Jun Ogawa

A Gut Microbial Metabolite of Linoleic Acid, 10-Hydroxy-cis-12-octadecenoic Acid, Ameliorates Intestinal Epithelial Barrier Impairment Partially via GPR40-MEK-ERK Pathway

Background: The physiological activity of gut microbial metabolites has recently attracted much attention. Results: A gut microbial metabolite of linoleic acid, 10-hydroxy-cis-12-octadecenoic acid (HYA), ameliorates intestinal epithelial barrier impairments by regulating TNFR2 expression via the GPR40-MEK-ERK pathway. Conclusion: HYA-induced GPR40 signaling contributes to the intestinal homeostasis. Significance: Our findings indicate a novel function of GPR40 in the inflamed intestine. Gut microbial metabolites of polyunsaturated fatty acids have attracted much attention because of their various physiological properties. Dysfunction of tight junction (TJ) in the intestine contributes to the pathogenesis of many disorders such as inflammatory bowel disease. We evaluated the effects of five novel gut microbial metabolites on tumor necrosis factor (TNF)-α-induced barrier impairment in Caco-2 cells and dextran sulfate sodium-induced colitis in mice. 10-Hydroxy-cis-12-octadecenoic acid (HYA), a gut microbial metabolite of linoleic acid, suppressed TNF-α and dextran sulfate sodium-induced changes in the expression of TJ-related molecules, occludin, zonula occludens-1, and myosin light chain kinase. HYA also suppressed the expression of TNF receptor 2 (TNFR2) mRNA and protein expression in Caco-2 cells and colonic tissue. In addition, HYA suppressed the protein expression of TNFR2 in murine intestinal epithelial cells. Furthermore, HYA significantly up-regulated G protein-coupled receptor (GPR) 40 expression in Caco-2 cells. It also induced [Ca2+]i responses in HEK293 cells expressing human GPR40 with higher sensitivity than linoleic acid, its metabolic precursor. The barrier-recovering effects of HYA were abrogated by a GPR40 antagonist and MEK inhibitor in Caco-2 cells. Conversely, 10-hydroxyoctadacanoic acid, which is a gut microbial metabolite of oleic acid and lacks a carbon-carbon double bond at Δ12 position, did not show these TJ-restoring activities and down-regulated GPR40 expression. Therefore, HYA modulates TNFR2 expression, at least partially, via the GPR40-MEK-ERK pathway and may be useful in the treatment of TJ-related disorders such as inflammatory bowel disease.

CHAPTER 5:Recent Advances in the Production of CLA and Conjugated Vegetable Oils: Microbial and Enzymatic Production of Conjugated Fatty Acids and Related Fatty Acids in Biohydrogenation Metabolism

Lactic acid bacteria produced CLA from linoleic acid. The produced CLA comprised a mixture of cis-9, trans-11-octadecadienoic acid (18:2) and trans-9, trans-11-18:2. Using washed cells of Lactobacillus plantarum AKU 1009a as a catalyst, CLA production from linoleic acid reached 40 mg/ml under the optimized conditions. Similar reactions were observed with C18 fatty acids with cis-9, cis-12 non-conjugated diene system such as α-linolenic acid, γ-linolenic acid, and stearidonic acid. Lactic acid bacteria transformed ricinoleic acid (12-hydroxy-cis-9-octadecenoic acid) to CLA. Castor oil, which is rich in the triacylglycerol form of ricinoleic acid, was also found to act as a substrate with the aid of lipase-catalysed triacylglycerol hydrolysis. Clostridium bifermentans saturated C20 PUFAs of arachidonic acid and EPA into corresponding partially saturated fatty acids with conjugated isomers of arachidonic acid and EPA as intermediates, respectively. The conjugated fatty acid synthesis was found to be a part reaction of biohydrogenation and the complex metabolic pathway was revealed. The enzyme system catalysing the biohydrogenation was found to consist of four enzymes, i.e., hydratase, dehydrogenase, isomerase and enone reductase. These enzymes are useful for the production of unique PUFA species, such as hydroxy, oxo, conjugated and partially saturated fatty acids.