Plant-derived drugs acting on cellular Ca2+ mobilization in vascular smooth muscle: tetramethylpyrazine and tetrandrine

Design and Comprehensive Characterization of Tetramethylpyrazine (TMP) for Targeted Lung Delivery as Inhalation Aerosols in Pulmonary Hypertension (PH): In Vitro Human Lung Cell Culture and In Vivo Efficacy

This is the first study reporting on the design and development innovative inhaled formulations of the novel natural product antioxidant therapeutic, tetramethylpyrazine (TMP), also known as ligustrazine. TMP is obtained from Chinese herbs belonging to the class of Ligusticum. It is known to have antioxidant properties. It can act as a Nrf2/ARE activator and a Rho/ROCK inhibitor. The present study reports for the first time on the comprehensive characterization of raw TMP (non-spray dried) and spray dried TMP in a systematic manner using thermal analysis, electron microscopy, optical microscopy, and Raman spectroscopy. The in vitro aerosol dispersion performance of spray dried TMP was tested using three different FDA-approved unit-dose capsule-based human dry powder inhaler devices. In vitro human cellular studies were conducted on pulmonary cells from different regions of the human lung to examine the biocompatibility and non-cytotoxicity of TMP. Furthermore, the efficacy of inhaled TMP as both liquid and dry powder inhalation aerosols was tested in vivo using the monocrotaline (MCT)-induced PH rat model.

Hernandezine, a novel AMPK activator induces autophagic cell death in drug-resistant cancers

Drug resistance hinder most cancer chemotherapies and leads to disease recurrence and poor survival of patients. Resistance of cancer cells towards apoptosis is the major cause of these symptomatic behaviours. Here, we showed that isoquinoline alkaloids, including liensinine, isoliensinine, dauricine, cepharanthine and hernandezine, putatively induce cytotoxicity against a repertoire of cancer cell lines (HeLa, A549, MCF-7, PC3, HepG2, Hep3B and H1299). Proven by the use of apoptosis-resistant cellular models and autophagic assays, such isoquinoline alkaloid-induced cytotoxic effect involves energy- and autophagy-related gene 7 (Atg7)-dependent autophagy that resulted from direct activation of AMP activated protein kinase (AMPK). Hernandezine possess the highest efficacy in provoking such cell death when compared with other examined compounds. We confirmed that isoquinoline alkaloid is structurally varied from the existing direct AMPK activators. In conclusion, isoquinoline alkaloid is a new class of compound that induce autophagic cell death in drug-resistant fibroblasts or cancers by exhibiting its direct activation on AMPK.

Ligustrazine for the Treatment of Unstable Angina: A Meta-Analysis of 16 Randomized Controlled Trials

Ligustrazine is a principal ingredient of chuanxiong. Concerns regarding the evaluation of the effectiveness of ligustrazine in the treatment of UA have resulted in a meta-analysis combined with recent clinical evidence. Seven computer databases that included the China hospital knowledge database (CHKD), Wanfang Med Online, the Chinese medical journal database (CMJD), PubMed, Cochrane, Embase (Ovid), and Medline (Ovid) were systematically searched. We included randomized controlled trials and quasi-randomized controlled trials. Our systematic review identified 16 RCTs that met our eligibility criteria. Ligustrazine combined with conventional medicine was associated with an increased rate of marked improvement in symptoms and an increased rate of marked improvement of ECG compared with conventional Western medicine alone. Additionally, the use of ligustrazine was associated with significant trends in the reduction of the consumption of nitroglycerin and the level of fibrinogen when compared with conventional Western medicine alone. No firm results were found between the intervention and the control method groups in the reduction of the time of onset or the frequency of acute attack angina due to the high level of heterogeneity. In conclusion, our meta-analysis found that ligustrazine was associated with some benefits for people with unstable angina.

Isolation and bioactivity of diterpenoids from the roots of Salvia grandifolia

A phytochemical investigation of root extracts of Salvia grandifolia led to isolation of six previously unreported diterpenoids, grandifolias A-F, along with eight known compounds. The structures of grandifolias A-F were primarily established by extensive 1D and 2D NMR spectroscopic analyses, as well as HRESIMS data. Their absolute configurations were assigned by their calculated and experimental electronic circular dichroism spectra or by X-ray diffraction analysis. All of the diterpenoids were evaluated for their vasorelaxant effects. Grandifolia B and isograndifoliol both exhibited dose-dependent vasorelaxant effects on rat aortic rings, preconstricted by KCl or norepinephrine, with EC50 values of 36.36-74.51μg/mL.

Protective effect of ligustrazine on lumbar intervertebral disc degeneration of rats induced by prolonged upright posture

Most chronic low back pain is the result of degeneration of the lumbar intervertebral disc. Ligustrazine, an alkaloid from Chuanxiong, reportedly is able to relieve pain, suppress inflammation, and treat osteoarthritis and it has the protective effect on cartilage and chondrocytes. Therefore, we asked whether ligustrazine could reduce intervertebral disc degeneration. To determine the effect of ligustrazine on disc degeneration, we applied a rat model. The intervertebral disc degeneration of the rats was induced by prolonged upright posture. We found that pretreatment with ligustrazine for 1 month recovered the structural distortion of the degenerative disc; inhibited the expression of type X collagen, matrix metalloproteinase (MMP)-13, and MMP3; upregulated type II collagen; and decreased IL-1β, cyclooxygenase (COX)-2, and inducible nitric oxide synthase (iNOS) expression. In conclusion, ligustrazine is a promising agent for treating lumbar intervertebral disc degeneration disease.

