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Biomedical subjects

M J Welch

Publications and source records attributed to M J Welch.

At least 73 records · Page 4Linked to original sources
PubMed1997

Capillary liquid chromatography/electrospray mass spectrometry for the separation and detection of catechins in green tea and human plasma.

The separation and detection of biologically active green tea catechins has been accomplished using capillary liquid chromatography/electrospray mass spectrometry (cLC/ESI-MS). Microscale determination (approximately 20 ng) of all six catechins in a green tea infusion, and the most extensively studied catechin, (-)epigallocatechin gallate (EGCG), in human plasma is demonstrated by cLC/ESI-MS with selected ion monitoring of protonated molecular ions. The overall quality of the analysis is shown to be dependent on the use of a capillary column with a deactivated, monomeric C18 stationary phase. The high chromatographic separation efficiency of this packed-capillary column, combined with the high sensitivity and selectivity afforded by the mass spectrometer as detector, provide a reliable approach to the analysis of picomolar quantities of these interesting compounds in complex matrices.

Catechin↗
PubMed1997

Measurement of upregulation of inducible nitric oxide synthase in the experimental autoimmune encephalomyelitis model using a positron emitting radiopharmaceutical.

Excess nitric oxide has been implicated in the pathogenosis of experimental autoimmune encephalomyelitis (EAE) which is an animal model for multiple sclerosis. Positron emission tomography (PET) is an imaging technique that has shown utility for studying enzyme systems in vivo. A positron-labeled inducible nitric oxide synthetase (iNOS) inhibitor has been studied in EAE-affected mice as well as controls. Greater uptake of the radiolabeled inhibitor was observed in the spinal cord of the affected mice than of control mice. Increased uptake was also observed in other organs not previously implicated in this experimental model. The increased uptake of the radiopharmaceutical in this model suggests that this tracer may have the potential for measuring increased levels of iNOS in humans by PET.

Animals↗
PubMed1997

Reactivity of p-[18F]fluorophenacyl bromide for radiolabeling of proteins and peptides.

Radiolabeling of the somatostatin analog octreotide was attempted with p-[18F]fluorophenacyl bromide ([18F]FPB). Following these unsuccessful trials, the reactivity of FPB was studied using benzyl mercaptan, phenyl acetic acid, benzyl alcohol, and benzyl amine as model compounds for amino acid functional groups. Structure and purity of products, relative reactivity of FPB in competition reactions, and radiolabeling experiments are described. In addition, improvement in labeling efficiency of HSA using [18F]FPB was achieved by pretreatment with 2-iminothiolane.

Acetophenones↗
PubMed1997

Evaluation of the in vitro stability of gadolinium (III) polyoxometalates.

The gadolinium chelates of lacunary polyoxometalates were evaluated for in vitro stability against rat serum, diethylenetriaminepentaacetic acid (DTPA), endogenous metal cations, and DTPA-doped rat serum. The chelates dissociated rapidly in rat serum. Challenges by DTPA gave relatively slower dissociation rates, whereas challenges by endogenous metal cations (Fe(III), Zn(II), and Cu(II)) occurred at a rate comparable to the serum challenge, suggesting the instability in serum is due to a transmetalation mechanism. Challenges by DTPA-doped serum gave slower rates of dissociation than in native serum, verifying the transmetalation mechanism.

Animals↗
PubMed1997

Efficient production of high specific activity 64Cu using a biomedical cyclotron.

