Sex-dependent expression and growth hormone regulation of class alpha and class mu glutathione S-transferase mRNAs in adult rat liver

Gstm1/Gstt1 is essential for reducing cisplatin ototoxicity in CBA/CaJ mice

Cisplatin is a widely used chemotherapeutic agent. However, its clinical utility is limited because of cisplatin-induced ototoxicity. Glutathione S-transferase (GST) was found to play a vital role in reducing cisplatin ototoxicity in mice. Deletion polymorphisms of GSTM1 and GSTT1, members of the GST family, are common in humans and are presumed to be associated with cisplatin-induced hearing impairment. However, the specific roles of GSTM1 and GSTT1 in cisplatin ototoxicity are not completely clear. Here, under cisplatin treatment, simultaneous deletion of Gstm1 and Gstt1 lead to a more profound hearing loss in CBA/CaJ mice (Gstm1/Gstt1-DKO) than in wild-type mice. The Gstm1/Gstt1-DKO mice, in which phase II detoxification genes were upregulated, exhibited more severe oxidative stress and higher outer hair cell apoptosis in the cochleae than the control mice. Thus, our study revealed that Gstm1 and Gstt1 protect auditory hair cells from cisplatin-induced ototoxicity in the CBA/CaJ mice, and genetic screening for GSTM1 and GSTT1 polymorphisms could help determine a standard cisplatin dose for cancer patients undergoing chemotherapy.

Protective effect of genistein pre-treatment on paraquat hepatotoxicity in rats

Paraquat (PQ), an herbicide widely used in agriculture, is considered a highly toxic compound. In hepatocytes, P-glycoprotein (P-gp/Abcb1) is a canalicular transporter involved in PQ extrusion from the cell. Previously, we demonstrated that genistein (GNT) induces P-gp in rat liver. In this study, the protective role of GNT pretreatment towards hepatic damage in a model of acute intoxication with PQ in rats, was investigated. Wistar rats were randomized in 4 groups: Control, GNT (5 mg/kg/day sc, 4 days), PQ (50 mg/kg/day ip, last day) and GNT+ PQ. Hepatic lipoperoxidation (LPO) was evaluated by the thiobarbituric acid reactive substances method. Hepatic levels of 4-hydroxynonenal protein adducts (4-HNEp-add) and glutathione-S-transferase alpha (GSTα) protein expression were evaluated by Western blotting. Hepatic glutathione levels and plasma levels of alanine transaminase (ALT) and aspartate transaminase (AST) were also measured. Biliary excretion of PQ was studied in vivo and in isolated perfused liver. PQ was quantified by HPLC. PQ significantly increased AST and ALT activities, malondialdehyde and 4-HNEp-add levels, whereby pretreatment with GNT ameliorated this effect. PQ biliary excretion remained unchanged after treatments in both experimental models. Hepatic GSTα expression was augmented in GNT group. GNT pretreatment increased hepatic glutathione levels in PQ + GNT group. These results agree with the lower content of 4-HNEp-adds in GNT + PQ group respect to PQ group. Unexpectedly, increased activity of P-gp did not enhance PQ biliary excretion. Thus, GNT protective mechanism is likely through the induction of GSTα which results in increased 4-HNE metabolism before formation of protein adducts.

Protective effect of glutathione S-transferase enzyme activity against aflatoxin B1 in poultry species: relationship between glutathione S-transferase enzyme kinetic parameters, and resistance to aflatoxin B1

Comparative studies designed to investigate the role of glutathione S-transferase (GST) activity on the enzyme catalyzed trapping of aflatoxin B1-8,9-epoxide (AFBO) with glutathione, and the relationship with aflatoxin B1 (AFB1) resistance have not been conducted in poultry. Hepatic cytosolic fractions of chickens, quail, turkeys and ducks were used to measure in vitro the enzymatic parameters maximal velocity (Vmax), Michaelis-Menten constant (Km) and intrinsic clearance (CLint) for GST activity. AFB1 used ranged from 2.0 to 157.5 µM and the AFB1-GSH produced was identified and quantitated by HPLC. Significant differences were found in GST Vmax values, being the highest in chickens, followed by quail, ducks and turkeys. The Km values were also significantly different, with chickens < ducks < turkeys < quail. Chickens had the higher CLint value in contrast to ducks. Differences by sex showed that duck females had a higher CLint value than the turkey and quail, whereas duck males had a CLint close to that of turkey. The ratio "AFBO production /AFB1-GSH production" follows the order duck>turkey>quail>chicken, in agreement with the known poultry sensitivity. The extremely high "AFB1 epoxidation activity/ GST activity" ratio observed in ducks might be the explanation for the development of hepatocellular carcinoma in this species.

GSTA4 mediates reduction of cisplatin ototoxicity in female mice

Cisplatin is one of the most widely used chemotherapeutic drugs for the treatment of cancer. Unfortunately, one of its major side effects is permanent hearing loss. Here, we show that glutathione transferase α4 (GSTA4), a member of the Phase II detoxifying enzyme superfamily, mediates reduction of cisplatin ototoxicity by removing 4-hydroxynonenal (4-HNE) in the inner ears of female mice. Under cisplatin treatment, loss of Gsta4 results in more profound hearing loss in female mice compared to male mice. Cisplatin stimulates GSTA4 activity in the inner ear of female wild-type, but not male wild-type mice. In female Gsta4^−/− mice, cisplatin treatment results in increased levels of 4-HNE in cochlear neurons compared to male Gsta4^−/− mice. In CBA/CaJ mice, ovariectomy decreases mRNA expression of Gsta4, and the levels of GSTA4 protein in the inner ears. Thus, our findings suggest that GSTA4-dependent detoxification may play a role in estrogen-mediated neuroprotection.

A common complication of cisplatin-based chemotherapy is hearing loss. Here, Park et al. show that glutathione transferase α4 (GSTA4) contributes to reducing cisplatin toxicity in the inner ear of female mice by removing 4-hydroxynonenal (4-HNE).

Genomics of sex hormone receptor signaling in hepatic sexual dimorphism

The liver plays a crucial role in a variety of physiological processes. Sexual dimorphism is markedly defined in liver disorders, such as fatty liver diseases and liver cancer, but barely addressed in the normal liver. Distinct sex hormone signaling between male and female livers is the major driving factor for hepatic sexual dimorphism. Over 6000 genes are differently expressed between male and female livers in mice. Here we address how sex hormone receptors, estrogen receptor alpha (ERα) and androgen receptor (AR), mediate sexually dimorphic gene expression in mouse livers. We identified 5192 ERα target genes and 4154 AR target genes using ChIP-Seq. Using liver-specific ERα or AR knockout mice, we further identified direct and functional target genes of ERα (123 genes) and AR (151 genes) that contribute to hepatic sexual dimorphism. We also found that the most significant sexually dimorphic gene expression was initiated at birth by comparing hepatic gene expression data from the embryonic stage E10.5 to the postnatal stage P60 during liver development. Overall, our study indicates that sex hormone receptor signaling drives sexual dimorphism of hepatic gene expression throughout liver development.

UPLC-MS/MS determination and gender-related pharmacokinetic study of five active ingredients in rat plasma after oral administration of Eucommia cortex extract

ETHNOPHARMACOLOGICAL RELEVANCE

Eucommiae cortex (EC), the bark of Eucommia ulmoides Oliv., has been traditionally used to treat many diseases in China for more than 2000 years. The pharmacological effects are primarily attributed to the presence of lignans, iridoids and phenolics, which are main active ingredients in EC.

AIM OF THE STUDY

First, to investigate the active ingredients that can be absorbed into the rat plasma according to which ingredients exhibit significant correlation of drug concentration-time curve. Second, to establish an efficient ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) method for simultaneous determination of ingredients absorbed in rat plasma. Finally, to investigate gender effect on the pharmacokinetics of the ingredients absorbed in male and female rats plasma after oral administration with EC extract.

