Glutathione S-transferases in rat testis microsomes: comparison with liver transferase

Mixed exposure effect of seminal metals on semen quality, mediation of total antioxidant capacity, and moderation of GSTM1/GSTT1 gene deletion in Chinese reproductive-aged men

BACKGROUND

The effects of metal exposure on semen quality and the role of oxidative damage in this process remain unclear.

METHODS

We recruited 825 Chinese male volunteers, and 12 seminal metals (Mn, Cu, Zn, Se, Ni, Cd, Pb, Co, Ag, Ba, Tl, and Fe), the total antioxidant capacity (TAC), and reduced glutathione were measured. Semen parameters and GSTM1/GSTT1-null genotypes were also detected. Bayesian kernel machine regression (BKMR) was applied to evaluate the effect of the mixed exposure to metals on semen parameters. The mediation of TAC and moderation of GSTM1/GSTT1 deletion were analyzed.

RESULTS

Most seminal metal concentrations were correlated with each other. The BKMR models revealed a negative association between the semen volume and metal mixture, with Cd (cPIP = 0.60) and Mn (cPIP = 0.10) as the major contributors. Compared to fixing all scaled metals at their median value (50th percentiles), fixing the scaled metals at their 75th percentiles decreased the TAC by 2.17 units (95%CI: -2.60, -1.75). Mediation analysis indicated that Mn decreased the semen volume, with 27.82% of this association mediated by TAC. Both the BKMR and multi-linear models showed that seminal Ni was negatively correlated with sperm concentration, total sperm count, and progressive motility, which was modified by GSTM1/GSTT1. Furthermore, Ni and the total sperm count showed a negative association in GSTT1 and GSTM1 null males (β[95%CI]: 0.328 [-0.521, -0.136]) but not in males with GSTT1 and/or GSTM1. Although Fe and the sperm concentration and total sperm count were positively correlated, they showed inverse "U" shapes in univariate analysis.

CONCLUSION

Exposure to the 12 metals was negatively associated with semen volume, with Cd and Mn as the major contributors. TAC may mediate this process. GSTT1 and GSTM1 can modify the reduction in the total sperm count caused by seminal Ni exposure.

Proteome mapping of the Drosophila melanogaster male reproductive system

The fruit fly Drosophila melanogaster is an excellent model organism for studying insect reproductive biology. Although the gene expression profiles of both male and female reproductive organs have been studied in detail, their proteomic profiles and functional characteristics largely remained to be clarified. In this study, we conducted proteome mapping of the male internal reproductive organs using 2-DE. We identified a total of 440 protein components from gels of the male reproductive organs (testis, seminal vesicle, accessory gland, ejaculatory duct, and ejaculatory bulb). A number of proteins associated with odorant/pheromone-binding, lipid metabolism, proteolysis, and antioxidation were expressed tissue specifically in the male reproductive system. Based on our proteomic data set, we constructed reference proteome maps of the reproductive organs, which will provide valuable information toward a comprehensive understanding of Drosophila reproduction.

Molecular cloning, phylogenetic analysis and expression of a MAPEG superfamily gene from the pufferfish Takifugu obscurus

The microsomal glutathione S-transferases (MGSTs) of membrane-associated proteins in eicosanoid and glutathione metabolism (MAPEG) superfamily play an important role in xenobiotics detoxification. Compared to mammals, there is limited information on MAPEGS from fish. We cloned a full length of cDNA sequence of a MGST gene from the river pufferfish (Takifugu obscurus), studied its phylogenetic relationship, and measured its expression in different tissues and in liver of fish exposed to cadmium. Phylogenetic analysis revealed that the identified gene encoded for MGST3. Liver showed the highest expression of MGST3 transcripts. When MSGT expression was compared with the expression of other GSTs (GST-Alpha, GST-Mu and GST-Theta), a similar pattern of highest expression was observed in the liver. Upon Cd exposure (5 ppm) for 96 h, the highest expression of MGST was observed at 24 h. GST-Mu also showed highest expression at 24 h. These findings indicate that MGSTs may be playing a role in detoxification of xenobiotics or free radicals generated by Cd-induced oxidative stress in fish.

