Sun J et al / Acta Pharmacol Sin 2002 Dec; 23 (12): 1142-1151

Effects of natural products on ischemic heart diseases and cardiovascular system

Jian SUN, Benny KH TAN, Shan-Hong HUANG¹, Matthew WHITEMAN¹, Yi-Zhun ZHU²

Department of Pharmacology, ¹Department of Biochemistry, Faculty of Medicine, National University of Singapore, Singapore

² Correspondence to Dr YZ ZHU. Department of Pharmacology, Faculty of Medicine, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260. Phn +65-874-3676. Fax +65-773-0579. E-mail phczhuyz@nus.edu.sg

Received 2002-09-12 Accepted 2002-10-14

KEY WORDS myocardial infarction; herbal medicine; antioxidants; cardiovascular system; Salvia miltiorrhiza

INTRODUCTION

Ischemic heart diseases remain the leading cause of death in most developed countries as seen over the past quarter-century. Reducing the mortality rate and prevention of myocardial infarction (MI) are of utmost importance. The use of Western medicinal drugs for the treatment of hypertension, congestive heart failure and post MI are widely accepted. Although some Traditional Chinese Medicines have been used in mainland, Hong Kong, Taiwan of China in clinics and other Chinese communities worldwide for centuries, our understanding of the scientific principles of these herbal drugs is still far from satisfactory. As a result, their wide spread use in patients is limited throughout the world, especially in Western societies, although some of them could be used as complementary medicines in the treatment of Western medicines or tonics to maintain good health. The mechanisms of action and interaction, and the chemicals they contain remain undetermined in most Chinese traditional medicines, and need to be further elucidated using modem biological tools.

As the medicinal value of Chinese traditional medicine cannot be ignored, researchers are gradually becoming interested in identification of the active prin ciples in the extracts with intensive follow-up study of their mechanisms of action. In this review, we mainly examine some natural products of Chinese herbal origin, and focus on elaborating the mechanisms of their beneficial effects on ischemic heart diseases, especially on myocardial infarction. In fact, there are a large number of natural products that have been confirmed to have such effects. Guided by publications indexed in Medline, we focus on herbal medicines (crude extracts and pure compounds) that have been deeply studied in recent ten years.

CARDIOPROTECTIVE EFFECTS OF HERBAL EXTRACTS AFTER MYOCARDIAL INFARCTION

Infarct size and survived myocardium The infarct size is an important parameter to evaluate the severity of acute myocardial infarction (MI). Pretreatment with trilinolein^[1] isolated from Panax pseudoginseng, or magnolol and honokiol ^[2,3], main components purified from Magnolia officinalis at the dosages of 0.1 and 0.01 mg/kg could significantly reduce the infarct size in rat models.

When compared the effects of Salvia miltiorrhiza Bunge (SMB, DanShen) with ramipril, an angiotensin converting enzyme (ACE) inhibitor, in rats induced with MI, Ji et al^[4] found that DanShen reduced the ratios of infarct size to the left ventricular size, total heart weight, left ventricular weight and right ventricular weight to body weight as effectively as ramipril. Similar effect could be seen in treatment with lithospermic acid B from the aqueous fraction of SMB in an ischemia/reperfusion (I/R) rabbit model^[5]. Radix stephania tetrandrae (RST) extract and its compound tetrandrine (TET) ^[6] also produced equally potent ameliorating effects on infarct size in isolated rat hearts which sustained I/R injury without reduced coronary artery flow. In contrast, fanchinoline (FAN), another effective compound of RST had no such effects.

Tetrahydropalmatine (THP) and its homologues: 1-stepholidine (SPD) and tetrahydroberberine (THB), found in several plants of the genus Corydalis including C. ambigua, also exhibited the effect of reducing infarct size in rats ^[7,8].

Capilary growth and myocardial microcirculation Vascular endothelial growth factors (VEGFs) are mitogenes for vascular endothelial cells, a key step for neovascularization. It is of interest that among many natural products, only SMB was demonstrated to have the ability to encourage capillary growth in blood vessels. A relevant study done by Huang et al ^[9] found that SMB could up-regulate the expression of VEGF and VEGF-B in vitro. Furthermore, the increased production of VEGF and VEGF-B was effective as judged by the proliferation of endothelial cells. This pharmacological profile of SMB suggests an important role for SMB in reconstruction of myocardial function after MI.

NATURAL PRODUCTS AND BLOOD PRESSURE REGULATION

Effects on vasorelaxation Endogenous nitric oxide (NO), once named endothelium-derived relaxing factor (EDRF), which plays a key role in numerous physiological and pathological processes, is synthesized from L-arginine by a family of nitric oxide synthase (NOS) isoenzymes including endothelial NOS (eNOS), neuronal NOS (nNOS) and inducible NOS (iNOS). NO acts as a vasodilator when produced by constitutive NOS, which is composed of eNOS and nNOS in endothelial cells^[10]. Several natural products have vasorelaxant effects due to the release of NO. Cheung and co-workers^[11] recently verified that magnesium tanshinoate B (MTB) purified from SMB stimulated the release of NO in human endothelial cells in vitro. Following treatment with magnesium tanshinoate B, the cellular NOS activities were enhanced with a concomitant increase in the levels of cNOS protein mass.

The extract of Uncaria rhynchophylla (UR) was found by Kuramochi et al^[12] to relax the NE-precontracted rat aorta mainly through endotheliumdependent mechanism, and partially via endothelium-independent way. This relaxation produced by UR was long-lasting.

Gallotannin, a component of Paeoniae radix, procyanidins, an active principle in Crataegus extract, and ginsenosides from the protopanaxatriol group were also proved to have an endothelium-dependent vasodilator effect on isolated rat aorta^[13-15].

