ACAT inhibitor HL-004 accelerates the regression of hypercholesterolemia in stroke-prone spontaneously hypertensive rats (SHRSP): stimulation of bile acid production by HL-004

Edible Red Seaweed Hypnea asiatica Ameliorates High-Fat Diet-Induced Metabolic Diseases in Mice

Metabolic diseases, including obesity, diabetes, and fatty liver disease, are dramatically increasing around the world. Seaweed is low in calories and rich in many active ingredients that are necessary for maintaining good health, and is expected to be effective for preventing metabolic diseases. The purpose of this study was to examine the effects of a traditional Japanese edible seaweed Hypnea asiatica (H. asiatica) on obesity, using a mouse model. H. asiatica was dried and powdered, mixed with a high-fat diet, and fed to male C57BL/6J mice for 13 weeks. On the last day of the experiment, blood samples were collected under anesthesia and biochemical parameters such as lipids and adipokines were measured. Liver and adipose tissue were excised, weighed, and oxidant/antioxidant parameters were measured. Some mice were perfused with a fixative solution containing formalin, and tissue specimens were prepared. A glucose tolerance test was used to assess insulin resistance. The inhibition of lipase activity was evaluated in vitro. Thirteen-week supplementation with H. asiatica suppressed body weight gain, body fat accumulation, and blood glucose levels. H. asiatica also improved fatty liver and hypercholesterolemia, and reduced the oxidant and inflammatory parameters of serum and liver. H. asiatica increased fecal triglyceride excretion and polyphenol-rich ethanol extract of H. asiatica inhibited lipase activity in vitro. These results suggest that polysaccharides and polyphenols in H. asiatica may ameliorate obesity and diabetes by inhibiting intestinal fat absorption and reducing oxidative stress and inflammation. H. asiatica may be useful in preventing metabolic diseases such as obesity, diabetes, and fatty liver.

The anti-obesity and anti-diabetic effects of the edible seaweed Gloiopeltis furcata (Postels et Ruprecht) J. Agardh in mice fed a high-fat diet

Obesity and diabetes are serious, chronic medical conditions associated with a wide range of life-threatening conditions. The aim of this study was to investigate the effects of the edible red seaweed Gloiopeltis furcata (Postels et Ruprecht) J. Agardh (G. furcata) on the development of obesity, diabetes and related metabolic diseases in mice. Male C57BL/6J mice were fed a high-fat (HF) diet (60% energy as fat), or an HF diet containing 2% (w/w) or 6% powdered G. furcata for 13 weeks. Polysaccharides of G. furcata were isolated and their anti-inflammatory effects were evaluated in lipopolysaccharide-stimulated RAW264.7 cells. The HF diet group showed greater weight gain, lipid accumulation in the body and liver, and increased serum levels of glucose and cholesterol in comparison to the normal group fed a normal diet (10% energy as fat). The treatment of HF diet mice with G. furcata reduced these changes and stimulated the fecal excretion of fat. In addition, G. furcata suppressed the HF diet-induced elevation of inflammation and oxidative stress markers in the serum and liver. The isolated sulfated polysaccharide from G. furcata inhibited pancreatic lipase activity and decreased the production of nitric oxide and TNF-α in the murine macrophage cell line RAW264.7. These results show that G. furcata treatment can attenuate obesity, diabetes, hepatic steatosis, and dyslipidemia in mice fed an HF diet, which is associated with inhibited intestinal fat absorption and reduced inflammation and oxidative stress by a sulfated polysaccharide.

Edible red seaweed Campylaephora hypnaeoides J. Agardh alleviates obesity and related metabolic disorders in mice by suppressing oxidative stress and inflammatory response

Background

The obesity epidemic has become a serious public health problem in many countries worldwide. Seaweed has few calories and is rich in active nutritional components necessary for health promotion and disease prevention. The aim of this study was to investigate the effects of the Campylaephora hypnaeoides J. Agardh (C. hypnaeoides), an edible seaweed traditionally eaten in Japan, on high-fat (HF) diet-induced obesity and related metabolic diseases in mice.

