Weight loss and the renin-angiotensin-aldosterone system

Multimarker approach to evaluate the incidence of the metabolic syndrome and longitudinal changes in metabolic risk factors: the Framingham Offspring Study

BACKGROUND

The metabolic syndrome (MetS) is associated with increased cardiovascular risk. We evaluated the relative contributions of circulating biomarkers representing distinct biological pathways to the incidence of MetS and to longitudinal changes of its constituent risk factors.

METHODS AND RESULTS

We measured 8 circulating biomarkers reflecting inflammation (C-reactive protein), hemostasis (plasminogen activator inhibitor-1, fibrinogen), neurohormonal activity (aldosterone, renin, B-type natriuretic peptide, N-terminal proatrial natriuretic peptide), and endothelial dysfunction (homocysteine) in 2292 Framingham Offspring Study participants (mean age, 57 years; 56% women). We related the biomarker panel to incidence of MetS on follow-up initially and then related biomarkers associated with incident MetS to longitudinal change in its components. On follow-up (mean, 2.9 years), 282 participants (of 1473 participants without prevalent MetS at baseline) developed MetS. After adjustment for clinical risk factors, the biomarker panel was associated with incident MetS (P=0.008). On backward elimination, plasminogen activator inhibitor-1 and aldosterone remained associated with incident MetS (multivariable-adjusted odds ratio per 1-SD increment log marker, 1.31 [P=0.004] and 1.21 [P=0.015], respectively). In multivariable analyses evaluating longitudinal change in MetS components (analyzed as continuous variables), plasminogen activator inhibitor-1 was significantly and positively associated with changes in fasting glucose, systolic blood pressure, and triglycerides (all P<0.05). Serum aldosterone was associated positively with change in systolic blood pressure (P=0.023) and inversely with change in high-density lipoprotein cholesterol (P=0.001).

CONCLUSIONS

Higher circulating plasminogen activator inhibitor-1 and aldosterone levels are associated with the development of MetS and with longitudinal change of its components, suggesting that these biomarkers and related pathways play a key role in mediating metabolic risk.

Retinol-binding protein 4 levels are elevated in polycystic ovary syndrome women with obesity and impaired glucose metabolism

OBJECTIVE

Insulin resistance and obesity are common features of the polycystic ovary syndrome (PCOS). Retinol-binding protein 4 (RBP4), a new fat-derived adipokine, has been described to be elevated in obesity and type 2 diabetes. The aim of the present study was to investigate whether serum RBP4 levels are correlated with metabolic parameters, indices of insulin resistance, and endocrine variables in German PCOS women.

DESIGN

We assessed the correlation between metabolic and endocrine parameters with RBP4 levels in 200 PCOS patients and 64 healthy controls.

METHODS

Serum RBP4 was measured by enzyme-linked immunosorbent assay (Immundiagnostik AG, Bensheim, Germany). In addition, anthropometric variables, clinical signs of hyperandrogenism, and body fat were evaluated, and a glucose tolerance test was performed to assess parameters of insulin resistance and glucose metabolism.

RESULTS

Taking the entire PCOS cohort, RBP4 levels were positively correlated with body mass index (BMI), body fat, waist circumference, fasting glucose, and area under the curve for glucose (all P<0.05), but not with indices of insulin resistance. On the other hand, PCOS women with impaired glucose metabolism had higher RBP4 levels than PCOS women with normal glucose metabolism (median 30.6, range 23.3-73.9 versus median 26.3, range 6.4-61.4, P<0.05). Furthermore, no differences were found in RBP4 levels between lean PCOS women and BMI-matched healthy controls.

CONCLUSION

In German PCOS women, serum RBP4 levels are associated with obesity and parameters of glucose metabolism but not with PCOS per se.

Treatment of hypertension in patients with diabetes mellitus

Antihypertensive treatment in diabetes mellitus, especially in diabetics known to have cardiac autonomic neuropathy, may have to consider the status of the autonomic nervous system. In diabetic subjects with cardiac autonomic neuropathy, vagal activity during the night is often reduced. The reduction results in relative or absolute sympathetic activation, which could increase cardiovascular risk. Pathophysiological and clinical data suggests that antihypertensive treatment should reduce rather than induce sympathetic activity in this setting. Beta blocking agents, ACE inhibitors, calcium antagonists of verapamil or diltiazem type and selective imidazoline receptor agonists reduce sympathetic activity and, therefore, may have a beneficial effect in diabetic patients with disturbed sympathovagal balance.

Angiotensin II increases adipose angiotensinogen expression

In addition to the well-defined contribution of the liver, adipose tissue has been recognized as an important source of angiotensinogen (AGT). The purpose of this study was to define the angiotensin II (ANG II) receptors involved in regulation of adipose AGT and the relationship of this control to systemic AGT and/or angiotensin peptide concentrations. In LDL receptor-deficient (LDLR(-/-)) male mice, adipose mRNA abundance of AGT was 68% of that in liver, and adipose mRNA abundance of the angiotensin type 1a (AT(1a)) receptor (AT(1a)R) was 38% of that in liver, whereas mRNA abundance of the angiotensin type 2 (AT(2)) receptor (AT(2)R) was 57% greater in adipose tissue than in liver. AGT and angiotensin peptide concentrations were decreased in plasma of AT(1a)R-deficient (AT(1a)R(-/-)) mice and were paralleled by reductions in AGT expression in liver. In contrast, adipose AGT mRNA abundance was unaltered in AT(1a)R(-/-) mice. AT(2)R(-/-) mice exhibited elevated plasma angiotensin peptide concentrations and marked elevations in adipose AGT and AT(1a)R mRNA abundance. Increases in adipose AGT mRNA abundance in AT(2)R(-/-) mice were abolished by losartan. In contrast, liver AGT and AT(1a)R mRNA abundance were unaltered in AT(2)R(-/-) mice. Infusion of ANG II for 28 days into LDLR(-/-) mice markedly increased adipose AGT and AT(1a)R mRNA but did not alter liver AGT and AT(1a)R mRNA. These results demonstrate that differential mRNA abundance of AT(1a)/AT(2) receptors in adipose tissue vs. liver contributes to tissue-specific ANG II-mediated regulation of AGT. Chronic infusion of ANG II robustly stimulated AT(1a)R and AGT mRNA abundance in adipose tissue, suggesting that adipose tissue serves as a primary contributor to the activated systemic renin-angiotensin system.

