Suppression of hepatic HMG-CoA reductase activity by beta-muricholic acid in mice fed a diet containing cholesterol and cholic acid

A diet containing cholesterol and cholic acid (SID) is known to induce the formation of cholesterol fatty liver as well as cholesterol gallstones. The activity of HMG-CoA reductase, one of the key enzymes for cholesterol synthesis in the liver, is significantly lowered by addition of beta-muricholic acid to SID. The prevention of fatty liver formation by beta-muricholic acid was accompanied by the suppression of HMG-CoA reductase activity.     

Skeletal changes in multiparous mice fed a nutrient-sufficient diet containing cadmium

Female mice were given nutrient-sufficient, purified diets containing either 0.25, 5, or 50 ppm Cd. One-half of the females were bred for 6 consecutive 42-day rounds of pregnancy/lactation (PL mice); remaining females were non-pregnant controls (NP mice). PL mice and NP controls were sacrificed after 1, 2, 4, or 6 consecutive rounds of pregnancy/lactation. No consistent, cadmium-dependent decreases in body weight, femur calcium content, or calcium/dry weight (Ca/DW) ratio occurred among the NP mice during the 252 days of cadmium exposure. In contrast, significant, cadmium-dependent decreases in body weight (3-11%), femur calcium content (15-27%), and Ca/DW ratio (5-7%) occurred in the multiparous mice exposed to 50 vs 0.25 ppm Cd. In addition, among the PL mice, the effect of cadmium was dose-dependent, with femur calcium contents decreasing significantly as the cadmium exposure level increased from 0.25 to 5 then 50 ppm Cd (P less than 0.05). Results demonstrate that dietary cadmium exposure had a greater effect on the skeletons of dams exposed to cadmium during the stresses of pregnancy and lactation than in non-pregnant controls. The results provide evidence that the combination of cadmium exposure and multiparity may have played a role in the etiology of Itai-Itai disease in Japan.     

Kidney changes in multiparous mice fed a nutrient-sufficient diet containing cadmium

Female mice were given nutrient-sufficient, purified diets containing cadmium at either 0.25, 5, or 50 ppm, as described in the accompanying publication. One-half of the females were bred for 6 consecutive 42-day rounds of pregnancy/lactation (PL mice); remaining females were non-pregnant controls (NP mice). PL mice and NP controls were sacrificed after 1, 2, 4, or 6 consecutive rounds of pregnancy/lactation. At all levels of dietary cadmium and after all reproductive rounds, kidney cadmium concentrations were 2-5-fold higher in PL than NP mice. After 6 rounds of reproduction, the mean concentration of cadmium in the kidneys of PL mice exposed to dietary cadmium at 50 ppm was 115 micrograms Cd/g kidney, close to the critical concentration for cadmium-induced renal damage (200 micrograms/g). No consistent increases in the concentrations of amino acids, protein, or cadmium in urine were observed in the NP or PL mice in our study, indicating that cadmium-induced renal dysfunction had not yet appeared. Very small increases in kidney concentrations of zinc and copper were observed with large increases in kidney cadmium concentrations. Threshold cadmium concentrations below which the concentrations of zinc and copper were relatively constant and independent of cadmium concentration were identified; they were 7.2 micrograms Cd/g kidney for zinc and 13 micrograms Cd/g kidney for copper. In this study, cadmium-induced decreases in bone-mineral content occurred in the PL mice exposed to cadmium at 5 and 50 ppm (see accompanying publication). Data presented here indicate that the latter bone changes occurred in the absence of cadmium-induced renal dysfunction of the type that results in increased aminoaciduria/proteinuria. They suggest that the bone disease of Itai-Ital patients may also have started prior to the onset of this type of renal dysfunction.     

