Circulating irisin and glucose metabolism in overweight/obese women: effects of α-lipoic acid and eicosapentaenoic acid

Irisin is a myokine/adipokine with potential role in obesity and diabetes. The objectives of the present study were to analyse the relationship between irisin and glucose metabolism at baseline and during an oral glucose tolerance test (OGTT) and to determine the effects of eicosapentaenoic acid (EPA) and/or α-lipoic acid treatment on irisin production in cultured human adipocytes and in vivo in healthy overweight/obese women following a weight loss program. Seventy-three overweight/obese women followed a 30% energy-restricted diet supplemented without (control) or with EPA (1.3 g/day), α-lipoic acid (0.3 g/day) or both EPA + α-lipoic acid (1.3 + 0.3 g/day) during 10 weeks. An OGTT was performed at baseline. Moreover, human adipocytes were treated with EPA (100-200 μM) or α-lipoic acid (100-250 μM) during 24 h. At baseline plasma, irisin circulating levels were positively associated with glucose levels; however, serum irisin concentrations were not affected by the increment in blood glucose or insulin during the OGTT. Treatment with α-lipoic acid (250 μM) upregulated Fndc5 messenger RNA (mRNA) and irisin secretion in cultured adipocytes. In overweight/obese women, irisin circulating levels decreased significantly after weight loss in all groups, while no additional differences were induced by EPA or α-lipoic acid supplementation. Moreover, plasma irisin levels were positively associated with higher glucose concentrations at beginning and at endpoint of the study. The data from the OGTT suggest that glucose is not a direct contributing factor of irisin release. The higher irisin levels observed in overweight/obese conditions could be a protective response of organism to early glucose impairments.

Effects of α-lipoic acid and eicosapentaenoic acid in overweight and obese women during weight loss

OBJECTIVE

To evaluate the potential body weight-lowering effects of dietary supplementation with eicosapentaenoic acid (EPA) and α-lipoic acid separately or combined in healthy overweight/obese women following a hypocaloric diet.

METHODS

This is a short-term double-blind placebo-controlled study with parallel design that lasted 10 weeks. Of the randomized participants, 97 women received the allocated treatment [Control, EPA (1.3 g/d), α-lipoic acid (0.3 g/d), and EPA+α-lipoic acid (1.3 g/d+0.3 g/d)], and 77 volunteers completed the study. All groups followed an energy-restricted diet of 30% less than total energy expenditure. Body weight, anthropometric measurements, body composition, resting energy expenditure, blood pressure, serum glucose, and insulin and lipid profile, as well as leptin and ghrelin levels, were assessed at baseline and after nutritional intervention.

RESULTS

Body weight loss was significantly higher (P<0.05) in those groups supplemented with α-lipoic acid. EPA supplementation significantly attenuated (P<0.001) the decrease in leptin levels that occurs during weight loss. Body weight loss improved lipid and glucose metabolism parameters but without significant differences between groups.

CONCLUSIONS

The intervention suggests that α-lipoic acid supplementation alone or in combination with EPA may help to promote body weight loss in healthy overweight/obese women following energy-restricted diets.

Leptin resistance and diet-induced obesity: central and peripheral actions of leptin

Obesity is a chronic disease that represents one of the most serious global health burdens associated to an excess of body fat resulting from an imbalance between energy intake and expenditure, which is regulated by environmental and genetic interactions. The adipose-derived hormone leptin acts via a specific receptor in the brain to regulate energy balance and body weight, although this protein can also elicit a myriad of actions in peripheral tissues. Obese individuals, rather than be leptin deficient, have in most cases, high levels of circulating leptin. The failure of these high levels to control body weight suggests the presence of a resistance process to the hormone that could be partly responsible of disturbances on body weight regulation. Furthermore, leptin resistance can impair physiological peripheral functions of leptin such as lipid and carbohydrate metabolism and nutrient intestinal utilization. The present document summarizes those findings regarding leptin resistance development and the role of this hormone in the development and maintenance of an obese state. Thus, we focused on the effect of the impaired leptin action on adipose tissue, liver, skeletal muscle and intestinal function and the accompanying relationships with diet-induced obesity. The involvement of some inflammatory mediators implicated in the development of obesity and their roles in leptin resistance development are also discussed.

