Trypsin inhibitors (TIs), root storage proteins, were purified from sweet potato (Ipomoea batatas[L.] Lam cv. Tainong 57) roots by trypsin affinity column according to the methods of Hou and Lin (Plant Sci. 1997, 126, 11-19 and Plant Sci. 1997, 128, 151-158). A single band of 33 kDa TI was obtained by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gels. This purified 33 kDa TI had scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. There was positive correlation between scavenging effects against DPPH (2 to 22%) and amounts of 33 kDa TI (1.92 to 46 pmol). The scavenging activities of 33 kDa TI against DPPH were calculated from linear regression to be about one-third of those of glutathione between 5 and 80 pmol. Using electron paramagnetic resonance (EPR) spectrometry for hydroxyl radical detection, it was found that 33 kDa TI could capture hydroxyl radical, and the intensities of EPR signal were significantly decreased from 1.5 to 6 pmol of 33 kDa TI compared to those of the controls. It is suggested that 33 kDa TI, one of the sweet potato root storage proteins, may play a role as an antioxidant in roots and may be beneficial to health when it is consumed.

To determine the effects of chromium (Cr) supplementations on oxidative stress of type 2 diabetes and euglycemic (EU) subjects, adult having HbA(1C) values of <6.0% (EU), 6.8-8.5% (mildly hyperglycemic, MH), and >8.5% (severely hyperglycemic, SH) were supplemented for 6 months with 1000 microg/day of Cr (as Cr yeast) or with a placebo. In the beginning, the levels of the plasma Cr in the MH and SH groups were 25-30% lower than those of the EU subjects. The values of thiobarbituric acid reactive substances (TBARS) and total antioxidative status (TAS) of the MH and SH groups were significantly higher than those of the EU ones. Following supplementations, the levels of plasma TBARS in the Cr groups of MH and SH groups were significantly decreased (the inverse was found in the EU) and showed no significant changes in the placebo group. The levels of plasma TAS in the Cr groups of EU and MH were significantly decreased (the inverse was found in the SH) and showed no significant changes in the placebo group. No significant difference was found in the antioxidant enzyme (superoxide dismutase, glutathione peroxidase, catalase) activities during supplementations. These data suggest that Cr supplementation was an effective treatment strategy to minimize increased oxidative stress in type 2 diabetes mellitus patients whose HbA(1C) level was >8.5%, and the Cr in EU groups might act as a prooxidant.

BackgroundThe metabolic syndrome (MS) is termed a cluster of multiple metabolic risk criteria which is positively correlated with cardiovascular disease and type 2 diabetes mellitus (DM). Yam dioscorins have been reported to exhibit biological activities, however, little is known their preventive effects on the MS. Therefore, a high-fat (HF) diet was used to induce Wistar rat obesity and then yam dioscorin (50 mg/kg, dio50) was intervened daily concurrent HF diet (HF diet + dio50) for five weeks to check the changes of weights of body and tissues, blood pressures, and impaired glucose tolerances. The in vitro peptic hydrolysates of dioscorin with molecular mass between 3 kDa and 10 kDa and less than 3 kDa were used to determine dipeptidyl peptidase IV (DPP IV) inhibitory activities which DPP IV inhibitor has been reported to prevent and treat type 2 DM.ResultsThere were no significant difference in body weights, feed intakes, feed conversion, and weights of adipose tissues of obese rats in groups of HF and (HF diet + dio50). However, the systolic blood pressures in obese rats of 2-, 3- and 4-week dioscorin interventions were showed significantly lower (P < 0.05) compared to the HF group. The dioscorin intervention (HF+ dio50) was showed significantly different (P < 0.05) and improved the impaired glucose tolerances compared to HF group in obese rats by the oral glucose tolerance tests. It was also found that the fraction with different molecular mass of dioscorin peptic hydrolysates (5 mg/ml) showed inhibitory activities against DPP IV using sitagliptin phosphate as positive controls.ConclusionsYam dioscorins exhibit improved MS activities in obese rats which the related mechanisms may need further investigations.Electronic supplementary materialThe online version of this article (doi:10.1186/s40529-015-0084-8) contains supplementary material, which is available to authorized users.