Obesity and hypertension: mechanisms, cardio-renal consequences, and therapeutic approaches

Fatty kidney, hypertension, and chronic kidney disease: the Framingham Heart Study

Ectopic fat depots may mediate local and systemic disease. Animal models of diet-induced obesity demonstrate increased fat accumulation in the renal sinus. The association of renal sinus fat with hypertension, chronic kidney disease, and other metabolic disorders has not been studied in a large, community-based sample. Participants from the Framingham Heart Study (n=2923; mean age: 54 years; 51% women) underwent quantification of renal sinus fat area using computed tomography. High renal sinus fat ("fatty kidney") was defined using sex-specific 90th percentiles in a healthy referent subsample. Multivariable linear and logistic regression was used to model metabolic risk factors as a function of fatty kidney and log-transformed renal sinus fat. Multivariable models were adjusted for age, sex, and outcome-specific covariates and then additionally adjusted for body mass index or abdominal visceral adipose tissue. The prevalence of fatty kidney was 30.1% (n=879). Individuals with fatty kidney had a higher odds ratio (OR) of hypertension (OR: 2.12; P<0.0001), which persisted after adjustment for body mass index (OR: 1.49; P<0.0001) or visceral adipose tissue (OR: 1.24; P=0.049). Fatty kidney was also associated with an increased OR for chronic kidney disease (OR: 2.30; P=0.005), even after additionally adjusting for body mass index (OR: 1.86; P=0.04) or visceral adipose tissue (OR: 1.86; P=0.05). We observed no association between fatty kidney and diabetes mellitus after adjusting for visceral adipose tissue. In conclusion, fatty kidney is a common condition that is associated with an increased risk of hypertension and chronic kidney disease. Renal sinus fat may play a role in blood pressure regulation and chronic kidney disease.

Development and reproducibility of a computed tomography-based measurement of renal sinus fat

Background

Renal sinus fat may mediate obesity-related vascular disease, although this fat depot has not been assessed in a community-based sample. We sought to develop a protocol to quantify renal sinus fat accumulation using multi-detector computed tomography (MDCT).

Methods

Protocol development was performed in participants in the Framingham Offspring cohort who underwent MDCT. Volumetric renal sinus fat was measured separately within the right and left kidneys, and renal sinus fat area within a single MDCT scan slice was measured in the right kidney. Due to the high correlation of volumetric and single-slice renal sinus fat in the right kidney (Pearson correlation [r] = 0.85, p < 0.0001), we optimized a single-slice protocol to capture renal sinus fat in the right kidney alone. Pearson correlation coefficients were used to compare to assess the correlation of volumetric and single-slice renal sinus fat in the right kidney with other measures of adiposity. Inter- and intra-reader reproducibility was assessed using intra-class correlation coefficients.

Results

Single-slice measurements were obtained in 92 participants (mean age 60 years, 49% women, median renal sinus fat 0.43 cm²). Intra- and inter-reader intra-class correlation coefficients were 0.93 and 0.86, respectively. Single-slice renal sinus fat was correlated with body mass index (r = 0.35, p = 0.0006), waist circumference (r = 0.31, p = 0.003), and abdominal visceral fat (r = 0.48, p < 0.0001). Similar correlations were observed for volumetric renal sinus fat in the right kidney.

Conclusions

Measuring renal sinus fat is feasible and reproducible using MDCT scans in a community-based sample.

Physical Activity in the Prevention of Chronic Kidney Disease

Chronic kidney disease (CKD) is an important risk factor for cardiovascular disease (CVD) and mortality. The increase in CKD in recent decades has paralleled increases in obesity, diabetes, and the metabolic syndrome. Physical inactivity is a modifiable risk factor that may affect the development and course of CKD. It is well established that exercise training improves a number of metabolic factors, including blood pressure and insulin resistance, which would be expected to preserve renal function as well as lower CVD risk. Epidemiological studies have suggested that partaking in vigorous physical activity may protect against kidney disease. However, to date few studies have rigorously measured physical activity levels. Instead, investigators have relied on subjective measures of physical activity and patient recall. This is particularly problematic when attempting to capture low- and very-low-intensity physical activity and in quantifying sedentary behavior. Improvements in vascular endothelial function, insulin sensitivity, adipocytokine profiles, and oxidative stress likely mediate the benefits of physical activity on the kidney. While formal exercise recommendations have been published for diabetes and hypertension, guidelines regarding the optimal type, frequency, intensity and duration of physical activity for preventing CKD have yet to be formalized.

