Leptin and atherosclerosis

Leptin, a 167-amino acid peptide hormone produced by white adipose tissue, is primarily involved in the regulation of food intake and energy expenditure. Leptin receptors are expressed in many tissues including the cardiovascular system. Plasma leptin concentration is proportional to body adiposity and is markedly increased in obese individuals. Recent studies suggest that hyperleptinemia may play an important role in obesity-associated cardiovascular diseases including atherosclerosis. Leptin exerts many potentially atherogenic effects such as induction of endothelial dysfunction, stimulation of inflammatory reaction, oxidative stress, decrease in paraoxonase activity, platelet aggregation, migration, hypertrophy and proliferation of vascular smooth muscle cells. Leptin-deficient and leptin receptor-deficient mice are protected from arterial thrombosis and neointimal hyperplasia in response to arterial wall injury. Several clinical studies have demonstrated that high leptin level predicts acute cardiovascular events, restenosis after coronary angioplasty, and cerebral stroke independently of traditional risk factors. In addition, plasma leptin correlates with markers of subclinical atherosclerosis such as carotid artery intima-media thickness and coronary artery calcifications. Inhibition of leptin signaling may be a promising strategy to slow the progression of atherosclerosis in hyperleptinemic obese subjects.

Identification of a non-mammalian leptin-like gene: characterization and expression in the tiger salamander (Ambystoma tigrinum)

Leptin is well established as a multifunctional cytokine in mammals. However, little is known about the evolution of the leptin gene in other vertebrates. A recently published set of ESTs from the tiger salamander (Ambystoma tigrinum) contains a sequence sharing 56% nucleotide sequence identity with the human leptin cDNA. To confirm that the EST is naturally expressed in the salamander, a 409bp cDNA was amplified by RT-PCR of salamander testis and stomach mRNAs. The coding sequence of the cDNA is predicted to encode 169 amino acids, and the mature peptide to consist of 146 residues, as in mammals. Although the overall amino acid identity with mammalian leptins is only 29%, the salamander and mammalian peptides share common structural features. An intron was identified between coding exons providing evidence that the sequence is present in the salamander genome. Phylogenetic analysis showed a rate of molecular divergence consistent with the accepted view of vertebrate evolution. The pattern of tissue expression of the leptin-like cDNA differed between metamorphosed adult individuals of different sizes suggesting possible developmental regulation. Expression was most prominent in the skin and testis, but was also detected in tissues in which leptin mRNA is present in mammals, including the fat body, stomach, and muscle. The characterization of a salamander leptin-like gene provides a basis for understanding how the structure and functions of leptin have altered during the evolution of tetrapod vertebrates.

Tumor necrosis factor alpha and glucocorticoid synergistically increase leptin production in human adipose tissue: role for p38 mitogen-activated protein kinase

CONTEXT

TNF increases plasma leptin in humans in vivo, but previous studies showed it decreases leptin in vitro.

OBJECTIVE AND PARTICIPANTS

The objective of this study was to determine the effect of TNF on leptin release from human adipose tissue (AT) from healthy subjects undergoing elective surgery or needle aspirations of AT at a university hospital.

DESIGN

Human omental and abdominal sc AT fragments from non- obese and obese subjects were placed in organ culture without or with TNF added in the presence or absence of insulin and/or dexamethasone (dex; a synthetic glucocorticoid) for up to 2 d.

RESULTS

In the absence of hormones, culture with TNF decreased leptin release. In contrast, when added in the presence of dex, TNF increased secreted leptin and leptin mRNA abundance in AT from nonobese and obese subjects. The TNF + dex-stimulated increase in leptin was associated with an increase in p38 MAPK activity and was totally blocked by p38 MAPK inhibitors. In contrast, inhibition of p38 MAPK only partially blocked the effect of TNF on IL-6 production. Culture of obese AT with either p38 or p44/42 MAPK inhibitors also blunted the spontaneous increase in media leptin that occurred from d 1-2 of culture in omental AT of obese subjects.

CONCLUSION

Synergistic effects of increased local or systemic TNF in combination with glucocorticoids may contribute to increased leptin expression in response to stress, including infection and obesity.

