Occupational Lead Exposure Ototoxicity Evaluated With Distortion-Product Otoacoustic Emissions.

OBJECTIVES: To evaluate the extent of hearing loss among pottery workers in Mexico exposed to lead. DESIGN: The authors conducted a cross-sectional study including 315 adult pottery workers. Auditory function was evaluated by air conduction pure-tone audiometry (pure-tone average) and distortion-product otoacoustic emission (DPOAE) levels (amplitude and signal-to-noise ratio). Lead exposure was assessed with a single blood sample test and classified as low, medium, and high according to blood lead tertiles. Logistic regression models were calculated for the association between blood lead levels, pure-tone average, and DPOAE records. RESULTS: Median (25th-75th) blood lead levels were 14 µg/dL (7.5-22.6 µg/dL). The audiometric pattern and DPOAE records were similar across blood lead levels groups in all frequencies, and no statistically significant differences were found. Adjusted logistic regression models showed no increase in the odds for hearing thresholds >25 dB (HL) and DPOAE absence associated with blood lead levels, and no dose-response pattern was observed ( p > 0.05). CONCLUSIONS: Given the results from this cross-sectional study, no association was found between blood lead levels and hearing loss assessed with DPOAE. Future longitudinal work should consider chronic lead exposure estimates among underrepresented populations, which can potentially inform safer work practices to minimize the risk of ototoxicity.

Effect of smoking on the redox status of knee osteoarthritis: A preliminary study.

Even though smoking has been scarcely studied in osteoarthritis (OA) etiology, it is considered a controversial risk factor for the disease. Exposure to tobacco smoke has been reported to promote oxidative stress (OS) as part of the damage mechanism. The aim of this study was to assess whether smoking increases cartilage damage through the generation of OS. Peripheral blood (PB) and synovial fluid (SF) samples from patients with OA were analyzed. The samples were stratified according to smoking habit, Kellgren-Lawrence score, pain, and cotinine concentrations in PB. Malondialdehyde (MDA), methylglyoxal (MGO), advanced protein oxidation products (APOPs), and myeloperoxidase (MPO) were assessed; the activity of antioxidant enzymes such as gamma-glutamyl transferase (GGT), glutathione S-transferase (GST) and catalase (CAT), as well as the activity of arginase, which favors the destruction of cartilage, was determined. When stratified by age, for individuals <60 years, the levels of MDA and APOPs and the activity of MPO and GST were higher, as well as antioxidant system activity in the smoking group (OA-S). A greater degree of pain in the OA-S group increased the concentrations of APOPs and arginase activity (P < 0.01 and P < 0.05, respectively). Arginase activity increased significantly with a higher degree of pain (P < 0.01). Active smoking can be an important risk factor for the development of OA by inducing systemic OS in young adults, in addition to reducing antioxidant enzymes in older adults and enhancing the degree of pain and loss of cartilage.

Relationship between urinary biomarkers of early kidney damage and exposure to inorganic toxins in a pediatric population of Apizaco, Tlaxcala, Mexico.

