The Ethanol Extract of Fructus trichosanthis Promotes Fetal Hemoglobin Production via p38 MAPK Activation and ERK Inactivation in K562 Cells

Pharmacological stimulation of fetal hemoglobin (HbF) expression may be a promising approach for the treatment of beta-thalassemia. In this study, the effects of Fructus trichosanthis (FT) were investigated in human erythroleukemic K562 cells for their gamma-globin mRNA and HbF-induction activities. The role of signaling pathways, including extracellular regulated protein kinase (ERK) and p38 mitogen-activated protein kinase (MAPK), was also investigated. It was found that the ethanol extract of FT significantly increased gamma-globin mRNA and HbF levels, determined by real-time reverse transcription polymerase chain reaction and enzyme linked immunosorbent assay, respectively, in dose- and time-dependent manner. Total Hb (THb) levels were also elevated in the concentrations without cytotoxicity (<80 μg mL(-1)). Pre-treatment with p38 MAPK inhibitor SB203580 blocked the stimulatory effects of FT extract in total and HbF induction. In contrast, no change in HbF was observed when treated with ERK inhibitor PD98059. Furthermore, FT ethanol extract activated p38 MAPK and inhibited ERK signaling pathways in K562 cells, as revealed in western blotting analysis. In addition, SB203580 significantly abolished p38 MAPK activation when the cells were treated with FT. In summary, the ethanol extract of FT was found to be a potent inducer of HbF synthesis in K562 cells. The present data delineated the role of ERK and p38 MAPK signaling as molecular targets for pharmacologic stimulation of HbF production upon FT treatment.

Relative contribution of individual oxidized components in ox-LDL to inhibition on endothelium-dependent relaxation in rat aorta

BACKGROUND AND AIM

Oxidized low-density lipoprotein (ox-LDL) causes atherosclerosis and endothelial dysfunction. No study up to the present date has examined the relative contribution of all the oxidized components in ox-LDL to inhibition on vascular function. Our aim was to investigate the effects of individual oxidized components at concentrations similar to those in ox-LDL on the impairment of endothelium-dependent relaxation in rat aorta.

METHODS AND RESULTS

Rat thoracic aorta was pre-treated with lysophosphatidylcholine (LPC), cholesterol oxidized products (COPs), oxidized linoleic acid (ox-18:2) and oxidized linolenic acid (ox-18:3) at concentrations similar to those in human ox-LDL. Ox-LDL as a whole caused 61% inhibition while LPC, COPs and ox-18:2 at concentrations similar to those in ox-LDL caused 12%, 24% and 19% inhibition, respectively, on endothelium-dependent relaxation, suggesting that COPs produced the most adverse effect followed by ox-18:2 and LPC in an additional way. Three COPs including 7-ketocholesterol, 7α-hydroxycholesterol and 7β-hydroxycholesterol showed inhibition on endothelium-dependent relaxation with E(max) being reduced to 79-87% compared with the control E(max) (95%). At Western blot analysis phosphorylation of eNOS at Ser1177 site and total eNOS were not altered by ox-LDL treatment, indicating that ox-LDL did not affect nitric oxide (NO) synthesis capacity. Ox-LDL might react directly with NO and lower NO bioavailability.

CONCLUSION

The present study demonstrated the relative contribution of individual oxidized components in ox-LDL in the inhibition of endothelium-dependent relaxation in rat aorta. This inhibitory effect could be caused by the reduction of NO bioactivity.

Differential gene expressions in atrial and ventricular myocytes: insights into the road of applying embryonic stem cell-derived cardiomyocytes for future therapies

