Regulation of fatty acid homeostasis in cells: novel role of leptin

Shedding light on the enigma of myocardial lipotoxicity: the involvement of known and putative regulators of fatty acid storage and mobilization

Excessive fatty acid (FA) uptake by cardiac myocytes is often associated with adverse changes in cardiac function. This is especially evident in diabetic individuals, where increased intramyocardial triacylglycerol (TG) resulting from the exposure to high levels of circulating FA has been proposed to be a major contributor to diabetic cardiomyopathy. At present, our knowledge of how the heart regulates FA storage in TG and the hydrolysis of this TG is limited. This review concentrates on what is known about TG turnover within the heart and how this is likely to be regulated by extrapolating results from other tissues. We also assess the evidence as to whether increased TG accumulation protects against FA-induced lipotoxicity through limiting the accumulations of ceramides and diacylglycerols versus whether it is a maladaptive response that contributes to cardiac dysfunction.

Loss of stearoyl-CoA desaturase 1 rescues cardiac function in obese leptin-deficient mice

The heart of leptin-deficient ob/ob mice is characterized by pathologic left ventricular hypertrophy along with elevated triglyceride (TG) content, increased stearoyl-CoA desaturase (SCD) activity, and increased myocyte apoptosis. In the present study, using an ob/ob;SCD1(-/-) mouse model, we tested the hypothesis that lack of SCD1 could improve steatosis and left ventricle (LV) function in leptin deficiency. We show that disruption of the SCD1 gene improves cardiac function in ob/ob mice by correcting systolic and diastolic dysfunction without affecting levels of plasma TG and FFA. The improvement is associated with reduced expression of genes involved in FA transport and lipid synthesis in the heart, as well as reduction in cardiac FFA, diacylglycerol, TG, and ceramide levels. The rate of FA beta-oxidation is also significantly lower in the heart of ob/ob;SCD1(-/-) mice compared with ob/ob controls. Moreover, SCD1 deficiency reduces cardiac apoptosis in ob/ob mice due to increased expression of antiapoptotic factor Bcl-2 and inhibition of inducible nitric oxide synthase and caspase-3 activities. Reduction in myocardial lipid accumulation and inhibition of apoptosis appear to be one of the main mechanisms responsible for improved LV function in ob/ob mice caused by SCD1 deficiency.

How much do we really know about our favorite cosmeceutical ingredients?

To date, we are unaware of a review that has investigated common cosmeceutical ingredients in order to answer the three specific questions proposed by the father of cosmeceuticals, Dr. Albert Kligman. It is the goal of this review to gather all the published scientific data on five common cosmeceutical ingredients, answer the three major questions about the scientific rationale for their use, and ascertain how much we really know about consumers' favorite cosmeceutical ingredients.Most of the research concerning cosmeceutical retinoid ingredients is based upon the effects of retinoic acid on the skin. Clinical trials concerning retinol and retinaldehyde are scant and lacking in statistical evaluation for significance. There is research substantiating the effects of kinetin in plants and also in-vitro antioxidant effects. However, proof of anti-aging activity remains elusive, and the clinical efficacy of kinetin is based on limited data. Niacinamide is the ingredient investigated that most closely upholds the "Kligman standards" of cosmeceutical-ingredient analysis. With the available scientific evidence on topical niacinamide, clinicians are able to adequately answer questions about permeability, mechanism, and clinical effect. Both green tea and soy have been popularized commercially based on their antioxidant effects, yet there is a paucity of clinical studies concerning their efficacy as topical anti-aging agents. It may be that soy and green tea are better at preventing the signs and symptoms of skin aging than actually reversing them. Since cosmeceutical products are claiming to therapeutically affect the structure and function of the skin, it is rational and necessary to hold them to specified scientific standards that substantiate efficacy claims.

Diabetes and apoptosis: lipotoxicity

Obesity is an established risk factor in the pathogenesis of insulin resistance, type 2 diabetes mellitus and cardiovascular disease; all components that are part of the metabolic syndrome. Traditionally, insulin resistance has been defined in a glucocentric perspective. However, elevated systemic levels of fatty acids are now considered significant contributors towards the pathophysiological aspects associated with the syndrome. An overaccumulation of unoxidized long-chain fatty acids can saturate the storage capacity of adipose tissue, resulting in a lipid 'spill over' to non-adipose tissues, such as the liver, muscle, heart, and pancreatic-islets. Under these circumstances, such ectopic lipid deposition can have deleterious effects. The excess lipids are driven into alternative non-oxidative pathways, which result in the formation of reactive lipid moieties that promote metabolically relevant cellular dysfunction (lipotoxicity) and programmed cell-death (lipoapoptosis). Here, we focus on how both of these processes affect metabolically significant cell-types and highlight how lipotoxicity and sequential lipoapoptosis are as major mediators of insulin resistance, diabetes and cardiovascular disease.

Sterol regulatory element-binding protein-1c knockdown protected INS-1E cells from lipotoxicity

OBJECTIVE

The reduction in insulin secretory capacity and beta-cell mass has been attributed, at least partially, to lipotoxicity, which may contribute to the development of type 2 diabetes. Chronic free fatty acids (FFA) exposure impairs pancreatic beta-cell function and induces beta-cell apoptosis. This study is to elucidate the underlying molecular mechanisms.

RESEARCH DESIGN AND METHODS

We exposed INS-1E pancreatic beta-cell line to palmitate or oleate, and measured the glucose stimulated insulin secretion (GSIS). The effect of FFA on sterol regulatory element-binding protein (SREBP)-1c lipogenic pathway, and expression of genes involved in beta-cell functions, including AMPK (AMP-activated protein kinase), UCP-2 (uncoupling protein-2), IRS-2 (insulin receptor substrate-2), PDX-1 (pancreatic duodenal homeobox-1), GLUT-2 (glucose transporter-2) and B cell lymphoma/leukaemia-2 (Bcl-2) were investigated. Apoptosis of these exposed cells was determined by MitoCapture, Annexin V-Cy3 or terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. Cell lipid accumulation was measured by oil red O staining or TG extraction. Also SREBP-1c expression knockdown were used.

RESULTS

FFA treatment resulted in SREBP-1c overexpression, impaired GSIS, lipid accumulation, apoptosis of INS-1E cells. In addition, the expression of lipogenic genes and UCP-2 were upregulated, but AMPK, IRS-2, PDX-1, GLUT-2 and Bcl-2 were downregulated in the exposed cells. However, these lipotoxic effects of FFA were largely prevented by induction of a SREBP-1c small interfering RNA.

CONCLUSIONS

These data suggest a strong correlation between FFA treatment and SREBP-1c activation in INS-1E cells. SREBP-1c might be a major factor responsible for beta-cell lipotoxicity, and SREBP-1c knockdown could protect INS-1E cells from lipotoxicity, which is implicating a therapeutic potential for treating diabetes related to lipotoxicity.

