Low level lead exposure and oxidative stress: Current opinions

A population-based assessment of blood lead levels in relation to inflammation

BACKGROUND

Some experimental and observational research suggests that inflammation may be an important mediator of lead toxicity. However, lead-induced inflammation has not been well-studied in non-occupationally exposed populations.

METHODS

Using data for 9,145 individuals >or=40 years of age from the National Health and Nutrition Examination Survey 1999-2004, we assessed the association between blood lead levels (BLLs) and C-reactive protein (CRP), fibrinogen, and white blood cell (WBC) count via ordinal logistic regression. We also examined the interaction between BLL and gender in relation to the inflammatory markers.

RESULTS

No evidence for an association between lead exposure and inflammatory markers was observed with odds ratios around or below the null. Although men but not women appeared to be at increased risk of lead-induced inflammation, no consistent dose-response patterns were observed across BLL quintiles.

CONCLUSION

Inflammation does not appear to be an important mediator of lead toxicity.

Inhibitory effect of Pb2+ on the transport cycle of the Na+,K+-ATPase

The effect of Pb(2+) on the transport cycle of the Na(+),K(+)-ATPase was characterized in detail at a molecular level by combining electrical and biochemical measurements. Electrical measurements were performed by adsorbing purified membrane fragments containing Na(+),K(+)-ATPase on a solid-supported membrane. Upon adsorption, the Na(+),K(+)-ATPase was activated by carrying out concentration jumps of different activating substrates, for example, Na(+) and ATP. Charge movements following Na(+),K(+)-ATPase activation were measured in the presence of various Pb(2+) concentrations to investigate the effect of Pb(2+) on different ion translocating steps of the pump cycle. These charge measurements were then compared to biochemical measurements of ATPase activity in the presence of increasing Pb(2+) concentration. Our results indicate that Pb(2+) inhibits cycling of the enzyme, but it does not affect cytoplasmic Na(+) binding and release of Na(+) ions at the extracellular side at concentrations below 10 muM. To explain the inhibitory effect of Pb(2+) on the Na(+),K(+)-ATPase, we propose that Pb(2+) may interfere with the hydrolytic cleavage of the phosphorylated intermediate E(2)P, which occurs in the K(+)-related branch of the pump cycle.

Lead accumulation as possible risk factor for primary open-angle glaucoma

We evaluated the association between hair lead concentrations and primary open-angle glaucoma. Ninety-eight Japanese patients (40 males, 58 females; average age 57.6 ± 10.8 years) with primary open-angle glaucoma and control subjects (131 males, 114 females; average age 56.0 ± 12.8 years) were recruited in this study. Hair lead levels were measured by inductively coupled plasma mass spectrometry. Hair lead concentrations between primary open-angle glaucoma and control groups were compared using Mann-Whitney U test. As a subgroup analysis, we compared hair lead concentrations between low-tension glaucoma, high-tension glaucoma, and control groups using one-factor analysis of variance. Lead accumulation levels were significantly higher in the female subjects with primary open-angle glaucoma compared to the control group (P=0.03). Lead accumulation levels were significantly higher in female patients with low intraocular pressure compared to control group 2 (P=0.02). A higher hair lead level, which reflects the total body burden of lead, was observed to be associated with primary open-angle glaucoma in females especially with low-tension glaucoma. Accumulation of lead may be an unrecognized risk factor of non-pressure-dependent glaucomatous optic neuropathy.

Natural antioxidants protect against lead-induced damage during pregnancy and lactation in rat's pups

The aim of this study was to add further evidence to the biochemical changes produced in lead-exposed pups and to investigate the potential role of natural antioxidants against the lead-induced damage. Pregnant Wistar rats received treatments with drinking water, divided into four groups, as follows: (1) distilled water; (2) lead (300mg/L); (3) lead+Zn (20mg/L)+vitamins A (50,000U/L), C (2g/L), E (500mg/L) and B(6) (500mg/L); and (4) vitamins+Zn solution. We found a significant decrease in haemoglobin and haematocrit values as well and an increase in haemolysis among lead-exposed pups. Vitamins and zinc supplementation were effective in restoring delta-aminolevulinic acid dehydratase, inhibited by lead in erythrocytes, but did not reach control values. Lead exposure increased the production of thiobarbituric acid reactive substances (TBARS) and catalase activity in kidneys and liver that were reduced by the co-administration of vitamins and zinc. Our findings suggest that administration of antioxidants during gestation and lactation could prevent some of the negative effects of lead.

