Effects of Poly (ADP-Ribose) Polymerase Inhibitors on the Sulfur Mustard-Induced Disruption of the Higher-Order Nuclear Structure of Human Lymphocytes

Abstract

Sulfur mustard (HD) is a potent vesicant that can cause severe lesions to skin, lung, and eyes (1). To develop therapeutic pretreatment or treatment regimens to prevent HD-initiated damage, a better understanding of the mechanisms of action of HD is required. Based on the initial findings by Herriott and Price (2), DNA was implicated as an important target in causing the cellular effects of HD. Berger et al. (3) proposed a hypothesis for the mechanism of cell death owing to exposure to alkylating agents, which was dependent on alkylation of the cell’ s DNA. The alkylation of the DNA results in DNA strand breaks, which cause activation of the nuclear enzyme poly (ADP-ribose) polymerase (PARP). Active PARP could deplete the cell of nicotinamide-adenine dinucleotide (NAD). The depletion of NAD would inhibit glycolysis and result in a loss of adenosine triphosphate (ATP). The ATP is needed as the major source of energy required for cell survival. Berger’s hypothesis has been extensively evaluated using the alkylator HD. It has been demonstrated in peripherial blood lymphocytes (PBLs) that HD lowers cell viability (4), NAD (5), and ATP (6) levels of the exposed cells. Protection against these HD-initiated losses could be shown using poly (ADP-ribose) polymerase inhibitors (PARPIs). Recent studies examined the effects of HD on Berger’s proposed primary target, the nucleus, and the effects of PARPIs were investigated. The most abundant nuclear proteins, histones, show altered solubility in PBLs exposed to HD. The structure of at least one histone, histone H2B, has been changed by what appears to be proteolytic cleavage (7). PARPIs appeared to have minimal effect on HD-induced changes in histones. This work attempts to address the effect of HD on DNA directly. The effects of HD on the DNA in PBLs were determined by both agarosegel electrophoresis and flow cytometry. HD caused a concentration and time-dependent fragmentation of the DNA in PBLs. When PARPIs were present in the PBL incubation mixture, they did not prevent the DNA cleavage initiated by HD, but they did alter the resulting cleavage patterns.KeywordsPropidium IodideSulfur MustardPolymerase InhibitorLadder PatternPeak ChannelThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.