Increased brain tumor microvessel permeability after intracarotid bradykinin infusion is mediated by nitric oxide

Nitric oxide (NO), a free radical gas implicated in a wide variety of biological reactions, is a novel signaling molecule that may regulate vasodilation, cerebral blood flow, and vascular permeability. This study was performed to determine whether NO mediates the selective increase in brain tumor microvessel permeability after intracarotid infusion of bradykinin in the RG2 rat glioma model. Intracarotid infusion of bradykinin selectively increased the transport of radiolabeled alpha-aminoisobutyric acid and dextran into brain tumors. Transport into normal brain was not increased. The administration of an NO synthase inhibitor, NG-nitro-L-arginine methyl ester, significantly inhibited the increased transport into tumors for both tracers. The inhibitory effect of NG-nitro-L-arginine methyl ester on the response to bradykinin was reversed by L-arginine. The expression of two NO synthase (NOS) isoforms in cultured RG2 glioma cell lines and intracerebral RG2 glioma was examined by immunohistochemistry and Western blot analysis. High levels of expression of neuronal NOS were detected in cultured and intracerebral RG2 cells but not in normal brain tissue, except in rare neuronal cells. The endothelial form of NOS was also expressed in cultured RG2 cells, but not as strongly as neuronal NOS expression. In intracerebral RG2 gliomas, expression of endothelial NOS in the tumor was detected at higher levels than in normal brain. These findings indicate that RG2 rat gliomas express high levels of NOS, which regulate the production of NO, compared with normal brain. We suggest that the selective permeability increase in brain tumor microvessels after bradykinin infusion is mediated by NO. Furthermore, the absence of high levels of NOS in normal brain may account for the attenuated permeability response to bradykinin in normal brain microvessels.

Enhanced tumor uptake of carboplatin and survival in glioma-bearing rats by intracarotid infusion of bradykinin analog, RMP-7

OBJECTIVE

Intracarotid infusion of the bradykinin analog, RMP-7, can increase permeability in brain tumor capillaries. This study sought to determine the following: 1) the unidirectional transport, Ki, of radiolabeled [14C]carboplatin into brain tumors with either intravenous or intracarotid RMP-7 infusions; 2) the duration and extent of increased permeability in tumor capillaries during continuous RMP-7 infusions; and 3) the effect on survival of carboplatin combined with RMP-7 treatment in rats with gliomas.

METHODS

Wistar rats with RG2 gliomas were used, and a unidirectional transfer constant, Ki, was determined using quantitative autoradiography. In the survival study, the rats were treated with intra-arterial carboplatin and RMP-7 at Days 5 and 7 after tumor implantation.

RESULTS

Intracarotid infusion of RMP-7 for 15 minutes increased the transport of [14C]carboplatin to tumors by 2.7-fold, as compared with saline infusion alone (P < 0.001). The transports of [14C]dextran and [14C]carboplatin into tumors were significantly higher with 15 minutes of intracarotid infusion of RMP-7 (0.1 microgram/kg/min), compared to those with 10-, 30-, or 60-minute infusions (P < 0.01). Rats treated at Days 5 and 7 after tumor implantation with carboplatin alone (10 mg/kg) exhibited a modest increase in survival at 31 days (37%, compared to < 10% of controls), while those given the combination of carboplatin with RMP-7 exhibited a significantly higher survival rate (74%).

CONCLUSION

Intracarotid infusion of RMP-7 can selectively increase transport of carboplatin into brain tumors and results in higher survival in rats with gliomas. These findings support the use of intracarotid infusion of RMP-7 to enhance the delivery of carboplatin to patients with malignant brain tumors.

The evolution of optical signals in human and rodent cortex

The time course of optical intrinsic signals was examined in order to characterize the evolution of response in human and rodent cortex. Both subtraction/ratio and principal component analyses were used to construct time-course curves. The time course began at a prestimulus baseline, responded with a finite delay, overcompensated, reduced to a maintenance level, and then disappeared. The magnitude, spatial involvement, and principal components demonstrated similar time-course curves both in human and in rodent. For acute stimuli, peak response was reached between 2 and 3 s and returned to baseline by 6 s poststimulation. The shape of the time-course curve is consistent with the need to satisfy neuronal demand and the contributions of vascular smooth muscle properties to the response behavior. The temporal delays and nonlinear phenomena observed in the time-course curves are consistent with a hydraulic model of neurovascular supply/demand behavior.

