A choline-deficient diet exacerbates fatty liver but attenuates insulin resistance and glucose intolerance in mice fed a high-fat diet

Liver fat accumulation is proposed to link obesity and insulin resistance. To dissect the role of liver fat in the insulin resistance of diet-induced obesity, we altered liver fat using a choline-deficient diet. C57Bl/6 mice were fed a low-fat (10% of calories) or high-fat (45% of calories) diet for 8 weeks; during the final 4 weeks, diets were either choline deficient or choline supplemented. In choline replete animals, high-fat feeding induced weight gain, elevated liver triglycerides (171%), hyperinsulinemia, and glucose intolerance. Choline deficiency did not affect body or adipose depot weights but amplified liver fat accumulation with high-fat diet (281%, P < 0.01). However, choline deficiency lowered fasting plasma insulin (from 983 +/- 175 to 433 +/- 36 pmol/l, P < 0.01) and improved glucose tolerance on a high-fat diet. In mice on 30% fat diet, choline deficiency increased liver mRNA levels of the rate-limiting enzyme in phosphatidylcholine synthesis and of enzymes involved in free fatty acid esterification, without affecting those of de novo lipogenesis or fatty acid oxidation. We conclude that liver fat accumulation per se does not cause insulin resistance during high-fat feeding and that choline deficiency may shunt potentially toxic free fatty acids toward innocuous storage triglyceride in the liver.     

PYY3-36 reinforces insulin action on glucose disposal in mice fed a high-fat diet

Peptide YY(3-36) (PYY(3-36)) is released by the gut in response to nutrient ingestion. It modulates the activities of orexigenic neuropeptide Y (NPY) neurons and anorexigenic proopiomelanocortin (POMC) neurons in the hypothalamus to inhibit food intake. Because both NPY and POMC have also been shown to impact insulin action, we wondered whether PYY(3-36) could improve insulin sensitivity. To address this question, we examined the acute effect of intravenous PYY(3-36) on glucose and free fatty acid (FFA) flux during a hyperinsulinemic-euglycemic clamp in mice maintained on a high-fat diet for 2 weeks before the experiment. We also evaluated the effects of PYY(3-36) infusion on glucose uptake in muscle and adipose tissue in this experimental context. Under basal conditions, none of the metabolic parameters were affected by PYY(3-36). Under hyperinsulinemic conditions, glucose disposal was significantly increased in PYY(3-36)-infused compared with vehicle-infused mice (103.8 +/- 10.9 vs. 76.1 +/- 11.4 micromol.min(-1).kg(-1), respectively; P = 0.001). Accordingly, glucose uptake in muscle and adipose tissue was greater in PYY(3-36)-treated animals, although the difference with controls did not reach statistical significance in adipose tissue (muscle: 2.1 +/- 0.5 vs. 1.5 +/- 0.5 micromol/g tissue, P = 0.049; adipose tissue: 0.8 +/- 0.4 vs. 0.4 +/- 0.3 micromol/g tissue, P = 0.08). In contrast, PYY(3-36) did not impact insulin action on endogenous glucose production or FFA metabolism. These data indicate that PYY(3-36) reinforces insulin action on glucose disposal in mice fed a high-fat diet, through a mechanism that is independent of food intake and body weight. In contrast, it leaves glucose production and lipid flux largely unaffected in this experimental context.     

Promoting effect of a high-fat/high-protein diet in DMBA-induced ductal pancreatic cancer in rats

