Several closely related glutathione S-transferase isozymes catalyzing conjugation of 4-hydroxynonenal are differentially expressed in human tissues

Anticancer Activity of Ω-6 Fatty Acids through Increased 4-HNE in Breast Cancer Cells

Simple Summary

Epidemiological evidence suggests that breast cancer risk is lowered by Ω-3 and increased by Ω-6 polyunsaturated fatty acids (PUFAs). Paradoxically, the Ω-6 PUFA metabolite 4-hydroxynonenal (4-HNE) inhibits cancer cell growth. This duality prompted us to study whether arachidonic acid (AA) would enhance doxorubicin (dox) cytotoxicity towards breast cancer cells. We found that supplementing AA or inhibiting 4-HNE metabolism potentiated doxorubicin (dox) toxicity toward Her2-dependent breast cancer but spared myocardial cells. Our results suggest that Ω-6 PUFAs could improve outcomes of dox chemotherapy in Her2-overexpressing breast cancer.

Abstract

Her2-amplified breast cancers resistant to available Her2-targeted therapeutics continue to be a challenge in breast cancer therapy. Dox is the mainstay of chemotherapy of all types of breast cancer, but its usefulness is limited by cumulative cardiotoxicity. Because oxidative stress caused by dox generates the pro-apoptotic Ω-6 PUFA metabolite 4-hydroxynonenal (4-HNE), we surmised that Ω-6 PUFAs would increase the effectiveness of dox chemotherapy. Since the mercapturic acid pathway enzyme RALBP1 (also known as RLIP76 or Rlip) that limits cellular accumulation of 4-HNE also mediates dox resistance, the combination of Ω-6 PUFAs and Rlip depletion could synergistically improve the efficacy of dox. Thus, we studied the effects of the Ω-6 PUFA arachidonic acid (AA) and Rlip knockdown on the antineoplastic activity of dox towards Her2-amplified breast cancer cell lines SK-BR-3, which is sensitive to Her2 inhibitors, and AU565, which is resistant. AA increased lipid peroxidation, 4-HNE generation, apoptosis, cellular dox concentration and dox cytotoxicity in both cell lines while sparing cultured immortalized cardiomyocyte cells. The known functions of Rlip including clathrin-dependent endocytosis and dox efflux were inhibited by AA. Our results support a model in which 4-HNE generated by AA overwhelms the capacity of Rlip to defend against apoptosis caused by dox or 4-HNE. We propose that Ω-6 PUFA supplementation could improve the efficacy of dox or Rlip inhibitors for treating Her2-amplified breast cancer.

Sensitivity of Osteosarcoma Cells to Concentration-Dependent Bioactivities of Lipid Peroxidation Product 4-Hydroxynonenal Depend on Their Level of Differentiation

4-Hydroxynonenal (HNE) is a major aldehydic product of lipid peroxidation known to exert several biological effects. Normal and malignant cells of the same origin express different sensitivity to HNE. We used human osteosarcoma cells (HOS) in different stages of differentiation in vitro, showing differences in mitosis, DNA synthesis, and alkaline phosphatase (ALP) staining. Differentiated HOS cells showed decreased proliferation (³H-thymidine incorporation), decreased viability (thiazolyl blue tetrazolium bromide-MTT), and increased apoptosis and necrosis (nuclear morphology by staining with 4′,6-diamidino-2-phenylindole-DAPI). Differentiated HOS also had less expressed c-MYC, but the same amount of c-FOS (immunocytochemistry). When exposed to HNE, differentiated HOS produced more reactive oxygen species (ROS) in comparison with undifferentiated HOS. To clarify this, we measured HNE metabolism by an HPLC method, total glutathione (GSH), oxidized GSH (ox GSH), glutathione transferase activity (GST), proteasomal activity by enzymatic methods, HNE-protein adducts by genuine ELISA and fatty acid composition by GC-MS in these cell cultures. Differentiated HOS cells had less GSH, lower HNE metabolism, increased formation of HNE-protein adducts, and lower proteasomal activity, in comparison to undifferentiated counterpart cells, while GST and oxGSH were the same. Fatty acids analyzed by GC-MS showed that there is an increase in C20:3 in differentiated HOS while the amount of C20:4 remained the same. The results showed that the cellular machinery responsible for protection against toxicity of HNE was less efficient in differentiated HOS cells. Moreover, differentiated HOS cells contained more C20:3 fatty acid, which might make them more sensitive to free radical-initiated oxidative chain reactions and more vulnerable to the effects of reactive aldehydes such as HNE. We propose that HNE might act as natural promotor of decay of malignant (osteosarcoma) cells in case of their differentiation associated with alteration of the lipid metabolism.

GSTM1 Modulates Expression of Endothelial Adhesion Molecules in Uremic Milieu

Deletion polymorphism of glutathione S-transferase M1 (GSTM1), a phase II detoxification and antioxidant enzyme, increases susceptibility to end-stage renal disease (ESRD) as well as the development of cardiovascular diseases (CVD) among ESRD patients and leads to their shorter cardiovascular survival. The mechanisms by which GSTM1 downregulation contributes to oxidative stress and inflammation in endothelial cells in uremic conditions have not been investigated so far. Therefore, the aim of the present study was to elucidate the effects of GSTM1 knockdown on oxidative stress and expression of a panel of inflammatory markers in human umbilical vein endothelial cells (HUVECs) exposed to uremic serum. Additionally, we aimed to discern whether GSTM1-null genotype is associated with serum levels of adhesion molecules in ESRD patients. HUVECs treated with uremic serum exhibited impaired redox balance characterized by enhanced lipid peroxidation and decreased antioxidant enzyme activities, independently of the GSTM1 knockdown. In response to uremic injury, HUVECs exhibited alteration in the expression of a series of inflammatory cytokines including retinol-binding protein 4 (RBP4), regulated on activation, normal T cell expressed and secreted (RANTES), C-reactive protein (CRP), angiogenin, dickkopf-1 (Dkk-1), and platelet factor 4 (PF4). GSTM1 knockdown in HUVECs showed upregulation of monocyte chemoattractant protein-1 (MCP-1), a cytokine involved in the regulation of monocyte migration and adhesion. These cells also have shown upregulated intracellular and vascular cell adhesion molecules (ICAM-1 and VCAM-1). In accordance with these findings, the levels of serum ICAM-1 and VCAM-1 (sICAM-1 and sVCAM-1) were increased in ESRD patients lacking GSTM1, in comparison with patients with the GSTM1-active genotype. Based on these results, it may be concluded that incubation of endothelial cells in uremic serum induces redox imbalance accompanied with altered expression of a series of cytokines involved in arteriosclerosis and atherosclerosis. The association of GSTM1 downregulation with the altered expression of adhesion molecules might be at least partly responsible for the increased susceptibility of ESRD patients to CVD.

DNA damage and oxidative stress induced by imidacloprid exposure in different tissues of the Neotropical fish Prochilodus lineatus

Imidacloprid (IMI), a systemic neonicotinoid insecticide widely used in worldwide scale, is reported in freshwater bodies. Nevertheless, there is a lack of information about IMI sublethal effects on freshwater fish. Thus, the aim of this study was to identify the potential hazard of this insecticide to the South American fish Prochilodus lineatus exposed for 120 h to four IMI concentrations (1.25, 12.5, 125, and 1250 μg L^-1). A set of biochemical, genotoxic and physiological biomarkers were evaluated in different organs of the fish. IMI exposure induced significant changes in the enzymatic profiles of P. lineatus, with alterations in the activity of biotransformation and antioxidant enzymes in different tissues. Redox balance of the tissues was affected, since oxidative damage such as lipoperoxidation (LPO) and protein carbonylation (PCC) were evidenced in the liver, gills, kidney and brain of fish exposed to different IMI concentrations. Fish exposed to all IMI concentrations showed decreased blood glucose indicating an increase of energetic demand. DNA damage was evidenced by the comet test, in the erythrocytes of fish all the concentrations evaluated. We integrated these results in the Integrated Biomarker Response (IBR) index, which evidenced that the organs most affected by IMI exposure were the liver and kidney, followed by the gills. Our results highlight the importance of investigating different target tissues after IMI exposure and show the sublethal effects of IMI in some of them; they also warn to the possible consequences that fish living in freshwater ecosystems can suffer due to IMI exposure.

