Triglyceride In Mice Research Articles

FR177391, A New Anti-hyperlipidemic Agent from Serratia

The pharmacological effect of FR177391, isolated from Serratia liquefaciens No. 1821, was studied in normal animals and various types of animal models of hypertriglyceridemia. Treatment of normal mice with FR177391 resulted in an increase in heparin-releasable lipoprotein lipase (LPL) activity in the blood and epididymal fat tissue. FR177391 treatment decreased triglyceride (TG) and increased high-density lipoprotein cholesterol in the blood in normal rats following 7 days treatment, suggesting potent LPL activating properties of FR177391. Both Triton WR1339-induced severe and fructose-induced mild hypertriglyceridemia in rats were attenuated by FR177391 treatment. Severely elevated levels of TG in db/db mice, an insulin resistant diabetic animal model, also significantly decreased from 14 days of treatment with FR177391. FR177391 treatment for 9 days caused a decrease in the elevated levels of TG in mice induced by intraperitoneal inoculation of murine lymphoma EL-4. Overall, this study demonstrated that FR177391 can be possibly a LPL activating agent and that FR177391 treatment improved hypertriglyceridemia in various rat and mouse animal models. These results suggest that FR177391 is a promising candidate compound for the management of hypertriglyceridemia.

Inherited Apolipoprotein A-V Deficiency in Severe Hypertriglyceridemia

Mutations in LPL or APOC2 genes are recognized causes of inherited forms of severe hypertriglyceridemia. However, some hypertrigliceridemic patients do not have mutations in either of these genes. Because inactivation or hyperexpression of APOA5 gene, encoding apolipoprotein A-V (apoA-V), causes a marked increase or decrease of plasma triglycerides in mice, and because some common polymorphisms of this gene affect plasma triglycerides in humans, we have hypothesized that loss of function mutations in APOA5 gene might cause hypertriglyceridemia. We sequenced APOA5 gene in 10 hypertriglyceridemic patients in whom mutations in LPL and APOC2 genes had been excluded. One of them was found to be homozygous for a mutation in APOA5 gene (c.433 C>T, Q145X), predicted to generate a truncated apoA-V devoid of key functional domains. The plasma of this patient was found to activate LPL in vitro less efficiently than control plasma, thus suggesting that apoA-V might be an activator of LPL. Ten carriers of Q145X mutation were found in the patient's family; 5 of them had mild hypertriglyceridemia. As predicted from animal studies, apoA-V deficiency is associated with severe hypertriglyceridemia in humans. This observation suggests that apoA-V regulates the secretion and/or catabolism of triglyceride-rich lipoproteins. Mutations in APOA5 gene might be the cause of severe hypertriglyceridemia in subjects in whom mutations in LPL or APOC2 genes have been excluded. We detected a nonsense mutation in APOA5 gene (Q145X) in a boy with hyperchylomicronemia syndrome. This is the first observation of a complete apoA-V deficiency in humans.

Peroxisome Proliferator-activated Receptor β/δ Regulates Very Low Density Lipoprotein Production and Catabolism in Mice on a Western Diet

The results of recent studies using selective agonists for peroxisome proliferator-activated receptor beta (PPARbeta) suggest that this receptor may have a role in regulating levels of serum lipids in animal models of obesity and insulin resistance. To further examine this possibility, serum lipid profiles of mice lacking a functional PPARbeta receptor were determined. PPARbeta-null mice maintained on either normal chow or a 10-week high fat (HF) diet, a condition that has been shown to induce insulin resistance and obesity in mice, have elevated levels of serum triglycerides primarily associated with very low density lipoprotein (VLDL) with no difference in either total cholesterol or phospholipids. Consistent with this finding, PPARbeta-null mice on a HF-diet were shown to have an increased rate of hepatic VLDL production as well as lowered lipoprotein lipase activity in serum compared with wild-type controls. The latter parallels an increase in the hepatic expression of the genes encoding angiopoietin-like proteins 3 and 4 in PPARbeta-null mice on a HF diet, both proteins of which have recently been shown to inhibit lipoprotein lipase (LPL) activity in vivo. Consistent with elevated VLDL production, a marked increase in plasma VLDL apoB48, -E, -AI, and -AII, as well as a sharp depletion of the hepatic lipid stores was also found in PPARbeta-null mice. In addition, PPARbeta-null mice on a HF diet were shown to have increased adiposity, despite lower total body weight. Together, these results indicate a clear role for PPARbeta in regulating levels of serum triglycerides in mice on a high fat Western diet by modulating both VLDL production and LPL-mediated catabolism of VLDL-triglycerides and also suggest a potential therapeutic role for PPARbeta in the improvement of serum lipids in the setting of metabolic syndrome.

