Daunorubicin-induced apoptosis in rat cardiac myocytes is inhibited by dexrazoxane. (25/155046)

-The clinical efficacy of anthracycline antineoplastic agents is limited by a high incidence of severe and usually irreversible cardiac toxicity, the cause of which remains controversial. In primary cultures of neonatal and adult rat ventricular myocytes, we found that daunorubicin, at concentrations /=10 micromol/L induced necrotic cell death within 24 hours, with no changes characteristic of apoptosis. To determine whether reactive oxygen species play a role in daunorubicin-mediated apoptosis, we monitored the generation of hydrogen peroxide with dichlorofluorescein (DCF). However, daunorubicin (1 micromol/L) did not increase DCF fluorescence, nor were the antioxidants N-acetylcysteine or the combination of alpha-tocopherol and ascorbic acid able to prevent apoptosis. In contrast, dexrazoxane (10 micromol/L), known clinically to limit anthracycline cardiac toxicity, prevented daunorubicin-induced myocyte apoptosis, but not necrosis induced by higher anthracycline concentrations (>/=10 micromol/L). The antiapoptotic action of dexrazoxane was mimicked by the superoxide-dismutase mimetic porphyrin manganese(II/III)tetrakis(1-methyl-4-peridyl)porphyrin (50 micromol/L). The recognition that anthracycline-induced cardiac myocyte apoptosis, perhaps mediated by superoxide anion generation, occurs at concentrations well below those that result in myocyte necrosis, may aid in the design of new therapeutic strategies to limit the toxicity of these drugs.  (+info)

Endothelial cells modulate the proliferation of mural cell precursors via platelet-derived growth factor-BB and heterotypic cell contact. (26/155046)

Embryological data suggest that endothelial cells (ECs) direct the recruitment and differentiation of mural cell precursors. We have developed in vitro coculture systems to model some of these events and have shown that ECs direct the migration of undifferentiated mesenchymal cells (10T1/2 cells) and induce their differentiation toward a smooth muscle cell/pericyte lineage. The present study was undertaken to investigate cell proliferation in these cocultures. ECs and 10T1/2 cells were cocultured in an underagarose assay in the absence of contact. There was a 2-fold increase in bromodeoxyuridine labeling of 10T1/2 cells in response to ECs, which was completely inhibited by the inclusion of neutralizing antiserum against platelet-derived growth factor (PDGF)-B. Antisera against PDGF-A, basic fibroblast growth factor, or transforming growth factor (TGF)-beta had no effect on EC-stimulated 10T1/2 cell proliferation. EC proliferation was not influenced by coculture with 10T1/2 cells in the absence of contact. The cells were then cocultured so that contact was permitted. Double labeling and fluorescence-activated cell sorter analysis revealed that ECs and 10T1/2 cells were growth-inhibited by 43% and 47%, respectively. Conditioned media from contacting EC-10T1/2 cell cocultures inhibited the growth of both cell types by 61% and 48%, respectively. Although we have previously shown a role for TGF-beta in coculture-induced mural cell differentiation, growth inhibition resulting from contacting cocultures or conditioned media was not suppressed by the presence of neutralizing antiserum against TGF-beta. Furthermore, the decreased proliferation of 10T1/2 cells in the direct cocultures could not be attributed to downregulation of the PDGF-B in ECs or the PDGF receptor-beta in the 10T1/2 cells. Our data suggest that modulation of proliferation occurs during EC recruitment of mesenchymal cells and that heterotypic cell-cell contact and soluble factors play a role in growth control during vessel assembly.  (+info)

Anti-monocyte chemoattractant protein-1/monocyte chemotactic and activating factor antibody inhibits neointimal hyperplasia in injured rat carotid arteries. (27/155046)

