Identification of the oxidized low-density lipoprotein scavenger receptor CD36 in plasma: a novel marker of insulin resistance

Protective Effects of Flavonoids in Diabetic Cardiomyopathy: A Comprehensive Review on the Mechanistic Insights

Diabetic cardiomyopathy (DCM) is one of the leading causes of mortality among diabetic patients. Flavonoid are the most abundant group of phytochemicals in fruits and vegetables, and have received increasing interest as potential chemopreventive antidiabetic agents. Flavonoids might contribute to prevent or delay DCM by regulating the cardiac metabolism, insulin signaling, oxidative stress, apoptosis, autophagy, and inflammation. Among other effects, flavonoids have been proved to enhance glucose uptake, decrease cellular lipid accumulation, or suppress oxidative stress. However, the mechanistic basis of these effects is not fully understood, and many points remain to be clarified. This review provides insight into the molecular mechanisms of flavonoid chemopreventive activity by summarizing cell culture and animal model studies.

Hyperactivity and Pro-inflammatory Functions of Platelets in Diabetes

Cardiovascular complications claim the lives of up to 70% of patients with diabetes mellitus (DM). The mechanisms increasing cardiovascular risk in DM remain to be fully understood and successfully addressed. Nonetheless, there is increasing evidence in the scientific literature of the participation of platelets in the cardiovascular complications of DM. Multiple reports describe the hyperactivity of platelets in DM and their participation in inflammatory responses. The understanding of the mechanisms underlying the contribution of platelets to cardiovascular pathologies in DM will help the development of targeted therapeutic strategies able to reduce cardiovascular risk in these patients. In this literature review, we summarise our current understanding of the molecular mechanisms leading to the contribution of platelets to cardiovascular risk in DM. Both platelet haemostatic activity leading to thrombus formation and their participation to inflammatory processes are stimulated by the biochemical conditions associated with DM. We also present evidence on how DM affect the efficacy of existing therapeutic treatments for thrombosis and, by converse, how antidiabetic drugs may affect platelet function and the haemostasis/thrombosis balance. Taken together, the growing evidence of the different and unexpected roles of platelets in the progression of DM provides a strong rationale for the design of cardiovascular drugs targeting specifically platelets, their pro-inflammatory activity and their activation mechanisms in this disease. Overall, this article provides an important up-to-date overview of the pathophysiological alterations of platelets in DM, which need to be taken into account for the effective management of cardiovascular health in this disease.

The polymorphism analysis for CD36 among platelet donors

CD36 may defect on platelets and/or monocytes in healthy individuals, which was defined as CD36 deficiency. However, we did not know the correlation between the molecular and protein levels completely. Here, we aim to determine the polymorphisms of the CD36 gene, RNA level, and CD36 on platelets and in plasma. The individuals were sequenced by Sanger sequencing. Bioinformational analysis was used by the HotMuSiC, CUPSAT, SAAFEC-SEQ, and FoldX. RNA analysis and CD36 protein detection were performed by qPCR, flow cytometry, and ELISA. In this study, we found c.1228_1239delATTGTGCCTATT (allele frequency = 0.0072) with the highest frequency among our cohort, and one mutation (c.1329_1354dupGATAGAAATGATCTTACTCAGTGTTG) was not present in the dbSNP database. 5 mutations located in the extracellular domain sequencing region with confirmation in deficient individuals, of which c.284T>C, c.512A>G, c.572C>T, and c.869T>C were found to have a deleterious impact on CD36 protein stability. Furthermore, the MFI of CD36 expression on platelets in the mutation-carry, deleterious-effect, and deficiency group was significantly lower than the no-mutation group (P < 0.0500). In addition, sCD36 levels in type II individuals were significantly lower compared with positive controls (P = 0.0060). Nevertheless, we found the presence of sCD36 in a type I individual. RNA analysis showed CD36 RNA levels in platelets of type II individuals were significantly lower than the positive individuals (P = 0.0065). However, no significant difference was observed in monocytes (P = 0.7500). We identified the most prevalent mutation (c.1228_1239delATTGTGCCTATT) among Kunming donors. Besides, our results suggested RNA level alterations could potentially underlie type II deficiency. Furthermore, sCD36 may hold promise for assessing immune reaction risk in CD36-deficient individuals, but more studies should be conducted to validate this hypothesis.

CD36 as a gatekeeper of myocardial lipid metabolism and therapeutic target for metabolic disease

The multifunctional membrane glycoprotein CD36 is expressed in different types of cells and plays a key regulatory role in cellular lipid metabolism, especially in cardiac muscle. CD36 facilitates the cellular uptake of long-chain fatty acids, mediates lipid signaling, and regulates storage and oxidation of lipids in various tissues with active lipid metabolism. CD36 deficiency leads to marked impairments in peripheral lipid metabolism, which consequently impact on the cellular utilization of multiple different fuels because of the integrated nature of metabolism. The functional presence of CD36 at the plasma membrane is regulated by its reversible subcellular recycling from and to endosomes and is under the control of mechanical, hormonal, and nutritional factors. Aberrations in this dynamic role of CD36 are causally associated with various metabolic diseases, in particular insulin resistance, diabetic cardiomyopathy, and cardiac hypertrophy. Recent research in cardiac muscle has disclosed the endosomal proton pump vacuolar-type H+-ATPase (v-ATPase) as a key enzyme regulating subcellular CD36 recycling and being the site of interaction between various substrates to determine cellular substrate preference. In addition, evidence is accumulating that interventions targeting CD36 directly or modulating its subcellular recycling are effective for the treatment of metabolic diseases. In conclusion, subcellular CD36 localization is the major adaptive regulator of cellular uptake and metabolism of long-chain fatty acids and appears a suitable target for metabolic modulation therapy to mend failing hearts.

Ligand-dependent CD36 functions in cancer progression, metastasis, immune response, and drug resistance

CD36, a multifunctional glycoprotein, has been shown to play critical roles in tumor initiation, progression, metastasis, immune response, and drug resistance. CD36 serves as a receptor for a wide range of ligands, including lipid-related ligands (e.g., long-chain fatty acid (LCFA), oxidized low-density lipoprotein (oxLDL), and oxidized phospholipids), as well as protein-related ligands (e.g., thrombospondins, amyloid proteins, collagens I and IV). CD36 is overexpressed in various cancers and may act as an independent prognostic marker. While it was initially identified as a mediator of anti-angiogenesis through its interaction with thrombospondin-1 (TSP1), recent research has highlighted its role in promoting tumor growth, metastasis, drug resistance, and immune suppression. The varied impact of CD36 on cancer is likely ligand-dependent. Therefore, we focus specifically on the ligand-dependent role of CD36 in cancer to provide a critical review of recent advances, perspectives, and challenges.

Association of oxidized ApoB and oxidized ApoA-I with high-risk coronary plaque features in cardiovascular disease

BACKGROUND

Oxidized apolipoprotein B (oxLDL) and oxidized ApoA-I (oxHDL) are proatherogenic. Their prognostic value for assessing high-risk plaques by coronary computed tomography angiography (CCTA) is missing.

METHODS

In a prospective, observational study, 306 participants with cardiovascular disease (CVD) had extensive lipoprotein profiling. Proteomics analysis was performed on isolated oxHDL, and atherosclerotic plaque assessment was accomplished by quantitative CCTA.

RESULTS

Patients were predominantly White, overweight men (58.5%) on statin therapy (43.5%). Increase in LDL-C, ApoB, small dense LDL-C (P < 0.001 for all), triglycerides (P = 0.03), and lower HDL function were observed in the high oxLDL group. High oxLDL associated with necrotic burden (NB; β = 0.20; P < 0.0001) and fibrofatty burden (FFB; β = 0.15; P = 0.001) after multivariate adjustment. Low oxHDL had a significant reverse association with these plaque characteristics. Plasma oxHDL levels better predicted NB and FFB after adjustment (OR, 2.22; 95% CI, 1.27-3.88, and OR, 2.80; 95% CI, 1.71-4.58) compared with oxLDL and HDL-C. Interestingly, oxHDL associated with fibrous burden (FB) change over 3.3 years (β = 0.535; P = 0.033) when compared with oxLDL. Combined Met136 mono-oxidation and Trp132 dioxidation of HDL showed evident association with coronary artery calcium score (r = 0.786; P < 0.001) and FB (r = 0.539; P = 0.012) in high oxHDL, whereas Met136 mono-oxidation significantly associated with vulnerable plaque in low oxHDL.

CONCLUSION

Our findings suggest that the investigated oxidized lipids are associated with high-risk coronary plaque features and progression over time in patients with CVD.

TRIAL REGISTRATION

CLINICALTRIALS

gov NCT01621594.

FUNDING

National Heart, Lung, and Blood Institute at the NIH Intramural Research Program.

