Leptin levels in human and rodent: measurement of plasma leptin and ob RNA in obese and weight-reduced subjects

Physical activity and low-fat diet: is it enough to maintain weight stability in the reduced-obese individual following weight loss by drug therapy and energy restriction?

OBJECTIVE

The anthropometric and physiological effects of a physical activity (PA) and a mildly energy-restricted low-fat diet (LFD) follow-up program after a long-term dietary restriction were studied in 12 men and 8 women.

RESEARCH METHODS AND PROCEDURES

The dietary restriction (approximately 700 kcal/day) was accompanied by a fenfluramine (60 mg/day) or placebo treatment for 15 weeks, whereas the mean duration of the PA-LFD follow-up was 18 weeks.

RESULTS

The long-term dietary restriction reduced body weight (-11.9 and -7.6 kg, p<.001), fat mass (FM) (-10.6 and -5.8 kg, p<0.01), resting metabolic rate (RMR) (-304 kcal/day, p<0.01 and -148 kcal/day, NS) in men and women, respectively. A decrease in fat-free mass (FFM) was also observed in women (-1.8 kg, p<0.05). The PA-LFD follow-up preserved weight stability at a reduced body weight and caused an additional significant decrease in FM for men (-3.4 kg, p<0.05). This part of the intervention also caused an increase in daily RMR for men (134 kcal/day, NS) to the point where this value no longer differed from the pre-energy restriction value. In contrast, RMR was further reduced in women (-200 kcal/day) to the point where it significantly differed from initial values (p<0.01). Resting seated heart rate was reduced by the PA-LFD follow-up in men leading it to differ significantly from both pre- and post-energy restriction values (-8.5 and -5.5 bpm, p<0.01).

DISCUSSION

In conclusion, these results suggest that a PA-LFD follow-up has the potential to permit body weight stability and may even accentuate fat loss in the reduced-obese state. Moreover, resting energy expenditure is increased under such conditions in men. These stimulating effects seem to be specific to energy metabolism since seated heart rate was either further reduced or remained stable in response to the PA-LFD follow-up.

Serum leptin levels in healthy ageing men: are decreased serum testosterone and increased adiposity in elderly men the consequence of leptin deficiency?

OBJECTIVE

The limited information on serum leptin levels in elderly men suggests the occurrence of an age-related decrease, with disruption of the relationship between fat mass and leptin levels. A relative leptin deficiency might thus be implicated in the increase of fat mass and decrease of serum testosterone levels in elderly men. Therefore, we have reevaluated the age-related changes in serum leptin levels and their relationship with adiposity and androgen levels in a large group of community dwelling men.

SUBJECTS AND MEASUREMENTS

Serum leptin and androgen levels were measured in 271 healthy, ambulatory elderly men (median age 74 years), as well as in 61 middle-aged (median 43 years) and 40 young (median 25.5 years) controls. Adiposity was assessed by anthropometrical measurements (body mass index; BMI) and by estimation of fat mass by the bio-impedance method.

RESULTS

Serum leptin levels, whether or not adjusted for BMI, were found to increase with age, the values tending to level off after the age of 45 years, and were strongly correlated to BMI (r = 0.77) and fat mass assessed by the bio-impedance method (r = 0.81). Linear regression analysis showed a similar slope for the relationship between BMI and serum leptin in the three age groups. Multiple linear regression analysis indicated BMI, age and serum insulin, but not serum testosterone, as significant independent correlates of serum leptin. Serum (free) testosterone levels were negatively correlated with age and serum leptin, also after partialization for BMI: rank correlation coefficients vs. age and serum leptin, respectively, were - 0.20 (P < 0.001) and - 0.16 (P < 0.01) for total testosterone and - 0.60 (P < 0.001) and - 0.23 (P < 0.001) for free testosterone. Dehydroepiandrosterone sulphate (DHEAS) and leptin levels emerged as significant independent correlates in a multiple linear regression model for total serum testosterone; BMI and serum insulin became highly significant correlates in the same model when leptin was omitted from the independent variables.

CONCLUSION

Ageing in men is accompanied by a rise of serum leptin levels with a maintained strong association between serum leptin and adiposity in elderly men. Testosterone does not appear to be a major determinant of serum leptin in healthy men, while leptin does emerge as a negative correlate of serum testosterone. Increased fat mass and decreased testosterone production in elderly men cannot be attributed to a relative leptin deficiency.

Fluctuation of serum leptin level in rats after ovariectomy and the influence of estrogen supplement

In order to understand the mechanism of increasing body fat in perimenopausal and postmenopausal women, an ovariectomy-induced obesity model was used to study the role of leptin. In this investigation, a long-term study lasted for 13 weeks was conducted to monitoring the change of serum leptin level in rats after the loss of estrogen, and also to examine the influence of estrogen replacement. The results showed that three weeks after the removal of ovaries the body weight of Ovx rats was already significantly higher than the other two groups, and continued to gain more weight thereafter. Accompanying with the significant weight gain was the changes in the serum leptin levels. The leptin concentration declined gradually during the first half of experimental period, dropping down to an almost undetectable level at week 7 (0.216+/-0.132 ng/ml). Subsequently, its concentration began to elevate, and by the end of experiment leptin level was significantly higher (3.182+/-0.936 ng/ml) than the value before the operation (0.818+/-0.242 ng/ml). This fluctuation of serum leptin level caused by ovariectomy was eliminated by the replacement of estrogen. The present data indicate that ovariectomy-induced weight gain is caused by the early drop in leptin level. The later rise in leptin production is connected to the increased body weight probably originated from a reduced sensitivity in leptin signal.

Hormonal, lifestyle, and dietary factors in relation to leptin among elderly men

BACKGROUND

Leptin, the adipocyte-secreted protein product of the ob gene, has been strongly linked to obesity and is believed to play a role in the regulation of the reproductive system. This study examines the potential influence of lifestyle and dietary factors, as well as of other hormones, on serum levels of leptin.

METHODS

The authors studied a population of 48 healthy elderly Greek men. Sera from these men were analyzed for leptin, several steroid hormones, sex hormone-binding globulin, and insulin-like growth factor 1. The authors also utilized data from food frequency questionnaires and information on demographic, anthropometric, and lifestyle (cigarette smoking, alcohol and coffee drinking) factors.

RESULTS

Using linear regression modeling, serum leptin levels were inversely associated with testosterone and positively associated with estradiol and dehydroepiandrosterone sulfate, after adjustment for the other hormones and body mass index (BMI). Leptin levels in men with a BMI >30 kg/m2 were 170% higher than in men with a BMI <27 kg/m2 (95% CI 63- 346%). Height was also positively associated with leptin, independent of BMI. No notable relationships were observed between leptin, on the one hand, and smoking, alcohol drinking, coffee drinking, or total energy intake, on the other. When total energy intake was separated into its three major components (carbohydrate, fat, and protein), it appeared that fat intake may have an isocalorically differential effect on serum leptin levels; one marginal quintile increase in fat intake corresponded to an 11% increase in leptin (95% CI 0-24%).

CONCLUSION

Serum levels of leptin may be influenced by other endocrine factors, especially testosterone and estradiol, and may be positively associated with excess fat intake independently of obesity.

Leptin serum levels are not correlated with disease activity in patients with rheumatoid arthritis

Leptin, the ob gene product, has been proposed as a mediator of inflammatory cytokine-dependent decreased food intake and cachexia in rodents. In humans, leptin serum levels increase after administration of tumor necrosis factor-alpha (TNF-alpha) or interleukin-2 or during septicemia. However, the effect of human chronic inflammatory disease on serum leptin is unknown. We therefore determined the serum leptin level (radioimmunoassay), body mass index (BMI), percent body fat ([%BF] bioelectrical impedance analysis), and disease activity (Disease Activity Score [DAS]) in 58 patients with rheumatoid arthritis (RA) and 16 controls. The BMI, %BF, serum leptin, and ratio of leptin to %BF (leptin/%BF) did not differ significantly in 25 patients with moderate RA activity (DAS, 3.6 +/- 0.5), 33 patients with low RA activity (DAS, 1.8 +/- 0.5), and controls. A positive correlation for serum leptin and %BF was detected in all groups. Our data indicate that in RA, a human chronic cytokine-mediated inflammatory disease, the serum leptin level is directly related to %BF but not to disease activity.

