Clinical significance of serum adipokines levels in lung cancer

Adipokines have a significant effect on metabolism, immunoinflammatory responses as well as on carcinogenesis; therefore, we aimed at evaluating their potential predictive and prognostic significance in lung cancer. Eighty patients--mean age 62.9 ± 9.2 years--with previously untreated lung cancer (61 NSCLC and 19 SCLC) of all stages and 40 healthy individuals were enrolled in this study. Serum levels of leptin, adiponectin and ghrelin were measured using human Radioimmunoassay kits. Serum leptin levels in lung cancer patients were lower compared to control (p < 0.0001), while adiponectin and ghrelin levels were significantly increased in patients (p = 0.0003 and p = 0.0043, respectively). Additionally, the leptin/adiponectin ratio was significantly lower in the patients group compared to controls (p < 0.0001]. There was no association between serum levels of adipokines and any of the patient clinicopathological characteristics or response to therapy. Nevertheless, patients with lower values of serum leptin had shorter overall survival (p = 0.014), whereas multivariate analysis revealed leptin levels as an independent prognostic factor for survival (p = 0.024, HR 0.452, CI 95 % 0.232-0.899). These results suggest that adipokines may play a role in the pathogenesis of lung cancer, while leptin serum levels might provide useful prognostic information.

Leptin overexpression in VTA trans-activates the hypothalamus whereas prolonged leptin action in either region cross-desensitizes

High-fat feeding or CNS leptin overexpression in chow-fed rats results in a region-specific cellular leptin resistance in medial basal hypothalamic regions and the ventral tegmental area (VTA). The present investigation examined the effects of targeted chronic leptin overexpression in the VTA as compared with the medial basal hypothalamus on long-term body weight homeostasis. The study also examined if this targeted intervention conserves regional leptin sensitivity or results in localized leptin resistance. Cellular leptin resistance was assessed by leptin-stimulated phosphorylation of signal transducers and activators of transcription 3 (STAT3). Tyrosine hydroxylase was measured in hypothalamus and VTA along with brown adipose tissue uncoupling protein 1. Leptin overexpression in VTA tempered HF-induced obesity, but to a slightly lesser extent than that with leptin overexpression in the hypothalamus. Moreover, the overexpression of leptin in the VTA stimulated cellular STAT3 phosphorylation in several regions of the medial basal hypothalamus, whereas verexpression in the hypothalamus did not activate STAT3 signaling in the VTA. This unidirectional trans-stimulation did not appear to involve migration of either the vector or the gene product. Long-term leptin overexpression in either the medial basal hypothalamus or VTA caused desensitization of leptin signaling in the treated region and cross-desensitization of leptin signaling in the untreated region. These results demonstrate a role of leptin receptors in the VTA in long-term body weight regulation, but the trans-activation of the hypothalamus following VTA leptin stimulation suggests that an integrative response involving both brain regions may account for the observed physiological outcomes.

Taurine may not alleviate hyperglycemia-mediated endoplasmic reticulum stress in human adipocytes

In obesity and diabetes, adipocytes show significant endoplasmic reticulum (ER) stress. Hyperglycemia-induced ER stress has not been studied in adipocyte differentiation and adipokine expression. Taurine has been known to protect the cells against ER stress. This study examined the effect of taurine on ER stress-induced adipocyte differentiation and adipokine expression to explain the therapeutic effect of taurine on diabetes and obesity. To do this, human preadipocytes were differentiated into adipocytes, in the presence or absence of taurine, under ER stress conditions. Changes in adipokine expression in adipocytes stimulated with IL-1β were investigated in the presence or absence of taurine. Human preadipocytes were treated with thapsigargin (10 nM) or high glucose concentrations (100 mM) as ER stress inducers during differentiation into adipocytes. Thapsigargin inhibited the differentiation of adipocytes in a dose-dependent manner, but the high glucose concentration treatment did not. Taurine 100 mM treatment did not block the inhibition of differentiation of preadipcytes into adipocytes. Furthermore, the high glucose concentration treatment inhibited the expression of adiponectin and increased the expression of leptin in human adipocytes. However, taurine treatment did not affect the expression of two adipokines. In conclusion, the therapeutic mechanism of taurine in diabetes and obesity does not appear to occur by alleviating hyperglycemia-mediated ER stress. To clarify the molecular mechanism by which taurine improves diabetic symptoms and obesity in animal models, the protective effect of taurine against hyperglycemia- or overnutrition-mediated ER stress should be further evaluated under various conditions or types of ER stress.