Macrophage immunometabolism in diabetes-associated atherosclerosis

Macrophages play fundamental roles in atherosclerotic plaque formation, growth, and regression. These cells are extremely plastic and perform different immune functions depending on the stimuli they receive. Initial in vitro studies have identified specific metabolic pathways that are crucial for the proper function of pro-inflammatory and pro-resolving macrophages. However, the plaque microenvironment, especially in the context of insulin resistance and type 2 diabetes, constantly challenges macrophages with several simultaneous inflammatory and metabolic stimuli, which may explain why atherosclerosis is accelerated in diabetic patients. In this mini review, we discuss how macrophage mitochondrial function and metabolism of carbohydrates, lipids, and amino acids may be affected by this complex plaque microenvironment and how risk factors associated with type 2 diabetes alter the metabolic rewiring of macrophages and disease progression. We also briefly discuss current challenges in assessing macrophage metabolism and identify future tools and possible strategies to alter macrophage metabolism to improve treatment options for diabetes-associated atherosclerosis.

The Rho guanine dissociation inhibitor α inhibits skeletal muscle Rac1 activity and insulin action

The molecular events governing skeletal muscle glucose uptake have pharmacological potential for managing insulin resistance in conditions such as obesity, diabetes, and cancer. With no current pharmacological treatments to target skeletal muscle insulin sensitivity, there is an unmet need to identify the molecular mechanisms that control insulin sensitivity in skeletal muscle. Here, the Rho guanine dissociation inhibitor α (RhoGDIα) is identified as a point of control in the regulation of insulin sensitivity. In skeletal muscle cells, RhoGDIα interacted with, and thereby inhibited, the Rho GTPase Rac1. In response to insulin, RhoGDIα was phosphorylated at S101 and Rac1 dissociated from RhoGDIα to facilitate skeletal muscle GLUT4 translocation. Accordingly, siRNA-mediated RhoGDIα depletion increased Rac1 activity and elevated GLUT4 translocation. Consistent with RhoGDIα's inhibitory effect, rAAV-mediated RhoGDIα overexpression in mouse muscle decreased insulin-stimulated glucose uptake and was detrimental to whole-body glucose tolerance. Aligning with RhoGDIα's negative role in insulin sensitivity, RhoGDIα protein content was elevated in skeletal muscle from insulin-resistant patients with type 2 diabetes. These data identify RhoGDIα as a clinically relevant controller of skeletal muscle insulin sensitivity and whole-body glucose homeostasis, mechanistically by modulating Rac1 activity.

Prospective Nutraceutical Effects of Cinnamon Derivatives Against Insulin Resistance in Type II Diabetes Mellitus-Evidence From the Literature

Apart from advances in pharmaceutical antidiabetic agents, efforts are being made toward hypoglycemic agents derived from natural sources. Cinnamon has been reported to have significant benefits for human health, particularly as an anti-inflammatory, antidiabetic, and anti-hypertriglyceridemic agent. The phytochemicals in cinnamon can be extracted from different parts of plant by distillation and solvent extraction. These chemicals help in decreasing insulin resistance and can act against hyperglycemia and dyslipidemia, inflammation and oxidative stress, obesity, overweight, and abnormal glycation of proteins. Cinnamon has shown to improve all of these conditions in in vitro, animal, and/or human studies. However, the mechanism of action of active ingredients found in cinnamon remains unclear. The current review presents the outstanding ability of cinnamon derivatives to control diabetes by various pathways modulating insulin release and insulin receptor signaling. It was also found that the type and dosage of cinnamon as well as subject characteristics including drug interactions are likely to affect the response to cinnamon. Future research directions based on this review include the synergistic usage of various cinnamon derivatives in managing and/or preventing diabetes and possible other relevant chronic diseases.

Sulforaphane Inhibits Foam Cell Formation and Atherosclerosis via Mechanisms Involving the Modulation of Macrophage Cholesterol Transport and the Related Phenotype

Sulforaphane (SFN), an isothiocyanate, is one of the major dietary phytochemicals found in cruciferous vegetables. Many studies suggest that SFN can protect against cancer and cardiometabolic diseases. Despite the proposed systemic and local vascular protective mechanisms, SFN's potential to inhibit atherogenesis by targeting macrophages remains unknown. In this study, in high fat diet fed ApoE-deficient (ApoE^-/-) mice, oral SFN treatment improved dyslipidemia and inhibited atherosclerotic plaque formation and the unstable phenotype, as demonstrated by reductions in the lesion areas in both the aortic sinus and whole aorta, percentages of necrotic cores, vascular macrophage infiltration and reactive oxygen species (ROS) generation. In THP-1-derived macrophages, preadministration SFN alleviated oxidized low-density lipoprotein (ox-LDL)-induced lipid accumulation, oxidative stress and mitochondrial injury. Moreover, a functional study revealed that peritoneal macrophages isolated from SFN-treated mice exhibited attenuated cholesterol influx and enhanced apolipoprotein A-I (apoA-I)- and high-density lipoprotein (HDL)-mediated cholesterol efflux. Mechanistic analysis revealed that SFN supplementation induced both intralesional and intraperitoneal macrophage phenotypic switching toward high expression of nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1) and ATP-binding cassette subfamily A/G member 1 (ABCA1/G1) and low expression of peroxisome proliferator-activated receptor γ (PPARγ) and cluster of differentiation 36 (CD36), which was further validated by the aortic protein expression. These results suggest that the regulation of macrophages' cholesterol transport and accumulation may be mainly responsible for SFN's potential atheroprotective properties, and the regulatory mechanisms might involve upregulating ABCA1/G1 and downregulating CD36 via the modulation of PPARγ and Nrf2.

Association of cluster determinant 36, scavenger receptor class B type 1, and major facilitator superfamily domain containing the 2a genetic polymorphism with serum lipid profile in aging population with type 2 diabetes mellitus

Background

Lipid metabolism disorder commonly happens in subjects with Type 2 diabetes mellitus (T2DM) which may be linked to genetic variants of lipid metabolism-related genes. However, few studies have explored the relationship between lipid metabolism-related gene polymorphism and serum lipid profile in aging subjects with T2DM. The present study was designed to explore the impact of genetic polymorphism of cluster determinant 36 (CD36) (rs1049673, rs1054516, rs2151916), scavenger receptor class B type 1 (SCARB1) (rs5888), and major facilitator superfamily domain containing the 2a (MFSD2A) (rs12083239, rs4233508, rs12072037) on the relationship between circulating lipids in aging subjects with T2DM.

Methods

205 T2DM patients and 205 age and gender matched control subjects were recruited. Information on demographic characteristics was collected by using a self-administered questionnaire. Fasting venous blood samples were taken for lipid-related gene genotyping and serum lipid profile measurement. The Chi-square test was used to compare percentage differences and to calculate P-value for Hardy-Weinberg equilibrium. Logistic regression and multiple linear regression were used to explore the risk or correlation between variables, and general linear model (GLM) was used to compare the means of serum lipids between the groups.

Results

In T2DM group, CD36 rs1054516 and MFSD2A rs12072037 were correlated with serum TC level. In control group, CD36 rs1049673 was correlated with serum HDL-C level. Meanwhile, T2DM subjects with MFSD2A rs12083239 (CG), MFSD2A rs4233508 (TT), and MFSD2A rs12072037 (AA) had higher TG level than control subjects. T2DM subjects with CD36 rs1049673 (CG, GG), CD36 rs1054516 (CT), CD36 rs2151916 (TT, CT), SCARB1 rs5888 (GG), MFSD2A rs12083239 (GG, CG), MFSD2A rs4233508 (TT), and MFSD2A rs12072037 (CA, AA) had lower HDL-C level than control subjects. T2DM subjects with MFSD2A rs12072037 (AA) had lower LDL-C level than control subjects. In dominant model, major genotype (GG) of SCARB1 gene was associated with the risk of T2DM (OR = 0.636, P = 0.032).

Conclusion

The genetic polymorphism of CD36 (rs1049673, rs1054516, rs2151916), SCARB1 (rs5888), and MFSD2A (rs12083239, rs4233508, rs12072037) were associated with serum lipids in T2DM subjects. The SCARB1 rs5888 major genotype (GG) was a protective factor for T2DM. Large scale cohort study is required to determine the relationship between lipid metabolism-related gene polymorphism, serum lipid profile and T2DM in aging subjects.

Impact of the interaction between the polymorphisms and hypermethylation of the CD36 gene on a new biomarker of type 2 diabetes mellitus: circulating soluble CD36 (sCD36) in Senegalese females

Background

Several predisposing factors for diabetes mellitus have been identified, including cluster determinant 36 (CD36) receptor expression. We aimed to determine the effects of CD36 gene polymorphisms and hypermethylation on the plasma CD36 protein levels in type 2 diabetes.

Materials and methods

We conducted a cross-sectional study involving 100 females (lean healthy control subjects and subjects with type 2 diabetes). This study was conducted at the Human Physiology Laboratory at the Dakar Faculty of Medicine in Senegal. Circulating sCD36 levels and DNA methyltransferase 3a levels were determined by enzyme-linked immunosorbent assay. The other biological parameters were evaluated in a biochemical laboratory. CD36 gene polymorphisms and methylation were explored by real-time polymerase chain reaction and methylation-specific polymerase chain reaction, respectively.