Systemic administration of lipopolysaccharide increases plasma leptin levels: blockade by soluble interleukin-1 receptor

Lipopolysaccharide (LPS) is known to produce several central and neuroendocrine effects and some of these effects are believed to be mediated through cytokines and other proteins. One such protein, leptin, produced by adipose tissue has been shown to cause anorexia, a central effect associated with LPS treatment. This raised the possibility that LPS-induced effects on feeding behavior may be mediated through leptin. This study was done to investigate the effects of systemic administration of LPS on plasma leptin levels in rats and the possible involvement of interleukin-1 (IL-1) in this mechanism. Adult male rats were implanted with indwelling jugular catheters and after collecting two pretreatment blood samples, the animals were injected (i.p.) with saline, 5 microg, 10 microg, or 25 microg/kg BW of LPS, or treated with 25 microg of soluble IL-1 receptor (sIL-1R) 5 min before and 90 min after 25 microg/kg BW of LPS. Posttreatment blood samples were collected at 30 min intervals for a period of 6 h. Plasma leptin concentrations were measured by radioimmunoassay. Treatment with saline did not produce any change in plasma leptin levels. In contrast, each of the three doses of LPS produced a dose-dependent increase in plasma leptin levels within 120 min. Leptin levels remained elevated for the next 4 h. Treatment with sIL-1 R completely blocked the LPS-induced increase in leptin levels, indicating that this effect is in fact mediated through IL-1. These results indicate that leptin could be a possible mediator of LPS-induced effects on feeding.

The role of agouti-related protein in regulating body weight

Defects in signaling by leptin, a hormone produced primarily by adipose tissue that informs the brain of the body's energy reserves, result in obesity in mice and humans. However, the majority of obese humans do not have abnormalities in leptin or its receptor but instead exhibit leptin resistance that could result from defects in downstream mediators of leptin action. Recently, two potential downstream mediators, agouti-related protein (Agrp) and its receptor, the melanocortin-4 receptor (Mc4r), have been identified. Agrp and Mc4r are excellent candidates for human disorders of body weight regulation and represent promising targets for pharmacological intervention in the treatment of these disorders.

Cyclical variations in the abundance of leptin receptors, but not in circulating leptin, correlate with NPY expression during the oestrous cycle

We have demonstrated previously that pharmacological doses of oestradiol decreased leptin receptor expression in the hypothalamus. We therefore analysed leptin receptor expression during the oestrous cycle in the rat, to establish if acute changes in oestradiol affect leptin receptor expression under physiological conditions. Radioactive in situ hybridization histochemistry was used to measure the gene expression under investigation. Total leptin receptor transcript levels were lowest in pro-oestrus in the choroid plexus, these changes correspond inversely with levels of circulating oestradiol in the rat 4-day oestrous cycle. In contrast full-length leptin receptor levels in both arcuate and ventromedial nuclei did not correspond to the levels of total leptin receptor in the same areas of the hypothalamus or serum levels of oestradiol. Full-length leptin receptor expression in the arcuate nucleus was negatively correlated with neuropeptide Y (NPY) expression (r = 0.447, p < 0. 05) in the same nucleus. Arcuate nucleus NPY expression did not correlate significantly with the expression of total leptin receptors in the arcuate nucleus (r = 0.080) or serum leptin levels (r = 0.251). Our results demonstrate that leptin receptor expression is regulated during the oestrous cycle. The unchanged serum leptin levels during the oestrous cycle together with the correlation between the expression of leptin-RL and NPY provide circumstantial evidence that regulation of leptin receptor abundance in the hypothalamus governs the biological actions of leptin.

High serum leptin concentrations during catch-up growth of children born with intrauterine growth retardation

The aim of the study was to investigate how leptin could be involved in catch-up growth of children born with intrauterine growth retardation (IUGR). The study population was made up of 70 newborns with IUGR longitudinally studied during the first 2 yr of life and 35 newborns and 32, 66, and 61 children with normal birth weight aged 3 days, 12 months, and 24 months, respectively. Postnatal patterns of body mass index (BMI) were similar in the 2 groups, but BMI remained significantly lower in IUGR over the study period. In contrast, children born with IUGR aged 1 yr had significantly higher serum leptin levels than normal children (P < 0.0001) independently of BMI. The correlation observed between BMI and serum leptin at birth in both groups and in the control group thereafter disappeared in children born with IUGR. Similarly, sexual dimorphism observed in normal children over the study period was not observed in the IUGR group during the first 2 yr of life. In summary, serum leptin is effective and regulated during the first years of life as it is in older children. Children born with IUGR demonstrate high serum leptin values during the first year of life, with a loss of the regulatory effect of BMI and gender. We suggest that these children develop an adaptative leptin resistance beneficial for their catch-up growth. An alternative hypothesis is that these observations could reflect an adipocyte dysfunction, a consequence of the special time course of adipose tissue development in children born with IUGR.

Advances in the molecular genetics of obesity

The past year has seen substantial progress in our understanding the molecular mechanisms of bodyweight regulation, particularly in the central and peripheral actions of the leptin and melanocortin signaling pathways (e.g. leptin stimulation of angiogenesis and suppression of cytokine production). Important advances also include the identification of mutations in components of the leptin and melanocortin pathways in human obese families. Expanding from the positional cloning of leptin some five years ago, the mouse continues to be a central focus of study, particularly the way in which different bodyweight-sensing pathways interact in different feeding states.

Impact of adipose tissue on plasma plasminogen activator inhibitor-1 in dieting obese women

The increased incidence of cardiovascular diseases in obese subjects could be partially attributed to impaired fibrinolysis due to elevated plasma levels of tissue plasminogen activator inhibitor 1 (PAI-1). The associations between changes in plasma PAI-1, metabolic variables, and adipose tissue during weight loss and regain were studied in 52 healthy, premenopausal, obese women participating in a weight reduction program with a hypocaloric diet. PAI-1, insulin, triglyceride, leptin, and adipsin levels were determined at entry, after the first week, after completion of the program, and after 5 months of follow-up. In the 33 obese women who completed the program, decreases in PAI-1 antigen (-54%), PAI activity (-74%), and leptin (-51%), but not of adipsin, were observed. Changes in PAI-1 were associated with changes in body mass index (BMI), body fat, leptin, and insulin. The decreased level of PAI-1 remained low after follow-up in the 14 women who maintained their reduced weight but increased in the 16 women who regained weight. This increase in PAI-1 was correlated with an increase in body fat and leptin. On multivariate analysis, BMI was the major determinant of PAI-1 level. In conclusion, during weight reduction with a hypocaloric diet, the decrease in PAI-1 is more closely related to changes in adipose tissue than to changes in metabolic variables, suggesting a significant role for adipose tissue in regulating plasma levels of PAI-1.

Leptin and its potential role in human obesity

Genetic studies in inbred obese mice have revealed the ob gene, its product leptin and the leptin receptor as important factors in the regulation of both appetite and energy expenditure. Treatment with recombinant leptin has resulted in a marked weight reduction in obese animals with ob gene mutations as well as in normal mice. Also mutations in the Ob receptor gene result in marked obesity in rodents. These data have given hope of new treatment options in obesity. Further support of leptin being involved in regulation of obesity in man comes from the observation that inactivating mutations in the human ob gene lead to profound early onset obesity. However, the role of leptin and its feedback system in man is still only partly revealed. This review focuses on our present knowledge and hypotheses about the leptin pathway in humans and its potential importance in the clinic of obesity.

Lack of association between changes in plasma leptin concentration and in food intake during the menstrual cycle

BACKGROUND

Changes in plasma leptin concentration and food intake occur during the menstrual cycle; because leptin regulates food intake, one could hypothesize that changes in plasma leptin concentration and in food intake are associated throughout the menstrual cycle. However, no data have ever been provided to support such a relationship. The aim of our study was to investigate, during the different phases of the menstrual cycle, (a) the changes in plasma leptin concentration and, if such changes were demonstrated, (b) the potential relationship between the changes in plasma leptin concentration and food intake.

DESIGN

The study was designed as an observational study. The plasma leptin concentration was determined in 16 healthy, young women during different phases of the menstrual cycle. At the same time, the basal metabolic rate (BMR), respiratory quotient (RQ) and food intake (FI) were also determined.

RESULTS

The plasma leptin concentration increased throughout the menstrual cycle (P < 0.01 for trend) and was significantly correlated with plasma progesterone concentration (r = 0.55, P < 0.007, for follicular phase, r = 0.58, P < 0.02, for the periovulatory period and r = 0.57, P < 0.02, for the luteal phase). No significant differences in BMR and fasting RQ throughout the different phases of the menstrual cycle were found. In contrast, FI significantly declined in the periovulatory phase. No significant correlations between BMR, RQ and FI values and fasting plasma leptin concentration at all menstrual phases were found.

CONCLUSION

Changes in plasma leptin concentration and in food intake were found at different phases of the menstrual cycle. Nevertheless, no correlation among those parameters at any phase of the menstrual cycle was observed.

