Leptin-deficient Obese Mice Research Articles

Low cytochrome oxidase 4I1 links mitochondrial dysfunction to obesity and type 2 diabetes in humans and mice.

Cytochrome oxidase (COX) dysfunction is associated with mitochondrial oxidative stress. We determined the association between COX expression, obesity and type 2 diabetes. COX4I1 and COX10 genes were measured in monocytes of 24 lean controls, 31 glucose-tolerant and 67 diabetic obese patients, and 17 morbidly obese patients before and after bariatric surgery. We investigated the effect of caloric restriction and peroxisome proliferator-activated receptor (PPAR) agonist treatment on Cox in obese diabetic mice, and that of diet-induced insulin resistance in Streptozotocin-treated mice. Low COX4I1 was associated with type 2 diabetes in obese patients, adjusting for age, gender, smoking, interleukin-6 and high-sensitivity C-reactive protein, all related to metabolic syndrome (MetS; odds ratio: 6.1, 95% confidence interval: 2.3-16). In contrast, COX10 was low in glucose-tolerant and diabetic obese patients. In morbidly obese patients, COX4I1 was lower in visceral adipose tissue collected at bariatric surgery. In their monocytes, COX4I1 decreased after bariatric surgery, and low COX4I1 at 4 months was associated with MetS at 7 years. In leptin-deficient obese diabetic mice, Cox4i1 was low in white visceral adipose tissue (n=13; P<0.001) compared with age-matched lean mice (n=10). PPARγ-agonist treatment (n=13), but not caloric restriction (n=11), increased Cox4i1 (P<0.001). Increase in Cox4i1 depended on the increase in glucose transporter 4 (Glut4) expression and insulin sensitivity, independent of the increase in blood adiponectin. In streptozotocin-treated mice (three groups of seven mice, diet-induced insulin resistance decreased Cox4i1 and Glut4 (P<0.001 for both). COX4I1 depression is related to insulin resistance and type 2 diabetes in obesity. In peripheral blood monocytes, it may be a diagnostically useful biomarker.

Pharmacokinetics (PK), pharmacodynamics (PD) and integrated PK/PD modeling of a novel long acting FGF21 clinical candidate PF-05231023 in diet-induced obese and leptin-deficient obese mice.

Pharmacological administration of fibroblast growth factor 21 (FGF21) improves metabolic profile in preclinical species and humans. FGF21 exerts its metabolic effects through formation of beta-klotho (KLB)/FGF receptor 1c FGFR1c complex and subsequent signaling. Data from various in vitro systems demonstrate the intact C- and N-terminus of FGF21 is required for binding with KLB, and interaction with FGFR1c, respectively. However the relative roles of the termini for in vivo pharmacological effects are unclear. Here we report PF-05231023, a long-acting FGF21 analogue which is unique in that the half-life and subcutaneous (SC) bioavailability of the intact C-terminus are significantly different from those of the intact N-terminus (2 vs. 22 hr for half-life and 4~7 vs. ~50% SC bioavailability). Therefore, this molecule serves as a valuable tool to evaluate the relative roles of intact C-terminus vs. N-terminus in in vivo pharmacology studies in preclinical species. We determined the effects of PF-05231023 administration on body weight (BW) loss and glucose reduction during an oral glucose tolerance test (OGTT) following SC and intravenous (IV) administration in diet-induced obese (DIO) and leptin-deficient obese (ob/ob) mice, respectively. Our data show that the intact N-terminus of FGF21 in PF-05231023 appears to be sufficient to drive glucose lowering during OGTT and sustain BW loss in DIOs. Further, PK/PD modeling suggests that while the intact FGF21 C-terminus is not strictly required for glucose lowering during OGTT in ob/ob mice or for BW reduction in DIO mice, the higher potency conferred by intact C-terminus contributes to a rapid initiation of pharmacodynamic effects immediately following dosing. These results provide additional insight into the strategy of developing stabilized versions of FGF21 analogs to harness the full spectrum of its metabolic benefits.

Taurine supplementation regulates pancreatic islet function in response to potentiating agents in leptin-deficient obese mice.