Leptin regulates gonadotropins and steroid receptors in the rats ovary

The leptin hormone is important to satiety and an important link between the nutritional status and reproductive processes. Owing to the contradictory effects of leptin on the ovary and the failure to clarify the precise mechanism by which leptin affects the ovary, our aim was to contribute to evaluation if leptin can directly regulate the gene expression of leptin itself and its receptors, and the expression of several genes related to the ovary function by a model of tissue culture. Ovaries from Wistar dams were used at 90 days of age and were submitted to medium with presence and absence of leptin. The results can demonstrate that leptin regulates gonadotropins and steroid receptors, which could suggest that the ovarian leptin role could be secondary to the changes in these receptors expression in rats.

The alternative Epac/cAMP pathway and the MAPK pathway mediate hCG induction of leptin in placental cells

Pleiotropic effects of leptin have been identified in reproduction and pregnancy, particularly in the placenta, where it works as an autocrine hormone. In this work, we demonstrated that human chorionic gonadotropin (hCG) added to JEG-3 cell line or to placental explants induces endogenous leptin expression. We also found that hCG increased cAMP intracellular levels in BeWo cells in a dose-dependent manner, stimulated cAMP response element (CRE) activity and the cotransfection with an expression plasmid of a dominant negative mutant of CREB caused a significant inhibition of hCG stimulation of leptin promoter activity. These results demonstrate that hCG indeed activates cAMP/PKA pathway, and that this pathway is involved in leptin expression. Nevertheless, we found leptin induction by hCG is dependent on cAMP levels. Treatment with (Bu)₂cAMP in combination with low and non stimulatory hCG concentrations led to an increase in leptin expression, whereas stimulatory concentrations showed the opposite effect. We found that specific PKA inhibition by H89 caused a significant increase of hCG leptin induction, suggesting that probably high cAMP levels might inhibit hCG effect. It was found that hCG enhancement of leptin mRNA expression involved the MAPK pathway. In this work, we demonstrated that hCG leptin induction through the MAPK signaling pathway is inhibited by PKA. We observed that ERK1/2 phosphorylation increased when hCG treatment was combined with H89. In view of these results, the involvement of the alternative cAMP/Epac signaling pathway was studied. We observed that a cAMP analogue that specifically activates Epac (CPT-OMe) stimulated leptin expression by hCG. In addition, the overexpression of Epac and Rap1 proteins increased leptin promoter activity and enhanced hCG. In conclusion, we provide evidence suggesting that hCG induction of leptin gene expression in placenta is mediated not only by activation of the MAPK signaling pathway but also by the alternative cAMP/Epac signaling pathway.

Effects of a moderate physical training on the leptin synthesis by adipose tissue of adult rats submitted to a perinatal low-protein diet

The aim of the study was to verify if moderate physical training affects leptin content in visceral and subcutaneous adipose tissue of adult rats subjected to a low-protein diet during the perinatal period. Male Wistar rats were divided into 2 groups according to their mother's diet during gestation and lactation: control (17% casein, C, n=12) and low-protein (8% casein, LP, n=12). On postnatal day 60, half of each group was submitted to moderate physical training (8 wks, 5 d · wk - 1, 60 min · d - 1, at 70% of VO2max, T) or not. After the physical training period, visceral and subcutaneous adipose tissues were removed. Leptin content was evaluated by western blotting. Starting from the fifth week on, T pups showed a reduction in the body weight. Similarly, LP+T offspring showed a lower body weight starting from the sixth week on. Western blotting analysis showed that leptin content in the visceral tissue was higher in the LP rats (p<0.01) and it was reversed in LP+T. No difference was found in the subcutaneous tissue. Moderate physical training attenuated the effects of a perinatal low-protein diet on the leptin content in visceral adipose tissue in adult offspring.

Angiotensin II Promotes Leptin Production in Cultured Human Fat Cells by an ERK1/2-dependent Pathway

OBJECTIVE

The fat cell hormone leptin is known to be implicated in the pathogenesis of hypertension and cardiovascular disease. Here we tested whether angiotensin (Ang) II is involved in the control of leptin release from human adipocytes.

RESEARCH METHODS AND PROCEDURES

Leptin secretion was assessed from in vitro differentiated human adipocytes by radioimmunoassay. Western blot experiments were used to test for the signaling pathway activated by Ang II.

