Sex difference in the principal cytochrome P-450 for tributyltin metabolism in rats

Sex differences in CYP450-based sodium dehydroacetate metabolism and its metabolites in rats

Sodium dehydroacetate (DHA-Na), a widely used preservative, can induce sex-differentiated coagulation disorders primarily resulting from its metabolism. However, the underlying mechanisms remain poorly understood. Here, we identified several Cytochrome P450 (CYP450) sub-enzymes involved in sex differences related to DHA-Na metabolism, along with two related DHA-Na metabolites. CYP1A2, CYP3A2, and CYP2D1 were primarily responsible for DHA-Na metabolism, which was stronger in male rats than in female rats. Inhibition of these isoforms separately resulted in the DHA-Na metabolic capacity in male rats becoming equal to, or even weaker than, that in female rats. Furthermore, Cyp1a2, Cyp3a2, Cyp2d1, and Cyp2c11 expression was higher in male rats than in female rats, suggesting these enzymes are related to exhibited sex differences in DHA-Na metabolism. Moreover, 3-glycoloyl-6-methy-2,3-dihydropyran-2,4-dione (C8H8O5) and 3-imino-6-methyl-2,3-dihydropran-2,4dione (C6H5O3N) were identified as the two main DHA-Na metabolites. These findings provide crucial insights into potential mechanisms underlying sex differences in DHA-Na metabolism and its metabolites in rats.

A Theoretical Study of Organotin Binding in Aromatase

The widely used organotin compounds are notorious for their acute toxicity. Experiments revealed that organotin might cause reproductive toxicity by reversibly inhibiting animal aromatase functioning. However, the inhibition mechanism is obscure, especially at the molecular level. Compared to experimental methods, theoretical approaches via computational simulations can help to gain a microscopic view of the mechanism. Here, in an initial attempt to uncover the mechanism, we combined molecular docking and classical molecular dynamics to investigate the binding between organotins and aromatase. The energetics analysis indicated that the van der Waals interaction is the primary driving force of binding the organic tail of organotin and the aromatase center. The hydrogen bond linkage trajectory analysis revealed that water plays a significant role in linking the ligand-water-protein triangle network. As an initial step in studying the mechanism of organotin inhibiting aromatase, this work provides an in-depth understanding of the binding mechanism of organotin. Further, our study will help to develop effective and environmentally friendly methods to treat animals that have already been contaminated by organotin, as well as sustainable solutions for organotin degradation.

Sexual Dimorphism in the Expression of Cytochrome P450 Enzymes in Rat Heart, Liver, Kidney, Lung, Brain, and Small Intestine

Cytochrome P450 (P450) enzymes are monooxygenases that are expressed hepatically and extrahepatically and play an essential role in xenobiotic metabolism. Substantial scientific evidence indicates sex-specific differences between males and females in disease patterns and drug responses, which could be attributed, even partly, to differences in the expression and/or activity levels of P450 enzymes in different organs. In this study, we compared the mRNA and protein expression of P450 enzymes in different organs of male and female Sprague-Dawley rats by real-time polymerase chain reaction and western blot techniques. We found significant sex- and organ-specific differences in several enzymes. Hepatic Cyp2c11, Cyp2c13, and Cyp4a2 showed male-specific expression, whereas Cyp2c12 showed female-specific expression. Cyp2e1 and Cyp4f enzymes demonstrated higher expression in the female heart and kidneys compared with males; however, they showed no significant sexual dimorphism in the liver. Male rats showed higher hepatic and renal Cyp1b1 levels. All assessed enzymes were found in the liver, but some were not expressed in other organs. At the protein expression level, CYP1A2, CYP3A, and CYP4A1 demonstrated higher expression levels in the females in several organs, including the liver. Elucidating sex-specific differences in P450 enzyme levels could help better understand differences in disease pathogeneses and drug responses between males and females and thus improve treatment strategies. SIGNIFICANCE STATEMENT: This study characterized the differences in the mRNA and protein expression levels of different cytochrome P450 (P450) enzymes between male and female rats in the heart, liver, lung, kidney, brain, and small intestine. It demonstrated unique sex-specific differences in the different organs. This study is considered a big step towards elucidating sex-specific differences in P450 enzyme levels, which is largely important for achieving a better understanding of the differences between males and females in the disease's processes and treatment outcomes.

