Lipoperoxidation of Rat Liver Microsomal Lipids induced by Carbon Tetrachloride

Abstract

IT has been known for 17 years¹ that d-α-tocopherol can protect rats from the lethal effects of carbon tetrachloride. Anti-oxidant protection implies that the reaction of the liver to the toxin involves destructive lipoperoxidation. Under certain circumstances, lipoperoxidation can be detected by following the evolution of malonaldehyde by means of the thiobarbituric acid (TBA) reaction. We have monitored malonaldehyde evolution in in vitro experiments utilizing the microsome-supernatant fraction of rat liver, and have found that carbon tetrachloride can act as a pro-oxidant in this system. Diethyl ether and heptane were inert. These in vitro findings support the hypothesis that the hepatotoxic chloroalkanes have as one of their vectors of toxicity the initiation of destructive lipoperoxidation. If carbon tetrachloride acts similarly in vivo, it should be possible to find supportive evidence. We have found that malonaldehyde is readily metabolized by rat liver mitochondria, hence the TBA reaction cannot be used as a tool in the search for evidence of lipoperoxidation in vivo. However, the appearance of malonaldehyde is only one index of destructive lipoperoxidation. It has been known for 20 years, from the work of Bolland and Koch², that during the course of autoxidation of ethyl linoleate there occurs a rearrangement of double bonds into diene conjugation. The spectra of normal conjugated dienes, that is, molecules such as butadiene, are characterized by a very intense absorption, the so-called K-band³, at 215 to 250 mµ. (ref. 4). The spectra of peroxidized lipids are characterized by an intense K-band at 233 mµ, with a shoulder, due to ketone dienes, in the region from 260 to 280 mµ (ref. 2). The appearance of diene conjugation in peroxidized, unsaturated fatty acids, or their derivatives, is due to resonance following free radical attack on methylene bridges separating the double bonds in these compounds⁵. It should be borne in mind that microsomal lipid is largely phospholipid.