Modulation of protein function by isoketals and levuglandins

Inflammation Biomarker Response to Oral 2-Hydroxybenzylamine (2-HOBA) Acetate in Healthy Humans

Inflammation is associated with the formation of reactive oxygen species (ROS) and the formation of lipid-derived compounds, such as isolevuglandins (IsoLGs), malondialdehyde, 4-hydroxy-nonenal, and 4-oxo-nonenal. The most reactive of these are the IsoLGs, which form covalent adducts with lysine residues and other cellular primary amines leading to changes in protein function, immunogenicity, and epigenetic alterations and have been shown to contribute to a number of inflammatory diseases. 2-Hydroxybenzylamine (2-HOBA) is a natural compound found in buckwheat seeds and reacts with all IsoLG adducts preventing adduct formation with proteins and DNA. Therefore, 2-HOBA is well positioned as an agent for the prevention of inflammatory-prone diseases. In this study, we examined the potential beneficial effects of 2-HOBA on oxidative stress and inflammatory biomarkers in two cohorts of healthy younger and older adults. We utilized the Olink® targeted inflammation panel before and after an oral 15-day treatment regimen with 2-HOBA. We found significant relative changes in the plasma concentration of 15 immune proteins that may reflect the in vivo immune targets of 2-HOBA. Treatment of 2-HOBA resulted in significant increased levels of CCL19, IL-12β, IL-20Rα, and TNFβ, whereas levels of TWEAK significantly decreased. Ingenuity Pathway Analysis identified canonical pathways regulated by the differentially secreted cytokines, chemokines, and growth factors upon 2-HOBA treatment and further points to biofunctions related to the recruitment, attraction, and movement of different immune cell types. In conclusion, 2-HOBA significantly altered the protein biomarkers CCL19, IL-12β, IL-20Rα, TNFβ, and TWEAK, and these may be responsible for the protective effects of 2-HOBA against reactive electrophiles, such as IsoLGs, commonly expressed in conditions of excessive oxidative stress. 2-HOBA has a role as a IsoLG scavenger to proactively improve immune health in a variety of conditions.

Oxidative Modification of Proteins: From Damage to Catalysis, Signaling, and Beyond

Significance: The systematic investigation of oxidative modification of proteins by reactive oxygen species started in 1980. Later, it was shown that reactive nitrogen species could also modify proteins. Some protein oxidative modifications promote loss of protein function, cleavage or aggregation, and some result in proteo-toxicity and cellular homeostasis disruption. Recent Advances: Previously, protein oxidation was associated exclusively to damage. However, not all oxidative modifications are necessarily associated with damage, as with Met and Cys protein residue oxidation. In these cases, redox state changes can alter protein structure, catalytic function, and signaling processes in response to metabolic and/or environmental alterations. This review aims to integrate the present knowledge on redox modifications of proteins with their fate and role in redox signaling and human pathological conditions. Critical Issues: It is hypothesized that protein oxidation participates in the development and progression of many pathological conditions. However, no quantitative data have been correlated with specific oxidized proteins or the progression or severity of pathological conditions. Hence, the comprehension of the mechanisms underlying these modifications, their importance in human pathologies, and the fate of the modified proteins is of clinical relevance. Future Directions: We discuss new tools to cope with protein oxidation and suggest new approaches for integrating knowledge about protein oxidation and redox processes with human pathophysiological conditions. Antioxid. Redox Signal. 35, 1016-1080.

Isolevuglandin-Modified Cardiac Proteins Drive CD4+ T-Cell Activation in the Heart and Promote Cardiac Dysfunction

BACKGROUND

Despite the well-established association between T-cell-mediated inflammation and nonischemic heart failure, the specific mechanisms triggering T-cell activation during the progression of heart failure and the antigens involved are poorly understood. We hypothesized that myocardial oxidative stress induces the formation of isolevuglandin (IsoLG)-modified proteins that function as cardiac neoantigens to elicit CD4+ T-cell receptor (TCR) activation and promote heart failure.

METHODS

We used transverse aortic constriction in mice to trigger myocardial oxidative stress and T-cell infiltration. We profiled the TCR repertoire by mRNA sequencing of intramyocardial activated CD4+ T cells in Nur77GFP reporter mice, which transiently express GFP on TCR engagement. We assessed the role of antigen presentation and TCR specificity in the development of cardiac dysfunction using antigen presentation-deficient MhcII-/- mice and TCR transgenic OTII mice that lack specificity for endogenous antigens. We detected IsoLG protein adducts in failing human hearts. We also evaluated the role of reactive oxygen species and IsoLGs in eliciting T-cell immune responses in vivo by treating mice with the antioxidant TEMPOL and the IsoLG scavenger 2-hydroxybenzylamine during transverse aortic constriction, and ex vivo in mechanistic studies of CD4+ T-cell proliferation in response to IsoLG-modified cardiac proteins.

RESULTS

We discovered that TCR antigen recognition increases in the left ventricle as cardiac dysfunction progresses and identified a limited repertoire of activated CD4+ T-cell clonotypes in the left ventricle. Antigen presentation of endogenous antigens was required to develop cardiac dysfunction because MhcII-/- mice reconstituted with CD4+ T cells and OTII mice immunized with their cognate antigen were protected from transverse aortic constriction-induced cardiac dysfunction despite the presence of left ventricle-infiltrated CD4+ T cells. Scavenging IsoLGs with 2-hydroxybenzylamine reduced TCR activation and prevented cardiac dysfunction. Mechanistically, cardiac pressure overload resulted in reactive oxygen species-dependent dendritic cell accumulation of IsoLG protein adducts, which induced robust CD4+ T-cell proliferation.

