Post-transcriptional regulation of vascular endothelial growth factor mRNA by the product of the VHL tumor suppressor gene

The VHL tumor suppressor gene is inactivated in patients with von Hippel-Lindau disease and in most sporadic clear cell renal carcinomas. Although VHL protein function remains unclear, VHL does interact with the elongin BC subunits in vivo and regulates RNA polymerase II elongation activity in vitro by inhibiting formation of the elongin ABC complex. Expression of wild-type VHL in renal carcinoma cells with inactivated endogenous VHL resulted in unaltered in vitro cell growth and decreased vascular endothelial growth factor (VEGF) mRNA expression and responsiveness to serum deprivation. VEGF is highly expressed in many tumors, including VHL-associated and sporadic renal carcinomas, and it stimulates neoangiogenesis in growing solid tumors. Despite 5-fold differences in VEGF mRNA levels, VHL overexpression did not affect VEGF transcription initiation or elongation as would have been suggested by VHL-elongin association. These results suggest that VHL regulates VEGF expression at a post-transcriptional level and that VHL inactivation in target cells causes a loss of VEGF suppression, leading to formation of a vascular stroma.

A comparison of the overnight and the standard metyrapone test for the differential diagnosis of adrenocorticotrophin-dependent Cushing's syndrome

OBJECTIVE

We wished to develop optimal criteria for interpreting the single-dose overnight metyrapone test and to compare the diagnostic efficiency of the overnight and the standard 6-dose metyrapone tests for the differential diagnosis of ACTH-dependent Cushing's syndrome.

DESIGN

Retrospective pilot study based on all patients who completed both metyrapone tests and whose diagnoses were subsequently confirmed surgically.

PATIENTS

Sixty-three patients, 57 with pituitary tumours and 6 with ectopic ACTH syndrome, were studied.

MEASUREMENTS

The sensitivity and specificity were determined using stimulation of plasma 11-deoxycortisol and suppression of plasma cortisol as endpoints for the overnight test and stimulation of urine 17-hydroxysteroid and plasma 11-deoxycortisol as endpoints for the standard test. The lest response that gave the highest sensitivity for the diagnosis of Cushing's disease, with 100% specificity, was determined for each test endpoint.

RESULTS

Both the stimulation of plasma 11-deoxycortisol and the suppression of plasma cortisol were expressed as the ratio of the post-metyrapone value to baseline. A plasma 11-deoxycortisol ratio > than 220 or a plasma cortisol ratio > 0.6 was associated with 100% specificity for diagnosis of Cushing's disease by the overnight test. When these two criteria were combined, the sensitivity was 65%, which was significantly higher than that obtained using either steroid alone: 42% for both plasma 11-deoxycortisol and plasma cortisol. The sensitivity of 65% for the overnight test, at 100% specificity, was nearly identical to that of the standard test in the same patients: 67% for the combined criterion of > 70% stimulation of urine 17-hydroxysteroid or > 480-fold increase of plasma 11-deoxycortisol. When the criteria for both the overnight and standard tests were combined, the sensitivity increased to 84%, which was higher than that obtained using the criteria for either test alone (P < 0.02).

CONCLUSION

The single-dose overnight metyrapone test, which can be performed in 24 hours and which avoids the disadvantages associated with timed urine collections, has a nearly identical sensitivity (for a specificity of 100%) as the 6-dose standard metyrapone test for the diagnosis of Cushing's disease. Furthermore, the diagnostic performance of a criterion that combines the results of both tests is significantly better than the best criterion for either test alone.

Mechanism of dexamethasone suppression of brain tumor-associated vascular permeability in rats. Involvement of the glucocorticoid receptor and vascular permeability factor

Brain tumor-associated cerebral edema arises because tumor capillaries lack normal blood-brain barrier function; vascular permeability factor (VPF, also known as vascular endothelial growth factor, VEGF) is a likely mediator of this phenomenon. Clinically, dexamethasone reduces brain tumor-associated vascular permeability through poorly understood mechanisms. Our goals were to determine if suppression of permeability by dexamethasone might involve inhibition of VPF action or expression, and if dexamethasone effects in this setting are mediated by the glucocorticoid receptor (GR). In two rat models of permeability (peripheral vascular permeability induced by intradermal injection of 9L glioma cell-conditioned medium or purified VPF, and intracerebral vascular permeability induced by implanted 9L glioma), dexamethasone suppressed permeability in a dose-dependent manner. Since 80% of the permeability-inducing activity in 9L-conditioned medium was removed by anti-VPF antibodies, we examined dexamethasone effects of VPF expression in 9L cells. Dexamethasone inhibited FCS- and PDGF-dependent induction of VPF expression. At all levels (intradermal, intracranial, and cell culture), dexamethasone effects were reversed by the GR antagonist mifepristone (RU486). Dexamethasone may decrease brain tumor-associated vascular permeability by two GR-dependent mechanisms: reduction of the response of the vasculature to tumor-derived permeability factors (including VPF), and reduction of VPF expression by tumor cells.

