PRO-THROMBOTIC EFFECTS OF A FOLIC-ACID DEFICIENT DIET IN RAT PLATELETS AND MACROPHAGES RELATED TO ELEVATED HOMOCYSTEINE AND DECREASED N-3 POLYUNSATURATED FATTY-ACIDS

Folic acid deficiency represents a Vitamin deficiency that may be due either to an inadequacy of the dietary supply or to an increased requi rement. It leads to a number of abnormalities including hematological, neurological and cardiovascular disorders. In this study, we investig ated whether folic acid deficiency would influence platelet and macrop hage activities. For 6 weeks, rats were fed a test diet containing a l ow amount of folic acid (250 mu g/kg) by comparison with a control die t (750 mu g/kg). We found 40 and 32% reductions (P < 0.05) of plasma a nd erythrocyte folates, respectively in the tested group. Peritoneal m acrophages of the folic acid deficient animals exhibited greater (20x) tissue factor (TF) activity than in the controls. We also found that folate depletion significantly enhanced the thrombin- and ADP-induced platelet aggregation (+64 and +13%, respectively). (1)Moreover, the re sults of incubations with radiolabeled arachidonic acid indicated that platelets of folic acid deficient animals incorporated more labeling than controls did. When stimulated with thrombin, the mobilization of arachidonate from platelet phospholipids and its subsequent formation of cyclooxygenase and lipoxygenase metabolites were enhanced in the de ficient animals. In particular, thromboxane biosynthesis was markedly increased. The analysis of the plasma fatty acid composition showed a decrease in the plasma unsaturation index related to a marked fall of long chain (n-3) fatty acids which was also observed in platelets. The se data suggested the occurrence of an oxidative stress in folic acid deficient animals which was confirmed by increases in plasma lipid per oxidation products (more than +20%) and an. enhanced susceptibility of erythrocytes to free radicals (+23%). Altogether these data suggested that folic acid deficiency altered the circulating and cellular fatty acid composition and thus influenced the balance of the platelet eico sanoid synthesis. In addition, total homocysteine and glutathione conc entrations were highly increased in plasma from folate-depleted rats. From these results, we conclude that folate deficiency can potentiate the coagulation pathway mediated by the macrophage TF as well as the p latelet activation process. It is suggested that these dysfunctions mi ght be related to the loss of (n-3) polyunsaturated fatty acids. The l atter could result from an increased lipid peroxidation triggered by t he folic acid deficiency-induced hyperhomocysteinemia.