Recent advances in the relationship between obesity, inflammation, and insulin resistance

It now appears that, in most obese patients, obesity is associated with a low-grade inflammation of white adipose tissue (WAT) resulting from chronic activation of the innate immune system and which can subsequently lead to insulin resistance, impaired glucose tolerance and even diabetes. WAT is the physiological site of energy storage as lipids. In addition, it has been more recently recognized as an active participant in numerous physiological and pathophysiological processes. In obesity, WAT is characterized by an increased production and secretion of a wide range of inflammatory molecules including TNF-alpha and interleukin-6 (IL-6), which may have local effects on WAT physiology but also systemic effects on other organs. Recent data indicate that obese WAT is infiltrated by macrophages, which may be a major source of locally-produced pro-inflammatory cytokines. Interestingly, weight loss is associated with a reduction in the macrophage infiltration of WAT and an improvement of the inflammatory profile of gene expression. Several factors derived not only from adipocytes but also from infiltrated macrophages probably contribute to the pathogenesis of insulin resistance. Most of them are overproduced during obesity, including leptin, TNF-alpha, IL-6 and resistin. Conversely, expression and plasma levels of adiponectin, an insulin-sensitising effector, are down-regulated during obesity. Leptin could modulate TNF-alpha production and macrophage activation. TNF-alpha is overproduced in adipose tissue of several rodent models of obesity and has an important role in the pathogenesis of insulin resistance in these species. However, its actual involvement in glucose metabolism disorders in humans remains controversial. IL-6 production by human adipose tissue increases during obesity. It may induce hepatic CRP synthesis and may promote the onset of cardiovascular complications. Both TNF-alpha and IL-6 can alter insulin sensitivity by triggering different key steps in the insulin signalling pathway. In rodents, resistin can induce insulin resistance, while its implication in the control of insulin sensitivity is still a matter of debate in humans. Adiponectin is highly expressed in WAT, and circulating adiponectin levels are decreased in subjects with obesity-related insulin resistance, type 2 diabetes and coronary heart disease. Adiponectin inhibits liver neoglucogenesis and promotes fatty acid oxidation in skeletal muscle. In addition, adiponectin counteracts the pro-inflammatory effects of TNF-alpha on the arterial wall and probably protects against the development of arteriosclerosis. In obesity, the pro-inflammatory effects of cytokines through intracellular signalling pathways involve the NF-kappaB and JNK systems. Genetic or pharmacological manipulations of these effectors of the inflammatory response have been shown to modulate insulin sensitivity in different animal models. In humans, it has been suggested that the improved glucose tolerance observed in the presence of thiazolidinediones or statins is likely related to their anti-inflammatory properties. Thus, it can be considered that obesity corresponds to a sub-clinical inflammatory condition that promotes the production of pro-inflammatory factors involved in the pathogenesis of insulin resistance.

A key regulatory role for histamine in experimental autoimmune encephalomyelitis: disease exacerbation in histidine decarboxylase-deficient mice

Histamine can modulate the cytokine network and influence Th1 and Th2 balance and Ab-isotype switching. Thus, pharmacological blockade or genetic deletion of specific histamine receptors has been shown to reduce the severity of experimental autoimmune encephalomyelitis (EAE), a prototypic Th1-mediated disease with similarities to human multiple sclerosis. To study the comprehensive contribution of endogenous histamine to the expression of EAE, we attempted to induce EAE in histidine decarboxylase-deficient mice, which are genetically unable to make histamine. In this study, we show that EAE is significantly more severe in HDC-/-, histamine-deficient mice, with diffuse inflammatory infiltrates, including a prevalent granulocytic component, in the brain and cerebellum. Unlike splenocytes from wild-type mice, splenocytes from HDC-/- mice do not produce histamine in response to the myelin Ag, whereas production of IFN-gamma, TNF, and leptin are increased in HDC-/- splenocytes in comparison to those from wild-type mice. Endogenous histamine thus appears to regulate importantly the autoimmune response against myelin and the expression of EAE, in this model, and to limit immune damage to the CNS. Understanding which receptor(s) for histamine is/are involved in regulating autoimmunity against the CNS might help in the development of new strategies of treatment for EAE and multiple sclerosis.

