Effects of stress on circulating nicotine and cotinine levels and in vitro nicotine metabolism in the rat.

The effects of physical and psychological stress on circulating nicotine levels and conversion of nicotine to cotinine were examined in the rat. Animals received one of three dosages of nicotine (0, 6, and 12 mg/kg) via miniosmotic pumps. On day 14 of drug infusion, animals from each drug condition were randomly assigned to one of three stress conditions (noise, rubber ligature, or no stress). After 2.5 h of stress exposure, animals were killed and plasma nicotine and cotinine were measured in vivo and hepatic conversion of nicotine to cotinine was determined in vitro. Stress lowered blood nicotine levels. However, this difference was statistically significant only among animals receiving 12 mg/kg per day nicotine. In contrast, stress had no consistent effect on either measure of conversion of nicotine to cotinine in rats. Taken together, these results suggest that stress lowers circulating nicotine levels. However, the mechanism by which this occurs remains unclear.

Consequences of overexpression of growth hormone in transgenic mice on liver cytochrome P450 enzymes.

The effect of growth hormone (GH) on cytochrome P450 (CYP) and P450-dependent monooxygenases was studied in 4-, 6-, 8-, and 10-month-old female bovine growth hormone (bGH) transgenic mice that overexpress GH. Nontransgenic female mice (C57/SJL) littermates were used for baseline determinations. The body weights of the bGH mice were approximately 35% greater than those of the controls. The liver weights were 2-fold higher than those of the controls, resulting in a 25-60% increase in liver/body weight ratio during the life span of the bGH mice when compared with the controls. Similar increases in heart and kidney weights were observed. Since the GH transgene was transcriptionally regulated by a metallothionein-I gene promoter, metallothionein concentrations in livers of transgenic and nontransgenic mice were measured. No significant differences were observed. In marked contrast to increases in liver weights, hepatic cytochrome P450 content, benzphetamine N-demethylase, and benzo [a] pyrene hydroxylase activities were decreased by 36, 42 and 75%, respectively. No age-related changes in the decrease of the monooxygenases were observed. Microsomal heme oxygenase (HO) in the liver was induced 44% above the control values. Immunoblot analysis also showed a marked increase in HO-1 in the bGH mice. These results indicate that GH suppresses the carcinogen-metabolizing enzyme benzo [a] pyrene hydroxylase and the drug-metabolizing enzyme benzphetamine N-demethylase. This suppression was accompanied by an induction of HO activity in bGH transgenic mice. The consequences of prolonged exposure to supraphysiological levels of this hormone cannot always be predicted from the known physiological actions of GH.

Species differences in the renal toxicity of the antiarthritic drug, gold sodium thiomalate.

Two gold compounds, gold sodium thiomalate (AuTM) and auranofin, are presently in clinical use in therapy of rheumatoid arthritis. In these studies, AuTM administered to Sprague-Dawley rats and three strains of mice, Swiss-Webster, C3H/HeJ, and DBA/2J, were studied with regard to its effect on liver and renal monooxygenases, metallothionein contents, and serum levels of alanine aminotransferase and urea nitrogen. These effects of AuTM were compared to those of cadmium, since the latter metal has exhibited tissue and species differences in the induction of metallothionein. Benzo(a)pyrene hydroxylase and benzphetamine N-demethylase activities were not altered by AuTM in livers of rats and the three strains of mice. Benzo(a)pyrene hydroxylase activity was significantly decreased in rat kidney, whereas this enzyme activity was not affected in the kidneys of mice. In rats, AuTM caused a sevenfold induction in liver metallothionein, while in mice, liver metallothionein was induced twofold in Swiss-Webster mice and about fivefold in the inbred strains. AuTM caused minimal changes in renal metallothionein contents in the three strains of mice studied. Serum alanine amino-transferase, an indicator of hepatotoxicity, was not altered by AuTM in rats and mice studied. Blood urea nitrogen, an indicator of kidney dysfunction, was increased threefold in rats, but not in AuTM-treated mice. These data demonstrate that AuTM, a nephrotoxic agent in rats and humans, showed no nephrotoxic effects in the mouse strains studied here.

Plasmodium berghei: sensitivity of chloroquine-resistant and chloroquine-sensitive strains to irradiation and the effect of irradiated malaria parasites on cytochrome P450-dependent monooxygenases.

