Maternal diet, rather than obesity itself, has a main influence on milk triacylglycerol profile in dietary obese rats

Triacylglycerols (TG) in milk derive from different sources, and their composition may be influenced by both maternal diet and obesity. We used two rat models to ascertain potential changes in TG composition in milk associated to maternal intake of an obesogenic diet during lactation and to distinguish them from the effects attributable to maternal adiposity. Milk samples were obtained from dams fed a cafeteria diet during lactation (CAF) and from dams made obese by cafeteria diet feeding, with dietary normalization before gestation (PCaf). Levels of specific TG species in milk collected at different time points of lactation were determined by shotgun lipidomics. CAF and PCaf dams presented a greater adiposity than their respective controls. The principal component analysis of TG peaks showed a clear separation between milk from CAF dams and milk from control and Pcaf dams, already evident at 5 days of lactation. Milk from CAF dams was enriched with TG species with greater number of carbons and double bonds and reduced in TG with lower number of carbons. TG composition of milk from Pcaf dams was similar to controls, although specific differences were observed at day 5 of lactation. Thus, the intake of a cafeteria diet during lactation, rather than maternal adiposity, alters milk composition. This effect is avoided with dietary normalization before gestation, although the remaining fat reserves may also influence TG composition at initial stages of lactation. Therefore, normalization of maternal diet prior to pregnancy should be considered as a strategy for achieving optimal milk composition.

TAS1R3 and UCN2 Transcript Levels in Blood Cells Are Associated With Sugary and Fatty Food Consumption in Children

CONTEXT

New types of dietary exposure biomarkers are needed to implement effective strategies for obesity prevention in children. Of special interest are biomarkers of consumption of food rich in simple sugars and fat because their intake has been associated with obesity development. Peripheral blood cells (PBCs) represent a promising new tool for identifying novel, transcript-based biomarkers.

OBJECTIVE

This study aimed to study potential associations between the transcripts of taste receptor type 1 member 3 (TAS1R3) and urocortin II (UCN2) genes in PBCs and the frequency of sugary and fatty food consumption in children.

DESIGN, SETTING, AND PARTICIPANTS

Four hundred sixty-three children from the IDEFICS cohort were selected to include a similar number of boys and girls, both normal-weight and overweight, belonging to eight European countries.

MAIN OUTCOME MEASURES

Anthropometric parameters (measured at baseline and in a subset of 193 children after 2 years), food consumption frequency and transcript levels of TAS1R3 and UCN2 genes in PBCs were measured.

RESULTS

Children with low-frequency consumption of sugary foods displayed higher TAS1R3 expression levels with respect to those with intermediate or high frequency. In turn, children with high-frequency consumption of fatty foods showed lower UCN2 expression levels with respect to those with low or intermediate frequency. Moreover, transcripts of TAS1R3 were related with body mass index and fat-mass changes after a 2-year follow-up period, with low expression levels of this gene being related with increased fat accumulation over time.

CONCLUSION

The transcripts of TAS1R3 and UCN2 in PBCs may be considered potential biomarkers of consumption of sugary and fatty food, respectively, to complement data of food-intake questionnaires.

Leptin intake in suckling rats restores altered T3 levels and markers of adipose tissue sympathetic drive and function caused by gestational calorie restriction

BACKGROUND

Maternal calorie restriction during gestation in rats has been associated with altered white adipose tissue (WAT) sympathetic innervation and function in offspring. Here, we aimed to investigate whether supplementation with oral leptin (a breast milk component) throughout the lactation period may revert the aforementioned adverse programming effects.

METHODS

Three groups of male and female rats were studied at the postnatal day 25: the offspring of control dams, the offspring of 20% calorie-restricted dams during pregnancy (CR) and CR rats supplemented with physiological doses of leptin throughout lactation (CR-Leptin). Tyrosine hydroxylase (TH) levels and its immunoreactive area, and mRNA expression levels of lipid metabolism-related genes and of deiodinase iodothyronine type II (Dio2) were determined in WAT. Triiodothyronine (T3) levels were determined in the blood.

RESULTS

In CR males, leptin treatment restored the decreased TH levels and its immunoreactive area in WAT, and partially normalized expression levels of genes related to lipolysis and fatty acid oxidation (adipose triglyceride lipase, hormone-sensitive lipase, carnitine palmitoyltransferase 1b and peroxisome proliferator-activated receptor gamma coactivator 1-alpha). Leptin treatment also reverted the decreased T3 plasma levels and WAT lipoprotein lipase mRNA levels occurring in CR males and females, and the decreased Dio2 mRNA levels in CR females.

CONCLUSIONS

Leptin supplementation throughout the lactation period reverts the malprogrammed effects on WAT structure and function induced by undernutrition during pregnancy. These findings support the relevance of the intake of leptin during lactation, bearing clear characteristics of essential nutrient, and provide a strategy to treat and/or prevent the programmed trend to obesity acquired by inadequate fetal nutrition.

Influence of breastfeeding on blood-cell transcript-based biomarkers of health in children

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

The expression of specific genes in peripheral blood cells (PBCs) may be used as biomarkers of the metabolic status. High levels of expression of CPT1A, SLC27A2, INSR, LEPR, FASN and PPARα in PBCs are indicative of a lower risk for the insulin resistant or dyslipidaemic state associated with obesity in children. Breastfeeding seems to confer protective effects against obesity and its related metabolic problems.

WHAT THIS STUDY ADDS

Children who had been breastfed showed higher expression levels of SLC27A2, FASN, PPARα and INSR in PBCs compared with formula-fed subjects. The relationship of the PBC transcript levels of SLC27A2, INSR, FASN and PPARα with insulin resistance and dyslipidaemia may be dependent on the type of infant feeding (breast vs. formula). The transcript levels of the mentioned biomarkers could be useful to distinguish the formula-fed children who are at higher risk of metabolic alterations.

BACKGROUND

Blood-cell transcripts have showed to be good biomarkers of metabolic alterations and their use in early detection and prevention of future disorders is promising.

OBJECTIVE

This study aimed to examine the relation between previously proposed transcriptional biomarkers of metabolic health (SLC27A2, CPT1A, FASN, PPARα, INSR, LEPR) in peripheral blood cells and the type of infant feeding in a subset of children from the IDEFICS (Identification and Prevention of Dietary- and Lifestyle-Induced Health Effects in Children and Infants) cohort.

