Hepatorenal syndrome

An increased consumption of fruit and vegetables has been associated with beneficial effects on the risk of disease. Citrus juices, especially orange juice and grapefruit juice, are rich sources of vitamin C. Recent reports suggest that drinking generous amounts of a mixture of juices improved the blood lipid profile, reduced oxidative stress, prevented atherogenic modifications of LDL cholesterol and platelet aggregation and improved HDL-cholesterol levels. However, no study has examined the bioavailability of vitamin C in orange juice and its possible beneficial effects on reducing isoprostane levels.

Isoprostanes are a family of eicosanoids of nonenzymatic origin that are produced by the random oxidation of phospholipids by oxygen radicals and that are elevated by oxidative stress. One of the isoprostanes, 8-epiprostaglandin F2 (8-epi-PG[F.sub.2[alpha]]) has been shown to act as a vasoconstrictor and are associated with the hepatorenal syndrome and pulmonary oxygen toxicity. Previous studies have showed decreased concentration of antioxidants and high concentrations of 8-isoprostanes among smokers, which may be due to a low level of antioxidants or a greater utilization of vitamin C by free radicals produced during smoking. Therefore, a recent study published in the American Journal of Clinical Nutrition assessed the bioavailability of vitamin C in orange juice and its effect on concentrations of 8-epi-PG[F.sub.2[alpha]] (F2-isoprostanes) in a healthy human population.

Six men and six women were enrolled in this study. The vitamin C bioavailability study was divided into two components, a dose-response test and a multiple-dose-response study. The subjects consumed 500 mL commercial fresh-squeezed orange juice per day for 14 days, corresponding to an intake of 250 mg ascorbic acid/day. On the first day of the study, the subjects drank the juice in one dose (dose-response study) and on days two and 14 they consumed 250 mL in the morning and 250 mL in the afternoon. Blood was collected every hour for six hours on the first day and again on days seven and 14. Dietary history data were obtained through a food-frequency questionnaire.

Baseline plasma vitamin C levels were significantly higher in the women than in the men. In the dose-response study, the maximum increase in plasma vitamin C occurred three hours postdose in all of the subjects. Vitamin C concentrations remained significantly higher on days seven and 14 than at baseline. Baseline concentrations of 8-epi-PG[F.sub.2[alpha]] were significantly higher among the men than the women, but decreased significantly by day 14 of the intervention. A significant inverse correlation was observed between vitamin C and 8-epi-PG[F.sub.2[alpha]] at baseline and on day 14 of the study. Among smokers, baseline vitamin C was lower, and 8-epi-PG[F.sub.2[alpha]] higher than among non-smokers.

The results showed that drinking two glasses of orange juice daily increases plasma vitamin C levels by 40% to 64%. Interestingly, changes in vitamin C levels were significantly and inversely correlated, with concentrations of 8-epi-PG[F.sub.2[alpha]] suggesting that vitamin C may play a critical role in reducing the formation of compounds produced by the random oxidation of phospholipids by oxygen radicals. These effects were accentuated among smokers than among non-smokers. This suggests that the protective effects of vitamin C is greater in persons with higher stress and that higher concentrations of vitamin C in tissues can be gained by drinking orange juice daily. Further research on the health-promoting properties of vitamin C in fruit is necessary.

Concepcion Sanchez-Moreno, Pilar Cano, Begona de Ancos, et al., Effect of Orange Juice Intake on Vitamin C Concentrations and Biomarkers of Antioxidant Status in Humans, Am J Clin Nutr 78: 454-460 (September 2003). [Address reprint requests to A Martin, Nutrition and Neurocognitive Laboratory, Jean Mayer USDA-HNRC on Aging At Tufts University, 711 Washington Street, 7th Floor, Boston, MA 02111. E-mail: antonio.martin@tufts.edu]

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