Methodological and analytical considerations for intra-operative microdialysis

BACKGROUND

Microdialysis is a technique that can be utilized to sample the interstitial fluid of the central nervous system (CNS), including in primary malignant brain tumors known as gliomas. Gliomas are mainly accessible at the time of surgery, but have rarely been analyzed via interstitial fluid collected via microdialysis. To that end, we obtained an investigational device exemption for high molecular weight catheters (HMW, 100 kDa) and a variable flow rate pump to perform microdialysis at flow rates amenable to an intra-operative setting. We herein report on the lessons and insights obtained during our intra-operative HMW microdialysis trial, both in regard to methodological and analytical considerations.

METHODS

Intra-operative HMW microdialysis was performed during 15 clinically indicated glioma resections in fourteen patients, across three radiographically diverse regions in each patient. Microdialysates were analyzed via targeted and untargeted metabolomics via ultra-performance liquid chromatography tandem mass spectrometry.

RESULTS

Use of albumin and lactate-containing perfusates impacted subsets of metabolites evaluated via global metabolomics. Additionally, focal delivery of lactate via a lactate-containing perfusate, induced local metabolic changes, suggesting the potential for intra-operative pharmacodynamic studies via reverse microdialysis of candidate drugs. Multiple peri-operatively administered drugs, including levetiracetam, cefazolin, caffeine, mannitol and acetaminophen, could be detected from one microdialysate aliquot representing 10 min worth of intra-operative sampling. Moreover, clinical, radiographic, and methodological considerations for performing intra-operative microdialysis are discussed.

CONCLUSIONS

Intra-operative HMW microdialysis can feasibly be utilized to sample the live human CNS microenvironment, including both metabolites and drugs, within one surgery. Certain variables, such as perfusate type, must be considered during and after analysis. Trial registration NCT04047264.

Blood-brain barrier disruption defines the extracellular metabolome of live human high-grade gliomas

The extracellular microenvironment modulates glioma behaviour. It remains unknown if blood-brain barrier disruption merely reflects or functionally supports glioma aggressiveness. We utilised intra-operative microdialysis to sample the extracellular metabolome of radiographically diverse regions of gliomas and evaluated the global extracellular metabolome via ultra-performance liquid chromatography tandem mass spectrometry. Among 162 named metabolites, guanidinoacetate (GAA) was 126.32x higher in enhancing tumour than in adjacent brain. 48 additional metabolites were 2.05-10.18x more abundant in enhancing tumour than brain. With exception of GAA, and 2-hydroxyglutarate in IDH-mutant gliomas, differences between non-enhancing tumour and brain microdialysate were modest and less consistent. The enhancing, but not the non-enhancing glioma metabolome, was significantly enriched for plasma-associated metabolites largely comprising amino acids and carnitines. Our findings suggest that metabolite diffusion through a disrupted blood-brain barrier may largely define the enhancing extracellular glioma metabolome. Future studies will determine how the altered extracellular metabolome impacts glioma behaviour.

Anti-PD-1 and Extended Half-life IL2 Synergize for Treatment of Murine Glioblastoma Independent of Host MHC Class I Expression

Glioblastoma (GBM) is the most common malignant brain tumor in adults, responsible for approximately 225,000 deaths per year. Despite preclinical successes, most interventions have failed to extend patient survival by more than a few months. Treatment with anti-programmed cell death protein 1 (anti-PD-1) immune checkpoint blockade (ICB) monotherapy has been beneficial for malignant tumors such as melanoma and lung cancers but has yet to be effectively employed in GBM. This study aimed to determine whether supplementing anti-PD-1 ICB with engineered extended half-life IL2, a potent lymphoproliferative cytokine, could improve outcomes. This combination therapy, subsequently referred to as enhanced checkpoint blockade (ECB), delivered intraperitoneally, reliably cures approximately 50% of C57BL/6 mice bearing orthotopic GL261 gliomas and extends median survival of the treated cohort. In the CT2A model, characterized as being resistant to CBI, ECB caused a decrease in CT2A tumor volume in half of measured animals similar to what was observed in GL261-bearing mice, promoting a trending survival increase. ECB generates robust immunologic responses, features of which include secondary lymphoid organ enlargement and increased activation status of both CD4 and CD8 T cells. This immunity is durable, with long-term ECB survivors able to resist GL261 rechallenge. Through employment of depletion strategies, ECB's efficacy was shown to be independent of host MHC class I-restricted antigen presentation but reliant on CD4 T cells. These results demonstrate ECB is efficacious against the GL261 glioma model through an MHC class I-independent mechanism and supporting further investigation into IL2-supplemented ICB therapies for tumors of the central nervous system.

