Antiapoptotic potential of herbal drugs in cardiovascular disorders: An overview

Abstract

Cardiomyocyte apoptosis has been reported in a number of cardiovascular disorders, including myocardial infarction, ischemia–reperfusion, end-stage heart failure, arrhythmogenic right ventricular dysplasia, and adriamycin-induced cardiomyopathy. Prevention of myocyte apoptosis has emerged as a potential new target in a multimodel therapeutic approach to cardiac disease. Herbal therapy may be an alternative strategy for the prevention and treatment of heart disease. The present review summarizes the list of plants/herbal formulations studied for their antiapoptotic activity in cardiovascular disorders. However, despite extensive positive research data from experimental studies for herbal drugs in cardiovascular disorders, and the anecdotal clinical experience of many practitioners and patients, its potential in the field of cardiac apoptosis remains largely untapped, and large scale clinical trials are needed to explore the potential of herbal medicines as a new treatment regime for targeting cardiovascular apoptosis.

Keywords::

• Apoptosis
• herbal medicine
• cardiovascular disorders

Introduction

Cardiovascular disease, including heart attack, stroke, and heart failure, is the leading cause of disease and death in the developed world, and is poised to become a significant health problem worldwide. Cardiovascular disorders are one of the main causes related to sudden death in man. In 1990, ischemic heart disease became the leading cause of death worldwide, killing more than 3.8 million men and 3.4 million women annually (World Health Organization, 2004). More people die of atherosclerosis and its complications, such as stroke, myocardial infarction, and arrhythmias, than all other medical problems combined. In the past few decades many treatment strategies have been developed based on different pathomechanisms of cardiovascular disease, but the morbidity and mortality due to heart failure and its complications still remain a clinical reality (Colucci & Braunwald, 1997). Heart failure is a heterogeneous syndrome that can result from primary cardiomyopathies or, more commonly, myocardial infarction, hypertension, and valvular heart disease, among other disorders.

Herbal products have been used since the dawn of civilization to maintain human health and as remedies for various diseases by the vast majority of the world’s population (Bei et al., 2004; Myagmar et al., 2004). In recent years, there has been growing interest in complementary and alternative medicine (CAM) for cardiovascular health (Lin et al., 2001). There has been a major increase in their use in the last few years in the developed countries, including the United States, Germany, and France (Kamboj, 2000). India is sitting on a goldmine of well-recorded and well-practiced knowledge of tradition herbal medicine. The basic requirements for gaining acceptance in developed countries include well-documented traditional use, single-plant medicines, medicinal plants free from pesticides, heavy metals, etc., standardization based on chemical constituents and activity profile, and safety and stability (Kamboj, 2000).

The keen interest in medicinal plants for cardioprotection has increased recently because they possess numerous cardioprotective mechanisms in addition to their known antioxidant activity (Ai et al., 2002). Hence, these herbal extracts used traditionally need to be evaluated significantly, with an aim to define the role of these agents in limiting the deleterious effects of myocardial and reperfusion injury, by providing scientific data to validate their use as prophylactic approaches or as an adjunct to standard treatment (synthetic compounds employed in conventional treatment protocols) of myocardial ischemia–reperfusion injury.

Despite remarkable advances in medical therapy and revascularization procedures, free radical mediated injury is a potential threat to viable myocardium, and this may deny the patient the full benefit of reperfusion (Becker & Ambrosio, 1987). Furthermore, oxidative stress is a major apoptotic, i.e., programmed cell death, stimulus in myocardial ischemia and reperfusion, among other cardiovascular diseases (Buttke & Sandstrom, 1994). A compromised heart due to cardiac ischemia and/or reperfusion injury further leads to progressive loss of cardiomyocytes by apoptosis and poses an additional workload on the remaining viable myocytes, causing further deterioration of cardiac function and resulting in activation of pathological death signal pathways (Haunstetter & Izumo, 1998). It has been reported that these programmed cell death pathways can be inhibited by antioxidants (Galang & Sasaki, 2000).

During the last few years, there has been increasing evidence from human and animal models suggesting that apoptosis or programmed cell death could be a key modulator, especially in the transition from “compensatory” hypertrophy to heart failure (Bardales et al., 1996). Cardiomyocyte apoptosis has been documented as a pivotal form of cell death in ischemia and reperfusion damage, with several reports documenting apoptotic rates of 2–12% in the border zone of human myocardial infarcts (Olivetti et al., 2005). Taking these values into account, it is not hard to imagine that such dramatic loss of viable tissue can have a disastrous effect on the geometry and function of the left ventricle. Human failing hearts in New York Heart Association (NYHA) classes III–IV typically display apoptotic rates ranging anywhere between 0.12 and 0.70% (Olivetti et al., 1997; Kang & Izumo, 2000). In the myocardium, equal results have been obtained using both TUNEL (terminal transferase-mediated DNA nick-end labeling) and Taq polymerase assays (Leri et al., 1998).

An understanding of the physiology of apoptosis and its clinical implications is important, because the therapeutic options may improve the outcome of patients who have heart failure. In fact, the attenuation and prevention of apoptotic pathways are new modes of therapy for congestive heart failure that will be applied in clinical practice within the next decade. However, a better understanding of the apoptotic process in the myocardium is clearly important, as it may lead to the identification of novel therapeutic strategies.

Apoptotic pathways in heart

Apoptosis among cardiomyocytes was first reported by Gottlieb et al. (1994). Cardiomyocyte apoptosis in heart failure has been the topic of research in many recent studies. Cardiomyocyte apoptosis has been reported in a variety of cardiovascular diseases, including myocardial infarction, ischemia–reperfusion, end-stage heart failure, arrhythmogenic right ventricular dysplasia, and adriamycin-induced cardiomyopathy (Kumar & Jugdutt, 2003).

