Effects of nicotinic receptor agonists on beta-amyloid beta-sheet formation. (25/3151)

Previously we demonstrated that nicotinic acetylcholine receptor stimulation protects neurons against beta-amyloid (Abeta)-induced cytotoxicity. In the present study, the effects of nicotinic receptor agonists on the beta-sheet formation were investigated using a thioflavin T (ThT)-based fluorescence assay. Nicotine, cytisine (an alpha4beta2 agonist), and 3-(2,4)-dimethoxybenzylidene anabaseine (DMXB, an alpha7 agonist) did not reduce fluorescence intensity when these agents were added to the beta-sheet-formed Abeta. Simultaneous incubation of Abeta with nicotinic agonists also did not cause a reduction in fluorescence intensity. This data suggests that nicotinic receptor agonists do not influence the formation of the beta-sheet structure.  (+info)

Glioma migration can be blocked by nontoxic inhibitors of myosin II. (26/3151)

Anaplastic gliomas are infiltrative tumors, and their ability to migrate through normal brain contributes to their highly malignant behavior. Invasion of brain requires cell motility, which in turn depends on the activity of the cytoskeleton. A cytoskeletal component central to this process is myosin II, the cytoplasmic analogue of smooth and skeletal muscle myosin. Myosin II activity is regulated by the enzyme myosin light chain kinase, which activates myosin II by phosphorylating it on its regulatory light chain. We have investigated the role of myosin II in glioma motility and invasiveness by examining the effects of two inhibitors of myosin light chain kinase, ML7 and KT5926. Both drugs are potent inhibitors of both glioma motility, as measured by a scrape motility assay, and an in vitro haptotaxis assay. The inhibition of in vitro haptotaxis follows the dose-response relationship expected for competitive inhibition of myosin light chain kinase by these drugs and is seen at drug concentrations that are nontoxic. These results highlight the important role that myosin II contributes to glioma invasiveness and suggest that it may serve as a target in future strategies at blocking invasion by these tumors.  (+info)

Tetrandrine inhibited chronic "inflammatory" pulmonary hypertension in rats. (27/3151)

AIM: To study the effects of tetrandrine (Tet), on pulmonary hypertension. METHODS: An "inflammatory" chronic pulmonary hypertension induced by monocrotaline (Mon) in rats was used. RESULTS: Tet 50, 100, and 150 mg.kg-1.d-1 i.g. 3 wk inhibited Mon-induced increase of pulmonary artery pressure (PAP) by 23.8%, 34.9% (P < 0.05), and 42.0%, (P < 0.05); the right heart index by 2.0%, 25.0%, and 30.0% (P < 0.05) respectively compared with those from Mon group, without significant influence on the systemic artery pressure (SAP). Using histological exam by Verhoeff elastic stain and computer scanning analysis, it was found that Tet (100 mg.kg-1.d-1) for 3 wk, inhibited the increase of medial thickness and cross sectional area by 57.8% (P < 0.01) and 54.6% (P < 0.01), respectively vs Mon group. CONCLUSION: Tet ameliorated the development of pulmonary vascular and lung tissue injury induced by Mon in rats.  (+info)

Dauricine inhibited L-type calcium current in single cardiomyocyte of guinea pig. (28/3151)

AIM: To study the effect of dauricine (Dau) on L-type calcium current in guinea pig ventricular myocytes. METHODS: Using whole-cell recording method to record L-type calcium current (ICa) in single ventricular cell of guinea pig. RESULTS: Dau 1, 10, and 100 mumol.L-1 markedly reduced ICa by 15.2% +/- 2.2%, 41% +/- 5%, and 82% +/- 8%, respectively. After washing out, ICa partially recovered. Dau inhibited ICa at 3 Hz and 1 Hz to a similar extent, its effect on ICa appeared to be not frequency-dependent. CONCLUSION: Dau had a calcium channel blocking effect.  (+info)

Modulation of multidrug resistance by three bisbenzyl-isoquinolines in comparison with verapamil. (29/3151)