SUBJECTS

A total of 237 children aged 2-9 years from eight European countries were studied.

RESULTS

Breastfed children showed higher expression levels of SLC27A2, FASN, PPARα and INSR, and lower risk of being overweight and of having high plasma triglyceride levels vs. formula-fed children. Besides, overweight formula-fed children presented higher HOMA-index than overweight breastfed children (1.90 vs. 1.62); however, this negative effect was absent in formula-fed children with high expression of SLC27A2. Moreover, formula-fed children with low expression of SLC27A2, FASN, PPARα and INSR presented higher triglyceride levels than subjects with high expression of these genes (77.7 mg dL(-1) vs. 44.8 mg dL(-1) ). This difference was absent in breastfed children.

CONCLUSIONS

Protective effects of breastfeeding are reflected in higher expression levels of SLC27A2, FASN, PPARα and INSR in blood cells. These biomarkers may also serve to discriminate the formula-fed children that are at higher risk of metabolic alterations.

[Physiological mechanisms in the development of adiposity]

The phenomenon of the so-called "obesity pandemic" having arisen over the last decades has to be, in large part, attributed to changes of lifestyle and the associated changes in dietary habits and physical activity observed world-wide. The resulting interference in energy homeostasis plays a central role in the development of obesity in a large proportion of the population worldwide. In this article, current knowledge about central biological mechanisms of energy intake, energy storage, and energy expenditure is summarized. This includes, for example, the feeling of hunger/satiety, lipid turnover with the two components of lipolysis and lipogenesis, adipogenesis, as well as energy-consuming processes like (adaptive) thermogenesis, resting metabolic rate, and physical activity energy expenditure. Based on examples, the possible influence of genetic polymorphisms contributing to the development of adiposity are illustrated.

Dietary l-leucine supplementation of lactating rats results in a tendency to increase lean/fat ratio associated to lower orexigenic neuropeptide expression in hypothalamus

The aim of this study was to assess the effects of dietary leucine supplementation in lactating dams, particularly on energy homeostasis through signaling mechanisms in the central nervous system. Dams were fed ad libitum with standard diet during pregnancy (control dams) or supplemented with 2% leucine (leucine-supplemented dams) from delivery onwards. Food intake, body weight and composition were periodically recorded. Hypothalamus was collected at the end of lactation, and the expression of neuropeptide Y (NPY), agouti-related protein (AgRP) pro-opiomelanocortin (POMC), cocaine and amphetamine regulated transcript (CART), insulin receptor (InsR), ghrelin receptor (GSHR), melanocortin receptor (MCR4), leptin receptor (Ob-Rb) and suppressor of cytokine signaling 3 (SOCS3) were analyzed. Dietary leucine supplementation to lactating rats increased plasma leucine by 56%, modulated body composition and contributed to a tendency of higher ratio of lean/fat mass content of dams during lactation, without affecting food intake, thermogenesis capacity or body or tissue/organs weights. No differences in body weight of offspring from control and leucine-supplemented dams were found. The expression of orexigenic peptides (NPY and AgRP) decreased in leucine-dams, whereas the expression of anorexigenic peptides (POMC and CART), the hypothalamic receptors of insulin, ghrelin, melanocortin and leptin and SOCS3 did not change by leucine supplementation. In conclusion, increased leucine intake during lactation may contribute to a healthier profile of body composition in dams, without compromising the growth and development of the progeny by a mechanism associated with lower expression of orexigenic neuropeptides in hypothalamus.

Moderate caloric restriction during gestation results in lower arcuate nucleus NPY- and alphaMSH-neurons and impairs hypothalamic response to fed/fasting conditions in weaned rats

AIM

We aimed to characterize the developmental programming effects of moderate caloric restriction during early pregnancy on factors involved in hypothalamic control of energy balance.

METHODS

Twenty-five-days-old offspring Wistar rats from 20% caloric restricted dams (from 1 to 12 days of pregnancy) (CR) and from control dams were studied under fed and 12 h fasting conditions. Morphometric studies on arcuate nucleus (ARC) and determinations of circulating parameters and hypothalamic levels of neuropeptide Y (NPY), proopiomelanocortin (POMC), long-form leptin receptor (ObRb), insulin receptor (InsR) and suppressor of cytokine signalling-3 (SOCS-3) mRNA were performed.

RESULTS

CR animals did not show different body weight with respect to their controls, but presented higher food intake. They exhibited lower neuropeptide Y- and alpha-melanocyte-stimulating hormone-neurons (decreases of 18 and 13% in males, and 10 and 18% in females respectively) and lower total cells (decrease of 3% in males and 18% in females) in ARC. Under fed conditions, CR animals presented lower circulating leptin and ghrelin levels (decreases of 37 and 43% in males, and 15 and 34% in females respectively); furthermore, hypothalamic POMC, NPY (only in females), ObRb and InsR mRNA levels were reduced (39, 16 and 26% in males, and 112, 33, 61 and 56% in females), and those of SOCS-3 were increased (86% in males and 74% in females). Unlike control animals, under fasting conditions, ObRb, InsR and POMC mRNA levels did not decrease in CR females, and NPY mRNA decreased instead of increase in CR males.

CONCLUSIONS

Moderate caloric restriction during gestation affects offspring hypothalamic structure and function, impairing its response to fed/fasting conditions, which suggests a predisposition to insulin and leptin resistance.

Response to carbohydrate and fat refeeding in the expression of genes involved in nutrient partitioning and metabolism: striking effects on fibroblast growth factor-21 induction

This study aimed to assess the effects of carbohydrate (CHO) and fat intake on the expression of key genes related with nutrient partitioning and metabolism in main tissues involved in energy metabolism (white adipose tissue, liver, and skeletal muscle). Rats were studied under different conditions: feeding state, 24 h fasting, and 12 h refeeding after 24 h fasting with isocaloric amounts of CHO or fat. Fat, but not CHO, refeeding was associated with an increase in serum and liver triglyceride content. Main changes in gene expression elicited by CHO compared with fat refeeding were: 1) higher expression levels of genes related with lipogenesis (PPARgamma2, ChREBP, FAS), glucose uptake and metabolism (GLUT4, HKII), fatty acid uptake (LPL, CD36), and lipolysis (ATGL, HSL) in white adipose tissue; 2) higher expression levels of genes related with lipogenesis (FAS, SCD1) but lower ones related with fatty acid uptake (CD36) and oxidation (PPARalpha, CPT1, PDK4) in liver; and 3) higher expression levels of GLUT4 but lower ones related with fatty acid oxidation (PDK4 and UCP3) in muscle. It is worth mentioning that both CHO and fat refeeding resulted in a robust increase in both hepatic mRNA and circulating levels of fibroblast growth factor-21, compared with fasted levels. In summary, these results, showing marked differences in gene expression after CHO and fat refeeding, can explain diet-associated differences in fuel handling and partitioning between tissues; in addition, a role of fibroblast growth factor-21 in metabolic adaptations, not only in the ketotic state but also to face an unbalanced nutritional situation, is suggested.

