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

Hernandezine induces autophagic cell death in human pancreatic cancer cells via activation of the ROS/AMPK signaling pathway

Hernandezine (Her) is a bisbenzylisoquinoline alkaloid extracted from the traditional Chinese herbal medicine Thalictrum glandulosissimum. Evidence shows that Her is a natural agonist of adenosine monophosphate (AMP)-activated protein kinase (AMPK) and induces apoptosis and autophagy in tumor cells. In this study, we investigated the role of autophagy in Her-induced cell death in human pancreatic cancer cell lines. We showed that Her dose-dependently suppressed cell proliferation, promoted autophagy and induced autophagic death in pancreatic ductal adenocarcinoma (PDAC) cell lines Capan-1 and SW1990. The IC50 values of Her in inhibition of Capan-1 and SW1990 cells were 47.7 μM and 40.1 μM, respectively. Immunoblotting showed that Her (1−40 μM) promoted the conversion of LC3-I to LC3-II, and Her exerted concentration-dependent and time-dependent effects on autophagy activation in PDAC cells. In transmission electron microscopy and fluorescence image analysis, we found that autophagic vacuoles were significantly increased in Her-treated cells. Knockdown of ATG5, a key gene in the autophagy pathway, alleviated the activation of autophagy by Her. These results demonstrated that Her induced autophagy in PDAC cells. Intensely activated autophagy could promote cell death. The autophagy inhibitors, BafA1 and HCQ significantly inhibited Her-induced cell death, implying that Her induced autophagic cell death in PDAC cells. Moreover, we showed that Her activated autophagy by increasing the phosphorylation of AMPK and decreasing the phosphorylation of mTOR/p70S6K. Knockdown of AMPKα relieves the autophagic cell death induced by Her. Furthermore, Her concentration-dependently enhanced reactive oxygen species (ROS) generation in PDAC cells. Antioxidants could reduce the phosphorylation of AMPK and suppress autophagic cell death induced by Her. Our study provides evidence for the development of Her as a therapeutic agent for the treatment of pancreatic cancer.

Hernandezine, a natural herbal alkaloid, ameliorates type 2 diabetes by activating AMPK in two mouse models

BACKGROUND

AMP-activated protein kinase (AMPK) is an effective target for treating diabetes. However, successful drug development is delayed due to issues including toxicity. Plant-derived natural product AMPK activators have emerged as a new way to treat diabetes due to its potential low safety risks. Here, we studied the effect of hernandezine (HER), a natural product derived from Thalictrum, in activating AMPK and treating T2D in mouse models.

METHOD

We tested HER in various cells and tissues, including primary hepatocytes, skeletal myotubes cell lines, as well as major metabolic tissues from diabetic (db/db) and diet-induced obesity (DIO) model mice. The effect of HER on glucose uptake via AMPK in vitro and in vivo was confirmed utilizing cell transfection and adenovirus interference analysis. Tissue staining assessed the effect of HER on adipogenesis. Real-time quantitative polymerase chain reaction (real-time PCR) was applied to verify the effect of HER on transcription factors. Western blot analysis was used to determine the activation of phosphorylated AMPK and ACC pathways.

RESULTS

Biochemically, we found that HER prevented pAMPK from dephosphorylation to prolong its activity, disproving previous direct activation model and providing a new model to explain HER-mediated AMPK activation. HER could be orally delivered to animals and has a 3-fold long half-life in vivo as compared to metformin. Importantly, long-term oral HER treatment potently reduced body weight and blood glucose in both type 2 diabetes mullitus (T2DM) mouse models by increasing glucose disposal and reducing lipogenesis, and appeared not to induce cardiac hypertrophy.

CONCLUSION

Natural product HER indirectly activates AMPK by suppressing its dephosphorylation. Oral HER effectively alleviated hyperglycemia and reduced body weight in T2D mouse models, appeared to have a low risk of causing cardiac hypertrophy, and might be a potential therapeutic option for T2DM.

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.

