Supplementary Material for: Healing Diabetic Foot Ulcers with Topical Timolol Improves Healed Epithelial Integrity

Abstract Introduction: Diabetic foot ulcers are a common complication in diabetes, leading to high amputation risk and significant healthcare costs. Given topical timolol's emergence as a potential wound-healing agent, our study explored its impact on epidermal integrity. Methods: This study was a post-hoc analysis conducted as part of a randomized controlled trial at the Veterans Affairs Northern California Health Care System. Twenty patients who had diabetic foot ulcers healed in the original trial, 10 in the timolol arm and 10 in the placebo arm, were enrolled in the study. The primary outcome was transepidermal water loss, measured monthly for three months post-healing using a closed-chamber device. The secondary outcome was re-ulceration rates over one year. Results: Transepidermal water loss at 1-, 2- and 3-months post-healing was significantly lower in the timolol group than in the placebo group (p<0.01). Linear mixed models identified contralateral foot transepidermal water loss as a significant predictor of healed diabetic foot ulcer site transepidermal water loss (Estimate = 0.76, p<0.001). The interaction between timolol treatment and months since healing significantly reduced transepidermal water loss over time (Estimate = -2.2, p=0.002). The use of a wheelchair was also associated with a significant decrease in transepidermal water loss (Estimate = -7.7, p=0.01). Initial transepidermal water loss values were higher in patients who re-ulcerated, but the difference was not statistically significant (p=0.42). There was no difference in re-ulceration rates in this small pilot study. Conclusion: Topical timolol significantly improved skin barrier function in healed diabetic foot ulcers, reducing transepidermal water loss. Although re-ulceration rates were not significantly different, the trend suggests potential benefits. Further studies with larger sample sizes and longer follow-up are needed to confirm these findings and explore transepidermal water loss’s predictive value for re-ulceration.