Effects of cigarette smoking and its cessation on body weight and plasma leptin levels

Smokers weigh less than age-matched nonsmokers, and most smokers gain weight after smoking cessation due to an increase in food intake and a decrease in energy expenditure. Leptin is an endocrine signal thought to regulate body fat stores through hypothalamic control of energy intake and expenditure. To determine whether the "weight-reducing" effects of smoking may be mediated by leptin, we measured plasma leptin concentrations in 22 middle-aged and older male smokers (body mass index [BMI], 28 +/- 1 kg/m2, mean +/- SEM) and 22 nonsmokers matched to the smokers for age (64 +/- 1 years) and BMI (28 +/- 1 kg/m2). The body weight and leptin concentration were remeasured at 3 and 6 months in 13 of the smokers who successfully stopped smoking. The leptin concentration correlated positively with the BMI in both smokers (r = .74, P < .001) and nonsmokers (r = .76, P < .001). However, the intercept of the regression line was higher for smokers versus nonsmokers (P < .05), with no difference in the slope. Thus, male smokers have a higher leptin level for a given BMI than nonsmokers. Following 6 months of smoking cessation, body weight increased by 7% (6.0 +/- 0.1 kg, n = 13, P < .01). Despite this weight gain, the mean leptin concentration did not increase with smoking cessation. On average, leptin levels were 25% lower than would be expected for the amount of weight gained after smoking cessation. These findings suggest that cigarette smoking directly elevates circulating plasma leptin concentrations, and this increase may be one mechanism for the lower body weight of smokers compared with nonsmokers.

Leptin and tumor growth in rats

We have examined the role of leptin in tumor-induced anorexia in 2 different tumor models. In rats bearing the Yoshida AH-130 ascites hepatoma, the reduction in food intake becomes important from day 6 after tumor inoculation. Interestingly, at day 4, when the animals do not show any anorectic behavior, circulating leptin levels were already reduced. Indeed, in all the tumor-bearing groups studied the levels of leptin were lower than in control animals. Moreover, the changes in the circulating levels paralleled changes in adipose tissue leptin mRNA expression, even at early stages following tumor inoculation when neither food intake nor fat stores were modified by the presence of a tumor. Interestingly, 7-day pair-fed controls showed changes similar to those present in tumor-bearing rats. These results agree with previous observations relating fasting to decreased leptin expression. Similar results were observed in another tumor model, the mouse Lewis lung carcinoma; i.e., at day 8 after tumor inoculation (when the animals did not show anorexia) both the circulating levels and the adipose leptin mRNA expression were also reduced. Our results suggest that experimental cancer-induced anorexia is not related to leptin changes.

Serum Leptin Concentration In Patients Infected With Human immunodeficiency virus

OBJECTIVE

To assess the potential effect of serum leptin levels in human immunodeficiency virus (HIV)-related wasting.

METHODS

Morning serum leptin levels of 94 randomly chosen HIV-infected patients were measured and correlated with age, sex, weight, height, body mass index (BMI), routine blood chemistries (SMA 18), complete blood cell count, HIV viral load, and CD4/CD8 ratio.

RESULTS

The mean serum leptin level was 7.0 +/- 6.9 ng/mL. Leptin levels were significantly higher in the 38 female patients than in the 56 male patients (10.0 +/- 8.4 ng/mL versus 5.0 +/- 4.9 ng/mL; P<0.001). Leptin levels were positively correlated with BMI (r = 0.71; P<0.05). The correlation of leptin levels with BMI was improved when the results were analyzed stratified by the sex of the patients (r = 0.74 for female patients; r = 0.81 for male patients).

CONCLUSION

This study showed that the serum leptin levels in HIV-infected patients with BMI between 18 and 25 kg/m 2 were comparable to leptin levels in lean, healthy subjects. Leptin distribution was positively correlated with BMI, as expected. These data do not support the hypothesis for a major role of serum leptin in HIV-related wasting.

Physiological and anatomical circuitry between Agouti-related protein and leptin signaling

Agouti-related protein (AGRP) is an orexigenic neuropeptide that acts via central melanocortin receptors, and whose messenger RNA (mRNA) levels are elevated in leptin-deficient mice. Fasting associated with a decline in circulating leptin normally causes a 15-fold elevation of hypothalamic Agrp mRNA levels but has no effect in leptin-deficient mice. Chronic hyperleptinemia associated with the tubby and Cpe(fat) mutations has no effect on Agrp mRNA levels, but short term leptin administration causes a 17% reduction of Agrp mRNA levels in nonmutant mice and a 700% reduction in leptin-deficient mice. In young nonobese animals, melanocortin receptor blockade associated with the Ay mutation causes complete resistance to leptin-induced weight loss. Dual in situ hybridization reveals that Agrp-expressing neurons in the medial portion of the arcuate nucleus constitute a subpopulation different from Pomc-expressing neurons, and that a significant proportion of Agrp-expressing neurons (10-25%) coexpresses the leptin receptor, Lepr-b. Immunocytochemistry confirms distinct locations of AGRP- and POMC-expressing cell bodies, but reveals an overlapping distribution of their terminal fields in the arcuate nucleus, the paraventricular hypothalamus, and the dorsomedial hypothalamus. These results suggest that in the fed state, AGRP is normally suppressed by leptin, and that release of this suppression during fasting leads to increased ingestive behavior.

Effects of mild aerobic exercise and a mild hypocaloric diet on plasma leptin in sedentary women

1. The present study was conducted to investigate whether mild aerobic exercise and a mild hypocaloric diet, instead of severe restrictions on caloric intake, would affect weight reduction and plasma leptin concentrations. 2. Forty-one middle-aged sedentary women (15 obese and 26 non-obese) participated in a 12 week lifestyle-modification programme to reduce cardiovascular risk factors. Bodyweight, body composition, plasma leptin concentrations, serum lipid profiles, fasting plasma glucose and fasting plasma insulin were measured before and after the 12 week intervention. The intervention consisted of aerobic exercise, corresponding to approximately 50% of maximal oxygen consumption, and personal diet counselling. 3. Bodyweight decreased by (mean +/- SD) 3.9 +/- 3.4 kg in the obese group (P < 0.05) and by 1.7 +/- 1.8 kg in the non-obese group (P < 0.05). The plasma leptin concentration decreased significantly from 14.7 +/- 5.3 to 8.9 +/- 3.6 ng/mL in the obese group (P < 0.001) and from 7.6 +/- 3.9 to 5.6 +/- 2.2 ng/mL in the non-obese group (P < 0.01). 4. Overall, for all subjects, both pre- and postintervention, the plasma leptin concentration was significantly correlated with body mass index (BMI; pre-intervention: r = 0.73, P < 0.0001; postintervention: r = 0.67, P < 0.0001), fat mass (FM; pre-intervention: r = 0.74, P < 0.0001; postintervention: r = 0.63, P < 0.0001) and fasting plasma insulin (pre-intervention: r = 0.66, P < 0.001; postintervention: r = 0.45, P < 0.01). The change in plasma leptin concentration was significantly correlated with the respective changes in BMI (r = 0.64, P < 0.0001), FM (r = 0.48, P < 0.01) and fasting plasma insulin (r = 0.58, P < 0.0001). Interestingly, the ratio of plasma leptin concentration to BMI or FM diminished significantly after intervention. In addition, we found that the plasma leptin concentration decreased in participants whose FM did not decrease. These results suggest that the production of leptin per unit FM decreased after intervention. 5. Mild aerobic exercise and a mild hypocaloric intake decreased body mass and the plasma leptin level in Japanese middle-aged sedentary women. This decrease in plasma leptin levels was likely to be associated with weight reduction plus some unknown factor(s).

Central leptin modulates behavioral and neural responsivity to CCK

The mechanisms through which leptin, the protein product of the ob gene, affects food intake remain to be determined. To assess whether the actions of leptin depend on modulation of within-meal satiety signals, we measured the effect of third ventricular leptin administration on the satiety actions of CCK. Leptin (10 micrograms) administered 1 h before 30-min access to a liquid diet had no effect on intake when administered alone, but doses of 3.5 or 10 micrograms dose dependently increased the suppression of intake produced by 1 nmol/kg CCK. Examination of patterns of c-Fos activation induced by 3.5 micrograms leptin and 1 nmol/kg CCK revealed that the combination produced significant c-Fos activation within the area postrema and the caudal and medial nucleus of the solitary tract (NST) compared with either leptin or CCK treatments alone. The leptin-CCK combination also resulted in increased c-Fos activation within the paraventricular nucleus of the hypothalamus above that produced by leptin alone. These data suggest that the actions of leptin in food intake are mediated through its ability to modulate responsivity to within-meal satiety signals.

