Direct and indirect healthcare costs of lung cancer CT screening in Denmark: a registry study

INTRODUCTION

A study based on the Danish Randomised Controlled Lung Cancer Screening Trial (DLCST) calculated the healthcare costs of lung cancer screening by comparing costs in an intervention group with a control group. Participants in both groups, however, experienced significantly increased negative psychosocial consequences after randomisation. Substantial participation bias has also been documented: The DLCST participants reported fewer negative psychosocial aspects and experienced better living conditions compared with the random sample.

OBJECTIVE

To comprehensively analyse the costs of lung cancer CT screening and to determine whether invitations to mass screening alter the utilisation of the healthcare system resulting in indirect costs. Healthcare utilisation and costs are analysed in the primary care sector (general practitioner psychologists, physiotherapists, other specialists, drugs) and the secondary care sector (emergency room contacts, outpatient visits, hospitalisation days, surgical procedures and non-surgical procedures).

DESIGN

To account for bias in the original trial, the costs and utilisation of healthcare by participants in DLCST were compared with a new reference group, selected in the period from randomisation (2004-2006) until 2014.

SETTING

Four Danish national registers.

PARTICIPANTS

DLCST included 4104 current or former heavy smokers, randomly assigned to the CT group or the control group. The new reference group comprised a random sample of 535 current or former heavy smokers in the general Danish population who were never invited to participate in a cancer screening test.

MAIN OUTCOME MEASURES

Total healthcare costs including costs and utilisation of healthcare in both the primary and the secondary care sector.

RESULTS

Compared with the reference group, the participants in both the CT group (offered annual CT screening, lung function test and smoking counselling) and the control group (offered annual lung function test and smoking counselling) had significantly increased total healthcare costs, calculated at 60% and 48% respectively. The increase in costs was caused by increased use of healthcare in both the primary and the secondary sectors.

CONCLUSION

CT screening leads to 60% increased total healthcare costs. Such increase would raise the expected annual healthcare cost per participant from EUR 2348 to EUR 3756. Cost analysis that only includes costs directly related to the CT scan and follow-up procedures most likely underestimates total costs. Our data show that the increased costs are not limited to the secondary sector.

TRIAL REGISTRATION NUMBER

NCT00496977.

Effect of Low-Dose Rapamycin on Senescence Markers and Physical Functioning in Older Adults with Coronary Artery Disease: Results of a Pilot Study

Rapamycin, an mTOR inhibitor affects senescence through suppression of senescence-associated secretory phenotype (SASP). We studied the safety and feasibility of low-dose rapamycin and its effect on SASP and frailty in elderly undergoing cardiac rehabilitation (CR). 13 patients; 6 (0.5mg), 6 (1.0mg), and 1 patient received 2mg oral rapamycin (serum rapamycin <6ng/ml) daily for 12 weeks. Median age was 73.9±7.5 years and 12 were men. Serum interleukin-6 decreased (2.6 vs 4.4 pg/ml) and MMP-3 (26 vs 23.5 ng/ml) increased. Adipose tissue expression of mRNAs (arbitrary units) for MCP-1 (3585 vs 2020, p=0.06), PPAR-γ (1257 vs 1166), PAI-1 (823 vs 338, p=0.08) increased, whereas interleukin-8 (163 vs 312), TNF-α (75 vs 94) and p16 (129 vs 169) decreased. Cellular senescence-associated beta galactosidase activity (2.2% vs 3.6%, p=0.18) tended to decrease. We observed some correlation between some senescence markers and physical performance but no improvement in frailty with rapamycin was noted. (NCT01649960).

Inflammatory characteristics of adipose tissue collected by surgical excision vs needle aspiration

Subcutaneous adipose tissue can be obtained for research during an elective, clinically indicated operation by standard surgical excision approaches and by needle aspiration in pure research settings. Whether measurements of inflammatory markers and cells made in tissue collected these two different ways are comparable is debatable. We sought to determine whether these two techniques yield systematically different results for measurements of inflammation, cellular senescence, and adipose tissue composition. Twelve subjects undergoing surgery participated. At the time of surgery abdominal subcutaneous adipose tissue from adjacent sites was removed by excision and needle aspiration. Stromovascular cell composition (flow cytometry), the number of senescent cells (senescence-associated-β-galactosidase staining), and IL-6, IL-1, TNF-α, MCP1 mRNA (RT-PCR) were measured in each sample. We found no statistically significant differences between the two sample collection approaches for any of the parameters measured. We conclude that these two methods of obtaining adipose tissue do not systematically differ in the results of cytokine mRNA content, cellular senescence, or stromovascular cell composition.

The thermic effect of food is reduced in older adults

The thermic effect of food accounts for ~10% of daily energy expenditure. A reduction in the thermic effect of food, which has been variably observed in the older adults, could predispose to fat gain. We tested whether the thermic effect of food is reduced in older adults compared with young adults by analyzing our database of standardized studies conducted at the Mayo Clinic between 1999 and 2009. Data were available from 136 older adult volunteers aged 60-88 (56 females) and 141 young adults aged 18-35 years (67 females). Basal energy expenditure was measured by indirect calorimetry to assess basal metabolic rate. Body fat, fat free mass, and visceral fat were measured using a combination of dual energy X-ray absorptiometry and an abdominal CT scan. The thermic effect of food and postprandial insulinemia were measured in 123 older adults (52 females) and 86 young adults (38 females) of these volunteers. Basal metabolic rate adjusted for fat-free mass was less in older adults (p=0.01) and the thermic effect of food was ~1% (p=0.02) less in the older adults. After controlling for meal size and fat-free mass, body fat and fat distribution did not predict the thermic effect of food. Both basal metabolic rate and the thermic effect of food are less in older adults than young adults, even when they have similar amounts of lean tissue and consume a similar size meal. These factors contribute to lower daily energy expenditure in the older adults.

Obesity Paradox should not interfere with public health efforts

The Obesity Paradox could result in confusing messages that derail beneficial environmental changes and lead to reduced efforts by physicians to provide healthy lifestyle treatment plans to their obese patients. The Obesity Paradox applies in the main to individuals who have a disease, and therefore observed associations with mortality illustrating the Paradox may be more susceptible to certain types of bias than would be found in healthy individuals. Although individualization of weight loss advice for patients with serious disease is appropriate in medical settings, this does not supplant the need for general efforts to prevent and treat obesity.

Clinical effects of high-fat meals and weight gain due to high-fat feeding

Overfeeding high-fat (HF) meals results in both short-term and long-term effects that vary depending upon adiposity status (obese vs nonobese) and family history of type 2 diabetes. Although more than 4 weeks of overeating produces mild insulin resistance, whether the same is true of a single, HF meal is not clear. We reviewed overfeeding studies of 4-8 weeks duration, studies of single HF meals and our own (unpublished) plasma insulin and glucose concentration data from 59 nonobese and 15 overweight/obese volunteers who consumed either a normal-fat (NF) breakfast or a breakfast matched for carbohydrate and protein, but with an additional 80 g of monounsaturated fat (HF). Four to eight weeks of overfeeding a HF diet causes an ∼10% reduction in insulin sensitivity. Some authors report that a single HF meal is associated with greater postprandial insulin concentrations, whereas other investigators have not confirmed such a response. We found that plasma glucose concentrations peaked later following a HF breakfast than a NF breakfast in both obese and nonobese adults and that daytime plasma insulin concentrations were not uniformly increased following a HF breakfast. We conclude that a single HF meal delays the postprandial peak in glucose concentrations, likely due to delayed gastric emptying. This will confound attempts to use insulinemia as a marker of insulin resistance. After 4-8 weeks of overeating a HF diet accompanied by 2-4 kg of fat gain, insulin sensitivity decreases by ∼10%. Although we could not demonstrate that baseline insulin resistance predicts visceral fat gain with overfeeding, normal-weight relatives of type 2 diabetes mellitus do tend to gain more weight and become more insulin resistant than those without a positive family history of type 2 diabetes mellitus. In summary, short-term weight gain from HF diets induces relatively mild metabolic disorders.

