Fatty acids modulate the effect of darglitazone on macrophage CD36 expression

Multi-target direct-acting SARS-CoV-2 antivirals against the nucleotide-binding pockets of virus-specific proteins

The nucleotide-binding pockets (NBPs) in virus-specific proteins have proven to be the most successful antiviral targets for several viral diseases. Functionally important NBPs are found in various structural and non-structural proteins of SARS-CoV-2. In this study, the first successful multi-targeting attempt to identify effective antivirals has been made against NBPs in nsp12, nsp13, nsp14, nsp15, nsp16, and nucleocapsid (N) proteins of SARS-CoV-2. A structure-based drug repurposing in silico screening approach with ADME analysis identified small molecules targeting NBPs in SARS-CoV-2 proteins. Further, isothermal titration calorimetry (ITC) experiments validated the binding of top hit molecules to the purified N-protein. Importantly, cell-based antiviral assays revealed antiviral potency for INCB28060, darglitazone, and columbianadin with EC50 values 15.71 μM, 5.36 μM, and 22.52 μM, respectively. These effective antivirals targeting multiple proteins are envisioned to direct the development of antiviral therapy against SARS-CoV-2 and its emerging variants.

Cox-2 Expressed with Insulin in Pancreatic Beta-Cells, and in the Infiltrated Leukocytes in Inflamed Islets of Diabetic Mice

In the event of the onset of type 1 diabetes (T1D) the circulating autoantibodies against the beta-cell of the pancreas are attacked by macrophages and autoreactive lymphocytes under the influence of different cytokines. Eventually, beta-cells are destroyed through apoptosis, or natural killer cells, or a scavenger process. Cyclooxygenase (COX)-2 is constitutively expressed in beta-cells, the possible role in insulin secretion and insulitis has been suggested. However, COX-2 with lymphocytes and other infiltrated leukocytes on diabetogenesis remains largely elusive. We injected diabetic lymphocytes of non-obese diabetic (NOD) mice to NOD/SCID mice for adoptive transfer. The diabetogenesis of adoptive transferred NOD/SCID mice was tested with supplements of COX-2 inhibitor or the substrate, arachidonic acid, in the diets under placebo control. The tissues of intestine and pancreas of BALB/c, NOD and NOD/SCID mice were immunohistochemically analyzed. COX-2 and insulin were revealed in the vesicles of beta-cells in intact islets of BALB/c mice. The lymphocyte tracking of the transferred lymphocytes and COX-2 expression in beta-cells and emerged leukocytes showed that celecoxib, or the substrate did not change the pattern of lymphocyte accumulation in the pancreas compared to placebo, even though the development of severe diabetes was slightly different. COX-2 was only expressed in macrophages, rather than infiltrated lymphocytes. Morphology showed that the emerged lymphocytes migrated from outside islets indicating that the disructive impact of COX-2 on beta cells is probably limited. The enhanced expression of COX-2 and insulin in random beta-cells is likely associated with the genesis of diabetes, a possible mechanism to increase or extend insulin secretion in the late period of insulitis.

Glucose-Dependent Insulinotropic Polypeptide Stimulates Osteopontin Expression in the Vasculature via Endothelin-1 and CREB

Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone with extrapancreatic effects beyond glycemic control. Here we demonstrate unexpected effects of GIP signaling in the vasculature. GIP induces the expression of the proatherogenic cytokine osteopontin (OPN) in mouse arteries via local release of endothelin-1 and activation of CREB. Infusion of GIP increases plasma OPN concentrations in healthy individuals. Plasma endothelin-1 and OPN concentrations are positively correlated in patients with critical limb ischemia. Fasting GIP concentrations are higher in individuals with a history of cardiovascular disease (myocardial infarction, stroke) when compared with control subjects. GIP receptor (GIPR) and OPN mRNA levels are higher in carotid endarterectomies from patients with symptoms (stroke, transient ischemic attacks, amaurosis fugax) than in asymptomatic patients, and expression associates with parameters that are characteristic of unstable and inflammatory plaques (increased lipid accumulation, macrophage infiltration, and reduced smooth muscle cell content). While GIPR expression is predominantly endothelial in healthy arteries from humans, mice, rats, and pigs, remarkable upregulation is observed in endothelial and smooth muscle cells upon culture conditions, yielding a "vascular disease-like" phenotype. Moreover, the common variant rs10423928 in the GIPR gene is associated with increased risk of stroke in patients with type 2 diabetes.