BACKGROUND: In recent years, chronic kidney disease has increased in the pediatric population and has been related to environmental factors. In the diagnosis of kidney damage, in addition to the traditional parameters, early kidney damage biomarkers, such as kidney injury molecule 1, cystatin C, and osteopontin, among others, have been implemented as predictors of early pathological processes. OBJECTIVE: This study aimed to evaluate the relationship between exposure to environmental pollutants and early kidney damage biomarkers. METHODS: A cross-sectional pilot study was conducted in February 2016 and involved 115 apparently healthy children aged 6-15 residing in Apizaco, Tlaxcala. Participant selection was carried out randomly from among 16,472 children from the municipality of Apizaco. A socio-demographic questionnaire included  age, sex, education, duration of residence in the area, occupation, water consumption and dietary habits, pathological history, and some non-specific symptoms. Physical examination included blood pressure, weight, and height. The urine concentrations of urinary aluminum, total arsenic, boron, calcium, chromium, copper, mercury, potassium, sodium, magnesium, manganese, molybdenum, lead, selenium, silicon, thallium, vanadium, uranium, and zinc, were measured. Four of the 115 participants selected for the study were excluded due to an incomplete questionnaire or lack of a medical examination, leaving a final sample population of 111 participants. RESULTS: The results showed a mean estimated glomerular filtration rate of 89.1 ± 9.98 mL/min/1.73m2 and a mean albumin/creatinine ratio of 12.9 ± 16.7 mg/g urinary creatinine. We observed a positive and significant correlation between estimated glomerular filtration rate with fluoride, total arsenic and lead, and a correlation of albumin/creatinine ratio with fluoride, vanadium, and total arsenic. There was also a significant correlation between the early kidney damage biomarkers and fluoride, vanadium, and total arsenic, except for cystatin C. CONCLUSION: In conclusion, our results show that four urinary biomarkers: α1-microglobulin, cystatin C, kidney injury molecule 1, and neutrophil gelatinase-associated lipocalin are related to environmental exposure to urinary fluoride, vanadium, and total arsenic in our pediatric population.

Fluoride exposure regulates the elongation phase of protein synthesis in cultured Bergmann glia cells.

Fluoride is an environmental pollutant present in dental products, food, pesticides and water. The latter, is the greatest source of exposure to this contaminant. Structural and functional damages to the central nervous system are present in exposed population. An established consequence of the neuronal is the release of a substantial amount of glutamate to the extracellular space, leading to an excitotoxic insult. Glutamate exerts its actions through the activation of specific plasma membrane receptors and transporters present in neurons and in glia cells and it is the over-activation of glutamate receptors and transporters, the biochemical hallmark of neuronal and oligodendrocyte cell death. In this context, taking into consideration that fluoride leads to degeneration of cerebellar cells, we took the advantage of the well-established model of cerebellar Bergmann glia cultures to gain insight into the molecular mechanisms inherent to fluoride neurotoxicity that might be triggered in glia cells. We could establish that fluoride decreases [(35)S]-methionine incorporation into newly synthesized polypeptides, in a time-dependent manner, and that this halt in protein synthesis is the result of a decrease in the elongation phase of translation, mediated by an augmentation of eukaryotic elongation factor 2 phosphorylation. These results favor the notion of glial cells as targets of fluoride toxicity and strengthen the idea of a critical involvement of glia cells in the function and dysfunction of the brain.

Oxidative stress, redox signaling, and autophagy: cell death versus survival.

SIGNIFICANCE: The molecular machinery regulating autophagy has started becoming elucidated, and a number of studies have undertaken the task to determine the role of autophagy in cell fate determination within the context of human disease progression. Oxidative stress and redox signaling are also largely involved in the etiology of human diseases, where both survival and cell death signaling cascades have been reported to be modulated by reactive oxygen species (ROS) and reactive nitrogen species (RNS). RECENT ADVANCES: To date, there is a good understanding of the signaling events regulating autophagy, as well as the signaling processes by which alterations in redox homeostasis are transduced to the activation/regulation of signaling cascades. However, very little is known about the molecular events linking them to the regulation of autophagy. This lack of information has hampered the understanding of the role of oxidative stress and autophagy in human disease progression. CRITICAL ISSUES: In this review, we will focus on (i) the molecular mechanism by which ROS/RNS generation, redox signaling, and/or oxidative stress/damage alter autophagic flux rates; (ii) the role of autophagy as a cell death process or survival mechanism in response to oxidative stress; and (iii) alternative mechanisms by which autophagy-related signaling regulate mitochondrial function and antioxidant response. FUTURE DIRECTIONS: Our research efforts should now focus on understanding the molecular basis of events by which autophagy is fine tuned by oxidation/reduction events. This knowledge will enable us to understand the mechanisms by which oxidative stress and autophagy regulate human diseases such as cancer and neurodegenerative disorders.