In addition, magnolol could relax vascular smooth muscle by releasing NO and inhibiting calcium influx through voltage-gated calcium channels in rat thoracic aorta in vitro^[16]. As excessive NO production due to elevated expression of iNOS may produce cytotoxic effects to cells in the vascular wall, magnolol and honokiol also could weakly inhibit inducible NO synthase (iNOS) enzyme activity, but potent decrease iNOS induction in lipopolysaccharide (LPS)-activated macrophages^[17].

Cheung et al found that Ginkgo biloba (Gb) extract selectively inhibited iNOS expression without affecting eNOS-mediated NO production in vitro^[18]. Such inhibition of iNOS induction could also be seen in treatment with wogonin, baicalein and baicalin, isolated from the dry roots of Scutellaria baicalensis Georgi, and the active stilbenes, isolated from the rhizome of Rheum undulatum L^[19,20]. But it was also demonstrated that baicalein and baicalin enhanced the phenylephrine-induced contraction through inhibiting production or/and release of endothelial nitric oxide in the isolated rat mesenteric artery rings^[21].

The relationship between NO and natural products, and the role NO plays in the treatment of ischemic heart diseases with natural products still need to be further elucidated.

Effects on calcium channel Calcium channel antagonism is the most common factor when we refer to antihypertensive or vasorelaxant effect. An active ingredient of Ligusticum wallichii Franchat, tetramethylpyrazine (TMP) is a commonly used Chinese herb to improve circulation. Both in vivo and in vitro studies of TMP showed that its hypotensive and direct vasorelaxant effects were due to calcium antagonism. TMP not only blocked the entry of extracellular calcium through calcium channels but also inhibited the release of intracellular stored calcium in vascular smooth muscle cells^[22]. In contrast, another compound which was also isolated from Ligusticum wallichii Franchat, butylidenephthalide (Bdph), was found by Ko and co-workers^[23] to inhibit calcium release from cal cium stores more selectively than calcium influx from extracellular space via voltage-dependent calcium channels using the rat's descending thoracic aorta in vitro.

Hirsutine, an indole alkaloid found in UR was shown in previous study that it could not only inhibit calcium release but also increase calcium uptake into the calcium store as well as block the voltage-dependent calcium channel leading to a reduction of intracellular Ca²⁺ level in isolated rat^[24].

Tetrandrine (TET) has a long history of use for the treatment of angina and hypertension in China^[7]. It has been shown to block Ca²⁺ channels in various tissues as a non-selective calcium channel antagonist^[25]. In addition, dehydroevodiamine (DeHE), a quinazolinocarboline alkaloid isolated from the fruit of Evodiac rutaecarpa also need to be noted as its vasorelaxant effect involved everal mechanisms which include endothelium dependence, -adrenoceptor blockade, K⁺ channel activation apart from Ca²⁺ channel blockade in vitro^[26].

ANTI-ARRHYTHMIC EFFECT

Many natural products show their effects on inhibition of ventricular tachycardia (VT), ventricular fibrillation (VF) and/or extrasystole during the period of I/R injury or AMI in animals. Pretreatment with magolol and honokiol significantly reduced the incidence and duration of ventricular arrhythmia including VT and VF in rats^[2,3]. Such effects may in part be relevant to an increased NO synthesis. In a similar model, trilinolein reduced or completely suppressed not only the incidence and duration of VT but the number of ectopic beats as well^[1].

Dauricine, an active compound found in Menispermum dauricum, ameliorate acute myocardial ischemia-induced VT and VF in anesthetized dogs^[27]. The mechanism of its antagonistic effect lies in its inhibition of K⁺, Na⁺ and Ca²⁺ in ventricular myocytes ^[28]. Berberine could also significantly suppress the ventricular premature beats and VT in both animal experiments and clinical observation^[29,30]. Neferine, isolated from the seeds of Nelumbo nucofera Gaertn, prevented the onset of re-entrant VT and sudden cardiac death after myocardial ischemic damage in vivo^[31].

Oxymatrine, isolated from the genus Sophora, increased diastolic excitability threshold and lengthened effective refractory periods (ERP) in dogs after myocardial infarction^[32]. But it had no effects on dispersion of ERP, VT and VF induced by programmed electric stimulation. In comparison, Crataegus oxyacantha presented contradictory results with regard to its anti-arrhythmic effects^[33,34]. In a recent study, it aggravated rather than prevented arrhythmias after long-term application while protective effects were previously reported in rats after short-term as well as long-term oral treatment.

The same effects can also be seen in in vitro study. The inhibition of VT and VF could be seen in treatment with TET or RST extract but not FAN during regional I/R injury without further reducing ischemia-reduced heart rate and coronary artery flow^[6]. Berbamine is very similar in structure to TET and seems to act in a virtually identical way on the cardiovascular system^[7]. Pretreatment with sinomenine^[35], a compound found in Sinomenium acutum, or TMPZ^[36] could also reduce the incidence of VT and VF in isolated perfused rat heart subject to I/R injury. The latter also enhanced the release of PGI₂ and diminished the outflow of TXB₂. Other natural products having anti-arrhythmic protection effects are: hirsutine, EGB761, and dehydroevodia-mine (DeHE). Hirsutine showed anti-arrhythmic action on membrane potentials of rabbit sino-atrial node and guinea-pig right ventricle and left atrium in vitro^[37].

It had direct effects on the action potential of cardiac muscle through inhibition of multiple ion channels, which might explain why its hypotensive effect was accompanied by negative chronotropic activity without reflex tachycardia. EGB761, a Ginkgo biloba extract, in combination with SOD could reduce the incidence of reperfusion-induced VF and VT in isolated rat hearts^[38]. DeHE was shown to depress arrhythmias in calcium-overloaded guinea-pig cardiac myocytes through its inhibitory actions on the Na⁺-dependent inward current, the transient inward current and, to a smaller extent, the L-type Ca²⁺ current. In the mean time, DeHE also had class III antiarrhythmic effect through a reduction of outward K⁺ currents across the sarcolemma^[39]. But the cause of the DeHE-induced bradycardia seemed unlikely to be due to antagonism of Ca²⁺ influx in isolated mouse hearts^[40].

