(1/3151) Development of muscarinic analgesics derived from epibatidine: role of the M4 receptor subtype.
Epibatidine, a neurotoxin isolated from the skin of Epipedobates tricolor, is an efficacious antinociceptive agent with a potency 200 times that of morphine. The toxicity of epibatidine, because of its nonspecificity for both peripheral and central nicotinic receptors, precludes its development as an analgesic. During the synthesis of epibatidine analogs we developed potent antinociceptive agents, typified by CMI-936 and CMI-1145, whose antinociception, unlike that of epibatidine, is mediated via muscarinic receptors. Subsequently, we used specific muscarinic toxins and antagonists to delineate the muscarinic receptor subtype involved in the antinociception evoked by these agents. Thus, the antinociception produced by CMI-936 and CMI-1145 is inhibited substantially by 1) intrathecal injection of the specific muscarinic M4 toxin, muscarinic toxin-3; 2) intrathecally administered pertussis toxin, which inhibits the G proteins coupled to M2 and M4 receptors; and 3) s.c. injection of the M2/M4 muscarinic antagonist himbacine. These results demonstrate that the antinociception elicited by these epibatidine analogs is mediated via muscarinic M4 receptors located in the spinal cord. Compounds that specifically target the M4 receptor therefore may be of substantial value as alternative analgesics to the opiates. (+info)
(2/3151) Phosphatidylinositol 3-kinase and protein kinase C are required for the inhibition of caspase activity by epidermal growth factor.
The mechanism by which growth factors exert an anti-apoptotic function on many cell types is not well understood. This issue is addressed in relation to epidermal growth factor (EGF) which inhibits apoptosis induced by staurosporine or wortmannin in an epithelial tumour cell line (CNE-2). The presence of EGF substantially reduced the in vitro Ac-DEVD-AMC hydrolytic activity and almost completely suppressed the intracellular cleavage of poly(ADP-ribose) polymerase in staurosporine- or wortmannin-treated cells. Staurosporine but not wortmannin caused the intracellular proteolytic processing of pro-caspase-3 and this event was transiently inhibited by EGF. Staurosporine-induced apoptosis was not inhibited by EGF in the presence of wortmannin or LY294002. Similarly, EGF failed to inhibit wortmannin-induced apoptosis in the presence of staurosporine, chelerythrine chloride or Go6850. These results suggest that phosphatidylinositol 3-kinase and protein kinase C play a role in the survival function of EGF but the reduction of cellular caspase activity cannot be satisfactorily explained by a lack of pro-caspase-3 activation. (+info)
(3/3151) Inhibition of human immunodeficiency virus type 1 replication by combination of transcription inhibitor K-12 and other antiretroviral agents in acutely and chronically infected cells.
8-Difluoromethoxy-1-ethyl-6-fluoro-1,4-dihydro-7-[4-(2-methoxyp hen yl)-1- piperazinyl]-4-oxoquinoline-3-carboxylic acid (K-12) has recently been identified as a potent and selective inhibitor of human immunodeficiency virus type 1 (HIV-1) transcription. In this study, we examined several combinations of K-12 and other antiretroviral agents for their inhibitory effects on HIV-1 replication in acutely and chronically infected cell cultures. Combinations of K-12 and a reverse transcriptase (RT) inhibitor, either zidovudine, lamivudine, or nevirapine, synergistically inhibited HIV-1 replication in acutely infected MT-4 cells. The combination of K-12 and the protease inhibitor nelfinavir (NFV) also synergistically inhibited HIV-1, whereas the synergism of this combination was weaker than that of the combinations with the RT inhibitors. K-12 did not enhance the cytotoxicities of RT and protease inhibitors. Synergism of the combinations was also observed in acutely infected peripheral blood mononuclear cells. The combination of K-12 and cepharanthine, a nuclear factor kappa B inhibitor, synergistically inhibited HIV-1 production in tumor necrosis factor alpha-stimulated U1 cells, a promonocytic cell line chronically infected with the virus. In contrast, additive inhibition was observed for the combination of K-12 and NFV. These results indicate that the combinations of K-12 and clinically available antiretroviral agents may have potential as chemotherapeutic modalities for the treatment of HIV-1 infection. (+info)
(4/3151) Replication-mediated DNA damage by camptothecin induces phosphorylation of RPA by DNA-dependent protein kinase and dissociates RPA:DNA-PK complexes.
