Simplified Quantification Method Research Articles

Hepatic Blood Perfusion Measured by 3-Minute Dynamic 18F-FDG PET in Pigs

There is an unmet clinical need for an imaging method for quantification of hepatic blood perfusion. The purpose of the present study was to develop and validate a PET method using blood-to-cell clearance (K(1)) of (18)F-FDG, 3-O-(11)C-methylglucose ((11)C-MG), or 2-(18)F-fluoro-2-deoxy-D-galactose ((18)F-FDGal) as a measure of hepatic blood perfusion without the need for portal venous blood samples. We aimed to make the method as simple as possible with the prospect of future application to clinical studies. For this purpose, we examined the possibility of using a 3-min data acquisition and a model-derived dual input calculated from measurements of radioactivity concentrations in a peripheral artery. Pigs (40 kg) underwent dynamic PET of the liver with (18)F-FDG, (11)C-MG, or (18)F-FDGal with simultaneous measurements of time-activity curves in blood sampled from a femoral artery and the portal vein (PV); blood flow rates were measured in the hepatic artery (HA) and PV by transit-time flow meters. Two input functions were compared: A measured dual input and a model-derived dual input, the latter with the PV time-activity curve estimated from the measured arterial time-activity curve and a previously validated 1-parametric PV model. (K(1)) was estimated for each tracer by fitting compartmental models to the data, comparing 3-min and 60-min data acquisitions and the 2 dual-input time-activity curves. Agreement between (K(1)) estimated using the measured and the model-derived dual input was good for all 3 tracers. For (18)F-FDG and (11)C-MG, (K(1)) (3-min data acquisition, model-derived dual input, and 1-tissue compartmental model) correlated to the measured blood perfusion (P = 0.01 and P = 0.07, respectively). For (18)F-FDGal, the correlation was not significant. A simplified method for quantification of hepatic blood perfusion using 3-min dynamic (18)F-FDG PET or (11)C-MG PET with blood sampling from only a peripheral artery was developed. Parametric (K(1)) images were constructed and showed homogeneous blood perfusion in these normal livers.

Direct quantification in bioanalytical LC–MS/MS using internal calibration via analyte/stable isotope ratio

The possibility to rationalize and simplify bioanalysis, without compromising the analytical quality, by omitting the calibration curves was studied. Using mass spectrometry (MS) and a stable isotope labeled internal standard it was possible to get equally good results by calculating the results directly from the analyte/internal standard area ratio and a predetermined response factor as by the traditional way, using a calibration curve run at the same occasion. To be able to use this simplified quantification method, that we call internal calibration, in its most simple form there are some prerequisites that must be considered: (1) The relative response should not be concentration dependent. (2) The relative response should be constant between batches/days. (3) The level of analyte in the internal standard should not be detectable. (4) There should be no influence from naturally occurring isotopes of the analyte on the internal standard peak area. A bioanalytical LC–MS/MS method for a research compound was validated both with and without calibration curves and no significant differences were found regarding precision and accuracy. It was shown that all four prerequisites above were fulfilled. Validation data were very good for the whole concentration range, 0.010–30 μmol/L. Long-term data for QC samples showed excellent precision and accuracy.

Seed-specific expression of the isopentenyl transferase gene (ipt) in transgenic tobacco

The Agrobacterium tumefaciens gene encoding isopentenyl transferase (ipt), a cytokinin biosynthetic gene, was fused to a promoter from a seed-specific gene, vicilin, and introduced into tobacco cells. Intact fertile plants were generated. The expression of the vicilin-ipt gene was shown to be confined to seed and resulted in enhanced levels of cytokinins in the developing seeds and increased seed protein content. Using a simplified quantification method, a significant increase in the levels of endogenous cytokinins was recorded at 16–21 days after flowering. The growth of the transgenic plants and the development of the seeds appeared to be normal.

A simplified quantification method of complex-release activity using peroxidase as immune complex antigen.

The complement-mediated solubilization of precipitable immune complexes (complex-release activity) in serum specimens was determined by a simplified method using peroxidase as an immune complex antigen. The results correlated well with the hemolytic activity via the classical complement pathway and that via the alternative complement pathway. This simplified method proved to be reliable and useful.