Molecularly imprinted coated graphene oxide solid-phase extraction monolithic capillary column for selective extraction and sensitive determination of phloxine B in coffee bean.

A method was developed to sensitively determine phloxine B in coffee bean by molecularly imprinted polymers (MIPs) coated graphene oxide (GO) solid-phase extraction (GO-MISPE) coupled with high-performance liquid chromatography and laser-induced fluorescence detection (HPLC-LIF). The GO-MISPE capillary monolithic column was prepared by water-bath in situ polymerization, using GO as supporting material, phloxine B, methacrylic acid (MAA), and ethylene dimethacrylate (EDMA) as template, functional monomer, and cross-linker, respectively. The properties of the homemade GO-MISPE capillary monolithic column, including capacity and specificity, were investigated under optimized conditions. The GO-MIPs were characterized by scanning electron microscopy (SEM) and Fourier transform-infrared spectroscopy (FT-IR). The mean recoveries of phloxine B in coffee bean ranged from 89.5% to 91.4% and the intra-day and inter-day relative standard deviation (RSD) values all ranged from 3.6% to 4.7%. Good linearity was obtained over 0.001-2.0 µg mL(-1) (r=0.9995) with the detection limit (S/N=3) of 0.075 ng mL(-1). Under the selected conditions, enrichment factors of over 90-fold were obtained and extraction on the monolithic column effectively cleaned up the coffee bean matrix. The results demonstrated that the proposed GO-MISPE HPLC-LIF method can be applied to sensitively determine phloxine B in coffee bean.

Chronic exposure to leucine in vitro induces ß-cell dysfunction in INS-1E cells and mouse islets.

Chronic hyperglycemia and hyperlipidemia cause deleterious effects on ß-cell function. Interestingly, increased circulating amino acid (AA) levels are also a characteristic of the prediabetic and diabetic state. The chronic effects of AAs on ß-cell function remain to be determined. Isolated mouse islets and INS-1E cells were incubated with or without excess leucine. After 72 h, leucine increased basal insulin secretion and impaired glucose-stimulated insulin secretion in both mouse islets and INS-1E cells, corroborating the existence of aminoacidotoxicity-induced ß-cell dysfunction. This took place concomitantly with alterations in proteins and genes involved in insulin granule transport, trafficking (e.g. collapsin response mediator protein 2 and GTP-binding nuclear protein Ran), insulin signal transduction (proteasome subunit α type 6), and the oxidative phosphorylation pathway (cytochrome c oxidase). Leucine downregulated insulin 1 gene expression but upregulated pancreas duodenum homeobox 1 and insulin 2 mRNA expressions. Importantly, cholesterol (CH) accumulated in INS-1E cells concomitantly with upregulation of enzymes involved in CH biosynthesis (e.g. 3-hydroxy-3-methylglutaryl-CoA reductase, mevalonate (diphospho) decarboxylase, and squalene epoxidase) and LDL receptor, whereas triglyceride content was decreased. Our findings indicate that chronic exposure to elevated levels of leucine may have detrimental effects on both ß-cell function and insulin sensitivity. Aminoacidotoxicity may play a pathogenic role in the development of type 2 diabetes.