An imbalance of the autonomic nervous system (ANS) is suggested to be involved in insulin hypersecretion in obesity. Taurine (Tau) shows anti-obesity effects and regulates pancreatic islet function. Here, we evaluated obesity development and insulin secretion in response to cholinergic/protein kinase (PK)-C and PKA activation in ob/ob mice supplemented with Tau. From weaning until 90 days of age, male and female C57Bl/6 (C) and ob/ob mice (ob) were supplemented (CT and obT), or not, with 5 % Tau. Female and male ob mice presented higher body weight and fat stores. Tau did not alter adiposity in the obT groups. Islets isolated from female and male ob mice hypersecreted insulin in response to 5.6 and 11.1 mM glucose without or with 100 μM Cch (carbachol), 100 nM PMA (phorbol-12-myristate-13-acetate) or 10 μM forskolin. Additionally, Cch-induced higher intracellular Ca2+ mobilization in ob islets. Islets from the female ob group were not responsive to the inhibitory action of phenylephrine (Phe). Tau decreased insulin release at 5.6 mM glucose without or with PMA in obT. At 11.1 mM glucose, the female obT group presented normal insulin secretion at Cch, PMA and Phe, whereas male obT partially decreased secretion following PMA and forskolin stimuli. Ca2+ mobilization induced by Cch is partially reduced in female obT. Therefore, ob islets presented hypersecretion in glucose and potentiating agents. Despite not preventing the development of obesity, the normalization of the cholinergic/PKC pathway and the improvement in the action of Phe, indicate that Tau may regulate the ANS actions upon endocrine pancreas in obesity.

Lean heart: Role of leptin in cardiac hypertrophy and metabolism.

Leptin is an adipokine that has been linked with the cardiovascular complications resulting from obesity such as hypertension and heart disease. Obese patients have high levels of circulating leptin due to increased fat mass. Clinical and population studies have correlated high levels of circulating leptin with the development of cardiac hypertrophy in obesity. Leptin has also been demonstrated to increase the growth of cultured cardiomyocytes. However, several animal studies of obese leptin deficient mice have not supported a role for leptin in promoting cardiac hypertrophy so the role of leptin in this pathological process remains unclear. Leptin is also an important hormone in the regulation of cardiac metabolism where it supports oxidation of glucose and fatty acids. In addition, leptin plays a critical role in protecting the heart from excess lipid accumulation and the formation of toxic lipids in obesity a condition known as cardiac lipotoxicity. This paper focuses on the data supporting and refuting leptin's role in promoting cardiac hypertrophy as well as its important role in the regulation of cardiac metabolism and protection against cardiac lipotoxicity.

유전성 비만 마우스에 대한 아프리칸 망고 추출물의 항비만 효과

This study investigated the anti-obesity effects of African mango (Irvingia gabonesis, IGOB 131™) extract in leptin-deficient obese mice. Experimental groups were treated with two different doses of IGOB 131™ (1% and 2% in each AIN93G supplement) for 8 weeks. Treatment of obese mice with both low and high dose of IGOB 131™ significantly reduced body weight gain by 10.9% and 13.3%, respectively, compared to control obese mice. Subcutaneous adipose tissue weight of mice was significantly reduced by 18% by low-dose and 23% by high-dose supplementation. This result was supported by micro-CT analysis around the abdominal regions of mice, indicating that the adipose tissue area and volume were significantly reduced by treatment with IGOB 131™. Serum levels of triglycerides in the low- and high-dose groups were reduced by 36.5% and 43.8%, respectively, upon treatment with IGOB 131™, whereas total cholesterol levels were reduced by 31.8% and 35.4%. Interestingly, the serum LDL level decreased upon treatment with IGOB 131™ while the serum level of HDL dramatically increased upon high-dose treatment with IGOB 131™, resulting in a significant reduction in the LDL to HDL ratio of 59.2%. These results were supported by the expression levels of enzymes and proteins related to lipid metabolism assessed by real-time PCR. There was a significant increase of in adiponectin expression as well as significant decreases in the expression of FAS, LPL, and lipid regulatory transcription factors such as PPAR-γ, C/EBP, and SREBP upon both low- and high-dose IGOB 131™ treatment. However, there was no statistical difference between low- and high-dose treatments. These results suggest that IGOB 131™ is able to regulate the serum lipid profiles by reducing triglyceride and increasing HDL levels as well as regulate expression of lipid metabolic factors, resulting in reduction of a weight gain in leptin-deficient obese mice.

