Regulation of metabolism and body fat mass by leptin

Effect of dietary lipoic acid on metabolic hormones and acute-phase proteins during challenge with infectious bovine rhinotracheitis virus in cattle

OBJECTIVE

To determine the effect of dietary supplemental lipoic acid (LA) on serum concentrations of metabolic hormones and acute-phase proteins of steers challenged with infectious bovine rhinotracheitis virus (IBRV).

ANIMALS

32 steers.

PROCEDURES

Steers were randomly assigned to 4 treatments: negative control (NC; no LA, no IBRV challenge), control (CON; no LA, IBRV challenge), 16 mg of LA/kg of body weight (BW)/d plus IBRV challenge (LA16), and 32 mg of LA/kg of BW/d plus IBRV challenge (LA32). Following a 21-day adaptation period, CON, LA16, and LA32 steers received IBRV (2 mL/nostril [day 0]); NC steers received saline (0.9% NaCl) solution. Blood samples, nasal swab specimens, BW, and rectal temperatures were obtained 0, 1, 3, 5, 7, 14, and 21 days after challenge. Serum was analyzed for concentrations of haptoglobin, amyloid-A, leptin, and anti-IBRV antibodies.

RESULTS

Steers fed LA32 began gaining BW by day 7, whereas BW of CON and LA16 steers declined. Serum haptoglobin concentration of LA32 steers was lower than that of CON and LA16 steers on day 7. Serum neutralization titers for 30 of 32 steers were negative for anti-IBRV antibodies before challenge; however, all steers (including NCs) had antibodies on day 21.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that LA supplementation augmented certain aspects of the immune response; LA32 steers had a more rapid recovery from IBRV viral challenge than did others.

Leptin and cancer

The prevalence of obesity has markedly increased over the past two decades, especially in the industrialized countries. While the impact of excess body weight on the development of cardiac disease and diabetes has been well documented, the link between obesity and carcinogenesis is just being recognized. This review will focus on the link between leptin, a cytokine that is elevated in obese individuals, and cancer development. First, we briefly discuss the biological functions of leptin and its signaling pathways. Then, we summarize the effects of leptin on different cancer types in experimental cellular and animal models. Next, we analyze epidemiological data on the relationship between obesity and the presence of cancer or cancer risk in patients. Finally, leptin as a target for cancer treatment and prevention will be discussed.

Leptin and ghrelin expression in adipose tissues and serum levels in gastric banding patients

BACKGROUND

To determine how leptin and ghrelin are expressed in the adipose tissues of obese adults undergoing gastric banding (LAGB), and to correlate tissue expression with serum concentrations and parameters of the metabolic syndrome.

MATERIALS AND METHODS

A cross-sectional analysis of 92 patients: 61 obese patients with a body mass index (BMI) 49.2 +/- 1 kg m(-2) received LAGB, 20 patients underwent band exchange (BMI, 36.6 +/- 1.4 kg m(-2)) and 11 adult patients (BMI, 24.3 +/- 0.6 kg m(-2)) with fundoplication served as controls. Clinical data such as BMI and blood pressure were evaluated along with subcutaneous and visceral adipose tissue gene expression and fasting levels of leptin and ghrelin. Tissue transcripts were measured using real-time PCR, serum protein concentrations radio-immunologically.

RESULTS

Leptin gene expression was highest in the primary LAGB group and more pronounced in subcutaneous fat in both sexes (P < 0.0001). Serum leptin concentrations were highest in the LAGB group (P < 0.001), whereby women exhibited higher serum levels than men. Leptin concentrations correlated positively to expression in subcutaneous fat (P < 0.0001), and leptin expression was also correlated to BMI and systolic blood pressure. We detected ghrelin gene expression in both types of fat. The ghrelin mRNA amounts in adipose tissues were similar in both sexes and comparable within groups; serum concentrations were lower in patients with primary LAGB than in controls (P < 0.05).

CONCLUSIONS

Human adipose tissue expression of leptin is weight-course dependent and ghrelin is constitutional. Serum levels of leptin, but not of ghrelin, are indicative of an adaptive pattern of local gene expression in obese subjects undergoing weight reduction.

Leptin regulates olfactory-mediated behavior in ob/ob mice

We have investigated olfactory-mediated pre-ingestive behavior in leptin (ob/ob) and leptin receptor (db/db) mutant mice compared to age- and gender-matched wild-type (wt) mice. Olfactory-mediated behavior was tested using a buried food paradigm 5 times/day at 2-h intervals for 6 days. Mean food-finding times of ob/ob and db/db mice were approximately 10 times shorter than those of wt mice. To test the effect of leptin replacement in ob/ob mice, leptin (1 or 5 microg/g body weight in sterile saline) or carrier was injected i.p. once daily prior to testing. Mean food finding times in ob/ob mice injected with carrier or with 1 microg/g leptin were similar and were 2-3 times faster than in wt mice. Mean food finding times in ob/ob mice injected with 5 microg/g leptin tripled compared to carrier-injected ob/ob mice and were of the same order of magnitude as those of wt mice, suggesting functional leptin replacement. A 3-factor repeated measures ANOVA demonstrated significant differences between the 6 cohorts (P = 0.0001), food finding times (P< or = 0.0001), and cohort by day interaction (P< or = 0.0001). Post hoc tests suggested that the ob/ob+5 mug/g leptin cohort performed more like the wt cohort in the food-finding test than like the ob/ob or ob/ob+carrier cohort. Potential local sites of leptin production and action were identified with immunohistochemistry and in situ hybridization in epithelial and gland cells of the olfactory and nasal mucosae. Our results strongly suggest that leptin acting through leptin receptors modulates olfactory-mediated pre-ingestive behavior.

Hyperleptinemia as a risk factor for high blood pressure in the elderly

CONTEXT

Studies have demonstrated that high serum leptin levels are associated with aging. However, we do not know whether hyperleptinemia is a relevant risk factor for high blood pressure (HBP) in the elderly.

OBJECTIVE

To determine the relationship between hyperleptinemia and HBP in the elderly.

DESIGN

A comparative cross-sectional study was carried out in a convenience sample of 70 healthy elderly persons comprising 46 women (mean age, 67 +/- 5.8 years) and 24 men (mean age, 73 +/- 7.5 years), and a group of 91 elderly persons with HBP, comprising 62 women (mean age, 67 +/- 8.2 years) and 29 men (mean age, 70 +/- 0.3 years). We measured serum leptin levels through the radioimmunoassay method.

RESULTS

The elderly subjects with HBP had significantly higher leptin levels than the healthy elderly subjects (P = .02). Furthermore, in female elderly subjects we observed a statistically significant correlation between systolic blood pressure and leptin (r = 0.37, P = .003), as well as systolic blood pressure and age (r = 0.29, P = .02), but not with diastolic blood pressure. In male elderly subjects, there was no correlation between leptin and systolic blood pressure or leptin and diastolic blood pressure. However, hyperleptinemia as risk factor for HBP was nearly 5 times higher in men than in women (men, odds ratio = 18.0, 95% confidence interval 3.2-100.9, P < .001 vs women, odds ratio = 3.33, 95% confidence interval 1.4-7.4, P = .003).

