Hypoxia-induced leptin production in human trophoblasts does not protect from apoptosis

OBJECTIVE

The ob-gene product, leptin, is an important regulator of placental and fetal development during pregnancy. Leptin, being induced by hypoxia in the placenta, is a known pro-apoptotic molecule in adipose tissue but is also known to inhibit apoptosis in other tissues like neuroblastoma cells. Based on these findings, we investigated if leptin has a pro- or anti-apoptotic effect on a trophoblastic cell line (JAr cells) in the presence or absence of oxygen.

METHODS AND RESULTS

Measurement of leptin in the supernatant by using ELISA showed hypoxia-induced leptin production in JAr cells in vitro. This could be confirmed by a leptin-specific RT-PCR. By analyzing leptin and/or hypoxia exposed cells with FACS cytometry we found that JAr cells can cope with hypoxia down to oxygen tensions of 1%. At this level, only a small number of cells underwent apoptosis. Interestingly, leptin added to the culture medium in high concentrations was not able to interfere with the rate of proliferation or apoptosis in these cells independent of the oxygen tension. Finally, an anti-caspase-3 and anti-caspase-9 Western blot was performed. Again, no difference in the expression of caspase-3 and -9 under the conditions tested was seen.

CONCLUSIONS

These results show that leptin, produced by placental cells after hypoxia in vitro, has no influence on the rate of proliferation of these cells. Furthermore, it does not influence apoptotic pathways in the trophoblastic cell line tested under hypoxic and non-hypoxic conditions.

Leptin-directed embryo implantation: leptin regulates adhesion and outgrowth of mouse blastocysts and receptivity of endometrial epithelial cells

Leptin is a 16-kDa multifunctional protein. Recent reports indicate that leptin is an important molecule during implantation and placentation, implicated in embryonic-maternal cross-talk and cytotrophoblast invasiveness, however, the role of leptin playing in the process of normal blastocyst implantation has not been well characterized. In the present study, the possible mechanisms of leptin playing in mouse blastocyst implantation were investigated. Leptin and receptor isoforms mRNAs were detected in whole mouse uteri during estrous cycle and peri-implantation periods. Immunofluorescent analysis further confirmed Ob-R protein was present in mouse uterus. The differential amounts of leptin and Ob-R isoforms suggested a role for leptin in such endometrial issues as blastocyst implantation. In vitro culture model for studying embryo implantation, leptin promoted mouse blastocyst adhesion and blastocyst outgrowth on fibronectin. Blastocysts treated with 300 ng/ml leptin had the greatest adhesion rate of 76.58+/-6.41% (P=0.046), and blastocysts treated with 30 ng/ml leptin had the greatest outgrowth rate of 78.64+/-8.48% (P=0.005). In isolated endometrial epithelial cells, leptin upregulated amounts of alpha v and beta 3 integrin, and promoted cell adhesion to such extracellular matrix proteins as fibronectin, laminin and type IV collagen, showing a dose- and time-dependent cell-adhesive capacity. Collectively, the information from the present study may partly account for leptin-induced mouse blatocyst implantation.

Regulation of leptin secretion from white adipocytes by insulin, glycolytic substrates, and amino acids

The aim of the present study was to determine the respective roles of energy substrates and insulin on leptin secretion from white adipocytes. Cells secreted leptin in the absence of glucose or other substrates, and addition of glucose (5 mM) increased this secretion. Insulin doubled leptin secretion in the presence of glucose (5 mM), but not in its absence. High concentrations of glucose (up to 25 mM) did not significantly enhance leptin secretion over that elicited by 5 mM glucose. Similar results were obtained when glucose was replaced by pyruvate or fructose (both 5 mM). L-Glycine or L-alanine mimicked the effect of glucose on basal leptin secretion but completely prevented stimulation by insulin. On the other hand, insulin stimulated leptin secretion when glucose was replaced by L-aspartate, L-valine, L-methionine, or L-phenylalanine, but not by L-leucine (all 5 mM). Interestingly, these five amino acids potently increased basal and insulin-stimulated leptin secretion in the presence of glucose. Unexpectedly, L-glutamate acutely stimulated leptin secretion in the absence of glucose or insulin. Finally, nonmetabolizable analogs of glucose or amino acids were without effects on leptin secretion. These results suggest that 1) energy substrates are necessary to maintain basal leptin secretion constant, 2) high availability of glycolysis substrates is not sufficient to enhance leptin secretion but is necessary for its stimulation by insulin, 3) amino acid precursors of tricarboxylic acid cycle intermediates potently stimulate basal leptin secretion per se, with insulin having an additive effect, and 4) substrates need to be metabolized to increase leptin secretion.