Human adipocytes induce an ERK1/2 MAP kinases-mediated upregulation of steroidogenic acute regulatory protein (StAR) and an angiotensin II — sensitization in human adrenocortical cells

OBJECTIVES

Hypertension is a major complication of overweight with frequently elevated aldosterone levels in obese patients. Our previous work suggests a direct stimulation of adrenal aldosterone secretion by adipocytes. Owing to aldosterone's important role in maintaining blood pressure homeostasis, its regulation in obesity is of major importance. One objective was to determine the signaling mechanisms involved in adipocyte-induced aldosterone secretion. In addition to a direct stimulation, a sensitization toward angiotensin II (AngII) might be involved. The second objective was to determine a possible adipokines-induced sensitization of human adrenocortical cells to AngII.

DESIGN

Human subcutaneous adipocytes and adrenocortical cells, and the adrenocortical cell line NCI-H295R were used. Adrenocortical cells were screened for signal transduction protein expression and phosphorylation. Subsequently, steroidogenic acute regulatory protein (StAR), cAMP response element-binding protein (CREB), cAMP and phosphorylated extracellular regulated kinase were analyzed by Western blot, enzyme-linked immunosorbent assay, quantitative PCR, reporter gene assay and confocal microscopy to investigate their role in adipocyte-mediated aldosterone secretion.

RESULTS

AngII-mediated aldosterone secretion was largely increased by preincubating H295R cells with adipocyte secretory products. StAR mRNA and StAR protein were upregulated in a time-dependent way. This steroidogenic effect was independent of the cAMP-protein kinase A (PKA) pathway as cellular cAMP was unaltered and inhibition of PKA by H89 failed to reduce aldosterone secretion. However, CREB reporter gene activity was moderately elevated. Upregulation of StAR was accompanied by ERK1/2 MAP kinase activation and nuclear translocation of the kinases. Inhibition of MAP kinase by UO126 abolished adipokine-stimulated aldosterone secretion from primary human adrenocortical and H295R cells, and inhibited StAR gene activity. Adipokines stimulated steroidogenesis also in primary human adrenocortical cells, supporting a role in human physiology and/or pathology.

CONCLUSIONS

Adipokines induce aldosterone secretion from human adrenocortical cells and sensitization of the cells to stimulation by AngII, possibly mediated via ERK1/2-dependent upregulation of StAR activity. This stimulation of aldosterone secretion could be one link between overweight and inappropriately elevated aldosterone levels.

Obesity and obesity-initiated metabolic syndrome: mechanistic links to chronic kidney disease

There is an epidemic of obesity and the metabolic syndrome in the United States and across the world. Both entities are associated with high mortality, mainly as a result of cardiovascular disease. The epidemic of obesity has been paralleled by an increase in the incidence of chronic kidney disease (CKD). Several recent epidemiologic studies have shown that obesity and the metabolic syndrome are independent predictors of CKD. In addition to diabetes and hypertension, several other mechanisms have been postulated to initiate and maintain kidney injury in patients with obesity and the metabolic syndrome. This article reviews the recent epidemiologic data linking obesity and the metabolic syndrome to CKD and summarizes the potential mechanisms of renal injury in this setting, with a focus on the role of inflammation, lipotoxicity, and hemodynamic factors. Potential preventive and therapeutic modalities based on the limited evidence available are discussed.

Direct Renin inhibition with aliskiren in obese patients with arterial hypertension

Current guidelines from the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure recommend first-line treatment with a thiazide diuretic but do not provide specific guidance for obese patients. The renin system is activated in obesity-associated arterial hypertension. Therefore, we tested the hypothesis that the oral direct renin inhibitor aliskiren could provide additive blood pressure lowering in obese patients with hypertension (body mass index >or=30 kg/m(2); mean sitting diastolic blood pressure: 95 to 109 mm Hg) who had not responded to 4 weeks of treatment with hydrochlorothiazide (HCTZ) 25 mg. After a 2- to 4-week washout, 560 patients received single-blind HCTZ (25 mg) for 4 weeks; 489 nonresponders were randomly assigned to double-blind aliskiren (150 mg), irbesartan (150 mg), amlodipine (5 mg), or placebo for 4 weeks added to HCTZ (25 mg), followed by 8 weeks on double the initial doses of aliskiren, irbesartan, or amlodipine. After 8 weeks of double-blind treatment (4 weeks on the higher dose), aliskiren/HCTZ lowered blood pressure by 15.8/11.9 mm Hg, significantly more (P<0.0001) than placebo/HCTZ (8.6/7.9 mm Hg). Aliskiren/HCTZ provided blood pressure reductions similar to those with irbesartan/HCTZ and amlodipine/HCTZ (15.4/11.3 and 13.6/10.3 mm Hg, respectively), with similar tolerability to placebo/HCTZ. Adverse event rates were highest with amlodipine/HCTZ because of a higher incidence of peripheral edema (11.1% versus 0.8% to 1.6% in other groups). In conclusion, combination treatment with aliskiren is a highly effective and well-tolerated therapeutic option for obese patients with hypertension who fail to achieve blood pressure control with first-line thiazide diuretic treatment.

Association of Adrenal Steroids With Hypertension and the Metabolic Syndrome in Blacks

Blacks have a high prevalence of hypertension and adrenal cortical adenomas/hyperplasia. We evaluated the hypothesis that adrenal steroids are associated with hypertension and the metabolic syndrome in blacks. Ambulatory blood pressures, anthropometric measurements, and measurements of plasma renin activity (PRA), aldosterone, fasting lipids, glucose, and insulin were obtained in 397 subjects (46% hypertensive and 50% female) after discontinuing antihypertensive and lipid-lowering medications. Hypertension was defined as average ambulatory blood pressure >130/85 mm Hg. Late-night and early morning salivary cortisol, 24-hour urine-free cortisol, and cortisone excretion were measured in a consecutive subsample of 97 subjects (40% hypertensive and 52% female). Compared with normotensive subjects, hypertensive subjects had greater waist circumference and unfavorable lipid profiles, were more insulin resistant, and had lower PRA and higher plasma aldosterone and both late-night and early morning salivary cortisol concentrations. Twenty-four-hour urine-free cortisol and cortisone did not differ. Overall, ambulatory blood pressure was positively correlated with plasma aldosterone (r=0.22; P<0.0001) and late-night salivary cortisol (r=0.23; P=0.03) and inversely correlated with PRA (r=-0.21; P<0.001). Plasma aldosterone correlated significantly with waist circumference, total cholesterol, triglycerides, insulin, and the insulin-resistance index. Based on Adult Treatment Panel III criteria, 17% of all of the subjects were classified as having the metabolic syndrome. Plasma aldosterone levels, but not PRA, were elevated in subjects with the metabolic syndrome (P=0.0002). The association of aldosterone with blood pressure, waist circumference, and insulin resistance suggests that aldosterone may contribute to obesity-related hypertension in blacks. In addition, we speculate that relatively high aldosterone and low PRA in these hypertensive individuals may reflect a mild variant of primary aldosteronism.

