Search PubMed⌕ Search

Biomedical subjects

K Hill

Publications and source records attributed to K Hill.

At least 73 records · Page 4Linked to original sources
PubMed1999

Purification of a highly modified RNA-aptamer. Effect of complete denaturation during chromatography on product recovery and specific activity.

To evaluate RNA-aptamers as potential drug candidates, efficient and scaleable purification protocols are needed. Because aptamers are highly structured and rigid molecules, denaturation during the purification process is a critical aspect to obtain a pure and active product. A two-step chromatographic procedure was developed to purify a synthetic anti-VEGF aptamer at the preparative scale. A reversed-phase chromatographic step was optimized with a highly hydrophobic ion pairing reagent, followed by ion-exchange chromatography in which heat and a chaotropic salt were used. Because of the presence of 2'-modified ribose, denaturation conditions had to be optimized in both chromatographic steps to achieve a fully active molecule.

Chromatography, High Pressure Liquid↗
PubMed1999

Sequence, assembly and analysis of pX01 and pX02.

Bacillus anthracis plasmids pX01 and pX02, harboured by the Sterne and Pasteur strains, respectively, have been sequenced by random 'shotgun' cloning and high throughout sequence analysis. These sequences have been assembled (Sequencher) to generate a circulate pX01 plasmid containing 181 656 bp and a single linear (gapped) pX02 contig containing at least 93.479 bp. Initial annotation suggests that the two plasmids combined contain at least 200 potential open reading frames (ORFs) with < 40% having significant similarity to sequences registered in open databases. Collectively, only 118 566 bp of the pX01 DNA (65%) represent predicted coding regions. This value is similar to published gene densities for other plasmids and is indicative of the larger intergenic spaces in plasmids vs those found in the chromosomes of the parental microbes (85-93% gene density). A 70 kbp region including the toxin genes (cya, lef and pag) is distinct from the remainder of the pX01 sequence: (1) it has a lower gene density (58 vs 70%) than the remaining 111 kbp; (2) it contains all but one of the co-regulated transcriptional fusions identified by transposon mutagenesis (Hoffmaster & Koehler 1997) and (3) it contains a significantly higher proportion of positive BLAST scores (62 vs 20%) for putative ORFs. These data suggest different origins for the two regions of pX01.

Bacillus anthracis↗
PubMed1999

Falls among healthy, community-dwelling, older women: a prospective study of frequency, circumstances, consequences and prediction accuracy.

OBJECTIVE: Most studies of falls among older people have focused on those with some degree of balance or mobility impairment. This study aimed to establish whether falls and associated injuries were a major problem among healthy, older women, whether there were some common features in the falls, and whether these falls could be accurately predicted. METHOD: Ninety-six healthy, active community-dwelling women in Melbourne, Australia, aged at least 70 years (mean 74.1 +/- 4.0) were initially measured on a comprehensive series of laboratory and clinical balance tests, gait, strength and psychometric measures. Subjects were monitored for falls events, circumstances and consequences by use of falls diaries and monthly phone calls. Baseline measures of clinical balance measures and gait were comparable to other studies reporting scores on these measures in samples of healthy older people. RESULTS: During the 12-month follow-up period, 49% of subjects fell, with 23% falling more than once; 9% suffered fractures as a result of their fall and 10% suffered strains or other moderate injuries. Many of the falls occurred during non-threatening activities such as walking, often under altered sensory or environmental conditions. Multivariate logistic regression identified gait symmetry and gait double support duration as the variables most strongly associated with prediction of multiple fallers. CONCLUSIONS: The results highlight that falls are a major problem among healthy active older women, and that targeted falls prevention programs are required for this group.

Accidental Falls↗
PubMed1999

Apolipoprotein B signal peptide polymorphism distribution among south Amerindian populations.