MATERIALS AND METHODS

18 ingredients from EC were detected by UPLC-MS/MS, 9 out of 18 ingredients were absorbed into rat plasma. And 5 ingredients exhibit significant correlation of drug concentration-time curve. They were pinoresinol di-O-β-d-glucopyranoside (PDG), geniposide (GE), geniposidic acid (GA), aucubin (AN) and chlorogenic acid (CA). The analytes were extracted from rat plasma via a simple protein precipitation procedure and osalmid was used as the internal standard. Chromatographic separation was achieved on a Waters ACQUITY HSS T3 column (2.1mm×100mm, 1.8μm) using a gradient elution program with acetonitrile and 0.1% formic acid water as the mobile phase, with a flow rate of 0.3mLmin(-1). The detection was performed on a triple-quadrupole tandem mass spectrometer by multiple reactions monitoring (MRM) mode in a positive ion mode via electrospray ionization (ESI). The transition monitored were /z 683.00[M+H](+)→235.10 for PDG, / z 389.00[M+H](+)→208.80 for GE, m/z 375.00[M+H](+)→194.79 for GA, m/z 364.00[M+NH4](+)→148.81 for AN, m/z 355.10[M+H](+)→162.84 for CA and m/z 230.03[M+H](+)→120.77 for internal standard.

RESULTS

The developed method showed good linearity over a wide concentration range, the lower limits of quantification and higher accuracy and precision for determination of the 5 analytes. Then the method was applied to study the pharmacokinetics in rats, and the results indicated that there were significant differences in pharmacokinetic parameters of the analytes between the male and female rats, and absorptions of these analytes in male group were all significantly higher than those in female group.

CONCLUSION

This study established an efficient, sensitive and selective UPLC-MS/MS method for simultaneous determination of the five ingredients in rat plasma, and it could be successfully applied to the comparative pharmacokinetic studies in male and female rats after oral administration with EC extract.

Hormonal regulation of hepatic drug biotransformation and transport systems

The human body is constantly exposed to many xenobiotics including environmental pollutants, food additives, therapeutic drugs, etc. The liver is considered the primary site for drug metabolism and elimination pathways, consisting in uptake, phase I and II reactions, and efflux processes, usually acting in this same order. Modulation of biotransformation and disposition of drugs of clinical application has important therapeutic and toxicological implications. We here provide a compilation and analysis of relevant, more recent literature reporting hormonal regulation of hepatic drug biotransformation and transport systems. We provide additional information on the effect of hormones that tentatively explain differences between sexes. A brief discussion on discrepancies between experimental models and species, as well as a link between gender-related differences and the hormonal mechanism explaining such differences, is also presented. Finally, we include a comment on the pathophysiological, toxicological, and pharmacological relevance of these regulations.

Effects of insulin-like growth factor 1 on glutathione S-transferases and thioredoxin in growth hormone receptor knockout mice

Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) have been shown to affect processes involved in cellular stress defense, aging, and longevity. This study was designed to identify possible mechanisms of a disrupted GH signaling pathway on stress resistance using growth hormone receptor knockout (GHRKO) mice. GHRKO mice are GH resistant due to the targeted disruption of the GH receptor/binding protein gene, thus preventing GH from binding and exerting its downstream effects. These mice have very low circulating IGF-1 levels and high GH levels, are obese yet insulin sensitive, and live longer than their wild-type controls. Wild-type or GHRKO mice were treated with saline or IGF-1 (WT saline, GHRKO saline, GHRKO IGF-1) two times daily for 7 days. Glutathione S-transferase (GST) activities, proteins, and gene expression were determined. Liver mitochondrial GSTA1, GSTA3, and GSTZ1 proteins were significantly higher in GHRKO when compared to those of WT mice. The 4-hydroxynonenal (4-HNE) GST activity was upregulated in GHRKO mice and was suppressed after IGF-1 administration. Interestingly, thioredoxin (Trx)1, Trx2, thioredoxin reductase (TrxR)1, and TrxR2 messenger RNA (mRNA) levels were significantly higher in the GHRKO as compared to WT mice, and IGF-1 treatment suppressed the expression of each. We also found that glutaredoxin (Grx)2 mRNA and cytosolic Grx activity were higher in GHRKO mice. These results suggest that the detoxification and stress response mechanisms in GHRKO mice are contributed in part by the circulating level of IGF-1.

Growth hormone alters the glutathione S-transferase and mitochondrial thioredoxin systems in long-living Ames dwarf mice

Ames dwarf mice are deficient in growth hormone (GH), prolactin, and thyroid-stimulating hormone and live significantly longer than their wild-type (WT) siblings. The lack of GH is associated with stress resistance and increased longevity. However, the mechanism underlying GH's actions on cellular stress defense have yet to be elucidated. In this study, WT or Ames dwarf mice were treated with saline or GH (WT saline, Dwarf saline, and Dwarf GH) two times daily for 7 days. The body and liver weights of Ames dwarf mice were significantly increased after 7 days of GH administration. Mitochondrial protein levels of the glutathione S-transferase (GST) isozymes, K1 and M4 (GSTK1 and GSTM4), were significantly higher in dwarf mice (Dwarf saline) when compared with WT mice (WT saline). GH administration downregulated the expression of GSTK1 proteins in dwarf mice. We further investigated GST activity from liver lysates using different substrates. Substrate-specific GST activity (bromosulfophthalein, dichloronitrobenzene, and 4-hydrox-ynonenal) was significantly reduced in GH-treated dwarf mice. In addition, GH treatment attenuated the activity of thioredoxin and glutaredoxin in liver mitochondria of Ames mice. Importantly, GH treatment suppressed Trx2 and TrxR2 mRNA expression. These data indicate that GH has a role in stress resistance by altering the functional capacity of the GST system through the regulation of specific GST family members in long-living Ames dwarf mice. It also affects the regulation of thioredoxin and glutaredoxin, factors that regulate posttranslational modification of proteins and redox balance, thereby further influencing stress resistance.

Sex dependent pharmacokinetics, tissue distribution and excretion of peimine and peiminine in rats assessed by liquid chromatography-tandem mass spectrometry

ETHNOPHARMACOLOGICAL RELEVANCE

Fritillaria thunbergii Miq. has been traditionally used in China as antitussive and expectorant herbs, and newly used in the clinical treatment of leukemia in recent years.

AIM

To investigate whether gender exerted a significant influence on the pharmacokinetics, tissue distribution and excretion of peimine and peiminine in Sprague-Dawley rats who were given a single oral administration of 4.25 g/kg Fritillaria thunbergii Miq. extract.

MATERIALS AND METHODS

Sprague-Dawley rats were assigned into two groups based on the gender and orally administered 4.25 g/kg Fritillaria thunbergii Miq. extract for each individual pharmacokinetics, tissue distribution and excretion study.

RESULTS

Compared with female rats, peimine and peiminine were eliminated slowly from male rat plasma, and significant gender-related differences were observed in the pharmacokinetic parameters. Drug blood and tissue levels in male rats were significantly higher than the female counterparts except for several tissues, such as fat, muscle and skin. Gender also exerted a significant influence on the urine excretion but such effect was not observed in the feces excretion study.

CONCLUSIONS

Gender exerted a significant influence on the pharmacokinetics, tissue distribution and urine excretion of peimine and peiminine. It is assumed that the sex-associated differences of peimine and peiminine in rats might be mainly result from sex-dependent expression and activity of drug metabolism enzymes and P-glycoprotein.

