Human mononuclear leukocytes (HML) respond to oxidative DNA damage by activation of ADP ribosylation and initiation of DNA repair synthesis (i.e. unscheduled DNA synthesis, UDS), whereas neutrophils do not. When neutrophils are added to HML cultures in ratios up to 4:1 ADP ribosylation becomes inhibited to approximately 50-60%. The ability of neutrophils to inhibit HML ADP ribosylation was shown to be dependent on H2O2, chloride ions and myeloperoxidase, which in turn are factors known to govern HOCl and N-chloramine production by phagocytic cells. HOCl and a model N-chloramine, chloramine T, were shown to give a dose-dependent inhibition of DNA repair using four independent estimates, namely ADP ribosylation, UDS and the repair of DNA strand breaks estimated by nucleoid sedimentation and alkaline elution profiles. All the DNA repair measurements used on HML were inhibited approximately 70-80% by 100 microM doses of HOCl or chloramine T, which was considered a biologically relevant dose because: (i) viable neutrophils equal in concentration to those found in blood could easily produce 100 microM levels in short-term culture; (ii) 100 microM doses of these agents were not acutely cytotoxic judged by trypan blue stained cells after 30-60 min exposure and under the conditions used for assay, but yet they abolished 86-95% of the growth response of HML to phytohemagglutinin.
Mononuclear leukocytes from 151 patients with cancer of various organs and from 467 apparently cancer-free individuals were exposed, in vitro, to H2O2 (100 microM) and the effects of the exposure on the activity of adenosine diphosphate ribosyl transferase (ADPRT) were determined. First, the reproducibility of this test procedure was established as satisfactory, by comparing the results of assays performed independently by two investigators, and by measuring ADPRT in cells from two individuals over a 9-week period. The test data were analyzed by multiple linear regression, and the correlation of cancer diagnosis, age, sex and smoking habits with ADPRT values was determined. The strongest correlate was cancer diagnosis. We considered categorizing ADPRT values as high and low, with a cut-off value that would substantially distinguish cancer from cancer-free individuals. When a cut-off value of 1200 c.p.m. TCA ppt [3H]NAD+/5 x 10(5) cells was applied to the complete test material, it was found that ADPRT values from cancer patients were more frequently below the cut-off than values from disease-free individuals: the relative risk estimate (odds ratio) was 13.8. When a similar analysis was done on values from lung cancer patients and smoking disease-free individuals, the odds ratio was 73.5. However, a cut-off value of 2000 c.p.m. TCA ppt [3H]NAD+/5 x 10(5) cells was most effective in distinguishing lung cancer patients (the largest cancer group, n = 96) from smoking non-cancer individuals: that value provided better sensitivity (85%) and specificity (81%) than other cut-off values tested in the range 1200-2000 c.p.m. Further, in the case of lung cancer, possible effects of anatomical site, and of staging and pathology on ADPRT values was analyzed by the chi-squared test: no significant associations were found. These data support the value of the ADPRT test in detecting early stage lung cancer regardless of location or pathological type.
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