Activity-Based Probes for Isoenzyme- and Site-Specific Functional Characterization of Glutathione S-Transferases

Glutathione S-transferases (GSTs) comprise a diverse family of phase II drug metabolizing enzymes whose shared function is the conjugation of reduced glutathione (GSH) to endo- and xenobiotics. Although the conglomerate activity of these enzymes can be measured, the isoform-specific contribution to the metabolism of xenobiotics in complex biological samples has not been possible. We have developed two activity-based probes (ABPs) that characterize active GSTs in mammalian tissues. The GST active site is composed of a GSH binding "G site" and a substrate binding "H site". Therefore, we developed (1) a GSH-based photoaffinity probe (GSTABP-G) to target the "G site", and (2) an ABP designed to mimic a substrate molecule and have "H site" activity (GSTABP-H). The GSTABP-G features a photoreactive moiety for UV-induced covalent binding to GSTs and GSH-binding enzymes. The GSTABP-H is a derivative of a known mechanism-based GST inhibitor that binds within the active site and inhibits GST activity. Validation of probe targets and "G" and "H" site specificity was carried out using a series of competition experiments in the liver. Herein, we present robust tools for the characterization of enzyme- and active site-specific GST activity in mammalian model systems.

Regulatory roles of glutathione-S-transferases and 4-hydroxynonenal in stress-mediated signaling and toxicity

Glutathione-S-Transferases (GSTs) have primarily been thought to be xenobiotic metabolizing enzymes that protect cells from toxic drugs and environmental electrophiles. However, in last three decades, these enzymes have emerged as the regulators of oxidative stress-induced signaling and toxicity. 4-Hydroxy-trans 2-nonenal (HNE) an end-product of lipid peroxidation, has been shown to be a major determinant of oxidative stress-induced signaling and toxicity. HNE is involved in signaling pathways, including apoptosis, proliferation, modulation of gene expression, activation of transcription factors/repressors, cell cycle arrest, and differentiation. In this article, available evidence for a major role of GSTs in the regulation of HNE-mediated cell signaling processes through modulation of the intracellular levels of HNE is discussed.

The Loss of GSTM1 Associates with Kidney Failure and Heart Failure

Glutathione S-transferase mu 1 (GSTM1) encodes an enzyme that catalyzes the conjugation of electrophilic compounds with glutathione to facilitate their degradation or excretion. The loss of one or both copies of GSTM1 is common in many populations and has been associated with CKD progression. With the hypothesis that the loss of GSTM1 is also associated with incident kidney failure and heart failure, we estimated GSTM1 copy number using exome sequencing reads in the Atherosclerosis Risk in Communities (ARIC) Study, a community-based prospective cohort of white and black participants. Overall, 51.2% and 39.8% of white participants and 25.6% and 48.5% of black participants had zero or one copy of GSTM1, respectively. Over a median follow-up of 24.6 years, 256 kidney failure events occurred in 5715 participants without prevalent kidney failure, and 1028 heart failure events occurred in 5368 participants without prevalent heart failure. In analysis adjusted for demographics, diabetes, and hypertension, having zero or one copy of GSTM1 associated with higher risk of kidney failure and heart failure (adjusted hazard ratio [95% confidence interval] for zero or one versus two copies of GSTM1: kidney failure, 1.66 [1.27 to 2.17]; heart failure, 1.16 [1.04 to 1.29]). Risk did not differ significantly between participants with zero and one copy of GSTM1 (P>0.10). In summary, the loss of GSTM1 was significantly associated with incident kidney and heart failure, independent of traditional risk factors. These results suggest GSTM1 function is a potential treatment target for the prevention of kidney and heart failure.

Antioxidant role of glutathione S-transferases: 4-Hydroxynonenal, a key molecule in stress-mediated signaling

4-Hydroxy-2-trans-nonenal (4HNE), one of the major end products of lipid peroxidation (LPO), has been shown to induce apoptosis in a variety of cell lines. It appears to modulate signaling processes in more than one way because it has been suggested to have a role in signaling for differentiation and proliferation. It has been known that glutathione S-transferases (GSTs) can reduce lipid hydroperoxides through their Se-independent glutathione-peroxidase activity and that these enzymes can also detoxify LPO end-products such as 4HNE. Available evidence from earlier studies together with results of recent studies in our laboratories strongly suggests that LPO products, particularly hydroperoxides and 4HNE, are involved in the mechanisms of stress-mediated signaling and that it can be modulated by the alpha-class GSTs through the regulation of the intracellular concentrations of 4HNE. We demonstrate that 4HNE induced apoptosis in various cell lines is accompanied with c-Jun-N-terminal kinase (JNK) and caspase-3 activation. Cells exposed to mild, transient heat or oxidative stress acquire the capacity to exclude intracellular 4HNE at a faster rate by inducing GSTA4-4 which conjugates 4HNE to glutathione (GSH), and RLIP76 which mediates the ATP-dependent transport of the GSH-conjugate of 4HNE (GS-HNE). The balance between formation and exclusion promotes different cellular processes - higher concentrations of 4HNE promote apoptosis; whereas, lower concentrations promote proliferation. In this article, we provide a brief summary of the cellular effects of 4HNE, followed by a review of its GST-catalyzed detoxification, with an emphasis on the structural attributes that play an important role in the interactions with alpha-class GSTA4-4. Taken together, 4HNE is a key signaling molecule and that GSTs being determinants of its intracellular concentrations, can regulate stress-mediated signaling, are reviewed in this article.

4-Hydroxy-nonenal-A Bioactive Lipid Peroxidation Product

This review on recent research advances of the lipid peroxidation product 4-hydroxy-nonenal (HNE) has four major topics: I. the formation of HNE in various organs and tissues, II. the diverse biochemical reactions with Michael adduct formation as the most prominent one, III. the endogenous targets of HNE, primarily peptides and proteins (here the mechanisms of covalent adduct formation are described and the (patho-) physiological consequences discussed), and IV. the metabolism of HNE leading to a great number of degradation products, some of which are excreted in urine and may serve as non-invasive biomarkers of oxidative stress.

Reactive oxygen species and energy machinery: an integrated dynamic model

The role of several important reactive oxygen species (ROS) on the Krebs cycle, the electron transport chain (ETC) and the two important shuttles has been modelled. Major part of the ROS is produced during oxygen reduction in the ETC, which has been kinetically simulated, and the changes in the final concentrations of several important metabolites were found. The simulation is based on chemical kinetics equation, and the associated set of differential equations was solved by the ordinary differential equation package in Octave. The validity of the model is checked by comparing the experimental results available in the literature with the simulations when a part of the ETC is blocked (80%) in the script. The present approach is versatile and flexible and has potential applications in various simulations. It is easy to study the change in concentrations of various metabolites when a particular enzyme or pathway is blocked (say by a drug). The Octave script is presented in the text.

Differential metabolism of 4-hydroxynonenal in liver, lung and brain of mice and rats

The lipid peroxidation end-product 4-hydroxynonenal (4-HNE) is generated in tissues during oxidative stress. As a reactive aldehyde, it forms Michael adducts with nucleophiles, a process that disrupts cellular functioning. Liver, lung and brain are highly sensitive to xenobiotic-induced oxidative stress and readily generate 4-HNE. In the present studies, we compared 4-HNE metabolism in these tissues, a process that protects against tissue injury. 4-HNE was degraded slowly in total homogenates and S9 fractions of mouse liver, lung and brain. In liver, but not lung or brain, NAD(P)+ and NAD(P)H markedly stimulated 4-HNE metabolism. Similar results were observed in rat S9 fractions from these tissues. In liver, lung and brain S9 fractions, 4-HNE formed protein adducts. When NADH was used to stimulate 4-HNE metabolism, the formation of protein adducts was suppressed in liver, but not lung or brain. In both mouse and rat tissues, 4-HNE was also metabolized by glutathione S-transferases. The greatest activity was noted in livers of mice and in lungs of rats; relatively low glutathione S-transferase activity was detected in brain. In mouse hepatocytes, 4-HNE was rapidly taken up and metabolized. Simultaneously, 4-HNE-protein adducts were formed, suggesting that 4-HNE metabolism in intact cells does not prevent protein modifications. These data demonstrate that, in contrast to liver, lung and brain have a limited capacity to metabolize 4-HNE. The persistence of 4-HNE in these tissues may increase the likelihood of tissue injury during oxidative stress.