Effect of high-fat diet feeding on leptin receptor expression in white adipose tissue in rats: depot- and sex-related differential response

Previous studies have illustrated the importance of leptin receptor (OB-Rb) mediated action on adipocytes in the regulation of body weight. The aim of the present study was to investigate in male and female rats the effects of high-fat (HF) diet feeding on the expression levels of OB-Rb in different depots of white adipose tissue (WAT), and its relation to fatty acid oxidation capacity. Male and female Wistar rats were fed until the age of 6 months with a normal-fat (NF) or non-isocaloric HF-diet (10 and 45% calories from fat, respectively). At this age, the weight of three different fat depots (retroperitoneal, mesenteric and inguinal) and the expression levels of OB-Rb, PPARalpha and CPT1 in these depots were measured. HF-diet feeding resulted in an increase in the weight of the different fat depots, the retroperitoneal depot being the one with the greatest increase in both sexes. In this depot, HF-diet feeding resulted in a significant decrease in OB-Rb mRNA levels, more marked in male than in female rats. In the mesenteric depot, the effects of HF-diet feeding on OB-Rb mRNA levels were sex-dependent: they decreased in males rats (associated with a decrease in PPARalpha and CPT1 mRNA levels), but increased in female rats. In the inguinal depot, OB-Rb expression was not affected by HF-diet feeding. These results show that a chronic intake of an HF-diet altered the expression of OB-Rb in WAT in a depot and sex-dependent manner. The decreased expression of OB-Rb in the internal depots of male rats under HF-diet feeding, with the resulting decrease in leptin sensitivity, can help to explain the higher tendency of males to suffer from obesity-linked disorders under HF-diet conditions.

On the role and fate of sugars in human nutrition and health. Introduction

The recently implemented European Regulation (EC) No. 1924/2006 on nutrition and health claims made on foods is fuelling scientific research efforts in the food and health arena. Essentially, it is now established that only claims that are scientifically substantiated will be allowed. Because this new legislation covers the idea that foods with health or nutritional claims might be perceived by consumers as having a health advantage over products without claims, it introduces a further requirement (enclosing the new concept of 'nutrient profile') to avoid a situation where claims could mislead consumers when trying to make healthy choices in the context of a balanced diet. Thus, only those foods having an appropriate nutrition profile (composition of different nutrients such as sugars and other substances with particularly relevant nutritional or physiological effects) will be allowed to bear claims. A scientific expert workshop was organized to critically review the available evidence behind current intake recommendations for sugars, focusing on the strength/gaps of the scientific evidence available and the identification of those fields where further research is needed. Work was distributed in the following topics covering potential effects of dietary sugars on (i) body weight control; (ii) diabetes-insulin resistance; (iii) dental health and (iv) micronutrient dilution. New approaches, including intervention studies and the application of nutrigenomic technologies, should be undertaken and interpreted bearing in mind that foods, food components and their combinations can have both positive and negative effects on health, thus requiring benefit-risk analysis.

The intake of physiological doses of leptin during lactation in rats prevents obesity in later life

BACKGROUND

There is epidemiological evidence that perinatal nutritional factors may have long-term effects on obesity. Which nutrients or food components are involved in this programming mechanism are unknown. Breast milk contains leptin, a hormone that regulates food intake and energy expenditure, and previous studies in rats have shown that leptin orally administered during lactation exerts anorexigenic effects.

OBJECTIVE

To evaluate whether supplementation with physiological doses of oral leptin during lactation has long-term effects on body weight regulation.

DESIGN

A daily oral dose of leptin (equivalent to five times the amount of leptin ingested normally from maternal milk during the suckling period) or the vehicle was given to suckling male rats during lactation. Animals were fed after weaning with a normal fat (NF) or a high-fat (HF) diet. We followed body weight and food intake of animals until the age of 6 months, and measured the size of adipose tissue depots, the thermogenic capacity, the expression of leptin in the stomach and adipose tissues and the expression of two appetite-related peptides (neuropeptide Y (NPY) and proopiomelanocortin (POMC)), leptin receptor (OB-Rb) and suppressor of cytokine signalling 3 (SOCS-3) in the hypothalamus at the age of 6 months.

RESULTS

Leptin-treated animals had, in adulthood, lower body weight and fat content and ate fewer calories than their untreated controls. Unlike adipocitary leptin production, adult animals that were leptin-treated during lactation displayed higher gastric leptin production without changes in OB-Rb mRNA levels. In addition, in response to HF diet, leptin-treated animals (contrary to controls) showed lower hypothalamic NPY/POMC mRNA ratio. Hypothalamic OB-Rb mRNA levels decreased in control animals as an effect of HF diet feeding, but remained unchanged in leptin-treated animals; SOCS-3 mRNA levels were lower in leptin-treated animals than in their controls, both under normal or HF diet.

CONCLUSION

The animals that received leptin during lactation become more protected against fat accumulation in adult life and seem to be more sensitive to the short- and long-term regulation of food intake by leptin. Thus, leptin plays an important role in the earlier stages of neonatal life, as a component of breast milk, in the prevention of later obesity.