Sex differences in the drug therapy for oncologic diseases

There are clear gender-dependent differences in response rates and the probability of side effects in patients treated with chemotherapy. Sex-biased expression levels of metabolic enzymes and transporters in liver and kidney leading to different pharmacokinetics have been described for most common anti-cancer drugs. In women, half-life is often longer, which is associated with improved survival, but also increased toxicity.Some chemotherapy protocols lead to a better response rate in women without increasing toxicity (e.g., cisplatin and irinotecan), while others only increase toxicity, but do not improve response rates in women (e.g., 5-fluorouracil). The increased toxicity often correlates with different pharmacokinetics, but women also show a higher sensitivity to some agents with shorter half-life (e.g., steroids). Organ-specific toxicities like cardiac toxicity after doxorubicin treatment or neurotoxicity associated with ifosfamide are more severe in women due to gender-specific changes in gene expression. Novel therapies like tyrosine kinase inhibitors or monoclonal antibodies show very complex, but clinical significant differences depending on gender. Antibodies often have a longer half-life in women, which is associated with an improved response to therapy.Side effects appear to be highly dependent on different tissue properties, as women have a higher incidence of oral mucositis, but lower rates of gut toxicity. Nausea and vomiting is a greater problem in females during therapy due to the lower activity of anti-emetic drugs. Nausea and vomiting pose a bigger challenge in female patients, as anti-emetic drugs seem to be less effective.

Effects of aging on mRNA profiles for drug-metabolizing enzymes and transporters in livers of male and female mice

Aging is a physiological process characterized by progressive functional decline in various organs over time. To reveal possible molecular mechanisms of altered xenobiotic disposition and toxicity in elderly individuals, age-dependent mRNA profiles for 101 xenobiotic-processing genes (XPGs), including seven uptake transporters, 41 phase I enzymes, 36 phase II enzymes, 10 efflux transporters, and seven transcription factors, were characterized in livers of male and female mice from 3 to 27 months of age. Gender differences across the lifespan (significant at five ages or more) were observed for 52 XPGs, including 15 male-predominant genes (e.g., Oatp1a1, Cyp3a11, Ugt1a6a, Comt, and Bcrp) and 37 female-predominant genes (e.g., Oatp1a4, Cyp2b10, Sult1a1, Ugt1a1, and Mrp3). During aging, the mRNA levels for 44% of the 101 XPGs changed in male mice and 63% changed in female mice. In male mice, mRNA levels for 40 XPGs (e.g., Oatp1a1, Ces2c, Gstm4, Gstp1, and Ces1e) were lower in aged mice (more than 21 months of age), whereas mRNA levels for four XPGs (e.g., Oat2 and Gstm2) were higher in aged mice. In female mice, mRNA levels for 43 XPGs (e.g., Oatp1a1, Cyp1a2, Ces1f, Sult3a1, Gstt2, Comt, Ent1, Fmo3, and Mrp6) were lower in aged mice, whereas mRNA levels for 21 XPGs (e.g., Oatp1a4, Nqo1, Adh7, Sult2a1/2, Gsta1, and Mrp4) were higher in aged mice. In conclusion, 51% of the 101 XPGs exhibited gender differences in liver mRNA levels across the lifespan of mice; the mRNA levels for 40% of the XPGs were lower in aged male mice and 43% were lower in aged female mice.

Circadian modulation of hepatic transcriptome in transgenic rats expressing human growth hormone

The secretory profile of growth hormone (GH) is sexually dimorphic in rats. In male transgenic (TG) rats expressing human GH (hGH) that we generated, the circulating levels of both hGH and endogenous GH are flattened with no male-type pulsatility. To elucidate the regulatory role of episodic GH profile on the liver, the hepatic transcriptome of male TG rats at the middle of the light and dark phases was characterized by genome-wide analyses as compared with that of male wild-type (WT) rats. Transcripts commonly up- or down-regulated regardless of the lighting conditions in TG rats were mainly enriched in the metabolism of xenobiotics. In TG rats, the gene expression profile was functionally feminized, verifying that the sexually dimorphic profile of GH rather than genetic sexuality is a stronger sex-determining factor on the hepatic transcriptome. The common transcripts which fluctuated during the day in both TG and WT rats were enriched in circadian rhythm signaling, and physiological rhythmicity was considered to be finely interconnected with liver metabolism via sexually dimorphic GH secretion. In contrast, some genes were differentially regulated in TG rats at only one of two time points measured, and others were fluctuated daily in only one genotype. In particular, some genes involved in the GH signaling pathway were included, suggesting the signal transduction is circadian-modulated depending upon the GH profile. Our transcriptome analyses clarified the regulatory role of episodic GH profile on the liver and strengthen the functional link between sexually dimorphic GH secretion, liver metabolism, and its circadian regulation.

Quantitative shot-gun proteomics and MS-based activity assay for revealing gender differences in enzyme contents for rat liver microsome

Liver microsomes are subcellular fractions that contain many metabolizing enzymes for drugs and endogeneous compounds. Some of these enzymes are regulated by sex hormonal control and exhibit sex-dependent expression pattern and metabolizing speed. Studying these enzymes, however, are complicated by the presence of isoforms such as cytochrome P450 (CYP450), which families share more than 50% amino acid identities. In this study, we applied quantitative shot-gun proteomics approach coupled with stable-isotope dimethyl labeling, two-dimensional reversed-phase peptide separation and tandem mass spectrometry (MS) to explore the gender-dependent expression of rat liver microsomal proteins. A total of 391 proteins were identified and quantified by this approach, and 56% of quantified proteins were enzymes. Although shot-gun approach is rarely used for identifying protein isoforms, we identified 53 isoforms by at least one unique peptide including 21 isoforms of CYP450s. Moreover, by quantitative and statistics assessment, we were able to classify them into 28 male dominant enzymes including CYP2C12 CYP2C11, CYP2C13, CYP2B3, CYP2C11, CYP2C70 and CYP3A2 which are known to be male specific, 21 female dominant enzymes including CYP2A1, CYP2C7, CYP2C12, CYP2D26, alcohol dehydrogenase 1, carboxylesterase 3, glutathione S-transferase, liver carboxylesterase 4, UDP-glucuronosyltransferase 2B1, and glyceraldehyde-3-phosphate dehydrogenase which are known to be female specific; and 125 sex-independent enzymes. However, most of the sex specificities revealed from this study, such as the male specificity of CYP2D1, were novel and not yet reported. We then conducted a mass spectrometry-multiple reaction mode (MS-MRM) based enzyme activity method to determine the catalyzing rate of CYP2D1 in male and female liver microsomes using carteolol as its specific substrate. The reaction rate catalyzed by CYP2D1 in female rats was determined to differ significantly with the rate in male rats. Moreover, the ratio (female/male) of reaction rate (0.68) was found to correlate with their relative protein abundance (0.72). This study revealed novel sex dependences of many rat liver enzymes and also demonstrated a unique MS-based analytical platform that could identify novel iso-enzymes and further quantify their abundance and enzyme activity.

Genotype-dependent gene expression profile of the antioxidant defense system (ADS) in the liver of a GH-transgenic zebrafish model

The aim of this study was to evaluate the effects of growth hormone (GH) overexpression on the gene expression profile of multiple components of the antioxidant defense system (ADS) of different genotypes of a GH-transgenic zebrafish (Danio rerio) model. Several ADS-related genes were analyzed by semiquantitative reverse transcription-PCR in the liver of hemizygous (HE) and homozygous (HO) transgenic zebrafish. The results showed a significant reduction in the glutamate cysteine ligase catalytic subunit (GCLC) and the gene expression of two glutathione S-transferase (GST) isoforms and an increase in the glutathione reductase gene in the HO group compared to non-transgenic controls. The expression of the Cu, Zn-superoxide dismutase (SOD1) and catalase (CAT) genes was reduced in HO and HE groups, respectively. Among the ten genes analyzed, two were altered in HE transgenic zebrafish and five were altered in HO transgenic zebrafish. These findings indicate a genotype-dependent gene expression profile of the ADS-related genes in the liver of our GH-transgenic zebrafish model and are in agreement with the general effects of GH hypersecretion in the fish and mouse, which involves a reduction in the capability of the tissues to deal with oxidative stress situations. The GH-transgenic zebrafish model used here seems to be an interesting tool for analyzing the effect of different GH expression levels on physiological processes.

