Effect of 3,4-di(OH)-cinnamate synthetic derivative on plasma and hepatic cholesterol level and antioxidant enzyme activities in high cholesterol-fed rats

The effect of 3,4-di(OH)-phenylpropionic acid (L-phenylalanine methyl ester) amide (SL-1063), a synthetic derivative of 3,4-di(OH)-cinnamate, on the cholesterol metabolism and antioxidant enzyme system was examined in rats. Diets that included either SL-1063 (0.046%, w/w) or lovastatin (0.02%, w/w) as a supplement, plus 1 g cholesterol/100 g diet were fed to rats ad libitum for 5 weeks. The total plasma cholesterol and triglyceride levels were significantly lowered by the SL-1063 supplement compared to the control group. Meanwhile, the levels of plasma HDL-cholesterol and ratio of HDL-cholesterol/total cholesterol (%) were significantly higher in the SL-1063 group than in the control group. However, the lovastatin supplement did not affect the plasma lipid level. The hepatic cholesterol level and 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity were significantly lowered in the lovastatin group compared to the SL-1063 group; however, the hepatic triglyceride level did not differ among the groups. The activity of hepatic acyl CoA: cholesterol acyltransferase (ACAT), the enzyme that catalyzes hepatic cholesterol esterification, was significantly lower in the lovastatin and SL-1063 groups than in the control group. Furthermore, the SL-1063 supplement elevated the excretion of fecal sterols. As regards the hepatic antioxidant enzyme system, the superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and glutathione reductase (GR) activities were all significantly higher in the SL-1063 group compared to the control group, whereas only the GR activity was significantly increased by the lovastatin supplement. No marked difference in the GSH levels and glucose-6-phosphate dehydrogenase (G6PD) activities was observed among the groups. The levels of plasma and hepatic thiobarbituric acid reactive substances (TBARS) were lowered by the SL-1063 supplement compared to the control group. Accordingly, the current results suggest that SL-1063, a synthetic derivative of 3,4-di(OH)-cinnamate, is effective in lowering the plasma lipids and improving the antioxidant enzyme system.     

Evaluation of hesperetin 7-O-lauryl ether as lipid-lowering agent in high-cholesterol-fed rats

The lipid-lowering efficacy of hesperetin was revealed in preliminary studies on experimental animals. As such, the current study compared the effect of hesperetin 7-O-lauryl ether, with that of hesperetin and lovastatin on the lipid profile and cholesterol-regulating mechanism in high-cholesterol-fed rats. Male rats were fed a high-cholesterol diet (1%, wt/wt) or high-cholesterol diet supplemented with lovastatin (1, 0.02%, wt/wt), hesperetin (2, 0.02%, wt/wt), or hesperetin 7-O-lauryl ether (3, 0.031%, wt/wt) for six weeks. The supplemental amount of 3 was 0.066mmol/100g diet as an equivalent to the supplemental amount of 2. The plasma total cholesterol and triglyceride levels were significantly lowered by the 2 and 3 supplements compared with the control or 1-supplemented group. The hepatic HMG-CoA reductase activities were also significantly lower in all the supplemented groups compared with the control group, and the hepatic ACAT activity was significantly lower in the 2- and 3-supplemented groups. The supplementation of 3 resulted in a higher excretion of total neutral sterol and total fecal sterol compared with the control or 1-supplemented group. Accordingly, overall, compound 3, exhibited a more potent plasma lipid-lowering effect than compound 1 based on inhibiting cholesterol biosynthesis and esterification, while also increasing the fecal sterol excretion.     

Antioxidative activity of naringin and lovastatin in high cholesterol-fed rabbits.

