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Biomedical subjects

J Clarke

Publications and source records attributed to J Clarke.

At least 109 records · Page 6Linked to original sources
PubMed1999

Cardiovascular responses to an orthostatic challenge and electrical-stimulation-induced leg muscle contractions in individuals with paraplegia.

The purpose of this study was to investigate the cardiovascular and haemodynamic responses that occur during moderate orthostatic challenge in people with paraplegia, and the effect of electrical stimulation (ES)-induced leg muscle contractions on their responses to orthostatic challenge. Eight males with complete spinal lesions between the 5th and 12th thoracic vertebrae (PARA) and eight able-bodied individuals (AB) volunteered for this study. Changes in heart rate (fc), stroke volume (SV), cardiac output (Qc), mean arterial pressure (MAP), total peripheral resistance (TPR), limb volumes and indices of neural modulation of fc, [parasympathetic (PNS) and sympathetic (SNS) nervous system indicators] were assessed during: (1) supine rest (REST), (2) REST with lower-body negative pressure at -30 torr (LBNP -30, where 1 torr = 133.32 N/m2), and (3) for PARA only, LBNP -30 with ES-induced leg muscle contractions (LBNP + ES). LBNP -30 elicited a decrease in SV (by 23% and 22%), Qc (by 15% and 18%) and the PNS indicator, but an increase in fc (by 10% and 9%), TPR (by 23% and 17%) and calf volume (by 1.51% and 4.04%) in both PARA and AB subjects, respectively. The SNS indicator was increased in the AB group only. Compared to LBNP -30, LBNP + ES increased SV (by 20%) and Qc (by 16%), and decreased TPR (by 12%) in the PARA group. MAP was unchanged from REST during all trials, for both groups. The orthostatic challenge induced by LBNP -30 elicited similar cardiovascular adaptations in PARA and AB subjects. ES-induced muscle contractions during LBNP -30 augmented the cardiovascular responses exhibited by the PARA group, probably via reactivation of the skeletal muscle pump and improved venous return.

Adult↗
PubMed1999

A new study of bacterial motion: superconducting quantum interference device microscopy of magnetotactic bacteria.

The recently developed "microscope" based on a high-Tc dc SQUID (superconducting quantum interference device) is used to detect the magnetic fields produced by the motion of magnetotactic bacteria, which have permanent dipole moments. The bacteria, in growth medium at room temperature, can be brought to within 15 micron of a SQUID at liquid nitrogen temperature. Measurements are performed on both motile and nonmotile bacteria. In the nonmotile case, we obtain the power spectrum of the magnetic field noise produced by the rotational Brownian motion of the ensemble of bacteria. Furthermore, we measure the time-dependent field produced by the ensemble in response to an applied uniform magnetic field. In the motile case, we obtain the magnetic field power spectra produced by the swimming bacteria. Combined, these measurements determine the average rotational drag coefficient, magnetic moment, and the frequency and amplitude of the vibrational and rotational modes of the bacteria in a unified set of measurements. In addition, the microscope can easily resolve the motion of a single bacterium. This technique can be extended to any cell to which a magnetic tag can be attached.

Biophysical Phenomena↗
PubMed1999

Evaluation of bovine lactoferrin as a topical therapy for chemotherapy-induced mucositis in the golden Syrian hamster.

Bovine lactoferrin was applied topically to the oral mucosa of Syrian hamsters and assessed for its ability to decrease the severity of chemotherapy-induced oral mucositis. Results indicated that the chemotherapy agent 5-fluorouracil (5-FU) administered to hamsters on days 0 and 2 produced severe leukopenia between days 4 and 7 of the trial, and that severity of oral mucositis coincided with the suppressed immune state in these animals. Bovine lactoferrin applied continuously to oral wounds in hamsters induced by a combination of chemotherapy treatment and mild abrasion of the cheek pouch, failed to decrease the severity of mouth ulcers relative to a group receiving BSA as a control protein source. Hamster cheek pouches treated twice daily with lactoferrin had a significantly worse condition score between days 6 and 8, and days 12 and 13 (p < 0.05 to p < 0.001), a higher ulcer score between days 6 and 15 (p < 0.05 to p < 0.001) and larger ulcer area between days 7 and 14 (p < 0.05 to p < 0.001) compared to animals administered the control protein. Body weight changes between treatment and control groups showed no significant difference over the trial period. In contrast to the pre-study hypothesis, we report a detrimental effect from topical administration of bovine lactoferrin to the wounded oral mucosa of immunocompromised hamsters.

