Increased skin tumorigenesis in mice lacking pi class glutathione S-transferases

Pre-pubertal obesity compromises ovarian oxidative stress, DNA repair and chemical biotransformation

Obesity in adult females impairs fertility by altering oxidative stress, DNA repair and chemical biotransformation. Whether prepubertal obesity results in similar ovarian impacts is under-explored. The objective of this study was to induce obesity in prepubertal female mice and assess puberty onset, follicle number, and abundance of oxidative stress, DNA repair and chemical biotransformation proteins basally and in response to 7,12-dimethylbenz(a)anthracene (DMBA) exposure. DMBA is a polycyclic aromatic hydrocarbon that has been shown to be ovotoxic. Lactating dams (C57BL6J) were fed either a normal rodent containing 3.5% kCal from fat (lean), or a high fat diet comprised of 60% kCal from fat, and 9% kCal from sucrose. The offspring were weaned onto the diet of their dam and exposed at postnatal day 35 to either corn oil or DMBA (1 mg/kg) for 7 d via intraperitoneal injection. Mice on the HFD had reduced (P < 0.05) age at puberty onset as measured by vaginal opening but DMBA did not impact puberty onset. Heart, spleen, kidney, uterus and ovary weight were increased (P < 0.05) by obesity and liver weight was increased (P < 0.05) by DMBA exposure in obese mice. Follicle number was largely unaffected by obesity or DMBA exposure, with the exception of primary follicle number, which were higher (P < 0.05) in lean DMBA exposed and obese control relative to lean control mice. There were also greater numbers (P < 0.05) of corpora lutea in obese relative to lean mice. In lean mice, DMBA exposure reduced (P < 0.05) the level of CYP2E1, EPHX1, GSTP1, BRCA1, and CAT but this DMBA-induced reduction was absent in obese mice. Basally, obesity reduced (P < 0.05) the abundance of CYP2E1, EPHX1, GSTP1, BRCA1, SOD1 and CAT. There was greater (P < 0.05) fibrotic staining in obese DMBA-exposed ovaries and PPP2CA was decreased (P < 0.05) in growing follicles by both obesity and DMBA exposure. Thus, prepubertal obesity alters the capacity of the ovary to respond to DNA damage, ovotoxicant exposure and oxidative stress.

LanCL2 Implicates in Testicular Redox Homeostasis and Acrosomal Maturation

Redox balance plays an important role in testicular homeostasis. While lots of antioxidant molecules have been identified as widely expressed, the understanding of the critical mechanisms for redox management in male germ cells is inadequate. This study identified LanCL2 as a major male germ cell-specific antioxidant gene that is important for testicular homeostasis. Highly expressed in the brain and testis, LanCL2 expression correlates with testicular maturation and brain development. LanCL2 is enriched in spermatocytes and round spermatids of the testis. By examining LanCL2 knockout mice, we found that LanCL2 deletion did not affect postnatal brain development but injured the sperm parameters of adult mice. With histopathological analysis, we noticed that LanCL2 KO caused a pre-maturation and accelerated the self-renewal of spermatogonial stem cells in the early stage of spermatogenesis. In contrast, at the adult stage, LanCL2 KO damaged the acrosomal maturation in spermiogenesis, resulting in spermatogenic defects with a reduced number and motility of spermatozoa. Furthermore, we show that this disruption of testicular homeostasis in the LanCL2 KO testis was due to dysbalanced testicular redox homeostasis. This study demonstrates the critical role of LanCL2 in testicular homeostasis and redox balance.

Regulation of antioxidants in cancer

Scientists in this field often joke, "If you don't have a mechanism, say it's ROS." Seemingly connected to every biological process ever described, reactive oxygen species (ROS) have numerous pleiotropic roles in physiology and disease. In some contexts, ROS act as secondary messengers, controlling a variety of signaling cascades. In other scenarios, they initiate damage to macromolecules. Finally, in their worst form, ROS are deadly to cells and surrounding tissues. A set of molecules with detoxifying abilities, termed antioxidants, is the direct counterpart to ROS. Notably, antioxidants exist in the public domain, touted as a "cure-all" for diseases. Research has disproved many of these claims and, in some cases, shown the opposite. Of all the diseases, cancer stands out in its paradoxical relationship with antioxidants. Although the field has made numerous strides in understanding the roles of antioxidants in cancer, many questions remain.

Prognostic biomarker GSTK1 in head and neck squamous cell carcinoma and its correlation with immune infiltration and DNA methylation

Background: Glutathione S-transferase kappa 1 (GSTK1) is critical in sarcoma and breast cancer (BRCA) development. However, the clinical significance of GSTK1 in head and neck squamous cell carcinoma (HNSC) remains unclear. This study is the first investigation into the role of GSTK1 in HNSC. Methods: All original data were downloaded from the Cancer Genome Atlas (TCGA) dataset and verified by R Base Package 4.2.0. The expression of GSTK1 in various cancers was explored with TIMER and TCGA databases. Prognostic value of GSTK1 was analyzed via survival module of Kaplan-Meier plotter and Human Protein Atlas database and Cox regression analysis. The association between GSTK1 and clinical features was evaluated by Wilcoxon signed-rank test and logistic regression analysis. The relationship between GSTK1 and immune infiltration and methylation level was further explored. The expression of GSTK1 and its correlation with immune cell infiltration was verified by Immunohistochemical staining (IHC). Results: GSTK1 was lower in HNSC, BRCA, Lung squamous cell carcinoma, and Thyroid carcinoma than in para-carcinoma. Low GSTK1 expression was associated with worse overall survival in Bladder urothelial carcinoma, Kidney renal papillary cell carcinoma, BRCA, and HNSC. However, only in BRCA and HNSC, GSTK1 expression in tumors was lower than that in normal tissues. Cox regression analyses confirmed that GSKT1 was an independent prognostic factor of overall survival in HNSC patients. The decrease in GSTK1 expression in HNSC was significantly correlated with high T stage and smoker history. IHC showed that the expression level of GSTK1 in HNSC was lower than that in para-carcinoma. In addition, GSEA showed that three pathways related to immune infiltration were positively correlated, while two pathways related to DNA methylation were negatively correlated with expression of GSTK1. Further analysis showed that GSTK1 was moderately positively correlated with the infiltration level of T cells and Cytotoxic cells, which was further confirmed by IHC. The methylation level of GSTK1 was associated with prognosis in patients with HNSC. Conclusion: Low GSTK1 expression may be a potential molecular marker for poor prognosis in HNSC and provide new insight for the development of diagnostic marker or therapeutic target.

The good Samaritan glutathione-S-transferase P1: An evolving relationship in nitric oxide metabolism mediated by the direct interactions between multiple effector molecules

Glutathione-S-transferases (GSTs) are phase II detoxification isozymes that conjugate glutathione (GSH) to xenobiotics and also suppress redox stress. It was suggested that GSTs have evolved not to enhance their GSH affinity, but to better interact with and metabolize cytotoxic nitric oxide (NO). The interactions between NO and GSTs involve their ability to bind and store NO as dinitrosyl-dithiol iron complexes (DNICs) within cells. Additionally, the association of GSTP1 with inducible nitric oxide synthase (iNOS) results in its inhibition. The function of NO in vasodilation together with studies associating GSTM1 or GSTT1 null genotypes with preeclampsia, additionally suggests an intriguing connection between NO and GSTs. Furthermore, suppression of c-Jun N-terminal kinase (JNK) activity occurs upon increased levels of GSTP1 or NO that decreases transcription of JNK target genes such as c-Jun and c-Fos, which inhibit apoptosis. This latter effect is mediated by the direct association of GSTs with MAPK proteins. GSTP1 can also inhibit nuclear factor kappa B (NF-κB) signaling through its interactions with IKKβ and Iκα, resulting in decreased iNOS expression and the stimulation of apoptosis. It can be suggested that the inhibitory activity of GSTP1 within the JNK and NF-κB pathways may be involved in crosstalk between survival and apoptosis pathways and modulating NO-mediated ROS generation. These studies highlight an innovative role of GSTs in NO metabolism through their interaction with multiple effector proteins, with GSTP1 functioning as a "good Samaritan" within each pathway to promote favorable cellular conditions and NO levels.

