Hepatic lipid peroxidation, sulfhydryl status, and toxicity of the blue-green algal toxin microcystin-LR in mice

Protective Effect of Opuntia dillenii Haw Fruit against Lead Acetate-Induced Hepatotoxicity: In Vitro and In Vivo Studies

Lead is one of the most common environmental contaminants in the Earth's crust, which induces a wide range of humans biochemical changes. Previous studies showed that Opuntia dillenii (OD) fruit possesses several antioxidant and anti-inflammatory properties. The present study evaluates OD fruit hydroalcoholic extract (OHAE) hepatoprotective effects against lead acetate- (Pb-) induced toxicity in both animal and cellular models. Male rats were grouped as follows: control, Pb (25 mg/kg/d i.p.), and groups 3 and 4 received OHAE at 100 and 200 mg/kg/d + Pb (25 mg/kg/d i.p.), for ten days of the experiment. Thereafter, we evaluated the levels of alkaline phosphatase (ALP), alanine aminotransferase (ALT), and aspartate aminotransferase (AST), catalase (CAT) activity and malondialdehyde (MDA) in serum, and liver histopathology. Additionally, the cell study was also done using the HepG2 cell line for measuring the direct effects of the extract on cell viability, oxidative stress MDA, and glutathione (GSH) and inflammation tumor necrosis factor-α (TNF-α) following the Pb-induced cytotoxicity. Pb significantly increased the serum levels of ALT, AST, ALP, and MDA and liver histopathological scores but notably decreased CAT activity compared to the control group (p < 0.001 for all cases). OHAE (100 and 200 mg/kg) significantly reduced the levels of serum liver enzyme activities and MDA as well as histopathological scores while it significantly increased CAT activity compared to the Pb group (p < 0.001-0.05 for all cases). OHAE (20, 40, and 80 μg/ml) concentration dependently and significantly reduced the levels of MDA and TNF-α, while it increased the levels of GSH and cell viability in comparison to the Pb group (p < 0.001-0.05 for all cases). These data suggest that OHAE may have hepatoprotective effects against Pb-induced liver toxicity both in vitro and in vivo by its antioxidant and anti-inflammatory activities.

Potential protective effects of the edible alga Arthrospira platensis against lead-induced oxidative stress, anemia, kidney injury, and histopathological changes in adult rats

Oxidative damage has been proposed as a possible mechanism involved in lead toxicity. This study investigated the possible protective effect of dietary Arthrospira platensis supplementation against lead acetate-induced kidney injury in adult male rats. Rats were divided into 4 groups: normal rats (control rats), rats treated with spirulina, rats treated with lead (Pb) (0.344 g/kg body weight), and rats treated with Pb and spirulina. The exposure of rats to Pb for 30 days provoked renal damage with significant increases in hematological parameters, oxidative stress-related parameters (i.e., thiobarbituric acid reactive substances, protein carbonyl content, advanced oxidation protein products, and hydrogen peroxide), creatinine and urea levels in plasma, and uric acid level in urine. Conversely, antioxidant enzyme activities (i.e., catalase, glutathione peroxidase, and superoxide dismutase) and levels of nonprotein thiols, plasma uric acid, and urinary creatinine and urea decreased. The administration of spirulina to Pb-treated rats significantly improved weight, peripheral blood parameters, oxidative stress-related parameters, renal biomarker levels, and antioxidant enzyme activities. Also, rats treated with Pb and spirulina had normal kidney histology. These healing effects are likely the result of the high phenol content and significant antioxidant capacity of A. platensis. Our data strongly suggest that spirulina supplementation improves kidney function and plays an important role in the prevention of complications of Pb intoxication.

