Ferrous-iron-induced oxidation in chicken liver slices as measured by hemichrome formation and thiobarbituric acid-reactive substances: effects of dietary vitamin E and beta-carotene.

Hemichrome formation in chicken liver slices was determined by employing a Heme Protein Spectra Analysis Program (HPSAP) on the visible spectrum of the liver tissue. Relative hemichrome formation (RHF) in liver tissue exposed to ferrous iron for 1 h at 37 degrees C could be predicted according to the general catalytic equation RHF = k.[Fe2+]/(Ap + [Fe2+]), with k = 132 +/- 30, where the factor Ap represents the additive antioxidative potential in the liver tissue. RHF in Fe2+ exposed liver slices incubated at 37 degrees C for 1 h correlated significantly with formation of thiobarbituric acid-reactive substances (TBARS) (r = .77, P < .0001). RHF was found to decrease significantly with increasing vitamin E concentration in liver tissue exposed to ferrous iron (1 h, 37 degrees C). However, the influence of beta-carotene on RHF in ferrous-iron exposed liver slices (1 h, 37 degrees C) was less evident, as the concentration of Fe2+ was found to be decisive for whether beta-carotene acted as an antioxidant or a prooxidant under the conditions in question. Results in the liver slice model system regarding the effect of vitamin E and beta-carotene on iron overload were supported in a subsequent in vivo iron injection experiment with chicks. These observations indicate that RHF is a sensitive marker for ferrous-iron-induced oxidative damage in the present tissue slice system.