Treatment with the NO-synthase inhibitor, methylene blue, moderates the decrease in serum leptin concentration in streptozotocin-induced diabetes

It was previously reported that serum leptin concentrations were decreased in rats with streptozotocin-induced diabetes. Also, simultaneous nitric oxide (NO)-synthase inhibitor treatment is known to partially attenuate streptozotocin-induced diabetes development. The aim of our study was to investigate the influence of the NO-synthase inhibitor, methylene blue, on serum leptin concentration and diabetes development. Body weight, blood glucose, glycated hemoglobin and leptin concentration were measured in a control group, diabetic (streptozotocin 70 mg/kg i.p.) group, methylene blue (40 mg/kg in the food) treated group and a diabetic group treated with methylene blue. After six weeks of experiments, blood glucose and glycated hemoglobin increased significantly in the diabetic group vs controls (27.31 vs 5.49 mmol.l(-1), 14.11 vs 6.79%, respectively) and this increase was partially attenuated by simultaneous methylene blue treatment (16.8 vs 27.31 mmol/l, p < 0.05). Body weight and serum leptin fell in diabetic rats vs controls (248.9 vs 342.8 g, 0.57 vs 3.46 ng.ml(-1)). Treatment with methylene blue significantly suppressed the drop of body weight and the increase in blood glucose and glycated hemoglobin concentrations in the diabetic group. The decrease of serum leptin levels was significantly inhibited by methylene blue in the first experiment (1.1 vs 0.57 ng. ml(-1), p < 0.05); the same trend was found in a second experiment but the differences did not reach statistical significance. We conclude that the drop of serum leptin levels in diabetic rats is probably mainly due to streptozotocin-induced insulin deficiency, which is partially attenuated by NO-synthase inhibitor treatment.

Leptin administration to lactating rats is unable to induce changes in lipid metabolism in white adipose tissue or mammary gland

During lactation in the rat, despite hyperphagia, there are no changes in either the plasma levels or the gene expression of leptin. Removal of the litter, however, results in an important increase in the circulating concentration of leptin. Administration of leptin to lactating rats resulted in no changes in the in vivo lipogenic rate and lipoprotein lipase (LPL) activity in either adipose tissue or mammary gland, although there was an increase in insulin levels as a consequence of leptin administration. Conversely, litter removal resulted in an important decrease of LPL activity and lipogenic rate in the mammary gland while an increase in these parameters took place in adipose tissue. It is concluded that leptin is not the signal responsible for the changes in lipid metabolism that take place both in adipose tissue and mammary gland following litter removal.

The effect of moxonidine on feeding and body fat in obese Zucker rats: role of hypothalamic NPY neurones

The antihypertensive agent moxonidine, an imidazoline Ii-receptor agonist, also induces hypophagia and lowers body weight in the obese spontaneously hypertensive rat, but the central mediation of this action and the neuronal pathways that moxonidine may interact with are not known. We studied whether moxonidine has anti-obesity effects in the genetically-obese and insulin-resistant fa/fa Zucker rat, and whether these are mediated through inhibition of the hypothalamic neuropeptide Y (NPY) neurones. Lean and obese Zucker rats were given moxonidine (3 mg kg(-1) day(-1)) or saline by gavage for 21 days. Moxonidine decreased food intake throughout by 20% in obese rats (P<0.001) and by 8% in lean rats (P<0.001), and reduced weight gain that final body weight was 15% lower in obese (P<0.001) and 7% lower in lean (P<0.01) rats than their untreated controls. Plasma insulin and leptin levels were decreased in moxonidine-treated obese rats (P<0.01 and P<0.05), but unchanged in treated lean rats. Uncoupling protein-1 gene expression in brown adipose tissue was stimulated by 40-50% (P< or =0.05) in both obese and lean animals given moxonidine. Obese animals given moxonidine showed a 37% reduction in hypothalamic NPY mRNA levels (P = 0.01), together with significantly increased NPY concentrations in the paraventricular nucleus (P<0.05), but no changes in the arcuate nucleus or other nuclei; this is consistent with reduced NPY synthesis in the arcuate nucleus and blocked release of NPY in the paraventricular nucleus. In lean animals, moxonidine did not affect NPY levels or NPY mRNA. The hypophagic, thermogenic and anti-obesity effects of moxonidine in obese Zucker rats may be partly due to inhibition of the NPY neurones, whose inappropriate overactivity may underlie obesity in this model.

Isoproterenol decreases leptin expression in adipose tissue of obese humans

OBJECTIVE

We investigated the effects of the non-selective beta-adrenergic agonist, isoproterenol (Iso), on leptin expression in human adipose tissue.

RESEARCH METHODS AND PROCEDURES

Subcutaneous (SQ) and omental adipose (OM) tissue taken during surgery from 12 morbidly obese subjects (10 women and 2 men) were cultured for up to 24 hours with insulin (7 nM) and/or dexamethasone (25 nM), a synthetic glucocorticoid, in the presence or absence of isoproterenol (10 microM). Adipose tissue was also acutely incubated for 3 hours in media alone with or without isoproterenol. Leptin secretion and leptin mRNA abundance were measured.

RESULTS

Iso acutely decreased leptin release by approximately 30% (vs. no hormone controls) in fragments of OM and SQ adipose tissue. In 24-hour culture, addition of Iso (in the presence of insulin) resulted in lower leptin accumulation in the medium (-20-30%) and leptin mRNA levels (-40-50%) from both tissue depots. Culture with insulin and dexamethasone increased leptin expression vs. insulin alone. Addition of Iso with insulin and dexamethasone decreased media leptin (-40-60%) and leptin mRNA levels were lower (-65%) in Iso-treated adipose tissue from both depots after 24 hours. Iso effects were not detectable after 5 hours of culture.

DISCUSSION

We conclude that stimulation of beta-adrenergic receptors may modulate leptin expression in human adipose tissue by two mechanisms: an acute effect on leptin release and a longer-term antagonism of stimulatory effects of insulin and dexamethasone on leptin mRNA expression. These mechanisms may contribute to the decline in serum leptin that occurs during fasting.

Metabolic, gastrointestinal, and CNS neuropeptide effects of brain leptin administration in the rat

To investigate whether brain leptin involves neuropeptidergic pathways influencing ingestion, metabolism, and gastrointestinal functioning, leptin (3.5 micrograms) was infused daily into the third cerebral ventricular of rats for 3 days. To distinguish between direct leptin effects and those secondary to leptin-induced anorexia, we studied vehicle-infused rats with food available ad libitum and those that were pair-fed to leptin-treated animals. Although body weight was comparably reduced (-8%) and plasma glycerol was comparably increased (142 and 17%, respectively) in leptin-treated and pair-fed animals relative to controls, increases in plasma fatty acids and ketones were only detected (132 and 234%, respectively) in pair-fed rats. Resting energy expenditure (-15%) and gastrointestinal fill (-50%) were reduced by pair-feeding relative to the ad libitum group, but they were not reduced by leptin treatment. Relative to controls, leptin increased hypothalamic mRNA for corticotropin-releasing hormone (CRH; 61%) and for proopiomelanocortin (POMC; 31%) but did not reduce mRNA for neuropeptide Y. These results suggest that CNS leptin prevents metabolic/gastrointestinal responses to caloric restriction by activating hypothalamic CRH- and POMC-containing pathways and raise the possibility that these peripheral responses to CNS leptin administration contribute to leptin's anorexigenic action.

Does estradiol mediate leptin's effects on adiposity and body weight?

The role of estradiol in mediating leptin's effects on body weight was assessed in ovariectomized (OVX) mice before and after the onset of obesity. Ovariectomy did not alter leptin levels before the onset of obesity, and estradiol adminstration (0.05-17 microgram/day for 14 days) did not significantly alter leptin levels if they were corrected for the estradiol-induced reduction in body fat. The converse was also true, in that leptin administration (0.4-140 microgram/day) did not alter estradiol levels in intact mice. Furthermore, neither estradiol reduction (via ovariectomy) nor addition (via exogenous administration) significantly altered leptin's ability to reduce fat mass. Leptin was equally effective in reducing body weight in lean or obese OVX mice and intact controls. Finally, estradiol did not change the magnitude of leptin's effect on fat mass reduction when it was given in combination with leptin to lean intact or OVX mice. Estradiol may have indirectly affected leptin efficacy, because leptin did not produce as large a change in fat mass at lower doses in lean OVX mice as it did in intact counterparts. Taken together, these data suggested that 1) estradiol does not directly regulate leptin secretion or its effects on fat mass and 2) leptin does not directly regulate estradiol secretion or its effects on fat mass. Leptin and estradiol, however, may interact in an indirect fashion to affect fat utilization.

Rodent mutant models of obesity and their correlations to human obesity

Obesity is a heath problem affecting a significant fraction of adult Americans and is on the rise globally. It is of importance to find treatments that achieve medically significant weight loss and successful long-term maintenance of a desired weight. Recent transgenic mouse studies and genetic characterization of spontaneous rodent obesity mutants, together with gene linkage analysis in humans, have led to an increased understanding of the physiologic and molecular mechanisms underlying obesity. However, much remains to be studied in this complex field of research. In this review, we discuss the physiology and genetics underlying obesity and how studies in rodents and humans are converging, producing a greater understanding of the mechanisms underlying this health problem.

