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

Postnatal regulation of hypothalamic neuropeptide expression by leptin: implications for energy balance and body weight regulation

Leptin is produced mainly by adipose tissue and has been shown to regulate feeding, energy balance and neuroendocrine function. Regulation of energy homeostasis by leptin is thought to be mediated by hypothalamic neuropeptides, at least in adult rodents. The neonatal period is a critical stage of development during which mammals have to optimize caloric intake to support growth and development, as well as maintain body temperature. It is likely that leptin is involved in the transition from preweaning to adult metabolism. To test this hypothesis, we compared the effect of leptin treatment on body weight and adiposity between neonatal and adult mice. We also determined whether well known hypothalamic neuropeptide targets, e.g. neuropeptide Y (NPY), proopiomelanocortin (POMC), agouti-related peptide (AGRP) and cocaine and amphetamine-regulated transcript (CART) were regulated in a pattern consistent with their presumed roles as mediators of leptin action. Once daily intraperitoneal leptin injection for 7 days did not alter body weight, fat content or expression of hypothalamic neuropeptide mRNAs in 10-day-old mice. In contrast, leptin decreased body weight and adiposity, increased CART and suppressed NPY and AGRP mRNA expression in adult mice. These results are consistent with previous studies showing that the timing of leptin's anorectic action develops after weaning. Furthermore, the association between leptin's ability to influence body weight in adult mice but not in neonates, and the regulation of hypothalamic neuropeptide mRNA expression, is consistent with the view that these peptides mediate leptin's effects on energy balance.

Intracerebroventricular injection of murine leptin enhances the postprandial metabolic rate in the rat

Energy balance is achieved by means of a concomitant control of both food intake and energy expenditure. Leptin, synthesized in the adipose tissue, acts on brain structures and lowers body weight by inhibiting food intake and in parallel by enhancing energy expenditure i.e. metabolism or one of its components. Recording distinctly these components allowed us to assess the effect of an acute intracerebroventricular injection of leptin on both feeding pattern and background metabolism (i.e. energy expenditure free from the part of locomotor activity), respiratory quotient, feeding-related metabolism and locomotor activity-related metabolism. Leptin injection to Sprague-Dawley male rats induced an inhibition of feeding that began 90 min after the treatment and lasted 1 h before to return to the control feeding pattern level. Considering this late behavioral effect, it appeared that leptin may act during the postprandial period so that we recorded the different metabolic parameters following a 3 g calibrated meal itself preceded by leptin vs. artificial cerebrospinal fluid injection. Postprandial respiratory quotient was rapidly lowered in leptin-treated animals and subsequent background metabolism increased for 6 h. Thus it appeared that leptin increased the duration of the postprandial metabolic rate via the recruitment of endogenous fat stores. Enhancement in the thermic effect of food may be the reason for feeding behavior inhibition to be delayed.

Serum leptin levels in young females with insulin-dependent diabetes and the relationship to hyperandrogenicity and microalbuminuria

To investigate the relationship between leptin levels and IDDM with and without microalbuminuria, fasting serum levels of leptin, insulin, insulin-like growth factor-1 (IGF-1), sex hormone-binding globulin (SHBG), testosterone (SHBG) ratio, blood pressure and body mass index (BMI) were measured in 18 normo- and 11 microalbuminuric females with >5 years of IDDM, and 24 healthy controls in late puberty. Leptin levels were higher in micro- than normoalbuminuric IDDM patients, and lower in healthy controls than in both IDDM groups (p < 0.05, respectively). In multiple regression analysis, presence of IDDM and BMI independently contributed to increased leptin values (R2 = 0.34, p < 0.001). Including IDDM females only, solely low IGF-1 and high testosterone/SHBG were associated with leptin (R2 = 0.39, p = 0.009). Albumin excretion rate (AER) was correlated to leptin (r = 0.48, p = 0.01). With AER as the dependent variable only serum leptin and diastolic blood pressure added to the regression (R2 = 0.59, p < 0.001). In conclusion, serum leptin, independently of BMI, is: (1) increased in IDDM females of late puberty; (2) associated with low IGF-1 and hyperandrogenemia, and (3) related to increased albumin excretion rate in IDDM females.

Study of serum leptin in cafeteria-diet-overfed rats. Influence of diet, insulin and corticosterone

In a group of 15 male Wistar rats overfed with cafeteria foods (delivering a mean fat percentage of 60%) during 5 months from the age of 8 weeks and in a control group of 15 rats fed with a standard chow for the same period, serum leptin, insulin and corticosterone were measured by RIA and body composition was determined by dual-energy X-ray absorptiometry. Significantly higher fasting serum concentrations of leptin, insulin and corticosterone were found in the cafeteria-diet group. Fasting leptin concentrations were significantly higher in rats with a body fat percentage of more than 25% compared to the others, irrespective of the type of feeding. The log serum leptin correlated positively with body fat percentage and fasting insulin concentration but not with corticosterone concentration. Leptin concentration corrected for body fat mass was, however, comparable between the two diet groups, while the leptin/insulin ratio was lower in the cafeteria-diet group. In conclusion, chronic overfeeding resulting in an increased body fat percentage in rats is associated with hyperleptinemia, hyperinsulinemia and hypercorticism. Serum leptin levels appear to primarily track total body fat percentage and are unaffected by dietary fat manipulation in cafeteria-diet-induced obese rats.

Longitudinal analysis of maternal serum leptin levels during pregnancy, at birth and up to six weeks after birth: relation to body mass index, skinfolds, sex steroids and umbilical cord blood leptin levels

Leptin is an important regulator of body fat mass and energy expenditure during adult life. The mechanisms by which maternal and fetal weight are regulated during pregnancy are poorly understood. In order to gain more insight into a potential role of leptin during gestation, a prospective, longitudinal study was carried out to measure leptin concentrations in maternal serum of 29 healthy women during pregnancy up to 6 weeks after birth and also in umbilical cord blood of their newborns. Leptin concentrations were measured using a specific RIA. In addition, estradiol, testosterone, and sex hormone binding globulin were determined using commercially available RIAs. The mothers' skinfolds were determined at four sites using a Holtain caliper. Leptin levels increased continuously during pregnancy and reached 25.8 +/- 14.7 ng/ml at 38-40 weeks. At birth, leptin concentrations were 23.5 +/- 15.4 ng/ml. Three days after delivery a significant decrease of leptin levels to 10.6 +/- 6.0 ng/ml was observed. Six weeks after birth the leptin concentration in maternal serum was 13.8 +/- 8.6 ng/ml. At birth, maternal serum levels were significantly higher than levels in cord blood and did not correlate with leptin levels in cord blood or neonatal weight. Furthermore, leptin levels did not correlate with maternal sex steroids and sex hormone binding globulin levels. At 6-8 weeks of pregnancy, maternal leptin serum levels correlated significantly with BMI (r = 0.81). The correlation coefficients (leptin vs. BMI) dropped with increasing gestational age and at birth only a poor correlation persisted (r = 0.50). Six weeks after birth there was again a high correlation between leptin levels in maternal serum and BMI (r = 0.76). Subscapular skinfold thickness was correlated to leptin concentrations in maternal serum during the whole period of the investigation. In conclusion, maternal leptin levels continuously increased from 6-8 weeks up to 38-40 weeks of pregnancy. Maternal leptin levels decreased dramatically after birth. Six weeks after delivery, leptin levels were comparable to the values measured at the beginning of pregnancy. We hypothesize that leptin might play an important role during pregnancy and fetal development.

Children born small-for-gestational age: postnatal growth and hormonal status

It is generally recognized that children born small-for-gestational age (SGA) have a 5-7 times higher risk of short stature than children born at normal size. It has been suggested that the programming of the endocrine axes occurs during critical phases of fetal development and is affected by intrauterine growth retardation. This study was undertaken to characterize the postnatal growth pattern and the final height of children born SGA, as part of a population- based study (n = 3,650), from birth to final height, and to evaluate the hormonal status in another group of prepubertal children born SGA (n = 134) without postnatal catch-up growth. The majority (88%) of 'healthy' full-term singleton SGA infants achieved catch-up growth during the first 2 years of life, and most of the increase in height occurred by 2 months of age. The SGA children who remained short at 2 years of age had a higher risk of short stature later in life. The risk of having a short final height (<-2 SDS) was five times higher for children with a low birth weight and seven times higher for those with a low birth length in comparison with children with a normal birth size. Moreover, about 20% of all children of short stature were born SGA. As a group, children born SGA will have a final height, expressed in SDS, as they had during the prepubertal years. This is in contrast to children, who became short postnatally. During puberty, these short children will have a mean height gain of 0.6 SDS for girls and 0.7 SDS for boys. The mean estimated secretion rate for growth hormone (GH) was lower in the short children born SGA compared with the reference groups born at an appropriate size for gestational age, of either short (p < 0.05) or normal stature (p < 0.001). Moreover, in the youngest children born SGA (2-6 years of age) a different pattern of GH secretion was found, with a high basal GH level, low peak amplitude, and high peak frequency. The majority of the children born SGA had levels of GH-binding protein within the range previously reported for normal children. However, the levels of insulin-like growth factor I (IGF-I), IGF-binding protein-3 (IGFBP-3) and leptin were significantly reduced compared with the reference values (p < 0.001, p < 0.01 and p < 0.001, respectively). In conclusion, the low spontaneous GH secretion rate and a disturbed GH secretion pattern, together with low serum levels of IGF-I, IGFBP-3 and leptin, might contribute to the reduced postnatal growth in some of the subgroup of children born SGA who remained short during childhood.

