Search PubMed⌕ Search

Biomedical subjects

P J Gray

Publications and source records attributed to P J Gray.

At least 19 recordsLinked to original sources
PubMed1996

Retinal detachment complicating scleral-sutured posterior chamber intraocular lens surgery.

Although retinal detachment has been reported in association with sutured posterior chamber intraocular lenses (PCIOL), detailed analysis of the pathogenesis, clinical features and risk factors is lacking. Thirty-nine patients who had undergone surgery for scleral-sutured PCIOL were therefore reviewed, revealing 8 patients with associated retinal tears or detachments. Retinal breaks resulted from vitreous incarceration by the intraocular suture (6), post-operative vitreous detachment (1), preretinal manipulation of the dislocated PCIOL (1), surgical entry-sites (1) and surgical induction of posterior vitreous detachment (1). An axial length > 25 mm was associated with the development of retinal tears (p < 0.05, Fisher's exact test). All patients had attached retina with median visual acuity of 6/12 (range 6/6 to CF) at last follow-up (median 15 months, range 1-41 months). In patients requiring a pars plana approach, careful attention to the posterior hyaloid face, basal gel, surgical entry-sites and suture tract is recommended to reduce the risk of retinal detachment associated with scleral-sutured PCIOL procedures.

Adult↗
PubMed1996

Effect of sulphur mustard on the initiation and elongation of transcription.

Sulphur mustard is a potent alkylating agent that causes severe vesication as well as systemic and genotoxic effects. Despite its long history as a chemical warfare agent, the mechanism of its toxicity remains unknown and no successful pharmacological intervention has yet been found. In this study we have examined the effects of mustard alkylation of DNA on transcriptional processes. Gel mobility shift analysis shows that mustard alkylation of the lac UV5 promoter increases the stability of the promoter-RNA polymerase binary complex. Following formation of the initiation complex and addition of elongation nucleotides, approximately 45% of the RNA polymerase in the initiated complex remained associated with the alkylated promoter, compared to only 7% remaining associated with the unalkylated promoter. For the RNA polymerase able to escape the initiation complex, mustard alkylation of the DNA template resulted in the production of truncated transcripts. Analysis of these truncated transcripts revealed that sulphur mustard alkylates DNA preferentially at 5'-AA, 5'-GG and 5'-GNC sequences on the DNA template strand and this is significantly different from the alkylation sites observed with nitrogen mustard. This study represents the first report at the molecular level of sulphur mustard-induced effects on transcriptional processes.

Alkylation↗
PubMed1996

The prevalence of eye disease in elderly Bengalis in Tower Hamlets.

The prevalence of eye disease and uncorrected refractive errors in a group of 167 elderly members of the Bangladeshi community which resides in the London Borough of Tower Hamlets was studied. Of the subjects screened 24.6% were found to have a significant and potentially treatable cause of visual loss and a further 32.3% were visually handicapped through the presence of uncorrected refractive errors. A high prevalence (53.3%) of cataract was found in the elderly Bengalis. The high prevalence of eye disease in this ethnic minority group, has important implications for health service planning.

Aged↗
PubMed1995

Sulphur mustards inhibit binding of transcription factor AP2 in vitro.

The bifunctional sulphur mustard (bis-(2-chloroethyl)sulphide, HD) and its monofunctional analogue (2-chloroethyl ethyl sulphide, CEES) are both vesicants. In this study, both mustards were shown to rapidly alkylate the AP2 consensus binding sequence incorporated in a 26mer oligonucleotide. The reaction was essentially complete within 10 min under the conditions employed in this study and -95% of the oligonucleotides were alkylated at least once using 500 microM HD and 1 mM CEES. Progressive alkylation of the consensus sequence was parallelled by a decrease in transcription factor binding. Under reaction conditions which alkylated approximately 95% of the oligonucleotides at least once, the binding of cloned human AP2 was reduced by 93 and 76% by HD and CEES, respectively, compared with control values. The interference with binding is a result of alkylation of the DNA and not damage to the transcription factor by mustard or its hydrolysis products. Interference with transcription factor binding would be expected to have a profound influence on the ability of the cell to function normally and to respond to DNA damage and may contribute significantly to the skin damage produced by these compounds.