Aldosterone inhibits uncoupling protein-1, induces insulin resistance, and stimulates proinflammatory adipokines in adipocytes

Aldosterone is a mineralocorticoid hormone that regulates blood pressure and salt/water balance. Increased aldosterone levels are found in states of disturbed energy balance such as the metabolic syndrome. Adipose tissue has been recognized to play a pivotal role in the regulation of energy homeostasis. We investigated direct aldosterone effects on brown adipocyte function. Aldosterone dose-dependently inhibited expression of uncoupling protein-1 (UCP-1) by 30% (p < 0.01). Furthermore, aldosterone dose-dependently impaired insulin-induced glucose uptake by about 25% (p < 0.01). On a transcriptional level, mRNA of the proinflammatory adipokines leptin and monocyte chemoattractant protein-1 (MCP-1) was increased by 5,000% and 40%, respectively, by aldosterone exposure (p < 0.05). This study demonstrates that aldosterone directly impacts on major adipose functions including stimulation of proinflammatory adipokines.

Dual roles of P2 purinergic receptors in insulin-stimulated leptin production and lipolysis in differentiated rat white adipocytes

ATP is co-localized with norepinephrine at the sympathetic nerve terminals and may be released simultaneously upon neuronal stimulation, which results in activation of purinergic receptors. To examine whether leptin synthesis and lipolysis are influenced by P2 purinergic receptor activation, the effects of ATP and other nucleotides on leptin secretion and glycerol release have been investigated in differentiated rat white adipocytes. Firstly, insulin-induced leptin secretion was inhibited by nucleotide treatment with the following efficacy order: 3'-O-(4-benzoyl)benzoyl ATP (BzATP) > ATP >> UTP. Secondly, treatment of adipocytes with ATP increased both intracellular Ca(2+) concentration and cAMP content. Intracellular calcium concentration was increased by ATP and UTP, but not BzATP, an effect attributed to phospholipase C-coupled P2Y(2). On the other hand, cAMP was generated by treatment with BzATP and ATPgammaS, but not UTP, indicating functional expression of adenylyl cyclase-coupled P2Y(11) receptors in white adipocytes. Thirdly, lipolysis was significantly activated by BzATP and ATP, which correlated with the characteristics of the P2Y(11) subtype. Taken together, the data presented here suggest that white adipocytes express at least two different types of P2Y receptors and that activation of P2Y(11) receptor might be involved in inhibition of leptin production and stimulation of lipolysis, suggesting that purinergic transmission can play an important role in white adipocyte physiology.

Early dietary intervention: long-term effects on blood pressure, brain neuropeptide Y, and adiposity markers

Early life nutrition impacts on subsequent risk of obesity and hypertension. Several brain chemicals responsible for both feeding and cardiovascular regulation are altered in obesity. We examined effects of early postnatal overnutrition on blood pressure, brain neuropeptide Y (NPY), and adiposity markers. Rat pup litters were adjusted to either 3 or 12 male animals (overnutrition and control, respectively) on day 1 of life. After weaning, rats were given either a palatable high-fat diet or standard chow. Smaller litter pups were significantly heavier by 17 days of age. By 16 wk, the effect of litter size was masked by that of diet, postweaning. Small and normal litter animals fed a high-fat diet had similar increases in body weight, plasma insulin, leptin, and adiponectin concentrations, leptin mRNA, and fat masses relative to chow-fed animals. An increase in 11beta-hydroxysteroid dehydrogenase-1 mRNA in white adipose tissue, and a decrease in uncoupling protein-1 mRNA in brown adipose tissue in both small litter groups at 16 wk of age, may represent a programming effect of the altered litter size. NPY concentration in the paraventricular nucleus of the hypothalamus was reduced in high fat-fed groups. Blood pressure was significantly elevated at 13 wk in high-fat-fed animals. This study demonstrates that overnourishment during early postnatal development leads to profound changes in body weight at weaning, which tended to abate with maturation. Thus the effects of long-term dietary intervention postweaning can override those of litter size-induced obesity.