Inferior petrosal sinus arginine vasopressin concentrations in normal volunteers and patients with Cushing's disease

In patients with Cushing's disease (CD), basal inferior petrosal sinus arginine vasopressin (AVP) concentrations are greater than peripheral levels and are further increased by the administration of CRH. AVP has an interpetrosal sinus gradient similar to that for ACTH, leading to the hypotheses that petrosal sinus AVP might either be derived from the corticotroph adenoma or be important for adenoma formation. To determine whether petrosal sinus AVP is truly increased in patients with CD, we compared inferior petrosal sinus and peripheral venous AVP and ACTH levels in 23 patients with CD and 9 healthy volunteers before and after iv ovine CRH. In both groups, AVP and ACTH showed interpetrosal lateralization, such that greater levels of both hormones were found at each time point in a single dominant petrosal sinus. When both hormones exhibited lateralization (an intersinus gradient > 1.5), ACTH and AVP always lateralized together. In patients with CD, the ACTH interpetrosal sinus lateralization correctly identified the side of the pituitary containing the tumor in 75% of evaluable patients, whereas the AVP interpetrosal sinus lateralization identified 63% (P = NS). Ovine CRH stimulated AVP in both the dominant and nondominant petrosal sinuses in patients with CD. Although basal AVP in the dominant petrosal sinus was not significantly different in patients with CD and normal volunteers (144 +/- 85 vs. 13.0 +/- 4.3 pmol/L; P = 0.058), dominant petrosal sinus AVP was significantly elevated in patients with CD compared to normal volunteers at 3 min (269 +/- 122 vs. 45.1 +/- 30.0 pmol/L; P < 0.05) and 5 min (315 +/- 120 vs 40.2 +/- 23.6 pmol/L; P < 0.05) after ovine CRH administration. Peripheral venous AVP levels were similar in all groups. We conclude that lateralization of AVP secretion occurs in both patients with CD and normal volunteers, but there is greater CRH-stimulated AVP secretion in the inferior petrosal sinuses of patients with CD.

Acute glucocorticoid deficiency is associated with plasma elevations of interleukin-6: does the latter participate in the symptomatology of the steroid withdrawal syndrome and adrenal insufficiency?

The cytokines tumor necrosis factor-alpha (TNF alpha), interleukin-1 (IL-1), and IL-6 are secreted at inflammatory sites in tandem and play a crucial role in the inflammatory and wound-healing processes. All three cytokines are potent activators of the hypothalamic-pituitary-adrenal axis, through which they restrain inflammation, whereas IL-6 itself plays a role in the termination of inflammation as well. To test the hypothesis that endogenous glucocorticoids exert a negative tonic effect on the secretion of these cytokines, we studied 17 patients with Cushing's disease and 2 patients with primary adrenal Cushing's syndrome before and after surgery. Plasma TNF alpha, IL-1 beta and IL-6 were measured before surgery, while the patients were hypercortisolemic; on postoperative day 4 or 5, when they were hypocortisolemic; and on postoperative day 9 or 10, when they were receiving glucocorticoid replacement. During severe hypocortisolism, on postoperative day 4 or 5, plasma IL-6 levels rose significantly, compared to the preoperative values (P < 0.001). During the same interval, TNF alpha and IL-1 beta also rose, albeit to a lesser extent. Over the same interval, patients with severe hypocortisolism experienced temperature elevation, fatigue, somnolence, flu-like symptoms, and anorexia, symptoms that have been traditionally attributed to glucocorticoid deficiency; these were also experienced by subjects that received recombinant human IL-6. There was no postoperative increase in any of the cytokines studied in the patients who were not hypocortisolemic after surgery and who also lacked the corresponding symptomatology. Plasma IL-6 concentrations decreased significantly, albeit not to normal levels, in the hypocortisolemic group of patients on postoperative day 9 or 10, when they were receiving glucocorticoid replacement. We conclude that the peripheral levels of IL-6 and to a lesser extent, those of TNF alpha and IL-1 beta are tonically inhibited by basal levels of glucocorticoids. The increased IL-6 production that occurs when cortisol levels fall might explain the symptomatology of acute glucocorticoid deficiency.