IMPROVEMENT OF OTHER CARDIAC PARAMETERS

Recent studies have suggested that the mitogen-activated protein kinases (MAPKs) may be implicated in apoptosis. p38 MAPK and c-Jun NH₂-terminal protein kinase (JNK/SAPK) are also called stress-regulated mitogen-activated protein kinases mediating apoptosis after I/R injury whereas extracellular signal-regulated kinase (ERK) plays a role in protecting cardiomyocytes^[41]. Magnesium tanshinoate B, a component of SMB could abolish the elevation in SAPK activity in isolated rat hearts and prevented the induction of apoptosis in reperfusion injury^[42]. Similar effect can be seen in another natural product, Flos carthami (FC). Siow et al^[43] used an aqueous Flos carthami extract to investigate its effect on SAP kinase in IR rats both in vivo and in vitro and found that FC extract, which protected the isolated heart against arrhythmia caused by I/R injury, significantly inhibited SAPK activity via two mechanisms. One is that it affects the interaction of SAP kinase with c-jun. The other is that it inhibits the phosphotransferase reaction. The administration of the FC extract may lead to a modulation of the apoptotic effect induced by SAP kinase.

Ischemic myocardial injury initiates an acute inflammatiory response in which polymorphonuclear leukocytes are major participants. Magnolol could significantly suppress N-formylmethionyl-leucyl-phenylalanine-activated human neutrophil migration as well as expression of VCAM-1 resulting in reduced adhesion of leukocytes in vitro^[44,45]. In cultured human umbilical vein endothelial cells, baicalein inhibited endothelial leukocyte adhesion molecule-1 and intercellular adhesion molecule-1 expression induced by thrombin and phorbol myristate acetate^[46].

In terms of myocardial metabolism, pretreatment with Polygonum multiflorum Thunb [PME) extract or Crataegus extract in isolated rat heart models could significantly attenuate LDH release, suggesting a preservation of the cell membrane from I/R damage^[47,48]. Meanwhile, the latter lowered the level of lactate during ischemia as well as accelerated the reperfusion-induced recovery of the energy metabolism including decreasing the level of AMP and increasing the level of energy charge potential^[49]. EGb 761 also suppressed the leakage of LDH as well as diminished the decrease in myocardial ascobate content concomitant with suppressing the increase of dehydroascorbate in cardiac I/R injury^[50]. Tetrahydropalmatine (THP) and its analogue were proved to ameliorate the increase of creatine kinase and aspartate aminotransferase in the serum of rats subject to I/R^[8].

Treatment with berberine in both anoxic and aerobic perfusion media in isolated rat hearts resulted in a significant reduction of creatine phosphokinase (CPK) release accompanied by amelioration of ultrastructural damage^[51]. Zhang and co-workers^[52] found similar results when they pretreated I/R rats with paeonol. Puerarin, an isoflavone isolated from plants of the genus Pueraria, has already been widely used in the treatment of angina and other ischemic diseases. In a clinical trial, it was shown that the frequency of angina events and myocardial oxygen consumption were reduced with improving abnormal rest ECG and increasing exercise duration^[53]. Such beneficial effects on myocardial function were consistent with previous studies in which puerarin preserved mitochondrial structure and decreased myocardial lactate production, oxygen consumption and CPK release after myocardial I/R injury in dogs^[54,55]. In addition, some reported that puerarin might play a role in regulating the imbalance of endothelin, rennin, and angiotensin II activity in patients with acute myocardial infarction^[56].

It is also necessary to be mindful of the protective effects of natural products on cardiac hemodynamics. Pretreatment with magnolol markedly enhanced the recovery of systolic wall thickening fraction 60 min after coronary artery reperfusion in anesthetized, open-chest rabbits^[57]. Berberine improved the impaired left ventricular function by its positive inotropic effect and mild systemic vasodilation^[58] and ameliorated the decreased cardiac output in dogs subject to IR injury^[29]. Scoparone could increase coronary flow and inhibit the depression of ST waves as an anti-anginal drug^[59]. Angelica sinensis (AS) increased the coronary blood flow with decreasing myocardial oxygen consumption^[60]. When AS was injected before I/R injury, the LVP and +/-dp/dt_max of the rabbit heart were significantly higher than those in the control group^[61].

ANTIOXIDANT EFFECTS OF NATURAL PRO-DUCTS

Healthy cells can scavenge free radicals effectively by means of the antioxidant. In general, this is a dynamic relationship between reactive oxygen species (ROS) and antioxidants in the human body. However, when cells suffer I/R injury, the sudden generation of ROS can dramatically upset this balance with an increased demand on the antioxidant defense system. Natural antioxidants including superoxide dismutase (SOD), catalase and glutathione peroxidase are depleted accompanied by accumulation of ROS. In such situation, natural products can play an important role in two aspects: enhance the activity of original natural an tioxidants and neutralize ROS work by nonenzymatic mechanisms.

With regard to the first aspect, SMB shows potent effects^[4]. It could reduce oxidant stress from MI by increasing the activities of hepatic-antioxidant enzymes, including superoxide dismutase, catalase, glutathione S-transferase, and tathione peroxidase (Tab 1). Other products including trilinolein, paeonol from Paeonia Radix, sinomenin from Sinomenium acutum, and Menispermum dauricum could also increase SOD in rats^[1,52,35,62]. Recent studies showed that after short-term supplementation of low concentration of trilinolein in rats^[63] or incubation at similar concentration in rat aortic smooth muscle cells^[64], the activity and mRNA levels of SOD were increased. However, when prolonging the time of incubation to seven days, these parameters were lowered in a dose-dependent manner. These phenomena imply that low dosage of trilinolein given short term stimulates endogenous antioxidant (SOD). By contrast, after long-term administration, it could replace the action of SOD in terms of an OFR scavenger. In addition, Polygonum multiflorum Thunb was found to have myocardial protection associated with an enhancement in myocardial glutathione antioxidant status impaired by IR-induced oxidative stress^[47].

