Hyperbaric Oxygen Therapy Mitigates Diaphragm Pathology After Spinal Cord Injury Through Antioxidant Upregulation

PURPOSE: Spinal cord injuries (SCI) at the cervical level produce respiratory dysfunction causing an increase in mortality following SCI. Diaphragm dysfunction after SCI can interfere with rehabilitation, thus a treatment to preserve diaphragm function is needed. Previously, we demonstrated that hyperbaric oxygen (HBO) therapy, delivered during the acute phase of SCI can attenuate diaphragm dysfunction. These experiments test the hypothesis that the protective effects of HBO treatment are mediated by upregulation of antioxidants SOD1, SOD2 and GPX1. METHODS: Adult Sprague-Dawley rats received a lateral C4 contusion, except for a spinal intact group (Intact-Normox-Saline), followed by HBO (1 hour/day, 10 consecutive days), N = 9 -12 per group. The control SCI group (SCI-Normox-Saline) and the intact group were at normal oxygen for the duration. To test if the antioxidants SOD1, SOD2, and/or GPX1 mediate beneficial effects of HBO therapy, we injected anti-sense oligonucleotides (ASOs) or saline i.p after each HBO therapy. The ASOs were given alone or as a Mix of all 3 (SCI-HBO-MIX). RESULTS: We measured oxygen consumption (JO2, pmol/sec/mg) in diaphragm muscle fibers. The SCI-Normox-saline group (774.55 ± 30.61) had a significantly reduced JO2 compared to Intact-Normox-Saline (869.45 ± 38.07, P ≤ 0.03). Importantly, HBO in the SCI-Saline group (865.58 ± 75.83) prevented SCI-induced decreases in JO2. As for the ASO treatments, SOD1 (759.99 ± 35.12, P ≤ 0.02), SOD2 (743.46 ± 26.48, P ≤ 0.01), and MIX (740.91 ± 31.03, P ≤ 0.01) had significantly reduced JO2 rate than the intact group, but GPX1 (751.74 ± 59.13) was not different. We also examined the contractile force of the diaphragm at stimulations from 1 - 160 Hz. All groups had reduced max force compared to Intact-Normox-Saline (25.41 ± 0.7, P ≤ 0.001) except for SCI-HBO-Saline (21.85 ± 2.3) which indicates that HBO is protective against SCI. Interestingly, both SOD1 ASO (17.9 ± 3.4, P ≤ 0.04) and SOD2 ASO (17.57 ± 3.3, P ≤ 0.02) prevented HBO-induced protection against SCI-induced muscle weakness, but GPX1 ASO (18.9 ± 2.6) and MIX ASO (19.32 ± 2.9) contractile forces were not different from SCI-HBO-Saline. CONCLUSIONS: These data identify antioxidants SOD1 and SOD2 as mediators of the therapeutic effects of HBO on the diaphragm following acute SCI. Funding: R01HL153140-04. R01HL153140-04