S. Balasubramaniam

On the effects of dietary n-3 fatty acids (Maxepa) on plasma lipids and lipoproteins in patients with hyperlipidaemia

An encapsulated preparation of fish oil (Maxepa) was administered to hyperlipidaemic patients in order to establish the responsiveness of the common lipid phenotypes to dietary supplementation with n-3 fatty acids. 13 patients took 6 g/day of fish oil and 12 patients took 16 g/day in a randomized, double-blind crossover study, whereby each subject took fish oil for 3 months and matching placebo for 3 months. The study was conducted against a background diet restricted in saturated fat and cholesterol. In Types IIa and IIb hyperlipoproteinaemia there was no substantial fall in plasma cholesterol concentration. Plasma triglyceride concentrations were reduced significantly in Types IIb and IV (28% and 41% respective reductions). In a separate study using 16 g/day of fish oil in patients with Type V hyperlipoproteinaemia, plasma triglycerides were reduced by 58% and plasma cholesterol concentration by 34%. The change in plasma triglyceride concentration was significantly correlated with the basal triglyceride level (r = -0.94), and was dose-related (33% fall on 6 g/day and 58% fall on 16 g/day). The fall in plasma triglyceride concentration was accompanied by a significant reduction in the concentration of very low-density lipoprotein cholesterol (-42%), a significant rise in low density lipoprotein cholesterol (+7%), and a significant rise in high-density lipoprotein cholesterol concentration (+6%), there being no significant change in the ratio of low density to high density lipoprotein cholesterol. There were changes in the fatty acid composition of plasma and platelet lipids which reflected dietary supplementation with n-3 fatty acids, notably an increase in the proportion of eicosapentaenoic and docosahexaenoic acids which occurred in a dose-dependent fashion. Despite these changes there was no significant variation in the bleeding time, platelet count or blood viscosity during the treatment.

On the effect of garlic on plasma lipids and lipoproteins in mild hypercholesterolaemia

The ingestion of garlic has been reported to have many cardiovascular effects, including a reduction in plasma cholesterol concentration and the susceptibility of LDL to oxidation. A double-blind, placebo-controlled, randomised crossover study was conducted in subjects with mild to moderate hypercholesterolaemia who were subject to strict dietary supervision and assessment. After a baseline dietary period of 28 days, subjects took Kwai garlic powder tablets 300 mg three times daily or matching placebo for 12 weeks, followed by 28 days washout, followed by a 12 weeks crossover on the alternative preparation. In the analysis hypercholesterolaemia was defined as those subjects in the range 5.5-8.05 mmol/l. Three subjects were withdrawn, one allocated to garlic and complaining of garlic body odour, one using placebo having intercurrent health problems, and one with a baseline cholesterol below 5.5 mmol/l, yielding analysable results in 28 subjects. Comparing the period on garlic with that on placebo, there were no significant differences in plasma cholesterol, LDL cholesterol, HDL cholesterol, plasma triglycerides, lipoprotein(a) concentrations, or blood pressure. Mean LDL cholesterol concentration was 4.64 +/- 0.52 mmol/l on garlic and 4.60 +/- 0.59 mmol/l on placebo. There was no demonstrable effect of garlic on oxidisability of LDL, on the ratio of plasma lathosterol/cholesterol (a measure of cholesterol synthesis), nor on LDL receptor expression in lymphocytes. This study found no demonstrable effect of garlic ingestion on lipids and lipoproteins.

The low-density lipoprotein receptor and cholesterol synthesis are affected differently by dietary cholesterol in the rat

In the hamster and the rabbit, the low-density lipoprotein (LDL) receptor and cholesterol synthesis are coordinately downregulated by dietary cholesterol. In the rat, cholesterol synthesis is downregulated but LDL kinetic studies suggest that the LDL receptor is not. The aim of this study was to determine the effect of dietary cholesterol on the expression of the hepatic LDL receptor in the rat. Young (2 months) hooded and albino Wistar rats and older (9 months) Sprague-Dawley rats were used because of their reported different propensities to develop hypercholesterolaemia when fed cholesterol. Hepatic LDL receptor activity was measured using a dot blot assay with LDL-gold and LDL receptor mass was measured using an electroblot assay with a polyclonal antibody. Dietary cholesterol had no effect on the plasma cholesterol concentration in both strains of young Wistar rats but increased it in the older Sprague-Dawley rats. Cholesterol synthesis as measured with 3H2O or as indicated by 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity or the ratio of plasma lathosterol to cholesterol was effectively downregulated by dietary cholesterol (1% w/w) in all three strains. In contrast, dietary cholesterol increased both hepatic LDL receptor activity and mass in the young Wistar rats and had no effect on either receptor activity or mass in the older Sprague-Dawley rats. Increases in receptor activity occurred despite increases in hepatic cholesterol especially when cholic acid was added to the cholesterol diet. The effect was systemic because CL 277082, an inhibitor of intestinal cholesterol absorption, prevented the increase in LDL receptor activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term treatment of hypercholesterolaemia with a new palatable formulation of guar gum.

Nineteen patients with primary hypercholesterolaemia previously stabilized on diet alone were treated with a new formulation of guar gum (6g t.d.s. with meals) in a placebo-controlled, single-blind study. Seventeen patients completed 3 months treatment without serious side effects, while 2 patients withdrew immediately because of severe diarrhoea. Thirteen patients have completed 12 months treatment with guar gum. There have been no significant changes in safety parameters. Plasma cholesterol was reduced by a significant 15% during the first 3 months of treatment (7.9 +/- 0.8 vs 6.7 +/- 1.0 mmol/l, P less than 0.001) and this effect has been sustained for 12 months. The fall in plasma cholesterol was associated with a significant 20% fall in LDL cholesterol, but with no change in HDL cholesterol. Plasma triglycerides did not change significantly. Percentage cholesterol absorption was reduced by guar gum in 4/5 normal subjects examined.

