Human leptin stimulates systemic nitric oxide production in the rat

Influence of genetic and cardiometabolic risk factors in Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder. Cardiometabolic and genetic risk factors play an important role in the trajectory of AD. Cardiometabolic risk factors including diabetes, mid-life obesity, mid-life hypertension and elevated cholesterol have been linked with cognitive decline in AD subjects. These potential risk factors associated with cerebral metabolic changes which fuel AD pathogenesis have been suggested to be the reason for the disappointing clinical trial results. In appreciation of the risks involved, using search engines such as PubMed, Scopus, MEDLINE and Google Scholar, a relevant literature search on cardiometabolic and genetic risk factors in AD was conducted. We discuss the role of genetic as well as established cardiovascular risk factors in the neuropathology of AD. Moreover, we show new evidence of genetic interaction between several genes potentially involved in different pathways related to both neurodegenerative process and cardiovascular damage.

Intensive Lifestyle Intervention Increases Plasma Midregional Proatrial Natriuretic Peptide Concentrations in Overweight Children

Background

Overweight adults have low circulating concentrations of ANP (atrial natriuretic peptide) and proANP fragments. We tested the hypothesis that an intensive lifestyle intervention with an intended weight loss would increase plasma concentrations of a proANP fragment in overweight children.

Methods and Results

We measured MR‐proANP (midregional proANP) concentrations in plasma from overweight children who participated in the OOIS (Odense Overweight Intervention Study). OOIS randomized 115 overweight children (11–13 years, 55% girls) to an intensive day‐camp intervention arm with increased physical activity and healthy diet or to a less intensive standard intervention arm for 6 weeks. We used linear mixed‐effects modeling for repeated measures to estimate the difference in the mean change with 95% CIs in fasting plasma MR‐proANP concentrations between the 2 arms, and we used partial least squares regression analysis to identify candidate mediators. Differences in weight, fitness, and metabolic factors were also analyzed. At baseline, fasting plasma MR‐proANP concentrations were (median [interquartile range]) 35.0 pmol/L (26.8–42.0) in the day‐camp intervention arm and 37.2 pmol/L (31.7–44.7) in standard intervention arm participants, respectively. After 6 weeks intervention, children in the day‐camp intervention arm had increased their MR‐proANP (5.4 pmol/L [0.8–10.0], P=0.022) and their fitness (2.33 mL O₂/min per kg [0.52–4.14], P=0.012) and they had deceased their body mass index (−2.12 kg/m² [−2.59 to −1.65], P<0.001) as compared with children in standard intervention arm. In the partial least squares analysis, decreases in fasting insulin and in estimated insulin resistance were associated with the observed increase in MR‐proANP concentrations.

Conclusions

An intensive lifestyle intervention increases plasma MR‐proANP among overweight children.

Registration

URL: https://www.clinicaltrials.gov; Unique identifier: NCT01574352.

Leptin as a Key between Obesity and Cardiovascular Disease

Obesity increases the risk of cardiovascular disease through various influencing factors. Leptin, which is predominantly secreted by adipose tissue, regulates satiety homeostasis and energy balance, and influences cardiovascular functions directly and indirectly. Leptin appears to play a role in heart protection in leptin-deficient and leptin-receptor-deficient rodent model experiments. Hyperleptinemia or leptin resistance in human obesity influences the vascular endothelium, cardiovascular structure and functions, inflammation, and sympathetic activity, which may lead to cardiovascular disease. Leptin is involved in many processes, including signal transduction, vascular endothelial function, and cardiac structural remodeling. However, the dual (positive and negative) regulator effect of leptin and its receptor on cardiovascular disease has not been completely understood. The protective role of leptin signaling in cardiovascular disease could be a promising target for cardiovascular disease prevention in obese patients.

Neuroinflammation, microglial activation, and glucose metabolism in neurodegenerative diseases

Alzheimer's disease is characterized by aggregated amyloid beta plaques and neurofibrillary tangles. Apart from the plaques and tangles, microglial activation plays a significant role in neurodegeneration and neuronal function. This review discusses the way in which microglial activation influences neurodegeneration and how systemic inflammation, type 2 diabetes mellitus, obesity and hypercholesterolemia influence neuroinflammation. Also reviewed is how systemic inflammation influences microglial activation along with the relationship between microglial activation and glucose metabolism.

Utility of Small Animal Models of Developmental Programming

Any effective strategy to tackle the global obesity and rising noncommunicable disease epidemic requires an in-depth understanding of the mechanisms that underlie these conditions that manifest as a consequence of complex gene-environment interactions. In this context, it is now well established that alterations in the early life environment, including suboptimal nutrition, can result in an increased risk for a range of metabolic, cardiovascular, and behavioral disorders in later life, a process preferentially termed developmental programming. To date, most of the mechanistic knowledge around the processes underpinning development programming has been derived from preclinical research performed mostly, but not exclusively, in laboratory mouse and rat strains. This review will cover the utility of small animal models in developmental programming, the limitations of such models, and potential future directions that are required to fully maximize information derived from preclinical models in order to effectively translate to clinical use.

Adiponectin, leptin, nitric oxide, and C-reactive protein levels in kidney transplant recipients: comparison with the hemodialysis and chronic renal failure

BACKGROUND

Cardiovascular disease (CVD) is the leading cause of mortality and morbidity in patients with chronic kidney disease (CKD) including kidney transplant recipients (KTR). Secondary lipid metabolism disorders, endothelial dysfunction, and inflammation enhance the risk of CVD development in these patients. The aim of the present study was to investigate the lipid profile, adiponectin, leptin, nitric oxide (NO), and high sensitivity C-reactive protein (hs-CRP) levels in KTR and to compare these parameters with those of the patients with chronic renal failure (CRF), hemodialysis (HD) patients, and healthy controls.

METHODS

Serum adiponectin and leptin levels were measured by radioimmunoassay; hs-CRP was determined immunoturbidimetrically. Determination of NO was based on the Griess reaction.

RESULTS

Compared with the control group, serum NO and adiponectin levels were significantly higher in the KTR, CRF, and HD groups; hs-CRP levels were significantly higher in the KTR and HD groups; leptin levels were significantly higher in the KTR. In addition, serum NO level was significantly higher in the KTR compared to CRF cases. Adiponectin correlated positively with high density lipoprotein-cholesterol in the control and patient groups. A positive correlation was observed between hs-CRP and NO in the KTR and the patients with CRF. Serum adiponectin levels were inversely correlated with hs-CRP and leptin in the HD group.

CONCLUSION

KTR suffer from inflammation and accompanying changes in levels of adipocytokines and NO which contribute to the increased risk of CVD in these patients.

