Brain Dopamine-Clock Interactions Regulate Cardiometabolic Physiology: Mechanisms of the Observed Cardioprotective Effects of Circadian-Timed Bromocriptine-QR Therapy in Type 2 Diabetes Subjects

Despite enormous global efforts within clinical research and medical practice to reduce cardiovascular disease(s) (CVD), it still remains the leading cause of death worldwide. While genetic factors clearly contribute to CVD etiology, the preponderance of epidemiological data indicate that a major common denominator among diverse ethnic populations from around the world contributing to CVD is the composite of Western lifestyle cofactors, particularly Western diets (high saturated fat/simple sugar [particularly high fructose and sucrose and to a lesser extent glucose] diets), psychosocial stress, depression, and altered sleep/wake architecture. Such Western lifestyle cofactors are potent drivers for the increased risk of metabolic syndrome and its attendant downstream CVD. The central nervous system (CNS) evolved to respond to and anticipate changes in the external (and internal) environment to adapt survival mechanisms to perceived stresses (challenges to normal biological function), including the aforementioned Western lifestyle cofactors. Within the CNS of vertebrates in the wild, the biological clock circuitry surveils the environment and has evolved mechanisms for the induction of the obese, insulin-resistant state as a survival mechanism against an anticipated ensuing season of low/no food availability. The peripheral tissues utilize fat as an energy source under muscle insulin resistance, while increased hepatic insulin resistance more readily supplies glucose to the brain. This neural clock function also orchestrates the reversal of the obese, insulin-resistant condition when the low food availability season ends. The circadian neural network that produces these seasonal shifts in metabolism is also responsive to Western lifestyle stressors that drive the CNS clock into survival mode. A major component of this natural or Western lifestyle stressor-induced CNS clock neurophysiological shift potentiating the obese, insulin-resistant state is a diminution of the circadian peak of dopaminergic input activity to the pacemaker clock center, suprachiasmatic nucleus. Pharmacologically preventing this loss of circadian peak dopaminergic activity both prevents and reverses existing metabolic syndrome in a wide variety of animal models of the disorder, including high fat-fed animals. Clinically, across a variety of different study designs, circadian-timed bromocriptine-QR (quick release) (a unique formulation of micronized bromocriptine-a dopamine D2 receptor agonist) therapy of type 2 diabetes subjects improved hyperglycemia, hyperlipidemia, hypertension, immune sterile inflammation, and/or adverse cardiovascular event rate. The present review details the seminal circadian science investigations delineating important roles for CNS circadian peak dopaminergic activity in the regulation of peripheral fuel metabolism and cardiovascular biology and also summarizes the clinical study findings of bromocriptine-QR therapy on cardiometabolic outcomes in type 2 diabetes subjects.

Serum Nonesterified Fatty Acids and Incident Stroke: The CHS

Background

Significant associations between total nonesterified fatty acid (NEFA) concentrations and incident stroke have been reported in some prospective cohort studies. We evaluated the associations between incident stroke and serum concentrations of nonesterified saturated, monounsaturated, polyunsaturated, and trans fatty acids.

Methods and Results

CHS (Cardiovascular Health Study) participants (N=2028) who were free of stroke at baseline (1996–1997) and had an archived fasting serum sample were included in this study. A total of 35 NEFAs were quantified using gas chromatography. Cox proportional hazards regression models were used to evaluate associations of 5 subclasses (nonesterified saturated, monounsaturated, omega (n)‐6 polyunsaturated, n‐3 polyunsaturated, and trans fatty acids) of NEFAs and individual NEFAs with incident stroke. Sensitivity analysis was conducted by excluding cases with hemorrhagic stroke (n=45). A total of 338 cases of incident stroke occurred during the median 10.5‐year follow‐up period. Total n‐3 (hazard ratio [HR], 0.77 [95% CI, 0.61–0.97]) and n‐6 (HR, 1.32 [95% CI, 1.01–1.73]) subclasses of NEFA were negatively and positively associated with incident stroke, respectively. Among individual NEFAs, dihomo‐γ‐linolenic acid (20:3n‐6) was associated with higher risk (HR, 1.29 [95% CI, 1.02–1.63]), whereas cis‐7‐hexadecenoic acid (16:1n‐9c) and arachidonic acid (20:4n‐6) were associated with a lower risk (HR, 0.67 [95% CI, 0.47–0.97]; HR, 0.81 [95% CI. 0.65–1.00], respectively) of incident stroke per standard deviation increment. After the exclusion of cases with hemorrhagic stroke, these associations did not remain significant.

Conclusions

A total of 2 NEFA subclasses and 3 individual NEFAs were associated with incident stroke. Of these, the NEFA n‐3 subclass and dihomo‐γ‐linolenic acid are diet derived and may be potential biomarkers for total stroke risk.

Metabolic Dysfunction-Associated Fatty Liver Disease (MAFLD)-A Condition Associated with Heightened Sympathetic Activation

Metabolic dysfunction-associated fatty liver disease (MAFLD) is the most common liver disease affecting a quarter of the global population and is often associated with adverse health outcomes. The increasing prevalence of MAFLD occurs in parallel to that of metabolic syndrome (MetS), which in fact plays a major role in driving the perturbations of cardiometabolic homeostasis. However, the mechanisms underpinning the pathogenesis of MAFLD are incompletely understood. Compelling evidence from animal and human studies suggest that heightened activation of the sympathetic nervous system is a key contributor to the development of MAFLD. Indeed, common treatment strategies for metabolic diseases such as diet and exercise to induce weight loss have been shown to exert their beneficial effects at least in part through the associated sympathetic inhibition. Furthermore, pharmacological and device-based approaches to reduce sympathetic activation have been demonstrated to improve the metabolic alterations frequently present in patients with obesity, MetSand diabetes. Currently available evidence, while still limited, suggests that sympathetic activation is of specific relevance in the pathogenesis of MAFLD and consequentially may offer an attractive therapeutic target to attenuate the adverse outcomes associated with MAFLD.