Obesity in adolescence is associated with left ventricular hypertrophy and hypertension

BACKGROUND

Obesity is a risk factor for hypertension (HTN) and left ventricular hypertrophy (LVH). However, the association between obesity, HTN or LVH in adolescents has not been studied in a large population.

METHOD

Utilizing a database of screening echocardiograms, we assessed for the presence of LVH and HTN (defined as systolic blood pressure (SBP) > 140 mmHg or diastolic blood pressure (DBP) > 90 mmHg) in obese adolescents (BMI > 30) using univariate and multivariate analysis.

RESULTS

A total of 2072 subjects were identified between the ages of 13-19 years. LVH was significantly more prevalent in obese subjects (47/166 [28.3%] vs. nonobese subjects (99/1612 [6.1%]) with a P-value of <0.001. Using multivariate analysis adjusting for age, gender and blood pressure, obesity remained strongly associated with the presence of LVH (OR 4.51, CI: 2.83-7.19, P < 0.001). Elevated SBP and DBP were also strongly associated with obesity. SBP > 140 was present in 38% of obese subjects (54/142) versus 12.7% of nonobese subjects (172/1, 353). DBP > 90 was present in 10.6% of obese subjects (15/141) of versus 3.1% of nonobese subjects (42/1352). After adjustment for age, gender and LVH, obesity remained independently associated with HTN (for SBP > 140, OR 2.24, CI: 1.46-3.45, P < 0.001, and for DBP > 90, OR 2.10, CI: 1.063-4.17, P = 0.03).

CONCLUSION

Obese adolescents have a significantly higher prevalence of HTN and LVH. Our analysis suggests a direct negative effect of obesity on cardiovascular function starting early in teenage years. (Echocardiography 2011;28:150-153).

Cardiovascular dysfunction in obesity and new diagnostic imaging techniques: the role of noninvasive image methods

Obesity is a major public health problem affecting adults and children in both developed and developing countries. This condition often leads to metabolic syndrome, which increases the risk of cardiovascular disease. A large number of studies have been carried out to understand the pathogenesis of cardiovascular dysfunction in obese patients. Endothelial dysfunction plays a key role in the progression of atherosclerosis and the development of coronary artery disease, hypertension and congestive heart failure. Noninvasive methods in the field of cardiovascular imaging, such as measuring intima-media thickness, flow-mediated dilatation, tissue Doppler, and strain, and strain rate, constitute new tools for the early detection of cardiac and vascular dysfunction. These techniques will certainly enable a better evaluation of initial cardiovascular injury and allow the correct, timely management of obese patients. The present review summarizes the main aspects of cardiovascular dysfunction in obesity and discusses the application of recent noninvasive imaging methods for the early detection of cardiovascular alterations.

Body mass index in midlife and late-life as a risk factor for dementia: a meta-analysis of prospective studies

The relationship between body mass index (BMI) (in midlife and late-life) and dementia was investigated in meta-analyses of 16 articles reporting on 15 prospective studies. Follow-ups ranged from 3.2 to 36.0 years. Meta-analyses were conducted on samples including 25 624 participants evaluated for Alzheimer's disease (AD), 15 435 participants evaluated for vascular dementia (VaD) and 30 470 followed for any type of dementia (Any Dementia). Low BMI in midlife was associated with 1.96 [95% confidence interval (CI): 1.32, 2.92] times the risk of developing AD. The pooled relative risks for AD, VaD and Any Dementia for overweight BMI in midlife compared with normal BMI were 1.35 (95% CI:1.19, 1.54), 1.33 (95% CI: 1.02, 1.75) and 1.26 (95% CI: 1.10, 1.44), respectively. The pooled relative risks of AD and Any Dementia for obese BMI in midlife compared to normal BMI were 2.04 (95% CI: 1.59, 2.62) and 1.64 (95% CI: 1.34, 2.00), respectively. Continuous BMI in late-life was not associated with dementia. Small numbers of studies included in pooled analyses reduce generalizability of findings, and emphasize the need for publication of additional findings. We conclude that underweight, overweight and obesity in midlife increase dementia risk. Further research evaluating late-life BMI and dementia is required.

