Scavenging Reactive Lipids to Prevent Oxidative Injury.

Oxidative injury due to elevated levels of reactive oxygen species is implicated in cardiovascular diseases, Alzheimer's disease, lung and liver diseases, and many cancers. Antioxidant therapies have generally been ineffective at treating these diseases, potentially due to ineffective doses but also due to interference with critical host defense and signaling processes. Therefore, alternative strategies to prevent oxidative injury are needed. Elevated levels of reactive oxygen species induce lipid peroxidation, generating reactive lipid dicarbonyls. These lipid oxidation products may be the most salient mediators of oxidative injury, as they cause cellular and organ dysfunction by adducting to proteins, lipids, and DNA. Small-molecule compounds have been developed in the past decade to selectively and effectively scavenge these reactive lipid dicarbonyls. This review outlines evidence supporting the role of lipid dicarbonyls in disease pathogenesis, as well as preclinical data supporting the efficacy of novel dicarbonyl scavengers in treating or preventing disease.

Elucidation of physico-chemical principles of high-density lipoprotein-small RNA binding interactions.

Extracellular small RNAs (sRNAs) are abundant in many biofluids, but little is known about their mechanisms of transport and stability in RNase-rich environments. We previously reported that high-density lipoproteins (HDLs) in mice were enriched with multiple classes of sRNAs derived from the endogenous transcriptome, but also from exogenous organisms. Here, we show that human HDL transports tRNA-derived sRNAs (tDRs) from host and nonhost species, the profiles of which were found to be altered in human atherosclerosis. We hypothesized that HDL binds to tDRs through apolipoprotein A-I (apoA-I) and that these interactions are conferred by RNA-specific features. We tested this using microscale thermophoresis and electrophoretic mobility shift assays and found that HDL binds to tDRs and other single-stranded sRNAs with strong affinity but did not bind to double-stranded RNA or DNA. Furthermore, we show that natural and synthetic RNA modifications influenced tDR binding to HDL. We demonstrate that reconstituted HDL bound to tDRs only in the presence of apoA-I, and purified apoA-I alone were able to bind sRNA. Conversely, phosphatidylcholine vesicles did not bind tDRs. In summary, we conclude that HDL binds to single-stranded sRNAs likely through nonionic interactions with apoA-I. These results highlight binding properties that likely enable extracellular RNA communication and provide a foundation for future studies to manipulate HDL-sRNA interactions for therapeutic approaches to prevent or treat disease.

Taxifolin inhibits NETosis through activation of Nrf2 and provides protective effects in models of lupus and antiphospholipid syndrome.

OBJECTIVES: Taxifolin (dihydroquercetin) is a bioactive plant flavonoid that exhibits anti-inflammatory and anti-oxidative properties. We hypothesized that taxifolin might be an effective dietary supplement to ameliorate symptoms arising from thrombo-inflammatory diseases such as lupus and antiphospholipid syndrome (APS). METHODS: We used in vitro assays and a mouse model to determine mechanisms by which taxifolin inhibits neutrophil extracellular trap (NET) formation (i.e., NETosis) and venous thrombosis in lupus and APS. RESULTS: At doses ranging from 0.1 to 1 µg/ml, taxifolin inhibited NETosis from control neutrophils stimulated with autoantibodies isolated from lupus and APS patients, and its suppressive effects were mitigated by blocking the antioxidant transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2). Furthermore, taxifolin at a dose as low as 20 mg/kg/day reduced in vivo NETosis in thrombo-inflammatory mouse models of lupus and APS while also significantly attenuating autoantibody formation, inflammatory cytokine production, and large-vein thrombosis. CONCLUSION: Our study is the first to demonstrate the protective effects of taxifolin in the context of lupus and APS. Importantly, our study also suggests a therapeutic potential to neutralize neutrophil hyperactivity and NETosis that could have relevance to a variety of thrombo-inflammatory diseases.

Myeloperoxidase-induced modification of HDL by isolevuglandins inhibits paraoxonase-1 activity.