Tab 1. Anti-oxidant status of the liver in DanShen-, saline- and ramipril-treated rats. n=6. Mean±SD. ^cP<0.01 vs corresponding saline group. ^fP<0.01 vs ramipril-treated group.

All assays were performed in duplicate at 25 ºC. One unit of SOD is defined as the amount of enzyme necessary to inhibit the superoxide-dependent oxidation of pyrogallol 10 mmol/L; 1 unit of catalase (CAT) defined as mmol H₂O₂ decomposed/min; 1 unit of glutathione peroxidase (GSH-Px) is defined as 1 mmol of reduced nicotinamide adenine dinucleotide phosphate (NADPH) converted to NADP⁺/min; 1 unit of glutathione S-transferase (GST) is defined as 1 mmol CDNB converted to CDNB-glutathione/min.

In an on-going project, initial screening of whole extracts of Rhizoma ligustici (RL), Herba leonuri (HL) and Radix Achyranthis bidentatae (RAB) has proved very interesting. RL, HL and RAB have been analysed for scavenging of peroxynitrite (ONOO^-), hydrochlorite (HOCl), hydroxyl radical (×OH), 2,2'-azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid) (ABTS×⁺) and diphenyl-1-plcrylhydrazyl (DPPH) as well as inhibition of Fe-induced lipid peroxidation and in each assay antioxidant activity greater than that, on a molar basis, than either ascorbic acid or Trolox, a water soluble analogue of vitamin E. We have shown that these compounds contain moieties other than phenolics that are responsible for the antioxidant activity (Fig 1).

Fig 1. A: Assessing the capacity of a compound to scavenge ABTS^·+ radicals in terms of ascorbic acid equivalent is known as Trolox-equivalent antioxidant capacity (TEAC). The average TEAC values for RAB, RL, and HL were 67 %, 481 %, and 237 %. B: The inhibition value of ascorbic-Ferric ion induced lipid peroxidantion by using borine brain extract is 21.6 % for RAB, 71 % for RL, and 79 % for HL. RL and HL inhibited more lipid peroxidation than ascorbic acid (21 %). C: DPPH (free radical) scavenging activity of drug extracts was determined. The final concentration of DPPH was 100 mmol/L in all tested samples. Control represented the control containing no antioxidants. D: Pyrogallolsulfonephtalein (PR) is easily to react with oxidant (peroxynitrite-ONOO or higypochlorite-HOCl). The drugs can inhibit oxidation of PR for HOCl.

Free radicals alter the structural and functional integrity of cells by a variety of mechanisms, including lipid peroxidation, sulfhydryl oxidation, proteolysis, and shearing of the nuclear material. Most research on natural products in recent years concentrates on the inhibition of lipid peroxidation.

Among these natural products, magnolol and honokiol show antioxidant effects 1000 times higher than that of alpha-tocopherol when oxygen consumption and MDA production were measured to quantitate lipid peroxidation in isolated rat heart^[65]. But magnolol and honokiol's free radical scavenging activities were less potent than alpha-tocopherol, consistent with another experiment showing that when compared with saturated and unsaturated lipid compounds (trilinolein, catechin, trolox, et al) by means of enhanced chemiluminescence^[1]. According to this data, trilinolein has the most post potent antioxidant effect, which in part explains its protection of mitochondrial ultrastruture, and improvement of erythrocyte deformability in vitro. The extract of Curcuma longa (CL)^[66,67] was tested for its effects on atherogenesis prevention, and found that it could decrease the susceptibility of low density lipoprotein (LDL) to lipid oxidation in atherosclerotic rabbits and lower the abnormally high values of human-plasma fibrinogen and apo B/ apo A ratio in clinical trials. Similar effect of preventing LDL from oxidation could also be seen in the treatment with SMB and its main components MTB and tanshinone II-A in vitro^[68-70].

Since superoxide, hydrogen peroxide, and hydroxyl ions are the three main free radicals involved in initiating a chain reaction of lipid peroxidation, some natural products have the ability to directly scavenge this kind of free radicals. Danshensu, an important compound of SMB, working as a preventive antioxidant, could scavenge superoxide anions generated from xanthine-xanthine oxidase system and protect the myocardial mitochondrial membranes from lipid peroxidation. And tanshinone, a chain-breaking antioxidant, scavenged the lipid free radicals generated from lipid peroxidation of the myocardial mitochondrial membranes^[71]. Shao et al^[72] found that baicalein could directly scavenge superoxide, hydrogen peroxide, and hydroxyl radicals, and significantly attenuate cell death after I/R in cardiomyocytes. Its chemical structure, o-di-hydroxyl group in the A ring, plays a key role^[73]. But recent study showed that baicalein and baicalin posed a different pathological pathway^[74]. The antioxidant function of baicalin was mainly based on scavenging superoxide radical whilst baicalein was a good xanthine oxidase inhibitor. Schisanhenol isolated from Fructus schizandrae scavenged hydroxyl radicals induced by adriamycin in rat heart mitochondria^[75]. And a recent study showed that some paeonol glycosides exhibited more potent radical scavenging effects than -tocopherol^[76]. Protykin, an all-natural extract of trans-resveratrol (20 %) and emodin (10 %) derived from the dried rhizome of Polygonum cuspidatum, also possessed potent peroxyl and hydroxyl radical scavenging activi ties in isolated rat hearts^[77].

