Measuring DNA Damage and Repair Capacity in Human Popula

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The direct role of DNA repair in cellular senescence, aging, sporadic disease susceptibility and incidence remains unclear except in the well know groups of heritable disorders associated with cancer susceptibility and premature aging such as Xeroderma Pigmentosum, Hereditary Non-polyposis Colorectal Carcinoma (HNPCC), and Werner?s syndrome among others. DNA repair capacity (DRC) of individuals may be a useful clinical tool in identifying individuals at risk for sporadically occurring disease. The clinical applications of the COMET Assay are varied ranging from assessment of chemotherapy agent geno- and cytotoxicity to correlation of oxidative DNA damage levels in spermatozoa with male infertility. Use of the Alkaline Comet Assay to assess DNA repair capacity (DRC) in human population studies has been limited by difficulties in controlling for inter-experimental variability, developing appropriate internal standards and establishing a methodology for cryopreserved lymphocytes appropriate for use in this assay. The aim of this work is to develop an accurate, reproducible and efficient comet assay methodology for evaluating DNA repair in cryopreserved lymphocytes. Our work thus far shows that unstimulated human cryopreserved lymphocytes can be used to accurately measure DRC using the comet assay. These refinements have been used to assess DRC in a clinical cohort of individuals in the Healthy Aging in Neighborhoods of Diversity across the Life Span (HANDLS) study. Healthy Aging in Neighborhoods of Diversity across the Life Span (HANDLS) study (HANDLS) is a community-based, epidemiologically driven multidisciplinary research effort designed to focus on evaluating health disparities in socioeconomically diverse Caucasians and African Americans in Baltimore. One of the domains of the HANDLS study examines the possible role of oxidative stress and defects in DNA repair in the development of age associated disease. The early appearance and increased severity of age-associated disease among African Americans and low SES individuals suggests that the factors contributing to the emergence of health disparities may also induce a phenotype of ?premature aging? or ?accelerated aging?. While we do not posit that health disparities result from genetic alterations in genes associated with the known heritable progeroid syndromes. We do hypothesize that in low SES populations with high rates of early onset age-associated disease the interaction of biologic, psychosocial, socioeconomic and environmental factors may result in a phenotype of accelerated aging biologically similar to these syndromes with increased susceptibility to oxidative stress, premature accumulation of oxidative DNA damage, defects in DNA repair and higher levels of biomarkers of oxidative stress. Health disparities therefore, may be the end product of this complex interaction in populations at high risk. We are examining the repair of DNA damage induced by ?-irradiation in lymphocytes from four age-matched groups of male and female Caucasians and African Americans between ages 30-64. DRC is being assessed using parameters described in the literature including half time of DNA repair and residual DNA damage after 30 min. Our preliminary findings however include the definition of a new repair parameter that we call ?initial rate of DNA repair. Our data suggest that the? initial rate of DNA repair? may approximate the fast component of DNA repair and that the ?residual DNA damage? measure may correspond to the slow DNA repair component discussed in the basic science DNA repair literature. The clinical implications of these parameters require further investigation.