Ginsenoside Rg3 Suppresses Palmitate-Induced Apoptosis in MIN6N8 Pancreatic beta-Cells

Chronic exposure to elevated levels of free fatty acids (FFA) causes beta-cell dysfunction and may induce beta-cell apoptosis in type 2 diabetes. The execution of beta-cell apoptosis occurs through activation of mitogen-activated protein kinases (MAPKs). Ginsenoside Rg3 (Rg3), one of the active ingredients of ginseng saponins, has not been known about the effects on beta-cell apoptosis mediated with FFA. The aims of this study were to investigate the in vitro protective effects of Rg3 on MIN6N8 mouse insulinoma beta-cells against FFA-induced apoptosis, as well as the modulating effects on p44/42 MAPK activation. Our results showed that Rg3 inhibited the palmitate-induced apoptosis through modulating p44/42 MAPK activation. We conclude that Rg3 has the potential role in suppressing the progression of type 2 diabetes by inhibiting FFA-mediated loss of beta-cells.

n-3 PUFA and lipotoxicity

Excess lipid accumulation in nonadipose tissues may occur in the setting of high levels of plasma free fatty acids or triglycerides (TGs) in a process called "lipotoxicity". Evidence from human studies and animal models suggests that lipid accumulation in the heart, skeletal muscle, pancreas, and liver play an important role in the pathogenesis of heart failure, obesity, metabolic syndrome, and type 2 diabetes mellitus (T2DM). During the past few years, several studies have shown that n-3 polyunsaturated fatty acids (PUFA) have potentially cardioprotective effects, especially in high-risk patients with dyslipidemia, and might therefore be expected to be of benefit in T2DM. Moreover, new information has demonstrated the beneficial effects of consuming n-3 PUFA in preventing the complications of lipotoxicity. n-3 PUFA dietary intake thus had positive effects on fatty liver in patients with non-alcoholic fatty liver disease (NAFLD), with an improvement in liver echotexture and a significant regression of hepatic brightness, associated with improved liver hemodynamics. The n-3 PUFA also had beneficial effects on ectopic fat accumulation inside the heart, with stabilization of cardiac myocytes and antiarrhythmic effects. On the other hand, recent data from animal models suggest that oral dosing of eicosapentaenoic acid (EPA) could contribute to protect against beta-cell lipotoxicity. This review discusses the latest hypotheses regarding lipotoxicity, concentrating on the impact of the n-3 PUFA that contribute to ectopic lipid storage, affecting organ function. Further human studies are needed to test the evidence and elucidate the mechanisms involved in this process.

Telmisartan attenuates fatty-acid-induced oxidative stress and NAD(P)H oxidase activity in pancreatic beta-cells

AIM

Angiotensin II receptor blockers (ARB) have been shown to lower insulin resistance in obese diabetic animal models and to reduce the risk of new-onset diabetes in hypertensive patients. In the present study, we studied whether telmisartan, an ARB with partial peroxisome proliferator-activated receptor-gamma (PPARgamma) activity, can exert a direct effect against fatty-acid-induced oxidative stress in pancreatic beta-cells.

METHODS

The effect of telmisartan on lipotoxicity was evaluated using mouse insulin-secreting clonal MIN6 and isolated mouse pancreatic islet cells. Reactive oxygen species, protein kinase-C (PKC) activity and NAD(P)H oxidase activity were examined to clarify the underlying mechanisms.

RESULT

Telmisartan decreased the accumulation of palmitate-induced reactive oxygen species in MIN6 cells by 25% and in mouse islet cells by 55%. Telmisartan also decreased palmitate-induced PKC activity by 36% and NAD(P)H oxidase activity by 32% in MIN6 cells.

CONCLUSION

These findings indicate that telmisartan attenuated fatty-acid-induced oxidative stress and NAD(P)H oxidase activity in pancreatic beta-cells. Our observations pave the way to the possible use of ARB as a means of protecting beta-cell survival and preserving insulin secretion capacity in patients with diabetes mellitus.

A minimal model for hepatic fatty acid balance during fasting: application to PPAR alpha-deficient mice

The purpose of this study is to identify the hierarchy of importance amongst pathways involved in fatty acid (FA) metabolism and their regulators in the control of hepatic FA composition. A modeling approach was applied to experimental data obtained during fasting in PPARalpha knockout (KO) mice and wild-type mice. A step-by-step procedure was used in which a very simple model was completed by additional pathways until the model fitted correctly the measured quantities of FA in the liver. The resulting model included FA uptake by the liver, FA oxidation, elongation and desaturation of FA, which were found active in both genotypes during fasting. From the model analysis we concluded that PPARalpha had a strong effect on FA oxidation. There were no indications that this effect changes during the fasting period, and it was thus considered to be constant. In PPARalpha KO mice, FA uptake was identified as the main pathway responsible for FA variation in the liver. The models showed that FA were oxidized at a constant and small rate, whereas desaturation of FA also occurred during fasting. The latter observation was rather unexpected, but was confirmed experimentally by the measurement of delta-6-desaturase mRNA using real-time quantitative PCR (QPCR). These results confirm that mathematical models can be a useful tool in identifying new biological hypotheses and nutritional routes in metabolism.

Metabolic characterization of a mouse deficient in all known leptin receptor isoforms

We have characterized a newly generated mouse model of obesity, a mouse strain deficient in all five previously described leptin receptor isoforms. These transgenic mice, named the db (333)/db (333) mice, were identified from an ENU mutagenesis screen and carry a point mutation in the seventh exon of the db gene encoding the leptin receptor, resulting in a premature stop codon (Y(333)Stop) and gene product that lacks STAT signaling domains. db (333)/db (333) mice have a morbidly obese phenotype, with body weights diverging from wild type as early as 4 weeks of age (P < 0.05). To determine the contribution of the short isoforms of the leptin receptor in this metabolic phenotype, we performed an extensive metabolic characterization of the db (333)/db (333) mouse in relation to the well-characterized db/db mouse lacking only the long form of the leptin receptor. db (333)/db (333) mice have similar endocrine and metabolic parameters as previously described in other leptin receptor transgenic mice including db/db mice that lack only the long isoform of the leptin receptor. However, db (333)/db (333) mice show a subtle trend toward higher body weight and insulin levels, lower oxygen, carbon dioxide production, respiratory exchange ratio (RER), and temperature than db/db mice suggesting the short isoforms may play an additional role in energy homeostasis.

COX-2-mediated inflammation in fat is crucial for obesity-linked insulin resistance and fatty liver

The aim was to examine the role of cyclooxygenase (COX)-2-mediated inflammation in the development of obese linked insulin resistance and fatty liver. The rats were fed separately regular diet (CONT), high-fat diet (HFD) ad libitum, or energy restrictedly for 12 weeks. Rats fed HFD ad libitum were further divided into three subgroups co-treated with vehicle (HFa), or a selective COX-2 inhibitor celecoxib (HFa-Cel) or mesulid (HFa-Mes). Euglycemic hyperinsulinemic clamp (EHC) experiment was performed at the end of study. Another set of rats with similar grouping was further divided into those with a 4, 8, or 12-week intervention period for hepatic sampling. Body weight was increased significantly and similarly in HFa, HFa-Cel, and HFa-Mes. Time-dependent increases in plasma insulin, glucose, 8-isoprostanes, leptin levels, homeostasis model assessment of insulin resistance (HOMA-IR) and hepatic triglyceride contents shown in HFa were significantly reversed in HFa-Cel and HFa-Mes. During EHC period, the reduction in stimulation of whole body glucose uptake, suppression of hepatic glucose production and metabolic clearance rate of insulin shown in HFa were significantly reversed in HFa-Cel and HFa-Mes. The enhanced COX-2 and tumor necrosis factor-alpha (TNF-alpha) but attenuated PPAR-gamma and C/EBP-alpha mRNA expressions in epididymal fat shown in HFa were significantly reversed in HFa-Cel and HFa-Mes. The increases in average cell size of adipocytes and CD68 positive cells shown in HFa were also significantly reversed in HFa-Cel and HFa-Mes. Our findings suggest that COX-2 activation in fat inflammation is important in the development of insulin resistance and fatty liver in high fat induced obese rats.

Impact of emodin and berberine on the mRNA expression of leptin receptor in HepG2 cells treated with high concentrations of leptin

AIM: To investigate the effect of the emodin and berberine on leptin in patients with non-alcoholic fatty liver disease and its mechanism.

