Relative neuroprotective effects hyperbaric oxygen treatment and TLR4 knockout in a mouse model of temporary middle cerebral artery occlusion

Purpose: To examine the effects of hyperbaric oxygen (HBO) therapy and knockout of toll-like receptor 4 (TLR4) on the outcome of temporary middle cerebral artery occlusion (MCAO) in a mouse model. Materials and Methods: MCAO was induced in anesthetized male C57Bl/6 mice (WT) and TLR4 knockout mice (TLR4^-/-) using an intra-arterial filament method. After 30 or 90 min, the filament was removed, and the mice were given either no treatment (WT and TLR4^-/- groups) or HBO (WT only). Mice were euthanized 24 h after MCAO, and the brain infarct area was examined using 2,3,5-triphenyltetrazolium chloride (TTC) staining. Results: In the WT group, without treatment, lesion volume was 120 ± 13 mm³ in the mice subjected to 30 min MCAO and 173 ± 23 mm³ in the mice subjected to 90 min MCAO. Respective values with HBO treatment were 66.5 ± 36.7 mm³ and 53.2 ± 17.2 mm³. The difference was significant only for 90-minute MCAO (p < 0.01, nonparametric test). In the TLR4^-/- group (all untreated), lesion volume was 95.9 ± 17.9 after 90 min of MCAO, which was significantly lower than in the untreated WT animals (p < 0.05, nonparametric test). Conclusions: A single treatment of HBO immediately after MCAO followed by 24 h reperfusion significantly reduces edema and may improve perfusion. TLR4 knockout protects mice from MCAO damage, but to a lesser extent than HBO treatment.