Carbon tetrachloride-induced alterations in hepatic glutathione and ascorbic acid contents in mice fed a diet containing ascorbate esters

The effects ofl-ascorbyl stearate andl-ascorbyl palmitate on carbon tetrachloride-induced alterations in glutathione and ascorbic acid content in mouse livers were investigated. Powdered food containing 1% ascorbate ester was given to mice for 3 days before and 1 day after a single injection of CCl₄ (0.1 ml/kg, i.p.). Biochemical parameters were determined 1 day after the CCl₄ administration. The ascorbate esters markedly attenuated CCl₄induced alterations such as reductions in ascorbate content and hepatic glutathioneS-transferase (GST) activity, and increases in glutathione and calcium content and serum GST activity. The CCl₄-induced rise in thiobarbituric acid-reactive substances, an index of lipid peroxidation, was not affected by ascorbate feeding. These findings suggest that exogenous ascorbate, in addition to endogenous glutathione, is available to maintain the intracellular milieu in a reduced state, and that this system operates more effectively in aqueous compartments than in membrane lipid bilayers.     

Trans fatty acids: chemical synthesis of eicosapentaenoic acid isomers and detection in rats fed a deodorized fish oil diet

Eicosapentaenoic acid (EPA) is a polyunsaturated fatty acid present in fish oils used for omega-3 enriched diets. The natural cis double bond geometry can be transformed to the trans configuration during the deodorization process utilized in the food industry. The analytical discrimination of the possible five monotrans regioisomers represents a limiting step for the recognition and structure-activity relationship in connection with the harmful effects of trans fatty acids in health. We carried out a dual synthetic strategy, providing new access to monotrans EPA isomers and valuable information on GC and NMR characteristics for further applications in metabolomics and lipidomics. This small library was used as an analytical reference for isomer determination in deodorized fish oils and the follow-up of rats fed fish oil diets, evidencing for the first time that monotrans EPA isomers are incorporated in liver mitochondrial membranes after dietary intake.     

Long-term feeding studies in mice fed a diet containing irradiated fish II. 90-day toxicity study

Three groups of mice (F_2b generation of Part I study) were fed for 90 days, either stock ration or diets containing 45% fish, either non-irradiated or irradiated with 1.75 kGy. Equal amounts of cod and redfish (ocean perch) constituted the fish portion of the diet. Haematological and clinical chemical examinations revealed no treatment-related effects. There were no untoward terminal gross or histopathological changes. An initial lag in weight gain of males fed fish diets was attributed to reduced food consumption, due to the difference in texture of the fish diets compared with the stock ration.     

Fatty acid composition in serum correlates with that in the liver and non-alcoholic fatty liver disease activity scores in mice fed a high-fat diet

In this study, we investigated the correlation between the serum fatty acid composition and hepatic steatosis, inflammation, hepatocellular ballooning scores, and liver fatty acids composition in mice fed a high-fat diet. Livers were collected for non-alcoholic fatty liver disease score analysis. Fatty acid compositions were analysed by gas chromatography. Correlations were determined by Pearson correlation coefficient. Exposed to a high-fat diet, mice developed fatty liver disease with varying severity without fibrosis. The serum fatty acid variation became more severe with prolonged exposure to a high-fat diet. This variation also correlated significantly with the variation in livers, with the types of fatty acids corresponding to liver steatosis, inflammation, and hepatocellular ballooning scores. Results of this study lead to the following hypothesis: the extent of serum fatty acid variation may be a preliminary biomarker of fatty liver disease caused by high-fat intake.     

Altered lipid metabolism and impaired clearance of plasma cholesterol in mice fed cyclopropenoid fatty acids

Swiss-Webster mice fed a diet containing 0.5% cyclopropenoid fatty acids (CPFA) for 6 weeks showed depressed growth rates and developed hypercholesteremia and increased concentrations of serum phospholipid and free cholesterol compared to control mice. No depression of cytochromes P-450 and b5 or microsomal mixed-function oxidase activities occurred to indicate impaired oxidative catabolism of serum cholesterol. Elimination of intragastrically administered [3H]cholesterol from blood was biphasic; there was no significant difference in first-order rate constants for absorption, distribution, and elimination processes between control and CPFA-fed animals. However, the area under the blood clearance curve for CPFA-fed animals was significantly increased (p less than or equal to 0.01) by 29% over controls, demonstrating a net increase in clearance time for exogenous cholesterol in CPFA-fed animals, thus contributing to their hypercholesteremia. In the CPFA-fed mice, the percentage of saturated fatty acid residues increased at the expense of monounsaturates in the cholesterol ester, triglyceride, and phosphatidyl choline fractions of serum lipids. Total polyene content of serum lipid was not altered; however, CPFA-fed animals demonstrated increased linoleic acid at the expense of arachidonic acid in all serum lipid fractions. Excessively saturated serum lipids may impede clearance of serum cholesterol in CPFA-fed animals by inhibited plasma lecithin-cholesterol acyltransferase (LCAT) and hepatic cholesterol esterase activities.     

