Effects of iron, copper, cobalt, and their chelators on the cytotoxicity of bleomycin.

Bleomycin is widely used for treating several types of human tumors as well as a variety of experimental tumors. The ability of this antibiotic to bind and to damage DNA has been proposed to be responsible for its antitumor effect. Bleomycin is also a good chelator for several metals, e.g., iron, copper, and others. Bleomycin:metal complexes have been investigated in detail particularly for their action on isolated DNA. The conclusions from these studies indicate that metal-chelated bleomycin either is ineffective or more effective in damaging DNA. In this paper, we tested the effect of iron, copper, cobalt, and their chelators on bleomycin cytotoxicity. Our results suggest that chelating bleomycin with copper or adding an iron chelator (deferoxamine), diethylenetriamine pentaacetic acid, and a copper chelator (penicillamine) shows no effect on bleomycin cytotoxicity. On the other hand, iron dextran and a metal chelator, diethyldithiocarbamate (DDC), with bleomycin show enhanced cytotoxicity. Cobalt-chelated bleomycin is not cytotoxic but is cytotoxic when combined with DDC. We suggest that different mechanisms are contributing to the enhanced toxicity of bleomycin with iron dextran and DDC. Bleomycin acts as a ferrous oxidase which promotes the iron toxicity. In the case of DDC, it can act as a reducing agent or it can help to maintain the bleomycin:metal complex in the reduced form which can generate radicals.

Amino acid and sugar transport incells permissively infected with simian virus 40.

Transport of alpha-aminoisobutyric acid and 2-deoxy-D-glucose in African green monkey kidney cells was measured 8 to 100 hr following permissive simian virus 40 infection. No differences in transport were detected during the time-period studies, and no significant differences were seen between the apparent Michaelis-Menten constants of normal and virally infected cells. The absence of transport enhancement in permissive simian virus 40 infection suggests that the augmented transport of viral-transformed cell lines devolves upon altered host genome function.

Impairment of Na+-dependent amino acid transport in a cultured human T-cell line by hyperthermia and irradiation.

We have examined the effects of hyperthermia and radiation on the ability of a human T-leukemic lymphocyte line (Molt-4) to transport the Na+-dependent amino acid, 2-aminoisobutyrate (AIB). Heating Molt-4 at 43 degrees for 1 to 4 hr damages the ability of these cells to accumulate AIB. The damage to the transport system at 43 degrees impairs only the maximal rate of AIB uptake, i.e., Vmax. The thermal effect on AIB transport parallels the radiation effects observed for this system. Preliminary data indicate that heat and radiation may induce irreversible transitions in the tertiary or quaternary structure of a plasma membrane protein involved in regulating Na+-dependent amino acid transport. However, the mechanism by which heat and radiation damage this protein is different.

Actin filament organization of the Dunning R3327 rat prostatic adenocarcinoma system: correlation with metastatic potential.

Recently, Volk, Geiger, and Raz (Cancer Res., 44: 811-824, 1984) addressed the question of whether variations in actin organization in clones of the murine K-1735 melanoma tumor correlated with their metastatic capability. Using immunofluorescence techniques, they found that clones which had a more ordered actin network were less metastatic, whereas clones having a diffuse actin staining pattern were more metastatic. Similarly, we have found that in the Dunning rat R3327 prostatic adenocarcinoma tumor system, the non-metastatic (less than 0.1%) H-prostatic tumor cell line has a prominent network of actin filament bundles, whereas the highly metastatic (greater than 90%) MatLyLu cell line has a diffuse actin staining pattern. In the low-metastatic (less than 10%) AT1 cell line an intermediate actin organization between H and MatLyLu was observed. Analysis of cell extracts from H- and MatLyLu-cells revealed differences in the level of activity of cellular proteins which affect actin filament assembly and structure in a manner similar to that of the cytochalasins, fungal metabolites which bind with high affinity to the fast-growing end of actin filaments. Extracts of MatLyLu were significantly more effective than those of H-cells in decreasing the extent of actin filament network formation and in inhibiting the rate of filament assembly by blocking monomer addition onto the fast-growing end. Measurements of spin-lattice nuclear magnetic resonance water proton relaxation times (T1) were made in surgically removed tumor tissue from four sublines (H, AT1, MatLyLu, and MatLu) of the Dunning R3327 tumor system. The highly metastatic cell lines had significantly longer water proton T1 relaxation times than did the lines with low metastatic potential. These differences in T1 may reflect the observed alterations in organization of actin filaments within these various sublines of the Dunning R3327 prostatic adenocarcinoma tumor system.

