On the use of liquid chromatography with radio- and ultraviolet absorbance detection coupled to mass spectrometry for improved sensitivity and selectivity in determination of specific radioactivity of radiopharmaceuticals

Molar activity of [18F]FP-(+)-DTBZ radiopharmaceutical: Determination and its effect on quantitative analysis of VMAT2 autoradiography

[¹⁸F]fluoropropyl-(+)-dihydrotetrabenazine ([¹⁸F]FP-(+)-DTBZ) is a rising positron tracer for imaging vesicular monoamine transporter II (VMAT2) in the central nervous system. The present work was to develop a novel chromatographic method capable of the molar activity (A_m) determination of [¹⁸F]FP-(+)-DTBZ. As a complement work of the A_m measurement, we also investigated the effect of A_m on the quantitative analysis of VMAT2 autoradiography with [¹⁸F]FP-(+)-DTBZ. The A_m determination was performed by high performance liquid chromatography (HPLC) using the non-radioactive standard (FP-(+)-DTBZ) for calibration plot of peak area against concentration. Based on this correlation, the A_m of [¹⁸F]FP-(+)-DTBZ was calculated and corrected to the end of synthesis. In the quantitative analysis of in vitro VMAT2 autoradiography, the striatum radioactivity uptake together with the uptake ratio of striatum versus cortex reduced along with the decrease of A_m and the increase of the FP-(+)-DTBZ content. Therefore, the A_m and the corresponding FP-(+)-DTBZ content have a significant effect on the quantitative analysis of VMAT2 autoradiography using [¹⁸F]FP-(+)-DTBZ.

Dopamine D1-like receptor antagonist attenuates Th17-mediated immune response and ovalbumin antigen-induced neutrophilic airway inflammation

Allergic airway inflammation is generally considered a Th2-type immune response. Recent studies, however, demonstrated that Th17-type immune responses also play important roles in this process, especially in the pathogenesis of neutrophilic airway inflammation, a hallmark of severe asthma. We previously reported that dendritic cells release dopamine to naive CD4(+) T cells in Ag-specific cell-cell interaction, in turn inducing Th17 differentiation through dopamine D1-like receptor (D1-like-R). D1-like-R antagonist attenuates Th17-mediated diseases such as experimental autoimmune encephalomyelitis and autoimmune diabetes. However, the effect of antagonizing D1-like-R on Th17-mediated airway inflammation has yet to be studied. In this study, we examined whether D1-like-R antagonist suppresses OVA-induced neutrophilic airway inflammation in OVA TCR-transgenic DO11.10 mice and then elucidated the mechanism of action. DO11.10 mice were nebulized with OVA or PBS, and some mice received D1-like-R antagonist orally before OVA nebulization. D1-like-R antagonist significantly suppressed OVA-induced neutrophilic airway inflammation in DO11.10 mice. It also inhibited the production of IL-17 and infiltration of Th17 cells in the lung. Further, D1-like-R antagonist suppressed the production of IL-23 by lung CD11c(+) APCs. In contrast, D1-like-R antagonist did not increase Foxp3(+) regulatory T cells in the lung. D1-like-R antagonist neither suppressed nonspecific LPS-induced neutrophilic airway inflammation nor OVA-induced eosinophilic airway inflammation. These results indicate that D1-like-R antagonist could suppress Th17-mediated neutrophilic airway inflammation, raising the possibility that antagonizing D1-like-R serves as a promising new strategy for treating neutrophil-dominant severe asthma.

Development and Validation of a Liquid Chromatographic Method for the Analysis of Positron Emission Tomography Radiopharmaceuticals with Ru(bpy)32+-KMnO4 Chemiluminescence Detection

A sensitive, selective and rapid high-performance liquid chromatographic (HPLC) method with chemiluminescence (CL) detection was developed and validated for the analysis of positron emission tomography (PET) radiopharmaceuticals. This method is based on the CL reaction of PET compounds with tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)] and acidic potassium permanganate [KMnO(4)]. After optimization of the reaction conditions, 12 of the 14 PET compounds investigated could be successfully detected and showed good performance in terms of sensitivity, linearity and reproducibility. In particular, for compounds with a tertiary amine functional group, the limits of detection were ppb levels for a 20 microL injection volume. Finally, this method was used to determine PET compounds for calculating of specific radioactivity in pharmaceutical samples.