Body composition determines direct FFA storage pattern in overweight women

Direct FFA storage in adipose tissue is a recently appreciated pathway for postabsorptive lipid storage. We evaluated the effect of body fat distribution on direct FFA storage in women with different obesity phenotypes. Twenty-eight women [10 upper body overweight/obese (UBO; WHR >0.85, BMI >28 kg/m(2)), 11 lower body overweight/obese (LBO; WHR <0.80, BMI >28 kg/m(2)), and 7 lean (BMI <25 kg/m(2))] received an intravenous bolus dose of [9,10-(3)H]palmitate- and [1-(14)C]triolein-labeled VLDL tracer followed by upper body subcutaneous (UBSQ) and lower body subcutaneous (LBSQ) fat biopsies. Regional fat mass was assessed by combining DEXA and CT scanning. We report greater fractional storage of FFA in UBSQ fat in UBO women compared with lean women (P < 0.01). The LBO women had greater storage per 10(6) fat cells in LBSQ adipocytes compared with UBSQ adipocytes (P = 0.04), whereas the other groups had comparable storage in UBSQ and LBSQ adipocytes. Fractional FFA storage was significantly associated with fractional VLDL-TG storage in both UBSQ (P < 0.01) and LBSQ (P = 0.03) adipose tissue. In conclusion, UBO women store a greater proportion of FFA in the UBSQ depot compared with lean women. In addition, LBO women store FFA more efficiently in LBSQ fat cells compared with UBSQ fat cells, which may play a role in development of their LBO phenotype. Finally, direct FFA storage and VLDL-TG fatty acid storage are correlated, indicating they may share a common rate-limiting pathway for fatty acid storage in adipose tissue.

Oxidation of Intracellular and Extracellular Fatty Acids in Skeletal Muscle: Application of kinetic modeling, stable isotopes and liquid chromatography/electrospray ionization ion-trap tandem mass spectrometry technology

Fatty acids are a major fuel for many tissues and abnormal utilization is implicated in diseases. However, tissue fatty acid oxidation has not been determined reliably in vivo. Furthermore, fatty acid oxidation has not been partitioned into intracellular and extracellular components. In this report, a one-pool model is described that enables direct quantitation of fluxes of intracellular and plasma fatty acids to mitochondria in skeletal muscle using dual stable isotopes and liquid chromatography/electrospray ionization ion-trap tandem mass spectrometry (LC/ESI-itMS²) technology. It is validated by the determination of palmitate oxidation by skeletal muscle in lean and obese rats and the regulation by insulin. Resting postabsorptive intramyocellular and plasma palmitate oxidation by gastrocnemius muscle was determined to be 3.47±0.8 and 2.06±0.5 nmol/g min in lean and 6.96±1.8 and 1.34±0.2 nmol/g min in obese rats, respectively. In obese rats, hyperinsulinemia (1 nmol/l) suppressed intramyocellular (by 59±5% to 2.88±0.3 nmol/g min P<0.05) but not plasma (1.41±0.14 nmol/g min, P>0.05) palmitate oxidation. The fractional turnover rate of palmitoylcarnitine (0.34±0.1/min vs. 0.83±0.2/min, P<0.05) was also suppressed by insulin. In obese and lean rats, there are 83% and 51%, respectively (P=0.08), of plasma fatty acids traverse triglyceride pool before being oxidized. The results demonstrated that the methodology is feasible and sensitive to metabolic alterations and thus can be used to study fatty acid utilization at tissue level in a compartmentalized manner for the firs time.

Adipose tissue metabolism -- an aspect we should not neglect?

Free fatty acids (FFAs) are the most metabolically important products of adipose tissue lipolysis. Experimentally creating high FFA concentrations can reproduce the metabolic abnormalities of obesity in lean, healthy persons and lowering FFA concentrations can improve the metabolic health of upper body obese individuals. FFA concentrations are determined by both the release of FFAs into the bloodstream and the clearance of FFAs from the bloodstream. Normal FFA release rates are different in men and women and total FFA release is closely linked to resting energy expenditure. Upper body subcutaneous fat, visceral fat, and leg fat depots contribute differently to the exposure of various tissues to FFAs. The implications of regional adipose tissue lipolysis to systemic FFA availability and the effect of different approaches to treatment of obesity are discussed.

Renal amino acid, fat and glucose metabolism in type 1 diabetic and non-diabetic humans: effects of acute insulin withdrawal

AIMS/HYPOTHESIS

The aim of this study was to test the hypothesis that type 1 diabetes alters renal amino acid, glucose and fatty acid metabolism.

MATERIALS AND METHODS

We studied five C-peptide-negative, type 1 diabetic subjects during insulin replacement (glucose 5.6 mmol/l) and insulin deprivation (glucose 15.5 mmol/l) and compared them with six non-diabetic subjects. Leucine, phenylalanine, tyrosine, glucose and palmitate tracers were infused after an overnight fast and samples were obtained from the renal vein, femoral vein and femoral artery.

RESULTS

Insulin deprivation significantly increased whole-body fluxes (20-25%) of phenylalanine, tyrosine and leucine, and leucine oxidation (50%). Kidney contributed 5-10% to the whole-body leucine and phenylalanine flux. A net uptake of phenylalanine, conversion of phenylalanine to tyrosine (5 micromol/min) and net release of tyrosine (approximately 5 micromol/min) occurred across the kidney. Whole-body (three-fold) and leg (two-fold) leucine transamination increased but amino acid metabolism in the kidney did not alter with diabetes or insulin deprivation. Insulin deprivation doubled endogenous glucose production, renal glucose production was unaltered by insulin deprivation and diabetes (ranging between 100 and 140 micromol/min). Renal palmitate exchange was unaltered by insulin deprivation.

CONCLUSIONS/INTERPRETATION

In conclusion, kidney post-absorptively accounts for 5-10% of whole-body protein turnover, 15-20% of leucine transamination and 10-15% of endogenous glucose production, and actively converts phenylalanine to tyrosine. During insulin deprivation, leg becomes a major site for leucine transamination but insulin deprivation does not affect renal phenylalanine, leucine, palmitate or glucose metabolism. Despite its key metabolic role, insulin deprivation in type 1 diabetic patients does not alter many of these metabolic functions.

Computational fluid dynamics modelling of hydraulics and sedimentation in process reactors during aeration tank settling

Aeration tank settling is a control method allowing settling in the process tank during high hydraulic load. The control method is patented. Aeration tank settling has been applied in several waste water treatment plants using the present design of the process tanks. Some process tank designs have shown to be more effective than others. To improve the design of less effective plants, computational fluid dynamics (CFD) modelling of hydraulics and sedimentation has been applied. This paper discusses the results at one particular plant experiencing problems with partly short-circuiting of the inlet and outlet causing a disruption of the sludge blanket at the outlet and thereby reducing the retention of sludge in the process tank. The model has allowed us to establish a clear picture of the problems arising at the plant during aeration tank settling. Secondly, several process tank design changes have been suggested and tested by means of computational fluid dynamics modelling. The most promising design changes have been found and reported.

Pioglitazone increases non-esterified fatty acid clearance in upper body obesity

AIMS/HYPOTHESIS

Plasma NEFA concentrations are largely determined by adipose tissue lipolysis. Insulin suppression of lipolysis is commonly impaired with insulin resistance and improves with thiazolidinedione treatment of type 2 diabetes. The present studies were designed to assess the effects of thiazolidinedione on NEFA (oleate) metabolism that are independent of improved glycaemic control.

MATERIALS AND METHODS

We measured plasma oleate concentration and flux ([(3)H]oleate), glucose kinetics ([6-(2)H(2)]glucose) and substrate oxidation (indirect calorimetry) before and after pioglitazone (30 mg/day for approximately 20 weeks) in 20 non-diabetic adults with upper body obesity. To assess the effects of improved insulin sensitivity per se we performed the same measurements in a matched group of volunteers treated with diet/exercise. Half of the two groups underwent these measurements during a hyperinsulinaemic-euglycaemic clamp, and the other half had their measurements taken during a (control) saline infusion before and after the intervention.

RESULTS

Both interventions increased insulin-stimulated glucose disposal and reduced plasma oleate concentrations during the insulin clamp. After diet/exercise, oleate flux decreased (p=0.03) during the insulin clamp and oleate clearance remained unchanged (p=0.55), whereas in the pioglitazone group, oleate flux during the clamp was unchanged (p=0.97) and oleate clearance increased (p=0.003). Oleate clearance in the saline control condition was increased in the pioglitazone group compared with the diet/exercise group (p=0.02).