Myocardial infarction has been the leading cause of morbidity and mortality in developed countries over the past few decades. The transplantation of cardiomyocytes offers a potential method of treatment. However, cardiomyocytes are in high demand and their supply is extremely limited. Embryonic stem cells (ESCs), which have been isolated from the inner cell mass of blastocysts, can self-renew and are pluripotent, meaning they have the ability to develop into any type of cell, including cardiomyocytes. This suggests that ESCs could be a good source of genuine cardiomyocytes for future therapeutic purposes. However, problems with the yield and purity of ESC-derived cardiomyocytes, among other hurdles for the therapeutic application of ESC-derived cardiomyocytes (e.g., potential immunorejection and tumor formation problems), need to be overcome before these cells can be used effectively for cell replacement therapy. ESC-derived cardiomyocytes consist of nodal, atrial, and ventricular cardiomyocytes. Specifically, for treatment of myocardial infarction, transplantation of a sufficient quantity of ventricular cardiomyocytes, rather than nodal or atrial cardiomyocytes, is preferred. Hence, it is important to find ways of increasing the yield and purity of specific types of cardiomyocytes. Atrial and ventricular cardiomyocytes have differential expression of genes (transcription factors, structural proteins, ion channels, etc.) and are functionally distinct. This paper presents a thorough review of differential gene expression in atrial and ventricular myocytes, their expression throughout development, and their regulation. An understanding of the molecular and functional differences between atrial and ventricular myocytes allows discussion of potential strategies for preferentially directing ESCs to differentiate into chamber-specific cells, or for fine tuning the ESC-derived cardiomyocytes into specific electrical and contractile phenotypes resembling chamber-specific cells.

4-aminopyridine-sensitive K+ channels contributes to NaHS-induced membrane hyperpolarization and relaxation in the rat coronary artery

The present study aimed at examining the role of potassium channels and endothelium in relaxations induced by sodium hydrogen sulphide (NaHS), which is the donor of gaseous hydrogen sulphide (H(2)S) and the effect of NaHS on endothelium-dependent relaxations in rat coronary arteries. Rat coronary arteries were suspended in a myograph for force measurement and changes of the membrane potential in arteries were determined by membrane potential-sensitive fluorescence dye. NaHS relaxed coronary arteries pre-contracted by U46619 and the relaxation was significantly less in high KCl-contracted rings. NaHS-induced relaxations were reduced by 4-aminopyridine (4-AP) but unaffected by glibenclamide, iberiotoxin, N(G)-nitro-L-arginine methyl ester, ODQ, indomethacin or by endothelium removal. The inhibitory effect of 4-AP was absent in NaHS-induced relaxations in high KCl-contracted rings. Addition of NaHS caused membrane hyperpolarization and this effect was inhibited by 4-AP but not by glibenclamide. NaHS causes endothelium-independent relaxations in rat coronary arteries partially through activation of 4-AP-sensitive potassium channel and ensuring hyperpolarization. Other potassium channels, Na(+)-K(+) pump or endothelium-derived relaxing factors play little role.

Therapeutically relevant concentrations of raloxifene dilate pressurized rat resistance arteries via calcium-dependent endothelial nitric oxide synthase activation

OBJECTIVE

Selective estrogen receptor modulators (SERMs) inhibit constriction of mammalian conduit arteries. However, it is unknown whether SERMs at therapeutically achievable concentrations could reduce vascular tone in resistance arteries. The present study aimed to examine roles of Ca(2+) influx in endothelium and endothelial nitric oxide synthase (eNOS) activation in dilatations induced by raloxifene, a second-generation SERM in myogenically active arteries.

METHODS AND RESULTS

Small mesenteric arteries from Sprague-Dawley rats were isolated and mounted in a pressure myograph for measurement of changes in vessel diameter. [Ca(2+)](i) images on native endothelial cells of intact arteries were determined by the fluorescence imaging technique, and phosphorylation of eNOS was assayed by Western blotting. Raloxifene (0.3 to 10 nmol/L) produced dilatations on established steady myogenic constriction. Female rat arteries dilated significantly more in response to raloxifene than male arteries. Raloxifene-induced dilatations of female arteries were blunted by N(G)-nitro-l-arginine methyl ester but unaffected by 1400W, charybdotoxin plus apamin, wortmannin, or LY294002. Raloxifene (3 nmol/L) triggered rises in endothelial cell [Ca(2+)](i) and increased eNOS phosphorylation at Ser1177. Both effects were greater in arteries from female rats than in arteries from male rats. Increases in endothelial cell [Ca(2+)](i) and in eNOS phosphorylation were prevented by removal of extracellular Ca(2+) ions. Finally, ICI 182,780 did not affect the raloxifene-stimulated rise in endothelial cell [Ca(2+)](i), eNOS phosphorylation, and vasodilatations. Chronic raloxifene treatment reduced myogenic constriction in arteries from female but not male rats.

