Adipose Tissue Renin-angiotensin System Research Articles

Lipotoxicity-Related Hematological Disorders in Obesity.

Lipotoxicity can mediate endothelial dysfunction in obesity. Altered endothelial cell phenotype during the pathobiological course of the lipotoxicity may lead to hemostatic abnormalities, which is a hallmark of several hematological disorders. Impaired hemostasis could also be directly related to numerous metabolic diseases such as hypertension, diabetes, and atherosclerosis. On the other hand, the local hematopoietic bone marrow (BM) renin-angiotensin system (RAS) contributes to the development of atherosclerosis via acting on the lipotoxicity processes. Local BM RAS, principally an autocrine/paracrine/intracrine hematological system, is located at the crossroads of cellular regulation, molecular interactions, and lipotoxicity-mediated vascular endothelial dysfunction. The positive regulatory role of plasma LDL on AT1 receptor-mediated hematopoietic stem cell (HSC) differentiation and the production of pro-atherogenic monocytes have been described. LDL-regulated HSC function may explain in part hypercholesterolemia-induced inflammation as well as the anti-inflammatory and anti-atherosclerotic effects of AT1 receptor blockers. The role of local adipose tissue RAS is directly related to the pathogenesis of metabolic derangements in obesity. There may be a crosstalk between local BM RAS and local adipose tissue RAS at the genomics and transcriptomics levels. This chapter aims to review hematological alterations propagating the pathological influences of lipotoxicity on the vascular endothelium.

The angiotensin II type 1 receptor blocker valsartan in the battle against COVID‐19

ObjectiveSevere acute respiratory syndrome‐coronavirus 2 (SARS‐CoV‐2) uses the host’s angiotensin‐converting enzyme 2 (ACE2) as a cellular entry point. Therefore, modulating ACE2 might impact SARS‐CoV‐2 viral replication, shedding, and coronavirus disease 2019 (COVID‐19) severity. Here, it was investigated whether the angiotensin II type 1 receptor blocker valsartan alters the expression of renin‐angiotensin system (RAS) components, including ACE2, in human adipose tissue (AT) and skeletal muscle.MethodsA randomized, double‐blind, placebo‐controlled clinical trial was performed, in which 36 participants (BMI 31.0 ± 0.8 kg/m2) with impaired glucose metabolism received either valsartan or placebo for 26 weeks. Before and after 26 weeks’ treatment, abdominal subcutaneous AT and skeletal muscle biopsies were obtained, and gene expression of RAS components was measured by quantitative reverse transcription polymerase chain reaction.ResultsValsartan treatment did not significantly impact the expression of RAS components, including ACE2, in AT and skeletal muscle.ConclusionsGiven the pivotal role of ACE2 in SARS‐CoV‐2 spread and the clinical outcomes in COVID‐19 patients, the data suggest that the putative beneficial effects of angiotensin II type 1 receptor blockers on the clinical outcomes of patients with COVID‐19 may not be mediated through altered ACE2 expression in abdominal subcutaneous AT.

Renin angiotensin system inhibition attenuates adipocyte-breast cancer cell interactions

Obesity is a significant breast cancer (BC) risk factor and is associated with 20–40% increased risk in obese post-menopausal women compared to their lean counterparts. Several obesity-related metabolic dysregulations have been linked to BC risk, including overactivation of the renin-angiotensin system (RAS). Currently, RAS inhibitors including angiotensin converting enzyme inhibitor (ACEi) and AT1 receptor blockers (ARBs), are used as safe and effective anti-hypertensive therapies in BC patients. However, it is uncertain how inhibition of RAS in adipose tissue impacts obesity-BC crosstalk. We hypothesized that adipose RAS inhibition will reduce BC cell motility and inflammation. We determined (1) the direct effects of Ang II, ACEi (captopril; Cap) or ARB (telmisartan; Tel) on receptor positive MCF-7 and receptor triple negative MDA-MB-231 cells; and (2) the effects of conditioned media (CM) from human mesenchymal stem cells differentiated into adipocytes, which were pretreated with RAS inhibitors, on BC cells. We demonstrated that direct treatments of BC cells with Ang II, Cap or Tel did not alter inflammatory cytokines in either BC cell line. However, CM from Ang II-pretreated adipocytes significantly increased secretion of pro-inflammatory markers at protein level. RAS inhibitors reduced their secretion in MDA-MB-231, but not in MCF-7 cells. Additionally, CM from adipocytes treated with RAS inhibitors significantly reduced markers of inflammation, fat synthesis, and angiogenesis in both BC cell lines. Furthermore, CM from ACEi pretreated adipocytes reduced cell motility in both BC cell lines. Findings from our study indicate an important role of adipose RAS inhibition in adipocyte and BC cell crosstalk.