Adenosine A1 receptors in mouse pontine reticular formation modulate nociception only in the presence of systemic leptin

Human obesity is associated with increased leptin levels and pain, but the specific brain regions and neurochemical mechanisms underlying this association remain poorly understood. This study used adult male C57BL/6J (B6, n=14) mice and leptin-deficient, obese B6.Cg-Lepob/J (obese, n=10) mice to evaluate the hypothesis that nociception is altered by systemic leptin levels and by adenosine A1 receptors in the pontine reticular formation. Nociception was quantified as paw withdrawal latency (PWL) in s after onset of a thermal stimulus. PWL was converted to percent maximum possible effect (%MPE). After obtaining baseline PWL measures, the pontine reticular formation was microinjected with saline (control), three concentrations of the adenosine A1 receptor agonist N6-p-sulfophenyladenosine (SPA), or super-active mouse leptin receptor antagonist (SMLA) followed by SPA 15min later, and PWL was again quantified. In obese, leptin-deficient mice, nociception was quantified before and during leptin replacement via subcutaneous osmotic pumps. SPA was administered into the pontine reticular formation of leptin-replaced mice and PWL testing was repeated. During baseline (before vehicle or SPA administration), PWL was significantly (p=0.0013) lower in leptin-replaced obese mice than in B6 mice. Microinjecting SPA into the pontine reticular formation of B6 mice caused a significant (p=0.0003) concentration-dependent increase in %MPE. SPA also significantly (p<0.05) increased %MPE in B6 mice and in leptin-replaced obese mice, but not in leptin-deficient obese mice. Microinjection of SMLA into the pontine reticular formation before SPA did not alter PWL. The results show for the first time that pontine reticular formation administration of the adenosine A1 receptor agonist SPA produced antinociception only in the presence of systemic leptin. The concentration–response data support the interpretation that adenosine A1 receptors localized to the pontine reticular formation significantly alter nociception.

Ob/ob mouse livers show decreased oxidative phosphorylation efficiencies and anaerobic capacities after cold ischemia.

BackgroundHepatic steatosis is a major risk factor for graft failure in liver transplantation. Hepatic steatosis shows a greater negative influence on graft function following prolonged cold ischaemia. As the impact of steatosis on hepatocyte metabolism during extended cold ischaemia is not well-described, we compared markers of metabolic capacity and mitochondrial function in steatotic and lean livers following clinically relevant durations of cold preservation.MethodsLivers from 10-week old leptin-deficient obese (ob/ob, n = 9) and lean C57 mice (n = 9) were preserved in ice-cold University of Wisconsin solution. Liver mitochondrial function was then assessed using high resolution respirometry after 1.5, 3, 5, 8, 12, 16 and 24 hours of storage. Metabolic marker enzymes for anaerobiosis and mitochondrial mass were also measured in conjunction with non-bicarbonate tissue pH buffering capacity.Results Ob/ob and lean mice livers showed severe (>60%) macrovesicular and mild (<30%) microvesicular steatosis on Oil Red O staining, respectively. Ob/ob livers had lower baseline enzymatic complex I activity but similar adenosine triphosphate (ATP) levels compared to lean livers. During cold storage, the respiratory control ratio and complex I-fueled phosphorylation deteriorated approximately twice as fast in ob/ob livers compared to lean livers. Ob/ob livers also demonstrated decreased ATP production capacities at all time-points analyzed compared to lean livers. Ob/ob liver baseline lactate dehydrogenase activities and intrinsic non-bicarbonate buffering capacities were depressed by 60% and 40%, respectively compared to lean livers.ConclusionsSteatotic livers have impaired baseline aerobic and anaerobic capacities compared to lean livers, and mitochondrial function indices decrease particularly from after 5 hours of cold preservation. These data provide a mechanistic basis for the clinical recommendation of shorter cold storage durations in steatotic donor livers.

C1q/TNF-related Protein 4 (CTRP4) Is a Unique Secreted Protein with Two Tandem C1q Domains That Functions in the Hypothalamus to Modulate Food Intake and Body Weight

CTRP4 is a unique member of the C1q family, possessing two tandem globular C1q domains. Its physiological function is poorly defined. Here, we show that CTRP4 is an evolutionarily conserved, ∼34-kDa secretory protein expressed in the brain. In human, mouse, and zebrafish brain, CTRP4 expression begins early in development and is widespread in the central nervous system. Neurons, but not astrocytes, express and secrete CTRP4, and secreted proteins form higher-order oligomeric complexes. CTRP4 is also produced by peripheral tissues and circulates in blood. Its serum levels are increased in leptin-deficient obese (ob/ob) mice. Functional studies suggest that CTRP4 acts centrally to modulate energy metabolism. Refeeding following an overnight fast induced the expression of CTRP4 in the hypothalamus. Central administration of recombinant protein suppressed food intake and altered the whole-body energy balance in both chow-fed and high-fat diet-fed mice. Suppression of food intake by CTRP4 is correlated with a decreased expression of orexigenic neuropeptide (Npy and Agrp) genes in the hypothalamus. These results establish CTRP4 as a novel nutrient-responsive central regulator of food intake and energy balance.

