Mature adipocytes inhibit in vitro differentiation of human preadipocytes via angiotensin type 1 receptors

Angiotensin II directly impairs adipogenic differentiation of human preadipose cells

Angiotensin II reduces adipogenic differentiation of preadipose cells present in the stroma-vascular fraction of human adipose tissue, which also includes several cell types. Because of the ability of non-adipose lineage cells in the stroma-vascular fraction to respond to angiotensin II, it is not possible to unequivocally ascribe the anti-adipogenic response to a direct effect of this hormone on preadipose cells. Therefore, we used the human Simpson-Golabi-Behmel syndrome (SGBS) preadipocyte cell strain to investigate the consequences of angiotensin II treatment on adipogenic differentiation under serum-free conditions, by assessing expression of typical adipocyte markers perilipin and fatty acid-binding protein 4 (FABP4), at the transcript and protein level. Reverse transcription-polymerase chain reaction showed that perilipin and FABP4 transcripts were, respectively, reduced to 0.33 ± 0.07 (P < 0.05) and 0.41 ± 0.19-fold (P < 0.05) in SGBS cells induced to adipogenic differentiation in the presence of angiotensin II. Western Blot analysis corroborated reduction of the corresponding proteins to 0.23 ± 0.21 (P < 0.01) and 0.46 ± 0.30-fold (P < 0.01) the respective controls without angiotensin II. Angiotensin II also impaired morphological changes associated with early adipogenesis. Hence, we demonstrated that angiotensin II is able to directly reduce adipogenic differentiation of SGBS preadipose cells.

Modulation of glucose metabolism by the renin-angiotensin-aldosterone system

The renin-angiotensin-aldosterone system (RAAS) is an enzymatic cascade functioning in a paracrine and autocrine fashion. In animals and humans, RAAS intrinsic to tissues modulates food intake, metabolic rate, adiposity, insulin sensitivity, and insulin secretion. A large array of observations shows that dysregulation of RAAS in the metabolic syndrome favors type 2 diabetes. Remarkably, angiotensin-converting enzyme inhibitors, suppressing the synthesis of angiotensin II (ANG II), and angiotensin receptor blockers, targeting the ANG II type 1 receptor, prevent diabetes in patients with hypertensive or ischemic cardiopathy. These drugs interrupt the negative feedback loop of ANG II on the RAAS cascade, which results in increased production of angiotensins. In addition, they change the tissue expression of RAAS components. Therefore, the concept of a dual axis of RAAS regarding glucose homeostasis has emerged. The RAAS deleterious axis increases the production of inflammatory cytokines and raises oxidative stress, exacerbating the insulin resistance and decreasing insulin secretion. The beneficial axis promotes adipogenesis, blocks the production of inflammatory cytokines, and lowers oxidative stress, thereby improving insulin sensitivity and secretion. Currently, drugs targeting RAAS are not given for the purpose of preventing diabetes in humans. However, we anticipate that in the near future the discovery of novel means to modulate the RAAS beneficial axis will result in a decisive therapeutic breakthrough.

Blood pressure control and weight loss in overweight or obese patients with previously treated or untreated mild to moderate hypertension given valsartan: An open-label study comparing pretreatment and posttreatment values

BACKGROUND

Hypertension is associated with obesity. Recent studies have indicated that therapy with an angiotensin II antagonist, in addition to having an antihypertensive effect, may cause a reduction in body weight.

OBJECTIVE

The aim of this study was to assess the efficacy and tolerability of valsartan in the treatment of overweight or obese patients with mild to moderate essential hypertension.

METHODS

Overweight or obese outpatients aged 18 to <70 years with previously treated or untreated mild to moderate essential hypertension were eligible for this open-label study conducted at the Department of Internal Medicine and Aging, Clinica Medica II, Policlinico S. Orsola-Malpighi (Bologna, Italy). After a 1-week pharmacologic washout period, patients were treated with valsartan capsules at a fixed dosage of 80 mg once daily for 8 weeks. The dosage was increased to 160 mg once daily if, at 8 weeks, diastolic blood pressure (DBP) was not normalized; otherwise, the 80-mg/d dosage was maintained. Treatment was continued for an additional 16 weeks. Patients' heart rate, systolic blood pressure (SBP) and DBP, body mass index (BMI), and waist-hip ratio (WHR) were measured/calculated at baseline (week 0) and 8, 16, and 24 weeks. Patients were asked to maintain a 1600-kcal/d diet throughout the study.

RESULTS

Forty-eight patients (28 men, 20 women; mean [SD] age, 57 [9] years) were included in the study. In the 45 patients (93.8%) who completed the study, mean SBP, DBP, and BMI were significantly decreased compared with baseline (all P < 0.001), but WHR was significantly increased (P < 0.05). After 24 weeks of treatment, 71.1 % of patients had SBP/DBP ≤ 140/≤90 mm Hg. Three patients (6.3%) withdrew from the study due to treatment-related adverse events.

CONCLUSION

In this population of overweight or obese patients with mild to moderate hypertension, valsartan was well tolerated, and could be effective in controlling blood pressure and achieving weight loss in such patients.

Distinct properties of telmisartan on agonistic activities for peroxisome proliferator-activated receptor γ among clinically used angiotensin II receptor blockers: drug-target interaction analyses

A proportion of angiotensin II type 1 receptor blockers (ARBs) improves glucose dyshomeostasis and insulin resistance in a clinical setting. Of these ARBs, telmisartan has the unique property of being a partial agonist for peroxisome proliferator-activated receptor γ (PPARγ). However, the detailed mechanism of how telmisartan acts on PPARγ and exerts its insulin-sensitizing effect is poorly understood. In this context, we investigated the agonistic activity of a variety of clinically available ARBs on PPARγ using isothermal titration calorimetry (ITC) and surface plasmon resonance (SPR) system. Based on physicochemical data, we then reevaluated the metabolically beneficial effects of telmisartan in cultured murine adipocytes. ITC and SPR assays demonstrated that telmisartan exhibited the highest affinity of the ARBs tested. Distribution coefficient and parallel artificial membrane permeability assays were used to assess lipophilicity and cell permeability, for which telmisartan exhibited the highest levels of both. We next examined the effect of each ARB on insulin-mediated glucose metabolism in 3T3-L1 preadipocytes. To investigate the impact on adipogenesis, 3T3-L1 preadipocytes were differentiated with each ARB in addition to standard inducers of differentiation for adipogenesis. Telmisartan dose-dependently facilitated adipogenesis and markedly augmented the mRNA expression of adipocyte fatty acid-binding protein (aP2), accompanied by an increase in the uptake of 2-deoxyglucose and protein expression of glucose transporter 4 (GLUT4). In contrast, other ARBs showed only marginal effects in these experiments. In accordance with its highest affinity of binding for PPARγ as well as the highest cell permeability, telmisartan superbly activates PPARγ among the ARBs tested, thereby providing a fresh avenue for treating hypertensive patients with metabolic derangement.

Atrial natriuretic peptide and type 2 diabetes development--biomarker and genotype association study

BACKGROUND

We have recently shown that low plasma levels of mid-regional atrial natriuretic peptide (MR-ANP) predict development of diabetes and glucose progression over time, independently of known risk factors for diabetes development. However, since MR-ANP levels might be influenced by unknown factors causing diabetes, we cannot rule out that such relationship might be confounded. Previous studies have shown an association of a single nucleotide polymorphism rs5068 on the natriuretic peptide precursor A (NPPA) locus gene with higher levels of circulating ANP. Since gene variants are inherited randomly and not subject to confounding, we aimed to investigate whether the variant rs5068 within the NPPA locus is associated with incident type 2 diabetes.