Metabolic studies with probucol in hypercholesterolaemia

Probucol (1 g/day) was administered for 6 months to 16 hypercholesterolaemic patients previously stabilized on diet alone. Total plasma cholesterol fell by 16%, LDL cholesterol by 14% and HDL cholesterol by 41%. The ratio of total cholesterol to HDL cholesterol increased by 40%. Total plasma triglycerides showed a slight upward trend. The extent of the fall in HDL cholesterol was directly proportional to the pre-treatment HDL cholesterol concentration. In 2 patients studied, treatment with Probucol produced a sustained increase in the excretion of endogenous faecal steroids, due to increased faecal bile acids. In 3 patients studied, Probucol increased the degree of cholesterol saturation in gall bladder bile. The Lithogenic Index approximated to pathological levels in 1 patient whose bile was previously relatively saturated with cholesterol. Probucol also appeared to cause a modest reduction in the degree of platelet activation in vivo, with reduced platelet prostaglandin synthesis and reduced release of platelet peptides.

On the mechanism by which an ACAT inhibitor (CL 277,082) influences plasma lipoproteins in the rat

CL 277,082 is an inhibitor of acyl-CoA: cholesterol acyltransferase (ACAT). The effects of this drug on lipoprotein metabolism have been examined in cholesterol-fed rats. An optimal dose of drug incorporated into the diet (0.1% w/w) for 7 days reduced plasma cholesterol by 48% and plasma triglycerides by 72%. The decrease in plasma cholesterol was due to a reduction in triglyceride-rich lipoproteins and in HDL cholesterol. There was a significant 72% reduction in intestinal ACAT activity, accompanied by a 41% reduction in hepatic cholesterol content. There was a smaller 21% reduction in hepatic ACAT activity. Hepatic HMG-CoA reductase activity increased 3-fold. HDL binding activity by liver membranes was not altered significantly. The decrease in plasma cholesterol with this ACAT inhibitor is most likely due to decreased absorption of dietary cholesterol resulting from inhibition of intestinal ACAT.

Fish oil and oat bran in combination effectively lower plasma cholesterol in the rat

Male rats were fed a semi-purified diet containing oat bran or wheat bran with or without a marine fish oil to investigate the effects of such combinations on lipid metabolism. Oat bran alone and wheat bran plus fish oil gave lower plasma cholesterol concentrations than wheat bran alone while oat bran plus fish oil gave the lowest. Oat bran increased plasma triacylglycerols compared with wheat bran but oat bran plus fish oil gave concentrations similar to those seen with wheat bran plus fish oil. Oat bran gave higher hepatic cholesterol synthesis rates and a higher activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase compared to wheat bran. The addition of fish oil to either bran diet decreased cholesterol synthesis but HMG CoA reductase activity was not reduced. Oat bran increased hepatic acyl coenzyme A:cholesterol acyl transferase (ACAT) activity and increased the ratio of esterified to unesterified cholesterol in hepatic microsomal membranes compared with wheat bran. Fish oil decreased hepatic LDL receptor activity and increased HDL binding activity when added to the wheat bran diet but these effects were not seen with oat bran. Oat bran also had no effect on hepatic lipoprotein receptor activity compared with wheat bran. These results show that fish oil and oat bran have complementary cholesterol lowering effects in the rat.

Coordinate diurnal regulation of hepatic acyl-coenzyme A: cholesterol acyltransferase and cellular levels of esterified cholesterol.

Hepatic ACAT, HMG-CoA reductase and both cellular free and esterified cholesterol were measured at 3 h intervals over a 24 h period in the rat. ACAT exhibited a characteristic low amplitude diurnal rhythm with maximum activity at the mid-light phase that was significantly higher than the minimum activity observed at the mid-dark phase. The cellular esterified cholesterol concentration showed a diurnal rhythm that closely paralleled the rhythm of ACAT activity. The cellular free cholesterol concentration was not significantly altered during the 24 h cycle. In rats fed cholesterol, the diurnal rhythm of ACAT was still maintained despite the increase in ACAT activity during the entire 24 h cycle suggesting that the ACAT rhythm is the result of changes in the level of ACAT protein expression. The results also indicate that the diurnal rhythms of ACAT and HMG-CoA reductase are generated by a process independent of the LDL receptor rhythm. All three rhythms are also independent of changes in the level of free cholesterol in the cell.

Effects of Ro 16-0521 on cholesterol metabolism in the rat.

Ro 16-0521 is a newly synthesized benzodiazepine derivative which is devoid of reactivity with the brain benzodiazepine receptor. The effects of this drug on plasma lipids and lipoproteins and hepatic cholesterol metabolism have been examined in the cholesterol-fed rat. Drug therapy was associated with dose-related falls in plasma cholesterol concentration, liver cholesterol content, and the activity of the liver enzyme Acyl-CoA cholesterol acyltransferase. Drug therapy abolished the lipid and lipoprotein changes induced by cholesterol feeding, including those associated with a diet supplemented with olive oil to facilitate cholesterol loading. Drug therapy was also associated with an increased activity of the enzyme HMG-CoA reductase and reduced hepatic microsomal cholesterol content. It is suggested that the cholesterol-fed rat will be a suitable model for further mechanistic studies.