The antiallodynic action of nortriptyline and terbutaline is mediated by β2 adrenoceptors and δ opioid receptors in the ob/ob model of diabetic polyneuropathy

Peripheral polyneuropathy is a frequent complication of diabetes. One of its consequences is neuropathic pain which is often chronic and difficult to treat. This pain management classically involves anticonvulsant drugs or tricyclic antidepressant drugs (TCA). We have previously shown that β2 adrenoceptors and δ opioid receptors are critical for TCA action in a traumatic model of neuropathic pain. In the present work, we used the obese leptin deficient mice (ob/ob) which are a genetic model of type 2 diabetes in order to study the treatment of diabetic polyneuropathy. ob/ob mice with hyperglycemia develop tactile bilateral allodynia. We investigated the action of the TCA nortriptyline and the β2 adrenoceptor agonist terbutaline on this neuropathic allodynia. The consequences of acute and chronic treatments were tested, and mechanical allodynia was assessed by using von Frey hairs. Chronic but not acute treatment with nortriptyline alleviates allodynia caused by the diabetic neuropathy. This effect depends on β2 adrenoceptors but not on α2 adrenoceptors, as shown by the blockade with repeated co-administration of the β2 adrenoceptor antagonist ICI118551 but not with repeated co-administration of the α2 adrenoceptor antagonist yohimbine. Direct stimulation of β2 adrenoceptors appears sufficient to relieve allodynia, as shown with chronic terbutaline treatment. δ but not mu opioid receptors seem important to these action since acute naltrindole, but not acute naloxonazine, reverses the effect of chronic nortriptyline or terbutaline treatment.

Erythropoietin Increases Erythropoiesis, Metabolism and Weight Loss In Mice

▪Erythropoietin is required for erythroid progenitor cell survival, proliferation and differentiation. Increasing evidence suggests that erythropoietin treatment in mice can stimulate erythropoiesis and also affect metabolic processes in a dose dependent manner. For example, medium to high dose erythropoietin treatment (600 U/kg or 3000 U/kg) in leptin deficient obese (ob/ob) mice three times a week for three weeks or more results in the expected increase in hematocrit as well as decrease in accumulated body fat and improved glucose tolerance. Phlebotomy to maintain normal hematocrit demonstrated that erythropoietin regulation of body weight was not dependent on increased red cell mass. In non-obese wild type C57BL/6 mice, erythropoietin treatment also demonstrated the expected increase in hematocrit as well as a 15% reduction in body weight and decreased fasting blood glucose. Erythropoietin receptor is expressed at the highest level in erythroid progenitor cells. The link between increased metabolism and erythropoietin stimulated erythroid differentiation was suggested by the increased oxygen consumption rate observed in vitro in primary cultures of erythropoietin stimulated erythroid progenitor cells. Erythropoietin also stimulated glucose uptake in differentiating erythroid progenitor cells in a dose dependent manner. Glucose uptake decreased with the down regulation of erythropoietin receptor during terminal differentiation. Relatively high erythropoietin receptor expression and erythropoietin activity that may also contribute to erythropoietin metabolic activity has been observed in non-hematopoietic mouse tissue including the hypothalamus and white adipose tissue (Teng R, Gavrilova O et al., Nat Commun 2011). The hypothalamus contributes importantly to appetite regulation and mice treated with erythropoietin exhibited a decrease in food intake compared with saline control. We found that pair-feeding decreased body weight and fat mass, and improved glucose tolerance, but no more than half that observed with erythropoietin treatment, providing evidence that erythropoietin regulation of food intake accounts for only part of the metabolic response observed with erythropoietin treatment. Adipocytes isolated from white adipose tissue in erythropoietin treated mice showed an increase in oxygen consumption compared with vehicle treated or pair-fed mice. To assess the role of direct erythropoietin response of white adipose tissue in regulation of fat mass accumulation, we engineered mice with targeted deletion of erythropoietin receptor in adipose tissue. Erythropoietin treatment gave rise to the expected increase in hematocrit but resulted in a reduced decrease in body weight compared with saline treatment. These data show that erythropoietin treatment can stimulate cell oxygen consumption and can contribute to regulation of metabolism and body weight in mice. Erythropoietin receptor expression on erythroid progenitor cells provides for erythropoietin response to promote erythropoiesis and increase cell metabolic activity including glucose uptake and oxygen consumption. In non-hematopoietic tissue, erythropoietin receptor expression further contributes to erythropoietin regulated metabolic activity such as control of food intake attributed in part to hypothalamus response and modulation of fat mass affected by direct erythropoietin response in white adipose tissue. Therefore, in addition to its critical role in promoting erythropoiesis, erythropoietin can contribute to metabolic homeostasis via its activity in erythroid tissue and beyond. Disclosures:No relevant conflicts of interest to declare.