[Insulin and angiotensin II signaling pathways cross-talk: implications with the association between diabetes mellitus, arterial hypertension and cardiovascular disease]

Insulin (Ins) and angiotensin II (AII) play pivotal roles in the control of two vital and closely related systems: the metabolic and the circulatory, respectively. A failure in the proper action of each of these hormones results, to a variable degree, in the development of two highly prevalent and commonly overlapping diseases--diabetes mellitus (DM) and hypertension (AH). In recent years, a series of studies has revealed a tight connection between the signal transduction pathways that mediate Ins and AII actions in target tissues. This molecular cross-talk occurs at multiple levels and plays an important role in phenomena that range from the action of anti-hypertensive drugs to cardiac hypertrophy and energy acquisition by the heart. At the extracellular level, the angiotensin-converting enzyme controls AII synthesis but also interferes with Ins signaling through the proper regulation of AII and the accumulation of bradykinin. At an early intracellular level, AII, acting through JAK-2/IRS-1/PI3-kinase, JNK and ERK, may induce the serine phosphorylation and inhibition of key elements of the Ins-signaling pathway. Finally, by inducing the expression of the regulatory protein SOCS-3, AII may impose a late control on the Ins signal. This review will focus on the main advances obtained in this field and will discuss the implications of this molecular cross-talk in the common clinical association between DM and AH.

Renin receptor expression in human adipose tissue

Adipose tissue synthesizes all components of the renin-angiotensin system. The renin receptor (RenR) is able, on renin binding, to increase its efficiency to generate angiotensin I from angiotensinogen. We demonstrate that RenR is specifically synthesized in the stromal portion of human adipose tissue in both isolated interadipocyte stromal cells and in stromal areas. RenR is expressed at the periphery of cells, strongly suggesting a membranal localization. RenR protein expression in primary cultures of human stromal cells decreased significantly during differentiation, whereas RenR mRNA levels did not change, demonstrating that RenR was expressed in both preadipocyte and nonpreadipocyte cells, and was regulated at a posttranscriptional level. Double-labeling immunohistochemistry of human adipose tissue sections revealed that RenR was colocalized with renin, whereas incubation of 3T3-L1, a preadipocyte cell line, with renin stimulated the phosphorylation state of the intracellular signaling pathway ERK 1/2, and short exposure of human adipose stromal cells in primary culture to renin was followed by a long-lasting dose-dependent increase of angiotensin I generation, indicating that adipose RenR is functional. We show, using a large set of human adipose tissue biopsies, that RenR expression was increased in visceral compared with subcutaneous adipose tissue of lean and obese patients. Taken together with our finding that RenR was colocalized with plasminogen activator inhibitor type 1, the main inhibitor of the fibrinolytic system in visceral adipose tissue, the above-mentioned data suggest that RenR plays a role in obesity-induced visceral adipose tissue accumulation and its accompanying cardiovascular complications.

Obesity-hypertension: an ongoing pandemic

Considerable evidence has suggested that excessive weight gain is the most common cause of arterial hypertension. This association has been observed in several populations, in different regions of the world. Obesity-hypertension, a term that underscores the link between these two deleterious conditions, is an important public health challenge, because of its high frequency and concomitant risk of cardiovascular and kidney diseases. The obesity-hypertension pandemic imposes a considerable economic burden on societies, directly reflecting on healthcare system costs. Increased renal sodium reabsorption and blood volume expansion are central features in the development of obesity-hypertension. Overweight is also associated with increased sympathetic activity. Leptin, a protein expressed in and secreted by adipocytes, is the main factor linking obesity, increased sympathetic nervous system activity and hypertension. The renin-angiotensin-aldosterone system has also been causally implicated in obesity-hypertension, because angiotensinogen is expressed in and secreted by adipose tissue. Hypoadiponectinemia, high circulating levels of free fatty acids and increased vascular production of endothelin-1 (ET-1) have been reported as potential mechanisms for obesity-hypertension. Lifestyle changes are effective in obesity-hypertension control, though pharmacological treatment is frequently necessary. Despite the consistency of the mechanistic approach in explaining the causal relation between hypertension and obesity, there is yet no evidence that one class of drug is superior to the others in controlling obesity-hypertension. In this review, we present the current knowledge and research in obesity-hypertension, exploring the epidemiologic evidence of the association, its probable pathophysiological mechanisms and treatment issues.

Endocrine role of the renin-angiotensin system in human adipose tissue and muscle: effect of beta-adrenergic stimulation

The renin-angiotensin system has been implicated in obesity-related hypertension and insulin resistance. We examined whether locally produced components of the renin-angiotensin system in adipose tissue and skeletal muscle play an endocrine role in vivo in humans. Furthermore, the effects of beta-adrenergic stimulation on plasma concentrations and tissue release of renin-angiotensin system components were investigated. Systemic renin-angiotensin system components and arteriovenous differences of angiotensin II (Ang II) and angiotensinogen (AGT) across abdominal subcutaneous adipose tissue and skeletal muscle were assessed in combination with measurements of tissue blood flow before and during systemic beta-adrenergic stimulation in 13 lean and 10 obese subjects. Basal plasma Ang II and AGT concentrations were not significantly different between lean and obese subjects. Ang II concentrations were increased in obese compared with lean subjects during beta-adrenergic stimulation (12.6+/-1.5 versus 8.1+/-1.0 pmol/L; P=0.04), whereas AGT concentrations remained unchanged. Plasma renin activity increased to a similar extent in lean and obese subjects during beta-adrenergic stimulation (both P<0.01). No net Ang II release across adipose tissue and skeletal muscle could be detected in both groups of subjects. However, AGT was released from adipose tissue and muscle during beta-adrenergic stimulation in obese subjects (both P<0.05). In conclusion, locally produced Ang II in adipose tissue and skeletal muscle exerts no endocrine role in lean and obese subjects. In contrast, AGT is released from adipose tissue and muscle in obese subjects during beta-adrenergic stimulation, which may contribute to the increased plasma Ang II concentrations during beta-adrenergic stimulation in obese subjects.

