Interrelationships between cadmium, zinc and antioxidants in the liver of the rat exposed orally to relatively high doses of cadmium and zinc

Pancreatic Antioxidative Defense and Heat Shock Proteins Prevent Islet of Langerhans Cell Death After Chronic Oral Exposure to Cadmium LOAEL Dose

Cadmium, a hazardous environmental contaminant, is associated with metabolic disease development. The dose with the lowest observable adverse effect level (LOAEL) has not been studied, focusing on its effect on the pancreas. We aimed to evaluate the pancreatic redox balance and heat shock protein (HSP) expression in islets of Langerhans of male Wistar rats chronically exposed to Cd LOAEL doses, linked to their survival. Male Wistar rats were separated into control and cadmium groups (drinking water with 32.5 ppm CdCl2). At 2, 3, and 4 months, glucose, insulin, and cadmium were measured in serum; cadmium and insulin were quantified in isolated islets of Langerhans; and redox balance was analyzed in the pancreas. Immunoreactivity analysis of p-HSF1, HSP70, HSP90, caspase 3 and 9, and cell survival was performed. The results showed that cadmium exposure causes a serum increase and accumulation of the metal in the pancreas and islets of Langerhans, hyperglycemia, and hyperinsulinemia, associated with high insulin production. Cd-exposed groups presented high levels of reactive oxygen species and lipid peroxidation. An augment in MT and GSH concentrations with the increased enzymatic activity of the glutathione system, catalase, and superoxide dismutase maintained a favorable redox environment. Additionally, islets of Langerhans showed a high immunoreactivity of HSPs and minimal immunoreactivity to caspase associated with a high survival rate of Langerhans islet cells. In conclusion, antioxidative and HSP pancreatic defense avoids cell death associated with Cd accumulation in chronic conditions; however, this could provoke oversynthesis and insulin release, which is a sign of insulin resistance.

Impact of cow, buffalo, goat or camel milk consumption on oxidative stress, inflammation and immune response post weaning time

Milk is a whitish liquid that is secreted from mammary glands; and considered as the primary source of nutrition for newborns since they are not able to digest solid food. However, it contains primary nutrients, as well as growth and immune factors. Early weaning is a critical issue that face women and their babies in developing countries. To avoid infant malnutrition, they tend to use other milk types instead of baby formula. Therefore, the present study aimed to evaluate the impact of cow, buffalo, goat or camel milk consumption on oxidative stress, inflammation and immune response in male and female Sprague Dawley rats post weaning time. The amino acids, fatty acids, minerals and vitamins in the tested milk types were evaluated. Animals were divided into 5 groups (control, cow, buffalo, goat and camel milk administrated groups) (10 rats/group); each animal was administrated by 3.4 ml/day. Rats were administered with milk for 6 weeks; at the end of the 5th week, five animals of each group were isolated and the remaining five animals were immunized with sheep red blood cells (SRBCs) and kept for another week to mount immune response. The effect of different milk types on rats' immune response towards SRBCs was evaluated through pro-inflammatory cytokines, antioxidants, ESR and CRP measurement; together, with the histopathological examination of spleen samples and hemagglutination assay. Camel milk consumption reduced oxidative stress and inflammation in spleen that resulted from SRBCs immunization; in addition to, B cell stimulation that was apparent from the high level of anti-SRBCs antibodies. Camel milk is recommended for newborn consumption, due to its high-water content, unsaturated fatty acids, and vitamin C, as well as low lactose and fat content.

Pancreas-Liver-Adipose Axis: Target of Environmental Cadmium Exposure Linked to Metabolic Diseases

Cadmium has been well recognized as a critical toxic agent in acute and chronic poisoning cases in occupational and nonoccupational settings and environmental exposure situations. Cadmium is released into the environment after natural and anthropogenic activities, particularly in contaminated and industrial areas, causing food pollution. In the body, cadmium has no biological activity, but it accumulates primarily in the liver and kidney, which are considered the main targets of its toxicity, through oxidative stress and inflammation. However, in the last few years, this metal has been linked to metabolic diseases. The pancreas-liver-adipose axis is largely affected by cadmium accumulation. Therefore, this review aims to collect bibliographic information that establishes the basis for understanding the molecular and cellular mechanisms linked to cadmium with carbohydrate, lipids, and endocrine impairments that contribute to developing insulin resistance, metabolic syndrome, prediabetes, and diabetes.

