Attenuation of Visceral and Somatic Nociception by Ghrelin Mimetics

Anti-nociceptive effect of STW 5-II in rodent models of stress and post-inflammatory visceral hypersensitivity

AIMS

Visceral hypersensitivity is a therapy-resistant hallmark of irritable bowel syndrome (IBS). Many IBS patients' symptoms develop following an acute colitis, and most report that stress worsens symptoms. STW 5-II, a combination of six herbal extracts, is a clinically proven treatment for IBS, but the mechanism is uncertain. Here, we employ two well-characterized rodent models to test the hypothesis that STW 5-II attenuates chronic colonic hypersensitivity.

MAIN METHODS

Separate cohorts of male rats were used for each model of colonic hypersensitivity. The first model used repeated water avoidance stress (1hr/day for 10 days), while the second model used intracolonic trinitrobenzene sulfonic acid to induce a short-lived colitis followed by post-inflammatory visceral hypersensitivity. Both models used sham treatment controls. Colonic sensitivity was quantified as the number of abdominal contractions to graded pressures (20-60 mmHg) of isobaric colorectal distension (CRD). Phosphorylation of extracellular signal-regulated kinase (pERK) was assessed via immunohistochemistry in the brain, spinal cord, and dorsal root ganglion (DRG). STW 5-II (10 ml/kg, p.o.) or vehicle (p.o.) was administered for 7 days, prior to CRD and pERK expression.

KEY FINDINGS

Rats exposed to either model developed significant colonic hypersensitivity. Both models enhanced CRD-evoked pERK in DRGs, spinal cord, and brain. STW 5-II decreased colonic hypersensitivity and reduced CRD-evoked brain, spinal, and DRG pERK.

SIGNIFICANCE

Both models induced colonic hypersensitivity and enhanced pERK expression. STW 5-II inhibited colonic hypersensitivity and decreased noxious neuronal activation in both models, which could explain its clinically proven efficacy in relieving visceral hypersensitivity-related symptoms in IBS.

In vitro pharmacological characterization of growth hormone secretagogue receptor ligands using the dynamic mass redistribution and calcium mobilization assays

Ghrelin modulates several biological functions via selective activation of the growth hormone secretagogue receptor (GHSR). GHSR agonists may be useful for the treatment of anorexia and cachexia, while antagonists and inverse agonists may represent new drugs for the treatment of metabolic and substance use disorders. Thus, the identification and pharmacodynamic characterization of new GHSR ligands is of high interest. In the present work the label-free dynamic mass redistribution (DMR) assay has been used to evaluate the pharmacological activity of a panel of GHSR ligands. This includes the endogenous peptides ghrelin, desacyl-ghrelin and LEAP2(1-14). Among synthetic compounds, the agonists anamorelin and HM01, the antagonists HM04 and YIL-781, and the inverse agonist PF-05190457 have been tested, together with HM03, R011, and H1498 from patent literature. The DMR results have been compared to those obtained in parallel experiments with the calcium mobilization assay. Ghrelin, anamorelin, HM01, and HM03 behaved as potent full GHSR agonists. YIL-781 behaved as a partial GHSR agonist and R011 as antagonist in both the assays. LEAP2(1-14) resulted a GHSR inverse agonist in DMR but not in calcium mobilization assay. PF-05190457, HM04, and H1498 behaved as GHSR inverse agonists in DMR experiments, while they acted as antagonists in calcium mobilization studies. In conclusion, this study provided a systematic pharmacodynamic characterization of several GHSR ligands in two different pharmacological assays. It demonstrated that the DMR assay can be successfully used particularly to discriminate between antagonists and inverse agonists. This study may be useful for the selection of the most appropriate compounds to be used in future studies.

Advances in the Development of Nonpeptide Small Molecules Targeting Ghrelin Receptor

Ghrelin is an octanoylated peptide acting by the activation of the growth hormone secretagogue receptor, namely, GHS-R1a. The involvement of ghrelin in several physiological processes, including stimulation of food intake, gastric emptying, body energy balance, glucose homeostasis, reduction of insulin secretion, and lipogenesis validates the considerable interest in GHS-R1a as a promising target for the treatment of numerous disorders. Over the years, several GHS-R1a ligands have been identified and some of them have been extensively studied in clinical trials. The recently resolved structures of GHS-R1a bound to ghrelin or potent ligands have provided useful information for the design of new GHS-R1a drugs. This perspective is focused on the development of recent nonpeptide small molecules acting as GHS-R1a agonists, antagonists, and inverse agonists, bearing classical or new molecular scaffolds, as well as on radiolabeled GHS-R1a ligands developed for imaging. Moreover, the pharmacological effects of the most studied ligands have been discussed.