Enhanced aldosterone signaling in the early nephropathy of rats with metabolic syndrome: possible contribution of fat-derived factors

Metabolic syndrome is an important risk factor for proteinuria and chronic kidney disease independent of diabetes and hypertension; however, the underlying mechanisms have not been elucidated. Aldosterone is implicated in target organ injury of obesity-related disorders. This study investigated the role of aldosterone in the early nephropathy of 17-wk-old SHR/NDmcr-cp, a rat model of metabolic syndrome. Proteinuria was prominent in SHR/NDmcr-cp compared with nonobese SHR, which was accompanied by podocyte injury as evidenced by foot process effacement, induction of desmin and attenuation of nephrin. Serum aldosterone level, renal and glomerular expressions of aldosterone effector kinase Sgk1, and oxidative stress markers all were elevated in SHR/NDmcr-cp. Mineralocorticoid receptors were expressed in glomerular podocytes. Eplerenone, a selective aldosterone blocker, effectively improved podocyte damage, proteinuria, Sgk1, and oxidant stress. An antioxidant tempol also alleviated podocyte impairment and proteinuria, along with inhibition of Sgk1. As for the mechanisms of aldosterone excess, visceral adipocytes that were isolated from SHR/NDmcr-cp secreted substances that stimulate aldosterone production in adrenocortical cells. The aldosterone-releasing activity of adipocytes was not inhibited by candesartan. Adipocytes from nonobese SHR did not show such activity. In conclusion, SHR/NDmcr-cp exhibit enhanced aldosterone signaling, podocyte injury, and proteinuria, which are ameliorated by eplerenone or tempol. The data also suggest that adipocyte-derived factors other than angiotensin II might contribute to the aldosterone excess of this model.

Influence of salt intake on renin-angiotensin and natriuretic peptide system genes in human adipose tissue

We tested the hypothesis that changes in sodium intake modulate adipose-tissue renin-angiotensin and natriuretic peptide system gene expression in humans. We studied 9 healthy young men in a metabolic ward at constant room temperature, humidity, and water, potassium, and calcium intake. Subjects were submitted to 4 different periods of sodium intake, and blood samples, microdialysis samples (interstitial fluid), and biopsies from subcutaneous abdominal adipose tissue were obtained at the end of the low-sodium period (0.7 mmol Na/kg per day) and at the end of the high-sodium period (7.7 mmol Na/kg per day). Urinary sodium excretion was 64+/-4 mmol per day with the low-sodium diet and 521+/-8 mmol per day with the high-sodium diet. Systemic and microdialysate sodium concentrations were similar with both interventions. With high-sodium intake, systemic renin activity and aldosterone levels were suppressed, angiotensin-converting enzyme activity did not change, and systemic levels of the atrial natriuretic peptide increased. High-sodium diet increased angiotensin-converting enzyme and atrial natriuretic peptide gene expression in adipose tissue. None of the other genes tested were influenced by changes in dietary sodium intake. Our findings suggest that the adipose-tissue renin-angiotensin system is not part of a feedback mechanism regulating sodium homeostasis and blood pressure. Systemic and adipose-tissue renin-angiotensin systems are regulated at least in part independently from each other. In contrast, systemic atrial natriuretic peptide and adipose-tissue atrial natriuretic peptide respond similarly to changes in sodium intake.

Hypertension and antihypertensive treatment of diabetic nephropathy

We are currently confronted with an epidemic of renal failure caused by diabetic nephropathy. It has become apparent that blood pressure is a major determinant of the risk of developing diabetic nephropathy; individuals with a genetic predisposition to hypertension are at increased risk of developing diabetes and diabetic nephropathy. Antihypertensive medication has an impact on development of diabetes; beyond blood-pressure lowering, the risk of diabetes is further reduced by blockade of the renin-angiotensin system (RAS). In experimental studies, blockade of the RAS in the pre-diabetic stage ameliorates the severity of subsequent diabetic nephropathy. Guidelines recommend a target blood pressure of 130/80 mmHg for diabetic patients without proteinuria and some guidelines recommend a target of less than 125/175 mmHg for diabetic patients with proteinuria. Above a systolic blood pressure of approximately 110 mmHg, the risk of progression of diabetic nephropathy increases progressively with increasing blood pressure. Blood-pressure lowering and blockade of the RAS delays or prevents onset of microalbuminuria, slows worsening of microalbuminuria and attenuates progression of diabetic nephropathy, even in advanced stages. In addition to blood pressure, proteinuria is a treatment target and should be reduced to below 1 g/24 h.

Retinol-binding protein 4 in human obesity

Studies in mice suggest that adipocytes serve as glucose sensors and regulate systemic glucose metabolism through release of serum retinol-binding protein 4 (RBP4). This model has not been validated in humans. RBP4 was highly expressed in isolated mature human adipocytes and secreted by differentiating human adipocytes. In contrast to the animal data, RBP4 mRNA was downregulated in subcutaneous adipose tissue of obese women, and circulating RBP4 concentrations were similar in normal weight, overweight, and obese women (n = 74). RBP4 was positively correlated with GLUT4 expression in adipose tissue, independent of any obesity-associated variable. Five percent weight loss slightly decreased adipose RBP4 expression but did not influence circulating RBP4. In another set of experiments, we stratified patients (n = 14) by low or high basal fasting interstitial glucose concentrations, as determined by the microdialysis technique. Venous glucose concentrations were similar throughout oral glucose tolerance testing, and basal RBP4 expression in adipose tissue and serum RBP4 concentrations were similar in the groups with higher and lower interstitial glucose levels. Our findings point to profound differences between rodents and humans in the regulation of adipose or circulating RBP4 and challenge the notion that glucose uptake by adipocytes has a dominant role in the regulation of RBP4.

Obesity, proteinuria and progression of renal failure

PURPOSE OF REVIEW

Recent studies have reported an alarming increase in the incidence of obesity-related glomerulopathy, in a context of a worldwide spread of obesity.

RECENT FINDINGS

Several epidemiological investigations have confirmed that obesity is a significant risk factor for the appearance of proteinuria and end-stage renal disease in a normal population. Obesity-induced hemodynamic changes and glomerular deposition of lipids (partly mediated by sterol regulatory element-binding proteins) play an important role in the pathogenesis of obesity-related renal disease. In addition, the renin-angiotensin-aldosterone system is markedly activated in obesity, adipocytes being an important source of these hormones. Weight loss induces a marked reduction in all renin-angiotensin-aldosterone system components. Patients with reduced renal mass of any origin appeared to be particularly susceptible to the detrimental influence of obesity: body mass index was the most important risk factor for the development of proteinuria and renal insufficiency in patients with unilateral renal agenesis, unilateral nephrectomy and remnant kidneys. Weight loss induces a very important reduction in proteinuria in chronic proteinuric nephropathies of different etiologies.

SUMMARY

Prevention and treatment of obesity should be a first-line objective in the therapeutic approach of patients with diabetic and nondiabetic chronic renal diseases.