METHODS

We genotyped the variant rs5068 within the NPPA locus in 27,307 individuals without known diabetes from the Malmö Diet Cancer Study. Incident diabetes was retrieved through national and regional registers (median follow-up time of 14 years, 2,823 incident diabetes cases).

RESULTS

In Cox regression analysis adjusted for age, sex and BMI, we found that the carriers of at least one copy of the G allele of rs5068 had lower likelihood of incident diabetes within 14 years (HR = 0.88, 95% CI 0.78-0.99, p = 0.037).

CONCLUSION

Our results indicate a role of the ANP system in the etiology of type 2 diabetes and might help provide insight in the metabolic actions of natriuretic peptides and the pathophysiology of type 2 diabetes.

Weighing in on adipocyte precursors

Obesity, defined as an excessive increase in white adipose tissue (WAT), is a global health epidemic. In obesity, WAT expands by increased adipocyte size (hypertrophy) and number (hyperplasia). The location and cellular mechanisms of WAT expansion greatly affect the pathogenesis of obesity. However, the cellular and molecular mechanisms regulating adipocyte size, number, and depot-dependent expansion in vivo remain largely unknown. This perspective summarizes previous work addressing adipocyte number in development and obesity and discusses recent advances in the methodologies, genetic tools, and characterization of in vivo adipocyte precursor cells allowing for directed study of hyperplastic WAT growth in vivo.

A meta-analysis of the effect of angiotensin receptor blockers and calcium channel blockers on blood pressure, glycemia and the HOMA-IR index in non-diabetic patients

OBJECTIVE

This study compared the efficacy of angiotensin receptor blockers (ARBs) and calcium channel blockers (CCBs) in the effect of insulin resistance (IR) as assessed using the homeostasis model assessment of insulin resistance (HOMA-IR) in non-diabetic patients.

METHODS

The MEDLINE, EMBASE, and Cochrane Library databases were searched to identify studies published before December 2012 that investigated the use of ARBs and CCBs to determine the effect on the HOMA-IR index in non-diabetics. Parameters on IR and blood pressure were collected. Review Manager 5.2 and Stata 12.0 were used to perform the meta-analysis. Fixed and random effects models were applied to various aspects of the meta-analysis, which assessed the therapeutic effects of the two types of drug using the HOMA-IR index in non-diabetic patients.

RESULTS

The meta-analysis included five clinical trials. Patient comparisons before and after treatment with ARBs and CCBs revealed that ARBs reduced the HOMA-IR index (weighted mean difference (WMD) -0.65, 95% confidence interval (CI) -0.93 to -0.38) and fasting plasma insulin (FPI) (WMD -2.01, 95% CI -3.27 to -0.74) significantly more than CCBs. No significant differences in the therapeutic effects of these two types of drug on blood pressure were observed.

CONCLUSION

Given that there are no significant differences in the therapeutic effects of ARBs and CCBs on blood pressure, as ARBs are superior to CCBs in their effect on the HOMA-IR index in non-diabetics, they might be a better choice in hypertension patients without diabetes.

The renin-angiotensin system in adipose tissue and its metabolic consequences during obesity

Obesity is a worldwide disease that is accompanied by several metabolic abnormalities such as hypertension, hyperglycemia and dyslipidemia. The accelerated adipose tissue growth and fat cell hypertrophy during the onset of obesity precedes adipocyte dysfunction. One of the features of adipocyte dysfunction is dysregulated adipokine secretion, which leads to an imbalance of pro-inflammatory, pro-atherogenic versus anti-inflammatory, insulin-sensitizing adipokines. The production of renin-angiotensin system (RAS) components by adipocytes is exacerbated during obesity, contributing to the systemic RAS and its consequences. Increased adipose tissue RAS has been described in various models of diet-induced obesity (DIO) including fructose and high-fat feeding. Up-regulation of the adipose RAS by DIO promotes inflammation, lipogenesis and reactive oxygen species generation and impairs insulin signaling, all of which worsen the adipose environment. Consequently, the increase of circulating RAS, for which adipose tissue is partially responsible, represents a link between hypertension, insulin resistance in diabetes and inflammation during obesity. However, other nutrients and food components such as soy protein attenuate adipose RAS, decrease adiposity, and improve adipocyte functionality. Here, we review the molecular mechanisms by which adipose RAS modulates systemic RAS and how it is enhanced in obesity, which will explain the simultaneous development of metabolic syndrome alterations. Finally, dietary interventions that prevent obesity and adipocyte dysfunction will maintain normal RAS concentrations and effects, thus preventing metabolic diseases that are associated with RAS enhancement.

Angiotensin II signaling in human preadipose cells: participation of ERK1,2-dependent modulation of Akt

The renin-angiotensin system expressed in adipose tissue has been implicated in the modulation of adipocyte formation, glucose metabolism, triglyceride accumulation, lipolysis, and the onset of the adverse metabolic consequences of obesity. As we investigated angiotensin II signal transduction mechanisms in human preadipose cells, an interplay of extracellular-signal-regulated kinases 1 and 2 (ERK1,2) and Akt/PKB became evident. Angiotensin II caused attenuation of phosphorylated Akt (p-Akt), at serine 473; the p-Akt/Akt ratio decreased to 0.5±0.2-fold the control value without angiotensin II (p<0.001). Here we report that the reduction of phosphorylated Akt associates with ERK1,2 activities. In the absence of angiotensin II, inhibition of ERK1,2 activation with U0126 or PD98059 resulted in a 2.1±0.5 (p<0.001) and 1.4±0.2-fold (p<0.05) increase in the p-Akt/Akt ratio, respectively. In addition, partial knockdown of ERK1 protein expression by the short hairpin RNA technique also raised phosphorylated Akt in these cells (the p-Akt/Akt ratio was 1.5±0.1-fold the corresponding control; p<0.05). Furthermore, inhibition of ERK1,2 activation with U0126 prevented the reduction of p-Akt/Akt by angiotensin II. An analogous effect was found on the phosphorylation status of Akt downstream effectors, the forkhead box (Fox) proteins O1 and O4. Altogether, these results indicate that angiotensin II signaling in human preadipose cells involves an ERK1,2-dependent attenuation of Akt activity, whose impact on the biological functions under its regulation is not fully understood.

Adipose tissue renin-angiotensin-aldosterone system (RAAS) and progression of insulin resistance

This review focuses on the expression of the key components of the renin-angiotensin-aldosterone axis in fat tissue. At the center of this report is the role of RAAS in normal and excessive fat mass enlargement, the leading etiology of insulin resistance. Understanding the expression and regulation of RAAS components in various fat depots allows insight not only into the processes by which these complex patterns are modified by the enlargement of adipose tissue, but also into their impact on local and systemic response to insulin.

Effects of angiotensin II type 1 receptor blocker and adiponectin on adipocyte dysfunction in stroke-prone spontaneously hypertensive rats

BACKGROUND

Hypoadiponectinemia in lipoatrophy may be related to worsening of hypertension in stroke-prone spontaneously hypertensive rats (SHRSP). One of the beneficial effects of candesartan (Angiotensin II Type 1 receptor blocker) for preventing hypertension may be increasing of adiponectin due to improvement of adipocyte dysfunction. In this study, we determined the effects of candesartan or adiponectin on pathophysiologic features and adipocyte dysfunction in SHRSP.

METHODS

Candesartan was administered to male SHRSP from 16 to 20 weeks of age (2 mg/kg/day). Adiponectin was cloned and intravenously administered to male SHRSP from 16 to 20 weeks of age. We examined biological parameters, as well as the expression and release of adipokines.