Resistin as a putative modulator of insulin action in the daily feeding/fasting rhythm

Resistin and adiponectin are adipokines with postulated opposite functions. Resistin has been related with insulin resistance in obesity, while adiponectin could be associated to higher insulin sensitivity. We have determined whether the production of these two adipokines during the day is related to the feeding rhythm in rats. Resistin mRNA levels in adipose tissue correlated positively with the gastric contents and serum insulin concentration, showing higher levels during the dark phase (period of the highest food intake), especially in the mesenteric depot, while levels decreased during the light phase. The diurnal pattern of resistin expression was not directly reflected in the circulating levels, but it showed a 6-h delay and correlated negatively with the gastric contents and serum insulin. Adiponectin expression followed an opposite pattern, not apparently related to feeding or insulin release, and not translated into changes in circulating levels. Moreover, considering that insulin stimulates resistin expression and that circulating resistin follows a contrary circadian pattern in comparison to insulin, resistin, apart from its role in the increased insulin resistance associated to obesity, could also act as a putative modulator of insulin in the daily feeding/fasting rhythm through a negative feedback regulation of its action.

[Nutrigenomics and obesity]

Obesity is a multifactorial disorder affected by multiple genetic and environmental factors, in particular nutrients, and their interrelationships. Increasing knowledge of the genes and molecules involved in the development of obesity is paving the way for new methods of obesity control. In this sense, Nutrigenomics--which represents a new approach in nutrition research that joints the application of powerful functional genomics technologies, bioinformatics and molecular biology with more traditional methodologies--may orientate the design and development of new functional foods for obesity, based on the scientific knowledge of the impact of specific nutrients on the mammalian body weight control system and their mechanisms of action.

Ontogenesis of leptin expression in different adipose tissue depots in the rat

Serum leptin levels and leptin mRNA expression by adipose tissue increase with age and are mainly associated with an increase in adiposity. Regional changes in both leptin production and fat distribution contribute to circulating leptin levels and may play a role in the regulation of body weight. a capacity that changes during development. Here, we have studied leptin mRNA expression in four different white adipose tissue depots (epididymal, retroperitoneal, mesenteric, inguinal; namely, EWAT, RWAT, MWAT, IWAT) and in interscapular brown adipose tissue (IBAT). We have also studied their relationship with lipid content and adiposity changes, together with serum leptin levels in male rats at different ages (18, 55, 93, 159, 212, 294 and 355 days). Serum leptin levels increased during development, reaching stable levels at the age of 7 months, and, as expected, were highly correlated with both the adiposity index (r=0.908, P<0.01) and body weight (r=0.906, P<0.01). Leptin mRNA expression also increased with age, following characteristic ontogenic patterns in every adipose tissue depot. The patterns were similar in EWAT and RWAT: leptin expression increased very rapidly during the first 55 days for EWAT and 3 months for RWAT, with a peak in the latter at 7 months, and high expression levels were retained for the rest of the study period. In IWAT and IBAT, leptin expression increased steadily during the 12-month period studied and was significantly lower than levels in EWAT and RWAT. Leptin expression in MWAT increased progressively with age to reach levels close to those of EWAT and RWAT in 10-month-old animals. The pattern of leptin expression in both EWAT and RWAT paralleled their lipid content, and leptin mRNA expression per unit of tissue lipid content was maintained high and constant from a very young age (about 2 and 3 months, respectively). However, the expression of mRNA for leptin (expressed per unit of tissue lipid concentration) in MWAT, IWAT and IBAT increased steadily during the whole period studied, without attaining the maximal levels observed in EWAT and RWAT. MWAT, IWAT and IBAT maintained their capacity to increase leptin mRNA expression in response to an additional accumulation of lipids. Our data demonstrate that there are regional-specific differences and different rates of increase of leptin gene expression within distinct depots of WAT and BAT. These changes cannot be uniquely explained by changes in adiposity or lipid content, implying that there are regional-specific regulatory mechanisms that may depend on the attenuation with age of the beta-adrenergic inhibitory signalling pathway upon leptin expression or on other factors.

Differential expression of genes for uncoupling proteins 1, 2 and 3 in brown and white adipose tissue depots during rat development

The different expression patterns of genes for uncoupling proteins (UCPs) 1, 2 and 3 (ucp1, ucp2 and ucp3) were studied in interscapular brown adipose tissue (BAT) and in four white adipose tissue (WAT) depots (epididymal, inguinal, mesenteric and retroperitoneal) in male rats of different ages (18 days-12 months). UCP mRNA expression levels were determined by Northern blotting. In BAT, there were high levels of expression of UCP1 and UCP3 mRNA, but no detectable levels of UCP2 mRNA. Both ucp1 and ucp3 followed a similar expression pattern with age, with high levels in suckling rats which decreased to 50% or less in rats just under 2 months old, declining thereafter until 5 months and then recovering with age. However, an additional peak of expression was observed for ucp3 at the age of 3 months. In WAT, ucp1 expression was rare: occasional expression was found for UCP1 mRNA in the retroperitoneal depot in suckling rats and in the epididymal and inguinal depots in suckling and mature adult rats. ucp2 and ucp3 had different developmental expression patterns, but these were similar for each gene in the different depots studied. UCP3 mRNA was highly expressed in rats soon after birth, it decreased until 3 months, and increased thereafter, except for the mesenteric WAT where ucp3 expression decreased until 7 months before recovering. The fact that changes with age of both ucp1 and ucp3 expression have a similar profile in BAT, which is also similar to the ucp3 and also ucp1 profiles in some WAT depots, might reflect a common regulatory pattern for the expression of these genes, and also a common function. In contrast to ucp1 and ucp3, ucp2 had a peak of expression at about 2 months, and lower expression at 3 months, suggesting different regulation and probably a different role for this UCP.

Opposite effects of feeding a vitamin A-deficient diet and retinoic acid treatment on brown adipose tissue uncoupling protein 1 (UCP1), UCP2 and leptin expression

The relationship between interscapular brown adipose tissue (IBAT) thermogenic potential and vitamin A status was investigated by studying the effects of feeding a vitamin A-deficient diet and all-trans retinoic acid (tRA) treatment on body weight and IBAT parameters in mice. Feeding a vitamin A-deficient diet tended to trigger opposite effects to those of tRA treatment, namely increased body weight, IBAT weight, adiposity and leptin mRNA expression, and reduced IBAT thermogenic potential in terms of uncoupling protein 1 (UCP1) mRNA and UCP2 mRNA expression. The results emphasize the importance of retinoids as physiological regulators of brown adipose tissue.

