Y. Lucas Yamamoto

Quantification of Glucose Utilization in an Experimental Brain Tumor Model by the Deoxyglucose Method

Reevaluation of lumped and rate constants is necessary when Sokoloffs 2-deoxyglucose (DG) method is used to measure glucose utilization in pathological tissue. We describe here a modification of Sokoloffs lumped constant measurement that permits simultaneous estimation of both lumped and rate constants from a single animal experiment. A subcutaneous tumor model (AA ascites tumor) was used for measurement of these constants with a procedure similar to Sokoloffs that kept the plasma tracer concentration constant. Measured constants were as follows: lumped constant, 0.654 ± 0.081; k*1, 0.196 ± 0.038 min−1; k*2, 0.262 ± 0.067 min−1; k*3, 0.117 ± 0.044 min−1. These constants were used to quantify glucose utilization in the implanted brain tumor. To test the validity of this method, we compared a fraction of the free DG pool calculated using the tumor constants with a fraction measured directly by chromatographic analysis of tissue samples from both subcutaneous tumor and implanted brain tumor. The values derived by chemical analysis agreed well with those predicted by the calculations. The value of k*4 varied from 0.0031 ± 0.0018 min−1 for the tumor tissue to 0.0214 ± 0.0024 min−1 for tumors with a large necrotic center. This method would be especially useful when applied to xenograft human gliomas in nude mice for quantification of glucose utilization in human gliomas by means of positron emission tomography.

An Improved Approach for Measurement of Regional Cerebral Rate Constants in the Deoxyglucose Method with Positron Emission Tomography

A new experimental approach was designed to measure regional rate constants for [18F]2-fluoro-2-d-deoxyglucose in the three-compartment model. A programmed infusion was used to keep the plasma tracer concentration constant for the first 20 min. Positron emission tomography images of the brain were taken every minute for 20 min in a low-resolution mode, then every 15–20 min for 2–3 h in a medium-resolution mode. Two simplified operational equations for the calculation of the regional rate constants were derived that incorporated the contribution of the vascular compartment to tissue activity. The first equation was applied to data collected during the initial 20 min (when the concentration of plasma tracer was constant) to estimate the values of k*1, k*2, k*3, and the fraction of the vascular compartment. The second equation was applied to data collected during the whole experimental period to find the value of k*4 and to provide a better estimate of k*3. The regional rate constants measured experimentally in three dogs and a brain tumor patient agreed well with those in the literature. This method permits estimation of the local CMRglu under pathological conditions using regionally measured rate constants and provides new information on the pathophysiological meaning of the rate constants.

Effect of Acute Fluoxetine Treatment on the Brain Serotonin Synthesis as Measured by the α-Methyl-l-Tryptophan Autoradiographic Method†

Abstract: The effect of treatment with acute fluoxetine, a serotonin reuptake inhibitor, on the rate of serotonin synthesis in the rat brain was studied through autoradiography following intravenous administration of α‐methyl‐l‐[3H]tryptophan. The rate of serotonin synthesis in fluoxetine‐treated rats was compared with the rate measured in sham‐treated rats (saline injection). Results showed a significant increase in the rate of synthesis in the majority of cerebral structures examined. The greatest increase (given as a percentage of rates in control animals) in the rate of serotonin synthesis was observed in the substantia nigra compacta (344%), hippocampus‐CA3 (337%), dorsal hippocampus (283%), and caudate‐putamen (232%). Fluoxetine had a less significant effect on the rate of synthesis in the pineal body (44%). Data suggest that acute fluoxetine treatment (30 mg/kg, i.p.) enhances the rate of serotonin synthesis in all the structures of rat brain examined in this work.