Animals↗
PubMed1999

Upregulation of basic fibroblast growth factor in breast carcinoma and its relationship to vascular density, oestrogen receptor, epidermal growth factor receptor and survival.

BACKGROUND: Angiogenesis, the process whereby endothelial cells divide and migrate to form new blood capillaries, has been assessed in tumours by measuring microvessel density. High microvessel density is a significant adverse prognostic factor in breast cancer. The angiogenic factor, basic fibroblast growth factor (bFGF), has been associated with tumourigenesis and metastasis in several human cancers. There are few quantitative studies of bFGF expression in normal tissues compared to cancer. PATIENTS AND METHODS: We have measured bFGF levels in 149 human primary breast carcinomas and assessed the findings in relation to microvessel density, oestrogen receptor (ER) and epidermal growth factor receptor (EGFR). Basic FGF levels were measured by ELISA. Western blotting and immunohistochemistry were carried out to confirm the presence of bFGF. RESULTS: Levels of bFGF were more than 10-fold higher in tumour cytosols compared to reduction mammoplasty tissue and 3-fold compared to non neoplastic cytosols from the same breast as the tumour (P < 0.0001). Immunohistochemistry showed bFGF protein was localised exclusively in the stroma whereas no bFGF staining was observed in the epithelial cells. High bFGF levels were significantly related to high ER (P = 0.01). Similarly, high bFGF levels were significantly related to low grade (P = 0.046) and to small tumour size (P = 0.04). No significant relationship was observed between bFGF and microvessel count, EGFR or age. In univariate analysis and in a Cox proportional hazard model bFGF did not reach significance for overall or relapse free survival. CONCLUSIONS: Our results show that although bFGF is elevated in breast carcinomas compared to normal breast tissue it is not related to microvessel density and it is not an independent predictor of survival in breast cancer patients. Basic FGF may be one of multiple factors that synergise with other growth factors such as VEGF to enhance angiogenesis.

Adult↗
PubMed1999

A human IFNGR1 small deletion hotspot associated with dominant susceptibility to mycobacterial infection.

The immunogenetic basis of severe infections caused by bacille Calmette-Guérin vaccine and environmental mycobacteria in humans remains largely unknown. We describe 18 patients from several generations of 12 unrelated families who were heterozygous for 1 to 5 overlapping IFNGR1 frameshift small deletions and a wild-type IFNGR1 allele. There were 12 independent mutation events at a single mutation site, defining a small deletion hotspot. Neighbouring sequence analysis favours a small deletion model of slipped mispairing events during replication. The mutant alleles encode cell-surface IFNgamma receptors that lack the intra-cytoplasmic domain, which, through a combination of impaired recycling, abrogated signalling and normal binding to IFNgamma exert a dominant-negative effect. We thus report a hotspot for human IFNGR1 small deletions that confer dominant susceptibility to infections caused by poorly virulent mycobacteria.

Adolescent↗
PubMed1999

Isolated limb perfusion with tumour necrosis factor-alpha and melphalan with or without interferon-gamma for the treatment of in-transit melanoma metastases: a multicentre randomized phase II study.

This open, multicentre, randomized phase II trial was conducted to determine the effect of isolated limb perfusion (ILP) with tumour necrosis factor-alpha (TNFalpha) in combination with melphalan with or without interferon-gamma (IFNgamma) in patients with in-transit metastases of melanoma of the limbs (MD Anderson stage IIIA or IIIAB, AJCC stage III). The 64 patients included were randomized to receive either a two- drug regimen consisting of TNFalpha and melphalan (TM-ILP) or a three-drug regimen consisting of TNFalpha, melphalan and INFgamma (TIM-ILP). Patients randomized to receive IFNgamma were pretreated for 2 days before the ILP with once daily 0.2 mg IFNgamma subcutaneously and also received the same amount of IFNgamma during ILP. A total of 47 complete responses (73%) were reported, 22 (69%) of which occurred in the TM-ILP group and 25 (78%) in the TIM-ILP group; the difference was not significant. The 14 partial responses (22%) were split evenly between the treatment groups. In the TM-ILP group, two cases of stable disease and one case of progressive disease were reported. The overall response rate (complete plus partial responses) was 100% in the TIM-ILP group and 91% in the TM-ILP group, yielding an overall response of 95% for this study. In the historical control data, where 103 patients had received melphalan alone (M-ILP), there were 54 records of complete responses (52%) and 80 of complete or partial responses (78%). The median survival time estimated by the Kaplan-Meier method was 819 days for the TM-ILP group, > 705 days for the TIM-ILP group and 873 days for the combined study population; estimates for time to local progression or recurrence were 327 days, in excess of 498 days and 405 days, respectively. The corresponding figure for the historical controls was 338 days. These data suggest that TNFalpha associated with melphalan may be superior to melphalan alone for ILP.

