Regulation of uncoupling protein-2 and -3 by growth hormone in skeletal muscle and adipose tissue in growth hormone-deficient adults

The newly described uncoupling proteins, UCP2 and UCP3, may play a role in regulating energy expenditure (EE) in humans. GH deficiency (GHD) is associated with decreased lean body mass, increased adiposity, and reduced EE, which are reversed by GH treatment. In the present study we investigated whether GH treatment for 4 months influenced the expression of UCPs in skeletal muscle and adipose tissue in 22 GHD patients who were investigated before and after GH (n = 11) or placebo (n = 11) treatment. GH treatment increased the amount of lean body mass by 4.5% (P < 0.05) and decreased body fat mass by 12% (P < 0.05), whereas no changes in these parameters were observed after placebo treatment. The level of UCP3 messenger ribonucleic acid (mRNA) increased 3-fold (P < 0.005) in skeletal muscle and almost 2-fold (P < 0.05) in adipose tissue after GH treatment, with no changes observed after placebo treatment. Skeletal muscle UCP2 mRNA was slightly (25%), but significantly (P < 0.05), decreased, whereas the level of UCP2 mRNA in adipose tissue was unaffected after GH treatment. The T4 level was positively correlated with skeletal muscle UCP2 and UCP3 expression (r = 0.518; P < 0.05 and r = 0.463; P < 0.05, respectively). Furthermore, plasma free fatty acids were positively correlated with the expression of UCP2 (r = 0.573; P < 0.01) and UCP3 (r = 0.518; P < 0.05) in skeletal muscle. The marked increase in UCP3 expression after GH treatment indicates that the UCPs might play a role in the effects of GH on EE in GHD patients. Finally, the strong association between thyroid hormone and skeletal muscle UCP and the correlation between plasma free fatty acids and UCP expression in skeletal muscle indicate that these hormones/metabolites might influence UCP expression in humans as previously demonstrated in rodents.     

Expression of insulin target genes in skeletal muscle and adipose tissue in adult patients with growth hormone deficiency: effect of one year recombinant human growth hormone therapy.

Our aim was to investigate the effects of one year recombinant human growth hormone (rhGH) therapy on the regulation by insulin of gene expression in muscle and adipose tissue in adults with secondary GH deficiency (GHD). Six GHD subjects without upper-body obesity were submitted to a 3-h euglycemic hyperinsulinemic clamp before and after one year of rhGH therapy. Muscle and abdominal subcutaneous adipose tissue biopsies were taken before and at the end of each clamp. The mRNA levels of insulin receptor, p85 alpha-phosphatidylinositol-3 kinase (p85 alpha PI-3K), insulin dependent glucose transporter (Glut4), hexokinase II, glycogen synthase, lipoprotein lipase (LPL) in muscle and in adipose tissue, hormone sensitive lipase and peroxisome proliferator-activated receptor gamma (PPAR gamma) in adipose tissue were quantified by RT-competitive PCR. One year treatment with rhGH (1.25 IU/day) increased plasma IGF-I concentrations (54+/-7 vs 154+/-11 ng/ml, P<0.01) but did not affect insulin-stimulated glucose disposal rate measured during the hyperinsulinemic clamp (74+/-9 vs 85+/-5 micromol/kg free fat mass/min). Insulin significantly increased p85 alpha PI-3K, hexokinase II and Glut4 mRNA levels in muscle both before and after rhGH treatment. One year of GH therapy increased LPL mRNA levels in muscle (38+/-2 vs 70+/-7 amol/microg total RNA, P<0.05) and in adipose tissue (2490+/-260 vs 4860+/-880 amol/microg total RNA, P<0.05), but did not change the expression of the other mRNAs. We conclude from this study that GH therapy did not alter whole body insulin sensitivity and the response of gene expression to insulin in skeletal muscle of adult GHD patients, but it did increase LPL expression in muscle and adipose tissue. This result could be related to the documented beneficial effect of GH therapy on lipid metabolism.     

