The potential therapeutic value of the natural plant compounds matrine and oxymatrine in cardiovascular diseases

Matrine (MT) and Oxymatrine (OMT) are two natural alkaloids derived from plants. These bioactive compounds are notable for their diverse pharmacological effects and have been extensively studied and recognized in the treatment of cardiovascular diseases in recent years. The cardioprotective effects of MT and OMT involve multiple aspects, primarily including antioxidative stress, anti-inflammatory actions, anti-atherosclerosis, restoration of vascular function, and inhibition of cardiac remodeling and failure. Clinical pharmacology research has identified numerous novel molecular mechanisms of OMT and MT, such as JAK/STAT, Nrf2/HO-1, PI3 K/AKT, TGF-β1/Smad, and Notch pathways, providing new evidence supporting their promising therapeutic potential against cardiovascular diseases. Thus, this review aims to investigate the potential applications of MT and OMT in treating cardiovascular diseases, encompassing their mechanisms, efficacy, and safety, confirming their promise as lead compounds in anti-cardiovascular disease drug development.

Matrine reduced intestinal stem cell damage in eimeria necatrix-infected chicks via blocking hyperactivation of Wnt signaling

BACKGROUND

Coccidiosis is a rapidly spreading and acute parasitic disease that seriously threatening the intestinal health of poultry. Matrine from leguminous plants has anthelmintic and anti-inflammatory properties.

PURPOSE

This assay was conducted to explore the protective effects of Matrine and the AntiC (a Matrine compound) on Eimeria necatrix (EN)-infected chick small intestines and to provide a nutritional intervention strategy for EN injury.

STUDY DESIGN

The in vivo (chick) experiment: A total of 392 one-day-old yellow-feathered broilers were randomly assigned to six groups in a 21-day study: control group, 350 mg/kg Matrine group, 500 mg/kg AntiC group, EN group, and EN + 350 mg/kg Matrine group, EN + 500 mg/kg AntiC group. The in vitro (chick intestinal organoids, IOs): The IOs were treated with PBS, Matrine, AntiC, 3 μM CHIR99021, EN (15,000 EN sporozoites), EN + Matrine, EN + AntiC, EN + Matrine + CHIR99021, EN + AntiC + CHIR99021.

METHODS

The structural integrity of chicks jejunal crypt-villus axis was evaluated by hematoxylin and eosin (H&E) staining and transmission electron microscopy (TEM). And the activity of intestinal stem cells (ISCs) located in crypts was assessed by in vitro expansion advantages of a primary in IOs model. Then, the changes of Wnt/β-catenin signaling in jejunal tissues and IOs were detected by Real-Time qPCR,Western blotting and immunohistochemistry.

RESULTS

The results showed that dietary supplementation with Matrine or AntiC rescued the jejunal injury caused by EN, as indicated by increased villus height, reduced crypt hyperplasia, and enhanced expression of tight junction proteins. Moreover, there was less budding efficiency of the IOs expanded from jejunal crypts of chicks in the EN group than that in the Matrine and AntiC group, respectively. Further investigation showed that AntiC and Matrine inhibited EN-stimulated Wnt/β-catenin signaling. The fact that Wnt/β-catenin activation via CHIR99021 led to the failure of Matrine and AntiC to rescue damaged ISCs confirmed the dominance of this signaling.

CONCLUSION

Our results suggest that Matrine and AntiC inhibit ISC proliferation and promote ISC differentiation into absorptive cells by preventing the hyperactivation of Wnt/β-catenin signaling, thereby standardizing the function of ISC proliferation and differentiation, which provides new insights into mitigating EN injury by Matrine and AntiC.

Matrine induces cardiotoxicity by promoting ferroptosis through the Nrf2 antioxidant system in H9c2 cells

Matrine (MT) has shown promising efficacy in various cancers and chronic hepatitis; however, its clinical application is limited because of its side effects. Our previous studies have indicated that MT can induce severe hepatotoxicity and nephrotoxicity. The current study aimed to investigate its cardiotoxicity and potential underlying mechanisms in H9c2 cells. Our results showed that MT induced H9c2 cell death and disrupted the cellular membrane integrity. Moreover, MT decreased glutathione (GSH) and cysteine (Cys) levels, and increased Fe2+, lipid peroxidation, reactive oxygen species (ROS), and MDA levels, ultimately leading to ferroptosis. Interestingly, these phenomena were alleviated by the ferroptosis inhibitor Fer-1, whereas MT-induced ferroptosis was exacerbated by the ferroptosis agonist RSL3. In addition, MT significantly reduced FTH, Nrf2, xCT, GPX4, and FSP1 protein levels and inhibited the transcriptional activity of Nrf2 while increasing TFR1 protein levels. Supplementation with Nrf2 agonist (Dimethyl fumarate, DMF) or selenium (Sodium selenite, SS) and CoQ10 alleviated MT-induced cytotoxic effects in H9c2 cells. These results suggest that ferroptosis, which is mediated by an imbalance in the Nrf2 antioxidant system, is involved in MT-induced cardiac toxicity.

Therapeutic Effects of Traditional Chinese Medicine on Cardiovascular Diseases: the Central Role of Calcium Signaling

Calcium, as a second messenger, plays an important role in the pathogenesis of cardiovascular diseases (CVDs). The malfunction of calcium signaling in endothelial cells and vascular smooth muscle cells promotes hypertension. In cardiomyocytes, calcium overload induces apoptosis, leading to myocardial infarction and arrhythmias. Moreover, the calcium–calcineurin–nuclear factor of activated T cells (NFAT) pathway is essential for expressing the cardiac pro-hypertrophic gene. Heart failure is also characterized by reduced calcium transient amplitude and enhanced sarcoplasmic reticulum (SR) calcium leakage. Traditional Chinese medicine (TCM) has been used to treat CVDs for thousands of years in China. Because of its multicomponent and multitarget characteristics, TCM's unique advantages in CVD treatment are closely related to the modulation of multiple calcium handling proteins and calcium signaling pathways in different types of cells involved in distinct CVDs. Thus, we systematically review the diverse mechanisms of TCM in regulating calcium pathways to treat various types of CVDs, ranging from hypertrophic cardiomyopathy to diabetic heart disease.