Quantitative Measurements of Regional Glucose Utilization and Rate of Valine Incorporation into Proteins by Double-Tracer Autoradiography in the Rat Brain Tumor Model

We examined the rate of glucose utilization and the rate of valine incorporation into proteins using 2-[18F]fluoro-2-deoxyglucose and L-[1-14C]-valine in a rat brain tumor model by quantitative double-tracer autoradiography. We found that in the implanted tumor the rate of valine incorporation into proteins was about 22 times and the rate of glucose utilization was about 1.5 times that in the contralateral cortex. (In the ipsilateral cortex, the tumor had a profound effect on glucose utilization but no effect on the rate of valine incorporation into proteins.) Our findings suggest that it is more useful to measure protein synthesis than glucose utilization to assess the effectiveness of antitumor agents and their toxicity to normal brain tissue. We compared two methods to estimate the rate of valine incorporation: “kinetic” (quantitation done using an operational equation and the average brain rate coefficients) and “washed slices” (unbound labeled valine removed by washing brain slices in 10% thrichloroacetic acid). The results were the same using either method. It would seem that the kinetic method can thus be used for quantitative measurement of protein synthesis in brain tumors and normal brain tissue using [11C]-valine with positron emission tomography.

Time-Dependent Changes of Lumped and Rate Constants in the Deoxyglucose Method in Experimental Cerebral Ischemia

Time-dependent changes in the lumped and rate constants in a bilateral middle cerebral artery (MCA) occlusion in cats were evaluated. These variables were measured in 11 cats after a sham operation, in five after a 1-h occlusion, in two after a 2-h occlusion, in five after a 4-h occlusion, and in four after a 16-h occlusion. The time course of the cerebral tissue radioactivity [Ci* (t)] was monitored by external coincidence counting during a programmed infusion of [18F]2-fluorodeoxyglucose (FDG). Arterial plasma concentration [Cp* (t)] of tracer was kept constant during the first 45 min. Comparison of k2* and k3* in the sham-operated group, estimated by external coincidence counting, and by the ratio of extraction fractions of glucose and [18F]2-FDG, demonstrated no significant difference between these rate constants in these two groups of animals. The rate and lumped constants were also estimated from Ci* (t) and Cp* (t), as well as from the ratio of extraction fractions of glucose and [18F]2-FDG, respectively, in the MCA occlusion group. Significant decrease in k3* was observed after 1 h of occlusion (20% lower than in the sham operation, p < 0.05); in ki* decrease occurred within 4 h of occlusion (21% lower than in the sham operation, p < 0.05). However, decrease in k2* was observed only after 16 h of occlusion (26% lower than in the sham operation, p < 0.05). Namely, decrease of rate constants occurred first in k3* then in k1* and k2*. In contrast to the rate constants where decrease was observed, a significant increase in the lumped constant occurred between 1 and 4 hours after occlusion (55% higher than in the 1-h occlusion, p < 0.05). However, the values of the lumped constant were not significantly different between the 4-h occlusion group and the 16-h occlusion group.

Influence of the input function on the calculation of the local cerebral metabolic rate for glucose in the deoxyglucose method

We describe here a modification of Sokoloffs deoxyglucose method which requires fewer blood samples but does not diminish accuracy. To calculate the local cerebral metabolism for glucose (LCMRglu), the input function containing the initial peak must be known. This requires many blood samples for accurate definition. To estimate the influence of the peak on the LCMRglu, a dummy input function was generated by extrapolating the data points after 2 min back to 0 min. Next, a biexponential curve, fitted to a reduced number of samples, was applied for the input function. The error introduced into the LCMRglu by using these different approximations was analyzed with an error function derived from an operational equation. The results indicate that the error of LCMRglu caused by neglecting the peak is <3%. Furthermore, the error of LCMRglu resulting from use of the biexponential approximation is a function of LCMRglu: the error decreases as the LCMRglu increases and remains at <3% even when only seven data points are used (half the usual number of the standard method). Finally, the LCMRglu was calculated by the biexponential curve-fitting, using the experimental data, and compared with that calculated by Sokoloffs computer program. Both methods were in good agreement. This modified method offers great advantage for simultaneous measurement of CMRglu, CBF, and other physiological parameters by means of the multiple tracer autoradiographic technique in the small laboratory animal.

Hemodynamic and metabolic effects of extracranial carotid disease.