CONCLUSIONS

Our data suggest that hyperleptinemia was a significant risk factor for HBP elderly individuals, mainly in men.

Intraperitoneal leptin regulates lipid metabolism in ethanol supplemented Mus musculas heart

Diseases of the heart and blood vessels are a major cause of illness and disability worldwide. The relationship between ethanol consumption and cardiovascular disease are both complex and interconnected. Our aim of this study was to explore the effect of leptin on lipid metabolism in ethanol supplemented mice. Male Swiss mice (Mus musculas) weighing 25+/-2 g were administered ethanol (6.32 g kg(-1) body weight) for the first 30 days. Subsequently, ethanol fed mice were given intraperitoneal injections of exogenous mouse recombinant leptin (230 microg kg(-1) body weight) every alternate day for 15 days. Food and water intake and total body weight were measured every day and at the end of the experimental period of 45 days, plasma and cardiac lipids were analyzed. Exogenous leptin injections to ethanol fed mice significantly (P < 0.05) prevented the accumulation of total cholesterol, phospholipids (PL), triglycerides (TG) and free fatty acids (FFA) in the mouse heart and blood as compared to the untreated ethanol fed mice whereas, the plasma concentration of free cholesterol was significantly increased on leptin administration as compared to normal untreated mice. Moreover leptin administration significantly elevated the activities of cardiac lipoprotein lipase (LPL) and plasma lecithin cholesterol acyl transferase (LCAT) and significantly reduced the activities of cardiac HMG CoA reductase and cholesterol ester synthase (CES) on leptin administration to ethanol fed mice. Thus we could postulate that an increase in systemic leptin level prevents the accumulation of lipids in the plasma and heart of ethanol treated mice.

Short-term leptin treatment increases fatty acids uptake and oxidation in muscle of high fat-fed rats

The purpose of this study was to measure the effects of short-term (10 days) leptin treatment on insulin sensitivity as it pertains to fatty acid (FA) uptake, oxidation, and muscle triglyceride (mTG) synthesis in animals that have been administered a high-fat (HF) diet for 3 months. Male Wistar rats were randomly assigned to 1 of 4 groups. One group was fed a control diet (CON) and 3 groups were fed a HF diet. The HF and HF-leptin (HF-LEP) groups were fed the HF diet ad libitum and the amount of food eaten by the HF-pair fed (HF-P) group was equal to that of the HF-LEP group. At the end of the dietary period, rats were injected daily either with saline (CON, HF, HF-P) or with leptin (HF-LEP; 10 mg.kg-1.d-1) for 10 days before hindlimb perfusion. The perfusate contained 600 micromol/L palmitate traced with [14C]palmitate, 9 mmol/L glucose, and 100 microU/mL insulin. As dictated by the protocol, energy expenditure was not significantly different (P>.05) between HF-LEP and HF-P. Palmitate uptake and oxidation as well as mTG synthesis were greater (P<.05) in HF (9.8+/-0.3, 2.0+/-0.1, and 1.9+/-0.2 nmol.min-1.g-1) than in CON (8.0+/-0.4, 1.4+/-0.1, and 1.1+/-0.1 nmol.min-1.g-1) and this was associated with higher levels of mTG in HF. Palmitate uptake and oxidation were higher (P<.05) in HF-LEP (10.3+/-0.6 and 2.0+/-0.1 nmol.min-1.g-1) than in HF-P (8.3+/-0.5 and 1.5+/-0.2 nmol.min-1.g-1, P<.05), but mTG synthesis and mTG levels were not changed significantly by leptin treatment (P>.05). High-fat feeding decreased glucose uptake by 41% when compared with CON (2.4+/-0.4 vs 4.1+/-0.4 micromol.h-1.g-1; P<.05) but pair feeding alone (4.7+/-0.4 micromol.h-1.g-1) or leptin treatment (3.8+/-0.3 micromol.h-1.g-1) similarly prevented the HF diet-induced decrease in glucose uptake. These data indicate that short-term leptin treatment in HF-fed rats alters muscle FA metabolism by increasing FA uptake and oxidation relative to pair feeding alone. This results in a decrease in the FA esterification-oxidation ratio.

Association of single nucleotide polymorphisms in the leptin gene with carcass and meat quality traits of beef cattle1

Studies with different populations are required to properly characterize the robustness of associations of polymorphisms in candidate genes with economically important traits across beef cattle populations before this sort of genetic information can be used efficiently in breeding and management decisions. The objective of this study was to evaluate the association of previously reported SNP in the bovine leptin gene with carcass and meat quality traits from a large sample of crossbred beef cattle. Five SNP (UASMS1, UASMS2, UASMS3, E2JW, and E2FB) were genotyped on 1,111 crossbred bulls, heifers, and steers. The measured traits included fat, lean, and bone yield (%) by partial rib dissection, grade fat, LM area, HCW, quality grade, LM i.m. fat, and tenderness evaluation of LM and semitendinosus muscle. Only four SNP were analyzed (UASMS1, UASMS2, E2JW, and E2FB), because UASMS1 and UASMS3 were completely linked. A uni-variate mixed-inheritance animal model was used to evaluate the association of either genotypes or haplo-types with the traits. The two leptin exon 2 SNP were associated with fat and lean yield and grade fat (E2JW, P < 0.01; E2FB, P < 0.05), and they interacted in their effect on LM tenderness (P < 0.01). The leptin promoter SNP were either not associated with any of the traits (UASMS2) or with fat yield only (UASMS1). Three haplotypes (TCAC, CCAT, TTAC) were at high frequency in the population (88%) and had similar effects on all the traits. Compared with the common haplotypes, one haplotype (CCTT) showed a significantly different effect on fat and lean yield and grade fat (P < 0.01), and one haplotype (TTTT) had a different effect on LM tenderness (P < 0.03). Therefore, important associations between SNP within the leptin gene with lean yield, fatness (fat yield and subcutaneous fat), and tenderness were detected. Results confirm some of the previously reported associations, but diverge with respect to others, showing that further efforts are required to validate some prospective associations.

