TOXICITY OF TRACE ELEMENTS IN TOBACCO SMOKE

Abstract

The potential to cause cellular damage by metal ions in conjunction with other constituents of tobacco smoke is enormous. Various studies have demonstrated the role of reactive oxygen species in the toxicity of transition metals, and the presence of many highly reactive metal ions in high concentrations in tobacco smoke indicates a role for metal ions in the subsequent toxicity and carcinogenicity of tobacco smoke. This review summarizes current information pertaining to the role of metal ions in the toxicity and carcinogenicity of tobacco smoke, and describes the mechanisms that may be involved. Evidence indicates that multiple mechanisms may be involved in the production of reactive oxygen species involving metal ions in tobacco smoke. Similar mechanisms involving redox cycling with the production of superoxide anion, hydrogen peroxide, and hydroxyl radical appear to be involved for iron, copper, and chromium. However, some metal ions, such as nickel, lead, cadmium, mercury, arsenic, and antimony, deplete glutathione and protein-bound sulfhydryls, thus contributing to an oxidative stress in this manner. Reactions involved in the production of reactive oxygen species may be commonly associated withmost membranous fractions of the lungs as mitochondria, microsomes, and peroxisomes. Furthermore, phagocytic cells accumulate in the lungs of smokers, and are another important source of reactive oxygen species. These phagocytic cells accumulate metal ions as iron, which catalyzes the formation of reactive oxygen species. Thus, a single metal ion may initiate formation of reactive oxygen species by more than a single mechanism, and involve more than one organelle or cell type. Metal ions can also act as catalysts for the formation of reactive oxygen species and various free radicals by numerous organic, redox cycling constituents such as hydroquinone and catechol, which are present in tobacco smoke, thus greatly enhancing the potential for tissue damaging effects in lungs. Finally, radioactive elements such as polonium-210 in tobacco smoke are additional contributing factors to the production of tissue damage. The cumulative and summative effects of metal ions are believed to play a significant role in the toxicity and carcinogenicity of tobacco smoke.