It should be noticed that two natural products present their antioxidant effects indirectly. One is Ginkgo biloba (Gb) and ginkgolides, which are terpenoids found in its leaves. Using hemodynamic and electron spin resonance (ESR) analyses, both in vivo and in vitro, Liebgott and co-workers^[78] found that part of the cardioprotection afforded by Gb extract involved a mechanism independent of direct scavenging of free radicals. This conclusion is consistent with a previous study showing that they appeared to inhibit free radical formation rather than directly scavenge free radical^[79]. The other is puerarin and Radix puerariae. Both of them were studied in live rats. Unlike Radix puerariae extract, puerarin seemed to act as an enzymatic inhibitor of the oxygen radical production mediated by the peroxidase/H₂O₂/luminol/enhancer radical reactions, rather than as a true antioxidant^[80].

According to the present knowledge, many natural products are involved in direct or indirect inhibition of lipid peroxidation. Aside from the natural products I mentioned above, tetrahydroprotoberberines decreased malondialdehyde (MDA) content, and xanthine oxidase activity and scavenge hydroxyl free radicals in vitro ^[81]. Ginsenosides and saponins from Panax ginseng decreased lipid peroxidation concomitant with increasing 6-keto-PGF₁a in vivo^[82]. Camellia sinensis, with flavan-3-ol tannins inhibited lipid peroxidation in rat heart mitochondria^[83]. Crataegus extracts showed cardioprotective effects via their radical scavenging and elastase inhibitory activities^[84]. Paeoniae Radix and Moutan cortex, both from the Paeoniaceae paeoniae family^[85], could suppress phenylhydroquinone-induced oxidative DNA cleavage.

CONCLUSION

In conclusion, the effects of most natural products on ischemic heart diseases are multiple and complex. In animal models, they show their abilities to improve myocardial function, promote capillary growth, relax vascular smooth muscle or myocardial contractility, inhibit arrhythmia induced by I/R injury and reduce myocardial infarct size. Meanwhile, compared to calcium antagonists or angiotensin converting enzyme inhibitors, some of them also have a unique profile, antioxidant activity, such as trilinolein, magnolol, and danshensu et al, which further strengthen their status in the treatment of ischemic heart diseases. All these effects partially explain why traditional Chinese medicines could have been widely used in Eastern countries for thousand years.

However, the more we study their mechanisms, the more complex they appear. For example, the relationship among apoptosis, ROS, and NO is very subtle in pathophysiology. It plays a key role in ischemic heart diseases, especially in myocardial infarction. Several natural products have already been demonstrated to be involved in this relationship. Flos carthami and MTB inhibited apoptosis by means of reducing SAP kinase activity; Gb extract, magnolol, and honokiol surpressed excessive NO production injury caused by iNOS expression. And many products mediate the balance between free radicals and NO via antioxidant activity. Further studies, especially clinical trials, still need to be done. Meanwhile, before we obtain more conclusive data on clinical efficacy and safety, herbal medications still need to be used prudently when accompanied with other Western drugs.