OBJECTIVE: To investigate whether a high-fat/high-protein diet (HFPD) acts as a promoter of the natural course of cancer growth in the 7,12-dimethylbenzanthracene (DMBA)-induced ductal pancreatic cancer model in rats. SUMMARY BACKGROUND DATA: DMBA implantation to the rat pancreas induces ductal adenocarcinoma. Information regarding the effects of diet and the presence of K-ras mutation in this model is not available. METHODS: Rats were randomly assigned to regular rat chow or a diet with a 30% content in fat and protein (HFPD). The presentation of cancer, the histologic spectrum of neoplasia at 1 and 9 months, and the prevalence of cancer in relation to diet were assessed. Histologic specimens comprising normal ducts, hyperplasia, dysplasia/carcinoma in situ, or carcinoma were designated by a pathologist and microdissected. Genomic DNA was extracted, and K-ras and H-ras gene mutations were determined by a mutant-enriched polymerase chain reaction assay and direct sequencing. RESULTS: Rats fed HFPD increased their weight significantly compared with controls. DMBA induced characteristic stages of neoplasia at the implant site but not elsewhere. Macroscopic cancers of the pancreatic head presented regularly with common bile duct and gastric outlet obstruction. The prevalence of K-ras mutations was proportional to the degree of epithelial abnormality. K-ras mutations were significantly more frequent in cancer than in normal and hyperplastic ducts. H-ras mutations were not found. At 1 month in the HFPD-fed rats, the prevalence of cancer (16%) and dysplasia (16%) was not significantly different from the prevalence of cancer (29%) and dysplasia (8%) in the chow-fed rats. At 9 months the prevalence of cancer in the HFPD-fed rats increased to 29%, whereas that in the chow-fed rats decreased to 17%. The combined prevalence of cancer and dysplasia at 9 months in the HFPD-fed rats (34%) significantly exceeded that in the chow-fed rats. CONCLUSIONS: DMBA induces characteristic stages of neoplasia in the evolution of ductal pancreatic cancer in rats. K-ras mutations occur progressively in the ladder of oncogenesis, as in human pancreatic neoplasms. The addition of a diet with a high fat and protein content acts as a promoter of carcinogenesis, possibly by interfering with repair mechanisms and natural regression of early lesions.     

Radical scavenging effect of gliclazide in diabetic rats fed with a high cholesterol diet

BACKGROUND: Gliclazide is a sulphonylurea antidiabetic drug with anti-oxidant effect due to its azabicyclo-octyl ring. We hypothesized that gliclazide may have a beneficial effect on diabetic nephropathy via radical scavenging. METHODS: Streptozotocin-induced diabetic rats fed a 4% cholesterol diet [high cholesterol-diabetes mellitus (HC-DM)] (N= 12) were treated with gliclazide (HC-DM + gliclazide) (N= 12) or glibenclamide (HC-DM + glibenclamide) (N= 12) after 2 weeks of the diabetes induction, and normal rat fed with 4% cholesterol served as control [high cholesterol-control (HC-control)] (N= 12). Renal expression of endothelial nitric oxide synthase (eNOS) and intracellular adhesion molecule-1 (ICAM-1), oxidative stress production via nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase and antioxidant enzyme manganese superoxide dismutase (MnSOD) were evaluated at 4 weeks and renal damage was examined at 8 weeks. RESULTS: HC-DM showed significant increase in renal NAD(P)H oxidase and reduction in MnSOD with a significant increase in urinary lipid peroxidation products and H2O2 excretion compared to HC-control. Gliclazide treatment, but not glibenclamide, significantly reduced the oxidative products and NAD(P)H oxidase. There was no difference in renal eNOS expression between HC-DM and HC-control rats, and only gliclazide treatment enhanced eNOS expression. Renal damage evaluated by increased glomerular macrophage migration via enhanced ICAM-1 expression, mesangial matrix expansion, and albuminuria was significantly increased in HC-DM, and they were ameliorated by gliclazide but not by glibenclamide. CONCLUSION: Gliclazide reduced oxidative stress in diabetic rats fed a high cholesterol diet with reduction of renal NAD(P)H oxidase expression, enhanced MnSOD and eNOS expression, and had a beneficial effect on glomerular macrophage infiltration and mesangial expansion.     

Decreased insulin binding, glucose transport, and glucose metabolism in soleus muscle of rats fed a high fat diet