Results

sCD36 was negatively correlated with HDL-cholesterol levels (r =  − 0.52 p = 0.0001) and triglyceride levels (r =  − 0.36 p = 0.01) in control subjects. However, in the type 2 diabetes group, sCD36 levels were positively correlated with total cholesterol levels (r = 0.28 p = 0.04). For rs3211867, control subjects harboring the CC genotypes had significantly higher sCD36 levels than control subjects harboring the AA/AC genotype (p = 0.02); in the type 2 diabetes group, the sCD36 level was not significantly lower in subjects harboring the AA/AC genotype than in subjects harboring the CC genotype (p = 0.27). CD36 gene methylation reduced the sCD36 level in the control subjects compared to control subjects without CD36 gene methylation (p = 0.03). This difference was not significant in the type 2 diabetes group comparing subjects with diabetes with CD36 gene methylation to subjects with diabetes without CD36 gene methylation (p = 0.09). We noted a nonsignificant increase in sCD36 levels in subjects with diabetes with CD36 gene methylation compared to control subjects with CD36 gene methylation (p = 0.27). A combination of the CD36 polymorphism effect and the CD36 methylation effect did not significantly reduce sCD36 levels in subjects with type 2 diabetes.

Conclusion

CD36 gene polymorphisms and CD36 gene methylation separately reduce sCD36 levels. Their impacts are compensated for in subjects with type 2 diabetes by an increase in sCD36 levels, the mechanism of which needs to be elucidated.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01337-2.

Association between polymorphisms and hypermethylation of CD36 gene in obese and obese diabetic Senegalese females

BACKGROUND

Obesity and related metabolic disorders are associated with genetic and epigenetic alterations. In this study, we have examined the association between polymorphisms and hypermethylation of the CD36 gene promoter with obesity in Senegalese females with or without type 2 diabetes mellitus to identify novel molecular markers of these pathologies (obesity and type 2 diabetes mellitus).

MATERIALS AND METHODS

The study was conducted in Senegal with healthy lean control, obese, and obese diabetic (age; 49.98 years ± 7.52 vs 50.50 years ± 8.76 vs 51.06 ± 5.78, and body mass index (BMI); 24.19 kg/m² ± 2.74 vs 34.30 kg/m² ± 4.41 vs 33.09 kg/m² ± 4.30). We determined three genetic polymorphisms of CD36 i.e., rs1761667, rs1527483, and rs3211867 by real-time polymerase chain reaction, and methylation of CPG islands of CD36 was assessed by methylation-specific polymerase chain reaction (MS-PCR) in DNA isolated from peripheral blood of each participant. Plasma sCD36 levels and DNA methyltransferase 3a (DNMT3a) levels were determined by enzyme-linked immunosorbent assay (ELISA). According to the standard laboratory protocol, all biochemical parameters were analyzed from fasting serum or plasma.

RESULTS

For rs1761667, obese and obese diabetic subjects had statistically significant different parameters depending on the genotypic distribution. These were waist size for obese and HDL cholesterol for obese diabetic, they were significantly higher in subjects harboring GG genotype of rs1761667 (respectively p = 0.04 and p = 0.04). For rs3211867, obese subjects harboring the AA/AC genotype had significantly higher BMI (p = 0.02) and total cholesterol (p = 0.03) than obese subjects harboring the CC genotype. At the same time, the obese diabetic subjects harboring the AA/AC genotype had total cholesterol levels significantly higher than the obese diabetic subjects harboring the CC genotype (p = 0.03). For rs1527483, only the control subjects had statistically significant different parameters depending on the genotypic distribution. The control subjects harboring the GG genotype had a significantly higher BMI than the control subjects harboring the AA/AG genotype (p = 0.003). The CD36 gene methylation was significantly 1.36 times more frequent in obese and obese diabetic compared to lean control (RR = 1.36; p = 0.04). DNMT3a levels were higher in subjects with CD36 gene methylation than in subjects without CD36 gene methylation in each group. Obese diabetic subjects with CD36 gene methylation had significantly fewer plasmas sCD36 (p = 0.03) and more LDL-cholesterol (p = 0.01) than obese diabetic subjects without CD36 gene methylation. In the control group, an increase in sCD36 levels would be associated with a decrease in total cholesterol and triglyceride levels (coef = -7647.56 p = 0.01 and coef = -2528.50 p = 0.048, respectively) would be associated with an increase in LDL cholesterol levels. For the obese group, an increase in sCD36 levels would be associated with an increase in fasting insulin levels (coef = 490.99 p = 0.02) and a decrease in glycated hemoglobin levels (coef = -1196.26 p = 0.03). An increase in the sCD36 levels would be associated with an increase in the triglyceride levels in the obese diabetic group (coef = 9937.41 p = 0.02). The AA/AC genotype of SNP rs3211867 polymorphism was significantly associated with CD36 gene methylation in the control and obese diabetic groups (respectively p = 0.05, p = 0.002; 95% CI).

CONCLUSION

These observations suggest that polymorphisms and epigenetic changes in CD36 gene promoters may be implicated in the onset of obesity and its related complication type 2 diabetes mellitus.

Oxidised Low-Density Lipoprotein-Induced Platelet Hyperactivity—Receptors and Signalling Mechanisms

Dyslipidaemia leads to proatherogenic oxidative lipid stress that promotes vascular inflammation and thrombosis, the pathologies that underpin myocardial infarction, stroke, and deep vein thrombosis. These prothrombotic states are driven, at least in part, by platelet hyperactivity, and they are concurrent with the appearancxe of oxidatively modified low-density lipoproteins (LDL) in the circulation. Modified LDL are heterogenous in nature but, in a general sense, constitute a prototype circulating transporter for a plethora of oxidised lipid epitopes that act as danger-associated molecular patterns. It is well-established that oxidatively modified LDL promote platelet activation and arterial thrombosis through a number of constitutively expressed scavenger receptors, which transduce atherogenic lipid stress to a complex array of proactivatory signalling pathways in the platelets. Stimulation of these signalling events underlie the ability of modified LDL to induce platelet activation and blunt platelet inhibitory pathways, as well as promote platelet-mediated coagulation. Accumulating evidence from patients at risk of arterial thrombosis and experimental animal models of disease suggest that oxidised LDL represents a tangible link between the dyslipidaemic environment and increased platelet activation. The aim of this review is to summarise recent advances in our understanding of the pro-thrombotic signalling events induced in platelets by modified LDL ligation, describe the contribution of individual platelet scavenger receptors, and highlight potential future challenges of targeting these pathways.

The Problem of Wound Healing in Diabetes—From Molecular Pathways to the Design of an Animal Model

Chronic wounds are becoming an increasingly common clinical problem due to an aging population and an increased incidence of diabetes, atherosclerosis, and venous insufficiency, which are the conditions that impair and delay the healing process. Patients with diabetes constitute a group of subjects in whom the healing process is particularly prolonged regardless of its initial etiology. Circulatory dysfunction, both at the microvascular and macrovascular levels, is a leading factor in delaying or precluding wound healing in diabetes. The prolonged period of wound healing increases the risk of complications such as the development of infection, including sepsis and even amputation. Currently, many substances applied topically or systemically are supposed to accelerate the process of wound regeneration and finally wound closure. The role of clinical trials and preclinical studies, including research based on animal models, is to create safe medicinal products and ensure the fastest possible healing. To achieve this goal and minimize the wide-ranging burdens associated with conducting clinical trials, a correct animal model is needed to replicate the wound conditions in patients with diabetes as closely as possible. The aim of the paper is to summarize the most important molecular pathways which are impaired in the hyperglycemic state in the context of designing an animal model of diabetic chronic wounds. The authors focus on research optimization, including economic aspects and model reproducibility, as well as the ethical dimension of minimizing the suffering of research subjects according to the 3 Rs principle (Replacement, Reduction, Refinement).

CD36, a signaling receptor and fatty acid transporter that regulates immune cell metabolism and fate

CD36 is a type 2 cell surface scavenger receptor widely expressed in many immune and non-immune cells. It functions as both a signaling receptor responding to DAMPs and PAMPs, as well as a long chain free fatty acid transporter. Recent studies have indicated that CD36 can integrate cell signaling and metabolic pathways through its dual functions and thereby influence immune cell differentiation and activation, and ultimately help determine cell fate. Its expression along with its dual functions in both innate and adaptive immune cells contribute to pathogenesis of common diseases, including atherosclerosis and tumor progression, which makes CD36 and its downstream effectors potential therapeutic targets. This review comprehensively examines the dual functions of CD36 in a variety of immune cells, especially macrophages and T cells. We also briefly discuss CD36 function in non-immune cells, such as adipocytes and platelets, which impact the immune system via intercellular communication. Finally, outstanding questions in this field are provided for potential directions of future studies.

Genetic variants, gene expression, and soluble CD36 analysis in acute coronary syndrome: Differential protein concentration between ST-segment elevation myocardial infarction and unstable angina

Background

Atherosclerosis plays an important role in the pathophysiology of acute coronary syndrome (ACS). CD36 is a scavenger receptor involved in lipid metabolism. Some single‐nucleotide variants in the non‐coding region could indirectly alter the expression and the function of the protein.

Objective

The aim of this study was to investigate the gene and protein expression associated with CD36 variants (rs1194182;C > G; rs1049654;C > A, rs1334512;G > T, and rs3211892;G > A) in ACS patients from the western Mexican population.

Methods

We recruited 310 ACS patients and 308 subjects in the control group (CG). Genotyping was determined by TaqMan SNP genotyping assays. CD36 expression at the mRNA level was quantified by TaqMan gene expression assays. Soluble CD36 (sCD36) was measured by enzyme‐linked immunosorbent assay.