We report the distribution of the APOB signal peptide polymorphism in 5 native populations of South America: 2 samples of Mataco and 1 sample each of Pilagá and Toba from the Argentinian Chaco and 1 sample of Ache from the Paraguay forest. A randomly selected subsample of a previously studied sample from the Cayapa of Ecuador (Scacchi et al. 1997) was reanalyzed to investigate probable differences attributable to sampling, laboratory techniques, or interobserver error. The polymorphism observed in the signal peptide region of the APOB gene among native populations of South America exhibits the same range of variation found among geographic continental populations, confirming the high genetic heterogeneity of South Amerindians. Extremes in the allele prevalences were found among the Mataco and Ache, populations not far apart geographically. The small differences in genotype and allele frequencies between the subsample of the Cayapa analyzed here and the original Cayapa sample and between the 2 Mataco samples were not statistically significant and most likely were due to sampling error.

Alleles↗
PubMed1998

Methylation of CpG dinucleotides in the lacI gene of the Big Blue transgenic mouse.

Cytosine residues at CpG dinucleotides can be methylated by endogenous methyltransferases in mammalian cells. The resulting 5-methylcytosine base may undergo spontaneous deamination to form thymine causing G/C to A/T transition mutations. Methylated CpGs also can form preferential targets for environmental mutagens and carcinogens. The Big Blue(R) transgenic mouse has been used to investigate tissue and organ specificity of mutations and to deduce mutational mechanisms in a mammal in vivo. The transgenic mouse contains approximately 40 concatenated lambda-like shuttle vectors, each of which contains one copy of an Escherichia coli lacI gene as a mutational target. lacI mutations in lambda transgenic mice are characterized by a high frequency of spontaneous mutations targeted to CpG dinucleotides suggesting an important contribution from methylation-mediated events. To study the methylation status of CpGs in the lacI gene, we have mapped the distribution of 5-methylcytosines along the DNA-binding domain and flanking sequences of the lacI gene of transgenic mice. We analyzed genomic DNA from various tissues including thymus, liver, testis, and DNA derived from two thymic lymphomas. The mouse genomic DNAs and methylated and unmethylated control DNAs were chemically cleaved, then the positions of 5-methylcytosines were mapped by ligation-mediated PCR which can be used to distinguish methylated from unmethylated cytosines. Our data show that most CpG dinucleotides in the DNA binding domain of the lacI gene are methylated to a high extent (>98%) in all tissues tested; only a few sites are partially (70-90%) methylated. We conclude that tissue-specific methylation is unlikely to contribute significantly to tissue-specific mutational patterns, and that the occurrence of common mutation sites at specific CpGs in the lacI gene is not related to selective methylation of only these sequences. The data confirm previous suggestions that the high frequency of CpG mutations in lacI transgenes is related to the presence of 5-methylcytosine bases.

Animals↗
PubMed1998

Tom40 forms the hydrophilic channel of the mitochondrial import pore for preproteins [see comment].

The mitochondrial outer membrane contains machinery for the import of preproteins encoded by nuclear genes. Eight different Tom (translocase of outer membrane) proteins have been identified that function as receptors and/or are related to a hypothetical general import pore. Many mitochondrial membrane channel activities have been described, including one related to Tim23 of the inner-membrane protein-import system; however, the pore-forming subunit(s) of the Tom machinery have not been identified until now. Here we describe the expression and functional reconstitution of Tom40, an integral membrane protein with mainly beta-sheet structure. Tom40 forms a cation-selective high-conductance channel that specifically binds to and transports mitochondrial-targeting sequences added to the cis side of the membrane. We conclude that Tom40 is the pore-forming subunit of the mitochondrial general import pore and that it constitutes a hydrophilic, approximately 22 A wide channel for the import of preproteins.

Amino Acid Sequence↗
PubMed1998

Changes in balance and locomotion measures during rehabilitation following stroke.