Eradication of established intracranial rat gliomas by transforming growth factor beta antisense gene therapy

Like human gliomas, the rat 9L gliosarcoma secretes the immunosuppressive transforming growth factor beta (TGF-beta). Using the 9L model, we tested our hypothesis that genetic modification of glioma cells to block TGF-beta expression may enhance their immunogenicity and make them more suitable for active tumor immunotherapy. Subcutaneous immunizations of tumor-bearing animals with 9L cells genetically modified to inhibit TGF-beta expression with an antisense plasmid vector resulted in a significantly higher number of animals surviving for 12 weeks (11/11, 100%) compared to immunizations with control vector-modified 9L cells (2/15, 13%) or 9L cells transduced with an interleukin 2 retroviral vector (3/10, 30%) (P < 0.001 for both comparisons). Histologic evaluation of implantation sites 12 weeks after treatment revealed no evidence of residual tumor. In vitro tumor cytotoxicity assays with lymph node effector cells revealed a 3- to 4-fold increase in lytic activity for the animals immunized with TGF-beta antisense-modified tumor cells compared to immunizations with control vector or interleukin 2 gene-modified tumor cells. These results indicate that inhibition of TGF-beta expression significantly enhances tumor-cell immunogenicity and supports future clinical evaluation of TGF-beta antisense gene therapy for TGF-beta-expressing tumors.

Occipital status epilepticus: an unusual case of post-traumatic blindness

Post-traumatic seizures can be a cause of multiple clinical and behavioral abnormalities. We present an unusual case of post-traumatic epilepsy resulting in blindness. The patient was a 35-year-old female with a past history of toxemia of pregnancy who was assaulted, sustaining a traumatic brain injury (TBI). Glasgow Coma Score upon presentation to the emergency department was 10. Initial CAT scan was negative. Subsequent MRI revealed occipital edema. On examination, she was found to be blind in both eyes. Consistent with cortical blindness, extra-ocular movements, pupillary reflexes and fundoscopic examination were normal. Unusual scanning eye movements were noted. Electroencephalography (EEG) revealed epileptiform discharges in both occipital regions consistent with occipital status epilepticus. Seizures were eventually controlled with Phenytoin and Phenobarbital, with subsequent conversion to Carbamazepine. Central vision returned, but peripheral sight was never regained. Follow up EEG revealed no evidence of epileptiform activity. Post-traumatic occipital status epilepticus is rare. Cortical blindness in TBI patients with minimal occipital pathology on imaging is generally transient. This case points out the need for the treating rehabilitation professional to be vigilant in assessing for post-traumatic seizures in patients with persisting visual deficits.

The temporal/spatial evolution of optical signals in human cortex

Intraoperative measures of functioning brain are an important aspect to understanding normal and diseased cortical response. Previous studies, in animal models, have used optical reflectance maps to illustrate the location and timing of functional activity. We used optical reflectance mapping in patients undergoing parietal tumor resection to reveal the temporal/spatial evolution of perfusion and other related metabolic responses of sensorimotor cortex to peripheral somesthetic stimulation. The somatosensory cortex of seven anesthetized patients was mapped in response to transcutaneous electrical median and ulnar nerve stimulation using optical reflectance imaging. The time course and spatial extent of this response were measured and correlated with evoked potential maps collected during the same conditions. Observable signals first appeared within 1-2 sec, peaked at 3 sec, and disappeared by 9 sec. These signals colocalized with the largest evoked potentials in both the sensory and motor regions and demonstrated topological specificity with median and ulnar nerve stimulation. Maps of this temporal/spatial resolution illustrate the integrative and dynamic nature of the neuronal, vascular, and metabolic responses of human cortex. These data also provide insight to the mechanisms responsible for signals obtained using other brain imaging techniques such as PET and fMRI.