A role for leptin in hemopoieses?

The recent discovery of leptin as a major controller of appetite has led to a detailed analysis of its specific actions in this process as well as any potential role in the etiology of obesity. It has also emerged that leptin has a wider spectrum of biological activities and has been strongly implicated in fertility and reproduction. The structural similarity between leptin and its receptor and cytokine-receptor systems that control hemopoiesis has also prompted investigation of the potential for this hormone to influence blood cell formation. Recent studies have shown that the leptin receptor is expressed on a diverse range of hemopoietic cells. Leptin itself appears to enhance proliferation of hemopoietic cells in vitro, particularly in combination with other cytokines and may augment some mature hemopoietic cell functions. Although only relatively minor hemopoietic deficiencies have been reported in mice lacking leptin or its receptor, these emerging studies suggest that further analysis of leptin actions in hemopoiesis may be warranted.

Discrepancy between serum leptin values and total body fat in response to the oral growth hormone secretagogue MK-677

OBJECTIVE

Growth hormone (GH) treatment decreases total body fat while this effect has not yet been documented for the oral GH secretagogue MK-677. In the present study, the effects of MK-677 treatment on serum levels of leptin, thyroid hormones and testosterone were determined.

DESIGN

This was a randomized, double-blind, and parallel study. Twenty-four healthy obese males, 19-49 years of age, with body mass index (BMI) > 30 kg/m2 and a waist:hip ratio > 0.95, were treated with MK-677 (25 mg/day; n = 12) or placebo (n = 12) for 8 weeks.

RESULTS

MK-677 treatment increased serum leptin levels and leptin/body fat ratio at 2 weeks of treatment (P < 0.05 vs. placebo) but no significant change was observed at 8 weeks. An increase in serum free 3, 5, 3'-triiodothyronine (free T3) was not detected until 8 weeks of MK-677 treatment (P < 0.05 vs. placebo). Peak serum thyroid stimulating hormone (TSH) concentration after MK-677 administration was similar to that after placebo administration at initiation of treatment and at 2 weeks. At 8 weeks of MK-677 treatment, mean peak serum TSH concentration was increased (P < 0.05 vs. placebo) although it remained within the normal range. Serum peak values of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were similar after MK-677 and placebo administration. MK-677 treatment reduced serum total testosterone (P < 0.05 vs. placebo) although total testosterone/sex hormone-binding globulin (SHBG) ratio (an index of free testosterone) was not changed.

CONCLUSION

Treatment with the oral GH secretagogue MK-677 transiently increased serum leptin levels and leptin/body fat ratio at 2 weeks of treatment, and increased serum free T3 after 8 weeks. These results indicate that MK-677 treatment is able to affect circulating factors of importance for adipose tissue mass and fuel metabolism.

Model for the regulation of energy balance and adiposity by the central nervous system

In 1995, we described a new model for adiposity regulation. Since then, data regarding the biology of body weight regulation has accumulated at a remarkable rate and has both modified and strengthened our understanding of this homeostatic system. In this review we integrate new information into a revised model for further understanding this important regulatory process. Our model of energy homeostasis proposes that long-term adiposity-related signals such as insulin and leptin influence the neuronal activity of central effector pathways that serve as controllers of energy balance.

Serum leptin response to the acute and chronic administration of growth hormone (GH) to elderly subjects with GH deficiency

In human studies, the principal determinant of serum leptin concentrations is fat mass (FM), but lean mass (LM) also has a significant negative influence. GH treatment in GH deficiency (GHD) alters body composition, increasing LM and decreasing FM, and thus would be expected to alter leptin concentrations. We have therefore examined the acute and chronic effects of GH on serum leptin in 12 elderly GHD subjects (ages 62-85 yr; 3 women and 9 men). FM (kilograms) and LM (kilograms) were determined by dual energy x-ray absortiometry. Leptin, insulin, insulin-like growth factor I (IGF-I), IGF-II, IGF-binding protein-1 (IGFBP-1), IGFBP-2, and IGFBP-3 were measured by specific immunoassays. Leptin, insulin, and IGFBP-1 concentrations were log10 transformed, and data were expressed as the geometric mean (-1, +1 tolerance factor). All other data are presented as the mean +/- SD. In the acute study, patients received a single bolus dose of GH (0.1 mg/kg BW) at time zero, with blood samples drawn at 0, 12, 24, 48, and 72 h and 1 and 2 weeks. There was a significant rise in leptin, insulin, and IGF-I at a median time of 24 h, followed by a significant fall, and nadir concentrations were reached at a median time of 1.5 weeks (leptin) or 2 weeks (insulin and IGF-I). IGFBP-3 concentrations were also significantly increased, but peak concentrations were not achieved until 48 h. IGF-II, IGFBP-1, and IGFBP-2 exhibited transient decreases before returning to baseline levels. There was no relationship between increased leptin concentrations and either insulin or IGF-I concentrations. In the chronic study, patients received daily GH treatment at doses of 0.17, 0.33, and 0.5 mg/day, each for 3 months (total time on GH, 9 months), and were then followed off GH for a further 3 months. Dual energy x-ray absortiometry was undertaken at 0, 3, 6, 9, and 12 months, and blood samples were drawn at these time points. Over 9 months on GH there was a significant fall in FM and a significant rise in LM, but no change in leptin. There were also significant increments in insulin, IGF-I, and IGFBP-3, whereas IGF-II, IGFBP-1, and IGFBP-2 did not change over 9 months of GH treatment. After 3 months off GH, there was a significant rise in FM and leptin. High dose single bolus GH led to an increase in serum leptin within 24 h apparently independent of changes in insulin or IGF-I. Despite the changes in body composition during chronic GH treatment, there was no change in leptin. However, discontinuation of GH led to a rapid reversal of the favorable body composition and a rise in serum leptin.

Regulation of body weight in humans

The mechanisms involved in body weight regulation in humans include genetic, physiological, and behavioral factors. Stability of body weight and body composition requires that energy intake matches energy expenditure and that nutrient balance is achieved. Human obesity is usually associated with high rates of energy expenditure. In adult individuals, protein and carbohydrate stores vary relatively little, whereas adipose tissue mass may change markedly. A feedback regulatory loop with three distinct steps has been recently identified in rodents: 1) a sensor that monitors the size of adipose tissue mass is represented by the amount of leptin synthesized by adipose cells (a protein encoded by the ob gene) which determines the plasma leptin levels; 2) hypothalamic centers, with specific leptin receptors, which receive and integrate the intensity of the signal; and 3) effector systems that influence the two determinants of energy balance, i.e., energy intake and energy expenditure. With the exception of a few very rare cases, the majority of obese human subjects have high plasma leptin levels that are related to the size of their adipose tissue mass. However, the expected regulatory responses (reduction in food intake and increase in energy expenditure) are not observed in obese individuals. Thus obese humans are resistant to the effect of endogenous leptin, despite unaltered hypothalamic leptin receptors. Whether defects in the leptin signaling cascade play a role in the development of human obesity is a field of great actual interest that needs further research. Present evidences suggest that genetic and environmental factors influence eating behavior of people prone to obesity and that diets that are high in fat or energy dense undermine body weight regulation by promoting an overconsumption of energy relative to need.

Circulating leptin in patients with chronic obstructive pulmonary disease

Unexplained weight loss is common in patients with chronic obstructive pulmonary disease (COPD). Since leptin, an obesity gene product, is known to play important roles in the control of body weight and energy expenditure, we investigated serum leptin levels, along with circulating tumor necrosis factor-alpha (TNF-alpha) and soluble TNF receptor (sTNF-R55 and -R75) levels, in 31 patients with COPD and 15 age-matched healthy controls. The body mass index (BMI) and percent body fat (%fat) were significantly lower in the COPD patients than in the healthy controls (BMI = 18.1 +/- 2.7 kg/m2 versus 22.8 +/- 2.2 kg/m2 [mean +/- SD]; p < 0.0001; %fat = 16.9 +/- 5.8% versus 24.3 +/- 4.9%; p < 0.001). Serum leptin levels were significantly lower in the COPD patients than in the healthy controls (1.14 +/- 1.17 ng/ml versus 2.47 +/- 2.01 ng/ml; p < 0.05). In contrast, serum TNF-alpha levels (6.59 +/- 1.92 pg/ml versus 5.41 +/- 1.60 pg/ml; p < 0.05), plasma sTNF-R55 (1.16 +/- 0.47 ng/ml versus 0.67 +/- 0.13 ng/ml; p < 0.0001) and sTNF-R75 (3.65 +/- 1.29 ng/ml versus 2.25 +/- 0.43 ng/ml; p < 0.0001) levels were significantly higher in the COPD patients than in the healthy controls. Importantly, circulating leptin levels (log transformed) did correlate well with BMI and %fat, but not with TNF-alpha or with sTNF-R levels in the COPD patients. These data suggest that circulating leptin is independent of the TNF-alpha system and is regulated physiologically even in the presence of cachexia in patients with COPD.

