Citrus aurantifolia (Christm.) Swingle (lime) Fruit Extract Inhibits the Activities of Polyol Pathway Enzymes

Abstract

Diabetes mellitus is associated with several complications, which may result from one or more factors including increased flux of polyol pathway. This study evaluated the inhibitory potential of four citrus fruits namely Citrus paradisi Macfad. (grape), Citrus limon (L.) Osbeck (lemon), Citrus aurantifolia (Christm.) Swingle (lime) and Citrus sinensis (L.) Osbeck (orange), on the activities of aldose reductase and sorbitol dehydrogenase – the two enzymes that mediate the polyol pathway. This is determined by incubating citrus extracts with appropriate enzymes and substrates. Fruit extract with the lowest half maximal inhibitory concentration (IC50) was used to assess the mode of inhibition of the enzymes by preparing Lineweaver–Burk plot. Citrus fruits tested inhibited sorbitol dehydrogenase more than aldose reductase, which resulted in lowered IC50 values. Of all the citrus fruits tested, lime fruit extract displayed potent inhibition of aldose reductase (IC50: 138.66 μg/mL) and sorbitol dehydrogenase (IC50: 47.21 μg/mL). Kinetic studies also revealed that lime fruit extract inhibited the activities of both enzymes in a competitive manner. In conclusion, the inhibition of the polyol pathway enzymes by the lime fruit extract may be attributed to the presence of phytochemicals such as flavonoids and limonoids.