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Hitoshi Shinotoh

Publications and source records attributed to Hitoshi Shinotoh.

7 recordsLinked to original sources
PubMed2005

Estimation of plasma IC50 of donepezil hydrochloride for brain acetylcholinesterase inhibition in monkey using N-[11C]methylpiperidin-4-yl acetate ([11C]MP4A) and PET.

Donepezil hydrochloride is a potent and selective inhibitor for brain acetylcholinesterase (AChE) and is currently used worldwide for the treatment of Alzheimer's disease. Until now, there is no in vivo study on the relation between the plasma concentration and the brain AChE inhibition. The purpose of this study was to estimate in vivo plasma IC(50) of donepezil in living monkeys by measuring plasma donepezil concentration (LC/MS/MS) and brain AChE activity with positron emission tomography (PET) and N-[(11)C]methylpiperidin-4-yl acetate, which is an acetylcholine analog recently developed by us for quantifying in vivo brain AChE activity. PET scans with donepezil at two doses, 100 microg/kg (donepezil-1; N=5) or 250 microg/kg (donepezil-2; N=5), were performed using the same monkeys at 4-week intervals. Before each PET scan, baseline PET scans (N=10 in total) were performed without donepezil. The plasma donepezil concentrations 14 min after intravenous injection were proportional to the doses, 17.2+/-2.9 ng/ml (donepezil-1) and 44.0+/-5.0 ng/ml (donepezil-2), and the mean AChE inhibitions in four neocortical regions as evaluated by PET were also dose-dependent, 27% (donepezil-1) and 53% (donepezil-2). In IC(50) estimation, measured plasma donepezil concentrations were corrected for the change during PET scan. The IC(50) values (estimate+/-SE) were 42+/-9.0 (ng/ml; donepezil-1), 34+/-3.2 (donepezil-2), and 37+/-4.1 (combined data). The present method may be useful for in vivo evaluation of other AChE inhibitors and novel drugs.

Acetylcholinesterase↗
PubMed2004

A simple method for the detection of abnormal brain regions in Alzheimer's disease patients using [11C]MP4A: comparison with [123I]IMP SPECT.

We have developed a radiolabeled lipophilic acetylcholine analogue, N-[11C]methylpiperidin-4-yl acetate ([11C]MP4A) to measure brain acetylcholinesterase (AChE) activity by positron emission tomography (PET) in vivo. Aiming to develop a new SPECT tracer similar to MP4A, we first proposed a simple method for diagnosing Alzheimer's disease (AD) using [11C]MP4A PET. We performed [11C]MP4A PET and N-isopropyl [123I]iodoamphetamine ([123I]IMP) SPECT in 13 patients with AD and in 17 normal controls (NC). We calculated the ratio of radioactivity of the cortical region of interest (ROI) to that of the cerebellum measured with [11C]MP4A PET (MP4A ratio) and the ratio of regional cerebral blood flow (rCBF) to that of the cerebellum measured with [123I]IMP SPECT (IMP ratio). Eleven cortical ROIs were placed in the frontal, sensorimotor, temporal, parietal, and occipital cortices in both hemispheres and in the posterior cingulate cortex, and z-score was calculated in each ROI in patients with AD compared with NC. When the z-score was 2 or more in a ROI, it was defined as a positive ROI. When a patient had 3 or more positive ROIs, the patient was diagnosed as having AD. The reduction in the MP4A ratio was greater than that in the IMP ratio in all cortical ROIs except for in the right parietal cortex and cingulate cortex in patients with AD. MP4A ratio method showed 92% sensitivity and the IMP ratio method 69% sensitivity for the diagnosis of AD. These results encourage us to develop a new SPECT tracer similar to MP4A for the diagnosis of AD.

Acetates↗
PubMed2004

Evaluation of simplified kinetic analyses for measurement of brain acetylcholinesterase activity using N-[11C]Methylpiperidin-4-yl propionate and positron emission tomography.

The applicability of two reference tissue-based analyses without arterial blood sampling for the measurement of brain regional acetylcholinesterase (AChE) activity using N-[11C]methylpiperidin-4-yl propionate ([11C]MP4P) was evaluated in 12 healthy subjects. One was a linear least squares analysis derived from Blomqvist's equation, and the other was the analysis of the ratio of target-tissue radioactivity relative to reference-tissue radioactivity proposed by Herholz and coworkers. The standard compartment analysis using arterial input function provided reliable quantification of k3 (an index of AChE activity) estimates in regions with low (neocortex and hippocampus), moderate (thalamus), and high (cerebellum) AChE activity with a coefficient of variation (COV) of 12% to 19%. However, the precise k3 value in the striatum, where AChE activity is the highest, was not obtained. The striatum was used as a reference because its time-radioactivity curve was proportional to the time integral of the arterial input function. Reliable k3 estimates were also obtained in regions with low-to-moderate AChE activity with a COV of less than 21% by striatal reference analyses, though not obtained in the cerebellum. Shape analysis, the previous method of direct k3 estimation from the shape of time-radioactivity data, gave k3 estimates in the cortex and thalamus with a somewhat larger COV. In comparison with the standard analysis, a moderate overestimation of k3 by 9% to 18% in the linear analysis and a moderate underestimation by 2% to 13% in the Herholz method were observed, which were appropriately explained by the results of computer simulation. In conclusion, simplified kinetic analyses are practical and useful for the routine analysis of clinical [11C]MP4P studies and are nearly as effective as the standard analysis for detecting regions with abnormal AChE activity.

