Lead induces oxidative stress, DNA damage and alteration of p53, Bax and Bcl-2 expressions in mice

Quercetin protects the rat kidney against oxidative stress-mediated DNA damage and apoptosis induced by lead

Quercetin, a flavonoid, effectively improved the lead-induced histology changes including structure damage and leukocyte infiltration in rat kidney. The present study was designed to explore the protective mechanism of quercetin against lead-induced oxidative DNA damage and apoptosis in rat kidney. We found that quercetin markedly decreased the ROS level and lowered the GSH/GSSG ratio in the kidney of lead-treated rat. The increase of 8-hydroxydeoxyguanosine level in the kidney of lead-treated rat was effectively suppressed by quercetin. Furthermore, quercetin markedly restored Cu/Zn-SOD, CAT and GPx activities in the kidney of lead-treated rat. TUNEL assay showed that lead-induced apoptosis in rat kidney was significantly inhibited by quercetin, which might be attributed to its antioxidant property. In conclusion, these results suggested that quercetin could protect the rat kidney against lead-induced injury by improving renal function, attenuating histopathologic changes, reducing ROS production, renewing the activities of antioxidant enzymes, decreasing DNA oxidative damage and apoptosis.

Genotoxic effects of lead: an updated review

Lead is a ubiquitous toxic heavy metal with unique physical and chemical properties that make it suitable for a great variety of applications. Because of its high persistence in the environment and its use since ancient times for many industrial activities, lead is a common environmental and occupational contaminant widely distributed around the world. Even though the toxic effects of lead and its compounds have been investigated for many years in a variety of systems, the data existing with regard to its mutagenic, clastogenic and carcinogenic properties are still contradictory. The International Agency for Research on Cancer has classified lead as possible human carcinogen (group 2B) and its inorganic compounds as probable human carcinogens (group 2A). Furthermore, although the biochemical and molecular mechanisms of action of lead remain still unclear, there are some studies that point out indirect mechanisms of genotoxicity such as inhibition of DNA repair or production of free radicals. This article reviews the works listed in the literature that use different parameters to evaluate the genotoxic effects of lead in vitro, in vivo and in epidemiological studies.

Impact of developmental lead exposure on splenic factors

Lead (Pb) is known to alter the functions of numerous organ systems, including the hematopoietic and immune systems. Pb can induce anemia and can lower host resistance to bacterial and viral infections. The anemia is due to Pb's inhibition of hemoglobin synthesis and Pb's induction of membrane changes, leading to early erythrocyte senescence. Pb also increases B-cell activation/proliferation and skews T-cell help (Th) toward Th2 subset generation. The specific mechanisms for many of the Pb effects are, as yet, not completely understood. Therefore, we performed gene expression analysis, via microarray, on RNA from the spleens of developmentally Pb-exposed mice, in order to gain further insight into these Pb effects. Splenic RNA microarray analysis indicated strong up-regulation of genes coding for proteolytic enzymes, lipases, amylase, and RNaseA. The data also showed that Pb affected the expression of many genes associated with innate immunity. Analysis of the microarray results via GeneSifter software indicated that Pb increased apoptosis, B-cell differentiation, and Th2 development. Direct up-regulation by Pb of expression of the gene encoding the heme-regulated inhibitor (HRI) suggested that Pb can decrease erythropoiesis by blocking globin mRNA translation. Pb's high elevation of digestive/catabolizing enzymes could generate immunogenic self peptides. With Pb's potential to induce new self-peptides and to enhance the expression of caspases, cytokines, and other immunomodulators, further evaluation of Pb's involvement in autoimmune phenomena, especially Th2-mediated autoantibody production, and alteration of organ system activities is warranted.

Quercetin protects rat liver against lead-induced oxidative stress and apoptosis

Quercetin, a flavonoid, effectively improved the lead-induced histology changes including structure damage and leukocyte infiltration in rat liver. The present study was designed to explore the protective mechanism of quercetin against lead-induced hepatic injury. We found that quercetin markedly decreased the MDA and H(2)O(2) levels and lowered the GSH/GSSG ratio in the liver of lead-treated rat. Moreover, quercetin markedly restored Cu/Zn-SOD, Mn-SOD, CAT and GPx activities and upregulated mRNA expression levels of these proteins in the liver of lead-treated rat. Western blot analysis showed that quercetin significantly inhibited apoptosis by modulating the ratio of Bax to Bcl-2 expression and suppressing the expression of phosphorylated JNK1/2 and cleaved caspase-3 in the liver of lead-treated rat. In conclusion, these data suggest that quercetin protects the rat liver from lead-induced injury by attenuating lipid peroxidation, renewing the activities of antioxidant enzymes and inhibiting apoptosis.