游离脂肪酸与胰岛素抵抗

胰岛素抵抗是 2型糖尿病的重要组成部分,是引起代谢综合征的病理基础,但它的发病机制还不是很清楚。近年来发现在许多胰岛素抵抗状态均伴随着游离脂肪酸 (freefattyacids,FFA)水平的升高,逐渐引起了人们注意,FFA不仅可以干扰葡萄糖代谢的不同环节,重要的是在胰岛素受体及受体后的信号转导方面发挥作用,降低胰岛素刺激的葡萄糖转运。噻唑烷二酮类药物(TZDs)是近年来上市的胰岛素增敏剂,其主要效应之一就是降低FFA水平。可见,以控制FFA代谢紊乱为目标设计具有新作用机制的药物,将会使胰岛素抵抗和 2型糖尿病的治疗前景变得更加广阔。     

Lipid profile in mice fed a high-fat diet after exogenous leptin administration

Previous studies suggest a possible link between leptin and decreased lipid levels, however, the role of leptin in high-fat diet-induced hyperlipidemia remains unclear. The aim of our study was to evaluate the effect of administering leptin on plasma and tissue lipids in mice fed a high-fat diet. Feeding a high-fat diet (2% cholesterol, 0.125% bile salts, 5% peanut oil) to four-week-old healthy mice for a period of 45 days, resulted in significantly elevated levels of plasma and tissue total cholesterol, phospholipids, free fatty acids and triglycerides as compared with those of the control mice. Subsequently after thirty days, exogenous leptin (230 microg/kg i.p.) was administered simultaneously with the daily dose of high-fat diet every alternate day for fifteen days. Leptin administration significantly reduced the levels of total cholesterol, phospholipids, free fatty acids and triglycerides in the plasma, liver, heart and kidney of both the control and high-fat diet fed mice. Moreover, leptin administration markedly reduced the levels of plasma LDL, VLDL and elevated plasma HDL and the activity of lipoprotein lipase as compared with the untreated control and high-fat diet fed mice. Thus, leptin administration was found to have a marked protective effect against hyperlipidemia and thus obesity, by virtue of its lipid lowering effects.     

Nrf2 deficiency improves glucose tolerance in mice fed a high-fat diet

Nrf2, a master regulator of intracellular redox homeostasis, is indicated to participate in fatty acid metabolism in liver. However, its role in diet-induced obesity remains controversial. In the current study, genetically engineered Nrf2-null, wild-type (WT), and Nrf2-activated, Keap1-knockdown (K1-KD) mice were fed either a control or a high-fat Western diet (HFD) for 12 weeks. The results indicate that the absence or enhancement of Nrf2 activity did not prevent diet-induced obesity, had limited effects on lipid metabolism, but affected blood glucose homeostasis. Whereas the Nrf2-null mice were resistant to HFD-induced glucose intolerance, the Nrf2-activated K1-KD mice exhibited prolonged elevation of circulating glucose during a glucose tolerance test even on the control diet. Feeding a HFD did not activate the Nrf2 signaling pathway in mouse livers. Fibroblast growth factor 21 (Fgf21) is a liver-derived anti-diabetic hormone that exerts glucose- and lipid-lowering effects. Fgf21 mRNA and protein were both elevated in livers of Nrf2-null mice, and Fgf21 protein was lower in K1-KD mice than WT mice. The inverse correlation between Nrf2 activity and hepatic expression of Fgf21 might explain the improved glucose tolerance in Nrf2-null mice. Furthermore, a more oxidative cellular environment in Nrf2-null mice could affect insulin signaling in liver. For example, mRNA of insulin-like growth factor binding protein 1, a gene repressed by insulin in hepatocytes, was markedly elevated in livers of Nrf2-null mice. In conclusion, genetic alteration of Nrf2 does not prevent diet-induced obesity in mice, but deficiency of Nrf2 improves glucose homeostasis, possibly through its effects on Fgf21 and/or insulin signaling.     

