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Biomedical subjects

D G Durham

Publications and source records attributed to D G Durham.

At least 19 recordsLinked to original sources
PubMed2001

Development of QSARs to investigate the bacterial toxicity and biotransformation potential of aromatic heterocylic compounds.

A series of aromatic heterocyclic and hydrocarbon compounds were tested for toxicity and biotransformation potential against two contrasting lux-marked whole-cell microbial biosensors. Toxicity was determined by inhibition of light output of a Pseudomonas fluorescens construct that expresses lux constitutively. Biotransformation was tested by increase in light output of P. fluorescens HK44 (pUTK21), which expresses lux when in the presence of a metabolic intermediate (salicylate). The data were then modelled against physical/chemical properties of the compounds tested to see if quantitative structure-activity relationships (QSARs) could be derived. Toxicity was found to be accurately predicted by log Kow (R2 = 0.95, Q2 = 0.88), with the basic (pyridine-ring containing) heterocycles modelled separately. The biotransformation data were best modelled using lowest unoccupied molecular orbital (LUMO) energies (R2 = 0.90, Q2 = 0.87).

Biotransformation↗
PubMed2001

Vancomycin resistance reversal in enterococci by flavonoids.

The development of clinical vancomycin-resistant strains of enterococci (VRE) is a major cause for concern. Here we show that a combination of galangin or 3,7-dihydroxyflavone with vancomycin may be used to sensitize resistant strains of Enterococcus faecalis and Enterococcus faecium to the level of vancomycin-sensitive strains. Minimum inhibitory concentrations (MICs) and viable counts were determined in Iso-sensitest broth using a microtitre method. MICs of vancomycin against 67% of resistant clinical isolates and a type strain of enterococci were lowered from > 250 microg mL(-1) to < 4 microg mL(-1) in the presence of galangin (12.5 microg mL(-1)) or 3,7-dihydroxyflavone (6.25 microg mL(-1)). Viable counts for type culture E. faecalis ATCC 51299 showed the flavonoids alone significantly lowered numbers of colony forming units (CFUs). CFUs were maintained at low levels (< 10(3) CFU mL(-1)) for 24 h by vancomycin/flavone combinations. This combinational action in reversing vancomycin resistance of enterococci highlights novel drug targets and has importance in the design of new therapeutic regimes against resistant pathogens.

Anti-Bacterial Agents↗
PubMed2000

Investigating the specificity of regulators of degradation of hydrocarbons and hydrocarbon-based compounds using structure-activity relationships.

Microbial biosensors which have genes for bioluminescence coupled to genes that control hydrocarbon degradation pathways can be used as reporters on the specificity of regulation of those pathways. Structure-activity relationships can be used to discover what governs that specificity, and can also be used to separate compounds into different groups depending on mode of action. Published data for four different bioluminescent biosensors, reporting on toluene (two separate biosensors), isopropylbenzene, and octane, were analyzed to develop structure-activity relationships between biological response and physical/chemical properties. Good QSARs (quantitative structure-activity relationships) were developed for three out of the four biosensors, with between 88 and 100 per cent of the variance explained. Parameters found to be important in controlling regulator specificity were hydrophobicity, lowest unoccupied molecular orbital energies, and molar volume. For one of the biosensors, it was possible to show that the biological response to chemicals tested fell into three separate classes (non-hydrocarbons, aliphatic hydrocarbons, and aromatic hydrocarbons). A statistically significant QSAR based on hydrophobicity was developed for the fourth biosensor, but was poor in comparison to the other three (44 per cent variance explained).

Bacterial Proteins↗
PubMed2000

Baicalin synergy with beta-lactam antibiotics against methicillin-resistant Staphylococcus aureus and other beta-lactam-resistant strains of S. aureus.