α-Lipoic acid treatment increases mitochondrial biogenesis and promotes beige adipose features in subcutaneous adipocytes from overweight/obese subjects

α-Lipoic acid (α-Lip) is a natural occurring antioxidant with beneficial anti-obesity properties. The aim of this study was to investigate the putative effects of α-Lip on mitochondrial biogenesis and the acquirement of brown-like characteristics by subcutaneous adipocytes from overweight/obese subjects. Thus, fully differentiated human subcutaneous adipocytes were treated with α-Lip (100 and 250μM) for 24h for studies on mitochondrial content and morphology, mitochondrial DNA (mtDNA) copy number, fatty acid oxidation enzymes and brown/beige characteristic genes. The involvement of the Sirtuin1/Peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (SIRT1/PGC-1α) pathway was also evaluated. Our results showed that α-Lip increased mitochondrial content in cultured human adipocytes as revealed by electron microscopy and by mitotracker green labeling. Moreover, an enhancement in mtDNA content was observed. This increase was accompanied by an up-regulation of SIRT1 protein levels, a decrease in PGC-1α acetylation and up-regulation of Nuclear respiratory factor 1 (Nrf1) and Mitochondrial transcription factor (Tfam) transcription factors. Enhanced oxygen consumption and fatty acid oxidation enzymes, Carnitine palmitoyl transferase 1 and Acyl-coenzyme A oxidase (CPT-1 and ACOX) were also observed. Mitochondria from α-Lip-treated adipocytes exhibited some morphological characteristics of brown mitochondria, and α-Lip also induced up-regulation of some brown/beige adipocytes markers such as cell death-inducing DFFA-like effector a (Cidea) and T-box 1 (Tbx1). Moreover, α-Lip up-regulated PR domain containing 16 (Prdm16) mRNA levels in treated adipocytes. Therefore, our study suggests the ability of α-Lip to promote mitochondrial biogenesis and brown-like remodeling in cultured white subcutaneous adipocytes from overweight/obese donors.

α-lipoic acid reduces fatty acid esterification and lipogenesis in adipocytes from overweight/obese subjects

OBJECTIVE

α-Lipoic acid (α-LA) is a natural occurring antioxidant with beneficial effects on obesity. The aim of this study was to investigate the putative effects of α-LA on triglyceride accumulation and lipogenesis in subcutaneous adipocytes from overweight/obese subjects and to determine the potential mechanisms involved.

METHODS

Fully differentiated human subcutaneous adipocytes were treated with α-LA (100 and 250 µM) during 24 h for studying triglyceride content, de novo lipogenesis, and levels of key lipogenic enzymes. The involvement of AMP-activated protein kinase (AMPK) activation was also evaluated.

RESULTS

α-LA down-regulated triglyceride content by inhibiting fatty acid esterification and de novo lipogenesis. These effects were mediated by reduction in fatty acid synthase (FAS), stearoyl-coenzyme A desaturase 1, and diacylglycerol O-acyltransferase 1 protein levels. Interestingly, α-LA increased AMPK and acetyl CoA carboxylase phosphorylation, while the presence of the AMPK inhibitor Compound C reversed the inhibition observed on FAS protein levels.

CONCLUSIONS

α-LA down-regulates key lipogenic enzymes, inhibiting lipogenesis and reducing triglyceride accumulation through the activation of AMPK signaling pathway in human subcutaneous adipocytes from overweight/obese subjects.

Cardiotrophin-1 eliminates hepatic steatosis in obese mice by mechanisms involving AMPK activation

BACKGROUND & AIMS

Cardiotrophin-1 (CT-1) is a hepatoprotective cytokine that modulates fat and glucose metabolism in muscle and adipose tissue. Here we analyzed the changes in hepatic fat stores induced by recombinant CT-1 (rCT-1) and its therapeutic potential in non-alcoholic fatty liver disease (NAFLD).