Methods

Male C57BL/6J mice were randomly divided into the following groups: normal diet group, HF diet group, HF diet supplemented with 2% C. hypnaeoides, and HF diet supplemented with 6% C. hypnaeoides. After 13 weeks of treatment, the weight of the white adipose tissue and liver, and the serum levels of glucose, insulin, adipokines, and lipids were measured. Hepatic levels of adipokines, oxidant markers, and antioxidant markers were also determined. Insulin resistance was assessed by a glucose tolerance test. Polysaccharides of C. hypnaeoides were purified and their molecular weight was determined by high-performance seize exclusion chromatography. The anti-inflammatory effects of purified polysaccharides were evaluated in RAW264.7 cells.

Results

Treatment of HF diet-induced obese mice with C. hypnaeoides for 13 weeks suppressed the increase in body weight and white adipose tissue weight. It also ameliorated insulin resistance, hyperglycemia, hepatic steatosis, and hypercholesterolemia. The ingestion of an HF diet increased serum levels of malondialdehyde (MDA), tumor necrosis factor α (TNF-α), and monocyte chemoattractant protein-1 (MCP-1), while it decreased serum adiponectin levels. In the liver, an HF diet markedly increased the MDA, TNF-α, and interleukin-6 (IL-6) levels, while it decreased glutathione and superoxide dismutase. These metabolic changes induced by HF diet feeding were ameliorated by dietary C. hypnaeoides. Purified polysaccharides and ethanol extract from C. hypnaeoides inhibited the lipopolysaccharide-induced overproduction of nitric oxide and TNF-α in macrophage RAW264.7 cells.

Conclusions

The present results indicated that C. hypnaeoides was able to alleviate HF diet-induced metabolic disorders, including obesity, hyperglycemia, hepatic steatosis, and hypercholesterolemia by attenuating inflammation and improving the antioxidant capacity in mice. Polysaccharides and polyphenols may be involved in these beneficial effects of C. hypnaeoides.

The Edible Brown Seaweed Sargassum horneri (Turner) C. Agardh Ameliorates High-Fat Diet-Induced Obesity, Diabetes, and Hepatic Steatosis in Mice

Sargassum horneri (Turner) C. Agardh (S. horneri) is edible brown seaweed that grows along the coast of East Asia and has been traditionally used as a folk medicine and a local food. In this study, we evaluated the effects of S. horneri on the development of obesity and related metabolic disorders in C57BL/6J mice fed a high-fat diet. S. horneri was freeze-dried, fine-powdered, and mixed with a high-fat diet at a weight ratio of 2% or 6%. Feeding a high-fat diet to mice for 13 weeks induced obesity, diabetes, hepatic steatosis, and hypercholesterolemia. Supplementation of mice with S. horneri suppressed high-fat diet-induced body weight gain and the accumulation of fat in adipose tissue and liver, and the elevation of the serum glucose level. In addition, S. horneri improved insulin resistance. An analysis of the feces showed that S. horneri stimulated the fecal excretion of triglyceride, as well as increased the fecal polysaccharide content. Furthermore, extracts of S. horneri inhibited the activity of pancreatic lipase in vitro. These results showed that S. horneri can ameliorate diet-induced metabolic diseases, and the effect may be partly associated with the suppression of intestinal fat absorption.