Dietary protein and exercise have additive effects on body composition during weight loss in adult women

This study examined the interaction of 2 diets (high protein, reduced carbohydrates vs. low protein, high carbohydrates) with exercise on body composition and blood lipids in women (n = 48, approximately 46 y old, BMI = 33 kg/m(2)) during weight loss. The study was a 4-mo weight loss trial using a 2 x 2 block design (Diet x Exercise). Diets were equal in total energy (7.1 MJ/d) and lipids ( approximately 30% energy intake) but differed in protein content and the ratio of carbohydrate:protein at 1.6 g/(kg . d) and <1.5 (PRO group) vs. 0.8 g/(kg . d) and >3.5 (CHO group), respectively. Exercise comparisons were lifestyle activity (control) vs. a supervised exercise program (EX: 5 d/wk walking and 2 d/wk resistance training). Subjects in the PRO and PRO + EX groups lost more total weight and fat mass and tended to lose less lean mass (P = 0.10) than the CHO and CHO + EX groups. Exercise increased loss of body fat and preserved lean mass. The combined effects of diet and exercise were additive for improving body composition. Serum lipid profiles improved in all groups, but changes varied among diet treatments. Subjects in the CHO groups had larger reductions in total cholesterol and LDL cholesterol, whereas subjects in the PRO groups had greater reductions in triacylglycerol and maintained higher concentrations of HDL cholesterol. This study demonstrated that a diet with higher protein and reduced carbohydrates combined with exercise additively improved body composition during weight loss, whereas the effects on blood lipids differed between diet treatments.

Leptin treatment induces loss of bone marrow adipocytes and increases bone formation in leptin-deficient ob/ob mice

Normal mice and leptin-deficient ob/ob mice were treated with leptin to study effects on osteogenesis and adipogenesis in bone marrow. Leptin treatment significantly decreased bone marrow adipocyte size and number in ob/ob mice while increasing bone formation, BMC, and BMD. The results suggest that, in leptin-sensitive animals, the reduction in marrow adipocytes has positive effects on bone formation.

INTRODUCTION

Adipocytes, osteoblasts, and osteoclasts have leptin receptors, and leptin can also affect bone metabolism indirectly through its receptors in the hypothalamus. We examined the effects of leptin treatment on bone formation, BMD, and marrow adipocyte population in normal mice and leptin-deficient ob/ob mice.

MATERIALS AND METHODS

At the age of 15 weeks, mice were implanted with Alzet osmotic pumps for subcutaneous delivery of treatment solutions (saline, 2.5 microg leptin/day, or 10 microg leptin/day) for 14 days at a delivery rate of 0.25 microl/h. Bone formation was assessed using fluorochrome labels, cell populations were quantified using histomorphometry, and bone densitometry was measured using DXA. We also used a Luminex Beadlyte assay system to quantify cell survival markers in bone marrow samples.

RESULTS AND CONCLUSIONS

Results indicate that both doses of leptin decreased the number of marrow adipocytes in ob/ob mice by >20% (p < 0.05) compared with PBS-treated ob/ob mice. The decrease in adipocyte number with leptin treatment is accompanied by an increase in concentration of the apoptosis marker caspase-3 in bone marrow adipocytes and hematopoietic cells. Both leptin doses also significantly (p < 0.05) increased the percentage of fluorochrome-labeled tibial endosteal surface by >30% compared with PBS-treated ob/ob mice. Leptin treatment increased whole body BMC by >30% in the ob/ob mice receiving the highest leptin dose. Leptin treatment provided no increase in bone formation, BMC, or BMD in normal, leptin-replete mice.

Leptin receptor activation depends on critical cysteine residues in its fibronectin type III subdomains

The leptin receptor (LR) complex is composed of a single subunit belonging to the class I cytokine receptor family and exists as a preformed complex. The extracellular portion contains two cytokine receptor homology (CRH) domains, separated by an Ig-like domain and followed by two membrane-proximal fibronectin type III (FNIII) domains. The mechanisms underlying ligand-induced receptor activation are still poorly understood. LRs can exist as disulfide-linked dimers at the cell surface, even in the absence of leptin. We evaluated the role of the two unpaired cysteine residues (Cys-672 and Cys-751) in the FNIII domains in receptor clustering, leptin binding, and biological activity. Although mutation of cysteine on position 751 to serine has hardly any effect on ligand binding and receptor activation, the C672S mutant exhibits a marked reduction in STAT3-dependent signaling. The double mutant was completely devoid of biological activity, although leptin binding remained unaffected. Mutation of both residues resulted in complete loss of disulfide bridge formation of FNIII domains in solution. In contrast, no difference was observed in ligand-independent oligomerization of the membrane-bound receptor, suggesting a role for cysteines in the CRH2 domain in formation of the preformed LR complex. We propose a model wherein leptin-induced clustering of two preformed dimers forms the activated LR complex. Disulfide bridge formation involving Cys-672 and Cys-751 may be necessary for JAK activation and hence signaling.

Plasma leptin status in young calves: effects of pre-term birth, age, glucocorticoid status, suckling, and feeding with an automatic feeder or by bucket

Plasma leptin concentrations depend on energy intake and fat stores and are modified by hormones, such as glucocorticoids. We have measured plasma leptin concentrations in pre-term calves (born on day 277 of gestation) during the first week of life, in full-term calves (290 days of gestation), fed similar amounts of nutrients with colostrum or a milk-derived formula, combined with or without dexamethasone treatment (to simulate a high glucocorticoid status), during the first five days of life, and in calves fed with an automatic feeder or by bucket or suckling on dams up to day 28. Leptin concentrations increased (P<0.05) from birth to day 7 in pre-term calves. In full-term calves leptin concentrations were stable from day 1 to day 4 in colostrum-fed animals, but decreased (P<0.05) and were lower (P<0.05) if fed a formula with similar amounts of energy and macronutrients as colostrum. Concentrations increased (P<0.05) from day 1 to day 2 in calves suckling on dams and then remained elevated, but did not change and were lower in calves fed with the automatic feeder or by bucket than in suckling calves. Dexamethasone only slightly elevated leptin concentrations. There was no episodic secretion pattern, and there were no consistent associations of leptin with various metabolites and hormones. In conclusion, plasma leptin in young calves with respect to effects of nutrition (low energy intake) and hormones (glucocorticoids) and in association with metabolic changes behaved differently from what is known in mature cattle.

Acute and chronic administration of immunomodulators induces anorexia in Zucker rats

To investigate the possible involvement of leptin signaling in lipopolysaccharide (LPS) anorexia, we compared the anorectic effect of LPS in genetically obese (fa/fa) Zucker rats and in their lean (Fa/?) counterparts. The effects of interleukin-1beta (IL-1beta) and muramyl dipeptide (MDP) were also tested. LPS [100 microg/kg body weight (BW)], IL-1beta (2 microg/kg BW) and MDP (2.2 mg/kg BW) injected intraperitoneally (i.p.) at lights out reduced food intake similarly in obese and lean rats. LPS injection at 500 or 1000 microg/kg BW (i.p.) also reduced food intake and BW similarly in obese and lean rats, but obese regained BW faster than lean rats. LPS (2.45 microg or 9.8 microg/h/rat) administered chronically with i.p. implanted osmotic pumps reduced food intake similarly on experimental day 1, regardless of the genotype. After day 3, the lean rats' anorectic response and recovery were dose-dependent, whereas the anorectic response in obese rats was minimally affected by dose (significant dose effect only on day 3). Again, obese rats regained lost BW faster than lean rats. These results do not support a role for leptin as the sole mediator of anorexia induced by bacterial products (LPS and MDP) and IL-1beta.

