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Biomedical subjects

M Stephens

Publications and source records attributed to M Stephens.

At least 55 records · Page 3Linked to original sources
PubMed1996

Chirality of a 1,10-bisacetoxymitosene compound. Impact on reductive activation, DNA interstrand cross-linking and antitumour activity.

The absolute configuration at the C-1 position of a 1,10-bisacetoxymitosene (WV15) appears to be important for enzymatic reduction, DNA interstrand cross-linking and in vitro antitumour activity of this compound. DNA cross-linking by the (-)-(S)-enantiomer of WV15 upon reduction with sodium dithionite (Na2S2O4) was more efficient than cross-linking by the (+)-(R)-enantiomer. Also, following enzymatic two-electron reduction by DT-diaphorase or one-electron reduction by xanthine oxidase, (-)-(S)-WV15 was more efficient in DNA cross-linking than (+)-(R)-WV15. However, the difference in cross-linking efficiency was less than upon chemical reduction, and in the case of enzymatic reduction that higher amount of DNA cross-links formed by (-)-(S)-WV15 can be explained by more efficient enzymatic activation of this enantiomer as compared to (+)-(R)-WV15. The enantiomeric preference upon chemical reduction can be explained by a second chemical reduction of DNA-bound WV15, which presumably does not occur upon enzymatic reduction. (-)-(S)-WV15 appeared to be more active than its (+)-(R) counterpart in A204 and L1210 tumour cell lines, with (+)-(R)/(-)-(S) toxicity ratios as high as 200 and 68, respectively. In Chinese hamster V79 cell lines, toxicity of the enantiomers was measured under oxic and hypoxic conditions. The oxic/hypoxic toxicity ratios of (+)-(R)-and (-)-(S)-WV15 in the Chinese hamster V79 cell line were 5.5 and 2.4, respectively. These different oxic/hypoxic toxicity ratios may indicate that different reducing enzymes are involved in the activation of the enantiomers. Generally, in biological systems, different activities of (+)-(R)- and (-)-(S)-WV15 appear not to be caused by different intrinsic cross-linking capacities of the enantiomers, but by more efficient enzymatic activation of (-)-(S)-WV15, as compared to (+)-(R)-WV15. The (-)-(S)-enantiomer of WV15 appears to be more active both in in vitro tumour models and in DNA cross-linking assays, and therefore the absolute configuration of mitosenes is indicated to be important for the antitumour activity of these compounds.

Animals↗
PubMed1996

The dielectrophoresis enrichment of CD34+ cells from peripheral blood stem cell harvests.

There is considerable interest in isolating the CD34+ cell population from leukaemic patients undergoing peripheral blood stem cell harvests. The techniques currently available make use of antibodies specific to the CD34+ surface markers. However, all of these techniques involve disturbance of the cell surface, are time-consuming and relatively expensive. In this study, we have used dielectrophoresis, which does not rely on the presence of cell-specific markers, to separate CD34+ cells from peripheral blood stem cell harvest samples containing an untreated natural mixed cell population. The separation is achieved by exploiting differences in the inherent dielectric properties of the various cell types. Samples obtained from peripheral blood stem cell harvests were resuspended in medium with a conductivity of less than 50 microS/cm and introduced into the dielectrophoretic separation chamber. Alternating field frequencies, from 500 kHz to 5 kHz, were used to collect cell fractions which were analysed by FACS, using a CD34-specific antibody, to quantify the CD34+ population within the fractions. On average a nearly five-fold increase in the frequency of the CD34+ cell population was observed in the fractions collected within the 50-10 kHz range. For this dielectrophoretic separation technique to be suitable in harvesting CD34+ cells for transplantation, it is important to demonstrate that the cells remain viable after the separation process. Cells obtained from each fraction grew when plated in colony assay cultures, GM-CFU and BFU-E, demonstrating that the cells remain normal, viable and capable of colony formation when cultured for 2 weeks. The number of colonies formed correlated with the percentage of CD34+ cells in each fraction. The dielectrophoretic separation technique is simple to operate, the separation is fast, the procedure non-invasive and although not tested has the potential to be incorporated as a batch-wise online facility with the standard harvesting equipment to increase the yield and speed of CD34+ cells in the PBSC harvest.

Antigens, CD34↗
PubMed1994

Potential antitumour mitosenes: relationship between in vitro DNA interstrand cross-link formation and DNA damage in Escherichia coli K-12 strains.

This investigation was aimed at determining the possible relationship between DNA interstrand cross-linking and the cytotoxic activity of potential antitumour mitosene compounds. Mitosenes, possessing two good leaving groups at C-1 and C-10, were found to be able to cross-link calf thymus DNA under hypoxic conditions following sodium dithionite (Na2S2O4) reduction at pH 7.0 and pH 5.5. DNA interstrand cross-linking was pH dependent for most of the mitosenes used, with a higher amount of cross-links formed at pH 5.5 compared to pH 7.0. Without reduction or under aerobic conditions no cross-link formation was detected. The importance of DNA damage for the toxic effect of these mitosenes was assayed by comparing the survival in a DNA repair deficient and a DNA repair proficient E. coli K-12 strain. A correlation between the number of cross-links formed in calf thymus DNA in vitro and the IC50 values in the DNA repair deficient E. coli strain was found. The effect of hypoxia on toxicity of mitosenes was studied in Chinese hamster V79 cells. In these cells, mitosenes appeared to be very active. Under severe hypoxic conditions toxicity of these mitosenes increased, most likely due to the increased lifetime of the activated mitosene species as compared to aerobic conditions. The results suggest that DNA cross-linking following reductive activation is important for the eventual activity of mitosenes in a bacterial system. Increased activity of mitosenes under hypoxic conditions in the V79 cells indicates that these mitosenes may be more active in hypoxic parts of tumours.

