Development of radioimmunoassay for human leptin

Leptin sensitizing effect of 1,3-butanediol and its potential mechanism

Leptin is an adipocyte-derived hormone that regulates appetite and energy expenditure via the hypothalamus. Since the majority of obese subjects are leptin resistant, leptin sensitizers, rather than leptin itself, are expected to be anti-obesity drugs. Endoplasmic reticulum (ER) stress in the hypothalamus plays a key role in the pathogenesis of leptin resistance. ATP-deficient cells are vulnerable to ER stress and ATP treatment protects cells against ER stress. Thus, we investigated the therapeutic effects of oral 1,3-butanediol (BD) administration, which increases plasma β-hydroxybutyrate and hypothalamic ATP concentrations, in diet induced obese (DIO) mice with leptin resistance. BD treatment effectively decreased food intake and body weight in DIO mice. In contrast, BD treatment had no effect in leptin deficient ob/ob mice. Co-administration experiment demonstrated that BD treatment sensitizes leptin action in both DIO and ob/ob mice. We also demonstrated that BD treatment attenuates ER stress and leptin resistance at the hypothalamus level. This is the first report to confirm the leptin sensitizing effect of BD treatment in leptin resistant DIO mice. The present study provides collateral evidence suggesting that the effect of BD treatment is mediated by the elevation of hypothalamic ATP concentration. Ketone bodies and hypothalamic ATP are the potential target for the treatment of obesity and its complications.

Blood leptin concentrations in Japanese Black cattle

The objective of this study was to examine the changes of serum leptin levels in heifers and steers during fattening. Seven steers and seven heifers at 14 months of age were used in the experiment. Live weight and serum leptin levels were determined at 2-month intervals. Initial live weight was greater in steers than heifers and a similar trend of growth was recorded during the experiment. As a result, live weight was higher in the steers than in the heifers during the experiment. Serum leptin concentration in both groups increased during the experiment and reached optimum level at 22 months of age and did not change thereafter. The increase in serum leptin level was more marked in heifers and leptin level was higher (P < 0·05) in heifers than steers between 18 and 26 months of age. The results suggest that serum leptin level increases during fattening in cattle and the trend is possibly affected by gender.

The relationships between leptin and vitamin A levels in plasma of fattening cattle supplemented with vitamin A

The objective of this study was to examine the effect of dietary vitamin A (retinol) on leptin in cattle. The relationship between plasma leptin and insulin was also examined. The experiment studies 16 9-month-old steers over the following 20-month fattening period. Four treatment diets were given to four steers in each of four groups. Cattle in treatment A were given a diet high in vitamin A (9000 to 10500 µg/day) throughout the experiment. Cattle in treatment B were given a diet low in vitamin A (300 to 4500 µg/day) for 0 to 10 months, after that they were given the high vitamin A diet during the period 10 to 20 months. Cattle in treatment C were given the low vitamin A diet for 0 to 14 months, after that they were given the high vitamin A diet for the period 14 to 20 months. Cattle in treatment D were given the low vitamin A diet throughout the experiment. Plasma samples were collected at 2-month intervals during the experiment to determine the plasma leptin, insulin and vitamin A concentrations. Plasma leptin concentration significantly increased over the fattening period (P< 0·001) but did not differ between the treatments (P> 0·05). Plasma leptin concentration was positively correlated with insulin concentration (r = 0·44,P< 0·001), although it was not correlated with plasma vitamin A concentration (r = –0·01,P> 0·05). It was concluded that dietary vitamin A in cattle does not affect plasma leptin concentration.

The relationships between leptin and insulin in blood plasma of growing lambs

The present study was designed to examine the pattern of changes in plasma leptin concentration during the early stage of young ruminants. Five crossbred lambs weaned at 45 days were housed individually in pens. The lambs were offered timothy hay, rolled barley and soya-bean meal to meet a 200 g daily gain, and were given free access to water and mineral block. Blood samples were collected just before the morning feeding and at 30-min intervals for 6 h after the morning feeding beginning at 0·5 months after weaning and thereafter monthly for the next 6 months. Plasma leptin level increased dramatically from 0·5 to 3 months after weaning. Thereafter, it dropped to a similar level to that at 2 months after weaning and remained at that level. Moreover, plasma leptin level was not affected by feeding, and no variation throughout the day of sampling was observed. Plasma insulin levels showed similarity to changes in plasma leptin levels. Plasma insulin levels were positively correlated (r = 0·63) with plasma leptin levels. This study shows that plasma leptin level dramatically increases after weaning. Additionally, it suggests that insulin contributes to the increase of leptin with growth in lambs.

Leptin modulates electrophysiological characteristics and isoproterenol-induced arrhythmogenesis in atrial myocytes

Background

Obesity is an important risk factor for atrial fibrillation (AF). Leptin is an important adipokine. However, it is not clear whether leptin directly modulates the electrophysiological characteristics of atrial myocytes.

Results

Whole cell patch clamp and indo-1 fluorescence were used to record the action potentials (APs) and ionic currents in isolated rabbit left atrial (LA) myocytes incubated with and without (control) leptin (100 nM) for 1 h to investigate the role of leptin on atrial electrophysiology. Leptin-treated LA myocytes (n = 19) had longer 20% of AP duration (28 ± 3 vs. 21 ± 2 ms, p < 0.05), but similar 50% of AP duration (51 ± 4 vs. 50 ± 3 ms, p > 0.05), and 90% of AP duration (89 ± 5 vs. 94 ± 4 ms, p > 0.05), as compared to the control (n = 22). In the presence of isoproterenol (10 nM), leptin-treated LA myocytes (n = 21) showed a lower incidence (19% vs. 54.2%, p < 0.05) of delayed afterdepolarization (DAD) than the control (n = 24). Leptin-treated LA myocytes showed a larger sodium current, but a smaller ultra-rapid delayed rectifier potassium current, and sodium-calcium exchanger current than the control. Leptin-treated and control LA myocytes exhibited a similar late sodium current, inward rectifier potassium current, transient outward current and L-type calcium current. In addition, the leptin-treated LA myocytes (n = 38) exhibited a smaller intracellular Ca²⁺ transient (0.21 ± 0.01 vs. 0.26 ± 0.01 R410/485, p < 0.05) and sarcoplasmic reticulum Ca²⁺ content (0.35 ± 0.02 vs. 0.43 ± 0.03 R410/485, p < 0.05) than the control LA myocytes (n = 42).

Conclusions

Leptin regulates the LA electrophysiological characteristics and attenuates isoproterenol-induced arrhythmogenesis.

Positive natural selection of TRIB2, a novel gene that influences visceral fat accumulation, in East Asia

Accumulation of visceral fat increases cardiovascular mortality in industrialized societies. However, during the evolution of the modern human, visceral fat may have acted as energy storage facility to survive in times of famine. Therefore, past natural selection might contribute to shaping the variation of visceral fat accumulation in present populations. Here, we report that the gene encoding tribbles homolog 2 (TRIB2) influenced visceral fat accumulation and was operated by recent positive natural selection in East Asians. Our candidate gene association analysis on 11 metabolic traits of 5,810 East Asians revealed that rs1057001, a T/A transversion polymorphism in 3'untranslated region (UTR) of TRIB2, was strongly associated with visceral fat area (VFA) and waist circumference adjusted for body mass index (P = 2.7 × 10(-6) and P = 9.0 × 10(-6), respectively). rs1057001 was in absolute linkage disequilibrium with a conserved insertion-deletion polymorphism in the 3'UTR and was associated with allelic imbalance of TRIB2 transcript levels in adipose tissues. rs1057001 showed high degree of interpopulation variation of the allele frequency; the low-VFA-associated A allele was found with high frequencies in East Asians. Haplotypes containing the rs1057001 A allele exhibited a signature of a selective sweep, which may have occurred 16,546-27,827 years ago in East Asians. Given the predominance of the thrifty gene hypothesis, it is surprising that the apparently non-thrifty allele was selectively favored in the evolution of modern humans. Environmental/physiological factors other than famine would be needed to explain the non-neutral evolution of TRIB2 in East Asians.

