Metallothionein and tissue damage.

Metallothioneins (MTs) are a class of small cysteine-rich heavy metal binding proteins produced in response to a variety of stresses, inflammation, and as components of the acute-phase response. Although the exact role of MT in this phase is not known, a number of reports have shown that expression of hepatic MT is markedly increased in response to bacterial infection, an effect mediated by lipopolysaccharides. More recently, it has been suggested that MT may play a major role in the prevention of tissue damage. Thus MT has been shown to be an efficient free radical scavenger. Indirect activation of macrophages and neutrophils during the acute phase of inflammation result in a massive release of various species of oxygen metabolites which may be indirectly responsible for the initiation of apoptosis. In addition, expression of MT also increases cell resistance to radiation damage. Together, these results suggest that MT could be part of a generalized protective system in mammalian cells.