Matrine-Type Alkaloids from the Seeds of Sophora alopecuroides and Their Potential Anti-inflammatory Activities

Three new matrine-type alkaloids, 8β-hydroxyoxysophoridine (1), 9β-hydroxysophoridine (2), 9β-hydroxyisosophocarpine (3), together with one known analog, 11,12-dehydromatrine (4), were isolated from the seeds of Sophora alopecuroides L. The structures of new compounds were elucidated using extensive spectroscopic techniques including the experimental and calculated ECD data. The anti-inflammatory activities of all the isolates on NO production in RAW 264.7 cells stimulated by lipopolysaccharide were evaluated. Among them, 8β-hydroxyoxysophoridine (1) showed a significant inhibitory effect with an IC₅₀ value of 18.26 μM.

Quinolizidine alkaloids from Sophora alopecuroides with anti-inflammatory and anti-tumor properties

Forty-three quinolizidine alkaloids (1-43), including twelve new matrine-type ones, sophalodes A-L (1-7, 17, 19 and 28-30), were isolated from the seeds of Sophora alopecuroides. Structurally, compounds 1-4 were the first examples of C-11 oxidized matrine-type alkaloids from Sophora plants. The structures and absolute configurations of new compounds were elucidated by extensive spectroscopic techniques, X-ray diffraction analysis, and quantum chemical calculation. In addition, the NMR data and absolute configuration of compound 18 was reported for the first time. All the isolates were evaluated for their inhibition on nitric oxide production induced by lipopolysaccharide in RAW 264.7 macrophages, among them, compounds 29, 38 and 42 exhibited the most significant activity with IC₅₀ values of 29.19, 25.86 and 33.30 μM, respectively. Further research about new compound 29 showed that it also suppressed the protein levels of iNOS and COX-2, which revealed its anti-inflammatory potential. Moreover, additional research showed that compound 16 exhibited marginal cytotoxicity against HeLa cell lines, with an IC₅₀ value of 24.27 μM.

Acute Ramelteon Treatment Maintains the Cardiac Rhythms of Rats during Non-REM Sleep

Sleep curtailment negatively affects cardiac activities and thus should be ameliorated by pharmacological methods. One of the therapeutic targets is melatonin receptors, which tune circadian rhythms. Ramelteon, a melatonin MT1/MT2 receptor agonist, has recently been developed to modulate sleep-wake rhythms. To date, the sleep-promoting effect of ramelteon has been widely delineated, but whether ramelteon treatment physiologically influences cardiac function is not well understood. To address this question, we recorded electrocardiograms, electromyograms, and electrocorticograms in the frontal cortex and the olfactory bulb of unrestrained rats treated with either ramelteon or vehicle. We detected vigilance states based on physiological measurements and analyzed cardiac and muscular activities. We found that during non-rapid eye movement (non-REM) sleep, heartrate variability was maintained by ramelteon treatment. Analysis of the electromyograms confirmed that neither microarousal during non-REM sleep nor the occupancy of phasic periods during REM sleep was altered by ramelteon. Our results indicate that ramelteon has a remedial effect on cardiac activity by keeping the heartrate variability and may reduce cardiac dysfunction during sleep.

Network Pharmacology-Based Analysis of the Pharmacological Mechanisms of Aloperine on Cardiovascular Disease

Background

Aloperine is an active component of Sophora alopecuroides Linn, which has been extensively applied for the treatment of cardiovascular disease (CVD). However, our current understanding of the molecular mechanisms supporting the effects of aloperine on CVD remains unclear.

Methods

Systematic network pharmacology was conducted to provide testable hypotheses about pharmacological mechanisms of the protective effects of aloperine against CVD. Detailed structure was obtained from Traditional Chinese Medicines Integrated Database (TCMID). Target genes of aloperine against CVD were collected from SwissTargetPrediction, DrugBank database, and Online Mendelian Inheritance in Man (OMIM) database. Gene Ontology (GO) enrichment analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway performance, and network construction were adopted to explore common target genes.

Results

Our findings showed that 25 candidate targets were the interacting genes between aloperine and CVD. GO analysis revealed biological process, cellular component, and molecular function of these target genes. More importantly, the majority of enrichment pathways was found to be highly associated with the nitrogen metabolism by KEGG analysis. Core genes particularly in nitrogen metabolism pathway including carbonic anhydrase (CA) III, CA IV, CA VA, CA VB, CA VI, CA VII, CA IX, CA XII, and CA XIV can be modulated by aloperine in the nitrogen metabolism.

Conclusion

Our work revealed the pharmacological and molecular mechanisms of aloperine against CVD and provided a feasible tool to identify the pharmacological mechanisms of single active ingredient of traditional Chinese medicines.

A review on plants and herbal components with antiarrhythmic activities and their interaction with current cardiac drugs

This paper aimed to compile information on plants or their compounds which have experimentally shown antiarrhythmic effect and to scrutinize the efficacy and potency of them and their potential interaction with conventional cardiac drugs. Literature searches were accomplished by using numerous electronic databases, and the available knowledge on different parts of herbs and their ingredients with antiarrhythmic effects up to 2019 were identified and collected. The results indicate that 36 herbs or their derivatives can be effective in the treatment of arrhythmias, especially in animal and cellular models. They affect various ionic channels in different action potential phases. The alterations in ionic currents lead to changing in the amplitude and duration of the action potential, effective refractory period, maximum velocity, resting membrane potential, channel trafficking, or intracellular calcium concentration. The agents that prolong action potential duration and effective refractory period such as dauricine and sophocarpine seem to be more beneficial if more comprehensive studies confirm their efficacy and safety. It is noteworthy that the consumption of some herbal agents for cardiovascular (e.g. Hawthorn and Ginseng) or other (e.g. Ginseng and Licorice) therapeutic purposes may boost the pro-arrhythmogenic effect of current cardiovascular drugs such as cardiac glycosides. This study accentuates known plants or their derivatives with anti-arrhythmic effects, potential interaction with other cardiac drugs, and the possible mechanisms involved. It can assist clinicians and scientists in research and therapeutic approaches to the management of cardiac arrhythmias.

