Beneficial Properties of Argon After Experimental Subarachnoid Hemorrhage: Early Treatment Reduces Mortality and Influences Hippocampal Protein Expression

Objectives: Until now, treatment ameliorating early brain injury following subarachnoid hemorrhage has been nonexistent. Here, we evaluate the neuroprotective properties of argon after experimental subarachnoid hemorrhage with mortality as the primary endpoint and functional outcome, as well as hippocampal cellular and molecular stress response as secondary endpoints.

Design: Randomized controlled animal study.

Setting: University research laboratory.

Subjects: Ninety-eight male Sprague-Dawley rats.

Interventions: One hour after subarachnoid hemorrhage induction via endovascular perforation technique or sham surgery, a breathing gas mixture containing 50 vol% argon/50 vol% oxygen (argon group) or 50 vol% nitrogen/50 vol% oxygen (control group) was applied for 1 hour.

Measurements And Main Results: The primary objective was mortality after subarachnoid hemorrhage. Additionally, outcome was assessed via 1) neurologic testing and 2) an open-field test 24 hours after subarachnoid hemorrhage, 3) protein analysis of hippocampal samples for hypoxia-inducible factor 1α and heme oxygenase 1, and 4) immunohistochemistry of hippocampal slices to quantify vital neurons. Animals were euthanized 6, 24, or 72 hours after subarachnoid hemorrhage or sham surgery. Occurrence of premature death (death prior to scheduled euthanasia) was assessed. Postconditioning with argon resulted in a reduction of risk with respect to premature death to 20.6% compared with the control group (95% CI, 4.39-96.7). Body weight was higher in the argon group over the entire observation period (p < 0.05). There was no difference in the neuroscore (p = 0.550). Expression of hypoxia-inducible factor 1α and heme oxygenase 1 in the hippocampus was increased in the argon group. Higher quantity of vital neurons in the hippocampal samples of the argon group was discovered 24 hours after subarachnoid hemorrhage.

Conclusions: Argon application after experimental subarachnoid hemorrhage met the primary endpoint of reducing the risk of mortality. In addition, higher body weight indicating good overall condition was observed in the argon group over the entire observation period. Regarding the mechanism of action, hypoxia-inducible factor 1α-induced heme oxygenase 1 expression resulting in improved survival of neurons may contribute to the beneficial effect of argon application after subarachnoid hemorrhage.