ABSTRACT
BACKGROUND: Stepwise gastric balloon distension progressively activates a 'visceral pain neuromatrix', ultimately inducing discomfort and pain. On the other hand, normal meal ingestion requires gastric volume expansion without induction of pain. The aim was to test the hypothesis that physiological gastric distension (liquid meal infusion) until maximal satiation elicits brain responses similar to balloon distension at discomfort threshold. METHODS: Brain H(2) (15) O-positron emission tomography (PET) was performed in two different groups of healthy volunteers (both n=14) during continuous and stepwise infusion of a liquid meal through a nasogastric tube, until maximal satiation. Brain (de)activation patterns were compared with historical controls in which discomfort was elicited using gastric balloon distension. This latter reference group was acquired on the same scanner using the same acquisition protocol; all data were analyzed using statistical parametric mapping (SPM2). Within each group, brain activity at maximal distension was compared to baseline activity and between-group comparisons were made. KEY RESULTS: Intragastric volumes and satiation/gastric sensation scores at endpoint were similar in all groups. Continuous and stepwise nutrient infusion was associated with progressive deactivations in key areas of the 'visceral pain neuromatrix' that were activated during balloon distension. Additionally, stepwise infusion progressively activated prefrontal areas and showed deactivations in 'default network' brain regions also found to be deactivated during balloon distension. CONCLUSIONS & INFERENCES: Compared to gastric balloon distension, physiological gastric distension using nutrient infusion elicits opposite brain responses in the 'visceral pain neuromatrix', but similar responses in other areas. We interpret this finding as a prerequisite for tolerance of normal meal volumes in health.
Subject(s)
Brain Mapping/methods , Brain/physiology , Catheterization/methods , Dilatation, Pathologic/physiopathology , Positron-Emission Tomography/methods , Stomach/physiology , Adult , Brain/anatomy & histology , Brain/diagnostic imaging , Dilatation, Pathologic/diagnostic imaging , Enteral Nutrition/methods , Female , Humans , Satiation/physiology , Sensation/physiology , Stomach/diagnostic imaging , Young AdultABSTRACT
2-(4'-[(18)F]fluorophenyl)-1,3-benzothiazole was synthesized as a fluorine-18 labelled derivative of the Pittsburg Compound-B (PIB), which has known affinity for amyloid beta and promising characteristics as tracer for in vivo visualisation of amyloid deposits in patients suffering from Alzheimer's disease (AD). Both the nitro-precursor 2-(4'-nitrophenyl)-1,3-benzothiazole and the non-radioactive reference compound were synthesized using a 1-step synthesis pathway. Labelling was achieved by direct aromatic nucleophilic substitution of the nitro-precursor using [(18)F]fluoride by heating for 20 min at 150 degrees C and with a radiochemical yield of 38%. The reference compound showed high affinity for amyloid in an in vitro competition binding study using human AD brain homogenates (K(i)=9.0 nM) and fluorescence imaging of incubated transgenic APP mouse brain slices confirmed binding to amyloid plaques. A biodistribution study in normal mice showed a high brain uptake at 2 min pi (3.20%ID/g) followed by a fast washout (60 min pi: 0.21%ID/g). A dynamic microPET study was performed in a transgenic APP and normal WT mouse, but, similar to [(11)C]PIB, no difference was seen in tracer retention between both kind of mice. The new (18)F-labelled 2-phenylbenzothiazole showed excellent preclinical characteristics comparable with those of the (11)C-labelled PIB.
Subject(s)
Benzothiazoles/chemistry , Chemistry, Pharmaceutical/methods , Fluorine Radioisotopes/chemistry , Alzheimer Disease/drug therapy , Amyloid/chemistry , Amyloid beta-Protein Precursor/genetics , Amyloid beta-Protein Precursor/metabolism , Animals , Benzothiazoles/chemical synthesis , Drug Design , Humans , Kinetics , Mice , Mice, Transgenic , Models, Chemical , Temperature , Tissue DistributionABSTRACT
Pittsburgh Compound-B (PIB) is currently being evaluated clinically for in vivo visualization of amyloid plaques in patients with Alzheimer's disease (AD). We have synthesized three structural isomers of 6-hydroxy-2-(4'-aminophenyl)-1,3-benzothiazole, performed radiolabelling with carbon-11 and investigated their in vivo and in vitro properties. Specific binding to amyloid plaques was demonstrated in vitro using post-mortem brain homogenates of AD patients, transgenic AD mice brain sections and post-mortem human AD brain sections. In normal mice, initial brain uptake (at 2 min p.i.) was high and was followed by a fast wash-out. The three structural analogues have a high potential as tracer agents for in vivo visualization of amyloid plaques in AD patients.