Enhanced food-anticipatory circadian rhythms in the genetically obese Zucker rat

This study examines the effects of the leptin receptor mutation in obese Zucker rats on entrainment of food-anticipatory rhythms to daily feeding schedules. Leptin is secreted by adipocytes in proportion to fat content, exhibits a daily rhythm in plasma that is synchronized to feeding time, and inhibits activity of arcuate neuropeptide Y neurons that stimulate feeding behavior and regulate metabolism. Activity within this neuropeptide Y system is enhanced by food deprivation and attenuated by overfeeding and diet-induced obesity. Diet-induced obesity, in turn, attenuates food-anticipatory rhythms. If the effects of obesity on food-entrained rhythms are mediated by leptin inhibition of neuropeptide Y neurons, then these rhythms may be enhanced in leptin-insensitive Zucker obese rats. Alternatively, if daily rhythms of leptin mediate the generation or entrainment of these rhythms, Zucker rats may fail to anticipate daily feedings. Zucker obese and lean rats received food for 3 h/day during the midlight period. Both groups exhibited significant food-anticipatory activity that persisted during three cycles of food deprivation, but this rhythm was significantly more robust in obese rats, when expressed as anticipation and persistence ratios, and as peak values. Anticipatory rhythms did not persist in either group when food was provided ad lib. These results indicate that central actions of leptin may mediate the inhibitory effects of obesity on the expression of food-anticipatory rhythms in rats, but do not mediate the inhibitory effects of ad lib food access, and do not serve as necessary internal entrainment cues or clock components for the food-entrainable circadian system.

Regulation of fatty acid homeostasis in cells: novel role of leptin

It is proposed that an important function of leptin is to confine the storage of triglycerides (TG) to the adipocytes, while limiting TG storage in nonadipocytes, thus protecting them from lipotoxicity. The fact that TG content in nonadipocytes normally remains within a narrow range, while that of adipocytes varies enormously with food intake, is consistent with a system of TG homeostasis in normal nonadipocytes. The facts that when leptin receptors are dysfunctional, TG content in nonadipocytes such as islets can increase 100-fold, and that constitutively expressed ectopic hyperleptinemia depletes TG, suggest that leptin controls the homeostatic system for intracellular TG. The fact that the function and viability of nonadipocytes is compromised when their TG content rises above or falls below the normal range suggests that normal homeostasis of their intracellular TG is critical for optimal function and to prevent lipoapoptosis. Thus far, lipotoxic diabetes of fa/fa Zucker diabetic fatty rats is the only proven lipodegenerative disease, but the possibility of lipotoxic disease of skeletal and/or cardiac muscle may require investigation, as does the possible influence of the intracellular TG content on autoimmune and neoplastic processes.

Plasma leptin concentrations in obese children: changes during 4-mo periods with and without physical training

BACKGROUND

Little is known about the effects of physical training on plasma leptin concentrations in children.

OBJECTIVE

We sought to determine the effects of 4-mo periods with and without physical training on leptin in obese children and to explore the determinants of leptin at baseline and in response to physical training.

DESIGN

Participants were 34 obese 7-11-y-old children randomly assigned to engage in physical training during either the first or second 4 mo of the 8-mo study.

RESULTS

Total body composition, visceral adiposity, and insulin were all positively correlated with leptin at baseline (P < or = 0.05); however, only fat mass was retained in the final stepwise regression (P = 0.0001, R2 = 0.57). Leptin decreased during the 4-mo periods of physical training and increased in the 4 mo after cessation of physical training (P < 0.001 for the time by group interaction). Decreases in leptin were greatest in children with higher pretraining leptin concentrations, those whose total mass increased least, and those whose insulin concentrations decreased most (P < or = 0.05); only pretraining leptin concentration (P = 0.009) and change in total mass (P = 0.0002) were retained in the final regression (R2 = 0.53).

CONCLUSIONS

In obese children, leptin concentration decreased during 4 mo of physical training and increased during a subsequent 4-mo period without physical training, fat mass was highly correlated with baseline leptin, and greater reductions in leptin during 4 mo of physical training were seen in children with higher pretraining leptin and in those whose total mass increased least.

Weight loss and leptin changes in individuals with type 2 diabetes

OBJECTIVE

To identify variables associated with leptin change in subjects with type 2 diabetes after 3 weeks and 20 weeks of weight loss.

RESEARCH METHODS AND PROCEDURES

Subjects with type 2 diabetes treated with diet or sulfonylureas (n = 54) were enrolled in a 20-week behavioral weight control program. Sulfonylureas were stopped > or =2 weeks before study entry. Seven subjects who restarted sulfonylureas after week 3 had their data analyzed separately after this point.

RESULTS

Leptin, fasting plasma glucose, and insulin levels were measured at baseline and at 3, 10, and 20 weeks. After 3 weeks, subjects lost 2.7+/-2.0 kg (p<0.001), and had significant decreases in leptin (5.2+/-7.0 ng/mL, p<0.001), fasting plasma glucose (1.8+/-1.8 mmol/L, p<0.001), and insulin (23+/-60 pmol/L, p<0.03). Between week 3 and week 20, subjects lost an additional 6.3+/-4.4 kg (p<0.001), but had no further changes in leptin. The primary determinants of leptin change at all time-points were weight loss and initial leptin level. Changes in insulin were not related to changes in leptin after controlling for the effects of weight loss. At week 20, more recent weight loss (week 10 to week 20) was as strong a predictor of overall change in leptin as overall weight loss (baseline to 20 week). Subjects who restarted sulfonylureas had an increase in both leptin levels (+1.9+/-9.0 ng/mL, p<0.05) and insulin levels (+23+/-65 pmol/L, p<0.05), despite significant overall weight loss (-7.4+/-4.0 kg, p<0.01). Initial changes in leptin (0 weeks to 3 weeks) did not affect subsequent ability to lose weight.

DISCUSSION

Both short- and long-term changes in weight had an effect on leptin changes in individuals with type 2 diabetes. Although physiological insulin changes did not independently influence changes in leptin concentration with weight loss, increases in insulin levels with sulfonylurea therapy were associated with increases in leptin levels despite weight loss.

Transcriptional regulation of fatty acid synthase gene by insulin/glucose, polyunsaturated fatty acid and leptin in hepatocytes and adipocytes in normal and genetically obese rats

Transcriptional regulation of the fatty acid synthase (FAS) gene by insulin/glucose, polyunsaturated fatty acids and leptin was investigated in hepatocytes and adipocytes of Wistar fatty rats and their lean littermates. The sequence spanning nucleotides -57 to -35 of FAS gene, which is responsive to insulin/glucose stimulation [Fukuda, H., Iritani, N. & Noguchi, T. (1997) FEBS Lett. 406, 243-248], was linked to a reporter gene containing a heterologous promoter and transfected into rat hepatocytes or adipocytes. The activity of the reporter, chloramphenicol acetyltransferase, in the presence of glucose alone was similar in the primary cultured cells from the lean and obese rats. In the presence of insulin/glucose, however, chloramphenicol acetyltransferase activity was markedly increased in hepatocytes of lean rats, but was not significantly increased in those of obese rats. The stimulation by insulin/glucose was reduced in arachidonic acid-treated cells of lean rats. Similarly, the stimulation by insulin/glucose was reduced in leptin-treated cells and in cells from lean rats containing an expression vector encoding leptin. However, neither polyunsaturated fatty acids nor leptin-treated cells from obese rats responded to insulin-stimulation. The same effects were observed at endogenous FAS mRNA and enzyme levels. Similar results were seen in adipocytes, although the stimulation and suppression were much smaller than in hepatocytes. The insulin-binding capacities of the receptors of liver and adipose tissue were reduced in the presence of leptin or polyunsaturated fatty acids. Leptin and polyunsaturated fatty acids appeared to suppress the insulin stimulation of FAS transcription by reducing the insulin-binding capacities of receptors. Leptin converged on the insulin/glucose response element of FAS gene and suppressed the transcription.