Involvement of mitochondria-mediated apoptosis in ethylbenzene-induced renal toxicity in rat

Ethylbenzene is an important industrial chemical that has recently been classified as a possible human carcinogen (International Agency of Research on Cancer class 2B), but the available data do not support the genotoxic mechanism of ethylbenzene-induced tumors in kidney. We investigated the effects of ethylbenzene on renal ultrastructure and explored the nongenotoxic mechanism of mitochondria-mediated apoptosis pathway. Forty male Sprague-Dawley rats were used as a vivo model with ethylbenzene inhalation for 13 weeks, and the metabolites of ethylbenzene, mandelic acid (MA), and phenylglyoxylic acid (PGA) in urine were examined by high-performance liquid chromatography. Meanwhile, the ultrastructure of renal tubular epithelial cells was observed, and cell apoptosis was detected via terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. Furthermore, we investigated the expression levels of messenger RNA (mRNA) and protein of bax, bcl-2, cytochrome c, caspase-9, and caspase-3 in rat kidney. With respect to levels of MA, PGA, and MA + PGA, a significant dose-dependent increase was observed in 4335 and 6500 mg/m(3) ethylbenzene-treated groups against the control group. The mitochondria of renal tubular epithelial cells became a compact and vacuolar structure in 6500 mg/m(3) ethylbenzene-treated group, and ethylbenzene induced a significant increase in the number of apoptotic cells as compared to the control group. In addition, enhanced mRNA and protein expression levels of all measured genes were observed in various ethylbenzene-treated groups except the decreased bcl-2 expression levels. Our results indicated that ethylbenzene may induce apoptosis of renal tubular epithelial cells via mitochondria-mediated apoptotic pathways. MA and PGA in urine might be a parameter of biological dose in vivo after ethylbenzene inhalation.

Oxidative stress and immunotoxic effects of lead and their amelioration with myrrh (Commiphora molmol) emulsion

The possible role of Commiphora molmol emulsion (CME) in protecting against lead (PbAc)-induced hepatotoxicity, oxidative stress and immunotoxicity in rabbits was assessed. Six groups of animals were used: groups I (control) and II (PbAc) were not supplemented with CME. Groups III (CME50) and IV (CME50+PbAc) were administered with CME in a dose rate of 50mg/kg bwt, while groups V (CME100) and VI (CME100+PbAc) were received 100mg CME/kg bwt daily p.o for successive 14 weeks. Groups II, IV and VI were given 80 mg PbAc/kg bwt/day orally for 6 weeks starting from the 9th week. At the 12th week, animals were subjected to immunization by a single dose of sheep RBCs. The PbAc-group showed 220% increase in hepatic malondialdehyde levels, while glutathione, glutathione s-transferase and glutathione peroxidase levels decreased. Lead-acetate induced hypoproteinemia and hypoalbuminemia, and increased aminotransferases activity. It reduced the values of lymphocyte transformation test, phagocytic activity, phagocytic index and antibody titer against sheep SRBCs. Interestingly, pretreatment with CME attenuated these adverse effects in a dose-dependent protection. CME, therefore, is a potent antioxidant, and can protect against PbAc-induced hepatic oxidative damage and immunotoxicity by reducing lipid peroxidation and enhancing the antioxidant and immune defense mechanisms.

Induction of micronuclei in rat bone marrow after chronic exposure to lead acetate trihydrate

Lead increasingly contributes to pollution of the environment and may play a role in the development of adverse effects in the human and animal body. Data concerning its mutagenic, clastogenic, and carcinogenic properties have been conflicting. In this study, we evaluated the frequency of micronuclei in bone marrow erythrocytes of rats treated with lead acetate trihydrate. Outbred Wistar rats were exposed to a daily dose of 100 mg/L drinking water for 125 days. The mean value of the total number of micronuclei observed in polychromatic erythrocytes of female rats was significantly higher than that found in the control group (13.375 ± 2.722 against 9.625 ± 3.204 micronuclei/1000 cells; P = 0.024 in ANOVA). In exposed female animals, no significant reduction of the ratio of polychromatic to normochromatic erythrocytes was observed (0.990 ± 0.228 against 1.208 ± 0.195; P = 0.060 in ANOVA). The effects of lead acetate trihydrate in male rats are both cytotoxic and genotoxic because of a decrease in ratio of polychromatic to normochromatic erythrocytes (0.715 ± 0.431 against 1.343 ± 0.306; P = 0.023, ANOVA followed by Tukey test) and an increase in frequency of micronucleated polychromatic erythrocytes (24.167 ± 7.859 against 4.0 ± 4.528 micronuclei/1000 cells; P ≤ 0.001, ANOVA followed by Tukey test), respectively.