Mechanisms underlying the antihypertensive effects of garlic bioactives

Cardiovascular disease remains the leading cause of death worldwide with hypertension being a major contributing factor to cardiovascular disease-associated mortality. On a population level, non-pharmacological approaches, such as alternative/complementary medicine, including phytochemicals, have the potential to ameliorate cardiovascular risk factors, including high blood pressure. Several epidemiological studies suggest an antihypertensive effect of garlic (Allium sativum) and of many its bioactive components. The aim of this review is to present an in-depth discussion regarding the molecular, biochemical and cellular rationale underlying the antihypertensive properties of garlic and its bioactive constituents with a primary focus on S-allyl cysteine and allicin. Key studies, largely from PubMed, were selected and screened to develop a comprehensive understanding of the specific role of garlic and its bioactive constituents in the management of hypertension. We also reviewed recent advances focusing on the role of garlic bioactives, S-allyl cysteine and allicin, in modulating various parameters implicated in the pathogenesis of hypertension. These parameters include oxidative stress, nitric oxide bioavailability, hydrogen sulfide production, angiotensin converting enzyme activity, expression of nuclear factor-κB and the proliferation of vascular smooth muscle cells. This review suggests that garlic and garlic derived bioactives have significant medicinal properties with the potential for ameliorating hypertension and associated morbidity; however, further clinical and epidemiological studies are required to determine completely the specific physiological and biochemical mechanisms involved in disease prevention and management.

Vasodilator compounds derived from plants and their mechanisms of action

The present paper reviews vasodilator compounds isolated from plants that were reported in the past 22 years (1990 to 2012) and the different mechanisms of action involved in their vasodilator effects. The search for reports was conducted in a comprehensive manner, intending to encompass those metabolites with a vasodilator effect whose mechanism of action involved both vascular endothelium and arterial smooth muscle. The results obtained from our bibliographic search showed that over half of the isolated compounds have a mechanism of action involving the endothelium. Most of these bioactive metabolites cause vasodilation either by activating the nitric oxide/cGMP pathway or by blocking voltage-dependent calcium channels. Moreover, it was found that many compounds induced vasodilation by more than one mechanism. This review confirms that secondary metabolites, which include a significant group of compounds with extensive chemical diversity, are a valuable source of new pharmaceuticals useful for the treatment and prevention of cardiovascular diseases.

Protective effect of tetramethylpyrazine isolated from Ligusticum chuanxiong on nephropathy in rats with streptozotocin-induced diabetes

PURPOSE

This study was designed to investigate the protective effect of tetramethylpyrazine isolated from Ligusticum chuanxiong, a traditional Chinese medicine, on diabetic nephropathy in a rat model, and to explore the possible mechanism involved in a protective function.

MATERIALS

Diabetes was induced in male Sprague-Dawley rats by a single intraperitoneal injection of 70mg/kg of streptozotocin. One week later, 200mg/kg/day of tetramethylpyrazine was administered intragastric gavage daily for 8 weeks. Renal functions and expression of vascular endothelial growth factor were examined at 4 and 8 weeks after tetramethylpyrazine administration.

RESULTS

Blood glucose and renal function were significantly improved in the tetramethylpyrazine-treated group compared to the untreated diabetic rats. Diabetic nephropathy resulted in an increase in the expression of vascular endothelial growth factor, while tetramethylpyrazine administration greatly decreased the expression.

CONCLUSIONS

Our results suggest that administration of tetramethylpyrazine may reduce kidney damage caused by diabetes. This protective effect may be mediated, in part, by downregulated expression of vascular endothelial growth factor in the kidney.

Evaluation of the Possible Mechanisms of Antihypertensive Activity of Loranthus micranthus: An African Mistletoe

Loranthus micranthus (LM), also called African mistletoe is a major Nigerian Loranthaceae plant used traditionally to treat hypertension. The methanolic leaf extract of the plant (LMME) has been shown to elicit anti-hypertensive activity in rats but mechanism remains unclear. This study was undertaken to study the effect of LM on pressor-induced contraction of rat aorta smooth muscles and serum lipid profiles in mice. The LMME was partitioned to produce n-butanol (NBF-LMME), chloroform (CF-LMME), ethyl acetate (EAF-LMME) and water (WF-LMME) fractions. The median effective concentrations and maximum relaxation of the fractions were determined against epinephrine and KCl pre-contracted rat aorta ring model. Serum lipid profiles and nitric oxide (NO) were determined spectrophotometrically in mice administered per orally 250 mg/kg b.w. of each fraction for 21 days. Data were analyzed statistically. NBF-LMME elicited the highest dose-dependent inhibitory effect on rat aorta pre-contracted with norepinephrine and KCl, followed in decreasing order by WF-LMME > CF-LMME > EAF-LMME. Similar order of activity was observed in the ability of these fractions to inhibit elevation in artherogenic lipids, raise serum nitric oxide and reduce cardiac arginase in mice. We conclude the anti-hypertensive activity of L. micranthus involve anti-artherogenic events, vasorelaxation, cardiac arginase reduction and NO elevation.

Endothelium-independent vasorelaxation by Ligusticum wallichii in isolated rat aorta: comparison of a butanolic fraction and tetramethylpyrazine, the main active component of Ligusticum wallichii

Ligusticum wallichii is an herb widely used to treat vascular disorders in Asian countries, and tetramethylpyrazine (TMP) has been identified as one of its vasorelaxant active components. This study was performed to examine the endothelium-independent relaxation produced by the butanol-soluble fraction of L. wallichii extract (LwBt) and its possible mechanisms of action in isolated rat aortic rings. The effects were compared with those of TMP. LwBt produced vasorelaxation that increased gradually after 2-3 min of LwBt administration and reached a maximum within 30 min. LwBt-induced relaxation was significantly attenuated by pretreatment with 4-aminopyridine and apamin. Additionally, LwBt attenuated CaCl(2)-induced vasoconstriction in high-potassium depolarized medium. Thus, LwBt-induced vasorelaxation apparently involved inhibition of calcium influx, mediated by the opening of voltage-dependent and/or Ca(2+)-activated potassium channels. On the other hand, the effect of TMP was significantly attenuated by pretreatment with glibenclamide, and 4-aminopyridine had no effect. In conclusion, LwBt-induced endothelium-independent vasorelaxation was mediated by the opening of voltage-dependent potassium channels, while TMP-induced relaxation was mediated by the opening of ATP-dependent potassium channels. These effects of LwBt may be due to a substance other than TMP.

Antihypertensive effect of Eucommia ulmoides Oliv. extracts in spontaneously hypertensive rats

AIM OF THE STUDY

To investigate the antihypertensive fractions of Eucommia ulmoides Oliv. and their underlying mechanisms in spontaneously hypertensive rats (SHRs).

