Cytochrome P450 in the liver mitochondrial outer membrane of 20-methyl cholanthrene or Aroclor treated rabbits

Polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs): biochemistry, toxicology, and mechanism of action

Polychlorinated and polybrominated biphenyls are industrial chemical mixtures which have been implicated in numerous human poisonings in Taiwan and Japan (PCBs) and Michigan (PBBs). Moreover, these polyhalogenated biphenyls have been widely detected in the environment including the air, water, fish, wildlife, human adipose tissue, and blood and breast milk. A major problem associated with the analysis and toxicology of this group of chemicals is their chemical complexity (e.g., there are 209 possible PCB isomers and congeners) and the remarkable effects of structure on activity. This article will discuss the effects of structure on the biologic and toxic effects of individual PCB and PBB congeners as well as reconstituted mixtures. The results clearly show that like "dioxin" (or 2,3,7,8-TCDD), the PCBs and PBBs elicit their effects through a cytosolic receptor protein which preferentially binds with the toxins which are approximate isostereomers of 2,3,7,8-TCDD. The evidence for this mechanism of action will be discussed in detail.

Epoxide hydrolase activity in the mitochondrial fraction of mouse liver

The intense interest in the metabolic fate of epoxidized xenobiotics is due to several factors. For instance, epoxides are often intermediates in the lipophile to hydrophile conversions necessary for the excretion of olefinic and aromatic compounds by living systems, and are widely encountered in man's diet from both natural and man-made sources. Some of these epoxidized compounds may alkylate proteins and nucleic acids and thus include some of the most potent cytotoxins, mutagens and carcinogens known. In mammals, epoxides may rearrange, deoxygenate to olefins, react with glutathione to form conjugates, or be hydrolysed by water to yield 1,2-diols with or without enzymatic catalysis. The enzymes which catalyse the formation of diols are known as epoxide hydrolases (EC 3.3.2.3), and their subcellular distribution is the subject of this report. Early data showed that styrene oxide hydrolase activity was associate with the microsomal subcellular fraction. Epoxide hydrolase activity was subsequently demonstrated on the nuclear, Golgi apparatus and plasma membranes, and in the cytosol of the cell, leaving the mitochondria as the last major cellular organelle assumed to be devoid of epoxide hydrolase activity. We now report strong evidence for the occurrence of substantial epoxide hydrolase activity in the mitochondria.

Covalent binding of polycyclic aromatic compounds to mitochondrial and nuclear DNA

Since the pioneering work of the Millers it has become clear that most chemical carcinogens require metabolism to reactive electrophiles and then exhibit their carcinogenic potential by reacting chemically with, and modifying, cellular macromolecules. At first modification of proteins was considered most likely to be of importance in carcinogenesis. Later, Brookes and Lawley demonstrated that the extent of binding of several polycyclic hydrocarbons to DNA, but not to RNA or protein isolated from the skin of mice treated topically with these compounds, correlated with their known carcinogenic potency to this tissue. Mammalian cells, particularly mouse embryo cells, treated with chemical carcinogens have often been used, and DNA has been involved almost exclusively from whole cells. However, mitochondria possess unique DNA which accounts for 0.1-1% of the total DNA present in mammalian cells, and three studies have shown that carcinogenic alkylating agents modify the michondrial DNA by a factor about five times greater than the nuclear DNA from the same cells. We demonstrate here that with six polycyclic aromatic compounds, all of which require metabolic activation and bind to DNA to a much smaller extent than direct than direct-acting alkylating agents, the binding to mitochondrial relative to DNA is dramatically increased by a factor of nearly 50 to over 500.