Pharmacological blood-brain barrier modification for selective drug delivery

Vasoactive agents have been identified through studies of peritumoral edema and effects on systemic capillaries. Abnormal blood-brain barrier or blood-tumor barrier can develop transient increases in permeability with the intraarterial delivery of vasoactive agents. Normal blood-brain barrier resists the effects of these compounds because of a biochemical barrier that may inactivate or become inert to vasoactive agents. Vasoactive compounds, including leukotrienes, bradykinin, and histamine appear to selectively increase permeability in abnormal brain capillaries. Intracarotid infusion of leukotrienes, bradykinin, and other vasoactive agents can increase drug delivery to diseased tissue.

High expression of the Glut1 glucose transporter in human brain hemangioblastoma endothelium

The principal glucose transporter at the blood-brain barrier is Glut1, and GLUT1 expression is downregulated in high grade gliomas. In the present study, glucose transporter expression was studied in surgically resected hemangioblastoma tissue. Light microscopic immunochemistry indicated the high expression of the Glut1 glucose transporter isoform throughout the central vascular endothelium of this tissue. Glial fibrillary acidic protein (GFAP) was observed only at the tumor border, with no GFAP immunoreactivity in stromal cells, pericytes or endothelia in the central tumor regions. It is generally believed that more Glut1 is found in erythrocytes than any other cell, but quantitative electron microscopic immunogold analyses of Glut1-immunoreactive sites per micron of capillary membrane showed the Glut1 density in tumor endothelial membranes glucose transporter was 2-3-fold higher than in human red cells. In the same tissue samples, qualitative immunogold electron microscopy of human serum albumin indicated that this protein (MW 65,000) moved freely from the vascular space into pericapillary regions, confirming the leaky barrier characteristics of the hemangioblastoma. These studies show that Glut1 expression may be high in endothelia that are highly permeable and devoid of astroglial contacts. Thus, human cerebral hemangioblastomas may provide a novel system for studying the induction of Glut1 in the blood-brain barrier.

Hyperacute thermal lesions: MR imaging evaluation of development in the brain

PURPOSE

To determine the natural time course of development of hyperacute thermal lesions in the brain.

MATERIALS AND METHODS

Ten interstitial lesions were created in five rabbit brains with a radio-frequency probe; an electrode-tip temperature of 80 degrees C was maintained for 60 seconds. Continuous fast spin-echo magnetic resonance (MR) imaging was used to follow lesion development for a minimum of 30 minutes. Temporal variations in lesion size and signal intensity were examined. Findings in final images were correlated with histologic findings.

RESULTS

Images demonstrated a focal hyperintense zone, which developed into an expanding ring of edema surrounding a necrotic center in about 10 minutes. Quantitative analysis revealed a 23% +/- 6 (standard deviation) increase in average signal intensity of the edema layer and a 152% +/- 41 increase in overall lesion size.

CONCLUSION

Full development of a thermal lesion is delayed for a period of minutes. Clinical implications of this effect should be considered when MR imaging-guided thermal ablation is performed.

Adenovirus-mediated p53 gene delivery inhibits 9L glioma growth in rats

Adenoviral vectors have recently been shown to effectively deliver genes into a variety of tissues. Since these vectors have some advantages over the more extensively investigated retroviruses, we studied the effect of two replication-defective adenovectors bearing human wild type tumor suppressor gene p53 (Adp53) and Escherichia coli beta-galactosidase gene (AdLacZ) on 9L glioma cells. Successful in vitro gene transfer was shown by DNA polymerase chain reaction (PCR), and expression was confirmed by reverse transcriptase RNA PCR and Western blot analyses. Transduction of 9L cells with the Adp53 inhibited cell growth and induced phenotypic changes consistent with cell death at low titers, while AdLacZ caused cytopathic changes only at high titers. Stereotactic injection of AdLacZ (10(7) plaque forming units) into tumor bed stained 25 to 30% of tumor cells at the site of vector delivery. Injection of Adp53 (10(7) plaque forming units), but not AdLacZ (controls), into established 4-day old 9L glioma brain tumors decreased tumor volume by 40% after 14 days. As a step toward gene therapy of brain tumors using replication-defective adenoviruses, these data support the use of tumor suppressor gene transfer for in vivo treatment of whole animal brain tumor models.

