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Biomedical subjects

D Talbot

Publications and source records attributed to D Talbot.

At least 55 records · Page 3Linked to original sources
PubMed1998

A randomised, concentration-controlled, comparison of standard (5-day) vs. prolonged (15-day) infusions of etoposide phosphate in small-cell lung cancer.

PURPOSE: This randomised trial was designed to investigate the activity and toxicity of continuous infusion etoposide phosphate (EP), targeting a plasma etoposide concentration of either 3 micrograms/ml for five days (5d) or 1 microgram/ml for 15 days (15d), in previously untreated SCLC patients with extensive disease. PATIENTS AND METHODS: EP was used as a single agent. Plasma etoposide concentration was monitored on days 2 and 4 in patients receiving 5d EP and on days 2, 5, 8 and 11 in patients receiving 15d EP, with infusion modification to ensure target concentrations were achieved. Treatment was repeated every 21 days for up to six cycles, with a 25% reduction in target concentration in patients with toxicity. RESULTS: The study has closed early after entry of 29 patients (14 with 5d EP, 15 with 15d EP). Objective responses were seen in seven of 12 (58%, confidence interval (CI): 27%-85%) evaluable patients after 5d EP, and two of 14 (14%, CI: 4%-42%) evaluable patients after 15d EP (P = 0.038). Grade 3 or 4 neutropenia or leucopenia during the first cycle of treatment was observed in six of 12 patients after 5d EP and 0/14 patients after 15d EP (P = 0.004), with median nadir WBC count of 2.6 x 10(9)/1 after 5d and 5.0 x 10(9)/1 after 15d EP (P = 0.017). Only one of 49 cycles of 15d EP was associated with grade 3 or worse haematological toxicity, compared to 14 of 61 cycles of 5d EP. CONCLUSIONS: Although the number of patients entered into this trial was small, the low activity seen at 1 microgram/ml in the 15d arm suggests that this concentration is below the therapeutic window in this setting. Further concentration-controlled studies with prolonged EP infusions are required.

Adult↗
PubMed1997

Baculovirus-mediated expression and characterization of the full-length murine DNA methyltransferase.

The original cDNA sequence reported for the murine DNA methyltransferase (MTase) was not full length. Recently, additional cDNA sequences have been reported that lie upstream of the original and contain an extended open reading frame with three additional ATGs in frame with the coding region [Tucker et al . (1996) Proc. Natl. Acad. Sci. USA , 93, 12920-12925; Yoder et al . (1996) J. Biol. Chem . 271, 31092-31097]. Genomic DNA upstream of this ATG contains two more ATGs in frame and no obvious splice site. We have constructed, and expressed in baculovirus, MTase clones that begin at each of these four ATGs and examined their properties. Constructs beginning with any of the first three ATGs as their initiator methionines give a predominant DNA MTase band of approximately 185 kDa on SDS-PAGE corresponding to translational initiation at the third ATG. The fourth ATG construct gives a much smaller protein band of 173 kDa. The 185 kDa protein was purified by HPLC, characterized by mass spectrometry and has a measured molecular mass of 184 +/- 0.5 kDa. All of these MTases were functional in vitro and steady state kinetic analysis showed that the recombinant proteins exhibit similar kinetic properties irrespective of their length. The homogeneous recombinant enzyme from the fourth ATG construct shows a 2.5-fold preference for a hemi-methylated DNA substrate as compared to an unmethylated substrate, whereas the 185 kDa protein is equally active on both substrates. The kinetic properties of the recombinant enzyme are similar to those reported for the native MTase derived from murine erythroleukemia cells. The new clones are capable of yielding large quantities of intact MTases for further structural and functional studies.

Amino Acid Sequence↗
PubMed1997

Multicenter randomized trial comparing tacrolimus (FK506) and cyclosporine in the prevention of renal allograft rejection: a report of the European Tacrolimus Multicenter Renal Study Group.