Structure and Interfacial Properties of Human Apolipoprotein A-V

Apolipoprotein A-V (apoA-V), the newest member of the plasma apolipoprotein family, was recently discovered by comparison of the mouse and human genomes. Studies in rodents and population surveys of human apoA-V polymorphisms have noted a strong effect of apoA-V on plasma triglyceride levels. Toward the elucidation of the biologic function of apoA-V, we used spectroscopic and surface chemistry techniques to probe its structure and interfacial activity. Computer-assisted sequence analysis of apoA-V predicts that it is very hydrophobic, contains a significant amount of alpha-helical secondary structure, and probably is composed of discrete structural regions with varying degrees of lipid affinity. Fluorescence spectroscopy of recombinant human apoA-V provided evidence of tertiary folding, and light scattering studies indicated that apoA-V transforms dimyristoylphosphatidylcholine vesicles into discoidal complexes with an efficiency similar to that of apoA-I. Surface chemistry techniques revealed that apoA-V displays high affinity, low elasticity, and slow binding kinetics at hydrophobic interfaces, properties we propose may retard triglyceride-rich particle assembly. Metabolic labeling and immunofluorescence studies of COS-1 cells transfected with human apoA-V demonstrated that apoA-V is poorly secreted, remains associated with the endoplasmic reticulum, and does not traffic to the Golgi. Given that overexpression of the apoA-V gene lowers plasma triglycerides in mice, these data together suggest that apoA-V may function intracellularly to modulate hepatic VLDL synthesis and/or secretion.

Lipoprotein production by the heart: a novel pathway of triglyceride export from cardiomyocytes

The current knowledge on lipoprotein secretion from the heart is examined in this article. The ability of cells to secrete apolipoprotein B (apo-B) containing lipoproteins depends on expression of the apo-B and microsomal triglyceride transfer protein (MTP) genes. Initially, it was shown that both genes are expressed in cardiac myocytes of mice and humans. Electron microscopy of human cardiac myocytes revealed lipoproteins in the secretory pathway and metabolic labelling studies demonstrated the secretion of LDL-like lipoproteins from minced heart biopsies. To examine the role of lipoprotein formation in the heart, we tested whether overexpression of a human apo-B transgene in the heart affects cardiac triglyceride accumulation. In wild-type mice, diabetes conferred an increase in heart triglycerides. In apo-B transgenic mice, diabetes did not affect heart triglycerides. Also, apo-B overexpression prevents fasting-induced heart triglyceride accumulation, whereas inhibition of MTP expression increases heart triglycerides in mice. In hypoxic human hearts, MTP mRNA expression was negatively associated with triglyceride contents. These findings suggest that lipoprotein formation rates affect cardiac triglyceride stores. The MTP mRNA levels are j 2-fold higher in hypoxic compared with normoxic human myocardium and in diabetic compared with non-diabetic mouse hearts. In both hypoxia and diabetes, the delivery of triglycerides to the heart exceeds their utilization for g -oxidation. Thus, endogenous lipoprotein secretion rates might be upregulated to remove surplus fat from the heart. Diabetes negatively affected indexes of systolic and diastolic function in wild-type mice. However, the diabetogenic effects on the heart were absent or much less pronounced in apo-B transgenic mice. This suggests that accelerated lipoprotein formation by the heart attenuates development of diabetic cardiomyopathy in mice. In conclusion, current evidence suggests that lipoprotein secretion from the heart plays an integrated role in cardiac lipid homeostasis and that it can affect the biomechanical function of the heart.

Plasma triglyceride reduction in mice after direct injections of muscle-specific lipoprotein lipase DNA.

The present study was conducted to determine if direct injections of plasmid pMCKhLPL DNA would lead to sufficient overexpression of lipoprotein lipase (LPL) to reduce plasma triglycerides in mice. After single intramuscular (i.m.) injections, human lipoprotein lipase (hLPL) mRNA was detectable in the quadriceps muscle for at least 21 days. Repeated intraperitoneal (i.p.) and i.m. DNA administration increased the LPL activity in skeletal muscle by 58% (i.p.) and 36% (i.m.) when compared with control-injected mice. A concomitant reduction of plasma triglycerides by 38% (i.p.) and 26% (i.m.) was obtained. Also, repeated measures of plasma triglycerides indicate that the triglyceride-lowering effect of pMCKhLPL can be noted early after DNA injections. Thus, the injection of pMCKhLPL into the peritoneum or quadriceps muscle results in plasma triglyceride reduction in mice.