Reduced activity of paraoxonase 1 (PON1), a high-density lipoprotein (HDL)-associated enzyme, has been implicated in the development of atherosclerosis. Post-translational modifications of PON1 may represent important mechanisms leading to reduced PON1 activity. Under atherosclerotic conditions, myeloperoxidase (MPO) is known to associate with HDL. MPO generates the oxidants hypochlorous acid and nitrogen dioxide, which can lead to post-translational modification of PON1, including tyrosine modifications that inhibit PON1 activity. Nitrogen dioxide also drives lipid peroxidation, leading to the formation of reactive lipid dicarbonyls such as malondialdehyde and isolevuglandins, which modify HDL and could inhibit PON1 activity. Because isolevuglandins are more reactive than malondialdehyde, we used in vitro models containing HDL, PON1, and MPO to test the hypothesis that IsoLG formation by MPO and its subsequent modification of HDL contributes to MPO-mediated reductions in PON1 activity. Incubation of MPO with HDL led to modification of HDL proteins, including PON1, by IsoLG. Incubation of HDL with IsoLG reduced PON1 lactonase and antiperoxidation activities. IsoLG modification of recombinant PON1 markedly inhibited its activity, while irreversible IsoLG modification of HDL before adding recombinant PON1 only slightly inhibited the ability of HDL to enhance the catalytic activity of recombinant PON1. Together, these studies support the notion that association of MPO with HDL leads to lower PON1 activity in part via IsoLG-mediated modification of PON1, so that IsoLG modification of PON1 could contribute to increased risk for atherosclerosis, and blocking this modification might prove beneficial to reduce atherosclerosis.

Kidney injury-mediated disruption of intestinal lymphatics involves dicarbonyl-modified lipoproteins.

Kidney disease affects intestinal structure and function. Although intestinal lymphatics are central in absorption and remodeling of dietary and synthesized lipids/lipoproteins, little is known about how kidney injury impacts the intestinal lymphatic network, or lipoproteins transported therein. To study this, we used puromycin aminoglycoside-treated rats and NEP25 transgenic mice to show that proteinuric injury expanded the intestinal lymphatic network, activated lymphatic endothelial cells and increased mesenteric lymph flow. The lymph was found to contain increased levels of cytokines, immune cells, and isolevuglandin (a highly reactive dicarbonyl) and to have a greater output of apolipoprotein AI. Plasma levels of cytokines and isolevuglandin were not changed. However, isolevuglandin was also increased in the ileum of proteinuric animals, and intestinal epithelial cells exposed to myeloperoxidase produced more isolevuglandin. Apolipoprotein AI modified by isolevuglandin directly increased lymphatic vessel contractions, activated lymphatic endothelial cells, and enhanced the secretion of the lymphangiogenic promoter vascular endothelial growth factor-C by macrophages. Inhibition of isolevuglandin synthesis by a carbonyl scavenger reduced intestinal isolevuglandin adduct level and lymphangiogenesis. Thus, our data reveal a novel mediator, isolevuglandin modified apolipoprotein AI, and uncover intestinal lymphatic network structure and activity as a new pathway in the crosstalk between kidney and intestine that may contribute to the adverse impact of kidney disease on other organs.

Modified sites and functional consequences of 4-oxo-2-nonenal adducts in HDL that are elevated in familial hypercholesterolemia.

The lipid aldehyde 4-oxo-2-nonenal (ONE) is a highly reactive protein crosslinker derived from peroxidation of n-6 polyunsaturated fatty acids and generated together with 4-hydroxynonenal (HNE). Lipid peroxidation product-mediated crosslinking of proteins in high-density lipoprotein (HDL) causes HDL dysfunction and contributes to atherogenesis. Although HNE is relatively well-studied, the role of ONE in atherosclerosis and in modifying HDL is unknown. Here, we found that individuals with familial hypercholesterolemia (FH) had significantly higher ONE-ketoamide (lysine) adducts in HDL (54.6 ± 33.8 pmol/mg) than healthy controls (15.3 ± 5.6 pmol/mg). ONE crosslinked apolipoprotein A-I (apoA-I) on HDL at a concentration of > 3 mol ONE per 10 mol apoA-I (0.3 eq), which was 100-fold lower than HNE, but comparable to the potent protein crosslinker isolevuglandin. ONE-modified HDL partially inhibited HDL's ability to protect against lipopolysaccharide (LPS)-induced tumor necrosis factor α (TNFα) and interleukin-1ß (IL-1ß) gene expression in murine macrophages. At 3 eq, ONE dramatically decreased apoA-I exchange from HDL, from ∼46.5 to ∼18.4% (p < 0.001). Surprisingly, ONE modification of HDL or apoA-I did not alter macrophage cholesterol efflux capacity. LC-MS/MS analysis revealed that Lys-12, Lys-23, Lys-96, and Lys-226 in apoA-I are modified by ONE ketoamide adducts. Compared with other dicarbonyl scavengers, pentylpyridoxamine (PPM) most efficaciously blocked ONE-induced protein crosslinking in HDL and also prevented HDL dysfunction in an in vitro model of inflammation. Our findings show that ONE-HDL adducts cause HDL dysfunction and are elevated in individuals with FH who have severe hypercholesterolemia.

