Impact of therapeutic X-ray exposure on collagen I and associated proteins

Biological tissues are exposed to X-rays in medical applications (such as diagnosis and radiotherapy) and in research studies (for example microcomputed X-ray tomography: microCT). Radiotherapy may deliver doses up to 50Gy to both tumour and healthy tissues, resulting in undesirable clinical side effects which can compromise quality of life. Whilst cellular responses to X-rays are relatively well-characterised, X-ray-induced structural damage to the extracellular matrix (ECM) is poorly understood. This study tests the hypotheses that ECM proteins and ECM-rich tissues (purified collagen I and rat tail tendons respectively) are structurally compromised by exposure to X-ray doses used in breast radiotherapy. Protein gel electrophoresis demonstrated that breast radiotherapy equivalent doses can induce fragmentation of the constituent α chains in solubilised purified collagen I. However, assembly into fibrils, either in vitro or in vivo, prevented X-ray-induced fragmentation but not structural changes (as characterised by LC-MS/MS and peptide location fingerprinting: PLF). In subsequent experiments exposure to higher (synchrotron) X-ray doses induced substantial fragmentation of solubilised and fibrillar (chicken tendon) collagen I. LC-MS/MS and PLF analysis of synchrotron-irradiated tendon identified structure-associated changes in collagens I, VI, XII, proteoglycans including aggrecan, decorin, and fibromodulin, and the elastic fibre component fibulin-1. Thus, exposure to radiotherapy X-rays can affect the structure of key tissue ECM components, although additional studies will be required to understand dose dependent effects.