Antioxidant and aldose reductase inhibitory capacities of Tephrosia humilis aerial parts' extracts

Tephrosia humilis (Leguminosae), is a tropical shrub endemic in central Africa. Species of this genus are used in traditional remedies as antimicrobial, tonic, diuretic, anthelminthic, blood purifier etc [1,2]. Phytochemical analysis of other Tephrosia species resulted in the isolation of coumarins, and several flavonoids [3–9]. The aim of this study was the evaluation of the antioxidant capacity of several plant extracts of Tephrosia humilis (DPPH assay and Co(II)/EDTA -induced luminol chemiluminescence test), as well as their ability to inhibit the aldose reductase enzyme (AR, ALR2, E.C. 1.1.1.21), indicating a potential of this plant to act against the long term diabetic complications [10,11]. After defatting, plant material was extracted in a soxhlet apparatus with methanol and the dry remaining was partitioned with solvents of increasing polarity, giving five different fractions (diethyl ether, ethyl acetate, ethyl acetate residue, n-butanol, water). Antioxidant results according to both tests proved the good antioxidant capacity of the ethyl acetate fraction in comparison to the standards used (trolox and quercetin) [12]. While according to the CL test all other fractions showed low hydroxyl radical scavenging ability, DPPH test results proved that the n-butanolic and ethyl acetate residue fractions are also effective radical scavengers. As about the ALR2 inhibition, all fractions, except the aqueous, were strong inhibitors at the concentration of 25µg/ml in comparison to sorbinil. The n-butanolic and the ethyl acetate fractions inhibited the enzyme above 75%. This research work proves in vitro the good antioxidant capacity of Tephrosia humilis extracts, as well as their strong inhibitory activity against ALR2 enzyme.

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