Alkylating Agents↗
PubMed1995

Nitrogen mustard inhibits transcription and translation in a cell free system.

Nitrogen mustard and its derivatives such as cyclophosphamide, chlorambucil and melphalan are widely used anti-cancer agents, despite their non-specific reaction mechanism. In this study, the effect of alkylation by nitrogen mustard of DNA and RNA (coding for a single protein) was investigated using both a translation system and a coupled transcription/translation system. When alkylated DNA was used as the template for coupled transcription and translation, a single translation product corresponding to the 62 kDa luciferase protein was synthesised. Production of the translated product encoded by this template was inhibited by mustard concentrations as low as 10 nM, and 50% inhibition occurred with 30 nM mustard. A primer extension assay employed to verify alkylation sites on the DNA revealed that all guanine residues on the DNA template are susceptible to alkylation by nitrogen mustard. Similarly, when alkylated RNA was used as the template for protein synthesis, the amount of the 62 kDa luciferase protein decreased with increasing mustard concentration and a range of truncated polypeptides was synthesised. Under these conditions 50% inhibition of translation occurred with approximately 300 nM mustard (i.e. approximately 10 times that required for similar inhibition using an alkylated DNA template). Furthermore, a gel mobility shift assay revealed that mustard alkylation of the RNA template results in the formation of a more stable retarded RNA complex. The functional activity of the luciferase protein decreased with alkylation of both the DNA and RNA templates, with a half-life of loss of activity of 1.1 h for DNA exposed to 50 nM mustard, and 0.5 h for RNA exposed to 50 microM mustard. The data presented support the notion that DNA is a critical molecule in the mode of action of mustards.

Alkylating Agents↗
PubMed1994

Molecular basis of nitrogen mustard effects on transcription processes: role of depurination.

DNA was alkylated with nitrogen mustard (HN2) and the rate of release of the alkylpurines was quantitated by HPLC. The half life of depurination of the major product (7-alkylguanine) was 9.1 h at 37 degrees C. End-labelled DNA was used to show that depurination occurred dominantly at 5'-GA, 5'-GG and 5'-GT sequences. Although extensive alkylation was observed at all 5'-GNC and 5'GNT sequences, no depurination was observed at these sites during a depurination time of 20 h at 37 degrees C. Since these sites are potential interstrand crosslinking sequences (G-adduct-G and G-adduct-A, both spanning an intervening base pair), this suggests that these regions have a greatly enhanced stability or that simultaneous depurination of both ends of the crosslink is necessary before these lesions are removed (with a predicted half-life of approximately 80 h at 37 degrees C). Depurination at the lac UV5 promoter impaired the association of Escherichia coli RNA polymerase with that promoter, while in the elongation phase two distinctly different sequence-specific processes were apparent. At 5'-GNC and 5'-GNT sequences transcriptional blockages were maintained with increasing elongation time, whereas at monoadduct sites, the blockage decreased with elongation time (predominantly at 5'-GG and 5'-GC sequences), with an average half-life of approximately 10.7 h. Collectively, these results suggest that the observed read-through past monoadduct sites is due to depurination of the DNA at those sites. E. coli RNA polymerase is therefore able to transcribe efficiently past apurinic sites and presumably does so by incorporating an incorrect base into the nascent RNA.

Alkylation↗
PubMed1993

Effect of alkylating agents on initiation and elongation of the lac UV5 promoter.

