Decreased reactive oxygen generation during H2O2 decomposition in the presence of samples from human rectal cancer

Reactive oxygen species (ROS) have generated a great deal of interest in the clinical field since experimental studies showed the involvement of these species in carcinogenesis. This paper reports the detection of ROS during the decomposition of H2O2 in the presence of samples obtained from tissues of 16 patients with rectal carcinoma (age 64 (plus-minus) 9 years) operated on in the Division of Surgical Oncology of Pomeranian Medical University, Szczecin (Poland). The samples were cut from the middle of the resected tumors and from the colonic mucosa (10 cm distant from the tumor and free of disease); they were processed and the supernatants, representing the soluble fraction, were used for measurements. Various methods for measuring free radical activity of the examined samples were used, such as chemiluminescence, fluorescent probe 2ʹ,7ʹ-dichlorodihydrofluorescein, spin trap 5,5-dimethylpyrroline-1-oxide and EPR, the spectrophotometrically examined formation of diformazan during reduction of the pnitroblue tetrazolium salt, and bleaching of p-nitrosodimethylalanine. A statistically significant difference (P < 0.001) was noticed in mean chemiluminescence (plus-minus) standard error of the mean in the presence of the tumor samples (42.6 (plus-minus) 7.3) in comparison to the control samples (234.6 (plus-minus) 36.0). Significantly decreased generation of ROS from the decomposition of H2O2 in the presence of the tumor samples in comparison to the control samples was also observed when the above-mentioned methods were used. Tumor samples had significantly lower superoxide dismutase activity (33 (plus-minus) 4 U/mg protein) than controls (93 (plus-minus) 14 U/mg, P < 0.001), which should contribute to a lower capacity of endogenous H2O2 production and therefore less ROS generation upon H2O2 decomposition. We conclude that the tested samples have different redox properties; this supports a possible role of ROS activity during carcinogenesis. Moreover, we propose a new, simple, and sensitive chemiluminescent method, which might be effective in sample differentiation.