Consumption of mercury-contaminated rice induces oxidative stress and free radical aggravation in rats.

OBJECTIVE: To study the oxidative stress induced by consumption of mercury-contaminated rice in rats, and to assess the possible public health risk of mercury contamination in Wanshan mining area. METHODS: Sprague Dawley rats were fed the mercury-contaminated rice produced from Wanshan area for 90 days. The antioxidant status and the free radicals in rat serum were evaluated. RESULTS: High mercury accumulation in organs of rats fed the mercury-contaminated rice confirmed the server pollution of mercury in Wanshan mining area. The intensity of electron spin resonance (ESR) signal increased by 87.38% in rats fed the rice from Wanshan compared with that in the control rats fed the rice from Shanghai, suggesting that chronic dietary consumption of rice from mercury mining area could induce an aggravation of free radicals. Feeding the mercury-contaminated rice was associated with significant decreases in the antioxidant enzymatic activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) and concentration of serum nitric oxide (NO), but it had no effect on serum nitric oxide synthase (NOS) activity. Feeding the mercury-contaminated rice raised the level of serum malonyldialdehyde (MDA), indicating the occurrence of oxidative stress. CONCLUSION: The long-term dietary consumption of mercury-contaminated rice induces the aggravation of free radicals and exerts oxidative stress.

Rice from mercury contaminated areas in Guizhou Province induces c-jun expression in rat brain.

OBJECTIVE: Mercury (Hg), as one of the priority pollutants and also a hot topic of frontier environmental research in many countries, has been paid higher attention in the world since the middle of the last century. Guizhou Province (at N24 degrees 30'-29 degrees 13', E103 degrees 1'-109 degrees 30', 1 100 m above the sea level, with subtropical humid climate) in southwest China is an important mercury production center. It has been found that the mercury content in most media of aquatics, soil, atmosphere and in biomass of corns, plants and animals, is higher than the national standard. The present study aims to explore the influence of mercury pollution on the health of local citizens. METHODS: The effect of rice from two mercury polluted experimental plots of Guizhou Province on the expression of c-jun mRNA in rat brain and c-jun protein in cortex, hippocampus and ependyma was observed using reverse transcription polymerase chain reaction (RT-PCR) and immunocytochemical methods. RESULTS: The results showed that the mercury polluted rice induced expression of c-jun mRNA and its protein significantly. Selenium can reduce Hg uptake, an antagonism between selenium and mercury on the expression of c-jun mRNA and c-jun protein. CONCLUSION: c-jun participates in the toxicity process of brain injury by mercury polluted rice, the expression of c-jun mRNA in brain, and c-jun protein in rat cortex and hippocampus can predict neurotoxicity of mercury polluted rice. People should be advised to be cautious in eating any kind of Hg-polluted foods. To reveal the relationship between c-jun induction and apoptosis, further examinations are required.

Neurotransmitter level changes in domestic ducks (Shaoxing duck) growing up in typical mercury contaminated area in China.

The neurotransmitter level changes of ducks exposed 8-month in a mercury-polluted site (Wanshan, China) and a reference site (Shanghai, China) were examined. Chemical analyses showed both higher mercury and selenium concentrations in the organ of Wanshan ducks. An increased content of acetylcholine (ACh) in brain and blood and a decreased activity of acetylcholinesterase (AChE) in blood were observed. Moreover, there was an increasing trend for nitric oxide synthase (NOS) activity and nitric oxide(NO) production in duck brain, but a reduction of NOS activity in duck serum. The possible explanations were due to the interactive effect of selenium accumulation and the sublethal exposure level of mercury in Wanshan area. The present study showed that AChE and NOS were sensitive to mercury contamination of real circumstance, suggesting that these two indexes have the potential to be biomarkers in assessment of health effects by mercury contamination.

[Effect of chronic exposure by mercury contaminated rice on neurotransmitter level changes in rat brain].

In order to survey the potential health risk of environmental exposure by mercury, Sprague-Dawley rats were reared by mercury contaminated rice from mercury mining area. The changes of neurotransmitter acetylcholine (ACh) and acetylcholinesterase (AChE) in rat brain were examined at different times. The results show that the mercury-contaminated rice significantly increase the content of ACh in rat brain after exposure for 7 days. ACh maintained at a high level even after exposure for 30 days, but decreased significantly after exposure for 90 days. The changes of AChE represented an inverse trend compared with that of ACh. The coexisting selenium in rice exhibited antagonistic effects on both mercury accumulation and toxicity. The findings suggested that neurotoxic effects of environmental mercury contamination had been significantly represented after chronically dietary exposure. Further studies are needed to examine the relationship between the neurotransmitter level changes and the Alzheimer's Disease (AD).

[Induction of free radicals after dietary exposure by mercury contaminated rice and protective effect of coexisting selenium].

