Obesity-induced hypertension: role of sympathetic nervous system, leptin, and melanocortins

Hypertension in postmenopausal women

Blood pressure is typically lower in premenopausal women than in men. However, after menopause, the prevalence of hypertension in women is higher than it is in men. Hypertension is a major risk factor for cardiovascular disease in women and men, but cardiovascular disease is the leading cause of death in women. Furthermore, there is evidence that blood pressure may not be as well-controlled in women as in men, despite the fact that most women adhere better to their therapeutic regimens and medications than do men, and have their blood pressures measured more frequently than do men. This review describes possible mechanisms by which blood pressure may be increased in postmenopausal women.

Sodium-retaining effect of insulin in diabetes

Insulin has long been hypothesized to cause sodium retention, potentially of enough magnitude to contribute to hypertension in obesity, metabolic syndrome, and Type II diabetes. There is an abundance of supportive evidence from correlational analyses in humans, acute insulin infusion studies in humans and animals, and chronic insulin infusion studies in rats. However, the absence of hypertension in human insulinoma patients, and negative results for sodium-retaining or blood pressure effects of chronic insulin infusion in a whole series of dog studies, strongly refute the insulin hypothesis. We recently questioned whether the euglycemic, hyperinsulinemia model used for most insulin infusion studies, including the previous chronic dog studies, was the most appropriate model to test the renal actions of insulin in obesity, metabolic syndrome, and Type II diabetes. In those circumstances, hyperinsulinemia coexists with hyperglycemia. Therefore, we tested the sodium-retaining effect of insulin in chronically instrumented, alloxan-treated diabetic dogs. We used 24 h/day intravenous insulin infusion to regulate plasma insulin concentration. Induction of diabetes (∼400 mg/dl) caused sustained natriuresis and diuresis. However, if we clamped insulin at baseline, control levels, i.e., prevented it from decreasing, then the sustained natriuresis and diuresis were completely reversed, despite the same level of hyperglycemia. We also found that 24 h/day intrarenal insulin infusion had the same effect in diabetic dogs but had no sodium-retaining action in normal dogs. This new evidence that insulin has a sodium-retaining effect during hyperglycemia may have implications for maintaining sodium balance in uncontrolled Type II diabetes.

Role of lipotoxicity in endothelial dysfunction

Vascular endothelial dysfunction is determined by both genetic and environmental factors that cause decreased bioavailability of the vasodilator nitric oxide. This is a hallmark of atherosclerosis, hypertension, and coronary heart disease, which are major complications of metabolic disorders, including diabetes and obesity. Several therapeutic interventions, including changes in lifestyle as well as pharmacologic treatments, are useful for improving endothelial dysfunction in the face of lipotoxicity. This review discusses the current understanding of molecular and physiologic mechanisms underlying lipotoxicity-mediated endothelial dysfunction as well as relevant therapeutic approaches to ameliorate dyslipidemia and consequent endothelial dysfunction that have the potential to improve cardiovascular and metabolic outcomes.

Effects of endurance exercise training, metformin, and their combination on adipose tissue leptin and IL-10 secretion in OLETF rats

Adipose tissue inflammation plays a role in cardiovascular (CV) and metabolic diseases associated with obesity, insulin resistance, and type 2 diabetes mellitus (T2DM). The interactive effects of exercise training and metformin, two first-line T2DM treatments, on adipose tissue inflammation are not known. Using the hyperphagic, obese, insulin-resistant Otsuka Long-Evans Tokushima Fatty (OLETF) rat model, we tested the hypothesis that treadmill training, metformin, or a combination of these reduces the secretion of proinflammatory cytokines from adipose tissue. Compared with Long-Evans Tokushima Otsuka (LETO) control rats (L-Sed), sedentary OLETF (O-Sed) animals secreted significantly greater amounts of leptin from retroperitoneal adipose tissue. Conversely, secretion of interleukin (IL)-10 by O-Sed adipose tissue was lower than that in L-Sed animals. Examination of leptin and IL-10 secretion from adipose tissue in OLETF groups treated with endurance exercise training (O-EndEx), metformin treatment (O-Met), and a combination of these (O-E+M) from 20 to 32 wk of age indicated that 1) leptin secretion from adipose tissue was reduced in O-Met and O-E+M, but not O-EndEx animals; 2) adipose tissue IL-10 secretion was increased in O-EndEx and O-E+M but not in O-Met animals; and 3) only the combined treatment (O-E+M) displayed both a reduction in leptin secretion and an increase in IL-10 secretion. Leptin and IL-10 concentrations in adipose tissue-conditioned buffers were correlated with their plasma concentrations, adipocyte diameters, and total adiposity. Overall, this study indicates that exercise training and metformin have additive influences on adipose tissue secretion and plasma concentrations of leptin and IL-10.

Leptin and the regulation of endothelial function in physiological and pathological conditions

Obesity and the accompanying metabolic syndrome are among the most important causes of cardiovascular pathologies associated with endothelial dysfunction, such as arterial hypertension and atherosclerosis. This detrimental effect of obesity is mediated, in part, by excessive production of the adipose tissue hormone leptin. Under physiological conditions leptin induces endothelium-dependent vasorelaxation by stimulating nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF). Leptin activates endothelial NO synthase (eNOS) through a mechanism involving AMP-activated protein kinase (AMPK) and protein kinase B/Akt, which phosphorylates eNOS at Ser(1177) , increasing its activity. Under pathological conditions, such as obesity and metabolic syndrome, the NO-mediated vasodilatory effect of leptin is impaired. Resistance to the acute NO-mimetic effect of leptin is accounted for by chronic hyperleptinaemia and may result from different mechanisms, such as downregulation of leptin receptors, increased levels of circulating C-reactive protein, oxidative stress and overexpression of suppressor of cytokine signalling-3. In short-lasting obesity, impaired leptin-induced NO production is compensated by EDHF; however, in advanced metabolic syndrome, the contribution of EDHF to the haemodynamic effect of leptin becomes inefficient. Resistance to the vasodilatory effects of leptin may contribute to the development of arterial hypertension owing to unopposed stimulation of the sympathetic nervous system by this hormone.

