Toshitsugu Ishikawa

Hypocholesterolemic effect of sesame lignan in humans

Dear Editors, Sesame, derived from Savanna areas in Africa, has been used and widely distributed as an important food all over the world. However, there are no reports concerning the physiological functions of sesame. Recently, it has been reported that sesamin, one kind of lignan in sesame seed, exhibits several physiological actions in animals [ l31. However, there are no clinical results on the effects of sesamin. In this study, the effect of sesamin on serum lipids was investigated in humans. Twelve male patients with hypercholesterolemia (8 Type IIa, 4 Type IIb) were randomly divided into two groups (one was the placebo group and the other was the sesamin-treated group). Experimental protocol was approved by the Institutional Review Board. The placebo group received capsules, each containing 180 mg wheat germ oil, with 18 mg vitamin E. The sesamin-treated group received capsules, each containing 3.6 mg sesamin and 18 mg vitamin E in 180 mg wheat germ oil. After a preobservation period of 4 weeks, each patient received 9 capsules per day (3 capsules x 3 times per day) for another 4 weeks, followed by 18 capsules per day (6 capsules x 3 times per day) for 4 weeks. They were instructed not to change their diet, any habits or alcoholic intake throughout the whole of the experimental period. Fasting blood samples were drawn before (0 weeks), 4 weeks and 8 weeks after administration of placebo or sesamin capsules. Serum total cholesterol (TC), triglyceride (TG), HDL-cholesterol (HDL-C), apoproteins and lipoproteins were determined using the enzymatic method, the polyanion precipitation method, immuno-nephelometry and the electrophoresis method respectively. LDL-cholesterol (LDL-C) was calculated by using Friedewald’s formula [4]. Statistical analyses were based on the Wilcoxon test and the Mann-Whitney U-test.

Delayed catabolism of high density lipoprotein apolipoproteins A-I and A-II in human cholesteryl ester transfer protein deficiency.

Deficiency of the cholesteryl ester transfer protein (CETP) in humans is characterized by markedly elevated plasma concentrations of HDL cholesterol and apoA-I. To assess the metabolism of HDL apolipoproteins in CETP deficiency, in vivo apolipoprotein kinetic studies were performed using endogenous and exogenous labeling techniques in two unrelated homozygotes with CETP deficiency, one heterozygote, and four control subjects. All study subjects were administered 13C6-labeled phenylalanine by primed constant infusion for up to 16 h. The fractional synthetic rates (FSRs) of apoA-I in two homozygotes with CETP deficiency (0.135, 0.134/d) were found to be significantly lower than those in controls (0.196 +/- 0.041/d, P < 0.01). Delayed apoA-I catabolism was confirmed by an exogenous radiotracer study in one CETP-deficient homozygote, in whom the fractional catabolic rate of 125I-apoA-I was 0.139/d (normal 0.216 +/- 0.018/d). The FSRs of apoA-II were also significantly lower in the homozygous CETP-deficient subjects (0.104, 0.112/d) than in the controls (0.170 +/- 0.023/d, P < 0.01). The production rates of apoA-I and apoA-II were normal in both homozygous CETP-deficient subjects. The turnover of apoA-I and apoA-II was substantially slower in both HDL2 and HDL3 in the CETP-deficient homozygotes than in controls. The kinetics of apoA-I and apoA-II in the CETP-deficient heterozygote were not different from those in controls. These data establish that homozygous CETP deficiency causes markedly delayed catabolism of apoA-I and apoA-II without affecting the production rates of these apolipoproteins.

Formation of N ε-(Hexanonyl)lysine in Protein Exposed to Lipid Hydroperoxide A PLAUSIBLE MARKER FOR LIPID HYDROPEROXIDE-DERIVED PROTEIN MODIFICATION

The objectives of this study were to estimate the structure of the lipid hydroperoxide-modified lysine residue and to prove the presence of the adducts in vivo. The reaction of lipid hydroperoxide toward the lysine moiety was investigated employingN-benzoyl-glycyl-l-lysine (Bz-Gly-Lys) as a model compound of Lys residues in protein and 13-hydroperoxyoctadecadienoic acid (13-HPODE) as a model of the lipid hydroperoxides. One of the products, compound X, was isolated from the reaction mixture of 13-HPODE and Bz-Gly-Lys and was then identified as N-benzoyl-glycyl-N ε-(hexanonyl)lysine. To prove the formation of N ε-(hexanonyl)lysine, named HEL, in protein exposed to the lipid hydroperoxide, the antibody to the synthetic hexanonyl protein was prepared and then characterized in detail. Using the anti-HEL antibody, the presence of HEL in the lipid hydroperoxide-modified proteins and oxidized LDL was confirmed. Furthermore, the positive staining by anti-HEL antibody was observed in human atherosclerotic lesions using an immunohistochemical technique. The amide-type adduct may be a useful marker for the lipid hydroperoxide-derived modification of biomolecules.

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.

Turnover of apoproteins A-I and A-II of high density lipoprotein and the relationship to other lipoproteins in normal and hyperlipidemic individuals.