Complementary and Alternative Medicine for Gliomas: Systematic Review and Critical Appraisal of Current Literature

BACKGROUND

Many patients with glioma and their caregivers seek complementary and alternative medicine (CAM) methods to comfort themselves, cope with cancer medication side effects, and feel they are taking control of their disease.

OBJECTIVE

To summarize existing evidence on safety and efficacy of CAM treatments for gliomas.

METHODS

We performed an exhaustive electronic literature search for in vitro, animal, and clinical studies (English language, all years available) on CAM modalities for gliomas.

RESULTS

A total of 378 studies (315 unique articles) were analyzed. Distribution was as follows: in vitro-274 (73%), animal-77 (20%), and clinical-26 (7%, 2491 patients). Most studies were conducted in China (n = 135, 43%), followed by the United States (n = 62, 20%) and Spain (n = 17, 5%-6%). Resveratrol was the most commonly investigated CAM therapy in the in vitro (n = 62) and in vivo (n = 17) setting. Safety/toxicity was examined in 21% of in vitro (cytotoxic at same dose in 48%), 39% of in vivo (no evidence of organ toxicity), and 50% of clinical studies (adverse events reported in 6). Cytotoxicity was the most frequent end point among in vitro (60%) and animal studies (56%), followed by synergistic action with chemotherapy and inhibition of invasiveness and migration. Finally, 7 of 26 studies found no clinical effect, whereas 5 reported possible impact on progression-free or overall survival, 3 demonstrated decrease or arrest of tumor progression, and 2 showed positive impact on symptoms and quality of life.

CONCLUSION

These findings will hopefully educate providers and patients and stimulate further research in the field of CAM therapy for gliomas.

Use of heparin to rescue immunosuppressive monocyte reprogramming by glioblastoma-derived extracellular vesicles

OBJECTIVE

The profound immunosuppression found in glioblastoma (GBM) patients is a critical barrier to effective immunotherapy. Multiple mechanisms of tumor-mediated immune suppression exist, and the induction of immunosuppressive monocytes such as myeloid-derived suppressor cells (MDSCs) is increasingly appreciated as a key part of this pathology. GBM-derived extracellular vesicles (EVs) can induce the formation of MDSCs. The authors sought to identify the molecular consequences of these interactions in myeloid cells in order to identify potential targets that could pharmacologically disrupt GBM EV-monocyte interaction as a means to ameliorate tumor-mediated immune suppression. Heparin-sulfate proteoglycans (HSPGs) are a general mechanism by which EVs come into association with their target cells, and soluble heparin has been shown to interfere with EV-HSPG interactions. The authors sought to assess the efficacy of heparin treatment for mitigating the effects of GBM EVs on the formation of MDSCs.

METHODS

GBM EVs were collected from patient-derived cell line cultures via staged ultracentrifugation and cocultured with monocytes collected from apheresis cones from healthy blood donors. RNA was isolated from EV-conditioned and unconditioned monocytes after 72 hours of coculture, and RNA-sequencing analysis performed. For the heparin treatment studies, soluble heparin was added at the time of EV-monocyte coculture and flow cytometry analysis was performed 72 hours later. After the initial EV-monocyte coculture period, donor-matched T-cell coculture studies were performed by adding fluorescently labeled and stimulated T cells for 5 days of coculture.

RESULTS

Transcriptomic analysis of GBM EV-treated monocytes demonstrated downregulation of several important immunological and metabolic pathways, with upregulation of the pathways associated with synthesis of cholesterol and HSPG. Heparin treatment inhibited association between GBM EVs and monocytes in a dose-dependent fashion, which resulted in a concomitant reduction in MDSC formation (p < 0.01). The authors further demonstrated that reduced MDSC formation resulted in a partial rescue of immune suppression, as measured by effects on activated donor-matched T cells (p < 0.05).