Walk-run transition speed training as an efficient exercise adjunct to dietary restriction in the management of obesity: a prospective intervention pilot study

OBJECTIVE

The aim of this study was to test the utility of preferred walk-run transition speed (WRTS) in exercise training adjunct to dietary restriction for obesity management in healthy obese women.

MATERIALS AND METHODS

37 obese women (age: 35 ± 9 years, body mass index (BMI): 34.9 ± 4.6 kg/m(2)) were assigned to an intervention pilot study during 6 months of restricted diet alone (RD) followed by 6 months of RD combined with WRTS (RD and WRTS) as a training exercise. Body mass, waist circumference (WC), fat mass (FM), fat free mass (FFM), active cell mass (ACM), fasting glucose, serum lipids (triacylglycerol (TG), total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), apo-lipoproteins A1 (ApoA1) and B (ApoB)], leptin and insulin concentrations, and HOMA-IR were assessed at baseline (T0), at the end of the RD alone (T1), and at the end of the RD and WRTS programme (T2).

RESULTS

Mean weight loss was 8.6 ± 4.9 kg and 2.2 ± 2.9 kg for (T0-T1) and (T1-T2), respectively. Significant BMI and WC reductions were reported at T1 and T2. FM decreased significantly both with RD and with RD and WRTS training whereas FFM and ACM increased with RD and WRTS training only. TG decreased significantly with the two phases of the programme. A significant increase in HDL-C, and a decrease in LDL-C and TC/HDL-C ratio were noticed with RD and WRTS training. Heart rate monitored in training improved significantly after RD and WRTS training. A significant relationship (r = 0.542, p < 0.02) was demonstrated between reductions in serum leptin and insulin concentrations observed with both RD and WRTS training.

CONCLUSION

The addition of WRTS training to RD promoted a greater reduction in body mass, WC, FM, leptin and insulin concentrations, improved metabolic and cardiovascular risk factors, and enhanced cardiovascular fitness.

Cardiovascular risk-benefit profile of sibutramine

Sibutramine is a combined norepinephrine and serotonin reuptake inhibitor used as an antiobesity agent to reduce appetite and promote weight loss in combination with diet and exercise. At a daily dose of 10-20 mg, it was initially considered to have a good safety profile, as it does not induce primary pulmonary hypertension or adverse effects on cardiac valves, in contrast to previous reports relating to some other antiobesity agents. However, it exerts disparate effects on cardiovascular risk factors. On the one hand, sibutramine may have antiatherogenic activities, as it improves insulin resistance, glucose metabolism, dyslipidemia, and inflammatory markers, with most of these effects resulting from weight loss rather than from an intrinsic effect of the drug. On the other hand, because of its specific mode of action, sibutramine exerts a peripheral sympathomimetic effect, which induces a moderate increase in heart rate and attenuates the reduction in BP attributable to weight loss or even slightly increases BP. It may also prolong the QT interval, an effect that could induce arrhythmias. Because of these complex effects, it is difficult to conclude what the final impact of sibutramine on cardiovascular outcomes might be. Sibutramine has been shown to exert favorable effects on some surrogate cardiovascular endpoints such as reduction of left ventricular hypertrophy and improvement of endothelial dysfunction. A good cardiovascular safety profile was demonstrated in numerous 1- to 2-year controlled trials, in both diabetic and nondiabetic well selected patients, as well as in several observational studies. However, since 2002, several cardiovascular adverse events (hypertension, tachycardia, arrhythmias, and myocardial infarction) have been reported in sibutramine-treated patients. This led to a contraindication of the use of this antiobesity agent in patients with established coronary heart disease, previous stroke, heart failure, or cardiac arrhythmias. SCOUT (Sibutramine Cardiovascular and Diabetes Outcome Study) was designed to prospectively evaluate the efficacy/safety ratio of sibutramine in a high-risk population. The efficacy/safety results of the first 6-week lead-in open period of treatment with sibutramine 10 mg/day were reassuring in 10 742 overweight/obese high-risk subjects (97% had cardiovascular disease, 88% had hypertension, and 84% had type 2 diabetes mellitus). However, the final results of SCOUT showed that long-term (5 years') treatment with sibutramine (10-15 mg/day) exposed subjects with pre-existing cardiovascular disease to a significantly increased risk for nonfatal myocardial infarction and nonfatal stroke, but not cardiovascular death or all-cause mortality. Because the benefit of sibutramine as a weight-loss aid seems not to outweigh the cardiovascular risks, the European Medicines Agency recommended the suspension of marketing authorizations for sibutramine across the EU. The US FDA stated that the drug should carry a 'black box' warning due to an increased risk of stroke and heart attack in patients with a history of cardiovascular disease. In conclusion, concern still persists about the safety profile of sibutramine regarding cardiovascular outcomes, and the drug should not be prescribed for overweight/obese patients with a high cardiovascular risk profile.