Hormones regulating lipid metabolism and plasma lipids in childhood obesity

OBJECTIVE

To review the mechanisms by which leptin, insulin and adiponectin influence lipid metabolism and plasma lipids in obesity, as well as to describe the associations between these hormones in prepubertal children.

METHOD

Revision of relevant papers published in the last 5 y related to the interactions of leptin, insulin and adiponectin, with special emphasis on those reporting potential mechanisms by which these hormones regulate lipid metabolism and plasma lipids. We also provide original results concerning the relationships found between plasma lipids and leptin, and insulin and adiponectin in prepubertal obese children.

RESULTS

Recent data in the literature shed new light to explain the effects of both leptin and adiponectin in the regulation of lipid metabolism in peripheral tissues. Activation of the AMP-dependent kinase pathway and subsequent increased fatty acid oxidation seems to be the main mechanism of action of these hormones in the regulation of lipid metabolism. In addition, we have found that insulin plasma levels are positively associated to leptin but negatively correlated with adiponectin in obese children. Adiponectin is negatively associated to plasma lipid markers of metabolic syndrome but positively related to HDL-cholesterol, whereas insulin and leptin show opposite patterns. These results support the effect of adiponectin in increasing insulin sensitivity and decreasing plasma triglycerides.

CONCLUSION

Leptin, insulin and adiponectin are associated hormones that regulate lipid metabolism in childhood. Adiponectin appears to be the missing link to explain the alterations in lipid metabolism and plasma lipids seen in obesity.

Metabolic adaptations to fasting and chronic caloric restriction in heart, muscle, and liver do not include changes in AMPK activity

Activation of adenosine monophosphate-activated protein kinase (AMPK) plays a central role in allowing cells to adapt to nutrient deprivation in vitro. This link between AMPK activity and nutritional status has raised the possibility that AMPK plays a role in the metabolic adaptation to acute and chronic nutritional stress. However, the effects of nutritional stress on AMPK activity in vivo have not been systematically evaluated. To address this, we measured the effects of 24 h of fasting and 4 mo of caloric restriction (CR) on AMPK alpha 1 and -alpha 2 activities in heart, skeletal muscle, and liver in mice. Although fasting caused the expected changes in body weight, plasma leptin, and free fatty acids, it did not increase AMPK activity in heart or skeletal muscle and only increased liver AMPK activity by approximately 20% (P = 0.10). Likewise, CR caused the expected changes in body weight, plasma leptin, and free fatty acids but did not alter AMPK activity in any of the three tissues. Although CR did not alter liver AMPK activity, it dramatically decreased the amount of phosphorylated acetyl-CoA carboxylase, and this was found to be due to decreased protein expression. Plasma leptin, a putative activator of AMPK, varied eightfold across the four groups of mice in the absence of changes in AMPK activity in any tissue. We conclude that, although the metabolic adaptations to fasting and CR include changes in plasma leptin concentration and phosphorylated acetyl-CoA carboxylase, these effects occur without changes in AMPK activity.

Reproductive Switch and Aging: The Case of Leptin Change in Dietary Restriction

We have proposed that normal food intake is geared toward optimizing the internal milieu for reproduction, despite some components of this milieu being detrimental to health. In dietary restriction, the animal is prevented from eating enough to attain or maintain reproductive capacity and this particular milieu does not materialize. Life extension occurs as a by-product. This idea provides a framework for exploring biomolecular changes in dietary restriction and their relevance to aging. Leptin is a case in point: here, a decrease in leptin level in dietary restriction is explored in the light of leptin's role in the complex signaling system of reproductive switch.

T3 and Triac inhibit leptin secretion and expression in brown and white rat adipocytes

Leptin regulates appetite, inhibits food intake, and seems to increase energy expenditure. We investigated the effect of triiodothyroacetic acid (Triac), a metabolite of T3, which seems to be more thermogenic than T3, on leptin secretion and mRNA expression. Rat primary cultures of white and brown adipocytes were treated with increasing concentrations of Triac and T3. The effect of different types of serum and insulin concentrations was also tested. Serum inhibited leptin secretion and mRNA expression. Leptin secretion was also clearly inhibited by Triac and T3 in a dose-dependent manner and with similar potency. In the presence of norepinephrine (NE), Triac and T3 had a similar inhibitory effect, but the inhibition was almost complete in white adipocytes. Parallel results were found at the mRNA level, where Triac and T3 had similar inhibitory potency, both alone and with NE. We also show that insulin induced dose- and time-dependent increases in leptin secretion, reaching maximum levels at 0.5 and 3 nM insulin for white and brown adipocytes, respectively. Leptin secretion was higher in white than in brown adipocytes. The increases in leptin secretion were preceded by increases in leptin mRNA. In conclusion, these data demonstrate for the first time that Triac, like T3 and serum, inhibits leptin secretion and expression in white and brown adipocytes, whereas insulin has the opposite effect.

Augmenting leptin circadian rhythm following a weight reduction in diet-induced obese rats: short- and long-term effects

The current study sought to examine whether leptin injections following a weight reduction in diet-induced obese rats would reduce both the enhanced food intake and body weight (BW) regain observed during the refeeding phase. Female Wistar rats (n = 100, 20 per group) were divided into 5 groups: (1) LEP rats were fed a high-fat (HF) diet (35% wt/wt) for 8 weeks to induce obesity and were then food-restricted (50% ad libitum) with a fortified high-fat diet for 2 weeks to induce a 20% BW loss. These rats were then refed the HF diet ad libtum for another 11 weeks. They were given leptin injections (200 microg/kg BW, twice daily, intraperitoneally ) for 19 days concomitant with the onset of refeeding. (2) SAL rats were treated in the same manner as LEP rats except that they were given saline injections; (3) PF rats were treated like SAL rats except that they were pair-fed with the LEP rats; (4) HFC rats were fed HF diet ad libitum; and (5) LFC rats were fed a low-fat (LF) diet (AIN-93M) ad libitum. Ten rats from each group were killed after leptin treatment and at the end of the study. Food and caloric intakes were monitored, and body composition and plasma glucose, insulin, and leptin levels were assessed at death. Leptin injections after a weight reduction briefly reduced energy intake during the first week only. After 19 days of treatment and to the end of the study, LEP and SAL rats were similar in energy intake, BW (LEP: 393 +/- 11.2 g, SAL: 371 +/- 14.1; difference not significant [NS]) and total body fat percent (LEP: 19.3 +/- 1.5, SAL: 17.6 +/- 1.5; NS). Leptin treatment induced hyperinsulinemia and insulin resistance. All of the metabolic abnormalities observed at the end of treatment period disappeared at the end of the study (8 weeks post-leptin injection). We conclude that bolus leptin injections to manipulate leptin circadian rhythm in diet-induced obese rats after a weight reduction caused temporary insulin resistance and hyperinsulinemia, and were ineffective in influencing food intake, BW, and fat content. Leptin resistance was evident following 1 week of treatment in this study. Leptin treatment had no effect on body fat content both short-term and long-term. Exogenous leptin treatment may, in the long run, increase leptin resistance in diet-induced obese animals. Hence, long-term leptin treatment may not be beneficial to obese individuals consuming a HF diet.