Preliminary experience with MR-guided thermal ablation of brain tumors

PURPOSE

To evaluate the feasibility of a technique of MR-guided stereotactic radio frequency ablation, which was developed as a minimally invasive treatment for brain tumors, and to determine MR characteristics and sequential evolution of radio frequency lesions created to ablate brain tumors.

METHODS

Fourteen lesions in 12 patients with primary and metastatic brain tumors were treated with this technique and followed for up to 10 months. The stereotactic coordinates of the tumor and the angle of the radio frequency probe were calculated on MR imaging. The radio frequency lesion was generated in the awake patient by increasing the temperature to 80 degrees C within the tumor for 1 minute. This was repeated until the entire tumor volume was destroyed. MR imaging was performed before, during, and immediately after the radio frequency procedure, and sequential MR was obtained during clinical follow-up.

RESULTS

MR imaging clearly showed well-defined radio frequency lesions and provided feedback for treatment planning. The radio frequency lesion boundary was well identified as a dark signal rim on T2-weighted images and showed ring enhancement on contrast-enhanced T1-weighted images. The sequential MR imaging showed the radio frequency lesions decreased in volume in all cases, suggesting focal control.

CONCLUSION

Stereotactic MR-guided radio frequency brain tumor ablation is a feasible and promising technique that can be an attractive brain tumor treatment alternative. MR provided not only accurate tumor location but also visualization of feedback of thermal tissue changes that reflected therapeutic effect.

Intracarotid infusion of RMP-7, a bradykinin analog: a method for selective drug delivery to brain tumors

The bradykinin analog, RMP-7, was investigated for its ability to selectively increase uptake of molecular tracers in RG2 glial tumors. When infused in low doses (0.1 microgram/kg/min) through the intracarotid artery ipsilateral to RG2 gliomas in rats, RMP-7 significantly increased the permeability of tumor capillaries to methotrexate and to four other tracers of varying molecular weights, compared to intracarotid infusion of vehicle alone. Tracers used to examine permeability included radiolabeled alpha-aminoisobutyric acid (M(r) 103 D), sucrose (M(r) 342 D), methotrexate (M(r) 454.5 D), inulin (M(r) 5000 D), and dextran (M(r) 70,000 D). Permeability was expressed as the unidirectional transfer constant, Ki (microliters/gm/min). The permeability (Ki) of tumors in the RMP-7 group compared to the vehicle control group was as follows: alpha-aminoisobutyric acid, 35.3 +/- 9.11 versus 12.7 +/- 4.56 (p < 0.001); sucrose, 16.5 +/- 3.83 versus 9.28 +/- 3.12 (p < 0.05); methotrexate, 26.3 +/- 10.3 versus 8.98 +/- 6.78 (p < 0.005); inulin, 13.5 +/- 3.23 versus 6.55 +/- 4.32 (p < 0.005); dextran, 15.2 +/- 3.42 versus 1.47 +/- 1.24 (p < 0.001). The permeability of RG2 gliomas to high-molecular-weight dextran (70,000 D) was 10.3-fold higher in the RMP-7 group than in the vehicle control group. Intracarotid infusion of RMP-7 did not significantly increase the blood volume in tumor or brain tissue. The permeability of normal brain capillaries was unaffected by intracarotid infusion of 0.1 microgram/kg/min RMP-7 relative to that achieved in tumor. These data support the idea that intracarotid infusion of RMP-7 will be a useful technique for selective delivery of antitumor compounds to brain tumors.