Quinolizidine alkaloids derivatives from Sophora alopecuroides Linn: Bioactivities, structure-activity relationships and preliminary molecular mechanisms

Quinolizidine alkaloids, as essential active ingredients extracted from Sophora alopecuroides Linn, have been well concerned in the past several decades owing to the unique structural features and numerous pharmacological activities. Quinolizidine alkaloids consist of matrine, oxymatrine, sophoridine, sophocarpine and aloperine etc. Additionally, quinolizidine alkaloids exert various excellent activities, including anti-cancer, anti-inflammation, anti-fibrosis, anti-virus and anti-arrhythmia regulations. In this review, we comprehensively clarify the pharmacological activities of quinolizidine alkaloids, as well as the relationship between biological function and structure-activity of substituted quinolizidine alkaloids. We believe that biological agents based on the pharmacological functions of quinolizidine alkaloids could be well applied in clinical practice.

Matrine suppresses KRAS-driven pancreatic cancer growth by inhibiting autophagy-mediated energy metabolism

Matrine is a natural compound extracted from the herb Sophora flavescens Ait which is widely used in traditional Chinese medicine for treating various diseases. Recently, matrine was reported to have antitumor effects against a variety of cancers without any obvious side effects; however, the molecular mechanisms of its antiproliferative effects on cancer are unclear. Here, we report that matrine inhibits autophagy-mediated energy metabolism, which is necessary for pancreatic cancer growth. We found that matrine significantly reduces pancreatic cancer growth in vitro and in vivo by insufficiently maintaining mitochondrial metabolic function and energy level. We also found that either pyruvate or α-ketoglutarate supplementation markedly rescues pancreatic cancer cell growth following matrine treatment. Inhibition of mitochondrial energy production results from matrine-mediated autophagy inhibition by impairing the function of lysosomal protease. Matrine-mediated autophagy inhibition requires stat3 downregulation. Furthermore, we found that the antitumor effect of matrine on pancreatic cancer growth depends on the mutation of the KRAS oncogene. Together, our data suggest that matrine can suppress the growth of KRAS-mutant pancreatic cancer by inhibiting autophagy-mediated energy metabolism.

Phytochemicals and PI3K Inhibitors in Cancer-An Insight

In today's world of modern medicine and novel therapies, cancer still remains to be one of the prime contributor to the death of people worldwide. The modern therapies improve condition of cancer patients and are effective in early stages of cancer but the advanced metastasized stage of cancer remains untreatable. Also most of the cancer therapies are expensive and are associated with adverse side effects. Thus, considering the current status of cancer treatment there is scope to search for efficient therapies which are cost-effective and are associated with lesser and milder side effects. Phytochemicals have been utilized for many decades to prevent and cure various ailments and current evidences indicate use of phytochemicals as an effective treatment for cancer. Hyperactivation of phosphoinositide 3-kinase (PI3K) signaling cascades is a common phenomenon in most types of cancers. Thus, natural substances targeting PI3K pathway can be of great therapeutic potential in the treatment of cancer patients. This chapter summarizes the updated research on plant-derived substances targeting PI3K pathway and the current status of their preclinical studies and clinical trials.

Synthesis, biological evaluation and mechanism studies of matrine derivatives as anticancer agents

A total of five matrine derivatives were synthesized and evaluated for their anti-proliferation activity using a panel of four human cancer cell lines, including A549 lung, BT20 breast, MCF-7 breast and U2OS osteosarcoma cells. The YF3-5, YF3-7 and YF3-9, three novel compounds, demonstrated increased anti-proliferation activity compared with matrine, of which YF3-5 revealed the strongest anti-proliferation activity with a half-maximal inhibitory concentration value of 15.49-16.67 µM against the four human cancer cell lines. The anti-proliferation mechanism underlying YF3-5 was investigated in the A549 human lung cancer cell line and the results demonstrated that YF3-5 exerted its anti-proliferation activity through the induction of apoptosis and oxidative stress, in addition to arresting the cell cycle at the G₁ phase in a dose-dependent manner.

Oxymatrine provides protection against Coxsackievirus B3-induced myocarditis in BALB/c mice

Oxymatrine is the primary pharmacological component of Sophora flavescens Ait. In the present study, we investigated the protective effect of oxymatrine against Coxsackievirus B3-induced myocarditis in mice. Coxsackievirus B3-infected HeLa cells were treated with oxymatrine and the viral titer, as well as the degree of cellular proliferation were determined. Additionally, BALB/c mice were infected with Coxsackievirus B3 and received differing concentrations of oxymatrine. On days 5 and 12 following treatment, mice were sacrificed, and serum lactate dehydrogenase, creatine kinase-MB isozyme, and tumor necrosis factor-α levels were quantified. The heart index and degree of myocardial tissue inflammation were also assessed. On day 5, the Coxsackievirus B3 TCID₅₀ values of the heart tissue, and the expression of NTR, IFN-γ, and TNF-α genes in the myocardial tissue were measured. Our results showed that oxymatrine exhibits potent antiviral effects on Coxsackievirus B3 as 50% inhibition was achieved at a concentration as low as 0.238 mg/mL. Oxymatrine markedly reduced the viral titer and inhibited cardiac myocyte pathology exhibited in viral myocarditis. Furthermore, oxymatrine treatment reduced the expression of Coxsackievirus B3 NTR and mouse TNF-α genes compared to the controls. Therefore, our findings indicate that oxymatrine is a promising potent antiviral agent against Coxsackievirus B3-induced myocarditis.

A novel matrine derivate inhibits differentiated human hepatoma cells and hepatic cancer stem-like cells by suppressing PI3K/AKT signaling pathways