Role of microRNA 690 in Mediating Angiotensin II Effects on Inflammation and Endoplasmic Reticulum Stress.

Overactivation of the renin–angiotensin system (RAS) during obesity disrupts adipocyte metabolic homeostasis and induces endoplasmic reticulum (ER) stress and inflammation; however, underlying mechanisms are not well known. We propose that overexpression of angiotensinogen (Agt), the precursor protein of RAS in adipose tissue or treatment of adipocytes with Angiotensin II (Ang II), RAS bioactive hormone, alters specific microRNAs (miRNA), that target ER stress and inflammation leading to adipocyte dysfunction. Epididymal white adipose tissue (WAT) from B6 wild type (Wt) and transgenic male mice overexpressing Agt (Agt-Tg) in adipose tissue and adipocytes treated with Ang II were used. Small RNA sequencing and microarray in WAT identified differentially expressed miRNAs and genes, out of which miR-690 and mitogen-activated protein kinase kinase 3 (MAP2K3) were validated as significantly up- and down-regulated, respectively, in Agt-Tg, and in Ang II-treated adipocytes compared to respective controls. Additionally, the direct regulatory role of miR-690 on MAP2K3 was confirmed using mimic, inhibitors and dual-luciferase reporter assay. Downstream protein targets of MAP2K3 which include p38, NF-κB, IL-6 and CHOP were all reduced. These results indicate a critical post-transcriptional role for miR-690 in inflammation and ER stress. In conclusion, miR-690 plays a protective function and could be a useful target to reduce obesity.

Açaí seed extract prevents the renin-angiotensin system activation, oxidative stress and inflammation in white adipose tissue of high-fat diet–fed mice

The role of the renin-angiotensin system (RAS), oxidative stress, and inflammation on the development of obesity and its comorbidities has been extensively addressed. Euterpe oleracea Mart. (açaí) seed extract (ASE), with antioxidant and anti-inflammatory properties and capable to modulate plasma renin levels, has been evidenced as a potential regulator of body mass. We hypothesized that the supplementation with ASE might exert beneficial effects on obesity-related white adipose tissue changes and metabolic disorders by interfering with the local adipose tissue overexpression of RAS, inflammation, and oxidative stress in C57BL/6 mice fed a high-fat (HF) diet. The animals were fed a standard diet (10% fat, control), 60% fat (HF), HF + ASE (300 mg/kg per day) and HF + ENA (enalapril, 30 mg/kg per day) for 12 weeks. ASE and ENA prevented weight gain and adiposity, adipocyte hypertrophy, dyslipidemia, and insulin resistance. In adipose tissue, ASE increased the insulin receptor expression and reduced renin and AT1 receptor expression, which was associated with decreased plasma levels of renin and angiotensin II. Differently, ENA increased the expression of angiotensin-conversing enzyme 2, AT2, B2, and Mas receptors in adipose tissue. Also, ASE but not ENA decreased malondialdehyde and 8-isoprostane levels in adipose tissue. Finally, ASE and ENA reduced the adipose tissue inflammatory markers tumor necrosis factor alpha and interleukin 6. These results demonstrate that ASE prevented the adipocyte hypertrophy, obesity, hyperlipidemia, hyperglycemia, and insulin resistance in HF diet–fed mice. The downregulation of RAS in adipose tissue, reducing oxidative stress and inflammation, may contribute to the prevention of obesity-related disorders.

