Oxidation and glycoxidation of phosphatidylserine and their effect in immune response : a lipidomic approach

Phosphatidylserine (PS) is a member of the class of phospholipids, and is distributed among all cells of mammalians, playing important roles in diverse biological processes, including blood clotting and apoptosis. When externalized, PS is a ligand that is recognized on apoptotic cells. It has been considered that before externalization PS is oxidized and oxPS enhance the recognition by macrophages receptors, however the knowledge about oxidation of PS is still limited. PS, like others phospholipids, has two fatty acyl chains and one polar head group, in this case is the amino acid serine. The modifications in PS structure can occur by oxidation of the unsaturated fatty acyl chains and by glycation of the polar head group, due to free amine group, thus increasing the susceptibility to oxidative events. The main goal of this work was to characterize and identify oxidized and glycoxidized PS, contributing to the knowledge of the biological role of oxidation products of PS, as well as of glycated PS, in immune and inflammatory processes. To achieve this goal, PS standards (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho- L-serine (POPS), 1,2-dipalmitoyl-sn-glycero-3-phospho-L-serine (DPPS), 1- palmitoyl-2-linoleoyl-sn-glycero-3-phospho-L-serine (PLPS) and 1-palmitoyl-2- arachidonoyl-sn-glycero-3-phospho-L-serine (PAPS)) and glycated PS (PAPS and POPS) were induced to oxidize in model systems, using different oxidant reagents: HO• and 2,2'-azobis-2-methyl-propanimidamide dihydrochloride (AAPH) . The detailed structural characterization of the oxidative products was performed by ESI-MS and MS/MS coupled to separation techniques such as off line TLC-MS and on line LC-MS, in order to obtained better characterization of the larger number of PS and glycated PS oxidation products. The results obtained in this work allowed to identify several oxidation products of PS and glycated PS with modifications in unsaturated fatty acyl chain. Also, oxidation products formed due to structural changes in the serine polar head with formation of terminal acetamide, terminal hydroperoxyacetaldehyde.and terminal acetic acid (glycerophosphacetic acid, GPAA) were identified. The mass spectrometric specific fragmentation pathway of each type of oxidation product was determined using different mass spectrometry approaches. Based on the identified fragmentation pathways, targeted lipidomic analysis was performed to detect oxidation products modified in serine polar head in HaCaT cell line treated with AAPH. The GPAA was detected in HaCaT cells treated with AAPH to induce oxidative stress, thus confirming that modifications in PS polar head is possible to occur in biological systems. Furthermore, it was found that glycated PS species are more prone to oxidative modifications when compared with non glycated PS. During oxidation of glycated PS, besides the oxidation in acyl chains, new oxidation products due to oxidation of the glucose moiety were identified, including PS advanced glycation end products (PSAGES). To investigate if UVA oxidative stress exerted changes in the lipidome of melanoma cell lines, particularly in PS profile, a lipidomic analysis was performed. The lipid profile was obtained using HILIC-LC-MS and GC-MS analysis of the total lipid extracts obtained from human melanoma cell line (SKMEL- 28) after UVA irradiation at 0, 2 and 24 hours. The results did not showed significant differences in PS content. At molecular level, only PS (18:0:18:1) decreased at the moment of irradiation. The most significant changes in phospholipids content occurred in phosphatidylcholines (PC) and phosphatidylinositol (PI) classes, with an increase of mono-unsaturated fatty acid (MUFA), similarly as observed for the fatty acid analysis. Overall, these data indicate that the observed membrane lipid changes associated with lipogenesis after UVA exposure may be correlated with malignant transformations associated with cancer development and progression. Despite of UVA radiation is associated with oxidative damage, in this work was not possible observe oxidation phospholipids. The anti/pro-inflammatory properties of the oxidized PLPS (oxPLPS) versus non-oxidized PLPS were tested on LPS stimulated RAW 264.7 macrophages. The modulation of intracellular signaling pathways such as NF-kB and MAPK cascades by oxPLPS and PS was also examined in this study. The results obtained from evaluation of anti/pro-inflammatory properties showed that neither PLPS or oxPLPS species activated the macrophages. Moreover only oxidized PLS were found to significantly inhibit NO production and iNOS and il1β gene transcription induced by LPS. The analysis at molecular level showed that this was the result of the attenuation of LPS-induced c-Jun-N-terminal kinase (JNK) and p65 NF-kB nuclear translocation. Overall these data suggest that oxPLPS, but not native PLPS, mitigates pro-inflammatory signaling in macrophages, contributing to containment of inflammation during apoptotic cell engulfment. The results obtained in this work provides new information on the modifications of PS, facilitating the identification of oxidized species in complex samples, namely under physiopathologic conditions and also contributes to a better understanding of the role of oxPS and PS in the inflammatory response, in the apoptotic process and other biological functions.

Studies of epithelial response to streptozotocin-induced hyperglycemia

A hiperglicemia é a principal característica da diabetes mellitus (DM), uma das causas de morte que mais cresce em Portugal, e cujas complicações a longo prazo são mais debilitantes e mais sobrecarregam os sistemas de saúde. No entanto, os mecanismos subjacentes à resposta fisiológica de alguns tecidos à hiperglicemia não estão completamente esclarecidos. Este estudo teve como objetivo avaliar de que forma o tempo de exposição à hiperglicemia afeta dois tecidos epiteliais, o endotélio e as glândulas salivares, que são frequentemente associados a complicações da DM, utilizando um modelo animal. Adicionalmente, procurou-se encontrar novos biomarcadores para avaliar a suscetibilidade a complicações orais em diabéticos, analisando as modificações pós-traducionais (PTMs) da família de proteínas mais representativa na saliva humana: proteínas ricas em prolina (PRPs). A disfunção vascular está na origem de várias complicações da diabetes. Neste sentido, observou-se uma progressiva disfunção endotelial com o aumento do tempo de exposição à hiperglicemia, que resulta do aumento de danos no endotélio e da diminuição da capacidade de mobilização de células progenitoras. Simultaneamente, o aumento observado na atividade da via de ativação do sistema de complemento mediada por lectinas (MBL), sugere um envolvimento do sistema de imunidade inata na patogénese da disfunção vascular. Outra complicação comum da DM é o desenvolvimento de doenças orais, nomeadamente as relacionadas com a redução da secreção salivar. Na análise às glândulas submandibulares, observou-se uma resposta inicial à hiperglicemia com fortes variações na expressão de proteínas, mas a longo prazo, estas variações foram atenuadas, sugerindo um mecanismo de adaptação à hiperglicemia crónica. Adicionalmente, as proteínas relacionadas com a secreção, como as anexinas, apresentaram-se sobre-expressas, enquanto as calicreinas e proteínas metabólicas estavam sub-expressas. Estas variações sugerem que, apesar de uma diminuição da capacidade de regeneração, as células tentam superar a perda de tecido por meio do aumento da secreção, embora sem êxito. O comprometimento funcional das glândulas salivares tem consequências na composição e funções da saliva. Analisando as PTMs das PRPs salivares humanas, observou-se um aumento da frequência de péptidos com ciclização de resíduos N-terminais de glutamina a piroglutamato, o que confere uma resistência à atividade proteolítica que, por sua vez, se encontra aumentada em diabéticos. Assim, a presença de péptidos com N-piroglutamato poderá ser um potencial biomarcador da suscetibilidade a complicações orais em diabéticos.