Sex differences in the expression of hepatic drug metabolizing enzymes

Sex differences in pharmacokinetics and pharmacodynamics characterize many drugs and contribute to individual differences in drug efficacy and toxicity. Sex-based differences in drug metabolism are the primary cause of sex-dependent pharmacokinetics and reflect underlying sex differences in the expression of hepatic enzymes active in the metabolism of drugs, steroids, fatty acids and environmental chemicals, including cytochromes P450 (P450s), sulfotransferases, glutathione transferases, and UDP-glucuronosyltransferases. Studies in the rat and mouse liver models have identified more than 1000 genes whose expression is sex-dependent; together, these genes impart substantial sexual dimorphism to liver metabolic function and pathophysiology. Sex differences in drug metabolism and pharmacokinetics also occur in humans and are due in part to the female-predominant expression of CYP3A4, the most important P450 catalyst of drug metabolism in human liver. The sexually dimorphic expression of P450s and other liver-expressed genes is regulated by the temporal pattern of plasma growth hormone (GH) release by the pituitary gland, which shows significant sex differences. These differences are most pronounced in rats and mice, where plasma GH profiles are highly pulsatile (intermittent) in male animals versus more frequent (nearly continuous) in female animals. This review discusses key features of the cell signaling and molecular regulatory mechanisms by which these sex-dependent plasma GH patterns impart sex specificity to the liver. Moreover, the essential role proposed for the GH-activated transcription factor signal transducer and activator of transcription (STAT) 5b, and for hepatic nuclear factor (HNF) 4alpha, as mediators of the sex-dependent effects of GH on the liver, is evaluated. Together, these studies of the cellular, molecular, and gene regulatory mechanisms that underlie sex-based differences in liver gene expression have provided novel insights into the physiological regulation of both xenobiotic and endobiotic metabolism.

Sex-different and growth hormone-regulated expression of microRNA in rat liver

Background

MicroRNAs (miRNAs) are short non-coding RNAs playing an important role in post-transcriptional regulation of gene expression. We have previously shown that hepatic transcript profiles are different between males and females; that some of these differences are under the regulation of growth hormone (GH); and that mild starvation diminishes some of the differences. In this study, we tested if hepatic miRNAs are regulated in a similar manner.

Results

Using microarrays, miRNA screening was performed to identify sex-dependent miRNAs in rat liver. Out of 324 unique probes on the array, 254 were expressed in the liver and eight (3% of 254) of those were found to be different between the sexes. Among the eight putative sex-different miRNAs, only one female-predominant miRNA (miR-29b) was confirmed using quantitative real-time PCR. Furthermore, 1 week of continuous GH-treatment in male rats reduced the levels of miR-451 and miR-29b, whereas mild starvation (12 hours) raised the levels of miR-451, miR-122a and miR-29b in both sexes. The biggest effects were obtained on miR-29b with GH-treatment.

Conclusion

We conclude that hepatic miRNA levels depend on the hormonal and nutritional status of the animal and show that miR-29b is a female-predominant and GH-regulated miRNA in rat liver.

Characterization of biliary conjugates of 4,4'-methylenedianiline in male versus female rats

4,4'-Methylenedianiline (4,4'-diaminodiphenylmethane; DAPM) is an aromatic diamine used in the production of numerous polyurethane foams and epoxy resins. Previous studies in rats revealed that DAPM initially injures biliary epithelial cells of the liver, that the toxicity is greater in female than in male rats, and that the toxic metabolites of DAPM are excreted into bile. Since male and female rats exhibit differences in the expression of both phase I and phase II enzymes, our hypothesis was that female rats either metabolize DAPM to more toxic metabolites or have a decreased capacity to conjugate metabolites to less toxic intermediates. Our objective was thus to isolate, characterize, and quantify DAPM metabolites excreted into bile in both male and female bile duct-cannulated Sprague Dawley rats. The rats were gavaged with [(14)C]-DAPM, and the collected bile was subjected to reversed-phase HPLC with radioisotope detection. Peaks eluting from HPLC were collected and analyzed using electrospray MS and NMR spectroscopy. HPLC analysis indicated numerous metabolites in both sexes, but male rats excreted greater amounts of glutathione and glucuronide conjugates than females. Electrospray MS and NMR spectra of HPLC fractions revealed that the most prominent metabolite found in bile of both sexes was a glutathione conjugate of an imine metabolite of a 4'-nitroso-DAPM. Seven other metabolites were identified, including acetylated, cysteinyl-glycine, glutamyl-cysteine, glycine, and glucuronide conjugates. While our prior studies demonstrated increased covalent binding of DAPM in the liver and bile of female compared to male rats, in these studies, SDS-PAGE with autoradiography revealed 4-5 radiolabeled protein bands in the bile of rats treated with [(14)C]-DAPM. In addition, these bands were much more prominent in female than in male rats. These studies thus suggest that a plausible mechanism for the increased sensitivity of female rats to DAPM toxicity may be decreased conjugation of reactive DAPM metabolites, leading to greater levels of protein adduct formation.

Isozyme- and gender-specific induction of glutathione S-transferases by flavonoids

Most dietary flavonoids have antioxidant activity in vitro however, secondary mechanisms such as the ability to influence gene expression with the consequent modulation of specific enzymatic activities involved in the intracellular response against oxidative stress, are being realized. In the following study, we examined the ability of the flavonoids: flavone, morin, naringenin, (+)-catechin, and quercetin to modulate the activity of glutathione S-transferases (GSTs) mGSTA, mGSTP and mGSTM in hepatic tissues of male and female Swiss Webster mice. Subchronic dietary exposure to morin, naringenin, (+)-catechin, and quercetin (2,500 mg/kg diet for 20 days) did not produce statistically significant changes in GST activity. Conversely, gender-, and isozyme-specific induction of mGSTs were observed in animals fed flavone. A sevenfold increase in total mGST activity was observed in female animals whereas a fourfold increase was observed in male animals. Enzyme specific assays indicate that there were greater increases of both mGSTM (eightfold) and mGSTP (fourfold) activities in females as compared to males (sixfold and twofold, respectively). As testosterone is involved in the regulation of GSTs in mice, castrated males were fed flavone for 5 days (2,500 mg/kg diet). In this case, dietary flavone resulted in similar fourfold increases in total GST activity in inact and castrated animals. Isozyme specific studies indicate that increases could be attributed to an induction of mGSTM and mGSTP.

Effect of chronic treatments with GH, melatonin, estrogens, and phytoestrogens on oxidative stress parameters in liver from aged female rats

The aging theory postulates that this process may be due to the accumulation of oxidative damage in cells and molecules. The present study has investigated the effect of castration in old female rats on various parameters related to the antioxidant properties of several cellular fractions obtained from the liver, and the influence of several chronic treatments on it, both in intact and castrated animals. Sixty-one 22-month-old Wistar female rats, were used. About 21 intact animals were divided into three groups and treated for 10 weeks with GH, melatonin or saline, and 40 ovariectomized (at 12 months of age) animals were divided into five groups and treated for the same time with GH, melatonin, estrogens (Eos), phytoestrogens (Phyt) or saline. All animals were sacrificed at 24 months of age by decapitation. The activity of glutathione peroxidase (GPx) in cytosolic fraction, glutathione-S-transferase (GST) in cytosol and microsomal fractions, and the levels of nitric oxide (NO) and cytochrome C in mitochondrial and cytosol fractions of liver were determined. A decrease in GST activity was detected in cytosol and in the microsomal fraction in ovariectomized animals as compared to intact rats. The activity of GPx was also decreased in ovariectomized as compared with the intact group. NO level was increased and cytochrome C decreased in the mitochondrial fraction of the liver in ovariectomized females as compared with the intact group, respectively. No significant changes after melatonin or GH treatments were found in GPx, GST activity and NO level in mitochondrial fraction in the intact group. Administration of GH, melatonin, Eos and Phyt in the ovariectomized groups significantly increased the GPx, and GST activity in the cytosol and microsomal fraction and decreased the level of NO in the mitochondrial fraction as compared with the untreated rats. A significant increase in the level of cytochrome C in the mitochondrial fraction and a decrease in the cytosol fraction were also found with all treatments. The administration of GH, melatonin, Eos and Phyt to castrated females seem to reduce oxidative changes in the liver from old ovariectomized rats.

