Examination on biological activities and fates of new steroids, steroid-17-yl methyl glycolate derivatives.
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A variety of acyl derivatives based on the "antedrug" concept were synthesized to evaluate their biological activities, in vitro fate in human serum and examine pharmacokinetics in rats. Among the prepared compounds, acetyl and pivaloyl derivatives (8 and 9) showed strong to vasoconstrictive activity in human, exceeding that of dexamethasone. In rats, topical administration of the compound 8 significantly reduced oxazolone-induced ear edema compared to that of control. These activities were almost equal to that of prednisolone, however 9 did not show any suppression of the oxazolone-induced edema. The in vitro half-lives of 8 and 9 in human serum were 18.2 and 43.8 hours, respectively. Prednisolone and dexamethasone were extremely stable under the used conditions. When compound 8 was intravenously administrated to rats, its metabolites, 20(R)-methyl dexamethasonate (4) and carboxylic acid (18), were found in the systemic blood. The total body clearance of 8 was 1734 ml x hr(-1) x kg(-1), which was about 12 times larger than that of dexamethasone. On the other hand, 9 was found to be metabolized instantaneously to methyl prednisolonate (1) in systemic serum. Acetyl derivative 8 derived from dexamethasone may thus be useful as a topical steroid which offers the advantage of a low potential for systemic and local side effects. (+info)
Effect of the synthetic glucocorticoid, deflazacort, on body growth, pulsatile secretion of GH and thymolysis in the rat.
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DESIGN: Deflazacort (DFZ) is a relatively new glucocorticoid that has been reported to exhibit fewer side-effects than other commonly used corticosteroids. The present study was designed to test the effects of DFZ on thymus gland involution (thymolysis), as compared with body growth and the secretory pattern of GH in the rat. Beginning at 38 days of age, male animals were treated for 8 consecutive days by s.c. injection of DFZ (0.15mg/day), cortisone (CORT) (5mg/day) or vehicle (control, CTRL). RESULTS: Both glucocorticoids had a similar thymolytic effect and caused growth failure, but the growth rate for the DFZ group was significantly higher than that of the CORT group. On day 46, pulsatile GH secretion was quantitated by blood sampling via an indwelling catheter at 10 min intervals for 6h. GH was assayed by RIA and analyzed by multiparameter deconvolution. CORT caused an increase in pulse frequency (5.8+/-0.4 (s.e.m.)) in comparison to DFZ (4.4+/-0. 4) and CTRL (3.8+/-0.3). Both glucocorticoids significantly shortened the interval between secretory bursts. In CTRL animals the interval between bursts was 69.3+/-4.5 min. In DFZ animals this was reduced to 58.5+/-7.1 min, and in CORT rats it was further reduced to 47.0+/-2.6 min. The mass of GH secreted per burst was reduced in CORT animals (52% of CTRL), while DFZ did not alter this parameter. A similar trend was observed for total GH production, with CORT causing a reduction and DFZ not affecting the secretion. CONCLUSION: Rats treated with glucocorticoid show a profound thymolytic effect, as well as important changes in growth. While CORT suppresses GH secretion and alters its pulsatile mode of release, DFZ causes a less significant alteration in the pattern of GH secretion and does not negatively affect the overall amount of GH secreted. (+info)
The pathway regulating MDM2 protein degradation can be altered in human leukemic cells.
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The MDM2 protein regulates the functional activity of the p53 tumor suppressor through direct physical association. Signals that control MDM2 expression are poorly understood but are likely to play an important role in the regulation of p53 activity. We show here that the half-life of MDM2 protein is shorter in proliferating than in quiescent peripheral blood mononuclear cells. We also demonstrate that MDM2 protein half-life is extended in some, but not all, p53 mutant human leukemic cell lines. In at least one of these p53 mutant lines, increased MDM2 protein stability is associated with higher amounts of MDM2 protein. Moreover, we demonstrate that MDM2 protein accumulates to a much greater extent in proteasome inhibitor-treated cells containing unstable MDM2 than in cells possessing stable MDM2. These results demonstrate that MDM2 expression is regulated by events that control the stability of the protein and suggest that the normal regulation of MDM2 turnover can be altered in tumor cell lines. (+info)
Transforming growth factor beta1 is a target for the von Hippel-Lindau tumor suppressor and a critical growth factor for clear cell renal carcinoma.
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The von Hippel-Lindau (VHL) tumor suppressor gene is mutated in patients with VHL disease and in the majority of patients with sporadic clear cell renal carcinoma (RCC). Overexpression of transforming growth factor (TGF) beta1 has been observed in patients with several cancers, including RCCs, with serum and urine levels correlating inversely with prognosis. We have demonstrated that the VHL tumor suppressor gene product represses TGF-beta1 mRNA and protein levels (approximately 3-4-fold) in 786-O RCC cells by decreasing the TGF-beta1 mRNA half-life. Exogenously added TGF-beta1 did not suppress the growth of 786-O cells in vitro, nor did the addition of neutralizing antibody (Ab) against TGF-beta have any effect. Indeed, 786-O cells were found to express no TGF-beta type II receptor protein, thus allowing them to escape from the negative growth control of TGF-beta1. In contrast to the in vitro data, neutralizing Ab to TGF-beta inhibited tumorigenesis and, in some cases, regressed established 786-O tumors in athymic mice. Immunohistochemistry for von Willebrand's factor revealed a 3-4-fold lower tumor microvessel count in the mice treated with TGF-beta Ab compared to controls, suggesting that the Ab was inhibiting angiogenesis. Our findings indicate that TGF-beta1 is a novel target for the VHL tumor suppressor and that antagonizing its paracrine action may provide novel avenues for treatment of RCCs as well as other tumors that secrete TGF-beta1. (+info)
In vivo disposition of 3-nitro-L-tyrosine in rats: implications on tracking systemic peroxynitrite exposure.