CONCLUSIONS

The authors demonstrated that GBM EVs induce broad but reproducible reprogramming in monocytes, with enrichment of pathways that may portend an immunosuppressive phenotype. The authors further demonstrated that GBM EV-monocyte interactions are potentially druggable targets for overcoming tumor-mediated immune suppression, with heparin inhibition of EV-monocyte interactions demonstrating proof of principle.

Superinduction of immunosuppressive glioblastoma extracellular vesicles by IFN-γ through PD-L1 and IDO1

Background

Glioblastoma (GBM), the most common primary brain tumor, has a median survival of 15-16 months. Immunotherapy is promising but GBM-mediated immunosuppression remains a barrier. GBMs express the interferon-gamma (IFN-γ)-responsive immunosuppressive molecules PD-L1 and IDO1. Extracellular vesicles (EVs) have also been implicated in GBM-mediated immunosuppression, in part through PD-L1. We therefore sought to determine if GBM IFN-γ exposure increased GBM EV-mediated immunosuppression and mechanisms underlying this.

Methods

Human GBM-derived cells were cultured in the presence/absence of IFN-γ. EV’s were harvested. PD-L1, IDO1, and EV-associated protein expression was assessed. GBM EV’s (+/-IFN-γ) were cultured with healthy donor monocytes. Immunosuppressive myeloid-derived suppressor cell (MDSC) and non-classical monocyte (NCM) frequency was determined. Impact of GBM (+/-IFN-γ) EV-treated monocytes on CD3/CD28-mediated T cell proliferation was assessed. The impact of PD-L1 and IDO1 knockdown in GBM EV’s in this system was evaluated.

Results

IFN-γ exposure increased PD-L1 and IDO1 expression in GBM cells and EV’s without altering EV size or frequency. IFN-γ-exposed GBM EVs induced more MDSC and NCM differentiation in monocytes and these monocytes caused more T cell inhibition than IFN-γ-naive GBM EVs. PD-L1 and/or IDO1 knockdown in GBM cells abrogated the immunosuppressive effects of IFN-γ-exposed GBM EVs on monocytes.

Conclusions

IFN-γ exposure such as might occur during an anti-tumor immune response results in superinduction of GBM EVs’ baseline immunosuppressive effects on monocytes. These effects are mediated by increased PD-L1 and IDO1 expression in GBM EV’s. This data highlights mechanisms of GBM EV-mediated immunosuppression and identifies therapeutic targets (PD-L1, IDO1) to reverse these effects.

Deploying Kinase Inhibitors to Study Pediatric Gliomas

Pediatric midline gliomas are a uniformly fatal disease for which there is no cure. The location of these tumors makes surgical resection impossible, and so novel therapies are urgently needed to improve outcomes. The biology of these tumors is increasingly understood, with the histone H3K27M mutation playing a critical role in the pathogenesis of these tumors. Efforts to inhibit the growth of these tumors have also focused on inhibiting the Aurora kinase and Janus-associated kinase (JAK)/signal transducer and activator of transcription (STAT) pathway in order to disrupt tumor proliferation. A number of small molecule inhibitors of these kinases have shown promise in early studies. Screening and preclinical assessment of such inhibitors requires a functional assay to assess the degree of kinase inhibition. We detail here a luciferase-based reporter assay for STAT3 transcriptional activity that we have employed frequently in order to assess the efficacy of kinase inhibitors in pediatric gliomas. The assay we describe is specific to STAT3, but the overall methodology is generalizable to other downstream targets of the kinase of interest.

Immunosuppression in Glioblastoma: Current Understanding and Therapeutic Implications

Glioblastoma (GBM) is the most common primary brain tumor in adults an carries and carries a terrible prognosis. The current regiment of surgical resection, radiation, and chemotherapy has remained largely unchanged in recent years as new therapeutic approaches have struggled to demonstrate benefit. One of the most challenging hurdles to overcome in developing novel treatments is the profound immune suppression found in many GBM patients. This limits the utility of all manner of immunotherapeutic agents, which have revolutionized the treatment of a number of cancers in recent years, but have failed to show similar benefit in GBM therapy. Understanding the mechanisms of tumor-mediated immune suppression in GBM is critical to the development of effective novel therapies, and reversal of this effect may prove key to effective immunotherapy for GBM. In this review, we discuss the current understanding of tumor-mediated immune suppression in GBM in both the local tumor microenvironment and systemically. We also discuss the effects of current GBM therapy on the immune system. We specifically explore some of the downstream effectors of tumor-driven immune suppression, particularly myeloid-derived suppressor cells (MDSCs) and other immunosuppressive monocytes, and the manner by which GBM induces their formation, with particular attention to the role of GBM-derived extracellular vesicles (EVs). Lastly, we briefly review the current state of immunotherapy for GBM and discuss additional hurdles to overcome identification and implementation of effective therapeutic strategies.