Expression and Function of Leptin Receptor Isoforms in Myeloid Leukemia and Myelodysplastic Syndromes: Proliferative and Anti-Apoptotic Activities

The receptor for the gene product of the obesity gene, leptin, was recently reported to be expressed on murine and human hematopoietic progenitor cells. Therefore, we studied the expression of the leptin receptor, OB-R, in normal myeloid precursors, human leukemia cell lines, and primary leukemic cells using reverse-transcriptase polymerase chain reaction. In normal hematopoiesis, OB-R was expressed in CD34+ cells. Normal promyelocytes (CD34−33+ and CD34−13+) expressed only very low levels of the short, presumably nonsignaling isoform. Both the long and short isoforms of OB-R were expressed in 10 of 22 samples from patients with newly diagnosed primary or secondary acute myeloid leukemia (AML), with a higher incidence of the long isoform in primary AML (87.6% v28.6%; P = .01). The incidence of OB-R expression was higher in recurrent than in newly diagnosed AML (P < .001), and samples from four patients with refractory AML showed strong expression of both isoforms. Both OB-R isoforms were also expressed in newly diagnosed and recurrent acute promyelocytic leukemia cells but were essentially absent in samples of chronic or acute lymphocytic leukemia. In vitro growth of myeloid leukemic cell lines and of blasts from 14 primary AMLs demonstrated that recombinant human leptin alone induced low level proliferation, significantly (P < .05) increased proliferation induced by recombinant human granulocyte colony-stimulating factor, interleukin 3, and stem cell factor in a subset of AML and increased colony formation (P < .005). Also, leptin reduced apoptosis induced by cytokine withdrawal in MO7E and TF-1 cells. Serum leptin levels correlated only with body mass index (P < .001) and gender (P = .03). Results confirm the reported expression of leptin receptor in normal CD34+ cells and demonstrate the frequent expression of leptin receptors in AML blasts. While normal promyelocytes lack receptor expression, leukemic promyelocytes express both isoforms. We also demonstrate proliferative effects of leptin alone and in combination with other physiologic cytokines, and anti-apoptotic properties of leptin. These findings could have implications for the pathophysiology of AML.

Is leptin concentration associated with the insulin resistance syndrome in nondiabetic men?

OBJECTIVE

Insulin resistance has been strongly associated with cardiovascular risk. Recently, leptin, a hormone that regulates appetite, has been associated with both obesity and insulin resistance. However, the possible relation of leptin to the insulin resistance syndrome has been controversial.

RESEARCH METHODS AND PROCEDURES

To explore this issue, we examined the relation of leptin to blood pressure, lipid levels, low density lipoprotein (LDL) size, and glucose levels in 87 normoglycemic men.

RESULTS

Leptin levels were significantly correlated with body mass index (BMI) (r = 0.494), fasting insulin (r = 0.576), whole-body glucose disposal rate (GDR) (r = -0.566), fasting glucose (r = 0.510) total triglycerides (r = 0.294), apolipoprotein B (r = 0.223), systolic blood pressure (r = 0.223), and LDL size (r = -0.244). After adjustment for BMI and GDR, leptin levels remained significantly correlated with fasting insulin, fasting glucose, triglyceride, apolipoprotein B, and systolic blood pressure. Leptin levels were also correlated with the number of metabolic risk factors (dyslipidemia, systolic blood pressure, and fasting glucose).

DISCUSSION

We conclude that leptin concentrations may be associated with several cardiovascular risk factors related to insulin resistance syndrome. These associations are only partly explained by leptin's relationship with BMI and GDR.

An inverse correlation between serum leptin levels and hemoglobin A1c in patients with non-insulin dependent diabetes mellitus

We measured serum leptin concentrations in 70 patients with diabetes mellitus to investigate the relationship between serum leptin levels and glycemic control. A positive correlation between serum leptin levels and body mass index or plasma insulin was obtained as reported previously. The present study also demonstrated an inverse association of serum leptin levels with hemoglobin A1c (HbA1c). Multiple regression analysis revealed that HbA1c was an independent determinant of serum leptin levels. These results suggest that HbA1c may be a factor to influence serum leptin levels and that hyperglycemia for a long period or poorly controlled diabetes may reduce leptin levels.

Postnatal changes of leptin levels in full-term and preterm neonates: their relation to intrauterine growth, gender and testosterone

The present study was carried out to investigate leptin levels in arterial and venous cord serum and in amniotic fluid in full-term infants at birth and on the 5th postnatal day to define the relationship of leptin to intrauterine growth rate, gender and early postnatal life. The relation of weight gain to serum leptin levels in male preterm infants was determined measuring leptin concentration weekly in the first 5 postnatal weeks. Testosterone levels were determined simultaneously to explore a possible relationship between leptin and testosterone concentrations. Fifty-three term newborn infants with mean birth weight and gestational age of 3,419 g (range 2,150-4,480) and 38.9 weeks (range 36-41) and 19 preterm male infants (mean birth weight and gestational age were 1,416 g (770-1,800) and 30.2 weeks (26-35) were enrolled into the study. Leptin and testosterone levels were determined by radioimmunoassay. It was demonstrated that serum leptin levels were markedly elevated in the cord blood without discernible arteriovenous differences. Cord blood leptin was found to correlate with birth weight (r = 0.40, p < 0.002), weight to length ratio (r = 0.40, p < 0.002) and body mass index (r = 0.35, p < 0.005). It was significantly lower in boys as opposed to girls (p < 0.01) and there was an apparent fall by the 5th postnatal day (p < 0.001). Amniotic fluid contained leptin in much less concentration than cord blood and it proved to be independent of intrauterine growth or gender. Serum leptin concentration in preterm infants at 1 week of age was significantly lower compared with term infants (p < 0.002) and it increased progressively with age (p < 0.01). An inverse relationship was found between leptin and testosterone level (r = -0.358, p < 0.01) and a positive correlation between leptin level and weight/height ratio (r = 0.674, p < 0.01). It is concluded that leptin derived either from placenta or fetal adipose tissue may be involved in regulating fetal growth and development and it may be related to energy intake, storage and expenditure. In preterm male infants serum leptin concentration increases with postnatal weight and testosterone may suppress leptin synthesis.

A review of endocrine changes in anorexia nervosa

Anorexia nervosa is a syndrome of unknown etiology. It is associated with multiple endocrine abnormalities. Hypothalamic monoamines (especially serotonin), neuropeptides (especially neuropeptide Y and cholecystokinin) and leptin are involved in the regulation of human appetite, and in several ways they are changed in anorexia nervosa. However, it remains to be clarified whether the altered appetite regulation is secondary or etiologic. Increased secretion of corticotropin-releasing hormone and proopiomelanocortin seems to be secondary to starvation, however, there is evidence that it may maintain and intensify anorexia, excessive physical activity and amenorrhea. Hypothalamic amenorrhea, which is a diagnostic criterion in anorexia nervosa, is not solely related to the low body weight and exercise. Growth hormone resistance with low production of insulin-like growth factor I and high growth hormone secretion reflect the nutritional deprivation. The nutritional therapy of patients with anorexia nervosa might be improved by administering an anabolic agent such as growth hormone or insulin-like growth factor I. So far none of the endocrine abnormalities have proved to be primary, however, there is increasing evidence that some of these might participate in a vicious circle.

Peroxisome proliferator activated receptor-gamma, leptin and tumor necrosis factor-alpha mRNA expression during very low calorie diet in subcutaneous adipose tissue in obese women

BACKGROUND

PPAR gamma, leptin and TNF alpha are three major factors that play a key role in influencing adipocyte differentiation and both adipose tissue function and metabolism. However, the regulation of these three genes during a dynamic period of weight loss is unknown. We therefore investigated the concomitant regulation of the mRNA expression of PPAR gamma, leptin and TNF alpha in adipose tissue during a 21-day very low calorie diet (VLCD) in 12 non-diabetic obese women.

METHODS

The mRNA levels of PPAR gamma, leptin and TNF alpha were quantified by quantitative RT-competitive PCR in abdominal subcutaneous adipose tissue before and during VLCD (940 kcal/day).

RESULTS

VLCD induced weight loss (approximately 6 kg) and improved insulin sensitivity. Simultaneously, VLCD induced the reduction in the adipose tissue mRNA abundances of PPAR gamma (-13%, p < 0.05) and of leptin (-58%, p < 0.005), whereas TNF alpha mRNA levels increased (+78%, p < 0.005). PPAR gamma and leptin mRNA levels were correlated before (r = 0.778, p < 0.01) and after VLCD (r = 0.797, p < 0.01). Serum HDL-cholesterol concentrations were positively associated with PPAR gamma (r = 0.696, p < 0.03) and leptin (r = 0.806, p < 0.01) mRNA levels.

CONCLUSIONS

The increase in TNF alpha mRNA levels suggested that a local increased expression of this cytokine in adipose tissue might play a role in the control of the fat mass during weight loss. PPAR gamma and leptin mRNA levels were positively associated both before and after VLCD, suggesting that common regulatory mechanism(s) might control their expression. More strikingly, we found strong positive correlations between circulating HDL-cholesterol and both PPAR gamma and leptin mRNA levels, suggesting the existence of physiological links between circulating lipoprotein metabolism and adipose tissue function.

