Chrysin Attenuates Oxidative Stress to Alleviate Sevoflurane-Induced Cognitive Impairments in Aged Rats

Abstract

Objective: Anesthesia-induced cognitive impairments are common for elder patients after surgery. Oxidative stress is the predominant factor contributing to the impairments. This study was to assess the therapeutic potential of an anti-oxidative naturally occurring flavonoid, chrysin, in attenuating sevoflurane-induced cognitive impairments in rat models.

Methods: Rat models of cognitive impairments were constructed by exposing aged rats (18 months old) to sevoflurane for 2 h. Chrysin was administered via oral gavage at the dose of 25, 50, and 100 mg/kg/day for seven days. The elevated plus maze test was used to assess anxiety and explorative behaviors. Spatial memory tests were performed using novel object recognition test, object location memory task, and water maze experiments. Oxidative stress was evaluated by measuring levels of malondialdehyde, nicotinamide adenine dinucleotide phosphate, 4-hydroxynonenal, and glutathione using colorimetric assays. Quantitative real-time polymerase chain reaction and Western blot were used to analyze how chrysin affects nuclear factor E2-related factor (Nrf) signaling.

Results: While sevoflurane anesthesia led to significant decline in cognitive performance in object recognition test, object location memory task, and water maze test, chrysin exerted significant effects in alleviating the impairments. Oxidative stress was also reduced in the hippocampus tissue of rats after chrysin intake. Nrf signaling was activated by chrysin treatment in sevoflurane-induced cognitive impairment models.

Conclusion: Chrysin was effective in alleviating cognitive impairments induced by sevoflurane anesthesia, which was at least in part facilitated by its effects in reducing oxidative stress via activating Nrf signaling.

Keywords: Anesthesia; Chrysin; Cognitive impairment; Nrf signaling; Oxidative stress.

Figure 1.

Effects of chrysin on sevoflurane-induced anxiety in aged rats. (A) Chrysin decreased the time spent in center. (B) Chrysin increased the time spent on the open arms and the time spent in the distal parts of the open arms (C) as well as total distance traveled (D). N=10 rats for each group. Brown-Forsythe ANOVA followed Dunn’s multiple comparisons test. ^*p<0.05; ^**p<0.01; ^***p<0.001. Sev, sevoflurane; Ch25, chrysin 25 mg/kg/day; Ch50, chrysin 50 mg/kg/day; Ch100, chrysin 100 mg/kg/day.

Figure 2.

Effects of chrysin on sevoflurane anesthesia-induced cognitive impairments of aged rats, determined by novel object recognition (NOR) assay (A and B) and object location memory (OLM) task (C and D). The recognition index was calculated as the proportion of time with the target or novel object out of the total time. N=10 rats for each group. Brown-Forsythe ANOVA followed Dunn’s multiple comparisons test. ^*p<0.05; ^**p<0.01; ^***p<0.001. Sev, sevoflurane; Ch25, chrysin 25 mg/kg/day; Ch50, chrysin 50 mg/kg/day; Ch100, chrysin 100 mg/kg/day.

Figure 3.

Effects of chrysin on sevoflurane anesthesia-induced spatial learning and memory impairments of aged rats by Morris Water Maze test. The escape latencies (A) and the average swim speed (B) were recorded based on three training sessions. The time in the target quadrant (C) and the number of platform site crossings during 60 s of test (D) were recorded. N=10 rats for each group. Brown-Forsythe ANOVA followed Dunn’s multiple comparisons test. ^*p<0.05; ^**p<0.01; ^***p<0.001. Sev, sevoflurane; Ch25, chrysin 25 mg/kg/day; Ch50, chrysin 50 mg/kg/day; Ch100, chrysin 100 mg/kg/day.

Figure 4.

Effects of chrysin on sevoflurane anesthesia-induced oxidative stress in hippocampus of aged rats. Levels of MDA (A), NADPH oxidase activity (B), HNE levels (C) and GSH activity (D) in hippocampus among different groups were measured. N=10 rats for each group. Data were presented with mean±standard deviation. Brown-Forsythe ANOVA followed Dunn’s multiple comparisons test. ^*p<0.05; ^**p<0.01; ^***p<0.001. MDA, malondialdehyde; NADPH, nicotinamide adenine dinucleotide phosphate; HNE, hydroxynonenal; GSH, glutathione; Sev, sevoflurane; Ch25, chrysin 25 mg/kg/day; Ch50, chrysin 50 mg/kg/day; Ch100, chrysin 100 mg/kg/day.

Figure 5.

Nrf2 signal in hippocampus of aged rats after sevoflurane anesthesia upon chrysin treatment. The levels of Nrf2 (A), HO-1 (B) and NQO-1 (C) mRNAs in hippocampus of aged rats after sevoflurane anesthesia were tested by RT-qPCR. (D) The protein levels of Nrf2, HO-1 and NQO-1 in hippocampus of aged rats after sevoflurane anesthesia were measured using western blot. GAPDH was used as a loading control and the expressions were normalized to control (E-G). N=3 repeats for each group (10 tissue homogenates were mixed for each group). Brown-Forsythe ANOVA followed Dunn’s multiple comparisons test.^*p<0.05; ^**p<0.01; ^***p<0.001. Nrf2, nuclear factor E2-related factor 2; HO-1, heme oxygenase-1; NQO-1, NAD(P)H:quinone oxidoreductase-1; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; Sev, sevoflurane; Ch25, chrysin 25 mg/kg/day; Ch50, chrysin 50 mg/kg/day; Ch100, chrysin 100 mg/kg/day.