TLR2 and TLR4 mediate an activation of adipose tissue renin-angiotensin system induced by uric acid

Both hyperuricemia and adipose tissue renin–angiotensin system (RAS) are closely associated with multiple metabolic and cardiovascular diseases. We previously reported that uric acid could upregulate tissue RAS in adipocytes. In the present study, we aimed to reveal the involvement of toll-like receptors (TLRs) in uric acid-induced RAS activation in adipose tissue. A hyperuricemia rat model fed with a high-fructose diet and rat primary adipocytes were used in this study. Here, we inhibited TLR2 and TLR4 expression in adipose tissue and cultured adipocytes using small interfering RNA (siRNA). We found that high fructose-fed rats had hyperuricemia, higher body weight and greater adipose tissue content. We also found that hyperuricemia rats had raising blood pressure, higher expression levels of inflammatory cytokines and RAS components in adipose tissue, which could be prevented by TLR2/4-siRNA infection. In vitro study, uric acid caused a dose- and time-dependent increase in the mRNA expression of TLR2 and TLR4 in rat adipocytes. Uric acid could increase inflammatory cytokines and upregulate tissue RAS in rat adipocytes, which were both blocked with TLR2/4-siRNA infection. TNF-α and IL-6 could also result in an activation of tissue RAS expression in adipocytes. In conclusion, TLR2/4 mediated adipose inflammation plays a key role in RAS activation induced by uric acid in adipose tissue.

Apelin-13 reduces oxidative stress induced by uric acid via downregulation of renin-angiotensin system in adipose tissue

Apelin-13, a novel adipocytokine, is found to be a powerful antioxidant. Our previous work reported that uric acid could induce oxidative stress via an activation of renin–angiotensin system (RAS) in 3T3-L1 adipocytes. In the present study, we tried to observe the effect of apelin-13 on uric acid-induced oxidative stress. We also tried to reveal the potential mechanisms. In vivo, the rats were fed with 60% fructose diet for 8 weeks to produce hyperuricemia. Then, the hyperuricemia rats were intraperitoneally injected with apelin-13 for 2 weeks or 12 weeks. In vitro, 3T3-L1 adipocytes were treated with apelin-13 in the presence of 600 μmol/L uric acid for 48 h. When injected with apelin-13 for 12 weeks, the hyperuricemia rats had ameliorated oxidative stress, downregulated RAS components and upregulated angiotensin type 1 receptor related protein (APJ) expression in adipose tissue. Serum uric acid levels were also decreased after treatment. However, 2-week apelin-13 treatment had no obvious effect on the rats with hyperuricemia. Consistent with the findings in vivo, in vitro study, apelin-13 could ameliorate oxidative stress, decrease tissue RAS components, and increase APJ expression in 3T3-L1 adipocytes stimulated by uric acid. In conclusion, apelin-13 reduces uric acid-induced oxidative stress in adipose tissue, maybe through the inhibition of adipose RAS expression.

Mechanisms Linking the Adipocyte Renin Angiotensin System, Inflammation and Endoplasmic Reticulum (ER) Stress

One of the critical pathways involved in obesity is the Renin angiotensin system (RAS) which is classically known to regulate blood pressure and fluid balance. Components of RAS are expressed in adipose tissue; however, mechanisms governing RAS‐obesity interactions are not well identified. Both ER stress and inflammation are increased in adipose tissue and we proposed that it is through ER stress and inflammatory pathways, that RAS contributes to obesity and regulates adipocyte function. This hypothesis was tested using male wild type C57BL/6 mice (Wt) and transgenic mice (Agt‐Tg) overexpressing angiotensinogen (Agt) via P2 promoter in the adipose tissue. Mice were fed a low fat (LF) or a high fat (HF) diet with or without RAS inhibition (captopril, an angiotensin converting enzyme inhibitor). Furthermore, for mechanistic analyses, we used mouse and human adipocytes treated with various inhibitors of RAS (Telmisartan, P‐186), inflammation (11‐7082), and ER stress (PBA).Markers of ER stress such as BiP (Binding immunoglobulin protein), ATF4 (activating transcription factor 4), XBP1 (X‐box binding protein 1) and CHOP (CCAAT/‐enhancer‐binding protein homologous protein) were significantly higher in Agt‐Tg mice compared to Wt mice. Moreover, adipose tissue mRNA and serum levels for pro‐inflammatory markers MCP‐1 (Monocyte Chemoattractant Protein‐1), and IL‐6 (interleukin‐6) were also significantly higher in Agt‐Tg compared to Wt mice. By contrast, anti‐inflammatory cytokine IL‐10 was significantly lower in Agt‐Tg mice compared to Wt mice. Captoril‐treated Agt‐Tg mice demonstrated a significantly lower expression of both ER stress and pro‐inflammatory markers indicating the importance of RAS in these metabolic pathways. To gain further insight into direct mechanisms by which RAS induces obesity, in vitro experiments were conducted. Inhibitors of angiotensin type 1 and type 2 receptors (Agtr) were used to determine the pathway through which RAS induces ER stress and inflammation. Inhibition of Agtr1 receptor significantly reduced RAS effect in both mouse and human adipocytes. As anticipated PBA and 11‐7082 reduced RAS‐induced ER stress and inflammation in vitro further confirming the involvement of RAS. In agreement with these findings, captopril and telmisartan prevented angiotensin‐II (Ang II) induced expression of ER stress, and pro inflammatory markers in both cell types. Further studies are ongoing in cultured adipocytes to dissect molecular mechanisms linking RAS to ER stress and inflammation in obesity.In conclusion, overexpression of RAS in adipose tissue and adipocytes increases inflammation and ER stress. These effects are mediated by Agtr1 receptors. These pathways could be used as potential targets to reduce RAS induced obesity and related metabolic diseases.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effects of Sleeve Gastrectomy on the Metabolic Profile and on the Expression of Renin-Angiotensin System in Adipose Tissue of Obese Rats.