BACKGROUND AND PURPOSE: This study aimed to examine the utility of a number of measures of balance and locomotion for the purpose of measuring change in a group of stroke patients undergoing in-patient rehabilitation. The aim was to select a core group of measures based on empirical evidence of usefulness rather than personal preference. METHODS: Twenty-nine stroke patients undergoing in-patient rehabilitation (mean age 71.8 +/- 10.5 years; 66% male) participated in the study. A prospective design was utilized with repeated measurement undertaken at four, six and eight weeks post-stroke. Static standing, the Clinical Test of Sensory Interaction of Balance (CTSIB) (Shumway-Cook & Horak, 1986), functional reach (FR), repetitive reach (RR), step test (ST), gait velocity, stride length and the Motor Assessment Scale (Carr et al., 1985) (walking item) were assessed at each interval. RESULTS: All measures of dynamic balance showed significant change over the four-week measurement period (p < 0.0036). Factor analysis identified two factors which grouped tests into static and dynamic, with a trend towards a third factor incorporating bipedal dynamic tests. Tests of static balance suffered from ceiling effects, whereas dynamic tests of balance and gait suffered from floor effects. Dynamic tests were more responsive (Standardized Response Measure (SRM) > 0.75) to change over the rehabilitation period than static tests. CONCLUSIONS: The findings suggest that a clinically useful and responsive balance and mobility test battery should include one component of the CTSIB (Shumway-Cook & Horak, 1986), RR (step stance), ST and gait velocity.

Aged↗
PubMed1998

Determination of flavopiridol (L86 8275; NSC 649890) in human plasma by reversed-phase liquid chromatography with electrochemical detection.

PURPOSE: Flavopiridol is a flavone which inhibits several cyclin-dependent kinases, and exhibits potent growth-inhibitory activity against a number of human tumor cell lines both in vitro, and when grown as xenografts in mice. It is currently being evaluated in a phase I clinical trial at the National Cancer Institute. The objective of this project was to develop and validate an analytical method for the assay of flavopiridol in human plasma, with sufficient sensitivity to permit the plasma pharmacokinetics of flavopiridol to be studied during clinical trials. METHODS: Flavopiridol was isolated from human plasma samples by extraction with t-butylmethyl ether following alkalinization with borate buffer (pH 8.0). The extract was evaporated, the residue was dissolved in mobile phase, and analyzed by reversed-phase high-pressure liquid chromatography. Chromatography was accomplished with a polymer-based C18 column eluted with a mobile phase consisting of methanol-phosphate buffer, pH 11.0 (53:47 v/v). Electrochemical detection (ECD) was employed. RESULTS: Flavopiridol was recovered from human plasma with an efficiency of 85-87%. Calibration curves were linear over the concentration range 10-500 nM (4.4-219 ng/ml). Plasma standard concentrations were measured with an accuracy and precision ranging from 3.2% to 10%. Regression analysis of flavopiridol concentrations of 15 clinical trial plasma samples ranging in concentration from approximately 50 to 4000 microM quantitated by both ECD and mass spectrometry showed close agreement. The equation of the regression line was y = 1.02x + 8 with a correlation coefficient of 0.969. Continuous infusion of flavopiridol in four patients for 72 h at a rate of 50 mg/m2 per day, resulted in mean steady-state plasma concentrations of from 200 to 300 nM. Levels declined in a biexponential manner following termination of the infusion, falling to approximately 10 nM after 48 h. CONCLUSIONS: An analytical method for the assay of flavopiridol in human plasma was developed with sensitivity to at least 10 nM. The assay is accurate, precise and specific, and is suitable for determination of plasma flavopiridol concentrations for pharmacokinetic studies during clinical trials.

Antineoplastic Agents↗
PubMed1998

The accuracy of mothers' reports of child vaccination: evidence from rural Egypt.

Estimates of immunization coverage in developing countries are typically made on a "card plus history" basis, combining information obtained from vaccination cards with information from mothers' reports, for children for whom such cards are not available. A recent survey in rural lower Egypt was able to test the accuracy of mothers' reports for a subset of children whose cards were not seen at round 1 of the survey but were seen a year later at round 3. Comparisons of the unsubstantiated reports at round 1 with information recorded from cards seen at round 3 indicate that mothers' reports are of very high quality; mothers' reports at round 1 were confirmed by card data at round 3 for between 83 and 93%, depending on vaccine, of children aged 12-23 months, and for 88 to 98% of children aged 24-35 months. Mothers of children who had not been vaccinated were more likely to give consistent responses than were mothers of vaccinated children. Thus, these "card plus history" estimates slightly understate true coverage levels. Most of the inconsistencies between round 1 and round 3 data apparently arose from interviewer or data processing error rather than from misreporting by mothers.

