The adipose renin-angiotensin system modulates systemic markers of insulin sensitivity and activates the intrarenal renin-angiotensin system

Ultra-processed foods and risk of declined renal function: a dose-response meta-analysis of 786,216 participants

OBJECTIVES

Earlier investigations have documented an association between elevated consumption of Ultra-Processed Foods (UPFs) and adverse renal outcomes. To explore this relationship further, we executed a comprehensive dose-response meta-analysis to examine the link between UPFs intake and the risk of declined renal function.

SETTING

A systematic search was completed utilizing the ISI Web of Science, Scopus, Embase as well as PubMed/MEDLINE databases (without any restrictions), up until September 5, 2024. Effect sizes of declined renal function were recalculated by applying a random effects model. The GRADE tool was adopted to assess the certainty of the evidence, while study quality and potential publication bias were examined via validated methods such as the Newcastle-Ottawa Scale, Egger's regression asymmetry and Begg's rank correlation test.

RESULTS

Thirty-three studies (comprising 786,216 participants) were incorporated in the quantitative analysis. The results demonstrated that a greater UPFs intake was significantly associated with an enhanced risk of declined renal function (RR = 1.16; 95% CI: 1.09, 1.23; I2 = 68.8%; p < 0.001; n = 37). Additionally, we observed that each 1-serving-per-day increase in UPFs consumption was associated to a 5% greater risk of reduced renal function (RR = 1.05; 95% CI: 1.02, 1.09; I2 = 80.9%; p = 0.013; n = 9). A positive, linear association between UPF intake and the risk of declined renal function (Pnonlinearity = 0.107, Pdose-response < 0.001) was further displayed in the non-linear dose-response analysis.

CONCLUSION

Greater exposure to UPFs is positively associated with the risk of declined renal function. The information emphasizes the importance of considering UPFs in the prevention and management of adverse renal outcomes.

Effect of Tissue-derived Angiotensinogen on Kidney Injury and Fibrosis in Obstructive Nephropathy

BACKGROUND/AIM

Angiotensinogen (AGT), a precursor of angiotensin II (AngII), contributes to regulating (patho)physiological conditions, including blood pressure changes, inflammation, and kidney fibrosis. However, the precise role of tissue-specific AGT in kidney fibrosis independent of blood pressure remains to be fully understood. This study investigated the source of intrarenal AGT and its role in kidney injury and fibrosis during obstructive nephropathy.

MATERIALS AND METHODS

Proximal tubule- (PT, major source secreting AGT in the kidney; PKO) or liver- (major source of circulating AGT; LKO) AGT knockout (KO) mice were subjected to unilateral ureteral obstruction (UUO), a blood pressure-independent fibrosis model.

RESULTS

UUO increased AGT mRNA and protein levels in the kidneys. PKO decreased AGT mRNA, but LKO enhanced it in UUO kidneys compared with the control. In contrast, the intrarenal protein levels of AGT increased in PKO, but not in LKO in UUO kidneys, indicating that the liver is a major source of intrarenal AGT protein. Expression of megalin, a PT receptor involved in the uptake of circulating AGT, was down-regulated in UUO kidneys and was independent of PKO or LKO. However, none of these changes prevented UUO-induced tubular injury and kidney fibrosis.

CONCLUSION

Hepatic and proximal tubule AGT play distinct roles in contributing to intrarenal AGT levels during UUO, and their genetic inhibitions fail to prevent kidney injury and fibrosis, suggesting a highly complicated signaling pathway of the renin-angiotensin system and an associated compensatory mechanism in obstructive nephropathy.

Obesity and the kidney: mechanistic links and therapeutic advances

Obesity is strongly associated with the development of diabetes mellitus and chronic kidney disease (CKD), but there is evidence for a bidirectional relationship wherein the kidney also acts as a key regulator of body weight. In this Review, we highlight the mechanisms implicated in obesity-related CKD, and outline how the kidney might modulate feeding and body weight through a growth differentiation factor 15-dependent kidney-brain axis. The favourable effects of bariatric surgery on kidney function are discussed, and medical therapies designed for the treatment of diabetes mellitus that lower body weight and preserve kidney function independent of glycaemic lowering, including sodium-glucose cotransporter 2 inhibitors, incretin-based therapies and metformin, are also reviewed. In summary, we propose that kidney function and body weight are related in a bidirectional fashion, and that this interrelationship affects human health and disease.

Double blind control trial of vitamin D fortified milk on the expression of lncRNAs and adiponectin for patients with metabolic syndrome

BACKGROUND

Metabolic syndrome (Mets) is a common metabolic disorder in which hypoadiponectinemia is one of the consequences for the body caused by inflammation, and vitamin D may help improve inflammatory symptoms. LncRNAs (long non-coding RNA) play several different regulatory roles in the body. The goal of this study was to see how adding vitamin D to milk affected the levels of adiponectin and inflammatory lncRNAs in the serum of people with Mets.

METHODS

This clinical trial was conducted on staff and students between the ages of 30 and 50 at Mashhad University of Medical Sciences and met the International Diabetes Federation's criteria for Mets. Eighty-two Mets were assigned randomly to one of two groups for ten weeks: fortified milk (FM) with 1500 IU vitamin D or non-fortified milk (NFM). Total RNA was extracted from both frozen clinical samples using Trizol reagent. APQ AS and MALAT1 lncRNA gene expression were measured by Real-Time PCR.

RESULTS

Serum adiponectin levels in the FM group increased significantly compared to the NFM group (p = 0.01). Also, the expression of APQ AS and MALAT1 genes decreased after ten weeks, which showed a significant decrease in APQ AS (p = 0.036).

CONCLUSION

As in FM, vitamin D may have anti-inflammatory effects and increase adiponectin levels in people with Mets via decreasing APQ AS gene expression.

Obesity-Related Chronic Kidney Disease: Principal Mechanisms and New Approaches in Nutritional Management

Obesity is the epidemic of our era and its incidence is supposed to increase by more than 30% by 2030. It is commonly defined as a chronic and metabolic disease with an excessive accumulation of body fat in relation to fat-free mass, both in terms of quantity and distribution at specific points on the body. The effects of obesity have an important impact on different clinical areas, particularly endocrinology, cardiology, and nephrology. Indeed, increased rates of obesity have been associated with increased risk of cardiovascular disease (CVD), cancer, type 2 diabetes (T2D), dyslipidemia, hypertension, renal diseases, and neurocognitive impairment. Obesity-related chronic kidney disease (CKD) has been ascribed to intrarenal fat accumulation along the proximal tubule, glomeruli, renal sinus, and around the kidney capsule, and to hemodynamic changes with hyperfiltration, albuminuria, and impaired glomerular filtration rate. In addition, hypertension, dyslipidemia, and diabetes, which arise as a consequence of overweight, contribute to amplifying renal dysfunction in both the native and transplanted kidney. Overall, several mechanisms are closely related to the onset and progression of CKD in the general population, including changes in renal hemodynamics, neurohumoral pathways, renal adiposity, local and systemic inflammation, dysbiosis of microbiota, insulin resistance, and fibrotic process. Unfortunately, there are no clinical practice guidelines for the management of patients with obesity-related CKD. Therefore, dietary management is based on the clinical practice guidelines for the nutritional care of adults with CKD, developed and published by the National Kidney Foundation, Kidney Disease Outcome Quality Initiative and common recommendations for the healthy population. Optimal nutritional management of these patients should follow the guidelines of the Mediterranean diet, which is known to be associated with a lower incidence of CVD and beneficial effects on chronic diseases such as diabetes, obesity, and cognitive health. Mediterranean-style diets are often unsuccessful in promoting efficient weight loss, especially in patients with altered glucose metabolism. For this purpose, this review also discusses the use of non-classical weight loss approaches in CKD, including intermittent fasting and ketogenic diet to contrast the onset and progression of obesity-related CKD.

The Renal Pathology of Obesity: Structure-Function Correlations

The kidney is one of the target organs that may show health disorders as a result of obesity. Obesity-related glomerulopathy (ORG) is a kidney disease category based on a biopsy diagnosis that may occur secondary to obesity. Detailed clinicopathologic observations of ORG have provided significant knowledge regarding obesity-associated renal complications. Glomerulomegaly with focal segmental glomerulosclerosis of perihilar locations is a typical renal histopathologic finding in ORG, which has long been considered to represent a state of single-nephron glomerular hyperfiltration. This hypothesis was recently confirmed in ORG patients by estimating single-nephron glomerular filtration rate using a combined image analysis and biopsy-based stereology. Overshooting in glomerulotubular and tubuloglomerular interactions may lead to glomerular hyperfiltration/hypertension, podocyte failure, tubular protein-traffic overload, and tubulointerstitial scarring, constituting a vicious cycle of a common pathway to the further loss of functioning nephrons and the progression of kidney functional impairment.