Apoptosis is a complex, multistep, biochemical process. Its morphological characteristics include plasma membrane blebbing, cell shrinkage, nuclear condensation, chromosomal DNA fragmentation, and formation of apoptotic bodies (Wyllie, 1997). Two major apoptotic pathways exists in cells, the “extrinsic” and “intrinsic” cascades. The “intrinsic” pathway utilizes mitochondria to propel cell death through opening of the mitochondrial permeability transition pore (MPTP) or rupture of the outer mitochondrial membrane, triggering the sudden and complete release of cytochrome c and other proteins from the intermembrane space of mitochondria into all other compartments of the cell. The “intrinsic” pathway is primarily activated in myocytes by cellular stimuli such as hypoxia, ischemia–reperfusion, and oxidative stress, which provoke the mitochondrial permeability transition, and increase permeability of the outer and inner mitochondrial membranes (Weiss et al., 2003). The “extrinsic” apoptotic pathway operates through the death receptor pathway, triggered by members of the death receptor superfamily, such as the Fas receptor or tumor necrosis factor receptor (TNFR).

The Bcl-2 family of proteins has emerged as a key regulatory component of the cell death process. The growing Bcl-2 family consists of death antagonists (Bcl-2, Bcl-xL) and death agonists (Bax, Bak), which function primarily to protect or disrupt the integrity of the mitochondrial membrane and control the release of (pro) apoptotic intermembrane proteins (Crow et al., 2004).

Recent studies have shown that methods based on the demonstration of caspase activation can be applied to detect apoptotic cells in tissue sections by light microscopy (Willingham, 1999). Measurement of the ratio of Bcl-2 to Bax illustrates the fate of apoptotic cell death. Specific DNA fragmentation at nucleosomal units is one of the most characteristic biochemical features of apoptosis. The major methods developed for the detection of DNA strand breaks involve the detection of 3′-OH ends of single-stranded DNA (in situ end-labeling; ISEL). The addition of labeled nucleotides to these ends, either using Escherichia coli polymerase (or its Klenow fragment) by in situ nick-translation (ISNT) or using TUNEL (Gavrieli et al., 1992), allows the cytochemical demonstration of free DNA strand ends.

Therapeutic implications: Apoptosis-targeted intervention

The discovery of apoptosis sheds a new light on the role of cell death in myocardial infarction and other cardiovascular diseases. There is mounting evidence that apoptosis plays an important role at multiple points in the evolution of myocardial infarction, and involves not only cardiomyocytes but also inflammatory cells, as well as cells of granulation tissue and fibrous tissue. Apoptosis, being a highly regulated process, is a potential target for therapeutic intervention.

Antiapoptotic therapeutic interventions offer an appealing platform for devising ways to retard the maladaptative growth associated with congestive heart failure. Numerous myocardial conditions and agents have been identified as inducers of cardiomyocyte apoptosis such as ischemia–reperfusion, cellular calcium overload, oxygen radicals, TNF-α, antinuclear factor (ANF), volume and pressure overload of cardiomyocytes, increased angiotensin-II levels, increased catecholamine levels, decreased coronary reserve, increased Fas ligand, increased p53 that lead to other cardiac disorders such as myocardial ischemia, myocardial infarction, dysrhythmias, contractile dysfunction, and cardiomyocyte apoptosis.

Caspase inhibitor zVAD.fmk (Yaoita et al., 1998; Armstrong et al., 2001), sodium-hydrogen exchanger inhibitors (Humphreys et al., 1999), poly (adenosine diphosphate ribose) synthetase inhibitors (Thiemermann et al., 1997), inhibitors of apoptosis proteins (Deveraux & Reed, 1999), up-regulation of insulin growth factor-1 (Li et al., 1997), ischemic preconditiong (Maulik et al., 1999), antioxidants (Oskarsson et al., 2000), TNF-α inhibitor (Krown et al., 1996), and cardiotrophin-1 (Sheng et al., 1997) are some of the most prominent antiapoptotic therapies, which are primarily investigational and without direct application to clinical practice.

Herbs used in cardiovascular disorders

Many herbal therapies have the potential of improving quality of life. Herbal therapies may be considered in the management of heart diseases. Herbal therapies should be integrated into the conventional care of patients with cardiovascular diseases. In the past decades, there has been a great increase in the use of complementary treatments such as herbal remedies in the treatment of diseases. Many traditional plants have been claimed to be useful for the control of problems due to ischemia and associated pathologies (Wu et al., 2007). Current estimates indicate that about 80% of people in developing countries still rely on traditional medicine, based largely on various species of plants and animals, for their primary healthcare because of better cultural acceptability, better compatibility with the human body, and fewer side effects. Thirty percent of the worldwide sales of drugs are based on natural products (Grabley & Thiericke, 1999). Commercially, these plant-derived medicines are worth about US$14 billion a year in the United States and $US40 billion worldwide (Wijesekara, 1991).

The use of herbal medicines among patients under cardiovascular pharmacotherapy is widespread. In one study, grape seed proanthocyanidins extract (GSPE) attenuated H₂O₂-induced oxidant stress in cardiomyocytes. Antioxidant action is associated with an increase in cardiomyocyte survival and contractile function. The extract had cardioprotective effects against reperfusion-induced injury by reducing or removing, directly or indirectly, free radicals in the myocardium of an isolated rat heart that was reperfused after ischemia (Wang et al., 2007). Another herb, green tea extract, has been shown to protect against cardiovascular and renal diseases in several in vitro and in vivo models (Stangl et al., 2006). Green tea catechins delay the oxidation reactions by inhibiting the formation of free radicals or interrupting the propagation of the free radical chain reaction caused by the toxic compounds. This protection attenuates the progress of atherosclerosis and thrombosis. Tea polyphenols act as antioxidants in vitro by scavenging reactive oxygen and nitrogen species and chelating redox-active transition metal ions (Wang et al., 2007).