The role of intracellular signaling in insulin-mediated regulation of drug metabolizing enzyme gene and protein expression

Endogenous factors, including hormones, growth factors and cytokines, play an important role in the regulation of hepatic drug metabolizing enzyme expression in both physiological and pathophysiological conditions. Diabetes, fasting, obesity, protein-calorie malnutrition and long-term alcohol consumption produce changes in hepatic drug metabolizing enzyme gene and protein expression. This difference in expression alters the metabolism of xenobiotics, including procarcinogens, carcinogens, toxicants and therapeutic agents, potentially impacting the efficacy and safety of therapeutic agents, and/or resulting in drug-drug interactions. Although the mechanisms by which xenobiotics regulate drug metabolizing enzymes have been studied intensively, less is known regarding the cellular signaling pathways and components which regulate drug metabolizing enzyme gene and protein expression in response to hormones and cytokines. Recent findings, however, have revealed that several cellular signaling pathways are involved in hormone- and growth factor-mediated regulation of drug metabolizing enzymes. Our laboratory has reported that insulin and growth factors regulate drug metabolizing enzyme gene and protein expression, including cytochromes P450 (CYP), glutathione S-transferases (GST) and microsomal epoxide hydrolase (mEH), through receptors which are members of the large receptor tyrosine kinase (RTK) family, and by downstream effectors such as phosphatidylinositol 3-kinase, mitogen activated protein kinase (MAPK), Akt/protein kinase B (PKB), mammalian target of rapamycin (mTOR), and the p70 ribosomal protein S6 kinase (p70S6 kinase). Here, we review current knowledge of the signaling pathways implicated in regulation of drug metabolizing enzyme gene and protein expression in response to insulin and growth factors, with the goal of increasing our understanding of how disease affects these signaling pathways, components, and ultimately gene expression and translational control.

Global effects of vitamin A deficiency on gene expression in rat liver: evidence for hypoandrogenism

Vitamin A (retinol) metabolites are ligands for transcription factors that regulate many genes. The liver is the main storage depot for retinol and plays a role in vitamin A homeostasis. To better understand the effects of vitamin A deficiency on liver gene expression, we produced retinol deficiency in male rats by feeding a diet low in retinol for 53 days after weaning and examined the effects on gene expression in liver using Affymetrix oligonucleotide microarrays. We detected expression of 41% of the 8799 probe sets represented on the RGU-34A GeneChips. Vitamin A deficiency resulted in major changes in liver gene expression: 805 genes (22% of all genes detected) differed at P<or=.05 (false discovery rate <0.143). Genes involved in fatty acid metabolism, peroxisomal function, glycolysis, glutamate metabolism and the urea cycle were altered. The expression of many sexually dimorphic genes was altered toward a feminized or senescent pattern of gene expression in the liver. Retinol deficiency also produces a shift toward increased protein and fat catabolism and decreased fatty acid synthesis.

Hormonal regulation of hepatic multidrug resistance-associated protein 2 (Abcc2) primarily involves the pattern of growth hormone secretion

Biliary excretion is the rate-limiting step in transfer of bilirubin, other organic anions, and xenobiotics across the liver. Multidrug resistance-associated protein 2 (Mrp2, Abcc2) is the major transporter for conjugated endo- and xenobiotic-conjugated compounds into bile. Hormones regulate bilirubin and xenobiotic secretion into bile, which have dimorphic differences. Therefore, we examined the possible role of sex steroids and growth hormone in the regulation of Mrp2. In approximately 8-wk-old rats, mRNA, transcriptional activity, and hepatic content of Mrp2 were selectively increased fourfold (P < 0.001) in females compared with males. In males, estrogens increased and testosterone decreased Mrp2 mRNA and protein, whereas no significant effect was measured in females, suggesting either a direct effect on the liver or an alteration in growth hormone secretory pattern. After hypophysectomy, Mrp2 mRNA was markedly reduced and the effects of estrogens and testosterone on Mrp2 were prevented, supporting the role of pituitary hormones in controlling Mrp2 expression. Mrp2 increased following growth hormone infusion in males. Mrp2 mRNA was decreased in growth hormone-deficient "Little" mice. Growth hormone infusions in hypophysectomized rats partially restored Mrp2 levels, whereas thyroxine addition returned Mrp2 mRNA and protein to basal levels. Morphology as well as biochemical measurements demonstrated that Mrp2 was localized to the bile canaliculus in equal density in both genders, whereas hormone replacements increased Mrp2 in hypophysectomized animals. In cultured hepatocytes, thyroxine did not have an effect, but growth hormone alone and combined with thyroxine increased Mrp2 mRNA levels. In conclusion, Mrp2 levels are regulated by the combination of thyroxine and different growth hormone secretory patterns.

Gene expression of drug metabolizing enzymes in adult and aged mouse liver: A modulation by immobilization stress

The role of stress in the regulation of enzymatic systems involved in the biotransformation of xenobiotics, as well as endogenous substrates in the liver was investigated using single immobilization stress as a model. Adult (3 months of age) and aged (26 months) C3H/a male mice were used. Cytochrome P450 1A1 and 1A2 (CYP1A1 and CYP1A2), glutathione S-transferase M1 (GSTM1), aryl hydrocarbon receptor (AHR), aryl hydrocarbon receptor nuclear translocator (ARNT) and catechol-O-methyltransferase (COMT) mRNA levels in the mouse liver were measured by a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) method. Excluding CYP1A1, experiments revealed significant differences in the expression of these genes between adult- and aged-control animals. The influence of stress on the expression of genes studied was shown to be higher in adult mice than in aged ones. Our results clearly demonstrate the lack of response or even the attenuation of gene expression in aged animals that may play an important role in age-related pathologies and diseases.

Sexual Dimorphism of Rat Liver Nuclear Proteins

Many genes are expressed in mammalian liver in a sexually dimorphic manner. DNA microarray analysis has shown that growth hormone (GH) and its sex-dependent pattern of pituitary secretion play a major role in establishing the sexually dimorphic patterns of liver gene expression. However, GH may exert effects on protein post-translational modification and nuclear localization that are not reflected at the mRNA level. To investigate these potential effects of GH, we used two-dimensional gel electrophoresis followed by LC-MS/MS to: 1) identify rat liver nuclear proteins whose abundance or state of post-translational modification displays sex-dependent differences; and 2) determine the role of the plasma GH profile in establishing these differences. Nuclear extracts prepared from livers of individual male (n=9) and female (n=5) adult rats, and from males given GH by continuous infusion for 7 days to feminize liver gene expression (n=5 rats), were resolved by two-dimensional electrophoresis. Image analysis of SYPRO Ruby-stained gels revealed 165 sexually dimorphic protein spots that differ in normalized volume between male and female groups by >1.5-fold at p<0.05. Sixty of these proteins exhibited female-like changes in spot abundance following continuous GH treatment. Comparison of male and GH-treated male groups revealed 130 proteins that displayed >1.5-fold differences in abundance, with 60 of these GH-responsive spots being sexually dimorphic. Thus, GH plays an important role in establishing the sex-dependent differences in liver nuclear protein content. Twenty-eight of the sexually dimorphic and/or GH-regulated protein spots were identified by LC-MS/MS. Proteins identified include regucalcin, nuclear factor 45, and heterogeneous nuclear ribonucleoproteins A3, D-like, and K, in addition to proteins such as GST, normally associated with cytosolic extracts but also reported to be localized in the nucleus.