Mechanism of protection against carbon tetrachloride toxicity. II. Lethality in rats fed a polyunsaturated fatty acid deficient diet

A PUFA-deficient diet causes deficiency symptoms and alters the fatty acid pattern in liver microsomal lipids. However, CCl4 lethality and sleeping time remain unchanged while the hepatic level of cytochrome P450 is only slightly lowered by the dietary regimen. In accordance, the amplitude of double bond shifting in microsomal lipids is far from being depressed in animals deprived of the peroxidative substrate. In fact, the experimental treatment does not impair intestinal absorption, liver uptake and metabolism of CCl4 given orally. Finally, both in vitro and in vivo peroxidative challenge of arachidonic acid content in hepatic microsomes causes comparable alterations of this parameter, whatever the initial fatty acid pattern following the dietary regimen. These findings provide evidence excluding an influence of the fatty acid composition of the diet on the severity of damages due to halogen-alkane exposure.     

Anti-atherogenic property of ferulic acid in apolipoprotein E-deficient mice fed Western diet: Comparison with clofibrate

Anti-atherogenic effect of ferulic acid (0.02%, w/w) was investigated in comparison with the clofibrate (0.02%, w/w) in apolipoprotein E-deficient (apo E^?/?) mice fed Western diet. Concentrations of total cholesterol (total-C), apolipoprotein B (apo B) in the plasma and epididymal adipose tissue weight were significantly lower in the ferulic acid and clofibrate supplemented groups compared to the control group. The ratio of apo B to apo A-I was also significantly lower in those groups than in the control group. Activities of hepatic ACAT and HMG-CoA reductase were only significantly lower in the ferulic acid and clofibrate groups, respectively than in the control group. The numbers of mice that exhibited aortic fatty plaque were 8/10 in control groups vs. 0/10 in the ferulic acid or clofibrate group. The activities of anti-oxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and paraoxonase) in the hepatocyte and erythrocyte were significantly higher in the ferulic acid group than in the control group. In contrast, hepatic TBARS level was only markedly lower in the ferulic acid group. These results provide a new insight into the anti-atherogenic property of ferulic acid in the apo E^?/? mice fed a Western diet.     

Cholesterol metabolism in serum and aorta of inbred mice fed a high-cholesterol diet

Biochemical characterization of the serum and aorta in inbred C57BL/6Cr mice fed a high-cholesterol diet was investigated by determining the total cholesterol (TC) and free cholesterol (FC) levels in serum, high density lipoprotein (HDL) and aorta. Serum lecithin:cholesterol acyltransferase (LCAT) activity was also determined. A modified fluoroenzymatic method for microdetermination of cholesterol was successfully used. TC and FC levels of the aorta in the mice were significantly increased by the high-cholesterol diet. Serum TC and FC levels of mice fed the high-cholesterol diet were increased about 80% and 110%, respectively, compared with the control. On the other hand, both HDL-TC and HDL-FC levels were decreased about 50%. The HDL-TC/serum-TC ratio was markedly decreased, while the atherogenic index was markedly increased with the high-cholesterol diet. LCAT activity was also strikingly decreased. A positive correlation was observed between LCAT activity and HDL-cholesterol. These changes in the serum may facilitate cholesterol accumulation in the aorta. The results indicate that a biochemical approach using mice may be possible for drug evaluation.     

