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Biomedical subjects

D Porter

Publications and source records attributed to D Porter.

At least 73 records · Page 4Linked to original sources
PubMed1996

Etoposide phosphate infusion with therapeutic drug monitoring in combination with carboplatin dosed by area under the curve: a cancer research campaign phase I/II committee study.

The area under the plasma concentration-time curve (AUC) following an intravenous dose of etoposide varies considerably among patients, which in part contributes to the unpredictability of toxicity and response seen in individual patients. This study evaluated the utility of therapeutic drug monitoring of etoposide in reducing the interpatient variability of etoposide steady-state concentrations during prolonged infusion. The etoposide prodrug etoposide phosphate (Etopophos; Bristol-Myers Squibb Company, Princeton, NJ) was administered by infusion using an adaptive dosing strategy. It was given in combination with carboplatin, which was dosed on an AUC basis. Patients with histologically or cytologically proven small cell lung cancer were treated with etoposide phosphate by continuous 120-hour infusion and carboplatin at a dose calculated by the Calvert formula to give an AUC of 5 mg/ mL.min. Blood samples were taken on days 2 through 5 of each treatment cycle, and high-performance liquid chromatography was used to measure the plasma etoposide concentration. The resultant concentrations were compared with target concentrations of 1 or 2 micrograms/mL and these data were used to calculate the rate of infusion for the following 24 hours. In the first cohort, the target etoposide concentration was 1 microgram/mL, and this was achieved (mean +/- SD = 1.05 +/- 0.24 micrograms/mL) by infusing etoposide phosphate doses of 21 to 109 mg (15 to 68 mg/m2) per day. In the second cohort, the target concentration of 2.0 micrograms/mL was achieved (mean +/- SD = 2.05 +/- 0.31 micrograms/mL) with infused etoposide phosphate doses of 69 to 193 mg (41 to 114 mg/m2) per day. This technique reduced the variation in plasma levels and resulted in predictable hematologic toxicity. Cumulative hematologic toxicity necessitated an extension of the treatment cycle from 3 to 4 weeks, however. Of six evaluable patients, two had a complete response and one had a partial response. Therapeutic drug monitoring was shown to reduce the interpatient variation in the plasma etoposide concentration by half and shows promise for individualizing treatment with combination chemotherapy. Exploiting the known relationships between the pharmacokinetics and pharmacodynamics of these two drugs by using therapeutic drug monitoring may lead to better therapeutic safety and efficacy.

Adult↗
PubMed1995

Dissection of the core and auxiliary sequences in the vegetative replication origin of promiscuous plasmid RK2.

The vegetative replication origin (oriV) of promiscuous IncP plasmid RK2 can function in many Gram-negative bacterial species when supplied with the plasmid-encoded replication protein TrfA and host-encoded replication proteins including DnaA. Nine TrfA binding sites (iterons) are known, and also two DnaA binding sites, box 1, between TrfA iterons 4 and 5, and box 2, downstream of repeat 9. The deletion analysis presented here shows that the core oriV requires DnaA box 1 for function in Escherichia coli and Pseudomonas putida. This DnA box is not essential in Pseudomonas aeruginosa, although its deletion does reduce plasmid copy number in this species. A putative IHF binding site is located upstream of DnaA box 1, but IHF deficiency in E. coli seems not to alter replication efficiency or copy number control. Cloned oriV can interfere with maintenance of an independent RK2 replicon. Analysis of replication inhibition functions associated with oriV showed that a short putative orf between TrfA iterons 1 and 2 is not necessary for replication inhibition, the presence of repeats 5 to 9 in target and inhibitor plasmid are not sufficient for efficient inhibition and inhibition does not correlate directly with the number of direct repeats present. Rather, the results showed that the isolated repeats 1 and 2 to 4, potentiate replication inhibition disproportionately to their effect on the number of TrfA binding sites. The results are consistent with the idea that repeats 1 to 4, arranged as a single copy and as an irregular group of three, potentiate the ability of the oriV region to form complexes which inhibit replication. We suggest that TrfA bound at these iterons may be more susceptible to forming pairs between oriV sequences on different plasmids.

Bacterial Proteins↗
PubMed1995

Evolution of T4-related phages.

