EFFECT OF DIETARY PHENOLIC-COMPOUNDS ON APOPTOSIS OF HUMAN CULTURED ENDOTHELIAL-CELLS INDUCED BY OXIDIZED LDL

1 Oxidized low density lipoproteins (LDL) are toxic to cultured endoth elial cells. Mildly oxidized LDL, characterized by relatively low leve ls of TEARS and only minor modifications of apoB, were obtained by usi ng 2 experimental model systems of oxidation, namely oxidation by u.v. radiation or ferrylmyoglobin (a two electron oxidation product from t he reaction of metmyoglobin with H2O2). 2 Toxic concentrations of mild ly oxidized LDL induce apoptosis (programmed cell death) of cultured e ndothelial cells, as shown by typical morphological features, by the i n situ TUNEL procedure and by DNA fragmentation revealed on gel electr ophoresis. This apoptosis is calcium-dependent and subsequent to the i ntense and sustained cytosolic [Ca2+](i) peak elicited by oxidized LDL . 3 Five naturally occurring phenolic compounds present in food and be verages were able to prevent, in a concentration-dependent manner, the apoptosis of endothelial cells induced by oxidized LDL. Among the com pounds tested, caffeic acid was the most effective. Under the conditio ns used, the protective effect of caffeic acid (IC50 8.3+/-2.1 mu mol l(-1)) in the prevention of apoptosis induced by oxidized LDL was sign ificantly higher than that of the other compounds tested (IC(50)s were 12.4+/-3.2, 14.1+/-4.1, 20.4+/-4.4 and 72.6+/-9.2 mu mol l(-1) for fe rulic, protocatechuic, ellagic and p-coumaric acids, respectively). 4 The anti-apoptotic effect of caffeic acid results from the addition of two effects, (i) the antioxidant effect which prevents LDL oxidation and subsequent toxicity ('indirect' protective effect); (ii) a 'direct ' cytoprotective effect, acting at the cellular level. 5 Effective con centrations of caffeic acid acted at the cellular level by blocking th e intense and sustained cytosolic [Ca2+](i) rise elicited by oxidized LDL. 6 In conclusion, phenolic acids (caffeic and ferulic acids being the most potent of the compounds tested under the conditions used) exh ibit a potent cytoprotective effect of cultured endothelial cells agai nst oxidized LDL. In addition to antioxidant effect delaying LDL oxida tion, caffeic acid acts as a cytoprotective agent, probably by blockin g the intracellular signalling triggered by oxidized LDL and culminati ng in the sustained calcium rise which is involved in oxidized LDL-ind uced apoptosis.