Subcutaneous adipose tissue expression of plasminogen activator inhibitor-1 gene during very low calorie diet in obese subjects

OBJECTIVE: To determine whether changes in subcutaneous adipose tissue plasminogen activator inhibitor-1 (PAI-1) expression influence plasma PAI-1 level during weight loss in obese humans. DESIGN: Study of the variations of PAI-1 levels both in plasma and in subcutaneous abdominal adipose tissue in 15 volunteer non-diabetic obese subjects, body mass index (BMI) 40.4.+/-1.9 kg/m2, aged 48+/-3 y, before and after a 3 week very low calorie diet (VLCD) programme (3.9+/-0.1 MJ/day). MEASUREMENTS: Plasma and adipose tissue PAI-1 protein levels were measured by enzyme-linked immunosorbent assay and PAI-1 mRNA levels were quantified by quantitative RT-competitive PCR. RESULTS: VLCD induced weight loss (5.8+/-0.8 kg) and decreased plasma PAI-1 concentration (-26% (P<0. 01)). Surprisingly, PAI-1 mRNA and protein abundance in subcutaneous adipose tissue increased by 87% (P<0.05) and by 44% (P<0.01), respectively. CONCLUSION: These data indicate thus that changes in subcutaneous adipose tissue PAI-1 expression are not involved in the decrease of plasma PAI-1 levels during VLCD in obese subjects. International Journal of Obesity (2000)24, 70-74     

NO-1886 (ibrolipim), a lipoprotein lipase activator, increases the expression of uncoupling protein 3 in skeletal muscle and suppresses fat accumulation in high-fat diet-induced obesity in rats

Although the lipoprotein lipase (LPL) activator NO-1886 shows antiobesity effects in high-fat-induced obese animals, the mechanism remains unclear. To clarify the mechanism, we studied the effects of NO-1886 on the expression of uncoupling protein (UCP) 1, UCP2, and UCP3 in rats. NO-1886 was mixed with a high-fat chow to supply a dose of 100 mg/kg to 8-month-old male Sprague-Dawley rats. The animals were fed the high-fat chow for 8 weeks. At the end of the administration period, brown adipose tissue (BAT), mesenteric fat, and soleus muscle were collected and levels of UCP1, UCP2, and UCP3 messenger RNA (mRNA) were determined. NO-1886 suppressed the body weight increase seen in the high-fat control group after the 8-week administration (585 +/- 39 vs 657 +/- 66 g, P < .05). NO-1886 also suppressed fat accumulation in visceral (46.9 +/- 10.4 vs 73.7 +/- 14.5 g, P < .01) and subcutaneous (43.1 +/- 18.1 vs 68.9 +/- 18.8 g, P < .05) tissues and increased the levels of plasma total cholesterol and high-density lipoprotein cholesterol in comparison to the high-fat control group. In contrast, NO-1886 decreased the levels of plasma triglycerides, nonesterified free fatty acid, glucose, and insulin. NO-1886 increased LPL activity in soleus muscle (0.082 +/- 0.013 vs 0.061 +/- 0.016 mumol of free fatty acid per minute per gram of tissue, P < .05). NO-1886 increased the expression of UCP3 mRNA in soleus muscle 3.14-fold (P < .01) compared with the high-fat control group without affecting the levels of UCP3 in mesenteric adipose tissue and BAT. In addition, NO-1886 did not affect the expression of UCP1 and UCP2 in BAT, mesenteric adipose tissue, and soleus muscle. In conclusion, NO-1886 increased the expression of UCP3 mRNA and LPL activity only in skeletal muscle. Therefore, a possible mechanism for NO-1886's antiobesity effects in rats may be the enhancement of LPL activity in skeletal muscle and the accompanying increase in UCP3 expression.     