Induction of proinflammatory cytokines by long-chain saturated fatty acids in human macrophages

Increased circulating free fatty acids in subjects with type 2 diabetes may contribute to activation of macrophages, and thus the development of atherosclerosis. In this study, we investigated the effect of the saturated fatty acids (SFA) palmitate, stearate, myristate and laurate, and the unsaturated fatty acid linoleate, on the production of proinflammatory cytokines in phorbol ester-differentiated THP-1 cells, a model of human macrophages. Palmitate induced secretion and mRNA expression of TNF-alpha, IL-8 and IL-1 beta, and enhanced lipopolysaccharide (LPS)-induced IL-1 beta secretion. Proinflammatory cytokine secretion was also induced by stearate, but not by the shorter chain SFA, myristate and laurate, or linoleate. Triacsin C abolished the palmitate-induced cytokine secretion, suggesting that palmitate activation to palmitoyl-CoA is required for its effect. Palmitate-induced cytokine secretion was decreased by knockdown of serine palmitoyltransferase and mimicked by C(2)-ceramide, indicating that ceramide is involved in palmitate-induced cytokine secretion. Palmitate phosphorylated p38 and JNK kinases, and blocking of these kinases with specific inhibitors diminished the palmitate-induced cytokine secretion. Palmitate also activated the AP-1 (c-Jun) transcription factor. Knockdown of MyD88 reduced the palmitate-induced IL-8, but not TNF-alpha or IL-1 beta secretion. In conclusion, our data suggest that the long-chain SFA induce proinflammatory cytokines in human macrophages via pathways involving de novo ceramide synthesis. This might contribute to the activation of macrophages in atherosclerotic plaques, especially in type 2 diabetes.

Zinc deficiency alters lipid metabolism in LDL receptor deficient mice treated with rosiglitazone

Zinc is a structural and functional component of PPAR and zinc deficiency may be associated with an increased risk for cardiovascular diseases. We tested the hypothesis that zinc deficiency compromises lipid metabolism in rosiglitazone (RSG)-treated mice lacking the LDL-receptor (LDL-R) gene. LDL-R-deficient mice were maintained for 3 wk on low-fat (7 g/100 g) diets that were either zinc deficient or zinc adequate. Subsequently, diets were adjusted to a high-fat (HF) (15 g/100 g) regimen for 1 wk to produce a biological environment of mild oxidative and inflammatory stress. One-half of the mice within each zinc group was gavaged daily with the PPARgamma agonist RSG starting 2 d prior to the HF feeding. Selected lipid parameters were studied. Zinc deficiency increased plasma total cholesterol, which was also elevated by RSG. Zinc deficiency also caused an increased lipoprotein-cholesterol distribution toward the non-HDL fraction (VLDL, intermediate density lipoprotein, LDL). Plasma total fatty acids tended to increase during zinc deficiency and RSG treatment resulted in similar changes in the fatty acid profile in zinc-deficient mice. Fatty acid translocase (FAT/CD36) expression in abdominal aorta was upregulated by RSG only in zinc-deficient mice. In contrast, RSG treatment markedly increased lipoprotein lipase (LPL) expression only in zinc-adequate mice. In vitro studies confirmed that adequate zinc is required for RSG-induced PPARgamma activity to transactivate target genes. These data suggest that in this atherogenic mouse model treated with RSG, lipid metabolism can be compromised during zinc deficiency and that adequate dietary zinc may be considered during therapy with the antidiabetic medicine RSG.

Do glucose and lipids exert independent effects on atherosclerotic lesion initiation or progression to advanced plaques?

It is becoming increasingly clear that suboptimal blood glucose control results in adverse effects on large blood vessels, thereby accelerating atherosclerosis and cardiovascular disease, manifested as myocardial infarction, stroke, and peripheral vascular disease. Cardiovascular disease is accelerated by both type 1 and type 2 diabetes. In type 1 diabetes, hyperglycemia generally occurs in the absence of elevated blood lipid levels, whereas type 2 diabetes is frequently associated with dyslipidemia. In this review article, we discuss hyperglycemia versus hyperlipidemia as culprits in diabetes-accelerated atherosclerosis and cardiovascular disease, with emphasis on studies in mouse models and isolated vascular cells. Recent studies on LDL receptor-deficient mice that are hyperglycemic, but exhibit no marked dyslipidemia compared with nondiabetic controls, show that diabetes in the absence of diabetes-induced hyperlipidemia is associated with an accelerated formation of atherosclerotic lesions, similar to what is seen in fat-fed nondiabetic mice. These effects of diabetes are masked in severely dyslipidemic mice, suggesting that the effects of glucose and lipids on lesion initiation might be mediated by similar mechanisms. Recent evidence from isolated endothelial cells demonstrates that glucose and lipids can induce endothelial dysfunction through similar intracellular mechanisms. Analogous effects of glucose and lipids are also seen in macrophages. Furthermore, glucose exerts many of its cellular effects through lipid mediators. We propose that diabetes without associated dyslipidemia accelerates atherosclerosis by mechanisms that can also be activated by hyperlipidemia.

