Aldose reductase inhibitors from Litchi chinensis Sonn.

Diabetes is one of the major risk factors for cataract. Aldose reductase has been reported to play an important role in sugar-induced cataract. In this study, we conducted pharmacological investigations upon experimental rat lenses using extracts of the fruits of Litchi chinensis (Sapindaceae). Of the extracts and organic fractions of L. chinensis tested, a MeOH extract and an EtOAc fraction were found to be potent inhibitors of rat lens aldose reductase (RLAR) in vitro--their IC(50) values being 3.6 and 0.3 microg/mL, respectively. From the active EtOAc fraction, four minor compounds with diverse structural moieties were isolated and identified as D-mannitol (1), 2,5-dihydroxybenzoic acid (2), delphinidin 3-O-beta-galactopyranoside-39,59-di-O-beta-glucopyranoside (3), and delphinidin 3-O-beta- galactopyranoside-39-O-beta-glucopyranoside (4). Among these, 4 was found to be the most potent RLAR inhibitor (IC(50) = 0.23 microg/mL), and may be useful in the prevention and/or treatment of diabetic complications.