Effect of Environmental Conditions on the α-Glucosidase Inhibitory Activity of Mulberry Leaves

Abstract

Mulberry leaves have been used as the sole food for silkworms in sericulture, and also as a traditional medicine for diabetes prevention. Mulberry leaf components, for example 1-deoxynojirimycin (1-DNJ), inhibit the activity of -glucosidase and prevent increased blood glucose levels, and they are highly toxic to caterpillars other than silkworms. The -glucosidase inhibitory activity of mulberry leaves changes with the season, but it is unknown which environmental conditions influence the -glucosidase inhibitory activity. We investigated in this study the relationship between the -glucosidase inhibitory activity and environmental conditions of temperature and photoperiod. The results demonstrate that low temperatures induced decreasing -glucosidase inhibitory activity, while the induction of newly grown shoots by the scission of branches induced increasing -glucosidase inhibitory activity. These results suggest that the -glucosidase inhibitory activity was related to the defense mechanism of mulberry plants against insect herbivores. Key words:-glucosidase inhibitor; 1-deoxynojirimycine; mulberry; resistance to insect herbivore Mulberry leaves have been historically used as feed for silkworms and consumed as a beverage or health food by humans. Mulberry leaf components inhibit the activity of a kind of digestive enzyme for sugar absorption, -glucosidase, and promote slow absorption of glucose into the blood vessels. [1][2][3] The most important substance in mulberry leaves, 1-deoxynojirimycin (1-DNJ), is known to be a strong intestinal -glucosidase inhibitor. Mulberry leaves contain 1-DNJ, 4) so that mulberry leaf products have been commercialized as health foods.In contrast, mulberry leaves are highly toxic to caterpillars other than the silkworm, Bombyx mori, because they contain 1-DNJ and other -glucosidase inhibitors that affect common insects. 5,6) The silkworm has evolved adaptive enzymes to circumvent the toxic effects of -glucosidase inhibitors and made it able to feed on mulberry leaves. 6,7) 1-DNJ and the -glucosidase inhibitor from mulberry leaves are therefore used to both improve the symptoms of diabetes mellitus, and to avoid caterpillars by inhibiting growth.Mulberry plants are distributed throughout the world, the number of mulberry cultivars in Japan alone being over 1,000. These cultivars match the climatic characteristics in various areas. The typical cultivars of mulberry plants are maintained and administered in Japan at the National Institute of Agrobiological Sciences (Tsukuba, Ibaraki, Japan) and the Experimental Farm of Textile Science and Technology of Shinshu University (Ueda, Nagano, Japan). It has been reported that the -glucosidase inhibitory activity and 1-DNJ concentration of mulberry leaves differ among various cultivars and seasons, [8][9][10][11] but it is unknown which environmental conditions influence the -glucosidase inhibitory activity. We therefore investigated in this study the relationship between the environmental conditions and -glucosidase inhibitory activity. Materia...

Seasonal Changes in Functional Component Contents in Mulberry (<i>Morus alba</i> L.) Leaves

“…However, the correlation coefficients with total temperature in their study were high at r = 0.92 (P = 0.02) in 2009 and r = 0.80 (P = 0.04) in 2010, suggesting a similar trend to the present study (data not shown). Kimura et al (2007) and Nakanishi et al (2011) reported that the DNJ contents in leaves peaked in August, and were affected by temperature. In our study, the DNJ contents in mulberry leaves increased slightly from late May to mid-July, peaked in August, and then decreased sharply after late August.…”

“…Consequently, we hypothesized that the harvest time may also affect the functional component concentrations in mulberry leaves. Kimura et al (2007) and Nakanishi et al (2011) reported that the contents of DNJ and α-glucosidase inhibitors increased in August, the hottest month of the year. In terms of polyphenol contents in mulberry leaves, Lee and Choi (2012) reported that the chlorogenic acid and flavonols contents were highest in May when leaves were harvested three times per year (in May, July, and September), although their results did not document seasonal changes in chlorogenic acid and flavonols contents.…”

A Comparison of Food-grade Folium mori Extract and 1-Deoxynojirimycin for Glycemic Control and Renal Function in Streptozotocin-induced Diabetic Rats

“…[2324] Among the proposed hypoglycemic FM components, 1-DNJ is one of the mostly studied compounds due to its α-glucosidase inhibitory role which is well established. [1625] Subsequently, a great effort has been made to improve the yield of 1-DNJ from natural resources such as the mulberry leaf and other microorganisms. [17] The present study reported the anti-diabetic activity of a commercial FM product to be effective at a dose as low as 1 mg/kg, which is equivalent to 10 mg/kg dried white mulberry (桑白皮 Sāng Bái Pí) leaf and is a much lower dose than what has been previously reported.…”

“…[151617] Studies on human beings have revealed that a 1-DNJ–enriched FM preparation is an effective hypoglycemic agent in control and type 2 DM patients. [918] However, a limited number of studies have been conducted on the hypoglycemic activity of purified 1-DNJ in diabetic animals.…”

Anti-hyperlipidemic effect of soybean extract fermented byBacillus subtilisMORI indb/dbmice

“…Despite the anti-obesity effects, some critical adverse effects of these medications such as gastro-intestinal effects [14], increases in blood pressure and pulse rate [15], and increased incidence of mood-related disorder are reported [16]. …”