Water Extract from Rice Bran Fermented with Lactobacillus plantarum Hong Inhibits Thromboxane A2 Production Associated Microsomal Enzyme Activity in Human Platelets

Abstract

In this study, we investigated the effect of rice bran water extract fermented with Lactobacillus plantarum Hong (RBLw), on activities of cyclooxygenase-1 (COX-1) and thromboxane A 2 synthase (TXAS), thromboxane A 2 (TXA 2 ) production associated microsomal enzymes and evaluated its the antiplatelet effect. RBLw, containing 13.5 mg of ferulic acid, dose-dependently inhibited ADP-induced platelet aggregation, and inhibited the production of TXA 2 , an aggregation molecule. In addition, RBLw directly inhibited COX-1 activity in a dose-dependent manner, but not TXAS activity in platelet microsomal fraction having cytochrome c reductase (an endoplasmic reticulum marker enzyme) activity and expressing COX-1 (72 kDa) and TXAS (60.5 kDa) proteins. These results suggest that RBLw selectively inhibited the activity of COX-1 rather than TXAS to attenuate TXA 2 production in ADP-activated platelets. Thus, we demonstrate that RBLw might have direct COX-1 antagonistic function for platelet aggregation-mediated diseases, such as thrombosis, myocardial infarction, atherosclerosis, and ischemic cerebrovascular disease.Key Words: Rice bran fermentation, Thromboxane A 2 , Microsomal fraction, Cyclooxygenase-1, Thromboxane A 2 synthase INTRODUCTIONThe aggregation-inducing molecule thromboxane A 2 (TXA 2 ) plays an important role in agonists (eg. collagen, thrombin, ADP)-induced platelet aggregation (Malmsten et al., 1975;Lewis and Watts, 1982;Li et al., 2010), which can cause cardiovascular diseases such as thrombosis, atherosclerosis and myocardial infarction (Schwartz et al., 1990).When diverse agonists such as collagen, thrombin, and ADP activate platelets, membrane phospholipids (i.e. phosphatidylinositol 4,5-bisphosphate) are broken down, and subsequently produce TXA 2 from arachidonic acid (AA). This potently induces platelet activation and vasoconstriction in an autacodial action (Hamberg et al., 1975;Samuelsson et al., 1978;Gresele et al., 1991). Agonists-produced TXA 2 interacts with its receptor in other platelets in an autacoidal reaction, and subsequently increases intracellular free Ca 2+ , a platelet aggregation-inducing molecule, via G αq of G proteincoupled receptor (Jennings, 2009;Cattaneo et al., 1991;Moriyama et al., 1988 -189 -are cyclooxygenase-1 (COX-1) and thromboxane A 2 synthase (TXAS), which are located in microsomes (Carey et al., 1982). COX-1 produces prostaglandin G 2 (PGG 2 ) from substrate AA, TXAS produces TXA 2 from prostaglandin H 2 (PGH 2 ) that is oxidized from PGG 2 by endoperoxidase.Therefore, inhibition of COX-1 or TXAS is very useful to evaluate an antiplatelet effect of any substance or compound.For instance, COX-1 inhibitor aspirin and TXAS inhibitor ozagrel are being used as anti-platelet agents (Patrono, 2001).Rice bran is produced as a by-product in the rice milling process by a method in which the outer layer of the rice grain is removed. Rice bran is known to have various biological effects, including anti-inflammatory, cholesterol-lowering, antioxidant and anti-diabetic activities ...