Obesity, Angiotensin-Blocking Drugs, and Acute Kidney Injury in Orthopedic Surgery

Postoperative acute kidney injury occurs in 7% to 11% of orthopedic surgeries. The effect of preoperative angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) on the development of postoperative acute kidney injury remains controversial. Adipose tissue has its own independently regulated angiotensin system. The primary aim of this study was to examine the effects of obesity and preoperative ACEIs and ARBs on postoperative acute kidney injury. Charts were reviewed of adult elective orthopedic surgery patients during a 2-year period when patients were instructed to take their ACEI or ARB on the morning of surgery. The patients were divided into an obese cohort (body mass index [BMI] ≥30 kg/m²) and a nonobese cohort (BMI <30 kg/m²). A multivariable model was created for the outcome of acute kidney injury, using obesity as a primary predictor and adjusting for demographics, medications, comorbidities, and intraoperative parameters in a logistic regression analysis. Obesity increased the likelihood of developing acute kidney injury after orthopedic surgery (odds ratio [OR], 1.86; 95% CI, 1.07-3.22; P=.028). For every 5-unit increase in BMI, the odds of acute kidney injury were 1.43 (95% CI, 1.26-1.62; P<.001). When receiving ACEIs or ARBs, only the nonobese patients had a statistically increased likelihood of postoperative acute kidney injury (OR, 3.30; 95% CI, 1.12-9.70; P=.030). Obesity is an independent risk factor for postoperative acute kidney injury. Obesity appears to influence the effect that preoperative ACEIs and ARBs have on postoperative acute kidney injury. [Orthopedics. 2021;44(2):e253-e258.].

Obesity and its impact on COVID-19

The severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) pandemic has proven a challenge to healthcare systems since its first appearance in late 2019. The global spread and devastating effects of coronavirus disease 2019 (COVID-19) on patients have resulted in countless studies on risk factors and disease progression. Overweight and obesity emerged as one of the major risk factors for developing severe COVID-19. Here we review the biology of coronavirus infections in relation to obesity. In particular, we review literature about the impact of adiposity-related systemic inflammation on the COVID-19 disease severity, involving cytokine, chemokine, leptin, and growth hormone signaling, and we discuss the involvement of hyperactivation of the renin-angiotensin-aldosterone system (RAAS). Due to the sheer number of publications on COVID-19, we cannot be completed, and therefore, we apologize for all the publications that we do not cite.

Autophagy in metabolic syndrome: breaking the wheel by targeting the renin-angiotensin system

Metabolic syndrome (MetS) is a complex, emerging epidemic which disrupts the metabolic homeostasis of several organs, including liver, heart, pancreas, and adipose tissue. While studies have been conducted in these research areas, the pathogenesis and mechanisms of MetS remain debatable. Lines of evidence show that physiological systems, such as the renin-angiotensin system (RAS) and autophagy play vital regulatory roles in MetS. RAS is a pivotal system known for controlling blood pressure and fluid balance, whereas autophagy is involved in the degradation and recycling of cellular components, including proteins. Although RAS is activated in MetS, the interrelationship between RAS and autophagy varies in glucose homeostatic organs and their cross talk is poorly understood. Interestingly, autophagy is attenuated in the liver during MetS, whereas autophagic activity is induced in adipose tissue during MetS, indicating tissue-specific discordant roles. We discuss in vivo and in vitro studies conducted in metabolic tissues and dissect their tissue-specific effects. Moreover, our review will focus on the molecular mechanisms by which autophagy orchestrates MetS and the ways future treatments could target RAS in order to achieve metabolic homeostasis.

Association between preterm birth and the renin-angiotensin system in adolescence: influence of sex and obesity

OBJECTIVES

Preterm birth appears to contribute to early development of cardiovascular disease, but the mechanisms are unknown. Prematurity may result in programming events that alter the renin-angiotensin system. We hypothesized that prematurity is associated with lower angiotensin-(1-7) in adolescence and that sex and obesity modify this relationship.

METHODS

We quantified angiotensin II and angiotensin-(1-7) in the plasma and urine of 175 adolescents born preterm and 51 term-born controls. We used generalized linear models to estimate the association between prematurity and the peptides, controlling for confounding factors and stratifying by sex and overweight/obesity.

RESULTS

Prematurity was associated with lower plasma angiotensin II (β: -5.2 pmol/l, 95% CI: -10.3 to -0.04) and angiotensin-(1-7) (-5.2 pmol/l, 95% CI: -8.4 to -2.0) but overall higher angiotensin II:angiotensin-(1-7) (3.0, 95% CI: 0.9-5.0). The preterm-term difference in plasma angiotensin-(1-7) was greater in women (-6.9 pmol/l, 95% CI: -10.7 to -3.1) and individuals with overweight/obesity (-8.0 pmol/l, 95% CI: -12.2 to -3.8). The preterm-term difference in angiotensin II:angiotensin-(1-7) was greater among those with overweight/obesity (4.4, 95% CI: 0.6-8.1). On multivariate analysis, prematurity was associated with lower urinary angiotensin II:angiotensin-(1-7) (-0.13, 95% CI: -0.26 to -0.003), especially among the overweight/obesity group (-0.38, 95% CI: -0.72 to -0.04).

CONCLUSION

Circulating angiotensin-(1-7) was diminished whereas urinary angiotensin-(1-7) was increased relative to angiotensin II in adolescents born preterm, suggesting prematurity may increase the risk of cardiovascular disease by altering the renin-angiotensin system. Perinatal renin-angiotensin system programming was more pronounced in women and individuals with overweight/obesity, thus potentially augmenting their risk of developing early cardiovascular disease.

Sex differences in the metabolic effects of the renin-angiotensin system

Obesity is a global epidemic that greatly increases risk for developing cardiovascular disease and type II diabetes. Sex differences in the obese phenotype are well established in experimental animal models and clinical populations. While having higher adiposity and obesity prevalence, females are generally protected from obesity-related metabolic and cardiovascular complications. This protection is, at least in part, attributed to sex differences in metabolic effects of hormonal mediators such as the renin-angiotensin system (RAS). Previous literature has predominantly focused on the vasoconstrictor arm of the RAS and shown that, in contrast to male rodent models of obesity and diabetes, females are protected from metabolic and cardiovascular derangements produced by angiotensinogen, renin, and angiotensin II. A vasodilator arm of the RAS has more recently emerged which includes angiotensin-(1-7), angiotensin-converting enzyme 2 (ACE2), mas receptors, and alamandine. While accumulating evidence suggests that activation of components of this counter-regulatory axis produces positive effects on glucose homeostasis, lipid metabolism, and energy balance in male animal models, female comparison studies and clinical data related to metabolic outcomes are lacking. This review will summarize current knowledge of sex differences in metabolic effects of the RAS, focusing on interactions with gonadal hormones and potential clinical implications.

Childhood adiposity, adult adiposity, and the ACE gene insertion/deletion polymorphism: evidence of gene-environment interaction effects on adult blood pressure and hypertension status in adulthood

BACKGROUND

Genetic variants may modify the associations of adiposity measures with blood pressure (BP) and hypertension. The insertion/deletion (I/D) polymorphism in the angiotensin-converting enzyme (ACE) gene is an attractive candidate.

AIMS

To examine interaction effects between I/D polymorphism and adiposity measures (BMI, waist circumference, waist-to-hip ratio, and skinfold thickness) during childhood and adulthood in relation to adult BP and hypertension.

METHODS

Data were available for 4835 participants from three prospective cohort studies. Multivariable linear regression models for adult SBP and DBP, and multivariable logistic regression models for hypertension were fit that included interaction effects between child or adult adiposity and I/D polymorphism.

RESULTS

Evidence for interaction effects on BP/hypertension were found across the three studies. Compared with childhood measures, the effect modification appeared to be more consistent when using adult adiposity. In particular, the adverse effects of greater adult waist circumference on increasing adult SBP and DBP appeared to be larger among carriers of ACE DD (or GG) [adjusted linear regression coefficients 0.26, 95% CI (0.21-0.31) and 0.28 (0.24-0.32) for SBP and DBP, respectively] and ID (or AG) genotypes [0.25 (0.21-0.29) and 0.25 (0.21-0.28), respectively], whereas those with II (or AA) genotypes had smaller effects [0.15 (0.09-0.21) and 0.19 (0.13-0.23)].