PhospholipaseA2: A key regulator of inflammatory signalling and a connector to fibrosis development in atherosclerosis

Atherosclerosis is a progressive inflammatory disease that takes place in the intima of the arterial wall. It is characterized by activation of endothelial cells, proliferation of smooth muscle cells and macrophages, accumulation of lipoproteins, deposition of extracellular matrix components and enhanced lipolytic enzyme activity. Phospholipase A(2) (PLA(2)) has been postulated to play an important role in the inflammatory process of atherosclerosis, but its molecular mechanism is uncertain. The secretory PLA(2) is expressed at increased levels in an atherosclerotic plaque and may hydrolyze low-density lipoproteins (LDL). This action promotes the production of pro-inflammatory lipids such as lysophospholipids, unsaturated fatty acids and eicosanoids. The current review highlights recent findings on how LDL-derived lipid mediators, generated by sPLA_2 modification of LDL, regulate pro-inflammatory activation and intracellular signaling in macrophages. Moreover, the review discusses how PLA_2 enzymes regulate signalling that promotes collagen accumulation and fibrotic plaque development. PLA_2 could therefore function as a connector between inflammation and fibrosis, the latter being an endpoint of chronic inflammation.

Inflammatory effects of very low-density lipoprotein and fatty acids

High plasma triacylglycerol (triglyceride, TG) levels is a risk factor for atherosclerosis. Very large lipoproteins, such as chylomicrons, alone are not considered atherogenic, but TG-rich remnant lipoproteins can penetrate into the vascular wall. Importantly, accumulating evidence suggests that all TG-rich lipoproteins stimulate cytokine expression in circulating monocytes. Very low-density lipoprotein (VLDL) stimulates monocyte adhesion to endothelial cells and expression of inflammatory genes in macrophages. Furthermore, fatty acids released from large lipoproteins can stimulate both vascular cells and circulating monocytes. It is likely that fatty acids released from TG-rich lipoproteins contribute to atherogenesis, but the role of fatty acids in ischemic heart disease is not as direct as that of cholesterol. Fatty acids influence plasma lipoprotein levels and either stimulate or suppress numerous cellular functions relevant to atherogenesis. While certain n-3 fatty acids are good for health, most other medium- to long-chain fatty acids appear to promote inflammation in cell culture studies and need to be studied further. Nevertheless, the existing evidence supports the general conclusion that TG-rich lipoproteins and fatty acids greatly accelerate the progression of atherosclerosis. This may be because of their inflammatory effects.

Fatty Acids Cause Alterations of Human Arterial Smooth Muscle Cell Proteoglycans That Increase the Affinity for Low-Density Lipoprotein

Objective— The dyslipidemia of insulin resistance, with high levels of albumin-bound fatty acids, is a strong cardiovascular disease risk. Human arterial smooth muscle cell (hASMC) matrix proteoglycans (PGs) contribute to the retention of apoB lipoproteins in the intima, a possible key step in atherogenesis. We investigated the effects of high NEFA levels on the PGs secreted by hASMCs and whether these effects might alter the PG affinity for low-density lipoprotein.

Methods and Results— hASMC exposed for 72 hours to high concentrations (800 μmol/L) of linoleate (LO) or palmitate upregulated the core protein mRNAs of the major PGs, as measured by quantitative PCR. Insulin (1 nmol/L) and the PPARγ agonist rosiglitazone (10 μmol/L) blocked these effects. In addition, high LO increased the mRNA levels of enzymes required for glycosaminoglycan (GAG) synthesis. Exposure to NEFA increased the chondroitin sulfate:heparan sulfate ratio and the negative charge of the PGs. Because of these changes, the GAGs secreted by LO-treated cells had a higher affinity for human low-density lipoprotein than GAGs from control cells. Insulin and rosiglitazone inhibited this increase in affinity.

Conclusions— The response of hASMC to NEFA could induce extracellular matrix alterations favoring apoB lipoprotein deposition and atherogenesis.

Conjugated linoleic acid and atherosclerosis: no effect on molecular markers of cholesterol homeostasis in THP-1 macrophages

Macrophage cholesterol homeostasis is a key process involved in the initiation and progression of atherosclerosis. Peroxisome proliferator-activated receptors (PPARs) regulate the transcription of the genes involved in cholesterol homeostasis and thus represent an important therapeutic target in terms of reducing atherosclerosis. Conjugated linoleic acid (CLA) is a potent anti-atherogenic dietary fatty acid in animal models of atherosclerosis and is capable of activating PPARs in vitro and in vivo. Therefore, this study examined whether the anti-atherogenic effects of CLA in vivo could be ascribed to altered cholesterol homeostasis in macrophages and macrophage derived foam cells. Of several genes that regulate cholesterol homeostasis investigated, CLA had most effect on the class B scavenger receptor CD36. The cis-9,trans-11 CLA (c9,t11-CLA) and trans-10,cis-12 CLA (t10,c12-CLA) isomers augmented CD36 mRNA expression (P<0.001). Confocal laser microscopy characterised the three-dimensional expression patterns of CD36 in THP-1 macrophages. Linoleic acid, CLA and the PPARgamma ligand rosiglitazone increased discrete cell surface CD36 localisation, with a heterogeneous punctate pattern of expression. In agreement with the observed increases in CD36 mRNA and cell surface expression, intracellular cholesterol concentrations were greater in macrophages exposed to linoleic acid and CLA. Further analysis of cholesterol metabolism showed that CLA had no effect on THP-1 derived foam cell cholesterol efflux to apo AI. Thus, altered cholesterol homeostasis in the macrophage may not explain the anti-atherogenic effects of CLA observed in vivo.