Obesity: molecular bases of a multifactorial problem

Obesity could well become the most common health problem of the 21st century. There are more opportunities to consume large quantities of food: big portions of tasty, varied food, at reasonable prices, are available everywhere. Moreover, our bodies are better adapted to combat weight loss than to combat weight gain, since for thousands of years our species evolved in circumstances where nutrients were in short supply. The response of each individual to diet and other environmental factors varies considerably, depending on the characteristics of his/her body weight control mechanisms. The differentiating element in the future, especially as regards the dietary and pharmacological control of obesity, will be knowledge of an individual's possible response depending on his/her genetic background. Obesity can occur as a result of genetic or acquired changes in three main types of biochemical processes, which are the main focus of this review: a)feeding control, which determines the sensations of satiety and hunger through processes that depend on an interplay between internal signals (notably leptin) and environmental factors; b) energy efficiency, in particular the activation of thermogenesis mediated by uncoupling proteins (UCPs) that makes it possible to dissipate part of the energy contained in food as heat instead of accumulating it as fat, and c) adipogenesis, the process by which cells specialised in fat storage (adipocytes) are formed, which is controlled by an interplay of transcription factors, including members of the C/EBP, PPARgamma and ADD families. The knowledge of a growing number of genes and molecules implicated in these three types of processes and of their metabolic relationships is leading toward a molecular understanding of the body weight regulatory system, and is paving the way for new methods of obesity control, especially pharmacological but also nutritional and possibly involving genetic intervention.

Secretory granules of endocrine and chief cells of human stomach mucosa contain leptin

BACKGROUND

Leptin plays an important role in the control of food intake and body weight homeostasis. In humans, leptin is produced by adipocytes, placental cells and secretory cells of the mammary epithelium. Recently, it has been reported that stomach glands produce leptin in rats.

OBJECTIVE

To test the expression of leptin protein in human stomach and localize, by immunocytochemistry, the specific cell type producing leptin.

DESIGN

Endoscopic stomach biopsies of six patients were used to investigate leptin production in the fundic epithelium using reverse transcription polymerase chain reaction (RT-PCR) of RNA. Leptin protein was detected by immunoblot analysis and localized by immunohistochemistry and ultrastructural immunocytochemistry (immunogold method).

RESULTS

Human gastric epithelium expresses leptin mRNA and leptin protein. The cells in the lower half of the stomach glands were immunoreactive for leptin. Ultrastructural immunocytochemistry showed leptin immunoreactivity in the pepsinogen granules of chief cells, but the granules of a specific endocrine cell type in the basal portion of the glands were also positive.

CONCLUSIONS

Our results suggest that gastric leptin could function in the short-term system to control feeding behaviour and is probably secreted in the stomach lumen by chief cells and into the stomach circulation by a special type of endocrine cell.

In vivo effects of CGP-12177 on the expression of leptin and uncoupling protein genes in mouse brown and white adipose tissues

OBJECTIVE

To assess the effect of chronic treatment with CGP-12177 a beta3-adrenergic receptor (AR) agonist with beta2/beta1-AR antagonist action, on the expression of the leptin gene and of genes coding for uncoupling proteins (ucp1, ucp2 and ucp3) in brown and white adipose tissues.

DESIGN

NMRI mice received a daily subcutaneous injection of CGP-12177 at a dose of 0.05, 0.2, 0.5 or 1 mg/kg for 15 days. The specific levels of the mRNAs of interest were analysed in interscapular brown adipose tissue (BAT) and in two white adipose tissue (WAT) depots, inguinal (IWAT) and epididymal (EWAT).

RESULTS

No changes in food intake or body weight were detected at any dose of CGP-12177. In the two WAT depots, the treatment led to enhanced expression of ucp1 and ucp3, but not of ucp2. In BAT, low doses (0.05 and 0.2 mg/kg) led to a decreased expression of the three ucp genes, whereas a slight stimulatory effect on the three ucp genes was elicited with a high dose (1 mg/kg). Treated animals displayed increased expression of leptin in BAT and, to a lesser extent, in IWAT, but not in EWAT.

CONCLUSION

The results reveal that simultaneous stimulation of the expression of certain ucp genes and the leptin gene can be achieved, and suggest that adrenergic regulation of the leptin gene and of genes of the ucp family in adipose tissues is the result of complex interactions between the different beta-AR pathways.

Brown adipose tissue response to cafeteria diet-feeding involves induction of the UCP2 gene and is impaired in female rats as compared to males

Noradrenaline-dependent brown adipose tissue (BAT) thermogenesis is activated by the cold and excess energy intake, largely depends on the activity of the uncoupling protein 1 (UCP1), and is mediated mainly through the beta3-adrenoceptor (beta3-AR). We investigated the expression of ucp2, a gene that encodes a putative UCP1-like uncoupling protein, along with that of ucp1 and beta3-ar, in the interscapular BAT (IBAT) of male and female rats chronically fed a cafeteria diet. After 3 months on this diet, male rats attained a 34% excess body mass and showed IBAT hypertrophy and increased IBAT thermogenic potential, in terms of both UCP1 and UCP2 mRNA expression (both by 1.6-fold), UCP1 protein expression (by 1.75-fold) and GDP binding to IBAT mitochondria (by 2.2-fold); female rats attained a larger excess body weight (50%) and their IBAT, although hypertrophied, showed no signs of increased thermogenic potential per gram of tissue. Interestingly, the IBAT of female rats was already activated compared to males. Treatment of mouse brown adipocytes in primary culture with noradrenaline also triggered a dose-dependent increase of the levels of UCP1 mRNA and UCP2 mRNA. Retroregulatory down-regulation of the beta3-AR mRNA levels was found in the two models used. The results support a physiological role for UCP2, along with UCP1, in rodent BAT thermogenesis.

2-Methoxyestradiol, an endogenous metabolite of 17beta-estradiol, inhibits adipocyte proliferation

The effects of 2-methoxyestradiol (2ME), a naturally occurring mammalian metabolite of 17beta-estradiol, on adipocyte growth has been investigated in mouse brown adipose tissue precursor cells developed in primary culture. 2ME inhibits brown adipocyte proliferation in a dose-response manner (IC50 = 1.7 x 10(-6) M for DNA synthesis), with much higher potency than its hormone precursor 17beta-estradiol, and cells acquire the typical differentiated morphology--more round with a higher content of triglycerides. 2ME causes similar effects in the immortal brown adipocyte tumor-derived hibernoma cell line HIB 1B and the immortal 3T3-F442A white adipocyte line. These findings suggest a possible role for 2ME in adipocyte proliferation, and probably in the differentiation process, entering the cells in the adipogenic program.