Thioacetamide differentially affects the expression and activity of glutathione-S-transferase in the liver of Wistar rats

Glutathione-S-transferase (GST) is a family of enzymes involved in the detoxification of toxic and carcinogenic compounds. In the present study, the effect of thioacetamide (TA), a hepatotoxic and hepatocarcinogenic compound, on the activity and expression of GST of Wistar female rats was tested. Animals were treated with a single dose of TA (250 mg/kg) for 12, 24, 48 and 72 hours. GST activity toward the broad substrate 1-chloro-2,4-dinitrobenzene was enhanced by TA. The protein level of the GST classes alpha and mu as well as the mRNA level of several GST subunits were also positively affected by the TA treatment. Female Wistar rats of the same age but from two other different colonies had their GST activity either inhibited or not affected by TA. The basal mRNA level of class alpha and class mu GST was also tested in female Wistar rats obtained from five different sources. Differences in the basal level of class alpha mRNA were observed in rats from at least three different sources, while class mu mRNA level was distinct in two groups of animals.

Influence of clinical factors, diet, and drugs on the human upper gastrointestinal glutathione system

BACKGROUND

Glutathione (GSH) and the cytosolic glutathione S-transferases (GSTs) protect the gastrointestinal mucosa against the toxic effects of a wide variety of compounds, such as reactive oxygen species and electrophiles.

AIMS

We wished to investigate the distribution along the upper gastrointestinal mucosa and the influence of clinical variables on components of the GSH system to learn more about factors which control its cytoprotective properties.

METHODS

Antral and duodenal biopsies of normal appearing mucosa were collected from 202 patients (104 males, 98 females; mean age 62 years) undergoing upper gastrointestinal endoscopy. GSH content was examined by high pressure liquid chromatography, GST enzyme activity by 1-chloro-, 2, 4-dinitrobenzene conjugation, and levels of the GST classes alpha, pi, and theta by western blot.

RESULTS

GSH, GST enzyme activity, and GST alpha levels were significantly lower (p<0.001) in the antrum than in the duodenum (antrum v duodenum: GSH 23.0 (0.7) v 35.0 (1.0) nmol/mg protein; GST activity 626 (19) v 832 (22) nmol/mg protein/min; GST alpha 4.5 (0.5) v 20.0 (0.7) microg/mg protein) while GST pi content was significantly higher (p<0.001) in antral than in duodenal biopsies (16.5 (0.7) v 11.2 (0.5) microg/mg protein). Antral GSH and GST activities were markedly lower in males compared with females (p<0.01). Some drugs (cisapride, diuretics, cortisol, analgesics) increased GST pi and GST alpha content but cytostatic drugs suppressed duodenal GST activity. High intake (>3 days a week) of vegetables enhanced duodenal GST alpha and GST pi and high intake of fruits the antral content of GST theta 1.

CONCLUSIONS

The gastrointestinal GSH system represents the antitoxic barrier of the mucosa; its activity is influenced by localisation, sex, and drugs, and its enzymes are stimulated by a high intake of vegetables and fruits.

Definition and mapping of epitopes recognized by specific monoclonal antibodies to Schistosoma bovis 28 kDa glutathione S-transferase: relation with anti-egg viability immunity

Monoclonal antibodies to the 28kDa glutathione S-transferase of Schistosoma bovis have been constructed in mice and used to characterize the epitope(s) potentially implied in the induction of anti-fecundity and anti-egg viability immune responses. Among the MoAbs produced three were particularly studied: Sb4-50 (IgG2a) and Sb4-56 (IgG1) which inhibited Sb28GST activity and Sb4-10 (IgG1) which did not. The use of overlapping peptides covering the entire amino acid sequence of Sb28GST, allowed us to define the linear epitopes recognized by these anti-Sb28GST MoAbs. Amino acid residues 202-211 were recognized by both MoAbs Sb4-50 and Sb4-56 and MoAb Sb4-10 recognized amino acid residues 58-67. Their capacity to inhibit GST activity suggested binding to the active site or to neighbouring regions, which include the C-terminal domain (a.a. 190-211) of the protein. When passively transferred into BALB/c mice MoAbs induced a significant reduction in egg hatching and an increase in immature eggs. Effects on worm burdens were, however, variable and no clear-cut association between the inhibition of enzyme activity and anti-fecundity or anti-viability activities was recorded. Our data indicate that beside the anti-fecundity and anti-viability immunity related to the impairment of GST activity, immune response to epitopes located in other regions of the molecule also contribute to the reduction of egg viability.

Sex-dependent metabolism of xenobiotics

Sex-dependent differences in xenobiotic metabolism have been most extensively studied in the rat. Because sex-dependent differences are most pronounced in rats, this species quickly became the most popular animal model to study sexual dimorphisms in xenobiotic metabolism. Exaggerated sex-dependent variations in metabolism by rats may be the result of extensive inbreeding and/or differential evolution of isoforms of cytochromes P450 in mammals. For example, species-specific gene duplications and gene conversion events in the CYP2 and CYP3 families have produced different isoforms in rats and humans since the species division over 80 million years ago. This observation can help to explain the fact that CYP2C is not found in humans but is a major subfamily in rats (Table 11). Animal studies are used to help determine the metabolism and toxicity of many chemical agents in an attempt to extrapolate the risk of human exposure to these agents. One of the most important concepts in attempting to use rodent studies to identify sensitive individuals in the human population is that human cytochromes P450 differ from rodent cytochromes P450 in both isoform composition and catalytic activities. Xenobiotic metabolism by male rats can reflect human metabolism when the compound of interest is metabolized by CYP1A or CYP2E because there is strong regulatory conservation of these isoforms between rodents and humans. However, problems can arise when rats are used as animal models to predict the potential for sex-dependent differences in xenobiotic handling in humans. Information from countless studies has shown that the identification of sex-dependent differences in metabolism by rats does not translate across other animal species or humans. The major factor contributing to this observation is that CYP2C, a major subfamily in rats, which is expressed in a sex-specific manner, is not found in humans. To date, sex-specific isoforms of cytochromes P450 have not been identified in humans. The lack of expression of sex-dependent isoforms in humans indicates that the male rat is not an accurate model for the prediction of sex-dependent differences in humans. Differences in xenobiotic metabolism among humans are more likely the consequence of intraindividual variations as a result of genetics or environmental exposures rather than from sex-dependent differences in enzyme composition. A major component of the drug discovery and development process is to identify, at as early a stage as possible, the potential for toxicity in humans. Earlier identification of individual differences in xenobiotic metabolism and the potential for toxicity will be facilitated by improving techniques to make better use of human tissue to prepare accurate in vitro systems such as isolated hepatocytes and liver slices to study xenobiotic metabolism and drug-induced toxicities. Accurate systems should possess an array of bioactivation enzymes similar to the in vivo expression of human liver. In addition, the compound concentrations and exposure times used in these in vitro test systems should mimic those achieved in the target tissues of humans. Consideration of such factors will allow the development of compounds with improved efficacy and low toxicity at a more efficient rate. The development of accurate in vitro systems utilizing human tissue will also aid in the investigation of the molecular mechanisms by which the CYP genes are regulated in humans. Such studies will facilitate the study of the basis for differences in expression of isoforms of CYP450 in humans.

Growth hormone- and testosterone-dependent regulation of glutathione transferase subunit A5 in rat liver

The class Alpha glutathione S-transferase (GST) subunit A5 is expressed in the livers of young male and female rats. After sexual maturation, this protein is no longer detectable in the livers of male rats, but is still expressed in female rats. We have previously demonstrated that the sexually dimorphic secretion of growth hormone regulates the levels of certain class Mu GSTs in rat liver, and this study was designed to investigate the hormonal regulation of GSTA5. Control and hypophysectomized rats of both sexes were used to study the role of growth hormone in the regulation of hepatic GSTA5; and the influence of testosterone on the expression of this same subunit was investigated in intact females and castrated males. Liver cytosols were subjected to SDS/PAGE and immunoblotting using antibodies directed towards rat (r)GSTA5, and to affinity purification on glutathione-Sepharose followed by reverse-phase HPLC in order to quantify the relative levels of rGSTA1, A2, A3, A4, M1 and M2 subunits. These analyses revealed that the expression of rGSTA5 is, indeed, regulated by both growth hormone and testosterone.