The relationship between diet and insulin sensitivity was examined in isolated soleus muscle from 10-wk-old lean Zucker rats. Rats were fed either a high fat or high carbohydrate diet that had 67% of calories as fat or carbohydrate, respectively, for 10 days. Plasma insulin but not plasma glucose concentrations were significantly elevated in high-fat-fed rats, indicating that a state of insulin resistance existed. The mechanisms responsible for the insulin resistance were studied by measuring insulin binding, 2-deoxyglucose uptake, and glucose metabolism in soleus muscle. The soleus muscle from the high-fat-fed rats bound significantly less insulin than high carbohydrate control rats under equilibrium binding conditions. The 35% decrease in insulin binding at maximal insulin concentrations resulted from a decrease in insulin receptor number but no change in receptor affinity. Maximal insulin-stimulated 2-deoxyglucose uptake was reduced in soleus muscle from high-fat-fed rats when compared with high carbohydrate controls. A decrease in postmembrane basal and insulin-stimulated glucose utilization was produced by high rat feeding and varied depending upon the pathway involved. An estimate of glycolysis (3H2O) formation from [5-3H]glucose) and glucose oxidation (14CO2 production from 14C-glucose) demonstrated a greater decrease in basal and insulin-stimulated utilization than in [5-3H]glucose conversion to [3H]glycogen. These results suggest that multiple sites are responsible for the observed insulin resistance in soleus muscle after high fat feeding.     

Immobilization and its effect on bone repletion in calcium-deficient rats fed a high calcium diet

In past work we demonstrated that, in growing rats, endosteal bone loss during a low calcium diet (depletion) was replaced when the animals were fed a normal calcium diet (repletion). Because past work showed that bone mechanical stress associated with weight bearing was increased les a result of bone depletion, the present study was undertaken to determine if immobilization during the repletion period would prevent bone repletion. In rats fed a 0% calcium diet (containing normal dietary phosphorus) for 12 days, there was a 460% increase in endosteal resorbing surface and a 38% increase in medullary area. When such animals were then fed a 1.2% calcium diet (normal phosphorus) for 15 days, the amount of endosteal resorbing surface decreased below the basal level to 0. Much of the endosteal resorbing surface was actually converted to forming surface, and les a result there was a 75% increase in the rate of endosteal bone formation compared with control (bone replete) animals. Bone replete animals subjected to immobilization of the left hind limb for 15 days by nerve transection had decreases of 31% and 33% in periosteal and endosteal bone formation rates, respectively, in the immobilized tibia. However, immobilization instituted at the start of the bone repletion period did not prevent or diminish the increment in the endosteal bone formation response during bone repletion over the intervening 15 days. Thus, the immobilized tibia from bone repleting rats exhibited an endosteal bone formation rate 128% greater than that in the immobilized limb of control (bone replete) rats. This increase was not less than that seen in bone repleting rats not subjected to immobilization. Thus, calcium repletion, even without mechanical stress, was sufficient to cause a marked increase in endosteal bone formation.     

Low-level laser therapy (LLLT) combined with swimming training improved the lipid profile in rats fed with high-fat diet

Obesity and associated dyslipidemia is the fastest growing health problem throughout the world. The combination of exercise and low-level laser therapy (LLLT) could be a new approach to the treatment of obesity and associated disease. In this work, the effects of LLLT associated with exercises on the lipid metabolism in regular and high-fat diet rats were verified. We used 64 rats divided in eight groups with eight rats each, designed: SC, sedentary chow diet; SCL, sedentary chow diet laser, TC, trained chow diet; TCL, trained chow diet laser; SH, sedentary high-fat diet; SHL, sedentary high-fat diet laser; TH, trained high-fat diet; and THL, trained high-fat diet laser. The exercise used was swimming during 8 weeks/90 min daily and LLLT (GA-Al-As, 830 nm) dose of 4.7 J/point and total energy 9.4 J per animal, applied to both gastrocnemius muscles after exercise. We analyzed biochemical parameters, percentage of fat, hepatic and muscular glycogen and relative mass of tissue, and weight percentage gain. The statistical test used was ANOVA, with post hoc Tukey–Kramer for multiple analysis between groups, and the significant level was p?<?0.001, p?<?0.01, and p?<?0.05. LLLT decreased the total cholesterol (p?<?0.05), triglycerides (p?<?0.01), low-density lipoprotein cholesterol (p?<?0.05), and relative mass of fat tissue (p?<?0.05), suggesting increased metabolic activity and altered lipid pathways. The combination of exercise and LLLT increased the benefits of exercise alone. However, LLLT without exercise tended to increase body weight and fat content. LLLT may be a valuable addition to a regimen of diet and exercise for weight reduction and dyslipidemic control.     