Engineering the gut microbiota to treat chronic diseases.

Gut microbes play vital roles in host health and disease. A number of commensal bacteria have been used as vectors for genetic engineering to create living therapeutics. This review highlights recent advances in engineering gut bacteria for the treatment of chronic diseases such as metabolic diseases, cancer, inflammatory bowel diseases, and autoimmune disorders. KEY POINTS: • Bacterial homing to tumors has been exploited to deliver therapeutics in mice models. • Engineered bacteria show promise in mouse models of metabolic diseases. • Few engineered bacterial treatments have advanced to clinical studies.

Modification by isolevuglandins, highly reactive γ-ketoaldehydes, deleteriously alters high-density lipoprotein structure and function.

Cardiovascular disease risk depends on high-density lipoprotein (HDL) function, not HDL-cholesterol. Isolevuglandins (IsoLGs) are lipid dicarbonyls that react with lysine residues of proteins and phosphatidylethanolamine. IsoLG adducts are elevated in atherosclerosis. The consequences of IsoLG modification of HDL have not been studied. We hypothesized that IsoLG modification of apoA-I deleteriously alters HDL function. We determined the effect of IsoLG on HDL structure-function and whether pentylpyridoxamine (PPM), a dicarbonyl scavenger, can preserve HDL function. IsoLG adducts in HDL derived from patients with familial hypercholesterolemia (n = 10, 233.4 ± 158.3 ng/mg) were found to be significantly higher than in healthy controls (n = 7, 90.1 ± 33.4 pg/mg protein). Further, HDL exposed to myeloperoxidase had elevated IsoLG-lysine adducts (5.7 ng/mg protein) compared with unexposed HDL (0.5 ng/mg protein). Preincubation with PPM reduced IsoLG-lysine adducts by 67%, whereas its inactive analogue pentylpyridoxine did not. The addition of IsoLG produced apoA-I and apoA-II cross-links beginning at 0.3 molar eq of IsoLG/mol of apoA-I (0.3 eq), whereas succinylaldehyde and 4-hydroxynonenal required 10 and 30 eq. IsoLG increased HDL size, generating a subpopulation of 16-23 nm. 1 eq of IsoLG decreased HDL-mediated [3H]cholesterol efflux from macrophages via ABCA1, which corresponded to a decrease in HDL-apoA-I exchange from 47.4% to only 24.8%. This suggests that IsoLG inhibits apoA-I from disassociating from HDL to interact with ABCA1. The addition of 0.3 eq of IsoLG ablated HDL's ability to inhibit LPS-stimulated cytokine expression by macrophages and increased IL-1ß expression by 3.5-fold. The structural-functional effects were partially rescued with PPM scavenging.

Isolevuglandins and cardiovascular disease.

Isolevuglandins are 4-ketoaldehydes formed by peroxidation of arachidonic acid. Isolevuglandins react rapidly with primary amines including the lysyl residues of proteins to form irreversible covalent modifications. This review highlights evidence for the potential role of isolevuglandin modification in the disease processes, especially atherosclerosis, and some of the tools including small molecule dicarbonyl scavengers utilized to assess their contributions to disease.

Scavenging dicarbonyls with 5'-O-pentyl-pyridoxamine increases HDL net cholesterol efflux capacity and attenuates atherosclerosis and insulin resistance.