Monocyte chemoattractant protein-1 (MCP-1)/monocyte chemotactic and activating factor (MCAF) has been suggested to promote atherogenesis. The effects of in vivo neutralization of MCP-1 in a rat model were examined in an effort to clarify the role of MCP-1 in the development of neointimal hyperplasia. Competitive polymerase chain reaction analysis revealed maximum MCP-1 mRNA expression at 4 hours after carotid arterial injury. Increased immunoreactivities of MCP-1 were also detected at 2 and 8 hours after injury. Either anti-MCP-1 antibody or nonimmunized goat IgG (10 mg/kg) was then administered every 12 hours to rats that had undergone carotid arterial injury. Treatment with 3 consecutive doses of anti-MCP-1 antibody within 24 hours (experiment 1) and every 12 hours for 5 days (experiment 2) significantly inhibited neointimal hyperplasia at day 14, resulting in a 27.8% reduction of the mean intima/media ratio (P<0.05) in experiment 1 and a 43.6% reduction (P<0.01) in experiment 2. This effect was still apparent at day 56 (55.6% inhibition; P<0.05). The number of vascular smooth muscle cells in the neointima at day 4 was significantly reduced by anti-MCP-1 treatment, demonstrating the important role of MCP-1 in early neointimal lesion formation. However, recombinant MCP-1 did not stimulate chemotaxis of vascular smooth muscle cells in an in vitro migration assay. These results suggest that MCP-1 promotes neointimal hyperplasia in early neointimal lesion formation and that neutralization of MCP-1 before, and immediately after, arterial injury may be effective in preventing restenosis after angioplasty. Further studies are needed to clarify the mechanism underlying the promotion of neointimal hyperplasia by MCP-1.  (+info)

Phospholamban is present in endothelial cells and modulates endothelium-dependent relaxation. Evidence from phospholamban gene-ablated mice. (28/155046)

Vascular endothelial cells regulate vascular smooth muscle tone through Ca2+-dependent production and release of vasoactive molecules. Phospholamban (PLB) is a 24- to 27-kDa phosphoprotein that modulates activity of the sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA). Expression of PLB is reportedly limited to cardiac, slow-twitch skeletal and smooth muscle in which PLB is an important regulator of [Ca2+]i and contractility in these muscles. In the present study, we report the existence of PLB in the vascular endothelium, a nonmuscle tissue, and provide functional data on PLB regulation of vascular contractility through its actions in the endothelium. Endothelium-dependent relaxation to acetylcholine was attenuated in aorta of PLB-deficient (PLB-KO) mice compared with wild-type (WT) controls. This effect was not due to actions of nitric oxide on the smooth muscle, because sodium nitroprusside-mediated relaxation in either denuded or endothelium-intact aortas was unaffected by PLB ablation. Relative to denuded vessels, relaxation to forskolin was enhanced in WT endothelium-intact aortas. The endothelium-dependent component of this relaxation was attenuated in PLB-KO aortas. To investigate whether these changes were due to PLB, WT mouse aorta endothelial cells were isolated. Both reverse transcriptase-polymerase chain reaction and Western blot analyses revealed the presence of PLB in endothelial cells, which were shown to be >98% pure by diI-acetylated LDL uptake and nuclear counterstaining. These data indicate that PLB is present and modulates vascular function as a result of its actions in endothelial cells. The presence of PLB in endothelial cells opens new fields for investigation of Ca2+ regulatory pathways in nonmuscle cells and for modulation of endothelial-vascular interactions.  (+info)

Ischemic tolerance in murine cortical cell culture: critical role for NMDA receptors. (29/155046)

Murine cortical cultures containing both neurons and glia (days in vitro 13-15) were exposed to periods of oxygen-glucose deprivation (5-30 min) too brief to induce neuronal death. Cultures "preconditioned" by sublethal oxygen-glucose deprivation exhibited 30-50% less neuronal death than controls when exposed to a 45-55 min period of oxygen-glucose deprivation 24 hr later. This preconditioning-induced neuroprotection was specific in that neuronal death induced by exposure to excitotoxins or to staurosporine was not attenuated. Neuroprotection was lost if the time between the preconditioning and severe insult were decreased to 7 hr or increased to 72 hr and was blocked if the NMDA antagonist 100 microM 3-((D)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid was applied during the preconditioning insult. This was true even if the duration of preconditioning was increased as far as possible (while still remaining sublethal). A similar preconditioning effect was also produced by sublethal exposure to high K+, glutamate, or NMDA but not to kainate or trans-1-aminocyclopentane-1, 3-dicarboxylic acid.  (+info)