Antihypertensive therapy in the obese hypertensive patient

PURPOSE OF REVIEW

Obesity is becoming recognized as one of the most important risk factors for the development of hypertension. The purpose of the review is to examine the latest evidence linking hypertension to obesity, summarize the benefits of weight reduction and present results of recent clinical trials evaluating antihypertensive treatment in obese patients.

RECENT FINDINGS

Adipose tissue has been directly implicated in the pathogenesis of hypertension. Obesity has been associated with unequivocal changes in cardiovascular structure and function. In contrast to earlier studies, several recent trials included overweight and obese patients. Evidence of potential benefits of angiotensin blockade in the management of obesity hypertension is growing. Hypertension management in obese individuals is complicated by poorer response to treatment, and the increased need for multiple medications. It is important to consider obstructive sleep apnea in obese patients with resistant hypertension.

SUMMARY

Several new lines of evidence suggest that drugs blocking the renin-angiotensin system might be considered as first-line therapy of obesity-related hypertension. Recent progress in understanding the mechanisms of obesity and associated disease processes might lead to development of novel therapeutic strategies. Further research in this area holds great promise for prevention of obesity-related cardiovascular disease.

From big fat cells to high blood pressure: a pathway to obesity-associated hypertension

PURPOSE OF REVIEW

The environment created by modern industrialized societies has caused an unprecedented rise in the prevalence of obesity and obesity-related disorders, including hypertension. Mechanisms that underlie the development of hypertension in obese individuals are not very well understood; they are thought to involve activation of the sympathetic nervous system, the renin-angiotensin-aldosterone system, and oxidative stress.

RECENT FINDINGS

Recent research suggests that obesity-associated hypertension may be causally related to the accumulation of 'dysfunctional' adipose tissue characterized by the presence of 'large' lipid-laden adipocytes.

SUMMARY

Excess energy-intake leads to an expansion of adipose tissue, a hallmark of obesity. But morphology of the expanded adipose tissue differs across individuals, including the size of adipocytes. The presence of 'large' rather than 'small' adipocytes is associated with functional and structural abnormalities of adipose tissue. These include increased production of bioactive molecules, such as leptin, angiotensinogen, pro-inflammatory cytokines, and reactive oxygen species; insufficient capacity to accommodate excess energy-intake leading to ectopic fat storage in tissues and in turn insulin resistance and hyperinsulinemia; and augmented macrophage infiltration enhancing the production of pro-inflammatory cytokines and reactive oxygen species. Such a 'dysfunctional' adipose tissue may, in turn, induce activation of the sympathetic nervous system and the renin-angiotensin-aldosterone system and oxidative stress and, hence, promote the development of obesity-associated hypertension.

Aldosteronism and Hypertension

A growing body of evidence suggests that hyperaldosteronism contributes significantly to the development and the severity of hypertension as well as to resistance to antihypertensive treatment. In cross-sectional analyses, plasma aldosterone levels have been shown to relate to BP levels, particularly in obese individuals. In these same individuals, BP was not related to plasma renin activity, suggesting an effect of aldosterone on BP independent of renin-angiotensin II. In a recent prospective analysis from the Framingham investigators, baseline serum aldosterone was strongly associated with development of hypertension during a 4-yr follow-up.

Plasma aldosterone is independently associated with the metabolic syndrome

The aim of this study was to analyze the associations of plasma aldosterone and plasma renin activity with the metabolic syndrome and each of its components. We analyzed data from a family based study in the Seychelles made up of 356 participants (160 men and 196 women) from 69 families of African descent. In multivariable models, plasma aldosterone was associated positively (P < 0.05) with blood pressure in older individuals (interaction with age, P < 0.05) and with waist circumference in men (interaction with sex, P < 0.05) and negatively with high-density lipoprotein cholesterol, in particular in individuals with elevated urinary potassium excretion (interaction with urinary potassium, P < 0.05); plasma renin activity was significantly associated with triglycerides and fasting blood glucose. Plasma aldosterone, but not plasma renin activity, was associated with the metabolic syndrome per se, independently of the association with its separate components. The observation that plasma renin activity was associated with some components of the metabolic syndrome, whereas plasma aldosterone was associated with other components of the metabolic syndrome, suggests different underlying mechanisms. These findings reinforce previous observations suggesting that aldosterone is associated with several cardiovascular risk factors and also suggest that aldosterone might contribute to the increased cardiovascular disease risk in individuals of African descent with the metabolic syndrome.

Hemodynamic and metabolic responses to interstitial angiotensin II in normal weight and obese men

OBJECTIVE

The expression of the AT1 receptor in adipose tissue is not decreased or even increased in obese subjects despite systemic activation of the renin-angiotensin system. Therefore, we hypothesized that peripheral tissues of obese subjects are hypersensitive to angiotensin (Ang) II.

METHODS

We characterized the effect of locally applied Ang II in skeletal muscle and subcutaneous adipose tissue of healthy non-obese (n = 12) and obese (n = 11) men using the microdialysis technique. Tissues were perfused with Ringer's solution + ethanol and incremental doses of Ang II (0.01, 0.1 and 1 micromol/l). Dialysate ethanol, glycerol, glucose, lactate, and pyruvate concentrations were measured to assess changes in blood flow (ethanol dilution technique), lipolysis and glycolysis, respectively.

RESULTS

In adipose tissue, basal ethanol ratio was significantly higher and dialysate metabolite concentrations were significantly lower in obese versus non-obese men. In muscle, basal dialysate glycerol was significantly higher in obese versus non-obese men. Ang II elicited small increases in ethanol ratio and decreases in dialysate glucose in adipose tissue and skeletal muscle in both non-obese and obese men. Dialysate lactate increased significantly in both tissues of obese, but not non-obese men. Dialysate glycerol increased in adipose tissue of non-obese (+ 40%) but not of obese and remained almost unchanged in muscle of both groups.

CONCLUSIONS

Interstitially applied Ang II elicits subtle changes in tissue perfusion and metabolism. However, we did not find a major increase in interstitial Ang II responsiveness in obese men.

Signaling by the angiotensin-converting enzyme

Inhibition of the angiotensin-converting enzyme (ACE) protects against the progression of several cardiovascular diseases. Because of its dual role in regulating angiotensin II and bradykinin levels, the positive clinical effects of ACE inhibitors were thought to be the consequence of concomitant reductions in the production of angiotensin II and the degradation of bradykinin. Recent evidence suggests that some of the beneficial effects of ACE inhibitors on cardiovascular function and homeostasis can be attributed to novel mechanisms. These include the accumulation of the ACE substrate N-acetyl-seryl-aspartyl-lysyl-proline, which blocks collagen deposition in the injured heart, as well as the activation of an ACE signaling cascade that involves the activation of the kinase CK2 and the c-Jun N-terminal kinase in endothelial cells and leads to changes in gene expression. Moreover, at least one other ACE homologue (ACE2) is proposed to counteract the detrimental effects associated with the activation of the classical renin-angiotensin system. These data reveal hitherto unexpected levels of internal regulation of the renin-angiotensin system.