Cholesterol and Triglyceride Fluctuations in Mice Tissues During Methylmercury Intoxication and Monothiols and Vitamin Therapy

The aim of this investigation is to check the efficacy of monothiols and vitamins in the restoration of cholesterol and triglycerides in mice pre-toxicated with methylmercury chloride (MMC). For th...

Human ApoA-II inhibits the hydrolysis of HDL triglyceride and the decrease of HDL size induced by hypertriglyceridemia and cholesteryl ester transfer protein in transgenic mice.

The plasma cholesteryl ester transfer protein (CETP) mediates the exchange of HDL cholesteryl esters with triglycerides of other lipoproteins. Subsequent lipolysis of the triglyceride-enriched HDL by hepatic lipase leads to reductions of HDL size and apoA-I content. To investigate a possible modulation of the effects of CETP by apoA-II, human CETP transgenic mice were cross-bred with transgenic mice expressing human apoA-II and, in some cases, human apoA-I and apoC-III (with human-like HDL and hypertriglyceridemia). CETP expression resulted in reductions of HDL and increases in VLDL cholesteryl ester in mice expressing human apoA-II, alone or in combination with apoA-I and apoC-III, indicating that apoA-II does not inhibit the cholesteryl ester transfer activity of CETP. However, CETP expression resulted in more prominent increases in HDL triglyceride in mice expressing both apoA-II and CETP, especially in CETP/apoA-II/apoAI-CIII transgenic mice. CETP expression caused dramatic reductions in HDL size and apoA-I content in apoAI-CIII transgenic mice, but not in apoA-II/AI-CIII transgenic mice. HDL prepared from mice of various genotypes showed inhibition of emulsion-based hepatic lipase activity in proportion to the apoA-II/apoA-I ratio of HDL. The presence of human apoA-II also inhibited mouse plasma hepatic lipase activity on HDL triglyceride. Thus, apoA-II does not inhibit the lipid transfer activity of CETP in vivo. However, coexpression of apoA-II with CETP results in HDL particles that are more triglyceride enriched and resistant to reductions in size and apoA-I content, reflecting inhibition of hepatic lipase by apoA-II. The inhibition of HDL remodeling by apoA-II could explain the relatively constant levels of HDL containing both apoA-I and apoA-II in human populations.

Metabolic effects of dietary stearic acid in mice: changes in the fatty acid composition of triglycerides and phospholipids in various tissues

The fatty acid patterns of triglycerides and phospholipids extracted from adipose tissue, liver, heart, kidney, spleen, and lung of 3 groups of C57BL/6 mice were determined after feeding diets rich in palmitic acid (16:0) (high palmitic: 16:0 = 45.1% of total fatty acids), stearic acid (18:0) (high stearic: 18:0 = 42.9% of total fatty acids) and oleic acid (18:1) (high oleic: 18:1 = 79.7% of total fatty acids) for 9 months. Triglyceride content of adipose, liver, heart, kidney, lung and spleen tissues was significantly enriched in palmitic acid in mice fed the high palmitic diet (range among all tissues: 19.9% ± 0.2% to 29.0% ± 1.9% of total fatty acids) and in oleic acid in mice fed the high oleic diet (range 56.0% ± 1.9% to 71.6% ± 1.2%). The stearic acid content of organ triglycerides in mice fed the high stearic diet ranged from 3.7% ± 0.3% to 10.8% ± 1.2%; however, the content of oleic acid on this diet (range; 57.0% ± 1.8% to 71.4% ± 1.7%) was similar to the one observed in mice fed the high oleic diet. In all organs, phospholipids had a significantly higher percentage of stearic acid (range: 23.5% ± 0.9% to 51.5% ± 6.6%) than triglycerides, regardless of diet. To evaluate the production of oleate from stearate and palmitate, 2 groups of mice were fed the high palmitic and the high stearic diets for 1 week and then injected intravenously with [1- 14C]palmitate and [1- 14C]stearate and the amount of labelled oleate in liver triglycerides was measured. In liver triglycerides of mice injected with [1- 14C]stearic acid, more than 80% of 14C label recovered was bound to oleic acid, while in mice injected with radioactive palmitate, the maximum recovery of label bound to oleate was 47.0% ± 6.9%. These data suggest that stearic acid is rapidly converted into oleic acid and could help explain why dietary stearic acid does not raise plasma cholesterol.