RESULTS

Ang II increased leptin secretion into the culture medium in a dose- and time-dependent fashion. At 10(-5) M Ang II, the leptin concentration in the medium was increased at 24 hours by 500+/-222% compared with control cultures (p<0.05). This effect was also seen at the mRNA level. Similar effects were seen after exposure of fat cells to Ang III and Ang IV. Preincubation of fat cells with candesartan, an angiotensin II type 1 receptor antagonist, or the extracellular-signal-regulated kinases 1 and 2 inhibitor UO126 completely abolished the effect of Ang II on leptin production. The peroxisome proliferator-activated receptor-gamma agonist troglitazone modestly attenuated leptin release.

DISCUSSION

In conclusion, Ang II and its metabolites stimulated leptin production in human adipocytes. This effect is mediated through an extracellular-signal-regulated kinases 1 and 2-dependent pathway and includes the angiotensin II type 1 receptor subtype.

Treatment with constitutive androstane receptor ligand during pregnancy prevents insulin resistance in offspring from high-fat diet-induced obese pregnant mice

The constitutive androstane receptor (CAR) has been reported to decrease insulin resistance even during pregnancy, while exposure to a high-fat diet (HFD) in utero in mice can induce a type 2 diabetes phenotype that can be transmitted to the progeny. Therefore, we examined whether treatment with a CAR ligand during pregnancy could prevent hypertension, insulin resistance, and hyperlipidemia in the offspring from HFD-induced obese pregnant mice (OH mice). We employed four groups of offspring from HFD-fed and control diet-fed pregnant mice with or without treatment with a CAR ligand. Treatment with a CAR ligand during pregnancy improved glucose tolerance and the levels of triglyceride and adipocytokine and restored the changes induced by HFD with amelioration of hypertension in the adult OH mice. This treatment also increased adiponectin mRNA expression, suppressed leptin expression in adipose tissues of OH mice, and abolished the effect of HFD on the epigenetic modifications of the genes encoding adiponectin and leptin in the offspring during immaturity and adulthood. Our data suggest that CAR might be a potential therapeutic target to prevent metabolic syndrome in adulthood of offspring exposed to an HFD in utero.

Resistance to obesity by repression of VEGF gene expression through induction of brown-like adipocyte differentiation

Adipose tissues are classified into white adipose tissue (WAT) and brown adipose tissue (BAT). WAT is responsible for energy storage, and malfunction is associated with obesity. BAT, on the contrary, consumes fat to generate heat through uncoupling mitochondrial respiration and is important in body weight control. Vascular endothelial growth factor (VEGF)-A is the founding member of the VEGF family and has been found highly expressed in adipose tissue. A genetic mouse model of an inducible VEGF (VEGF-A) repression system was used to study VEGF-regulated energy metabolism in WAT. VEGF-repressed mice demonstrated lower food efficiency, lower body weight, and resistance to high-fat diet-induced obesity. Repression of VEGF expression caused morphological and molecular changes in adipose tissues. VEGF repression induced brown-like adipocyte development in WAT, up-regulation of BAT-specific genes including PRDM16, GATA-1, BMP-7, CIDEA, and UCP-1 and down-regulation of leptin, a WAT-specific gene. VEGF repression up-regulated expression of VEGF-B and its downstream fatty acid transport proteins. Relative levels of VEGF/VEGF-B may be important switches in energy metabolism and of pharmaceutical significances.

The source of leptin, but not leptin depletion in response to food restriction, changes during early pregnancy in mice

Maternal food restriction during pregnancy results in adverse consequences for offspring, including obesity and cardiovascular disease. Early pregnancy is a critical period for this programming effect. Leptin is a regulator of energy homeostasis that also affects placental and fetal development. As food restriction results in decreased serum leptin levels, at least in non-pregnant animals, leptin depletion may be one mechanism by which food restriction affects development. The objective of this study was to test whether moderate food restriction affects serum leptin concentrations during the first half of pregnancy. We found that restriction to 50% of ad libitum consumption levels resulted in a significant decrease in serum leptin concentrations in both pregnant and non-pregnant female mice. There was no significant difference in serum leptin concentrations between non-pregnant females and at pregnancy day 11.5 when fed ad libitum. However, there was a difference in the source of leptin during pregnancy, with greater production in visceral fat in pregnant mice, and greater production in subcutaneous fat in non-pregnant mice. Leptin concentrations were dependent on time of day and time of sampling relative to feeding, particularly in restricted mice. There was a significant difference in serum leptin concentrations between fed and restricted mice when they were fed and sampled in afternoon, but not when they were fed and sampled in morning. We conclude that food restriction results in a significant decrease in leptin concentration during the first half of pregnancy in mice, but that detection of this relationship is subject to experimental design considerations.