Obese adipocytes show ultrastructural features of stressed cells and die of pyroptosis

We previously suggested that, in obese animals and humans, white adipose tissue inflammation results from the death of hypertrophic adipocytes; these are then cleared by macrophages, giving rise to distinctive structures we denominated crown-like structures. Here we present evidence that subcutaneous and visceral hypertrophic adipocytes of leptin-deficient (ob/ob and db/db) obese mice exhibit ultrastructural abnormalities (including calcium accumulation and cholesterol crystals), many of which are more common in hyperglycemic db/db versus normoglycemic ob/ob mice and in visceral versus subcutaneous depots. Degenerating adipocytes whose intracellular content disperses in the extracellular space were also noted in obese mice; in addition, increased anti-reactive oxygen species enzyme expression in obese fat pads, documented by RT-PCR and immunohistochemistry, suggests that ultrastructural changes are accompanied by oxidative stress. RT-PCR showed NLRP3 inflammasome activation in the fat pads of both leptin-deficient and high-fat diet obese mice, in which formation of active caspase-1 was documented by immunohistochemistry in the cytoplasm of several hypertrophic adipocytes. Notably, caspase-1 was not detected in FAT-ATTAC transgenic mice, where adipocytes die of apoptosis. Thus, white adipocyte overexpansion induces a stress state that ultimately leads to death. NLRP3-dependent caspase-1 activation in hypertrophic adipocytes likely induces obese adipocyte death by pyroptosis, a proinflammatory programmed cell death.

Effect of Caloric Restriction and AMPK Activation on Hepatic Nuclear Receptor, Biotransformation Enzyme, and Transporter Expression in Lean and Obese Mice

Fatty liver alters liver transporter expression. Caloric restriction (CR), the recommended therapy to reverse fatty liver, increases Sirtuin1 deacetylase activity in liver. This study evaluated whether CR and CR mimetics reversed obesity-induced transporter expression in liver and hepatocytes. mRNA and protein expression was determined in adult lean (lean) and leptin-deficient obese (OB) mice fed ad libitum or placed on 40% (kCal) reduced diet. Hepatocytes were isolated from lean and OB mice, treated with AMP Kinase activators, and gene expression was determined. CR decreased Oatp1a1, Oatp1b2, and Abcb11 mRNA expression in lean, but not OB mice. CR increased Abcc2 mRNA OB livers, whereas protein expression increased in both genotypes. CR increased Abcc3 protein expression increased in OB livers. CR did not alter Abcc1, 4 and 5 mRNA expression in lean mice but decreased expression in livers of OB mice. CR increased Abcc4 protein in lean, but not OB mice. CR restriction reversed the expression of some, but not all transporters in livers of OB mice. Overall, these data indicate a potential for CR to restore some hepatic transporter changes in OB mice, but suggest a functional leptin axis is needed for reversal of expression for some transporters.

Quantification of Hepatic Steatosis With Dual-Energy Computed Tomography

The aim of this study was to compare dual-energy computed tomography (DECT) and magnetic resonance imaging (MRI) for fat quantification using tissue triglyceride concentration and histology as references in an animal model of hepatic steatosis. This animal study was approved by our institution's Research Animal Resource Center. After validation of DECT and MRI using a phantom consisting of different triglyceride concentrations, a leptin-deficient obese mouse model (ob/ob) was used for this study. Twenty mice were divided into 3 groups based on expected levels of hepatic steatosis: low (n = 6), medium (n = 7), and high (n = 7) fat. After MRI at 3 T, a DECT scan was immediately performed. The caudate lobe of the liver was harvested and analyzed for triglyceride concentration using a colorimetric assay. The left lateral lobe was also extracted for histology. Magnetic resonance imaging fat-fraction (FF) and DECT measurements (attenuation, fat density, and effective atomic number) were compared with triglycerides and histology. Phantom results demonstrated excellent correlation between triglyceride content and each of the MRI and DECT measurements (r(2) ≥ 0.96, P ≤ 0.003). In vivo, however, excellent triglyceride correlation was observed only with attenuation (r(2) = 0.89, P < 0.001) and MRI-FF (r(2) = 0.92, P < 0.001). Strong correlation existed between attenuation and MRI-FF (r(2) = 0.86, P < 0.001). Nonlinear correlation with histology was also excellent for attenuation and MRI-FF. Dual-energy computed tomography (CT) data generated by the current Gemstone Spectral Imaging analysis tool do not improve the accuracy of fat quantification in the liver beyond what CT attenuation can already provide. Furthermore, MRI may provide an excellent reference standard for liver fat quantification when validating new CT or DECT methods in human subjects.