Lipostat in the lean rat: evidence for a non-causal relationship between glucocorticoids and leptin levels

In order to assess the long-term impact of a complete depletion of glucocorticoids on plasma leptin levels, we bilaterally adrenalectomized 20 lean rats, and analysed glucocorticoids and leptin levels for 20 consecutive days. Results demonstrate that the adrenalectomy (ADX) significantly lowered the leptin levels, as compared to sham-operated controls. On the other hand, a significant increase in leptin levels was noticeable from day 1 to day 20 of the experiment in the sham-operated controls, even though corticosterone levels remained stable during that same period. Plasma leptin concentration was proportional to body fat content. These results would indicate a non-causal relationship between glucocorticoids and leptin levels in the context of a lipostat in the lean rat.

Gender-dependent differences in plasma leptin in essential hypertension

Leptin, the gene product of the ob gene, is influenced by gender and insulin sensitivity. Because in human hypertension there are important endocrine-hemodynamic gender-dependent differences, we compared plasma leptin in 39 essential hypertensives (EH) and in 27 normotensive healthy subjects (HS) matched for gender, age, and fat mass. Fat mass was measured by bioelectrical impedance analysis (BIA), plasma leptin by a sensitive radioimmunoassay RIA (intraassay CV < 6%), and insulin sensitivity by the HOMA-R index. Both in essential hypertensives and in normotensive subjects plasma leptin was consistently higher in females than in males and was strictly related to fat mass. Gender differences in plasma leptin were not explained by differences in fat mass. Separate analysis of data by gender showed that leptin was significantly higher (P < .05) in hypertensive men (median, 5.4 ng/mL; interquartile range, 4.1-9.5) than in normotensive men (4.6 ng/mL, 2.6-7.4) whereas it was identical in hypertensive and normotensive women. In essential hypertensives, in a multiple regression model only fat mass, gender, and the HOMA-R index were independently linked to plasma leptin. Similarly, fat mass and gender were independent predictors of plasma leptin in normotensive subjects. In the combined group of hypertensive and normotensive men, heart rate as well as systolic and diastolic pressure were univariate predictors of leptin. However, in a multivariable model only heart rate was independently related to leptin, and neither systolic nor diastolic pressure contributed significantly to explain the variability in plasma leptin. No relationship was found between leptin and heart rate or systolic or diastolic pressure in women. These results support the notion that leptin may participate in the gender-dependent variability of human hypertension.

Role of adipose tissue in body-weight regulation: mechanisms regulating leptin production and energy balance

Adipose tissue performs complex metabolic and endocrine functions. Among the endocrine products produced by adipose tissue are tumour necrosis factor alpha, interleukin 6, acylation-stimulating protein and leptin. The present review will focus primarily on mechanisms regulating leptin production and leptin action, and the implications of this regulation in the control of energy balance. Leptin acts in the central nervous system where it interacts with a number of hypothalamic neuropeptide systems to regulate feeding behaviour and energy expenditure. The presence of extreme obesity in animals and human subjects with mutations of the leptin gene or the leptin receptor demonstrates that normal leptin production and action are critical for maintaining energy balance. Insulin is the major regulator of leptin production by adipose tissue. Insulin infusions increase circulating leptin concentrations in human subjects. Plasma leptin levels are markedly decreased in insulin-deficient diabetic rodents, and the low leptin levels contribute to diabetic hyperphagia. Based on in vitro studies, the effect of insulin to stimulate leptin production appears to involve increased glucose metabolism. Blockade of glucose transport or glycolysis inhibits leptin expression and secretion in isolated adipocytes. Evidence suggests that anaerobic metabolism of glucose to lactate does not stimulate leptin production. Alterations in insulin-mediated glucose metabolism in adipose tissue are likely to mediate the effects of energy restriction to decrease, and refeeding to increase, circulating leptin levels. Changes in glucose metabolism may also explain the observation that high-fat meals lower 24h circulating leptin levels relative to high-carbohydrate meals in human subjects, suggesting a mechanism that may contribute to the effects that high-fat diets have in promoting increased energy intake, weight gain and obesity. The decreased circulating leptin observed during energy restriction is related to increased sensations of hunger in human subjects. Thus, decreases in leptin during energy-restricted weight-loss regimens may contribute to the strong propensity for weight regain. A better understanding of the precise mechanisms regulating leptin production and leptin action may lead to new approaches for managing obesity.

Thyroid hormones influence serum leptin levels in patients with Graves' disease during suppression of beta-adrenergic receptors

Leptin is a protein product of the ob gene, mainly produced by adipocytes. Leptin is thought to play an important role in the homeostasis of body weight by suppressing appetite and increasing energy consumption. The aim of this study was to investigate the possible effect of thyroid hormone on the regulation of the leptin system during suppression of beta-adrenergic receptors in Graves' patients. We studied 15 adult female patients with Graves' disease. Thyroid function, serum levels of leptin, and percent body fat (%BF) were examined at four different clinical conditions during therapy (A, untreated; B, beta-adrenergic antagonist only [A, B; hyperthyroid], C, beta-adrenergic antagonist and antithyroid drug; D, antithyroid drug only [C, D; euthyroid]). The use of beta-adrenergic antagonist significantly reduced heart rate in spite of hyperthyroid state, indicating sufficient suppression of beta-adrenergic receptors. During treatment with beta-adrenergic antagonist, leptin percentage of body fat (%BF) ratio significantly decreased in euthyroid state compared to that in hyperthyroid state (from 38.7 +/- 21.3 to 18.1 +/- 19.3, p = 0.003). Moreover, there was a significantly positive correlation between delta leptin/%BF and delta free thyroxine (FT4) (r = 0.51, p = 0.008). Under a euthyroid state induced by antithyroid drug treatment, leptin/%BF did not change in spite of withdrawal of beta-adrenergic antagonist. Our data indicate that thyroid hormones could increase serum leptin level during suppression of beta-adrenergic receptors in Graves' patients. Our data also suggest that the beta-adrenergic action of thyroid hormones might be partly mediated by regulation of leptin.

Plasma leptin in moderately obese men: independent effects of weight loss and aerobic exercise

The independent effects of weight loss and exercise on plasma leptin and total (AT), subcutaneous (SAT), and visceral (VAT) adipose tissue were investigated in 52 obese men. Subjects were randomly assigned to four 12-wk protocols: 1) control (C, n = 8), 2) diet-induced weight loss (DWL, n = 14), 3) exercise-induced weight loss (EWL, n = 14), and 4) exercise with weight maintenance (EWS, n = 16). Plasma leptin was unchanged in C (from 7.8 +/- 1.3 to 7.7 +/- 1.0 ng/ml). Equivalent weight loss (7.5 kg) decreased leptin significantly but similarly (DWL, from 8.5 +/- 1.0 to 4.8 +/- 0.6 ng/ml; EWL, from 10.1 +/- 1.0 to 5.0 +/- 0.6 ng/ml). Exercise in the absence of weight loss did not alter leptin levels (from 10.1 +/- 1. 3 to 9.2 +/- 1.2 ng/ml). Changes in leptin correlated with changes in AT and SAT (both P < 0.05) but not in VAT. We conclude that reduction in adipose tissue after weight loss results in a collateral decrease in circulating leptin, and exercise, independent of its effects on weight loss, has no profound influence on leptin secretion.

Pharmacology of appetite suppression

Despite a rising worldwide epidemic of obesity there is currently only a very small number of anti-obesity drugs available to manage the problem. Large numbers of differing pharmacological agents reliably produce a reduction in food intake when administered acutely to animals, and when administered chronically they result in a significant decrease in body mass. Behavioural analysis of drug-induced anorexia in animals demonstrates that various compounds profoundly effect feeding behaviour in differing ways. This indicates the variety of mechanisms by which pharmacological agents can induce changes in food intake, body weight and eventually body composition. Some of the same drugs produce decreases in food intake and weight loss in humans. Some of these drugs do so by modifying the functioning of the appetite system as measured by subjective changes in feelings of hunger and fullness (indices of satiety). Such drugs can be considered as "appetite suppressants" with clinical potential as anti-obesity agents. Other drugs induce changes in food intake and body weight through various physiological mechanisms inducing feelings of nausea or even by side effect related malaise. Of the drugs considered suitable candidates for appetite suppressants are agents which act via peripherally satiety peptide systems (such as CCK, Bombesin/GRP, Enterostatin and GLP-1), or alter the CNS levels of various hypothalamic neuropeptides (NPY, Galanin, Orexin and Melanocortins) or levels of the key CNS appetite monoamine neurotransmitters such as serotonin (5-HT) and noradrenaline (NA). Recently, the hormone leptin has been regarded as a hormonal signal linking adipose tissue status with a number of key central nervous system circuits. The peptide itself stimulates leptin receptors and it links with POMC and MC-4 receptors. These receptors may also provide drug targets for the control of appetite. Any changes induced by a potential appetite suppressant should be considered in terms of the (i) psychological experience and behavioural expression of appetite, (ii) metabolism and peripheral physiology, and (iii) functioning of CNS neural pathways. In humans, modulation of appetite may involve changes in total caloric consumption, subjective changes in feelings of hunger and fullness, preferences for specific food items, and general macronutrient preferences. These may be expressed behaviourally as changes in meal patterns, snacking behaviour and food choice. Within the next 20 years it is certain that clinicians will have a new range of anti-obesity compounds available to choose from. Such novel compounds may act on a single component of the appetite system or target a combination of these components detailed in this review. Such compounds used in combination with lifestyle changes and dietary intervention may be useful in dealing with the rising world epidemic of obesity.