The effect of Cushing's disease on bone mineral density, body composition, growth, and puberty: a report of an identical adolescent twin pair

As endogenous Cushing's syndrome (CS) in children occurs during a critical developmental period, when the majority of peak bone mass is acquired, we hypothesized that children with CS might be at an increased risk of osteoporosis. To determine the effects of CS on bone density, bone metabolism, and growth, we studied a 15-yr-old female identical twin pair, one of whom had CS (twin A), and the other of whom was healthy (twin B). Before therapy for CS, twin A showed a severe loss of bone mineral density [BMD; -3.2SD at the lumbar spine (LS)] compared to twin B (-0.1 SD), which in twin A was associated with low serum osteocalcin levels and urinary pyridinium cross-link excretion. Cure of CS in twin A led to a marked increase in these bone markers, suggesting a state of active bone remodeling. After 27 months of follow-up, even though twin A's BMD improved significantly, it still remained abnormal [-1.9 SD at LS compared with that of twin B (0 SD)], suggesting that twin A continued to be at increased long term risk of osteoporosis. In addition, as a consequence of CS, twin A's final height was 21 cm less than that of her identical twin. We recommend that all children with CS should have BMD monitored after treatment to determine the long term risk of osteoporosis.

Loss of nitric oxide synthase immunoreactivity in cerebral vasospasm

To determine the distribution of nitric oxide synthase (NOS) in the primate cerebral artery nervi vasorum and to examine the potential role of NOS in cerebral vasospasm after subarachnoid hemorrhage (SAH) in primates, the distribution of NOS immunoreactivity (NOS-IR) in the major cerebral arteries was examined immunohistochemically in cynomolgus monkeys by the use of whole, mounted preparations of the circle of Willis. In four normal monkeys, NOS-IR was localized to the endothelial and adventitial layers of the large cerebral arteries. On the abluminal side, NOS-IR staining was densely concentrated in perivascular nerve fibers (nervi vasorum) of the anterior circulation. Staining was less prominent in the posterior circulation. In six monkeys with vasospasm on Day 7 after placement of preclotted arterial blood to form an SAH around the right middle cerebral artery (MCA) (42% +/- 8.3% decrease of MCA area, mean +/- standard deviation), NOS-IR was virtually absent in nerve fibers around the spastic right MCA but was normal on the contralateral side. In five monkeys in which vasospasm resolved by Day 14 after SAH (36% +/- 14% decrease of right MCA area on Day 7, and 5% +/- 14% decrease on Day 14), NOS-IR was also absent in the right MCA adventitial nerve fibers and remained normal in the left MCA. Adventitial NOS-IR was also normal in cerebral vessels of a sham-operated, nonspastic monkey. These findings provide further evidence that nitric oxide (NO) functions as a neuronal transmitter to mediate vasodilation in primates and indicate a role for adventitial NO in the pathogenesis of cerebral vasospasm after SAH in humans.

Hyperosmolar blood-brain barrier disruption in baboons: an in vivo study using positron emission tomography and rubidium-82

Hyperosmolar blood-brain barrier (BBB) disruption remains controversial as an adjuvant therapy to increase delivery of water-soluble compounds to extracellular space in the brain in patients with malignant brain tumors. To understand the physiological effects of BBB disruption more clearly, the authors used positron emission tomography (PET) to study the time course of BBB permeability in response to the potassium analog rubidium-82 (82Rb, halflife 75 seconds) following BBB disruption in anesthetized adult baboons. Mannitol (25%) was injected into the carotid artery and PET scans were performed before and serially at 8-to 15-minute intervals after BBB disruption. The mean influx constant (K1), a measure of permeability-surface area product, in ipsilateral, mannitol-perfused mixed gray- and white-matter brain regions was 4.9 +/-2.4 microliter/min/ml (+/- standard deviation) at baseline and increased more than 100% (delta K1=9.4 +/-5.1 microliter/min/ml, 18 baboons) in brain perfused by mannitol. The effect of BBB disruption on K1 correlated directly with the total amount of mannitol administered (p< 0.005). Vascular permeability returned to baseline with a halftime of 24.0 +/- 14.3 minutes. The mean brain plasma volume rose by 0.57 +/- 0.34 ml/100 ml in ipsilateral perfused brain following BBB disruption. This work provides a basis for the in vivo study of permeability changes induced by BBB disruption in human brain and brain tumors.

Microvascular anatomy of dural arteriovenous abnormalities of the spine: a microangiographic study

Although most vascular abnormalities of the spinal cord are now ascribed to an abnormal communication between a dural artery and a medullary vein on the dura near a sensory nerve root, these lesions are too small for their anatomy to be demonstrated directly by spinal arteriography. Thus, it is unknown whether the site of dural arteriovenous shunting is an arteriovenous malformation (AVM), implying a congenital origin, or is a direct arteriovenous fistula (AVF), implying an acquired etiology. The authors treated six patients by en bloc resection of the involved dural root sleeve, proximal nerve root, and adjacent spinal dura. All of the patients presented with myelopathy and their arteriograms were consistent with a spinal dural vascular malformation. The lesions occurred between T-6 and T-12, levels at which clinical deficits from such resection are minimal. The dural artery or medullary vein associated with the vascular malformation was cannulated and a dilute solution of barium sulfate was injected during sequential fine-grain radiography. In all of the lesions the artery split into daughter vessels that coalesced one to three times to form a skein of arterial loops in the dura that invariably emptied into a medullary vein without an intervening capillary plexus. Several medium-to-small collateral vessels arising from adjacent intercostal or lumbar arteries were commonly present in the dura and converged at the site of the AVF to join a single medullary vein. These results show that spinal dural AVMs are direct AVFs that link the dural branch of the radiculo-medullary-dural artery with the intradural medullary vein. They also provide an anatomical explanation for the presence of a multiple segmental arterial supply and a single draining medullary vein of spinal dural AVFs, and the propensity for reestablishment of flow through the arteriovenous shunt after embolic occlusion.