Results

We show that rs1194182G > C variant provides a protective effect with a 1.7‐fold lower susceptibility to develop ACS (p  = 0.03); however, this association was masked by diabetes and dyslipidemia. We observed a higher sCD36 concentration in patient with ST‐segment elevation myocardial infarction (STEMI) compared with patients with unstable angina (UA) (p  = 0.038). Likewise, in diabetic patients versus non‐diabetic (p < 0.001). We observed in patients an increase in CD36 mRNA expression (1.91 times higher) than in the CG (p  = 0.02).

Conclusion

The rs1194182 seems to be associated with diabetes in a risky manner, in ACS patients and protective for dyslipidemia in both groups. The concentration of sCD36 seems to be associated with the clinical spectrum of the ACS patients and the presence of diabetes, since patients with STEMI present significantly elevated level compared with UA.

Metabolic regulation of (-)-epicatechin and the colonic metabolite 2,3-dihydroxybenzoic acid on the glucose uptake, lipid accumulation and insulin signalling in cardiac H9c2 cells

Epicatechin (EC) and main colonic phenolic acids derived from flavonoid intake have been suggested to exert healthful effects, although their mechanism of action remains unknown. Heart damage is highly prevalent in metabolic diseases, and the failure of this organ is a major cause of death worldwide. In this study, the modulation of the energy metabolism and insulin signalling by the mentioned compounds in cardiac H9c2 cells was evaluated. Incubation of cells with EC (1-20 μM) and 2,3-dihydroxybenzoic acid (DHBA, 10 μM) reduced glucose uptake, and both compounds decreased lipid accumulation at concentrations higher than 0.5 μM. EC and DHBA also increased the tyrosine phosphorylated and total insulin receptor (IR) levels, and activated the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway in cardiac H9c2 cells. Interestingly, EC and DHBA did not modify glucose transporters (SGLT-1 and GLUT-1) levels, and increased GLUT-4 values. In addition, EC and DHBA decreased cluster of differentiation 36 (CD36) and fatty acid synthase (FAS) values, and enhanced carnitine palmitoyl transferase 1 (CPT1) and proliferator activated receptor α (PPARα) levels. By using specific inhibitors of AKT and 5'-AMP-activated protein kinase (AMPK), the participation of both proteins in EC- and DHBA-mediated regulation on glucose uptake and lipid accumulation was shown. Taken together, EC and DHBA modulate glucose uptake and lipid accumulation via AKT and AMPK, and reinforce the insulin signalling by activating key proteins of this pathway in H9c2 cells.

Markers of insulin resistance in Polycystic ovary syndrome women: An update

Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders, affecting 5%-10% of women of reproductive age. The importance of this syndrome lies in the magnitude of associated comorbidities: infertility, metabolic dysfunction, cardiovascular disease (CVD), plus psychological and oncological complications. Insulin resistance (IR) is a prominent feature of PCOS with a prevalence of 35%-80%. Without adequate management, IR with compensatory hyperinsulinemia contributes directly to reproductive dysfunction in women with PCOS. Furthermore, epidemiological data shows compelling evidence that PCOS is associated with an increased risk of impaired glucose tolerance, gestational diabetes mellitus and type 2 diabetes. In addition, metabolic dysfunction leads to a risk for CVD that increases with aging in women with PCOS. Indeed, the severity of IR in women with PCOS is associated with the amount of abdominal obesity, even in lean women with PCOS. Given these drastic implications, it is important to diagnose and treat insulin resistance as early as possible. Many markers have been proposed. However, quantitative assessment of IR in clinical practice remains a major challenge. The gold standard method for assessing insulin sensitivity is the hyperinsulinemic euglycemic glucose clamp. However, it is not used routinely because of the complexity of its procedure. Consequently, there has been an urgent need for surrogate markers of IR that are more applicable in large population-based epidemiological investigations. Despite this, many of them are either difficult to apply in routine clinical practice or useless for women with PCOS. Considering this difficulty, there is still a need for an accurate marker for easy, early detection and assessment of IR in women with PCOS. This review highlights markers of IR already used in women with PCOS, including new markers recently reported in literature, and it establishes a new classification for these markers.

Exosomes in Cardiovascular Diseases: Pathological Potential of Nano-Messenger

Cardiovascular diseases (CVDs) represent a major global health problem, due to their continued high incidences and mortality. The last few decades have witnessed new advances in clinical research which led to increased survival and recovery in CVD patients. Nevertheless, elusive and multifactorial pathophysiological mechanisms of CVD development perplexed researchers in identifying efficacious therapeutic interventions. Search for novel and effective strategies for diagnosis, prevention, and intervention for CVD has shifted research focus on extracellular vesicles (EVs) in recent years. By transporting molecular cargo from donor to recipient cells, EVs modulate gene expression and influence the phenotype of recipient cells, thus EVs prove to be an imperative component of intercellular signaling. Elucidation of the role of EVs in intercellular communications under physiological conditions implied the enormous potential of EVs in monitoring and treatment of CVD. The EVs secreted from the myriad of cells in the cardiovascular system such as cardiomyocytes, cardiac fibroblasts, cardiac progenitor cells, endothelial cells, inflammatory cells may facilitate the communication in physiological and pathological conditions. Understanding EVs-mediated cellular communication may delineate the mechanism of origin and progression of cardiovascular diseases. The current review summarizes exosome-mediated paracrine signaling leading to cardiovascular disease. The mechanistic role of exosomes in cardiovascular disease will provide novel avenues in designing diagnosis and therapeutic interventions.

Beneficial effects of cinnamon and its extracts in the management of cardiovascular diseases and diabetes

Cardiovascular diseases (CVDs) and diabetes are the leading causes of death worldwide, which underlines the urgent necessity to develop new pharmacotherapies. Cinnamon has been an eminent component of spice and traditional Chinese medicine for thousands of years. Numerous lines of findings have elucidated that cinnamon has beneficial effects against CVDs in various ways, including endothelium protection, regulation of immune response, lowering blood lipids, antioxidative properties, anti-inflammatory properties, suppression of vascular smooth muscle cell (VSMC) growth and mobilization, repression of platelet activity and thrombosis and inhibition of angiogenesis. Furthermore, emerging evidence has established that cinnamon improves diabetes, a crucial risk factor for CVDs, by enhancing insulin sensitivity and insulin secretion; regulating the enzyme activity involved in glucose; regulating glucose metabolism in the liver, adipose tissue and muscle; ameliorating oxidative stress and inflammation to protect islet cells; and improving diabetes complications. In this review, we summarized the mechanisms by which cinnamon regulates CVDs and diabetes in order to provide a theoretical basis for the further clinical application of cinnamon.

β-patchoulene protects against non-alcoholic steatohepatitis via interrupting the vicious circle among oxidative stress, histanoxia and lipid accumulation in rats

Non-alcoholic steatohepatitis (NASH), an extreme progressive subtype of metabolic associated fatty liver disease, is well characterized by hepatic steatosis, injury and inflammation. It causes irreversible hepatic damage and there are no approved interventions for it. β-PAE, a representatively pharmacological active substance isolated from Pogostemon cablin, has been indicated to alleviate hepatic steatosis and injury through modulating lipid metabolism in rats with simple steatosis. However, its protection against NASH remains unclear. Here, this study explored the potential effect of β-PAE against high-fat diet-induced NASH in rats. The results displayed that β-PAE significantly reduced the gains of body weight and epididymal adipose tissue, liver index and attenuated liver histological damages in NASH rats. It also markedly alleviated hepatic inflammation by inhibiting NLRP3 inflammasome activation. In NASH, the active NLRP3 inflammasome is caused by hepatic lipid abnormal accumulation-induced oxidative stress. Excessive oxidative stress results in hepatic histanoxia, which exacerbates lipid metabolism disorders by elevating CD36 to suppress AMPK signalling pathways. Moreover, the lipid accumulation led by lipid metabolism dysfunction intensifies oxidative stress. A vicious circle is formed among oxidative stress, histanoxia and lipid accumulation, eventually, but β-PAE effectively interrupted it. Interestingly, soluble CD36 (sCD36) was tightly associated not only with hepatic steatosis and injury but also with inflammation. Collectively, β-PAE exerted a positive effect against NASH by interrupting the vicious circle among oxidative stress, histanoxia and lipid accumulation, and sCD36 may be a promising non-invasive tool for NASH diagnosis.

Circulating CD36 is increased in hyperlipidemic mice: Cellular sources and triggers of release

CD36 is a multifunctional transmembrane glycoprotein abundantly expressed in several cell types. Recent studies have identified CD36 in circulation (cCD36) in several chronic inflammatory diseases, including type 2 diabetes and chronic kidney disease, and proposed cCD36 to be a biomarker of disease activity. Whether cCD36 is present in hyperlipidemia, a condition characterized by oxidative stress and low-grade inflammation, is not known. In addition, the cellular origin of cCD36 and triggers of CD36 release have not been elucidated. We now demonstrate that plasma cCD36 level is increased in hyperlipidemic ApoE^-/- and Ldlr^-/- mice. Using several cell-specific CD36 knockout mice, we showed that multiple cell types contribute to cCD36 generation in hyperlipidemic conditions, with a particularly strong contribution from endothelial cells. In vitro studies have demonstrated that oxidized phospholipids, ligands for CD36 (oxPC_CD36), which are known to accumulate in circulation in hyperlipidemia, induce a robust release of CD36 from several cell types. In vivo studies have demonstrated CD36 release into the circulation of WT mice in response to tail-vein injection of oxPC_CD36. These findings document the presence of cCD36 in hyperlipidemia and identify a link between cCD36 and oxidized phospholipids generated under oxidative stress and low-grade inflammation associated with hyperlipidemia.

