Modulation of 7,12-dimethylbenz[a]anthracene disposition and hepatocarcinogenesis by dieldrin and chlordecone in rainbow trout

The present study examined whether modified xenobiotic transport, resulting from chlordecone (CD) or dieldrin pretreatment, would alter polycyclic aromatic hydrocarbon (PAH) or organochlorine (OC) target organ doses and subsequent tumor organospecificity or incidence rates in rainbow trout. Additionally, the potential for exposure to dieldrin or CD, following PAH exposure, to enhance tumor incidence was assessed. Evaluation of CD pretreatment effects on [14C]CD disposition in trout was conducted following two i.p. (0-15 mg/kg) and two dietary (0-0.4 mg/kg/d) pretreatment regimes. To assess the influence of OC pretreatment on cancer induced by the PAH 7,12-dimethylbenz[a]anthracene (DMBA), juvenile trout were fed control, CD (0.1, 0.4 mg/kg/d), or dieldrin (0.1, 0.3 mg/kg/d) diets for 9 wk, received a waterborne [3H]DMBA exposure (1 mg/L, 20 h), and resumed control, CD, or dieldrin diets for 33 wk. [3H]DMBA disposition and hepatic [3H]DMBA binding were examined immediately and 24 h after exposure. Hepatic and stomach tumor incidences were determined 33 wk after DMBA exposure. CD pretreatment did not influence [14C]CD or [3H]DMBA hepatic concentrations, hepatic [3H]DMBA DNA binding, or hepatic/stomach tumor incidence. It did, however, elevate bile [14C]CD and [3H]DMBA concentrations. Postinitiation exposure to CD weakly enhanced DMBA-induced hepatic tumor incidence at the low but not the high CD dose. Dieldrin pretreatment did not influence stomach [3H]DMBA equivalents or stomach tumor incidence but did cause an elevation in biliary and hepatic concentrations of [3H]DMBA equivalents. [3H]DMBA binding to liver DNA was significantly increased and hepatic tumor incidence was elevated by dieldrin pretreatment. Dieldrin treatment following DMBA initiation did not enhance hepatic or stomach tumor incidence. Ecoepidemiology studies, to date, have reported correlations between the co-occurrence of PAHs and OCs and elevated tumor incidence in feral fish, but cause-and-effect relationships have been difficult to establish. The results of the present study confirm that OCs, such as dieldrin and CD, play a role in modifying PAH-induced carcinogenesis in fish.

Ultrastructural, protein, and lipid changes in liver associated with chlordecone treatment of mice

Pretreatment of mice with chlordecone (CD) reduced hepatic accumulation of a subsequent dose of [14C]CD without significantly changing [14C]CD biotransformation. To determine if CD-induced changes in hepatic [14C]CD accumulation were coincident with altered cell composition, we examined the effects of CD on hepatic protein and lipid content, on fatty acid profiles of liver and kidney, and on the ultrastructure of hepatocytes. SDS-polyacrylamide gel electrophoresis detected an apparent CD dose-related increase in a microsomal protein with a molecular weight of about 23 kDa. Total liver or kidney lipid contents were not altered by CD but relative amounts of several hepatic fatty acids were changed. CD caused marked hepatic mitochondrial swelling, increased amounts of endoplasmic reticulum, apparently increased numbers of peroxisome-like structures, and decreased numbers of lipid droplets in cytoplasm of hepatocytes. Numbers of lipid droplets were not decreased in perisinusoidal fat storage cells. In addition, the numbers of cytoplasmic lipoprotein vesicles were apparently increased in some hepatocytes. Overall these changes indicated an increased hepatocyte secretory activity and suggested that CD changed hepatocellular lipid transport, storage, and metabolism pathways.

