Influence of age on arsenic-induced oxidative stress in rat

Association of low blood arsenic exposure with level of malondialdehyde among Chinese adults aged 65 and older

High environmental arsenic exposure can increase chronic oxidative stress in experimental studies and in occupational epidemiology studies. Many regulatory agencies have put forth arsenic exposure limits, it is still unclear that whether low environmental arsenic exposure was associated with adverse health outcome in general population. This study aimed to explore the association of low blood arsenic with malondialdehyde in community-dwelling older adults. We used a cross-sectional study of 2384 older adult individuals aged ≥65 years (mean age: 85 years) from the Healthy Aging and Biomarkers Cohort Study in 2017. The median blood arsenic level was 1.41 μg/L. High oxidative stress was categorized according to the 95th percentile of MDA levels (7.47 nmol/mL). Restricted cubic spline models showed that blood arsenic levels were positively associated with malondialdehyde levels (P < 0.01); and the risk of high oxidative stress was no longer significantly increased when blood arsenic level up to 8.74 μg/L. After adjusting for potential confounders, the odds ratios of high oxidative stress for the second, third, and fourth quartiles of blood arsenic were 2.35 (1.11-4.96), 3.87 (1.90-7.91), and 4.18 (2.00-8.72) (P_trend < 0.01), compared with the first quartile. We concluded that even low arsenic exposure was associated with higher risk of oxidative stress, in a nonlinear dose-response.

Biomarkers of mercury toxicity: Past, present, and future trends

Mercury (Hg) toxicity continues to represent a global health concern. Given that human populations are mostly exposed to low chronic levels of mercurial compounds (methylmercury through fish, mercury vapor from dental amalgams, and ethylmercury from vaccines), the need for more sensitive and refined tools to assess the effects and/or susceptibility to adverse metal-mediated health risks remains. Traditional biomarkers, such as hair or blood Hg levels, are practical and provide a reliable measure of exposure, but given intra-population variability, it is difficult to establish accurate cause-effect relationships. It is therefore important to identify and validate biomarkers that are predictive of early adverse effects prior to adverse health outcomes becoming irreversible. This review describes the predominant biomarkers used by toxicologists and epidemiologists to evaluate exposure, effect and susceptibility to Hg compounds, weighing on their advantages and disadvantages. Most importantly, and in light of recent findings on the molecular mechanisms underlying Hg-mediated toxicity, potential novel biomarkers that might be predictive of toxic effect are presented, and the applicability of these parameters in risk assessment is examined.

Molecular insight of arsenic-induced carcinogenesis and its prevention

Population of India and Bangladesh and many other parts of the world are badly exposed to arsenic through drinking water. Due to non-availability of safe drinking water, they are dependent on arsenic-contaminated water. Generally, poverty level is high in those areas with lack of proper nutrition. Arsenic is considered to be an environmental contaminant and widely distributed in the environment due to its natural existence and anthropogenic applications. Contamination of arsenic in both human and animal could occur through air, soil, and other sources. Arsenic exposure mainly occurs in food materials through drinking water with high levels of arsenic in it. High levels of arsenic in groundwater have been found to be associated with various health-related problems including arsenicosis, skin lesions, cardiovascular diseases, reproductive problems, psychological, neurological, immunotoxic, and carcinogenesis. The mechanism of arsenic toxicity consists in its transformation in metaarsenite, which acylates protein sulfhydryl groups, affect on mitochondria by inhibiting succinic dehydrogenase activity and can uncouple oxidative phosphorylation with production of active oxygen species by tissues. A variety of dietary antioxidant supplements are useful to protect the carcinogenetic effects of arsenic. They play crucial role for counteracting oxidative damage and protect carcinogenesis by chelating with heavy metal moiety. Phytochemicals and chelating agents will be beneficial for combating heavy metal-induced carcinogenesis through its biopharmaceutical properties.

Prenatal Exposure to Arsenic Impairs Behavioral Flexibility and Cortical Structure in Mice

Exposure to arsenic from well water in developing countries is suspected to cause developmental neurotoxicity. Although, it has been demonstrated that exposure to sodium arsenite (NaAsO₂) suppresses neurite outgrowth of cortical neurons in vitro, it is largely unknown how developmental exposure to NaAsO₂ impairs higher brain function and affects cortical histology. Here, we investigated the effect of prenatal NaAsO₂ exposure on the behavior of mice in adulthood, and evaluated histological changes in the prelimbic cortex (PrL), which is a part of the medial prefrontal cortex that is critically involved in cognition. Drinking water with or without NaAsO₂ (85 ppm) was provided to pregnant C3H mice from gestational days 8 to 18, and offspring of both sexes were subjected to cognitive behavioral analyses at 60 weeks of age. The brains of female offspring were subsequently harvested and used for morphometrical analyses. We found that both male and female mice prenatally exposed to NaAsO₂ displayed an impaired adaptation to repetitive reversal tasks. In morphometrical analyses of Nissl- or Golgi-stained tissue sections, we found that NaAsO₂ exposure was associated with a significant increase in the number of pyramidal neurons in layers V and VI of the PrL, but not other layers of the PrL. More strikingly, prenatal NaAsO₂ exposure was associated with a significant decrease in neurite length but not dendrite spine density in all layers of the PrL. Taken together, our results indicate that prenatal exposure to NaAsO₂ leads to behavioral inflexibility in adulthood and cortical disarrangement in the PrL might contribute to this behavioral impairment.