In one study, Scutellaria baicalensis extract (SbE) and baicalein attenuated the oxidation of intracellular fluorescent probes in chick cardiomyocytes exposed to ischemia–reperfusion. A rapid antioxidant protection by baicalein in the cardiomyocyte model was observed. As the system is devoid of other sources of reactive oxygen species (ROS) such as neutrophils or endothelial cells, the reduction of fluorescence clearly indicates rapid intracellular scavenging by baicalein. It was postulated that the flavonoid structure and a low-molecular weight endow such molecules with intracellular antioxidant properties (Wang et al., 2007). In another study (Kitts et al., 2000), American ginseng extract showed antioxidant activity in both lipid-soluble and water-soluble media by chelating metal ions and directly scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radicals. In another study, ginsenosides extracted from American ginseng inhibited the activation of protein tyrosine kinase induced by ischemia–reperfusion, another antioxidant mechanism (Dou et al., 2001).

Table 1 summarizes a few herbal drugs used in cardiovascular disorders.

Table 1.  Herbal drugs used in cardiovascular disorders.

S. no.	Experimental model used	Herb/herbal formulation/active constituent	Type of heart disease	Mechanism of cardioprotection	Reference
1	Adriamycin (doxorubicin)-induced myocardial toxicity	Curcumin	Cardiomyopathy	Inhibition of lipid peroxidation, augmentation of endogenous antioxidants	Venkatesan, 1998
		p-Coumaric, a polyphenolic acid from tea, coffee, etc.	Myocardial ischemia	Decreased serum LDH and creatine phosphokinase (CPK) activities, reduced lipid peroxidation, increased antioxidant enzyme activities	Abdel-Wahab et al., 2003
		Ethanolic extract of Nardostachys jatamansi	Cardiovascular diseases	Decrease in serum and cardiac lipids (cholesterol, triglycerides, free fatty acids, and phospholipids), low density lipoproteins (LDL), very low density lipoproteins (VLDL), and rise in high density lipoproteins (HDL)	Subashini et al., 2007
		Ethanolic extract of Picrorhiza kurroa	Cardiomyopathy	Inhibition of rise in the levels of marker enzymes (alanine aminotransferase (ALT), aspartate amino-transferase (AST), lactate dehydrogenase (LDH), and creatine phoshokinase (CPK)) in plasma and lipid peroxidation in the heart tissue and concomitant decline in the level of reduced glutathione (GSH) and the activities of glutathione dependent antioxidant enzymes (GPx and GST) and antiperoxidative enzymes (SOD and CAT)	Rajaprabhu et al., 2007
		Butanolic fraction of Terminalia arjuna bark (TA-05)	Cardiovascular diseases	Increased cardiac antioxidant enzymes, decreased in serum CK-MB levels, and reduced lipid peroxidation as compared to Dox-treated animals. Decreased Dox-induced histological alteration such as mitochondrial swelling, Z-band disarray, focal dilatation of smooth endoplasmic reticulum (SER), and lipid inclusions	Singh et al., 2008
		Panax notoginseng saponins (PNS) of Panax notoginseng, a traditional Chinese herb	Cardiovascular diseases	Decreased levels of serum LDH, CK, and CK-MB, minimal morphological changes in hearts, and normalization of myocardial superoxide dismutase, glutathione peroxidase, and catalase activities	Liu et al., 2008
2	Open-chest anesthetized rat model of myocardial ischemia–reperfusion injury	Magnolol, an active component from the Chinese medicinal herb Magnolia officinalis	Cardiovascular diseases	Suppressed the incidence of ventricular fibrillation and mortality, reduced the total duration of ventricular tachycardia and ventricular fibrillation, reduction in infarct size, reduced superoxide anion production and myeloperoxidase activity, in vitro studies of magnolol suppressed N-formylmethionyl-leucyl-phenylalanine (fMLP)-activated human neutrophil migration	Lee et al., 2001
		Tetramethylpyrazine (TMP), an active ingredient of Chinese medicinal herb, Ligusticum wallichii Franchat	Myocardial ischemia	Reduction in infarct size, induced HO-1 expression in ischemic myocardium, and suppressed fMLP (800 nM)-activated human neutrophil migration and respiratory burst	Chen et al., 2006
3	Myocardial ischemia–reperfusion injury	Curcuma longa	Myocardial infarction	Suppression of oxidative stress	Mohanty et al., 2004a
		Schisandrin B (Sch B), ingredient isolated from Schisandra chinensis	Hepatic and cardiac diseases	Induction of Hsp25 and Hsp70 expression contributed to the cardioprotection	Chiu and Ko, 2004
		Dang-Gui Buxue Tang (DBT, a decoction of Astragali and Angelica roots) and its component herb extracts	Myocardial infarction	Enhancement of myocardial mitochondrial as well as red blood cell (RBC) glutathione status, increasing resistance to oxidative stress-induced	Mak et al., 2006
		Euryale ferox (fox nut or gorgon nut)	Myocardial ischemia	Increased amounts of thioredoxin-1 (Trx-1) and thioredoxin-related protein-32 (TRP32), potent reactive oxygen species scavenging activities	Das et al., 2006
		Salvia miltiorrhiza (SM) herb extracts	Myocardial ischemia	Reduced production of 15-F2t-isoprostane, a specific index of oxidative stress-induced lipid peroxidation, during ischemia, optimal post-ischemic myocardial functional recovery, reduced myocardial infarct size	Nie et al., 2007
		Alcoholic extract of Terminalia arjuna	Myocardial ischemia	Reduction in TBARS, and rise in SOD, GSH, catalase, induced myocardial HSP72, and augmented myocardial endogenous antioxidants	Gauthaman et al., 2008
4	Left coronary artery ligation	Salvia miltiorrhiza	Acute myocardial infarction	Antioxidant, inhibition of lipid peroxidation, prevention of DNA damage	Sun et al., 2005
		Puerarin (isolated from Pueraria lobata Ohwi) and Danshensu (isolated from the Chinese herb, Salvia miltiorrhiza)	Acute myocardial ischemia	Antioxidant, anti-lipid peroxidation	Wu et al., 2007
		Shu-Mai-Tang (mixture of seven medicinal components: Astragalus mongholicus Bunge, Salvia miltiorrhiza Bge, Eupolyphaga sinensis Walker, Trichosanthes kirilowii Maxim, Panaxpseudo ginseng N. Wallich, Hirudo nipponica Whitman, and Moschus berezovskii	Ischemic heart diseases	Decreased myocardial fibrosis, phospho-p38 MAPK, TIMP-1, and TNFα proteins, and serum TNFα level, accompanied by improved cardiac function	Yin et al., 2008
