Novel structural templates for estrogen-receptor ligands and prospects for combinatorial synthesis of estrogens.
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BACKGROUND: The development of estrogen pharmaceutical agents with appropriate tissue-selectivity profiles has not yet benefited substantially from the application of combinatorial synthetic approaches to the preparation of structural classes that are known to be ligands for the estrogen receptor (ER). We have developed an estrogen pharmacophore that consists of a simple heterocyclic core scaffold, amenable to construction by combinatorial methods, onto which are appended 3-4 peripheral substituents that embody substructural motifs commonly found in nonsteroidal estrogens. The issue addressed here is whether these heterocyclic core structures can be used to prepare ligands with good affinity for the ER. RESULTS: We prepared representative members of various azole core structures. Although members of the imidazole, thiazole or isoxazole classes generally have weak binding for the ER, several members of the pyrazole class show good binding affinity. The high-affinity pyrazoles bear close conformational relationship to the nonsteroidal ligand raloxifene, and they can be fitted into the ligand-binding pocket of the ER-raloxifene X-ray structure. CONCLUSIONS: Compounds such as these pyrazoles, which are novel ER ligands, are well suited for combinatorial synthesis using solid-phase methods. (+info)
Antifungal susceptibility testing of Candida species by flow cytometry.
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The feasibility of flow cytometric antifungal susceptibility testing has been studied using the fluorescent anionic membrane potential probe, bis-(1,3-dibutylbarbituric acid) trimethine oxonol [DiBAC4(3)]. The in vitro antifungal susceptibility testing of amphotericin B was performed on 8 Candida isolates from clinical specimens and 2 ATCC strains by flow cytometry with the results compared to those of the National Committee of Clinical Laboratory Standards (NCCLS) M27-T, broth macrodilution method. The flow cytometric method is based on an increase of fluorescence given out by DiBAC4(3) in fungi when they are killed by antifungal agents. Minimum inhibitory concentration (MIC) of amphotericin B ranged from 0.25 to 1 microg/mL. All results agreed within +/-2 dilution between the flow cytometric method and the M27-T method. MIC with ATCC strains were within recommended ranges of M27-T. The new flow cytometric method revealed a clear and distinct reproducible test end point. A four hr of incubation was sufficient for the test. In conclusion, flow cytometry using DiBAC4(3) is a rapid and accurate in vitro antifungal susceptibility testing method. (+info)
The induction of GSH synthesis by nanomolar concentrations of NO in endothelial cells: a role for gamma-glutamylcysteine synthetase and gamma-glutamyl transpeptidase.
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Nitric oxide protects cells from oxidative stress through a number of direct scavenging reactions with free radicals but the effects of nitric oxide on the regulation of antioxidant enzymes are only now emerging. Using bovine aortic endothelial cells as a model, we show that nitric oxide, at physiological rates of production (1-3 nM/s), is capable of inducing the synthesis of glutathione through a mechanism involving gamma-glutamylcysteine synthetase and gamma-glutamyl transpeptidase. This novel nitric oxide signalling pathway is cGMP-independent and we hypothesize that it makes an important contribution to the anti-atherosclerotic and antioxidant properties of nitric oxide. (+info)
Assessment of the effect of amphotericin B on the vitality of Candida albicans.
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The processes involved in cell death are complex, and individual techniques measure specific fractions of the total population. The interaction of Candida albicans with amphotericin B was measured with fluorescent probes with different cellular affinities. These were used to provide qualitative and quantitative information of physiological parameters which contribute to fungal cell viability. SYBR Green I and 5,(6)-carboxyfluorescein were used to assess membrane integrity, and bis-(1,3-dibutylbarbituric acid)trimethine oxonol and 3,3-dihexyloxacarbocyanine iodide were used to evaluate alterations in membrane potential. The fluorescent indicators were compared with replication competency, the conventional indicator of viability. By using these tools, the evaluation of the response of C. albicans to amphotericin B time-kill curves delineated four categories which may represent a continuum between alive and dead. The data showed that replication competency (CFU per milliliter) as determined by conventional antifungal susceptibility techniques provided only an estimate of inhibition. Interpretation of fluorescent staining characteristics indicated that C. albicans cells which were replication incompetent after exposure to greater than 0.5 microgram of amphotericin B per ml still maintained degrees of physiological function. (+info)
Pharmacological evidence for a KATP channel in renin-secreting cells from rat kidney.