Sleeve gastrectomy (SG) has been used as a multipurpose surgical procedure for the treatment of obesity. The present study aimed to assess the effects of SG on the metabolic and inflammatory profile and renin-angiotensin system (RAS) expression in the white adipose tissue of male rats with obesity induced by a high-fat diet. Male Wistar rats were treated with a standard diet or high-fat diet and submitted to SG or sham surgery. The glycemic and lipid profiles and gene expression of inflammatory markers and RAS components in adipose tissue were evaluated. SG led to weight loss, decreased adiposity (p < 0.01) and a reduction in plasma glucose (p < 0.05), C-peptide (p < 0.05), insulin (p < 0.001) and total cholesterol (p < 0.05) levels. In addition, SG led to a decrease in the expression of tumor necrosis factor-alpha (TNF-α) (p < 0.01), interleukin- 6 (IL-6) (p < 0.001), angiotensinogen (AGT) (p < 0.001) and angiotensin converting enzyme (ACE) (p < 0.05) and increased the expression of angiotensin converting enzyme 2 (ACE2) (p < 0.05) in white adipose tissue. No statistically significant differences were observed for AT1 (p = 0.10) and Mas (p = 0.22) receptors. This study showed that SG leads to weight loss and improves metabolic parameters. Changes in the expression of RAS components and of inflammatory molecules in adipose tissue seem to play a role the before beneficial effects of the SG.

Regulation and Functions of the Renin-Angiotensin System in White and Brown Adipose Tissue.

The renin angiotensin system (RAS) is a major regulator of blood pressure, fluid, and electrolyte homeostasis. RAS precursor angiotensinogen (Agt) is cleaved into angiotensin I (Ang I) and II (Ang II) by renin and angiotensin converting enzyme (ACE), respectively. Major effects of Ang II, the main bioactive peptide of this system, is mediated by G protein coupled receptors, Angiotensin Type 1 (AGTR1, AT1R) and Type 2 (AGTR2, AT2R) receptors. Further, the discovery of additional RAS peptides such as Ang 1-7 generated by the action of another enzyme ACE2 identified novel functions of this complex system. In addition to the systemic RAS, several local RAS exist in organs such as the brain, kidney, pancreas, and adipose tissue. The expression and regulation of various components of RAS in adipose tissue prompted extensive research into the role of adipose RAS in metabolic diseases. Indeed, animal studies have shown that adipose-derived Agt contributes to circulating RAS, kidney, and blood pressure regulation. Further, mice overexpressing Agt have high blood pressure and increased adiposity characterized by inflammation, adipocyte hypertrophy, and insulin resistance, which can be reversed at least in part by RAS inhibition. These findings highlight the importance of this system in energy homeostasis, especially in the context of obesity. This overview article discusses the depot-specific functions of adipose RAS, genetic and pharmacological manipulations of RAS, and its applications to adipogenesis, thermogenesis, and overall energy homeostasis. © 2017 American Physiological Society. Compr Physiol 7:1137-1150, 2017.

