title: Sphingomyelins suppress the targeted disruption of lysosomes/endosomes by the photosensitizer NPe6 during photodynamic therapy.
abstract: Recent studies have described a biochemical pathway whereby lysosome disruption and the released proteases initiate the intrinsic apoptotic pathway. Irradiation of murine hepatoma 1c1c7 cells preloaded with the lysosomal photosensitizer NPe6 (N-aspartyl chlorin e6) caused a rapid loss of Acridine Orange staining of acidic organelles, release of cathepsin D from late endosomes/lysosomes and the activation of procaspase-3. Pretreatment of NPe6-loaded cultures with 10-50 microM 3-O-MeSM (3-O-methylsphingomyelin) caused a concentration-dependent suppression of apoptosis following irradiation. This suppression reflected a stabilization of lysosomes/endosomes, as opposed to an inhibition of the accumulation of photosensitizer in these organelles. Exogenously added sphingomyelin, at comparable concentrations, offered some protection, but less than 3-O-MeSM. Fluorescence microscopy showed that 3-O-MeSM competed with NBD-C6-sphingomyelin (6-{[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]hexanoyl} sphingosyl phosphocholine) for co-localization with LysoTracker Red in acidic organelles. Pre-treatment of 1c1c7 cultures with 3-O-MeSM also suppressed the induction of apoptosis by TNFalpha (tumour necrosis factor alpha), but offered no protection against HA14-1 [ethyl 2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate], staurosporine, tunicamycin or thapsigargin. These results suggest that exogenously added 3-O-MeSM is trafficked to and stabilizes late endosomes/lysosomes against oxidant-induced damage, and further implicate a role for lysosomal proteases in the apoptotic processes initiated by TNFalpha and lysosomal photosensitizers.
authors.affiliation: Institute of Environmental Health Sciences, Wayne State University, Detroit, MI 48201, USA.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Caruso
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Mathieu
authors.forename: John J
authors.initials: JJ
authors.lastname: Reiners
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002402:Cathepsin D / Q000378:metabolism; D045744:Cell Line, Tumor; D003513:Cycloheximide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D011992:Endosomes / Q000187:drug effects* / Q000378:metabolism; D004789:Enzyme Activation; D008027:Light; D008247:Lysosomes / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011166:Porphyrins / Q000494:pharmacology*; D013109:Sphingomyelins / Q000378:metabolism / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: C508074:3-O-methylsphingomyelin; D017319:Photosensitizing Agents; D011166:Porphyrins; D013109:Sphingomyelins; D014409:Tumor Necrosis Factor-alpha; D003513:Cycloheximide; C505409:Casp3 protein, mouse; C506434:Casp9 protein, mouse; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases; D002402:Cathepsin D; C053434:Talaporfin