RESULTS

The SHRSP exhibited severe atrophy of visceral fat and progression of severe hypertension. The expression and release of leptin and adiponectin were impaired at 6 and 20 weeks of age. Candesartan suppressed the development of lipoatrophy and reduced the incidence of stroke at 20 weeks of age. Candesartan also enhanced the expression of adiponectin and leptin by inducing the overexpression of peroxisome proliferator activated receptor γ. Circulating level of leptin was significantly higher in candesartan group than in the control group, whereas adiponectin was similar in both groups. Intravenous administration of adiponectin resulted in enhancement of adiponectin expression in adipose tissue, but no remarkable effects were found in pathophysiology in SHRSP.

CONCLUSIONS

Our results indicate that candesartan protects against hypertension and adipocyte dysfunction in SHRSP. The induction of leptin expression appeared to be important factor in the inhibition of stroke lesions, whereas adiponectin was not a major regulator of blood pressure in SHRSP with genetic hypertension. Further studies are needed to elucidate the role of the renin-angiotensin system in adipose tissue dysfunction in relation to hypertensive end-organ damage.

The renin angiotensin aldosterone system and insulin resistance in humans

Alterations in the renin angiotensin aldosterone system (RAAS) contribute to the underlying pathophysiology of insulin resistance in humans; however, individual differences in the treatment response of insulin resistance to RAAS blockade persist. Thus, understanding inter-individual differences in the relationship between the RAAS and insulin resistance may provide insights into improved personalized treatments and improved outcomes. The effects of the systemic RAAS on blood pressure regulation and glucose metabolism have been studied extensively; however, recent discoveries on the influence of local tissue RAAS in the skeletal muscle, heart, vasculature, adipocytes, and pancreas have led to an improved understanding of how activated tissue RAAS influences the development of insulin resistance and diabetes in humans. Angiotensin II (ANGII) is the predominant RAAS component contributing to insulin resistance; however, other players such as aldosterone, renin, and ACE2 are also involved. This review examines the role of local ANGII activity on insulin resistance development in skeletal muscle, adipocytes, and pancreas, followed by a discussion of the other RAAS components implicated in insulin resistance, including ACE2, Ang1-7, renin, and aldosterone.

Association of angiotensin-converting enzyme and angiotensin II type I receptor gene polymorphisms with extreme obesity in Polish individuals

There is strong evidence for the presence of a functional renin-angiotensin system in human adipose tissue. The aim of our study was to investigate the association of polymorphic variants of angiotensin-converting enzyme gene (ACE I/D) and angiotensin II type I receptor gene (AGTR1 A1166C) with extreme obesity and obesity-associated type 2 diabetes mellitus (T2DM) and to examine their combined effect on extremely obese patients. Overall, no significant associations were detected between ACE and AGTR1 gene polymorphisms and extreme obesity. However, extremely obese patients with T2DM showed an increased frequency of ACE II genotype compared with controls (p<0.05) and with non-diabetic extremely obese patients (p<0.01). The results suggest that II genotype of ACE was a significant contributor to extreme obesity in AA homozygotes of AGTR1 gene, regardless of the presence of T2DM. Moreover, the analysis of genetic polymorphisms demonstrated that ACE II and AGTR1 AC genotypes were most frequently observed in patients with extreme obesity and T2DM. On the basis of our results, we suggest that ACE II homozygosity may be a significant predictor of extreme obesity and T2DM and that the interaction between ACE and AGTR1 genes may be considered a predisposing factor for extreme obesity and extreme obesity-associated T2DM development.

Arsenic-stimulated lipolysis and adipose remodeling is mediated by G-protein-coupled receptors

Arsenic in drinking water promotes a number of diseases that may stem from dysfunctional adipose lipid and glucose metabolism. Arsenic inhibits adipocyte differentiation and promotes insulin resistance; however, little is known of the impacts of and mechanisms for arsenic effects on adipose lipid storage and lipolysis. Based on our earlier studies of arsenic-signaling mechanisms for vascular remodeling and inhibition of adipogenesis, we investigated the hypothesis that arsenic acts through specific adipocyte G-protein-coupled receptors (GPCRs) to promote lipolysis and decrease lipid storage. We first demonstrated that 5-week exposure of mice to 100 μg/l of arsenic in drinking water stimulated epididymal adipocyte hypertrophy, reduced the adipose tissue expression of perilipin (PLIN1, a lipid droplet coat protein), and increased perivascular ectopic fat deposition in skeletal muscle. Incubating adipocytes, differentiated from adipose-derived human mesenchymal stem cell, with arsenic stimulated lipolysis and decreased both Nile Red positive lipid droplets and PLIN1 expression. Arsenic-stimulated lipolysis was not associated with increased cAMP levels. However, preincubation of adipocytes with the Gi inhibitor, Pertussis toxin, attenuated As(III)-stimulated lipolysis and lipid droplet loss. Antagonizing Gi-coupled endothelin-1 type A and B receptors (EDNRA/EDNRB) also attenuated arsenic effects, but antagonizing other adipose Gi-coupled receptors that regulate fat metabolism was ineffective. The endothelin receptors have different roles in arsenic responses because only EDNRA inhibition prevented arsenic-stimulated lipolysis, but antagonists to either receptor protected lipid droplets and PLIN1 expression. These data support a role for specific GPCRs in arsenic signaling for aberrant lipid storage and metabolism that may contribute to the pathogenesis of metabolic disease caused by environmental arsenic exposures.

Control of adipogenesis by the autocrine interplays between angiotensin 1-7/Mas receptor and angiotensin II/AT1 receptor signaling pathways

Angiotensin II (AngII), a peptide hormone released by adipocytes, can be catabolized by adipose angiotensin-converting enzyme 2 (ACE2) to form Ang(1-7). Co-expression of AngII receptors (AT1 and AT2) and Ang(1-7) receptors (Mas) in adipocytes implies the autocrine regulation of the local angiotensin system upon adipocyte functions, through yet unknown interactive mechanisms. In the present study, we reveal the adipogenic effects of Ang(1-7) through activation of Mas receptor and its subtle interplays with the antiadipogenic AngII-AT1 signaling pathways. Specifically, in human and 3T3-L1 preadipocytes, Ang(1-7)-Mas signaling promotes adipogenesis via activation of PI3K/Akt and inhibition of MAPK kinase/ERK pathways, and Ang(1-7)-Mas antagonizes the antiadipogenic effect of AngII-AT1 by inhibiting the AngII-AT1-triggered MAPK kinase/ERK pathway. The autocrine regulation of the AngII/AT1-ACE2-Ang(1-7)/Mas axis upon adipogenesis has also been revealed. This study suggests the importance of the local regulation of the delicately balanced angiotensin system upon adipogenesis and its potential as a novel therapeutic target for obesity and related metabolic disorders.

Inflammation and hypertension: are there regional differences?

Hypertension is a chronic disease with global prevalence and incidence rapidly increasing in low and medium income countries. The surveillance of cardiovascular risk factors, such as hypertension, is a global health priority in order to estimate the burden and trends, to appropriately direct resources, and to measure the effect of interventions. We propose here that the adoption of Western lifestyles in low and middle incomes countries has dramatically increased the prevalence of abdominal obesity, which is the main source of proinflammatory cytokines, and that the vascular systemic inflammation produced by adipose tissue contributes to the development of hypertension. The concentration of proinflammatory cytokines is higher in the Latin American population than that reported in developed countries, suggesting a higher susceptibility to develop systemic low-degree inflammation at a given level of abdominal obesity. These particularities are important to be considered when planning resources for health care programs. Moreover, studying these singularities may provide a better understanding of the causes of the burden of cardiovascular risk factors and the remarkable variability in the prevalence of these medical conditions within and between countries.

The role of Siglec-1 and SR-BI interaction in the phagocytosis of oxidized low density lipoprotein by macrophages

Background

Macrophages play a proatherosclerotic role in atherosclerosis via oxLDL uptake. As an adhesion molecular of I-type lectins, Siglec-1 is highly expressed on circulating monocytes and plaque macrophages of atherosclerotic patients, but the exact role of Siglec-1 has not been elucidated.

