Muscle Sympathetic Nerve Activity Is Associated With Elements of the Plasma Lipidomic Profile in Young Asian Adults

BACKGROUND

Asian subjects are at increased cardio-metabolic risk at comparatively lower body mass index (BMI) compared with white subjects. Sympathetic nervous system activation and dyslipidemia, both characteristics of increased adiposity, appear to be related. We therefore analyzed the association of muscle sympathetic nerve activity (MSNA) with the plasma lipidomic profile in young adult Asian and white subjects.

METHODS

Blood samples were collected from 101 participants of either Asian or white background (age, 18 to 30 years; BMI, 28.1 ± 5.9 kg/m2). Lipids were extracted from plasma and analyzed using electrospray ionization-tandem mass spectrometry. MSNA was quantified using microneurography. The association of MSNA and obesity with lipid species was examined using linear regression analysis.

RESULTS

The plasma concentrations of total dihydroceramide, ceramide, GM3 ganglioside, lysoalkylphosphatidylcholine, alkenylphosphatidylethanolamine, and lysophosphatidylinositol were elevated in the Asian subjects relative to the white subjects. After adjustment for confounders, diacylglycerols and triacylglycerols, cholesterol esters, phosphatidylinositols, phosphatidylethanolamines, and phosphatidylglycerols bore significant associations with MSNA but only in the Asian subjects. These associations remained significant after further adjustment for the participants' degree of insulin resistance and appeared not to be related to differences in diet macronutrient content between groups.

CONCLUSIONS

The lipidomic profile differs between Asian and white subjects. There exists a strong relationship between certain lipid species and MSNA. The association is stronger in Asian subjects, despite their lower BMI. This study demonstrates an association between circulating lipids and central sympathetic outflow. Whether the stronger association between the lipid profile and sympathetic activation underpins the apparent greater risk posed by increased adiposity in Asian individuals merits further attention.

Neck Circumference Is Associated with Muscle Sympathetic Nerve Activity in Overweight and Obese Men but Not Women

Background: Neck circumference (NC) is a predictor of cardiometabolic risk. The objective of this study was to explore the relationship of NC to muscle sympathetic nerve activity (MSNA) within an overweight and obese population.

Methods: The study design was a retrospective cross-sectional analysis. Un-medicated persons (72 men, 53 postmenopausal women) aged 56 ± 1 years (mean ± SEM) with body mass index (BMI) 32.8 ± 0.4 kg/m², were studied. NC was measured together with traditional anthropometric measures, supine blood pressure, fasting blood lipids, insulin, and glucose. Insulin sensitivity was assessed by homeostasis model (HOMA-IR) and Matsuda Insulin Sensitivity Index (ISI) derived from 75-g oral glucose tolerance test. Resting multiunit MSNA was recorded by microneurography in the peroneal nerve and expressed as burst frequency and burst incidence.

Results: Men within the highest tertile of NC had significantly higher fasting and post-glucose plasma insulin levels (insulin AUC₀₋₁₂₀), HOMA-IR, non-esterified fatty acids, MSNA (45 ± 2 vs. 36 ± 2 bursts per min; 69 ± 3 vs. 58 ± 3 bursts per 100 hb) and heart rate, and lower Matsuda ISI compared to men in the lowest tertile (P all <0.05). In stepwise regression analyses, NC alone explained 12%, and together with insulin AUC₀₋₁₂₀ it accounted for 22%, of the variance in MSNA in men. In women, NC was associated with anthropometric measures but not with MSNA or metabolic indices.

Conclusions: Among overweight and obese men, NC was independently associated with elevated MSNA and hyperinsulinemia, and thus may be relevant to cardiometabolic risk prediction. The biological basis of gender differences merits further elucidation.

Norepinephrine transporter expression is inversely associated with glycaemic indices: a pilot study in metabolically diverse persons with overweight and obesity

Objective

The objective of this study was to examine the cross‐sectional relationship between the expression of norepinephrine transporter (NET), the protein responsible for neuronal uptake‐1, and indices of glycaemia and hyperinsulinaemia, in overweight and obese individuals.