Much progress has been made in understanding T-even phage biology in the last 50 years. We now know the entire sequence of T4, encoding nearly 300 genes, only 69 of which have been shown to be essential under standard laboratory conditions; no specific function is yet known for about 140 of them. The origin of most phage genes is unclear, and only 42 genes in T4 have significant similarity to anything currently included in GenBank. Comparative analysis of related phages is now being used to gain insight into both the evolutionary origins and interrelationships of these phage genes, and the functions of their protein products. The genomes of phages isolated from Tbilisi hospitals, Long Island sewage plants, the Denver zoo, and Khabarovsk show basic similarity. However, these phages show substantial insertions and deletions in a number of regions relative to each other, and closer investigation of specific sequences often reveals much more complex relationships. There are only a few cases in T4-related phages in which there is evidence for evolution through DNA duplication. These include the fibrous products of genes 12, 34, and 37; head proteins gp23 and gp24; and the Alt enzyme and its downstream neighbors. T4 also contains 13 apparent relatives of group I and group II intron homing endonucleases. Distal portions of the tail fibers of various T-even phages contain segments closely related to tail-fiber regions of other DNA coliphages, such as Mu, P1, P2, and lambda. Horizontal gene transfer clearly emerges as a major factor in the evolution of at least the tail-fiber regions, where site-specific recombination probably is involved in the exchange of host-range determinants.

Amino Acid Sequence↗
PubMed1995

The mission of social history of medicine: an historical view.

This paper analyses the shift in the Society for the Social History of Medicine from public health professionals to full-blooded approaches drawn from social history. The Bulletin of the Society reflected its vigorous interdisciplinary meetings programme: during the 1980s this matured into a fully fledged Journal and a monographs series as the Society took a crucial role in delivering the disciplinary functions of the history of medicicine.

Historiography↗
PubMed1995

Ultrasonography to evaluate adults for appendicitis: decision making based on meta-analysis and probabilistic reasoning.

OBJECTIVES: To review ultrasonography (US) test performance and to develop recommendations for the use of US to aid in the evaluation of potential appendicitis. METHODS: A meta-analysis was conducted using all English-language articles published since 1986 (17 studies; 3,358 patients) to ascertain sensitivity and specificity of US for diagnosing appendicitis in adults and teenagers. Calculation of the predictive value of US was performed for three groups of patients: group I--usually operated on (prevalence of appendicitis = 80%); group II--usually observed in hospital (prevalence = 40%); and group III--usually released home (prevalence 2%). RESULTS: Overall sensitivity was 84.7% (95% CI: 81.0-87.8%), and specificity 92.1% (88.0-95.2). The accuracy and usefulness of US were related to the likelihood of appendicitis. In group I, a positive test was accurate [positive predictive value (PPV) = 97.6%], but a negative study could not rule out appendicitis [negative predictive value (NPV) = 59.5%]. The converse was true for group III patients (PPV = 19.5%, NPV = 99.7%). Test performance accuracy was balanced only for group II patients (PPV = 87.3%, NPV = 89.9%). CONCLUSIONS: 1) US should not be used to exclude appendicitis for patients who have "classic" signs/symptoms, due to the underlying high false-negative rate. 2) US is most useful for patients who have an indeterminate probability of disease after the initial evaluation--if US is positive, the patient should have an operation; otherwise, he or she should be observed. 3) US is not recommended for screening patients who have a low probability of appendicitis, due to the low prevalence of disease and high false-positive rate in this group.

Adult↗
PubMed1995

Encapsidation and serial passage of a poliovirus replicon which expresses an inactive 2A proteinase.