Methods

In this study, oxLDL was used to stimulate Siglec-1 and some oxLDL receptors (SR-BI, CD64, CD32B, LOX-1 and TLR-4) expression on bone marrow-derived macrophages, whereas small interfering RNA was used to down-regulate Siglec-1. Meanwhile, an ELISA-based assay for Siglec-1-oxLDL interaction was performed, and co-immunoprecipitation (co-IP) and laser scanning confocal microscopy (LSCM) were used to determine the role of Siglec-1 in oxLDL uptake by macrophages.

Results

We found that oxLDL could up-regulate the expression of various potential oxLDL receptors, including Siglec-1, in a dose-dependent manner. Moreover, down-regulation of Siglec-1 could attenuate oxLDL uptake by Oil red O staining. LSCM revealed that Siglec-1 and CD64/SR-BI may colocalize on oxLDL-stimulated macrophage surface, whereas co-IP showed that Siglec-1 and SR-BI can be immunoprecipitated by each other. However, no direct interaction between Siglec-1 and oxLDL was found in the in vitro protein interaction system.

Conclusions

Thus, Siglec-1 can interact with SR-BI in the phagocytosis of oxLDL by macrophages, rather than act as an independent receptor for oxLDL.

Intrinsic dynamics of the fat graft: in vitro interactions between the main cell actors

BACKGROUND

Successful soft-tissue reconstruction requires autologous tissue transfer in respect to the increasingly important "replace like-with-like" principle. Autologous lipoaspirate material for fat grafting can easily be obtained in large amounts without substantial donor-site morbidity. The exact nature and fate of the different cells in the transplanted fat graft and their contribution to tissue reconstruction, however, remain largely unknown.

METHODS

Adipose tissue was harvested from healthy female patients. CD34+ adipose-derived stem cells were isolated through magnetic-activated cell sorting and brought into co-culture with mature adipocytes in various culture medium conditions. Proliferation and differentiation of the adipose-derived stem cells were examined through histology, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays, and polymerase chain reaction assays.

RESULTS

This study demonstrates that adipose-derived stem cells from fresh adipose tissue can be isolated within a few hours via magnetic-activated cell sorting with selection for CD34+ cells. All unpassaged adipose-derived stem cells in fresh adipose tissue are CD34+. Subsets include CD34+ CD31+ and CD34+ CD271+. No CD34+ CD45+ cells were present. Histological staining, polymerase chain reaction, and MTT assays confirm that purified mature adipose cells incite adipose-derived stem cells proliferation and adipose differentiation in vitro.

CONCLUSIONS

This in vitro study demonstrates important interactions between the main actors in the adipose graft, the adipose-derived stem cells and the mature adipocytes. Although the eventual fate of these cells in a clinically implemented fat graft is still largely unknown, the results of this study support the theory that lipofilling can be conceived as an in vivo tissue engineering approach in which the mature adipocytes within fat grafts support proliferation and differentiation in the co-grafted stromal cell population.

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.

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.

Increased cord blood angiotensin II concentration is associated with decreased insulin sensitivity in the offspring of mothers with gestational diabetes mellitus

OBJECTIVE

To determine cord blood angiotensin II (Ang II) concentration and assess its relationship to fetal insulin sensitivity in the offspring of mothers with gestational diabetes mellitus (GDM) at birth.

STUDY DESIGN

Thirty women with GDM and 30 healthy women were evaluated at elective cesarean delivery. Cord blood was obtained for measurement of Ang II, glucose and insulin. Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated and used to estimate fetal insulin sensitivity.

RESULT

The offspring of mothers with GDM had higher ponderal index (PI), HOMA-IR and cord Ang II and insulin concentrations than the offspring of healthy mothers. Cord insulin concentration and HOMA-IR were positively associated with PI in all the offspring. Cord Ang II concentration was positively associated with HOMA-IR in the offspring of mothers with GDM.

CONCLUSION

Increased cord Ang II concentration is associated with decreased insulin sensitivity in the offspring of mothers with GDM.

Arsenic activates endothelin-1 Gi protein-coupled receptor signaling to inhibit stem cell differentiation in adipogenesis

Dysfunctional lipid and glucose metabolism contribute to metabolic syndrome-a major public health concern that enhances cardiovascular disease risk. Arsenic (As(III)) exposure may increase metabolic syndrome and cardiovascular disease risk by impairing adipose tissue differentiation, function, and insulin sensitivity through pathogenic mechanisms that remain unclear. We hypothesized that As(III) signals through the Pertussis toxin (Ptx) sensitive, Gi protein-coupled receptor (GPCR) to impair adipogenesis, as previously demonstrated for its stimulation of vascular oxidant generation, angiogenesis, and remodeling. Because both As(III) and GPCR ligands inhibit progenitor cell differentiation into adipocytes, we investigated the hypothesis in a model of low-passage human mesenchymal stem cells (hMSC). As(III) (0.1-1.0 µM) suppressed dexamethasone/insulin-induced hMSC adipogenesis, as indicated by decreased transcriptional promoters of differentiation, decreased fat droplet formation, and decreased expression of differentiated adipocyte markers, such as adiponectin and perilipin. Preincubating hMSC with Ptx prevented 90% of the suppressive effect of As(III). Selective competitive antagonists of Gi-coupled endothelin-1 type A and B receptors were ~60% effective in blocking As(III) inhibition and combination of antagonists to both receptors were 85% effective. In contrast, antagonists to the sphingosine-1-phosphate type 1 receptor (previously shown to mediate As(III) vascular effects) or the angiotensin II type 1 receptor were ineffective in blocking As(III) effects. These studies suggest a majority of arsenic-inhibited adipocyte differentiation, and metabolism requires endothelin-1 GPCRs and that As(III) effects on GPCR signaling are tissue and context specific. This may represent a significant mechanism for the contribution of arsenic exposure to increased metabolic and cardiovascular diseases.

Multilineage co-culture of adipose-derived stem cells for tissue engineering

Stem cell interactions through paracrine cell signalling can regulate a range of cell responses, including metabolic activity, proliferation and differentiation. Moving towards the development of optimized tissue-engineering strategies with adipose-derived stem cells (ASCs), the focus of this study was on developing indirect co-culture models to study the effects of mature adipocytes, chondrocytes and osteoblasts on bovine ASC multilineage differentiation. For each lineage, ASC differentiation was characterized by histology, gene expression and protein expression, in the absence of key inductive differentiation factors for the ASCs. Co-culture with each of the mature cell populations was shown to successfully induce or enhance lineage-specific differentiation of the ASCs. In general, a more homogeneous but lower-level differentiation response was observed in co-culture as compared to stimulating the bovine ASCs with inductive differentiation media. To explore the role of the Wnt canonical and non-canonical signalling pathways within the model systems, the effects of the Wnt inhibitors WIF-1 and DKK-1 on multilineage differentiation in co-culture were assessed. The data indicated that Wnt signalling may play a role in mediating ASC differentiation in co-culture with the mature cell populations.

The adipose tissue renin-angiotensin system and metabolic disorders: a review of molecular mechanisms

The renin-angiotensin system (RAS) is classically known for its role in regulation of blood pressure, fluid and electrolyte balance. In this system, angiotensinogen (Agt), the obligate precursor of all bioactive angiotensin peptides, undergoes two enzymatic cleavages by renin and angiotensin converting enzyme (ACE) to produce angiotensin I (Ang I) and angiotensin II (Ang II), respectively. The contemporary view of RAS has become more complex with the discovery of additional angiotensin degradation pathways such as ACE2. All components of the RAS are expressed in and have independent regulation of adipose tissue. This local adipose RAS exerts important auto/paracrine functions in modulating lipogenesis, lipolysis, adipogenesis as well as systemic and adipose tissue inflammation. Mice with adipose-specific Agt overproduction have a 30% increase in plasma Agt levels and develop hypertension and insulin resistance, while mice with adipose-specific Agt knockout have a 25% reduction in Agt plasma levels, demonstrating endocrine actions of adipose RAS. Emerging evidence also points towards a role of RAS in regulation of energy balance. Because adipose RAS is overactivated in many obesity conditions, it is considered a potential candidate linking obesity to hypertension, insulin resistance and other metabolic derangements.