Up-regulation of muscle uncoupling protein 3 gene expression in mice following high fat diet, dietary vitamin A supplementation and acute retinoic acid-treatment

OBJECTIVE: To analyse the impact of vitamin A supplementation of both a normal fat (NF) diet and a high fat (HF) diet and of acute retinoic acid (RA)-treatment on the expression of uncoupling protein 3 (UCP3) in mice. DESIGN: C57BL/6J mice were fed for 18 weeks a NF or a HF diet (10 and 45 energy% as fat, respectively), both with the normal vitamin A content or an excess vitamin A (8 mg and 320 mg retinyl palmitate/kg diet, respectively). Body weight and energy intake were recorded periodically. UCP3 mRNA and UCP3 protein levels in skeletal muscle (soleus/gastrocnemius) were analysed, as well as UCP1, UCP2 and UCP3 mRNA levels in interscapular brown adipose tissue (BAT), and UCP2 mRNA, UCP2 protein and leptin mRNA levels in white adipose tissue (WAT) depots. The effect of acute RA-treatment (100 mg/kg/day, 4 days) on UCP3 mRNA levels in skeletal muscle and BAT of NMRI mice was also assessed. RESULTS: Vitamin A supplementation of a NF diet led to increased levels of UCP3 mRNA and UCP3 protein in muscle, UCP1 mRNA in BAT, and UCP2 mRNA in inguinal WAT, but had no impact on body weight or adiposity of B6 mice. HF diet promoted obesity and increased levels of UCP3 mRNA and UCP3 protein in skeletal muscle, and of the mRNAs for all three UCPs in BAT. Supplementing the HF diet with vitamin A had little effect on the final obesity reached and did not lead to further increases of muscle UCP3 mRNA nor BAT UCP1 mRNA over the levels achieved with the non-supplemented HF diet. Adipose leptin mRNA levels were down regulated after vitamin A supplementation, independently of the fat content of the diet. Up-regulation of muscle, but not BAT, UCP3 mRNA levels was also found after acute RA-treatment in NMRI mice. CONCLUSION: The results provide evidence of a stimulatory effect of retinoids on muscle UCP3 expression in vivo, and a differential retinoid-regulation of the UCP3 gene in muscle and BAT.     

The effects of underfeeding on whole-body carbohydrate partitioning, thermogenesis and uncoupling protein 3 expression in human skeletal muscle

AIM: Underfeeding is known to reduce resting energy expenditure (REE) as an energy-conserving mechanism and may also reduce insulin sensitivity. Uncoupling protein 1 is known to have a significant role in energy expenditure (EE) in small mammals, but the role of UCPs in humans is unclear. UCP3 is primarily expressed in human skeletal muscle, a significant site of whole-body EE in lean individuals and therefore has a potential role in human metabolism. Here, we examine the effects of short-term underfeeding on UCP3 skeletal muscle expression, and on whole-body insulin sensitivity, substrate utilization and thermogenesis. METHODS: Eleven non-obese men [age 22.8 +/- 1.34 years, body mass index 23.4 +/- 0.71 kg/m(2), mean +/- s.e.m.] were fed for two periods of 6 days, an underfeeding diet (UF) (50% predicted requirements for weight maintenance) and an eucaloric diet (EU), with the same macronutrient composition, in random order. Subjects visited the laboratory on four separate occasions, before and after each dietary period. REE, metabolites and muscle biopsies (vastus lateralis) were taken and the thermogenic response to a hyperinsulinaemic euglycaemic clamp was measured over a 2-h period. UCP3 mRNA levels were measured using Taqman. RESULTS: After underfeeding for 6 days, REE fell by 0.43 +/- 0.17 kJ/min (p = 0.032), with weight loss of 2.05 +/- 0.34 kg (p < 0.001). Baseline fasting glucose was significantly lower at 4.26 +/- 0.07 mmol/l (p = 0.005), with a corresponding fall in carbohydrate oxidation (0.08 +/- 0.03 g/min; p = 0.04). Fasting free fatty acids (FFA) increased by 0.13 +/- 0.03 mmol/l (p < 0.001), with an increase in beta-hydroxybutyrate concentrations of 0.41 +/- 0.07 mM (p < 0.001) compared with post-EU. There was no significant change in UCP3 mRNA levels pre- and post-UF [10.4 +/- 6.8 arbitrary units (au); p = 0.16] compared with pre- and post-EU (3.2 +/- 7.3 au; p = 0.67). There was no thermogenic response to the clamp after 6 days of underfeeding and a significant reduction in glucose disposal rates (from 46.35 +/- 2.15 to 39.46 +/- 1.12 micromol/min/kg; p = 0.003). Carbohydrate oxidation rates were lower by 0.08 +/- 0.03 g/min (p = 0.011) compared with pre-UF, with no change in glucose storage rates (28.2 +/- 2.4 micromol/min/kg pre-UF; 27.0 +/- 2.3 micromol/min/kg post-UF; p = 0.7). EU resulted in a mildly underfed state with marginal weight loss (0.55 +/- 0.28 kg; p = 0.08), and fasting FFA increased by 0.13 +/- 0.03 mmol/l (p < 0.001) and beta-hydroxybutyrate concentrations by 0.05 +/- 0.02 mM (p = 0.03) compared with pre-EU. There was no change in glucose disposal or storage rates compared with pre-EU. CONCLUSIONS: Underfeeding for 6 days has no significant effect on UCP3 mRNA expression in skeletal muscle in non-obese men but is associated with changes in carbohydrate fuel partitioning, REE and the thermogenic response to the glucose clamp. Mild underfeeding had no effect on insulin sensitivity, but more severe energy restriction reduced insulin-stimulated glucose oxidation without affecting glucose storage.     

