Protective effect of deferoxamine on chromium (VI)-induced DNA single-strand breaks, cytotoxicity, and lipid peroxidation in primary cultures of rat hepatocytes

Signaling Pathways and Genes Associated with Hexavalent Chromium-Induced Hepatotoxicity

Exposure to hexavalent chromium [Cr(VI)] causes human and animal hepatotoxicity. However, it is unclear how Cr(VI) induces hepatotoxicity, nor is it clear which pathways and genes may be involved. This study aimed to identify the key molecular pathways and genes engaged in Cr(VI)-induced hepatotoxicity. Publicly available microarray GSE19662 was downloaded from the Gene Expression Omnibus database. GSE19662 consists of primary rat hepatocyte (PRH) groups treated with or without 0.10 ppm potassium dichromate (PD), with three samples per group. Compared to the control group, a total of 400 differentially expressed genes were obtained. Specially 262 and 138 genes were up- and downregulated in PD-treated PRHs, respectively. Gene ontology (GO) enrichment indicated that those DEGs were primarily engaged in many biological processes, including androgen biosynthetic process, the positive regulation of cell death, the response to activity, the toxic substance and hepatocyte growth factor stimulus, and others. Kyoto Encyclopedia of Genes and Genomes (KEGG) suggested that the DEGs are fundamentally enriched in hepatocellular carcinoma (HCC), hepatitis B, p53, PI3K-Akt, MAPK, AMPK, metabolic pathways, estrogen, cGMP-PKG, metabolic pathways, etc. Moreover, many genes, including UBE2C, TOP2A, PRC1, CENPF, and MKI67, might contribute to Cr(VI)-induced hepatotoxicity. Taken together, this study enhances our understanding of the regulation, prevention, and treatment strategies of Cr(VI)-induced hepatotoxicity.

Improvement of Experimentally Induced Hepatic and Renal Disorders in Rats using Lactic Acid Bacteria-fermented Soybean Extract (BiofermenticsTM)

The effects of lactic acid bacteria-fermented soybean extract (Biofermentics; BF) on experimental models of hepatic and renal disorders were investigated in vivo and in vitro. In rat, hepatitis induced by feeding of deoxycholic acid (DCA, 0.5 wt/wt, n = 6) or intraperitoneal injection of d-galactosamine (GMN, 500 mg/body wt, n = 6), the increase in serum AST (aspartate aminotransferase) and ALT (alanine aminotransferase) levels were inhibited significantly (P < 0.05) by feeding a diet containing 5% dried BF. Moreover, the BF-administered rat group showed lower concentrations of blood urea nitrogen and a larger amount of urine as compared with values in the control group. Pretreatment of primary cell cultures of rat hepatic and renal cells with BF prior to exposure to dichromate (K(2)Cr(2)O(7)) resulted in a marked decrease of dichromate-induced cytotoxicity as evaluated by the leakage of lactate dehydrogenase The levels of dichromate-induced lipid peroxidation, as monitored by malondialdehyde formation, were also reduced by pretreatment of hepatocytes with BF. These results suggest that BF may play a role in hepatic and renal disorders, and may be useful for maintaining health in humans as well.

Toxicity of hepatotoxins: new insights into mechanisms and therapy

Liver injury caused by hepatotoxins, such as carbon tetrachloride (CCl4), ethanol, and acetaminophen (APAP), is characterised by varying degrees of hepatocyte degeneration and cell death via either apoptosis or necrosis. The generation of reactive intermediate metabolites from the metabolism of hepatotoxins, and the occurrence of reactive oxygen species (ROS) during the inflammatory reaction account for a variety of pathophysiologic pathways leading to cell death, such as covalent binding, disordered cytosolic calcium homeostasis, glutathione (GSH) depletion, onset of mitochondrial permeability transition (MPT) and associated lipid peroxidation. The metabolism of hepatotoxins by cytochrome P-450 enzyme subtypes is a key step of the intoxication; therefore, enzyme inhibitors are shown to minimise the hepatotoxin-associated liver damage. Understanding the function of transcription factors, such as nuclear factor kappaB (NF-kappaB) in acute liver injury, may provide some answers as to the molecular mechanisms of toxic insults. Moreover, substantial evidence exists that MPT is involved in ROS-associated hepatocellular injury and new findings offer a novel therapeutic approach to attenuate cell damage by blocking the onset of MPT. Thus, oxidant stress and lipid peroxidation are crucial elements leading to hepatotoxin-associated liver injury. In addition to specific treatment for a given hepatotoxin, the general strategy for prevention and treatment of the damage includes reducing the production of reactive metabolites of the hepatotoxins, using anti-oxidative agents, and selectively targeting therapeutics to Kupffer cells or hepatocytes for on-going processes, which play a role in mediating a second phase of the injury.