Animal models of male subfertility targeted on LanCL1-regulated spermatogenic redox homeostasis

Oxidative stress in spermatozoa is a major contributor to male subfertility, which makes it an informed choice to generate animal models of male subfertility with targeted modifications of the antioxidant systems. However, the critical male germ cell-specific antioxidant mechanisms have not been well defined yet. Here we identify LanCL1 as a major male germ cell-specific antioxidant gene, reduced expression of which is related to human male infertility. Mice deficient in LanCL1 display spermatozoal oxidative damage and impaired male fertility. Histopathological studies reveal that LanCL1-mediated antioxidant response is required for mouse testicular homeostasis, from the initiation of spermatogenesis to the maintenance of viability and functionality of male germ cells. Conversely, a mouse model expressing LanCL1 transgene is protected against high-fat-diet/obesity-induced oxidative damage and subfertility. We further show that germ cell-expressed LanCL1, in response to spermatogenic reactive oxygen species, is regulated by transcription factor specific protein 1 (SP1) during spermatogenesis. This study demonstrates a critical role for the SP1-LanCL1 axis in regulating testicular homeostasis and male fertility mediated by redox balance, and provides evidence that LanCL1 genetically modified mice have attractive applications as animal models of male subfertility.

Implications of glutathione-S transferase P1 in MAPK signaling as a CRAF chaperone: In memory of Dr. Irving Listowsky

Glutathione-S transferase P1 (GSTP1) is one of the glutathione-S transferase isozymes that belong to a family of phase II metabolic isozymes. The unique feature of GSTP1 compared with other GST isozymes is its relatively high expression in malignant tissues. Thus, clinically, GSTP1 serves as a tumor marker and as a refractory factor against certain types of anticancer drugs through its primary function as a detoxifying enzyme. Additionally, recent studies have identified a chaperone activity of GSTP1 involved in the regulation the function of various intracellular proteins, including factors of the growth signaling pathway. In this review, we will first describe the function of GSTP1 and then extend the details onto its role in the mitogen-activated protein kinase signal pathway, referring to the results of our recent study that proposed a novel autocrine signal loop formed by the CRAF/GSTP1 complex in mutated KRAS and BRAF cancers. Finally, the possibilities of new therapeutic approaches for these cancers by targeting this complex will be discussed.

GSTP1 positive prostatic adenocarcinomas are more common in Black than White men in the United States

GSTP1 is a member of the Glutathione-S-transferase (GST) family silenced by CpG island DNA hypermethylation in 90-95% of prostate cancers. However, prostate cancers expressing GSTP1 have not been well characterized. We used immunohistochemistry against GSTP1 to examine 1673 primary prostatic adenocarcinomas on tissue microarrays (TMAs) with redundant sampling from the index tumor from prostatectomies. GSTP1 protein was positive in at least one TMA core in 7.7% of cases and in all TMA cores in 4.4% of cases. The percentage of adenocarcinomas from Black patients who had any GSTP1 positive TMA cores was 14.9%, which was 2.5 times higher than the percentage from White patients (5.9%; P < 0.001). Further, the percentages of tumors from Black patients who had all TMA spots positive for GSTP1 (9.5%) was 3-fold higher than the percentage from White patients (3.2%; P<0.001). In terms of association with other molecular alterations, GSTP1 positivity was enriched in ERG positive cancers among Black men. By in situ hybridization, GSTP1 mRNA expression was concordant with protein staining, supporting the lack of silencing of at least some GSTP1 alleles in GSTP1-positive tumor cells. This is the first report revealing that GSTP1-positive prostate cancers are substantially over-represented among prostate cancers from Black compared to White men. This observation should prompt additional studies to determine whether GSTP1 positive cases represent a distinct molecular subtype of prostate cancer and whether GSTP1 expression could provide a biological underpinning for the observed disparate outcomes for Black men.

Glutathione S-Transferase P Influences Redox Homeostasis and Response to Drugs that Induce the Unfolded Protein Response in Zebrafish

We have created a novel glutathione S-transferase π1 (gstp1) knockout (KO) zebrafish model and used it for comparative analyses of redox homeostasis and response to drugs that cause endoplasmic reticulum (ER) stress and induce the unfolded protein response (UPR). Under basal conditions, gstp1 KO larvae had higher expression of antioxidant nuclear factor erythroid 2-related factor 2 (Nrf2) accompanied by a more reduced larval environment and a status consistent with reductive stress. Compared with wild type, various UPR markers were decreased in KO larvae, but treatment with drugs that induce ER stress caused greater toxicities and increased expression of Nrf2 and UPR markers in KO. Tunicamycin and 0²-{2,4-dinitro-5-[4-(N-methylamino)benzoyloxy]phenyl}1-(N,N-dimethylamino)diazen-1-ium-1,2-diolate (PABA/nitric oxide) activated inositol-requiring protein-1/X-box binding protein 1 pathways, whereas thapsigargin caused greater activation of protein kinase-like ER kinase/activating transcription factor 4/CHOP pathways. These results suggest that this teleost model is useful for predicting how GSTP regulates organismal management of oxidative/reductive stress and is a determinant of response to drug-induced ER stress and the UPR. SIGNIFICANCE STATEMENT: A new zebrafish model has been created to study the importance of glutathione S-transferase π1 in development, redox homeostasis, and response to drugs that enact cytotoxicity through endoplasmic reticulum stress and induction of the unfolded protein response.

A CRAF/glutathione-S-transferase P1 complex sustains autocrine growth of cancers with KRAS and BRAF mutations

A strategy to overcome therapeutic obstacles of mKRAS and mBRAF cancers is devised based on the finding, here, that the RAF/MEK/ERK cascade is by-passed by an autocrine signal loop established by interaction of CRAF with GSTP1. The interaction evokes stabilization of CRAF from proteosomal degradation and facilitation of RAF-dimer formation. Thus, blocking CRAF/GSTP1 interactions should generate additive antiproliferative effects.

The Ras/RAF/MEK/ERK pathway is an essential signaling cascade for various refractory cancers, such as those with mutant KRAS (mKRAS) and BRAF (mBRAF). However, there are unsolved ambiguities underlying mechanisms for this growth signaling thereby creating therapeutic complications. This study shows that a vital component of the pathway CRAF is directly impacted by an end product of the cascade, glutathione transferases (GST) P1 (GSTP1), driving a previously unrecognized autocrine cycle that sustains proliferation of mKRAS and mBRAF cancer cells, independent of oncogenic stimuli. The CRAF interaction with GSTP1 occurs at its N-terminal regulatory domain, CR1 motif, resulting in its stabilization, enhanced dimerization, and augmented catalytic activity. Consistent with the autocrine cycle scheme, silencing GSTP1 brought about significant suppression of proliferation of mKRAS and mBRAF cells in vitro and suppressed tumorigenesis of the xenografted mKRAS tumor in vivo. GSTP1 knockout mice showed significantly impaired carcinogenesis of mKRAS colon cancer. Consequently, hindering the autocrine loop by targeting CRAF/GSTP1 interactions should provide innovative therapeutic modalities for these cancers.

GSTZ1-1 downregulates Wnt/β-catenin signalling in hepatocellular carcinoma cells

Glutathione S-transferase Zeta 1-1 (GSTZ1-1), an enzyme involved in the catabolism of phenylalanine and the detoxification of xenobiotics, plays a tumour suppressor role in hepatocellular carcinoma (HCC), but the underlying mechanism remains largely unknown. Here, we further explored the function of GSTZ1-1 in HCC through transcriptome analysis by RNA sequencing. The analysis revealed that 223 genes were upregulated and 290 genes were downregulated in GSTZ1-1-overexpressing Huh7 cells. Gene Ontology analysis showed that these differentially expressed genes (DEGs) were highly enriched for protein phosphorylation, cell cycle arrest and metabolic processes. Pathway analysis revealed that metabolic pathways were the predominant enriched pathways among the upregulated genes, while the TGF-β and Wnt/β-catenin signalling pathways were prominent in the downregulated clusters. Pathway interaction networks also showed that the Wnt/β-catenin pathway was located in the centre of the cluster. The expression levels of selected DEGs were validated by qRT-PCR, and Wnt/β-catenin involvement was validated by luciferase assays, western blotting and immunohistochemical analysis in vitro and in vivo. These results provide a comprehensive overview of the transcriptome in GSTZ1-1-overexpressing Huh7 cells and indicate that GSTZ1-1 may play a tumour suppressor role by inactivating the Wnt/β-catenin signalling pathway.

piR-31470 epigenetically suppresses the expression of glutathione S-transferase pi 1 in prostate cancer via DNA methylation

Inactivation of glutathione S-transferase pi 1 (GSTP1) via hypermethylation is an early and common event in prostate carcinogenesis. Functional inactivation of GSTP1 increases the susceptibility to oxidative stress and enhance progression risk of the prostatic carcinoma. In this study, we hypothesized that the Piwi-interacting RNA (piRNA) could be a sequence-recognition and guidance molecule for induction of promoter methylation of GSTP1 facilitating prostate carcinogenesis. We found that piR-31470 was highly expressed in prostate cancer cells, and piR-31470 could bind to piwi-like RNA-mediated gene silencing 4 (PIWIL4) to form the PIWIL4/piR-31470 complex. This complex could bind to the nascent RNA transcripts of GSTP1, and recruit DNA methyltransferase 1, DNA methyltransferase 3 alpha and methyl-CpG binding domain protein 2 to initiate and maintain the hypermethylation and inactivation of GSTP1. Our data demonstrated that the overexpression of piR-31470 inhibited the levels of GSTP1 and increased vulnerability to oxidative stress and DNA damage in human prostate epithelial RWPE1 cells. In conclusion, this study characterized the roles of the PIWIL4/piR-31470 complex in the regulation of the transcription of GSTP1 by methylating the CpG island of GSTP1. This discovery may provide a novel therapeutic strategy by targeting piRNAs for the epigenetic treatment of prostate cancer.

