Fumonisin B1 does not prevent apoptosis in A431 human epidermoid carcinomacells after photosensitization with a silicon phthalocyanine

Photodynamic therapy with the phthalocyanine photosensitizer Pc 4 (Pc 4-PDT ), an apoptosis inducer, is associated with accumulation of ceramide in var ious cell lines. The role of ceramide in Pc 4-PDT-induced apoptosis was inv estigated in A431 cells. Caspase-3 (casp-3) was activated and TUNEL positiv e cells began to appear 30 and 60 min post-Pc 4-PDT, respectively. A rapid increase (10 min) in cellular ceramide levels was observed after Pc 4-PDT. Induced ceramide accumulation was maintained over 60 min. Acid sphingomyeli nase, a ceramide-generating enzyme, was inhibited after photosensitization with Pc 4, suggesting that the enzyme was not required for stimulated ceram ide accumulation. Co-treatment of A431 cells with fumonisin B1, a ceramide synthase inhibitor, and Pc 4-PDT led to a decrease in ceramide levels witho ut any effect on induced casp-3 activity or apoptosis. In the presence of z VAD, a pan-caspase inhibitor, apoptosis was abolished, while ceramide level s remained elevated after Pc 4-PDT. Exposure of A431 cells to exogenous C6- ceramide for 22 h, led to induction of apoptosis, and the process was abrog ated by zVAD. In conclusion, C6-ceramide-, like Pc 4-PDT-induced apoptosis, is zVAD-sensitive. Furthermore, Pc 4 photosensitization can lead to apopto sis without FB-sensitive elevation in ceramide levels upstream of caspases. (C) 2000 Elsevier Science S.A. All rights reserved.