METHODS

rCT-1 was administered to two murine NAFLD models: ob/ob and high fat diet-fed mice. Livers were analyzed for lipid composition and expression of genes involved in fat metabolism. We studied the effects of rCT-1 on lipogenesis and fatty acid (FA) oxidation in liver cells and the ability of dominant negative inhibitor of AMP-activated protein kinase (AMPK) to block these effects.

RESULTS

CT-1 was found to be upregulated in human and murine steatotic livers. In two NAFLD mouse models, treatment with rCT-1 for 10days induced a marked decrease in liver triglyceride content with augmented proportion of poly-unsaturated FA and reduction of monounsaturated species. These changes were accompanied by attenuation of inflammation and improved insulin signaling. Chronic administration of rCT-1 caused downregulation of lipogenic genes and genes involved in FA import to hepatocytes together with amelioration of ER stress, elevation of NAD(+)/NADH ratio, phosphorylation of LKB1 and AMPK, increased expression and activity of sirtuin1 (SIRT1) and upregulation of genes mediating FA oxidation. rCT-1 potently inhibited de novo lipogenesis and stimulated FA oxidation in liver cells both in vitro and in vivo. In vitro studies showed that these effects are mediated by activated AMPK.

CONCLUSIONS

rCT-1 resolves hepatic steatosis in obese mice by mechanisms involving AMPK activation. rCT-1 deserves consideration as a potential therapy for NAFLD.

Lipoic acid inhibits adiponectin production in 3T3-L1 adipocytes

Lipoic acid (LA) is a naturally occurring compound with antioxidant properties. Recent attention has been focused on the potential beneficial effects of LA on obesity and related metabolic disorders. Dietary supplementation with LA prevents insulin resistance and upregulates adiponectin, an insulin-sensitizing adipokine, in obese rodents. The aim of this study was to investigate the direct effects of LA on adiponectin production in cultured adipocytes, as well as the potential signaling pathways involved. For this purpose, fully differentiated 3T3-L1 adipocytes were treated with LA (1-500 μM) during 24 h. The amount of adiponectin secreted to media was detected by ELISA, while adiponectin mRNA expression was determined by RT-PCR. Treatment with LA induced a dose-dependent inhibition on adiponectin gene expression and protein secretion. Pretreatment with the PI3K inhibitor LY294002 inhibited adiponectin secretion and mRNA levels, and significantly potentiated the inhibitory effect of LA on adiponectin secretion. The AMPK activator AICAR also reduced adiponectin production, but surprisingly, it was able to reverse the LA-induced inhibition of adiponectin. The JNK inhibitor SP600125 and the MAPK inhibitor PD98059 did not modify the inhibitory effect of LA on adiponectin. In conclusion, our results revealed that LA reduces adiponectin secretion in 3T3-L1 adipocytes, which contrasts with the stimulation of adiponectin described after in vivo supplementation with LA, suggesting that an indirect mechanism or some in vivo metabolic processing is involved.

Effects of lipoic acid on AMPK and adiponectin in adipose tissue of low- and high-fat-fed rats

BACKGROUND

Lipoic acid (LA) is an antioxidant with antiobesity and antidiabetic properties. Adiponectin is an adipokine with potent anti-inflammatory and insulin-sensitizing properties. AMP-activated protein kinase (AMPK) is a key enzyme involved in cellular energy homeostasis. Activation of AMPK has been considered as a target to reverse the metabolic abnormalities associated with obesity and type 2 diabetes.

AIM OF THE STUDY

The aim of this study was to determine the effects of LA on AMPK phosphorylation and adiponectin production in adipose tissue of low-fat (control diet) and high-fat diet-fed rats.