Associations of Serum Nonesterified Fatty Acids With Coronary Heart Disease Mortality and Nonfatal Myocardial Infarction: The CHS (Cardiovascular Health Study) Cohort

Background

Significant associations have been reported between serum total nonesterified fatty acid (NEFA) concentrations and coronary heart disease (CHD) mortality and incident nonfatal myocardial infarction (MI) in some prospective cohort studies. Little is known about whether individual or subclasses (saturated, polyunsaturated [n‐6 and n‐3], and trans fatty acids) of serum NEFAs relate to CHD mortality and nonfatal MI.

Methods and Results

CHS (Cardiovascular Health Study) participants (N=1681) who had no history of MI, angina, or revascularization or were free of MI at baseline (1996–1997) were included. NEFAs were quantified using gas chromatography. Cox regression analysis was used to evaluate associations of 5 subclasses and individual NEFAs with CHD composite (CHD mortality and nonfatal MI), CHD mortality, and incident nonfatal MI. During a median follow‐up of 11.7 years, 266 cases of CHD death and 271 cases of nonfatal MI occurred. In the fully adjusted model, no significant associations were identified between individual NEFA and CHD composite. Exploratory analyses indicated that lauric acid (12:0) was negatively associated (hazard ratio [HR], 0.76; 95% CI, 0.59–0.98; P=0.0328) and dihomo‐γ‐linolenic acid (20:3n‐6) was positively associated with CHD mortality (HR, 1.34; 95% CI, 1.02–1.76; P=0.0351). Elaidic acid (18:1n‐7t) was positively associated with incident nonfatal MI (HR, 1.46; 95% CI, 1.01–2.12; P=0.0445). No significant associations were observed for NEFA subclass and any outcomes.

Conclusions

In CHS participants, 2 NEFAs, dihomo‐γ‐linolenic and elaidic acids, were positively associated with CHD mortality and nonfatal MI, respectively, suggesting potential susceptibility biomarkers for risks of CHD mortality and nonfatal MI.

Circadian-timed quick-release bromocriptine lowers elevated resting heart rate in patients with type 2 diabetes mellitus

OBJECTIVE

Sympathetic nervous system (SNS) overactivity is a risk factor for insulin resistance and cardiovascular disease (CVD). We evaluated the impact of bromocriptine-QR, a dopamine-agonist antidiabetes medication, on elevated resting heart rate (RHR) (a marker of SNS overactivity in metabolic syndrome), blood pressure (BP) and the relationship between bromocriptine-QR's effects on RHR and HbA1c in type 2 diabetes subjects.

DESIGN AND SUBJECTS

RHR and BP changes were evaluated in this post hoc analysis of data from a randomized controlled trial in 1014 type 2 diabetes subjects randomized to bromocriptine-QR vs placebo added to standard therapy (diet ± ≤2 oral antidiabetes medications) for 24 weeks without concomitant antihypertensive or antidiabetes medication changes, stratified by baseline RHR (bRHR).

RESULTS

In subjects with bRHR ≥70 beats/min, bromocriptine-QR vs placebo reduced RHR by -3.4 beats/min and reduced BP (baseline 130/79; systolic, diastolic, mean arterial BP reductions [mm Hg]: -3.6 [P = .02], -1.9 [P = .05], -2.5 [P = .02]). RHR reductions increased with higher baseline HbA1c (bHbA1c) (-2.7 [P = .03], -5 [P = .002], -6.1 [P = .002] with bHbA1c ≤7, >7, ≥7.5%, respectively] in the bRHR ≥70 group and more so with bRHR ≥80 (-4.5 [P = .07], -7.8 [P = .015], -9.9 [P = .005]). Subjects with bRHR <70 had no significant change in RHR or BP. With bHbA1c ≥7.5%, %HbA1c reductions with bromocriptine-QR vs placebo were -0.50 (P = .04), -0.73 (P = .005) and -1.22 (P = .008) with bRHR <70, ≥70 and ≥80, respectively. With bRHR ≥70, the magnitude of bromocriptine-QR-induced RHR reduction was an independent predictor of bromocriptine-QR's HbA1c lowering effect.

CONCLUSION

Bromocriptine-QR lowers elevated RHR with concurrent decrease in BP and hyperglycaemia. These findings suggest a potential sympatholytic mechanism contributing to bromocriptine-QR's antidiabetes effect and potentially its previously demonstrated effect to reduce CVD events.

Mechanistic Links Between Obesity, Diabetes, and Blood Pressure: Role of Perivascular Adipose Tissue

Obesity is increasingly prevalent and is associated with substantial cardiovascular risk. Adipose tissue distribution and morphology play a key role in determining the degree of adverse effects, and a key factor in the disease process appears to be the inflammatory cell population in adipose tissue. Healthy adipose tissue secretes a number of vasoactive adipokines and anti-inflammatory cytokines, and changes to this secretory profile will contribute to pathogenesis in obesity. In this review, we discuss the links between adipokine dysregulation and the development of hypertension and diabetes and explore the potential for manipulating adipose tissue morphology and its immune cell population to improve cardiovascular health in obesity.

The Effect of Renal Denervation on Plasma Adipokine Profile in Patients with Treatment Resistant Hypertension

Background: We previously demonstrated the effectiveness of renal denervation (RDN) to lower blood pressure (BP) at least partially via the reduction of sympathetic stimulation to the kidney. A number of adipocyte-derived factors are implicated in BP control in obesity.

Aim: The aim of this study was to examine whether RDN may have salutary effects on the adipokine profile in patients with resistant hypertension (RH).

Methods: Fifty seven patients with RH undergoing RDN program have been included in this study (65% males, age 60.8 ± 1.5 years, BMI 32.6 ± 0.7 kg/m², mean ± SEM). Throughout the study, the patients were on an average of 4.5 ± 2.7 antihypertensive drugs. Automated seated office BP measurements and plasma concentrations of leptin, insulin, non-esterified fatty acids (NEFA), adiponectin and resistin were assessed at baseline and the 3 months after RDN.