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In many pathological conditions such as inflammatory and neurodegenerative diseases, the in vivo toxicity of nitric oxide has been attributed to the toxic oxidant peroxynitrite. Interaction of peroxynitrite with biological molecules can modify tyrosine residues on the proteins at the ortho position resulting in the formation of the stable end-product, 3-nitro-L-tyrosine (3-NT). Recent investigations indicate that changes in the circulating concentrations of 3-NT in pathological conditions may reflect the extent of nitric oxide-dependent oxidative damage and peroxynitrite toxicity. In the present study, we examined the in vivo disposition characteristics of 3-NT in rats after either a single i.v. bolus dose (10 mg/kg) or a loading and maintenance infusion at 10 or 30 mg/kg. Plasma concentrations of 3-NT were analyzed by a reversed-phase HPLC method. After a single bolus dose of 3-NT at 10 mg/kg, the average half-life of the elimination phase for the drug was 68.5+/-18.4 min (n = 5). Infusions of 3-NT at two different doses (10 and 30 mg/kg) indicated that the pharmacokinetic properties of 3-NT below plasma concentrations of 100 microM were both linear and stationary. Urinary excretion of unchanged 3-NT was minimal, but two distinct metabolites of 3-NT were identified in the urine collected throughout the study. These findings may be useful in the interpretation of the plasma and urine 3-NT concentrations as possible indices of systemic peroxynitrite exposure. (+info)
Pharmacokinetics of aminolevulinic acid after oral and intravenous administration in dogs.
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The purpose of these studies was to examine the pharmacokinetics, oral bioavailability, and systemic side effects of aminolevulinic acid (ALA) in beagle dogs after oral and i.v. administration. Oral and i.v. doses of ALA (128 mg of ALA hydrochloride, equivalent to 100 mg of ALA) were administered to four animals using a crossover design. Animals were allowed a 2-week washout period between doses. Plasma ALA concentrations were determined using precolumn fluorescent derivatization and reversed-phase HPLC. Plasma concentrations after i.v. administration declined rapidly with a terminal half-life of 19.5 +/-2.5 min (mean +/- S.D.). Total body clearance and volume of distribution at steady state averaged 6.79+/-1.77 ml/min/kg and 259+/- 128 ml/kg, respectively. Peak plasma concentrations of ALA after oral administration ranged from 1.27 to 9.42 microgram/ml. Oral bioavailability in these animals averaged 41.2+/-14.8% (range, 23.5-58.5%). These studies demonstrate that oral administration may provide a convenient and efficient route of delivery of ALA for photodynamic therapy in patients. (+info)
The lifespan of major histocompatibility complex class I/peptide complexes determines the efficiency of cytotoxic T-lymphocyte responses.
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Major histocompatibility complex (MHC)/peptide association and stability are determined by specific amino acid interactions between peptide antigens and the MHC groove, and are regarded as a critical feature in ensuring efficient monitoring by T cells. In this investigation we examined the relationship between MHC/peptide stability and the immunostimulatory capacity of MHC/peptide complexes. For this purpose we compared synthetic peptide analogues derived from the immunodominant HLA-A11-presented IVTDFSVIK (IVT) epitope, for their capacity to reactivate IVT-specific memory cytotoxic T-lymphocyte (CTL) responses. The analogues differentiated from the wild-type epitope by single amino acid substitution at position 2. All peptides showed similar affinity for HLA-A11 molecules and were recognized by IVT-specific CTL clones, but induced HLA-A11 complexes at the cell surface with different lifespan. This model offered the possibility of comparing the capacity of an immunogenic epitope to stimulate a unique population of T-cell precursors depending on the lifespan of its presentation at the cell surface. We demonstrated that stable HLA-A11/peptide complexes efficiently stimulate IVT-specific CTL responses, while HLA-A11/peptide complexes with short lifespan do not. The precise identification of the role of amino acid residues in the formation of stable MHC/peptide complexes may be relevant for the design of wild-type-derived epitopes with high immunogenicity. These analogues may have important applications in the immunotherapy of infectious diseases and immunogenic tumours. (+info)
Changes in the suppressive effects of recombinant inhibin A on FSH secretion in ram lambs during sexual maturation: evidence for alterations in the clearance rate of inhibin.
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We have investigated the effectiveness of human recombinant inhibin A (hr-inhibin A) to suppress the secretion of follicle-stimulating hormone (FSH) in ram lambs from 1 to 18 months of age. Seventeen rams (nine castrated, eight intact) were used. At 1, 3, 6, 9, 12 and 18 months of age the rams were given an i.v. injection of either vehicle or hr-inhibin A (0.64 microgram/kg). Blood samples were taken over 24 h. Plasma concentrations of FSH were suppressed in castrated and intact rams following injection of hr-inhibin A with maximal suppression occurring 6 h after injection. Vehicle injection had no effect. At 12 months of age the suppression in FSH was most rapid in castrated rams and was maximal in intact rams. The clearance rate of inhibin was greatest at older ages but during the period of seasonally induced testicular activity, there was a significant decrease in the inhibin clearance. The testicular weight was reduced in rams treated with hr-inhibin A, indicating the importance of FSH for testicular development during the pubertal period. There was no effect of hr-inhibin A on plasma concentrations of luteinizing hormone. We conclude that inhibin is capable of suppressing the secretion of FSH in rams from 1 month of age onwards and that the pituitary gland becomes maximally responsive to the actions of inhibin by the age of puberty. (+info)