Contraction of the ROS Scavenging Enzyme Glutathione S-Transferase Gene Family in Cetaceans

Cetaceans are a group of marine mammals whose ancestors were adaptated for life on land. Life in an aquatic environment poses many challenges for air-breathing mammals. Diving marine mammals have adapted to rapid reoxygenation and reactive oxygen species (ROS)-mediated reperfusion injury. Here, we considered the evolution of the glutathione transferase (GST) gene family which has important roles in the detoxification of endogenously-derived ROS and environmental pollutants. We characterized the cytosolic GST gene family in 21 mammalian species; cetaceans, sirenians, pinnipeds, and their terrestrial relatives. All seven GST classes were identified, showing that GSTs are ubiquitous in mammals. Some GST genes are the product of lineage-specific duplications and losses, in line with a birth-and-death evolutionary model. We detected sites with signatures of positive selection that possibly influence GST structure and function, suggesting that adaptive evolution of GST genes is important for defending mammals from various types of noxious environmental compounds. We also found evidence for loss of alpha and mu GST subclass genes in cetacean lineages. Notably, cetaceans have retained a homolog of at least one of the genes GSTA1, GSTA4, and GSTM1; GSTs that are present in both the cytosol and mitochondria. The observed variation in number and selection pressure on GST genes suggest that the gene family structure is dynamic within cetaceans.

Benzo[ a]pyrene Induction of Glutathione S-Transferases: An Activity-Based Protein Profiling Investigation

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants generated from combustion of carbon-based matter. Upon ingestion, these molecules can be bioactivated by cytochrome P450 monooxygenases to oxidized toxic metabolites. Some of these metabolites are potent carcinogens that can form irreversible adducts with DNA and other biological macromolecules. Conjugative enzymes, such as glutathione S-transferases or UDP-glucuronosyltransferases, are responsible for the detoxification and/or facilitate the elimination of these carcinogens. While responses to PAH exposures have been extensively studied for the bioactivating cytochrome P450 enzymes, much less is known regarding the response of glutathione S-transferases in mammalian systems. In this study, we investigated the expression and activity responses of murine hepatic glutathione S-transferases to benzo[ a]pyrene exposure using global proteomics and activity-based protein profiling for chemoproteomics, respectively. Using this approach, we identified several enzymes exhibiting increased activity including GSTA2, M1, M2, M4, M6, and P1. The activity of one GST enzyme, GSTA4, was found to be downregulated with increasing B[ a]P dose. Activity responses of several of these enzymes were identified as being expression-independent when comparing global and activity-based data sets, possibly alluding to as of yet unknown regulatory post-translational mechanisms.

Molecular Pathology of High-Grade Prostatic Intraepithelial Neoplasia: Challenges and Opportunities

A better understanding of the early stages of prostate cancer initiation, potentially arising from precursor lesions, may fuel development of powerful approaches for prostate cancer prevention or interception. The best-known candidate for such a precursor lesion has been referred to as high-grade prostatic intraepithelial neoplasia (HGPIN). Although there is significant evidence supporting the notion that such HGPIN lesions can give rise to invasive adenocarcinomas of the prostate, there are also numerous complicating considerations and evidence that cloud the picture in many instances. Notably, recent evidence has suggested that some fraction of such lesions that are morphologically consistent with HGPIN may actually be invasive carcinomas masquerading as HGPIN-a state that we term "postinvasive intraepithelial carcinoma" (PIC). Although the prevalence of such PIC lesions is not fully understood, this and other factors can confound the potential of identifying prostate precursors that can be targeted for disease prevention, interception, or treatment. Here, we review our current understanding of the morphological and molecular pathological features of prostate cancer precursor lesions.

If this is true, what does it imply? How end-user antibody validation facilitates insights into biology and disease

Antibodies are employed ubiquitously in biomedical sciences, including for diagnostics and therapeutics. One of the most important uses is for immunohistochemical (IHC) staining, a process that has been improving and evolving over decades. IHC is useful when properly employed, yet misuse of the method is widespread and contributes to the "reproducibility crisis" in science. We report some of the common problems encountered with IHC assays, and direct readers to a wealth of literature documenting and providing some solutions to this problem. We also describe a series of vignettes that include our approach to analytical validation of antibodies and IHC assays that have facilitated a number of biological insights into prostate cancer and the refutation of a controversial association of a viral etiology in gliomas. We postulate that a great deal of the problem with lack of accuracy in IHC assays stems from the lack of awareness by researchers for the critical necessity for end-users to validate IHC antibodies and assays in their laboratories, regardless of manufacturer claims or past publications. We suggest that one reason for the pervasive lack of end-user validation for research antibodies is that researchers fail to realize that there are two general classes of antibodies employed in IHC. First, there are antibodies that are "clinical grade" reagents used by pathologists to help render diagnoses that influence patient treatment. Such diagnostic antibodies, which tend to be highly validated prior to clinical implementation, are in the vast minority (e.g. < 500). The other main class of antibodies are "research grade" antibodies (now numbering >3 800 000), which are often not extensively validated prior to commercialization. Given increased awareness of the problem, both the United States, National Institutes of Health and some journals are requiring investigators to provide evidence of specificity of their antibody-based assays.

Glutathione S-Transferase P1 313 (A > G) Ile105Val Polymorphism Contributes to Cancer Susceptibility in Indian Population: A Meta-analysis of 39 Case-Control Studies

GSTP1 involved in the metabolism of carcinogens and toxins, reduces damage of DNA and act as a suppressor of carcinogenesis. Many studies have reported that 313 A > G polymorphism is associated with different cancer in Indian population, but the results remain conflicting rather than conclusive. Therefore, we have performed meta-analysis to clarify the more precise association of GSPT1 313 A > G polymorphism with cancer risk in Indian population. We retrieved all relevant published literature from PubMed (Medline) and Google scholar web database and included those study only based on the established inclusion criteria. Pooled ORs and 95% CIs were used to appraise the strength of association. Publication bias and sensitivity analysis was also evaluated. A total of 6581 confirmed cancer cases and 8218 controls were included from eligible thirty nine case-controls studies. Pooled analysis suggested that the variant genotypes significantly increased the risk of cancer in allele (G vs. A: OR 1.266, 95% CI 1.129-1.418, p = 0.001), heterozygous (AG vs. AA: OR 1.191, 95% CI 1.047-1.355, p = 0.008), homozygous (GG vs. AA: OR 1.811, 95% CI 1.428-2.297, p = 0.001), dominant (GG + AG vs. AA: OR 1.276, 95% CI 1.110-1.466, p = 0.001) and recessive (GG vs. AG + AA: OR 1.638, 95% CI 1.340-2.002, p = 0.001) genetic models. The stability of these observations was confirmed by a sensitivity analysis. Begger's funnel plot and Egger's test did not reveal any publication bias. This meta-analysis suggests that the GSTP1 313 A > G polymorphism may contribute to genetic susceptibility to cancer in Indian population. However, larger studies and randomized clinical trial will be required to elucidate the biological and molecular mechanism of GSTP1 gene in cancer.