Replication protein A (RPA) is a DNA single-strand binding protein essential for DNA replication, recombination and repair. In human cells treated with the topoisomerase inhibitors camptothecin or etoposide (VP-16), we find that RPA2, the middle-sized subunit of RPA, becomes rapidly phosphorylated. This response appears to be due to DNA-dependent protein kinase (DNA-PK) and to be independent of p53 or the ataxia telangiectasia mutated (ATM) protein. RPA2 phosphorylation in response to camptothecin required ongoing DNA replication. Camptothecin itself partially inhibited DNA synthesis, and this inhibition followed the same kinetics as DNA-PK activation and RPA2 phosphorylation. DNA-PK activation and RPA2 phosphorylation were prevented by the cell-cycle checkpoint abrogator 7-hydroxystaurosporine (UCN-01), which markedly potentiates camptothecin cytotoxicity. The DNA-PK catalytic subunit (DNA-PKcs) was found to bind RPA which was replaced by the Ku autoantigen upon camptothecin treatment. DNA-PKcs interacted directly with RPA1 in vitro. We propose that the encounter of a replication fork with a topoisomerase-DNA cleavage complex could lead to a juxtaposition of replication fork-associated RPA and DNA double-strand end-associated DNA-PK, leading to RPA2 phosphorylation which may signal the presence of DNA damage to an S-phase checkpoint mechanism. KEYWORDS: camptothecin/DNA damage/DNA-dependent protein kinase/RPA2 phosphorylation (+info)
(5/3151) Effects of prostaglandin F2 alpha on intracellular pH, intracellular calcium, cell shortening and L-type calcium currents in rat myocytes.
OBJECTIVE: We have studied the mechanisms underlying the positive inotropic action of prostaglandin F2 alpha (PGF2 alpha) by monitoring intracellular calcium transients, intracellular pH, L-type calcium currents and cell shortening in isolated ventricular myocytes. METHODS: Rat myocytes were loaded with fura-2AM for intracellular calcium measurements, or BCECF-AM for pH measurements. Cell shortening was recorded using an edge detection system, and L-type calcium currents measured using whole cell patch clamping. RESULTS: PGF2 alpha (3 nmol l-1-3 mumol l-1 increased single myocyte shortening and reduced resting cell length in a concentration-dependent manner. While myocyte shortening was increased by PGF2 alpha, this was not associated with any change in the amplitude of intracellular calcium transients, diastolic calcium, or L-type calcium currents. However, the same myocytes were capable of responding to catecholamines with increases in calcium transient amplitude and L-type calcium currents. PGF2 alpha (3 mumol l-1 caused a reversible rise in intracellular pH of 0.08 +/- 0.01 pH units (n = 5, p < 0.05). The Na(+)-H+ exchanger inhibitor, HOE 694 (10 mumol l-1, abolished the PGF2 alpha-induced rise in pH and the increase in cell shortening. PGF2 alpha-induced increases in cell shortening and intracellular pH were also attenuated by the protein kinase C (PKC) inhibitor, chelerythrine (2 mumol l-1. CONCLUSION: The positive inotropic action of PGF2 alpha appears to be mediated via activation of the Na(+)-H+ exchanger with the possible involvement of PKC. This suggests that PGF2 alpha-produces intracellular alkalosis, which then sensitizes cardiac myofilaments to calcium. (+info)
(6/3151) Morphine preconditioning attenuates neutrophil activation in rat models of myocardial infarction.
