Isolation and identification of metallothionein isoforms (MT-1 and MT-2) in the rat testis

Phthalate-Induced Fetal Leydig Cell Dysfunction Mediates Male Reproductive Tract Anomalies

Male fetal Leydig cells in the testis secrete androgen and insulin-like 3, determining the sexual differentiation. The abnormal development of fetal Leydig cells could lead to the reduction of androgen and insulin-like 3, thus causing the male reproductive tract anomalies in male neonates, including cryptorchidism and hypospadias. Environmental pollutants, such as phthalic acid esters (phthalates), can perturb the development and differentiated function of Leydig cells, thereby contributing to the reproductive toxicity in the male. Here, we review the epidemiological studies in humans and experimental investigations in rodents of various phthalates. Most of phthalates disturb the expression of various genes encoded for steroidogenesis-related proteins and insulin-like 3 in fetal Leydig cells and the dose-additive effects are exerted after exposure in a mixture.

Role of metallothionein-like cadmium-binding protein (MTLCdBP) in the protective mechanism against cadmium toxicity in the testis

The role of metallothionein (MT)-like cadmium (Cd) binding protein (MTLCdBP) in protecting the testes against Cd toxicity was examined. In the acute Cd exposure treatment, cadmium chloride was intraperitoneally injected at 2 mg Cd/kg to Wistar male rats. In the chronic Cd toxicity treatments, 20 mg Cd/kg/d was orally administered for 5 d a week for 5, 10, and 15 wk. MT (-I,-II) and MTLCdBP were measured using ELISA and Cd-Hem methods, respectively. Testicular tissues were immunostained with antibodies of MT-I,-II, MT-III, and MTLCdBP. Expression of HO1, OGG, iNOS, COX2, and p53 was measured by RT-PCR. Cd concentration in the testis increased dose-dependently in response to Cd exposure. MTLCdBP concentration increased markedly with increasing Cd accumulation. Significant increases in expression of iNOS, HO1, COX2, and OGG1 were observed in the acute exposure treatment. In the chronic oral administration group, expression of MT-I, MT-II, MT-III, iNOS, HO1, and COX2 did not change. Positive immunostaining of MTLCdBP was observed in testicular interstitial tissue. In the testis protected from Cd toxicity, MTLCdBP induction increased significantly with increasing Cd accumulation. Our results suggest that MTLCdBP plays an important role in protecting the testis against Cd toxicity.

Cadmium specific proteomic responses of a highly resistantPseudomonas aeruginosasan ai

Pseudomonas aeruginosa san ai is a promising candidate for bioremediation of cadmium pollution, as it resists a high concentration of up to 7.2 mM of cadmium. Leaving biomass of P. aeruginosa san ai exposed to cadmium has a large biosorption potential, implying its capacity to extract heavy metal from contaminated medium. In the present study, we investigated tolerance and accumulation of cadmium on protein level by shotgun proteomics approach based on liquid chromatography and tandem mass spectrometry coupled with bioinformatics to identify proteins. Size exclusion chromatography was used for protein prefractionation to preserve native forms of metalloproteins and protein complexes. Using this approach a total of 60 proteins were observed as up-regulated in cadmium-amended culture. Almost a third of the total numbers of up-regulated were metalloproteins. Particularly interesting are denitrification proteins which are over expressed but not active, suggesting their protective role in conditions of heavy metal exposure. P. aeruginosa san ai developed a complex mechanism to adapt to cadmium, based on: extracellular biosorption, bioaccumulation, the formation of biofilm, controlled siderophore production, enhanced respiration and modified protein profile. An increased abundance of proteins involved in: cell energy metabolism, including denitrification proteins; amino acid metabolism; cell motility and posttranslational modifications, primarily based on thiol-disulfide exchange, were observed. Enhanced oxygen consumption of biomass in cadmium-amended culture versus control was found. Our results signify that P. aeruginosa san ai is naturally well equipped to overcome and survive high doses of cadmium and, as such, has a great potential for application in bioremediation of cadmium polluted sites.

When exposed to cadmium a highly resistant strain P. aeruginosa san ai responds by an increased metalloprotein expression (particularly denitrification proteins), an enhanced respiration, and a pronounced thiol-disulfide protein modifications.