Vascular smooth muscle-specific deletion of the leptin receptor attenuates leptin-induced alterations in vascular relaxation

Obesity is a risk factor for cardiovascular disease and is associated with increased plasma levels of the adipose-derived hormone leptin. Vascular smooth muscle cells (VSMC) express leptin receptors (LepR); however, their physiological role is unclear. We hypothesized that leptin, at levels to mimic morbid obesity, impairs vascular relaxation. To test this, we used control and VSM-LepR knockout mice (VSM-LepR KO) created with a tamoxifen-inducible specific Cre recombinase to delete the LepR gene in VSMC. Control (10-12 wk old) and VSM-LepR KO (10-12 wk old) mice were fed a diet containing tamoxifen (50 mg/kg) for 6 wk, after which vascular reactivity was studied in isolated carotid arteries using an organ chamber bath. Vessels were incubated with leptin (100 ng/ml) or vehicle (0.1 mM Tris·HCl) for 30 min. Leptin treatment resulted in significant impairment of vessel relaxation to the endothelial-specific agonist acetylcholine (ACh). When these experiments were repeated in the presence of the superoxide scavenger tempol, relaxation responses to ACh were restored. VSM-LepR deletion resulted in a significant attenuation of leptin-mediated impaired ACh-induced relaxation. These data show that leptin directly impairs vascular relaxation via a VSM-LepR-mediated mechanism, suggesting a potential pathogenic role for leptin to increase cardiovascular risk during obesity.

Renal hemodynamic and morphological changes after 7 and 28 days of leptin treatment: the participation of angiotensin II via the AT1 receptor

The role of hyperleptinemia in cardiovascular diseases is well known; however, in the renal tissue, the exact site of leptin’s action has not been established. This study was conducted to assess the effect of leptin treatment for 7 and 28 days on renal function and morphology and the participation of angiotensin II (Ang II), through its AT₁ receptor. Rats were divided into four groups: sham, losartan (10 mg/kg/day, s.c.), leptin (0.5 mg/kg/day for the 7 days group and 0.25 mg/kg/day for the 28 days group) and leptin plus losartan. Plasma leptin, Ang II and endothelin 1 (ET-1) levels were measured using an enzymatic immuno assay. The systolic blood pressure (SBP) was evaluated using the tail-cuff method. The renal plasma flow (RPF) and the glomerular filtration rate (GFR) were determined by p-aminohippuric acid and inulin clearance, respectively. Urinary Na⁺ and K⁺ levels were also analyzed. Renal morphological analyses, desmin and ED-1 immunostaining were performed. Proteinuria was analyzed by silver staining. mRNA expression of renin-angiotensin system (RAS) components, TNF-α and collagen type III was analyzed by quantitative PCR. Our results showed that leptin treatment increased Ang II plasma levels and progressively increased the SBP, achieving a pre-hypertension state. Rats treated with leptin 7 days showed a normal RPF and GFR, but increased filtration fraction (FF) and natriuresis. However, rats treated with leptin for 28 showed a decrease in the RPF, an increase in the FF and no changes in the GFR or tubular function. Leptin treatment-induced renal injury was demonstrated by: glomerular hypertrophy, increased desmin staining, macrophage infiltration in the renal tissue, TNF-α and collagen type III mRNA expression and proteinuria. In conclusion, our study demonstrated the progressive renal morphological changes in experimental hyperleptinemia and the interaction between leptin and the RAS on these effects.

Pulmonary vasoreactivity in spontaneously hypertensive rats--effects of endothelin-1 and leptin

Background

Systemic hypertension may be associated with an increased pulmonary vascular resistance, which we hypothesized could be, at least in part, mediated by increased leptin.

Methods

Vascular reactivity to phenylephrine (1 μmol/L), endothelin-1 (10 nmol/L) and leptin (0.001–100 nmol/L) was evaluated in endothelium-intact and -denuded isolated thoracic aorta and pulmonary arteries from spontaneously hypertensive versus control Wistar rats. Arteries were sampled for pathobiological evaluation and lung tissue for morphometric evaluation.

Results

In control rats, endothelin-1 induced a higher level of contraction in the pulmonary artery than in the aorta. After phenylephrine or endothelin-1 precontraction, leptin relaxed intact pulmonary artery and aortic rings, while no response was observed in denuded arteries. Spontaneously hypertensive rats presented with increased reactivity to phenylephrine and endothelin-1 in endothelium-intact pulmonary arteries. After endothelin-1 precontraction, endothelium-dependent relaxation to leptin was impaired in pulmonary arteries from hypertensive rats. In both strains of rats, aortic segments were more responsive to leptin than pulmonary artery. In hypertensive rats, pulmonary arteries exhibited increased pulmonary artery medial thickness, associated with increased expressions of preproendothelin-1, endothelin-1 receptors type A and B, inducible nitric oxide synthase and decreased endothelial nitric oxide synthase, together with decreased leptin receptor and increased suppressor of cytokine signaling 3 expressions.

Conclusions

Altered pulmonary vascular reactivity in hypertension may be related to a loss of endothelial buffering of vasoconstriction and decreased leptin-induced vasodilation in conditions of increased endothelin-1.

Leptin-induced endothelial dysfunction is mediated by sympathetic nervous system activity

BACKGROUND

The adipocyte-derived hormone leptin is elevated in obesity and may contribute to vascular risk associated with obesity. The mechanism(s) by which leptin affects vascular disease is unclear, although leptin has been shown to increase sympathetic activity. The aim of this study was to investigate the effect of leptin treatment on endothelial function and the role of the local sympathetic nervous system in mediating these effects.

METHODS AND RESULTS

Recombinant leptin was administered to C57BL6/J mice every other day for 1 week. Mesenteric arteriole myography revealed that leptin treatment caused significant impairment of endothelium-dependent vasorelaxation. Although leptin alone did not raise aortic blood pressure, leptin treatment augmented the blood pressure response to angiotensin II. The effects of leptin on mesenteric arteriolar function and aortic blood pressure response to angiotensin II were neutralized following sympathetic denervation to the mesenteric vasculature. The superoxide scavenger TEMPOL was also effective in preventing the effects of leptin on endothelial dysfunction.

CONCLUSIONS

Leptin causes endothelial dysfunction and enhances the effects of angiotensin II on blood pressure. These effects of leptin are mediated by sympathetic nervous system activation and superoxide and may contribute to vascular stiffness and hypertension in obesity.