BACKGROUND: To confirm the results of a number of studies conducted in Europe, the United States, and Japan, this multicenter, randomized trial compared the 12-month efficacy and safety of tacrolimus- and cyclosporine-based immunosuppressive regimens in the prevention of renal allograft rejection. METHODS: A total of 448 renal transplant recipients were recruited from 15 centers and assigned to receive triple-drug therapy consisting of tacrolimus (n=303) or cyclosporine (n=145) in conjunction with azathioprine and low-dose corticosteroids. RESULTS: At 12 months after transplantation, tacrolimus therapy was associated with a significant reduction in the frequency of both acute (tacrolimus 25.9% vs. cyclosporine 45.7%; P<0.001 [absolute difference: 19.8%, 95% confidence interval: 10.0-29.6%]) and corticosteroid-resistant rejection (11.3% vs. 21.6%; P=0.001 [absolute difference: 10.3%, 95% confidence interval: 2.5-18.2%]). Actuarial 1-year patient (tacrolimus 93.0% vs. cyclosporine 96.5%; P=0.140) and graft survival rates (82.5% vs. 86.2%; P=0.380) did not differ significantly between the two treatment groups. Overall, the safety profiles of the tacrolimus- and cyclosporine-based regimens were quite comparable. Infections, renal impairment, neurological complications, and gastrointestinal complaints were frequently reported but were mostly reversible in both groups. Higher incidences of elevated serum creatinine, tremor, diarrhea, hyperglycemia, diabetes mellitus, and angina pectoris were reported in the tacrolimus treatment group, whereas acne, arrhythmia, gingival hyperplasia, and hirsutism were more frequent with cyclosporine treatment. CONCLUSIONS: The significant reduction in the incidence of episodes of allograft rejection observed with tacrolimus therapy may have important long-term implications given the prognostic influence of rejection on graft survival.

Adolescent↗
PubMed1997

Examination of the mechanism by which heparin antagonizes activation of a model endothelium by interferon-gamma (IFN-gamma).

IFN-gamma increases the potential immunogenicity of vascular endothelial cells by up-regulation of intercellular adhesion molecule-1 (ICAM-1) and class I MHC antigen expression and by induction of class II MHC antigens and certain chemokines. In this study the mechanism by which the glycosaminoglycan (GAG) heparin antagonizes the activation of a model endothelium by IFN-gamma was investigated. Radioligand binding assays demonstrated that total binding of 125I-IFN-gamma to the EAhy.926 endothelial hybridoma cell line was reduced in the presence of heparin or heparan sulphate (HS); the structurally dissimilar GAG chondroitin sulphate had no effect. Treatment of the cells with chlorate, a metabolic inhibitor of GAG sulphation, was found to reduce both the subsequent binding of IFN-gamma and its ability to induce expression of class II MHC antigens. Treatment with heparinase II dramatically reduced the binding of IFN-gamma, while chondroitin ABC lyase had no effect. A cationic peptide from the C-terminal region of IFN-gamma was also found to reduce binding of intact IFN-gamma to the cells. These results appear to demonstrate that IFN-gamma is sequestered at the surface of endothelial cells by electrostatic interaction between specific basic amino acid residues and sulphated domains on HS, the most abundant endothelial GAG. This interaction is competitively inhibited by heparin, which is structurally related to HS. These observations are consistent with the model that IFN-gamma is bound by membrane-associated HS before engagement with the high-affinity receptor and signal transduction. Inhibition of the interaction between proinflammatory cytokines and membrane-associated GAG molecules may provide a mechanism for inducing clinically useful immunosuppression.

Cell Division↗
PubMed1997

Recovery of kidneys from older donors: is it worthwhile?

One factor that is considered in the search for viable organs is the age of the potential donor. Retrospective data analysis on older donors (those aged 65 years and above) was performed to examine graft outcome. Data were collected on all older donors retrieved in one region from 1990 to 1995. Of those recipients transplanted locally (mean age, 57.6 years), creatinine values were recorded at 3 and 12 months. A recipient control group was selected from younger donors over the same period. Grafts were considered functional if the recipient was dialysis free. After 1 year, 24 recipients (82.3%) remained dialysis free, whereas 28 in the control group (90.3%) remained dialysis free during the same period. No significant differences were found in 1-year graft survival between kidneys retrieved from older donors versus those retrieved from younger donors. It therefore can be concluded that recovery from older donors is worthwhile.