Does it matter how blood pressure is lowered in patients with metabolic risk factors?

Abdominal obesity is an important cardiovascular risk factor. It is a primary driver of the metabolic syndrome, the cluster of metabolic risk factors that includes insulin resistance and dyslipidemia, and often occurs in association with hypertension. The aim of antihypertensive therapy in patients with metabolic risk factors is to reduce cardiovascular risk, but some antihypertensive agents can exert adverse metabolic effects. For example, beta-blockers produce significant weight gain, and are associated with an increased incidence of diabetes. By contrast, agents that inhibit the renin-angiotensin system (RAS), such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs), have been shown to be associated with a decreased risk of new-onset diabetes. This reflects the finding that increased activation of the RAS in obese individuals can contribute to the development of the metabolic syndrome. The ARB telmisartan has been shown to act as a selective peroxisome proliferator-activated receptor (PPAR)-gamma modulator. It is known that PPAR-gamma plays a role in the regulation of multiple genes affecting carbohydrate and lipid metabolism; however, the clinical significance of this remains to be established. The potential metabolic effects of RAS blockade should be considered in the choice of antihypertensive therapy for patients with metabolic risk factors, including obesity.

Deficiency of angiotensin type 1a receptors in adipocytes reduces differentiation and promotes hypertrophy of adipocytes in lean mice

Adipocytes express angiotensin receptors, but the direct effects of angiotensin II (AngII) stimulating this cell type are undefined. Adipocytes express angiotensin type 1a receptor (AT1aR) and AT2R, both of which have been implicated in obesity. In this study, we determined the effects of adipocyte AT1aR deficiency on adipocyte differentiation and the development of obesity in mice fed low-fat (LF) or high-fat (HF) diets. Mice expressing Cre recombinase under the control of the aP2 promoter were bred with AT1aR-floxed mice to generate mice with adipocyte AT1aR deficiency (AT1aR(aP2)). AT1aR mRNA abundance was reduced significantly in both white and brown adipose tissue from AT1aR(aP2) mice compared with nontransgenic littermates (AT1aR(fl/fl)). Adipocyte AT1aR deficiency did not influence body weight, glucose tolerance, or blood pressure in mice fed either LF or high-fat diets. However, LF-fed AT1aR(aP2) mice exhibited striking adipocyte hypertrophy even though total fat mass was not different between genotypes. Stromal vascular cells from AT1aR(aP2) mice differentiated to a lesser extent to adipocytes compared with controls. Conversely, incubation of 3T3-L1 adipocytes with AngII increased Oil Red O staining and increased mRNA abundance of peroxisome proliferator-activated receptor γ (PPARγ) via AT1R stimulation. These results suggest that reductions in adipocyte differentiation in LF-fed AT1aR(aP2) mice resulted in increased lipid storage and hypertrophy of remaining adipocytes. These results demonstrate that AngII regulates adipocyte differentiation and morphology through the adipocyte AT1aR in lean mice.

Implications of 2H-labeling of DNA protocol to measure in vivo cell turnover in adipose tissue

Adipose tissue expansion in obesity involves a series of cycles of adipocyte hyperplasia, hypertrophy and hypoplasia due to alterations in adipogenesis, adipocyte cellular metabolism and cell death, respectively. Increased frequency of these cycles may lead to deterioration of adipocyte function and viability, accelerated exhaustion of the adipocyte progenitor pool and extensive adipose tissue remodeling, all leading to impaired expandability of subcutaneous adipose tissue, ectopic lipid accumulation and insulin resistance. Understanding the mechanisms that contribute to adipocyte turnover is thus important. We have recently refined and published an existing method to assess in vivo adipogenesis using incorporation of the stable isotope deuterium into the DNA of isolated adipocytes and adipocyte progenitors from adipose tissue. In this commentary, we highlight further implications of this method to determine the rate of adipocyte hypertrophy and adipocyte death that will enhance our understanding of adipocyte cell turnover and cellular mechanisms that control regional adipose tissue growth.

Adipocyte induction of preadipocyte differentiation in a gradient chamber

Adipose tissue expansion involves enlargement of mature adipocytes and the formation of new adipocytes through the differentiation of locally resident preadipocytes. Factors released by the enlarged adipocytes are potential cues that induce the differentiation of the preadipocytes. Currently, there are limited options to investigate these cues in isolation from confounding systemic influences. A gradient generating microfluidic channel-based cell culture system was designed to enable solution patterning, while supporting long-term culture and differentiation of preadipocytes. Solution patterning was confirmed by selectively staining a fraction of uniformly seeded preadipocytes. An adipogenic cocktail gradient was used to induce the differentiation of a fraction of uniformly seeded preadipocytes and establish a spatially defined coculture of adipocytes and preadipocytes. Varying the adipogenic cocktail gradient generated cocultures of preadipocytes and adipocytes with different compositions. Transient application of the cocktail gradient, followed by basal medium treatment showed a biphasic induction of differentiation. The two phases of differentiation correlated with a spatial gradient in adipocyte size. Our results provide in vitro data supporting the size-dependent release of preadipocyte differentiation factors by enlarged adipocytes. Prospectively, the coculture system developed in this study could facilitate controlled, yet physiologically meaningful studies on paracrine interactions between adipocytes and preadipocytes during adipose tissue development.

Characterizing and quantifying leukocyte populations in human adipose tissue: impact of enzymatic tissue processing

Adipose tissue inflammation is a major mechanistic link between obesity and chronic disease. To isolate and characterize specific leukocyte populations, e.g. by flow cytometry, tissue needs to be processed to digest the extracellular matrix. We have systematically compared the impact of different commonly used collagenase preparations, digestion times, and normalization strategies on the reproducibility of flow cytometric phenotyping of adipose tissue leukocyte populations. Subcutaneous adipose tissue was obtained from 11 anonymous donors undergoing elective procedures at a plastic surgery clinic in Seattle, WA. We found that collagenase alone consistently produced better cell yields (p=0.007) than when combined with additional proteases such as the commercially available liberases. Moreover, liberase significantly degraded the cell surface expression of CD4 (p<0.001) on T cells and to a lesser extent CD16 (p=0.058) on neutrophils. Extension of the digestion interval from 30 to 120 min did not significantly impact cell viability (p=0.319) or yield (p=0.247). Normalization by either 'live-gate' or percentage of CD45(pos) leukocytes exhibited the lowest coefficient of variation for tissue digests between 60 and 75 min, compared to normalization per gram of tissue, which consistently exhibited the greatest variability. Our data suggest that digestion of adipose tissue using pure collagenase for 60-75 min provides the best cell yield and viability, with minimal degradation of cell surface markers used to identify immune cell subpopulations, and best reproducibility independent of the normalization strategy.

1, 25-Dihydroxyvitamin D3Modulation of Adipocyte Glucocorticoid Function

OBJECTIVE

1,25-Dihydroxyvitamin D3 dose dependently increases intracellular calcium in human adipocytes. We have demonstrated that suppression of circulating 1,25-dihydroxyvitamin D3 levels by increasing dietary calcium reduces adipocyte intracellular calcium and reduces adiposity in both humans and rodents, with preferential loss of trunk fat. Autocrine production of cortisol by adipocytes of mice overexpressing 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD 1) in adipose tissue increases visceral adiposity, whereas knockout of 11beta-HSD 1 appears to attenuate truncal obesity. Accordingly, our objective was to investigate the role of 1,25-dihydroxyvitamin D3 in the modulation of adipocyte glucocorticoid metabolism.

