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.
Answers to all your Biology Questions
