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: Joseph A Caruso, Patricia A Mathieu, John J Reiners Jr
• Journal: The Biochemical journal (Biochem J) Vol. 392 Issue Pt 2 Pg. 325-34 (Dec 01 2005) ISSN: 1470-8728 [Electronic] England
• PMID: 15943580 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• 3-O-methylsphingomyelin
• Photosensitizing Agents
• Porphyrins
• Sphingomyelins
• Tumor Necrosis Factor-alpha
• Cycloheximide
• Casp3 protein, mouse
• Casp9 protein, mouse
• Caspase 3
• Caspase 9
• Caspases
• Cathepsin D
• Talaporfin

Topics

• Animals
• Apoptosis (drug effects, physiology)
• Caspase 3
• Caspase 9
• Caspases (metabolism)
• Cathepsin D (metabolism)
• Cell Line, Tumor
• Cycloheximide (pharmacology)
• Dose-Response Relationship, Drug
• Endosomes (drug effects, metabolism)
• Enzyme Activation
• Light
• Lysosomes (drug effects, metabolism)
• Mice
• Photochemotherapy
• Photosensitizing Agents (pharmacology)
• Porphyrins (pharmacology)
• Sphingomyelins (metabolism, pharmacology)
• Tumor Necrosis Factor-alpha (metabolism)