Lactobacillus rhamnosus GG administration partially prevents diet-induced insulin resistance in rats: a comparison with its heat-inactivated parabiotic

Insulin resistance and type 2 diabetes are obesity-related health alterations, featuring an ever-increasing prevalence. Besides inadequate feeding patterns, gut microbiota alterations stand out as potential contributors to these metabolic disturbances. The aim of this study was to investigate whether the administration of a probiotic (Lactobacillus rhamnosus GG) effectively prevents diet-induced insulin resistance in rats and to compare these potential effects with those exerted by its heat-inactivated parabiotic. For this purpose, 34 male Wistar rats were fed a standard or a high-fat high-fructose diet, alone or supplemented with viable or heat-inactivated Lactobacillus rhamnosus GG. The body and white adipose tissue weight increases, induced by the obesogenic diet, were prevented by probiotic and parabiotic administration. The trend towards higher basal glucose levels and significantly higher serum insulin concentration observed in the non-treated animals fed with the obesogenic diet were effectively reverted by both treatments. Similar results were also found for serum adiponectin and leptin, whose levels were brought back by the probiotic and parabiotic administration to values similar to those of the control animals. Noteworthily, parabiotic administration significantly reduced skeletal muscle triglyceride content and activated CPT-1b compared to the non-treated animals. Finally, both treatments enhanced Akt and AS160 phosphorylation in the skeletal muscle compared to the non-treated animals; however, only parabiotic administration increased GLUT-4 protein expression in this tissue. These results suggest that heat-inactivated Lactobacillus rhamnosus GG seem to be more effective than its probiotic of origin in preventing high-fat high-fructose diet-induced insulin resistance in rats.

Role of chemerin in the control of glucose homeostasis

Chemerin is an adipokine produced by the white adipose tissue and other tissues, which plays various roles in the pathogenesis of inflammatory and metabolic diseases in multiple organs. The present review aims at gathering scientific evidence reported in the last ten years, concerning the relationship of chemerin with alterations of glycaemic control, such as insulin resistance, type 2 diabetes and gestational diabetes in humans. Although the vast majority of the studies have shown a positive correlation between the chemerin level and a bad glycaemic control, a general consensus has not been reached. The reported results come from case-control and observational longitudinal studies, thereby limiting their interpretation. In fact, it cannot be stated whether insulin resistance and diabetes lead to an increase in chemerin levels or, on the contrary, if high levels of chemerin contribute to an impaired glycaemic control. Elevated levels of circulating chemerin are also associated with gestational diabetes mellitus. Chemerin gene polymorphisms could be proposed as mediators of glucose-related diseases. Nevertheless, to date very little is known about their implication in glucose metabolism. With regard to the mechanisms of action, chemerin impairs insulin cascade signaling by acting on several proteins of this cascade and by inducing inflammation.

Pterostilbene modifies triglyceride metabolism in hepatic steatosis induced by high-fat high-fructose feeding: a comparison with its analog resveratrol

The use of phenolic compounds as a new therapeutic approach against NAFLD has emerged recently. In the present study, we aim to study the effect of pterostilbene in the prevention of liver steatosis developed as a consequence of high-fat (saturated) high-fructose feeding, by analysing the changes induced in metabolic pathways involved in triglyceride accumulation. Interestingly, a comparison with the anti-steatotic effect of its parent compound resveratrol will be made for the first time. Rats were distributed into 5 experimental groups and fed either a standard laboratory diet or a high-fat high-fructose diet supplemented with or without pterostilbene (15 or 30 mg per kg per d) or resveratrol (30 mg per kg per d) for 8 weeks. Serum triglyceride, cholesterol, NEFA and transaminase levels were quantified. Liver histological analysis was carried out by haematoxylin-eosin staining. Different pathways involved in liver triglyceride metabolism, including fatty acid synthesis, uptake and oxidation, triglyceride assembly and triglyceride release, were studied. Pterostilbene was shown to partially prevent high-fat high-fructose feeding induced liver steatosis in rats, demonstrating a dose-response pattern. In this dietary model, it acts mainly by reducing de novo lipogenesis and increasing triglyceride assembly and release. Improvement in mitochondrial functionality was also appreciated. At the same dose, the magnitude of pterostilbene and resveratrol induced effects, as well as the involved mechanisms of action, were similar.

The influence of dietary conditions in the effects of resveratrol on hepatic steatosis

Non-alcoholic fatty liver disease (NAFLD) is considered the major cause for the development of chronic liver alterations.

Has the adipokine profile an influence on the catch-up growth type in small for gestational age infants?

Infants born small for gestational age (SGA) are at increased risk of perinatal morbidity, persistent short stature, and metabolic alterations in later life. Moreover, the post-natal growth pattern of SGA infants may be an important contributor to health outcomes later in life, which can be influenced by adipokines. The aims of this study were to compare plasma adipokine profiles (leptin, adiponectin, vaspin, chemerin, and nephroblastoma overexpressed (NOV/CCN3)) among SGA newborns aged 3 months, with low, normal, or high catch-up, to search for potential differences between males and females and to analyze the evolution of several adipokines in plasma from SGA newborns between 3 and 24 months. This prospective, longitudinal study was addressed in SGA Caucasian subjects at Hospital Universitario de Álava-Txagorritxu. We observed that infants with fast catch-up showed significantly lower birth weight than the other two groups. As far as adipokines are concerned, they could have an influence on catch-up type because differences among the three experimental groups were found. It may be proposed that health prognoses in infants with slow and fast catch-up are opposite, not only in adulthood but also during their first months. Finally, adipokine evolution patterns during the first 24 months of age differ, depending on the adipokine, and 24-month-old males show lower levels of leptin, adiponectin, and omentin than females.

A randomised controlled trial of a program based on the theory of planned behavior to promote fruit and vegetable intake among schoolchildren: PROFRUVE study protocol

BACKGROUND

The PROFRUVE study is a controlled intervention based on the Theory of Planned Behavior (TPB), which follows those behavioral theories that have proved to be the most effective at changing infant fruit and vegetable (FV) intake pattern. The main purpose of the study is to evaluate the effectiveness of an intervention program in increasing FV consumption in schoolchildren aged 8 to 10 and based on TPB.

METHODS

Eligible classrooms within schools from Vitoria-Gasteiz (Basque Country, Spain) will be randomly assigned to the intervention (classrooms n = 4; children n = 86) or control (classrooms n = 4; children n = 86) group. The intervention group will receive 14 sessions of 60 min during an academic year (October to June). These sessions, designed by a multidisciplinary team, are based on TPB and are directed at modifying determinants of behavior (attitudes, subjective norms, perceived behavioral control and intention of consumption), and intake of FV itself. Both the process and the evolution of consumption and determinants of behavior will be evaluated (before, during, shortly after and a year after) using validated surveys, 7 day food records, 24 h reminders and questionnaires.

DISCUSSION

This study will provide a valid and useful tool to achieve changes in the consumption of FV at school level. A negative result will be helpful in redefining new strategies in the framework of changing habits in the consumption of FV.

TRIAL REGISTRATION

This study has been retrospectively registered at ClinicalTrials.gov. Identifier: NCT03400891 . Data registered: 17/01/2018.