Clinical utility of brain biopsy for presumed CNS relapse of systemic lymphoma

OBJECTIVE

The objective of this study was to determine the frequency with which brain biopsy for presumed CNS relapse of systemic hematological malignancies yields new, actionable diagnostic information. Hematological malignancies represent a disparate group of genetic and histopathological disorders. Proclivity for brain involvement is dependent on the unique entity and may occur synchronously or metasynchronously with the systemic lesion. Diffuse large B-cell lymphomas (DLBCLs) have a high propensity for brain involvement. Patients in remission from systemic DLBCL may present with a lesion suspicious for brain relapse. These patients often undergo brain biopsy. The authors' a priori hypothesis was that brain biopsy in patients with a history of systemic DLBCL and a new brain MRI lesion would have lower diagnostic utility compared with patients with non-DLBCL systemic malignancies.

METHODS

The authors performed a retrospective review of patients who underwent brain biopsy between 2000 and 2019. Inclusion criteria were patients ≥ 18 years of age with a prior systemic hematological malignancy in remission presenting with a new brain MRI lesion concerning for CNS relapse. Patients with a history of any CNS neoplasms, demyelinating disorders, or active systemic disease were excluded. The main outcome was the proportion of patients with a distinct histopathological brain diagnosis compared with the systemic malignancy. The authors secondarily assessed overall survival, procedure-related morbidity, and 30-day mortality.

RESULTS

Sixty patients met inclusion criteria (40 males and 20 females); the median age at brain biopsy was 67 years (range 23-88 years). The median follow-up was 8.5 months (range 0.1-231 months). Thirty-nine (65.0%) patients had DLBCL and 21 (35%) had non-DLBCL malignancies. Thirty-five of 36 (97.2%) patients with prior systemic DLBCL and a diagnostic biopsy had histopathological confirmation of the original systemic disease versus 0 of 21 patients with non-DLBCL systemic malignancies (p < 0.001). Morbidity and 30-day mortality were 8.3% and 10.0%, respectively; 2 of 6 30-day mortalities were directly attributable to the biopsy. The median overall survival following brain biopsy was 10.8 months.

CONCLUSIONS

Patients with a history of systemic DLBCL and presumed CNS relapse gained minimal clinical benefit from brain biopsy but were at high risk of morbidity and mortality. In patients with a history of non-DLBCL systemic malignancies, brain biopsy remained critical given the high likelihood for discovery of distinct diagnostic entities. It was determined that patients with a prior systemic DLBCL and presumed brain relapse should likely receive empirical therapy obviating treatment delay and the risks of brain biopsy.

Does pituitary compression/empty sella syndrome contribute to MRI-negative Cushing's disease? A single-institution experience

OBJECTIVE

Cushing's disease arises from functioning adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas. These tumors can be very small and evade detection by MRI. Empty sella syndrome is a phenomenon by which an arachnoid outpouching of CSF into the sella leads to compression of the pituitary, likely due to intracranial hypertension (a common issue in Cushing's disease), further leading to difficulty in visualizing the pituitary gland that may contribute to difficulty in finding a tumor on MRI, so-called MRI-negative Cushing's disease. The authors sought to examine the association between empty sella syndrome and MRI-negative Cushing's disease.

METHODS

A single-institution database of Cushing's disease cases from 2000 to 2017 was reviewed, and 197 cases were included in the analysis. One hundred eighty patients had a tissue diagnosis of Cushing's disease and 17 had remission with surgery, but no definitive tissue diagnosis was obtained. Macroadenomas (tumors > 1 cm) were excluded. The degree of empty sella syndrome was graded on the degree of CSF visualized in the sella on midline sagittal T1-weighted MRI.