METHODS: The concentration of emodin and berberine-treating HepG2 cells was screened by MTT assay. Then high concentration of leptin was added (10^-6 mol/L) to the HepG2 cells to establish a model group, and emodin, berberine and dexamethasone were given in the model group respectively. RT-PCR was used to detect the level of leptin receptor long-and short-receptor mRNA expression.

RESULTS: Compared with the normal control group, mRNA expression levels of leptin long- receptor and short-receptor in cells were significantly elevated in model group (P < 0.01). Emodin, berberine and dexamethasone obviously improved the expression (P < 0.01) compared with normal group. However, no significant change was noted (P > 0.05).

CONCLUSION: Emodin and berberine are effective for high-concentration leptin-induced non-alcoholic fatty liver disease through up-regulating the mRNA expression of leptin receptor.

Skeletal changes associated with the onset of type 2 diabetes in the ZDF and ZDSD rodent models

The incidence and prevalence of type 2 diabetes (T2D) continue to escalate at an unprecedented rate in the United States, particularly among populations with high rates of obesity. The impact of T2D on bone mass, geometry, architecture, strength, and resistance to fracture has yet to be incontrovertibly characterized because of the complex and heterogeneous nature of this disease. This study utilized skeletally mature male diabetic rats of the commonly used Zucker diabetic fatty (ZDF) and Zucker diabetic Sprague-Dawley (ZDSD) strains as surrogate models to assess alterations in bone attributable to T2D-like states. After the animals were euthanized, bone data were collected using dual-energy X-ray absorptiometry, peripheral quantitative tomography, and micro-CT imaging modalities and via three-point bending or compression mechanical testing methods. ZDF and ZDSD diabetic rats exhibited lower bone mineral densities, which coincided with declines in structural strength and increased fragility at the femoral midshaft and the L4 vertebral body in response to monotonic loading. Vertebral trabecular morphology was compromised in both diabetic rodent strains, and ZDSD diabetic rats exhibited additional phenotypic impairments to bone material properties at the spine. Because the metabolic origin of the T2D-like state that develops in the ZDSD rat strain is highly relevant to adult-onset diabetes, it is a particularly attractive novel model for future preclinical research.

Saturated with fat: new perspectives on lipotoxicity

PURPOSE OF REVIEW

To present current perspectives on the mediators and mechanisms of cyto-lipotoxic events and their relevance to human health.

RECENT FINDINGS

The relatively recent isolation of lipid acyltransferase genes from yeast to mice and humans has resulted in a paradigm shift that now establishes all fatty acids as toxic, albeit in tissue specific patterns and by different mechanisms. Furthermore, the dysregulation of glucose homeostasis in combination with excess fatty acids provides a synergistic effect leading to glucolipotoxicity and cell death. These findings are relevant to the development of disease states associated with the pathogenesis of the metabolic syndrome.

SUMMARY

In an era when an astounding number of people are diagnosed with metabolic disorders, it is imperative that we understand the consequences of a chronic metabolic surplus. Excessive fat, saturated or otherwise, has to be accommodated. Multiple aspects of this homeostasis are emerging, some of which are described here.

Obesity and diabetes: lipids, 'nowhere to run to'

Although specific pathogenic entities contributing to diabetic risk, such as central adiposity, ectopic fat accumulation, hyperlipidaemia and inflammation, are well-characterized, the response of cellular systems to such insults are less well understood. This short review highlights the effect of increasing fat mass on ectopic fat accumulation, the role of triacylglycerols (triglycerides) in Type 2 diabetes mellitus and cardiovascular disease pathogenesis, and selected current therapeutic strategies used to ameliorate these risk factors.

Examination of 'lipotoxicity' in skeletal muscle of high-fat fed and ob/ob mice

Excess lipid accumulation resulting from an elevated supply of plasma fatty acids is linked to the pathogenesis of the metabolic syndrome and heart disease. The term 'lipotoxicity' was coined to describe how lipid accumulation leads to cellular dysfunction and death in non-adipose tissues including the heart, pancreas and liver. While lipotoxicity has been shown in cultured skeletal muscle cells, the degree of lipotoxicity in vivo and the functional consequences are unresolved. We studied three models of fatty acid overload in male mice: 5 h Intralipid((R)) and heparin infusion, prolonged high fat feeding (HFF) and genetic obesity induced by leptin deficiency (ob/ob mice). Markers of apoptosis, proteolysis and autophagy were assessed as readouts of lipotoxicity. The Intralipid((R)) infusion increased caspase 3 activity in skeletal muscle, demonstrating that enhancing fatty acid flux activates pro-apoptotic pathways. HFF and genetic obesity increased tissue lipid content but did not influence apoptosis. Gene array analysis revealed that HFF reduced the expression of 31 pro-apoptotic genes. Markers of autophagy (LC3beta and beclin-1 expression) were unaffected by HFF and were associated with enhanced Bcl(2) protein expression. Proteolytic activity was similarly unaffected by HFF or in ob/ob mice. Thus, contrary to our previous findings in muscle culture in vitro and in other non-adipose tissues in vivo, lipid overload did not induce apoptosis, autophagy or proteolysis in skeletal muscle. A broad transcriptional suppression of pro-apoptotic proteins may explain this resistance to lipid-induced cell death in skeletal muscle.

Impact of increased adipose tissue mass on inflammation, insulin resistance, and dyslipidemia

Obesity is associated with increased prevalence of metabolic disorders, such as inflammation, insulin resistance, and dyslipidemia, which can predispose an individual to develop diabetes and cardiovascular disease. Adipose tissue (AT) is now recognized as a metabolically active organ that controls plasma free fatty acid levels and contributes to systemic metabolic homeostasis by secreting adipokines. In obesity, the recruitment of immune cells, such as T cells and macrophages, to AT causes inflammation, which is thought to contribute to local insulin resistance. This loss of insulin sensitivity within AT can lead to uncontrolled release of fatty acids, secretion of inflammatory cytokines, and alterations in the balance of adipokines, which ultimately impact lipoprotein metabolism and insulin sensitivity systemically. Thus, AT itself plays an important role in the increased risk of diabetes and cardiovascular disease that is associated with obesity.

Molecular analysis of db gene-related pancreatic beta cell dysfunction; evidence for a compensatory mechanism inhibiting development of diabetes in the db gene heterozygote

The db gene homozygous, but not heterozygous, mice develop diabetes with severe beta-cell damage. We investigated the molecular mechanism underlying db gene-associated pancreatic beta-cell dysfunction. Islet morphology, beta-cell function, and gene expression profiles specific for pancreatic islet cells were compared among db gene homozygous(db/db), heterozygous (db/m) and unrelated m/m mice. The beta-cell ratio decreased in db/db mice with age, but not in non-diabetic db/m and m/m mice. The islet insulin content was lower, but the triglyceride content was higher in db/db than other mice. The islet cell specific gene expression profiles analyzed by laser capture microdissection method and morphological findings suggested an augmentation of beta-cell apoptosis, oxidative stress and ER stress in db/db mice. Interestingly, insulin I and II, anti-apoptotic bcl-2, and proliferation promoting ERK-1 gene expressions were significantly upregulated in db/m mice. An impaired glucose tolerance was shown in m/m mice fed a high fat diet, but not in db/m mice, in which a higher insulin response and increased beta-cell mass were observed. Expressions of insulin I and II, bcl-2, and ERK-1 gene were increased in db/m mice, but not in m/m fed a high fat diet. The present results strongly suggest that the db gene heterozygote, but not homozygote, acquires a compensatory mechanism suppressing beta-cell apoptosis and augmenting the capacity of beta-cell function.

