Induction of AT-specific DNA-interstrand crosslinks by bizelesin in genomic and simian virus 40 DNA.
Bizelesin is a bifunctional AT-specific DNA alkylating drug. Our study characterized the ability of bizelesin to induce interstrand crosslinks, a potential lethal lesion. In genomic DNA of BSC-1 cells, bizelesin formed from approx. 0.3 to 6.03+/-0.85 interstrand crosslinks per 106 base pairs, at 5-100 nM drug concentration, respectively, comparable to the number of total adducts previously determined in the same system (J.M. Woynarowski, M.M. McHugh, L.S. Gawron, T.A. Beerman, Biochemistry 34 (1995) 13042-13050). Bizelesin did not induce DNA-protein crosslinks or strand breaks. A model defined target, intracellular simian virus 40 (SV40) DNA, was employed to map at the nucleotide level sites of bizelesin adducts, including potential interstrand crosslinks. Preferential adduct formation was observed at AT tracts which are abundant in the SV40 matrix associated region and the origin of replication. Many sites, including each occurrence of 5'-T(A/T)4A-3', co-mapped on both DNA strands suggesting interstrand crosslinks, although monoadducts were also formed. Bizelesin adducts in naked SV40 DNA were found at similar sites. The localization of bizelesin-induced crosslinks in AT-rich tracts of replication-related regions is consistent with the potent anti-replicative properties of bizelesin. Given the apparent lack of other types of lesions in genomic DNA, interstrand crosslinks localized in AT-rich tracts, and to some extent perhaps also monoadducts, are likely to be lethal effects of bizelesin. (+info)
Prior exposure to neurotrophins blocks inhibition of axonal regeneration by MAG and myelin via a cAMP-dependent mechanism.
MAG is a potent inhibitor of axonal regeneration. Here, inhibition by MAG, and myelin in general, is blocked if neurons are exposed to neurotrophins before encountering the inhibitor; priming cerebellar neurons with BDNF or GDNF, but not NGF, or priming DRG neurons with any of these neurotrophins blocks inhibition by MAG/myelin. Dibutyryl cAMP also overcomes inhibition by MAG/myelin, and cAMP is elevated by neurotrophins. A PKA inhibitor present during priming abrogates the block of inhibition. Finally, if neurons are exposed to MAG/myelin and neurotrophins simultaneously, but with the Gi protein inhibitor, inhibition is blocked. We suggest that priming neurons with particular neurotrophins elevates cAMP and activates PKA, which blocks subsequent inhibition of regeneration and that priming is required because MAG/myelin activates a Gi protein, which blocks increases in cAMP. This is important for encouraging axons to regrow in vivo. (+info)
Single synaptic events evoke NMDA receptor-mediated release of calcium from internal stores in hippocampal dendritic spines.
We have used confocal microscopy to monitor synaptically evoked Ca2+ transients in the dendritic spines of hippocampal pyramidal cells. Individual spines respond to single afferent stimuli (<0.1 Hz) with Ca2+ transients or failures, reflecting the probability of transmitter release at the activated synapse. Both AMPA and NMDA glutamate receptor antagonists block the synaptically evoked Ca2+ transients; the block by AMPA antagonists is relieved by low Mg2+. The Ca2+ transients are mainly due to the release of calcium from internal stores, since they are abolished by antagonists of calcium-induced calcium release (CICR); CICR antagonists, however, do not depress spine Ca2+ transients generated by backpropagating action potentials. These results have implications for synaptic plasticity, since they show that synaptic stimulation can activate NMDA receptors, evoking substantial Ca2+ release from the internal stores in spines without inducing long-term potentiation (LTP) or depression (LTD). (+info)
Role of dexamethasone dosage in combination with 5-HT3 antagonists for prophylaxis of acute chemotherapy-induced nausea and vomiting.
Dexamethasone (20 mg) or its equivalent in combination with 5-HT3 antagonists appears to be the gold-standard dose for antiemetic prophylaxis. Additional to concerns about the use of corticosteroids with respect to enhanced tumour growth or impaired killing of the tumour cells, there is evidence that high-dosage dexamethasone impairs the control of delayed nausea and emesis, whereas lower doses appear more beneficial. To come closer to the most adequate dose, we started a prospective, single-blind, randomized trial investigating additional dosage of 8 or 20 mg dexamethasone to tropisetron (Navoban), a 5-HT3 receptor antagonist, in cis-platinum-containing chemotherapy. After an interim analysis of 121 courses of chemotherapy in 69 patients, we have been unable to detect major differences between both treatment alternatives. High-dose dexamethasone (20 mg) had no advantage over medium-dose dexamethasone with respect to objective and subjective parameters of acute and delayed nausea and vomiting. In relation to concerns about the use of corticosteroids in non-haematological cancer chemotherapy, we suggest that 8 mg or its equivalent should be used in combination with 5-HT3 antagonists until further research proves otherwise. (+info)
Pharmacology of LY315920/S-5920, [[3-(aminooxoacetyl)-2-ethyl-1- (phenylmethyl)-1H-indol-4-yl]oxy] acetate, a potent and selective secretory phospholipase A2 inhibitor: A new class of anti-inflammatory drugs, SPI.