Progressive obesity alters ovarian insulin, phosphatidylinositol-3 kinase, and chemical metabolism signaling pathways and potentiates ovotoxicity induced by phosphoramide mustard in mice

Mechanisms underlying obesity-associated reproductive impairment are ill defined. Hyperinsulinemia is a metabolic perturbation often observed in obese subjects. Insulin activates phosphatidylinositol 3-kinase (PI3K) signaling, which regulates ovarian folliculogenesis, steroidogenesis, and xenobiotic metabolism. The impact of progressive obesity on ovarian genes encoding mRNA involved in insulin-mediated PI3K signaling and xenobiotic biotransformation [insulin receptor (Insr), insulin receptor substrate 1 (Irs1), 2 (Irs2), and 3 (Irs3); kit ligand (Kitlg), stem cell growth factor receptor (Kit), protein kinase B (AKT) alpha (Akt1), beta (Akt2), forkhead transcription factor (FOXO) subfamily 1 (Foxo1), and subfamily 3 (Foxo3a), microsomal epoxide hydrolase (Ephx1), cytochrome P450 family 2, subfamily E, polypeptide 1 (Cyp2e1), glutathione S-transferase (GST) class Pi (Gstp1) and class mu 1 (Gstm1)] was determined in normal wild-type nonagouti (a/a; lean) and lethal yellow mice (KK.CG-Ay/J; obese) at 6, 12, 18, or 24 weeks of age. At 6 weeks, ovaries from obese mice had increased (P < 0.05) Insr and Irs3 but decreased (P < 0.05) Kitlg, Foxo1, and Cyp2e1 mRNA levels. Interestingly, at 12 weeks, an increase (P < 0.05) in Kitlg and Kit mRNA, pIRS1Ser302, pAKTThr308, EPHX1, and GSTP1 protein level was observed due to obesity, while Cyp2e1 mRNA and protein were reduced. A phosphoramide mustard (PM) challenge increased (P < 0.05) ovarian EPHX1 protein abundance in lean but not obese females. In addition, lung tissue from PM-exposed animals had increased (P < 0.05) EPHX1 protein with no impact of obesity thereon. Taken together, progressive obesity affected ovarian signaling pathways potentially involved in obesity-associated reproductive disorders.

The multifaceted role of glutathione S-transferases in cancer

Glutathione S-transferases (GSTs) are phase II detoxifying enzymes involved in the maintenance of cell integrity, oxidative stress and protection against DNA damage by catalyzing the conjugation of glutathione to a wide variety of electrophilic substrates. Though enzymes of the glutathione synthesis and salvage pathways have been well characterized in the past, there is still a lack of comprehensive understanding of their independent and coordinate regulatory mechanisms in carcinogenesis. The present review discusses implication of GST in cancer development and progression, gene polymorphism, drug resistance, signaling and epigenetic regulation involving their role in cancer. It is anticipated that GST especially the GSTP1 class can be developed as a biomarker either used alone or in combination with other biomarkers for early cancer detection and/or diagnosis as well as for future targeted preventive and therapeutic interventions with dietary agents.

Alteration of benzo(a)pyrene biotransformation by resveratrol in ApcMin/+ mouse model of colon carcinogenesis

Epidemiological surveys have revealed that environmental and dietary factors contribute to most of the human cancers. Our earlier studies have shown that resveratrol (RVT), a phytochemical reduced the tumor number, size and incidence of dysplasias induced by benzo(a)pyrene (BaP), an environmental toxicant in the Apc^Min/+ mouse model of colon cancer. In this study we investigated to ascertain whether the preventive effects of RVT on BaP-induced colon carcinogenesis is a result of altered BaP biotransformation by RVT. For the first group of mice, 100 μg BaP/kg bw was administered in peanut oil via oral gavage over a 60 day period. For the second group, 45 μg RVT/kg bw was co-administered with BaP. For the third group, RVT was administered for 1 week prior to BaP exposure. Blood, colon and liver were collected from control and BaP/RVT-treated mice at 60 days post-BaP & RVT exposure. We have assayed activities and expression (protein & mRNA) of drug metabolizing enzymes such as cytochrome P4501A1 (CYP1A1), CYP1B1, and glutathione-S-transferase (GST) in colon and liver samples from the treatment groups mentioned above. An increased expression of CYP1A1 in liver and colon and of CYP1B1 in liver of BaP-treated mice was seen, while RVT inhibited the extent of biotransformation mediated by these enzymes in the respective tissue samples. In the case of GST, an increased expression in colon of BaP alone-treated mice was noted when RVT was administered prior to BaP or simultaneously with BaP. However, there is no change in liver GST expression between BaP and RVT treatment groups. The concentrations of BaP aqueous (phase II) metabolites were found to be greater than the organic (phase I) metabolites, suggesting that RVT slows down the phase I metabolism (metabolic activation) of BaP, while enhancing phase II metabolism (detoxification). Additionally, the BaP-DNA adduct concentrations measured in colon and liver of BaP + RVT-treated mice were low relative to their BaP counterparts. Taken together, our findings strongly suggest that RVT alleviates BaP-induced colon carcinogenesis by impairing biotransformation pathways and DNA adduct formation, and therefore holds promise as a chemopreventive agent.

GSTP1 c.341C>T gene polymorphism increases the risk of oral squamous cell carcinoma

Glutathione S Transferases (GST) are anti-oxidant enzymes involved in detoxification of cellular and exogenous carcinogens and oxidative products of reactive oxygen species. Genetic polymorphisms can attenuate the detoxification capacity of GST and consequently increase the susceptibility to carcinogenesis. There are eight classes of GST enzymes of which pi subtype is the predominant form expressed in the oral mucosa. c.341C > T single nucleotide polymorphism (rs1138272) in GSTP1 gene, is a functional variation that reduces the enzymatic activity of GST pi. We carried out a 1:2 case-control study involving 270 individuals to determine the association of c.341C > T variation with the risk of oral squamous cell carcinoma. GSTP1 c.341C > T variation was genotyped by PCR-RFLP method. GST pi expression in the tumour sample was determined by immunohistochemistry. Tobacco consumption was the major risk factor among cancer patients. The odds ratio for the risk of oral squamous cell carcinoma in individuals with the minor allele was 4.5 (0.95 CI = 2.3-8.9; P = 0.000004). The genotype was found to follow dominant mode of inheritance (OR 4.4 [0.95 CI = 2.1-9.2]; P = 0.00006). Our results support the conclusion that c.341C > T variation in GSTP1 increases the risk of OSCC in patients habituated to tobacco consumption.

S-Glutathionylation of estrogen receptor α affects dendritic cell function

Glutathione S-transferase Pi (GSTP) is a thiolase that catalyzes the addition of glutathione (GSH) to receptive cysteines in target proteins, producing an S-glutathionylated residue. Accordingly, previous studies have reported that S-glutathionylation is constitutively decreased in cells from mice lacking GSTP (Gstp1/p2^-/-). Here, we found that bone marrow-derived dendritic cells (BMDDCs) from Gstp1/p2^-/- mice have proliferation rates that are greater than those in their WT counterparts (Gstp1/p2^+/+). Moreover, Gstp1/p2^-/- BMDDCs had increased reactive oxygen species (ROS) levels and decreased GSH:glutathione disulfide (GSSG) ratios. Estrogen receptor α (ERα) is linked to myeloproliferation and differentiation, and we observed that its steady-state levels are elevated in Gstp1/p2^-/- BMDDCs, indicating a link between GSTP and ERα activities. BMDDCs differentiated by granulocyte-macrophage colony-stimulating factor had elevated ERα levels, which were more pronounced in Gstp1/p2^-/- than WT mice. When stimulated with lipopolysaccharide for maturation, Gstp1/p2^-/- BMDDCs exhibited augmented endocytosis, maturation rate, cytokine secretion, and T-cell activation; heightened glucose uptake and glycolysis; increased Akt signaling (in the mTOR pathway); and decreased AMPK-mediated phosphorylation of proteins. Of note, GSTP formed a complex with ERα, stimulating ERα S-glutathionylation at cysteines 221, 245, 417, and 447; altering ERα's binding affinity for estradiol; and reducing overall binding potential (receptor density and affinity) 3-fold. Moreover, in Gstp1/p2^-/- BMDDCs, ERα S-glutathionylation was constitutively decreased. Taken together, these findings suggest that GSTP-mediated S-glutathionylation of ERα controls BMDDC differentiation and affects metabolic function in dendritic cells.

Promoter methylation and gene polymorphism are two independent events in regulation of GSTP1 gene expression

Breast carcinogenesis is a multistep process, involving both genetic and epigenetic modification process of genes, involved in diverse pathways ranging from DNA repair to metabolic processes. This study was undertaken to assess the role of promoter methylation of GSTP1 gene, a member of glutathione-S-transferase family of enzymes, in relation to its expression, polymorphism, and clinicopathological parameters. Tissue samples were taken from breast cancer patients and paired with their normal adjacent tissues. A total of 51 subjects were studied, in which the frequency of promoter methylation in cancerous tissue was 37.25% as against 11% in the normal tissues ( p ≤ 0.001). The hypermethylated status of the gene was significantly associated with the loss of the protein expression ( r = −0.449, p = 0.001, odds ratio = 7.42, 95% confidence interval = 2.05–26.92). Furthermore, when compared with the clinical parameters, the significant association was found between the promoter hypermethylation and lymph node metastasis ( p ≤ 0.001), tumor stage ( p = 0.039), tumor grade ( p = 0.028), estrogen receptor status ( p = 0.018), and progesterone receptor status ( p = 0.046). Our study is the first of its kind in Kashmiri population, which indicates that GSTP1 shows aberrant methylation pattern in the breast cancer with the consequent loss in the protein expression. Furthermore, it also shows that the gene polymorphism (Ile105Val) at codon 105 is not related to the promoter methylation and two are the independent events in breast cancer development.