Involvement of nitric oxide in endothelium-dependent arterial relaxation by leptin

Leptin is a polypeptide, mainly produced in white adipose tissue, and increases sympathetic nerve activity. A few studies investigated leptin's effect on peripheral vessels. We examined the vasorelaxant effects of human leptin on rat arteries. Arterial rings were precontracted with 1 x 10(-6) mol/l of phenylephrine, and leptin was superfused. Leptin relaxed phenylephrine-precontracted arterial rings in a dose-dependent manner. ED50 was calculated to 8.4 microg/ml. Removal of endothelium abolished the effects of leptin. Indomethacin (1 x 10(-5) mol/l) did not affect the vasorelaxation by leptin, whereas 1 x 10(-4) mol/l of N(omega)-nitro-L-arginine methyl ester (L-NAME) completely suppressed it. The inhibition was antagonized by 1 x 10(-4) mol/l of L-arginine. Leptin normally relaxed arterial rings during superfusion of K channel blockers, including 3 x 10(-5) mol/l of glibenclamide, 1 x 10(-6) of mol/l apamin, and 5 x 10(-7) mol/l of charybdotoxin. Low Cl(-) solution (8. 3 mmol/l) inhibited leptin-induced relaxation, but endothelium-independent vasodilatation by nitroprusside was not impaired at low Cl(-) solution. These results suggest that arterial relaxation by leptin is mediated by nitric oxide released from endothelium, and Cl(-) plays an important role in leptin-induced nitric oxide release.

The co-ordinated cytokine/hormone response to acute injury incorporates leptin

Recent studies have implicated leptin as a "stress" hormone and highlighted its association with increases in inflammatory cytokines, C-reactive protein and cortisol. In order to investigate the exact temporal leptin response to stress we undertook a detailed longitudinal study of circulating leptin concentrations during the well defined surgical injury of cholecystectomy. Circulating concentrations of cortisol, free fatty acids, leptin and C-reactive protein were measured at 3, 6, 9, 12, 18, 24, 48 and 72 h from the start of surgery in nine patients. There was a significant correlation between baseline concentrations of leptin and BMI (r=0. 893, P<0.001). Over the 72 h from the start of surgery there were significant (P<0.05) increases in the concentrations of all analytes (peak median concentrations); cortisol (6 h), free fatty acids (9 h), leptin (18 h) and C-reactive protein (48 h). Interestingly the timing of the leptin peak at approximately 18 h after an acute inflammatory stimulus is exactly the same as previously reported for interleukin 6. These data support the suggestion that the relationship between cortisol and leptin mirrors that of cortisol and another cytokine, interleukin 6, i.e. stimulatory in acute and suppressive in chronic situations. They also imply a physiological role for leptin in acute injury.

Relationship between serum leptin immunoreactivity and body fat mass as estimated by use of a novel gas-phase Fourier transform infrared spectroscopy deuterium dilution method in cats

OBJECTIVE

To validate a recently developed commercially available leptin radioimmunoassay (RIA) for use with feline serum and evaluate the relationship between serum leptin concentrations and body fat mass in domestic cats.

ANIMALS

19 sexually intact male specific-pathogen-free domestic cats that weighed 3.8 to 7.1 kg and were 1.1 to 3.5 years old.

PROCEDURE

Specificity for feline leptin was evaluated by use of gel filtration chromatography and reverse-phase high-performance liquid chromatography fractionation of serum. Body fat mass was determined by use of the deuterium oxide (D2O) dilution method. Serum water D2O enrichment was measured by use of gas-phase Fourier transform infrared spectroscopy.

RESULTS

Body fat mass and percentage body fat ranged from 0.3 to 2.3 kg and 7.5 to 34.9%, respectively. Serum leptin concentrations were lower in the unfed versus the fed state and ranged between 1.6 and 4.9 ng/ml human equivalent (HE); mean +/- SD value was 2.9 +/- 0.2 ng/ml HE. Leptin concentrations increased with increasing body fat mass and percentage of body fat.

CONCLUSIONS

Leptin is in the serum of domestic cats in free (> 78%) and apparently bound forms. The relationship between body fat and serum leptin concentration was similar to that observed in humans and rodents and indicative of a lipostatic role for leptin in cats. Cats that have an overabundance of body fat appear to be less sensitive to the weight-normalizing action of leptin than cats of ideal body condition.

Integration of metabolism and intake regulation: a review focusing on periparturient animals

There has been great interest in dry matter intake regulation in lactating dairy cattle to enhance performance and improve animal health and welfare. Predicting voluntary dry matter intake (VDMI) is complex and influenced by numerous factors relating to the diet, management, housing, environment and the animal. The objective of this review is to identify and discuss important metabolic factors involved in the regulation of VDMI and their integration with metabolism. We have described the adaptations of intake and metabolism and discussed mechanisms of intake regulation. Furthermore we have reviewed selected metabolic signals involved in intake regulation. A substantial dip in VDMI is initiated in late pregnancy and continues into early lactation. This dip has traditionally been interpreted as caused by physical constraints, but this role is most likely overemphasized. The dip in intake coincides with changes in reproductive status, fat mass, and metabolic changes in support of lactation, and we have described metabolic signals that may play an equally important role in intake regulation. These signals include nutrients, metabolites, reproductive hormones, stress hormones, leptin, insulin, gut peptides, cytokines, and neuropeptides such as neuropeptide Y, galanin, and corticotrophin-releasing factor. The involvement of these signals in the periparturient dip in intake is discussed, and evidence supporting the integration of the regulation of intake and metabolism is presented. Still, much research is needed to clarify the complex regulation of VDMI in lactating dairy cows, particularly in the periparturient animal.

Serum leptin levels in post-hepatitis liver cirrhosis

BACKGROUND/AIMS

Little information is available on the involvement of leptin in clinical conditions associated with malnutrition, such as liver cirrhosis. The behaviour of serum leptin in patients with different Child-Pugh score, post-hepatitis liver cirrhosis and insulin sensitivity has therefore been investigated and compared with that in alcoholic Child C patients.

METHODS

Sixty-four patients, aged 51 to 62 years, with different degrees of post-hepatitis cirrhosis or Child C alcoholic cirrhosis were compared with 15 age-matched control subjects. Body composition was estimated by skinfold thickness. Serum leptin, glucose and insulin were assayed.

RESULTS

In post-hepatitis patients a significant reduction in leptin levels was observed as the Child-Pugh score worsened (men: 2.94+/-1.61 in Child C vs 6.78+/-2.49 ng/ml in controls, p<0.001; women: 4.14+/-0.66 in Child C vs 16.16+/-3.90 ng/ml in controls, p<0.02). Conversely, only the men with alcoholic liver cirrhosis showed a significant difference in leptin concentration compared to controls (8.5+/-2.1 vs 16.4+/-7.9 kg, p<0.05). In particular, Child C, alcoholic cirrhotic women had a significantly (p=0.03) higher level of leptin than post-hepatitis matched women. A positive correlation was observed between leptin and fat mass (men R2=0.59, p<0.0001 and women R2=0.65, p<0.0001). While fasting levels of serum leptin correlated significantly with insulin concentrations in controls, a similar relationship was not observed in the cirrhotic population, which displayed higher insulin concentrations than controls.

CONCLUSIONS

In contrast to findings in alcoholic cirrhotic women, low leptin values in post-hepatitis cirrhotic patients mainly represent the expression of a reduced fat mass.

The common pentanucleotide polymorphism of the 3'-untranslated region of the leptin receptor gene is associated with serum insulin levels and the risk of type 2 diabetes in non-diabetic men: a prospective case-control study

OBJECTIVES

The purpose of the study was to test whether the pentanucleotide insertion/deletion polymorphism in the 3'-untranslated region (3'-UTR) of the leptin receptor gene, which has previously been associated with serum insulin levels in obese subjects, is associated with insulin levels and the risk of type 2 diabetes in non-diabetic middle-aged men.

SUBJECTS AND DESIGN

We studied these associations in a prospective population-based nested case-control study in 41 men who developed type 2 diabetes during 4-year follow-up and 81 controls who were matched for age, obesity, baseline glucose and insulin and other strongest risk factors. Both the cases and the controls came from a cohort of 985 men who had no diabetes at baseline.

RESULTS

There was one homozygote and 22 heterozygotes for the 3'-UTR insertion allele amongst all 122 men. The carrier frequency of this allele was 9.8% amongst the cases and 23.5% amongst the controls. At baseline, the mean fasting serum insulin was 12.2 mU L-1 in the 23 men who were heterozygous or homozygous for the insertion allele and 17.1 mU L-1 in the 99 men who were homozygous for the deletion allele (P = 0.005). In a logistic regression model adjusting for four strongest non-matched predictors of type 2 diabetes, the carriers of the insertion allele had a 79% reduced risk of diabetes (OR = 0.21; 95% CI = 0.06-0.77, P = 0.019), compared with non-carriers.