Involvement of sulfhydryl groups in the action of the insulin and radiation on thymocyte Na+-dependent amino acid transport.

1,p-Chloromercuribenzene sulfonate concentrations less than 10(-5) M stimulate the uptake by thymocytes of 2-aminoisobutyrate, a non-metabolized amino acid. At concentrations greater than 10(-5) M of this reagent, transport is impaired and cell viability is effected. In contrast, 5,5'-dithiobis-(2-nitrobenzoate) between 10(-4) and 10(-6) M produces only stimulation of 2-aminoisobutyrate uptake after treating for 10 min. 2. Treatment of thymocytes with 10(-4)M 5,5'-dithiobis-(2-nitrobenzoate) reveals at least three categories of reactive SH groups. Titration of the most rapidly reacting category, 4 - 10(7)-7 - 10(7)/cell, activates 2-aminoisobutyrate transport to the same extent as does p-chloromercuribenzene sulfonate. Cells treated with 10(-6) M insulin showed a 30-50% reduction in the number of sulfhydryl groups that could be titrated with 5,5'-dithiobis-(2-nitrobenzoate). In thymocytes treated with 10(-6) M p-chloro(203Hg)mercuribenzene sulfonate, addition of 10(-6) or 10(-9) M insulin before treatment with the sulhydryl reagent again reduces the number of titrable SH groups by 20%. 3. Insulin (10(-10)-10(-6) M) also stimulates 2-aminoisobutyrate uptake, but the effects of insulin and SH blocker are not additive. 4. Insulin, but not p-chloromercuribenzene sulfonate, prevents the impairment of 2-aminoisobutyrate transport caused by gamma-irradiation. Treatment of cells with p-chloromercuribenzene sulfonate prior to irradiation increases the radiation impairment of 2-aminoisobutyrate transport. 5. gamma-irradiation reduces the number of 5,5'-dithiobis-(2-nitrobenzoate) reactive sulfhydryl residues by 37%. 6. A model for the action of insulin and irradiation on 2-aminoisobutyrate transport is presented.

Altered surface topology and membrane functions of rat thymocytes eluted from nylon wool columns.

(1) Following incubation of thymocytes with nylon wool at 37 degrees C, the eluted cells showed an increase in the number of microvilli per cell and a concominant elongation of the microvilli (0.22 mum versus 1.15 mum. (2) Cyclic adenosine monophosphate (cylic AMP) levels were lowered by 30-50% in nylon wool-treated thymocytes. (3) Nylon wool-treated cells showed an impaired Na+-dependent amino acid transport system (2-aminoisobutyrate) whereas the Na+-independent amino acid transport system (1-aminocyclopentane-1-carboxylate) was unaffected.

Tumor retention of 5-fluorouracil following irradiation observed using 19F nuclear magnetic resonance spectroscopy.

PURPOSE: The combination of 5-fluorouracil (5FU) and radiation results in improved tumor control in a variety of gastrointestinal cancers. We propose the enhancement is related to radiation potentiating the antitumor effects of 5FU. To better understand the mechanism of the 5FU-radiation interaction, 19F nuclear magnetic resonance (NMR) spectroscopy experiments were performed to observed the tumor clearance and metabolism of 5FU. METHODS AND MATERIALS: Experiments were performed on 10 3-6-week-old female (Nu/Nu) athymic nude mice. Flank tumors measuring approximately 1.0 cm in diameter 3 weeks following a subcutaneous injection of 1 x 10(6) human colon adenocarcinoma (HT-29) cells were studied. In our first group, all animals received an intravenous bolus injection of 5FU (100 mg/kg) immediately before spectroscopic analysis. Animals in the second group were first treated with a single tumor radiation dose of 10 Gy just before the 5FU injection and subsequent spectroscopy. Spectroscopic analysis was performed with a 2.0-T NMR spectroscopy system. RESULTS: The tumor retention of 5FU was prolonged in animals receiving radiation before the drug infusion. The tumor clearance rate of the 5FU for nonirradiated animals was 0.0178 +/- 0.0082/min vs. 0.0055 +/- 0.0027/min for irradiated animals, reflecting a threefold reduction in drug clearance in the irradiated tumors. The difference was significant at p < 0.005. CONCLUSION: Our preliminary experiments suggest the enhanced cytotoxicity seen with concurrent 5FU and radiation is related to prolonged tumor retention of 5FU induced by radiation. This is consistent with the hypothesis that radiation is potentiating the cytotoxic effects of 5FU.

