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Biomedical subjects

A Nicholls

Publications and source records attributed to A Nicholls.

At least 19 recordsLinked to original sources
PubMed1996

Pharmacokinetics and bioavailability of mycophenolate mofetil in healthy subjects after single-dose oral and intravenous administration.

A randomized, crossover study of 12 healthy volunteers was conducted with single, 1.5-g doses of mycophenolate mofetil (MMF), a prodrug of mycophenolic acid (MPA), after oral and intravenous administration. During the intravenous infusion, phase systemic plasma clearance of MMF was approximately 10 L/min and the half-life (t1/2) was a few minutes. After oral administration, however, plasma MMF was below quantitation limits at all times. The plasma MPA profile of oral MMF showed a sharp peak at approximately 1 hour and a secondary peak at 8 to 12 hours. Mean apparent plasma t1/2 of MPA was similar for both routes (approximately 17 hours). The area under the concentration-time curve (AUC) from time 0 to 24 hours was statistically higher for intravenous than for oral administration, but total AUC showed statistical equivalence (80-120 rule), with mean bioavailability of MPA from oral administration of MMF estimated as 94.1% relative to the intravenous route. Total plasma AUC of mycophenolic acid glucuronide (MPAG), the sole metabolite of MPA, was four- to five-fold higher than MPA. Total 48-hour MPAG recovery in urine was statistically equivalent for the two routes and represented a mean of 70% of administered drug; corresponding MPA recovery was less than 1%. Renal clearance (ClR) values required transport mechanisms for MPAG, but not for MPA. The ClR of MPAG was statistically higher after intravenous administration than oral administration. MMF administered orally undergoes rapid, complete absorption and essentially complete presystemic deesterification. There was presystemic removal of MPA, but enterohepatic circulation compensated for the first pass loss. Renal metabolism of MPA also may have occurred.

Administration, Oral↗
PubMed1996

Free-energy determinants of alpha-helix insertion into lipid bilayers.

A detailed treatment is provided of the various free-energy terms that contribute to the transfer of a polyalanine alpha-helix from the aqueous phase into lipid bilayers. In agreement with previous work, the hydrophobic effect is found to provide the major driving force for helix insertion. However, an opposing effect of comparable magnitude is also identified and is attributed to the large free-energy penalty associated with the desolvation of peptide hydrogen bonds on transfer to the low dielectric environment of the bilayer. Lipid perturbation effects as well as the entropy loss associated with helix immobilization in the bilayer are also evaluated. Two configurations of a membrane-bound 25mer polyalanine helix were found to be lower in free energy than the isolated helix in the aqueous phase. The first corresponds to the case of vertical insertion, in which a helix terminus protrudes from each side of the bilayer. The second minimum is for the case of horizontal insertion, for which the helix is adsorbed upon the surface of the bilayer. The calculated free-energy minima are found to be in good agreement with recent measurements of related systems. Large free-energy barriers resulting from desolvation of unsatisfied hydrogen-bonding groups at the helix termini are obtained for both insertion processes. The barriers for insertion are significantly reduced if the helix termini are assumed to be "capped" through the formation of hydrogen bonds with polar sidechains. For uncapped helices, our results support recently proposed models in which helices are inserted by first adsorbing on the membrane surface and then having one terminus "swing around" so as to penetrate the bilayer.

Biophysical Phenomena↗
PubMed1996

Pharmacokinetics of mycophenolate mofetil (RS61443): a short review.

Overall, the PK of MMF is reasonably straightforward and relatively unaffected by the complex pathophysiological changes involved in the management of renal transplant recipients. The ability to relate plasma MPA concentrations to efficacy through the PK/PD correlation implies that, unlike for many other drugs, plasma PK has direct relevance to the clinical outcome. These features should not only greatly help the exploration of immunosuppressive regiments using MMF but also the development of clinical use of MMF in situations other than renal transplantation.

Body Weight↗
PubMed1995

Classical electrostatics in biology and chemistry.