Methods

Thirteen non‐medicated, non‐smoking subjects, aged 58 ± 1 years (mean ± standard error of the mean), body mass index (BMI) 31.4 ± 1.0 kg m⁻², with wide‐ranging plasma glucose and haemoglobin A1c (HbA1c, range 5.1% to 6.5%) participated. They underwent forearm vein biopsy to access sympathetic nerves for the quantification of NET by Western blot, oral glucose tolerance test (OGTT), euglycaemic hyperinsulinaemic clamp, echocardiography and assessments of whole‐body norepinephrine kinetics and muscle sympathetic nerve activity.

Results

Norepinephrine transporter expression was inversely associated with fasting plasma glucose (r = −0.62, P = 0.02), glucose area under the curve during OGTT (AUC_0–120, r = −0.65, P = 0.02) and HbA1c (r = −0.67, P = 0.01), and positively associated with steady‐state glucose utilization during euglycaemic clamp (r = 0.58, P = 0.04). Moreover, NET expression was inversely related to left ventricular posterior wall dimensions (r = −0.64, P = 0.02) and heart rate (r = −0.55, P = 0.05). Indices of hyperinsulinaemia were not associated with NET expression. In stepwise linear regression analysis adjusted for age, body mass index and blood pressure, HbA1c was an independent inverse predictor of NET expression, explaining 45% of its variance.

Conclusions

Hyperglycaemia is associated with reduced peripheral NET expression. Further studies are required to identify the direction of causality.

Comparable Attenuation of Sympathetic Nervous System Activity in Obese Subjects with Normal Glucose Tolerance, Impaired Glucose Tolerance, and Treatment Naïve Type 2 Diabetes following Equivalent Weight Loss

Background and Purpose: Elevated sympathetic nervous system (SNS) activity is a characteristic of obesity and type 2 diabetes (T2D) that contributes to target organ damage and cardiovascular risk. In this study we examined whether baseline metabolic status influences the degree of sympathoinhibition attained following equivalent dietary weight loss.

Methods: Un-medicated obese individuals categorized as normal glucose tolerant (NGT, n = 15), impaired glucose tolerant (IGT, n = 24), and newly-diagnosed T2D (n = 15) consumed a hypocaloric diet (29% fat, 23% protein, 45% carbohydrate) for 4-months. The three groups were matched for baseline age (56 ± 1 years), body mass index (BMI, 32.9 ± 0.7 kg/m²), and gender. Clinical measurements included whole-body norepinephrine kinetics, muscle sympathetic nerve activity (MSNA, by microneurography), spontaneous cardiac baroreflex sensitivity (BRS), and oral glucose tolerance test.

Results: Weight loss averaged −7.5 ± 0.8, −8.1 ± 0.5, and −8.0 ± 0.9% of body weight in NGT, IGT, and T2D groups, respectively. T2D subjects had significantly greater reductions in fasting glucose, 2-h glucose and glucose area under the curve (AUC₀₋₁₂₀) compared to NGT and IGT (group effect, P <0.001). Insulinogenic index decreased in IGT and NGT groups and increased in T2D (group × time, P = 0.04). The magnitude of reduction in MSNA (−7 ± 3, −8 ± 4, −15 ± 4 burst/100 hb, respectively) and whole-body norepinephrine spillover rate (−28 ± 8, −18 ± 6, and −25 ± 7%, respectively), time effect both P <0.001, did not differ between groups. After adjustment for age and change in body weight, Δ insulin AUC₀₋₁₂₀ was independently associated with reduction in arterial norepinephrine concentration, whilst Δ LDL-cholesterol and improvement in BRS were independently associated with decrease in MSNA.

Conclusions: Equivalent weight loss through hypocaloric diet is accompanied by similar sympathoinhibition in matched obese subjects with different baseline glucose tolerance. Attenuation of hyperinsulinemia and hyperlipidemia, rather than glycemic indices, is associated with reduction in SNS activity following weight loss intervention.

Reduction in peripheral vascular resistance predicts improvement in insulin clearance following weight loss

Background

The hyperinsulinemia of obesity is a function of both increased pancreatic insulin secretion and decreased insulin clearance, and contributes to cardiovascular risk. Whilst weight loss is known to enhance insulin clearance, there is a paucity of data concerning the underlying mechanisms. This study was conducted to examine the inter-relationships between changes in sympathetic nervous system (SNS) activity, vascular function and insulin clearance during a weight loss program.