Nutrient modulation of insulin secretion

The presence of different nutrients regulates the beta-cell response to secrete insulin to maintain glucose in the physiological range and appropriate levels of fuels in different organs and tissues. Glucose is the only nutrient secretagogue capable of promoting alone the release of insulin release. The mechanisms of Insulin secretion are dependent or independent of the closure of ATP-sensitive K(+) channels. In addition, insulin secretion in response to glucose and other nutrients is modulated by several hormones as incretins, glucagon, and leptin. Fatty acids (FAs), amino acids, and keto acids influence secretion as well. The exact mechanism for which nutrients induce insulin secretion is complicated because nutrient signaling shows one of the most complex transduction systems, which exists for the reason that nutrient have to be metabolized. FAs in the absence of glucose induce FA oxidation and insulin secretion in a lesser extent. However, FAs in the presence of glucose produce high concentration of malonyl-CoA that repress FA oxidation and increase the formation of LC-CoA amplifying the insulin release. Long-term exposure to fatty acids and glucose results in glucolipotoxicity and decreases in insulin release. The amino acid pattern produced after the consumption of a dietary protein regulates insulin secretion by generating anaplerotic substrates that stimulates ATP synthesis or by activating specific signal transduction mediated by mTOR, AMPK, and SIRT4 or modulating the expression of genes involved in insulin secretion. Finally, dietary bioactive compounds such as isoflavones play an important role in the regulation of insulin secretion.

White adipose tissue as endocrine organ and its role in obesity

Due to the public health problem represented by obesity, the study of adipose tissue, particularly of the adipocyte, is central to the understanding of metabolic abnormalities associated with the development of obesity. The concept of adipocyte as endocrine and functional cell is not totally understood and can be currently defined as the capacity of the adipocyte to sense, manage, and send signals to maintain energy equilibrium in the body. Adipocyte functionality is lost during obesity and has been related to adipocyte hypertrophy, disequilibrium between lipogenesis and lipolysis, impaired transcriptional regulation of the key factors that control adipogenesis, and lack of sensitivity to external signals, as well as a failure in the signal transduction process. Thus, dysfunctional adipocytes contribute to abnormal utilization of fatty acids causing lipotoxicity in non-adipose tissue such as liver, pancreas and heart, among others. To understand the metabolism of the adipocyte it is necessary to have an overview of the developmental process of new adipocytes, regulation of adipogenesis, lipogenesis and lipolysis, endocrine function of adipocytes and metabolic consequences of its dysfunction. Finally, the key role of adipose tissue is shown by studies in transgenic animals or in animal models of diet-induced obesity that indicate the contribution of adipose tissue during the development of metabolic syndrome. Thus, understanding of the molecular process that occurs in the adipocyte will provide new tools for the treatment of metabolic abnormalities during obesity.

Dramatic reversal of derangements in muscle metabolism and left ventricular function after bariatric surgery

OBJECTIVE

The study objective was to define muscle metabolic and cardiovascular changes after surgical intervention in clinically severe obese patients.

METHODS

Obesity is a state of metabolic dysregulation that can lead to maladaptive changes in heart and skeletal muscle, including insulin resistance and heart failure. In a prospective longitudinal study, 43 consecutive patients underwent metabolic profiling, skeletal muscle biopsies, and resting echocardiograms at baseline and 3 and 9 months after bariatric surgery.

RESULTS

Body mass index decreased (mean changes, 95% confidence interval [CI]): 7.7 kg/m(2) (95% CI, 6.70-8.89) at 3 months and 5.6 kg/m(2) (95% CI, 4.45-6.80; P<.0001) at 9 months after surgery, with restoration of insulin sensitivity and decreases in plasma leptin at the same time points. Concurrent with these changes were dramatic decreases in skeletal muscle transcript levels of stearoyl coenzyme-A desaturase and pyruvate dehydrogenase kinase-4 at 3 and 9 months (P<.0001, for both) and a significant decrease in peroxisome proliferation activated receptor-alpha-regulated genes at 9 months. Left ventricular relaxation impairment, assessed by tissue Doppler imaging, normalized 9 months after surgery.

CONCLUSION

Weight loss results in the reversal of systemic and muscle metabolic derangements and is accompanied by a normalization of left ventricular diastolic function.

Leptin regulates peripheral lipid metabolism primarily through central effects on food intake

The metabolic effects of leptin may involve both centrally and peripherally mediated actions with a component of the central actions potentially independent of alterations in food intake. Ob/ob mice have significant abnormalities in lipid metabolism, correctable by leptin administration. We used ob/ob mice to study the relative importance of the subtypes of actions of leptin (central vs. peripheral; food intake dependent vs. independent) on lipid metabolism. Mice were treated for 3 d with leptin, either centrally [intracerebroventricular (icv)] or peripherally (ip), and compared with mice pair-fed to the leptin-treated mice (PF) and with ad libitum-fed controls (C). All treatment groups (icv, ip, PF) showed indistinguishable changes in liver weight; hepatic steatosis; hepatic lipidemic profile; and circulating free fatty acids, triglycerides, and cholesterol lipoprotein profile. Changes in the expression of genes involved in lipogenesis and fatty acid oxidation in liver, muscle, and white fat were broadly similar in ip, icv, and PF groups. Leptin (both icv and ip) stimulated expression of both mitochondrial and peroxisomal acyl-coenzyme A oxidase (liver) and peroxisomal proliferator-activated receptor-alpha (skeletal muscle) to an extent not replicated by pair feeding. Leptin had profound effects on peripheral lipid metabolism, but the majority were explained by its effects on food intake. Leptin had additional centrally mediated effects to increase the expression of a limited number of genes concerned with fatty acid oxidation. Whereas we cannot exclude direct peripheral effects of leptin on certain aspects of lipid metabolism, we were unable to detect any such effects on the parameters measured in this study.

Glycerolipid metabolism and signaling in health and disease

Maintenance of body temperature is achieved partly by modulating lipolysis by a network of complex regulatory mechanisms. Lipolysis is an integral part of the glycerolipid/free fatty acid (GL/FFA) cycle, which is the focus of this review, and we discuss the significance of this pathway in the regulation of many physiological processes besides thermogenesis. GL/FFA cycle is referred to as a "futile" cycle because it involves continuous formation and hydrolysis of GL with the release of heat, at the expense of ATP. However, we present evidence underscoring the "vital" cellular signaling roles of the GL/FFA cycle for many biological processes. Probably because of its importance in many cellular functions, GL/FFA cycling is under stringent control and is organized as several composite short substrate/product cycles where forward and backward reactions are catalyzed by separate enzymes. We believe that the renaissance of the GL/FFA cycle is timely, considering the emerging view that many of the neutral lipids are in fact key signaling molecules whose production is closely linked to GL/FFA cycling processes. The evidence supporting the view that alterations in GL/FFA cycling are involved in the pathogenesis of "fatal" conditions such as obesity, type 2 diabetes, and cancer is discussed. We also review the different enzymatic and transport steps that encompass the GL/FFA cycle leading to the generation of several metabolic signals possibly implicated in the regulation of biological processes ranging from energy homeostasis, insulin secretion and appetite control to aging and longevity. Finally, we present a perspective of the possible therapeutic implications of targeting this cycling.

Boc5, a non-peptidic glucagon-like Peptide-1 receptor agonist, invokes sustained glycemic control and weight loss in diabetic mice

Background

Our recent discovery of the substituted cyclobutane Boc5, one of the first non-peptidic agonists at glucagon-like peptide-1 receptors, offers the potential of combining oral availability with full agonism capable of eliciting antidiabetic and antiobesity effects. The present study was aimed at determining the in vivo pharmacologic properties of Boc5 in both normal and diabetic mice following chronic administration, with emphasis on glycemic control and weight loss.