The Mechanisms of the Development of Atherosclerosis in Prediabetes

Lifestyle changes, such as overeating and underexercising, can increase the risk of prediabetes. Diabetes is one of the leading causes of atherosclerosis, and recently it became clear that the pathophysiology of atherosclerosis progresses even before the onset of diabetic symptoms. In addition to changes in platelets and leukocytes in the hyperglycemic state and damage to vascular endothelial cells, extracellular vesicles and microRNAs were found to be involved in the progression of prediabetes atherosclerosis. This review discusses the cellular and molecular mechanisms of these processes, with an intention to enable a comprehensive understanding of the pathophysiology of prediabetes and atherosclerosis.

Controversies and Opportunities in the Use of Inflammatory Markers for Diagnosis or Risk Prediction in Fatty Liver Disease

In the Western society, non-alcoholic fatty liver disease (NAFLD), characterized by the excessive accumulation of fat in the liver, represents the most common cause of chronic liver disease. If left untreated, approximately 15%-20% of patients with NAFLD will progress to non-alcoholic steatohepatitis (NASH), in which lobular inflammation, hepatocyte ballooning and fibrogenesis further contribute to a distorted liver architecture and function. NASH initiation has significant effects on liver-related mortality, as even the presence of early stage fibrosis increases the chances of adverse patient outcome. Therefore, adequate diagnostic tools for NASH are needed, to ensure that relevant therapeutic actions can be taken as soon as necessary. To date, the diagnostic gold standard remains the invasive liver biopsy, which is associated with several drawbacks such as high financial costs, procedural risks, and inter/intra-observer variability in histology analysis. As liver inflammation is a major hallmark of disease progression, inflammation-related circulating markers may represent an interesting source of non-invasive biomarkers for NAFLD/NASH. Examples for such markers include cytokines, chemokines or shed receptors from immune cells, circulating exosomes related to inflammation, and changing proportions of peripheral blood mononuclear cell (PBMC) subtypes. This review aims at documenting and critically discussing the utility of such novel inflammatory markers for NAFLD/NASH-diagnosis, patient stratification and risk prediction.

Soluble Receptors Affecting Stroke Outcomes: Potential Biomarkers and Therapeutic Tools

Soluble receptors are widely understood to be freestanding moieties formed via cleavage from their membrane-bound counterparts. They have unique structures, are found among various receptor families, and have intriguing mechanisms of generation and release. Soluble receptors’ ability to exhibit pleiotropic action by receptor modulation or by exhibiting a dual role in cytoprotection and neuroinflammation is concentration dependent and has continually mystified researchers. Here, we have compiled findings from preclinical and clinical studies to provide insights into the role of soluble/decoy receptors, focusing on the soluble cluster of differentiation 36, the soluble cluster of differentiation 163, and soluble lipoprotein-related protein 1 (sCD36, sCD163, and sLRP1, respectively) and the functions they could likely serve in the management of stroke, as they would notably regulate the bioavailability of the hemoglobin and heme after red blood cell lysis. The key roles that these soluble receptors play in inflammation, oxidative stress, and the related pharmacotherapeutic potential in improving stroke outcomes are described. The precise pleiotropic physiological functions of soluble receptors remain unclear, and further scientific investigation/validation is required to establish their respective role in diagnosis and therapy.

Treatment of Fatty Liver Disease: The Present and the Future

Non-alcoholic fatty liver disease (NAFLD) progressing to non-alcoholic steatohepatitis (NASH), cirrhosis, end-stage liver disease (ESRD), and hepatocellular carcinoma (HCC) is emerging as a global epidemic. Obesity, diabetes, and metabolic syndrome are some of the leading risk factors for NAFLD. The most prevalent treatment to stop the progression is aimed at dietary modification and lifestyle changes. Bariatric surgery is indicated for patients with morbid obesity with NAFLD. The progression of NAFLD to NASH and HCC can be arrested at various stages of pathogenesis by the already prevalent drugs and the emerging newer molecular and genetic targets. This review article analyzed various preclinical animal trials and clinical trials and has summarized various groups of drugs that can be life-altering in patients diagnosed with NAFLD. This study also discusses the obstacles in taking these clinical trials to bedside treatment.

Understanding lipotoxicity in NAFLD pathogenesis: is CD36 a key driver?

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide. NAFLD stages range from simple steatosis (NAFL) to non-alcoholic steatohepatitis (NASH) which can progress to cirrhosis and hepatocellular carcinoma. One of the crucial events clearly involved in NAFLD progression is the lipotoxicity resulting from an excessive fatty acid (FFA) influx to hepatocytes. Hepatic lipotoxicity occurs when the capacity of the hepatocyte to manage and export FFAs as triglycerides (TGs) is overwhelmed. This review provides succinct insights into the molecular mechanisms responsible for lipotoxicity in NAFLD, including ER and oxidative stress, autophagy, lipoapotosis and inflammation. In addition, we highlight the role of CD36/FAT fatty acid translocase in NAFLD pathogenesis. Up-to-date, it is well known that CD36 increases FFA uptake and, in the liver, it drives hepatosteatosis onset and might contribute to its progression to NASH. Clinical studies have reinforced the significance of CD36 by showing increased content in the liver of NAFLD patients. Interestingly, circulating levels of a soluble form of CD36 (sCD36) are abnormally elevated in NAFLD patients and positively correlate with the histological grade of hepatic steatosis. In fact, the induction of CD36 translocation to the plasma membrane of the hepatocytes may be a determining factor in the physiopathology of hepatic steatosis in NAFLD patients. Given all these data, targeting the fatty acid translocase CD36 or some of its functional regulators may be a promising therapeutic approach for the prevention and treatment of NAFLD.

Complement Properdin Regulates the Metabolo-Inflammatory Response to a High Fat Diet

Background and objectives: Overnutrition leads to a metabolic and inflammatory response that includes the activation of Complement. Properdin is the only amplifier of complement activation and increases the provision of complement activation products. Its absence has previously been shown to lead to increased obesity in mice on a high fat diet. The aim of this study was to determine ways in which properdin contributes to a less pronounced obese phenotype. Materials and Methods: Wild type (WT) and properdin deficient mice (KO) were fed a high-fat diet (HFD) for up to 12 weeks. Results: There was a significant increase in liver triglyceride content in the KO HFD group compared to WT on HFD. WT developed steatosis. KO had an additional inflammatory component (steatohepatitis). Analysis of AKT signalling by phosphorylation array supported a decrease in insulin sensitivity which was greater for KO than WT in liver and kidney. There was a significant decrease of C5L2 in the fat membranes of the KO HFD group compared to the WT HFD group. Circulating microparticles in KO HFD group showed lower presence of C5L2. Expression of the fatty acid transporter CD36 in adipose tissue was increased in KO on HFD and was also significantly increased in plasma of KO HFD mice compared to WT on HFD. CD36 was elevated on microparticles from KO on HFD. Ultrastructural changes consistent with obesity-associated glomerulopathy were observed for both HFD fed genotypes, but tubular strain was greater in KO. Conclusion: Our work demonstrates that complement properdin is a dominant factor in limiting the severity of obesity-associated conditions that impact on liver and kidney. The two receptors, C5L2 and CD36, are downstream of the activity exerted by properdin.

New molecular basis associated with CD36-negative phenotype in the sub-Saharan African population

BACKGROUND

CD36 glycoprotein is expressed by various cell types, including platelets (PLTs), monocytes, and erythroid precursors, and is also the receptor for several ligands. However, absence of CD36 expression seems asymptomatic and is poorly described in Caucasians. In contrast, the frequency reaches 7% and 11% in African Caribbean and Asian persons, respectively. Lack of CD36 expression exposes to the risk of immunization in case of pregnancy or PLT transfusion. Two types of deficiency have been described: in Type I, PLTs and monocytes lack CD36 expression and the subjects are homozygous or compound heterozygous for CD36 mutations, whereas in Type II, only PLTs (Type IIa), and rarely also erythroid cells (Type IIb), are affected. Molecular events leading to Type II deficiency are poorly understood.

CASE REPORT

An African girl, diagnosed with homozygous sickle cell disease and regularly transfused, was assessed for PLT CD36 expression by immunofluorescence microscopy. The deficiency was then confirmed by monoclonal antibody immobilization of PLT antigen (MAIPA) assay, and the subtype was assessed by flow cytometry. The underlying molecular basis was characterized by DNA sequencing. Furthermore, we tested the serum for possible anti-CD36 immunization.

