Reducing plasma free fatty acids by acipimox improves glucose tolerance in high-fat fed mice

To study whether free fatty acids (FFAs) contribute to glucose intolerance in high-fat fed mice, the derivative of nicotinic acid, acipimox, which inhibits lipolysis, was administered intraperitoneally (50 mg kg(-1)) to C57BL/6J mice which had been on a high-fat diet for 3 months. Four hours after administration of acipimox, plasma FFA levels were reduced to 0.46 +/- 0.06 mmol L(-1) compared with 0.88 +/- 0.10 mmol L(-1) in controls (P < 0.001). At this point, the glucose elimination rate after an intravenous glucose load (1 g kg(-1)) was markedly improved. Thus, the elimination constant (KG) for the glucose disposal between 1 and 50 min after the glucose challenge was increased from 0.54 +/- 0.01% min-1 in controls to 0.66 +/- 0.01% min-1 by acipimox (P < 0.001). In contrast, the acute insulin response to glucose (1-5 min) was not significantly different between the groups, although the area under the insulin for the entire 50-min period after glucose administration was significantly reduced by acipimox from 32.1 +/- 2.9 to 23.9 +/- 1.2 nmol L(-1) x 50 min (P = 0.036). This, however, was mainly because of lower insulin levels at 20 and 50 min because of the lowered glucose levels. In contrast, administration of acipimox to mice fed a normal diet did not affect plasma levels of FFA or the glucose elimination or insulin levels after the glucose load. It is concluded that reducing FFA levels by acipimox in glucose intolerant high-fat fed mice improves glucose tolerance mainly by improving insulin sensitivity making the ambient islet function adequate, suggesting that increased FFA levels are of pathophysiological importance in this model of glucose intolerance.     

Japanese herbal medicines shosaikoto,inchinkoto, and juzentaihoto inhibit high‐fat diet‐induced nonalcoholic steatohepatitis in db/db mice

Few studies have investigated the effects of Japanese herbal medicines on nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH). To the best of our knowledge, only one study has examined whether high‐fat (HF) diet‐fed db/db mice are appropriate animal models of NASH. We investigated the effects of four types of Japanese herbal medicines (shosaikoto (TJ‐9), inchinkoto (TJ‐135), juzentaihoto (TJ‐48), and keishibukuryogan (TJ‐25)) on hepatic lesions of HF diet‐fed db/db mice. Db/db mice were divided into six groups: control diet (control); HF diet (HF); and HF diet supplemented with TJ‐9, TJ‐135, TJ‐48, or TJ‐25 (TJ‐9, TJ‐135, TJ‐48, and TJ‐25, respectively). Mice were killed after 6 weeks of treatment, and biochemical and pathological analyses were performed. Mice in the HF group consistently developed histopathological features consistent with definite NASH, and marked necroinflammation occurred. Serum alanine aminotransferase levels in the TJ‐9, TJ‐135, and TJ‐48 groups were significantly improved compared with those in the HF group. With regard to liver histology, TJ‐9 and TJ‐48 significantly improved lobular inflammation, and TJ‐135 significantly improved ballooning degeneration. We have shown that HF diet‐fed db/db mice are animal models that correctly recapitulate the histopathology of human NASH and that TJ‐9, TJ‐135, and TJ‐48 inhibit necroinflammatory activity in this model.     

