Impaired intestinal free fatty acid transport followed by chylomicron malformation, not pancreatic insufficiency, cause metabolic defects in cystic fibrosis.

Intestinal disease is one of the earliest manifestations of cystic fibrosis (CF) in children and is closely tied to deficits in growth and nutrition, both of which are directly linked to future mortality. Patients are treated aggressively with pancreatic enzyme replacement therapy and a high-fat diet to circumvent fat malabsorption, but this does not reverse growth and nutritional defects. We hypothesized that defects in chylomicron production could explain why CF body weights and nutrition are so resistant to clinical treatments.

The Isolation of Flowing Mesenteric Lymph in Mice to Quantify In Vivo Kinetics of Dietary Lipid Absorption and Chylomicron Secretion.

Intestinal lipoproteins, especially triglyceride-rich chylomicrons, are a major driver of metabolism, inflammation, and cardiovascular diseases. However, isolating intestinal lipoproteins is very difficult in vivo because they are first secreted from the small intestine into the mesenteric lymphatics. Chylomicron-containing lymph then empties into the subclavian vein from the thoracic duct to deliver components of the meal to the heart, lungs, and, ultimately, whole-body circulation.

Hepatocyte-derived GDF15 suppresses feeding and improves insulin sensitivity in obese mice.

Growth differentiation factor 15 (GDF15) is a stress-induced secreted protein whose circulating levels are increased in the context of obesity. Recombinant GDF15 reduces body weight and improves glycemia in obese models, which is largely attributed to the central action of GDF15 to suppress feeding and reduce body weight. Despite these advances in knowledge, the tissue-specific sites of GDF15 production during obesity are unknown, and the effects of modulating circulating GDF15 levels on insulin sensitivity have not been evaluated directly.

A single-day mouse mesenteric lymph surgery in mice: an updated approach to study dietary lipid absorption, chylomicron secretion, and lymphocyte dynamics.

The intestine plays a crucial role in regulating whole-body lipid metabolism through its unique function of absorbing dietary fat. In the small intestine, absorptive epithelial cells emulsify hydrophobic dietary triglycerides (TAGs) prior to secreting them into mesenteric lymphatic vessels as chylomicrons. Except for short- and medium-chain fatty acids, which are directly absorbed from the intestinal lumen into portal vasculature, the only way for an animal to absorb dietary TAG is through the chylomicron/mesenteric lymphatic pathway.

Cardiolipin deficiency elevates susceptibility to a lipotoxic hypertrophic cardiomyopathy.

Cardiolipin (CL) is a unique tetra-acyl phospholipid localized to the inner mitochondrial membrane and essential for normal respiratory function. It has been previously reported that the failing human heart and several rodent models of cardiac pathology have a selective loss of CL. A rare genetic disease, Barth syndrome (BTHS), is similarly characterized by a cardiomyopathy due to reduced levels of cardiolipin.

Petite Integration Factor 1 (PIF1) helicase deficiency increases weight gain in Western diet-fed female mice without increased inflammatory markers or decreased glucose clearance.

Petite Integration Factor 1 (PIF1) is a multifunctional helicase present in nuclei and mitochondria. PIF1 knock out (KO) mice exhibit accelerated weight gain and decreased wheel running on a normal chow diet. In the current study, we investigated whether Pif1 ablation alters whole body metabolism in response to weight gain.

Adropin reduces blood glucose levels in mice by limiting hepatic glucose production.

Adropin is a liver- and brain-secreted peptide hormone with striking effects on fuel metabolism regulation in a number of tissues. Previous studies demonstrated that adropin secretion is decreased in obese mice subjected to a long-term high-fat diet (HFD), and that whole-body loss of adropin expression resulted in systemic insulin resistance. Treatment of obese mice with adropin improves glucose tolerance, which has been linked to increased glucose oxidation and inhibition of fatty acid utilization in isolated skeletal muscle homogenates.

Hepatocyte-Specific Ablation or Whole-Body Inhibition of Xanthine Oxidoreductase in Mice Corrects Obesity-Induced Systemic Hyperuricemia Without Improving Metabolic Abnormalities.

Systemic hyperuricemia (HyUA) in obesity/type 2 diabetes facilitated by elevated activity of xanthine oxidoreductase (XOR), which is the sole source of uric acid (UA) in mammals, has been proposed to contribute to the pathogenesis of insulin resistance/dyslipidemia in obesity. Here, the effects of hepatocyte-specific ablation of , the gene encoding XOR (HXO), and whole-body pharmacologic inhibition of XOR (febuxostat) on obesity-induced insulin resistance/dyslipidemia were assessed. Deletion of hepatocyte substantially lowered liver and plasma UA concentration.