Sex-associated differences in cold-induced UCP1 synthesis in rodent brown adipose tissue

The effects of acute and chronic acclimation to cold on uncoupling protein 1 (UCP1) levels, as well as on GDP-binding to mitochondria, cytochrome c oxidase activity and mitochondrial protein concentration in brown adipose tissue (BAT) of intact male and female rats have been analyzed. Results reveal that females rats are more sensitive to cold because their threshold temperature for the thermogenic response is set at a higher value (around 22 degreesC) than that of males (around 18 degreesC), hence leading to differences in BAT UCP1 levels between the sexes at different environmental temperatures. In vitro experiments showed that steroid hormones, beta-estradiol, estrone and progesterone, can reduce norepinephrine-induced UCP1 synthesis in brown adipocytes differentiated in primary culture. Thus the different sex-associated response of cold-induced thermogenesis in rats does not appear to be explained by a direct action of sex steroids upon the adipocyte, implying that other factors in the thermogenic regulatory system must be involved.

Stimulation of uncoupling protein synthesis in white adipose tissue of mice treated with the beta 3-adrenergic agonist CGP-12177

The effects of chronic treatment with the beta 3-adrenergic receptor agonist CGP-12177 on uncoupling protein (UCP) synthesis in interscapular brown adipose tissue (IBAT), various white fat depots and skeletal muscle have been examined in the mouse (daily injection for 15 days at a dose of 0.5 mg/kg). The treatment increased the IBAT UCP content and led to the expression of UCP in inguinal white adipose tissue. The increase in IBAT UCP content took place in the absence of tissue hypertrophy, and despite the increase in total body UCP content, no changes in body weight were observed after the treatment. The results confirm that ectopic expression of UCP in non-BAT tissues can be induced after chronic adrenergic stimulation.

The uncoupling protein, thermogenin

The uncoupling protein (UCP) or thermogenin is a 33 kDa inner-membrane mitochondrial protein exclusive to brown adipocytes in mammals that functions as a proton transporter, allowing the dissipation as heat of the proton gradient generated by the respiratory chain and thereby uncoupling oxidative phosphorylation. Thermogenesis (heat production) in brown adipose tissue, which is activated in response to cold exposure or chronic overeating, depends largely on UCP activity. Norepinephrine, released from sympathetic terminals and acting via beta-adrenoceptors and cAMP, is the main positive regulator of both UCP synthesis and activity. Brown fat thermogenesis plays a critical role in thermoregulation and in overall energy balance, at least in rodents. Manipulation of thermogenesis, whether through UCP or through analogous uncoupling proteins, could be an effective strategy against obesity.

Rats receiving the slimming agent oleoyl-estrone in liposomes (Merlin-2) decrease food intake but maintain thermogenesis

Oleoyl-estrone given i.v.--incorporated in liposomes to mimic lipoprotein delivery--(Merlin-2) to normal weight rats, induces a dose-dependent weight loss. Analysis of body composition showed that body protein concentration was preserved and fat stores wasted. The respiratory quotient was consistent with the massive oxidation of body fat, since the diet contained practically no lipid. Appetite was affected by Merlin-2, and thus food intake showed a transient decrease. But oxygen consumption (and basal metabolic rates) was kept practically unchanged at the levels of the controls, i.e. higher than needed to oxidize the food ingested during the weight loss period. Brown adipose tissue uncoupling protein levels were proportionally preserved with a 2-week treatment, but it lost a substantial amount of lipid. In conclusion, Merlin-2 is a slimming agent with considerable potential given its powerful fat-wasting action, since it maintains thermogenesis despite lowered energy intake.

In vitro and in vivo induction of brown adipocyte uncoupling protein (thermogenin) by retinoic acid

The effects of retinoic acid (RA) isomers (all-trans-RA and 9-cis-RA) on the appearance of uncoupling protein (UCP; thermogenin), the only unequivocal molecular marker of the brown adipocyte differentiated phenotype, have been investigated in primary cultures of brown adipocytes, in the brown adipocyte cell line HIB 1B and directly in intact mice. The results obtained with cultured cells indicate that retinoids function as inducers of the appearance of UCP and, at the same time, partially inhibit brown adipocyte cell proliferation. The two RA isomers displayed similar effectiveness as UCP inducers, their effect being comparable with that triggered by noradrenaline, so far considered to be the main modulator of UCP gene expression. The effectiveness of retinoids as UCP inducers was dependent on the stage of brown adipocyte differentiation, being maximal in confluent primary cells and in the medium-late differentiation stage of HIB 1B cells. Corroborating the results obtained in vitro, we show that administration of all-trans-RA or 9-cis-RA to mice leads to an increase in their brown adipose tissue specific UCP content. 9-cis-RA treatment also prevented the loss of UCP on cold deacclimation. To our knowledge, this is the first report of a stimulatory effect of retinoid compounds on UCP induction in vivo.

Effect of selective beta-adrenoceptor stimulation on UCP synthesis in primary cultures of brown adipocytes

Given the co-existence of the three beta-adrenoceptor (beta AR) subtypes (beta 1AR, beta 2AR and beta 3AR) in brown adipocytes, the present study was undertaken to determine the relative importance of these in the induction of UCP synthesis in mouse BAT precursor cells in primary culture. Cells at different stages of differentiation were exposed to different beta AR agonists: prenalterol (a selective beta 1AR agonist), salbutamol or clenbuterol (selective beta 2AR agonists), or BRL 37344 (a selective beta 3AR agonist). As with the endogenous agonist, noradrenaline, and the non-selective beta AR agonist, isoprenaline, all four beta AR agonists induced UCP in the confluent stage of the cells, but with different potencies, and with the highest induction being seen after clenbuterol or BRL 37344 treatment. Cells in the confluent stage of development were the most sensitive to the effects of the agonists, although clenbuterol and BRL 37344 induced a weak UCP synthesis in pre-confluent cells. None of these beta AR agonists were able to induce UCP synthesis in the post-confluent period. The responses to prenalterol and salbutamol were inhibited by propranolol at relatively low concentrations, suggesting their effects were mediated by beta 1AR and beta 2AR, respectively. However, propranolol was a particularly weak antagonist of BRL 37344 and, unexpectedly, of the clenbuterol UCP responses, which suggests that both induce UCP synthesis via the beta 3AR. In summary, the beta 3AR is the most important adrenoceptor coupled to the induction of UCP synthesis, although both beta 1AR and beta 2AR activation may make a contribution. However, all three beta AR subtypes do not become fully functional until cultured cells become confluent.