Leptin reverts pro-apoptotic and antiproliferative effects of α-linolenic acids in BCR-ABL positive leukemic cells: involvement of PI3K pathway

It is suspected that bone marrow (BM) microenvironmental factors may influence the evolution of chronic myeloid leukaemia (CML). In this study, we postulated that adipocytes and lipids could be involved in the progression of CML. To test this hypothesis, adipocytes were co-cultured with two BCR-ABL positive cell lines (PCMDS and K562). T cell (Jurkat) and stroma cell (HS-5) lines were used as controls. In the second set of experiments, leukemic cell lines were treated with stearic, oleic, linoleic or α-linolenic acids in presence or absence of leptin. Survival, proliferation, leptin production, OB-R isoforms (OB-Ra and OB-Rb), phosphoinositide 3-kinase (PI3k) and BCL-2 expression have been tested after 24h, 48h and 72h of treatment. Our results showed that adipocytes induced a decrease of CML proliferation and an increase in lipid accumulation in leukemic cells. In addition, CML cell lines induced adipocytes cell death. Chromatography analysis showed that BM microenvironment cells were full of saturated (SFA) and monounsaturated (MUFA) fatty acids, fatty acids that protect tumor cells against external agents. Stearic acid increased Bcl-2 expression in PCMDS, whereas oleic and linoleic acids had no effects. In contrast, α-linolenic acid decreased the proliferation and the survival of CML cell lines as well as BCL-2 and OB-R expression. The effect of α-linolenic acids seemed to be due to PI3K pathway and Bcl-2 inhibition. Leptin production was detected in the co-culture medium. In the presence of leptin, the effect of α-linolenic acid on proliferation, survival, OB-R and BCl-2 expression was reduced.

Developmental plasticity in adrenal function and leptin production primed by nicotine exposure during lactation: gender differences in rats

Neonate male rats whose mothers were nicotine-treated during lactation have higher adiposity, hyperleptinemia, and adrenal dysfunction. At adulthood, they still present higher adiposity and hyperleptinemia, but there was no report about their adrenal function. Also, there was no report of this developmental plasticity on females. Here, we evaluated the adrenal function and leptin content in adipocytes and muscle of male and female adult offspring whose mothers were nicotine-treated during lactation. On the 2nd postnatal day (PN2), dams were subcutaneously implanted with osmotic minipumps releasing nicotine (NIC-6 mg/kg/day) or saline for 14 days (12 litters/group and 2 rats/litter). Male and female offspring were killed on PN180. Significant data were p<0.05. Male NIC offspring presented higher adrenal catecholamine content (+ 89%) and TH expression (+ 38%), lower "in vitro" catecholamine release (- 19%), and higher adrenergic β3 receptor (ADRB3, + 59%) content in visceral adipose tissue (VAT). Serum corticosterone was higher (+ 77%) in male NIC group, coherent with the increase of both CRH and ACTH immunostaining in hypothalamus and pituitary, respectively. Leptin content was higher in VAT (+ 23%), which may justify the observed hyperleptinemia. Female NIC offspring presented lower ADRB3 content in VAT (- 39%) and lower leptin content in subcutaneous adipose tissue (SAT) (- 46%), but higher leptin content in soleus muscle (+ 22%), although leptinemia was normal. We evidenced a sex dimorphism in the model of maternal nicotine exposure during lactation. The adrenal function in adult offspring was primed only in male offspring while the female offspring displayed relevant alterations in leptin content on muscle and adipocytes.

Angiotensinogen and angiotensin-converting enzyme mRNA decrease and AT1 receptor mRNA and protein increase in epididymal fat tissue accompany age-induced elevation of adiposity and reductions in expression of GLUT4 and peroxisome proliferator-activated receptor (PPARγ)

