Photosensitized oxidation of phosphatidylethanolamines monitored by electrospray tandem mass spectrometry

Abstract

Photodynamic therapy combines visible light and a photosensitizer (PS) in the presence of molecular oxygen to generate reactive oxygen species able to modify biological structures such as phospholipids. Phosphatidylethanolamines (PEs), being major phospholipid constituents of mammalian cells and membranes of Gram-negative bacteria, are potential targets of photosensitization. In this work, the oxidative modifications induced by white light in combination with cationic porphyrins (Tri-Py(+)-Me-PF and Tetra-Py(+)-Me) were evaluated on PE standards. Electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS) were used to identify and characterize the oxidative modifications induced in PEs (POPE: PE 16:0/18:1, PLPE: PE 16:0/18:2, PAPE: PE 16:0/20:4). Photo-oxidation products of POPE, PLPE and PAPE as hydroxy, hydroperoxy and keteno derivatives and products due to oxidation in ethanolamine polar head were identified. Hydroperoxy-PEs were found to be the major photo-oxidation products. Quantification of hydroperoxides (PE-OOH) allowed differentiating the potential effect in photodamage of the two porphyrins. The highest amounts of PE-OOH were notorious in the presence of Tri-Py(+)-Me-PF, a highly efficient PS against bacteria. The identification of these modifications in PEs is an important key point in the understanding cell damage processes underlying photodynamic therapy approaches.

Electrochemical oxidation of phosphatidylethanolamines studied by mass spectrometry

“…This is a typical neutral loss of PE in positive ion mode, which confirmed that the assigned products were oxidized PEs and that the oxidation did not occur in the polar head. All the MS/MS spectra acquired in negative ion mode showed the typical fragmentation pathways of PEs . These include the formation of carboxylate anions of the fatty acids esterified to the sn‐1 and sn‐2 positions and the formation of ions due to losses of the modified fatty acyl chain from the sn‐2 position as ketene derivative (−R 2 =C=O), with the formation of lysoPE ions.…”

“…Nowadays, the study of enzymatic and nonenzymatic oxidation mechanisms should start from in vitro biomimetic systems, able to predict the reactions that normally lead to the production of oxidized PE. In these biomimetic approaches, the oxidized PE species can be identified by MS and the fragmentation patterns studied by tandem MS, aiming to find diagnostic fragment ions for targeted in vivo analysis . Facing a great variability of possible oxidation derivatives, an ideal biomimetic tool should be able to mimic as much as possible the oxidation chemistry that is likely to occur in vivo.…”

Mass spectrometry strategies to unveil modified aminophospholipids of biological interest

“…Oxidation of the fatty acyl chains (Khaselev and Murphy, ; Gugiu et al, ; Maskrey et al, ; Tyurin et al, ; Tyurina et al, ; Domingues et al, ; Tyurin et al, ; Simões et al, ; Thomas et al, ; Tyurina et al, ; Morgan et al, ; Tyurina et al, ; Tyurina et al, ; Clark et al, ; Hammond et al, ; Melo et al, ,; Maciel et al, ; Simões et al, );…”

“…Similarly, in vitro irradiation of PE standards with white light in the presence of cationic porphyrins as photosensitizers (photo‐oxidation) led to oxidative deamination of the ethanolamine group, with the generation of the polar head modified as terminal acetaldehyde (Fig. ) (Melo et al, ).…”

“…APL are prone to be modified by oxidation (Domingues et al, ; Simões et al, ; Maciel et al, ; Melo et al, ), glycation (Simões et al, ; Maciel et al, ; Melo et al, ; Annibal et al, ), and reactive molecules such as electrophilic aldehydes (Bernoud‐Hubac et al, ; Bacot et al, ). These changes in native APL may occur under physiological and pathological conditions through non‐enzymatic reactions with reactive oxygen species (ROS), glucose, and other carbonyl compounds, or through enzyme‐catalyzed reactions, generating a vast number of differently modified derivatives which display several biological functions.…”