Leptin gene expression and systemic levels in healthy men: effect of exercise, carbohydrate, interleukin-6, and epinephrine

Leptin, an adipose tissue-derived cytokine, is correlated with adipose mass as obese persons have increased levels of leptin that decrease with weight loss. Previous studies demonstrate that high-energy-expenditure exercise decreases circulating leptin levels, whereas low-energy-expenditure exercise has no effect. We aimed to test the hypothesis that acute exercise reduced leptin mRNA levels in human adipose tissue and that this effect would be ameliorated by carbohydrate supplementation. Because exercise markedly increases circulating IL-6 and epinephrine, we investigated whether the changes in leptin seen with acute exercise could be mediated by IL-6 or epinephrine infusion. Abdominal subcutaneous adipose tissue mRNA and plasma levels of leptin were measured in healthy men in response to 3-h ergometer exercise with or without carbohydrate (CHO) ingestion ( n = 8) and in response to infusion with recombinant human (rh)IL-6 ( n = 11) or epinephrine ( n = 8) or saline. Plasma leptin declined in response to exercise ( P < 0.05) compared with rest, whereas mRNA expression in adipose tissue was unaffected. The exercise-induced decrease in plasma leptin was attenuated by CHO ingestion ( P < 0.001). A 3-h epinephrine infusion decreased plasma leptin ( P < 0.001) to the same level seen with 3 h of exercise, whereas leptin levels were unaffected by rhIL-6 infusion. In conclusion, both acute exercise and epinephrine infusion decreased plasma leptin to a similar extent, whereas there was no effect with rhIL-6 infusion. Acute exercise solely affected leptin plasma levels, as mRNA levels were unchanged. The exercise-induced decrease in circulating leptin was counteracted by CHO ingestion, suggesting a posttranscriptional regulatory mechanism of leptin involving substrate availability.

Fatty acids and expression of adipokines

Adipose tissue has been recognised as the quantitatively most important energy store of the human body for many years, in addition to its functions as mechanical and thermic insulator. In mammals, the adipose organ is localised in several depots including white as well as brown adipose tissues. The largest depots are found subcutaneously and in the abdominal region. Several secretory proteins are synthesised in adipose tissue including leptin, resistin, adiponectin, tumor necrosis factor (TNFalpha), angiotensinogen, adipsin, acylation-stimulating protein, retinol-binding protein (RBP), interleukin (IL)-1b, IL-6, IL-8, IL-10, plasminogen activator inhibitor-1 (PAI-1), fasting-induced adipose factor, fibrinogen-angiopoietin-related protein, metallothionein, tissue factor (TF), complement C3, fibronectin, haptoglobin, entactin/nidogen, collagen VI alpha 3, pigment epithelium-derived factor (PEDF), hippocampal cholinergic neurostimulating peptide (HCNP), neutrophil gelatinase-associated lipocalin (NGAL) and adiponutrin. Fatty acids may influence the expression of adipokines like leptin, resistin or adiponectin directly by interaction with transcription factors, or indirectly via unknown mechanisms possibly linked to fatty acid oxidation, synthesis or storage. Because fatty acids are the main components of adipose tissue, it is of essential interest to clarify the biological effects of different types of fatty acids on the expression of relevant adipokines.

Metabolic regulation of leptin production in adipocytes: a role of fatty acid synthesis intermediates

In addition to a signal arising from the physical "stretching" of the adipocytes, metabolic and endocrine regulation of leptin production seems to operate in adipocytes. There is however a paucity of literature examining direct role of fatty acid synthesis in regulating adipocytes leptin production. To clarify the relation between fatty acid synthesis and leptin release in adipocytes, we examined leptin release from primary cultured rat epididymal adipocytes with several substances relevance to de novo fatty acid syntyhesis. Bezafibrate (0.5 or 1.0 mM), known to inhibit acetyl-CoA carboxylase, decreased leptin release to 60.3 +/- 7.2 or 47.3 +/- 11.9%, while cerulenin (15, 30, or 75 mM), an inhibitor of fatty acid synthase, increased it by 20.5 +/- 7.7, 58.5 +/- 12.1 or 105.0 +/- 35.0% of the control. Exogenous pyruvate (2.5, 5.0, or 10.0 mM) and malonyl-CoA (10, 20, or 40 mM), substrates and intermediate of fatty acid synthesis, increased leptin release by 11.0 +/- 3.3, 21.5 +/- 5.4, or 61.0 +/- 10.7%, and 11.1 +/- 3.0, 41.1 +/- 9.7 or 56.7 +/- 7.9% of the control, respectively. Considering difference in the site of action of bezafibrate and cerulenin along fatty acid synthesis pathway, one plausible explanation is that malonyl-CoA levels act as a signal of fuel availability to trigger leptin synthesis and/or secretion in adipocytes.