CONCLUSION

Our findings support the hypothesis that alterations in the leptin signalling system could contribute to serum insulin levels and the development of type 2 diabetes.

Leptin regulation of neuroendocrine systems

The discovery of leptin has enhanced understanding of the interrelationship between adipose energy stores and neuronal circuits in the brain involved in energy balance and regulation of the neuroendocrine axis. Leptin levels are dependent on the status of fat stores as well as changes in energy balance as a result of fasting and overfeeding. Although leptin was initially thought to serve mainly as an anti-satiety hormone, recent studies have shown that it mediates the adaptation to fasting. Furthermore, leptin has been implicated in the regulation of the reproductive, thyroid, growth hormone, and adrenal axes, independent of its role in energy balance. Although it is widely known that leptin acts on hypothalamic neuronal targets to regulate energy balance and neuroendocrine function, the specific neuronal populations mediating leptin action on feeding behavior and autonomic and neuroendocrine function are not well understood. In this review, we have discussed how leptin engages arcuate hypothalamic neurons expressing putative orexigenic peptides, e.g., neuropeptide Y and agouti-regulated peptide, and anorexigenic peptides, e.g., pro-opiomelanocortin (precursor of alpha-melanocyte-stimulating hormone) and cocaine- and amphetamine-regulated transcript. We show that leptin's effects on energy balance and the neuroendocrine axis are mediated by projections to other hypothalamic nuclei, e.g., paraventricular, lateral, and perifornical areas, as well as other sites in the brainstem, spinal cord, and cortical and subcortical regions.

Genetic determinants of variation in gallbladder disease in the Mexican-American population

Since there have not been any studies that quantify the influence of genetic factors on gallbladder disease (GBD) in humans using information from families, we utilized pedigree data to explore the genetic control of variation in liability to GBD. Using an extension of a variance components approach, we performed genetic analyses of GBD using information from 32 low-income Mexican-American families with two slightly different general models incorporating several sex-specific GBD risk factors. After evaluating the relative magnitudes of the covariate effects from these two models, we identified a parsimonious model including only significant predictors of GBD. According to this model, heritability for GBD was high (h2 = 0.44+/-0.18), after accounting for the significant effects of age, leptin in both sexes, total cholesterol, and HDL cholesterol in males only. We have shown quantitatively that variation in GBD is under strong genetic control. However, there are two major limitations to our findings: (1) since GBD was defined by a self-reported clinical history rather than an ultrasound examination, the prevalence of GBD could have been underestimated; and (2) since our design did not allow for shared environmental effects, our estimate of heritability may have been inflated.

Linkage analysis of candidate obesity genes among the Mexican-American population of Starr County, Texas

Recent advances in the molecular basis of body fat regulation have identified several genes in which genetic variation may influence obesity and related measures in human populations. Genes that have been shown to have a regulatory function in the control of body fat utilization, eating behavior, and/or metabolic rate in rodent models of obesity include leptin (LEP), leptin receptor (LEPR), neuropeptide Y (NPY), NPY Y1 receptor (NPYY1), glucagon-like peptide-1 (GLP-1), GLP-1 receptor (GLP1R), and uncoupling protein 1 (UCP1). We have typed microsatellite markers located within or near these seven candidate obesity genes in 302 non-diabetic individuals from 59 Mexican-American families from Starr County, Texas. Sib pair linkage analysis was used to examine linkage between these genes and obesity status (obese siblings only; n = 170 pairs) and several obesity-related quantitative variables (all siblings; n = 545 total sibling pairs). Significant linkage (P = 0.042) was found between obesity and NPY within the obese sibling pairs. No other candidate gene was linked to obesity status in this subsample. Consistent with the obese sib pair linkage results, NPY showed evidence of linkage to body weight (P = 0.020), abdominal circumference (P = 0.031), hip circumference (P = 0.012), diastolic blood pressure (P = 0.005), and a composite measure of body mass and size (P = 0.048) in the entire sibling sample. Other significant linkages observed were between LEP and waist/hip ratio (P = 0.010), total cholesterol (P = 0.030), and HDL cholesterol (P = 0.026) and between LEPR and fasting blood glucose (P = 0.018) and diastolic blood pressure (P = 0.003). These results support further investigation of NPY, LEP, and LEPR to identify genetic variation that may influence obesity status, glucose and lipid metabolism, and blood pressure in Mexican Americans.

Leptin, but not immune function, is linked to reproductive responsiveness to photoperiod

Energetic demands are high while energy availability is minimum during winter. To cope with this energetic bottleneck, animals exhibit numerous energy-conserving adaptations during winter, including changes in immune and reproductive functions. A majority of individual rodents within a population inhibits reproductive function (responders) as winter approaches. A substantial proportion of small rodents within a species, however, fails to inhibit reproduction (nonresponders) during winter in the field or in the laboratory when maintained in winter-simulated day lengths. In contrast, immune function is bolstered by short day lengths in some species. The specific mechanisms that link reproductive and immune functions remain unspecified. Leptin is a hormone produced by adipose tissue, and several studies suggest that leptin modulates reproductive and immune functions. The present study sought to determine if photoperiodic alterations in reproductive function and leptin concentrations are linked to photoperiod-modulated changes in immune function. Siberian hamsters (Phodopus sungorus) were housed in either long (LD 16:8) or short (LD 8:16) day lengths for 9 wk. After 9 wk, blood samples were collected during the middle of the light and dark phase to assess leptin concentrations. One week later, animals were injected with keyhole limpet hemocyanin to evaluate humoral immunity. Body mass, body fat content, and serum leptin concentrations were correlated with reproductive responsiveness to photoperiod; short-day animals with regressed gonads exhibited a reduction in these measures, whereas short-day nonresponders resembled long-day animals. In contrast, immune function was influenced by photoperiod but not reproductive status. Taken together, these data suggest that humoral immune function in Siberian hamsters is independent of photoperiod-mediated changes in leptin concentrations.

The in vivo and in vitro effects of exogenous leptin on ovulation in the rat

Leptin, a hormonal product of the Lep gene, is expressed by adipocytes and is thought to play a role in regulating food intake and reproduction. The leptin protein has been localized in many reproductive tissues, including the ovary. Several publications indicate that the ovary is directly affected by leptin and that leptin may be a factor linking obesity and reproductive dysfunction. In this study, the effect of systemic leptin administration on ovulation in the rat ovary, both in vivo and in vitro, was investigated. Ip administration of leptin (30 microg at 3 hourly intervals for 15 h) to immature gonadotropin-primed rats caused a decline in ovulation in vivo, from 15.9+/-2.0 oocytes in the control animals to 5.3+/-1.6 oocytes in the leptin-treated animals (P < 0.001). Plasma progesterone and estradiol levels were analyzed immediately before ovulation, and neither was altered significantly in animals receiving the leptin treatment. Food consumption and body weight decreased following leptin treatment; however, a loss in body weight alone (pair-fed controls) was insufficient to explain the decrease in ovulation observed in the leptin-treated animals. In vitro perfusion of FSH-primed whole ovaries showed that treatment with leptin in combination with LH significantly decreased ovulations from 5.7+/-1.6 per ovary perfused with LH alone to 1.3+/-0.6 in those with LH and 1 microg/ml leptin (P < 0.05). Progesterone and estradiol levels in the samples taken during the perfusion period were unaffected by leptin treatment. In summary, leptin administration resulted in fewer ovulations, both in vivo and in vitro, but did not influence steroid levels. Systemic leptin administration at these doses can therefore inhibit ovulation, a process that occurs through a direct effect on the ovary.

The effect of ovarian steroids and photoperiod on body fat stores and uncoupling protein 2 in the marsupial Sminthopsis crassicaudata

To determine the effects of photoperiod and ovarian steroids on fat stores in the marsupial S. crassicaudata, animals were ovariectomised (OVX) or sham operated, and maintained under either short-day (SD) or long-day (LD) photoperiods for 104 days. Photoperiod had no effect on body weight in the sham animals. In the LD OVX animals, body weight fell and remained below baseline for about 45 days, whereafter it returned to baseline. In contrast, body weight of SD OVX animals increased over the first 45 days then returned to baseline. Tail width (a reflection of body fat stores) increased in both sham and OVX animals exposed to SD. When exposed to LD, tail width increased only in the OVX animals. There was no effect of either photoperiod or OVX on total cumulative energy intake. Leptin mRNA expression was increased in the LD OVX animals compared to the shams. Photoperiod had no effect on UCP2 mRNA expression in any tissue; however, OVX decreased UCP2 mRNA expression in muscle. These data indicate that in S. crassicaudata: (a) fat mass increases in response to both SD photoperiod and OVX and they have additive effects; (b) the effects of photoperiod on fat mass are mediated by both gonadal steroid dependent and independent mechanisms; (c) alterations in UCP2 mRNA expression may mediate the effect of OVX, but not photoperiod; and (d) UCP2 mRNA is differentially regulated in muscle and fat.