5	Isoproterenol-induced myocardial infarction	Test drug (Lipistat) comprising equal proportions of extracts of Terminalia arjuna, Inula racemosa Hook, latex of Commiphora mukul	Ischemic heart diseases	Prevention of loss of myocardial high energy phosphates (HEP) stores and accumulation of lactate content, confirmed by histopathology	Seth et al., 1998
		Hydro-alcoholic extract of Withania somnifera	Cardiovascular diseases	Augmentation of endogenous antioxidants, maintenance of the myocardial antioxidant status, and significant restoration of most of the altered hemodynamic parameters	Mohanty et al., 2004b
		Garlic oil (Allium sativum)	Myocardial necrosis	Decreased iron content with a significant increase in plasma iron binding capacity, ceruloplasmin activity, and glutathione (GSH) level, decrease in lipid peroxide levels and increase in antioxidant enzyme activities, e.g., superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST), and glutathione reductase (GRD)	Saravanan & Prakash, 2004
		Aegle marmelos extract	Myocardial infarction	Decreased levels of CK, LDH, TBARS, HP and other lipids and lipoprotein levels with subsequent increase in the level of HDL cholesterol	Rajadurai & Prince, 2005
		Ocimum sanctum	Ischemic heart diseases	Augmentation of basal endogenous antioxidants, suppression of oxidative stress, improved ventricular function	Arya et al., 2006
		Ferulic acid (from carrot, tomato, wheat, etc.)	Atherosclerosis	Reduced triglycerides, total cholesterol, free fatty acids, free and ester cholesterol in both serum and cardiac tissue	Yogeeta et al., 2006
		Ethanolic extract of Zingiber officinale	Myocardial injury	Increased the levels of endogenous myocardial antioxidants (catalase, superoxide dismutase, and tissue glutathione), decreased the levels of serum marker enzymes (lactate dehydrogenase, creatine kinase, aspartate transaminase, and alanine transaminase), and increased myocardial lipid peroxides, confirmed by histological examination	Ansari et al., 2006
		Total flavonoids of Fructus chorspondiatis (TFFC), a potential effective component from Chorspomias axillaries Batt et Hill, a well-known Chinese herb	Angina pectoris	Inhibited the up-regulated serum level of creatine kinase and lactate dehydrogenase, increased a potent tissue protective polypeptide, transforming growth factor β1 (TGF-β1) level as well as its receptors TβRI and TβRII, and inhibited the expression of a redox-sensitive transcription factor, nuclear factor κB (NF-κB)	Ao et al., 2007
		Alcoholic extract of T. chebula	Myocardial injury	Decrease in the level of lactate, decrease in enzyme activities of tricarboxylic acid cycle (TCA), mitochondrial respiration, levels of adenosine triphosphate (ATP), and oxidative phosphorylation as compared to ISO-treated group. Further confirmed by electron microscope studies	Suchalatha et al., 2007
		Hydro-alcoholic lyophilized extract of Bacopa monneira (Bm)	Myocardial necrosis	Restoration of endogenous antioxidant defense (SOD, CAT, GSH, GSHPx), myocardial LDH, and CK-MB and decreased MDA, reconfirmed by histopathological and ultrastuctural finidngs	Nandave et al., 2007
		Grape seed proanthocyanidins	Myocardial injury	Maintained levels of the marker enzymes (AST, ALT, LDH, and CK), no significant change in the basal levels of myocardial TBARS, GST, SOD, and CAT on administration of GSP when compared to ISO-injected rats	Karthikeyan et al., 2007
		Ethanolic extract of Momordica cymbalaria	Myocardial injury	Reduced elevation of serum marker enzymes, lactate dehydrogenase (LDH), creatinine kinase-MB fraction (CK-MB), aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP) and alterations in oxidative stress markers such as lipid peroxidase (LPO), glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD), confirmed by histological findings	Raju et al., 2008
		Hydro-alcoholic extract of Tribulus terresris Linn.	Myocardial infarction	Increased activities of SOD, CAT, GSHPx, tissue GSH, inhibition of lipid peroxidation. Decreased CK-MB, LDH enzymes, correction of mean arterial pressure, heart rate, LVEDP, preservation of histoarchitectural and ultrastructural alteration	Ojha et al., 2008
		Astragali radix, Chinese medical herb	Myocardial infarction	Antioxidant property and partial prevention of changes in protein and gene expression of cardiac sarcoplasmic reticulum Ca^2+ regulatory proteins mediated through the cAMP pathway	Xu et al., 2008
		Curcumin	Myocardial infarction	Decreased serum lactate dehydrogenase, creatine kinase, aspartate transaminase, alanine transaminase, and myocardial lipid peroxide levels and increased levels of myocardial endogenous antioxidants (superoxide dismutase, catalase, and tissue glutathione), confirmed by histological examination	Ansari et al., 2008
6	Zucker diabetic fatty (ZDF) rats model and ngiotensin II-stimulated embryonic rat heart-derived H9c2 cells and neonatal rat cardiac fibroblasts model	Salacia oblonga (SOE) water extract, an ayurvedic medicine and its prominent component mangiferin (MA)	Antidiabetic and antiobesity medicine, obesity- and diabetes-associated cardiac hypertrophy	SOE-treated ZDF rats showed less cardiac hypertrophy (decrease in weights of the hearts and left ventricles and reduced cardiomyocyte cross-sectional areas), suppressed cardiac overexpression of ANP, brain natriuretic peptide (BNP) and AT(1) mRNAs and AT(1) protein in ZDF rats. SOE and MA suppressed angiotensin II-induced ANP mRNA overexpression and protein synthesis in H9c2 cells and also inhibited angiotensin II-stimulated [^3H]thymidine incorporation by cardiac fibroblasts	Huang et al., 2007
7	Angiotensin II-induced proliferative and hypertrophic response in cardiac fibroblast	Resveratrol, extracted from root of the rhizoma Polygoni cuspidate	Cardiovascular diseases	Increased nitric oxide (NO) and nitric oxide synthase (NOS) levels in culture medium, increased intracellular cyclic GMP (cGMP) level in cardiac fibroblasts, and decreased ANP and BNP levels in culture medium	Wang et al., 2007
8	Phenylephrine-induced cardiac hypertrophy in neonatal rat ventricular myocytesCardiac hypertrophy induced by aortic banding and phenylephrine infusion	Curcumin	Cardiac hypertrophy	Abrogation of histone acetylation, GATA4 acetylation, DNA-binding activity through blocking p300-HAT activity. Disruption of p300-HAT-dependent signaling pathways and downstream GATA4, NF-κB, and TGF-α–Smad signaling pathways.	Li et al., 2008