RESEARCH METHODS AND PROCEDURES

We examined the effect of 1,25-dihydroxyvitamin D3 or angiotensin II on cortisol production and expression using real-time reverse transcriptase-polymerase chain reaction of 11beta-HSD 1, angiotensin II receptor type 1 (AT1), and AT2 receptor in human adipocytes.

RESULTS

Adipocytes produced negligible cortisol in the absence of substrate (cortisone). In the presence of cortisone (1 to 10 nM), there was significant cortisol production, which was dose dependently augmented (2- to 6-fold, p < 0.001) by 1,25-dihydroxyvitamin D3 (0.1 to 10 nM). 1,25-Dihydroxyvitamin D3 dose dependently increased 11beta-HSD 1 expression up to 2-fold (p < 0.01) in both the presence and absence of cortisone. In contrast, 1,25-dihydroxyvitamin D3 dose dependently decreased adipocyte AT1 expression (by 30% to 50%, p < 0.001) in both the presence and absence of cortisone, suggesting compensatory down-regulation of AT(1).

DISCUSSION

We conclude that 1,25-dihydroxyvitamin D3 directly regulates adipocyte 11beta-HSD 1 expression and, consequently, local cortisol levels and that this may contribute to the preferential loss of visceral adiposity by high-calcium diets.

Analysis of in vitro secretion profiles from adipose-derived cell populations

Background

Adipose tissue is an attractive source of cells for therapeutic purposes because of the ease of harvest and the high frequency of mesenchymal stem cells (MSCs). Whilst it is clear that MSCs have significant therapeutic potential via their ability to secrete immuno-modulatory and trophic cytokines, the therapeutic use of mixed cell populations from the adipose stromal vascular fraction (SVF) is becoming increasingly common.

Methods

In this study we have measured a panel of 27 cytokines and growth factors secreted by various combinations of human adipose-derived cell populations. These were 1. co-culture of freshly isolated SVF with adipocytes, 2. freshly isolated SVF cultured alone, 3. freshly isolated adipocytes alone and 4. adherent adipose-derived mesenchymal stem cells (ADSCs) at passage 2. In addition, we produced an ‘in silico’ dataset by combining the individual secretion profiles obtained from culturing the SVF with that of the adipocytes. This was compared to the secretion profile of co-cultured SVF and adipocytes. Two-tailed t-tests were performed on the secretion profiles obtained from the SVF, adipocytes, ADSCs and the ‘in silico’ dataset and compared to the secretion profiles obtained from the co-culture of the SVF with adipocytes. A p-value of < 0.05 was considered statistically different. To assess the overall changes that may occur as a result of co-culture we compared the proteomes of SVF and SVF co-cultured with adipocytes using iTRAQ quantitative mass spectrometry.

Results

A co-culture of SVF and adipocytes results in a distinct secretion profile when compared to all other adipose-derived cell populations studied. This illustrates that cellular crosstalk during co-culture of the SVF with adipocytes modulates the production of cytokines by one or more cell types. No biologically relevant differences were detected in the proteomes of SVF cultured alone or co-cultured with adipocytes.

Conclusions

The use of mixed adipose cell populations does not appear to induce cellular stress and results in enhanced secretion profiles. Given the importance of secreted cytokines in cell therapy, the use of a mixed cell population such as the SVF with adipocytes may be considered as an alternative to MSCs or fresh SVF alone.

Visceral adipose tissue: emerging role of gluco- and mineralocorticoid hormones in the setting of cardiometabolic alterations

Several clinical and experimental lines of evidence have highlighted the detrimental effects of visceral adipose tissue excess on cardiometabolic parameters. Besides, recent findings have shown the effects of gluco-and mineralocorticoid hormones on adipose tissue and have also underscored the interplay existing between such adrenal steroids and their respective receptors in the modulation of adipose tissue biology. While the fundamental role played by glucocorticoids on adipocyte differentiation and storage was already well known, the relevance of the mineralocorticoids in the physiology of the adipose organ is of recent acquisition. The local and systemic renin–angiotensin–aldosterone system (RAAS) acting on adipose tissue seems to contribute to the development of the cardiometabolic phenotype so that its modulation can have deep impact on human health. A better understanding of the pathophysiology of the adipose organ is of crucial importance in order to identify possible therapeutic approaches that can avoid the development of such cardiovascular and metabolic sequelae.

The link between the renin-angiotensin-aldosterone system and renal injury in obesity and the metabolic syndrome

Obesity is a risk factor for type 2 diabetes mellitus (DM) and is associated with chronic kidney disease. Activation of the renin-angiotensin-aldosterone system (RAAS) is common in obesity. The RAAS is an important mediator of hypertension. Mechanisms involved in activation of the RAAS in obesity include sympathetic stimulation, synthesis of adipokines in the RAAS by visceral fat, and hemodynamic alterations. The RAAS is known for its role in regulating blood pressure and fluid and electrolyte homeostasis. The role of local/tissue RAAS in specific tissues has been a focus of research. Urinary angiotensinogen (UAGT) provides a specific index of the intrarenal RAAS. Investigators have demonstrated that sex steroids can modulate the expression and activity of the different components of the intrarenal RAAS and other tissues. Our data suggest that obese women without DM and hypertension have significantly higher levels of UAGT than their male counterparts. These differences existed without any background difference in the ratio of microalbumin to creatinine in the urine or the estimated glomerular filtration rate, raising a question about the importance of baseline gender differences in the endogenous RAAS in the clinical spectrum of cardiovascular diseases and the potential utility of UAGT as a marker of the intrarenal RAAS. Animal studies have demonstrated that modifying the amount of angiotensin, the biologically active component of the RAAS, directly influences body weight and adiposity. This article reviews the role of the RAAS in renal injury seen in obesity and the metabolic syndrome.

Does interference with the renin-angiotensin system protect against diabetes? Evidence and mechanisms

Agents interfering with the renin-angiotensin system (RAS) were consistently shown to lower the incidence of type 2 diabetes mellitus (T2DM), as compared to other antihypertensive drugs, in hypertensive high-risk populations. The mechanisms underlying this protective effect of RAS blockade using angiotensin-converting enzyme inhibitors or angiotensin-receptor blockers on glucose metabolism are not fully understood. In this article, we will review the evidence from randomized controlled trials and discuss the proposed mechanisms as to how RAS interference may delay the onset of T2DM. In particular, as T2DM is characterized by β-cell dysfunction and obesity-related insulin resistance, we address the mechanisms that underlie RAS blockade-induced improvement in β-cell function and insulin sensitivity.

Telmisartan at 80 mg/day increases high-molecular-weight adiponectin levels and improves insulin resistance in diabetic patients

INTRODUCTION

The clinical dose of telmisartan necessary for activation of peroxisome proliferator-activated receptor gamma (PPAR-gamma) has not been established. The authors investigated the effect of high-dose telmisartan on serum levels of the high-molecular-weight (HMW) adiponectin in patients with diabetes and hypertension.

METHODS

In this open-label, prospective, randomized study, patients with type 2 diabetes and hypertension with poor control of blood pressure by 40 mg/day telmisartan were randomly assigned into the telmisartan 80 mg/day (Tel80) group (dose increase from 40 to 80 mg/day) or the telmisartan 40 mg + amlodipine 5 mg (Tel40 + Aml5) group. Serum levels of HMW adiponectin and parameters of glucose and lipid metabolism were measured at baseline and end of 3-months of treatment.

