Species differences in hepatic drug oxidation in mammals and fishes in relation to thermal acclimation

Determination of temporal changes in hepatic drug-oxidizing capacity using plasma metabolite/caffeine ratios in non-pregnant and pregnant goats

Caffeine (CF) is a metabolic probe drug used in the determination of the hepatic drug-oxidizing capacity. The aim of this study was to investigate temporal changes in the hepatic drug-oxidizing capacity using plasma metabolite/CF ratios in non-pregnant goats (n = 11) and pregnant goats (n = 23). CF (5 mg/kg, intravenous) was administered in six periods (Period 1-6) with 45 days between two periods. The plasma levels of CF and its metabolites, theophylline (TP), theobromine (TB) and paraxanthine (PX), were determined by HPLC-UV. To evaluate hepatic drug-oxidizing capacity in terms of enzymes that play a role in CF metabolism, the plasma metabolic ratios including TB/CF, PX/CF, TP/CF and TB + PX + TP/CF were determined at 10 h following CF administration. Plasma metabolite/CF ratios were similar between non-pregnant and pregnant goats. However, plasma metabolite/CF ratios in Period 3 (45 days in pregnant goats) were significantly higher than those other periods in both pregnant and non-pregnant goats. The effect of pregnancy may not be observed on drugs that are substrates of enzymes involved in CF metabolism in goats.

Down regulation of bisphenol A glucuronidation in carp during the winter pre-breeding season

Environmental pollution by bisphenol A is prevalent in many rivers. The influence of bisphenol A on the reproductive organs of carp has been demonstrated to be serious, especially in the winter pre-breeding season. Although bisphenol A is detoxified as bisphenol A-glucuronide in carp organs, principally the intestine, the seasonal variation in the efficiency of the detoxification is not known. To estimate the seasonal risk of bisphenol A in carp, we investigated seasonal changes in microsomal UDP-glucuronosyltransferase activity toward bisphenol A in male-carp. Seasonal elimination efficiency of bisphenol A was also examined by organ perfusion in everted intestine. No marked seasonal differences were observed in UDP-glucuronosyltransferase activity toward 1-naphthol, but high activity toward sex steroid hormones (testosterone and estradiol) was observed in the winter pre-breeding season. Low UDP-glucuronosyltransferase activity toward bisphenol A was indicated in winter. The addition of bisphenol A into the mucosal fluid of the everted intestine resulted in excretion of bisphenol A into the mucosal side of the intestine as the metabolite, bisphenol A-glucuronide. Excretion of bisphenol A-glucuronide from carp intestine was highest in summer (proximal intestine: 13.3 nmol; middle intestine: 8.3 nmol; distal intestine: 7.9 nmol) and lowest in winter (proximal intestine: 1.0 nmol; middle intestine: 1.0 nmol; distal intestine: 0.9 nmol). These results suggest that metabolism and excretion of bisphenol A in carp hepatopancreas and intestine are impaired by down regulation of UDP-glucuronosyltransferase activity in the winter pre-breeding season.

Nongenetic variation, genetic-environmental interactions and altered gene expression. I. Temperature, photoperiod, diet, pH and sex-related effects

The use of protein electrophoretic data for determining the relationships among species or populations is widespread and generally accepted. However, many confounding factors may alter the results of an electrophoretic study in such a way as to allow erroneous conclusions to be drawn in taxonomic, systematic or population studies. Such variables as temperature, photoperiod, salinity, pH and diet have been shown to influence enzymes and proteins both quantitatively and qualitatively. Production of distinct "cold" and "warm" isozymes or "seasonal" isozymes have been found in a variety of organisms. The factors that are or may be responsible for the appearance of these isozymes is discussed. Most studies that have demonstrated some apparent form of environmentally induced genetic expression have not determined that mechanisms responsible. However, proteolytic modification has been shown to produce seasonal isozymes of fructose 1,6-bisphosphatase in rabbit liver and may account for other seasonal isozymes. Acclimating organisms to various conditions may actually allow detection of cryptic genetic variation and provide valuable data. There are many aspects to consider in designing acclimation experiments, and the conditions used will vary according to the aim of the research. Polyploidy may contribute to the genesis of environmentally regulated isozymes. A review of this literature follows with additional hypotheses and conclusions. Recommendations are given for the resolution of real and potential problems.

The influence of dietary energy levels with and without PCB induction on the growth of tilapia, Oreochromis niloticos x O. aureus

The effects of three dietary energy levels, 323, 365 and 408 Kcal/100g diet, on the growth performance of hybrid tilapia, Oreochromis niloticus x O. aureus, were studied. The experiment was carried out for 3 months in a recirculating rearing system. Growth and feed conversion ratios were significantly reduced (p<0.05) in fish exposed to 100 ppm polychlorinated biphenyl (PCB), fed high energy diets (365 and 408 Kcal/100g diet). The hepatic cytochrome P-450 and NADPH-cytochrome c reductase activities were also significantly (p<0.05) lower in PCB-treated fish fed high energy diets (365 and 408 Kcal/100g diet) than fish fed lower energy diet (323 Kcal/100g diet). The malic enzyme activity and the body lipid content in fish generally increased as the dietary energy level increased.