Epigenetic characterization of the CpG islands of bovine Leptin and POU5F1 genes in cloned bovine fetuses

Abnormal development and fetal loss during postimplantation period are concerns for production of nuclear transferred animals. Aberrant DNA methylation is one of the reasons for poor survival of cloned animals. In mammalian genome DNA, CpG islands are preferentially located at the start of transcription of housekeeping genes and are associated with tissue-specific genes. The correct and consecutive mechanisms of DNA methylation in the CpG islands are necessary for selective gene expressions that determine the properties of individual cells, tissues, and organs. In this study, we investigated the methylation status of the CpG islands of the bovine Leptin and POU5F1 genes in fetal and placental tissues from fetuses produced by artificial insemination (AI) and nuclear transfer (NT) at days 48 and 59 of pregnancy. Altered DNA methylation was observed in the normal and cloned fetal, placental, and endometrial tissues using bisulfite sequencing and pyrosequencing. Different tissue-specific methylated regions in the bovine Leptin and POU5F1 genes show a variable methylation status in NT fetuses compared to AI control.

Variation in expression of gastric leptin according to differentiation and growth pattern in gastric adenocarcinoma

Leptin is an adipocyte-derived hormone that regulates body fat stores and feeding behavior. The presence of leptin in stomach epithelium was recently demonstrated in the rat and humans, and gastric leptin has been linked to the control of meal size, local inflammatory responses, and paracrine and autocrine functions through leptin receptors in the stomach. We compared the expression patterns of leptin and of the long variant of the leptin receptor (Ob-Rb) between areas with non-ulcerated mucosa and with hyperplastic polyps, adenoma, or adenocarcinoma to evaluate the expression relative to different disease states. Leptin and Ob-Rb were expressed in hyperplastic polyps, adenoma, and adenocarcinoma. In the gastric adenocarcinoma, leptin was expressed significantly less in the poorly differentiated and diffuse-type groups than in the well-differentiated and moderately differentiated groups or in the intestinal type. Based upon our findings, we suggest the possibility that leptin expression can have a pathophysiologic role about the differentiation or growth pattern of gastric adenocarcinoma. A further series of experiments is necessary to elucidate the pathophysiological role of leptin in the differentiation of gastric adenocarcinoma.

Differential effect of antioxidant treatment on plasma and tissue paraoxonase activity in hyperleptinemic rats

Recent studies suggest that adipose tissue hormone, leptin, is involved in atherogenesis, especially in obese subjects. Previously, we have demonstrated that experimentally induced hyperleptinemia decreases plasma paraoxonase 1 (PON1) activity. The aim of this study was to investigate whether treatment with synthetic antioxidant, Tempol, modulates the effect of leptin on plasma and tissue PON1 in the rat. Leptin was administered at a dose of 0.25 mgkg-1 s.c. twice daily for 7 days and Tempol was added to the drinking water at a concentration of 2 mM. Leptin reduced plasma PON1 activity toward paraoxon, phenyl acetate and gamma-decanolactone to 71.1, 72.3 and 57.1% of control, respectively. In addition, leptin decreased PON1 activity toward paraoxon in aorta, renal cortex and medulla to 78.6, 49.2 and 48.0% of control, respectively, but had no effect on PON1 in heart, lung and liver. PON1 activity toward phenyl acetate was lower following leptin treatment only in aorta. Leptin increased plasma concentration and urinary excretion of isoprostanes as well as malonyldialdehyde + 4-hydroxyalkenals level in aorta, renal cortex and renal medulla. Coadministration of Tempol prevented leptin-induced oxidative stress and normalized PON1 activity in aorta and kidney. However, Tempol had no effect on plasma PON1 in leptin-treated rats. These data indicate that hyperleptinemia decreases tissue PON1 activity through oxidative stress-dependent mechanism. In contrast, leptin-induced downregulation of plasma PON1 is not mediated by oxidative stress.

Direct effect of ghrelin on leptin production by cultured rat white adipocytes

OBJECTIVE

Because ghrelin is known to stimulate adipogenesis, we tested whether ghrelin could contribute to the maintenance of homeostasis, directly affecting rat white adipocyte leptin production.

RESEARCH METHODS AND PROCEDURES

Isolated retroperitoneal adipocytes were cultured for 0.5 to 48 hours without (baseline) or with (0.001 to 1 nM) ghrelin alone or in combination with insulin (0.01 to 10 nM) or dexamethasone (1 to 100 nM). Adipocytes were also incubated with ghrelin and inhibitors either of RNA (actinomycin D) or protein synthesis (cycloheximide) or with several concentrations (10 to 1000 nM) of a specific ghrelin antagonist. When cultures were terminated, we evaluated adipocyte leptin secretion and ob mRNA expression.