Methods

Seventeen non-smoking, un-medicated individuals aged 55 ± 1 years (mean ± SEM), body mass index (BMI) 33.9 ± 1.7 kg/m², underwent a 4-month hypocaloric diet (HCD), using a modified Dietary Approaches to Stop Hypertension diet, whilst seventeen age- and BMI-matched subjects acted as controls. Insulin sensitivity and insulin clearance were assessed via euglycemic hyperinsulinemic clamp (exogenous insulin clearance); hepatic insulin extraction was calculated as fasting C-peptide to insulin ratio (endogenous insulin clearance); SNS activity was quantified by microneurographic nerve recordings of muscle sympathetic nerve activity (MSNA) and whole-body norepinephrine kinetics; and vascular function by calf venous occlusion plethysmography and finger arterial tonometry.

Results

Weight loss averaged −8.3 ± 0.6 % of body weight in the HCD group and was accompanied by increased clamp-derived glucose utilization (by 20 ± 9 %, P = 0.04) and exogenous insulin clearance (by 12 ± 5 %, P = 0.02). Hepatic insulin extraction increased from 6.3 ± 0.8 to 7.1 ± 0.9 (P = 0.09). Arterial norepinephrine concentration decreased by −12 ± 5 %, whole-body norepinephrine spillover rate by −14 ± 8 %, and MSNA by −9 ± 5 bursts per 100 heartbeats in the HCD group (P all >0.05 versus control group). Step-wise regression analysis revealed a bidirectional relationship between enhanced exogenous insulin clearance post weight loss and reduction in calf vascular resistance (r = −0.63, P = 0.01) which explained 40 % of the variance. Increase in hepatic insulin extraction was predicted by enhanced finger reactive hyperaemic response (P = 0.006) and improvement in oral glucose tolerance (P = 0.002) which together explained 64 % of the variance.

Conclusions

Insulin clearance is independently and reciprocally associated with changes in vascular function during weight loss intervention.

Trial registration ClinicalTrials.gov: NCT01771042 and NCT00408850

Pioglitazone treatment enhances the sympathetic nervous system response to oral carbohydrate load in obese individuals with metabolic syndrome

CONTEXT

Insulin resistance is associated with blunted sympathetic nervous system (SNS) response to carbohydrate ingestion which may contribute to postprandial hypotension and impaired body weight homeostasis.

OBJECTIVE

This study was conducted to examine the effects of pharmacological insulin sensitization on whole-body norepinephrine kinetics during a standard 75-g oral glucose tolerance test (OGTT) in obese, insulin resistant subjects with metabolic syndrome.

METHODS

Un-medicated individuals (n=42, mean age 56±0.8 yrs, body mass index 34±0.6 kg/m(2)) were randomised to 12-weeks pioglitazone (PIO, 15 mg for 6 weeks, then 30 mg daily) or placebo using a double-blind, parallel group design. Whole-body norepinephrine kinetics (arterial norepinephrine concentration, calculated spillover and clearance rates), spontaneous cardiac baroreflex sensitivity, heart rate and blood pressure were measured at times 0, 30, 60, 90 and 120 minutes during OGTT. Insulin sensitivity was assessed by euglycemic hyperinsulinemic clamp (M) and Matsuda index.

RESULTS

PIO increased clamp derived glucose utilisation by 35% (P<0.001) and there were concurrent reductions in inflammatory status and plasma triglycerides (P<0.05). Fasting norepinephrine kinetic parameters were unaltered. PIO treatment was associated with lower plasma insulin incursions, greater reduction in diastolic blood pressure and enhanced baroreflex sensitivity during OGTT (P all <0.05). The overall norepinephrine spillover response (AUC(0-120)) increased significantly in the PIO group (group × time interaction, P=0.04), with greatest increment at 30 minutes post-glucose (101±38 ng/min at baseline versus 241±48 ng/min post treatment, P=0.04) and correlated with percent improvement in M.

CONCLUSIONS

PIO enhances the early postprandial SNS response to carbohydrate ingestion.

Arterial norepinephrine concentration is inversely and independently associated with insulin clearance in obese individuals with metabolic syndrome

CONTEXT

Impaired insulin clearance contributes to the hyperinsulinemia of obesity, yet relatively little is known concerning the pathophysiological determinants of insulin clearance in obese populations.

OBJECTIVE

To examine the cross-sectional relationship between insulin clearance and resting sympathetic nervous system activity in a cohort of obese subjects with metabolic syndrome.