The consumption of a cholesterol-enriched diet increases the degree of lipid peroxidation, which is one of the early processes of atherosclerosis. The aim of this trial was to determine the antioxidative effects of the citrus bioflavonoid, naringin, a potent cholesterol-lowering agent, compared to the cholesterol-lowering drug, lovastatin, in rabbits fed a high cholesterol diet. Male rabbits were served a high-cholesterol (0.5%, w/w) diet or high-cholesterol diet supplemented with either naringin (0.5% cholesterol, 0.05% naringin, w/w) or lovastatin (0.5% cholesterol, 0.03% lovastatin, w/w) for 8 weeks to determine the plasma and hepatic lipid peroxide, plasma vitamin A and E levels, and hepatic hydrogen peroxide levels, along with the hepatic antioxidant enzyme activities and gene expressions. Only the lovastatin group showed significantly lower plasma and hepatic lipid peroxide levels compared to the control group. The naringin supplementation significantly increased the activities of both hepatic SOD and catalase by 33% and 20%, respectively, whereas the lovastatin supplementation only increased the catalase activity by 23% compared to control group. There was no difference in the GSH-Px activities between the various groups. Content of H2O2 in hepatic mitochondria was significantly lower in groups supplemented with lovastatin and naringin than in control group. However, there was no difference in cytosolic H2O2 content in liver between groups. The concentration of plasma vitamin E was significantly increased by the naringin supplementation. When comparing the antioxidant enzyme gene expression, the mRNA expression of SOD, catalase and GSH-Px was significantly up-regulated in the naringin-supplemented group. Accordingly, these results would appear to indicate that naringin, a citrus bioflavonoid, plays an important role in regulating antioxidative capacities by increasing the SOD and catalase activities, up-regulating the gene expressions of SOD, catalase, and GSH-Px, and protecting the plasma vitamin E. In contrast, lovastatin exhibited an inhibitory effect on the plasma and hepatic lipid peroxidation and increased the hepatic catalase activity in high-cholesterol fed rabbits.     

Regulation of cholesterol biosynthesis in sitosterolemia: effects of lovastatin, cholestyramine, and dietary sterol restriction.

We investigated the effects of lovastatin, cholestyramine, and dietary sterol restriction on cholesterol synthesis and low density lipoprotein receptor function in freshly isolated mononuclear leukocytes from two unrelated sitosterolemic families. Total plasma sterol concentrations were elevated in the two homozygous sitosterolemic subjects (343 and 301 vs. 185 mg/dl in controls) and contained increased amounts of plant sterols and 5 alpha-saturated stanols (20% and 8% vs. less than 1% in controls), but were not significantly different from controls in the two heterozygous subjects. The rates of conversion of acetate to cholesterol by mononuclear leukocytes were subnormal in all homozygous and heterozygous subjects and correlated with markedly reduced microsomal 3-hydroxy-3-methylglutaryl co-enzyme A (HMG-CoA) reductase activity. In the two homozygous subjects, cholestyramine treatment decreased plasma sterols 29% and 35%, and yet was associated with a paradoxical decline in mononuclear leukocyte HMG-CoA reductase activity. In contrast, plasma sterol concentrations decreased 14% and 5%, and mononuclear leukocyte HMG-CoA reductase activities increased 13% and 46% in three control and one heterozygous subjects treated with cholestyramine, respectively. Plasma sterol concentrations in the homozygous subjects unexpectedly failed to decline during treatment with lovastatin or a low sterol diet. In distinction, plasma sterol concentrations in three control and one heterozygous subjects dropped 28% and 31%, respectively, during treatment with lovastatin. Both cholestyramine and low dietary sterols stimulated low density lipoprotein receptor function. These results demonstrate a marked abnormality in cholesterol homeostasis in patients with homozygous sitosterolemia with xanthomatosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Astragalus polysaccharides lowers plasma cholesterol through mechanisms distinct from statins