Dehydroepiandrosterone is a complete hepatocarcinogen and potent tumor promoter in the absence of peroxisome proliferation in rainbow trout

Dehydroepiandrosterone (DHEA), fed for 30 weeks to rainbow trout after initiation with the hepatocarcinogen aflatoxin B1 (AFB1), produced a dose-dependent enhancement of carcinogenesis as measured by increased tumor incidence, multiplicity and size. Significant enhancement was observed at 222 p.p.m., which corresponds to a daily dosage one-half that previously administered to humans in clinical trials. DHEA was also capable of acting as a complete carcinogen in this model, producing liver tumors at doses as low as 222-444 p.p.m. Tumors isolated from trout treated with DHEA alone contained mutations in Ki-ras, primarily codon 12[1] G-->A transitions, providing the first suggestive evidence that DHEA could be a genotoxic carcinogen. The carcinogenicity of DHEA in trout is independent of peroxisome proliferation, as measurements of peroxisomal beta-oxidation and catalase activity support previous observations that trout, like humans, are weak responders to peroxisome proliferators.

Temperature-modulated incidence of aflatoxin B1-initiated liver cancer in rainbow trout

Rainbow trout (initial weight of 4 or 5 g) were acclimated at a cool, 11.0 degrees C (C), a warm, 18.0 degrees C (W), or an intermediate temperature 14.5 degrees C (I) for 1 month. There was a slight difference in hepatic microsomal content of one of six cytochrome P450 isozymes between acclimation groups. Monounsaturated fatty acids in hepatic phosphotidylethanolamine but not phosphotidylcholine increased at lower acclimation temperatures. Saturated fatty acid content decreased with temperature for both phospholipid classes. Fish were exposed to 0.08-0.12 ppm waterborne aflatoxin B1 (AFB1) for 30 min at respective acclimation temperatures or after acute temperature shifts (24 hr) and reared for 9 months at C, I, or W. With exposure concentrations which delivered equivalent target organ doses, trout acclimated, exposed, and reared at C, I, or W had liver tumor incidences of 4, 35, and 61%, respectively. The average number of tumors per liver increased from 1.25-1.34 at C to 2.46-2.66 at W. There were no temperature-dependent differences in tumor diameter. When C- and W-acclimated fish were AFB1 exposed and reared at I, tumor incidence was 12.5% for W-I-shifted fish and 26.5% for C-I-shifted fish. This was consistent with previous work which demonstrated acute downward temperature shift reduced [3H]AFB1 adduction to hepatic DNA. Tumor incidence and multiplicity data suggested manipulation of temperature permitted selective modulation of cancer initiation and promotion in rainbow trout.

In vitro and in vivo temperature modulation of hepatic metabolism and DNA adduction of aflatoxin B1 in rainbow trout

Alterations in membrane lipid composition during temperature acclimation of poikilotherms is hypothesized to compensate for direct effects of temperature on membrane fluidity. Temperature also influences disposition and actions of some xenobiotics. This suggests the potential for complex interactions between temperature and metabolism of chemical carcinogens. Whole livers and hepatic microsomes from rainbow trout acclimated at 18 degrees C have more saturated fatty acids and less mono- and polyunsaturated fatty acids than those from fish acclimated at 10 degrees C. Such changes are consistent with a role for membrane lipid fluidity in temperature compensation. When 10 and 18 degrees C acclimated fish are ip injected with 0.4 mg/kg [3H]aflatoxin B1 (AFB1) at their respective acclimation temperatures, hepatic disposition of AFB1, DNA adduction, and biliary metabolites are similar. An acute shift of 18 degrees C acclimated trout to 14 degrees C reduces [3H]AFB-DNA adduct formation, while [3H]AFB1 adduction after acute shift of 10 degrees C acclimated fish to 14 degrees C is no different than in non-shifted fish. Hepatic microsomes isolated from 10 or 18 degrees C acclimated trout, incubated with 10 microM [3H]AFB1 and calf thymus DNA between 6 and 22 degrees C exhibit no differences in the "break points" of Arrhenius plots (16 degrees C in both groups). There is, however, more in vitro DNA adduction of [3H]AFB1 by microsomes from 18 degrees C acclimated fish, a difference abolished by 0.5 mM alpha-naphthoflavone (ANF). These results suggest that temperature acclimation of trout differentially modifies activities of cytochrome P-450 isozymes. When assayed at respective acclimation temperatures, hepatic cytosol from 18 degrees C fish produces more aflatoxicol, a detoxication product of AFB1, than cytosol from 10 degree C fish. Therefore, this soluble enzyme does not exhibit ideal temperature compensation. Such temperature-induced differences in microsomal cytochrome P-450 isozymes and cytosolic dehydrogenase partially explain temperature-modulated AFB1 genotoxicity.

