Functional association of retinoic acid and hedgehog signaling in Xenopus primary neurogenesis.
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Previous work has shown that the posteriorising agent retinoic acid can accelerate anterior neuronal differentiation in Xenopus laevis embryos (Papalopulu, N. and Kintner, C. (1996) Development 122, 3409-3418). To elucidate the role of retinoic acid in the primary neurogenesis cascade, we investigated whether retinoic acid treatment of whole embryos could change the spatial expression of a set of genes known to be involved in neurogenesis. We show that retinoic acid expands the N-tubulin, X-ngnr-1, X-MyT1, X-&Dgr;-1 and Gli3 domains and inhibits the expression of Zic2 and sonic hedgehog in the neural ectoderm, whereas a retinoid antagonist produces opposite changes. In contrast, sonic and banded hedgehog overexpression reduced the N-tubulin stripes, enlarged the neural plate at the expense of the neural crest, downregulated Gli3 and upregulated Zic2. Thus, retinoic acid and hedgehog signaling have opposite effects on the prepattern genes Gli3 and Zic2 and on other genes acting downstream in the neurogenesis cascade. In addition, retinoic acid cannot rescue the inhibitory effect of Notch(ICD), Zic2 or sonic hedgehog on primary neurogenesis. Our results suggest that retinoic acid acts very early, upstream of sonic hedgehog, and we propose a model for regulation of differentiation and proliferation in the neural plate, showing that retinoic acid might be activating primary neurogenesis by repressing sonic hedgehog expression. (+info)
Glioma cells release excitotoxic concentrations of glutamate.
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Elevated levels of extracellular glutamate ([Glu]o) cause uncontrolled Ca2+ increases in most neurons and are believed to mediate excitotoxic brain injury following stroke and other nervous system insults. In the normal brain, [Glu]o is tightly controlled by uptake into astrocytes. Because the vast majority of primary brain tumors (gliomas) are derived from astrocytes, we investigated glutamate uptake in glioma cells surgically isolated from glioma patients (glioblastoma multiforme) and in seven established human glioma cell lines, including STTG-1, D-54 MG, D-65 MG, U-373 MG, U-138 MG, U-251 MG, and CH-235 MG. All glioma cells studied showed impaired glutamate uptake, with a Vmax < 10% that of normal astrocytes. Moreover, rather than removing glutamate from the extracellular fluid, glioma cells release large amounts of glutamate, resulting in elevations of [Glu]o in excess of 100 microM within hours in a space that is 1000-fold larger than the cellular volume. Exposure of cultured hippocampal neurons to glioma-conditioned medium elicited sustained [Ca2+]i elevations that were followed by widespread neuronal death. Similarly, coculturing of hippocampal neurons and glioma cells, either with or without direct contact, resulted in neuronal death. Glioma-induced neuronal death could be completely prevented by treating neurons with the N-methyl-D-aspartate receptor antagonists MK-801/D(-)-2-amino-5-phosphonopentanoic acid or by depletion of glutamate from the medium. Interestingly, several phenylglycine derivatives including the metabotropic glutamate receptor agonist/antagonist (S)-4-carboxyphenylglycine (S-4CPG) potently and selectively inhibited glutamate release from glioma cells and prevented neurotoxicity. These data suggest that growing glioma tumors may actively kill surrounding neuronal cells through the release of glutamate. This glutamate release may also be responsible in part for tumor-associated seizures that occur frequently in conjunction with glioma. These data also suggest that neurotoxic release of glutamate by gliomas may be prevented by phenylglycine derivatives, which may thus be useful as an adjuvant treatment for brain tumors. (+info)
Pharmacokinetic-pharmacodynamic modeling of the immunomodulating agent susalimod and experimentally induced tumor necrosis factor-alpha levels in the mouse.