Copper-64 (T 1/2 = 12.7 h) is an intermediate-lived positron-emitting radionuclide that is a useful radiotracer for positron emission tomography (PET) as well as a promising radiotherapy agent for the treatment for cancer. Currently, copper-64 suitable for biomedical studies is produced in the fast neutron flux trap (irradiation of zinc with fast neutrons) at the Missouri University Research Reactor. Access to the fast neutron flux trap is only possible on a weekly basis, making the availability of this tracer very limited. In order to significantly increase the availability of this intermediate-lived radiotracer, we have investigated and developed a method for the efficient production of high specific activity Cu-64 using a small biomedical cyclotron. It has been suggested that it may be possible to produce Cu-64 on a small biomedical cyclotron utilizing the 64Ni(p,n)64Cu nuclear reaction. We have irradiated both natural nickel and enriched (95% and 98%) Ni-64 plated on gold disks. Nickel has been electroplated successfully at thicknesses of approximately 20-300 mm and bombarded with proton currents of 15-45 microA. A special water-cooled target had been designed to facilitate the irradiations on a biomedical cyclotron up to 60 microA. We have shown that it is possible to separate Cu-64 from Ni-64 and other reaction byproducts rapidly and efficiently by using ion exchange chromatography. Production runs using 19-55 mg of 95% enriched Ni-64 have yielded 150-600 mCi of Cu-64 (2.3-5.0 mCi/microAh) with specific activities of 94-310 mci/microgram Cu. The cyclotron produced Cu-64 had been used to radiolabel PTSM [pyruvaldehyde bis-(N4-methylthiosemicarbazone), used to quantify myocardial, cerebral, renal, and tumor blood flow], MAb 1A3 [monoclonal antibody MAb to colon cancer], and octreotide. A recycling technique for the costly Ni-64 target material has been developed. This technique allows the nickel eluted off the column to be recovered and reused in the electroplating of new targets with an overall efficiency of greater than 90%.

Copper Radioisotopes↗
PubMed1997

Synthesis and evaluation of [18F] labeled benzamides: high affinity sigma receptor ligands for PET imaging.

We have synthesized and characterized four new fluorinated halobenzamides as sigma receptor ligands for use with positron emission tomography (PET). All the compounds were found to have high sigma-1 affinities (Ki = 0.38-0.98 nM), and the 4-fluoro-substituted benzamides were found to be more potent sigma-2 ligands (Ki = 3.77-4.02 nM) than their corresponding 2-fluoro analogs (Ki = 20.3-22.8 nM). The [18F] radiochemical syntheses of two of the analogs gave overall yields between 3-10% (EOS), radiochemical purities > 99%, and specific activities between 800-1200 Ci/mmol (29.6-44.4 TBq/mmol). Rat biodistribution and blocking experiments were performed with 2-[18F](N-fluorobenzylpiperidin-4yl)-4-iodobenzamide, the analog with the best Ki value for sigma-1 sites (0.38 nM). Results of these experiments demonstrate specific uptake of the compound in tissues believed to contain sigma receptors, such as lungs, kidneys, heart, brain, and spleen and indicate its potential as a candidate for use in PET imaging of tissues containing these receptors.

Animals↗
PubMed1997

Radiation dosimetry of [18F] (N-methyl)benperidol as determined by whole-body PET imaging of primates.

Radiation absorbed doses due to IV administration of [18F](N-methyl) benperidol ([18F]NMB) were estimated by whole-body PET imaging of nonhuman primates. Time-activity curves were obtained for nine compartments (striatum, eyes, heart, lungs, liver, gallbladder, intestines, kidneys, bladder) by using dynamic PET scans of three different baboons given the radiotracer. These time-activity curves were used to calculate the residence times of radioactivity in these tissues. Human absorbed dose estimates were calculated using the updated MIRDOSE 3 S values and assuming the same biodistribution. Based on an average of three studies, the critical organs were the lower large intestine, gallbladder, and liver, receiving doses of 585, 281, and 210 mrad/mCi, respectively. The brain received a dose of 13 mrad/mCi; other organs received doses between 32-77 mrad/mCi. These results indicate that up to 8.5 mCi of [18F]NMB can be safely administered to human subjects for PET studies of D2 receptor binding.

Animals↗
PubMed1997

Retardation of 17-oxidation of 16 alpha-[18F]fluoroestradiol-17 beta by substitution of deuterium for hydrogen in the 17 alpha position(6).