Impaired compensatory beta‐cell function and growth in response to high‐fat diet in LDL receptor knockout mice

In this study, we investigated the effect of low density lipoprotein receptor (LDLr) deficiency on gap junctional connexin 36 (Cx36) islet content and on the functional and growth response of pancreatic beta-cells in C57BL/6 mice fed a high-fat (HF) diet. After 60 days on regular or HF diet, the metabolic state and morphometric islet parameters of wild-type (WT) and LDLr−/− mice were assessed. HF diet-fed WT animals became obese and hypercholesterolaemic as well as hyperglycaemic, hyperinsulinaemic, glucose intolerant and insulin resistant, characterizing them as prediabetic. Also they showed a significant decrease in beta-cell secretory response to glucose. Overall, LDLr−/− mice displayed greater susceptibility to HF diet as judged by their marked cholesterolaemia, intolerance to glucose and pronounced decrease in glucose-stimulated insulin secretion. HF diet induced similarly in WT and LDLr−/− mice, a significant decrease in Cx36 beta-cell content as revealed by immunoblotting. Prediabetic WT mice displayed marked increase in beta-cell mass mainly due to beta-cell hypertrophy/replication. Nevertheless, HF diet-fed LDLr−/− mice showed no significant changes in beta-cell mass, but lower islet–duct association (neogenesis) and higher beta-cell apoptosis index were seen as compared to controls. The higher metabolic susceptibility to HF diet of LDLr−/− mice may be explained by a deficiency in insulin secretory response to glucose associated with lack of compensatory beta-cell expansion.     

Analysis of rapid oscillations of glucose and free fatty acids in plasma

Summary The authors analyzed rapid oscillations of blood sugar (GL) and free fatty acid levels (FFA) in serum of healthy subjects. They investigated a series of blood samples taken under conditions of absolute rest from the cubital vein at 15-s intervals for a period of 6 min. In addition to common statistical parameters, they calculated the course of autocorrelation and cross-correlation functions and periodograms. The magnitude of oscillations is significantly higher than the error of the biochemical methods. In some sequences periodicities were detected which were statistically significant in 23.8% of GL and in 38.1% of FFA. 24-point series of GL collected in parallel from both arms correlate in 36.3% positively, in 27.3% negatively, and in 36.4% they do not correlate. Series of FFA and GL collected simultaneously from one site correlate mutually in almost all instances either positively or negatively, frequently with a time shift. The oscillations may be due to (a) feedback regulations of the levels of the two metabolites, (b) permanent mutual interaction between the FFA and glucose level and (c) an uneven concentration of the two metabolites in different parts of the circulation. The above factors may combine, and the list of possible factors may not be complete.     

Sources of hepatic triglyceride accumulation during high‐fat feeding in the healthy rat

Hepatic triglyceride (HTG) accumulation from peripheral dietary sources and from endogenous de novo lipogenesis (DNL) was quantified in adult Sprague–Dawley rats by combining in vivo localized ¹H MRS measurement of total hepatic lipid with a novel ex vivo ²H NMR analysis of HTG ²H enrichment from ²H‐enriched body water. The methodology for DNL determination needs further validation against standard methodologies. To examine the effect of a high‐fat diet on HTG concentrations and sources, animals (n = 5) were given high‐fat chow for 35 days. HTG accumulation, measured by in vivo ¹H MRS, increased significantly after 1 week (3.85 ± 0.60% vs 2.13 ± 0.34% for animals fed on a standard chow diet, P < 0.05) and was maintained until week 5 (3.30 ± 0.60% vs 1.12 ± 0.30%, P < 0.05). Animals fed on a high‐fat diet were glucose intolerant (13.3 ± 1.3 vs 9.4 ± 0.8 mM in animals fed on a standard chow diet, for 60 min glycemia after glucose challenge, P < 0.05). In control animals, DNL accounted for 10.9 ± 1.0% of HTG, whereas in animals given the high‐fat diet, the DNL contribution was significantly reduced to 1.0 ± 0.2% (P < 0.01 relative to controls). In a separate study to determine the response of HTG to weaning from a high‐fat diet, animals with raised HTG (3.33 ± 0.51%) after 7days of a high‐fat diet reverted to basal HTG concentrations (0.76 ± 0.06%) after an additional 7 days of weaning on a standard chow diet. These studies show that, in healthy rats, HTG concentrations are acutely influenced by dietary lipid concentrations. Although the DNL contribution to HTG content is suppressed by a high‐fat diet in adult Sprague–Dawley rats, this effect is insufficient to prevent overall increases in HTG concentrations. Copyright © 2008 John Wiley & Sons, Ltd.     