To determine the efficacy and underlying mechanism of Astragalus polysaccharides (APS) on plasma lipids in hypercholesterolemia hamsters. The effect of APS (0.25 g/kg/d) on plasma and liver lipids, fecal bile acids and neutral sterol, cholesterol absorption and synthesis, HMG-CoA reductase activity, and gene and protein expressions in the liver and small intestine was investigated in twenty-four hypercholesterolemia hamsters. Treatment periods lasted for three months. APS significantly lowered plasma total cholesterol by 45.8%, triglycerides by 30%, and low-density lipoprotein-cholesterol by 47.4%, comparable to simvastatin. Further examinations revealed that APS reduced total cholesterol and triglycerides in the liver, increased fecal bile acid and neutral sterol excretion, inhibited cholesterol absorption, and by contrast, increased hepatic cholesterol synthesis and HMG-CoA reductase activity. Plasma total cholesterol or low-density lipoprotein-cholesterol levels were significantly correlated with cholesterol absorption rates. APS up-regulated cholesterol-7α-hydroxylase and LDL-receptor gene expressions. These new findings identify APS as a potential natural cholesterol lowering agent, working through mechanisms distinct from statins.     

Naringenin 7-O-cetyl ether as inhibitor of HMG-CoA reductase and modulator of plasma and hepatic lipids in high cholesterol-fed rats

Numerous studies in vitro have shown a close relationship between the chemical structure and biologic activity of flavonoids, whereby their basic structure is modified to increase or decrease their biologic activity. The effects of naringenin (1) and its synthetic derivative, naringenin 7-O-cetyl ether (2), on the lipid profile, the cholesterol-regulating enzyme activity and the excretion of sterol were compared in rats fed a high-cholesterol (1% wt/wt) diet. Either 1 or 2 was supplemented with a high-cholesterol diet for 6 weeks at a dose of 0.073 mmol/100g diet. The supplementation of 1 or 2 significantly lowered the levels (mean+/-SE) of the plasma total cholesterol (4.93+/-0.19 and 4.75+/-0.16 mmol/L vs 5.87+/-0.36 mmol/L, p<0.05) and hepatic triglyceride (0.12+/-0.01 and 0.11+/-0.01 mmol/g vs 0.18+/-0.01 mmol/g, p<0.05) and cholesterol (0.23+/-0.01 and 0.21+/-0.01 mmol/g vs 0.31+/-0.01 mmol/g, p<0.05) compared to those of the control. The compound 1 or 2 supplementation appeared to decrease the excretion of neutral sterols. The plasma HDL-cholesterol concentration and ratio of HDL to total cholesterol were significantly higher in 1 and 2 groups than in control group. Although the biological effect of 2 on inhibiting hepatic HMG-CoA reductase and ACAT activities was only significant compared to the control group, both compounds exhibited a significant hypocholesterolemic effect in rats fed a high-cholesterol diet. The results suggest that cholesterol biosynthesis and esterification were concomitantly reduced by 2, as indicated by the decreased HMG-CoA reductase and ACAT activities.     

Hypocholesterolemic and antioxidant properties of 3-(4-hydroxyl)propanoic acid derivatives in high-cholesterol fed rats

The purpose of the present study was to evaluate the in vivo efficacy of two cinnamic acid synthetic derivatives (allyl 3-[4-hydroxyphenyl]propanoate; HPP304, 1-naphthyl-methyl 3-[4-hydroxyphenyl]propanoate; HPP305) in high-cholesterol fed rats and compare their actions to that of cinnamic acid. Cinnamic acid and its synthetic derivatives were supplemented with a high-cholesterol diet for 42 days at a dose of 0.135 mmol/100 g of diet. The supplementation of HPP304 and HPP305 significantly lowered cholesterol and triglyceride levels in the plasma and liver with a simultaneous increase in the HDL-cholesterol concentration, whereas cinnamic acid only lowered the plasma cholesterol concentration. Cinnamic acid lowered hepatic HMG-CoA reductase activity in high-cholesterol fed rats, however, its synthetic derivatives (HPP304 and HPP305) did not affect HMG-CoA reductase activity compared to the control group. Instead, the HPP304 and HPP305 supplements significantly lowered hepatic acyl coenzyme A:cholesterol acyltransferase activity and increased the fecal bile acid. The SOD activity of the erythrocytes and liver was not different between the groups, however, the activities of CAT and GSH-Px, and the level of GSH in the erythrocytes were significantly higher in the HPP304 and HPP305 groups than in the control group. On the other hand, the activities of CAT and GSH-Px, and the level of malondialdehyde in the liver were significantly lower in the HPP304 and HPP305 groups. The antioxidant activities of these cinnamic acid synthetic derivatives were similar to the cinnamic acid in the high-cholesterol fed rats. In addition, HPP304 and HPP305 lowered amniotransferase activity in the plasma. These results suggest that two cinnamic acid synthetic derivatives (HPP304 and HPP305) exert lipid-lowering action and antioxidant properties without hepatotoxicity in high-cholesterol fed rats.     