Elevated adiposity is one of the accompanying features of increased age in humans and animals. Angiotensin II (Ang II) is considered as growth promoting peptide to be involved in hypertrophic enlargement of adipose tissue. However, systemic renin-angiotensin system (RAS) seems to decrease with increased age of rats. Local adipose tissue RAS might be independent of the systemic one. Therefore we performed a comprehensive study using rats with increased age from 9 to 26 weeks and evaluated angiotensinogen, angiotensin-converting enzyme (ACE) and AT(1) receptor mRNA in epididymal adipose tissue by RT-PCR. In addition, we determined AT(1) receptor protein by Western blotting and Ang II binding. These RAS parameters were correlated with expression of selected adiposity-dependent proteins such as leptin, adiponectin, insulin-dependent glucose transporter (GLUT4) and PPARgamma. Angiotensinogen and ACE expression decreased with increased age and adiposity. On the contrary, AT(1) receptor mRNA and protein was significantly elevated in 26-week-old rats though the Ang II binding was not different between 9 and 26-week-old animals. These results suggest dynamic adaptation of local adipose tissue RAS components to increased age and adiposity most likely by decreasing local Ang II formation which is thereafter compensated by increased expression of AT(1) receptor. However, this increase in AT(1) receptor mRNA and protein is not reflected in increased receptor binding. We believe that this complex regulation of adipose tissue RAS slows down the negative age and adiposity related changes in adipose tissue leptin, adiponectin, GLUT4 and PPARgamma.

Glioblastoma-derived leptin induces tube formation and growth of endothelial cells: comparison with VEGF effects

BACKGROUND

Leptin is a pleiotropic hormone whose mitogenic and angiogenic activity has been implicated in the development and progression of several malignancies, including brain tumors. In human brain cancer, especially in glioblastoma multiforme (GBM), leptin and its receptor (ObR) are overexpressed relative to normal tissue. Until present, the potential of intratumoral leptin to exert proangiogenic effects on endothelial cells has not been addressed. Using in vitro models, we investigated if GBM can express leptin, if leptin can affect angiogenic and mitogenic potential of endothelial cells, and if its action can be inhibited with specific ObR antagonists. Leptin effects were compared with that induced by the best-characterized angiogenic regulator, VEGF.

RESULTS

We found that GBM cell lines LN18 and LN229 express leptin mRNA and LN18 cells secrete detectable amounts of leptin protein. Both lines also expressed and secreted VEGF. The conditioned medium (CM) of LN18 and LN 229 cultures as well as 200 ng/mL pure leptin or 50 ng/mL pure VEGF stimulated proliferation of human umbilical vein endothelial cells (HUVEC) at 24 h of treatment. Mitogenic effects of CM were ~2-fold greater than that of pure growth factors. Furthermore, CM treatment of HUVEC for 24 h increased tube formation by ~5.5-fold, while leptin increased tube formation by ~ 80% and VEGF by ~60% at 8 h. The mitogenic and angiogenic effects of both CM were blocked by Aca 1, a peptide ObR antagonist, and by SU1498, which inhibits the VEGF receptor. The best anti-angiogenic and cytostatic effects of Aca1 were obtained with 10 nM and 25 nM, respectively, while for SU1498, the best growth and angiogenic inhibition was observed at 5 μM. The combination of 5 μM SU1498 and Aca1 at 25 nM (growth inhibition) or at 10 nM (reduction of tube formation) produced superior effects compared with single agent treatments.

CONCLUSIONS

Our data provide the first evidence that LN18 and LN 229 human GBM cells express leptin mRNA and might produce biologically active leptin, which can stimulate tube formation and enhance proliferation of endothelial cells. Furthermore, we demonstrate for the first time that a peptide ObR antagonist inhibits proangiogenic and growth effects of leptin on endothelial cells, and that the pharmacological potential of this compound might be combined with drugs targeting the VEGF pathway.

Higher white adipocyte area and lower leptin production in adult rats overfed during lactation

Litter size reduction during lactation is a good model for childhood obesity since it induces overnutrition and programming for obesity at adulthood. Adult offspring develop higher fat mass content, hyperinsulinemia and insulin resistance, hypertension, lower HDL cholesterol, hyperphagia, and leptin resistance. Leptin resistance is often associated with hyperleptinemia. Although we observed higher SOCS3 and lower STAT3 in the hypothalamus of rats raised in small litters featuring a central leptin resistance, they showed unexpected normoleptinemia at 180 days old. Then, to clarify why early overfed rats did not develop hyperleptinemia when adult, we studied the leptin production by the visceral and subcutaneous adipose tissue and skeletal muscle as well as the morphology in the 2 different fat depots. To induce EO, litter size was reduced to 3 pups/litter (SL group) on the 3 (rd) day of life. In controls (NL group), litter size was adjusted to 10 pups/litter. Rats were killed at 180 days old. The programming of adipose tissue morphology by early overnutrition is specific between the different fat depots with hypertrophy only in the visceral compartment. In addition, the visceral adipocyte showed lower leptin content that may indicate a reduced leptin synthesis. These data suggest that adipocytes from SL rats are dysfunctional, since a higher leptin production in larger adipose cells is expected. In conclusion, postnatal nutrition is determinant for future leptin production by different fat depots as well as adipocyte morphology. These changes seem to be related to the severity of obesity and its metabolic consequences.

