Relaxation effect of a novel Danshensu/tetramethylpyrazine derivative on rat mesenteric arteries

Abstract

Danshen (Radix Salviae miltiorrhizae) and ChuanXiong (Ligusticum wallichii) are two traditional herbal medicines commonly used in China for the treatment of cardiovascular diseases. The active components in Danshen and ChuanXiong are Danshensu (DSS, (R)-3, 4-dihydroxyphenyllactic acid) and tetramethylpyrazine (TMP), respectively. In the present study, a new compound named ADTM, which is a conjugation of DSS and TMP, was synthesized and its effect on the contractility of rat mesenteric arteries was examined. The relaxation effect of ADTM on rat mesenteric arteries was studied using myography. The effects of ADTM on Ca²⁺ channels were measured by Ca²⁺ imaging and patch-clamp techniques. The results showed that ADTM caused a concentration-dependent relaxation of rat mesenteric arteries. This relaxation effect was not affected by the removal of endothelium or inhibitors of nitric oxide synthase, cyclooxygenase, guanylyl cyclase and adenylyl cyclase. Potassium channel blockers including tetraethylammonium, iberiotoxin, apamin, 4-aminopyridine, BaCl₂ and glibenclamide also failed to inhibit the relaxation response to ADTM. ADTM inhibited CaCl₂-induced contractions and reduced the Ca²⁺ influx in isolated mesenteric arterial muscle cells. Our results suggest that ADTM may be a novel relaxing agent. Its mechanism of action involves the direct blockade of voltage-gated Ca²⁺ channels in vascular smooth muscle cells, resulting in a decrease in Ca²⁺ influx into the cells.

Introduction

Danshen (root of Salvia miltiorrhiza) is a traditional herbal medicine commonly used in China. According to the theory of Chinese Medicine, Danshen can promote blood circulation and relieve hematological disorders (Qiao et al., 2011). It has been used clinically in the treatment of cardiovascular diseases such as myocardial infarction, stroke, coronary heart disease and hyperlipidemia in the Chinese population (Lam et al., 2007, Zhou et al., 2005). Danshensu [3-(3,4-dihydroxyphenyl)-2-hydroxy-propanoic acid; DSS] is the major biologically active and water soluble component in Danshen. In vitro and in vivo experiments have demonstrated that DSS has antioxidant, antiatherosclerotic and endothelial cell protective effects (Hung et al., 2010, Qiao et al., 2011, Tang et al., 2011, Yang et al., 2010, Zeng et al., 2012).

Chuan Xiong (Ligustium wallichii Franch), another traditional Chinese medicine, is also commonly used for the treatment of cardiovascular and cerebrovascular diseases such as ischemia and stroke (Chun-sheng et al., 1978, Guo et al., 1983, Wu et al., 1999). The active ingredient in Chuan Xiong is tetramethylpyrazine (TMP), which has been shown to produce an antithrombotic effect, induce vasodilation, reduce endotoxic shock and protect the brain against ischemic injury in both in vivo and in vitro models (Kao et al., 2006, Liu and Sylvester, 1990, Rhyu et al., 2004, Zeng et al., 1998).

The combined use of Danshen and Chuan Xiong can lower the incidence of myocardial damage and is effective in patients with angina pectoris and ischemic heart failure (Jia et al., 2013, Wang et al., 2011). The therapeutic effects of Danshen and Chuan Xiong are synergistic. Recently a compound known as ADTM was synthesized by coupling DSS to the carboxyl position of TMP and three hydroxyl groups in DSS were acetylated (Fig. 1). The biological effects of ADTM are unclear, however, it is known that it exerts protective effects against tert-butylhydroperoxide-induced injury in the cardiomyoblast cell line H9c2 and myocardial ischemia in rats (Cui et al., 2013). In this study, we determined whether ADTM affected the contractility of rat mesenteric arteries. Its mechanism of action and the potential therapeutic implications are also discussed.