Fructose-rich diet differently affects angiotensin II receptor content in the nucleus and a plasma membrane fraction of visceral adipose tissue.

The adipose tissue renin-angiotensin system (RAS) is proposed to be a pathophysiological link between adipose tissue dysregulation and metabolic disorders induced by a fructose-rich diet (FRD). RAS can act intracellularly. We hypothesized that adipocyte nuclear membranes possess angiotensin receptor types 1 and 2 (AT1R and AT2R), which couple to nuclear signaling pathways and regulate oxidative gene expression under FRD conditions. We analyzed the effect of consumption of 10% fructose solution for 9 weeks on biochemical parameters, adipocyte morphology, and expression of AT1R, AT2R, AT1R-associated protein (ATRAP), NADPH oxidase 4 (NOX4), matrix metalloproteinase-9 (MMP-9), and manganese superoxide dismutase (MnSOD) in adipose tissue of Wistar rats. We detected AT1R and AT2R in the nuclear fraction. FRD reduced the level of angiotensin receptors in the nucleus, while increased AT1R and decreased AT2R levels were observed in the plasma membrane. FRD increased the ATRAP mRNA level and decreased MnSOD mRNA and protein levels. No significant differences were observed for MMP-9 and NOX4 mRNA levels. These findings coincided with hyperleptinemia, elevated blood pressure and triglycerides, and unchanged visceral adipose tissue mass and morphology in FRD rats. Besides providing evidence for nuclear localization of angiotensin receptors in visceral adipose tissue, this study demonstrates the different effects of FRD on AT1R expression in different cellular compartments. Elevated blood pressure and decreased antioxidant capacity in visceral fat of fructose-fed rats were accompanied by an increased AT1R level in the plasma membrane, while upregulation of ATRAP and a decrease of nuclear membrane AT1R suggest an increased capacity for attenuation of excessive AT1R signaling and visceral adiposity.

Lipotoxicity-Related Hematological Disorders in Obesity.

Lipotoxicity can mediate endothelial dysfunction in obesity. Altered endothelial cell phenotype during the pathobiological course of the lipotoxicity may lead to the hemostatic abnormalities, which is a hallmark of several hematological disorders. Impaired hemostasis could also be directly related to the numerous metabolic diseases such as hypertension, diabetes and atherosclerosis. On the other hand, local hematopoietic bone marrow (BM) renin-angiotensin system (RAS) contributes to the development of atherosclerosis via acting on the lipotoxicity processes. Local BM RAS, principally an autocrine/ paracrine/ intracrinehematological system, is located at the crossroads of cellular regulation, molecular interactions and the lipotoxicity-mediated vascular endothelial dysfunction. The positive regulatory role of plasma LDL on AT1 receptor-mediated hematopoietic stem cell (HSC) differentiation and the production of pro-atherogenic monocytes had been described. LDL-regulated HSC function may explain in part hypercholesterolemia-induced inflammation as well as the anti-inflammatory and anti-atherosclerotic effects of AT1 receptor blockers. The role of local adipose tissue RAS is directly related to the pathogenesis of metabolic derangements in obesity. There may be a crosstalk between local BM RAS and local adipose tissue RAS at the genomics and transcriptomics levels. The aim of this chapter is to review hematological alterations propagating the pathological influences of lipotoxicity on the vascular endothelium.

Angiotensin-converting enzyme insertion/deletion polymorphism association with obesity and some related disorders in Egyptian females: a case-control observational study.