Subject(s)
Alzheimer Disease/metabolism , Amyloid beta-Peptides/analysis , Aniline Compounds/chemistry , Thiazoles/chemistry , Amyloid beta-Peptides/metabolism , Aniline Compounds/chemical synthesis , Aniline Compounds/metabolism , Animals , Benzothiazoles/chemistry , Benzothiazoles/metabolism , Brain/metabolism , Carbon Radioisotopes/chemistry , Fluorine Radioisotopes/chemistry , Humans , Hydroxides/chemistry , Isomerism , Mice , Radioactive Tracers , Staining and Labeling , Thiazoles/chemical synthesis , Thiazoles/metabolismABSTRACT
99mTc-exametazime (99mTc-d,l-HMPAO, 99mTc-d,l-hexamethylpropyleneamine oxime) is a neutral rather unstable complex of short-lived 99mTc (t(1/2)=6 h) with the d,l-isomer (mixture of D,D- and L,L-isomers) of a bis-amine bis-oxime tetraligand. It is widely used for measurement of regional cerebral perfusion in nuclear medicine. The meso-isomer (D,L-form) should not be present in a preparation as it is not retained in brain and thus does not provide clinically useful information. Meso-HMPAO is removed from the ligand during the synthesis procedure by repeated recrystallization, but can still be present as impurity in d,l-isomer. Due to the lack of a suitable chromatographic method for analysis of the isomeric purity of 99mTc-exametazime preparations, United States Pharmacopoeia 25 (USP 25) prescribes a biological test in rats for quality control purpose. In this study, we developed a suitable high-performance liquid chromatography (HPLC) method which allows to demonstrate the relative amounts of d,l- and meso-isomer in 99mTc-exametazime and so obviates the need for a biodistribution test in animals as part of the quality control. Due to the low concentrations in which 99mTc-d,l-HMPAO is obtained (typically 2-6 ng/ml), confirmation of the identity of 99mTc-d,l-HMPAO in the monograph of the European Pharmacopoeia is now performed only indirectly by TLC and assessment of its retention time on RP-HPLC. To investigate the potential of radio-LC-MS for assessment of the identity of 99mTc-exametazime, 99mTc-d,l-HMPAO and 99mTc-meso-HMPAO prepared using a Tc-rich eluate were analyzed using a radio-LC-MS system equipped with a time-of-flight mass spectrometer with electrospray ionization. The main peak in the radiometric channel coincided with the molecular ion mass of 99mTc-d,l-HMPAO in the mass spectrometer channel and the measured accurate mass differed only by 0.26 ppm from the theoretical mass. The identity of 99mTc-meso-HMPAO was also confirmed. Thus, radio-LC-MS allowed to obtain strong evidence for the structure of 99mTc-d,l-HMPAO and 99mTc-meso-HMPAO at nanomolar concentration. It is concluded that radio-LC-MS can become a sensitive aid in quality control of "no carrier added" radiopharmaceutical preparations.
Subject(s)
Butanones/analysis , Drug Contamination , Technetium/analysis , Technology, Pharmaceutical/methods , Butanones/chemistry , Chromatography, High Pressure Liquid/methods , Chromatography, Liquid/methods , Mass Spectrometry/methods , Technetium/chemistryABSTRACT
Micellar electrokinetic capillary chromatography (MEKC) was examined for analysis of cefalexin and its related substances. Good selectivity was obtained with two different buffer solutions: a sodium acetate buffer (50 mM, pH 5.25) containing sodium dodecyl sulfate (50 mM SDS) or sodium phosphate buffer (40 mM, pH 7.0) containing 100 mM SDS. Both methods permit cefalexin to be completely separated from its ten related substances within 20 min. The robustness of the method, using pH 5.25 acetate buffer, was examined by means of a full-fraction factorial design to test the influence of buffer pH, concentration of SDS and buffer concentration. The parameters for validation such as linearity, precision, limit of detection and limit of quantitation are also reported. The results show that method 1 is suitable for the analysis of cefalexin.
Subject(s)
Cephalexin/isolation & purification , Cephalexin/analogs & derivatives , Cephalexin/chemistry , Chromatography, Micellar Electrokinetic Capillary/methods , Molecular StructureABSTRACT
A method is developed and validated for analysis of the antibiotic cefadroxil using micellar electrokinetic capillary chromatography. It permits cefadroxil to be completely separated from ten of its known related substances within 15 min (including the washing procedure). The separation is performed in an acetate buffer (50 mM, pH 5.25) containing sodium dodecyl sulfate (SDS; 110 mM). The fused-silica capillary was 44 cm long (36 cm effective length), 50 microm ID; the voltage, 18 kV; temperature, 15 degrees C; and the detection wavelength; 254 nm. The influence of the type of buffer, buffer pH and concentration, and of the SDS concentration was investigated. The robustness of the method was examined by means of a full-fraction factorial design. The parameters for validation such as linearity, precision, limit of detection and limit of quantitation are also reported.
