Inhibition of monoamine oxidase type A, but not type B, is an effective means of inducing anticonvulsant activity in the kindling model of epilepsy.
The anticonvulsant activity of inhibitors of monoamine oxidase (MAO) was reported early after the development of irreversible MAO inhibitors such as tranylcypromine, but was never clinically used because of the adverse effects of these compounds. The more recently developed reversible MAO inhibitors with selectivity for either the MAO-A or MAO-B isoenzyme forms have not been studied extensively in animal models of epilepsy, so it is not known which type of MAO inhibitor is particularly effective in this respect. We compared the following drugs in the kindling model of epilepsy: 1) L-deprenyl (selegiline), i.e., an irreversible inhibitor of MAO-B, which, however, also inhibits MAO-A at higher doses, 2) the novel reversible MAO-B inhibitor LU 53439 (3,4-dimethyl-7-(2-isopropyl-1,3, 4-thiadiazol-5-yl)-methoxy-coumarin), which is much more selective for MAO-B than L-deprenyl, 3) the novel reversible and highly selective MAO-A inhibitor LU 43839 (esuprone; 7-hydroxy-3, 4-dimethylcoumarin ethanesulfonate), and 4) the irreversible nonselective MAO inhibitor tranylcypromine. Esuprone proved to be an effective anticonvulsant in the kindling model with a similar potency as L-deprenyl. In contrast to esuprone and L-deprenyl, the selective MAO-B inhibitor LU 53439 was not effective in the kindling model; this substantiates the previous notion that the anticonvulsant activity of L-deprenyl is not related to MAO-B inhibition, but to other effects of this drug, such as inhibition of MAO-A. Drugs inhibiting both MAO-A and MAO-B to a similar extent (tranylcypromine) or combinations of selective MAO-A and MAO-B inhibitors (esuprone plus LU 53439) had no advantage over MAO-A inhibition alone, but were less well tolerated. The data thus suggest that selective MAO-A inhibitors such as esuprone may be an interesting new approach for the treatment of epilepsy. (+info)
7-ethoxycoumarin deethylation activity in perfused isolated rat brain.
7-ethoxycoumarin (7-EC) deethylation activity was measured in the perfused rat brain in situ. Infusion of 7-EC into a brain through an internal carotid artery resulted in the formation of 7-hydroxycoumarin (7-HC) and its conjugates in the effluent perfusate collected from the superior vena cava. The rate of formation of products was 200 nmol/h/g when 130 microM 7-EC was infused. This value was much higher (more than 100 times) than that determined from the brain microsomal activity ( approximately 1 nmol/h/g), indicating that the activity determined with microsomes was an underestimate. This value was comparable to the activity in the perfused liver (30-50%), suggesting that drug metabolizing enzymes can play important roles within the brain. Pretreatment of rats with P-450 inducers such as phenobarbital and beta-naphthoflavone increased the deethylation activity in the perfused brain, as in the perfused liver. We conclude that the perfused brain is suitable for evaluating drug metabolizing activities under physiological conditions. (+info)
Effect of praeruptorin C on spontaneous [Ca2+]i transients in cultured myocardial cells of neonatal rats.
AIMS: To study the effects of praeruptorin C (Pra-C) on [Ca2+]i transients in cultured neonatal myocardiocytes. METHOD: Using Ca(2+)-sensitive fluorescent indicator, Fura 2-AM, spontaneous cytosolic Ca2+ transients were measured in cultured myocardial cells of neonatal rats. RESULTS: Pra-C 10, 30 mumol.L-1 caused a decrease in the peak of Ca2+ transients. Pra-C 30 mumol.L-1 and 10-30 mumol.L-1 inhibited partly the stimulatory effects of CaCl2 4.8 mmol.L-1 and Bay k 8644 100 nmol.L-1 on peak Ca2+ transients, respectively. Pra-C did not cause any marked change in the basal [Ca2+]i level between beats. Pra-C inhibited the reduced [Ca2+]i transients after inhibition of sarcoplasmic reticulum Ca2+ release in ryanodine pretreated cells. CONCLUSIONS: Pra-C inferred with the Ca2+ influx responsible for excitation-contraction coupling in myocardiocytes. (+info)
Effects of praeruptorine C on the intracellular free calcium in normal and hypertrophied rat ventricular myocytes.
AIM: To study the intracellular free calcium ([Ca2+]i) in normal and hypertrophic left ventricular myocytes isolated from adult rat hearts and the effects of praeruptorine C (Pra-C) on them. METHODS: [Ca2+]i of single myocyte was measured with Fura 2-AM. RESULTS: The resting [Ca2+]i was 87 +/- 4 nmol.L-1 in normal left ventricular myocytes, 123 +/- 7 nmol.L-1 in hypertrophied myocytes. After exposure to KCl (20, 40, and 60 mmol.L-1), the [Ca2+]i were increased by 66%, 141%, and 268% in normal myocytes, and 77%, 185%, and 243% in hypertrophic myocytes, respectively. Pra-C (1, 10, and 100 mumol.L-1) concentration-dependently inhibited the [Ca2+]i elevation caused by KCl (35 mmol.L-1) or norepinephrine (20 mumol.L-1) in both normal and hypertrophied myocytes. All of the effects of Pra-C were similar to that of nifedipine. CONCLUSION: [Ca2+]i of hypertrophied myocytes was higher than that of normal ones and Pra-C decrease the [Ca2+]i elevation in left ventricular myocytes resulted from its calcium channel blockade. (+info)
Rapid identification of Staphylococcus aureus by using fluorescent staphylocoagulase assays.