RESULTS

Our data indicate that ghrelin directly enhanced adipocyte leptin release and ob mRNA expression, that the leptin-releasing activity of ghrelin was additive to the action of both insulin and dexamethasone and was abrogated by protein synthesis inhibitors, and that effects of ghrelin on adipocyte ob mRNA expression and release were blocked by coincubation with the specific growth hormone secretagogue receptor 1a antagonist.

DISCUSSION

Our study supports the ability of ghrelin to enhance white adipose tissue leptin production by a direct receptor-mediated effect. This activity of ghrelin could play a potentially significant role in rapid restoration of homeostasis after food intake.

Arguments raised by the recent discovery that insulin and leptin are expressed in and secreted by human ejaculated spermatozoa

The recent findings demonstrating that insulin and leptin are expressed in and secreted by human ejaculated spermatozoa raise the controversial issue related to mRNA function in male gamete. Capacitated sperm display an increased metabolism and overall energy expenditure presumably to affect the changes in sperm signaling and function during capacitation. However the relationship between the signaling events associated with capacitation and the change in sperm metabolism energy is poorly understood. It emerges from the findings here reported that both leptin and insulin may be crucial in ejaculated spermatozoa to manage their energy status. Immunoistochemical analysis revealed that in uncapacitated sperm insulin was located at the subacrosomial level, in the midpiece and through the tail while leptin was immunodetected at the equatorial segment and at the midpiece. Capacitated sperm display an overall decrease and a more uniform distribution in the signal for both hormones and this is in agreement with their enhanced release in the medium. Both hormones in ejaculated sperm somehow recapitulate the cross-talk between their signalling transductional pathways in somatic cells, resulting in the increase of phosphoinositide 3-kinase (PI3K) activity, AKT S473 and Glycogen synthase kinase 3 (GSK-3)-S9 phosphorylations. During capacitation GSK-3 phosphorylation was abolished suggesting how in capacitating sperm there is a block in glycogen synthesis. This reasonably indicates how during capacitation glycogen reserve is mobilized and this makes the glucose as energy substrate available. For instance insulin dismissed by ejaculated spermatozoa up-regulates Glucose 6-Phosphate Dehydrogenase (G6PDH), the rate-limiting enzyme in the pentose phosphate pathway (PPP), which has be shown to be crucial in the acquisition of fertilizing capability as well as to mediate gamete fusion. Insulin immunoneutralization or blockage of its release, dramatically down regulated G6PDH. Interestingly, in the presence of a disruptor of insulin signaling wortmannin, an inhibitor of PI3K, the intrinsic activity of G6PDH drops. Leptin appears to play similar action to that of insulin on G6PDH in sperm (data in progress). The enhanced activity of this enzyme induced by both hormones produces an increase of NADPH that is essential for fatty acid synthesis from acetyl CoA. These fatty acids have two possible fates: beta-oxidation to produce ATP or reesterification back into triacylglycerol. Inter-relationships of the classes of substrates of free fatty acids (FFA) and glucose utilized for energy, has been long established [Randle, P.J., 1964. The interrelationships of hormones, fatty acid and glucose in the provision of energy. Postgrad. Med. J. 40, 457-463]. The authors observed in ejaculated spermatozoa what it occurs in somatic cells: FFA beta-oxidation tested utilizing the octanoil-CoA as substrate, appears to be stimulated by leptin and down-regulated by the contemporaneous presence of insulin in uncapacitated sperms. FFA beta-oxidation activity dramatically increases when capacitation starts, so it may be assumed the possibility that leptin may work to stimulate such enzymatic activity providing additional metabolic fuel to triggering capacitation process. The autonomous capability of sperm to release insulin and leptin suggests that they through an autocrine short loop may provide the recruitment of energy substrate according to sperm metabolic needs. This occurs independently by the systemic regulation and may represent a protective mechanism which preserves sperm fertilizing capability by any detrimental effects produced by long calorie restriction or by alterations occurring in the energy homeostasis at systemic level.