Leptin in hepatocellular carcinoma

The risk factors for hepatocellular carcinoma (HCC) development have been established, and include chronic hepatitis B and C, heavy alcohol consumption, and aflatoxins. In fact, 5%-30% of patients with HCC still lack a readily identifiable risk factor. It has been reported that the majority of ‘‘cryptogenic’’ HCC may be attributed to nonalcoholic fatty liver disease, the hepatic presentation of the metabolic syndrome (MS). Obesity is associated with the development of the MS. Recently, adipose tissue has been considered as an endocrine organ because of its capacity to secrete a variety of cytokines, which are collectively known as the adipokines. Leptin, the product of the obese gene, is mainly produced by adipose tissue. Since leptin was first characterized in 1994, accumulated literature has demonstrated the involvement of this adipokine in several areas of human physiology. After binding to its receptor, leptin initiates a cascade of signaling events and subsequent cellular effects. In addition to being the regulatory mediator of energy homeostasis, several in vitro studies have demonstrated the fibrogenic role of leptin in the liver. Furthermore, the deregulated expression of leptin and its receptor have been demonstrated to be associated with a variety of metabolic disorders as well as human cancers. Most importantly, direct evidence supporting the inhibitory and/or activating role of leptin in the process of carcinogenesis and progression of human HCC has been accumulating rapidly. This review aims to provide important insights into the potential mechanisms of leptin in the development of HCC. Hopefully, further investigations will shed light on a new therapeutic target in HCC.

Derivation of new reference tables for human heart weights in light of increasing body mass index

As body weights and body mass indices have increased over time, we questioned the validity of correlating heart weight with body weight and whether tables from previous decades remain relevant. We investigated this by collecting details of heart weight, body weight, height, gender and age from 384 autopsy cases with no obvious heart or lung disease. Heart weights, body weights and heights showed a normal distribution for both genders. Heart weight correlated slightly better with body surface area than body weight and we present new reference charts derived from these data. The correlation between heart weight and body weight has changed little, despite increases in body weight and body mass index. As life expectancy is increasing, we investigated the effect of age on heart weight and demonstrated a small increase in heart weight relative to body surface area for both genders, in contrast to a previous study.

Submandibular gland and caries susceptibility in the obese Zucker rat

BACKGROUND

Obesity is a prevalent disorder characterized as marked insulin resistance and low grade inflammation. We tested the hypothesis that obesity upregulates inflammatory markers in the submandibular gland in association with derangements of its architecture and pre-disposition to caries in obese Zucker rats (OZR). We also examined the potential impact of chromium picolinate (Cr(Pic)3), a nutritional supplement suggested to improve glycemic control, on the aforementioned parameters.

DESIGN

Male OZR were treated with diets lacking and containing 5 or 10 mg/kg chromium (as Cr(Pic)3) from 6 weeks to about 6 months of age; lean Zucker rats (LZR) served as controls. Thereafter, glycemic status, salivary tissue architecture, and the levels of several inflammatory markers were determined in association with caries susceptibility.