Progesterone-induced blocking factor (PIBF) and trophoblast invasiveness

Controlled trophoblast invasion is a key process during human placentation and a prerequisite for successful pregnancy. Progesterone is one of the factors to regulate trophoblast invasiveness. Progesterone-induced blocking factor (PIBF) is a progesterone-induced molecule expressed by the trophoblast, and also by tumors. The distribution of PIBF within the first-trimester decidua coincides with sites of trophoblast invasion. Another molecule that has been implicated in the control of trophoblast invasiveness is placental leptin. Leptin inhibits the secretion of progesterone by cytotrophoblast. The aim of this work was to investigate the possible interaction of PIBF and leptins in regulating trophoblast invasion. Paraffin-embedded sections from normal first-trimester placentae, partial moles, complete moles, and choriocarcinomas were reacted with PIBF, leptin, and leptin receptor specific antibodies. PIBF-deficient trophoblast cells were generated using siRNA and leptin receptor was detected on Western blot analysis. The lysates of PIBF-treated cells were used for detecting leptin expression in a protein array. PIBF was expressed in both normal first-trimester villous trophoblast and in partial mole. Compared with this, PIBF expression was markedly decreased in complete mole and absent in choriocarcinoma. Neither leptinR nor leptin were detected in partial mole, whereas both of these molecules were present in complete mole and choriocarcinoma. Leptin receptor expression was upregulated in PIBF-deficient cells, while leptin expression was decreased in PIBF-treated cells. These data suggest that PIBF affects the expression of leptin and its receptor, and that PIBF expression is inversely related to trophoblast invasiveness.

Cold-induced alteration of adipokine profile in humans

Adipose tissue function and sympathetic nervous system (SNS) activity are tightly interconnected. Adipose tissue is densely innervated by the SNS. Adipokines secreted by adipose tissue are implicated in maintaining energy homeostasis, the control of blood pressure, immune system function, hemostasis, and atherosclerosis. Little is known about a direct effect of SNS activation on influencing adipose tissue endocrine function in humans. In 10 lean, healthy male volunteers, SNS was activated by whole-body exposure to cold for 2 hours; a group of 10 subjects served as controls. Vital parameters were evaluated, plasma adipokine levels were measured, and adipokine gene expression in subcutaneous abdominal adipose tissue was determined. Cold exposure caused an increase in cold sensation and a drop in body temperature and heart rate. Norepinephrine, but not epinephrine, plasma levels were elevated. Adiponectin plasma concentrations were acutely and significantly decreased. There was a trend of increased monocyte chemoattractant protein-1 plasma concentrations. Interleukin-6 and leptin levels increased and decreased, respectively, in both groups. Vascular endothelial growth factor plasma levels were unaffected. Subcutaneous adipokine gene expression was unchanged. Cold exposure caused SNS activation and differentially influenced adipokine secretion. Adiponectin levels were acutely reduced, whereas monocyte chemoattractant protein-1 concentrations tended to increase. No specific changes in leptin and IL-6 concentrations were detectable. The observed alterations appeared to be posttranscriptional because adipokine gene expression was found to be unaltered.

[Relationship between insulin, leptin, and melatonin contents in patients with metabolic syndrome]

Melatonin, leptin, and insulin secretion was studied in 25 men with metabolic syndrome (MS) verified against IDF criteria (2005) (mean age 44 +/- 2 yr). The control group was constituted by 23 healthy men (mean age 45.1 yr). Melatonin secretion was estimated from 6-oxymelatonin sulfate (6-OMS) level in urine samples collected at 4 a.m. (in the darkness). It was shown to increase at this time in both groups but was lower in MS patients than in controls (t = 2, p < 0.05). The Pearson correlation analysis revealed moderate negative correlation between 6-SOMT level in urine and insulin and glucose levels in plasma (r = 0.95). Peak 6-SOMT level showed strong negative correlation with the leptin level. Multiple regression analysis demonstrated strong linear relationship of 6-OMS and insulin levels (r = 0.93) and 6SOMT and leptin levels (r = 0.95). The calculated odds ratio suggests that the risk of insulin resistance in patients displaying a peakless melatonin secretion profile is 3 times that in control subjects (OR = 3.0; 95% CI = 1.3-7). It is concluded that patients with MS present with disturbances of melatonin secretion manifest as the absence of its physiological elevation at night hours; they are characterized by negative correlation between melatonin, leptin and insulin levels and changes in melatonin secretion in relation to abnormal production of insulin and leptin.