Glutathione S-Transferase P-Mediated Protein S-Glutathionylation of Resident Endoplasmic Reticulum Proteins Influences Sensitivity to Drug-Induced Unfolded Protein Response

AIMS

S-glutathionylation of cysteine residues, catalyzed by glutathione S-transferase Pi (GSTP), alters structure/function characteristics of certain targeted proteins. Our goal is to characterize how S-glutathionylation of proteins within the endoplasmic reticulum (ER) impact cell sensitivity to ER-stress inducing drugs.

RESULTS

We identify GSTP to be an ER-resident protein where it demonstrates both chaperone and catalytic functions. Redox based proteomic analyses identified a cluster of proteins cooperatively involved in the regulation of ER stress (immunoglobulin heavy chain-binding protein [BiP], protein disulfide isomerase [PDI], calnexin, calreticulin, endoplasmin, sarco/endoplasmic reticulum Ca²⁺-ATPase [SERCA]) that individually co-immunoprecipitated with GSTP (implying protein complex formation) and were subject to reactive oxygen species (ROS) induced S-glutathionylation. S-glutathionylation of each of these six proteins was attenuated in cells (liver, embryo fibroblasts or bone marrow dendritic) from mice lacking GSTP (Gstp1/p2^-/-) compared to wild type (Gstp1/p2^+/+). Moreover, Gstp1/p2^-/- cells were significantly more sensitive to the cytotoxic effects of the ER-stress inducing drugs, thapsigargin (7-fold) and tunicamycin (2-fold).

INNOVATION

Within the family of GST isozymes, GSTP has been ascribed the broadest range of catalytic and chaperone functions. Now, for the first time, we identify it as an ER resident protein that catalyzes S-glutathionylation of critical ER proteins within this organelle. Of note, this can provide a nexus for linkage of redox based signaling and pathways that regulate the unfolded protein response (UPR). This has novel importance in determining how some drugs kill cancer cells.

CONCLUSIONS

Contextually, these results provide mechanistic evidence that GSTP can exert redox regulation in the oxidative ER environment and indicate that, within the ER, GSTP influences the cellular consequences of the UPR through S-glutathionylation of a series of key interrelated proteins. Antioxid. Redox Signal. 26, 247-261.

A combined linkage and association strategy identifies a variant near the GSTP1 gene associated with BMI in the Mexican population

Obesity is a major public health concern in Mexico and worldwide. Although the estimated heritability is high, common variants identified by genome-wide association studies explain only a small proportion of this heritability. A combination of linkage and association strategies could be a more robust and powerful approach to identify other obesity-susceptibility variants. We thus sought to identify novel genetic variants associated with obesity-related traits in the Mexican population by combining these methods. We performed a genome-wide linkage scan for body mass index (BMI) and other obesity-related phenotypes in 16 Mexican families using the Sequential Oligogenic Linkage Analysis Routines Program. Associated single-nucleotide polymorphisms (SNPs) were tested for associations in an independent cohort. Two suggestive BMI-linkage peaks (logarithm of odds ⩾1.5) were observed at chromosomal regions 11q13 and 13q22. Only rs614080 in the 11q13 region was significantly associated with BMI and related traits in these families. This association was also significant in an independent cohort of Mexican adults. Moreover, this variant was significantly associated with GSTP1 gene expression levels in adipose tissue. In conclusion, the rs614080 SNP near the GSTP1 gene was significantly associated with BMI and GSTP1 expression levels in the Mexican population.

Does maternal exposure to artificial food coloring additives increase oxidative stress in the skin of rats?

Glutathione-S-transferase (GST) and cytochrome P450 family 1 subfamily A polypeptide 1 (CYP1A1) metabolize and detoxify carcinogens, drugs, environmental pollutants, and reactive oxygen species. Changes of GST expression in tissues and gene mutations have been reported in association with many neoplastic skin diseases and dermatoses. Widely used artificial food coloring additives (AFCAs) also reported to effect primarily behavioral and cognitive function and cause neoplastic diseases and several inflammatory skin diseases. We aimed to identify the changes in expression of GSTs, CYP1A1, and vascular endothelial growth factor (VEGF) in rat skin which were maternally exposed AFCAs. A rat model was designed to evaluate the effects of maternal exposure of AFCAs on skin in rats. "No observable adverse effect levels" of commonly used AFCAs as a mixture were given to female rats before and during gestation. Immunohistochemical expression of GSTs, CYP1A1, and VEGF was evaluated in their offspring. CYP1A1, glutathione S-transferase pi (GSTP), glutathione S-transferase alpha (GSTA), glutathione S-transferase mu (GSTM), glutathione S-transferase theta (GSTT), and VEGF were expressed by epidermal keratinocytes, dermal fibroblasts, sebaceous glands, hair follicle, and subcutaneous striated muscle in the normal skin. CYP1A1, GSTA, and GSTT were expressed at all microanatomical sites of skin in varying degrees. The expressions of CYP1A1, GSTA, GSTT, and VEGF were decreased significantly, while GSTM expression on sebaceous gland and hair follicle was increased. Maternal exposure of AFCAs apparently effects expression of the CYP1A1, GSTs, and VEGF in the skin. This prominent change of expressions might play role in neoplastic and nonneoplastic skin diseases.

Bioactive benzofuran-chalcanes as potential NQO1 inducers from Millettia pulchra (Benth) kurzvar-laxior (Dunn) Z.Wei

Five chalcanes ((α'R)-2, α'-dimethoxy-furano-[4″, 5'': 3', 4'] chalcane, (α'R, βR)-2', α', β-trimethoxy-furano-[4″, 5'': 3', 4'] chalcane, (α'S, βR)-2', α', β-trimethoxy-furano-[4″, 5'': 3', 4'] chalcane, (α'R, βR)-2', β-dimethoxy-α'-hydroxyethoxy-furano-[4″, 5'': 3', 4'] chalcane, (α'S, βR)-2', β-dimethoxy-α'-hydroxyethoxy-furano-[4″, 5'': 3', 4'] chalcane) and a flavonoid glycoside (3', 7-dihydroxy-6-methoxy-4', 5'-methylenedioxyisoflavone 6-O-β-D- glucopyranoside), together with 15 known components, were isolated from the leaves of Millettia pulchra (Benth) Kurzvar-laxior (Dunn) Z. Wei, a traditional Zhuang medicine. Their chemical structures were established by extensive analysis of NMR, mass spectrometry and ECD spectra. Furthermore compounds (α'R, βR)-2', β-dimethoxy-α'-hydroxyethoxy-furano-[4″, 5'': 3', 4'] chalcane, (α'S, βR)-2', β-dimethoxy-α'-hydroxyethoxy-furano-[4″, 5'': 3', 4'] chalcane, quercetin, methyl 2-O-β-D-glucopyranosylbenzoate, 6,7-dimethoxy-3',4'-methylenedioxyisoflavone and lyoniresinol were suggested to be potential chemopreventive agents because of their significant activity in inducing NQO1 ([NAD(P)H quinine oxidoreductase 1], a phase II metabolism enzyme).

Biochemical Characterization of the Detoxifying Enzyme Glutathione Transferase P1-1 from the Camel Camelus Dromedarius

Glutathione transferase (GST, EC 2.5.1.18) is a primary line of defense against toxicities of electrophile compounds and oxidative stress and therefore is involved in stress-response and cell detoxification. In the present study, we investigated the catalytic and structural properties of the glutathione transferase (GST) isoenzyme P1-1 from Camelus dromedarius (CdGSTP1-1). Recombinant CdGSTP1-1 was produced in Escherichia coli BL21(DE3) and purified to electrophoretic homogeneity. Kinetic analysis revealed that CdGSTP1-1 displays broad substrate specificity and shows high activity towards halogenated aryl-compounds, isothiocyanates and hydroperoxides. Computation analysis and structural comparison of the catalytic and ligand binding sites of CdGSTP1-1 with other pi class GSTs allowed the identification of major structural variations that affect the active site pocket and the catalytic mechanism., Affinity labeling and kinetic inhibition studies identified key regions that form the ligandin-binding site (L-site) and gave further insights into the mechanism of non-substrate ligand recognition. The results of the present study provide new information into camelid detoxifying mechanism and new knowledge into the diversity and complex enzymatic functions of GST superfamily.

