Stability of the oxidative stress marker, urinary 8-hydroxy-2'-deoxyguanosine (8-OH-dG), when the sample urine undergoes several cycles of freezing and thawing

Abstract

We examined the stability of urinary 8-hydroxy-2'-deoxyguanosine (8-OH-dG) when the sample urine undergoes several cycles of freezing and thawing. One hundred and two frozen samples (85 males and 17 females aged 22-79 years) were used. The concentration of urinary 8-OH-dG was measured by HPLC using two-step separations. We compared the 8-OH-dG level of samples after a second cycle of freezing and thawing with the level of samples after the first cycle (n=82). The mean urinary 8-OH-dG concentration after the first cycle and the concentration after the second cycle were 5.4 ± 2.8 ng/ml and 5.2 ± 2.8 ng/ml, respectively. There was no significant difference by the paired t-test. Regression analysis, with the 8-OH-dGconcentration after the second cycle as y and the 8-OH-dG concentration after the first cycle as x yielded y =0.97 × - 0.04 (R2=0.91, p<0.01). We then compared the 8-OH-dG level of samples after a third cycle with the level after the first cycle (n=20). The mean urinary 8-OH-dG concentration after the first cycle and the concentration after the third cycle were 5.9 ± 5.0 ng/ml and 6.2 ± 5.1 ng/ml, respectively. There was no significant difference by the paired t-test. Regression analysis, with the 8-OH-dG concentration after the third cycle as y and the 8-OH-dG concentration after first cycle as x yielded y = 1.0 × + 0.29 (R2 =0.96, p<0.01). We concluded that if the research purpose is the determination of urinary 8-OH-dG, samples can undergo at least three cycles of freezing and thawing without significant change.