Beneficial effects by intake of Euphausiacea pacifica on high-fat diet-induced obesity

Obesity is a major health problem showing increased incidence in developed and developing countries. We examined the effect of Euphausia pacifica (E. pacifica) (Pacific Krill) on high-fat diet (HFD)-induced obesity in C57BL/6 mice. No significant differences were observed in average food intake between the HFD and HFD with E. pacifica group, or the low-fat diet (LFD) and LFD with E. pacifica group for 18 weeks. The increased ratio of body weight in the HFD containing E. pacifica group was significantly reduced, being 10% lower than that with HFD group in the 18th week (HFD, 298.6±18.8% vs. HFD with E. pacifica, 267.8±16.2%; p<0.05), while the ratio for the LFD containing E. pacifica group was reduced by 4% compared with LFD group (LFD, 244.2±11.6% vs. LFD with E. pacifica, 234.1±18.0%). There were no effects of E. pacifica on total cholesterol levels in serum and liver, whereas the supplement of E. pacifica tended to decrease triglyceride levels in the HFD groups. The leptin level in serum was significantly decreased in the HFD group (p<0.01) by E. pacifica. The adipocyte area (1926±1275 μm(2)) in the HFD containing E. pacifica group was significantly reduced by 20% (p<0.001) compared with the HFD group. These results suggested that E. pacifica supplementation in the diet is beneficial for the prevention of HFD-induced obesity.

Amylin improves the effect of leptin on insulin sensitivity in leptin-resistant diet-induced obese mice

Leptin enhances insulin sensitivity in addition to reducing food intake and body weight. Recently, amylin, a pancreatic β-cell-derived hormone, was shown to restore a weight-reducing effect of leptin in leptin-resistant diet-induced obesity. However, whether amylin improves the effect of leptin on insulin sensitivity in diet-induced obesity is unclear. Diet-induced obese (DIO) mice were infused with either saline (S), leptin (L; 500 μg·kg⁻¹·day⁻¹), amylin (A; 100 μg·kg⁻¹·day⁻¹), or leptin plus amylin (L/A) for 14 days using osmotic minipumps. Food intake, body weight, metabolic parameters, tissue triglyceride content, and AMP-activated protein kinase (AMPK) activity were examined. Pair-feeding and weight-matched calorie restriction experiments were performed to assess the influence of food intake and body weight reduction. Continuous L/A coadministration significantly reduced food intake, increased energy expenditure, and reduced body weight, whereas administration of L or A alone had no effects. L/A coadministration did not affect blood glucose levels during ad libitum feeding but decreased plasma insulin levels significantly (by 48%), suggesting the enhancement of insulin sensitivity. Insulin tolerance test actually showed the increased effect of insulin in L/A-treated mice. In addition, L/A coadministration significantly decreased tissue triglyceride content and increased AMPKα2 activity in skeletal muscle (by 67%). L/A coadministration enhanced insulin sensitivity more than pair-feeding and weight-matched calorie restriction. In conclusion, this study demonstrates the beneficial effect of L/A coadministration on glucose and lipid metabolism in DIO mice, indicating the possible clinical usefulness of L/A coadministration as a new antidiabetic treatment in obesity-associated diabetes.

A morbid obese Japanese woman with a body mass index of 83.2 kg/m2: before and after sleeve gastrectomy

A 34-year-old Japanese woman presented at our institution weighing 182.7 kg, 148.2 cm tall, and with a body mass index of 83.2 kg/m(2). She had been overweight since childhood, but no abnormality was found to explain her obesity. Treatments, including mazindol, bofu-tsusho-san, dietary restriction, and BioEnterics Intragastric Balloon, did not result in improvement of her obesity. Finally, we performed sleeve gastrectomy, and she has maintained her weight within 130-140 kg without rebounding for 2 and a half years. We followed the clinical changes before and after the operation. This case provides potentially interesting information regarding operative treatment for morbid obesity in Japanese.

Therapeutic impact of leptin on diabetes, diabetic complications, and longevity in insulin-deficient diabetic mice

OBJECTIVE

The aim of the current study was to evaluate the long-term effects of leptin on glucose metabolism, diabetes complications, and life span in an insulin-dependent diabetes model, the Akita mouse.

RESEARCH DESIGN AND METHODS

We cross-mated Akita mice with leptin-expressing transgenic (LepTg) mice to produce Akita mice with physiological hyperleptinemia (LepTg:Akita). Metabolic parameters were monitored for 10 months. Pair-fed studies and glucose and insulin tolerance tests were performed. The pancreata and kidneys were analyzed histologically. The plasma levels and pancreatic contents of insulin and glucagon, the plasma levels of lipids and a marker of oxidative stress, and urinary albumin excretion were measured. Survival rates were calculated.

RESULTS

Akita mice began to exhibit severe hyperglycemia and hyperphagia as early as weaning. LepTg:Akita mice exhibited normoglycemia after an extended fast even at 10 months of age. The 6-h fasting blood glucose levels in LepTg:Akita mice remained about half the level of Akita mice throughout the study. Food intake in LepTg:Akita mice was suppressed to a level comparable to that in WT mice, but pair feeding did not affect blood glucose levels in Akita mice. LepTg:Akita mice maintained insulin hypersensitivity and displayed better glucose tolerance than did Akita mice throughout the follow-up. LepTg:Akita mice had normal levels of plasma glucagon, a marker of oxidative stress, and urinary albumin excretion rates. All of the LepTg:Akita mice survived for >12 months, the median mortality time of Akita mice.

CONCLUSIONS

These results indicate that leptin is therapeutically useful in the long-term treatment of insulin-deficient diabetes.

P-selectin glycoprotein ligand-1 deficiency is protective against obesity-related insulin resistance

OBJECTIVE

An inflammatory process is involved in the mechanism of obesity-related insulin resistance. Recent studies indicate that monocyte chemoattractant protein-1 (MCP-1) is a major chemokine that promotes monocyte infiltration into adipose tissues; however, the adhesion pathway in adipose tissues remains unclear. We aimed to clarify the adhesion molecules that mediate monocyte infiltration into adipose tissue.

RESEARCH DESIGN AND METHODS

We used a DNA microarray to compare the gene expression profiles in epididymal white adipose tissues (eWAT) between db/db mice and C57/BL6 mice each fed a high-fat diet (HFD) or a low-fat diet (LFD). We investigated the change of insulin resistance and inflammation in eWAT in P-selectin glycoprotein ligand-1 (PSGL-1) homozygous knockout (PSGL-1⁻(/)⁻) mice compared with wild-type (WT) mice fed HFD.

RESULTS

DNA microarray analysis revealed that PSGL-1, a major ligand for selectins, is upregulated in eWAT from both db/db mice and WT mice fed HFD. Quantitative real-time RT-PCR and immunohistochemistry showed that PSGL-1 is expressed on both endothelial cells and macrophages in eWAT of obese mice. PSGL-1⁻(/)⁻ mice fed HFD showed a remarkable reduction of macrophage accumulation and expression of proinflammatory genes, including MCP-1 in eWAT. Moreover, adipocyte hypertrophy, insulin resistance, lipid metabolism, and hepatic fatty change were improved in PSGL-1⁻(/) ⁻mice compared with WT mice fed HFD.

CONCLUSIONS

These results indicate that PSGL-1 is a crucial adhesion molecule for the recruitment of monocytes into adipose tissues in obese mice, making it a candidate for a novel therapeutic target for the prevention of obesity-related insulin resistance.

Leptin modulates ACAT1 expression and cholesterol efflux from human macrophages

Leptin is an adipose tissue-derived hormone implicated in atherosclerosis and macrophage foam cell formation. The current study was conducted to examine the effect of leptin on cholesteryl ester accumulation in human monocytes/macrophages. Exogenously added leptin at 5 nM during differentiation of monocytes into macrophages for 7 days accelerated acetylated LDL (acetyl-LDL)-induced cholesteryl ester accumulation by 30-50%. Leptin did not affect endocytic uptake of acetyl-LDL; however, it increased ACAT activity 1.8-fold and ACAT-1 protein expression 1.9-fold. Among the four ACAT-1 mRNA transcripts, two shorter transcripts (2.8 and 3.6 kb) were upregulated approximately 1.7-fold upon leptin treatment. The enhanced expression of ACAT-1 protein by leptin was suppressed by inhibitors of Janus-activated kinase2 (JAK2) and phosphatidylinositol 3-kinase (PI3K). HDL-mediated cholesterol efflux was suppressed by leptin, which was canceled by K-604, an ACAT-1 inhibitor. Expression of long form of leptin receptor was upregulated during monocytic differentiation into macrophages and sustained after differentiation. Thus, the results suggest that leptin accelerates cholesteryl ester accumulation in human monocyte-derived macrophages by increasing ACAT-1 expression via JAK2 and PI3K, thereby suppressing cholesterol efflux.