KEYWORDS

Leptin secretion; Fatty acid synthesis; Malonyl-CoA; Rat adipocytes.

Isoproterenol decreases leptin release from rat and human adipose tissue through posttranscriptional mechanisms

In vivo and in vitro studies indicate that beta-adrenergic receptor agonists decrease leptin release from fat cells in as little as 30 min. Our objective was to determine whether alterations in leptin biosynthesis or secretion were involved in the short-term adrenergic regulation of leptin in human and rat adipose tissue. Isoproterenol (Iso) decreased leptin release from incubated adipose tissue of both nonobese and obese subjects to similar extent (-28 vs. -21% after 3 h). Inhibition of protein synthesis with cycloheximide did not block the effect of Iso on leptin release from human adipose tissue, suggesting that the Iso effect is independent of leptin synthesis. Iso also tended to increase tissue leptin content at the end of the 3-h incubation, as expected from the observed inhibition of release. Consistent with a posttranslational mechanism, Iso treatment did not affect leptin mRNA levels or relative rate of leptin biosynthesis as directly assessed by [35S]methionine incorporation into immunoprecipitable leptin. In contrast to these results in human adipose tissues, Iso did not decrease basal leptin release from rat adipose tissue. However, Iso did decrease insulin-stimulated leptin release by inhibiting the ability of insulin to increase leptin biosynthesis without detectably affecting leptin mRNA levels. Thus, in both human and rat, adrenergic regulation of posttranscriptional events (secretion in humans, translation in rats) may contribute to the rapid decline in circulating leptin that occurs when the sympathetic nervous system is activated, such as during fasting and cold exposure. Furthermore, the rat does not provide an ideal model to study mechanisms of cellular leptin regulation in humans.

[Cloning of human obesity gene and its expression in E. coli]

OBJECTIVE

To clone the obesity gene of Chinese and express human leptin in E.coli.

METHOD

The obesity gene was amplified from the total RNA isolated from cultured human adipocytes of Chinese by reverse transcriptional PCR, inserted into TA-vector and cloned into the expression plasmid pBV220 after sequence identification.

RESULTS

DNA sequencing confirmed that the isolated obesity gene was identical to the previously reported sequence. The recombinant plasmid pBV220-OB was constructed and leptin successfully expressed in E.coli.

CONCLUSION

Successful cloning and expression of human obesity gene in E.coli may facilitate further research of the mechanism of fat metabolism and adipocyte differentiation.

Melatonin enhances leptin expression by rat adipocytes in the presence of insulin

Leptin and melatonin play an important role in the regulation of body mass and energy balance. Both hormones show a circadian rhythm, with increasing values at night. In addition, melatonin receptors were recently described in adipocytes, where leptin is synthesized. Here, we investigated the influence of melatonin and its interaction with insulin and dexamethasone on leptin expression. Isolated rat adipocytes were incubated with melatonin (1 nM) alone or in combination with insulin (5 nM) and/or dexamethasone (7 nM) for 6 h. Melatonin or insulin alone did not affect leptin expression, but together they increased it by 120%. Dexamethasone increased leptin mRNA content (105%), and this effect was not enhanced by melatonin. Simultaneous treatment with the three hormones provoked a further increase in leptin release (250%) and leptin mRNA (100%). Melatonin prevented the forskolin-induced inhibition (95%) of leptin expression. In addition, melatonin's ability to stimulate leptin release (in the presence of insulin) was completely blocked by pertussis toxin and luzindole. To gain further insight into the molecular basis of melatonin and insulin synergism, the insulin-signaling pathway was investigated. Melatonin increased the insulin-induced insulin receptor-beta tyrosine phosphorylation, which led to an increased serine phosphorylation of the downstream convergent protein Akt. We concluded that melatonin interacts with insulin and upregulates insulin-stimulated leptin expression. These effects are caused by melatonin binding to the pertussis toxin-sensitive G(i) protein-coupled membrane receptor (MT1 subtype) and the cross talk with insulin, since insulin receptor and its convergent target Akt are coactivated by melatonin.

