Mercury, selenium, and glutathione peroxidase in dental personnel

Biomarkers of selenium status and antioxidant effect in workers occupationally exposed to mercury

The present observation based research was designed to evaluate the influence of occupational human exposure to metallic mercury (Hg°) vapor on the biomarkers of selenium status involved in the antioxidant defense system. For this purpose we determined Hg and selenium (Se) concentrations in body fluids, the markers of antioxidant effect measured as an activity of Se-dependent enzymes (red blood cell and plasma glutathione peroxidase: GPx1-RBC and GPx3-P), concentration of selenoprotein P in the plasma (SeP-P) and total antioxidant activity in the plasma (TAA-P) in 131 male workers from a chloralkali plant exposed to Hg° and 67 non-exposed males (control group). The mRNA expression levels of glutathione peroxidases (GPX1, GPX3), selenoprotein P (SEPP1), thioredoxin reductase 1 (TRXR1), thioredoxin 1 (TRX1), peroxiredoxins (PRDX1, PRDX2) were also examined in the leukocytes of peripheral blood. Hg concentration in the blood (Hg-B) and urine (Hg-U) samples was determined using the thermal decomposition amalgamation/atomic absorption spectrometry (TDA-AAS) method and Se concentrations in plasma (Se-P) and urine (Se-U) using the inductively coupled plasma mass spectrometry (ICP-MS) method. Activities of GPx1-RBC, GPx3-P and TAA-P were determined using the kinetic and spectrophotometric method, respectively. Gene expression analysis was performed using the quantitative Real-Time PCR. The results showed significant higher Hg levels among the Hg°-exposed workers in comparison to control group (12-times higher median for Hg-B and almost 74-times higher median for Hg-U concentration in chloralkali workers). Se-P was also significantly higher (Me (median): 82.85 μg/L (IQR (interquartile range) 72.03-90.28 μg/L) for chloralkali workers vs. Me: 72.74 μg/L (IQR 66.25-80.14 μg/L) for control group; p = 0.0001) but interestingly correlated inversely with Hg-U in chloralkali workers suggesting depletion of the Se protection among the workers with the highest Hg-U concentration. The mRNA level for GPX1, PRXD1 were markedly but significantly higher in the workers compared to the control group. Moreover, concentrations of Hg-B and Hg-U among the workers were significantly positively correlated with the levels of selenoprotein P at both the mRNA and selenoprotein levels. In the multivariate model, after adjusting to cofounders (dental amalgam fillings, age, BMI, job seniority time, smoking), we confirmed that Hg-U concentration was inversely correlated with genes expression of TRXR1. This is the first comprehensive assessment of the impact of occupational exposure of workers to Hg° at both the mRNA and selenoprotein levels, with investigation of fish intake obtained by means of a questionnaire. These findings suggest that exposure to Hg° alters gene expression of the antioxidant enzymes and the level of Se-containing selenoproteins.

The effects of amalgam restorations on plasma mercury levels and total antioxidant activity

OBJECTIVE

This study evaluated the effects of amalgam restorations on plasma mercury levels and total antioxidant activities (TAA).

DESIGN

The study was comprised of 48 subjects ranging in age from 20 to 32 years. Of these, 33 had dental amalgam restorations and 15 had no dental amalgam restorations. In those patients with amalgams, the total number of amalgam restorations and surfaces were counted, and the total and occlusal areas (mm(2)) of restorations were measured using a Counting Measurement Machine. Blood samples were collected from all participants. Plasma mercury levels were measured using an Atomic Absorption Spectrometer and Hydride System, and plasma TAA levels were measured using an Antioxidant Assay Kit. Statistical analysis was performed using the SPSS 10.01 software program. Data was evaluated by t test and correlation analysis.

RESULTS

Plasma mercury (P-Hg) levels were found to be significantly higher in subjects with amalgam restorations when compared to subjects without amalgams (p<0.01); the differences in P-TAA levels between subjects with and without amalgams were not found to be statistically significant (p>0.05). No significant correlations were found between P-Hg concentrations and P-TAA levels (p>0.05). Significant positive correlations were found between P-Hg concentrations and the number of amalgam restorations (p<0.01), number of amalgam surfaces (p<0.05), total amalgam surface area (p<0.05) and amalgam occlusal surface area (p<0.01). However, no significant correlations were found between these parameters and P-TAA (p>0.05).

