Repeated preconditioning with hyperbaric oxygen induces neuroprotection against forebrain ischemia via suppression of p38 mitogen activated protein kinase

We previously reported in rats that preconditioning with hyperbaric oxygen (HBO; 100% O2 3.5-atomsphere absolute (ATA), 1 h/day for 5 days) provided neuroprotection against transient (8 min) forebrain ischemia possibly through protein synthesis relevant to neurotrophin receptor and inflammatory–immune system. A recent report suggested that HBO-induced neuroprotection is relevant to brain derived neurotrophic factor and its downstream event involving suppression of p38 mitogen activated protein kinase (p38) activation. In the present study, we first performed a dose comparison (1, 2, and 3.5 ATA) of HBO-induced neuroprotection and then investigated pharmacological modification by 10 mg/kg anisomycin (a protein synthesis inhibitor and potent activator for p38) and 200 μg/kg SB203580 (a p38 inhibitor), which were given intraperitoneally 60 and 30 min before every 3.5 ATA-HBO treatment, respectively. Most prominent protective effect on hippocampal CA1 neurons was observed with 3.5 ATA-HBO (survived neurons: 69% [62–73%] vs. untreated: 3.9% [2–8%], 1 ATA: 8.8% [0–26%], 2 ATA-HBO: 46% [22–62%] (median [range]) (7 days after ischemia). Anisomycin abolished a neuroprotective effect (survived neuron: 1.2% [0–7%]). SB203580, when given between administration of anisomycin and HBO treatment, resumed a neuroprotective effect (survived neuron: 52% [37–62%]). The level of phosphorylated p38 at 10-min reperfusion was significantly decreased in 3.5 ATA-HBO group (32% [12–53%] of sham). Single pretreatment with 100 and 200 μg/kg of SB203580 exerted a similar neuroprotective effect (39% [25–51%] and 59% [50–72%]) to 2 and 3.5 ATA-HBO preconditioning, respectively. It is concluded that suppression of p38 phosphorylation plays a key role in HBO-induced neuroprotection and that pretreatment with a p38 inhibitor (SB203580) can provide similar neuroprotection.