Hepatic 3-hydroxy-3-methylglutaryl Coenzyme A Research Articles

N-3 Fatty Acids Abrogate Dyslipidemia-Induced Changes in Bile Acid Uptake, Synthesis, and Transport in Young and Aged Dyslipidemic Rats.

In this study, the effect of n-3 fatty acids (FA) [α-linolenic acid (ALA) and eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA)] on the intestinal bile acid (BA) uptake, hepatic BA synthesis, and enterohepatic bile acid transporters (BAT) was assessed in young and aged dyslipidemic rats. Dyslipidemia was induced in young and aged rats by feeding a high-fat (HF) diet. Experimental groups received diets containing canola oil (HF + CNO) and fish oil (HF + FO) as a source of ALA and EPA + DHA, respectively. After 60 days of feeding, intestinal BA uptake and expression of apical sodium-dependent bile acid transporter (Asbt), organic solute transporter-alpha/beta (Osta/b) messenger RNA (mRNA), and hepatic expression of Na+ taurocholate cotransporting polypeptide (Ntcp), bile salt export pump (Bsep), cholesterol 7-α hydroxylase A1 (Cyp7a1), Farnesoid X receptor (Fxr), small heterodimer partner-1 (Shp), liver receptor homolog-1 (Lrh-1), and hepatic nuclear factor-4 alpha (Hnf4a) mRNA were measured. Hepatic 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase activity and total BA in serum, liver, and feces were assessed. The dyslipidemic HF group had: (1) increased intestinal BA uptake and Asbt and Osta/b mRNA expression, (2) increased BA in serum, (3) decreased hepatic expression of Ntcp, Bsep, and Cyp7a1 mRNA, (4) increased activity of HMG-CoA reductase, (5) increased hepatic expression of Fxr and Shp mRNA, (6) decreased hepatic expression of Lrh-1 and Hnf4a mRNA, and (7) decreased BA in feces, when compared to control, HF + CNO, and HF + FO groups. Immunostaining revealed increased expression of intestinal Asbt and hepatic Ntcp protein in the HF group when compared to control, HF + CNO, and HF + FO groups. n-3 FA abrogated dyslipidemia-induced changes in the intestinal uptake, hepatic synthesis, and enterohepatic transporters of BA in both young and aged rats. EPA + DHA was more effective than ALA in modulating dyslipidemia-induced changes.

Effects of dietary red yeast (Sporidiobolus pararoseus) on production performance and egg quality of laying hens.

The purpose of this study was to evaluate the effect of dietary red yeast (Sporidiobolus pararoseus) on production performance and egg quality of laying hens. A total of 200 Esa Brown laying hens (23weeks of age) were allocated equally to negative control group (no yeast supplement); positive control group (2g/kg of Saccharomyces cerevisiae); 0.5, 1, 2g/kg red yeast respectively. The experiment was lasted for 12weeks. Feed intake, hen-day egg production and egg weight were not different between control and supplemented groups. However, yeast-supplemented groups were significantly improved feed efficiency (p<.05). Incremental levels of red yeast increased the colour score of egg yolk (p<.05). The cholesterol and triglyceride of serum and yolk were significantly (p<.05) lower in the laying hens fed dietary administration red yeast compared to the control diet; however, no significant (p>.05) differences among yeast-supplemented groups were observed. The hepatic hydroxymethylglutaryl-coenzymeA (HMG-CoA) reductase activity was significantly lower (p<.05) in the 2g/kg red yeast-supplemented group compared to the control and other red yeast-supplemented groups. Concentrations of caecal short-chain fatty acids was increased (p<.05) in laying hens fed 1 and 2g/kg red yeast as compared to the control group. Dietary administration of 2g/kg red yeast (S.pararoceus) significantly improved egg yolk colour, decrease serum and egg yolk cholesterol levels.