RESULTS

Dietary supplementation with LA reduced body weight and adiposity in control and high-fat-fed rats. LA also reduced basal hyperinsulinemia as well as the homeostasis model assessment (HOMA) levels, an index of insulin resistance, in high-fat-fed rats, which was in part independent of their food intake lowering actions. Furthermore, AMPK phosphorylation was increased in white adipose tissue (WAT) from LA-treated rats as compared with pair-fed animals. Dietary supplementation with LA also upregulated adiponectin gene expression in WAT, while a negative correlation between adiposity-corrected adiponectin levels and HOMA index was found. Our present data suggest that the ability of LA supplementation to prevent insulin resistance in high-fat diet-fed rats might be related in part to the stimulation of AMPK and adiponectin in WAT.

Role of cardiotrophin-1 in obesity and insulin resistance

Cardiotrophin-1 (CT-1) is a member of the gp130 family of cytokines. In a recent study we examined the metabolic features of ct-1 null mice and the effects on body composition, glucose and lipid metabolism of acute and chronic administration of recombinant CT-1. Our data revealed that CT-1 is a key regulator of energy metabolism with potential applications in the treatment of obesity and the metabolic syndrome. This commentary discusses the significance of these findings in the context of other key studies in the field of obesity and insulin resistance.

Cardiotrophin-1 is a key regulator of glucose and lipid metabolism

Cardiotrophin-1 (CT-1) is a member of the gp130 family of cytokines. We observed that ct-1(-/-) mice develop mature-onset obesity, insulin resistance, and hypercholesterolemia despite reduced calorie intake. Decreased energy expenditure preceded and accompanied the development of obesity. Acute treatment with rCT-1 decreased blood glucose in an insulin-independent manner and increased insulin-stimulated AKT phosphorylation in muscle. These changes were associated with stimulation of fatty acid oxidation, an effect that was absent in AMPKα2(-/-) mice. Chronic rCT-1 treatment reduced food intake, enhanced energy expenditure, and induced white adipose tissue remodeling characterized by upregulation of genes implicated in the control of lipolysis, fatty acid oxidation, and mitochondrial biogenesis and genes typifying brown fat phenotype. Moreover, rCT-1 reduced body weight and corrected insulin resistance in ob/ob and in high-fat-fed obese mice. We conclude that CT-1 is a master regulator of fat and glucose metabolism with potential applications for treatment of obesity and insulin resistance.

A dysregulation in CES1, APOE and other lipid metabolism-related genes is associated to cardiovascular risk factors linked to obesity

OBJECTIVE

The aim of the present study was to investigate the relationship between the differential expression of genes related to lipid metabolism in subcutaneous adipose tissue and metabolic syndrome features in lean and obese subjects with habitual high fat intake.

METHODS

Microarray and RT-PCR analysis were used to analyze and validate differential gene expression in subcutaneous abdominal adipose tissue samples from lean and obese phenotype subjects.

RESULTS

Several genes and transcripts involved in lipolysis were down-regulated, such as AKAP1, PRKAR2B, Gi and CIDEA, whereas NPY1R and CES1 were up-regulated, when comparing obese to lean subjects. Similarly, transcripts associated with cholesterol and lipoprotein metabolism showed a differential expression, with APOE and ABCA being decreased and VLDLR being increased in obese versus lean subjects. In addition, positive correlations were found between different markers of the metabolic syndrome and CES1 and NPY1R mRNA expressions, while APOE showed an inverse association with some of them.

CONCLUSION

Different expression patterns in transcripts encoding for proteins involved in lipolysis and lipoprotein metabolism were found between lean and obese subjects. Moreover, the dysregulation of genes such as CES1 and APOE seems to be associated with some physiopathological markers of insulin resistance and cardiovascular risk factors in obesity.

