Michio Suzukawa

Inhibitory effect of tea flavonoids on the ability of cells to oxidize low density lipoprotein

Dietary flavonoid intake has been reported to be inversely related to mortality from coronary heart disease, and the anti-atherosclerotic effect of flavonoids is considered to be due probably to their antioxidant properties. Oxidation of low density lipoprotein (LDL) has been reported to be induced by the constituent cells of the arterial wall. Accordingly, we examined the effect of pretreatment with tea flavonoids, such as theaflavin digallate, on the ability of cells to oxidize LDL. Theaflavin digallate pretreatment of macrophages or endothelial cells reduced cell-mediated LDL oxidation in a concentration- (0-400 microM) and time- (0-4 hr) dependent manner. This inhibitory effect of flavonoids on cell-mediated LDL oxidation was in the order of theaflavin digallate > theaflavin > or = epigallocatechin gallate > epigallocatechin > gallic acid. Further, we investigated the mechanisms by which flavonoids inhibited cell-mediated LDL oxidation using macrophages and theaflavin digallate. Theaflavin digallate pretreatment decreased superoxide production of macrophages and chelated iron ions significantly. These results suggest that tea flavonoids attenuate the ability of the cell to oxidize LDL, probably by reducing superoxide production in cells and chelating iron ions.

Effect of in-vivo supplementation with low-dose vitamin E on susceptibility of low-density lipoprotein and high-density lipoprotein to oxidative modification.

OBJECTIVES We have examined the effects of in-vivo supplementation with low-dose vitamin E on the susceptibility of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) to oxidative modification, and compared the oxidizability of HDL with that of LDL. METHODS Normal humans (n = 8) ingested vitamin E (150 mg/day for 1 week, followed by 300 mg/day for 3 weeks) in divided doses with meals. The subjects did not use any medications or vitamins before being enrolled in this study. Fasting blood samples were drawn before and at the end of supplementation. LDL and HDL were separated by sequential ultracentrifugation and susceptability to copper-mediated oxidation was measured. RESULTS After vitamin E supplementation, vitamin E content of LDL increased 1.9-fold and that of HDL increased 1.8-fold. Lag time before initiation of LDL oxidation lengthened significantly (+20%, p < 0.01), and the propagation rate of LDL decreased significantly (-10%, p < 0.05). The lag time of HDL oxidation did not change significantly, but the propagation rate of HDL oxidation decreased significantly (-24%, p < 0.001). The lag time of HDL oxidation was shorter than that of LDL. HDL contained the same or higher concentrations of vitamin E relative to lipid mass as LDL, but contained lower concentration of CoQ10 relative to lipid mass and fewer molecules of vitamin E and beta-carotene per particle than LDL. CONCLUSIONS We conclude that in-vivo supplementation of low-dose vitamin E protects LDL against oxidative modification and decreases the propagation rate of HDL oxidation significantly. We suggest that supplementation with low-dose vitamin E would be beneficial for ameliorating atherosclerosis.

Endothelium-dependent flow-mediated vasodilation in the postprandial state in type 2 diabetes mellitus

This study examined the effects of fat- plus sucrose-rich meals on endothelium-dependent flow-mediated vasodilation in diabetic patients. Flow-mediated vasodilation in the postprandial state decreased significantly, and the decrease correlated inversely with the magnitude of postprandial hyperglycemia, suggesting that endothelial function in diabetic patients becomes impaired postprandially.

Beneficial effect of gemfibrozil on the chemical composition and oxidative susceptibility of low density lipoprotein: a randomized, double-blind, placebo-controlled study

Previous reports have shown that administration of fibrates can reduce coronary events and also improve plasma lipid levels. Oxidative modification of low density lipoprotein has been implicated in the pathogenesis of atherosclerosis, and the resistance of low density lipoprotein (LDL) to in vitro oxidation has been found to be correlated with the extent of atherosclerosis. We performed a double-blind, placebo-controlled intervention trial to establish whether gemfibrozil could improve resistance of LDL to oxidation in patients with hyperlipidemia. Patients were randomly assigned to treatment with gemfibrozil (450 mg, twice a day, n = 10) or placebo (n = 9) for 8 weeks. Blood samples were obtained after an overnight (12 h) fast. Gemfibrozil administration significantly reduced total plasma cholesterol and triglyceride levels and changed the LDL from small, dense particles (pattern B, < or = 25.5 nm) to larger, more buoyant particles (pattern A, > 25.5 nm). Gemfibrozil significantly increased the lag time of LDL oxidation in vitro by 18.2% from 45.5 +/- 8.0 min at week 0 to 53.4 +/- 11.4 min at week 8, but did not change LDL vitamin E and beta-carotene concentrations. Surprisingly, gemfibrozil significantly decreased LDL lipid peroxides by -33.1% and increased the LDL vitamin E/lipid peroxide ratio by 67.6% from 1.3 +/- 0.5 at week 0 to 2.1 +/- 0.9 at week 8. These results demonstrate that gemfibrozil treatment can render LDL less susceptible to oxidative modification while reducing plasma cholesterol and triglyceride and improving LDL subclass pattern. This antioxidative effect of gemfibrozil on LDL may be one of the factors which could delay the progression of atherosclerosis.

