Semaglutide single-dose pen-injector: Post hoc analysis of summative usability testing for weight management

Subcutaneous semaglutide, at a 2.4 mg once-weekly maintenance dose, is approved in the United States for weight management in individuals with a body mass index (BMI) of 30 kg/m² or higher, or with a BMI of 27 kg/m² or higher and at least one obesity-related co-morbidity. To investigate the usability of the semaglutide pen-injector in individuals who met these criteria, we report post hoc analysis of the summative (human factors validation) usability testing and safety analysis involving patients with type 2 diabetes (an obesity-related co-morbidity) with the same pen-injector, limited to the 26 out of 30 patients with a BMI of 27 kg/m² or higher (11 pen-injector-naïve, 15 pen-injector-experienced) and 15 non-pharmacist healthcare professionals (HCPs). Participants performed two simulated injections into an injection pad. No potentially serious use errors occurred. Mean subjective ease-of-use rating on a seven-point scale, where 1 = difficult and 7 = easy, was 6.9 for the second injection in all three groups. These results suggest that the semaglutide pen-injector is easy to use and not associated with serious use errors when used by pen-injector-naïve or pen-injector-experienced patients meeting the requirement for weight management with semaglutide treatment, and by non-pharmacist HCPs.

Comparison of the injection-site experience of the starting doses with semaglutide and dulaglutide: A randomized, double-blind trial in healthy subjects

This double-blind, randomized, single-site, crossover trial compared the injection-site experience with the starting doses of semaglutide and dulaglutide. Healthy subjects (aged 18-75 years; body mass index ≥ 25 kg/m² ; n = 104) were randomized 1:1, using a pregenerated list, to semaglutide 0.25 mg as the first injection and dulaglutide 0.75 mg as the second injection or vice versa; each was administered using their proprietary pen-injectors, according to instructions for use. The primary endpoint was intensity of injection-site pain, measured using a visual analogue scale (VAS; 0 mm = no pain, 100 mm = unbearable pain). Exploratory endpoints included intensity category, duration and quality of injection-site pain, and comparative assessment of injection-site pain with the two injections. The point estimate of the VAS score for injection-site pain intensity was 11.5 mm with dulaglutide versus 5.6 mm with semaglutide; mean (95% confidence interval) estimated treatment difference 5.9 (3.6; 8.2) mm; p < .0001. Other endpoints corroborated a less painful injection experience with semaglutide versus dulaglutide. Safety was consistent with reported data for the drugs. In conclusion, the injection-site experience with semaglutide was rated as less painful than that with dulaglutide.

Association of plasma nitrite levels with obesity and metabolic syndrome in the Old Order Amish

OBJECTIVES

Plasma nitrite is a metabolite of nitric oxide and reflects endogenous nitric oxide synthase (NOS) activity. Although plasma nitrites were previously linked with obesity and metabolic syndrome (MetS), the direction of association remains inconsistent, possibly due to sample heterogeneity. In a relatively homogeneous population, we hypothesized that nitrite levels will be positively associated with overweight/obesity and MetS.

METHODS

Fasting nitrite levels were measured in 116 Old Order Amish (78% women). We performed age-and-sex-adjusted ancovas to compare nitrite levels between three groups (a) overweight/obese(-)MetS(-), (b) overweight/obese(+)MetS(-) and (c) overweight/obese(+)MetS)(+). Multivariate linear regressions were conducted on nitrite associations with continuous metabolic variables, with successive adjustments for demographics, body mass index, C-reactive protein and neopterin.

RESULTS

Nitrite levels were higher in the obese/overweight(+)MetS(+) group than in the other two groups (p < 0.001). Nitrites were positively associated with levels of triglycerides (p < 0.0001), total cholesterol (p = 0.048), high-density lipoprotein/cholesterol ratio (p < 0.0001) and fasting glucose (p < 0.0001), and negatively correlated with high-density lipoprotein-cholesterol (p < 0.0001). These associations were robust to adjustments for body mass index and inflammatory markers.

CONCLUSION

Further investigation of the connection between obesity/MetS and plasma nitrite levels may lead to novel dietary and pharmacological approaches that ultimately may contribute to reducing the increasing burden of obesity, MetS and cardiovascular morbidity and mortality.

Genome-wide physical activity interactions in adiposity - A meta-analysis of 200,452 adults

Physical activity (PA) may modify the genetic effects that give rise to increased risk of obesity. To identify adiposity loci whose effects are modified by PA, we performed genome-wide interaction meta-analyses of BMI and BMI-adjusted waist circumference and waist-hip ratio from up to 200,452 adults of European (n = 180,423) or other ancestry (n = 20,029). We standardized PA by categorizing it into a dichotomous variable where, on average, 23% of participants were categorized as inactive and 77% as physically active. While we replicate the interaction with PA for the strongest known obesity-risk locus in the FTO gene, of which the effect is attenuated by ~30% in physically active individuals compared to inactive individuals, we do not identify additional loci that are sensitive to PA. In additional genome-wide meta-analyses adjusting for PA and interaction with PA, we identify 11 novel adiposity loci, suggesting that accounting for PA or other environmental factors that contribute to variation in adiposity may facilitate gene discovery.

Body weight gain in free-living Pima Indians: effect of energy intake vs expenditure

BACKGROUND

Obesity results from a chronic imbalance between energy intake and energy expenditure. However, experimental evidence of the relative contribution of interindividual differences in energy intake and expenditure (resting or due to physical activity) to weight gain is limited.

