Introduction
Dyslipidaemia is a common metabolic disease that is closely related to the occurrence and development of atherosclerotic cardiovascular disease (ASCVD) [
1]. Elevated low-density lipoprotein cholesterol (LDL-C) levels are considered to be independent risk factors for cardiovascular events. Statins can effectively reduce LDL-C and reduce the incidence of cardiovascular events, and they have become the cornerstone of ASCVD prevention and treatment. However, although the comprehensive control of traditional cardiovascular risk factors has been effective, after standard treatments guided by current clinical evidence, including the treatment of traditional risk factors such as smoking, unhealthy lifestyles, hypercholesterolaemia, hypertension, hyperglycaemia and obesity, patients are still at risk of major vascular and microvascular events; that is, the residual cardiovascular risk remains [
2]. Hypertriglyceridaemia (HTG), the most common type of dyslipidaemia in China, is worthy of attention for its correlation with residual cardiovascular risk [
3]. Studies have shown that patients with high TG levels (2.26–5.64 mmol/L) have higher residual cardiovascular risk, worse cardiovascular outcomes and higher overall medical costs after treatment with statins [
4,
5], for every 1 mmol/L increase in TG, the risk of ASCVD increased by 13% [
6]. Thus, Further reductions in ASCVD risk can potentially be achieved with drugs that lower triglyceride levels [
7] .
Xuezhitong (XZT) is a single-prescription traditional Chinese medicine that is enriched, purified and refined from the natural edible and medicinal plant Allium macrostemon Bunge, which is also known as Xie Bai. Xie Bai is an ancient Chinese medicinal plant that is widely used to treat CVDs in China. Modern pharmacological studies have shown that Allium macrostemon contains a variety of active ingredients, such as methyl allyl trisulfide, saponins, and adenosines [
8]. Preliminary studies have proven that XZT can significantly reduce blood lipids, inhibit platelet aggregation, confer anti-thrombosis, and prevent and treat atherosclerosis [
9]. Xuezhikang (XZK) is another natural lipid-lowering drug extracted from fermented red yeast rice, which contains lovastatin and statin homologue and a variety of essential amino acids, unsaturated fatty acid, sterol, and small amounts of flavonoids [
10]. Studies have shown that the effect of XZK in reducing TC and LDL-C levels is equivalent to that of statins under conventional doses, and that it is better than statins in increasing HDL-C levels. More importantly, the treatment is more tolerable and safer than statins [
11]. Xu et al. found that XZK can not only affect the level of blood lipids, but also significantly reduce atherosclerotic small LDL subfractions, oxidative stress and inflammatory markers [
12].
The objectives of this study were to assess the effects of XZT (vs XZK and placebo) on TG and other blood lipids and to determine its tolerability and safety profiles in patients with HTG.
Discussion
According to an epidemiological survey of China in 2010, among 97,409 residents over 18 years old, the prevalence rates of HTG, low HDL-C and high LDL-C were 11.3%, 44.8%, and 2.1%, respectively, [
16]. The DYSIS study, which covers 6 regions, 27 provinces and 122 hospitals in China, included 25,317 patients who had taken statins for at least 3 months. The results showed that there were still as many as 47.6% of patients with HTG and/or low HDL-C; in the very high-risk group (patients were considered to be those with CHD or ischaemic stroke plus diabetes, or acute coronary syndrome), the proportion was as high as 74.2% [
17]. Persistent hypertriglyceridaemia indicates a significant residual cardiovascular risk, even in patients with well-controlled LDL cholesterol levels achieved by high-intensity statin regimens [
18]. Currently, some components are available that can decrease TG, namely, fibrates, Omega-3 fatty acids, and nicotinic acid [
19]. However, high-purity Omega-3 fatty acids products are not clinically available, and nicotinic acid drugs may raise blood sugar in patients [
20]. It is urgent to find and research new TG-lowering drugs.