Loss of total body potassium during rapid weight loss does not depend on the decrease of potassium concentration in muscles. Different methods to evaluate body composition during a low energy diet

OBJECTIVE: The aim of the study was to elucidate whether combustion of skeletal muscle glycogen during a very low calorie diet (VLCD) was associated with decreased muscle potassium content. A comparison between different methods was also performed to evaluate body composition during a VLCD and a low calorie diet (LCD). DESIGN: Dietary treatment of obese women by VLCD and LCD. Measurements after 1 and 2 weeks of VLCD and 6 months of LCD. SUBJECTS: Fifteen perimenopausal obese women aged 46.5+/-1.3 y and 15 of 48.0+/-0.7 y of age. MEASUREMENTS: Skeletal muscle biopsies under local anaesthesia. Body composition measurements by means of deal-energy X-ray absorptiometry (DEXA), and measurements of total body potassium (40K) and total body nitrogen (TBN). Measurements of electrolytes and glycogen concentration in muscle samples. RESULTS: In the first study (1 week of VLCD) skeletal muscle glycogen decreased (P<0.01), but muscle potassium increased (P<0.01). Muscle sodium decreased (P<0.01), while muscle magnesium was unaltered. Body weight decreased by 2.9+/-0.5 kg and 40K decreased. Fat-free mass (FFM) calculated from 40K and DEXA decreased by 2.7 vs 1.9 kg (P<0.001). Body fat measured with DEXA decreased by 1.1 kg (P<0.01), but not body fat calculated from 40K. TBN decreased by 0.03+/-0.01 kg (P<0.05) and FFM calculated from TBN by 2.9+/-0.5 kg (P<0.002). In the second study, 6 months on the LCD resulted in 17.0+/-2.0 kg weight reduction and this was mainly due to reduced body fat, 14. 0+/-2.0 kg measured with DEXA and from 40K (P<0.001). The decrease in FFM was slight. CONCLUSION: One week of VLCD resulted in muscle glycogen depletion but increased muscle potassium content in spite of decreased total body potassium. FFM contributed to the main part of body weight loss during short periods of severe energy restriction, but remained unchanged during long-term dietary treatment. Body fat became mostly responsible for the body weight loss during long-term LCD. Calculations of changes of FFM from 40K and TBN seem to overestimate the FFM decrease associated with short-term VLCD. International Journal of Obesity (2000)24, 101-107     

Reduced expression of uncoupling proteins-2 and -3 in adipose tissue in post-obese patients submitted to biliopancreatic diversion

