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      Leptin Stimulated C-Reactive Protein Production by Human Coronary Artery Endothelial Cells

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          Abstract

          Background: Obesity and cardiovascular disease are closely related. Leptin, an adipocyte-produced hormone, is associated with increased cardiovascular risk. Increased plasma levels of leptin are measurable in the plasma of obese individuals. However, the possible links between obesity and cardiovascular disease are not completely understood. C-reactive protein (CRP) is a predictor of future cardiovascular events and plays a role in atherothrombotic disease. Thus, we evaluated whether leptin might play a role in cardiovascular disease, investigating its effects on CRP production by human coronary artery endothelial cells in culture. Methods and Results: Leptin induced CRP mRNA transcription as demonstrated by semiquantitative and real-time polymerase chain reaction as well as the release of CRP in the culture medium in a concentration-dependent fashion. Leptin-induced production of CRP was mediated through the RhoA activation of protein kinase Cβ since both protein kinase C and RhoA pathway inhibitors prevented these leptin effects. Lovastatin, a hydroxymethylglutaryl coenzyme A reductase inhibitor, by modulating the RhoA activation, significantly reduced leptin-induced CRP production. Conclusions: This study describes the close relationship between leptin and CRP, providing support to the view that this adipokine, besides being involved in the pathophysiology of obesity, might play a relevant role as an active partaker in obesity, inflammation and atherothrombosis.

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          Most cited references 22

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          Intracellular signalling pathways activated by leptin.

          Leptin is a versatile 16 kDa peptide hormone, with a tertiary structure resembling that of members of the long-chain helical cytokine family. It is mainly produced by adipocytes in proportion to fat size stores, and was originally thought to act only as a satiety factor. However, the ubiquitous distribution of OB-R leptin receptors in almost all tissues underlies the pleiotropism of leptin. OB-Rs belong to the class I cytokine receptor family, which is known to act through JAKs (Janus kinases) and STATs (signal transducers and activators of transcription). The OB-R gene is alternatively spliced to produce at least five isoforms. The full-length isoform, OB-Rb, contains intracellular motifs required for activation of the JAK/STAT signal transduction pathway, and is considered to be the functional receptor. Considerable evidence for systemic effects of leptin on body mass control, reproduction, angiogenesis, immunity, wound healing, bone remodelling and cardiovascular function, as well as on specific metabolic pathways, indicates that leptin operates both directly and indirectly to orchestrate complex pathophysiological processes. Consistent with leptin's pleiotropic role, its participation in and crosstalk with some of the main signalling pathways, including those involving insulin receptor substrates, phosphoinositide 3-kinase, protein kinase B, protein kinase C, extracellular-signal-regulated kinase, mitogen-activated protein kinases, phosphodiesterase, phospholipase C and nitric oxide, has been observed. The impact of leptin on several equally relevant signalling pathways extends also to Rho family GTPases in relation to the actin cytoskeleton, production of reactive oxygen species, stimulation of prostaglandins, binding to diacylglycerol kinase and catecholamine secretion, among others.
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            Leptin signaling, adiposity, and energy balance.

