Benzo pyrene hepatic microsomal

Little PJ, MO James, JB Pritchard, JR Bend (1984) Benzo(a)pyrene metabolism in hepatic microsomes from feral and 3-methylcholanthrene-treated southern flounder, Paralichthys lethostigma. J Environ Pathol Toxicol Oncol 5 309-320. 

Enzymes of the hepatic microsomes of most marine organisms, with the notable exception of certain molluscs, metabolize xeno-biotic substrates however, as much as 600-fold variations in enzyme activities have been noted between different species of marine teleosts (40). The hepatic enzyme activities of aquatic species are generally lower, with most substrates tested, than the hepatic enzymes of mammals (40). The mixed function oxidase enzymes in marine organisms are inducible by hydrocarbons, such as 3-methylcholanthrene or benzo[a]pyrene. Moreover, it is known... 

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. 

Several properties of hepatic microsomal AHH activity were compared in control and DBA-pretreated male little skates as shown in Table I. Following treatment there was an approximately 35-fold increase in specific enzyme activity, as quantitated by fluorescence of the phenolic metabolites formed (3, 21). The pH optimum, which was fairly broad, and the concentration of benzo(a)-pyrene (0.06 mM) that had to be added to the incubation mixture to achieve maximum enzyme activity were the same for both control and induced skate hepatic microsomes. The shorter periods observed for linearity of product formation with microsomes from the induced skates is thought to be related to the much higher AHH activity present, and may be due to substrate depletion or the formation of products which are inhibitory (i.e., compete with the MFO system as they are substrates themselves). A similar explanation may be relevant for the loss of linear product formation at lower microsomal protein concentrations in the induced animals. 

The apparent kinetic constants were obtained from Lineweaver-Burk plots of AHH activities recorded in the presence of increasing concentrations of benzo(a)pyrene (0.001-1.0 mM). The plots were linear for both untreated and DBA-induced animals. The apparent V was 20- to 30-fold higher in hepatic microsomes from the induced skates whereas the apparent K values were of the same magnitude in control and treated fish. 

Bend, J. R., Hall, P., and Foureman, G. L. Comparison of benzo(a)pyrene hydroxylase (aryl hydrocarbon hydroxylase, AHH) activities in hepatic microsomes from untreated and 1,2,3,4-dibenzanthracene (DBA)-induced little skate (Raja erinacea). Bull. Mt. Desert Island Biol. Lab. (1976) 16. 3-5. 

The induction of carboxylesterase activity has also been observed in animals exposed to PAHs (Nousiainen et al. 1984). Benzo[a]pyrene, benz[a]anthracene, and chrysene were moderate inducers of hepatic carboxylesterase activity in rats that were intragastrically administered 50,100, and 150 mg/kg/day (100 mg/kg/day for chrysene), respectively, for 4 days. However, rats administered 100 mg/kg/day anthracene or phenanthrene did not exhibit induction of hepatic carboxylesterase activity. Induction of hepatic microsomal enzymes generally results in enhanced biotransformation of other xenobiotics (to either more or less toxic forms). 

Hepatic microsomes from rats induced with 3-methylcholanthrene convert benzo[a]pyrene to benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE) 10 times faster than untreated microsomes. The rate-limiting step in BPDE formation is the competition for P-450 between benzo[a]pyrene and the... 

Govindwar SP, Kachole MS, Pawar SS. 1988. Effect of caffeine on the hepatic microsomal mixed function oxidase system during phenobarbital and benzo[a]pyrene treatment in rats. Toxicol Lett 42(2) 109-115. 

Hall M. Grover PL. 1987. Differential stereoselectivity in the metabolism of benzo(a)pyrene and anthracene by rabbit epidermal and hepatic microsomes. Cancer Lett 38 57-64. 

Rats were dosed with soil suspensions, by gavage, either once or for four consecutive days. Total TCDD dosages administered to rats were either 10 ug TCDD/kg or 40 ug/ TCDD/kg. Rats were sacrificed 24 hours after the final dose, autopsied, and hepatic microsomal fractions were collected. Aryl hydrocarbon hydroxylase (AHH) levels were determined in the microsomes, using the fluorescent assay of the product of the metabolism of benzo(a)pyrene to 3-OH benzo(a)pyrene (16). 

Figure 9.1. Sex-differences in rat hepatic microsomal drug metabolism. Data shown are based on enzyme assays in rat liver microsomes using the three indicated xenobiotic substrates ethylmorphine (EM), benzo[o] pyrene (BP), and hexobarbital (HB). Ethylmorphine A -demethylase and benzo[a]pyrene hydroxylase activities are expressed as nmol product formed per minute per mg microsomal protein, whereas hexobarbital hydroxylase activity is expressed as nmol product formed per 30 min per g liver. Also shown is hepatic microsomal total cytochrome P450 content, which is expressed as nmol per mg microsomal protein (values multiplied by 10). The data are shown as mean SD for 4 or 5 rats, except for ethylmorphine W-demethylase and total P450 which are based on a pool of 6 livers.

Chae, Y.H. et al.. Effects of synthetic and naturally occurring flavonoids on benzo[a]pyrene metabolism by hepatic microsomes prepared from rats heated with cytochrome P-450 inducers. Cancer Lett., 60, 15, 1991. 

James MO, Khan MAQ, Bend JR (1979b) Hepatic microsomal mixed-function oxidase activities in several marine species common to coastal Florida. Comp Biochem Physiol 62C 155-164 James MO, Sherman B, Fisher SA, Bend JR (1982) Benzo(a)pyrene metabolism in reconstituted monooxygenase systems containing cytochrome P-450 from lobster Homarus americanus) hepatopancreas fractions and N ADPH-cytochrome P-450 reductase from pig liver. Bull Mt Desert Isl Biol Lab 22 37-39... 

Sediments and biota collected from the Hersey River, Michigan, in 1978, were heavily contaminated with phenanthrene, benz[a]anthracene, and benzo[a]pyrene when compared to a control site. Elevated PAH concentrations were recorded in sediments, whole insect larvae, crayfish muscle, and flesh of lampreys (family Petromyzontidae), brown trout (Salmo trutta), and white suckers (Catostomus commersoni), in that general order (Black et al. 1981). The polluted collection locale was the former site of a creosote wood preservation facility between 1902 and 1949, and, at the time of the study, received Reed City wastewater treatment plant effluent, described as an oily material with a naphthalene-like odor (Black et al. 1981). In San Francisco Bay, elevated PAH concentrations in fish livers reflected elevated sediment PAH concentrations (Stehr et al. 1997). In Chesapeake Bay, spot (Leiostomus xanthurus) collected from a PAH-contaminated tributary (up to 96 mg PAHs/kg DW sediment) had elevated cytochrome P-450 and EROD activity in liver and intestine microsomes (Van Veld et al. 1990). Intestinal P-450 activity was 80 to 100 times higher in fish from highly contaminated sites than in conspecifics from reference sites intestinal EROD activity had a similar trend. Liver P-450 and EROD activity was about 8 times higher in spot from the contaminated sites when compared to the reference sites. Liver P-450 activity correlated positively with sediment PAH, but intestinal P-450 activity seemed to reflect dietary exposure (Van Veld et al. 1990). The poor correlation between hepatic concentrations of PAHs and P-4501A is attributed to the rapid metabolism of these compounds (van der Weiden et al. 1994). 

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... 

Bompart G, Puig P, Pipy B, et al. 1989. In vitro influence of molybdenum on benzo[a]pyrene metabolism in hepatic and pulmonary rat microsomes. J Toxicol Environ Health 26(4) 459-468. 

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