RESULTS

Although the antihypertensive effects of the two doses of telmisartan were similar, a significant increase in HMW adiponectin levels was noted only in the Tel80 group. The increase was evident particularly in a group of patients whose HMW adiponectin levels were less than 4.0 μg/dL. A significant improvement in homeostasis model assessment of insulin resistance (HOMA-IR), a measure of insulin resistance, was also observed in the Tel80 group only.

CONCLUSIONS

In diabetic patients with hypertension, high-dose telmisartan increased HMW adiponectin levels and improved insulin resistance through activation of PPAR-gamma.

Valsartan improves adipose tissue function in humans with impaired glucose metabolism: a randomized placebo-controlled double-blind trial

BACKGROUND

Blockade of the renin-angiotensin system (RAS) reduces the incidence of type 2 diabetes mellitus. In rodents, it has been demonstrated that RAS blockade improved adipose tissue (AT) function and glucose homeostasis. However, the effects of long-term RAS blockade on AT function have not been investigated in humans. Therefore, we examined whether 26-wks treatment with the angiotensin II type 1 receptor blocker valsartan affects AT function in humans with impaired glucose metabolism (IGM).

METHODOLOGY/PRINCIPAL FINDINGS

We performed a randomized, double-blind, placebo-controlled parallel-group study, in which 38 subjects with IGM were treated with valsartan (VAL, 320 mg/d) or placebo (PLB) for 26 weeks. Before and after treatment, an abdominal subcutaneous AT biopsy was collected for measurement of adipocyte size and AT gene/protein expression of angiogenesis/capillarization, adipogenesis, lipolytic and inflammatory cell markers. Furthermore, we evaluated fasting and postprandial AT blood flow (ATBF) ((133)Xe wash-out), systemic inflammation and insulin sensitivity (hyperinsulinemic-euglycemic clamp). VAL treatment markedly reduced adipocyte size (P<0.001), with a shift toward a higher proportion of small adipocytes. In addition, fasting (P = 0.043) and postprandial ATBF (P = 0.049) were increased, whereas gene expression of angiogenesis/capillarization, adipogenesis and macrophage infiltration markers in AT was significantly decreased after VAL compared with PLB treatment. Interestingly, the change in adipocyte size was associated with alterations in insulin sensitivity and reduced AT gene expression of macrophage infiltration markers. VAL did not alter plasma monocyte-chemoattractant protein (MCP)-1, TNF-α, adiponectin and leptin concentrations.

CONCLUSIONS/SIGNIFICANCE

26-wks VAL treatment markedly reduced abdominal subcutaneous adipocyte size and AT macrophage infiltration markers, and increased ATBF in IGM subjects. The VAL-induced decrease in adipocyte size was associated with reduced expression of macrophage infiltration markers in AT. Our findings suggest that interventions targeting the RAS may improve AT function, thereby contributing to a reduced risk of developing cardiovascular disease and type 2 diabetes.

TRIAL REGISTRATION

Trialregister.nl NTR721 (ISRCTN Registry: ISRCTN42786336).

Adipogenic differentiation of adipose tissue-derived human mesenchymal stem cells: effect of gastric bypass surgery

BACKGROUND

Adipose tissue dysfunction is an important feature of obesity characterized by enlarged adipocytes and marked changes in secretion of cytokines. These changes result in insulin resistance, chronic vascular inflammation, oxidative stress, and activation of the renin-angiotensin system (RAS), eventually leading to type 2 diabetes, obesity-related hypertension, and cardiovascular disease (CVD). Several trials have shown that bariatric surgery significantly reduces these comorbidities. However, there is a gap in knowledge regarding the mechanisms whereby bariatric surgery reduces the burden of CVD in obese individuals.

METHOD

Mesenchymal stem cells (MSCs) were isolated from adipose tissue collected from three groups: (1) nonobese control subjects, (2) obese subjects undergoing gastric bypass surgery (GBS), and (3) subjects 1 year or more after GBS. In the study, MSCs were induced to adipogenic differentiation, and RAS-related gene expressions were determined by quantitative polymerase chain reaction. The effect of angiotensin II (Ang II) on adipogenic differentiation of MSCs also was investigated.

RESULTS

Angiotensinogen mRNA levels in MSCs and differentiated adipocytes were significantly higher in the obese group than in the nonobese control subjects. Renin mRNA levels were significantly higher in the obese group MSCs than in the nonobese and post-GBS groups. Angiotensin-converting enzyme mRNA levels were significantly lower in the MSCs derived from the post-GBS group than in the obese and nonobese control subjects. Serum Ang II levels were significantly lower in the post-GBS group (52.1 ± 4.2 pg/ml) than in the nonobese (85.4 ± 12.4 pg/ml) and obese (84.7 ± 10.0 pg/ml) groups. Ang II treatment inhibited adipogenesis of MSCs in a dose-dependent manner. The inhibitory effect of Ang II was mainly abolished by PD123319, a receptor 2 blocker.

CONCLUSIONS

The adipogenesis of MSCs is inhibited by Ang II treatment. Obese individuals are characterized by an upregulation of the RAS-related gene expressions in adipose tissue. This upregulation resolves in post-GBS subjects.

Bisphenol A-mediated suppression of LPL gene expression inhibits triglyceride accumulation during adipogenic differentiation of human adult stem cells

The endocrine disrupting chemical, bisphenol A (BPA), has been shown to accelerate the rate of adipogenesis and increase the amount of triglyceride accumulation during differentiation of 3T3-L1 preadipocytes. The objective of this study was to investigate if that observation is mirrored in human primary cells. Here we investigated the effect of BPA on adipogenesis in cultured human primary adult stem cells. Continuous exposure to BPA throughout the 14 days of differentiation dramatically reduced triglyceride accumulation and suppressed gene transcription of the lipogenic enzyme, lipoprotein lipase (LPL). Results presented in the present study show for the first time that BPA can reduce triglyceride accumulation during adipogenesis by attenuating the expression of LPL gene transcription. Also, by employing image cytometric analysis rather than conventional Oil red O staining techniques we show that BPA regulates triglyceride accumulation in a manner which does not appear to effect adipogenesis per se.

Physiological, pathological and potential therapeutic roles of adipokines

Formerly regarded purely as passive energy storage, adipose tissue is now recognized as a vital endocrine organ. Adipocytes secrete diverse peptide hormones named adipokines, which act in a autocrine, paracrine or endocrine way to influence several biological functions. Adipokines comprise diverse bioactive substances, including cytokines, growth, and complement factors, which perform essential regulatory functions related to energy balance, satiety and immunity. Presently adipokines have been widely implicated in obesity, diabetes, hypertension and cardiovascular diseases. In this article we aim to present a brief description of the roles and potential therapeutic modulation of adipokines, such as leptin, resistin, adiponectin, apelin, visfatin, FABP-4, tumor necrosis factor-α (TNF-α), interleukin-6 and plasminogen activator inhibitor-1 (PAI-1).

Metabolic rate regulation by the renin-angiotensin system: brain vs. body

Substantial evidence supports a role for the renin-angiotensin system (RAS) in the regulation of metabolic function, but an apparent paradox exists where genetic or pharmacological inhibition of the RAS occasionally has similar physiological effects as chronic angiotensin infusion. Similarly, while RAS targeting in animal models has robust metabolic consequences, effects in humans are more subtle. Here, we review the data supporting a role for the RAS in metabolic rate regulation and propose a model where the local brain RAS works in opposition to the peripheral RAS, thus helping to explain the paradoxically similar effects of RAS supplementation and inhibition. Selectively modulating the peripheral RAS or brain RAS may thus provide a more effective treatment paradigm for obesity and obesity-related disorders.