CONCLUSIONS

Our study demonstrates an important role of reactive oxygen species-induced formation of IsoLG-modified cardiac neoantigens that lead to TCR-dependent CD4+ T-cell activation within the heart.

Pyridoxamine reduces postinjury fibrosis and improves functional recovery after acute kidney injury

Acute kidney injury (AKI) is a common and independent risk factor for death and chronic kidney disease (CKD). Despite promising preclinical data, there is no evidence that antioxidants reduce the severity of injury, increase recovery, or prevent CKD in patients with AKI. Pyridoxamine (PM) is a structural analog of vitamin B6 that interferes with oxidative macromolecular damage via a number of different mechanisms and is in a phase 3 clinical efficacy trial to delay CKD progression in patients with diabetic kidney disease. Because oxidative stress is implicated as one of the main drivers of renal injury after AKI, the ability of PM to interfere with multiple aspects of oxidative damage may be favorable for AKI treatment. In these studies we therefore evaluated PM treatment in a mouse model of AKI. Pretreatment with PM caused a dose-dependent reduction in acute tubular injury, long-term postinjury fibrosis, as well as improved functional recovery after ischemia-reperfusion AKI (IR-AKI). This was associated with a dose-dependent reduction in the oxidative stress marker isofuran-to-F2-isoprostane ratio, indicating that PM reduces renal oxidative damage post-AKI. PM also reduced postinjury fibrosis when administered 24 h after the initiating injury, but this was not associated with improvement in functional recovery after IR-AKI. This is the first report showing that treatment with PM reduces short- and long-term injury, fibrosis, and renal functional recovery after IR-AKI. These preclinical findings suggest that PM, which has a favorable clinical safety profile, holds therapeutic promise for AKI and, most importantly, for prevention of adverse long-term outcomes after AKI.

Accumulation of isolevuglandin-modified protein in normal and fibrotic lung

Protein lysine modification by γ-ketoaldehyde isomers derived from arachidonic acid, termed isolevuglandins (IsoLGs), is emerging as a mechanistic link between pathogenic reactive oxygen species and disease progression. However, the questions of whether covalent modification of proteins by IsoLGs are subject to genetic regulation and the identity of IsoLG-modified proteins remain unclear. Herein we show that Nrf2 and Nox2 are key regulators of IsoLG modification in pulmonary tissue and report on the identity of proteins analyzed by LC-MS following immunoaffinity purification of IsoLG-modified proteins. Gene ontology analysis revealed that proteins in numerous cellular pathways are susceptible to IsoLG modification. Although cells tolerate basal levels of modification, exceeding them induces apoptosis. We found prominent modification in a murine model of radiation-induced pulmonary fibrosis and in idiopathic pulmonary fibrosis, two diseases considered to be promoted by gene-regulated oxidant stress. Based on these results we hypothesize that IsoLG modification is a hitherto unrecognized sequelae that contributes to radiation-induced pulmonary injury and IPF.

Treatment with a γ-ketoaldehyde scavenger prevents working memory deficits in hApoE4 mice

Both inflammation and oxidative injury are features of Alzheimer's disease (AD), but the contribution of these intertwined phenomena to the loss of working memory in this disease is unclear. We tested the hypothesis that highly reactive γ-ketoaldehydes that are formed both by non-enzymatic free radical catalyzed lipid peroxidation and by cyclooxygenases may be causally linked to the development of memory impairment in AD. We found that levels of γ-ketoaldehyde protein adducts were increased in the hippocampus of brains obtained postmortem from patients with AD compared to age-matched controls, but that levels of γ-ketoaldehyde protein adducts in the cerebellum were not different in the two groups. Moreover, immunohistochemistry revealed that adducts localized to hippocampal pyramidal neurons. We tested the effect of an orally available γ-ketoaldehyde scavenger, salicylamine, on the development of spatial working memory deficits in hApoE4 targeted replacement mice, a mouse model of dementia. Long-term salicylamine supplementation did not significantly alter body weight or survival, but protected against the development of age-related deficits in spatial working memory in 12-14 month old ApoE4 mice. These findings suggest that γ-ketoaldehyde adduct formation is associated with damage to hippocampal neurons in patients with AD and can contribute to the pathogenesis of spatial working memory deficits in hApoE4 mice. These data provide a rational basis for future studies exploring whether γ-ketoaldehyde scavengers may mitigate the development of cognitive dysfunction in patients with AD.

Isoketals form cytotoxic phosphatidylethanolamine adducts in cells

Levuglandins and their stereo- and regio-isomers (termed isolevuglandins or isoketals) are gamma-ketoaldehydes (IsoK) that rapidly react with lysines to form stable protein adducts. IsoK protein adduct levels increase in several pathological conditions including cardiovascular disease. IsoKs can induce ion channel dysfunction and cell death, potentially by adducting to cellular proteins. However, IsoKs also adduct to phosphatidylethanolamine (PE) in vitro, and whether PE adducts form in cells or contribute to the effects of IsoKs is unknown. When radiolabeled IsoK was added to HEK293 cells, 40% of the radiolabel extracted into the chloroform lower phase suggesting the possible formation of PE adducts. We therefore developed methods to measure IsoK-PE adducts in cells. IsoK-PE was quantified by LC/MS/MS after hydrolysis to IsoK-ethanolamine by Streptomyces chromofuscus phospholipase D. In HEK293 and human umbilical vein endothelial cells (HUVEC), IsoK dose-dependently increased PE adduct concentrations to a greater extent than protein adduct. To test the biological significance of IsoK-PE formation, we treated HUVEC with IsoK-PE. IsoK-PE dose dependently induced cytotoxicity (LC(50) 2.2 muM). These results indicate that cellular PE is a significant target of IsoKs, and that formation of PE adducts may mediate some of the biological effects of IsoKs relevant to disease.