Increased repair of gamma-induced DNA double-strand breaks at lower dose-rate in CHO cells

DNA double-strand breaks (DSBs) are highly cell damaging. We asked whether for a given dose a longer irradiation time would be advantageous for the repair of DSBs. Varying the gamma-irradiation dose and its delivery time (0.05 Gy/min low dose-rate (LDR) compared with 3.5 Gy/min high dose-rate), confluent Chinese hamster ovary cells (CHO-K1) and Ku80 mutant cells (xrs-6) deficient in nonhomologous end-joining (NHEJ) were irradiated in agarose plugs at room temperature using a cesium-137 gamma-ray source. We used pulsed-field gel electrophoresis (PFGE) to measure DSBs in terms of the fraction of activity released (FAR). At LDR, one third of DSBs were repaired in CHO-K1 but not in xrs-6 cells, indicating the involvement of NHEJ in the repair of gamma-induced DSBs at a prolonged irradiation incubation time. To improve DSB measurements, we introduced in our PFGE protocol an antioxidant at the cell lysis step, thus avoiding free-radical side reactions on DNA and spurious DSBs. Addition of the metal chelator deferoxamine (DFO) decreased more efficiently the basal DSB level than did reduced glutathione (GSH), showing that measuring DSBs in the absence of DFO reduces precision and underestimates the role of NHEJ in the dose-rate effect on DSB yield.

Zinc has ambiguous effects on chromium (VI)-induced oxidative stress and apoptosis

Zinc is an important cellular antioxidant. We investigated its role in chromium-induced oxidative stress and apoptosis in human tumor cell line Hep-2. The measured parameters included intracellular labile zinc content (Zinquin-E fluorescence), cell viability (WST-1 assay), oxidative stress (spectrophotometry), mitochondrial potential (flow cytometry), caspase-3 activity, and PARP cleavage (immunofluorescence). We found that Hep-2 cells contain abundant labile zinc stores that may be depleted by the ionophore TPEN or increased by external zinc supplementation. Chromium (VI)-induced cytotoxicity and apoptosis were enhanced in zinc-depleted cells after 24 h, in particular at chromium (VI) concentrations of 50 and 150 micromol/l. On the other hand, elevated levels of labile zinc were able to protect against apoptosis induced by 10 micromol/l chromium (VI) but at higher chromium (VI) concentrations (50 and 150 micromol/l) acted synergistically, significantly enhancing oxidative stress and the course of apoptosis, possibly through oxidative stress and mitochondrial damage.

Acute toxicity of hexavalent chromium in isolated teleost hepatocytes

Acute toxic effects of hexavalent chromium [Cr(VI)], a widely recognised carcinogenic, mutagenic and redox active metal, were investigated in isolated hepatocytes of goldfish (Carassius auratus). Exposure to 250 microM Cr(VI) induced a significant decrease of cell viability from 94% in controls to 88% and 84% after 30 min and 4 h of exposure, respectively. Cr-toxicity was associated with a concentration-dependent stimulation of the formation of reactive oxygen species (ROS). As one potential source of ROS formation we identified the lysosomal Fe(2+) pool, since the ferric ion chelator deferoxamin inhibited ROS formation by approximately 15%. Lysosomal membranes remained nevertheless intact during Cr-exposure, as determined from neutral red retention in this compartment. Another significant source of ROS appear to be the mitochondria, where a presumably uncoupled increase of respiration by 20-30% was triggered by the metal. Inhibition of mitochondrial respiration by cyanide caused an approximately 40% decrease of Cr-induced ROS-formation, whereas the uncoupling agent carbonyl cyanide m-chlorophenyl hydrazine was without effect. Cellular Ca(2+) homeostasis was not disturbed by Cr(VI) and thus played no role in this scenario. Overall, our data show that Cr(VI) is acutely toxic to goldfish hepatocytes, and its toxicity is associated with the induction of radical stress, presumably involving lysosomes and mitochondria as important sources of ROS formation.