Results: There was a significant reduction in mean office systolic (168.75 ± 2.57 vs. 155.23 ± 3.17 mmHg, p < 0.001) and diastolic (90.68 ± 2.31 vs. 83.74 ± 2.36 mmHg, p < 0.001) BP 3 months after RDN. Body weight, plasma leptin and resistin levels and heart rate remained unchanged. Fasting insulin concentration significantly increased 3 months after the procedure (20.05 ± 1.46 vs. 29.70 ± 2.51 uU/ml, p = 0.002). There was a significant drop in circulating NEFA at follow up (1.01 ± 0.07 vs. 0.47 ± 0.04 mEq/l, p < 0.001). Adiponectin concentration was significantly higher after RDN (5,654 ± 800 vs. 6,644 ± 967 ng/ml, p = 0.024).

Conclusions: This is the first study to demonstrate that RDN is associated with potentially beneficial effects on aspects of the adipokine profile. Increased adiponectin and reduced NEFA production may contribute to BP reduction via an effect on metabolic pathways.

Clinical Trial Registration Number: NCT00483808, NCT00888433.

A cohort study of unstable overdose patients treated with intravenous lipid emulsion therapy

Objectives

Intravenous lipid emulsion (ILE) has been used increasingly over the last decade for a range of drug overdoses. Although the use of ILE in local anesthetic toxicity (LAST) is well established, the hemodynamic effectiveness of ILE in non-LAST poisonings is still unclear. Thus, the primary objective of this study was to examine a cohort of poisoned patients in whom ILE was administered.

Methods

Consecutive patients were identified by calls to a regional poison center from May 1, 2012 to May 30, 2014. Patients were enrolled if they ingested a drug, developed hemodynamic instability, failed conventional treatment, and received ILE therapy. Data were collected by medical record review. The primary outcome was the change in mean arterial pressure (MAP) in the first hour after ILE administration. Secondary outcomes included survival, length of stay, and the effect of drug class on patient outcome.

Results

Thirty-six patients were enrolled. Agents ingested included calcium channel blockers and beta blockers (10/36, 27.8%), tricyclic antidepressants (5/36, 13.9%), bupropion (3/36, 8.3%), and antiepileptic agents (1/36, 2.8%). Seventeen patients (47.2%) ingested multiple agents. Twenty-five patients survived (69.0%). Overall, MAP increased by 13.79 mm Hg (95% CI 1.43–26.15); this did not meet oura prioridefinition of clinical significance.

Conclusions

Our study did not find a clinically important improvement in MAP after ILE administration. Until future research is done to more definitively study its efficacy, ILE should remain a potential treatment option for hemodynamically unstable overdose patients only after conventional therapy has failed.

Levels of F2-isoprostanes, F4-neuroprostanes, and total nitrate/nitrite in plasma and cerebrospinal fluid of patients with traumatic brain injury

Several events occurring during the secondary damage of traumatic brain injury (TBI) can cause oxidative stress. F(2)-isoprostanes (F(2)-IsoPs) and F(4)-neuroprostanes (F(4)-NPs) are specific lipid peroxidation markers generated from arachidonic acid and docosahexaenoic acid, respectively. In this study, we evaluated oxidative stress in patients with moderate and severe TBI. Since sedatives are routinely used to treat TBI patients and propofol has been considered an antioxidant, TBI patients were randomly treated with propofol or midazolam for 72 h postoperation. We postoperatively collected cerebrospinal fluid (CSF) and plasma from 15 TBI patients for 6-10 d and a single specimen of CSF or plasma from 11 controls. Compared with the controls, the TBI patients exhibited elevated levels of F(2)-IsoPs and F(4)-NPs in CSF throughout the postsurgery period regardless of the sedative used. Compared with the group of patients who received midazolam, those who received propofol exhibited markedly augmented levels of plasma F(2)-IsoPs, which were associated with higher F(4)-NPs levels and lower total nitrate/nitrite levels in CSF early in the postsurgery period. Furthermore, the higher CSF F(2)-IsoPs levels correlated with 6-month and 12-month worse outcomes, which were graded according to the Glasgow Outcome Scale. The results demonstrate enhanced oxidative damage in the brain of TBI patients and the association of higher CSF levels of F(2)-IsoPs with a poor outcome. Moreover, propofol treatment might promote lipid peroxidation in the circulation, despite possibly suppressing nitric oxide or peroxynitrite levels in CSF, because of the increased loading of the lipid components from the propofol infusion.

Caloric restriction decreases orthostatic tolerance independently from 6° head-down bedrest

Astronauts consume fewer calories during spaceflight and return to earth with an increased risk of orthostatic intolerance. Whether a caloric deficiency modifies orthostatic responses is not understood. Thus, we determined the effects of a hypocaloric diet (25% caloric restriction) during 6° head down bedrest (an analog of spaceflight) on autonomic neural control during lower body negative pressure (LBNP). Nine healthy young men completed a randomized crossover bedrest study, consisting of four (2 weeks each) interventions (normocaloric bedrest, normocaloric ambulatory, hypocaloric bedrest, hypocaloric ambulatory), each separated by 5 months. Muscle sympathetic nerve activity (MSNA) was recorded at baseline following normocaloric and hypocaloric interventions. Heart rate (HR) and arterial pressure were recorded before, during, and after 3 consecutive stages (7 min each) of LBNP (-15, -30, -45 mmHg). Caloric and posture effects during LBNP were compared using two-way ANOVA with repeated measures. There was a strong trend toward reduced basal MSNA following caloric restriction alone (normcaloric vs. hypocaloric: 22±3 vs. 14±4 burst/min, p = 0.06). Compared to the normocaloric ambulatory, both bedrest and caloric restriction were associated with lower systolic blood pressure during LBNP (p<0.01); however, HR responses were directionally opposite (i.e., increase with bedrest, decrease with caloric restriction). Survival analysis revealed a significant reduction in orthostatic tolerance following caloric restriction (normocaloric finishers: 12/16; hypocaloric finishers: 6/16; χ2, p = 0.03). Caloric restriction modifies autonomic responses to LBNP, which may decrease orthostatic tolerance after spaceflight.