Cumulative lead exposure and tooth loss in men: the normative aging study

BACKGROUND

Individuals previously exposed to lead remain at risk because of endogenous release of lead stored in their skeletal compartments. However, it is not known if long-term cumulative lead exposure is a risk factor for tooth loss.

OBJECTIVES

We examined the association of bone lead concentrations with loss of natural teeth.

METHODS

We examined 333 men enrolled in the Veterans Affairs Normative Aging Study. We used a validated K-shell X-ray fluorescence (KXRF) method to measure lead concentrations in the tibial midshaft and patella. A dentist recorded the number of teeth remaining, and tooth loss was categorized as 0, 1-8 or > or = 9 missing teeth. We used proportional odds models to estimate the association of bone lead biomarkers with tooth loss, adjusting for age, smoking, diabetes, and other putative confounders.

RESULTS

Participants with > or = 9 missing teeth had significantly higher bone lead concentrations than those who had not experienced tooth loss. In multivariable-adjusted analyses, men in the highest tertile of tibia lead (> 23 microg/g) and patella lead (> 36 microg/g) had approximately three times the odds of having experienced an elevated degree of tooth loss (> or = 9 vs. 0-8 missing teeth or > or = 1 vs. 0 missing teeth) as those in the lowest tertile [prevalence odds ratio (OR) = 3.03; 95% confidence interval (CI), 1.60-5.76 and OR = 2.41; 95% CI, 1.30-4.49, respectively]. Associations between bone lead biomarkers and tooth loss were similar in magnitude to the increased odds observed in participants who were current smokers.

CONCLUSION

Long-term cumulative lead exposure is associated with increased odds of tooth loss.

Lead exposure, polymorphisms in genes related to oxidative stress, and risk of adult brain tumors

There is some evidence that oxidative stress plays a role in lead-induced toxicity. Mechanisms for dealing with oxidative stress may be of particular relevance in the brain given the high rate of oxygen metabolism. Using a hospital-based case-control study, we investigated the role of oxidative stress in the potential carcinogenicity of lead through examination of effect modification of the association between occupational lead exposure and brain tumors by single nucleotide polymorphisms in genes with functions related to oxidative stress. The study included 362 patients with glioma (176 of which had glioblastoma multiforme), 134 patients with meningioma, and 494 controls. Lead exposure was estimated by expert review of detailed job history data for each participant. We evaluated effect modification with 142 single nucleotide polymorphisms using likelihood ratio tests that compared nested unconditional logistic regression models that did and did not include a cross-product term for cumulative lead exposure and genotype. When the analyses were restricted to cases with glioblastoma multiforme, RAC2 rs2239774 and two highly correlated GPX1 polymorphisms (rs1050450 and rs18006688) were found to significantly modify the association with lead exposure (P Collapse

Key Words

• glioma
• meningioma
• lead exposure
• oxidative stress
• polymorphism

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MESH Headings

• Adolescent
• Adult
• Aged
• Aged, 80 and over
• Brain Neoplasms/chemically induced
• Brain Neoplasms/genetics
• Female
• Genetic Predisposition to Disease
• Glutathione Peroxidase/genetics
• Humans
• Lead/adverse effects
• Male
• Middle Aged
• Occupational Diseases/genetics
• Occupational Exposure/adverse effects
• Oxidative Stress/genetics
• Polymerase Chain Reaction
• Polymorphism, Single Nucleotide
• Risk Factors
• Young Adult
• rac GTP-Binding Proteins/genetics
• Glutathione Peroxidase GPX1
• RAC2 GTP-Binding Protein

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Grants

• N01CO12400 NCI NIH HHS
• NIH0011946573 Intramural NIH HHS
• Z01 CP010135-12 Intramural NIH HHS
• N01-CO-12400 NCI NIH HHS

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Affiliation(s)

Parveen Bhatti Department of Health ad Human Services, Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, Bethesda, Maryland, USA.
Patricia A Stewart
Amy Hutchinson
Nathaniel Rothman
Martha S Linet
Peter D Inskip
Preetha Rajaraman