RESULTS AND CONCLUSION

Flow cytometric analysis on the patient's blood samples allowed the diagnosis of Type I CD36 deficiency. CD36 antibodies, probably due to her past history of red blood cell transfusions, were identified by MAIPA and by Luminex technology assay. Interestingly, we identified through sequencing a new molecular basis involved in CD36 deficiency: two adenines were replaced by one guanine in Exon 4 (c.367_368delAAinsG) leading to a stop codon at Position 76.

The Multifunctionality of CD36 in Diabetes Mellitus and Its Complications-Update in Pathogenesis, Treatment and Monitoring

CD36 is a multiligand receptor contributing to glucose and lipid metabolism, immune response, inflammation, thrombosis, and fibrosis. A wide range of tissue expression includes cells sensitive to metabolic abnormalities associated with metabolic syndrome and diabetes mellitus (DM), such as monocytes and macrophages, epithelial cells, adipocytes, hepatocytes, skeletal and cardiac myocytes, pancreatic β-cells, kidney glomeruli and tubules cells, pericytes and pigment epithelium cells of the retina, and Schwann cells. These features make CD36 an important component of the pathogenesis of DM and its complications, but also a promising target in the treatment of these disorders. The detrimental effects of CD36 signaling are mediated by the uptake of fatty acids and modified lipoproteins, deposition of lipids and their lipotoxicity, alterations in insulin response and the utilization of energy substrates, oxidative stress, inflammation, apoptosis, and fibrosis leading to the progressive, often irreversible organ dysfunction. This review summarizes the extensive knowledge of the contribution of CD36 to DM and its complications, including nephropathy, retinopathy, peripheral neuropathy, and cardiomyopathy.

Hepatic cholesterol synthesis and lipoprotein levels impaired by dietary fructose and saturated fatty acids in mice: Insight on PCSK9 and CD36

OBJECTIVES

The aim of this study was to investigate the uncertain effects of high saturated fatty acids (SFAs) or fructose intake on cholesterol and lipoproteins with an insight of proprotein convertase subtilisin/kexin type 9 (PCSK9)- and cluster of differentiation 36 (CD36)-induced mechanisms.

METHODS

Forty male C57 BL/6 mice (8 wks of age) were divided into four groups and fed ad libitum with standard chow or three isocaloric diets containing high SFAs (SFA group), monounsaturated fatty acids (MUFA group, vehicle), or fructose for 15 wks. Subsequently, mice were sacrificed and blood, liver, and heart were collected for further analysis.

RESULTS

Consequently, fructose or SFA intake resulted in higher plasma and liver total cholesterol (TC) levels, plasma low-density lipoprotein cholesterol (LDL-C), non-high-density lipoprotein cholesterol (HDL-C), apolipoprotein (Apo)-B levels, TC/HDL-C, and LDL-C/HDL-C ratios, and lower plasma levels of HDL-C and Apo-A1 (P < 0.05). Levels of 3-hydroxy-3-methylglutaryl-CoA reductase and acetyl-CoA acetyltransferase 1 enzymes in liver and CD36 levels in plasma were elevated by high SFAs and fructose intake (P < 0.05), whereas plasma PCSK9 levels were not significantly changed. Fructose and SFA intake increased PCSK9 and CD36 levels in the heart, along with increased CD36 levels in the liver (P < 0.05). Furthermore, plasma LDL-C was found to be positively correlated with liver PCSK9 (r = 0.85, P = 0.02), and CD36 (r = 0.70, P = 0.02) in the SFA and fructose groups.

CONCLUSION

High intakes of dietary SFAs and fructose might induce dysregulations in the cholesterol synthesis and blood lipoprotein levels via proposed nutrient-sensitive biomarkers PCSK9 and CD36 in liver and extrahepatic tissues involved in cholesterol homeostasis.

The Circulating Fatty Acid Transporter Soluble CD36 Is Not Associated with Carotid Atherosclerosis in Subjects with Type 1 and Type 2 Diabetes Mellitus

This study aimed to determine the association of fatty acid transporter plasma soluble cluster of differentiation 36 (sCD36) with subclinical carotid atherosclerosis (SCA). A cross-sectional study was conducted in 1023 subjects, 225 with type 1 diabetes (T1D), 276 with type 2 diabetes (T2D) and 522 who were nondiabetic. Carotid atherosclerotic plaque (CAP) presence was determined using B-mode carotid ultrasound imaging. sCD36 were analysed by ELISA, and CD36 surface receptor and mRNA expression were measured by flow cytometry and real-time PCR. Logistic regression models were used to evaluate sCD36 as a biomarker of SCA. Up to 376 (36.75%) participants had at least one CAP, 76 T1D, 164 T2D and 136 without diabetes, while the remaining 647 (63.25%) did not have any CAP. There were no differences in sCD36 between patients with and without CAP in T1D (p = 0.287) or T2D (p = 0.513). Although nondiabetic subjects with plaques had lower sCD36 levels than those without (p = 0.023), the multivariate models revealed no association of sCD36 with CAP in any of the three study groups. No differences were found in surface CD36 or CD36 mRNA expression between the patients with and without CAP. sCD36 is not associated with SCA in type 1 or type 2 diabetic or in nondiabetic subjects.

The Role of CD36 in Type 2 Diabetes Mellitus: β-Cell Dysfunction and Beyond

Impaired β-cell function is the key pathophysiology of type 2 diabetes mellitus, and chronic exposure of nutrient excess could lead to this tragedy. For preserving β-cell function, it is essential to understand the cause and mechanisms about the progression of β-cells failure. Glucotoxicity, lipotoxicity, and glucolipotoxicity have been suggested to be a major cause of β-cell dysfunction for decades, but not yet fully understood. Fatty acid translocase cluster determinant 36 (CD36), which is part of the free fatty acid (FFA) transporter system, has been identified in several tissues such as muscle, liver, and insulin-producing cells. Several studies have reported that induction of CD36 increases uptake of FFA in several cells, suggesting the functional interplay between glucose and FFA in terms of insulin secretion and oxidative metabolism. However, we do not currently know the regulating mechanism and physiological role of CD36 on glucolipotoxicity in pancreatic β-cells. Also, the downstream and upstream targets of CD36 related signaling have not been defined. In the present review, we will focus on the expression and function of CD36 related signaling in the pancreatic β-cells in response to hyperglycemia and hyperlipidemia (ceramide) along with the clinical studies on the association between CD36 and metabolic disorders.

Plasma CD36 and Incident Diabetes: A Case-Cohort Study in Danish Men and Women

BACKGROUND

Membrane CD36 is a fatty acid transporter implicated in the pathogenesis of metabolic disease. We aimed to evaluate the association between plasma CD36 levels and diabetes risk and to examine if the association was independent of adiposity among Danish population.

METHODS

We conducted a case-cohort study nested within the Danish Diet, Cancer and Health study among participants free of cardiovascular disease, diabetes and cancer and with blood samples and anthropometric measurements (height, weight, waist circumference, and body fat percentage) at baseline (1993 to 1997). CD36 levels were measured in 647 incident diabetes cases that occurred before December 2011 and a total of 3,515 case-cohort participants (236 cases overlap).

RESULTS

Higher plasma CD36 levels were associated with higher diabetes risk after adjusting for age, sex and other lifestyle factors. The hazard ratio (HR) comparing high versus low tertile of plasma CD36 levels was 1.36 (95% confidence interval [CI], 1.00 to 1.86). However, the association lost its significance after further adjustment for different adiposity indices such as body mass index (HR, 1.23; 95% CI, 0.87 to 1.73), waist circumference (HR, 1.21; 95% CI, 0.88 to 1.68) or body fat percentage (HR, 1.20; 95% CI, 0.86 to 1.66). Moreover, raised plasma CD36 levels were moderately associated with diabetes risk among lean participants, but the association was not present among overweight/obese individuals.

CONCLUSION

Higher plasma CD36 levels were associated with higher diabetes risk, but the association was not independent of adiposity. In this Danish population, the association of CD36 with diabetes risk could be either mediated or confounded by adiposity.

Physical resistance training-induced changes in lipids metabolism pathways and apoptosis in prostate

BACKGROUND

Altered lipid metabolism is an important characteristic of neoplastic cells, with androgens and growth factors being major regulatory agents of the lipid metabolism process. We investigated the effect of physical resistance training on lipid metabolism and apoptosis in the adult Wistar rat prostate.

METHODS

Two experimental groups represented sedentary and physical resistance training. Three days per week for 13 weeks, rats performed jumps in water carrying a weight load strapped to their chests as part of a physical resistance exercise protocol. Two days after the last training session, rats were anesthetized and sacrificed for blood and prostate analysis.

RESULTS

Physical exercise improved feeding efficiency, decreased weight gain, regulated the serum-lipid profile, and modulated insulin-like growth factor-1 (IGF-1) and free testosterone concentration. Furthermore, upregulation of cluster of differentiation 36 (CD36), sterol regulatory element binding protein-1 (SREBP-1), sterol regulatory element-binding protein cleavage-activating protein (SCAP), and reduced lysosome membrane protein (LIMPII) expression were also observed in the blood and prostates of trained rats. Consistent with these results, caspase-3 expression was upregulating and the BCL-2/Bax index ratio was decreased in trained rats relative to sedentary animals.