Comparative effects of energy restriction and resveratrol intake on glycemic control improvement

Resveratrol (RSV) has been proposed as an energy restriction mimetic. This study aimed to compare the effects of RSV and energy restriction on insulin resistance induced by an obesogenic diet. Any additive effect of both treatments was also analyzed. Rats were fed a high-fat high-sucrose diet for 6 weeks. They were then distributed in four experimental groups which were either fed a standard control diet (C), or treated with RSV (30 mg/kg/d), or submitted to energy restriction (R, 15%), or treated with RSV and submitted to energy restriction (RR). A glucose tolerance test was performed, and serum glucose, insulin, fructosamine, adiponectin, and leptin concentrations determined. Muscle triacylglycerol content and protein expression of insulin receptor (IRβ), protein kinase B (Akt), Akt substrate of 160 kDa (AS160) and glucose transporter 4 (GLUT-4) were measured. In RSV rats, fructosamine concentrations were reduced, HOMA-IR remained unchanged, but glucose tolerance was improved, without changes in phosphorylation of IRβ, Akt, and AS160 or in GLUT-4 protein expression. Rats under energy restriction showed an improvement in all the markers related to glycemic control, as well as increased phosphorylation of AS160 and protein expression of GLUT-4. In rats from RR group the results were similar to R group, with the exception of IRβ and Akt phosphorylation, which were increased. In conclusion, mild energy restriction is more efficient than intake of RSV within a standard balanced diet, and acts by means of a different mechanism from that of RSV. No additive effects between RSV and energy restriction were observed. © 2017 BioFactors, 43(3):371-378, 2017.

Olive oil in the prevention and management of type 2 diabetes mellitus: a systematic review and meta-analysis of cohort studies and intervention trials

Background/Objectives:

Olive oil (OO) as food is composed mainly of fatty acids and bioactive compounds depending from the extraction method. Both had been discussed as health promoting with still open questions. Thus, we conducted a meta-analysis to illustrate the impact of this food on type 2 diabetes (T2D) by investigating the association between OO intake and risk of T2D, and the effect of OO intake in the management of T2D.

Subjects/Methods:

Searches were performed in PubMed, Cochrane Library and google scholar. First, we conducted a random effect meta-analysis of prospective cohort studies and trials investigating the association between OO and risk of T2D. Second, a meta-analysis was performed to detect the effects of olive oil on glycemic control in patients with T2D.

Results:

Four cohort studies including 15 784 T2D cases and 29 trials were included in the meta-analysis. The highest OO intake category showed a 16% reduced risk of T2D (RR: 0.84; 95% CI: 0.77, 0.92) compared with the lowest. However, we observed evidence for a nonlinear relationship. In T2D patients OO supplementation resulted in a significantly more pronounced reduction in HbA1c (MD: −0.27% 95% CI: −0.37, −0.17) and fasting plasma glucose (MD: −0.44 mmol l⁻¹; 95% CI −0.66, −0.22) as compared with the control groups.

Conclusions:

This meta-analysis provides evidence that the intake of OO could be beneficial for the prevention and management of T2D. This conclusion regards OO as food, and might not been valid for single components comprising this food.

MicroRNAs involved in the browning process of adipocytes

The present review focuses on the role of miRNAs in the control of white adipose tissue browning, a process which describes the recruitment of adipocytes showing features of brown adipocytes in white adipose tissue. MicroRNAs (miRNAs) are a class of short non-coding RNAs (19-22 nucleotides) involved in gene regulation. Although the main effect of miRNAs is the inhibition of the translational machinery, thereby preventing the production of the protein product, the activation of protein translation has also been described in the literature. In addition to modifying translation, miRNAs binding to its target mRNAs also trigger the recruitment and association of mRNA decay factors, leading to mRNA destabilization, degradation, and thus to the decrease in expression levels. Although a great number of miRNAs have been reported to potentially regulate genes that play important roles in the browning process, only a reduced number of studies have demonstrated experimentally an effect on this process associated to changes in miRNA expressions, so far. These studies have shown, by using either primary adipocyte cultures or experimental models of mice (KO mice, mice overexpressing a specific miRNA), that miR-196a, miR-26, and miR-30 are needed for browning process development. By contrast, miR-155, miR-133, miR-27b, and miR-34 act as negative regulators of this process [corrected]. Further studies are needed to fully describe the miRNA network-involved white adipose tissue browning regulation.

Potential application of non-flavonoid phenolics in diabetes: antiinflammatory effects

Polyphenols are members of a very large family of plant-derived compounds that may have beneficial effects on human health, and thus their study has become an increasingly important area of human nutrition research. Considering that it is increasingly accepted that chronic sub-acute inflammation plays an important role in the development of insulin resistance and of diabetes in animals and in humans, the aim of the present review is to compile information concerning the anti-inflammatory effects of non-flavonoid polyphenols on diabetes prevention and/or treatment. Most of these studies have been carried out with different cultured cells and using animal models displaying different types of diabetes, such as diabetes induced by streptozotocin or streptozotocin-nicotinamide, genetic diabetes or diabetes induced by high-fat feeding. In general terms, non-flavonoid polyphenols reduce the production of inflammatory mediators, such as IL-1β, IL-8, MCP-1, COX-2 or iNOS in these animal models of diabetes. This effect is accompanied in the vast majority of these studies by improved insulin action. In addition, some of the non-flavonoid polyphenols are also able to ameliorate or prevent several pathological alterations associated with the development of diabetes, such as nephropathy, cardiopathy or retinopathy. Very little information has been reported with regard to human studies to date. Thus, new studies are needed to confirm if the beneficial effects observed in preclinical studies can apply to human beings.

Shifts in microbiota species and fermentation products in a dietary model enriched in fat and sucrose

The gastrointestinal tract harbours a 'superorganism' called the gut microbiota, which is known to play a crucial role in the onset and development of diverse diseases. This internal ecosystem, far from being a static environment, can be manipulated by diet and dietary components. Feeding animals with high-fat sucrose (HFS) diets entails diet-induced obesity, a model which is usually used in research to mimic the obese phenotype of Western societies. The aim of the present study was to identify gut microbiota dysbiosis and associated metabolic changes produced in male Wistar rats fed a HFS diet for 6 weeks and compare it with the basal microbial composition. For this purpose, DNA extracted from faeces at baseline and after treatment was analysed by amplification of the V4-V6 region of the 16S ribosomal DNA (rDNA) gene using 454 pyrosequencing. Short-chain fatty acids, i.e. acetate, propionate and butyrate, were also evaluated by gas chromatography-mass spectrometry. At the end of the treatment, gut microbiota composition significantly differed at phylum level (Firmicutes, Bacteroidetes and Proteobacteria) and class level (Erisypelotrichi, Deltaproteobacteria, Bacteroidia and Bacilli). Interestingly, the class Clostridia showed a significant decrease after HFS diet treatment, which correlated with visceral adipose tissue, and is likely mediated by dietary carbohydrates. Of particular interest, Clostridium cluster XIVa species were significantly reduced and changes were identified in the relative abundance of other specific bacterial species (Mitsuokella jalaludinii, Eubacterium ventriosum, Clostridium sp. FCB90-3, Prevotella nanceiensis, Clostridium fusiformis, Clostridium sp. BNL1100 and Eubacterium cylindroides) that, in some cases, showed opposite trends to their relative families. These results highlight the relevance of characterising gut microbial population differences at species level and contribute to understand the plausible link between diet and specific gut bacterial species that are able to influence the inflammatory status, intestinal barrier function and obesity development.

Pterostilbene improves glycaemic control in rats fed an obesogenic diet: involvement of skeletal muscle and liver

This study aims to determine whether pterostilbene improved glycaemic control in rats showing insulin resistance induced by an obesogenic diet.