The protective role of thiola and soybean seeds against the genotoxicity induced by potassium dichromate in mice

The genotoxic potential of potassium dichromate (K(2)Cr(2)O(7)) was evaluated in vivo in mice using different mutagenic end points. Chromosomal aberrations in bone-marrow and spermatocytes as well as sperm abnormalities in the tested mice were determined. The doses used were 3, 6, 12 mg K(2)Cr(2)O(7)kg(-1) body weight which correspond to 1/16, 1/8, 1/4 the experimental LD(50), respectively. The protective roles of i.p. injection with thiola (a synthetic sulfhydryl compound) at 20 mg kg(-1) body weight and feeding treatment with soybean seeds (30% of the diet) were also studied. For chromosomal aberration analysis, subacute treatment for a period of 3 weeks were performed. All the tested doses of K(2)Cr(2)O(7) induced a statistically significant increase in the percentage of chromosomal aberrations in both somatic and germ cells with dose and time relationships. The percentage of the induced chromosomal aberrations was significantly minimized in all groups of mice i.p. treated with thiola or fed soybean seeds during the period of treatment. Potassium dichromate also induced a significant increase (P<0.01) in the percentage of abnormal sperms at the doses 6 and 12 mg kg(-1) body weight. Such percentage reached 7.52+/-0.45, 5.50+/-0.53 and 4.28+/-0.45 in mice treated with the highest tested dose of K(2)Cr(2)O(7), K(2)Cr(2)O(7) and thiola; K(2)Cr(2)O(7) and soybean, respectively compared with 2.14+/-0.33 for the control. In conclusion, the results demonstrate the genotoxic effect of potassium dichromate in mice. The results also confirm the protective role of thiola and soybean seeds against the genotoxicity of potassium dichromate.

Mechanisms of chromium toxicity, carcinogenicity and allergenicity: review of the literature from 1985 to 2000

Laboratory and clinical reports about the pathogenesis of the carcinogenicity and allergenicity of chromium compounds published between 1985 and 2000 have been reviewed as a basis for consideration of the pathogenetic mechanisms involved. There is good evidence from the clinic and the laboratory that Cr[VI] is the ion responsible for most of the toxic actions, although much of the underlying molecular damage may be due to its intracellular reduction to the even more highly reactive and short-lived chemical species Cr[III] and Cr[V]. Exposure to Cr[VI] can result in various point mutations in DNA and to chromosomal damage, as well as to oxidative changes in proteins and to adduct formation. The relative importance of these effects of chromium ions and of the free oxidising radicals they may generate in the body in causing tumours and allergic sensitisation remain to be demonstrated. Biochemical studies of the DNA-damaging effects and of the pathogenesis of the allergic reactions to chromium ions have not kept up with advances in understanding of the molecular basis of the effects of other carcinogens and allergens.

Mitochondrial involvement in cocaine-treated rat hepatocytes: effect of N-acetylcysteine and deferoxamine

The cytotoxicity of cocaine (0 - 1000 microM), was studied on parameters related to the mitochondrial role and the cascade of events that lead to apoptosis in hepatocyte cultures from phenobarbitone (PB) pretreated rats. Cytotoxicity was dose-dependent and LDH leakage was significantly enhanced above 100 microM cocaine. Apoptosis was visualized by DNA fragmentation on agarose gel, and appeared at 50 and 100 microM cocaine. Cocaine induced biphasic changes in mitochondrial transmembrane potential and significantly increased the mitochondrial release of cytochrome c, the caspase-3 like DEVDase activity and the level of 20 kDa subunit, a product of pro-caspase-3 cleavage. The protective effect of N-acetylcysteine (NAC) and deferoxamine (DFO) on all these parameters confirmed the involvement of oxygen radicals in cocaine-induced necrosis/apoptosis. We conclude: first, that the biphasic changes recorded in mitochondrial inner membrane potential by the effect of cocaine, were parallel to apoptosis; second, that caspase-3 activity and cleavage to it p20 subunit increased sharply in parallel to the translocation of cytochrome c from mitochondria to cytosol; and third, that the antioxidants, NAC or DFO exerted a noticeable protective role in counteracting the cytotoxicity of cocaine, these effects being more pronounced in the case of DFO than NAC. These findings demonstrate that cocaine cytotoxicity involves mitochondrial damage.

Effect of N-acetylcysteine and deferoxamine on endogenous antioxidant defense system gene expression in a rat hepatocyte model of cocaine cytotoxicity

In the present study we investigated on cultures of hepatocytes from phenobarbital-pretreated rats, the effect of the antioxidants, 0.5 mM N-acetylcysteine (NAC) or 1.5 mM deferoxamine (DFO), previously incubated for 24 h and coincubated with cocaine (0-1000 microM) for another 24 h. Cocaine cytotoxicity was monitored by either the lysis of the cell membranes or apoptosis. Lysis of the cell membranes was evidenced by lactate dehydrogenase leakage, apoptosis was observed by detecting a hypodiploid peak (<2C) in DNA histograms obtained by flow cytometry, peroxide production was quantified with 2', 7'-dichlorodihydrofluorescein diacetate and gene expression of the antioxidant enzymes: Mn- and Cu,Zn-superoxide dismutases, catalase and glutathione peroxidase were measured by Northern blot analysis. NAC and DFO significantly decreased the extent of lysis of cell membranes and apoptosis, and the antiapoptotic effect was parallel to peroxide generation. By the effect of NAC and DFO, significant increases were detected in the levels of mRNA of catalase, manganese superoxide dismutase and glutathione peroxidase. From these results we conclude that NAC or DFO, when incubated in the presence of cocaine, exerted a protective effect against cocaine toxicity at the level of both lysis of the membranes and apoptosis. This protective effect, in the case of NAC, was directed towards an increase in antioxidant enzyme expression, and in the case of DFO against reactive oxygen species generation.