Green tea (Camellia sinensis) alleviates arsenic-induced damages to DNA and intestinal tissues in rat and in situ intestinal loop by reinforcing antioxidant system

This study elucidates the protective role of Green tea (Camellia sinensis or CS) against arsenic-induced mutagenic DNA-breakage/intestinal (small) damages in female rats. Intestinal epithelial cells receive ingested arsenic initially. Though, the possibility of damages in this tissue is immense and the therapeutic strategies against this damage are of great concern, reports on either issue are scanty. Our earlier study on arsenic-exposed human unveils a link between carcinogenesis and mutagenic DNA damage. Here, we demonstrate that supplementation of CS-extract (10 mg/mL water) with NaAsO2 (0.6 ppm)/100 g b.w. for 28 days to rats offered a significant protection against arsenic-induced oxidative damages to DNA and intestinal (small) tissues by buttressing antioxidant systems. Necrotic and apoptotic damages and their CS-protection are shown in DNA-fragmentation, comet-assay, and histoarchitecture (hematoxylin and eosin and periodic acid-schiff staining) results. Only arsenic exposure significantly decreased intestinal superoxide dismutase, catalase activities, and level of soluble thiol with a concomitant increase in malondialdehyde/conjugated dienes. Alteration of serum necrotic marker lactate dehydrogenase and the metabolic inflammatory marker c-reactive protein also indicate the impairment may be occurring at transcription and/or cellular signal transduction level. In addition, in situ incubation in rat intestinal loop filled for 24 h with NaAsO2 alone (250 µM) or with aqueous CS-extract (250 mg/mL) suggests that small intestinal epithelial cells are significantly protected by CS against arsenic-associated necrotic/mutagenic damages, which is observed in DNA-breakage studies. In conclusion, besides intensifying endogenous antioxidant system, CS polyphenols also offer a direct role on free radical scavenging activity that is associated to the protection from mutagenic DNA-breakages and prevention of tissue necrosis/carcinogenesis generated by arsenic.

Oxidative stress-related liver dysfunction by sodium arsenite: Alleviation by Pistacia lentiscus oil

CONTEXT

Pistacia lentiscus L. (Anacardiaceae) is an evergreen shrub widely distributed throughout the Mediterranean region. Pistacia lentiscus oil (PLo) was particularly known in North African traditional medicine. Thus, people of these regions have used it externally to treat sore throats, burns and wounds, as well as they employed it internally for respiratory allergies. PLo is rich in essential fatty acids, vitamin E and polyphenols. As a very active site of metabolism, liver is reported to be susceptible to arsenic (As) intoxication.

OBJECTIVE

The present study evaluates the protective effect of PLo against sodium arsenite-induced hepatic dysfunction and oxidative stress in experimental Wistar rats.

MATERIALS AND METHODS

Twenty-eight rats were equally divided into four groups; the first served as a control, the remaining groups were respectively treated with PLo (3.3 mL/kg body weight), sodium arsenite (5.55 mg/kg body weight) and a combination of sodium arsenite and PLo. After 21 consecutive days, cellular functions were evaluated by hematological, biochemical and oxidative stress markers.

RESULTS

A significant decrease in the levels of red blood cells, haemoglobin (p ≤ 0.001), hematocrit (p ≤ 0.001), reduced glutathione and metallothionein (p ≤ 0.05) associated with a significant increase of malondialdehyde (p ≤ 0.001) were noticed in the arsenic-exposed group when compared to the control. The As-treated group also exhibited an increase in hepatic antioxidant enzymes namely superoxide dismutase, glutathione peroxidase (p ≤ 0.01) and catalase (p ≤ 0.05). However, the co-administration of PLo has relatively reduced arsenic effect.

CONCLUSION

The results showed that arsenic intoxication disturbed the liver pro-oxidant/antioxidant status. PLo co-administration mitigates arsenic-induced oxidative damage in rat.