Elevated metabolic rate and skeletal muscle oxidative metabolism contribute to the reduced susceptibility of NF-κB p50 null mice to obesity.

Mice with a deletion of the p50 subunit of the proinflammatory nuclear factor kappa B pathway (NF-κB p50) have reduced weight compared to wild-type control mice. However, the physiological underpinning of this phenotype remains unknown. This study addressed this issue.

Adipose tissue-derived free fatty acids initiate myeloid cell accumulation in mouse liver in states of lipid oversupply.

Accumulation of myeloid cells in the liver, notably dendritic cells (DCs) and monocytes/macrophages (MCs), is a major component of the metainflammation of obesity. However, the mechanism(s) stimulating hepatic DC/MC infiltration remain ill defined. Herein, we addressed the hypothesis that adipose tissue (AT) free fatty acids (FFAs) play a central role in the initiation of hepatic DC/MC accumulation, using a number of mouse models of altered FFA supply to the liver.

DNA methylation alters transcriptional rates of differentially expressed genes and contributes to pathophysiology in mice fed a high fat diet.

Objective: Overnutrition can alter gene expression patterns through epigenetic mechanisms that may persist through generations. However, it is less clear if overnutrition, for example a high fat diet, modifies epigenetic control of gene expression in adults, or by what molecular mechanisms, or if such mechanisms contribute to the pathology of the metabolic syndrome. Here we test the hypothesis that a high fat diet alters hepatic DNA methylation, transcription and gene expression patterns, and explore the contribution of such changes to the pathophysiology of obesity.

Kupffer cells facilitate the acute effects of leptin on hepatic lipid metabolism.

Leptin has potent effects on lipid metabolism in a number of peripheral tissues. In liver, an acute leptin infusion (~120 min) stimulates hepatic fatty acid oxidation (~30%) and reduces triglycerides (TG, ~40%), effects that are dependent on phosphoinositol-3-kinase (PI3K) activity. In the current study we addressed the hypothesis that leptin actions on liver-resident immune cells are required for these metabolic effects.

Similar degrees of obesity induced by diet or aging cause strikingly different immunologic and metabolic outcomes.

In obesity, adipose tissue (AT) and liver are infiltrated with Th-1 polarized immune cells, which are proposed to play an important role in the pathogenesis of the metabolic abnormalities of obesity. Aging is also associated with increased adiposity, but the effects of this increase on inflammation and associated metabolic dysfunction are poorly understood. To address this issue, we assessed insulin resistance (IR) andATand liver immunophenotype in aged, lean (AL) and aged, obese (AO) mice, all of whom were maintained on a standard chow diet (11% fat diet) throughout their lives.

Dendritic cells promote macrophage infiltration and comprise a substantial proportion of obesity-associated increases in CD11c+ cells in adipose tissue and liver.

Obesity-associated increases in adipose tissue (AT) CD11c(+) cells suggest that dendritic cells (DC), which are involved in the tissue recruitment and activation of macrophages, may play a role in determining AT and liver immunophenotype in obesity. This study addressed this hypothesis. With the use of flow cytometry, electron microscopy, and loss-and-gain of function approaches, the contribution of DC to the pattern of immune cell alterations and recruitment in obesity was assessed.

Mice lacking NKT cells but with a complete complement of CD8+ T-cells are not protected against the metabolic abnormalities of diet-induced obesity.

The contribution of natural killer T (NKT) cells to the pathogenesis of metabolic abnormalities of obesity is controversial. While the combined genetic deletion of NKT and CD8(+) T-cells improves glucose tolerance and reduces inflammation, interpretation of these data have been complicated by the recent observation that the deletion of CD8(+) T-cells alone reduces obesity-induced inflammation and metabolic dysregulation, leaving the issue of the metabolic effects of NKT cell depletion unresolved. To address this question, CD1d null mice (CD1d(-/-)), which lack NKT cells but have a full complement of CD8(+) T-cells, and littermate wild type controls (WT) on a pure C57BL/6J background were exposed to a high fat diet, and glucose intolerance, insulin resistance, dyslipidemia, inflammation, and obesity were assessed.

Depletion of liver Kupffer cells prevents the development of diet-induced hepatic steatosis and insulin resistance.

Objective: Increased activity of the innate immune system has been implicated in the pathogenesis of the dyslipidemia and insulin resistance associated with obesity and type 2 diabetes. In this study, we addressed the potential role of Kupffer cells (liver-specific macrophages, KCs) in these metabolic abnormalities.