Leptin in Cerebrospinal Fluid from Children: Correlation with Plasma Leptin, Sexual Dimorphism, and Lack of Protein Binding

Background: Previous studies in adults have established that leptin is present at very low concentrations in cerebrospinal fluid (CSF), but few data exist concerning CSF leptin in children. Current evidence suggests that CSF leptin concentrations interact with hypothalamic centers controlling food intake. Serum leptin concentrations manifest a sexual dimorphism that arises during puberty.

Methods: Leptin concentrations were determined in CSF from 42 pre- and postpubertal children who had been objectively classified into non-neurological disease or aseptic meningitis groups. Multivariate analysis of the dependence of CSF leptin on gender, pubertal state, body mass index (BMI), presence of aseptic meningitis, and CSF protein concentration was performed.

Results: CSF leptin concentrations correlated with log-transformed plasma leptin concentrations in concomitantly collected samples (r = 0.582; P = 0.029). BMI and gender were significant determinants of CSF leptin in postpubertal children, but only BMI was significant in prepubertal children. Analysis with HPLC to separate protein-bound and free forms of leptin found only free leptin in CSF.

Conclusions: CSF leptin concentrations in children reflect plasma leptin concentrations, including the advent of sexual dimorphism at puberty. Only free leptin is detectable in CSF, suggesting that it is the biologically active form.

Associations of leptin with body fat distribution and metabolic parameters in non-insulin-dependent diabetic patients: no effect of apolipoprotein E polymorphism

Leptin levels have been shown previously to be associated with anthropometric parameters such as the body mass index (BMI), total body fat, and subcutaneous fat. Since apolipoprotein E (apoE) polymorphism is known to be a genetic marker affecting the relationship between certain anthropometric and metabolic parameters, we evaluated whether the leptin level and/or associations between the leptin level and body composition in non-insulin-dependent diabetic patients could be determined by apoE polymorphism. In 171 type 2 diabetic patients (105 male and 66 female), body composition (BMI, waist to hip ratio [WHR], fat mass, and visceral fat) was measured and fasting blood samples were obtained to determine the apoE genotype, leptin, glucose, and insulin levels, and the lipid profile. The mean leptin level for the whole group was 11.7 +/- 9.3 ng/mL, with a significant difference (P < .001) between men (7.1 +/- 4.9 ng/mL) and women (19.0 +/- 10.1 ng/mL). No difference was found for leptin levels or anthropometric variables between the 3 different apoE genotypes (E3/E3 homozygotes, E2 carriers, and E4 carriers). Only low-density lipoprotein (LDL) cholesterol was significantly different between the 3 apoE subgroups. The correlations of leptin with anthropometric variables, especially visceral fat, tended to be different between the 3 apoE groups, but this was not independent and no effect was found after controlling for the other parameters in the model. A multiple regression model containing gender, subcutaneous fat, fasting glucose, triglycerides, and high-density lipoprotein (HDL) cholesterol explained 81% of the variance in leptin levels. We conclude that apoE polymorphism has no effect on the leptin level or its associations with other anthropometric and metabolic parameters.

Relationship between serum leptin and thyroid hormones in children

BACKGROUND

Because leptin decreases food intake and increases energy expenditure, the possible influence of thyroid status on the leptin system has been investigated mainly in adults and animals. However, the data available at present are very confusing. The aim of the present study was to assess the possible interaction of thyroid hormones with the leptin system.

METHODS

Serum free thyroxine (FT4), a biologically active thyroid hormone, and thyroid stimulating hormone (TSH), a sensitive and reliable index of thyroid status, were examined in 51 children (19 males, 32 females) with mass screening-detected congenital hypothyroidism on continuous L-thyroxine (L-T4) substitution therapy. The subjects were divided into younger (n = 35, aged 1 month-5 years) and older (n = 16, 6 years-11 years) children groups. Serum levels of leptin and thyroid hormones were measured in the subjects. Body mass index (BMI) was estimated by the formula bodyweight (kg)/height x height (m2), which is known as the Kaup index in younger children and BMI in older children and adults.

RESULTS

In the younger children group, serum leptin levels showed no correlation with serum TSH, FT4 or T4. In the older children group, serum leptin concentrations significantly correlated with T4 (r = 0.510, P < 0.05) and BMI (n = 16, r = 0.647, P < 0.01), but not with TSH or FT4.

CONCLUSION

The role of thyroid hormones in modulating leptin synthesis and secretion seems to have little, if any, clinical or biological relevance.

Hyperleptinemia is more closely associated with adipose cell hypertrophy than with adipose tissue hyperplasia

OBJECTIVES

To investigate the relationships of fat cell weight (FCW) as well as of estimated total adipose cell number to fasting plasma leptin concentration.

DESIGN

Cross-sectional correlational study.

SUBJECTS

A sample of 63 men (mean age+/-s.d.: 36+/-4 y) and 42 premenopausal women (35+/-5 y).

MEASUREMENTS

Adipose tissue (AT) biopsies were obtained in order to determine FCW as well as estimated adipose cell number. Fasting plasma leptin and insulin concentrations as well as various fatness and body fat distribution variables (underwater weighing and computed tomography) were also measured.

RESULTS

In both genders, mean FCW as well as the estimated adipose cell number were significantly correlated with body fatness and AT distribution variables (0.41</=r</=0.84). Larger abdominal (P<0.005) and femoral (P<0.0001) FCW were found in women than in men. This gender difference in adipose cell size was associated with increased leptin concentrations in women compared with men. In both genders, increased abdominal FCW was associated with higher plasma leptin concentrations (men: r=0.38, P<0.005 and women: r=0.55, P<0.0001). However, the association between femoral FCW and leptinemia was only significant in women (r=0.45, P<0.005). Contrary to women, plasma leptin concentrations were associated with estimated adipose cell number in men (r=0.59, P<0.0001). Multiple regression analyses revealed that gender (43.3%), mean FCW (16.2%) and the estimated adipose cell number (10.1%) were significant predictors of fasting leptinemia.

CONCLUSIONS

Results of the present study indicate that in men and women, adipose cell hypertrophy is associated with increased plasma leptin concentrations. This finding provides further support to the observation that adipose tissue leptin secretion may be regulated, at least to a certain extent, by adipocyte size. Thus, the present study suggests that the higher plasma leptin concentrations found in women than in men could be partly explained by the well documented gender difference in adipose cell size and number.

Evidence for leptin expression in fishes

Tissues from bony fish were screened with anti-mouse leptin antibodies to detect the presence of the fat-regulating hormone in fishes. Low molecular-weight (16 kDa) immunoreactive bands were detected in blood, brain, heart and liver of green sunfish (Lepomis cyanellus), bluegill sunfish (Lepomis macrochirus), largemouth bass (Micropterus salmoides), white crappie (Pomonix annularis), channel catfish (Ictalurus punctatus), and rainbow trout (Oncorhynchus mykiss). To further verify that we had identified leptin, the response of fish "leptin" was measured in fed and fasted green sunfish. Fed sunfish had approximately threefold higher concentration of leptin in blood than did fasted sunfish (fed vs. fasted; 0.599 +/- 0.03 microg/microl vs. 0.196 +/- 0.04 microg/microl; P > F = 0.0001), which is consistent with mammalian models of leptin function. Brain leptin concentration is also positively correlated with percent body fat in white crappie and bluegill. Based upon electrophoretic mobility, immunoreactivity, response to fasting, and correlation with adiposity, we believe we have the first evidence for leptin expression in an ectotherm.

Centrally administered murine-leptin stimulates the hypothalamus-pituitary- adrenal axis through arginine-vasopressin

Starvation induces a decrease in circulating leptin levels and activation of the hypothalamus-pituitary-adrenal (HPA) axis. Leptin inhibits the HPA axis in unfed rodents or genetically leptin-deficient ob/ob mice, whereas it stimulates corticotropin-releasing hormone (CRH) gene expression in the paraventricular nucleus (PVN). However, the interactions between leptin, CRH and the HPA axis are poorly understood and are likely to be complex. We recently demonstrated that central leptin administration caused increases in plasma arginine-vasopressin (AVP) and AVP gene expression of the PVN in nonstressful rats. AVP stimulates the release of adrenocorticotropic hormone (ACTH), but it also potentiates the action of CRH on ACTH release. In this study, we investigated the effects of leptin on plasma ACTH and corticosterone levels, CRH mRNA of the PVN and proopiomelanocortin (POMC) mRNA of the pituitary in nonstrained rats. Intracerebroventricularly administered leptin caused increases in plasma ACTH and corticosterone levels in dose-dependent manners. In Northern blot analyses, the leptin injection induced significant increases in the expression of CRH mRNA in the PVN and POMC mRNA in the pituitary. The increased plasma ACTH and corticosterone levels by leptin were attenuated with intracerebroventricular pretreatment of a V(1a) receptor antagonist (OPC-21268) or a V(1a)/V(1b) receptor antagonist (dP[Tyr(Me)(2)]AVP), but not with that of a V(2) receptor antagonist (OPC-31260). The leptin-induced CRH mRNA expression in the PVN and POMC mRNA expression in the pituitary were also reduced by the pretreatment with OPC-21268 and dP[Tyr(Me)(2)]AVP. These results suggest that intracerebroventricular leptin administration activates the HPA axis by AVP receptor activation through V(1a) receptors in the PVN which in turn activates CRH neurons to drive ACTH and corticosterone secretion in concert with AVP in nonstrained rats.