PARTICIPANTS AND METHODS

Unmedicated, nonsmoking subjects (31 male, 27 female; aged 56 ± 1 year; body mass index 33.7 ± 0.6 kg/m(2)) underwent euglycemic hyperinsulinemic clamp to determine insulin sensitivity (M) and insulin clearance, assessment of norepinephrine kinetics, peripheral arterial tonometry, Doppler echocardiography, and oral glucose tolerance test.

RESULTS

Univariate correlation analyses showed inverse associations between insulin clearance and arterial norepinephrine concentration (r = -0.44, P = .0006), calculated norepinephrine spillover rate (r = -0.33, P = .01), augmentation index (AI, r = -0.37, P = .005), and positive associations with M (r = 0.30, P = .02), Matsuda insulin sensitivity index (r = 0.27, P = .04), and cardiac output (r = 0.27, P = .04). Insulin clearance and sensitivity did not differ between genders, however females had higher AI compared to males (35 ± 3% versus 14 ± 2%, P < .001). In age and gender adjusted stepwise regression analyses, arterial norepinephrine concentration alone explained 19% of the variance in insulin clearance. When all significant variables were entered into the regression model, arterial norepinephrine, AI, gender, and M were independent predictors of insulin clearance, together explaining 41% of the variance.

CONCLUSIONS

Arterial norepinephrine concentration is inversely and independently associated with whole-body insulin clearance rate in obese individuals with metabolic syndrome. Prospective studies are needed to determine the direction of causality and the chronology of interactions between insulin clearance and sympathetic neural activity.

A randomized controlled trial of the effects of pioglitazone treatment on sympathetic nervous system activity and cardiovascular function in obese subjects with metabolic syndrome

CONTEXT

Insulin resistance and sympathetic nervous system overactivity are closely associated and contribute to cardiovascular risk.

OBJECTIVE

The objective of the study was to test the hypotheses that pharmacological improvement in insulin sensitivity would (1) attenuate sympathetic neural drive and (2) enhance neuronal norepinephrine uptake.

PARTICIPANTS AND METHODS

A randomized, double-blind trial was conducted in 42 obese, unmedicated individuals with metabolic syndrome (mean age 56 ± 1 y, body mass index 34 ± 0.6 kg/m(2)) who received 12 weeks of pioglitazone (PIO; 15 mg for 6 wk, then 30 mg daily) or matched placebo. Clinical measurements included whole-body norepinephrine kinetics [spillover rate, plasma clearance, and the steady state ratio of tritiated 3,4-dihydroxyphenylglycol to tritiated norepinephrine ([(3)H]-DHPG to [(3)H]-NE) as an index of neuronal uptake-1], muscle sympathetic nerve activity, spontaneous baroreflex sensitivity, euglycemic hyperinsulinemic clamp, oral glucose tolerance test, ambulatory blood pressure, and Doppler echocardiography.

RESULTS

PIO treatment increased glucose uptake by 35% and was accompanied by significant reductions in diastolic blood pressure and improved left ventricular diastolic and endothelial function. Resting muscle sympathetic nerve activity burst frequency decreased by -6 ± 3 burst/min compared with baseline (P = .03), but the magnitude of change was not different from placebo (P = .89). Norepinephrine spillover and clearance rates and baroreflex sensitivity were unchanged. Post hoc subgroup analyses revealed an 83% increase in [(3)H]-DHPG to [(3)H]-NE ratio in hyperinsulinemic (P = .04) but not normoinsulinemic subjects (time × group interaction, P = .045). Change in [(3)H]-DHPG to [(3)H]-NE ratio correlated with improvements in diastolic blood pressure (r = -0.67, P = .002), the ratio of early (E) to late (A) peak transmitral diastolic inflow velocity (r = 0.62, P = .008), E wave deceleration time (r = -0.48, P = .05), and Δinsulin area under the curve0-120 during the oral glucose tolerance test (r = -0.42, P = .08).

CONCLUSIONS

Compared with placebo, PIO does not affect resting sympathetic drive or norepinephrine disposition in obese subjects with metabolic syndrome. Treatment induced changes in the [(3)H]-DHPG to [(3)H]-NE ratio related to reduction in hyperinsulinemia and improvements in diastolic function.