             ERIC JÉQUIER (2002)
            A chronic minor imbalance between energy intake and energy expenditure may lead to obesity. Both lean and obese subjects eventually reach energy balance and their body weight regulation implies that the adipose tissue mass is "sensed", leading to appropriate responses of energy intake and energy expenditure. The cloning of the ob gene and the identification of its encoded protein, leptin, have provided a system signaling the amount of adipose energy stores to the brain. Leptin, a hormone secreted by fat cells, acts in rodents via hypothalamic receptors to inhibit feeding and increase thermogenesis. A feedback regulatory loop with three distinct steps has been identified: (1) a sensor (leptin production by adipose cells) monitors the size of the adipose tissue mass; (2) hypothalamic centers receive and integrate the intensity of the leptin signal through leptin receptors (LRb); (3) effector systems, including the sympathetic nervous system, control the two main determinants of energy balance-energy intake and energy expenditure. While this feedback regulatory loop is well established in rodents, there are many unsolved questions about its applicability to body weight regulation in humans. The rate of leptin production is related to adiposity, but a large portion of the interindividual variability in plasma leptin concentration is independent of body fatness. Gender is an important factor determining plasma leptin, with women having markedly higher leptin concentrations than men for any given degree of fat mass. The ob mRNA expression is also upregulated by glucocorticoids, whereas stimulation of the sympathetic nervous system results in its inhibition. Furthermore, leptin is not a satiety factor in humans because changes in food intake do not induce short-term increases in plasma leptin levels. After its binding to LRb in the hypothalamus, leptin stimulates a specific signaling cascade that results in the inhibition of several orexigenic neuropeptides, while stimulating several anorexigenic peptides. The orexigenic neuropeptides that are downregulated by leptin are NPY (neuropeptide Y), MCH (melanin-concentrating hormone), orexins, and AGRP (agouti-related peptide). The anorexigenic neuropeptides that are upregulated by leptin are alpha-MSH (alpha-melanocyte-stimulating hormone), which acts on MC4R (melanocortin-4 receptor); CART (cocaine and amphetamine-regulated transcript); and CRH (corticotropin-releasing-hormone). Obese humans have high plasma leptin concentrations related to the size of adipose tissue, but this elevated leptin signal does not induce the expected responses (i.e., a reduction in food intake and an increase in energy expenditure). This suggests that obese humans are resistant to the effects of endogenous leptin. This resistance is also shown by the lack of effect of exogenous leptin administration to induce weight loss in obese patients. The mechanisms that may account for leptin resistance in human obesity include a limitation of the blood-brain-barrier transport system for leptin and an inhibition of the leptin signaling pathways in leptin-responsive hypothalamic neurons. During periods of energy deficit, the fall in leptin plasma levels exceeds the rate at which fat stores are decreased. Reduction of the leptin signal induces several neuroendocrine responses that tend to limit weight loss, such as hunger, food-seeking behavior, and suppression of plasma thyroid hormone levels. Conversely, it is unlikely that leptin has evolved to prevent obesity when plenty of palatable foods are available because the elevated plasma leptin levels resulting from the increased adipose tissue mass do not prevent the development of obesity. In conclusion, in humans, the leptin signaling system appears to be mainly involved in maintenance of adequate energy stores for survival during periods of energy deficit. Its role in the etiology of human obesity is only demonstrated in the very rare situations of absence of the leptin signal (mutations of the leptin gene or of the leptin receptor gene), which produces an internal perception of starvation and results in a chronic stimulation of excessive food intake.
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              Plasma leptin and the risk of cardiovascular disease in the west of Scotland coronary prevention study (WOSCOPS).

              Leptin plays a role in fat metabolism and correlates with insulin resistance and other markers of the metabolic syndrome, independent of total adiposity. Therefore, we hypothesized that raised leptin levels may identify men at increased risk of a coronary event in the West of Scotland Coronary Prevention Study (WOSCOPS). Methods and Results- Plasma leptin levels were measured at baseline in 377 men (cases) who subsequently experienced a coronary event and in 783 men (controls) who remained free of an event during the 5-year follow-up period of the study. Controls were matched to cases on the basis of age and smoking history and were representative of the entire WOSCOPS cohort. Leptin levels were significantly higher in cases than controls (5.87+/-2.04 ng/mL versus 5.04+/-2.09 ng/mL, P<0.001). In univariate analysis, for each 1 SD increase in leptin, the relative risk (RR) of an event increased by 1.25 (95% confidence interval [CI], 1.10 to 1.43; P<0.001). There was minimal change in this RR with correction for body mass index (RR, 1.24; 95% CI, 1.06 to 1.45; P=0.006) or with further correction for classic risk factors, including age, lipids, and systolic blood pressure (RR, 1.20; 95% CI, 1.02 to 1.42; P=0.03). Leptin correlated with C-reactive protein (r=0.24, P<0.001) and, even with this variable added to the model, leptin retained significance as a predictor of coronary events (RR, 1.18; 95% CI, 1.00 to 1.39; P=0.05) at the expense of C-reactive protein. We show, for the first time, in a large prospective study that leptin is a novel, independent risk factor for coronary heart disease.
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                Author and article information

                Journal
                JVR
                J Vasc Res
                10.1159/issn.1018-1172
                Journal of Vascular Research
                S. Karger AG
                1018-1172
                1423-0135
                2009
                October 2009
                30 June 2009
                : 46
                : 6
                : 609-617
                Affiliations
                Division of Cardiology, University of Naples Federico II, Naples, Italy
                Article
                226229 J Vasc Res 2009;46:609–617
                10.1159/000226229
                19571581
                © 2009 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 5, References: 38, Pages: 9
                Categories
                Research Paper

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