Vitamin C inhibits leptin secretion and some glucose/lipid metabolic pathways in primary rat adipocytes

Antioxidant-based treatments are emerging as an interesting approach to possibly counteract obesity fat accumulation complications, since this is accompanied by an increased systemic oxidative stress. The aim of this study was to analyze specific metabolic effects of vitamin C (VC) on epididymal primary rat adipocytes. Cells were isolated and incubated for 72 h in culture medium, in the absence or presence of 1.6 nM insulin, within a range of VC concentrations (5-1000 microM). Glucose- and lipid-related variables as well as the secretion/expression patterns of several obesity-related genes were assessed. It was observed that VC dose dependently inhibited glucose uptake and lactate production, and also reduced glycerol release in both control and insulin-treated cells. Also, VC caused a dramatic concentration-dependent fall in leptin secretion especially in insulin-stimulated cells. In addition, VC (200 microM) induced Cdkn1a and Casp8, partially inhibited Irs3, and together with insulin drastically reduced Gpdh (listed as Gpd1 in the MGI database) gene expressions. Finally, VC and insulin down-regulatory effects were observed on extracellular and intracellular reactive oxygen species production respectively. In summary, this experimental assay describes a specific effect of VC in isolated rat adipocytes on glucose and fat metabolism, and on the secretion/expression of important obesity-related proteins.

Association between leptin receptor (LEPR) and brain-derived neurotrophic factor (BDNF) gene variants and obesity: a case-control study

INTRODUCTION

Human and animal studies provide evidence for a relevant role of the leptin receptor (LEPR) and the brain-derived neurotrophic factor (BDNF) genes in energy homeostasis.

AIM

To assess the association between human LEPR and BDNF genetic variants with adult obesity.

DESIGN AND METHODS

Case-control study in Pamplona (Navarra, Spain) with adult obese subjects (n = 159) and normal weight controls (n = 154). Four common polymorphisms of the LEPR gene (Lys109Arg, Gln223Arg, Ser343Ser, Lys656Asn) and 17 variants of the BDNF gene, including the Val66Met variant, were genotyped.

RESULTS

No significant case-control differences were found in allele/genotype frequencies after adjusting for relevant co-variates. Haplotype analysis did not detect any significant association between LEPR or BDNF variants and obesity. No associations were found between LEPR variants and serum leptin levels.

CONCLUSIONS

Our results do not support a major role of LEPR or BDNF common polymorphisms in multifactorial adult obesity.

Lipoic acid prevents body weight gain induced by a high fat diet in rats: effects on intestinal sugar transport

Several studies have suggested that oxidative stress might cause and aggravate the inflammatory state associated with obesity and could be the link between excessive weight gain and its related disorders such as insulin resistance and cardiovascular diseases. Thus, antioxidant treatment has been proposed as a therapy to prevent and manage obesity and associated complications. Therefore, the aim of the present study was to investigate the effects of supplementation of a standard or high fat diet with the antioxidant lipoic acid (LA) during 56 days, on body weight gain, adiposity, feed efficiency and intestinal sugar absorption, in male Wistar rats. LA supplementation induced a lower body weight gain and adipose tissue size in both control or high fat fed rats accompanied by a reduction in food intake. The group fed on a high fat diet and treated with LA (OLIP group) showed a lower body weight gain than its corresponding Pair-Fed (PF) group (P < 0.05), which received the same amount of food than LA-treated animals but with no LA. In fact, LA induced a reduction on feed efficiency and also significantly decreased intestinal alpha-methylglucoside (alpha-MG) absorption both in lean and obese rats. These results suggest that the beneficial effects of dietary supplementation with LA on body weight gain are mediated, at least in part, by the reduction observed in food intake and feed efficiency. Furthemore, the inhibitory action of LA on intestinal sugar transport could explain in part the lower feed efficiency observed in LA-treated animals and therefore, highlighting the beneficial effects of LA on obesity.