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The main objective of this study was to explore the concentration-effect relationship between the immunomodulating agent susalimod and lipopolycaccharide (LPS)-induced elevated serum levels of the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). Bacterial LPS (1 mg/kg) was given i.p. along with different doses of susalimod (0, 25, 50, 100, and 200 mg/kg) to female CD-1 mice. Blood samples were drawn at different time points (15-300 min), and serum was analyzed with respect to susalimod and TNF-alpha. The concentration-effect relationship was explored by modeling the data from all dose levels simultaneously using specially written program models, i.e., a three-compartment pharmacokinetic model, including biliary excretion, and an indirect mechanistically based pharmacodynamic model. The models, which were successfully fitted to the experimental data, showed that LPS induced the TNF-alpha synthesis during approximately 70 min and that during this time course, the synthesis rate was governed by the serum phamacokinetics of susalimod. Because the results supported the assumption that the maximum inhibitory effect was equal to full inhibition of the synthesis, the in vivo potency (IC(50)) of susalimod could be estimated to 293 microM. In conclusion, susalimod decreased the LPS-induced TNF-alpha mouse serum levels in a concentration-related manner. The compound is suggested to inhibit the synthesis of TNF-alpha. The integrated pharmacokinetic-pharmacodynamic model estimated the in vivo potency of susalimod in the mouse to be 293 microM. (+info)
Disposition and chemical stability of telmisartan 1-O-acylglucuronide.
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Telmisartan 1-O-acylglucuronide, the principal metabolite of telmisartan in humans, was characterized in terms of chemical stability and the structure of its isomerization products was elucidated. In addition, pharmacokinetics of telmisartan 1-O-acylglucuronide were assessed in rats after i.v. dosing. Similar to other acylglucuronides, telmisartan 1-O-acylglucuronide and diclofenac 1-O-acylglucuronide, which was used for comparison, showed the formation of different isomeric acylglucuronides on incubation in aqueous buffer. The isomeric acylglucuronides of telmisartan consisted of the 2-O-, 3-O-, and 4-O-acylglucuronides (alpha,beta-anomers). First order degradation half-lives of 26 and 0. 5 h were observed on incubation in buffer of pH 7.4 for the 1-O-acylglucuronides of telmisartan and diclofenac, respectively. This indicated that the 1-O-acylglucuronide of telmisartan was among the most stable acylglucuronides reported to date. The high stability of telmisartan 1-O-acylglucuronide was confirmed by in vitro experiments that indicated only very low covalent binding of telmisartan acylglucuronide to human serum albumin but a considerable amount of covalently bound radioactivity with the acylglucuronide of diclofenac. After i.v. dosing to rats, telmisartan 1-O-acylglucuronide was rapidly cleared from plasma with a clearance of 180 ml/min/kg, compared with 15.6 ml/min/kg for the parent compound. Because telmisartan 1-O-acylglucuronide exhibited a comparably high chemical stability together with a high clearance that resulted in low systemic exposure, the amount of covalent binding to proteins should be negligible compared with other frequently used drugs, such as furosemide, ibuprofen, or salicylic acid. (+info)
Inhibition of angiogenesis and intrahepatic growth of colon cancer by TAC-101.
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We demonstrated in this study that inhibition of intra-hepatic growth of colon cancer by TAC-101 is mediated by inhibition of angiogenesis. In vitro experiments showed that TAC-101 inhibited the proliferation of murine hepatic sinusoidal endothelial (HSE) cells induced by coculture with murine colon 26-L5 (L5) cells. HSE cell proliferation was also enhanced by conditioned medium of L5 cells (CM-L5), and this enhancement of proliferation was abrogated by anti-vascular endothelial growth factor antibody. CM-L5 also induced in vitro tube formation of HSE cells on Matri-gel, and this activity of CM-L5 was abrogated by TAC-101 in a concentration-dependent manner. On the other hand, p.o. administration of TAC-101 inhibited tumor-induced angiogenesis in vivo and decreased the weights of L5 tumors in the mouse liver. Reverse transcriptase-PCR analysis using in vivo tumor tissue suggested that repression of vascular endothelial growth factor expression by TAC-101 was associated with the antiangiogenic activity. TAC-101 alone and 5-fluorouracil (5-FU)/D,L-leucovorin (LV) significantly inhibited the intrahepatic growth of L5 tumors (P = 0.002 and 0.001, respectively), whereas 5-FU alone did not (P = 0.088). When TAC-101 was administered with 5-FU/LV, marked enhancement of antitumor activity was observed (95% inhibition; P<0.001). This enhanced antitumor effect was also observed in experiments using Co-3 human colon adenocarcinoma. Concurrent treatment with TAC-101 and 5-FU/LV and sequential treatment with 5-FU/LV followed by TAC-101 resulted in significant augmentation of antitumor activity against Co-3 (overall P = 0.007 and 0.015, respectively). These findings indicate that TAC-101 inhibits tumor angiogenesis and suggest that it may be effective against hepatic metastasis of colon cancer. (+info)
Angiotensin II receptor antagonists in the treatment of hypertension.