Free fatty acid availability is closely related to myocardial lipid storage and cardiac function in hypoglycemia counterregulation

Hypoglycemia, a major side effect of intensive glucose-lowering therapy, was recently linked to increased cardiovascular risk in patients with diabetes. Whether increased circulating free fatty acids (FFA) owing to catecholamine-induced lipolysis affect myocardial energy metabolism and thus link hypoglycemia to cardiac vulnerability is unclear. Therefore, this study investigated the impact of hypoglycemia counterregulation (± inhibition of lipolysis) on myocardial lipid content (MYCL) and left ventricular function in healthy subjects. Nine healthy men were studied in randomized order: 1) insulin/hypoglycemia test (IHT; ins+/aci-), 2) IHT during inhibition of adipose tissue lipolysis by acipimox (ins+/aci+), 3) normoglycemia with acipimox (ins-/aci+), and 4) normoglycemia with placebo (ins-/aci-). MYCL and cardiac function were assessed by employing magnetic resonance spectroscopy/imaging at baseline and at 2 and 6 h. In response to acute hypoglycemia, plasma FFA (P<0.0001) and ejection fraction (EF; from 63.2±5.5 to 69.6±6.3%, P=0.0001) increased significantly and were tightly correlated with each other (r=0.68, P=0.0002); this response was completely blunted by inhibition of adipose tissue lipolysis. In the presence of normoglycemia, inhibition of lipolysis was associated with a drop in EF (from 59.2±5.5 to 53.9±6.9%,P=0.005) and a significant decrease in plasma FFA, triglycerides, and MYCL (by 48.5%, P=0.0001). The present data indicate that an intact interorgan cross-talk between adipose tissue and the heart is a prerequisite for catecholamine-mediated myocardial contractility and preservation of myocardial lipid stores in response to acute hypoglycemia.

Are we waking up to the effects of NEFA?

NEFA are mobilised from adipose tissues during fasting or stress. Under conditions of acute or chronic NEFA excess, skeletal muscle and hepatic insulin resistance may ensue. Hence, a wealth of literature has focused on the crosstalk between NEFA and glucose in the pathogenesis of insulin resistance. Sleep restriction has also been shown to acutely induce insulin resistance, and self-reported short sleep duration is associated with diabetes. In this issue of Diabetologia (DOI: 10.1007/s00125-015-3500-4), Broussard and colleagues examine the impact of acute sleep restriction on detailed 24 h metabolic profiles, including plasma NEFA. Here, we address the potential clinical relevance of these findings and pose questions for further research.

Metabolic syndrome: a sympathetic disease?

Metabolic syndrome is associated with adverse health outcomes and is a growing problem worldwide. Although efforts to harmonise the definition of metabolic syndrome have helped to better understand the prevalence and the adverse outcomes associated with the disorder on a global scale, the mechanisms underpinning the metabolic changes that define it are incompletely understood. Accumulating evidence from laboratory and human studies suggests that activation of the sympathetic nervous system has an important role in metabolic syndrome. Indeed, treatment strategies commonly recommended for patients with metabolic syndrome, such as diet and exercise to induce weight loss, are associated with sympathetic inhibition. Pharmacological and device-based approaches to target activation of the sympathetic nervous system directly are available and have provided evidence to support the important part played by sympathetic regulation, particularly for blood pressure and glucose control. Preliminary evidence is encouraging, but whether therapeutically targeting sympathetic overactivity could help to prevent metabolic syndrome and attenuate its adverse outcomes remains to be determined.

Sympathetic neural regulation of blood pressure: influences of sex and aging

Sex and age have important influences on sympathetic neural control of blood pressure in humans. Young women are relatively protected against risk of hypertension due to greater peripheral vasodilator influences compared with young men and older people. This protective effect is lost at menopause. Older men and women have higher sympathetic nerve activity and tighter coupling between SNA and blood pressure, contributing to the increased risk of hypertension with aging.

Gender differences in the relationship between blood pressure and body mass index during adolescence

OBJECTIVE

In adults, gender and obesity play significant roles in the regulation of blood pressure (BP). This study investigated the effects of gender and body mass index (BMI) on BP during adolescence.

DESIGN AND SETTING

A cross-sectional and longitudinal study involving 6838 students under twenty years old (median, eighteen years old; male, 4624; female, 2214) at Osaka University visited the Healthcare Center for their matriculation health examination from April to May in the years 2008, 2009, and 2010, and re-visited the Healthcare Center for their student health examination from May to June in the years 2011, 2012, and 2013.

METHODS

Height, body weight, and BP were measured in students both on and 3 years after admission to Osaka University.

RESULTS

On admission, the slope of the regression line for BMI and systolic BP (SBP) in non-underweight students was significantly different between genders. SBP and diastolic BP (DBP) increased in both genders during the observation period. Among male students who had a normal BMI on admission, those who had an increase in BMI of over 4% during the observation period showed a greater increase in SBP than those who had a change in BMI of -4% to 4%. On the other hand, female students showed no change in BP with the increase in BMI.

CONCLUSIONS

The magnitude of BP elevation with increased BMI was associated with gender during adolescence. This may be a cause of the higher prevalence of hypertension in adult males.

Simvastatin but not ezetimibe reduces sympathetic activity despite similar reductions in cholesterol levels

The relationship between the sympatholytic effects of statins and their lipid-lowering activity remains unclear. Ezetimibe lowers cholesterol, but its sympatholytic activity is unknown. The purpose of study was to compare the influence of equipotent doses of simvastatin and ezetimibe on sympathetic activity. This randomized double-blinded study was performed in 22 hypertensive patients (age, 45.6 ± 2.2 years; female/male, 2/20) with untreated hypercholesterolemia. The subjects were administered 20 mg/d of simvastatin (n = 11) or 20 mg/d of ezetimibe (n = 11) for 6 weeks. Pre- and post-treatment measurements of muscle sympathetic nerve activity (MSNA), baroreceptor control of heart rate (baroreflex sensitivity), and impedance cardiography were recorded. Simvastatin and ezetimibe produced similar reductions of total (-58.0 ± 23.4 vs. -45.2 ± 17.2 mg/dL; P = .15, respectively) and low-density lipoprotein cholesterol (-52.6 ± 20.9 vs. -37.9 ± 17.6 mg/dL; P = .09, respectively). There was a significant difference in the effect of simvastatin and ezetimibe on muscle sympathetic nerve activity (-8.5 ± 5.1 vs. -0.7 ± 3.5 bursts/min; P = .0005). Simvastatin improved baroreflex sensitivity as compared with ezetimibe (10.0 ± 14.3 vs. -2.8 ± 6.1 ms/mm Hg; P = .01). There was no difference in the effect of both treatments on blood pressure, heart rate, cardiac output, stroke volume, total peripheral resistance, high-density lipoprotein, and triglycerides. Simvastatin reduced sympathetic activity via lipid-independent mechanisms, but ezetimibe exerts no sympatholytic effects.