Effect of conjugated linoleic acid on body composition and plasma lipids in humans: an overview of the literature

Studies in mice have indicated that feeding diets containing 0.5-1% conjugated linoleic acid (CLA) considerably reduces body fat. These findings have attracted much interest because of the potential use of CLA as a tool to promote weight loss in humans. Several CLA studies in humans have now been published, and the objective of the present review was to give an overview of these experiments. Most of the studies were done in free-living subjects and were not strictly controlled for nutrient and energy intakes. None of the studies found a significant reduction in body weight, and only 2 studies showed a significant but relatively small body fat-lowering effect. Some studies suggested that CLA may have a tendency to increase lean body mass. Furthermore, there are indications from animal studies that CLA may have effects on plasma lipids. However, only one study in humans showed a significant HDL-cholesterol-lowering effect of CLA; in all the other studies, there were no significant effects on plasma total, LDL-, and HDL-cholesterol concentrations or on plasma triacylglycerol concentrations. Thus, the results of the studies in humans indicate that the effect of CLA on body fat is considerably less than that anticipated from mice studies and that CLA has no major effect on plasma lipids.

Modulatory effect of leptin on nitric oxide production and lipid metabolism in term placental tissues from control and streptozotocin-induced diabetic rats

Leptin production by placental tissues contributes to its circulating levels and functions. The diabetic pathology induces alterations in leptin levels. In the present study, leptin levels were evaluated in placental tissue from control and neonatal streptozotocin-induced (n-STZ) diabetic rats during late gestation. The effects of leptin levels on the generation of nitric oxide (NO), prostaglandin (PG) E2 production and lipid metabolism were examined. Leptin levels were diminished in placentas from n-STZ diabetic rats compared with controls (P < 0.01). These differences were also evident when leptin was evaluated immunohistochemically. Addition of leptin (1 nm) in vitro enhanced NO production in control (66%) and diabetic placentas (134%) by stimulating NO synthase activity (by 38% and 54%, respectively). The addition of leptin increased PGE2 production in placentas from control (173%) and diabetic rats (83%) and produced a 50% decrease in placental lipid levels (phospholipids, triacylglycerides, cholesterol and cholesteryl ester) without involving a reduction in de novo lipid synthesis. These data indicate that leptin enhances the production of placental NO and PGE2, vasoactive agents that modify placental blood flow, and that leptin stimulates placental lipid metabolism, probably generating more lipids for transfer to the fetus. In the diabetic rat, placental leptin was reduced, probably as a response to the maternal environment to locally regulate the transfer of nutrients to the developing fetus.

Response of Plasma Leptin Concentration to Jugular Infusion of Glucose or Lipid Is Dependent on the Stage of Lactation of Holstein Cows

In this study we investigated the hormonal and metabolite responses to isoenergetic jugular infusions of glucose or lipid in early- and late-lactation Holstein cows. Six Holstein cows were used in a replicated Latin square design with jugular infusions of either 1) control (CON; saline), 2) glucose (GLU; 50% dextrose) or 3) lipid (LIP; 20% Intralipid). Treatments did not affect dry matter intake, with the exception of a hypophagic effect of LIP in late lactation. The GLU-induced hyperglycemia and hyperinsulinemia were greater in late-lactation than in early-lactation cows. The GLU treatment did not affect plasma leptin and insulin-like growth factor-1 (IGF-1) concentrations in early-lactation cows, but it increased them in late-lactation cows. The LIP treatment did not affect plasma leptin, insulin and IGF-1 concentrations in early-lactation cows, despite a marked LIP-induced increase in plasma nonesterified fatty acid and beta-hydroxybutyrate concentrations and a reduction in growth hormone (GH) concentration. Compared with the delayed leptin response to GLU, the stimulatory effect of LIP on leptin secretion in late-lactation cows was relatively rapid and occurred in the absence of any significant changes in plasma insulin, IGF-1 or GH. We propose that insulin-mediated glucose metabolism may be involved in the stimulatory effects of glucose on leptin secretion in late-lactation animals but that the stimulatory effects of lipid are independent of insulin or IGF-1. In early-lactation animals a strong inhibitory effect of GH on leptin expression and release, in addition to low adipose reserves and/or energy balance, might override any short-term stimulatory effect of glucose or lipid on leptin secretion.

Plasma leptin and exercise: recent findings

It is established that plasma leptin is associated with satiety and that leptin stimulates lipid metabolism, and increases energy expenditure. These effects implicate leptin as a major regulator of energy homeostasis, which may serve to limit excess energy storage. As plasma leptin concentrations are tightly coupled with fat mass in humans, decreases in adipose mass with weight loss coincide with decreased concentrations of circulating leptin. However, due to many confounding factors, the effects of exercise on circulating leptin are less clear. The data from investigations examining single exercise bouts suggest that serum leptin concentrations are unaltered by short duration (41 minutes or less), non-exhaustive exercise, but may be affected by short duration, exhaustive exercise. More convincingly, studies investigating long duration exercise bouts indicate that serum leptin concentrations are reduced with exercise durations ranging from one to multiple hours. These findings raise speculation that exercise-associated reductions in leptin may be due to alterations in nutrient availability or nutrient flux at the level of the adipocytes, the primary site of leptin production and secretion. Thus, one purpose of this review is to discuss the effects of exercise on circulating leptin concentrations with special emphasis on studies that have examined single exercise bouts that are associated with high levels of energy expenditure and energy deficit. In addition, a 'nutrient sensing pathway' (the hexosamine biosynthetic pathway), which regulates leptin gene expression, will be discussed as a possible mechanism by which exercise-induced energy deficit may modulate serum leptin concentrations.

The implications of weight changes with antipsychotic treatment

Patients receiving treatment with atypical antipsychotics commonly experience weight gain, which can cause considerable distress and can have deleterious effects on cardiovascular health. Because of the associated weight gain and potential direct effects on glucose metabolism, atypical antipsychotics have also been linked to the development of type II diabetes mellitus. Data on long-term treatment with these agents show that clozapine and olanzapine, followed by risperidone, were associated with the greatest degree of weight gain. A large body of data suggests that during long-term treatment, patients receiving the atypical antipsychotic quetiapine experience minimal weight gain. Data also suggest that quetiapine treatment does not increase the risk of developing type II diabetes. The use of atypical antipsychotics is increasing, as these agents are being prescribed for schizophrenia in lieu of conventional antipsychotics. Furthermore, these drugs have efficacy for treating other conditions such as bipolar disorder. Physicians prescribing atypical antipsychotics must be aware of the risk of weight gain and its associated comorbidities.