OBJECTIVE

To assess prospectively the association between baseline measurements of daily energy metabolism and weight changes by studying free-living adult Pima Indians, one of the most obese populations in the world.

DESIGN

A study of the pathogenesis of obesity in the Pima Indians living in Southwestern Arizona. The participants were 92 nondiabetic Pima Indians (64M/28F, 35+/-12 y, 35+/-9% body fat; mean+/-s.d.). At baseline, free-living daily energy metabolism was assessed by doubly labeled water and resting metabolic rate (RMR) by indirect calorimetry. Data on changes in body weight (5.8+/-6.5 kg) over a follow-up period of 4+/-3 y were available in 74 (49M/25F) of the 92 subjects.

RESULTS

The baseline calculated total energy intake (r=0.25, P=0.028) and RMR (r=-0.28, P=0.016) were significantly associated with changes in body weight. The baseline energy expenditure due to physical activity was not associated with changes in body weight.

CONCLUSION

Using state-of-the-art methods to assess energy intake and expenditure in free-living conditions, we show for the first time that the baseline calculated total energy intake is a determinant of changes in body weight in Pima Indians. These data also confirm that a low RMR is a risk factor for weight gain in this population.

Spontaneous physical activity in a respiratory chamber is correlated to habitual physical activity

OBJECTIVE

During a stay in a respiratory chamber without an exercise protocol, physical activity is limited to activities of daily living, change of posture and 'fidgeting,' collectively referred to as spontaneous physical activity (SPA). SPA is quite variable among individuals and is a heritable trait. A low SPA during a chamber stay is a predictor of weight gain in men. However, it remains to be established whether physical activity in a respiratory chamber relates to physical activity under habitual, free-living conditions. The purpose of the present study was to determine whether physical activity in a chamber is correlated to habitual, free-living physical activity.

DESIGN

Fifty healthy, non-diabetic Pima Indians (30 M/20 F, 30+/-6 y; 37+/-10% body fat; means+/-s.d.) completed a 24 h stay in the respiratory chamber followed by a 7 day measurement of habitual, free-living energy expenditure by doubly labeled water. Free-living physical activity was expressed as activity energy expenditure (AEE(FL); daily energy expenditure-(sleeping metabolic rate+thermic effect of food)), physical activity level (PAL(FL); daily energy expenditure/sleeping metabolic rate) and body-size independent activity units. Activity during the chamber stay was expressed as PAL(Ch), AEE(Ch), and based on radar sensor measurements, as percentage of time with activity (SPA(Radar)).

RESULTS

AEE(FL) (averaging 930+/-310 kcal/day (3.89+/-1.30 MJ/day)) was correlated to AEE(CH) (averaging 440+/-160 kcal/day (1.84+/-0.67 MJ/day)) and higher in men than in women (r=0.53, P=0.003) and r=0.53, P=0.02, respectively). Likewise, PAL(FL) (averaging 1.75+/-0.21) was correlated to PAL(Ch) (averaging 1.42+/-0.10) and higher in men than in women (r=0.49, P=0.006 and r=0.42, P=0.02, respectively). Free-living activity expressed in body-size independent activity units (averaging 17.8+/-7.0) was correlated to SPA(Radar) (averaging 6.4+/-1.7) with no effect of sex (r=0.30, P=0.03).

CONCLUSION

Physical activity in a respiratory chamber was correlated to habitual physical activity, whether expressed as AEE, PAL or body-size independent activity units, providing a plausible explanation for the demonstrated association between a low SPA in the chamber and weight gain. The study encourages further studies of the genetic and non-genetic determinants of SPA and non-exercise activity thermogenesis (NEAT).

Ethnic differences in insulinemia and sympathetic tone as links between obesity and blood pressure

Hyperinsulinemia and increased sympathetic nervous system (SNS) activity are thought to be pathophysiological links between obesity and hypertension. In the present study, we examined the relation among heart rate (HR), blood pressure (BP), and percent body fat (hydrodensitometry or DEXA), fasting plasma insulin concentration, and muscle sympathetic nerve activity (MSNA, microneurography) in male, normotensive whites (n=42) and Pima Indians (n=77). Pima Indians have a high prevalence of obesity and hyperinsulinemia but a relatively low prevalence of hypertension. Compared with whites, Pima Indian men had a higher percent body fat (28% versus 21%) and higher fasting insulin concentrations (210 versus 132 pmol/L) but lower MSNA (27 versus 33 bursts/min) (all P<0.001). In both ethnic groups, HR and BP were positively related to percent body fat and MSNA, and both were significant independent determinants of HR and BP in multiple regression analyses. However, MSNA was positively related to percent body fat and the fasting insulin concentration in whites (r=0.60 and r=0.47, both P<0.01) but not in Pima Indians (r=0.15 and r=0.03, NS) (P<0.01 for ethnic differences in the slope of the regression lines). These results confirm the physiological importance of the SNS in normal BP regulation but indicate that the roles of hyperinsulinemia and increased SNS activity as mediators for the relation between obesity and hypertension can differ between different ethnic groups. The lack of an increase in SNS activity with increasing adiposity and insulinemia in Pima Indians may contribute to the low prevalence of hypertension in this population.