CONCLUSION

ACE genetic variation may modify the effect of adult adiposity on increasing BP and risk of hypertension in adulthood. Individuals with ACE DD (or GG) and/or ID (or AG) genotypes, compared with those with II (or AA) genotype, appear more vulnerable to the impact of excess adiposity.

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.

Skeletal muscle insulin resistance: role of mitochondria and other ROS sources

At present, obesity is one of the most important public health problems in the world because it causes several diseases and reduces life expectancy. Although it is well known that insulin resistance plays a pivotal role in the development of type 2 diabetes mellitus (the more frequent disease in obese people) the link between obesity and insulin resistance is yet a matter of debate. One of the most deleterious effects of obesity is the deposition of lipids in non-adipose tissues when the capacity of adipose tissue is overwhelmed. During the last decade, reduced mitochondrial function has been considered as an important contributor to 'toxic' lipid metabolite accumulation and consequent insulin resistance. More recent reports suggest that mitochondrial dysfunction is not an early event in the development of insulin resistance, but rather a complication of the hyperlipidemia-induced reactive oxygen species (ROS) production in skeletal muscle, which might promote mitochondrial alterations, lipid accumulation and inhibition of insulin action. Here, we review the literature dealing with the mitochondria-centered mechanisms proposed to explain the onset of obesity-linked IR in skeletal muscle. We conclude that the different pathways leading to insulin resistance may act synergistically because ROS production by mitochondria and other sources can result in mitochondrial dysfunction, which in turn can further increase ROS production leading to the establishment of a harmful positive feedback loop.

The Renal Pathology of Obesity

Obesity causes various structural, hemodynamic, and metabolic alterations in the kidney. Most of these are likely to be compensatory responses to the systemic increase in metabolic demand that is seen with obesity. In some cases, however, renal injury becomes clinically apparent as a result of compensatory failure. Obesity-related glomerulopathy is the best known of such disease states. Factors that may sensitize obese individuals to renal compensatory failure and associated injury include the severity and number of obesity-associated conditions or complications, including components of metabolic syndrome, and the mismatch of body size to nephron mass, due to nephron reductions of congenital or acquired origin.

Renal and Systemic Effects of Calorie Restriction in Patients With Type 2 Diabetes With Abdominal Obesity: A Randomized Controlled Trial

In individuals with type 2 diabetes with abdominal obesity, hyperfiltration is a risk factor for accelerated glomerular filtration rate (GFR) decline and nephropathy. In this academic, single-center, parallel-group, prospective, randomized, open-label, blinded end point trial, consenting patients with type 2 diabetes aged >18 years, with waist circumference >94 (males) or >80 (females) cm, serum creatinine <1.2 mg/dL, and normoalbuminuria were randomized (1:1) with permuted blocks to 6 months of a 25% calorie restricted (CR) or standard diet (SD). Primary outcome was measured GFR (iohexol plasma clearance). Analyses were by modified intention to treat. At 6 months, GFR significantly decreased in 34 patients on CR and did not change appreciably in 36 on SD. Changes were significantly different between the groups. GFR and body weight reduction were correlated. GFR reduction was larger in hyperfiltering (GFR >120 mL/min) than nonhyperfiltering patients and was associated with BMI, waist circumference, blood pressure, heart rate, HbA_1c, blood glucose, LDL-to-HDL cholesterol ratio, C-reactive protein, angiotensin II, and albuminuria reduction and with increased glucose disposal rate (measured by hyperinsulinemic-euglycemic clamps). Protein and sodium intake and concomitant treatments were similar between the groups. CR was tolerated well. In patients with type 2 diabetes with abdominal obesity, CR ameliorates glomerular hyperfiltration, insulin sensitivity, and other cardiovascular risk factors, effects that might translate into long-term nephro- and cardioprotection.

The renin angiotensin system, oxidative stress and mitochondrial function in obesity and insulin resistance

Obesity is a complex disease characterized by excessive expansion of adipose tissue and is an important risk factor for chronic diseases such as cardiovascular disorders, hypertension and type 2 diabetes. Moreover, obesity is a major contributor to inflammation and oxidative stress, all of which are key underlying causes for diabetes and insulin resistance. Specifically, adipose tissue secretes bioactives molecules such as inflammatory hormone angiotensin II, generated in the Renin Angiotensin System (RAS) from its precursor angiotensinogen. Accumulated evidence suggests that RAS may serve as a strong link between obesity and insulin resistance. Dysregulation of RAS also occurs in several other tissues including those involved in regulation of glucose and whole body homeostasis as well as insulin sensitivity such as muscle, liver and pancreas and heart. Here we review the scientific evidence for these interactions and potential roles for oxidative stress, inflammation and mitochondrial dysfunction in these target tissues which may mediate effects of RAS in metabolic diseases. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.

The effect of vitamin D administration on serum leptin and adiponectin levels in end-stage renal disease patients on hemodialysis with vitamin D deficiency: A placebo-controlled double-blind clinical trial

BACKGROUND

The prevalence of vitamin D deficiency is higher in end-stage renal disease (ESRD) patients compared to healthy populations. This deficiency could lead to several complications with different mechanisms and might result in reduced survival in patients. Leptin and adiponectin are messenger proteins with endocrine secretion from adipocytes and various effects in cellular mechanisms. The goal of this study was to find the effect of vitamin D administration on serum levels of leptin and adiponectin in ESRD patients.

MATERIALS AND METHODS

This double-blind randomized placebo-controlled clinical trial was carried out on 64 ESRD patients on hemodialysis in the Amin and Noor hospitals of Isfahan, Iran. Patients were categorized into two groups, on control and intervention; serum levels of vitamin D, leptin, and adiponectin were measured in both groups before and after the study. The intervention group was treated with vitamin D pearls, while the control group received placebo in the same manner.

RESULTS

The mean [standard deviation (SD)] ages of the patients were 62 (21) years and 60 (19) years in the control and treated groups, respectively.

CONCLUSION

The change in serum level of vitamin D was statistically significant in the treatment group but not in the control group. The serum level of leptin was reduced in the treatment group, while the serum level of adiponectin increased significantly, but none of these changes were statistically significant in the control group. This study showed that vitamin D administration is associated with an increase in adiponectin and a decrease in leptin level in ESRD patients.

RNA-Seq Analysis of Abdominal Fat in Genetically Fat and Lean Chickens Highlights a Divergence in Expression of Genes Controlling Adiposity, Hemostasis, and Lipid Metabolism

Genetic selection for enhanced growth rate in meat-type chickens (Gallus domesticus) is usually accompanied by excessive adiposity, which has negative impacts on both feed efficiency and carcass quality. Enhanced visceral fatness and several unique features of avian metabolism (i.e., fasting hyperglycemia and insulin insensitivity) mimic overt symptoms of obesity and related metabolic disorders in humans. Elucidation of the genetic and endocrine factors that contribute to excessive visceral fatness in chickens could also advance our understanding of human metabolic diseases. Here, RNA sequencing was used to examine differential gene expression in abdominal fat of genetically fat and lean chickens, which exhibit a 2.8-fold divergence in visceral fatness at 7 wk. Ingenuity Pathway Analysis revealed that many of 1687 differentially expressed genes are associated with hemostasis, endocrine function and metabolic syndrome in mammals. Among the highest expressed genes in abdominal fat, across both genotypes, were 25 differentially expressed genes associated with de novo synthesis and metabolism of lipids. Over-expression of numerous adipogenic and lipogenic genes in the FL chickens suggests that in situ lipogenesis in chickens could make a more substantial contribution to expansion of visceral fat mass than previously recognized. Distinguishing features of the abdominal fat transcriptome in lean chickens were high abundance of multiple hemostatic and vasoactive factors, transporters, and ectopic expression of several hormones/receptors, which could control local vasomotor tone and proteolytic processing of adipokines, hemostatic factors and novel endocrine factors. Over-expression of several thrombogenic genes in abdominal fat of lean chickens is quite opposite to the pro-thrombotic state found in obese humans. Clearly, divergent genetic selection for an extreme (2.5-2.8-fold) difference in visceral fatness provokes a number of novel regulatory responses that govern growth and metabolism of visceral fat in this unique avian model of juvenile-onset obesity and glucose-insulin imbalance.