Hypolipidemic effects of Solidago chilensis hydroalcoholic extract and its major isolated constituent quercetrin in cholesterol-fed rats

Context: Despite several studies on the effects of Solidago chilensis Meyen (Asteraceae), the phytochemical and hypolipidemic properties remain underappreciated.Objective: This study evaluates the hypolipidemic and antioxidant effects of hydroalcoholic extract (HE) and quercetrin from S. chilensis aerial parts in cholesterol-fed rats.Materials and methods: The HE was analyzed by high-performance liquid chromatography, followed by quercetrin isolation. Hypercholesterolemic rats (1% cholesterol and 0.5% cholic acid for 15 d) were treated with HE (150, 300, and 600 mg/kg p.o.; n = 6), simvastatin (4 mg/kg p.o.; n = 6), or quercetrin (10 mg/kg p.o.; n = 6) once a day for 30 d. During this period, a high-cholesterol diet was maintained until the 30th day of treatment.Results: Rats treated with HE (150, 300, and 600 mg/kg) and quercetrin showed decreased serum levels of total cholesterol (−19.9, −27.5, −31.0, and −39.4%), lipoprotein-cholesterol (−36.0, −37.5, −43.3, and −59.4%), and triacylglycerides (−15.6, −23.5, −29.8, and −27.2%) when compared with the control group similar to simvastatin. Moreover, treatment with HE and quercetrin decreased hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity (35.1% on average) and increased fecal cholesterol levels (38.2% on average).Discussion and conclusions: Our results suggest that hypolipidemic effects of HE are associated with it modulating the activity of HMG-CoA reductase and its interference in the reabsorption and/or excretion of intestinal lipids. Solidago chilensis and its main constituent, quercetrin, may thus be effective as cholesterol-lowering agents and in preventing atherosclerosis.

Impact of Chicory-Supplemented Diet on HMG-CoA Reductase, Acetyl-CoA Carboxylase, Visfatin and Anti-Oxidant Status in Triton WR-1339-Induced Hyperlipidemia

Hyperlipidemia is a major risk factor for cardiovascular diseases. The present study was conducted to evaluate the potential role of chicory (Cichorium intybus Linn.) against hyperlipidemia and its subsequent effect in rats. Sixty male albino rats were randomly and equally divided into four groups. Hyperlipidemia was induced via intraperitoneal injection of Triton WR-1339 at a dose of 250 mg/kg body weight three times a week for 2 weeks. Chicory-supplemented diet (10 g/100 g diet) was given for 4 weeks to group II and group IV. Chicory caused significant improvement in lipid profile and decreased the liver and heart acetyl-CoA carboxylase activity, atherogenic indices, hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase mRNA level and visfatin level. Meanwhile, significant increase in paraoxonase-1, superoxide dismutase and catalase activity was recorded. In conclusion, chicory has the potential role of being hypolipidemic, anti-lipotoxic, anti-oxidant and anti-atherogenic factor. Practical Applications Herbal treatments for hyperlipidemia are relatively cheap and locally available. The results showed that chicory (Cichorium intybus) has the potential of being hypolipidemic, anti-oxidant, anti-inflammatory, and decreased the atherogenic risk indices and anti-steatotic. Thus, it may represent a new source of natural food supplement aimed at preventing dyslipidemic risk for atherosclerosis, cardiac and hepatic steatosis.

Hypolipidemic effect of dandelion (Taraxacum officinale) extracts via fecal lipid excretion in C57BL/6 mice fed an atherogenic diet

Hypolipidemic effects of dandelion (Taraxacum officinale) extracts were investigated in C57BL/6 mice fed atherogenic diet for 6 weeks. Control, DWE (I and II) (1.5 and 3% dandelion water extract) and DEE (I and II) (1.5 and 3% dandelion ethanol extract) groups were used. Plasma triglyceride (TG), total cholesterol, and low density lipoprotein (LDL) cholesterol levels and the atherogenic index of dandelion groups were significantly (p<0.05) reduced, compared to controls. Hepatic total lipids, TG, and cholesterol levels were significantly (p<0.05) decreased in DEE groups, while the cholesterol level was significantly (p<0.05) decreased in DWE II group, compared to controls. Fecal lipid excretion was significantly (p<0.05) increased in DEE groups. Expression of hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase was significantly (p<0.05) down-regulated in DWE groups and up-regulated in DEE groups, compared to controls. DWE and DEE exert a hypolipidemic effect via decreased HMG CoA reductase expression and increased fecal lipid excretion.