Purification and characterisation of hepatic glutathione transferases from a herbivorous marsupial, the brushtail possum (Trichosurus vulpecula)

A single glutathione transferase isoenzyme was purified from hepatic cytosol of the brushtail possum and shown to represent 3.6 +/- 0.3% of the total cytosolic protein. Characterisation of the enzyme, termed Possum GST 1-1, indicated that it possessed similar catalytic activity and structural homology with isoenzymes belonging to the alpha class of glutathione transferases. This homodimeric GST exhibited a single band with an apparent molecular mass of 25.4 kDa on sodium dodecyl sulphate-polyacrylamide gels and an apparent pI of 9.8. Inhibition studies demonstrated that Possum GST 1-1 displays binding affinity for a range of inhibitors similar to that shown by alpha class GSTs purified from other mammals. Immunoblot analysis demonstrated immuno-cross reactivity between Possum GST 1-1 and antisera raised against human alpha GST, while this GST did not cross-react with antisera raised against human mu and pi GST. N-terminal sequencing of purified Possum GST 1-1 revealed that the N-terminus of the protein is chemically blocked. Sequence analysis of three internal peptide sequences demonstrated homology with mammalian alpha GSTs. Of particular interest is the significant substrate specificity that Possum GST 1-1 displays with both organic and inorganic hydroperoxides. It is proposed that this substrate specificity is an evolutionary adaptation to a diet high in potentially toxic plant allelochemicals.

Interaction of a novel sex-dependent, growth hormone-regulated liver nuclear factor with CYP2C12 promoter

CYP2C12 is a steroid hydroxylase cytochrome P450 whose female-specific expression in adult rat liver is transcriptionally activated by the continuous plasma growth hormone (GH) profile characteristic of adult female rats. DNase I footprinting and gel mobility shift analysis of the 5'-flank of the CYP2C12 gene were carried out to identify cis-acting elements and trans-acting factors that may contribute to the GH-regulated, sex-dependent transcription of this P450 gene. DNase I footprinting analysis revealed sex- and GH-regulated DNase I hypersensitivity sites at the boundaries of several protein binding sites detected along a 1560-nucleotide upstream segment of CYP2C12. Five distinct sites bound a novel continuous GH-regulated nuclear factor, GHNF, which is enriched in adult female and continuous GH-treated male liver nuclear extracts compared to untreated male liver nuclear extracts. Two other footprinted sites correspond to binding sites for the liver transcription factors C/EBP and albumin D element-binding protein and a third to an HNF1 binding site. A specific binding site for GHNF was also found in the 5'-proximal promoter of CYP2C11, an adult male-specific liver P450 gene, suggesting that GHNF may contribute to the down-regulation of that gene by continuous GH. GHNF was distinguished from the nuclear factors that bind to a GH response element upstream of the rat Spi 2.1 gene and is also distinct from the GH-activatable latent cytoplasmic transcription factors STAT 1, STAT 3, and STAT 5. These findings support the hypothesis that continuous GH-activated transcription of CYP2C12 in adult female rat liver (a) involves the activation of a novel GH-regulated nuclear factor which binds to multiple sites along the 5'-flank of this cytochrome P450 gene, and (b) proceeds via a signaling pathway distinct from the GH pulse-activated STAT5 pathway proposed to induce CYP2C11 and other male-expressed liver genes.

Regulation of rat olfactory glutathione S-transferase expression. Investigation of sex differences, induction, and ontogenesis

The glutathione S-transferases (GSTs) of rat olfactory epithelium have been characterised with regard to sex differences, induction, and developmental regulation, and compared to those of the liver. Olfactory cytosolic GST activity with 1-chloro-2,4-dinitrobenzene (CDNB) as substrate was similar in both male and female animals, and there were no differences in subunit profile. Administration of trans-stilbene oxide and beta-naphthoflavone had no effect on olfactory GST activity with CDNB, although phenobarbitone treatment resulted in a small, but significant, increase in activity (130% compared to controls). HPLC analysis of subunit profiles indicated that all three agents induced olfactory subunit 1b and decreased subunit 6. The effect of age (3 to 84 days) on both cytosolic and microsomal CDNB activity was examined. In the liver, cytosolic activity was low at 3 days and climbed steadily to reach maximal levels around 28 days, but microsomal activity was relatively constant at all ages. Olfactory cytosolic activity was similar at all ages; microsomal activity was low until 21 days and then increased to reach a maximum at 56 days. Changes in individual cytosolic subunits were assessed by SDS-PAGE followed by immunoblotting. The significance of these results with regard to putative physiological roles for olfactory GSTs is discussed.

Rat kidney glutathione S-transferase 1 subunits have C-terminal truncations

Cytosolic glutathione S-transferases (GSTs) from rat kidneys were purified by a combination of glutathione and S-hexylglutathione affinity columns. The isolated GSTs were subjected to reverse-phase HPLC and electrospray MS analysis. The major GST isoenzymes expressed in kidney are subunits 1, 2, 7 and 8. GST 1',3 and 4 are expressed in minor amounts. GST 10 is barely detectable in the male kidney cytosol. The molecular masses of these rat kidney GST subunits were determined by MS. The values obtained for subunits 1', 2, 3, 4, 7, 8 and 10 are identical with those obtained for rat liver GSTs. Rat kidney GST 1 consists of three polypeptides, with molecular masses of 25517, 25372 and 24982 Da. Results from peptide mapping, MS and amino-acid-sequencing analyses indicate that the major components were generated by deleting the C-terminal phenylalanine (24982 Da) and the C-terminal IFKF tetrapeptide (25372 Da) from the GST 1 subunit, respectively. The 1-chloro-2,4-dinitrobenzene-conjugating and peroxidase activities of kidney GST 1 are substantially lower than for its counterpart from rat liver. In addition, rat kidney GST 1 has an arginine and a valine residue at positions 151 and 207 respectively. The results are in contradiction with the SWISS-PROT and GenBank rat liver GST 1 cDNA-sequencing data, which give a lysine and a methionine at the corresponding positions. Further analyses indicate that rat liver GST 1 also has a C-terminal phenylalanine deletion, and an arginine and a valine residue at positions 151 and 207 respectively. However, the C-terminal-tetrapeptide-deleted form was not observed for rat liver GST 1.

Growth hormone activation of Stat 1, Stat 3, and Stat 5 in rat liver. Differential kinetics of hormone desensitization and growth hormone stimulation of both tyrosine phosphorylation and serine/threonine phosphorylation

Intermittent plasma growth hormone (GH) pulses, which occur in male but not female rats, activate liver Stat 5 by a mechanism that involves tyrosine phosphorylation and nuclear translocation of this latent cytoplasmic transcription factor (Waxman, D. J., Ram, P. A., Park, S. H., and Choi, H. K. (1995) J. Biol. Chem. 270, 13262-13270). We demonstrate that physiological levels of GH can also activate Stat 1 and Stat 3 in liver tissue, but with a dependence on the dose of GH and its temporal plasma profile that is distinct from Stat 5 and with a striking desensitization following a single hormone pulse that is not observed with liver Stat 5. GH activation of the two groups of Stats leads to their selective binding to DNA response elements upstream of the c-fos gene (c-sis-inducible enhancer element; Stat 1 and Stat 3 binding) and the beta-casein gene (mammary gland factor element; liver Stat 5 binding). In addition to tyrosine phosphorylation, GH is shown to stimulate phosphorylation of these Stats on serine or threonine in a manner that either enhances (Stat 1 and Stat 3) or substantially alters (liver Stat 5) the binding of each Stat to its cognate DNA response element. These findings establish the occurrence of multiple, Stat-dependent GH signaling pathways in liver cells that can target distinct genes and thereby contribute to the diverse effects that GH and its sexually dimorphic plasma profile have on liver gene expression.