Joint statement of the European Association for the Study of Obesity and the European Society of Hypertension: obesity and difficult to treat arterial hypertension

Obese patients are prone to arterial hypertension, require more antihypertensive medications, and have an increased risk of treatment-resistant arterial hypertension. Obesity-induced neurohumoral activation appears to be involved. The association between obesity and hypertension shows large inter-individual variability, likely through genetic mechanisms. Obesity affects overall cardiovascular and metabolic risk; yet, the relationship between obesity and cardiovascular risk is complex and not sufficiently addressed in clinical guidelines. The epidemiological observation that obesity may be protective in patients with established cardiovascular disease is difficult to translate into clinical experience and practice. Weight loss is often recommended as a means to lower blood pressure. However, current hypertension guidelines do not provide evidence-based guidance on how to institute weight loss. In fact, weight loss influences on blood pressure may be overestimated. Nevertheless, weight loss through bariatric surgery appears to decrease cardiovascular risk in severely obese patients. Eventually, most obese hypertensive patients will require antihypertensive medications. Data from large-scale studies with hard clinical endpoints on antihypertensive medications specifically addressing obese patients are lacking and the morbidity from the growing population of severely obese patients is poorly recognized or addressed. Because of their broad spectrum of beneficial effects, renin-angiotensin system inhibitors are considered to be the most appropriate drugs for antihypertensive treatment of obese patients. Most obese hypertensive patients require two or more antihypertensive drugs. Finally, how to combine weight loss strategies and antihypertensive treatment to achieve an optimal clinical outcome is unresolved.

Leptin as a link between the immune system and kidney-related diseases: leading actor or just a coadjuvant?

Food intake and nutritional status modify the physiological responses of the immune system to illness and infection and regulate the development of chronic inflammatory processes, such as kidney disease. Adipose tissue secretes immune-related proteins called adipokines that have pleiotropic effects on both the immune and neuroendocrine systems, linking metabolism and immune physiology. Leptin, an adipose tissue-derived adipokine, displays a variety of immune and physiological functions, and participates in several immune responses. Here, we review the current literature on the role of leptin in kidney diseases, linking adipose tissue and the immune system with kidney-related disorders. The modulation of this adipose hormone may have a major impact on the treatment of several immune- and metabolic-related kidney diseases.

Fetal cardiac autonomic control during breathing and non-breathing epochs: the effect of maternal exercise

We explored whether maternal exercise during pregnancy moderates the effect of fetal breathing movements on fetal cardiac autonomic control assessed by metrics of heart rate (HR) and heart rate variability (HRV). Thirty women were assigned to Exercise or Control group (n=15/group) based on the modifiable physical activity questionnaire (MPAQ). Magnetocardiograms (MCG) were recorded using a dedicated fetal biomagnetometer. Periods of fetal breathing activity and apnea were identified using the fetal diaphragmatic magnetomyogram (dMMG) as a marker. MCG R-waves were marked. Metrics of fetal HR and HRV were compared using 1 breathing and 1 apneic epoch/fetus. The main effects of group (Exercise vs. Control) and condition (Apnea vs. Breathing) and their interactions were explored. Fetal breathing resulted in significantly lower fetal HR and higher vagally-mediated HRV. Maternal exercise resulted in significantly lower fetal HR, higher total HRV and vagally-mediated HRV with no difference in frequency band ratios. Significant interactions between maternal exercise and fetal breathing were found for metrics summarizing total HRV and a parasympathetic metric. Post hoc comparison showed no group difference during fetal apnea. Fetal breathing was associated with a loss of Total HRV in the Control group and no difference in the Exercise group. Both groups show enhanced vagal function during fetal breathing; greater in the Exercise group. During in utero breathing movements, the fetus of the exercising mother has enhanced cardiac autonomic function that may give the offspring an adaptive advantage.

Obesity-related hypertension: epidemiology, pathophysiology, treatments, and the contribution of perivascular adipose tissue

The advent of the obesity epidemic has highlighted the need to re-assess more closely the pathophysiology of obesity-related hypertension with the aim of identifying new therapies. In this article, we review the role of the renin-angiotensin-aldosterone system, sympathetic nervous system, and inflammation in relation to the pathophysiology of this condition. We also discuss the potential role of the perivascular adipose tissue in the context of obesity-related hypertension.

Telmisartan prevents high-fat diet-induced hypertension and decreases perirenal fat in rats

We sought to investigate the effects of telmisartan on high-fat diet-induced hypertension and to explore the possible underlying mechanisms. Rats receiving high-fat diet were randomly divided into two groups, the telmisartan group (n = 9) and the high-fat diet group (n = 10). The control group consisted of age-matched rats on a regular diet (n = 10). At the end of the treatment, the body weight, blood pressure, insulin sensitivity and serum adiponectin levels of all rats were examined, and their visceral fat was extracted and weighed. Our results showed that telmisartan improved insulin resistance and dyslipidemia and increased serum adiponectin levels. Telmisartan also lowered both systolic blood pressure and diastolic blood pressure, and decreased the accumulation of perirenal fat associated with high-fat diet. Furthermore, telmisartan increased adiponectin mRNA expression in the perirenal fat. Correlation analysis showed that both systolic blood pressure and diastolic blood pressure were positively correlated with perirenal fat. These effects of telmisartan may be mediated through decreases in perirenal fat and contributed to the improvement of perirenal fat function. Our findings suggested a strong link between perirenal fat and high-fat diet-induced hypertension, and identified telmisartan as a potential drug for the treatment of obesity-related hypertension.