Is leptin a significant predictor of bone mineral density in postmenopausal Turkish women?

The objective of the present study was to investigate the relationship between leptin and bone mineral density in postmenopausal Turkish women. A total of 122 healthy postmenopausal women were enrolled in this cross-sectional study. Blood samples were obtained for analysis of serum leptin. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry at the lumbar spine, femoral neck and trochanter on the same day. Leptin levels was significantly correlated with BMD of L(1-4) (P = 0.04), but not of femoral neck (P = 0.13), and trochanter (P = 0.39). However, Z scores of L(1-4) (P = 0.009), femur neck (P = 0.009), and femur trochanter (P = 0.025) were positively correlated with leptin levels. In multiple linear regression analysis, leptin was not found to be a statistically significant independent predictor for BMD. Leptin was associated with BMD and Z scores at various body sites; however, it was not an independent predictor of BMD.

Analysis of plasma adipocytokines related to clinical and laboratory data in the maintenance hemodialysis patients

BACKGROUND

Atherosclerotic vascular diseases such as cerebrovascular and cardiovascular diseases are major causes for fatality of hemodialysis (HD) patients. Since adipocytokines are key players for arteriosclerosis in the concept of metabolic syndrome (MetS), we aimed to determine whether circulating levels of major three adipocytokines, adiponectin, TNF-alpha, and leptin, could be associated with various parameters and clinical events in HD patients who are diagnosed as MetS using a new criteria designed for the Japanese population.

PATIENTS AND METHODS

We enrolled 53 very stable patients under maintenance HD at Minami-Senju Hospital. Basically, clinical and laboratory data were taken just before HD therapy. HD sessions were performed regularly and all the participants took oral administration and injection as usual. A cross-sectional study was performed to evaluate clinical and laboratory data related to three major adipocytokines, adiponectin, TNF-alpha and leptin.

RESULTS

We observed no significant differences of three adipocytokines when the participants were divided in accordance with existence of MetS or past cerebrocascular/cardiovascular diseases. Only the serum adiponectin levels were significantly different in two groups categorized by existence of diabetes mellitus. Serum triglycerides (TG) were significantly correlated with two circulating adipocytokines, adiponectin (r=-0.328, p<0.016) and leptin (r=0.397, p<0.003), when we analyzed all 53 patients together.

CONCLUSION

Plasma adiponectin and leptin are expected as contributors related to dyslipidemia, suggesting these may be targets of prevention of vascular diseases in maintenance HD patients.

The relationship between maternal plasma leptin levels and fetal growth restriction

Leptin is a satiety hormone secreted from the adipose tissue and human placenta. We previously demonstrated that severe preeclampsia up-regulated leptin mRNA expression in the placenta and elevated maternal plasma leptin concentrations. Preeclampsia is frequently related to generation of small for gestational age (SGA) infant especially in cases with severe preeclampsia. However, it is still controversial whether the increase in maternal plasma leptin levels is associated with fetal growth restriction without complication of preeclampsia. Therefore, the aim of the present study was to explore the relationship between maternal plasma leptin levels and fetal growth in non-preeclamptic (n = 98) and preeclamptic (n = 40) women. In non-preeclamptic pregnant women, plasma leptin levels in SGA group (n = 11) were significantly higher than those in appropriate for gestational age (AGA) group (n = 87, P<0.05). In pregnant women with preeclampsia, likewise, plasma leptin levels in SGA group (n = 15) were significantly higher than those in AGA group (n = 25, P<0.05). In multiple linear regression analysis, maternal BMI, mean arterial blood pressure and Delta SD of neonatal body weight were significant factors for determining maternal plasma leptin levels in all population studied. Maternal BMI and Delta SD of neonatal body weight showed positive correlation with maternal plasma leptin levels when analysis was performed in non-preeclamptic subjects alone. In conclusion, maternal plasma leptin levels reflect, at least partly, deterioration in fetal growth.

Perinatal and postnatal exposure to bisphenol a increases adipose tissue mass and serum cholesterol level in mice

AIM

To investigate whether the perinatal and postnatal exposure of mice to bisphenol A (BPA) caused the development of obesity and/or hyperlipidemia.

METHODS

Pregnant mice were exposed to BPA in drinking water at concentrations of either 1 microg/mL (LD group) or 10 microg/mL (HD group) from gestation day 10 and throughout the lactating period. After weaning, the pups were allowed free access to drinking water containing the appropriate concentrations of BPA. The body weight, adipose tissue weight, and serum lipid levels were measured in the offspring at postnatal day 31.

RESULTS

In females, the mean body weight increased by 13% in the LD group (p<0.05) and 11% in the HD group (p<0.05) compared with the control group. The mean adipose tissue weight increased by 132% in the LD group (p<0.01). The mean total cholesterol level increased by 33% in the LD group (p<0.01) and 17% in the HD group (p<0.05). In males, the mean body weight and mean adipose tissue weight increased by 22% (p<0.01) and 59% (p<0.01), respectively, in the HD group compared with the control group. The mean triacylglycerol level increased by 34% in the LD group (p<0.05).

CONCLUSIONS

The continuous exposure of mice to BPA during the perinatal and postnatal periods caused the development of obesity and hyperlipidemia.

Do low levels of circulating adiponectin represent a biomarker or just another risk factor for the metabolic syndrome?

The metabolic syndrome is currently defined by various combinations of insulin resistance, obesity, dyslipidaemia and hypertension. The tendency for these risk factors to appear simultaneously suggests a single aetiologic basis. A low level of circulating adiponectin is associated with the appearance of each metabolic syndrome risk factor. The following review summarizes a large body of evidence that suggests a low level of circulating adiponectin represents an independent risk factor and a possible biomarker for the metabolic syndrome. An association between the metabolic syndrome and low adiponectin supports the view that the development of the metabolic syndrome may be triggered by a single underlying mechanism. Clinical studies in the future may show that a low level of circulating adiponectin is a primary biomarker for a specific cluster of metabolic syndrome risk factors rather than all the possible combinations of risk factors currently used to identify the metabolic syndrome. The significance of low circulating adiponectin in risk assessment models should ultimately be compared against insulin resistance, obesity, dyslipidaemia, hypertension and other metabolic syndrome risk factors presently under consideration. Adiponectin can be measured reliably in a clinical setting; circulating values of adiponectin do not fluctuate on a diurnal basis as much as insulin, glucose, triglycerides or cholesterol and only 2-4 microl of blood are currently needed for its measurement.

An alpha1-receptor blocker reduces plasma leptin levels in hypertensive patients with obesity and hyperleptinemia

Obesity is often complicated by hypertension, and both conditions are risk factors for atherosclerosis. Leptin has attracted attention as a possible cause of hypertension in obese persons. We investigated the effect of a slow-release alpha1-receptor blocker, bunazosin hydrochloride, on leptin levels and insulin resistance in obese hypertensive patients with hyperleptinemia. The subjects were 17 patients (12 men and 5 women aged 56.1 +/- 12.2 years) with essential hypertension who were not receiving alpha1-receptor blockers. They had a body mass index (BMI) > or = 25 kg/m2 and a plasma leptin concentration > or = 5 ng/ml. They received oral therapy with bunazosin hydrochloride at doses of up to 9 mg/day. The plasma leptin concentration, body weight, blood pressure, heart rate, fasting blood glucose, plasma insulin concentration, and free fatty acid level were compared between before and after treatment. Although there was no significant change of BMI, there was a significant decrease of plasma leptin after treatment (10.6 +/- 5.4 ng/ml vs. 8.7 +/- 3.4 ng/ml, p = 0.0128), as well as a significant decrease of plasma insulin (9.8 +/- 4.8 microU/ml vs. 8.1 +/- 4.6 microU/ml, p = 0.0494) and HOMA-R (2.9 +/- 2.1 vs. 2.2 +/- 1.5, p = 0.0237). In conclusion, bunazosin hydrochloride reduced the plasma leptin level and improved insulin resistance in hypertensive patients with obesity and hyperleptinemia.