Relationship of muscle sympathetic nerve activity to insulin sensitivity

PURPOSE

An association between insulin resistance and activation of the sympathetic nervous system has been reported in previous studies. However, potential interactions between insulin sensitivity and sympathetic neural mechanisms in healthy people remain poorly understood. We conducted a study to determine the relationship between sympathetic activity and insulin resistance in young, healthy humans.

METHODS

Thirty-seven healthy adults (18-35 years, BMI <28 kg m(-2)) were studied. Resting muscle sympathetic nerve activity (MSNA) was measured with microneurography and insulin sensitivity of glucose and free fatty acid metabolism was measured during a hyperinsulinemic-euglycemic clamp with two levels of insulin.

RESULTS

During lower doses of insulin, we found a small association between lower insulin sensitivity and higher MSNA (P < 0.05) but age was a cofactor in this relationship. Overall, we found no difference in insulin sensitivity between groups of low and high MSNA, but when women were analyzed separately, insulin sensitivity was lower in the high MSNA group compared with the low MSNA group of women.

CONCLUSIONS

These data suggest that MSNA and insulin sensitivity are only weakly associated with young healthy individuals and that age and sex may be important modifiers of this relationship.

Statins and the autonomic nervous system

Statins (3-hydroxy-3-methylglutaryl-CoA reductase inhibitors) reduce plasma cholesterol and improve endothelium-dependent vasodilation, inflammation and oxidative stress. A ‘pleiotropic’ property of statins receiving less attention is their effect on the autonomic nervous system. Increased central sympathetic outflow and diminished cardiac vagal tone are disturbances characteristic of a range of cardiovascular conditions for which statins are now prescribed routinely to reduce cardiovascular events: following myocardial infarction, and in hypertension, chronic kidney disease, heart failure and diabetes. The purpose of the present review is to synthesize contemporary evidence that statins can improve autonomic circulatory regulation. In experimental preparations, high-dose lipophilic statins have been shown to reduce adrenergic outflow by attenuating oxidative stress in central brain regions involved in sympathetic and parasympathetic discharge induction and modulation. In patients with hypertension, chronic kidney disease and heart failure, lipophilic statins, such as simvastatin or atorvastatin, have been shown to reduce MNSA (muscle sympathetic nerve activity) by 12–30%. Reports concerning the effect of statin therapy on HRV (heart rate variability) are less consistent. Because of their implications for BP (blood pressure) control, insulin sensitivity, arrhythmogenesis and sudden cardiac death, these autonomic nervous system actions should be considered additional mechanisms by which statins lower cardiovascular risk.

Relation between serum free fatty acids and adiposity, insulin resistance, and cardiovascular risk factors from adolescence to adulthood

The objective of this study was to describe longitudinal relations of serum total free fatty acids (FFAs) to insulin resistance (IR) and cardiovascular (CV) risk factors from adolescence into adulthood. The cohort included participants in a longitudinal study of obesity and IR with complete data, including anthropometric measures, FFAs, IR measured by euglycemic clamp, blood pressure, fasting serum lipids, and insulin at mean 15 and 22 years of age (n = 207) and their parents (n = 272). FFAs and IR were not significantly related at mean 15 years of age but were significantly related at mean age 22 years. FFA did not relate to BMI at either age. FFA at 15 years of age estimated IR at 22 years of age. In parents (mean age 51 years), FFA was significantly correlated with BMI, percent body fat, systolic blood pressure, LDL, and IR. Associations with all risk factors except IR in parents were attenuated by adjustment for BMI. Most 22 years of age correlations with parents were higher than corresponding 15 years of age correlations. This study finds that FFA is associated with IR starting in young adulthood. The relation between FFA and CV risk factors does not become significant until later adulthood. The results support a significant impact of early metabolic dysfunction on later CV risk.

Sympathetic support of energy expenditure and sympathetic nervous system activity after gastric bypass surgery

OBJECTIVE

This study was designed to determine how gastric bypass affects the sympathetically-mediated component of resting energy expenditure (REE) and muscle sympathetic nerve activity (MSNA).

DESIGN AND METHODS

We measured REE before and after beta-blockade in seventeen female subjects approximately three years post-gastric bypass surgery and in nineteen female obese individuals for comparison. We also measured MSNA in a subset of these subjects.

RESULTS

The gastric bypass subjects had no change in REE after systemic beta-blockade, reflecting a lack of sympathetic support of REE, in contrast to obese subjects where REE was reduced by beta-blockade by approximately 5% (P < 0.05). The gastric bypass subjects, while still overweight (BMI = 29.3 vs 38.0 kg·m(-2) for obese subjects, P < 0.05), also had significantly lower MSNA compared to obese subjects (10.9 ± 2.3 vs. 21.9 ± 4.1 bursts·min(-1) , P < 0.05). The reasons for low MSNA and a lack of sympathetically mediated support of REE after gastric bypass are likely multifactorial and may be related to changes in insulin sensitivity, body composition, and leptin, among other factors.

CONCLUSIONS

These findings may have important consequences for the maintenance of weight loss after gastric bypass. Longitudinal studies are needed to further explore the changes in sympathetic support of REE and if changes in MSNA or tissue responsiveness are related to the sympathetic support of REE.

Management of hyperglycemia during enteral and parenteral nutrition therapy

Hyperglycemia is a frequent complication of enteral and parenteral nutrition in hospitalized patients. Extensive evidence from observational studies indicates that the development of hyperglycemia during parenteral and enteral nutrition is associated with an increased risk of death and infectious complications. There are no specific guidelines recommending glycemic targets and effective strategies for the management of hyperglycemia during specialized nutritional support. Managing hyperglycemia in these patients should include optimization of carbohydrate content and administration of intravenous or subcutaneous insulin therapy. The administration of continuous insulin infusion and insulin addition to nutrition bag are efficient approaches to control hyperglycemia during parenteral nutrition. Subcutaneous administration of long-acting insulin with scheduled or corrective doses of short-acting insulin is superior to the sliding scale insulin strategy in patients receiving enteral feedings. Randomized controlled studies are needed to evaluate safe and effective therapeutic strategies for the management of hyperglycemia in patients receiving nutritional support.