Adult↗
PubMed1999

Burns.

Explore the source record for details and available documents.

Burns↗
PubMed1998

The dependence of chemical exchange on boundary selection in a fibronectin type III domain from human tenascin.

The third fibronectin type III domain from human tenascin adopts a compact beta-sandwich fold. Its boundaries were originally selected to encode a 90-residue domain (TNfn31-90). We conclude that the dynamic properties of TNfn3 are more accurately represented when the C terminus is extended by the two naturally succeeding residues. Longitudinal (R1) and transverse (R2) 15N relaxation rates, and ¿1H-15N¿ NOE enhancements at pH 4.9 and 300 K are presented for TNfn31-90 and TNfn31-92, the extended form, at two field strengths (11.74 and 14.10 T). Nearly identical results confirm their similar motional properties over a broad range of timescales. However, a number of residues near the C terminus in TNfn31-90 exhibit elevated transverse relaxation rates and broadened signals in 1H-15N HSQC spectra. Explicit rates of chemical exchange for five residues in TNfn31-90 were determined by measuring transverse relaxation rates in a series of CPMG experiments with spin-echo refocusing delays increasing from 311 to 1436 micros. Calculated exchange rates average 1000(+/-311) s-1, with individual uncertainties near 20%. Homonuclear TOCSY experiments collected between pH 4 and 7 reveal the coincident titration of two acidic clusters in TNfn31-90 at pH 5. 64(+/-0.47). The repulsive electrostatic interaction of the C-terminal carboxylate with one of these clusters may promote chemical exchange in the shorter domain. Additionally, NOE and chemical shift data suggest hydrogen bond formation between the added residues and adjacent loops. The data affirm the importance of judiciously selecting domain boundaries prior to the characterization of molecular properties.

Fibronectins↗
PubMed1998

The effect of boundary selection on the stability and folding of the third fibronectin type III domain from human tenascin.

Correct selection of domain boundaries is critical for structural analysis of single domains from multimodular proteins. Folding and stability studies of the third fibronectin type III domain from human tenascin (TNfn31-90) have shown that it is moderately stable (Delta G(D-N)(H2O) approximately 5 kcal mol-1) and folds with two-state kinetics. In an attempt to stabilize the protein, five domains were constructed with different combinations of extensions to the N- and C-termini. Thermal denaturation studies show that a specific two amino acid (Gly-Leu) extension at the C-terminus is primarily responsible for a significant increase in stability. The Delta Delta G(D-N)(H2O) of the Gly-Leu extension (TNfn3(1-92)) is 2.7 +/- 0.3 kcal mol-1. Refolding kinetics do not differ significantly, but unfolding is slowed 40-fold. Mutation of leucine 92 to alanine does not affect stability, indicating that the stability of the extension does not come from the packing of the leucine side chain. Hydrogen exchange data suggest that the extension adds new hydrogen bonds and strengthens existing hydrogen bonds in the C-terminal interaction with the A-B and E-F loops. Removal of a very small number of hydrogen bonds substantially increases the unfolding rate, a phenomenon which may be important in stress-relaxation of FNIII-containing muscle proteins such as titin. These experiments demonstrate the importance of a small number of additional long-range interactions in the overall formation of a compact independently folding beta-sheet module.

Alanine↗
PubMed1998

Physical assault in New Zealand: the experience of 21 year old men and women in a community sample.

AIM: To obtain epidemiological information on physical assault in a high risk group of New Zealanders. METHOD: Rates of physical assault in the preceding twelve months were ascertained by interview in a cohort of 21 year old, Dunedin-born men (n = 482) and women (n = 462). RESULTS: Forty-five percent of the men and one quarter of the women reported at least one physical assault, either completed, attempted or threatened. A small proportion of these received medical treatment. Most serious assaults were by a perpetrator who was thought to have been drinking alcohol. Most assaults on men were by strangers but partners carried out more assaults against women, especially those receiving medical treatment. One quarter of all assaults on women were by other women, compared to 15% of the assaults on men. Differences between patterns of assaults on women and on men are discussed. CONCLUSION: It is important for doctors to be aware of the widespread occurrence of interpersonal violence in New Zealand and its underreporting.

Adult↗
PubMed1998

Characterisation of urea-denatured states of an immunoglobulin superfamily domain by heteronuclear NMR.