Effect of citrus flavonoids on lipid metabolism and glucose-regulating enzyme mRNA levels in type-2 diabetic mice

Flavonoids have been identified as the antidiabetic components in a number of traditional ethnic remedies. However, the mechanisms whereby these compounds exert their hypoglycemic and hypolipidemic action in type-2 diabetes have rarely been investigated. Therefore, this study investigated the effect of the flavonoids hesperidin and naringin on glucose and lipid regulation in C57BL/KsJ-db/db mice. Hesperidin and naringin both significantly increased the glucokinase mRNA level, while naringin also lowered the mRNA expression of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase in the liver. In addition, the hepatic glucose transporter 2 protein expression was significantly reduced, while the expression of adipocyte glucose transporter 4 and hepatic and adipocyte peroxisome proliferator-activated receptor gamma were elevated in the hesperidin and naringin groups when compared with the control group. Furthermore, hesperidin and naringin effectively lowered the plasma free fatty acid and plasma and hepatic triglyceride levels, and simultaneously reduced the hepatic fatty acid oxidation and carnitine palmitoyl transferase activity. These changes were seemingly attributable to a suppression of the hepatic fatty acid synthase, glucose-6-phosphate dehydrogenase, and phosphatidate phosphohydrolase activities and an increase in the fecal triglycerides. The two flavonoids also led to a decrease in the plasma and hepatic cholesterol levels that may have been partly due to the decreased hepatic 3-hydroxy-3-methylglutaryl-coenzyme (HMG-CoA) reductase and acyl CoA: cholesterol acyltransferase (ACAT) activities and increased fecal cholesterol. Consequently, the current results suggest that hesperidin and naringin are beneficial for improving hyperlipidemia and hyperglycemia in type-2 diabetic animals by partly regulating the fatty acid and cholesterol metabolism and affecting the gene expression of glucose-regulating enzymes.     

Lipid-lowering efficacy of 3,4-di(OH)-phenylpropionic L-leucine in high-cholesterol fed rats

A preliminary study revealed that 3,4-di(OH)-hydrocinnamate (HC), a polyphenolic compound, lowered the plasma lipids in high-cholesterol fed rats. Accordingly, this study was designed to test the lipid-lowering efficacy of a synthetic derivative, 3,4-di(OH)-phenylpropionic (L-leucine) amide (PPLA), in rats fed a high-cholesterol (1%, wt/wt) diet. As such, HC or PPLA was given as supplement to a high-cholesterol diet for 6 weeks at a dose of 0.137 mmol/100 g diet. The supplementation of HC and PPLA significantly lowered the plasma and hepatic cholesterol and triglyceride levels compared to the control group. The activities of hepatic HMG-CoA reductase (164 +/- 9.12 and 124.74 +/- 17.09 pmol/min/mg protein vs. 245.41 +/- 13.01 pmol/min/mg protein, p < 0.05) and ACAT (411.49 +/- 11.48 and 334.35 +/- 17.68 pmol/min/mg protein vs. 490.41 +/- 16.69 pmol/min/mg protein, p < 0.05) were significantly lower in the HC- and PPLA-supplemented groups than in the control group. However, PPLA was more effective in inhibiting the enzyme activities than HC. The excretion of neutral sterol was significantly higher in HC- and PPLA-supplemented groups than in the control group. Therefore, these results indicate that PPLA, a leucine-attached version of HC, exhibited a similar significant hypocholesterolemic effect to HC in rats fed a high-cholesterol diet.     