Research Design And Methods: Rats were depleted of KCs by administration of gadolinium chloride, after which all animals were exposed to a 2-week high-fat or high-sucrose diet.

Leptin augments the acute suppressive effects of insulin on hepatic very low-density lipoprotein production in rats.

It is well established that leptin increases the sensitivity of carbohydrate metabolism to the effects of insulin. Leptin and insulin also have potent effects on lipid metabolism. However, the effects of leptin on the regulation of liver lipid metabolism by insulin have not been investigated.

Inhibition or deletion of the lipopolysaccharide receptor Toll-like receptor-4 confers partial protection against lipid-induced insulin resistance in rodent skeletal muscle.

Aims/hypothesis: A role for increased activity of the innate immune system in the pathogenesis of insulin resistance is supported by a number of studies. The current study assessed the potential role of the lipopolysaccharide receptor known as Toll-like receptor-4 (TLR-4), a component of the innate immune system, in mediating lipid-induced insulin resistance in skeletal muscle.

Methods: The effects of TLR-4 inhibition/deletion on lipid-induced insulin resistance was determined in skeletal muscle of TLR-4 null mice in vivo and in rat L6 myotubes in vitro.

Leptin, skeletal muscle lipids, and lipid-induced insulin resistance.

Leptin-induced increases in insulin sensitivity are well established and may be related to the effects of leptin on lipid metabolism. However, the effects of leptin on the levels of lipid metabolites implicated in pathogenesis of insulin resistance and the effects of leptin on lipid-induced insulin resistance are unknown. The current study addressed in rats the effects of hyperleptinemia (HL) on insulin action and markers of skeletal muscle (SkM) lipid metabolism in the absence or presence of acute hyperlipidemia induced by an infusion of a lipid emulsion.

Hepatic steatosis and plasma dyslipidemia induced by a high-sucrose diet are corrected by an acute leptin infusion.

High sucrose (HS) feeding in rats induces hepatic steatosis and plasma dyslipidemia. In previous reports (Huang W, Dedousis N, Bhatt BA, O'Doherty RM. J Biol Chem 279: 21695-21700, 2004; and Huang W, Dedousis N, Bandi A, Lopaschuk GD, O'Doherty RM.

Liver triglyceride secretion and lipid oxidative metabolism are rapidly altered by leptin in vivo.

Leptin has potent lipid-lowering effects in peripheral tissues and plasma that are proposed to be important for the prevention of cellular lipotoxicity and insulin resistance. The current study addressed in vivo the effects of acute leptin delivery on liver triglyceride (TG) metabolism, the consequence of hepatic leptin action on whole-body TG homeostasis, and the mechanisms of leptin action. A 120-min iv leptin infusion (plasma leptin, approximately 14 ng/ml) decreased liver TG levels (53 +/- 3%; P = 0.

Diet-induced obesity and acute hyperlipidemia reduce IkappaBalpha levels in rat skeletal muscle in a fiber-type dependent manner.

Increased activity of proinflammatory/stress pathways has been implicated in the pathogenesis of insulin resistance in obesity. However, the effects of obesity on the activity of these pathways in skeletal muscle, the major insulin-sensitive tissue by mass, are poorly understood. Furthermore, the mechanisms that activate proinflammatory/stress pathways in obesity are unknown.

Impaired activation of phosphatidylinositol 3-kinase by leptin is a novel mechanism of hepatic leptin resistance in diet-induced obesity.

Obesity is associated with the development of leptin resistance. However, the effects of leptin resistance on leptin-regulated metabolic processes and the biochemical defects that cause leptin resistance are poorly understood. We have addressed in rats the effect of dietinduced obesity (DIO), a situation of elevated tissue lipid levels, on the well described lipid-lowering effect of leptin in liver, an action that is proposed to be important for the prevention of tissue lipotoxicity and insulin resistance.

Simultaneous glutamate and perfusion fMRI responses to regional brain stimulation.

Functional magnetic resonance imaging (fMRI) rests on the assumption that regional brain activity is closely coupled to regional cerebral blood flow (rCBF) in vivo. To test the degree of coupling, cortical brain activity was locally stimulated in rats by reversed microdialysis infusion of picrotoxinin, alphagamma-aminobutyric acid-A antagonist. Before and during the first 30 minutes of infusion, simultaneous fMRI (rCBF) and neurochemical (interstitial glutamate concentration) measures of brain activity were highly correlated (r = 0.