The sympathetic nervous system and obesity: role in aetiology and treatment

The sympathetic nervous system (SNS) is an important component of the autonomic nervous system, and thus plays a major role in the maintenance of homeostasis. The SNS is of particular importance in the control of the cardiovascular system and of a number of metabolic processes. Alterations in SNS effects on metabolism have been implicated in the development and maintenance of obesity, and the SNS is a potential therapeutic target in the treatment of obesity. This review provides an overview of the anatomical and physiological aspects of the SNS, before considering the evidence showing a role for the SNS in the development or treatment of obesity.

A novel polymorphism in the proximal UCP3 promoter region: effect on skeletal muscle UCP3 mRNA expression and obesity in male non-diabetic Pima Indians

OBJECTIVE

UCP2 and UCP3 are newly discovered uncoupling proteins, which are thought to underlie the variability in energy metabolism in humans. Mutations in the UCP2 and/or UCP3 gene have been associated with sleeping metabolic rate. Recently we reported that skeletal muscle UCP3 mRNA expression was positively correlated with sleeping metabolic rate in Pima Indians. To study whether genetic variation in the promoter region of UCP3 contributed to the variation in expression of UCP3, we screened part of the proximal promoter region for polymorphisms.

METHODS

In the first part of the study, the proximal promoter region of UCP3 was screened by direct sequencing in 24 non-diabetic Pima Indians (range body mass index (BMI): 18-47 kg/m2) (Schrauwen et al. Diabetes 1999; 48: 146-149) and skeletal muscle UCP3 mRNA expression was measured by RT-PCR. In the second part of the study, we typed the polymorphism found in the first part of the study in 67 Pima Indians (32 males, 35 females) from the upper and lower extremes of the BMI distribution.

RESULTS

We identified a novel C to T substitution in the UCP3 promoter, 6bp upstream of the putative TATA signal, and 55bp upstream of the transcription starting site. Among 18 male subjects, skeletal muscle UCP3 mRNA expression was significantly higher in the C/T & T/T group compared to the C/C homozygotes (P<0.02). However, in the group of 67 Pima Indians genotype frequencies were not different in the obese and lean groups.

CONCLUSION

We identified a novel polymorphism in the proximal promoter region of UCP3, which was associated with increased skeletal muscle expression of UCP3 in male non-diabetic Pima Indians. Considering the suggested role of UCP3 in energy metabolism, this polymorphism might be of physiological importance in the regulation of energy balance.

Energy metabolism in African Americans: potential risk factors for obesity

BACKGROUND

Recent reports have identified a lower resting metabolic rate in African Americans than in whites, but most studies included only females and used short-term measurements with ventilated-hood systems.

OBJECTIVE

Our objective was to compare 24-h measurements of energy metabolism between African American and white women and men using a respiratory chamber.

DESIGN

Thirty-eight African American (x +/- SD: 32 +/- 7 y of age, 24 +/- 10% body fat) and 288 white (31 +/- 7 y of age, 26 +/- 12% body fat) subjects spent 24 h in a respiratory chamber for measurement of 24-h energy expenditure (24EE), sleeping metabolic rate (SMR), 24-h respiratory quotient (24RQ), and substrate oxidation rates.

RESULTS

After adjustment for sex, age, and body composition (by hydrodensitometry), African Americans had lower SMR (-301 +/- 105 kJ/d; P < 0.01) and higher 24RQ (0.014 +/- 0.004; P < 0.001) than whites, whereas 24EE was similar. A sex-specific analysis, using a subset of 38 whites with an equal sex distribution and similar age and body weight, revealed that African American women had lower SMR (-442 +/- 182 kJ/d; P < 0.05) and lower 24EE (-580 +/- 232 kJ/d; P < 0.05), but similar 24RQ values compared with white women. African American men tended to have lower SMRs than white men (-355 +/- 188 kJ/d; P = 0. 07), but had higher 24RQ values, accounting for a 992 +/- 327-kJ/d lower 24-h fat oxidation rate (P < 0.005).

CONCLUSIONS

These data not only confirm the findings of a lower metabolic rate in African American than in white women, but also suggest that fat oxidation is lower in African American men than in white men.

Determinants of energy expenditure and fuel utilization in man: effects of body composition, age, sex, ethnicity and glucose tolerance in 916 subjects

BACKGROUND

24-h energy expenditure (24-EE) and 24-h respiratory quotient (24-RQ) are important measurements in obesity research, but their accurate assessment is limited to few specialized laboratories.

OBJECTIVES

1) To provide comprehensive prediction equations for 24-EE, sleeping metabolic rate (SMR) and 24-RQ, based on a large number of Caucasian and Pima Indian subjects, covering a wide range of body weight and composition, body fat distribution, and age and 2) to test whether Pima Indians have lower metabolic rate and/or higher 24-RQ than Caucasians.

SUBJECTS AND METHODS

916 non-diabetic subjects, aged 31.5 +/- 11.9 y, body weight 90.5 +/- 26.1 kg (mean +/- s.d.), (561 males, 355 females; 416 Caucasians, 500 Pima Indians; 720 with normal (NGT) and 196 with impaired (IGT) glucose tolerance) spent 24 h in a respiratory chamber for measurements of 24-EE, SMR and 24-RQ. Fat-free mass (FFM) and fat mass (FM) were assessed by either hydrodensitometry or DEXA. Waist circumference and waist-to-thigh ratio (WTR) were determined as measures of body fat distribution.