Cadmium-Zinc Interaction in Mus musculus Fibroblasts

This work aimed to evaluate the effects of zinc (Zn) relating to cadmium (Cd)-induced toxicity and the role played by MTF-1. This transcription factor regulates the expression of genes encoding metallothioneins (MTs), some Zn transporters and the heavy chain of γ-glutamylcysteine synthetase. For this reason, two cell lines of mouse fibroblasts were used: a wild-type strain and a knockout strain to study the effects. Cells were exposed to complete medium containing: (1) 50 μM ZnSO₄ (Zn), (2) 1 μM CdCl₂ (Cd 1), (3) 2 μM CdCl₂ (Cd 2), (4) 50 μM ZnSO₄ + 1 μM CdCl₂ (ZnCd 1) and (5) 50 μM ZnSO₄ + 2 μM CdCl₂ (ZnCd 2) for 4, 18 and 24 h. Following exposure, cell viability, the intracellular content of metals, glutathione (GSH) and MT and the gene expression of the two isoforms of MT was evaluated. The results obtained suggest that a lower Cd content in the co-treatments is responsible for the protection offered by Zn due to the probable competition for a common transporter. Furthermore, Zn determines an increase in GSH in co-treatments compared to treatments with Cd alone. Finally, the MTF-1 factor is essential for the expression of MT-1 but not of MT-2 nor probably for the heavy chain of γ-glutamylcysteine synthetase.

GSH and Zinc Supplementation Attenuate Cadmium-Induced Cellular Stress and Stimulation of Choline Uptake in Cultured Neonatal Rat Choroid Plexus Epithelia

Choroid plexus (CP) sequesters cadmium and other metals, protecting the brain from these neurotoxins. These metals can induce cellular stress and modulate homeostatic functions of CP, such as solute transport. We previously showed in primary cultured neonatal rat CP epithelial cells (CPECs) that cadmium induced cellular stress and stimulated choline uptake at the apical membrane, which interfaces with cerebrospinal fluid in situ. Here, in CPECs, we characterized the roles of glutathione (GSH) and Zinc supplementation in the adaptive stress response to cadmium. Cadmium increased GSH and decreased the reduced GSH-to-oxidized GSH (GSSG) ratio. Heat shock protein-70 (Hsp70), heme oxygenase (HO-1), and metallothionein (Mt-1) were induced along with the catalytic and modifier subunits of glutamate cysteine ligase (GCL), the rate-limiting enzyme in GSH synthesis. Inhibition of GCL by l-buthionine sulfoximine (BSO) enhanced stress protein induction and stimulation of choline uptake by cadmium. Zinc alone did not induce Hsp70, HO-1, or GCL subunits, or modulate choline uptake. Zinc supplementation during cadmium exposure attenuated stress protein induction and stimulation of choline uptake; this effect persisted despite inhibition of GSH synthesis. These data indicated up-regulation of GSH synthesis promotes adaptation to cadmium-induced cellular stress in CP, but Zinc may confer cytoprotection independent of GSH.