Influence of HMG-CoA Reductase Inhibitors on Leptin-Induced Endothelial Cell Proliferation, Migration, and Capillary-Like Tube Formation

Objective: This study investigated the impact of the hepatic hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) on the leptin-induced human umbilical vein endothelial (HUVE) cell proliferation, migration, and capillary-like tube formation. Methods: The HUVE cells were isolated and cultured, and stimulated with leptin, statins (cerivastatin, fluvastatin, simvastatin), mevalonate, farnesyl pyrophosphate, geranylgeranyl pyrophosphate, or methyl-β-cyclodextrin. The endothelial cell proliferation was assessed using the Neubauer counting chamber. The migration of HUVE cells was examined with the planar migration assay. In vitro capillary sprouting was quantified by measuring the sprout length, number, and cumulative sprout length. Results: The HMG-CoA reductase inhibitors significantly reduced leptin-induced proliferation and migration, which was reversed by mevalonate. Further, the inhibitory effect of the statins on leptin-induced migration was shown to be modulated by the prenylation of farnesyl pyrophosphate and geranylgeranyl pyrophosphate. Although stimulation with a leptin showed no significant effect, a marked increase in capillary-like tube formation was observed with a joint stimulation with HMG-CoA reductase inhibitors. Although statins caused inhibition of proliferation and migration, the same dose of the agents amplified the selective growth of capillary-like tube formation. Membranous cholesterol depletion by methyl-β-cyclodextrin showed a weaker effect compared with statins. Conclusion: Through modulation of prenylation, leptin-induced pro-atherosclerotic events including proliferation and migration were inhibited by HMG-CoA reductase inhibitors.

Effects of broccoli stems and leaves meal on production performance and egg quality of laying hens

A total of 384 Roman brown shell laying hens were used to study the effects of increasing dietary inclusion of 0, 30, 60 and 90 g/kg of dried broccoli stems and leaves meal (BSLM) on production performance and egg quality. Hens were randomly allocated to four groups with six replicates of 16 chickens. The results showed that dietary supplementation of BSLM had no effect (P > 0.05) on production performance of laying hens. Incremental levels of BSLM linearly and quadratically increased the xanthophyll content of egg yolk, the yolk color (P < 0.05) and linearly decreased the content of cholesterol in egg yolk (P < 0.05). However, supplementation with BSLM had no effect (P > 0.05) on albumen height, haugh unit, shell thickness and shell strength of eggs. Hepatic hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase activity was decreased (P < 0.05) and concentrations of cecal short chain fatty acids were increased (P < 0.05) linearly and quadratically with increasing BSLM supplementation. The results indicate that supplementation with BSLM in laying hens improves egg quality with more yolk pigmentation and less yolk cholesterol. The decreased cholesterol of the egg fed BSLM may be partly caused by an alteration in the synthesis of cholesterol, which might result from the changes in cecal fermentation.

Regulation of hepatic cholesterol biosynthesis by berberine during hyperhomocysteinemia

Hyperhomocysteinemia, an elevation of blood homocysteine levels, is a metabolic disorder associated with dysfunction of multiple organs. We previously demonstrated that hyperhomocysteinemia stimulated hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase leading to hepatic lipid accumulation and liver injury. The liver plays an important role in cholesterol biosynthesis and overall homeostasis. HMG-CoA reductase catalyzes the rate-limiting step in cholesterol biosynthesis. Hepatic HMG-CoA reductase is a major target for lowering cholesterol levels in patients with hypercholesterolemia. The aim of the present study was to examine the effect of berberine, a plant-derived alkaloid, on hepatic cholesterol biosynthesis in hyperhomocysteinemic rats and to identify the underlying mechanism. Hyperhomocysteinemia was induced in Sprague-Dawley rats by feeding a high-methionine diet for 4 wk. HMG-CoA reductase activity was markedly elevated in the liver of hyperhomocysteinemic rats, which was accompanied by hepatic lipid accumulation. Activation of HMG-CoA reductase was caused by an increase in its gene expression and a reduction in its phosphorylation (an inactive form of the enzyme). Treatment of hyperhomocysteinemic rats with berberine for 5 days inhibited HMG-CoA reductase activity and reduced hepatic cholesterol content. Such an inhibitory effect was mediated by increased phosphorylation of HMG-CoA reductase. Berberine treatment also improved liver function. These results suggest that berberine regulates hepatic cholesterol biosynthesis via increased phosphorylation of HMG-CoA reductase. Berberine may be therapeutically useful for the management of cholesterol homeostasis.