Fat on the brain

The study by Borg and colleagues featured in this issue of The Journal of Physiology suggests that a high fat diet could quite literally leave you with ‘fat on the brain’ (Borg et al. 2012). According to this research, an excess intake of dietary fat translates into increased lipid content of brain tissues, which is likely to have significant (and probably negative) consequences for brain function. This work builds on previous studies in both animals and humans which have shown that consuming excessive amounts of fat in the diet leads to an increased accumulation of lipid in peripheral tissues which aren't designed for fat storage, particularly the skeletal muscle and liver, in a process referred to as ectopic fat storage (Frayn, 2001; Kopecky et al. 2002). The resulting increase in the fat content of these tissues interferes with their ability to function normally, and is implicated in many of the co-morbidities associated with diet-induced obesity, in particular insulin resistance (Kopecky et al. 2002; Ravussin & Smith, 2002). In the skeletal muscle and liver, for example, increases in lipids such as ceramide and diacylglycerol block insulin signalling, leading to reduced glucose uptake in the muscle and impaired suppression of glucose output by the liver, both of which contribute to peripheral hyperglycaemia and ultimately lead to whole body insulin resistance (Kopecky et al. 2002). Whilst the association between high fat diets and increased fat accumulation is well established and has been looked at in a range of important metabolic tissues, including the pancreas, liver and muscle, the study by Borg and colleagues is the first to show that this also occurs in the brain. In this study, mice were fed for 12 weeks on either a low fat diet, which supplied 5% energy from fat, or a micro-nutrient-matched high fat diet, supplying 59% energy from fat. The hypothalami (a region known to be critical for the regulation of energy balance) of the mice were then collected and examined for signs of lipid accumulation. These investigations revealed that the levels of several lipids, particularly those known to be involved in insulin resistance, were significantly elevated in the brains of the mice on the high fat diet at the end of the feeding period. Importantly, further studies showed that the accumulation of lipid in the brains of these mice was specifically related to consumption of a high fat diet and not obesity per se, since genetically obese leptin-deficient mice consuming a low fat diet didn't show increased brain lipid levels, despite being of a similar body weight to the diet-induced obese mice. It will be interesting in future studies to determine what happens to brain lipid levels in animals who are resistant to diet-induced obesity, since the results of the Borg paper suggest that even if these animals remain lean, they could still exhibit significant lipid accumulation in the brain and the associated adverse consequences in the long term. The other question addressed in this paper is the all-important one of reversibility. In previous studies, exercise has proved to be an effective approach for promoting fat oxidation, reducing triglyceride content in skeletal muscle and improving peripheral insulin sensitivity (Snel et al. 2012). Based on this, it might be expected that placing high-fat-fed mice on an exercise regimen might help to reverse the accumulation of brain lipids. However, the results of this paper clearly showed that even when mice consuming a high-fat diet were placed on a fairly substantial programme of treadmill running for 6 weeks, brain lipid content was not significantly different from high-fat-fed mice who were sedentary. This was despite positive effects of the exercise intervention on fitness (running capacity), fasting glucose levels and glucose tolerance. So, whilst it might be possible to overcome some of the negative effects of a high fat diet by exercise, it would appear that the only way to reduce brain lipid levels is by reducing the intake of fat in the diet. This paper clearly shows that consuming a high fat diet can literally result in fat on (or rather in) the brain. Knowing what we do about the negative effects of increased lipid accumulation on the function of other tissues, it seems highly likely that accumulation of excess lipid in brain tissues will have negative effects on the many crucial regulatory systems of the brain. Following on from these findings, it will be important to move towards determining the full impact of lipid accumulation on brain function and investigating potential strategies for preventing and reversing this process.

