Effect of diet on the response in rats to lead acetate given orally or in the drinking water

Abdel Moneim, El-Khadragy MF. Coenzyme Q10 Activates the Antioxidant Machinery and Inhibits the Inflammatory and Apoptotic Cascades Against Lead Acetate-Induced Renal Injury in Rats

The kidney is among the metabolic organs most susceptible to injury, particularly following exposure to xenobiotics and heavy metals. We aimed to explore the potential protective impacts of coenzyme Q10 (CoQ10) on lead acetate (PbAc)-induced nephrotoxicity in rats. Four experimental groups (n = 7) were applied as follows: control group, CoQ10 alone (10 mg/kg), PbAc alone (20 mg/kg), and PbAc with CoQ10. Exposure to PbAc led to the accumulation of Pb in the kidney and increased urea and creatinine serum levels. The deposition of Pb coupled with the elevation of malondialdehyde and nitrate/nitrite levels along with the upregulation of inducible nitric oxide synthase. Additionally, upon PbAc poisoning, glutathione content and the antioxidant enzymes were depleted along with the downregulation of Nrf2 and HO-1 expression. Moreover, PbAc injection increased the protein and mRNA levels of pro-inflammatory cytokines namely, tumor necrosis factor-alpha and interleukin-1 beta, while decreased the levels of interleukin-10, an anti-inflammatory cytokine, in the kidney. Furthermore, exposure to PbAc correlated with increased levels of pro-apoptotic markers, Bax and caspase-3, and reduced levels of the anti-apoptotic marker Bcl-2. The administration of CoQ10 alleviated the molecular, biochemical and histological changes following PbAc intoxication. Thus, CoQ10 reduces the deleterious cellular side effects of PbAc exposure due to its antioxidant, anti-inflammatory and anti-apoptotic effects.

Oxidative stress biomarkers in Eurasian eagle owls (Bubo bubo) in three different scenarios of heavy metal exposure

The main aim of the present study is the assessment of oxidative stress related to metals in the Eurasian eagle owl (Bubo bubo) from three areas (agricultural and rural area, industrial area, and mining area) of Murcia, Southern Spain. Mean blood metal concentrations were Cd=0.07±0.21, Pb=3.27±5.21, Cu=10.62±4.77, Zn=311.47±67.14, Hg=2.32±3.83 μg/dl wet weight. Although individuals from the mining area had significant higher Pb and Hg concentrations, and significant lower glutathione-S-transferase (GST) and catalase (CAT) activities in red blood cells (RBC); the lack of differences in oxidative damage to membrane lipids (TBARS) among areas suggests that the antioxidant capacity of the different populations is able to deal with oxidant species and maintain TBARS levels in the same amount. Despite the low levels of metals, several oxidative stress biomarkers were correlated with metal concentrations. This study provides threshold concentrations at which metals cause effects on the antioxidant system in Eagle owls. Blood Cd concentrations greater than 0.3 μg/dl produced an inhibition in GPx (32%) and CAT (26%) activity in RBC. However, Cd concentrations higher than 0.02 μg/dl were enough to produce an inhibition of these enzymes. Regarding Pb levels, blood concentrations above 2 μg/dl produced an inhibition of 8% and 10.5% in GPx and CAT activities, respectively, in RBC. A depletion of 16% and 4% in tGSH levels was associated with Pb concentrations higher than 15 and 3 μg/dl, respectively, in individuals from the ancient mine site. In addition, Pb concentrations above 2 and 10 μg/dl produced a TBARS induction of 10% and 28%, respectively, in individuals from both the industrial and the mining area. Finally, Hg concentrations greater than 3 and 10 μg/dl resulted in a TBARS induction of 102% and 190%, respectively, in Eurasian eagle owls from the industrial area. Our findings show that Pb may produce effects on oxidative stress biomarkers in Strigiformes at lower concentrations than those typically accepted for considering physiological effects in Falconiformes (20 µg/dl in blood). In addition, we provide new data on Hg and Cd concentrations related to effects in the antioxidant system.