Glucose intolerance in young TallyHo mice is induced by leptin-mediated inhibition of insulin secretion

The pathophysiology of TallyHo mouse, a recently established animal model for type 2 diabetes mellitus, was analyzed at prediabetic state to examine the inherent defects which contribute to the development of diabetes. At 4 weeks of age, the TallyHo mice already revealed glucose intolerance while their peripheral tissues exhibited normal insulin sensitivity. On the other hand, decreased plasma insulin concentration was observed with little differences in pancreatic insulin contents, indicating the impaired insulin secretion. Such defect, however, was not found in the isolated islets, which suggests a role of endocrine factor in impaired insulin secretion of TallyHo mice. Treatment of leptin inhibited the glucose-stimulated insulin secretion from the isolated islets of TallyHo mice, while in vivo administration of anti-leptin antibody lowered plasma glucose concentration with increased insulin level in TallyHo mice. Expression of glucokinase mRNA was decreased both in whole pancreas and leptin treated islets of TallyHo mice compared with whole pancreas in C57BL/6 mice and untreated islets of TallyHo mice, respectively. These results suggest that elevated plasma leptin can, through the inhibition of insulin secretion, induce glucose intolerance in TallyHo mice.

Leptin regulates insulin sensitivity via phosphatidylinositol-3-OH kinase signaling in mediobasal hypothalamic neurons

To investigate whether phosphatidylinositol-3 kinase (PI3K) signaling mediates the metabolic effects of hypothalamic leptin action, adenoviral gene therapy was used to direct expression of leptin receptors to the area of the hypothalamic arcuate nucleus (ARC). This intervention markedly improved insulin sensitivity in genetically obese, leptin-receptor-deficient Koletsky (fa(k)/fa(k)) rats via a mechanism that was not dependent on reduced food intake but was attenuated by approximately 44% by third-ventricular infusion of the PI3K inhibitor LY294002. Conversely, ARC-directed expression of a constitutively active mutant of protein kinase B (PKB/Akt, an enzyme activated by PI3K) mimicked the insulin-sensitizing effect of restored hypothalamic leptin signaling in these animals, despite having no effect on food intake or body weight. These findings suggest that hypothalamic leptin signaling is an important determinant of glucose metabolism and that the underlying neuronal mechanism involves PI3K.

Role of endothelin-1-dependent up-regulation of leptin in oral mucosal repair

Leptin, a multifunctional hormone that regulates food intake and energy expenditure, has emerged recently as an important modulator of inflammatory cascades associated with wound healing. In this study, we applied the animal model of buccal mucosal ulcer to investigate the role of endothelin-1 (ET-1) and leptin in soft oral tissue repair. Using groups of rats with experimentally induced buccal mucosal ulcers we show that ulcer onset was characterized by a marked increase in the mucosal level of ET-1 and leptin. However, while the ET-1 level gradually declined with healing, the mucosal level of leptin increased reaching maximum expression on the 4th day of healing. Therapeutic administration of phosphoramidon, an inhibitor of ECE-1 activity, not only led to a 53.2% drop in the ET-1, but also produced a dose-dependent reduction (up to 50.9%) in the mucosal level of leptin and up to 42.3% decline in the rate of ulcer healing. A marked drop (54.2%) in the mucosal level of leptin and the reduction (46.8%) in the rate of ulcer healing was also attained in the presence of ETA receptor antagonist BQ610 administration, but not the ETB receptor antagonist BQ788. Moreover, administration of ERK inhibitor, PD98059 in the presence of ETB receptor antagonist, but not the ETA receptor antagonist, caused the reduction the mucosal leptin level as well as a decline in the rate of ulcer healing. Our findings are the first to implicate the requirement for both ET-1 and leptin in orderly progression of the events of soft oral tissue repair. We also show that ET-1 is a key factor in up-regulation of leptin production associated with oral mucosal ulcer healing , and that the effect of ET-1 on leptin production is a consequence of ETA receptor activation and subsequent signaling through MAPK/ERK.

Gene-transfer technology: a preventive neurotherapy to curb obesity, ameliorate metabolic syndrome and extend life expectancy

Leptin insufficiency at crucial target sites in the hypothalamic circuitries that integrate energy intake and expenditure underlies abnormal rates of fat accumulation. The payload of this "fat burden" is metabolic syndrome, a cluster of life-threatening metabolic afflictions, and a shorter lifespan. Currently available therapies employed to combat obesity have disadvantages such as poor compliance for lifestyle modification or transient effectiveness and undesirable side-effects of pharmacological interventions. Recent studies suggest that neurotherapy comprising a single central administration of recombinant adeno-associated virus vector encoding the leptin gene severely depletes fat and ameliorates the major symptoms of metabolic syndrome for extended periods in rodents. These persistent benefits avert the deleterious impact of the "fat burden" and extend life expectancy. Thus, the novel approach of central gene-transfer technology has distinct advantages over current therapies and has the potential to correct or slow the progression of inherited or acquired hypothalamic diseases.