Quercetin can reduce insulin resistance without decreasing adipose tissue and skeletal muscle fat accumulation

Quercetin exhibits a wide range of biological functions. The first aim of the present work was to analyze the effects of quercetin on fat accumulation in adipose tissue and glycemic control in rats. Any potential involvement of muscle fatty acid oxidation in its effect on glycemic control was also assessed. Animals were fed a high-fat high-sucrose diet either supplemented with quercetin (30 mg/kg body weight/day), or not supplemented, for 6 weeks. One week before killing, a glucose tolerance test was carried out. Muscle triacylglycerol content, serum glucose, insulin, fructosamine and free fatty acids were measured, and homeostatic model assessment for insulin resistance (HOMA-IR) was calculated. The activities of lipogenic enzymes and lipoprotein lipase in adipose tissue, carnitine palmitoyl transferase-1b (CPT-1b) and citrate synthase in skeletal muscle, and the expression of several genes, ACO, CD36, CPT-1b, PPAR-α, PGC-1α, UCP3, TFAM and COX-2 in skeletal muscle were analyzed. Quercetin caused no significant reduction in body weight or adipose tissue sizes. However, fructosamine, basal glucose and insulin, and consequently HOMA-IR, were significantly reduced by quercetin. No changes were observed in the activity of lipogenic enzymes and lipoprotein lipase. Muscle triacylglycerol content was similar in both experimental groups. The expression of ACO, CD36, CPT-1b, PPAR-α, PGC-1α, UCP3, TFAM and COX-2 remained unchanged. It can be concluded that quercetin is more effective as an anti-diabetic than as an anti-obesity biomolecule. The improvement in insulin resistance induced by this flavonoid is not mediated by a delipidating effect in skeletal muscle.

The combination of resveratrol and conjugated linoleic acid attenuates the individual effects of these molecules on triacylglycerol metabolism in adipose tissue

PURPOSE

The combination of resveratrol + conjugated linoleic acid (RSV + CLA) did not show the body fat-lowering effect exhibited by these molecules when administered separately. This study aimed to find metabolic explanations for this situation in an experimental model of diet-induced obesity.

METHODS

Thirty-six male Wistar rats were divided into four groups: rats treated with saline (control), resveratrol (RSV), conjugated linoleic acid (CLA) and a combination of these molecules (RSV + CLA).

RESULTS

Rats treated with RSV + CLA did not show the reduction in heparin-releasable lipoprotein lipase (HR-LPL) and fatty acid synthase activities observed in RSV group or the increased HSL expression found in RSV and CLA groups. These animals showed reduced sirtuin 1 expression and CLA isomer amounts in adipose tissue. Finally, intracellular Ca(2+) concentration was increased.

CONCLUSION

The attenuation of the effects induced in adipose tissue triacylglycerol metabolism by RSV and CLA separately, such as the decrease in lipogenesis and fatty acid uptake and the increase in lipolysis, contributes to explain the lack of body fat-lowering effect of the combination RSV + CLA.

Several statins increase body and liver fat accumulation in a model of metabolic syndrome

Statins are a family of drugs used in hypercholesterolemia. The aim of this study was to analyze the effect of statins on body and liver fat accumulation in obese Zucker rats. Seventy Zucker (fa/fa) rats were divided into seven groups. Rats from six statin groups were treated with pravastatin, simvastatin, atorvastatin, rosuvastatin, fluvastatin and lovastatin respectively, at a dose of 0.6 mg/kg body weight/day. After 6 weeks, liver and white adipose tissue from intra-abdominal and subcutaneous locations were dissected and weighed. Subcutaneous adipose tissue from rosuvastatin, atorvastatin, fluvastatin and lovastatin treated rats was significantly increased. Fatty acid synthase (FAS) activity was increased by the administration of fluvastatin and lovastatin, as was glucose-6-P dehydrogenase (G6PDH) by the administration of atorvastatin and lovastatin. No changes were observed in malic enzyme (ME) activity. Furthermore, heparin-releasable lipoprotein lipase (HR-LPL) was increased in all groups where the subcutaneous depot was increased, and total LPL increased only in rosuvastatin and fluvastatin-treated groups. With regard to liver, there were no changes in weight but the amount of triacylglycerols was increased in rosuvastatin group, as well as its liver damage was higher. In this group FAS and G6PDH activities were increased and no changes were observed in ME, acyl CoA oxidase (ACO) and carnitine palmitoyltransferase-1a (CPT-1a) activities. All statins, with the exception of simvastatin, worsen insulin resistance. These results show that statins have different effects on body fat accumulation. Moreover, rosuvastatin also shows a prosteatotic effect. These results should be taken into account for statin choice in prescription.

Dietary glycemic index/load and peripheral adipokines and inflammatory markers in elderly subjects at high cardiovascular risk

BACKGROUND AND AIMS

Epidemiological and clinical studies suggest that low-glycemic index diets could protect against weight gain. However, the relationship between these diets and adipokines or inflammatory markers is unclear. In the present study we examine how the dietary glycemic index (GI) and dietary glycemic load (GL) are associated with several adipokines and related metabolic risk markers of obesity and diabetes in a cross-sectional and longitudinal manner.

METHODS AND RESULTS

511 elderly community-dwelling men and women at high cardiovascular risk were recruited for the PREDIMED trial. Dietary data were collected at baseline and after 1 year of follow-up. The GI and GL were calculated. Plasma leptin, adiponectin and other metabolic risk markers were measured at baseline and after 1 year. At baseline, subjects in the highest quartiles of GI showed significantly higher levels of TNF and IL-6 than those in the lowest quartiles. Dietary GI index was negatively related to plasma leptin and adiponectin levels. After 1 year of follow-up, subjects with a higher increase in dietary GI or GL showed a greater reduction in leptin and adiponectin plasma levels. There was no association between GI or GL and the other metabolic markers measured.

CONCLUSION

Our results suggest that the consumption of high-GI or high-GL diets may modulate plasma concentrations of leptin and adiponectin, both adipostatic molecules implicated in energy balance and cardiometabolic risk.

Effects of different doses of resveratrol on body fat and serum parameters in rats fed a hypercaloric diet

Recently resveratrol, a compound naturally occurring in various plants, has been proposed as a potential anti-obesity compound. The aim of the present work was to analyse the effects of different doses of resveratrol on body fat and serum parameters in rats. Thirty-two male Sprague-Dawley rats were randomly divided into four groups and fed on a hypercaloric diet for 6 weeks. The doses oftrans-resveratrol used were 6, 30 and 60 mg/kg body weight/d in RSV1, RSV2 and RSV3 groups respectively. The stability of resveratrol when added to the diet was evaluated. Blood samples were collected, and white adipose tissue from different anatomical locations, interscapular brown adipose tissue, gastrocnemious muscles and liver were weighed. Commercial kits were used to measure serum cholesterol, glucose, triacylglycerols and non-esterified fatty acids. While the lowest dose did not have a body fat reducing effect, the intermediate dose reduced all the white adipose depots. The highest dose significantly reduced mesenteric and subcutaneous depots but not epididymal and perirenal tissues. Although the reduction in all the anatomical locations analysed was 19% in the RSV3 group, in the RSV2 group it was 24%. No significant differences among the experimental groups were found in brown adipose tissue, gastrocnemious muscle or liver weights. Serum parameters were not affected by resveratrol intake because no differences among the experimental groups were observed. These results suggest that resveratrol is a molecule with potential anti-obesity effect. The most effective of the three experimental doses was 30 mg/kg body weight/d.