Plasma advanced glycation end products (AGEs) and NF-κB activity are independent determinants of diastolic and pulse pressure

BACKGROUND

High levels of circulating advanced glycation end products (AGEs) can initiate chronic low-grade activation of the immune system (CLAIS) with each of these factors independently associated with cardiovascular (CV) morbidity and mortality. Therefore, our objective was to characterize the relationship between serum AGEs, CLAIS and other risk factors for CV disease in normotensive non-diabetic individuals.

METHODS

We measured body mass index (BMI), waist-to-hip ratio (WHR), blood pressure, lipid and glucose profile in 44 non-diabetic volunteers (17 female, 27 males). Carboxymethyl-lysine (CML) was measured by ELISA as a marker for circulating AGEs and NF-κB p65 activity as an inflammatory marker by DNA-binding in peripheral blood mononuclear cells lysates (PBMC).

RESULTS

Plasma CML concentrations were related to diastolic blood pressure (r=-0.51, p<0.01) independently of age, sex, BMI and WHR (p<0.05). Diastolic blood pressure was also related to NF-κB activity in PBMC (r=0.47, p<0.01) before and after adjustment for age, sex, BMI and WHR (p<0.05). Plasma CML concentrations were related to the pulse pressure before (r=0.42; p<0.05) and after adjustment for age, sex, BMI and waist (p<0.05). Neither CML nor NF-κB activity were related to systolic blood pressure (both p=ns). Plasma CML concentrations were not associated with plasma lipid or glucose concentrations (all p=ns).

CONCLUSIONS

Plasma AGE levels and NF-κB activity in PBMC were independent determinants of diastolic and pulse pressure in healthy normotensive individuals. This association suggests a role for AGEs in the etiology of hypertension, possibly via the initiation of CLAIS and aortic stiffening.

The effects of dietary weight loss on indices of norepinephrine turnover: modulatory influence of hyperinsulinemia

OBJECTIVES

This study was conducted to examine (1) the effects of dietary weight loss on indices of norepinephrine (NE) turnover and (2) whether baseline hyperinsulinemia modulates sympathetic neural adaptations.

METHODS

Obese individuals aged 56 ± 1 year, BMI 32.5 ± 0.4 kg/m(2) , with metabolic syndrome, underwent a 12-week hypocaloric diet (HCD, n = 39) or no treatment (n = 26). Neurochemical measurements comprised arterial dihydroxyphenylalanine (DOPA), 3,4-dihydroxyphenylglycol (DHPG), and NE concentrations, the steady-state ratio of [3H]-DHPG to [3H]-NE, as an index of neuronal uptake, and calculated whole-body plasma NE clearance and spillover rates.

RESULTS

Body weight decreased by -7.4 ± 0.5% in HCD group (P < 0.001) and was accompanied by reductions in DOPA, NE, and DHPG averaging -14 ± 5% (P = 0.001), -23 ± 4% (P <0.001), and -5 ± 4% (P = 0.03), respectively. NE spillover rate decreased by -88 ± 39 ng/min (P = 0.01), whereas neuronal uptake and NE plasma clearance were unchanged. Despite similar weight loss, hyperinsulinemic subjects exhibited greater reductions in NE and NE spillover rate, compared to normoinsulinemic subjects (group by time interaction P < 0.05).

CONCLUSIONS

Weight loss is associated with down-regulation of sympathetic nervous activity but no overall alteration in disposition indices. Hyperinsulinemic subjects derive a greater sympathoinhibitory benefit during weight loss.

The relation of glucose metabolism to left ventricular mass and function and sympathetic nervous system activity in obese subjects with metabolic syndrome

CONTEXT

Altered cardiac structure and function have been reported in prediabetic and diabetic populations; however, the contribution of the sympathetic nervous system (SNS) to these changes has yet to be delineated.

OBJECTIVE

Our objective was to examine interrelationships between glucose metabolism, left ventricular mass and function, and SNS activity in obese metabolic syndrome subjects.

PARTICIPANTS AND METHODS

Unmedicated impaired glucose tolerant (IGT) (n = 31) or treatment-naive type 2 diabetic (T2D) (n = 25) subjects, matched for age (mean 58 ± 1 years), gender, body mass index (32.2 ± 0.5 kg/m(2)), and blood pressure, participated. They underwent echocardiography and assessments of whole-body norepinephrine kinetics, muscle sympathetic nerve activity, and insulin sensitivity by euglycemic clamp (M value).