RESULTS

OZR showed reduced insulin sensitivity, increased ratio of phospho-nuclear factor-kappa B (NF-κB) to total NF-κB, and increased intercellular adhesion molecule-1 level but similar histological features compared to LZR. Importantly, compared to LZR, OZR displayed rampant caries and a tendency for reduced dentin mineral density. Treatment of OZR with Cr(Pic)3 attenuated upregulation of these proinflammatory indicators in association with reduced severity of caries without improving insulin sensitivity.

CONCLUSIONS

Obesity promotes proinflammatory changes within the submandibular gland, without affecting glandular architecture, in association with rampant caries; Cr(Pic)3 treatment provided some protective effects.

Correlates of echocardiographic indices of cardiac remodeling over the adult life course: longitudinal observations from the Framingham Heart Study

BACKGROUND

The heart progressively remodels over the life course, yet longitudinal data characterizing such remodeling in the community are limited.

METHODS AND RESULTS

Using multilevel modeling, we analyzed up to 4 serial echocardiographic observations obtained over a 16-year period in 4062 Framingham Heart Study participants (mean age 45 years, 54% women; 11 485 person-observations). We related left ventricular (LV) wall thickness, LV systolic and diastolic dimensions, and fractional shortening to age, sex, body mass index, blood pressure (including antihypertensive medication use), smoking, and diabetes mellitus (separate analyses for each echocardiographic measure). With advancing age, LV dimensions decreased, whereas fractional shortening and LV wall thickness increased concomitantly. Male sex, body mass index, and blood pressure indices/hypertension treatment were significantly related to both greater LV dimensions and LV wall thickness. The effect of age on cardiac remodeling was influenced by key covariates (P<0.05 for all interactions): Women and individuals with diabetes mellitus experienced greater age-associated increases in LV wall thickness; presence of diabetes or a higher blood pressure was associated with a lesser decrease in LV diastolic dimensions with increasing age; and antihypertensive medication use was a marker of an attenuated increase in fractional shortening with aging.

CONCLUSIONS

Cardiac remodeling over the adult life course is characterized by a distinct pattern of increasing LV wall thickness, decreasing LV dimensions, and increasing fractional shortening with advancing age. Overall, female sex, greater blood pressure load, and presence of diabetes mellitus serve to attenuate this remodeling pattern. These observations suggest a mechanism for the preponderance of women with hypertension and individuals with diabetes among patients with diastolic heart failure.

Estrogen receptor-{beta}-selective ligands alleviate high-fat diet- and ovariectomy-induced obesity in mice

Obesity is an epidemic problem affecting millions of people in the Western hemisphere and costs the United States economy more than $200 billion annually. Currently, there are no effective treatments to combat obesity. Recent studies have implicated the constitutive activity of estrogen receptor (ER) β as an important regulator of metabolic diseases. However, the potential of ER-β-selective ligands to offset obesity is not clear. We evaluated the pharmacological effect of ER-β-selective ligands (β-LGNDs) in animal models of high-fat diet- and ovariectomy-induced obesity. Ligand binding, transactivation, and uterotrophic studies with β-LGNDs demonstrated selectivity for ER-β over ER-α. Animals fed a high-fat diet showed a significant increase in body weight, and this weight gain was attenuated by β-LGNDs. High-fat diet-mediated increases in serum cholesterol, leptin, glucose, and fat accumulation in organs were also reduced by β-LGNDs. In addition, MRI scanning indicated that β-LGNDs altered body composition by reducing fat mass and increasing lean body mass. Organ weights and gene expression analyses demonstrated that adipose tissue is the center of action for β-LGNDs, and the reduction in body weight is likely due to increased energy expenditure. In vitro and in vivo mechanistic studies indicated that the anti-obesity effects of β-LGNDs were due to indirect peroxisome proliferator-activated receptor γ antagonistic actions requiring the ligand binding domain of ER-β and through abrogation of the ability of PGC-1 to coactivate peroxisome proliferator-activated receptor γ. In conclusion, these studies indicate that ligand-activated ER-β is a potential therapeutic target to combat obesity and obesity-related metabolic diseases.