Association between Vitamin D and Adiponectin and Its Relationship with Body Mass Index: The META-Health Study

Background: Low vitamin D and adiponectin levels are both associated with obesity and cardiovascular disease. Previous studies have indicated that vitamin D levels are directly associated with adiponectin, and that this association varies across body mass index (BMI) categories; stronger with increasing BMI. Few studies examined this association in African-Americans (AA), known to have lower levels of vitamin D and adiponectin, and in whites.

Methods: We assessed whether serum vitamin D is associated with serum adiponectin in a biracial population-based sample. Cross-sectional analyses were performed on 426 non-diabetic participants (218 whites and 208 AA) from the META-Health Study, a random sample from the metro Atlanta. Age-adjusted correlations and multivariable linear regression were used for analyses. We investigated the effect modification of the BMI categories of lean, overweight, and obese as defined by standard cut-points (25 and 30 kg/m²).

Results: The mean (SD) age of our study sample was 50.5 (9) years. The mean (SD) levels of vitamin D were 27.4 (9.8) ng/mL in white women, 25.5 (9.3) ng/mL in white men, 16.9 (7.3) ng/mL in AA women, and 18.8 (7.3) ng/mL in AA men. The mean (SD) levels of adiponectin were 17.0 (17.1) μg/mL in white women, 9.9 (11.3) μg/mL in white men, 6.6 (4.8) μg/mL in AA women, and 9.4 (11.6) μg/mL in AA men. Among lean white women (n = 63), there was a significant direct association between vitamin D and adiponectin (β = 0.02, p = 0.04) after adjustment for age, systolic blood pressure, HDL-cholesterol, triglycerides, income, and season of blood drawing. On the contrary, in lean AA women (n = 23), there was a significant inverse association (β = −0.06, p = 0.01).

Conclusion: The association of vitamin D and adiponectin is dependent on race, gender, and BMI category. Among lean white women, there was a significant direct association, whereas in lean AA women the association was inverse. No association was present among obese individuals.

Maternal high-fat diet programs rat offspring hypertension and activates the adipose renin-angiotensin system

OBJECTIVE

A maternal high-fat diet creates an increased risk of offspring obesity and systemic hypertension. Although the renal renin-angiotensin system (RAS) is known to regulate blood pressure, it is now recognized that the RAS is also activated in adipose tissue during obesity. We hypothesized that programmed offspring hypertension is associated with the activation of the adipose tissue RAS in the offspring of obese rat dams.

STUDY DESIGN

At 3 weeks of age, female rats were weaned to a high-fat diet (60% k/cal; n = 6) or control diet (10% k/cal; n = 6). At 11 weeks of age, these rats were mated and continued on their respective diets during pregnancy. After birth, at 1 day of age, subcutaneous adipose tissue was collected; litter size was standardized, and pups were cross-fostered to either control or high-fat diet dams, which created 4 study groups. At 21 days of age, offspring were weaned to control or high-fat diet. At 6 months of age, body fat and blood pressure were measured. Thereafter, subcutaneous and retroperitoneal adipose tissue was harvested from male offspring. Protein expression of adipose tissue RAS components were determined by Western blotting.

RESULTS

The maternal high-fat diet induced early and persistent alterations in offspring adipose RAS components. These changes were dependent on the period of exposure to the maternal high-fat diet, were adipose tissue specific (subcutaneous and retroperitoneal), and were exacerbated by a postnatal high-fat diet. Maternal high-fat diet increased adiposity and blood pressure in offspring, regardless of the period of exposure.

CONCLUSION

These findings suggest that programmed adiposity and the activation of the adipose tissue RAS are associated with hypertension in offspring of obese dams.

High levels of cystatin C predict the metabolic syndrome: the prospective Malmö Diet and Cancer Study

OBJECTIVE

Cystatin C is a novel marker of cardiovascular disease (CVD); however, the underlying mechanisms remain unclear. Here, we prospectively investigated whether plasma levels of cystatin C predict new-onset metabolic syndrome (MetS) as well as long-term progression and incidence of the different components of the MetS.

METHODS

Cystatin C was measured in 1502 individuals included in the Malmö Diet and Cancer cardiovascular cohort (mean age 56 years, 59% women) who were free from the MetS at baseline and subsequently underwent a follow-up examination after a median of 16 years. MetS was defined according to the NCEP-ATP-III guidelines. Logistic regression was used to adjust for covariates.

MAIN OUTCOME MEASURES

Metabolic syndrome and long-term progression as well as incidence of the different components of the MetS.

RESULTS

During follow-up, 428 subjects developed new-onset MetS. In age- and sex-adjusted analysis, compared with the lowest quartile of cystatin C, the odds ratios (95% confidence interval) for incident MetS in subjects with cystatin C levels in quartiles 2, 3 and 4 were 1.00 (0.71-1.40), 1.48 (1.06-2.07) and 1.91 (1.37-2.68), respectively (Ptrend  < 0.001); this linear association remained significant even after full multivariate adjustment (Ptrend  = 0.041). Interestingly, in this fully adjusted model, long-term progression of abdominal obesity was the only component of the MetS significantly associated with increasing quartiles of baseline cystatin C levels (Ptrend  = 0.008).

CONCLUSION

These findings suggest that cystatin C may adversely affect metabolic factors, particularly abdominal obesity, thus contributing to development of the MetS. Our results may help to explain the link between cystatin C and development of CVD.

The role of the renin-angiotensin-aldosterone system in obesity-related renal diseases

Obesity is an independent risk factor for the development and progression of chronic kidney disease and one of the emerging reasons for end-stage renal disease owing to its dramatic increase worldwide. Among the potential underlying pathophysiologic mechanisms, activation of the renin-angiotensin-aldosterone-system (RAAS) plays a central role. Increased angiotensin II (AngII) levels also are central in hypertension, dyslipidemia, and insulin resistance, which, taken together with obesity, represent the metabolic syndrome. Increased AngII levels contribute to hyperfiltration, glomerulomegaly, and subsequent focal glomerulosclerosis by altering renal hemodynamics via afferent arteriolar dilation, together with efferent renal arteriolar vasoconstriction as well as by its endocrine and paracrine properties linking the intrarenal and the systemic RAAS, adipose tissue dysfunction, as well as insulin resistance and hypertension. The imbalance between increased AngII levels and the angiotensin converting enzyme 2/Ang (1-7)/Mas receptor axis additionally contributes to renal injury in obesity and its concomitant metabolic disturbances. As shown in several large trials and experimental studies, treatment of obesity by weight loss is associated with an improvement of kidney disease because it also is beneficial in dyslipidemia, hypertension, and diabetes. The most promising data have been seen by RAAS blockade, pointing to the central position of RAAS within obesity, kidney disease, and the metabolic syndrome.

The influence of sodium- and calcium-regulatory hormone interventions on adipocytokines in obesity and diabetes

OBJECTIVE

The renin-angiotensin-aldosterone system (RAAS), vitamin D, and parathyroid hormone have all been implicated as regulators of adipocytokines and inflammation. We evaluated human interventional study protocols to investigate whether controlled modulations of these calcium- and sodium-regulatory hormones could influence adipocytokines and inflammation in obesity and diabetes.

METHODS

Post-hoc analyses of two separate human protocols (Protocol 1, n=14; Protocol 2, n=24) conducted in a clinical research setting after rigorous control of diet, posture, medications, and diurnal rhythm, were performed. Protocol 1 evaluated obese hypertensives with vitamin D deficiency who received an infusion of angiotensin II (AngII) before and after 1month of vitamin D3 therapy. Protocol 2 evaluated obese subjects with type 2 diabetes who also received AngII. Adipocytokines and inflammatory markers were measured before and after vitamin D3 therapy, and also before and after infusions of AngII.

RESULTS

Vitamin D3 therapy significantly raised 25(OH)D and 1,25(OH)2D concentrations, and lowered parathyroid hormone, but had no effect on concentrations of adiponectin, resistin, leptin, IL-6, PAI-1, urinary TGFβ1, or HOMA-IR. AngII infusions, despite significant elevations in blood pressure and serum aldosterone, did not influence adipocytokine concentrations in either protocol.

CONCLUSION

In contrast to prior studies conducted in healthy populations, or those that could not control major regulators of the RAAS or adipocytokines, we observed that robust modulations in calcium- and sodium-regulatory hormones did not influence adipocytokines or inflammation in obesity or diabetes. Adipose-tissue physiology in these conditions may alter the hormonal regulation of inflammatory parameters.

