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Title: Defining a role for xanthine oxidoreductase in promoting the healing of chronic ulcers
Author: Bennett, Emily Jane
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2006
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Chronic ulcers are a major healthcare problem characterised by ineffectual healing and infection. Xanthine oxidoreductase (XOR, EC, incorporated into a dressing or graft may provide enhanced healing and antibacterial activity. XOR is a complex molybdoflavoprotein with broad substrate specificity, and in aerobic conditions, generates superoxide (0₂̇⁻) and hydrogen peroxide (H₂O₂) through purine catabolism. Low levels of these species from XOR are known to enhance the proliferation of many mammalian cells including human dermal fibroblasts, essential for the healing process (Murrell et al, 1990). XOR also generates nitric oxide (̇NO) from physiological levels of nitrite, optimally at low pH in anoxic conditions (cf the conditions prevailing in a chronic ulcer). Nitric oxide contributes to healing in general by increasing perfusion, stimulating angiogenesis and killing bacteria. Chronic wounds are known to harbour a range of anaerobic and facultative bacteria, many of which are detrimental to wound healing. It has been shown that the simultaneous generation of 0₂̇⁻ and ̇NO by XOR in low oxygen, results in the rapid production of peroxynitrite (ONOO⁻), a very much more potent bactericidal species than 0₂̇⁻, ̇NO or H₂O₂. Experiments were performed to characterise the effects of XOR activities on factors pertinent to healing to test the hypothesis that XOR incorporated into a dressing or dermograft will facilitate ulcer healing. Superoxide generation by xanthine oxidase (XO) was characterised, and shown to vary in biological media commonly used for the growth of either fibroblasts or bacteria in the laboratory setting. In support of existing research, superoxide generation by XO in low oxygen (1%) was reduced when compared with air. Nevertheless, peroxynitrite generation was also observed in low oxygen (1%). This thesis supports previous research showing that XO enhances the proliferation of adult human dermal fibroblasts (HDF) using standard culture conditions in air. In the presence of 21% oxygen (air), high levels of XO (10-50mU ml⁻¹) were shown to be cytotoxic to adult fibroblasts whereas lower levels appeared to increase DNA synthesis suggesting enhanced proliferation (lmUml⁻¹). This thesis also extends these findings showing a similar effect on neonatal HDF. The novel findings in this thesis are that at low oxygen tension (p0₂ below 5%) the growth of adult HDF is not adversely affected in the presence of high XO concentrations (5-50mU ml⁻¹ XO); in fact, HDF appear to show some evidence of enhanced proliferation under these conditions. Bacterial strains relevant to the chronic wound responded differentially to XO but showed growth inhibition at 10 and 50mU ml⁻¹ XO. Overall, these findings suggest that an XO-incorporating graft or dressing may deliver both proliferative and antimicrobial effects in a hypoxic ulcer setting.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available