A brain leptin-renin angiotensin system interaction in the regulation of sympathetic nerve activity

The sympathetic nervous system, leptin, and renin-angiotensin system (RAS) have been implicated in obesity-associated hypertension. There is increasing evidence for the presence of both leptin and angiotensin II receptors in several key brain cardiovascular and metabolic control regions. We tested the hypothesis that the brain RAS plays a facilitatory role in the sympathetic nerve responses to leptin. In rats, intracerebroventricular (ICV) administration of losartan (5 μg) selectively inhibited increases in renal and brown adipose tissue (BAT) sympathetic nerve activity (SNA) produced by leptin (10 μg ICV) but did not reduce the SNA responses to corticotrophin-releasing factor (CRF) or the melanocortin receptor agonist MTII. In mice with deletion of angiotensin II type-1a receptors (AT(1a)R(-/-)), increases in renal and BAT SNA induced by leptin (2 μg ICV) were impaired whereas SNA responses to MTII were preserved. Decreases in food intake and body weight with ICV leptin did not differ in AT(1a)R(-/-) vs. AT(1a)R(+/+) mice. ICV leptin in rats increased AT(1a)R and angiotensin-converting enzyme (ACE) mRNA in the subfornical organ and AT(1a)R mRNA in the arcuate nucleus, suggesting leptin-induced upregulation of the brain RAS in specific brain regions. To evaluate the role of de novo production of brain angiotensin II in SNA responses to leptin, we treated rats with captopril (12.5 μg ICV). Captopril attenuated leptin effects on renal and BAT SNA. In conclusion, these studies provide evidence that the brain RAS selectively facilitates renal and BAT sympathetic nerve responses to leptin while sparing effects on food intake.

Central leptin replacement enhances chemorespiratory responses in leptin-deficient mice independent of changes in body weight

Previous studies showed that leptin-deficient (ob/ob) mice develop obesity and impaired ventilatory responses to CO(2) (V(E) - CO(2)). In this study, we examined if leptin replacement improves chemorespiratory responses to hypercapnia (7 % CO(2)) in ob/ob mice and if these effects were due to changes in body weight or to the direct effects of leptin in the central nervous system (CNS). V(E) - CO(2) was measured via plethysmography in obese leptin-deficient- (ob/ob) and wild-type- (WT) mice before and after leptin (10 μg/2 μl day) or vehicle (phosphate buffer solution) were microinjected into the fourth ventricle for four consecutive days. Although baseline V(E) was similar between groups, obese ob/ob mice exhibited attenuated V(E) - CO(2) compared to WT mice (134 ± 9 versus 196 ± 10 ml min(-1)). Fourth ventricle leptin treatment in obese ob/ob mice significantly improved V(E) - CO(2) (from 131 ± 15 to 197 ± 10 ml min(-1)) by increasing tidal volume (from 0.38 ± 0.03 to 0.55 ± 0.02 ml, vehicle and leptin, respectively). Subcutaneous leptin administration at the same dose administered centrally did not change V(E) - CO(2) in ob/ob mice. Central leptin treatment in WT had no effect on V(E) - CO(2). Since the fourth ventricle leptin treatment decreased body weight in ob/ob mice, we also examined V(E) - CO(2) in lean pair-weighted ob/ob mice and found it to be impaired compared to WT mice. Thus, leptin deficiency, rather than obesity, is the main cause of impaired V(E) - CO(2) in ob/ob mice and leptin appears to play an important role in regulating chemorespiratory response by its direct actions on the CNS.

Adipocyte dysfunction and hypertension

Obesity is increasingly a public health problem due to its high risk of developing insulin resistance, diabetes, atherosclerosis, hypertension, chronic kidney disease, and increased cardiovascular morbidity and mortality. In particular, the association of obesity and hypertension is well recognized; however, the underlying mechanisms are not fully understood. This article reviews recent advancements of cellular and molecular mechanisms by which adipocyte dysfunction and obesity contribute to hypertension through endocrine and paracrine effects of the adipose tissue-derived adipokines on the function of vascular endothelial cells, smooth muscle cells and macrophages.

Longitudinal changes in blood pressure during weight loss and regain of weight in obese boys and girls

OBJECTIVE

To investigate blood pressure (BP) in relation to changes in body mass index (BMI) in obese children during weight loss and subsequent weight regain.

DESIGN

A longitudinal study of obese boys and girls investigated through a 12-week weight loss intervention with follow-up investigations spanning 28 months. Results shown are from baseline; day 14, 33, and 82 during weight loss; and at months 10, 16 and 28 during follow-up.

PATIENTS

One hundred and fifteen obese children, 53 boys and 62 girls (8-15 years) with a median BMI standard deviation score (SDS) at baseline of 2.78 in boys, and 2.70 in girls. Ninety children completed the weight loss programme and 68 children entered the follow-up programme.

METHODS

Height, weight, systolic blood pressure (SBP), and diastolic BP (DBP) were recorded and analysed using a general linear mixed model.