Expression and secretion of inflammation-related adipokines by human adipocytes differentiated in culture: integrated response to TNF-alpha

The expression profile of a series of adipokine genes linked to inflammation has been examined by quantitative PCR during the differentiation of human preadipocytes to adipocytes in primary culture, together with the integrated effects of TNF-alpha on the expression of these adipokines in the differentiated adipocytes. Expression of the genes encoding adiponectin, leptin, and haptoglobin was highly differentiation dependent, the mRNA being undetectable predifferentiation with the level peaking 9-15 days postdifferentiation. Although angiotensinogen (AGT) and monocyte chemoattractant protein-1 (MCP-1) were both expressed before differentiation, the mRNA level increased markedly on differentiation. The expression of nerve growth factor (NGF) and plasminogen activator inhibitor-1 (PAI-1) fell after differentiation, whereas that of TNF-alpha and IL-6 changed little. Measurement of adiponectin, leptin, MCP-1, and NGF in the medium by ELISA showed that the protein secretion pattern paralleled cellular mRNA levels. Treatment of differentiated human adipocytes with TNF-alpha (5 or 100 ng/ml for 24 h) significantly decreased the level of adiponectin, AGT, and haptoglobin mRNA (by 2- to 4-fold), whereas that of leptin and PAI-1 was unchanged. In contrast, TNF-alpha induced substantial increases in IL-6, TNF-alpha, metallothionein, MCP-1, and NGF mRNAs, the largest increase being with MCP-1 (14.5-fold). MCP-1 and NGF secretion increased 8- to 10-fold with TNF-alpha, whereas leptin and adiponectin did not change. These results demonstrate that there are major quantitative changes in adipokine gene expression during differentiation of human adipocytes and that TNF-alpha has a pleiotropic effect on inflammation-related adipokine production, the synthesis of MCP-1 and NGF being highly induced by the cytokine.

[Influence of hypoxia on leptin and leptin receptor gene expression of C57BL/6J mice]

OBJECTIVE

To investigate the influence of hypoxia on leptin and leptin receptor gene expression of C57BL/6J mice.

METHODS

C57BL/6J mice, exposed to hypoxia in the man-made auto pressure and hypoxia control cabin (XQ-I), were divided into 3 groups: the normal control group, 24 h hypoxia group and 48 h hypoxia group. Reverse transcription-polymerase chain reaction (RT-PCR) was used to measure the mRNA levels of leptin and leptin receptor.

RESULTS

(1) Compared with the normal control group (0.508 +/- 0.207), the leptin mRNA level of 24 h hypoxia group (0.903 +/- 0.190) and 48 h hypoxia group (0.856 +/- 0.336) were up-regulated markedly (all < 0.05); (2) Compared with the normal control group (Ra 0.630, Rb 0.258 +/- 0.049, Rc 0.133), the Ra, Rb, Rc mRNA levels of 24 h hypoxia group (Ra 0.724, Rb 0.381 +/- 0.038, Rc 0.299) and 48 h hypoxia group (Ra 0.700, Rb 0.345 +/- 0.042, Rc 0.292) were up-regulated to different degrees.

CONCLUSIONS

As an independent factor, hypoxia can stimulate increased expression of leptin, leptin receptor Ra, Rb, Rc mRNA. It is suggested that leptin play an important role in positive regulation of respiratory function.

Expression of placental leptin and leptin receptors in preeclampsia

This study investigated the expression profile of placental leptin and leptin receptor isoforms in preeclampsia, using placental tissue from normal pregnancies that were matched in gestational age and birth weight as controls. A total of 29 cases of preeclampsia were studied by immunohistochemistry, including 16 severe and 13 mild preeclampsia cases. Reverse transcriptase-polymerase chain reaction (RT-PCR) was further performed using RNA extracted from frozen tissue (10 severe preeclampsia, 10 mild preeclampsia, and 20 normal third trimester placentas). In all tissue sections, immunostaining signal was shown in the cytoplasmic compartment of the trophoblastic cells. Both the severe and mild preeclampsia groups showed significantly higher immunostaining for leptin compared with normal controls (p < 0.05), but there was no significant difference between the severe and mild preeclampsia groups (p > 0.05). There was no significant difference in immunostaining for leptin receptor between both severe and mild preeclampsia compared with controls (p > 0.05). RT-PCR showed significantly higher levels of mRNA transcripts of leptin in severe preeclampsia (p < 0.05), but not mild preeclampsia (p > 0.05), compared with normal controls. No significant difference in expression of all the receptor isoforms was demonstrated between both severe and mild preeclampsia groups compared with controls (p > 0.05). In conclusion, we confirmed an up-regulated expression of leptin in placental tissue in preeclampsia. However, there was no difference in the expression of all leptin receptor isoforms in placental tissue between preeclamptic and normal pregnancies. The leptin signal probably does not play a major primary role in the pathogenesis of preeclampsia.