Differential sensitivity to 4-hydroxynonenal for normal and malignant mesenchymal cells

Normal and malignant cells of various origin differ in their sensitivity to oxidative stress. Therefore, we used normal and malignant mesenchymal cells--human osteosarcoma cells (HOS and 143B), human fibroblasts (WI38) and two primary cultures of normal human osteoblasts to test sensitivity to reactive aldehyde 4-hydroxynonenal (HNE), known as a second messenger of free radicals and a signaling molecule. Upon HNE-treatment, decrease in cell viability (by Trypan-blue), apoptosis induction (by TiterTACS TUNEL assay), HNE-protein binding (by HNE-His ELISA) were higher in malignant than in normal cells, while glutathione content was higher in normal cells. These results indicate that HNE affects the growth of malignant mesenchymal cells more than normal and that this effect was mainly related to lower glutathione concentration and higher binding of HNE to the cellular proteins. We thus assume that HNE and GSH homeostasis play an important role in the growth regulation of normal and malignant mesenchymal cells.

Protein modification by oxidized phospholipids and hydrolytically released lipid electrophiles: Investigating cellular responses

Oxygen is essential for the growth and function of mammalian cells. However, imbalances in oxygen or abnormalities in the ability of a cell to respond to oxygen levels can result in oxidative stress. Oxidative stress plays an important role in a number of diseases including atherosclerosis, rheumatoid arthritis, cancer, neurodegenerative diseases and asthma. When membrane lipids are exposed to high levels of oxygen or derived oxidants, they undergo lipid peroxidation to generate oxidized phospholipids (oxPL). Continual exposure to oxidants and decomposition of oxPL results in the formation of reactive electrophiles, such as 4-hydroxy-2-nonenal (HNE). Reactive lipid electrophiles have been shown to covalently modify DNA and proteins. Furthermore, exposure of cells to lipid electrophiles results in the activation of cytoprotective signaling pathways in order to promote cell survival and recovery from oxidant stress. However, if not properly managed by cellular detoxification mechanisms, the continual exposure of cells to electrophiles results in cytotoxicity. The following perspective will discuss the biological importance of lipid electrophile protein adducts including current strategies employed to identify and isolate protein adducts of lipid electrophiles as well as approaches to define cellular signaling mechanisms altered upon exposure to electrophiles. This article is part of a Special Issue entitled: Oxidized phospholipids-their properties and interactions with proteins.

The balance between 4-hydroxynonenal and intrinsic glutathione/glutathione S-transferase A4 system may be critical for the epidermal growth factor receptor phosphorylation of human esophageal squamous cell carcinomas

Oxidative stress might participate in the carcinogenesis of human esophageal squamous cell carcinomas (hESCC). 4-Hydroxynonenal (HNE) is a major product of membrane lipid peroxidation with short life. It might act as an important mediator through the generation of adducts and activate epidermal growth factor receptor (EGFR) signaling. It is mainly trapped with glutathione (GSH) and catalyzed by glutathione S-transferases (GSTs). This study aimed to elucidate the possible participation of HNE, GSH/GST system, and EGFR signaling in hESCC development. Immunohistochemistry of HNE adducts, EGFR, and phosphorylated EGFR (pEGFR) was performed with hESCC specimens. The effect of HNE on the phosphorylation of EGFR and its downstream PhospholipaseCγ1 (PLCγ1) was investigated with KYSE30 cell-line. Pretreatment with GSH inducer N-acetylcysteine (NAC) or GSH inhibitor Buthionine sulfoximine (BSO) and mandatory transfection of hGSTA4 gene in KYSE30 were conducted to investigate the relationship between HNE and GSH/GST system. Immunoreactants of HNE adducts, EGFR, and pEGFR were increased in hESCC compared to non-cancerous epithelium with positive correlations. The treatment of HNE ligand-independently induced the phosphorylation of EGFR and PLCγ1 accompanying the diminishment of intracellular GSH level. NAC increased GSH contents but BSO decreased in dose-dependent manners. Reflecting changes in GSH, HNE-induced EGFR phosphorylation was suppressed by NAC, whereas it was promoted by BSO. Mandatory expression of hGSTA4 suppressed HNE-induced events. We first demonstrated that the ligand-independent activation of EGFR by the balance between the stimulation of HNE and the prevention of intrinsic GSH/GST system might participate in the development of hESCC.

Interactions of glutathione transferases with 4-hydroxynonenal

Electrophilic products of lipid peroxidation are important contributors to the progression of several pathological states. The prototypical α,β-unsaturated aldehyde, 4-hydroxynonenal (HNE), triggers cellular events associated with oxidative stress, which can be curtailed by the glutathione-dependent elimination of HNE. The glutathione transferases (GSTs) are a major determinate of the intracellular concentration of HNE and can influence susceptibility to toxic effects, particularly when HNE and GST levels are altered in disease states. In this article, we provide a brief summary of the cellular effects of HNE, followed by a review of its GST-catalyzed detoxification, with an emphasis on the structural attributes that play an important role in the interactions with alpha-class GSTs. Some of the key determining characteristics that impart high alkenal activity reside in the unique C-terminal interactions of the GSTA4-4 enzyme. Studies encompassing both kinetic and structural analyses of related isoforms will be highlighted, with additional attention to stereochemical aspects that demonstrate the capacity of GSTA4-4 to detoxify both enantiomers of the biologically relevant racemic mixture while generating a select set of diastereomeric products with subsequent implications. A summary of the literature that examines the interplay between GSTs and HNE in model systems relevant to oxidative stress will also be discussed to demonstrate the magnitude of importance of GSTs in the overall detoxification scheme.

Germline polymorphisms of glutathione-S-transferase GSTM1, GSTT1 and p53 codon 72 in cervical carcinogenesis

The clinical significance of glutathione-S-transferase GSTM1, GSTT1 and p53 codon 72 polymorphisms in cervical carcinogenesis was investigated. Germline polymorphisms of GSTM1, GSTT1 and p53 codon 72 together with human papillomavirus (HPV) types were examined in a total of 457 blood and cervical smear samples from normal healthy women and the patients with premalignant and malignant cervical lesions. The 167 patients with low-grade squamous intraepithelial lesion (LSIL), 49 with high-grade SIL (HSIL) and 83 with squamous cell carcinoma (SCC) had significantly higher frequency of high-risk HPV than 158 controls. The 49 patients with HSIL and 83 with SCC had statistically higher frequency of null GSTT1 genotype than 158 controls. There was an increased odds ratio for null GSTT1 genotype in HSIL and SCC cases compared with controls among 191 patients with high-risk HPV. The 67 cases with HPV types 16 and/or 18 had higher frequency of the GSTT1 null genotype than 186 with other types of HPV. There was no statistical difference in the polymorphic frequency of GSTM1 and p53 codon 72 genotypes between SILs and controls with or without high-risk HPV. These results suggest that GSTT1 null genotype may increase the risk of cervical cancer particularly in the cases with high-risk HPV types in a Japanese population.

Glutathione S-transferase pi localizes in mitochondria and protects against oxidative stress

Glutathione S-transferases (GSTs) are multifunctional enzymes involved in the protection of cellular components against anti-cancer drugs or peroxidative stress. Previously we found that GST pi, an isoform of the GSTs, is transported into the nucleus. In the present study, we found that GST pi is present in mitochondria as well as in the cytosol and nucleus in mammalian cell lines. A construct comprising the 84 amino acid residues in the amino-terminal region of GST pi and green fluorescent protein was detected in the mitochondria. The mutation of arginine to alanine at positions 12, 14, 19, 71, and 75 in full-length GST pi completely abrogated the ability to distribute in the mitochondria, suggesting that arginine, a positively charged residue, is required for the mitochondrial transport of GST pi. Chemicals generating reactive oxygen species, such as rotenone and antimycin A, decreased cell viability and reduced mitochondrial membrane potential. The overexpression of GST pi diminished these changes. GST pi-targeting siRNA abolished the protective effect of GST pi on the mitochondria under oxidative stress. The findings indicate that the peptide signal is conducive to the mitochondrial localization of GST pi under steady-state conditions without alternative splicing or posttranslational modifications such as proteolysis, suggesting that GST pi protects mitochondria against oxidative stress.