Higher leptin is associated with hypertension: the Multi-Ethnic Study of Atherosclerosis

Adipokines are secreted from adipose tissue, influence energy homeostasis and may contribute to the association between obesity and hypertension. Among 1897 participants enrolled in the Multi-Ethnic Study of Atherosclerosis, we examined associations between blood pressure and leptin, tumor necrosis factor-α (TNFα), resistin and total adiponectin. The mean age and body mass index (BMI) was 64.7 years and 28.1, respectively, and 50% were female. After adjustment for risk factors, a 1-s.d.-increment higher leptin level was significantly associated with higher systolic (5.0 mm Hg), diastolic (1.9), mean arterial (2.8) and pulse pressures (3.6), as well as a 34% higher odds for being hypertensive (P<0.01 for all). These associations were not materially different when the other adipokines, as well as BMI, waist circumference or waist-to-hip ratio, were additionally added to the model. Notably, the associations between leptin and hypertension were stronger in men, but were not different by race/ethnic group, BMI or smoking status. Adiponectin, resistin and TNFα were not independently associated with blood pressure or hypertension. Higher serum leptin, but not adiponectin, resistin or TNFα, is associated with higher levels of all measures of blood pressure, as well as a higher odds of hypertension, independent of risk factors, anthropometric measures and other selected adipokines.

Leptin and the regulation of endothelial function in physiological and pathological conditions

Obesity and the accompanying metabolic syndrome are among the most important causes of cardiovascular pathologies associated with endothelial dysfunction, such as arterial hypertension and atherosclerosis. This detrimental effect of obesity is mediated, in part, by excessive production of the adipose tissue hormone leptin. Under physiological conditions leptin induces endothelium-dependent vasorelaxation by stimulating nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF). Leptin activates endothelial NO synthase (eNOS) through a mechanism involving AMP-activated protein kinase (AMPK) and protein kinase B/Akt, which phosphorylates eNOS at Ser(1177) , increasing its activity. Under pathological conditions, such as obesity and metabolic syndrome, the NO-mediated vasodilatory effect of leptin is impaired. Resistance to the acute NO-mimetic effect of leptin is accounted for by chronic hyperleptinaemia and may result from different mechanisms, such as downregulation of leptin receptors, increased levels of circulating C-reactive protein, oxidative stress and overexpression of suppressor of cytokine signalling-3. In short-lasting obesity, impaired leptin-induced NO production is compensated by EDHF; however, in advanced metabolic syndrome, the contribution of EDHF to the haemodynamic effect of leptin becomes inefficient. Resistance to the vasodilatory effects of leptin may contribute to the development of arterial hypertension owing to unopposed stimulation of the sympathetic nervous system by this hormone.

Leptin and Nitric Oxide Production in Normotensive and Hypertensive Men

OBJECTIVE

Recent findings have shown that leptin, the product of the obesity gene, may actively participate in the regulation of blood pressure and other cardiovascular functions through the nitric oxide (NO)-dependent mechanism.

RESEARCH METHODS AND PROCEDURES

In this study, to test the hypothesis that leptin regulation of NO metabolism is impaired in hypertension, we examined the possible relationship between circulating leptin and plasma NO metabolite level in normotensive (NT) and hypertensive (HT) men.

RESULTS

There were significant correlations between circulating leptin and BMI in both the NT and HT groups (NT: r = 0.64, n = 26, p < 0.01; HT: r = 0.59, n = 22, p < 0.01). The concentration of circulating leptin was similar between the NT and HT men, although the plasma NO metabolite level (nitrite and nitrate) was significantly reduced in the HT men compared with the NT men (NT: 51.0 +/- 4.9 microM, n = 26; HT: 37.1 +/- 2.5 microM, n = 22, p < 0.05). The circulating leptin was significantly correlated with the plasma NO metabolite level in the overall analysis of the NT and HT men (r = 0.35, n = 48, p < 0.05). When the analysis of the correlation for the NT and HT men was performed separately, there was a significant correlation between circulating leptin and plasma NO metabolites in the NT men (r = 0.45, n = 26, p < 0.05) but not in the HT men (r = 0.15, n = 22). The results of this study are consistent with the hypothesis that leptin-related metabolism of NO might be altered in HT men.

Effects of Chronic Nitric Oxide Inhibition on the Renal Excretory Response to Leptin

OBJECTIVE

Previous investigations have demonstrated that leptin promotes natriuresis with a renal tubular effect. However, the mechanisms involved in this response are unclear. The present study was designed to examine the hypothesis that the natriuretic response to leptin in normotensive Sprague-Dawley rats is regulated by nitric oxide (NO).

RESEARCH METHODS AND PROCEDURES

The hemodynamic and renal excretory effects of intravenous bolus administration of pharmacological doses of synthetic murine leptin were examined in groups of control Sprague-Dawley rats (n = 8), Sprague-Dawley rats treated for 4 days with the NO synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) (n = 8), and Sprague-Dawley rats treated for 4 days with L-NAME followed by acute treatment with sodium nitroprusside (n = 8).

RESULTS

In the control group (n = 8), an intravenous bolus of leptin, 400 microg/kg body weight, increased urinary sodium excretion 4- to 6-fold. In the Sprague-Dawley rats chronically administered l-NAME (n = 8), an intravenous bolus of 400 microg/kg of leptin did not increase sodium excretion. Acute sodium nitroprusside infusion to Sprague-Dawley rats chronically treated with L-NAME (n = 8) was associated with partial restoration of the sodium excretory response to leptin administration.

DISCUSSION

Collectively, these results are interpreted to suggest that the natriuretic and diuretic responses to leptin observed in the Sprague-Dawley rat require a functional NO system.

Neuroprotection by leptin in a rat model of permanent cerebral ischemia: effects on STAT3 phosphorylation in discrete cells of the brain

In addition to its effects in the hypothalamus to control body weight, leptin is involved in the regulation of neuronal function, development and survival. Recent findings have highlighted the neuroprotective effects of leptin against ischemic brain injury; however, to date, little is known about the role performed by the signal transducer and activator of transcription (STAT)-3, a major mediator of leptin receptor transduction pathway in the brain, in the beneficial effects of the hormone. Our data demonstrate that systemic acute administration of leptin produces neuroprotection in rats subjected to permanent middle cerebral artery occlusion (MCAo), as revealed by a significant reduction of the brain infarct volume and neurological deficit up to 7 days after the induction of ischemia. By combining a subcellular fractionation approach with immunohistofluorescence, we observe that neuroprotection is associated with a cell type-specific modulation of STAT3 phosphorylation in the ischemic cortex. The early enhancement of nuclear phospho-STAT3 induced by leptin in the astrocytes of the ischemic penumbra may contribute to a beneficial effect of these cells on the evolution of tissue damage. In addition, the elevation of phospho-STAT3 induced by leptin in the neurons after 24 h MCAo is associated with an increased expression of tissue inhibitor of matrix metalloproteinases-1 in the cortex, suggesting its possible involvement to the neuroprotection produced by the adipokine.

Leptin promotes melanoma tumor growth in mice related to increasing circulating endothelial progenitor cells numbers and plasma NO production

Background

Epidemiological studies propose that obesity increases the risk of several cancers, including melanoma. Obesity increases the expression of leptin, a multifunctional peptide produced predominantly by adipocytes which may promote tumor growth. Several recently experiments have suggested that the tumors growth is in need of endothelial progenitor cell (EPC) dependent generation of new blood vessels.