Gene expression of GLUT3 and GLUT1 glucose transporters in human brain tumors

GLUT3 glucose transporter gene expression is confined to neurons, while GLUT1 gene expression is limited to endothelial cells in normal brain. Thus far, neither of the GLUT genes has been shown to be consistently expressed in glial cells in adult brain in vivo under normal conditions. However, GLUT gene expression may be aberrant in human brain glial tumors. The present investigation shows that the GLUT1 and GLUT3 transcripts are differentially expressed in a series of 20 human brain tumors. The GLUT1/actin mRNA ratio increased in parallel to the astrocytoma grade, compared to a control human brain cortex, although no change in this ratio was seen in 5 meningiomas. Immunoreactive GLUT1 protein was not detectable in human brain tumors, including high-grade gliomas. Both 4.2 or 2.7 kb GLUT3/actin mRNA ratios showed a linear correlation with the glioma grade (P < 0.025), and the GLUT3-immunoreactive protein was also expressed in high grade gliomas. These studies provide evidence for induction of GLUT1 and GLUT3 gene expression in malignant glial cells, and the mRNA levels correlate with the biologic aggressiveness of the tumor. The detection of immunoreactive GLUT3, but not GLUT1, in the high grade gliomas suggest the GLUT3 isoform may be the predominant glucose transporter in highly malignant glial cells of human brain.

Stereotactic delivery of a recombinant adenovirus into a C6 glioma cell line in a rat brain tumor model

The dismal results of conventional therapy for primary malignant brain tumors has justified exploring gene therapy approaches for this disease. Transduction of animal brain tumor models in vivo has been reported previously with retroviruses and herpes viruses. Because adenoviruses have the advantage of transducing quiescent and actively dividing tumor cells, they may prove to be more effective in such therapy. We used a replication-deficient recombinant adenovirus bearing the Escherichia coli beta-galactosidase gene in a rat C6 glioma tumor model. Transduced cells were detected by X-5-bromo-4-chloro-3-indolyl beta-D-galactoside staining to reveal beta-galactosidase activity. Initial experiments in vitro showed 50% and 90% transduction at vector titers of approximately 10(7) and 10(8) plaque-forming units/ml, respectively. Although no cytopathic effects were seen at 10(7) plaque-forming units/ml, more than 50% reduction in tumor cell growth was noted at 10(8) plaque-forming units/ml both in vitro and in vivo. Stereotactic delivery of the recombinant adenovirus into the frontal lobe of normal rat brains resulted in intense staining of all cell types, that is, neurons, astrocytes, and ependymal cells. Stereotactic injection into C6 glioma brain tumors in rats stained 25 to 30% of the tumor cells. We conclude that adenovirus vectors can be used to transfer genes to central nervous system tumors in vivo. Using stereotactic delivery, adenovirus vectors can transfer genes into the central nervous system intended for tumor therapy.

Enzymatic barrier protects brain capillaries from leukotriene C4

Leukotriene C4 (LTC4) increases vascular permeability in systemic, brain tumor, and ischemic brain capillaries, but not in normal brain capillaries. This study examines whether the abundance of gamma-glutamyl transpeptidase (gamma-GTP) in normal brain capillaries might act as an enzymatic barrier to vasoactive leukotrienes in the brain. Blood-brain barrier (BBB) permeability was determined by quantitative autoradiography using 14C-aminoisobutyric acid. Ischemia was produced by occluding the middle cerebral artery. Seventy-two hours after occlusion, gamma-GTP activity in ischemic brain disappeared, and LTC4 (4-micrograms total dose), which was infused into the carotid artery ipsilateral to the occlusion, selectively increased permeability, Ki, approximately twofold within core ischemic tissue and adjacent tissue, compared to vehicle alone in seven brains (15.53 +/- 6.03 vs. 7.29 +/- 3.36, p < 0.05, and 8.76 +/- 4.02 vs. 4.32 +/- 2.65, p < 0.05, respectively). No effect on BBB was seen in nonischemic brain tissue. Twenty-four hours postocclusion, gamma-GTP activity was still present, and LTC4 infusion did not increase permeability within ischemic tissue. However, inhibition of gamma-GTP with acivicin allowed LTC4 to increase permeability even 24 hours after occlusion in ischemic core and adjacent tissue compared to vehicle alone in seven brains (17.21 +/- 16.32 vs. 8.23 +/- 6.58, p < 0.05, and 11.78 +/- 7.96 vs. 4.56 +/- 1.93, p < 0.01, respectively). Acivicin almost completely blocked both the histochemical activity of gamma-GTP in brain capillaries and the metabolism of LTC4 in isolated bovine capillaries. These findings suggest that gamma-GTP may help normal brain capillaries resist the vasoactive effects of LTC4. In contrast, gamma-GTP is lost in injured brain capillaries, which allows LTC4 (in combination with other factors) to increase vascular permeability in ischemic brain and brain tumors.