A major revival in the use of classical electrostatics as an approach to the study of charged and polar molecules in aqueous solution has been made possible through the development of fast numerical and computational methods to solve the Poisson-Boltzmann equation for solute molecules that have complex shapes and charge distributions. Graphical visualization of the calculated electrostatic potentials generated by proteins and nucleic acids has revealed insights into the role of electrostatic interactions in a wide range of biological phenomena. Classical electrostatics has also proved to be successful quantitative tool yielding accurate descriptions of electrical potentials, diffusion limited processes, pH-dependent properties of proteins, ionic strength-dependent phenomena, and the solvation free energies of organic molecules.

Biochemistry↗
PubMed1995

Elective ventilation of potential organ donors.

Elective ventilation describes the procedure of transferring selected patients dying from rapidly progressive intracranial haemorrhage from general medical wards to intensive care units for a brief period of ventilation before confirmation of brain stem death and harvesting of organs. This approach in Exeter has led to a rate of kidney retrieval and transplant higher than has been achieved elsewhere in the United Kingdom, with a stabilisation of numbers on patients on dialysis. Recently doubt has been cast on the legality of our practice of elective ventilation on the grounds that relatives are not permitted to consent to treatment of an incompetent person when that treatment is not in the patient's best interests. We are thus faced with the dilemma of a protocol that is ethical, practical, and operates for the greater good but which may be illegal. This article explores various objections to the protocol and calls for public, medical, and legal debate on the issues.

Brain Death↗
PubMed1995

Evolution of spinal bone loss and biochemical markers of bone remodeling after menopause in normal women.

The main objective of this study was to describe longitudinal patterns of spinal bone loss in normal women who undergo a natural menopause. The second objective was to determine if a proportion of women suffer excessively rapid postmenopausal bone loss from the spine. If this was the case it was the aim to devise a means of predicting the woman at excess risk; but if all women lost bone at similar rates, the aim was to document changing loss rates over the first 5-8 postmenopausal years. Responding women in six suburban general practices recalled for cervical smears who had their last menstrual period 9- 36 months previously were invited to participate in a longitudinal study of bone loss and the biochemical markers plasma osteocalcin and urinary hydroxyproline. Sixty-four subjects agreed to participate, a response rate of 80%. In the ensuing 5 years, six received hormone replacement therapy and are not reported on. The main outcome measures were rates of spinal bone loss over 5 years, measured by dual photon absorptiometry, and radial bone loss over the first 2 years measured to quantitative computed tomography. Spinal bone loss was similar between individuals, with 94% of the variability in the data being accounted for by a statistical model that assumed parallel rates of bone loss. A less restrictive model allowing women to have different rates of spinal bone loss accounted for 12% more of the remaining variance in the data than the previous model. However, rates of radial bone loss were more dissimilar between women than rates of spinal loss. The results of the biochemical data collected serially showed that the plasma osteocalcin rose slowly to a plateau at 5 years postmenopause; in contrast, the hydroxyproline fell progressively with time over the whole period of study. These results were interpreted as being consistent with diminishing rates of bone destruction which gradually reequilibrated with bone formation as time passed after menopause.

Absorptiometry, Photon↗
PubMed1995

Ocular and renal sarcoidosis.

Sarcoidosis commonly presents in young adults with bilateral hilar lymphadenopathy, lung parenchymal disease and/or skin lesions. Ocular symptoms are the presenting feature in up to 10% of cases, but eye involvement can be demonstrated in around a quarter of all patients. Renal disease is much rarer, and may manifest with hypercalcaemic nephropathy, granulomatous interstitial nephritis, tubular dysfunction or glomerulonephritis. Eye and renal involvement are rarely found together, and may be confused with Wegener's granulomatosis or polyarteritis. We report a case of a young man who developed renal failure due to sarcoidosis soon after presenting with uveitis. The case illustrates an unusual combination of systemic features that may not be widely recognized.

Acute Kidney Injury↗
PubMed1994

The arthropathy of the Muckle-Wells syndrome.

Muckle-Wells syndrome (MWS) is a rare condition characterized by urticaria, arthralgias, deafness and amyloid nephropathy. The arthropathy is poorly documented. We describe the arthropathy occurring in four cases of MWS and discuss the management. Each patient developed recurrent bouts of transient synovitis. One patient developed a persistent sterile pyoarthrosis.

