Effect of Fenofibrate on Plasma Lipoprotein Composition and Kinetics in Patients With Complete Hepatic Lipase Deficiency

Rosa rugosa flavonoids exhibited PPARα agonist-like effects on genetic severe hypertriglyceridemia of mice

ETHNOPHARMACOLOGICAL RELEVANCE

Rosa rugosa Thunb. is a traditional Chinese medicine that was used in the treatment of cardiovascular diseases and relative risk factors such as diabetes, hyperlipidemia, hypertension, and inflammation. Rosa rugosa flavonoids (RRFs) are the main components in Rosa rugosa Thunb. Several studies have demonstrated that RRFs can regulate plasma lipid contents, but the related mechanism of which has not yet been elucidated clearly.

AIM OF THE STUDY

The goal of this study was to clarify the effects of RRFs on triglyceride metabolism and its related mechanisms.

MATERIALS AND METHODS

RRFs were obtained by ethanol extraction from Rosa rugosa Thunb.. Transgenic mice expressing human Apolipoprotein C3 (ApoC3) were used as a mouse model of hypertriglyceridemia. Fenofibrate (FNB), a PPARα agonist, was used as a positive control drug of decreasing high triglyceride. FNB (100 mg/kg) or RRFs (300 mg/kg) were given to the mice by gavage daily. Two weeks later, the changes of plasma lipid levels in the mice were measured by commercial kits, the clearance of triglyceride was evaluated by oral fat load test, and expression of the genes related to lipid β-oxidation and synthesis was detected in the mice livers by real time PCR.

RESULTS

RRFs, as well as FNB, were found to significantly reduce plasma triglyceride (TG) levels in ApoC3 transgenic mice after administration of the drug for two weeks. Plasma lipid clearance rate was increased and lipid content in the mice livers was reduced after administration of RRF. Treatment with RRFs up-regulated mRNA expression of PPARα and its downstream gene of ACOX, while down-regulated mRNA expression of the genes related to fatty acid synthesis (FASN, SREBP-1c, and ACC1). The expression of LPL was raised, while the expression of ApoC3 was decreased, and Foxo1 was inhibited by RRFs in the mice livers.

CONCLUSION

RRFs can reduce plasma TG levels by repressing the expression of ApoC3 and inducing the expression of LPL in liver. RRFs could also reduce triglyceride in hepatocytes through increasing β-oxidation and decreasing synthesis of the lipids. These findings show the potency of further clinical application of RRFs as a hypolipidemic drug for treatment of cardiovascular diseases.

Hepatic Lipase: a Comprehensive View of its Role on Plasma Lipid and Lipoprotein Metabolism

Hepatic lipase (HL) is a key enzyme catalyzing the hydrolysis of triglycerides (TG) and phospholipids (PLs) in several lipoproteins. It is generally recognized that HL is involved in the remodeling of remnant, low-density lipoprotein (LDL), high-density lipoprotein (HDL) and the production of small, dense low-density lipoproteins (sd-LDLs).On the other hand, it is unclear whether HL accelerates or retards atherosclerosis. From the clinical point of view, HL deficiency may provide useful information on answering this question, but the rarity of this disease makes it impossible to conduct epidemiological study.In this review, we describe a comprehensive and updated view of the clinical significance of HL on lipid and lipoprotein metabolism.

Peroxisome proliferator-activated receptor (PPAR α/γ) agonists as a potential target to reduce cardiovascular risk in diabetes

The disappointing results of glucose lowering studies have highlighted the ongoing need to develop new therapeutic strategies to reduce cardiovascular risk in patients with type 2 diabetes. The presence of a range of metabolic abnormalities in diabetic patients presents a number of potential targets for therapeutic intervention. While modulation of peroxisome proliferator activated receptors (PPARs) represents an attractive approach, the results of studies of pharmacological agonists have been variable. The findings of these studies and rationale for development of dual PPAR-α/γ agonists will be reviewed.