Adolescent↗
PubMed1998

Urea kinetic modelling--are any of the 'bedside' Kt/V formulae reliable enough?

BACKGROUND: Longevity on dialysis is determined by many factors. One of these has increasingly been seen to be 'dialysis dose'. There are several methods for calculating dialysis dose. We wanted prospectively to test 'gold-standard' UKM-Kt/V with various shortcut bedside formulae, to see whether reliance on the latter approach was likely to lead to errors in over- or underprescribing dialysis regimens. METHODS: Ten bedside formulae for the calculation of Kt/V (urea) were compared with UKM Kt/V values, in a month-long study involving 507 dialysis sessions in 50 patients in a single-centre in-patient haemodialysis unit. RESULTS: For patients with UKM Kt/V<0.8 (median 0.69, n=140), simplified formulae had a difference (delta) of 0.094-0.396 from the calculated UKM resulting in an inter-method variability ranging from 13 to 57%. The least difference was seen with the Calzavara formula (P=NS), maximum difference with the Barth formulae (P<0.05). No statistically significant differences were seen when comparing Daugirdas 1 and 2 and Keshaviah formulae with UKM, for patients with UKM Kt/V<0.8. For patients with UKM Kt/V in the range 0.8-1.4 (median 1.06, n=285) the extreme recorded values from simplified formulae were 0.012 (least different) and 0.245 (most different) from the UKM mean, with an inter-method variability ranging between 1.1% (Basile method) to 23.1% (Calzavara). No statistically significant difference were seen when comparing Daugirdas 1 and 2, Keshaviah, and Lowrie formulae with UKM, for patients with UKM Kt/V 0.8-1.4. For patients with the highest UKM Kt/V values (>1.4; median 1.58, n=72), all simplified formulae gave Kt/V values lower than UKM Kt/V: the minimum difference was 0.070 using Jindal (P=NS, intermethod variability of 4.4%), while the maximum was seen when using Calzavara (P<0.05; difference = 0.69; intermethod variability of 43.7%). There was also no statistically significant difference for Basile and Kerr methods. For the group as a whole the biggest difference from UKM mean values was obtained using Barth's and Calzavara's formulae (delta of 0.171 and 0.140 respectively (P<0.05)). CONCLUSIONS: The best correlations were seen with the Daugirdas 2 formula (r2=0.953). Also, comparing grouped formulae containing ln(Co/Ct) terms with those incorporating the (Co-Ct)/Co ratio (i.e. the urea reduction) there was a better correlation for all formulae employing the logarithmic transformation (r2=0.951-0.953 cf. r2=0.939-0.940). Nevertheless no bedside formula had the accuracy of UKM-Kt/V.

Adult↗
PubMed1998

A high-conductance solute channel in the chloroplastic outer envelope from Pea.

The pea chloroplastic outer envelope protein OEP24 can function as a general solute channel. OEP24 is present in chloroplasts, etioplasts, and non-green root plastids. The heterologously expressed protein forms a voltage-dependent, high-conductance (Lambda = 1.3 nS in 1 M KCl), and slightly cation-selective ion channel in reconstituted proteoliposomes. The highest open probability (P open approximately 0. 8) is at 0 mV, which is consistent with the absence of a transmembrane potential across the chloroplastic outer envelope. The OEP24 channels allow the flux of triosephosphate, dicarboxylic acids, positively or negatively charged amino acids, sugars, ATP, and Pi. Structure prediction algorithms and circular dichroism spectra indicate that OEP24 contains seven amphiphilic beta strands. The primary structure of OEP24 shows no homologies to mitochondrial or bacterial porins on a primary sequence basis, and OEP24 is functionally not inhibited by cadaverine, which is a potent inhibitor of bacterial porins. We conclude that OEP24 represents a new type of solute channel in the plastidic outer envelope.

Amino Acid Sequence↗
PubMed1998

Phase I trial of continuous infusion flavopiridol, a novel cyclin-dependent kinase inhibitor, in patients with refractory neoplasms.