Chlordecone pretreatment alters [14C]chlordecone and [14C]cholesterol transport kinetics in the perfused rat liver

Previous work demonstrated that pretreatment of mice with low doses of the organochlorine insecticide chlordecone (CD) altered the tissue disposition of a subsequent [14C]CD or [14C]cholesterol challenge dose. The profile of these changes was consistent with the induction of a protein integral to hepatic CD/cholesterol turnover. The present study was undertaken to confirm similar in vivo effects in the rat and to analyze potential CD-induced changes in hepatic transport kinetics in the perfused rat liver. For in vivo experiments, male, Sprague-Dawley rats were treated with CD (5, 15, or 40 mg/kg) and challenged 3 or 7 days later with a 5 mg/kg [14C]CD tracer dose. Rats challenged 3 days after treatment and evaluated 16 hr later showed a dose-dependent decrease in hepatic [14C]CD relative to controls. This decrease could not be attributed to alterations in liver mass or total liver lipid. For kinetics studies, rats received 15 mg/kg CD and livers were perfused 3 days later. Following a brief (5-7 min) single-pass perfusion, the perfusate was replaced with recirculating buffer containing albumin-bound [3H]oleic acid or high-density lipoprotein-bound [14C]CD or [14C]cholesterol. Livers from pretreated animals had significantly decreased rates of [14C]CD and [14C]cholesterol uptake. Efflux of [14C]CD and biliary excretion of [14C]cholesterol were increased. No changes were observed in uptake or biliary excretion of [3H]oleic acid. SDS-PAGE of hepatic cytosol revealed an enhanced band intensity corresponding to a M(r) of 25,600 in livers from pretreated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic dieldrin exposure increases hepatic disposition and biliary excretion of [14C]dieldrin in rainbow trout

Previous work demonstrated that exposure of laboratory animals including fish to certain organochlorine (OC) insecticides altered the tissue distribution of a subsequent tracer dose of the same [14C]OC. In the present study, 10- to 20-g rainbow trout were exposed to 15 ppm dieldrin in the diet. Fish were subsequently challenged at 2-week intervals with an intraperitoneal injection of 0.1 mg/kg [14C]dieldrin and viscera (liver, bile, mesenteric fat, kidney, and intestine) analyzed for radioactivity, 24 hr later. After 10 and 12 weeks of dieldrin pretreatment, [14C]dieldrin was significantly elevated relative to controls in liver (200%), bile (500%), and fat (500 and 1200% for 10 and 12 weeks, respectively) of pretreated fish. Other tissues were unchanged. Chloroform/methanol extractions revealed a time-dependent increase in label disposition to carcass lipid in controls but not in pretreated fish. Altered disposition could not be explained by changes in total body lipid or induction of total cytochrome P-450 or ethoxyresorufin-O-deethylase, pentoxyresorufin-O-deethylase, glutathione S-transferase, or UDP glucuronosyltransferase activities. In vivo assessment of [14C]dieldrin metabolism revealed no increase in hepatic and only a slight (22%) increase in biliary polar:nonpolar concentration ratio after 9 weeks 20 ppm dieldrin pretreatment. Results suggest that constitutive changes in liver integral to dieldrin sequestration, transport, or excretion may be an adaptive response of trout to chronic OC exposure.

Alterations in lipid peroxidation, antioxidant enzymes, and carcinogen metabolism in liver microsomes of vitamin E-deficient trout and rat

Feeding rainbow trout for 16 weeks a diet in which the levels of vitamin E were reduced 70-fold resulted in marked depletion (18-fold) of vitamin E levels in liver microsomes from these fish. The susceptibility of hepatic microsomes to lipid peroxidation in vitro and the levels of plasma and liver microsomal lipid hydroperoxides generated in vivo were markedly elevated in vitamin E-depleted trout. No appreciable alterations were observed in the liver microsomal cytochrome P450-dependent mixed-function oxidase system or in the fatty acid composition of trout liver microsomal membranes. Livers from rats fed a vitamin E-deficient diet for 10 weeks also had significantly lower levels of microsomal vitamin E. In addition, total cytochrome P450 levels were depressed (15%) and cytosolic glutathione was enhanced (40%) in livers from rats fed the vitamin E-depleted diet. Covalent binding of [3H]-(+)-benzo[a]pyrene-7,8-dihydrodiol to exogenous DNA in vitro was enhanced with liver microsomes from vitamin E-deficient trout and these fish were much more sensitive to the acute toxicity of this carcinogenic polycyclic aromatic hydrocarbon. These results indicate that trout may be a useful model for studying the significance of peroxidative pathways in carcinogenesis and their manipulation by dietary antioxidants.