Mechanisms for cholesterol homeostasis in rat jejunal mucosa: effects of cholesterol, sitosterol, and lovastatin

The effects of feeding cholesterol, sitosterol, and lovastatin on cholesterol absorption, biosynthesis, esterification, and LDL receptor function were examined in the rat jejunal mucosa. Cholesterol absorption was measured by the dual-isotope plasma ratio method; the rate-limiting enzyme of cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, was measured as total and expressed enzyme activities (in the absence and presence of a phosphatase inhibitor, NaF, respectively); mucosal total and esterified cholesterol concentrations were determined by gas-liquid chromatography; LDL receptor function was assayed as receptor-mediated binding of (125)I-labeled LDL to mucosal membranes. Feeding 2% sitosterol or 0.04% lovastatin for 1 week significantly (P < 0.01) decreased the amounts of cholesterol absorbed per day (-85% and -63%, respectively). In contrast, feeding 2% cholesterol for 1 week increased the amounts of absorbed cholesterol 27-fold, even though the percent absorption significantly decreased. With all three treatments, there was a coordinate regulation of total HMG-CoA reductase activity and receptor-mediated LDL binding. Cholesterol feeding downregulated both total jejunal HMG-CoA reductase activity (P < 0.05) and receptor-mediated LDL binding (P < 0.01), whereas lovastatin- and sitosterol-supplemented diets significantly upregulated both of these parameters. In the control, cholesterol-fed, and sitosterol-fed animals, about half of the total jejunal HMG-CoA reductase activity was expressed (in functional dephosphorylated form). However, in the lovastatin-treated rats with 4-fold stimulation of HMG-CoA reductase, only 23% of the total enzyme activity was expressed. Changes in total HMG-CoA reductase activity and receptor-mediated LDL binding in all tested groups occurred with no change in total concentrations of mucosal cholesterol, and only cholesterol-fed animals had increased mucosal esterified cholesterol concentrations. Thus, in response to various fluxes of dietary or newly formed cholesterol, HMG-CoA reductase and receptor-mediated LDL binding are coordinately regulated to maintain constant cellular cholesterol concentrations in the jejunum.     

Lovastatin treatment inhibits sterol synthesis and induces HMG-CoA reductase activity in mononuclear leukocytes of normal subjects

The mechanism by which competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase decrease serum cholesterol is incompletely understood. The few available data in humans suggest that chronic administration of the competitive inhibitor, lovastatin, decreases serum cholesterol with little or no change in total body sterol synthesis. To further define the effect of lovastatin on cholesterol synthesis in normal subjects, we investigated the effect of a single oral dose of lovastatin and a 4-week treatment period of lovastatin on mononuclear leukocyte (ML) sterol synthesis as a reflection of total body sterol synthesis. In parallel, we measured serum lipid profiles and HMG-CoA reductase activity in ML microsomes that had been washed free of lovastatin. ML sterol synthesis did not significantly decrease (23 +/- 5%, mean +/- SEM) at 3 h after a single 40-mg dose of lovastatin. With a single oral 80-mg dose, ML sterol synthesis decreased by 57 +/- 10% (P less than 0.05) and remained low for the subsequent 6 h. With both doses, total HMG-CoA reductase enzyme activity in microsomes prepared from harvested mononuclear leukocytes was induced 4.8-fold (P less than 0.01) over baseline values. Both the 20-mg bid dose and the 40-mg bid dose of lovastatin administered for a 4-week period decreased serum cholesterol by 25-34%. Lovastatin at 20 mg bid decreased ML sterol synthesis by 23 +/- 6% (P less than 0.02) and increased ML HMG-CoA reductase 3.8 times (P less than 0.001) the baseline values. Twenty four hours after stopping lovastatin, ML sterol synthesis and HMG-CoA reductase enzyme activity had returned to the baseline values. The higher dose of lovastatin (40 mg bid) decreased ML sterol synthesis by 16 +/- 3% (P less than 0.05) and induced HMG-CoA reductase to 53.7 times (P less than 0.01) the baseline value at 4 weeks. Stopping this higher dose effected a rebound in ML sterol synthesis to 140 +/- 11% of baseline (P less than 0.01), while HMG-CoA reductase remained 12.5 times baseline (P less than 0.01) over the next 3 days. No rebound in serum cholesterol was observed. From these data we conclude that in normal subjects lovastatin lowers serum cholesterol with only a modest effect on sterol synthesis. The effect of lovastatin on sterol synthesis in mononuclear leukocytes is tempered by an induction of HMG-CoA reductase enzyme quantity, balancing the enzyme inhibition by lovastatin.(ABSTRACT TRUNCATED AT 400 WORDS)     