Alanine aminotransferase decreases with age: the Rancho Bernardo Study

Background

Serum alanine aminotransferase (ALT) is a marker of liver injury. The 2005 American Gastroenterology Association Future Trends Committee report states that serum ALT levels remain constant with age. This study examines the association between serum ALT and age in a community-dwelling cohort in the United States.

Methods

A cross-sectional study of 2,364 (54% female) participants aged 30–93 years from the Rancho Bernardo Study cohort who attended a research clinic visit in 1984–87. Demographic, metabolic co-variates, ALT, bilirubin, gamma glutamyl transferase (GGT), albumin, and adiposity signaling biomarkers (leptin, IL-6, adiponectin, ghrelin) were measured. Participants were divided into four-groups based upon age quartile, and multivariable-adjusted least squares of means (LSM) were examined (p for trend <0.05).

Results

ALT decreased with increasing age, with mean ALT levels (IU/L) of 23, 21, 20, and 17 for those between quartile ages 30–62, 63–71, 72–77, and 78–93 years (p<0.0001). Trends of decreasing LSM ALT with age and the decreasing prevalence of categorically defined elevated serum ALT with age remained robust after adjusting for sex, alcohol use, metabolic syndrome components, and biomarkers of adiposity (p-value <0.0001), and was not materially changed after adjusting for bilirubin, GGT, and albumin.

Conclusions

ALT levels decrease with age in both men and women independent of metabolic syndrome components, adiposity signaling biomarkers, and other commonly used liver function tests. Further studies are needed to understand the mechanisms responsible for a decline in ALT with age, and to establish the optimal cut-point of normal ALT in the elderly.

Region-specific diet-induced and leptin-induced cellular leptin resistance includes the ventral tegmental area in rats

Diet-induced obesity (DIO) results in region-specific cellular leptin resistance in the arcuate nucleus (ARC) of the hypothalamus in one strain of mice and in several medial basal hypothalamic regions in another. We hypothesized that the ventral tegmental area (VTA) is also likely susceptible to diet-induced and leptin-induced leptin resistance in parallel to that in hypothalamic areas. We examined two forms of leptin resistance in F344xBN rats, that induced by 6-months of high fat (HF) feeding and that induced by 15-months of central leptin overexpression by use of recombinant adeno-associated viral (rAAV)-mediated gene delivery of rat leptin. Cellular leptin resistance was assessed by leptin-stimulated phosphorylation of signal transducers and activators of transcription 3 (STAT3) in medial basal hypothalamic areas and the VTA. The regional pattern and degree of leptin resistance with HF was distinctly different than that with leptin overexpression. Chronic HF feeding induced a cellular leptin resistance that was identified in the ARC and VTA, but absent in the lateral hypothalamus (LH), ventromedial hypothalamus (VMH), and dorsomedial hypothalamus (DMH). In contrast, chronic central leptin overexpression induced cellular leptin resistance in all areas examined. The identification of leptin resistance in the VTA, in addition to the leptin resistance in the hypothalamus, provides one potential mechanism, underlying the increased susceptibility of leptin resistant rats to HF-induced obesity.

Zinc-alpha2-glycoprotein: a new biomarker of breast cancer?

BACKGROUND/AIM

Obesity increases the risk of breast cancer. It is established that adipocyte secretions, i.e. adipokines, may play a role in mammary carcinogenesis. We have shown that two major adipokines, leptin and adiponectin, were expressed in mammary adenocarcinoma.

PATIENTS AND METHODS

Here, we evaluated zinc-alpha2-glycoprotein (ZAG) expression in tumor (n=55) and healthy (n=6) breast tissue by immunohistochemistry and examined whether it was correlated with that of major adipokines, usual tumor biomarkers (sex steroids receptors, i.e. estrogen (ER) and progesterone; Ki-67; cErb2), or apoptosis markers (Bcl2 and Bax).

RESULTS

ZAG expression was detected in ductal carcinoma and normal epithelial adjacent tissue but not in normal tissue of healthy women. In cancer tissue, its expression was correlated positively to leptin receptor and negatively to adiponectin receptor and ER.

CONCLUSION

These preliminary results suggest both a relationship between ZAG expression and pathways involving adipokines or estrogen and that ZAG may be a potential breast cancer biomarker.

