Colonic Dysmotility Associated With High Fat Diet-Induced Obesity: Involvement of Endogenous Adenosine via a2B Receptors

Introduction. Increasing evidence points out an active role of adenosine in altered tissue functions associated with diabetes and obesity via A2B receptors (A2BR). However, the contribution of adenosine to enteric dysmotility associated with obesity has not been investigated. This study examines the involvement of A2BR in the alterations of colonic neuromuscular functions in a mouse model of diet-induced obesity (DIO). Methods. C57BL/6 male mice (age 6 weeks) were fed with regular diet (RD; 9% calories from fat) or high fat diet (HFD; 60% calories from fat) for 8 weeks to obtain a murine model of DIO. Body weight, blood fasting total cholesterol, triglycerides and glucose levels, as well as fecal pellet frequency and stool water content, were evaluated the day before sacrifice. Then, epididymal fat weight and colonic malondialdehyde (MDA) concentration were assessed. The expression and localization of A2BR and the neuronal marker HuC/D were assessed by immunofluorescence. Colonic longitudinal muscle strips (LMS) were set up in organ baths with Krebs solution containing guanethidine and connected to isometric transducers. The effects of MRS-1754 (MRS, 0.01 µM; A2BR antagonist) were assayed on contractile responses evoked by electrical stimulation (ES; 0.5 ms, 28 V, 10 Hz), carbachol or SP (1 µM in the presence of tetrodotoxin). Results. DIO mice displayed altered blood metabolic indices, increments of body weight, epididymal fat weight and colonic MDA levels, as well as reduced fecal pellet frequency and decreased stool water content, as compared with RD mice (Table 1). In DIO mice, the colonic distribution of A2BR immunoreactivity was significantly increased in myenteric HuC/ D + neurons. MRS did not affect ES-induced contractions in LMS from RD mice, while it enhanced the electrically evoked responses in colonic preparations from DIO mice (+32.1±3.5%). This enhancing effect was not affected upon blockade of nitrergic pathways with the NO synthase inhibitor L-Nw -nitroarginine methyl ester (L-NAME) [+35.6±2.8%]. By contrast, the enhancing effect of MRS was no longer observed on ES-induced cholinergic contractions evoked in the presence of L-NAME, L-732.138, GR159897 and SB218795 (NK1 , NK2 and NK3 receptor antagonists, respectively). Under ES-induced NK1 -mediated tachykininergic contractions (incubation with atropine, L-NAME, NK2 and NK3 antagonists), the increasing motor effect of MRS was still evident (+27.6±5.7%). MRS did not affect contractions elicited by carbachol or exogenous SP. Conclusions. In the model of HFDinduced obesity, metabolic alterations are associated with colonic oxidative stress and motor dysfunctions. In this setting, endogenous adenosine takes part to a significant inhibitory control on NK1 -mediated tachykininergic colonic contractions, which is likely mediated by an increased expression of A2BR at level of myenteric neurons. Effects of regular diet (RD) and high fat diet (HFD) on body weight gain, blood metabolic indices, fecal pellet frequency, stool water content and colonic oxidative stress [malondialdehyde (MDA)].