Acetylcholinesterase↗
PubMed2004

Acetylcholinesterase imaging: its use in therapy evaluation and drug design.

Several cholinesterase (ChE) inhibitors have been labeled with carbon-11 for visualizing binding sites on acetylcholinesterase (AChE) by positron emission tomography (PET). Following intravenous injection of 1,2,3,4-tetrahydro-9-[(11)C]methylaminoacridine or [(11)C]donepezil, however, the radioactivity distribution does not reflect the regional distribution of AChE in the brain of animals, probably because these compounds have high non-specific binding and/or other specific binding sites in vivo in the brain. PET studies with [(11)C]physostigmine and [(11)C]CP-126,998 in the brain of healthy subjects have shown a radioactivity distribution corresponding to the regional distribution of AChE activity measured in postmortem human brains. These radiotracers may be useful for measuring the occupancy of binding sites on AChE by AChE inhibitors, and for investigating the cerebral pharmacokinetics of such therapeutic drugs. An alternative approach to map AChE is the use of acetylcholine analogue substrates. We have developed N-methylpiperidinyl esters labeled with carbon-11 for quantitative measurement of AChE activity. Currently, two N-[(11)C]methylpiperidine esters, N-[(11)C]methylipiperidin-4-ylacetate (MP4A) and N-[(11)C]methylpiperidin-4-yl propionate (MP4P or PMP), have been used for clinical studies of Alzheimer's disease and other neurodegenerative diseases. Both [(11)C]MP4A- and [(11)C]MP4P-PET have demonstrated not only the reduction of AChE activity in the cerebral cortex of patients with Alzheimer's disease (AD) but also the inhibitory effects of donepezil and rivastigmine on AChE activity in the brain of AD patients. AChE imaging should prove useful for therapeutic monitoring of the effects of ChE inhibitors, including determination of the appropriate clinical doses of newly developed compounds, and can thus prompt the development of novel drugs targeting AChE.

Acetylcholinesterase↗
PubMed2003

Biopterin metabolism in patients with malignant syndrome.

We examined the autopsied brains of two parkinsonian patients who had malignant syndrome (MS). Neopterin and biopterin contents, and GTP cyclohydrolase I activity were measured in various region of the brain. We found relatively higher GTP cyclohydrolase I activities in the hypothalamus compared with other regions of the brain from patients with MS. This finding suggested a possible involvement of biopterin metabolism in pathophysiology of MS. This is the first report on biopterin metabolism in the brains of patients with MS.

Aged↗
PubMed2002

Positron emission tomography: quantitative measurement of brain acetylcholinesterase activity using radiolabeled substrates.

A new method for quantitative measurement of brain acetylcholinesterase (AChE) activity in living human brain using positron emission tomography (PET) is described. We tested several radiolabeled lipophilic acetylcholine analogs, e.g., N-methylpiperidyl esters, which readily entered the brain via the blood-brain barrier, were hydrolyzed selectively by AChE, and were then trapped in the brain. Among them, and tested and N-[11C]methylpiperidin-4-yl acetate ([11C]MP4A) was chosen as the tracer for PET. Quantitative measurement of cortical AChE was accomplished by fitting the time course of cerebral radioactivity concentration measured by PET and the metabolite-corrected arterial plasma input function using a nonlinear least-squares fitting method. Normal control studies of subjects with a wide range in age (24-89 years) showed no decrease in AChE activity in the cerebral cortex with age. Studies on patients with Alzheimer's disease demonstrated a widespread reduction of AChE activity in the cerebral cortex (more profound in early-onset than in late-onset Alzheimer's disease). Parkinson's disease and progressive supranuclear palsy, clinically similar disorders, could be differentiated with [11C]MP4A/PET studies. Simple methods without using an arterial input function are also proposed. The method provides a quantitative measure of the cholinergic aspect of brain function and proved to be useful in diagnosis of neurodegenerative disorders including Alzheimer's disease.

Acetylcholinesterase↗