Hepatic Gene Expression Changes in Mice Associated with Prolonged Sublethal Microcystin Exposure

Microcystin-LR (MCLR) is an acute hepatotoxicant and suspected carcinogen. Previous chronic studies have individually described hepatic morphologic changes, or alterations in the cytoskeleton, cell signaling or redox pathways. The objective of this study was to characterize chronic effects of MCLR in wild-type mice utilizing gene array analysis, morphology, and plasma chemistries. MCLR was given daily for up to 28 days. RNA from the 28-day study was hybridized onto mouse genechip arrays. RNA from 4 hours, 24 hours, 4 days, 1 day, and 28 days for selected genes was processed for quantitative-PCR. Increases in plasma hepatic enzyme activities and decreases in total protein, albumin and glucose concentrations were identified in MCLR-treated groups at 14 and 28 days. Histologically, marked hepatokaryomegaly was identified in the 14-day MCLR group with the addition of giant cells at 28 days. Major gene transcript changes were identified in the actin organization, cell cycle, apoptotic, cellular redox, cell signaling, albumin metabolism, and glucose homeostasis pathways, and the organic anion transport polypeptide system. Using toxicogenomics, we have identified key molecular pathways involved in chronic sublethal MCLR exposure in wild-type mice, genes participating in those critical pathways and related them to cellular and morphologic alterations seen in this and other studies.

Effect of cyanobacteria on immune function of crucian carp (Carassius auratus) via chronic exposure in diet

Cyanobacterial blooms caused by water eutrophication have become a worldwide problem. Microcystins (MCs) released during cyanobacterial blooms exert toxicity on fish. Up to now, immunotoxicity of MCs on fish has been rarely reported. The present study investigated immune response of crucian carp (Carassius auratus) to cyanobacteria via chronic exposure in diet. Fish were fed with diets containing 20% (low dose group) and 40% (high dose group) of cyanobacteria lyophilized powder. After exposure of 30 d, a batch of assays was determined for assessing immunotoxicity of MCs. The head kidney and spleen indexes significantly increased in high dose group. Blood nitroblue tetrazolium activity in high dose group was nearly twice as much as that in control group with no cyanobacteria additive. Marked haemorrhage and hyperemia were observed in kidney and spleen in high dose group. The edematous mitochondria, deformation of the nucleus and compaction of chromatin occurred in lymphocytes of head kidney and spleen in both cyanobacteria groups. Lysozyme activity showed an obvious increase in low dose group but a sharp decrease in high dose group. Significant increase of macrophage bactericidal activity was detected in low dose group. The present findings indicate that via chronic diet exposure of different cyanobacteria levels, fish exhibit various immune responses. Fish immunity tends to proceed toward the direction of immunostimulative response at low MCs concentrations but toward the trend of immunosuppressive answer at high MCs concentrations.

Involment of p53, Bax, and Bcl-2 pathway in microcystins-induced apoptosis in rat testis

It has been reported that microcystins (MCs) could accumulate in the gonads of mammals and MCs exposure exerts obvious toxic effects on male reproductive system of mammals. We have comfirmedthat MCs could accumulate and induce apoptosis in rat testis. The p53, Bax, and Bcl-2 protein play important roles in mitochondria-dependent apoptotic pathway, and this study aimed to investigate whether the p53, Bax, and Bcl-2 pathway is involved in microcystins-induced apoptosis in rat testis and discussed the possible mechanisms. Our results show that MCs led to persistent increase of transcriptional and protein level of P53 and Bax expression but led to decrease of Bcl-2 expression, resulting in an increased ratio of Bax to Bcl-2, which might contribute to apoptotic cell death of rat testis following MCs treatment. The increased ratio of expression of Bax to that of Bcl-2 induced by MCs suggests their important role in MCs-induced apoptosis in rat testis tissue.