REFERENCES

• 1 Chan P, Tomlinson B. Antioxidant effects of Chinese traditional medicine: focus on trilinolein isolated from the Chinese herb Sanchi (Panax pseudoginseng). J Clin Pharmacol 2000; 40: 457-61.
• 2 Hong CY, Huang SS, Tsai SK. Magnolol reduces infarct size and suppresses ventricular arrhythmia in rats subjected to coronary ligation. Clin Exp Pharmacol Physiol 1996; 23: 660-4.
• 3 Tsai SK, Huang SS, Hong CY. Myocardial protective effect of honokiol: an active component in magnolia officialis. Planta Med 1996; 62: 503-6.
• 4 Zhu YZ, Zhu YC. Rediscovering remedies. Science 2002; 297: 1231.
• 5 Fung KP, Zeng LH, Wu J, Wong HNC, Lee CM, Hon PM, et al. Demonstration of the myocardial salvage effect of lithospermic acid B isolated from the aqueous extract of Salvia miltiorrhiza. Life Sci 1993; 52: 239-44.
• 6 Yu XC, Wu S, Wang GY, Shan J, Wong TM, Chen CF, et al. Cardiac effects of the extract and active components of radix stephaniae tetrandrae. Life Sci 2001; 68: 2863-72.
• 7 Sutter MC, Wang YX. Recent cardiovascular drugs from Chinese medical plants. Cardiovasc Res 1993; 27: 1891-901.
• 8 Xuan B, Li DX, Wang W. Protective effects of tetrahydroprotoberberines on experimental myocardial infarction in rats. Acta Pharmacol Sin 1992; 13: 167-71.
• 9 Huang JL, Chen Y, Huang YQ. Induction of vascular endothelial growth factor genes expression by Dan Shen (Radix Salviae miltiorrhizae) in human fibroblasts. Available at www.ustcma.org/AJTCM/vol1-2-2000/JanLi-HUANG.htm.
• 10 Chung HT, Pae HO, Choi BM, Billiar TR, Kim YM. Nitric oxide as a bioregulator of apoptosis. Biochem Biophys Res Commun 2001; 282: 1075-9
• 11 O K, Cheung F, Sung FL, Zhu DY, Siow LY. Effect of magnesium tanshinoate B on the production of nitric oxide in endothelial cells. Mol Cell Biochem 2000; 207: 35-9.
• 12 Kuranochi T, Chu J, Suga T. Gou-teng (from Uncaria rhynchophylla Miquel)-induced endothelium-dependent and -independent relaxations in the isolated rat aorta. Life Sci 1994; 54: 2061-9.
• 13 Goto H, Shimada Y, Akechi Y, Kohta K, Hattori M, Terasawa K. Endothelium-dependent vasodilator effect of extract prepared from the roots of Paeonia lactiflora on isolated rat aorta. Planta Med 1996; 62: 436-9.
• 14 Kang SY, Schini-Kerth VB, Kim ND. Ginsenosides of the protopanaxatriol group cause endothelium-dependent relaxation in the rat aorta. Life Sci 1995; 56: 1577-86.
• 15 Kim SH, Kang KW, Kim KW, Kim ND. Procyanidins in crataegus extract evoke endothelium-dependent vasorelaxation in rat aorta. Life Sci 2000; 67: 121-31.
• 16 Teng CM, Yu SM, Chen CC, Huang YL, Huang TF. EDRF-release and Ca²⁺-channel blockade by magnolol, an antiplatelet agent isolated from Chinese herb magnolia officinalis, in rat thoracic aorta. Life Sci 1990; 47: 1153-61.
• 17 Matsuda H, Kageura T, Oda M, Morikawa T, Sakamoto Y, Yoshikawa M. Effects of constituents from the bark of Magnolia obovata on nitric oxide production in lipopolysaccharide-activated macrophages. Chem Pharm Bull (Tokyo) 2001; 49: 716-20.
• 18 Cheng F, Siow YL, OK. Inhibition by ginkgolides and bilobalide of the production of nitric oxide in macrophages (THP-1) but not in endothelial cells (HUVEC). Biochem Pharmacol 2001; 61: 503-10.
• 19 Chen YC, Shen SC, Chen LG, Lee TJ, Yang LL. Wogonin, baicalin, and baicalein inhibition of inducible nitric oxide synthase and cyclooxygenase-2 gene expressions induced by nitric oxide synthase inhibitors and lipopolysaccharide. Biochem Pharmacol 2001; 61: 1417-27.
• 20 Matsuda H, Kageura T, Morikawa T, Toguchida I, Harima S, Yoshikawa M. Effects of stilbene constituents from rhubarb on nitric oxide production in lipopolysaccharide-activated macrophages. Bioorg Med Chem Lett 2000; 10: 323-7.
• 21 Huang Y, Yao XQ, Tsang SY, Lau CW, Chen ZY. Role of endothelium/nitric oxide in vascular response to flavonoids and epicatechin. Acta Pharmacol Sin 2000; 21: 1119-24.
• 22 Pang PK, Shan JJ, Chiu KW. Tetramethylpyrazine, a calcium antagonist. Planta Med 1996; 62: 431-5.
• 23 Ko WC, Charing CY, Sheu JR, Tzeng SH, Chen CM. Effect of butylidenephthalide on calium in isolated rat aorta. J Pharm Pharmacol 1998; 50: 1365-9.
• 24 Horie S, Yano S, Aimi N, Sakai S, Watanabe K. Effects of hirsutine, an antihypertensive indole alkaloid from Uncaria rhynchophylla, on intracellular calcium in rat thoracic aorta. Life Sci 1992; 50: 491-8.
• 25 Takemura H, Imoto K, Ohshika H, Kwan CY. Tetrandrine as a calcium antagonist. Clin Exp Pharmacol Physiol 1996; 23: 751-3.
• 26 Chiou WF, Liao JF, Shum AY, Chen CF. Mechanisms of vasorelaxant effect of dehydroevodiamine: a bioactive isoquinazolinocarboline alkaloid of plant origin. J Cardiovasc Pharmacol 1996; 27: 845-53.
• 27 Zhu JQ, Zeng FD, Hu CJ. Protective and anti-arrhythmic effects of dauricine and verapamil on acute myocardial infarction in anesthetized dogs. Acta Pharmacol Sin 1992; 13: 249-51.
• 28 Xia JS, Guo DL, Zhang Y, Zhou ZN, Zeng FD, Hu CJ. Inhibitory effects of dauricine on potassium currents in guinea pig ventricular myocytes. Acta Pharmacol Sin 2000; 21: 60-4.
• 29 Huang WM, Wu ZD, Gan YQ. Effects of berberine on ischemic ventriculararrhythmia. Chin J Cardiol 1989; 17: 300-1, 319.
• 30 Huang W. Ventricular tachyarrhythmias treated with berberine. Chin J Cardiol 1990; 18: 155-6.
• 31 Guo Z. Electrophysiological effects of neferine against ischemic ventricular tachyarrhythmias. Chin J Cardiol 1992; 20: 119-22, 134.