MATERIALS AND METHODS

In vivo study, Eucommia ulmoides lignans (EuL) and Eucommia ulmoides iridoids (EuI) were administrated to Sprague-Dawley (SD) rats and SHRs, and their blood pressures were measured. Plasma level of nitric oxide (NO) was measured by colorimetric method, and renin activity (RA) and plasma concentration of angiotensin II (Ang II) were measured by radioimmunoassay. In vitro study, rat mesenteric artery was treated with EuL and the vessel relaxation responses were determined.

RESULTS

EuL could lower blood pressures of both SD rats and SHR dose-dependently by either intravenous (i.v.) or intragastric (i.g.) administration, but EuI failed to affect blood pressure in the two kinds of rats. Meanwhile, no synergistic effect was observed with the combination of EuL and EuI. The plasma level of NO in SHR treated with EuL 300 mg/kg twice a day was markedly increased. Both plasma RA and Ang II level were decreased with long-term oral treatment of EuL 150 and 300 mg/kg twice a day. In perfusion experiment, EuL relaxed mesenteric artery quickly and dose-dependently and the effect on the artery with and without endothelium was the same.

CONCLUSIONS

EuL may be the effective fraction to lowering blood pressure and its antihypertensive effect is probably associated with regulating NO and renin-angiotensin system (RAS) and directly relaxing artery.

Antihypertensive and anti-arrhythmic effects of an extract of Radix Stephaniae Tetrandrae in the rat

In this study, we determined the effects of an extract of Radix Stephaniae Tetrandrae (RST) on arterial blood pressure and heart weight in deoxycorticosterone acetate-salt (DOCA-salt) hypertensive rats. We also determined the effects of the extract on arrhythmia and infarct induced by myocardial ischaemia and reperfusion in anaesthetized rats. We further compared the effects of the extract with those of tetrandrine, which makes up 7% of the extract and is known to act as a calcium-channel antagonist, and verapamil, a prototype calcium-channel antagonist. Treatment with RST extract returned the arterial blood pressure, cardiac compliance and coronary flow towards normal, and reduced right ventricular hypertrophy in the DOCA-salt hypertensive rat. In the anaesthetized rat, the RST extract reduced arrhythmia and infarct size induced by myocardial ischaemia and reperfusion; the effects were similar to those of tetrandrine and verapamil. The findings indicate that the RST extract acts like a calcium-channel antagonist. It may be used in the treatment of cardiovascular diseases, as are the calcium-channel antagonist and tetrandrine. More interestingly, the effects of the RST extract were of the same potency as tetrandrine. Since only 7% of the extract was tetrandrine, the observation indicates that tetrandrine was not the only component that was responsible for the actions of the extract.

Tetramethylpyrazine inhibits activities of glioma cells and glutamate neuro-excitotoxicity: potential therapeutic application for treatment of gliomas

We tested the herbal extract 2,3,5,6-tetramethylpyrazine (TMP) for possible therapeutic efficacy against a glioma cell line and against gliomas transplanted into rat brains. In the cultured glioma cells, 50 muM TMP significantly inhibited glutamate-induced increase in intracellular calcium. Significant cell damage (30%) and proliferation suppression (10%), however, occurred only at higher concentrations (200-400 microM). Gliomaneuronal co-culturing resulted in significant neuronal damage and higher proliferation of the glioma cells (140%) compared with single cultures. Low concentrations of TMP (< or =200 microM) attenuated the neuronal damage, suppressed glioma migration, and decreased glioma proliferation in the neuronal-glioma co-culture. Gliomas transplanted into the frontal cortical area exhibited high proliferation, with untreated rats dying 10-23 days later. TMP treatment inhibited tumor growth and significantly extended survival time. The results indicate that TMP can suppress glioma activity, including growth, and protect neurons against glioma-induced excitotoxicity, suggesting that TMP may have therapeutic potential in the treatment of malignant gliomas.

A systematic review of mechanisms by which natural products of plant origin evoke vasodilatation

This article reviews the body of work aimed at elucidating the mechanisms of action by which natural products of plant origin exert a vasodilatory effect at the level of the vasculature. The search was restricted to 4 mechanisms: the nitric oxide system and (or) reactive oxygen species, the eicosanoid system, potassium channel function, and calcium channel function. The National Library of Medicine database was searched using "PubMed" without restriction to language. The search generated 266 references on 15 November 2005. Most studies were in vitro in nature and of these, most involved studies in the rat aorta. Many of the natural products evoked vasodilatation through an endothelium-dependent mechanism. The vasodilatation was attenuated or abolished by a nitric oxide synthase inhibitor and, in some of these studies, by an inhibitor of guanylate cyclase. A few studies reported a cyclooxygenase component, but most found no effect of the cyclooxygenase inhibitor, indomethacin. The vasorelaxation evoked by several natural products was attenuated by various potassium channel blocking agents, suggesting that some natural products exerted their effect either directly or indirectly through activation of potassium channels. Finally, a significant number of natural products evoked vasodilatation either through blockade of calcium channels or by inhibiting the release of calcium from intracellular stores. Many natural products evoked vasodilatation through multiple mechanisms. The information in this review on mechanisms of action should facilitate good clinical practice by increasing the predictive capabilities of the practitioner, notably the ability to predict adverse effects and interactions among medications. The knowledge should also help to provide leads to the ultimate goal of developing new therapeutic medications.

Effect of Ligustrazine on liver injury after burn trauma

This study was designed to investigate the effect of Ligustrazine on burn-induced liver injury as well as the activation of nuclear factor kappaB (NF-kappaB) in severely burned rats. Sprague-Dawley rats were divided into three groups: (1) sham group, rats who underwent sham burn; (2) control group, rats given third-degree burns over 30% total body surface area (TBSA) and lactated Ringer solution for resuscitation; (3) Ligustrazine group, rats given burn and lactated Ringer's solution with Ligustrazine inside for resuscitation. Liver injury was assessed at 24 h post-burn by serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), as well as liver wet/dry weight ratio. Liver myeloperoxidase (MPO) activity was also analyzed. Hepatic NF-kappaB activity was examined by electrophoretic mobility shift assay (EMSA). Burn results in hepatic dysfunction and increased hepatic NF-kappaB activity, elevated liver wet/dry ratio and hepatic MPO activity. Ligustrazine inhibited these changes and alleviated burn-mediated hepatic dysfunction. The data indicated that Ligustrazine has a protective effect on burn-induced liver injury and possible mechanism may be attributed to its inhibitory action on the activation of NF-kappaB following burn trauma.