Constitutive production of human leptin by fed-batch culture of recombinant rpoS- Escherichia coli

High-level production of human leptin by fed-batch culture of recombinant Escherichia coli using constitutive promoter system was investigated. For the constitutive expression of the obese gene encoding human leptin, the strong constitutive HCE promoter cloned from the D-amino acid aminotransferase gene of Geobacillus toebii was used. To develop an optimal host-vector system, several different recombinant E. coli strains were compared for leptin production. In flask cultures, E. coli FMJ123, which is a rpoS mutant strain, showed the highest level of leptin production (41% of total proteins). By comparing the expression levels of leptin in several different rpoS- and rpoS+ strains, it could be concluded that rpoS mutation positively affected constitutive production of leptin. For the large-scale production of human leptin, fed-batch cultures of recombinant E. coli FMJ123 were carried out using three different feeding solutions--chemically defined, yeast extract-containing, and casamino acid-containing feeding solutions. Among these, the use of casamino acid-containing feeding solution allowed production of leptin up to 2.1 g/L, which was 2.1- and 1.8-fold higher than that obtained with chemically defined and yeast extract-contained feeding solutions, respectively. These results suggest that the HCE promoter can be used for the efficient production of leptin, and most likely other recombinant proteins, in a constitutive manner.

Enhanced expression of leptin and leptin receptor (OB-R) in human breast cancer

PURPOSE

To evaluate leptin and leptin receptor (OB-R) expression in human breast cancer and determine whether it could be effective for the prevention and treatment of breast cancer.

EXPERIMENTAL DESIGN

Immunohistochemical staining using specific antibodies was used to evaluate the protein expression of leptin and OB-R in 76 invasive ductal carcinomas and 32 samples of corresponding normal mammary gland, and the relationship between the expression of OB-R and leptin and clinicopathological features was analyzed.

RESULTS

Normal mammary epithelial cells did not express a significant level of Ob-R, whereas carcinoma cells showed positive staining for OB-R in 63 (83%) cases. Both normal epithelial cells and carcinoma cells expressed a significant level of leptin. However, overexpression of leptin, as determined by staining intensity, was observed in 70 cancers (92%) but in no normal epithelium. The expression of OB-R showed a significant correlation with the level of leptin expression. Interestingly, distant metastasis was detected in 21 (34%) of 61 OB-R-positive tumors with leptin overexpression, but in none of the 15 tumors that lacked OB-R expression or leptin overexpression (P < 0.05). Consequently, patients with the former tumors showed significantly lower survival than those with the latter.

CONCLUSIONS

Leptin may have a promoting effect on the carcinogenesis and metastasis of breast cancer, possibly in an autocrine manner. Functional inhibition of leptin may be effective for the prevention and treatment of breast cancer.

[Expression of leptin mRNA in luteinized granulosa cells and leptin levels in serum and follicular fluid of non-obese infertile patients with polycystic ovary syndrome]

OBJECTIVE

To investigate the expression of leptin mRNA in luteinized granulose cells and the leptin level in serum and follicular fluid of non-obese patients with polycystic ovary syndrome (PCOS).

METHODS

Granulosa cells were collected from the puncture fluid of follicle of 16 obese infertile patients with PCOS to undergo external fertilization. Fasting venous blood was collected while collecting the ova. RT-PCR was used to detect the expression of leptin mRNA in the granulosa cells. ELISA was used to detect the leptin level in the serum and follicular fluid. Twenty normal women undergoing external fertilization because of male infertility of their husbands were used as controls.

RESULTS

The expression of leptin mRNA (A value) was 1.5 +/- 0.4 in the obese infertile patients with PCOS and was 1.8 +/- 0.6 (P > 0.05) in the controls. Both the leptin levels of serum and follicular fluid were not different between the obese infertile patients with PCOS and controls (both P > 0.05). The leptin level in follicular fluid was significantly correlated with both the serum leptin level in the obese infertile patients with PCOS (r(s) = 0.838, P = 0.000) and the control group (r(s) = 0.712, P = 0.000). The expression level of leptin mRNA in the luteinized was not correlated with the leptin level of follicular fluid in both the obese infertile patients with PCOS and the control group (both P > 0.05). The fertility rate was not different between the obese infertile patients with PCOS (7/16) and the controls (9/24) (P = 0.693).

CONCLUSION

The expression of leptin mRNA is normal in the follicular fluid of the obese infertile patients with PCOS. The leptin levels in serum and follicular fluid of the obese infertile patients with PCOS are similar to those of normal women. The leptin level in follicular fluid depends mainly on the circulating leptin level.