Germline polymorphism of cancer susceptibility genes in gynecologic cancer

The multifactorial process of carcinogenesis involves mutations in oncogenes, or tumor suppressor genes, as well as the influence of environmental etiological factors. Common DNA polymorphisms in low penetrance genes have emerged as genetic factors that seem to modulate an individual's susceptibility to malignancy. Genetic studies, which lead to a true association, are expected to increase understanding of the pathogenesis of each malignancy and to be a powerful tool for prevention and prognosis in the future. Here, we review the findings of genetic association studies of gene polymorphisms in gynecologic cancer with special reference to glutathione-S-transferase, FAS/CD95 and p53 genes including our recent research results.

The chemistry of cell signaling by reactive oxygen and nitrogen species and 4-hydroxynonenal

During the past several years, major advances have been made in understanding how reactive oxygen species (ROS) and nitrogen species (RNS) participate in signal transduction. Identification of the specific targets and the chemical reactions involved still remains to be resolved with many of the signaling pathways in which the involvement of reactive species has been determined. Our understanding is that ROS and RNS have second messenger roles. While cysteine residues in the thiolate (ionized) form found in several classes of signaling proteins can be specific targets for reaction with H(2)O(2) and RNS, better understanding of the chemistry, particularly kinetics, suggests that for many signaling events in which ROS and RNS participate, enzymatic catalysis is more likely to be involved than non-enzymatic reaction. Due to increased interest in how oxidation products, particularly lipid peroxidation products, also are involved with signaling, a review of signaling by 4-hydroxy-2-nonenal (HNE) is included. This article focuses on the chemistry of signaling by ROS, RNS, and HNE and will describe reactions with selected target proteins as representatives of the mechanisms rather attempt to comprehensively review the many signaling pathways in which the reactive species are involved.

The stereochemical course of 4-hydroxy-2-nonenal metabolism by glutathione S-transferases

4-Hydroxy-2-nonenal (HNE) is a toxic aldehyde generated during lipid peroxidation and has been implicated in a variety of pathological states associated with oxidative stress. Glutathione S-transferase (GST) A4-4 is recognized as one of the predominant enzymes responsible for the metabolism of HNE. However, substrate and product stereoselectivity remain to be fully explored. The results from a product formation assay indicate that hGSTA4-4 exhibits a modest preference for the biotransformation of S-HNE in the presence of both enantiomers. Liquid chromatography mass spectrometry analyses using the racemic and enantioisomeric HNE substrates explicitly demonstrate that hGSTA4-4 conjugates glutathione to both HNE enantiomers in a completely stereoselective manner that is not maintained in the spontaneous reaction. Compared with other hGST isoforms, hGSTA4-4 shows the highest degree of stereoselectivity. NMR experiments in combination with simulated annealing structure determinations enabled the determination of stereochemical configurations for the GSHNE diastereomers and are consistent with an hGSTA4-4-catalyzed nucleophilic attack that produces only the S-configuration at the site of conjugation, regardless of substrate chirality. In total these results indicate that hGSTA4-4 exhibits an intriguing combination of low substrate stereoselectivity with strict product stereoselectivity. This behavior allows for the detoxification of both HNE enantiomers while generating only a select set of GSHNE diastereomers with potential stereochemical implications concerning their effects and fates in biological tissues.

Association between long-term neuro-toxicities in testicular cancer survivors and polymorphisms in glutathione-s-transferase-P1 and -M1, a retrospective cross sectional study

Background

To assess the impact of polymorphisms in Glutathione S-transferase (GST) -P1, -M1, and -T1 on self-reported chemotherapy-induced long-term toxicities in testicular cancer survivors (TCSs).

Methods

A total of 238 TCSs, who had received cisplatin-based chemotherapy at median twelve years earlier, had participated in a long-term follow-up survey which assessed the prevalence of self-reported paresthesias in fingers/toes, Raynaud-like phenomena in fingers/toes, tinnitus, and hearing impairment. From all TCSs lymphocyte-derived DNA was analyzed for the functional A→G polymorphism at bp 304 in GSTP1, and deletions in GST-M1 and GST-T1. Evaluation of associations between GST polymorphisms and self-reported toxicities included adjustment for prior treatment.

Results

All six evaluated toxicities were significantly associated with the cumulative dose of cisplatin and/or bleomycin. Compared to TCSs with either GSTP1-AG or GSTP1-AA, the 37 TCSs with the genotype GSTP1-GG, were significantly less bothered by paresthesias in fingers and toes (p = 0.039, OR 0.46 [0.22–0.96] and p = 0.023, OR 0.42 [0.20–0.88], respectively), and tinnitus (p = 0.008, OR 0.33 [0.14–0.74]). Furthermore, absence of functional GSTM1 protected against hearing impairment (p = 0.025, OR 1.81 [1.08–3.03]).

Conclusion

In TCSs long-term self-reported chemotherapy-induced toxicities are associated with functional polymorphisms in GSTP1 and GSTM1. Hypothetically, absence of GST-M1 leaves more glutathione as substrate for the co-expressed GST-P1. Also intracellular inactivation of pro-apoptotic mediators represents a possible explanation of our findings. Genotyping of these GSTs might be a welcomed step towards a more individualized treatment of patients with metastatic testicular cancer.

Cisplatin-induced long-term hearing impairment is associated with specific glutathione s-transferase genotypes in testicular cancer survivors

PURPOSE

Cisplatin, a cornerstone of combination chemotherapy in the treatment of testicular cancer, induces hearing impairment with considerable interindividual variations. These differences might be a result of functional polymorphisms in cisplatin-detoxifying enzymes like glutathione S-transferases (GSTs).

PATIENTS AND METHODS

We identified 173 cisplatin-treated testicular cancer survivors (TCSs) who had participated in a long-term survey that included audiometric testing and lymphocyte sampling. The hearing decibel thresholds at 4,000 Hz were categorized into leveled scales by normative decibel percentiles. Known functional polymorphisms (positive or negative) in GSTT1 and GSTM1 and codon 105 A/G (Ile/Val) in GSTP1 were analyzed by multiplex polymerase chain reaction, followed by restriction enzyme cutting, and separated by gel electrophoresis.

RESULTS

The risk of having an inferior audiometric result was more than four times higher in TCSs with 105Ile/105Ile-GSTP1 or 105Val/105Ile-GSTP1 compared with 105Val/105Val-GSTP1 (odds ratio [OR] = 4.21; 95% CI, 1.99 to 8.88; P < .001 when modeled by ordinal logistic regression [OLR]). GSTM1 positivity was detrimental for hearing ability. Two combined genotypes were associated with hearing ability. The presence of pattern 1 (GSTT1 positive, GSTM1 positive, and 105Ile/105Ile-GSTP1) was associated with hearing impairment (OR = 2.76; 95% CI, 1.35 to 5.64; P = .005, OLR). TCSs with pattern 2 (GSTT1 positive, GSTM1 positive, and 105Val/105Val-GSTP1) had better hearing ability than TCSs without this pattern (OR = 5.35; 95% CI, 2.25 to 12.76; P < .001, OLR).

CONCLUSION

The presence of both alleles of 105Val-GSTP1 offered protection against cisplatin-induced hearing impairment. Two genotype patterns with good and poor protection against cisplatin-induced ototoxicity were identified.