Our objectives in the present study were to examine the effects of leptin on melanoma growth, circulating EPCs number and plasma levels of nitric oxide metabolites (NOx).

Methods

2 × 10⁶ B16F10 melanoma cells were injected to thirty two C57BL6 mice subcutaneously. The mice were randomly divided into 4 groups (n = 8) in 8th day. Two groups were received twice daily intraperitoneal(i.p) injections of either PBS or recombinant murine leptin (1 μg/g initial body weight). Two groups were received i.p. injections of either 9F8 an anti leptin receptor antibody or the control mouse IgG at 50 μg/mouse every 3 consecutive days. By the end of the second week the animals were euthanized and blood samples and tumors were analyzed.

Results

The tumor weight, EPC numbers and NOx level in leptin, PBS, 9F8, and IgG group were (3.2 ± 0.6, 1.7 ± 0.3, 1.61 ± 0.2,1.7 ± 0.3 g), (222.66 ± 36.5, 133.33 ± 171, 23.33 ± 18, 132.66 ± 27.26/ml of blood), and (22.47 ± 5.5, 12.30 ± 1.5, 6.26 ± 0.84, 15.75 ± 6.3 μmol/L) respectively. Tumors weight and size, circulating EPC numbers and plasma levels of NOx were significantly more in the leptin than 9f8 and both control groups (p < 0.05). The plasma concentration of NOx significantly decreased in 9f8 treated mice compare to control group (p < 0.05).

Conclusions

In conclusion, our observations indicate that leptin causes melanoma growth likely through increased NO production and circulating EPC numbers and consequently vasculogenesis.

Role of leptin in delayed embryonic development in the Indian short-nosed fruit bat, Cynopterus sphinx

An adiposity-associated rise in leptin occurs at the time of delayed embryonic development in Cynopterus sphinx. The aim of present study was to examine the mechanism by which leptin may inhibit progesterone, and therefore could be responsible for delayed development. The study showed a significant increase in circulating leptin level during the period of increased fat accumulation, which coincided with significant decrease in serum progesterone level and delayed embryonic development in C. sphinx. The study showed increased Ob-R expression in the corpus luteum and in the utero-embryonic unit during the period of delayed embryonic development. The in vitro study showed suppressive effect of leptin on progesterone synthesis. The effect of high dose of leptin on ovarian steroidogenesis was found to be mediated through decreased expression of StAR and LH-R proteins in the ovary. The treatment with leptin caused increased expression of STAT 3 and iNOS proteins in the ovary, which correlated with decreased expression of StAR protein in the ovary. The inhibitory effects of leptin on progesterone synthesis in the ovary are thus mediated through STAT 3 and iNOS-NO signaling pathways. This study further demonstrated low expression of PCNA coinciding with the increased concentration of the leptin receptor in the utero-embryonic unit and high circulating leptin level during November. In conclusion, adiposity associated increased leptin level during November-December might play role in suppressing progesterone synthesis in the corpus luteum as well as suppressing the rate of cell-proliferation in the utero-embryonic unit thereby causing delayed embryonic development in C. sphinx.

Leptin regulates ACE activity in mice

Leptin is a hormone related to metabolism. It also influences blood pressure, but the mechanisms triggered in this process are not yet elucidated. Angiotensin-I converting enzyme (ACE) regulates cardiovascular functions and recently has been associated with metabolism control and obesity. Here, we used ob/ob mice, a model lacking leptin, to answer the question whether ACE and leptin could interact to influence blood pressure, thereby linking the renin-angiotensin system and obesity. These mice are obese and diabetic but have normal 24 h mean arterial pressure. Our results show that plasma and lung ACE activities as well as ACE mRNA expression were significantly decreased in ob/ob mice. In agreement with these findings, the hypotensive effect produced by enalapril administration was attenuated in the obese mice. Plasma renin, angiotensinogen, angiotensin I, bradykinin, and angiotensin 1-7 were increased, whereas plasma angiotensin II concentration was unchanged in obese mice. Chronic infusion of leptin increased renin activity and angiotensin II concentration in both groups and increased ACE activity in ob/ob mice. Acute leptin infusion restored ACE activity in leptin-deficient mice. Moreover, the effect of an ACE inhibitor on blood pressure was not changed in ob/+ mice during leptin treatment but increased four times in obese mice. In summary, our findings show that the renin-angiotensin system is altered in ob/ob mice, with markedly reduced ACE activity, which suggests a possible connection between the renin-angiotensin system and leptin. These results point to an important interplay between the angiotensinergic and the leptinergic systems, which may play a role in the pathogenesis of obesity, hypertension, and metabolic syndrome.

Leptin reduces plasma ANP level via nitric oxide-dependent mechanism

Leptin is a circulating adipocyte-derived hormone that influences blood pressure (BP) and metabolism. This study was designed to define the possible role of leptin in regulation of the atrial natriuretic peptide (ANP) system using acute and chronic experiments. Intravenous infusion of rat leptin (250 μg/kg injection plus 2 μg·kg−1·min−1 for 20 min) into Sprague-Dawley rats increased BP by 25 mmHg and decreased plasma level of ANP from 80.3 ± 3.45 to 51.8 ± 3.3 pg/ml. Reserpinization attenuated the rise in BP, but not the reduction of plasma ANP during leptin infusion. Nω-nitro-l-arginine methyl ester prevented the effects of leptin on the reduction of ANP level. In hyperleptinemic rats that received adenovirus containing rat leptin cDNA (AdCMV-leptin), BP increased during first 2 days and then recovered to control value. Plasma concentration of ANP and expression of ANP mRNA, but not of atrial ANP, in hyperleptinemic rats were lower than in the control groups on the first and second week after administration of AdCMV-leptin. These effects were not observed by the pretreatment with Nω-nitro-l-arginine methyl ester. No differences in renal function and ANP receptor density in the kidney were found between hyperleptinemic and control rats. Basal ANP secretion and isoproterenol-induced suppression of ANP secretion from isolated, perfused atria of hyperleptinemic rats were not different from those of other control groups. These data suggest that leptin inhibits ANP secretion indirectly through nitric oxide without changing basal or isoproterenol-induced ANP secretion.