RESULTS

Fifty-one percent of the obese children were pre or hypertensive at baseline. Both DBP and SBP declined significantly with weight loss, but a divergent response was found in the timing of the rebound in hypertension during the weight regain phase, that is DBP increased during weight regain, whereas SBP remained lower than baseline during 28 months of continuous weight regain.

CONCLUSION

The effect of weight reduction upon obesity-associated hypertension is noticeable and suggests the importance of an intensified childhood obesity treatment strategy in order to reduce the burden of future cardiovascular disease.

Sympathetic nervous system: role in hypertension and in chronic kidney disease

PURPOSE OF REVIEW

A number of cardiovascular disease have been shown to be characterized by a marked increase in sympathetic drive to the heart and peripheral circulation. This is the case for essential hypertension, congestive heart failure, obesity, metabolic syndrome and chronic renal failure. This review focuses on the most recent findings documenting the role of sympathetic neural factors in the development and progression of the hypertensive state as well as of target organ damage. It also reviews the participation of sympathetic neural factors in the development of the earlier stages of renal failure.

RECENT FINDINGS

A marked increase in sympathetic neural discharge, as assessed via the microneurographic technique, has been shown to occur in the predialytic stage of chronic renal failure. Recent evidence, however, indicates that also in the earlier clinical phases of kidney disease, sympathetic activation is detectable. Further data show that sympathetic neural mechanisms participate in renal and/or hypertensive disease progression, favouring the development of target organ damage. Finally, recent findings indicate that the metabolic disarray frequently complicating the high blood pressure state (metabolic syndrome, dislipidemia, insulin resistance) may have as pathophysiological background a sympathetic overdrive. Altogether these data represent the rationale for employing in hypertension (and particularly in resistant hypertension) therapeutic interventions such as carotid baroreceptor stimulation and renal denervation, capable of exerting sympathoinhibitory effects.

SUMMARY

The sympathetic nervous system represents a major pathophysiological hallmark of both hypertension and renal failure and is an important target for the therapeutic intervention.

Dietary fat and heart failure: moving from lipotoxicity to lipoprotection

There is growing evidence suggesting that dietary fat intake affects the development and progression of heart failure. Studies in rodents show that in the absence of obesity, replacing refined carbohydrate with fat can attenuate or prevent ventricular expansion and contractile dysfunction in response to hypertension, infarction, or genetic cardiomyopathy. Relatively low intake of n-3 polyunsaturated fatty acids from marine sources alters cardiac membrane phospholipid fatty acid composition, decreases the onset of new heart failure, and slows the progression of established heart failure. This effect is associated with decreased inflammation and improved resistance to mitochondrial permeability transition. High intake of saturated, monounsaturated, or n-6 polyunsaturated fatty acids has also shown beneficial effects in rodent studies. The underlying mechanisms are complex, and a more thorough understanding is needed of the effects on cardiac phospholipids, lipid metabolites, and metabolic flux in the normal and failing heart. In summary, manipulation of dietary fat intake shows promise in the prevention and treatment of heart failure. Clinical studies generally support high intake of n-3 polyunsaturated fatty acids from marine sources to prevent and treat heart failure. Additional clinical and animals studies are needed to determine the optimal diet in terms of saturated, monounsaturated, and n-6 polyunsaturated fatty acids intake for this vulnerable patient population.

Selenate enhances STAT3 transcriptional activity in endothelial cells: differential actions of selenate and selenite on LIF cytokine signaling and cell viability

Sodium selenate may have utility in treating Alzheimer's disease and diabetes; however, its impact on the associated proinflammatory cytokine signaling of endothelial cells has not been investigated. We report that treatment of human microvascular endothelial cells with sodium selenate at a pharmacological dose (100 μM) enhanced tyrosine phosphorylation of nuclear STAT3 on Y705 in response to IL-6-type cytokine, leukemia inhibitory factor (LIF), indicative of enhanced STAT3 activity. Accordingly, STAT3 nuclear binding to DNA was increased, as well as LIF-induced gene expression of chemokine (C-C motif) ligand 2 (CCL2). CCL2 plays a key role in inflammatory processes associated with neuronal degenerative and vascular diseases. The enhancing action of selenate on LIF-induced STAT3 Y705 phosphorylation was replicated by vanadate and a specific inhibitor of protein tyrosine phosphatase, non-receptor type 1 (PTP1B). Moreover, we observed that selenite, the cellular reduction bioproduct of selenate but not selenate itself, inhibited enzymatic activity of human recombinant PTP1B. Our findings support the conclusion that in human microvascular endothelial cells selenate has a vanadate-like effect in inhibiting PTP1B and enhancing proinflammatory STAT3 activation. These findings raise the possibility that beneficial actions of supranutritional levels of selenate for treating Alzheimer's and diabetes may be offset by a proinflammatory action on endothelial cells.

Activation of the central melanocortin system contributes to the increased arterial pressure in obese Zucker rats