AIM: To compare cycleanine (Cyc), insularine (Insr), insulanoline (Insn) and verapamil (Ver) in modulation of multidrug resistance (MDR) in vitro. METHODS: The cytotoxic effect was determined by 3-[4, 5-dimethylthiazol-2-yl], 5-diphenyl tetarzolium bromide (MTT) assay. The intracellular doxorubincin (Dox) accumulation was assayed by spectrofluorometer. RESULTS: Cyc, Insr, Insn, and Ver showed significant activities in modulating Dox and vincristine resistances in acquired resistant MCF-7/Adr and KBv200 cell lines in a dose-dependent manner. Cyc, Insr, Insn, and Ver increased intracellular Dox accumulation in MCF-7/Adr cells. Cyc and Insr had greater activities than Ver in modulating MDR, while Insn had similar activity to that of Ver. CONCLUSION: MDR was modulated by Cyc, Insr, and Insn, due to the increase of intracellular Dox accumulation.  (+info)

Nuclear factor-kappaB plays an essential role in the late phase of ischemic preconditioning in conscious rabbits. (30/3151)

Although it is recognized that late preconditioning (PC) results from upregulation of cardioprotective genes, the specific transcription factor(s) that govern this genetic adaptation remains unknown. The aim of this study was to test the hypothesis that the development of late PC is mediated by nuclear factor-kappaB (NF-kappaB) and to elucidate the mechanisms that control the activation of NF-kappaB after an ischemic stimulus in vivo. A total of 152 chronically instrumented, conscious rabbits were used. A sequence of six 4-minute coronary occlusion/4-minute reperfusion cycles, which elicits late PC, induced rapid activation of NF-kappaB, as evidenced by a marked increase in p65 content (+164%; Western immunoblotting) and NF-kappaB DNA binding activity (+306%; electrophoretic mobility shift assay) in nuclear extracts isolated 30 minutes after the last reperfusion. These changes were attenuated 2 hours after ischemic PC and resolved by 4 hours. Competition and supershift assays confirmed the specificity of the NF-kappaB DNA complex signals. The mobility of the NF-kappaB DNA complex was shifted by anti-p65 and anti-p50 antibodies but not by anti-c-Rel antibodies, indicating that the subunits of NF-kappaB involved in gene activation after ischemic PC consist of p65-p50 heterodimers. Pretreatment with the NF-kappaB inhibitor diethyldithiocarbamate (DDTC; 150 mg/kg IP 15 minutes before ischemic PC) completely blocked the nuclear translocation and increased DNA binding activity of NF-kappaB. The same dose of DDTC completely blocked the cardioprotective effects of late PC against both myocardial stunning and myocardial infarction, indicating that NF-kappaB activation is essential for the development of this phenomenon in vivo. The ischemic PC-induced activation of NF-kappaB was also blocked by pretreatment with Nomega-nitro-L-arginine (L-NA), a nitric oxide synthase (NOS) inhibitor, N-2-mercaptopropionyl glycine (MPG), a reactive oxygen species (ROS) scavenger, chelerythrine, a protein kinase C (PKC) inhibitor, and lavendustin A, a tyrosine kinase inhibitor (all given at doses previously shown to block late PC), indicating that ischemic PC activates NF-kappaB via formation of NO and ROS and activation of PKC- and tyrosine kinase-dependent signaling pathways. A subcellular redistribution and increased DNA binding activity of NF-kappaB quantitatively similar to those induced by ischemic PC could be reproduced pharmacologically by giving the NO donor diethylenetriamine/NO (DETA/NO) (at a dose previously shown to elicit late PC), demonstrating that NO in itself can activate NF-kappaB in the heart. Taken together, these results provide direct evidence that activation of NF-kappaB is a critical step in the signal transduction pathway that underlies the development of the late phase of ischemic PC in conscious rabbits. The finding that four different pharmacological manipulations (L-NA, MPG, chelerythrine, and lavendustin A) produced similar inhibition of NF-kappaB suggests that this transcription factor is a common downstream pathway through which multiple signals elicited by ischemic stress (NO, ROS, PKC, tyrosine kinases) act to induce gene expression. To our knowledge, this is the first demonstration that NO can promote NF-kappaB activation in the heart, a finding that identifies a new biological function of NO and may have important implications for various pathophysiological conditions in which NO is involved and for nitrate therapy.  (+info)