Pulmonary microangiography. A comparison of in vitro versus in vivo perfusion techniques in dogs.

Because of a need to correlate pulmonary microvascular changes with physiologic data during lung injury, in vitro and in vivo pulmonary capillary microangiography was performed on normal dogs and those subjected to oleic acid injury and glass bead microembolization. During these studies, no significant differences were found between microangiograms obtained after in vitro and in vivo perfusion techniques. This work therefore suggests that in vitro microangiography yields reliable morphologic information more conveniently than more expensive and difficult in vivo techniques. In vitro pulmonary capillary microangiography can provide reliable structural information which can be correlated with physiologic data.

Magnetic resonance imaging and spectroscopy of small ring-enhancing lesions using a rat glioma model.

RATIONALE AND OBJECTIVES: We sought to demonstrate the usefulness of proton and fluorine magnetic resonance spectroscopy (MRS) techniques in characterizing small ring enhancing lesions produced by experimental malignant gliomas. METHODS: The growth characteristics of a rat glioma model (RT2) were studied using contrast-enhanced magnetic resonance imaging scans of the tumors and histologic correlates obtained at various times. Changes in tumor metabolite levels were monitored on a serial basis using water-suppressed proton spectroscopy. The existence of tumor hypoxia was established using 19F MRS in combination with a fluorinated nitroimidazole and subsequently confirmed by immunohistochemical staining of tumor sections. RESULTS: Ring-enhancing lesions are produced by RT2 rat brain gliomas approximately 7 days after intracerebral implantation. Beginning at day 5, marked deviations in brain metabolite levels are observed on proton MR spectra. However, while the signal from the fluorinated nitroimidazole is first detected by 19F MRS at day 7, immunohistochemical staining of tissue sections reveals bound drug as early as day 5, when the first histologic signs of necrosis become apparent. CONCLUSIONS: Magnetic resonance imaging of RT2 rat brain glioma exhibits ring-enhancing characteristics similar to those observed in clinical studies. The appearance of the ring enhancement corresponds with the development of central necrosis and could serve as an indicator for rapid growth. Proton and fluorine MRS may be useful in confirming that a small ring-enhancing lesion represents an active tumor process early in its development.

In vitro NMR evaluation of human thyroid lesions.

In vitro analysis of spin-lattice relaxation times (T1), water self-diffusion coefficients (DH2O), and proton NMR spectroscopy were performed in a study of 88 patients with thyroid lesions in order to determine the usefulness of these parameters in the differentiation of benign and malignant tissues. Thyroid tissue sample proton NMR spectral patterns were examined at 360 MHz. Proton NMR spectra were different for normal thyroid tissues, benign, and cancerous lesions. Significantly prolonged T1 (0.5T) and decreased DH2O were found in cancerous thyroid lesions relative to normal thyroid tissues. Considerable overlap was found, however, in comparing T1 and DH2O values for benign and malignant thyroid lesions. This study suggests that proton NMR spectroscopy may be more useful than T1 and DH2O in differentiating benign and malignant thyroid lesions.

A comparison of the effects of hyperthermia on cell growth in human T and B lymphoid cells: relationship to alterations in plasma membrane transport properties.

Hyperthermic exposure (39-43 degrees C) for 1 or 2 hr impairs growth and Na+-dependent amino acid transport in both a radiosensitive human T (Molt-4) and a radioresistant B (RPMI 1788) lymphoid cell line. The heat damage to Na+-dependent amino acid transport in both cell lines is reversible under the conditions tested. Cell growth, as judged by increases in cell number, is decreased in both cell lines after hyperthermic treatment (43 degrees C, 1-hr exposure). This decrease in growth correlated with the damage to, and recovery of, the Na+-dependent amino acid transport system. However, the sensitivity to heat of both growth and Na+-dependent amino acid transport appears to differ in Molt-4 which is somewhat more sensitive to hyperthermia (T-cell line) vs RPMI-1788 (B-cell line). In the case of Molt-4, the rate of growth is decreased for about 60-80 hr after cells are exposed for 1 hr at 43 degrees C; whereas increases in cell number in the RPMI 1788 is observed within 40 hr after the heat treatment. The differences observed in cell growth and transport in these two lymphoid cell lines are attributed to the manner in which heat affects (i) the transport parameters in Molt-4 vs RPMI 1788 (i.e., the Michaelis-Menten constants Km and Vmax) and (ii) the putative plasma membrane sulfhydryl protein(s) which modulates Na+-dependent amino acid transport.