二甲双胍对地塞米松作用下SD大鼠骨密度的影响及可能的机制

目的研究不同干预剂量和时间的二甲双胍对地塞米松作用下SD大鼠骨密度(bone mineral density,BMD)的影响及可能的机制。方法将72只雌性SD大鼠随机均分为对照组、地塞米松组和二甲双胍100(Met 100)、200(Met 200)、300(Met 300)、500(Met 500)mg组。除对照组外,各组均每周2次肌注5 mg/kg的地塞米松。各二甲双胍组每日给予相应剂量的二甲双胍灌胃1次。连续干预12周,每2周测体重1次并调整药物剂量。分别在干预前和干预后4、8及12周测大鼠BMD及体成分。实验结束时采集血样测定大鼠I型胶原C端肽(CTX-I)、骨钙素(OCN)等指标。结果干预前及干预4周,各组间的BMD比较差异无统计学意义(均P>0.05)。干预8周,地塞米松组BMD低于对照组(P<0.05);地塞米松组与各地塞米松联合二甲双胍组的BMD比较差异无统计学意义(均P>0.05)。干预12周,地塞米松组BMD仍低于对照组(P<0.05);Met 100组和Met 200组的BMD高于地塞米松组(均P<0.05);Met 300组和Met 500组的BMD与地塞米松组相比无差异(均P>0.05)。干预12周,对照组、Met 100组、Met 200组和Met 300组的CTX-I水平均低于地塞米松组(均P<0.05),而OCN水平均高于地塞米松组(均P<0.05)。结论二甲双胍可通过促进骨形成及抑制骨吸收改善地塞米松作用下SD大鼠的BMD,并与干预的时间和剂量有关。     

Bone repletion in calcium deficient rats fed a high calcium diet

The changes in the tibial diaphysis as a result of feeding a high calcium diet to rats previously fed a calcium free diet were determined. The calcium free diet resulted in an increase in the medullary area, and the subsequent feeding of a high calcium diet caused a reduction in medullary area. However, the amount of endosteal bone lost during ten days of feeding a calcium free diet was not completely restored after 78 days of feeding a high calcium diet. The decrease in medullary area was brought about by decreased endosteal bone resorption and particularly by increased endosteal bone formation. Bone formation at the periosteum and at the epiphyses were unchanged, indicating that the high calcium diet did not cause a generalized increase in bone formation. The increase in endosteal bone formation was limited to those sites along endosteum where greatest loss of bone had occurred during the calcium depletion period. This indicates that a local factor is at least partially responsible for the stimulation of endosteal bone formation during calcium repletion. Mechanical stress, which stimulates bone formation, was increased in calcium deficient animals and returned to normal during calcium repletion. In addition, mechanical stress was probably greatest in those sites where the greatest amount of bone repletion occurred and may have been the factor which contributed to the increase in endosteal bone formation during calcium repletion.This study was supported in part by a grant from the U.S. Public Health Service (AM09096).     

巴戟天醇提取物对卵巢切除大鼠在高脂饮食状态下骨质量的影响

目的通过研究巴戟天醇提取物干预卵巢切除大鼠,探讨巴戟天醇提取物对卵巢切除大鼠在高脂饮食状态下骨小梁形态、骨密度(Bone mineral density,BMD)、胫骨最大载荷影响。方法采用切除雌性SD大鼠双侧卵巢建立绝经后骨质疏松症模型。将SD大鼠随机分成假手术组、正常饮食模型组、高脂饮食模型组、高脂饮食巴戟天醇提取物组,其中高脂饮食巴戟天组用巴戟天醇提取物灌胃干预,余下各组用生理盐水干预。运用双能X线仪测定骨密度,万能材料试验机检测骨组织的最大载荷。石蜡包埋切片Masson染色,观察骨组织形态。结果卵巢切除组相对假手术组,BMD、胫骨最大载荷均有不同程度降低(P0.05),骨的微观结构发生明显改变,其中以高脂饮食组改变最为明显。与高脂饮食巴戟天组相比,正常饮食模型组和高脂饮食模型组,各组BMD均呈现不同程度的下降;各组的胫骨最大载荷也呈现不同程度下降(P0.05);骨的微观结构也发生不同的改变。结论高脂饮食能加重卵巢切除大鼠骨质量及骨的微观结构的破坏。巴戟天醇提取物能够抑制卵巢切除术后大鼠的骨量流失,在一定程度上维持骨的微观结构,提高骨的最大载荷。     