Effects of dietary cadmium supplementation on production performance, cadmium residue in eggs, and hepatic damage in laying hens

This study was conducted to investigate the adverse effects of cadmium (Cd) on the production performance, serum biochemistry, liver antioxidant status, histopathology, and egg residue in laying hens. A total of 72 healthy Hy-Line brown laying hens at 40-week-old were randomly assigned to four diets containing 0 (control diet), 15, 30, or 60 mg/kg Cd for 6 weeks. Laying hens exposed to 60 mg/kg Cd had lower egg production rate and worse feed to egg ratio (P < 0.05). Dietary Cd exposure (≥ 15 mg/kg) significantly decreased hepatic glutathione peroxide (GPX) activities, while increasing malondialdehyde (MDA) (P < 0.05). Hepatic histopathology and ultrastructure also showed damage and the symptoms were exacerbated in a dose-dependent manner. The residue of Cd in the yolk was increased with increasing dietary Cd concentration. The mRNA expression levels of mt4L, mt3, sod1, sod2, gpx1, gpx3, and gpx4 in the liver of laying hens exposed to 60 mg Cd/kg feed were significantly decreased (P < 0.05). In conclusion, dietary Cd exposure at ≥ 15 mg/kg induced hepatic damage in laying hens, indicating that the content of Cd in feed must be critically controlled.

The impact of polar fraction of the fine particulate matter on redox responses in different rat tissues

Particulate matter (PM) contains different chemical substances that have been associated with health effects and an increased risk of mortality due to their toxicity. In this study, fine particulate matter (PM_2.5) samples were collected in a region with rural characteristics (Seropédica (Se)) and another with some industries (Duque de Caxias (DC)) (Brazil, RJ). Rats were exposed to PM_2.5 extracts daily for 25 days at different dilutions: 10×, 5×, and a concentrated solution (CS). Biochemical analyses were investigated for total antioxidant capacity (ACAP), lipid peroxidation (LPO) levels, reduced glutathione (GSH) concentration, activity of glutamate cysteine ligase (GCL), and activity of glutathione S-transferase (GST). The liver showed a significant increase in GCL (DC-5×, DC-CS and Se-CS) and GST activities (DC-CS and Se-CS) in both regions when compared to the control group. In the renal cortex, GCL activity decreased in most of the tested groups while GST activity increased only in the 5× groups of both regions (DC and Se). In the renal medulla, GCL activity decreased for Se-10× and DC-CS but increased for Se-5×, and GST activity increased in the Se-10×, DC-5×, and DC-CS groups. Lung GCL increased in all groups for both regions. Moreover, this organ also showed an increase in GST activity when higher metal concentrations were present (5× and CS). TBARS levels were increased for all tissues in most tested concentrations. These data indicate that soluble compounds (e.g., metals) from PM_2.5 sampled in areas with different pollution indexes can change the redox status and cause damage to different tissues.

Cadmium overload modulates piroxicam-regulated oxidative damage and apoptotic pathways

Cadmium (Cd) is a common environmental pollutant that threatens humans' and animals' health. Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used drugs due to their wide therapeutic action; however, they have significant side effects. Since, under many circumstances, humans and animals may be co-exposed to Cd and NSAIDs, the current investigation was assigned to explore the intertwining relationship between Cd and NSAIDs. Four groups of male Wister rats were used: control group: rats received saline; Cd group: rats received cadmium (Cd, 2 mg/kg) orally; Px group: rats received a NSAID (piroxicam, Px, 7 mg/kg, i.p.); and Cd+Px group: rats received both Cd+Px. All treatments were given once a day for 28 consecutive days. Then, blood samples, stomach, liver, and kidney tissues were collected. The results indicated that Px provoked gastric ulcer indicated by high ulcer index, while Cd had no effect on the gastric mucosa. In addition, treatment with Cd or Px alone significantly induced liver and kidney injuries indicated by serum elevations of AST, ALT, ALP, ALB, total protein, creatinine, and urea along with histopathological alterations. Significant increases in malondialdehyde and reduction in GSH and CAT contents were reported along with up-regulated expression of Bax and Bcl-2 after Cd or Px exposure. However, when Cd and Px were given in a combination, Cd obviously potentiated the Px-inflicted cellular injury and death in the liver and kidney but not in the stomach when compared to their individual exposure. This study concluded that oxidative stress mechanisms were supposed to be the main modulator in promoting Cd and Px toxicities when given in combination.

