Keizo Sekiya

Selective inhibition of platelet lipoxygenase by baicalein

Abstract The effects of various flavonoids on platelet lipoxygenase and cyclooxygenase activities were studied. Baicalein selectively inhibited platelet lipoxygenase. The concentration for 50% inhibition (ID 50 ) was 0.12 μM for platelet lipoxygenase and 0.83 mM for platelet cyclooxygenase. Therefore, the ID 50 value for the cyclooxygenase was 6917 times that for the lipoxygenase. Baicalin also selectively inhibited the lipoxygenase, but it was less potent (ID 50 =100 μM). Other flavonoids tested had no inhibitory effect on either enzyme.

Flavanone exhibits PPARγ ligand activity and enhances differentiation of 3T3-L1 adipocytes.

Flavanones are class of polyphenolic compounds, some of which are found in foods and provide health benefits. In this study, we show that flavanone significantly enhances differentiation of 3T3-L1 preadipocytes. During adipogenesis, flavanone enhanced expression of genes and accumulation of proteins that are involved in adipocyte function. Some reports have indicated that flavanone inhibits proliferation of mammalian cells, and down-regulates expression of growth-related proteins. Such proteins include phosphorylated ERK1/2, cyclins, and Cdks that are important for an early event in adipogenesis, mitotic clonal expansion (MCE). We demonstrated that flavanone did not inhibit MCE or expression of MCE-related proteins, except for a modest inhibition of cyclin D1 expression. Using luciferase reporter assays, we found that flavanone acted as a peroxisome proliferator-activated receptor gamma (PPARgamma) ligand in a dose-dependent manner. Together, our results suggest that flavanone enhances adipogenesis, at least in part, through its PPARgamma ligand activity.

A fraction of unripe kiwi fruit extract regulates adipocyte differentiation and function in 3T3-L1 cells

Adipocyte dysfunction is strongly associated with the development of insulin resistance and diabetes, and regulation of adipogenesis is important in prevention of diabetes. We prepared a 100% methanol fraction of methanolic extract from unripe kiwi fruit (Actinidia deliciosa), designated KMF (kiwi fruit methanol fraction). When applied to 3T3‐L1 preadipocyte cells, KMF promoted adipocyte differentiation, increased glycerol‐3‐phosphate dehydrogenase (GPDH) activity, and increased triglyceride (TG) content. KMF markedly increased mRNA expression of peroxisome proliferator‐activated receptor γ (PPARγ)—the master adipogenic transcription factor—and its target genes. Moreover, KMF increased mRNA expression and protein secretion of adiponectin, whereas mRNA expression and secretion of monocyte chemoattractant protein‐1 (MCP‐1) and interleukin‐6 (IL‐6) were decreased. Compared with troglitazone, KMF decreased the production of reactive oxygen species (ROS) and nuclear factor‐kappaB (NFκB) activation. Glucose uptake was stimulated by KMF in differentiated 3T3‐L1 adipocytes. Taken together, these results indicate that KMF may exert beneficial effects against diabetes via its ability to regulate adipocyte differentiation and function.

Inhibitory action of soluble elastin on thromboxane B2 formation in blood platelets

Soluble elastin, prepared from insoluble elastin by treatment with oxalic acid or elastase, was found to inhibit the formation of thromboxane B2 both from [1-14C]arachidonic acid added to washed platelets and from [1-14C]arachidonic acid in prelabeled platelets on stimulation with thrombin. In both systems, the formation of 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) was accelerated. Oxalic acid-treated soluble elastin at 1 and 10 mg/ml inhibited the formation of thromboxane B2 from exogenously supplied arachidonic acid 21 and 59%, respectively, and the formation of thromboxane B2 in prelabeled platelets stimulated by thrombin 44 and 94%, respectively. These concentrations of elastin increased the formation of 12-HETE from exogenously supplied arachidonic acid about 3.4- and 7.3-times, respectively. Almost all the added arachidonic acid was converted to metabolites. In prelabeled platelets, soluble elastin at 1 and 10 mg/ml increased the formation of 12-HETE stimulated by thrombin about 1.3- and 2.8-times, respectively, and inhibited the thrombin-induced total productions of thromboxane B2 (12-hydroxy-5,8,10-heptadecatrienoic acid (12-HETE) and free arachidonic acid by 26 and 25%, respectively. Elastase-treated digested elastin also inhibited the formation of thromboxane B2 and stimulated the formation of 12-HETE in prelabeled platelets stimulated by thrombin. This inhibitory action of elastin was not replaced by desmosine. The level of cAMP in platelets was not affected by soluble elastin. Soluble elastin was also found to inhibit platelet aggregation induced by thrombin. However, the inhibitory action of soluble elastin on platelet aggregation cannot be explained by inhibition of thromboxane B2 formation by the elastin.

Lipolytic activities of p-aminophenol and n-decylamine in endogenous lipid droplets from rat adipocytes

Lipolytic agents such as adrenaline (epinephrine), dibutyryl cyclic AMP (DBcAMP) and theophylline possess common structural characteristics, the existence of a positive charge and a hydrophobic area. p-Aminophenol, which has the same structural characteristics, was found to induce lipolysis in the endogenous lipid droplets from rat adipocytes. It was demonstrated that the positive group and the hydrophobic area of p-aminophenol are essential requirements for its lipolytic activity. Among various amine derivatives, only n-decylamine was found to induce lipolysis in the endogenous lipid droplets. Although the lipolytic action of n-decylamine is fairly low, it possesses remarkable inhibitory effects on both adrenaline- and DBcAMP-induced lipolytic activities. Furthermore, n-decylamine is found to inhibit competitively the DBcAMP-induced lipolysis.