Angiotensin-converting enzyme inhibition reduces food intake and weight gain and improves glucose tolerance in melanocortin-4 receptor deficient female rats

Functional loss of melanocortin-4 receptor (MC4R) activity leads to hyperphagia and an obese, glucose intolerant phenotype. We have previously established that inhibition of angiotensin-converting enzyme (ACE) reduces food intake, body weight and glucose homeostasis in diet-induced obesity. The current study assessed the effect of ACE inhibitor treatment in MC4R-deficient female rats on body weight, adiposity and glucose tolerance. Rats homozygous (HOM) for a loss of function Mc4r mutation had an obese phenotype relative to their wildtype (WT) littermates. Inhibition of ACE for 8weeks produced reductions in body weight gain in both HOM and WT rats; however, food intake was only reduced in HOM rats. Weight loss following ACE inhibitor treatment was specific to fat mass while lean mass was unaffected. HOM rats were severely glucose intolerant and insensitive to exogenous insulin injection, and treatment with an ACE inhibitor improved both glucose tolerance and insulin sensitivity in HOM rats although not fully to that of the level of WT rats. The current study indicates that HOM rats are sensitive to the anorectic effects of ACE inhibition, unlike their WT littermates. This resulted in a more rapid reduction in body weight gain and a more substantial loss of adipose mass in HOM animals, relative to WT animals, treated with an ACE inhibitor. Overall, these data demonstrate that MC4R signaling is not required for weight loss following treatment with an ACE inhibitor.

An increased circulating angiotensin II concentration is associated with hypoadiponectinemia and postprandial hyperglycemia in men with nonalcoholic fatty liver disease

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) is a condition associated with type 2 diabetes (T2D). Insulin resistance, a common pathogenesis of NAFLD and T2D, is partially caused by alterations in angiotensin II (Ang II) and is accompanied by hypoadiponectinemia. We aimed to investigate whether the circulating Ang II and adiponectin concentrations are related to hyperglycemia in male NAFLD patients.

METHODS

Thirty-five controls and 85 NAFLD patients without prior known T2D were enrolled. All participants were non-smoking men who performed 75-g oral glucose tolerance tests. According to the American Diabetes Association (ADA) criteria, the NAFLD patients were divided into the euglycemia and hyperglycemia groups. The NAFLD patients with hyperglycemia were further divided into the isolated impaired fasting glucose (I-IFG) and postprandial hyperglycemia subgroups. The fasting serum Ang II and adiponectin concentrations were measured.

RESULTS

Among the 85 NAFLD patients, 40 (47%) had hyperglycemia, including I-IFG (18%) and postprandial hyperglycemia (29%). The serum Ang II concentrations in the euglycemia and hyperglycemia groups were significantly higher than those observed in the control and euglycemia groups, respectively; whereas the serum adiponectin concentrations were significantly lower. The serum Ang II concentrations were significantly higher in the postprandial hyperglycemia subgroup than in the I-IFG subgroup. The serum Ang II and adiponectin concentrations were found to be independent predictors of hyperglycemia in the NAFLD patients. The serum Ang II concentration was significantly associated with the serum adiponectin and 2-hour postprandial glucose concentrations in the NAFLD patients.

CONCLUSION

An increased circulating Ang II concentration is associated with hypoadiponectinemia and postprandial hyperglycemia in male NAFLD patients and may be involved in the pathogenesis of T2D in NAFLD patients.

Transcriptomic and metabolomic profiling of chicken adipose tissue in response to insulin neutralization and fasting

BACKGROUND

Domestic broiler chickens rapidly accumulate adipose tissue due to intensive genetic selection for rapid growth and are naturally hyperglycemic and insulin resistant, making them an attractive addition to the suite of rodent models used for studies of obesity and type 2 diabetes in humans. Furthermore, chicken adipose tissue is considered as poorly sensitive to insulin and lipolysis is under glucagon control. Excessive fat accumulation is also an economic and environmental concern for the broiler industry due to the loss of feed efficiency and excessive nitrogen wasting, as well as a negative trait for consumers who are increasingly conscious of dietary fat intake. Understanding the control of avian adipose tissue metabolism would both enhance the utility of chicken as a model organism for human obesity and insulin resistance and highlight new approaches to reduce fat deposition in commercial chickens.

RESULTS

We combined transcriptomics and metabolomics to characterize the response of chicken adipose tissue to two energy manipulations, fasting and insulin deprivation in the fed state. Sixteen to 17 day-old commercial broiler chickens (ISA915) were fed ad libitum, fasted for five hours, or fed but deprived of insulin by injections of anti-insulin serum. Pair-wise contrasts of expression data identified a total of 2016 genes that were differentially expressed after correction for multiple testing, with the vast majority of differences due to fasting (1780 genes). Gene Ontology and KEGG pathway analyses indicated that a short term fast impacted expression of genes in a broad selection of pathways related to metabolism, signaling and adipogenesis. The effects of insulin neutralization largely overlapped with the response to fasting, but with more modest effects on adipose tissue metabolism. Tissue metabolomics indicated unique effects of insulin on amino acid metabolism.

CONCLUSIONS

Collectively, these data provide a foundation for further study into the molecular basis for adipose expansion in commercial poultry and identify potential pathways through which fat accretion may be attenuated in the future through genetic selection or management practices. They also highlight chicken as a useful model organism in which to study the dynamic relationship between food intake, metabolism, and adipose tissue biology.

The renin-angiotensin system: a link between obesity, inflammation and insulin resistance

The renin-angiotensin system (RAS) is classically known for its role in regulation of blood pressure, fluid and electrolyte balance. Recently, several local RASs in organs such as brain, heart, pancreas and adipose tissue have also been identified. Evidence from clinical trials suggests that in addition to anti-hypertensive effects, pharmacological inhibition of RAS also provides protection against the development of type-2 diabetes. Moreover, animal models with targeted inactivation of RAS genes exhibit improved insulin sensitivity and are protected from high-fat diet-induced obesity and insulin resistance. Because there is evidence for RAS overactivation in obesity, it is possible that RAS is a link between obesity and insulin resistance. This review summarizes the evidence and mechanistic insights on the associations between RAS, obesity and insulin resistance, with special emphasis on the role of adipose tissue RAS in the pathogenesis of metabolic derangements in obesity.

Overproduction of angiotensinogen from adipose tissue induces adipose inflammation, glucose intolerance, and insulin resistance

Although obesity is associated with overactivation of the white adipose tissue (WAT) renin-angiotensin system (RAS), a causal link between the latter and systemic insulin resistance is not established. We tested the hypothesis that overexpression of angiotensinogen (Agt) from WAT causes systemic insulin resistance via modulation of adipose inflammation. Glucose tolerance, systemic insulin sensitivity, and WAT inflammatory markers were analyzed in mice overexpressing Agt in the WAT (aP2-Agt mice). Proteomic studies and in vitro studies using 3T3-L1 adipocytes were performed to build a mechanistic framework. Male aP2-Agt mice exhibited glucose intolerance, insulin resistance, and lower insulin-stimulated glucose uptake by the skeletal muscle. The difference in glucose tolerance between genotypes was normalized by high-fat (HF) feeding, and was significantly improved by treatment with angiotensin-converting enzyme (ACE) inhibitor captopril. aP2-Agt mice also had higher monocyte chemotactic protein-1 (MCP-1) and lower interleukin-10 (IL-10) in the WAT, indicating adipose inflammation. Proteomic studies in WAT showed that they also had higher monoglyceride lipase (MGL) and glycerol-3-phosphate dehydrogenase levels. Treatment with angiotensin II (Ang II) increased MCP-1 and resistin secretion from adipocytes, which was prevented by cotreating with inhibitors of the nuclear factor-κB (NF-κB) pathway or nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. In conclusion, we show for the first time that adipose RAS overactivation causes glucose intolerance and systemic insulin resistance. The mechanisms appear to be via reduced skeletal muscle glucose uptake, at least in part due to Ang II-induced, NADPH oxidase and NFκB-dependent increases in WAT inflammation.