Transcription factor activating enhancer-binding protein-2beta. A negative regulator of adiponectin gene expression

We previously reported the association between the activating enhancer-binding protein-2beta (AP-2beta) transcription factor gene and type 2 diabetes. This gene is preferentially expressed in adipose tissue, and subjects with the disease-susceptible allele of AP-2beta showed stronger expression in adipose tissue than those without the susceptible allele. Furthermore, overexpression of AP-2beta leads to lipid accumulation by enhancing glucose transport and inducing insulin resistance in 3T3-L1 adipocytes. In this study we demonstrated that overexpression of AP-2beta in 3T3-L1 adipocytes decreased the expression and secretion of adiponectin and increased those of interleukin-6 (IL-6). Interestingly, the effects of AP-2beta on the expressions of adiponectin and IL-6 and the mechanisms by which AP-2beta modulated their expressions were different. We found that the promoter activity of adiponectin gene was inhibited by AP-2beta overexpression and enhanced by knockdown of endogenous AP-2beta, whereas IL-6 was unaffected. Electrophoretic mobility shift assays revealed the existence of putative responsive elements for AP-2beta and NF-YA in human and mouse adiponectin promoter regions, and mutation of this AP-2beta binding site abolished the inhibitory effect of AP-2beta. Furthermore, chromatin immunoprecipitation assays demonstrated that AP-2beta and NF-YA competitively bind to the same region of the adiponectin promoter. Our results clearly demonstrated that AP-2beta directly inhibits adiponectin gene expression by displacing NF-YA and binding to its promoter. We conclude that AP-2beta might modulate the expression of adiponectin by directly inhibiting its transcriptional activity.

Expression of Endothelin-1 and Adrenomedullin Was Not Altered by Leptin or Resistin in Bovine Brain Microvascular Endothelial Cells

Hypertension frequently occurs in obese subjects. It has been reported that leptin and resistin induce endothelin-1 expression in vascular endothelial cells. Altered function of brain microvascular endothelial cells may be related to increased occurrences of stroke in hypertensive patients. In the present study, we therefore studied the effects of leptin and resistin on the expression of endothelin-1 and adrenomedullin in bovine brain microvascular endothelial cells. Northern blot analysis showed that leptin (10(-10)-10(-8) mol/l), resistin (10(-10)-10(-8) mol/l) or a combination of leptin and resistin (10(-8) mol/l for each) had no significant effects on the expression of endothelin-1 mRNA or adrenomedullin mRNA in cultured bovine brain microvascular endothelial cells. On the other hand, hypoxia induced, and tumor necrosis factor-alpha (10 ng/ml) decreased, the expression levels of endothelin-1 and adrenomedullin mRNAs, indicating that the bovine brain microvascular endothelial cells were able to respond to hypoxia and tumor necrosis factor-alpha. Consistent with the results of Northern blot analysis, immunoreactive endothelin and immunoreactive adrenomedullin concentrations in the medium were not significantly changed by the treatment with leptin, resistin, or a combination of leptin and resistin. The present study thus showed that neither leptin nor resistin affects the expression of endothelin-1 or adrenomedullin in bovine brain microvascular endothelial cells.

Sleep oxygen desaturation and circulating leptin in obstructive sleep apnea-hypopnea syndrome

BACKGROUND

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is characterized by repeated oxygen desaturation. Obesity and visceral fat accumulation (VFA) are risk factors for the development of OSAHS. Circulating leptin increases in accordance with body mass index (BMI), and under experimental conditions intermittent hypoxia stimulates leptin production.

METHODS

The primary objective of this study was to investigate whether hypoxemia during sleep influences the levels of circulating leptin and whether the location of body fat deposits, ie, the distribution of VFA and subcutaneous fat accumulation (SFA), affects circulating leptin levels in patients with OSAHA who are not obese. We assessed VFA and SFA by abdominal CT scan and measured circulating levels of leptin in 96 male patients with OSAHS and 52 male patients without OSAHS matched for BMI. To be matched for BMI in the two groups, patients whose BMIs were < 27 were selected for the OSAHS group.

RESULTS

In the whole study group, circulating leptin levels correlated with BMI (r = 0.30), VFA (r = 0.44), SFA (r = 0.28), apnea-hypopnea index (AHI) [r = 0.48], sleep mean arterial oxygen saturation (Sao(2)) [r = 0.59], and sleep lowest Sao(2) (r = 0.37). Multiple regression analysis showed that average Sao(2) (p < 0.01) and lowest Sao(2) (p = 0.03) were explanatory variables for serum leptin values, but AHI (p = 0.054), BMI (p = 0.33), VFA (p = 0.11), and SFA (p = 0.36) were not.

CONCLUSIONS

These results suggest that sleep hypoxemia may be the main determinant of circulating leptin levels, although the location of body fat deposits could contribute to the elevated circulating leptin levels in patients with OSAHS who are not obese.

Fat accumulation, leptin, and hypercapnia in obstructive sleep apnea-hypopnea syndrome

BACKGROUND

Obesity and visceral fat accumulation (VFA) are risk factors for the development of obstructive sleep apnea-hypopnea syndrome (OSAHS), and a subgroup of OSAHS patients acquire hypoventilation. Circulating leptin, an adipocyte-derived signaling factor, increases in accordance with body mass index (BMI); under experimental conditions, leptin selectively decreases visceral adiposity and it is also a respiratory stimulant.

OBJECTIVE

To investigate whether the location of body fat deposits, ie, the distribution of VFA and subcutaneous fat accumulation (SFA), contributes to hypoventilation and whether circulating levels of leptin are involved in the pathogenesis of hypoventilation, which is often observed in OSAHS.

METHODS

We assessed VFA and SFA by abdominal CT scan, and measured lung function and circulating levels of leptin in 106 eucapnic and 79 hypercapnic male patients with OSAHS.

RESULTS

In the whole study group, circulating leptin levels correlated with BMI (r = 0.56), VFA (r = 0.24), and SFA (r = 0.47), but not with Po(2) or sleep mean arterial oxygen saturation (Sao(2)). BMI, percentage of predicted vital capacity, FEV(1)/FVC ratio, apnea-hypopnea index, sleep mean Sao(2), VFA, and SFA were not significantly different between two groups. Circulating leptin levels were higher in the hypercapnic group than in the eucapnic group. Logistic regression analysis indicated that serum leptin was the only predictor for the presence of hypercapnia (beta = 0.21, p < 0.01).

CONCLUSIONS

These results suggest that the location of body fat deposits may not contribute to the pathogenesis of hypoventilation, and circulating leptin may fail to maintain alveolar ventilation in hypercapnic patients with OSAHS.

Changes in serum leptin concentrations in overweight Japanese men after exercise

AIM

To investigate the link between serum leptin concentrations and exercise.

DESIGN

Cross-sectional and longitudinal studies of an exercise intervention.

SUBJECTS

110 Japanese overweight men aged 32-59 years were recruited. At baseline, the average body mass index (BMI) was 28.5 +/- 2.5 kg/m2. From this group, we used data of 36 overweight men (BMI, 28.9 +/- 2.3) for a 1-year exercise programme.

MEASUREMENTS

Leptin was measured at baseline and after 1 year. Fat distribution was evaluated by visceral fat (V) and subcutaneous fat (S) areas measured with computed tomography (CT) scanning at umbilical levels. Anthropometric parameters, aerobic exercise level, muscle strength and flexibility were also investigated at baseline and after 1 year.

RESULTS

In the first analysis, using cross-sectional data, leptin was significantly correlated with total body fat (r = 0.760, p < 0.01), V (r = 0.383, p < 0.01) and S (r = 0.617, p < 0.01) areas. In the second analysis, using longitudinal data, leptin was significantly reduced after 1 year (pre 6.7 +/- 4.0 ng/ml vs. post 5.1 +/- 3.1 ng/ml, p < 0.01). Results showed that steps per day were increased, and aerobic exercise level, weight-bearing index (WBI) and insulin resistance were significantly improved. Although, there was a positive correlation between Delta leptin(positive changes in leptin after 1 year) and anthropometric measurements such as Delta body weight, Delta BMI and Delta body fat, leptin/body weight, leptin/BMI and leptin/body fat ratios were significantly reduced during exercise intervention.

CONCLUSION

The present study indicated exercise significantly lowers serum leptin concentrations, and thus it may improve the leptin resistance observed in overweight Japanese men.