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1. Openers of the ATP-sensitive potassium channel (KATP channel) increase and blockers decrease renin secretion. Here we report the effects of levcromakalim (LCRK, a channel opener) and glibenclamide (GBC, a blocker) on membrane potential, whole-cell current and the cytoplasmic Ca2+ concentration of renin-secreting cells (RSC). Studies were performed on afferent arterioles from the kidney of Na+-depleted rats. 2. As monitored with the fluorescent oxonol dye DiBAC4(3), LCRK (0.3 and 1 microM) induced a hyperpolarization of approximately 15 mV which was abolished by GBC (1 microM). 3. Whole-cell current-clamp experiments showed that RSC had a membrane potential of -61 +/- 1 mV (n = 16). LCRK (1 microM) induced a hyperpolarization of 9.9 +/- 0.2 mV (n = 16) which, in the majority of cells, decreased slowly with time. 4. Capacitance measurements showed a strong electrical coupling of the cells in the preparation. 5. At -60 mV, LCRK induced a hyperpolarizing current in a concentration-dependent manner with an EC50 of 152 +/- 31 nM and a maximum current of about 200 pA. 6. Application of GBC (1 microM) produced no effect; however, when applied after LCRK (300 nM), GBC inhibited the opener-induced hyperpolarizing current with an IC50 of 103 +/- 36 nM. 7. LCRK (0.3 and 1 microM) did not significantly affect the cytoplasmic Ca2+ concentration either at rest or after stimulation by angiotensin II. 8. The data show that LCRK induces a GBC-sensitive hyperpolarizing current in rat RSC. This current presumably originates from the activation of KATP channels which pharmacologically resemble those in vascular smooth muscle cells. The stimulatory effect of KATP channel opening on renin secretion is not mediated by a decrease in intracellular Ca2+ concentration. (+info)
Newer immunosuppressive drugs: a review.
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In recent years, many new immunosuppressive drugs have been discovered and developed for clinical use in transplantation. This review focuses on those drugs (leflunomide, mycophenolate mofetil, sirolimus, tacrolimus) that have been shown to have immunosuppressive activity in patients. Different anti-interleukin-2 receptor antibodies are also reviewed as an example of a resurgence of development in the area of monoclonal antibodies. The price for reducing the incidence of allograft rejection by improved immunosuppression was thought to be a proportional increase in the incidence of infection and malignancy. Data from Phase III clinical trials of new immunosuppressants, however, show a statistically significant reduction in the incidence of acute rejection produced by these new drugs, which has not been accompanied by increases in infection and malignancy rates. The wide array of new drugs offers the opportunity to use combinations that block different pathways of immune activation while at the same time selecting drug combinations with nonoverlapping toxicity profiles so that doses of each single drug can be reduced below toxicity levels. The immunosuppressive therapy for patients can be tailored according to their individual needs. (+info)
Induction of gadd153 mRNA by nutrient deprivation is overcome by glutamine.
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The growth arrest and DNA damage-inducible (gadd) genes are co-ordinately activated by a variety of genotoxic agents and/or growth-cessation signals. The regulation of gadd153 mRNA was investigated in renal proximal tubular epithelial cells (LLC-PK1) cultured in a nutrient- and serum-deprived medium. The addition of glutamine alone to LLC-PK1 cells cultured in Earl's balanced salt solution (EBSS) is sufficient to suppress gadd153 mRNA expression, and the removal of only glutamine from Dulbecco's modified Eagle's medium (DMEM) is also sufficient to induce gadd153 mRNA expression. Consistent with these findings, the inhibition of glutamine utilization with acivicin and 6-diazo-5-oxo-l-norleucine (DON) in cells grown in a glutamine-containing medium effectively induces gadd153 expression. Glutamine can be used as an energy source in cultured mammalian cells. However, it is unlikely that deficits in cellular energy stores (ATP) are coupled to gadd153 mRNA expression, because concentrations of ATP, UTP and GTP are all elevated in EBSS-exposed cells, and the addition of alpha-oxoglutarate to cells grown in EBSS has no effect on gadd153 mRNA expression. In contrast, concentrations of CTP decline substantially in EBSS and glutamine-deprived DMEM-cultured cells. Glutamine also serves as a precursor for the synthesis of protein and DNA. The addition of glutamine to cells grown in EBSS partly restores CTP concentrations. The addition of pyrimidine ribonucleosides (cytidine and uridine) to LLC-PK1 cells also restores CTP concentrations, in a manner commensurate with their relative abilities to overcome gadd153 expression. Finally, glutamine does not completely suppress DNA damage-induced gadd153 expression, suggesting that multiple signalling pathways lead to the expression of gadd153 mRNA under conditions of nutrient deprivation and DNA damage. (+info)
Pharmacokinetics, safety, and efficacy of combination treatment with methotrexate and leflunomide in patients with active rheumatoid arthritis.
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OBJECTIVE: To examine the safety and pharmacokinetics of and clinical response to leflunomide, a de novo pyrimidine synthesis inhibitor, when administered to patients with active rheumatoid arthritis (RA) who have been receiving long-term methotrexate therapy. METHODS: This was an open-label, 52-week study in which 30 patients with RA that remained active despite therapy with methotrexate at 17+/-4 mg/week (mean +/- SD) for > or =6 months were given leflunomide, 10-20 mg/day. Patients were assessed for adverse effects, pharmacokinetic measurements of leflunomide and methotrexate, and clinical response by American College of Rheumatology (ACR) 20% response criteria. RESULTS: Twenty-three patients completed 1 year of treatment. No significant pharmacokinetic interactions between leflunomide and methotrexate were noted. This combination therapy was generally well tolerated clinically, with the exception of elevations of liver enzyme levels. Seven patients withdrew from the treatment regimen: 2 withdrawals were voluntary, 3 were due to persistent elevation of plasma transaminase levels, and 2 were due to lack of efficacy. Of the patients, 16 (53%) met ACR 20% response criteria. Two met ACR criteria for remission after 1 year. CONCLUSION: The combination of methotrexate and leflunomide has therapeutic potential in RA. (+info)