The multiple roles of the viral proteinase 2A in poliovirus replication have been difficult to assess because, to date, it has not been possible to isolate and characterize a viral genome with an inactive 2Apro. We have previously reported that a poliovirus replicon containing an inactive 2Apro by virtue of a change at amino acid 109 from a cysteine to a serine (C109S) was replication competent when transfected into cells previously infected with vaccinia virus (R. Pal-Ghosh and C. D. Morrow, J. Virol. 67:4621-4629, 1993). To further develop this system, we have used a poliovirus replicon which contains the human immunodeficiency virus type 1 (HIV-1) gag gene positioned between nucleotides 1174 and 2470 of the poliovirus genome and have engineered a second mutation within this replicon to change the codon for amino acid 109 of the 2Apro from cysteine to serine (2AC109S). Transfection of this replicon into cells previously infected with vaccinia virus results in the replication and expression of a protein with a molecular mass consistent with that of a P1-HIV-1 Gag-2A fusion protein. Using a recently described complementation system which relies on the capacity of a recombinant vaccinia virus (VV-P1) to provide the capsid precursor (P1) in trans (D. C. Ansardi, D. C. Porter, and C. D. Morrow, J. Virol. 67:3684-3690, 1993; and D. C. Porter, D. C. Ansardi, W. S. Choi, and C. D. Morrow, J. Virol. 67:3712-3719, 1993), we have encapsidated this replicon containing the 2AC109S mutation. By using reverse transcription PCR, we demonstrated that after 15 serial passages the encapsidated replicon still contained the 2AC109S mutation. Infection of cells with a stock of encapsidated replicon, either in the presence or in the absence of vaccinia virus, resulted in the expression of the P1-HIV-1 Gag-2A fusion protein. Expression of the P1-HIV-1 Gag fusion protein in cells infected with the encapsidated replicon containing the 2AC109S mutation was reduced compared with the expression of P1-HIV-1 Gag in those cells infected with a replicon containing a wild type 2A gene. The protein expression and replication of the replicon RNA in cells containing the 2AC109S mutation was maintained for a longer period of time than for the replicons containing the wild-type 2A gene, possibly because of a reduced cytopathic effect.(ABSTRACT TRUNCATED AT 400 WORDS)

Base Sequence↗
PubMed1995

Differential expression of multiple glutaminase mRNAs in LLC-PK1-F+ cells.

LLC-PK1-F+ cells are porcine proximal tubule-like cells that have been used to model the renal ammoniagenic response to metabolic acidosis. A 3.2-kb porcine glutaminase (GA) cDNA (pGA201) containing 528 bp of coding sequence and 2.7 kb of 3'-untranslated region was cloned and sequenced. Probes derived from both porcine and rat GA cDNAs were used to characterize the expression of putative GA mRNAs in LLC-PK1-F+ cells. Two larger putative GA mRNAs (approximately 5.0 and 4.5 kb in length) were resolved and a smaller 2.5-kb species was also observed. The level of the 5.0-kb mRNA is detectable in freshly split LLC-PK1-F+ cells and increases as the cells reach confluence. In contrast, the amount of the 4.5-kb GA mRNA is greatest in freshly split cells and decreases gradually as the cells approach confluence. The levels of the 5.0- and 2.5-kb mRNAs are also affected by refeeding the cells, and the 2.5-kb mRNA accumulates to high levels if cells are retained in the same media for 4 days. Exposure to acidic media had little or no effect on the levels of GA mRNAs expressed in confluent or postconfluent cells, whereas, in growing and undifferentiated cells, this treatment did affect the level of the 4.5-kb mRNA. Thus the putative GA mRNA species are differentially expressed. Given this complexity, a careful assessment of GA mRNA species, of basal expression, and of growth conditions are essential for a meaningful analysis of GA mRNA levels in cultured cells.

Acids↗
PubMed1994

Determination of the monomer-dimer equilibrium of interleukin-8 reveals it is a monomer at physiological concentrations.

Interleukin-8 has been shown by X-ray crystallography and NMR to be a homodimer, suggesting that this is the form which binds to its receptor. Here we measure, for the first time, the monomer-dimer equilibrium of interleukin-8 using analytical ultracentrifugation and titration microcalorimetry and find that it dissociates readily to monomers with an equilibrium dissociation constant of 18 +/- 6 microM at 37 degrees C. The present findings suggest that the monomer is the form which binds to the receptor. Comparison of experimental and structure-based calculated thermodynamics of interleukin-8 dimerization argues for limited subunit conformational changes upon dissociation to monomer.

Calorimetry↗
PubMed1994

A fluorometric assay for DNA cleavage reactions characterized with BamHI restriction endonuclease.