Matrine is an alkaloid extracted from a Chinese herb Sophora flavescens Ait, which has shown chemopreventive potential against various cancers. In this study, we evaluated the anticancer efficacy of a novel derivative of matrine, (6aS, 10S, 11aR, 11bR, 11cS)-10- methylamino-dodecahydro- 3a,7a-diazabenzo (de) (MASM), against human hepatocellular carcinoma (HCC) cells and their corresponding sphere cells in vitro and in vivo. Human HCC cell lines (Hep3B and Huh7) were treated with MASM. Cell proliferation was assessed using CCK8 and colony assays; cell apoptosis and cell cycle distributions were examined with flow cytometry. The expression of cell markers and signaling molecules was detected using Western blot and qRT-PCR analyses. A sphere culture technique was used to enrich cancer stem cells (CSC) in Hep3B and Huh7 cells. The in vivo antitumor efficacy of MASM was evaluated in Huh7 cell xenograft model in BALB/c nude mice, which were administered MASM (10 mg·kg-1·d-1, ig) for 3 weeks. After the treatment was completed, tumor were excised and weighed. A portion of tumor tissue was enzymatically dissociated to obtain a single cell suspension for the spheroid formation assays. MASM (2, 10, 20 μmol/L) dose-dependently inhibited the proliferation of HCC cells, and induced apoptosis, which correlated with a reduction in Bcl-2 expression and an increase in PARP cleavage. MASM also induced cell cycle arrest in G0/G1 phase, which was accompanied by increased p27 and decreased Cyclin D1 expression. Interestingly, MASM (2, 10, and 20 μmol/L) drastically reduced the EpCAM+/CD133+ cell numbers, suppressed the sphere formation, inhibited the expression of stem cell marker genes and promoted the expression of mature hepatocyte markers in the Hep3B and Huh7 spheroids. Additionally, MASM dose-dependently suppressed the PI3K/AKT/mTOR and AKT/GSK3β/β-catenin signaling pathways in Hep3B and Huh7 cells. In Huh7 xenograft bearing nude mice, MASM administration significantly inhibited Huh7 xenograft tumor growth and markedly reduced the number of surviving cancer stem-like cells in the tumors. MASM administration also reduced the expression of stem cell markers while increasing the expression of mature hepatocyte markers in the tumor tissues. The novel derivative of matrine, MASM, markedly suppresses HCC tumor growth through multiple mechanisms, and it may be a promising candidate drug for the treatment of hepatocellular carcinoma.

MASM, a Matrine Derivative, Offers Radioprotection by Modulating Lethal Total-Body Irradiation-Induced Multiple Signaling Pathways in Wistar Rats

Matrine is an alkaloid extracted from Sophora flavescens Ait and has many biological activities, such as anti-inflammatory, antitumor, anti-fibrosis, and immunosuppressive properties. In our previous studies, the matrine derivative MASM was synthesized and exhibited potent inhibitory activity against liver fibrosis. In this study, we mainly investigated its protection against lethal total-body irradiation (TBI) in rats. Administration of MASM reduced the radiation sickness characteristics and increased the 30-day survival of rats before or after lethal TBI. Ultrastructural observation illustrated that pretreatment of rats with MASM significantly attenuated the TBI-induced morphological changes in the different organs of irradiated rats. Gene expression profiles revealed that pretreatment with MASM had a dramatic effect on gene expression changes caused by TBI. Pretreatment with MASM prevented differential expression of 53% (765 genes) of 1445 differentially expressed genes induced by TBI. Pathway enrichment analysis indicated that these genes were mainly involved in a total of 21 pathways, such as metabolic pathways, pathways in cancer, and mitogen-activated protein kinase (MAPK) pathways. Our data indicated that pretreatment of rats with MASM modulated these pathways induced by TBI, suggesting that the pretreatment with MASM might provide the protective effects on lethal TBI mainly or partially through the modulation of these pathways, such as multiple MAPK pathways. Therefore, MASM has the potential to be used as an effective therapeutic or radioprotective agent to minimize irradiation damages and in combination with radiotherapy to improve the efficacy of cancer therapy.

Valsartan Upregulates Kir2.1 in Rats Suffering from Myocardial Infarction via Casein Kinase 2

Purpose

Myocardial infarction (MI) results in an increased susceptibility to ventricular arrhythmias, due in part to decreased inward-rectifier K+ current (IK1), which is mediated primarily by the Kir2.1 protein. The use of renin-angiotensin-aldosterone system antagonists is associated with a reduced incidence of ventricular arrhythmias. Casein kinase 2 (CK2) binds and phosphorylates SP1, a transcription factor of KCNJ2 that encodes Kir2.1. Whether valsartan represses CK2 activation to ameliorate IK1 remodeling following MI remains unclear.

Methods

Wistar rats suffering from MI received either valsartan or saline for 7 days. The protein levels of CK2 and Kir2.1 were each detected via a Western blot analysis. The mRNA levels of CK2 and Kir2.1 were each examined via quantitative real-time PCR.

Results

CK2 expression was higher at the infarct border; and was accompanied by a depressed IK1/Kir2.1 protein level. Additionally, CK2 overexpression suppressed KCNJ2/Kir2.1 expression. By contrast, CK2 inhibition enhanced KCNJ2/Kir2.1 expression, establishing that CK2 regulates KCNJ2 expression. Among the rats suffering from MI, valsartan reduced CK2 expression and increased Kir2.1 expression compared with the rats that received saline treatment. In vitro, hypoxia increased CK2 expression and valsartan inhibited CK2 expression. The over-expression of CK2 in cells treated with valsartan abrogated its beneficial effect on KCNJ2/Kir2.1.

Conclusions

AT1 receptor antagonist valsartan reduces CK2 activation, increases Kir2.1 expression and thereby ameliorates IK1 remodeling after MI in the rat model.

Matrine compromises mouse sperm functions by a [Ca(2+)]i-related mechanism

Matrine, a bioactive alkaloid widely used in Chinese medicine, inhibits mouse sperm functions in vitro. In this study, we investigated the reproductive toxicity of matrine to male mice in vivo. C57BL/6J mice were administered with daily doses of 0, 1, 10 and 50mg/kg matrine by intraperitoneal injection for 30 days. The results showed that matrine did not affect testis size, testis weight, sperm count and sperm viability, but it significantly inhibited total motility, progressive motility, linear velocity, capacitation and the progesterone-induced acrosome reaction of mouse sperm. Furthermore, the intracellular Ca(2+) concentration ([Ca(2+)]i), a key regulator of sperm function, was reduced in sperm of matrine-exposed mice. The current and gene expression of the sperm specific Ca(2+) channel, CatSper, which modulates Ca(2+) influx in sperm, were decreased in testes of matrine-exposed mice. These results indicate that matrine inhibits mouse sperm functions by a [Ca(2+)]i-related mechanism via CatSper channel.

Valsartan ameliorates KIR2.1 in rats with myocardial infarction via the NF-κB-miR-16 pathway

BACKGROUND

MicroRNAs have an important role in regulating arrhythmogenesis. MicroRNA-16 (miR-16) is predicted to target KCNJ2. The regulation of miR-16 is primarily due to NF-κB. Whether valsartan could downregulate miR-16 via the inhibition of NF-κB after MI and whether miR-16 targets KCNJ2 remain unclear.

METHODS

MI rats received valsartan or saline for 7days. The protein levels of NF-κB p65, inhibitor κBα (IκBα), and Kir2.1 were detected by Western blot analysis. The mRNA levels of Kir2.1 and miR-16 were examined by quantitative real-time PCR. Whole cell patch-clamp techniques were applied to record IK1.