Previous results from our laboratory have suggested that morphine can attenuate neutrophil activation in patients with acute myocardial infarction. To elucidate if morphine preconditioning (PC) has the same effects via activation of neutrophil endopeptidase 24.11 (NEP), we measured serum levels of intercellular adhesion molecule-1 (ICAM-1), gp100MEL14 and NEP in adult Wistar rats subjected to ten different protocols (n = 10 for each) at baseline, immediately after and 2 h after morphine PC. All groups were subjected to 30 min of occlusion and 2 h of reperfusion. Similarly, morphine-induced PC was elicited by 3-min drug infusions (100 micrograms/kg) interspersed with 5-min drug-free periods before the prolonged 30-min occlusion. Infarct size (IS), as a percentage of the area at risk (AAR), was determined by triphenyltetrazolium staining. Pretreatment with morphine increased NEP activities (9.86 +/- 1.98 vs. 5.12 +/- 1.10 nmol/mg protein in control group; p < 0.001). Naloxone (mu-opioid receptor antagonist) (4.82 +/- 1.02 nmol/mg protein) and phosphoramidon (NEP inhibitor) (4.66 +/- 1.00 nmol/mg protein) inhibited morphine-activated NEP, whereas glibenclamide (ATP-sensitive potassium channel antagonist) and chelerythrine (protein kinase C inhibitor) had no effects. The ICAM-1 and gp100MEL14 of the third sampling were lowest for those with morphine PC (280 +/- 30 ng/ml and 2.2 +/- 0.7 micrograms/ml; p < 0.001), but naloxone (372 +/- 38 ng/ml and 3.8 +/- 0.9 micrograms/ml) and phosphoramidon (382 +/- 40 ng/ml and 4.2 +/- 1.1 micrograms/ml) abolished the above phenomenon. IS/AAR were definitely lowest for those with morphine PC (24 +/- 7%; p < 0.05). Morphine preconditioning increases NEP activities to attenuate shedding of gp100MEL14 and to ICAM-1 and, thus, provides myocardial protection. (+info)
(7/3151) Altered pharmacokinetics of a novel anticancer drug, UCN-01, caused by specific high affinity binding to alpha1-acid glycoprotein in humans.
The large species difference in the pharmacokinetics/pharmacodynamics of 7-hydroxystaurosporine (UCN-01) can be partially explained by the high affinity binding of UCN-01 to human alpha1-acid glycoprotein (AGP) (Fuse et al, Cancer Res., 58: 3248-3253, 1998). To confirm whether its binding to human AGP actually changes the in vivo pharmacokinetics, we have studied the alteration in its pharmacokinetics after simultaneous administration of human AGP to rats: (a) the protein binding of UCN-01 was evaluated by chasing its dissociation from proteins using dextran-coated charcoal. The UCN-01 remaining 0.1 h after adding dextran-coated charcoal to human plasma or AGP was approximately 80%, although the values for other specimens, except monkey plasma (approximately 20%), were <1%, indicating that the dissociation from human AGP was specifically slower than from other proteins; and (b) the pharmacokinetics of UCN-01 simultaneously administered with human AGP has been determined. The plasma concentrations after i.v. administration of UCN-O1 with equimolar human AGP were much higher than those after administration of UCN-01 alone. The steady-state distribution volume and the systemic clearance were reduced to about 1/100 and 1/200, respectively. Human AGP thus reduced the distribution and elimination of UCN-01 substantially. On the other hand, dog AGP, which has a low binding affinity for UCN-01, did not change the pharmacokinetics of UCN-01 so much. Furthermore, human AGP markedly reduced the hepatic extraction ratio of UCN-01 from 0.510 to 0.0326. Also, human AGP (10 microM) completely inhibited the initial uptake of UCN-01 (1 microM) into isolated rat hepatocytes, whereas the uptake of UCN-01 was unchanged in the presence of human serum albumin (10 microM). In conclusion, the high degree of binding of UCN-01 to human AGP causes a reduction in the distribution and clearance, resulting in high plasma concentrations in humans. (+info)
(8/3151) Comparison between huperzine A, tacrine, and E2020 on cholinergic transmission at mouse neuromuscular junction in vitro.
AIM: To compare the effects of huperzine A (Hup A), tacrine, and E2020 on cholinergic transmission at mouse neuromuscular junction in vitro. METHODS: The isolated mouse phrenic nerve-hemidiaphragm preparations were used with the conventional intracellular recording technique. The miniature end-plate potentials (MEPP), the mean quantal content of end-plate potentials (EPP), and the resting membrane potentials of muscle fiber were recorded. RESULTS: Hup A, tacrine, and E2020 at the concentration of 1.0 mumol.L-1 increased the amplitude, time-to-peak, and half-decay time of MEPP in the potencies of E2020 > Hup A > tacrine. Hup A did not significantly change the frequency of MEPP, the appearance of giant MEPP or slow MEPP, the resting membrane potentials, and the mean quantal content of EPP. CONCLUSION: Hup A is a selective and potent cholinesterase inhibitor, by which activity it facilitates the cholinergic transmission at mouse neuromuscular junction, and devoid of pre- and post-synaptic actions. (+info)