Teratological study of Fischer rats fed diet containing added vomitoxin

Vomitoxin (deoxynivalenol), a tricothecene mycotoxin produced by Fusarium species, has been detected in corn, wheat and other cereal grains intended for consumption by man and by animals used for food. The teratogenic potential of vomitoxin administered in the diet was studied by feeding a vomitoxin-containing certified rat feed ad lib. to groups of Fischer 344 rats during the entire course of pregnancy. The vomitoxin was added to the diet at a level of 0.0, 0.5, 2.0 or 5.0 ppm. There were no overt signs of toxicity in the dams, and no statistically significant differences in feed consumption at any level compared to the control group. Dams in the two groups receiving the highest levels of vomitoxin tended to weigh less at term than other females, and after removal of the pups and uterus their carcass weights were significantly lower than those in the control group. Term foetuses were examined by standard teratological techniques. Male and female pup weights were unaffected by the maternal treatment. Vomitoxin had no statistically significant adverse effects on the incidence of gross, skeletal or visceral abnormalities. Neither dams nor pups showed any significant histopathological changes.     

Free and esterified fatty acids of guar gum

Guar gum consists essentially of the polysaccharide galactomannan. However, small amounts of various lipid soluble compounds, including long chain fatty acids, are also present. In this investigation free and esterified fatty acids of guar gum were analysed by GLC-MS. Palmitate (hexadecanoate), oleate (9-octadecenoate) and linoleate (9,12-octadecadienoate) were found to be the main components of the lipid fraction, but several long chain saturated acids and at least two 2-hydroxy-derivatives of fatty acids are also present.     

A gastrointestinal lipase inhibitor reduces progression of atherosclerosis in mice fed a western-type diet

To investigate whether gastrointestinal lipase inhibition reduces the progression of a western-type diet induced atherosclerosis, male apolipoprotein-E knockout (apoE KO) mice were administered orlistat ((S)-1-[[(S, 2S, 3S)-3-hexyl-4-oxo-2-oxetanyl] methyl]dodecyl-(S)-2-formamido-4-methylvalerate) mixed with a western-type diet for 8 weeks. Orlistat significantly reduced plasma triglyceride levels, but not total cholesterol levels, at 4 and 8 weeks of treatment. Increase in plasma triglyceride levels after oral olive oil loading in the mice fed a western-type diet was significantly suppressed in the orlistat treated group at 4 weeks of treatment. After 8 weeks treatment, atherosclerotic lesion area in the aorta of the orlistat treated group was significantly smaller than that of the control group. These results suggest that gastrointestinal lipase inhibition reduces the progression of atherosclerosis through a triglyceride-lowering effect, via inhibition of fat absorption.     

Long-term feeding studies in mice fed a diet containing irradiated fish I. Multigeneration reproduction,mutagenicity, teratology,and longevity studies

A wholesomeness feeding study was carried out in mice fed equal amounts of cod or redfish, comprising 45% of the diet. Three groups of animals received either irradiated [1.75 kGy (175 krad)] fish, non-irradiated fish or stock ration. A 90-day subchronic study,a multigeneration reproduction, a dominant lethality and a teratology study were carried out together with an 80-week oncogenic study on the F₁ generation. No adverse effects were noted on growth, reproduction and litter behaviour, in relation to dominant lethality, teratogenicty or oncogenicity.     

Free fatty acid receptors and drug discovery

Utilizing the human genome database, the recently developed G-protein-coupled receptor (GPCR) deorphanizing strategy successfully identified multiple receptors of free fatty acids (FFAs) and is proposed to play a critical role in a variety of physiologic homeostasis mechanisms. GPR40 and GPR120 are activated by medium- and long-chain FFAs, whereas GPR41 and GPR43 are activated by short-chain FFAs. GPR40, which is preferentially expressed in pancreatic beta-cells, mediates insulin secretion. On the other hand, GPR120, which is abundantly expressed in the intestine, functions as a receptor for unsaturated long-chain FFAs and promotes the secretion of glucagon-like peptide-1 (GLP-1). In this review, we summarize the identification, structure, and pharmacology of the receptors and speculate on the respective physiologic roles that FFA receptor family members may play.