Nitric oxide mediation of chemoregulation but not autoregulation of cerebral blood flow in primates

The authors sought to develop a model for assessing in vivo regulation of cerebral vasoregulation by nitric oxide (NO), originally described as endothelial-derived relaxing factor, and to use this model to establish the role of NO in the regulation of cerebral blood flow (CBF) in primates. By using regional intraarterial perfusion, the function of NO in cerebral vasoregulation was examined without producing confounding systemic physiological effects. Issues examined were: whether resting vasomotor tone requires NO; whether NO mediates vasodilation during chemoregulation and autoregulation of CBF; and whether there is a relationship between the degree of hypercapnia and hypotension and NO production. Twelve anesthetized (0.5% isoflurane) cynomolgus monkeys were monitored continuously for cortical CBF, PaCO2, and mean arterial pressure (MAP), which were systematically altered to provide control and experimental curves of chemoregulation (CBF vs. PaCO2) and autoregulation (CBF vs. MAP) during continuous intracarotid infusion of 1) saline and 2) an NO synthase inhibitor (NOSI), either L-n-monomethyl arginine or nitro L-arginine. During basal conditions (PaCO2 of 38-42 mm Hg) NOSI infusion of internal carotid artery (ICA) reduced cortical CBF from 62 (saline) to 53 ml/100 g/per minute (p<0.01), although there was no effect on MAP. Increased CBF in response to hypercapnia was completely blocked by ICA NOSI. The difference in regional (r)CBF between ICA saline and NOSI infusion increased linearly with PaCO2 when PaCO2 was greater than 40 mm Hg, indicating a graded relationship of NO production, increasing PaCO2, and increasing CBF. Diminution of CBF with NOSI infusion was reversed by simultaneous ICA infusion of L-arginine, indicating a direct role of NO synthesis in the chemoregulation of CBF. Hypotension and hypertension were induced with trimethaphan camsylate (Arfonad) and phenylephrine at constant PaCO2 (40 +/- 1 mm Hg). Autoregulation in response to changes in MAP from 50 to 140 mm Hg was unaffected by ICA infusion of NOSI. In primates, cerebral vascular tone is modulated in vivo by NO; continuous release of NO is necessary to maintain homeostatic cerebral vasodilation; vasodilation during chemoregulation of CBF is mediated directly by NO production; autoregulatory vasodilation with hypertension is not mediated by NO; and increasing PaCO2 induces increased NO production.

Nelson's syndrome associated with a somatic frame shift mutation in the glucocorticoid receptor gene

Nelson's syndrome is the appearance and/or progression of ACTH-secreting pituitary macroadenomas in patients who had previously undergone bilateral adrenalectomy for Cushing's disease. Extremely high plasma ACTH levels and aggressive neoplastic growth might be explained by the lack of appropriate glucocorticoid negative feedback due to defective glucocorticoid signal transduction. To study the glucocorticoid receptor (GR) gene in Nelson's syndrome, DNA was extracted from pituitary adenomas and leukocytes of four patients with this condition and amplified by PCR for direct sequence analysis. In one of the tumors, a heterozygous mutation, consisting of an insertion of a thymine between complementary DNA nucleotides 1188 and 1189, was found in exon 2. This frame-shift mutation led to premature termination at amino acid residue 366 of the wild-type coding sequence, excluding the expression of a functioning receptor protein from the defective allele. The mutation was not detected in the sequence of the GR gene in the patient's leukocyte DNA, indicating a somatic origin. By lowering the receptor number in tumorous cells, this defect might have caused local resistance to negative glucocorticoid feedback similar to that caused by the presence of a null allele in a kindred with the generalized glucocorticoid resistance syndrome. P53 protein accumulation, previously reported in 60% of corticotropinomas, could not be detected in any of the four pituitary tumors examined by immunohistochemistry. We suggest that a somatic GR defect might have played a pathophysiological role in the tumorigenesis of the corticotropinoma bearing this mutation.

