N-Acylphosphatidylethanolamines as Novel Regulators of Gastrointestinal Motility in the Mouse

Abstract

Background: N-acylethanolamines (NAEs) are long chain fatty acid ethanolamides which are present in almost all mammalian tissues including the gastrointestinal (GI) tract. NAEs are synthesized from the hydrolysis of phospholipid precursors N-acylphosphatidylethanolamines (NAPEs) by N-acylphosphatidylethanolamine-hydrolyzing phospholipase D (NAPEPLD). Despite their abundance, the physiologic roles of C16:0 and C18:1 NAPEs in the GI tract are not known. They may induce their effects directly or by conversion to Npalmitoylethanolamine (C16:0) or N-oleoylethanolamine (C18:1). We examined whether i) C16:0 or C18:1 NAPE regulates GI motility in the mouse, and ii) if these effects are through the endocannabinoid system involving NAPE-PLD and the cannabinoid 1 (CB1) receptor. Methods: Wild type, NAPE-PLD -/or CB1-/mice were used. The effects of C16:0 and C18:1 NAPEs on contractility of the intestine to electrical field stimulation (EFS; 4Hz, 60 Volts) and bethanechol (10μM) were studied in an organ bath In Vitro. Whole gut transit of an Evans blue marker after treatment with NAPEs (1-10 mg/kg i.p.) was studied In Vivo. NAPE-PLD mRNA expression after treatment with NAPEs was measured by real-time PCR. Results: C16:0 NAPE (up to 10 μM) reduced EFS induced contractions by ~ 41% in the ileum and ~ 44% in the colon of wild type mice. C18:1 NAPE had no effect in either region of the intestine. AM251 (100nM), a CB1 antagonist, blocked the effect of C16:0 NAPE on EFS contractility in the ileum but not the colon. Organ bath experiments on CB1-/mice confirmed these findings, as C16:0 NAPE did not have any effect in the ileum of those mice; however, it was still active in the colon. In NAPE-PLD -/mice, the effect of C16:0 NAPE was completely abolished in the ileum but not the colon (~42% inhibition at 10 μM). C16:0 or C18:1 NAPE had no effect on contractions induced by bethanechol. C16:0 NAPE dose-dependently increased whole gut transit time with ~100% increase at 10 mg/kg compared to the vehicle treated mice. AM251 blocked this effect. C18:1 NAPE had no effect on whole gut transit up to 10mg/kg. C16:0 or C18:1 NAPE (50 mg/kg i.p.) did not change NAPE-PLD mRNA expression in either ileum or colon of wild type mice. Conclusion: C16:0 but not C18:1 NAPE modulates GI motility. This effect requires the conversion of the NAPEs to a CB1 receptor ligand by NAPE-PLD in the ileum, but it involves other pathways in the colon. This study suggests some NAPEs may have a role as physiologic regulators of GI motility.