Absorption of intestinal free cholesterol is lowered by supplementation of Areca catechu L. extract in rats

Areca extracts exhibiting a strong inhibitory activity against pancreatic cholesterol esterase (pCEase) in vitro were previously found to lower the absorption of dietary cholesteryl ester. Therefore, to determine whether a combined Areca extract also affects the absorption of intestinal free cholesterol, male rats were fed a diet containing free cholesterol (1%, w/w) either with or without an Areca nut extract supplement (0.5%, w/w). The Areca extract supplement significantly lowered the plasma cholesterol concentration by 25% without any change in the plasma triglyceride concentration, when compared to the control group. The supplement also significantly lowered the small intestinal pCEase activity by 39.1% compared to that of the control group. As regards the hepatic and intestinal ACAT activities, only the intestinal enzyme activity was significantly lowered by the supplement, when compared to the control group. The absorbed cholesterol that appeared in the blood after an oral dose of [1,2(n)-3H] free cholesterol was significantly lower in the rats supplemented with the Areca nut extract, compared with the control group. These results suggest that the inhibition of intestinal ACAT and possibly pCEase may facilitate the metabolic efficiency of the Areca nut extract as regards the absorption of intestinal free cholesterol. The structure and chemical properties of the active compound in the water-soluble Areca extract remain to be elucidated.     

Variations of hepatic cholesterol precursors during altered flows of endogenous and exogenous squalene in the rat

Hepatic and serum levels of cholesterol precursors were analyzed in rats under basal (control) conditions and when cholesterol synthesis was activated by feeding 1% squalene or 5% cholestyramine. Exogenous squalene stimulated the activity of acyl-coenzyme A:cholesterol acyltransferase (ACAT) but strongly inhibited the activity of hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase; cholestyramine did not affect ACAT but increased HMG-CoA reductase several-fold, indicating enhanced production of endogenous squalene. Activation of cholesterol synthesis by the two methods markedly increased the hepatic and serum contents of cholesterol precursor sterols. However, the sterol profiles were clearly different. Thus, exogenous squalene raised most significantly (up to 109-fold) free and esterified methyl sterols, and less so (up to 2-fold) demethylated C27 sterols (desmosterol and cholestenols) and also esterified cholesterol. Activation of endogenous squalene production by cholestyramine was associated with a depletion of esterified cholesterol and by a marked, up to 8-fold, increase of the free demethylated sterol precursor levels, whereas the increase of methyl sterols, up to 5-fold, was less conspicuous than during the squalene feeding. The changes were mostly insignificant for esterified sterols. The altered serum sterol profiles were quite similar to those in liver. Serum cholestenols and especially their portion of total serum precursor sterols were closely correlated with the hepatic activity of HMG-CoA reductase.     

Alteration of biliary ursodeoxycholic acid in guinea pig during early stages of cholestyramine feeding

The effects of cholestyramine feeding on biliary ursodeoxycholic acid, fecal excretion of bile acids and neutral sterols on cholesterol 7α-hydroxylase and hepatic HMG-CoA reductase were examined in the guinea pig. In the bile there was a 57% decrease in the concentration of ursodeoxycholic acid while an increase was observed in the concentration of chenodeoxycholic acid. Cholestyramine feeding for ten days resulted in a decrease in plasma cholesterol levels and an increase in both hepatic HMG-CoA reductase and cholesterol 7α-hydroxylase activities. The fecal excretion of both bile acids and neutral sterols was significantly increased.     

