OBJECTIVE: As indications for adjuvant radiation therapy (XRT) have expanded in recent years, an increasing number of breast cancer patients are receiving XRT as a component of treatment. Although XRT is highly effective, it often damages the skin and soft tissues of the breast. Radiation-induced damage to dermal type I collagen reduces cutaneous elasticity and strength, which can ultimately limit patient candidacy for expander-based breast reconstruction. In the present study, we utilized amifostine (AMF) as a prophylactic radioprotectant with the objective of mitigating dermal type I collagen injury associated with XRT. To investigate this, we utilized Raman spectroscopy to analyze the chemical properties of dermal type I collagen in a murine model of irradiated expander-based breast reconstruction.
METHODS: Female Lewis rats were grouped (n = 7/group): expander without XRT (Control); expander + XRT (XRT); and expander + AMF + XRT (AMF). Expanders were surgically placed in a submusculocutaneous plane on the dorsum of the animal and filled to achieve a final volume of 15 ml. Both the XRT and AMF group received a total XRT dose of 35 Gy. The AMF group received AMF pretreatment 30 minutes before XRT. After a 20-day recovery period, tissues overlying the expander were harvested and sectioned. Raman spectroscopy was performed to study the chemical properties of dermal type I collagen.
RESULTS: Based on the (853 + 877)/1,657 cm−1 band intensity ratio (Pro+Hyp/Amide-I ratio), collagen turnover was impaired in expanded, irradiated tissues (mean ratio, 0.492; SD, 0.086) compared to the control group (mean ratio, 0.660; SD, 0.089). This impaired collagen synthesis was not observed in animals receiving AMF pretreatment (mean ratio, 0.685; SD, 0.098), supporting its efficacy as a radioprotectant. Additionally, based on the 853/877 cm−1 band intensity ratio (Hyp/Pro ratio), the hydroxylation of proline within collagen was reduced in expanded, irradiated tissues compared to controls. This decrease in the Hyp/Pro ratio was paralleled and supported by the observed reduction in collagen synthesis (Pro+Hyp/Amide-I ratio). This reduction in hydroxylation of collagen proline was mitigated by AMF pretreatment. The 1,656/1,673 cm−1 intensity ratio (α-helix/β-sheet ratio) was evaluated to detect changes in collagen secondary structure, and interestingly, no significant changes in the α-helix/β-sheet ratio were found between irradiated and non–irradiated-expanded tissues. These results suggest that radiotherapy reduces collagen synthesis, but the integrity of collagen secondary structure is preserved.
CONCLUSION: This study further elucidated the mechanism of dermal type I collagen radiation injury. Pathologic changes in the chemical composition of irradiated tissues were detected utilizing Raman spectroscopy. Radiation significantly impaired collagen synthesis, resulting in a marked reduction in the collagen content of irradiated tissues. Amifostine was shown to mitigate these detrimental effects, as AMF pretreatment demonstrated a significant preservation in type I collagen synthesis in this model of irradiated expander-based breast reconstruction. Utilizing AMF as a prophylactic radioprotectant in breast cancer patients has the potential to increase reconstructive options available to patients and their plastic surgeons and improve surgical outcomes in the aftermath of radiotherapy.