RESUMO
Active fractions and constituents with antioxidant and lipid-lowering activities were investigated using bio-assay-guided isolation and identification. The data showed that the antioxidant fraction of A. cepa was AC50%, the main constituents of which were quercetin and isoquercitrin, by way of both ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS) and bio-assay-guided purification and elucidation. Similarly, the lipid-lowering active fraction of A. cepa was AC30% with the main constituents of 3,4-dihydroxybenzoic acid and quercetin 3,4'-O-diglucoside. Also, bio-assay-guided isolation led to the isolation and identification of five known compounds with a purity of more than 98%, and quercetin was both the best free radical scavenger and lipid-lowering constituent. Moreover, the mechanism of the lipid-lowering effect of AC30% might be its reduction in mRNA expression levels of sterol regulatory element binding protein 2 (SREBP2) and FAS gene in lipid synthesis. Otherwise, reducing the mRNA expression level of lipid synthesis genes, including SREBP1, SREBP2, fatty acid synthetase (FASN), ß-Hydroxy ß-methylglutaryl-CoA (HMGCR), stearoyl CoA desaturase 1 (SCD1), and increasing the mRNA expression level of lipid decomposition gene, such as carnitine palmitoyl transferease-1 (CPT1), might be involved in the lipid-lowering activity of quercetin. This study suggested that Allium cepa might be used to prevent and treat oxidative stress and dislipidemia-related disorders, including NAFLD.
RESUMO
The effects of chironomid larval (Propsilocerus akamusi) bioturbation on sediment phosphorus (P) mobility were studied over the course of 34 days using the indoor larval cultivation method on in situ sediment cores. High-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) techniques were used to record fine-scale changes of soluble and DGT-labile P and iron (Fe) concentrations in the sediment. The larval-driven irrigation of the overlying water into their burrows significantly increased the oxygen penetration depth (OPD) and redox state (Eh) in sediments. In addition, the soluble and DGT-labile P and Fe decreased with the increase of OPD and Eh in larval-bioturbated sediments. The greatest decrease in the mean concentration of SRP, soluble Fe, and DGT-labile P in the Propsilocerus group was observed on Day 15 of the experiment, with a decrease by over half of the mean concentration of the control group. Furthermore, two-dimensional measurements of DGT-labile P concentration showed notable reductions of DGT-labile P around larval burrows. The DGT-induced fluxes in sediments (DIFS) model also exhibited a much longer response time (420 s) and a much higher rate of P adsorption (0.002 s-1) in the bioturbation sediments than those in the control sediments (116 s and 0.009 s-1, respectively). A significant correlation was shown for DGT-labile P and DGT-labile Fe. We conclude that Fe(II) oxidation and its enhanced adsorption were the major mechanisms responsible for the decrease of soluble and DGT-labile P in sediments.