Search PubMed⌕ Search

Biomedical subjects

D A Smith

Publications and source records attributed to D A Smith.

At least 37 records · Page 2Linked to original sources
PubMed2002

Are chemically reactive metabolites responsible for adverse reactions to drugs?

Low molecular weight organic chemicals can be transformed by normal drug-metabolising systems into short-lived metabolites that are inherently reactive towards cellular macromolecules. There is direct evidence that the formation of such chemically reactive metabolites may lead to mutagenesis, carcinogenicity, apoptosis and necrosis in both cell and animal models. A number of drugs associated with non-pharmacological drug toxicities in man have been shown to undergo bioactivation either in vivo or in vitro. We have therefore examined the evidence for the role of reactive metabolites in the three most common drug-induced toxicities: hepatotoxicity, skin reactions and blood dyscrasias.

Animals↗
PubMed2001

Beta(2)-microglobulin and its deamidated variant, N17D form amyloid fibrils with a range of morphologies in vitro.

Amyloid fibrils formed by incubation of recombinant wild-type human beta(2)-microglobulin (beta(2)M) ab initio in vitro at low pH and high ionic strength are short and highly curved. By contrast, fibrils extracted from patients suffering from haemodialysis-related amyloidosis and those formed by seeding growth of the wild-type protein in vitro with fibrils ex vivo are longer and straighter than those previously produced ab initio in vitro. Here we explore the effect of growth conditions on morphology of beta(2)M fibrils formed ab initio in vitro from the wild-type protein, as well as a variant form of beta(2)M in which Asn17 is deamidated to Asp (N17D). We show that deamidation results in significant destabilisation of beta(2)M at neutral pH. Despite this, acidification is still necessary to form amyloid from the mutant protein in vitro. Interestingly, at low pH and low ionic strength long, straight fibrils of recombinant beta(2)M are formed in vitro. The fibrils comprise three distinct morphological types when examined using electron microscopy (EM) and atomic force microscopy (AFM) that vary in periodicity and the number of constituent protofibrils. Using kinetic experiments we suggest that the immature fibrils observed previously do not represent intermediates in the assembly of fully mature amyloid, at least under the conditions studied here.

Amino Acid Substitution↗
PubMed2001

Serum levels of the antiinflammatory cytokine interleukin-10 are decreased in patients with unstable angina.

BACKGROUND: Proinflammatory cytokines play a role in acute coronary events. However, the potential role of antiinflammatory cytokines in the modulation of the atherosclerotic process remains unknown. Interleukin (IL)-10, which is expressed in human atherosclerotic plaques, has potent deactivating properties in macrophages and T cells. The aim of this study was to assess whether serum concentrations of IL-10 differed between patients with unstable and stable angina pectoris. METHODS AND RESULTS: A total of 95 patients with angina pectoris and angiographically documented coronary artery disease were studied. Of these, 50 patients had chronic stable angina (with stable symptoms over 3 months), and 45 patients had Braunwald class IIIB unstable angina with ST-segment changes. Serum IL-10 and IL-6 concentrations were measured on admission using commercially available immunoassays. Serum IL-10 concentrations were lower in unstable angina patients compared with those who had chronic stable angina (28.4 versus 14.0 pg/mL; 95% CI, 9.8 to 19.0; P<0.0001), even after adjustment for variables that were significantly different on univariate analysis. IL-6 concentrations were higher in the unstable angina group (20.9 versus 11.4 pg/mL; 95% CI, 1.0 to 12.6; P=0.04). CONCLUSIONS: Patients with unstable angina had significantly lower serum IL-10 concentrations than did patients with chronic stable angina. This important finding is in keeping with previous data from animal model studies that suggest that IL-10 has a protective role in atherosclerosis.

Acute Disease↗
PubMed2001

UV Raman evidence of a tyrosine in apo-human serum transferrin with a low pK(a) that is elevated upon binding of sulphate.

The binding of sulphate to human serum apo-transferrin has been examined by ultraviolet absorption and ultraviolet resonance Raman difference spectroscopies between pH 6.0 and 9.0. The ultraviolet absorption data reveals a negative feature at 245 nm that increases in magnitude with pH, with an apparent pK(a) of 7.57, which the Raman difference data reveals to be due to tyrosine. The pK(a) of this tyrosine is unusually low and is measured at 7.84 by the Raman difference method and is elevated to greater than 9.0 upon addition of sulphate. Previous studies on the N-lobe imply that Tyr 188 is the tyrosine with a low pK(a) and also that Arg 124 is the primary binding site for the sulphate. The functional relevance may be that with sulphate bound, both carbonate binding and the deprotonation of Tyr will be disfavoured, and as a result so is iron binding.