Neurotoxicity of the human immunodeficiency virus type 1 tat transactivator to PC12 cells requires the Tat amino acid 49-58 basic domain

The acquired immunodeficiency syndrome (AIDS) frequently involves the central nervous system (CNS) and manifests as dementia due to encephalitis or diffuse neurodegeneration. Human immunodeficiency virus type 1 (HIV-1) proteins, potentially transported into the CNS by mononuclear inflammatory cells, have been implicated in the etiology of this HIV-1 associated neurological dysfunction. Here we investigate the neurotoxicity of the essential HIV-1 regulator protein Tat in vivo after microinfusion into the rat brain and in vitro using PC12, NG108-15, and GT17 neuronal cell lines. Infusion of either chemically synthesized Tat (Tat86) or recombinant Tat (rTat) into the striatal gray matter in Sprague-Dawley rats resulted in postural deviation ipsilateral to the infusion, a clinical presentation in rats associated with complete striatal dysfunction. Histologic examination 3 days after infusion revealed massive necrosis in the area of the distribution of the infusion. Infusion of heat denatured rTat, peptide Tat49-58, or peptide Tat57-86 did not result in clinically or histologically detectable brain damage. After 3 days incubation in vitro, the lethal dose for half (LD50) of PC12 cells due to rTat was 5 micrograms/ml. The LD50 for Tat86 under the same conditions was 10 micrograms/ml. Tat49-58 and Tat57-86 peptides were not toxic in vitro even at 10-fold higher doses. At 5 micrograms/ml, rTat was toxic to 100% of GT17 cells after 24 hr. At 5 micrograms/ml, Tat86 was toxic to 90% of the NG108-15 cells after 7 days of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective venous sampling from the cavernous sinuses is not a more reliable technique than sampling from the inferior petrosal sinuses in Cushing's syndrome

The purpose of this study was to compare ACTH levels in unstimulated samples obtained from the cavernous sinuses (CS) to unstimulated and CRH-stimulated samples obtained from the inferior petrosal sinuses (IPS) in 15 patients with surgically proven Cushing's disease. After unstimulated samples were obtained through 5-French catheters placed in both IPS, tracker catheters were introduced into both cavernous sinuses, and unstimulated samples were obtained within 5 min of the initial set. The Tracker catheters were removed, CRH was administered, and CRH-stimulated samples were obtained from the IPS. We compared the central to peripheral ACTH ratios in unstimulated samples from the cavernous sinuses to unstimulated and CRH-stimulated samples from the IPS as a basis for distinguishing pituitary from ectopic ACTH production. In addition, we compared the ability of the intercavernous and interpetrosal ACTH ratios to correctly predict the site of the microadenoma. Unstimulated levels of ACTH in the cavernous sinuses were generally higher than unstimulated levels of ACTH in the petrosal sinuses. However, 3 of 15 patients failed to show central to peripheral ACTH ratios greater than 2 in unstimulated samples from the cavernous sinuses and were thus falsely negative for the diagnosis of Cushing's disease (test sensitivity, 80%). By comparison, the test sensitivity for the petrosal sinus samples was 87% for the unstimulated samples and 100% for the CRH-stimulated samples. Lateralization was correct in 6 of 15 patients based on CS samples and in 9 of 15 patients based on IPS samples. Because of the 20% false negative rate, CS sampling without CRH stimulation is not recommended for the differential diagnosis of ACTH-dependent hypercortisolism.

Intraoperative ultrasound-directed resection of pituitary tumors

Microadenomas of the pituitary vary in size, particularly those related to Cushing's disease. They are often not visualized on preoperative magnetic resonance (MR) imaging and may be difficult to find during surgical exploration of the pituitary. To enhance intraoperative localization of pituitary adenomas, we assessed the feasibility of using ultrasound to detect and localize pituitary tumors. Intraoperative ultrasound (IS) in the axial and sagittal planes was performed with an Intrascan system using a 12-MHz mechanically oscillating, end-firing transducer. Interpretation of the scans was performed by two individuals, who were usually blinded to the results of preoperative MR imaging or petrosal sinus sampling. Twenty-eight patients were examined. Eighteen of these patients had microadenomas (1.5-7 mm), all with Cushing's disease; nine had macroadenomas (10-20 mm), three of which were adrenocorticotropic hormone-secreting, three growth hormone-secreting, two thyroid-stimulating hormone-secreting, and one nonfunctioning; and one patient had an intrasellar craniopharyngioma. Normal sellar and parasellar structures, such as intrapituitary cysts, the intracavernous carotid arteries, and the diaphragma sella were easily visualized. Twenty-three of the 28 tumors, including 13 of the 18 microadenomas, were detected on IS (82% sensitivity). Tumors were seen as hyperechoic masses in 19 patients, mixed echogenicity in three, and isoechoic in one. In most macroadenomas IS allowed visualization of the interface between the tumor and the normal pituitary gland. These results indicate the potential of IS to aid the intraoperative localization and definition of pituitary tumors.