CONCLUSIONS/INTERPRETATION

In insulin-resistant, non-diabetic adults, pioglitazone increases NEFA clearance during physiological hyperinsulinaemia, whereas improved insulin sensitivity achieved by diet/exercise does not alter NEFA clearance but enhances insulin suppression of NEFA release. This action of pioglitazone may contribute to improved glucose metabolism in type 2 diabetes.

Accelerated intramyocellular triglyceride synthesis in skeletal muscle of high-fat-induced obese rats

OBJECTIVE

To test the hypothesis that the synthesis of intramyocellular triglycerides (imcTG) in skeletal muscle is increased in obese rats in which the content of imcTG is known to be abnormally high.

ANIMALS

Sprague-Dawley male lean and high-fat-induced obese rats were studied at the age of 4, 8 and 12 months after an overnight fast, awake.

MEASUREMENTS

[U-(14)C]glycerol was continuously infused intravenously for 2 h followed by muscle biopsies, and intracellular glycerol incorporation into imcTG was determined. imcTG content, intramyocellular free glycerol concentration and specific activity, systemic glycerol flux and plasma glycerol, free fatty acid (FFA) and glucose concentrations were also determined.

RESULTS

The rates of incorporation of intramyocellular glycerol into imcTG (nmol/g wet muscle/h) were markedly accelerated in obese rats compared to their lean littermates at all ages: 66+/-12 vs 12+/-2 (P=0.02) for gastrocnemius and 74+/-29 vs 31+/-7 (P=0.09) for soleus when 4 months old; 223+/-29 vs 58+/-27 (P=0.001) for gastrocnemius, 224+/-28 vs 70+/-21 (P=0.001) for soleus and 294+/-78 vs 49+/-22 (P=0.02) for tibialis anterior when 8 months old; and 25+/-4 vs 11+/-2 (P=0.01) for gastrocnemius and 22+/-8 vs 8.4+/-3 (P=0.04) for soleus when 12 months old. As expected, this was accompanied by a higher imcTG content in virtually all muscles at all ages tested.

CONCLUSION

The synthesis of imcTG in skeletal muscle is grossly increased in obese rats, which likely contributes to abnormal imcTG accumulation.

Fate of fatty acids at rest and during exercise: regulatory mechanisms

Fatty acids are a major fuel source for humans both at rest and during exercise. Plasma free fatty acids (FFA), although present only in micromolar concentrations, are the major circulating lipid fuel. FFA availability can increase two- to four-fold with moderate intensity exercise. Other potential sources of fatty acids include circulating very low-density lipoprotein (VLDL) triglycerides (TGs) ( approximately 1/5 the fuel availability of FFA) and intramyocellular TGs ( approximately 2 mmol kg-1 muscle). At rest approximately 40% of systemic FFA uptake occurs in the splanchnic bed and uptake in legs is approximately 15-20%. During leg exercise the uptake of FFA in leg tissue increases to 30-60% of systemic uptake and splanchnic uptake decreases to 15%. The fate of VLDL TG fatty acids has not been adequately studied. Intramyocellular TG hydrolysis increases during exercise, but the factors that regulate this response are not clear. The fact that contraction of isolated muscles can stimulate the hydrolysis and oxidation of intramyocellular TGs (in the absence of hormonal or neural input) suggests an intracellular regulation of this process. Additional regulation from changes in catecholamines and insulin may also occur. During moderate intensity exercise circulating FFA and intramyocellular TG provide roughly equal portions of fatty acids for oxidation. In addition to endurance training, dietary factors have been shown to modulate the fatty acid oxidation response to exercise. Much remains to be learned about fatty acid trafficking during exercise. What role do VLDL TG play? How is the oxidation of intramyocellular TGs regulated? Techniques to address these questions in humans are only now becoming available.

Strength training for obesity prevention in midlife women

OBJECTIVE

The primary goal of this study was to assess whether increases in fat-free mass (FFM) and decreases in total and percentage fat mass from 15 weeks of twice weekly supervised strength training would be maintained over 6 months of unsupervised exercise in a randomized controlled trial.

DESIGN

In all, 60 women aged 30-50 y, body mass index between 20 and 35 kg/m(2), were randomized to control or treatment groups. The treatment group performed twice-weekly supervised strength training followed by 6 months of unsupervised training. Measurements at baseline, 15, and 39 weeks included body weight and body composition by dual-energy X-ray absorptiometry. Repeated measures regression was used to assess between-group differences for changes over time.

RESULTS

Almost 90% of prescribed exercise sessions were completed. The body composition treatment effects over 15 weeks were largely maintained over 6 months of unsupervised exercise. Over the total 39 weeks of strength training, the treatment group gained +0.89 kg more in FFM, lost -0.98 kg more in fat mass, and lost -1.63% more in percent body fat when compared to the control group. P-values for these between-group differences in 39-week changes were 0.009, 0.06, and 0.006, respectively. Strength training did not result in any significant weight loss or waist circumference attenuation. Adjustment for changes in energy intake and physical activity did not alter these results.

CONCLUSIONS

Twice-weekly strength training is behaviorally feasible for busy midlife women and the favorable body composition changes resulting from supervised strength training can be maintained over time. These findings lay the groundwork for determining the long-term health benefits of this behaviorally feasible exercise prescription, potentially including prevention of age-associated fat gains.

Sources of blood glycerol during fasting

To determine the source(s) of blood and very low density lipoprotein (VLDL)-triglyceride glycerol during fasting, four men ingested (2)H(2)O from 14 to 20 h into a 60-h fast to achieve ~0.5% body water enrichment. At 60 h of fasting, glycerol flux was measured using [2-(14)C]glycerol. Blood was taken for measurement of (2)H enrichment at carbon 6 of glucose and at carbon 3 of free glycerol and VLDL-triglyceride glycerol. (2)H enrichment of the 2 hydrogens bound to carbon 3 of VLDL-triglyceride glycerol was 105 +/- 2% of the (2)H enrichment of the 2 hydrogens bound to carbon 6 of glucose, indicating isotopic equilibrium between hepatic glyceraldehyde 3-P and glycerol 3-P. The (2)H enrichment of the 2 hydrogens bound to carbon 3 of free glycerol was 17 +/- 3% of VLDL-triglyceride glycerol, indicating that a significant percentage of free glycerol in blood originated from the hydrolysis of circulating VLDL-triglyceride or a pool of glycerol with similar (2)H enrichment. Glycerol flux was 6.3 +/- 1.1 micromol. kg(-1). min(-1). Glycerol appearing from nonadipose tissue sources was then approximately 1.1 micromol. kg(-1). min(-1). Seven other subjects were fasted for 12, 42, and 60 h. A small percentage of glycerol in the circulation after 12 h of fasting was enriched with (2)H. The enrichment of the 2 hydrogens bound to carbon 3 of free glycerol in the longer periods of fasting was approximately 16% of the enrichment of the 2 hydrogens bound to carbon 6 of glucose. Therefore, as much as 15-20% of systemic glycerol turnover during fasting is not from lipolysis of adipose tissue triglyceride.

Lipid metabolism during fasting

These studies were conducted to understand the relationship between measures of systemic free fatty acid (FFA) reesterification and regional FFA, glycerol, and triglyceride metabolism during fasting. Indirect calorimetry was used to measure fatty acid oxidation in six men after a 60-h fast. Systemic and regional (splanchnic, renal, and leg) FFA ([(3)H]palmitate) and glycerol ([(3)H]glycerol) kinetics, as well as splanchnic triglyceride release, were measured. The rate of systemic FFA reesterification was 366 +/- 93 micromol/min, which was greater (P < 0.05) than splanchnic triglyceride fatty acid output (64 +/- 6 micromol/min), a measure of VLDL triglyceride fatty acid export. The majority of glycerol uptake occurred in the splanchnic and renal beds, although some leg glycerol uptake was detected. Systemic FFA release was approximately double that usually present in overnight postabsorptive men, yet the regional FFA release rates were of the same proportions previously observed in overnight postabsorptive men. In conclusion, FFA reesterification at rest during fasting far exceeds splanchnic triglyceride fatty acid output. This indicates that nonhepatic sites of FFA reesterification are important, and that peripheral reesterification of FFA exceeds the rate of simultaneous intracellular triglyceride fatty acid oxidation.