Chemopreventive effects of β-ionone and geraniol during rat hepatocarcinogenesis promotion: distinct actions on cell proliferation, apoptosis, HMGCoA reductase, and RhoA

Chemopreventive activities of the dietary isoprenoids β-ionone (βI) and geraniol (GOH) were evaluated during the promotion phase of hepatocarcinogenesis. Over 5 consecutive weeks, rats received daily 16 mg/100 g body weight (b.w.) of βI (βI group), 25 mg/100 g b.w. of GOH (GOH group), or only corn oil (CO group, controls). Compared to the CO group, the following was observed: only the βI group showed a decrease in the mean number of visible hepatocyte nodules ( P<.05); βI and GOH groups had reduced mean number of persistent preneoplastic lesions (pPNLs) ( P<.05), but no differences regarding number of remodeling PNL (rPNLs) were observed; only the βI group exhibited smaller rPNL size and percentage of liver sections occupied by pPNLs ( P<.05), whereas the GOH group displayed a smaller percentage of liver sections occupied by rPNLs ( P<.05); a trend was observed in the βI group, which showed reduced cell proliferation of pPNLs ( P<.10), and the GOH group had increased apoptosis in pPNLs and rPNLs ( P<.05); only the βI group displayed reduced total plasma cholesterol concentrations ( P<.05) and increased hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase mRNA levels ( P<.05); only the GOH group had lower hepatic membrane RhoA protein levels ( P<.05); both the βI- and GOH-treated groups had higher hepatic concentrations of βI and GOH, respectively ( P<.05). Given these data, βI and GOH show promising chemopreventive effects during promotion of hepatocarcinogenesis by acting through distinct mechanism of actions: βI may inhibit cell proliferation and modulate HMGCoA reductase, and GOH can induce apoptosis and inhibit RhoA activation.

Beneficial Role of Dietary Folic Acid on Cholesterol and Bile Acid Metabolism in Ethanol-Fed Rats

Cholesterol metabolism is altered by chronic ethanol consumption. In previous articles, we demonstrated the anti-oxidant capacity of folic acid, which may be useful in the prevention of damage provoked by ethanol. We want to determine the effects of ethanol on cholesterol and bile metabolism and whether a folic acid-supplemented diet could change alterations provoked by a chronic ethanol intake in rats. We used four experimental groups: (1) control, (2) alcohol, (3) alcohol supplemented with folic acid, and (4) control supplemented with folic acid. In all the experimental groups, we measured hepatic 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, and cholesterol and bile acids in serum, liver, bile, and feces. We have found that the alcohol-fed groups showed high hepatic HMG-CoA reductase activity, total hepatic and serum cholesterol concentration, bile cholesterol secretion concentration, and cholesterol enterohepatic circulation. Total serum and hepatic cholesterol levels decreased when alcohol-fed rats were supplemented with folic acid. The hepatic bile acid concentration increased in both chronic ethanol groups. Folic acid supplementation significantly increased bile cholesterol secretion, the bile acids in bile, and fecal bile acid excretion in ethanol-exposed rats. The independent bile acid fraction showed no significant differences between both ethanol groups with respect to Na+, K+, and Cl- concentrations. Folic acid increases bile flow, bile acid synthesis from cholesterol, and bile acid excretion via feces, thus provoking a decrease in serum and hepatic cholesterol. However none of these actions were observed in supplemented control rats. This, therefore, could be yet another beneficial effect of folic acid on alcoholic patients.

Statin Therapy-Evidence Beyond Lipid Lowering Contributing to Plaque Stability

Primarily statin drugs inhibit hepatic 3-hydroxy 3-methylglutaryl coenzyme A (HMG-CoA) reductase, which is responsible for the reduction in circulating low-density lipoprotein (LDL) cholesterol. Several findings from recent research studies indicate that statins have multiple actions that favorably influence key factors involved in the atherogenic process. These so-called pleiotropic properties affect various aspects of cell function, inflammation, coagulation, and vasomotor activity. These effects are mediated either indirectly through LDL cholesterol reduction or via a direct effect on cellular functions. Such actions may contribute to the early cardiovascular benefit observed in several outcome trials with statin drugs therapy. Although many of the pleiotropic properties of statins may be a class effect, some may be unique to certain agents and account for differences in their pharmacological activity. This review summarise the results of the major outcome trials of statins and non-statins therapy and the possible mechanisms beyond lipid lowering contributing to plaque stability.

