Effect of benzo(a)pyrene exposure on fluoranthene metabolism by mouse adipose tissue microsomes.

The present study has been undertaken to examine whether exposure to benzo(a)pyrene (BaP), a polycyclic aromatic hydrocarbon (PAH) compound, influences the metabolism of fluoranthene (FLA), another PAH compound. Microsomes were isolated from the adipose tissue of mice that received 50 microg/kg BaP and incubated with FLA (3 microM) alone; FLA in combination with BaP at equimolar concentrations, and a control group that received nothing. Post-incubation, samples were extracted with ethyl acetate and analyzed for FLA metabolites by reverse-phase HPLC with fluorescence detection. The rate of FLA metabolism (pmol of metabolite/min/mg protein) was increased when microsomes from BaP-treated mice were exposed to FLA alone and FLA in combination with BaP, compared to controls. On the other hand, the difference in FLA metabolic rate between microsomes that were exposed to FLA + BaP was higher than the ones that received FLA. The microsomes from BaP-pre-treated mice produced a considerably higher proportion of FLA 2, 3-diol, and 2, 3 D FLA when microsomes were incubated with FLA. There were no differences in the FLA metabolite types formed when BaP-pre-treated mice were co-incubated with BaP and FLA than with FLA alone. The enhanced biotransformation of FLA as a result of prior and concomitant exposure to BaP may have implications for assessment of risks arising from human exposure to PAH mixtures.

Dietary fat-influenced development of colon neoplasia in Apc Min mice exposed to benzo(a)pyrene.

Colorectal cancer, responsible for 50,000 deaths per year, is a contributing factor for considerable mortalities in the United States. Consumption of well-done red meat and saturated fats rich in polycyclic aromatic hydrocarbons may be one of the causative factors for sporadic colon cancer. The objective of this study was to investigate whether the formation of colon tumors in adult Apc(Min) mice was influenced by the ingestion of different types of fat containing benzo(a)pyrene [B(a)P], a polycyclic aromatic hydrocarbon compound. Treatment consisted of 50 and 100 microg B(a)P/kg body weight dissolved in peanut or coconut oil (representatives of unsaturated and saturated fats, respectively) administered daily to six-week-old male Apc(Min) mice via oral gavage for sixty days. At the end of exposure, mice were sacrificed; jejunum and colons were retrieved and preserved in 10% formalin for observation for gross pathological changes. An increased prevalence of adenomas in colons of mice that ingested B(a)P through saturated dietary fat compared to unsaturated fat and controls (p < .05) was noticed. Interestingly, we also observed adenomas with high-grade dysplasia in the B(a)P + saturated fat group, and these incidences were frequent at the 100 microg/kg B(a)P dose. On the other hand, the B(a)P-alone and unsaturated-fat groups did not show significant differences in the numbers of adenomas and invasive tumors in the both jejunum and the colon. Our studies established that dietary fat, especially saturated fat, potentiates the development of colon tumors caused by B(a)P in the Apc(Min) mouse.

Comparative metabolism of benzo(a)pyrene by ovarian microsomes of various species.

Knowledge of the ability of the female reproductive system to metabolize polycyclic aromatic hydrocarbons (PAHs) is critical to the diagnosis and management of female infertility and for risk assessment purposes. The PAHs are a family of widespread pollutants that are released into the environment from automobile exhausts, cigarette smoke, burning of refuse, industrial emissions, and hazardous waste sites. In exposed animals, PAHs become activated to reactive metabolites that interfere with target organ function and as a consequence cause toxicity. The extent of susceptibility to PAH exposure may depend on the ability of animals to metabolize these chemicals. The present study has been undertaken to assess whether any differences exist among mammals in the metabolism of benzo(a)pyrene (BaP), a prototypical PAH compound. Microsomes isolated from the liver and ovaries of rats, mice, goats, sheep, pigs, and cows were incubated with 5 microM BaP. Postincubation, samples were extracted with ethyl acetate and analyzed for BaP/metabolites by reverse-phase HPLC with fluorescence detection. The rate of metabolism (pmol of metabolite/min/mg protein) was found to be more in liver than in ovary in all the species studied (P < 0.05). The differences in metabolite concentrations were statistically significant (P < 0.0001) among the various species in both organs studied. Multiple species comparison also revealed that the differences were statistically significant (P < 0.001) between rodents (rat and mouse) and higher mammals (ewe, sow, and cow). Even among the higher mammals, in a majority of the cases, the differences in metabolite concentrations were significantly different (P < 0.001) both in ovary and liver. The BaP metabolites identified were 4,5-diol; 7,8-diol; 9,10-diol; 3-hydroxy BaP; and 9-hydroxy BaP. The rodent microsomes produced considerably higher proportion of BaP 4,5-diol and 9,10-diol than did cow, sow, goat, and sheep. However, microsomes from higher mammals converted a greater proportion of BaP to 3-hydroxy and 9-hydroxy BaP, the detoxification products of BaP. Overall, our results revealed a great variation among species to metabolize BaP.

