Alterations in Bacillus subtilis transforming DNA induced by beta-propiolactone and 1,3-propane sultone, two mutagenic and carcinogenic alkylating agents.
(9/1894)Transforming DNA was exposed to either beta-propiolactone or 1,3-propane sultone and then used for transformation of competent bacteria to nutritional independence from tyrosine and tryptophan (linked markers) and leucine (an unlinked marker). The ability to transform was progressively lost by the DNA during incubation with either of these two chemicals. For all three markers the inactivation curve was biphasic, with a short period of rapid inactivation followed by one characterized by a much slower rate. The overall rate of inactivation was different for all three markers and presumably was related to the size of the marker. The decrease in the transforming activity was in part due to the slower rate of penetration of alkylated DNA through the cellular membrane and its inability to enter the recipient bacteria. This decrease in the rate of cellular uptake, even for DNA eventually destined to enter the cell, began almost immediately after its exposure to the chemical and ended up with an almost complete lack of recognition of the heavily alkylated DNA by the specific surface receptors of competent cells. Such DNA attached to sites on the surface of competent bacteria which were different from receptors specific for the untreated nucleic acid. This attachment was not followed by uptake of the altered DNA. Presence of albumin during the incubation with a carcinogen further increased the degree of inactivation, indicating that the artificial nucleoproteins produced under such conditions were less efficient in the transformation assay than was the naked DNA. Cotransfomration of close markers progressively decreased, beginning immediately after the start of incubation of DNA with the chemicals. Extensively alkylated DNA fractionated by sedimentation through sucrose density gradients showed a peculiar distribution of cotransforming activity for such markers; namely, molecules larger than the bulk of DNA ("megamolecules") showed less ability to transform the second marker than did some of the apparently smaller molecules which sedimented more slowly through the gradient. An increase in cotransformation of distant markers was evident in DNA molecules after a short exposure to an alkylating agent, but cotransformation of such markers was absent in DNA treated for longer periods. The observed changes in the transforming and cotransforming activities of the alkylated DNA can be explained by what is known about the physicochemistry of such DNA and in particular about the propensity of the alkylated and broken molecules to form complexes with themselves and with other macromolecules. (+info)
Diverse oxygenations catalyzed by carbazole 1,9a-dioxygenase from Pseudomonas sp. Strain CA10.
(10/1894)Carbazole 1,9a-dioxygenase (CARDO) from Pseudomonas sp. strain CA10 is a multicomponent enzyme that catalyzes the angular dioxygenation of carbazole, dibenzofuran, and dibenzo-p-dioxin. It was revealed by gas chromatography-mass spectrometry and 1H and 13C nuclear magnetic resonance analyses that xanthene and phenoxathiin were converted to 2,2',3-trihydroxydiphenylmethane and 2,2',3-trihydroxydiphenyl sulfide, respectively. Thus, for xanthene and phenoxathiin, angular dioxygenation by CARDO occurred at the angular position adjacent to the oxygen atom to yield hetero ring-cleaved compounds. In addition to the angular dioxygenation, CARDO catalyzed the cis dihydroxylation of polycyclic aromatic hydrocarbons and biphenyl. Naphthalene and biphenyl were converted by CARDO to cis-1, 2-dihydroxy-1,2-dihydronaphthalene and cis-2,3-dihydroxy-2, 3-dihydrobiphenyl, respectively. On the other hand, CARDO also catalyzed the monooxygenation of sulfur heteroatoms in dibenzothiophene and of the benzylic methylenic group in fluorene to yield dibenzothiophene-5-oxide and 9-hydroxyfluorene, respectively. These results indicate that CARDO has a broad substrate range and can catalyze diverse oxygenation: angular dioxygenation, cis dihydroxylation, and monooxygenation. The diverse oxygenation catalyzed by CARDO for several aromatic compounds might reflect the differences in the binding of the substrates to the reaction center of CARDO. (+info)
Population pharmacokinetics of 2% topical dorzolamide in the aqueous humor of humans.