High ambient temperature reverses hypothalamic MC4 receptor overexpression in an animal model of anorexia nervosa

The potential involvement of the melanocortin system in the beneficial effects of heat application in rats submitted to activity-based anorexia (ABA), an analogous model of anorexia nervosa (AN), was studied. Once ABA rats had lost 20% of body weight, half of the animals were exposed to a high ambient temperature (HAT) of 32 degrees C, whereas the rest were maintained at 21 degrees C. Control sedentary rats yoked to ABA animals received the same treatment. ABA rats (21 degrees C) showed increased Melanocortin 4 (MC4) receptor and Agouti gene Related Peptide (AgRP) expression, and decreased pro-opiomelanocortin (POMC) mRNA levels (Real Time PCR), with respect to controls. Heat application increased weight gain and food intake, and reduced running rate in ABA rats, when compared with ABA rats at 21 degrees C. However, no changes in body weight and food intake were observed in sedentary rats exposed to heat. Moreover, heat application reduced MC4 receptor, AgRP and POMC expression in ABA rats, but no changes were observed in control rats. These results indicate that hypothalamic MC4 receptor overexpression could occur on the basis of the characteristic hyperactivity, weight loss, and self-starvation of ABA rats, and suggest the involvement of hypothalamic melanocortin neural circuits in behavioural changes shown by AN patients. Changes in AgRP and POMC expression could represent an adaptative response to equilibrate energy balance. Moreover, the fact that HAT reversed hypothalamic MC4 receptor overexpression in ABA rats indicates the involvement of brain melanocortin system in the reported beneficial effects of heat application in AN. A combination of MC4 receptor antagonists and heat application could improve the clinical management of AN.

Adiposity and serum parameters in hamsters fed energy restricted diets supplemented or not with trans-10,cis-12 conjugated linoleic acid

Numerous studies have demonstrated that conjugated linoleic acid (CLA) modulates body composition, reducing body fat accumulation in various mammalian species. However, very few studies have been carried out to assess the effect of CLA on previously stored body fat. The aim of the present work was to analyse the effectiveness of trans-10,cis-12 CLA in improving alterations produced by high-fat feeding in body fat and serum parameters when it was included in an energy-restricted diet. For this purpose male Syrian Golden hamsters were fed on high-fat diet for 7 weeks in order to increase their body fat content, and a further 25% energy-restricted diet supplemented or not with 0.5% trans-10,cis-12 CLA for 3 weeks. Adipose tissues, liver and gastrocnemious muscles were dissected and weighed. Adipocyte diameter and number were assessed in epididymal adipose tissue. Total cholesterol, triacylglycerols, non-esterified fatty acids and glucose were measured in serum. Three weeks of energy restriction resulted in a reduction in body weight and white adipose tissue size in all anatomical locations, without changes in liver and gastrocnemious muscle weights. Epididymal adipocyte size was reduced, but total adipocyte number remained unchanged. Serum cholesterol, triacylglycerols and glucose were significantly reduced. No differences were observed between the restricted groups (control and CLA supplemented). In conclusion, under our experimental conditions, the addition of trans-10,cis-12 CLA to the diet does not increase the benefits produced by energy restriction.

Effects of fluoxetine administration on hypothalamic melanocortin system in obese Zucker rats

The aim of the present work was to study the potential involvement of melanocortin system in the anorectic mechanism of fluoxetine, a selective serotonin reuptake inhibitors, in obese Zucker rats. Male obese Zucker (fa/fa) rats were administered fluoxetine (10 mg/kg; i.p.) daily for two weeks. The control group was given 0.9% NaCl solution. RT-PCR for pro-opiomelanocortin (POMC), Agouti gene related peptide (AgRP) and melanocortin receptor 4 (MC4-R) in the hypothalamus, as well as regional immunostaining for alpha-melanocyte stimulating hormone (alpha-MSH) and MC4-R were carried out. Fluoxetine administration increased POMC expression and reduced MC4-R expression in the hypothalamus, without changes in AgRP mRNA levels. Moreover, an increase in the numbers of alpha-MSH positively immunostained neural cells in the hypothalamic arcuate nucleus (ARC), as well as a significant decrease in the numbers of neural cells positively immunostained for MC4-R in the paraventricular nucleus (PVN), without changes in lateral hypothalamic area (LHA), were observed. These results suggest the involvement of alpha-MSH in central fluoxetine anorectic action.

Expanding role for the apelin/APJ system in physiopathology

Apelin is a bioactive peptide known as the ligand of the G protein-coupled receptor APJ. Diverse active apelin peptides exist under the form of 13, 17 or 36 amino acids, originated from a common 77-amino-acid precursor. Both apelin and APJ mRNA are widely expressed in several rodent and human tissues and have functional effects in both the central nervous system and peripheral tissues. Apelin has been shown to be involved in the regulation of cardiovascular functions, fluid homeostasis, vessel formation and cell proliferation. More recently, apelin has been described as an adipocyte-secreted factor (adipokine), up-regulated in obesity. By acting as circulating hormone or paracrine factor, adipokines are involved in physiological regulations (fat depot development, energy storage, metabolism or eating behavior) or in the promotion of obesity-associated disorders (type 2 diabetes and cardiovascular dysfunctions). In this regard, expression of apelin gene in adipose tissue is increased by insulin and TNFalpha. This review will consider the main roles of apelin in physiopathology with particular attention on its role in energy balance regulation and in obesity-associated disorders.

Quantitative gas chromatographic method for the analysis of cis-9, trans-11 and trans-10, cis-12 isomers of the conjugated linoleic acid in liver

A quantitative GC method for conjugated linoleic acid (CLA) isomers of physiological significance (cis-9, trans-11 CLA and trans-10, cis-12 CLA) as non-esterified fatty acids (NEFA) or triacylglycerols (TAG) was developed. Furthermore, the effect of the internal standard addition point (sample or fat extract) was studied. Response linearity, recovery and precision assays, detection and quantification limits were determined. Linearity was demonstrated over a range from 0.1 to 10 microg/mL. When CLA isomers were present as NEFA, the recovery significantly decreased (P< or =0.05) from 76% to 27.1% (cis-9, trans-11 CLA) and 28.5% (trans-10, cis-12 CLA) when the standards were added to the fat extract or to the initial tissue, respectively. As an application, liver samples from hamsters fed a diet supplemented with both CLA isomers were analyzed. The CLA isomers in liver samples were detected with reasonable reproducibility.

Effects of trans-10,cis-12 conjugated linoleic acid on body fat and serum lipids in young and adult hamsters

The aim of the present work was to determine whether t-10, c-12 conjugated linoleic acid (CLA) feeding was able to reduce body fat accumulation and improve the serum lipid profile in adult hamsters fed an atherogenic diet, in order to compare these effects with those observed in young growing hamsters. Young and adult hamsters were fed semi-purified atherogenic diets supplemented with 0.5 % linoleic acid or 0.5% t-10, c-12 CLA for 6 weeks. Body weight and food intake were measured every two days. Adipose tissue from different anatomical locations, liver and gastrocnemious muscle were dissected and weighed. Cholesterol, triacylglycerols, non-esterified fatty acids and proteins were determined spectrophotometrically and water content by gravimetry. In young hamsters, no significant differences were found in food intake, final body weight and gastrocnemious muscle weight. White adipose tissue weights were reduced, liver weight was increased and cholesterol and triacyl-glycerols in both serum and liver were reduced. In adult hamsters, CLA feeding decreased food intake and adipose tissue weights. No changes were observed in other parameters. The present study demonstrates that age has an influence in hamster responsiveness to t-10, c-12 CLA because, although when this isomer is added to an atherogenic diet it reduces body fat accumulation in both young and adults hamsters, the lessening of the effects on serum lipids brought about by atherogenic feeding is only observed in young animals. Moreover, it is clear that liver is a target for CLA in young but not in adult hamsters.