Intracarotid infusion of bradykinin selectively increases blood-tumor permeability in 9L and C6 brain tumors

This study investigated the effects of bradykinin on blood-tumor barrier (BTB) permeability in transplanted 9L gliosarcomas (9L) and C6 gliomas (C6) in rats. Permeability, expressed as the unidirectional transfer constant, Ki (microliter/g/min), was measured by quantitative autoradiography. Tracers used to examined permeability included radiolabeled alpha-aminoisobutyric acid ([14C]AIB), sucrose ([14C]sucrose) and dextran ([14C]dextran). Intracarotid infusion of bradykinin (10 mg/kg/min) significantly increased the BTB permeability in both 9L and C6 tumors to [14C]AIB and [14C]sucrose, but did not increase permeability to [14C]dextran. Blood-brain barrier (BBB) permeability in normal (non-tumor) brain was not significantly increased to any of the tracers by intracarotid bradykinin infusion. Ki values for [14C]AIB, [14C]sucrose and [14C]dextran of 9L tumors in the bradykinin group versus control group were 41.6 +/- 12.6 vs. 24.8 +/- 6.30 (P < 0.02), 17.5 +/- 9.34 vs. 9.05 +/- 4.36 (P < 0.05), and 3.90 +/- 2.59 vs. 2.42 +/- 1.76, respectively (mean +/- S.D.). Ki values to [14C]AIB, [14C]sucrose and [14C]dextran of C6 tumors in the bradykinin group versus control group were 41.4 +/- 19.0 vs. 19.5 +/- 11.4 (P < 0.01), 18.0 +/- 8.88 vs. 7.06 +/- 3.05 (P < 0.01), and 4.07 +/- 1.45 vs. 2.27 +/- 1.26, respectively (mean +/- S.D.). Intracarotid infusion of bradykinin did not significantly increase the blood volume in tumor or brain tissue despite its known vasodilative effect. Intracarotid infusion of bradykinin may be a useful technique for selective delivery of compounds to brain tumors.

Bradykinin selectively opens blood-tumor barrier in experimental brain tumors

Bradykinin, infused in low doses (10 micrograms/kg/min) through the carotid artery ipsilateral to RG2 glioma in rats, significantly increased the permeability in tumor capillaries to six different tracers of varying molecular weights compared with intracarotid infusion of saline alone. Permeability in normal brain capillaries was not significantly increased by intracarotid bradykinin infusion. Tracers used to examined permeability included radiolabeled alpha-aminoisobutyric acid (AIB; MW 103), sucrose (MW 342.3), inulin (MW 5000), and dextran (MW 70,000), horseradish peroxidase (HRP) and Evans blue (EB). Permeability was expressed as the unidirectional transfer constant K(i) (microliter/g/min). The permeabilities (K(i)) of tumors in the bradykinin group versus the control saline group for AIB, sucrose, inulin, and dextran were 25.91 +/- 6.78 vs. 13.95 +/- 4.29 (p < 0.01), 17.90 +/- 2.65 vs. 10.75 +/- 4.55 (p < 0.01), 23.92 +/- 6.99 vs. 6.20 +/- 4.37 (p < 0.01), and 17.84 +/- 1.00 vs. 1.47 +/- 1.24 (p < 0.001), respectively (mean +/- SD). Permeability of RG2 gliomas to high molecular weight dextran (70,000) was 12-fold higher in the bradykinin group than in the saline infusion group. Intracarotid infusion of bradykinin did not significantly increase the blood volume in tumor or brain tissue despite its known vasodilative effect. The permeability of normal brain capillaries was unaffected by intracarotid bradykinin infusion. The increased permeability was reversed 20 min after stopping the intracarotid infusion. Electron microscopic and gross qualitative analysis was performed using HRP and EB. Intracarotid bradykinin infusion increased HRP and EB within tumor tissue but not normal tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Trans retinoic acid inhibits in vivo tumour growth of C6 glioma in rats: effect negatively influenced by nerve growth factor

