Nitro-Oleic Acid Reduces J774A.1 Macrophage Oxidative Status and Triglyceride Mass: Involvement of Paraoxonase2 and Triglyceride Metabolizing Enzymes

Developmental changes in lipid and fatty acid metabolism and the inhibition by in ovo feeding oleic acid in Muscovy duck embryogenesis

Hepatic lipid and fatty acid (FA) metabolism are critical for regulating energetic homeostasis during embryogenesis. At present, it remains unclear how an exogenous FA intervention affects embryonic development in an avian embryo model. In Exp. 1, 30 fertilized eggs were sampled on embryonic days (E) 16, 19, 22, 25, 28, 31 and the day of hatch (DOH) to determine the critical period of lipid metabolism. In Exp. 2, a total of 120 fertilized eggs were divided into two groups (60 eggs/group) for in ovo feeding (IOF) procedures on E25. Eggs were injected into the yolk sac with PBS as the control group and with oleic acid (OA) as the IOF-OA treatment group. Samples were collected on E28 and E31. In Exp. 1, hepatic triacylglycerol (TG) and cholesterol (CHO) contents increased while serum TG content decreased from E16 to DOH (P < 0.05). Both serum and liver displayed an increase in unsaturated FA and a decrease in saturated FA (P < 0.05). There was a quadratic increase in the target gene and protein expression related to hepatic FA de novo synthesis and oxidation (P < 0.05), whose inflection period was between E22 and E28. In Exp. 2, compared with the control embryos, IOF-OA embryos had an increased yolk sac TG content on E28 and E31, and a decreased serum TG and CHO content on E28 (P < 0.05). The IOF-OA embryos had less OA in the yolk sac and liver on E28, and less unsaturated FA in the serum and liver on E31 than did the control embryos (P < 0.05). Hepatic gene mRNA expression related to FA uptake, synthesis, and oxidation on E28 was lower in IOF-OA than in control embryos (P < 0.05), not on E31 (P > 0.05). Maximal metabolic changes in lipid and FA metabolism occurred on E22-E28 in Muscovy duck embryogenesis, along with the altered target gene and protein expression related to lipogenesis and lipolysis. IOF-OA intervention on E25 could inhibit the target gene expression related to FA uptake, synthesis, and oxidation, which may influence the normal FA metabolism on E28 during embryogenesis.

Chemoproteomic profiling reveals cellular targets of nitro-fatty acids

Nitro-fatty acids are a class of endogenous electrophilic lipid mediators with anti-inflammatory and cytoprotective effects in a wide range of inflammatory and fibrotic disease models. While these beneficial biological effects of nitro-fatty acids are mainly attributed to their ability to form covalent adducts with proteins, only a small number of proteins are known to be nitro-alkylated and the scope of protein nitro-alkylation remains undetermined. Here we describe the synthesis and application of a clickable nitro-fatty acid probe for the detection and first global identification of mammalian proteins that are susceptible to nitro-alkylation. 184 high confidence nitro-alkylated proteins were identified in THP1 macrophages, majority of which are novel targets of nitro-fatty acids, including extended synaptotagmin 2 (ESYT2), signal transducer and activator of transcription 3 (STAT3), toll-like receptor 2 (TLR2), retinoid X receptor alpha (RXRα) and glucocorticoid receptor (NR3C1). In particular, we showed that 9-nitro-oleate covalently modified and inhibited dexamethasone binding to NR3C1. Bioinformatic analyses revealed that nitro-alkylated proteins are highly enriched in endoplasmic reticulum and transmembrane proteins, and are overrepresented in lipid metabolism and transport pathways. This study significantly expands the scope of protein substrates targeted by nitro-fatty acids in living cells and provides a useful resource towards understanding the pleiotropic biological roles of nitro-fatty acids as signaling molecules or as multi-target therapeutic agents.

Analysis of Low Molecular Weight Substances and Related Processes Influencing Cellular Cholesterol Efflux

Cholesterol efflux is the key process protecting the vascular system from the development of atherosclerotic lesions. Various extracellular and intracellular events affect the ability of the cell to efflux excess cholesterol. To explore the possible pathways and processes that promote or inhibit cholesterol efflux, we applied a combined cheminformatic and bioinformatic approach. We performed a comprehensive analysis of published data on the various substances influencing cholesterol efflux and found 153 low molecular weight substances that are included in the Chemical Entities of Biological Interest (ChEBI) database. Pathway enrichment was performed for substances identified within the Reactome database, and 45 substances were selected in 93 significant pathways. The most common pathways included the energy-dependent processes related to active cholesterol transport from the cell, lipoprotein metabolism and lipid transport, and signaling pathways. The activators and inhibitors of cholesterol efflux were non-uniformly distributed among the different pathways: the substances influencing ‘biological oxidations’ activate cholesterol efflux and the substances influencing ‘Signaling by GPCR and PTK6’ inhibit efflux. This analysis may be used in the search and design of efflux effectors for therapies targeting structural and functional high-density lipoprotein deficiency.

Pro-atherogenic and pro-oxidant crosstalk between adipocytes and macrophages

PURPOSE

Obesity, which is characterized by triglyceride accumulation mainly in adipocytes but also in arterial wall cells such as macrophages, is a major risk factor for developing atherosclerosis. We aimed to identify the crosstalk related to lipid metabolism and oxidation status between adipocytes and macrophages.

METHODS

We used a co-culture model system with J477A.1 cultured macrophages and 3T3L1 cultured adipocytes. For an in-vivo co-culture system, we used C57BL/6 mouse peritoneal macrophages and visceral or subcutaneous adipose tissue.