Obesity-related metabolic syndrome: mechanisms of sympathetic overactivity

The prevalence of the metabolic syndrome has increased worldwide over the past few years. Sympathetic nervous system overactivity is a key mechanism leading to hypertension in patients with the metabolic syndrome. Sympathetic activation can be triggered by reflex mechanisms as arterial baroreceptor impairment, by metabolic factors as insulin resistance, and by dysregulated adipokine production and secretion from visceral fat with a mainly permissive role of leptin and antagonist role of adiponectin. Chronic sympathetic nervous system overactivity contributes to a further decline of insulin sensitivity and creates a vicious circle that may contribute to the development of hypertension and of the metabolic syndrome and favor cardiovascular and kidney disease. Selective renal denervation is an emerging area of interest in the clinical management of obesity-related hypertension. This review focuses on current understanding of some mechanisms through which sympathetic overactivity may be interlaced to the metabolic syndrome, with particular regard to the role of insulin resistance and of some adipokines.

Vascular effects of intravenous intralipid and dextrose infusions in obese subjects

Hyperglycemia and elevated free fatty acids (FFA) are implicated in the development of endothelial dysfunction. Infusion of soy-bean oil-based lipid emulsion (Intralipid®) increases FFA levels and results in elevation of blood pressure (BP) and endothelial dysfunction in obese healthy subjects. The effects of combined hyperglycemia and high FFA on BP, endothelial function and carbohydrate metabolism are not known. Twelve obese healthy subjects received four random, 8-h IV infusions of saline, Intralipid 40 mL/h, Dextrose 10% 40 mL/h, or combined Intralipid and dextrose. Plasma levels of FFA increased by 1.03±0.34 mmol/L (p=0.009) after Intralipid, but FFAs remained unchanged during saline, dextrose, and combined Intralipid and dextrose infusion. Plasma glucose and insulin concentrations significantly increased after dextrose and combined Intralipid and dextrose (all, p<0.05) and were not different from baseline during saline and lipid infusion. Intralipid increased systolic BP by 12±9 mmHg (p<0.001) and diastolic BP by 5±6 mmHg (p=0.022),and decreased flow-mediated dilatation (FMD) from baseline by 3.2%±1.4% (p<0.001). Saline and dextrose infusion had neutral effects on BP and FMD. The co-administration of lipid and dextrose decreased FMD by 2.4%±2.1% (p=0.002) from baseline, but did not significantly increase systolic or diastolic BP. Short-term Intralipid infusion significantly increased FFA and BP; in contrast, FFA and BP were unchanged during combined infusion of Intralipid and dextrose. Combined Intralipid and dextrose infusion resulted in endothelial dysfunction similar to Intralipid alone.

Effects of acute and one-week fatty acid lowering on cardiac function and insulin sensitivity in relation with myocardial and muscle fat and adiponectin levels

BACKGROUND/AIM

We tested the hypothesis that a persistent reduction in free fatty acid (FFA) levels improves cardiac function and systemic insulin sensitivity via a reduction in the myocardial and skeletal muscle adiposities and a modulation in adipokine release.

METHODS

Study subjects (body mass index 22-30 kg/m(2), 57 ± 3 yr old) underwent magnetic resonance imaging and spectroscopy to measure the cardiac function and the amounts of fat inside and around the myocardium and skeletal muscle, before (n = 10) and after acute (n = 8) and 1 wk (n = 7, one excluded from analysis) lowering of circulating FFA by acipimox. Circulating adipokines (leptin, adiponectin, resistin, TNFα, IL-6, IL-8, plasminogen activator inhibitor-I, macrophage chemoattractant protein-1) were measured.

RESULTS

The ejection fraction (62 ± 2 vs. 56 ± 1%, P = 0.0035), cardiac output (6.6 ± 0.3 vs. 5.5 ± 0.2 liters/min, P = 0.0018), and forward work (708 ± 49 vs. 539 ± 44 mm Hg × liters/min, P = 0.018) were significantly lower after 1 wk of FFA lowering. In the six subjects undergoing all sessions, the stroke and end-diastolic volumes were also reduced, insulin sensitivity was increased by 33%, and adiponectinemia was decreased (-26%, P = 0.03). No change in intracellular cardiac and skeletal muscle triglyceride levels was observed. Metabolic changes correlated with the lowering of FFA. The reduction in cardiac function was related with changes in glycemia and insulin sensitivity, whereas the deflection in left ventricular work was correlated with the decline in FFA, lipid, and blood pressure levels.

CONCLUSIONS

A 1-wk FFA depletion suppressed cardiac function and improved insulin sensitivity. Intracellular triglyceride deposits in the heart and skeletal muscle played no role in the observed changes. Our data show that FFA participate in the physiological regulation of adipokine levels.

Intake of polyphenol-rich pomegranate pure juice influences urinary glucocorticoids, blood pressure and homeostasis model assessment of insulin resistance in human volunteers