Low dose chlordecone pretreatment altered cholesterol disposition without induction of cytochrome P-450

Pretreatment of mice with low doses of chlordecone (CD) alters the pattern of distribution of a subsequent tracer dose of [14C]CD. We call this preexposure effect a pretreatment disposition response (PDR) and suggest that it reflects important cellular responses to lipophilic compounds. The present study examined three possible mechanisms for CD-induced PDR (CD-PDR). The first was that CD-PDR occurred with induction of the cytochrome P-450 system. A cumulative dose of 45 mg/kg CD caused a PDR, increased the content of cytochrome P-450, and elevated the activities of ethoxyresorufin- and ethoxycoumarin-O-deethylases (EROD and ECOD). A cumulative dose of 10 mg/kg caused a PDR, but did not affect cytochrome P-450, EROD, or ECOD, indicating that an induction of the cytochrome P-450 system in not necessary for PDR. A second possibility examined was that CD-PDR resulted because of an altered affinity of a subcellular fraction. Following a pretreatment regimen designed to produce PDR, amounts of [14C]CD in each fraction paralleled homogenate values in the liver and the kidney. However, when values were calculated as percentages of total label recovered, it was apparent that [14C]CD levels were higher in the microsomal fraction of the liver. Finally, the possibility that CD-PDR occurred because of an interaction of CD with proteins involved in cholesterol synthesis and transport was addressed. CD pretreatment increased disposition of a dose of [14C]cholesterol to the fat at the expense of [14C]cholesterol in the liver and kidney.

Biliary excretion appears rate limiting for hepatic elimination of benzo[a]pyrene by temperature-acclimated rainbow trout

Previous work demonstrated that mixed function oxidase activities of hepatic microsomes from cold- and warm-acclimated rainbow trout were similar when assayed at temperatures to which fish were acclimated. This "ideal temperature compensation" was partially explained by constitutive differences in microsomes. In the work reported here, rainbow trout were acclimated at 10 or 18 degrees C for 4 weeks and then ip injected with 10 mumol [3H] or [14C]benzo[a]pyrene (BP)/kg in one of two temperature regimens. First, fish were acclimated and exposed at the same temperature and killed after 4, 24, or 48 hr. Concentrations of [3H]BP equivalents in liver, bile, and fat but not in plasma, muscle, intestine, gill, or kidney increased with time. There were no differences in hexane or ethyl acetate extractable [3H] or [14C]BP tissue concentrations in 10 and 18 degrees C-acclimated fish exposed at their acclimation temperatures. At 24 hr after injection, biliary excretion of [3H]BP equivalents was about twofold higher at 18 degrees C than at 10 degrees C. Therefore, warmer temperature stimulated biliary excretion without a marked effect on in vivo BP metabolism. In the second regimen, 10 and 18 degrees C-acclimated fish were shifted to 14 degrees C, injected with [3H] or [14C]BP 1 hr later, and killed after an additional 24 hr. There were no differences in tissue concentrations of total [3H]BP equivalents between acclimation groups at 14 degrees C. However, the biliary concentration of [14C]BP not extracted by ethyl acetate was significantly higher in bile from 10 degrees C-acclimated fish than from 18 degrees C-acclimated fish when both groups were exposed at 14 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

2,3,7,8-Tetrachlorodibenzo-p-dioxin pretreatment of female mice altered tissue distribution but not hepatic metabolism of a subsequent dose

