Ascorbic acid attenuates activation and cytokine production in sepsis-like monocytes

Abstract

Objective To investigate the effects of high dose ascorbic acid (AA) on monocyte polarization and cytokine production in vitro Design Experimental in vitro study of cells from healthy subjects and patients with sepsis Setting University research laboratory and academic hospital Subjects Six healthy controls and three patients with sepsis Interventions Monocytes were isolated from whole blood of healthy donors (n=6) and polarized in vitro for 48hrs using LPS or LTA. Polarization was confirmed by surface marker expression using flow cytometry. As a comparison, monocytes were also isolated from septic patients (n=3) and analyzed for polarization markers. The effect of AA on monocyte polarization was evaluated. As a functional assay, AA-treated monocytes were analyzed for cytokine production of TNF and IL-8 by intracellular staining and flow cytometry following activation with LPS or LTA. Measurements and Main Results Both LPS and LTA induced polarization in healthy monocytes in vitro, with increased expression of both pro- (CD40 and PDL1, p<0.05) and anti-inflammatory (CD16 and CD163, p<0.05) polarization markers, with non-significant effects on CD86 and CD206. This pattern resembled, at least partly, that of monocytes from septic patients. Treatment with AA significantly inhibited the upregulation of surface expression of CD16 and CD163 (p<0.05) in a dose dependent manner, but not CD40 or PDL-1. Finally, AA attenuated LPS or LTA-induced cytokine production of IL-8 and TNF in a dose-dependent manner (both p<0.05). Conclusions AA inhibits upregulation of anti-, but not pro-inflammatory related markers in LPS or LTA polarized monocytes. Additionally, AA attenuates cytokine production from in vitro polarized monocytes, displaying functional involvement. This study provides important insight into the immunological effects of high dose AA on monocytes, and potential implications in sepsis.