RESULTS

MiR-16 expression was higher in the infarct border, and was accompanied by a depressed IK1/KIR2.1 level. Additionally, miR-16 overexpression suppressed KCNJ2/KIR2.1 expression. In contrast, miR-16 inhibition or binding-site mutation enhanced KCNJ2/KIR2.1 expression, establishing KCNJ2 as a miR-16 target. In the MI rats, compared to saline treatment, valsartan reduced NF-κB p65 and miR-16 expression and increased IκBα and Kir2.1 expression. In vitro, angiotensin II increased miR-16 expression and valsartan inhibited it. Overexpressing miR-16 in cells treated with valsartan abrogated its beneficial effect on KCNJ2/Kir2.1. NF-κB activation directly upregulates miR-16 expression.

CONCLUSIONS

miR-16 controls KCNJ2 expression, and valsartan ameliorates Kir2.1 after MI partly depending on the NF-κB-miR-16 pathway.

Synergistic Anticancer Activities of Natural Substances in Human Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is highly resistant to currently available chemotherapeutic agents. The clinical outcome of HCC treatment remains unsatisfactory. Therefore, new effective and well-tolerated therapy strategies are needed. Natural products are excellent sources for the development of new medications for disease treatment. Recently, we and other researchers have suggested that the combined effect of natural products may improve the effect of chemotherapy treatments against the proliferation of cancer cells. In addition, many combination treatments with natural products augmented intracellular reactive oxygen species (ROS). In this review we will demonstrate the synergistic anticancer effects of a combination of natural products with chemotherapeutic agents or natural products against human HCC and provide new insight into the development of novel combination therapies against HCC.

The alkaloid matrine of the root of Sophora flavescens prevents arrhythmogenic effect of ouabain

Matrine, a alkaloid of the root of Sophora flavescens, has multiple protective effects on the cardiovascular system including cardiac arrhythmias. However, the molecular and ionic mechanisms of matrine have not been well investigated. Our study aimed at to shed a light on the issue to investigate the antiarrhythmic effects of matrine by using ouabain to construct an arrhythmic model of cardiomyocytes. In this experiment, matrine significantly and dose-dependently increased the doses of ouabain required to induce cardiac arrhythmias and decreased the duration of arrhythmias in guinea pigs. In cardiomyocytes of guinea pigs, ouabain 10 μM prolonged action potential duration by 80% (p<0.05) and increased L-type Ca(2+) currents and Ca(2+) transients induced by KCl (p<0.05). Matrine 100 μM shortened the prolongation of APD and prevented the increase of L-type Ca(2+) currents and Ca(2+) transients induced by ouabain. Taken together, these findings provide the first evidence that matrine possessed arrhythmogenic effect of ouabain by inhibiting of L-type Ca(2+) currents and Ca(2+) overload in guinea pigs.

Matrine inhibits proliferation and induces apoptosis of human colon cancer LoVo cells by inactivating Akt pathway

The present study has investigated the anti-tumor activity and the underlying mechanisms of matrine on human colon cancer LoVo cells. Matrine inhibited the proliferation of the cells in dose- and time-dependent manners. The concentration required for 50 % inhibition (IC50) was 1.15, 0.738, and 0.414 mg/ml, when cell were incubated with matrine for 24, 48, and 72 h, respectively. Matrine induced cell cycle arrest at G1 phase by downregulating cyclin D1 and upregulating p27 and p21. Matrine induced cell apoptosis by reducing the ratio of Bcl-2/Bax and increasing the activation of caspase-9 in a dose-dependent manner. Matrine displayed its anti-tumor activity by inactivating Akt, the upstream factor of the above proteins. Matrine significantly reduced the protein levels of pAkt, and increased the protein levels of other downstream factors, pBad and pGSK-3β. Specific inhibition of pAkt induced cell apoptosis, and synergized with matrine to inhibit the proliferation of LoVo cells; whereas activation of Akt neutralized the inhibitory effect of matrine on cell proliferation. The present study has demonstrated that matrine inhibits proliferation and induces apoptosis of human colon cancer LoVo cells by inactivating Akt pathway, indicating matrine may be a potential anti-cancer agent for colon cancer.

Downregulation of miR-151-5p contributes to increased susceptibility to arrhythmogenesis during myocardial infarction with estrogen deprivation

Estrogen deficiency is associated with increased incidence of cardiovascular diseases. But merely estrogen supplementary treatment can induce many severe complications such as breast cancer. The present study was designed to elucidate molecular mechanisms underlying increased susceptibility of arrhythmogenesis during myocardial infarction with estrogen deprivation, which provides us a new target to cure cardiac disease accompanied with estrogen deprivation. We successfully established a rat model of myocardial ischemia (MI) accompanied with estrogen deprivation by coronary artery ligation and ovariectomy (OVX). Vulnerability and mortality of ventricular arrhythmias increased in estrogen deficiency rats compared to non estrogen deficiency rats when suffered MI, which was associated with down-regulation of microRNA-151-5p (miR-151-5p). Luciferase Reporter Assay demonstrated that miR-151-5p can bind to the 3′-UTR of FXYD1 (coding gene of phospholemman, PLM) and inhibit its expression. We found that the expression of PLM was increased in (OVX+MI) group compared with MI group. More changes such as down-regulation of Kir2.1/I_K1, calcium overload had emerged in (OVX+MI) group compared to MI group merely. Transfection of miR-151-5p into primary cultured myocytes decreased PLM levels and [Ca²⁺]_i, however, increased Kir2.1 levels. These effects were abolished by the antisense oligonucleotides against miR-151-5p. Co-immunoprecipitation and immunofluorescent experiments confirmed the co-localization between Kir2.1 and PLM in rat ventricular tissue. We conclude that the increased ventricular arrhythmias vulnerability in response to acute myocardial ischemia in rat is critically dependent upon down-regulation of miR-151-5p. These findings support the proposal that miR-151-5p could be a potential therapeutic target for the prevention of ischemic arrhythmias in the subjects with estrogen deficiency.