(11/1894)PURPOSE: To evaluate the concentration and kinetics of dorzolamide in the aqueous humor after its topical application. METHODS: Samples of aqueous humor were collected at the beginning of routine cataract surgery at defined intervals after topical application of a 2% solution of dorzolamide. After deep-frozen storage of the samples, drug extraction was achieved with a mixture of solvents. Quantification was carried out by high-performance liquid chromatography on a reversed-phase column. RESULTS: Peak concentrations of dorzolamide in aqueous humor were reached approximately 2 hours after application with 1000 ng/ml. Average values were approximately 1000 to 700 ng/ml after 4 to 6 hours and approximately 200 ng/ml after 12 hours. Mean half-life of absorption was 1.2 hours and for elimination 3.0 hours. CONCLUSIONS: Pharmacokinetics of dorzolamide in the aqueous humor of humans are in comparable dimensions as previously reported in experimental trials in pigmented rabbits. There is a clear linear absorption and elimination kinetic, which is demonstrated using the Bateman function. A better knowledge of the distribution and kinetics of dorzolamide will help to explain its reported effects on intraocular hemodynamics, distinct from its intraocular pressure lowering effect. (+info)
Clinical estimation of corneal endothelial pump function.
(12/1894)PURPOSE: To develop a technique to estimate the corneal endothelial pump rate in human subjects. METHODS: Corneal hydration control is thought to be maintained by a pump-leak mechanism whereby the leak of solutes and fluid across the endothelial barrier into the stroma is, in the steady state, exactly balanced by the pumping of solutes and passive fluid transfer across the endothelium to the aqueous humor. Overall corneal hydration control can be measured from the rate at which the swollen cornea thins (deswells), and a measure of the leak can be obtained simultaneously from the endothelial permeability to fluorescein. From the pump-leak hypothesis, the deswelling rate is directly proportional to the pump rate and inversely proportional to the leak rate. The relative endothelial pump rate can be estimated as the product of the normalized deswelling rate and the normalized endothelial permeability. This procedure was used to obtain the relative endothelial pump rate in 41 patients with diabetes mellitus, 12 patients with long-term corneal transplants, 20 long-term wearers of contact lenses, and 19 normal volunteer subjects after the short-term administration of topical dorzolamide. RESULTS: The relative endothelial pump rate did not differ significantly from that of control subjects in diabetics, in contact lens wearers, and after dorzolamide administration, but was markedly decreased in the patients with corneal transplants, despite a reduction in permeability (reduced leak). CONCLUSIONS: This method allows the estimation of both the barrier and pump arms of corneal endothelial function and should be useful in the investigation of causes and mechanisms of functional endothelial insufficiency. (+info)
Antifolate resistance mediated by the multidrug resistance proteins MRP1 and MRP2.
(13/1894)Transfection of multidrug resistance proteins (MRPs) MRP1 and MRP2 in human ovarian carcinoma 2008 cells conferred a marked level of resistance to short-term (1-4 h) exposure to the polyglutamatable antifolates methotrexate (MTX; 21-74-fold), ZD1694 (4-138-fold), and GW1843 (101-156-fold). Evidence for MRP-mediated antifolate efflux relies upon the following findings: (a) a 2-3.3-fold lower accumulation of [3H]MTX and subsequent reduced formation of long-chain polyglutamate forms of MTX; (b) reversal of MTX resistance by probenecid in both transfectants, and (c) ATP-dependent uptake of [3H]MTX in inside-out vesicles of MRP1 and MRP2 transfectants. This report provides a mechanistic basis for resistance to polyglutamatable antifolates through an MRP-mediated drug extrusion. (+info)
Molecular analysis of the Na+ channel blocking actions of the novel class I anti-arrhythmic agent RSD 921.
(14/1894)RSD 921 is a novel, structurally unique, class I Na+ channel blocking drug under development as a local anaesthetic agent and possibly for the treatment of cardiac arrhythmias. The effects of RSD 921 on wild-type heart, skeletal muscle, neuronal and non-inactivating IFMQ3 mutant neuronal Na+ channels expressed in Xenopus laevis oocytes were examined using a two-electrode voltage clamp. RSD 921 produced similarly potent tonic block of all three wild-type channel isoforms, with EC50 values between 35 and 47 microM, whereas the EC50 for block of the IFMQ3 mutant channel was 110+5.5 microM. Block of Na+ channels by RSD 921 was concentration and use-dependent, with marked frequency-dependent block of heart channels and mild frequency-dependent block of skeletal muscle, wild-type neuronal and IFMQ3 mutant channels. RSD 921 produced a minimal hyperpolarizing shift in the steady-state voltage-dependence of inactivation of all three wild-type channel isoforms. Open channel block of the IFMQ3 mutant channel was best fit with a first order blocking scheme with k(on) equal to 0.11+/-0.012x10(6) M(-1) s(-1) and k(off) equal to 12.5+/-2.5 s(-1), resulting in KD of 117+/-31 microM. Recovery from open channel block occurred with a time constant of 14+/-2.7 s(-1). These results suggest that RSD 921 preferentially interacts with the open state of the Na+ channel, and that the drug may produce potent local anaesthetic or anti-arrhythmic action under conditions of shortened action potentials, such as during anoxia or ischaemia. (+info)
Effects of (-)-tertatolol, (-)-penbutolol and (+/-)-pindolol in combination with paroxetine on presynaptic 5-HT function: an in vivo microdialysis and electrophysiological study.