The kinetics of the major apoproteins of high density lipoproteins (HDL), A-I(apoA-I) and A-II(apoA-II), were studied from the specific activity-time curves of these apoproteins, after reinjection of radioiodine-labeled HDL. In all 20 subjects, HDL apoprotein kinetics conformed to a two-pool model. The total fractional removal rates for the two apoproteins were similar, although the irreversible fractional removal rate appeared to be slightly greater for apoA-I. The mean transport for A-I and A-II was 12.2 mg/kg/day and 5.0 mg/kg/day, respectively. The mass of the apoprotein pools was strongly correlated with apoprotein production rate and also, to a lesser degree and inversely, with the irreversible fractional catabolic rate. Transport was directly correlated with body weight. Higher fractional catabolic rates, including the transfer rates between the two pools, were observed in five hypertriglyceridemic subjects; in contrast, five subjects with familial hypercholesterolemia tended to show lower fractional catabolic rates. These findings were supported by (1) a strongly positive correlation between the transport rates of HDL A-I and of very low density lipoprotein (VLDL) apoB, determined simultaneously in 10 subjects; and (2) a significant inverse correlation between the irreversible fractional removal rate of HDLA-I and the concentration of low density lipoprotein (LDL) apoB, measured in 15 subjects. These observations underline the metabolic interrelationships of the major lipoprotein classes. Two subjects with familial hyperalphalipoproteinemia showed enlarged pool sizes, but normal transport, with irreversible fractional removal rates that were in the lower range for the group of 20 subjects.

Increased catabolic rate of low density lipoproteins in humans with cholesteryl ester transfer protein deficiency.

The cholesteryl ester transfer protein (CETP) transfers lipids among lipoprotein particles and plays a central role in lipoprotein metabolism. Humans with genetic deficiency of CETP have both elevated HDL cholesterol and apolipoprotein A-I concentrations as well as decreased LDL cholesterol and apolipoprotein B levels. The present study was undertaken to elucidate the metabolic basis for the decreased LDL cholesterol and apo B levels in CETP deficiency. We conducted a series of in vivo apo B kinetic studies in tow unrelated homozygotes with CETP deficiency and in control subjects. A primed constant infusion of stable isotopically labeled phenylalanine was administered to the two CETP deficient subjects and control subjects and apo B kinetic parameters in VLDL, intermediate density lipoproteins, and LDL were obtained by using a multicompartmental model. The fractional catabolic rates (FCR) of LDL apo B were significantly increased in the CETP-deficient subjects (0.56 and 0.75/d) compared with the controls (mean FCR of 0.39/d). Furthermore, the production rates of apo B in VLDL and intermediate density lipoprotein were decreased by 55% and 81%, respectively, in CETP deficiency compared with the controls. In conclusion, CETP-deficient subjects were demonstrated to have substantially increased catabolic rates of LDL apo B as the primary metabolic basis for the low plasma levels of LDL apo B. This result indicates that the LDL receptor pathway may be up-regulated in CETP deficiency.

Effects of alcohol on lipoprotein lipase, hepatic lipase, cholesteryl ester transfer protein, and lecithin:cholesterol acyltransferase in high-density lipoprotein cholesterol elevation

The mechanism whereby alcohol increases high-density lipoprotein cholesterol (HDL-C) levels is unclear. Lipoprotein lipase (LPL), hepatic lipase (HL), cholesteryl ester transfer protein (CETP) and lecithin:cholesterol acyltransferase (LCAT) act on lipoprotein metabolism. The purpose of the present study is to determine which one or what combination of these factors is responsible for the rise in HDL-C levels following alcohol ingestion. After 3 weeks of abstinence, 12 men consumed 0.5 g/kg bw of alcohol per day for 4 weeks; 13 abstaining men served as controls. Mean plasma total cholesterol (TC) levels were unchanged in either group throughout the study. Among the alcohol consumers, plasma triglycerides (TG), HDL-C, apolipoprotein (apo) A-I and A-II levels increased significantly after 3 weeks of alcohol loading but were unchanged in the control group. High-density lipoprotein3 cholesterol (HDL3-C) levels increased significantly in the alcohol consumers after 4 weeks of alcohol loading whereas high-density lipoprotein2 cholesterol (HDL2-C) levels were unaffected. In the controls, neither HDL2-C nor HDL3-C changed significantly. Post-heparin plasma (PHP) LPL activity and mass increased significantly (P < 0.01) after the alcohol ingestion (controls remained unchanged) without changing LPL specific activity. HL, CETP and LCAT activities were unaffected in both groups. We conclude that of the factors considered, LPL contributed the most to the alcohol-induced rise in HDL-C.

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.

Effects of gammalinolenic acid on plasma lipoproteins and apolipoproteins

Nineteen hypercholesterolemic patients (10 without and 9 with hypertriglyceridemia) were given evening primrose oil rich in gammalinolenic acid (GLA, 18: 3n - 6), in a placebo controlled cross-over design, over 16 weeks (8 + 8 weeks), with safflower oil as the placebo. During supplementation with evening primrose oil, dihomogammalinolenic acid (20: 3n - 6) increased in plasma lipids and red blood cells, and in subjects without hypertriglyceridemia there was a significant decrease in low density lipoprotein-cholesterol and plasma apolipoprotein B compared with the levels observed during safflower oil administration. Our results confirmed that evening primrose oil is effective in lowering low density lipoprotein in hypercholesterolemic patients.