Effects of some natural products on sugar cataract studied with nuclear magnetic resonance spectroscopy

Liquid chromatography-tandem mass spectrometry analysis allows the simultaneous characterization of C-glycosyl and O-glycosyl flavonoids in stingless bee honeys

The analysis of the phytochemicals present in stingless bee honey samples has been a difficult task due to the small amounts of samples available and to the complexity of the phytochemical composition that often combines flavonoid glycosides and aglycones. Honey samples produced in Venezuela from Melipona species were analyzed using a combination of solid-phase extraction and HPLC-DAD-MSn/ESI methodologies with specific study of the fragment ions produced from flavonoid glycosides. The analyses revealed that flavonoid glycosides were the main constituents. The honey samples analyzed contained a consistent flavonoid pattern composed of flavone-C-glycosides, flavonol-O-glycosides and flavonoid aglycones. The HPLC-DAD-MSn/ESI analysis and the study of the fragment ions obtained allowed the characterization and quantification for the first time of five apigenin-di-C-glycosides, and ten quercetin, kaempferol and isorhamnetin O-glycosides (di- and tri- glycosides), and the aglycones pinobanksin, quercetin, kaempferol and isorhamnetin in the different samples. This is the first report of flavonoid-C-glycosides in honey. The results show that the content of flavonoid-glycosides (mean values of 2712 μg/100 g) in stingless bee honeys is considerably higher than the content of flavonoid aglycones (mean values of 315 μg/100 g). This differs from previous studies on Apis mellifera honeys that consistently showed much higher aglycone content and smaller flavonoid glycoside content. The occurrence of relevant amounts of flavonoid glycosides, and particularly C-glycosides, in stingless bee honeys could be associated with their putative anticataract properties.

Magnetic resonance imaging of the galactosemic dog eye using magnetization transfer contrast

Magnetization transfer contrast (MTC) enhanced magnetic resonance (MR) imaging is a technique that generates high contrast images based on characteristic tissue differences resulting from the interaction of water and macromolecules. In this study, the feasibility of applying this technique to documenting the progression of osmotic sugar cataract formation was investigated in male beagles, initially 6 or 24 month old, fed a diet containing 30% galactose. MTC enhanced magnetic resonance imaging was periodically conducted on these animal's eyes at 2-Tesla. The lens MR images were compared to photographs obtained by photo-slit lamp and retroillumination photography. The MTC technique provided improved image details of the lens and anterior segment that documented osmotic changes from initial cortical vacuole formation to cortical and nuclear changes associated with advanced sugar cataracts. The latter could not be observed by photo-slit lamp or retroillumination photography.

Inhibition of aldose reductase: 13C NMR studies in isolated peripheral nerve

We report 13C NMR measurements of the flux through aldose reductase in isolated rat sciatic nerve, and its inhibition by an aldose reductase inhibitor of the sulphonylnitromethane class. [1-13C] galactose was used as substrate, and the rate of production of [1-13C] dulcitol was measured. Quantitation required the use both of internal extracellular, and external, standards. The mean net forward flux (+/- SD) was 20 +/- 11 nmol/(mL nerve water)/min (n = 10). In the presence of the inhibitor, flux was reduced significantly (p < 0.001) to 13% of control. Since dulcitol is symmetrical, an estimate of the backward flux, to [6-13C] galactose, is also possible; under our conditions, this was negligible.