We have previously demonstrated that leptin-mediated activation of the central nervous system (CNS) melanocortin system reduces appetite and increases sympathetic activity and blood pressure (BP). In the present study we examined whether endogenous melanocortin system activation, independent of leptin's actions, contributes to the regulation of BP and metabolic functions in obese Zucker rats, which have mutated leptin receptors. The long-term cardiovascular and metabolic effects of central melanocortin-3/4 receptor (MC3/4R) antagonism with SHU-9119 were assessed in lean (n = 6) and obese (n = 8) Zucker rats. BP and heart rate (HR) were measured 24-h/day by telemetry and an intracerebroventricular cannula was placed in the brain lateral ventricle. After stable control measurements, SHU-9119 was infused intracerebroventricularlly (1 nmol/h) for 10 days followed by a 10-day recovery period. Chronic CNS MC3/4R antagonism significantly increased food intake and body weight in lean (20 ± 1 to 45 ± 2 g and 373 ± 11 to 432 ± 14 g) and obese (25 ± 2 to 35 ± 2 g and 547 ± 10 to 604 ± 11 g) rats. No significant changes were observed in plasma glucose levels in lean or obese rats, whereas plasma leptin and insulin levels markedly increased in lean Zucker rats during CNS MC3/4R antagonism. Chronic SHU-9119 infusion in obese Zucker rats reduced mean arterial pressure (MAP) and HR by 6 ± 1 mmHg and 24 ± 5 beats/min, whereas in lean rats SHU-9119 infusion reduced HR by 31 ± 9 beats/min while causing only a transient decrease in MAP. These results suggest that in obese Zucker rats the CNS melanocortin system contributes to elevated BP independent of leptin receptor activation.

Development of melanoma-targeted polymer micelles by conjugation of a melanocortin 1 receptor (MC1R) specific ligand

The incidence of malignant melanoma is rising faster than that of any other cancer in the United States. Because of its high expression on the surface of melanomas, MC1R has been investigated as a target for selective imaging and therapeutic agents against melanoma. Eight ligands were screened against cell lines engineered to overexpress MC1R, MC4R, or MC5R. Of these, compound 1 (4-phenylbutyryl-His-dPhe-Arg-Trp-NH(2)) exhibited high (0.2 nM) binding affinity for MC1R and low (high nanomolar) affinities for MC4R and MC5R. Functionalization of the ligand at the C-terminus with an alkyne for use in Cu-catalyzed click chemistry was shown not to affect the binding affinity. Finally, formation of the targeted polymer, as well as the targeted micelle formulation, also resulted in constructs with low nanomolar binding affinity.

Leptin action in the dorsomedial hypothalamus increases sympathetic tone to brown adipose tissue in spite of systemic leptin resistance

Leptin regulates body weight in mice by decreasing appetite and increasing sympathetic nerve activity (SNA), which increases energy expenditure in interscapular brown adipose tissue (iBAT). Diet-induced obese mice (DIO) are resistant to the anorectic actions of leptin. We evaluated whether leptin still stimulated sympathetic outflow in DIO mice. We measured iBAT temperature as a marker of SNA. We found that obese hyperleptinemic mice have higher iBAT temperature than mice on regular diet. Conversely, obese leptin-deficient ob/ob mice have lower iBAT temperature. Additionally, leptin increased SNA in obese (DIO and ob/ob) and control mice, despite DIO mice being resistant to anorectic action of leptin. We demonstrated that neurons in the dorsomedial hypothalamus (DMH) of DIO mice mediate the thermogenic responses to hyperleptinemia in obese mammals because blockade of leptin receptors in the DMH prevented the thermogenic effects of leptin. Peripheral Melotan II (MTII) injection increased iBAT temperature, but it was blunted by blockade of DMH melanocortin receptors (MC4Rs) by injecting agouti-related peptide (AgRP) directly into the DMH, suggesting a physiological role of the DMH on temperature regulation in animals with normal body weight. Nevertheless, obese mice without a functional melanocortin system (MC4R KO mice) have an increased sympathetic outflow to iBAT compared with their littermates, suggesting that higher leptin levels drive sympathoexcitation to iBAT by a melanocortin-independent pathway. Because the sympathetic nervous system contributes in regulating blood pressure, heart rate, and hepatic glucose production, selective leptin resistance may be a crucial mechanism linking adiposity and metabolic syndrome.

Intensified effect of adiposity on blood pressure in overweight and obese children

In children, blood pressure (BP) and risk for hypertension are proportional to degree of adiposity. Whether the relationship to BP is similar over the full range of adiposity is less clear. Subjects from a cohort study (n=1111; 50% male and 42% black) contributed 9102 semiannual BP and height/weight assessments. The mean enrollment age was 10.2 years, and mean follow-up was 4.5 years. Adiposity was expressed as body mass index percentile, which accounted for effects of age and sex. The following observations were made. The effect of relative adiposity on BP was minimal until the body mass index percentile reached 85, beginning of the overweight category, at which point the effect of adiposity on BP increased by 4-fold. Similarly intensified adiposity effects on BP were observed in children aged ≤10, 11 to 14 years, and ≥15 years. Serum levels of the adipose tissue-derived hormone, leptin, together with heart rate, showed an almost identically patterned relation to BP to that of body mass index percentile and BP, thus implicating a possible mediating role for leptin. In conclusion, there is a marked intensification of the influence of adiposity on BP when children reach the categories of overweight and obese. Among the possible pathways, leptin may be a potentially important mediator acting through the sympathetic nervous system (reflected in heart rate). The findings have relevance to interventions designed to prevent or treat adiposity-related increases in BP and to the analytic approaches used in epidemiological studies.

Chronic blood pressure and appetite responses to central leptin infusion in rats fed a high fat diet

OBJECTIVE

Obesity has been suggested to induce selective leptin resistance whereby leptin's anorexic effects are attenuated, whereas the effects to increase sympathetic nervous system activity and blood pressure remain intact. Most studies, however, have tested only the acute responses to leptin administration. This study tested whether feeding a high-fat diet causes resistance to the appetite and cardiovascular responses to chronic central leptin infusion.

METHODS

Sprague-Dawley rats were fed high-fat diet (40% kcal from fat, n=5) or normal-fat diet (13% kcal from fat, n=5) for a year. Radiotelemeters were implanted for continuous monitoring of mean arterial pressure (MAP) and heart rate (HR). A 21G steel cannula was implanted in the lateral cerebral ventricle [intracerebroventricular (ICV)]. After recovery, leptin was infused ICV at 0.02 μg/kg per min for 10 days.