Benoxacor is enantioselectively metabolized by rat liver subcellular fractions

This study investigated the enantioselective metabolism of benoxacor, an ingredient of herbicide formulations, in microsomes or cytosol prepared from female or male rat livers. Benoxacor was incubated for ≤30 min with microsomes or cytosol, and its enantioselective depletion was measured using gas chromatographic methods. Benoxacor was depleted in incubations with active microsomes in the presence and absence of NADPH, suggesting its metabolism by hepatic cytochrome P450 enzymes (CYPs) and microsomal carboxylesterases (CESs). Benoxacor was depleted in cytosolic incubations in the presence of glutathione, consistent with its metabolism by glutathione S-transferases (GSTs). The depletion of benoxacor was faster in incubations with cytosol from male than female rats, whereas no statistically significant sex differences were observed in microsomal incubations. The consumption of benoxacor was inhibited by the CYP inhibitor 1-aminobenzotriazole, the CES inhibitor benzil, and the GST inhibitor ethacrynic acid. Estimates of the intrinsic clearance of benoxacor suggest that CYPs are the primary metabolic enzyme responsible for benoxacor metabolism in rats. Microsomal incubations showed an enrichment of the first eluting benoxacor enantiomer (E₁-benoxacor). A greater enrichment occurred in incubations with microsomes from female (EF = 0.67 ± 0.01) than male rats (EF = 0.60 ± 0.01). Cytosolic incubations from female rats resulted in enrichment of E₁-benoxacor (EF = 0.54 ± 0.01), while cytosolic incubations from male rats displayed enrichment of the second eluting enantiomer (E₂-benoxacor; EF = 0.43 ± 0.01). Sex-dependent differences in the metabolism of benoxacor in rats could significantly impact ecological risks and mammalian toxicity. Moreover, changes in the enantiomeric enrichment of benoxacor may be a powerful tool for environmental fate and transport studies.

Tributyltin: Advancing the Science on Assessing Endocrine Disruption with an Unconventional Endocrine-Disrupting Compound

Tributyltin (TBT) has been recognized as an endocrine disrupting chemical (EDC) for several decades. However, only in the last decade, was its primary endocrine mechanism of action (MeOA) elucidated-interactions with the nuclear retinoid-X receptor (RXR), peroxisome proliferator-activated receptor γ (PPARγ), and their heterodimers. This molecular initiating event (MIE) alters a range of reproductive, developmental, and metabolic pathways at the organism level. It is noteworthy that a variety of MeOAs have been proposed over the years for the observed endocrine-type effects of TBT; however, convincing data for the MIE was provided only recently and now several researchers have confirmed and refined the information on this MeOA. One of the most important lessons learned from years of research on TBT concerns apparent species sensitivity. Several aspects such as the rates of uptake and elimination, chemical potency, and metabolic capacity are all important for identifying the most sensitive species for a given chemical, including EDCs. For TBT, much of this was discovered by trial and error, hence important relationships and important sensitive taxa were not identified until several decades after its introduction to the environment. As recognized for many years, TBT-induced responses are known to occur at very low concentrations for molluscs, a fact that has more recently also been observed in fish species. This review explores the MeOA and effects of TBT in different species (aquatic molluscs and other invertebrates, fish, amphibians, birds, and mammals) according to the OECD Conceptual Framework for Endocrine Disruptor Testing and Assessment (CFEDTA). The information gathered on biological effects that are relevant for populations of aquatic animals was used to construct Species Sensitivity Distributions (SSDs) based on No Observed Effect Concentrations (NOECs) and Lowest Observed Effect Concentrations (LOECs). Fish appear at the lower end of these distributions, showing that they are as sensitive as molluscs, and for some species, even more sensitive. Concentrations in the range of 1 ng/L for water exposure (10 ng/g for whole-body burden) have been shown to elicit endocrine-type responses, whereas mortality occurs at water concentrations ten times higher. Current screening and assessment methodologies as compiled in the OECD CFEDTA are able to identify TBT as a potent endocrine disruptor with a high environmental risk for the original use pattern. If those approaches had been available when TBT was introduced to the market, it is likely that its use would have been regulated sooner, thus avoiding the detrimental effects on marine gastropod populations and communities as documented over several decades.

Hepatic Transcript Levels for Genes Coding for Enzymes Associated with Xenobiotic Metabolism are Altered with Age

Metabolism studies are crucial for data interpretation from rodent toxicity and carcinogenicity studies. Metabolism studies are usually conducted in 6 to 8 week old rodents. Long-term studies often continue beyond 100 weeks of age. The potential for age-related changes in transcript levels of genes encoding for enzymes associated with metabolism was evaluated in the liver of male F344/N rats at 32, 58, and 84 weeks of age. Differential expression was found between the young and old rats for genes whose products are involved in both phase I and phase II metabolic pathways. Thirteen cytochrome P450 genes from CYP families 1–3 showed alterations in expression in the older rats. A marked age-related decrease in expression was found for 4 members of the Cyp3a family that are critical for drug metabolism in the rat. Immunohistochemical results confirmed a significant decrease in Cyp3a2 and Cyp2c11 protein levels with age. This indicates that the metabolic capacity of male rats changes throughout a long-term study. Conducting multiple hepatic microarray analyses during the conduct of a long-term study can provide a global view of potential metabolic changes that might occur. Alterations that are considered crucial to the interpretation of long-term study results could then be confirmed by subsequent metabolic studies.

Evaluation of hepatotoxicity and cholestasis in rats treated with EtOH extract of Fructus Psoraleae

ETHNOPHARMACOLOGICAL RELEVANCE

Fructus Psoraleae (FP) has been widely used to heal skin diseases as well as osteoporosis, osteomalacia, and bone fracture. There also exist many clinical reports about FP-induced hepatotoxicity associated with acute cholestatic hepatic injury. However, the FP-induced hepatotoxicity and the underlying mechanisms remain unclear.

