Model Studies Related to Vanadium Detoxification
- Model studies related to vanadium biochemistry: recent advances and perspectives
Contamination of the environment by vanadium has dramatically increased in recent years, especially in the most developed countries, due to the increasing use of fossil fuels, which liberate V2O5 during combustion.79 Therefore, the toxicology and detoxification of vanadium constitute an area of increasing development.
The degree of toxicity depends on the route of administration, oxidation and chemical form and it is also to some extent species-dependent. Vanadium compounds, especially V2O5, are strong irritants of the airways and the eyes. Acute and chronic exposure gives rise to conjunctivitis, rhinitis, reversible irritation of the respiratory tract, and to bronchitis, bronchospasms, and asthma-like diseases in more severe cases. It has shown that it can produce gastrointestinal distress, fatigue, cardiac palpitation, and kidney damage. In humans, acute vanadium toxicity has been observed in vanadium miners, as well as other industrial workers exposed to high concentrations of the element. The classic symptoms of this malady, referred to as "green tongue" syndrome, are a green discoloration of the tongue, accompanied by some of the cited disorders.80,81
It has been usually accepted that vanadium toxicity increases with increasing oxidation state, vanadium(V) being the most toxic.80,81
Living systems have developed defense mechanisms to deal with the reactive and potentially harmful by-products that arise from cellular metabolism and to control the effects of exogenous substances that eventually invade the organism (biological detoxification). Drugs have been developed to chelate metal ions in vivo, not only to eliminate excesses of essential metals but also to prevent possible damage caused by nonessential, toxic elements (chemical detoxification).
Some of the systems mentioned in this account are evidently relevant to the toxicity and detoxification of vanadium. Some of the metabolic processes (glutathione-, ascorbate- or cysteine- mediated reduction of vanadates(V); complexation of VO2+ by different biomolecules; accumulation of vanadium in hard tissues) must play an important role in biological vanadium detoxification.81
Most of the systems assayed for chemical detoxification contain chelating or reducing/chelating agents.81 Animal studies have demonstrated that the best detoxification agent may be L-ascorbic acid.81-83 Its action is related to the facility with which it reduces vanadium(V) to VO2+ and to the possibility that the oxocation generated may be complexed by its oxidation products, as discussed above.
Better knowledge of the fundamental metabolic steps and a thorough characterization of new vanadium species with chelating or reducing agents may be useful for the development of more potent and specific detoxification agents for vanadium.
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