One-step enzyme-linked immunosorbent assay (ELISA) for measurement of serum free leptin

In man, circulating leptin levels are increased with obesity and are regulated by a complex of hormonal, feeding and body-weight changes. Accurate and precise methods to quantitate circulating serum free leptin (f-leptin) concentrations are needed for physiological and clinical studies. We developed a one-step enzyme immunoassay to measure human f-leptin in serum. The detection limit was 0.40 ng/ml. The recovery of leptin added to serum was 90.8-102.8%. The within-run and between-day coefficients of variation (C.V.) ranged from 2.8 to 7.7 and 5.7 to 9.7%, respectively, and the immunoassay had an overall recovery rate for serial dilution in the range of 94. 0-109.9%. Measured serum f-leptin concentrations in 201 adults correlated (r=0.449, P<0.001) directly with body mass index (BMI kg/m(2)), particularly when results were separated by gender (r=0. 709 for male, P<0.001; r=0.643 for female, P<0.001). We conclude that this one-step enzyme immunoassay is accurate for measuring f-leptin in human serum.

Leptina: o diálogo entre adipócitos e neurônios

A descoberta da leptina trouxe consigo um interesse renovado sobre o estudo do controle homeostático da energia. Sabe-se agora que o tecido adiposo branco é o maior sítio de produção da leptina. Uma vez na circulação sangüínea ela se liga a receptores específicos no cérebro, levando ao sistema nervoso central um sinal de saciedade que reflete a quantidade existente de energia em forma de gordura no organismo. Agindo por intermédio de receptores que fazem uso da via JAK/SAT de transdução do sinal intracelular, a leptina modifica a expressão e a atividade de inúmeros peptídeos hipotalâmicos que regulam o apetite e o gasto de energia. Além disso, a leptina sinaliza o estado nutricional do organismo a outros sistemas fisiológicos, modulando a função de várias glândulas alvo. Mais recentemente, a leptina recombinante foi administrada com sucesso numa paciente obesa com deficiência do hormônio devido a uma mutação do gene ob. Por outro lado, os efeitos da leptina recombinante no único estudo em pacientes com obesidade e concentrações elevadas de leptina foram menos impressionantes. Nesta revisão, discutiremos a complexidade das ações da leptina com ênfase no seu papel integrativo de sinalizadora do estado nutricional para o organismo.

Interaction between leptin and sympathetic nervous system in hypertension

Leptin is a protein produced by adipose tissue that acts in the central nervous system (CNS) to decrease appetite and increase energy expenditure. Leptin thus functions as the afferent component of a negative feedback loop that maintains stable adipose tissue mass. Intravenous leptin increases norepinephrine turnover and sympathetic nerve activity to thermogenic brown adipose tissue. Leptin also increases sympathetic nerve activity to tissues not usually considered thermogenic, including the kidney, hindlimb, and adrenal gland. Chronic systemic CNS administration of leptin increases arterial pressure and heart rate in conscious animals. However, leptin has additional cardiovascular actions that may act to oppose sympathetically mediated vasoconstriction. These actions include natriuresis, insulin sensitization, endothelium-dependent dilatation, and angiogenesis. Thus, the overall effect of leptin on arterial pressure has been unclear. Recent studies have demonstrated that leptin-deficient ob/ob obese mice have lower arterial pressure than lean controls with normal leptin levels. These studies suggest that leptin contributes physiologically to maintenance of arterial pressure. Leptin expression and plasma leptin concentrations are elevated in obese humans. Abnormalities in the generation or actions of leptin may, therefore, have implications for the sympathetic, cardiovascular, and renal changes associated with obesity.

Transcellular transport of leptin by the short leptin receptor isoform ObRa in Madin-Darby Canine Kidney cells

Leptin is an adipocyte-derived hormone that acts in specific regions of the brain to regulate body weight and neuroendocrine function. The mechanism by which leptin enters the brain is unknown. We previously reported that rat brain microvessels, which constitute the blood-brain barrier, contain large amounts of messenger RNA encoding a short form of the leptin receptor (ObRa), suggesting that this site may be important for receptor-mediated transport of leptin into the brain. The purpose of this study was to determine whether ObRa is capable of transcellular transport of intact leptin. A transwell system in which Madin-Darby Canine Kidney (MDCK) cells stably expressing ObRa are grown in a monolayer was used to determine receptor distribution on apical or basolateral cell surfaces and the capacity for directional transport of 125I-leptin. Binding of 125I-leptin was greater on the apical vs. the basolateral cell surface and transport of 125I-leptin occurred only in the apical to basolateral direction. 11% of transported radioactivity appearing in the basolateral chamber represented intact leptin as assessed by TCA precipitation analysis and by SDS-PAGE. Parental MDCK cells did not express leptin receptors and did not bind or transport 125I-leptin. Epidermal growth factor (EGF) binding and transport via endogenous EGF receptors in MDCK cells also was assessed. In contrast to leptin, specific binding of 125I-EGF occurred primarily on the basolateral cell surface and transport of 125I-EGF occurred predominantly in the basolateral to apical direction. These data show that ObRa is preferentially targeted to the apical cell membrane in MDCK cells and that leptin transport occurs, albeit at a low rate, in a unidirectional manner in the apical to basolateral direction. These findings may be relevant to the putative role of ObRa in receptor-mediated transport of leptin from the circulation into the brain.

Plasma concentrations of a novel, adipose-specific protein, adiponectin, in type 2 diabetic patients

Adiponectin is a novel, adipose-specific protein abundantly present in the circulation, and it has antiatherogenic properties. We analyzed the plasma adiponectin concentrations in age- and body mass index (BMI)-matched nondiabetic and type 2 diabetic subjects with and without coronary artery disease (CAD). Plasma levels of adiponectin in the diabetic subjects without CAD were lower than those in nondiabetic subjects (6.6+/-0.4 versus 7.9+/-0.5 microg/mL in men, 7.6+/-0.7 versus 11.7+/-1.0 microg/mL in women; P<0.001). The plasma adiponectin concentrations of diabetic patients with CAD were lower than those of diabetic patients without CAD (4.0+/-0.4 versus 6.6+/-0.4 microg/mL, P<0.001 in men; 6.3+/-0.8 versus 7.6+/-0. 7 microg/mL in women). In contrast, plasma levels of leptin did not differ between diabetic patients with and without CAD. The presence of microangiopathy did not affect the plasma adiponectin levels in diabetic patients. Significant, univariate, inverse correlations were observed between adiponectin levels and fasting plasma insulin (r=-0.18, P<0.01) and glucose (r=-0.26, P<0.001) levels. In multivariate analysis, plasma insulin did not independently affect the plasma adiponectin levels. BMI, serum triglyceride concentration, and the presence of diabetes or CAD remained significantly related to plasma adiponectin concentrations. Weight reduction significantly elevated plasma adiponectin levels in the diabetic subjects as well as the nondiabetic subjects. These results suggest that the decreased plasma adiponectin concentrations in diabetes may be an indicator of macroangiopathy.

Basal metabolic rate in anorexia nervosa: relation to body composition and leptin concentrations

BACKGROUND

Leptin is thought to represent a peripheral signal involved in the regulation of energy balance. Its action has been studied in animals and obese subjects. Little is known about leptin's role during negative energy balance.

OBJECTIVE

The objective was to evaluate the relation between energy turnover, body composition, and plasma leptin concentrations in anorexia nervosa (AN).

DESIGN

Sixteen weight-stable women with AN were compared with 22 control subjects and 14 rehabilitated AN patients (R-AN). Basal metabolic rate (BMR) was measured by indirect calorimetry; fat-free mass (FFM) and fat mass (FM) were calculated according to a 4-compartment model. Plasma leptin was determined by radioimmunoassay.

RESULTS

The BMR of AN patients (2.73 +/- 0.37 kJ/min) was significantly lower than that of control subjects (3.45 +/- 0.34 kJ/min) (P < 0.001), even after adjustment for FFM (2.92 +/- 0.33 kJ/min in AN patients and 3.30 +/- 0.26 kJ/min in control subjects; P < 0.004). Plasma leptin concentrations in AN patients were 76% lower than in control subjects, even after body fat was controlled for. In R-AN patients, BMR was not significantly different from that of control subjects and leptin concentrations were generally close to normal. Plasma leptin concentrations correlated significantly with FM (r(2) = 0.53, P < 0.0000) and BMR, even after adjustment for FFM (r(2) = 0.21, P < 0.0003).

CONCLUSIONS

BMR and plasma leptin concentrations are depressed in patients with AN; this is not explained by body-composition changes. The relation between leptin and BMR suggests that leptin plays a role in the energy sparing response to exposure to chronic energy deficiency. The return of BMR to normal and the significant increase in leptin concentrations in R-AN patients suggests a full reversibility of this adaptation mechanism.