Methodology/Principal Findings

C57BL/6J and db/db mice were treated daily with Boc5 for 4 weeks and a range of pharmacologic parameters, including hemoglobin A1c, intraperitoneal glucose tolerance, insulin tolerance, fasting insulin and leptin levels, food intake, body weight and fat mass, were assessed before and after the treatment. Effects on food intake, gastric emptying, and insulinogenic index were also investigated in animals acutely administered with Boc5. Boc5 (3 mg) was able to induce a durable restoration of glycemic control (normalization of both hemoglobin A1c and intraperitoneal glucose tolerance) in db/db mice, following 4 weeks of daily administration. As with peptidic glucagon-like peptide-1 receptor agonists, its glycemic benefit and weight (fat) loss were associated with dose-dependent effects that included reduction in food intake, slowing of gastric emptying (both of which reduce nutrient-drive at β-cells), stimulation of insulin secretion (which was glucose-dependent), and elevation in insulin sensitivity. There was little effect on normal mice treated in the same manner.

Conclusions/Significance

Our findings suggest that Boc5 is the only non-peptidic molecule reported thus far to simultaneously activate this spectrum of antidiabetic effects.

Nutrigenomics, beta-cell function and type 2 diabetes

INTRODUCTION

The present investigation was designed to investigate the accuracy and precision of lactate measurement obtained with contemporary biosensors (Chiron Diagnostics, Nova Biomedical) and standard enzymatic photometric procedures (Sigma Diagnostics, Abbott Laboratories, Analyticon).

MATERIALS AND METHODS

Measurements were performed in vitro before and after the stepwise addition of 1 molar sodium lactate solution to samples of fresh frozen plasma to systematically achieve lactate concentrations of up to 20 mmol/l.

RESULTS

Precision of the methods investigated varied between 1% and 7%, accuracy ranged between 2% and -33% with the variability being lowest in the Sigma photometric procedure (6%) and more than 13% in both biosensor methods.

CONCLUSION

Biosensors for lactate measurement provide adequate accuracy in mean with the limitation of highly variable results. A true lactate value of 6 mmol/l was found to be presented between 4.4 and 7.6 mmol/l or even with higher difference. Biosensors and standard enzymatic photometric procedures are only limited comparable because the differences between paired determinations presented to be several mmol. The advantage of biosensors is the complete lack of preanalytical sample preparation which appeared to be the major limitation of standard photometry methods.

Pioglitazone attenuates fatty acid-induced oxidative stress and apoptosis in pancreatic beta-cells

AIMS

Thiazolidinediones (TZDs), ligands for peroxisome proliferator-activated receptor gamma, are antidiabetic agents that improve hyperglycemia by decreasing insulin resistance in obese diabetic animal models and patients with type 2 diabetes. We have studied whether pioglitazone, a TZD, can exert a direct effect against pancreatic beta-cell lipoapoptosis.

METHODS

MIN6 cells were cultured in medium containing either 5.6 (low glucose) or 25 mM glucose (high glucose) in the presence or absence of 0.5 mM palmitate for 48 h. We examined the effect of 10 microM pioglitazone on MIN6 cells on glucose-stimulated insulin secretion, cellular ATP, uncoupling protein-2 (UCP-2) mRNA expression, intracellular triglyceride content, reactive oxygen species production, the number of apoptotic cells and nuclear factor-kappaB (NF-kappaB) activity.

RESULTS

Pioglitazone recovered partly impaired glucose-stimulated insulin secretion and cellular ATP in MIN6 cell exposed to high glucose with 0.5 mM palmitate. Pioglitazone suppressed intracellular triglyceride accumulation in cells exposed to high glucose with 0.5 mM palmitate. Palmitate-induced upregulation of UCP-2 mRNA levels was suppressed by pioglitazone in a dose-dependent manner. Pioglitazone decreased palmitate-induced reactive oxygen species production in MIN6 cells by 24% and in mouse islet cells by 53%. Pioglitazone also decreased palmitate-induced NF-kappaB activity by 40% and protected beta-cells from palmitate-induced apoptosis by 22% in MIN6 cell.

CONCLUSIONS

Pioglitazone attenuated fatty acid-induced oxidative stress and apoptosis in pancreatic beta-cells. TZDs might be used as a mean for maintaining beta-cell survival and preserving capacity of insulin secretion in patients with diabetes mellitus.

Fructose-1,6-bisphosphatase overexpression in pancreatic beta-cells results in reduced insulin secretion: a new mechanism for fat-induced impairment of beta-cell function

OBJECTIVE

Fructose-1,6-bisphosphatase (FBPase) is a gluconeogenic enzyme that is upregulated in islets or pancreatic beta-cell lines exposed to high fat. However, whether specific beta-cell upregulation of FBPase can impair insulin secretory function is not known. The objective of this study therefore is to determine whether a specific increase in islet beta-cell FBPase can result in reduced glucose-mediated insulin secretion.

RESEARCH DESIGN AND METHODS

To test this hypothesis, we have generated three transgenic mouse lines overexpressing the human FBPase (huFBPase) gene specifically in pancreatic islet beta-cells. In addition, to investigate the biochemical mechanism by which elevated FBPase affects insulin secretion, we made two pancreatic beta-cell lines (MIN6) stably overexpressing huFBPase.

RESULTS

FBPase transgenic mice showed reduced insulin secretion in response to an intravenous glucose bolus. Compared with the untransfected parental MIN6, FBPase-overexpressing cells showed a decreased cell proliferation rate and significantly depressed glucose-induced insulin secretion. These defects were associated with a decrease in the rate of glucose utilization, resulting in reduced cellular ATP levels.

CONCLUSIONS

Taken together, these results suggest that upregulation of FBPase in pancreatic islet beta-cells, as occurs in states of lipid oversupply and type 2 diabetes, contributes to insulin secretory dysfunction.

Hyperleptinemia without obesity in male mice lacking androgen receptor in adipose tissue

Insulin resistance occurs through an inadequate response to insulin by insulin target organs such as liver, muscle, and adipose tissue with consequent insufficient glucose uptake. In previous studies we demonstrated that whole body androgen receptor (AR) knockout (AR(-/y)) mice develop obesity and exhibit insulin and leptin resistance at advanced age. By examining adipose tissue-specific AR knockout (A-AR(-/y)) mice, we found A-AR(-/y) mice were hyperleptinemic but showed no leptin resistance, although body weight and adiposity index of A-AR(-/y) mice were identical with those of male wild-type control mice. Hypotriglyceridemia and hypocholesterolemia found in nonobese A-AR(-/y) mice suggested a beneficial effect of high leptin levels independent of fat deposition. Further examination showed that androgen-AR signaling in adipose tissue plays a direct regulatory role in leptin expression via enhanced estrogen receptor transactivation activity due to elevated intraadipose estrogens. The present study in A-AR(-/y) mice suggests a differential tissue-specific role of AR in energy balance control in males.

Treatment of obesity and diabetes in mice by transplant of gut cells engineered to produce leptin

Leptin injections evoke weight loss by causing a reduction in food consumption and an increase in energy expenditure. Also, the administration of leptin lowers blood glucose levels in some rodent models of diabetes and in humans with lipodystrophy. We explored the therapeutic potential of delivering leptin to obese, diabetic ob/ob mice and to mice fed on a high-fat diet (HFD), by transplanting gut-derived cells engineered to produce leptin, under the regulation of an inducing agent, mifepristone. These cells expressed and released leptin in a mifepristone dose-dependent and time-dependent manner. The engineered cells were either transplanted into the mice under the kidney capsule or were encapsulated in alginate and injected into the intraperitoneal cavity, while mifepristone was delivered by implanting 14-day release pellets. In ob/ob mice, leptin delivery by this method caused a significant reduction in food intake and profound weight loss, which was controllable by adjusting the dose of mifepristone. These transplants also achieved rapid and persistent amelioration of diabetes. However, mice fed on a HFD were resistant to the leptin therapy. These results indicate that gut cells can be modified to express leptin in an inducible manner and that the transplantation of these cells has a therapeutic effect in leptin-deficient mice, but not in mice fed on a HFD.