Taurine attenuates the development of hepatic steatosis through the inhibition of oxidative stress in a model of nonalcoholic fatty liver disease in vivo and in vitro

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease. It is characterized by the accumulation of triglyceride within hepatocytes. Taurine is a sulfur-containing-β-amino acid that is widely distributed in mammalian tissues. The objective of this study was to examine the effects of taurine on the development of hepatic steatosis in a model of NAFLD in vivo and in vitro. Male C57BL/6J mice were fed a high-fat diet (HFD) supplemented with 2% (w/v) or 5% (w/v) taurine for 12 weeks. An in vitro study was performed in HepG2 cells loaded with fatty acids. Twelve weeks of supplementation with an HFD increased the hepatic lipid levels and oxidative stress as well as the body weight and liver weight. Taurine significantly suppressed these changes, which was accompanied by a decrease in the hepatic level of thiobarbituric acid-reactive substances (TBARS). In addition, taurine treatment suppressed the HFD-induced reduction of the enzyme activity of hepatic superoxide dismutase and catalase and the reduction of the hepatic level of reduced glutathione and ATP. In HepG2 cells, taurine suppressed the fatty acid-induced lipid accumulation, production of reactive oxygen species and TBARS level, and amelioration of the fatty acid-induced disruption of the mitochondrial membrane potential. These results showed that taurine was effective in alleviating hepatic steatosis by reducing oxidative stress. Taurine may, therefore, be of therapeutic value in reducing the risks associated with NAFLD.

Over-expression of hepatic neutral cytosolic cholesteryl ester hydrolase in mice increases free cholesterol and reduces expression of HMG-CoAR, CYP27, and CYP7A1

Hepatic neutral cytosolic cholesteryl ester hydrolase (hncCEH) is a key enzyme in the regulation of hepatic free cholesterol (FC). In examining the effects of over-expression of this enzyme on cholesterol homeostasis, mice were infected with a recombinant adenovirus construct (AdCEH) of the rat hncCEH cDNA driven by the human cytomegalovirus promoter. Cholesteryl esterase and p-nitrophenylcaprylate (PNPC) esterase activities were measured in liver postmitochondrial supernatants at 1, 3, 7, and 11 d after infection with AdCEH or a control virus expressing beta-galactosidase (AdbetaGAL). The PNPC esterase activity of AdCEH mice peaked threefold higher than controls on day 2, declining on subsequent days. In contrast, cholesteryl esterase peaked eightfold higher than controls on day 3, indicating a shift in substrate selectivity of hncCEH. Hepatic FC peaked at 144% of controls, 7 d postinfection. The mRNAs for cholesterol 7alpha-hydroxylase, sterol 27-hydroxylase, and HMG-CoA reductase decreased to 47, 46, and 58% of controls, respectively, on day 7, coinciding with peak FC concentrations. Coinciding with increased cholesteryl esterase activity, hepatic esterified cholesterol dropped precipitously from day 3 onward, to 11% of controls by day 11. Hepatic TAG levels also declined, consistent with the reported TAG lipase activity of hncCEH. These results demonstrate elevation of FC and depletion of cholesteryl esters by over-expression of hncCEH, which were resistant to compensatory responses by other enzymes of cholesterol homeostasis.

Effects of dietary soybean lecithin on plasma lipid transport and hepatic cholesterol metabolism in rats

Dietary lecithin can stimulate bile formation and biliary lipid secretion, particularly cholesterol output in bile. Studies also suggested that the lecithin-rich diet might modify hepatic cholesterol homeostasis and lipoprotein metabolism. Therefore, we examined hepatic activities of 3-hydroxy-3 methylglutaryl coenzyme A reductase "HMG -CoA reductase", cholesterol 7 alpha-hydroxylase and acyl-CoA: cholesterol acyltransferase "ACAT" as well as plasma lipids and lipoprotein composition in rats fed diets enriched with 20% of soybean lecithin during 14 days. We also evaluated the content of hepatic canalicular membrane proteins involved in lipid transport to the bile (all P-glycoproteins as detected by the C 219 antibody and the sister of P-glycoprotein "spgp" or bile acid export pump) by Western blotting. As predicted, lecithin diet modified hepatic cholesterol homeostasis. The activity of hepatic HMG-CoA reductase and cholesterol 7 alpha-hydroxylase was enhanced by 30 and 12% respectively, while microsomal ACAT activity showed a dramatic decrease of 75%. As previously reported from ACAT inhibition, the plasma level and size of very low-density lipoprotein (VLDL) were significantly decreased and bile acid pool size and biliary lipid output were significantly increased. The canalicular membrane content of lipid transporters was not significantly affected by dietary lecithin. The current data on inhibition of ACAT activity and related metabolic effects by lecithin mimic the previously reported effects following drug-induced inhibition of ACAT activity, suggesting potential beneficial effects of dietary lecithin supplementation in vascular disease.