Diagnosis and management of hypertension in obesity

Cardiovascular risk in a patient with obesity hypertension increases with the extent of risk factor clustering. It is therefore important to determine the global risk of a patient with hypertension rather than to focus solely on blood pressure. Every hypertensive should be screened for other than blood pressure risk factors, target organ damage and concomitant diseases or accompanying clinical conditions. Assessment of blood pressure and target organ damage might be more difficult in obese hypertensives than in normal-weight patients. Intensive lifestyle interventions can reduce weight, and decrease blood pressure and cardiovascular risk in obese hypertensive patients. Current guidelines do not provide specific recommendation for pharmacological management of the hypertensive patients with obesity. Recent trials have consistently shown that therapy involving beta-blockers and diuretics may induce more new-onset diabetes compared with other combination therapies. Several lines of evidence suggest that anti-hypertensive agents that block the renin-angiotensin system may be especially beneficial in treating obese hypertensive patients. Hypertension management in obese individuals is complicated by poorer response to treatment, and the increased need for multiple medications. It is important to consider obstructive sleep apnoea in the differential diagnosis of hypertensive patients who respond poorly to combination therapy with anti-hypertensive medications.

The obese patient with diabetes mellitus: from research targets to treatment options

Abdominal obesity is a recognized risk factor for both type 2 diabetes mellitus and cardiovascular disease. The metabolic consequences of obesity, such as insulin resistance and impaired glucose tolerance, are primarily attributable to visceral, rather than to subcutaneous, adipose tissue. As a result, liposuction, which mainly removes subcutaneous fat, has no significant effect on insulin sensitivity; by contrast, weight loss resulting from bariatric surgical procedures is associated with resolution of type 2 diabetes in almost 80% of patients. Even modest weight loss in overweight or obese individuals is associated with significant reductions in the risk of diabetes and increased survival. Recent studies have suggested that the renin-angiotensin system (RAS) functions in the regulation of adipogenesis. Activation of this system is increased in obese individuals and angiotensin II, acting via angiotensin type 1 receptors, inhibits the differentiation of preadipocytes into mature adipocytes. This might be expected to result in ectopic storage of fat in tissues such as skeletal muscle and liver, thereby decreasing insulin sensitivity. Evidence from animal studies suggests that angiotensin-receptor blockers can promote redistribution of excess fat from these ectopic sites to mature adipocytes, resulting in improved insulin sensitivity. Clinical trials with telmisartan are currently investigating the effects of RAS blockade on insulin sensitivity in humans.

Heart and kidney: fatal twins?

The importance of renal function as both a marker of and risk factor for cardiovascular disease is increasingly recognized. This link is apparent even in the earliest stages of renal dysfunction, at levels that are conventionally considered "normal." These findings are of considerable importance, given the prevalence of high-normal levels of albuminuria (i.e., 10 to 20 mg/L) in the general population. There is also a close link between the progression of albuminuria and the development of insulin resistance and type 2 diabetes mellitus, such that kidney disease--far from being simply a consequence of the metabolic syndrome--may be considered a component of it. It may be hypothesized that minor derangements of renal function, such as microalbuminuria or reduced glomerular filtration rate, can lead to dysfunction of the endothelium, with the consequence of sensitizing the vasculature to the injurious effects of hypertension, dyslipidemia, and other risk factors. The renin-angiotensin system (RAS) is highly activated in patients with the metabolic syndrome, and this presumably is also true for the intrarenal RAS systems. Both angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers are known to reduce the progression of renal damage. Still to be resolved, however, is the optimal dosage; several recent studies indicate that the dosage required for maximal blood pressure reduction is insufficient to provide maximal renoprotection.

The tissue renin-angiotensin system and intracellular signalling

PURPOSE OF REVIEW

The renin-angiotensin system is not what it was, or for that matter not necessarily where we thought it should be. For example, there is a novel angiotensin I-metabolizing enzyme that generates angiotensin 1-7 rather than angiotensin II. Moreover, we are slowly realizing the importance of local rather than circulating angiotensin II.

RECENT FINDINGS

Rather than concentrating on the systemic renin-angiotensin system, recent work has concentrated on elucidating the consequences of increasing angiotensin II production within specific organs, such as the heart and vasculature, as well as in the pancreas and in adipose tissue. Inhibition of angiotensin II production either using angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers not only reverses remodelling but also increases tissue insulin sensitivity. Targeting the renin-angiotensin system clinically delays the onset of type 2 diabetes, but the mechanisms involved are not clearly understood. Moreover, at least one other angiotensin-converting enzyme homologue (ACE2) plays a significant role in the regulation of heart and kidney function, and as it generates angiotensin 1-7 from angiotensin I, it is proposed to counteract the detrimental effects associated with the activation of the classic renin-angiotensin system.

SUMMARY

There is a need to re-evaluate the role(s) played by the molecular components of the "extended" local renin-angiotensin system and their role in vascular disease and type 2 diabetes.

Oestrogen and weight loss decrease isoproterenol-induced Fos immunoreactivity and angiotensin type 1 mRNA in the subfornical organ of female rats

Studies from our laboratory and others show that oestrogen reduces angiotensin II (Ang II)-induced water intake by ovariectomized rats. Elimination of endogenous oestrogen by ovariectomy causes weight gain that can be reversed or prevented by oestrogen replacement. Changes in body weight modify cardiovascular responses to Ang II but whether such changes have similar effects on central and behavioural responses to Ang II is unknown. The goal of this study was to evaluate the contributions of oestrogen and weight loss to isoproterenol (isoprenaline; Iso)-induced Fos immunoreactivity (IR) and to angiotensin type 1 (AT1) receptor mRNA in forebrain regions implicated in the control of fluid balance. Isoproterenol significantly increased Fos IR in the hypothalamic paraventricular and supraoptic nuclei, the subfornical organ (SFO), and the organum vasculosum of the lamina terminalis, but had no effect on AT1 mRNA expression. However, both Iso-induced Fos IR and the AT1 mRNA were attenuated in the SFO of the oestrogen and weight loss groups compared with that of the control group. Consequently, we examined the effect of weight loss on Iso-induced water intake and plasma renin activity (PRA) and found that weight loss decreased water intake after Iso, but had no effect on PRA. Thus, we propose that weight loss decreases Ang II-elicited water intake in the female rat by down-regulating the expression of the AT1 receptor.