Natural Bizbenzoquinoline Derivatives Protect Zebrafish Lateral Line Sensory Hair Cells from Aminoglycoside Toxicity

Moderate to severe hearing loss affects 360 million people worldwide and most often results from damage to sensory hair cells. Hair cell damage can result from aging, genetic mutations, excess noise exposure, and certain medications including aminoglycoside antibiotics. Aminoglycosides are effective at treating infections associated with cystic fibrosis and other life-threatening conditions such as sepsis, but cause hearing loss in 20–30% of patients. It is therefore imperative to develop new therapies to combat hearing loss and allow safe use of these potent antibiotics. We approach this drug discovery question using the larval zebrafish lateral line because zebrafish hair cells are structurally and functionally similar to mammalian inner ear hair cells and respond similarly to toxins. We screened a library of 502 natural compounds in order to identify novel hair cell protectants. Our screen identified four bisbenzylisoquinoline derivatives: berbamine, E6 berbamine, hernandezine, and isotetrandrine, each of which robustly protected hair cells from aminoglycoside-induced damage. Using fluorescence microscopy and electrophysiology, we demonstrated that the natural compounds confer protection by reducing antibiotic uptake into hair cells and showed that hair cells remain functional during and after incubation in E6 berbamine. We also determined that these natural compounds do not reduce antibiotic efficacy. Together, these natural compounds represent a novel source of possible otoprotective drugs that may offer therapeutic options for patients receiving aminoglycoside treatment.

Trans-resveratrol simultaneously increases cytoplasmic Ca(2+) levels and nitric oxide release in human endothelial cells

SCOPE

The aim of this study was to investigate whether the dietary polyphenol trans-resveratrol (t-Resv) increases [Ca(2+)](c) in endothelial cells, leading to a simultaneous augmentation of nitric oxide (NO) biosynthesis.

METHODS AND RESULTS

We have separately and simultaneously measured [Ca(2+)](c) and NO in human endothelial cells using the Ca(2+) indicator fura-2 and the NO-sensitive fluorescent probe 4,5-diaminofluorescein. In ∼30% of cells, t-Resv (30 μM) induced an increase in [Ca(2+)](c) with a transient as well as sustained component and a simultaneous increase in NO biosynthesis. This effect was reduced by non-selective Ca(2+) channel blockers, inhibition of intracellular Ca(2+) release, inhibition of endothelial nitric oxide synthase (eNOS) and, to a lesser extent, inhibition of extracellular signal-regulated kinase 1/2 (ERK 1/2) or 5' adenosine monophosphate-activated protein kinase (AMPK). t-Resv did not modify in vitro eNOS activity, suggesting that the observed stimulation of NO generation proceeds via mobilisation of Ca(2+) and not through direct effects on eNOS.

CONCLUSION

We therefore show, for the first time, that t-Resv induces a concentration-dependent, simultaneous increase in [Ca(2+)](c) and NO biosynthesis that could be linked to its endothelium-dependent vasorelaxant effect. Under the assumption that t-Resv exhibits similar behaviour in human blood vessels in vivo, the pharmacological properties described here may contribute to the beneficial cardiovascular effects of this polyphenol by improving endothelial function.

Alpha-naphthoflavone induces vasorelaxation through the induction of extracellular calcium influx and NO formation in endothelium

The effect of alpha-naphthoflavone (alpha-NF) on vascular function was studied in isolated ring segments of the rat thoracic aorta and in primary cultures of human umbilical vein endothelial cells (HUVECs). alpha-NF induced concentration-dependent relaxation of the phenylephrine-precontracted aorta endothelium-dependently and -independently at lower and higher concentrations, respectively. The cGMP, but not cAMP, content was increased significantly in alpha-NF-treated aorta. Pretreatment with N(omega)-nitro- l-arginine methyl ester (L-NAME) or methylene blue attenuated both alpha-NF induced vasorelaxation and the increase of cGMP content significantly. The increase of cGMP content induced by alpha-NF was also inhibited by chelating extracellular Ca(2+) with EGTA. These results suggest that the endothelium-dependent vasorelaxation induced by alpha-NF is mediated most probably through Ca(2+)-dependent activation of NO synthase and guanylyl cyclase. In HUVECs, alpha-NF induced concentration-dependent formation of NO and Ca(2+) influx. alpha-NF-induced NO formation was abolished by removal of extracellular Ca(2+) and by pretreatment with the Ca(2+) channel blockers SKF 96365 and Ni(2+), but not by the L-type Ca(2+) channel blocker verapamil. The Ca(2+) influx, as measured by (45)Ca(2+) uptake, induced by alpha-NF was also inhibited by SKF 96365 and Ni(2+). Our data imply that alpha-NF, at lower concentrations, induces endothelium-dependent vasorelaxation by promoting extracellular Ca(2+) influx in endothelium and the activation of the NO-cGMP pathway.