Animals↗
PubMed1994

Evaluation of the optimal hand-scrub duration prior to total hip arthroplasty.

Orthopaedic surgeons in many major arthroplasty centres advocate the use of a prolonged surgical hand-scrub prior to total joint replacement. In this study we evaluated the antimicrobial efficacy of a 5 compared with a 10 min scrub before both long (> 90 min) and short (< 90 min) operations for total hip arthroplasty. Surgical hand disinfection was performed on one occasion for 5 min and on a second for 10 min by 41 surgeons and theatre nurses using 4% chlorhexidine gluconate as a detergent formulation ('Hibiscrub', ICI Pharmaceuticals). None of the subjects had previously scrubbed on the day of each test. Bacterial colony counts on the fingers were measured using the method described by Rotter (vide infra) before scrubbing, immediately after scrubbing, and at the end of each operation. Our results showed that for arthroplasty procedures lasting less than 90 min (35 operations) a 5 min hand-scrub was equally as effective as one of 10 min. However, following longer procedures (36 operations) colony counts were significantly higher on subjects who had scrubbed for 10 min than on those who only scrubbed for 5 (P < 0.05, Mann-Whitney U-Test). This study suggests that the practice of a prolonged scrub before total joint replacement does not have a scientific basis and that such a policy should be discontinued where it is still practised.

Aerosols↗
PubMed1994

Follicular toxic pustuloderma associated with allopurinol.

Allopurinol is widely prescribed for primary and secondary hyperuricaemia, and cutaneous adverse reactions are seen in 0.8-2.1% of recipients. The majority of these are mild and include pruritus, diffuse or maculo-papular erythema, urticaria and ichthyosis. More severe reactions are well recognized and include exfoliative dermatitis, toxic epidermal necrolysis and a generalized hypersensitivity syndrome. The latter typically comprises fever, rash, hepatic and renal dysfunction and eosinophil leucocytosis. The occurrence of toxic pustuloderma due to allopurinol, confirmed by re-challenge, is reported.

Allopurinol↗
PubMed1994

Calcaneal dome osteotomy: a new procedure for revising triple arthrodesis.

A preliminary report of a new calcaneal osteotomy is presented. Five patients ranging in age from 18 to 35 years underwent a calcaneal dome osteotomy. They all had painful and significant foot deformity, recurrent tenosynovitis, callosities, and shoe wear problems. The osteotomy was developed to correct the deformity present in patients that had a previous triple arthrodesis. The crescentic shape of the osteotomy allowed for the correction of various degrees and patterns of deformity with accuracy and provided a broad area of contact resulting in osteotomy union. The results achieved by this new technique showed that deformity was corrected, callosities had disappeared, and all the osteotomies were healed. All patients were satisfied by the procedure.

Adolescent↗
PubMed1994

Irreducible dislocation of the fifth metatarsophalangeal joint: a case report.

Metatarsophalangeal joint dislocations are unusual in children and usually occur in the hallux. We are reporting a case of irreducible traumatic dislocation of the fifth metatarsophalangeal joint. At open reduction, the metatarsal head was incarcerated under the flexor digitorum longus. After returning the flexor digitorum longus tendon to its anatomical position, the metatarsophalangeal joint reduced and was stable.

Child↗
PubMed1993

Angiosarcoma in congenital hereditary lymphoedema (Milroy's disease)--diagnostic beacons and a review of the literature.

In cases of congenital lymphoedema the finding of ulceration, violaceous nodules or papules, or apparent traumatic ecchymoses should act as a diagnostic beacon warning of dangers. A case is reported of a high-grade angiosarcoma developing in a patient with congenital hereditary lymphoedema (Milroy's disease). This is the second paper to report this complication, the third case report and the first case in which the diagnosis is substantiated by immunohistochemistry and lectin histochemistry. A review of cases of angiosarcoma complicating congenital hereditary and non-hereditary lymphoedema is also presented.

Adult↗
PubMed1993

(+)-Anatoxin-a is a potent agonist at neuronal nicotinic acetylcholine receptors.

The effects of the nicotinic agonist (+)-anatoxin-a have been examined in four different preparations, representing at least two classes of neuronal nicotinic receptors. (+)-Anatoxin-a was most potent (EC50 = 48 nM) in stimulating 86Rb+ influx into M10 cells, which express the nicotinic receptor subtype comprising alpha 4 and beta 2 subunits. A presynaptic nicotinic receptor mediating acetylcholine release from hippocampal synaptosomes was similarly sensitive to (+)-anatoxin-a (EC50 = 140 nM). alpha-Bungarotoxin-sensitive neuronal nicotinic receptors, studied using patch-clamp recording techniques, required slightly higher concentrations of this alkaloid for activation: Nicotinic currents in hippocampal neurons were activated by (+)-anatoxin-a with an EC50 of 3.9 microM, whereas alpha 7 homooligomers reconstituted in Xenopus oocytes yielded an EC50 value of 0.58 microM for (+)-anatoxin-a. In these diverse preparations, (+)-anatoxin-a was between three and 50 times more potent than (-)-nicotine and approximately 20 times more potent than acetylcholine, making it the most efficacious nicotinic agonist thus far described.

Acetylcholine↗