Skin tumorigenic potential of aflatoxin B1 in mice

Aflatoxin B1 (AFB1) has been classified as a category I human carcinogen, which is responsible for a high incidence of hepatocellular carcinoma. Since exposure to AFB1 can occur through skin contact in addition to ingestion and inhalation, the carcinogenic potential of topically applied AFB1 on mouse skin was investigated. Our results show that single topical application of AFB1 (80 nmol) as a tumor initiator, followed by twice weekly application of 12-tetradecanoyl phorbol myristate acetate (TPA, 4 nmol), resulted in tumor formation after 13 weeks. However, no tumorigenic potential was observed when AFB1 (16 nmol) was used either as a complete carcinogen or as a tumor promoter (4 nmol). Histological analysis of skin showed squamous cell carcinoma in the AFB1/TPA treated group. The application of AFB1 as a complete carcinogen, an initiator or a promoter after 24 weeks demonstrated widespread degenerative and necrotic changes in hepatic tissue as well, suggesting liver to be the target organ following percutaneous absorption. Additionally, twice weekly topical application of AFB1 caused significant induction of cutaneous CYP IA monoxygenases without any effect on hepatic levels while glutathione-S-transferase activity was induced more in the liver than skin. The topical application of AFB1 also resulted in increased hepatic and cutaneous lipid peroxidation with concomitant depletion of glutathione content. It is likely that due to higher induction of hepatic GST activity, products of lipid peroxidation may be detoxified and therefore unable to cause DNA damage making mice resistant to hepatic tumor formation. The overall results indicate a tumor initiating potential of AFB1 in mice and suggest that continued dermal exposure of AFB1, even at low doses, might lead to degenerative changes in hepatocytes.

Several glutathione S-transferase isozymes that protect against oxidative injury are expressed in human liver mitochondria

The mitochondrial environment is rich in reactive oxygen species (ROS) that may ultimately peroxidize membrane proteins and generate unsaturated aldehydes such as 4-hydroxy-2-nonenal (4HNE). We had previously demonstrated the presence of hGSTA4-4, an efficient catalyst of 4HNE detoxification, in human liver mitochondria to the exclusion of the cytosol. In the present study, GSH-affinity chromatography was used in conjunction with biochemical and proteomic analysis to determine the presence of additional cytosolic glutathione S-transferases (GSTs) in human hepatic mitochondria. HPLC-subunit analysis of GSH affinity-purified liver mitochondrial proteins indicated the presence of several potential mitochondrial GST isoforms. Electrospray ionization-mass spectrometry analysis of eluted mitochondrial GST subunits yielded molecular masses similar to those of hGSTP1, hGSTA1 and hGSTA2. Octagonal matrix-assisted laser desorption/ionization time of flight mass spectrometry and proteomics analysis using MS-FIT confirmed the presence of these three GST subunits in mitochondria, and HPLC analysis indicated that the relative contents of the mitochondrial GST subunits were hGSTA1>hGSTA2>hGSTP1. The mitochondrial localization of the alpha and pi class GST subunits was consistent with immunoblotting analysis of purified mitochondrial GST. Enzymatic studies using GSH-purified mitochondrial GST fractions demonstrated the presence of significant GST activity using the nonspecific GST substrate 1-chloro-2,4-dinitrobenzene (CDNB), as well as 4HNE, delta(5)-androstene-3,17-dione (ADI), and cumene hydroperoxide (CuOOH). Interestingly, the specific mitochondrial GST activities toward 4HNE, a highly toxic alpha,beta-unsaturated aldehyde produced during the breakdown of membrane lipids, exceeded that observed in liver cytosol. These observations are suggestive of a role of GST in protecting against mitochondrial injury during the secondary phase of oxidative stress, or modulation of 4HNE-mediated mitochondrial signaling pathways. However, other properties of mitochondrial GST, such as conjugation of environmental chemicals and binding of lipophilic non-substrate xenobiotics and endogenous compounds, remain to be investigated.

Formation of acetaldehyde adducts of glutathione S-transferase A3 in the liver of rats administered alcohol chronically

Hepatic tissue damage induced by chronic exposure to alcohol is mediated through acetaldehyde and associated with reactive oxygen species, which impair cellular defense mechanisms. Because glutathione S-transferases (GSTs) play an important role in the detoxification of xenobiotics and reactive oxygen species, the current study was undertaken to test the effect of alcohol administration on structural and functional characteristics of rat (r) liver Alpha class rGSTs. Western blot analysis revealed an appreciable change in the expression of rGSTA3 subunit levels, whereas no change was observed in activity after chronic alcohol treatment. Reverse-phase high performance liquid chromatographic analysis of rat liver GSTs that were affinity purified with glutathione showed a 1.07-fold increase in rGSTA3 subunit levels in rats treated with alcohol chronically. In addition, liquid chromatographic-electrospray ionization mass spectrometric analysis of GSTs that were affinity purified with glutathione showed the formation of acetaldehyde adducts to the rGSTA3 subunit. Given the abundant expression of rGSTA3 subunit and acetaldehyde adduct formation, results of the current study support the suggestion that modification of rGSTA3 subunit, and thus its impaired function, in alcohol-exposed rats may contribute to the progression of alcohol-induced liver damage.

Cloning and expression of alpha class glutathione S-transferase gene from the small hermaphroditic fish Rivulus marmoratus (Cyprinodontiformes, Rivulidae)

In order to assess its potential as a biomarker of aquatic pollution, an alpha class glutathione S-transferase gene (GSTalpha gene) was cloned from the small hermaphroditic fish Rivulus marmoratus. The R. marmoratus GSTalpha gene spanned 1.3 kb, consisting of 6 exons encoding 221 amino acid residues. It showed high similarity to zebrafish GST. We named this R. marmoratus GSTalpha gene as rm-GSTalpha. The cDNA of the rm-GSTalpha gene was also investigated for its phylogeny, tissue-specific and chemical-induced expression. Rm-GSTalpha was subcloned into a 6 x His-tagged pCRT7 TOPO TA expression vector to produce the recombinant 6 x His-tagged rm-GST protein. This will be used in future to raise an rm-GSTalpha antibody for use in the study of phase II metabolism involved in detoxification. We also exposed R. marmoratus to 300 microg/l of 4-nonylphenol in water, and found approximately 4-fold induction of R. marmoratus GSTalpha mRNA in the treated animals. In this paper, we discuss the characteristics of the R. marmoratus GSTalpha gene as well as its potential use in relation to environmental pollution.

Regulation of 4‐Hydroxynonenal Mediated Signaling By Glutathione S‐Transferases

4-Hydroxy-trans-2-nonenal (HNE) was initially considered to be merely a toxic end product of lipid peroxidation that contributed to oxidative stress-related pathogenesis. However, in recent years its physiological role as an important "signaling molecule" has been established. HNE can modulate various signaling pathways in a concentration-dependent manner. Glutathione S-transferases (GSTs) are major determinants of the intracellular concentration of HNE, because these enzymes account for the metabolism of most cellular HNE through its conjugation to glutathione. Evidence is emerging that GSTs are involved in the regulation of the HNE-mediated signaling processes. Against the backdrop of our current understanding on the formation, metabolism, and role of HNE in signaling processes, the physiological role of GSTs in regulation of HNE-mediated signaling processes is critically evaluated in this chapter. Available evidence strongly suggests that besides their well-established pharmacological role of detoxifying xenobiotics, GSTs also play an important physiological role in the regulation of cellular signaling processes.

Nuclear glutathione S-transferase pi prevents apoptosis by reducing the oxidative stress-induced formation of exocyclic DNA products

We previously found that nuclear glutathione S-transferase pi (GSTpi) accumulates in cancer cells resistant to anticancer drugs, suggesting that it has a role in the acquisition of resistance to anticancer drugs. In the present study, the effect of oxidative stress on the nuclear translocation of GSTpi and its role in the protection of DNA from damage were investigated. In human colonic cancer HCT8 cells, the hydrogen peroxide (H(2)O(2))-induced increase in nuclear condensation, the population of sub-G(1) peak, and the number of TUNEL-positive cells were observed in cells pretreated with edible mushroom lectin, an inhibitor of the nuclear transport of GSTpi. The DNA damage and the formation of lipid peroxide were dependent on the dose of H(2)O(2) and the incubation time. Immunological analysis showed that H(2)O(2) induced the nuclear accumulation of GSTpi but not of glutathione peroxidase. Formation of the 7-(2-oxo-hepyl)-substituted 1,N(2)-etheno-2'-deoxyguanosine adduct by the reaction of 13-hydroperoxyoctadecadienoic acid (13-HPODE) with 2'-deoxyguanosine was inhibited by GSTpi in the presence of glutathione. The conjugation product of 4-oxo-2-nonenal, a lipid aldehyde of 13-HPODE, with GSH in the presence of GSTpi, was identified by LS/MS. These results suggested that nuclear GSTpi prevents H(2)O(2)-induced DNA damage by scavenging the formation of lipid-peroxide-modified DNA.

