Bilirubin Induces Pain Desensitization in Cholestasis by Activating 5-Hydroxytryptamine 3A Receptor in Spinal Cord

Erliang Kong; Hongqian Wang; Xiaoqiang Wang; Yan Zhang; Jinmin Zhang; Weifeng Yu; Xudong Feng; Yuming Sun; Feixiang Wu

doi:10.3389/fcell.2021.605855

Bilirubin Induces Pain Desensitization in Cholestasis by Activating 5-Hydroxytryptamine 3A Receptor in Spinal Cord

Front Cell Dev Biol. 2021 Apr 1:9:605855. doi: 10.3389/fcell.2021.605855. eCollection 2021.

Authors

Erliang Kong^{1

2}, Hongqian Wang^{1

3}, Xiaoqiang Wang⁴, Yan Zhang⁵, Jinmin Zhang¹, Weifeng Yu⁴, Xudong Feng², Yuming Sun¹, Feixiang Wu⁶

Affiliations

¹ Department of Anesthesiology, Shanghai Eastern Hepatobiliary Surgery Hospital, Naval Medical University, Shanghai, China.
² Department of Anesthesiology, The 988th Hospital of Joint Logistic Support Force of PLA, Zhengzhou, China.
³ Department of Anesthesiology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, China.
⁴ Department of Anesthesiology, Renji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
⁵ Department of Anesthesiology, Zhejiang Province Zhoushan Hospital, Zhoushan, China.
⁶ Department of Critical Care Medicine, Shanghai Eastern Hepatobiliary Surgery Hospital, Naval Medical University, Shanghai, China.

Abstract

Background: Cholestasis patients often suffer from pain desensitization, resulting in serious complications in perioperative period. This study was aim to investigate the mechanism of bilirubin in cholestasis mediating pain desensitization through 5-hydroxytryptamine 3A (5-HT_3A ) receptor activation in spinal dorsal horn (SDH).

Methods: A cholestasis model was established by bile duct ligation (BDL) in rats. Pain thresholds of rats were measured after BDL or intrathecally injecting bilirubin in the presence or absence of agonist (mCPBG) and antagonists (ondansetron, bicuculline, or CGP55845). Expression of 5-HT₃ receptors, and the affinity and binding mode of bilirubin to 5-HT_3A receptor were determined. Effects of bilirubin on γ-aminobutyric acid (GABA) pathway and the interactions with 5-HT_3A receptor were tested.

Results: Bilirubin was elevated significantly in both serum and CSF in BDL rats, accompanied with the up-regulation of pain thresholds. Both of 5-HT_3A receptor and GABA _A receptor antagonists could reverse the increased pain threshold in BDL rats. Further, 5-HT_3A and GABA _A receptor expressions were increased in BDL rats or intervention with bilirubin. Molecular docking suggested that bilirubin entered the hydrophobic pocket pre-formed in 5-HT_3A receptor with potential hydrogen bonding. Bilirubin also increased GABA concentrations in CSF and GABAergic spontaneous inhibitory postsynaptic current in spinal cord, and directly induced inward currents in HEK293 cells which were overexpressed 5-HT_3A receptor by lentivirus.

Conclusion: In conclusion, bilirubin induced pain desensitization in cholestasis by activating 5-HT_3A receptor in spinal cord. The activation of 5-HT_3A receptor might regulate pain threshold by acting on the GABA pathway.

Keywords: 5-HT3A receptor; GABA; bilirubin; cholestasis; pain desensitization.