Chromate-induced human erythrocytes haemoglobin oxidation and peroxidation: influence of vitamin E, vitamin C, salicylate, deferoxamine, and N-ethylmaleimide

In order to attenuate or to prevent chromate-induced human erythrocytes injury, the influence of vitamin E, vitamin C, salicylate, deferoxamine, and N-ethylmaleimide on chromate-induced human erythrocytes haemoglobin oxidation and peroxidation were investigated. It was observed that pretreatment of human erythrocytes with vitamin E (20 microM), vitamin C (1 mM), salicylate (3 mM), and deferoxamine (4 mM) significantly increased (P=0.0001) chromate-induced human erythrocytes haemoglobin oxidation in a time dependent manner, while it was significantly decreased (P=0.0001) by pretreatment with N-ethylmaleimide (1 mM). In contrast, pretreatment of human erythrocytes with deferoxamine (4 mM) immediately inhibited (P=0.0001) chromate-induced human erythrocytes peroxidation, while it was significantly increased (P=0.0001) by pretreatment with N-ethylmaleimide (1 mM) during the first 4 h of cells exposition to chromate. For time periods superior to 6 h pretreatment with N-ethylmaleimide (1 mM) significantly decreased (P=0.0001) chromate-induced human erythrocytes peroxidation. It was concluded that care must be taken as these drugs are used to prevent against toxicity induced by chromium(VI) compounds.

Human erythrocytes are protected against chromate-induced peroxidation

In previous studies performed in this laboratory it was realized that in a broad concentration range (0.5-8 mM) dichromate does not induced red blood cell (RBC) peroxidation. To investigate the reasons behind RBC protection against chromate-induced peroxidation, the effects of 8 mM dichromate on white ghost and RBC peroxidation, RBC antioxidant system and hemoglobin status, as well as RBC osmotic fragility and morphology, were studied in more detail. It was observed that the peroxidation level induced by dichromate on RBCs is practically negligible when compared with the peroxidation induced in white ghosts. Furthermore, the osmotic fragility of RBCs exposed to dichromate is not altered, but the cells undergo echinocytic transformation, probably due to chromate-induced structural RBC membrane modifications. The activities of catalase, gluthatione peroxidase, and superoxide dismutase of RBCs exposed to dichromate were similar to those observed in controls, but the gluthatione reductase and GSH levels were significantly reduced (P<0. 05). Concomitantly, GSSG and methemoglobin levels increased and NADH-methemoglobin reductase activity decreased. These results indicate that chromate does not induce RBC peroxidation, but does promote echinocytic shape transformation, oxidation of hemoglobin and GSH, and inhibition of gluthatione reductase and methemoglobin reductase. The enzymatic antioxidant defense system and hemoglobin oxidation are probably involved in the mechanism of RBC proctection against chromate-induced peroxidation, as is discussed.

Protective effect of diethyldithiocarbamate pretreatment on chromium (VI)-induced cytotoxicity and lipid peroxidation in primary cultures of rat hepatocytes

Pretreatment of primary cultures of rat hepatocytes with sodium diethyldithiocarbamate (DDTC) for 15 min prior to exposure to K2Cr2O7 resulted in a marked decrease in dichromate-induced cytotoxicity, as evaluated by the leakage of lactate dehydrogenase, and in lipid peroxidation, as monitored by malondialdehyde formation. In addition, pretreatment with DDTC attenuated the suppression of the level of vitamin E attributed to K2Cr2O7. However, DDTC pretreatment had no effect on the cellular levels of glutathione or vitamin C or on the activity of the glutathione reductase, glutathione peroxidase, superoxide dismutase or alkaline phosphatase suppressed by dichromate. Under the same experimental conditions, cellular uptake or distribution of chromium was not affected by DDTC. These results indicate that the protective effect of DDTC on chromium (VI)-induced cytotoxicity as well as lipid peroxidation may be associated with the level of nonenzymatic antioxidants such as vitamin E.