LY315920 is a potent, selective inhibitor of recombinant human, group IIA, nonpancreatic secretory PLA2 (sPLA2). In a chromogenic isolated enzyme assay, LY315920 inhibited sPLA2 activity with an IC50 of 9 +/- 1 nM or 7.3 x 10(-6) mole fraction, which approached the stiochiometric limit of this assay. The true potency of LY315920 was defined using a deoxycholate/phosphatidylcholine assay with a mole fraction of 1.5 x 10(-6). LY315920 was 40-fold less active against human, group IB, pancreatic sPLA2 and was inactive against cytosolic PLA2 and the constitutive and inducible forms of cyclooxygenase. Human sPLA2-induced release of thromboxane A2 (TXA2) from isolated guinea pig lung bronchoalveolar lavage cells was inhibited by LY315920 with an IC50 of 0.79 microM. The release of TXA2 from these cells by N-formyl-methionyl-leucyl-phenylalanine or arachidonic acid was not inhibited. The i.v. administration of LY315920, 5 min before harvesting the bronchoalveolar lavage cells, resulted in the inhibition of sPLA2-induced production of TXA2 with an ED50 of 16.1 mg/kg. Challenge of guinea pig lung pleural strips with sPLA2 produced contractile responses that were suppressed in a concentration-dependent manner by LY315920 with an apparent KB of 83 +/- 14 nM. Contractile responses induced by arachidonic acid were not altered. Intravenous or oral administration of LY315920 to transgenic mice expressing the human sPLA2 protein inhibited serum sPLA2 activity in a dose-related manner over a 4-h time course. LY315920 is a potent and selective sPLA2 inhibitor and represents a new class of anti-inflammatory agent designated SPI. This agent is currently undergoing clinical evaluation and should help to define the role of sPLA2 in various inflammatory disease states. (+info)
Glomerular size-selective dysfunction in NIDDM is not ameliorated by ACE inhibition or by calcium channel blockade.
BACKGROUND: In patients with insulin-dependent diabetes mellitus (IDDM) and overt nephropathy glomerular barrier size-selectivity progressively deteriorates with time and is effectively improved by angiotensin converting enzyme (ACE) inhibition. Whether similar glomerular functional changes develop in proteinuric patients with non-insulin-dependent diabetes mellitus (NIDDM), and whether antihypertensive agents can favorably affect glomerular filtration of macromolecules in these patients, has not been documented yet. METHODS: We investigated renal hemodynamics and fractional clearance of neutral dextrans of graded sizes, in nine proteinuric patients with NIDDM and renal biopsy findings of typical diabetic glomerulopathy. Six healthy volunteers served as controls. We also investigated the effects of an ACE inhibitor and of a calcium channel blocker, both given in doses targeted to achieve a comparable level of systemic blood pressure control, on glomerular hemodynamics and sieving function. Theoretical analysis of glomerular macromolecule transport was adopted to evaluate intrinsic glomerular membrane permeability properties. RESULTS: Fractional clearance of large macromolecules (42 to 66 A in radius) was significantly higher in diabetic patients than in controls, and the distribution of membrane pore radii was calculated to be shifted towards larger pore sizes in diabetics (mean radius increased from 55 to 60 A). Despite effective blood pressure control, neither antihypertensive affected glomerular hemodynamics to any significant extent. Fractional clearance of dextrans, as well as of albumin and IgG, and total urinary proteins were not modified by either treatments. CONCLUSIONS: These data indicate that patients with NIDDM and overt nephropathy develop abnormalities in size-selective function of the glomerular barrier and, at variance to IDDM, such changes were not ameliorated either by ACE inhibition or calcium channel blockade. (+info)
Involvement of p21 in the PKC-induced regulation of the G2/M cell cycle transition.
Activation of protein kinase C (PKC) inhibits cell cycle progression at the G1/S and G2/M transitions. We found that phorbol 12-myristate 13-acetate (PMA) induced upregulation of p21, not only in MCF-7 cells arrested in the G1 phase as previously shown, but also in cells delayed in the G2 phase. This increase in p21 in cells accumulated in the G1 and G2/M phases of the cell cycle after PMA treatment was inhibited by the PKC inhibitor GF109203X. This indicates that PKC activity is required for PMA-induced p21 upregulation and cell cycle arrest in the G1 and G2/M phases of the cell cycle. To further assess the role of p21 in the PKC-induced G2/M cell cycle arrest independently of its G1 arrest, we used aphidicolin-synchronised MCF-7 cells. Our results show that, in parallel with the inhibition of cdc2 activity, PMA addition enhanced the associations between p21 and either cyclin B or cdc2. Furthermore, we found that after PMA treatment p21 was able to associate with the active Tyr-15 dephosphorylated form of cdc2, but this complex was devoid of kinase activity indicating that p21 may play a role in inhibition of cdc2 induced by PMA. Taken together, these observations provide evidence that p21 is involved in integrating the PKC signaling pathway to the cell cycle machinery at the G2/M cell cycle checkpoint. (+info)
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)