Effect of taurine on cholesterol metabolism in hamsters: up-regulation of low density lipoprotein (LDL) receptor by taurine

The effects of taurine on hepatic cholesterol metabolism were investigated in hamsters fed a high-fat diet or normal chow. Two weeks-treatment of taurine at 1% in drinking water prevented high-fat diet-induced increase in cholesterol levels of serum and liver. The decrease in serum cholesterol by taurine was due to decrease in non-HDL cholesterols. A similar tendency was noted in serum and liver cholesterol levels of hamsters fed a normal diet. In hamsters fed a high-fat diet, taurine prevented elevation in hepatic activity of acyl-CoA:cholesterol acyltransferase (ACAT) and increased the activity of cholesterol 7alpha-hydroxylase. Taurine also increased cholesterol 7alpha-hydroxylase activity in hamsters fed normal chow. Studies on liver membranes revealed that taurine increased 125I-labeled LDL binding by 52% and 58% in hamsters fed either a normal chow or high-fat diet, respectively. Furthermore, LDL kinetic analysis showed that taurine intake resulted in significant faster plasma LDL fractional catabolic rates (FCR). These results suggest that taurine elevates hepatic LDL receptor and thereby decreases serum cholesterol levels, an event which may be the result of hepatic cholesterol depletion as a consequence of increased bile acid synthesis via enhancement of cholesterol 7alpha-hydroxylase activity. Thus, up-regulation of the LDL receptor and subsequent increase in receptor- mediated LDL turnover may be a key event in the cholesterol-lowering effects of taurine in hamsters.

Effect of SMP-500, a novel ACAT inhibitor, on hepatic cholesterol disposition in rats

The effects of SMP-500, a novel ACAT inhibitor, on serum lipid levels, hepatic lipid secretion rate, and hepatic lipid disposition in rats were studied to clarify its lipid-lowering action. SMP-500 reduced the serum cholesterol level in a dose-dependent manner in rats fed a hypercholesterolemic diet. SMP-500 also reduced hepatic free cholesterol content in addition to hepatic total and esterified cholesterol contents. Biliary concentrations of cholesterol and bile acid were increased by SMP-500; however, the bile flow and lithogenic index were not affected. SMP-500 increased cholesterol 7a-hydroxylase mRNA level. Therefore, it is suggested that the increase in concentrations of cholesterol and bile acid in bile is due to both the increase of bile acid production through the increase of cholesterol 7alpha-hydroxylase and the decrease of hepatic free cholesterol content. An inhibitory effect of SMP-500 both on the cholesterol secretion and on the TG secretion from liver was observed. SMP-500 reduced the serum TG level in sucrose-fed rats. From these results, one may hypothesize that the suppression of hepatic VLDL secretion probably plays an important role on both cholesterol- and TG-lowering effects of SMP-500.

Effects of long-term treatment with taurine in mice fed a high-fat diet: improvement in cholesterol metabolism and vascular lipid accumulation by taurine

Hypocholesterolemic effects of taurine in rats fed a high-fat and high-cholesterol diet are well established. However, there are few studies on long-term effects of taurine on cholesterol metabolism. In the present study, taurine was dissolved in drinking water and given to C57BL/6J mice during 6 months-feeding of a high fat diet. Taurine treatment significantly decreased serum LDL and VLDL cholesterol, while it significantly increased serum HDL cholesterol. In the liver, taurine decreased cholesteryl ester contents, accompanied by decrease in acyl CoA:cholesterol acyltransferase (ACAT) activity. Hepatic activity of cholesterol 7alpha-hydroxylase, a rate-limiting enzyme for bile acid synthesis, was doubled with taurine. Taurine reduced by 20% the high-fat diet-induced arterial lipid accumulation. Thus, taurine prevented elevation of serum and liver cholesterol levels, as possibly related to accelerated cholesterol elimination from the body through the stimulation of bile acid synthesis. Long-term treatment with taurine is beneficial for prevention of hypercholesterolemia and atherosclerosis.

