Polycyclic hydrocarbons, hepatic microsomal

Anderson, R.S., J.E. Doos, and F.L. Rose. 1982. Differential ability of Ambystoma tigrinum hepatic microsomes to produce mutagenic metabolites from polycyclic aromatic hydrocarbons and aromatic amines. Cancer Lett. 16 33-41. 

In general, our studies with cytochrome P-450-dependent metabolism have emphasized the similarity of the hepatic MFO system in marine fish to that found in mammals. Thus, in the little skate (Raja erinaoea), a marine elasmobranch, enzyme activity is localized in the microsomal fraction, requires NADPH and molecular oxygen for maximum activity, and can be inhibited with CO (1, 2). Moreover, when hepatic microsomes from the little skate were solubilized and separated into cytochrome P-450, NADPH-cytochrome P-450 reductase, and lipid fractions, all three fractions were required for maximal MFO activity in the reconstituted system (3). We have also found, as have others, that the administration of polycyclic hydrocarbons (3-methylcholanthrene, 1,2,3,4-dibenzanthracene [DBA]), 2,3,7,8-tetrachlorodibenzo-p-dioxin... 

In this report we compare several properties of hepatic microsomal AHH activity in control and DBA-treated little skates (including metabolic profiles obtained from c-benzo(a)pyrene as elucidated by high pressure liquid chromatography [HPLC]), we describe the partial purification of two different forms of cytochrome P-450 (cytochrome P-448 and cytochrome P-451) from hepatic microsomes of DBA-pretreated little skates and we report polycyclic hydrocarbon-like induction in large numbers of winter flounder assayed in Maine during June, July, and August, which was quite different than data obtained with sheepshead examined in Florida during the same period. 

An obvious difference was also noted between control and induced skate hepaticdnicrosomal AHH activity in the presence of a-naphthoflavone (10 M). This compound, when added in vitro at this or higher concentrations, caused significant stimulation of AHH activity in control animals (about 3-fold) but inhibition (80%) was found in DBA-pretreated skates. Similar results were earlier reported for control and 3-methylcholanthrene-treated rats (23), where it appears that the response is due to differential effects of a-naphthoflavone on hepatic microsomal cytochrome P-450 (stimulated) and cytochrome P-448 (inhibited) (24). Our data suggests that there may be a novel form of cytochrome P-450 synthesized in skate liver in response to polycyclic hydrocarbon administration, even though there was no hypsochromic shift in the carbon monoxide difference spectrum of dithionite reduced hepatic microsomes from DBA-treated skates (relative to hepatic microsomes from control fish). 

The alteration of hemoprotein(s) P-450 subpopulations in the rat may be observed spectrally, because after treatment of rats with polycyclic aromatic hydrocarbons, the Soret maximum of the carbonmonoxyferrocytochrome complex undergoes a hypsochromic shift from 450 to 448nm (50). This blue shift was not seen with rainbow trout hepatic microsomes (29,30). However, this does not preclude the induction of novel hemoproteins P-450 since (a) the induced hemoprotein(s) maty not differ spectrally from the constitutive enzymes and (b) the induced-hemoprotein may account for only a small proportion of total hemoprotein P-450, and hence its contribution to the position of the Soret maximum of carbon monoxide-treated reduced microsomes may be negligible. The latter suggestion is supported by the work of Bend et al. with the little skate. These workers have shown that hepatic microsomes from 1, 2,3,4-dibenzanthracene treated skates did not exhibit a hypsochromic shift when compared to control microsomes, however, partially purified hemoprotein exhibited an absorbance maxima at 448 nm (51). 

Statham, C.N., Elcombe, C.R., Szyjka, S.P. and Lech, J.J. Effect of polycyclic aromatic hydrocarbons on hepatic microsomal enzymes and disposition of methylnaphthalene in rainbow trout in vivo. Xenobiotica. (1978) j3 65-71. 

Hansen, A.R. and Fouts, J.R. Some problems in Michaelis-Menten kinetic analysis of benzpyrene hydroxylase in hepatic microsomes from polycyclic aromatic hydrocarbon-pretreated animals. Chem. Biol. Interactions. (1972) 5 167-182. 

Occasionally, the cytochrome P-450 system converts some chemieals to reactive species with carcinogenic potential (e.g., polycyclic hydrocarbons). The hepatic microsomal cytochrome P-450 system is inducible by many of its substrates. The cytoehrome P-450 of adrenal cortical mitochondria is involved in steroid hydroxylase reactions, and this system contains iron-sulfur (Fc2S2) proteins. 

Epoxide Hydrolase. Epoxide hydrolase (EH) activity has been studied in numerous tissues with many different substrates (71-72). Hepatic microsomal EH has been shown to be induced by polycyclic aromatic hydrocarbons, but is insensitive to cytochrome P-450 type inducers (73). Epoxide hydrolase has been related to the activation of polycyclic aromatic hydrocarbons into reactive carcinogens (70). Epoxide hydrolase activity has been determined... 

Hepatic and extrahepatic CarbE activities have been studied after the exposure of rats to polycyclic aromatic hydrocarbons. In dose- and time-dependent studies, benz(a)anthracene, benzo(a)pyrene, and 3-methylcholanthrene moderately induced the hepatic cytosolic and kidney microsomal CarbEs activities, while anthracene, phenanthrene, and chrysene had... 

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