BackgroundAccording to the WHO report in 2015, obesity is the fifth leading cause of death worldwide, and the prevalence of Egyptian female obesity is 37.5 %. Since obesity is highly influenced by genetics, and adipose tissue renin-angiotensin system is over-activated in obesity, the effect of angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism on obesity and related disorders was studied in several populations, because of its effect on ACE activity. Our objective was to study the association of ACE I/D polymorphism with obesity and certain related disorders, namely hypertension, insulin resistance and metabolic syndrome, in Egyptian females.MethodsEighty female volunteers were recruited, blood pressure and body measurements were recorded and a fasting blood sample was obtained for the quantitation of glucose, lipid profile, insulin, leptin and identification of ACE I/D polymorphs. Subjects were grouped based on hypertension and obesity states. Comparisons of continuous parameters were made with independent sample t-test between two groups. The frequencies of ACE genotypes and alleles, and the association between gene polymorphism and metabolic parameters were assessed using chi-square or Fisher's exact test.ResultsGenotype frequencies were in Hardy-Weinberg equilibrium for all groups. Genotype distribution did not differ significantly between controls and cases of all the studied disorders. Although DD carriers had apparently higher parameters of blood pressure, lipid profile and insulin resistance, only diastolic blood pressure was almost significant (p = 0.057). I-carriers were significantly less susceptible to hypertension than DD carriers having normal waist/hip ratio (p = 0.007, OR = 17.29, CI = 1.81–164.96) and normal conicity index (p = 0.024, OR = 7.00, CI = 1.36–35.93). In DD genotype carriers, a significant association was found between insulin resistance and high body mass index (p = 0.004, OR = 8.89, CI = 1.94–40.71), waist circumference (p = 0.003, OR = 9.63, CI = 2.14–43.36) and waist/height ratio (p = 0.034, OR = 6.86, CI = 1.25–37.61), although the variations in percentages between DD and I-carriers were not high enough to conclude an effect of ACE I/D on such an association.ConclusionsIn this sample of Egyptian females, ACE I/D polymorphism was not significantly associated with obesity nor with any of its related disorders studied. The I allele seemed protective against hypertension in subjects with normal, not high, waist/hip ratio and conicity index compared to DD genotype carriers.

Free Fatty Acids Activate Renin-Angiotensin System in 3T3-L1 Adipocytes through Nuclear Factor-kappa B Pathway.

The activity of a local renin-angiotensin system (RAS) in the adipose tissue is closely associated with obesity-related diseases. However, the mechanism of RAS activation in adipose tissue is still unknown. In the current study, we found that palmitic acid (PA), one kind of free fatty acid, induced the activity of RAS in 3T3-L1 adipocytes. In the presence of fetuin A (Fet A), PA upregulated the expression of angiotensinogen (AGT) and angiotensin type 1 receptor (AT1R) and stimulated the secretion of angiotensin II (ANG II) in 3T3-L1 adipocytes. Moreover, the activation of RAS in 3T3-L1 adipocytes was blocked when we blocked Toll-like receptor 4 (TLR4) signaling pathway using TAK242 or NF-κB signaling pathway using BAY117082. Together, our results have identified critical molecular mechanisms linking PA/TLR4/NF-κB signaling pathway to the activity of the local renin-angiotensin system in adipose tissue.

Circulating RAS in Mice with Prorenin Receptor Gene Deletion Specificly in Adipose Tissue

IntroductionAdipose tissue (AT) renin‐angiotensin system (RAS) has been involved in the pathogenesis of obesity, where the role of the prorenin/renin receptor [(P)RR], which acts in an angiotensin‐dependent and ‐independent manner is not clear yet. Our previous results suggest the (P)RR plays a role in the regulation of body weight (BW), fat mass and insulin sensitivity (IS).Material and methodsMice with deletion of the (P)RR gene specificly in AT (KO) created by cre‐loxp technology, were kept either on regular chow (ND) or high‐fat/high‐carbohydrate diet (HF/HC) for 10 weeks. BW measured weekly. Body composition assessed by Echo‐MRI. Glucose homeostasis evaluated by OGTT. At the end of protocol, mice euthanized, subcutaneous, visceral (VF) fat pads separated, weighed, flash frozen. Plasma renin activity (PRA), Angiotensin I (Ang‐I) concentration were measured by immunoassay (DBC, Canada).ResultsMale KO mice had a 20% lower BW compared to wild‐type mice (WT), p0.001, whereas KO female mice had a 4.3% decrease on ND, p&lt;0.01 and 14.12%, p0.001 on HF/HC. The VF mass in KO male mice was lower by 2.4 fold, p0.001 compared to WT, in female KO mice ‐1.3 fold lower on ND, p0.01 and 2.4 folds on HF/HC, p0.001. In addition, although KO and WT mice had similar glycemia during OGTT, fasting and stimulated insulinemia were lower in KO mice which suggests an improved IS. These phenotypes were not associated with any changes in circulating Ang‐I and PRA.ConclusionOur results suggest that AT specific deletion of the (P)RR regulates body weight, fat mass, glucose homeostasis without changing circulating RAS.