Serum leptin levels in patients with hyperlipidemias

Leptin is a protein hormone produced by adipocytes that reflects the body fat content. The aim of our study was to compare serum leptin levels in randomly selected untreated males and females with hypercholesterolemia and combined hyperlipidemia and in healthy control subjects matched for age and body mass index and to study the relations between leptin and serum lipids and lipoproteins. No statistically significant differences in serum leptin levels were found between the male control group (5.26 +/- 2.81 ng/mL(-1)) and the male group with hypercholesterolemia (8.16 +/- 3.85 ng/mL(-1)) or combined hyperlipidemia (7.51 +/- 4.83 ng/mL(-1)) and between the female control group (13.0 +/- 8.12 ng/mL(-1)) and the female group with hypercholesterolemia (15.36 +/- 8.89 ng/mL(-1)) or combined hyperlipidemia (18.63 +/- 10.15 ng/mL(-1)). Leptin concentration in male group with hypercholesterolemia did not differ significantly from the female control group; in the other male groups, leptin levels were significantly lower than those of the other female groups. Serum leptin levels in all studied groups except for the male group with hypercholesterolemia positively correlated with body mass index. Serum leptin levels correlated negatively with high-density lipoprotein cholesterol in the female group with hypercholesterolemia (r = -0.67, P < 0.01) and the male group with combined hyperlipidemia (r = -0.56, P < 0.01). A positive correlation between serum leptin and high-density lipoprotein cholesterol (r = 0.67, P < 0.01) and between leptin and lipoprotein (a) (r = 0.71, P < 005) was found in female group with combined hyperlipidemia. No other significant relationships between leptin and serum lipids or lipoproteins were found. We conclude that serum leptin levels in patients with hyperlipidemias do not significantly differ from those healthy control subjects matched by age and body mass index.

Negative regulation of leptin by chronic high-glycemic index starch diet

The response of plasma leptin to a high-glycemic index (high-GI) starch diet after a short (3 weeks) and prolonged (12 weeks) period was determined in Sprague-Dawley rats. Age-matched rats were fed an identical isocaloric diet except that the carbohydrates were from either mung bean starch (low-GI) or waxy cornstarch (high-GI). After a single test meal of the high-GI starch diet, postprandial plasma glucose (P < .05) and insulin (P < .01) peaks and plasma glucose (P < .014) and insulin (P < .05) areas were higher versus the low-GI starch diet (n = 8 per group). Other age-matched control rats were fed the same diets for a longer period. After 3 weeks, ob mRNA levels were decreased by 50% (P < .005) in the epididymal adipose tissue of high-GI-fed rats versus low-GI-fed rats, without a significant decrease in plasma leptin. After 12 weeks of the high-GI starch diet, both plasma leptin and ob mRNA were decreased by 34% (P < .005) and 41% (P < .05), respectively, compared with the low-GI diet. Both relative epididymal adipose tissue weight (adjusted per 100 g body weight) and total fat mass, as measured by dual-energy x-ray absorptiometry (DEXA), were unchanged by the high-GI starch diet. Basal nonfasting plasma insulin, glucose, and triglycerides were not altered by the high-GI starch diet, whereas free fatty acids were significantly elevated and associated with a trend (P < .13) for increased plasma free glycerol. Plasma leptin levels were negatively correlated with free fatty acid levels (r = .56, P < .05). Despite low leptin, rats fed on the high-GI diet did not increase their food intake, suggesting increased leptin sensitivity. These findings might precede weight gain and the increase in fat mass. Chronic nutritional factors might alter plasma leptin via several overlapping factors independently of energy intake.

Differential and genetically separable associations of leptin with obesity-related traits

OBJECTIVE

The extent to which leptin protects against obesity is unknown. By intercrossing New Zealand obese mice with lean C57BL/6J mice, we have separated the genes controlling leptin and other weight-related phenotypes. This has allowed us to determine whether hyperleptinaemia is associated with reduced food intake and increased physical activity in mice spanning a large range in body weight.

METHODS

Plasma leptin, glucose and insulin, body weight, food intake, running wheel activity, and four adipose depots were measured in 587 adult F2 and backcross mice

RESULTS

When mice were categorized by adiposity, a plot of food intake vs leptin illustrated a U-shaped curve. Food intake decreased as leptin levels rose to approximately 15 ng/ml, beyond which the relationship reversed. A negative relationship was observed between activity and leptin with a maximal decrease in activity once leptin reached approximately 15 ng/ml.

CONCLUSION

Leptin has differential responses to food intake and activity, suggesting that it has limited potential to defend against obesity. A genetic defect in leptin sensitivity is unlikely to be the primary cause of obesity in these mice, since hyperleptinaemia was not coinherited with both hyperphagia and inactivity as body weight increased.

Leptin levels in relation to body composition and insulin concentration in patients with endogenous Cushing's syndrome compared to controls matched for body mass index

Cushing's syndrome (CS) is associated with weight gain and visceral obesity. We examined the relationship between regional fat distribution and serum levels of leptin, cortisol and insulin. Twenty-three consecutive patients with recently diagnosed CS (18 with pituitary adenoma, 5 with adrenal tumor), where compared to obese controls, matched for age, sex and Body Mass Index (BMI). Serum insulin, leptin, cortisol, C-peptide and body composition determined by DEXA were measured. Serum leptin levels were significantly increased in patients with CS (36.9+/-3.8 vs 18.9+/-2.4 ng/ml, p<0.001; women: 40.1+/-4.6 vs 21.7+/-2.9 ng/ml, p<0.01; men: 27.9+/-5.7 vs 10.9+/-2.3 ng/ml; p<0.05), the same were fasting insulin levels (178+/-30 vs 81+/-10 pmol/l; p<0.01) and C-peptide (1.51+/-0.12 vs 0.77+/-0.07 nmol/l; p<0.001). In a subgroup of 12 patients, truncal fat mass was significantly elevated when compared to obese controls (19.2 kg vs 14.7 kg, p<0.01, and 42% vs 36% in percentage of truncal body tissue, p<0.05), whereas total fat mass was insignificantly increased. Serum leptin correlated positively to total body fat (%) as in patients with CS (r=0.94, p<0.001) as in controls (r=0.68, p<0.01). The correlation to truncal body fat (%) was also significant in both groups (CS: r=0.84, p<0.001; controls: r=0.63, p<0.01). Multiple regression showed that percent total body fat was the predictor of leptin concentrations among patients with CS (r2=0.88, p<0.001) whereas insulin did not contribute significantly to the variance in leptin concentrations. In controls, both leptin and insulin (r2=0.65, p<0.001) contributed significantly to the variations in leptin levels. Controlled for the differences in total body fat, patients with endogenous CS have significantly increased serum leptin levels, compared to BMI-matched obese controls. This suggests that hyperleptinemia in CS not primarily reflects changes in body composition, but is the result of different hormonal influences on adipose tissue.

Leptin and metabolic control of reproduction

Leptin treatment prevents the effects of fasting on reproductive processes in a variety of species. The mechanisms that underlie these effects have not been elucidated. Progress in this area of research might be facilitated by viewing reproductive processes in relation to mechanisms that maintain fuel homeostasis. Reproduction, food intake, and fuel partitioning can be viewed as homeostatic responses controlled by a sensory system that monitors metabolic signals. These signals are generated by changes in intracellular metabolic fuel availability and oxidation rather than by changes in the amount of body fat or by changes in any aspect of body composition. Leptin might be viewed as either a mediator or as a modulator of the intracellular metabolic signal. Consistent with its purported action as a mediator of the metabolic signal, leptin synthesis and secretion are influenced acutely by changes in metabolic fuel availability, and these changes might lead to changes in reproductive function. The effects of leptin treatment on reproduction are blocked by treatments that inhibit intracellular fuel oxidation. Metabolic signals that inhibit reproduction in leptin-treated animals might act via neural pathways that are independent of leptin's action. Alternatively, both leptin and metabolic inhibitors might interact at the level of intracellular fuel oxidation. In keeping with the possibility that leptin modulates the metabolic signal, leptin treatment increases fuel availability, uptake, and oxidation in particular tissues. Leptin might affect reproduction indirectly by altering fuel oxidation or other peripheral processes such as gastric emptying. Reproductive processes are among the most energetically expensive in the female repertoire. Because leptin increases energy expenditure while simultaneously inhibiting energy intake, it may have limited use as a long-term treatment for infertility.

Fasting, but not adrenalectomy, reduces transport of leptin into the brain

Food deprivation and adrenalectomy are associated with low concentrations of leptin in blood and the absence of obesity. Because leptin is known to cross the blood-brain barrier (BBB) by a saturable transport system, we examined whether fasting and adrenalectomy (ADX) also act at the BBB. Multiple-time regression analysis showed that fasting, but not ADX, significantly decreased the entry of leptin into mouse brain. After 3 days of food deprivation, the influx of leptin became indistinguishable from that of the vascular control (albumin); 5 h of refeeding significantly reversed this reduced rate of influx. Thus, the results indicate that the BBB provides a dynamic site for the regulation of physiological processes involving leptin.

Low plasma leptin concentration and low rates of fat oxidation in weight-stable post-obese subjects

OBJECTIVE

A low resting metabolic rate for a given body size and composition, a low rate of fat oxidation, low levels of physical activity, and low plasma leptin concentrations are all risk factors for body weight gain. The aim of the present investigation was to compare resting metabolic rate (RMR), respiratory quotient (RQ), levels of physical activity, and plasma leptin concentrations in eight post-obese adults (2 males and 6 females; 48.9 +/- 12.2 years; body mass index [BMI]: 24.5 +/- 1.0 kg/m2; body fat 33 +/- 5%; mean +/- SD) who lost 27.1 +/- 21.3 kg (16 to 79 kg) and had maintained this weight loss for > or =2 months (2 to 9 months) to eight age- and BMI-matched control never-obese subjects (1 male and 7 females; 49.1 +/- 5.2 years; BMI 24.4 +/- 1.0 kg/m2; body fat 33 +/- 7%).