The Disposition and Bioavailability of35S-GSH from35S-GSSG in BSS PLUS®in Rabbit Ocular Tissues

The purpose of this study was to evaluate the biodistribution and uptake of 35S-GSH into intraocular tissues following the administration of BSS PLUS containing 35S-GSSG by either an anterior chamber or intravitreal injection. This study evaluated the disposition and uptake of the 35S-radiolabel, the intracellular concentrations of 35S-GSH from extracellular 35S-GSSG, and the percentage of 35S-GSH to the total cellular GSH pool. Glutathione was analyzed by high-performance liquid chromatography (HPLC) using fluorescence detection after derivitizing the thiols in situ with monobromobimane. The effluent from the GSH peak was then collected for measurement of 35S-GSH. After an anterior chamber injection of 35S-BSS PLUS, 35S-radioactivity rapidly disappeared from the aqueous humor between 0.5 and 2 hours; corneal 35S-radioactivity remained constant over time. 35S-GSH was detected in the iris and ciliary body. However, in the cornea, 35S-GSH became the predominant radioactive thiol in the stroma, endothelium, and epithelium; the corneal stroma appeared to be a possible GSH reservoir for the adjacent corneal layers. After an intravitreal injection, 35S-radioactivity slowly decreased in the vitreous humor but was readily taken up by the tissues of the posterior segment, especially the retina and choroid, which showed the greatest concentrations of 35S-GSH of all tissues studied. The data from this study demonstrate that 35S-GSSG in BSS PLUS is metabolized and taken up by ocular cells and that 35S-GSH becomes incorporated into the intracellular GSH pool of ocular tissues.

Transfection with 4-hydroxynonenal-metabolizing glutathione S-transferase isozymes leads to phenotypic transformation and immortalization of adherent cells

4-Hydroxy-2-trans-nonenal (4-HNE), one of the major end products of lipid peroxidation, has been shown to induce apoptosis in a variety of cell lines. It appears to modulate signaling processes in more than one way because it has been suggested to have a role in signaling for differentiation and proliferation. We show for the first time that incorporation of 4-HNE-metabolizing glutathione S-transferase (GST) isozyme, hGSTA4-4, into adherent cell lines HLE B-3 and CCL-75, by either cDNA transfection or microinjection of active enzyme, leads to their transformation. The dramatic phenotypic changes due to the incorporation of hGSTA4-4 include rounding of cells and anchorage-independent rapid proliferation of immortalized, rounded, and smaller cells. Incorporation of the inactive mutant of hGSTA4-4 (Y212F) in cells by either microinjection or transfection does not cause transformation, suggesting that the activity of hGSTA4-4 toward 4-HNE is required for transformation. This is further confirmed by the fact that mouse and Drosophila GST isozymes (mGSTA4-4 and DmGSTD1-1), which have high activity toward 4-HNE and subsequent depletion of 4-HNE, cause transformation whereas human GST isozymes hGSTP1-1 and hGSTA1-1, with minimal activity toward 4-HNE, do not cause transformation. In cells overexpressing active hGSTA4-4, expression of transforming growth factor beta1, cyclin-dependent kinase 2, protein kinase C betaII and extracellular signal regulated kinase is upregulated, whereas expression of p53 is downregulated. These studies suggest that alterations in 4-HNE homeostasis can profoundly affect cell-cycle signaling events.

Antioxidant role of glutathione S-transferases: protection against oxidant toxicity and regulation of stress-mediated apoptosis

It has been known that glutathione S-transferases (GSTs) can reduce lipid hydroperoxides through their Se-independent glutathione peroxidase activity and that these enzymes can also detoxify lipid peroxidation end products such as 4-hydroxynonenal (4-HNE). In this article, recent studies suggesting that the Alpha class GSTs provide a formidable defense against oxidative stress are critically evaluated and the role of these enzymes in the regulation of oxidative stress-mediated signaling is reviewed. Available evidence from earlier studies together with results of recent studies in our laboratories strongly suggests that lipid peroxidation products, particularly hydroperoxides and 4-HNE, are involved in the mechanisms of stress-mediated signaling and that it can be modulated by the Alpha class GSTs through the regulation of the intracellular concentrations of 4-HNE.

Ethanol fraction of Aralia elata Seemann enhances antioxidant activity and lowers serum lipids in rats when administered with benzo(a)pyrene

Aralia elata Seemann is an edible mountain vegetable in Korea containing saponin, alkaloid, palmitic acid, linoleic acid, methyl eicosanoate and hexacosol, and is known to manifest an effect on cardiac infarction, gastric ulcer, colitis, and enervation. This study has examined the effects of Aralia elata Seemann ethanol extract on antioxidant enzyme systems and lipid metabolism in rats along with benzo(a)pyrene (B(a)P) administration. Rats were divided into four groups: control (C), an extract fed group (CE), a B(a)P fed group (CB), and a B(a)P and extract fed group (CBE). The ethanol extracts of Aralia elata Seemann (50 mg/kg body weight) were fed to the rats for 4 weeks by stomach tubing. Extract administration increased the antioxidant activities of glutathione sulfur transferase (GST). Total superoxide dismutase (SOD) and Cu,Zn-SOD activities were stimulated. Catalase activities were increased by 50% with extract feeding. Cu,Zn-SOD was greatly enhanced from 0.10 unit to 0.18 unit and catalase activity also was increased. Serum alpha-tocopherol was markedly increased by the extracts. The ethanol fraction of Aralia elata Seemann decreased total serum cholesterol. However, serum HDL-cholesterol was increased by 35% (p<0.05). The results indicate that Aralia elata Seemann exerts antioxidant and strong hypocholesterolemic and hypolipidemic effects in vivo with the administration of B(a)P.

Glutathione S-Transferase GSTM1, GSTT1 and p53 Codon 72 Polymorphisms in Human Tumor Cells

The genes of the glutathione S-transferase (GST) family encode enzymes that appear to be critical in cellular protection against the cytotoxic effects, whereas p53 is a tumor suppressor gene. Despite a large number of studies on germline polymorphisms of GSTM1, GSTT1 and p53 genes, there have been very few reports on genotyping of these genes in human malignant tumor cells. In this study, we investigated GSTM1, GSTT1 and p53 codon 72 polymorphisms in a variety of human tumor cell lines originating from different organs to clarify tissue-specific polymorphic frequency of these genes in human solid tumors. The GSTM1 and GSTT1 genetic polymorphisms were evaluated using multiplex PCR techniques and PCR-RFLP analysis was conducted to identify p53 codon 72 genotypes. Gene expression of GSTM1 or GSTT1 was detected by RT-PCR in the cells with respective present genotype for each. Polymorphisms of p53 codon 72 detected by PCR-RFLP were also confirmed using SSCP and sequence analyses. GSTM1 and GSTT1 genotypes were various in 104 cell lines examined. Null GSTM1 genotype was dominant in small cell lung, kidney and ovarian carcinoma cells, whereas null GSTT1 genotype was dominant in cervical and endometrial carcinoma cells. GSTM1 and GSTT1 genotypes in ovarian carcinoma cells were quite similar to those in small cell lung carcinoma cells. Polymorphic frequency of p53 codon 72 was also various among the cells, however, the Pro allele was found in only 1 of 6 kidney, 14 cervical and 4 endometrial carcinoma cell lines. There was a significant difference in GSTM1 and p53 genotypes between 34 small cell and 24 non small cell lung carcinoma cells (P < 0.01). Combined study on the distribution of GSTM1, GSTT1 and p53 genotypes revealed that null GSTM1 genotype was associated with the Arg allele of p53 codon 72 in 58 lung carcinoma cells and null GSTT1 genotype was associated with the Pro/Pro homozygote in 104 tumor cell lines examined. This is the first study examining GSTM1, GSTT1 and p53 codon 72 polymorphisms in a variety of human solid tumor cells and suggesting that polymorphic frequency of these genes may be tissue- and organ-specific. The molecular interaction between GST gene defects and p53 codon 72 genotype in the development of human malignant tumors should be further investigated.

