Glucopyranoside flavonoids isolated from leaves of Spinacia oleracea (spinach) inhibit the formation of advanced glycation end products (AGEs) and aldose reductase activity (RLAR)

Abstract

Background and purpose: The formation and accumulation of advanced glycation end products (AGEs) and rat lens aldose reductase (RLAR) generated in the glycation process play an outstanding role in the complications of diabetes. Owing to the adverse effects of AGEs on diabetic patients, the search for new anti-AGE agents from plants without side effects has had significant interest from the researchers in the last decades for the development of a therapy that improves diabetic complications. Spinach could reverse the formation of AGEs and RLAR. This study aimed to investigate the ability of 10 known glucopyranosides flavonoids isolated from Spinacia oleracea on the formation of AGEs and RLAR in vitro and in vivo experiments.

Materials and methods: Methanol extract of leaves of spinach was subjected to bioassay-guided fractionation using to silica gel column chromatographic followed by gel filtration by Sephadex LH-20. BSA glucose system and in vitro bioassays using rat lens aldose reductase (RLAR) were employed to evaluated inhibitory activity on the formation of AGEs. The induced diabetes in zebrafish by immersing in a 111 mM glucose solution for 14 days, revealed increased glycation of proteins in the eyes. Measurements of glycated hemoglobin and fructosamine were used to verify the anti-AGEs effect of the isolated flavonoids.

Key results: Through bioassay-guided fractionation of methanol extract of leaves spinach, ten known glucopyranoside flavonoids (1-10) have been isolated, and spectroscopic studies established their structures. Among the isolated compounds are: patuletin-3-O-(2"-coumaroylglucosyl)-(1→6)-[apiosyl-(1→2)]- β-d-glucopyranoside (7), patuletin 3-O-(2"-feruloyl glucosyl)-(1→6)-[apiosyl-(1→2)]- β-d-glucopyranoside (8), they have shown potent inhibition on AGEs formation, stronger than the positive controls used in the different experiments.

Conclusion and implications: The findings indicated that glucopyranoside flavonoids found in Spinacia oleracea might have therapeutic potential for decreasing protein glycation, and might ameliorate AGE-related diabetic complications.

Keywords: Aldose reductase; Glucopyranosides flavonoids; Glycation; Spinacia oleracea; Zebrafish.