Mechanism of the vasodilator effect of 12-O-methylcurine in rat aortic rings

The vasodilator effects of 12-O-methylcurine (OMC), a bisbenzylisoquinoline alkaloid isolated from Chondrodendron platyphyllum (Menispermaceae), and its respective mechanism of action were investigated in rat aorta. In either endothelium-intact or endothelium-denuded aortic rings, OMC induced concentration-dependent relaxation in vessels pre-contracted with 0.1 microM phenylephrine (IC50 = 63.2+/-8.8 microM and 73.9+/-5.3 microM, respectively), 100 microM 5-hydroxytryptamine (IC50=49.6+/-13 microM and 49.9+/-10 microM, respectively) and 50 mM KCl (IC50= 19.9+/-6.8 microM and 21.1+/-4.5 microM, respectively). OMC also inhibited in a concentration-dependent and non-competitive manner the concentration-response curves induced by CaCl2 in high K+ (IC50 = 16.7+/-1.6 microM). In addition, OMC (100 microM) strongly inhibited phenylephrine-induced contractions dependent on calcium influx in the absence and presence of nifedipine (10 microM). In Ca2+-free medium, the transient contractions induced by phenylephrine (0.1 microM) were strongly inhibited by OMC (100 microM), whereas those induced by caffeine (20 mM) were not altered. H-89 (1 microM) and Rp-8-pCPT-cGMPs (3 microM), selective inhibitors of protein kinase A and G, respectively, did not change the relaxant effect of OMC in aortic rings pre-contracted with phenylephrine. Finally, OMC induced a concentration-dependent relaxation (IC50 = 62.8+/-12.5 microM) of the sustained contractions induced by the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate in normal, but not in Ca2+-free, solution. The above results suggest that OMC induces a vasodilator effect in rataortic rings by a mechanism independent of the presence of functional endothelium and dependent on the influx of calcium ions through voltage- and receptor-operated calcium channels. Furthermore, it can also be suggested that the inhibition of calcium influx activated by protein kinase C is involved in the vasodilator effect of OMC.

Adverse effects of herbal treatment of cardiovascular disease: what the physician must know

The increasing use of herbal products by patients with cardiovascular disease represents a clinical challenge to physicians. The use of herbal products is increasing in our society, and less than 50% of patients using herbal products report this information to their physicians. In addition, physicians often lack the knowledge base for herbal medications to effectively counsel patients regarding adverse effects and potential herb-drug interactions. This article reviews Western and traditional Chinese herbs that are commonly used by patients with cardiovascular diseases, herbs noted to have adverse cardiovascular effects, and herbs that may potentially interact with commonly prescribed cardiovascular medications.

Effects of inhibitors for tyrosine kinase and non-selective cation channel on capacitative Ca(2+) entry in rat ileal smooth muscle

The effects of tyrosine kinase inhibitors and non-selective cation channel blockers on capacitative Ca(2+) entry were examined in the presence of methoxyverapamil in rat ileal smooth muscles. In Ca(2+)-free solution, carbachol or caffeine produced a rapid contraction mediated by Ca(2+) release from the stores (Ca(2+)-release response), and then led to Ca(2+) depletion of the stores. Subsequently, reintroduction of Ca(2+) caused a transient contraction due to capacitative Ca(2+) entry. Tyrosine kinase inhibitors, genistein and tyrphostin 47 but not herbimycin A, suppressed the responses to Ca(2+)-reintroduction much greater than Ca(2+)-release responses to carbachol or caffeine. Similar inhibitory effects on the responses to Ca(2+)-reintroduction were obtained with daidzein and tyrphostin A1, respective inactive analogue of genistein and tyrphostins. After continuous depletion of the stores with thapsigargin, Ca(2+)-reintroduction produced a sustained contraction, which was inhibited by these agents to different extents, but not by herbimycin A. In beta-escin-treated skinned muscles, genistein slightly reduced Ca(2+)-induced contraction. In fura-2-loaded tissues, SK&F 96365 inhibited contractile and [Ca(2+)](i) responses to Ca(2+)-reintroduction but minimally affected Ca(2+)-release responses. Tetrandrine suppressed both responses to Ca(2+)-reintroduction and to Ca(2+)-release. These results suggest that genistein and tyrphostin 47 inhibit capacitative Ca(2+) entry through an inhibition of Ca(2+) entry channels rather than tyrosine kinase. SK&F 96365, but not tetrandrine, seems to selectively inhibit the contractile responses to capacitative Ca(2+) entry in rat ileal smooth muscles.