Protective role of erdosteine on vancomycin-induced oxidative stress in rat liver

Drug-induced liver toxicity is a common cause of liver injury. This study was designed to elucidate whether high dose vancomycin (VCM) induces oxidative stress in liver and to investigate the protective effects of erdosteine, an expectorant agent. Twenty-two young Wistar rats were divided into three groups as follows: control group, VCM, and VCM plus erdosteine. VCM was administered intraperitoneally in the dosage of 200 mg/kg twice daily for 7 days. Erdosteine was administered orally administered once a day at a dose of 10 mg/kg body weight. The activities of antioxidant enzymes such as superoxide dismutase and catalase as well as the concentration of malondialdehyde, as an indicator of lipid peroxidation, were measured to evaluate oxidative stress in homogenates of the liver. VCM administration increased malondialdehyde levels (p < 0.001), superoxide dismutase (p < 0.01) and catalase (p < 0.001) activities. Erdosteine co-administration with VCM injections caused significantly decreased malondialdehyde levels (p < 0.001), superoxide dismutase (p < 0.01) and catalase (p < 0.001) activities in liver tissue when compared with VCM alone. It can be concluded that erdosteine may prevent VCM-induced oxidative changes in liver by reducing reactive oxygen species.

Damage of cell membrane and antioxidative system in human erythrocytes incubated with microcystin-LR in vitro

The effect of the exposure of human erythrocytes to different concentrations of microcystin-LR were studied. Lipid peroxidation, membrane fluidity, cell morphology, haemoglobin oxidation and changes in the activity of antioxidant enzymes were investigated. Human erythrocytes were incubated with microcystin-LR at concentrations of 1-1000 nM for 1, 6, 12 and 24 h. We observed that microcystin-LR induces a significant increase of the level of thiobarbituric acid reactive substances (TBARS), formation of echinocytes, haemolysis, conversion of oxyhaemoglobin to methaemoglobin, decrease of membrane fluidity on the level of 16 carbon atom fat acids. The compound also changed antioxidative enzymes activities: catalase, superoxide dismutase and glutathione reductase and formation of reactive oxygen species (ROS). All of the observed changes point out that 100 nM of Microcistin LR is the liminal (threshold) toxic dose for human erythrocytes. This dose caused most of the described changes. Observed damages of erythrocytes membrane and antioxidative enzymes may be the result of direct covalent binding of microcystin-LR with -SH residues of proteins and indirectly be related with reactive oxygen species formation.

Induction of Apoptosis in Mouse Liver by Microcystin-LR

Microcystins (MCs) are a family of cyclic heptapeptide hepatotoxins produced by freshwater species of cyanobacteria that have been implicated in the development of liver cancer, necrosis, and even deadly intrahepatic bleeding. MC-LR, the most toxic MC variant, is also the most commonly encountered in a contaminated aquatic system. This study presents the first data in the toxicological research of MCs that combines the use of standard apoptotic assays with transcriptomics, proteomic technologies, and computer simulations. By using histochemistry, DNA fragmentation assays, and flow cytometry analysis, we determined that MC-LR causes rapid, dose-dependent apoptosis in mouse liver when BALB/c mice are treated with MC-LR for 24 h at doses of either 50, 60, or 70 microg/kg of body weight. We then used gene expression profiling to demonstrate differential expressions (>2-fold) of 61 apoptosis-related genes in cells treated with MC-LR. Further proteomic analysis identified a total of 383 proteins of which 35 proteins were up-regulated and 30 proteins were down-regulated more than 2.5-fold when compared with controls. Combining computer simulations with the transcriptomic and proteomic data, we found that low doses (50 microg/kg) of MC-LR lead to apoptosis primarily through the BID-BAX-BCL-2 pathway, whereas high doses of MC-LR (70 microg/kg) caused apoptosis via a reactive oxygen species pathway. These results indicated that MC-LR exposure can cause apoptosis in mouse liver and revealed two independent pathways playing a major regulatory role in MC-LR-induced apoptosis, thereby contributing to a better understanding of the hepatotoxicity and the tumor-promoting mechanisms of MCs.