Beneficial Effects of Alcohol Withdrawal on LDL Particle Size Distribution and Oxidative Susceptibility in Subjects With Alcohol-Induced Hypertriglyceridemia

LDL subclass pattern B, reported to have a higher prevalence in hypertriglyceridemics (HTGs), is considered to be associated with an increased risk for coronary artery disease, and the small dense LDL characteristic of this pattern is susceptible to oxidative modification. Alcohol is considered one of the most frequent causes of increases in plasma triglyceride (TG) levels. We investigated the effects of alcohol withdrawal on LDL subclass distribution and oxidizability in drinkers with different plasma TG levels. Thirty-seven male subjects with relatively heavy alcohol-consumption habits were divided into four groups; normotriglyceridemic (NTG)/withdrawal (n = 11), NTG/control (n = 8), hypertriglyceridemic (HTG)/withdrawal (n = 10), and HTG/control (n = 8). Both withdrawal groups abstained form alcohol for 4 weeks, while the control subjects maintained their usual intake of alcohol. Peak LDL particle diameter (PPD) was smaller in the combined HTG groups than in the combined NTG groups before abstinence, although PPD increased significantly (P < .01) from 25.5 to 26.1 nm in the HTG/withdrawal group. Before abstinence, lag times preceding LDL oxidation in the combined HTG groups were shorter than in the combined NTG groups; after withdrawal, lag time was prolonged significantly (P < .01) from 49.9 to 57.3 minutes in the HTG-withdrawal group. No significant changes in PPD and lag time were observed in the other three groups. Significant correlations (P < .05) were observed between the change (delta) in the lag time and delta TG and between delta lag time and delta PPD. We conclude that in alcohol-induced HTG subjects, alcohol withdrawal has beneficial effects on the LDL profile by shifting the particle size from smaller to larger and decreasing its susceptibility to oxidation.

Effects of alcohol consumption on antioxidant content and susceptibility of low-density lipoprotein to oxidative modification.

OBJECTIVE The effects of moderate alcohol intake on antioxidant content of low-density lipoprotein (LDL) and the susceptibility of LDL to oxidative modification were examined in 12 healthy adult males. DESIGN Volunteers abstained from alcohol for 3 weeks and then 12 subjects (alcohol intake group) consumed alcohol (0.5 g/kg/day) as brandy for 4 weeks; 4 subjects (control abstinence group) did not consume any alcohol for the entire study. RESULTS In the alcohol intake group, plasma total cholesterol (TC), triglyceride (TG), phospholipids (PL), free cholesterol (FC) and apoprotein B (apoB) levels in LDL decreased significantly after alcohol intake; however, since TC/apoB, TG/apoB, PL/apoB and FC/apoB ratios did not change significantly, it is clear that LDL particle numbers decreased. Vitamin E and vitamin A levels in plasma, and vitamin E content of LDL also did not change significantly. Beta-carotene levels in plasma and in LDL decreased significantly in the alcohol intake group. In the abstinence group, lipid levels and vitamin levels did not change. Lag time before the onset of LDL oxidation and propagation rate of LDL oxidation in the alcohol intake group did not change significantly. CONCLUSIONS Moderate alcohol intake decreases particle numbers of LDL without any changes in chemical composition, vitamin E content and susceptibility of LDL to oxidative modification. However, beta-carotene content was decreased significantly by even moderate alcohol intake.

Vitamin E reduces cholesterol esterification and uptake of acetylated low density lipoprotein in macrophages

The effects of vitamin E on cholesteryl ester (CE) metabolism in 1774 cells were examined. Pretreatment of 1774 cells with vitamin E at concentrations above 50 μM significantly decreased acetylated low density lipoprotein (LDL)-induced incorporation of [14C]oleate into CF in cells in a dose-dependent manner. This was partly due to vitamin E Also significantly inhibiting the uptake of [3H]CE-labeled acetylated LDL by 1774 cells. A trend existed toward suppression of acyl-CoA:cholesterol acyltransferase (ACAT) activity in the cell lysate at high vitamin E concentration, but there was no effect on hydrolysis of CE. These data indicate that vitamin E reduces the uptake of modified LDL and suppresses ACAT activity, resulting in less cholesterol esterification in macrophages; a novel mechanism underlying the antiatherogenic properties of vitamin E.