RESEARCH METHODS AND PROCEDURES

Following 3 days of weight maintenance diet (50% carbohydrate and 30% fat), RMR and RQ were measured after a 10-hour fast using indirect calorimetry and plasma leptin concentrations were measured using radioimmunoassay. Levels of physical activity were estimated using an accelerometer over a 48-hour period in free living conditions.

RESULTS

After adjustment for fat mass and fat-free mass, post-obese subjects had, compared with controls, similar levels of physical activity (4185 +/- 205 vs. 4295 +/- 204 counts) and similar RMR (1383 +/- 268 vs. 1430 +/- 104 kcal/day) but higher RQ (0.86 +/- 0.04 vs. 0.81 +/- 0.03, p < 0.05). Leptin concentration correlated positively with percent body fat (r = 0.57, p < 0.05) and, after adjusting for fat mass and fat-free mass, was lower in post-obese than in control subjects (4.5 +/- 2.1 vs. 11.6 +/- 7.9 ng/mL, p < 0.05).

DISCUSSION

The low fat oxidation and low plasma leptin concentrations observed in post-obese individuals may, in part, explain their propensity to relapse.

Pathophysiological role of leptin in obesity-related hypertension

To explore the pathophysiological role of leptin in obesity-related hypertension, we examined cardiovascular phenotypes of transgenic skinny mice whose elevated plasma leptin concentrations are comparable to those seen in obese subjects. We also studied genetically obese KKA(y) mice with hyperleptinemia, in which hypothalamic melanocortin system is antagonized by ectopic expression of the agouti protein. Systolic blood pressure (BP) and urinary catecholamine excretion are elevated in transgenic skinny mice relative to nontransgenic littermates. The BP elevation in transgenic skinny mice is abolished by alpha(1)-adrenergic, beta-adrenergic, or ganglionic blockers at doses that do not affect BP in nontransgenic littermates. Central administration of an alpha-melanocyte-stimulating hormone antagonist causes a marked increase in cumulative food intake but no significant changes in BP. The obese KKA(y) mice develop BP elevation with increased urinary catecholamine excretion relative to control KK mice. After a 2-week caloric restriction, BP elevation is reversed in nontransgenic littermates with the A(y) allele, in parallel with a reduction in plasma leptin concentrations, but is sustained in transgenic mice overexpressing leptin with the A(y) allele, which remain hyperleptinemic. This study demonstrates BP elevation in transgenic skinny mice and obese KKA(y) mice that are both hyperleptinemic, thereby suggesting the pathophysiological role of leptin in some forms of obesity-related hypertension.

Predictors of weight gain: the biological-behavioural debate

The rapidly increasing prevalence of obesity, in spite of an unchanged gene pool, makes it interesting to search for biological factors which increase the susceptibility at the individual level as well as searching for the responsible environmental factors. Among the identified metabolic factors is a low resting metabolic rate for given body size and composition, a high respiratory quotient (RQ) indicating a low fat oxidation and a low spontaneous physical activity, all factors which are regarded as being under substantial genetic influence. Among the environmental factors, it is low levels of physical activity, increasing inactivity and a high fat diet that are probably the most important ones. In this review we have focused on controversies in this area. Understanding the interaction between the constitutional biological factors and the environmentally determined lifestyle factors it is important to produce better options for both the prevention and treatment of obesity.

The relationship between different subcutaneous adipose tissue layers, fat mass and leptin in obese children and adolescents

We studied the relationships of subcutaneous adipose tissue layers (SAT-layers), body fat mass (FM) and waist-to-hip ratio (WHR) with leptin in obese children and adolescents. Twenty-nine obese children and adolescents (12 boys: age: 11.3 +/- 3.7 yr; body mass index [BMI]: 28.5 +/- 4) and 17 girls (age: 12.2 +/- 2.2 yr; BMI: 29.8 +/- 4.7) (mean +/- SD) were studied. FM was estimated by bioelectrical impedance. SAT-layers were determined at 15 different body sites from 1-neck to 15-calf by the Lipometer optical device. Leptin and insulin were determined by RIA. Maturity was associated with a greater thickness of certain SAT-layers from the upper body and with a lower thickness of SAT-layers from the abdominal region and lower extremities. Significant correlations were found for all estimates of adiposity and leptin (all p<0.001). Waist and hip circumferences were not correlated to leptin after adjustment for FM. SAT-layers from the upper body were significantly and positively correlated to leptin. Multiple regression analysis revealed FM as a main contributor to the variation in leptin (R2=0.53, p<0.0001). FM together with SAT-layers 5-front chest and 13-rear thigh explained 72% of the variation in leptin (p<0.0001). In a body fat distribution model, hip circumference together with SAT-layers 4-upper back and 2-triceps explained 75% of the variation in leptin (p< 0.0001). The results suggest that SAT-layers and their topography are main determinants for leptin in obese children and adolescents. Maturity in obese children is associated with higher values of upper body SAT-layers and lower values of abdominal and lower extremities SAT-layers. Whether leptin is under the control of certain subcutaneous adipose tissue depots from the upper body remains to be elucidated by longitudinal studies.

Insulin increases leptin mRNA expression in abdominal subcutaneous adipose tissue in humans

Insulin regulates expression and production of leptin in rodents but whether this is also true in humans remains unclear. To test the effects of acute hyperinsulinemia on expression of leptin mRNA in humans, percutaneous needle biopsies of abdominal subcutaneous adipose tissue were performed at baseline and immediately following a 200-min two-step hyperinsulinemic-euglycemic glucose clamp in 16 Pima Indians (8M/8F). Leptin mRNA was quantified by reverse transcription, PCR amplification and expressed relative to actin mRNA. Leptin mRNA levels were higher in women than men (25.6 +/- 1.7 v 16.9 +/- 2.1 relative units, P = 0.003) at baseline. Baseline levels were directly related to percentage body fat (r = 0.54, P = 0. 03) and fasting plasma glucose concentrations (r = 0.57, P = 0.02) and were negatively correlated to glucose disposal at physiologic insulin concentrations (750 +/- 40 pmol/L) during the clamp (r = -0. 51, P = 0.04). Acute hyperinsulinemia (final insulin concentration 11560 +/- 950 pmol/L) increased leptin mRNA levels in 13 of 16 individuals an average of 13% (21.3 +/- 1.7 to 24.2 +/- 1.2 relative units, P = 0.01). Changes in leptin mRNA were directly related to glucose disposal rates during physiologic hyperinsulinemia (r = 0.54, P < 0.04). These results suggest that the expression of leptin mRNA is regulated by insulin in humans, as it is in rodents.

Gene expressions of leptin, insulin receptors and lipogenic enzymes are coordinately regulated by insulin and dietary fat in rats

Regulation of the gene expressions of leptin, insulin receptors and lipogenic enzymes was investigated after refeeding a fat-free diet or a 10 g/100 g corn oil diet to food-deprived rats. Plasma glucose and insulin concentrations began to increase 30 min after the feeding and further increased up until 8 h. In these rats, the expression of leptin mRNA in adipose tissue began to increase significantly only 30 min after feeding, and reached a maximum at 8-16 h. However, plasma leptin levels did not increase until 4 h after refeeding, then markedly increased and reached the maximal level after 8 h. The expression of leptin mRNA and plasma leptin concentrations generally were greater in rats fed the corn oil diet compared to those fed the fat-free diet. Insulin receptor mRNA concentrations in the liver and adipose tissue began to decrease 30 min after the refeeding, in contrast to the plasma insulin increase, and continued to decrease until 8 h. The expression of acetyl-CoA carboxylase and fatty acid synthase mRNA began to increase 4-8 h after feeding and reached maximal levels at 16-24 h. Leptin treatment suppressed the expression of lipogenic enzyme mRNA in rats fed the fat-free diet but not in corn oil-fed rats, in which the expression was suppressed by polyunsaturated fatty acids and leptin expression was higher. Thus, we suggest that the glucose and insulin-dependent expressions of leptin, insulin receptors and lipogenic enzymes are coordinately and/or mutually regulated by dietary manipulation.

Weight gain associated with valproate in childhood

Weight gain is a common side effect of valproate treatment. Several mechanisms have been suggested for its pathophysiology; of these, impairment of beta-oxidation of fatty acids and increased insulin secretion have been supported by clinical studies. To investigate whether changes in carnitine and insulin levels had a role in the weight gain occurring with valproate treatment in children, 20 patients with epilepsy were randomly assigned to receive either carnitine or placebo supplementation in addition to valproate. After a follow-up period of 3 months, weight gain was observed in both groups. The mean insulin concentration and insulin/glucose ratios increased. Weight gain did not correlate with carnitine levels. These results suggest that weight gain during valproate treatment is not related to a decrease in carnitine levels. However, an increase in insulin levels together with a decrease in glucose levels may cause weight gain, possibly by stimulating appetite.