Effect of intracarotid nitric oxide on primate cerebral vasospasm after subarachnoid hemorrhage

The continuous release of nitric oxide (NO) is required to maintain basal cerebrovascular tone. Oxyhemoglobin, a putative spasmogen, rapidly binds NO, implicating loss of NO in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH). If vasospasm is mediated by depletion of NO in the vessel wall, it should be reversible by replacement with NO. To investigate this hypothesis, the authors placed blood clots around the right middle cerebral artery (RMCA) of four cynomolgus monkeys; four unoperated animals served as controls. Arteriography was performed before and 7 days after surgery to assess the presence and degree of vasospasm, which was quantified in the anteroposterior (AP) projection by computerized image analysis. On Day 7, cortical cerebral blood flow (CBF) in the distribution of the right MCA was measured during four to six runs in the right internal carotid artery (ICA) of brief infusions of saline followed by NO solution. Arteriography was performed immediately after completing the final NO infusion in three of the four animals with vasospasm. Right MCA blood flow velocities were obtained using transcranial Doppler before, during, and after NO infusion in two vasospastic animals. After ICA NO infusion, arteriographic vasospasm resolved (mean percent of preoperative AP area, 55.9%); that is, the AP areas of the proximal portion of the right MCA returned to their preoperative values (mean 91.4%; range 88%-96%). Compared to ICA saline, during ICA NO infusion CBF increased 7% in control animals and 19% in vasospastic animals (p < 0.002) without significant changes in other physiological parameters. During NO infusion, peak systolic right MCA CBF velocity decreased (130 to 109 cm/sec and 116 to 76 cm/sec) in two vasospastic animals. The effects of ICA NO on CBF and CBF velocity disappeared shortly after terminating NO infusion. Intracarotid infusion of NO in a primate model of vasospasm 1) increases CBF, 2) decreases cerebral vascular resistance, 3) reverses arteriographic vasospasm, and 4) decreases CBF velocity in the vasospastic artery without producing systemic hypotension. These findings indicate the potential for the development of targeted therapy to reverse cerebral vasospasm after SAH.

Convection-enhanced distribution of large molecules in gray matter during interstitial drug infusion

Many novel experimental therapeutic agents, such as neurotrophic factors, enzymes, biological modifiers, and genetic vectors, do not readily cross the blood-brain barrier. An effective strategy to deliver these compounds to the central nervous system is required for their application in vivo. Under normal physiological conditions, brain interstitial fluid moves by both bulk flow (convection) and diffusion. It has recently been shown that interstitial infusion into the white matter can be used to increase bulk flow, produce interstitial convection, and efficiently and homogeneously deliver drugs to large regions of brain without significant functional or structural damage. In theory, even more uniform distribution is likely in gray matter. In the current study, four experiments were performed to examine if convection-enhanced delivery could be used to achieve regional distribution of large molecules in gray matter. First, the volume and consistency of anatomical distribution of 20 microliters of phaseolus vulgaris-leukoagglutinin (PHA-L; molecular weight (MW) 126 kD) after continuous high-flow microinfusion into the striatum of five rats over 200 minutes were determined using immunocytochemistry and quantified with image analysis. Second, the concentration profile of 14C-albumin (MW 69 kD) infused under identical conditions was determined in four hemispheres using quantitative autoradiography. Third, the volume of distribution after convection-enhanced infusion of 250 or 500 microliters biotinylated dextran (b-dextran, MW 10 kD), delivered over 310 minutes into the caudate and putamen of a rhesus monkey from one (250 microliters) or two (500 microliters) cannulas, was determined using immunocytochemistry and quantified with image analysis. Finally, the ability to target all dopaminergic neurons of the nigrostriatal tract via perfusion of the striatum with subsequent retrograde transport was assessed in three experiments by immunohistochemical analysis of the mesencephalon following a 300-minute infusion of 27 microliters horseradish peroxidase-labeled wheat germ agglutinin (WGA-HRP) into the striatum. Convection-enhanced delivery reproducibly distributed the large-compound PHA-L throughout the rat striatum (the percent volume of the striatum perfused, Vs, was 86% +/- 5%; mean +/- standard deviation) and produced a homogeneous tissue concentration in the perfused region (concentration of 14C-albumin relative to infusate concentration 30% +/- 5%). In the monkey, the infusion widely distributed b-dextran within the striatum using one cannula (caudate and putamen Vs = 76% and 76%) or two cannulas (Vs = 90% and 71%).(ABSTRACT TRUNCATED AT 400 WORDS)

Toxicity studies and distribution dynamics of retroviral vectors following intrathecal administration of retroviral vector-producer cells