Retinoic acid (RA) and nerve growth factor (NGF) are both differentiation factors for central nervous system tumours. Mouse-derived NGF inhibits proliferation of C6 glioma cells in vivo in the absence of serum. Retinoic acid inhibits in vivo growth of C6 gliomas in the subcutaneous tissue of rats. This study evaluated the response of C6 cells implanted in the rat cortex to NGF, RA, or a combination of the two in 89 rats. Tumour size, cellular density and morphology were analysed using light microscopy. Treatment with RA alone resulted in tumour volumes that were 38% of control and 48% of NGF-treated groups. There was no significant difference in the tumour volumes or in cell morphology in C6 cells treated with NGF alone compared to controls. Tumours treated with a combination of RA and NGF were larger however, than tumours treated with RA alone. This suggests that despite the growth inhibitory effects of NGF in vitro, NGF acts to prevent the growth inhibitory effect of RA in vivo.

Thallium-201 SPECT and positron emission tomography equal predictors of glioma grade and recurrence

Quantitative indexes based on regions of interest ratios from preoperative thallium-201 SPECT and F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) scans were compared for their ability to predict the histological grade of cerebral gliomas. Of the five different ratios used to determine the index for each PET scan, the ratio of tumour versus ipsilateral hemisphere in the same plane as the tumour showed the most significant correlation with glioma grade (p < 0.001). A large study of 62 thallium-201 SPECT scans showed equally good correlation with glioma grade (p < 0.0005). The use of thallium-201 SPECT for detection of tumour recurrence had 100% sensitivity in this series, while PET scans had 90.9% sensitivity. Patients with a rate of change in serial thallium indexes of 0.475 +/- 0.278 per month survived 5.93 +/- 2.25 months from onset of index increase, while those with little change in the index (0.069 +/- 0.063 per month) survived 17.93 +/- 5.25 months from onset of index increase. Results indicate thallium-201 SPECT correlates well with tumour grade and is equally efficient as PET in screening for glioma recurrence.

Intracarotid histamine infusion increases blood tumour permeability in RG2 glioma

Histamine will alter blood flow and permeability in systemic and cerebral vessels. We reported that intracarotid infusion of histamine selectively increased the blood flow in experimental brain tumours and caused extravassation of Evans blue within tumours. In this study, the effects of histamine on tumour and brain capillary permeability were quantified using autoradiography. RG2 glioma cells were implanted in female Wistar rats. Seven days after implantation, either low doses of histamine (1 or 10 micrograms kg-1 min-1) or saline as a control was infused through the carotid artery of rats. Regional permeability was measured by autoradiography using [14C] aminoisobutyric acid, and the unidirectional transfer constant, Ki (microliters g-1 min-1), was calculated. Intracarotid infusion of 10 micrograms kg-1 min-1 histamine resulted in significant increase in brain tumour permeability, compared to controls. The permeability, Ki, for the 10 micrograms kg-1 min-1 histamine group, the 1 micrograms kg-1 min-1 histamine group, and the control group was 18.8 +/- 4.6 (p < 0.05), 14.9 +/- 5.2, 13.9 +/- 3.7 microliters g-1 min-1, respectively. There was no significant change in blood brain permeability in other brain regions. The effect of increased permeability by 10 micrograms kg-1 min-1 histamine was suppressed by the H2-blocker, cimetidine. This suggests that the effect of histamine on tumour capillaries is mediated by H2-receptors. Intracarotid histamine infusion selectively increases permeability in brain tumours.