CONCLUSION

Raloxifene at therapeutically relevant concentrations inhibits myogenic constriction by an NO-dependent mechanism that causally involves the elevated [Ca(2+)](i) in endothelial cells and subsequent eNOS activation. Raloxifene dilates resistance arteries more effectively in female rats, indicating its significant gender-related action on endothelial cells in microcirculation.

Raloxifene, tamoxifen and vascular tone

1. Oestrogen deficiency causes progressive reduction in endothelial function. Despite the benefits of hormone-replacement therapy (HRT) evident in earlier epidemiological studies, recent randomized trials of HRT for the prevention of heart disease found no overall benefit. Instead, HRT users had higher incidences of stroke and heart attack. Most women discontinue HRT because of its many side-effects and/or the increased risk of breast and uterine cancer. This has contributed to the development of selective oestrogen receptor modulators (SERMs), such as tamoxifen and raloxifene, as alternative oestrogenic agents. 2. A SERM is a molecule that binds with high affinity to oestrogen receptors but has tissue-specific effects distinct from oestrogen, acting as an oestrogen agonist in some tissues and as an antagonist in others. Clinical and animal studies suggest multiple cardiovascular effects of SERMs. For example, raloxifene lowers serum levels of cholesterol and homocysteine, attenuates oxidation of low-density lipoprotein, inhibits endothelial-leucocyte interaction, improves endothelial function and reduces vascular smooth muscle tone. 3. Available evidence suggests that raloxifene and tamoxifen are capable of acting directly on both endothelial cells and the underlying vascular smooth muscle cells and cause a multitude of favourable modifications of the vascular wall, which jointly contribute to improved local blood flow. The outcome of the Raloxifene Use for the Heart (RUTH) trial will determine whether raloxifene, currently approved for the treatment of post-menopausal osteoporosis, could substitute for HRT in alleviating cardiovascular symptoms in post-menopausal women.

Ectopic expression of systemic RNA interference defective protein in embryonic stem cells

RNA interference (RNAi), a post-transcriptional gene silencing mechanism originally described in Caenorhabditis elegans, involves sequence-specific mRNA degradation mediated by double-stranded RNAs (dsRNAs). Passive dsRNA uptake has been uniquely observed in C. elegans due to the expression of systemic RNA interference defective-1 (SID-1). Here we investigated the ability of ectopic SID-1 expression to enable passive cellular uptake of short interfering RNA (siRNA) or double stranded RNA (dsRNA) in pluripotent mouse embryonic stem cells (mESCs). When SID-1-GFP and the Firefly luciferase reporter gene (luc(Fir)) were co-expressed in mESCs, luc(Fir) activity could be suppressed by simple incubation with dsRNAs/siRNAs that were designed to specifically target luc(Fir). By contrast, suppression was not observed in mESCs expressing luc(Fir) and GFP alone or when either GFP- or SID-1-GFP-expressing cells were incubated with control dsRNAs/siRNAs (non-silencing or Renilla luciferase-specific). These results may lead to high-throughput experimental strategies for studying ESC differentiation and novel approaches to genetically inhibit or eliminate the tumorigenicity of ESCs.

Tamoxifen and estrogen attenuate enhanced vascular reactivity induced by estrogen deficiency in rat carotid arteries

Recent clinical trials showed that estrogen usage in postmenopausal women did not affect coronary heart disease incidence, in contrast to several laboratory studies showing that estrogen decreased vascular reactivity. We speculated that, in some arteries, estrogen deficiency enhances endothelial function to compensate for the increased vascular smooth muscle reactivity. In this study, we examined the role of endothelium-derived vasoactive factors and the influence of in vivo estrogen and/or tamoxifen treatment on vascular reactivity of estrogen-deficient rats. Common carotid arteries were isolated from sham-operated (control), ovariectomized (Ovx), estrogen- or tamoxifen-treated Ovx rats, and Ovx rats co-treated with estrogen and tamoxifen. U46619 or phenylephrine induced similar contractions in endothelium-intact rings from all groups. Interestingly, removal of endothelium unmasked enhanced contractions in Ovx rats, which was prevented by estrogen, tamoxifen, or estrogen+tamoxifen treatment. Contractions to high K(+) were higher in both endothelium-intact and endothelium-denuded arteries from Ovx rats. Estrogen or tamoxifen treatment normalized high K(+)-induced contraction. A gap junction blocker, 18alpha-glycyrrhetinic acid, revealed enhanced contractions to U46619 in the absence or presence of l-NNA. Western blotting showed enhanced expressions of gap junctional connexin 43 in Ovx group. This study suggests that ovariectomy increases functional expression of gap junction-mediated endothelium-derived hyperpolarizing factor. Also, vascular effects of ovariectomy can be reversed by estrogen, tamoxifen or estrogen+tamoxifen treatment, suggesting that tamoxifen confers estrogenic effects in the vascular system.