Herbs with antiapoptotic potential in cardiovascular disorders

The consequence of myocardial infarction is excessive cell death. It is patent that preventing cell death is a potential target for therapeutic intervention. Although several potential therapeutic agents have been tested in animal models of ischemia–reperfusion heart injury with some success, nearly none of the specific antiapoptotic agents have reached the stage of clinical research.

Table 2 summarizes the list of plants/herbal formulations studied for their antiapoptotic activity in cardiovascular disorders.

Table 2.  Plants studied for antiapoptotic potential in cardiovascular disorders.

Name of herb	Component/part used	Dose	Model	Therapeutic use reported	Parameters estimated	Inference	Reference
Elsholtzia blanda (Benth.) Benth., a traditional Chinese medicine	Total flavones	100 mg/kg p.o., 200 mg/kg p.o.	Coronary occlusion model of myocardial infarction in rats	Acute myocardial ischemia, coronary heart disease, hepatitis, dysentery, gastroenteritis, pyelonephritis	Serum creatine kinase-MB, infarct size determination, in situ detection of cell death, DNA fragme-ntation, TUNEL assay, Western blot assay of Bcl-2 and Bax proteins	Reduction in CK-MB activity, reduction of TUNEL positive cells, absence of DNA-laddering, decreased infarct, greater Bcl-2 and attenuated Bax expression	Ling & Lou, 2005
Perilla frutescens	Rosmarinic acid (RA), a natural polyphenolic component	H9c2 cardiac muscle cells exposed to RA (20 µg/ml)	ADR-induced apoptosis in H9c2 cardiac muscle cells	Antioxidant and anti-inflammatory	Western blot analysis,caspase-3 activity, cytoflu-orometric asses-sment of mitoc-hondrial membrane potential, DCFDA assay, electrophoretic mobility shift assay, total gluta-thione measurement in ADR-treated H9c2 cells	RA reversed the down-regulation of GSH, SOD, Bcl-2, activated c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK), transcri-ptional factor-activator-protein (AP)-1	Kim et al., 2005
Ocimum sanctum, and Curcuma longa	Hydro-alcoholic lyophilized extract of Ocimum sanctum and aqueous extract of Curcuma longa	75 mg/kg p.o. (Ocimum sanctum) and 100 mg/kg p.o. (Curcuma longa)	Ischemia reperfusion (IR) model of myocardial injury	Wound healing, urinary tract infections, liver ailments, adatogenic, antioxidant (Curcuma longa); cardiovascular disorders, diabetes, asthma (Ocimum sanctum)	Hemodynamic variables, immun-ostaining for the localizationof Bax and Bcl-2 proteins, TUNEL assay, histopathological studies	Chronic treatment with Curcuma longa signifi-cantly reduced TUNEL positivity, Bax protein, and up-regulated Bcl-2 and demonstrated mitigating effects on several myocardial injury-induced hemo-dynamic ((+)LVdP/dt, (–) LVdP/dt and LVEDP) and histop-athological perturbations. Chronic Os treatmentresulted in modest modulation of the hemodynamic alterations (MAP, LVEDP) but failed to demo-nstrate any significant antia-poptotic effects and prevent the histo-pathological alterations	Mohanty et al., 2006
Ocimum sanctum, Withania somnifera, and Curcuma longa	Combination of herbal extracts of Ocimum sanctum, Withania somnifera, and Curcuma longa (HCB)	Ocimum sanctum (75 mg/kg), Withania somnifera (50 mg/kg), and Curcuma longa (100 mg/kg) orally	Left anterior descending coronary artery (LAD) ischemia and reperfusion (IR) experimental model	Wound healing, urinary tract infections, liver ailments, adatogenic, antioxidant (Curcuma longa); immuno-modulatory, adatogenic, antioxidant, hypoglycemic, anticancer (Withania somnifera); cardiovascular disorders, diabetes, asthma (Ocimum sanctum)	Hemodynamic variables, biochemical parameters (MDA assay, GSH, GSHPx, SOD, CAT, CPK), histopathological studies, immun-ostaining for the localization of Bax and Bcl-2 protiens, TUNEL assay	Reduced the surrogate preload marker LVEDP, improved inotropic and lusitropic function of the heart, increased GSH content, SOD, CAT, GSHPx, decreased TBARS, decreased Bax, up-regulated Bcl-2 expression, and attenuated TUNEL positivity	Mohanty et al., 2007
Dracocephalum rupestre Hance, a Chinese traditional herb	Naringenin-7-O-glucoside, the main active constituent	H9c2 cells treated with naringenin-7-O-glucoside (10, 20, 40, 80 µM)	Doxorubicin-induced apoptosis in H9c2 cells	Therapeutic potential for cardiovascular diseases	DNA fragmentation assay, MTT assay, flow cytometric detection, reverse transcriptase-polymerase chain reaction (RT-PCR), Western blot analysis	Enhanced cardiomyocyte proliferation relative to that of doxorubicin, incre-ased the protein levels of heme oxygenase-1 (HO-1) and Bcl-2 in cardiomyocytes (as detected by Western blotting), and suppressed the mRNA expression of caspase-3 and caspase-9 (as detected by RT-PCR)	Han et al., 2008
Danshen (Chinese herb, Radix salvia miltiorrhiza)	Tanshinone IIA (TSN), a major lipid-soluble pharmacologic constituent	Cultured cardiomyocytes treated with tanshinone IIA (0.5–2 µmol/L)	Adriamycin (ADR)-induced apoptosis in neonatal rat cardiomyocytes	Cardiovascular diseases, including coronary heart diseases, hypertension, and chronic heart failure	3-(4,5-Dimethyl thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, Hoechst staining, and flow cytometry, fluorescent probes 2,’7′-dichlorofluorescein diacetate and dihydroethidium detection, Western blotting	Reduced ratio of Bcl-2/Bax, increased cell viability, reduced oxidant production	Gao et al., 2008
Withania somnifera	Purified extract (1.5% withanolides)	300 mg/kg orally	Doxorubicin-induced apoptosis in rats	Cardioprotective, reduces myelosuppression and urotoxicity, chemopreventive	Biochemical estimation (AST, CAT, SOD, lipid peroxidation, MPO, total antioxidant capacity, TBARS, calcium level determination), histopathology, TUNEL assay, immunohistochemical analysis of Bcl-2	Attenuation of doxorubicin-induced biochemical and histochemical alterations, decreased the number of Bcl-2 positive cells in doxorubicin-treated group	Hamza et al., 2008
Ginkgo biloba	Ginkgo biloba extract (EGb) 761	EGb761 (25 µg/mL) (in vitro), 5 mg/kg i.p. (in vivo)	Doxorubicin-induced cardiac toxicity in vitro and in vivo	Cytoprotective	p53 mRNA, Bcl-2 family protein expression, mitochondrial membrane potential	Suppressed p53 mRNA expression, Bcl-2 family protein disbalance, improved disrupted mitochondrial membrane potential, and precipitated mitochondrion-dependent apoptotic signaling, reduced apoptotic cell death, and improved viability of cardiomyocytes	Liu et al., 2008
Epimedium, a traditional Chinese herb	Ethanol extract of Epimedium (EPI-ext)		Isoproterenol-induced congestive heart failure (CHF) in rats	Coronary heart disease, impotence, and osteoporosis	Cardiac morphometric and hemodynamic parameters, serum levels of tumor necrosis factor α, norepinephrine, angiotensin II, and brain natriuretic peptide, expression of matrix metalloproteinase-2 and -9, Bcl-2/Bax axle	Reversed changes of cardiac morphometric and hemodynamic parameters, decresed serum levels of tumor necrosis factor α, norepinephrine, angiotensin II, and brain natriuretic peptide, improved histological changes including cardiocyte hypertrophy, cadiocyte degeneration, inflammatory infiltration, and cardiac desmoplasia. Blocked the expression and activities of matrix metalloproteinase-2 and -9, regulated Bcl-2/Bax axle	Song et al., 2008