Pyruvate kinase activity and δ-aminolevulinic acid dehydratase activity as biomarkers of toxicity in workers exposed to lead

Lead (Pb(2+)) is a heavy metal that has long been used by humans for a wide range of technological purposes, which is the main reason for its current widespread distribution. Pb(2+) is thought to enter erythrocytes through anion exchange and to remain in the cell by binding to thiol groups. Pyruvate kinase (PK) is a thiol-containing enzyme that plays a key role in erythrocyte cellular energy homeostasis. δ-aminolevulinic acid dehydratase (δ-ALAD) is the second enzyme in the heme biosynthetic pathway and plays a role in the pathogenesis of Pb poisoning. Our primary objective was to investigate the effect of Pb(2+) on the activity of the thiolenzymes δ-ALAD and PK and on the concentration of glutathione (GSH), a nonenzymatic antioxidant defense, in erythrocytes from Pb-exposed workers. The study sample comprised 22 male Pb workers and 21 normal volunteers (15 men and 6 women). The Pb-exposed workers were employed in manufacturing and recycling of automotive batteries. Basic red-cell parameters were assayed and total white blood cell counts performed. PK and δ-ALAD activity and blood Pb (BPb) concentrations were determined in all subjects. Pb-exposed individuals had significantly greater BPb levels than controls. Both PK and δ-ALAD activity levels were significantly lower in Pb-exposed individuals than in controls. Pb significantly inhibited PK and δ-ALAD activity in a dose-dependent manner. We found that erythrocyte GSH levels were lower in Pb-exposed individuals than normal volunteers. Pb-exposed individuals had lower values than controls for several red cell parameters (hemoglobin, hematocrit, red blood cell count, mean corpuscular volume). These results suggest that Pb inhibits δ-ALAD and PK activity by interacting with their thiol groups. It is therefore possible that Pb disrupts energy homeostasis and may be linked with decreased glucose metabolism because it affects the heme synthesis pathway in erythrocytes, contributing to the cell dysfunction observed in these in Pb-exposed individuals. These results indicate an apparent dose-effect relationship between PK activity and BPb. PK activity in human erythrocytes can be used for biological monitoring of Pb exposure. Study of the mechanisms by which Pb acts may contribute to greater understanding of the symptoms caused by Pb.

The redox status in rats treated with flaxseed oil and lead-induced hepatotoxicity

Lead is a persistent environmental pollutant, and its toxicity continues to be a major health problem due to its interference with natural environment. In the present study, we have evaluated the effect of flaxseed oil on lead acetate-mediated hepatic oxidative stress and toxicity in rats. Lead acetate enhanced lipid peroxidation and nitric oxide production in both serum and liver with concomitant reduction in glutathione, catalase, superoxide dismutase, glutathione reductase, glutathione-S-transferase, and glutathione peroxidase activities, these findings were associated with DNA fragmentation. In addition, lead acetate caused liver injury as indicated by histopathological changed of the liver with an elevation in total bilirubin, serum alanine aminotransferase, aspartate aminotransferase, γ-glutamyl transpeptidase, and alkaline phosphatase. Treatment of rats with flaxseed oil resulted in marked improvement in most of the studied parameters as well as histopathological features. On the basis of the above results it can hypothesized that flaxseed oil is a natural product can be protect against lead acetate-mediated hepatic cytotoxicity.

Involvement of some low-molecular thiols in the peroxidative mechanisms of lead and ethanol action on rat liver and kidney

The involvement of low-molecular thiols, such as reduced glutathione (GSH) and metallothionein (Mt), in the mechanisms of the peroxidative action of lead (Pb) and ethanol (EtOH) in liver and kidney was investigated on rats treated with 500 mg Pb/l (in drinking water) and 5 g EtOH/kg body wt./24h (p.o.), alone and in conjunction with each other for 12 weeks. Beside of GSH and Mt, concentration of total and non-protein SH groups (TSH and NPSH, respectively) in these organs as well as the blood activity of dehydratase of delta-aminolevulinic acid (delta-ALAD) and the urinary concentration of delta-aminolevulinic acid (delta-ALA) were determined. The exposure to Pb and EtOH alone and in conjunction with each other led to a decrease in the blood delta-ALAD activity and an increase in the urinary delta-ALA concentration, and these effects were more markedly advanced at co-exposure. In the liver and kidney of rats treated with Pb and/or EtOH, a decrease in concentrations of GSH and NPSH was noted, compared to control. However, in the Pb+EtOH group, only the liver concentrations of NPSH and GSH were lower also compared to the Pb and EtOH groups. The liver concentration of TSH decreased in the rats exposed to EtOH alone and in conjunction with Pb, whereas the kidney concentration of TSH decreased only at co-exposure to Pb and EtOH. Mt concentration was unchanged except for an increase in the liver in the Pb and Pb+EtOH groups. Two-way analysis of variance (ANOVA/MANOVA) revealed that the changes noted at the co-exposure to Pb and EtOH resulted from an independent action of the two xenobiotics as well as from their interactive action. Negative correlations noted between the liver and kidney concentrations of GSH and/or NPSH and recently reported malondialdehyde (MDA, an indicator of lipid peroxidation) concentration in both organs of those rats indicate the relationship between the content of SH groups and the intensity of the Pb and/or EtOH-induced lipid peroxidation. The results allow for the conclusion that the decrease in the liver and kidney concentrations of GSH and NPSH are involved in the mechanisms of the peroxidative action of Pb and EtOH alone and at co-exposure in these organs.

