Effect of betaine on hepatic insulin resistance through FOXO1-induced NLRP3 inflammasome.

In the present study, we attempted to elucidate whether molecular modulation of inflammation by betaine through the forkhead box O1 (FOXO1)-induced NLRP3 inflammasome improves insulin resistance. Betaine is a major water-soluble component of Lycium chinense. It mainly functions as an oxidative metabolite of choline by suppressing superoxide-induced free radicals by donating methyl groups. The FOXO1 transcription factor regulates various genes involved in cellular metabolic processes related to cell death as well as oxidative stress responses through binding to the thioredoxin-interacting protein (TXNIP). Betaine is known to inhibit FOXO1 phosphorylation through phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) in liver cells exposed to insulin. To elucidate the molecular mechanism of inactivation of insulin-induced FOXO1 by the antioxidant betaine, we used HepG2 cells and the liver of db/db mice treated with betaine at a dose of 50 mg/kg/day for 3 weeks. We found that the activation of NLRP3 inflammasome genes was reduced by betaine, which resulted in the suppression of reactive species (RS) production in liver cells. In addition, betaine inhibited insulin-induced PI3K/AKT and FOXO1 activation. Therefore, betaine suppressed the cytokine interleukin-1β production by inhibiting the activation of the NLRP3 inflammasome via interaction of FOXO1 and TXNIP. Our results suggest that betaine inhibits the FOXO1 binding to TXNIP, leading to the suppression of RS-induced NLRP3 inflammasome activation in a diabetic liver.