Raloxifene prevents endothelial dysfunction in aging ovariectomized female rats

Lack of an appropriate animal model has delayed the better understanding of mechanisms related to higher cardiovascular risk in women after menopause. The aging female rat may share some menopausal changes observed in women. However, most studies have attempted to mimic menopause by ovariectomizing young (6-12 weeks old) animals without taking into accounts the influence of aging and of declining ovarian function. Therefore, the present study examined changes in vascular reactivity in the aging (15 months old) female rat after ovariectomy and the effects of chronic raloxifene therapy on vascular reactivity and eNOS protein expression. Aortic rings were prepared from the three experimental groups of rats: sham-operated control, ovariectomized and ovariectomized aging rats receiving daily oral administration of raloxifene for 3 months. Aortic rings were suspended in organ baths for the measurement of isometric tension. Rings with endothelium contracted significantly more to phenylephrine after inhibition of nitric oxide/cyclic GMP-signaling pathway by L-NAME or ODQ (as an index of basal nitric oxide release) in control and raloxifene-treated ovariectomized rats than in ovariectomized rats. This effect was abolished upon mechanical removal of the endothelium. Phenylephrine induced greater contractions only in rings with endothelium from ovariectomized rats as compared with control rats and raloxifene treatment normalized this response. In the presence of L-NAME or ODQ, phenylephrine-induced contraction was similar in rings from the three groups. Rings relaxed more to thapsigargin and acetylcholine in raloxifene-treated ovariectomized rats than in ovariectomized rats. There was no significant difference in aortic eNOS protein contents among the different groups. These results suggest that chronic oral administration of raloxifene to aging ovariectomized female rats augmented the bioavailability of endothelial nitric oxide in isolated aortic rings without altering eNOS protein levels.

A multifunctional aromatic residue in the external pore vestibule of Na+ channels contributes to the local anesthetic receptor

Voltage-gated Na(+) (Na(v)) channels are responsible for initiating action potentials in excitable cells and are the targets of local anesthetics (LA). The LA receptor is localized to the cytoplasmic pore mouth formed by the S6 segments from all four domains (DI-DIV) but several outer pore-lining residues have also been shown to influence LA block (albeit somewhat modestly). Many of the reported amino acid substitutions, however, also disrupt the inactivated conformations that favor LA binding, complicating the interpretation of their specific effects on drug block. In this article, we report that an externally accessible aromatic residue in the Na(v) channel pore, DIV-Trp1531, when substituted with cysteine, completely abolished LA block (e.g., 300 microM mexiletine induced a use-dependent block with 65.0 +/- 2.9% remaining current and -11.0 +/- 0.6 mV of steady-state inactivation shift of wild-type (WT) channels versus 97.4 +/- 0.7% and -2.4 +/- 2.1 mV of W1531C, respectively; p < 0.05) without destabilizing fast inactivation (complete inactivation at 20 ms at -20 mV; V(1/2) = -70.0 +/- 1.6 mV versus -48.6 +/- 0.5 mV of WT). W1531C also abolished internal QX-222 block (200 microM; 98.4 +/- 3.4% versus 54.0 +/- 3.2% of WT) without altering drug access. It is interesting that W1531Y restored WT blocking behavior, whereas W1531A channels exhibited an intermediate phenotype. Together, our results provide novel insights into the mechanism of drug action, and the structural relationship between the LA receptor and the outer pore vestibule.