Tetramethylpyrazine downregulates angiotensin II-induced endothelin-1 gene expression in vascular endothelial cells

1. Tetramethylpyrazine (TMP) is one of the active ingredients of the Chinese herb Ligusticum wallichii Franchat. It is well documented that TMP exerts a cardiovascular protective effect. The aims of the present study were to examine whether TMP alters angiotenisn (Ang) II-induced endothelin (ET)-1 gene expression and to identify the putative underlying signalling pathways in vascular endothelial cells. 2. Cultured vascular endothelial cells were pre-incubated with TMP, stimulated with AngII and ET-1 gene expression was then examined. The effects of TMP pretreatment on AngII-induced extracellular signal-regulated kinase (ERK) phosphorylation were investigated to elucidate the intracellular mechanism responsible for the effects of TMP on ET-1 gene expression. 3. Tetramethylpyrazine inhibited AngII-induced ET-1 gene expression, as revealed by nothern blotting and a promoter activity assay. Tetramethylpyrazine also inhibited the AngII-induced increase in intracellular reactive oxygen species (ROS), as measured by the redox sensitive fluorescent dye 2' 7'-dichlorofluorescin diacetate and ERK phosphorylation. 4. In summary, we have demonstrated, for the first time, that TMP inhibits AngII-induced ROS generation, ERK phosphorylation and ET-1 gene expression in vascular endothelial cells. Thus, the present study delivers important new insights into the molecular pathways that may contribute to the proposed beneficial effects of TMP in the cardiovascular system.

The control of vascular smooth muscle function: my life-long learning and continuous discovery with Professor E.E. Daniel

This communication is neither a comprehensive review of my research, nor a description about my recent new original scientific findings in smooth muscle or in cell Ca2+. For that intention, I will choose to publish via a regular channel, certainly not in this special edition. My intention is to take this opportunity to recapitulate Dr. Daniel's thoughts and spirits through the progress of my research, teaching, and personal development at McMaster University, stemming largely from Dr. Daniel's life-long interest in the regulation of Ca2+ in the control of smooth muscle function, specifically the vascular smooth muscle. Being a culturally adsorbent person, I am sure that my thoughts and behavior must have been substantially influenced by Dr. Daniel over 27 years of our collaboration. His influence may have molded me into whom and what I am today, both socially and scientifically. Equally, I may also have influenced him in some particular or peculiar way. Dr. Daniel's academic contribution is globally well known for, but not limited to, his insightful and productive research in smooth muscle, but also for his effective application of problem-based learning to education in pharmacology and his influence on students and colleagues.

A NOVEL IN VITRO ENDOTHELIUM-DEPENDENT VASCULAR RELAXANT EFFECT OF APOCYNUM VENETUM LEAF EXTRACT

1. In the present study, a novel in vitro vascular relaxant effect of Apocynum venetum leaf extract (AVLE; also called 'Luobuma'), obtained from a traditional Chinese medicinal herb with known antihypertensive effects, is reported in isometric contraction studies of rat aorta and superior mesenteric artery. At low concentrations (0.3-10 microg/mL), AVLE had no effect on the resting tension of either blood vessel and caused relaxation in agonist-precontracted vessels with functionally intact endothelium. 2. We demonstrated pharmacologically that the AVLE-induced vasorelaxation was mediated selectively by the endothelial cells in both blood vessels. Using NG-nitro-L-arginine methyl ester (L-NAME) and a low concentration of KCl (15 mmol/L), we also demonstrated that AVLE acted by releasing endothelium-derived relaxation factors; nitric oxide (NO) in the rat aorta and NO plus endothelium-derived hyperpolarizing factor in the rat mesenteric artery. 3. The vascular relaxation following brief exposure to AVLE appeared to persist even after subsequent prolonged washout; this was manifested as an attenuated contraction to subsequent application of phenylephrine (PE) compared with the PE-induced contraction after exposure to carbachol (CCh) and subsequent similar washout. The addition of L-NAME at this point in the absence of AVLE totally restored the contraction to PE, suggesting that enzymatic generation of endothelial NO persisted even after brief exposure to AVLE. 4. Unlike the endothelium-dependent NO-mediated relaxation induced by CCh, which is mediated by endothelial muscarinic receptors (and inhibited by atropine), the relaxation induced by AVLE was not inhibited by atropine and, thus, was not mediated by muscarinic receptors. However, similar to CCh-induced relaxation, AVLE-induced relaxation was associated with the activation of K+ channels. 5. These results provide a strong scientific basis for the folk use of AVLE decoction for antihypertensive therapy in traditional Chinese medicine.

Role of cGMP signals in tetramethylpyrazine induced relaxation of the isolated rat aortic strip

In the present study, role of guanosine-3',5'-cyclic monophosphate (cGMP) in the vasodilatation of tetramethylpyrazine (TMP), one of the active ingredients of the Chinese herb Chuang-xion, was investigated. We found that the TMP could decrease the vascular tone of isolated rat aorta precontracted with phenylephrine (10(-8) M) in a concentration-dependent manner from 10(-5) M to 10(-3) M. Also, the TMP-induced relaxation was reduced by 1H-(1,2,4)-oxadiazol-(4,3-a)-quinoxalin-1-one (ODQ) or methylene blue, the inhibitor of soluble guanylyl cyclase. Moreover, the vasodilative response to TMP was enhanced significantly in the presence of sildenafil, a well-known inhibitor of phosphodiestrase type 5 that is sensitive to cGMP. In addition, TMP could increase the cGMP level in the isolated aortic rings and TMP-induced vasodilatation was deleted by cGMP-dependent protein kinases (PKG) blockade. These results suggest that relaxation of rat aortic strip by TMP is induced in the cGMP-dependent manner.