We describe the synthesis, in vitro metabolism and biodistribution of [17 alpha-2H]16 alpha-[18F]fluoroestradiol ([18F]DFES). The clinically useful breast cancer imaging agent, 16 alpha-[18F]fluoroestradiol-17 beta ([18F]FES), was deuterated at the C-17 alpha position to lower the rate of C-17 alcohol oxidation. Metabolism studies in immature female rat and mature female baboon isolated hepatocytes showed [18F]DFES being consumed ca. 2.5 times slower than [18F]FES. Biodistribution studies and time-activity curve measurements in female rats showed [18F]DFES to have superior uptake characteristics compared to [18F]FES for imaging estrogen-receptor rich targets.

Aging↗
PubMed1997

Synthesis, estrogen receptor binding, and tissue distribution of [18F]fluorodoisynolic acids.

Doisynolic acids, D-ring seco-steroids derived from alkaline fusion of estrones, are hormonal curiosities: Their binding affinity for the estrogen receptor is low (ca. 1-2% that of estradiol), but their in vivo potency is high and they have a long duration of action. To study the in vivo behavior of the doisynolic acids, we prepared fluorine-substituted analogs of both trans-doisynolic acid (with the natural 14 alpha-hydrogen configuration, trans-FDA) and the more active cis-doisynolic acid (with the unnatural 14 beta-hydrogen configuration, cis-FDA) from estrone and 14 beta-estrone, respectively. Modification of the D-ring haloform cleavage approach of Meyers allowed us to introduce fluorine (or fluorine-18) on the carbon atom derived from C-16 in the estrones. Fluorine substitution had little effect on the estrogen receptor binding affinity of the doisynolic acids. Tissue distribution of the fluorodoisynolic acids (trans-[18F]FDA and cis-[18F]FDA) was unusual and very different from that of typical, high-affinity ligands for the estrogen receptor. At 1-3 h in immature female rats, trans-[18F]FDA shows low and rather nonselective uptake in the principal estrogen target tissue (uterus) and slow clearance. By contrast, cis-[18F]FDA shows high uptake in nearly all tissues, with significant uterine uptake that continues to increase over the 1-6-h period. The uterine uptake of this isomer was blocked at the later times by a sufficiently high dose of unlabeled cis-FDA. After administration of the trans-[18F]FDA, a more polar metabolite slowly accumulates in the blood. The cis-[18F]FDA, however, showed no apparent metabolism, with 84% of the blood activity at 5 h assigned as the unmetabolized radioligand. After 5 h, only limited clearance from blood, liver, and kidneys has occurred. No metabolite from this isomer accumulates in the uterus. Although fluorodoisynolic acids will not be useful breast-tumor imaging agents, their behavior was found to be interesting as it deviates from that of other F-18 estrogens. Further long-term studies of cis-doisynolic acid, labeled with tritium, may be needed to explicate fully its unusual distribution properties and high in vivo activity.

Animals↗
PubMed1997

Application of a novel phenylpiperazine formation reaction to the radiosynthesis of a model fluorine-18-labeled radiopharmaceutical (18FTFMPP).

The labeled serotonin agonist 3-[18F]fluoro-N-(alpha,alpha,alpha-trifluoro-m-tolyl)piperazine (18FTFMPP) was prepared rapidly using the labeling procedure for trifluorotoluenes, [18F]fluoro-for-nitro exchange, followed by an alumina-supported bis-alkylation. After normal-phase HPLC purification, the labeled product was obtained in 20-32% (n = 20) decay-corrected radiochemical yield with a radiochemical purity > 98% and a specific activity of 100 GBq/mumol. The synthesis time including purification was 3 h. The receptor binding affinity of FTFMPP to rat brain membranes was found to be similar to that of the nonfluorinated parent compound (TFMPP). Although TFMPP has been proposed by others as an agent for the imaging of serotonin receptors, only minimal receptor-mediated uptake was observed.

Animals↗
PubMed1997

Pilot study of bronchodilator response to inhaled albuterol delivered by metered-dose inhaler and a novel dry powder inhaler.