AHR2 morpholino knockdown reduces the toxicity of total particulate matter to zebrafish embryos

The zebrafish embryo has been proposed as a 'bridge model' to study the effects of cigarette smoke on early development. Previous studies showed that exposure to total particulate matter (TPM) led to adverse effects in developing zebrafish, and suggested that the antioxidant and aryl hydrocarbon receptor (AHR) pathways play important roles. This study investigated the roles of these two pathways in mediating TPM toxicity. The study consisted of four experiments. In experiment I, zebrafish embryos were exposed from 6h post fertilization (hpf) until 96hpf to TPM0.5 and TPM1.0 (corresponding to 0.5 and 1.0μg/mL equi-nicotine units) in the presence or absence of an antioxidant (N-acetyl cysteine/NAC) or a pro-oxidant (buthionine sulfoximine/BSO). In experiment II, TPM exposures were performed in embryos that were microinjected with nuclear factor erythroid 2-related factor 2 (Nrf2), AHR2, cytochrome P450 1A (CYP1A), or CYP1B1 morpholinos, and deformities were assessed. In experiment III, embryos were exposed to TPM, and embryos/larvae were collected at 24, 48, 72, and 96hpf to assess several genes associated with the antioxidant and AHR pathways. Lastly, experiment IV assessed the activity and protein levels of CYP1A and CYP1B1 after exposure to TPM. We demonstrate that the incidence of TPM-induced deformities was generally not affected by NAC/BSO treatments or Nrf2 knockdown. In contrast, AHR2 knockdown reduced, while CYP1A or CYP1B1 knockdowns elevated the incidence of some deformities. Moreover, as shown by gene expression the AHR pathway, but not the antioxidant pathway, was induced in response to TPM exposure, providing further evidence for its importance in mediating TPM toxicity.

Attenuation of lung fibrosis in mice with a clinically relevant inhibitor of glutathione-S-transferase π

Idiopathic pulmonary fibrosis (IPF) is a debilitating lung disease characterized by excessive collagen production and fibrogenesis. Apoptosis in lung epithelial cells is critical in IPF pathogenesis, as heightened loss of these cells promotes fibroblast activation and remodeling. Changes in glutathione redox status have been reported in IPF patients. S-glutathionylation, the conjugation of glutathione to reactive cysteines, is catalyzed in part by glutathione-S-transferase π (GSTP). To date, no published information exists linking GSTP and IPF to our knowledge. We hypothesized that GSTP mediates lung fibrogenesis in part through FAS S-glutathionylation, a critical event in epithelial cell apoptosis. Our results demonstrate that GSTP immunoreactivity is increased in the lungs of IPF patients, notably within type II epithelial cells. The FAS-GSTP interaction was also increased in IPF lungs. Bleomycin- and AdTGFβ-induced increases in collagen content, α-SMA, FAS S-glutathionylation, and total protein S-glutathionylation were strongly attenuated in Gstp-/- mice. Oropharyngeal administration of the GSTP inhibitor, TLK117, at a time when fibrosis was already apparent, attenuated bleomycin- and AdTGFβ-induced remodeling, α-SMA, caspase activation, FAS S-glutathionylation, and total protein S-glutathionylation. GSTP is an important driver of protein S-glutathionylation and lung fibrosis, and GSTP inhibition via the airways may be a novel therapeutic strategy for the treatment of IPF.

Synthesis, evaluation, and metabolism of novel [6]-shogaol derivatives as potent Nrf2 activators

Oxidative stress is a central component of many chronic diseases. The Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2 p45-related factor 2 (Nrf2) system is a major regulatory pathway of cytoprotective genes against oxidative and electrophilic stress. Activation of the Nrf2 pathway plays crucial roles in the chemopreventive effects of various inducers. In this study, we developed a novel class of potent Nrf2 activators derived from ginger compound, [6]-shogaol (6S), using the Tg[glutathione S-transferase pi 1 (gstp1):green fluorescent protein (GFP)] transgenic zebrafish model. Investigation of structure-activity relationships of 6S derivatives indicates that the combination of an α,β-unsaturated carbonyl entity and a catechol moiety in one compound enhances the Tg(gstp1:GFP) fluorescence signal in zebrafish embryos. Chemical reaction and in vivo metabolism studies of the four most potent 6S derivatives showed that both α,β-unsaturated carbonyl entity and catechol moiety act as major active groups for conjugation with the sulfhydryl groups of the cysteine residues. In addition, we further demonstrated that 6S derivatives increased the expression of Nrf2 downstream target, heme oxygenase-1, in both a dose- and time-dependent manner. These results suggest that α,β-unsaturated carbonyl entity and catechol moiety of 6S derivatives may react with the cysteine residues of Keap1, disrupting the Keap1-Nrf2 complex, thereby liberating and activating Nrf2. Our findings of natural product-derived Nrf2 activators lead to design options of potent Nrf2 activators for further optimization.

Oxygen stress: impact on innate immune system, antioxidant defence system and expression of HIF-1α and ATPase 6 genes in Catla catla

Catla catla catla (2.28 ± 0.1 g) were exposed to six different levels of dissolved oxygen: 1 (DO-1), 3 (DO-3), 5 (DO-5), 7 (DO-7), 9 (DO-9) and 11 (DO-11) mg/L. DO-5 served as control. In DO-1 and DO-3, the number of red blood cells (RBC), lysozyme, respiratory burst activity and nitric oxide synthase were significantly (p < 0.05) lower compared to the control one. In DO-7 and DO-9, RBC and lysozyme were significantly (p < 0.05) higher compared to the control one. Thiobarbituric acid reactive substances was significantly (p < 0.05) higher in catla exposed at low (1 and 3 mg/L) and high (9 and 11 mg/L) dissolved oxygen compared to others. In muscles and hepatopancreas, reduced glutathione was significantly (p < 0.05) higher in DO-5 and DO-7 and in gills of DO-5 compared to others after 1 h. In muscles, glutathione S-transferase (GST) was significantly (p < 0.05) lower in DO-5 and DO-7 compared to others. In hepatopancreas, GST and glutathione peroxidise (GPx) were significantly (p < 0.05) higher in DO-1 and DO-3 compared to others. In gills, GPx was higher in DO-9 and DO-11 after 48 h. In brain, hypoxia-inducible factor (HIF)-1α mRNA level was induced in DO-1 and DO-3 compared to others after 1 h of exposure. In gills and hepatopancreas, HIF-1α mRNA level was significantly (p < 0.05) higher in DO-1 compared to others after 1 h. The ATPase 6 mRNA level was significantly (p < 0.05) higher in brain and hepatopancreas of DO-1 after 1 h and in gills and hepatopancreas of DO-3 and DO-9, respectively, after 48 h compared to others.

Altered protein S-glutathionylation identifies a potential mechanism of resistance to acetaminophen-induced hepatotoxicity

Acetaminophen (APAP) is the most commonly used over-the-counter analgesic. However, hepatotoxicity induced by APAP is a major clinical issue, and the factors that define sensitivity to APAP remain unclear. We have previously demonstrated that mice nulled for glutathione S-transferase Pi (GSTP) are resistant to APAP-induced hepatotoxicity. This study aims to exploit this difference to delineate pathways of importance in APAP toxicity. We used mice nulled for GSTP and heme oxygenase-1 oxidative stress reporter mice, together with a novel nanoflow liquid chromatography-tandem mass spectrometry methodology to investigate the role of oxidative stress, cell signaling, and protein S-glutathionylation in APAP hepatotoxicity. We provide evidence that the sensitivity difference between wild-type and Gstp1/2(-/-) mice is unrelated to the ability of APAP to induce oxidative stress, despite observing significant increases in c-Jun N-terminal kinase and extracellular signal-regulated kinase phosphorylation in wild-type mice. The major difference in response to APAP was in the levels of protein S-glutathionylation: Gstp1/2(-/-) mice exhibited a significant increase in the number of S-glutathionylated proteins compared with wild-type animals. Remarkably, these S-glutathionylated proteins are involved in oxidative phosphorylation, respiratory complexes, drug metabolism, and mitochondrial apoptosis. Furthermore, we found that S-glutathionylation of the rate-limiting glutathione-synthesizing enzyme, glutamate cysteine ligase, was markedly increased in Gstp1/2(-/-) mice in response to APAP. The data demonstrate that S-glutathionylation provides an adaptive response to APAP and, as a consequence, suggest that this is an important determinant in APAP hepatotoxicity. This work identifies potential novel avenues associated with cell survival for the treatment of chemical-induced hepatotoxicity.