Endothelin-1-dependent leptin induction in gastric mucosal inflammatory responses to Helicobacter pylori lipopolysaccharide

Leptin, a multifunctional hormone that regulates food intake and energy expenditure, has emerged recently as an important modulator of gastric mucosal responses to Helicobacter pylori infection. We applied the animal model of H. pylori LPS-induced gastritis to investigate the role of endothelin-1 (ET-1) in the mucosal leptin production. We show that the histologic pattern of inflammation reached a maximum on the fourth day following the LPS and was reflected in a marked increase in the mucosal level of ET-1 and leptin. Therapeutic administration of phosphoramidon, an inhibitor of ECE-1 activity, led to a 61.2% decline in the mucosal ET-1 level and a 64.1% reduction in leptin, while the severity of mucosal inflammatory involvement increased by 28.6%. A drop in the level of leptin and the increase in severity of the inflammatory involvement elicited by the LPS was also attained in the presence of ET(A) receptor antagonist BQ610, but not the ET(B) receptor antagonist BQ788. Moreover, administration of ERK inhibitor, PD98059, in the presence of ET(B) receptor antagonist, but not the ET(A) receptor antagonist, caused reduction in the mucosal leptin level. Our findings are the first to implicate ET-1 as a key factor in up-regulation of gastric mucosal leptin-associated H. pylori infection. We also show that the effect of ET-1 on leptin production is a consequence of ET(A) receptor activation.

Potential role of leptin in increase of fatty acid synthase gene expression in chicken liver

Leptin is reported to have direct effects on lipogenesis in peripheral tissues that are independent of its central effects on food intake and body weight. These experiments have been mainly carried out in rodents (different models of obesity) in which lipogenesis occurs in both adipose tissue and liver. Such effects are unknown in birds in which lipogenesis occurs essentially in the liver. In this study, leptin gene expression and circulating leptin levels were examined in two chicken lines, selected for high (FL) or low (LL) abdominal fat pad size, at different nutritional states (fasted and fed state). In addition, effects of recombinant chicken leptin on liver metabolism were investigated. Hepatic leptin and fatty acid synthase (FAS) gene expression and plasma leptin levels were significantly higher in FL than in LL chickens (P < 0.05). In both lines, fasting significantly reduced hepatic leptin and FAS mRNA levels (P < 0.05). Continuous administration of recombinant chicken leptin (8 microg/kg/h) during 6 h significantly inhibited food intake (51%) and increased leptinemia (23-fold) compared to untreated group. Despite the decrease of food intake, leptin significantly induced the expression of FAS in chicken liver. These changes were accompanied by a significant down-regulation of leptin receptor gene expression, however SREBP-1, the main transcription factor of lipogenic genes, remained unchanged. This result suggests a local potential role of leptin in the regulation of avian hepatic lipogenesis, and explain, at least partly, the metabolic changes evolved during the divergent selection of FL and LL chickens.

Leptin regulates chondrocyte differentiation and matrix maturation during endochondral ossification

Leptin has been suggested to mediate a variety of actions, including bone development, via its ubiquitously expressed receptor (Ob-Rb). In this study, we investigated the role of leptin in endochondral ossification at the growth plate. The growth plates of wild-type and ob/ob mice were analyzed. Effects of leptin on chondrocyte gene expression, cell cycle, apoptosis and matrix mineralization were assessed using primary chondrocyte culture and the ATDC5 cell differentiation culture system. Immunohistochemistry and in situ hybridization showed that leptin was localized in prehypertrophic chondrocytes in normal mice and that Ob-Rb was localized in hypertrophic chondrocytes in normal and ob/ob mice. Growth plates of ob/ob mice were more fragile than those of wild-type mice in a mechanical test and were broken easily at the chondro-osseous junction. The growth plates of ob/ob mice showed disturbed columnar structure, decreased type X collagen expression, less organized collagen fibril arrangement, increased apoptosis and premature mineralization. Leptin administration in ob/ob mice led to an increase in femoral and humeral lengths and decrease in the proportional length of the calcified hypertrophic zone to the whole hypertrophic zone. In primary chondrocyte culture, the matrix mineralization in ob/ob chondrocytes was stronger than that of wild-type mice; this mineralization in both types of mice was abolished by the addition of exogenous leptin (10 ng/ml). During ATDC5 cell differentiation culture, exogenous leptin at a concentration of 1-10 ng/ml (equivalent to the normal serum concentration of leptin) altered type X collagen mRNA expression and suppressed apoptosis, cell growth and matrix calcification. In conclusion, we demonstrated that leptin modulates several events associated with terminal differentiation of chondrocytes. Our finding that the growth plates of ob/ob mice were fragile implies a disturbance in the differentiation/maturation process of growth plates due to depletion of leptin signaling in ob/ob mice. These findings suggest that peripheral leptin signaling plays an essential role in endochondral ossification at the growth plate.