XZT is synthesized from Allium macrostemon extract. It has proven that Allium macrostemon contains methyl allyl trisulfide, macrostemonoside A and other sulphur compounds, which have the effect of lipid lowering and anti-atherosclerosis [
8]. The pharmacological action of XZT on the cardiovascular system is to reduce the levels of TC, TG and LDL-C in the blood, increase the level of HDL-C, inhibit the aggregation of platelets and thrombosis, protect against myocardial injury caused by hypoxia ischaemia and ischaemia-reperfusion, and prevent and control atherosclerosis at the same time [
21]. Daily treatment with XZT and XZK resulted in statistically and clinically significant improvement from baseline to week 12 in terms of the reduction of TG and the percent reduction of TG. XZT and XZK enabled approximately 70% of the subjects to achieve ≥20% reductions in TG level from baseline. XZT and XZK also significantly improved the success rate of lipid control and improved the levels of other atherogenic lipids, such as the reduction/increase, percent reduction/increase and effective rate of TC, LDL-C and HDL-C. Our efficacy data are largely consistent with the results from previous studies [
9,
22]. Therefore, these agents may provide clinical benefits for patients with CV residual risk/CV events based on the treatment of statins, or they can be used as alternative drugs for patients with intolerance of statins.
In the present study, XZT and XZK proved to be effective in the treatment of dyslipidemia, and the mechanisms are still being explored. Zhao et al. investigated the effects of XZK on the TG level compared with simvastatin in the setting of an equivalent LDL-C lowering power, and found that XZK has stronger hypotriglyceridemic performance than simvastatin, which is attributed to more apolipoprotein A5 (apoA5) up-regulation by XZK through peroxisome proliferator-activated receptor α (PPARα) signalling pathway [
23]. Our present study demonstrated that XZT and XZK have similar performance of reducing TG and LDL-C levels, but XZT has stronger ability to increase HDL-C level. HDL-C, as the acceptor of cholesterol, can transport cholesterol from surrounding tissues (including macrophages and atherosclerotic plaques) to the liver for recycling or excretion in the form of cholic acid. This process is called reverse cholesterol transport (RCT), through which can reduce the cholesterol level in plasma and blood vessel wall and anti-atherosclerosis [
24]. Meng et al. detected the mechanism of XZT in the treatment of dyslipidemia involving RCT. The study indicated that XZT improved blood lipid dysfunction by induced RCT activation and increased the HDL levels of high fat diet-fed ApoE
−/−mice [
25].
Similar frequencies of adverse events (chiefly GI effects) were observed in the 3 groups. Although 1 subject receiving XZT experienced muscle symptoms, none had myopathy. In previous trials, XZT proved to be safe and well tolerated among patients with pre-existing abnormal liver function tests or statin-associated myalgia. Allium macrostemon is a dual-purpose plant used for medicine and food, so the XZT extracted and synthesized from it has good tolerability and safety.
Strengths, Limitations and Future Work
Our study had strengths and limitations. To the best of our knowledge, this is the first multicentre, randomized, double-blind, double simulation, positive drug and placebo parallel control study to evaluate the efficacy and safety of XZT using a large sample size. The 17 sites participated in our study are located in various regions of China, and the results are representative. Moreover, all patients have undergone a 2-week therapeutic lifestyle change period before inclusion, so that the enrolled patients are most in need of drug treatment, making the results of the study more reliable. In addition, XZT is extracted from a medicine food homology plant, which not only has a good efficacy of dyslipidemia, but also has a good tolerability and safety, it provides a new direction for the development of new lipid-modulating drugs.
However, there were also several limitations in our study. Firstly, this study only evaluated the lipid-modulating efficacy and safety of XZT treatment for 12 weeks, while the efficacy of the drug, especially the safety, needs to be tested for a longer time. Secondly, this study only included patients with moderate TG levels (2.3 mmol/L~5.6 mmol/L), but not patients with severe TG level (>5.6 mmol/L), which may make the results biased. Thirdly, HTG is closely related to residual cardiovascular risk, and the present study only evaluated the effect of XZT on triglyceride-lowering performance, but the effect among patients who have achieved statins therapy on residual cardiovascular risk is not available here. Lastly, patients with type 2 diabetes are often associated with HTG, but there is no further subgroup study on diabetes in this study. Moreover, only one dose of each drug was tested and dose response curves have not been performed.
Future study should enlarge the sample size, include with sever HTG patients with well-controlled LDL-C levels by statins, and each patient treated for an extended period (at least 1.5~2 years), and observe the clearer primary endpoint (CV death, MI, stroke, hospitalization for unstable angina requiring unplanned revascularization) to evaluate the efficacy and safety of XZT on residual cardiovascular risk [
26]. Most of all, more studies are needed to clarify the possible mechanism involved in the lipid-modulating effect of XZT.
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