The body fat-lowering effect of conjugated linoleic acid: a comparison between animal and human studies

Different reasons which justify differences between rodents and humans in body fat reduction produced by conjugated linoleic acid (CLA) could be proposed. The doses used in humans are lower than those used in rodents. Human experiments have been performed with CLA isomer mixtures instead of isolated isomers. The variable dilution of t-10, c-12, the active isomer, among different preparations might explain the reduced responsiveness in humans. Diet composition may modulate CLA effects on body fat accumulation. As far as human studies are concerned, a specific dietary pattern has not been established. As a result differences among studies and also among subjects in the same study are likely. In rodents, the effects of CLA vary with genotype, suggesting that genetic predisposition to fat accumulation can play an important role in the effectiveness of CLA. Human volunteers with different body mass index have participated in the published studies and even in the same experiment. So, differences in lipid metabolism among subjects could help to explain the discrepancies observed in the literature. Age and maturity may also be crucial. Experiments using rodents have been conducted with growing animals and there is little evidence of CLA effectiveness in adult animals. By contrast, human studies have been performed with adults. Inhibition of lipogenesis in white adipose tissue is one of the mechanisms which have been proposed to explain the body-fat lowering effect of CLA, but lipogenesis in this tissue is very low in humans. Another mechanism suggested is increased fatty acid oxidation in the liver associated with peroxisome proliferation, but humans are relatively insensitive to this effect.

Effects of cis-9, trans-11 and trans-10, cis-12 CLA isomers on liver and adipose tissue fatty acid profile in hamsters

The aim of the present study was to investigate the effect of cis-9,trans-11 and trans-10,cis-12 CLA on FA composition of TAG in epididymal adipose tissue and liver, and of hepatic phospholipids PL. Twenty-four Syrian Golden hamsters were randomly divided into three groups of eight animals each and fed semipurified atherogenic diets supplemented with either 0.5 g/100 g diet of linoleic acid or cis-9,trans-11 or trans-12,cis-9 CLA for 6 wk. Total lipids were extracted, and TAG and PL were separated by TLC. FA profile in lipid species from liver and adipose tissue, as well as in feces, was determined by GC. Trans-10,cis-12 CLA feeding significantly reduced linoleic and linolenic acids in TAG from both tissues, leading to reduced total PUFA content. Moreover, in the epididymal adipose tissue docosenoic and arachidonic acids were significantly increased. In liver PL, although no changes in individual FA were observed, total saturated FA (SFA) were decreased. No changes in TAG and PL FA profiles were induced by the cis-9,trans-11 CLA. TAG and PL incorporated cis-9,trans-11 more readily than trans-10,cis-12 CLA. This difference was not due to differential intestinal absorption, as shown by the analysis of feces. We concluded that only trans-10,cis-12 CLA induces changes in FA composition. Whereas increased PUFA content was observed in either liver or adipose tissue TAG, decreased SFA were found in liver PL. Incorporation of cis-9,trans-11 CLA in TAG is greater than that of trans-10,cis-12 CLA, but this is not due to differences in intestinal absorption.

Body fat-lowering effect of conjugated linoleic acid is not due to increased lipolysis

The ability of conjugated linoleic acid (CLA) to reduce adiposity may be due to changes in energy expenditure and/or direct effects on adipocyte lipid metabolism. The aim of the present work was to analyse if CLA supplementation modifies lipolytic activity in adipose tissue from hamsters fed on high-fat diet. Hamsters were divided into two groups and fed on diets supplemented with either 0.5% linoleic acid (control) or 0.5% trans-10,cis-12 CLA. After 6 weeks, animals were fasted overnight and adipose tissues were dissected and weighed. Adipocytes were isolated by collagenase digestion and incubated in Krebs-Ringer bicarbonate buffer with or without several agents acting at different levels of the lipolytic cascade. Adipocyte diameters were measured by microscopy. Adipose tissue DNA content was assessed by spectrophotometry. Animals fed on CLA diet showed significantly reduced adipose tissue mass. No differences between both groups was found for basal lipolysis, lipolytic effects of isoproterenol, forskolin, dibutyryl-cAMP and isobutylmethylxanthine, and pD2 for isoproterenol. A similar total DNA amount was found in adipose tissue of both groups, showing that CLA diet had no effect on total cell number per fat pad. Although DNA content per gram tissue, an indirect reverse index of cell size, was significantly increased in CLA fed hamsters, microscopy did not reveal differences in medium mature adipocyte diameter, nor in cell size distribution between both groups. These results suggest that adipose tissue size reduction induced by trans-10,cis-12 CLA intake is not due to changes in lipolysis. Reduced preadipocyte differentiation into mature adipocytes may account for this fat-lowering effect.

Effects of conjugated linoleic acid on body fat accumulation and serum lipids in hamsters fed an atherogenic diet

Conjugated linoleic acid (CLA) refers to a mixture of naturally occurring positional and geometric isomers of linoleic acid that exist in dairy products and meat. The aim of the present work was to study the effects of c-9,t-11 and t-10,c-12 CLA isomers on body fat accumulation and serum lipids in hamsters fed an atherogenic diet. Hamsters were divided in four groups: one group was fed a chow diet (control) and the other three groups were given semi-purified atherogenic diets with 0.5% linoleic acid (LA), c-9,t-11 or t-10,c-12 CLA. Body weight and food intake were measured daily. After 6 weeks, adipose tissues from different anatomical locations and liver were dissected and weighed. Serum glucose, total cholesterol, HDL-c, LDL-c and triacylglycerol levels, as well as total and free cholesterol, triacylglycerol and phospholipid content in liver were determined by enzymatic methods. No differences in either energy intake or final body weight were found. The addition of t-10,c-12 CLA reduced fat accumulation and led to lower serum cholesterol, as compared with LA group. Nevertheless the level remained higher than in the control animals. The reduction in serum cholesterol was limited to LDL-c. This isomer also reduced triacylglycerol content in liver but did not modify serum triacylglycerol level. In summary, the present study demonstrates that t-10,c-12 CLA is the biologically active agent when anti-obesity and hypocholesterolaemic properties of CLA are considered. In contrast, the isomer c-9,t-11 has no effect on lipid metabolism in hamsters.

[Role of uncoupling proteins in obesity]

The discovery of a protein of the internal mitochondrial membrane of the brown adipocytes, the UCP1, marked an important advance in the understanding of the thermogenic process, as well as of the working of the brown adipose tissue. This protein is only of importance in the newly born and small animals, however the later discovery of proteins that were analogues of UCP1 (UCP2, widely distributed, and UCP3, mainly present in the muscle) with a similar functioning and also present in human tissue, created new perspectives and scientific goals. These proteins uncouple the respiratory chain of the oxidative phosphorylation, thus dissipating energy in the form of heat without producing ATP, by means of a mechanism that is still the subject of debate. From the studies of regulation that have been made, it emerges that their activity is modified when facing different physiological and nutritional stimuli, with greater activity observed in situations where an increase of energy expenditure is required. The studies carried on humans seem to corroborate the results obtained in experiments on animals, and action can thus be proposed on the activity, or the quantity, of these proteins in humans, as a means for fighting overweightedness and obesity. However, there is still an evident need to complete and improve the existing information on the importance of these proton transporting proteins in humans.

Lipolysis induced by leptin in rat adipose tissue from different anatomical locations

The aim of the present work is to compare the lipolytic response of three fat depots (subcutaneous, epididymal and perirenal) to leptin under in vitro conditions in rats. Moreover an assessment of the potential differences between young and mature rats in terms of the response of these tissues to leptin is made. Adipocytes from 6- and 20-wk-old rats were isolated by collagenase digestion and incubated in vitro both in the absence and the presence of either leptin (10(-12)-10(-6) M) or isoproterenol (10(-6) M). Lipolysis was measured by the release of glycerol into the incubation medium over 2 hours of incubation. Adipocytes responded in a dose-dependent manner to leptin concentrations ranging from 10(-12) M to 10(-6) M. The lowest leptin concentration inducing a significant lipolytic effect was 10(-9) M in all tissues. No significant differences in the effect of the maximal concentration of leptin (10(-6) M) were observed among tissues for either age. The lipolytic effect of isoproterenol (10(-6) M) was significantly reduced in adipose tissues from mature rats; in contrast no significant differences in the effect of leptin (10(-6) M) were observed between young and mature rats. In summary, no anatomical-specific differences exist in the response of rat adipose tissue to lipid mobilization induced by leptin. Furthermore, this leptin action is not decreased in mature rats compared with young ones.