RESULTS

In a stepwise multiple regression analysis, FFM, FM, sex, age, WTR, and ethnicity were significant independent determinants of 24-EE (2258 +/- 422 kcal/d), explaining 85% of its variability (24-EE (kcal/d)=696 + 18.9 FFM (kg) + 10.O FM (kg) + 180 male -1.9 age (y) + 7.1 WTR (per decimal) + 44 Pima Indian). SMR (1623 +/- 315kcal/d) was determined (78% of variability) by FFM, FM, sex, age, WTR, and glucose tolerance (SMR (kcal/d) = 443 +/- 14.6 FFM (kg) + 6.9 FM (kg) + 79 male - 1.0 age (y) + 5.8 WTR (per decimal) + 38 IGT), but not by ethnicity. Adjustment for the respective variables reduced the variance in 24-EE from 422 to 162 kcal/d and in SMR from 315 to 146kcal/d. 24-RQ (0.854 +/- 0.026) was determined by waist circumference and energy balance (24-RQ = 0.88429-0.00175 waist circumference (cm) + 0.00004 energy balance (%)), but not by sex, ethnicity or glucose tolerance. With this equation only 13% of the variability in 24-RQ could be explained (residual variance 0.024). Compared to Caucasians, Pima Indians had higher 24-EE, but similar SMR and 24-RQ.

CONCLUSIONS

This analysis provides comprehensive prediction equations for 24-EE, SMR and 24-RQ from their major known determinants. It confirms the previous findings that, even after adjustment for body composition, age, sex, ethnicity, and glucose tolerance, there is still considerable variability in energy expenditure and substrate oxidation that may, in part, be genetically determined. In adult Pima Indians, we found no evidence for lower metabolic rate or impaired fat oxidation that could explain the propensity towards obesity in this ethnic group.

Hypothalamic-pituitary-adrenal axis and sympathetic nervous system activities in Pima Indians and Caucasians

It has been proposed that both hypercortisolism and low sympathetic nervous system (SNS) activity contribute to obesity. Because glucocorticoids inhibit SNS activity, we hypothesized that hypercortisolism and low SNS activity may be found in association in Pima Indians, a population with a high prevalence of obesity. We therefore measured indices of hypothalamic-pituitary-adrenal (HPA) axis and SNS activities in 39 nondiabetic men, 20 Pimas (age, 30+/-5 years; weight, 94+/-26 kg; 35%+/-8% body fat [mean +/- SD]) and 19 Caucasians (33+/-9 years, 91+/-23 kg, 28%+/-11% body fat). HPA axis activity was assessed by measurements of morning fasting plasma corticotropin (ACTH) and cortisol concentrations and 24-hour urinary free cortisol (UFC) excretion. SNS activity was assessed as muscle sympathetic nerve activity (MSNA) by microneurography and by measurement of catecholamines (fasting plasma concentration and 24-hour urinary excretion). Plasma ACTH and cortisol and UFC were similar in Pimas and Caucasians. MSNA was positively correlated with percent body fat (r = .49, P = .002) and was lower in Pimas compared with Caucasians after adjustment for percent body fat (24+/-9 v 31+/-10 bursts/min, P = .04). We conclude that Pima Indians, a population with a high prevalence of obesity, have lower SNS activity but normal HPA axis activity compared with Caucasians.

No effect of Trp64Arg beta3-adrenoceptor polymorphism on the plasma leptin concentration in Pima Indians

In rodents, administration of leptin promotes beta3-adrenergic stimulation of thermogenesis in brown adipose tissue. Conversely, administration of a beta3-adrenoceptor (beta3-AR) agonist decreases leptin mRNA expression and secretion, suggesting that leptin and sympathetic nervous system activity mediated through the beta3-AR comprise a negative-feedback loop. It has recently been proposed that a defect in the beta3-AR in humans may contribute to a resistance to the sympathetically mediated effects of leptin on thermogenesis and lipolysis, thus leading to obesity and type 2 diabetes mellitus. We thus hypothesized that the Trp64Arg variant in the human beta3-AR would be associated with elevated plasma leptin concentrations. We studied 101 healthy nondiabetic Pima Indians: 11 Arg64 homozygotes, 35 Trp64 homozygotes, and 55 heterozygotes. The fasting plasma leptin concentration as an absolute value or after adjustment for percent body fat and sex was not associated with the beta3-AR genotype. Thus, the data do not support an influence of the Trp64Arg variant on the plasma leptin concentration.

Respiratory quotient is inversely associated with muscle sympathetic nerve activity

The relative amounts of the macronutrients oxidized by an individual are reflected in the respiratory quotient (RQ), which varies inversely with lipid oxidation. A high RQ, indicating a relatively low lipid oxidation, and a low activity of the sympathetic nervous system have both been identified as risk factors for body weight gain. The stimulatory effect of norepinephrine on lipid oxidation suggests that low lipid oxidation may contribute to the relationship between low sympathetic nervous activity and body weight gain. The purpose of the present study was to determine whether low basal muscle sympathetic nerve activity (MSNA), a direct measure of sympathetic nervous outflow, is independently associated with low lipid oxidation. Intraneural recordings of basal MSNA were performed in 39 healthy, nondiabetic males, 19 Caucasians (mean +/-SD, 33 +/- 9 yr, 91 +/- 23 kg, and 28 +/- 11% body fat) and 20 Pima Indians (30 +/- 5 yr, 94 +/- 25 kg, and 35 +/- 8% fat) immediately after measurement of 24-h RQ in a respiratory chamber. Basal MSNA, energy balance, and age were independent determinants of 24-h RQ, together explaining 45% of its variability. Accordingly, 24-h RQ adjusted for energy balance and age was inversely related to MSNA (r = -0.41; P = 0.01). Race, percent body fat, and fasting plasma insulin were not independent determinants of 24-h RQ. Although MSNA explained only a limited part of the variability in 24-h RQ, the results support the hypothesis that an effect on lipid oxidation contributes to the demonstrated relationship between low activity of the sympathetic nervous system and body weight gain.

