Vol. 187, No. 3, 1992 BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS September 30, 1992 Pages 1256-l 261 INHIBITION OF APOPTOSIS BY ZINC: A REAPPRAISAL Daniela Barbieri, Leonarda Troiano, Emanuela Grassilli, Caterina Agnesini, Elizabeth A. Cristofalo, Daniela Monti, Miriam Capri, Andrea Cossarizza and Claudio Franceschi Istituto di Patologia Generale, University of Modena Via Campi 287, 41100 Modena, Italy Received August 3, 1992 Apoptosis - or programmed cell death - is an active type of cell death, occurring in several pathophysiological conditions. One of the most important characteristics of apoptosis is that cell death is preceded by DNA fragmentation, consequent to the activation of nuclear calcium- and magnesium-dependent endonuclease(s). DNA fragmentation can be inhibited by zinc ions. By using several techniques, such as DNA agarose gel electrophoresis, cytofluorimetric analysis of DNA content and of cell cycle, 3H-thymidine incorporation and trypan blue dye exclusion test, we show that zinc, despite completely inhibiting DNA fragmentation and the consequent loss of nuclear DNA content, does not protect rat thymocytes from spontaneous or dexamethasone- induced death. Our data also suggest that DNA fragmentation, although characteristic, is not a critical event for thymocyte death of apoptotic type. 0 1992 Academic Press, Inc. Two types of death are recognized, i.e., necrosis and apoptosis. Necrosis is a pathological event associated with cessation of synthetic function. On the contrary, apoptosis is apparently a regulated event dependent upon active metabolism and protein synthesis by the dying cells. It occurs in physiological circumstances such as embryogenesis and methamorphosis. Apoptosis is particularly important for the physiology of the immune system [I]. Indeed, apoptosis is the model of death of centroblasts with low affinity for antigen within germinal centers, cells killed by specific cytotoxic T lymphocytes or natural killer cells, as well as thymocytes bearing high-affinity T-cell receptors for self antigens that are clonally deleted during thymus development. The biochemical and molecular mechanisms that mediate apoptosis are poorly understood [2]. One of the most important characteristics of apoptosis is that cell death is preceded by DNA fragmentation. The DNA of apoptotic cells is nonrandomly degraded by endogenous calcium- and magnesium-dependent endonuclease(s). This enzyme(s) gives fragments of 200 base pairs (bp) or multiples of 200 bp by cutting the linker DNA running between nucleosomes [3]. Thus, DNA appears to be a most important target of the process which leads to cell suicide. Recently, it has been suggested that cells die not because of DNA breaks but because of active metabolic events triggered by DNA breaks, such as activation of 0006-291X/92 $4.00 Copyright 0 1992 by Academic Press. Inc. All rights of reproduction in any form reserved. 1256