Results of the META-Health Study Suggest Pathways by Which Vitamin D Affect Obesity and Cardiovascular Risk through Adiponectin Levels may Require Further Characterization in Subgroups.

Recent review of Bidulescu and colleagues’ article on the association between vitamin D and adiponectin and its relationship with body mass index in African-Americans, as compared to Whites, reinforced the value of conducting stratified analyses using more resolute subpopulation/subgroup data (1). Although potential mechanisms were carefully considered and described by the investigators of the META-Health Study, the mixed results raised questions about how vitamin D and adiponectin interact in the presence of normal weight versus obesity. For example, the authors hypothesized that the inverse association between vitamin D and adiponectin among lean African-American women may be due to a possible reduced negative regulation of the adipose-tissue renin-angiotensin system by vitamin D metabolites. While this explanation has some support in the literature (2, 3), the significant direct association between vitamin D and adiponectin among lean White women and the lack of association found among obese individuals suggest biological pathways by which vitamin D affects adiponectin expression may be more complex in subgroups and may require further characterization. Prior studies have indicated that adiponectin secretion is paradoxically decreased in obesity, likely as a result of the inhibitory effects of inflammatory factors secreted by hypertrophic adipocytes (i.e., as in obesity) (3–5). Taken together, the results of the META-Health Study suggest that further research may be needed to characterize how vitamin D actually mediate obesity and cardiovascular risk through adiponectin levels by race, gender, and body mass index categories. As indicated by the authors, these study data, in spite of their inherent limitations, could be used to inform if and how randomized controlled trials and other studies on vitamin D supplementation should be conducted. An added value of Bidulescu et al.’s investigation is the contribution of mixed results to the evidence base in this field. All too often, publication bias impedes release of these kinds of null or mixed result findings, especially as they relate to subpopulations or subgroups with high burden of obesity, diabetes, and/or cardiovascular disease. In the “real” world setting, e.g., in health policy and clinical practice, negative or mixed results frequently have as much of an impact as positive results on decision-making.

Uric acid induces oxidative stress via an activation of the renin–angiotensin system in 3T3-L1 adipocytes

Hyperuricemia is recently reported involving in various obesity-related cardiovascular disorders, especially hypertension. However, the underlying mechanisms are not completely understood. In the present study, we investigated whether uric acid upregulates renin-angiotensin system (RAS) expression in adipocytes. We also examined whether RAS activation plays a role in uric acid-induced oxidative stress in adipocytes. The adipocytes of different phenotypes were incubated with uric acid for 48h, respectively. Losartan (10(-4)M) or captopril (10(-4)M) was used to block adipose tissue RAS activation. mRNA expressions of angiotensinogen (AGT), angiotensin-converting enzyme-1 (ACE-1), renin, angiotensin type 1 receptor (AT1R), and angiotensin type 2 receptor (AT2R) were evaluated with real-time PCR. Angiotensin II concentrations in supernatant were measured by ELISA. Intracellular reactive species (ROS) levels were measured by fluorescent probe DCFH-DA, DHR, or NBT assay. The uric acid upregulated both RAS (AGT, ACE1, renin, AT1R, and AT2R) mRNA expressions and angiotensin II protein secretion and caused a significant increase in ROS production in 3T3-L1 adipocytes. These effects could be prevented by RAS inhibitors, either losartan or captopril. RAS activation has been causally implicated in oxidative stress induced by uric acid in 3T3-L1 adipocytes, suggesting a plausible mechanism through which hyperuricemia contributes to the pathogenesis of obesity-related cardiovascular diseases.

Effects of angiotensin converting enzyme inhibition on adiponectin levels and lipid profile in the ovariectomized-aged rats