Effect of dietary lipids on plasma fatty acid profiles and prostaglandin and leptin production in gilthead seabream (Sparus aurata)

The aim of this study was to investigate the effects of different levels of substitution of fish oil by vegetable oils rich in oleic, linoleic and linolenic acids on gilthead seabream plasma and leukocyte fatty acid compositions and prostaglandin (PG) and leptin production. Juvenile seabream of 24 g initial body mass were fed four iso-energetic and iso-proteic experimental diets for 281 days. Fatty acid composition of plasma lipids was markedly affected by the inclusion of vegetable oils (VO). ARA (arachidonate), EPA (eicosapentaenoate) and DHA (docosahexaenoate) were preferentially incorporated into polar lipids of plasma, and DHGLA (di-homogammalinoleate) accumulated with increased vegetable oil inclusion. Dietary treatments resulted in alterations of DHGLA/ARA ratios, but not ARA/EPA. ARA-derived PGE(2) production in plasma was not affected by vegetable oils, in agreement with similar eicosanoid precursor ratio (ARA/EPA) in leukocytes total lipids and plasma phospholipids among fish fed with the different dietary treatments. Feeding vegetable oils leads to a decrease in plasma EPA which in turn reduced plasma PGE(3) concentration. Moreover, PGE(3) was the major prostaglandin produced in plasma of fish fed fish oil based diet. Such findings point out the importance of EPA as a precursor of prostaglandins in marine fish, at least for the correct function of the blood cells, and correlates well with the predominant role of this fatty acid in immune regulation in this species. A negative correlation was found between plasma PGE(2) and leptin plasma concentration, suggesting that circulating levels of leptin may act as a metabolic signal modulating PGE(2) release. The present study has shown that increased inclusion of vegetable oils in diet for gilthead seabream may profoundly affect the fatty acid composition of plasma and leukocytes, specially HUFA (highly unsaturated fatty acids), and consequently the production of PGE(3), which can be a major PG in plasma. Alteration in the amount and type of PG produced can be at least partially responsible for the changes in the immune system and health parameters of fish fed diets with high inclusion of VO.

Endothelin-1-dependent up-regulation of leptin production in gastric mucosal injury by indomethacin

Leptin, a multifunctional hormone that regulates food intake and metabolic and endocrine responses, has emerged recently as an important modulatory factor in gastric mucosal resistance to injury. In this study, we applied the animal model of gastric mucosal injury caused by indomethacin to investigate the role of endothelin-1 (ET-1) in the mucosal leptin production. Using groups of rats subjected to intragastric administration of indomethacin (at 0-60 mg/kg), we show that gastric mucosal damage reached a maximum 4 h following the drug, and was accompanied by a marked elevation (up to 3.5-fold) in the mucosal leptin level, up to 4-fold enhancement in the expression of endothelin-converting enzyme-1 (ECE-1) activity and up to 4.5-fold increase in ET-1 generation. Pretreatment with phosphoramidon, an inhibitor of ECE-1 activity, not only led to a decline in ECE-1 and ET-1 generation, but also produced a dose-dependent reduction in the mucosal level of leptin and the extent of mucosal damage caused by indomethacin. This effect of phosphoramidon, however, was subject to suppression by the exogenous ET-1 administration. Moreover, a marked drop in the mucosal level of leptin and the reduction in the severity of mucosal damage was attained following pretreatment with ET(A) receptor antagonist BQ610, but not by ET(B) receptor antagonist BQ788. The results implicate ET-1 as a key factor in the regulation of leptin production associated with gastric mucosal response to injury, and show that the stimulatory effect of ET-1 on leptin production occurs via ET(A) receptor activation.