Differences in sensitivities of chloroquine-sensitive and chloroquine-resistant strains of Plasmodium berghei were observed following irradiation of the parasites. A dose of 15 kilorads from a cobalt-60 source killed the erythrocytic stages of the chloroquine-sensitive strain and no parasitemias were observed when mice were injected with these irradiated parasites. In contrast, when the chloroquine-resistant strain was irradiated with the same dose of cobalt-60 and injected into mice, an infection rate of 12.5% was observed, indicating that the latter strain was more resistant to inactivation by irradiation. Following injection of these irradiated strains of P. berghei into mice, significant decreases in mouse hepatic cytochrome P450 and benzo(a)pyrene hydroxylase activity, with no significant effect on N-demethylase activity, were observed. Serum glutamic-oxaloacetic transaminase (SGOT) and glutamic-pyruvic transaminase (SGPT) levels of mice injected with the irradiated parasites fell within the range of the serum enzyme levels in normal laboratory mice.

Metabolism of benzo(a)pyrene by lung microsomes from rabbits pretreated with polychlorinated biphenyls and 2,3,4,7,8-pentachlorodibenzofuran.

The polychlorinated biphenyls (PCBs) mixture, Aroclor 1254, is a weak inducer of aryl hydrocarbon hydroxylase (AHH) activity in rabbit lung. In contrast, 2,3,4,7,8-pentachlorodibenzofuran (PCDF), like 3-methylcholanthrene (3-MC), caused a 3-fold increase in pulmonary AHH activity. An important finding of the present studies was that AHH activity, whether assayed by the flourometric or HPLC methods, was dependent on the buffer used in the incubation mixture. The metabolism of benzo(a)pyrene (BP) to its oxidative metabolites, as assayed by HPLC, revealed that PCBs, PCDF and 3-MC pretreatments caused greater than 15-fold and about 3- to 4-fold increase in the formation of the tumorigenic metabolites 9,10- and 7,8-dihydrodiols, respectively. In contrast to 3-MC and PCDF, PCBs caused a 75% decrease in the formation of the K-region metabolite, BP-4,5-dihydrodiol. These studies strongly suggest that the catalysis of BP metabolism is mediated by more than one isoform of cytochrome P450 (P450).

Comparisons of hepatic and renal cytochromes P-450-dependent monooxygenases from fuzzy and Sprague-Dawley rats.

The differences in monooxygenase activities between the fuzzy rat, a variant of the hairless rat, and the Sprague-Dawley rat were examined. Benzo(a)pyrene hydroxylase and benzphetamine N-demethylase activities and cytochrome P-450 contents were significantly lower in the livers of fuzzy rats than in the livers of the Sprague-Dawley rats. The hydroxylase activity in the kidneys of the two strains were not significantly different from each other. In comparison to the Sprague-Dawley rats, the induction of these enzymic activities by phenobarbital and 3-methylcholanthrene were of a lesser magnitude in the fuzzy rats, indicating that regulation of the hepatic monooxygenases differed in the two strains. Immunoblot data showed that cross-reactivity between antirat P-450IIB1 and microsomal protein from phenobarbital-treated rats appeared to be lower in the fuzzy rat when compared with the Sprague-Dawley rat. These differences in the constitutive enzymes and the differences in the induction of hepatic monooxygenases between the two strains of rats may be important determinants in studies involving metabolism of drugs and other chemicals following cutaneous exposure.

Effects of cage beddings on microsomal oxidative enzymes in rat liver.

The purpose of the present studies was to evaluate the effects of some commercially available cage beddings on rat liver microsomal cytochrome P-450-dependent drug-metabolizing enzyme, ethylmorphine N-demethylase, and the carcinogen-metabolizing enzyme, benzo(a)pyrene hydroxylase. Sprague-Dawley rats were housed in cages containing cedar chip, corncob or heat-treated pinewood bedding for 3 weeks. Control rats were housed in cages on wire bottom floors containing no bedding material. Rats housed in cages containing cedar chip showed 18, 46 and 49% increases in liver cytochrome P-450 content, ethylmorphine N-demethylase and benzo(a)pyrene hydroxylase activities, respectively. The liver enzyme activities of rats housed in cages containing corncob bedding were similar to those obtained with control rats. In contrast, the pinewood-bedded rats showed a 21% decrease in ethylmorphine N-demethylase activity without affecting cytochrome P-450 content and benzo(a)pyrene hydroxylase activity. Hexobarbital-induced sleep times of the variously bedded rats were similar to those of control animals. These data suggest that the commercial bedding materials differ in their abilities to affect liver microsomal enzymes. Thus, interlaboratory variability in basal enzyme activities reported in the literature may be partly due to bedding materials used in the animal's cages.

