NMR and proteomic analysis of Cornus officinalis extract reveals abundance of 5-hydroxymethylfurfural and induced expression of Nrf2 and superoxide dismutase-2 in 1.1B4 human pancreatic β-cells and murine islets

Abstract

We aimed to identify and isolate the metabolically active compounds from Cornus officinalis (C. officinalis) that underlie the biological effects previously observed in our in vitro and in vivo studies. Our prior findings demonstrated that C. officinalis promoted activation of the Keap1/Nrf2 pathway in a pancreatic β-cell line and delayed the onset of type 1 diabetes (T1D) in non-obese diabetic (NOD) mice. To characterize the metabolically active compounds within C. officinalis, the concentrated extract was fractionated by column chromatography, and evaluated for their effect on β-cell metabolic activity and expression of Nrf2 targets such as heme oxygenase-1 (HO1) and superoxide dismutase 2 (SOD2). Highly concentrated compounds of interest within metabolically active fractions were isolated using high performance liquid chromatography (HPLC). Elucidation of a highly abundant compound within C. officinalis extract was identified by mass spectrometry and nuclear magnetic resonance (NMR) as 5-hydroxymethylfurfural (5-HMF) which was demonstrated by immunoblotting to significantly increase SOD2 expression. Quantitative proteomics was performed on 5-HMF treated murine non-obese diabetic (NOD) islets and revealed increased expression of Nrf2 and downstream targets such as SOD2, GSTA3, GSTA4 and GCLC. Our findings suggest that 5-HMF is a highly abundant and metabolically active compound within C. officinalis that stimulates partial activation of the Keap1/Nrf2 pathway.