CONCLUSIONS

The results of our study showed that dental amalgams are a major source of plasma mercury; however, amalgam restorations were not found to have a significant effect on plasma-total antioxidant activities.

Serum mercury concentration in relation to survival, symptoms, and diseases: results from the prospective population study of women in Gothenburg, Sweden

A prospective population study of women in Gothenburg, Sweden was started in 1968-69 and comprised 1462 women aged 38, 46, 50, 54, or 60 years at baseline. Follow-up studies were carried out in 1974-75, 1980-81, and 1992-93. The baseline study included an extensive medical and dental examination. Serum mercury concentration (beta-HG) was determined in deep-frozen samples from all participants in 1968-69 and in a random subsample of sera from participants in 1980-81, about 20 years after the baseline examination. S-Hg was statistically significantly correlated with number of amalgam fillings at both examinations. Of 30 defined symptoms and 4 different clusters of symptoms, no one was independently correlated with S-Hg measured in the samples from 1968-69, while there was a negative statistically significant correlation with over-exertion and poor appetite in 1980-81. Blood hemoglobin and serum B-12 concentrations in 1968-69 were statistically significantly and positively correlated with S-Hg, while erythrocyte sedimentation rate and the serum concentrations of potassium and triglycerides were significantly and negatively correlated with S-Hg, also after including potential confounders. Blood hematocrit examined in 1980-81 was negatively correlated with S-Hg. When including potential confounders, serum IgA was also statistically significantly correlated with S-Hg, but not in univariate analysis. No statistically significant correlation was observed between S-Hg, on the one hand, and the incidence of diabetes, myocardial infarction, stroke, or cancer on the other, while a statistically significant negative correlation was observed with overall mortality when age and education were included as background variables. There were some correlations between biological variables and S-Hg, probably of no negative clinical significance, and we conclude that there is no association between disease and S-Hg on a population basis in middle-aged and older women.

Methylmercury and inorganic mercury in serum--correlation to fish consumption and dental amalgam in a cohort of women born in 1922

Methylmercury in serum (S-MeHg) was assessed from serum concentrations of total (S-TotHg) and inorganic mercury (S-InoHg), determined by cold vapor-atomic absorption spectrometry. The samples were collected from 135 women on two occasions, in 1968-1969 and 1980-1981. In a subgroup of 29 women, an association was found between S-MeHg and the amount of fish consumed in 1968-1969 (r = 0.38, P = 0.04). The association was stronger (r = 0.50; P = 0.006) when the individuals' mean S-MeHg from 1968-1969 and 1980-1981 were plotted vs fish consumption 1968-1969. In the group, as a whole, there was an association between S-InoHg and number of dental amalgam surfaces, in both 1968-1969 (r = 0.48, P = 0.0001) and 1980-1981 (r = 0.57, P < 0.0001). The S-InoHg increased by approximately 0.1 nmol/L per amalgam tooth surface, corresponding to an uptake of approximately 0.2 microgram/day per amalgam surface, but with considerable interindividual differences. The levels were lower in 1980-1981 than in 1968-1969 for both MeHg and InoHg. The medians and ranges (nmol/L) were for MeHg 1968-1969: 3.6 (0.3-11.9); MeHg 1980-1981, 2.0 (-0.4-8.7); InoHg 1968-1969, 3.3 (0.7-11.8); InoHg 1980-1981, 1.7 (0.1-11.8); TotHg 1968-1969, 7.2 (1.9-18.8); and TotHg 1980-1981, 3.9 (1.0-14.2). The decrease in S-MeHg is probably due to a decreased consumption of MeHg via contaminated fish. The decrease in S-InoHg may reflect a decrease in environmental exposure, but the possibility of contamination of the 1968-1969 samples at sampling and/or storage cannot be excluded.

