Trichloromethyl proteins

Methods for Determining Biomarkers of Exposure and Effect. Covalent adducts between reactive carbon tetrachloride metabolites (e.g., the trichloromethyl radical) and cellular proteins, lipids and nucleic acids are known to occur, but at present these can only be measured using radiolabeled carbon tetrachloride. Development of immunological or other methods to detect such adducts in humans exposed to carbon tetrachloride could be of value in estimating past exposures to carbon tetrachloride. 

Carbon tetrachloride causes centrilobular liver necrosis and steatosis after acute exposure, and liver cirrhosis, liver tumors, and kidney damage after chronic administration. The mechanism underlying the acute toxicity to the liver involves metabolic activation by cytochrome P-450 to yield a free radical (trichloromethyl free radical). This reacts with unsaturated fatty acids in the membranes of organelles and leads to toxic products of lipid peroxidation including malondialdehyde and hydroxynonenal. This results in hepatocyte necrosis and inhibition of various metabolic processes including protein synthesis. The latter leads to steatosis as a result of inhibition of the synthesis of lipoproteins required for triglyceride export. 

Carbon tetrachloride is metabolized by cytochrome P-450 to the reactive metabolites trichloromethyl free radical and trichloromethylperoxy free radical. The trichloromethyl free radical may bind directly to cellular macromolecules such as lipids and proteins, and also to DNA, disrupting cell processes and breaking down membranes. The free radical can take part in anaerobic reactions, subsequently forming such toxic compounds as chloroform, hexachloroethane, and carbon monoxide. Aerobic biotransformation of the... 

FIGURE 7.6 The microsomal enzyme mediated metabolic activation of carbon tetrachloride to the trichloromethyl radical. This radical may either react with oxygen or abstract a hydrogen atom from a suitable donor (R) to yield a secondary radical, or react covalently with lipid or protein. If R is a polyunsaturated lipid, (R) a lipid radical (R.) is formed which can undergo peroxidation (see figure 6.9). 

Cellular disruption leading to hepatocellular necrosis results from damage to cellular macromolecules by trichloromethyl radicals. Cellular disruption involves alteration of calcium homeostasis, " impaired oxidative phosphorylation, and trichloromethyl radical binding to cellular proteins, nucleic acids, and induction of lipid peroxidation. Histologically there is preferential necrosis of zone three hepatocytes in the liver acinus so called centrizonal necrosis as well as zone three steatosis. 

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