Fatty acids and glucose in high concentration down-regulates ATP synthase beta-subunit protein expression in INS-1 cells

Chronic hyperglycemia and hyperlipidemia exert deleterious effects on beta-cell function and impair glucose-induced insulin release, referred to as glucotoxicity and lipotoxticity. These abnormalities are associated with decreased glucose-induced ATP production; ATP serves as an important signal for insulin secretion. To investigate the mechanism of the impaired ATP formation, we examined the effects of elevated glucose and fatty acids levels on ATP synthase beta-subunit expression, ATP content and insulin secretion in INS-1 insulinoma beta-cells. ATP synthase beta-subunit expression was measured by western blot, ATP content was monitored by ATP luminescence and insulin secretion detected by radio immunoassay. Our result indicated that chronic exposure to high doses of fatty acids together with high levels glucose produced a marked decrease in ATP synthase beta-subunit protein expression. Reduction of ATP synthase beta-subunit protein expression occurred with a decreased intracellular ATP concentration and insulin secretion at high fatty acid concentrations. These results indicate that high glucose together with fatty acids impair the production of ATP in beta-cells through the suppression of mitochondrial ATP synthesis. We conclude that ATP synthase beta-subunit may have an important role in the glucolipotoxicity of islet cells and suggest that ATP synthase beta-subunit might be a target of lipotoxicity in beta-cells.

Soy protein ameliorates metabolic abnormalities in liver and adipose tissue of rats fed a high fat diet

Chronic consumption of high-fat or -carbohydrate diets is associated with the development of obesity; however, it is not well established whether dietary protein plays a role in the development of abnormalities of lipid metabolism that occur during obesity. To determine the effect of different types of protein during diet-induced obesity on hepatic and adipocyte lipid metabolism, rats were fed casein (CAS) or soy (SOY) protein diets with 5% fat or high-fat diets with 25% fat (HF-CAS and HF-SOY) for 180 d. Rats fed soy diets had lower hepatic sterol regulatory element binding protein-1 (SREBP-1) expression and higher SREBP-2 expression than those fed casein diets, leading to less hepatic lipid deposition. On the other hand, long-term HF-SOY consumption prevented hyperleptinemia in comparison with rats fed HF-CAS. Rats fed soy protein diet showed higher adipocyte perilipin mRNA expression and smaller adipocyte area than those fed casein diets, which was associated with a lower body fat content. Furthermore, the lipid droplet area in brown adipose tissue was significantly lower in rats fed soy diets than in those fed casein diets and it was associated with higher uncoupling protein-1 (UCP-1) expression. As a result, rats fed the soy diets gained less weight than those fed the casein diets, in part due to an increase in the thermogenic capacity mediated by UCP-1. These results suggest that the type of protein consumed and the presence of fat in the diet modulate lipid metabolism in adipose tissue and liver.

Disruption of leptin receptor expression in the pancreas directly affects beta cell growth and function in mice

Obesity is characterized by hyperinsulinemia, hyperleptinemia, and an increase in islet volume. While the mechanisms that hasten the onset of diabetes in obese individuals are not known, it is possible that the adipose-derived hormone leptin plays a role. In addition to its central actions, leptin exerts biological effects by acting in peripheral tissues including the endocrine pancreas. To explore the impact of disrupting leptin signaling in the pancreas on beta cell growth and/or function, we created pancreas-specific leptin receptor (ObR) KOs using mice expressing Cre recombinase under the control of the pancreatic and duodenal homeobox 1 (Pdx1) promoter. The KOs exhibited improved glucose tolerance due to enhanced early-phase insulin secretion, and a greater beta cell mass secondary to increased beta cell size and enhanced expression and phosphorylation of p70S6K. Similar effects on p70S6K were observed in MIN6 beta cells with knockdown of the ObR gene, suggesting crosstalk between leptin and insulin signaling pathways. Surprisingly, challenging the KOs with a high-fat diet led to attenuated acute insulin secretory response to glucose, poor compensatory islet growth, and glucose intolerance. Together, these data provide direct genetic evidence, from a unique mouse model lacking ObRs only in the pancreas, for a critical role for leptin signaling in islet biology and suggest that altered leptin action in islets is one factor that contributes to obesity-associated diabetes.

Leptin signaling and obesity: cardiovascular consequences

Leptin, among the best known hormone markers for obesity, exerts pleiotropic actions on multiple organ systems. In this review, we summarize major leptin signaling pathways, namely Janus-activated kinase/signal transducers and activators of transcription and mitogen-activated protein kinase, including possible mechanisms of leptin resistance in obesity. The effects of leptin on the cardiovascular system are discussed in detail, including its contributions to hypertension, atherosclerosis, depressed myocardial contractile function, fatty acid metabolism, hypertrophic remodeling, and reduction of ischemic/reperfusion injury. The overall goal is to summarize current understanding of how altered leptin signaling in obesity contributes to obesity-related cardiovascular disease.

A topical lipophilic niacin derivative increases NAD, epidermal differentiation and barrier function in photodamaged skin

The effects of myristyl nicotinate (MN), a nicotinic acid derivative designed to deliver nicotinic acid to skin without vasodilatation, on subjects with photodamaged skin have been studied. MN increased skin cell nicotinamide adenine dinucleotide (NAD) by 25% (P = 0.001) demonstrating effective delivery of nicotinic acid to skin. Relative to placebo, MN treatment of photodamaged facial skin increased stratum corneum thickness by approximately 70% (P = 0.0001) and increased epidermal thickness by approximately 20% (P = 0.001). In two separate studies, MN treatment increased rates of epidermal renewal by 6% (P = 0.003) to 11% (P = 0.001) and increased the minimal erythemal dose by 8.9 (P = 0.07) and 10% (P = 0.05) relative to placebo. MN treatment resulted in reductions in the rates of transepidermal water loss (TEWL) of approximately 20% relative to placebo on cheeks (P = 0.012) and arms (P = 0.017) of study subjects. Results of a tape stripping challenge before and after MN treatment demonstrated a significant correlation (P = 0.03) between increased skin NAD content and resistance to changes in TEWL for MN treated but not placebo subjects. Rates of TEWL changed more rapidly and to a greater extent in atopic subjects compared with normal subjects. The results indicate that MN enhances epidermal differentiation and barrier function in skin, suggesting that this method of nicotinic acid delivery may prove useful in limiting progression of actinic skin damage and possibly in treating other conditions involving skin barrier impairment.

Adipose triglyceride lipase and hormone-sensitive lipase protein expression is decreased in the obese insulin-resistant state

AIM/HYPOTHESIS

Obesity is associated with increased triacylglycerol (TAG) storage in adipose tissue and insulin resistance. The mobilization of stored TAG is mediated by hormone-sensitive lipase (HSL) and the recently discovered adipose triglyceride lipase (ATGL). The aim of the present study was to examine whether ATGL and HSL mRNA and protein expression are altered in insulin-resistant conditions. In addition, we investigated whether a possible impaired expression could be reversed by a period of weight reduction.

METHODS

Adipose tissue biopsies were taken from obese subjects (n = 44) with a wide range of insulin resistance, before and just after a 10-wk hypocaloric diet. ATGL and HSL protein and mRNA expression was determined by Western blot and quantitative RT-PCR, respectively.