Leptin treatment during lactation programs leptin synthesis, intermediate metabolism, and liver microsteatosis in adult rats

Epidemiological and experimental studies have associated development of metabolic syndrome with stressful events (nutritional, hormonal, or environmental) in early life. This phenomenon is known as programing and changes in adipokines levels in early life, especially leptin, seem to be involved with its development. We have shown that neonatal hyperleptinemia on lactation programs for leptin resistance, hyperthyroidism, and higher corticosterone and catecholamines levels with cardiovascular consequences. In the present study, we evaluated the effect of hyperleptinemia during lactation on the glucose and lipid metabolism and liver morphology of adult rats, which were saline or leptin-treated (8 microg/100 g of body weight) daily, for the first 10 days of life. Leptin group had lower body mass during treatment, but higher body mass and hyperleptinemia at adulthood, without difference in fat mass. We showed that the probable source of hyperleptinemia is the higher leptin content in the subcutaneous adipose tissue. The programed rats showed hyperinsulinemia and hypoadiponectinemia with higher expression of the hypothalamic Suppressor of Cytokine Signaling 3 (SOCS3), suggesting insulin resistance. Besides, they presented higher liver glycogen and hypertriglyceridemia. We also observed liver microsteatosis in the leptin-programed adult rats. Our data show that neonatal hyperleptinemia alters glucose metabolism, which seems to be partially compensated by the hyperinsulinemia. However, changes in the lipid metabolism are not compensated. It is probable that these changes induced by neonatal hyperleptinemia result from a selective tissue specific resistance both to insulin and leptin at adulthood, and the increase of SOCS3 may play an important role in this process.

The different satiating capacity of CHO and fats can be mediated by different effects on leptin and ghrelin systems

Leptin and ghrelin are known to be the main hormones involved in the control of food intake, with opposite effects. Here we aimed to assess whether changes in leptin and ghrelin systems can be involved in the different satiating capacities of carbohydrates (CHO) and fat. Adult male Wistar rats were studied under 24h fasting conditions and after 24h fasting followed by a 12h re-feeding period with 64 kcal of CHO or fat, consisting of a mixture of wheat starch and sucrose or bacon, respectively. Serum levels of leptin and ghrelin, and mRNA levels of leptin and ObRb in the retroperitoneal and inguinal adipose tissue and of NPY, POMC, ObRb and GSHR in the hypothalamus were measured. CHO re-feeding resulted in higher leptin mRNA expression levels in the retroperitoneal adipose tissue and in higher circulating leptin levels compared with those after fat re-feeding. Moreover, circulating ghrelin levels and ghrelin/leptin ratio were significantly higher after fat re-feeding compared with CHO re-feeding, and hypothalamic expression levels of ghrelin receptor increased after fat, but not after CHO, re-feeding. Hence, expression levels of hypothalamic neuropeptides involved in food intake control and regulated by these hormones, particularly the orexigenic NPY and the anorexigenic pro-opiomelanocortin (POMC)-derived alpha-melanocyte-stimulating hormone, were also differently affected by CHO and fat re-feeding, resulting in a significantly lower NPY/POMC ratio after CHO re-feeding than after fat re-feeding. In conclusion, different effects on the leptin and ghrelin systems can account, at least in part, for the lower satiating capacity of fat compared to CHO.

Adenovirus-mediated leptin expression normalises hypertension associated with diet-induced obesity

In our previous study, moderate increases in plasma leptin levels achieved via administration of recombinant adenovirus containing the rat leptin cDNA were shown to correct the abnormal metabolic profile in rats with diet-induced obesity, suggesting that these animals had developed resistance to the metabolic effects of leptin, which could be reversed by leptin gene over-expression. However, the effect of this therapeutic strategy on blood pressure was not investigated. The present study aimed to determine whether a moderate increase of endogenous plasma leptin levels affected arterial blood pressure in rats with diet-induced obesity and hypertension. The major finding from the present study was that the natural rise in plasma leptin with weight-gain is insufficient to counterbalance high blood pressure associated with obesity, additional increases of circulating leptin levels with adenoviral leptin gene therapy led to normalisation of blood pressure in high-fat diet-induced obese and hypertensive rats. Mechanistically, the reduction of blood pressure by leptin in obese rats was likely independent of alpha-adrenergic and acetylcholinergic receptor mediation. This is the first study to demonstrate that further increases in circulating leptin levels by leptin gene transfer during obesity could reduce blood pressure.