OBJECTIVE: Oxidative stress contributes to the development of insulin resistance (IR) and atherosclerosis. Peroxidation of lipids produces reactive dicarbonyls such as Isolevuglandins (IsoLG) and malondialdehyde (MDA) that covalently bind plasma/cellular proteins, phospholipids, and DNA leading to altered function and toxicity. We examined whether scavenging reactive dicarbonyls with 5'-O-pentyl-pyridoxamine (PPM) protects against the development of IR and atherosclerosis in Ldlr-/- mice. METHODS: Male or female Ldlr-/- mice were fed a western diet (WD) for 16 weeks and treated with PPM versus vehicle alone. Plaque extent, dicarbonyl-lysyl adducts, efferocytosis, apoptosis, macrophage inflammation, and necrotic area were measured. Plasma MDA-LDL adducts and the in vivo and in vitro effects of PPM on the ability of HDL to reduce macrophage cholesterol were measured. Blood Ly6Chi monocytes and ex vivo 5-ethynyl-2'-deoxyuridine (EdU) incorporation into bone marrow CD11b+ monocytes and CD34+ hematopoietic stem and progenitor cells (HSPC) were also examined. IR was examined by measuring fasting glucose/insulin levels and tolerance to insulin/glucose challenge. RESULTS: PPM reduced the proximal aortic atherosclerosis by 48% and by 46% in female and male Ldlr-/- mice, respectively. PPM also decreased IR and hepatic fat and inflammation in male Ldlr-/- mice. Importantly, PPM decreased plasma MDA-LDL adducts and prevented the accumulation of plaque MDA- and IsoLG-lysyl adducts in Ldlr-/- mice. In addition, PPM increased the net cholesterol efflux capacity of HDL from Ldlr-/- mice and prevented both the in vitro impairment of HDL net cholesterol efflux capacity and apoAI crosslinking by MPO generated hypochlorous acid. Moreover, PPM decreased features of plaque instability including decreased proinflammatory M1-like macrophages, IL-1ß expression, myeloperoxidase, apoptosis, and necrotic core. In contrast, PPM increased M2-like macrophages, Tregs, fibrous cap thickness, and efferocytosis. Furthermore, PPM reduced inflammatory monocytosis as evidenced by decreased blood Ly6Chi monocytes and proliferation of bone marrow monocytes and HSPC from Ldlr-/- mice. CONCLUSIONS: PPM has pleotropic atheroprotective effects in a murine model of familial hypercholesterolemia, supporting the therapeutic potential of reactive dicarbonyl scavenging in the treatment of IR and atherosclerotic cardiovascular disease.

Apolipoprotein A5, a unique modulator of fasting and postprandial triglycerides.

The discovery of apolipoprotein A5 (APOA5) in 2001 has raised a number of intriguing questions about its role in lipid transport and triglyceride (TG) homeostasis. Genome-wide association studies have consistently identified APOA5 as a regulator of plasma TG levels, which is further supported by studies in transgenic and knockout mouse models. The present review describes recent concepts pertaining to the roles of APOA5 in TG metabolism as related to the vascular compartment, liver, adipose tissue and the gut. Recent evidence indicates that APOA5 may also affect postprandial TG metabolism through influencing chylomicron formation and transport by the intestine into the intestinal lymph. While substantial evidence supports the notion that APOA5 plays both extracellular and intracellular roles in TG homeostasis, mysteries remain on how this low-abundance, liver-derived protein may modulate TG homeostasis, including via the gut. Given the strong correlation between elevated plasma TG and cardiometabolic diseases, there is great scientific and public interest in understanding the intriguing mysteries presented by APOA5.

Dicarbonyl-modified lipoproteins contribute to proteinuric kidney injury.

Lipoprotein modification by reactive dicarbonyls, including isolevuglandin (IsoLG), produces dysfunctional particles. Kidneys participate in lipoprotein metabolism, including tubular uptake. However, the process beyond the proximal tubule is unclear, as is the effect of kidney injury on this pathway. We found that patients and animals with proteinuric injury have increased urinary apolipoprotein AI (apoAI), IsoLG, and IsoLG adduct enrichment of the urinary apoAI fraction compared with other proteins. Proteinuric mice, induced by podocyte-specific injury, showed more tubular absorption of IsoLG-apoAI and increased expression of lipoprotein transporters in proximal tubular cells compared with uninjured animals. Renal lymph reflects composition of the interstitial compartment and showed increased apoAI and IsoLG in proteinuric animals, supporting a tubular cell-interstitium-lymph pathway for renal handling of lipoproteins. IsoLG-modified apoAI was not only a marker of renal injury but also directly damaged renal cells. IsoLG-apoAI increased inflammatory cytokines in cultured tubular epithelial cells (TECs), activated lymphatic endothelial cells (LECs), and caused greater contractility of renal lymphatic vessels than unmodified apoAI. In vivo, inhibition of IsoLG by a dicarbonyl scavenger reduced both albuminuria and urinary apoAI and decreased TEC and LEC injury, lymphangiogenesis, and interstitial fibrosis. Our results indicate that IsoLG-modified apoAI is, to our knowledge, a novel pathogenic mediator and therapeutic target in kidney disease.

Isolevuglandins as mediators of disease and the development of dicarbonyl scavengers as pharmaceutical interventions.