Resveratrol attenuates obesity-associated peripheral and central inflammation and improves memory deficit in mice fed a high-fat diet

Obesity-induced diabetes is associated with chronic inflammation and is considered a risk factor for neurodegeneration. We tested the hypothesis that an AMP-activated protein kinase activator, resveratrol (RES), which is known to exert potent anti-inflammatory effects, would attenuate peripheral and central inflammation and improve memory deficit in mice fed a high-fat diet (HFD). C57BL/6J mice were fed an HFD or an HFD supplemented with RES for 20 weeks. Metabolic parameters in serum were evaluated, and Western blot analysis and immunohistochemistry in peripheral organs and brain were completed. We used the Morris water maze test to study the role of RES on memory function in HFD-treated mice. RES treatment reduced hepatic steatosis, macrophage infiltration, and insulin resistance in HFD-fed mice. In the hippocampus of HFD-fed mice, the protein levels of tumor necrosis factor-α and Iba-1 expression were reduced by RES treatment. Choline acetyltransferase was increased, and the phosphorylation of tau was decreased in the hippocampus of HFD-fed mice upon RES treatment. In particular, we found that RES significantly improved memory deficit in HFD-fed mice. These findings indicate that RES reverses obesity-related peripheral and central inflammation and metabolic derangements and improves memory deficit in HFD-fed diabetic mice.     

Increased 1,25-dihydroxyvitamin D3 synthesis in rats fed a high-phosphorus diet

Summary Rats fed vitamin D-deficient diets containing 0.6% Ca and 0.3%, 0.6%, 1.2%, or 1.8% P exhibited progressive increments of hypocalcemia and hyperphosphatemia. In vitro assay of 25-hydroxyvitamin D₃-1-α-hydroxylase (1-α-hydroxylase) activity in isolated kidney cortical mitochondria showed that hyperphosphatemia in the presence of hypocalcemia was associated with an increase in enzyme activity. The results indicate that the stimulation of 1-α-hydroxylase associated with depressed plasma Ca in rats fed a high-P diet overrides any inhibition of the enzyme that may be caused by excess plasma phosphate.     

The effect of metformin treatment on the basal and gonadotropin-stimulated steroidogenesis in male rats with type 2 diabetes mellitus

Type 2 diabetes mellitus impairs reproductive functions in men, and important tasks are deciphering the mechanisms of testicular dysfunctions in diabetes and the search of effective approaches to their correction. The purpose was to study the effect of four-week metformin treatment (120 mg kg⁻¹ day⁻¹) of male Wistar rats with high-fat diet/low-dose streptozotocin-induced type 2 diabetes on basal and gonadotropin-stimulated steroidogenesis, intratesticular content of leptin and the leptin and luteinising hormone receptors and on spermatogenesis. Diabetic rats had hyperleptinaemia, androgen deficiency and reduced sperm count and quality, and in the testes, they had the increased leptin level and the decreased content of the leptin and luteinising hormone receptors and 17-hydroxyprogesterone. The stimulating effects of chorionic gonadotropin on testosterone production and expression of steroidogenic genes (Star, Cyp11a1) were decreased. Metformin restored basal and gonadotropin-stimulated blood testosterone levels. In the testes, it restored gonadotropin-stimulated 17-hydroxyprogesterone, androstenedione and testosterone levels, Star expression and the content of leptin and the leptin and luteinising hormone receptors. Metformin also improved epididymal sperm count and morphology. We concluded that metformin treatment normalises the testicular steroidogenesis in diabetic rats, which is due to restoration of the gonadotropin and leptin systems in the testes and is associated with an improvement in spermatogenesis.     

Protective effect of doxycycline on germinal epithelial loss caused by a high-fat diet

Introduction

A high-fat diet and male obesity are aspects associated with germinal epithelial alterations and male infertility. Some reports have shown that certain tetracyclines can protect the germinal epithelium from toxic drugs. The aim of the present study design was to evaluate the possible effect of doxycycline on testicular germ cells in individuals fed a Western diet (atherogenic), using a murine model.