Effect of low-dose simvastatin on cholesterol levels, oxidative susceptibility, and antioxidant levels of low-density lipoproteins in patients with hypercholesterolemia : a pilot study

In this pilot study, 12 patients (6 men, 6 postmenopausal women) with hypercholesterolemia were treated with low-dose (5 mg/d) simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, for 4 weeks. Low-density lipoprotein (LDL) samples were isolated at the beginning (week 0) and at the end (week 4) of the treatment regimen. Simvastatin caused significant decreases of total cholesterol (-18.1%), LDL cholesterol (-27.6%), and apolipoprotein B (-21.8%), and significantly reduced total cholesterol, free cholesterol, cholesterol esters, phospholipids, and protein in LDL without significantly changing the component ratios and fatty acid levels of LDL. However, simvastatin therapy had no major effects on either antioxidant levels in LDL or the oxidative susceptibility of LDL. We conclude that low-dose simvastatin significantly reduces LDL cholesterol levels without increasing the oxidative susceptibility of LDL or decreasing the antioxidant levels of LDL, and thus may reduce the risk of coronary artery disease.

Effects of beta-blockers on HMG CoA reductase and LDL receptor activity in cultured human skin fibroblasts

SummaryPrevious reports, based on clinical trials and animal experiments, suggest that beta-blockers may be useful in the prevention of atherosclerosis. Betaxolol, a new beta1-selective blocker, was shown to decrease plasma total and LDL cholesterol levels or to have no adverse effect on those [1–4]. While many reports deal with the metabolism of triglyceride and high density lipoprotein, fewer publications about cholesterol metabolism are currently available. To clarify the mechanism by which beta-blockers affect lipid metabolism, we examined the effects of beta-blockers on HMG CoA reductase and LDL receptor activity in cultured human skin fibroblasts. L-propranolol, a nonselective betablocker, increased HMG CoA reductase activity and decreased LDL receptor activity. However, d-propranolol had no major effects on HMG CoA reductase activity. These results suggest that beta-blockers act on HMG CoA reductase through the beta receptors. Beta1-blocking action should decrease HMG CoA reductase activity and increase LDL receptor activity. In fact, betaxolol, a beta1-selective blocker, decreased HMG CoA reductase activity and increased LDL receptor activity, but metoprolol had no major effect. We speculate that the discrepancy between betaxolol and metoprolol in the effect on HMG CoA reductase and the LDL receptor might be due to the difference of the extent of beta1-selectivity. We conclude that beta1-selective blockers are antihypertensive agents potentially valuable in the prevention of atherosclerosis.

Effects of ketanserin tartrate on 3-hydroxy, 3-methylglutaryl coenzyme a reductase activity in cultured human skin fibroblasts

SummaryKetanserin tartrate (ketanserin) is a new antihypertensive drug that is a selective 5HT2 serotonergic receptor antagonist and at high concentrations antagonizes the alpha1-adrenergic receptor. Several reports have indicated that ketanserin clinically decreases plasma low density lipoprotein (LDL) cholesterol. In order to clarify the mechanisms of this LDL cholesterol reduction by ketanserin, we investigated the effects of ketanserin on 3-hydroxy, 3-methylglutaryl coenzyme A(HMG CoA) reductase activity to cultured human skin fibroblasts. We also studied the effects of ritanserin (a 5HT2 serotonergic receptor antagonist) and prazosin HCl (an alpha1-adrenergic receptor antagonist) on HMG CoA reductase activity in cultured human skin fibroblasts. Human skin fibroblasts were cultured in Dulbeccos modified Eagles (DME) medium containing 10% fetal calf serum. Before the cells reached confluence, the medium was changed to DME containing 10% lipoprotein-deficient serum. After incubation for 48–72 hours, the drugs under investigation were added to the medium. The cells were incubated for 14 hours and harvested after washing with phosphate buffered saline. In our study, ketanserin decreased HMG CoA reductase activity in a dose-dependent manner up to 300 ng/ml (550 nM). Prazosin also decreased HMG CoA reductase activity in a dose-dependent manner up to 40 ng/ml (95 nM); ritanserin decreased HMG CoA reductase activity at concentrations of 100 nM and 200 nM. These findings suggest that the combination of alpha1-adrenergic receptor and 5HT2 serotenergic receptor antagonist effects of ketanserin inhibits HMG CoA reductase activity and that this suppression is probably one of the mechanisms for the plasma LDL cholesterol reduction resulting from ketanserin treatment.