Potent and selective nonpeptide inhibitors of caspases 3 and 7 inhibit apoptosis and maintain cell functionality.
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Caspases have been strongly implicated to play an essential role in apoptosis. A critical question regarding the role(s) of these proteases is whether selective inhibition of an effector caspase(s) will prevent cell death. We have identified potent and selective non-peptide inhibitors of the effector caspases 3 and 7. The inhibition of apoptosis and maintenance of cell functionality with a caspase 3/7-selective inhibitor is demonstrated for the first time, and suggests that targeting these two caspases alone is sufficient for blocking apoptosis. Furthermore, an x-ray co-crystal structure of the complex between recombinant human caspase 3 and an isatin sulfonamide inhibitor has been solved to 2.8-A resolution. In contrast to previously reported peptide-based caspase inhibitors, the isatin sulfonamides derive their selectivity for caspases 3 and 7 by interacting primarily with the S(2) subsite, and do not bind in the caspase primary aspartic acid binding pocket (S(1)). These inhibitors blocked apoptosis in murine bone marrow neutrophils and human chondrocytes. Furthermore, in camptothecin-induced chondrocyte apoptosis, cell functionality as measured by type II collagen promoter activity is maintained, an activity considered essential for cartilage homeostasis. These data suggest that inhibiting chondrocyte cell death with a caspase 3/7-selective inhibitor may provide a novel therapeutic approach for the prevention and treatment of osteoarthritis, or other disease states characterized by excessive apoptosis. (+info)
Antagonism of adenosine 5'-triphosphate-induced relaxation by 2-2'-pyridylisatogen in the taenia of guinea-pig caecum.
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1. 2-2' Pyridylisatogen tosylate (PIT) (greater than 2.5 muM) relaxed the guinea-pig isolated taenia caeci by an unknown mechanism. 2. With higher concentrations of PIT (greater than 12.5 muM) subsequent applications of adenosine 5'-triphosphate (ATP) (2-600 muM) revealed a blockade of the ATP receptors. The antagonism was characterized by a delayed onset of action (greater than 10 min incubation with 50 muM PIT) and eventually became irreversible (greater than 50 muM PIT for greater than 30 minutes). The antagonism was specific for ATP, was not competitive, and was not dependent upon the relaxant effect. 3. The presence of either acetylcholine (0.05-1.0 muM) or carbachol (0.05-1.0 muM) increased the antagonistic effect of PIT (50 muM) approximately five-fold. 4. Following prolonged exposure, PIT (50 muM for 90 min) did not block the inhibitory effects of fiedl stimulation (2 Hz, 10 s) of the taenia caeci in the presence of hyoscine (0.33 muM). These results do not support the purinergic nerve hypothesis. (+info)
Synthesis and pharmacological activities of hydrazones, Schiff and Mannich bases of isatin derivatives.
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Schiff bases and phenyl hydrazone of isatins were prepared by reacting isatin and the appropriate aromatic primary amine/hydrazines. A new series of the corresponding N-mannich bases were synthesized by reacting them with formaldehyde and diphenylamine. The chemical structures were confirmed by means of their 1H-NMR, IR spectral data and elemental analysis. The compounds were screened for analgesic, antiinflammatory and antipyretic activity. 1-Diphenylaminomethyl-3-(1-naphthylimino)-1,3-dihydroindol-3-one (4), 3-(1-naphthylimino)-5-bromo-1,3-dihydroindol-2-one (2) and 1-diphenylaminomethyl-3-(4-methylphenylimino)-1,3-dihydroindol-3-one (7) were found to exhibit the highest analgesic, anti-inflammatory and antipyretic activity respectively. 1-Diphenylaminomethyl-3-(4-methylphenylimino)-1,3-dihydroindol-3-one (7) was found to be the most active compound of the series. (+info)
Characterization of a major form of human isatin reductase and the reduced metabolite.
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Isatin, an endogenous indole, has been shown to inhibit monoamine oxidase, and exhibit various pharmacological actions. However, the metabolism of isatin in humans remains unknown. We have found high isatin reductase activity in the 105,000 g supernatants of human liver and kidney homogenates, and have purified and characterized a major form of the enzyme in the two tissues. The hepatic and renal enzymes showed the same properties, including an M(r) of 31 kDa, substrate specificity for carbonyl compounds and inhibitor sensitivity, which were also identical to those of recombinant human carbonyl reductase. The identity of the isatin reductase with carbonyl reductase was immunologically demonstrated with an antibody against the recombinant carbonyl reductase. About 90% of the soluble isatin reductase activity in the liver and kidney was immunoprecipitated by the antibody. The Km (10 microm) and k(cat)/K(m) (1.7 s(-1) x microm(-1)) values for isatin at pH 7.0 were comparable to those for phenanthrenequinone, the best xenobiotic substrate of carbonyl reductase. The reduced product of isatin was chemically identified with 3-hydroxy-2-oxoindole, which is also excreted in human urine. The inhibitory potency of the reduced product for monoamine oxidase A and B was significantly lower than that of isatin. The results indicate that the novel metabolic pathway of isatin in humans is mediated mainly by carbonyl reductase, which may play a critical role in controlling the biological activity of isatin. (+info)
The effects of isatin (indole-2, 3-dione) on pituitary adenylate cyclase-activating polypeptide-induced hyperthermia in rats.
