oa Comet Assay: An Exposure Biomarker for Human Biomonitoring

A global concern on the adverse effects of chemicals to human health has led toxicologists, and in particular genetic toxicologists, to identify environmental genotoxins. The conventional method of identification involves techniques such as Ames test, chromosomal aberrations, micronucleus assay, alkaline elution assay, etc. However, these methods are cumbersome, time consuming as well as resource-intensive. During the last two decades, a state-of-the-art technique, the single cell gel electrophoresis (SCGE) /Comet assay, has gained importance as a rapid, visual and sensitive technique for qualitative and quantitative assessment of DNA damage and repair. It is a valuable technique for detection of a variety of DNA damages, which include single and double strand breaks, alkali labile sites and oxidative base damages. Comet assay can be performed on any eukaryotic and some prokaryotic cells and may be used for both in vitro and in vivo screening of geno- and anti-genotoxic potential of chemicals. Its non-invasive nature and requirement of few cells for processing has made this assay widely accepted for monitoring human genotoxicity. Its sensitivity has enabled genetic toxicologists to monitor low-level, long-term exposure to chemicals, thus predicting genetic damage at an early stage. Our studies, in the Indian population, using the alkaline Comet assay have revealed significant gender-related differences in the extent of DNA damage in lymphocytes. DNA damage was also found to vary with eating and smoking habits, age, exercise as well as occupational exposure. In vitro Comet assay studies have also been performed using human peripheral blood lymphocytes and cell lines such as MCF-7, CHO, JM-1 to assess the genotoxic potential of environmental chemicals. The versatility of the Comet assay has indeed proven it to be a Rosetta Stone in the garden of Genetic Toxicology.