Regulation of Ca2+ movements by cyclovirobuxine D in ECV304 endothelial cells

In Fura-2/loaded ECV304 endothelial cells cyclovirobuxine D promoted a transient increase in cytosolic free Ca2+ originating from both an intracellular pool sensitive to the endoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin and the extracellular space. The intracellular pool was apparently different from that mobilized by other agents acting through IP3 generation. The integrity of the plasma membrane was an absolute requirement. In cells treated with digitonin, cyclovirobuxine D did not promote any Ca2+ release from the intracellular stores even at high concentrations and in the absence or presence of thapsigargin or sodium azide, the inhibitors of the endoplasmic reticular or mitochondrial Ca2+ uptake. Furthermore, cyclovirobuxine D was effective in halting the persistent increase in cytosolic Ca2+ caused by thapsigargin, inhibiting the operation of the "capacitative" Ca2+ membrane channels as demonstrated by the decrease in the extent of both Ca2+-overshoot and Mn2+ influx. Additional effects of cyclovirobuxine D included a depolarization of plasma membrane apparently related to an enhanced influx of Na+ from the extracellular space. The results obtained indicate that cyclovirobuxine D markedly affects intracellular Ca2+ homeostasis in ECV304 endothelial cells by both promoting a discharge of intracellular pools and by interfering with the operation of store-dependent channels via plasma membrane depolarization.

INHIBITION OF CYCLIC STRAIN-INDUCED ENDOTHELIN-1 SECRETION BY TETRAMETHYLPYRAZINE

1. Chuanxiong is a Chinese herb that has been used widely in China to treat vascular disorders. 2,3,5,6-Tetramethylpyrazine (TMP) is one of the major components purified from chuanxiong. Many studies have demonstrated that TMP is effective in the treatment of cardiovascular diseases. However, the mechanism of action by which TMP exerts relaxation in vascular vessels remains unclear. 2. Endothelin (ET)-1 is a potent vasopressor synthesised by endothelial cells both in culture and in vivo. The aims of the present study were to test the hypothesis that TMP may alter strain-induced ET-1 secretion and to identify the putative underlying signalling pathways in endothelial cells. 3. We showed that TMP inhibits strain-induced ET-1 secretion. 2,3,5,6-Tetramethylpyrazine also inhibits the strain-induced formation of reactive oxygen species (ROS) and phosphorylation of extracellular signal-regulated kinases (ERK) 1/2. Furthermore, pretreating cells with TMP or the anti-oxidant N-acetyl-cysteine decreased strain-induced increases in ET-1 secretion and ERK1/2 phosphorylation. Using a reporter gene assay, TMP and N-acetyl-cysteine were demonstrated to also attenuate the strain-induced activity of the activator protein-1 reporter. 4. In summary, we have demonstrated, for the first time, that TMP inhibits strain-induced ET-1 gene expression, in part by interfering with the ERK1/2 pathway via attenuation of ROS formation. Thus, the present study provides important new insights into the molecular pathways that may contribute to the proposed beneficial effects of TMP in the vascular system.

Differential Cl- and HCO3- mediated anion secretion by different colonic cell types in response to tetromethylpyrazine

AIM: Colonic epithelium is known to secrete both Cl^- and HCO₃^-, but the secretory mechanisms of different colonic cell types are not fully understood. The present study aimed to investigate the differential activation of Cl^- and HCO₃^-secretion by tetramethylpyrazine (TMP) in human crypt-like cell line, T84, and villus-like cell line, Caco-2, in comparison to the TMP-induced secretory response in freshly isolated rat colonic mucosa.

METHODS: Colonic epithelial anion secretion was studied by using the short circuit current (I_SC) technique. RT-PCR was used to examine the expression of Na⁺-HCO₃^-- cotranspoter in different epithelial cell types.

RESULTS: TMP produced a concentration-dependent I_SC which was increase in both T84 and Caco-2 cells. When extracellular Cl^- was removed, TMP-induced I_SC was abolished by 76.6% in T84 cells, but not in Caco-2 cells. However, after both Cl^- and HCO₃^- were removed, TMP-induced I_SC in Caco-2 cells was reduced to 10%. Bumetanide, an inhibitor of Na⁺-K⁺-Cl^--cotranspoter, inhibited the TMP-induced I_SC by 96.7% in T84 cells, but only 47.9% in Caco-2 cells. In the presence of bumetanide and 4, 4’-diisothiocyanostilbene-2, 2’-disulfonic acid, an inhibitor of Na⁺-HCO₃^- cotransporter, inhibited the TMP-induced current in Caco-2 cells by 93.3%. In freshly isolated rat colonic mucosa, TMP stimulated distinct I_SC responses similar to that observed in T84 and Caco-2 cells depending on the concentration used. RT-PCR revealed that the expression of Na⁺-HCO₃^- cotransporter in Caco-2 cells was 4-fold more greater than that in T84 cells.

CONCLUSION: TMP exerts concentration-dependent differential effects on different colonic cell types with stimulation of predominant Cl^- secretion by crypt cells at a lower concentration, but predominant HCO₃^- secretion by villus cells at a higher concentration, suggesting different roles of these cells in colonic Cl^- and HCO₃^- secretion.

Tetramethylpyrazine elicits disparate responses in cardiac contraction and intracellular Ca(2+) transients in isolated adult rat ventricular myocytes

Tetramethylpyrazine (TMP) is the biologically active ingredient isolated from a popular Chinese medicinal plant, Ligusticum wallichil franchat, which has been used effectively since the 1970s to treat ischemic heart disease, cerebrovascular and thrombotic vascular diseases. The direct action of TMP on cardiac contractile function, however, is largely unclear. This study was designed to examine the effect of TMP on ventricular contractile function at the single cardiac myocyte level. Adult rat ventricular myocytes were isolated and stimulated to contract at 0.5 Hz, and mechanical and intracellular Ca(2+) properties were evaluated using an IonOptix Myocam system. Contractile properties analyzed included peak shortening (PS), time-to-peak shortening (TPS), time-to-90% relengthening (TR(90)), maximal velocity of shortening/relengthening (+/-dl/dt), resting intracellular Ca(2+) level, Ca(2+)-induced Ca(2+) release (CICR) and decay. TMP (10(-10)-10(-5) M) exhibited an increase in PS with a maximal increase of 30.9%. TMP had no effect on +/-dl/dt, TPS/TR(90) or CICR but lowered resting intracellular Ca(2+) level and slowed intracellular Ca(2+) decay. Pretreatment with either the nonspecific nitric oxide synthase (NOS) inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME, 100 microM) or inducible NOS inhibitor W1400 effectively abolished the positive effect of TMP on myocyte shortening. Our data demonstrate a direct positive inotropic effect of TMP in cardiac myocytes, which may be related, at least in part, to NO production.