Leptin-stimulated endothelial nitric-oxide synthase via an adenosine 5'-monophosphate-activated protein kinase/Akt signaling pathway is attenuated by interaction with C-reactive protein

The AMP-activated protein kinase (AMPK) lies upstream of Akt in the pathway leading to endothelial NO synthase (eNOS) activation. Whether leptin promotes eNOS activation via AMPK-dependent activation of Akt, and which of the two AMPKalpha catalytic subunits is involved, remains unknown. Leptin resistance may be partly attributed to interaction between leptin and C-reactive protein (CRP). We hypothesized that leptin effect on eNOS activation in human aortic endothelial cells might be blunted by direct interaction with human recombinant CRP. Small interfering RNAs (siRNAs) were used to knock down expression of alpha1- or alpha2-AMPK in transient transfection assay to evaluate which is involved in this pathway and whether leptin effect on eNOS activation in human aortic endothelial cells might be blunted by direct interaction with human CRP. siRNA-mediated down-regulation of AMPKalpha1, but not AMPKalpha2, abolished leptin-induced Akt-Ser(473) phosphorylation, eNOS-Ser(1177) phosphorylation, eNOS activation, and cGMP accumulation. By contrast, siRNA-mediated knockdown of Akt1 did not affect AMPKalpha1 phosphorylation, but it abolished leptin-induced phosphorylation of Akt-Ser(473) and eNOS-Ser(1177), suggesting that Akt functions downstream of AMPKalpha1. Preincubation of leptin with human recombinant CRP impaired leptin-induced AMPK activation, eNOS-Ser(1177) phosphorylation, eNOS activity, and intracellular cGMP accumulation. The data are consistent with a model implicating an AMPKalpha1-->Akt-->eNOS pathway leading to NO production in response to leptin supporting the idea that interaction between leptin and CRP may have a role in impairing leptin effect on eNOS activation, suggesting a link between leptin resistance, low-grade inflammation, and endothelial dysfunction.

Leptin and its metabolic interactions: an update

Obesity results from an abnormal accumulation of fat in the white adipose tissue. Recent research utilizing genetic models of obesity in rodents has implicated a major role of leptin as a controller of obesity. Leptin is a 167-amino acid peptide hormone encoded by the obesity gene (ob), which is secreted by adipocytes and plays an important role in regulating food intake, energy expenditure and adiposity. Leptin receptors (OB-R) are expressed in the central nervous system mainly in afferent satiety centres of hypothalamus and in peripheral organs such as adipose tissues, skeletal muscles, pancreatic beta-cells and liver, thus indicating the autocrine and paracrine role of leptin in energy regulation. In human beings, a highly organized circadian pattern of leptin secretion is observed with peak levels in the midnight probably resulting from cumulative hyperinsulinemia of entire day. Leptin has a dual role in weight maintenance. Leptin reflects total body adipose tissue mass whereas in conditions of negative and positive energy balance, the dynamic changes in plasma leptin concentration function as a sensor of energy balance and influence the efferent energy regulation pathways. Many effects of leptin on metabolism are mediated by interaction with Insulin and also by synergistic action with cholecystokinin. Besides physiological roles, leptin may influence pathological conditions like obesity-associated atherosclerosis, oxidative stress and cancers. The purpose of the present review is to summarize the important aspects of the biology, actions, and regulation of leptin and to serve as an update of new information.

Metabolic and hemodynamic markers of endothelial dysfunction in patients with hypertension and patients with type 2 diabetes during the cold pressor test

Leptin, a 167-amino acid peptidic hormone secreted by adipose tissue, acts mainly in the arcuate hypothalamus nucleus as a satiety signal, but given its closed connections with inflammatory and endothelial systems, a probable regulatory role in blood pressure (BP) control by interaction with nitric oxide (NO) and C-reactive protein (CRP) has also been described. The cold pressor test (CPT) is a simple test that indirectly determines endothelial dysfunction. In this work, biochemical indicators (CRP, leptin, and NO) and hemodynamic indicators (systolic and diastolic BP) were performed and evaluated in patients with hypertension, patients with type 2, and control subjects during a single CPT for assessment of endothelial dysfunction. A total of 43 subjects aged 25 to 60 years were divided into three groups: 15 healthy volunteers, 13 patients with hypertension, and 15 patients with type 2 diabetes were included in the study. A complete clinical history was obtained from each subject and a complete physical examination, including an electrocardiogram, was carried out. During the 30-minute assay, 0.9% saline solution was infused intravenously. CPT was performed to assess the cardiovascular reactivity at 15 minutes. The cardiovascular variables (systolic and diastolic BP) were measured at 0, 16, and 30 minutes. In addition, serum variables were extracted at the beginning and at the end of the experiment and statistical analysis was performed. CPT caused in all subjects a significant increase in BP and pulse. There were no significant differences in CRP or leptin in all groups, although we observed significant differences for NO (P < 0.05). Sensibility and specificity for all biochemical variables resulted in nonsignificant statistical or clinical importance as markers of endothelial dysfunction; however, a positive association was found when leptin and NO were evaluated together (sensibility, 0.2; specificity, 0.8). CRP, leptin, and NO did not show any direct or significant association with the hemodynamic variables in this study, although a relationship was observed in NO according to group and among biochemical variables when studied together.

Leptin-induced endothelial dysfunction in obesity

Hyperleptinemia accompanying obesity affects endothelial nitric oxide (NO) and is a serious factor for vascular disorders. NO, superoxide (O(2)(-)), and peroxynitrite (ONOO(-)) nanosensors were placed near the surface (5+/-2 microm) of a single human umbilical vein endothelial cell (HUVEC) exposed to leptin or aortic endothelium of obese C57BL/6J mice, and concentrations of calcium ionophore (CaI)-stimulated NO, O(2)(-), ONOO(-) were recorded. Endothelial NO synthase (eNOS) expression and L-arginine concentrations in HUVEC and aortic endothelium were measured. Leptin did not directly stimulate NO, O(2)(-), or ONOO(-) release from HUVEC. However, a 12-h exposure of HUVEC to leptin increased eNOS expression and CaI-stimulated NO (625+/-30 vs. 500+/-24 nmol/l control) and dramatically increased cytotoxic O(2)(-) and ONOO(-) levels. The [NO]-to-[ONOO(-)] ratio ([NO]/[ONOO(-)]) decreased from 2.0+/-0.1 in normal to 1.30+/-0.1 in leptin-induced dysfunctional endothelium. In obese mice, a 2.5-fold increase in leptin concentration coincided with 100% increase in eNOS and about 30% decrease in intracellular L-arginine. The increased eNOS expression and a reduced l-arginine content led to eNOS uncoupling, a reduction in bioavailable NO (250+/-10 vs. 420+/-12 nmol/l control), and an elevated concentration of O(2)(-) (240%) and ONOO(-) (70%). L-Arginine and sepiapterin supplementation reversed eNOS uncoupling and partially restored [NO]/[ONOO(-)] balance in obese mice. In obesity, leptin increases eNOS expression and decreases intracellular l-arginine, resulting in eNOS an uncoupling and depletion of endothelial NO and an increase of cytotoxic ONOO(-). Hyperleptinemia triggers an endothelial NO/ONOO(-) imbalance characteristic of dysfunctional endothelium observed in other vascular disorders, i.e., atherosclerosis and diabetes.