Effect of selenomethionine supplementation in food on the excretion and toxicity of arsenic exposure in female mice.

Selenium (Se) is an essential component of several major metabolic pathways and controls immune function. Arsenic (As) is a human carcinogen with immunotoxic and genotoxic activities, functioning mainly by producing oxidative stress. Due to the ability of Se to interact with As and to possibly block its toxic effects, we investigated the impact of dietary Se-methionine (Se-Met) supplementation on the toxicity of As exposure in vivo in a mouse model. Sufficient and excess levels of Se-Met (0.2 and 2 ppm, respectively) were fed to C57BL/6N female mice exposed to sodium arsenite (3, 6 and 10 mg/kg) in tap water for 9 days. We observed that As exposure increased Se-Met excretion in the urine. Se-Met supplementation increased the relative liver weight and decreased the concentration of total liver proteins in animals exposed to 10 mg/kg of As. Se-Met supplementation maintained a normal pool of glutathione in the liver and increased glutathione peroxidase concentration, although the lipoperoxidation level was increased by Se-Met even without As exposure. Se-Met supplementation helped to maintain the CD4/CD8 ratio of lymphocytes in the spleen, although it increased the proportion of B cells. Se-Met supplementation prior to As exposure increased the secretion of interleukin-4, IL-12 and interferon-γ and the stimulation index of the spleen cells in in vitro assays. Se-Met intake improved the basal immunological parameters but did not reduce the damage caused by oxidative stress after low-dose As exposure.

Identification of the GST-T1 and GST-M1 null genotypes using high resolution melting analysis.

Glutathione S-transferases, including GST-T1 and GST-M1, are known to be involved in the phase II detoxification pathways for xenobiotics as well as in the metabolism of endogenous compounds. Polymorphisms in these genes have been linked to an increased susceptibility to carcinogenesis and associated with risk factors that predispose to certain inflammatory diseases. In addition, GST-T1 and GST-M1 null genotypes have been shown to be responsible for interindividual variations in the metabolism of arsenic, a known human carcinogen. To assess the specific GST genotypes in the Mexican population chronically exposed to arsenic, we have developed a multiplex High Resolution Melting PCR (HRM-PCR) analysis using a LightCycler480 instrument. This method is based on analysis of the PCR product melting curve that discriminates PCR products according to their lengths and base sequences. Three pairs of primers that specifically recognize GST-T1, GST-M1, and ß-globin, an internal control, to produce amplicons of different length were designed and combined with LightCycler480 High Resolution Melting Master Mix containing ResoLight, a completely saturating DNA dye. Data collected from melting curve analysis were evaluated using LightCycler480 software to determine specific melting temperatures of individual melting curves representing target genes. Using this newly developed multiplex HRM-PCR analysis, we evaluated GST-T1 and GST-M1 genotypes in 504 DNA samples isolated from the blood of individuals residing in Zimapan, Lagunera, and Chihuahua regions in Mexico. We found that the Zimapan and Lagunera populations have similar GST-T1 and GST-M1 genotype frequencies which differ from those of the Chihuahua population. In addition, 14 individuals have been identified as carriers of the double null genotype, i.e., null genotypes in both GST-T1 and GST-M1 genes. Although this procedure does not distinguish between biallelic (+/+) and monoallelic (+/-) genotypes, it can be used in an automated workflow as a simple, sensitive, and time and money saving procedure for rapid identification of the GST-T1 and GST-M1 positive or null genotypes.

Epigenetic changes in individuals with arsenicosis.

Inorganic arsenic (iAs) is an environmental toxicant currently poisoning millions of people worldwide, and chronically exposed individuals are susceptible to arsenicosis or arsenic poisoning. Using a state-of-the-art technique to map the methylomes of our study subjects, we identified a large interactome of hypermethylated genes that are enriched for their involvement in arsenic-associated diseases, such as cancer, heart disease, and diabetes. Notably, we have uncovered an arsenic-induced tumor suppressorome, a complex of 17 tumor suppressors known to be silenced in human cancers. This finding represents a pivotal clue in unraveling a possible epigenetic mode of arsenic-induced disease.