DNA containing the lac UV5 promoter was alkylated using bifunctional sulfur and nitrogen mustards and a monofunctional sulfur mustard. The alkylation sites were mapped using Taq polymerase, and the effect of alkylation on the formation of the DNA-RNA polymerase complex was determined using gel retardation. Alkylation was observed at all G residues in the template strand. Exposure of the alkylated DNA to Escherichia coli RNA polymerase resulted in the formation of a DNA-enzyme complex that was more stable, prior to initiation, than the complex formed with nonalkylated DNA. The DNA-RNA polymerase complex formed with the alkylated DNA also demonstrated decreased ability to progress along the full length of the DNA template. These observations show that, in addition to inducing transcriptional blockages, mustards also influence the interaction between RNA polymerase and its promoter. The ability to interfere with protein-DNA interactions may contribute significantly to the effects of these compounds in eukaryotic systems with their complex array of transcription factors.

Alkylating Agents↗
PubMed1993

Effects of the nerve agents soman and tabun on the uptake and release of GABA and glutamate in synaptosomes of guinea pig cerebral cortex.

1. Crude and purified synaptosomes were prepared from the cerebral cortex of the rat or the guinea pig and used to study the uptake and release of [3H]GABA and [3H]glutamate. 2. Baclofen at 10(-5) M inhibited stimulated release of [3H]GABA from crude rat and guinea pig synaptosomes, but not from purified rat synaptosomes. 3. 1-2 mM tabun decreased the uptake of [3H]GABA and increased the uptake of [3H]glutamate by purified guinea pig synaptosomes. 4. Soman and tabun at 10(-6) M and 10(-5) M inhibited basal release of [3H]GABA and [3H]glutamate from crude guinea pig synaptosomes. Tabun at 10(-5) M decreased stimulated release of [3H]GABA while soman had no effect. 5. The results do not sustain the possibility that nerve agents cause convulsions by affecting the uptake or release of GABA or glutamate. However indirect evidence was obtained that soman and tabun inhibit catabolism of GABA and glutamate.

Animals↗
PubMed1993

Analysis of errors in the calculation of irreversible enzyme inhibition kinetic constants.

The kinetic constants for irreversible enzyme inhibition are determined by non-linear least-square regression using a new optimisation technique. An analysis is given of how calculation of the dissociation constant and the unimolecular rate constant is affected both by the inherent error involved in fitting an exponential curve to the plot of product concentration against time, and by the ill-conditioned nature of the equations relating these constants to the parameters of the exponential. The analysis is applied to simulated sets of product concentration curves.

Acetylcholinesterase↗
PubMed1992

Diffractive multifocal intraocular lens implants for unilateral cataracts in prepresbyopic patients.

Multifocal intraocular lenses allow pseudophakic patients to obtain good near and distance visual acuities without an additional near correction. We report our experiences in implanting diffractive multifocal intraocular lenses in prepresbyopic patients with acquired unilateral cataracts and assess their postoperative visual acuities and stereoscopic vision. Accommodative function in patients following cataract surgery is discussed.

Accommodation, Ocular↗
PubMed1991

In vitro transcription analysis of DNA alkylation by nitrogen mustard.

A synchronized in vitro transcription assay has been used to probe the sequence specificity of alkylation of DNA by nitrogen mustard. Transcriptional blockages were detected with use of a 497-base-pair PvuII/SalI restriction fragment of a modified pBR322 vector when initiation of transcription was commenced after the DNA had been alkylated but not if the initiated transcription complex was subjected to alkylation before the elongation phase. The intensity of transcriptional blockages increased with alkylation time and was maximal after 1.5 h at a mustard concentration of 200 microM. There was also evidence of alkylation of the promoter region with increasing mustard concentration. The transcriptional blockage pattern changed at some sites as elongation time was increased and three types of blockages were observed-partial transcription (one or two nucleotides) past an initial blockage site, delayed but normal transcription past some sites, and complete termination at most sites. Eight of the nine blockage sites detected were at G or GG sequences on the template strand, with an apparent specificity for 5'-CTGT sequences of the template strand. Seven of the nine sites were capable of inter- or intrastrand cross-links, including three possible G-G interstrand cross-links spanning an intervening base-pair. In the 103-bp segment probed by this procedure, transcriptional blockages were detected (with one exception) only at sites corresponding to G on the template strand where inter- or intrastrand cross-linking was possible but not for similar sequences on the non-template strand.

Alkylation↗