Oxidized Lipids: Common Immunogenic Drivers of Non-Alcoholic Fatty Liver Disease and Atherosclerosis

The prevalence of non-alcoholic fatty liver disease (NAFLD), ranging from simple steatosis to inflammatory steatohepatitis (NASH) and cirrhosis, continues to rise, making it one of the major chronic liver diseases and indications for liver transplantation worldwide. The pathological processes underlying NAFLD not only affect the liver but are also likely to have systemic effects. In fact, growing evidence indicates that patients with NAFLD are at increased risk for developing atherosclerosis. Indeed, cardiovascular complications are the leading cause of mortality in NAFLD patients. Here, we aim to address common pathophysiological molecular pathways involved in chronic fatty liver disease and atherosclerosis. In particular, we focus on the role of oxidized lipids and the formation of oxidation-specific epitopes, which are important targets of host immunity. Acting as metabolic danger signals, they drive pro-inflammatory processes and thus contribute to disease progression. Finally, we summarize encouraging studies indicating that oxidized lipids are promising immunological targets to improve intervention strategies for NAFLD and potentially limit the risk of developing atherosclerosis.

Epilipidomics platform for holistic profiling of oxidized complex lipids in blood plasma of obese individuals

Lipids are a structurally diverse class of biomolecules which can undergo a variety of chemical modifications. Among them, lipid (per)oxidation attracts most of the attention due to its significance in regulation of inflammation, cell proliferation and death programs. Despite their apparent regulatory significance, the molecular repertoire of oxidized lipids remains largely elusive as accurate annotation of lipid modifications is challenged by their low abundance and largely unknown, biological context-dependent structural diversity. Here we provide a holistic workflow based on the combination of bioinformatics and LC-MS/MS technologies to support identification and relative quantification of oxidized complex lipids in a modification type- and position-specific manner. The developed methodology was used to identify epilipidomics signatures of lean and obese individuals with and without type II diabetes. Characteristic signature of lipid modifications in lean individuals, dominated by the presence of modified octadecanoid acyl chains in phospho- and neutral lipids, was drastically shifted towards lipid peroxidation-driven accumulation of oxidized eicosanoids, suggesting significant alteration of endocrine signalling by oxidized lipids in metabolic disorders.

Immunogenic ferroptosis and where to find it?

Ferroptosis is a recently discovered form of regulated cell death that is morphologically, genetically, and biochemically distinct from apoptosis and necroptosis, and its potential use in anticancer therapy is emerging. The strong immunogenicity of (early) ferroptotic cancer cells broadens the current concept of immunogenic cell death and opens up new possibilities for cancer treatment. In particular, induction of immunogenic ferroptosis could be beneficial for patients with cancers resistant to apoptosis and necroptosis. However, ferroptotic cancer cells may be a rich source of oxidized lipids, which contribute to decreased phagocytosis and antigen cross-presentation by dendritic cells and thus may favor tumor evasion. This could explain the non-immunogenicity of late ferroptotic cells. Besides the presence of lactate in the tumor microenvironment, acidification and hypoxia are essential factors promoting ferroptosis resistance and affecting its immunogenicity. Here, we critically discuss the crucial mediators controlling the immunogenicity of ferroptosis that modulate the induction of antitumor immunity. We emphasize that it will be necessary to also identify the tolerogenic (ie, immunosuppressive) nature of ferroptosis, which can lead to tumor evasion.

80. Heme Oxygenase-1 Gene promoter and associations with inflammation and subclinical vascular disease in Ugandan adolescents with and without HIV