Evaluation of a fluorinated 2-nitroimidazole binding to hypoxic cells in tumor-bearing rats by 19F magnetic resonance spectroscopy and immunohistochemistry.

We have examined a hexafluorinated 2-nitroimidazole, CCI-103F, as a probe for hypoxic tumor cells by in vivo 19F magnetic resonance spectroscopy (MRS). Following initial intraperitoneal injections of the drug in tumor-bearing (Dunning R3327-AT1-Matlylu) rats, 19F spectra were obtained on an Otsuka 2.0T Vivospec spectrometer using a 1.5-cm surface coil. Signal at 1- and 2-h time points indicated initial biodistribution of drug in the tumor. At 4 and 8 h, a progressive increase in signal intensity was observed, indicating retention of drug within the tumor. Tumor signal remained detectable in 4 of 10 rats at 24 h, indicating possible nitroreductive bioactivation by hypoxic cells. Immunohistochemistry of these tumors revealed a staining pattern consistent with labeling of hypoxic cells. No detectable 19F signal was found at 24 h for the other rats, indicating complete washout of unbound drug. Immunohistochemical assessment of these tumors revealed some staining for bound drug at the periphery of necrotic zones. 31P-MRS of the tumors showed good correlation with the presence or absence of hypoxia as evaluated by 19F-MRS, T1- and T2-weighted images, and immunohistochemistry. These results provide the groundwork for further studies using this misonidazole analog for noninvasive identification of hypoxic tumor cells in vivo by MRS.

The effects of ionizing radiation on the pulmonary endothelial cell uptake of alpha-aminoisobutyric acid and synthesis of prostacyclin.

The effects of gamma irradiation (150-3000 rad) on prostacyclin synthesis (PGI2) and Na+-dependent amino acid uptake (alpha-aminoisobutyric acid, AIB) were assessed in vitro in bovine pulmonary artery endothelial cells grown in plastic culture dishes. A dose-dependent increase in both PGI2 synthesis and AIB was found 24 h after irradiation at exposure levels greater than 600 rad. The increase in PGI2 synthesis [297% of sham-irradiated values at 3000 rad, P less than 0.01] was due to an increase in release of arachidonic acid from plasma membrane stores as well as stimulation of cyclooxygenase and/or prostacyclin synthetase enzymes. The increase in AIB uptake (75% increase at 3000 rad compared to sham-exposure values) correlated with the increased synthesis of PGI2 (r = 0.94). There was also a dose-dependent increase in the number of cells that became detached from the culture dishes during the 24-h period after irradiation. The changes in PGI2 synthesis and AIB uptake induced by gamma irradiation differed if the endothelial cells were grown on cover slips, indicating that the endothelial response to irradiation may be dependent on the interaction between the endothelial cell and its extracellular basement membrane matrix.

The effects of ionizing radiation on the pulmonary vasculature of intact rats and isolated pulmonary endothelium.

We studied the effects of ionizing radiation on the morphology of the pulmonary circulation using an in vivo rat model and an in vitro pulmonary artery endothelial cell model. Gamma radiation was given as either an acute (30 Gy) or fractionated (5 X 6 Gy) dose to one hemithorax of rats. An acute 30-Gy dose delivered resulted in a 70% decrease in pulmonary arterial perfusion, using technetium-99m microaggregated albumin (99mTc-MAA), in the irradiated lung by 2-3 weeks after irradiation. Pulmonary microradiographs, using a barium sulfate perfusion method, obtained 2-3 weeks after irradiation demonstrated widespread loss of capillary filling and segmentation of the vessels. Histologic examination demonstrated intact capillaries, suggesting that the alterations in pulmonary perfusion were at the precapillary level. Similar abnormalities in lung perfusion and morphology were found after delivery of fractionated doses of radiation, but the onset of the changes was delayed, occurring 4-6 weeks postirradiation. Using cultured pulmonary endothelial cell monolayers, cell sloughing and retraction from the surface substrate were observed within 24 h after in vitro delivery of 30 Gy. Similar findings occurred in monolayers given fractionated doses (5 X 6 Gy) of radiation 2-3 days after the final dose. The in vivo animal and in vitro endothelial cell models offer a useful means of examining the morphologic alterations involved in radiation lung vascular damage.