Influence of growth hormone on the hepatic mixed function oxidase and transferase systems of rainbow trout

The effect of GH treatment on hepatic cytochrome P450 content, aryl hydrocarbon hydroxylase (AHH), aminopyrine-N-demethylase (AND), testosterone hydroxylase, testosterone 5α- and 5β-reductase, UDP-glucuronyl transferase (UDPGT) and glutathione S-transferase (GST) activities in immature rainbow trout were investigated. Hepatic cytochrome P450 content, AHH and GST activities were measured in both GH implanted and GH injected animals whereas other activities were assayed in GH implanted trout only.GH implants significantly decreased cytochrome P450 content at 15 days compared to the control but no significant effect was observed at 15 or 30 d when GH was injected biweekly. In both cases, AHH activity was significantly decreased by GH treatment compared to the control whereas GST remained unchanged. Compared to the control, GH implanted fish exhibited a pronounced inhibition of AND, a decreased 6β and 16β-testosterone hydroxylation, an inhibition of UDPGT with testosterone as substrate and an enhanced 17β-testosterone oxidation.

Intermittent plasma growth hormone triggers tyrosine phosphorylation and nuclear translocation of a liver-expressed, Stat 5-related DNA binding protein. Proposed role as an intracellular regulator of male-specific liver gene transcription

Growth hormone (GH) exerts sexually dimorphic effects on liver gene transcription that are regulated by the temporal pattern of pituitary GH release, which is intermittent in male rats and nearly continuous in females. To investigate the influence of these GH secretory patterns on intracellular hepatocyte signaling, we compared the pattern of liver nuclear protein tyrosine phosphorylation in male and female rats. An M(r) approximately 93,000 polypeptide, p93, was found to be tyrosine phosphorylated to a high level in male but not female rats. GH, but not prolactin, rapidly stimulated p93 tyrosine phosphorylation in hypophysectomized rats. Intermittent plasma GH pulses triggered repeated p93 phosphorylation, while continuous GH exposure led to desensitization and a dramatic decline in liver nuclear p93. p93 was cross-reactive with two monoclonal antibodies raised to mammary Stat 5, whose tyrosine phosphorylation is stimulated by prolactin. Intermittent GH pulsation translocated liver Stat 5/p93 protein from the cytosol to the nucleus and also activated its DNA binding activity, as demonstrated using a mammary Stat 5-binding DNA element derived from the beta-casein gene. p93 is thus a liver-expressed, Stat 5-related DNA binding protein that undergoes tyrosine phosphorylation and nuclear translocation in response to intermittent plasma GH stimulation and is proposed to be an intracellular mediator of the stimulatory effects of GH pulses on male-specific liver gene expression.

The glutathione S-transferase supergene family: regulation of GST and the contribution of the isoenzymes to cancer chemoprotection and drug resistance

The glutathione S-transferases (GST) represent a major group of detoxification enzymes. All eukaryotic species possess multiple cytosolic and membrane-bound GST isoenzymes, each of which displays distinct catalytic as well as noncatalytic binding properties: the cytosolic enzymes are encoded by at least five distantly related gene families (designated class alpha, mu, pi, sigma, and theta GST), whereas the membrane-bound enzymes, microsomal GST and leukotriene C4 synthetase, are encoded by single genes and both have arisen separately from the soluble GST. Evidence suggests that the level of expression of GST is a crucial factor in determining the sensitivity of cells to a broad spectrum of toxic chemicals. In this article the biochemical functions of GST are described to show how individual isoenzymes contribute to resistance to carcinogens, antitumor drugs, environmental pollutants, and products of oxidative stress. A description of the mechanisms of transcriptional and posttranscriptional regulation of GST isoenzymes is provided to allow identification of factors that may modulate resistance to specific noxious chemicals. The most abundant mammalian GST are the class alpha, mu, and pi enzymes and their regulation has been studied in detail. The biological control of these families is complex as they exhibit sex-, age-, tissue-, species-, and tumor-specific patterns of expression. In addition, GST are regulated by a structurally diverse range of xenobiotics and, to date, at least 100 chemicals have been identified that induce GST; a significant number of these chemical inducers occur naturally and, as they are found as nonnutrient components in vegetables and citrus fruits, it is apparent that humans are likely to be exposed regularly to such compounds. Many inducers, but not all, effect transcriptional activation of GST genes through either the antioxidant-responsive element (ARE), the xenobiotic-responsive element (XRE), the GST P enhancer 1(GPE), or the glucocorticoid-responsive element (GRE). Barbiturates may transcriptionally activate GST through a Barbie box element. The involvement of the Ah-receptor, Maf, Nrl, Jun, Fos, and NF-kappa B in GST induction is discussed. Many of the compounds that induce GST are themselves substrates for these enzymes, or are metabolized (by cytochrome P-450 monooxygenases) to compounds that can serve as GST substrates, suggesting that GST induction represents part of an adaptive response mechanism to chemical stress caused by electrophiles. It also appears probable that GST are regulated in vivo by reactive oxygen species (ROS), because not only are some of the most potent inducers capable of generating free radicals by redox-cycling, but H2O2 has been shown to induce GST in plant and mammalian cells: induction of GST by ROS would appear to represent an adaptive response as these enzymes detoxify some of the toxic carbonyl-, peroxide-, and epoxide-containing metabolites produced within the cell by oxidative stress. Class alpha, mu, and pi GST isoenzymes are overexpressed in rat hepatic preneoplastic nodules and the increased levels of these enzymes are believed to contribute to the multidrug-resistant phenotype observed in these lesions. The majority of human tumors and human tumor cell lines express significant amounts of class pi GST. Cell lines selected in vitro for resistance to anticancer drugs frequently overexpress class pi GST, although overexpression of class alpha and mu isoenzymes is also often observed. The mechanisms responsible for overexpression of GST include transcriptional activation, stabilization of either mRNA or protein, and gene amplification. In humans, marked interindividual differences exist in the expression of class alpha, mu, and theta GST. The molecular basis for the variation in class alpha GST is not known. (ABSTRACT TRUNCATED)

Naturally occurring human glutathione S-transferase GSTP1-1 isoforms with isoleucine and valine in position 104 differ in enzymic properties

Glutathione S-transferase P1-1 isoforms, differing in a single amino acid residue (Ile104 or Val104), have been previously identified in human placenta [Ahmad, H., Wilson, D. E., Fritz, R. R., Singh, S. V., Medh, R. D., Nagle, G. T., Awasthi, Y. C. & Kurosky, A. (1990) Arch. Biochem. Biophys. 278, 398-408]. In the present report, the enzymic properties of these two proteins are compared. [I104]glutathione S-transferase P1-1 has been expressed from its cDNA in Escherichia coli and purified to homogeneity by affinity chromatography; the cDNA has been mutated to replace Ile104 by Val104, and [V104]glutathione S-transferase P1-1 was expressed and isolated as described for [I104]glutathione S-transferase P1-1. The two enzymes differed in their specific activity and affinity for electrophilic substrates (KM values for 1-chloro-2,4-dinitrobenzene were 0.8 mM and 3.0 mM for [I-104]glutathione S-transferase P1-1 and [V-104]glutathione S-transferase P1-1, respectively), but were identical in their affinity for glutathione. In addition, the two enzymes were distinguishable by their heat stability, with half-lives at 45 degrees C of 19 min and 51 min, respectively. The resistance to heat denaturation was differentially modulated by the presence of substrates. These data, in conjunction with molecular modeling, indicate that the residue in position 104 helps to define the geometry of the hydrophobic substrate-binding site, and may also influence activity by interacting with residues directly involved in substrate binding.