Induction of Metallothionein in Rat Liver by Zinc Exposure: A Dose and Time Dependent Study

Metallothioneins (MTs) are low molecular weight ubiquitous metalloproteins with high cysteine (thiol) content. The intracellular concentration of zinc (Zn) is tightly regulated and MT plays a crucial role in it. The present study investigates the relationship between the Zn status (as a function of Zn concentration and time) in the rat liver and the occurrence of hepatic MT. For dose dependent study, four experimental groups, one control and three receiving different levels of metal supplementation, were chosen [Group 1 control and Group 2, Group 3, Group 4 receiving subcutaneous dose of 10, 50 and 100 mg of Zn/kg body weight (in the form of ZnSO₄·7H₂O), respectively]. For the time dependent expression of MT, again four experimental groups, i.e. Group 5 control and Group 6, Group 7, Group 8 receiving 50 mg of Zn/kg body weight (in the form of ZnSO₄·7H₂O) subcutaneously and sacrificed at different time intervals after last injection i.e. 6, 18, 48 h, respectively were chosen. Isolation of MT was done by using combination of gel filtration and ion exchange chromatography while characterization of MT fraction was carried in the wavelength range 200-400 nm. Expression of MT was studied by using Western blot analysis. The results revealed that the MT expression increases with increasing the dose of Zn administered and maximum at 18 h after last Zn injection. Accumulation of MT with increase dose would help in maintaining the intracellular Zn concentration by its sequestration which further reduces the possibility of undesirable binding of Zn to other proteins significantly and maintains Zn homeostasis. The maximum expression of MT at 18 h is indicative of its half life.

Melatonin promotes the proliferation of GC-1 spg cells by inducing metallothionein-2 expression through ERK1/2 signaling pathway activation

Synthesized by the pineal gland, melatonin is a neurohormone implicated in diverse physiological functions via several mechanisms. However, the role of melatonin in spermatogenesis and its underlying mechanisms have yet to be completely understood. In the present study, transcriptome sequencing was performed to characterize the mechanism of melatonin-induced GC-1 spg proliferation. Gene ontology (GO) enrichment and pathway analyses were also conducted to identify the signaling pathways and biological processes involved in differential mRNA expression. Results revealed 28 differential genes. Of these genes, 11 were upregulated and 17 were downregulated. Melatonin increased the expression of metallothionein-2 (Mt2), a gene that acts as a protector to sequester nonessential toxic heavy metals. Functional investigations demonstrated that Mt2 overexpression promoted the proliferation of GC-1 spg cells, but Mt2 knockdown significantly suppressed their proliferation and increased their apoptosis. Mechanistic analysis indicated that the extracellular-signal-regulated kinase 1/2 (ERK1/2) pathway participated in melatonin-promoted proliferation of GC-1 spg cells. Therefore, melatonin induces the proliferation of GC-spg 1 cells by stimulating Mt2 expression, and this process is mediated by the ERK1/2 signaling pathway.

Unravelling the Role of Metallothionein on Development, Reproduction and Detoxification in the Wall Lizard Podarcis sicula

Metallothioneins (MTs) are an evolutionary conserved multigene family of proteins whose role was initially identified in binding essential metals. The physiological role of MT, however, has been revealed to be more complex than expected, since not only are MTs able to bind to toxic heavy metals, but many isoforms have shown specialized and alternative functions. Within this uncertainty, the information available on MTs in non-mammalian vertebrates, particularly in neglected tetrapods such as the reptiles, is even more scant. In this review, we provide a summary of the current understanding on metallothionein presence and function in the oviparous lizard Podarcis sicula, highlighting the results obtained by studying MT gene expression in most representative adult and embryonic tissues. The results demonstrate that in adults, cadmium induces MT transcription in a dose- and tissue-specific manner. Thus, the MT mRNAs appear, at least in some cases, to be an unsuitable tool for detecting environmental ion contamination. In early embryos, maternal RNAs sustain developmental needs for MT protein until organogenesis is well on its way. At this time, transcription starts, but again in a tissue- and organ-specific manner, suggesting an involvement in alternative roles. In conclusion, the spatiotemporal distribution of transcripts in adults and embryos definitively confirms that MT has deserved the title of elusive protein.