Matrine inhibits the adhesion and migration of BCG823 gastric cancer cells by affecting the structure and function of the vasodilator-stimulated phosphoprotein (VASP)

AIM

Vasodilator-stimulated phosphoprotein (VASP) expression is upregulated in human cancers and correlates with more invasive advanced tumor stages. The aim of this study was to elucidate the mechanisms by which matrine, an alkaloid derived from Sophora species plants, acted on the VASP protein in human gastric cancer cells in vitro.

METHODS

VASP was expressed and purified. Intrinsic fluorescence spectroscopy was used to study the binding of matrine to VASP. CD spectroscopy was used to examine the changes in the VASP protein secondary structure. Human gastric carcinoma cell line BGC823 was tested. Scratch wound and cell adhesion assays were used to detect the cell migration and adhesion, respectively. Real-time PCR and Western blotting assays were used to measure mRNA and protein expression of VASP.

RESULTS

In the fluorescence assay, the dissociation constant for binding of matrine to VASP protein was 0.86 mmol/L, thus the direct binding between the two molecules was weak. However, matrine (50 μg/mL) caused obvious change in the secondary structure of VASP protein shown in CD spectrum. Treatments of BGC823 cells with matrine (50 μg/mL) significantly inhibited the cell migration and adhesion. The alkaloid changed the subcellular distribution of VASP and formation of actin stress fibers in BGC823 cells. The alkaloid caused small but statistically significant decreases in VASP protein expression and phosphorylation, but had no significant effect on VASP mRNA expression.

CONCLUSION

Matrine modulates the structure, subcellular distribution, expression and phosphorylation of VASP in human gastric cancer cells, thus inhibiting the cancer cell adhesion and migration.

Matrine activates PTEN to induce growth inhibition and apoptosis in V600EBRAF harboring melanoma cells

Here, we report a natural chemical Matrine, which exhibits anti-melanoma potential with its PTEN activation mechanism. Matrine effectively inhibited proliferation of several carcinoma cell lines, including melanoma ^V600EBRAF harboring M21 cells. Flow cytometry analysis showed Matrine induced G₀/G₁ cell cycle arrest in M21 cells dose-dependently. Apoptosis in M21 cells induced by Matrine was identified by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) analysis and Annexin-V/FITC staining. Molecular mechanistic study suggested that Matrine upregulated both mRNA level and protein expression level of phosphatase and tensin homolog deleted on chromosome ten (PTEN), leading to inhibition of the PI3K/Akt pathway. Downregulation of phosphor-Akt^ser473 by Matrine activated p21 and Bax, which contributed to G₀/G₁ cell cycle and apoptosis. Besides, Matrine enhanced the PI3K/Akt inhibition effects to inhibit the cell proliferation with PI3K inhibitor, LY2940002. In summary, our findings suggest Matrine is a promising antitumor drug candidate with its possible PTEN activation mechanisms for treating cancer diseases, such as melanomas.

Synthesis, characterization and activity evaluation of matrinic acid derivatives as potential antiproliferative agents

A series of new matrinic acid derivatives 5a–e was synthesized. The chemical structures of the synthesized compounds were confirmed by ¹H-NMR, ¹³C-NMR, and electrospray ionization mass spectroscopy. The anti-tumor activities were also investigated in vitro by evaluating the effect of synthesized compounds on the proliferation of A375, A549, HeLa, and HepG2 cells. Compound 5e was found to be the most potent against A375 and HeLa cells, with IC₅₀ values of 37 and 75.5 μg/mL, respectively. Compounds 5b, 5c, 5g, and 5h also exhibited antiproliferative activities against A549 cells, with IC₅₀ values within the 36.2–47 μg/mL range. For HepG2 cells, 5e and 5i, with IC₅₀ values of 78.9 and 61 μg/mL, respectively, showed higher antiproliferative activity than taxol.

Protective role of autophagy in matrine‑induced gastric cancer cell death

Matrine has potent antitumor activity against a broad variety of cancer cells and our previous study showed that both autophagy and apoptosis were activated during matrine-induced gastric cancer cell death. The aim of the present study was to determine the significance of autophagy in antineoplastic effects of matrine and the molecular mechanism by which matrine induces autophagy in gastric cancer cells. Western blot analysis showed that exposure of gastric cancer cells to matrine resulted in the extent of autophagy increasing in a dose- and time-dependent manner by detecting micro-tubule-associated protein 1 light chain 3 (LC3). This induction was due to activation of autophagic flux, as supported using the lysosome inhibitor, bafilomycin A1, which produced an accumulation of LC3-II. Propidium iodide staining demonstrated that matrine induced cell death in a dose-dependent manner and the autophagy inhibitor 3-methyladenine (3-MA) or bafilomycin A1 enhanced lethality of matrine against gastric cancer cells. Moreover, after pretreatment with 3-MA, some of the gastric cancer cells treated with matrine exhibited prototypical characteristics of apoptosis by transmission electron microscopy. The ability of 3-MA to increase matrine-induced apoptosis was further confirmed by Annexin V-FITC/PI staining. Also, the combination of matrine and 3-MA was more potent than matrine alone in inhibiting the proliferation of SGC-7901 cells assessed by sulphorhodamine B assay. Furthermore, administration of the pan-caspase inhibitor zVAD-fmk or autophagy inducer rapamycin decreased the matrine-induced cell death. In addition, matrine treatment did not inhibit the phosphorylation of Akt and its downstream effectors mammalian target of rapamycin (mTOR) as well as p70 ribosomal protein S6 kinase (p70S6K), although the levels of the total Akt and mTOR were decreased. These results suggest that autophagy was activated as a protective mechanism against matrine-induced apoptosis and inhibition of autophagy may be an attractive strategy for enhancing the antitumor potential of matrine in gastric cancer.

Arsenic trioxide-induced hERG K(+) channel deficiency can be rescued by matrine and oxymatrine through up-regulating transcription factor Sp1 expression

The human ether-a-go-go-related gene (hERG) encodes the rapidly activating, delayed rectifier potassium channel (IKr) important for cardiac repolarization. Dysfunction of the hERG channel can cause Long QT Syndrome (LQTS). A wide variety of structurally diverse therapeutic compounds reduce the hERG current by acute direct inhibition of the hERG current or/and selective disruption of hERG protein expression. Arsenic trioxide (As(2)O(3)), which is used to treat acute promyelocytic leukemia, can cause LQTS type 2 (LQT2) by reducing the hERG current through the diversion of hERG trafficking to the cytoplasmic membrane. This cardiotoxicity limits its clinical applications. Our aim was to develop cardioprotective agents to decrease As(2)O(3)-induced cardiotoxicity. We reported that superfusion of hERG-expressing HEK293 (hERG-HEK) cells with matrine (1, 10 μM) increased the hERG current by promoting hERG channel activation. Long-term treatment with 1 μM matrine or oxymatrine increased expression of the hERG protein and rescued the hERG surface expression disrupted by As(2)O(3). In addition, Matrine and oxymatrine significantly shortened action potential duration prolonged by As(2)O(3) in guinea pig ventricular myocytes. These results were ascribed to the up-regulation of hERG at both mRNA and protein levels via an increase in the expression of transcription factor Sp1, an established transactivator of the hERG gene. Therefore, matrine and oxymatrine may have the potential to cure LQT2 as a potassium channel activator by promoting hERG channel activation and increasing hERG channel expression.