Fluorescently labeled oligonucleotides and DNA fragments have promise in nucleic acid research with applications that include DNA hybridization, automated DNA sequencing, fluorescence anisotropy, and resonance energy transfer studies. Past concerns with fluorescent-labeled DNA arose from interactions between fluorophores and DNA that result in quenched fluorescence. This quenching phenomenon is most problematic in fluorescence resonance energy transfer studies because quenching of the donor fluorescence could result from either resonance energy transfer or nontransfer effects. In the present study, relief of nontransfer quenching of a 14-mer fluorescein 5-isothiocyanate (FITC)-labeled oligonucleotide containing the BamHI restriction site was characterized with both steady-state and time-resolved fluorescence techniques. The FITC-labeled single strand was best fit by a triexponential decay with lifetimes of 0.5, 2.7, and 4.2 ns. The 4.2-ns component was found to contribute more than 80% of the total steady-state intensity. Upon annealing with an unmodified complementary strand, the contribution from the 4.2-ns component was significantly decreased, resulting in twofold quenching of total fluorescence. We reasoned that this quenching phenomenon should be a reversible process and could be employed to study strand separation processes in molecular biology. Hence, cleavage of the fluorescently labeled substrate was examined using DNAase I and BamHI restriction endonuclease. Our results show that the quenched fluorescence is totally recovered upon cleavage (compared to that of the single strand). The extent of cleavage measured by fluorescence was confirmed by nondenaturing polyacrylamide gel electrophoresis analysis. We believe this fluorescence "dequenching" technique may be used to quantify the kinetics of other DNA strand separation and cleavage processes in molecular biology.

Base Sequence↗
PubMed1994

Emotional and neurocognitive deficits in fragile X.

We have studied the neurocognitive deficit in premutation and full mutation women as compared to control women and to explore the relationship between those deficits and the incidence of emotional problems. Four groups of women were examined: two fragile X (fra(X)) negative control groups, one of which grew up in fra(X) families and one not; and two DNA positive groups, one with a premutation (CGG repeats < 200) and one with an expanded mutation (CGG repeats > 200). All women were assessed using the MMPI-2, the SADS-L, and a battery of neuropsychological tests. Full mutation women had lower scores on composite measures of executive function and nonverbal function. There was no difference between the groups in terms of the lifetime incidence of depressive and anxiety disorders on the SADS-L. Full mutation women displayed Lie scales higher than the other groups on the MMPI-2. Neurocognitive measures were not related to SADS-L diagnoses but were related to the Lie scale on the MMPI-2. Finally, number of CGG repeats was related to the neuropsychological variables and the Lie scale.

Adult↗
PubMed1994

Abnormal haem biosynthesis in the chronic anaemia of rheumatoid arthritis.

OBJECTIVES: The chronic microcytic anaemia of rheumatoid arthritis (RA) occurs despite the presence of adequate reticulo-endothelial iron stores. The red cell microcytosis is evidence of impaired haemoglobin production. This study has examined possible abnormalities of erythroid haem biosynthesis that may contribute to the anaemia. METHODS: 5-Aminolaevulinate (ALA) synthase and ferrochelatase activities were assayed in whole bone marrow and in purified erythroblasts from patients with RA and in control subjects. All patients were iron replete with demonstrable iron in the bone marrow. RESULTS: ALA synthase activity was significantly reduced in both whole bone marrow and purified erythroblasts from patients with the anaemia of RA. Erythrocyte protoporphyrin levels were raised in nine of 12 patients tested while ferrochelatase activity was normal. CONCLUSION: These abnormalities provide absolute evidence of abnormal erythroblast haem biosynthesis and iron metabolism in the anaemia of RA and most likely reflect decreased ALA synthase mRNA translation and some abnormality of erythroblast iron transport. Further studies using highly purified erythroblast populations will attempt to identify the causal factors leading to this abnormal erythroblast metabolism.

5-Aminolevulinate Synthetase↗
PubMed1992

Triaxial force transducer for investigating stresses at the stump/socket interface.

Although normal pressures at the stump socket interface of the lower-limb amputee have been investigated, little is known about the shear stresses that also occur. Studies suggest that the combination of both shear and normal stresses significantly exacerbates discomfort and vascular and tissue damage. A means of simultaneously measuring normal and shear stresses will aid in the investigation and improvement of prosthetic fit. A miniature triaxial force transducer (4.9 x 16 mm diameter) has been developed which can be recessed into the socket wall. The principle of operation, construction, performance and limitations of the device are described. Preliminary measurements of the interface stress variations over the gait cycle in a supra-condylar PTB socket are presented. These show clear differences in the stress patterns present when two different prosthetic feet are used.

Amputation Stumps↗