Selenium and zinc protections against metal-(loids)-induced toxicity and disease manifestations: A review

Metals are ubiquitous in the environment due to huge industrial applications in the form of different chemicals and from extensive mining activities. The frequent exposures to metals and metalloids are crucial for the human health. Trace metals are beneficial for health whereas non-essential metals are dangerous for the health and some are proven etiological factors for diseases including cancers and neurological disorders. The interactions of essential trace metals such as selenium (Se) and zinc (Zn) with non-essential metals viz. lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg) in biological system are very critical and complex. A huge number of studies report the protective role of Se and Zn against metal toxicity, both in animal and cellular levels, and also explain the numerous mechanisms involved. However, it has been considered that a tiny dyshomeostasis in the metals/trace metals status in biological system could induce severe deleterious effects that can manifest to numerous diseases. Thus, in this particular review, we have demonstrated the critical protection mechanism/s of Se and Zn against Cd, Pb, As and Hg toxicity in a one by one manner to clarify the up-to-date findings and perspectives. Furthermore, biomolecular consequences are comprehensively presented in light of particular cellular/biomolecular events which are somehow linked to a subsequent disease. The analyzed reports support significant protection potential of Se and Zn, either alone or in combination with other agents, against each of the abovementioned non-essential metals. However, Se and Zn are still not being used as detoxifying agents due to some unexplained reasons. We hypothesized that Se could be a potential candidate for detoxifying As and Hg regardless of their chemical speciations, but requires intensive clinical trials. However, particularly Zn-Hg interaction warrants more investigations both in animal and cellular level.

Grape skin extract mitigates tissue degeneration, genotoxicity, and oxidative status in multiple organs of rats exposed to cadmium

The aim of this study was to investigate whether grape skin extract can mitigate the noxious activities induced by cadmium exposure in multiple organs of rats. For this purpose, histopathological analysis for the liver, genotoxicity, and oxidative status in the blood and liver were investigated in this setting. A total of 20 Wistar rats weighing 250 g, on average, and 8 weeks of age were distributed into four groups (n=5) as follows: control group (nontreated group); cadmium group (Cd); and grape skin extract groups (Cd+GS) at 175 or 350 mg/l. Histopathological analysis in liver showed that animals treated with grape skin extract showed improved tissue degeneration induced by cadmium intoxication. Genetic damage was reduced in blood and hepatocytes as indicated by comet and micronucleus assays in animals treated with grape skin extract. Copper-zinc superoxide dismutase and cytochrome c gene expression increased in groups treated with grape skin extract in liver cells. Grape skin extract also reduced the 8-hydroxy-2'-deoxyguanosine levels in liver cells compared with the cadmium group. Taken together, our results indicate that grape skin extract can mitigate tissue degeneration, genotoxicity, and oxidative stress induced by cadmium exposure in multiple organs of Wistar rats.

Effects of Nano-zinc on Biochemical Parameters in Cadmium-Exposed Rats

Cadmium (Cd) is a toxic environmental and occupational pollutant with reported toxic effects on the kidneys, liver, lungs, bones, and the immunity system. Based on its physicochemical similarity to cadmium, zinc (Zn) shows protective effects against cadmium toxicity and cadmium accumulation in the body. Nano-zinc and nano-zinc oxide (ZnO), recently used in foods and pharmaceutical products, can release a great amount of Zn²⁺ in their environment. This research was carried out to investigate the more potent properties of the metal zinc among sub-acute cadmium intoxicated rats. Seventy-five male Wistar rats were caged in 15 groups. Cadmium chloride (CdCl₂) was used in drinking water to induce cadmium toxicity. Different sizes (15, 20, and 30 nm) and doses of nano-zinc particles (3, 10, 100 mg/kg body weight [bw]) were administered solely and simultaneously with CdCl₂ (2-5 mg/kg bw) for 28 days. The experimental animals were decapitated, and the biochemical biomarkers (enzymatic and non-enzymatic) were determined in their serum after oral exposure to nano-zinc and cadmium. Statistical analysis was carried out with a one-way ANOVA and t test. P < 0.05 was considered as statistically significant. The haematocrit (HCT) significantly increased and blood coagulation time significantly reduced in the nano-zinc-treated rats. AST, ALT, triglyceride, total cholesterol, LDL, and free fatty acids increased significantly in the cadmium- and nano-zinc-treated rats compared with the controls. However, albumin, total protein, and HDLc significantly decreased in the cadmium- and nano-zinc-treated rats compared with the controls (P < 0.05). It seems that in the oral administration of nano-zinc, the smaller sizes with low doses and the larger sizes with high doses are more toxic than metallic zinc. In a few cases, an inverse dose-dependent relationship was seen as well. This research showed that in spite of larger sizes of zinc, smaller sizes of nano-zinc particles are not suitable for protection against cadmium intoxication.