Genetic Deficiency of Glutathione S-Transferase P Increases Myocardial Sensitivity to Ischemia-Reperfusion Injury

RATIONALE

Myocardial ischemia-reperfusion (I/R) results in the generation of oxygen-derived free radicals and the accumulation of lipid peroxidation-derived unsaturated aldehydes. However, the contribution of aldehydes to myocardial I/R injury has not been assessed.

OBJECTIVE

We tested the hypothesis that removal of aldehydes by glutathione S-transferase P (GSTP) diminishes I/R injury.

METHODS AND RESULTS

In adult male C57BL/6 mouse hearts, Gstp1/2 was the most abundant GST transcript followed by Gsta4 and Gstm4.1, and GSTP activity was a significant fraction of the total GST activity. mGstp1/2 deletion reduced total GST activity, but no compensatory increase in GSTA and GSTM or major antioxidant enzymes was observed. Genetic deficiency of GSTP did not alter cardiac function, but in comparison with hearts from wild-type mice, the hearts isolated from GSTP-null mice were more sensitive to I/R injury. Disruption of the GSTP gene also increased infarct size after coronary occlusion in situ. Ischemia significantly increased acrolein in hearts, and GSTP deficiency induced significant deficits in the metabolism of the unsaturated aldehyde, acrolein, but not in the metabolism of 4-hydroxy-trans-2-nonenal or trans-2-hexanal; on ischemia, the GSTP-null hearts accumulated more acrolein-modified proteins than wild-type hearts. GSTP deficiency did not affect I/R-induced free radical generation, c-Jun N-terminal kinase activation, or depletion of reduced glutathione. Acrolein exposure induced a hyperpolarizing shift in INa, and acrolein-induced cell death was delayed by SN-6, a Na(+)/Ca(++) exchange inhibitor. Cardiomyocytes isolated from GSTP-null hearts were more sensitive than wild-type myocytes to acrolein-induced protein crosslinking and cell death.

CONCLUSIONS

GSTP protects the heart from I/R injury by facilitating the detoxification of cytotoxic aldehydes, such as acrolein.

Proteome-wide identification and quantification of S-glutathionylation targets in mouse liver

Protein S-glutathionylation is a reversible post-translational modification regulating sulfhydryl homeostasis. However, little is known about the proteins and pathways regulated by S-glutathionylation in whole organisms and current approaches lack the sensitivity to examine this modification under basal conditions. We now report the quantification and identification of S-glutathionylated proteins from animal tissue, using a highly sensitive methodology combining high-accuracy proteomics with tandem mass tagging to provide precise, extensive coverage of S-glutathionylated targets in mouse liver. Critically, we show significant enrichment of S-glutathionylated mitochondrial and Krebs cycle proteins, identifying that S-glutathionylation is heavily involved in energy metabolism processes in vivo. Furthermore, using mice nulled for GST Pi (GSTP) we address the potential for S-glutathionylation to be mediated enzymatically. The data demonstrate the impact of S-glutathionylation in cellular homeostasis, particularly in relation to energy regulation and is of significant interest for those wishing to examine S-glutathionylation in an animal model.

Glutathione S-transferase P protects against cyclophosphamide-induced cardiotoxicity in mice

High-dose chemotherapy regimens using cyclophosphamide (CY) are frequently associated with cardiotoxicity that could lead to myocyte damage and congestive heart failure. However, the mechanisms regulating the cardiotoxic effects of CY remain unclear. Because CY is converted to an unsaturated aldehyde acrolein, a toxic, reactive CY metabolite that induces extensive protein modification and myocardial injury, we examined the role of glutathione S-transferase P (GSTP), an acrolein-metabolizing enzyme, in CY cardiotoxicity in wild-type (WT) and GSTP-null mice. Treatment with CY (100-300 mg/kg) increased plasma levels of creatine kinase-MB isoform (CK · MB) and heart-to-body weight ratio to a significantly greater extent in GSTP-null than WT mice. In addition to modest yet significant echocardiographic changes following acute CY-treatment, GSTP insufficiency was associated with greater phosphorylation of c-Jun and p38 as well as greater accumulation of albumin and protein-acrolein adducts in the heart. Mass spectrometric analysis revealed likely prominent modification of albumin, kallikrein-1-related peptidase, myoglobin and transgelin-2 by acrolein in the hearts of CY-treated mice. Treatment with acrolein (low dose, 1-5 mg/kg) also led to increased heart-to-body weight ratio and myocardial contractility changes. Acrolein induced similar hypotension in GSTP-null and WT mice. GSTP-null mice also were more susceptible than WT mice to mortality associated with high-dose acrolein (10-20 mg/kg). Collectively, these results suggest that CY cardiotoxicity is regulated, in part, by GSTP, which prevents CY toxicity by detoxifying acrolein. Thus, humans with low cardiac GSTP levels or polymorphic forms of GSTP with low acrolein-metabolizing capacity may be more sensitive to CY toxicity.

Transgenic mice and metabolomics for study of hepatic xenobiotic metabolism and toxicity

INTRODUCTION

The study of xenobiotic metabolism and toxicity has been greatly aided by the use of genetically modified mouse models and metabolomics.

AREAS COVERED

Gene knockout mice can be used to determine the enzymes responsible for the metabolism of xenobiotics in vivo and to examine the mechanisms of xenobiotic-induced toxicity. Humanized mouse models are especially important because there exist marked species differences in the xenobiotic-metabolizing enzymes and the nuclear receptors that regulate these enzymes. Humanized mice expressing CYPs and nuclear receptors including the pregnane X receptor, the major regulator of xenobiotic metabolism and transport were produced. With genetically modified mouse models, metabolomics can determine the metabolic map of many xenobiotics with a level of sensitivity that allows the discovery of even minor metabolites. This technology can be used for determining the mechanism of xenobiotic toxicity and to find early biomarkers for toxicity.

EXPERT OPINION

Metabolomics and genetically modified mouse models can be used for the study of xenobiotic metabolism and toxicity by: i) comparison of the metabolomics profiles between wild-type and genetically modified mice, and searching for genotype-dependent endogenous metabolites; ii) searching for and elucidating metabolites derived from xenobiotics; and iii) discovery of specific alterations of endogenous compounds induced by xenobiotics-induced toxicity.

MicroRNA Regulating Glutathione S-Transferase P1 in Prostate Cancer

Glutathione S-transferase P1 (GSTP1), an enzyme involved in detoxification process, is frequently inactivated in prostate cancer due to epigenetic modifications. Through in silico analysis we identified a subset of miRNAs that are putative targets in regulating GSTP1. miRNAs are small endogenous non-coding RNA that are critical regulators of various physiologic and pathologic processes and their level of expression may play a precise role in early diagnosis and prognosis of cancer. These small molecules have been detected in a wide variety of human biological specimens including blood, serum, urine, ejaculate and tissues, which could be utilized as clinically useful biomarker in early detection and prognosis of prostate cancer. The chapter summarizes the current knowledge about miRNA involved in GSTP1 regulation in prostate cancer and their potential as useful biomarkers of disease for early detection and prognosis, along with challenges and limitations in this development.

Ezatiostat hydrochloride for the treatment of myelodysplastic syndromes

INTRODUCTION

Myelodysplastic syndromes (MDSs) are associated with significant morbidity due to ineffective hematopoiesis. Given the limited number of drugs approved by the FDA, there is a need for new therapeutic options. Ezatiostat is a novel agent targeting oxidative stress via inhibition of glutathione S-transferase 1.

AREAS COVERED

Herein, the authors summarize the standard of care in order to build the framework for therapeutic advancements. The purpose of this paper is to review the body of preclinical and clinical research literature on the investigational agent ezatiostat hydrochloride (TLK199) for the treatment of MDSs. The article includes details of the pathophysiology, pharmacology, toxicity and efficacy of ezatiostat hydrochloride from controlled studies in patients with myelodysplasia.

EXPERT OPINION

MDS clonal heterogeneity and clonal architecture complexity has presented a significant technical challenge in developing effective therapies. Ezatiostat offers a unique and specific mechanism to improve the transfusion burden associated with myelodysplasia. Since it is tolerable as a monotherapy, combining ezatiostat with agents such as lenalidomide may have the most potential benefit.

