Amantadine attenuates sepsis-induced cognitive dysfunction possibly not through inhibiting toll-like receptor 2

Abstract

Amantadine has been shown to reduce anesthesia and surgery-induced neuroinflammation and cognitive dysfunction. It is known that sepsis can impair brain function. We determined whether amantadine-attenuated sepsis-induced neuroinflammation and dysfunction of learning and memory and whether toll-like receptors (TLRs) play a role in the effects. Six- to eight-week-old mice were subjected to cecal ligation and puncture (CLP). Amantadine at 30 mg/kg/day was injected intraperitoneally for 3 days. CU-CPT22, a TLR1/TLR2 inhibitor, at 3 mg/kg/day was injected intraperitoneally for 2 days. Mice were subjected to Barnes maze and fear conditioning tests from 1 week after CLP. CLP induced neuroinflammation and cognitive dysfunction. CLP also increased the expression of toll-like receptor 2 (TLR2), TLR4, and TLR9, three major TLRs in the brain, in CD-1 male mice. Amantadine attenuated CLP-induced neuroinflammation and dysfunction of learning and memory but did not have significant effects on the expression of TLRs. CU-CPT22 also attenuated sepsis-induced neuroinflammation and cognitive dysfunction. Similarly, sepsis induced neuroinflammation and cognitive dysfunction in the C57BL/6J mice. Interestingly, sepsis also induced neuroinflammation and cognitive dysfunction in the TLR2 knockout mice. The effects of amantadine on the neuroinflammation and cognitive dysfunction were still apparent in these knockout mice. TLR2 contributes to sepsis-induced neuroinflammation and cognitive dysfunction. However, inhibiting TLR2 may not be a major mechanism for amantadine to inhibit sepsis-induced neuroinflammation and cognitive dysfunction.

Key messages: Sepsis induces neuroinflammation and cognitive impairment, which were attenuated by amantadine. Toll-like receptors 2 mediates these sepsis effects but may not be the major target for amantadine to reduce these effects.

Keywords: Amantadine; Cognitive function; Neuroinflammation; Sepsis; Toll-like receptors.

Fig. 1

Amantadine attenuated sepsis-induced learning and memory dysfunction in CD-1 mice. Mice were subjected to Barnes maze and fear conditioning from 1 week after CLP. a Scheme of experimental protocol. b Training sessions of Barnes maze. c One day after the training sessions. d Eight days after training sessions. e Context-related fear conditioning. f Tone-related fear conditioning. Results are mean ± SD (n = 15). *P < 0.05 compared with the corresponding values on day 1. ^P < 0.05 compared with control. #P < 0.05 compared with CLP alone. Aman: amantadine; D: day

Fig. 2

Sepsis increased IL-1β and IL-6 concentrations in the hippocampus of CD-1 mice. Hippocampus was harvested 24 h after CLP. a IL-1β levels in mice subjected to CLP and treated with amantadine. b IL-6 levels in mice subjected to CLP and treated with amantadine. c IL-1β levels in mice subjected to CLP and treated with CU-CPT22. d IL-6 levels in mice subjected to CLP and treated with CU-CPY22. Results are mean ± SD (n = 5–6). *P < 0.05 compared with control. ^P < 0.05 compared with CLP alone. CU: CU-CPT22

Fig. 3

Sepsis increased the expression of TLRs in the hippocampus of CD-1 mice. Hippocampus was harvested 6 or 24 h after CLP. a TLR expression in the plasma membrane harvested 6 h after CLP. b TLR expression in the plasma membrane harvested 24 h after CLP. c TLR expression in the whole cell extract harvested 6 h after CLP. d TLR expression in the whole cell extract harvested 24 h after CLP. In each panel, representative images are presented in the top and quantification data are presented in the bottom. Results are mean ± SD (n = 5–6). *P < 0.05 compared with control. Ama: amantadine

Fig. 4

Co-expression of TLR2 with NeuN and Iba-1 in the brain sections of CD-1 mice

Fig. 5

CU-CPT22 attenuated sepsis-induced learning and memory dysfunction in CD-1 mice. Mice were subjected to Barnes maze and fear conditioning from 1 week after CLP. a Scheme of experimental protocol. b Training sessions of Barnes maze. c One day after the training sessions. d Eight days after training sessions. e Context-related fear conditioning. f Tone-related fear conditioning. Results are mean ± SD (n = 15). *P < 0.05 compared with the corresponding values on day 1. ^P < 0.05 compared with control. #P < 0.05 compared with CLP alone. Aman: amantadine; CU: CU-CPT22; D: day

Fig. 6

Effects of TLR2 knockout on sepsis-induced learning and memory dysfunction in mice. C57BL/6J mice (wild-type mice) and TLR2^−/− mice were subjected to Barnes maze and fear conditioning from 1 week after CLP. a Scheme of experimental protocol. b Training sessions of Barnes maze. c One day after the training sessions. d Eight days after training sessions. e Context-related fear conditioning. f Tone-related fear conditioning. Results are mean ± SD (n = 7–9). *P < 0.05 compared with the corresponding values on day 1. ^P < 0.05 compared with control. Aman: amantadine; D: day

Fig. 7

Effects of TLR2 knockout on sepsis-induced increase of IL-1β and IL-6 concentrations in mice. Hippocampus of C57BL/6J mice (wild-type mice) and TLR2^−/− mice was harvested 24 h after CLP. a IL-1β levels in mice subjected to CLP and treated with amantadine. b IL-6 levels in mice subjected to CLP and treated with amantadine. Results are mean ± SD (n = 6–10). *P < 0.05 compared with control