Selective Compensatory Induction of Hepatic HMG-CoA Reductase in Response to Inhibition of Cholesterol Absorption

The effect of the potent inhibitor of cholesterol absorption, ezetimibe, on serum cholesterol levels was tested in diabetic and thyroidectomized male Sprague-Dawley rats. Feeding diets supplemented with 1% cholesterol to the diabetic rats raised serum cholesterol levels from 132 to 514 mg/dl while decreasing hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase protein and mRNA levels. Addition of 10 mg/kg/day of ezetimibe to the diets of these animals lowered the serum cholesterol level to 90 mg/dl and produced a large compensatory increase in hepatic HMG-CoA reductase protein without significantly increasing mRNA levels, indicating a post-transcriptional effect. Hepatic LDL receptor protein levels in these diabetic rats were unaffected by ezetimibe treatment. In contrast, ezetimibe treatment of these young normal Sprague-Dawley rats, known to express high levels of hepatic HMG-CoA reductase, did not lower serum cholesterol levels. In thyroidectomized rats, dietary cholesterol increased serum cholesterol levels from 116 to 135 mg/dl and ezetimibe treatment lowered these elevated cholesterol levels to 85 mg/dl. Cholesterol feeding of thyroidectomized rats severely reduced hepatic HMG-CoA reductase protein, while ezetimibe treatment restored reductase protein to normal levels. Again, hepatic LDL receptor protein levels were unaffected by ezetimibe treatment of cholesterol-fed thyroidectomized rats. The data demonstrate that the cholesterol absorption inhibitor ezetimibe profoundly lowers serum cholesterol levels in animals expressing very low rates of hepatic cholesterol synthesis and produces large compensatory increases in hepatic HMG-CoA reductase expression without significantly affecting expression of hepatic LDL receptors. This indicates that ezetimibe should be most effective in lowering serum cholesterol levels in people with low rates of cholesterol synthesis/high rates of cholesterol absorption.

The Role of Mannosylated Enzyme and the Mannose Receptor in Enzyme Replacement Therapy

Lysosomal acid lipase (LAL) is the critical enzyme for the hydrolysis of triglycerides (TGs) and cholesteryl esters (CEs) in lysosomes. LAL defects cause Wolman disease (WD) and CE storage disease (CESD). An LAL null (lal-/-) mouse model closely mimics human WD/CESD, with hepatocellular, Kupffer cell and other macrophage, and adrenal cortical storage of CEs and TGs. The effect on the cellular targeting of high-mannose and complex oligosaccharide-type oligosaccharide chains was tested with human LAL expressed in Pichia pastoris (phLAL) and CHO cells (chLAL), respectively. Only chLAL was internalized by cultured fibroblasts, whereas both chLAL and phLAL were taken up by macrophage mannose receptor (MMR)-positive J774E cells. After intraperitoneal injection into lal-/- mice, phLAL and chLAL distributed to macrophages and macrophage-derived cells of various organs. chLAL was also detected in hepatocytes. Ten injections of either enzyme over 30 d into 2- and 2.5-mo-old lal-/- mice produced normalization of hepatic color, decreased liver weight (50%-58%), and diminished hepatic cholesterol and TG storage. Lipid accumulations in macrophages were diminished with either enzyme. Only chLAL cleared lipids in hepatocytes. Mice double homozygous for the LAL and MMR deficiences (lal-/-;MMR-/-) showed phLAL uptake into Kupffer cells and hepatocytes, reversal of macrophage histopathology and lipid storage in all tissues, and clearance of hepatocytes. These results implicate MMR-independent and mannose 6-phosphate receptor-independent pathways in phLAL uptake and delivery to lysosomes in vivo. In addition, these studies show specific cellular targeting and physiologic effects of differentially oligosaccharide-modified human LALs mediated by MMR and that lysosomal targeting of mannose-terminated glycoproteins occurs and storage can be eliminated effectively without MMR.

Degradation of HMG-CoA reductase in rat liver is cholesterol and ubiquitin independent

In contrast with the accelerated degradation observed in tumor cells in response to sterols, hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase turnover in whole animals was not increased by dietary cholesterol. Furthermore, treating rats with lovastatin to lower hepatic cholesterol levels did not decrease the rate of degradation. The half-life remained in the 6 h range. Co-immunoprecipitation studies revealed that the amount of ubiquitin associated with the reductase was entirely dependent upon the amount of microsomal protein subjected to immunoprecipitation. The results indicate that in liver, neither the rate of reductase protein degradation nor the ubiquitin-proteasome system appear to play roles in mediating changes in HMG-CoA reductase protein levels in response to dietary cholesterol.