Sibutramine decreases body weight gain and increases energy expenditure in obese Zucker rats without changes in NPY and orexins

The aim of the present work was to describe the effects of sibutramine on body weight and adiposity and to establish the potential involvement of neuropeptide Y (NPY) and orexins in the anorectic action of this drug. Male obese Zucker rats were daily administered with sibutramine (10 mg/kg, intraperitoneal) for two weeks. Carcass composition was assessed using the official methods of the Association of Official Analytical Chemists. Total body oxygen consumption was measured daily for 60 min before sibutramine or saline injection and for 30 min (from 60 to 90 min) after drug or saline injection. Hypothalamic arcuate and paraventricular nuclei, and the lateral hypothalamic area were immunostained for NPY, orexin A and orexin B. Commercial kits were used for serum determinations. Reductions in body weight and adipose tissue weights were observed after sibutramine treatment in obese Zucker rats. No changes in NPY immunostaining in the arcuate and paraventricular nuclei were found. Orexin A and orexin B immunostaining was not modified in the lateral hypothalamic area in treated rats. The reduction in body weight and adiposity induced by sibutramine was achieved by both a reduction in food intake and an increase in energy expenditure. NPY and orexins do not seem to be involved in the anorectic effect of sibutramine.

Nefazodone alters NPY immunostaining in rat arcuate-paraventricular projection without changes in food intake and body weight

Nefazodone is an antidepressant drug that inhibits serotonin and noradrenaline reuptake. The aim of the present work was to study the effects of nefazodone on food intake, body weight, adiposity and hypothalamic NPY immunostaining in rats. For this purpose, male Sprague-Dawley rats (3-month-old) were administered with nefazodone (20 mg/kg; i.p) daily for two weeks. The control group was given 0.9% NaCl solution. Hypothalamic arcuate, paraventricular, periventricular, supraoptic and suprachiasmatic nuclei and the lateral hypothalamic area were immunostained for NPY. Chronic nefazodone administration in rats did not modify food intake, body weight and adipose depot size (subcutaneous, perirenal and epididymal white adipose tissues, and interscapular brown adipose tissue). However, a significant decrease in paraventricular NPY immunostaining was found in the nefazodone group compared with the control group. No changes in other hypothalamic regions such as arcuate, periventricular, supraoptic and suprachiasmatic nuclei, and lateral and medial preoptic areas were observed. Because nefazodone is an alpha1-adrenoceptor antagonist, it can be proposed that the expected decrease in food intake after nefazodone administration, due to its effects on NPY arcuate-paraventricular projection, could be masked by the opposite orexigenic effect of alpha1-adrenoceptor blockade.

Lipoprotein lipase and lipogenic enzyme activities in adipose tissue from rats fed different lipid sources

This work was designed to study the effect of different lipid sources on the activities of lipoprotein lipase and lipogenic enzymes in adipose tissue from rats fed ad libitum or energy-controlled diets. Male Wistar rats were fed diets containing 40% of energy as fat (olive oil, sunflower oil, palm oil or beef tallow), for 4 wk. Under ad libitum feeding no differences were found among dietary fat groups in final body weight, adipose tissue weights and total body fat. Under energy-controlled feeding, despite isoenergetic intake, rats fed the beef tallow diet gained significantly less weight than rats fed the other three diets. Beef tallow fed rats showed the lowest values for adipose tissue weights and total body fat. When rats had free access to food no effect of dietary lipid source on lipogenic enzyme activities was found. In contrast, under energy-controlled feeding rats fed the beef tallow diet showed significantly higher activities of glucose-6-phosphate dehydrogenase and fatty acid synthase than rats fed the other three diets. Heparin-releasable lipoprotein lipase activity in perirenal and subcutaneous adipose tissues was not different among rats fed olive oil, safflower oil, palm oil or beef tallow. When comparing both adipose tissue anatomical locations, significantly higher activities were found in subcutaneous than in perirenal fat pad independently of dietary fat. In conclusion, under our experimental protocol, lipogenesis in rat adipose tissue does not seem to be affected by dietary fat type.

Effects of the whole seed and a protein isolate of faba bean (Vicia faba) on the cholesterol metabolism of hypercholesterolaemic rats

The aim of the present work was to analyse the hypocholesterolaemic efficiency of a Vicia faba-protein isolate in relation to the intact legume. In addition, the mechanisms underlying the effects of this isolate were investigated. Hypercholesterolaemic rats were divided into three groups and fed high-fat diets rich in cholesterol-containing casein, whole seeds of Vicia faba or the protein isolate of faba beans as protein source, for 2 weeks ad libitum. The protein isolate was prepared by isoelectric precipitation and spray dried. Analyses of serum, liver and faeces, as well as of the activity of hepatic 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase, were assessed by enzymatic methods. The rats fed on Vicia faba diets showed significantly lower body weights and energy intakes than rats fed on casein diets. The whole-seed diet induced a significant reduction in plasma triacylglycerol. Feeding rats on diets containing faba bean seeds, or the protein isolate, induced a significant decrease in plasma (LDL+VLDL)-cholesterol but not in HDL-cholesterol. Hepatic cholesterol and triacylglycerol were also reduced. The hypocholesterolaemic effects of Vicia faba were not the result of a reduction in cholesterol synthesis as assessed from HMG-CoA reductase activity, but the result of an increase in steroid faecal excretion. The faba bean-protein isolate obtained under our experimental conditions was useful in improving the metabolic alterations induced by feeding with a hypercholesterolaemic diet compared with casein. The effectiveness of the whole seeds was higher than that of the protein isolate.

Differential effects of diets that provide different lipid sources on hepatic lipogenic activities in rats under ad libitum or restricted feeding

This work was designed to study the effect of different lipid sources on hepatic lipogenic enzyme activity in rats fed ad libitum or energy-controlled diets. Male Wistar rats were fed diets containing 40% of energy as fat (olive oil, sunflower oil, palm oil, or beef tallow) for 4 wk. In experiment 1 rats had free access to food, and in experiment 2 rats were fed a controlled amount of food. In both experiments, rats fed the olive oil diets had higher activities of glucose-6-phosphate dehydrogenase, malic enzyme, fatty acid synthase, and acetyl-CoA carboxylase (P < 0.05) than rats fed the other fats. It is unlikely that this effect could be attributed to the stimulation by insulin or triiodothyronine because serum values did not differ among the groups. Enzymatic activities were positively and significantly correlated with liver triacylglycerol content, but not with serum triacylglycerol levels. No interaction between lipid source and feeding protocol was found. Oleic acid and components in olive oil other than fatty acids, such as phytosterols, may account for the effects of dietary fat on lipogenic enzyme activity.