Hemodynamic and metabolic responses to valsartan and atenolol in obese hypertensive patients

OBJECTIVE

None of the current hypertension guidelines provides specific guidance regarding pharmacological management of obese hypertensive patients. Treatment recommendations for lean hypertensives may not be simply extrapolated to obese hypertensive persons.

DESIGN

Randomized, double-blind, parallel-group study with a 13-week treatment period.

SETTING

Multicenter study in Germany.

PATIENTS

Obese patients with mild to moderate uncomplicated essential hypertension.

INTERVENTION

Patients were treated with valsartan at a maximal dose of 160 mg/day or with atenolol at a maximal dose of 100 mg/day. Hydrochlorothiazide at doses of 12.5-25 mg was added in patients with blood pressure > 140/90 mmHg on monotherapy.

MAIN OUTCOME MEASURES

Blood pressure, lipid and glucose metabolism, and highly sensitive C-reactive protein (hsCRP) were monitored.

RESULTS

Sixty-seven patients were randomized to valsartan and 65 patients to atenolol. With valsartan, systolic blood pressure (SBP) decreased from 160.8 +/- 8.9 to 140.5 +/- 13.3 mmHg and diastolic blood pressure (DBP) from 96.1 +/- 7.0 to 85.1 +/- 8.1 mmHg by the end of the study. With atenolol, SBP decreased from 159.3 +/- 6.8 to 139.8 +/- 14.5 mmHg and DBP from 95.0 +/- 6.8 to 83.5 +/- 7.5 mmHg (P = 0.91 for SBP and P = 0.34 for DBP between interventions). Body weight did not change with either treatment. We did not see a significant difference in the response of lipid levels or hsCRP between interventions. To assess the cumulative effect of each intervention on glucose metabolism over the trial duration, we calculated individual areas under the curve for homeostasis model assessment for insulin resistance (HOMA-IR) over time. The resulting area under the curve was significantly smaller with valsartan compared with atenolol (P = 0.02).

CONCLUSIONS

Beta-adrenoreceptor blockers and AT1-receptor blockers, particularly in combination with low-dose diuretics, effectively lower blood pressure in obese hypertensives. However, metabolic responses differ between both treatment strategies, with beneficial effects of AT1-receptor blockers. AT1-receptor blockers are a good choice in obese hypertensives, given the profoundly increased diabetes risk in this population.

Obesity and the renin- angiotensin-aldosterone system

The renin-angiotensin-aldosterone system (RAAS) is a key regulator of cardiovascular function. RAAS activity is upregulated in obesity despite concurrent renal sodium retention, which is a hallmark and principle determinant of obesity-associated hypertension. The contribution of adipose tissue to increased angiotensinogen and aldosterone plasma levels in obesity is probably due to the secretion of angiotensinogen and, as yet, unidentified aldosterone secretagogues by adipocytes. Increased circulating renin activity, on the other hand, is probably due to increased sympathetic activity in the obese. Modest weight reduction significantly reduces RAAS activity by uncertain mechanisms. Pharmacological blockade of the RAAS yielded promising results, both with regard to cardiovascular function and metabolic complications of obesity. These studies suggest that the activated RAAS is a prime pharmacological target for reducing the cardiometabolic risk in obese patients.

C-344T polymorphism of the aldosterone synthase gene and blood pressure in the elderly: a population-based study

OBJECTIVES

Whether the C-344T polymorphism of the aldosterone synthase gene is important for blood pressure control remains controversial. It has been proposed that an association between this polymorphism and blood pressure might be evident in elderly subjects. The aim of the present study was to test this hypothesis in an epidemiological context.

DESIGN

A cross-sectional epidemiological evaluation of a highly homogeneous unselected general population of elderly Caucasians.

METHODS

Lifestyle, medical history, anthropometrics, skinfold thickness, supine blood pressure, heart rate and biochemical measures were recorded in 437 subjects aged > or = 65 years living in a secluded valley. All were genotyped for C-344T allele status and underwent measurements of plasma aldosterone and renin.

RESULTS

The C-344T genotypic frequency did not deviate from Hardy-Weinberg equilibrium. The aldosterone to renin ratio was 19% lower in the CC than in the TT genotype. Systolic blood pressure was significantly lower in subjects with the CC genotype, higher in the TT (+9.6 mmHg versus CC) and intermediate in the CT (+7.9 mmHg versus CC). Adjustment for age, gender, smoking and antihypertensive treatment did not affect this association. Diastolic blood pressure did not differ across genotypes. A significant increase of systolic blood pressure with increasing age and with increasing skinfold thickness was observed in the TT homozygotes but not in the C-carriers.

CONCLUSIONS

These data support the concept that the C-344T polymorphism plays a role in controlling systolic blood pressure and the age-related increase in systolic blood pressure in response to age and to body fat, possibly through differences in modulation of aldosterone synthesis.

Influences of AT1 receptor blockade on tissue metabolism in obese men

ANG II applied to the interstitial space influences carbohydrate and lipid metabolism in a tissue-specific fashion. Thus endogenous ANG II may have a tonic effect on tissue metabolism that could be reversed with ANG II type 1 (AT1) receptor blockade, particularly during adrenergic stimulation. We studied 14 obese men. They were treated for 10 days with the AT1 receptor blocker irbesartan or with placebo in a double-blind and crossover fashion. At the end of each treatment period, we assessed skeletal muscle and adipose tissue metabolism using the microdialysis technique. The ethanol dilution technique was applied to follow changes in tissue blood flow. Measurements were obtained at baseline and during application of incremental isoproterenol concentrations through the microdialysis catheter. Blood pressure decreased from 133 ± 3/84 ± 3 to 128 ± 3/79 ± 2 mmHg for systolic and diastolic blood, respectively ( P = 0.02 and 0.006, respectively) with AT1 receptor blockade. Isoproterenol perfusion caused a dose-dependent increase in dialysate glycerol in adipose tissue and in skeletal muscle. Irbesartan slightly reduced the isoproterenol-induced glycerol response in adipose tissue ( P < 0.05 by ANOVA). Ethanol ratio, interstitial glucose supply, and lactate production in adipose tissue and skeletal muscle were similar with placebo and irbesartan. We conclude that AT1 receptor blockade in obese men does not reveal a major tonic ANG II effect on interstitial glucose supply, lipolysis, or glycolysis in skeletal muscle, either at rest or during β-adrenergic stimulation. Endogeneous ANG II may slightly increase adipose tissue lipolysis. The mechanism may promote the redistribution of triglycerides from adipose tissue toward other organs.