• 32 Zeng JX, Cao HY, Li Q, Xu Z, Guo ZB. Effects of oxymatrine on arrhythmia in dogs with myocardial infarction. Acta Pharmacol Sin 1996; 17: 379-82.
• 33 Rothfuss MA, Pascht U, Kissling G. Effect of long-term application of Crataegus oxyacantha on ischemia and reperfusion induced arrhythmias in rats. Arzneimittelforschung 2001; 51: 24-8.
• 34 Al Makdessi S, Sweidan H, Dietz K, Jacob R. Protective effect of Crataegus oxyacantha against reperfusion arrhythmias after global no-flow ischemia in the rat heart. Basic Res Cardiol 1999; 94: 71-7.
• 35 Xie SX, Jian QQ. Prevention of sinomenine on isolated rat myocardial reperfusion injury. Acta Pharmacol Sin 1993; 14 Suppl: S12-5.
• 36 Feng J, Wu GZ, Tang SB. The effects of tetramethylpyrazine on the incidence of arrhythmias and the release of PGI ₂ and TXA₂ in the ischemic rat heart. Planta Med 1999; 65: 268-70.
• 37 Masumiya H, Saitoh T, Tanaka Y, Horie S, Aimi N, Takayama H, et al. Effects of hirsutine and dihydrocorynantheine on the action potentials of sino-atrial node, atrium and ventricle. Life Sci 1999; 65: 2333-41.
• 38 Tosaki A, Droy-Lefaix MT, Pali T, Das DK. Effects of SOD, catalase, and a novel antiarrhythmic drug, EGb 761, on reperfusion-induced arrhythmias in isolated rat hearts. Free Rad Biol Med 1993; 14: 361-70.
• 39 Loh SH, Lee AR, Huang WH, Lin CI. Ionic mechanisms responsible for the antiarrhythmic action of dehydroevodiamine in guinea-pig isolated cardiomyocytes. Br J Pharmacol 1992; 106: 517-23.
• 40 Wong KK. Lack of calcium-antagonizing activity of dehydroevodiamine on the chronotropic and inotropic activities of mouse isolated atria. Planta Med 1996; 62: 246-9.
• 41 Yue TL, Wang C, Gu JL, Ma XL, Kumar S, Lee JC, et al. Inhibition of extracellular signal-regulated kinase enhances ischemia/reoxygenation-induced apoptosis in cultured cardiac myocytes and exaggerates reperfusion injury in isolated perfused heart. Cir Res 2000; 86: 692-9.
• 42 Au-Yeung KKW, Zhu DY, O K, Siow YL. Inhibition of stress-activated protein kinase in the ischemic/reperfused heart: role of magnesium tanshinoated B in preventing apoptosis. Biochem Pharmacol 2001; 62: 483-93.
• 43 Siow YL, Choy PC, Leung WMK, O K. Effect of Flos Carthami on stress-activated protein kinase activity in the isolated reperfused rat heart. Mol Cell Biochem 2000; 207: 41-7.
• 44 Lee YM, Hsiao G, Chen HR, Chen YC, Sheu JR, Yen MH. Magnolol reduces myocardial ischemia/reperfusion injury via neutrophil inhibition in rats. Eur J Pharmacol 2001; 422: 159-67.
• 45 Chen YH, Lin SJ, Chen JW, Ku HH, Chen YL. Magnolol attenuates VCAM-1 expression in vitro in TNF-alpha-treated human aortic endothelial cells and in vivo in the aorta of cholesterol-fed rabbits. Br J Pharmacol 2002; 135: 37-47.
• 46 Kimura Y, Matsushita N, Yokoi-Hayashi K, Okuda H. Effects of baicalein isolated from Scutellaria baicalensis radix on adhesion molecule expression induced by thrombin and thrombin receptor agonist peptide in cultured human umbilical vein endothelial cells. Planta Med 2001; 67: 331-4.
• 47 Yim TK, Wu WK, Mak DHF, Ko KM. Myocardial protective effect of an anthraquinone-containing extract of polygonum multiflorum ex vivo. Planta Med 1998; 64: 607-11.
• 48 Makdessi SA, Sweidan H, Mullner S, Jacob R. Myocardial protection by pretreatment with crataegus oxyacantha. Arzneimittelforschung 1996; 46: 25-7.
• 49 Nasa Y, Hashizume H, Ehsanul Hoque AN, Abiko Y. Protective effect of crataegus extract on the cardiac mechanical dysfunction in isolated perfused working rat heart. Arzneimittelforschung 1993; 43: 945-9.
• 50 Haramaki N, Aggarwal S, Kawabata T, Droy-Lefaix MTT, Packer L. Effects of natural antioxidant Ginkgo biloba extract (Egb 761) on myocardial ischemia-reperfusion injury. Free Radit Biol Med 1994; 16: 789-94.
• 51 Huang Z, Chen S, Zhang G, Xu S, Huang W, Han Y, et al. Protective effects of berberine and phentolamine on myocardial reoxygenation damage. Chin Med Sci J 1992; 7: 221-5.
• 52 Zhang WG, Zhang ZS. Anti-ischemia reperfusion damage and anti-lipid peroxidation effects of paeonol in rat heart. Acta Pharm Sin 1994; 29: 145-8.
• 53 Zhao Z, Yang X, Zhang Y. Clinical study of puerarin in treatment of patients with unstable angina. Chin J Integrated Tradit West Med 1998; 18: 282-4.
• 54 Fan LL, Sun LH, Li J, Yue XH, Yu HX, Wang SY, et al. Protective effect of puerarin against myocardial reperfusion injury. Myocardial metabolism and ultrastructure. Chin Med J (Engl) 1992; 105: 451-6.
• 55 Fan LL, Sun LH, Li J, Yue SH, Yu HX, Wang SY. The protective effect of puerarin against myocardial reperfusion injury. Study on cardiac function. Chin Med J (Engl) 1992; 105: 11-7.
• 56 Li SM, Liu B, Chen HF. Effect of puerarin on plasma endothelin, renin activity and angiotensin II in patients with acute myocardial infarction. Chin J Integrated Tradit West Med 1997; 17: 339-41.
• 57 Huang CH, Hong CY, Tsai SK, Lai ST, Weng ZC, Chih CL, et al. Intravenous pretreatment with magnolol protects myocardium against stunning. Planta Med 2000; 66: 516-20.
• 58 Huang WM, Yan H, Jin JM, Yu C, Zhang H. Beneficial effects of berberine on hemodynamics during acute ischemic left ventricular failure in dogs. Chin Med J (Engl) 1992; 105: 1014-9.
• 59 Yamahara J, Kobayashi G, Matsuda H, Katayama T, Fujimura H. The effect of scoparone, a coumarin derivative isolated from the Chinese crude drug Artemisiae capillaries flos, on the heart. Chem Pharmacol Bull (Tokyo) 1989; 37: 1297-9.