Apoproteins↗
PubMed2001

Smads mediate signaling of the TGFbeta superfamily in normal keratinocytes but are lost during skin chemical carcinogenesis.

The Smads are the signaling mediators of the TGFbeta superfamily. In the present study, we examined Smad expression in mouse epidermis and chemically-induced skin tumors. Mutations in Smad2 and -4 genes were also screened. Transcripts of Smad1 through -5 were constantly expressed in the epidermis regardless of changes in TGFbeta signaling, state of differentiation and stages of carcinogenesis. Smad7 transcripts were barely detectable in keratinocytes, but were induced by TGFbeta1 treatment and in chemically-induced skin tumors. At the protein level, Smad1 was detected throughout the epidermis, whereas Smad2 through -5 exhibited greater levels in suprabasal layers than basal keratinocytes. In cultured keratinocytes, Smad2, -3 and -4 underwent nuclear translocation upon TGFbeta1 treatment. Furthermore, nuclear translocation of Smads correlated with decreased BrdU labeling in proliferative keratinocytes. Although no mutations were detected in the Smad2 and -4 genes in tumors, proteins of Smad1 through -5 were partially or completely lost in carcinomas. These data document that Smads are expressed at high levels in the epidermis and mediate signaling of the TGFbeta superfamily. During skin carcinogenesis, loss of Smad1 through -5 and overexpression of Smad7 may contribute to the loss of growth inhibition mediated by TGFbeta superfamily members, thus resulting in tumor progression.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2001

UV resonance Raman study of streptavidin binding of biotin and 2-iminobiotin: comparison with avidin.

UV resonance Raman (UVRR) spectroscopy is used to study the binding of biotin and 2-iminobiotin by streptavidin, and the results are compared to those previously obtained from the avidin-biotin complex and new data from the avidin-2-iminobiotin complex. UVRR difference spectroscopy using 244-nm excitation reveals changes to the tyrosine (Tyr) and tryptophan (Trp) residues of both proteins upon complex formation. Avidin has four Trp and only one Tyr residue, while streptavidin has eight Trp and six Tyr residues. The spectral changes observed in streptavidin upon the addition of biotin are similar to those observed for avidin. However, the intensity enhancements observed for the streptavidin Trp Raman bands are less than those observed with avidin. The changes observed in the streptavidin Tyr bands are similar to those observed for avidin and are assigned exclusively to the binding site Tyr 43 residue. The Trp and Tyr band changes are due to the exclusion of water and addition of biotin, resulting in a more hydrophobic environment for the binding site residues. The addition of 2-iminobiotin results in spectral changes to both the streptavidin and avidin Trp bands that are very similar to those observed upon the addition of biotin in each protein. The changes to the Tyr bands are very different than those observed with the addition of biotin, and similar spectral changes are observed in both streptavidin and avidin. This is attributable to hydrogen bond changes to the binding site Tyr residue in each protein, and the similar Tyr difference features in both proteins supports the exclusive assignment of the streptavidin Tyr difference features to the binding site Tyr 43.

Avidin↗
PubMed2001

Hidden-Markov methods for the analysis of single-molecule actomyosin displacement data: the variance-Hidden-Markov method.

In single-molecule experiments on the interaction between myosin and actin, mechanical events are embedded in Brownian noise. Methods of detecting events have progressed from simple manual detection of shifts in the position record to threshold-based selection of intermittent periods of reduction in noise. However, none of these methods provides a "best fit" to the data. We have developed a Hidden-Markov algorithm that assumes a simple kinetic model for the actin-myosin interaction and provides automatic, threshold-free, maximum-likelihood detection of events. The method is developed for the case of a weakly trapped actin-bead dumbbell interacting with a stationary myosin molecule (Finer, J. T., R. M. Simmons, and J. A. Spudich. 1994. Nature. 368:113-119). The algorithm operates on the variance of bead position signals in a running window, and is tested using Monte Carlo simulations to formulate ways of determining the optimum window width. The working stroke is derived and corrected for actin-bead link compliance. With experimental data, we find that modulation of myosin binding by the helical structure of the actin filament complicates the determination of the working stroke; however, under conditions that produce a Gaussian distribution of bound levels (cf. Molloy, J. E., J. E. Burns, J. Kendrick-Jones, R. T. Tregear, and D. C. S. White. 1995. Nature. 378:209-212), four experiments gave working strokes in the range 5.4-6.3 nm for rabbit skeletal muscle myosin S1.