In situ lipolytic responses to isoproterenol and physiological stressors are similar in obese Pima Indians and Caucasians

Evidence suggests that impaired lipolysis may contribute to fat accumulation. To test whether the lipolytic response to adrenergic stimulation is lower in Pima Indians, a population prone to obesity and type 2 diabetes mellitus, than in Caucasians, 48 healthy, non-diabetic subjects were studied: 27 Pima Indians (12 males and 15 females, 30 +/- 7 yr, 85 +/- 18 kg, 36 +/- 10% body fat; mean +/- SD) and 21 Caucasians (11 males and 10 females, 34 +/- 7 yr, 105 +/- 26 kg, 39 +/- 11% body fat). Lipolysis in the abdominal s.c. adipose tissue was assessed in situ by glycerol concentration in microdialysis samples at baseline and during local infusion of the nonselective beta-adrenergic agonist isoproterenol (10(-6) mol/L), mental stress, and submaximal exercise. The baseline dialysate glycerol concentrations were similar in Pima Indians and Caucasians. Lipolytic response (relative increment in dialysate glycerol concentration, percentage above the baseline) was similar in Pima Indians and Caucasians in response to local isoproterenol infusion (77 +/- 36% and 76 +/- 40%) and exercise (38 +/- 38% and 41 +/- 41%). During mental stress, the dialysate concentration did not change significantly from baseline in either group. Changes in local blood flow, determined by ethanol dilution, did not differ between the two groups. In conclusion, the high propensity for obesity in Pima Indians does not seem to be due to an impaired lipolytic response to stimuli.

Increase in insulin action and fat oxidation after treatment with CL 316,243, a highly selective beta3-adrenoceptor agonist in humans

Stimulation of beta3-adrenoceptors by selective agonists improves insulin action and stimulates energy metabolism in various rodent models of obesity and type 2 diabetes. Whether selective beta3-adrenoceptor stimulation exerts metabolic actions in humans remains to be proven. The effects of a highly selective beta3-adrenoceptor agonist on insulin action, energy metabolism, and body composition were assessed in 14 healthy young lean male volunteers (age 22.5 +/- 3.3 years, 15 +/- 5% body fat [mean +/- SD]) randomly assigned to 8 weeks of treatment with either 1,500 mg/day of CL 316,243 (n = 10) or placebo (n = 4). Insulin-mediated glucose disposal (IMGD), nonoxidative glucose disposal (NOGD), oxidative glucose disposal (OGD) (indirect calorimetry), and splanchnic glucose output (SGO; beta3-[H3]glucose) were determined during a 100-min hyperinsulinemic-euglycemic glucose clamp (40 mU x m(-2) x min(-1)) before and after 4 and 8 weeks of treatment. The 24-h energy expenditure (24-EE), 24-h respiratory quotient (24-RQ), and the oxidation rates of fat and carbohydrate were determined in a respiratory chamber before and after 8 weeks. After 4 weeks, treatment with CL 316,243 increased IMGD (+45%, P < 0.01) in a plasma concentration-dependent manner (r = 0.76, P < 0.02). This effect was due to an 82% increase in NOGD (P < 0.01), while OGD and SGO remained unchanged. The effects on insulin action were markedly diminished after 8 weeks; this was significantly related to an unexpected decline in the plasma concentrations of CL 316,243 (-36%, P = 0.08). At this time, 24-RQ was lowered (P < 0.001), corresponding to a 23% increase in fat oxidation (P < 0.01) and a 17% decrease in carbohydrate oxidation (P = 0.05). The 24-EE after 8 weeks did not differ from baseline, and there was no change in body weight or body composition. Plasma concentrations of glucose, insulin, and leptin were unaffected by treatment, while free fatty acid concentrations increased by 41% (P < 0.05), again linearly with the achieved plasma concentration of CL 316,243 (r = 0.67, P < 0.05). Treatment with CL 316,243 had no effect on heart rate or blood pressure and caused no cases of tremors. We conclude that treatment of lean male subjects with CL 316,243 increases insulin action and fat oxidation, both in a plasma concentration-dependent manner. This is the first study to demonstrate unequivocal metabolic effects of a highly selective beta3-adrenoceptor agonist in humans.