Genetic induction of phosphate toxicity significantly reduces the survival of hypercholesterolemic obese mice

Objective The adverse effects of metabolic disorders in obesity have been extensively studied; however, the pathologic effects of hyperphosphatemia or phosphate toxicity in obesity have not been studied in similar depth and detail, chiefly because such an association is thought to be uncommon. Studies have established that the incidence of obesity-associated nephropathy is increasing. Because hyperphosphatemia is a major consequence of renal impairment, this study determines the in vivo effects of hyperphosphatemia in obesity. Methods and results We genetically induced hyperphosphatemia in leptin-deficient obese ( ob/ ob) mice by generating ob/ ob and klotho double knockout [ ob/ ob- klotho −/−] mice. As a control, we made ob/ ob mice with hypophosphatemia by generating ob/ ob and 1- alpha hydroxylase double knockout [ ob/ ob-1 α( OH) ase −/−] mice. Compared to the wild-type mice, all three obese background mice, namely ob/ ob, ob/ ob- klotho −/−, and ob/ ob-1 α( OH) ase −/− mice developed hypercholesterolemia. In addition, the hyperphosphatemic, ob/ ob- klotho −/− genetic background induced generalized tissue atrophy and widespread soft-tissue and vascular calcifications, which led to a shorter lifespan; no such changes were observed in the hypophosphatemic, ob/ ob-1 α( OH) ase −/− mice. Significantly, in contrast to the reduced survival of the ob/ ob- klotho −/− mice, lowering serum phosphate levels in ob/ ob-1 α( OH) ase −/− mice showed no such compromised survival, despite both mice being hypercholesterolemic. Conclusion These genetic manipulation studies suggest phosphate toxicity is an important risk factor in obesity that can adversely affect survival.

Serotonin Receptor Type 3 Antagonists Improve Obesity-Associated Fatty Liver Disease in Mice

Obesity is a major cause for nonalcoholic fatty liver disease (NAFLD). Previous studies suggested that alterations in intestinal motility and permeability contribute to the development of NAFLD. Serotonin and serotonin receptor type 3 (5-HT(3)R) are key factors in the regulation of intestinal motility and permeability. Therefore, we studied the effect of the 5-HT(3)R antagonists tropisetron and palonosetron on the development of NAFLD in leptin-deficient obese mice. Four-week-old ob/ob mice and lean controls were treated for 6 weeks orally with tropisetron or palonosetron at 0.2 mg/kg per day. We determined markers of liver damage and inflammation, portal endotoxin levels, and duodenal concentrations of serotonin, serotonin-reuptake transporter (SERT), occludin, and claudin-1. Tropisetron treatment significantly reduced liver fat content (-29%), liver inflammation (-56%), and liver cell necrosis (-59%) in ob/ob mice. The beneficial effects of tropisetron were accompanied by a decrease in plasma alanine aminotransferase and portal vein plasma endotoxin levels, an attenuation of enhanced MyD88 and tumor necrosis factor-α mRNA expression in the liver, and an increase of tight junction proteins in the duodenum. Tropisetron treatment also caused a reduction of elevated serotonin levels and an increase of SERT in the duodenum of ob/ob mice. Palonosetron had similar effects as tropisetron with regard to the reduction of liver fat and other parameters. Tropisetron and palonosetron are effective in attenuating NAFLD in a genetic mouse model of obesity. The effect involves the intestinal nervous system, resulting in a reduction of endotoxin influx into the liver and subsequently of liver inflammation and fat accumulation.

Ob/ob serum promotes a mesenchymal cell phenotype in B16BL6 melanoma cells

In 2009, malignant melanoma was responsible for approximately 9,000 deaths in the US. These deaths are often associated with aggressive metastasis to secondary sites such as the lungs. Epidemiological and animal studies suggest that obesity is a risk factor for melanoma. Others have shown that B16BL6 melanoma cells metastasize more aggressively in obese ob/ob than in lean mice. However, the mechanism by which obesity promotes B16BL6 melanoma metastasis in ob/ob mice has not been identified. In the present study, we used serum obtained from control and ob/ob leptin-deficient obese mice to determine if obese serum increases the aggressive phenotype of melanoma cells. Results showed that ob/ob serum has higher levels of resistin, insulin, tPAI1, IL-6, TNF-α, and MCP-1 compared to control serum. We showed that ob/ob serum increases the invasive ability of B16BL6 melanomas. To further determine the mechanism by which ob/ob serum increases the invasive ability of melanomas, we determined the effect of ob/ob and control serum on genes associated with the epithelial-to-mesenchymal transition (EMT). Cancer cells with a mesenchymal phenotype have a higher metastatic ability. Snai1 and Twist are genes that are strongly associated with EMT and metastasis of melanomas. Our results showed that ob/ob serum increases the expression of Snai1 and Twist. Moreover, ob/ob serum increased matrix metalloproteast 9 (MMP9) activity and decreased the expression of E-cadherin and the metastasis suppressor gene Kiss1. In summary, results suggest that obesity may increase the metastatic ability of melanoma by promoting a mesenchymal cell phenotype.

