Abstract:
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.
Introduction
Cataract, the leading cause of blindness worldwide, is associated with several risk factors, a major one of which is considered to be diabetes. Various pharmacological intervention strategies aimed at the prevention of diabetes are currently being investigated. Among these, aldose reductase inhibitors (ARIs) have received considerable attention owing to the proposed involvement of aldose reductase (AR) in the pathophysiology of diabetic complications, including cataract [1]. A vast literature exists demonstrating that cataract progression can be slowed or prevented by the use of natural therapies, and particularly by the use of plants having high flavonoid contents, which have exhibited considerable in vivo AR inhibitory effects [2].
Litchi (Litchi chinensis Sonn., Sapindaceae) is a tropical to subtropical crop that originated in South-East Asia. With the gradual consumer acceptance of litchi fruits for their delicious taste and attractive red skin, there has been a steady increase in litchi production over recent decades, with increasing exports into Europe and North America from production areas in both the Southern and Northern hemispheres. Litchi fruit pericarp (LFP) accounts forapproximately 15% by weight of the whole fresh fruit and comprises significant amounts of flavonoids. Consequently, litchi LFP tissues may be a potentially important source of AR-inhibiting compounds [3]. Previous pharmacological and phytochemical studies on litchi have revealed the fruit to be a rich source of anthocyanins [4] and several flavone glycosides [5]. Duan et al. (2007) reported that anthocyanins from LFP tissues strongly inhibited linoleic acid oxidation and exhibited a dose-dependent free-radical scavenging activity against diphenylpicrylhydrazyl (DPPH) radicals, superoxide anions, and hydroxyl radicals. Wang et al. [6] reported that an LFP extract exhibited potential in vitro and in vivo anticancer activity against hepatocellular carcinoma. Furthermore, the LFP extract exhibited a dose-dependent, time-inhibitory effect on cancer cell growth. The anticancer activity of LFP water-soluble crude ethanolic extract might result, at least in part, from the inhibition of DNA synthesis, proliferation, and apoptosis induction in cancer cells [7].
However, the biological activity of LFP has not been investigated in detail. From this perspective, various inhibitors, such as the inhibitors of rat lens aldose reductase (RLAR), are presently being developed as novel potential therapeutic agents. Therefore, we have screened LFP for its ability to inhibit RLAR in vitro.
In our continuing search for the bioactive principles from crude plant extracts, we have evaluated the extracts and fractions of L. chinensis, particularly in relation to their inhibitory effects on RLAR. Here, the effects of compound isolate