RESULTS

Fasting insulin levels and the degree of insulin resistance (using the homeostasis model assessment index for insulin resistance) were negatively correlated with ATGL and HSL protein expression, independent of age, gender, fat cell size, and body composition. Both mRNA and protein levels of ATGL and HSL were reduced in insulin-resistant compared with insulin-sensitive subjects (P < 0.05). Weight reduction significantly decreased ATGL and HSL mRNA and protein expression. A positive correlation between the decrease in leptin and the decrease in ATGL protein level after weight reduction was observed. Finally, ATGL and HSL mRNA and protein levels seem to be highly correlated, indicating a tight coregulation and transcriptional control.

CONCLUSIONS

In obese subjects, insulin resistance and hyperinsulinemia are strongly associated with ATGL and HSL mRNA and protein expression, independent of fat mass. Data on weight reduction indicated that also other factors (e.g. leptin) relate to ATGL and HSL protein expression.

Prolonged exposure to homocysteine results in diminished but reversible pancreatic beta-cell responsiveness to insulinotropic agents

BACKGROUND

Plasma homocysteine levels may be elevated in poorly controlled diabetes with pre-existing vascular complications and/or nephropathy. Since homocysteine has detrimental effects on a wide diversity of cell types, the present study examined the effects of long-term homocysteine exposure on the secretory function of clonal BRIN-BD11 beta-cells.

METHODS

Acute insulin secretory function, cellular insulin content and viability of BRIN-BD11 cells were assessed following long-term (18 h) exposure to homocysteine in culture. RT-PCR and Western blot analysis were used to determine the expression of key beta-cell genes and proteins. Cells were cultured for a further 18 h without homocysteine to determine any long-lasting effects.

RESULTS

Homocysteine (250-1000 micromol/L) exposure reduced insulin secretion at both moderate (5.6 mmol/L) and stimulatory (16.7 mmol/L) glucose by 48-63%. Similarly, insulin secretory responsiveness to stimulatory concentrations of alanine, arginine, 2-ketoisocaproate, tolbutamide, KCl, elevated Ca2+, forskolin and PMA, GLP-1, GIP and CCK-8 were reduced by 11-62% following culture with 100-250 micromol/L homocysteine. These inhibitory effects could not simply be attributed to changes in cellular insulin content, cell viability, H2O2 generation or any obvious alterations of gene/protein expression for insulin, glucokinase, GLUT2, VDCC, or Kir6.2 and SUR1. Additional culture for 18 h in standard culture media after homocysteine exposure restored secretory responsiveness to all agents tested.

CONCLUSION

These findings suggest that long-term exposure to high homocysteine levels causes a reversible impairment of pancreatic beta-cell insulinotropic pathways. The in vivo actions of hyperhomocysteinaemia on islet cell function merit investigation.

Defective mitochondrial biogenesis: a hallmark of the high cardiovascular risk in the metabolic syndrome?

The metabolic syndrome is a group of risk factors of metabolic origin that are accompanied by increased risk for type 2 diabetes mellitus and cardiovascular disease. These risk factors include atherogenic dyslipidemia, elevated blood pressure and plasma glucose, and a prothrombotic and proinflammatory state. The condition is progressive and is exacerbated by physical inactivity, advancing age, hormonal imbalance, and genetic predisposition. The metabolic syndrome is a particularly challenging clinical condition because its complex molecular basis is still largely undefined. Impaired cell metabolism has, however, been suggested as a relevant pathophysiological process underlying several clinical features of the syndrome. In particular, defective oxidative metabolism seems to be involved in visceral fat gain and in the development of insulin resistance in skeletal muscle. This suggests that mitochondrial function may be impaired in the metabolic syndrome and, thus, in the consequent cardiovascular disease. We have recently found that mitochondrial biogenesis and function are enhanced by nitric oxide in various cell types and tissues, including cardiac muscle. Increasing evidence suggests that this mediator acts as a metabolic sensor in cardiomyocytes. This implies that a defective production of nitric oxide might be linked to dysfunction of the cardiomyocyte metabolism. Here we summarize some recent findings and propose a hypothesis for the high cardiovascular risk linked to the metabolic syndrome.

Neonatal leptin treatment programmes leptin hypothalamic resistance and intermediary metabolic parameters in adult rat

We previously showed that neonatal leptin treatment programmes higher body weight and food intake in adult rats. Here we investigate whether leptin treatment during lactation affects the anorectic effect of leptin on adult rats and their hypothalamic leptin receptors (OB-Rb) and whether those changes could have consequences on intermediary metabolism. When the offspring were born, pups were divided into two groups: the Lep group, injected daily with leptin (8μg/100g body weight, subcutaneously) for the first 10d of lactation, and the control group, injected daily with saline. After weaning (day 21), body weight and food intake were monitored until the rats were 150d old. Food intake was higher in the Lep group (approximately 14%,p<0·05) from day 133 onwards, and body weight was higher (approximately 10%,p<0·05) from day 69 onwards, compared with the control group. At 150d of age, the rats were tested for food intake in response to either leptin (05mg/kg body weight intraperitoneally; groups CL and LepL) or saline (groups CSal and LepSal). The CL group showed a decrease in food intake, but no response was observed in the LepL group, suggesting leptin resistance. The Lep group demonstrated a decrease in OB-Rb expression (−40%p<0·05), hyperleptinaemia (+78%,p<0·05), hyperinsulinaemia (+100%,p<0·02), hypertriacylglycerolaemia (+17%,p<0·05) and a higher protein content in the body (+16%,p<0·05) without changes in fat mass and glycaemia. We conclude that neonatal leptin treatment programmes both hyperleptinaemia and hyperinsulinaemia in adulthood, which leads to leptin resistance by reducing the expression of the hypothalamic leptin receptor.

Leptin predicts the development of diabetes in Mauritian men, but not women: a population–based study

OBJECTIVE

To determine if levels of the adipocyte-derived hormone, leptin, predict the development of type 2 diabetes.

METHODS

Population-based surveys were undertaken in the multiethnic nation of Mauritius in 1987, 1992 and 1998. Questionnaires, anthropometric measurements, and a 2-h 75-g oral glucose tolerance test were included. A cohort of 2330 participants who were free of diabetes, aged 25-79 years in 1987, and who were followed-up in 1992 and 1998 was studied. Serum leptin was measured in baseline samples. Glucose tolerance was classified according to WHO (World Health Organization) 1999 criteria.

RESULTS

In total, 456 subjects developed diabetes over 11 years with similar incidences in all ethnic groups (P=0.2). Baseline leptin correlated positively with anthropometric measurements, fasting and postload insulin and homeostasis model assessment indices (all P<0.001), and inversely with subsequent weight increase. Participants with incident diabetes had higher serum levels of leptin at baseline than those remaining nondiabetic (P<0.001). After adjustment for confounders, high leptin levels and high leptin/body mass index ratio were independently associated with incident diabetes over 11 years in men (odds ratio for top versus bottom quartile of leptin 2.18; 95% CI: 1.09-4.35), but not in women.

CONCLUSION

We conclude that high leptin levels are associated with the future development of diabetes, and the association is independent of other factors in men, but not in women.