Expression and Function of Leptin Receptor Isoforms in Myeloid Leukemia and Myelodysplastic Syndromes: Proliferative and Anti-Apoptotic Activities

The receptor for the gene product of the obesity gene, leptin, was recently reported to be expressed on murine and human hematopoietic progenitor cells. Therefore, we studied the expression of the leptin receptor, OB-R, in normal myeloid precursors, human leukemia cell lines, and primary leukemic cells using reverse-transcriptase polymerase chain reaction. In normal hematopoiesis, OB-R was expressed in CD34+ cells. Normal promyelocytes (CD34−33+ and CD34−13+) expressed only very low levels of the short, presumably nonsignaling isoform. Both the long and short isoforms of OB-R were expressed in 10 of 22 samples from patients with newly diagnosed primary or secondary acute myeloid leukemia (AML), with a higher incidence of the long isoform in primary AML (87.6% v28.6%; P = .01). The incidence of OB-R expression was higher in recurrent than in newly diagnosed AML (P &lt; .001), and samples from four patients with refractory AML showed strong expression of both isoforms. Both OB-R isoforms were also expressed in newly diagnosed and recurrent acute promyelocytic leukemia cells but were essentially absent in samples of chronic or acute lymphocytic leukemia. In vitro growth of myeloid leukemic cell lines and of blasts from 14 primary AMLs demonstrated that recombinant human leptin alone induced low level proliferation, significantly (P &lt; .05) increased proliferation induced by recombinant human granulocyte colony-stimulating factor, interleukin 3, and stem cell factor in a subset of AML and increased colony formation (P &lt; .005). Also, leptin reduced apoptosis induced by cytokine withdrawal in MO7E and TF-1 cells. Serum leptin levels correlated only with body mass index (P &lt; .001) and gender (P = .03). Results confirm the reported expression of leptin receptor in normal CD34+ cells and demonstrate the frequent expression of leptin receptors in AML blasts. While normal promyelocytes lack receptor expression, leukemic promyelocytes express both isoforms. We also demonstrate proliferative effects of leptin alone and in combination with other physiologic cytokines, and anti-apoptotic properties of leptin. These findings could have implications for the pathophysiology of AML.

Serum leptin concentrations in women taking oral contraceptives

OBJECTIVES

To investigate serum leptin concentrations in women taking oral contraceptives containing the same gestagen and different doses of ethinyl estradiol.

STUDY DESIGN

30 women received tablets containing 20 microg of ethinyl estradiol (EE) and 150 microg of desogestrel (DSG) (Mercilon) whereas another group of 30 women received 30 microg of EE and 150 microg of DSG (Marvelon). Serum leptin concentrations were estimated using a Leptin RIA kit (Linco Research USA) after an overnight fast on the first day of the cycle prior to the onset of therapy as well as after the 3rd and 6th treated cycles.

RESULTS

In both groups a positive correlation between serum leptin and body mass index (BMI) was found (r=0.56; P<0.001 and r=0.67; P<0.001). The initial serum leptin concentration in the Mercilon group was 7.62+/-8.46 ng/ml. This value was not statistically different from values after 3 months (9.31 8.23 ng/ml) and after 6 months (10.53+/-8.03 ng/ml) of treatment. Very similar results were found in patients receiving Marvelon: 8.81+/-6.56 ng/ml initially; 11.62+/-11.16 ng/ml at 3 months, and 10.38+/-7.32 ng/ml at 6 months. The statistical analysis did not reveal any significant difference at each investigated time point in either study group.

CONCLUSIONS

Modern low dose OC containing third generation gestagen and low dose of ethinyl estradiol, does not have any influence on serum leptin or BMI, and therefore does not exert a significant influence on body energy metabolism.

Acute effects of exercise on circulating leptin in lean and genetically obese fa/fa rats

Mechanisms of regulation of plasma leptin in lean and genetically obese animals are not completely understood. In particular a relation has been proposed between energy metabolism and leptin. However, it is not clear how energy expenditure and leptin are related under exercise in lean and obese animals. To clarify these aspects we investigated lean and genetically obese (fa/fa) Zucker rats undergoing a single bout (30 min) of swimming and measured several biochemical and hormonal parameters of energy metabolism and leptin changes throughout the study. Moreover ob-gene expression in adipose tissue was also measured. Our results showed that plasma leptin is decreased by 30% at the end of exercise in lean animals while resulting unaffected in obese animals. Leptin changes in lean rats are concomitant with the peak of NEFA and glycerol release from adipose tissue rather than with the reduction of plasma insulin. Ob-gene expression in adipose tissue was markedly increased in fa/fa compared to lean rats, but was not modified by exercise both in lean and obese animals. In conclusion our data show that leptin changes during exercise are related to lipolytic events in adipose tissue and support a link between leptin and energy expenditure.

Increased high density lipoprotein (HDL), defective hepatic catabolism of ApoA-I and ApoA-II, and decreased ApoA-I mRNA in ob/ob mice. Possible role of leptin in stimulation of HDL turnover

Abnormalities of plasma high density lipoprotein (HDL) levels commonly reflect altered metabolism of the major HDL apolipoproteins, apoA-I and apoA-II, but the regulation of apolipoprotein metabolism is poorly understood. Two mouse models of obesity, ob/ob and db/db, have markedly increased plasma HDL cholesterol levels. The purpose of this study was to evaluate mechanisms responsible for increased HDL in ob/ob mice and to assess potential reversibility by leptin administration. ob/ob mice were found to have increased HDL cholesterol (2-fold), apoA-I (1.3-fold), and apoA-II (4-fold). ApoA-I mRNA was markedly decreased (to 25% of wild-type) and apoA-II mRNA was unchanged, suggesting a defect in HDL catabolism. HDL apoprotein turnover studies using nondegradable radiolabels confirmed a decrease in catabolism of apoA-I and apoA-II and a 4-fold decrease in hepatic uptake in ob/ob mice compared with wild-type, but similar renal uptake. Low dose leptin treatment markedly lowered HDL cholesterol and apoA-II levels in both ob/ob mice and in lean wild-type mice, and it restored apoA-I mRNA to normal levels in ob/ob mice. These changes occurred without significant alteration in body weight. Moreover, ob/ob neuropeptide Y-/- mice, despite marked attenuation of diabetes and obesity phenotypes, showed no change in HDL cholesterol levels relative to ob/ob mice. Thus, increased HDL levels in ob/ob mice reflect a marked hepatic catabolic defect for apoA-I and apoA-II. In the case of apoA-I, this is offset by decreased apoA-I mRNA, resulting in apoA-II-rich HDL particles. The studies reveal a specific HDL particle catabolic pathway that is down-regulated in ob/ob mice and suggest that HDL apolipoprotein turnover may be regulated by obesity and/or leptin signaling.

Concentrations of leptin in the serum of pregnant, lactating, and cycling rats and of leptin messenger ribonucleic acid in rat placental tissue

Leptin concentrations were measured in the serum of cycling, pregnant, and lactating Sprague-Dawley rats. Serum leptin concentrations did not vary significantly during the estrous cycle. In contrast, as gestation advanced, serum leptin concentrations increased significantly, p < 0.0001. Following delivery, leptin concentrations declined and remained stable during lactation. Leptin messenger ribonucleic acid (mRNA) was identified in the visceral adipose tissue and placenta of rats sacrificed on days 14 and 21 of pregnancy. The relative abundance of placental leptin mRNA increased approximately 4 to 5 fold from day 14 to 21 of gestation. The pattern of elevated leptin concentrations in the serum of late pregnant rats is similar to that reported in pregnant women, therefore the rat may be a useful model for the study of leptin during pregnancy. The increase in leptin in the serum of late pregnant rats, as well as an increase in placental mRNA, raises the possibility that leptin may serve a physiological role for the late parturient rat and/or its young.

Serum leptin concentrations in obese women with Down syndrome and Prader-Willi syndrome

We have evaluated serum leptin concentrations in two forms of genetic obesity. The subjects examined were eight women with Down syndrome and eight women with Prader-Willi syndrome. All patients were in the reproductive age range and were obese (body mass index > or = 27 kg/m2). Plasma leptin values, analyzed as a function of body mass index showed a statistically significant correlation in both Prader-Willi (r = 0.985; p < 0.001) and Down syndrome patients (r = 0.943; p < 0.001). Obese Down syndrome women exhibited significantly lower leptin values (10.8 +/- 1.1) as compared to patients with Prader-Willi syndrome (31 +/- 2.6; p < 0.01). The linear correlation between leptin and insulin in the two groups of patients was not statistically significant. The data suggested that obesity in Prader-Willi subjects could be caused by failure of leptin to reach its target in the brain, as a consequence of defects in the receptor or in postreceptor processing, whereas data on obese patients with Down syndrome could be due to a different pathogenetic origin.