Adrenergic effects on plasma levels of glucagon,insulin, glucose and free fatty acids in rabbits—influences of selective blocking drugs

Species differences concerning the effects of alpha-and beta-receptor stimulation on glucagon release and carbohydrate metabolism have been reported. The aim of the present study was to investigate how the subtypes of alpha-and beta-receptors regulate the plasma levels of glucagon, insulin, glucose and free fatty acids in fasted rabbits. Epinephrine-induced 1) hyperglucagonaemia, 2) hypoinsulinaemia and 3) hyperglycaemia were significantly inhibited by alpha-2 receptor blockade (yohimbine), and not influenced by alpha-1 receptor blockade (prazosin). Isoproterenol-induced 1) hyperglucagonaemia was not affected by beta-1 or beta-2 receptor blockade, 2) hyperinsulinaemia was inhibited by a lower dose of beta-2 (ICI 118.551) than beta-1 receptor blockade (metoprolol), 3) hyperglycaemia was inhibited by beta-2 receptor blockade and 4) increases in the plasma levels of free fatty acids were blocked by beta-1 receptor blockade. It is concluded that in fasted rabbits: 1) plasma levels of glucagon are mainly increased by alpha-2 receptor stimulation, 2) plasma levels of insulin are decreased by alpha-2 receptor stimulation, and increased more by beta-2 than by beta-1 receptor stimulation, 3) plasma levels of glucose are increased by alpha-2 and beta-2 receptor stimulation and 4) the plasma levels of free fatty acids are increased by beta-1 receptor stimulation.     

The effect of high‐fat diet on the morphological properties of the forelimb musculature in hypertrophic myostatin null mice

Obesity is a worldwide nutritional disorder affecting body performance, including skeletal muscle. Inhibition of myostatin not only increases the muscle mass but also it reduces body fat accumulation. We examined the effect of high‐fat diet on the phenotypic properties of forelimb muscles from myostatin null mice. Male wild‐type and myostatin null mice were fed on either a normal diet or a high‐fat diet (45% fat) for 10 weeks. Musculus triceps brachii Caput longum; M. triceps brachii Caput laterale; M. triceps brachii Caput mediale; M. extensor carpi ulnaris and M. flexor carpi ulnaris were processed for fiber type composition using immunohistochemistry and morphometric analysis. Although the muscle mass revealed no change under a high‐fat diet, there were morphometric alterations in the absence of myostatin. We show that high‐fat diet reduces the cross‐sectional area of the fast (IIB and IIX) fibers in M. triceps brachii Caput longum and M. triceps brachii Caput laterale of both genotypes. In contrast, increases of fast fiber areas were observed in both M. extensor carpi ulnaris of wild‐type and M. flexor carpi ulnaris of myostatin null mice. Meanwhile, a high‐fat diet increased the area of the fast IIA fibers in wild‐type mice; myostatin null mice display a muscle‐dependent alteration in the area of the same fiber type. The combined high‐fat diet and myostatin deletion shows no effect on the area of slow type I fibers. Although a high‐fat diet causes a reduction in the area of the peripheral IIB fibers in both genotypes, only myostatin null mice show an increase in the area of the central IIB fibers. We provide evidence that a high‐fat diet induces a muscle‐dependent fast to slow myofiber shift in the absence of myostatin. The data suggest that the morphological alterations of muscle fibers under a combined high‐fat diet and myostatin deletion reflect a functional adaptation of the muscle to utilize the high energy intake.     