Protein and amino acid intake in cafeteria fed obese rats

Food selection pattern and portal blood amino acid profile were examined in rats given a cafeteria diet. Compared to standard-diet fed rats, cafeteria-diet fed rats consumed more energy. Increase in energy intake was attributable to an increase in fat intake. Protein intake was slightly higher and carbohydrate intake remained constant and was similar to levels consumed by standard-diet fed rats. The cafeteria rats took up higher quantities of Phenylalanine+Tyrosine, Arginine, Histidine, Lysine, Leucine, Isoleucine, Valine, Threonine, and Glycine, lower quantities of Tryptophan and the same quantity of Methionine+Cysteine vs. control rats. Portal concentrations of Serine, Threonine, Tryptophan and Lysine were significantly higher in cafeteria-diet fed rats than in standard-diet fed rats. This can be interpreted in such a way that, on the whole, the quality of protein ingested by cafeteria and control rats is similar. No statistical differences in the ingestion of individual amino acids were observed between different days of the period of cafeteria diet feeding, thus the idea of a strict control of protein ingestion irrespective of the obese status is reinforced.

Decrease of the pool of amino acids adsorbed on blood cell membranes caused by starvation in rats

The effect of 24 h starvation on the pool of amino acids adsorbed on the blood cell membranes was determined in Wistar rats. Aortic and iliac blood was analysed. 24 h starvation induced a significant decrease in the combined essential amino acids adsorbed on the blood cell membranes, in both arterial and venous blood, without affecting whole-blood levels (adsorbed + non-adsorbed). The same tendency was extended to most of the individual amino acids. This finding indicates that this pool of adsorbed amino acids has a rapid turnover and probably plays a physiological role in a situation of exogenous food deprivation.

Stabilization of the mRNA for the uncoupling protein thermogenin by transcriptional/translational blockade and by noradrenaline in brown adipocytes differentiated in culture: a degradation factor induced by cessation of stimulation?

The stability of the mRNA coding for the uncoupling protein thermogenin was investigated in mouse brown-fat cells differentiated in culture. After 7 days in culture, the cells were stimulated for 24 h with noradrenaline, and a high level of thermogenin mRNA was then observed. If noradrenaline treatment was continued, the mRNA level remained high, but, upon withdrawal of noradrenaline, the level decreased rapidly, with a half-life of only 2.7 h. The presence of transcriptional (actinomycin) or translational (cycloheximide) inhibitors prolonged the apparent half-life by about 50%. The presence of noradrenaline during transcriptional blockade led to a further stabilization of thermogenin mRNA. It was concluded that an induced (or short-lived) gene product is important for thermogenin mRNA degradation. Direct interaction of noradrenaline with the cultured brown adipocytes could apparently not mimic the paradoxical destabilization of thermogenin mRNA in vivo, previously observed in the cold-exposed mouse [Jacobsson, Cannon and Nedergaard (1987) FEBS Lett. 244, 353-356], indicating significant differences between the systems in vitro and in vivo.

Blood amino acid compartmentation in obese rats is specifically altered in the iliac vein

Amino acid concentration in blood cells and plasma and the calculated blood cell to plasma gradients (C/P) were measured in different blood vessels (aortic artery and portal, hepatic, iliac and renal veins) from both control and cafeteria diet obese rats. Essential amino acids are increased in plasma in all blood vessels in obese rats. The iliac vein was the only vessel in which cell concentration of amino acids, and mainly the mean of the combined non-essential amino acids, was affected by obesity. Only in the iliac vein were C/P values of the combined amino acids, including both essential and non-essential, significantly lower in obese versus control rats. These results also show that there are differences between sampling sites which should be noted in the design of physiological studies of amino acid metabolism.

Blood cell to plasma gradients of amino acids in arterial and venous blood in fed and fasted rats

Measurement of amino acid concentrations in blood cells and plasma, and the calculated blood cell to plasma gradients (C/P) from both afferent and efferent vessels to tissues, allowed evaluation of the effect of several tissues (splanchnic bed, skeletal muscle and kidney) on blood amino acid distribution in fed and starved rats. Combined effects of tissues and erythrocyte transport capabilities determined specific C/P values for each amino acid. For amino acids related to the L-system, the high capacity of this erythrocyte transport many buffer some C/P changes as an effect of tissue metabolism. For less permeable amino acids (like Asp and Glu) plasma changes were mainly responsible for changes in C/P values, whereas for other amino acids (such as basic amino acids) blood cells became the main determinants of C/P changes, mainly in starvation. In general, the role of erythrocytes in amino acid transport was enhanced in starvation.

Opposite response to starvation of Trp/LNAA ratio in lean and obese Zucker rats

Total blood and plasma free amino acids and plasma urea levels were studied in fed and 24 h fasted Zucker rats. In fed animals there were no differences between obese and lean rats in the overall essential and non essential blood free amino acids. However, starvation reduced blood amino acid levels in the obese animals compared to the lean group, mainly due to changes in the plasma compartment. The reduction of available amino acids from plasma in the obese rats during starvation affected most of the amino acids, including the branched chain amino acids, which showed higher levels in the fed situation than in lean rats. Of particular interest is the opposite response to starvation in lean and obese Zucker rats concerning the plasma ratio of tryptophan (Trp) to the large neutral amino acids (LNAA) which could be implicated in the alteration of food intake and energy expenditure characteristic of obesity.

Regulation of rat erythrocyte l-glutamine, 1-glutamate and l-lysine uptake by short term starvation

1. The kinetic parameters (Km, Vmax and Kd) of L-glutamine, L-glutamate and L-lysine uptake by isolated red blood cells in fed and 24 hr starved rats have been determined. 2. L-Lysine and L-glutamine uptake was best fitted by a two transport component: a saturable component and a diffusion one. 3. Starvation brought about important decreases in the Km and Vmax for both L-lysine and L-glutamine uptake. 4. The Kd for L-glutamine showed a significant increase whereas that corresponding to L-lysine did not change by starvation. 5. L-Glutamate uptake adjusted to diffusion kinetics, with a Kd which did not change due to starvation. 6. It is concluded that the amino acid uptake showed specific regulation by starvation. 7. The mechanism involved is not dependent on protein synthesis--given the unnucleated nature of mammal red cells. 8. The magnitude of the changes observed in the uptake kinetic parameters may account for the extent of the blood amino acid pool changes as those produced in vivo over physiological limits.