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BACKGROUND: Previous studies have demonstrated that centrally administered natriuretic peptides and pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38) have hyperthermic properties. Isatin (indole-2, 3-dione) is an endogenous indole that has previously been found to inhibit hyperthermic effects of natriuretic peptides. In this study the aim was to investigate the effects of isatin on thermoregulatory actions of PACAP-38, in rats. RESULTS: One microg intracerebroventricular (icv.) injection of PACAP-38 had hyperthermic effect in male, Wistar rats, with an onset of the effect at 2 h and a decline by the 6th h after administration. Intraperitoneal (ip.) injection of different doses of isatin (25-50 mg/kg) significantly decreased the hyperthermic effect of 1 microg PACAP-38 (icv.), whereas 12.5 mg/kg isatin (ip.) had no inhibiting effect. Isatin alone did not modify the body temperature of the animals. CONCLUSION: The mechanisms that participate in the mediation of the PACAP-38-induced hyperthermia may be modified by isatin. The capability of isatin to antagonize the hyperthermia induced by all members of the natriuretic peptide family and by PACAP-38 makes it unlikely to be acting directly on receptors for natriuretic peptides or on those for PACAP in these hyperthermic processes. (+info)
Synthesis of isatin semicarbazones as novel anticonvulsants--role of hydrogen bonding.
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PURPOSE: A series of substituted isatin semicarbazones and related bioisosteric hydrazones were designed and synthesised to meet the structural requirements essential for anticonvulsant properties. METHODS: The structures of all synthesised compounds were confirmed by means of infrared, proton magnetic resonance spectroscopy and by elemental analyses. All compounds were evaluated for their anticonvulsant activity by maximal electroshock (MES), subcutaneous metrazol (ScMet) and subcutaneous strychnine (ScSty) induced seizure methods and their neurotoxic effects were determined by rotorod test. RESULTS: A number of isatin semicarbazones exhibited significant protection after intraperitoneal administration at the dose of 100 and 300mg/kg. Some of them showed good anticonvulsant activity in MES test in rats after per oral administration at the dose of 30mg/kg. The bioisosteric hydrazone derivatives were inactive in all tests. Compound 6-chloroisatin-3- (4-bromophenyl)-semicarbazone has emerged as the most active analogue of the series showing good activity in all the three tests and was more active than phenytoin and valproic acid. CONCLUSIONS: The results evidenced the importance of hydrogen bonding and suggested a new pharmacophore model with four binding sites essential for anticonvulsant activity. (+info)
Investigating antibody-catalyzed ozone generation by human neutrophils.
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Recent studies have suggested that antibodies can catalyze the generation of previously unknown oxidants including dihydrogen trioxide (H(2)O(3)) and ozone (O(3)) from singlet oxygen ((1)O(2)(*)) and water. Given that neutrophils have the potential both to produce (1)O(2)(*) and to bind antibodies, we considered that these cells could be a biological source of O(3). We report here further analytical evidence that antibody-coated neutrophils, after activation, produce an oxidant with the chemical signature of O(3). This process is independent of surface antibody concentration down to 50% of the resting concentration, suggesting that surface IgG is highly efficient at intercepting the neutrophil-generated (1)O(2)(*). Vinylbenzoic acid, an orthogonal probe for ozone detection, is oxidized by activated neutrophils to 4-carboxybenzaldehyde in a manner analogous to that obtained for its oxidation by ozone in solution. This discovery of the production of such a powerful oxidant in a biological context raises questions about not only the capacity of O(3) to kill invading microorganisms but also its role in amplification of the inflammatory response by signaling and gene activation. (+info)
Insights into the mode of inhibition of human mitochondrial monoamine oxidase B from high-resolution crystal structures.
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Monoamine oxidase B (MAO-B) is an outer mitochondrial membrane-bound enzyme that catalyzes the oxidative deamination of arylalkylamine neurotransmitters and has been a target for a number of clinically used drug inhibitors. The 1.7-A structure of the reversible isatin-MAO-B complex has been determined; it forms a basis for the interpretation of the enzyme's structure when bound to either reversible or irreversible inhibitors. 1,4-Diphenyl-2-butene is found to be a reversible MAO-B inhibitor, which occupies both the entrance and substrate cavity space in the enzyme. Comparison of these two structures identifies Ile-199 as a "gate" between the two cavities. Rotation of the side chain allows for either separation or fusion of the two cavities. Inhibition of the enzyme with N-(2-aminoethyl)-p-chlorobenzamide results in the formation of a covalent N(5) flavin adduct with the phenyl ring of the inhibitor occupying a position in the catalytic site overlapping that of isatin. Inhibition of MAO-B with the clinically used trans-2-phenylcyclopropylamine results in the formation of a covalent C(4a) flavin adduct with an opened cyclopropyl ring and the phenyl ring in a parallel orientation to the flavin. The peptide bond between the flavin-substituted Cys-397 and Tyr-398 is in a cis conformation, which allows the proper orientation of the phenolic ring of Tyr-398 in the active site. The flavin ring exists in a twisted nonplanar conformation, which is observed in the oxidized form as well as in both the N(5) and the C(4a) adducts. An immobile water molecule is H-bonded to Lys-296 and to the N(5) of the flavin as observed in other flavin-dependent amine oxidases. The active site cavities are highly apolar; however, hydrophilic areas exist near the flavin and direct the amine moiety of the substrate for binding and catalysis. Small conformational changes are observed on comparison of the different inhibitor-enzyme complexes. Future MAO-B drug design will need to consider "induced fit" contributions as an element in ligand-enzyme interactions. (+info)