Conjugated linoleic acid deteriorates insulin resistance in obese/diabetic mice in association with decreased production of adiponectin and leptin

Dietary supplementation of conjugated linoleic acids (CLA) is known to have some beneficial effects such as anti-carcinogenic and anti-obesity effects in several animal species, while it also induces insulin resistance and fatty liver, especially in mice. To explore the possible factors responsible for the CLA-induced insulin resistance, we examined the plasma and mRNA expression levels of several adipocytokines, which are likely involved in the regulation of insulin sensitivity, in normal C5 7BL, mildly obese/diabetic KK and morbidly obese/diabetic KKAy mice. Feeding a diet supplemented with 0.5%, CLA oil consisting of 30.5/% c9, t11-CLA and 28.9% t10, c12-CLA for 4 wk resulted in a decrease in white adipose tissue (WAT), an increase in liver weight with excess accumulation of triglyceride, and insulin resistance associated with hyperglycemia and hyperinsulinemia. The plasma and WAT mRNA levels of leptin were higher in KK and KKAy mice than C57BI. mice, whereas those of adiponectin were higher in C5 7BL mice. CLA-feeding decreased the levels of leptin, adiponectin and resistin, especially in KK and KKAy mice. In contrast, tumor necrosis factor-alpha (TNFalpha) mRNA levels were higher in KK and KKAy mice than C57BL mice, and were increased by CLA feeding. The present results thus indicate that CLA feeding promotes insulin resistance in obese/diabetic mice by at least inverse regulation of leptin and adiponectin, and TNFalpha, adipocytokines known to either ameliorate or deteriorate insulin sensitivity, respectively.

Lack of the effect of mycotoxins-aflatoxin B1 and ochratoxin A on some functions of rat adipocytes

Mycotoxins-aflatoxin B1 (AFB1) and ochratoxin A (OTA)-compounds which are strong carcinogenic, mutagenic and cytotoxic factors-are also known to evoke a decrease of food intake and body weight gains. The purpose of our study was to determine the direct influence of AFB1 and OTA incubated with isolated rat fat cells on the lipogenesis, lipolysis and leptin secretion. Adipocytes were isolated from the epididymal fat tissue by the collagenase digestion. Toxins used at concentrations 1, 10 and 100 microM were incubated for 90 min with adipocytes. Basal and insulin-stimulated lipogenesis-determined by the measure of [U-14C]glucose conversion to total lipids-was abated by AFB1 only at the highest concentration. At two lower ones, AFB1 did not affect the process. OTA at all used concentrations decreased insulin-stimulated lipogenesis but the effect was not dose-dependent. The lipolysis was determined by the measure of glycerol release from adipocytes. The basal lipolysis was unchanged by both toxins. The epinephrine-stimulated lipolysis was intensified by AFB1 only at the highest concentration, however, the process was not altered by OTA. The antilipolytic action of insulin was unaffected by both compounds (10 microM). To determine the influence of the tested toxins on leptin secretion, adipocytes were incubated for 120 min in the presence of glucose and insulin as stimulators of hormone secretion. AFB1 and OTA added to the incubation medium (1, 10 and 100 microM) had no significant influence on the leptin release. The results obtained in this experiment demonstrate that adipocytes are susceptible to the direct action of AFB1 and OTA. This susceptibility is, however, rather weak and is exhibited by a slight restriction of the lipogenesis (in the case of both toxins) and by a slight increase of the lipolysis (in the case of AFB1).

The emerging role of adipocytokines as inflammatory mediators in inflammatory bowel disease

Anorexia, malnutrition, altered body composition and development of mesenteric obesity are well known features of inflammatory bowel disease (IBD). Recent data suggest that dysregulation of protein secretion by white adipose tissue is involved in these manifestations of patients with IBD. Adipocytes are recently recognized as endocrine cells that secrete a variety of bioactive substances known as adipocytokines. There is evidence that adipocytokines are involved in inflammatory and metabolic pathways in human beings. Overexpression of adipocytokines such as leptin, adiponectin and resistin in mesenteric adipose tissue of operated patients with Crohn's disease has recently been reported, suggesting that mesenteric adipocytes in IBD may act as immunoregulating cells. Therefore, it could be suggested that adipocytokines play an important role in the disease pathogenesis. Moreover, modulators of mesenteric adipose function have been suggested as potential therapeutic drugs in IBD. In this review, the importance of white adipose tissue function and adipocytokines, is discussed with respect to IBD.