technetium-tc-99m-exametazime and diethyl-maleate

Technetium-99m-d,l-hexamethylpropylene amine oxime ((99m)Tc-HMPAO) retention in the brain monitored by single photon emission computed tomography (SPECT) is currently used as a marker of cerebral blood flow. The purported mechanism by which (99m)Tc-HMPAO accumulates in the brain is through its intracellular conversion from a lipophilic form to more hydrophilic derivatives within the brain parenchyma. The issue of the contribution of different cell types on (99m)Tc-HMPAO retention was investigated in vitro by studying the accumulation of (99m)Tc-HMPAO in primary cultures of mouse cortical astrocytes and neurons. Results show that (99m)Tc-HMPAO retention predominates in astrocytes over neurons by a factor of approximately 2.5 (0.26 +/- 0.05 vs. 0.095 +/- 0.042 fmol/mg protein after 120 minutes, respectively). Diethyl maleate (60 micromol/L), ethacrynic acid (1 mmol/L) and buthionine sulfoximine (1 mmol/L), 3 agents which significantly reduced glutathione levels also decreased (99m)Tc-HMPAO retention in both astrocytes (29%, 3%, and 46% of control, respectively) and neurons (69%, 11% and 63% of control). Decrease did not always correlate with glutathione levels, however, which suggests that other factors could be involved. The possibility that cell energy status determines (99m)Tc-HMPAO retention was also assessed. Agents that activate (glutamate, azide) or inhibit (cytochalasin B) glucose utilization in astrocytes, as measured by the (3)H-2-deoxyglucose method, were without effect on (99m)Tc-HMPAO retention. In conclusion, the data presented indicate that astrocytes may constitute a prominent site of (99m)Tc-HMPAO retention and most likely contribute significantly to the SPECT signal. In addition, the data also suggest that specific alterations in glial cell metabolism could explain flow-independent changes in (99m)Tc-HMPAO retention in the brain as observed by SPECT in some pathologies.

Topics: Animals; Astrocytes; Biological Transport; Buthionine Sulfoximine; Cells, Cultured; Cerebral Cortex; Enzyme Inhibitors; Ethacrynic Acid; Glutathione; Maleates; Mice; Neurons; Radiopharmaceuticals; Technetium Tc 99m Exametazime

To investigate whether [(99m)Tc]-hexamethyl propyleneamine oxime ([(99m)Tc]-HMPAO) is applicable for evaluating glutathione (GSH) localization in tumor, the difference of distribution between [(99m)Tc]-d,l- and meso-HMPAO was studied using a mouse tumor model. Biodistribution of [(99m)Tc]-d,l- or meso-HMPAO was studied in GSH-depleted and control Ehrlich tumor-bearing mice. GSH levels in tumors in GSH-depleted and control mice were measured in another set of mice. The uptake of [(99m)Tc]-d,l-HMPAO in tumor was significantly decreased by the diethyl maleate (DEM) treatment. On the other hand, the DEM treatment increased the accumulation of [(99m)Tc]-meso-HMPAO in tumor. Meanwhile, the content of GSH was lowest in tumor among the tissues tested and decreased in a manner similar to other tissues on preloading of DEM. [(99m)Tc]-d,l-HMPAO may be useful for estimating the GSH status in a certain tumor and thereby contribute to the diagnosis of anticancer therapy.

Topics: Animals; Brain; Carcinoma, Ehrlich Tumor; Glutathione; Kidney; Liver; Lung; Male; Maleates; Mice; Mice, Inbred Strains; Neoplasm Transplantation; Organ Specificity; Radionuclide Imaging; Spleen; Stereoisomerism; Technetium Tc 99m Exametazime; Tissue Distribution

The aim of this study was to explain the contribution of mitochondria to the accumulation of 99mTc-meso-hexamethyl propyleneamine oxime (HMPAO) in the brain, after examinations were performed.. We studied subcellular distribution of 99mTc-meso-HMPAO and glutathione (GSH) in normal and diethyl maleate (DEM)-administered mice.. In normal brain, major radioactivity was found in the mitochondrial (49.0%) and cytosolic fractions (33.0%), while the GSH content was high in the cytosol (63.2%) and mitochondria (30.6%). The radioactivity in mitochondrial, cytosolic, microsomal and nuclear fractions was decreased in a dose-dependent manner by DEM, a GSH depleting agent, to 32.2% (mitochondrial) and 24.7% (cytosolic) of the control by a dose of 550 mg/kg. The GSH content in mitochondrial and cytosolic fractions also decreased in a dose-dependent manner on DEM treatment to 29.3% (mitochondrial) and 30.0% (cytosolic) of the control by 550 mg/kg of DEM. A good correlation was found between the uptake of 99mTc-meso-HMPAO and GSH content in mitochondrial, cytosolic and nuclear fractions, with a correlation coefficient (r) of 0.814, 0.834 and 0.784, respectively.. Mitochondria are a major subcellular fraction for the uptake of 99mTc-meso-HMPAO by the brain, and GSH in mitochondria contributes to the accumulation of 99mTc-meso-HMPAO.