RESULTS

T2D subjects had higher left ventricular mass index (LVMI) (93.6 ± 3.5 vs 77.2 ± 3.4 g/m(2), P = .002) and Doppler-derived isovolumetric relaxation and deceleration times (both P < .05) and lower early/late transmitral inflow velocities (E/A) (P = .02) compared with IGT. Total muscle sympathetic nerve activity and arterial norepinephrine concentration were higher in the T2D group (by 18% and 32%, respectively, both P ≤ .05), whereas plasma norepinephrine clearance was reduced (1.94 ± 0.11 vs 2.26 ± 0.10 L/min, P = .02). M value correlated inversely with left ventricular septal thickness (r = -0.46, P = .007). Whole-body noradrenaline spillover rate correlated with LVMI in the T2D subgroup (r = 0.47, P = .03). In the pooled cohort, LVMI was independently predicted by pulse pressure (r = 0.38, P = .004) and E/A ratio by 2-hour glucose (r = -0.38, P = .005).

CONCLUSIONS

Transition from IGT to T2D is associated with cardiac enlargement and diastolic dysfunction, which relate to metabolic, hemodynamic, and SNS alterations.

Neuroadrenergic dysfunction along the diabetes continuum: a comparative study in obese metabolic syndrome subjects

Neuroadrenergic function in type 2 diabetic (T2D) patients without neuropathy is poorly characterized. We therefore compared sympathetic nervous system activity at rest and during an oral glucose tolerance test in obese metabolic syndrome (MetS) subjects classified as glucose intolerant (impaired glucose tolerance [IGT]; n = 17) or treatment-naive T2D (n = 17). Untreated subjects, matched for age (mean 59 ± 1 year), sex, BMI (32.4 ± 0.6 kg/m(2)), and family history of diabetes were studied. We measured resting muscle sympathetic nerve activity (MSNA) by microneurography, whole-body norepinephrine kinetics by isotope dilution, insulin sensitivity by euglycemic-hyperinsulinemic clamp (steady-state glucose utilization adjusted for fat-free mass and steady-state insulin concentration [M/I]), and MetS components. T2D subjects had higher resting MSNA burst incidence (67 ± 4 versus 55 ± 3 bursts per 100 heartbeats; P = 0.05) and arterial norepinephrine levels (264 ± 33 versus 167 ± 16 pg/mL; P = 0.02), lower plasma norepinephrine clearance (by 17%; P = 0.03), and reduced neuronal reuptake compared with IGT subjects (by 46%; P = 0.04). Moreover, norepinephrine spillover responses to glucose ingestion were blunted in T2D subjects. The M/I value independently predicted whole-body norepinephrine spillover (r = -0.47; P = 0.008), whereas fasting insulin level related to neuronal norepinephrine reuptake (r = -0.35, P = 0.047). These findings demonstrate that progression to T2D is associated with increased central sympathetic drive, blunted sympathetic responsiveness, and altered norepinephrine disposition.

Baseline sympathetic nervous system activity predicts dietary weight loss in obese metabolic syndrome subjects

CONTEXT

The sympathetic nervous system is an important physiological modulator of basal and postprandial energy expenditure.

OBJECTIVE

Our objective was to investigate whether the variability of weight loss attained during hypocaloric dietary intervention is related to individual differences in baseline sympathetic drive and nutritional sympathetic nervous system responsiveness.

PARTICIPANTS AND METHODS

Untreated obese subjects (n = 42; body mass index = 32.1 ± 0.5 kg/m(2)), aged 57 ± 1 yr, who fulfilled Adult Treatment Panel III metabolic syndrome criteria participated in a 12-wk weight loss program using a modified Dietary Approaches to Treat Hypertension (DASH) diet. Muscle sympathetic nerve activity (MSNA) was measured by microneurography at rest and in a subset of subjects during a standard 75-g oral glucose tolerance test.