PURPOSE: We conducted a phase I trial of the cyclin-dependent kinase inhibitor, flavopiridol (National Service Center [NSC] 649890), to determine the maximum-tolerated dose (MTD), toxicity profile, and pharmacology of flavopiridol given as a 72-hour infusion every 2 weeks. PATIENTS AND METHODS: Seventy-six patients with refractory malignancies with prior disease progression were treated with flavopiridol, with first-cycle pharmacokinetic sampling. RESULTS: Forty-nine patients defined our first MTD, 50 mg/m2/d x 3 with dose-limiting toxicity (DLT) of secretory diarrhea at 62.5 mg/kg/d x 3. Subsequent patients received antidiarrheal prophylaxis (ADP) to define a second MTD, 78 mg/m2/d x 3 with DLT of hypotension at 98 mg/m2/d x 3. Other toxicities included a proinflammatory syndrome with alterations in acute-phase reactants, particularly at doses >50 mg/ m2/d x 3, which in some patients prevented chronic therapy every 2 weeks. In some patients, ADP was not successful, requiring dose-deescalation. Although approximately 70% of patients displayed predictable flavopiridol pharmacology, we observed unexpected interpatient variability and postinfusion peaks in approximately 30% of cases. At the two MTDs, we achieved a mean plasma flavopiridol concentration of 271 nM (50 mg/m2/d x 3) and 344 nM (78 mg/m2/d x 3), respectively. One partial response in a patient with renal cancer and minor responses (n=3) in patients with non-Hodgkin's lymphoma, colon, and renal cancer occurred. CONCLUSION: The MTD of infusional flavopiridol is 50 mg/m2/d x 3 with dose-limiting secretory diarrhea at 62.5 mg/m2/d x 3. With ADP, 78 mg/m2/d x 3 was the MTD, with dose-limiting hypotension at 98 mg/m2/d x 3. Based on chronic tolerability, 50 mg/m2/d x 3 is the recommended phase II dose without ADP. Antitumor effect was observed in certain patients with renal, prostate, and colon cancer, and non-Hodgkin's lymphoma. Concentrations of flavopiridol (200 to 400 nM) needed for cyclin-dependent kinase inhibition in preclinical models were achieved safely.

Adult↗
PubMed1998

Causes of childhood deaths in Bangladesh: results of a nationwide verbal autopsy study.

While knowledge of causes of deaths is important for health sector planning, little is known from conventional sources about the causes of deaths in Bangladesh. This is partly due to deficiencies in the registration system and partly because few deaths are attended by qualified physicians. The present study was undertaken to update the information available on causes of deaths among under-5-year-olds, taking advantage of advances in verbal autopsy methodology and of the national Bangladesh Demographic and Health Survey conducted in 1993-94. About 25% of the deaths were associated with acute lower respiratory infections (ALRI) and about 20% with diarrhoea. Neonatal tetanus and measles remained important causes of death, and drowning was a major cause for 1-4-year-olds. Research and programmes to enable mothers to identify ALRI cases, particularly pneumonia, and to encourage timely and appropriate care-seeking and strengthening of ALRI case management at the primary care facilities are important priorities. While promotion of oral rehydration for watery diarrhoea and antibiotic treatment for dysentery should continue, broader preventive interventions including provision of safe water and sanitation, and improvements in personal hygiene require more attention. Further intensification of immunization programmes and innovative experimental interventions to reduce childhood from drowning should be designed and tested.

Age Distribution↗
PubMed1997

Reconstitution of a chloroplast protein import channel.

The chloroplastic outer envelope protein OEP75 with a molecular weight of 75 kDa probably forms the central pore of the protein import machinery of the outer chloroplastic membrane. Patch-clamp analysis shows that heterologously expressed, purified and reconstituted OEP75 constitutes a voltage-gated ion channel with a unit conductance of Lambda = 145pS. Activation of the OEP75 channel in vitro is completely dependent on the magnitude and direction of the voltage gradient. Therefore, movements of protein charges of parts of OEP75 in the membrane electric field are required either for pore formation or its opening. In the presence of precursor protein from only one side of the bilayer, strong flickering and partial closing of the channel was observed, indicating a specific interaction of the precursor with OEP75. The comparatively low ionic conductance of OEP75 is compatible with a rather narrow aqueous pore (dporeapproximately equal to 8-9 A). Provided that protein and ion translocation occur through the same pore, this implies that the environment of the polypeptide during the transit is mainly hydrophilic and that protein translocation requires almost complete unfolding of the precursor.