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Bone lead levels are associated with measures of memory impairment in older adults

Accumulating evidence suggests a link between lead exposure and memory impairment but assessments based on predictive and validated measures are lacking. We conducted a pilot study of 47 healthy subjects 55-67 years of age to examine associations between bone lead levels and 4 tests sensitive to the natural history of Mild Cognitive Impairment (MCI) and Alzheimer's disease (AD). These include three subtests of the Cambridge Neuropsychological Test Automated Battery (delayed match-to-sample, paired associates learning and spatial recognition memory) and the Montreal Cognitive Assessment Test. Bone lead concentrations were measured at the mid-shaft of the tibia and the calcaneus with K X-ray fluorescence. Higher tibial and calcaneal bone lead values were significantly (p<0.05) associated with lower performance levels on delayed match-to-sample and paired associates learning in unadjusted analyses with Spearman rank correlation coefficients of about 0.4. Multiple linear regression analyses (i.e., least-squares means of cognitive test scores across tertiles of lead exposure) adjusted for age, education and smoking status continued to show an association of higher calcaneal lead levels with increasing memory impairments on delayed match-to-sample (p=0.07). As might be expected, additional adjustment for history of hypertension reduced the strength of this association (p=0.19). Given the demonstrated impact of lead exposure on hypertension and the vascular etiology of certain dementias, we speculate that hypertension could play a mediating role in the association between lead exposure and memory impairment.

Placental lead-induced oxidative stress and preterm delivery

It has been reported that impaired oxidant/antioxidant status is involved in a variety of pregnancy complications. To elucidate the possible free radical mediated mechanism of preterm delivery due to lead exposure by determining the placental lead level and oxidant/antioxidant status in women with the preterm and full-term deliveries. Twenty-nine women with preterm deliveries (gestational age 28-37 weeks) and 31 women with full-term deliveries (gestational age >37 weeks) attending a local hospital of Lucknow, India were recruited. Placental lead level, thiobarbituric acid reactive species (TBARS) level, as an end product of lipid peroxidation, antioxidant molecule glutathione (GSH) level, and activity of antioxidant enzymes; superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione S-transferase (GST) were measured in the placental tissue. In the group with preterm delivery, significantly higher placental lead levels were recorded than in those of full-term (0.39μg/g vs. 0.27μg/g; p<0.05). TBARS was significantly higher while GSH was significantly lower in the placenta of women with the preterm deliveries as compared to the full-term deliveries (p<0.05 for each). Activity of antioxidant enzymes; SOD, CAT, GPx, and GR were significantly higher in the placenta of women having preterm deliveries than those of the full-term (p<0.05 for each). Furthermore, placental lead has significant positive correlations with TBARS (r=0.34, p<0.05), SOD (r=0.30, p<0.05) and CAT (r=0.41, p<0.05), and negative correlation with GSH (r=-0.31, p<0.05). There may be a number of plausible reasons for increased oxidative stress in preterm delivery. However, results of this pilot study suggest that lead-induced oxidative stress may be one of the underlying mechanism(s) of preterm delivery and emphasizes the importance of evaluating the impact of persistent environmental pollutants on adverse pregnancy outcome.

A comparison of the effect of lead nitrate on rat liver chromatin, DNA and histone proteins in solution

Although lead is widely recognized as a toxic substance in the environment and directly damage DNA, no studies are available on lead interaction with chromatin and histone proteins. In this work, we have examined the effect of lead nitrate on EDTA-soluble chromatin (SE chromatin), DNA and histones in solution using absorption and fluorescence spectroscopy, thermal denaturation and gel electrophoresis techniques. The results demonstrate that lead nitrate binds with higher affinity to chromatin than to DNA and produces an insoluble complex as monitored at 400 nm. Binding of lead to DNA decreases its Tm, increases its fluorescence intensity and exhibits hypochromicity at 210 nm which reveal that both DNA bases and the backbone participate in the lead-DNA interaction. Lead also binds strongly to histone proteins in the absence of DNA. The results suggest that although lead destabilizes DNA structure, in the chromatin, the binding of lead introduces some sort of compaction and aggregation, and the histone proteins play a key role in this aspect. This chromatin condensation, upon lead exposure, in turn may decrease fidelity of DNA, and inhibits DNA and RNA synthesis, the process that introduces lead toxicity at the chromatin level.