Cardiovascular and metabolic responses to thermoneutrality and cold ambient temperature in lean and obese leptin deficient mice

Cardiovascular and metabolic responses to thermoneutrality and cold ambient temperature in lean and obese leptin deficient mice

Expression of Monocyte Chemotactic Protein 3 Following Simulated Birth Trauma in a Murine Model of Obesity

To determine the effect of obesity on simulated birth trauma in leptin-deficient obese mice as measured by relative monocyte chemotactic protein 3 (MCP-3) expression. A total of 25 wild-type and 25 obese C57BL/6 virgin female mice underwent 1 hour of vaginal distension (VD), sham VD, or anesthesia without VD. Pelvic organ tissues were then harvested either immediately or 24-hours post VD and subsequent real-time polymerase chain reaction analysis was performed. Urethral MCP-3 levels in wild-type mice were elevated from baseline at 0 hours with a return to baseline at 24 hours in both VD and sham VD groups. In obese mice, there was a 6-fold elevation in MCP-3 levels at 0 hours after sham VD vs control (P <.05), which then returned to baseline levels at 24 hours. After undergoing VD, MCP-3 levels increased to 6-fold baseline values (P = .002) at 0 hours, with continued elevation in MCP-3 levels to 15 times control levels (P = .0003) at 24 hours. MCP-3 is significantly over-expressed in the urethral tissues of both wild-type and obese mice immediately after any urethral manipulation. At 24 hours, the MCP-3 expression patterns become divergent between VD and sham VD in obese mice. With a greater degree of trauma, MCP-3 continued to rise at 24 hours, suggesting that the underlying obesity resulted in alterations in response to tissue injury, paralleling the degree of injury. Such associations warrant further investigation into the role of MCP-3 as a chemokine for stem cell migration, with implications for subsequent tissue repair mechanisms after birth trauma.

Deficiency in the extracellular signal-regulated kinase 1 (ERK1) protects leptin-deficient mice from insulin resistance without affecting obesity

Extracellular signal-regulated kinase (ERK) activity is increased in adipose tissue in obesity and type 2 diabetes mellitus and strong evidences suggests that it is implicated in the downregulation of insulin signalling and action in the insulin-resistant state. To determine the role of ERK1 in obesity-associated insulin resistance in vivo, we inactivated Erk1 (also known as Mapk3) in obese leptin-deficient mice (ob/ob). Mice of genotype ob/ob-Erk1⁻(/)⁻ were obtained by crossing Erk1⁻(/)⁻ mice with ob/ob mice. Glucose tolerance and insulin sensitivity were studied in 12-week-old mice. Tissue-specific insulin sensitivity, insulin signalling, liver steatosis and adipose tissue inflammation were determined. While ob/ob-Erk1⁻(/)⁻ and ob/ob mice exhibited comparable body weight and adiposity, ob/ob-Erk1⁻(/)⁻ mice did not develop hyperglycaemia and their glucose tolerance was improved. Hyperinsulinaemic-euglycaemic clamp studies demonstrated an increase in whole-body insulin sensitivity in the ob/ob-Erk1⁻(/)⁻ mice associated with an increase in both insulin-stimulated glucose disposal in skeletal muscles and adipose tissue insulin sensitivity. This occurred in parallel with improved insulin signalling in both tissues. The ob/ob-Erk1⁻(/)⁻ mice were also partially protected against hepatic steatosis with a strong reduction in acetyl-CoA carboxylase level. These metabolic improvements were associated with reduced expression of mRNA encoding inflammatory cytokine and T lymphocyte markers in the adipose tissue. Our results demonstrate that the targeting of ERK1 could partially protect obese mice against insulin resistance and liver steatosis by decreasing adipose tissue inflammation and by increasing muscle glucose uptake. Our results indicate that deregulation of the ERK1 pathway could be an important component in obesity-associated metabolic disorders.