Influence of different dietary fats on triacylglycerol deposition in rat adipose tissue

It has been demonstrated that triacylglycerol (TAG) mobilization from adipose tissue is selective and depends on fatty acid (FA) chain length, unsaturation and positional isomerism. The present study was performed to determine the influence of dietary fat on the composition of TAG stored in rat perirenal and subcutaneous adipose tissues. These results may provide information on the susceptibility of stored TAG to hydrolysis and further mobilization, and may help to establish an interrelationship between dietary composition and the FA efflux from adipose tissue. TAG molecular species and FA composition were determined by HPLC and GLC respectively. No significant differences were found in either FA or TAG composition between perirenal and subcutaneous adipose depots. The major FA in the dietary fats were present in the adipose tissues of the animals; in most cases, in similar proportions. However, differences were found between dietary and adipose tissue content of minor FA, which suggests that dietary FA composition is altered between ingestion and deposition in adipose tissue. The TAG molecular species of rat adipose tissue were enriched with the FA characteristic of each dietary fat. Dietary sunflower oil was responsible for enrichment with the most polar TAG. This finding may suggest easier mobilization of stored TAG. In conclusion, the process of fatty acid and TAG deposition in rat adipose tissue is selective, and depends on the composition of the diet.

In vivo lipolysis in adipose tissue from two anatomical locations measured by microdialysis

In this study, the difference in lipolytic response in inguinal subcutaneous and epididymal adipose tissues of male Sprague-Dawley rats was assessed in vivo by microdialysis. Probes were perfused with Ringer solution in which increasing concentrations of isoproterenol (10(-7) - 10(-4) mol/L) were added. Glycerol release, expressed as extracellular glycerol concentration, was used as lipolytic index. The effect of isoproterenol on local blood flow was investigated using the ethanol technique. No differences were found in the interstitial glycerol concentration between both adipose tissues under basal conditions. When isoproterenol was perfused, a dose-response increase in glycerol production was induced in both tissues. Interstitial glycerol concentration from epididymal adipose tissue was higher than that of inguinal subcutaneous depot at all isoproterenol concentrations. No vasodilatory effect of isoproterenol was found. These results suggest that epididymal adipose tissue is more responsive in vivo to beta-adrenergic lipolysis stimulation than is subcutaneous fat pad from the inguinal region.

Lipid and glucose utilization in hypercholesterolemic rats fed a diet containing heated chickpea (Cicer aretinum L.): a potential functional food

This feeding trial evaluated the influence of a diet containing heated chickpea in a dietary induced rat model of hypercholesterolemia in order to assess some possible protective and therapeutic effects on lipid and carbohydrate metabolism disorders as found with other legumes. Rats fed a diet enriched with coconut oil (25%) and cholesterol (1%) for 42 days (HH) showed a situation of type IIa hyperlipoproteinemia. However, these lipid alterations were improved in the hypercholesterolemic rats receiving control (HC) and legume (HL) diets for 16 days. Moreover, results confirm that the chickpea was more effective than the control diet containing casein in the normalization of triglycerides as well as total and LDL-cholesterol levels. On the other hand, the HH group showed a marked reduction in the liver glycogen content and Glucose-6-Phase activity (involved in glyconeogenesis) and an increase in Glucokinase (GK) activity (involved in glucose utilization). In contrast, the rats receiving chickpea re-established the liver glycogen deposition as compared to the HH group. Also, the chickpea intake increased the GK activity as compared to the control diet. The overall results support that chickpea intake may be recommended in humans with altered lipid profile such as type IIa hyperlipoproteinemia. Additionally, data concerning carbohydrate utilization indicated its potential positive effects in diabetes therapy and their role as biological active food supplements.

Modifications induced by dietary lipid source in adipose tissue phospholipid fatty acids and their consequences in lipid mobilization

The aim of the present work was to assess the influence of dietary lipid source on fatty acid phospholipid profiles and on lipid mobilization. Forty male Wistar rats were divided into four groups and fed on high-fat diets which provided olive oil, sunflower oil, palm oil or beef tallow. All rats received the same amount of energy to avoid hyperphagia and differences in energy intake among groups. Phospholipid fatty acids were determined by GC. Lipolysis was stimulated in subcutaneous and perirenal isolated adipocytes by several lipolytic agents, and assessed by the determination of released glycerol. After 4 weeks of feeding, differences in body and adipose tissue weights were not observed. Dietary regimens caused great changes in adipose tissue phospholipid composition: rats fed on palm oil and beef tallow had higher concentrations of saturated fatty acids and animals fed on olive oil or sunflower oil had greater amounts of oleic and linoleic acids, respectively. These modifications did not lead to important changes in adipocyte lipolysis. Significant differences were only observed between palm-oil- and beef-tallow-fed groups when lipolysis was stimulated by isoproterenol in subcutaneous adipocytes. The fact that our feeding protocol did not induce differences in fat accumulation among groups avoids misinterpretations due to adiposity changes. The differences observed between both saturated-fat-fed groups, therefore, should only be attributable to dietary lipids. Despite this effect, the data from this work indicate that some diet-induced changes in adipose tissue fatty acid composition may have little effect on overall function.

Effect of high-fat diet on lypolisis in isolated adipocytes from visceral and subcutaneous WAT

Variations in total energy intake and composition of daily food play an important role in the regulation of metabolic processes and so, in the control of body weight. This study was designed in order to investigate the effect of a high-fat diet on lipolysis in isolated adipocytes. For this purpose, fourteen Wistar rats were divided into two groups and fed either a standard-fat diet or a high-fat diet ad libitum for 7 weeks. Adipocytes were prepared from fat pads by collagenase digestion and incubated in vitro in the absence or presence of various lipolytic agents. Lipolysis was measured by the release of glycerol into the medium during 90 min of incubation. We observed that a high amount of fat in the diet induced an enlargement of adipose tissue, which was accompanied by a reduction of beta-adrenergic agonist-induced lipolysis, that could be due to a loss of beta(1) and beta(3)-adrenoceptor number or to alterations of their coupling to adenylate-cyclase through the guanine nucleotide regulatory protein. New data about regional differences were provided by comparing two adipose locations (subcutaneous and visceral).

Effects of dietary fat content on adiposity during energy restriction in genetically obese rats

The effects of the amount of fat provided in a restricted diet on weight loss and body composition were studied in this work. Lean male (Fa/?) Zucker rats were fed a control diet ad libitum. Obese (fa/fa) Zucker rats were divided into three groups: one group was fed a control diet ad libitum and the other two groups were fed 75% energy-restricted diets, which provided 10 or 50% of calories as fat. After 4 weeks, energy restriction normalized body weight but not body composition in the genetically obese rats. Reductions in adipose tissue weights and adipocyte size, without changes in the cellularity, were observed. Differences only reached statistical significance in subcutaneous adipose tissue. A standard fat content in the diet induced the same fat-free mass reduction as a higher amount of this macronutrient, but a greater body fat reduction. This suggests that the restriction of dietary fat, as well as energy, is necessary to achieve dietary management in obesity.

Energy restriction with high-fat diet enriched with coconut oil gives higher UCP1 and lower white fat in rats

OBJECTIVE

To investigate the effects of overfeeding on a high fat diet, enriched in coconut oil, and the influence of food restriction on the uncoupling protein (UCP1) expression and on body fat content.

DESIGN AND SUBJECTS

In experiment I, female Wistar rats were fed ad libitum either a normal-fat diet (control group, C) or a high-fat diet (HF), enriched in coconut oil, for 7 weeks. In experiment II, HF rats after finishing experiment I were fed (for 3 weeks) either the normal-fat diet (group CAHF, Control After High Fat) or food restricted diets which provided 60% of the energy intake of group CAHF: a group fed a low-energy, normal-fat diet (LENF) and another fed a low-energy, high-fat diet (LEHF).

MEASUREMENTS

Body and fatty depot weights. Food intake. Protein and UCP1 levels of interscapular brown adipose tissue.

