The effect of mercury and vitamin E on tissue glutathione peroxidase activity and thiobarbituric acid values

Methylmercury effects on avian brains

Methylmercury (MeHg) is a concerning contaminant due to its ubiquity and harmful effects on organisms. Although birds are important models in the neurobiology of vocal learning and adult neuroplasticity, the neurotoxic effects of MeHg are less understood in birds than mammals. We surveyed the literature on MeHg effects on biochemical changes in the avian brain. Publication rates of papers related to neurology and/or birds and/or MeHg increased with time and can be linked with historical events, regulations, and increased understanding of MeHg cycling in the environment. However, publications on MeHg effects on the avian brain remain relatively low across time. The neural effects measured to evaluate MeHg neurotoxicity in birds changed with time and researcher interest. The measures most consistently affected by MeHg exposure in birds were markers of oxidative stress. NMDA, acetylcholinesterase, and Purkinje cells also seem sensitive to some extent. MeHg exposure has the potential to affect most neurotransmitter systems but more studies are needed for validation in birds. We also review the main mechanisms of MeHg-induced neurotoxicity in mammals and compare it to what is known in birds. The literature on MeHg effects on the avian brain is limited, preventing full construction of an adverse outcome pathway. We identify research gaps for taxonomic groups such as songbirds, and age- and life-stage groups such as immature fledgling stage and adult non-reproductive life stage. In addition, results are often inconsistent between experimental and field studies. We conclude that future neurotoxicological studies of MeHg impacts on birds need to better connect the numerous aspects of exposure from molecular physiological effects to behavioural outcomes that would be ecologically or biologically relevant for birds, especially under challenging conditions.

The influence of nutrition on methyl mercury intoxication

This article reviews progress in the research of methyl mercury (MeHg) and nutrient interactions during the past two decades. Special emphasis is placed on the following three major areas: a) effects on kinetics, b) effects on toxicity, and c) possible mechanisms. Dietary information is not usually collected in most epidemiologic studies examining of the effects of MeHg exposure. However, inconsistency of the MeHg toxicity observed in different populations is commonly attributed to possible effects of dietary modulation. Even though the mechanisms of interaction have not been totally elucidated, research in nutritional toxicology has provided insights into the understanding of the effects of nutrients on MeHg toxicity. Some of this information can be readily incorporated into the risk assessment of MeHg in the diets of fish-eating populations. It is also clear that there is a need for more studies designed specifically to address the role of nutrition in the metabolism and detoxification of MeHg. It is also important to collect more detailed dietary information in future epidemiologic studies of MeHg exposure.

Effect of vitamin E and synthetic antioxidants on the survival rate of mercury-poisoned Japanese quail

The effect of vitamin E and the synthetic antioxidants, 6-ethyoxy,1,2-dihydro 2,2,4-trimethylquinoline (ethoxyquin), 2,6 bis(1,1 dimethyethyl)-4-methylphenol (BHT), N,N-diphenyl-p-phenylene diamine (DPPD), bis-(diethyl thiocarbamoyl) disulfide (Antabuse), and 2 tertiary-butyl-4-methoxyphenol (BHA) on organic mercury-induced mortality was investigated in Japanese quail. When the synthetic antioxidants, ethoxyquin, BHT, and Antabuse were fed at 1% of the diet, they induced mortality. Ethoxyquin was less toxic in combination with mercury (Hg) than when it or mercury was given alone. Of the antioxidants tested at .5% of the diet, only Antabuse was toxic as shown by increased mortality. At .5% of the diet, both ethoxyquin and DPPD reduced mortality associated with organic Hg poisoning. Neither BHA nor BHT had any effect in reducing Hg toxicity. In fact, mortality from organic Hg was greater when organic Hg was given in combination with .5% BHT than when given alone. Vitamin E was equal or superior to all synthetic antioxidants tested in alleviating the toxicity of organic Hg poisoning. The cause of observed antioxidant protection during organic Hg stress is not known but the protection may result from the ability to scavenge free radicals generated by induction of in vivo peroxidation by the Hg compound.