Pleiotropic functions of glutathione S-transferase P

Glutathione S-transferase P (GSTP) is one member of the GST superfamily that is prevalently expressed in mammals. Known to possess catalytic activity through deprotonating glutathione allowing formation of thioether bonds with electrophilic substrates, more recent discoveries have broadened our understanding of the biological roles of this protein. In addition to catalytic detoxification, other properties so far ascribed to GSTP include chaperone functions, regulation of nitric oxide pathways, regulation of a variety of kinase signaling pathways, and participation in the forward reaction of protein S-glutathionylation. The expression of GSTP has been linked with cancer and other human pathologies and more recently even with drug addiction. With respect to human health, polymorphic variants of GSTP may determine individual susceptibility to oxidative stress and/or be critical in the design and development of drugs that have used redox pathways as a discovery platform.

The shifting perception on antioxidants: the case of vitamin E and β-carotene

Antioxidants are vital for aerobic life, and for decades the expectations of antioxidants as health promoting agents were very high. However, relatively recent meta-analyses of clinical studies show that supplementation of antioxidants does not result in the presumed health benefit, but is associated with increased mortality. The dilemma that still needs to be solved is: what are antioxidants in the end, healthy or toxic? We have evaluated this dilemma by examining the presumed health effects of two individual antioxidants with opposite images i.e. the “poisonous” β-carotene and the “wholesome” vitamin E and focused on one aspect, namely their role in inducing BPDE-DNA adducts. It appears that both antioxidants promote DNA adduct formation indirectly by inhibition of the protective enzyme glutathione-S-transferase π (GST π). Despite their opposite image, both antioxidants display a similar type of toxicity. It is concluded that, in the appreciation of antioxidants, first their benefits should be identified and substantiated by elucidating their molecular mechanism. Subsequently, the risks should be identified including the molecular mechanism. The optimal benefit–risk ratio has to be determined for each antioxidant and each individual separately, also considering the dose.

•

To date, the debate on the health benefit of antioxidants continues.

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The effect of vitamin E and β-carotene on BPDE-DNA adduct formation was evaluated.

•

Both antioxidants promote DNA adduct formation by inhibition of GST π.

•

Accurate benefit–risk analyses give a balanced view on the effects of antioxidants.

Glutathione transferases P1/P2 regulate the timing of signaling pathway activations and cell cycle progression during mouse liver regeneration

Glutathione transferases (GST) are phase II enzymes catalyzing the detoxification of endogenous noxious compounds and xenobiotics. They also regulate phosphorylation activities of MAPKinases in a catalytic-independent manner. Previous studies have demonstrated the regulation of JNK-dependent pathway by GSTP1/2. Considering the crucial role of JNK in the early steps of the hepatocyte cell cycle, we sought to determine whether GSTP1/2 were essential for hepatocyte proliferation following partial hepatectomy (PH). Using a conventional double knockout mouse model for the Gstp1 and Gstp2 genes, we found that the lack of GSTP1/P2 reduced the rate of DNA replication and mitotic index during the first wave of hepatocyte proliferation. The lowered proliferation was associated with the decrease in TNFalpha and IL-6 plasma concentrations, reduced hepatic HGF expression and delayed and/or altered activation of STAT3, JNK and ERK1/2 signaling pathways. In addition, the expression and/or activation of cell cycle regulators such as Cyclin D1, CDK4, E2F1 and MCM7 was postponed demonstrating that the absence of GSTP1/2 delayed the entry into and progression through the G1 phase of the cell cycle and impaired the synchrony of proliferation in hepatocytes following PH. Furthermore, while JNK and its downstream targets c-Jun and ATF2 were activated during the early steps of the liver regeneration in wild-type animals, the constitutively active JNK found in the quiescent liver of Gstp1/2 knockout mice underwent a decrease in its activity after PH. Transient induction of antioxidant enzymes and nitric oxide synthase were also delayed or repressed during the regenerative response. Altogether our results demonstrate that GSTP1/2 are a critical regulators of hepatocyte proliferation in the initial phases of liver regeneration.

Chemopreventive flavonoids from Millettia pulchra Kurz var-laxior (Dunn) Z.Wei (Yulangsan) function as Michael reaction acceptors

Natural NQO1 [NAD(P)H quinine oxidoreductase 1] inducing agents play a critical role in cancer chemoprevention. The expression of NQO1 is regulated by Michael reaction acceptors (MRAs) via the Keap1/Nrf2/ARE signaling pathway. The aims of this study were to identify and characterize novel effective chemopreventive agents from naturally occurring products. Using bioassay-guided isolation approaches 16 bioactive MRAs from Millettia pulchra Kurz var-laxior (Dunn) Z.Wei, also called Yulangsan as a famous Zhuang medicine. The structures were elucidated as chalcone (1-7), flavonone (8-14), flavanone (15) and isoflavan (16). Their electrophilic abilities and NQO1 inducing activity were assessed using GSH (glutathione) rapid screening, and in vitro cell-based (Hepa 1c1c7 cells) assay, respectively. Compounds 3, 4, 6, 13, and 14 showed to have NQO1 inducing activity. Among them, compounds 4 and 14 interact with NQO1 at Gly 149, Gly 150, Phe 106, Typ 105 and His 161, revealed by molecular docking studies.

Tissue specific dysregulated protein subnetworks in type 2 diabetic bladder urothelium and detrusor muscle

Diabetes mellitus is well known to cause bladder dysfunction; however, the molecular mechanisms governing this process and the effects on individual tissue elements within the bladder are poorly understood, particularly in type 2 diabetes. A shotgun proteomics approach was applied to identify proteins differentially expressed between type 2 diabetic (TallyHo) and control (SWR/J) mice in the bladder smooth muscle and urothelium, separately. We were able to identify 1760 nonredundant proteins from the detrusor smooth muscle and 3169 nonredundant proteins from urothelium. Pathway and network analysis of significantly dysregulated proteins was conducted to investigate the molecular processes associated with diabetes. This pinpointed ERK1/2 signaling as a key regulatory node in the diabetes-induced pathophysiology for both tissue types. The detrusor muscle samples showed diabetes-induced increased tissue remodeling-type events such as Actin Cytoskeleton Signaling and Signaling by Rho Family GTPases. The diabetic urothelium samples exhibited oxidative stress responses, as seen in the suppression of protein expression for key players in the NRF2-Mediated Oxidative Stress Response pathway. These results suggest that diabetes induced elevated inflammatory responses, oxidative stress, and tissue remodeling are involved in the development of tissue specific diabetic bladder dysfunctions. Validation of signaling dysregulation as a function of diabetes was performed using Western blotting. These data illustrated changes in ERK1/2 phosphorylation as a function of diabetes, with significant decreases in diabetes-associated phosphorylation in urothelium, but the opposite effect in detrusor muscle. These data highlight the importance of understanding tissue specific effects of disease process in understanding pathophysiology in complex disease and pave the way for future studies to better understand important molecular targets in reversing bladder dysfunction.

Co-administration of adjuvants along with Moringa oleifera attenuates beryllium-induced oxidative stress and histopathological alterations in rats

CONTEXT

Moringa oleifera Lam. (Moringaceae) is a rich source of antioxidants. All parts of the plant are medicinally important and have been used as traditional medicine for a variety of human ailments in India.

OBJECTIVE

Therapeutic efficacy of adjuvants with M. oleifera (MO) root extract was investigated against beryllium-induced oxidative stress.

MATERIALS AND METHODS

Hydroalcoholic (50% v/v) root extract of M. oleifera (150 mg/kg, p.o.) alone and combinations of M. oleifera with either piperine (2.5 mg/kg, p.o.) or curcumin (5.0 mg/kg, p.o.) daily for 1 week were administered in experimental rats against beryllium toxicity (1.0 mg/kg, i.p. daily for 5 weeks). Oxidative stress parameters including blood sugar, G-6-Pase in liver, and DNA damage were analyzed. Histopathological changes in liver and kidney were also observed.

RESULTS

Beryllium enhanced lipid peroxidation (LPO), depleted reduced glutathione (GSH) and antioxidant enzymes activities, decreased blood sugar and G-6-Pase activity, and did not damage DNA. Histologically, liver was observed with structural loss and disintegration of hepatocytes, heavy vacuolation in hepatocytes, and kidney was observed with constriction of glomeruli and hypertrophy in epithelial cells of uriniferous tubules. Therapy of M. oleifera with piperine was effective; however, combination of M. oleifera with curcumin showed better therapeutic effect by reduction of LPO, elevated GSH level, maintained antioxidant enzymes activities, restored blood sugar, and G-6-Pase activity in liver together with almost normal histoarchitecture of liver and kidney.

DISCUSSION AND CONCLUSION

Curcumin enhanced therapeutic efficacy of M. oleifera root extract and showed better antioxidant potential against beryllium toxicity.