[Role of Nrf2 in the protective effects of hydrogen against cerebral dysfunction in septic mice]

To investigate the role of nuclear factor erythroid 2-related factor 2 (Nrf2) in the protective effects of hydrogen against cerebral dysfunction in a mouse model of sepsis.

Male ICR mice were randomly divided into sham operation group, hydrogen control group, sepsis group and hydrogen treatment group, with 20 in each group. Sepsis model was reproduced by cecal ligation and puncture (CLP). 2% hydrogen inhalation was given for 1 hour at 1 hour and 6 hours after operation in hydrogen treatment group. The brain tissues were obtained at 24 hours after operation. The histopathologic changes and neuron apoptosis in the hippocampus were observed under the microscope. The expressions of nucleus and total Nrf2 in hippocampus were detected by Western Blot. The activities of superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA) and 8-iso-prostaglandin F2α (8-iso-PGF2α) in hippocampus were also detected. The changes of learning and memory abilities were observed by Morris water maze test at day 4 to 9 after operation.

Compared with the sham operation and hydrogen control groups, in the sepsis group, the number of normal pyramidal neurons in the hippocampal CA1 region was markedly reduced, the apoptotic index was marked increased, the expressions of nucleus and total Nrf2 were partly increased, the activities of SOD and CAT in the hippocampus were significantly decreased, and the levels of MDA and 8-iso-PGF2α were markedly increased, the escape latency at day 4 to 8 after operation was significantly extended, and there was no difference in swimming speed, the percentage of time in the target quadrant and the times of the platform crossing were significantly decreased on probe day. Compared with the sepsis group, in the hydrogen treatment group, the number of normal pyramidal neurons in the hippocampal CA1 region was markedly increased (67.33 ± 6.89 vs. 42.33 ± 6.02, P<0.01), the apoptotic index was dramatically reduced [(30.00 ± 4.77)% vs. (80.50 ± 6.99)%, P<0.01], the expressions of nucleus and total Nrf2 were significantly increased [nucleus Nrf2 (A value): 5.07 ± 0.35 vs. 3.04 ± 0.34, total Nrf2 (A value): 4.24 ± 0.58 vs. 2.91 ± 0.37, both P<0.01], the activities of SOD and CAT in the hippocampus were significantly increased [SOD (U/mg): 120.96 ± 13.44 vs. 81.16 ± 12.28, CAT (U/mg): 9.11 ± 1.28 vs. 5.64 ± 1.88, both P<0.01], and the levels of MDA and 8-iso-PGF2α were markedly reduced [MDA (nmol/mg): 16.12 ± 1.49 vs. 27.64 ± 1.87, 8-iso-PGF2α (pg/mg): 183.43 ± 13.07 vs. 864.07 ± 49.92, both P<0.01], the escape latency at day 5 to 8 after operation was significantly shortened, and there was no difference in swimming speed, the percentage of time in the target quadrant [(37.06 ± 1.16)% vs. (24.42 ± 1.82)%, P<0.01] and the times of the platform crossing (7.13 ± 0.98 vs. 4.88 ± 0.99, P<0.01) were significantly increased on probe day. There was no statistical difference in above indexes between sham operation group and hydrogen control group.

Hydrogen inhalation can ameliorate pathological injury in brain and impairment of learning and memory abilities of septic mice, which may be associated with the up-regulation of Nrf2, the increase of antioxidant enzymes activities and the decrease of oxidative products.