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The sixth report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC-VI) includes recommendations for the assessment of overall cardiovascular risk and the need for active antihypertensive drug therapy. Once the decision to initiate antihypertensive drug therapy has been made, JNC-VI recommends one of three paths for the choice of initial therapy: one path for patients with uncomplicated hypertension, another for those with well-defined indications for certain drugs and a third path for patients with various concomitant conditions in which one or another drug has favorable effects. At this time, the place for the newest class of antihypertensive drugs, the angiotensin II receptor antagonists, remains uncertain. Currently, they are considered reasonable alternatives for patients who have a compelling need for an angiotensin-converting enzyme (ACE) inhibitor but develop a cough while taking this medication. When data from ongoing trials become available, angiotensin II receptor antagonists may prove to be a good choice for initial therapy in many patients because of the favorable side effect profile of this class of drugs. (+info)
Initial reactions in anaerobic oxidation of m-xylene by the denitrifying bacterium Azoarcus sp. strain T.
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The initial enzymatic steps in anaerobic m-xylene oxidation were studied in Azoarcus sp. strain T, a denitrifying bacterium capable of mineralizing m-xylene via 3-methylbenzoate. Permeabilized cells of m-xylene-grown Azoarcus sp. strain T catalyzed the addition of m-xylene to fumarate to form (3-methylbenzyl)succinate. In the presence of succinyl coenzyme A (CoA) and nitrate, (3-methylbenzyl)succinate was oxidized to E-(3-methylphenyl)itaconate (or a closely related isomer) and 3-methylbenzoate. Kinetic studies conducted with permeabilized cells and whole-cell suspensions of m-xylene-grown Azoarcus sp. strain T demonstrated that the specific rate of in vitro (3-methylbenzyl)succinate formation accounts for at least 15% of the specific rate of in vivo m-xylene consumption. Based on these findings, we propose that Azoarcus sp. strain T anaerobically oxidizes m-xylene to 3-methylbenzoate (or its CoA thioester) via (3-methylbenzyl)succinate and E-(3-methylphenyl)itaconate (or its CoA thioester) in a series of reactions that are analogous to those recently proposed for anaerobic toluene oxidation to benzoyl-CoA. A deuterium kinetic isotope effect was observed in the (3-methylbenzyl)succinate synthase reaction (and the benzylsuccinate synthase reaction), suggesting that a rate-determining step in this novel fumarate addition reaction involves breaking a C-H bond. (+info)
3-Geranyl-4-hydroxy-5-(3'-methyl-2'-butenyl)benzoic acid as an anti-inflammatory compound from Myrsine seguinii.
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Bioassay-guided isolation of anti-inflammatory compounds from the methanol extract of Myrsine seguinii yielded an anti-inflammatory compound (1). The structure of compound 1 was elucidated to be 3-geranyl-4-hydroxy-5-(3'-methyl-2'-butenyl)benzoic acid on the basis of its spectroscopic data. Compound 1 strongly suppressed 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation on mouse ears at a dose of 500 micrograms (inhibitory effect (IE): 65%). The acetate and the methyl ether of 1 showed moderate activity at a 500-microgram application, with IE 38% and 27%, respectively. However, the methyl ester and the dimethyl derivative of 1 did not show activity at the same dose. The related compounds of 1, o-, m- and p-hydroxybenzoic acids also did not exhibit notable activity. These results indicate that the carboxylic acid and lipophilic terpene moieties of 1 were significant structural features for anti-inflammatory activity. (+info)