Adipose tissue metabolism in benign symmetric lipomatosis

Type 2 benign symmetric lipomatosis (BSL) is characterized by abnormal growth of adipose tissue in the upper back, deltoid region, upper arms, hips, and upper thigh region. Studies of lipomatous tissue in vitro have suggested that defective lipolysis may account for excess fat accumulation; however, in vivo adipose tissue metabolism has not been evaluated. We measured systemic adipose tissue lipolysis and regional adipose tissue fatty acid uptake in a patient with type 2 BSL scheduled for elective brachioplasty. We found increased, rather than decreased, rates of systemic free fatty acid release coupled with normal fatty acid oxidation. The uptake of fatty acids was 19% greater in deltoid region lipomatous tissue than in abdominal sc fat, whereas in control studies the relative uptake of fatty acids in deltoid fat averaged 29% less than that in abdominal fat. Adipocyte size was smaller than expected in lipomatous tissue. These results suggest that type 2 BSL is a hyperplastic adipose tissue abnormality that does not impair systemic lipolysis. The pathophysiology appears similar to what has been termed hyperplastic obesity. A better understanding of this condition could lead to insights into the mechanisms of hyperplastic obesity.

Systemic and regional free fatty acid metabolism in type 2 diabetes

To determine whether type 2 diabetes mellitus alters systemic and regional free fatty acid ([3H]palmitate) metabolism, 14 nondiabetic (ND) and 14 type 2 diabetic (D) subjects underwent hyperinsulinemic-hyperglycemic (approximately 9.3 mM) clamps. The subjects were matched for age, body mass index, percent body fat, and fat-free mass. D subjects had more (P < 0.05) visceral fat than ND. During somatostatin, replacement growth hormone, and glucagon infusions, insulin was infused to achieve moderate (approximately 75 pmol/l) and high (approximately 150 pmol/l) physiological insulin levels. D subjects had greater (P < 0.02) systemic and regional (splanchnic and leg) palmitate release than ND subjects during both insulin infusion intervals. The relative contributions of splanchnic, leg, and nonsplanchnic upper body regions to systemic palmitate release did not differ between groups, although the last contributed the most (approximately 75%) to systemic palmitate release. Visceral fat area correlated with systemic palmitate flux (r = 0.45, P < 0.03) during both insulin infusions. We conclude that type 2 diabetes is associated with a generalized impairment in insulin suppression of lipolysis compared with equally obese ND individuals.

Physiological levels of glucagon do not influence lipolysis in abdominal adipose tissue as assessed by microdialysis

To determine whether glucagon stimulates lipolysis in adipose tissue, seven healthy young male volunteers were studied, with indwelling microdialysis catheters placed sc in abdominal adipose tissue. Subjects were studied three times: 1) during euglucagonemia (EG; glucagon infusion rate, 0.5 ng/kg.min); 2) during hyperglucagonemia (HG; (glucagon infusion rate, 1.5 ng/kg.min); and 3) during EG and a concomitant glucose infusion mimicking the glucose profile from the day of HG (EG+G). Somatostatin (450 microg/h) was infused to suppress hormonal secretion, and replacement doses of insulin and GH were administered. Sampling was done every 30 min for 420 min. Baseline circulating values of insulin, C-peptide, glucagon, GH, glycerol, and free fatty acids were comparable in all three conditions. During EG and EG+G, plasma glucagon was maintained at fasting level (20-40 ng/L); whereas, during HG, it increased (110-130 ng/L). Interstitial concentrations of glycerol were similar in the three conditions [30,870 +/- 5,946 (EG) vs. 31,074 +/- 7,092 (HG) vs. 29,451 +/- 6,217 (EG+G) micromol/L.120 min, P = 0.98]. Plasma glycerol (ANOVA, P = 0.5) and free fatty acids (ANOVA, P = 0.3) were comparable during the different glucagon challenges. We conclude that HG per se does not increase interstitial glycerol (and thus lipolysis) in abdominal sc adipose tissue; nor does modest hyperglycemia, during basal insulinemia and glucagonemia, influence indices of abdominal sc lipolysis.

Energy expenditure of nonexercise activity

BACKGROUND

We found recently that changes in nonexercise activity thermogenesis (NEAT) mediate resistance to weight gain with overfeeding in sedentary adults. A potentially important, yet seldom investigated, component of NEAT is the energy expenditure of fidgeting-like activities.

OBJECTIVE

Our goal was to measure changes in energy expenditure with fidgeting-like activities.

DESIGN

Energy expenditure was measured in 24 subjects (17 women and 7 men x+/- SD body weight: 76 +/- 21 kg) while recumbent at rest, sitting motionless, standing motionless, partaking of self-selected fidgeting-like movements while seated and while standing, and walking on a treadmill at 1.6, 3.2, and 4.8 km/h (1, 2, and 3 mph). Measurements were performed by using a high-precision, indirect calorimeter connected to the subject via a transparent, lightweight facemask that enabled almost unrestricted movement.

RESULTS

Compared with metabolic rate in the supine position (5.4 +/- 1.5 kJ/min), energy expenditure increased while sitting motionless by 4 +/- 6%, while fidgeting while seated by 54 +/- 29% (P: < 0.0001), while standing motionless by 13 +/- 8% (P: < 0.0001), while fidgeting while standing by 94 +/- 38% (P: < 0.0001), while walking at 1.6 km/h by 154 +/- 38% (P: < 0.0001), while walking at 3.2 km/h by 202 +/- 45% (P: < 0.0001), and while walking at 4.8 km/h by 292 +/- 81% (P: < 0.0001). There was a significant, positive correlation between changes in energy expenditure and body weight for fidgeting-like activities while standing (r = 0.43, P: = 0.02) but not while seated.

CONCLUSIONS

There is marked variance between subjects in the energy expenditure associated with self-selected fidgeting-like activities. The thermogenic potential of fidgeting-like and low-grade activities is sufficiently great to substantively contribute to energy balance.

Kinetics of intramuscular triglyceride fatty acids in exercising humans

A pulse ([(14)C]palmitate)-chase ([(3)H]palmitate) approach was used to study intramuscular triglyceride (imTG) fatty acid and plasma free fatty acid (FFA) kinetics during exercise at approximately 45% peak O(2) consumption in 12 adults. Vastus lateralis muscle was biopsied before and after 90 min of bicycle exercise; (3)H(2)O production, breath (14)CO(2) excretion and lipid oxidation (indirect calorimetry) rates were measured during exercise.

RESULTS

during exercise, 8.2+/-1.2 and 8.4+/-0.7 micromol x kg(-1) x min(-1) of imTG fatty acids and plasma FFA, respectively, were oxidized according to isotopic measurements. The sum of these two values was not different (P = 0.6) from lipid oxidation by indirect calorimetry (15.4 +/-1.6 micromol x kg(-1) x min(-1)); the isotopic and indirect calorimetry values were correlated (r = 0.79, P<0.005). During exercise, imTG turnover rate was 0.32+/-0.07%/min (6.0+/-2.0 micromol of imTG x kg wet muscle(-1) x min(-1)) and plasma FFA were incorporated into imTG at a rate of 0.7+/-0.1 micromol x kg wet muscle(-1) x min(-1). The imTG pool size did not change during exercise. This pulse-chase, dual tracer appears to be a reasonable approach to measure oxidation and synthesis kinetics of imTG.

Body composition and resting energy expenditure in humans: role of fat, fat-free mass and extracellular fluid

OBJECTIVE

The objective of this study was to determine whether there are independent effects of extracellular fluid volume (ECF) and fat mass (FM) on resting energy expenditure (REE) relative to fat-free mass (FFM) in adult men and women.

METHODS

Multiple linear regression analysis was used to relate REE, as determined by indirect calorimetry, to FFM and FM (measured using dual energy X-ray absorptiometry) and ECF (measured using bromide space and/or the radiosulfate washout space) in 153 women and 100 men with varying amounts of body fat.

RESULTS

REE correlated significantly with FFM and FM in women (r=0.65 and r=0.63, both P<0.001) and men (r=0.62 and r=0.48, both P<0.001, FFM and FM, respectively). In a multiple linear regression analysis FFM, FM and age significantly contributed to the ability to predict REE in both genders. The models that were derived were not significantly different between women and men. In women the contribution to REE from FM was easier to detect when FM was greater. Adjustment of FFM for ECF did not improve the relationship between FFM and REE.