150 kDa glycoprotein isolated from Solanum nigrum Linne enhances activities of detoxicant enzymes and lowers plasmic cholesterol in mouse

This study was carried out to investigate the modulation of detoxicant enzyme activity and plasma lipidemic levels by 150 kDa glycoprotein isolated from Solanum nigrum Linne (SNL), which has been used as a hepatoprotective and anticancer agent in folk medicine. Our results in this study showed that SNL glycoprotein has a band with 150 kDa on the 10% sodium dodecyl sulfate polyacrylamide gel, and that it has a strong scavenging activity against lipid peroxyl radicals. We also evaluated the lipidemic levels of SNL glycoprotein, based on lipoproteins and activities of detoxicant enzymes in treatment with Triton WR-1339 or corn oil in vivo. When mice were treated with either Triton WR-1339 or corn oil in the absence of SNL glycoprotein, the number of plasma lipoproteins [triglyceride (TG), total cholesterol (TC) and low density lipoprotein (LDL)] increased. However, when the mice were treated with either Triton WR-1339 or corn oil in the presence of SNL glycoprotein, the plasma lipoprotein levels (TG, TC and LDL) were significantly reduced. Similar results of SNL glycoprotein treatment were also produced in the activities of detoxicant enzymes. Namely, the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were remarkably increased after treatment with SNL glycoprotein. In addition, the activity of hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase was reduced by SNL glycoprotein in cholestyramine-treated mice. For example, we found that it inhibits the activity of cholestyramine-induced hepatic HMG-CoA reductase at 40 μg head body weight g −1 SNL glycoprotein. Collectively, these results pointed out that SNL glycoprotein can enhance the activities of detoxicant enzymes and bring about the inhibition of HMG-CoA reductase activity in vivo. Therefore, we speculate that SNL glycoprotein can be used as a cholesterol-lowering agent even at low concentrations.

Hepatic HMG-CoA Reductase Expression and Resistance to Dietary Cholesterol

The premise that the intrinsic level of expression of hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase determines the relative sensitivity to the serum cholesterol raising action of dietary cholesterol was examined in 9 strains of rat. For further comparison purposes, hamsters were also examined. The basal expression of hepatic HMG-CoA reductase, extent of feedback regulation by cholesterol, and changes in serum cholesterol levels and the hepatic low-density lipoprotein (LDL) receptor in response to cholesterol challenge were determined in these animals. The Sprague-Dawley, Wistar-Furth, Spontaneously Hypertensive, Lewis, and Wistar-Kyoto rats were all very resistant to dietary cholesterol and exhibited hepatic HMG-CoA reductase activities above 150 pmol / min(-1) / mg(-1). The Buffalo, Brown Norway, and Copenhagen 2331 rats had hepatic HMG-CoA reductase activities below 90 pmol / min(-1) / mg(-1) and had increases in serum cholesterol levels ranging from 12 to 33 mg/dl when given a 4-day, 1% cholesterol challenge. The extent of feedback regulation was reduced to only 3-fold in the Fisher 344 and Brown Norway rats that exhibited significant increases in serum cholesterol levels when given a cholesterol challenge. The Golden Syrian hamsters exhibited the largest increase (197 mg/dl) in serum cholesterol levels in response to dietary cholesterol and the lowest basal expression of hepatic HMG-CoA reductase (3.3 pmol / min(-1) / mg(-1)). Hepatic LDL receptor levels were not significantly decreased by dietary cholesterol in any of the animals. The data from these inbred rats and the hamsters strongly support the conclusion that the animals expressing the highest levels of hepatic HMG-CoA reductase are the most resistant to the serum cholesterol raising action of dietary cholesterol.

Suppression of 7,12-dimethylbenz[alpha]anthracene-induced carcinogenesis and hypercholesterolaemia in rats by tocotrienol-rich fraction isolated from rice bran oil.

