Hyperbaric oxygen treatment reverses radiation-induced oxidative stress responses in a rat model Oscarsson N1, Ny L2, Mölne J3, Ricksten S-E1,Seeman-Lodding H1, Giglio D2 1Department of Anaesthesiology and Intensive Care, 2Department of Oncology, 3Department of Pathology, all at Sahlgrenska University Hospital and Sahlgrenska Academy, University of Gothenburg, Sweden Statistics Values from luminosity measurements were checked for normal distribution using the Shapiro-Wilk test and homogeneity using the Levens test. Significance between groups was calculated using ANOVA and Tukey HSD post hoc Background Radiotherapy for cancer can cause late radiation-induced injuries. An elevated production of reactive oxygen species (ROS) and an activation of the innate immune response is seen in irradiated tissue. These responses may lead to the development of chronic inflammation and fibrosis, which significantly impairs organ function, sometimes leading to severe symptoms and reduced QoL for affected patients. Previous studies have also shown that elevated oxidative stress in the urothelium alone can cause physiological alterations of the bladder function. Hyperbaric Oxygen Therapy (HBOT) has emerged as a treatment modality for late radiation-induced injuries. The time from radiation until HBOT is given has an impact on the treatment results, where early treatment is favored. HBOT seems to be able to sustainably reverse some of the late radiation-induced injuries. Interestingly, it also seems to be able to prevent adverse effects of radiation if given prophylactically. Little is known about the effects of HBOT administered at a subacute time-point. We assessed whether HBOT may reverse sub-acute induced oxidative stress in a newly developed rat model for radiation cystitis and HBOT treatment. Results The average body weight of the rats was 302±39 g at the time of euthanisation. The average weight of the urinary bladder was 100±22 mg. No body or bladder weight differences were observed between the groups. Bladder irradiation induced a pronounced up-regulation of the oxidative stress marker 8-hydroxy-deoxyguanosine (8-OHdG) particularly in the urothelium. A-C: In the urothelium of irradiated bladders (Group C), 8-OHdG was 34.3±14.3% compared with 4.7±2.2% in controls (Group A) p<0.001. C-D: The up-regulation was totally attenuated in irradiated rats treated with HBOT (Group D) 11.4±4.9%; p<0.001. A-B: In bladders only exposed to HBOT (Group B) 8-OHdG was 5.0±2.3, which did not differ from controls (p=0.82). Method Sprague-Dawley rats (n=40) were allocated into one of four groups. No treatment and only 20 sessions of HBOT (sham control group and HBOT sham group, respectively). Bladder irradiation of 20 Gy only and irradiation followed fourteen days later by 20 sessions of HBOT under a period of 14 days (radiation sham group and intervention group, respectively). Pathological examinations, immunofluorescence and q-PCR were used to analyze changes in the urinary bladder. Adobe Photoshop CS6 (Version 13.0.1 x64) was used for measurements of luminosity of the immunohistochemically stained slides. The mean value from three representative areas from each slide was chosen for luminosity measurements. The pixel intensity value for the measured RGB-channel was converted to a percentage of the maximum value of 255 Discussion/Conclusion Radiation induced a significant elevation of oxidative stress. All sub-acute changes were completely reversed by HBOT whereas HBOT in non-irradiated bladder had no effect on any of the factors investigated. Our results give support to the hypothesis that HBOT can be used prophylactically in order to prevent late radiation-induced injuries. The model used seems to be appropriate for studies on late radiation-induced injuries, but a more chronic study is warranted to analyze the effects of fibrosis itself. For additional information, please contact: Nicklas Oscarsson, MD Email: nicklas.oscarsson@vgregion.se