BACKGROUND: The metered-dose inhaler is currently one of the most prescribed methods of delivering drugs to the lungs. In the United States, most currently marketed metered dose inhalers use chlorofluorocarbons as the system propellant and require patient breath coordination. These factors lead to the need for a delivery system that is independent of propellants and patient coordination. OBJECTIVE: To compare the magnitude and time course of bronchodilation between albuterol delivered by Ventolin metered dose inhaler and albuterol sulfate powder (Rotacaps) delivered by a novel dry powder inhaler that generates a respirable drug aerosol over a range of inspiratory flow rates. METHODS: A single-center, single-dose, randomized, placebo-controlled, partial-blind, 3-way crossover study was conducted in an outpatient asthma Clinical Research Center. Twelve mild to moderate asthmatic patients 12 to 36 years of age participated in this study that involved three treatments, each separated by three to eight days, consisting of 2 puffs (90 micrograms/puff) albuterol by Ventolin metered-dose inhaler, two inhalations (100 micrograms/puff) albuterol sulfate powder (Rotacaps) by dry powder inhaler, and two inhalations (12.5 mg/inhalation) lactose powder by dry powder inhaler. Spirometry, blood pressure, and heart rate were measured at 30 minutes, 15 minutes, and immediately before treatment and then at 15, 30, 45, 60, 90, 120, 180, 240, and 300 minutes after each treatment. Serum potassium and glucose, and electrocardiograms were measured at 30 minutes before, and 30, 60, 90, and 180 minutes after each treatment. Endpoints were compared with analysis of variance. RESULTS: Five patients (one metered-dose inhaler and four dry powder inhaler) did not respond with > 15% FEV1 increase over baseline within 30 minutes. Metered-dose inhaler and dry powder inhaler mean FEV1 results, respectively, for 11 and 8 responders were 15 minutes in onset, 202.9 and 185.4 minutes in duration, 24.8% and 25.1% maximum change, and 18.6 and 18.2 area-under-FEV1-bronchodilation-curve. Statistical analysis of all patients and responders-only revealed both active treatments to be different from placebo (P = .0018), but not different from each other (P = .1291). No safety endpoints were significantly different among all three treatments (P > .10 for all safety endpoints). CONCLUSIONS: In this study, the dry powder inhaler safely and effectively delivered a commercially available albuterol sulfate powder (Rotacaps) into human lungs with bronchodilation comparable to Ventolin metered-dose inhaler.

Administration, Inhalation↗
PubMed1997

In vivo kinetics of [18F](N-methyl)benperidol: a novel PET tracer for assessment of dopaminergic D2-like receptor binding.

A novel D2-like receptor-binding radioligand, [18F](N-methyl)benperidol ([18F]NMB), was evaluated via positron emission tomographic (PET) imaging studies of baboons. [18F]NMB rapidly localized in vivo within dopaminergic receptor-rich cerebral tissues, and striatum-to-cerebellum ratios as high as 35 were achieved after 3 hours. Pretreatment of an animal with unlabeled receptor-specific antagonists before injection of [18F]NMB confirmed that the radioligand bound specifically to central D2-like receptors in vivo, and not to S2- or D1-like receptors. Unlabeled eticlopride displaced striatal [18F]NMB in vivo, showing that D2-like binding is reversible. Receptor-binding by the radioligand was resistant to competitive displacement by synaptic dopamine, as illustrated by the lack of effect of intravenous d-amphetamine on the in vivo localization of [18F]NMB. Studies involving sequential intravenous administration of [18F]NMB, d-amphetamine, and eticlopride show that the radioligand does not undergo agonist-mediated internalization with subsequent trapping. The feasibility of applying a three-compartment non-steady state model for quantification of [18F]NMB receptor binding was demonstrated. These in vivo characteristics give [18F]NMB distinct advantages over the PET radiopharmaceuticals currently used for clinical investigation of D2-like receptor binding.