The RAAS in the pathogenesis and treatment of diabetic nephropathy

Angiotensin II and other components of the renin-angiotensin-aldosterone system (RAAS) have a central role in the pathogenesis and progression of diabetic renal disease. A study in patients with type 1 diabetes and overt nephropathy found that RAAS inhibition with angiotensin-converting-enzyme (ACE) inhibitors was associated with a reduced risk of progression to end-stage renal disease and mortality compared with non-RAAS-inhibiting drugs. Blood-pressure control was similar between groups and proteinuria reduction was responsible for a large part of the renoprotective and cardioprotective effect. ACE inhibitors can also prevent microalbuminuria in patients with type 2 diabetes who are hypertensive and normoalbuminuric; in addition, ACE inhibitors are cardioprotective even in the early stages of diabetic renal disease. Angiotensin-II-receptor blockers (ARBs) are renoprotective (but not cardioprotective) in patients with type 2 diabetes and overt nephropathy or microalbuminuria. Studies have evaluated the renoprotective effect of other RAAS inhibitors, such as aldosterone antagonists and renin inhibitors, administered either alone or in combination with ACE inhibitors or ARBs. An important task for the future will be identifying which combination of agents achieves the best renoprotection (and cardioprotection) at the lowest cost. Such findings will have major implications, particularly in settings where money and facilities are limited and in settings where renal replacement therapy is not available and the prevention of kidney failure is life saving.

Therapeutic potential of endothelin receptor antagonists for chronic proteinuric renal disease in humans

Diabetes and arterial hypertension continue to be the main causes of chronic renal failure in 2010, with a rising prevalence in part due to the worldwide obesity epidemic. Proteinuria is a main feature of chronic renal disease and mediated by defects in the glomerular filtration barrier and is as a good predictor of cardiovascular events. Indeed, chronic renal disease due to glomerulosclerosis is one of the important risk factors for the development of coronary artery disease and stroke. Glomerulosclerosis develops in response to inflammatory activation and increased growth factor production. Preclinical and first preliminary clinical studies provide strong evidence that endogenous endothelin-1 (ET-1), a 21-amino-acid peptide with strong growth-promoting and vasoconstricting properties, plays a central role in the pathogenesis of proteinuria and glomerulosclerosis via activation of its ET(A) subtype receptor involving podocyte injury. These studies have not only shown that endothelin participates in the disease processes of hypertension and glomerulosclerosis but also that features of chronic renal disease such as proteinuria and glomerulosclerosis are reversible processes. Remarkably, the protective effects of endothelin receptors antagonists (ERAs) are present even on top of concomitant treatments with inhibitors of the renin-angiotensin system. This review discusses current evidence for a role of endothelin for proteinuric renal disease and podocyte injury in diabetes and arterial hypertension and reviews the current status of endothelin receptor antagonists as a potential new treatment option in renal medicine.

Associations of metabolic factors, especially serum retinol-binding protein 4 (RBP4), with blood pressure in Japanese--the Tanno and Sobetsu study

Excess secretion of various adipocyte-derived molecules has been linked with insulin resistance, obesity, diabetes, inflammation, atherosclerosis, and cardiovascular disease. Retinol-binding protein 4 (RBP4), one of the new adipocytokine, is recently reported to provide a link between insulin resistance and features of metabolic factors. Hypertension is one of the most influential risk factors among cardiovascular disease. We examined the relationship between systolic blood pressure (BP) levels and metabolic factors including homeostasis model assessment of insulin resistance (HOMA-R), high sensitivity c-reactive protein (hs-CRP), adiponectin, and RBP4. The subjects were 153 men aged 59 ± 14 years and 224 women aged 57 ± 14 years who had undergone medical check-ups in rural communities in 2007. Systolic BP was positively correlated with HOMA-R, hs-CRP and RBP4 but not with adiponectin in women. There was a positive significant relationship between serum RBP4 levels and blood pressure in women, but such a relationship was not found in men. Serum RBP4 levels were not correlated with HOMA-R in either men or women. Serum RBP4 levels negatively were correlated with estimated glomerular filtration rate (eGFR) in women but not in men. Multiple regression analysis revealed that serum RBP4 levels significantly were related to systolic BP independently of age, sex, body mass index (BMI), total cholesterol levels and eGFR. Our study showed that increased levels of RBP4 as well as HOMA-R and hs-CRP in women were significantly associated with increased levels of systolic BP.