Matrine induces apoptosis in human acute myeloid leukemia cells via the mitochondrial pathway and Akt inactivation

Acute myeloid leukemia (AML) is a hematological malignancy characterized by a rapid increase in the number of immature myeloid cells in bone marrow. Despite recent advances in the treatment, AML remains an incurable disease. Matrine, a major component extracted from Sophora flavescens Ait, has been demonstrated to exert anticancer effects on various cancer cell lines. However, the effects of matrine on AML remain largely unknown. Here we investigated its anticancer effects and underlying mechanisms on human AML cells in vitro and in vivo. The results showed that matrine inhibited cell viability and induced cell apoptosis in AML cell lines as well as primary AML cells from patients with AML in a dose- and time-dependent manner. Matrine induced apoptosis by collapsing the mitochondrial membrane potential, inducing cytochrome c release from mitochondria, reducing the ratio of Bcl-2/Bax, increasing activation of caspase-3, and decreasing the levels of p-Akt and p-ERK1/2. The apoptotic effects of matrine on AML cells were partially blocked by a caspase-3 inhibitor Z-DEVD-FMK and a PI3K/Akt activator IGF-1, respectively. Matrine potently inhibited in vivo tumor growth following subcutaneous inoculation of HL-60 cells in SCID mice. These findings indicate that matrine can inhibit cell proliferation and induce apoptosis of AML cells and may be a novel effective candidate as chemotherapeutic agent against AML.

Matrine, a novel autophagy inhibitor, blocks trafficking and the proteolytic activation of lysosomal proteases

Autophagy has been referred to as a double-edged sword in tumorigenesis and tumor progression. Emerging evidence suggests that pharmacological modulation of autophagy is a promising therapeutic strategy for cancer. However, few autophagy-modulating compounds are currently approved for clinical use in humans. Matrine is a natural compound extracted from traditional Chinese medicine that is widely used for treatment of a variety of diseases without any obvious side effects. Recently, matrine has been reported to induce autophagy and autophagic cell death in cancer cells, although the underlying mechanisms have yet to be elucidated. Here, we systematically examined the autophagic events induced by matrine in SGC7901 cells. The accumulation of autophagic vacuoles in matrine-treated cells was verified by the conversion of microtubule-associated protein light chain 3 as well as confocal and transmission electron microscopy. Furthermore, we demonstrated that matrine blocked autophagic degradation by impairing the activities of lysosomal proteases. Moreover, confocal microscopy and gradient ultracentrifugation revealed that the trafficking processes and proteolytic activation of cathepsins were inhibited by matrine. Using a pH sensor probe, we found elevated pH values in endosomes/lysosomes in response to matrine treatment. Therefore, matrine seems to be a novel autophagy inhibitor that can modulate the maturation process of lysosomal proteases.

Matrine modulates HSC70 levels and rescues ΔF508-CFTR

Cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-dependent Cl(-) channel located in the plasma membrane, and its malfunction results in cystic fibrosis (CF), the most common lethal genetic disease in Caucasians. Most CF patients carry the deletion of Phe508 (ΔF508 mutation); this mutation prevents the delivery of the CFTR to its correct cellular location, the apical (lumen-facing) membrane of epithelial cells. Molecular chaperones play a central role in determining the fate of ΔF508-CFTR. In this report, we show that the Matrine, a quinolizidine alkaloid, downregulates the expression of the molecular chaperone HSC70 and increases the protein levels of ΔF508-CFTR in human alveolar basal epithelial cells (A549 cell line), stably transfected with a ΔF508-CFTR-expressing construct. Moreover, Matrine induced ΔF508-CFTR release from endoplasmic reticulum to cell cytosol and its localization on the cell membrane. Interestingly, downregulation of HSC70 resulted in increased levels of ΔF508-CFTR complexes with the co-chaperone BAG3 that in addition appeared to co-localize with the mutated protein on the cell surface. These results shed new light on ΔF508-CFTR interactions with proteins of the chaperones/co-chaperones system and could be useful in strategies for future medical treatments for CF.

Neuroprotective effect of early and short-time applying sophoridine in pMCAO rat brain: down-regulated TRAF6 and up-regulated p-ERK1/2 expression, ameliorated brain infaction and edema

BACKGROUND

Matrine has been proven to protect ischemic injury in brain and sophoridine (SOP) is an isomeride of matrine. It is unknown whether SOP has this protective effect on ischemic injury in brain. We therefore investigated the potential neuroprotective role of SOP and the underlying mechanism.

METHODS

Male, Sprague-Dawley rats were randomly assigned into five groups: Vehicle (pMCAO+saline), High dose (pMCAO+SOP 10 mg/kg), Middle dose (pMCAO+SOP 5 mg/kg), Low dose (pMCAO+SOP 2.5 mg/kg) and Sham operated group. Permanent middle cerebral artery occlusion (pMCAO) model was used and SOP was administered intraperitoneally immediately after cerebral ischemia and once daily in the following days. Neurological deficit was evaluated using a modified six point scale; brain water content and infarct volume were measured. The expression of TRAF6 and ERK1/2 were measured by immunohistochemistry, Western blotting.

RESULTS

Compared with Vehicle group, the cerebral edema was alleviated in High dose group (P<0.05), and the infarct volume was decreased in Low dose group (P<0.05). Consistent with these results, immunohistochemistry and Western blot analysis indicated that TRAF6 expression was significantly decreased in SOP administrated groups at 24 h, and the expression of phosphorylated ERK1/2 increased in Low dose at 72 h.