Arsenic(III) methylation in betaine-nontronite clay-water suspensions under environmental conditions.

This paper reports arsenic methylation in betaine-nontronite clay-water suspensions under environmental conditions. Two nontronites (<0.05 mm), NAu-1 (green color, Al-enriched) and NAu-2 (brown color, Al-poor, contains tetrahedral Fe) from Uley Mine - South Australia were selected for this study. Betaine (pK(a)=1.83) was selected as methyl donor. The reaction between 5 g L(-1) clay, 20 ppm As(III), and 0.4M betaine at 7< or =pH(0)< or =9 under anoxic conditions was studied. The presence of nontronite clays were found to favor As(III) conversion to monomethylarsenic (MMA). Arsenic conversion was found to be as high as 50.2 ng MMA/ng As(III)(0). Conversion of As was found to be more quantitative in the presence of NAu-2 ((Na(0.72)) [Si(7.55) Al(0.16)Fe(0.29)][Al(0.34) Fe(3.54) Mg(0.05)] O(20)(OH)(4)) than NAu-1 ((Na(1.05)) [Si(6.98) Al(0.95)Fe(0.07)][Al(0.36) Fe(3.61) Mg(0.04)] O(20)(OH)(4)). The inherent negative charge at the nontronite tetrahedral layer stabilizes positively charged organic intermediate-reaction species, thereby leading to decreases in the overall methylation activation energy. The outcome of this work shows that nontronite clays catalyze As methylation to MMA via non-enzymatic pathway(s) under environmental conditions.

Tissue levels of arsenicals and skin tumor response following administration of monomethylarsonous acid and arsenite to K6/ODC mice.

The effects of monomethylarsonous acid (MMA[III]) and arsenite, administered in drinking water on tissue levels of arsenicals, cytogenetics, and mouse skin tumorigenicity were determined. A low-methionine diet modified the pattern of arsenical tissue concentrations and decreased the tissue arsenical concentrations, particularly in kidney and urinary bladder, less so in liver, and had little effect in the lungs. In mice given 75 ppm arsenite and a low-methionine diet, the urinary bladder tissue levels were only 29%, 26%, and 38% of the inorganic arsenic (iAs), MMA, and dimethylarsinic acid (DMA) concentrations found in mice eating the control diet. In K6/ODC transgenic mice that consumed a normal diet (Purina 5002), a 26-week drinking water exposure to 10 ppm arsenite resulted in 5% of the treated animals having squamous skin tumors. Exposure to 10, 50, 75, or 150 ppm MMA(III) caused 5%, 6.7%, 5%, or 0% tumor-bearing animals. A low-methionine diet did not markedly change the incidence of skin tumors--10 ppm arsenite led to 10% tumors. With a low-methionine diet, 10 and 50 ppm, MMA(III) caused 5% and 6.7% tumor-bearing animals. In comparing the frequency of tumors in the concurrent control groups (1/70, 1.4%) with the frequency of tumors in the pooled arsenical-treated responsive groups (8/122, 6.6%), there is an excess of 6 mouse skin tumors observed in the pooled arsenical-responsive treatment groups compared to the expected number of tumors based on frequency of tumors observed in concurrent control mice. In summary, studies with MMA(III) and arsenite-treated K6/ODC transgenic mice showed (1) a low-methionine diet substantially altered mouse tissue arsenical levels and (2) numerically elevated incidence of mouse skin tumors following arsenical exposures.

Inorganic arsenic exposure affects pain behavior and inflammatory response in rat.

