The concentration of circulating DNA (cirDNA) and deoxyribonuclease activity in blood plasma of healthy donors and patients with colon or stomach cancer were analyzed. The concentration of DNA was measured using Hoechst 33258 fluorescent assay after the isolation by the glass-milk protocol. A 1-kbp PCR product labeled with biotinylated forward and fluorescein-labeled reverse primers was used as a substrate for DNase. DNase activity was estimated from the data of immunochemical detection of the nonhydrolyzed amplicon. The average concentration of cirDNA in the plasma of healthy donors was low (34 +/- 34 ng/mL), and was accompanied with high DNase activity (0.356 +/- 0.410 U/mL). The increased concentrations of cirDNA in blood plasma of patients with colon and stomach cancer were accompanied by a decrease in DNase activity below the detection level of the assay. The data obtained demonstrate that low DNase activity in blood plasma of cancer patients can cause an increase in the concentration of cirDNA.

The DNase activity and circulating DNA (cirDNA) concentration in blood plasma of healthy donors, patients with chronic prostatitis, and patients with prostate tumors were analyzed. The concentration of the cirDNA from plasma was determined by PicoGreen fluorescent assay. DNase activity in blood was measured using the immunoassay based on the cleavage of a hapten-labeled 974-bp DNA substrate. The mean cirDNA concentration in the plasma of healthy donors was low (21 +/- 4 ng/mL total blood) and was accompanied by high DNase activity (0.17 +/- 0.04 U/mL blood). The mean cirDNA concentration was 90 ng/mL blood (10-234 ng/mL) in the patients with nonmalignant prostate tumors and 115 ng/mL blood (13-339 ng/mL) in those with prostate cancer. The mean DNase activity in blood plasma of the patients with prostate tumors was 0.06 U/mL blood (0-0.12 U/mL). The results obtained demonstrate that increased concentrations of cirDNA in blood of the patients with prostate tumors is accompanied by a decreased DNase activity, confirming our previous data that a low DNase activity in blood plasma of cancer patients is one reason for a high cirDNA concentration.

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