Cerebral blood flow (CBF), cerebral blood volume (CBV), the CBF/CBV ratio - an index of the hemodynamic reserve capacity - the rate of oxygen metabolism (CMRO2), and the fractional extraction of oxygen by the brain (OEF) were studied by positron emission tomography (PET) in the cortical territory of both internal carotid arteries in 15 cases of transiently symptomatic or progressive extracranial atherosclerotic carotid disease. None of the patients had a major stroke or had a significant neurological deficit except 1 whose damaged hemisphere is excluded from study. All were asymptomatic at the time of PET scanning. Values were obtained in the middle cerebral artery (MCA) distribution, and in the anterior and posterior borderzone regions. Eight cases had unilateral carotid stenosis of 80% or greater and 7 had unilateral or bilateral occlusion of the origin of the internal carotid artery. Results obtained in patients were compared using Students t-test, to those obtained in neurologically normal, elderly volunteers. Patients with carotid stenosis had a significantly decreased CBF (p less than .025) and CBF/CBV ratio (p less than .025) selectively in the anterior borderzone regions. This was accompanied by a trend toward elevated OEF and declining CMRO2 values. Patients with carotid occlusion had significantly decreased CBF (p less than .005), decreased CBF/CBV ratio (p less than .005) and decreased CMRO2 (p less than .025) in the ipsilateral anterior borderzone and MCA territories. Similar changes were present in the opposite hemisphere of patients with bilateral carotid disease. These results indicate that carotid stenosis is associated with hypoperfusion and diminished hemodynamic reserve capacity in the anterior borderzone, and that carotid occlusion produces more widespread hypoperfusion and metabolic depression.

Regional glucose utilization and blood flow in experimental brain tumors studied by double tracer autoradiography

SummaryCoupling of regional glucose utilizatio (GLU) and blood flow (CBF) was examined in rats with implanted brain tumors (AA ascites tumor) by quantitative double tracer autoradiography using 18F-2-fluorodeoxyglucose and 14C-iodoantipyrine. Four to 13 days after implantation, the animals were injected with the two tracers to obtain autoradiograms from the same brain section before and after the decay of 18F. The autoradiograms were then analyzed by an image processor to obtain a metabolic coupling index (MCI = GLU/ CBF).In the tumor, high GLU and low CBF were uncoupled to give a high MCI which implied anerobic glycolysis. In large tumors, the CBF was even lower. In the peri-tumoral region, GLU was reduced (especially in gray matter) and reduction was lowest around the larger tumors. CBF in the peri-tumoral region was also reduced, but this reduction became less as the distance from the tumor margin increased. These changes in the peri-tumoral region may be secondary to edema. The GLU and CBF of white matter was little influenced by the presence of tumors except for some reduction in these values in relation to the larger tumors.On a narrow margin of tumor and brain, corresponding to a zone of increased vascularity, CBF was moderately high. The MCI in the tumor was higher than in the cortex of the same as well as the opposite hemisphere. These findings indicate that the metabolism and blood flow of the tumor and surrounding brain are variable and directly related to tumor size.

The sequential changes in DNA synthesis, glucose utilization, protein synthesis, and peripheral benzodiazepine receptor density in C6 brain tumors after chemotherapy to predict the response of tumors to chemotherapy

Monitoring therapy in patients with brain tumors is very difficult and unreliable. It has been shown that there is no good correlation between tumor sensitivity measured in vitro and in situ tumor response to therapies.

Permeability change and brain tissue damage after intracarotid administration of cisplatin studied by double-tracer autoradiography in rats.

SummaryThe present study was designed to find the reliable parameter(s) for the detection of early neurotoxicity following intracarotid (IC) administration of cisplatin. IC administration was performed for 60 minutes in female Wistar rats derived into four groups according to the dose given (1 mg, 1.2 mg, and 1.5 mg of cisplatin, and normal saline in control rats). Blood-brain barrier (BBB) permeability and local cerebral blood flow (LCBF) were measured by a double-tracer autoradiography technique using 1-[14 C]-α-aminoisobutyric acid (14 C-AIB) and 4-[18 F] fluoroantipyrine (18 F-FAP), respectively. Blood chemistry and neuropathology were also examined. BBB permeability was incereased only on the ipsilateral side. This increase was dose-dependent, preceded the brain necrosis, and was statistically significant in the hypothalamus [1.2 mg group), auditory cortex and caudoputamen (1.5 mg group). Renal dysfunction was often observed. The changes in the LCBF did not occur until brain necrosis was noticeable. These findings demonstrate that the increase in the BBB permeability provides a sensitive and reliable indication of an early toxicity to brain tissue following IC administration of cisplatin.