Differential induction of oxidative impairments in brain regions of male mice following subchronic consumption of Khesari dhal (Lathyrus sativus) and detoxified Khesari dhal

Neurolathyrism is a neurodegenerative disease caused by the chronic consumption of Khesari dhal (Lathyrus sativus L). It is generally accepted that beta-N-oxalylamino-l-alanine (b-ODAP), a non-protein amino acid present in the seeds is the primary causative agent. Based on in vitro studies with beta-ODAP, both excitotoxic and oxidative stress mechanisms have been speculated to be responsible for its neurotoxic effects. However, occurrence and the involvement of oxidative stress mechanisms in experimental animals following Khesari dhal consumption in vivo is less well understood. Accordingly in the present study, we have addressed primarily two questions: (i) whether dietary intake of Khesari dhal (KD) causes oxidative impairment in specific regions of brain, such as cortex and cerebellum and (ii) if there is any significant reduction in the oxidative damage induction following consumption of detoxified Khesari dhal (DKD). Adult male mice were fed either normal, KD or DKD incorporated diet (30%) for a period of 4 or 12 weeks. Biochemical markers of oxidative stress, such as lipid peroxidation (LPO), generation of reactive oxygen species (ROS), activity of antioxidant enzymes, protein carbonyls in brain regions (cortex, cerebellum) were determined. Mice fed KD diet showed enhanced LPO levels and ROS generation in brain, while the levels of LPO and ROS were unaltered in DKD mice. Interim sampling (4 weeks) also showed a similar trend though the degree of oxidative damage was lower. Depletion of reduced GSH, significant alterations in the activity of various antioxidant enzymes and enhanced protein carbonyls in brain in KD fed mice suggested that a state of oxidative stress exists in vivo. Interestingly, no significant induction of oxidative damage was evident in the brain of mice fed DKD. However, altered cholinergic function was discernible among both treatment groups. KD consumption resulted in a marked reduction of brain AChE activity at both sampling times (cortex, 38-43%; cerebellum, 22-41%), while DKD consumption resulted in less robust reduction (cortex, 11-17%; cerebellum, 11-13%). Taken together, these data suggest that dietary KD has the propensity to induce marked oxidative damage in brain of male mice, while DKD failed to induce any significant degree of oxidative impairments. Based on these results, it is hypothesized that oxidative stress mechanisms may wholly or in part contribute towards the development of neuro-degeneration associated with human consumption of L. sativus.

Nickel-induced oxidative stress in testis of mice: evidence of DNA damage and genotoxic effects

Oxidative stress (OS) mechanisms are speculated to play a significant role in nickel-induced toxic effects and their carcinogenic potency. Although nickel-induced oxidative damage in somatic tissues is well demonstrated, evidence of the involvement of a similar mechanism(s) in nickel-induced testicular dysfunction and associated genotoxic effects is scarce. Hence, the present study aimed to investigate the nickel-induced OS response in testis and the associated genotoxic implications in vivo. Initially, the toxicity profile of nickel chloride was determined in adult albino mice (CFT-Swiss) following administration (intraperitoneal) of single doses. Subsequently, multiple sublethal doses (1.25, 2.5, and 5.0 micromol/100 g of body weight per day for 3 days) were used to characterize effects on testicular histoarchitecture, lipid peroxidation (LPO) in testis (homogenates, microsomal or mitochondrial fractions) and epididymal sperm, DNA damage, induction of apoptosis in testis, and incidence of sperm head abnormalities. Although short-term doses of nickel induced only a minimal LPO response, multiple doses elicited a moderate (15% to 30%) increase in LPO in whole homogenates and higher dose-related increases in both mitochondrial (20% to 50%) and microsomal fractions (25% to 60%). This was associated with a significant increase in DNA damage in the testis as evidenced by increased single-strand breaks (fluorimetric analysis of DNA unwinding assay). Further, at higher doses, nickel-induced apoptosis was demonstrable in the testis biochemically. Although caudal sperm counts determined at all sampling weeks showed no alterations, analysis for head abnormalities revealed a nearly 3- to 4-fold increase in the percentage of abnormal sperms among the nickel-treated males during the first 3 weeks. Furthermore, mating of nickel-treated (2.5 micromol/100 g of body weight per day for 5 days) males sequentially for a period of 5 weeks with untreated females resulted in a significant increase in male-mediated dominant lethal-type mutations (the frequency of dead implantations) during the first 3 weeks, suggesting a stage-specific effect on postmeiotic germ cells. These findings suggest that testicular toxicity of nickel compounds may be related to enhanced production of reactive oxygen species, probably mediated through oxidative damage to macromolecules, including damage to DNA.