Metallothionein expression and synthesis in the testis of the lizard Podarcis sicula under natural conditions and following estrogenic exposure

Metallothionein (MT) is the main protein involved in the homeostasis of metallic micronutrients and in cellular defence against heavy metals and reactive oxygen species. Found in almost all vertebrate tissues, MT presence and localization in the testis has been controversial. In the present study, by using in situ hybridization and immunohistochemical analysis we assessed the localization of both MT transcript and protein in Podarcis sicula testes during two different phases of the reproductive cycle: the autumnal resumption and the springearly summer mating period. In addition, with the same methodological approach, we verified the effect of estradiol-1711and nonylphenol, a potent xenoestrogen, on MT expression and synthesis. These results, the first collected in a non-mammalian oviparous vertebrate, demonstrated that the expression profile of MT mRNA and protein changes during the reproductive cycle. In the fall resumption, MT transcripts are absent in spermatogonia and present in all the other cells of tubules, including spermatozoa; vice versa, the MT protein is evident only in spermatozoa and somatic cells. In the mating period, both MT transcripts and proteins are present in spermatogonia, spermatocytes and spermatids, whereas in the spermatozoa only the proteins are detected, thus suggesting that the MTs translated in the earlier germinal stages are stored up to spermatozoa. Results also demonstrated that in lizard testis the expression of MT gene undergoes a cell-specific regulation after estrogenic exposure; the possible role and the mechanism by which this regulation occurs have been discussed.

Ultrastructural Demonstration of Mercury Granules in the Placenta of Metallothionein-Null Pregnant Mice after Exposure to Mercury Vapor

The placenta plays an important role in the regulation of maternal to fetal transfer of toxic substances, including nonessential metals. Metallothioneins (MTs), which are known to have protective effects against heavy metal toxicity, exist in the placenta, but the exact localization of placental MTs (both MT-I and MT-III) and their physiological role in the placenta exposed to mercury are unclear. The present study was performed to examine the localization of MTs and mercury granules in the placenta of mice exposed to mercury vapor. On gestational day 16, MT-I & II-null and wild-type mice were exposed to mercury vapor at 4.9 to 5.9 mg/m3 for 2 hours. At 24 and 48 hours after exposure, the placentas were examined for mercury distribution (autometallography), MT immunoreactivity, and MT mRNA expression (in situ hybridization). No histological changes were observed in the placentas of either MT-null or wild-type mice. Mercury deposition was demonstrated along the boundary between the junctional zone and the labyrinth zone, as well as in the yolk sac, maternal decidual cells, and labyrinth trophoblasts of both MT-null and wild-type mice. MT-I & -II immunoreactivity, which was confined to wild-type mice, was demonstrated in the yolk sac and decidual cells; mercury was also shown in both structures, suggesting that mercury granules were bound to MTs. MT-III mRNA expression was observed in the yolk sac, decidual cells, and spongiotrophoblasts in both MT-null and wild-type mice. There was, however, no evidence of MT at the boundary between the junctional and labyrinth zones, where substantial mercury deposits were demonstrated. These results suggest that placental MTs and the other unknown molecules may be related to the barrier to the placental transfer of mercury.

Protective Effects of Zinc Against Acute Arsenic Toxicity by Regulating Antioxidant Defense System and Cumulative Metallothionein Expression

Arsenic (As), a toxic metalloid, is one of the major global concerns. The toxicity resulting from As exposure is linked to the generation of reactive oxygen intermediates during their redox cycling and metabolic activation processes that cause lipid peroxidation (LPO). Zinc (Zn), a redox-inactive metal, helps to maintain cellular functions because of its prominent role in antioxidant network through multiple mechanisms. The present study, therefore, explores the effectiveness of administered Zn to combat against acute As toxicity by analysis of antioxidant defense status, alkaline phosphatase (ALP) activity, histological profile, MT expression, and elemental status in rat liver. To achieve this goal, four experimental groups, one control and three receiving different metal supplementations, were chosen (group 1, control; group 2, Zn supplemented; group 3, As substituted; group 4, Zn + As supplemented). The levels of reduced glutathione (GSH) and activities of glutathione reductase (GR) and ALP were lowered, whereas LPO levels and activity of superoxide dismutase (SOD) were elevated with no significant change in catalase (CAT) activity. Histopathological changes were also observed in the As substituted group in comparison to the control. Particle-induced X-ray emission (PIXE) analysis showed decrease in Fe and S concentration in rat liver after As intoxication, whereas As was below detection limit, i.e., <1 ppm. Zn administration almost restored the antioxidants, ALP activity, histopathological changes, and elemental status. A cumulative increase in MT expression was found with the combined treatment of Zn and As. Also, Zn alone caused no significant change in the antioxidant defense system. It can be concluded that restoration of antioxidant activity and increased MT expression are the two independent protective mechanisms of Zn to reduce acute As toxicity.