Environmental-induced oxidative stress in neurodegenerative disorders and aging

The aetiology of most neurodegenerative disorders is multifactorial and consists of an interaction between environmental factors and genetic predisposition. Free radicals derived primarily from molecular oxygen have been implicated and considered as associated risk factors for a variety of human disorders including neurodegenerative diseases and aging. Damage to tissue biomolecules, including lipids, proteins and DNA, by free radicals is postulated to contribute importantly to the pathophysiology of oxidative stress. The potential of environmental exposure to metals, air pollution and pesticides as well as diet as risk factors via the induction of oxidative stress for neurodegenerative diseases and aging is discussed. The role of genetic background is discussed on the light of the oxidative stress implication, focusing on both complex neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis) and monogenic neurological disorders (Huntington's disease, Ataxia telangiectasia, Friedreich Ataxia and others). Emphasis is given to role of the repair mechanisms of oxidative DNA damage in delaying aging and protecting against neurodegeneration. The emerging interplay between environmental-induced oxidative stress and epigenetic modifications of critical genes for neurodegeneration is also discussed.

Chronic nickel-induced DNA damage and cell death: the protection role of ascorbic acid

High consumption of nickel-containing products leads to more exposure of humans to nickel and its by-products. Except the lethal effect of acute nickel poison, chronic nickel exposure is also harmful to humans, but the mechanism of chronic nickel-induced cytotoxicity remains unclear. Here, we found that long-term exposure of Ni(2+) led to significant DNA fragmentation, cell death, and reactive oxygen species (ROS) generation in human leukemia HL-60 cells. Induction of Ni(2+) on DNA fragmentation and cell death could be prevented by the antioxidants ascorbic acid (ASA) or N-acetyl-cysteine (NAC), or enhanced by H(2)O(2), indicating the involvement of ROS generation in the chronic nickel cytotoxicity in cells. Long-term exposure of mice to low Ni(2+) also led to a significant increase in both the ROS generation in the serum and the DNA fragmentation in the peripheral blood mononuclear cells (PBMC), while coadministration of ASA with Ni(2+) together significantly decreased both the DNA fragmentation and the ROS generation. Collectively, these results proved that ROS generation is at least one mechanism of the cytotoxicity of chronic nickel exposure, while ASA is probably useful for people to prevent the chronic nickel cytotoxicity, especially for those who work or live near a mining area or a factory related with nickel.

Statin adverse effects : a review of the literature and evidence for a mitochondrial mechanism

HMG-CoA reductase inhibitors (statins) are a widely used class of drug, and like all medications, have potential for adverse effects (AEs). Here we review the statin AE literature, first focusing on muscle AEs as the most reported problem both in the literature and by patients. Evidence regarding the statin muscle AE mechanism, dose effect, drug interactions, and genetic predisposition is examined. We hypothesize, and provide evidence, that the demonstrated mitochondrial mechanisms for muscle AEs have implications to other nonmuscle AEs in patients treated with statins. In meta-analyses of randomized controlled trials (RCTs), muscle AEs are more frequent with statins than with placebo. A number of manifestations of muscle AEs have been reported, with rhabdomyolysis the most feared. AEs are dose dependent, and risk is amplified by drug interactions that functionally increase statin potency, often through inhibition of the cytochrome P450 3A4 system. An array of additional risk factors for statin AEs are those that amplify (or reflect) mitochondrial or metabolic vulnerability, such as metabolic syndrome factors, thyroid disease, and genetic mutations linked to mitochondrial dysfunction. Converging evidence supports a mitochondrial foundation for muscle AEs associated with statins, and both theoretical and empirical considerations suggest that mitochondrial dysfunction may also underlie many nonmuscle statin AEs. Evidence from RCTs and studies of other designs indicates existence of additional statin-associated AEs, such as cognitive loss, neuropathy, pancreatic and hepatic dysfunction, and sexual dysfunction. Physician awareness of statin AEs is reportedly low even for the AEs most widely reported by patients. Awareness and vigilance for AEs should be maintained to enable informed treatment decisions, treatment modification if appropriate, improved quality of patient care, and reduced patient morbidity.