CONCLUSIONS

In this work, physical resistance training can alter lipid metabolism and increase markers of apoptosis in the prostate, suggesting physical resistance training as a potential novel therapeutic strategy for treating prostate cancer.

Contribution of rare coding mutations in CD36 to type 2 diabetes and cardio-metabolic complications

We sequenced coding regions of the cluster of differentiation 36 (CD36) gene in 184 French individuals of European ancestry presenting simultaneously with type 2 diabetes (T2D), arterial hypertension, dyslipidemia, and coronary heart disease. We identified rare missense mutations (p.Pro191Leu/rs143150225 and p.Ala252Val/rs147624636) in two heterozygous cases. The two CD36 mutation carriers had no family history of T2D and no clustering of cardio-metabolic complications. While the p.Pro191Leu mutation was found in 84 heterozygous carriers from five ethnic groups from the genome aggregation database (global frequency: 0.0297%, N = 141,321), only one European carrier of the p.Ala252Val mutation was identified (global frequency: 0.00040%, N = 125,523). The Pro191 and Ala252 amino acids were not conserved (74.8% and 68.9% across 131 animal species, respectively). In vitro experiments showed that the two CD36 mutant proteins are expressed and trafficked to the plasma membrane where they bind modified low-density-lipoprotein (LDL) cholesterol as normal. However, molecular modelling of the recent CD36 crystal structure showed that Pro191 was located at the exit/entrance gate of the lipid binding chamber and Ala252 was in line with the chamber. Overall, our data do not support a major contribution of CD36 rare coding mutations to T2D and its cardio-metabolic complications in the French population.

Plasma sCD36 as non-circadian marker of chronic circadian disturbance in shift workers

Shift work induces chronic circadian disturbance, which might result in increased health risks, including cardio-metabolic diseases. Previously, we identified sCD36 as a potential non-circadian biomarker of chronic circadian disturbance in mice. The aim of the current study (n = 232 individuals) was to identify whether sCD36 measured in plasma can be used as a non-circadian marker of chronic circadian disturbance in humans, which would allow its use to measure the effects of interventions and monitoring in large-scale studies. We compared levels of plasma sCD36 of day workers with recent (< 2 years) and experienced (> 5 years) night-shift workers within the Klokwerk study. We detected no differences in sCD36 levels between day workers and recent or experienced night-shift workers, measured during a day or afternoon shift. In addition, sCD36 levels measured directly after a night shift were not different from sCD36 levels measured during day or afternoon shifts, indicating no acute effect of night shifts on sCD36 levels in our study. In summary, our study does not show a relation between night-shift work experience (recent or long-term) and plasma levels of sCD36. Since we do not know if and for which time span night-shift work is associated with changes in sCD36 levels, and our study was relatively small and cross-sectional, further evidence for an association between chronic circadian disruption and this candidate biomarker sCD36 should be gathered from large cohort studies.

Oral fatty acid taste sensitivity in healthy young individuals of both sexes is related to body mass index and soluble CD36 serum levels

Introduction

Introduction: CD36 is a membrane protein that functions as a lingual receptor for lipids. The soluble CD36 fraction (sCD36) may correlate oral fatty acid fat taste sensitivity to body mass index (BMI) and adiposity. Objectives: to determine if the oral fatty acid taste sensitivity in healthy young individuals of both sexes is related to serum sCD36 levels, adiposity and BMI. Methods: a cross-sectional study was conducted in 72 healthy young individuals (18-25 years). Serum sCD36 was quantified for all subjects. Oral fatty acid taste sensitivity was determined using an ascending series of the three-alternate forced choice methodology. Additionally, BMI was calculated using anthropometry, and adiposity was determined by bioelectric impedance analysis. Results: there was a positive correlation between BMI and the oral fatty acid taste sensitivity threshold (r = 0.277, p < 0.05) and a negative correlation between BMI and serum sCD36 levels (r = -0.035, p < 0.01). Adiposity negatively correlated with the sCD36 levels only in women (r = -0.359, p < 0.05). The threshold for oral sensitivity to fatty acids in overweight individuals was 1.0 (IQR 1.16) mM vs 0.2 (IQR 0.29) mM in healthy weight individuals (p < 0.05), while sCD36 levels were 26.1 pg/ml (IQR 32.9) and 77.97 pg/ml (IQR 560.66) in overweight and normal weight individuals, respectively (p < 0.05). Conclusions: BMI positively correlates with the oral sensitivity threshold of fatty acids and negatively correlates with serum sCD36 levels. The threshold of oral sensitivity to fatty acids was significantly higher in overweight subjects, while sCD36 levels were significantly higher in the group of normal weight individuals.

The expression patterns of SNMP1 and SNMP2 underline distinct functions of two CD36-related proteins in the olfactory system of the tobacco budworm Heliothis virescens

In insects, male and female pheromone signals are detected by olfactory sensory neurons (OSNs) expressing the "sensory neuron membrane protein type 1". SNMP1 is supposed to function as a co-receptor involved in the transfer of pheromones to adjacent pheromone receptors. In the moth Heliothis virescens, we previously found OSNs that project their dendrites into pheromone-responsive trichoid sensilla and are associated with cells containing transcripts for the HvirSNMP1-related protein HvirSNMP2. Like HvirSNMP1, HvirSNMP2 belongs to the CD36-family of two-transmembrane domain receptors and transporters for lipophilic compounds, but its role in the olfactory system is unknown. Here, we generated polyclonal anti-peptide antibodies against HvirSNMP2 as well as HvirSNMP1 and conducted an in-depth immunohistochemical analysis of their subcellular localization in the antenna of both sexes. In line with a function in pheromone detection, HvirSNMP1 was immunodetected in the somata and the dendrites of distinct OSNs in subsets of trichoid sensilla. These trichoid sensilla contained only one α-SNMP1-positive OSN in males and clusters of 2-3 labeled cells in females. In contrast, experiments with α-SNMP2-antibodies revealed a broad labeling of non-neuronal support cells (SCs) that are associated with OSNs in likely all trichoid and basiconic sensilla of the antenna with no differences between sexes. Detailed confocal microscope examinations of olfactory sensilla revealed SNMP2-like immunoreactivity close to the apical membrane of SCs and interestingly inside the sensillum. Together, these findings indicate a potential function of SNMP2 in pheromone- as well as general odorant-responsive sensilla and a role fundamentally different from SNMP1.

Circulating exosomes deliver free fatty acids from the bloodstream to cardiac cells: Possible role of CD36

Regulation of circulating free fatty acid (FFA) levels and delivery is crucial to maintain tissue homeostasis. Exosomes are nanomembranous vesicles that are released from diverse cell types and mediate intercellular communication by delivering bioactive molecules. Here, we sought to investigate the uptake of FFAs by circulating exosomes, the delivery of FFA-loaded exosomes to cardiac cells and the possible role of the FFA transporter CD36 in these processes. Circulating exosomes were purified from the serum of healthy donors after an overnight fast (F) or 20 minutes after a high caloric breakfast (postprandial, PP). Western blotting, Immunogold Electron Microscopy and FACS analysis of circulating exosomes showed that CD36 was expressed under both states, but was higher in postprandial-derived exosomes. Flow cytometry analysis showed that circulating exosomes were able to take-up FFA directly from serum. Importantly, preincubation of exosomes with a blocking CD36 antibody significantly impeded uptake of the FFA analogue BODIPY, pointing to the role of CD36 in FFA exosomal uptake. Finally, we found that circulating exosomes could delivery FFA analogue BODIPY into cardiac cells ex vivo and in vivo in a mice model. Overall, our results suggest a novel mechanism in which circulating exosomes can delivery FFAs from the bloodstream to cardiac tissue. Further studies will be necessary to understand this mechanism and, in particular, its potential involvement in metabolic pathologies such as obesity, diabetes and atherosclerosis.

Circulating Soluble CD36 is Similar in Type 1 and Type 2 Diabetes Mellitus versus Non-Diabetic Subjects

The aim of this study was to determine whether plasma concentrations of sCD36 (soluble CD36) are associated with the presence of type 1 or type 2 diabetes. Plasma levels of sCD36 were analysed in 1023 subjects (225 type 1 diabetes (T1D) patients, 276 type 2 diabetes (T2D) patients, and 522 non-diabetic control subjects) using an enzyme-linked immunosorbent assay (ELISA). Multinomial and logistic regression models were performed to evaluate associations with sCD36 and its association with diabetes types. There were no significant differences in sCD36 (p = 0.144) among study groups, neither in head-to-head comparisons: non-diabetic versus T1D subjects (p = 0.180), non-diabetic versus T2D subjects (p = 0.583), and T1D versus T2D patients (p = 0.151). In the multinomial model, lower sCD36 concentrations were associated with older age (p < 0.001), tobacco exposure (p = 0.006), T2D (p = 0.020), and a higher-platelets count (p = 0.004). However, in logistic regression models of diabetes, sCD36 showed only a weak association with T2D. The current findings show a weak association of circulating sCD36 with type 2 diabetes and no association with T1D.

Associations of plasma CD36 and body fat distribution

CONTEXT

CD36 is a class B scavenger-receptor involved in the uptake of fatty acids in liver and adipose tissue. It is unknown whether plasma CD36 levels are related to liver fat content or adipose tissue in the general population.