Association between obesity and insulin resistance with UCP2-UCP3 gene variants in Spanish children and adolescents

A number of studies have yielded controversial results on the association between polymorphisms in UCP2 and UCP3 genes with obesity and its comorbidities. The discrepancy among studies might be partially explained by the lack of consideration of the effect of adjacent loci in the same haplotype and the exclusion of key lifestyle factors in the statistical analysis. In this study, we have assessed the association between three genetic variants of the UCP2-UCP3 gene cluster, the -866G/A (rs659366) and the 45bp insertion (in position 173247 of the AC019121) of the UCP2 gene, the -55C/T (rs1800849) polymorphism of the UCP3 gene and their estimated haplotypes with childhood obesity and insulin resistance. This research was designed as a case-control study and information about several environmental parameters such as leisure time physical activity and time spent watching television were included. The study sample consisted in 193 obese children and adolescents (cases) and 170 controls aged 6-18. We found that the individual polymorphisms were not associated with obesity, but the (-866G; rs659366)-(Del; 45bp)-(-55T; rs1800849) haplotype was significantly associated with obesity and its presence in the control group increased about nine times the insulin resistance risk. Thus, the (-866A; rs659366)-(Ins; 45bp)-(-55C; rs1800849) haplotype may protect against insulin resistance in the obese population group.

Linoleic acid decreases leptin and adiponectin secretion from primary rat adipocytes in the presence of insulin

Obesity rates have dramatically increased over the last few decades and, at the same time, major changes in the type of fatty acid intake have occurred. Linoleic acid, an n-6 polyunsaturated fatty acid, is an essential fatty acid occurring in high amounts in several western diets. A potential role of this fatty acid on obesity has been suggested. Controversial effects of linoleic acid on insulin sensitivity have also been reported. Thus, the aim of this study was to examine the direct effects of linoleic acid on leptin and adiponectin production, two adipokines known to influence weight gain and insulin sensitivity. Because insulin-stimulated glucose metabolism is an important regulator of leptin production, the effects of linoleic acid on adipocyte metabolism were also examined. For this purpose, isolated rat adipocytes were incubated with linoleic acid (1-200 microM) in the absence or presence of insulin. Linoleic acid (1-200 microM) significantly decreased insulin-stimulated leptin secretion and expression (P < 0.05), however, no changes in basal leptin production were observed. Linoleic acid also induced a significant decrease (approximately 20%) in adiponectin secretion (P < 0.05), but only in the presence of insulin and at the highest concentration tested (200 microM). This fatty acid did not modify either glucose uptake or lactate production and the percentage of glucose metabolized to lactate was not changed either. Together, these results suggest that linoleic acid seems to interfere with other insulin signalling pathway different from those controlling glucose uptake and metabolism, but involved in the regulation of leptin and adiponectin production.

Eicosapentaenoic acid actions on adiposity and insulin resistance in control and high-fat-fed rats: role of apoptosis, adiponectin and tumour necrosis factor-alpha

n-3 PUFA have shown potential anti-obesity and insulin-sensitising properties. However, the mechanisms involved are not clearly established. The aim of the present study was to assess the effects of EPA administration, one of the n-3 PUFA, on body-weight gain and adiposity in rats fed on a standard or a high-fat (cafeteria) diet. The actions on white adipose tissue lipolysis, apoptosis and on several genes related to obesity and insulin resistance were also studied. Control and cafeteria-induced overweight male Wistar rats were assigned into two subgroups, one of them daily received EPA ethyl ester (1 g/kg) for 5 weeks by oral administration. The high-fat diet induced a very significant increase in both body weight and fat mass. Rats fed with the cafeteria diet and orally treated with EPA showed a marginally lower body-weight gain (P = 0.09), a decrease in food intake (P < 0.01) and an increase in leptin production (P < 0.05). EPA administration reduced retroperitoneal adipose tissue weight (P < 0.05) which could be secondary to the inhibition of the adipogenic transcription factor PPARgamma gene expression (P < 0.001), and also to the increase in apoptosis (P < 0.05) found in rats fed with a control diet. TNFalpha gene expression was significantly increased (P < 0.05) by the cafeteria diet, while EPA treatment was able to prevent (P < 0.01) the rise in this inflammatory cytokine. Adiposity-corrected adiponectin plasma levels were increased by EPA. These actions on both TNFalpha and adiponectin could explain the beneficial effects of EPA on insulin resistance induced by the cafeteria diet.