MELAS syndrome: imaging and proton MR spectroscopic findings.

PURPOSE: To evaluate imaging findings in MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, strokes) syndrome for the presence and location of infarctions and the presence of lactate. METHODS: Eight patients were studied with MR (n = 8) and CT (n = 2). One patient underwent single-photon emission CT with technetium 99m hexamethyl-propyleneamine oxime and one patient had conventional catheter angiography. One fixed brain was studied with MR imaging. Five patients underwent single volume proton MR spectroscopy. Imaging studies were evaluated for atrophy, edema, and infarctions. Proton MR spectroscopy was visually analyzed for presence or absence of lactate. RESULTS: One patient showed a cerebral infarction, and later a second distant infarction developed. One patient showed a transient area of cortical edema. Two patients had small nonspecific periventricular white matter abnormalities and one patient had diffuse white matter hyperintensities. Two patients had nonspecific MR abnormalities (probably age-related changes), and two had normal MR findings. None had basal ganglia involvement. Proton MR spectroscopy showed presence of lactate in one case with transient cortical edema; in two cases with nonspecific (probably age-related) brain findings; and in two patients with normal MR findings. CONCLUSIONS: Patients with MELAS have a variety of MR findings. The fact that proton MR spectroscopy showed lactate in all five cases studied, regardless of MR findings, indicates that proton MR spectroscopy may be more sensitive in the detection of MELAS-associated abnormalities than MR imaging.

Extraneous lipid contamination in single-volume proton MR spectroscopy: phantom and human studies.

PURPOSE: To determine the degree of extraneous lipid contamination in defined volumes of interest studied with single-volume proton MR spectroscopy. METHODS: Single-volume proton MR spectroscopy was performed on a fat/water phantom and in three volunteers using the stimulated-echo acquisition mode (STEAM) and point-resolved spectroscopy (PRESS) localization methods. Three different volumes of interest (8, 27, and 64 cm3) were examined at echo times of 20, 135, and 270 for the STEAM sequences and 135 and 270 for the PRESS acquisitions in both the phantom and the volunteers (volumes of interest were placed adjacent to but not encompassing fat-containing structures, such as the scalp and retroorbital fat). The degree of lipid contamination was then correlated with measurements of the section profiles. RESULTS: The PRESS method resulted in less extraneous lipid contamination in both phantom and volunteer studies. The STEAM method had the highest level of lipid contamination signal in phantom and human studies. In the volunteers, volumes of interest abutting fat-containing structures obtained with PRESS or STEAM sequences showed no lipid contamination. However, the STEAM sequences showed lipid signal in the volume of interest adjacent to orbital fat whereas the PRESS sequences did not. These observations are supported by the section profile studies, which showed that the actual volume excited by the STEAM sequence was 7% to 32% larger than that originally selected, while with PRESS the actual excited volume was 12% to 16% smaller than that originally selected. CONCLUSION: In our MR unit, short-echo-time STEAM sequences (< or = 135 milliseconds) resulted in extraneous lipid contamination in phantom and human studies adjacent to the orbits. PRESS sequences showed no lipid contamination in volumes abutting fat structures in phantoms or humans. These results correlated closely with the configuration of the section profiles. Although these findings might be dependent on the MR unit used, our study could help determine extraneous lipid contamination for other MR units.

Effects of contrast material on single-volume proton MR spectroscopy.

BACKGROUND AND PURPOSE: Administration of contrast material before proton MR spectroscopy may allow more accurate placement of the volume of interest, particularly in tumors; yet, some data have suggested that contrast material may alter the results of MR spectroscopy. To determine the validity of this contention, we performed pre- and postcontrast MR spectroscopy in patients with brain tumors and compared the results with those obtained from a phantom. METHODS: Ten patients with astrocytomas were examined with single-volume MR spectroscopy before and after administration of contrast material. Voxel placement was identical for all studies. Peak area, peak height, and width at half maximum were measured for N-acetyl aspartate (NAA), creatine (Cr), and choline (Cho) in all studies. A phantom containing a 10 mmol concentration of NAA, Cr, and Cho was prepared in phosphate-buffered saline and mixed with contrast concentrations varying from 0.1 to 1.0 mmol. The phantom was studied by MR spectroscopy with the same parameters as used for the clinical studies. RESULTS: No significant differences were found between the pre- and postcontrast MR spectroscopy studies for the three parameters measured. In phantom studies, there was a significant decline in the Cho peak area and height and an increase in the width at half maximum as the concentration of contrast material increased from 0.1 to 1.0 mmol. NAA and Cr peaks showed no significant changes in peak height or area. CONCLUSION: Contrast material may be administered before clinical MR spectroscopy without affecting its interpretation.