Resistance to IP leptin-induced adipose apoptosis caused by high-fat diet in mice

The objectives of this experiment were to determine whether leptin causes adipocyte apoptosis in mice, whether peripheral administration is an effective means of studying leptin-induced adipocyte apoptosis, and whether high-fat feeding results in reduced responsiveness to leptin-induced adipocyte apoptosis. Continuous 13-day intraperitoneal infusion of 10 microg/day leptin significantly increased adipocyte apoptosis in the epididymal/parametrial fat pads of male and female mice, but only male mice developed reduced responsiveness to leptin-induced adipocyte apoptosis after high-fat (45% fat) feeding for 5 or 15 weeks. There was a positive correlation between serum leptin concentration and percent apoptotic adipocytes. These findings demonstrate that leptin administered peripherally is effective in inducing adipocyte apoptosis in mice, thus extending the possibility of studying this effect of leptin in a wider variety of animal models. In addition, high-fat feeding has a gender-specific effect on development of reduced responsiveness to leptin-induced adipocyte apoptosis.

Effect of leptin administration on plasma and tissue lipids in alcohol induced liver injury

Previous studies suggest a possible link between leptin and hepatic inflammation; however the role of leptin in liver diseases remains unclear. The purpose of the present study was to evaluate the effect of leptin on plasma and tissue lipids in experimental hepatotoxicity. Administering ethanol (6.32 g/kg body weight) to 4-week-old healthy mice for 45 days resulted in significantly elevated levels of plasma and tissue phospholipids, triglycerides and free fatty acids as compared with those of the control animals. Subsequent to the experimental induction of hepatotoxicity (i.e., the initial period of 30 days) exogenous leptin was simultaneously administered (230 microg/kg body weight) every alternate day for 15 days along with the daily dose of alcohol. Leptin administration to control and alcohol-treated mice reduced the weight gain and significantly lowered the levels of plasma and tissue lipids as compared with the untreated control and alcohol supplemented mice. It is postulated that the increase in systemic leptin levels lower the plasma and tissue lipids of alcohol-treated mice, which operates independently of changes in food intake, body weight and the size of the fat stores.

The hypothalamus in episodic brain disorders

Episodic brain disorders (EBD) form an intriguing group of neurological diseases in which at least some of the symptoms occur in attacks. The hypothalamus integrates many brain functions, including endocrine and autonomic control, and governs various body rhythms. It seems a likely site in which the initiation of attacks of EBD can be modulated. Indeed, the hypothalamus has a crucial role in EBD such as narcolepsy and cluster headache. The same may be true for migraine and depression. Here we summarise the evidence supporting an important role for the hypothalamus in the initiation of disease episodes in various EBD. Study of the various pathophysiological concepts of EBD within the context of the hypothalamus may prove a fruitful example of cross-fertilisation between various research areas.

Gender difference in the leptin response to feeding in peroxisome-proliferator-activated receptor-alpha knockout mice

OBJECTIVE

Peroxisome-proliferator-activated receptor-alpha (PPARalpha) has a central role in lipid metabolism. Mice lacking PPARalpha accumulate hepatic fat and are prone to late onset obesity. Leptin, an adipocyte-derived hormone, also plays an important role in regulating energy balance. In order to test the hypothesis that leptin secretion increases in response to PPARalpha knockout, we determined leptin concentrations including the effect of nutritional status in male and female PPARalpha knockout mice compared with wild-type controls.

DESIGN

We studied the effect of 16 h fasting and 4 h refeeding on plasma leptin concentrations in male and female wild-type and PPARalpha-knockout mice, aged 14 weeks. In female mice the effect of daily growth hormone (GH) injection on the leptin response to refeeding was determined.

RESULTS

Circulating leptin concentrations were higher in female mice compared with males and increased in both sexes after PPARalpha-knockout. There was no change in leptin levels after a 16 h fast, compared with ad libitum feeding. However leptin increased with refeeding, to the greatest extent in female PPARalpha-knockout mice. Intermittent GH administration decreased leptin concentrations in female, wild-type and PPARalpha-knockout animals and abolished the exaggerated leptin response to refeeding.

CONCLUSIONS

Leptin concentrations are increased in PPARalpha-knockout mice. There are gender differences in the leptin response to feeding which may be due to differences in insulin sensitivity.

An experimental paradigm for studying the cellular and molecular mechanisms of cancer inhibition by energy restriction

With a rapid-emergence, chemically induced animal model for breast cancer, an experiment designed to test the hypothesis that energy restriction (ER) induces the loss of carcinogen-initiated cells from the mammary gland, thereby conferring a permanent protective effect against the development of cancer, failed to support this hypothesis. Nonetheless, this experiment served to define an experimental approach and a time frame on which to focus mechanistic inquiry. With an ER and energy repletion (ER-REP) protocol as a tool for identifying potential mediators of the cancer-inhibitory activity of ER, concomitant changes in plasma corticosterone and insulin-like growth factor 1 during energy restriction and repletion were observed. The relationship of the timing of these hormonal changes to the time frame of change in the carcinogenic response during ER-REP was consistent with the role of both hormones in mediating the protective effects of ER. However, a similar pattern of change in the energy-regulated hormone leptin indicated that its role in cancer inhibition also merits consideration.

Leptin activates cardiac fatty acid oxidation independent of changes in the AMP-activated protein kinase-acetyl-CoA carboxylase-malonyl-CoA axis

Leptin regulates fatty acid metabolism in liver, skeletal muscle, and pancreas by partitioning fatty acids into oxidation rather than triacylglycerol (TG) storage. Although leptin receptors are present in the heart, it is not known whether leptin also regulates cardiac fatty acid metabolism. To determine whether leptin directly regulates cardiac fatty acid metabolism, isolated working rat hearts were perfused with 0.8 mm [9,10-(3)H]palmitate and 5 mm [1-(14)C]glucose to measure palmitate and glucose oxidation rates. Leptin (60 ng/ml) significantly increased palmitate oxidation rates 60% above control hearts (p < 0.05) and decreased TG content by 33% (p < 0.05) over the 60-min perfusion period. In contrast, there was no difference in glucose oxidation rates between leptin-treated and control hearts. Although leptin did not affect cardiac work, oxygen consumption increased by 30% (p < 0.05) and cardiac efficiency was decreased by 42% (p < 0.05). AMP-activated protein kinase (AMPK) plays a major role in the regulation of cardiac fatty acid oxidation by inhibiting acetyl-CoA carboxylase (ACC) and reducing malonyl-CoA levels. Leptin has also been shown to increase fatty acid oxidation in skeletal muscle through the activation of AMPK. However, we demonstrate that leptin had no significant effect on AMPK activity, AMPK phosphorylation state, ACC activity, or malonyl-CoA levels. AMPK activity and its phosphorylation state were also unaffected after 5 and 10 min of perfusion in the presence of leptin. The addition of insulin (100 microunits/ml) to the perfusate reduced the ability of leptin to increase fatty acid oxidation and decrease cardiac TG content. These data demonstrate for the first time that leptin activates fatty acid oxidation and decreases TG content in the heart. We also show that the effects of leptin in the heart are independent of changes in the AMPK-ACC-malonyl-CoA axis.