Lipid partitioning of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) inadequately explains its tissue distribution since higher concentrations occur in liver than fat except at high doses. This study provides in vivo evidence that an inducible, saturable system plays a predominant role in disposition of [14C]TCDD in female mice at doses between 5 and 20 micrograms/kg. Female C57BL/6J mice were gavaged with 0, 5, or 15 micrograms TCDD/kg, received a subsequent gavage of 5 or 20 micrograms [14C]TCDD after 6 days, and were killed 1 day later. In mice pretreated with 5 and 15 micrograms TCDD/kg and subsequently dosed with 20 micrograms [14C]TCDD/kg, liver weight and [14C]TCDD concentration increased. Total liver [14C]TCDD burden increased about 50% in both pretreatment groups. Concentrations of [14C]TCDD in kidney, fat, heart, lung, gastrointestinal tract, but not plasma or splenic lymphocytes, decreased in a reciprocal manner. Alterations in absorption, concentrations of polar metabolites of [14C]TCDD in liver, and hepatic lipid content failed to explain these results. About 97% of hepatic 14C was hexane extractable. HPLC of this extract indicated [14C]TCDD was the only significant nonpolar form of radiolabel in liver. In mice pretreated with 5 micrograms TCDD/kg and subsequently dosed with 5 micrograms [14C]TCDD/kg, a more marked pretreatment disposition response was observed. These results are consistent with a predominant role for an inducible, high affinity, low capacity system in whole animal pharmacokinetics of TCDD.

The effect of thermal acclimation on the activity of arylhydrocarbon hydroxylase in rainbow trout (Oncorhynchus mykiss)

1. The possibility that temperature acclimation (to 10 or 18 degrees C for 28 days) would alter the cytochromes P-450 of rainbow trout was addressed. 2. The specific content of LM4b (P-450 IA1), the trout isozyme responsible for activation of polynuclear aromatic hydrocarbons, was lower in 18 degrees C fish than it was in 10 degrees C fish. 3. Kinetic analysis of aryl hydrocarbon hydroxylase indicated that, while thermal acclimation caused no change in Vmax, it lowered the apparent Km of this enzyme for benzo[a]pyrene when assayed at acutely shifted temperatures. 4. Thermal acclimation of fish may have significance when feral populations are subjected to acute temperature shifts.

A characterization of chlordecone pretreatment-altered pharmacokinetics in mice

Lipophilic chlorinated hydrocarbons pose a potential health hazard to humans and animals and the toxicity of a number of these compounds has been well documented. Despite the low environmental concentrations of most of these chemicals, much of the research conducted to date has used maximally tolerated doses. Our research, conducted with low, apparently nontoxic, doses of the insecticide chlordecone (CD), showed that the administration of CD (5 mg/kg ip) to mice (C57BL/6N and DBA/2N strains) caused a time-dependent alteration in the pattern of distribution of a subsequently administered dose of [14C]CD. Livers of CD-pretreated animals contained less label than did those from controls and CD pretreatment increased amounts of label in kidney, lung, fat, and muscle. Changes did not appear to be due to an altered rate of metaboLism and analysis of total CD in tissues (unlabeled plus [14C]CD) indicated that these responses were not due to a simple redistribution phenomenon. We have termed this preexposure effect a pretreatment disposition response (PDR) and feel it may reflect an important cellular response to lipophilic compounds. CD-induced PDR is dose related, exhibits a threshold, and is saturable at a given level of induction. In addition, PDR exhibits some specificity, inasmuch as pretreating mice with CD (5 mg/kg) does not alter the distribution of subsequently administered [14C]dieldrin. The characteristics of threshold, saturability, and specificity are consistent with the premise that CD-induced PDR is a protein-mediated phenomenon.

Hepatic uroporphyrin accumulation and uroporphyrinogen decarboxylase activity in cultured chick-embryo hepatocytes and in Japanese quail (Coturnix coturnix japonica) and mice treated with polyhalogenated aromatic compounds

