Apple Leaf Extract as a Potential Candidate for Suppressing Postprandial Elevation of the Blood Glucose Level

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While the industrial value of fruits has long been recognized, only recently have the leaves of fruit trees been considered to have immense and mostly-untapped potential. In the present study, the physiological effects of apple leaf extract in mice were investigated. In addition, we sought to elucidate the active principle(s) and examined its potential for application. Apple leaf extract suppressed postprandial elevation of the blood glucose level and increased the residual amount of glucose in the small intestine in glucose-loaded mice compared with those in control mice. Bioassay-guided fractionation led to an active component that was identified as phloridzin, a known SGLT inhibitor, based on an analysis of its spectral data. With regard to an anti-hyperglycemic effect, extraction with ethanol from leaves of apple tree gave the best results. These effects decreased with heating during the extraction procedure. Since bolus ingestion of the extract did not affect blood glucose levels in normal mice with or without an overnight fast, the inhibitory effects on glucose absorption were not considered to be associated with unspecific gastrointestinal impairment and the extract did not cause hypoglycemia at a normally effective dose. Therefore, the leaf parts of apple tree may be a promising candidate as an industrial resource for maintaining good health in the future.