Sp1-mediated transcription is involved in the induction of leptin by insulin-stimulated glucose metabolism

We have previously demonstrated that insulin-stimulated glucose metabolism, and not insulin per se, mediates the effects of insulin to increase the transcriptional activity of the leptin promoter in adipocytes. Here, we sought to identify the specific cis-acting DNA elements required for the upregulation of leptin gene transcription in response to insulin-mediated glucose metabolism. To accomplish this, 3T3-L1 cells and primary rat adipocytes were transfected with a series of luciferase reporter genes containing portions of the mouse leptin promoter. Using this method, we identified an element between -135 and -95 bp (relative to the transcriptional start site) that mediated transcription in response to insulin-stimulated glucose metabolism in adipocytes. This effect was abolished by incubation with 2-deoxy-d-glucose, a competitive inhibitor of glucose metabolism. Gel shift electrophoretic mobility shift assays confirmed that the stimulatory effect of insulin-mediated glucose metabolism on leptin transcription was mediated by a previously identified Sp1 site. Consistent with these findings, incubation of primary rat adipocytes with WP631, a specific inhibitor of specificity protein (Sp)1-dependent transcription, inhibited glucose- and insulin-stimulated, but not basal, leptin secretion. Together, these findings support a key role for Sp1 in the transcriptional activation of the leptin gene promoter by insulin-mediated glucose metabolism.

A novel mutation Thr162Arg of the melanocortin 4 receptor gene in a Spanish children and adolescent population

OBJECTIVE

The melanocortin 4 receptor gene (MC4R) is involved in body weight regulation. While many studies associated MC4R mutations with childhood obesity, information on MC4R mutations in Spanish children and adolescents is lacking. Our objective was to screen a population of children and adolescents from the north of Spain (Navarra) for MC4R mutations and to study the phenotypes of carriers and their families. In addition, functional assays were performed for a novel MC4R mutation.

METHODS

The study was composed of 451 Spanish children and adolescents (49% boys), aged 5-18 year. According to the International Obesity Task Force (IOTF) criteria, the groups included 160 obese, 132 overweight and 159 normal-weight control subjects.

RESULTS

One novel (Thr162Arg) and three known nonsynonymous mutations in the MC4R gene (Ser30Phe, Thr150Ile, Ala244Glu) were detected heterozygously. The MC4R mutations were found in three male (one obese and two overweight) and two female subjects (one obese and one overweight). The novel mutation did not appear to lead to an impaired receptor function. An unequivocal relationship of MC4R mutations with obesity in pedigrees together with an impaired function of the encoded receptor could not be established for any of the mutations.

CONCLUSIONS

The presence of heterozygous MC4R mutations in obese and overweight subjects indicates that these mutations may be a susceptibility factor for obesity development, but lifestyle factors, such as exercise or sedentary activities, may modify their effect.

Predictor factors for childhood obesity in a Spanish case-control study

OBJECTIVE

The aim of this study was to identify and characterize factors associated with childhood obesity risk related to lifestyle and perinatal life influences (dietary pattern, physical activity, family history of obesity, breast-feeding, sedentary behavior, and birth weight) in a case-control study design.

METHODS

Cases were 185 obese (body mass index >97th percentile) children and adolescents (6-18 y old) from the Navarra region of Spain and control subjects were matched by sex and age. Anthropometric data were collected, and a personal interview about lifestyle parameters (dietary patterns, physical activity, family history of obesity, breast-feeding and sedentary behaviors) was performed with each participant. Conditional logistic regression was used to identify predictive factors of obesity.

RESULTS

Leisure time physical activity proved to be a protector factor against obesity (odds ratio [OR] 0.94, 95% confidence interval [CI] 0.92-0.96), whereas family history of obesity (OR 4.18, 95% CI 2.20-8.62), watching television (OR 2.02, 95% CI 1.09-3.77), and sugar-sweetened beverage consumption (OR 1.74, 95% CI 1.05-2.89) were associated with a higher obesity risk.