Changes in liver PPARα mRNA expression in response to two levels of high-safflower-oil diets correlate with changes in adiposity and serum leptin in rats and mice

The ligand-dependent transcription factor peroxisome proliferator-activated receptor alpha (PPARalpha) is known to be activated by common fatty acids and to regulate the expression of genes of various lipid oxidation pathways and transport. High-fat diets provide more fatty acids, which presumably could enhance lipid catabolism through up-regulation of PPARalpha signaling. However, high intake of fat could also lead to obesity. To examine PPARalpha signaling in high-fat feeding and obesity, this study examined the hepatic mRNA expression of PPARalpha and some of its target genes in Wistar rats and C57BL/6J mice fed two levels (20% or 30% wt/wt) of high-safflower-oil (SFO; oleic-acid-rich) diets until animals showed significantly higher body weight (13 weeks for rats and 22 weeks for mice) than those of control groups fed a 5% SFO diet. At the end of these respective feeding periods, only the rats fed 30% SFO and the mice fed 20% SFO among the two groups fed high-fat diets showed significantly higher body weight, white adipose tissue weight, serum leptin and mRNA expression of PPARalpha (P<.05) compared to the respective control groups. Despite elevated acyl-CoA (a PPARalpha target gene) protein and activity in both groups fed high-fat diets, the mRNA expression level of most PPARalpha target genes examined correlated mainly to PPARalpha mRNA levels and not to fat intake or liver lipid levels. The observation that the liver PPARalpha mRNA expression in groups fed high-fat diets was significantly higher only in obese animals with elevated serum leptin implied that obesity and associated hyperleptinemia might have a stronger impact than dietary SFO intake per se on PPARalpha-regulated mRNA expression in the liver.

The relationship between the metabolic syndrome and energy-utilization deficit in the pathogenesis of obesity-induced osteoarthritis

We propose that the pathogenesis of obesity-induced osteoarthritis may be explained by the metabolic changes in the striated muscle induced by the interaction of insulin resistance and systemic inflammation in obese individuals with metabolic syndrome being osteoarthritis the latest consequence by the physiological changes seen in the metabolic syndrome. Increased levels of TH1 cytokines are produced by activated macrophages in the presence of an acute or chronic infectious disease and suppress the sensitivity of insulin receptors on the membrane of muscle cell and adipocytes. Both cells are activated by inflammatory cytokines and contribute to enhance acute inflammation and to maintain a state of chronic, low-grade inflammation in apparently healthy obese individuals. The increased number of macrophage in the adipose tissue of obese individuals acts as an amplifier of inflammation. Patients with osteoarthritis and metabolic syndrome frequently are complaining about hotness and recurrent edema of feet and hands. It is probable that hyperinsulinemia in the presence of insulin resistance and inflammation, induce vasodilation through the TNF mediated-iNOS overexpression. Patients with metabolic syndrome express clinically the consequence of a poor uptake, storage and energy expenditure by the muscle and any other insulin dependent tissue and the consequence of high insulin plasma levels are vasodilation and increased protein synthesis. The fatigue and muscle weakness induced by insulin resistance and inflammation in obese patients with metabolic syndrome increase the frequency and the intensity of traumatic events of peripheral or axial joints that result in stretch and breaking of tenoperiosteal junction and abrasive damage of cartilage and therefore in these patients with metabolic syndrome and pro-inflammatory state the reparative process of cartilage and periarticular tissues would be severely modified by the growth factor activity in presence of high levels of insulin.

ApoO, a novel apolipoprotein, is an original glycoprotein up-regulated by diabetes in human heart

Obesity is an independent risk factor for cardiac failure. Obesity promotes excessive deposition of fat in adipose and nonadipose tissues. Intramyocardial lipid overload is a relatively common finding in nonischemic heart failure, especially in obese and diabetic patients, and promotes lipoapoptosis that contributes to the alteration of cardiac function. Lipoprotein production has been proposed as a heart-protective mechanism through the unloading of surplus cellular lipids. We previously analyzed the heart transcriptome in a dog nutritional model of obesity, and we identified a new apolipoprotein, regulated by obesity in heart, which is the subject of this study. We detected this new protein in the following lipoproteins: high density lipoprotein, low density lipoprotein, and very low density lipoprotein. We designated it apolipoprotein O. Apolipoprotein O is a 198-amino acid protein that contains a 23-amino acidlong signal peptide. The apolipoprotein O gene is expressed in a set of human tissues. Confocal immunofluorescence microscopy colocalized apolipoprotein O and perilipins, a cellular marker of the lipid droplet. Chondroitinase ABC deglycosylation analysis or cell incubation with p-nitrophenyl-beta-d-xyloside indicated that apolipoprotein O belongs to the proteoglycan family. Naringenin or CP-346086 treatments indicated that apolipoprotein O secretion requires microsomal triglyceride transfer protein activity. Apolipoprotein O gene expression is up-regulated in the human diabetic heart. Apolipoprotein O promoted cholesterol efflux from macrophage cells. To our knowledge, apolipoprotein O is the first chondroitin sulfate chain containing apolipoprotein. Apolipoprotein O may be involved in myocardium-protective mechanisms against lipid accumulation, or it may have specific properties mediated by its unique glycosylation pattern.

Chromatin remodeling complex interacts with ADD1/SREBP1c to mediate insulin-dependent regulation of gene expression

Insulin plays a critical role in whole-body energy homeostasis by regulating lipid and glucose metabolism. In fat and liver tissues, ADD1/SREBP1c is a key transcription factor to mediate insulin-dependent regulation of gene expression. Although transcriptional and proteolytic activation of ADD1/SREBP1c has been studied intensively, the mechanism by which insulin regulates expression of its target genes with ADD1/SREBP1c at the chromatin level is unclear. Here, we reveal that SWI/SNF chromatin remodeling factors interact with the ADD1/SREBP1c and actively regulate insulin-dependent gene expression. Insulin enhanced recruitment of SWI/SNF chromatin remodeling factors to its target gene promoters with concomitant changes in the chromatin structures as well as gene expression. Furthermore, in vivo overexpression of BAF155/SRG3, a component of the SWI/SNF complex, substantially promoted insulin target gene expression and insulin sensitivity. Taken together, our results suggest that the SWI/SNF chromatin remodeling complexes confer not only insulin-dependent gene expression but also insulin sensitivity in vivo via interaction with ADD1/SREBP1c.

AMP-activated protein kinase signaling in metabolic regulation

AMP-activated protein kinase (AMPK) is an energy sensor that regulates cellular metabolism. When activated by a deficit in nutrient status, AMPK stimulates glucose uptake and lipid oxidation to produce energy, while turning off energy-consuming processes including glucose and lipid production to restore energy balance. AMPK controls whole-body glucose homeostasis by regulating metabolism in multiple peripheral tissues, such as skeletal muscle, liver, adipose tissues, and pancreatic beta cells--key tissues in the pathogenesis of type 2 diabetes. By responding to diverse hormonal signals including leptin and adiponectin, AMPK serves as an intertissue signal integrator among peripheral tissues, as well as the hypothalamus, in the control of whole-body energy balance.

Patogenia de la lipodistrofia y de las alteraciones metabólicas asociadas a la infección por el VIH

Lipodystrophy, and the metabolic alterations (dislipemia, insulin-resistance) associated with human immunodeficiency virus (HIV) infection, is a multifactorial syndrome due to the interaction of host related factors (cellular immune status, diet, gene mutations), viral factors (cytokine synthesis, polyunsaturated fatty acid or PUFA depletion), and pharmacological effects (mitochondrial DNA-polymerase inhibition, lipolysis inhibition, adiponectin synthesis reduction). HIV probably modifies the adipocyte differentiation and the lipid metabolism. This retroviral effect is mediated by proinflammatory cytokines (tumor necrosis factor) and the participation of other factors (drugs, diet), all in the context of a particular host genetic setting. The adipocyte (and several cellular receptors, fatty acids, membrane proteins, and cytokines) plays a central role in the pathogenesis of HIV-associated lipodystrophy.