Feedback inhibition of the cholesterol biosynthetic pathway in patients with Smith-Lemli-Opitz syndrome as demonstrated by urinary mevalonate excretion

Smith-Lemli-Opitz syndrome (SLOS) is a genetic disorder characterized by low plasma cholesterol and high 7-dehydrocholesterol (7-DHC). Synthesis of cholesterol and 7-DHC and its metabolites is regulated by HMG-CoA reductase, whose activity can be measured by 24-h excretion of its product mevalonate. We devised a simple, non-invasive method for collecting 24-h urine in our subjects. With a background of a very low cholesterol diet, mean mevalonate excretion did not differ between controls and SLOS children, indicating that SLOS subjects have normal HMG-CoA reductase activity. In a short term feeding study, the effects of a high cholesterol diet in SLOS subjects include a significant 55% increase in plasma cholesterol levels and 39% decrease in mevalonate excretion and no change in plasma 7-DHC levels. However, in four SLOS subjects, fed a high cholesterol diet for 2-3 years, plasma cholesterol levels continued to increase, urinary mevalonate excretion remained low and total 7-DHC decreased significantly, likely from decreased total sterol synthesis. Thus, in SLOS subjects, HMG-CoA reductase activity was normal and was subject to normal cholesterol induced feedback inhibition. However, total sterol synthesis in SLOS may still be decreased because of increased diversion of mevalonate into the shunt pathway away from sterol synthesis.     

Role of naringin supplement in regulation of lipid and ethanol metabolism in rats

The current study was performed to investigate the effect of naringin supplements on the alcohol, lipid, and antioxidant metabolism in ethanol-treated rats. Male Sprague-Dawley rats were randomly divided into six groups (n = 10) based on six dietary categories: ethanol and naringin-free, ethanol (50 g/L) plus low-naringin (0.05 g/L), ethanol plus high-naringin (0.125 g/L), and three corresponding pair-fed groups. The pair-fed control rats received an isocaloric diet containing dextrin-maltose instead of ethanol for 5 wks. Among the ethanol treated groups, the naringin supplements significantly lowered the plasma ethanol concentration with a simultaneous increase in the ADH and/or ALDH activities. However, among the ethanol-treated groups, naringin supplementation resulted in a significant decrease in the hepatic triglycerides and plasma and hepatic total cholesterol compared to that in the naringin-free group. Naringin supplementation significantly increased the HDL-cholesterol and HDL-C/total-C ratio, while lowering the AI value among the ethanol-treated groups. Hepatic lipid accumulation was also significantly reduced in the naringin-supplemented groups compared to the naringin-free group among the ethanol-treated groups, while no differences were found among the pair-fed groups. Among the ethanol-treated groups, the low-naringin supplementation resulted in a significant decrease in the levels of plasma and hepatic TBARS, whereas it resulted in higher SOD and GSH-Px activities and gluthathion levels in the liver. Accordingly, naringin would appear to contribute to alleviating the adverse effect of ethanol ingestion by enhancing the ethanol and lipid metabolism as well as the hepatic antioxidant defense system.     