The independent association between 25-hydroxyvitamin D and adiponectin and its relation with BMI in two large cohorts: the NHS and the HPFS

Low 25-hydroxyvitamin D (25(OH)D) and adiponectin levels are both associated with obesity and cardiovascular disease. Cross-sectional studies have suggested that 25(OH)D concentrations are positively associated with adiponectin, and that this relation may strengthen with increasing BMI. However, these studies had small samples sizes and did not account for many known confounders of adiponectin levels. We evaluated whether 25(OH)D was independently associated with circulating adiponectin in two large populations, and whether BMI modified this relationship. Cross-sectional analyses were performed on 1,206 women from the Nurses' Health Study I (NHS) and 439 men from the Health Professionals Follow-Up Study. Multivariable linear regression was used to analyze the independent association between 25(OH)D and adiponectin after controlling for potential confounders. Effect modification by BMI was examined by creating interaction terms between vitamin D and BMI. 25(OH)D concentrations were positively associated with circulating adiponectin in univariate analyses, and also independently associated with adiponectin after multivariable adjustments in both populations (women: β = 0.06, P < 0.001; men: β = 0.07, P < 0.05). BMI did not significantly modify the relation between 25(OH)D and adiponectin in either population. Higher 25(OH)D concentrations were independently associated with higher adiponectin concentrations in large populations of women and men. Since lower levels of 25(OH)D and adiponectin are associated with higher cardio-metabolic risk, assessing the effect of vitamin D supplementation on adiponectin levels is warranted.

Renin-angiotensin system activity in vitamin D deficient, obese individuals with hypertension: An urban Indian study

BACKGROUND

Elevated renin-angiotensin-aldosterone system (RAAS) activity is an important mechanism in the development of hypertension. Both obesity and 25-hydroxy vitamin D [25(OH)D] deficiency have been associated with hypertension and augmented renin-angiotensin system (RAS) activity. We tried to test the hypothesis that vitamin D deficiency and obesity are associated with increased RAS activity in Indian patients with hypertension.

MATERIALS AND METHODS

Fifty newly detected hypertensive patients were screened. Patients with secondary hypertension, chronic kidney disease, or coronary artery disease were excluded. Patients underwent measurement of vitamin D and plasma renin and plasma aldosterone concentrations. They were divided into three groups according to their baseline body mass index (BMI; normal <25 kg/m(2), overweight 25-29.9 kg/m(2) and obese ≥30 kg/m(2)) and 25(OH)D levels (deficient <20 ng/ml, insufficient 20-29 ng/ml and optimal ≥30 ng/ml).

RESULTS

A total of 50 (male:female - 32:18) patients were included, with a mean age of 49.5 ± 7.8 years, mean BMI of 28.3 ± 3.4 kg/m(2) and a mean 25(OH)D concentration of 18.5 ± 6.4 ng/ml. Mean systolic blood pressure (SBP) was 162.4 ± 20.2 mm Hg and mean diastolic blood pressure (DBP) was 100.2 ± 11.2 mm Hg. All the three blood pressure parameters [SBP, DBP and mean arterial pressure (MAP)] were significantly higher among individuals with lower 25(OH)D levels. The P values for trends in SBP, DBP and MAP were 0.009, 0.01 and 0.007, respectively. Though all the three blood pressure parameters (SBP, DBP and MAP) were higher among individuals with higher BMIs, they were not achieving statistical significance. Increasing trends in PRA and PAC were noticed with lower 25(OH)D and higher BMI levels.

CONCLUSION

Vitamin D deficiency and obesity are associated with stimulation of RAAS activity. Vitamin D supplementation along with weight loss may be studied as a therapeutic strategy to reduce tissue RAS activity in individualswith Vitamin D deficiency and obesity.

The influence of body mass index and renin-angiotensin-aldosterone system activity on the relationship between 25-hydroxyvitamin D and adiponectin in Caucasian men

OBJECTIVE

Previous studies have suggested that circulating adiponectin concentrations are associated positively with vitamin D and negatively with body mass index (BMI) but have not accounted for the influence of the renin-angiotensin-aldosterone system (RAAS) in this relationship. This is particularly relevant because increased RAAS activity is associated with obesity and is known to lower adiponectin levels. We evaluated the association between adiponectin and 25-hydroxyvitamin D (25(OH)D) after controlling RAAS activity with dietary sodium equilibration and also evaluated whether this relationship was influenced by BMI.

DESIGN

Cross-sectional study of 115 hypertensive Caucasian men from the Hypertensive Pathotype Consortium.

METHODS

To manipulate RAAS activity, all subjects underwent 1 week of high dietary sodium (HS) diet to suppress RAAS and 1 week of low dietary sodium (LS) diet to stimulate RAAS. Linear regression was used to evaluate the association between adiponectin and 25(OH)D, and the effect of BMI on this relationship, in each dietary condition.

RESULTS

Adiponectin was higher on HS, where circulating RAAS activity was low, when compared with LS (HS=2.9 versus LS=2.4 μg/ml, P<0.0001). 25(OH)D levels were positively associated with adiponectin, and BMI was a statistically significant effect modifier of the relationship between 25(OH)D and adiponectin on both diets (P interaction <0.01 between BMI and 25(OH)D).

CONCLUSIONS

Higher 25(OH)D concentrations were independently associated with higher adiponectin levels, particularly when BMI was high. Dietary sodium balance and circulating RAAS activity did not appear to affect this relationship. Future studies should explore whether vitamin D supplementation increases adiponectin levels in obesity.

The association of plasma resistin with dietary sodium manipulation, the renin-angiotensin-aldosterone system, and 25-hydroxyvitamin D3 in human hypertension

OBJECTIVE

Both resistin and vitamin D have been associated with the renin-angiotensin-aldosterone system (RAAS). We investigated the association between resistin and the RAAS, and resistin and vitamin D under controlled dietary sodium conditions.

DESIGN

Retrospective cross-sectional study of subjects from the HyperPATH Consortium, who were maintained in high dietary sodium (HS) and low dietary sodium (LS) balance for 1 week each.

PATIENTS

Caucasian subjects with hypertension (n=177).

MEASUREMENTS

25-Hydroxyvitamin D (25[OH]D) levels were used to assess vitamin D status. Plasma resistin and RAAS measures were evaluated on each dietary intervention.

RESULTS

Resistin levels were significantly higher in LS, where RAAS activity was high, when compared with HS balance, where RAAS activity was suppressed (6.36 vs 5.86 μg/l, P < 0.0001); however, resistin concentrations were not associated with plasma renin activity or serum aldosterone on either diet. 25(OH)D levels were positively and independently associated with resistin in both dietary conditions (HS: β=0.400, P-trend=0.027; LS: β=0.540, P-trend=0.014).

CONCLUSIONS

Dietary sodium loading reduced resistin levels, possibly by suppressing the RAAS; however, circulating RAAS components were not related to resistin concentrations within each specific dietary sodium condition. 25(OH)D was positively associated with resistin and may be involved in resistin regulation through an unknown mechanism. Further studies to understand resistin regulation in human hypertension better are warranted.

Energy-restricted high-fat diets only partially improve markers of systemic and adipose tissue inflammation

This study aimed at investigating whether the weight loss due to energy-restricted high-fat diets is accompanied with parallel improvements in metabolic markers and adipose tissue inflammation. Eight-week-old C57BL/6J mice were given free access to a low-fat (LF) or a high-fat (45% of energy from fat-HF) diet for 6 months. Restricting intake of the HF diet by 30% (HFR) during the last 2 months of the HF feeding trial decreased fasting plasma insulin, homeostasis model assessment of insulin resistance (HOMA(IR)), and plasma triglyceride levels and improved hepatic steatosis compared to ad libitum HF feeding, indicating an improved metabolic profile. Further, analysis of gonadal white adipose tissue (GWAT) gene expression by microarray and quantitative PCR analyses demonstrated that HFR downregulated expression of genes linked to cell and focal adhesion, cytokine-cytokine receptor interaction, and endoplasmic reticulum (ER)-associated degradation pathway. However, HFR had no effect on circulating plasminogen activator inhibitor-1 (PAI-1) and nonesterified fatty acid levels, which were persistently higher in both HF and HFR groups compared to the LF group. Furthermore, HFR had a negative effect on plasma total adiponectin level. Finally, while HFR decreased GWAT monocyte chemotactic protein-1 (MCP-1), interleukin-2 (IL-2), and PAI-1 levels, it did not affect several other cytokines including granulocyte-macrophage colony-stimulating factor, interferon-γ, IL-1β, IL-6, and IL-10. In summary, energy-restricted high-fat diets improve insulin sensitivity, while only partially improving markers of systemic and adipose tissue inflammation. In conclusion, our study supports the recommended low-fat intake for overall cardiovascular health.

Scope and mechanisms of obesity-related renal disease

PURPOSE OF REVIEW

Obesity is established as an important contributor of increased diabetes mellitus, hypertension, and cardiovascular disease, all of which can promote chronic kidney disease (CKD). Recently, there is a growing appreciation that, even in the absence of these risks, obesity itself significantly increases CKD and accelerates its progression.