Animals↗
PubMed1997

Dose-ranging study of the clinical efficacy of twice-daily triamcinolone acetonide inhalation aerosol in moderately severe asthma.

OBJECTIVES: This multicenter, double-blind, placebo-controlled study evaluated the dose response to 6 weeks of triamcinolone acetonide inhalation aerosol (TAA, 100 microg per puff) in patients with moderately severe asthma. STUDY DESIGN: A total of 285 patients were randomly assigned to treatment with 1, 2, 4, or 8 puffs TAA (total daily doses of 200, 400, 800, and 1,600 microg, respectively), administered twice daily, or matching placebos. Efficacy was assessed by changes in FEV1, asthma symptom scores, albuterol use, and peak flow rates. RESULTS: Linear trend analyses showed a dose response for all efficacy variables across the dose range of 200 to 1,600 microg daily. Therapeutic activity was evident at a dose of 200 microg daily for all variables, with significant clinical efficacy (p<0.05) demonstrated for all doses except for reduction in inhaled albuterol use which achieved statistical significance at 400 microg/d. Daily doses of 400 microg and higher showed response plateaus at 3 weeks of treatment that were maintained for the remainder of the trial. The incidence of adverse events was similar in all treatment groups, although more patients treated with TAA reported pharyngitis in a dose-related manner. CONCLUSIONS: Our findings suggest that most patients with chronic, moderately severe asthma can be treated adequately with doses of TAA between 200 microg (1 puff bid) and 800 microg (4 puffs bid) daily. At this dose range, clinically significant improvements are evident in symptoms, pulmonary function, and rescue medication use.

Administration, Inhalation↗
PubMed1997

Synthesis, in vivo evaluation and PET study of a carbon-11-labeled neuronal nitric oxide synthase (nNOS) inhibitor S-methyl-L-thiocitrulline.

UNLABELLED: Reports have implicated neuronal nitric oxide synthetase (nNOS) in the pathological effects of neurodegenerative diseases. S-Methyl-L-thiocitrulline (MTICU), a potent and selective nNOS inhibitor (Ki = 1.2 nM), was chosen as our initial target molecule for positron emitter labeling as a potential nNOS tracer. We report the synthesis, biological evaluation and primate brain images of S-[11C]methyl-L-thiocitrulline ([I11C]MTICU). METHODS: The two-step synthesis of [11C]MTICU consisted of the S-alkylation of alpha-N-Boc-L-thiocitrulline t-butyl ester with [11C]Mel followed by TFA hydrolysis and HPLC purification. The final product was obtained within 50 min (yield = 9.1%-12.5%, based on [11C]Mel S.A. = 27-680 Ci/mmol at end of synthesis). The lipophilicity of [11C]MTICU was determined by octanol/water partition coefficient (LogP). Blood stability of this tracer in vitro and in vivo was measured by HPLC analysis. Biodistribution using female Sprague-Dawley rats was performed, including examination of uptake in cerebellum and olfactory bulb (high nNOS) as well as cortex and brain stem (low nNOS). Carbon-11-MTICU was administered to a female baboon and brain images were obtained using a Siemens ECAT EXACT scanner for determination of brain regional uptake and blood-brain barrier permeability. RESULTS: At 30 min postinjection, [11C]MTICU remained 64% intact in vivo and 95% intact in vitro. Lipophilicity estimation gave Log p = 1.08 +/- 0.08 (n = 6). The brain (0.11% ID/g)-to-blood (0.20% ID/g) ratio was 1:2 at 30 min postinjection. Uptake in the cerebellum was 20% higher than in either the cortex or the brain stem (p < 0.05). Blockage using 1 mg/kg MTICU reduced uptake in the cerebellum and the cortex by 22%, but did not affect the brain stem. PET imaging showed that [11C]MTICU brain uptake, corrected for blood volume, was stable from 10 min to 1 hr at approximately 0.4% ID/organ. PET images of a baboon brain showed increased uptake in the region of the olfactory bulb compared to uniform biodistribution in the rest of the brain. CONCLUSION: The [11C]MTICU is a tracer that is potentially useful in determining nNOS levels in vivo.