Effect of diet-induced obesity on kinetic parameters of amino acid uptake by rat erythrocytes

The effects of cafeteria diet-induced obesity upon in vitro uptake of L-Alanine, Glycine, L-Lysine, L-Glutamine, L-Glutamic acid, L-Phenylalanine and L-Leucine by isolated rat erythrocytes have been studied. The total Phe and Leu uptakes followed Michaelis-Menten kinetics. The Glu uptake was fitted to diffusion kinetics. The uptakes of Ala, Gly, Lys and Gln were best explained by a two-component transport: one saturable and one diffusion. Obesity increased the Km value for Ala, Gln and Leu, and the Vmax value for Ala, but decreased the Vmax for Lys. Kinetic parameters of Phe uptake were unaffected by obesity. In addition, the pseudo-first order rate constant (Vmax/Km) for Ala, Gly, Gln, Lys and Leu uptake decreased as a result of cafeteria diet-induced obesity. The Kd value for Ala, Gly, Gln and Glu decreased and that of Lys increased as result of obesity. These adaptations could, at least in part, explain alterations in amino acid distribution between blood cells and plasma related to overfeeding or obesity.

Tissue composition in persistent dietary obesity after early and adulthood overfeeding in the rat

The objective of this study was to assess the effects of prolonged cafeteria-diet feeding on tissue composition in adult rats comparing those that had been overfed in early life and then in adulthood with a group that was only overfed in adulthood, and to determine whether any alterations were related to the high energy diet per se or to obesity. In addition to following the body weight changes in detail, tissue masses and composition were determined at selected points of this long term dietary experiment. The marked changes in body weight and tissue composition of cafeteria-fed obese rats were sustained for at least 84 days after returning to the standard diet, and the obesity was exaggerated if these animals were pre-exposed to the palatable diet in early life. Three patterns of tissue composition in response to cafeteria feeding could be discerned: Liver and brown adipose tissue developed cell hypertrophy without apparent hyperplasia. In contrast, the retroperitoneal white adipose depot developed hyperplasia whereas the intestine and kidneys were not associated with marked changes in lipid composition. These adaptations were not recovered to control levels by prolonged standard diet feeding. Previous obesity influenced the adaptations in adipose tissue during the subsequent return to standard diet feeding, and differences between cafeteria-induced obese animals became more apparent when the cafeteria diet was removed. These results indicated the important effects of early dietary experience in subsequent responses to overfeeding.

Short term starvation-induced changes in the kinetic parameters of rat red cell L-alanine and glycine uptake

Na(+)-dependent L-Alanine and Glycine uptake by rat red blood cells were best fit to a common model of two transport components, saturable transport and diffusion. 24 hours of food deprivation provoked statistically significant increases of the Km and Vmax red cells L-Alanine uptake, whereas the diffusion constant did not change in response to starvation. The Glycine uptake kinetics poorly follows the L-Alanine pattern and no significant response to starvation can be outlined. The physiological meaning of these adaptations has to be related to short term food deprivation regulation, independent of protein synthesis in the erythrocytes. Such mechanisms could be important to account for the previously described changes in the distribution patterns of amino acids between the blood plasma and blood cell compartments in response to short term starvation.

A significant pool of amino acids is adsorbed on blood cell membranes

It is well known that the amino acids in the blood are distributed between the plasma and inside the cells. This study was conducted to determine whether amino acids can be located adsorbed on blood cell membranes. The amino acid concentration in the deproteinized haemolysed blood was higher than that in the fraction of blood after removal of the blood cell membranes by centrifugation. These results showed that a pool of amino acids representing 21.1% of the whole blood cell amino acids was adsorbed on the blood cell membranes of adult Wistar rats. The non-polar amino acids showed high adsorption on the membrane, whereas out of the polar amino acid group, only the non-ionic amino acids did adsorb.

Sustained changes in blood alpha amino nitrogen compartmentation during recovery from cafeteria feeding in rats

We have previously reported that blood urea and blood cell amino acids levels are reduced in rats obese by feeding a palatable cafeteria diet. In order to distinguish whether these changes result from the altered diet, or from the obesity per se, we have studied cafeteria fed rats after returning to standard diet. As in previous studies, obesity induced by cafeteria feeding (for 90 days) was maintained when the cafeteria diet was removed and rats were fed standard diet only. After removal of the cafeteria diet, blood urea levels of 24 h starved obese rats were lower (23%) than those of starved control rats. Blood cell amino acid levels of obese were lower than control ones from day 50 onwards, during and after cafeteria feeding (21% lower on day 100 of life), and thus coincided with divergence of body weights; these differences were maintained despite removal of cafeteria diet. The effects of starvation on plasma amino acid levels were more marked in obese than control rats, during and after cafeteria feeding. Thus the effects on blood amino acids and urea levels in cafeteria diet induced obese rats are related to the obese status rather than to the diet composition.

Alternating sequential endocrine therapy: tamoxifen and medroxyprogesterone acetate versus tamoxifen in postmenopausal advanced breast cancer patients

The effects of tamoxifen (TAM) versus the alternating sequential combination of TAM plus medroxy-progesterone acetate (MPA) has been evaluated in 20 postmenopausal patients with advanced breast cancer in a randomized controlled trial. In the TAM arm, patients received 20 mg b.i.d. of TAM. In the TAM-MPA arm, patients received only 20 mg b.i.d. of TAM for 7 days and, on the following 7 days. TAM plus an oral daily dose of 500 mg of MPA, in alternating sequence. Objective tumor reduction was achieved in 22 (41%) of the 54 patients in the TAM arm and in 25 (43%) of the 58 patients in the TAM-MPA arm. With regard to the stabilization of disease, a significant difference was observed between patients treated with the TAM-MPA combination and those treated with TAM alone (47% vs 22%). The percentage of nonresponders was also significantly higher in the TAM group (37%) than in the TAM-MPA group (10%). The time to progression was significantly shorter for the TAM arm than for the TAM-MPA arm (median, 7 vs 15 months), but the duration of remission was not significantly different for either treatment.