A Multifunctional Aromatic Residue in the External Pore Vestibule of Na+ Channels Contributes to the Local Anesthetic Receptor

Voltage-gated Na(+) (Na(v)) channels are responsible for initiating action potentials in excitable cells and are the targets of local anesthetics (LA). The LA receptor is localized to the cytoplasmic pore mouth formed by the S6 segments from all four domains (DI-DIV) but several outer pore-lining residues have also been shown to influence LA block (albeit somewhat modestly). Many of the reported amino acid substitutions, however, also disrupt the inactivated conformations that favor LA binding, complicating the interpretation of their specific effects on drug block. In this article, we report that an externally accessible aromatic residue in the Na(v) channel pore, DIV-Trp1531, when substituted with cysteine, completely abolished LA block (e.g., 300 microM mexiletine induced a use-dependent block with 65.0 +/- 2.9% remaining current and -11.0 +/- 0.6 mV of steady-state inactivation shift of wild-type (WT) channels versus 97.4 +/- 0.7% and -2.4 +/- 2.1 mV of W1531C, respectively; p < 0.05) without destabilizing fast inactivation (complete inactivation at 20 ms at -20 mV; V(1/2) = -70.0 +/- 1.6 mV versus -48.6 +/- 0.5 mV of WT). W1531C also abolished internal QX-222 block (200 microM; 98.4 +/- 3.4% versus 54.0 +/- 3.2% of WT) without altering drug access. It is interesting that W1531Y restored WT blocking behavior, whereas W1531A channels exhibited an intermediate phenotype. Together, our results provide novel insights into the mechanism of drug action, and the structural relationship between the LA receptor and the outer pore vestibule.

Critical intra-linker interactions of HCN1-encoded pacemaker channels revealed by interchange of S3-S4 determinants

Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels contribute to the spontaneous rhythmic activities in cardiac and neuronal cells. Recently, we reported that the S3-S4 linker of HCN1 channels influences activation, and that part of the linker is helical with the determinants G231, M232, and E235 clustered on one side. Here we explored the undefined role of the G(231)E(235)M(232) triplet by systematic substitutions. Replacing G231 or M232 next to the "neighboring" E235 in the S3-S4 helix with an anionic residue (i.e., G231E, M232E) rendered channels non-functional although they were localized on the membrane surface. Interestingly, this loss of function could be readily rescued either by introducing a countercharge at position 235 (G231E/E235R, M232E/E235R) or by interchanging residues 231 or 232 and 235 (G231E/E235G, M232E/E235M). We conclude that residues 231, 232, and 235 are in close spatial proximity to each other, and uniquely interact with one another to shape the phenotypes of HCN channels.

Differential regulation of K+ and Ca2+ channel gene expression by chronic treatment with estrogen and tamoxifen in rat aorta

The beneficial effect of estrogen on the vascular system is partly associated with its ability to reduce vascular contractility. Estrogen acutely activates large-conductance Ca(2+)-activated K(+) channel (BK(Ca)) and inhibits L-type voltage-gated Ca(2+) channel (VGCC) in vascular smooth muscle cells. However, a long-term influence of estrogen, estrogen deficiency, or selective estrogen receptor modulators on gene expression of these ion channels is unclear. This study was therefore aimed to determine the relative mRNA expression levels of alpha- and beta-subunits of BK(Ca), K(V)1.5 subtype of delayed rectifier K(+) channel (K(V)), and alpha(1C) subunit of L-type VGCC in endothelium-denuded aortas from female rats by a semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis. Rats were divided into four experimental groups: (i) sham-operated control, (ii) ovariectomized, (iii) ovariectomized with 17 beta-estradiol treatment and (iv) ovariectomized with tamoxifen treatment. The results showed that ovariectomy decreased the mRNA expression of K(V)1.5 while it increased the mRNA expression of alpha(1C) subunit of L-type VGCC. Ovariectomy-induced modulation of gene expression of these ion channels was completely prevented in ovariectomized rats receiving chronic treatment with estrogen or tamoxifen. In contrast, the expression levels of genes encoding both alpha- and beta-subunits of BK(Ca) remained the same in the four animal groups. The present study has provided the first line of evidence suggesting the long-term beneficial effects of estrogen and tamoxifen therapy on vascular ion channel expressions, which may be an important mechanism by which the favorable modulation of vessel tone by estrogen or selective estrogen receptor modulators is mediated.