RECENT FINDINGS

Experimental and clinical studies reveal that adipose tissue, especially visceral fat, elaborates bioactive substances that contribute to the pathophysiologic renal hemodynamic and structural changes leading to obesity-related nephropathy. Adipocytes contain all the components of the renin-angiotensin-aldosterone system, plasminogen activator inhibitor, as well as adipocyte-specific metabolites such as free fatty acids, leptin, and adiponectin, which affect renal function and structure. In addition, fat is infiltrated by macrophages that can alter their phenotype and foster a proinflammatory milieu, which advances pathophysiologic changes in the kidney associated with obesity.

SUMMARY

Obesity is an independent risk factor for development and progression of renal damage. Although the current therapies aimed at slowing progressive renal damage include reduction in weight and rely on inhibition of the renin-angiotensin system, the approach will likely be supplemented by interventions aimed at obesity-specific targets including adipocyte-driven cytokines and inflammatory factors.

Expression changes of angiotensin II pathways and bioactive mediators during human preadipocytes-visceral differentiation

Obesity is a worldwide serious health problem; and it may result in a wide range of complications, such as hypertension and diabetes mellitus. As a consequence, molecular identification on the differentiation of preadipocytes and the generation of bioactive mediators is crucial in understanding the formation and development of obesity and obesity-associated health problems. In addition, exhaustive exhibition and purposeful control of adipocytes formation also play critical roles in the plastic and reconstructive surgical procedures. The primary purpose of this study was to exhibit the expression changes of angiotensin II (Ang II) pathways and 2 vital adipokines, leptin and resistin, during human preadipocytes-visceral differentiation by real-time quantitative reverse transcription-polymerase chain reaction. The present result indicated that the generation of Ang II during preadipocytes differentiation was achieved through both renin-angiotensin system pathway and non-renin-angiotensin system pathways, and the latter may be more important in this process. Gene expression of Ang II receptor type 1 and 2 increased in the initial phase of differentiation and then quickly decreased after 9 days. Moreover, the expression of both leptin and resistin increased significantly during preadipocyte-adipocyte conversion. The present work provided a fundamental understanding of human visceral preadipocytes differentiation molecularly. It may promote the understanding of obesity and obesity-associated diseases to some extent. However, there is still a long way to go to treat obesity and its complications effectively; and more efforts should be devoted urgently.

Combination of captopril and allopurinol retards fructose-induced metabolic syndrome

BACKGROUND

Both ACE inhibitors and allopurinol have been shown to partially prevent metabolic syndrome induced by fructose. We tested the hypothesis that combined therapy might be more effective at blocking the metabolic syndrome induced with fructose.

METHODS

Male Sprague-Dawley rats were fed a high fructose diet with or without allopurinol, captopril, or the combination for 20 weeks. A control group received a normal diet. All groups were pair-fed to assure equivalent caloric intake.

RESULTS

Despite reduced energy intake, the fructose-fed rats developed features of metabolic syndrome including elevated blood pressure, abdominal obesity, hypertriglyceridemia, hyperuricemia and hyperinsulinemia. While both allopurinol and captopril alone tended to reduce features of the metabolic syndrome, the combined therapy was synergistic, with significant reduction in blood pressure, less accumulation of abdominal fat, an improvement in the dyslipidemia and a complete prevention of insulin resistance.

CONCLUSION

A high fructose diet can induce metabolic syndrome even in the setting of caloric restriction. Captopril and allopurinol synergistically reduce features of the metabolic syndrome, especially hypertension, insulin resistance and dyslipidemia. Combination allopurinol and ACE inhibitor therapy might provide a superior means to prevent diabetes and cardiovascular disease.

Aliskiren reduces body-weight gain, adiposity and plasma leptin during diet-induced obesity

BACKGROUND AND PURPOSE

Overfeeding increases adipose tissue mass and leptin production and up-regulates the renin-angiotensin system in adipose tissue in rodents. Here, we determined the effect of chronic treatment with the renin inhibitor, aliskiren, in a model of diet-induced obesity in mice, on: (i) body weight, adipose tissue weight and plasma leptin; (ii) food intake and caloric efficiency; and (iii) angiotensin II (Ang II) in adipose tissue.

EXPERIMENTAL APPROACH

Four-week-old C57BL/6J mice (n= 40) received aliskiren (50 mg.kg(-1).day(-1); 6 weeks) by means of a subcutaneous osmotic Alzet minipump. Animals were given either a low-fat (10% kcal from fat) or a high-fat diet (45% kcal from fat) during this period. Food-intake and body-weight variation were monitored during treatment.

KEY RESULTS

In addition to a decrease of plasma renin activity, aliskiren reduced body-weight gain, adipose pads and plasma leptin concentration, independent of the diet. In adipose tissue, local concentrations of Ang II were also reduced by aliskiren.

CONCLUSIONS AND IMPLICATIONS

Aliskiren limited the gain of adiposity in young mice. This effect was not due to changes in food intake or caloric efficiency and might be related to a down-regulation of the local renin-angiotensin system in adipose tissue. These effects were accompanied by reduced plasma leptin levels. As Ang II favours differentiation of adipocytes, it is possible that the decreased adipose tissue was linked to changes in adipocyte size and number.

Obesity-related focal and segmental glomerulosclerosis: normalization of proteinuria in an adolescent after bariatric surgery

Obesity-related glomerulopathy (ORG) is a secondary form of focal and segmental glomerulosclerosis (FSGS) occurring in severely obese patients. A significant percentage of individuals with ORG will develop renal insufficiency or end stage renal disease. We report here a 17-year-old girl with morbid obesity (body mass index 56.8 kg/m(2)) and ORG presenting with nephrotic range proteinuria, who failed to improve following treatment with diet, exercise and angiotensin-converting enzyme inhibitor (ACEi)/angiotensin receptor blocker (ARB) therapy. Laparoscopic gastric bypass surgery was performed, and within 2 weeks following the surgery, the patient had lost 5.7 kg body weight and showed a remarkable decrease in protein excretion to one tenth of pre-surgery levels. More than 1 year after surgery, the patient's urine protein and kidney function have remained normal while off renin-angiotensin system inhibition therapy. This is the first report of successful use of gastric bypass surgery for obesity-related glomerulopathy in an adolescent. We propose that gastric bypass surgery be considered for patients with ORG.

Deficiency of angiotensin type 2 receptor rescues obesity but not hypertension induced by overexpression of angiotensinogen in adipose tissue

Increased angiotensinogen (AGT) production by white adipose tissue has been related to not only obesity but also hypertension. Several studies have highlighted the importance of the angiotensin II type 2 receptor (AT2) in the regulation of blood pressure and fat mass, but the relevance of this transporter in a physiopathological model of increased AGT production, as it occurs in obesity, has not yet been investigated. We used transgenic mice that display either a deletion of AT2 (AT2 KO), an overexpression of AGT (OVEX), or both compound mutants (KOVEX). Results demonstrated that adipocyte hypertrophy and increased lipogenic gene expression induced by adipose AGT overproduction was rescued by deletion of AT2. In line with AGT overexpression, KOVEX and OVEX mice have similar increased plasma AGT levels. However, KOVEX mice display a higher blood pressure than OVEX mice. In kidney, renin expression was clearly reduced in OVEX mice, and its expression was normalized in KOVEX mice. Taken together, we demonstrated that the loss of AT2 expression was sufficient to rescue obesity induced by adipose tissue AGT overexpression and confirmed the necessary role of AT2 for the onset of obesity in this model. Furthermore, despite a reduction of adipose mass in KOVEX, AT2 deficiency caused increased renin production, further worsening the hypertension caused by AGT overexpression.

Renin dynamics in adipose tissue: adipose tissue control of local renin concentrations

The renin-angiotensin system (RAS) has been implicated in a variety of adipose tissue functions, including tissue growth, differentiation, metabolism, and inflammation. Although expression of all components necessary for a locally derived adipose tissue RAS has been demonstrated within adipose tissue, independence of local adipose RAS component concentrations from corresponding plasma RAS fluctuations has not been addressed. To analyze this, we varied in vivo rat plasma concentrations of two RAS components, renin and angiotensinogen (AGT), to determine the influence of their plasma concentrations on adipose and cardiac tissue levels in both perfused (plasma removed) and nonperfused samples. Variation of plasma RAS components was accomplished by four treatment groups: normal, DOCA salt, bilateral nephrectomy, and losartan. Adipose and cardiac tissue AGT concentrations correlated positively with plasma values. Perfusion of adipose tissue decreased AGT concentrations by 11.1%, indicating that adipose tissue AGT was in equilibrium with plasma. Cardiac tissue renin levels positively correlated with plasma renin concentration for all treatments. In contrast, adipose tissue renin levels did not correlate with plasma renin, with the exception of extremely high plasma renin concentrations achieved in the losartan-treated group. These results suggest that adipose tissue may control its own local renin concentration independently of plasma renin as a potential mechanism for maintaining a functional local adipose RAS.

