Supplementation with linoleic acid-rich soybean oil stimulates macrophage foam cell formation via increased oxidative stress and diacylglycerol acyltransferase1-mediated triglyceride biosynthesis

The interplay between nonalcoholic fatty liver disease and atherosclerotic cardiovascular disease

Therapeutic approaches that lower circulating low-density lipoprotein (LDL)-cholesterol significantly reduced the burden of cardiovascular disease over the last decades. However, the persistent rise in the obesity epidemic is beginning to reverse this decline. Alongside obesity, the incidence of nonalcoholic fatty liver disease (NAFLD) has substantially increased in the last three decades. Currently, approximately one third of world population is affected by NAFLD. Notably, the presence of NAFLD and particularly its more severe form, nonalcoholic steatohepatitis (NASH), serves as an independent risk factor for atherosclerotic cardiovascular disease (ASCVD), thus, raising interest in the relationship between these two diseases. Importantly, ASCVD is the major cause of death in patients with NASH independent of traditional risk factors. Nevertheless, the pathophysiology linking NAFLD/NASH with ASCVD remains poorly understood. While dyslipidemia is a common risk factor underlying both diseases, therapies that lower circulating LDL-cholesterol are largely ineffective against NASH. While there are no approved pharmacological therapies for NASH, some of the most advanced drug candidates exacerbate atherogenic dyslipidemia, raising concerns regarding their adverse cardiovascular consequences. In this review, we address current gaps in our understanding of the mechanisms linking NAFLD/NASH and ASCVD, explore strategies to simultaneously model these diseases, evaluate emerging biomarkers that may be useful to diagnose the presence of both diseases, and discuss investigational approaches and ongoing clinical trials that potentially target both diseases.

Macrophage polarization by potential nutraceutical compounds: A strategic approach to counteract inflammation in atherosclerosis

Chronic inflammation represents a main event in the onset and progression of atherosclerosis and is closely associated with oxidative stress in a sort of vicious circle that amplifies and sustains all stages of the disease. Key players of atherosclerosis are monocytes/macrophages. According to their pro- or anti-inflammatory phenotype and biological functions, lesional macrophages can release various mediators and enzymes, which in turn contribute to plaque progression and destabilization or, alternatively, lead to its resolution. Among the factors connected to atherosclerotic disease, lipid species carried by low density lipoproteins and pro-oxidant stimuli strongly promote inflammatory events in the vasculature, also by modulating the macrophage phenotyping. Therapies specifically aimed to balance macrophage inflammatory state are increasingly considered as powerful tools to counteract plaque formation and destabilization. In this connection, several molecules of natural origin have been recognized to be active mediators of diverse metabolic and signaling pathways regulating lipid homeostasis, redox state, and inflammation; they are, thus, considered as promising candidates to modulate macrophage responsiveness to pro-atherogenic stimuli. The current knowledge of the capability of nutraceuticals to target macrophage polarization and to counteract atherosclerotic lesion progression, based mainly on in vitro investigation, is summarized in the present review.

Effects of increasing intake of soybean oil on synthesis of testosterone in Leydig cells

Background

Soybean oil is a very common edible oil in daily life. With the changes in the dietary composition, the intake of soybean oil increased. However, the effects of dietary intake of soybean oil on testosterone production are still unclear.

Methods

In order to study the effects of increasing intake of soybean oil on the synthesis of testosterone in Leydig cells, we fed male C57BL/6 mice on the diet which added 20% soybean salad oil (SOY group). We detected the hormone levels by enzyme-linked immunosorbent assay (ELISA) kits and serum fatty acid composition by gas chromatography, and analyzed the expression of steroidogenic enzymes by Real-Time PCR or immunoblotting analysis.

Results

After the 16-week feeding period, serum linoleic acid (LA) and α-linolenic acid (ALA) significantly increased and serum palmitic acid (PA) significantly decreased in SOY group mice. Compared to the normal diet (ND group), increasing intake of soybean oil raised the luteinizing hormone (LH) levels and up-regulated luteinizing hormone/chorionic gonadotropin receptor (LHCGR), steroidogenic acute regulatory protein (StAR) and cytochrome P450 family 11 subfamily A member I (CYP11A1). Testosterone levels in SOY group were higher than that in the ND group, and significantly difference showed.

Conclusions

Increasing intake of soybean oil could raise the serum LA and ALA levels and decrease serum PA levels. This could activate the LH/LHCGR pathway and improve the function of steroid synthesis in Leydig cells, and finally lead to the elevated testosterone levels.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12986-021-00580-1.

Soybean Oil Modulates the Gut Microbiota Associated with Atherogenic Biomarkers

During the last few decades there has been a staggering rise in human consumption of soybean-oil (SO). The microbiome and specific taxa composing it are dramatically affected by diet; specifically, by high-fat diets. Increasing evidence indicates the association between dysbiosis and health or disease state, including cardiovascular diseases (CVD) and atherosclerosis pathogenesis in human and animal models. To investigate the effects of high SO intake, C57BL/6 mice were orally supplemented with SO-based emulsion (SOE) for one month, followed by analyses of atherosclerosis-related biomarkers and microbiota profiling by 16S rRNA gene sequencing of fecal DNA. SOE-supplementation caused compositional changes to 64 taxa, including enrichment in Bacteroidetes, Mucispirillum, Prevotella and Ruminococcus, and decreased Firmicutes. These changes were previously associated with atherosclerosis in numerous studies. Among the shifted taxa, 40 significantly correlated with at least one atherosclerosis-related biomarker (FDR < 0.05), while 13 taxa positively correlated with the average of all biomarkers. These microbial alterations also caused a microbial-derived metabolic-pathways shift, including enrichment in different amino-acid metabolic-pathways known to be implicated in CVD. In conclusion, our results demonstrate dysbiosis following SOE supplementation associated with atherosclerosis-related biomarkers. These findings point to the microbiome as a possible mediator to CVD, and it may be implemented into non-invasive diagnostic tools or as potential therapeutic strategies.