Beneficial role of monoesters of meso-2,3-dimercaptosuccinic acid in the mobilization of lead and recovery of tissue oxidative injury in rats

We investigated the therapeutic efficacy of meso-2,3-dimercaptosuccinic acid (DMSA) and two of its analogues, monomethyl dimercaptosuccinic acid (MmDMSA) and mono-cyclohexyl dimercaptosuccinic acid (MchDMSA) in reducing lead concentration in blood and soft tissues, and in recovering lead induced oxidative stress in rats. Male wistar rats were exposed to lead acetate in drinking water for 20 weeks, followed by 5 days of oral treatment with DMSA (100mg/kg, oral, once daily), MmDMSA or MchDMSA (50 and 100mg/kg). Biochemical variables indicative of oxidative stress along with lead, zinc and copper concentration were evaluated in blood and other soft tissues. Exposure to lead caused a significant decrease in blood delta-aminolevulinic acid dehydratase (ALAD) activity and glutathione (GSH) level. These changes were accompanied by inhibition of kidney ALAD and an increase in delta-aminolevulinic acid synthatase (ALAS) activity in liver and kidneys. Also seen were a pronounced depletion of brain GSH, glutathione peroxidase (GPx), glutathione-S-transferase (GST) and decreased superoxide dismutase (SOD) activity and an increase in thiobarbituric acid reactive substances (TBARS) and reactive oxygen species (ROS) levels. These biochemical changes were correlated with an increased uptake of lead in blood and soft tissues. Blood and kidneys zinc concentration decreased significantly following lead exposure while, copper concentration remained unchanged. No effect of chelation on hepatic zinc concentration was noted, only liver copper concentration showed significant depletion on treatment with DMSA and MmDMSA (100mg/kg). Treatment with DMSA, MmDMSA and MchDMSA provided significant recovery in altered biochemical variables and brain DNA damage besides significant depletion of tissue lead burden. Among the chelating agents used, MchDMSA and MmDMSA provided better recovery in altered biochemical variables and depletion of lead concentration in tissues compared to DMSA. The above results suggest DMSA monoesters to be a better treatment option than DMSA in eliciting recovery to the altered biochemical variables and in the depletion of body lead burden.

Combined efficacies of lipoic acid and 2,3-dimercaptosuccinic acid against lead-induced lipid peroxidation in rat liver

Oxidative stress with subsequent lipid peroxidation has been postulated as one mechanism for lead toxicity. Hence in assessing the protective effects of lipoic acid (LA) and meso 2,3-dimercaptosuccinic acid (DMSA) on lead toxicity, they were tested either separately or in combination for their effects on selected indices of hepatic oxidative stress. Elevated levels of lipid peroxides were accompanied by altered antioxidant defense systems. Lead acetate (Pb - 0.2%) was administered in drinking water for five weeks to induce toxicity. LA (25 mg kg(-1) body wt. day(-1) i.p) and DMSA (20 mg kg(-1) body wt. day(-1) i.p) were administered individually and also in combination during the sixth week. Lead damage to the liver was evident in the decreases in hepatic enzymes alanine transaminase (-38%), aspartate transaminase (-42%) and alkaline phosphatase (-43%); increases in lipid peroxidation (+38%); decreases in the antioxidant enzymes catalase (-45%), superoxide dismutase (-40%), glutathione peroxidase (-46%) and decreases in glutathione (-43%) and decreases in glutathione metabolizing enzymes, glutathione reductase (-59%), glucose-6-phosphate dehydrogenase (-27%) and glutathione-S-transferase (-42%). In combination LA and DMSA completely ameliorated the lead induced oxidative damage. Either compound alone was however only partially protective against lead damage.