Grape juice concentrate (G8000(®) ) intake mitigates testicular morphological and ultrastructural damage following cadmium intoxication

Cadmium is a well-known testicular toxicant, and parts of the world population are exposed chronically by inhalation or by food and water intake. Grape products have been highlighted as important sources of bioactive compounds, having anti-inflammatory, anti-oxidant and metal chelating properties. Since maintenance of tissue morphology is essential for testicular sperm development and hence male fertility, we analysed the protective effect of grape juice concentrate (GJC) (G8000(®) ) consumption on testicular morphology in rats exposed to cadmium. Thus, four groups of male Wistar rats (n = 6 per group), 50 days old, ingested either water or G8000(®) (2 g/kg/day) until they had completed one spermatogenic cycle in adult life (136 days old). Cadmium (1.2 mg / kg) was injected intraperitoneally when the animals were 80 days old into one of the water and one of the G8000 groups; intraperitoneal saline was used as a control in the other two groups. Animals anaesthetised and exsanguinated at 136 days and then perfused with Karnovsky's fixative and then the testes were collected for morphological analysis. We describe evident disruption of testicular morphology by cadmium, with alteration in tissue component proportions, reduced Leydig cells volume and initial signs of an inflammatory process. Ultrastructural analysis showed greater damage, suggesting spermatogenesis disruption. G8000(®) ingestion allowed tissue architecture to be re-established, as was corroborated by our stereological and morphometric findings. Animals from the group where G8000(®) had been administered together with cadmium revealed a significant reduction in macrophages and blood vessel volume, suggesting diminished inflammation, when compared to animals that received only cadmium. Moreover, smaller number of ultrastructural alterations was noted, revealing fewer areas of degeneration and disorganized interstitium. In conclusion, our results demonstrate that GJC consumption prevented the spermatogenic disruption promoted by cadmium, and thus could be a promising form of therapy against male infertility.

Cadmium stress: an oxidative challenge

At the cellular level, cadmium (Cd) induces both damaging and repair processes in which the cellular redox status plays a crucial role. Being not redox-active, Cd is unable to generate reactive oxygen species (ROS) directly, but Cd-induced oxidative stress is a common phenomenon observed in multiple studies. The current review gives an overview on Cd-induced ROS production and anti-oxidative defense in organisms under different Cd regimes. Moreover, the Cd-induced oxidative challenge is discussed with a focus on damage and signaling as downstream responses. Gathering these data, it was clear that oxidative stress related responses are affected during Cd stress, but the apparent discrepancies observed in between the different studies points towards the necessity to increase our knowledge on the spatial and temporal ROS signature under Cd stress. This information is essential in order to reveal the exact role of Cd-induced oxidative stress in the modulation of downstream responses under a diverse array of conditions.

Expression of metallothionein-1 (MT-1) mRNA in the rat testes and liver after cadmium injection

Metallothioneins (MTs) belong to the family of stress proteins that are present in the majority of living organisms. The MTs play an important task in detoxifying heavy metals. The mammalian scrotal testis is known to be susceptible to cadmium (Cd) exposure. The present work focuses on the MT-1 isoform and aims to ascertain and confirm previous findings to answer whether rodent testes indeed contain MT-1 mRNA, whether its level is increased with Cd injection in liver and testes, and lastly what is the relative difference in the expression of MT-1 mRNA in liver and testes both with and without Cd injection. Adult male Wistar rats weighing 270-290 g received a subcutaneous injection of 4.0 mumol Cd/kg and were sacrificed by cervical dislocation 6 h later. RNA was isolated from testes as well as the liver. There were 2 replicates per treatment for RNA analyses. MT-1 mRNA levels were determined by semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) analysis and then assessed by densitometry scanning. The results of RT-PCR clearly demonstrated that the rodent testes express MT-1 mRNA. The densitometry data shows that the expression of MT-1 mRNA increases with Cd treatment in testes. The relative level of MT1-mRNA is greater in the control-liver than in the control-testes. However, upon Cd injection, the level of testes MT-1 mRNA increases 2.16 fold. These results suggest that the testes respond to Cd for at least 6 h post injection through a transcriptional mechanism.