OBJECTIVE: Little is known about the physiological role and the regulation of uncoupling proteins-2 and -3 (UCP-2 and -3) in adipose tissue. We investigated whether the expression of UCP-2 and -3 in adipose tissue was affected by weight loss due to a biliopancreatic diversion (BPD) and related to the daily energy expenditure (24-h EE). DESIGN: Ten morbidly obese subjects (mean body mass index +/- s.e.m.=49.80 +/- 2.51 kg/m(2)) were studied before and 18+/-2 Months after BPD. METHODS: We determined body composition using tritiated water and 24-h EE in a respiratory chamber. Adipose tissue UCP-2 and -3 mRNA, plasma insulin, glucose, free fatty acids (NEFA), free triiodothyronine (FT3), free thyroxine (FT4) and leptin were assayed before and after BPD. RESULTS: BPD treatment resulted in a marked weight loss (P<0.001) mainly due to a fat mass reduction. A significant decrease in 24-h EE/fat-free mass (FFM) (P<0.05) and in UCP-2 (P<0.05) and UCP-3 (P<0.05) mRNA was observed. A significant reduction in plasma insulin, glucose, NEFA, FT3, FT4 and leptin was seen after BPD. The decline in plasma leptin and FFA was tightly correlated with the decrease in both UCP-2 and -3. A significant correlation was found between changes in FT3 and variations in 24-h EE (r=0.64, P<0.05). In a multiple-regression analysis changes in 24-h EE/FFM after BPD were significantly correlated with changes in UCP-3 expression (P<0.05). CONCLUSION: These findings suggest that UCPs in adipose tissue may play a role in the reduction in 24-h EE observed in post-obese individuals.     

The effect of mild cold exposure on UCP3 mRNA expression and UCP3 protein content in humans

OBJECTIVE: In rodents, adaptive thermogenesis in response to cold exposure and high-fat feeding is accomplished by the activation of the brown adipose tissue specific mitochondrial uncoupling protein, UCP1. The recently discovered human uncoupling protein 3 is a possible candidate for adaptive thermogenesis in humans. In the present study we examined the effect of mild cold exposure on the mRNA and protein expression of UCP3. SUBJECTS: Ten healthy male volunteers (age 24.4 +/- 1.6 y; height 1.83 +/- 0.02 m; weight 77.3 +/- 3.0 kg; percentage body fat 19 +/- 2). DESIGN: Subjects stayed twice in the respiration chamber for 60 h (20.00-8.00 h); once at 22 degrees C (72 degrees F), and once at 16 degrees C (61 degrees F). After leaving the respiration chamber, muscle biopsies were taken and RT-competitive-PCR and Western blotting was used to measure UCP3 mRNA and protein expression respectively. RESULTS: Twenty-four-hour energy expenditure was significantly increased at 16 degrees C compared to 22 degrees C (P<0.05). At 16 degrees C, UCP3T (4.6 +/- 1.0 vs 7.7 +/- 1.5 amol/microg RNA, P=0.07), UCP3L (2.0 +/- 0.5 vs 3.5 +/- 0.9 amol/microg RNA, P=0.1) and UCP3S (2.6 +/- 0.6 vs 4.2 +/- 0.7 amol/microg RNA, P=0.07) mRNA expression tended to be lower compared with at 22 degrees C, whereas UCP3 protein content was, on average, not different. However, the individual differences in UCP3 protein content (16-22 degrees C) correlated positively with the differences in 24 h energy expenditure (r=0.86, P<0.05). CONCLUSION: The present study suggests that UCP3 protein content is related to energy metabolism in humans and might help in the metabolic adaptation to cold exposure. However, the down-regulation of UCP3 mRNA with mild cold exposure suggests that prolonged cold exposure will lead to lower UCP3 protein content. What the function of such down-regulation of UCP3 could be is presently unknown.     

Downregulation of uncoupling protein 2 mRNA in women treated with glucocorticoids.