Turmeric [Curcuma longa, Linn. (Zingiberaceae)], a common Indian dietary pigment and spice, has been shown to possess a wide range of therapeutic utilities in traditional medicine. The active component of turmeric, identified as curcumin, exhibits a variety of pharmacological effects including adatogenic, antioxidant, anti-inflammatory, and anti-infective (Dikshit & Rastogi, 1995). Its role in wound healing, urinary tract infections, and liver ailments is well documented (Dixit & Jain, 1998). In one study, the cardioprotective potential of Curcuma longa (Cl) was evaluated in the ischemia–reperfusion (IR) model of myocardial infarction (MI) (Mohanty et al., 2004b). Cl treatment resulted in restoration of the myocardial antioxidant status and altered hemodynamic parameters as compared to control IR. Furthermore, IR-induced lipid peroxidation was significantly inhibited by Cl treatment. The beneficial cardioprotective effects also translated into the functional recovery of the heart.

Ocimum sanctum, Linn. (Labiateae), commonly known as Tulsi in India, is a local herb. The ancient systems of medicine including Ayurveda, Greek, Roman, Siddha, and Unani have mentioned its therapeutic application in cardiovascular disorders, diabetes, and asthma (Devi & Ganasoundari, 1999). It contains potent antioxidant flavanoids (orientin, vicenin) and phenolic compounds (eugenol, cirsilineol, apigenin) (Gupta et al., 2002). The cardioprotective potential of Ocimum sanctum (Os) was measured in isoproterenol-induced myocardial infarction in rats (Sharma et al., 2001). Os at the dose of 25, 50, 75, and 100 mg/kg significantly reduced glutathione (GSH), superoxide dismutase (SOD), and lactate dehydrogenase (LDH) levels. It also inhibited lipid peroxidation as observed by the reduced thiobarbituric acid reactive substances (TBARS) levels (Sharma et al., 2001). Os may be of therapeutic and prophylactic value in the treatment of MI.

