Astaxanthin Attenuates Environmental Tobacco Smoke-Induced Cognitive Deficits: A Critical Role of p38 MAPK

Abstract

Increasing evidence indicates that environmental tobacco smoke (ETS) impairs cognitive function and induces oxidative stress in the brain. Recently, astaxanthin (ATX), a marine bioactive compound, has been reported to ameliorate cognitive deficits. However, the underlying pathogenesis remains unclear. In this study, ATX administration (40 mg/kg and 80 mg/kg, oral gavage) and cigarette smoking were carried out once a day for 10 weeks to investigate whether the p38 MAPK is involved in cognitive function in response to ATX treatment in the cortex and hippocampus of ETS mice. Results indicated that ATX administration improved spatial learning and memory of ETS mice (p < 0.05 or p < 0.01). Furthermore, exposure to ATX prevented the increases in the protein levels of the p38mitogen-activated protein kinase (p38 MAPK; p < 0.05 or p < 0.01) and nuclear factor-kappa B (NF-κB p65; p < 0.05 or p < 0.01), reversed the decreases in the mRNA and protein levels of synapsin I (SYN) and postsynaptic density protein 95 (PSD-95) (all p < 0.05 or p < 0.01). Moreover, ATX significantly down-regulated the increased levels of pro-inflammatory cytokines including interleukin-6 (IL-6) and tumor necrosis factor (TNF-α) (all p < 0.05 or p < 0.01). Meanwhile, the increased level of malondialdehyde (MDA) and the decreased activities of superoxide dismutase (SOD), glutathione (GSH), and catalase (CAT) were suppressed after exposure to ATX (all p < 0.05 or p < 0.01). Also, the results of the molecular docking study of ATX into the p38 MAPK binding site revealed that its mechanism was possibly similar to that of PH797804, a p38 MAPK inhibitor. Therefore, our results indicated that the ATX might be a critical agent in protecting the brain against neuroinflammation, synaptic plasticity impairment, and oxidative stress in the cortex and hippocampus of ETS mice.

Keywords: antioxidant inflammatory; astaxanthin; cigarette smoke exposure; p38 MAPK; synaptic-associated plasticity.

Figure 1

Effects of chronic astaxanthin (ATX) treatment on environment tobacco smoke (ETS) induced cognitive decline (n = 12). (A) Escape latency appeared during the training and the probe sessions. Data are reported as mean ± SE. (* p < 0.05) versus Group Control at the corresponding days; ^# p < 0.05 versus Group ETS at the corresponding days). (B) The swimming speed among the four groups during the five-day period. Data are reported as mean ± SE (p > 0.05). (C) The percentage of time spent in the target quadrant during the probe trial. Data are reported as mean ± SE. (* p < 0.05 versus Group Control; ^# p < 0.05 versus Group ETS). (D) The number of crossings of the platform area. Data are reported as mean ± SE (* p < 0.05 versus Group Control; ^# p < 0.05 versus Group ETS).

Figure 2

Effects of ATX on parameters of oxidative stress in the mouse brain (n = 12). (A) The level of MDA. Data are reported as mean ± SE. (** p < 0.01 versus Group Control; ^# p < 0.05 versus Group ETS; ^## p < 0.01 versus Group ETS). (B) The activity of SOD. Data are reported as mean ± SE. (** p < 0.01 versus Group Control; ^# p < 0.05 versus Group ETS; ^## p < 0.01 versus Group ETS). (C) The activity of CAT (** p < 0.01 versus Group Control; ^# p < 0.05 versus Group ETS; ^## p < 0.01 versus Group ETS). (D) The level of GSH. Data are reported as mean ± SE. (** p < 0.01 versus Group Control; ^# p < 0.05 versus Group ETS; ^## p < 0.01 versus Group ETS).

Figure 3

Effects of ATX on inflammation in the hippocampus and cortex (n = 12). (A) The levels of TNF-α. Data are reported as mean ± SE. (** p < 0.01 versus Group Control; ^# p < 0.05 versus Group ETS; ^## p < 0.01 versus Group ETS). (B) The levels of IL-6. Data are reported as mean ± SE. (** p < 0.01 versus Group Control; ^# p < 0.05 versus Group ETS; ^## p < 0.01 versus Group ETS).

Figure 4

Effects of ATX on the expressions of NF-κB p65 in the cortex and hippocampus (n = 12). The levels of NF-κB p65 in the hippocampus and cortex of mice. Data are reported as mean ± SE. (** p < 0.01 versus Group Control; ^# p < 0.05 versus Group ETS; ^## p < 0.01 versus Group ETS).

Figure 5

Effects of ATX on the expressions of p38 and p-p38 in the cortex and hippocampus (n = 12). The levels of p-p38 in the hippocampus and cortex of mice. Data are reported as mean ± SE. (** p < 0.01 versus Group Control; ^# p < 0.05 versus Group ETS; ^## p < 0.01 versus Group ETS).

Figure 6

Effects of ATX on the expression of SYN mRNA and PSD-95 mRNA in the mouse brain (n = 12). (A) The levels of SYN mRNA. Data are reported as mean ± SE. (** p < 0.01 versus Group Control; ^# p < 0.05 versus Group ETS; ^## p < 0.01 versus Group ETS). (B) The levels of PSD-95 mRNA. Data are reported as mean ± SE. (** p < 0.01 versus Group Control; ^# p < 0.05 versus Group ETS; ^## p < 0.01 versus Group ETS).

Figure 7

Effects of ATX on the expression of synaptic proteins in the mouse brain (n = 12). (A) The levels of SYN in the hippocampus and cortex of mice. Data are reported as mean ± SE. (** p < 0.01 versus Group Control; ^# p < 0.05 versus Group ETS; ^## p < 0.01 versus Group ETS). (B) The levels of PSD-95 in the hippocampus and cortex of mice. Data are reported as mean ± SE. (** p < 0.01 versus Group Control; ^# p < 0.05 versus Group ETS; ^## p < 0.01 versus Group ETS).

Figure 8

Effects of ATX on the structure and morphology of the hippocampal neurons (n = 12). Nissl stained neurons in the hippocampal CA1 subfield (A) and cortex (B). Bar = 20 μm.

Figure 9

Molecular docking model for ATX (green and stick) with the active site of the ATP pocket of p38 alpha and the p38 alpha with the p38 inhibitor PH797804. (A) The whole picture of the molecular docking model for ATX with the p38 alpha. (B) Molecular docking model for ATX with the p38 alpha. Highlighting the hydrogen bonds (red dashed lines) coordination between the oxygen atoms in ATX and residues Glu-71 and Arg-49. (C) Molecular docking model for p38 MAPK with p38 MAPK inhibitor PH797804 binding pocket. The red color bonds indicate hydrogen bonds.

Figure 10

Schematic figure of the treatment protocol (n = 12).