Differential gene-expression of metallothionein 1M and 1G in response to zinc in sertoli TM4 cells

BACKGROUND

Zinc (Zn) as an important trace element is essential for testicular development and spermatogenesis. Molecular mechanism of Zn action in the reproductive system may be related to metal binding low-molecular weight proteins, metallothioneins (MT). Our objective was to determine the effect of Zn on two important isoforms of MT, MT1M and MT1G genes expression on testicular sertoli cells.

METHODS

Cultured sertoli TM4 cells were exposed to different concentrations of Zn at different time points. Cellular uptake of Zn was tested using flame atomic absorption spectrometry. The cellular viability and gene expression were assessed by MTT and real-time PCR methods, respectively.

RESULTS

The treated cells resulted in higher Zn concentration and cellular viability. The expression of MT1M and MT1G genes in the treated cells were greater than those of the untreated cells (P less than 0.05). In the high dosage treated group (100 and 500 muM), Zn concentration and expression of MT1M and MT1G genes increased three h after treatment; MT1G gene expression increased more at sixth h. At 18th h of treatment, the expression of both genes especially MT1G, increased dramatically while Zn concentration decreased.

CONCLUSION

Since the increase of MT1G mRNA was coincident with cellular Zn level, it seems that MT1G has a more prominent role than MT1M in the homeostasis of Zn. In addition, Zn at dosage of 50 muM (pharmacologic concentration) may protect cells by increasing the expression of MT genes at longer periods.

Cadmium-induced testicular injury

Cadmium (Cd) is an environmental toxicant and an endocrine disruptor in humans and rodents. Several organs (e.g., kidney, liver) are affected by Cd and recent studies have illustrated that the testis is exceedingly sensitive to Cd toxicity. More important, Cd and other toxicants, such as heavy metals (e.g., lead, mercury) and estrogenic-based compounds (e.g., bisphenols) may account for the recent declining fertility in men among developed countries by reducing sperm count and testis function. In this review, we critically discuss recent data in the field that have demonstrated the Cd-induced toxicity to the testis is probably the result of interactions of a complex network of causes. This is likely to involve the disruption of the blood-testis barrier (BTB) via specific signal transduction pathways and signaling molecules, such as p38 mitogen-activated protein kinase (MAPK). We also summarize current studies on factors that confer and/or regulate the testis sensitivity to Cd, such as Cd transporters and metallothioneins, the impact of Cd on the testis as an endocrine disruptor and oxidative stress inducer, and how it may disrupt the Zn(2+) and/or Ca(2+) mediated cellular events. While much work is needed before a unified mechanistic pathway of Cd-induced testicular toxicity emerges, recent studies have helped to identify some of the likely mechanisms and/or events that take place during Cd-induced testis injury. Furthermore, some of the recent studies have shed lights on potential therapeutic or preventive approaches that can be developed in future studies by blocking or minimizing the destructive effects of Cd to testicular function in men.

Modelling metallothionein induction in the liver of Sparus aurata exposed to metal-contaminated sediments

Metallothionein (MT) in the liver of gilthead seabreams (Sparus aurata L., 1758) exposed to Sado estuary (Portugal) sediments was quantified to assess the MT induction potential as a biomarker of sediment-based contamination by copper (Cu), cadmium (Cd), lead (Pb) and arsenic (As). Sediments were collected from two control sites and four sites with different levels of contamination. Sediment Cu, Cd, Pb, As, total organic matter (TOM) and fine fraction (FF) levels were determined. Generalized linear models (GLM) allowed integration of sediment parameters with liver Cu, Cd, Pb, As and MT concentrations. Although sediment metal levels were lower than expected, we relate MT with liver Cd and also with interactions between liver and sediment Cu and between liver Cu and TOM. We suggest integrating biomarkers and environmental parameters using statistical models such as GLM as a more sensitive and reliable technique for sediment risk assessment than traditional isolated biomarker approaches.