RESULTS

Of the 197 cases identified, 40 (20%) presented with MRI-negative disease, and empty sella syndrome was present in 49 cases (25%). MRI-negative disease was found in 18 (37%) of 49 empty sella cases versus 22 (15%) of 148 cases without empty sella syndrome present. Empty sella syndrome was significantly associated with MRI-negative disease (OR 3.32, 95% CI 1.61-6.74, p = 0.0018). Decreased thickness of the pituitary gland was also associated with MRI-negative disease (mean thickness 5.6 vs 6.8 mm, p = 0.0002).

CONCLUSIONS

Empty sella syndrome is associated with an increased rate of MRI-negative Cushing's disease. Pituitary compression causing a relative reduction in the volume of the pituitary for imaging is a plausible cause for not detecting the tumor mass with MRI.

Plasma extracellular vesicles as a source of biomarkers in traumatic brain injury

OBJECTIVE

The objective of this study was to isolate extracellular vesicles (EVs) from plasma in a cohort of patients with traumatic brain injury (TBI) and analyze their contents for novel biomarkers that could prove useful for rapid diagnosis and classification of brain injury during initial evaluation.

METHODS

Plasma EVs were isolated by serial ultracentrifugation from patients with TBI (n = 15) and healthy controls (n = 5). Samples were obtained from the TRACK-TBI biorepository (2010–present). Size and concentration were determined by nanoparticle tracking. Glial fibrillary acidic protein (GFAP) concentration was determined in EV protein. EV RNA was isolated and deep sequencing of short noncoding RNA was performed.

RESULTS

Plasma EVs are physically similar but contained approximately 10 times more GFAP in TBI patients with altered consciousness than patients and controls with normal consciousness. Eleven highly differentially expressed microRNAs (miRNAs) were identified between these groups. Genes targeted by these miRNAs are highly associated with biologically relevant cellular pathways, including organismal injury, cellular development, and organismal development. Multiple additional coding and noncoding RNA species with potential biomarker utility were identified.

CONCLUSIONS

Isolating plasma EVs in patients with TBI is feasible. Increased GFAP concentration—a validated plasma TBI marker—in EVs from TBI patients with altered consciousness, along with differential expression of multiple miRNAs targeting TBI-relevant pathways, suggests that EVs may be a useful source of TBI biomarkers. Additional evaluation in larger patient cohorts is indicated.

The role of extracellular vesicles and PD-L1 in glioblastoma-mediated immunosuppressive monocyte induction

BACKGROUND

Immunosuppression in glioblastoma (GBM) is an obstacle to effective immunotherapy. GBM-derived immunosuppressive monocytes are central to this. Programmed cell death ligand 1 (PD-L1) is an immune checkpoint molecule, expressed by GBM cells and GBM extracellular vesicles (EVs). We sought to determine the role of EV-associated PD-L1 in the formation of immunosuppressive monocytes.

METHODS

Monocytes collected from healthy donors were conditioned with GBM-derived EVs to induce the formation of immunosuppressive monocytes, which were quantified via flow cytometry. Donor-matched T cells were subsequently co-cultured with EV-conditioned monocytes in order to assess effects on T-cell proliferation. PD-L1 constitutive overexpression or short hairpin RNA-mediated knockdown was used to determined the role of altered PD-L1 expression.

RESULTS

GBM EVs interact with both T cells and monocytes but do not directly inhibit T-cell activation. However, GBM EVs induce immunosuppressive monocytes, including myeloid-derived suppressor cells (MDSCs) and nonclassical monocytes (NCMs). MDSCs and NCMs inhibit T-cell proliferation in vitro and are found within GBM in situ. EV PD-L1 expression induces NCMs but not MDSCs, and does not affect EV-conditioned monocytes T-cell inhibition.

CONCLUSION

These findings indicate that GBM EV-mediated immunosuppression occurs through induction of immunosuppressive monocytes rather than direct T-cell inhibition and that, while PD-L1 expression is important for the induction of specific immunosuppressive monocyte populations, immunosuppressive signaling mechanisms through EVs are complex and not limited to PD-L1.

