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Effects of HIF-1alpha on vascular relaxation to hypoxia in healthy Sprague-Dawley rats exposed to hyperbaric oxygenation

Introduction: Hypoxia and reactive oxygen species or reactive nitrogen species may stimulate HIF-1α stabilization and its cellular signal pathway activation. However, the role of HIF-1α in vascular function in conditions of elevated oxidative stress and exposure to hyperbaric oxygenation is still underinvestigated. This study aimed to test the effects of HIF-1α inhibition on the hypoxia– induced relaxation (HIR) of isolated rat aortic rings and to examine HIF-1alpha mRNA and protein expression in aortic tissue after different hyperbaric exposure protocol. Methods: Healthy 9-12 weeks old Sprague-Dawley rats (n=64) were divided in 4 groups ; Control group (no treatment, n=16), A-HBO2 (acute HBO2 group exposed to HBO2 single 120’ session of 100% O2 at 2.0 bars, n=16), 24H-HBO2 (tested 24h after HBO2 exposure, n=16) and 4D-HBO2 (4 consecutive days of exposure, tested on 5th day, n=16). Response to reduced pO2 (bath gas mixture from 95% O2, 5% CO2 switched to bath gas mixture of 95% N2, 5% CO2) were tested in norepinephrine-precontracted aortic rings in the absence/presence of the LW6 HIF-1α inhibitor. HIF- 1mRNA expression and HIF-1α protein expression in aorta were determined byqPCR method and Western blot, respectively. All experimental procedures conformed to the European Guidelines for the Care and Use of Laboratory Animals (directive 86/609) and were approved by the local and national Ethical Committee #2158/61-02-139/2-06. Results: HIR was impaired in A-HBO2 group compared to other groups, and elevated in 24-HBO2 and 4D-HBO2 groups compared to CTRL group. HIR was partially blocked by LW6 inhibitor in 24-HBO2 group compared to baseline relaxation. HIF- 1alpha mRNA expression was significantly increased in 24H-HBO2 and 4D-HBO2 groups compared to CTRL and A-HBO2.Protein expression was similar among groups. Conclusion: These results suggest HIF-1alpha activation by hyperbaric oxygenation and its involvement in hypoxia-induced relaxation. Acknowledgment: Supported by grants of Ministry of Science, Education and Sports, Croatia, #219-2160133- 2034 and Faculty of Medicine Osijek VIF-2016 grant (PI Drenjancevic I).

HIF-1alpha, hyperbaric oxigenation, vascular function, Sprague-Dawley rats

Funded by: VIF2017-MEFOS-4 ; PI: Ines Drenjančević