The effects of tetrandrine on the contractile function and microvascular permeability in the stunned myocardium of rats

The effects of tetrandrine (Tet) on the contractile function and microvascular permeability in stunned rat myocardium in vivo were studied. Stunned myocardium was induced by 15 (MS(15) group) or 20 (MS(20) group) min of myocardial ischemia plus 60 min of reperfusion. The following was shown. (1) FITC-BSA concentration was 166.0 +/- 7. 9 microg/g myocardium in the control group. The concentrations in ischemic myocardium increased by 35.4 and 45.6% in MS(15) and MS(20) groups respectively (p<0.05). (2) Administration of Tet (64.2 and 96. 3 micromol/kg, I.P.) 20 min before ischemia not only ameliorated the contractile function, but also reduced the FITC-BSA concentrations in ischemic myocardium. At 60 min after reperfusion, the contractile function parameters in Tet-treated groups were significantly superior to those in corresponding stunning groups. FITC-BSA concentrations in Tet-treated groups were lower than those in stunning groups. Then, there was already no significant difference in FITC-BSA concentrations between Tet-treated groups and the control group. The FITC-BSA concentrations at the end of experiments were correlated negatively with dp/dt(max) (r = -0.83, p<0.01). (3) Tet inhibited KCl-induced calcium influx in isolated cardiomyocytes. The results suggest that Tet given before ischemia may be involved in the reduction of microvascular permeability in stunned myocardium, which might be associated with its calcium channel blocking effect.

Agonist-stimulated calcium entry in primary cultures of human cerebral microvascular endothelial cells

Primary cultures of human cerebral microvascular endothelial cells (HCMEC) were loaded with fura-2. The intracellular free Ca2+ concentration ([Ca2+]i) was measured by digital imaging microscopy. Agonists ATP (100 micro), thrombin (10 units/ml), and histamine (25 microM) induced a transient [Ca2+]i increase. Histamine (100 microM) induced a biphasic [Ca2+]i increase with an initial [Ca2+]i peak followed by a [Ca2+]i plateau. The [Ca2+]i plateau was blocked by the receptor-operated Ca2+ channel (ROC) blockers SK&F 96365 and NCDC, indicating a contribution by Ca2+ influx through ROC to the [Ca2+]i plateau. However, this [Ca2+]i plateau was not blocked by the voltage-gated Ca2+ channel (VGC) blocker diltiazem (DTZ). Depolarization with 80K+ or application of the VGC agonist BAY K 8644 did not alter the resting [Ca2+]i; but 80K+ reduced the histamine (100 microM) induced [Ca2+]i plateau. These results show that HCMEC are devoid of functional VGC. Thus the membrane potential (Em) regulates Ca2+ entry mainly by enhancing the electrochemical Ca2+ gradient, such that hyperpolarization increases while depolarization decreases [Ca2+]i. Blockade of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) by CPA increased [Ca2+]i. This effect was dependent on extracellular Ca2+ and reduced by iberiotoxin (IBTX) blockade of Ca2+-activated K+ channels (Kca), suggesting a role for Kca in regulating Ca2+ influx. Ca2+ is the principal activator of endothelial nitric oxide synthase (eNOS), which stimulates cyclic GMP production. The final result that the eNOS inhibitor L-NAME enhanced the histamine (100 microM) induced [Ca2+]i plateau suggests a negative feedback loop (via cGMP) of endothelial NO on its own synthesis in the regulation of endothelial [Ca2+]i signal.

Plant alkaloid tetrandrine downregulates protein kinase C-dependent signaling pathway in T cells