Leptin-induced endothelial dysfunction in obesity

Hyperleptinemia accompanying obesity affects endothelial nitric oxide (NO) and is a serious factor for vascular disorders. NO, superoxide (O(2)(-)), and peroxynitrite (ONOO(-)) nanosensors were placed near the surface (5+/-2 microm) of a single human umbilical vein endothelial cell (HUVEC) exposed to leptin or aortic endothelium of obese C57BL/6J mice, and concentrations of calcium ionophore (CaI)-stimulated NO, O(2)(-), ONOO(-) were recorded. Endothelial NO synthase (eNOS) expression and L-arginine concentrations in HUVEC and aortic endothelium were measured. Leptin did not directly stimulate NO, O(2)(-), or ONOO(-) release from HUVEC. However, a 12-h exposure of HUVEC to leptin increased eNOS expression and CaI-stimulated NO (625+/-30 vs. 500+/-24 nmol/l control) and dramatically increased cytotoxic O(2)(-) and ONOO(-) levels. The [NO]-to-[ONOO(-)] ratio ([NO]/[ONOO(-)]) decreased from 2.0+/-0.1 in normal to 1.30+/-0.1 in leptin-induced dysfunctional endothelium. In obese mice, a 2.5-fold increase in leptin concentration coincided with 100% increase in eNOS and about 30% decrease in intracellular L-arginine. The increased eNOS expression and a reduced l-arginine content led to eNOS uncoupling, a reduction in bioavailable NO (250+/-10 vs. 420+/-12 nmol/l control), and an elevated concentration of O(2)(-) (240%) and ONOO(-) (70%). L-Arginine and sepiapterin supplementation reversed eNOS uncoupling and partially restored [NO]/[ONOO(-)] balance in obese mice. In obesity, leptin increases eNOS expression and decreases intracellular l-arginine, resulting in eNOS an uncoupling and depletion of endothelial NO and an increase of cytotoxic ONOO(-). Hyperleptinemia triggers an endothelial NO/ONOO(-) imbalance characteristic of dysfunctional endothelium observed in other vascular disorders, i.e., atherosclerosis and diabetes.

Role of leptin in reverse epidemiology in chronic kidney disease

Leptin is mainly produced by adipocytes and metabolized in the kidney. Leptin is taken up into the central nervous system by a saturable transport system, and controls appetite in rodents and in healthy subjects. Leptin acts on peripheral tissue and increases the inflammatory response by stimulating the production of tumor necrosis factor alpha, interleukin-6 and interleukin-12. In healthy humans, serum leptin concentration is related to the size of adipose tissue mass in the body. The majority of obese subjects have inappropriately high levels of circulating plasma leptin concentrations, indicating leptin resistance. In healthy subjects increased leptin concentration constitutes a biomarker for increased cardiovascular risk. On the other hand, a recent prospective long-term study in patients with chronic kidney disease stage 5 on hemodialysis therapy showed that reduced serum leptin concentration is an independent risk factor for mortality in these patients.

Low serum leptin predicts mortality in patients with chronic kidney disease stage 5

OBJECTIVE

Leptin, secreted from adipose tissue, regulates food intake, energy expenditure, and immune function. It is unknown whether leptin predicts mortality in patients with chronic kidney disease stage 5 on hemodialysis therapy.

RESEARCH METHODS AND PROCEDURES

We performed a prospective cohort study of 71 patients with chronic kidney disease stage 5 in an outpatient hemodialysis center. Subjects were recruited in June 1998 and followed for 83 months. Survival was compared by the Kaplan-Meier method.

RESULTS

After 83 months of follow-up, 48 patients (68%) had died. Serum leptin concentrations at study entry were lower among all deceased patients compared with those patients who survived (5.2 +/- 9.0 microg/L; n = 48; vs. 7.7 +/- 7.8 microg/L; n = 23; p = 0.005). Baseline serum leptin concentrations were significantly lower in patients who died from cardiovascular diseases (4.7 +/- 9.4 microg/L, n = 32) or infections (4.0 +/- 2.7 microg/L; n = 10; each p < 0.05), but not cancer (9.4 +/- 7.9 microg/L; n = 6), than in survivors (7.7 +/- 7.8 microg/L; n = 23; p = 0.003). The relative risk for mortality in patients with serum leptin concentrations below the median (<2.6 microg/L) compared with patients above the median was 1.96 (95% confidence interval, 1.01 to 3.79; p = 0.04). Survival was shorter in patients with leptin concentrations below the median compared with those whose leptin concentrations were above the median (all-cause mortality, chi(2) = 5.05; p = 0.02).

DISCUSSION

Low serum leptin concentration is an independent predictor of mortality in patients with chronic kidney disease stage 5 on hemodialysis therapy.

The Sir David Cuthbertson Medal Lecture. Hunting for new pieces to the complex puzzle of obesity

Disentangling the neuroendocrine systems that regulate energy homeostasis and adiposity has been a long-standing challenge in pathophysiology, with obesity being an increasingly important public health problem. Adipose tissue is no longer considered a passive bystander in body-weight regulation. It actively secretes a large number of hormones, growth factors, enzymes, cytokines, complement factors and matrix proteins, at the same time as expressing receptors for most of these elements, which influence fuel storage, mobilisation and utilisation at both central and peripheral sites. Thus, an extensive cross talk at a local and systemic level in response to specific external stimuli or metabolic changes underpins the multifunctional characteristics of adipose tissue. In addition to the already-known adipokines, such as IL, TNFalpha, leptin, resistin and adiponectin, more recently attention has been devoted to 'newcomers' to the 'adipose tissue arena', which include aquaporin, caveolin, visfatin, serum amyloid A and vascular endothelial growth factor. While in vitro and in vivo experiments have provided extremely valuable information, the advances in genomics, proteomics and metabolomics are offering a level of information not previously attainable to help unlock the molecular basis of obesity. The potential and power of combining pathophysiological observations with the wealth of information provided by the human genome, knock-out models, transgenesis, DNA microarrays, RNA silencing and other emerging technologies offer a new and unprecedented view of a complex disease, conferring novel insights into old questions by identifying new pieces to the unfinished jigsaw puzzle of obesity.

Leptin and hypertension in obesity

Leptin, a peptide discovered more than 10 years ago, decreases food intake and increases sympathetic nerve activity to both thermogenic and non-thermogenic tissue. Leptin was initially believed to be an anti-obesity hormone, owing to its metabolic effects. However, obese individuals, for unknown reasons, become resistant to the satiety and weight-reducing effect of the hormone, but preserve leptin-mediated sympathetic activation to non-thermogenic tissue such as kidney, heart, and adrenal glands. Leptin has been shown to influence nitric oxide production and natriuresis, and along with chronic sympathetic activation, especially to the kidney, it may lead to sodium retention, systemic vasoconstriction, and blood pressure elevation. Consequently, leptin is currently considered to play an important role in the development of hypertension in obesity.