AIMS OF THE STUDY

The present study aims to determine the hepatotoxicity of FP in Sprague-Dawley (SD) rats and to investigate the underlying mechanisms.

MATERIALS AND METHODS

Sprague-Dawley rats of both sexes were intragastrically administered with the EtOH extract of FP (EEFP) at doses of 1.875, 1.25 and 0.625 g/kg for 28 day. Body weight, relative liver weight, biochemical analysis, histopathology, the mRNA and protein expression of Cholesterol 7α-hydroxylase (CYP7A1), farnesoid X receptor (FXR), bile-salt export pump (BSEP), multidrug resistance-associated protein 2 (MRP2), multidrug resistance-associated protein 3 (MRP3) were evaluated to study the EEFP-induced hepatotoxicity and its underlying mechanisms.

RESULTS

Many abnormalities were observed in the EEFP-treated groups including suppression of weight gain and food intake, change of some parameters in serum biochemistry, increased weight of liver, and decreased concentration of bile acid in bile. The mRNA and protein expression of CYP7A1, MRP3, MRP2, BSEP increased and the expression of FXR decreased in EEFP-treated female groups; the mRNA and protein of FXR and CYP7A1 decreased and that of the others remained the same in EEFP-treated male groups.

CONCLUSION

In conclusion, we provide evidence for the first time that EEFP can induce sex-related cholestatic hepatotoxicity, and that female rats are more sensitive to EEFP-induced hepatotoxicity, which involves the destruction of the biosynthesis and transportation of bile acid. Further investigation is still needed to uncover the mechanism of the sex-dimorphic EEFP-induced hepatotoxicity.

Fenofibrate-induced decrease of expression of CYP2C11 and CYP2C6 in rat

This short communication is aimed to investigate whether the widely used hypolipidemic drug fenofibrate affects CYP2C11 and CYP2C6 in rats, both counterparts of human CYP2C9, known to metabolise many drugs including S-warfarin and largely used non-steroidal antiinflammatory drugs such as ibuprofen, diclofenac and others. The effects of fenofibrate on the expression of rat liver CYP2C11 and CYP2C6 were studied in both healthy Wistar rats and hereditary hypertriglyceridemic rats. Both strains of rats were fed on diet containing fenofibrate (0.1% w/w) for 20 days. Fenofibrate highly significantly suppressed the expression of mRNA of CYP2C11 and less that of CYP2C6 in liver microsomes of both rat strains; this effect was associated with a corresponding decrease in protein levels. The results indicate that the combination of fenofibrate with drugs metabolised by CYP2C9 in humans should be taken with caution as it may lead, for example, to the potentiation of warfarin effects. This type of drug interaction has been observed previously and the results presented here could contribute to the explanation of their mechanism.

Metabolism of tributyltin and triphenyltin by Dall's porpoise hepatic microsomes

The in vitro metabolism of tributyltin (TBT) and triphenyltin (TPT) by the hepatic microsomal cytochrome P-450 system enzymes of Dall's porpoises (Phocoenoides dalli) was comparatively elucidated with those enzymes of the Sprague Dawley rat in the present study. Our results suggested firstly a limited metabolic capacity for TBT and especially TPT to their metabolites in the Dall's porpoises, and documented a similar mechanism of a relatively stronger metabolic rate of TBT to its metabolites than that of TPT in the microsome of porpoises and rat. However, the metabolic capacity to degrade both TBT and TPT were much lower in the microsome of porpoises than that in the rats.

[Comparative study of five trialkyltin compounds: their metabolites in rat organs 24 hours after single oral treatment]

OBJECTIVE

The objective of this study is to provide basic information on the metabolic fate of five trialkyltins, namely, trimethyltin, triethyltin, tripropyltin, tributyltin, and trioctyltin, in rats.

METHODS

The levels of trialkyltin and its metabolites in the liver, kidneys, brain, and blood of rats and mice were determined 24h after single oral treatment with trimethyltin, triethyltin, tripropyltin, tributyltin, and trioctyltin by gas chromatography. The doses (as tin) of the trialkyltin compounds were 2.98 mg/kg for trimethyltin and triethyltin, 18.23 mg/kg for tripropyltin and tributyltin and 24.09 mg/kg for trioctyltin.

RESULTS

For the trimethyltin and triethyltin treatments, no metabolites of either trialkyltin accumulated in the organs, except for the kidney in the triethyltin treatment. The levels of trimethyltin and triethyltin in the blood of the rats were markedly higher than those of the mice. For the tripropyltin and tributyltin treatments, the predominant metabolites in the liver and kidneys were found to be dialkyltins. Furthermore, despite the higher dose, the level of total tin in the organs 24 h after treatment with trioctyltin were markedly lower than those of the other trialkyltins tested.

CONCLUSION

There are clear differences in the metabolic fates of the tin metabolites of the five trialkyItins studied. These results should be considered when carrying out toxicological research on trialkyltins.