Whole body fat oxidation is related to in situ adipose tissue lipolytic response to isoproterenol in males

A high 24-h respiratory quotient (RQ), i.e., low fat oxidation, predicts weight gain. To determine whether impaired fat mobilization (lipolysis) may contribute to weight gain, we studied the relation between lipolytic response to nonselective beta-adrenergic stimulation and RQ measured in a respiratory chamber in 21 males (11 Caucasians, 10 Pima Indians; age 32 +/- 5 yr, weight 93 +/- 24 kg, body fat 30 +/- 8%; means +/- SD) and 23 females (10 Caucasians, 13 Pima Indians; age 32 +/- 9 yr, weight 95 +/- 26 kg, body fat 44 +/- 8%). Lipolytic response was assessed as the relative increase in dialysate glycerol concentration (% above baseline) when isoproterenol (1 micromol/l) was added to the perfusate of a microdialysis probe inserted in the abdominal subcutaneous adipose tissue. In males, but not in females, basal RQ measured during sleep from 0500 to 0630 and adjusted for waist circumference was negatively correlated to lipolytic response (r = -0.66, P = 0.001). The results suggest that in males, impaired beta-adrenergic-mediated lipolysis may contribute to low rates of fat oxidation, a condition known to predispose to weight gain.

Pima Indian males have lower beta-adrenergic sensitivity than Caucasian males

The sympathetic nervous system controls cardiovascular homeostasis and regulates energy metabolism. Pima Indians, a population with a low prevalence of hypertension and a high prevalence of obesity, have low sympathetic nervous activity, compared with Caucasians. Preliminary findings suggest that they may also have a low beta-adrenergic sensitivity. We studied beta-adrenergic sensitivity in 87 nondiabetic normotensive individuals [52 Pima Indians (35 males/17 females) and 35 Caucasians (24 males/11 females)], matched for age and body weight. Chronotropic sensitivity to beta-adrenergic stimulation was assessed by the dose of isoproterenol necessary to increase heart rate by 25 beats per minute [chronotropic dose-25 (CD25)]. Despite a similar basal heart rate and arterial blood pressure, Pimas tended to have lower beta-adrenergic sensitivity than Caucasians (CD25 = 2.37 +/- 2.27 vs. 1.57 +/- 1.38 microg, P = 0.07; mean +/- SD). This difference was significant in males (CD25 = 3.03 +/- 2.39 vs. 1.85 +/- 1.56 microg, P = 0.02) but not in females (CD25 = 1.01 +/- 1.17 vs. 0.96 +/- 0.61 microg, P = 0.99). In males only, CD25 was positively correlated to percent body fat (r = 0.36, P < 0.01). After adjustment for percent body fat, beta-adrenergic sensitivity was still significantly lower in Pima than in Caucasian males (CD25 = 3.44 +/- 2.24 vs. 2.57 +/- 1.60 microg, P = 0.05). In conclusion, our data suggest that increased adiposity is accompanied by decreased beta-adrenergic sensitivity in males only. However, at each level of adiposity, Pima Indian males have lower beta-adrenergic sensitivity than Caucasian males. In combination with a low sympathetic nervous system activity, a reduced beta-adrenergic sensitivity may contribute to the low prevalence of hypertension and the high prevalence of obesity observed in Pima Indians.

Relationship between muscle sympathetic nerve activity and plasma leptin concentration

In humans, basal muscle sympathetic nerve activity (MSNA), a direct measure of sympathetic nervous outflow, is correlated with percentage of body fat. The underlying physiological mechanism is unknown. On the basis of the observation that leptin increases sympathetic nervous outflow in the ob/ob mouse, we hypothesized that leptin, a hormone secreted by the adipose tissue, may act as a peripheral signal to increase sympathetic nervous outflow from the central nervous system. We therefore tested whether basal MSNA is correlated with plasma leptin concentration. Fasting plasma samples and recordings of basal MSNA in the peroneal nerve were obtained from 37 healthy, nondiabetic men (35 whites and 2 Mexican-Americans; 29 +/- 7 years, 86 +/- 14 kg, 24 +/- 10% body fat; mean +/- SD) who were fed a weight-maintenance diet on a metabolic ward. As expected, plasma leptin concentration (geometric mean, 6.4 ng/mL; 95% confidence interval, 4.6 ng/mL to 9.0 ng/mL) correlated with % body fat (r = 0.93, p < 0.001). Basal MSNA was 31.6 +/- 10.0 bursts/min and correlated with % body fat (r = 0.53, p < 0.001) and with plasma leptin concentration (r = 0.44, p < 0.01). In conclusion, the results demonstrate a correlation between MSNA and plasma leptin concentration of a magnitude similar to that between MSNA and % body fat. Leptin may therefore be the peripheral signal explaining the correlation between MSNA and % body fat. A full understanding of the relationship between leptin and the activity of the sympathetic nervous system requires further studies, including the administration of leptin in humans.

No effect of the Trp64Arg beta 3-adrenoceptor variant on in vivo lipolysis in subcutaneous adipose tissue

