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Promotion of DNA Strand Breaks in Cocultured Mononuclear Leukocytes by Protein Kinase C-dependent Prooxidative Interactions of Benoxaprofen, Human Polymorphonuclear Leukocytes, and Ultraviolet Radiation¹

Division of Immunology, Department of Medical Microbiology, Institute of Pathology, University of Pretoria [G. S., R. A.]; and the Departments of Medical Physiology [A. D. B.] and Internal Medicine [A. E. N.], Faculty of Medicine, University of Stellenbosch, Tygerberg; Republic of South Africa

At concentrations of 5 µg/ml and greater the nonsteroidal antiinflammatory drug benoxaprofen caused dose-related activation of lucigeninenhanced chemiluminescence in human polymorphonuclear leukocytes (PMNL). Benoxaprofen-mediated activation of lucigenin-enhanced chemiluminescence by PMNL was increased by UV radiation and was particularly sensitive to inhibition by the selective protein kinase C inhibitor H-7. To identify the molecular mechanism of the prooxidative activity of benoxaprofen, the effects of the nonsteroidal antiinflammatory drug on the activity of purified protein kinase C in a cell-free system were investigated. Benoxaprofen caused a dose-related activation of protein kinase C by interaction with the binding site for the physiological activator phosphatidylserine, but could not replace diacylglycerol. When autologous mononuclear leukocytes (MNL) were cocultured with PMNL and benoxaprofen in combination, but not individually, the frequency of DNA strand breaks in MNL was markedly increased. UV radiation significantly potentiated damage to DNA mediated by benoxaprofen and PMNL. Inclusion of superoxide dismutase, H-7, and, to a much lesser extent, catalase during exposure of MNL to benoxaprofen-activated PMNL prevented oxidant damage to DNA. These results clearly demonstrate that potentially carcinogenic prooxidative interactions, which are unlikely to be detected by conventional assays of mutagenicity, may occur between phagocytes, UV radiation, and certain pharmacological agents.

¹ This investigation was supported by individual investigator research grants awarded by the National Cancer Association and the Arthritis Foundation of South Africa to R. Anderson and by The South African Medical Research Council to A. E. Nel.

² To whom requests for reprints should be addressed, at Institute of Pathology, P. O. Box 2034, Pretoria 0001, Republic of South Africa.

Received 10/23/87. Revised 2/11/88. Accepted 3/ 3/88.