Withania somnifera (L.) (Solanaceae), most commonly known as Ashwagandha, has been a valuable drug in Ayurveda, the ancient Indian system of medicine. Administration of Withania extract was found to reduce the myelosuppression (Davis & Kuttan, 1998) and urotoxicity (Davis & Kuttan, 2000) induced by antineoplastic agents such as cyclophosphamide in mice. Although its therapeutic potential on account of its immunomodulatory, adaptogenic, hypoglycemic, and anticancer activities are reported, very few studies assessing its cardioprotective potential are currently available (Dhuley, 2000). The cardioprotective effects of Withania have also been documented against myocardial damage induced by strophanthin-K (Dhuley, 2000) and by isoproterenol (Mohanty et al., 2004b) in different animal models. Augmentation of endogenous antioxidants, maintenance of the myocardial antioxidant status, and significant restoration of most of the altered hemodynamic parameters contributed to its cardioprotective effect (Mohanty et al., 2004b). Withania roots have also shown a specific chemopreventive efficacy against skin carcinogenesis in mice (Padmavathi et al., 2005). In one study, the effect of Curcuma longa (Cl) and Ocimum sanctum (Os) on myocardial apoptosis and cardiac function was studied in an ischemia and reperfusion (IR) model of myocardial injury. Chronic treatment with Cl significantly reduced TUNEL positivity and Bax protein and up-regulated Bcl-2 expression in comparison to the control IR group. In addition, Cl demonstrated mitigating effects on several myocardial injury-induced hemodynamic [(+) LVdP/dt, (–) LVdP/dt and LVEDP] and histopathological perturbations. Chronic Os treatment resulted in modest modulation of the hemodynamic alterations (MAP, LVEDP) as compared to the control IR group. There was significant cardioprotection, and functional recovery demonstrated by Cl may be attributed to its antiapoptotic property (Mohanty et al., 2006).

In another study, the efficacy of the combination of herbal extracts of Ocimum sanctum, Withania somnifera, and Curcuma longa (HCB) in an open chest left-anterior descending coronary artery (LAD) ischemia and reperfusion (IR) experimental model was evaluated (Mohanty et al., 2007). In addition, to understand the underlying mechanism of their beneficial therapeutic effects, various hemodynamic, immunohistochemical, and biochemical parameters were studied. HCB treatment significantly reduced the surrogate preload marker left ventricular end diastolic pressure (LVEDP) and improved inotropic and lusitropic function of the heart. It increased GSH content, SOD, catalase (CAT), and glutathione peroxidase (GSHPx), decreased TBARS, decreased Bax, up-regulated Bcl-2 expression, and attenuated TUNEL positivity. Cardioprotection by HCB treatment was attributed to its favorable hemodynamic effects, and myocardial adaptogenic, antioxidant, and antiapoptotic properties (Mohanty et al., 2007).

In recent years, Chinese medicinal herbs and their extracts have received great attention in the prevention of acute myocardial infarction (AMI). Rosmarinic acid (RA), a natural phenolic, is found in many Lamiaceae herbs, such as Perilla frutescens Linn., sage, basil, and mint. The medicinal value of RA has been well recognized, especially in regard to its antioxidant and anti-inflammatory activities (Ito et al., 1998). RA has been reported to inhibit complement-dependent inflammatory processes (Zupko et al., 2001) and may have therapeutic potential (al-Sereiti et al., 1999). The inhibitory effect of RA on adriamycin (ADR)-induced apoptosis in H9c2 cardiac muscle cells at a mechanistic level was evaluated. In vitro, ADR significantly decreased the viabilities of H9c2 cells, and this was accompanied by apoptotic features, such as a change in nuclear morphology and caspase protease activation. RA was found to markedly inhibit these apoptotic characteristics by reducing intracellular ROS generation and by restoring the mitochondria membrane potential (Dc) (Kim et al., 2005).

Elsholtzia blanda (Benth.) Benth. (TFEB) (Lamiaceae) is a traditional Chinese medicine used for Xiong-Bi symptoms, which in traditional Chinese medicine refers to the syndromes of coronary heart disease. Total flavones from Elsholtzia blanda (TFEB) significantly reduced the infarct size in canine models with coronary occlusion, which was confirmed by lower serum activity of creatine kinase-MB (CK-MB); TFEB produced a marked and progressive vasorelaxation effect on the coronary artery; TFEB reversed hemodynamic compromise as evidenced by ±(dp/dt)max and LVEDP (Ling et al., 2004). Lou et al. (2003a) found that TFEB significantly decreased the infarct size in coronary ligated rats and reversed the elevated T amplitude of the electrocardiogram (ECG) in rats with AMI induced by intravenous pituitrin (Lou et al., 2003b). The anti-ischemic effect of total flavones from Elsholtzia blanda was evaluated in a coronary occlusion model of myocardial infarction in rats. In the study, treatment with TFEB was found to be related to an up-regulated level of the antiapoptotic protein, Bcl-2, and a down-regulated pro-apoptotic protein, Bax, suggesting that TFEB exhibited an inhibitory effect on apoptotic cell death due to myocardial ischemia through modulation of the Bcl-2 family (Ling & Lou, 2005).

The Chinese traditional medicine Dracocephalum rupestre Hance (Lamiaceae), a wild perennial herb found throughout western China, is a rich resource of flavonoids (Wu & Li, 1977). Some research groups have reported that flavonoids exhibit protective effects against cardiomyopathy and cardiomyocyte apoptosis induced by doxorubicin (Hüsken et al., 1995; Bagchi et al., 2003). Flavonoids, a group of polyphenols, possess potent cardioprotective efficacy and significantly reduce the risk of cardiovascular disease (Peluso, 2006; Bast et al., 2007). Therefore, it has therapeutic potential for cardiovascular diseases. Naringenin-7-O-glucoside (10, 20, and 40 μM) greatly decreased the loss of cell viability and significantly attenuated doxorubicin-induced H9c2 cell apoptosis. Furthermore, naringenin-7-O-glucoside increased the protein levels of heme oxygenase-1 (HO-1) and Bcl-2 in cardiomyocytes (as detected by Western blotting) and suppressed the mRNA expression of caspase-3 and caspase-9 (as detected by reverse transcriptase-polymerase chain reaction (RT-PCR)). The results suggested that naringenin-7-O-glucoside had protective effects against doxorubicin-induced apoptosis (Han et al., 2008).