The insulin-like growth axis in patients with autoimmune thyrotoxicosis: effect of antithyroid drug treatment

OBJECTIVE

Hyperthyroidism is associated with altered growth hormone (GH) secretion. Many patients with thyroid dysfunction experience several poorly described complications such as symptoms and signs also seen in patients with growth hormone deficiency (GHD). We have therefore prospectively evaluated a possible relationship between the thyroid function, body composition, leptin levels and insulin-like growth factor (IGF) related peptides in patients with Graves' disease. DESIGN, PATIENTS, AND MEASUREMENTS: In a prospective group of 24 fasting female patients with Graves' disease (mean age (CI 95%): 40 years (33-47)), we measured serum thyroxine, triiodothyronine, thyrotropine (TSH), TSH receptor antibodies, anti-thyroid peroxidase, leptin, body composition, body mass index (BMI) and IGF-related peptides at diagnosis and after 12 months of treatment with thiamazol (ATD).

RESULTS

In thyrotoxic patients IGF-I plus IGF-II correlated positively with IGFBP-3 at baseline (r = 0.90, p < 0.1 x 10(16)) and after 12 months follow-up (r = 0.87, p < 0.1 x 10(-16)). In the thyrotoxic state total IGF-I, IGF-II, IGF binding protein 3 (IGFBP-3) and acid-labile subunit (ALS) but not free IGF-I decreased significantly from 223 microg/L (189-260) (mean (CI 95%), 877 microg/L (801-953), 4165 microg/L (3772-4577) and 22 mg/L (18-26)) to 198 microg/L (172-226), 788 microg/L (711-865), 3431 microg/L (3135-3741) and 19 mg/L (16-26) (p <0.006), respectively, after 12 months of ATD despite an increase in BMI from 22 (21-23) to 23 kg/m(2) (22-25) (p < 0.0004) but no significant changes in leptin.

CONCLUSIONS

The complex IGF systems seemed intact in thyrotoxic patients but change in body composition and the regulation of leptin and insulin secretion during treatment of autoimmune thyroid disease influence IGF-related peptides leaving the patient in a state somewhat similar to partial GHD, but the mechanism behind these alterations remains unclear.

Significant increase in maternal plasma leptin concentration in induced delivery: a possible contribution of pro-inflammatory cytokines to placental leptin secretion

Maternal plasma leptin concentration is significantly increased during pregnancy. However, its roles in pregnancy, especially in labor, have not been fully clarified. We measured plasma leptin concentrations in pregnant women during the course of induced labor, just after spontaneous vaginal delivery and Cesarean section at term. We also studied the regulation of leptin secretion from term placental tissue and BeWo cells, a trophoblastic cell-line. Plasma leptin concentrations increased significantly during labor (58.9 +/- 9.2 ng/ml) compared to those before labor induction (37.5 +/- 5.8 ng/ml, P<0.05), then decreased 3-6 days postpartum (14 +/- 3 ng/ml, n = 6, P<0.0001) to the levels of normal nonpregnant women. Leptin concentrations within an hour and 24 hours after spontaneous vaginal delivery were significantly higher than those after Cesarean section (P<0.05 for both comparisons). Similarly, leptin mRNA expression in placental tissues obtained after spontaneous vaginal delivery was significantly greater than that in those obtained after Cesarean section without labor (P<0.05). IL-1alpha and TNF-alpha treatment significantly stimulated leptin secretion and leptin mRNA expression in explant culture of human term placental tissue and in BeWo cells as compared with those in vehicle controls (P<0.05, for all comparisons). By contrast, oxytocin and prostaglandin F(2alpha) treatment had no effects on leptin secretion from explant culture of human term placental tissue or from BeWo cells. These data indicate that pro-inflammatory cytokines might stimulate placental leptin secretion, thus finally contributing to the increase in plasma leptin concentration during labor.

The leptin, a new hormone of adipose tissue: clinical findings and perspectives in geriatrics

Obesity has gained a great importance during the last decades, and this fact stimulated numerous studies regarding the genetic causes of this disease. A recently discovered new molecule, called leptin, raised a wide interest. It is a product of the adipocytes, it exerts inhibitory effects on the center of appetite and increases the energy expenditure of the organism. The present study evaluated blood leptin levels in 57 elderly subjects and searched for eventual correlations between this parameter and the age, the body mass index (BMI), the fat body mass (fat%), the waist (W) and hip (H) circumference, as well as the ratio (R) of these latter two values (WHR). Blood leptin levels do not correlate with age, body height and the WHR, but display significant positive correlations with the body weight, the BMI, the fat%, the W, H and WHR. A deeper knowledge on leptin and the correlations of this hormone with other body parameters might be helpful in a better understanding of several pathogenetic mechanisms related to aging and involved in a deterioration of the quality of life in elderly, like multiple atherosclerotic and metabolic diseases (diabetes, dyslipidemias).

Free-to-total leptin ratio in maternal plasma is constant throughout human pregnancy

To clarify the mechanism of leptin resistance during pregnancy, we measured plasma leptin concentrations, free to total leptin ratio (percent free leptin) and soluble leptin receptor concentrations in pregnant women, and compared the results with those in non-pregnant women. We collected plasma samples from 23 non-pregnant and 31 pregnant women in the third trimester. Plasma samples from 5 pregnant women were collected longitudinally in each trimester. Plasma leptin concentrations in pregnant women in the second trimester (17.4 +/- 3.2 ng/ml) were higher than those in the first trimester of pregnancy (11.0 +/- 2.8 ng/ml, n = 5), as previously reported. However, percent free leptin did not change significantly throughout pregnancy. Percent free leptin correlated with total leptin concentrations (ng/ml) in non-pregnant women (r = 0.727, P < 0.0001), but not in women in the third trimester of pregnancy (r = 0.006). Constant percent free leptin during pregnancy despite increased leptin concentrations indicates increased leptin binding capacity in pregnant women, that might partly contribute to the establishment of leptin resistance. On the other hand, soluble leptin receptor concentrations showed significant negative correlation with BMI and plasma leptin concentrations in pregnant women (r = -0.470, P < 0.01 and r = -0.493, P < 0.01, respectively) but not in non-pregnant women. These data suggest the possibility that soluble leptin receptor is a minor component of leptin binding capacity in the plasma of pregnant women.

Interaction of leptin with gastric myofibroblast transdifferentiation in Helicobacter pylori-infected Mongolian gerbils: the effect of rebamipide

BACKGROUND

Our recent histochemical studies have revealed the marked increase of myofibroblasts in the Helicobacter pylori-infected Mongolian gerbil fundic mucosa, while the mediators, which facilitate the conversion of fibroblasts to the myofibroblasts have remained unknown.

AIM

The present study was undertaken to clarify the alteration of leptin in the control and H. pylori-infected Mongolian gerbil stomach. The effector sites of rebamipide were also investigated in relation to leptin.

METHODS

The localization of leptin was investigated by the indirect immunofluorescence. Plasma leptin levels were determined by ELISA method. The localization of 3H-rebamipide binding sites was investigated by autoradiography.

RESULTS

Serum leptin content in H. pylori-infected Mongolian gerbils was significantly increased. The presence of leptin immunoreactivity was recognized in the endothelial cells of the microcirculatory network and very weakly in the glandular cells in the control group, while in the H. pylori-infected group leptin was markedly recognized in the mesenchymal cells. Rebamipide bound to the fibroblasts and surface mucous cells and decreased the leptin immunoreactivity in the gastric mucosa.

CONCLUSIONS

Leptin was mostly found in the mesenchymal cells. Rebamipide administration brought about the decrease of leptin in the gastric mucosaof the H. pylori-infected gerbils.

Effects of obstructive sleep apnea syndrome on serum aminotransferase levels in obese patients

PURPOSE

Obesity has been associated with obstructive sleep apnea and hepatic steatosis. We investigated the effects of obstructive sleep apnea and treatment with nasal continuous positive airway pressure (CPAP) on serum aminotransferase levels in obese patients.

METHODS

We studied 40 obese men with obstructive sleep apnea syndrome. None had hepatitis B antigen or C antibody, autoimmune disease, or an excessive intake of alcohol. Serum levels of aspartate aminotransferase, alanine aminotransferase, triglyceride, glucose, insulin, and leptin were determined in the afternoon and in the morning immediately after sleep, before and after nasal CPAP treatment.