Chloroplasts↗
PubMed1997

Spontaneous mutation frequencies and spectra in p53 (+/+) and p53 (-/-) mice: a test of the 'guardian of the genome' hypothesis in the Big Blue transgenic mouse mutation detection system.

TSG-p53/Big Blue double transgenic mice offer a powerful tool for examining the effect of a p53 germline mutation on spontaneous somatic mutation in vivo. After sequencing the DNA-binding domain of the lacI gene, we previously reported no differences in mutant frequency between p53 nullizygous (-/-) and p53 wild-type (+/+) mice in liver, spleen and brain. However, jackpot mutations elsewhere in the gene may have obscured a real difference in mutation frequency and the small sample size of mutations not at CpG dinucleotides (n = 23) may have been insufficient to reveal differences in mutation spectra. Herein we have sequenced the entire lacI gene, including the promoter and lacZ operator regions. 123 additional independent mutations have been found including 70 mutations not at CpG sites. The mutation frequency was determined by correcting for jackpot mutations. There were no statistically significant differences in mutation frequency or spectrum between the p53 (+/+) and p53 (-/-) genotypes in any of the three tissues.

Animals↗
PubMed1997

Recruitment for controlled clinical trials: literature summary and annotated bibliography.

This article is a literature summary and annotated bibliography of research on recruitment for controlled clinical trials published through 1995. It extends and revises a similar review published in this journal a decade ago. The current commentary focuses on intervening developments in recruitment, including diverse populations, HIV trials, primary prevention trials, recruitment strategies, overall planning and management, patient and physician attitudes, adherence, generalizability, and cost. Profound barriers may exist in the recruitment of diverse populations, involving language, cultural factors, beliefs about medical research, and the appropriateness of available protocols. Extensive literature exists on patient and physician barriers to participation. Trials in HIV-infected or AIDs-diagnosed individuals introduce special considerations, including issues of confidentiality, parallel track design, and populations difficult to define and track. Recruitment strategies such as patient registries, occupational screening, direct mail, and the media are now prominent in the literature. Successful planning and management of an overall recruitment plan include piloting strategies, monitoring recruitment by data tracking systems, and hiring quality staff. Generalizability of study results is influenced by the characteristics of participants and by their adherence to study protocol. With increasingly limited funding to conduct clinical trials, efforts to quantify and reduce recruitment costs are being made. While over 4000 titles were identified, primarily by MEDLINE literature search, the articles summarized emphasize data-supported and -confirmed conclusions, and broad coverage of disease areas. We annotate here 91 outstanding articles useful for formulation of overall recruitment approaches in clinical trials.

Clinical Trials as Topic↗
PubMed1997

Spinal anesthesia versus intravenous sedation for transvaginal oocyte retrieval: reproductive outcome, side-effects and recovery profiles.

Transvaginal ultrasonically guided oocyte retrieval is commonly performed as part of in vitro fertilization efforts. The impact of anesthetic management on patient outcome from this procedure has not been well characterized. At our institution, patients are offered a choice of either heavy intravenous sedation or spinal anesthesia with minimal or no sedatives. In this pilot study, we retrospectively reviewed the anesthetic management, reproductive outcome and recovery room experience for all patients having oocyte retrieval during a 2-year interval (n = 95). Fifty-one oocyte retrievals were performed under spinal anesthesia, while 44 patients received solely intravenous sedatives. Both groups had similar reproductive outcomes. The intravenous sedation group required a significantly longer period until recovery room discharge criteria were met (P = 0.03), and were more likely to have postoperative emetic episodes (46% versus 6% in the spinal anesthesia group: P < 0.01). Two unplanned hospital admissions occurred in the intravenous sedation group: both were related to uncontrolled nausea and vomiting. We conclude that spinal anesthesia may have advantages over intravenous sedation for oocyte retrieval.

Journal Article↗