Effects of Cyclic Fatty Acid Monomers from Heated Vegetable Oil on Markers of Inflammation and Oxidative Stress in Male Wistar Rats

This study assesses the effects of cyclic fatty acid monomers (CFAM) from heated vegetable oils on oxidative stress and inflammation. Wistar rats were fed either of these four diets for 28 days: canola oil (CO), canola oil and 0.5% CFAM (CC), soybean oil (SO), and soybean oil and 0.5% CFAM (SC). Markers of oxidative stress and inflammation were determined by micro liquid chromatography tandem mass spectrometry (micro-LC-MS/MS) and enzyme-linked immunosorbent assay (ELISA) kits, respectively. Analysis of variance (ANOVA) for a 2 × 2 factorial design was performed to determine the CFAM and oil effects and interactions between these two factors at P ≤ 0.05. For significant interactions, a post hoc multiple comparison test was performed, i.e., Tukey HSD (honest significant difference) test. CFAM induced higher plasma levels of 15-F_2t-IsoP (CC, 396 ± 43 ng/mL, SC, 465 ± 75 ng/mL vs CO, 261 ± 23 ng/mL and SO, 288 ± 35 ng/mL, P < 0.05). Rats fed the SC diet had higher plasma 2,3-dinor-15-F_2t-IsoP (SC, 145 ± 9 ng/mL vs CC, 84 ± 8 ng/mL, CO, 12 ± 1 ng/mL, and SO, 12 ± 1 ng/mL, P < 0.05), urinary 2,3-dinor-15-F_2t-IsoP (SC, 117 ± 12 ng/mL vs CC, 67 ± 13 ng/mL, CO, 15 ± 2 ng/mL, and SO, 18 ± 4 ng/mL, P < 0.05), and plasma IL-6 (SC, 57 ± 10 pg/mL vs CC, 48 ± 11 pg/mL, CO, 46 ± 9 pg/mL, and SO, 44 ± 4 pg/mL, P < 0.05) than the other three diet groups. These results indicate that CFAM increased the levels of markers of oxidative stress, and those effects are exacerbated by a CFAM-high-linoleic acid diet.

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.

Relative levels of dietary EPA and DHA impact gastric oxidation and essential fatty acid uptake

Previous research showed that increasing the proportion of docosahexaenoic acid (DHA) in marine lipid supplements significantly reduces associated health benefits compared with balanced eicosapentaenoic acid (EPA):DHA supplementation Dasilva et al., 2015 [1]. It was therefore hypothesized that the EPA and DHA molecules might have differential resistance to oxidation during gastric digestion and that the oxidation level achieved could be inversely correlated with intestinal absorption and, hence, with the resultant health benefits. Accordingly, we tested this proposed mechanism of action by investigating the degree of oxidation in the stomach, and the levels of bioaccessible lipids, of varying molar proportions of DHA and EPA (2:1, 1:1 and 1:2) using the dynamic gastrointestinal tract model TIM-1. In addition, small intestine enterocyte absorption and metabolism were simulated by Caco-2 cell monolayers that were incubated with these same varying proportions of DHA and EPA, and comparing oxidized and nonoxidized polyunsaturated fatty acids (PUFAs). The results show an inverse correlation between lipid oxidation products in the stomach and the levels of bioaccessible lipids. The balanced 1:1 EPA:DHA diet resulted in lower oxidation of PUFAs during stomach digestion relative to the other ratios tested. Finally, cell-based studies showed significantly lower assimilation of oxidized EPA and DHA substrates compared to nonoxidized PUFAs, as well as significant differences between the net uptake of EPA and DHA. Overall, the present work suggests that the correct design of diets and/or supplements containing marine lipids can strongly influence the stability and bioaccessibility of PUFAs during gastrointestinal digestion and subsequent absorption. This could modulate their health benefits related with inflammation, oxidative stress and metabolic disorders.

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.

20-Hydroxyeicosatetraenoic Acid (20-HETE) Modulates Canonical Transient Receptor Potential-6 (TRPC6) Channels in Podocytes

The arachidonic acid metabolite 20-hydroxyeicosatetraenoic acid (20-HETE) regulates renal function, including changes in glomerular function evoked during tubuloglomerular feedback (TGF). This study describes the cellular actions of 20-HETE on cultured podocytes, assessed by whole-cell recordings from cultured podocytes combined with pharmacological and cell-biological manipulations of cells. Bath superfusion of 20-HETE activates cationic currents that are blocked by the pan-TRP blocker SKF-96365 and by 50 μM La³⁺, and which are attenuated after siRNA knockdown of TRPC6 subunits. Similar currents are evoked by a membrane-permeable analog of diacylgycerol (OAG), but OAG does not occlude responses to maximally-activating concentrations of 20-HETE (20 μM). Exposure to 20-HETE also increased steady-state surface abundance of TRPC6 subunits in podocytes as assessed by cell-surface biotinylation assays, and increased cytosolic concentrations of reactive oxygen species (ROS). TRPC6 activation by 20-HETE was eliminated in cells pretreated with TEMPOL, a membrane-permeable superoxide dismutase mimic. Activation of TRPC6 by 20-HETE was also blocked when whole-cell recording pipettes contained GDP-βS, indicating a role for either small or heterotrimeric G proteins in the transduction cascade. Responses to 20-HETE were eliminated by siRNA knockdown of podocin, a protein that organizes NADPH oxidase complexes with TRPC6 subunits in this cell type. In summary, modulation of ionic channels in podocytes may contribute to glomerular actions of 20-HETE.