Hypocholesterolemic and choleretic effects of three dimethoxycinnamic acids in relation to 2,4,5-trimethoxycinnamic acid in rats fed with a high-cholesterol/cholate diet

Abstract

Background

2,4,5-Trimethoxycinnamic acid (2,4,5-TMC) is the major and non-toxic metabolite of α-asarone, which retains hypocholesterolemic and choleretic activities. We compared the activities of 2,4,5-TMC with those of 2,4-dimethoxycinnamic acid (2,4-DMC), 3,4-DMC and 3,5-DMC, to understand the role of the methoxyls on carbons 2, 4 and 5 on the pharmacologic properties of these compounds.

Methods

The methoxycinnamic acids were administered to high-cholesterol/cholate-fed rats. We measured bile flow, and quantified bile acids, phospholipids and cholesterol in bile, and cholesterol and cholesterol-lipoproteins in serum. The inhibition of HMG-CoA reductase by the methoxycinnamic acids was evaluated in vitro.

Results

The four methoxycinnamic acids decreased serum cholesterol, without affecting the concentration of HDL-cholesterol. 2,4,5-TMC produced the highest decrease in LDL-cholesterol, 73.5%, which exceeds the range of statins (20–40%), and produced the highest inhibition of the activity of HMG-CoA reductase. 3,4-DMC produced the highest increase in bile flow, bile acids and phospholipids concentrations, and reduction in bile cholesterol, which led to a decrease in the biliary cholesterol saturation index.

Conclusions

2,4,5-TMC (which has three methoxyls) had the highest hypocholesterolemic activity, while 3,4-DMC, which lacks the methoxyl in carbon 2 but conserves the two other methoxyls in an adjacent position, had the highest choleretic activity and a probable cholelitholytic activity. In methoxycinnamic acids with two methoxyls in non-adjacent positions (2,4-DMC and 3,5-DMC), the hypocholesterolemic and choleretic activities were not as evident. 2,4,5-TMC and 3,4-DMC, which did not cause liver damage during the treatment period, should be further explored as a hypocholesterolemic and choleretic compounds in humans.

Introduction

Yumel (Guatteria gaumeri, Greenman, Annonaciae) is a native plant from Yucatán, Mexico, that has been used as a bark infusion in traditional medicine for the treatment of gallstones [1]. α-asarone (2,4,5-trimethoxy-1-propenylbenzene), the active substance of G. gaumeri, decreases rat and human cholesterol serum levels [2]. α-asarone has hypocholesterolemic [2] and hypolipidemic properties attributed to the inhibition of HMG-CoA reductase [EC 1.1.1.34 (R)-mevalonate:NADP⁺ oxidoreductase (CoA-acylating)] [3], but it cannot be used in clinical trials because of its genotoxic and hepato-carcinogenic properties in rodents [4]. 2,4,5-Trimethoxycinnamic acid (TMC), the major metabolite of α-asarone, does not have the above-mentioned toxicity [4], but it retains the beneficial properties of α-asarone: it decreases total serum cholesterol and serum LDL-cholesterol, but has no effect on serum HDL-cholesterol. α-asarone and 2,4,5-TMC also increase bile flow, bile acids and bile phospholipids, and decrease bile cholesterol and biliary cholesterol saturation index (CSI) in hypercholesterolemic rats [5].

High levels of serum cholesterol and LDL-cholesterol correlate with an increased occurrence of atherosclerosis [6], [7], therefore, it is important to develop efficient therapies for the treatment of hypercholesterolemia. Statins are considered as the most effective drugs for the treatment of hypercholesterolemia; however, they have some adverse effects, such as renal dysfunction, myalgia, arthralgia and cardiac failure [8], [9]. In this study, we evaluated the role of the methoxyls on carbons 2, 4 and 5 of 2,4,5-TMC on its pharmacological properties. We evaluated three 2,4,5-TMC derivatives, which lack one methoxyl and have the other two methoxyls in different positions on their aromatic rings: 2,4-DMC, 3,4-DMC and 3,5-DMC (Fig. 1), in order to find out which DMC retains most of the pharmacological properties of 2,4,5-TMC. DMCs could be used as therapeutic hypocholesterolemic and choleretic agents.