Ontogenic differences in human liver 4-hydroxynonenal detoxification are associated with in vitro injury to fetal hematopoietic stem cells

4-hydroxynonenal (4HNE) is a highly mutagenic and cytotoxic alpha,beta-unsaturated aldehyde that can be produced in utero during transplacental exposure to prooxidant compounds. Cellular protection against 4HNE injury is provided by alcohol dehydrogenases (ADH), aldehyde reductases (ALRD), aldehyde dehydrogenases (ALDH), and glutathione S-transferases (GST). In the present study, we examined the comparative detoxification of 4HNE by aldehyde-metabolizing enzymes in a panel of adult and second-trimester prenatal liver tissues and report the toxicological ramifications of ontogenic 4HNE detoxification in vitro. The initial rates of 4HNE oxidation and reduction were two- to fivefold lower in prenatal liver subcellular fractions as compared to adult liver, and the rates of GST conjugation of 4HNE were not detectable in either prenatal or adult cytosolic fractions. GSH-affinity purification of hepatic cytosol yielded detectable and roughly equivalent rates of GST-4HNE conjugation for the two age groups. Consistent with the inefficient oxidative and reductive metabolism of 4HNE in prenatal liver, cytosolic fractions prepared from prenatal liver exhibited a decreased ability to protect against 4HNE-protein adduct formation relative to adults. Prenatal liver hematopoietic stem cells (HSC), which constitute a significant percentage of prenatal liver cell populations, exhibited ALDH activities toward 4HNE, but little reductive or conjugative capacity toward 4HNE through ALRD, ADH, and GST. Cultured HSC exposed to 5 microM 4HNE exhibited a loss in viability and readily formed one or more high molecular weight 4HNE-protein adduct(s). Collectively, our results indicate that second trimester prenatal liver has a lower ability to detoxify 4HNE relative to adults, and that the inefficient detoxification of 4HNE underlies an increased susceptibility to 4HNE injury in sensitive prenatal hepatic cell targets.

Role of 4-hydroxynonenal in stress-mediated apoptosis signaling

In this mini review we summarize recent studies from our laboratory, which show the involvement of 4-hydroxynonenal (4-HNE) in cell cycle signaling. We demonstrate 4-HNE induced apoptosis in various cell lines is accompanied with c-Jun-N-terminal kinase and caspase-3 activation. Cells exposed to mild, transient, heat or oxidative stress acquire capacity to exclude intracellular 4-HNE at a faster rate by inducing hGST5.8 which conjugate 4-HNE to GSH, and RLIP76 which mediates the ATP-dependent transport of the GSH-conjugate of 4-HNE. The cells preconditioned with mild transient stress acquire resistance to H(2)O(2) and 4-HNE induced apoptosis by excluding intracellular 4-HNE at an accelerated pace. Furthermore, a decrease in intracellular concentration of 4-HNE achieved by transfecting cells with mGSTA4-4 or hGSTA4-4 results in a faster growth rate. These studies strongly suggest a role of 4-HNE in stress mediated signaling.

Intracellular metabolism of 4-hydroxynonenal

4-hydroxynonenal (HNE) is a major aldehydic product of lipid peroxidation known to exert a multitude of biological, cytotoxic, and signal effects. Mammalian cells possess highly active pathways of HNE metabolism. The metabolic fate of HNE was investigated in various mammalian cells and organs such as hepatocytes, intestinal enterocytes, renal tubular cells, aortic and brain endothelial cells, synovial fibroblasts, neutrophils, thymocytes, heart, and tumor cells. The experiments were carried out at 37 degrees C at initial HNE concentrations between 1 microM--that means in the range of physiological and pathophysiologically relevant HNE levels--to 100 microM. In all cell types which were investigated, 90-95% of 100 microM HNE were degraded within 3 min of incubation. At 1 microM HNE the physiological blood serum level of about 0.1-0.2 microM was restored already after 10-30 s. As primary products of HNE in hepatocytes and other cell types the glutathione-HNE-1:1-conjugate, the hydroxynonenoic acid and the corresponding alcohol of HNE, the 1,4-dihydroxynonene, were identified. Furthermore, the beta-oxidation of hydroxynonenoic acid including the formation of water was demonstrated. The quantitative share of HNE binding to proteins was low with about 2-8% of total HNE consumption. The glycine-cysteine-HNE, cysteine-HNE adducts and the mercapturic acid from glutathione-HNE adduct were not formed in the most cell types, but in kidney cells and neutrophils. The rapid metabolism underlines the role of HNE degrading pathways in mammalian cells as important part of the secondary antioxidative defense mechanisms in order to protect proteins from modification by aldehydic lipid peroxidation products.

Mercapturate metabolism of 4-hydroxy-2-nonenal in rat and human cerebrum

4-Hydroxy-2-nonenal (HNE), a potent toxin formed in the brain from oxidation of polyunsaturated fatty acids, is increased in Alzheimer disease (AD), where it is a proposed effector of amyloid beta peptide-mediated neurotoxicity. Detoxification of HNE via the mercapturic acid pathway (MAP) is the primary means by which other organs, such as liver, limit its toxic effects. Here we examined the distribution and activity of MAP detoxification for HNE in cerebrum. Our results showed that rat cerebral cortex and especially synaptosomes were less well equipped to detoxify HNE via the MAP than liver. Glutathione transferases (GSTs) catalyze the committed step in the MAP; GST-mu and GST-pi, but not OST-alpha, were detected in neurons and astrocytes in cerebrum from AD patients and controls. MAP activity in frontal cortex of AD patients was modestly but significantly increased compared to controls. These data suggest that lipid peroxidation may present a greater toxic burden to cerebrum than to other organs, and that a component of response to injury in late stage AD is a slight increase in MAP activity.

Toxic, halogenated cysteine S-conjugates and targeting of mitochondrial enzymes of energy metabolism

Several haloalkenes are metabolized in part to nephrotoxic cysteine S-conjugates; for example, trichloroethylene and tetrafluoroethylene are converted to S-(1,2-dichlorovinyl)-L-cysteine (DCVC) and S-(1,1,2,2-tetrafluoroethyl)-L-cysteine (TFEC), respectively. Although DCVC-induced toxicity has been investigated since the 1950s, the toxicity of TFEC and other haloalkene-derived cysteine S-conjugates has been studied more recently. Some segments of the US population are exposed to haloalkenes either through drinking water or in the workplace. Therefore, it is important to define the toxicological consequences of such exposures. Most halogenated cysteine S-conjugates are metabolized by cysteine S-conjugate beta-lyases to pyruvate, ammonia, and an alpha-chloroenethiolate (with DCVC) or an alpha-difluoroalkylthiolate (with TFEC) that may eliminate halide to give a thioacyl halide, which reacts with epsilon-amino groups of lysine residues in proteins. Nine mammalian pyridoxal 5'-phosphate (PLP)-containing enzymes catalyze cysteine S-conjugate beta-lyase reactions, including mitochondrial aspartate aminotransferase (mitAspAT), and mitochondrial branched-chain amino acid aminotransferase (BCAT(m)). Most of the cysteine S-conjugate beta-lyases are syncatalytically inactivated. TFEC-induced toxicity is associated with covalent modification of several mitochondrial enzymes of energy metabolism. Interestingly, the alpha-ketoglutarate- and branched-chain alpha-keto acid dehydrogenase complexes (KGDHC and BCDHC), but not the pyruvate dehydrogenase complex (PDHC), are susceptible to inactivation. mitAspAT and BCAT(m) may form metabolons with KGDHC and BCDHC, respectively, but no PLP enzyme is known to associate with PDHC. Consequently, we hypothesize that not only do these metabolons facilitate substrate channeling, but they also facilitate toxicant channeling, thereby promoting the inactivation of proximate mitochondrial enzymes and the induction of mitochondrial dysfunction.