Inorganic arsenic (iAs) contamination of drinking water is a worldwide problem associated with an increased risk for the development of various types of cancer and noncancerous damage. In vitro studies have suggested that iAs can modulate the activity of macrophages producing an over-expression of cyclooxygenase-2 (COX-2) and resulting in an increase in prostaglandin E(2) (PGE(2)) concentrations in endothelial cells. These effects may lead to an in vivo enhancement of inflammatory and pain responses. Our aim was to determine the effect of a single dose of arsenic or subchronic exposure to arsenic on pain behavior and tissue inflammation in rats. Rats were given a single dose of sodium arsenite (0.1, 1 and 10 mg/kg i.p.) or submitted to subchronic exposure to arsenic added to the drinking water for 4 weeks (0.1, 1, 10 and 100 ppm). Inflammatory pain was assessed by using the formalin and tail-flick tests, while inflammation was evaluated with the carrageenan model. Arsenite did not induce pain or significant inflammation by itself. In contrast, arsenite in both single dose administration and subchronic exposure increased not only the inflammatory process and the underlying hyperalgesic pain, but also induced a decrease in the pain threshold. Alterations in pain processing were dependent on the arsenic dose and the length of exposure, and the underlying mechanism involved an increased release of local PGE(2). These results suggest that inorganic arsenic exposure enhances pain perception and exacerbates the pathological state of inflammatory diseases.

Non-optimal levels of dietary selenomethionine alter splenocyte response and modify oxidative stress markers in female mice.

Many studies evaluating the effects of selenium (Se) status on immunity utilize inorganic Se, although selenomethionine (Se-Met) has been suggested to be more bioavailable and less toxic. In the current study, we investigated the effects of dietary Se-Met on immune system function and cellular redox status in C57BL/6N female mice fed with low (0.02 ppm), sufficient (0.2 ppm, control group), or excess Se-Met (2 ppm) in the diet for 50 days. Low Se-Met intake reduced glutathione peroxidase (GPx) activity and glutathione concentration without modifying lipoperoxidation. While low Se-Met intake also reduced the number of B cells in the spleen, it increased mitogen-induced proliferation, IL-4 and IL-12 secretion when compared to the sufficient Se-Met intake group. In comparison to controls, excess Se-Met intake increased splenocyte proliferation and reduced B cell numbers, IL-4, and IL-12 secretion without affecting oxidative stress markers. These data suggest that Se-Met supplementation should be carefully evaluated as it many influence immune function.

Endogenous reductants support the catalytic function of recombinant rat cyt19, an arsenic methyltransferase.

The postulated scheme for the metabolism of inorganic As involves alternating steps of oxidative methylation and of reduction of As from the pentavalent to the trivalent oxidation state, producing methylated compounds containing AsIII that are highly reactive and toxic. S-Adenosyl-L-methionine:AsIII methyltransferase purified from rat liver catalyzes production of methyl and dimethyl arsenicals from inorganic As. This protein is encoded by the cyt19 gene orthologous with cyt19 genes in mouse and human. The reductants dithiothreitol or tris(2-carboxylethyl)phosphine support catalysis by recombinant rat cyt19 (rrcyt19). Coupled systems containing an endogenous reductant (thioredoxin/thioredoxin reductase/NADPH, glutaredoxin/glutathione/glutathione reductase/NADPH, or lipoic acid/thioredoxin reductase/NADPH) support inorganic As methylation by rrcyt19. Although glutathione alone does not support rrcyt19's catalytic function, its addition to reaction mixtures containing other reductants increases the rate of As methylation. Aurothioglucose, an inhibitor of thioredoxin reductase, reduces the rate of As methylation by rrcyt19 in thioredoxin-supported reactions. Addition of guinea pig liver cytosol, a poor source of endogenous As methyltransferase activity, to reaction mixtures containing rrcyt19 shows that endogenous reductants in cytosol support the enzyme's activity. Methylated compounds containing either AsIII or AsV are detected in reaction mixtures containing rrcyt19, suggesting that cycling of As between oxidation states is a component of the pathway producing methylated arsenicals. This enzyme may use endogenous reductants to reduce pentavalent arsenicals to trivalency as a prerequisite for utilization as substrates for methylation reactions. Thus, cyt19 appears to possess both AsIII methyltransferase and AsV reductase activities.