A Trp64Arg variant in the human beta 3-adrenoceptor is associated with earlier onset of non-insulin-dependent diabetes mellitus and obesity in several populations. The present study investigated in vivo lipolysis in individuals homozygous for the 'variant' allele coding for arginine (Arg) in position 64 of the beta 3-adrenoceptor or homozygous for the 'wild type' tryptophan (Trp) allele. Subjects were 25 healthy, non-diabetic Pima Indians, 8 Arg (2 males, 6 females; aged 34 +/- 9 years, BMI 36.2 +/- 7.7 kg/m2, 43 +/- 11% body fat [mean +/- SD]), and 17 Trp (9 males, 8 females; aged 30 +/- 5 years, BMI 30.4 +/- 6.1 kg/m2, 39 +/- 9% body fat). After an overnight fast, a microdialysis probe was inserted in the subcutaneous adipose tissue and perfused with Ringer's solution. Dialysate was collected in 10-min fractions during a 30-min baseline and during 40 min with isoproterenol, a non-selective beta-adrenergic agonist, added to the perfusate (1 mumol/l). Changes in rate of lipolysis were assessed as changes in dialysate glycerol concentration. The relative changes in dialysate glycerol concentrations in response to isoproterenol, expressed as percent over baseline, were similar in the two groups (i.e. 63 +/- 30 and 74 +/- 28% in the Arg and Trp subjects, respectively). The results were also similar in the two groups after adjustment for sex and percentage of body fat. No differential effect of isoproterenol on blood flow was demonstrated between the two groups (assessed by the ethanol dilution technique). These results are consistent with in vitro studies showing no functional effect of the beta 3-adrenoceptor variant, and/or indicate that the beta 3-adrenoceptor is not very important for subcutaneous adipose tissue lipolysis.

Ad libitum food intake in humans after manipulation of glycogen stores

It is controversial whether food intake in humans is under day-to-day regulation to maintain constant body glycogen stores. In eight white males with a mean (+/-SD) age of 30 +/- 4 y, body weight of 82 +/- 20 kg, and percentage body fat of 22 +/- 5%, exercise and diets were used to produce either high (HG) or low glycogen (LG) stores in a randomized crossover design. After each treatment a vastus lateralis muscle biopsy was obtained. Subsequent ad libitum food intake was measured with an automated food-selection system during 2 d in a respiratory chamber. Despite a 46 +/- 21% difference in muscle glycogen between the two treatments, ad libitum 2-d food intakes (energy, weight, or macronutrients) were similar between treatments (HG: 23.80 +/- 4.67 MJ/d; LG: 21.20 +/- 6.73 MJ/d). However, energy intake on the second day of ad libitum feeding was negatively correlated with carbohydrate balance on the first day, adjusted for the effect of total energy intake and treatment. Adjusted carbohydrate balance on day 1 only explained 9% of the variance in energy intake on day 2. The 24-h respiratory quotient on the first day after treatment was higher after the HG than after the LG treatment: 0.94 +/- 0.04 and 0.88 +/- 0.07 (P < 0.001). The findings suggest that 1) body glycogen stores play at most a minor role in short-term food intake regulation, and 2) in the short term, imbalances in glycogen stores are corrected by adjustments of macronutrient oxidation rates.

Effects of glucocorticoids on energy metabolism and food intake in humans

The effect of glucocorticoid administration on energy metabolism and food intake was studied in 20 healthy, nondiabetic Caucasian male volunteers [27 +/- 5 (SD) yr, 72 +/- 9 kg, 20 +/- 7% body fat] randomly and blindly assigned to glucocorticoid (methylprednisolone, METH; n = 10) or placebo (PLAC; n = 10) treatment. Each subject was studied twice: during a weight maintenance diet and during ad libitum food intake. Energy metabolism was measured by indirect calorimetry and food intake by an automated food-selection system. Twenty-four-hour urinary norepinephrine excretion (24-h NE) was used as an estimate of sympathetic nervous system activity. During weight maintenance, METH intravenous infusion (125 mg/30 min) increased energy expenditure compared with PLAC, and after 4 days of oral therapy, METH (40 mg/day) decreased 24-h NE and increased energy expenditure compared with PLAC. During ad libitum food intake, after 4 days of METH (40 mg/day) or PLAC oral therapy, both groups increased their energy intake over weight maintenance, but the increase was significantly larger in the METH group compared with the PLAC group (4,554 +/- 1,857 vs. 2,867 +/- 846 kcal/day; P = 0.04). Our data suggest that therapeutic doses of glucocorticoids induce obesity mostly by increasing energy intake, an effect which may be related to the ability of glucocorticoids to act directly or indirectly on the central regulation of appetite.

Decreased ratio of fat to carbohydrate oxidation with increasing age in Pima Indians

BACKGROUND

Some metabolic changes related to age may increase the prevalence of obesity. Previous studies have shown that a low relative metabolic rate and a low ratio of fat to carbohydrate utilization are predictors of body weight gain. However, a possible relationship between age and energy substrate utilization (respiratory quotient; RQ = VCO2/VO2) has not been reported.

OBJECTIVE

To determine whether RQ increases and therefore fat oxidation decreases with age in Pima Indian men, independent of body fat and energy balance.

METHODS

We analyzed longitudinal data collected in seven non-diabetic Pima Indian men (31 +/- 6 years, 167 +/- 8 cm, 111.0 +/- 23.7 kg and 41 +/- 9% fat at baseline) who had repeated measurements of 24-hour RQ 7 years apart. On both admissions, subjects were fed a weight maintenance diet (50% carbohydrate, 30% fat and 20% protein) for 3 days before spending 1 day within a respiratory chamber for measurements of 24-hour energy expenditure, basal metabolic rate, sleeping metabolic rate and 24-hour RQ. Paired t-test was used to determine differences between the first and last measurement of 24-hour RQ. Cross-sectional data in 131 Pima Indian men (28 +/- 9 years, 171 +/- 6 cm, 94.5 +/- 24.4 kg, and 32 +/- 9% fat) were also analyzed to determine the relationship between 24-hour RQ and age. Multiple regression analysis was used to adjust 24-hour RQ for differences in energy balance (intake/expenditure in %) and percent body fat and metabolic rate for differences in body size and composition.