CONCLUSION

Our results suggest that leisure time physical activity, family history of obesity, watching television, and sugar-sweetened beverage consumption are important predictive variables for childhood obesity, whereas other factors including breast-feeding, birth weight, and time spent sleeping did not appear to play an important role in the development of childhood obesity.

Conjugated linoleic acid inhibits glucose metabolism, leptin and adiponectin secretion in primary cultured rat adipocytes

Conjugated linoleic acid (CLA) supplementation has been reported to induce insulin resistance in animals and humans, however, the underlying mechanisms remain unclear. The aim of this study was to examine the direct effects of CLA on leptin and adiponectin secretion, two hormones with actions known to influence insulin sensitivity. Isolated rat adipocytes were incubated with CLA (1-200microM) in the absence and presence of insulin (1.6nM). CLA inhibited both basal and insulin-stimulated leptin gene expression and secretion (-30 to -40%, P<0.05-0.01). CLA also inhibited basal adiponectin production (-20 to -40%, P<0.05-0.01), but not in the presence of insulin. CLA (50-200muM) decreased basal glucose uptake (P<0.05-0.01) and significantly increased the proportion of glucose metabolized to lactate (P<0.01). Insulin treatment partially prevented the inhibitory effects of CLA on glucose uptake and induced a significant increase (P<0.05-0.01) in the percentage of glucose metabolized to lactate. A strong inverse relationship was observed between the increase in the anaerobic utilization of glucose and the decreases of both leptin and adiponectin secretion. In addition, lipolysis and the expression of the adipogenic transcription factor PPARgamma were decreased by CLA. These results indicate that CLA inhibits leptin and adiponectin secretion and suggest that increased anaerobic metabolism of glucose may be involved in these effects. The inhibition of PPARgamma could also mediate the inhibition of adiponectin induced by CLA. Furthermore, the inhibition of leptin and adiponectin production induced by CLA may contribute to insulin resistance observed in CLA-treated animals and humans.

Differences in short-term metabolic responses to a lipid load in lean (resistant) vs obese (susceptible) young male subjects with habitual high-fat consumption

OBJECTIVE

To determine the role of macronutrients oxidation ability in the postprandial response to a high lipid load in the mechanisms conferring resistance or susceptibility to obesity.

SUBJECTS AND DESIGN

Nine lean and nine obese young male subjects with habitual similar high-fat intake (>40 % of energy) and comparable physical activity were selected and categorized as 'resistant', those who remained lean (body mass index (BMI) <25 kg/m2), and 'susceptible', those who were obese (BMI>30 kg/m2). Fasting blood samples were taken for the evaluation of blood metabolic and hormonal variables. Resting metabolic rate (RMR) and substrates oxidation were measured by indirect calorimetry, in the fasting state and every 30 min for 3 h after a rich lipid meal (fat 94.7%) supplied to cover the 50% of the volunteers energy requirements. The study was performed at the Metabolic Unit of the University of Navarra.

RESULTS

Fasting RMR and lipid oxidation were higher in obese-susceptible subjects. However, similar values were found in both groups after adjustment for fat mass and free fat mass. The cumulative postprandial fat oxidation was also similar in both groups (despite having different tissue metabolic activity), whereas cumulative carbohydrate oxidation was lower in the obese-susceptible group. The thermic effect of food (% of dietary induced thermogenesis) was lower (P<0.05) in the susceptible-obese subjects. The energy and fat balance were more positive in the obesity-susceptible individuals after the high fat load, who also showed higher fasting homeostatic model assessment index, low-density lipoprotein-cholesterol and triacylglyceride levels, hyperleptinemia and hypoadiponectinemia.

CONCLUSION

Lean-resistant individuals came closer to achieving fat balance than obese-susceptible subjects. These metabolic and hormonal differences are probably genetically determined.