Background Heme oxygenase-1 (HO-1) is a cytoprotective enzyme with potent anti-inflammatory, and anti-oxidant effects. The HO-1 response is modulated by functional polymorphisms (a dinucleotide (GT)n repeat length variation) in the HO-1 gene promoter region which have been associated with cardiovascular disease (CVD) susceptibility in adults. HO-1 polymorphisms and their associations with markers of inflammation and CVD in Ugandan adolescents with (HIV+) and without HIV (HIV-) have not been investigated. Methods We included 177 children (92 HIV+, 85 HIV-) enrolled in an ongoing observational cohort study at the Joint Clinical Research Center, Kampala, Uganda. All HIV+ participants were on ART. HO-1 (GT)n allele genotypes were determined by PCR of the (GT)n repeat region followed by fragment size determination on a capillary sequencer in DNA extracted from blood samples. Allele designations were assigned by number of (GT)n repeats: S < 27, M 27-34, or L > 34 repeats. We measured mean common carotid artery intima-media thickness (IMT) as a marker of CVD, markers of systemic inflammation (hsCRP, IL6, sTNFRI), monocyte activation (sCD14 and sCD163), and T-cell activation (expression of CD38 and HLA-DR on CD4+ and CD8+) , oxidized lipids, markers of gut integrity and fungal translocation (BDG). Results Median age (IQR) was 13 (11, 14), 44% were females, 86% had viral load < 20 copies/mL. 19% had a short allele genotype, 37% had a medium allele genotype and 44% had a long allele genotype (Figure). The shortest and longest allele length correlated with lower IMT in HIV- only (r=-0.36 and -0.30, respectively, p≤ 0.01 for both). Among biomarkers, only the medium allele correlated with oxidized lipids in HIV+ and with hsCRP and BDG in HIV- (p≤ 0.05). After adjusting for age, sex, and BMI, the presence of a long allele was associated with lower IMT. This was no longer significant after adjusting for markers of inflammation or oxidized lipids (Table). Heme Oxygenase-1 genotype allele length frequency in Ugandan cohort of HIV+ and HIV- youth 1: Models are adjusted for age (years), sex (male vs female), BMI (kg/m2) and HIV status (positive vs negative) 2: Models are adjusted for age (years), sex (male vs female), BMI (kg/m2), sCD14 (pg/mL) and HIV status (positive vs negative) 3: Models are adjusted for age (years), sex (male vs female), BMI (kg/m2), high sensitivity C reactive protein (ng/mL) and HIV status (positive vs negative) 4: Models are adjusted for age (years), sex (male vs female), BMI (kg/m2), oxidized lipids and HIV status (positive vs negative) Conclusion These findings underscore the potential of the HO pathways in modulating future risk for CVD in adolescents through inflammation. HIV status in this setting, likely influences the associations with the genotype with the risk of CVD. Further studies to validate our findings in this population are required. Disclosures Grace A. McComsey, MD, Gilead (Consultant, Advisor or Review Panel member)Janssen (Consultant, Advisor or Review Panel member)Merck (Consultant, Grant/Research Support, Scientific Research Study Investigator, Advisor or Review Panel member)Redhill (Research Grant or Support)Roche (Grant/Research Support)Tetraphase, Astellas (Research Grant or Support)Theratechnologies (Consultant)Vanda (Grant/Research Support)ViiV/GSK (Scientific Research Study Investigator, Advisor or Review Panel member)

Determination of Oxidized Lipids in Commonly Consumed Foods and a Preliminary Analysis of Their Binding Affinity to PPARγ

Foods rich in poly unsaturated fatty acids (PUFA) are vulnerable to oxidation. While it is well established that endogenously derived oxidized lipids are ligands of the transcription factor PPARγ, the binding ability of diet-derived oxidized lipids is unknown. Our two-fold objective was to determine the oxidized lipid content and PPARγ binding ability of commonly consumed foods. Extracted food lipids were assayed for the peroxide value, conjugated dienes, and aldehydes, and PPARγ binding was assessed by an in vitro PPARγ ligand screening assay. Oxidized lipids were present in all foods tested at the time of purchase, and oxidation did not increase during storage. The peroxide values for walnuts, sunflower seeds, and flax meal were significantly lower at the end of three months as compared to the day of purchase (peroxide value: 1.26 ± 0.13 vs. 2.32 ± 0.4; 1.65 ± 0.23 vs. 2.08 ± 0.09; 3.07 ± 0.22 vs. 9.94 ± 0.75 mEq/kg fat, p ≤ 0.05, respectively). Lipids extracted from French fries had the highest binding affinity (50.87 ± 11.76%) to PPARγ compared to other foods. Our work demonstrates that oxidized lipids are present in commonly consumed foods when purchased, and for the first time demonstrates that some contain ligands of PPARγ.

1H NMR Study of the In Vitro Digestion of Highly Oxidized Soybean Oil and the Effect of the Presence of Ovalbumin

Oxidized lipids containing a wide variety of potentially toxic compounds can be ingested through diet. However, their transformations during digestion are little known, despite this knowledge being essential in understanding their impact on human health. Considering this, the in vitro digestion process of highly oxidized soybean oil, containing compounds bearing hydroperoxy, aldehyde, epoxy, keto- and hydroxy groups, among others, is studied by 1H nuclear magnetic resonance. Lipolysis extent, oxidation occurrence and the fate of oxidation products both present in the undigested oil and formed during digestion are analyzed. Furthermore, the effect during digestion of two different ovalbumin proportions on all the aforementioned issues is also addressed. It is proved that polyunsaturated group bioaccessibility is affected by both a decrease in lipolysis and oxidation occurrence during digestion. While hydroperoxide level declines throughout this process, epoxy-compounds, keto-dienes, hydroxy-compounds, furan-derivatives and n-alkanals persist to a great extent or even increase. Conversely, a,b-unsaturated aldehydes, especially the very reactive and toxic oxygenated ones, diminish, although part of them remains in the digestates. While a low ovalbumin proportion hardly affects oil evolution during digestion, at a high level it diminishes oxidation and reduces the concentration of potentially bioaccessible toxic oxidation compounds.