Pomegranate juice (PJ; also known as pomegreat pure juice) provides a rich and varied source of polyphenolic compounds that may offer cardioprotective, anti-atherogenic and antihypertensive effects. The aim of this study was to investigate the effect of PJ consumption on glucocorticoids levels, blood pressure (BP) and insulin resistance in volunteers at high CVD risk. Subjects (twelve males and sixteen females) participated in a randomised, placebo-controlled cross-over study (BMI: 26·77 (sd 3·36) kg/m²; mean age: 50·4 (sd 6·1) years). Volunteers were assessed at baseline, and at weeks 2 and 4 for anthropometry, BP and pulse wave velocity. Cortisol and cortisone levels in urine and saliva were determined by specific ELISA methods, and the cortisol/cortisone ratio was calculated. Fasting blood samples were obtained to assess plasma lipids, glucose, insulin and insulin resistance (homeostasis model assessment of insulin resistance). Volunteers consumed 500 ml of PJ or 500 ml of a placebo drink containing a similar amount of energy. Cortisol urinary output was reduced but not significant. However, cortisol/cortisone ratios in urine (P = 0·009) and saliva (P = 0·024) were significantly decreased. Systolic BP decreased from 136·4 (sd 6·3) to 128·9 (sd 5·1) mmHg (P = 0·034), and diastolic BP from 80·3 (sd 4·29) to 75·5 (sd 5·17) mmHg (P = 0·031) after 4 weeks of fruit juice consumption. Pulse wave velocity decreased from 7·5 (sd 0·86) to 7·44 (sd 0·94) m/s (P = 0·035). There was also a significant reduction in fasting plasma insulin from 9·36 (sd 5·8) to 7·53 (sd 4·12) mIU/l (P = 0·025) and of homeostasis model assessment of insulin resistance (from 2·216 (sd 1·43) to 1·82 (sd 1·12), P = 0·028). No significant changes were seen in the placebo arm of the study. These results suggest that PJ consumption can alleviate key cardiovascular risk factors in overweight and obese subjects that might be due to a reduction in both systolic and diastolic BP, possibly through the inhibition of 11β-hydroxysteroid dehydrogenase type 1 enzyme activity as evidenced by the reduction in the cortisol/cortisone ratio. The reduction in insulin resistance might have therapeutic benefits for patients with non-insulin-dependent diabetes, obesity and the metabolic syndrome.

Rapid onset of renal sympathetic nerve activation in rabbits fed a high-fat diet

Hypertension and elevated sympathetic drive result from consumption of a high-calorie diet and deposition of abdominal fat, but the etiology and temporal characteristics are unknown. Rabbits instrumented for telemetric recording of arterial pressure and renal sympathetic nerve activity (RSNA) were fed a high-fat diet for 3 weeks then control diet for 1 week or control diet for 4 weeks. Baroreflexes and responses to air-jet stress and hypoxia were determined weekly. After 1 week of high-fat diet, caloric intake increased by 62%, accompanied by elevated body weight, blood glucose, plasma insulin, and leptin (8%, 14%, 134%, and 252%, respectively). Mean arterial pressure, heart rate, and RSNA also increased after 1 week (6%, 11%, and 57%, respectively). Whereas mean arterial pressure and body weight continued to rise over 3 weeks of high-fat diet, heart rate and RSNA did not change further. The RSNA baroreflex was attenuated from the first week of the diet. Excitatory responses to air-jet stress diminished over 3 weeks of high-fat diet, but responses to hypoxia were invariant. Resumption of a normal diet returned glucose, insulin, leptin, and heart rate to control levels, but body weight, mean arterial pressure, and RSNA remained elevated. In conclusion, elevated sympathetic drive and impaired baroreflex function, which occur within 1 week of consumption of a high-fat, high-calorie diet, appear integral to the rapid development of obesity-related hypertension. Increased plasma leptin and insulin may contribute to the initiation of hypertension but are not required for maintenance of mean arterial pressure, which likely lies in alterations in the response of neurons in the hypothalamus.

Obesity and adipokines: effects on sympathetic overactivity

Excess body weight is a major risk factor for cardiovascular disease, increasing the risk of hypertension, hyperglycaemia and dyslipidaemia, recognized as the metabolic syndrome. Adipose tissue acts as an endocrine organ by producing various signalling cytokines called adipokines (including leptin, free fatty acids, tumour necrosis factor-α, interleukin-6, C-reactive protein, angiotensinogen and adiponectin). A chronic dysregulation of certain adipokines can have deleterious effects on insulin signalling. Chronic sympathetic overactivity is also known to be present in central obesity, and recent findings demonstrate the consequence of an elevated sympathetic outflow to organs such as the heart, kidneys and blood vessels. Chronic sympathetic nervous system overactivity can also contribute to a further decline of insulin sensitivity, creating a vicious cycle that may contribute to the development of the metabolic syndrome and hypertension. The cause of this overactivity is not clear, but may be driven by certain adipokines. The purpose of this review is to summarize how obesity, notably central or visceral as observed in the metabolic syndrome, leads to adipokine expression contributing to changes in insulin sensitivity and overactivity of the sympathetic nervous system.

The effects of dietary weight loss with or without exercise training on liver enzymes in obese metabolic syndrome subjects

AIM

Insulin resistance and visceral adiposity are predisposing factors for fatty liver disease. The main objectives of this study were (i) to compare the effects of caloric restriction (CR) alone or together with moderate-intensity aerobic exercise training (CR+EX) on liver enzymes, a surrogate marker of liver injury, in obese metabolic syndrome (MetS) subjects and (ii) to identify anthropometric, metabolic, cardiovascular and dietary predictors of changes in liver enzymes.

METHODS

Sedentary men and women (n = 63), aged 55 ± 6 (s.d.) years with body mass index 32.7 ± 4.1 kg/m(2) and confirmed MetS, were randomized to 12-week CR, CR+EX or no treatment (Control).

RESULTS

Weight loss averaged 7.6% in the CR and 9.1% in the CR+EX group (time effect, p < 0.001; group effect, p = 0.11); insulin sensitivity improved by 49 and 45%, respectively (both p < 0.001). Fitness (maximal oxygen consumption) increased by 19% in the CR+EX group only (p < 0.001). Alanine aminotransferase (ALT) levels decreased by 20% in the CR and 24% in the CR+EX group (time effect, both p < 0.001; group effect, p = 0.68); corresponding values for γ-glutamyltransferase (GGT) were -28 and -33%, respectively (time effect, both p < 0.001; group effect, p = 0.28). Reduction in abdominal fat mass (measured by DXA from L1 to L4) independently predicted ΔALT (r = 0.42, p = 0.005) and ΔGGT (r = 0.55, p < 0.001), whereas change in dietary saturated fat intake was independently associated with ΔALT (r = 0.35, p = 0.03).

CONCLUSIONS

Reductions in central adiposity and saturated fat intake are key drivers of improvement in liver enzymes during lifestyle interventions. Exercise training did not confer significant incremental benefits in this study.