CONCLUSIONS

FFM, FM and age are significant, independent predictors of REE in both men and women. Adjustment of FFM for ECF does not improve the ability of FFM to predict REE, which suggests that ECF is a highly integrated component of FFM in healthy adults. Expressing REE relative to FFM alone will introduce errors when lean and obese populations are compared.

Meal fatty acid uptake in adipose tissue: gender effects in nonobese humans

We tested for gender differences in dietary fatty acid metabolism in 12 nonobese men and 12 nonobese women using the meal fatty acid tracer/adipose tissue biopsy study design. In addition to determining body composition, measurements of regional adipose tissue lipoprotein lipase activity, blood flow, and fat cell size were performed to place the meal fatty acid kinetic studies in perspective. Twenty-four hours after ingesting the test meal, the concentration of meal fatty acids was greater (P < 0.05) in abdominal subcutaneous than in thigh adipose tissue in both men (0. 61 +/- 0.12 vs. 0.45 +/- 0.09 mg/g) and women (0.59 +/- 0.10 vs. 0. 43 +/- 0.05) but was not different between men and women. A greater percentage of dietary fat was stored in subcutaneous adipose tissue in women than in men (38 +/- 3 vs. 24 +/- 3%, respectively, P < 0. 05), and a greater portion of meal fatty acid disposal was unaccounted for in men. Significant gender differences in regional adipose tissue blood flow after meal ingestion were noted; the differences were in the direction that could support greater nutrient storage in lower body fat in women.

Meal fatty acid uptake in human adipose tissue: technical and experimental design issues

The adipose tissue uptake of dietary fat has been studied using fatty acid radiotracers incorporated into a meal, followed by adipose tissue biopsies. A number of experimental design issues, including the use of isotopic tracers to measure meal fatty acid oxidation and plasma appearance of tracer, as well as the heterogeneity of adipose tissue fatty acid uptake, have been addressed. We examined these questions in a study of 24 volunteers (12 men and 12 women) who consumed a meal containing [(3)H]triolein and [(14)C]triolein. Slight differences in the purity of [(3)H]triolein vs. [(14)C]triolein were found, which could affect the apparent adipose tissue uptake of meal fatty acids. The adipose tissue triglyceride specific activity from bilateral biopsy sites agreed well, implying that a unilateral biopsy is satisfactory for measuring tracer uptake. Meal fatty acid oxidation measured using [(3)H]triolein and [(14)C]triolein was well correlated (r = 0.79, P < 0.0001). The peak tracer appearance in plasma chylomicrons occurred 1 h after the ingestion of a second, unlabeled meal. Our findings have implications for the experimental design of future meal fatty acid tracer/adipose tissue biopsy studies.

Prospective evaluation of Roux-en-Y gastric bypass as primary operation for medically complicated obesity

OBJECTIVE

To determine prospectively the results of Roux-en-Y gastric bypass (RYGB) used as the primary weight-reducing operation in patients with medically complicated ("morbid") obesity. The RYGB procedure combines the advantages of a restrictive physiology (pouch of 10 mL) and a "dumping physiology" for high-energy liquids without requiring an externally reinforced (banded) stoma.

PATIENTS AND METHODS

Between April 1987 and December 1998, a total of 191 consecutive patients with morbid obesity (median weight, 138 kg [range, 91-240 kg]; median body mass index, 49 kg/m2 [range, 36-74 kg/m2]), all of whom had directly weight-related morbidity, underwent RYGB and prospective follow-up.

RESULTS

Hospital mortality was 0.5% (1/191), and hospital morbidity occurred in 10.5% (20/191). Good long-term weight loss was achieved, and patients adapted well to the required new eating habits. The mean +/- SD weight loss at 1 year after operation (113 patients) was 52 +/- 1 kg or 68% +/- 2% of initial excess body weight. By 3 years postoperatively (74 patients), weight loss was still 66% +/- 2% of excess body weight. Overall, 53 (72%) of 74 patients had achieved and maintained a weight loss of 50% or more of their preoperative excess body weight 3 years after the operation. In addition, only 1 (1%) of 98 patients had persistent postoperative vomiting 1 or more times per week.

CONCLUSION

We believe that RYGB is a safe, effective procedure for most patients with morbid obesity and thus may be the current procedure of choice in patients requiring bariatrics++ surgery for morbid obesity.

Obesity is associated with a decreased leptin transport across the blood-brain barrier in rats

Leptin exerts important effects on the regulation of food intake and energy expenditure by acting in the brain. Leptin is secreted by adipocytes into the bloodstream and must gain access to specific regions in the brain involved in regulating energy balance. Its action is mediated by interaction with a receptor that is mainly expressed in the hypothalamus but is also present in other cerebral areas. To reach these target areas, leptin most likely needs to cross the blood-brain barrier (BBB). In this study, we compared the permeability of leptin at the BBB in homozygous lean (FA/FA), high-fat diet-induced (HFD) obese rats (FA/FA rats on a highfat diet), and genetically obese fa/fa Zucker rats by quantifying the permeability coefficient surface area (PS) product after correction for the residual plasma volume (Vp) occupied by leptin in the vessel bed of different brain regions. The intravenous bolus injection technique was used in the cannulated brachial vein and artery using leptin radioiodinated with 2 isotopes of iodine (125I and 131I) to separately determine the PS and Vp values. The PS for leptin at the BBB in lean FA/FA rats ranged from 11.0 +/- 1.6 at the cortex to 14.8 +/- 1.4 x 10(-6) ml x g(-1) x ml(-1) at the posterior hypothalamus. The PS for leptin in HFD obese FA/FA and obese fa/fa rats ranged from 3.0- to 4.0-fold lower than in lean FA/FA rats. The Vp values were not significantly different among the 3 groups studied. SDS-PAGE analysis of the radioiodinated leptin after 60 min of uptake revealed intact protein in the 8 different brain regions. Plasma leptin levels were significantly higher in both obese rat groups compared with those in lean FA/FA rats. Leptin levels in cerebrospinal fluid were not significantly different among the 3 groups of rats. These findings strongly suggest that the leptin receptor (OB-R) in the BBB can be easily saturated. Saturation of the BBB OB-R in obese individuals would explain the defect in leptin transport into the brain described in this study.

Genetic and environmental contributions

There is a remarkable variability in insulin action in humans. Depending upon the definition of the insulin resistance syndrome, different inheritability/environmental influences on insulin action are reported. The environmental contributions to insulin resistance appear to account for approximately 50% of this syndrome. Obese and sedentary insulin-resistant individuals can see dramatic improvement in insulin sensitivity with weight reduction and fitness training. The degree to which obesity is determined by genetic influences will have a substantial impact on insulin resistance in the Western populations. Familial components also appear to account for approximately 50% of the variation and insulin action (as commonly defined by glucose metabolic effects).

The long form of the leptin receptor (OB-Rb) is widely expressed in the human brain

Leptin exerts important effects on the regulation of food intake and energy expenditure by acting in the brain. Leptin action is mediated by the interaction with a receptor that is alternatively spliced, resulting in at least five different isoforms. The long form (OB-Rb) has a long intracellular domain that is essential for intracellular signal transduction. The specific aim of this study was to further investigate the role that the brain may play in the pathogenesis of obesity in humans. We studied the expression of OB-R mRNA (both short or common and long isoforms) in the brains of obese, lean and diabetic subjects, by in situ hybridization, semiquantitative RT-PCR and Northern blots analysis. We used two alternative probes: one that recognizes all known splice variants (OB-Ra) and a second that recognizes only the long form, OB-Rb. Several brain regions, including hypothalamus, cerebellum, neocortex, entorrhinal cortex, amygdala, and rostral medulla, were evaluated. In situ hybridization studies revealed that both OB-Ra and OB-Rb mRNAs are widely distributed in the human brain. The specific hybridization signal with both probes was detected exclusively in the cytoplasm of the cell body, dendrites and proximal axons of neurons. Hypothalamic nuclei, Purkinje cells and dentate nuclei of the cerebellum, inferior olivary and cranial nerves nuclei in the medulla, amygdala and neurons from both neocortex and entorrhinal cortex demonstrated positive signals. The hybridization signal obtained in ependyma was lower than that in neurons and no specific hybridization was detected in glial cells. No significant differences were identified among the regions or among the three groups studied. These results match those previously obtained by us [Couce et al.: Neuroendocrinology 1997;66:145] in which the distribution of the OB-R protein in the human brain was first described. RT-PCR indicated that the OB-Rb was highly expressed in the hypothalamus and cerebellum. No significant differences of OB-Ra or OB-Rb mRNA expression were identified in lean or obese individuals in these two cerebral regions. The levels of OB-Rb were significantly higher in cerebellum compared to hypothalamus in lean and obese individuals. The original hypothesis that OB-Rb is present only in the hypothalamus needs to be reconsidered. This OB-Rb isoform seems to be widely expressed in the human brain with highest levels in the cerebellum. Obesity and hyperleptinemia appears not to be associated with down-regulation of the OB-Rb in the human brain.