RESULTS

High-fat diet feeding promoted an increase in body fat content, body weight and UCP1 levels. Energy restriction induced similar body weight reduction in groups LENF and LEHF. However, some adipose depots were more strongly reduced in the rats fed the high-fat diet enriched in coconut oil (group LEHF) than in the rats fed the normal-fat diet (Group LENF). Specific UCP1 was 2.0 (group LENF) and 3.4 (group LEHF) times higher than in controls (group CAHF).

CONCLUSION

The coconut-oil enriched diet is effective in stimulating UCP1 expression during ad libitum feeding and in preventing its down regulation during food restriction, and this goes hand in hand with a decrease of the white fat stores.

Expression of retinoic acid, triiodothyronine, and glucocorticoid hormone nuclear receptors is decreased in the liver of rats fed a hypercholesterolemia-inducing diet

Several studies have shown that dietary factors modulate cell signaling pathways. The aim of this study was to determine whether a hypercholesterolemia-inducing diet rich in saturated fat and cholesterol modifies rat liver expression of the nuclear receptors of retinoic acid (RAR), triiodothyronine (TR), and glucocorticoid hormone (GR), which are transcriptional factors. The experimental diet contained coconut oil 25 g/100 g as a source of lipids, cholesterol 1 g/100 g, and cholic acid 0.5 g/100 g, and the control diet contained olive oil 5 g/100 g. After 26 days of feeding the hypercholesterolemia-inducing diet, a lower binding capacity of the nuclear receptors and a smaller amount of their mRNA were observed. Moreover, the activities of malic enzyme (ME) and tyrosine aminotransferase (TAT), whose gene promotors contain a response element to TR and GR, respectively, were significantly decreased. These changes occurred in a cellular environment characterized by a high level of cholesterol and free fatty acids (FFAs). Thus, two nonexclusive hypotheses can be proposed to explain this decreased expression of nuclear receptors, one emphasizing the effect of lipidic components on the cellular amount of receptor ligands (retinoic acid [RA] and triiodothyronine [T3]), the other emphasizing a modification of the balance between nuclear receptors that could impede the upregulation of TR and RAR.

Fatty acid profiles in subcutaneous and mesenteric adipose tissues from Zucker rats after energy restriction. Influence of dietary fat

Several disturbances concerning lipid metabolism are found in obese Zucker rats. The present study was designed to determine the effect of energy restriction on fatty acid profile of adipose tissue triglycerides from two different anatomic locations, in genetically obese rats. The impact of the addition of a high amount of olive oil to a restricted diet was also considered. Lean and obese male Zucker rats, 11 weeks old, were used. The former (n = 7) were fed a control diet ad libitum during 4 weeks, and the latter (n = 21) were randomized into 3 groups and fed either a control diet ad libitum or diets restricted to 75% of lean rat intake which provided different amounts of olive oil as fat source. Obesity induced strong modifications in fatty acid profiles from subcutaneous and mesenteric adipose tissues that were not corrected when a standard-fat 25% energy-restricted diet was used for feeding. In contrast, when a high amount of olive oil was included into the restricted diet, a new fatty acid profile in adipose tissue from obese rats, that mirrors the one of lean rats, was observed. Significant differences between two anatomic locations were found in the pattern of modifications produced by obesity, but not by dietary treatments.

Desensitization effect of in vivo treatment with metaproterenol on beta1, beta2 and beta3-adrenergic responsiveness in rat adipocytes

The desensitization process of beta-adrenergic system was assessed by in vivo administration to 7-week old rats of a mixed beta-agonist, metaproterenol (3,5-dehydroxyphenyl-N-isopropyl-amine-beta-ethanol sulphate; T1/2=6 hours), (2 mg/kg/d) in treatments of 12 hours, 2 days and 10 days. The in vitro lipolytic effect of selective beta-adrenergic agonists, dobutamine, salbutamol and BRL 37344, as well as plasma free fatty acid concentrations were measured in treated and control animals given vehicle. Different times of exposure to a beta-agonist induced a loss of responsiveness on lipolytic response mediated by beta1 and beta2-adrenoceptors, as demonstrated by decreased affinity and intrinsic activity (maximal effect) of dobutamine and salbutamol. In contrast, no changes were found in beta3 mediated lipolysis. These observations suggest that beta1, beta2 and beta3-adrenoceptors follow different regulatory patterns. Lack of beta3-adrenoceptor desensitization may have important physiological and therapeutic consequences in the treatment of diseases such as obesity and heart failure.

Lipolytic effects of beta1, beta2 and beta3-adrenergic agonists in isolated human fat cells from omental and retroperitoneal adipose tissues

The presence of beta1- and beta2-adrenoceptors has been clearly established in human fat cells. There is some controversy about the presence and function of beta3-adrenoceptors. It is well established that there are marked regional variations in catecholamine-induced lipolysis. In this work the possibility that a beta3-adrenoceptor plays a significant role in the control of lipid mobilization is studied and also its importance in comparison to beta1- and beta2-adrenoceptors in isolated human fat cells, is evaluated, by measuring the in vitro lipolysis induced by dobutamine, salbutamol, metaproterenol, BRL 37344 and CGP 12177A. Human adipocytes from omental and retroperitoneal fat deposits exhibited an "atypical" beta-adrenergic response but, given the small lipolytic effect initiated by BRL 37344 and CGP 12177A, they are probably poorly equipped in functional beta3-adrenoceptors.

Analysis of the interactions between growth hormone and metaproterenol on lipid mobilization

The possible modification of the in vitro lipolytic action of rat growth hormone (rGH) or a mixed beta-adrenergic agonist (metaproterenol) on rat adipose tissue after a previous acute treatment with these compounds was assessed by measuring glycerol release from adipocytes. The involvement of adenosine deaminase (ADA) and dexamethasone, was also considered. The results showed that the previous acute treatment with rGH or the beta-adrenergic agonist did not alter the in vitro rGH or metaproterenol lipolytic response. The presence of ADA at a non-lipolytic concentration per se (0.02 U/ml) potentiated the lipolytic response of both compounds. Also, the addition of non-lipolytic concentrations of dexamethasone (0.5 microM) or beta-adrenergic agonist (10(-7)M) to the incubation medium potentiated the rGH lipolytic response, while the metaproterenol-induced glycerol release was not affected by the simultaneous addition of a rGH concentration (2 x 10(-7) M) which had no lipolytic effect per se.

Effects of the beta-adrenergic agonist salbutamol and its withdrawal on protein metabolism of lambs

Rasa Aragonesa lambs were used to evaluate the repartitioning effects of a beta-adrenergic agonist and its withdrawal on nutrient metabolism. One group of animals (T-I) was fed salbutamol at a dose of 2 mg x kg-1 diet x day-1 for 38 days, while in another group (T-II) the beta-adrenergic agonist was discontinued in the diet 5 days before slaughter on the 43rd day. The semitendinosus muscle protein content increased (p < 0.05), while fat and collagen content decreased (p < 0.05) in the T-I group. These differences were not apparent in the group from which salbutamol was withdrawn. Muscle protein degradation was diminished (p < 0.05) in both treated groups. The serum free fatty acid level was markedly enhanced (p < 0.05) in the T-I group. Total essential amino acid serum levels were reduced (p < 0.05) after the withdrawal period. Ketogenic and urea cycle amino acids were reduced (p < 0.05) in the salbutamol-fed T-I group and glycogenic amino acids were diminished (p < 0.05) in the T-II experimental group. The data show that salbutamol is able to increase muscle content at the expense of fat stores in productive animals. However, these repartitioning effects are circumvented by a 5-day period of withdrawal, in which concomitant metabolic changes in lipid and protein turnover and plasma amino acid profiles occur.