Biology subjects

Tavakkoli, A. D.

Publications and source records attributed to Tavakkoli, A. D..

3 recordsLinked to original sources

bioRxiv2025

Intermediate tissue oxygen level is required to observe murine FLASH skin sparing

ObjectiveThis study evaluated the hypothesis that baseline tissue oxygen (pO2) would modulate FLASH toxicity sparing in murine skin, using a wide range of pO2 values, with ultra-high dose rate (UHDR) versus conventional dose rate (CDR) irradiation. ApproachMurine leg tissue pO2 was systematically varied and measured during irradiation from a FLASH Mobetron 9 MeV linac at 25 Gy, comparing UHDR ({approx}240 Gy/s) to CDR ({approx}0.16 Gy/s), for radiation induced skin toxicity outcomes. Baseline tissue pO2 was systematically modulated in 5 different treatment cohorts, using different ranges of inhaled gas (room air, 100% oxygen, or carbogen) and through varying limb vascular compression (partial or full). Radiolytic oxygen consumption, gO2 (mmHg/Gy), was quantified in vivo, and induced macroscopic skin toxicity was scored daily post treatment. Main ResultsFLASH skin sparing was observed at a fixed dose of 25 Gy in groups with partial leg clamping (pO2{approx}7{+/-}4mmHg), inhaled air (pO2{approx}12{+/-}6mmHg) and 100% oxygen (pO2{approx}16{+/-}4mmHg), while reduction in ulceration progression was significant only in the air inhalation group. No FLASH effect was observed under anoxic conditions, via complete blood flow occlusion (pO2{approx}0{+/-}1mmHg), or when modulated by inhaled carbogen (pO2{approx}21{+/-}7mmHg). In vivo measurements of radiolytic oxygen consumption, gO2, correlated to initial pO2 under UHDR conditions (pO2{approx}4-16mmHg), with ulceration predominantly occurring at pO2 values above 16mmHg. Inspired carbogen induced the highest pO2 at which point there was no FLASH sparing, for any dose groups between 25 to 15 Gy, despite having large changes in damage with dose. At the specific dose level of 25 Gy studied, the toxicity scores under anoxia for both UHDR and CDR were low (toxicity scores < 1) with no differences observed. SignificanceThese findings point to the fact that moderate and low tissue pO2 is associated with diminished oxygen-mediated damage at UHDR but not CDR, seen with inspired room air or 100% oxygen. Anoxic and hyperoxic murine skin are associated with minimal and maximal radiation damage respectively, but also exhibit no apparent FLASH toxicity sparing effect, with further investigation warranted into if the FLASH toxicity sparing effect persists at higher doses under anoxia.

cancer biology↗

bioRxiv2025

Anesthesia is a Potent Determinant of Ultra-High Dose Rate Sparing in the Murine Total Abdominal Irradiation Model

Radiation therapy is a mainstay of treatment for numerous gastrointestinal (GI) malignancies, where our ability to deliver dose to tumors is limited by acute GI toxicity. Ultra-high dose-rate (UHDR) FLASH irradiation can spare normal tissue, yet its dependence on physiological variables remains incompletely defined. We compared FLASH and conventional dose-rate (CDR) 9 MeV electron total abdominal irradiation (TAI) in C57BL/6 mice anesthetized with either intraperitoneal ketamine/xylazine or inhaled isoflurane in room air, deliberately omitting supplemental oxygen. Single doses of 14 or 16 Gy were delivered, and normal-tissue injury was quantified by time-to-25% body-weight loss. At 14 Gy, UHDR under K/X produced a marked survival advantage: by day 14, 80% of animals had not reached the weight-loss endpoint versus 40% after CDR K/X; no FLASH benefit was discernible with ISO anesthesia. Raising the dose to 16 Gy accentuated these trends; 40% of UHDR K/X mice were still below the endpoint at study termination, whereas all CDR K/X mice met it by day 7. Again, ISO abolished sparing at both dose rates. To probe mechanism, intraperitoneal oxygen tension was measured with an optical reporter in six mice. ISO anesthesia yielded significantly higher pO2 (62 {+/-} 4 mmHg) than K/X (26 {+/-} 10 mmHg), a 2.5-fold difference. These findings identify anesthetic-dependent oxygenation as a reproducible confounder in pre-clinical FLASH studies: elevated pO2 under ISO negates abdominal sparing, whereas K/X preserves it across two clinically relevant doses. Rigorous control and reporting of factors that alter tissue oxygenation are therefore essential when designing experiments and, ultimately, translating FLASH radiotherapy.

cancer biology↗

bioRxiv2023

Anesthetic oxygen use and sex are critical factors in the FLASH sparing effect

IntroductionUltra-high dose-rate (UHDR) radiation has been reported to spare normal tissue compared to conventional dose-rate (CDR) radiation. However, reproducibility of the FLASH effect remains challenging due to varying dose ranges, radiation beam structure, and in-vivo endpoints. A better understanding of these inconsistencies may shed light on the mechanism of FLASH sparing. Here, we evaluate whether sex and/or use of 100% oxygen as carrier gas during irradiation contribute to the variability of the FLASH effect. MethodsC57BL/6 mice (24 male, 24 female) were anesthetized using isoflurane mixed with either room air or 100% oxygen. Subsequently, the mice received 27 Gy of either 9 MeV electron UHDR or CDR to a 1.6 cm2 diameter area of the right leg skin using the Mobetron linear accelerator. The primary post-radiation endpoint was time to full thickness skin ulceration. In a separate cohort of mice (4 male, 4 female) skin oxygenation was measured using PdG4 Oxyphor under identical anesthesia conditions. ResultsIn the UHDR group, time to ulceration was significantly shorter in mice that received 100% oxygen compared to room air, and amongst them female mice ulcerated sooner compared to males. However, no significant difference was observed between male and female UHDR mice that received room air. Oxygen measurements showed significantly higher tissue oxygenation using 100% oxygen as the anesthesia carrier gas compared to room air, and female mice showed higher levels of tissue oxygenation compared to males under 100% oxygen. ConclusionThe FLASH sparing effect is significantly reduced using oxygen during anesthesia compared to room air. The FLASH sparing was significantly lower in female mice compared to males. Both tissue oxygenation and sex are likely sources of variability in UHDR studies. These results suggest an oxygen-based mechanism for FLASH, as well as a key role for sex in the FLASH skin sparing effect.

cancer biology↗