Cholesterol-Lowering Effect of Agemaki, a Kind of Shellfish, in Mice.

Agemaki (Sinonovacula constricta) is an edible and popular shellfish in the western part of Japan. The present study demonstrated the effects of feeding Agemaki on cholesterol and triglyceride concentrations in mice plasma and liver. Mice were fed a diet containing 0.1% cholesterol and 0.1% Na-cholate for 1 week, and then a cholesterol-free diet or a cholesterol-enriched one for 2 weeks. To both diets, freeze-dried Agemaki was added at a 5% level. There was no statistically significant effect on the body-weight gain, food intake, and liver weight by feeding Agemaki in both dietary regimens. However, Agemaki significantly lowered the concentrations of plasma and liver cholesterol and also of plasma triglyceride in mice feeding on the cholesterol-rich diet. A similar tendency was also observed for the mice feeding on the cholesterol-free diet. The analysis of freeze-dried Agemaki revealed a relatively larger proportion of n-3 polyunsaturated fatty acids and plant sterols, which may possibly decrease plasma lipids. So far as we know, this is the first report showing hypolipidemic effect of Agemaki.

Tumor extracellular triglycerides in mice during growth of Ehrlich ascites carcinoma.

Our earlier work with Swiss-Webster mice has shown that most of the lipid in Ehrlich ascites tumor extracellular fluid is in the form of free fatty acids. This finding is in direct contradiction to earlier and subsequent reports from another laboratory that has found free fatty acids to be a very minor component and triglycerides to be the major lipid of Ehrlich ascites tumor extracellular fluid. In light of these contradictory reports, we have carried out a study patterned after that of other workers, but using our Swiss-Webster mice. As predicted from our earlier study, we have found very little triglyceride in Ehrlich ascites tumor extracellular fluid. Although we could demonstrate a significant, transient hypertriglyceridemia during tumor growth, maximum plasma triglyceride concentrations were an order of magnitude lower than those reported by other workers. In addition, and again in contrast to other reports, we found that plasma triglyceride and tumor extracellular fluid triglyceride levels in tumorous mice fell significantly with fasting. Thus, interesting differences in triglyceride metabolism between mouse and/or tumor strains seem to exist. Our present findings suggest, but do not prove, that triglycerides in the tumor extracellular fluid probably are not a major source of the rapidly turning over, tumor extracellular fluid free fatty acid in our mice.

Plasma lipoproteins and the synthesis and turnover of plasma triglyceride in normal and genetically obese mice

1. Lipoproteins in the plasma of mice were characterized by agarose-gel chromatography and polyacrylamide-gel electrophoresis: genetically obese (ob/ob) mice exhibited hyperlipoproteinaemia (compared with lean mice), largely owing to an increase in the concentration of cholesterol in high-density lipoprotein. Plasma concentrations of triglyceride and phospholipid were not markedly increased in genetically obese mice. 2. The formation of glycerolipids in liver and plasma was investigated with (14)C-labelled precursors. The synthesis of hepatic triglyceride and phospholipid from glucose or palmitate was enhanced in ob/ob mice, compared with lean mice. The rate of entry of triglyceride into plasma, calculated from the time-course of incorporation of (14)C from [(14)C]palmitate into plasma triglyceride, was increased in ob/ob mice (0.5mumol of fatty acid/min, compared with 0.2 in lean mice). 3. The removal from plasma of murine lipoprotein triglyceride-[(14)C]fatty acid was increased in ob/ob mice (half-time 2.2min, compared with 7.2min in lean mice). Similar results were obtained with an injected lipid emulsion (Intralipid). 4. From these measurements, estimates of the rates of turnover of plasma triglyceride in mice (fed on a mixed diet, female, 3 months old) are about 1.0mumol of fatty acid/min in ob/ob mice, and 0.25 in lean mice. 5. The major precursor of hepatic and plasma triglyceride in lean and ob/ob mice was calculated to be plasma free fatty acid. 6. These results are discussed, in connexion with the role of the liver in triglyceride metabolism in mice, especially in relation to genetic obesity.