Brain cancer induces systemic immunosuppression through release of non-steroid soluble mediators

Immunosuppression of unknown aetiology is a hallmark feature of glioblastoma and is characterized by decreased CD4 T-cell counts and downregulation of major histocompatibility complex class II expression on peripheral blood monocytes in patients. This immunosuppression is a critical barrier to the successful development of immunotherapies for glioblastoma. We recapitulated the immunosuppression observed in glioblastoma patients in the C57BL/6 mouse and investigated the aetiology of low CD4 T-cell counts. We determined that thymic involution was a hallmark feature of immunosuppression in three distinct models of brain cancer, including mice harbouring GL261 glioma, B16 melanoma, and in a spontaneous model of diffuse intrinsic pontine glioma. In addition to thymic involution, we determined that tumour growth in the brain induced significant splenic involution, reductions in peripheral T cells, reduced MHC II expression on blood leucocytes, and a modest increase in bone marrow resident CD4 T cells. Using parabiosis we report that thymic involution, declines in peripheral T-cell counts, and reduced major histocompatibility complex class II expression levels were mediated through circulating blood-derived factors. Conversely, T-cell sequestration in the bone marrow was not governed through circulating factors. Serum isolated from glioma-bearing mice potently inhibited proliferation and functions of T cells both in vitro and in vivo. Interestingly, the factor responsible for immunosuppression in serum is non-steroidal and of high molecular weight. Through further analysis of neurological disease models, we determined that the immunosuppression was not unique to cancer itself, but rather occurs in response to brain injury. Non-cancerous acute neurological insults also induced significant thymic involution and rendered serum immunosuppressive. Both thymic involution and serum-derived immunosuppression were reversible upon clearance of brain insults. These findings demonstrate that brain cancers cause multifaceted immunosuppression and pinpoint circulating factors as a target of intervention to restore immunity.

Adjuvant radiation for WHO grade II and III intracranial meningiomas: insights on survival and practice patterns from a National Cancer Registry

INTRODUCTION

WHO grades II (atypical) and III (malignant) meningiomas are associated with significant morbidity and mortality. The role of adjuvant radiotherapy (RT) in management remains controversial. The goal of this study was to evaluate the impact of adjuvant RT on 5-year survival in patients with atypical and malignant meningiomas. We secondarily aimed to assess contemporary practice patterns and the impact of sociodemographic factors on outcome.

METHODS

We queried the National Cancer Database for patients ≥ 18 years of age with cranial atypical or malignant meningiomas from 2010 through 2015 who underwent surgical resection with or without adjuvant radiotherapy. Subjects with unknown WHO grade or radiation status and those not receiving any surgical procedure were excluded from analysis.

RESULTS

The study includes 7486 patients, 6788 with atypical and 698 with malignant meningiomas. Overall 5-year survival was 76.9% (95% CI 75.5-78.3%) and 43.3% (95% CI 38.8-48.2%) among patients with WHO grades II and III meningiomas, respectively. Adjuvant RT correlated with improved survival in a multivariable model in patients with grade II tumors (HR 0.78; p = 0.029) regardless of the extent of resection. Age (HR 2.33; p < 0.001), male sex (HR 1.27; p < 0.001), Black race (HR 1.27; p = 0.011) and Charlson-Deyo Score ≥ 2 (1.35; p = 0.001) correlated with poorer survival whereas private insurance (HR 0.71; p < 0.001) correlated with improved survival. Adjuvant RT was also associated with improved 5-year survival among those with grade III tumors on univariate analysis (log-rank p = 0.006) but was underpowered for multivariable modeling. Utilization of adjuvant radiotherapy was only 28.4% and correlated with private insurance status. Academic institutions (25.3%) and comprehensive community cancer programs (21.4%) had lower radiotherapy utilization rates compared with integrated network cancer programs (30.5%) and community cancer programs (29.7%).

CONCLUSIONS

Adjuvant RT may correlate with improved overall survival in patients with grades II and III intracranial meningiomas regardless of the extent of resection. There is poor utilization of adjuvant RT for patients with grades II and III meningiomas likely due to a paucity of quality data on the subject. These findings will be strengthened with prospective data evaluating the role of adjuvant RT.

Effect of surgery and chemotherapy on long-term survival in infants with congenital glioblastoma: an integrated survival analysis

OBJECTIVE

Glioblastoma (GBM) during infancy is rare, and the clinical outcomes of congenital GBM are not well understood. Correspondingly, the aim of this study was to present a long-term survivor case from the authors' institution, and establish an integrated cohort of cases across the published literature to better understand the clinical course of this disease in this setting.