The relationship between hepatic uroporphyrin accumulation and uroporphyrinogen decarboxylase (EC 4.1.1.37) activity was investigated in cultured chick-embryo hepatocytes, Japanese quail (Coturnix coturnix japonica) and mice that had been treated with polyhalogenated aromatic compounds. Chick-embryo hepatocytes treated with 3,3',4,4'-tetrachlorobiphenyl accumulated uroporphyrin in a dose-dependent fashion without a detectable decrease in uroporphyrinogen decarboxylase activity when either pentacarboxyporphyrinogen III or uroporphyrinogen III were used as substrates in the assay. Other compounds, such as hexachlorobenzene, parathion, carbamazepine and nifedipine, which have been shown previously to cause uroporphyrin accumulation in these cells, did not decrease uroporphyrinogen decarboxylase activity. Japanese quail treated with hexachlorobenzene for 7-10 days also accumulated hepatic uroporphyrin without any decrease in uroporphyrinogen decarboxylase activity. In contrast, hepatic uroporphyrin accumulation in male C57BL/6 mice treated with iron and hexachlorobenzene was accompanied by a 20-80% decrease in uroporphyrinogen decarboxylase activity, demonstrating that the assay used for uroporphyrinogen decarboxylase, using pentacarboxyporphyrinogen III as substrate, could detect decreased enzyme activity. Our results with chick hepatocytes and quail, showing uroporphyrin accumulation without a decrease in uroporphyrinogen decarboxylase activity, are consistent with a new two-stage model of the uroporphyria: initially uroporphyrinogen is oxidized by a cytochrome P-450-mediated reaction, followed in rodents by a progressive decrease in uroporphyrinogen decarboxylase activity.

A comparison of the effects of hexachlorobenzene, beta-naphthoflavone, and phenobarbital on cytochrome P-450 and mixed-function oxidases in Japanese quail

Hexachlorobenzene (HCB), beta-naphthoflavone (BNF), or phenobarbital (PB) was administered to Japanese quail to determine their effects on hepatic porphyrin levels and drug-metabolizing enzymes. While HCB increased porphyrin levels, PB slightly reduced them, and BNF had no effect. HCB was an excellent inducer in quail, increasing the specific content of cytochrome P-450 to levels similar to those produced by BNF. Additional similarities between HCB- and BNF-treated quail included a comparable hypsochromic absorption shift in the CO-reduced difference spectra of cytochrome P-450 and similar effects on the activities of cytosolic glutathione S-transferase (GSH-t), biphenyl hydroxylase (BPH), and ethoxyresorufin O-deethylase (EROD). However, a differential response to HCB and BNF treatment was seen in the activities of hepatic NADPH-cytochrome P-450 reductase, epoxide hydrolase, GSH-t (microsomal), aryl hydrocarbon hydroxylase (AHH), and ethoxycoumarin O-deethylase (ECOD). The activities of NADPH-cytochrome P-450 reductase, AHH, and ECOD following treatment with HCB were similar to those found after dosing with PB. HCB caused a pattern of induction that was distinct from either BNF or PB and appeared to be a "mixed-type" inducer. The rapidity of the HCB-induced porphyrogenic response of Japanese quail, as compared to mammals, may provide unique advantages for making correlations between the in vivo metabolism of haloaromatic hydrocarbons and their effects on porphyrin metabolism.

The effect of tetrachlorohydroquinone on hexachlorobenzene-induced porphyria in Japanese quail

Female Japanese quail received either hexachlorobenzene (HCB, 100 mg/kg . d) or tetrachlorohydroquinone (TCHQ, 175 mg/kg . d) for 10 d as a primary treatment. Following this, a secondary treatment of HCB (100 mg/kg . d) or TCHQ (175 mg/kg . d), alone or in combination, was administered for 1, 5, 10 or 15 d. The primary HCB treatment caused elevated delta-aminolevulinic acid synthetase (ALA-S) activities and small increases in porphyrin concentrations. Subsequent treatment of these birds with lactose resulted in no further increases in porphyrins or ALA-S. TCHQ treatment caused increases in porphyrins similar to those seen with continued HCB treatment. Apparently, despite the fact that TCHQ alone had no affect on ALA-S or porphyrin levels, this compound is able, in the presence of elevated ALA levels to cause porphyria. A combination of HCB and TCHQ administered to HCB-pretreated animals caused a more severe porphyria than did follow-up treatment with either HCB or TCHQ alone.

