TRPV1 agonist monoacylglycerol increases UCP1 content in brown adipose tissue and suppresses accumulation of visceral fat in mice fed a high-fat and high-sucrose diet.

The administration of such a transient receptor potential vanilloid 1 (TRPV1) agonist as capsaicin, which is a pungent ingredient of red pepper, promotes energy metabolism and suppresses visceral fat accumulation. We have recently identified monoacylglycerols (MGs) having an unsaturated long-chain fatty acid as the novel TRPV1 agonist in foods. We investigated in this present study the effects of dietary MGs on uncoupling protein 1 (UCP1) expression in interscapular brown adipose tissue (IBAT) and on fat accumulation in mice fed with a high-fat, high-sucrose diet. The MG30 diet that substituted 30% of all lipids for MGs (a mixture of 1-oleoylglycerol, 1-linoleoylglycerol and 1-linolenoylglycerol) significantly increased the UCP1 content of IBAT and decreased the weight of epididymal white adipose tissue, and the serum glucose, total cholesterol and free fatty acid levels. The diet containing only 1-oleoylglycerol as MG also increased UCP1 expression in IBAT. MGs that activated TRPV1 also therefore induced the expression of UCP 1 and prevented visceral fat accumulation as well as capsaicin.

Monoacylglycerols activate capsaicin receptor, TRPV1.

Transient receptor potential vanilloid subtype 1 (TRPV1) is known as capsaicin (CAP) receptor and activated by CAP. Activation of TRPV1 by CAP increases energy expenditure and thermogenesis in rodents or human. Therefore, TRPV1 may be target for energy expenditure enhancement and thermogenesis. To search for novel TRPV1 agonist, we screened 19 types of foods by using TRPV1-expressing HEK293 cells. TRPV1 was activated by hexane extract of wheat flour, and its functional compounds were 1-monoacylglycerols containing oleic, linoleic, and alpha-linolenic acids. Their potencies (EC50) were about 50 times larger than that of CAP and their efficacies (maximal response) were about half of that of CAP. TRPV1 was activated by 1-monoacylglycerols (MGs) having C18 and C20 unsaturated and C8-C12 saturated fatty acid (FA). Moreover, 2-MGs having C18 and C20 unsaturated FA acted on TRPV1 with the same potency. On the other hand, no activation of TRPV1 was induced by MGs having C16 and C18 saturated FA, di- or triacylglycerols of C18:1 FA. Pain-relating aversive responses were induced when TRPV1-activating 1-monoacylglycerols (50 mM) was administered subcutaneously into rat hind paw. These effects were inhibited by the co-injection of capsazepine (10 mM) which is a TRPV1 competitive antagonist. These results suggested that these 1-monoacylglycerols activate TRPV1 in vitro and in vivo.