29th Annual Meeting of the American Society of Photobiology

Downtown Marriot

Chicago, Il.

Characterization of Plasmenylcholine Vesicle Photooxidation Products Formed via AlPcS₄^4- Sensitization

Abstract-
Oxidative damage to plasmenyl-type lipids may contribute to decreased membrane barrier function, loss of membrane structure and formation of nonlamellar defects in membrane bilayers. Since plasmalogen lipids, in particular the plasmenylcholines and plasmenylethanolamines, are significant components of sarcoplasma and myelin membrane lipids, we sought to characterize the products of plasmenylcholine (PlsC) (1-alk-1Z-enyl-2-palmitoyl-sn-glycero-3-phosphocholine) photooxidation. Previous results from this laboratory have shown that the membrane-soluble sensitizers, zinc phthalocyanine or bacteriochlorophyll a, mediated photooxidation of PlsC vesicles, with the subsequent creation of lamellar defect structures, vesicle contents leakage, and membrane-membrane fusion. This study addressed the photooxidation of PlsC vesicles in the presence of the water-soluble sensitizer, aluminum phthalocyanine tetrasulfonate (AlPcS44-). Attack of photogenerated ¹O₂ on PlsC lipids was expected to generate dioxetane and ene-type photoproducts. The products formed during continuous aerobic irradiation (28 mW/cm², 610 nm) were separated via reversed-phase HPLC with electrochemical (ECD) or evaporative light scattering (ELSD) detection. Photooxidation of DPPC-cholesterol vesicles (control) was used to optimize the HPLC-ECD conditions. ECD was found to be most sensitive for PlsC hydroperoxides, while ELSD was more sensitive for non-hydroperoxide photoproducts. Three main HPLC fractions were collected and the isolated photoproducts characterized by 1H NMR and mass spectrometry. Peaks eluting first were identified as the dioxetane cleavage products, 1-formyl-2-palmitoyl-sn-glycero-3-phosphocholine and 1-hydroxy-2-palmitoyl-sn-glycero-3-phosphocholine. The peak eluting last from the column was identified as a PlsC hydroperoxide of unknown regiochemistry. The third photoproduct is tentatively identified as a cross-linked, oligomeric PlsC species.

Keywords: photooxidation, lipid peroxidation, sensitization