Effects of Minocycline on expression of TLR4, NF-κBp65 and TNF-α in an developing rat model of hypoxic-ischemic brain damage

Objective To explore the mechanism of neuroprotective effects of Minocycline, and observe the expression of TLR4, NF-κBp65 and TNF-α in immature rats with hypoxic-ischemic brain damage. Methods 160 Sprague-Dawley rats at the age of postnatal day 2(P2) were randomly divided into 4 groups : normal control group, sham operation group, HIBD group and HIBD+MN group. HIBD group and HIBD+MN group were subjected to the left common carotid artery ligation(CCAL) and exposure to 8% oxygen for 4 h. The HIBD+MN group received a dose of minocycline(45 mg / kg) in PBS and the HIBD group received the same dose of sterile phosphate buffered saline(PBS)(pH 7.4) intraperitoneally immediately after the hypoxic exposure. 24, 48 and 72 hours after the HI insult, the expressions of TLR4, NF-κBp65 and TNF-α were detected by Western blotting. Brain tissues were collected on 72 hours and 4 weeks after HI for hematoxylin-eosin staining and histological scoring. Rats underwent behavioral tests on postnatal day 30. Results 72 hours and 4 weeks after the HI insult, the pathological changes were improved in HIBD+MN group compared with the HIBD group. Compared with the HIBD group, histological scores in the left cerebral hemisphere of HIBD+ MN group was significantly lower 72 hours and 4 weeks after HI(P0.05). Western blotting showed that the expression of TLR4,NF-κBp65 and TNF-α protein in HIBD+MN group were lower than that in HIBD group, and higher than normal group and sham group in 24, 48 and 72 hours after the HI insult. The outcomes of neurobehavioral test of HIBD group were abnormal.In the hanging test and inclined plane test, the scores of the HIBD+MN group had no statistical significance compared with the normal group and sham group(P0.05), but was higher than HIBD group. In the open field test,there was no significant statistical difference between the HIBD group and HIBD+MN group(P=0.375), but there was significant difference between these two groups and the normal group, sham group(P 0.05). During exploratory activity in the cylinder test,the percent use of left forelimb and right forelimb in the HIBD+MN group had no statistical significance compared with the normal group and sham group(P0.05); but the percent use of left forelimb in the HIBD group was significantly higher than the normal group, sham group and HIBD +MN group(P 0.01). Conclusion Minocycline exerts well protection on hypoxic-ischemic brain damage in immature rats after only used one dose of minocycline, and the effects of protection may be related with repressing activation of TLR4-NF- κBp65—TNF-α signal pathway.