Adult↗
PubMed1996

Complementation of methylation deficiency in embryonic stem cells by a DNA methyltransferase minigene.

Previous attempts to express functional DNA cytosine methyltransferase (EC 2.1.1.37) in cells transfected with the available Dnmt cDNAs have met with little or no success. We show that the published Dnmt sequence encodes an amino terminal-truncated protein that is tolerated only at very low levels when stably expressed in embryonic stem cells. Normal expression levels were, however, obtained with constructs containing a continuation of an ORF with a coding capacity of up to 171 amino acids upstream of the previously defined start site. The protein encoded by these constructs comigrated in SDS/PAGE with the endogenous enzyme and restored methylation activity in transfected cells. This was shown by functional rescue of Dnmt mutant embryonic stem cells that contain highly demethylated genomic DNA and fail to differentiate normally. When transfected with the minigene construct, the genomic DNA became remethylated and the cells regained the capacity to form teratomas that displayed a wide variety of differentiated cell types. Our results define an amino-terminal domain of the mammalian MTase that is crucial for stable expression and function in vivo.

Amino Acid Sequence↗
PubMed1996

Cyclosporine nephrotoxicity in the ischemic kidney and the protective effect of pentoxifylline--a study in the rat.

In order to prevent cyclosporine nephrotoxicity in the ischemic kidney, pentoxifylline was used in a rat model. Seventy-two rats were divided into six groups according to treatment after right nephrectomy: Group I was the control, group II was treated with 25 mg/kg cyclosporine, group III underwent renal ischemia for 45 min, group IV was given 25 mg/kg cyclosporine and subjected to renal ischemia, and group V was subjected to renal ischemia and given 45 mg/kg pentoxifylline (repeated at 12, 36, and 48 hr), group VI underwent renal ischemia and was then given both cyclosporine and pentoxifylline. BUN, creatinine, and potassium levels were significantly elevated 24 hr after cyclosporine (group II), ischemia (group III), and cyclosporine and ischemia (group IV). Sodium levels remained unaffected. BUN levels normalized in all but groups III and IV after 48 hr. Creatinine levels normalized in all but group IV after 48 hr. Creatinine clearance fell in all groups and remained low even after 48 hr. Pentoxifylline prevented dramatic rises in BUN and creatinine and levels nearly normalized after 48 hr. It also histologically prevented extensive tissue damage seen after ischemia. In conclusion, pentoxifylline has a protective effect upon the kidney when subjected to cyclosporine in the presence of ischemia.

Animals↗
PubMed1996

Flow cytometric crossmatching in renal transplantation--outcome after five years.

The association of a positive flow cytometric crossmatch between recipient IgG directed against donor T lymphocytes and poor outcome is well described in renal transplantation. Until now, no long-term follow-up on such patients has been available. A total of 117 renal transplant patients were followed up for a period of 5 years. Of these, 21 were known to have donor T cell-directed IgG and 5 had B lymphocyte-directed IgG. Both groups of patients with these antibodies had a significantly poorer outcome at 5 years than did the group of patients without IgG (P < 0.0001 Handel Maenzel test). Patients with antibody detected preoperatively were tested again, either at the time of graft failure or at 5 years posttransplantation. The sera were tested against stored donor cells and the intensity of surface IgG compared with the preoperative levels. In those recipients who lost their grafts, the levels increased in 60% of cases but those that retained their grafts also had an increase in levels of donor-directed antibody in 50% of cases. The changing levels of antibody therefore appeared to have little relevance to outcome. However, when IgG isotypes were considered, for those who experienced graft failure and also had a gamma 3 isotype, a rise in IgG was demonstrated in all cases. Conversely, successful grafts with gamma 3 had a decline in levels between preoperative and 5-year samples in three of the four cases (p not significant).

Flow Cytometry↗