Colloid cyst of the third ventricle: imaging-pathologic correlation.

Colloid cysts are relatively rare intracranial lesions located in the rostral aspect of the third ventricle. They may produce acute hydrocephalus, brain herniation, and lead to death. Although the clinical and imaging features of colloid cysts are well known, their etiology and the factors responsible for their imaging features continue to be a subject of debate. We present the imaging-pathologic correlation of a patient with a colloid cyst as well as data supporting the fact that the presence of cholesterol is probably responsible for the MR imaging features exhibited by some colloid cysts.

Proton MR spectroscopy in patients with acute temporal lobe seizures.

BACKGROUND AND PURPOSE: Decreases in N-acetyl aspartate (NAA) as seen by proton MR spectroscopy are found in hippocampal sclerosis, and elevated levels of lipids/lactate have been observed after electroconvulsive therapy. Our purpose was to determine whether increased levels of lipids/lactate are found in patients with acute seizures of hippocampal origin. METHODS: Seventeen patients with known temporal lobe epilepsy underwent proton MR spectroscopy of the mesial temporal lobes within 24 hours of their last seizure. Four of them were restudied when they were seizure-free. Five healthy individuals were used as control subjects. All MR spectroscopy studies were obtained using a single-voxel technique with TEs of 135 and 270. The relationship between the presence of lipids/lactate and seizures was tested using Fisher's exact test. Mean and standard deviations for NAA/creatine (Cr) were obtained in the hippocampi in patients with seizures on initial and follow-up studies and these values were compared with those in the control subjects. RESULTS: Seizure lateralization was obtained in 15 patients. Of the 17 seizure locations that involved hippocampi, 16 showed lipids/lactate by proton MR spectroscopy. Of the 13 hippocampi not directly affected by seizures, 10 showed no lipids/lactate and three showed lipids/lactate. The relationship between lipids/lactate and seizure location was confirmed. A comparison of NAA/Cr ratios for the involved hippocampi with those in control subjects showed significant differences on initial MR spectroscopy; however, no significant difference was found between acute and follow-up NAA/Cr ratios in hippocampi affected by seizures. CONCLUSION: Lipids/lactate were present in the hippocampi of patients with acute seizures and decreased when the patients were seizure-free. Thus, lipids/lactate may be a sensitive marker for acute temporal lobe seizures.

Correlation of myo-inositol levels and grading of cerebral astrocytomas.

BACKGROUND AND PURPOSE: In a limited number of patients, the level of myo-inositol (MI), as seen by proton magnetic resonance spectroscopy (HMRS), has been shown to differ for gliomas of different histologic grades. We sought to determine if MI levels correlate with cerebral astrocytoma grade. METHODS: Five control subjects, 14 patients with low-grade astrocytoma, 10 patients with anaplastic astrocytoma, and 10 patients with glioblastoma multiforme (GBM) underwent single-volume HMRS with an echo time of 20 ms. Twenty-five patients had received surgery, chemotherapy, and/or radiation therapy previously. Using the curve-fitting program supplied by the manufacturer, peak areas for n-acetyl aspartate (NAA), choline (Cho), and MI were normalized with respect to the peak area of creatine (Cr). Ratios for MI/Cr, Cho/Cr, and NAA/Cr were obtained for each lesion and retrospectively compared with the histologic grade of the lesion. RESULTS: Levels of MI/Cr were higher (0.82 +/- 0.25) in patients with low-grade astrocytoma, intermediate (0.49 +/- 0.07) in control subjects, and lower in patients with anaplastic astrocytoma (0.33 +/- 0.16) and GBM (0.15 +/- 0.12). CONCLUSION: Our study shows a trend toward lower MI levels in the presence of anaplastic astrocytomas and GBMs compared with those of low-grade astrocytomas. MI levels may have implications in the grading of cerebral astrocytomas.