The anti-tumour and anti-cholesterol impacts of tocotrienol-rich fraction (TRF) were investigated in rats treated with the chemical carcinogen 7,12-dimethylbenz [alpha]anthracene (DMBA), which is known to induce mammary carcinogenesis and hypercholesterolaemia. DMBA administration to rats was associated with the appearance of multiple tumours on mammary glands after 6 months. Alkaline phosphatase (ALP) and glutathione-S-transferase (GST) are used as marker enzymes to monitor the severity of carcinogenesis. Although no tumours were visible on livers, hepatic ALP and GST activities of DMBA-treated rats were profoundly elevated in comparison to enzyme activities of normal control rats. Feeding of TRF (10 mg/kg body weight/day) for 6 months, isolated from rice bran oil (RBO), to DMBA-administered rats, reduced the severity and extent of neoplastic transformation in the mammary glands. Similarly, plasma and mammary ALP activities increased during carcinogenesis (95% and 43%, respectively), were significantly decreased in TRF-treated rats, whereas TRF mediated a further increase of 51% in hepatic ALP activity. TRF treatment to rats maintained low levels of GST activities in liver ( approximately 32%) and mammary glands ( approximately 21%), which is consistent with anti-carcinogenic properties of TRF. Administration of DMBA also caused a significant increase of 30% in plasma total cholesterol and 111% in LDL-cholesterol levels compared with normal control levels. Feeding of TRF to rats caused a significant decline of 30% in total cholesterol and 67% in LDL-cholesterol levels compared with the DMBA-administered rats. The experimental hypercholesterolaemia caused a significant increase in enzymatic activity (23%) and protein mass (28%) of hepatic 3-hydroxy-3-methylglutaryl co-enzyme A (HMG-CoA) reductase. Consistent with TRF-mediated reduction in plasma lipid levels, enzymatic activity and protein mass of HMG-CoA reductase was significantly reduced. These results indicate that TRF has potent anti-cancer and anti-cholesterol effects in rats.

Molecular mechanisms of altered cholesterol metabolism in rats with spontaneous focal glomerulosclerosis

Imai rats exhibit spontaneous focal glomerulosclerosis (FGS), which is marked by heavy proteinuria, severe hyperlipidemia, and progressive renal insufficiency beginning at 8 to 10 weeks of age. In an earlier study, we reported severe skeletal muscle and adipose tissue lipoprotein lipase, and very low-density lipoprotein (VLDL) receptor deficiencies, which account for elevated plasma VLDL and triglycerides in Imai rats at 34 weeks of age. In this study, we investigated key factors involved in cholesterol metabolism. Male Imai and Sprague-Dawley control rats were fed a regular rat chow and observed from age 8 through 34 weeks. Hepatic 3-hydroxy-3 methylglutaryl coenzyme A (HMG-CoA) reductase, cholesterol 7alpha-hydroxylase, low-density lipoprotein (LDL) receptor and acyl Co A:cholesterol acyltransferase (ACAT) were measured by Western blot and plasma lecithin:cholesterol acyltransferase (LCAT) protein was measured by enzyme-linked immunosorbent assay (ELISA). At 34 weeks of age, the Imai rats showed severe proteinuria, hypoalbuminemia, 60% reduction in glomerular filtration rate (GFR), elevated plasma total and LDL cholesterol and LDL/high-density lipoprotein (HDL) ratio. Imai rats showed a twofold elevation of hepatic HMG-CoA reductase, the rate-limiting step in cholesterol biosynthesis, but no significant change in cholesterol 7alpha-hydroxylase, the rate-limiting enzyme in cholesterol catabolism to bile acids. This was accompanied by and largely due to a threefold down-regulation of hepatic LDL receptor, which limits hepatic uptake of LDL; and a threefold up-regulation of hepatic ACAT (P < 0.01), which augments esterification of hepatocyte free cholesterol, thus, limiting cholesterol-mediated feedback regulation of cholesterol synthesis and catabolism. Moreover, plasma LCAT concentration was severely depressed (by fourfold) in Imai rats. This abnormality can impair HDL-mediated cholesterol transport from extrahepatic tissues to the liver. The study revealed marked abnormalities of the key proteins involved in regulation of hepatic cholesterol metabolism. These abnormalities can account for severe dysregulation of cholesterol metabolism in Imai rats with spontaneous FGS, which closely resembles FGS in humans.