OBJECTIVE: Glucocorticoids are well-known regulators of energy turnover and adipose tissue metabolism. We investigated the effect of glucocorticoids on the expression of the human uncoupling protein 2 (UCP 2) gene, which has been implicated in energy expenditure. DESIGN: Prednisolone (25 mg) was administered orally daily for 7 days. Subcutaneous adipose tissue UCP 2 mRNA was measured before and after treatment. SUBJECTS: Eight healthy female subjects (age 52-63 y; body mass index 25-34 kg/m2). RESULTS: No differences in body weight, waist-to-hip ratio or plasma-values of FFA or glucose were found after prednisolone treatment, as compared to pre-treatment values under these conditions. In contrast, plasma insulin levels were significantly increased by glucocorticoid administration, 54+/-6 before vs 70+/-12 (mean+/-sem) pmol/l after treatment (P=0.028). Furthermore, using RT-competitive-PCR, the UCP 2 mRNA level in abdominal subcutaneous adipose tissue was found to be down-regulated by half (6.3+/-0.4 vs 3.1+/-0.8 amol/microg RNA, P=0.012) after glucocorticoid treatment. No difference in expression levels of the reference gene 18SrRNA was observed before, as compared to after prednisolone exposure (249+/-11 vs 248+/-30 amol/microg RNA, P=0.87). CONCLUSION: These data suggest that glucocorticoids may play a role in the regulation of UCP 2 mRNA expression in human adipose tissue in vivo.     

Changes in FAT/CD36, UCP2, UCP3 and GLUT4 gene expression during lipid infusion in rat skeletal and heart muscle

OBJECTIVE: It has been reported that an increased availability of free fatty acids (NEFA) not only interferes with glucose utilization in insulin-dependent tissues, but may also result in an uncoupling effect of heart metabolism. We aimed therefore to investigate the effect of an increased availability of NEFA on gene expression of proteins involved in transmembrane fatty acid (FAT/CD36) and glucose (GLUT4) transport and of the uncoupling proteins UCP2 and 3 at the heart and skeletal muscle level. STUDY DESIGN: Euglycemic hyperinsulinemic clamp was performed after 24 h Intralipid(R) plus heparin or saline infusion in lean Zucker rats. Skeletal and heart muscle glucose utilization was calculated by 2-deoxy-[1-(3)H]-D-glucose technique. Quantification of FAT/CD36, GLUT4, UCP2 and UCP3 mRNAs was obtained by Northern blot analysis or RT-PCR. RESULTS: In Intralipid(R) plus heparin infused animals a significant decrease in insulin-mediated glucose uptake was observed both in the heart (22.62+/-2.04 vs 10.37+/-2.33 ng/mg/min; P<0.01) and in soleus muscle (13.46+/-1.53 vs 6.84+/-2.58 ng/mg/min; P<0.05). FAT/CD36 mRNA was significantly increased in skeletal muscle tissue (+117.4+/-16.3%, P<0.05), while no differences were found at the heart level in respect to saline infused rats. A clear decrease of GLUT4 mRNA was observed in both tissues. The 24 h infusion of fat emulsion resulted in a clear enhancement of UCP2 and UCP3 mRNA levels in the heart (99.5+/-15.3 and 80+/-4%) and in the skeletal muscle (291.5+/-24.7 and 146.9+/-12.7%). CONCLUSIONS: As a result of the increased availability of NEFA, FAT/CD36 gene expression increases in skeletal muscle, but not at the heart level. The augmented lipid fuel supply is responsible for the depression of insulin-mediated glucose transport and for the increase of UCP2 and 3 gene expression in both skeletal and heart muscle.     

