Optimal timing and frequency of bone marrow soup therapy for functional restoration of salivary glands injured by single‐dose or fractionated irradiation

Injections of bone marrow (BM) cell extract, known as ‘BM soup’, were previously reported to mitigate ionizing radiation (IR) injury to salivary glands (SGs). However, the optimal starting time and frequency to maintain BM soup therapeutic efficacy remains unknown. This study tested the optimal starting time and frequency of BM soup injections in mice radiated with either a single dose or a fractionated dose. First, BM soup treatment was started at 1, 3 or 7 weeks post‐IR; positive (non‐IR) and negative (IR) control mice received injections of saline (vehicle control). Second, BM soup‐treated mice received injections at different frequencies (1, 2, 3 and 5 weekly injections). Third, a 'fractionated‐dose radiation' model to injure mouse SGs was developed (5 Gy × 5 days) and compared with the single high dose radiation model. All mice ( n = 65) were followed for 16 weeks post‐IR. The results showed that starting injections of BM soup between 1 and 3 weeks mitigated the effect of IR‐induced injury to SGs and improved the restoration of salivary function. Although the therapeutic effect of BM soup lessens after 8 weeks, it can be sustained by increasing the frequency of weekly injections. Moreover, both single‐dose and fractionated‐dose radiation models are efficient and comparable in inducing SG injury and BM soup treatments are effective in restoring salivary function in both radiation models. In conclusion, starting injections of BM soup within 3 weeks post‐radiation, with 5 weekly injections, maintains 90–100% of saliva flow in radiated mice.