FREE-RADICALS SCAVENGING ACTION AND ANTI-ENZYME ACTIVITIES OF PROCYANIDINES FROM VITIS-VINIFERA - A MECHANISM FOR THEIR CAPILLARY PROTECTIVE ACTION

The scavenging by procyanidines (polyphenol oligomers from Vitis vinifera seeds, CAS 85594-37-2) of reactive oxygen species (ROS) involved in the onset (HO degrees) and the maintenance of microvascular injury (lipid radicals R degrees, RO degrees, ROO degrees) has been studied in phosphatidylcholine liposomes (PCL), using two different models of free radical generation: a) iron-promoted and b) ultrasound- induced lipid peroxidation. In a) lipid peroxidation was assessed by determination of thiobarbituric acid-reactive substances (TBARS); in b) by determination of conjugated dienes, formation of breakdown carbonyl products (as 2,4-dinitrophenylhydrazones) and loss of native phosphatidylcholine. In the iron-promoted (Fenton-driven) model, procyanidines had a remarkable, close-dependent antilipoperoxidant activity (IC50 = 2.5 mu mol/l), more than one order of magnitude greater than that of the monomeric unit catechin (IC50 = 50 mu mol/l), activity which is due, at least in part, to their metal-chelating properties. In the more specific model b), which discriminates between the initiator (hydroxyl radical from water sonolysis) and the propagator species of lipid peroxidation (the peroxyl radical, from autooxidation of C-centered radicals), procyanidines are highly effective in preventing conjugated diene formation in both the induction (IC50 = 0.1 mu mol/l) and propagation (IC50 = 0.05 mu mol/l) phases (the scavenging effect of a-tocopherol was weaker, with IC50 of 1.5 and 1.25 mu mol/l). In addition, procyanidines at 0.5 mu mol/l markedly delayed tire onset of the breakdown phase (48 h), totally inhibiting during this time the formation of degradation products (the lag-time induced by alpha-tocopherol was only of 24 h at 10 mu mol/l concentration). The HO degrees entrapping capacity of these compounds was further confirmed by UV studies and by electron spin resonance (ESR) spectro-scopy, using DMPO as spin trapper: procyanidines markedly reduce, in a dose-dependent fashion, the signal intensity of the DMPO-OH radical spin adduct (100 % inhibition at 40 mu mol/l). The results of the second part of this study show that procyanidines, in addition to free radical scavening action, strongly and non-competitively, inhibit xanthine oxidase activity, the enzyme which triggers the oxy radical cascade (IC50 = 2.4 umol/l). In addition procyanidines non-competitively inhibit the activities of the proteolytic enzymes collagenase (IC50 = 38 mu mol/l) and elastase (IC50 = 4.24 mu mol/l) and of the glycosidases hyaluronidase and beta-glucuronidase (IC50 = 80 mu mol/l and 1.1 mu mol/l), involved in the tunzover of the main structural components of the extravascular matrix collagen, elastin and hyaluronic acid. All these findings provide a strong molecular basis for the capillary protective action of procyanidines, which is probably a pluricentric mechanism, based on radical quenching and antioxidant effects and on the inhibition of some key enzymes of the microvascular endothtelium and extravascular matrix.