Bacterial resistance to antibiotics is a serious global problem and includes strains of beta-lactam-resistant Staphylococcus aureus and methicillin-resistant S. aureus (MRSA). Novel antimicrobials and/or new approaches to combat the problem are urgently needed. The Chinese herb Xi-nan Huangqin (Scutellaria amoena C.H. Wright) has been used in traditional Chinese medicine to treat a wide range of infectious diseases. In this study we have examined the antibacterial action of baicalin, a flavone isolated from the herb. When combined with 16 microg mL(-1) baicalin, minimum inhibitory concentrations (MICs) of benzylpenicillin against MRSA and penicillin-resistant S. aureus were reduced from 125 and 250 microg mL(-1) to 4 and 16 microg mL(-1), respectively. This activity of baicalin was dose-dependent. Viable counts showed that the killing of MRSA and beta-lactam-resistant S. aureus cells by 10 to 50 microg mL(-1) ampicillin, amoxycillin, benzylpenicillin, methicillin and cefotaxime was potentiated by 25 microg mL(-1) baicalin. From the study it was concluded that baicalin has the potential to restore the effectiveness of beta-lactam antibiotics against MRSA and other strains of beta-lactam-resistant S. aureus. In view of its limited toxicity baicalin offers potential for the development of a valuable adjunct to beta-lactam treatments against otherwise resistant strains of microorganisms.

Ampicillin↗
PubMed1994

Molecular modelling of the inclusion complexes between beta-cyclodextrin and (R)/(S)-methylphenobarbitone and its application to HPLC.

Molecular modelling of beta-cyclodextrin and optimisation of its potential energy suggests that a favoured conformation is that distorted from a symmetrical torus. The inclusion of water molecules into the torus cavity simulates the increased stability in an aqueous solvent. Complexes of beta-cyclodextrin with (R)- and (S)-enantiomers of methylphenobarbitone have been modelled and energetically optimised by the application of molecular mechanics. The simulations suggests that the guest molecules adopt an orientation in which the phenyl ring is projected into the torus cavity, with in each case the plane of the ring parallel to a longer axis of the distorted torus and slightly displaced from the axis through the torus cavity. It is suggested that the asymmetry in the macrocyclic ring contributes to chiral recognition as a result of additional discriminatory binding to the barbiturate ring residue of each enantiomer, which occupy different 3D geometries. The enantiomers form complexes of different minimum potential energies. The resulting difference in complex stability can be related to the behaviour of beta-cyclodextrin, as a mobile phase additive in reverse-phase HPLC to effect chiral separation of rac-methylphenobarbitone during chromatography.

Chromatography, High Pressure Liquid↗
PubMed1994

A triterpene from Rubus pinfaensis.

A new pentacyclic triterpene, pinfaensin, was isolated from the roots of Rubus pinfaensis and the structure elucidated by 13C NMR methods. This triterpene, a glycoside of pinfaensic acid (glucosyl 23-formyl-2 alpha,3 beta,19 alpha-trihydroxyurs-12-en-28-oate), in order to achieve purification and characterization, was hydrolysed to previously unreported pinfaensic acid which on acetylation and methylation gave methyl diacetoxypinfaensate (methyl 2 alpha,3 beta-diacetoxy-23-formyl-19 alpha-hydroxyurs-12-en-28-oate).

Carbohydrate Sequence↗
PubMed1986

Development of a stability-indicating assay for nafimidone [1-(2-naphthoylmethyl)imidazole hydrochloride] by high-performance liquid chromatography.

The rational development of a stability-indicating assay for nafimidone [1-(2-naphthoylmethyl)imidazole hydrochloride] is demonstrated. It allows resolution of the decomposition products, obtained both on melting and resulting from decomposition in solution. Ion-pair chromatography was used to elute the solution decomposition products before the parent compound, thus producing maximum sensitivity of detection of these in the presence of undecomposed reactant. Stability data in terms of first-order rate constants were obtained in two different buffer solutions both from conventional integrated-rate equations using reactant concentration measurements, and by the initial rate method using decomposition product concentrations. In the light of this investigation, additional criteria for stability-indicating assays are suggested, which exploit the sensitivity as well as specificity of high-performance liquid chromatography.

Chromatography, High Pressure Liquid↗
PubMed1979

Extended wear of hydrophilic contact lenses in aphakia - an alternative to intraocular lens implantation.

Since not every patient will be a candidate for an intraocular lens, there will always be a portion of aphakic patients who are candidates for extended wear hydrophilic lenses. Aphakic patients to be fitted successfully with extended wear contacts must be motivated, aware of the risks, and require frequent lens cleaning and replacement on an individual basis. While future improvement of hydrophilic lenses is to be expected and anticipated, the extent of these improvements is still uncertain. However, preliminary reports are encouraging. Extended wear contact lenses are not the only answer to aphakia. They are but one alternative available to the ophthalmologist for maximizing the visual rehabilitation of the aphakic patient. Even with the increasing use and acceptance of intraocular lenses, the use of extended soft lens wear has a place in this rehabilitation.

Aphakia, Postcataract↗