RESULTS

High-fat rats were heavier than normal-fat rats (582±12 vs. 511±19 g) and exhibited significantly higher MAP (114±3 vs. 96±7 mmHg). Although the acute (24 h) effects of leptin were attenuated in high-fat rats, chronic ICV leptin infusion decreased caloric intake in both groups similarly (50±8 vs. 40±10%) by day 5. Despite decreased food intake and weight loss, leptin infusion significantly increased MAP and HR in both high-fat and normal-fat rats (7±2 and 5±1 mmHg; 18±11 and 21±10 b.p.m., respectively).

CONCLUSION

These results suggest that obesity induced by feeding a high-fat diet blunts the acute anorexic effects of leptin but does not cause significant resistance to the chronic central nervous system effects of leptin on appetite, MAP, or HR.

Postmenopausal hypertension

Cardiovascular disease is the leading cause of morbidity and mortality in postmenopausal women. Hypertension is a major risk factor for cardiovascular disease. The mechanisms responsible for postmenopausal hypertension have not been completely elucidated. However, various mechanisms have been implicated to play a role. For example, there is evidence that changes in estrogen/androgen ratios favoring increases in androgens, activation of the renin-angiotensin and endothelin systems, activation of the sympathetic nervous system, metabolic syndrome and obesity, inflammation, increased vasoconstrictor eicosanoids, and anxiety and depression may be important in the pathogenesis of postmenopausal hypertension. There is also evidence that hypertension is less well controlled in aging women than in aging men, but the reasons for this gender difference is not clear. Postmenopausal hypertension is likely multifactorial. Future studies will be necessary to determine the contribution of these systems listed above in mediating postmenopausal hypertension and to design treatment strategies that encompass these mechanisms to improve the quality of life of postmenopausal women as they age.

Chronic HO-1 induction with cobalt protoporphyrin (CoPP) treatment increases oxygen consumption, activity, heat production and lowers body weight in obese melanocortin-4 receptor-deficient mice

Objective

Heme oxygenase-1 induction (HO-1) elicits chronic weight loss in several rodent models of obesity. Despite these findings, the mechanism by which HO-1 induction reduces body weight is unclear. Chronic HO-1 induction does not alter food intake suggesting other mechanisms such as increases in metabolism and activity may be responsible for the observed reduction of body weight. In this study, we investigated the mechanism of weight loss elicited by chronic HO-1 induction in a model of genetic obesity due to melanocortin-4 receptor (MC4R) deficiency.

Design

Experiments were performed on loxTB MC4R deficient mice as well as lean controls. Mice were administered cobalt protoporphyrin (CoPP, 5 mg/kg), an inducer of HO-1, once weekly from 4 to 23 weeks of age. Body weights were measured weekly and fasted blood glucose and insulin as well as food intake were determined at 18 weeks of age. O₂ consumption, CO₂ production, activity, and body heat production were measured at 20 weeks of age.

Results

Chronic CoPP treatment resulted in a significant decrease in body weight from 5 weeks on in loxTB mice. Chronic CoPP treatment resulted in a significant decrease in fasted blood glucose levels, plasma insulin, and a significant increase in plasma adiponectin levels in MC4R deficient mice. Chronic CoPP treatment increased O₂ consumption (47 ± 4 vs. 38 ± 3 ml/kg/min, P<0.05) and CO₂ production (44 ± 7 vs. 34 ± 4 ml/kg/min, P<0.05) in treated versus non-treated, MC4R deficient mice (n=4). Heat production (10%) and activity (18%) were also significantly (P<0.05) increased in CoPP treated MC4R deficient mice.

Conclusion

Our results suggest that chronic HO-1 induction with CoPP induction elicits weight loss by increasing metabolism and activity by an MC4R independent pathway.

Control of blood pressure, appetite, and glucose by leptin in mice lacking leptin receptors in proopiomelanocortin neurons

Although the central nervous system melanocortin system is an important regulator of energy balance, the role of proopiomelanocortin (POMC) neurons in mediating the chronic effects of leptin on appetite, blood pressure, and glucose regulation is unknown. Using Cre/loxP technology we tested whether leptin receptor deletion in POMC neurons (LepR(flox/flox)/POMC-Cre mice) attenuates the chronic effects of leptin to increase mean arterial pressure (MAP), enhance glucose use and oxygen consumption, and reduce appetite. LepR(flox/flox)/POMC-Cre, wild-type, LepR(flox/flox), and POMC-Cre mice were instrumented for MAP and heart rate measurement by telemetry and venous catheters for infusions. LepR(flox/flox)/POMC-Cre mice were heavier, hyperglycemic, hyperinsulinemic, and hyperleptinemic compared with wild-type, LepR(flox/flox), and POMC-Cre mice. Despite exhibiting features of metabolic syndrome, LepR(flox/flox)/POMC-Cre mice had normal MAP and heart rate compared with LepR(flox/flox) but lower MAP and heart rate compared with wild-type mice. After a 5-day control period, leptin was infused (2 μg/kg per minute, IV) for 7 days. In control mice, leptin increased MAP by ≈5 mm Hg despite decreasing food intake by ≈35%. In contrast, leptin infusion in LepR(flox/flox)/POMC-Cre mice reduced MAP by ≈3 mm Hg and food intake by ≈28%. Leptin significantly decreased insulin and glucose levels in control mice but not in LepR(flox/flox)/POMC-Cre mice. Leptin increased oxygen consumption in LepR(flox/flox)/POMC-Cre and wild-type mice. Activation of POMC neurons is necessary for the chronic effects of leptin to raise MAP and reduce insulin and glucose levels, whereas leptin receptors in other areas of the brain other than POMC neurons appear to play a key role in mediating the chronic effects of leptin on appetite and oxygen consumption.

