Dexmedetomidine attenuates sevoflurane‑induced neurocognitive impairment through α2‑adrenoceptors

Abstract

It has been reported that sevoflurane induces neurotoxicity in the developing brain. Dexmedetomidine is an α2 adrenoceptor agonist used for the prevention of sevoflurane‑induced agitation in children in clinical practice. The aim of the present study was to determine whether dexmedetomidine could prevent sevoflurane‑induced neuroapoptosis, neuroinflammation, oxidative stress and neurocognitive impairment. Additionally, the involvement of α2 adrenoceptors in the neuroprotective effect of dexmedetomidine was assessed. Postnatal day (P)6 C57BL/6 male mice were randomly divided into four groups (n=6 in each group). Mice were pretreated with dexmedetomidine, either alone or together with yohimbine, an α2 adrenoceptor inhibitor, then exposed to 3% sevoflurane in 25% oxygen. Control mice either received normal saline alone or with sevoflurane exposure. Following sevoflurane exposure, the expression of cleaved caspase‑3 was detected by immunohistochemistry in hippocampal tissue sections. In addition, the levels of tumor necrosis factor‑α (TNF‑α), interleukin (IL)‑1β, IL‑6 and malondialdehyde, as well as superoxide dismutase (SOD) activity in the hippocampus were measured. At P35, the learning and memory abilities were assessed in each mouse using a Morris water maze test. Dexmedetomidine significantly decreased the expression of activated caspase‑3 following sevoflurane exposure. Moreover, dexmedetomidine significantly decreased the levels of TNF‑α, IL‑1β and IL‑6 in the hippocampus. SOD activity also increased in a dose‑dependent manner in dexmedetomidine‑treated mice. MDA decreased in a dose‑dependent manner in dexmedetomidine‑treated mice. Lastly, sevoflurane‑induced learning and memory impairment was reversed by dexmedetomidine treatment. By contrast, co‑administration of yohimbine significantly attenuated the neuroprotective effects of dexmedetomidine. These findings suggested that dexmedetomidine exerted a neuroprotective effect against sevoflurane‑induced apoptosis, inflammation, oxidative stress and neurocognitive impairment, which was mediated, at least in part, by α2 adrenoceptors.

Keywords: dexmedetomidine; neuroapoptosis; sevoflurane; inflammation; oxidative stress; α2 adrenoceptor.

Figure 1.

Dexmedetomidine reverses sevoflurane-induced cognitive impairment. (A) Effects of Sevoflurane on mice escape latency. Postnatal day 35–41 mice exposed to 3% sevoflurane exhibit increased escape latency, and Sevoflurane induced mice administered dexmedetomidine with yohimbine show the similar results. (B) Effects of Sev, Sev + Dex, and Sev + Dex and Yoh. Postnatal day 36 mice exposed to 3% sevoflurane exhibit decreased platform crossing times. Sev-induced mice administered with Dexmedetomidine exhibited similar results. (C) Changes in the expression levels of the learning and memory marker CREB were detectable by western blotting after sevoflurane and dexmedetomidine treatment. n=6 in each group. *P<0.05 and **P<0.01 vs. NS + Air; ^#P<0.05 vs. Dex20 + Sev. Dex20, dexmedetomidine 20 µg/kg; Sev, sevoflurane; Yoh, yohimbine; NS, normal saline; CREB, cAMP response element-binding protein; p, phosphorylated.

Figure 2.

Dexmedetomidine reverses sevoflurane-induced neuroapoptosis. (A) Caspase-3 expression increased in mice exposed to 3% sevoflurane alone, compared with NS + Air. Dex20 treatment reduced sevoflurane-induced neuroapoptosis. Scale bar, 200 µm; (B) Apoptosis rate changes following dexmedetomidine (20 µg/kg) with air, Sev or Sev + Yoh treatment. n=6 in each group. PI/FITC. +/− (Q1), percentage of necrotic cells; PI/FITC +/+ (Q2), percentage of late apoptotic cells; PI/FITC −/− (Q3), percentage of viable cells; and PI/FITC −/+ (Q4), percentage of early apoptotic cells. *P<0.05, **P<0.01; ***P<0.001; ****P<0.0001 vs. NS + Air; ^#P<0.05 vs. Dex20 + Sev. Dex20, dexmedetomidine 20 µg/kg; Sev, sevoflurane; Yoh, yohimbine; NS, normal saline; PI, propidium iodide.

Figure 3.

Dexmedetomidine attenuates sevoflurane-induced proinflammatory cytokine secretion (A) IL-1β, (B) IL-6 and (C) TNF-α release. n=6 in each group. *P<0.05 vs. NS + Air; ^#P<0.05 vs. Dex20 + Sev. Dex5/10/20, dexmedetomidine 5, 10 or 20 µg/kg; Sev, sevoflurane; Yoh, yohimbine; NS, normal saline; IL, interleukin; TNF-α, tumor necrosis factor-α.

Figure 4.

Dexmedetomidine attenuates sevoflurane-induced oxidative stress. (A) MDA and (B) SOD levels detected using ELISA following dexmedetomidine treatment in sevoflurane-induced mice. n=6 in each group. *P<0.05 vs. NS + Air; ^#P<0.05 vs. Dex20 + Sev. Dex5/10/20, dexmedetomidine 5, 10 or 20 µg/kg; Sev, sevoflurane; Yoh, yohimbine; NS, normal saline; MDA, malondialdehyde; SOD, superoxide dismutase.