The effect of PPAR-alpha agonism on apolipoprotein metabolism in humans

Metabolic syndrome, diabetes and obesity are frequently associated with hypertriglyceridemia, hypercholesterolemia and low HDL levels, a phenotype known as atherogenic dyslipidemia. Atherogenic dyslipidemia and hypertriglyceridemia are frequently treated with fibric acid derivatives which activate the nuclear receptor PPAR-alpha leading to reduce plasma triglycerides and an increase in HDL cholesterol levels. The mechanism by which activation of PPAR-alpha with fibrates improves the plasma lipid profile in patients with atherogenic dyslipidemia and hypertriglyceridemia has been examined in several small studies measuring lipoprotein kinetics. The results of these studies indicate that the changes in lipoprotein metabolism observed in response to fibrate treatment vary according to lipoprotein phenotype. In general, fibrates act to reduce VLDL apoB-100 through enhanced fractional catabolism (clearance) of VLDL apoB-100 with additional effects on reducing VLDL apoB-100 production. LDL apoB-100 levels generally decrease in response to fibrates due to increased LDL fractional catabolism except in those patients with high to very high plasma triglyceride levels (>400mg/dL). Fibrates also increase HDL apoA-I and apoA-II levels by enhancing apoA-I and apoA-II production, although this is partially counteracted by increasing fractional catabolism of these apolipoproteins. The potent and specific PPAR-alpha agonist LY518674, reduced VLDL apoB-100 levels through enhanced fractional catabolism similar to what is seen with fibrates. In contrast to fibrates, LY518674 did not change HDL apoA-I levels in response to due to an increased turnover of apoA-I where an increased fractional catabolic rate entirely counteracted the increase in apoA-I production. The changes in apoB metabolism in response to PPAR-alpha activation with fibrates and specific PPAR-alpha agonists would be expected to reduce the risk of cardiovascular disease. However, the benefit of the enhanced turnover of HDL apoA-I in response to PPAR-alpha activation remains to be determined.

Potent and selective PPAR-alpha agonist LY518674 upregulates both ApoA-I production and catabolism in human subjects with the metabolic syndrome

OBJECTIVE

The study of PPAR-alpha activation on apoA-I production in humans has been limited to fibrates, relatively weak PPAR-alpha agonists that may have other molecular effects. We sought to determine the effect of a potent and highly specific PPAR-alpha agonist, LY518674, on apoA-I, apoA-II, and apoB-100 kinetics in humans with metabolic syndrome and low levels of HDL cholesterol (C).

METHODS AND RESULTS

Subjects were randomized to receive LY518674 (100 microg) once daily (n=13) or placebo (n=15) for 8 weeks. Subjects underwent a kinetic study using a deuterated leucine tracer to measure apolipoprotein production and fractional catabolic rates (FCR) at baseline and after treatment. LY518674 significantly reduced VLDL-C (-38%, P=0.002) and triglyceride (-23%, P=0.002) levels whereas LDL-C and HDL-C levels were unchanged. LY518674 significantly reduced VLDL apoB-100 (-12%, P=0.01) levels, attributable to an increased VLDL apoB-100 FCR with no change in VLDL apoB-100 production. IDL and LDL apoB-100 kinetics were unchanged. LY518674 significantly increased the apoA-I production rate by 31% (P<0.0001), but this was accompanied by a 33% increase in the apoA-I FCR (P=0.002), resulting in no change in plasma apoA-I. There was a 71% increase in the apoA-II production rate (P<0.0001) accompanied by a 25% increase in the FCR (P<0.0001), resulting in a significant increase in plasma apoA-II.

CONCLUSIONS

Activation of PPAR-alpha with LY518674 (100 microg) in subjects with metabolic syndrome and low HDL-C increased the VLDL apoB-100 FCR consistent with enhanced lipolysis of plasma triglyceride. Significant increases in the apoA-I and apoA-II production rates were accompanied by increased FCRs resulting in no change in HDL-C levels. These data indicate a major effect of LY518674 on the production and clearance of apoA-I and HDL despite no change in the plasma concentration. The effect of these changes on reverse cholesterol transport remains to be determined.

The clinical significance of the size of low-density-lipoproteins and the modulation of subclasses by fibrates

BACKGROUND

Beyond total low-density-lipoproteins (LDL) levels, increasing evidence suggests that the 'quality' of LDL exerts a great influence on the cardiovascular risk. Several studies have also shown that the therapeutic modulation of LDL size is of benefit in reducing the risk of cardiovascular events. Hypolipidaemic treatment is able to alter LDL subclass distribution but strong variations have been noticed among different agents. Fibrates have a major impact on triglyceride metabolism and in modulating LDL size and subclasses, but variations exist among the different molecules.

METHODOLOGY

A literature search (by Medline and Scopus) was performed using the following headings: 'small dense LDL', 'LDL size', 'LDL subfractions', 'LDL subclasses', 'LDL distribution' and 'fenofibrate', 'bezafibrate', 'ciprofibrate' and 'gemfibrozil' up to 20 January 2007. The authors also manually reviewed the references of selected articles for any pertinent material.

RESULTS

Analysis of all published studies revealed that treatment with fenofibrate, ciprofibrate, bezafibrate and gemfibrozil is usually beneficial, and fenofibrate may be more efficacious than the other molecules. This is supported by using all the available techniques in subjects with a very wide range of lipid alterations.

CONCLUSION

Among the different agents, fenofibrate has been found to be particularly effective in modulating LDL size and subclasses in patients at higher cardiovascular risk, such as those with type 2 diabetes or the metabolic syndrome.