Hexachlorobenzene-induced porphyria in Japanese quail: an in vitro study of changes in cytochrome P-450 and monooxygenases

The ability of hexachlorobenzene (HCB) to cause changes in the isozymic composition of hepatic monooxygenases of Japanese quail was assessed. HCB-induced changes in the relative concentrations of benzo[a]pyrene metabolites produced in vitro were apparent. HCB treatment also resulted in changes in the responsiveness of ethoxycoumarin O-deethylase (ECOD) and ethoxyresorufin O-deethylase (EROD) to the in vitro cytochrome P-450 inhibitors metyrapone, SKF-525A, and alpha-naphthoflavone. These changes may be indicative of alterations in the major cytochrome P-450 isozymes present following HCB treatment. Of these changes, only an increased responsiveness of ECOD to SKF-525A correlated with the onset of porphyria. The response of Japanese quail to the porphyrogenic action of HCB is more rapid than that found with more commonly used mammalian models. This rapid response is probably due either to the ability of quail to produce greater amounts of porphyrogenic metabolites of HCB than mammals or to a greater sensitivity of the heme pathway in quail to metabolites produced. In either case, this rapid response makes Japanese quail a good model for studying the biochemical mechanism for HCB-induced porphyria. The work presented here extends previous in vivo studies by using in vitro techniques to address the possibility that changes in the proportions of the major cytochrome P-450 isozymes occur in response to HCB and these changes, rather than changes in the total concentration of cytochrome P-450, are important to the development of porphyria.

Hexachlorobenzene-induced porphyria in Japanese quail: changes in microsomal enzymes

Hexachlorobenzene (HCB) was administered orally (500 mg/kg d) for 1, 2, 5, or 10d) to sexually mature Japanese quail to compare altered hepatic porphyrin levels with changes that occur in hepatic xenobiotic metabolizing enzymes. Porphyrin levels rapidly increased following the administration of HCB (three times control levels after a single dose of HCB), and birds began to develop porphyria (i.e., porphyrin levels were at least 10 times higher than controls) following 5 d of treatment. Following 10 d of HCB treatment, 3 of 4 treated quail were porphyric. Coincident with the HCB-induced disruption of the heme biosynthetic pathway were increases in various hepatic constituents. Changes included elevation of microsomal protein concentrations and increases in the specific content of cytochrome P-450, in the activities of aryl hydrocarbon hydroxylase (AHH), biphenyl hydroxylase (BPH), ethoxyresorufin-O-deethylase (EROD), and ethoxycoumarin-O-deethylase (ECOD), and in cytosolic and microsomal glutathione S-transferase (GSH-t) levels. In addition, the lambda max of the CO versus CO-reduced absorption spectra of hepatic microsomes from HCB-dosed birds showed a hypsochromic shift of 450 to 448 nm. The activity of NADPH-cytochrome P-450 reductase was increased following 10 d of HCB, and the activity of epoxide hydrolase was increased following 5 d of HCB. Most of these changes occurred with a single HCB treatment, and no further alterations developed in the nature of the response with repetitive dosing. Only weight loss, increased cytochrome P-450 content, and increases in GSH-t activity occurred simultaneously with the induction of porphyria.

Hexachlorobenzene-induced porphyria in Japanese quail. Effect of pretreatment with phenobarbital or beta-naphthoflavone

In an effort to determine the role that metabolism by the cytochrome P-450 system plays in the development of hexachlorobenzene (HCB)-induced porphyria, Japanese quail were pretreated with either beta-naphthoflavone (BNF) or phenobarbital (PB) and then treated with HCB. PB or BNF pretreatment appeared to have no effect on the response of quail hepatic enzymes to HCB. There were no differences between the two groups in either the content of cytochrome P-450 or the activities of NADPH-cytochrome c reductase, glutathione transferase (microsomal or cytosolic), ethoxycoumarin-O-deethylase or ethoxyresorufin-O-deethylase following HCB treatment. These pretreatments did, however, markedly influence the development of porphyria in quail. BNF-treated birds had higher delta-aminolevulinic acid-synthetase (ALA-S) activities and developed porphyria much more rapidly than birds treated with HCB alone. Birds pretreated with PB did not exhibit porphyria even following 10 days of HCB. Although the ALA-S activities in this group were elevated slightly following HCB, they were about one-half of those seen in the BNF-pretreated HCB-treated group. These results may reflect a difference between the PB and BNF groups in the production of a porphyrogenic metabolite of HCB.