Influence of combined antioxidants against cadmium induced testicular damage

Acute effects of cadmium (Cd) and combined antioxidants were evaluated in Sprague-Dawley rat testes. The rats were subdivided into four groups. Cadmium chloride (2mg/kgday) injected intraperitoneally during 8 days. Vitamin C (250mg/kgday), vitamin E (250mg/kgday) and sodium selenate (0.25mg/kgday) were pretreated by gavage in both of control and cadmium injected rats. Testis lipid peroxidation and glutathione levels were determined by spectrophotometrically. In Cd treated rats, lipid peroxidation levels were increased and glutathione levels were decreased and combined antioxidants treatment was effective in preventing of lipid peroxidation and normalizing glutathione. In Cd treated animals, the degenerative changes were observed, but not observed in the administrated rats with Cd and antioxidants under the light microscope. Proliferating cell nuclear antigen, metallothionein and caspase-3 activities were evaluated by immunohistochemically. Proliferation activity was not seen in the spermatogonial cells of cadmium treated testis. Treatment with antioxidants in cadmium administrated testis leads to pronounced increase in proliferation activity. Cytoplasmic caspase-3 activity was determined in the spermatogenic cells but not spermatogonia in treatment of antioxidants with Cd. In control and treated with antioxidants animals, metallothionein expressions were localized in the cells of seminiferous tubules, although the expression only was observed in the interstitial cells of cadmium treated rats. Results demonstrated beneficial effects of combined vitamin C, vitamin E and selenium treatment in Cd toxicity.

Localization and role of metallothioneins in the olfactory pathway after exposure to mercury vapor

We have investigated the localization and physiological roles of metallothioneins (MTs) in the olfactory pathway after exposure to mercury (Hg0) vapor. Male MT-null and wild-type mice were examined for the distribution of mercury, MT immunoreactivity and MT-III mRNA expression. There were no signs of histological changes in MT-null or wild-type mice. Light and electron microscopy of the samples stained with autometallography demonstrated chronological transfer of exposed mercury granules to the olfactory bulb by way of the olfactory tract. Basal expression of MT-I and -II immunoreactivity was observed in supporting cells, basal cells and acinar cells of the Bowman's gland of the olfactory mucosa in wild-type mice even without mercury exposure. In situ hybridization showed that signals for MT-III mRNA dominated in the olfactory cells of the olfactory mucosa, neurons in the olfactory bulb and those of brain in MT-null and wild-type mice. No difference in these findings was observed between samples taken at any interval after mercury exposure.

Cytokines and junction restructuring during spermatogenesis—a lesson to learn from the testis

In the mammalian testis, preleptotene and leptotene spermatocytes residing in the basal compartment of the seminiferous epithelium must traverse the blood-testis barrier (BTB) at late stage VIII through early stage IX of the epithelial cycle during spermatogenesis, entering the adluminal compartment for further development. However, until recently the regulatory mechanisms that regulate BTB dynamics remained largely unknown. We provide a critical review regarding the significance of cytokines in regulating the 'opening' and 'closing' of the BTB. We also discuss how cytokines may be working in concert with adaptors that selectively govern the downstream signaling pathways. This process, in turn, regulates the dynamics of either Sertoli-Sertoli tight junction (TJ), Sertoli-germ cell adherens junction (AJ), or both junction types in the epithelium, thereby permitting TJ opening without compromising AJs, and vice versa. We also discuss how adaptors alter their protein-protein association with the integral membrane proteins at the cell-cell interface via changes in their phosphorylation status, thereby altering adhesion function at AJ. These findings illustrate that the testis is a novel in vivo model to study the biology of junction restructuring. Furthermore, a molecular model is presented regarding how cytokines selectively regulate TJ/AJ restructuring in the epithelium during spermatogenesis.

