Chlorpromazine induces apoptosis in activated human lymphoblasts - A mechanism supporting the induction of drug-induced lupus erythematosus?

Objective. Drug-induced lupus erythematosus is a serious side effect of cer tain medications, such as procainamide, quinidine, hydralazine, chlorpromaz ine, and isoniazid, the underlying pathogenesis of which is unresolved. In this study, we examined the influence of these drugs on the regulation of a poptosis, or programmed cell death, in quiescent and activated human lympho cytes, We also discuss the dysregulation of apoptosis as a pathogenetic fac tor in systemic lupus erythematosus. Methods. Peripheral blood mononuclear cells or activated lymphoblasts from normal donors were incubated with different concentrations of each of the a bove-mentioned drugs. Results. We did not find induction of apoptosis in quiescent cells over a b road concentration range. In contrast, lymphoblasts readily underwent apopt osis when cultured with chlorpromazine, but not any of the other drugs, aft er stimulation with interleukin-2 (IL-2) in a dose-, time- and cell cycle-d ependent manner. By several lines of evidence, toxicity was ruled out. Char acteristic features of apoptosis-like incorporation of propidium iodide (PI ), such as increased annexin V binding, changes in mitochondrial membrane p otential, and induction of DNA breaks (as evidenced by TUNEL techniques), c ould be induced in lymphoblasts after chlorpromazine treatment. Chlorpromaz ine did not cause apoptosis: by inhibition of cytokine binding or blockade of early intracellular signaling. The protease inhibitor Z-VAD and the cera mide inhibitor sphingosine 1-phosphate effectively blocked chlorpromazine-i nduced apoptosis (by PI staining and by externalization of phosphatidylseri ne), in contrast to the caspase 3/CPP32 inhibitor DEVD, which had only mino r effects. Western blot analysis revealed IL-2-mediated phosphorylation of extracellular signal-regulated kinase, which was sensitive to chlorpromazin e. Using lymphoblasts from a patient with Canale-Smith syndrome, we found t hat chlorpromazine-mediated apoptosis is Fas/ APO-1 independent. Conclusion. These data suggest that chlorpromazine mediates apoptosis in hu man lymphoblasts through specific activation of intracellular proapoptotic signaling cascades. This mechanism might lead to an unsynchronized inflow o f apoptotic break-down products and thereby to the induction of (auto)immun ity against nuclear components.