RESULTS

Over a 7-year period, mean unadjusted and adjusted 24-hour RQ increased (p < 0.01). Cross-sectional data analysis showed that both the unadjusted (r = 0.19, p < 0.03) and adjusted (r = 0.19, p < 0.03) 24-hour RQ correlated with increasing age while adjusted BMR (r = -0.21, p < 0.02) correlated inversely with age.

CONCLUSIONS

Despite a higher body fat content, older individuals utilize less fat than their younger counterparts. Reduced fat utilization and decreased BMR with age may both contribute to increasing obesity in older individuals.

Gender differences in muscle sympathetic nerve activity: effect of body fat distribution

Muscle sympathetic nerve activity (MSNA) has been correlated with percent body fat (%BF) in males. Because MSNA is typically lower and %BF higher in females, we tested whether this relationship could be generalized to females. Because abdominal-visceral body fat in men may be responsible for elevated sympathetic activity, we hypothesized that an estimate [waist-to-thigh ratio (W/T)] would correlate positively with MSNA in both genders and account for higher MSNA in males. Microneurography, hydrodensitometry, and W/T measures were obtained in 14 males and 14 females with a large range of %BF and W/T. Regression analyses revealed positive correlations between MSNA and %BF in males (r = 0.55, P = 0.04) and in females (r = 0.63, P = 0.02), with no difference in the slopes of the regression lines but a higher intercept in males (P < 0.01). When genders were pooled, MSNA and W/T were correlated (r = 0.68, P < 0.0001); this positive correlation was also found in males (r = 0.57, P = 0.04) but not as strongly in females (r = 0.49, P = 0.07). Forward stepwise multiple-regression analysis using %BF, W/T, gender, and age indicated that W/T was the primary factor related to MSNA (R2 = 0.46); the other factors were not independent predictors. It is concluded that %BF is related to MSNA in both males and females but that the regression line is shifted downward in females because of lower levels of MSNA. W/T is a better correlate of MSNA than %BF and partially explains the higher MSNA in males. These findings may be relevant to the cardiovascular and metabolic disease risk associated with abdominal obesity.

No differential effects of porcine and human insulin on muscle sympathetic nerve activity during euglycaemia or hypoglycaemia

On the basis of some clinical studies in diabetic patients, and experimental studies in normal humans, it has been suggested that hypoglycaemic autonomic responses are augmented with porcine (PI) compared to human insulin (HI). A difference in sensory processing has been reported following insulin-induced hypoglycaemia with PI compared to HI, and has been interpreted as different insulin effects on the central nervous system. In a double blind crossover comparison of HI and PI in nine healthy subjects, microneurographic recordings of muscle sympathetic nerve activity (MSNA) were performed, as well as measurements of cardiovascular and hormonal responses during a low dose hyperinsulinaemic euglycaemic glucose clamp (plasma insulin 60.1 +/- 1.9 mU ml-1 (mean +/- SEM)), followed by a period of insulin-induced hypoglycaemia. Plasma insulin and glucose were identical in the two sessions. Plasma glucose nadir during hypoglycaemia was 2.4 +/- 0.2 mmol l-1 for HI and 2.5 +/- 0.1 mmol l-1 for PI. During euglycaemia, MSNA increased from 24 +/- 2 to 34 +/- 3 and 23 +/- 2 to 30 +/- 2 burst/min (P:NS) for HI and PI, respectively, and during hypoglycaemia to 49 +/- 4 and 45 +/- 2 bursts min-1 (P:NS), respectively. The maximal hypoglycaemic increments of MSNA were not different (HI 15 +/- 4; PI 15 +/- 2 bursts min-1 (P:NS)) Responses of plasma noradrenaline and haemodynamic parameters did not differ either. This study does not indicate differing sympathetic responses to PI and HI in healthy humans. Evidence for a modulating effect of insulin on central sympathetic outflow was not found.

Thermic effect of food in humans: methods and results from use of a respiratory chamber

During the past two decades, many investigators have measured the thermic effect of food (TEF) in humans and have speculated on its role in the development of obesity. In this study we compared different ways of computing TEF from daily energy expenditure measurements in a respiratory chamber, evaluated the determinants of TEF, and more importantly assessed for the first time the relation between TEF and change in body weight. In 471 subjects, TEF was 1697 +/- 857 kJ/d (mean +/- SD), ie, 18 +/- 9% of energy intake. In 114 subjects studied more than once, intraindividual TEF variability was very high (CV = 48%). TEF correlated positively with the level of spontaneous physical activity (SPA) and negatively with fasting plasma glucose and insulin concentrations. TEF correlated inversely with age (males only) and body weight, percent body fat, and waist-to-hip ratio (females only). The level of SPA and fasting plasma glucose concentration were the only significant determinants of TEF, explaining 15% of its variance. In 137 subjects in whom body weight was measured > or = 6 mo after TEF measurement (mean follow-up duration of 2.9 +/- 1.7 y), a low TEF was not predictive of body weight gain. We conclude that, despite the low reproducibility of TEF from use of a respiratory chamber, data in a large number of subjects suggest that TEF is increased by higher SPAs and that insulin resistance is associated with a low TEF. More important, longitudinal data indicate that the variability in TEF is not associated with changes in body weight.