RESULTS

Adipocytes significantly increased reactive oxygen species generation, up to twofold, and decreased cholesterol content by 22% in the co-cultured macrophages. Macrophages significantly increased triglyceride-biosynthesis rate by twofold and decreased triglyceride-degradation rate by 30%, resulting in increased triglyceride accumulation in the co-cultured adipocytes by up to 72%. In the in-vivo mouse model, visceral adipose tissue crosstalk with macrophages resulted in a significant pro-atherogenic phenotype with respect to cellular cholesterol metabolism. In contrast, the interaction between subcutaneous adipose tissue and macrophages mostly affected cellular triglyceride metabolism. There were no significant effects on mitochondrial respiration capacity in the macrophages. Upon oxidative-stress reduction in the co-cultured cells using the polyphenol-rich antioxidant, pomegranate juice, the expression of genes related to cellular lipid accumulation was significantly reduced.

CONCLUSIONS

We reveal, for the first time, that paracrine interactions between adipocytes and macrophages result in oxidative stress and lipids metabolic alterations in both cells, toward increased atherogenicity which can be reversed by phenolic antioxidants.

Leucine supplementation attenuates macrophage foam-cell formation: Studies in humans, mice, and cultured macrophages

Whereas atherogenicity of dietary lipids has been largely studied, relatively little is known about the possible contribution of dietary amino acids to macrophage foam-cell formation, a hallmark of early atherogenesis. Recently, we showed that leucine has antiatherogenic properties in the macrophage model system. In this study, an in-depth investigation of the role of leucine in macrophage lipid metabolism was conducted by supplementing humans, mice, or cultured macrophages with leucine. Macrophage incubation with serum obtained from healthy adults supplemented with leucine (5 g/d, 3 weeks) significantly decreased cellular cholesterol mass by inhibiting the rate of cholesterol biosynthesis and increasing cholesterol efflux from macrophages. Similarly, leucine supplementation to C57BL/6 mice (8 weeks) resulted in decreased cholesterol content in their harvested peritoneal macrophages (MPM) in relation with reduced cholesterol biosynthesis rate. Studies in J774A.1 murine macrophages revealed that leucine dose-dependently decreased cellular cholesterol and triglyceride mass. Macrophages treated with leucine (0.2 mM) showed attenuated uptake of very low-density lipoproteins and triglyceride biosynthesis rate, with a concurrent down-regulation of diacylglycerol acyltransferase-1, a key enzyme catalyzing triglyceride biosynthesis in macrophages. Similar effects were observed when macrophages were treated with α-ketoisocaproate, a key leucine metabolite. Finally, both in vivo and in vitro leucine supplementation significantly improved macrophage mitochondrial respiration and ATP production. The above studies, conducted in human, mice, and cultured macrophages, highlight a protective role for leucine attenuating macrophage foam-cell formation by mechanisms related to the metabolism of cholesterol, triglycerides, and energy production. © 2018 BioFactors, 44(3):245-262, 2018.

Inflammatory signaling and metabolic regulation by nitro-fatty acids

The addition of nitrogen dioxide (NO2) to the double bond of unsaturated fatty acids yields an array of electrophilic nitro-fatty acids (NO2-FA) with unique biochemical and signaling properties. During the last decade, NO2-FA have been shown to exert a protective role in various inflammatory and metabolic disorders. NO2-FA exert their biological effects primarily by regulating two central physiological adaptive responses: the canonical inflammatory signaling and metabolic pathways. In this mini-review, we summarize current knowledge on the regulatory role of NO2-FA in the inflammatory and metabolic response via regulation of nuclear factor kappa B (NF-κB) and peroxisome proliferator-activated receptor γ (PPARγ), master regulators of inflammation and metabolism. Moreover, the engagement of novel signaling and metabolic pathways influenced by NO2-FA, beyond NF-κB and PPAR signaling, is discussed herein.

Acrolein increases macrophage atherogenicity in association with gut microbiota remodeling in atherosclerotic mice: protective role for the polyphenol-rich pomegranate juice

The unsaturated aldehyde acrolein is pro-atherogenic, and the polyphenol-rich pomegranate juice (PJ), known for its anti-oxidative/anti-atherogenic properties, inhibits macrophage foam cell formation, the hallmark feature of early atherosclerosis. This study aimed to investigate two unexplored areas of acrolein atherogenicity: macrophage lipid metabolism and the gut microbiota composition. The protective effects of PJ against acrolein atherogenicity were also evaluated. Atherosclerotic apolipoprotein E-deficient (apoE^-/-) mice that were fed acrolein (3 mg/kg/day) for 1 month showed significant increases in serum and aortic cholesterol, triglycerides, and lipid peroxides. In peritoneal macrophages isolated from the mice and in J774A.1 cultured macrophages, acrolein exposure increased intracellular oxidative stress and stimulated cholesterol and triglyceride accumulation via enhanced rates of their biosynthesis and over-expression of key regulators of cellular lipid biosynthesis: sterol regulatory element-binding proteins (SREBPs), 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCR), and diacylglycerol acyltransferase1 (DGAT1). Acrolein-fed mice demonstrated a major shift in the gut microbiota composition, including a significant phylum-level change in increased Firmicutes and decreased Bacteroidetes. At the family level, acrolein significantly increased the prevalence of Ruminococcaceae and Lachnospiraceae of which the Coprococcus genus was significantly and positively correlated with serum, aortic and macrophage lipid levels and peroxidation. The pro-atherogenic effects of acrolein on serum, aortas, macrophages, and the gut microbiota were substantially abolished by PJ. In conclusion, these findings provide novel mechanisms by which acrolein increases macrophage lipid accumulation and alters the gut microbiota composition in association with enhanced atherogenesis. Moreover, PJ was found as an effective strategy against acrolein atherogenicity.