Gastroprotective and Ulcer Healing Effects of Camel Milk and Urine in HCl/EtOH, Non-steroidal Anti-inflammatory Drugs (Indomethacin), and Water-Restraint Stress-induced Ulcer in Rats

Background:

Camel milk has been reportedly used to treat dropsy, jaundice, tuberculosis, and diabetes while camel urine is used to treat diarrhea and cancer. However, there is no scientific evidence on the antiulcer activity of camel milk and urine. Thus, the present is designed to investigate the gastroprotective and ulcer healing effect of camel milk and urine on experimentally induced gastric ulcer models in rats.

Materials and Methods:

The gastroprotective effect was investigated in HCl/EtOH, water-restraint stress (WRS) and non-steroidal anti-inflammatory drugs (indomethacin)-induced ulcer models while ulcer healing activity was investigated in indomethacin-induced ulcer model. Cimetidine (100 mg/kg) was used as a standard antiulcer drug.

Results:

Acute toxicity study done up to a dosage of 10 ml/kg of camel milk and urine showed no signs of toxicity and mortality among the rats, indicating the present dosage of 5 ml/kg is safe to be administered to the rats. In the HCl/EtOH model, oral administration of cimetidine (100 mg/kg), camel urine (5 ml/kg), and camel milk (5 ml/kg) significantly (P < 0.05) inhibited gastric lesions by 83.7, 60.5 and 100%, respectively. In the WRS-induced model, cimetidine, and camel urine showed an ulcer inhibition of 100% while camel milk showed an inhibition of 50%. Similarly, in the indomethacin-induced ulcer model, cimetidine, camel milk, and urine showed an ulcer inhibition of 100, 33.3, and 66.7%, respectively. In addition, camel milk and urine also showed a significant (P < 0.05) ulcer healing effect of 100% in indomethacin-induced ulcer model, with no ulcers observed as compared to that of cimetidine, which offers a healing effect of 60.5%.

Conclusion:

The antiulcer activity of camel milk and urine may be attributed to its cytoprotective mechanism and antioxidant properties.

SUMMARY

Acute toxicity findings revealed the dosage of 10 ml/kg of camel milk and urine seems no toxic and indicating the dosage of 5 ml/kg is safe to be administered to the rats

Oral administration of cimetidine (100 mg/kg), camel urine (5 ml/kg), and camel milk (5 ml/kg) significantly inhibited gastric lesions by 83.7, 60.5 and 100% in the HCl/EtOH experimental model

The results of this investigation have proven that camel milk and urine showed strong ulcer healing effect in indomethacin-induced gastric damage.

Abbreviations used: NSAIDs: Non-steroidal anti-inflammatory drugs, UI: Ulcer index, ANOVA: One-way analysis of variance, WRS: Water-restraint stress, ROS: Reactive oxygen species

Can zinc supplementation ameliorate cadmium-induced alterations in the bioelement content in rabbits?