Vehicle-dependent disposition kinetics of fluoranthene in Fisher-344 rats.

The objective of this study was to evaluate how the vehicles of choice affect the pharmacokinetics of orally administered Fluoranthene [FLA] in rats. Fluoranthene is a member of the family of Polycyclic Aromatic Hydrocarbon chemicals. Fluoranthene exposure to humans may occur as a result of cigarette smoking, consumption of contaminated food and water, heating woods in stoves and boilers, industrial sources such as coal gasification, carbon and graphite electrode manufacturing. Adult male Fisher-344 rats were given single oral doses of 25 and 50 microg/kg FLA in tricaprylin, peanut oil, cod liver oil, Tween 80/isotonic saline (1:5) and 2% Alkamuls-EL620 through gavage. After administration, the rats were housed individually in metabolic cages and sacrificed at 2, 4, 6, 8, 10 and 12 hours post FLA exposure. Blood, lung, liver, small intestine, adipose tissue samples, urine, and feces were collected at each time point. Samples were subjected to a liquid-liquid extraction using methanol, chloroform, and water. The extracts were analyzed by a reverse-phase HPLC, equipped with a fluorescence detector. The results revealed a dose-dependent increase in FLA concentrations in plasma and tissues for all the vehicles used. Plasma and tissue FLA concentrations were greater for peanut oil; cod liver oil, and tricaprylin vehicles compared to Alkamuls (p < 0.05), and Tween 80/isotonic saline (1:5). Most of the FLA administered through peanut oil, cod liver oil and tricaprylin was cleared from the body by 8 hours (90%) and 12 hours (80%) post administration for the 25 microg/kg and 50 microg/kg dose groups, respectively. With both doses employed, the metabolism of FLA was highest when cod liver oil was used as a vehicle and lowest in vehicles containing detergent/water [cod liver oil > peanut oil > tricaprylin > alkamuls > Tween 80/isotonic saline (1:5)]. These findings suggest that uptake and elimination of FLA is accelerated when administered through oil-based vehicles. The low uptake of FLA from Alkamuls and Tween 80/isotonic saline may have been a result of the poor solubility of the chemical. In summary, our findings reiterate that absorption characteristics of FLA were governed by the dose as well as the dosing vehicle. The vehicle-dependent bioavailability of FLA suggests a need for the judicious selection of vehicles in evaluating oral toxicity studies for risk assessment purposes.

Species-specific testicular and hepatic microsomal metabolism of benzo(a)pyrene, an ubiquitous toxicant and endocrine disruptor.

Information on the metabolism of the environmental toxicant, benzo(a)pyrene (BaP) in the male reproductive system is crucial for understanding BaP-induced infertility. Microsomes were isolated from the liver and testes of rat, mouse, hamster, ram, boar, bull, and monkey and incubated with BaP. Post-incubation, samples were extracted with ethyl acetate and analyzed for BaP/metabolites by reverse-phase HPLC with fluorescence detection. A great variation among species to metabolize BaP was observed. The rodent testicular microsomes produced higher proportions of BaP 4,5-diol and 9,10-diol than did boar, ram, bull, and monkey. On the other hand, hepatic microsomes from higher mammals converted a greater proportion of BaP to 3-hydroxy and 9-hydroxy BaP, the detoxification products of BaP. Given the ability of BaP 7-8-diol 9, 10-epoxide, 3-, and 9-hydroxy BaP to bind with DNA and form adducts, there is a likelihood of risk arising from the accumulation of BaP metabolites in testicular tissues. These metabolites may interfere with the formation and function of gametes, eventually contributing to infertility.