Effects of temperature acclimation on the expression of hepatic cytochrome P4501A mRNA and protein in the fish Fundulus heteroclitus

Previous studies showed that hydrocarbon induction of hepatic microsomal monooxygenase activity is attenuated in the teleost fish Fundulus heteroclitus acclimated to low temperature. The basis of that attenuation, and the effects of temperature on monooxygenase activity, were examined by analyzing liver cytochrome P4501A (CYP1A) mRNA, protein, and catalytic activity in control and beta-naphthoflavone (BNF)-treated F. heteroclitus acclimated to 6 or 16 degrees C. There were no temperature-related differences in total P450 content, NADPH-cytochrome c (P450) reductase activity, ethoxyresorufin O-deethylase (EROD) activity, or immunoquantified CYP1A content in hepatic microsomes of untreated fish. Fish acclimated to 16 degrees C and given a single intraperitoneal injection of BNF exhibited a rapid rise and fall in CYP1A mRNA content and an induction of EROD activity and CYP1A protein that was undiminished over 7 days. Similarly treated fish acclimated at 6 degrees C showed an increase in CYP1A mRNA content greater than that in 16 degrees C fish, but with no significant increase in EROD activity or CYP1A content over 7 days. Examined over a longer term, microsomal EROD activity was significantly induced by BNF in fish at both temperatures; activity peaked at 5-7 days in 16 degrees C fish, while in 6 degrees C fish the activity continued to rise slowly over 25 days. However, the greatest activity reached in 6 degrees C fish (0.68 nmol/min/mg) was less than half that seen in the warmer animals (1.46 nmol/min/mg). Immunodetectable CYP1A content showed the same trend as EROD activity, and the turnover number (nmol product formed/min/nmol CYP1A) for EROD activity was about the same in all groups, indicating that concentration of the catalyst alone could account for the different patterns of microsomal activity. CYP1A mRNA content was again induced to a similar degree by BNF in both the 6 and the 16 degrees C fish; the apparent half-life of the mRNA was substantially longer in cold-acclimated than in warm-acclimated BNF-treated fish. Comparing the levels of CYP1A mRNA and protein at the two acclimation temperatures following BNF treatment indicates that translational activity, rather than transcriptional activity, is the sensitive point in the effect of temperature on CYP1A induction in these fish.

Cytochrome P-450-dependent metabolism in isolated liver cells from fed and starved rainbow trout,Salmo gairdneri

The cytochrome P-450 content in liver cells from rainbow trout was not affected by starvation for 12 weeks whereas the rate of cytochrome P-450-dependent deethylation of 7-ethoxycoumarin in liver cells from 6 or 12 weeks starved fish was 60% of the rate in fed fish. Treatment of fish with β-naphthoflavone increased the 7-ethoxycoumarin metabolism several-fold in both starved and fed fish.Optimal cytochrome P-450 monooxygenation in liver cells from fed or starved fish was not affected by addition of glucose or 2-bromooctanoate, an inhibitor of fatty acid β-oxidation which is the main source of metabolic fuel in trout liver. The cellular content of NADPH, an obligatory cofactor for cytochrome P-450 monooxygenation, was not affected by addition of substrate to cytochrome P-450, inhibition of fatty acid β-oxidation or inhibition of the oxidative phosphorylation. This indicates a great capacity of rainbow trout liver cells to retain high NADPH/NADP(+) ratios. These results suggest that the cytochrome P-450 mediated metabolism of xenobiotics in liver cells from fed or starved trout is not limited by the availability of reducing equivalents.

Influence of environmental temperature on the induction of xenobiotic metabolism by beta-naphthoflavone in rainbow trout, Salmo gairdneri

The response of hepatic microsomal cytochrome P-450 monooxygenase and UDPglucuronosyltransferase to a common inducer, beta-naphthoflavone, was investigated in rainbow trout acclimated to 5 or 17 degrees C. The hepatic microsomal 7-ethoxycoumarin-O-deethylase, 7-ethoxyresorufin-O-deethylase, and benzo[a]pyrene hydroxylase activities, measured at 5 or 17 degrees C, were induced at both acclimation temperatures. Maximum response of 7-ethoxyresorufin-O-deethylase and 7-ethoxycoumarin-O-deethylase activities to beta-naphthoflavone was obtained with doses of 5 mg/kg and above, both in warm- and cold-acclimated trout. In warm-acclimated trout the maximum degree of induction of cytochrome P-450-dependent activities was already evident on the day following treatment with beta-naphthoflavone (100 mg/kg), whereas these activities reached maximum values after 3 days in cold-acclimated fish. Furthermore, the maximum induced values of 7-ethoxyresorufin-O-deethylase and benzo[a]pyrene hydroxylase activities were higher in cold-acclimated than in warm-acclimated fish. beta-Naphthoflavone treatment caused a slight but significant increase (1.6-fold) in UDPglucuronosyltransferase activity in warm-acclimated fish when measured at 5 or 17 degrees C, whereas in cold-acclimated fish a significant elevation was seen only when the activity was determined at environmental temperature (5 degrees C).

