Effect of select antioxidants on malondialdehyde modification of proteins.

To determine whether commonly used antioxidants alter malondialdehyde (MDA) modification of proteins, a known mechanism of free radical-related tissue injury, we studied the effect of adding 1 mg/mL of pycnogenol, 5 mM of alpha-tocopherol, 5 mM of ascorbate, and 0.2 mg/mL of an ethanol equivalent of red and white wine on MDA-protein content of endothelial cells in culture. The addition of pycnogenol but not of the other antioxidants was associated with significant reduction in MDA-protein content compared with controls (0.521 +/- 0.041 in arbritrary units versus 1.011 +/- 0.021, P < 0. 001). To determine whether the observed effect occurs distal to MDA generation, the effect of these antioxidants on the modification of bovine serum albumin with MDA generated in a cell-free system was studied. In this cell-free assay, pycnogenol but not the other antioxidants reduced MDA-BSA generation by approximately 50%. It is concluded that pycnogenol may reduce MDA modification of proteins at a step distal to MDA generation. This may be an additional mechanism of protective effects of pycnogenol against oxidative stress.