• 60 Mei QB, Tao JY, Cui B. Advances in the pharmacological studies of radix Angelica sinensis (oliv) diels (Chinese danggui). Chin Med J 1991; 104: 776-81.
• 61 Chen SG, Li CC, Zhuang XX, Chen HZ, Shi GG. Protective effects of Angelica sinensis injection on myocardial ischemia/reperfusion injury in rabbits. Chin J Integrated Tradit West Med 1995; 15: 486-8.
• 62 Wang F, Qu L, Lu Q, Guo LJ. Effect of phenolic alkaloids from Menispermum dauricum on myocardial-cerebral ischemia-reperfusion injury in rabbits. Acta Pharmacol Sin 2001; 22: 1130-4.
• 63 Chan P, Huang WP, Liu JC, Chen YJ, Cheng JT. Changes in superoxide dismutase activity and mRNA in vivo after short-term supplementation with trilinolein in rats. Zhonghua Yi Xue Za Zhi (Taipei) 2000; 63: 355-60.
• 64 Chan P, Tomlinson B. Antioxidant effects of Chinese traditional medicine: focus on trilinolein isolated from the Chinese herb sanchi (Panax pseudoginseng). J Clin Pharmacol 2000; 40: 457-61.
• 65 Lo YC, Teng CM, Chen CF, Chen CC, Hong CY. Magnolol and honokiol isolated from magnolia officinalis protect rat heart mitochondria against lipid peroxidation. Biochem Pharmacol 1994; 47: 549-53.
• 66 Ramirez-Tortosa MC, Mesa MD, Aguilera MC, Quiles JL, Baro L, Ramirez-Tortosa CL, et al. Oral administration of a turmeric extract inhibits LDL oxidation and has hypocholesterolemic effects in rabbits with experimental atherosclerosis. Atherosclerosis 1999; 147: 371-8.
• 67 Ramirez-Bosca A, Soler A, Carrion MA, Diaz-Alperi J, Bernd A, Quintanilla C, et al. An hydroalcoholic extract of Curcuma longa lowers the apo B/apo A ratio implications for atherogenesis prevention. Mech Ageing Dev 2000; 119: 41-7.
• 68 OK, Lynn EG, Vazhappily R, Au-Yeung KKW, Zhu DY, Siow YL. Magnesium tanshinoate B (MTB) inhibits low density lipoprotein oxidation. Life Sci 2001; 68: 903-12.
• 69 Wu YJ, Hong CY, Lin SJ, Wu P, Shiao MS. Increase of vitamin E content in LDL and reduction of atherosclerosis in cholesterol-fed rabbits by a water-soluble antioxidant-rich fraction of Salvia miltiorrhiza. Arterioscler Thromb Vasc Biol 1998; 18: 481-6.
• 70 Niu XL, Ichimori K, Yang X, Hirota Y, Hoshiai K, Li M, Nakazawa H. Tanshinone II-A inhibits low density lipoprotein oxidation in vitro. Free Rad Res 2000; 33: 305-12.
• 71 Zhao BL, Jiang W, Zhao Y, Hou JW, Xin WJ. Scavenging effects of salvia miliorrhiza on free radicals and its protection for myocardial mitochondrial membranes from ischemia-reperfusion injury. Biochem Mol Biol Int 1996; 38: 1171-82.
• 72 Shao ZH, Vanden Hoek TL, Becker LB, Schumacker PT, Wu JA, Attele AS, et al. Extract from scutellaria baicalensis Georgi attenuates oxidant stress in cardiomyocytes. J Mol Cell Cardiol 1999; 31: 1885-95.
• 73 Gao Z, Huang K, Yang X, Xu HB. Free radical scavenging and antioxidant activities of flavonoids extracted from the radix of scutellaria baicalensis Georgi. Biochim Biophys Acta 1999; 1472: 643-50.
• 74 Shieh DE, Liu LT, Lin CC. Antioxidant and free radical scavenging effects of baicalein, baicalin and wogonin. Anticancer Res 2000; 20: 2861-5.
• 75 Lin TJ, Liu GT, Pan Y, Liu Y, Xu GZ. Protection by schisanhenol against adriamycin toxicity in rat heart mitochondria. Biochem Pharmacol 1991; 42: 1805-10.
• 76 Matsuda H, Ohta T, Kawaguchi A, Yoshikawa M. Bioactive constituents of Chinese natural medicines. VI. moutan cortex. (2): structures and radical scavenging effects of suffruticosides A,B,C,D and E and galloyl-oxypaeoniflorin. Chem Pharm Bull 2001; 49: 69-72.
• 77 Sato M, Maulik G, Bagchi D, Das DK. Myocardial protection by protykin, a novel extract of trans-resveratrol and emodin. Free Radic Res 2000; 32: 135-44.
• 78 Liebgott T, Miollan M, Berchadsky Y, Drieu K, Culcasi M, Pietri S. Complementary cardioprotective effects of flavonoid metabolites and terpenoid constituents of Ginkgo biloba extract (EGb 761) during ischemia and reperfusion. Basic Res Cardiol 2000; 95: 368-77.
• 79 Pietri S, Maurelli E, Drieu K, Culcasi M. Cardioprotective and anti-oxidant effects of the terpenoid constituents of Ginkgo biloba extract (EGb 761). J Mol Cell Cardiol 1997; 29: 733-42.
• 80 Guerra MC, Speroni E, Broccoli M, Cangini M, Pasini P, Minghett A, et al. Comparison between Chinese medical herb Pueraria lobata crude extract and its main isoflavone puerarin antioxidant properties and effects on rat liver CYP-catalysed drug metabolism. Life Sci 2000; 67: 2997-3006.
• 81 Jin XL, Shao Y, Wang MJ, Chen LJ, Jin GZ. Tetrahydroprotoberberines inhibit lipid peroxidation and scavenge hydroxyl free radicals. Acta Pharmacol Sin 2000; 21: 477-80.
• 82 Chen X. Cardiovascular protection by ginsenosides and their nitric oxide releasing action. Clin Exp Pharmacol Physiol 1996; 23: 728-32.
• 83 Hong CY, Wang CP, Lo YC, Hsu FL. Effect of flavan-3-ol tannins purified from Camellia sinensis on liquid peroxidation of rat heart mitochondria. Am J Chin Med 1994; 22: 285-92.
• 84 Chatterjee SS, Koch E, Jaggy H, Krzeminski T. In vitro and in vivo studies on the cardioprotective action of oligomeric procyanidins in a Crataegus extract of leaves and blooms. Arzneimittelforschung 1997; 47: 821-5.
• 85 Okubo T, Nagai F, Seto T, Satoh K, Ushiyama K, Kano I. The inhibition of phenylhydroquinone-induced oxidative DNA cleavage by constituents of Moutan Cortex and Paeoniae Radix. Biol Pharm Bull 2000; 23: 199-203.