Dietary calcium regulates ROS production in aP2-agouti transgenic mice on high-fat/high-sucrose diets

OBJECTIVE: We have previously demonstrated that 1alpha, 25(OH)2D3 promotes adipocyte reactive oxygen species (ROS) production. We have now evaluated whether decreasing 1alpha, 25(OH)2D3 levels by increasing dietary calcium will decrease oxidative stress in vivo. METHODS: We fed low-calcium (0.4% Ca) and high-calcium (1.2% Ca from CaCO3) obesity-promoting (high sucrose/high fat) diets to aP2-agouti transgenic mice and assessed regulation of ROS production in adipose tissue and skeletal muscle. RESULTS: Mice on the high-calcium diet gained 50% of the body weight (P=0.04) and fat (P<0.001) as mice on the low-calcium diet (0.4% Ca). The high-calcium diet significantly reduced adipose intracellular ROS production by 64 and 18% (P<0.001) and inhibited adipose tissue nicotinamide adenine dinucleotide phosphate oxidase expression by 49% (P=0.012) and 63% (P=0.05) in visceral and subcutaneous adipose tissue, respectively. Adipocyte intracellular calcium ([Ca2+]i) levels were suppressed in mice on the high-calcium diet by 73-80% (P<0.001). The high-calcium diet also induced 367 and 191% increases in adipose mitochondrial uncoupling protein 2 (UCP2) expression (P<0.001) in visceral and subcutaneous adipose tissue, respectively. The pattern of UCP3 expression and indices of ROS production in skeletal muscle were consistent with those in adipose tissue. The high-calcium diet also suppressed 11beta-hydroxysteroid dehydrogenase (11beta-HSD) expression in visceral adipose tissue by 39% (P=0.034). 11beta-HSD expression was markedly higher in visceral vs subcutaneous adipose tissue in mice on the low-calcium diet (P=0.034), whereas no difference was observed between the fat depots in mice on the high-calcium diet. CONCLUSION: These data support a potential role for dietary calcium in the regulation of obesity-induced oxidative stress.     

Skeletal muscle low attenuation area and maximal fat oxidation rate during submaximal exercise in male obese individuals.

BACKGROUND: Muscle triacylglycerols (TG) are known to be a source of energy during submaximal exercise. OBJECTIVE: The aim of this study was to assess whether an index of muscle fat content is related to maximal fat oxidation rate (FATOXmax) in 58 obese men (mean age 46.0+/-0.8 (s.e.) y, body weight 96.4+/-1.4 kg, percentage fat: 31.9+/-0.5%) [corrected]. DESIGN: FATOXmax was defined as the highest value of fat oxidation rate, measured by indirect calorimetry, while walking on a treadmill (4.3 km/h) at three different slopes: 0% (40+/-1% of VO2max), 3% (47+/-1% of VO2max) and 6% (58+/-1% of VO2max). Fat-free mass (FFM) and fat mass (FM) were measured with the underwater technique and scans were obtained by computed tomography (CT) at the mid thigh level to assess areas of adipose tissue within skeletal muscle, ie deep adipose tissue (DAT), subcutaneous adipose tissue (SAT), skeletal muscle (M) and low attenuation skeletal muscle (LAM, range of attenuation values: 0-34 Hounsfield units). LAM and DAT were used as indices of skeletal muscle fat content. RESULTS: FATOXmax, adjusted for age, was correlated with FFM (r=0.26, P<0.05), LAM (r=0.29, P<0.05), abdominal visceral adipose tissue (r=0.30, P<0.05) and plasma free fatty acid (FFA) levels (r=0.33, P<0.05) but not with SAT (r=0.03) and DAT (r=0.21) [corrected]. In a stepwise linear multiple regression, plasma FFA, age and LAM significantly predicted FATOXmax (r2=0.27). Each independent variable explained about 9% of the FATOXmax variance. CONCLUSION: LAM makes a significant but weak contribution to the modulation of fat oxidation during submaximal exercise in obese men.     