RESULTS

Aminotransferase levels were abnormal in 35% (n = 14) of patients. Before treatment, mean (+/- SD) aspartate aminotransferase levels were higher in the morning than in the previous afternoon (presleep, 34 +/- 20 IU/L; postsleep, 39 +/- 28 IU/L; P = 0.006). The overnight mean increases in aminotransferase levels were less marked after the first night of nasal CPAP treatment (aspartate aminotransferase: from 6 +/- 11 IU/L to 2 +/- 6 IU/L, P = 0.0003; alanine aminotransferase: from 5 +/- 9 IU/L to 2 +/- 6 IU/L, P = 0.006). Leptin levels (n = 23) decreased significantly after treatment (P = 0.0002), whereas insulin resistance (calculated by the homeostasis model assessment method) and triglyceride levels were unchanged. Improvements in aspartate and alanine aminotransferase levels were maintained after 1 and 6 months of nasal CPAP treatment.

CONCLUSION

Nasal CPAP therapy may have beneficial effects on serum aminotransferase abnormalities in obese patients who have obstructive sleep apnea.

Potential association between endogenous leptin and sympatho-vagal activities in young obese Japanese women

Leptin is an adipocyte-derived hormone that decreases food intake and increases energy expenditure through the activation of the sympathetic nervous system (SNS). Notwithstanding recent intensive research, the underlying physiological mechanism of leptin as well as the etiology of obesity in humans remains elusive. The present study attempted to investigate the potential association between endogenous circulating leptin and sympatho-vagal activities in age- and height-matched obese and nonobese healthy young women. Plasma leptin concentrations were measured by radioimmunoassay. The autonomic nervous system activity was assessed during the resting condition by means of a recently devised power spectral analysis of heart rate variability, which serves to identify three separate frequency components, very low (VLO), low (LO), and high (HI). Plasma leptin concentrations were greater in the obese than in the control group (45.7 +/- 5.89 vs. 11.2 +/- 1.10 ng. ml(-1), P < 0.01). As to the contribution of endogenous leptin to SNS activity, both the ratios of the VLO frequency component reflecting thermoregulatory sympathetic function and the global SNS index [(VLO + LO)/HI] to plasma leptin concentration were markedly reduced in the obese compared to the control group (VLO per leptin: 5.9 +/- 1.39 vs. 37.8 +/- 8.1 ms(2). ml. ng(-1), P < 0.01; SNS index per leptin: 0.04 +/- 0.008 vs. 0.33 +/- 0.01 ml c. ng(-1), P < 0.01). Additionally, a nonlinear regression analysis revealed that these ratios exponentially decreased as a function of body fat content (VLO per leptin r(2) = 0.57, P < 0.01; SNS index per leptin r(2) = 0.53, P < 0.01). Our data suggest that reduced sympathetic responsiveness to endogenous leptin production, implying peripheral leptin resistance, might be a pathophysiological feature of obesity in otherwise healthy young women. The findings regarding the association of leptin, body fat content, and SNS activity further indicate that the 30% of total body fat, which has been used as a criterion of obesity, might be a critical point at which leptin resistance is induced.

Characterization of leptin binding in bovine kidney membranes

The interactions of leptin with its receptor and other leptin binding sites is not well described or understood. We have used Scatchard analysis of saturation binding data to characterize the affinity of leptin for binding sites in bovine kidney membranes. 125I-Leptin was used in saturation studies, over a range of concentrations from 50 pM to 9 nM. 125I-Leptin differentiated a high affinity binding site from an abundant low affinity site. The high affinity/low density binding site (putative leptin receptor) had K(d)=0.098 nM and B(max)=46.2f mol/mg protein. An additional class of low affinity, highly abundant sites with an apparent K(d)=175 nM, and B(max)=574 fmol/mg protein was characterized. The association and dissociation kinetics for 125I-leptin binding were also studied. Dissociation of the leptin-receptor complex was very rapid, and this necessitated the use of a specially developed separation method for radioligand binding studies (precipitation with PEG and filtration). Competitive displacement of 125I-leptin by mouse and human leptin and polyclonal anti-bovine leptin antibodies was dose-dependent. Specificity of binding was shown as bound 125I-leptin was not displaced by insulin or control antibodies. These data indicate that leptin binds the bovine leptin receptor with high affinity and that a pool of leptin is bound to abundant cell membrane-associated proteins. These observations are consistent with the plasma concentration range for leptin and imply that free leptin concentration in the tissues may be partially buffered by cell-associated and bound forms in plasma. Thus, acute changes in leptin secretion may have little effect at the leptin receptor. The development of leptin agonists/antagonists should facilitate further characterization of leptin binding and clarify the role of abundant low affinity binding sites at the leptin axis.

Clinical implications of leptin and its potential humoral regulators in long-term low-calorie diet therapy for obese humans

OBJECTIVE

To address the clinical implications of leptin and to re-examine the relationship between leptin and its potential humoral regulators such as insulin, nonesterified fatty acids (NEFA) and triiodothyronine (T3) in low-calorie diet (LCD) for obese humans.

DESIGN

Longitudinal study.

SETTING

University and foundation hospitals.

SUBJECTS

Ten obese men and 10 premenopausal obese women.

INTERVENTIONS

Five men and five women took 800 kcal/day LCD and another five men and five women took 1400 kcal/day balanced deficit diet (BDD) during 4 weeks.

RESULTS

Plasma leptin levels in the LCD group decreased more markedly (46.2+/-14.6 to 13.2+/-3.6 ng/ml) than that expected for the decrement in percentage fat (39.0+/-1.7 to 35.9+/-1.7%) and body mass index (BMI; 35.4+/-2.4 to 33.1+/-2.2 kg/m(2)), while that in the BDD group did not decrease significantly (14.9+/-3.5 to 13.4+/-2.8 ng/ml). The ratio of the decrease in leptin levels to that of BMI during the first week was significantly greater than that during the following 3 weeks (39.5+/-2.7 vs 29.3+/-2.1%, P=0.017). The plasma insulin and T3 levels also fell substantially in the first week and continued to decrease during the entire course. Plasma leptin levels measured weekly in each subject were correlated well with insulin (r=0.586, P=0.0003) and T3 (r=0.785, P=0.0004). Multiple regression analyses after adjustment for the time course and BMI revealed that serum levels of T3 were independently correlated with plasma leptin levels (r=0.928, P<0.0001). The plasma NEFA level was markedly elevated during the first 2 weeks and decreased thereafter.

CONCLUSIONS

A rapid fall in leptin during the first week of LCD, coordinated by insulin, T3 and NEFA, should be beneficial for responding to decreased energy intake. Inversely, in view of the powerful effect of leptin on energy dissipation, the present findings suggest the potential usefulness of leptin in combination with caloric restriction for the treatment of obesity.

SPONSORSHIP

The Ministry of Education, Culture, Sports, Science and Technology of Japan and the Ministry of Health, Labour and Welfare of Japan.

Direct in vitro effects of androgens and estrogens on ob gene expression and leptin secretion in human adipose tissue

In the present study, we have explored, in vitro, the possibility that short exposure to androgens and estrogens for 24 h may directly influence leptin expression (ARNm and secretion) in sc adipose tissue from men and women. In men, only dihydrotestosterone at high concentration (100 nM) induced a reduction in leptin secretion and ob mRNA level. In women, 17beta-estradiol (10-100 nM) increased ob mRNA expression (+180 to +500%) and leptin release (+75%). Moreover, in adipose tissue of women, the estrogen precursors testosterone (100 nM) and dehydroepiandrosterone (1 microM) also induced an increase in leptin secretion (+84 and +96%, respectively), an effect that was prevented by the aromatase inhibitor letrozole. Finally, the stimulatory effect of 17beta-estradiol observed in women was antagonized by the antiestrogen ICI182780. Altogether, these results suggest that the sexual dimorphism of leptinemia in humans is mainly owing to the estrogen receptor-dependent stimulation of leptin expression in adipose tissue by estrogens and estrogen precursors in women.

Plasma leptin levels and cardiac sympathetic function in patients with obstructive sleep apnoea-hypopnoea syndrome

BACKGROUND

The control of body weight and cardiac sympathetic function in patients with obstructive sleep apnoea-hypopnoea syndrome (OSAHS) are important because both factors have significant effects on the mortality of these patients. It has recently been reported that OSAHS has a significant effect on the secretion of leptin, a hormone involved in the control of body weight and sympathetic nerve activity. In addition to the circadian rhythm of leptin secretion, the effects of one night of treatment with nasal continuous positive airway pressure (nCPAP) and the mechanism of the effects of nCPAP on nocturnal leptin secretion in patients with OSAHS has not yet been elucidated.