The structural and dynamic properties of an immunoglobulin superfamily domain (IgSF), Ig 18', have been characterised by NMR at 285 K, in the presence of 4.2 M and 6.0 M urea, respectively. Analysis of chemical shift deviations, 3JHNHalpha coupling constants, sequential NOE pattern, and 15N relaxation data reveals that although the two urea-denatured states are highly disordered, some local turn-like residual structures do exist. Moreover, some distinct differences between the properties of the two denatured states are observed. In 4.2 M urea-denatured Ig 18', regions 80-83 and 86-92 adopt turn-like conformations, furthermore, region 84-93 is involved in slow exchange processes that occur on a micro- to millisecond time-scale. In the 6.0 M urea-denatured state, these turn-like conformations are less occupied, and chemical exchange processes in region 84-93 are largely reduced. In contrast, region 32-36 has persistent turn-like structures in both urea-denatured states. Some correlation between the spectral density function at 0 frequency, Jeff(0), for the urea-denatured states and the secondary structure elements of the folded state have been observed. Except for the terminal regions, residues corresponding to beta-strands have higher Jeff(0) values compared to residues corresponding to loops. The characterisation and comparison of the two urea-denatured states highlight residues that possess properties that may be crucial for the initiation of folding of this domain.

Immunoglobulins↗
PubMed1998

Folding intermediates of wild-type and mutants of barnase. II. Correlation of changes in equilibrium amide exchange kinetics with the population of the folding intermediate.

There is an unanswered question from previous studies of 1H/2H-exchange of amide protons of barnase. Under certain conditions, there is a relatively abrupt change from EX2 towards EX1 kinetics as the temperature is slightly increased. The change in kinetics for different mutants is not directly related to their changes in stability. We have measured the stability of the folding intermediate of barnase (I) in 2H2O under a variety of conditions and calculated its population at different temperatures. The change in kinetics correlates with the change in the population of the folding intermediate. At higher temperatures and pH, the free energy of I becomes higher than that of the denatured state, D, and the kinetics becomes EX1. The data fit a simple kinetic scheme. Such changes in kinetics may be used to detect the presence of intermediates in the folding reaction at equilibrium in native conditions, but cannot distinguish whether they are on or off-pathway.

Amides↗
PubMed1998

SQUID detected NMR and NQR. Superconducting Quantum Interference Device.

The dc Superconducting QUantum Interference Device (SQUID) is a sensitive detector of magnetic flux, with a typical flux noise of the order 1 muphi0 Hz(-1/2) at liquid helium temperatures. Here phi0 = h/2e is the flux quantum. In our NMR or NQR spectrometer, a niobium wire coil wrapped around the sample is coupled to a thin film superconducting coil deposited on the SQUID to form a flux transformer. With this untuned input circuit the SQUID measures the flux, rather than the rate of change of flux, and thus retains its high sensitivity down to arbitrarily low frequencies. This feature is exploited in a cw spectrometer that monitors the change in the static magnetization of a sample induced by radio frequency irradiation. Examples of this technique are the detection of NQR in 27Al in sapphire and 11B in boron nitride, and a level crossing technique to enhance the signal of 14N in peptides. Research is now focused on a SQUID-based spectrometer for pulsed NQR and NMR, which has a bandwidth of 0-5 MHz. This spectrometer is used with spin-echo techniques to measure the NQR longitudinal and transverse relaxation times of 14N in NH4ClO4, 63+/-6 ms and 22+/-2 ms, respectively. With the aid of two-frequency pulses to excite the 359 kHz and 714 kHz resonances in ruby simultaneously, it is possible to obtain a two-dimensional NQR spectrum. As a third example, the pulsed spectrometer is used to study NMR spectrum of 129Xe after polariza-tion with optically pumped Rb. The NMR line can be detected at frequencies as low as 200 Hz. At fields below about 2 mT the longitudinal relaxation time saturates at about 2000 s. Two recent experiments in other laboratories have extended these pulsed NMR techniques to higher temperatures and smaller samples. In the first, images were obtained of mineral oil floating on water at room temperature. In the second, a SQUID configured as a thin film gradiometer was used to detect NMR in a 50 microm particle of 195Pt at 6 mT and 4.2 K.

Aluminum↗
PubMed1998

Hydrogen exchange and protein folding.

Amide hydrogen-deuterium exchange is a sensitive probe of the structure, stability and dynamics of proteins. The significant increase in the number of small, model proteins that have been studied has allowed a better understanding of the structural fluctuations that lead to hydrogen exchange. Recent technical advances enable the methodology to be applied to the study of protein-protein interactions in much larger, more complex systems.

Hydrogen↗