Metabolomic biomarkers in wound healing and infection

Abstract

Deficiencies in wound healing processes result in chronic wounds which have varying consequences. Some of these include a negative impact on patients’ quality of life, increasing financial healthcare costs and an association with significant morbidity and mortality. Multiple “omic” technologies have been utilised to provide a deeper understanding of pathways responsible for normal and impaired wound healing. Infection also remains a major contributor to delayed wound healing and although the chronic wound microbiome has been well investigated; its temporal variation in acute wound healing and its association to wound healing processes have been underreported. The identification of biomarkers through metabolomics is an emerging field and yet currently remains understudied in wound healing and infection. There is an unmet need for additional diagnostic, monitoring and therapeutic tools that can detect, observe and treat wound infections, respectively. There is however a lack of relevant pre-clinical human wound biofilm models available to investigate these further. Volatile organic compounds (VOCs) are a sub-class of metabolic biomarkers, which have potential applications to wound healing and infection. In light of these needs and limitations, the objectives of this thesis were to investigate the role of VOCs in wound healing and wound infection in addition to attempt to address the paucities described above. The first phase of this research led to the successful development and validation of bacterial biofilm formation in novel clinically relevant human ex vivo incisional and excisional cutaneous wound models. This was done through the use of multiple microscopy techniques and quantitative assays. In addition, bacteria-specific volatile signatures were identified and VOCs were significantly affected by biofilm development, model used and biofilm growth phase. VOCs also correlated with biofilm metabolic activity and biomass. The second phase successfully explored the feasibility of utilising VOCs to monitor biofilm treatment response. Significant variations were noted in the relative abundance of VOCs in biofilms exposed to treatment when compared to controls. Furthermore, due to the occurrence and increase of antibiotic resistance there has been a growing demand for alternative treatment methods. In view of this, the antimicrobial efficacy of electrical stimulation (ES) was also investigated. In vitro and ex vivo results demonstrated significantly reduced biofilm viability, metabolic activity and biomass following ES treatment compared to controls. In the final phase, a multi-part temporal study was undertaken involving healthy human subjects where over 300 metabolite features were analytically identified from sequential acute wounds using multiple sampling methods. Parallel to this, wound healing was quantified using non-invasive devices and multivariate and shape statistical analyses identified VOC biomarkers that corresponded to wound healing processes. Additionally, microbial communities were sequenced and significant correlations between collagen, Propionibacterium and Staphylococcus were found. In conclusion, these studies effectively evaluate the role of metabolomics in wound healing and in wound infection. They support the association between metabolic VOC biomarkers and the phases of wound healing. In addition, they demonstrate the potential clinical translatability in utilising these biomarkers in the diagnosis and staging of wound infections and their ability to monitor treatment response. Furthermore, the biofilm wound models formed and validated provide a vehicle for further human skin-relevant biofilm studies.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	M.T. Alonso-Rasgado (Supervisor) & Ardeshir Bayat (Supervisor)