The effect of arsenic on some antioxidant enzyme activities and lipid peroxidation in various tissues of mirror carp (Cyprinus carpio carpio)

The effect of arsenic bioaccumulation in liver, kidney, skin, muscle, and intestinal tissues of mirror carp (Cyprinus carpio carpio) was investigated on lipid peroxidation and certain antioxidant enzyme activities. In this study, three aquarium groups were formed from mirror carp: control group, 0.5-, and 1-mg/L arsenic concentrations. The fish were dissected after 1 month. Arsenic bioaccumulation, malondialdehyde (MDA) levels, catalase (CAT), and superoxide dismutase (SOD) enzyme activities were determined in the tissues. Results showed that arsenic was accumulated in liver, kidney, muscle, skin, and intestinal tissues. As the final product of lipid peroxidation, MDA levels were determined to have increased in all tissues with the exception of muscle. On the other hand, CAT and SOD enzyme activities in the fish tissues were decreased as compared to the control group. In the muscle tissue, differences were observed in the enzyme activities depending on arsenic concentration. Considering the increases in enzyme inhibition and MDA levels, liver was observed to be the main tissue affected in response to the arsenic toxicity.

Tert-butylhydroquinone as a phenolic activator of Nrf2 antagonizes arsenic-induced oxidative cytotoxicity but promotes arsenic methylation and detoxication in human hepatocyte cell line

Oxidative stress plays crucial roles in exerting a variety of damages upon arsenic exposure. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a master transcriptional regulator protecting cells and tissues from oxidative injuries. The objective of this study was to test whether tert-butylhydroquinone (tBHQ), a well-known synthetic Nrf2 inducer, could protect human hepatocytes against arsenic-induced cytotoxicity and oxidative injuries. Our results showed that 5 and 25 μmol/l tBHQ pretreatment suppressed the arsenic-induced hepatocellular cytotoxicity, reactive oxygen species generation, and hepatic lipid peroxidation, while relieved the arsenic-induced disturbances of intracellular glutathione balance. In addition, we also observed that tBHQ treatment promoted the arsenic biomethylation process and upregulated Nrf2-regulated downstream heme oxygenase-1 and NADPH: quinine oxidoreductase 1 mRNA expressions. Collectively, we suspected that Nrf2 signaling pathway may be involved in the protective effects of tBHQ against arsenic invasion in hepatocytes. These data suggest that phenolic Nrf2 inducers, such as tBHQ, represent novel therapeutic or dietary candidates for the population at high risk of arsenic poisoning.

Effects of sodium arsenate exposure on liver fatty acid profiles and oxidative stress in rats

The present study aimed to evaluate the effect of arsenic on liver fatty acids (FA) composition, hepatotoxicity and oxidative status markers in rats. Male rats were randomly devised to six groups (n=10 per group) and exposed to sodium arsenate at a dose of 1 and 10 mg/l for 45 and 90 days. Arsenate exposure is associated with significant changes in the FA composition in liver. A significant increase of saturated fatty acids (SFA) in all treated groups (p<0.01) and trans unsaturated fatty acids (trans UFA) in rats exposed both for short term for 10 mg/l (p<0.05) and long term for 1 and 10 mg/l (p<0.001) was observed. However, the cis UFA were significantly decreased in these groups (p<0.05). A markedly increase of indicator in cell membrane viscosity expressed as SFA/UFA was reported in the treated groups (p<0.001). A significant increase in the level of malondialdehyde by 38.3 % after 90 days of exposure at 10 mg/l was observed. Compared to control rats, significant liver damage was observed at 10 mg/l of arsenate by increasing plasma marker enzymes after 90 days. It is through the histological investigations in hepatic tissues of exposed rats that these damage effects of arsenate were confirmed. The antioxidant perturbations were observed to be more important at groups treated by the high dose (p<0.05). An increase in the level of protein carbonyls was observed in all treated groups (p<0.05). The present study provides evidence for a direct effect of arsenite on FA composition disturbance causing an increase of SFA and TFAs isomers, liver dysfunction and oxidative stress. Therefore, arsenate can lead to hepatic damage and propensity towards liver cancer.

Resveratrol ameliorates the oxidative damage induced by arsenic trioxide in the feline lung

The objective of this study was to evaluate the possible protection of resveratrol against lung injury induced by arsenic trioxide (As2O3). Twenty-four healthy Chinese Dragon Li cats of either sex were randomly divided into four groups: control (1 ml/kg physiological saline), As2O3 (1 mg/kg), resveratrol (3 mg/kg) and resveratrol (3 mg/kg) + As2O3 (1 mg/kg). The resveratrol + As2O3- treated group was given resveratrol 1 hr before As2O3 (1 mg/kg) administration. We found that pretreatment with resveratrol in a clinically comparable dose regimen can reversed the changes in morphological and biochemical parameters induced by As2O3 in the lung. Resveratrol treatment also upregulated the activities of antioxidant enzymes and attenuated As2O3-induced increases in reactive oxygen species, 8-hydroxydeoxyguanosine and malondialdehyde production in the lung. In addition, resveratrol attenuated the As2O3-induced reduction in the ratio of reduced glutathione to oxidized glutathione, the content of total glutathione and lung arsenic burden. These findings indicated that resveratrol can provide significant protection against As2O3-induced oxidative damage.