Methods

Two groups of male mice (BALB/c) were fed a high-fat Western diet (HFD). One of these two groups was given doxycycline at a dose of 10 mg/kg/day (HFD+Dox). A third group was fed a standard rodent diet (SD group). After 6 months, the mice were euthanized and morphologic and histopathologic analyses were performed.

Results

Germinal epithelial height was similar between the SD group (54 μm) and the HFD+Dox group (53 μm) (p = 0.26), and it was significantly reduced in the HFD group (47 μm) (p = 0.0001). The degree of germinal epithelial loss (DGEL) was significantly lower in the SD (10) and HFD+Dox (12.5) groups than in the HFD group (30) (p = 0.0001 and =0.007, respectively). There were no differences in the DGEL between the SD and HFD+Dox groups (p = 0.42).

Conclusions

Doxycycline administration was shown to prevent germinal epithelial loss in the testes of mice fed a high-fat diet. Future studies are necessary to evaluate the clinical usefulness of doxycycline or its analogs in persons with a habitual high-fat diet.     

长期高脂饮食诱导大鼠胰腺急慢性损伤的机制研究

目的 探究长期高脂饮食诱导胰腺急慢性损伤的发病机制.方法 建立2,4,6,10,18周高脂饮食大鼠模型,HE和天狼猩红饱和苦味酸染色法观察胰腺组织病理学改变,测定血清甘油三酯(TG)水平,检测胰腺组织中超氧化物岐化酶(superoxide dismutase,SOD)活性、丙二醛(Malondial-dehyde,MDA)及游离脂肪酸(Free fatty acid,FFA)含量,免疫组化法检测胰腺组织中α-平滑肌肌动蛋白(smooth muscle actin,α-SMA),结蛋白(desmin),转化生长因子β1(TGF-β1)和血小板衍生性生长冈子受体β(PDGFR-β)的表达.结果 长期高脂饮食导致大鼠胰腺早期发生急性炎症反应,最终导致局部腺泡萎缩,胰腺纤维化.胰腺组织中FFA和MDA含量增加,TGF-β1和PDGFR-β表达增加,并且胰腺星状细胞(pancreatic stellate cell,PSC))数量增加,纤维化区域α-SMA阳性染色的星状细胞数量增加.结论 胰腺组织中游离脂肪酸和脂质过氧化产物浓度增高在长期高脂饮食诱导的胰腺急性损伤和慢性纤维化过程中发挥重要作用.     

Mesangial kinetics after partial nephrectomy in rats fed a normal or a low-protein diet

Mesangial kinetics of aggregated BSA (aggBSA) were studied inrats subjected to 1 1/3 nephrectomy (47sol;6 Nx) fed eithera normal (16%) or a low-protein (8%) diet. At 4 weeks postsurgery,ablated rats exhibited modest elevations in blood pressure buthad neither significant proteinuria nor evidence of glomerulardamage. Following injection of aggBSA into 4/6 Nx rats (16%diet) there was a marked increase in mesangial localizationat 4 h compared with control animals, followed by rapid clearanceover 4–8 h, in keeping with increased trafficking in thismodel. The increased trafficking was significantly reduced bydietary protein restriction with 4/6 Nx rats fed an 8% proteindiet exhibiting mesangial kinetics not significantly differentfrom control animals. Control animals exhibited identical kineticsirrespective of diet. In separate studies, the 8% protein diet significantly reducedproteinuria and glomerulosclerosis when compared with untreatedanimals when studied at 30 weeks postsurgery.     

The effect of high sodium intake on bone mineral content in rats fed a normal calcium or a low calcium diet

The effect of high sodium intake on bone mineral content of rats fed a normal (0.6% Ca) or a low (0.02% Ca) calcium diet was studied. Rats on a normal calcium diet given 1.8% sodium chloride to drink showed persistent and significant hypercalciuria and subnormal bone mineral content. Total calcium content of femur was significantly lower after 4 months (p<0.02) and 12 months (p<0.001). In rats maintained on a low calcium diet (0.02% Ca), a high sodium diet for 8 weeks caused a significant loss of calcium in bone similar to that seen in animals fed a normal calcium diet for 4 months. We conclude that high sodium intake reduces bone mineral content, especially if the diet is low in calcium.