Acyl-coenzyme A: cholesterol acyltransferase modulates the generation of the amyloid beta-peptide

The pathogenic event common to all forms of Alzheimer's disease is the abnormal accumulation of the amyloid beta-peptide (Abeta). Here we provide strong evidence that intracellular cholesterol compartmentation modulates the generation of Abeta. Using genetic, biochemical and metabolic approaches, we found that cholesteryl-ester levels are directly correlated with Abeta production. Acyl-coenzyme A:cholesterol acyltransferase (ACAT), the enzyme that catalyses the formation of cholesteryl esters, modulates the generation of Abeta through the tight control of the equilibrium between free cholesterol and cholesteryl esters. We also show that pharmacological inhibitors of ACAT, developed for the treatment of atherosclerosis, are potent modulators of Abeta generation, indicating their potential for use in the treatment of Alzheimer's disease.

Overexpression of SR-BI in hamsters treated with a novel ACAT inhibitor (F12511)

The effect of a novel acyl-coenzyme A: cholesterol acyltransferase (ACAT) inhibitor on cholesterol metabolism was studied in hamsters. Oral administration of F12511 (10 mg/kg/d) for 4 weeks produced a decrease in dietary cholesterol absorption (-18%) and in the liver concentration of esterified cholesterol (-75%), as compared with control values in untreated hamsters. While the hepatic expression of LDLr was unchanged by the treatment, that of SR-BI was increased (+142%), which suggests that the hepatic expression of SR-BI could be upregulated by a depletion of the cholesterol stores, due to ACAT inhibition. This SR-BI overexpression, however, did not induce a fall in plasma HDL-cholesterol concentration, in contrast with previous reports in transgenic mice overexpressing SR-BI at a higher extent.

Inhibitory effect of TS-962 on the formation of early atherosclerotic lesions in high fat-fed hyperlipidemic hamsters

The hypocholesterolemic and anti-atherosclerotic effect of TS-962, a specific ACAT inhibitor, was investigated in a hamster model fed a high fat diet containing 10% coconut oil and 0.05% cholesterol. Lipid accumulated atherosclerotic lesions were detected by using oil red O staining in the lesion-prone aortic arch. A high dose, estimated to be 15 mg/kg, of TS-962 decreased serum cholesterol to normal levels with reduction of liver cholesterol contents below normal levels, and as a consequence, entirely inhibited the lipid accumulation in the aortic arch. Furthermore, a low dose, estimated to be 1.5 mg/kg, of TS-962 remarkably inhibited aortic lipid accumulation by 73% compared with the control group, without changing either serum cholesterol level or liver cholesterol content. These findings suggest that TS-962 is effective in the primary prevention of atherosclerosis by directly suppressing the formation of foam cells in arteries.

Acyl-coenzyme A:cholesterol acyltransferase inhibitor, avasimibe, stimulates bile acid synthesis and cholesterol 7alpha-hydroxylase in cultured rat hepatocytes and in vivo in the rat