METHODS

The authors report the outcomes of an institutional case of congenital GBM diagnosed within the first 3 months of life, and performed a comprehensive literature search for published cases from 2000 onward for an integrated survival analysis. All cases were integrated into 1 cohort, and Kaplan-Meier estimations, Fisher's exact test, and logistic regression were used to interrogate the data.

RESULTS

The integrated cohort of 40 congenital GBM cases consisted of 23 (58%) females and 17 (42%) males born at a median gestational age of 38 weeks (range 22-40 weeks). Estimates of overall survival (OS) at 1 month was 67%, at 1 year it was 59%, and at 10 years it was 45%, with statistically superior outcomes for subgroups in which patients survived to be treated by resection and chemotherapy. In the overall cohort, multivariable analysis confirmed resection (p < 0.01) and chemotherapy (p < 0.01) as independent predictors of superior OS. Gestational age > 38 weeks (p < 0.01), Apgar scores ≥ 7 at 5 minutes (p < 0.01), absence of prenatal hydrocephalus (p < 0.01), and vaginal delivery (p < 0.01) were associated with greater odds of surgical diagnosis versus autopsy diagnosis.

CONCLUSIONS

Congenital GBM can deviate from the expected poor prognosis of adult GBM in terms of OS. Both resection and chemotherapy confer statistically superior prognostic advantages in those patients who survive within the immediate postnatal period, and should be first-line considerations in the initial management of this rare disease.

Outcomes in single-level posterior cervical spine surgeries performed in the sitting and prone positions

OBJECTIVE

The sitting or semisitting position in neurosurgery allows for several technical advantages, including improved visualization of the surgical field. However, it has also been associated with an increased risk of venous air embolisms and positioning-related complications that limit its commonplace adoption. The authors report a large, single-center series of cervical spine procedures performed with patients in the sitting or prone position in order to assess the perceived risk of intraoperative and postoperative complications associated with the sitting position.

METHODS

Noninstrumented, single-level posterior cervical spine procedures performed with patients in the sitting/semisitting or prone position from 2000 to 2016 at a single institution were reviewed. Institutional abstraction tools (DataMart and Chart Plus) were used to collect data from the medical records. The two positions were compared with regard to preoperative factors, intraoperative variables, and postoperative outcomes. Multivariable logistic regression models were fitted for 30-day readmission, 30-day return to the operating room, and complication rates.

RESULTS

A total of 750 patients (sitting, n = 480; prone, n = 270) were analyzed. The median age was 53 years for those who underwent surgery in the prone position and 50 years for those who underwent surgery in the sitting position (IQRs 45-62 years and 43-60 years, respectively), and 35% of the patients were female. Sitting cases were associated with significantly longer anesthetic times (221 minutes [range 199-252 minutes] vs 205 minutes [range 179-254 minutes]) and operative times (126 minutes [range 101-163 minutes] vs 149 minutes [120-181 minutes]). Cardiorespiratory events in the postanesthesia care unit (PACU) were comparable between the two groups, with the exception of episodes of apnea (2.6% vs 0.6%, p = 0.041) and hypoventilation (4.4% vs 0.8%, p < 0.003), which were more frequent in the prone-position cohort. On multivariable analysis, the effect of the sitting versus the prone position was not significant for 30-day readmission (OR 0.77, 95% CI 0.34-1.71, p = 0.52) or reoperation (OR 0.71, 95% CI 0.31-1.60, p = 0.40). The sitting position was associated with lower odds of developing any complication (OR 0.31, 95% CI 0.16-0.62, p < 0.001).

CONCLUSIONS

Based on the intraoperative and postoperative complications chosen in this study, the sitting position confers a similar safety profile to the prone position. This can be explained by a more anatomic positioning accounting for reduced temporary neurological deficits and reduced PACU-associated hypoventilation noted in this series. Nevertheless, the findings may also reflect institutional familiarity, experience, and mastery of this position type, and outcomes may not reflect practices in general.

Glioblastoma Recurrence Versus Treatment Effect in a Pathology-Documented Series

OBJECTIVE

Patients diagnosed with glioblastoma (GBM) are treated with surgery followed by fractionated radiotherapy with concurrent and adjuvant temozolomide. Patients are monitored with serial magnetic resonance imaging (MRI). However, treatment-related changes frequently mimic disease progression. We reviewed a series of patients undergoing surgery for presumed first-recurrence GBM, where pathology reports were available for tissue diagnosis, in order to better understand factors associated with a diagnosis of treatment-related changes on final pathology.

