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Increased Serum Levels of 8-Hydroxy-2'-Deoxyguanosine in Clinical Depression

From the Faculty of Health Sciences (M.J.F.), Simon Fraser University, Burnaby, British Columbia, Canada; and the Department of Psychology (G.E.M.), University of British Columbia, Vancouver, British Columbia, Canada.

Address correspondence and reprint requests to Michael J. Forlenza, PhD, MPH, Faculty of Health Sciences, Simon Fraser University, West Mall Centre 2812, 8888 University Drive, Burnaby, B.C. V5A 1S6, Canada. E-mail: forlenza{at}sfu.ca.

Objective: We sought to understand the pathophysiological effects of depression by examining group differences in serum levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a biomarker of oxidative damage.

Methods: Our sample consisted of 169 participants. Eight-four of these participants met diagnostic criteria for clinical depression. The 85 participants in our comparison group were matched on age, gender, and ethnicity to the depressed group. 8-OHdG was measured by enzyme-linked immunosorbent assay.

Results: After adjusting for age, gender, race/ethnicity, years of education, daily smoking, average number of alcoholic drinks per week, average amount of physical activity per week, and body mass index, participants in the depressed group had significantly higher levels of oxidative DNA damage compared with participants in the control group. Pairwise comparisons showed that participants with major depression had significantly higher levels of 8-OHdG than control subjects and marginally higher levels of 8-OHdG compared with those with minor depression. Furthermore, participants with recurrent episodes of depression had more oxidative damage than participants with single episodes, who in turn had more damage than healthy control subjects. Finally, participants with recurrent episodes of major depression had more DNA damage than other depressed participants, who in turn had more damage than healthy control subjects.

Conclusions: Our findings suggest that increased oxidative damage may represent a common pathophysiological mechanism, whereby depressed individuals become vulnerable to comorbid medical illness.

Key Words: depression • DNA damage • oxidative damage • comorbidity

Abbreviations: 8-OHdG = 8-hydroxy-2'-deoxyguanosine; DSM-IV= Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition; DISH = Depression Interview and Structured Hamilton Interview; ELISA = enzyme-linked immunosorbent assay; HPLC-EC = high-performance liquid chromatography with electrochemical detection; GC-MS= gas chromatography–mass spectrometry; BMI= body mass index.