Genotoxic consequences associated with oxidative damage in testis of mice subjected to iron intoxication

While iron-induced testicular dysfunction has been demonstrated adequately, the mechanism(s) involved and the genotoxic implications are not fully understood. In order to understand the genotoxic effects of iron intoxication, initially induction of oxidative stress response in testis of adult albino mice (CFT-Swiss) was ascertained following administration (i.p.) of acute sub-lethal doses of iron dextran (ID). Subsequently, multiple sub-lethal doses (50, 100 and 200 mg/kg bw/day) were employed to characterize effects on lipid peroxidation (LPO) in testis (homogenates, microsomal/mitochondrial fractions), DNA damage and incidence of abnormal sperms. While acute doses of ID induced only a marginal increase in LPO response in testis at 24 h of administration, multiple doses elicited a moderate (30-40%) increase in LPO in whole homogenates and significant dose-related elevation in both mitochondrial (20-45%) and microsomal fractions (25-65%). This was associated with significant increase in DNA damage in the testis as evidenced by increased single strand breaks in a fluorimetric analysis of DNA unwinding (FADU) assay. Further, evidences of oxidative damage in testis was evident in terms of increased protein carbonyls and altered antioxidant enzymic activities. The genotoxic implications were investigated by quantification of the frequency of abnormal sperms sampled at specific periods during spermatogenetic cycle. Nearly three- to seven-fold increase in percent abnormal sperms among the ID treated males were evident during the first 3 weeks although the counts were unaffected. Interestingly, in a classical dominant lethal (DL) assay, mating of ID treated (100 mg/kg bw/day for 5 days) males sequentially for a period of 5 weeks with untreated females resulted in a significant increase in male-mediated dominant lethal type mutations (the frequency of dead implants) during the first 3 weeks only indicating a stage-specific effect on post-meiotic germ cells. These findings provide an account of the early oxidative damage in testis in vivo following exposure to low levels of iron which may be wholly or in part responsible for the genotoxic consequences observed in this model of iron overload.

Microsomal glutathione S-transferase A1-1 with glutathione peroxidase activity from sheep liver: molecular cloning, expression and characterization

A 25 kDa subunit of glutathione S-transferase (GST) from sheep liver microsomes (microsomal GSTA1-1) with a significant selenium-independent glutathione peroxidase activity has been isolated and characterized. Several analytical criteria, including EDTA stripping, protease protection assay and extraction with alkaline Na(2)CO(3), indicate that the microsomal GSTA1-1 is associated with the inner microsomal membrane. The specific cDNA nucleotide sequence reveals that the enzyme is made up of 222 amino acid residues and shares approx. 73-83% sequence similarity to Alpha-class GSTs from different species. The molecular mass, as determined by electrospray mass ionization, is 25611.3 Da. The enzyme is distinct from the previously reported rat liver microsomal GST in both amino acid sequence and catalytic properties [Morgenstern, Guthenberg and DePierre (1982) Eur. J. Biochem. 128, 243-248]. The microsomal GSTA1-1 differs from the sheep liver cytosolic GSTs, reported previously from this laboratory, in its substrate specificity profile and molecular mass [Reddy, Burgess, Gong, Massaro and Tu (1983) Arch. Biochem. Biophys. 224, 87-101]. In addition to catalysing the conjugation of 4-hydroxynonenal with GSH, the enzyme also exhibits significant glutathione peroxidase activity towards physiologically relevant fatty acid hydroperoxides, such as linoleic and arachidonic acid hydroperoxides, as well as phosphatidylcholine hydroperoxide, but not with H(2)O(2). Thus the microsomal GSTA1-1 isoenzyme might have an important role in the protection of biological membranes against oxidative damage.