Fast-induced changes in plasma glucose, insulin and free fatty acid concentration compared in rats during the night and day

Changes in PG, PI and PFFA were examined and compared in fed rats or after 0 to 12 hours of fasting, during the night or during the day. At night, a progressive decrease in PG and PI and an increase in PFFA were induced by 0 to 12 hours of food deprivation. During the light period a decrease in PG occurred only from the 6th hour of fasting. A slight, progressive increase in PFFA levels was induced from 0 to 12 hours of fasting, while no significant variation of PI levels was observed. The results are discussed in terms of relationships between blood glucose, PFFA levels, and food intake in control rats over the circadian cycle.     

Decreased levels of keratin 8 sensitize mice to streptozotocin‐induced diabetes

Aim

Diabetes is a result of an interplay between genetic, environmental and lifestyle factors. Keratin intermediate filaments are stress proteins in epithelial cells, and keratin mutations predispose to several human diseases. However, the involvement of keratins in diabetes is not well known. K8 and its partner K18 are the main β‐cell keratins, and knockout of K8 (K8^?/?) in mice causes mislocalization of glucose transporter 2, mitochondrial defects, reduced insulin content and altered systemic glucose/insulin control. We hypothesize that K8/K18 offer protection during β‐cell stress and that decreased K8 levels contribute to diabetes susceptibility.

Methods

K8‐heterozygous knockout (K8^+/?) and wild‐type (K8^+/+) mice were used to evaluate the influence of keratin levels on endocrine pancreatic function and diabetes development under basal conditions and after T1D streptozotocin (STZ)‐induced β‐cell stress and T2D high‐fat diet (HFD).

Results

Murine K8^+/? endocrine islets express ~50% less K8/K18 compared with K8^+/+. The decreased keratin levels have little impact on basal systemic glucose/insulin regulation, β‐cell health or insulin levels. Diabetes incidence and blood glucose levels are significantly higher in K8^+/? mice after low‐dose/chronic STZ treatment, and STZ causes more β‐cell damage and polyuria in K8^+/? compared with K8^+/+. K8 appears upregulated 5 weeks after STZ treatment in K8^+/+ islets but not in K8^+/?. K8^+/? mice showed no major susceptibility risk to HFD compared to K8^+/+.

Conclusion

Partial K8 deficiency reduces β‐cell stress tolerance and aggravates diabetes development in response to STZ, while there is no major susceptibility to HFD.

     

Evaluation of high‐fat high‐fructose diet treatment in factor VIII (coagulation factor)‐deficient mouse model

Non‐alcoholic fatty liver disease (NAFLD)‐like conditions enhance the production and action of clotting factors in humans. However, studies examining the effect of NAFLD due to high‐fat high‐fructose (HFHF) diet in factor VIII‐deficient (haemophilia A) animals or patients have not been reported previously. In this study, we investigated the individual role of factor VIII in the progression of diet‐induced NAFLD in the factor 8^?/? (F8^?/?) mouse model system and its consequences on the haemophilic status of the mice. The F8^?/? mice were fed with HFHF diet for 14 weeks. Physiological, biochemical, haematological, molecular, pathological, and immune histochemical analyses were performed to evaluate the effect of this diet. The F8^?/? mice developed hepatic steatosis after 14 weeks HFHF diet and displayed lower energy metabolism, higher myeloid cell infiltration in the liver, decreased platelet count, upregulated de novo fatty acid synthesis, lipid accumulation, and collagen deposition. This study helps to understand the role of factor VIII in NAFLD pathogenesis and to analyse the severity and consequences of steatosis in haemophilic patients as compared to normal population. This study suggests that haemophilic animals (F8^?/? mice) are highly prone to hepatic steatosis and thrombocytopenia.     