The study was designed to investigate the influence of zinc (Zn) supplementation on cadmium-induced alterations in zinc, copper (Cu), and magnesium (Mg) status in rabbits. For this purpose, the concentrations of cadmium (Cd), Zn, Cu, and Mg were estimated in the blood, liver, kidney, and bone. The rabbits were divided in a control group, a Cd group-animals intoxicated orally with Cd (10 mg kg-1 bw, as aqueous solution of Cd-chloride), and a Cd+Zn group-animals intoxicated with the same dose of Cd and co-treated with Zn (20 mg kg-1 bw, as aqueous solution of Zn-sulphate). Solutions were administered orally, every day for 28 days. Sample mineralisation was performed with concentrated nitric acid (HNO3) and perchloric acid (HClO4) (4:1) and metal concentrations were determined by atomic absorption spectrophotometry (AAS). Zinc supplementation improved some of Cd-induced disturbances in bioelement levels in the investigated tissues. Beneficial effects of Zn on Zn and Cu levels were observed in blood, as well as on the Cu kidney level. The calculated values for Cu/Zn, Mg/Zn, and Mg/Cu ratios in blood suggest that Zn co-treatment reduces Cd-induced changes in bioelement ratios in blood.

Purple carrot extract protects against cadmium intoxication in multiple organs of rats: Genotoxicity, oxidative stress and tissue morphology analyses

The aim of this study was to investigate if purple carrot extract is able to protect against the noxious activities induced by cadmium exposure in multiple organs of rats. For this purpose, histopathological analysis, genotoxicity and oxidative status were investigated in this setting. A total of twenty Wistar rats weighing 250g on the average, and 8 weeks age were distributed into four groups (n=5), as follows: Control group (non-treated group, CTRL); Cadmium group (Cd) and Purple carrot extract groups at 400mg/L or 800mg/L. Histopathological analysis revealed that liver from animals treated with purple carrot extract improved tissue degeneration induced by cadmium intoxication. Genetic damage was reduced in blood and hepatocytes as depicted by comet and micronucleus assays in animals treated with purple carrot extract. SOD-CuZn and cytocrome C gene expression increased in groups treated with purple carrot extract. Purple carrot extract also reduced the 8OHdG levels in liver cells when compared to cadmium group. Taken together, our results demonstrate that purple carrot extract is able to protect against cadmium intoxication by means of reducing tissue regeneration, genotoxicity and oxidative stress in multiple organs of Wistar rats.

Insight into the oxidative stress induced by lead and/or cadmium in blood, liver and kidneys

Besides being important occupational hazards, lead and cadmium are nowadays metals of great environmental concern. Both metals, without any physiological functions, can induce serious adverse health effects in various organs and tissues. Although Pb and Cd are non-redox metals, one of the important mechanisms underlying their toxicity is oxidative stress induction as a result of the generation of reactive species and/or depletion of the antioxidant defense system. Considering that the co-exposure to both metals is a much more realistic scenario, the effects of these metals on oxidative status when simultaneously present in the organism have become one of the contemporary issues in toxicology. This paper reviews short and long term studies conducted on Pb or Cd-induced oxidative stress in blood, liver and kidneys as the most prominent target organs of the toxicity of these metals and proposes the possible molecular mechanisms of the observed effects. The review is also focused on the results obtained for the effects of the combined treatment with Pb and Cd on oxidative status in target organs and on the mechanisms of their possible interactions.

Antimutagenic and antigenotoxic potential of grape juice concentrate in blood and liver of rats exposed to cadmium

The aim of this study was to evaluate the antimutagenic and antigenotoxic potential of grape juice concentrate in rodent organs exposed to cadmium chloride intoxication. A total of 15 Wistar rats were distributed into three groups (n = 5), as follows: control group (CTRL; nontreated group), cadmium group (Cd), and cadmium-grape juice group (Cd + GJ). Exposed animals received intraperitoneal injection of cadmium chloride (1.2 mg/kg body weight) diluted in water and, after 15 days, Cd + GJ group received grape juice concentrate for 15 days, by gavage (0.8 mL, 1.18 mg of polyphenols kg(-1) day(-1)). Grape juice concentrate was able to decrease genotoxic effects induced by cadmium in peripheral blood and liver cells as depicted by single cell gel (comet) and micronucleus assays. A decrease for anti-8-hydroxy-20-deoxyguanosine (8OHdG) expression in hepatocytes of animals exposed to cadmium and treated with grape juice concentrate was also detected. Higher CuZn-SOD activity was observed in liver cells of the Cd + GJ group. No remarkable differences were seen regarding Mn-SOD activity among groups. Taken together, our results demonstrate that grape juice concentrate was able to exert antimutagenic and antigenotoxic activities in blood and liver cells of rats exposed to cadmium.