Objective:To investigate the relationship between angiotensin converting enzyme (ACE) and adiponectin and lipid profile in the ovariectomized-aged rats.Materials and Methods:Wistar albino rats were first divided into two groups; control (C) and ovariectomized (OVX). Bilateral ovariectomy were carried out on rats (n = 30) except control group (n = 10). After 6 weeks from ovariectomy, ovariectomized rats were subdivided into three groups; one group received no treatment (OVX), two groups received low dose (OVX + Cap5; 5 mg/kg/day) and high dose (OVX + Cap20; 20 mg/kg/day) captopril (Cap). Body weights were monitored weekly. Adiponectin, triglyceride, cholesterol, high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), and very low density lipoprotein cholesterol (VLDL-C) levels were measured at the end of the 6 weeks.Results:In the OVX group, body weights increased (P < 0.001). In the OVX + Cap20 group, body weights significantly decreased compared with the OVX group during weeks 5 and 6 (P < 0.05). While adiponectin levels increased in the OVX + Cap5 group (P = 0.014), triglyceride and cholesterol levels decreased in the OVX + Cap20 group (P = 0.016 and P < 0.001, respectively) compared to the OVX group. HDL-C and VLDL-C levels decreased only in OVX + Cap20 group (P < 0.005).Conclusions:ACE inhibitors may be decreasing the ovariectomy-induced weight gain by increasing adiponectin levels, and by affecting lipid profiles. The adipose tissue renin-angiotensin system (RAS) may be playing an important role in the development of adiposity.

Effects of Ang II receptor blocker irbesartan on adipose tissue function in mice with metabolic disorders.

Recent studies indicate that the functional renin-angiotensin system (RAS) exists in the adipose tissue. The adipose tissue RAS is proposed in the pathophysiology of metabolic disorders. In the present study, we examined therapeutic effects of irbesartan, an angiotensin II (Ang II) type 1 receptor (AT1R)-specific blocker, in genetically obese diabetic KKAy mice, a model of human metabolic disorders without any dietary loading, with our focus on the analysis on possible effect of irbesartan on the adipose tissue. The treatment with irbesartan significantly lowered systolic blood pressure with a concomitant decrease in body weight in KKAy mice. In addition, irbesartan significantly decreased the adipose leptin mRNA expression and tended to decrease IL-6 mRNA expression in the adipose tissue of KKAy mice. Furthermore irbesartan preserved the adipose gene expression of AT1R-associated protein (ATRAP), an endogenous inhibitory molecule of tissue AT1R signaling, with a concomitant tendency of up-regulation of adipose tissue ATRAP/AT1R ratio. Collectively, these results suggest that the irbesartan-induced beneficial suppressive effect on the leptin-IL-6 axis in the adipose tissue in KKAy mice is partly mediated by a trend of up-regulation of the adipose ATRAP/AT1R ratio as one of pleiotropic effects of irbesartan.

Angiotensinogen Gene Silencing Reduces Markers of Lipid Accumulation and Inflammation in Cultured Adipocytes

Inflammatory adipokines secreted from adipose tissue are major contributors to obesity-associated inflammation and other metabolic dysfunctions. We and others have recently documented the contribution of adipose tissue renin-angiotensin system to the pathogenesis of obesity, inflammation, and insulin resistance. We hypothesized that adipocyte-derived angiotensinogen (Agt) plays a critical role in adipogenesis and/or lipogenesis as well as inflammation. This was tested using 3T3-L1 adipocytes, stably transfected with Agt-shRNA or scrambled Sc-shRNA as a control. Transfected preadipocytes were differentiated and used to investigate the role of adipose Agt through microarray and PCR analyses and adipokine profiling. As expected, Agt gene silencing significantly reduced the expression of Agt and its hormone product angiotensin II (Ang II), as well as lipid accumulation in 3T3-L1 adipocytes. Microarray studies identified several genes involved in lipid metabolism and inflammatory pathways which were down-regulated by Agt gene inactivation, such as glycerol-3-phosphate dehydrogenase 1 (Gpd1), serum amyloid A 3 (Saa3), nucleotide-binding oligomerization domain containing 1 (Nod1), and signal transducer and activator of transcription 1 (Stat1). Mouse adipogenesis PCR arrays revealed lower expression levels of adipogenic/lipogenic genes such as peroxisome proliferator activated receptor gamma (PPARγ), sterol regulatory element binding transcription factor 1 (Srebf1), adipogenin (Adig), and fatty acid binding protein 4 (Fabp4). Further, silencing of Agt gene significantly lowered expression of pro-inflammatory adipokines including interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and monocyte chemotactic protein-1 (MCP-1). In conclusion, this study directly demonstrates critical effects of Agt in adipocyte metabolism and inflammation and further support a potential role for adipose Agt in the pathogenesis of obesity-associated metabolic alterations.