CONCLUSIONS

SOP protected the brain from damage caused by pMCAO, and this effect may be through down-regulation of TRAF6 expression and up-regulation of ERK1/2 phosphorylation expression.

Berberine alleviates ischemic arrhythmias via recovering depressed I(to) and I(Ca) currents in diabetic rats

The present study was designed to elucidate the potential mechanism underlying that berberine suppressed ischemic arrhythmias in a rat model of diabetes mellitus (DM). Streptozotocin (STZ)-induced diabetic rats were subjected to ischemia by the occlusion of left anterior descending (LAD) coronary artery. Berberine was orally administered for 7 days before ischemic injury in diabetic rats. Whole-cell patch-clamp was performed to measure the transient outward K⁺ current (I(to)) and L-type Ca²⁺ current (I(Ca)). Results showed that oral administration of berberine (100 mg/kg) attenuated ischemia-induced arrhythmias in diabetic rats. Berberine significantly shortened the prolonged QTc interval from 214 ± 6ms to 189 ± 5ms in ischemic diabetic rats, and also restored the diminished I(to) and I(Ca) current densities in the same animal model rats. In conclusion, the ability of berberine to protect diabetic rats against cardiac arrhythmias makes it possible to be a prospective therapeutic agent in clinical management of cardiac disease secondary to diabetes.

Effects of matrine on proliferation and apoptosis in gallbladder carcinoma cells (GBC-SD)

Although matrine, a primary active component of dried Sophora flavescens root (ku shen), is known to induce apoptosis in a variety of tumor cells in vitro, the molecular mechanism of such apoptosis remains elusive. This analysis of the cell cycle and apoptosis in matrine-treated human gallbladder carcinoma cells (GBC-SD) showed that matrine can indeed inhibit cell proliferation and induce G1 cell cycle arrest and apoptosis in a dose- and time-dependent manner. An additional western blot analysis of matrine-treated cells also showed caspase-3 and Bcl-2 activation, as well as cyclinE down-regulation. Overall, the results indicate that matrine perturbs gallbladder cancer cell progression during the G1 phase by down-regulating cyclinE and induces apoptosis by decreasing the expression of the antiapoptotic protein Bcl-2 and increasing expression of the proapoptotic protein Bax.

Matrine inhibits pacing induced atrial fibrillation by modulating I(KM3) and I(Ca-L)

AIM

To elucidate the protective effects of Matrine on atrial fibrillation (AF) induced by electric pacing in mice and underlying molecular and ion channel mechanisms.

METHODS

AF was introduced by electric pacing in mice and the incidence and duration of AF were evaluated. Functional expression of M(3) receptor (M(3)-R) and Cav1.2 were explored by western and Real-time PCR, action potential (AP) and the density of (I(KM3)) L-type calcium channel (I(Ca-L)) were both recorded using whole-cell patch in isolated atrial cardiomyocytes.

RESULTS

In control group, incidence and duration of AF induced by electric pacing were 50 ± 17% and 3.68 ± 1.84 s, respectively; after application of carbachol 50 µg/kg both incidence and duration of AF were significantly increased to 86 ± 24% and 65.2 ± 29.0 s. Compared with control group, pretreatment of Matrine for 15 days significantly reduced AF incidence and duration in dose-dependent manner. Atrial membrane-protein expression of M(3)-R was decreased and membrane Cav1.2 expression was up-regulated. In single Matrine-treated atrial cardiomyocyte the density of I(KM3) was significantly decreased by 39% as well compared with control group, P < 0.05, whereas, I(Ca-L) density of atrium was increased by 40%.

CONCLUSION

These data demonstrated at the first time that the anti-AF effects of Matrine may due, at least in part, to down-regulation of I(KM3) density and M(3)-R expression and up-regulation of I(Ca-L )density and α1C/Cav1.2 expression.

Electrophysiological mechanisms of sophocarpine as a potential antiarrhythmic agent

AIM

To examine the electrophysiological effects of sophocarpine on action potentials (AP) and ionic currents of cardiac myocytes and to compare some of these effects with those of amiodarone.

METHODS

Langendorff perfusion set-up was used in isolated guinea pig heart, and responses to sophocarpine were monitored using electrocardiograph. Conventional microelectrode, voltage clamp technique and perforated patch were employed to record fast response AP (fAP), slow response AP (sAP) and ionic currents in guinea pig papillary muscle or rabbit sinus node cells.

RESULTS

Tachyarrhythmia produced by isoprenaline (15 μmol/L) could be reversed by sophocarpine (300 μmol/L). Sophocarpine (10 μmol/L) decreased the amplitude by 4.0%, maximal depolarization velocity (V(max)) of the fAP by 24.4%, and Na(+) current (I(Na)) by 18.0%, while it prolonged the effective refractory period (ERP) by 21.1%. The same concentration of sophocarpine could also decrease the amplitude and V(max) of the sAP, by 26.8% and 25.7%, respectively, and attenuated the Ca(2+) current (I(CaL)) and the K(+) tail current substantially. Comparison of sophocarpine with amiodarone demonstrated that both prolonged the duration and the ERP of fAP and sAP, both decreased the amplitude and V(max) of the fAP and sAP, and both slowed the automatic heart rate.

CONCLUSION

Sophocarpine could reverse isoprenaline-induced arrhythmia and inhibit I(Na), I(CaL), and I(Kr) currents. The electrophysiological effects of sophocarpine are similar to those of amiodarone, which might be regarded as a prospective antiarrhythmic agent.

Antiarrhythmic effects and ionic mechanisms of oxymatrine from Sophora flavescens

Accumulating evidence indicates that oxymatrine may exert protective effects on the cardiovascular system. This study was designed to evaluate the antiarrhythmic effects as well as the electrophysiological properties of oxymatrine. The antiarrhythmic activity of oxymatrine was observed in a rat model of arrhythmia induced by coronary ligation. Action potential duration (APD), L-type calcium current (I(Ca-L) ), transient outward potassium current (I(to) ) and inward rectifier potassium current (I(K1)) in rat ventricular myocytes were recorded by utilizing the whole cell patch-clamp technique. The results showed that administration of oxymatrine significantly delayed the onset of ventricular arrhythmia, decreased the duration of ventricular arrhythmia and reduced the arrhythmia score of arrhythmic rats. The beneficial effects of oxymatrine may be related to the shortening of APD through reduction of I(Ca-L) , enhancement of I(to) and inhibition of I(K1).