Two rapid (1-h) assays for the detection of Staphylococcus aureus staphylocoagulase were developed by using the fluorogenic thrombin substrates N-t-boc-Val-Pro-Arg-7-amido-4-methylcoumarin (VPA) and N-t-boc-beta-benzyl-Asp-Pro-Arg-7-amido-4-methylocoumarin (BB). The assays were compared to the tube coagulase test and latex agglutination (LA) (Sanofi Diagnostics Pasteur, Guildford, Surrey, United Kingdom) by using 406 clinical isolates of staphylococci, and they produced positive and negative predictive values of 99.2 and 99. 1% for LA, 98.9 and 92.7% for VPA, and 98.9 and 99.1% for BB. Fluorescent assays used colonies from solid media, thereby eliminating the need for broth cultures, and were performed in microtiter trays, thus making them suitable for large-scale screening. (+info)
Caspase-dependent activation of calpain during drug-induced apoptosis.
We have previously demonstrated that calpain is responsible for the cleavage of Bax, a proapoptotic protein, during drug-induced apoptosis of HL-60 cells (Wood, D. E., Thomas, A., Devi, L. A., Berman, Y., Beavis, R. C., Reed, J. C., and Newcomb, E. W. (1998) Oncogene 17, 1069-1078). Here we show the sequential activation of caspases and calpain during drug-induced apoptosis of HL-60 cells. Time course experiments using the topoisomerase I inhibitor 9-amino-20(S)-camptothecin revealed that cleavage of caspase-3 substrates poly(ADP-ribose) polymerase (PARP) and the retinoblastoma protein as well as DNA fragmentation occurred several hours before calpain activation and Bax cleavage. Pretreatment with the calpain inhibitor calpeptin blocked calpain activation and Bax cleavage but did not inhibit PARP cleavage, DNA fragmentation, or 9-amino-20(S)-camptothecin-induced morphological changes and cell death. Pretreatment with the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (Z-VAD-fmk) inhibited PARP cleavage, DNA fragmentation, calpain activation, and Bax cleavage and increased cell survival by 40%. Interestingly, Z-VAD-fmk-treated cells died in a caspase- and calpain-independent manner that appeared morphologically distinct from apoptosis. Our results suggest that excessive or uncontrolled calpain activity may play a role downstream of and distinct from caspases in the degradation phase of apoptosis. (+info)
Activation of Xenopus eggs by proteases: possible involvement of a sperm protease in fertilization.
Egg activation in cross-fertilization between Xenopus eggs and Cynops sperm may be caused by a protease activity against Boc-Gly-Arg-Arg-MCA in the sperm acrosome. To determine the role of the sperm protease in fertilization, the protease was purified from Cynops sperm using several chromatographic techniques. We found that purified sperm protease readily hydrolyzes Boc-Gly-Arg-Arg-MCA and Z-Arg-Arg-MCA, that protease activity was inhibited by the trypsin inhibitors aprotinin and leupeptin, and that not only the purified protease, but also cathepsin B, induces activation in Xenopus eggs. We inseminated unfertilized Xenopus eggs with homologous sperm in the presence of various peptidyl MCA substrates or protease inhibitors and demonstrated that trypsin inhibitors or MCA substrates containing Arg-Arg-MCA reversibly inhibited fertilization of both fully jellied and denuded eggs. Sperm motility was not affected by the reagents. An extract obtained from Xenopus sperm showed hydrolytic activity against Boc-Gly-Arg-Arg-MCA, Z-Arg-Arg-MCA, and Arg-MCA. These results suggest that the tryptic protease in Xenopus sperm is involved in fertilization, most likely by participating in egg activation. (+info)
Core RNA polymerase from E. coli induces a major change in the domain arrangement of the sigma 70 subunit.
Luminescence resonance energy transfer measurements were used to show that binding of E. coli core RNA polymerase induced major changes in interdomain distances in the sigma 70 subunit. The simplest model describing core-induced changes in sigma 70 involves a movement of the conserved region 1 by approximately 20 A and the conserved region 4.2 by approximately 15 A with respect to conserved region 2. The core-induced movement of region 1 (autoinhibition domain) and region 4.2 (DNA-binding domain) provides structural rationale for allosteric regulation of sigma 70 DNA binding properties by the core and suggests that this regulation may not only involve directly the autoinhibition domain of sigma 70 but also could involve a modulation of spacing between DNA-binding domains of sigma 70 induced by binding of core RNAP. (+info)