Tetrandrine, a purified traditional Chinese medicinal herb that acts as an immunosuppressant and a Ca2+ channel blocker, has been clinically used to treat patients with arthritis, silicosis and hypertension. Since T cells play a critical role as autoreactive and pathogenic population in autoimmune diseases, in this study, we examined the immunosuppressive effect of tetrandrine on human peripheral blood T cells. We showed that tetrandrine inhibited phorbol 12-myristate 13-acetate (PMA) + ionomycin-induced T cell proliferation, interleukin-2 secretion and the expression of the T cell activation antigen, CD71. Further investigation of the molecular mechanism demonstrated that tetrandrine inhibited the expression of the protein kinase C-dependent interleukin-2 receptor alpha chain and CD69 but not the expression of the Ca2+-dependent CD40 ligand and CD69. Interestingly, when tetrandrine and cyclosporin A were added together, significant synergism in the suppression of T cell activation was observed. Moreover, of the several tetrandrine analogues studied, hernandezine was the most potent inhibitor of protein kinase C signaling events. These results also suggest that the protein kinase C-inhibitory capacity of tetrandrine and its analogues may not be associated with their function as Ca2+ channel blockers. Lastly, we showed that, within therapeutic concentrations, tetrandrine and its analogues could induce cellular apoptosis, which is defective in autoimmune diseases. In conclusion, our findings provide novel information about the molecular mechanism of the immunosuppressive effect of tetrandrine and its analogues in human peripheral blood T cells.

Alpha-adrenoceptor interaction of tetrandrine and isotetrandrine in the rat: functional and binding assays

The action of 1S,1'S-tetrandrine, a bisbenzyltetrahydroisoquinoline alkaloid, on alpha1-adrenoceptors has been compared with that of its isomer 1R,1'S-isotetrandrine. The work includes binding assays to analyse the affinity of these products for the [3H]prazosin binding site of rat cerebral cortical membranes and functional studies on rat isolated aorta to examine the effects of both alkaloids on intracellular calcium processes related or not to alpha-adrenoceptor activation. A radioligand receptor-binding study showed that both compounds interacted with the alpha1-adrenoceptors displacing [3H]prazosin from the specific binding site. The Ki values (inhibition constants) were 0.69+/-0.12 and 1.6+/-0.4 microM for tetrandrine and isotetrandrine, respectively. The functional studies showed that both alkaloids concentration-dependently inhibited noradrenaline-induced contraction in Ca2+-free solution (IC50 values, i.e. the concentrations needed to induce 50% inhibition, were 252.8 and 174.9 microM for tetrandrine and isotetrandrine, respectively), the spontaneous contractile response elicited by extracellular calcium after depletion of noradrenaline-sensitive intracellular stores (increase in resting tone; IC50 values 11.6 and 19.6 microM for tetrandrine and isotetrandrine, respectively) and the refilling of intracellular Ca2+ stores sensitive to noradrenaline (IC50 values 7.4 and 14.9 microM for tetrandrine and isotetrandrine, respectively). The results show that tetrandrine and isotetrandrine interact with alpha1-adrenoceptors by displacing the [3H]prazosin binding site and that both compounds inhibit mainly the Ca2+-dependent process and have less action on alpha1-adrenoceptors. Tetrandrine is more potent than isotetrandrine.

Mobilization of internal Ca2+ by vasoactive intestinal polypeptide in endothelial cells

The aims of the present study were to establish whether vasoactive intestinal polypeptide (VIP) could mobilize internally-stored Ca2+ and whether Ca2+ release could trigger Ca2+ influx from the extracellular space. Bovine pulmonary artery endothelial cells from an established cell line were loaded with fura-2/AM and cells were studied in suspension or were imaged in monolayers at 40-80% confluency. In Ca2+ imaging studies, VIP evoked Ca2+ transients in Ca2+-free medium containing 50 microM EGTA. This was observed in 33 out of 122 cells examined on 29 separate trials. With each cell, the spread of Ca2+ appeared to occur from the periphery of the cell to the central core. Cells which did not respond to VIP responded to other stimulants such as bradykinin, endoplasmic reticulum Ca2+ pump inhibitors, (cyclopiazonic acid and thapsigargin), and endoplasmic reticulum Ca2+ release channel opener, ryanodine. The reintroduction of Ca2+ following VIP-induced Ca2+ release did not evoke a Ca2+ response in 5 cells imaged. Cells in suspension showed typical biphasic responses to bradykinin, thapsigargin or cyclopiazonic acid in the presence of external Ca2+. Stimulation with VIP caused transient Ca2+ responses in Ca2+-free physiological saline containing 50 microM EGTA. However, only 1 out of 4 cells tested showed a response to Ca2+ when it was reintroduced to the bathing medium. This study provided direct evidence for the first time in these bovine endothelial cells for VIP-mediated elevation of cytosolic concentration of Ca2+. The results also suggested that other mechanisms might prevail preventing capacitative Ca2+ entry following the release of internally-stored Ca2+.