Inducible genetic suppression of neuronal excitability. (30/155046)

Graded, reversible suppression of neuronal excitability represents a logical goal of therapy for epilepsy and intractable pain. To achieve such suppression, we have developed the means to transfer "electrical silencing" genes into neurons with sensitive control of transgene expression. An ecdysone-inducible promoter drives the expression of inwardly rectifying potassium channels in polycistronic adenoviral vectors. Infection of superior cervical ganglion neurons did not affect normal electrical activity but suppressed excitability after the induction of gene expression. These experiments demonstrate the feasibility of controlled ion channel expression after somatic gene transfer into neurons and serve as the prototype for a novel generalizable approach to modulate excitability.  (+info)

Identification of the Kv2.1 K+ channel as a major component of the delayed rectifier K+ current in rat hippocampal neurons. (31/155046)

Molecular cloning studies have revealed the existence of a large family of voltage-gated K+ channel genes expressed in mammalian brain. This molecular diversity underlies the vast repertoire of neuronal K+ channels that regulate action potential conduction and neurotransmitter release and that are essential to the control of neuronal excitability. However, the specific contribution of individual K+ channel gene products to these neuronal K+ currents is poorly understood. We have shown previously, using an antibody, "KC, " specific for the Kv2.1 K+ channel alpha-subunit, the high-level expression of Kv2.1 protein in hippocampal neurons in situ and in culture. Here we show that KC is a potent blocker of K+ currents expressed in cells transfected with the Kv2.1 cDNA, but not of currents expressed in cells transfected with other highly related K+ channel alpha-subunit cDNAs. KC also blocks the majority of the slowly inactivating outward current in cultured hippocampal neurons, although antibodies to two other K+ channel alpha-subunits known to be expressed in these cells did not exhibit blocking effects. In all cases the blocking effects of KC were eliminated by previous incubation with a recombinant fusion protein containing the KC antigenic sequence. Together these studies show that Kv2.1, which is expressed at high levels in most mammalian central neurons, is a major contributor to the delayed rectifier K+ current in hippocampal neurons and that the KC antibody is a powerful tool for the elucidation of the role of the Kv2.1 K+ channel in regulating neuronal excitability.  (+info)

Thyroid hormone promotes the phosphorylation of STAT3 and potentiates the action of epidermal growth factor in cultured cells. (32/155046)

We have examined the effects of l-thyroxine (T4) on the activation of signal transducer and activator of transcription 3 (STAT3) and on the STAT3-dependent induction of c-Fos expression by epidermal growth factor (EGF). T4, at a physiological concentration of 100 nM, caused tyrosine phosphorylation and nuclear translocation (i.e. activation) of STAT3 in HeLa cells in as little as 10-20 min. Activation by T4 of STAT3 was maximal at 30 min (15+/-4-fold enhancement; mean+/-S.E.M.) in 18 experiments. This effect was reproduced by T4-agarose (100 nM) and blocked by CGP 41251, genistein, PD 98059 and geldanamycin, inhibitors of protein kinase C (PKC), protein tyrosine kinase (PTK), mitogen-activated protein kinase (MAPK) kinase and Raf-1 respectively. Tyrosine-phosphorylated MAPK also appeared in nuclear fractions within 10 min of treatment with T4. In the nuclear fraction of T4-treated cells, MAPK immunoprecipitate also contained STAT3. The actions of T4 were similar in HeLa and CV-1 cells, which lack thyroid hormone receptor (TR), and in TR-replete skin fibroblasts (BG-9). T4 also potentiated the EGF-induced nuclear translocation of activated STAT1alpha and STAT3 and enhanced the EGF-stimulated expression of c-Fos. Hormone potentiation of EGF-induced signal transduction and c-Fos expression was inhibited by CGP 41251, geldanamycin and PD 98059. Therefore the non-genomically induced activation by T4 of STAT3, and the potentiation of EGF by T4, require activities of PKC, PTK and an intact MAPK pathway.  (+info)