Fat tissue metabolism and adrenal steroid secretion

Obesity has reached epidemic proportions in Western societies, contributing to metabolic diseases, hypertension, and vascular diseases. White adipose tissue has traditionally been regarded merely as lipid, and consequently, as energy storage. However, recent data revealed the importance of adipose tissue as a highly active endocrine organ and its involvement in the body's metabolism and homeostasis. Obesity is associated with several endocrine disorders, including adrenocortical malfunction. Because of the central role of adrenal function in the body's homeostasis, adrenal malfunction is important in the development of other obesity-related abnormalities. Therefore, in this short review, we summarize recent data on obesity-induced changes in adrenocortical mineralocorticoid, glucocorticoid, and androgen secretions and their consequences for metabolism.

Adipose tissue as source and target for novel therapies

The physiology of adipose tissue has a key role in the pathogenesis of the metabolic syndrome and related cardiovascular disorders. Three main functions of adipocytes have been proposed to explain this role: the secretion of adipocyte-derived hormones (so-called adipokines), energy dissipation/thermogenesis, and energy storage. There is mounting evidence that this repertoire of actions and reactions contributes to whole-body glucose and energy homeostasis, the control of blood pressure, immune-system function, haemostasis and atherosclerosis. In this article we highlight the most recent examples of adipocyte-based therapies and discuss future pharmacological options for exploiting this triad of adipocyte functions.

The metabolic syndrome: role of skeletal muscle metabolism

Skeletal muscle constitutes the largest insulin-sensitive tissue in the body and is the primary site for insulin-stimulated glucose utilization. Skeletal muscle resistance to insulin is fundamental to the metabolic dysregulation associated with obesity and physical inactivity, and contributes to the development of the metabolic syndrome (MS). The inability to efficiently take up and store fuel, and to transition from fat to glucose as the primary source of fuel during times of caloric abundance (high insulin) or scarcity (low insulin) has been termed metabolic inflexibility which contributes to a whole body metabolic dysregulation and cardiovascular risk. Potential mechanisms contributing to reduced insulin signaling and action in skeletal muscle includes adipose tissue expansion and increased inflammatory adipokines, increased renin-angiotensin-aldosterone system (RAAS) activity, decreases in muscle mitochondrial oxidative capacity, increased intramuscular lipid accumulation, and increased reactive oxygen species. Future research is focused upon understanding these and other potential mechanisms in order to identify therapeutic targets for reducing MS risk. Strategies will include adequate physical activity and maintaining a healthy weight, but may also require specific pharmacologic interventions.

Primary aldosteronism: Diagnostic and therapeutic considerations

Recent evaluations indicate that primary aldosteronism (PA) is common in patients with hypertension. In patients with mild to moderate hypertension the prevalence of PA is 5% to 10%, whereas in subjects with resistant hypertension the prevalence is approximately 20%. As such, PA has become the most common secondary cause of hypertension. Such high prevalence rates are distinctly different from earlier assessments in which PA was found to be rare, with a prevalence of generally less than 1% of hypertensive patients. Why PA is seemingly so much more common now than when first described remains unknown. Accurate identification of PA allows for specific therapy with aldosterone antagonists or with surgical resection of aldosterone-producing adenomas. Determination of the plasma aldosterone to plasma renin activity ratio is an effective screen for PA in that it has a high negative predictive value even in the setting of ongoing antihypertensive therapy. Its specificity, however, is low such that a high ratio is suggestive of PA but must be confirmed by demonstration of high and autonomous secretion of aldosterone.

Activation of the peripheral endocannabinoid system in human obesity

Obesity is the main risk factor for the development of type 2 diabetes. Activation of the central endocannabinoid system increases food intake and promotes weight gain. Blockade of the cannabinoid type 1 (CB-1) receptor reduces body weight in animals by central and peripheral actions; the role of the peripheral endocannabinoid system in human obesity is now being extensively investigated. We measured circulating endocannabinoid concentrations and studied the expression of CB-1 and the main degrading enzyme, fatty acid amide hydrolase (FAAH), in adipose tissue of lean (n = 20) and obese (n = 20) women and after a 5% weight loss in a second group of women (n = 17). Circulating levels of anandamide and 1/2-arachidonoylglycerol were increased by 35 and 52% in obese compared with lean women (P < 0.05). Adipose tissue mRNA levels were reduced by -34% for CB-1 and -59% for FAAH in obese subjects (P < 0.05). A strong negative correlation was found between FAAH expression in adipose tissue and circulating endocannabinoids. Circulating endocannabinoids and CB-1 or FAAH expression were not affected by 5% weight loss. The expression of CB-1 and FAAH was increased in mature human adipocytes compared with in preadipocytes and was found in several human tissues. Our findings support the presence of a peripheral endocannabinoid system that is upregulated in human obesity.

Caloric restriction versus drug therapy to delay the onset of aging diseases and extend life

There are two firmly established methods of prolonging life. Calorie restriction (CR) using nutrient-rich diets to prolong life in lower animals, and life saving medications in humans to delay the development of the major diseases of middle and old age. These two approaches have different mechanisms of action. In rats, CR at 40% below ad libitum intake begun soon after weaning and continued until death, reduces body weight by about 40% and increases lifespan. There have been no lifelong CR studies performed on humans. However, in healthy adult human subjects about 20% CR over a period of 2-15 years, lowers body weight by about 20% and decreases body mass index (BMI) to about 19. This CR treatment in humans reduces blood pressure and blood cholesterol to a similar extent as the specific drugs used to delay the onset of vascular disease and so extend human life. These same drugs may act by mechanisms that overlap with some of the mechanisms of CR in retarding these pathologies and thus may have similar antiaging and life prolonging actions. Such drugs may be regarded as CR mimetics which inhibit the development of certain life shortening diseases, without the need to lower calorie intake. In developed countries, better medical care, drug therapy, vaccinations, and other public health measures have extended human life by about 30 years during the 20th century without recourse to CR, which is so effective in the rat. The percentage gain in human life expectancy during the 20th century is twice that achieved by CR in rat survival. However, rat longevity studies now use specific pathogen-free animals and start CR after weaning or later, thereby excluding deaths from infectious diseases and those associated with birth and early life. There is a need to develop CR mimetics which can delay the development of life-threatening diseases in humans. In the 21st century due to the human epidemic of overeating with a sedentary lifestyle, it may necessary to utilize CR to counter the aging effects of overweight. Since the greatest life-extending effects of CR in the rodent occur when started early in life, long-term antiaging therapy in humans should be initiated soon after maturity, when physiological systems have developed optimally.