Low plasma level of atrial natriuretic peptide predicts development of diabetes: the prospective Malmo Diet and Cancer study

CONTEXT

The cardiac natriuretic peptides are involved in blood pressure regulation, and large cross-sectional studies have shown lower plasma levels of N-terminal pro-natriuretic peptide levels [N-terminal atrial natriuretic peptide (N-ANP) and N-terminal brain natriuretic peptide (N-BNP)] in patients with insulin resistance, obesity, and diabetes.

OBJECTIVE

In this study, we prospectively tested whether plasma levels of mid-regional ANP (MR-ANP) and N-BNP predict new-onset diabetes and long-term glucose progression.

DESIGN, SETTING, AND PATIENTS

MR-ANP and N-BNP were measured in 1828 nondiabetic individuals of the Malmö Diet and Cancer cohort (mean age 60 yr; 61% women) who subsequently underwent a follow-up exam including an oral glucose tolerance test after a median follow-up time of 16 yr. Logistic regression was used to adjust for covariates.

RESULTS

During follow-up, 301 subjects developed new-onset diabetes. After full multivariate adjustment, MR-ANP was significantly inversely associated with incident diabetes (OR = 0.85; 95% CI = 0.73-0.99; P = 0.034) but not N-BNP (OR = 0.92; 95% CI = 0.80-1.06; P = 0.262). In fully adjusted linear regression models, the progression of fasting glucose during follow-up was significantly inversely related to baseline levels of MR-ANP (P = 0.004) but not N-BNP (P = 0.129). Quartile analyses revealed that the overall association was mainly accounted for by excess risk of incident diabetes in subjects belonging to the lowest quartile of MR-ANP. After full adjustment, the odds ratio for incident diabetes in the bottom compared with the top quartile of MR-ANP was 1.65 (OR = 1.08-2.51, P = 0.019) and 1.43 (OR = 1.04-1.96, P = 0.027) compared with all other subjects.

CONCLUSION

Low plasma levels of MR-ANP predict development of future diabetes and glucose progression over time, suggesting a causal role of ANP deficiency in diabetes development.

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.

The relationship between fat depot-specific preadipocyte differentiation and metabolic syndrome in obese women

OBJECTIVE

Obesity is strongly associated with metabolic syndrome, but not all obese individuals display a clustering of metabolic risk factors. Recent studies have shown that in vitro subcutaneous (SC)-preadipocyte differentiation is negatively associated with obesity. These results suggest that impaired adipogenesis is an important factor linking obesity to metabolic disorders. We examined whether in vitro preadipocyte differentiation is associated with metabolic syndrome, independent of obesity.

DESIGN/PATIENTS/MEASUREMENTS

Paired adipose tissue samples were obtained from the 13 nonobese women and the 65 obese women. The CD34(+)/CD31(-) cells were isolated from the stromal-vascular fraction of both SC and omental (OM) fat depots by immune magnetic separation, and the subset was cultured with a differentiation cocktail. Then, we analysed the relationship between the degree of preadipocyte differentiation and metabolic factors.

RESULTS

Obese women without metabolic syndrome (n = 37) had significantly higher SC-preadipocyte differentiation than equally obese women with metabolic syndrome (n = 28); however, OM-preadipocyte differentiation was similar in both groups. SC-preadipocyte differentiation was strongly correlated with triglycerides, HDL cholesterol, homoeostasis model assessment of insulin resistance and OM-adipocyte size. However, OM-preadipocyte differentiation was not correlated with any of these parameters.

CONCLUSIONS

This study identified that SC-preadipocyte differentiation is associated with metabolic syndrome independent of obesity, whereas OM-preadipocyte differentiation is not. These findings suggest that, in the setting of obesity, an enhanced adipogenic capacity of SC depots could be protective for metabolic syndrome. Our data underscores an interaction between adipose tissue homoeostasis and metabolic disorder.

The renin-angiotensin system in the pathophysiology of type 2 diabetes

Increased activation of the renin-angiotensin system (RAS) has been related to cardiovascular disease and type 2 diabetes mellitus. Most randomized clinical trials have demonstrated that RAS blockade reduces the incidence of type 2 diabetes, which has been explained by improved insulin secretion and insulin sensitivity. In this review, an overview of the mechanisms that may underlie the association between the RAS and type 2 diabetes will be provided, with focus on skeletal muscle and adipose tissue function. This will include discussion of several human studies performed in our laboratory to investigate the metabolic and hemodynamic effects of the RAS, combining in vivo measurements of whole-body and tissue metabolism with molecular and immunohistochemical approaches. Available data suggest that the detrimental effects of the RAS on insulin secretion are mediated by a reduction in pancreatic blood flow and induction of islet fibrosis, oxidative stress as well as inflammation, whereas both impaired skeletal muscle function and adipose tissue dysfunction may underlie RAS-induced insulin resistance. Thus, although future studies in humans are warranted, current evidence supports that targeting the RAS in intervention studies may improve metabolic and cardiovascular function in conditions of insulin resistance like obesity and type 2 diabetes.

Adipocyte-specific deficiency of angiotensinogen decreases plasma angiotensinogen concentration and systolic blood pressure in mice

Previous studies demonstrated that overexpression of angiotensinogen (AGT) in adipose tissue increased blood pressure. However, the contribution of endogenous AGT in adipocytes to the systemic renin-angiotensin system (RAS) and blood pressure control is undefined. To define a role of adipocyte-derived AGT, mice with loxP sites flanking exon 2 of the AGT gene (Agt(fl/fl)) were bred to transgenic mice expressing Cre recombinase under the control of an adipocyte fatty acid-binding protein 4 promoter (aP2) promoter to generate mice with adipocyte AGT deficiency (Agt(aP2)). AGT mRNA abundance in adipose tissue and AGT secretion from adipocytes were reduced markedly in adipose tissues of Agt(aP2) mice. To determine the contribution of adipocyte-derived AGT to the systemic RAS and blood pressure control, mice were fed normal laboratory diet for 2 or 12 mo. In males and females of each genotype, body weight and fat mass increased with age. However, there was no effect of adipocyte AGT deficiency on body weight, fat mass, or adipocyte size. At 2 and 12 mo of age, mice with deficiency of AGT in adipocytes had reduced plasma concentrations of AGT (by 24-28%) compared with controls. Moreover, mice lacking AGT in adipocytes exhibited reduced systolic blood pressures compared with controls (Agt(fl/fl), 117 ± 2; Agt(aP2), 110 ± 2 mmHg; P < 0.05). These results demonstrate that adipocyte-derived AGT contributes to the systemic RAS and blood pressure control.

Effects of whey protein supplements on metabolism: evidence from human intervention studies

PURPOSE OF REVIEW

Epidemiological studies indicate that the consumption of milk and dairy products is inversely associated with a lower risk of metabolic disorders and cardiovascular diseases. In particular, whey protein seems to induce these effects because of bioactive compounds such as lactoferrin, immunoglobulins, glutamine and lactalbumin. In addition, it is an excellent source of branch chained amino acids. This review summarizes recent findings on the effects of whey protein on metabolic disorders and the musculoskeletal system.

RECENT FINDINGS

We identified 25 recently published intervention trials examining chronic and/or acute effects of whey protein supplementation on lipid and glucose metabolism, blood pressure, vascular function and on the musculoskeletal system. Whey protein appears to have a blood glucose and/or insulin lowering effect partly mediated by incretins. In addition, whey protein may increase muscle protein synthesis. In contrast there are no clear-cut effects shown on blood lipids and lipoproteins, blood pressure and vascular function. For bone metabolism the data are scarce.

SUMMARY

In summary, whey protein may affect glucose metabolism and muscle protein synthesis. However, the evidence for a clinical efficacy is not strong enough to make final recommendations with respect to a specific dose and the duration of supplementation.