Tissue-selective acute effects of inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase on cholesterol biosynthesis in lens

Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the key enzyme that regulates cholesterol synthesis, lower serum cholesterol by increasing the activity of low density lipoprotein (LDL) receptors in the liver. In rat liver slices, the dose-response curves for inhibition of [14C]acetate incorporation into cholesterol were similar for the active acid forms of lovastatin, simvastatin, and pravastatin. The calculated IC50 values were approximately 20-50 nM for all three drugs. Interest in possible extrahepatic effects of reductase inhibitors is based on recent findings that some inhibitors of HMG-CoA reductase, lovastatin and simvastatin, can cause cataracts in dogs at high doses. To evaluate the effects of these drugs on cholesterol synthesis in the lens, we developed a facile, reproducible ex vivo assay using lenses from weanling rats explanted to tissue culture medium. [14C]Acetate incorporation into cholesterol was proportional to time and to the number of lenses in the incubation and was completely eliminated by high concentrations of inhibitors of HMG-CoA reductase. At the same time, incorporation into free fatty acids was not inhibited. In marked contrast to the liver, the dose-response curve for pravastatin in lens was shifted two orders of magnitude to the right of the curves for lovastatin acid and simvastatin acid. The calculated IC50 values were 4.5 +/- 0.7 nM, 5.2 +/- 1.5 nM, and 469 +/- 42 nM for lovastatin acid, simvastatin acid, and pravastatin, respectively. Thus, while equally active in the liver, pravastatin was 100-fold less inhibitory in the lens compared to lovastatin and simvastatin. Similar selectivity was observed with rabbit lens. Following oral dosing, ex vivo inhibition of [14C]acetate incorporation into cholesterol in rat liver was similar for lovastatin and pravastatin, but cholesterol synthesis in lens was inhibited by lovastatin by as much as 70%. This inhibition was dose-dependent and no inhibition in lens was observed with pravastatin even at very high doses. This tissue-selective inhibition of sterol synthesis by pravastatin was likely due to the inability of pravastatin to enter the intact lens since pravastatin and lovastatin acid were equally effective inhibitors of HMG-CoA reductase enzyme activity in whole lens homogenates. We conclude that pravastatin is tissue-selective with respect to lens and liver in its ability to inhibit cholesterol synthesis.     

Selective inhibition of cholesterol synthesis in liver versus extrahepatic tissues by HMG-CoA reductase inhibitors

Hepatic specificity of inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase may be achieved by efficient first-pass liver extraction resulting in low circulating drug levels, as with lovastatin, or by lower cellular uptake in peripheral tissues, seen with pravastatin. BMY-21950 and its lactone form BMY-22089, new synthetic inhibitors of HMG-CoA reductase, were compared with the major reference agent lovastatin and with the synthetic inhibitor fluindostatin in several in vitro and in vivo models of potency and tissue selectivity. The kinetic mechanism and the potency of BMY-21950 as a competitive inhibitor of isolated HMG-CoA reductase were comparable to the reference agents. The inhibitory potency (cholesterol synthesis assayed by 3H2O or [14C]acetate incorporation) of BMY-21950 in rat hepatocytes (IC50 = 21 nM) and dog liver slices (IC50 = 23 nM) equalled or exceeded the potencies of the reference agents. Hepatic cholesterol synthesis in vivo in rats was effectively inhibited by BMY-21950 and its lactone form BMY-22089 (ED50 = 0.1 mg/kg p.o.), but oral doses (20 mg/kg) that suppressed liver synthesis by 83-95% inhibited sterol synthesis by only 17-24% in the ileum. In contrast, equivalent doses of lovastatin markedly inhibited cholesterol synthesis in both organs. In tissue slices from rat ileum, cell dispersions from testes, adrenal, and spleen, and in bovine ocular lens epithelial cells, BMY-21950 inhibited sterol synthesis weakly in vitro with IC50 values 76- and 188-times higher than in hepatocytes; similar effects were seen for BMY-22089. However, the IC50 ratios (tissue/hepatocyte) for lovastatin and fluindostatin were near unity in these models. Thus, BMY-21950 and BMY-22089 are the first potent synthetic HMG-CoA reductase inhibitors that possess a very high degree of liver selectivity based upon differential inhibition sensitivities in tissues. This cellular uptake-based property of hepatic specificity of BMY-21950 and BMY-22089, also manifest in pravastatin, is biochemically distinct from the pharmacodynamic-based disposition of lovastatin, which along with fluindostatin exhibited potent inhibition in all tissues that were exposed to it.