We adapted the Alkaline Comet Assay to examine whether demographic and epidemiologic factors, such as age, sex, race, BMI, hypertension, tobacco or alcohol use, affect the repair capacity of single strand breaks (SSB) in humans. We examined repair of gamma-radiation-induced DNA damage in unstimulated cryopreserved peripheral blood mononuclear cells (PBMCs) from four age- and sex-matched groups of whites and African-Americans between ages 30-64. We found that age, race and sex affect the fast component of DNA repair, while the slow component was unaffected. We analyzed the strength of effect of demographic and health-related variables on the ability of cells to repair their DNA damage which we have termed single strand break repair capacity (SSB-RC). One-way and two-way ANOVA as well as t-tests were used to detect significant differences in SSB-RC between groups characterized by independent variables including sex, race, age (stratified into groups), hypertension, current and past ethanol and tobacco use and family history of cancer. Simple linear regression analyses were applied to investigate relationships between continuous independent variable (age, BMI or pack-years) and dependent variable (SSB-RC or intercellular variability in DNA damage). Simple regression analyses were performed in subsets of the 96-individual cohort characterized by sex or race or both sex and race. A statistically significant interaction between age and race was found for females when SSB DNA repair capacity was expressed using parameters related to the fast component of DNA repair, the logarithm of the initial rate of DNA repair (p <0.005) and the logarithm of the half-time of DNA repair (p <0.05). The interaction between age and sex was detected in African-Americans when SSB-RC was measured by the logarithm of the initial rate of DNA repair (p <0.05) and the logarithm of the half-time of DNA repair (p = 0.052). The bi-exponential repair model describes fast and slow DNA repair components and residual non-repairable DNA damage. Both fast and slow repair components are usually characterized by their half-times and fractions of initial DNA damage repaired. Thus, there is a decrease in the fast component of DNA repair with age in African-American females when compared with white females or African-American males. We detected no interaction between age and sex in whites for any DNA repair parameter. However, when we analyzed the data using the simpler model with no interaction, we found that SSB-RC measured by the logarithm of the half-time of DNA repair and the residual DNA damage after 30 min are significantly affected by sex (p <0.01 and p <0.05). Sex also affects SSB-RC as measured by the logarithm of the initial rate of DNA repair;however, this relationship is not statistically significant (p = 0.056). These results indicate that the rate of fast component of DNA repair is higher in white males than white females. We also found that the logarithm of the initial rate of DNA repair increases with age in whites (p <0.02). Finally, there is no effect of age on SSB-RC in whites and no difference in SSB-RC between white males and African-American males. We also found that there is no effect of body mass index (BMI), hypertension, alcohol or tobacco use and family cancer history on SSB-RC in our 93-individual cohort as assessed by t-tests, ANOVA and regression analyses. In addition to assessing DNA repair capacity in the HANDLS cohort, we used our small comet study to correlate single strand break (SSB) level with single strand break repair capacity (SSB-RC) and markers of oxidant stress and inflammation. We found that females have higher single strand break (SSB) levels than males (p=0.013). There was a significant negative correlation between SSB-RC and SSB level (p=0.041). There was a positive correlation between SSBs in African American males with both heme degradation products (p=0.008) and high-sensitivity C-reactive protein (hs-CRP) (p=0.022). We found a significant interaction between hs-CRP and sex in their effect on residual DNA damage (p=0.002). Red blood cell reduced glutathione concentration was positively correlated with the levels of oxidized bases detected by endonuclease III (p=0.047), heme degradation products (p=0.015) and hs-CRP (p=0.020). However, plasma carbonyl levels showed no significant correlation with other markers. The data from the literature and from our very limited study suggest a complex relationship between measures of oxidative stress and frequently used clinical parameters believed to reflect inflammation or oxidative stress. Oxidative stress and inflammation has been assessed in clinical settings by measuring levels of high-sensitivity C-reactive protein (hs-CRP). CRP is an acute phase protein that is associated with risk of coronary artery disease, peripheral arterial disease, stroke, diabetes and metabolic syndrome. Since hs-CRP is linked to chronic inflammation that is a consequence of oxidative stress, it is relevant to examine the importance of hs-CRP as a biomarker of disease states related to oxidative stress. We have begun to evaluate another marker of oxidant stress and oxidative DNA damage that can be detected in serum, the common DNA base modification 8-oxo-7,8-dihydroguanine (8-oxo-G) and its correlation with inflammation, aging and other clinical parameters. We have assessed the relationship of 8-oxo-G levels with selected clinical and laboratory measures in a select part of our cohort. Our preliminary analyses revealed that the relationship between both systolic blood pressure and pulse pressure were significant. The relationship between 8-oxo-G and poverty status with race were not significant. 8-oxo-G levels increase with age and though we found no relationship between hs-CRP with SSB we have found that 8-oxo-G levels increase with increasing hs-CRP levels, suggesting a potential important relationship between a marker of inflammation and a marker of oxidative stress.
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