Impact of body composition, fat distribution and sustained weight loss on cardiac function in obesity

BACKGROUND

Obesity is associated with alterations in left ventricular function varying along with the degree of fatness, but the mechanisms underlying this co-variation are not clear. In a case-control study we examined how sustained weight losses affect cardiac function and report on how body composition and fat distribution relate to the left ventricular performance.

METHODS

At the 10-year follow-up of the Swedish obese subjects (SOS) study cohort we identified 44 patients with sustained weight losses after bariatric surgery (surgery group) and 44 matched obese control patients who remained weight stable (obese group). We also recruited 44 matched normal weight subjects (lean group). Dual-energy X-ray absorptiometry, computed tomography and echocardiography were performed to evaluate body composition, fat distribution and cardiac function.

RESULTS

BMI was 42.5 kg/m(2), 31.5 kg/m(2) and 24.4 kg/m(2) for the obese, surgery and lean groups respectively. Increasing degree of obesity was associated with larger left ventricular volumes (p < 0.001), higher cardiac output (p < 0.001), reduced systolic myocardial velocity (p<0.001) and impaired ventricular relaxation (p = 0.015). In multivariate analyses, left ventricular volume, stroke volume and cardiac output primarily associated with lean body mass, whereas blood pressure, heart rate and variables reflecting cardiac dysfunction were more related to total body fat and visceral adiposity.

CONCLUSION

Obesity is associated with discrete but distinct disturbances in the left ventricular performance appearing to be related to both the total amount of body fat and degree of visceral adiposity. Patients with sustained weight losses display superior left ventricular systolic and diastolic functions as compared with their obese counterparts remaining weight stable.

Resistant hypertension in the high-risk metabolic patient

The metabolic syndrome is a constellation of metabolic and vascular abnormalities that include insulin resistance with compensatory hyperinsulinemia, central or visceral obesity, hypertension, dyslipidemia, microalbuminuria, and oxidative stress as well as prothrombotic and inflammatory abnormalities that contribute to a hypercoagulable state and systemic endothelial dysfunction. Visceral adipose tissue is now known to secrete into the circulation a number of protein and nonprotein factors that regulate glucose metabolism in traditional insulin-sensitive tissue as well as nontraditional insulin-sensitive tissue including cardiovascular tissue. Collectively, this constellation of factors that lead to metabolic dysregulation contributes to a substantial risk for adverse cardiovascular and renal outcomes. The development of a particularly resistant form of hypertension in these individuals can be attributed to a number of factors including vasoconstriction from increased sympathetic activation, proinflammatory cytokines, and inappropriate activation of the renin-angiotensin-aldosterone system. The management of hypertension in such patients can be challenging and generally requires nonpharmacologic as well as pharmacologic interventions.

Cardiovascular and sympathetic effects of disrupting tyrosine 985 of the leptin receptor

Leptin acts in the brain to regulate food intake and energy expenditure. Leptin also increases renal sympathetic nerve activity and arterial pressure. The divergent signaling capacities of the leptin receptor (ObRb) mediate the stimulation of various intracellular pathways that are important for leptin control of physiological processes. We evaluated the cardiovascular and sympathetic consequences of disrupting the signal emanating from tyrosine985 of ObRb. For this, we used Lepr(L985) (l/l) mice, which carry a loss of function mutation replacing tyrosine985 of ObRb with leucine. Body weight of l/l mice was not significantly different from wild-type controls. In contrast, radiotelemetry measurements revealed that the l/l mice had higher arterial pressure and heart rate as compared with controls. Ganglionic blockade caused a greater arterial pressure fall in the l/l mice relative to controls. In addition, leptin treatment induced a larger increase in arterial pressure and heart rate in the l/l versus wild-type mice. Finally, we compared the response of renal and brown adipose tissue sympathetic nerve activity to intracerebroventricular injection of leptin (2 μg) between l/l and control mice. Leptin-induced increase in renal sympathetic nerve activity was greater in l/l mice relative to controls. In contrast, the brown adipose tissue sympathetic nerve activity response to leptin was attenuated in the l/l mice relative to controls. These data indicate that selective loss of leptin receptor signaling emanating from tyrosine985 enhances the cardiovascular and renal sympathetic effects of leptin. These findings provide important insight into the molecular mechanisms underlying leptin's effects on the sympathetic cardiovascular function and arterial pressure.

[Renal consequences of obesity]

The steady increase in the prevalence of obesity contributes to the increase in the prevalence of chronic kidney disease, through renal damages associated with type-2 diabetes and hypertension. Obesity is also an independent risk factor for the kidney, since it is associated with an increased risk of albuminuria and glomerulosclerosis, and worsens the course of chronic kidney disease regardless of the primary renal disease. The existence of a metabolic syndrome, constant in type-2 diabetes, and associated with abdominal obesity, is not the only requirement for renal anomalies of which the translation is a functional hyperfiltration, a clinical microalbuminuria and histologically a glomerulomegaly and glomerulosclerosis. The estimated glomerular filtration rate (GFR) in obese patients is strongly influenced by the weight or indexation to body surface area, and it is logical to take into account the value of non-indexed GFR to assess renal risk and treatment effects, especially if they lead to weight loss. Hypertension is promoted by salt sensitivity, potentially reversible, and overactivity of the renin-angiotensin system (RAS) in part due to adipose tissue. The cytokines secreted by adipose tissue (adipokines), induce sympathetic hyperactivity through leptin, and low-grade inflammatory state that contributes to the development of glomerular sclerosis lesions, especially because a resistance to adiponectin. The treatment relies on weight loss, possibly through bariatric surgery, and antagonists of the RAS.