Differential induction of hepatic drug metabolizing enzymes in Japanese quail by 1,2,4-trichlorobenzene

The effects of single oral administration of 1,2,4-trichlorobenzene (TCB), 200, 400, 800 or 1600 mg/kg, and of daily oral administration of TCB, 400 mg/kg, for 3 consecutive days, on components of the microsomal monooxygenase system, glutathione, and the activities of cytosolic glutathione S-transferase and microsomal epoxide hydrolase in Japanese quail liver were studied. Cytochromes P-450 and b5 contents of liver microsomes and the activities of 7-ethoxyresorufin deethylase (7-ERD) and glutathione S-transferase were significantly increased 1 day after administration of single doses of TCB. Liver GSH and 7-ethoxycoumarin deethylase (7-ECD) activity were unchanged. Microsomal epoxide hydrolase activity was significantly decreased at TCB doses above 400 mg/kg. Increases in cytochromes and activities of 7-ERD and glutathione S-transferase were also seen following the 3-day administration of TCB, 400 mg/kg. In addition, liver GSH and the activity of NADPH-cytochrome c reductase were significantly increased whereas 7-ECD was significantly decreased by the 3-day treatment. These findings indicate that in Japanese quail, TCB is an inducer of 7-ERD and glutathione S-transferase but not of 7-ECD and epoxide hydrolase.

Studies on the porphyrinogenic action of 1,2,4-trichlorobenzene in birds

The porphyrinogenic action of 1,2,4-trichlorobenzene (TCB) was examined in 17-day-old embryos, day-old chicks, 18-day-old chickens and adult Japanese quail. The quail was found to be the most sensitive species towards TCB induced porphyria whereas the chick embryo was totally non-responsive. The liver porphyrins of Japanese quail were increased in a dose-dependent manner 1 day after TCB. Elevation in porphyrin levels in quail was associated with comparable increases in delta-aminolevulinic acid synthetase (ALA-S) activity 1 day after TCB treatment. In contrast, ferrochelatase activity was found to be unchanged 1 day after TCB. Multiple administration of TCB produced only a slight increase in liver porphyrin levels and ALA-S activity in quail. However, there was a marked induction in ferrochelatase activity suggesting increased porphyrin turnover. Liver glutathione and glutathione S-transferase activity were also significantly increased following repeated administration of TCB in quail, which could indicate an enhancement of detoxication of reactive metabolites of TCB. Thus, it is suggested that the inability of low multiple doses of TCB to cause porphyria in Japanese quail may be related to the low responsiveness of ALA-S but high inducibility of ferrochelatase liver GSH and glutathione S-transferase.

Acetaminophen nephrotoxicity: studies on renal acetylation and deacetylation

Acetaminophen (N-acetyl-p-aminophenol; APAP) inhibits both the acetylation and uptake of p-aminohippurate (PAH) by slices of mouse kidney cortex; p-aminophenol (PAP) is more potent than APAP in inhibiting the acetylation of PAH, but has no effect on uptake of PAH. Since PAP itself is acetylated by the kidney, the action of PAP on the acetylation of PAH might be competitive. However, from kinetic analysis the inhibition is principally noncompetitive in nature. In studies on deacetylation, PAP was generated from APAP both in slices and homogenates of kidneys; acetylated PAH was relatively stable. PAP is a known nephrotoxin but has not been identified previously as a metabolite of APAP. The data indicate that the kidney has the capacity to generate a potent nephrotoxin, PAP, from a relatively benign precursor, APAP. This potentiality should be considered in further studies on the pathogenesis of analgesic nephropathy.

Uptake and acetylation of p-aminohippurate by slices of mouse kidney cortex

In slices of mouse kidney cortex, p-aminohippurate (PAH) is taken up by the organic anion transport system and then rapidly acetylated to p-acetylaminohippurate acid (PAAH), so that there is little net accumulation of PAH itself. The basic characteristics of this system have been described. Uptake may be measured as the total of PAH and PAAH combined. Both uptake and acetylation are dependent on aerobic metabolism. Succinate strongly inhibits net accumulation but has only a slight effect on the amount acetylated. This is attributed to the stimulation of efflux by succinate. In the mouse, the degree of acetylation as well as uptake varies with sex and strain, as well as with the drug used as substrate. When organic anion transport is employed as a test system for the assay of nephrotoxicity, it is proposed that slices from the mouse possess advantages over some other species in that acetylation and uptake provide dual endpoints.