Endothelium-dependent vasorelaxant effects of the aqueous extracts of the Eucommia ulmoides Oliv. leaf and bark: implications on their antihypertensive action

The vascular effects of three extract preparations from the Chinese medicinal herb, Eucommia ulmoides Oliv., which is historically an active ingredient commonly used in antihypertensive herbal prescriptions in China, were investigated with isometric contraction using isolated rat aortic and dog carotid rings. Both aqueous extracts isolated from eucommia leaf (L) and bark (B) concentration dependently caused endothelium-dependent relaxation in vessels precontracted with 1 microM phenylephrine (PE), but the methanol extract of the leaf (M) had no effect. Vessels precontracted with KCl and de-endothelialized vessels precontracted with PE were not affected by B or L. The endothelium-dependent relaxation evoked by B and L was either abolished or substantially inhibited by NG-nitro-L-arginine methyl ester (L-NAME) and methylene blue (MB), indicating the involvement of the nitric oxide (NO) synthase pathway in the vasorelaxant action of B and L. The relaxation to the aqueous extract of eucommia bark was not inhibited with 1 microM atropine, but was inhibited by 3-5 mM tetraethylammonium (TEA) and 3 mM 4-aminopyridine. This suggests that the endothelium-dependent, NO-mediated relaxation evoked by the aqueous eucommia extracts was not mediated via the activation of endothelium muscarinic receptors and may involve the activation of K+ -channels. Results in this study have provided the first evidence on the in vitro vasorelaxant action of E. ulmoides Oliv. that forms the pharmacological basis for its well-documented antihypertensive action.

Mechanisms responsible for the in vitro relaxation of ligustrazine on porcine left anterior descending coronary artery

In this study, we have evaluated the underlying mechanisms responsible for the relaxation response of ligustrazine (2,3,5,6-tetra-methyl-pyrazine; 2,3,5,6-MP) and its structural analogues (2-methyl-pyrazine (2-MP); ethyl-pyrazine (EP); 2,3-di-methyl-pyrazine (2,3-MP); 2,5-di-methyl-pyrazine (2,5-MP); 2,6-di-methyl-pyrazine (2,6-MP) and 2,3,5-tri-methyl-pyrazine (2,3,5-MP)) in porcine left anterior descending coronary artery (tertiary branch, O.D. </=1 mm). In 5-hydroxytryptamine (3 microM) precontracted preparations, cumulative administration (0.1-300 microM) of all pyrazine analogues caused an endothelium-independent, concentration-dependent relaxation. The relative inhibitory potency, as compared at concentration with which 50% relaxation occurred, was 2,3,5,6-MP>2,3,5-MP>EP>2,5-MP>/=2,6-MP>/=2,3-MP>2-MP. Besides, salbutamol and forskolin caused an endothelium-independent relaxation. The relaxation response of ligustrazine, salbutamol and forskolin was blunted in the presence of cis-N-(2-phenylcyclopentyl) azacyclotridec-1-en-2-amine (MDL 12330A) (10 microM, an adenylate cyclase inhibitor) and N-[2-((bromocinnamyl)amino)ethyl]-5-isoquinoline-sulphonamide (H-89, a protein kinase A inhibitor, 3 microM). Patch-clamp, whole-cell electrophysiological studies using single smooth muscle cells of the left anterior descending coronary artery revealed that ligustrazine (300 microM), salbutamol (30 microM) and forskolin (1 microM) inhibited the nifedipine-sensitive L-type Ca(2+) channels, and the inhibitory effect was eradicated by MDL 12330A (10 microM) and H-89 (1 microM). However, neither the Ca(2+)-dependent K(+) channel nor the ATP-dependent K(+) channel was modified by ligustrazine (300 microM). In conclusion, our results indicate that ligustrazine-mediated left anterior descending coronary artery relaxation is due to the activation of adenylate cyclase/protein kinase A cascade and the subsequent inhibition of nifedipine-sensitive, voltage-dependent L-type Ca(2+) channels. However, opening of K(+) channels seems to play no role in mediating the relaxation effect of ligustrazine.

Tetrandrine cytotoxicity and its dual effect on oxidative stress-induced apoptosis through modulating cellular redox states in Neuro 2a mouse neuroblastoma cells

Tetrandrine (TET), a plant alkaloid, is known primarily as a non-selective Ca(2+) channel blocker. On the contrary to the cytoprotective effect on ischemia/reperfusion injury, TET has also been reported to cause cytotoxicity. In this study, we wished to understand the apparently disparate effects of this potential drug and thus investigated molecular mechanisms on proliferation and apoptosis and its effect on oxidative stress-induced apoptosis in Neuro 2a mouse neuroblastoma cells. We showed that TET, at high concentrations, induced cell cycle arrest and apoptosis through oxidative stress with following observations. Firstly, 10 microM TET elevated the reactive oxygen species (ROS) level and accordingly depleted glutathione (GSH) content. Secondly, pretreatment with antioxidants (NAC or GSH) protected cells from TET-induced apoptosis. We also demonstrated that treatment with 10 microM TET caused not only induction of p53, p21(waf1), and Bax, but also nuclear translocation of p53 and hypo-phosphorylation of pRb concurrently. Our important finding is that the concentration-dependent dual effect of TET, either inhibiting or promoting cell death induced by H(2)O(2) was observed, probably through regulating redox balance, which was well reflected on the GSH content in each condition. Besides, inhibition of Ca(2+) influx protected cells from H(2)O(2)-induced apoptosis even in the presence of 10 microM TET. Taken together, our data suggest that TET regulation of cellular redox states may play a major role in its dual action of cytotoxicity and cytoprotection.

