The role of structural changes of the urinary bladder extracellular matrix in the occurrence of different grades of adverse events after radiation therapy

Aim. To investigate the role of structural changes of the urinary bladder extracellular matrix in the occurrence of different grades of adverse events after radiation therapy. Materials and methods. The connective tissue matrix was studied using 126 images obtained from the histological sections of the bladder biopsy specimens of 12 patients classified according to the clinical presentation and the grades of late bladder toxicity according to RTOG/EORTC Late Radiation Morbidity Scoring Scheme. Control images of the normal bladder (n=23) were collected from the autopsy samples. We used nonlinear microscopy imaging method capturing the second harmonic generation (SHG) signal and two-photon excitation auto-fluorescence (TPEA). Results. The findings of nonlinear microscopy of urinary bladder histological sections showed that the structural changes in the connective tissue differed depending on the grade of adverse events: grade II adverse events were associated with the preservation of the structure of collagen fibers and their compression, grade III adverse events caused pronounced disorganization of collagen fibers, blurring without a definite fiber direction. At the same time, in a normal bladder, the structure of collagen fibers was visualized; they had a spiral shape and in some areas were collected in bundles. Collagen fibers and bundles were loosely arranged and accompanied by elastic fibers. The findings suggest that the grade of urinary bladder radiation injury correlates with the data detected by nonlinear microscopy. Discussion. The mosaic structure of radiation-induced alterations of the bladder tissue, even in the areas most affected by radiation (posterior bladder wall, bladder trigone, and bladder neck) indicates that patients with radiation-induced high-grade toxicity need comprehensive care designed to preserve the bladder functional reserves and capacity. The prevention of radiation-related adverse events before radiation therapy should be based on urologic care aimed to detect and treat chronic inflammatory diseases of the bladder and preserve its functional reserves. Another way to improve outcomes is to optimize the management of adverse events. Conclusion. The examination of bladder tissue specimens taken from different parts of the bladder carried out using nonlinear microscopy in the SHG and TPEA modes revealed that the degree of structural changes in the connective tissue matrix in the post-radiation period varies and correlates with the grades of the radiation bladder toxicity. The results of this study can be used to substantiate measures to prevent the onset of high-grade toxicity after radiation therapy of pelvic malignancies.

urinary bladder, extracellular matrix, radiation therapy