Metabolic complications of obesity. Pathophysiologic considerations

Given a specific research interest in human fatty acid metabolism, this article focuses primarily on the evidence surrounding the hypothesis that dysregulation of the fuel release function of fat cells (lipolysis) is an important contributing factor to the health hazards of obesity.

Measuring leg muscle and fat mass in humans: comparison of CT and dual-energy X-ray absorptiometry

Dual-energy X-ray absorptiometry (DEXA) is reported to be inferior to computed tomography (CT) to measure changes in appendicular soft tissue composition. We compared CT- and DEXA-measured thigh muscle and fat mass to evaluate the random and systematic discrepancies between these two methods. Thigh skeletal muscle area (single-slice CT) was suboptimally (r(2) = 0.74, P < 0.0001) related to DEXA-measured thigh fat-free mass (FFM). In contrast, thigh muscle and adipose tissue volumes (multislice CT) were highly related to DEXA-measured thigh FFM and fat (both r(2) = 0.96, P < 0.0001). DEXA-measured leg fat was significantly less than multislice-CT-measured leg adipose tissue volume, whereas multislice-CT-measured leg muscle mass was less (P < 0.0001) than DEXA-measured leg FFM. The systematic discrepancies between the two approaches were consistent with the 10-15% nonfat components of adipose tissue. In conclusion, CT and DEXA measures of appendicular soft tissue are highly related. Systematic differences between DEXA and CT likely relate to the underlying principles of the techniques.

Effects of type 2 diabetes on the ability of insulin and glucose to regulate splanchnic and muscle glucose metabolism: evidence for a defect in hepatic glucokinase activity

Insulin-induced stimulation of muscle glucose uptake (MGU) is impaired in people with type 2 diabetes. To determine whether insulin-induced stimulation of splanchnic glucose uptake (SGU) is also impaired, we simultaneously measured leg glucose uptake (LGU) and SGU in 14 nondiabetic subjects and 16 subjects with type 2 diabetes using a combined organ catheterization-tracer infusion technique. Glucose was clamped at approximately 9.3 mmol/l, while insulin concentrations were maintained at approximately 72 pmol/l (low) and approximately 150 pmol/l (high) for 3 h each. Endogenous hormone secretion was inhibited with somatostatin. Total body glucose disappearance was lower (P < 0.01) and glucose production higher (P < 0.01) during both insulin infusions in the diabetic compared with the nondiabetic subjects, indicating insulin resistance. Splanchnic glucose production was higher (P < 0.05) in the diabetic subjects during the low but not the high insulin infusion. SGU was slightly lower in the diabetic than in the nondiabetic subjects during the low insulin infusion and 50-60% lower (P < 0.05) during the high insulin infusion. LGU (P < 0.001), but not SGU, was inversely correlated with the degree of visceral adiposity. The contribution of the indirect pathway to hepatic glycogen synthesis did not differ in the diabetic and nondiabetic subjects. In contrast, both flux through the UDP-glucose pool (P < 0.05) and the contribution of the direct pathway to glycogen synthesis (P < 0.01) were lower in the diabetic than in the nondiabetic subjects, indicating decreased uptake and/or phosphorylation of extracellular glucose. On the other hand, glycogenolysis was equally suppressed in both groups. In summary, type 2 diabetes impairs the ability of insulin to stimulate both MGU and SGU. The defect appears to reside at a proximal (e.g., glucokinase) metabolic step and is not related to the degree of visceral adiposity. These data suggest that impaired hepatic glucose uptake as well as MGU contribute to hyperglycemia in people with type 2 diabetes.

Leg free fatty acid kinetics during exercise in men and women

We previously reported that epinephrine stimulates leg free fatty acid (FFA) release in men but not in women. The present studies were conducted to determine whether the same is true during exercise. Six men and six women bicycled for 90 min at 45% of peak O(2) consumption, during which time systemic and leg FFA kinetics ([9, 10-(3)H]palmitate) were measured. The catecholamine and hormonal responses to exercise were not different in men and women. The baseline systemic and leg palmitate release was 94 +/- 15 vs. 114 +/- 5 micromol/min and 16 +/- 2 and 20 +/- 3 micromol/min, respectively, in men and women [P = nonsignificant (NS)]. Systemic and leg palmitate release increased (both P < 0.001) to 251 +/- 18 vs. 212 +/- 16 micromol/min and 73 +/- 19 vs. 80 +/- 12 micromol/min in men and women, respectively, during the last 30 min of exercise (P = NS, men vs. women). We conclude that the systemic and leg adipose tissue lipolytic response to exercise is not different in nonobese men and women.

Androgen effect on body composition and fat metabolism

Recognizing the adverse metabolic effects of predominantly visceral body fat distribution associated with low testosterone levels, researchers have investigated the effects of androgen treatment on body fat distribution in men. This presentation reviews the results of research on acute and longer-term effects of treatment with testosterone and dihydrotestosterone. Methods for investigating these results, including measurement of lipoprotein lipase activity and of radiolabeled fat uptake and turnover, are described and discussed.

Echocardiographic improvement over time after cessation of use of fenfluramine and phentermine

OBJECTIVE

To determine the echocardiographic changes over time of valvular heart lesions in patients who took the weight loss drugs fenfluramine and phentermine.

SUBJECTS AND METHODS

This prospective cohort study began at the termination of a randomized, double-blind, placebo-controlled weight loss trial of 18 obese women and 13 obese men (mean age, 42 years; mean body mass index, 33.4 kg/m2) who had been assigned randomly to treatment with fenfluramine and phentermine or to placebo. Echocardiograms were obtained at termination of the trial when fenfluramine was withdrawn from the market and 6 months later. They were interpreted independently by 3 cardiologists blinded to treatment assignment and temporal sequence of the echocardiograms. The main outcome measure was the change in drug-related valvular disease over time.

RESULTS

One subject assigned to receive the drugs was lost to follow-up, and 3 subjects who did not meet a weight loss goal of 10 kg crossed over from placebo to drug treatment. Echocardiograms were obtained in 19 subjects who received the drugs and 11 subjects who received placebo, and 6-month follow-up echocardiograms were obtained in 15 subjects who received the drugs and 3 who received placebo. Subjects had taken fenfluramine and phentermine a mean of 41 weeks (range, 8-73 weeks). Five of 19 subjects who received the drugs (26%; 95% confidence interval, 7%-46%) and 1 of 11 who received placebo (9%) (odds ratio, 3.6; 95% confidence interval, 0.4-35.6) had findings that met criteria established for drug-related valvular disease. All 5 subjects (4 women and 1 man) receiving the drugs had mild aortic regurgitation, and 1 also had pulmonary hypertension (estimated pulmonary artery pressure, 59 mm Hg). Six months later, the echocardiographic findings had improved in all 5 subjects (P=.06), and 3 no longer met the criteria for drug-related valvular disease. Pulmonary artery pressures decreased to near normal in the subject with pulmonary hypertension (37 mm Hg). Overall, the echocardiographic valvular features improved in 8 of 15 subjects who received the drugs and had echocardiograms performed at both time periods (P=.008).

CONCLUSIONS

Valvular heart disease did not appear to progress after cessation of use of fenfluramine and phentermine, and echocardiographic valvular features appeared to improve over time.

Relationship between urinary albumin excretion, body composition, and hyperinsulinemia in normotensive glucose-tolerant adults

OBJECTIVE

Elevated urinary albumin excretion (UAE) has been associated with insulin resistance and is suggested to be elevated in prediabetic individuals. Upper body obesity, especially visceral obesity, predicts insulin resistance and development of type 2 diabetes. We examined whether UAE clusters with obesity-associated insulin resistance traits in healthy glucose-tolerant normotensive subjects.

