Background: The national programs for the harmonization of hemoglobin (Hb)A1c measurements in the US [National Glycohemoglobin Standardization Program (NGSP)], Japan [Japanese Diabetes Society (JDS)/Japanese Society of Clinical Chemistry (JSCC)], and Sweden are based on different designated comparison methods (DCMs). The future basis for international standardization will be the reference system developed by the IFCC Working Group on HbA1c Standardization. The aim of the present study was to determine the relationships between the IFCC Reference Method (RM) and the DCMs.
Methods: Four method-comparison studies were performed in 2001–2003. In each study five to eight pooled blood samples were measured by 11 reference laboratories of the IFCC Network of Reference Laboratories, 9 Secondary Reference Laboratories of the NGSP, 3 reference laboratories of the JDS/JSCC program, and a Swedish reference laboratory. Regression equations were determined for the relationship between the IFCC RM and each of the DCMs.
Results: Significant differences were observed between the HbA1c results of the IFCC RM and those of the DCMs. Significant differences were also demonstrated between the three DCMs. However, in all cases the relationship of the DCMs with the RM were linear. There were no statistically significant differences between the regression equations calculated for each of the four studies; therefore, the results could be combined. The relationship is described by the following regression equations: NGSP-HbA1c = 0.915(IFCC-HbA1c) + 2.15% (r2 = 0.998); JDS/JSCC-HbA1c = 0.927(IFCC-HbA1c) + 1.73% (r2 = 0.997); Swedish-HbA1c = 0.989(IFCC-HbA1c) + 0.88% (r2 = 0.996).
Conclusion: There is a firm and reproducible link between the IFCC RM and DCM HbA1c values.
Sterol regulatory element binding protein-1a (SREBP-1a) is a transcription factor that is a major player in lipid metabolism and insulin action. We have generated human liver cells (HepG2) overexpressing active SREBP-1a constitutively called SREBP-1a (+). These cells show massive intracellular lipid accumulation. To elucidate the effect of SREBP-1a on lipid metabolism at the level of the cellular protein network, we have analyzed the protein pattern of mitochondria using the novel technique two-dimensional difference gel electrophoresis (2D-DIGE). Mitochondria were enriched by subcellular fractionation using differential and isopyknic centrifugation. Proteins of isolated organelles were labeled with Cy dyes and separated on 2D gels. These gels revealed more than 100 protein spots, which were significantly different in their abundance between wild-type and SREBP-1a (+) cells. MALDI mass spectrometry showed that 68% of identified proteins belong to mitochondria. In SREBP-1a (+) cells, several enzymes involved in lipid metabolism were significantly altered, suggesting that cellular lipid metabolism is triggered by accumulation of fatty acids rather than by its degradation. To test the possible functional relevance of this finding, intracellular fatty acid (FA) patterns were analyzed by gas chromatography. The results showed a significant increase in total fatty acid content with a shift in composition to long-chain unsaturated FAs. Therefore, the detected protein differences might be an explanation for the observed intracellular lipid accumulation and might link SREBP-1a to features like steatosis hepatis.
Comparative studies of high-performance liquid chromatographic and liquid chromatographic/mass spectrometric methods for the quantitative determination of glibenclamide in patient serum are described. The 4-methylcyclohexyl analogue of glibenclamide [N-(4-(beta-5-chloro-2-methoxybenzamidoethyl)benzenesulfonyl-N'-(4-methylcyclohexyl)-urea] is used as internal standard for both methods. After acidification of the sample, the analyte and internal standard are extracted with chloroform. For HPLC analysis, the glibenclamide and internal standard are derivatized to a highly fluorescent amine with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-chloride). The glibenclamide derivative is detected by a fluorescence detector. For APCI LC/MS assay, a derivatization of the analyte is not required and the compounds are measured by selected ion monitoring (SIM). The accuracy, precision, and recovery of the compared methods are presented and discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.