Chromatographic and catalytic properties of multiple forms of rabbit pulmonary cytochromes P-450.

Rabbit pulmonary cytochrome P-450 forms 2, 5, and 6 were resolved using anion-exchange high-performance liquid chromatography (HPLC) and their properties compared with rabbit liver cytochrome P-450 isozymes LM2 and LM6. Although rabbit pulmonary form 2 and liver LM2 had similar electrophoretic mobilities and similar substrate specificities in reconstitution experiments, they differed in their HPLC elution profiles. High-performance liquid chromatography of pulmonary microsomes from rabbits treated with 3-methylcholanthrene (3-MC) revealed the induction of form 6 isozyme, which had a retention time, electrophoretic mobility, and substrate specificity similar to those of rabbit liver LM6. In reconstitution experiments, forms 2 and 6 showed the highest substrate specificities toward benzphetamine and 7-ethoxyresorufin, respectively. Rabbit lung cytochrome P-450 form 5 was relatively inactive toward all substrates tested.

Acute nephropathy induced by gold sodium thiomalate: alterations in renal heme metabolism and morphology.

Gold compounds are used clinically in rheumatoid arthritis therapy. Acute renal toxicity is observed in some patients receiving chrysotherapy. The present study addresses morphofunctional and biochemical changes in rat kidneys during the first 8 days following a single ip injection of gold sodium thiomalate (AuTM), one of the gold compounds presently in clinical use. Compared to controls, AuTM pretreatment resulted in increased urine output and elevated serum creatinine and urea nitrogen concentrations. Also, by Day 8, treated rats had decreased body weights and increased kidney weights. Postmortem examination on Day 1 showed pale and mottled kidneys and diffusely pale inner cortex. Microscopically, there was severe coagulative necrosis of the proximal tubular epithelium. Epithelial regeneration was prominent by Day 4 and was nearly complete by Day 8. The regenerating epithelium was hyperplastic with basophilic cytoplasm and pleomorphic nuclei. Alterations in renal heme biosynthesis and drug metabolism paralleled the morphologic changes. The activity of delta-aminolevulinic acid dehydratase and benzo[a]pyrene hydroxylase were inhibited on Days 1, 2, and 4 following AuTM administration. Decreases in monooxygenase activity were accompanied by decreases in renal cytochrome P-450 levels. In contrast, renal microsomal heme oxygenase activity was elevated 9.5-fold on Day 1 and 2.5-fold on Day 2. By Day 8, all renal enzymatic activities assayed for were similar to those obtained with untreated rats.

Regulation of heme metabolism and monooxygeneses in liver and kidney: influence of therapeutically used gold compounds.

Two gold compounds, gold sodium thiomalate (AuTM) and auranofin (AF) are presently in clinical use in therapy of rheumatoid arthritis. The effects of varying doses of AF administered to rats by either the p.o. or the i.p. route on heme metabolism were determined. Twenty four hours after a single dose of AF, decreases in the sulfhydryl-containing enzymes, delta-aminolevulinic acid dehydratase and ferrochelatase activities were observed in the liver and kidneys. These decreases in heme biosynthetic enzymes were accompanied by decreases in cytochrome P-450-dependent enzymic activities and increases in microsomal heme oxygenase activity. These changes were observed with AF dosages as low as 5 mg/kg, with maximal changes occurring at a p.o. dose of about 15 mg of AF per kg and an i.p. dose of 5 to 10 mg of AF per kg. Dose-response studies with AuTM showed that maximal changes in heme metabolism occur at a lower dose of AF than of AuTM, even though AF was administered p.o. and AuTM was administered parenterally. In addition, the kidneys appeared to be more susceptible to the inhibitory effects of the two chrysotherapeutic agents than did the liver. The present studies demonstrate the p.o. drug AF affects heme metabolism in a manner similar to that reported previously with the parenterally administered AuTM.

Differences in the in vivo and in vitro effects of the carbamate insecticide, carbaryl on rat hepatic monooxygenases.