Combined amylin-leptin treatment lowers blood pressure and adiposity in lean and obese rats

OBJECTIVE

To examine the cardiovascular effects of combined amylin (AMN) and leptin (LEP) treatment in lean and obese rats.

RESEARCH DESIGN

Rats were instrumented for telemetry and given LEP (300 μg kg(-1) day(-1)), AMN (100 μg kg(-1) day(-1)), AMN+LEP or vehicle (VEH; 0.9% normal saline) via a subcutaneous mini-osmotic pump for 7 days. The VEH group was subdivided into ad libitum fed and pair-fed to the amount of food AMN+LEP animals ate daily. Rats were housed in metabolic chambers for analysis of cardiovascular physiology and metabolism.

SUBJECTS

Male Fisher 344 × Brown Norway (FBNF1; Harlan; age=3-5 months; n=72) rats were placed on standard rodent chow (LEAN, n=41) or moderately high-fat diet (OBESE; n=31) to produce obesity.

RESULTS

AMN+LEP potently reduced food intake (LEAN: 57% OBESE: 59%) and abdominal fat mass (LEAN: 56% OBESE: 41%). Pair-fed rats displayed bradycardia and metabolic suppression. In contrast, AMN+LEP increased heart rate and oxygen consumption above levels in LEP or AMN-treated rats. LEP reduced blood pressure in both lean and obese rats but AMN had no effect. LEP-induced reductions in blood pressure were not altered by AMN+LEP treatment. Thus, AMN+LEP treatment decreased food intake, body fat and blood pressure in lean and obese rats.

CONCLUSION

We conclude that the potent anti-adiposity actions of AMN+LEP are due in part to prevention of the bradycardia and metabolic suppression typically observed with negative energy balance. Furthermore, the hypotensive actions of peripheral LEP treatment are observable in spite of the potent AMN+LEP activation of anorexic and thermogenic mechanisms in the central nervous system.

Body mass index, leptin, and ambulatory blood pressure variability in healthy adults

OBJECTIVE

To investigate the association between body mass index (BMI) and 24-h ambulatory blood pressure (ABP) variability, and to assess whether leptin might act as a mediator of this association.

METHODS

A cross-sectional study in healthy, normotensive men and women (n = 156). BMI was derived from direct height and weight measurements made on each participant. All participants underwent 24-h ABP monitoring, and two measures of ABP variability were derived--the weighted standard deviation (wSD) and the average real variability (ARV). Plasma leptin was measured using an enzyme lined immunosorbant assay.

RESULTS

In linear regression models adjusted for demographic factors, glucose, creatinine, lipids, and mean ABP, BMI showed positive and statistically significant associations with diastolic wSD, and systolic and diastolic ARV. For those in the low, intermediate, and high BMI groups, mean values for diastolic wSD were 7.7, 7.9, and 8.5 mmHg, respectively (p = .02); mean values of systolic ARV were 8.2, 8.2, and 9.0 mmHg, respectively (p=.02); and mean values of diastolic ARV were 6.7, 7.0, and 7.5 mmHg, respectively (p = .01). Similarly, leptin showed positive and statistically significant associations with measures of wSD and ARV. When BMI was entered as an ordinal variable in regression models for wSD and ARV, adjustment for leptin attenuated significant ordinal BMI coefficients by as much as 60%, suggesting a mediating role for leptin.

CONCLUSION

In healthy adults, BMI and leptin show positive associations with ABP variability, and leptin may play a mediating role in this association.

Activation of the melanocortin-4 receptor causes enhanced excitation in presympathetic paraventricular neurons in obese Zucker rats

Sympathetic nerve activity is increased in obesity-related hypertension. However, the central mechanisms involved in the increased sympathetic outflow remain unclear. The hypothalamic melanocortin system is important for regulating energy balance and sympathetic outflow. To understand the mechanisms by which the melanocortin systems regulates sympathetic outflow, we investigated the role of melanocortin 4 receptors (MC4R) in regulating presympathetic paraventricular nucleus (PVN) neurons. We performed whole-cell patch-clamp recordings on retrogradely labeled PVN neurons projecting to the rostral ventrolateral medulla in brain slices from obese zucker rats (OZRs) and lean zucker rats (LZRs). The MC4R agonists melanotan II (MTII) and α-melanocyte-stimulating hormone (α-MSH) increased the firing activity and depolarized the labeled PVN neurons from both LZRs and OZRs in a concentration-dependent manner. MTII produced significant greater increase in the firing activity in OZRs than in LZRs. Blocking MC4R with the specific antagonist SHU9119 had no effect on the basal firing rate but abolished the MTII-induced increase in the firing rate in both OZRs and LZRs. Furthermore, intracellular dialysis of guanosine 5'-O-(2-thodiphosphate), but not bath application of kynurenic acid and bicuculline, eliminated the MTII-induced increase in firing activity. In addition, MTII had no effect on the frequency and amplitude of glutamatergic excitatory postsynaptic currents and GABAergic inhibitory postsynaptic currents in labeled PVN neurons. Collectively, our findings suggest that MC4R contributes to the elevated excitability of PVN presympathetic neurons, which may be involved in obesity-related hypertension.