Dissecting the structural and functional roles of the S3-S4 linker of pacemaker (hyperpolarization-activated cyclic nucleotide-modulated) channels by systematic length alterations

If or Ih, a key player in neuronal and cardiac pacing, is encoded by the hyperpolarization-activated cyclic nucleotide-modulated (HCN) channel gene family. We have recently reported that the S3-S4 linker (i.e. residues 229EKGMDSEVY237 of HCN1) prominently influences the activation phenotypes of HCN channels and that part of the linker may conform a secondary helical structure. Here we further dissected the structural and functional roles of this linker by systematic alterations of its length. In contrast to voltage-gated K+ channels, complete deletion of the S3-S4 linker (Delta229-237) did not produce functional channels. Similarly, the deletions Delta229-234, Delta232-234, and Delta232-237 also abolished normal current activity. Interestingly, Delta229-231, Delta233-237, Delta234-237, Delta235-237, Delta229-231/Delta233-237, Delta229-231/Delta234-237, and Delta229-231/Delta235-237 all yielded robust hyperpolarization-activated inward currents, indicating that loss-of-function caused by deletion could be rescued by keeping the single functionally important residue Met232 alone. Whereas shortening the linker by deletion generally shifted steady-state activation in the depolarizing direction (e.g. DeltaV1/2 of Delta229-231, Delta233-237, Delta235-237 > +10 mV relative to wild type), linker prolongation by duplicating the entire linker (Dup229-237) or by glutamine insertion (InsQ233Q, InsQQ233QQ and InsQQQ233QQQ, or Ins237QQQ) produced length-dependent progressive hyperpolarizing activation shifts (-35 mV < DeltaV1/2 < -4 mV). Based on these results, we conclude that only Met232 is prerequisite for channels to function, but the length and other constituents of the S3-S4 linker shape the ultimate activation phenotype. Our results also highlight several evolutionary similarities and differences between HCN and voltage-gated K+ channels. Manipulations of the S3-S4 linker length may provide a flexible approach to customize HCN gating for engineering electrically active cells (such as stem cell-derived neuronal and cardiac pacemakers) for gene- and cell-based therapies.

Development of Effective Therapeutics Targeting the GABAA Receptor: Naturally Occurring Alternatives

The enhancement of GABA-mediated synaptic transmission underlies the pharmacotherapy of various neurological diseases. GABAA receptors are thus targets for neuroactive drugs, including classical benzodiazepines, mediating their anxiolytic, hypnotic and anticonvulsant effects via the benzodiazepine site (BZS). Based on findings that low intrinsic efficacy and subtype selectivity can greatly improve the specificity of drugs targeting the BZS, recent research has identified possible drug leads with apparently little side effects. In particular, drug leads of natural sources have been identified as promising candidates. This review describes the advances in the design of effective therapeutics targeting the GABAA receptor, focusing on the more recent research on naturally occurring drug leads. This includes discussion on the isolation of neuroactive alkaloids and flavonoids from herbal medicines and their rational development based on structure-activity relationships studies. Interest in the development of effective therapeutics from natural sources is clear and awaits to be seen whether their medicinal potential can be fulfilled.

Inhibition of nitric oxide/cyclic GMP-mediated relaxation by purified flavonoids, baicalin and baicalein, in rat aortic rings

The dried roots of Scutellaria baicalensis Georgi (Huangqin) are widely used in traditional Chinese medicine. We purified two flavonoids, baicalin and baicalein from S. baicalensis Georgi and examined their effects on isolated rat aortic rings. Baicalin (3-50 microM) inhibited endothelium/nitric oxide (NO)-dependent relaxation induced by acetylcholine (Ach) or cyclopiazonic acid (CPA). Baicalein at 50 microM abolished Ach-induced relaxation and markedly reduced CPA-induced relaxation. Treatment with 1mM L-arginine partially but significantly reversed the effects of baicalin (50 microM) or baicalein (50 microM) on Ach-induced relaxation. In endothelium-denuded rings, treatment with baicalin, baicalein or methylene blue partially inhibited relaxations induced by the NO donors, sodium nitroprusside (SNP) and hydroxylamine. Both flavonoids markedly reduced the increase in cyclic GMP levels stimulated by Ach in endothelium-intact rings and by SNP in endothelium-denuded rings. In contrast, exposure of endothelium-denuded rings to baicalin or baicalein did not affect relaxations induced by pinacidil or NS 1619, putative K+ channel activators. Neither flavonoids affected agonist-induced increase in the endothelial [Ca2+]i. Our results indicate that baicalin and baicalein attenuated NO-mediated aortic relaxation and cyclic GMP increases, likely through inhibition of NO-dependent guanylate cyclase activity.