Quality control of PET radiopharmaceuticals using HPLC with electrochemical detection

The usefulness of high-performance liquid chromatography with electrochemical detection (HPLC/ECD) in the quality control of positron emission tomography (PET) radiopharmaceuticals was evaluated for a number of substances. Chromatographic separation was performed using a reversed phase column and acetonitrile or 20 mM sodium phosphate buffer as the mobile phase. The effluent from the column was introduced into an electrochemical detector equipped with a glassy carbon electrode versus Ag/AgCl electrode operated in the direct current mode. In 19 of 21 PET radiopharmaceuticals studied, the compounds and corresponding precursors used in the synthesis of the radiopharmaceuticals could be successfully detected by the HPLC/ECD method. For 17 compounds with electroactive functional groups, such as aliphatic amines, phenols and aromatic amines, the detection limits were ppb levels for a 20-mul injection volume; this was significantly better compared with ultraviolet (UV) detection. This method could be applied to the analysis of [11C]MP4A, useful PET radiopharmaceutical for measuring acetylcholinesterase activity in the brain with no available UV absorbance.

Optimization of labeling and metabolite analysis of copper-64-labeled azamacrocyclic chelators by radio-LC-MS

The cross-bridged tetraamine ligand 4,11-bis(carboxymethyl)-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (H2CB-TE2A) allows formation of a radio-copper complex with higher in vivo stability than that of the corresponding non-cross-bridged analog 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (TETA). The structure of the natCu(II) complex of CB-TE2A has been previously determined by X-ray crystallography; however, direct high-pressure liquid chromatography (HPLC) characterization of the corresponding 64Cu complex was inaccessible due to the inability to detect the complex by ultraviolet absorbance at the radiotracer level. A reverse-phase HPLC separation of a series of natCu(II)-tetraazamacrocyclic complexes, both traditional and cross-bridged, was developed and applied toward characterization and assessment of the purity of the corresponding no-carrier-added 64Cu-labeled complexes. Verification of the identity of copper-64-labeled compounds was also achieved by coupling this HPLC method with mass spectrometry. The radio-liquid chromatography/mass spectrometry methodology was further extended to study the in vivo metabolic fates of 64Cu-azamacrocyclic complexes.

Determination of specific radioactivity for (76)Br-labeled compounds measuring the ratio between (76)Br and (79)Br using packed capillary liquid chromatography mass spectrometry

Packed capillary liquid chromatography with electrospray mass spectrometry was used for direct determination of the specific radioactivity by calculation of isotope ratios between the (76)Br- and (79)Br-labeled analogues of N-((3-aminomethyl)benzyl)-4-bromobenzamide. Using 20 microL injections on packed capillary columns, sufficient mass sensitivity was attained for the determination on an injected amount of radioactivity corresponding to approximately 2 MBq (0.3 pmol of the (76)Br isotopic analogue).

Determination of raclopride in human plasma by on-column focusing packed capillary liquid chromatography-electrospray ionisation mass spectrometry

A packed capillary liquid chromatography-electrospray ionisation mass spectrometry method was developed for the quantitative determination of raclopride in human plasma samples. Plasma samples containing the drug and its isotopically substituted analogue (2H3)raclopride as internal standard were extracted on solid-phase extraction discs, evaporated and reconstituted in a solvent with less elution strength than the mobile phase. Packed capillary columns of 100 mm x 500 microm I.D. were used to obtain high mass sensitivity in the analysis and large volume injections (20 microl) were performed with analyte enrichment on top of the column. The assay exhibited satisfactory accuracy and precision over the concentration range of 0.2-15 nM (70-5200 pg/ml) with a limit of quantification of 0.2 nM. Raclopride in plasma was determined after intravenous injection in a positron emission tomography study performed in the tracer dose range.