Effects of dietary broccoli on rat testicular xenobiotic metabolizing enzymes

The effects of vegetables on the activities of various metabolizing enzymes in liver and intestine have been studied intensively, whereas studies on effects on testicular metabolizing enzymes are lacking. The present report is the first describing the effects of dietary broccoli on the activities of a number of xenobiotic metabolizing enzymes from rat testes. Groups of male Wistar rats were fed a semisynthetic diet with 10% (w/w) freeze-dried broccoli for 1 week. Different broccoli samples with varying content of glucosinolates were used. Dietary broccoli significantly increased the activities of two testicular phase II enzymes--glutathione S-transferase (1.6-fold) and UDP-glucuronosyl transferase (1.8-fold). The activities of these enzymes differed significantly depending on the conditions during cultivation of the broccoli, because of differences in the content of glucosinolates and other secondary plant metabolites. The levels of two glutathione S-transferase subunits, rGSTM2 and rGSTA, were determined using Western blotting analysis and the levels of both subunits were reduced in animals fed broccoli grown at low S-fertilizer level. Broccoli did not statistically significantly modulate the activities of the phase I enzymes, epoxide hydrolase or NAD(P)H quinone-oxidoreductase, or the phase II enzyme p-sulphotransferase, or the anti-oxidative enzymes catalase and total glutathione peroxidase in rat testes. In general, dietary broccoli affects phase I and phase II enzyme levels in rat testes much less than found in liver, however, two rat testicular phase II xenobiotic metabolizing enzymes were induced.

Glutathione S-transferase-M1 'null' genotype and alcohol-induced disorders of human spermatogenesis

The association between alcohol-induced disorders of human spermatogenesis and glutathione S-transferase-M1 genotype was investigated in an autopsy study comprising 271 subjects, including interviews with relatives or close acquaintances on the alcohol consumption of the deceased. Of the 50 moderate drinking men (reported mean daily alcohol consumption < 40 g), 21 (42.0%) had normal spermatogenesis, whereas 24 men (48.0%) had partial, and five (10.0%) complete arrest of spermatogenesis. Of the 21 men with normal spermatogenesis, nine (42.9%) had GST M1 'null' genotype, while this genotype was found in 13 (44.8%) of the 29 men with partial or complete spermatogenic arrest. Of 212 heavy-drinking men (reported mean daily alcohol consumption > 80 g), only 45 (21.2%) had normal spermatogenesis, whereas 77 (36.3%) had partial spermatogenic arrest. Complete arrest of spermatogenesis was found in 81 men (38.2%) and nine men had Sertoli-cell-only syndrome (4.2%). Of the 45 heavy drinkers with normal spermatogenesis, 27 (60%) men had GST M1 'null' genotype (OR 2.7 with 95% confidence intervals: 1.0-4.0, when compared to those with disorders of spermatogenesis). The frequency of GST M1 'null' genotype in heavy drinkers with normal spermatogenesis also differed from that of corresponding moderate drinkers, whereas the frequency of GST M1 'null' genotype in heavy drinkers with disorders of spermatogenesis was similar to moderate drinkers with or without disorders of spermatogenesis. The finding that > 20% of men in the heavy-drinking group had normal spermatogenesis suggests individual variations in sensitivity to alcohol-induced disorders of this process. Heavy drinkers with GST M1 'null' genotype were slightly less prone to develop disorders of spermatogenesis. Thus, the GST M1 locus may be associated with susceptibility to develop alcohol-induced disorders of spermatogenesis.