Early decline in the catecholamine release-inhibitory peptide catestatin in humans at genetic risk of hypertension

BACKGROUND

Hypertension is a complex trait with an ill-defined genetic predisposition, in which adrenergic mechanisms seem to be involved even at the early stages. Chromogranin A is a pro-hormone stored and released with catecholamines by exocytosis; its fragment catestatin, formed in vivo, inhibits further catecholamine release as an antagonist at the physiologic trigger for secretion, the neuronal nicotinic cholinergic receptor.

METHODS

We measured catestatin by radioimmunoassay in n = 277 subjects stratified by blood pressure (n = 61 hypertensive, n = 216 normotensive), and if normotensive by genetic risk of developing hypertension: family history positive (n = 176) versus negative (n = 40). Maximum likelihood analysis tested for bimodality. Involvement of catestatin in pathophysiology was probed by measurements of catecholamines and leptin, and the hemodynamic responses to environmental (cold) stress.

RESULTS

The normotensive offspring of patients with hypertension already had diminished catestatin (P = 0.024), and family history was a better predictor of catestatin than age, ethnicity or gender (P = 0.014). Greater catestatin variance among family history-positive individuals (P = 0.021) suggested heterogeneity in this group, and a bimodal distribution (P < 0.001) identified 4.3% of individuals in a lower mode of catestatin values, all with positive family histories (P = 0.05). Catestatin correlated inversely with body mass index (r = -0.215, r(2) = 0.046, n = 276, P < 0.001) and plasma leptin (r = -0.203, r(2) = 0.041, n = 212, P = 0.003), while body mass index and leptin correlated directly (r = 0.59, r(2) = 0.350, n = 212, P < 0.001). Family history-positive individuals had greater epinephrine excretion (P = 0.037) in addition to diminished catestatin, suggesting an inhibitory effect of catestatin on chromaffin cells in vivo. Low plasma catestatin predicted enhanced pressor response to a sympathoadrenal stressor (cold stress; r = -0.184, r(2) = 0.034, n = 211, P = 0.007), suggesting an adrenergic mechanism whereby diminished catestatin might predispose to later development of hypertension. In white subjects, diminished catestatin also predicted greater systemic vascular resistance responses to cold stress (r = -0.307, r(2) = 0.094, n = 75, P = 0.007), a relationship not found in Blacks (r = 0.122, r(2) = 0.015, n = 94, P = 0.243).

CONCLUSIONS

We conclude that catestatin is diminished early in the course of development of hypertension, even in the normotensive offspring of patients with the disease. Low catestatin predicts augmented adrenergic pressor responses, suggesting a mechanism whereby diminished catestatin might increase the risk for later development of hypertension.

The leptin-like effects of 3-d peripheral administration of a melanocortin agonist are more marked in genetically obese Zucker (fa/fa) than in lean rats

The effects of a 3-d peripheral administration of an alpha-MSH agonist, MTII, on body weight and the expression of uncoupling proteins (UCPs) and carnitine palmitoyltransferase-1 were determined in lean and genetically obese fa/fa rats by comparing MTII-treated animals with two different control groups, one being ad libitum fed, the other pair-fed to the amount of food consumed by MTII-treated rats. MTII treatment of lean and obese rats lowered food intake and body weight, the effects being more marked in obese than in lean rats. In both groups, MTII administration suppressed the increased plasma FFA levels brought about by food restriction. In lean rats, MTII prevented the decrease in brown adipose tissue UCP1, UCP2, and UCP3 expression and muscle UCP3 occurring during food restriction. In obese animals, MTII markedly increased brown adipose tissue (7-fold) and muscle (2.5-fold) UCP3 expression. The decrease in liver carnitine palmitoyltransferase-1 elicited by food restriction in lean and obese rats was prevented by MTII administration. In summary, the effects of MTII resemble those of leptin and are more marked in obese than in lean animals, in keeping with their reported reduced endogenous melanocortin tone. Melanocortin agonists may be useful in the treatment of obesity associated with impaired leptin signaling.

Brain evolution and lifespan regulation: conservation of signal transduction pathways that regulate energy metabolism

Mechanisms for sensing, acquiring, storing and using energy are fundamental to the survival of organisms at all levels of the phylogenetic scale. Single-cell organisms evolved surface receptors that sense an energy source and, via signal transduction pathways that couple the receptors to the cell cytoskeleton move towards the energy source. Mutlicellular organisms evolved under conditions that favored species that developed complex mechanisms for obtaining food, with nervous systems being critical mediators of energy acquisition and regulators of energy metabolism. A conserved signaling system involved in regulating cellular and organismal energy metabolism, and in sensing and responding to energy/food-related environmental signals, involves receptors coupled to the phosphatidylinositol-3-kinase-Akt signaling pathway. Prominent activators of this pathway are insulin, insulin-like growth factors and brain-derived neurotrophic factor (BDNF). Recent studies in diverse organisms including nematodes, flies and rodents have provided evidence that insulin-like signaling in the nervous system can control lifespan, perhaps by modulating stress responses and energy metabolism. Interestingly, the lifespan-extending effect of dietary restriction in rodents is associated with increased BDNF signaling in the brain, and a related increase of peripheral insulin sensitivity, suggesting a mechanism whereby the brain can control lifespan. Thus a prominent evolutionarily conserved function of the nervous system is to regulate food acquisition and energy metabolism, thereby controlling lifespan.

Body-weight changes are clearly reflected in plasma concentrations of leptin in female mink (Mustela vison)

The mink is a seasonal breeder with a propensity for seasonal fatness, and it is very responsive to changes in energy supply. The objectives of the present study were first, to validate a multi-species leptin assay for mink (Mustela vison) plasma, and second, to evaluate how plasma leptin and insulin concentrations responded to energy restriction and body-weight loss and refeeding with restoration of body reserves. The study was performed with six very fat yearling females (initial mean body weight 1,451 (SD 119) g, i.e. approximately 300 g more than for a female in normal body condition). The animals were fed in restricted amounts (about 35 % metabolizable energy requirement for maintenance) in order to reach a very lean body condition. The target weight of 800 g was reached after about 1 month of restriction. The animals were then refed ad libitum until almost complete weight recovery. Blood samples were taken on days 1, 24, 34 (end of restriction), 44, 55 and 71 (end of experiment) and analysed for plasma concentrations of leptin and insulin. Three females were mated on day 44. Leptin and insulin concentrations mirrored each other and clearly reflected changes in body weight. Significant (P<0.001) Pearson correlation coefficients of 0.75 (leptin-insulin), 0.72 (leptin-body weight) and 0.59 (insulin-body weight) were found. Two of the three females that were mated gave birth to normal litters. It was concluded that the leptin assay yielded acceptable results for animals with body weight:fat content within the range investigated here, and that plasma leptin reflected body fat mass.