Differential regulation of leptin synthesis in rats during short-term hypoxia and short-term carbon monoxide inhalation

Leptin is a circulating hormone that is secreted primarily by adipose tissue. However, recent studies have demonstrated leptin production by other tissues, including placenta, stomach, kidney, liver, and lung, a process not only activated by stimuli such as insulin or corticosteroids, but also by hypoxia, which is mediated by the hypoxia inducible factor-1. In contrast to this fact, smokers have lower plasma leptin levels. The purpose of this study was to determine whether tissue hypoxygenation [induced by lack of oxygen] or inhalation of carbon monoxide (CO) are sufficient to up-regulate leptin in fat cells as well as in peripheral organs such as lung, liver, and kidney of rats. In hypoxic rats, leptin expression was unchanged or even reduced in adipose tissue. In contrast, in liver, kidney, and lung we observed an increase in leptin expression compared with normoxic controls, whereas plasma levels were unchanged. When animals were exposed to CO, generating a functional anemia known to activate the HIF-1-dependent transcription, a significant decrease in leptin gene expression in adipose tissue and in all organs tested was observed. Plasma leptin concentrations after CO exposure were significantly diminished compared with those in control animals. These findings suggest that tissue hypoxygenation up-regulates leptin expression in nonadipose tissue. However, this is not sufficient to raise plasma leptin levels in rats. Inhalation of CO leads to a significant decrease in leptin mRNA and protein concentration in the plasma of the animals, suggesting a negative effect of CO on leptin transcription.

Obesity and the female sex, risk factors for knee osteoarthritis that may be attributable to systemic or local leptin biosynthesis and its cellular effects

Obesity and the female sex represent significant risk factors for osteoarthritis (OA). Few studies have demonstrated a metabolic link between obesity and OA, strengthening the likelihood that biomechanical factors mediate this relationship, possibly via the redistribution of increased body mass to weight-bearing joints. However, it is less plausible that the biomechanical factors that contribute toward the incidence of OA at weight-bearing joints, such as the knee, are similar to those at non-weight bearing joints, such as in the hand. This may suggest that non-examined or unidentified biomechanical and/or systemic factors may be important contributors to the aetiology of OA. Recent developments that have helped to better appreciate the pathophysiology of obesity offer new hope to understanding the link between obesity and OA. The discovery of the obesity gene (ob) and its product leptin may have important implications for the onset and progression of OA. For instance, the greater total body fat of the average adult female may partially account for the gender disparity toward OA, given that females theoretically demonstrate higher levels of adipose derived systemic leptin concentrations than their male counterparts. However, while it was previously thought that adipose cells were only capable of leptin production, osteoblasts and chondrocytes are also capable of leptin synthesis and secretion, inferring that local leptin production may be of great importance. For instance, significant levels of leptin were observed in the cartilage and osteophytes of people with OA, yet few chondrocytes produced leptin in the cartilage of healthy people. Leptin has also been demonstrated to induce anabolic activity in the chondrocytes of rats, which may ultimately confer structural joint changes. This paper hypothesizes that leptin may be an unexamined systemic or local factor that may mediate the metabolic link between obesity and OA and partially account for the gender disparity toward the disease.

Leptin expression in human primary skeletal muscle cells is reduced during differentiation

We found leptin to be strongly expressed in undifferentiated human myoblasts derived from biopsies of the thigh (Musculus vastus lateralis). Both mRNA expression and secretion of leptin were reduced during in vitro differentiation into primary myotubes. However, the expression of the leptin receptor (OB-Rb) mRNA, was unchanged during differentiation of the muscle cells. Administration of recombinant leptin had no effect on leptin, myogenin, myoD, or GLUT4 mRNA expressions during the period of cellular differentiation. A functional leptin receptor was demonstrated by an acute leptin-induced 1.5-fold increase in ERK activity (P = 0.029). Although mRNA expression of regulation of suppressor of cytokine signaling-3 (SOCS-3) mRNA expression was unaltered, leptin significantly stimulated fatty acid oxidation after 6 h measured as acid soluble metabolites (ASM). Palmitic acid (PA), oleic acid (OA), and eicosapentaenoic acid (EPA), known to modulate leptin expression in other tissues, had no effect on mRNA expression or secretion of leptin from human myotubes. In conclusion, we demonstrate that leptin is highly expressed in undifferentiated human myoblasts and the expression is reduced during differentiation to mature myotubes. The role of leptin in these cells needs to be further characterized.