Thermal acclimatization of hepatic polysubstrate monooxygenase and UDP-glucuronosyltransferase of mature rainbow trout (Salmo gairdneri)

The thermal acclimatization of hepatic cytochrome P-450-dependent polysubstrate monooxygenase (PSMO) and UDP-glucuronosyltransferase of mature rainbow trout (Salmo gairdneri) was studied. The results indicate that the PSMO system, 7-ethoxycoumarin and benzo(a)pyrene as substrates, shows almost ideal acclimatization pattern in autumn during water cooling. The enzyme activities were identical if measurements were carried out at acclimatization (=environmental) temperatures which were 20 degrees C in August and 5 degrees C in November. If a constant incubation temperature (18 degrees C) was used, the PSMO activities were significantly higher in cold (5 degrees C)-acclimatized fish. The acclimatization process could be seen both in specific and total activities. The content of cytochrome P-450 remains at constant level from August to November. In early summer during water warming the PSMO activities increased considerably in both sexes in all incubation conditions. The specific and total UDP-glucuronosyltransferase activities were significantly higher in warm-acclimatized fish both in the autumn and in the spring if the activities were measured at environmental temperature. No differences could be detected if the measurements were carried out at constant experimental temperature (18 degrees C).

Metabolism of benzo[a]pyrene by fish cells in culture

Benzo[a]pyrene (BaP) metabolism was studied in cell lines derived from rainbow trout (RTG-2), bluegill fry (BF-2), and fathead minnow (FHM). Confluent cultures were exposed to 3H-BaP (0.5 nmol/ml), and, after various exposure times, metabolites were extracted from the media with an organic solvent and analyzed by high-pressure liquid chromatography. BF-2 and RTG-2 cells converted 63% of the BaP to water-soluble metabolites within 24 h, while FHM cells converted only 12%. BF-2 and RTG-2 cells metabolized more than 90% of the BaP by 48 h, while only 67% of the BaP was converted to water-soluble metabolites by FHM cells after 96 h. The major organic-solvent-extractable metabolites in all three cell lines were 9,10-dihydroxy-9,10-dihydrobenzo[a]pyrene and unidentified polar metabolites. Of the water-soluble metabolites formed by BF-2, FHM, and RTG-2 cells, 67, 42, and 19%, respectively, were converted to ethyl-acetate-extractable metabolites by treatment with beta-glucuronidase. All three cell lines formed a glucuronide of 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (7,8-diol); in BF-2 and FHM cells, the 7,8-diol represented almost half of the metabolites released by beta-glucuronidase treatment. Thus, cell lines derived from three widely distributed species of freshwater fish have the capacity to metabolize BaP to a form that is a proximate carcinogen in rodents and to produce a water-soluble conjugate of this metabolite.

Effects of polychlorinated biphenyls and environmental temperature on in vitro formation of benzo[a]pyrene metabolites by liver of trout (Salmo gairdneri)

Rainbow trout (Salmo gairdneri) held at 7 degrees and 16 degrees were given Aroclor 1254 (PCB) (10 mg/kg body wt) via intraperitoneal injections. The binding of [3H]benzo[a]pyrene (BaP) to deproteinized salmon sperm DNA was assayed (pmoles BaP equivalents per mg DNA per mg protein) using the post-mitochondrial supernatant (S 10) fractions from livers of fish at 24-168 hr after the PCB exposure. Liver enzymes from the untreated fish acclimated at 7 degrees yielded an average binding value (0.37 +/- 0.17) which was significantly greater (P less than 0.05) than the value (0.07 +/- 0.03) for untreated fish at 16 degrees. Liver supernatant fractions from PCB-induced fish acclimated at 16 degrees and sampled at 24-120 hr showed a substantial increase (P less than 0.05) in the binding (average value 2.4 +/- 1.8) compared to the value obtained with untreated fish at 16 degrees. At 24, 48 and 120 hr after the PCB treatment of fish held at 7 degrees, there was no significant increase in the binding value or extent of metabolism of BaP compared to that obtained with the untreated fish at 7 degrees. However, at 168 hr, three of four fish at 7 degrees responded to the PCB treatment with significantly (P less than 0.05) increased binding values (3.3 +/- 1.6). Chromatographic analyses of the ethyl acetate-soluble metabolites revealed that 3-hydroxy BaP and 7,8- and 9,10-dihydrodiols were the major metabolites; K-region metabolites were formed in trace amounts in untreated and PCB-treated fish at both temperatures. No marked qualitative differences were observed in metabolite profiles after the PCB treatment; however, overall metabolism of BaP and production of reactive metabolites by liver enzymes were considerably (P less than 0.05) enhanced in the PCB-induced fish at both 7 degrees and 16 degrees.