(15/1894)The antidepressant efficacy of selective serotonin reuptake inhibitors (SSRIs) might be enhanced by co-administration of 5-HT1A receptor antagonists. Thus, we have recently shown that the selective 5-HT1A receptor antagonist, WAY 100635, blocks the inhibitory effect of an SSRI on 5-HT cell firing, and enhances its ability to elevate extracellular 5-HT in the forebrain. Here we determined whether the beta-adrenoceptor/5-HT1A receptor ligands (+/-)-pindolol, (-)-tertatolol and (-)-penbutolol, interact with paroxetine in a similar manner. Both (-)-tertatolol (2.4 mg kg(-1) i.v.) and (-)-penbutolol (2.4 mg kg(-1) i.v.) enhanced the effect of paroxetine (0.8 mg kg(-1) i.v.) on extracellular 5-HT in the frontal cortex, whilst (+/-)-pindolol (4 mg kg(-1) i.v.) did not. (-)-Tertatolol (2.4 mg kg(-1) i.v.) alone caused a slight increase in 5-HT however, (-)-penbutolol (2.4 mg kg(-1) i.v.) alone had no effect. In electrophysiological studies (-)-tertatolol (2.4 mg kg(-1) i.v.) alone had no effect on 5-HT cell firing but blocked the inhibitory effect of paroxetine. In contrast, (-)-penbutolol (0.1-0.8 mg kg(-1) i.v.) itself inhibited 5-HT cell firing, and this effect was reversed by WAY 100635 (0.1 mg kg(-1) i.v.). We have recently shown that (+/-)-pindolol inhibits 5-HT cell firing via a WAY 100635-sensitive mechanism. Our data suggest that (-)-tertatolol enhances the effect of paroxetine on forebrain 5-HT via blockade of 5-HT1A autoreceptors which mediate paroxetine-induced inhibition of 5-HT cell firing. In comparison, the mechanisms by which (-)-penbutolol enhances the effect of paroxetine on extracellular 5-HT is unclear, since (-)-penbutolol itself appears to have agonist properties at the 5-HT1A autoreceptor. Indeed, the agonist action of (+/-)-pindolol at 5-HT1A autoreceptors probably explains its inability to enhance the effect of paroxetine on 5-HT in the frontal cortex. Overall, our data suggest that both (-)-tertatolol and (-)-penbutolol are superior to (+/-)-pindolol in terms of enhancing the effect of an SSRI on extracellular 5-HT. Both (-)-tertatolol and (-)-penbutolol are worthy of investigation for use as adjuncts to SSRIs in the treatment of major depression. (+info)
Effects of isoprothiolane on cell growth of cultured bovine mammary epithelial cells.
(16/1894)This study was performed to investigate the effects of isoprothiolane on cell growth and the production of interleukin (IL)-1 and IL-6 by bovine mammary epithelial cells in vitro. Isoprothiolane increased proliferation of mammary epithelial cells in a dose-dependent manner at the concentration of 0.05 to 5 microM when cultured either with or without serum-supplemented medium. In contrast, isoprothiolane (0.0005-5 microM) significantly inhibited the production of IL-1 and IL-6 by mammary epithelial cells. Moreover, the cytokines, IL-1alpha, IL-1beta, IL-6, and tumor necrosis factor (TNF)-alpha tended to inhibit the proliferation of mammary epithelial cells in a dose-dependent manner. These results indicated that isoprothiolane regulated mammary epithelial cell growth in vitro possibly by modulating the production of cytokines. (+info)