Camel Milk as a Potential Therapy as an Antioxidant in Autism Spectrum Disorder (ASD)

Extensive studies have demonstrated that oxidative stress plays a vital role in the pathology of several neurological diseases, including autism spectrum disorder (ASD); those studies proposed that GSH and antioxidant enzymes have a pathophysiological role in autism. Furthermore, camel milk has emerged to have potential therapeutic effects in autism. The aim of the current study was to evaluate the effect of camel milk consumption on oxidative stress biomarkers in autistic children, by measuring the plasma levels of glutathione, superoxide dismutase, and myeloperoxidase before and 2 weeks after camel milk consumption, using the ELISA technique. All measured parameters exhibited significant increase after camel milk consumption (P < 0.5). These findings suggest that camel milk could play an important role in decreasing oxidative stress by alteration of antioxidant enzymes and nonenzymatic antioxidant molecules levels, as well as the improvement of autistic behaviour as demonstrated by the improved Childhood Autism Rating Scale (CARS).

Glutathione and its dependent enzymes' modulatory responses to toxic metals and metalloids in fish--a review

Toxic metals and metalloid are being rapidly added from multiple pathways to aquatic ecosystem and causing severe threats to inhabiting fauna including fish. Being common in all the type of aquatic ecosystems such as freshwater, marine and brackish water fish are the first to get prone to toxic metals and metalloids. In addition to a number of physiological/biochemical alterations, toxic metals and metalloids cause enhanced generation of varied reactive oxygen species (ROS) ultimately leading to a situation called oxidative stress. However, as an important component of antioxidant defence system in fish, the tripeptide glutathione (GSH) directly or indirectly regulates the scavenging of ROS and their reaction products. Additionally, several other GSH-associated enzymes such as GSH reductase (GR, EC 1.6.4.2), GSH peroxidase (EC 1.11.1.9), and GSH sulfotransferase (glutathione-S-transferase (GST), EC 2.5.1.18) cumulatively protect fish against ROS and their reaction products accrued anomalies under toxic metals and metalloids stress conditions. The current review highlights recent research findings on the modulation of GSH, its redox couple (reduced glutathione/oxidised glutathione), and other GSH-related enzymes (GR, glutathione peroxidase, GST) involved in the detoxification of harmful ROS and their reaction products in toxic metals and metalloids-exposed fish.

Effects of heavy metals on the expression of a zinc-inducible metallothionein-III gene and antioxidant enzyme activities in Crassostrea gigas

Sequestration by metallothioneins and antioxidant defense are two kinds of important defense mechanisms employed by mollusks to minimize adverse effects caused by heavy metal contaminants in marine environment. In the present study, a novel metallothionein gene, CgMT-III, was cloned from Crassostrea gigas, consisting of eighteen conserved cysteine residues and encoding a MT III-like protein with two tandem β domains. The expression level of CgMT-III transcript induced by zinc was much higher than that induced by cadmium exposure. It suggested that CgMT-III was perhaps mainly involved in homeostatic control of zinc metabolism, which was distinct from previously identified MTs in C. gigas. Among the tested antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), SOD and GPx showed varying up-regulations in a tissue-specific manner, while CAT activities were inhibited in both gill and hepatopancreas from C. gigas exposed to heavy metals. It can be inferred that CgMT-III was mainly involved in zinc homeostasis, and CgMT-III gene together with CAT enzyme could be potential biomarkers to indicate heavy metal, especially zinc pollution in marine organisms.