Evaluation of the effects of pre-injury exercise in a mouse hindlimb model of secondary lymphedema

Abstract

Background and Purpose. Lymphedema is a common but distressing sequela after cancer treatment. A curative treatment is not yet available; thus, prevention is a vital part of its management. This study aims to determine the effect of exercise before injury, i.e., lymph node resection and radiation, on the development of lymphedema in mice hindlimb.

Methods. BALB/c mice were randomized into 2 groups: exercise (n=7) and no exercise (n=7). The exercise group performed 30 minutes of moderate exercise on a treadmill, 5 days a week for 4 weeks, while the no exercise group was placed on a stationary treadmill for the same amount of time. Lymphedema was induced by unilateral popliteal lymph node resection and 20 Gy lower limb irradiation. Caliper measurements of ankle diameter and hindpaw thickness were obtained weekly for 6 weeks, and the percentages of excess ankle diameter (PED) and hindpaw thickness (PET) relative to the intact control limb were calculated. Weekly indocyanine green (ICG) lymphangio-imaging was performed to visualize dermal backflow patterns. Histopathological analysis on the 6th week post injury was also done to evaluate skin thickness and lymphatic vessel density.

Results. The exercise group exhibited a significantly lower PED compared to the no exercise group at weeks 3, 4, 5, and 6 after injury, as well as significantly lower PET at weeks 5 and 6 after injury. ICG imaging showed that the no exercise group had a significantly higher proportion of mice demonstrating the more severe stardust and diffuse patterns at weeks 1, 4 and 5 after injury. On hematoxylin and eosin slides, the exercise group showed a significantly lower increase in epidermal and dermal thickness. On immunohistochemistry staining with anti-LYVE-1, the exercise group showed a higher lymphatic vessel density than the no exercise group.

Conclusion. Exercise before lymphatic injury may attenuate the development of secondary lymphedema induced by lymph node resection and radiation in mice hindlimb. This may have implications for the role of prehabilitation in human lymphedema.