Products of lipid peroxidation include a number of reactive lipid aldehydes such as malondialdehyde, 4-hydroxy-nonenal, 4-oxo-nonenal, and isolevuglandins (IsoLGs). Although these all contribute to disease processes, the most reactive are the IsoLGs, which rapidly adduct to lysine and other cellular primary amines, leading to changes in protein function, cross-linking and immunogenicity. Their rapid reactivity means that only IsoLG adducts, and not the unreacted aldehyde, can be readily measured. This high reactivity also makes it challenging for standard cellular defense mechanisms such as aldehyde reductases and oxidases to dispose of them before they react with proteins and other cellular amines. This led us to seek small molecule primary amines that might trap and inactivate IsoLGs before they could modify cellular proteins or other endogenous cellular amines such as phosphatidylethanolamines to cause disease. Our studies identified 2-aminomethylphenols including 2-hydroxybenzylamine as IsoLG scavengers. Subsequent studies showed that they also trap other lipid dicarbonyls that react with primary amines such as 4-oxo-nonenal and malondialdehyde, but not hydroxyalkenals like 4-hydroxy-nonenal that preferentially react with soft nucleophiles. This review describes the use of these 2-aminomethylphenols as dicarbonyl scavengers to assess the contribution of IsoLGs and other amine-reactive lipid dicarbonyls to disease and as therapeutic agents.

Progressively decreasing plasma high-density lipoprotein cholesterol levels preceding diagnosis of smoldering myeloma.

We report a case of disappearing high-density lipoprotein (HDL) syndrome caused by oxidative modification of HDL and by autoantibodies against modified HDL, with subsequent diagnosis of myeloma. An elderly Caucasian man had normal lipid levels with HDL cholesterol (HDL-C) levels in the upper 70 mg/dL range from 1999 to 2003. In 2003, his HDL-C levels began to progressively fall, and by 2011, they were undetectable (<5 mg/dL) when measured with a Beckman Synchron LX auto analyzer. Analyses of the plasma sample from 2011 using ultracentrifugation (Vertical Auto Profile), nuclear magnetic resonance, and Ace EXCEL auto analyzer have shown that HDL-C levels were easily detectable (47-54 mg/dL), although reduced compared with his pre-2003 values. Analyses of his plasma sample from 2011 also showed the presence of lipid-adducted apolipoprotein A1 (apoA1) and high titer of antibodies against the adducted apoA1. Interestingly, a negative correlation between HDL-C levels and the titer of antibodies against apoA1 adducts was found in the control cohort. Finally, we show that in the mouse system, an antibody against apoA1 increases the clearance of HDL from plasma. This case of smoldering myeloma preceded by acquired, severe HDL-C deficiency, likely because of oxidative modifications of the HDL protein leading to the formation of autoantibodies, interference with clinical measurement of HDL-C, and increased plasma clearance of HDL, adds to the list of diagnostic considerations for unexplained HDL-C decreases over time.

Administration of N-Acyl-Phosphatidylethanolamine Expressing Bacteria to Low Density Lipoprotein Receptor-/- Mice Improves Indices of Cardiometabolic Disease.

Obesity increases the risk for cardiometabolic diseases. N-acyl phosphatidylethanolamines (NAPEs) are precursors of N-acylethanolamides, which are endogenous lipid satiety factors. Incorporating engineered bacteria expressing NAPEs into the gut microbiota retards development of diet induced obesity in wild-type mice. Because NAPEs can also exert anti-inflammatory effects, we hypothesized that administering NAPE-expressing bacteria to low-density lipoprotein receptor (Ldlr)-/- mice fed a Western diet would improve various indices of cardiometabolic disease manifested by these mice. NAPE-expressing E. coli Nissle 1917 (pNAPE-EcN), control Nissle 1917 (pEcN), or vehicle (veh) were given via drinking water to Ldlr-/- mice for 12 weeks. Compared to pEcN or veh treatment, pNAPE-EcN significantly reduced body weight and adiposity, hepatic triglycerides, fatty acid synthesis genes, and increased expression of fatty acid oxidation genes. pNAPE-EcN also significantly reduced markers for hepatic inflammation and early signs of fibrotic development. Serum cholesterol was reduced with pNAPE-EcN, but atherosclerotic lesion size showed only a non-significant trend for reduction. However, pNAPE-EcN treatment reduced lesion necrosis by 69% indicating an effect on preventing macrophage inflammatory death. Our results suggest that incorporation of NAPE expressing bacteria into the gut microbiota can potentially serve as an adjuvant therapy to retard development of cardiometabolic disease.