Kinetic analysis of inhibition of α-glucosidase by leaf powder from Morus australis and its component iminosugars.

Mulberry leaves contain iminosugars, such as 1-deoxynojirimycin (1-DNJ), fagomine, and 2-O-α-D-galactopyranosyl deoxynojirimycin (GAL-DNJ) that inhibit α-glucosidase. In this study, we quantified iminosugars in Morus australis leaves and made the kinetic analysis in the hydrolysis of maltose by α-glucosidase. By LC-MS/MS, the concentrations of 1-DNJ, fagomine, and GAL-DNJ in the powdered leaves were 4.0, 0.46, and 2.5 mg/g, respectively, and those in the roasted ones were 1.0, 0.24, and 0.73 mg/g, respectively, suggesting that the roasting process degraded iminosugars. Steady-state kinetic analysis revealed that the powdered and roasted leaves exhibited competitive inhibition. At pH 6.0 at 37ºC, the IC50 values of the extracts from the boiled powdered or roasted leaves were 0.36 and 1.1 mg/mL, respectively. At the same condition, the IC50 values of 1-DNJ, fagomine, and GAL-DNJ were 0.70 µg/mL, 0.18 mg/mL, and 2.9 mg/mL, respectively. These results suggested that in M. australis, 1-DNJ is a major inhibitor of α-glucosidase. ABBREVIATIONS: 1-DNJ: 1-deoxynojirimycin; GAL-DNJ: 2-O-α-D-galactopyranosyl-DNJ.

Seasonal variations of iminosugars in mulberry leaves detected by hydrophilic interaction chromatography coupled with tandem mass spectrometry.

A rapid, sensitive, and validated method was developed for the simultaneous determination of four iminosugars, 1-deoxynojirimycin (DNJ), d-fagomine (FAG), 2-O-a-d-galactopyranosyl-DNJ (Gal-DNJ), and 4-O-ß-d-glucopyranosyl-fagomine (Glu-FAG), in mulberry leaves. The method used hydrophilic interaction chromatography coupled with tandem mass spectrometry. Based on this method, the seasonal variations of iminosugars in the leaves of different mulberry species (Morus alba, Morus multicaulis Perr, Morus atropurpurea Roxb. and Morus wittiorum Hand-Mazz.) collected in Guangzhou, China, during 10 consecutive months in 2013 were investigated. The results indicated that the maximum content of DNJ in the leaves of all four species occurred in summer (June or July). The highest FAG level was found in spring (April or May). The highest levels of Gal-DNJ and Glu-FAG were recorded in autumn (September or October).

Advances in the analysis of iminocyclitols: Methods, sources and bioavailability.

Iminocyclitols are chemically and metabolically stable, naturally occurring sugar mimetics. Their biological activities make them interesting and extremely promising as both drug leads and functional food ingredients. The first iminocyclitols were discovered using preparative isolation and purification methods followed by chemical characterization using nuclear magnetic resonance spectroscopy. In addition to this classical approach, gas and liquid chromatography coupled to mass spectrometry are increasingly used; they are highly sensitive techniques capable of detecting minute amounts of analytes in a broad spectrum of sources after only minimal sample preparation. These techniques have been applied to identify new iminocyclitols in plants, microorganisms and synthetic mixtures. The separation of iminocyclitol mixtures by chromatography is particularly difficult however, as the most commonly used matrices have very low selectivity for these highly hydrophilic structurally similar molecules. This review critically summarizes recent advances in the analysis of iminocyclitols from plant sources and findings regarding their quantification in dietary supplements and foodstuffs, as well as in biological fluids and organs, from bioavailability studies.

Analysis of iminosugars and other low molecular weight carbohydrates in Aglaonema sp. extracts by hydrophilic interaction liquid chromatography coupled to mass spectrometry.

A method by hydrophilic interaction liquid chromatography coupled to tandem mass spectrometry (HILIC-MS(2)) has been successfully developed for the simultaneous analysis of bioactive iminosugars and other low molecular weight carbohydrates in Aglaonema leaf extracts. Among other experimental chromatographic conditions, mobile phase eluents, additives and column temperature were evaluated in terms of retention time, resolution, peak width and symmetry provided for target carbohydrates. In general, narrow peaks (wh: 0.2-0.6min) with good symmetry (As: 0.9-1.3) and excellent resolution (Rs>1.8) were obtained for iminosugars using an acetonitrile:water gradient with 5mM ammonium acetate in both eluents at 55°C. Tandem mass spectra were used to confirm the presence of previously detected iminosugars in Aglaonema extracts and to tentatively identify for the first time others such as miglitol isomer, glycosyl-miglitol isomers and glycosyl-DMDP isomers. Concentration of total iminosugars varied from 1.35 to 2.84mgg(-1) in the extracts of the different Aglaonema samples analyzed. To the best of our knowledge, this is the first time that a HILIC-MS(2) method has been proposed for the simultaneous analysis of iminosugars and other low molecular weight carbohydrates of Aglaonema sp. extracts.

Improvement of a gas chromatographic method for the analysis of iminosugars and other bioactive carbohydrates.

The analysis of derivatised iminosugars and other bioactive low molecular weight carbohydrates present at low concentrations in different vegetable extracts (hyacinth, mulberry and buckwheat) required the improvement of a previously developed gas chromatographic method. Among the different parameters optimized, the temperature of the injection port, evaluated for the first time, resulted to be the most important. Thus, 240 °C was chosen as a tradeoff to achieve the required volatility, to avoid degradation and to provide symmetric peaks for bioactive carbohydrates highly retained such as glycosyl inositols. GC-MS operating under selective ion monitoring (SIM) acquisition mode and GC-FID provided limits of detection and quantitation for the target compounds of 0.2 and 0.7 ng g(-1) and of 1 and 3 ng g(-1) on average, respectively. Therefore, both methodologies could be considered appropriate to extend the range of quantitation of these bioactives.