METHODS

Blood samples were obtained at 21.00 hours, 00.00 hours, 03.00 hours, and 06.30 hours from 21 subjects with OSAHS (mean apnoea and hypopnoea index 52.4/h), with and without nCPAP treatment. Iodine-123 (I(123))-meta-iodobenzylguanidine (MIBG) imaging was used to evaluate myocardial sympathetic function before nCPAP treatment.

RESULTS

Plasma leptin reached a peak level at 00:00 hours (p<0.01) in patients with OSAHS, both with and without nCPAP treatment. The first night of nCPAP treatment significantly decreased the plasma leptin levels at 03.00 hours (without nCPAP: mean (SE) 21.6 (4.7) ng/ml; with nCPAP: 19.3 (4.1) ng/ml, p<0.02) and at 06.30 hours (without nCPAP: 17.6 (3.8) ng/ml; with nCPAP: 15.2 (3.2) ng/ml, p<0.01). The magnitude of the decrease in leptin levels after nCPAP treatment was significantly correlated with cardiac sympathetic function measured before nCPAP treatment (p<0.03).

CONCLUSIONS

Patients with OSAHS undergo nocturnal increases in leptin levels in spite of interruption of sleep due to apnoea and hypopnoea, a trend seen in normal subjects. Plasma leptin levels in patients with OSAHS decreased significantly after the first night of nCPAP treatment. Enhanced cardiac sympathetic function in these patients may contribute to the leptin levels before nCPAP treatment and vice versa.

Circulating leptin: a marker of health in female students

We studied the relationship between serum leptin concentration and lifestyle factors in female nursing students. Serum leptin was estimated by radioimmunoassay and the correlation between these concentrations with serum lipids, physical fitness and Health-promoting Lifestyle Profile score was investigated. A total of 247 students took part in the study: mean age, 19.0 +/- 2.0 years; mean body mass index (BMI), 21.7 +/- 2.9 kg/m2; and mean serum leptin concentration, 10.8 +/- 11.5 ng/ml. Serum leptin was positively correlated with BMI, systolic and diastolic blood pressure, total cholesterol and serum triglyceride. Serum leptin level concentration inversely correlated with physical fitness score and lifestyle score. When the subjects were grouped according to BMI, the high-BMI group (BMI: > or = 24 kg/m2; n = 40) showed significantly lower fitness and lifestyle scores than the low-BMI group (BMI < or = 20 kg/m2; n = 70). Higher leptin, blood pressure, total cholesterol and triglyceride were seen in high-BMI compared with low-BMI subjects. We suggest that leptin is a useful marker for monitoring good health and may be useful as a motivational aid towards achieving and maintaining a healthy lifestyle.

[Potential molecular targets for anti-obesity drugs--after the discovery of leptin]

The discovery of the adipose-derived hormone leptin has generated interest in the interaction between peripheral signals and brain targets involved in the regulation of feedings and energy balance. Potential anti-obesity drugs can be based on any intervention between the neuropeptide and its receptor that would alter the biological responses mediated by the neuronal network, in particular, food intake, metabolism and energy expenditure. Modulation of neurons in the arcuate nucleus by leptin results in reduced expression of neuropeptide Y and agouti-related protein, and increased expression of pro-opiomelanocortin (the precursor of a-melanocyte-stimulating hormone) and cocaine- and amphetamine- regulated transcript. Whether leptin finds its way into general usage as an anti-obesity drug, the use of modern methods to identify and target the components of leptin signaling pathway will form the basis for new pharmacological approaches to the treatment of obesity.

Effect of long-term changes in diet and exercise on plasma leptin concentrations

BACKGROUND

Although it is known that plasma leptin concentrations correlate with the amount of adipose tissue in the body, little information is available on the long-term effects on leptin concentrations of changes in diet and exercise.

OBJECTIVE

We wanted to examine whether changes in dietary energy sources and exercise-mediated energy expenditure, alone or in combination, affect plasma leptin concentrations.

DESIGN

In a randomized, 2 x 2 factorial trial, 186 men with metabolic syndrome were divided into 4 groups: diet, exercise, a combination of diet and exercise, and control. Data on dietary intake, physical fitness, and demographics were collected and plasma leptin concentrations were measured before and after a 1-y intervention period.

RESULTS

Plasma leptin concentrations, body mass index, and fat mass decreased in association with long-term reductions in food intake as well as increased physical activity. By adjusting for either body mass index or fat mass, we observed a highly significant reduction in plasma leptin concentration after both the diet and the exercise interventions. There was no interaction between the interventions, suggesting a direct and additive effect of changes in diet and physical activity on plasma leptin concentrations.

CONCLUSION

Long-term changes in lifestyle consisting of decreased intake of dietary fat and increased physical activity reduced plasma leptin concentrations in humans beyond the reduction expected as a result of changes in fat mass.

Downregulation of leptin by free fatty acids in rat adipocytes: effects of triacsin C, palmitate, and 2-bromopalmitate

Free fatty acid (FFA) has been reported to decrease leptin mRNA levels in 3T3-L1 adipocytes. When using this cell line, it is difficult to determine the protein levels because a very small amount of leptin is secreted into the medium. The effect of FFA on leptin secretion from adipocytes has not yet been determined. In addition, in vivo studies have failed to demonstrate a FFA-induced decrease in plasma leptin levels. To clarify the effect of FFA on leptin production, we investigated the leptin protein level in the medium and the mRNA level in primary cultured rat adipocytes treated with triacsin C, which is a potent inhibitor of acyl-coenzyme A (CoA) synthetase, palmitate, and 2-bromopalmitate. Triacsin C (0 to 5 x 10(-5) mol/L) decreased leptin concentrations in the culture medium in a dose-dependent manner. Leptin mRNA levels were decreased to 10% of the control in the presence of triacsin C. The concentration of triacsin C needed to suppress leptin production was similar to the Ki value (approximately 10(-5) mol/L) for inhibition of acyl-CoA synthetase. Both palmitate and 2-bromopalmitate decreased leptin concentra-tions but did not affect the triacsin C-induced decrease in leptin additively. In conclusion, both protein and mRNA levels of leptin were decreased by triacsin C and FFA in primary cultured rat adipocytes. Our findings suggest that FFA is involved in the regulation of leptin production in adipocytes.

Changes in intra-abdominal visceral fat and serum leptin levels in patients with obstructive sleep apnea syndrome following nasal continuous positive airway pressure therapy

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is a common disorder in obese subjects. Visceral fat accumulation (VFA) is a better predictor of coronary heart disease than body mass index. Leptin is a hormone involved in the control of body weight and fat distribution. The effect of nasal continuous positive airway pressure (NCPAP) treatment on VFA and serum leptin levels in OSAS patients has not been known.

METHODS AND RESULTS

VFA and subcutaneous fat accumulation (SFA) were assessed by CT before and after NCPAP treatment in 22 OSAS patients (mean apnea and hypopnea index >50 episodes/h). Serum leptin levels of another 21 OSAS patients were measured before and after 3 to 4 days of NCPAP to gain insight into the mechanism by which NCPAP affects fat distribution. VFA and SFA decreased significantly after 6 months of NCPAP treatment (236+/-16 to 182+/-14cm(2), P=0.0003 and 215+/-21 to 189+/-18 cm(2), P=0.003, respectively). VFA decreased significantly in the body weight reduction group (n=9, P<0.01) and the no body weight reduction group (n=13, P<0.03). In contrast, SFA changed significantly in the body weight reduction group only (P<0.01). Leptin levels decreased significantly following 3 to 4 days of NCPAP (P<0.01), whereas body weight, fasting insulin, and cortisol levels did not change significantly.

CONCLUSIONS

Correction of sleep disordered breathing by NCPAP may be used to reduce VFA in OSAS patients. OSAS may have significant effects on the serum leptin levels.

Paradoxical decrease of an adipose-specific protein, adiponectin, in obesity

We isolated the human adipose-specific and most abundant gene transcript, apM1 (Maeda, K., et al., Biochem. Biophys. Res. Commun. 221, 286-289, 1996). The apM1 gene product was a kind of soluble matrix protein, which we named adiponectin. To quantitate the plasma adiponectin concentration, we have produced monoclonal and polyclonal antibodies for human adiponectin and developed an enzyme-linked immunosorbent assay (ELISA) system. Adiponectin was abundantly present in the plasma of healthy volunteers in the range from 1.9 to 17.0 mg/ml. Plasma concentrations of adiponectin in obese subjects were significantly lower than those in non-obese subjects, although adiponectin is secreted only from adipose tissue. The ELISA system developed in this study will be useful for elucidating the physiological and pathophysiological role of adiponectin in humans.