The metabolic syndrome

The "metabolic syndrome" (MetS) is a clustering of components that reflect overnutrition, sedentary lifestyles, and resultant excess adiposity. The MetS includes the clustering of abdominal obesity, insulin resistance, dyslipidemia, and elevated blood pressure and is associated with other comorbidities including the prothrombotic state, proinflammatory state, nonalcoholic fatty liver disease, and reproductive disorders. Because the MetS is a cluster of different conditions, and not a single disease, the development of multiple concurrent definitions has resulted. The prevalence of the MetS is increasing to epidemic proportions not only in the United States and the remainder of the urbanized world but also in developing nations. Most studies show that the MetS is associated with an approximate doubling of cardiovascular disease risk and a 5-fold increased risk for incident type 2 diabetes mellitus. Although it is unclear whether there is a unifying pathophysiological mechanism resulting in the MetS, abdominal adiposity and insulin resistance appear to be central to the MetS and its individual components. Lifestyle modification and weight loss should, therefore, be at the core of treating or preventing the MetS and its components. In addition, there is a general consensus that other cardiac risk factors should be aggressively managed in individuals with the MetS. Finally, in 2008 the MetS is an evolving concept that continues to be data driven and evidence based with revisions forthcoming.

Association of visceral and subcutaneous adiposity with kidney function

BACKGROUND AND OBJECTIVES

Obesity is a risk factor for incident chronic kidney disease (CKD). Visceral (VAT) and subcutaneous adipose tissue (SAT) may confer differential metabolic risk profiles. The relations of VAT and SAT were analyzed with CKD as estimated by creatinine- and cystatin-based estimating equations.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Participants from the Framingham Offspring Study who underwent abdominal computed tomography for VAT and SAT quantification were included (n = 1299; 53% women; mean age 60 yr). CKD was defined as estimated GFR <60 ml/min per 1.73 m(2), as estimated using creatinine (n = 89) in the Modification of Diet in Renal Disease (MDRD) formula or by cystatin C (n = 136). Regression models evaluated the cross-sectional relations between VAT and SAT with CKD and cystatin C, with age and gender adjustment and cardiovascular risk factor adjustment.

RESULTS

Neither VAT nor SAT was associated with CKD as estimated by the MDRD equation. In contrast, both VAT and SAT were associated with CKD when defined using cystatin-based equations. The estimated decrease in estimated GFR by cystatin C per 1-SD increase of VAT was 1.9 ml/min per 1.73 m(2) and for SAT was 2.6 ml/min per 1.73 m(2) in a multivariable-adjusted model.

CONCLUSIONS

VAT and SAT were associated with CKD when defined using cystatin C estimating equations but not when using a creatinine-based estimating equation. Mechanisms linking adipose tissue to cystatin C warrant further research.

Local adipose tissue renin-angiotensin system

A local renin-angiotensin system (RAS) has been proposed in adipocytes. Adipocytes are a suggested source of components of the RAS, with regulation of their production related to obesity-hypertension. Both angiotensin type 1 and 2 receptors have been localized to adipocytes. Angiotensin II has been demonstrated to regulate adipocyte growth and differentiation, lipid metabolism, and expression and release of adipokines and RAS components, and to promote oxidative stress. Differences in regional expression of RAS components in visceral versus subcutaneous adipose tissue have been suggested as a link between abdominal obesity and cardiovascular disease. Finally, several studies support antihypertensive efficacy of RAS blockade in patients with type 2 diabetes and obesity. Future studies should address the role of adipocyte-specific deficiency of RAS components to definitively determine the relevance of the adipose RAS to normal physiology and to the development of hypertension.

Adiposity gain during childhood, ACE I/D polymorphisms and metabolic outcomes

We aimed to (i) determine the relative importance of childhood gain in upper body adiposity for insulin resistance (IR) and triglyceridemia (TG); (ii) examine whether the associations between adiposity and metabolic indices were more evident in those with the ACE DD genotype. We examined a birth cohort study of 292 children with measures in the neonatal period (day 4) including subscapular and triceps skinfolds; repeat skinfold measures at age 8, cardiorespiratory (CR) fitness, IR by the homeostasis model assessment (HOMA) equation (HOMA-IR) and serum triglyceride (TG) concentrations and measures of ACE I/D gene variants. A multiple linear regression analysis incorporating a life course approach was undertaken. Childhood gain in upper body adiposity was positively associated with HOMA-IR and TG independently of neonatal skinfolds (P < or = 0.02). The magnitude of these associations was higher among those of the ACE DD genotype. For example, subscapular skinfold gain was not strongly associated with HOMA-IR or TG among those with II or ID genotype (b = 0.03, P = 0.05; b = 0.02, P = 0.18 respectively) but was positively associated among those with the DD genotype (b = 0.11, P = 0.001; b = 0.08, P = 0.003); difference in effect P = 0.05; P = 0.01 respectively. Upper body fat accumulation during childhood was positively associated with HOMA-IR and TG independently of neonatal skinfolds. Further, the stronger associations for those with the ACE DD genotype is consistent with randomised controlled trial findings that ACE inhibition is associated with a reduced risk of developing type 2 diabetes. Further work is required to confirm and extend these findings.

Effect of ARB on expression of CD68 and MCP-1 in adipose tissue of rats on long-term high fat diet

In adipose tissue of rats on long-term high fat diet, the inflammatory changes the roles of angiotensin receptor blocker (ARB) in pimelitis and insulin resistance (IR) were observed. IR rat model was established by feeding high calorie and high fat diet. The change in insulin sensitivity was detected by euglycemic-hyperinsulinemic clamp technique 8 weeks after intervention by valsartan. The expression levels of CD68 and MCP-1 mRNA and proteins in adipose tissue were examined by RT-PCR and immunohistochemistry respectively. The parameters of blood glucose, insulin and blood lipid were analyzed. The results showed that in high fat diet group intra-abdominal obesity developed, the content of visceral fat and the number of inflammatory cells in local adipose tissue were significantly increased (P<0.01), the levels of serum triglyceride, free fatty acids and fasting serum insulin were markedly increased, the insulin sensitivity was significantly lowered (P<0.01), and the expression of CD68 and MCP-1 was significantly increased as compared with control group (P<0.01). In ARB interventional group, the content of visceral fat, the number of inflammatory cells and the expression of CD68 and MCP-1 in local adipose tissue were significantly reduced (all P<0.01), but the insulin sensitivity was significantly enhanced (P<0.01) as compared with high fat diet group. There were pimelitis and IR in rats with obesity induced by long-term high calorie and high fat diet. The ARB can significantly inhibit the infiltration of macrophages and the expression of MCP-1 in adipose tissue, thereby attenuating the inflammation and improving IR in rats.

Cardiotrophin-1 is expressed in adipose tissue and upregulated in the metabolic syndrome

Adipose tissue is a target for cardiotrophin-1 (CT-1), a cytokine member of the IL-6 family of cytokines that is involved in cardiac growth and dysfunction. However, it is unknown whether adipocytes are a source of CT-1 and whether CT-1 is overexpressed in diseases characterized by increased fat depots [i.e., the metabolic syndrome (MS)]. Thus this work aimed 1) to test whether adipose tissue expresses CT-1 and whether CT-1 expression can be modulated and 2) to compare serum CT-1 levels in subjects with and without MS diagnosed by National Cholesterol Education Program Adult Treatment Panel III criteria. Gene and protein expression of CT-1 was determined by real-time RT-PCR, ELISA, and Western blotting. CT-1 expression progressively increased, along with differentiation time from preadipocyte to mature adipocyte in 3T3-L1 cells. CT-1 expression was enhanced by glucose in a dose-dependent manner in these cells. mRNA and protein CT-1 expression was also demonstrated in human adipose biopsies. Immunostaining showed positive staining in adipocytes. Finally, increased CT-1 serum levels were observed in patients with MS compared with control subjects (127 +/- 9 vs. 106 +/- 4 ng/ml, P < 0.05). Circulating levels of CT-1 were associated with glucose levels (r = 0.2, P < 0.05). Taken together, our data suggest that adipose tissue can be recognized as a source of CT-1, which could account for the high circulating levels of CT-1 in patients with MS.