Cytoplasmic fatty acid‐binding protein facilitates fatty acid utilization by skeletal muscle

The intracellular transport of long‐chain fatty acids in muscle cells is facilitated to a great extent by heart‐type cytoplasmic fatty acid‐binding protein (H‐FABP). By virtue of the marked affinity of this 14.5‐kDa protein for fatty acids, H‐FABP dramatically increases their concentration in the aqueous cytoplasm by non‐covalent binding, thereby facilitating both the transition of fatty acids from membranes to the aqueous space and their diffusional transport from membranes (e.g. sarcolemma) to other cellular compartments (e.g. mitochondria). Striking features are the relative abundance of H‐FABP in muscle, especially in oxidative muscle fibres, and the modulation of the muscular H‐FABP content in concert with the modulation of other proteins and enzymes involved in fatty acid handling and utilization. Newer studies with mice carrying a homozygous or heterozygous deletion of the H‐FABP gene show that, in comparison with wild‐type mice, hindlimb muscles from heterozygous animals have a markedly lowered (?66%) H‐FABP content but unaltered palmitate uptake rate, while in hindlimb muscles from homozygous animals (no H‐FABP present) palmitate uptake was reduced by 45%. These findings indicate that H‐FABP is present in relative excess and plays a substantial, but merely permissive role in fatty acid uptake by skeletal muscles.     

Interaction of exercise and diet on GLUT‐4 protein and gene expression in Type I and Type II rat skeletal muscle

We determined the interaction of exercise and diet on glucose transporter (GLUT‐4) protein and mRNA expression in type I (soleus) and type II [extensor digitorum longus (EDL)] skeletal muscle. Forty‐eight Sprague Dawley rats were randomly assigned to one of two dietary conditions: high‐fat (FAT, n=24) or high‐carbohydrate (CHO, n=24). Animals in each dietary condition were allocated to one of two groups: control (NT, n=8) or a group that performed 8 weeks of treadmill running (4 sessions week^–1 of 1000 m @ 28 m min^–1, RUN, n=16). Eight trained rats were killed after their final exercise bout for determination of GLUT‐4 protein and mRNA expression: the remainder were killed 48 h after their last session for measurement of muscle glycogen and triacylglycerol concentration. GLUT‐4 protein expression in NT rats was similar in both muscles after 8 weeks of either diet. However, there was a main effect of training such that GLUT‐4 protein was increased in the soleus of rats fed with either diet (P < 0.05) and in the EDL in animals fed with CHO (P < 0.05). There was a significant diet–training interaction on GLUT‐4 mRNA, such that expression was increased in both the soleus (100% ↑P < 0.05) and EDL (142% ↑P < 0.01) in CHO‐fed animals. Trained rats fed with FAT decreased mRNA expression in the EDL (↓ 45%, P < 0.05) but not the soleus (↓ 14%, NS). We conclude that exercise training in CHO‐fed rats increased both GLUT‐4 protein and mRNA expression in type I and type II skeletal muscle. Despite lower GLUT‐4 mRNA in muscles from fat‐fed animals, exercise‐induced increases in GLUT‐4 protein were largely preserved, suggesting that control of GLUT‐4 protein and gene expression are modified independently by exercise and diet.     

Impaired glucose tolerance plus hyperlipidaemia induced by diet promotes retina microaneurysms in New Zealand rabbits

With the increasing prevalence of diabetes mellitus and metabolic syndrome worldwide, experimental models are required to better understand the pathophysiology and therapeutic approaches to preserve pancreatic beta cells, attenuate atherosclerosis and protect target organs. The aims of this study were to develop an experimental model of impaired glucose tolerance combined with hypercholesterolaemia induced by diet and assess metabolic alterations and target organ lesions. New Zealand male rabbits were fed high-fat/high-sucrose (10/40%) and cholesterol-enriched diet for 24 weeks, when they were sacrificed. Biochemistry, fundus photographs with fluorescein angiography and pathological analyses were performed. Cholesterol-fed and normal animals of same age were compared. Results: The animals with diet-induced impaired glucose tolerance combined with hypercholesterolaemia gained weight, increased blood glucose, total cholesterol, LDL-C and triglycerides and decreased HDL-C (P < 0.05 vs. baseline). Fructosamine levels and the homeostasis model assessment of insulin resistance (HOMA-IR) index were increased, while there was a reduction in the HOMA-β (P < 0.05 for all vs. baseline). Histomorphologic findings of this model were aortic atherosclerosis, hepatic steatofibrosis and glomerular macrophage infiltration. Early clinical features of diabetic retinopathy with hyperfluorescent dots consistent with presence of retina microaneurysms were seen since week 12, progressing up to the end of the experiment (P < 0.0005 vs. baseline and 12 weeks). Our model reproduced several metabolic characteristics of human diabetes mellitus and promoted early signs of retinopathy. This non-expensive model is suitable for studying mechanistic pathways and allowing novel strategic approaches.     

