oral solution is an effective treatment for stimulation of appetite in dogs and represents the first ghrelin receptor agonist shown to be effective for this indication.

Capromorelin oral solution (ENTYCE®) increases food consumption and body weight when administered for 4 consecutive days to healthy adult Beagle dogs in a randomized, masked, placebo controlled study

Background

Dogs can suffer from inappetence caused by a variety of medical conditions. This may present as anorexia (complete loss of appetite), hyporexia (decreased appetite) or dysrexia (change in food preferences). A drug with a new mechanism of action, capromorelin, has potential to stimulate appetite in dogs. Capromorelin is a ghrelin receptor agonist, which mimics the action of endogenous ghrelin. It is a member of the growth hormone secretagogue (GHS) class of drugs. Capromorelin oral solution (ENTYCE®) was tested in healthy adult male and female Beagle dogs (n = 6 males and 6 females per group) for its effect on food consumption and body weight. A randomized, masked, placebo controlled study was conducted to measure the effects of a daily 3 mg/kg oral dose given over 4 days. Dogs were observed for clinical signs, physical examinations were completed prior to and at the end of treatment, and blood was drawn before and after treatment for evaluation of serum chemistry and hematology parameters.

Results

Capromorelin was well-tolerated, with no abnormalities seen on physical examination or clinical pathology. Some dogs showed increased salivation. Capromorelin treated dogs had increased mean (±SD) food consumption compared to placebo treated dogs (60.55 ± 39.87% versus -11.15 ± 14.23% respectively, P < 0.001). Treated dogs also had increased mean body weights compared to placebo treated dogs (5.96 ± 1.76% versus 0.053 ± 1.14% respectively, P < 0.001).

Conclusions

This study supports the effectiveness of capromorelin oral solution as an appetite stimulant in dogs. Treatment with the oral solution resulted in dramatic increases in appetite, as measured by food consumption, of over 60% compared to placebo. The drug was well tolerated. Capromorelin is the first ghrelin receptor agonist developed for appetite stimulation in any species, and represents a novel mechanism of action for this clinical use.