Inhibitory effects of potassium channel blockers on tetramethylpyrazine-induced relaxation of rat aortic strip in vitro

Tetramethylpyrazine (TMP) is one of the active principles contained in Ligusticum chuanxiong Hort. (Umbelliferae), a herb that has been widely used to treat vascular disorders in China. In the present study, role of potassium channel in the vasodilatation of TMP was investigated using the effect of potassium channel blocker on TMP induced relaxation in isolated aortic rings from Wistar rats. TMP produced a concentration-dependent relaxation in the aortic rings precontracted with vasopressin or phenylephrine. Similar effect of TMP on vasoconstrictions by phenylephrine and vasopressin, induced through two different receptors, indicating the direct vasodilatation of TMP. Specific inhibitors for potassium channel were used to characterize the role of potassium channel in this action of TMP. Only the inhibitors specific to small conductance calcium-activated potassium (SK(Ca)) channel or ATP-sensitive potassium (K(ATP)) channel inhibited the action of TMP. Also, the TMP-induced relaxation was reversed by the inhibitor of soluble guanylyl cyclase in a way similar to that of K(ATP) channel blockade. The obtained results indicated that vasodilatation induced by TMP is related to the opening of SK(Ca) and K(ATP) channels.

Efficacy of the bisbenzylisoquinoline alkaloids in acute and chronic Trypanosoma cruzi murine model

We have shown previously that daphnoline and cepharanthine are active against Trypanosoma cruzi and inhibited trypanothione reductase. The effects of oral treatments with daphnoline, cepharanthine and benznidazole were examined in Balb/c mice infected with T. cruzi acutely and chronically. In acute infections, parasitaemia was significantly reduced in the daphnoline-treated mice compared with controls and benznidazole-treated mice. The parasitological cure rate was increased in mice treated with daphnoline. Fifty days after infection, the negative serological response in both models was significantly different for the three tested drugs. Daphnoline showed the highest negative serological rate (48%). In chronically infected mice treated with daphnoline, we were unable to detect parasites in 70% of mice. The results obtained of oral treatment of daphnoline suggest that this bisbenzylisoquinoline may be useful in the treatment of acute and chronic Chagas' disease. This was not seen with cepharanthine, an excellent trypanothione reductase inhibitor.

Tetramethylpyrazine, a Chinese drug, blocks coronary vasoconstriction by endothelin-1 and decreases plasma endothelin-1 levels in experimental animals

The purpose of this study was to investigate effects of tetramethylpyrazine (TMP), a Chinese plant-derived medicine, on coronary vasoconstriction and related electrocardiographic and histologic changes caused by endothelin-1 (ET-1), and on plasma ET-1 levels. ET-1 (75 pmol) was administered into the left coronary artery (LCA) in anesthetized closed-chest dogs with and without prior infusion of TMP (80 mg/kg). Coronary arterial diameter (CAD) was determined by coronary arteriography (CAG). Blood pressure and electrocardiogram (ECG) were monitored continuously. Histologic damage in tissues was ascertained microscopically. Plasma ET-1 and 6-keto-PGF1 levels were determined by RIA 90 min after i.v. injection of TMP (25 mg/kg; n = 5) in rabbits. Intracoronary injection of ET-1 resulted in a significant vasoconstriction of the entire vascular bed of the LCA, with a decrease in CAD of 35.9 +/- 5.7% (n = 5; p < 0.01) and ischemic changes on ECG and in tissues of endocardium, myocardium, coronary endothelial cells, and capillary vessels. Pretreatment with TMP produced a significant increase in CAD by 38.5 +/- 7.8% (n = 5; p < 0.01) and greatly suppressed the vasoconstriction produced by ET-1. The myocardial tissue damage estimated from the ratio of ischemic area for the entire area after ET-1 injection (35.6%) was completely abolished by TMP (0.6%). In addition, TMP injection induced a significant decrease in plasma ET-1 levels and an increase in 6-keto-PGF1 levels in rabbits. The Chinese medicine TMP could be a useful therapeutic agent in ischemic heart disease by suppressing coronary vasoconstriction and ischemic changes in the tissues produced by ET-1.

Cytotoxicity to macrophages of tetrandrine, an antisilicosis alkaloid, accompanied by an overproduction of prostaglandins

Tetrandrine, an anti-inflammatory immunosuppressive bisbenzylisoquinoline alkaloid of Chinese herbal origin, is widely used to treat silicosis and interferes with the regulation of calcium in many cell types. We investigated its effect on the cellular integrity of macrophages and on their ability to generate prostaglandins and nitric oxide, mediators of inflammation with immunomodulatory roles. Tetrandrine at 10(-7) M to 10(-4) M caused dose- and time-dependent loss of cell viability of mouse peritoneal macrophages, guinea-pig alveolar macrophages and mouse macrophage-like J774 cells. Loss of viability (50%) occurred within 1-3 hr and required approximately 5 x 10(-6) M tetrandrine. Loss of macrophage viability after tetrandrine treatment was accompanied by the generation of large amounts of prostaglandin E2 (PGE2), to levels 285-877% of control. Coincubation with indomethacin abolished PGE2 generation, but did not prevent cell death. Tetrandrine did not cause generation of nitric oxide. Verapamil also reduced the viability of mouse peritoneal macrophages and J774 cells, but did not cause PGE2 overproduction, except at 10(-4) M in mouse peritoneal macrophages. In macrophages cultured with lipopolysaccharide and interferon-gamma to induce the generation of large amounts of both PGE2 and nitric oxide, tetrandrine reduced mediator release and their forming enzymes (cyclo-oxygenase-2 and inducible nitric oxide synthase), secondary to cytotoxicity. The predominant action of tetrandrine is to exert a cytotoxic effect on macrophages, perhaps by interfering with calcium homeostasis; this leads to overproduction of immunomodulatory but proinflammatory prostaglandin. This may be relevant to its protective actions in human fibrosing silicosis, in which there is alveolar macrophage involvement.