Mercury vapor release from dental amalgam in patients with symptoms allegedly caused by amalgam fillings

The aim of this study was to determine whether a group of patients with symptoms, self-related to their amalgam restorations, experienced an exposure to mercury vapor from their amalgam restorations that reached the range at which subtle symptoms have been reported in the literature. Furthermore, the aim was to determine whether the mercury exposure for these patients was significantly higher than for controls with no reported health complaints. The symptom group consisted of 10 consecutively selected patients from a larger group, referred by their physicians for investigation into any correlation between subjective symptoms and amalgam restorations. The control group consisted of 8 persons with no reported health complaints. The intra-oral release of mercury vapor was measured between 7:45 a.m. and 9:00 p.m. at intervals of 30-45 min, following a standardized schedule. The mercury levels in plasma, erythrocytes, and urine were also determined. The calculated daily uptake of inhaled mercury vapor, released from the amalgam restorations, was less than 5% of the daily uptake calculated at the lower concentration range given by the WHO (1991), at which subtle symptoms have been found in particularly sensitive individuals. The symptom group had neither a higher estimated daily uptake of inhaled mercury vapor, nor a higher mercury concentration in blood and urine than in the control group. The study provides no scientific support for the belief that the symptoms of the patients examined originated from an enhanced mercury release from their amalgam restorations.

Oxidative stress from environmental pollutants

Recently progress has been made on O2 toxicity and pathology related to numerous environmental contaminants in insects. The pro-oxidants studied included: dioxin, paraquat, and an assorted array of quinones, 8-methoxypsorlen, arsenic, and mercury. The responses to these oxidants are diverse, but they arise from the reactive oxygen species. These pro-oxidants in insects cause lipid peroxidation, protein and enzyme oxidation, and GSH depletion. Potentially, they may also cause DNA oxidation, and form DNA adducts. Oxidative challenge is alleviated by antioxidant compounds, but more importantly by the induction of antioxidant enzymes, which are crucial for the termination of O2 radical cascade and lipid peroxidation chain reaction. Insects exhibit a wasting syndrome under sub-acute stress. In acute toxicity vital physiological processes impaired are hemolymph melanization and diuresis. Thus, insects resemble vertebrates in both the response to oxidative stress and its pathological consequences. These results raise the prospect that insects may serve as non-mammalian model species for monitoring the oxidative-stress component of environmental toxicity.

Number of amalgam fillings in relation to cardiovascular disease, diabetes, cancer and early death in Swedish women

Altogether 1462 women aged 38, 46, 50, 54 and 60 yr were initially examined in 1968-69 in a combined medical and dental population study in Gothenburg, Sweden. Number of tooth surfaces restored with amalgam fillings was assessed. The incidences of myocardial infarction, stroke, diabetes, cancer and overall mortality were determined during a 20-yr follow-up period. Women with few amalgam tooth fillings had increased incidence of myocardial infarction, stroke, diabetes and early death compared with women with a large number of fillings. However, the significant inverse correlations between number of amalgam tooth fillings and the endpoints studied disappeared when number of teeth and socioeconomic group were included in a multivariate analysis. The study thus did not provide any evidence for a correlation between amalgam fillings and cardiovascular disease, diabetes, cancer or early death.

Serum selenium and glutathione-peroxidase activities and their interaction with toxic metals in dialysis and renal transplantation patients

Selenium, aluminum, cadmium, and magnesium concentrations and glutathione-peroxidase activities in sera of 35 healthy individuals, 30 renal transplants, and 30 hemodialysis patients were measured. Serum selenium, aluminum, and cadmium concentrations in both groups of patients were higher than the controls (p less than 0.001), whereas the serum glutathione-peroxidase levels were lower (p less than 0.001). According to our results, it can be concluded that the patients receiving hemodialysis are subjected to more toxic elements than the transplantation patients. These findings imply that dietary selenium supplement may be suggested in renal failure for the detoxification of elements, such as cadmium and mercury. The essential trace element selenium takes part not only in the direct protection of endothelial cells against the accumulation of aggressive oxygen species, but also in the prevention of the toxic effects of cadmium or in the modulation of the active calcium transport.