Signal transduction in spontaneous myogenic tone in isolated arterioles from rat skeletal muscle. (31/3151)

OBJECTIVE: The mechanism of spontaneous myogenic tone was investigated in isolated arteriolar segments. METHODS: Arterioles were isolated from rat cremaster muscle. Segments were endothelium-denuded and mounted in a pressure myograph at 75 mmHg. Under this condition, segments spontaneously constricted from a passive diameter of 167 +/- 3 to 82 +/- 4 microns (n = 41). The effects of several inhibitors were tested on the maintenance of myogenic tone. RESULTS: Gadolinium (10(-6)-10(-4) M), a putative inhibitor of stretch-activated cation channels, was ineffective. The phospholipase C (PLC) inhibitor 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (NCDC) induced a dose-dependent inhibition of tone. NCDC inhibited phenylephrine- (10(-6) M), but not potassium buffer-induced (100 mM) constriction. The protein kinase C (PKC) inhibitors staurosporine, chelerythrine and calphostin C inhibited myogenic tone in a concentration-dependent manner. At an intermediate concentration, calphostin C selectively inhibited phenylephrine-induced constriction. However, all PKC inhibitors abolished responses to phenylephrine and potassium buffer at higher concentrations. The cytochrome P450 inhibitor 17-ODYA (0.3-3 x 10(-6) M) did not inhibit myogenic tone. CONCLUSIONS: No evidence was found for a role of gadolinium-sensitive, stretch-activated cation channels or cytochrome P450 metabolites. On the other hand, both PLC and PKC contribute to the maintenance of myogenic tone.  (+info)

PKC-dependent activation of p44/p42 MAPKs during myocardial ischemia-reperfusion in conscious rabbits. (32/3151)

Using conscious rabbits, we examined the effect of ischemic preconditioning (PC) on p44 and p42 mitogen-activated protein kinases (MAPKs). We found that both isoforms contribute significantly to total MAPK activity in the heart (in-gel kinase assay: p44, 59 +/- 1%; p42, 41 +/- 1%). Ischemic PC (6 cycles of 4-min occlusion/4-min reperfusion) elicited a pronounced increase in total cellular MAPK activity (+89%). This increase, which occurred exclusively in the nuclear fraction, was contributed by both isoforms (in-gel kinase assay: p44, +97%; p42, +210%) and was accompanied by migration of the two proteins from the cytosolic to the nuclear compartment. In control rabbits, MAPK kinase (MEK)1 and MEK2, direct activators of p44 and p42 MAPKs, were located almost exclusively in the cytosolic fraction. Ischemic PC induced a marked increase in cytosolic MEK activity (+164%), whereas nuclear MEK activity did not change, indicating that MEK-induced activation of MAPKs occurred in the cytosolic compartment. Activation of MAPKs after ischemic PC was completely blocked by the protein kinase C (PKC) inhibitor chelerythrine. Selective overexpression of PKC-epsilon in adult rabbit cardiomyocytes induced activation of both p44 and p42 MAPKs and reduced lactate dehydrogenase release during simulated ischemia-reperfusion, which was abolished by the MEK inhibitor PD-98059. The results demonstrate that 1) ischemic PC induces a rapid activation of p44 and p42 MAPKs in hearts of conscious rabbits; 2) the mechanism of this phenomenon involves activation of p44 and p42 MAPKs in the cytosol and their subsequent translocation to the nucleus; and 3) it occurs via a PKC-mediated signaling pathway. The in vitro data implicate PKC-epsilon as the specific isoform responsible for PKC-induced MAPK activation and suggest that p44/p42 MAPKs contribute to PKC-epsilon-mediated protection against simulated ischemia. The results are compatible with the hypothesis that p44 and p42 MAPKs may play a role in myocardial adaptations to ischemic stress.  (+info)