Actin Cytoskeleton↗
PubMed2001

Models of motor-assisted transport of intracellular particles.

One-dimensional models are presented for the macroscopic intracellular transport of vesicles and organelles by molecular motors on a network of aligned intracellular filaments. A motor-coated vesicle or organelle is described as a diffusing particle binding intermittently to filaments, when it is transported at the motor velocity. Two models are treated in detail: 1) a unidirectional model, where only one kind of motor is operative and all filaments have the same polarity; and 2) a bidirectional model, in which filaments of both polarities exist (for example, a randomly polarized actin network for myosin motors) and/or particles have plus-end and minus-end motors operating on unipolar filaments (kinesin and dynein on microtubules). The unidirectional model provides net particle transport in the absence of a concentration gradient. A symmetric bidirectional model, with equal mixtures of filament polarities or plus-end and minus-end motors of the same characteristics, provides rapid transport down a concentration gradient and enhanced dispersion of particles from a point source by motor-assisted diffusion. Both models are studied in detail as a function of the diffusion constant and motor velocity of bound particles, and their rates of binding to and detachment from filaments. These models can form the basis of more realistic models for particle transport in axons, melanophores, and the dendritic arms of melanocytes, in which networks of actin filaments and microtubules coexist and motors for both types of filament are implicated.

Actins↗
PubMed2001

Female meadow voles housed in long and short daylengths respond to exogenous estrogen with similar mating latencies.

After weaning, adult female meadow voles were maintained for 7 weeks in either long (LD, 14 h light/day) or short photoperiods (SD, 10 h light/day). They were then ovariectomized and implanted with 3-week, timed-release estrogen pellets (0.0, 0.001, 0.05, or 0.5 mg/pellet of 17-beta-estradiol). An additional group received a sham ovariectomy (intact) and a 0.0-mg/pellet control (no estrogen) pellet. One week after surgery, females were paired with an LD sexually experienced male. Each pair was videotaped continuously until the first intromission or for 2 weeks. LD sham animals mated significantly earlier than did SD sham animals (P=.05). However, there were no differences in mating latencies between LD and SD control groups or between any of the LD and SD groups receiving estrogen replacement (P>.05). In addition, no ovariectomized animals receiving either the control or the 0.001-mg/pellet estrogen dosage mated within the 2-week time period, while all shams and all animals receiving either the 0.05- or 0.5-mg/pellet doses mated. The results indicate that there is some minimal amount of estrogen that is necessary for meadow voles to enter behavioral estrus and that LD and SD females do not differ in their sensitivity to estrogen, since animals in both photoperiods mate with similar latencies as long as enough estrogen is present.

Animals↗
PubMed2001

Neurosurgery 2000.

Explore the source record for details and available documents.

Evidence-Based Medicine↗
PubMed2001

Lipophilicity in PK design: methyl, ethyl, futile.

Lipophilicity, often expressed as distribution coefficients (log D) in octanol/water, is an important physicochemical parameter influencing processes such as oral absorption, brain uptake and various pharmacokinetic (PK) properties. Increasing log D values increases oral absorption, plasma protein binding and volume of distribution. However, more lipophilic compounds also become more vulnerable to P450 metabolism, leading to higher clearance. Molecular size and hydrogen bonding capacity are two other properties often considered as important for membrane permeation and pharmacokinetics. Interrelationships among these physicochemical properties are discussed. Increasing size (molecular weight) often gives higher potency, but inevitably also leads to either higher lipophilicity, and hence poorer dissolution/solubility, or to more hydrogen bonding capacity, which limits oral absorption. Differences in optimal properties between gastrointestinal absorption and uptake into the brain are addressed. Special attention is given to the desired lipophilicity of CNS drugs. In examples using beta-blockers, Ca channel antagonists and peptidic renin inhibitors we will demonstrate how potency and pharmacokinetic properties need to be balanced.

1-Octanol↗