Antioxidant enzyme activity and lipid peroxidation in liver and kidney of rats exposed to microcystin-LR administered intraperitoneally

The effect of acute exposure of intraperitoneal injection of microcystin-LR (MCLR) on antioxidant enzymes and lipid peroxidation has been studied in liver and kidney of rats. Rats were treated with two doses, i.e. 100 and 150 microg of pure MCLR/kg body weight or saline solution. The enzyme activities of glutathione peroxidase (GSH-Px), glutathione reductase (GR), superoxide dismutase (SOD) and catalase (CAT) in the liver were significantly decreased in MCLR-treated rats. The decrease of GR activity in the liver was 60%, followed by GSH-Px, SOD and CAT. Similarly, a decrease in the antioxidant enzymes was found in the kidney of MCLR-treated rats, such as GSH-Px (27-31%), GR (22%), SOD (42%) and CAT (25-28%). Concomitantly, significant increases in lipid peroxidation levels were recorded in liver (121 and 196% for 100 and 150 microg/kg, respectively) and kidney (48 and 58% for 100 and 150 microg/kg, respectively) from MCLR-treated rats. In conclusion, acute exposure to MCLR results in a decrease in the antioxidant enzymes and an increase in lipid peroxidation in liver and kidney rats, suggesting the oxidative stress as an important role in the pathogenesis of MCLR-induced toxicity. Antioxidant enzymes were significantly consumed in the liver and a minor decrease was found in kidney, confirming the organ-specific effects of MCLR.

An investigation into the detoxification of microcystin-LR by the glutathione pathway in Balb/c mice

Toxin-producing cyanobacteria pose a world-wide health threat to humans and animals due to their increasing presence in both drinking and recreational waters. The predominant cyanotoxin, microcystin-LR (MCLR), targets the liver and its toxicity depends on the uptake and removal rates in the liver. The role of the glutathione detoxification pathway in protecting the liver from the effects of MCLR was investigated. Mice exposed to a single 75% LD(50) dose of pure MCLR were sacrificed at 8, 16, 24 and 32 h post-exposure (pe). Toxin induced liver damage was observed 8 and 16 h pe as evidenced by raised serum ALT and LDH levels, reduced glycogen levels and liver histology. A significant increase in lipid peroxidation was seen at 16 h pe that decreased after 24 and 32 h pe, the time-points which showed significant increases in GPX activity. An increase in soluble GST activity was noted between 8 and 16 h pe, levels of total GSH increased at 24 h while oxidised glutathione increased throughout the investigation. The increase in activity of both GPX and GST corresponded with increased transcription of these enzymes, as well as the rate-limiting enzyme in GSH synthesis, gamma-glutamyl transferase. In conclusion, this study confirms that an increase in GST activity is critical for the detoxification of MCLR, that this is regulated at the transcriptional level, and that exposure to MCLR induces the de novo synthesis of GSH. Finally, we report the involvement of GPX in the removal of MCLR-induced lipid hydroperoxides.

An investigation of the role of vitamin E in the protection of mice against microcystin toxicity

The presence of cyanobacterial toxins in drinking and recreational waters represents a potential public health risk. Microcystin-LR (MC-LR) is a potent cyclic heptapeptide hepatotoxin produced by the blue-green alga Microcystis aeruginosa. Chemoprotectant studies have indicated that membrane-active antioxidants such as vitamin E may offer protection against microcystin toxicity. This study investigated the effect of vitamin E supplementation on microcystin toxicity in mouse liver. Groups of mice were fed vitamin E supplements (8.33 or 33.3 U/mouse/day) for 4 weeks, with intraperitoneal doses of MC-LR extract (70% LD(50)) every 3 days from day 8. The potential benefits of vitamin E were evaluated based on lipid peroxidation, alanine transaminase (ALT), and glutathione S-transferase (GST) levels. Vitamin E supplementation at 33.3 U/mouse/day offered some protection against lipid peroxidation induced by repeated exposure to MC-LR extract and limited both the toxin-induced increase in ALT leakage and decrease in GST activity. Vitamin E supplementation at 66.6 U/mouse/day significantly increased the time to death and reduced the increase in liver percentage body weight induced in mice given a lethal dose challenge of MC-LR extract. Therefore, vitamin E, taken as a dietary supplement, may have a protective effect against chronic exposure to MC-LR.