Regulation of lipoprotein lipase and hormone-sensitive lipase activity and gene expression in adipose and muscle tissue by growth hormone treatment during weight loss in obese patients

It is well known that growth hormone (GH) treatment reduces fat mass (FM), which presumably is mediated through stimulation of triglyceride breakdown and inhibition of adipose tissue lipoprotein lipase activity (AT-LPL). However, it is unknown which of the 2 GH-regulated pathways are of most importance for the reduction in FM. We investigated the effect of weight loss together with GH treatment on the activity and gene expression of LPL and hormone-sensitive lipase (HSL) in AT and muscle tissue. A very-low-calorie diet ([VLCD] 740 kcal/d) was given to 18 obese women (body mass index [BMI] > 35 kg/m2) and half of them were treated with GH (0.04 IU/kg) for 4 weeks in a randomized double-blind placebo-controlled study. Subcutaneous fat and muscle biopsies were taken before and after 4 weeks. Weight loss after 4 weeks was similar in the 2 groups, with a reduction of 4.5% (placebo) and 4.6% (GH) and a reduction of FM by 7.4% and 9.0% ([NS] nonsignificant). The weight loss resulted in a small and NS reduction of AT-LPL activity by 20% +/- 12% in the placebo group, but in the GH group, AT-LPL was significantly reduced by 65% +/- 8% (P < .01). Muscle LPL (M-LPL) activity was not affected by the weight loss alone, but a significant reduction was observed in the GH group (20.4% +/- 10%, P < .05). AT-HSL activity was significantly enhanced after weight loss, but GH had no additional effect on this minor increment. This is in accordance with the finding that the increment in free fatty acid (FFA) after weight loss was similar in the 2 groups. GH treatment was associated with a significant reduction of high-density lipoprotein (HDL) cholesterol (P < .05). In conclusion, GH significantly inhibited AT-LPL activity but had no additional effect on the hypocaloric-induced loss of FM, indicating that under such circumstances, AT-LPL does not directly regulate adipose tissue mass. GH was not found to have opposite effects on the activity of LPL in adipose tissue and muscle, since GH treatment reduced them both (by 65% and 20%, respectively). The VLCD-induced weight loss was associated with a minor enhanced activity of AT-HSL with no independent effect of GH. Thus, concerning body weight, FM, and lipolytic activity, treatment with GH offers no extra benefits during a VLCD for 4 weeks.     

Expression of rat uncoupling protein family mRNA levels by chronic treatment with thyroid hormone

The present study was conducted to assess the effects of chronic treatment with triiodothyronine (T3) on mRNA expression of uncoupling protein (UCP) family in male Wistar King A rats. Subcutaneous injection of T3 (37 nmol/body weight 100 g) over 7 d increased mRNA expression of UCP1 in brown adipose tissue (BAT), UCP2 in white adipose tissue (WAT), and UCP3 in skeletal muscle (MSL) mRNA by 1.3, 1.7, and 2.0-fold, respectively. In contrast, the expression of ob gene mRNA in WAT and serum leptin level in the T3-treated rats decreased by 0.5-fold of the controls. These results suggest that T3 may increase UCP family expression independent of leptin action.     

Apelin, an APJ receptor ligand, regulates body adiposity and favors the messenger ribonucleic acid expression of uncoupling proteins in mice

Apelin, the endogenous ligand of the APJ receptor, has been identified in a variety of tissues, including stomach, heart, skeletal muscle, and white adipose tissue. We sought to clarify the effects of apelin on body adiposity and the expression of uncoupling proteins (UCPs) in C57BL/6 mice. Treatment with ip apelin at a dose of 0.1 mumol/kg.d for 14 d decreased the weight of white adipose tissue and serum levels of insulin and triglycerides, compared with controls, without influencing food intake. Apelin treatment also decreased body adiposity and serum levels of insulin and triglycerides in obese mice fed a high-fat diet. Apelin increased the serum adiponectin level and decreased that of leptin. Additionally, apelin treatment increased mRNA expression of UCP1, a marker of peripheral energy expenditure, in brown adipose tissue (BAT) and of UCP3, a regulator of fatty acid export, in skeletal muscle. In addition, immunoblot bands and relative densities of UCP1 content in BAT were also higher in the apelin group than controls. Furthermore, apelin treatment increased body temperature and O(2) consumption and decreased the respiratory quotient. In conclusion, apelin appears to regulate adiposity and lipid metabolism in both lean and obese mice. In addition, apelin regulates insulin resistance by influencing the circulating adiponectin level, the expression of BAT UCP1, and energy expenditure in mice.