High phosphatidylcholine hydroperoxide level in plasma of guinea pigs with low and excess supplementation of ascorbic acid

Graded amounts (0, 50, 500 and 5,000 mg/liter) of ascorbic acid (AsA) were given in drinking water to guinea pigs for 21 days to prepare AsA-deficient, low-AsA, moderate-AsA and excess-AsA animals, and the plasma phospholipid hydroperoxide level and lipid concentration were quantitatively determined to investigate the antioxidant effect of AsA in vivo. Phosphatidylcholine hydroperoxide (PCOOH) was a predominant phospholipid hydroperoxide present in the plasma, and the PCOOH concentration was significantly higher in AsA-deficient, low-AsA and excess-AsA animals (80.4nM, 54.8nM and 42.2nM, respectively) as compared with that in moderate-AsA animals (27.2nM). Hyperlipidemic plasma characterized as high cholesterol and high triacylglycerol concentrations was confirmed in AsA-deficient animals. Molar ratios of plasma AsA and a-tocopherol against 10⁴ moles of phospholipids were significantly lower in AsA-deficient and low-AsA animals (0.6-2.1 and 5.5-8.5, respectively) than in moderate-AsA and excess-AsA animals (14.2-18.0 and 11.2-11.9, respectively). In plasma, a high correlation coefficient (r=0.979) was observed between PCOOH and AsA for which there was optimum AsA level to keep the low PCOOH and such correlation was stronger than that (r=0.558) observed with a-tocopherol. The results indicated that AsA has an important function to control the phospholipid hydroperoxide level in plasma and that moderate supplementation of AsA is required to reveal its optimal antioxidant effect in vivo. The present study also showed that AsA-deficiency especially invites an increase in plasma PCOOH together with a hyperlipidemic state which are risk factors in developing atherogenesis.