RESEARCH DESIGN AND METHODS

There were 49 volunteers with a wide range of body fat and body fat distribution studied. All had normal blood pressure and glucose tolerance and were maintained on a controlled diet for 2 weeks. UAE was assessed from three overnight urine collections, and body composition was assessed by whole-body dual-energy X-ray absorptiometry scanning and abdominal computed tomography scanning.

RESULTS

Fasting insulin and insulin responses to oral glucose were significantly increased in obese subjects, who also tended to have more dyslipidemia, greater blood pressure, and more visceral fat than lean subjects. These differences were more apparent in upper body obese subjects. UAE was normal in obese and upper body obese subjects and not different from that of lean subjects. UAE ranged from 0.3 to 8.3 micrograms/min in lean subjects and from 0.2 to 7.2 micrograms/min in obese subjects. UAE was not significantly correlated with body composition, plasma insulin, glucose, or lipids.

CONCLUSIONS

Obese subjects (even upper body obese subjects) with increased visceral and total body fat, high plasma insulin and triglycerides, and low HDL cholesterol concentrations do not have elevated UAE. This suggests that UAE is not closely associated with these characteristics and implies a later onset of abnormal albuminuria in the course of the insulin resistance syndrome.

Blood glycerol is an important precursor for intramuscular triacylglycerol synthesis

The utilization of blood glycerol and glucose as precursors for intramuscular triglyceride synthesis was examined in rats using an intravenous infusion of [2-(14)C]glycerol and [6-(3)H]glucose or [6-(14)C]glucose. In 24-h fasted rats, more glycerol than glucose was incorporated into intramuscular triglyceride glycerol in soleus (69 +/- 23 versus 4 +/- 1 nmol/micromol triglyceride/h, respectively, p = 0.02 glycerol versus glucose) and in gastrocnemius (25 +/- 5 versus 9 +/- 2 nmol/micromol triglyceride/h, respectively, p = 0.02). Blood glucose was utilized more than blood glycerol for triglyceride glycerol synthesis in quadriceps. In fed rats, the blood glycerol incorporation rates (4 +/- 2, 8 +/- 3, and 9 +/- 3 nmol/micromol triglyceride/h) were similar (p > 0.3) to those of glucose (5 +/- 2, 8 +/- 2, and 5 +/- 2 nmol/micromol triglyceride/h for quadriceps, gastrocnemius, and soleus muscle, respectively). Glucose incorporation into intramuscular triglycerides was less with [6-(3)H]glucose than with [6-(14)C]glucose, suggesting an indirect pathway for glucose carbon entry into muscle triglyceride. The isotopic equilibrium between plasma and intramuscular free glycerol ([U-(13)C]glycerol) was complete in quadriceps and gastrocnemius, but not soleus, within 2 h after beginning the tracer infusion. We conclude that blood glycerol is a direct and important precursor for muscle triglyceride synthesis in rats, confirming the presence of functionally important amounts of glycerol kinase in skeletal muscle.

Leptin responses to overfeeding: relationship with body fat and nonexercise activity thermogenesis

Administration of leptin to rodents results in weight loss through decreased food intake and increased energy expenditure that occurs in part through increased spontaneous activity. In humans, low levels of spontaneous physical activity and below normal plasma leptin concentrations predict subsequent excess weight gain. We recently found that failure to increase nonexercise activity thermogenesis (NEAT) with overfeeding results in greater fat gain in humans, and subsequently evaluated whether changes in leptin are related to NEAT activation. We measured plasma leptin concentrations and adipose tissue leptin messenger ribonucleic acid together with the components of energy expenditure in 16 nonobese humans before and after overfeeding to assess the relationship between leptin responses to overfeeding and the changes in NEAT. Adipocyte leptin expression was up-regulated with overfeeding, and leptin concentrations increased. Leptin concentrations correlated with body fat before and after overfeeding. Changes in leptin with overfeeding were strongly related to changes in body fat, but not to changes in NEAT. Changes in NEAT correlated inversely with fat gain. It is, therefore, unlikely that leptin mediates activation of NEAT with overfeeding in nonobese humans; rather, leptin directly reflects body fat mass and fat mass gain.

Regional postprandial fatty acid metabolism in different obesity phenotypes

To examine if postprandial splanchnic/hepatic free fatty acid (FFA) delivery is increased in upper-body (UB) obesity, and to determine the adipose tissue depots responsible for the greater postprandial FFA availability, we measured systemic and regional uptake and release of FFAs ([1-(14)C]palmitate) before and during a 5-h frequent-feeding mixed meal in eight UB and eight lower-body (LB) obese women. Postabsorptive FFA flux and splanchnic FFA delivery were not different in UB and LB obese women; however, postprandial FFA concentrations (257 +/- 45 vs. 81 +/- 12 micromol/l, P < 0.0001), FFA flux (8.5 +/- 1.2 vs. 3.9 +/- 0.8 micromol x kg(-1) fat-free mass x min(-1), P < 0.0001), splanchnic FFA delivery (275 +/- 45 vs. 88 +/- 24 micromol/min, respectively, P < 0.005), and estimated hepatic FFA delivery were greater in UB than LB obese women. Nonsplanchnic UB adipose tissue FFA release was greater in UB than in LB obese women (276 +/- 71 vs. 97 +/- 37 micromol/min, respectively, P < 0.05) and accounted for the greater postprandial FFA availability in UB obesity. Postprandial leg glucose uptake was less in UB than in LB obese women (8.4 +/- 5.1 vs. 22.9 +/- 2.6 micromol x kg(-1) leg fat-free mass x min(-1), P < 0.05). We conclude that the elevated postprandial FFA release observed in UB obese women originates from the nonsplanchnic UB fat, not visceral fat. These results suggest that visceral fat may be a marker for, but not the source of, excess postprandial FFAs in obesity.

Collection and interpretation of plasma leptin concentration data in humans

OBJECTIVE

To reassess the relationship between body fat and plasma leptin concentrations when a) replicate measures of leptin are made; b) energy intake is controlled at isoenergetic levels before the study; and c) body fat and percent body fat are measured with dual energy X-ray absorptiometry (DXA).

RESEARCH METHODS AND PROCEDURES

Two separate studies were conducted. In the first study, four plasma samples were collected for measurement of leptin over 30 minutes on a single day in 43 lean and obese men and women. For the second study, plasma samples were collected on four consecutive days from a group of 50 lean and obese men and women. Percent body fat (and body fat mass) was related to log-transformed mean plasma leptin concentrations using linear regression analysis; multiple linear regression analysis was used to determine whether there was an effect of gender on this relationship, and the analysis of Choi was used to examine whether percent body fat or body fat mass better predicts plasma leptin concentrations.

RESULTS

For the first study, percent body fat was highly correlated (r=0.96, p<0.0001) with log-transformed mean leptin concentrations. No difference in the relationship between leptin and percent body fat in men and women was detected. The second study confirmed this observation; the relationship between ln leptin and percent body fat was virtually identical (r=0.93, p<0.001). Analysis of the pooled data suggests that percent body fat is a better predictor of plasma leptin concentration than body fat mass. The use of multiple (as opposed to a single) leptin measurements did not significantly improve the leptin/body fat relationship.

DISCUSSION

When robust body composition techniques and diet control measures are taken into consideration, the relationship between ln plasma leptin concentrations and percent body fat is not different in men and women.

Regional glycerol and free fatty acid metabolism before and after meal ingestion

We measured splanchnic and leg glycerol [and free fatty acid (FFA)] uptake and release in 11 healthy volunteers before and after meal ingestion to assess whether regional FFA-to-glycerol release ratios mirror systemic release ratios. Basal splanchnic triglyceride release was also assessed. Although basal splanchnic glycerol uptake (111 +/- 18 micromol/min) accounted for most of systemic glycerol rate of appearance (156 +/- 20 micromol/min), leg glycerol uptake was also noted. The basal, systemic FFA-to-glycerol release ratio was less (2.6 +/- 0.2, P < 0.05) than the splanchnic ratio of 6.1 +/- 1.3, and the leg FFA-to-glycerol release ratio under fed conditions was less than the systemic ratio (0.9 +/- 0.1 vs. 1.6 +/- 0.2, respectively, P < 0.05). Basal splanchnic triglyceride production rates were 74 +/- 20 micromol/min, which could produce equimolar amounts of glycerol in the peripheral circulation via lipoprotein lipase action. In summary, 1) regional FFA-to-glycerol release ratios do not mirror systemic ratios, 2) leg glycerol uptake occurs in humans, and 3) splanchnic triglyceride production rates are substantial relative to systemic glycerol appearance. Glycerol appearance rates may not be a quantitative index of whole body lipolysis.

