Enteric Neuropathy Can Be Induced by High Fat Diet In Vivo and Palmitic Acid Exposure In Vitro

Abstract

ObjectiveObese and/or diabetic patients have elevated levels of free fatty acids and increased susceptibility to gastrointestinal symptoms. Since the enteric nervous system is pivotal in regulating gastrointestinal functions alterations or neuropathy in the enteric neurons are suspected to occur in these conditions. Lipid induced intestinal changes, in particular on enteric neurons, were investigated in vitro and in vivo using primary cell culture and a high fat diet (HFD) mouse model.DesignMice were fed normal or HFD for 6 months. Intestines were analyzed for neuronal numbers, remodeling and lipid accumulation. Co-cultures of myenteric neurons, glia and muscle cells from rat small intestine, were treated with palmitic acid (PA) (0 – 10−3 M) and / or oleic acid (OA) (0 – 10−3 M), with or without modulators of intracellular lipid metabolism. Analyses were by immunocyto- and histochemistry.ResultsHFD caused substantial loss of myenteric neurons, leaving submucous neurons unaffected, and intramuscular lipid accumulation in ileum and colon. PA exposure in vitro resulted in neuronal shrinkage, chromatin condensation and a significant and concentration-dependent decrease in neuronal survival; OA exposure was neuroprotective. Carnitine palmitoyltransferase 1 inhibition, L-carnitine- or alpha lipoic acid supplementation all counteracted PA-induced neuronal loss. PA or OA alone both caused a significant and concentration-dependent loss of muscle cells in vitro. Simultaneous exposure of PA and OA promoted survival of muscle cells and increased intramuscular lipid droplet accumulation. PA exposure transformed glia from a stellate to a rounded phenotype but had no effect on their survival.ConclusionsHFD and PA exposure are detrimental to myenteric neurons. Present results indicate excessive palmitoylcarnitine formation and exhausted L-carnitine stores leading to energy depletion, attenuated acetylcholine synthesis and oxidative stress to be main mechanisms behind PA-induced neuronal loss.High PA exposure is suggested to be a factor in causing diabetic neuropathy and gastrointestinal dysregulation.

The enteric nervous system of P2Y13 receptor null mice is resistant against high-fat-diet- and palmitic-acid-induced neuronal loss

“…It is also notable that the P2Y 13 −/− mice fed with ND displayed an even higher number of neurons per millimetre section in colon compared with ND-fed P2Y 13 +/+ littermates. The finding that PA induces loss of myenteric neurons from P2Y 13 +/+ mice in vitro is well in line with previous findings, describing PA-induced loss of cultured myenteric neurons from rat [22]. The current study also shows that cultured myenteric neurons from P2Y 13 −/− mice are resistant to PAinduced loss.…”

“…The study confirmed previous findings on HFD-fed C57BL/6 mice [22], in that HFD induced a significant loss of myenteric neurons in both the ileum and colon in the P2Y 13 +/+ mice. Surprisingly, the P2Y 13 −/− mice showed a remarkable protection against HFD-induced neuronal loss.…”

“…The current study also shows that cultured myenteric neurons from P2Y 13 −/− mice are resistant to PAinduced loss. In rat, the mechanisms behind PA-induced neuronal loss was found to be complex, but excessive palmitoylcarnitine formation and exhausted L-carnitine stores leading to energy depletion, low acetylcholine synthesis and oxidative stress were identified as important events [22]. The present study shows that absence of the P2Y 13 receptor or presence of MRS2211 abolished PA-induced neuronal loss in vitro.…”

“…Gene profiling and phenotypic analysis of P2Y 13 −/− mice confirm that they hold altered lipoprotein, cholesterol and HDL metabolism [20]. HFD has previously been shown to increase lipid droplet accumulation in intestinal muscularis propria in C57BL/6 mice [22]. In contrast, P2Y 13 −/− mice fed with HFD did not accumulate lipid droplets in muscularis propria, which suggestively underlines the possibility of an altered lipid metabolism.…”

“…It was recently shown that feeding mice with high-fat diet (HFD) for 6 months results in a substantial loss of myenteric neurons in both the ileum and colon [22]. The saturated free fatty acid (FFA), palmitic acid (PA), was put forward as a putative mediator of this effect, as PA exposure in vitro caused substantial neuronal loss.…”