RESULTS

Weight loss (6.7 ± 0.5 kg) was independently predicted by baseline resting MSNA burst incidence (r = 0.38; P = 0.019), which accounted for 14.3% of the variance after adjustment for age and baseline body weight. Weight loss-resistant subjects in the lower tertile of weight loss (4.4 ± 0.3%) had significantly blunted MSNA responses to oral glucose at baseline compared with successful weight losers (9.6 ± 0.8%). Absolute Δ MSNA averaged -7 ± 2, -6 ± 5, and -3 ± 3 bursts per 100 heartbeats at 30, 60, and 90 min after glucose in the weight loss-resistant group. Corresponding values in the successful weight loss group were 9 ± 3, 12 ± 3, and 15 ± 4 bursts per 100 heartbeats (time × group interaction, P = 0.004).

CONCLUSIONS

These findings indicate that baseline sympathetic drive and nutritional sympathetic responsiveness may be important prognostic biological markers for weight loss outcome.

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.

First Australian experiences with an oral volume restriction device to change eating behaviors and assist with weight loss

Eating behaviors impact satiety and caloric intake so should be considered in any weight-loss program. A novel custom-made oral device has been designed to be worn in the upper palate while eating in order to slow eating-rate and aid weight loss. The aim of this study was to assess the device's potential impact on weight-loss and gain first impressions among overweight/obese Australians. Twenty participants (M: 6, F: 14, mean age 36 years, BMI 27-33 kg/m(2)) were enrolled in a 4-month open-label trial. Each received a device and nutritionist-delivered diet plan. Weight, compliance, and acceptability were assessed fortnightly. Anthropometry, biochemical and clinical outcomes were measured at baseline and 16 weeks. Sixteen participants completed the study. Mean weight-loss was 4.9 ± 0.9 kg, or 5.2 ± 0.9% initial bodyweight (P < 0.001, n = 20, intention-to-treat). There were no significant adverse events (AEs), but 65% of participants required device adjustment by the dentist. Compliance (defined as >5 uses/week) was achieved by 80% of participants and correlated positively with weight-loss (R = 0.68, P = 0.001). All reported that the device was comfortable and reduced bite-size, promoted chewing and slowed eating-rate. Most observed either no change, or increased satiety, despite reduced meal sizes. For most, speech difficulties discouraged device use in social settings. All reported greater awareness of food choices, portion sizes and eating-rate. Subjective control of dietary behaviors, measured by the Three Factor Eating Questionnaire (TFEQ), improved significantly. The device should be explored as an adjunct to dietary composition change in weight-management programs, to assist patients to modify eating behaviors and achieve successful weight-loss.

The effects of weight loss versus weight loss maintenance on sympathetic nervous system activity and metabolic syndrome components

CONTEXT

Sympathetic nervous system (SNS) overactivity participates in both the pathogenesis and adverse clinical complications of metabolic syndrome (MetS) obesity.

OBJECTIVE

We conducted a prospective lifestyle intervention trial to compare the effects of active weight loss and extended weight loss maintenance on SNS function and MetS components.

METHODS

Untreated subjects (14 males, four females; mean age, 53 ± 1 yr; body mass index, 30.9 ± 0.9 kg/m(2)) who fulfilled Adult Treatment Panel III criteria were randomized to 12-wk hypocaloric diet alone (n = 8) or together with aerobic exercise training (n = 10). This was followed by a 4-month weight maintenance period. Measurements of muscle sympathetic nerve activity (MSNA) by microneurography, whole-body norepinephrine kinetics, substrate oxidation by indirect calorimetry, baroreflex sensitivity, plasma renin activity (PRA), and MetS components were performed.

RESULTS

Body weight decreased by 9.3 ± 0.8% at wk 12 (P < 0.001), and this was maintained. During active weight loss, norepinephrine spillover rate decreased by 23 ± 16% (P = 0.004), MSNA by 25 ± 3 bursts per 100 heartbeats (P < 0.001), and PRA by 0.25 ± 0.09 ng/ml · h (P = 0.007), whereas baroreflex sensitivity increased by 5.2 ± 2.2 msec/mm Hg (P = 0.005). After weight maintenance, beneficial effects of weight loss on norepinephrine spillover rate were preserved, whereas PRA and MSNA rebounded (by 0.24 ± 0.11 ng/ml · h, P = 0.02; and 20 ± 5 bursts/100 heartbeats, P = 0.0003), and baroreflex sensitivity was attenuated.

CONCLUSIONS

Divergent effects of successful weight loss maintenance on whole-body norepinephrine spillover rate and MSNA suggest organ-specific differentiation in SNS adaptation to weight loss under conditions of negative vs. stable energy balance.