The use of intrathecal, retroviral-mediated transfer of the herpes simplex thymidine kinase (HStk) gene and subsequent ganciclovir (GCV) administration has recently been shown to improve survival in a rat model of leptomeningeal carcinomatosis. Clinical application of this approach is attractive because access to the cerebrospinal fluid (CSF) space is relatively noninvasive and distribution of producer cells and vectors may be facilitated by circulation of CSF, overcoming distribution problems inherent in solid tumors. However, meningeal inflammation, transduction and injury to normal CNS tissue, proliferation of the xenogeneic producer cells in the subarachnoid space, immune-mediated injury, and development of hydrocephalus are possible complications of intraventricular or intrathecal administration of vector-producer cells. In addition, the dynamics of producer cell and vector distribution in the CSF are unknown. To address these issues, we evaluated the safety of this approach for gene delivery and assessed the dynamics of distribution of producer cells and retroviral vectors in rats and non-human primates. In rats, transduction of normal central nervous system (CNS) structures surrounding the subarachnoid space was evaluated after intrathecal and intraventricular injections of beta-galactosidase and HStk vector-producer cells, with and without GCV. In primates, beta-galactosidase and HStk vector-producer cells were injected intraventricularly and GCV was administered either intrathecally or intravenously. Toxicity was evaluated by neurologic examination, serial gadolinium-enhanced MRI scans of the brain, and blood and CSF profiles. A subgroup of monkeys received repeated intraventricular injection of vector-producer cells and intravenous GCV. The titer of retroviral-vector was measured in cisternal and lumbar CSF samples after repeated producer cell injection.(ABSTRACT TRUNCATED AT 250 WORDS)

In situ cyclopentenyl cytosine infusion for the treatment of experimental brain tumors

Cyclopentenylcytosine (CPEC; NSC 375575) is a pyrimidine nucleoside analogue that has potent antitumor effects when tested in vitro and also when tested in experimental tumors outside the central nervous system. CPEC exerts its antiproliferative effect through inhibition of CTP synthetase and consequent depletion of CTP and dCTP pools required for cell replication. Due to its poor penetration of the bloodbrain barrier, CPEC has failed to demonstrate therapeutic efficacy in experimental brain tumors after systemic administration. We therefore examined the in vivo activation, distribution, and antitumor effect of CPEC after long-term regional infusion of the drug directly into experimental brain tumors in rats. HPLC analysis of CPEC incubated with homogenized human brain and brain tumor tissue showed minimal degradation of the drug over 24 h. Analysis of rat cerebral 9L gliosarcoma infused with tritium-labeled CPEC demonstrated intratumoral accumulation of the active metabolite CPEC-triphosphate and concomitant depletion of CTP to a much greater extent in tumor tissue than in the adjacent brain. Tumor tissue UTP also decreased, but no significant effects on other ribonucleoside triphosphates were detected. Only trace amounts (< 1%) of CPEC and its metabolites reached peripheral sites, including the liver and kidneys, after intratumoral infusion. Rats treated with continuous intratumoral infusion of CPEC for 4 weeks using s.c. implanted osmotic pumps survived significantly longer than control rats receiving intratumoral saline or i.p. CPEC (P < 0.0001). Long-term intratumoral infusion of CPEC was not associated with any detectable toxicity. Our results support the feasibility of using intratumoral administration of CPEC as a regional therapy for malignant brain tumors.

Surgical interruption of intradural draining vein as curative treatment of spinal dural arteriovenous fistulas

To establish if interruption of the intradural draining spinal vein or surgical excision are curative treatments for spinal dural arteriovenous fistulas (AVFs), the medical records and radiographic studies of 19 patients with spinal dural AVFs and progressive myelopathy were reviewed. Spinal arteriograms were obtained before and within 2 weeks after surgery in 19 patients, and after a delay of 4 months or more in 11 patients. The mean clinical and arteriographic follow up was at 37 and 35 months, respectively. In the 11 patients who underwent excision of the dural AVF there was no evidence of a residual lesion upon immediate or delayed postoperative arteriography. Surgery in eight patients consisted of simple interruption of the intradural draining vein as it entered the subarachnoid space. In six of these patients the vein draining the AVF intrathecally provided the only venous drainage of the AVF. In these six patients there was no immediate (six of six) or delayed (four of six) arteriographic evidence of residual or recurrent flow through the AVF. Two patients had an AVF with both intra- and extradural venous drainage; after intradural division of the draining vein there was residual flow through the AVF into the extradural venous system. In one of these two patients intrathecal venous drainage was reestablished, which required additional therapy. In the other patient the extradural AVF spontaneously thrombosed and was not evident on delayed follow-up arteriography. In patients with spinal dural AVFs with only intrathecal medullary venous drainage, which includes most patients with these lesions, surgical interruption of the intradural draining vein provides lasting and curative treatment. In patients with both intra- and extradural drainage of the AVF, complete excision of the fistula or interruption of the intra- and extradural venous drainage of the fistula is indicated. In patients in whom a common vessel supplies the spinal cord and the dural AVF, simple surgical interruption of the vein draining the AVF is the treatment of choice, as it provides lasting obliteration of the fistula and it is the only treatment that does not risk arterial occlusion and cord infarction. Simple interruption of the venous drainage of a spinal dural AVF provides lasting occlusion of the fistula, as it does for cranial dural AVFs, if all pathways of venous drainage are interrupted. This result provides further evidence that the venous approach to the treatment of dural AVFs can be used successfully.