METHODS

We measured plasma CD36 from 575 participants of the community-based PopGen-cohort who underwent magnetic resonance imaging (MRI) to quantify visceral (VAT) and subcutaneous (SAT) adipose tissue and liver signal intensity (LSI), a proxy for liver fat content. Non-alcoholic fatty liver disease (NAFLD) was defined as LSI ≥3.0 in the absence of high alcohol intake. The relations between plasma CD36 and body mass index (BMI), VAT, SAT, LSI, and NAFLD were evaluated using multivariable-adjusted linear and logistic regression analysis.

RESULTS

Plasma CD36 concentrations were correlated with BMI (r=0.11; P=0.01), SAT (r=0.16; P<0.001), and VAT (r=0.15, P<0.001), but not with LSI (P=0.44). In multivariable-adjusted regression models, mean BMI values rose across CD36-quartiles (Q1: 27.8 kg/m2; Q4: 28.9 kg/m2; P-trend=0.013). Similarly, VAT (Q1: 4.13 dm3; Q4: 4.71 dm3; P-trend<0.001) and SAT (Q1: 7.61 dm3; Q4: 8.74 dm3; P-trend<0.001) rose across CD36 quartiles. Plasma CD36 concentrations were unrelated to LSI (P-trend=0.36), and NAFLD (P-trend=0.64). Participants with NAFLD and elevated alanine aminotransferase (ALT), a marker for liver damage, had higher CD36 compared to NAFLD participants with normal ALT.

CONCLUSIONS

Higher plasma concentrations of CD36 were associated with greater general and abdominal adiposity, but not with liver fat content or NAFLD in this community-based sample. However, plasma CD36 may reflect more severe liver damage in NAFLD.

Fatty acid transport receptor soluble CD36 and dietary fatty acid pattern in type 2 diabetic patients: a comparative study

Recently, it has been remarked that dietary fatty acids and fatty acid receptors might be involved in the aetiology of diabetes. Therefore, this study was conducted to determine the relationship between dietary fatty acid pattern, fatty food preferences and soluble CD36 (sCD36) and insulin resistance in type 2 diabetes mellitus (DM). The study was carried out with thirty-eight newly diagnosed type 2 DM patients and thirty-seven healthy volunteers, aged 30-65 years. In the study, socio-demographic characteristics, dietary fat type and fatty acid pattern of individuals were recorded. After anthropometric measurements were taken, blood CD36, glucose, TAG and insulin levels were analysed. The results showed that although the type of fatty acid intake did not differ between the groups (P>0·05), the consumption of olive oil in the type 2 DM group was lower than the control group (P0·05). Crucially, elevated sCD36 levels increased the type 2 DM risk (OR 1·21, P<0·05). In conclusion, sCD36 level may be a possible biomarker, independent from the dietary fatty acid pattern, for type 2 DM owing to its higher levels in these patients. Therefore, the new insights make CD36 attractive as a therapeutic target for diabetes.

Bariatric surgery reduces CD36-bearing microvesicles of endothelial and monocyte origin

Background

Bariatric surgery is a widely adopted treatment for obesity and its secondary complications. In the past decade, microvesicles (MVs) and CD36 have increasingly been considered as possible biomarkers for obesity, the metabolic syndrome (MetSy), type 2 diabetes mellitus (T2DM). Thus, the purpose of this study was to investigate how weight loss resulting from bariatric surgery affects levels of specific MV phenotypes and their expression of CD36 scavenger receptor. Additionally, we hypothesised that subjects with MetSy had higher baseline concentrations of investigated MV phenotypes.

Methods

Twenty individuals undergoing Roux-en-Y gastric bypass surgery were evaluated before and 3 months after surgery. MVs were characterised by flow cytometry at both time points and defined as lactadherin-binding particles within a 100-1000 nm size gate. MVs of monocyte (CD14) and endothelial (CD62E) origin were defined by cell-specific markers, and their expression of CD36 was investigated.

Results

Following bariatric surgery, subjects incurred an average BMI reduction (delta) of − 8.4 ± 1.4 (p < 0.0001). Significant reductions were observed for the total MVs (− 66.55%, p = 0.0017) and MVs of monocyte (− 36.11%, p = 0.0056) and endothelial (− 40.10%, p = 0.0007) origins. Although the bulk of CD36-bearing MVs were unaltered, significant reductions were observed for CD36-bearing MVs of monocyte (− 60.04%, p = 0.0192) and endothelial (− 54.93%, p = 0.04) origin. No differences in levels of MVs were identified between subjects who presented with MetSy at baseline (n = 13) and those that did not (n = 7).

Conclusion

Bariatric surgery resulted in significantly altered levels of CD36-bearing MVs of monocyte and endothelial origin. This likely reflects improvements in ectopic fat distribution, plasma lipid profile, low-grade inflammation, and oxidative stress following weight loss. Conversely, however, the presence of MetSy at baseline had no impact on MV phenotypes.

Electronic supplementary material

The online version of this article (10.1186/s12986-018-0309-4) contains supplementary material, which is available to authorized users.

Association between plasma CD36 levels and incident risk of coronary heart disease among Danish men and women

BACKGROUND AND AIMS

CD36 is a cholesterol receptor involved in the uptake of oxidized low-density lipoprotein cholesterol and development of atherosclerotic plaques. Cross-sectional studies have shown correlations between plasma CD36 and atherosclerosis but no prospective study has examined the association yet. We prospectively examined the association between plasma CD36 levels and risk of incident coronary heart disease (CHD) in a Danish population.

METHODS

Plasma CD36 levels were measured in a case-cohort study nested within the Danish population-based cohort, the Diet, Cancer and Health Study. A total of 1963 incident CHD events occurred between baseline (1993-1997) and 2008, and a sub-cohort of 1759 participants were randomly selected as reference. Cox proportional hazard regression models were used to compute the hazard ratio (HR) and corresponding 95% confidence interval (CI).

RESULTS

After adjusting for CHD risk factors, including history of hypercholesterolemia and diabetes, elevated plasma CD36 levels were not associated with higher CHD risk in the total population, and the HR comparing the highest versus lowest tertile of CD36 levels was 1.02 (95% CI: 0.84-1.23). High CD36 levels were only found to be associated with risk of CHD in combination with prevalent diabetes (HR = 2.83, 95% CI: 1.08-7.45) vs. the joint reference group of lowest CD36 tertile and no diabetes.

CONCLUSIONS

Plasma CD36 levels were not predictive of CHD risk in the general population.

Cardioprotective effect of β-d-mannuronic acid (M2000) as a novel NSAID on gene expression of oxLDL scavenger receptors in the experimental diabetic model

CONTEXT

The investigations have shown that patients with diabetes have the elevated levels of glucose and oxLDL. These two play an important role in increased expression levels of oxLDL scavenger receptors on the surface of macrophages and endothelial cells that leads to deposition of oxLDL and macrophages in vascular walls.

OBJECTIVE

The present study intends to show the effects of β-d-mannuronic acid (M2000) on the expression profile of ox-LDL scavenger receptors (including SR-A, LOX-1, CD36, and CD68) in an experimental model of diabetes.

MATERIALS AND METHODS

Eighteen Sprague-Dawley rats were randomly divided into three 6-member groups of the healthy control, diabetic control, and treated rats by M2000. Diabetes was induced in rats by intraperitoneal (IP) administration of 60 mg/kg streptozotocin. The treated rats were given daily intraperitoneal injections of M2000 with a dose of 25 mg/kg for 28 days and at the end of the 28th day, their aortas were removed. The qRT-PCR technique was then used to evaluate the expression levels of the proposed gene.

RESULTS

The gene expression levels of the SR-A, LOX-1, CD36, and CD68 significantly declined in the diabetic group that received M2000 compared with untreated diabetic rats.

CONCLUSIONS

The M2000, as a novel NSAID is able to modify by lowering the gene expression levels of SR-A, LOX-1, CD36, and CD68 in treated rats compared to the untreated diabetic group, which may play an important role in preventing the complications that could lead to a cardioprotective efficacy.

CD36 gene polymorphism and plasma sCD36 as the risk factor in higher cholesterolemia

INTRODUCTION

The receptor CD36 has been reported to play an important role in atherogenicity. The aim of this study was to gain insight into the relationship between CD36 gene polymorphisms or the plasma concentration of sCD36 and clinical or biochemical parameters in children.

PATIENTS AND METHODS

The study groups comprised Caucasian children with and without hypercholesterolemia. The alterations in the CD36 gene were detected by DHPLC and the plasma concentrations of sCD36 were measured by ELISA.

RESULTS

The data presented suggest that the IVS4-10A allele of CD36 (rs3211892) is associated with a lower risk of hypercholesterolemia. We observed a negative correlation of the sCD36 concentration with uric acid and insulin concentrations, the HOMA-IR ratio, weight, waist and hip circumference, systolic blood pressure, body mass index, waist-hip ratio and mean arterial pressure ratio, but a positive correlation with HDL cholesterol and ApoA1 concentrations. Female gender was a significant independent predictor of a higher plasma sCD36 concentration.

CONCLUSIONS

The data presented suggest a possible protective effect of a higher sCD36 concentration in relation to metabolic syndrome components.