The obese gene product, leptin: possible role in obesity-related hypertension in adolescents

OBJECTIVE

The mechanism of the association between obesity and hypertension is not clear. The recently discovered obese gene product, leptin, the levels of which increase in obese subjects, has been shown to reduce food intake and increase sympathetic nervous system activity in animal studies. The present study was undertaken to elucidate the relationship between blood pressure and factors related to obesity, including leptin, in different age groups.

METHODS

The subjects were 348 Japanese male adolescents (15-17 years old) and 165 men (40-59 years old) not taking medication for hypertension, diabetes mellitus or hyperlipidaemia. Height, weight, blood pressure, heart rate, plasma glucose, lipid profiles, serum insulin and leptin levels were measured in the morning after an overnight fast

RESULTS

Body mass index (BMI), serum leptin level and the homeostasis model insulin resistance index increased in the order of blood-pressure category (i.e. normotensive < high normal < hypertensive) in both the male adolescents and the middle-aged men. In addition, simple linear regressions revealed that both systolic and diastolic blood pressure correlated significantly with serum leptin and the insulin resistance index in both groups. Even after adjustment for age and BMI, the correlation of mean blood pressure with leptin remained in the obese adolescents (r2 = 0.390, P = 0.02). The heart rate also correlated with leptin in the adolescents (r = 0.18, P< 0.001), but not in the middle-aged subjects (r = 0.04). Even after adjustment for age and BMI in adolescents, serum leptin correlated significantly with heart rate.

CONCLUSION

These results suggest a role for leptin in obesity-related hypertension, especially in adolescents.

The relationship between the serum leptin concentrations of thyrotoxic patients during treatment and their total fat mass is different from that of normal subjects

OBJECTIVE

Previous studies of leptin in thyrotoxic human subjects have been short-term and cross-sectional. We have measured serum leptin concentrations in thyrotoxic patients in order to study the influence of endogenous thyroid hormones on the relationship between serum leptin and fat mass. DESIGN PATIENTS, MEASUREMENTS: In 10 fasting thyrotoxic patients (8 females, 2 males, mean age: 51 years) we measured serum leptin (microgram/l), total thyroxine (TT4), total triiodothyronine (TT3), thyrotropin (TSH) and by Dual Energy X-ray Absorptiometry (DEXA) total fat mass (TFM, kg) at time of diagnosis (0 months, baseline) and during 12 months treatment with thiamazole. For comparison 16 fasting thiamazole-treated euthyroid patients (14 females, 2 males, mean age: 38 years) were studied after one year follow-up (26 months (15-48)) and 18 normal controls (12 females, 6 males, mean age: 39 years).

RESULTS

The serum leptin concentration was 9.1 (1.3 micrograms/l (mean (SEM) in the thyrotoxic patients and increased significantly to 16.0 (1.3 micrograms/l (P < 0.0005) after 12 months treatment compared to both normal subjects and their own baseline. There was a significant correlation between serum leptin concentration and TFM in the normal control group (r = 0.79, P < 0.00009), in the thiamazole-treated euthyroid group (r = 0.85, P < 0.00003) and in the baseline thyrotoxic group (r = 0.84, P < 0.002) but the serum leptin/TFM ratio increased significantly during 12 months of antithyroid drug treatment from 0.34 (1.2 micrograms/l/kg to 0.53 (1.2 micrograms/l/kg (P < 0.03).

CONCLUSION

The thiamazole-treated thyrotoxic patients increased their serum leptin concentrations during 12 months antithyroid drug treatment without a significant corresponding degree of changes in TFM as expected from normal controls. It is suggested that the metabolic state in thyrotoxic patients can influence the regulation of serum leptin concentrations without any associated changes in TFM.

Effect of obesity on estradiol level, and its relationship to leptin, bone maturation, and bone mineral density in children

The purpose of this study was to investigate 24-h estradiol and leptin levels in obese and nonobese children to further understand the roles of estradiol and leptin in obesity and puberty. We measured serum estradiol, leptin, insulin, glucose, and GH levels every hour for 24 h in 18 obese (12 females and 6 males) and 30 nonobese (11 females and 19 males) prepubertal and early pubertal (stages 1-2) children. Bone age and dual energy x-ray absortiometry (DEXA) were obtained upon completion of the 24-h study. Obese children were significantly younger than nonobese children, with no difference in pubertal stage, height, or bone age between the 2 groups. Obese children had greater bone age to chronological age ratios than nonobese children, indicating a more advanced rate of bone maturation. Mean 24-h estradiol levels correlated significantly with chronological age and bone age as well as with insulin-like growth factor I, insulin-like growth factor-binding protein-3, dehydroepiandrosterone sulfate, mean 24-h GH, and lean body mass. Mean 24-h estradiol levels did not differ between obese and nonobese children [1.65+/-1.47 us. 2.75+/-3.30 pmol/L (0.45+/-0.40 vs. 0.75+/-0.90 pg/mL), respectively]. Similar mean 24-h estradiol levels in obese and nonobese children are consistent with the increased bone maturation of the obese children. Estradiol did not correlate significantly with DEXA fat mass, body mass index, or arm fat measures of adiposity. Obese children had higher 24-h mean leptin concentrations than nonobese children (28.6+/-17.4 vs. 6.8+/-7.1 ng/mL; P < 0.001). Leptin concentrations positively correlated with DEXA fat mass, body mass index, and arm fat measurement of adiposity. Girls had higher 24-h mean leptin levels than boys when controlling for adiposity. Estradiol and leptin concentrations fluctuated over a 24-h period in both groups, with all children having higher leptin concentrations at night and higher estradiol concentrations in the morning. This diurnal rhythm was of a similar pattern, but at higher levels for leptin and lower levels for estradiol in the obese children compared to nonobese children. There was no significant correlation between estradiol and leptin levels. Bone mineral density, as measured by DEXA, did not differ between obese and nonobese children. Similar bone mineral density values in obese and nonobese children are consistent with the increased bone maturation of the obese children. Bone mineral density was not correlated with estradiol or leptin level in these children. In conclusion, obese children had similar estradiol levels and equivalent bone ages at a younger chronological age than nonobese children. Leptin was higher in these obese children, but did not correlate with estradiol level or bone age. These findings suggest that the role of leptin in both obesity and pubertal development is not directly correlated with the estradiol level.

Development of a sensitive ELISA for human leptin, using monoclonal antibodies

A new, sensitive ELISA for human leptin in plasma and cerebrospinal fluid (CSF) was developed, using monoclonal antibodies. The lower limit of detection of this ELISA was 0.78 pg/assay. Both intra- and interassay imprecision values were &lt;7%. The dilution curves of plasma and CSF showed good linearity, and the recovery was 83.2–95.6%. There was good correlation between plasma leptin concentrations by the ELISA and a commercially available RIA (r = 0.99). Our ELISA is advantageous because it does not require radioisotopes, it produces results in hours rather than days, and more importantly, it improves on the detection limit and plasma interference of the RIA kit. The new ELISA enables measurement of low concentrations of leptin, as are seen in CSF and in plasma of patients with anorexia nervosa.

A rapid, quantitative functional assay for measuring leptin

At present, leptin is quantitated using immuno-assays that measure leptin mass. Leptin biological activity is determined using protocols that measure feed consumption and weight reduction. These in vivo protocols are semi-quantitative and require large quantities of leptin. We describe a rapid, sensitive and quantitative in vitro assay for leptin using HEK-293 cells stably co-transfected with the leptin receptor Ob-Rb isoform and a STAT-inducible promoter regulating the firefly luciferase cDNA. The assay, performed in a 96-well format, has an EC50 of 150 pM and is linear from 3 to 700 pM of leptin. We demonstrate that the assay is capable of measuring leptin in plasma samples. We demonstrate that bacterially-expressed, recombinant leptin and in vivo expressed leptin are equipotent. Furthermore, we demonstrate that a leptin-derived peptide, leptin fragment 22-56, previously shown to be capable of reducing feed intake following ICV injection does not act directly through the leptin receptor.