Ceramide generation in response to photodynamic treatment of L5178Y mouse lymphoma cells.
Photodynamic therapy, a novel cancer treatment using a photosensitive dye and visible light, produces an oxidative stress in cells, often leading to apoptotic cell death. Because ceramide is a second messenger that has been associated with stress-induced apoptosis, we investigated a possible link between photodynamic treatment (PDT), ceramide, and apoptosis in L5178Y-R (LY-R) cells. The cells undergo rapid apoptosis, initiating within 30 min of PDT. After a dose of PDT producing a 99.9% loss of clonogenicity, LY-R cells responded by an increased production of ceramide, which reached a maximum level in 60 min. For a constant light fluence and varying concentrations of the phthalocyanine photosensitizer Pc 4 [HOSiPcOSi(CH3)2(CH2)3N(CH3)2], the ED50 for ceramide generation (46 nM) was similar to the LD50 for clonogenic cell death (40 nM). We suggest that the PDT-stimulated increase in synthesis of ceramide in LY-R cells may be coupled to PDT-induced apoptosis. When the cells were exposed to exogenous N-acetyl-sphingosine (10 microM), apoptotic changes were observed only after 12-24 h. The delayed apoptotic response to the synthetic ceramide may be due to an induction of apoptosis by a different route than the one used by PDT.
Separovic
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Department of Radiology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4942, USA. dxs66@po.cwru.edu
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Oleinick
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D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002518:Ceramides / Q000378:metabolism*; D053938:DNA Fragmentation; D007940:Leukemia L5178; D051379:Mice; D010778:Photochemotherapy / Q000379:methods*; D013110:Sphingosine / Q000031:analogs & derivatives / Q000494:pharmacology; D013997:Time Factors
D002518:Ceramides; C064769:N-acetylsphingosine; D013110:Sphingosine