Danshen (Radix Salvia miltiorrhiza), which is a well known traditional Chinese herb, has been used frequently in China for the treatment of cardiovascular diseases, including coronary heart disease, hypertension, and chronic heart failure. Tanshinone IIA (TSN), which is one of the major lipid-soluble pharmacologic constituents of Danshen, is the most abundant form of tanshinone extracted from Danshen and possesses the most characteristic structure. TSN has antioxidative properties and can protect against oxidative stress in vitro and in vivo (Lin et al., 2006; Meng et al., 2006). In another study, TSN attenuated atherosclerotic calcification by inhibition of oxidative stress in a rat model (Tang et al., 2007). The effect of tanshinone IIA on ADR-induced apoptosis in neonatal rat cardiomyocytes was examined. Tanshinone IIA (2 µmol/L) markedly attenuated ADR-induced reactive oxygen species production. Western blotting revealed that tanshinone IIA prevented the ADR-mediated reduction of the ratio of Bcl-2/Bax. Tanshinone IIA significantly inhibited ADR-induced cardiomyocyte apoptosis in a dose dependent manner (Gao et al., 2008).

Antioxidant herbs: Potential target for apoptosis in cardiovascular disorders

Reactive oxygen species (ROS) generated by disturbance of the oxidation/reduction state of the cell have been implicated in the pathogenesis of various vascular diseases, cancer, and neurodegenerative disorders (Cooke et al., 2003; Madamanchi et al., 2005). The intervention of oxidative damage using compounds with antioxidant properties may therefore relieve or prevent diseases in which oxidative stress is a primary causal factor. Herbs are found to be a potent source of natural antioxidants. Some have been used for thousand of years, and their clinical and pharmacological effects have been extensively studied from various view-points (Scartezzini & Speroni, 2000; Govindarajan et al., 2003).

Induction of apoptosis is implicated in myocardial IR injury among other cardiovascular diseases (MacLellan & Schneider, 1997; Haunstetter & Izumo, 1998). Various studies have demonstrated that not only ROS per se, but also their oxidation products and other secondary messenger molecules generated by ROS, can trigger the programmed cell death (Buttke & Sandstrom, 1994). It has been reported that these programmed cell death pathways can be inhibited by antioxidants (Hockenbery et al., 1993; Cook et al., 1999). Leading the way in the new understanding is the discovery of herbs as potent free-radical scavengers: antioxidants (Pinn, 2000). Evidence of deleterious effects of free radicals in the pathophysiology of ischemic heart disease (IHD) is clear and indisputable (Burton et al., 1984). IHD is perhaps one of the human conditions in which the role of oxidative stress has been extensively investigated. The free radicals and consequent expression of oxidative damage have been demonstrated during post-ischemic–reperfusion injury in humans. The protective role of antioxidants has been validated in several experimental studies addressing the pathophysiology of acute ischemia (Dhalla et al., 2000). The multitude of free radicals generated during oxidative stress associated with isoproterenol (ISP)-induced myocardial necrosis can damage every major cellular component, including carbohydrate, membrane lipids, protein, and DNA (Downye, 1990). Extensive studies show that myocardial ischemia and reperfusion are associated with increased generation of ROS (Bernier et al., 1986). These oxygen free radicals may result in depression in contractile function, arrhythmias, depletion of the endogenous antioxidant network, and membrane permeability changes resulting in an increase in myocardial malondialdehyde (MDA) content (Curello et al., 1986). Oxidative stress may also depress the sarcolemmal Ca²⁺ transport and result in the development of intracellular Ca²⁺ overload and heart dysfunction (Tappia et al., 2001). There is comprehensive experimental and clinical evidence that antioxidants attenuate the myocardial injury following myocardial infarction (Hearse, 1991; Bernier et al., 1989). Several medicinal plants have been reported to possess strong antioxidant activity, and their health benefits have been suggested to be related to their antioxidant activity (Fugh-Berman, 2000).

However, there are few studies addressing the inhibition of apoptosis by herbal drugs and the effects on myocardial contractility. Since apoptosis is a genetically regulated process, hence, a better understanding of the cellular mechanisms that control apoptosis could lead to defining novel and effective therapeutic strategies to limit the amount of tissue damage in patients with MI (MacLellan & Schneider, 1997; Haunstetter & Izumo, 1998).

Discussion

Apoptosis or programmed cell death is a genetically regulated, cellular suicide response that plays a pivotal role in a variety of homeostatic and pathological processes. It is a normal phenomenon in the development and health of multicellular organisms (Ribble et al., 2005). Cardiomyocyte apoptosis is a precisely orchestrated process that is hard-wired into all metazoan cells.

The prevention of myocyte apoptosis has emerged as a potential new treatment approach for cardiac disease. Although the molecular biology of apoptosis in general and myocyte apoptosis in particular allows for the definition of potential antiapoptotic targets, there are still several open questions that need to be addressed. In addition, the safety and side effects of chronic antiapoptotic treatment remain a major concern. Keeping the concerns associated with chronic inhibition of apoptosis in mind, an antiapoptotic approach for cardiac disease still figures among the most attractive future therapeutic options for cardiac disease.

Antiapoptotic pharmaceutical agents have the highest potential to become clinically important as a therapeutic option. These medications could be administered preoperatively as an adjunct to the priming solution of the cardiopulmonary circuit or intraoperatively as an adjunct to the cardioplegic solution. However, the safety and long-term consequences of these therapies have not been adequately investigated. The prevention or attenuation of cardiocytic apoptosis is a very appealing therapeutic goal in the treatment of congestive heart failure, and as we accumulate more data, the spectrum of therapeutic methods will widen. It is vital for physicians to understand the available treatment options and to incorporate them to the best possible extent into the practice of modern heart failure medicine and surgery.

Herbal medicine is increasingly gaining greater acceptance from the public and medical profession due to greater advances in the understanding of the mechanisms by which herbs positively influence health and quality of life (Fugh-Berman, 2000). It is apparent that experimental evaluation of herbal drugs for the treatment of cardiovascular diseases is rather impressive, but very few have reached clinical trials and still fewer have been marketed. Hence, pharmacologists need to take more active interest in the evaluation of herbal drugs for potential antiapoptotic activity and their standardization to allow them to be clinically effective and globally competitive.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.