Up-regulation of acyl-coenzyme A:cholesterol acyltransferase (ACAT) in nephrotic syndrome

We have previously demonstrated that hypercholesterolemia in rats with puromycin-induced nephrotic syndrome (NS) is associated with up-regulation of hepatic 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase and relative down-regulation of cholesterol 7alpha-hydroxylase (Ch-7alpha), which represent the rate-limiting steps in cholesterol biosynthesis and catabolism. Expression of HMG-CoA reductase is inhibited and Ch-7alpha is augmented by intracellular free cholesterol, which is avidly esterified by acyl-CoA:cholesterol acyltransferase (ACAT). Therefore, we hypothesized that NS may result in up-regulation of hepatic ACAT. Hepatic tissue ACAT mRNA (Northern blot), protein (Western blot) and enzymatic activity were determined in rats with puromycin-induced NS, placebo-treated control rats and Nagase hypoalbuminemic (NAG) rats. The NS group exhibited heavy proteinuria, hypoalbuminemia, normal creatinine clearance, severe hypercholesterolemia and hypertriglyceridemia. Despite severe hypoalbuminemia, NAG rats with inherited hypoalbuminemia exhibited only a mild elevation of plasma cholesterol and triglycerides. Severe hypercholesterolemia in the NS group was coupled with depressed liver tissue free cholesterol concentration and marked increases in hepatic ACAT mRNA, protein and enzymatic activity. In contrast, ACAT mRNA and protein contents of the liver were normal and ACAT activity was mildly elevated in the NAG group. NS results in marked up-regulation of hepatic ACAT, which is primarily due to proteinuria and not hypoalbuminemia, since the latter alone, as seen in NAG rats, does not significantly impact ACAT expression. Elevated ACAT in NS can contribute to dysregulation of cholesterol biosynthesis and catabolism by limiting the normal cholesterol signaling involved in regulation of these processes.

Effects of high-dose simvastatin on adrenal and gonadal steroidogenesis in men with hypercholesterolemia

In view of the role of both the de novo biosynthesis and receptor-mediated uptake of cholesterol for normal steroidogenesis, we evaluated whether extending the therapeutic dose of the hepatic hydroxymethyl glutaryl coenzyme A (HMG-CoA) reductase inhibitor, simvastatin, to 80 mg/d would affect adrenal and gonadal steroid synthesis in men with hypercholesterolemia. To evaluate this question, we enrolled men into a multicenter randomized, placebo-controlled study lasting 12 weeks. Men with serum low-density lipoprotein cholesterol (LDL-C) more than 145 mg/dL after 6 weeks of a lipid-lowering diet were randomized to 80 mg simvastatin or placebo. Half of the subjects were asked to undergo a 6-hour infusion of corticotropin (ACTH) to evaluate cortisol synthesis, and the entire cohort received a human chorionic gonadotropin (hCG) stimulation test to assess gonadal hormone secretion using pooled serum samples taken 15 minutes apart. A total of 81 men (age, 45 ± 11 years; 93% Caucasian) with baseline serum LDL-C of 197 mg/dL (placebo, n = 39) and 184 mg/dL (simvastatin 80 mg, n = 42) completed the study. After 12 weeks, serum LDL-C, triglycerides, and high-density lipoprotein cholesterol (HDL-C) in the simvastatin group changed by −43%, −25%, and 8%, respectively (all P < .001). The basal cortisol level and the peak serum cortisol and area under the curve response to the 6-hour ACTH infusion were comparable between the two treatment groups at baseline and after 12 weeks. The pooled total testosterone level at baseline was 541 and 513 ng/dL in the placebo and simvastatin-treated groups, respectively, which declined to 536 ± 20.5 ng/dL (−1.5%) and 474 ± 30.4 ng/dL (−13.6%, P = .09) after treatment (mean ± SD). The pooled free testosterone declined by 6.3% in the simvastatin group, versus a 4.9% increase in the placebo group (P = .588), while pooled bioavailable testosterone declined 10.2% in the simvastatin group and increased 1.4% in the placebo group (P = 035). There were no changes in serum gonadotropin levels or sex hormone-binding globulin (SHBG). After administration of hCG, there were no differences in the peak total pooled testosterone level before or after 12 weeks of treatment. Simvastatin 80 mg was well tolerated compared with placebo. In conclusion, basal and stimulated cortisol production was unaffected by the use of simvastatin 80 mg versus placebo. As reported with other statins and cholestyramine, there were small declines in the simvastatin-treated group for pooled total, free, and bioavailable testosterone after 12 weeks, although there was no compensatory increase in serum follicle-stimulating hormone (FSH) or luteinizing hormone (LH) levels.