Policosanol modulates HMG-CoA reductase activity in cultured fibroblasts.
ABSTRACT Cholesterol biosynthesis is strictly controlled by 3-hydroxy-3-methylglutaryl Coenzyme A (HMG-CoA) reductase.
Transfer of cultured fibroblasts to a lipid-depleted medium (LDM) up-regulates the enzyme levels. This, in turn, is followed by an accelerated biosynthesis of cholesterol.
Exposure of Vero fibroblasts to LDM and policosanol (0.5-50 microg/mL), a new cholesterol-lowering drug purified from sugarcane (Saccharum officinarum L.) wax, decreased in a dose-dependent manner cholesterol biosynthesis from [14C]-acetate and 3H-water, but not from [14C]-mevalonate.
This suggests an effect on HMG-CoA reductase, the rate-controlling enzyme in cholesterol biosynthesis. When enzyme activity was measured in the presence of various concentrations of policosanol (0.5-50 microg/mL), reductase was not suppressed. Therefore, there was no evidence for a competitive or noncompetitive inhibition of enzyme activity. However, after treatment of intact cells with policosanol (50 microg/mL) in the presence of LDM, a suppressive effect on enzyme activity was observed, suggesting a modulatory effect of policosanol on reductase activity. The previous inhibition of enzyme up-regulation by policosanol suggests to date a depression of de novo synthesis of HMG-CoA reductase and/or stimulation of its degradation. However, the exact mechanism by which policosanol inhibits the activity of HMG-CoA reductase still remains unclear. Further studies are needed to clarify the precise mechanism of its inhibitory action on cholesterol biosynthesis.
- SourceAvailable from: InTechBiochemistry, 03/2012; , ISBN: 978-953-51-0076-8
- The British journal of nutrition 01/2007; 97:381-8. · 3.45 Impact Factor
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ABSTRACT: Hypercholesterolaemia is a risk factor for coronary heart disease (CHD). Clinical studies have shown that lowering elevated serum total cholesterol (TC) levels, and particularly low density lipoprotein-cholesterol (LDL-C) levels, reduces the frequency of coronary morbidity and deaths, whereas high serum levels of high density lipoprotein-cholesterol (HDL-C) protect against CHD. Policosanol is a cholesterol-lowering drug purified from sugar cane wax with a therapeutic dosage range from 5-20 mg/day. Atorvastatin is an HMG-CoA reductase inhibitor which across its dosage range (10-80 mg/day) has shown significantly greater lipid-lowering effects than all previously marketed statins. This study was undertaken to compare the efficacy and tolerability of policosanol with atorvastatin in older patients with type II hypercholesterolaemia. This randomised, single-blind, parallel-group study was conducted in older patients (60-80 years) with type II hypercholesterolaemia. After 4 weeks on a cholesterol-lowering diet, 75 patients were randomised to policosanol or atorvastatin 10mg tablets taken once daily with the evening meal for 8 weeks. An interim and final check-up were performed at 4 and 8 weeks, respectively, after treatment was initiated. At 4 (p < 0.0001) and 8 (p < 0.00001) weeks, policosanol 10 mg/day significantly lowered serum LDL-C levels by 17.5 and 23.1%, respectively compared with baseline; corresponding values for atorvastatin were 28.4 and 29.8%. At study completion, policosanol significantly (p < 0.0001) reduced serum TC (16.4%), LDL-C/HDL-C ratio (25.5%) and TC/HDL-C ratio (19.3%), as well as (p < 0.001) triglyceride levels (15.4%). Atorvastatin significantly (p < 0.0001) decreased serum TC (22.6%), LDL-C/HDL-C (26.2%) and TC/HDL-C (19.8%) ratios, as well as (p < 0.001) triglyceride levels (15.5%). Atorvastatin was significantly more effective than policosanol in reducing LDL-C and TC, but similar in reducing both atherogenic ratios and triglyceride levels. Policosanol, but not atorvastatin, significantly (p < 0.05) increased serum HDL-C levels by 5.3%. Both treatments were well tolerated. At study completion, atorvastatin mildly, but significantly (p < 0.05) increased creatine phosphokinase (CPK) and creatinine, whereas policosanol significantly reduced AST and glucose (p < 0.01) and CPK (p < 0.05) levels. All individual values, however, remained within normal limits. Three atorvastatin but no policosanol patients withdrew from the study because of adverse events: muscle cramps (1 patient), gastritis (1 patient) and uncontrolled hypertension, abdominal pain and myalgia (1 patient). Overall, no policosanol and seven atorvastatin patients (18.9%) reported a total of nine mild or moderate adverse events during the study (p < 0.01). This study shows that policosanol (10 mg/day) administered for 8 weeks was less effective than atorvastatin (10 mg/day) in reducing serum LDL-C and TC levels in older patients with type II hypercholesterolaemia. Policosanol, but not atorvastatin, however, significantly increased serum HDL-C levels, whereas both drugs similarly reduced atherogenic ratios and serum triglycerides. Policosanol was better tolerated than atorvastatin as revealed by patient withdrawal analysis and overall frequency of adverse events. Nevertheless, further studies must be conducted in larger sample sizes and using dose-titration methods to achieve target lipid levels in order to reach wider conclusions.Drugs & Aging 01/2003; 20(2):153-63. · 2.50 Impact Factor