Adult↗
PubMed1993

Organ donation.

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Ethics, Medical↗
PubMed1992

Detection and characterisation of an overmodified type III collagen by analysis of non-cutaneous connective tissues in a patient with Ehlers-Danlos syndrome IV.

The clinical and biochemical observations in a patient with a mild form of Ehlers-Danlos syndrome (EDS) type IV are described. The patient's skin fibroblasts produced markedly diminished amounts of type III collagen. SDS-polyacrylamide gel electrophoresis of collagens produced by cells obtained from other, non-cutaneous tissues showed two forms of collagen alpha 1(III) chains, a normal and a slow migrating, mutant form. Further analysis confirmed that the type III collagen molecules containing mutant alpha chains which were overmodified had a lower thermal stability and were poorly secreted into the extracellular medium. The protein defect was mapped by in situ cyanogen bromide digestion and was located in alpha 1(III) CB9, the C-terminal peptide of the collagen triple helix. This study shows that non-cutaneous connective tissues can be a useful source for the study of type III collagen defects in patients with EDS type IV.

Cells, Cultured↗
PubMed1992

Localized scleroderma and hemiatrophy in association with antibodies to double-stranded DNA.

Localized scleroderma involves primarily skin but also muscle, bone and synovium. Further associations and transitional forms have been reported. We report here two cases showing associations between localized scleroderma and vasculitis, mononeuritis multiplex, juvenile chronic arthritis and hemiatrophy. In particular our cases both possess antibodies to double-stranded DNA, a finding not previously reported.

Adolescent↗
PubMed1991

Extracting hydrophobic free energies from experimental data: relationship to protein folding and theoretical models.

Solubility and vapor pressure measurements of hydrocarbons in water are generally thought to provide estimates of the strength of the hydrophobic effect in the range 20-30 cal/(mol.A2). Our reassessment of the solubility data on the basis of new developments in solution thermodynamics suggests that the hydrophobic surface free energy for hydrocarbon solutes is 46-47 cal/(mol.A2), although the actual value depends strongly on curvature effects [Nicholls et al. (1991) Proteins (in press); Sharp et al. (1991) Science 252, 106-109]. The arguments to support such a significant increase in the estimate of the hydrophobic effect stem partly from theoretical considerations and partly from the experimental results of De Young and Dill [(1990) J. Phys. Chem. 94, 801-809] on benzene partition between water and alkane solvents. Previous estimates of the hydrophobic effect derive from an analysis of solute partition data, which does not fully account for changes in volume entropy. We show here how the ideal gas equations, combined with experimental molar volumes, can account for such changes. Revised solubility scales for the 20 amino acids, based on cyclohexane to water and octanol to water transfer energies, are derived. The agreement between these scales, particularly the octanol scale, and mutant protein stability measurements from Kellis et al. [(1989) Biochemistry 28, 4914-4922] and Shortle et al. [(1990) Biochemistry 29, 8033-8041] is good. The increased strength of the hydrophobic interaction has implications for the energetics of protein folding, substrate binding, and nucleic acid base stacking and the interpretation of computer simulations.

Alkanes↗
PubMed1991

Reconciling the magnitude of the microscopic and macroscopic hydrophobic effects.

The magnitude of the hydrophobic effect, as measured from the surface area dependence of the solubilities of hydrocarbons in water, is generally thought to be about 25 calories per mole per square angstrom (cal mol-1 A-2). However, the surface tension at a hydrocarbon-water interface, which is a "macroscopic" measure of the hydrophobic effect, is approximately 72 cal mol-1 A-2. In an attempt to reconcile these values, alkane solubility data have been reevaluated to account for solute-solvent size differences, leading to a revised "microscopic" hydrophobic effect of 47 cal mol-1 A-2. This value, when used in a simple geometric model for the curvature dependence of the hydrophobic effect, predicts a macroscopic alkane-water surface tension that is close to the macroscopic value.

Hydrocarbons↗