The effects of one of the most widely used insecticides, carbaryl, on the hepatic cytochrome P-450-dependent monooxygenases were determined. Addition of carbaryl to liver microsomes from untreated or phenobarbital (PB)-pretreated rats resulted in a weak Type I binding spectrum. A much stronger spectral Type I interaction was observed when microsomes from 3-methylcholanthrene(3-MC)-treated rats were used. In vitro, carbaryl caused marked inhibition of ethylmorphine and benzphetamine N-demethylases, benzo(a)pyrene hydroxylase, 7-ethoxycoumarin and 7-ethoxyresorufin O-deethylase in liver microsomes. Kinetic studies demonstrated that carbaryl was a competitive inhibitor of ethylmorphine N-demethylase activity. Daily administration of carbaryl for 4 days by gavage or intraperitoneally resulted in no significant alterations in hepatic cytochrome P-450 levels, ethylmorphine N-demethylase or benzo(a)-pyrene hydroxylase activities. The lack of effect of carbaryl in vivo may be due to the rapid metabolism of the insecticide, such that the insecticide may not be present in the liver endoplasmic reticulum to cause the inhibitory effects observed in vitro.

Selective induction and inhibition of liver and lung cytochrome P-450-dependent monooxygenases by the PCBs mixture, Aroclor 1016.

The effects of the widely used industrial PCBs mixture, Aroclor 1016, as modifiers of monooxygenases were studied in rats and rabbits. From data presented, it is not possible to generalize the biological effects of PCBs observed with rats, namely, that they are potent, non-specific inducers of monooxygenase activities. In rat liver, Aroclor 1016 exhibited primarily the potent inducing effects of the barbiturate class of inducers. In contrast, in rabbits pretreated with Aroclor 1016, although cytochrome P-450 content of the liver was significantly increased, benzphetamine N-demethylase and benzo[a]pyrene hydroxylase activities were decreased 30-35%; and no changes in the O-deethylation of 7-ethoxycoumarin and 7-ethoxyresorufin were observed. These results strongly suggest differences in the regulation of cytochrome P-450 isozymes in the liver by the PCBs. A similar conclusion can be drawn from the pulmonary studies of Aroclor 1016-pretreated rabbits. In the lung, cytochrome P-450, form 2 and associated enzymic activities were markedly decreased, with little or no effect on the form 5 isozyme. Electrophoretic and chromatographic studies confirmed these findings. The induction and the repression of a form or forms of cytochrome P-450 by environmentally-derived chemicals may be important determinants of organ-targeted chemical toxicity.

Regulation of hepatic monooxygenases by phenobarbital, 3-methylcholanthrene, and polychlorinated biphenyls in rapid and slow acetylator mice.

A/J and C57BL/6J inbred mouse strains have been previously used as models of slow and fast acetylators, respectively, of human acetylator polymorphism. Studies were carried out to characterize possible differences in basal activities of hepatic monooxygenases and the response of these mouse strains to microsomal enzyme inducers. No significant difference in cytochrome P-450 content and associated enzyme activities of ethylmorphine N-demethylase and benzo(a)pyrene hydroxylase were observed between the two strains. The administration of the inducers, phenobarbital or the polychlorinated biphenyl mixture Aroclor 1254, resulted in significant increases in cytochrome P-450 and ethylmorphine N-demethylase activity and minimal changes in benzo(a)pyrene hydroxylase activity in both strains. Pretreatment with 3-methylcholanthrene resulted in little or no increase in N-demethylase activity in both strains. The polycyclic hydrocarbon caused a CO difference spectral shift to a lower wavelength only in the C57BL/6J mice. Further, it increased benzo(a)pyrene hydroxylase activity in both strains, but to a greater extent in the C57BL/6J strain. Electrophoretic studies using solubilized microsomal preparations confirmed the findings that the fast acetylators were highly responsive to the inducing properties of the polycyclic aromatic hydrocarbon, whereas the slow acetylators were relatively much less responsive to its inducing properties. The latter strain appeared to be more responsive to the inducing properties of the phenobarbital class of inducers, as reflected in the inducibility of cytochrome P-450 and the associated enzymic activities in the liver.

Pulmonary cytochromes P-450 from rabbits treated with phenobarbital.