Plasma leptin and exercise: recent findings

The cloning of murine and human obese genes in 1994, and the subsequent identification that the product of the obese gene, leptin, is secreted from adipose tissue, stimulated a tremendous amount of interdisciplinary interest in adipose tissue endocrinology and the potential role of this tissue in the regulation of energy balance. Exercise, with concomitant changes in fuel flux, systemic hormone levels and energy expenditure, may contribute to the regulation of plasma leptin levels and presumably, leptin action. The initial work characterising the leptin-exercise relationship was equivocal. Cross-sectional studies provided some mixed evidence regarding the relationship between aerobic capacity or habitual physical activity and plasma leptin. In contrast, studies on acute bouts of exercise and exercise training interventions have, with few exceptions, suggested that exercise does not alter systemic leptin independent of changes in fat mass. In general, these studies did not carefully control for energy balance, and sampled only a single fasting plasma leptin level. Two recent studies utilising experimental designs in which energy balance was controlled and 24-hour profiles of plasma leptin were determined have provided the most compelling evidence to date of the interaction between exercise, energy balance and systemic leptin in humans. These studies provide a clear explanation for the apparent lack of an acute effect of exercise on systemic leptin and underscore the importance of clearly defining the balance between energy intake and energy expenditure when studying the physiology of leptin. The aim of this brief review is to provide an overview of the interaction between energy expenditure during physical activity and systemic leptin level. Special emphasis will be placed on those studies in which energy intake/balance was carefully controlled.

Seasonally inappropriate body weight induced by food restriction: effect on hypothalamic gene expression in male Siberian hamsters

Male Siberian hamsters undergo physiological weight change in changing photoperiod. Weight loss was induced by food restriction in long days to mimic short-day weight loss, or by food restriction superimposed on short-day weight loss, to test the hypothesis that the hypothalamus differentiates between weight change induced by imposed negative energy balance (inappropriate body weight) and seasonal, appropriate, body weight change, even when these are of similar magnitude. Short-day weight loss was accompanied by reduced POMC and leptin receptor (OB-Rb) mRNA in the arcuate nucleus but elevated cocaine- and amphetamine-regulated transcript. Melanocortin 3-receptor gene expression was reduced in the arcuate nucleus but elevated in the ventromedial nucleus compared with ad libitum-fed long-day controls. Weight loss in long-day restricted animals generated a gene expression profile typical of negative energy balance with low cocaine- and amphetamine-regulated transcript mRNA and elevated OB-Rb. Melanocortin 3-receptor mRNA levels were indistinguishable in short-day and long-day food-restricted hamsters. The hypothalamic correlates of food restriction in short days included up-regulated anabolic neuropeptides and increased OB-Rb mRNA. Low plasma leptin is integrated differently in short-day and long-day restricted animals, and seasonally-inappropriate body weight in either photoperiod engages the compensatory neuropeptide systems involved in the defense of body weight.

The adipocyte: a model for integration of endocrine and metabolic signaling in energy metabolism regulation

The ability to ensure continuous availability of energy despite highly variable supplies in the environment is a major determinant of the survival of all species. In higher organisms, including mammals, the capacity to efficiently store excess energy as triglycerides in adipocytes, from which stored energy could be rapidly released for use at other sites, was developed. To orchestrate the processes of energy storage and release, highly integrated systems operating on several physiological levels have evolved. The adipocyte is no longer considered a passive bystander, because fat cells actively secrete many members of the cytokine family, such as leptin, tumor necrosis factor-alpha, and interleukin-6, among other cytokine signals, which influence peripheral fuel storage, mobilization, and combustion, as well as energy homeostasis. The existence of a network of adipose tissue signaling pathways, arranged in a hierarchical fashion, constitutes a metabolic repertoire that enables the organism to adapt to a wide range of different metabolic challenges, such as starvation, stress, infection, and short periods of gross energy excess.

Inhibition of preadipocyte differentiation by myostatin treatment in 3T3-L1 cultures

Myostatin, a new TGF-beta family member, is known as a muscle growth inhibitor, but its role in adipocyte development has not been studied. To test the role of Myostatin in 3T3-L1 preadipocyte differentiation, we treated cultured 3T3-L1 preadipocytes with Myostatin dissolved in 0.1% trifluoroacetic acid (TFA) during differentiation after they had become confluent. Myostatin treatment significantly decreased glycerol-3-phosphate dehydrogenase (GPDH) activity and oil Red-O staining compared to controls that did not receive Myostatin. Western blot analysis showed that the expression levels of CCAAT/enhancer binding protein alpha (C/EBP alpha) and peroxisome proliferator-activated receptor gamma (PPAR gamma) were significantly decreased by Myostatin treatment (P < 0.05). However, the expression of C/EBP beta was not significantly changed by the treatment (P > 0.05). From RT-PCR result, the relative level of leptin mRNA in Myostatin-treated cells was not significantly different (P > 0.1) from the level in cells without Myostatin treatment. Our data show that Myostatin, a secreted protein from muscle, inhibits preadipocyte differentiation in 3T3-L1 cells, which is mediated, in part, by altered regulation of C/EBP alpha and PPAR gamma.

Hypothalamic neuropeptide mechanisms for regulating energy balance: from rodent models to human obesity

In small rodents there is compelling evidence of a lipostatic system of body mass regulation in which peripheral signals of energy storage are decoded in the hypothalamus. The ability of small mammals to defend an appropriate mass against imposed energy imbalance has implicated hypothalamic neuroendocrine systems in body mass regulation. The effect of the neuropeptide systems involved in this regulation is primarily compensatory. However, small mammals can also effect changes in the level of body mass that they will defend, as exemplified by seasonal species. Regulatory control over fat mass may be relatively loose in humans; the sizes of long-term storage depots may not themselves be regulated, but rather may be a consequence of temporal variations in the matching of supply and demand. Whether food intake is regulated to match energy demand, or to match demand and to regulate storage, it is clear that physiological defects or genetic variation in hypothalamic and peripheral feedback systems will have profound implications for fat storage. Study of mechanisms implicated in energy homeostasis in laboratory rodents is likely to continue to identify targets for pharmacological manipulation in the management of human obesity.