Epoxyeicosatrienoic acids alleviate methionine‐choline‐deficient diet–induced non‐alcoholic steatohepatitis in mice

The epoxyeicosatrienoic acids (EETs) are products of cytochrome P450 epoxygenases and have recently been found to have an anti‐inflammatory activity. However, the role of EETs in non‐alcoholic steatohepatitis has not been fully understood. In this study, we investigated the protective role of EETs in methionine‐choline‐deficient (MCD) diet–induced non‐alcoholic steatohepatitis (NASH) in mice and the potential mechanisms. We used 1‐trifluoromethoxyphenyl‐3‐(1‐propionylpiperidin‐4‐yl)urea(TPPU), a soluble epoxide hydrolase inhibitor, to increase the endogenous EET level in mice. Upon TPPU treatment, the liver steatosis and inflammatory damage were significantly ameliorated in mice with steatohepatitis, paralleled by the downregulation of pro‐inflammatory cytokines (TNF‐α, IL‐1β, IL‐6) as well as chemokines (CXCL1, MCP‐1). Compared with untreated NASH mice, mRNA levels of sterol regulatory element binding protein 1c (SREBP1c) and inflammation relevant adhesion molecules (ICAM‐1, VCAM‐1) were downregulated, whereas mRNA level of peroxisome proliferator–activated receptor α(PPAR‐α) was elevated in TPPU‐treated mice. In vitro, 11,12‐EET treatment remarkably attenuated free fatty acid (FFA)–induced inflammation in HepG2 and THP‐1 cells. Further, 11,12‐EET inhibited the activation of NF‐κB signalling pathway in macrophages from mice with steatohepatitis. Collectively, these results suggest that EETs play a protective role and alleviate the MCD diet–induced steatohepatitis in mice mainly by downregulating activation of NF‐κB pathway in macrophages.     

TRIM8在高糖高脂诱导的小鼠心肌细胞凋亡中的作用

目的:探讨含三基序蛋白8(TRIM8)对高糖高脂(HGHF)诱导的小鼠心肌细胞(MCMs)凋亡的影响及机制。方法:将MCMs分为正常糖(NG)组(葡萄糖浓度为5.5 mmol/L)、高糖(HG)组(葡萄糖浓度为33 mmol/L)、高脂(HF)组(软脂酸钠浓度为300μmol/L)和HGHF组(葡萄糖浓度为33 mmol/L,软脂酸钠浓度为300μmol/L);用siRNA沉默MCMs中TRIM8的表达后,再将MCMs分为对照(control)组(仅给予转染试剂)、Scra-siRNA/PBS组(转染scrambled siRNA)、TRIM8-siRNA/PBS组(转染TRIM8特异性siRNA)、Scra-siRNA/HGHF组和TRIM8-siRNA/HGHF组;为探索TRIM8在HGHF诱导的MCMs损伤中的可能作用机制,将MCMs分为HGHF/DMSO组、HGHF+TRIM8-siRNA+DMSO(HGHF+Ts/DMSO)组、HGHF/ML385组和HGHF+TRIM8-siRNA+ML385(HGHF+Ts/ML385)组。采用流式细胞术检测心肌细胞凋亡率;流式细胞术及D...