Pretreatment of rabbits with phenobarbital caused significant increases in total pulmonary cytochrome P-450 content, benzo(a)pyrene hydroxylase and 7-ethoxycoumarin O-deethylase activities and to a lesser extent in benzphetamine N-demethylase activity in lung microsomes. However, 7-ethoxyresorufin O-deethylase activity was not significantly altered. In addition, the pulmonary concentration of the cytochrome P-450-metyrapone complex was increased significantly. Column chromatography of the pulmonary monooxygenases demonstrated that in untreated and phenobarbital-treated rabbits, cytochromes P-450I and P-450II constituted the major forms of cytochrome P-450 isozymes. In addition, the chromatographic studies showed that pretreatment with phenobarbital caused an increase in the content of cytochrome P-450I, but not of cytochrome P-450II. These observations were confirmed by subjecting the pulmonary cytochromes to gel electrophoresis, and staining of the gels for protein and heme.

Impairment of hepatic cytochrome P-450-dependent monooxygenases by the malaria parasite Plasmodium berghei.

The effect of Plasmodium berghei infection on hepatic monooxygenase activities and cytochrome P-450 contents was investigated in mice. NIH/NMRI or A/J mice infected with active P. berghei showed 30-40% decreases in hepatic cytochrome P-450 contents and the ability to metabolize the test substrates, ethylmorphine and benzo(a)pyrene. These decreases were observed during the erythrocytic stage of the infection, but not during the initial exoerythrocytic stage, or after heat-inactivated sporozoites were injected. These results strongly suggest that malaria infections may significantly impair the capacity of the liver to metabolize drugs, carcinogens, and other foreign compounds.

Comparative effects of ethanol administration on hepatic monooxygenases in rats and mice.

The inducing effects of chronic ethanol ingestion on hepatic monooxygenases in Sprague-Dawley and Long-Evans rats, and A/J and C57BL/6J mice, were studied. Cytochrome P-450 content was significantly increased in livers of all animals receiving the experimental ethanol-containing liquid diet. The CO-difference spectra of microsomes from ethanol-treated animals showed a shift in the absorbance maximum to 451-452 nm, compared to the absorbance maximum of 450 nm observed with microsomes from control animals. Ethylmorphine N-demethylase and benzo[a]pyrene hydroxylase activities in livers of ethanol-treated animals were minimally affected. The shift in the absorbance maxima to longer wavelengths in the CO-difference spectrum and the minimal effects on the metabolism of ethylmorphine and benzo[a]pyrene demonstrate that ethanol differs in its inducing properties, when compared to the properties of the two widely used hepatic microsomal enzyme inducers, phenobarbital and 3-methylcholanthrene. In contrast to the minimal effects observed on the metabolism of ethylmorphine and benzo[a]pyrene, several fold increases were observed in hepatic 7-ethoxycoumarin 0-deethylase and aniline hydroxylase activities in the treated animals. Polyacrylamide gel electrophoresis of hepatic microsomes from those animals receiving ethanol revealed protein band(s) in the cytochrome P-450 molecular weight region, the intensities of which were markedly increased relative to that from control animals. The heme-associated peroxidase activity was also increased in the same molecular weight region. The results of the present spectral, catalytic, and electrophoretic studies demonstrate that in mice, as in rats, chronic ethanol treatment causes the induction of specific cytochrome(s) P-450 with preferential activity toward aniline and 7-ethoxycoumarin.

Effect of heme on allylisopropylacetamide-induced changes in heme and drug metabolism in the rhesus monkey (Macaca mulatta).

In rhesus monkeys, in which porphyria was induced by the administration of allylisopropylacetamide (AIA), hepatic delta-aminolevulinic acid synthase (ALA-S) was increased. Cytochrome P-450 and associated monooxygenase activities and microsomal heme oxygenase activity were decreased in these animals. Administration of heme for 4 days concurrently with AIA prevented the induction of hepatic ALA-S but produced further decreases in cytochrome P-450 and monooxygenase activities. The decrease in heme oxygenase activity elicited by AIA alone was partially reversed. Administration of heme alone caused an impairment of hepatic drug metabolism but had no significant effect on heme metabolism. The porphyric monkeys showed elevation of porphyrin levels in blood and urine. When heme was administered concurrently with AIA, blood porphyrin levels were further elevated, while the urinary excretion of porphyrins was lower than that following treatment of monkeys with AIA. Following the administration of heme alone, blood and urinary porphyrin levels were minimally affected. These results suggest that repeated heme administration in the primate may adversely affect drug metabolism by the liver.