The roles of metallothionein on cadmium-induced testes damages in Sprague-Dawley rats

The present study was to investigate whether metallothionein (MT) was involved in sensitivity of testis to cadmium (Cd) and protection of rats from Cd-induced testis damages. The rats were treated by intraperitoneal injection with 0.2, 0.4, and 0.8mg Cd/kg BW for 7 days. The atomic absorption spectrophotometry and cadmium hemoglobin affinity assay were applied to evaluate the contents of Cd and MT in testis and liver. The testis glutathione (GSH), malondialdehyde (MDA) and daily sperm production were measured. There were substantial increases of both Cd and MT in the liver after Cd exposure. The testis Cd and MT contents were lower than those in the corresponding liver in Cd-exposed rats. Low doses of Cd (0.2 and 0.4mg/kg BW) induced MT in testis, while a significant decline of MT was found in rats treated with 0.8mg Cd/kg BW. By a concomitant decrease of MT, there was an obvious increase of MDA and marked decreases of GSH, daily sperm production in rats treated with 0.8mg Cd/kg BW. These findings suggested MT was more difficult to be induced in the testis than in the liver by Cd, which might account for the high susceptibility of testis to Cd. MT, increased by a low dose of Cd, played an important role in protecting testis against Cd toxicity by sequestering and antioxidating.

PCR-based subtraction analyses for upregulated gene transcription in cadmium-exposed rat lung type 2 epithelial cells

The aim of this study was to gain insight into early events in the lung epithelial cells following acute Cd exposure. We adopted the polymerase chain reaction (PCR)-based subtraction technique and found several genes that were upregulated in immortalized rat lung type 2 epithelial cells (SV40T2). The upregulation of those genes was confirmed by Northern blot analysis and categorized into three groups (highly, moderately, and weakly inducible genes). Heme oxygenase-1 (HO-1), HSP 72, hepatic steroid hydroxylase/CYPIIA2, and Cd-inducible gene 1 (cdig1, a new gene, Accession Nos. AB086233 and AB086234) were highly inducible genes, testosterone-repressed prostate message 2 mRNA was moderately inducible, and collagen-binding protein and cdig2 (another new gene, Accession No. AB086193) mRNAs were weakly inducible. The expression of cdig1 increased linearly with time up to 9h, while that of HO-1 reached the maximum value at 4h in response to 10 microM Cd.

Tissue-dependent induction of heme oxygenase-1 and metallothionein-1/2 by methyl methanesulfonate

Methyl methanesulfonate (MMS), a methylating agent, is known to be a genotoxicant in testis. The purpose of this study was to investigate roles of oxidative stress-responsive proteins, heme oxygenase-1 (HO-1) and metallothionein-1/2 (MT-1/2), in genotoxicity of MMS. Cadmium, a potent genotoxicity inducer, induced HO-1 and MT-1/2 in rat livers and kidneys. Then we comparatively investigated MMS-induced HO-1 and MT-1/2 in rat livers, kidneys and testes. We found that a single administration of MMS (40 mg/kg) resulted in the induction of MT-1/2 mRNA in the liver, but not HO-1 mRNA, reaching maximum level at 6 hr and returning to the control levels by 24 hr. Interestingly, MMS induced both HO-1 and MT-1/2 mRNAs in the kidney. In contrast, MMS induced HO-1 mRNA, but not MT-1/2 mRNA in the testis. Since HO-1 and MT-1/2 have been recognized to respond to various oxidative stimuli, we further examined the inducing effect of MMS on these two proteins. MMS at dosages of 20 to 40 mg/kg for 2 consecutive weeks induced HO-1 mRNA (123 to 187% of the control) and protein (274 to 404% of the control) in rat testes. However, MT-1/2 mRNA was not induced by MMS administration, although a high level of expression was observed in comparison with the liver and kidney. These findings suggest that MMS induces HO-1 and/or MT-1/2 mRNA and its protein tissue-dependently, and the heme catabolites by HO-1 in the testis may contribute in some manner to its genotoxicity.

Expression of metallothionein gene at different time in testicular interstitial cells and liver of rats treated with cadmium

AIM: Rodent testes are generally more susceptible to cadmium (Cd)-induced toxicity than liver. To clarify the molecular mechanism of Cd-induced toxicity in testes, we compared metallothionein (MT) gene expression, MT protein accumulation, and Cd retention at different time in freshly isolated testicular interstitial cells and liver of rats treated with Cd.

METHODS: Adult male Sprague-Dawley rats weighing 250-280 g received a s.c injection of 4.0 μmol Cd/kg and were euthanized by CO₂ asphyxiation 1 h, 3 h, 6 h, or 24 h later. Tissue was sampled and testicular interstitial cells were isolated. There were three replicates per treatment and 3 animals per replicate for RNA analyses, others, three replicates per treatment and one animal per replicate. MT1 and MT2 mRNA levels were determined by semi-quantitative RT-PCR analysis followed by densitometry scanning, and MT was estimated by the enzyme-linked immunosorbent assay (ELISA) method. Cadmium content was determined by atomic absorption spectrophotometry. The same parametersd were also analyzed in the liver, since this tissue unquestionably accumulate MT.