Sprague-Dawley rats were reared by environmental mercury contaminated rice to survey the potential health risk of Wanshan mercury mining area. Electron spin resonance (ESR) was introduced to detect the species and the intensities of free radicals, using spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). The results showed that the mercury-contaminated rice significantly increased the levels of free radicals and MDA in rat brain at 7 days (p < 0.05). ESR spectrums showed that the principal spin adducts resulted from the trapping of alkyl free radical (alphaH = 22.7 x 10(-4)T +/- 1.6 x 10(-4)T, alphaN = 15.5 x 10(-4)T +/- 0.5 x 10(-4)T), and hydroxyl radical. Levels of free radicals and MDA increased slowly until after 90-day exposure period (83%, 100%). Element correlation analysis showed high correlations of mercury and selenium in the brain of rat fed with Wanshan rice, suggesting that the coexisting selenium in rice exhibited antagonistic effects on both mercury accumulation and toxicity. The slight increases of free radicals in rat brain at 7, 20 and 30-day exposure periods should be related with the scavenger effect of Se.

[Expression of c-FOS protein in rat hippocampus by inducing of mercury contaminated rice].

In order to probe into the biological effects of mercury in typical mercury contaminated area and try to apply the expression of immediately early gene c-fos in brain to early predict the neurotoxicity of mercury in typical polluted areas, the expression of c-FOS protein in rat hippocampus is observed using immunocytochemical methods. The results show the mercury pollutes rice induced significantly the expression of c-FOS protein in hippccampus;the antagonisis between selenium and mercury on the exposure process. It is suggested that c-fos can be used as an effective index of detecting and assessing neurotoxicology of mercury polluted areas.

[Antagonistic effects of selenium on the expression of c-fos in central nerval system of rat included by mercury contaminated rice].

The objective of this paper is to study the antagonisms between selenium and mercury and the effect of different species mercury on the brain injury. The expression of c-fos mRNA and c-FOS protein in rat brain induced by Hg-contaminated rice was observed by using reverse transcriptions polymerase chain reaction (RT-PCR) and immunocytochemical methods. The results show the Hg-contaminated rice induced significantly the expression of c-fos mRNA and c-FOS protein; selenium could antagonize mercury accumulative level in brain. Antagonistic effects of selenium on the expression of c-fos included by mercury and the molecule mechanism of the antagonisms between selenium and mercury was probed, too.

[Correlation of mercury, selenium and other elements in the tissues of fishes from the regions at different mercury exposure level].

The contents of selenium and other elements in fish liver and muscle tissues collected from mercury polluted area of Wanshan, Guizhou province of China and non-known mercury polluted one of Beijing were determined with instrumental neutron activation analysis, and that of mercury was determined with atomic fluorescence spectrometry. The correlation among the determined elements, especially between mercury and selenium, in the fish tissues were studied. For most of the elements significant difference of elemental content was found between tissues of liver and muscle, and mostly the content in liver was higher than that in muscle. It was interesting to note that the average content of mercury in Guizhou fish liver was 25-fold higher than that in Beijing one, and 5-fold higher in Guizhou fish muscle than that in Beijing one. For most of the elements no significant difference on the average content was found between the same tissues of the two areas. The molar ratio of Hg/Se increased with the increasing of Hg content at the low Hg level, but the alteration trend became gently and reached to a higher constant value (about 0.2) at the higher Hg level. Only the element of bromine and rubidium was found to have strong linear correlation between the two different tissues of liver and muscle. Though certain correlation existed among the different elements of fish tissues from the two areas, the most significant and the closest one existed between the mercury and selenium of muscle tissue of Guizhou fishes. A closer correlation was also found between them of liver tissue of Guizhou fishes. As for Beijing fish tissues, the correlation of mercury and selenium only existed in liver but no correlation of them was found in muscle. Our results confirm the fact that a certain interaction exists between mercury and selenium in organisms including fish, and it is more evident as the mercury-exposed level is higher. Some significant correlation was also observed between other elements, such as potassium and sodium, cesium and rubidium, iron and zinc, in fish tissues and it could be well explained by their similar chemical and physical properties or their different biological functions.

[Effect of methylmercury on expression of immediate early gene c-jun mRNA in rat brain].

In order to probe into the early prediction molecular index and the signal transduction molecular mechanism of methyl mercury chloride (MMC) neurotoxicity, the expression of c-jun mRNA in rat brains induced by different concentration MMC for different times were observed by using reverse transcription polymerase chain reaction (RT-PCR) methods (the control group was physiological saline of 0.9%, the concentrations of expose groups were 0.05, 0.5, 5 mg x kg(-1) respectively, the sampling times were 20, 60, 240, 1440 min). The result showed the expression of c-jun mRNA in rat brains was prior to the accumulation of mercury, and the expression of c-jun mRNA in rat brains could early predict the neurotoxicity of MMC. IEG (c-jun) participated in the toxicity process of injury by MMC.

[Mercury pollution and its ecosystem effects in Wanshan mercury miner area, Guizhou].

Samples of water, soil, plants, crops and animals collected from Wanshan mercury miner area, Guzhou Province, were analyzed with an AMA-254 liquid/solid mercury analyzer. It was shown that mercury pollution is mainly in soil and air; except water from a pool, no anomaly mercury is found in waters. Mercury content in soil is 24.31-347.52 mg.kg-1, two or three magnitude higher than the average value of Chinese soils; mercury content in plants is 0.47-331.4 mg.kg-1, and moss can enrich much mercury. Due to the long time of exploration and smelting, abundant mercury are accumulated in the local ecosystem, and healthy of local people are threatened seriously.