Topics: Animals; Brain; Cell Nucleus; Cytosol; Glutathione; Kinetics; Maleates; Mice; Mice, Inbred Strains; Microsomes; Mitochondria; Technetium Tc 99m Exametazime; Tissue Distribution

To clarify whether the content of glutathione (GSH) in the brain can be estimated by the uptake of 99mTc-meso-HMPAO, we conducted the following in vivo and in vitro experiments.. We investigated the effect of diethyl maleate (DEM) and buthionine sulfoximine (BSO) administration on the brain uptake of 99mTc-meso-HMPAO in the mouse, rat and rabbit, and the chemical specificity of in vitro interaction of 99mTc-HMPAO to GSH using measurements of octanol-extractable radioactivity as an index of remaining intact tracer.. The uptake of 99mTc-meso-HMPAO in the mouse and rat brain were reduced together with decreased content of GSH by preloading of DEM, a GSH depletor that acts through glutathione S-transferase. Neither 99mTc-meso-HMPAO uptake nor GSH content was affected in the rabbit brain. Similarly, the uptake of 99mTc-meso-HMPAO and GSH content in the mouse brain was reduced by preinjection of BSO, a GSH depletor that acts through gamma-glutamylcysteine synthetase. In an in vitro study, 99mTc-HMPAO showed reactivity to the molecules possessing a -SH group, but were not specific to GSH. The order of 99mTc-meso-HMPAO reactivity to the mouse brain homogenate agreed with the order of GSH concentration: normal > BSO > DEM. GSH was a major contributor to the conversion reaction of 99mTc-meso-HMPAO to hydrophilic complex in mouse brain homogenate.. GSH may have a major responsibility for trapping 99mTc-HMPAO in the brain, suggesting the possibility of in vivo measurement of brain GSH with 99mTc-meso-HMPAO.

Topics: Animals; Brain; Buthionine Sulfoximine; Glutathione; In Vitro Techniques; Maleates; Mice; Organotechnetium Compounds; Oximes; Rabbits; Radiopharmaceuticals; Rats; Rats, Wistar; Sulfhydryl Compounds; Technetium Tc 99m Exametazime

To visualize the regional localization of glutathione (GSH) in the brain, the relationship between the concentrations of tissue GSH and uptake of [99mTc]meso-hexamethyl propyleneamine oxime ([99mTc] meso-HMPAO) or [99mTc]d,l-hexamethyl propyleneamine oxime ([99mTc]d,l-HMPAO) was studied in mice.. The uptake of [99mTc]meso-HMPAO in the mouse brain was decreased to 35% of control paralleling the decrease in GSH content by pre-loading of diethyl maleate (DEM), an agent to reduce GSH. In contrast, pre-treatment with DEM scarcely affected the 99mTc-d,l-HMPAO uptake in the brain.. The DEM treatment decreased the GSH content in liver, kidney, spleen, fat and lung but did not affect the uptake of [99mTc]meso-HMPAO in those tissues except lung. The images of rat brain acquired with a gamma camera showed a significant reduction of [99mTc]meso-HMPAO uptake by DEM treatment.. Technetium-99m-meso-HMPAO may be a potential tool to assess GSH content and to estimate antioxidative ability in the brain.

Topics: Animals; Brain; Glutathione; Maleates; Mice; Organotechnetium Compounds; Oxidation-Reduction; Oxidative Stress; Oximes; Rats; Rats, Wistar; Stereoisomerism; Sulfhydryl Compounds; Technetium Tc 99m Exametazime; Tissue Distribution

The accumulation and retention mechanisms of 99mTc-d, 1-hexamethylpropyleneamine oxime (99mTc-d, 1-HMPAO) were investigated in cultures of the dissociated rat cerebellum. Our experiments indicate a linear dependency of the uptake on incubation time and on the concentration of the radioligand. Upon chloroform extraction and distribution between the lipophilic and the hydrophilic phases, we located 69.1% of the retained radioactivity in the hydrophilic phase, 24.1% in a bound state and 6.8% in the lipophilic phase. The water-soluble, unbound radioactive contents of the cultures were identified as 99mTcO4- by HPLC analysis. Treatment of cultures with diethyl maleate (DEM) inhibited the accumulation of radioactivity along with a reduction of the GSH contents of the cultures. However, even in the absence of GSH, significant amounts of radioactivity were accumulated. DEM reduced the radioactive contents of cultures predominantly by diminishing the aqueous phase of the chloroform-extracted material. By contrast, the metabolic state, manipulated by treating the cultures with oligomycin B or 2,4-dinitrophenol, had no significant effect on the accumulation of radioactivity. Our experiments suggest two major mechanisms for the retention of radioactivity following the exposure of neuronal tissue to 99mTc-d, 1-HMPAO: Conversion of the lipophilic complex to the hydrophilic product, 99mTcO4-, and binding to non-diffusible cell components.

Topics: 2,4-Dinitrophenol; Animals; Cells, Cultured; Cerebellum; Chromatography, High Pressure Liquid; Dinitrophenols; Half-Life; Maleates; Oligomycins; Organotechnetium Compounds; Oximes; Radionuclide Imaging; Rats; Technetium; Technetium Tc 99m Exametazime; Time Factors