Peripheral benzodiazepine stimulates secretion of growth hormone and mitochondrial proliferation in pituitary tumour GH3 cells

High affinity receptors for peripheral benzodiazepines (PBD) are present within the pituitary gland. Whether these receptors influence cell growth, mitochondrial morphology and secretion of growth hormone was examined in pituitary tumour GH3 cells. Cells were incubated in medium with either 10% calf serum, or serum free medium, or serum free medium plus 10 nM of selective PBD ligands (PK11195 or Ro5-4864) or a central benzodiazepine ligand (clonazepam). Peripheral or central ligands had no effect on cell growth. Quantitative electron micrography, however, revealed that cells treated with PBDs had a 2.5-fold increase in the total mitochondrial area within cells, a 1.6-fold increase in the number of mitochondria, and a 2.0 to 2.7-fold increase on the number of dividing mitochondria compared to serum free controls. The activity of DNA polymerase gamma, which replicates mitochondrial DNA, was increased approximately 3 times the initial value after 6 h exposure to PBDs. The number of nucleolar organizer regions (NORs), which relate to the ultimate synthesis of cellular protein, showed a 1.4-fold increase in PBDs treated cells. Secretion of growth hormone was stimulated (240% of serum free control) by exposure to PBDs for 12 h. The central benzodiazepine ligand, clonazepam, had little effect on mitochondrial morphology or secretion of growth hormone. These findings suggest that PBD receptors may be involved in mitochondrial proliferation and may affect the secretion of pituitary hormones.

Differential tissue expression of immunoreactive dehydropeptidase I, a peptidyl leukotriene metabolizing enzyme

We previously reported that intracarotid infusion of leukotriene C4 (LTC4) causes a selective increase in vascular permeability within brain tumor capillaries in experimental rat brain tumor. Normal brain capillaries are rich in gamma-glutamyl transpeptidase (gamma-GTP), an enzyme which converts LTC4 to leukotriene D4 (LTD4), and acts as an 'enzymatic barrier' to the vasoactive effects of LTC4. Metabolism of LTD4 in brain capillaries is, however, not known. In this study, rat renal dipeptidase (dehydropeptidase-I, microsomal dipeptidase; EC 3.4.13.11), which converts LTD4 to leukotriene E4 (LTE4) in kidney, was purified from rat kidney and the distribution of immunoreactive dipeptidase in multiple rat organs was determined. Immunocytochemical multi-organ analysis in the rat, which included brain, lung, heart, liver, spleen, small intestine, and testis, was performed. The antigen corresponding to renal dipeptidase was recognized in lung, liver, and testis. There was no antigen in the brain, heart, spleen, and small intestine. In order to confirm the absence of dipeptidase activity in brain capillaries, the metabolism of LTD4 by isolated brain capillaries were examined by reversed phase high performance liquid chromatography. When LTD4 was incubated with the isolated rat brain capillary, no measurable conversion of [3H] LTD4 to LTE4 and leukotriene F4 (LTF4) by brain capillaries was observed with 30 min of incubation. These findings suggest that although gamma-GTP acts as an enzymatic barrier and inactivates LTC4, brain capillaries do not have metabolic activity against LTD4.

The petrosal approach with hearing preservation

Twenty-six patients with petroclival lesions were operated on via a petrosal approach designed to preserve hearing. The surgical pathology included 14 meningiomas, three chordomas, three epidermoid cysts, four vertebrobasilar aneurysms, and two pontine cavernous malformations. The approach allowed complete resection of 14 of 20 tumors and definitive treatment of all six vascular lesions. Complications included cerebrospinal fluid leakage in three patients, high-frequency sensorineural hearing loss in three, meningitis in one, and cranial nerve palsies (which were usually transient). This approach allows a wide exposure of the petroclival region with decreased operating distance. Cerebellar and temporal lobe retraction are minimized, dural sinus patency is maintained, and the inner ear structures are not sacrificed. The approach is suitable for neoplastic or vascular lesions involving the petroclival region, the ventral pons, or the basilar artery trunk. The surgical technique, indications, and neuro-otological considerations are discussed.