Report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

Subjects of the past decade in the dental literature are reflected in this year's Committee report. We note the decrease in the prevalence of caries, the influence of dental implants, the advancements in dental materials, and the continued efforts to control adhesive events in the oral cavity. This year we included comments from and about many significant review articles published this past year. The Committee continues to be concerned about the quality of some of the work reported and the quality of the reporting. We have attempted to select the distinguished work, that which provides new information to our profession. The subjects covered include pulp biology, caries prevention, periodontics, implants, craniomandibular function and dysfunction, occlusion, and dental materials.

Mobilized mercury in subjects with varying exposure to elemental mercury vapour

In a mercury mobilization test, 0.3 g of the complexing agent sodium 2,3-dimercaptopropane-1-sulfonate (DMPS) was given orally to 10 workers with moderate occupational exposure to elemental mercury vapour, to 8 dentists with slight exposure, to 18 matched controls, and to 5 referents without amalgam fillings. In the workers, DMPS caused an increase in 24-h urinary mercury excretion by a factor of 10; in the dentists, 5.9; in the controls, 5.3; and in the amalgam-free referents, 3.8. Of the mercury excreted during 24 h, 59% appeared during the first 6 h. Close, albeit non-linear, associations were found between mobilized mercury and the premobilization mercury levels in plasma and urine, but not with the duration of occupational exposure or the rough estimate of the integrated function of blood levels vs time. The present data indicate that mercury mobilized after a single DMPS dose in close connection with exposure is mainly an index of recent exposure and is not significantly affected by slow body pools or long-term exposure.

The influence of dental amalgam placement on mercury, selenium, and glutathione peroxidase in man

Amalgam restorations were inserted in eight healthy persons, previously unprovided with dental restorations, who had several severe carious lesions. The mean number of surfaces restored were 16.1 (range, 11 to 22). The total mean calculated amount of mercury inserted was 2.9 g (range, 1.5 to 4.3 g). Blood and urinary levels were measured on seven occasions during a 4-month period before and a 3-month period after amalgam placement. One and 3 months after placement, the P-mercury mean values were almost equal to the preplacement values (3.3 nmol/l). After placement U-mercury increased continuously; 3 months after placement a statistically significantly higher (p less than 0.05) mean U-mercury value (0.58 nmol/mmol creatinine) was found compared with the mean preplacement value (0.34 nmol/mmol creatinine). No statistically significant correlation was found between the P- and U-mercury concentrations and the total number of amalgam surfaces. Selenium levels in plasma and urine and erythrocyte glutathione peroxidase showed no systematic change of pattern. The results show that the insertion of amalgam fillings contributed to the U-mercury concentration, but apparently even more extensive amalgam therapy and/or longer exposure periods are needed to affect the P-mercury concentration. No negative effects on the P- and U-selenium or the erythrocyte glutathione peroxidase levels could be found during the 3 months immediately after an extensive amalgam placement. The supplementary blood and urine analyses were not influenced by the insertion of amalgam fillings.

Mercury, selenium, and glutathione peroxidase before and after amalgam removal in man

In 10 healthy persons all amalgam fillings were replaced with gold inlays. Blood and urinary levels were measured on 10 occasions during a 4-month period before and a 12-month period after amalgam removal. These variables were also measured three times in 10 healthy controls. A strong statistically significant relation was found between plasma mercury values and both the total number of amalgam surfaces (r = 0.71, p = 0.0006) and the total surface area of the fillings (r = 0.73, p = 0.0004). In the immediate postremoval phase plasma mercury rose three- to four-fold, whereas the urinary and erythrocyte mercury rose about 50%. These peak values declined to the preremoval level at about 1 month. Twelve months after the removal the plasma and urinary mercury levels were significantly reduced to 50% and 25%, respectively, of the initial values for the experimental group. Apart from the significantly lower plasma selenium values 5 and 10 days after removal no significant differences were found with regard to plasma selenium or erythrocyte glutathione peroxidase either within or between the experimental and the control groups. A large number of supplementary biochemical analyses did not show any influence on organ functions or any differences between the groups before or after the amalgam removal. Amalgam fillings considerably contributed to the plasma and urinary mercury levels.