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) inhibitors are currently in clinical development as potential lipid-lowering and antiatherosclerotic agents. We investigated the effect of avasimibe (Cl- 1011), a novel ACAT inhibitor, on bile acid synthesis and cholesterol 7alpha-hydroxylase in cultured rat hepatocytes and rats fed different diets. Avasimibe dose-dependently decreased ACAT activity in rat hepatocytes in the presence and absence of beta-migrating very low-density lipoproteins (betaVLDL) (by 93% and 75% at 10 micromol/L) and reduced intracellular storage of cholesteryl esters. Avasimibe (3 micromol/L) increased bile acid synthesis (2.9-fold) after preincubation with betaVLDL and cholesterol 7alpha-hydroxylase activity (1.7- and 2.6-fold, with or without betaVLDL), the latter paralleled by a similar induction of its messenger RNA (mRNA). Hepatocytes treated with avasimibe showed a shift from storage and secretion of cholesteryl esters to conversion of cholesterol into bile acids. In rats fed diets containing different amounts of cholesterol and cholate, avasimibe reduced plasma cholesterol (by 52% to 71%) and triglyceride levels (by 28% to 62%). Avasimibe did not further increase cholesterol 7alpha-hydroxylase activity and mRNA in cholesterol-fed rats, but prevented down-regulation by cholate. Avasimibe did not affect sterol 27-hydroxylase and oxysterol 7alpha-hydroxylase, 2 enzymes in the alternative pathway in bile acid synthesis. No increase in the ratio of biliary excreted cholesterol to bile acids was found, indicating that ACAT inhibition does not result in a more lithogenic bile. Avasimibe increases bile acid synthesis in cultured hepatocytes by enhancing the supply of free cholesterol both as substrate and inducer of cholesterol 7alpha-hydroxylase. These effects may partially explain the potent cholesterol-lowering effects of avasimibe in the rat.

Effects of NTE-122, a novel acyl-CoA:cholesterol acyltransferase inhibitor, on cholesterol esterification and secretions of apolipoprotein B-containing lipoprotein and bile acids in HepG2

We studied the effect of NTE-122 (trans-1,4-bis[[1-cyclohexyl-3-(4-dimethylamino phenyl) ureido]methyl]cyclohexane), a novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, on intracellular cholesterol esterification and the secretion of apolipoprotein B100 (apoB)-containing lipoprotein and bile acids in the human hepatoma cell line HepG2. NTE-122 markably inhibited [3H]oleate incorporation into cholesteryl esters in HepG2 cells incubated with 5 microg/ml 25-hydroxycholesterol as a stimulus for ACAT (IC50=6.0 nM). On the other hand, NTE-122 did not affect [3H]oleate incorporation into triglycerides and phospholipids and [14C]acetate incorporation into cholesterol. The stimulation of ACAT by 25-hydroxycholesterol caused significant increases in the secretion of radiolabeled cholesteryl esters, radiolabeled triglycerides and apoB mass. NTE-122 pronouncedly inhibited the secretion of radiolabeled cholesteryl esters in proportion to the inhibition of cellular cholesterol esterification, and it significantly reduced the secretion of radiolabeled triglycerides and apoB mass in HepG2 cells incubated with 25-hydroxycholesterol. Furthermore, NTE-122 increased the secretion of bile acids synthesized from [14C]-cholesterol. These results suggest that NTE-122 is capable of exhibiting anti-hyperlipidemic effects by reducing both the cholesterol content and the amount of secreted very low-density lipoprotein and enhancing the excretion of bile acid from the liver.

The ACAT inhibitor HL-004 inhibits cholesterol absorption and lowers serum cholesterol in rats

1. HL-004 decreased absorption of cholesteryl ester from the intestine into the lymph in a rat lymph-fistula model. 2. HL-004 reduced serum cholesterol level in acute cholesterol-fed rats. 3. HL-004 simultaneously decreased hepatic cholesteryl ester content and increased free cholesterol in cholesterol-fed rats. 4. These findings suggest that: (1) the hypocholesterolemic effect of HL-004 is principally due to inhibition of cholesterol absorption via inhibition of ACAT in the intestine; and (2) changes in hepatic cholesterol metabolism due to direct inhibition by HL-004 of hepatic ACAT may account in part for reduction of serum cholesterol level by HL-004.