Studies on oxidative damage induced by cyanobacteria extract in primary cultured rat hepatocytes

Contamination of water by cyanobacteria (blue-green algae) is a serious health problem around the world, largely due to the toxic effects of microcystins, a group of potent hepatotoxins. However, the mechanisms responsible for the cytotoxicity of microcystins have not been fully elucidated. In the present study, oxidative damage caused by lyophilized freshwater cyanobacteria extract was evaluated on primary cultured rat hepatocytes. A time- and dose-dependent increase of lactate dehydrogenase (LDH) leakage was observed in hepatocytes treated with cyanobacteria extract. Lipid peroxidation, a main manifestation of oxidative damage, was also studied and a time- and dose-dependent increase in malondiadehyde was observed. In addition, by using a fluorescent probe, 2',7'-dichlorofluorescein diacetate, it was found that cyanobacteria extract was able to enhance intracellular production of reactive oxygen species (ROS) in a dose- and time-dependent manner. Moreover, desferrioxamine, a specific iron chelator, could significantly decrease LDH leakage and ROS production caused by cyanobacteria extract treatment. These findings thus provide experimental evidence that oxidative damage is involved in cyanobacteria extract-induced hepatotoxicity. The understanding of this mechanism is believed to be beneficial to the prevention and control of the toxicity of microcystin and cyanobacteria contamination.

Evaluation of potential chemoprotectants against microcystin-LR hepatotoxicity in mice

Microcystin-LR (MCLR) is a potent cyclic heptapeptide hepatotoxin produced by the blue-green algae, Microcystis aeruginosa. Toxic blooms of this cyanobacteria have been reported throughout the temperate world. In spite of the potential economic loss and health hazard posed by this toxin, few studies on the development of an antidote have been conducted. Thus, a number of biologically active compounds were tested in mice for effectiveness in preventing the toxicity of a lethal dose of MCLR (100 micrograms kg-1). Efficacy was evaluated based upon the percentage of surviving mice, time to death and serum lactate dehydrogenase activity 45 min after treatment with the toxin. The biologically active compounds were separated into groups based upon proposed mechanisms of action. Enzyme induction by phenobarbital but not by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) resulted in partial protection against toxicity. Calcium channel blockers, free-radical scavengers and water-soluble antioxidants produced little protection against toxicity. The membrane-active antioxidants vitamin E and silymarin, as well as glutathione and the monoethyl ester of glutathione, produced significant protection from lethality. Rifampin and cyclosporin-A, both immunosuppressive and membrane-active agents, which also block the bile acid uptake system of hepatocytes, produced complete protection from the toxicity of MCLR. Thus, lipophilic antioxidants provide partial protection against MCLR toxicity while cyclosporin-A and rifampin are highly effective and potentially useful antidotes. The toxicity of MCLR may depend upon stimulation of the immune system and may be mediated by membrane alterations.

Cyclosporin A--a chemoprotectant against microcystin-LR toxicity

Microcystin-LR (MCLR) is a potent hepatotoxin that rapidly produces death in experimental animals. We have shown that cyclosporin A (CsA) can prevent the toxic and lethal effects of MCLR in mice. The LD50 of MCLR in mice is approximately 61 micrograms/kg, and 100 micrograms/kg produces death in 100% of treated mice. The minimum dose of CsA which prevented lethality in mice given 100 micrograms MCLR/kg i.p. was 10 mg/kg. This dose of CsA did not protect mice against higher doses of MCLR. Survival of all mice given 100 micrograms MCLR/kg was achieved if 10 mg CsA/kg was given 0.5-3 h prior to the MCLR but not if the CsA was co-administered or given after the MCLR. The results indicate that CsA effectively protects mice against a lethal dose of MCLR, but that the time of administration and the dose of CsA are critical determinants of the chemoprotective effects.