Ligustrazine-induced endothelium-dependent relaxation in pulmonary arteries via an NO-mediated and exogenous L-arginine-dependent mechanism

1. Ligustrazine (tetramethylpyrazine, TMP) is a vasodilator that has been reported to have pulmonary selective properties in vivo, but not in vitro. Although TMP is generally described as being endothelium-independent, we provide evidence here that TMP may have an endothelium-dependent and nitric oxide (NO)-mediated mechanism in pulmonary arteries that could predominate at concentrations used therapeutically in China. 2. The study was performed on isolated pulmonary (1-2 mm i.d.), intrapulmonary (200-850 microns) and mesenteric (200-400 microns) arteries of the rat using a Mulvaney-Halpen small vessel myograph, following preconstriction with phenylephrine (PE, 10 microM), prostaglandin F2 alpha (PGF2 alpha, 100 microM), or 75 mM K+ (KPSS, equimolar substitution for Na+). Values are shown as mean +/- s.e.mean, or for EC50S as mean [+/-95% confidence limits]. 3. TMP caused a concentration-dependent relaxation against all three agonists in both large (1.56 +/- 0.04 mm) and small (399 +/- 20 microM) pulmonary arteries; it was more potent in small compared to large arteries constricted with PE or PGF2 alpha (P < 0.05), but not those constricted with KPSS. The NO synthase (NOS) inhibitor, NG-monomethyl-L-arginine (L-NMMA, 100 microM) caused a significant shift to the right of these relationships, such that the EC50 for TMP in large pulmonary arteries constricted with PE increased from 522 [+130, -104] microM (n = 12) to 1828 [+395, -325] microM (n = 6, P < 0.01). Both removal of the endothelium and methylene blue (10 microM) had similar effects. 4. L-Arginine substantially reduced the EC50 for TMP in pulmonary arteries; in the presence of 400 microM L-arginine the EC50 for TMP in large arteries constricted with PE was 14.7 [+21.0, -8.6] microM, (n = 6, P < 0.001), and with 10 microM L-arginine 96.7 [+45.1, -30.7] microM, (n = 6, P < 0.001). Similar effects were seen in small arteries. L-Arginine had no effect in the absence of an endothelium. D-Arginine was ineffective, and inhibition of L-arginine uptake with L-lysine blocked the action of L-arginine. L-Arginine (400 microM) had no significant effect on TMP-induced relaxation in mesenteric arteries (n = 5). 5. L-Arginine itself caused a concentration-dependent relaxation in intrapulmonary arteries (639 +/- 34 microM) constricted with PE, reaching a maximum relaxation around 100-400 microM (42.4 +/- 3.0%, n = 16), but this was independent of the endothelium. TMP (10 and 100 microM) significantly enhanced the relaxation to L-arginine, with a maximum relaxation in the presence of 100 microM TMP of 81.7 +/- 6.2% (n = 5, P < 0.01), but the effect of TMP was entirely dependent on the endothelium. A similar effect was observed in PGF2 alpha-constricted pulmonary arteries. 6. These results show that TMP stimulates NO production at low concentrations in pulmonary arteries, via an apparently novel endothelium-resident mechanism that is dependent on exogenous L-arginine. Normal plasma L-arginine levels of around 150 microM would allow this mechanism to be maximally activated. As mesenteric arteries do not seem to express the mechanism to any significant extent, at low concentrations TMP would be effectively selective to the pulmonary vasculature, and may thus have potential as a therapeutic agent in pulmonary vascular disease.

Plant alkaloids, tetrandrine and hernandezine, inhibit calcium-depletion stimulated calcium entry in human and bovine endothelial cells

Depletion of internal Ca2+ stores causes capacitative Ca2+ entry which occurs through non-selective cation channels sensitive to blockade by SK&F 96365. Recently, alkaloids of Chinese herbal medicinal origin, tetrandrine and hernandezine, have been shown to possess actions including inhibition of Ca2+ channels in non-excitable cell types. In this study, we compared the actions of these novel inhibitors to those of SK&F 96365 in fura-2-loaded endothelial cells from human umbilical vein and bovine pulmonary artery. Depletion of Ca2+ from the internal stores was accomplished in Ca(2+)-free medium using an endoplasmic reticulum Ca2+ pump inhibitor, cyclopiazonic acid (CPA) or receptor agonists, histamine and bradykinin. Stimulation with histamine or bradykinin caused a marked and rapid transient increase in Ca2+ signal whereas CPA caused a smaller amplitude increase of longer duration. Restoring Ca2+ to the medium caused marked and sustained increases in the fluorescence indicating movement of Ca2+ into the cytosol presumably stimulated by the emptied Ca2+ stores. SK&F 96365 as well as tetrandrine and hernandezine antagonized depletion-induced Ca2+ entry. The results suggest that these putative inhibitors interact with Ca2+ entry triggered by depletion of the internal Ca2+ stores and their action is presumed to be on the non-selective cation channels. Their effectiveness may be enhanced by the mechanisms which lead to the opening of the Ca2+ influx channel.

Vascular effects of selected antihypertensive drugs derived from traditional medicinal herbs

1. The pharmacological actions of the active ingredients extracted or purified from two selected traditional Chinese medicinal plants on vascular smooth muscles are briefly reviewed. The active ingredients of these herbal drugs include tetrandrine (TET) and total ginseng saponins (TGS). These natural products have been clinically used in China for the treatment of cardiovascular diseases due to their vasodilatory and antihypertensive actions. 2. Studies from this laboratory have confirmed previously reported characteristics of these drugs as Ca2+ antagonists in vascular tissues. On the other hand, they also elicited inhibitory effects in response to a wide variety of receptor stimulations as indicated by contractility studies using isolated vascular tissues and radioligand binding studies using isolated subcellular membranes. 3. TET has been demonstrated as an effective but not very selective Ca2+ antagonist. Other than the vasodilatory action on arteries and veins, TET also shows a vasoconstrictive effect in veins. 4. TGS from panax notoginseng may be acting as a novel and selective Ca2+ antagonist that does not interact with the L-type Ca2+ channel (e.g. in KCl-induced contraction) but may interact with the putative receptor operated Ca2+ channel (e.g. in phenylephrine-induced contraction). TGS from panax quinquefolium, on the other hand, enhanced the vasoconstrictor effect produced by phenylephrine, but not KCl.