Resting heart rate as a predictor of metabolic dysfunctions in obese children and adolescents

BACKGROUND

Recent studies have identified that a higher resting heart rate (RHR) is associated with elevated blood pressure, independent of body fatness, age and ethnicity. However, it is still unclear whether RHR can also be applied as a screening for other risk factors, such as hyperglycemia and dyslipidemia. Thus, the purpose of the presented study was to analyze the association between RHR, lipid profile and fasting glucose in obese children and adolescents.

METHODS

The sample was composed of 180 obese children and adolescents, aged between 7-16 years. Whole-body and segmental body composition were estimated by Dual-energy X-ray absorptiometry. Resting heart rate (RHR) was measured by heart rate monitors. The fasting blood samples were analyzed for serum triglycerides, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and glucose, using the colorimetric method.

RESULTS

Fasting glucose, TC, triglycerides, HDL-C, LDL-C and RHR were similar in both genders. The group of obese subjects with a higher RHR presented, at a lower age, higher triglycerides and TC. There was a significant relationship between RHR, triglycerides and TC. In the multivariate model, triglycerides and TC maintained a significant relationship with RHR independent of age, gender, general and trunk adiposity. The ROC curve indicated that RHR has a high potential for screening elevated total cholesterol and triglycerides as well as dyslipidemia.

CONCLUSION

Elevated RHR has the potential to identify subjects at an increased risk of atherosclerosis development.

Regulation of subcutaneous adipose tissue blood flow is related to measures of vascular and autonomic function

Appropriate blood vessel function is important to cardiovascular health. Adipose tissue plays an important role in metabolic homoeostasis, and subcutaneous abdominal ATBF (adipose tissue blood flow) is responsive to nutritional stimuli. This response is impaired in obesity, suggesting parallels with endothelial function. In the present study, we assessed whether regulation of ATBF is related to the regulation of endothelial function, assessed by FMD (flow-mediated vasodilatation) of the brachial artery. Impaired FMD is a marker of atherosclerotic risk, so we also assessed relationships between ATBF and a marker of atherosclerosis, common carotid artery IMT (intima-media thickness). As ATBF is responsive to sympatho-adrenal stimuli, we also investigated relationships with HRV (heart rate variability). A total of 79 healthy volunteers (44 female) were studied after fasting and after ingestion of 75 g of glucose. FMD, fasting ATBF and the responsiveness of ATBF to glucose were all negatively related to BMI (body mass index), confirming the adverse cardiovascular effects of adiposity. FMD was related to fasting ATBF (rs=0.32, P=0.008) and, at least in males, this relationship was independent of BMI (P=0.02). Common carotid artery IMT, measured in a subset of participants, was negatively related to fasting ATBF [rs=-0.51, P=0.02 (n=20)]. On the other hand, ATBF responsiveness to glucose had no relationship with either FMD or IMT. In multiple regression models, both fasting and stimulated ATBF had relationships with HRV. In conclusion, our results show that the regulation of ATBF has features in common with endothelial function, but also relationships with autonomic cardiovascular control as reflected in HRV.

Drugs and pharmaceuticals: management of intoxication and antidotes

The treatment of patients poisoned with drugs and pharmaceuticals can be quite challenging. Diverse exposure circumstances, varied clinical presentations, unique patient-specific factors, and inconsistent diagnostic and therapeutic infrastructure support, coupled with relatively few definitive antidotes, may complicate evaluation and management. The historical approach to poisoned patients (patient arousal, toxin elimination, and toxin identification) has given way to rigorous attention to the fundamental aspects of basic life support--airway management, oxygenation and ventilation, circulatory competence, thermoregulation, and substrate availability. Selected patients may benefit from methods to alter toxin pharmacokinetics to minimize systemic, target organ, or tissue compartment exposure (either by decreasing absorption or increasing elimination). These may include syrup of ipecac, orogastric lavage, activated single- or multi-dose charcoal, whole bowel irrigation, endoscopy and surgery, urinary alkalinization, saline diuresis, or extracorporeal methods (hemodialysis, charcoal hemoperfusion, continuous venovenous hemofiltration, and exchange transfusion). Pharmaceutical adjuncts and antidotes may be useful in toxicant-induced hyperthermias. In the context of analgesic, anti-inflammatory, anticholinergic, anticonvulsant, antihyperglycemic, antimicrobial, antineoplastic, cardiovascular, opioid, or sedative-hypnotic agents overdose, N-acetylcysteine, physostigmine, L-carnitine, dextrose, octreotide, pyridoxine, dexrazoxane, leucovorin, glucarpidase, atropine, calcium, digoxin-specific antibody fragments, glucagon, high-dose insulin euglycemia therapy, lipid emulsion, magnesium, sodium bicarbonate, naloxone, and flumazenil are specifically reviewed. In summary, patients generally benefit from aggressive support of vital functions, careful history and physical examination, specific laboratory analyses, a thoughtful consideration of the risks and benefits of decontamination and enhanced elimination, and the use of specific antidotes where warranted. Data supporting antidotes effectiveness vary considerably. Clinicians are encouraged to utilize consultation with regional poison centers or those with toxicology training to assist with diagnosis, management, and administration of antidotes, particularly in unfamiliar cases.

Central sympathetic outflow to skeletal muscle: the major link between non-esterified fatty acids and elevated blood pressure?

Sympathetic nervous system activation is a hallmark of several conditions associated with an adverse prognosis, including hypertension and the metabolic syndrome. Proposed mediators of increased sympathetic drive include hyperinsulinaemia, leptin, NEFAs (non-esterified fatty acids), pro-inflammatory cytokines, baroreflex impairment and others. The role of NEFAs appears to be of particular importance given the increased levels observed in human obesity and the experimental results linking the NEFA-induced pressor response to sympathetic activation. Findings from human studies have yielded conflicting results with regards to a sympathetically mediated association between NEFAs and elevated arterial blood pressure. In the present issue of Clinical Science, Florian and Pawelczyk present some interesting results obtained from a small number of healthy normotensive lean volunteers who were exposed to NEFA infusion and cardiovascular and sympathetic monitoring using state of the art methodology that appears to be in support of such a link. However, several methodological and conceptual considerations need to be taken into account when interpreting the results from this study. Put into perspective, the case for a substantial sympathetically mediated pressor response to NEFA infusion does not appear to be a very strong one.