MAGL inhibition modulates gastric secretion and motility following NSAID exposure in mice

Abstract

Non-steroidal anti-inflammatory drugs (NSAIDs) are common analgesic drugs that also cause well-known, negative gastrointestinal (GI) side effects. The physiological mechanism(s) of NSAID-induced GI damage are unclear and are likely due to multiple causes. The most studied contributing mechanisms are increased gastric acid secretion and increased gastric motility. The present study was designed to determine which ulcerogenic effects of the NSAID diclofenac sodium are reversed by blocking the endocannabinoid catabolic enzyme monoacylglycerol lipase (MAGL). Both male and female mice were used to identify possible sex differences. We hypothesized that the MAGL inhibitor JZL184 would attenuate diclofenac-induced increases in both gastric acid secretion and gastric motility. Diclofenac dose-dependently induced gastric hemorrhages to a similar extent in both male and female mice. Gastric hemorrhage severity significantly correlated with gastric levels of myeloperoxidase, an objective measure of neutrophil infiltration. Similarly, JZL184 reduced gastric acidity, in controls as well as mice treated with pentagastrin, which stimulates gastric acid release. As hypothesized, JZL184 decreased gastric motility. Surprisingly, diclofenac also slowed gastric emptying, indicating that diclofenac-induced ulcers most likely occur through increased gastric acid secretion, and not increased gastric motility, as measured in the present study. Thus, MAGL inhibition may proffer gastroprotection through modulating the secretory pathway of gastric hemorrhage. These data underscore the importance of sampling multiple time points and using both sexes in research, in addition to multiple mechanistic targets, and contribute to the basic understanding of NSAID-induced gastric inflammation.

Introduction

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most commonly used pharmaceutical therapies for pain (Lanas, 2009). Approximately 20% of chronic NSAID users develop gastric hemorrhages in the stomach or duodenum that require medical intervention (Wallace, 2001). The physiological mechanisms through which NSAIDs induce gastric hemorrhages are not clear (Schubert, 2008). The most characterized mechanisms include NSAID-induced increases in gastric acid secretion and stomach contractions (Takeuchi, 2012, Wallace, 2008, Wallace, 2001, Yano et al., 1978). To prevent NSAID-induced hemorrhages, proton pump inhibitors (PPI) are regularly co-prescribed to reduce gastric acid secretion (Mössner, 2016). Chronic PPI use is also associated with negative side effects including gastric polyps, tumors, infection, vitamin deficiencies, bone fractures, cancer, and dementia (Kuller, 2016, Lodato et al., 2010, Mössner, 2016). The negative side effects of both NSAIDs and PPIs emphasize the need for new gastroprotective therapeutics.

The psychoactive component of Cannabis, i.e., Δ⁹-tetrahydrocannabinol (THC), strongly inhibits NSAID-induced gastric hemorrhages in mice (Kinsey et al., 2011, Kinsey and Cole, 2013). Similarly, synthetic cannabinoid receptor agonists suppress gastric acid secretion, in pentagastrin- and histamine-stimulated animal models via the CB₁ cannabinoid receptor (Adami et al., 2002, Coruzzi et al., 2006, Coruzzi et al., 1999, Pazos et al., 2008). The effects of cannabinoids on gastric ulceration and acid production suggest that the endogenous cannabinoid (endocannabinoid) system modulates gastric physiology. Inhibiting the catabolism of endocannabinoid agonists blocks gastric hemorrhage development (Kinsey et al., 2011, Naidu et al., 2009). For example, inhibiting the catabolic enzyme monoacylglycerol lipase (MAGL) blocks the formation of NSAID-induced ulcers (Ignatowska-Jankowska et al., 2014, Kinsey et al., 2011). Furthermore, the anti-ulcerogenic effects of the MAGL inhibitor, JZL184, occur through CB₁, indicating that endocannabinoids modulate ulcer formation (Kinsey et al., 2011). JZL184 also increases stomach levels of the endocannabinoid 2-arachidonoylglycerol (2-AG) (Kinsey et al., 2011). Thus, the endocannabinoid influences pathogenic effects of NSAID-induced gastric hemorrhages, albeit through unknown mechanisms.

While synthetic cannabinoid receptor agonists decrease gastric acid secretions (Adami et al., 2002, Coruzzi et al., 2006, Coruzzi et al., 1999), it is unknown whether MAGL inhibition, per se, modulates gastric acid output. 2-AG decreases gastric motility through a CB₁ mechanism of action (Aviello et al., 2008). However, cannabinoids have not been evaluated in the context of altered gastric motility following NSAID exposure. Therefore, the primary goal of this study was to evaluate the role of MAGL inhibition on gastric acid production and gastric motility. The present study also evaluated myeloperoxidase (MPO) as a potential biomarker for gastric hemorrhage severity. After initial damage, epithelial cells recruit and activate white blood cells, including neutrophils (Wallace, 2008, Wallace et al., 1990). MPO is an enzyme that is expressed within circulating neutrophils and is commonly used to indirectly quantify neutrophil activity in tissue (Liu et al., 1998, Loria et al., 2008). Thus, MPO level for each mouse was correlated with an established visual measure of hemorrhage severity.

Finally, published reports of cannabinoid modulation of gastric pathology have used only male animals. Sex differences have been noted in multiple cannabinoid studies (Craft, 2005, Craft et al., 2013a, Craft et al., 2013b). Thus, a goal of the present study was to establish the NSAID-induced gastric hemorrhage model, as well as its attenuation by MAGL inhibition, in female mice. The ultimate goal of this research is to improve the lives of patients taking NSAIDs by informing the development of new, cannabinoid-based gastroprotective therapeutics.