| 1-Deoxynojirimycin (DNJ) is naturally-occurred alkaloid with promising physiological activities in vivo (i.e., inhibition of intestinal a-glucosidase) (1). The compound is a D-glucose analogue, in which the pyranose ring oxygen is replaced by nitrogen (Fig. 1). In 1976, DNJ was isolated from mulberry tree (Morus alba) for the first time. This DNJ isolation prompted the concept that dietary mulberry DNJ might be beneficial for the suppression of abnormally high blood glucose levels, thereby preventing diabetes.
Fig. 1. Chemical strucuture of 1-deoxynojirimycin (DNJ).
Various mulberry products (i.e., tea, powder and tablet) have been now commercially available in Japan and many countries. These products appeal the bioavailability of DNJ, but their DNJ contents are not specified because of lack of method to measure DNJ. Kimura et al. have therefore previously developed a method for determining DNJ by hydrophilic interaction chromatography with evaporative light scattering detection (HILIC-ELSD) (2, 3) (Fig. 2). Using HILIC-ELSD, it was confirmed that DNJ contents in mulberry products are relatively low as about 0.1 % (100 mg/100 g dry product), and, surprisingly, there are some products with a trace amount of DNJ (less than 0.05 %) (Table 1). Development of DNJ-enriched product is therefore desired. Pharmacological administration of DNJ-enriched product may be a promising therapeutic approach for diabetes prevention.
Fig. 2. HILIC-ELSD/MS analysis of 1-deoxynojirimycin (DNJ) present in mulberry leaves. A, ELSD chromatogram. B, Single ion plot of the mass corresponding to the [M+H]+ ion of DNJ (m/z 164.1). C, MS spectrum of the peak detected at 24.5 min in the chromatogram B. Leaf extract from Kairyonezumikaeshi, a popular mulberry cultivar in Japan, was analyzed by HILIC-ELSD/MS following optimal conditions; column TSKgel Amide-80 (4.6 × 250 mm); mobile phase, a mixture of acetonitrile and distilled water (81:19; containing 6.5 mM ammonium acetate; pH 5.5); flow rate, 1 mL/min; column temperature, 40oC.
In order to develop DNJ-enriched product, DNJ concentrations in mulberry leaves obtained from different cultivars, harvest seasons and harvest regions were determined and compared by HILIC-ELSD, and mulberry leaves containing the higher level of DNJ were selected. As results, it was found that young mulberry leaves from top part of branch contain relatively high amount of DNJ (0.2-0.5%). After optimization of harvesting, drying and extraction processes of mulberry leaves, food-grade mulberry powder enriched with DNJ (1.0%) could be successfully produced. Human studies indicated that the developed DNJ-enriched powder has an effect of lowering blood-sugar level. Therefore, the DNJ-enriched product may be used therapeutically in the oral treatment of the non-insulin-dependent diabetes mellitus (type 2 diabetes). This possibility is now being investigated in clinical studies, to obtain approval of “Food for Specified Health Use (FOSHU)” status in Japan.
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References
1. Watson, A.A., Fleet, G.W.J., Asano, N., Molyneux, R.J., and Nash, R.J., Polyhydroxylated alkaloids-natural occurrence and therapeutic applications. Phytochemistry, 56, 265?295 (2001)
2. Kimura, T., Nakagawa, K., Saito, Y., Yamagishi, K., Suzuki, M., Yamaki, K., Shinmoto, H., and Miyazawa, T., Determination of 1-deoxynojirimycin in mulberry leaves using hydrophilic interaction chromatography with evaporative light scattering detection. J. Agric. Food Chem., 52, 1415-1418 (2004)
3. Kimura, T., Nakagawa, K., Saito, Y., Yamagishi, K., Suzuki, M., Yamaki, K., Shinmoto, H., and Miyazawa T., Simple and rapid determination of 1-deoxynojirimycin in mulberry leaves. Biofactors, 22, 341-345 (2004)
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