Combined efficacies of lipoic acid and meso-2,3-dimercaptosuccinic acid on lead-induced erythrocyte membrane lipid peroxidation and antioxidant status in rats

One of the most intriguing phenomenon observed during lead toxicity has been attributed to lead-induced oxidative stress. The combined effect of DL-alpha-lipoic acid (LA) and meso-2,3-dimercaptosuccinic acid (DMSA) on lead-induced alterations in selected parameters, which are indicators of oxidative stress in erythrocytes, have been studied. Lead acetate (Pb, 0.2%) was administered in drinking water for 5 weeks to induce toxicity. LA (25 mg/ kg body weight per day i.p.) and DMSA (20 mg/kg body weight per day i.p.) were administered individually and also in combination during week 6. Clinical evidence of toxic exposure was evident from the elevated blood lead levels (BPb) along with lowered levels of haemoglobin (Hb) and haematocrit (Ht). Lead-exposed animals showed enhanced membrane lipid peroxidation (LPO) in the erythrocytes. Damage to the erythrocyte membrane was evident from the decline in the activities of the transmembrane enzymes, viz., Na+, K(+)-ATPase, Ca(2+)-ATPase and Mg(2+)-ATPase. Lead-exposed rats also suffered an onslaught on the antioxidant defence system witnessed by lowered activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and reduced glutathione (GSH). Serum glutamic-oxoloacetic transaminase (SGOT) and serum glutamic-pyruvic transaminase (SGPT) were also elevated in lead-exposed rats. Treatment with either LA or DMSA reversed the lead-induced biochemical disturbances encountered by the erythrocytes, but combined treatment with LA and DMSA was very effective in mitigating all the parameters indicative of oxidative stress.

Recommending calcium to reduce lead toxicity in children: a critical review

Assertions that adequate or supplemental calcium intake can reduce lead absorption in children are based on liberal extrapolation from animal studies, experiments with human adults, and cross-sectional studies of children that have a variety of methodologic weaknesses. Without stronger supporting evidence, statements that diet can ameliorate the deleterious effects of environmental lead could provide a false sense of efficacy and divert efforts from lead abatement and from behavioral modifications that might have more impact.

Can antioxidants be beneficial in the treatment of lead poisoning?

Recent studies have shown that lead causes oxidative stress by inducing the generation of reactive oxygen species, reducing the antioxidant defense system of cells via depleting glutathione, inhibiting sulfhydryl-dependent enzymes, interfering with some essential metals needed for antioxidant enzyme activities, and/or increasing susceptibility of cells to oxidative attack by altering the membrane integrity and fatty acid composition. Consequently, it is plausible that impaired oxidant/antioxidant balance can be partially responsible for the toxic effects of lead. Where enhanced oxidative stress contributes to lead-induced toxicity, restoration of a cell's antioxidant capacity appears to provide a partial remedy. Several studies are underway to determine the effect of antioxidant supplementation following lead exposure. Data suggest that antioxidants may play an important role in abating some hazards of lead. To explain the importance of using antioxidants in treating lead poisoning the following topics are addressed: (i) Oxidative damage caused by lead poisoning; (ii) conventional treatment of lead poisoning and its side effects; and (iii) possible protective effects of antioxidants in lead toxicity.

Effect on blood, liver, and kidney variables of age and of dosing rats with lead acetate orally or via the drinking water

Levels of lead in the livers and kidneys of rats increased in proportion to the dose of lead acetate that the rats were given orally or in the drinking water. The activities of delta-aminolevulinic acid dehydratase (DALAD) in blood and liver decreased when the rats were dosed with lead, whereas glutathione levels in the blood increased. The decrease in the activity of blood DALAD was the most sensitive indicator of lead toxicity. Levels of lead in the livers and kidneys decreased after 3, 7, and 14 d of lead withdrawal. The activities of blood DALAD increased after 3 d of lead withdrawal. Groups of rats that initially weighted an average of 140 g were killed at weekly intervals for 6 wk. Blood hematocrits and liver glutathione levels increased, and blood DALAD and activated DALAD from blood decreased with increasing age of the rats. Activated DALAD activities from liver increased after the first week of the study.