Abstract
Metallothionein is a cysteine-rich low molecular weight protein with a high affinity for metals such as cadmium, zinc, copper and mercury, and is induced by these metals and many other factors such as glucocorticoids and cytokines. Metallothionein has been found in a variety of organisms ranging from prokaryotes, eukaryotic microorganisms, plants, invertebrates to vertebrates (fishes, amphibians, reptiles, birds and mammals). Quite a few research groups reported metallothionein as a biochemical marker which reflect exposed level and effects of heavy metals. Induced amounts of metallothionein by exposure to heavy metals such as cadmium and mercury have been reported in human, harbor seal, seabirds, snail, earthworm and fish. Significant correlation between metallothionein levels and cadmium concentrations or exposure doses of cadmium have been established in harbor seal, seabirds, snail, earthworm and several kinds of fish. In people living in cadmium-polluted areas or those occupationally exposed to this metal, the elevated amounts of metallothionein excreted into urine were found to be more sensitive and specific marker than urinary cadmium for renal dysfunction found in these human populations. Metallothionein mRNA level has been also increased by exposure to cadmium or mercury in the blood of human or the liver of fish, respectively, Recently, hepatic metallothionein has been induced by glucocorticoid or violent air-pumping stress in fish. In conclusion, metallothionein is a very useful biomarker for monitoring heavy metal pollution in man and the wild-life.