Animals↗
PubMed1996

Synthesis and evaluation of two positron-labeled nitric oxide synthase inhibitors, S-[11C]methylisothiourea and S-(2-[18F]fluoroethyl)isothiourea, as potential positron emission tomography tracers.

In an effort to develop a tracer for probing inducible nitric oxide synthase (iNOS) levels in vivo utilizing positron emission tomography, we have synthesized and evaluated two positron-emitting iNOS selective inhibitors: S-[11C]methylisothiourea (1b) and S-(2-[18F]fluoroethyl)-isothiourea (3b). Prior to fluorine-18 labeling, the nonradioactive fluoro derivative S-(2-fluoroethyl)isothiourea (3a) was prepared and determined to have a 9-fold higher selectivity for iNOS compared to endothelial NOS (eNOS). Radiochemical synthesis of both compounds, in high radiochemical purity and at high specific activity, was accomplished by the S-alkylation reaction of labeled precursors (11CH3I or 18FCH2CH2OTf) with thiourea. An in vitro model, J774 macrophage cell line, was used to assess the uptake of radiolabeled iNOS inhibitor in response to iNOS induction at the cellular level. Increased cell uptake of these two labeled compounds at stimulated iNOS levels, as well as blocking under controlled in vitro conditions, was observed. Lipophilicity (log P o/w), stability, and tissue biodistribution data of both compounds are reported. Serum stability studies indicate that 3b metabolized much more rapidly compared to the relatively stable 1b in vitro and in vivo. Based on in vitro cell uptake data, both tracers were further evaluated in lipopolysaccharide (LPS)-pretreated rats. LPS has been reported to induce iNOS protein expression in the liver, lung, heart, and kidney and other tissues. The uptake for LPS-pretreated rats (6 h post-treatment) was significantly increased in the liver, kidney, and heart for 3b at 10 min and in the liver and lung for 1b at 30 min. The results suggest that this first generation of radiolabeled inhibitors may be useful for assessing induction of iNOS in vivo with PET.

Animals↗
PubMed1996

Evaluation of the stability and animal biodistribution of gadolinium (III) benzylamine-derivatized diethylenetriaminepentaacetic acid.

The need for a readily available Gd(III) bifunctional chelate for protein conjugation has led to the development of LDTPA (N,N-bis[2-[N',N'-bis(carboxymethyl)amino]- ethyl]-4-amino-L-phenyl-alanine). The benzylamine group is readily converted to the isothiocyanato group (SCN-LDTPA) by treatment of the lithium salt of LDTPA with thiophosgene. SCN-LDTPA was successfully conjugated to three proteins, BSA (bovine serum albumin), mannose BSA, and galactose BSA. All protein conjugates were labeled with 111In3+ or 153Gd3+. Competition of Gd-LDTPA with DTPA (diethylenetriaminepentaacetic acid) resulted in a log stability constant of 21.2. The thermodynamic stability constant of Gd-LDTPA was also measured. The log Gd(III) stability constant (log K) is 21.99, and the log protonation constants (pKa's) are 10.16, 8.92, 5.35, 3.93, 2.71, and 1.89. Comparison of the thermodynamic stability constants for Gd(LDTPA)2- with other DTPA derivatives indicates that the stability of Gd(LDTPA)2- is similar to Gd(DTPA)2- (log K = 22.4), and higher than DTPA derivatives with one or more carboxylate arm(s) functionalized. The biodistribution of 153Gd-LDTPA-protein conjugates is consistent with the in vitro stability measurements. By monitoring the bone accumulation of 153Gd3+, 153Gd-LDTPA-protein shows a higher in vivo stability than 153Gd-DTPA-protein, the radiolabeled protein conjugate formed by the reaction of DTPA dianhydride with proteins.

Animals↗