Contribution of Na+ -Ca2+ exchanger to pinacidil-induced relaxation in the rat mesenteric artery

1 Pinacidil relaxes blood vessels through opening the K(ATP) channels with a resultant membrane hyperpolarization and inhibition of Ca(2+) influx. The aim of this study was to examine the mechanisms thereby pinacidil induces K(+) channel-independent relaxation in isolated endothelium-denuded rat mesenteric artery. 2 Pinacidil-induced relaxation was inhibited by glibenclamide (1-10 micro M) in phenylephrine-preconstricted rings, but was unaffected by glibenclamide after inhibition of K(+) channels and VGCCs. Pinacidil-induced K(+) channel-independent relaxation remained unchanged after treatment with cyclopiazonic acid (10 micro M), thapsigargin (1 micro M), ouabain (100 micro M), propranolol (10 micro M), Rp-cAMPS triethylamine (30 micro M), L-NNA (100 micro M), or ODQ (10 micro M). 3 Pinacidil induced more relaxant effect in the presence of nifedipine than in the presence of 60 mM K(+) plus nifedipine. Pretreatment with Na(+)-Ca(2+) exchanger inhibitors, nickel (30-300 micro M) or benzamil (20 micro M) attenuated pinacidil-induced relaxation in normal or in nifedipine-containing solution. Pinacidil (1 micro M) produced less relaxant effect with decreasing extracellular Na(+) concentration. Na(+)-free condition abolished the inhibitory effect of benzamil. Both nickel and benzamil inhibited pinacidil-induced relaxation in the presence of glibenclamide (10 micro M). Nickel (300 micro M) did not affect the relaxant response to sodium nitroprusside. 4 Pinacidil relaxed the rings preconstricted by active phorbol and U46619 with similar potency. 5 The present results indicate that stimulation of the forward mode Na(+)-Ca(2+) exchange pathway is in part responsible for pinacidil-induced K(+) channel-independent vasorelaxation. Pinacidil also induces K(+) channel-dependent but VGCCs-independent relaxation. The PKC-mediated cellular pathway may be a target site for pinacidil only in higher concentrations.

Inhibition of tumor-induced angiogenesis and matrix-metalloproteinase expression in confrontation cultures of embryoid bodies and tumor spheroids by plant ingredients used in traditional chinese medicine

Tumor-induced angiogenesis is a prerequisite for excessive tumor growth. Blood vessels invade the tumor tissue after degradation of the extracellular matrix scaffold by matrix metalloproteinases (MMPs). Inhibition of MMPs has been therefore suggested to be a useful tool to abolish neoangiogenesis of solid tumors. In the present study, antioxidative plant ingredients used in traditional Chinese medicine were investigated for their capacity to down-regulate MMP expression and to inhibit angiogenesis in embryonic stem cell-derived embryoid bodies and tumor-induced angiogenesis in confrontation cultures consisting of embryoid bodies and multicellular DU-145 prostate tumor spheroids. Embryoid bodies transiently expressed MMP-1, MMP-2, and MMP-9 during the time of differentiation of capillary-like structures. In confrontation cultures, MMP expression was increased compared with control tumor spheroids and embryoid bodies cultivated separately. The increased expression of MMPs in confrontation cultures was a result of elevated levels of reactive oxygen species (ROS) upon confrontation culture and was totally abolished in the presence of the free radical scavenger vitamin E. Incubation of embryoid bodies with baicalein, epicatechin, berberine, and acteoside, which are herbal ingredients used in traditional Chinese medicine, significantly inhibited angiogenesis in embryoid bodies and decreased intracellular ROS levels. Tumor-induced angiogenesis in confrontation cultures was totally abolished in the presence of the free radical scavenger vitamin E. Because herbal ingredients down-regulated MMP expression, we conclude that ROS generated during confrontation culture induce the expression of MMPs that are necessary for endothelial cell invasion into the tumor tissue.