Equol, a soybean metabolite with estrogen-like functions, decreases lipopolysaccharide-induced human neutrophil extracellular traps in vitro

Abstract

Objective Neutrophil extracellular traps (NETs) defend against acute infections. However, their overexpression causes organ failure during sepsis. Control of NET formation may improve the outcomes of patients with sepsis. Equol, a soybean isoflavone, is a female hormone analog, which prevents inflammation. We evaluated the effects of equol on NET formation in human neutrophils during inflammatory stimulation in vitro. Methods Healthy volunteers provided blood samples. An enzyme-linked immunosorbent assay (ELISA) assessed serum equol concentrations. NET formation in neutrophils was induced by lipopolysaccharide (LPS) treatment. ELISA quantified DNA-binding elastase, and immunostaining assessed NET formation. Reverse-transcription quantitative PCR and western blotting detected G-protein-coupled receptor 30 (GPR30) or peptidyl arginine deiminase 4 (PAD4) expression. Flow cytometry assessed neutrophil phagocytic ability with inactivated Escherichia coli. Results In neutrophils derived from males with low-serum equol levels (low-serum equol group), equol significantly decreased DNA-binding elastase levels and NET formation. Equol did not decrease NETs in neutrophils from males with high-serum equol levels. GPR30 expression of neutrophils was higher in the low-serum than in the high-serum equol group. PAD4 mRNA levels and nuclear PAD4 protein expression also decreased than the vehicle control in the low-serum equol group. Equol did not alter the phagocytic ability of neutrophils. In neutrophils from young females, equol had no inhibitory effect on NET formation. Conclusions Equol decreases LPS-induced NET formation in neutrophils from males via inhibition of PAD4 expression. Our findings provide a rationale for investigating a new therapeutic approach using equol to control neutrophil activity during sepsis.