Adenovirally mediated gene transfer into experimental solid brain tumors and leptomeningeal cancer cells

Among the appealing features of adenoviruses as vectors for transfer of genes into the central nervous system (CNS) are that they are not neurotoxic, they can accommodate the insertion of several large genes, they are not associated with the hazards of insertional mutagenesis, and they can be concentrated to a high-titer preparation. The authors evaluated the feasibility of using adenovirally mediated gene transfer into cultured human glioma cells and in rat models of solid brain tumors and meningeal cancer. Replication-deficient adenoviral vector particles carrying a nuclear-localizing lacZ gene were injected into established 9L cerebral gliomas in Fischer rats. In addition, the adenoviral vector was injected into the subarachnoid space, either simultaneously with intrathecal tumor inoculation or after establishing leptomeningeal cancer. The brains and spinal cords were removed at various intervals for histochemical evaluation for beta-galactosidase activity using X-Gal staining. Additional rats received a stereotactic intracerebral injection of the vector into normal brain. No clinical abnormalities were observed in the injected rats. Injection of the adenoviral vector into normal brain resulted in diffuse transduction of astrocytes, microglia, neurons, and endothelial cells at the injection site. Injection of a high-concentration vector preparation into cerebral gliomas resulted in effective tumor transduction. Intrathecal injection of the vector in rats with meningeal cancer resulted in transduction of the infiltrating tumor in the subarachnoid space when injections were given simultaneously with, or 7 days after, tumor inoculation. Transduction rates of both solid and leptomeningeal tumors correlated with the number of injected particles. These results suggest that adenoviral vectors can efficiently transduce solid brain tumors and that the vectors survive in the cerebrospinal fluid for a sufficient period of time to allow leptomeningeal tumor transduction. Adenoviral vector should be evaluated for its potential use in therapeutic gene transfer approaches in malignancies of the CNS.

Isolated hyponatremia after transsphenoidal pituitary surgery

A retrospective analysis was performed to study the fluid and sodium status of patients undergoing transsphenoidal surgery (TS) for Cushing's disease. We evaluated the time of onset, duration, and relative incidence of isolated hyponatremia and identified possible factors associated with it. Of 58 patients that underwent TS over 1 yr, 52 without postoperative diabetes insipidus or volume depletion were studied. Isolated hyponatremia after TS for Cushing's disease occurred in 21%, and symptomatic hyponatremia (plasma sodium, < or = 125 mmol/L) with new onset headache, nausea, and emesis occurred in 7.0% of all operated. These later patients escaped monitoring and intervention for 24 h. The development of hyponatremia began early in the postoperative period and progressed slowly over 7 days. Maximum antidiuresis occurred on postoperative day 7. Vasopressin levels measured in two patients while hypoosmolar suggested that unregulated vasopressin release contributed to the hyponatremia. Cortisol levels, glucocorticoid replacement, and pituitary adenoma size were similar in normonatremic and hyponatremic patients. Patients combining a history of an estrogenic milieu and documented posterior pituitary trauma at surgery experienced lower nadir plasma sodium. All hyponatremic patients were fluid restricted, and none developed progressive neurological symptoms, morbidity, or mortality. We speculate that the mild degree and slow rate of development of hyponatremia and/or active monitoring and intervention contributed to the good outcome.

Reversal of hemiparkinsonian syndrome in nonhuman primates by amnion implantation into caudate nucleus

Although recent animal and human experiments suggest that tissue implantation can ameliorate parkinsonism, there is controversy about what mechanism underlies recovery. Secretion of dopamine from the graft seems unlikely to be the sole restorative factor. Regenerative sprouting by the host brain may also underlie behavioral recovery. Fetal amnion and term amnion, which were shown to produce and secrete a factor that supports the outgrowth of neurite processes in vitro, were implanted in hemiparkinsonian monkeys. Fetal amnion implants induced sprouting of dopaminergic fibers from the host brain and behavioral improvement, despite failure of the grafts to survive. Animals implanted with term amnion also had some sprouted dopaminergic fibers and behavioral improvement, but these were limited and were similar to the recovery, in prior experiments using the same primate model of parkinsonism, of animals that received surgical cavitation only. Recovery after central nervous system grafting with fetal amnion, a fetal accessory tissue, does not require secretion of a deficient neurotransmitter(s) from the graft and occurs despite the failure of graft survival. Recovery after cerebral implantation of fetal tissues appears to depend more on the regenerative and recuperative processes of the host brain than on graft replacement of deficient neurotransmitters or development of functional synaptic connections between the graft and the host brain.