Monitoring of human populations for early markers of cadmium toxicity: A review

Exposure of human populations to cadmium (Cd) from air, food and water may produce effects in organs such as the kidneys, liver, lungs, cardiovascular, immune and reproductive systems. Since Cd has been identified as a human carcinogen, biomarkers for early detection of susceptibility to cancer are of an importance to public health. The ability to document Cd exposure and uptake of this element through biological monitoring is a first step towards understanding its health effects. Interpretation and application of biological monitoring data for predicting human health outcomes require correlation with biological measures of organ system responses to the documented exposure. Essential to this understanding is the detection and linkage of early biological responses toxic effects in target cell populations. Fortunately, advances in cell biology have resulted in the development of pre-clinical biological markers (biomarkers) that demonstrate measurable and characteristic molecular changes in organ systems following chemical exposures that occur prior to the onset of overt clinical disease or development of cancer. Technical advances have rendered a number of these biomarkers practical for monitoring Cd-exposed human populations. Biomarkers will be increasingly important in relation to monitoring effects from the exposure to new Cd-based high technology materials. For example, cadmium-selenium (CdSe), nano-materials made from combinations of these elements have greatly altered cellular uptake characteristics due to particle size. These differences may greatly alter effects at the target cell level and hence risks for organ toxicities from such exposures. The value of validated biomarkers for early detection of systemic Cd-induced effects in humans cannot be underestimated due to the rapid expansion of nano-material technologies. This review will attempt to briefly summarize the applications, to date, of biomarker endpoints for assessing target organ system effects in humans and experimental systems from Cd exposure. Further, it will attempt to provide a prospective look at the possible future of biomarkers. The emphasis will be on the detection of early toxic effects from exposure to Cd in new products such as nano-materials and identification of populations at special risk for Cd toxicity.