Leptin acts on human marrow stromal cells to enhance differentiation to osteoblasts and to inhibit differentiation to adipocytes

Both bone mass and serum leptin levels are increased in obesity. Because osteoblasts and adipocytes arise from a common precursor in bone marrow, we assessed the effects of human recombinant leptin on a conditionally immortalized human marrow stromal cell line, hMS2-12, with the potential to differentiate to either the osteoblast or adipocyte phenotypes. By RT-PCR and Western immunoblot analysis, the hMS2-12 cells expressed messenger RNA (mRNA) and protein for the leptin receptor. Leptin did not affect hMS2-12 cell proliferation, but resulted in dose- and time-dependent increases in mRNA and protein levels of alkaline phosphatase, type I collagen, and osteocalcin, and in a 59% increase in mineralized matrix. Leptin increased mRNA levels of lipoprotein lipase at 3 days, but decreased mRNA levels of adipsin and leptin at 9 days and decreased lipid droplet formation by 50%. Leptin did not affect the expression of Cbfa1 or peroxisome proliferator-activated receptor-gamma2, transcription factors involved in commitment to the osteoblast and adipocyte pathways, respectively. Thus, leptin acts on human marrow stromal cells to enhance osteoblast differentiation and to inhibit adipocyte differentiation. Our data support the hypothesis that leptin is a previously unrecognized, physiological regulator of these two differentiation pathways, acting primarily on maturation of stromal cells into both lineages.

Leptin acts on human marrow stromal cells to enhance differentiation to osteoblasts and to inhibit differentiation to adipocytes

Both bone mass and serum leptin levels are increased in obesity. Because osteoblasts and adipocytes arise from a common precursor in bone marrow, we assessed the effects of human recombinant leptin on a conditionally immortalized human marrow stromal cell line, hMS2-12, with the potential to differentiate to either the osteoblast or adipocyte phenotypes. By RT-PCR and Western immunoblot analysis, the hMS2-12 cells expressed messenger RNA (mRNA) and protein for the leptin receptor. Leptin did not affect hMS2-12 cell proliferation, but resulted in dose- and time-dependent increases in mRNA and protein levels of alkaline phosphatase, type I collagen, and osteocalcin, and in a 59% increase in mineralized matrix. Leptin increased mRNA levels of lipoprotein lipase at 3 days, but decreased mRNA levels of adipsin and leptin at 9 days and decreased lipid droplet formation by 50%. Leptin did not affect the expression of Cbfa1 or peroxisome proliferator-activated receptor-gamma2, transcription factors involved in commitment to the osteoblast and adipocyte pathways, respectively. Thus, leptin acts on human marrow stromal cells to enhance osteoblast differentiation and to inhibit adipocyte differentiation. Our data support the hypothesis that leptin is a previously unrecognized, physiological regulator of these two differentiation pathways, acting primarily on maturation of stromal cells into both lineages.

Role of nonexercise activity thermogenesis in resistance to fat gain in humans

Humans show considerable interindividual variation in susceptibility to weight gain in response to overeating. The physiological basis of this variation was investigated by measuring changes in energy storage and expenditure in 16 nonobese volunteers who were fed 1000 kilocalories per day in excess of weight-maintenance requirements for 8 weeks. Two-thirds of the increases in total daily energy expenditure was due to increased nonexercise activity thermogenesis (NEAT), which is associated with fidgeting, maintenance of posture, and other physical activities of daily life. Changes in NEAT accounted for the 10-fold differences in fat storage that occurred and directly predicted resistance to fat gain with overfeeding (correlation coefficient = 0.77, probability < 0.001). These results suggest that as humans overeat, activation of NEAT dissipates excess energy to preserve leanness and that failure to activate NEAT may result in ready fat gain.

Serum leptin and weight gain over 8 years in African American and Caucasian young adults

OBJECTIVE

There is considerable interest in how to prevent weight gain in adulthood. Leptin, a peptide hormone expressed in adipose tissue, is believed to signal the central nervous system about the level of body fat stores, and thereby may control appetite. Little information exists on whether the serum leptin concentration influences long-term weight changes in the free-living population.

RESEARCH METHODS AND PROCEDURES

From an ongoing cohort study of young African American and white adults, we selected a sample of participants (n=492), stratified on sex, race, and weight changes over 8 years. Serum leptin was measured on stored specimens using a radioimmunoassay. Weight change was modeled in relation to baseline leptin concentrations.

RESULTS

Cross-sectionally, leptin concentration was associated positively with body mass index, negatively with physical activity level, and was higher in women than men. These variables explained 72% of the variance in serum leptin. Over the 8 years, the sample gained an average of 7.8 kg (standard deviation = 10.8). There was no evidence that 8-year weight change was associated with initial leptin concentration: 8-year weight change was only 0.5 kg less (95% confidence interval =-1.8 to 0.8, p = 0.47) per each 10 ng/ mL increment (approximately one standard deviation) of baseline leptin. In contrast, leptin change correlated highly (r=0.62) with weight change.

DISCUSSION

Our data corroborate evidence that adiposity determines leptin levels but do not support the hypothesis that leptin deficiency plays an important role in obesity in the general population.

Insulin regulation of regional free fatty acid metabolism

Studies were conducted to determine whether regional free fatty acid (FFA) release is differentially regulated by insulin. Systemic, leg, and splanchnic palmitate rate of appearance ([9,10-(3)H]palmitate) was measured in 26 healthy adults using the euglycemic-hyperinsulinemic clamp technique to achieve a physiological range of plasma insulin concentrations. We found that insulin inhibited systemic, leg, and splanchnic palmitate release in a dose-dependent fashion over the range of insulin infused (0-1.0 mU x kg(-1) x min(-1)). Progressive hyperinsulinemia changed the leg from a net producer to a net FFA consumer, whereas the splanchnic bed converted from a net FFA consumer to a net producer. At the 0.5 mU x kg(-1) x min(-1) insulin infusion rate, leg FFA release was almost completely suppressed, whereas even with the 1.0 mU x kg(-1) x min(-1) insulin infusion rate, splanchnic FFA release decreased by only approximately 65% (P < 0.05 leg vs. splanchnic). These results demonstrate the regional heterogeneity of insulin-regulated FFA release in vivo, and indicate that visceral adipose tissue lipolysis is more resistant to insulin suppression than is leg lipolysis in humans.

Regional leptin kinetics in humans

BACKGROUND

Leptin is known to be cleared by the kidney, a tissue with substantial leptin receptor mRNA expression; however, lung, liver, and muscle tissues also express leptin receptor messenger RNA and it is not known whether these tissues also clear leptin from the circulation.

OBJECTIVE

This study was conducted to determine whether net leptin clearance takes place in the pulmonary, splanchnic, and leg tissue beds to a similar extent as in the kidney.

DESIGN

Plasma leptin concentrations were measured in blood entering and exiting the renal bed, pulmonary bed, splanchnic bed, and leg in 4 groups of subjects. Regional plasma flow was measured in 3 of the 4 groups.

RESULTS

Renal leptin uptake was substantial, whereas no net uptake of leptin by the splanchnic or pulmonary vascular beds was detected; leg tissue was a net leptin producer. Net leptin release by leg tissue, relative to leg adipose tissue mass, was comparable with that reported previously for abdominal subcutaneous adipose tissue.

CONCLUSION

These results confirm that the kidney is a significant site of leptin clearance in humans, whereas pulmonary and splanchnic beds are not.

Medical management of obesity

Obesity is a heterogeneous condition. Some individuals suffer severe, life-threatening medical complications as a result of their obesity, whereas others appear to remain healthy for their entire lives despite substantially greater-than-normal amounts of body fat. A personal or family history of adverse health consequences of obesity and an upper-body fat distribution suggests that the patient will have greater health risks from obesity, and these patients stand to benefit more from successful treatment. Therefore, one can justify more aggressive approaches in helping them to make permanent changes in eating and exercise behavior, which are the cornerstones of obesity management. Supplementing these interventions with behavior therapy is necessary for patients unable to make lifestyle changes by themselves. Pharmacotherapy is appropriate for patients with medically complicated obesity in whom other approaches have not succeeded.