Apple leaf extract as a potential candidate for suppressing postprandial elevation of the blood glucose level.

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.

Peach leaf contains multiflorin a as a potent inhibitor of glucose absorption in the small intestine in mice.

Peach leaf extract has anti-hyperglycemic effects on the postprandial blood glucose level in glucose-loaded mice. In our previous study, the mechanism of action was considered to be the inhibition of glucose absorption in the small intestine. To elucidate the active principle in peach leaf, purification of the active compound and a structure determination were performed. With the use of bioassay-guided fractionation using glucose-loaded mice, the acetylated kaempferol glycoside multiflorin A (MFA), a potent inhibitor of glucose absorption from the intestine, was isolated from the MeOH extract of leaf of the edible peach Prunus persica. The structure was identified by HPLC using thiazolizine derivatives and by an analysis of its spectral data. The inhibitory effect of MFA against glucose absorption was demonstrated in the dose dependent manner in mice. However, as the deacetylated analog of MFA, multiflorin B did not show the activity at the in vivo, the activity of MFA was suggested to depend on the acetyl group on the sugar moiety. This is the first report of anti-hyperglycemic activity of MFA in peach leaf extract. MFA may be useful in functional foods or medicines for preventing the postprandial absorption of glucose in hyperglycemia.

Suppressive effect of peach leaf extract on glucose absorption from the small intestine of mice.

The crude extract of peach leaves dose-dependently suppressed the postprandial elevation in the blood glucose level after an oral administration of soluble starch to mice. This study examines the mechanism for this suppressive effect in vivo. An oral carbohydrate-loading test on mice showed that the peach leaf extract suppressed the glucose-induced increase in the blood level of glucose, but without affecting the insulin level. An enteral soluble starch and glucose loading test on mice also showed that the crude extract (1,000 mg/kg) significantly suppressed the postprandial elevation of the blood glucose level and increased the amount of glucose that remained in the intestine to within the same range as that with phloridzin (500 mg/kg), a natural sodium-dependent glucose transporter (SGLT)-specific inhibitor. In contrast, the extract did not suppress the postprandial elevation of the blood triglyceride and cholesterol levels in mice, and did not affect the normal blood glucose level in a feeding test for 21 d. These results reveal that the extract of peach leaves suppressed the postprandial elevation of blood glucose level by inhibiting the absorption of glucose in the small intestine of mice.

Anti-inflammatory effects of seeds of the tropical fruit camu-camu (Myrciaria dubia).

The methanolic extract of seeds of the tropical fruit camu-camu was screened for its anti-inflammatory activity in carrageenan-induced paw edema model mice. The extract significantly suppressed both the formation of edema in mice by oral administration and the release of nitric oxide from macrophage-derived RAW 264.7 cells in vitro. Based on the results of a spectroscopic analysis, the active compound was identified by in vivo bioassay-guided fractionation to be 3ß-hydroxy-lup-20(29)-en-28-oic acid, betulinic acid, known as an anti-inflammatory triterpenoid. These findings suggest that camu-camu seed extract is a potentially useful material as a source of betulinic acid and as a functional food for prevention of immune-related diseases.

Anti-hyperglycemic activity of kiwifruit leaf (Actinidia deliciosa) in mice.

The methanol extract of kiwifruit leaf suppressed the postprandial blood glucose level after an oral administration of soluble starch or sucrose in mice. The mechanism of action is proposed to be due to the alpha-amylase-inhibiting activity in the 90% aqueous methanol fraction and alpha-glucosidase-inhibiting activity in the n-buthanol fraction, based on the results of in vitro experiments.