The inhibitory effect of leptin on angiotensin II-induced vasoconstriction in vascular smooth muscle cells is mediated via a nitric oxide-dependent mechanism

Leptin inhibits the contractile response induced by angiotensin (Ang) II in vascular smooth muscle cells (VSMCs) of the aorta. We studied in vitro and ex vivo the role of nitric oxide (NO) in the effect of leptin on the Ang II-induced vasoconstriction of the aorta of 10-wk-old Wistar rats. NO and nitric oxide synthase (NOS) activity were assessed by the Griess and (3)H-arginine/citrulline conversion assays, respectively. Stimulation of inducible NOS (iNOS) as well as Janus kinases/signal transducers and activators of transcription (JAK/STAT) and phosphoinositide 3-kinase (PI3K)/Akt signaling pathways were determined by Western blot. The contractile responses to Ang II were evaluated in endothelium-denuded aortic rings using the organ bath system. Changes in intracellular Ca(2+) were measured in VSMCs using fura-2 fluorescence. Leptin significantly (P < or = 0.01) stimulated NO release and NOS activity in VSMCs. Leptin's effect on NO was abolished by the NOS inhibitor, N(G)-monomethyl l-arginine, or the iNOS selective inhibitor L-N(6)-(1-iminoethyl)-lysine. Accordingly, leptin increased iNOS protein expression, with a comparable time course with that of NO production and NOS activity. Leptin also significantly increased STAT3 (P < or = 0.01) and Akt (P < or = 0.001) phosphorylation. Moreover, either the JAK2 inhibitor, AG490, or the PI3K inhibitor, wortmannin, significantly (P < or = 0.05) abrogated the leptin-induced increase in iNOS protein. Finally, both N(G)-monomethyl L-arginine and L-N(6)-(1-iminoethyl)-lysine inhibitors completely blunted (P < or = 0.001) the leptin-mediated inhibition of the Ang II-induced VSMC activation and vasoconstriction. These findings suggest that the endothelium-independent depressor action of leptin is mediated by an increase of NO bioavailability in VSMCs. This process requires the up-regulation of iNOS through mechanisms involving JAK2/STAT3 and PI3K/Akt pathways.

Plasma Leptin and its Relationship with Lipid Peroxidation and Nitric Oxide in Obese Female Patients with or without Hypertension

BACKGROUND

Recent evidence suggested that leptin-induced oxidative stress in human endothelial cells in vivo and increased oxidative stress in human essential hypertension may further contribute to both the development of atherosclerosis and other cardiovascular diseases. We investigated the association of plasma leptin levels with plasma lipid peroxidation and nitric oxide metabolites (NOx) in obese hypertensive atherosclerosis model.

METHODS

Plasma leptin, lipid peroxidation and NOx levels were determined in age-matched non-obese normotensive female subjects (n = 30), obese normotensive female subjects (n = 45), and obese hypertensive female subjects (n = 50). Plasma leptin levels were determined by immunoradiometric method. Lipid peroxidation was determined as thiobarbituric acid reactive substances (TBARS) using spectrophotometric method. NOx levels were determined using enzymatic method.

RESULTS

We found that plasma leptin and TBARS levels were increased in obesity, and obese hypertensives have significantly higher plasma leptin and TBARS levels than obese normotensives (p <0.001 and p <0.001). Obese hypertensives have significantly lower plasma NOx levels than obese normotensives (p <0.001). In univariate and multivariate regression analysis, plasma leptin levels were significantly correlated with TBARS (p <0.01 and p <0.01) in obese subjects. Plasma TBARS were also inversely correlated with NOx in hypertensive obese subjects (r = -0.412, p <0.01).

CONCLUSIONS

Our results have shown that elevated leptin levels may be associated with increased oxidative stress and free-radical-induced decreased NOx levels. Therefore, hyperleptinemia may be an important contributor to the generation of hypertension in obesity.

Role of leptin in blood pressure regulation and arterial hypertension

Leptin is a 16-kDa protein secreted by white adipose tissue that is primarily involved in the regulation of food intake and energy expenditure. Plasma leptin concentration is proportional to the amount of adipose tissue and is markedly increased in obese individuals. Recent studies suggest that leptin is involved in cardiovascular complications of obesity, including arterial hypertension. Acutely administered leptin has no effect on blood pressure, probably because it concomitantly stimulates the sympathetic nervous system and counteracting depressor mechanisms such as natriuresis and nitric oxide (NO)-dependent vasorelaxation. By contrast, chronic hyperleptinemia increases blood pressure because these acute depressor effects are impaired and/or additional sympathetic nervous system-independent pressor effects appear, such as oxidative stress, NO deficiency, enhanced renal Na reabsorption and overproduction of endothelin. Although the cause-effect relationship between leptin and high blood pressure in humans has not been demonstrated directly, many clinical studies have shown elevated plasma leptin in patients with essential hypertension and a significant positive correlation between leptin and blood pressure independent of body adiposity both in normotensive and in hypertensive individuals. In addition, leptin may contribute to end-organ damage in hypertensive individuals such as left ventricular hypertrophy, retinopathy and nephropathy, independent of regulating blood pressure. Here, current knowledge about the role of leptin in the regulation of blood pressure and in the pathogenesis of arterial hypertension is presented.

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.

Role of nitric oxide and endothelium-derived hyperpolarizing factor (EDHF) in the regulation of blood pressure by leptin in lean and obese rats

We investigated the role of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) in hemodynamic action of leptin. The effect of leptin (1 mg/kg i.p.) on systolic blood pressure (SBP) was examined in lean rats and in rats made obese by feeding highly palatable diet for either 1 or 3 months. Separate groups received NO synthase inhibitor, L-NAME, or EDHF inhibitors, the mixture of apamin+charybdotoxin or sulfaphenazole, before leptin administration. Leptin increased NO production, as evidenced by increase in plasma and urinary NO metabolites and cyclic GMP. This effect was impaired in both obese groups. In lean rats either leptin or EDHF inhibitors had no effect on blood pressure. L-NAME increased blood pressure in lean animals and this effect was prevented by leptin. However, when leptin was administered to animals pretreated with both L-NAME and EDHF inhibitors, blood pressure increased even more than after L-NAME alone. In the 1-month obese group leptin had no effect on SBP, however, pressor effect of leptin was observed in animals pretreated with EDHF inhibitors. In the 3-month obese group leptin alone increased SBP, and EDHF inhibitors did not augment its pressor effect. The results suggest that leptin may stimulate EDHF when NO becomes deficient, e.g. after NOS blockade or in short-term obesity. Although the effect of leptin on NO production is impaired in the 1-month obese group, BP does not increase, probably because EDHF compensates for NO deficiency. In contrast, leptin increases BP in 3-month obesity because its effect on EDHF is also attenuated.