Comparative expression of two alpha class glutathione S-transferases in human adult and prenatal liver tissues

The ability of the fetus to detoxify transplacental drugs and chemicals can be a critical determinant of teratogenesis and developmental toxicity. Developmentally regulated expression of alpha class glutathione S-transferases (GSTs) is of particular interest, since these isozymes have high activity toward peroxidative byproducts of oxidative injury that are linked to teratogenesis. The present study was initiated to examine the expression and catalytic activities of alpha class GST isozymes in human prenatal liver. Northern analysis demonstrated the presence of hGSTA1 and/or A2 (hGSTA1/2) and hGSTA4 steady-state mRNAs in second trimester prenatal livers. Western blotting of prenatal liver proteins provided corroborating evidence via detection of an hGSTA1/2-reactive protein in both cytosol and mitochondria and of hGSTA4-4-reactive protein in mitochondria alone. Catalytic studies demonstrated that prenatal liver cytosolic GSTs were active toward 1-chloro-2,4-dinitrobenzene (a general GST reference substrate), delta5-androstene-3,17-dione (relatively specific for hGSTA1-1), and 4-hydroxynonenal, a highly mutagenic alpha,beta-unsaturated aldehyde produced during oxidative damage and a substrate for hGSTA4-4. Total GSH-peroxidase and GST-dependent peroxidase activities were 9- and 18-fold higher, respectively, in adult liver than in prenatal liver. Multiple tissue array analyses demonstrated considerable tissue-specific and developmental variation in GST mRNA expression. In summary, our results demonstrate the presence of two important alpha class GSTs in second trimester human prenatal tissues, and indicate that mitochondrial targeting of GST may represent an important pathway for removal of cytotoxic products in prenatal liver. Furthermore, the relatively inefficient prenatal reduction of hydroperoxides may underlie an increased susceptibility to maternally transferred pro-oxidant drugs and chemicals.

Accelerated metabolism and exclusion of 4-hydroxynonenal through induction of RLIP76 and hGST5.8 is an early adaptive response of cells to heat and oxidative stress

To explore the role of lipid peroxidation (LPO) products in the initial phase of stress mediated signaling, we studied the effect of mild, transient oxidative or heat stress on parameters that regulate the cellular concentration of 4-hydroxynonenal (4-HNE). When K562 cells were exposed to mild heat shock (42 degrees C, 30 min) or oxidative stress (50 microM H2O2, 20 min) and allowed to recover for 2 h, there was a severalfold induction of hGST5.8, which catalyzes the formation of glutathione-4-HNE conjugate (GS-HNE), and RLIP76, which mediates the transport of GS-HNE from cells (Awasthi, S., Cheng, J., Singhal, S. S., Saini, M. K., Pandya, U., Pikula, S., Bandorowicz-Pikula, J., Singh, S. V., Zimniak, P., and Awasthi, Y. C. (2000) Biochemistry 39, 9327-9334). Enhanced LPO was observed in stressed cells, but the major antioxidant enzymes and HSP70 remained unaffected. The stressed cells showed higher GS-HNE-conjugating activity and increased efflux of GS-HNE. Stress-pre-conditioned cells with induced hGST5.8 and RLIP76 acquired resistance to 4-HNE and H2O2-mediated apoptosis by suppressing a sustained activation of c-Jun N-terminal kinase and caspase 3. The protective effect of stress pre-conditioning against apoptosis was abrogated by coating the cells with anti-RLIP76 IgG, which inhibited the efflux of GS-HNE from cells, indicating that the cells acquired resistance to apoptosis by metabolizing and excluding 4-HNE at a higher rate. Induction of hGST5.8 and RLIP76 by mild, transient stress and the resulting resistance of stress-pre-conditioned cells to apoptosis appears to be a general phenomenon since it was not limited to K562 cells but was also evident in lung cancer cells, H-69, H-226, human leukemia cells, HL-60, and human retinal pigmented epithelial cells. These results strongly suggest a role of LPO products, particularly 4-HNE, in the initial phase of stress mediated signaling.

The interplay of glutathione-related processes in antioxidant defense

This review summarizes current knowledge on glutathione (GSH) associated cellular processes that play a central role in defense against oxidative stress. GSH itself is a critical factor in maintaining the cellular redox balance and has been demonstrated to be involved in regulation of cell signalling and repair pathways. Enhanced expression of various enzymes involved in GSH metabolism, including glutathione peroxidases, γ-glutamyl cysteinyl synthetase (γ-GCS), glutathione S-transferases (GST) and membrane proteins belonging to the ATP-binding cassette family, such as the multidrug resistance associated protein, have all been demonstrated to play a prominent role in cellular resistance towards oxidative stress. This review stresses the fact that aco-ordinateinterplay between these systems is essential for efficient protection against oxidative stress.

Transfection of mGSTA4 in HL-60 cells protects against 4-hydroxynonenal-induced apoptosis by inhibiting JNK-mediated signaling

The mammalian alpha-class glutathione S-transferase (GST) isozymes mGSTA4-4, rGSTA4-4, and hGSTA4-4 are known to utilize 4-hydroxynonenal (4HNE) as a preferred substrate. During the present studies, we have examined the effect of transfecting human myeloid HL-60 cells with mGSTA4, on 4-HNE-induced apoptosis and the associated signaling mechanisms. Results of these studies show that treatment of the wild-type or vector-only-transfected HL-60 cells with 20 microM 4-HNE caused apoptosis within 2 h. The cells transfected with mGSTA4 did not undergo apoptosis under these conditions even after 4 h. In the wild-type and vector-transfected cells, apoptosis was preceded by JNK activation and c-Jun phosphorylation within 30 min, and an increase in AP-1 binding within 2 h of treatment with 20 microM 4-HNE. In mGSTA4-transfected cells, JNK activation and c-Jun phosphorylation were observed after 1 h, and increased AP-1 binding was observed after 8 h under these conditions. In the control cells, 20 microM 4-HNE caused caspase 3 activation and poly(ADP-ribose) polymerase cleavage within 2 h, while in mGSTA4-transfected cells, a lesser degree of these effects was observed even after 8 h. Transfection with mGSTA4 also provided protection to the cells from 4-HNE and doxorubicin cytotoxicity (1.6- and 2.6-fold, respectively). These results show that 4-HNE mediates apoptosis through its effects on JNK and caspase 3, and that 4-HNE metabolizing GST isozyme(s) may be important in the regulation of this pathway of oxidative-stress-induced apoptosis.

Role of glutathione S-transferases in protection against lipid peroxidation. Overexpression of hGSTA2-2 in K562 cells protects against hydrogen peroxide-induced apoptosis and inhibits JNK and caspase 3 activation

The physiological significance of the selenium-independent glutathione peroxidase (GPx) activity of glutathione S-transferases (GSTs), associated with the major Alpha class isoenzymes hGSTA1-1 and hGSTA2-2, is not known. In the present studies we demonstrate that these isoenzymes show high GPx activity toward phospholipid hydroperoxides (PL-OOH) and they can catalyze GSH-dependent reduction of PL-OOH in situ in biological membranes. A major portion of GPx activity of human liver and testis toward phosphatidylcholine hydroperoxide (PC-OOH) is contributed by the Alpha class GSTs. Overexpression of hGSTA2-2 in K562 cells attenuates lipid peroxidation under normal conditions as well as during the oxidative stress and confers about 1.5-fold resistance to these cells from H(2)O(2) cytotoxicity. Treatment with 30 microm H(2)O(2) for 48 h or 40 microm PC-OOH for 8 h causes apoptosis in control cells, whereas hGSTA2-2-overexpressing cells are protected from apoptosis under these conditions. In control cells, H(2)O(2) treatment causes an early (within 2 h), robust, and persistent (at least 24 h) activation of JNK, whereas in hGSTA2-2-overexpressing cells, only a slight activation of JNK activity is observed at 6 h which declines to basal levels within 24 h. Caspase 3-mediated poly(ADP-ribose) polymerase cleavage is also inhibited in cells overexpressing hGSTA2-2. hGSTA2 transfection does not affect the function of antioxidant enzymes including GPx activity toward H(2)O(2) suggesting that the Alpha class GSTs play an important role in regulation of the intracellular concentrations of the lipid peroxidation products that may be involved in the signaling mechanisms of apoptosis.