Olanzapine-induced weight gain and disturbances of lipid and glucose metabolism

Among the atypical antipsychotics, clozapine and olanzapine are known to cause significant weight gain. Along with quetiapine, they may impair glucose metabolism and increase the risk for type 2 diabetes. They are also associated with a rise in triglyceride levels and an increased risk for coronary artery disease. Clinicians should take these risks seriously in prescribing these antipsychotics and employ intelligent safeguards if and when they use them.

Effects of retinoic acid administration and dietary vitamin A supplementation on leptin expression in mice: lack of correlation with changes of adipose tissue mass and food intake

Retinoic acid (RA) administration and chronic vitamin A supplementation were reported to inhibit adipose tissue leptin expression in rodents, but the impact of this effect on food intake and its relationship with changes of body adiposity was not analyzed. Here, we have studied the effects of RA administration at three different doses on body weight, adipose tissue mass, food intake, adipose tissue leptin expression and circulating leptin levels in NMRI mice; the effects of chronic vitamin A supplementation with a 40-fold excess retinyl palmitate on the same parameters in NMRI and C57BL/6J mice; and the effects of RA and retinoid receptors agonists on leptin expression in brown and white adipocyte cell model systems. The results show that vitamin A down-regulates leptin expression in white and brown adipose tissue and circulating leptin levels independently of changes of adipose tissue mass and, for the first time to our knowledge, that this effect does not correlate with increased food intake. They also demonstrate a direct inhibitory effect of RA on leptin expression in both white and brown adipocyte cell cultures, and constitute first proof of the involvement of both RA receptors (RARs) and rexinoid receptors (RXRs) in this effect. Reduction of leptin levels by specific nutrients is of potential interest from a clinical point of view.

Interleukin-6 regulates human adipose tissue lipid metabolism and leptin production in vitro

Adipose tissue IL-6 expression is increased in obesity and is a strong predictor of abnormalities in adipocyte and systemic metabolism. We used adipose tissue organ culture to test the direct effects of IL-6 on leptin expression, lipolysis, and lipoprotein lipase activity. To assess possible interactions with the hormonal milieu, IL-6 effects were tested in the presence or absence of insulin and/or glucocorticoid [dexamethasone (dex)]. Because omental (Om) and abdominal sc depots differ in IL-6 expression, their responses to exogenous IL-6 were compared. Although IL-6 had no significant effects under basal conditions, culture with the combination of IL-6 and dex, compared with dex alone, for 2 d increased leptin in both depots [+95 +/- 30% (sc) and +67 +/- 19% (Om), P < 0.01]; IL-6 did not affect leptin production when added in the presence of insulin. Culture with IL-6 in the absence of hormones moderately increased lipolysis during culture in both sc and Om [+79 +/- 23% (sc) and +26 +/- 9% (Om), each P < 0.01]. IL-6 markedly reduced the high levels of lipoprotein lipase activity in tissue cultured with insulin plus dex. We conclude that high local concentrations of IL-6 can modulate leptin production and lipid metabolism in human adipose tissue.

Prenatal programming of postnatal obesity: fetal nutrition and the regulation of leptin synthesis and secretion before birth

Exposure to either an increased or decreased level of intrauterine nutrition can result in an increase in adiposity and in circulating leptin concentrations in later life. In animals such as the sheep and pig in which fat is deposited before birth, leptin is synthesised in fetal adipose tissue and is present in the fetal circulation throughout late gestation. In the sheep a moderate increase or decrease in the level of maternal nutrition does not alter fetal plasma leptin concentrations, but there is evidence that chronic fetal hyperglycaemia and hyperinsulinaemia increase fetal fat mass and leptin synthesis within fetal fat depots. Importantly, there is a positive relationship between the relative mass of the 'unilocular' component of fetal perirenal and interscapular adipose tissue and circulating fetal leptin concentrations in the sheep. Thus, as in the neonate and adult, circulating leptin concentrations may be a signal of fat mass in fetal life. There is also evidence that leptin can act to regulate the lipid storage, leptin synthetic capacity and potential thermogenic functions of fat before birth. Thus, leptin may act as a signal of energy supply and have a 'lipostatic' role before birth. Future studies are clearly required to determine whether the intrauterine and early postnatal nutrient environment programme the endocrine feedback loop between adipose tissue and the central and peripheral neuroendocrine systems that regulate energy balance, resulting in an enhanced risk of obesity in adult life.