Influence of intravenously administered leptin on nitric oxide production, renal hemodynamics and renal function in the rat

We investigated the effect of leptin on systemic nitric oxide (NO) production, arterial pressure, renal hemodynamics and renal excretory function in the rat. Leptin (1 mg/kg) was injected intravenously and mean arterial pressure (MAP), heart rate (HR), renal blood flow (RBF) and renal cortical blood flow (RCBF), were measured for 210 min after injection. Urine was collected for seven consecutive 30-min periods and blood samples were withdrawn at 15, 45, 75, 105, 135, 165 and 195 min after leptin administration. Leptin had no effect on MAP, HR, RBF, RCBF and creatinine clearance, but increased urine output by 37.8% (0-30 min), 32.4% (31-60 min) and 27.0% (61-90 min), as well as urinary sodium excretion by 175.8% (0-30 min), 136.4% (31-60 min) and 124.2% (61-90 min). In contrast, leptin had no effect on potassium and phosphate excretion. Plasma concentration of NO metabolites, nitrites + nitrates (NOx), increased following leptin injection at 15, 45, 75 and 105 min by 27.7%, 178.1%, 156.4% and 58.7%, respectively. Leptin increased urinary NOx excretion by 241.6% (0-30 min), 552.6% (31-60 min), 430.7% (61-90 min) and 88.9% (91-120 min). This was accompanied by increase in plasma and urinary cyclic GMP. These data indicate that leptin stimulates systemic NO production but has no effect on arterial pressure and renal hemodynamics.

Nitric Oxide Mediates Inhibitory Effect of Leptin on Insulin-Like Growth Factor I Augmentation of 17β-Estradiol Production in Human Granulosa Cells1

In the present study the authors investigated if the inhibitory effect of leptin in the ovary was mediated via nitric oxide (NO) using human granulosa cells (GCs). Human GCs were obtained from preovulatory follicles of women who underwent IVF. Reverse transcription-polymerase chain reaction (RT-PCR) demonstrated that human GCs expressed mRNA of leptin and mRNA of isoforms of leptin receptor, including one long form and two types of short forms. Exposure of human GCs to leptin at concentrations of 3-30 ng/ml for 60 min dose-dependently increased the fluorescence of 4,5-diaminofluorescein (DAF-2), an NO-sensitive dye. The effect of leptin on DAF-2 fluorescence was inhibited by pretreatment of human GCs with 100 microM nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase (NOS), indicating that the increase in DAF-2 fluorescence properly reflected the intracellular NO production. FSH (1 ng/ ml) and IGF-I (30 ng/ml) stimulated 17beta-estradiol (E2) production in human GCs, respectively. FSH plus IGF-I induced a further increase in E2 production. Leptin did not significantly alter basal or FSH-dependent E2 production, but it inhibited the effect of IGF-I on E2 production and the synergistic effect of IGF-I on FSH-stimulated E2 production. The inhibitory effect of leptin on IGF-I argumentation of E2 production was attenuated by pretreatment of human GCs with 100 microM L-NAME. In conclusion, leptin could induce NO production in human GCs. The inhibitory effect of leptin on IGF-I augmentation of E2 production in human GCs was attenuated by L-NAME, strongly suggesting that NO may mediate the action of leptin in human GCs.

Stimulatory effect of leptin on nitric oxide production is impaired in dietary-induced obesity

OBJECTIVE

We investigated the effect of leptin on nitric oxide production in lean and rats made obese by a high-calorie diet.

RESEARCH METHODS AND PROCEDURES

The animals were placed in metabolic cages, and urine was collected in 2-hour periods after leptin (1 mg/kg intraperintoneally) or vehicle administration. Blood was obtained 0.5, 1, 2, 4, or 6 hours after injection.

RESULTS

Leptin had no effect on systolic blood pressure in either lean or obese animals. Plasma concentration of NO metabolites (nitrites + nitrates, NOx) increased in lean rats by 31.5%, 58.0%, and 27.9% at 1, 2, and 4 hours after leptin injection, respectively. In the obese group, plasma NOx increased only at 2 hours (+36.5%). Leptin increased urinary NOx excretion by 31.8% in the first 2-hour period after injection in lean but not in obese rats. In lean animals, leptin elevated plasma cyclic 3',5'-guanosine monophosphate (cGMP) at 1, 2, and 4 hours by 35.3%, 96.3%, and 57.3%, respectively. In the obese group, plasma cGMP was higher only at 2 and 4 hours (+44.6% and +32.1%, respectively). Urinary excretion of cGMP increased in lean animals by 67.1% in the first period and by 50.4% in the second period. In the obese group, leptin induced a 53.9% increase in urinary cGMP excretion only in the first 2-hour period.

DISCUSSION

The stimulatory effect of leptin on NO production is impaired in dietary-induced obesity; however, leptin does not increase blood pressure in obese animals, suggesting that other NO-independent depressor mechanisms are stimulated.

Oxidative stress, nitric oxide production, and renal sodium handling in leptin-induced hypertension

Chronic hyperleptinemia induces arterial hypertension in experimental animals and may contribute to the development of hypertension in obese humans; however, the mechanism of hypertensive effect of leptin is not completely elucidated. We investigated the effect of leptin on whole-body oxidative stress, nitric oxide production, and renal sodium handling. The study was performed on male Wistar rats divided into 3 groups: 1) control, fed standard chow ad libitum, 2) leptin-treated group, receiving leptin injections (0.25 mg/kg twice daily s.c. for 7 days), 3) pair-fed group, in which food intake was adjusted to the leptin group. Leptin caused 30.5% increase in systolic blood pressure. Plasma concentration and urinary excretion of 8-isoprostanes in animals receiving leptin was 46.4% and 49.2% higher, respectively. The level of lipid peroxidation products, malonyldialdehyde + 4-hydroxyalkenals, increased by 52.5% in the renal cortex and by 48.4% in the renal medulla following leptin treatment, whereas aconitase activity decreased in these regions of the kidney by 45.3% and 39.2%, respectively. Urinary excretion of nitric oxide metabolites (NOx) was 55.0% lower, and fractional excretion of NOx was 55.8% lower in the leptin-treated group. Urinary excretion of cGMP decreased in leptin-treated rats by 26.3%. Following leptin treatment, absolute and fractional sodium excretion decreased by 35.0% and 41.2%, respectively. These results indicate that hyperleptinemia induces systemic and intrarenal oxidative stress, decreases the amount of bioactive NO possibly due to its degradation by reactive oxygen species, and causes renal sodium retention by stimulating tubular sodium reabsorption. NO deficiency and abnormal renal Na+ handling may contribute to leptin-induced hypertension.