RESULTS: The rat testis expressed MT1 and MT2, the major isoforms. We also found that untreated animals contained relatively high basal levels of both isoform mRNA, which were increased after Cd treatment in liver and peaked at 3 h, followed by a decline. In contrast, the mRNA levels in interstitial cells peaked at 6 h. Interestingly, the induction of MT1 mRNA was lower than MT2 mRNA in liver of rat treated with Cd, but it was opposite to interstitial cells. Cd exposure substantially increased hepatic MT (3.9-fold increase), but did not increase MT translation in interstitial cells.

CONCLUSION: Cd-induced expression of MT isoforms is not only tissue dependent but also time-dependent. The inability to induce the metal-detoxicating MT-protein in response to Cd, may account for a higher susceptibility of testes to Cd toxicity and carcinogenesis compared to liver.

Cadmium-induced testicular damage in a rat model of subchronic intoxication

Background: Cadmium (Cd)-induced testicular damage in relation to spermatogenesis has not been well studied. We studied the mechanism of Cd-induced testicular damage in a rat model of subchronic intoxication. Methods:  Male Sprague-Dawley rats were subcutaneously injected with 0.6 mg Cd/kg per day for 6 weeks. The concentration of Cd in urine, serum and testes was measured by using atomic absorption spectrophotometry. Testicular damage was evaluated by counting the spermatogonia (SG) and spermatocytes (SC) on one cut-surface of five seminiferous tubules in stages VII or VIII of spermatogenesis every week. The location of intratesticular cadmium was determined by using oxine-fluorescent cytochemistry. Results: There were no differences in the testes/bodyweight ratio between the study and control groups. The concentration of Cd in the testes increased more than 100-fold that in serum after week 2, suggesting active testicular Cd accumulation (1-3 mg/g tissue). Cadmium accumulation was detected in SG and SC. The number of SG and SC diminished significantly in the study group (week 2: SG 74%, SC 90%; week 4: SG 47%, SC 75%; week 6: SG 30%, SC 54% of the control, respectively). Conclusions: Cadmium accumulated in SG and SC, consequently reduced the number of these cells, and disturbed the spermatogenesis in this rat model of subchronic Cd intoxication. Therefore, the number of SG decreased in this rat model of subchronic Cd intoxication. (Reprod Med Biol 2002; 1: 59-63).

Application of the S-pyridylethylation reaction to the elucidation of the structures and functions of proteins

Cysteine (Cys) and cystine residues in proteins are unstable under conditions used for acid hydrolysis of peptide bonds. To overcome this problem, we proposed the use of the S-pyridylethylation reaction to stabilize Cys residues as pyridylethyl-cysteine (PEC) protein derivatives. This suggestion was based on our observation that two synthetic derivatives formed by pyridylethylation of the SH group of Cys with either 2-vinylpyridine (2-VP) or 4-vinylpyridine (4-VP), designated as S-beta-(2-pyridylethyl)-L-cysteine (2-PEC) and S-beta-(4-pyridylethyl)-L-cysteine (4-PEC), were stable under acid conditions used to hydrolyze proteins. This was also the case for protein-bound PEC groups. Since their discovery over 30 years ago, pyridylethylation reactions have been widely modified and automated for the analysis of many structurally different proteins at levels as low as 20 picomoles, to determine the primary structures of proteins and to define the influence of SH groups and disulfide bonds on the structures and functional, enzymatic, medical, nutritional, pharmacological, and toxic properties of proteins isolated from plant, microbial, marine, animal, and human sources. Pyridylethylation has been accepted as the best method for the modification of Cys residues in proteins for subsequent analysis and sequence determination. The reaction has also been proposed to measure D-Cys, homocysteine, glutathione, tryptophan, dehydroalanine, and furanthiol food flavors. This integrated overview of the diverse literature on these reactions emphasizes general concepts. It is intended to serve as a resource and guide for further progress based on the reported application of pyridylethylation reactions to more than 150 proteins.