METHODS

Patient records at a single institution between 2005 and 2015 were retrospectively reviewed. Pathology reports were reviewed to determine diagnosis of recurrent GBM or treatment effect. Survival analysis was performed interrogating overall survival (OS) and progression-free survival (PFS). Correlation with radiation treatment plans was also examined.

RESULTS

One-hundred-twenty-three patients were identified. One-hundred-sixteen patients (94%) underwent resection and seven underwent biopsy. Treatment-related changes were reported in 20 cases (16%). These patients had longer median OS and PFS from the time of recurrence than patients with true disease progression. However, there was no significant difference in OS from the time of initial diagnosis. Treatment effect was associated with surgery within 90 days of completing radiation. In patients receiving radiation at our institution (n = 53), larger radiation target volume and a higher maximum dose were associated with treatment effect.

CONCLUSION

Treatment effect was associated with surgery nearer to completion of radiation, a larger radiation target volume, and a higher maximum point dose. Treatment effect was associated with longer PFS and OS from the time of recurrence, but not from the time of initial diagnosis.

Pituitary adenomas in the setting of multiple endocrine neoplasia type 1: a single-institution experience

OBJECTIVE

Multiple endocrine neoplasia type 1 (MEN1) is a rare, autosomal-dominant tumor disorder characterized by the development of pituitary tumors and other endocrine neoplasms. Diagnosis is made clinically based on the development of 2 or more canonical lesions (parathyroid gland, anterior pituitary, and enteropancreatic tumors) or in family members of a patient with a clinical diagnosis of MEN1 and the occurrence of one of the MEN1-associated tumors. The goal of this study was to characterize pituitary tumors arising in the setting of MEN1 at a single institution. The probability of tumor progression and the likelihood of surgical intervention in patients with asymptomatic nonfunctional pituitary adenomas were also analyzed.

METHODS

A retrospective review of a prospectively maintained institutional database was performed for patients with MEN1 diagnosed from 1970 to 2017. Data included patient demographics, tumor characteristics, treatment strategies, and outcomes.

RESULTS

A review of the database identified 268 patients diagnosed with MEN1, of whom 158 (59%) were female. Among the 268 patients, 139 (51.8%) had pituitary adenomas. There was a higher prevalence in women than in men (65% vs 35%, p < 0.005). Functional adenomas (57%) were more common. Prolactin-secreting adenomas were the most common functional tumors. Macroadenomas were seen in 27% of patients and were more likely to be symptomatic and locally aggressive (p < 0.001). Forty-nine patients (35%) underwent transsphenoidal resection at some point during their disease course. In 52 patients who were initially observed with MEN1 asymptomatic nonfunctional adenomas, only 5 (10%) progressed to need surgery. In MEN1 patients, an initial parathyroid lesion is most likely followed in order by pituitary, pancreatic, adrenal, and, finally, rare carcinoid tumors.

CONCLUSIONS

Asymptomatic nonfunctional pituitary adenomas in patients with MEN1 may be followed safely with MRI. In this series, parathyroid tumors developed at the lowest median age of all cardinal tumors, and development of additional cardinal MEN1 lesions followed a predictable pattern. This pattern of disease progression could have significant implications for disease surveillance in clinical practice and may help to target clinical resources to the lesions most likely to develop next. This may aid with early detection and treatment and warrants further study.

SCIDOT-34. BRAIN INJURY SIGNALS SYSTEMIC IMMUNOSUPPRESSION THROUGH THYMIC INVOLUTION

Systemic immunosuppression following neurological insults including stroke, traumatic brain injury, and glioblastoma (GBM) causes mortality and leads to failure of immune-modulating therapies. Exact immunological nature and the underlying mechanisms of this immunosuppression are unknown. Our goal was to define effects of neurological insults given exclusively to the brain on the thymus. The thymus is the primary immune organ responsible for T-cell development and maintenance both in children and in adults. We evaluated the brain-thymus communication using the following neurological insults: physical injury, CNS viral infection, sterile injury, tumor implantation, and seizures. All insults resulted in significant thymic involution that was reversible upon clearance of the insult. Thymic involution did not occur following similar peripheral insults. We next demonstrated that the GL261 model of GBM recapitulates hallmark features of peripheral immunosuppression observed in GBM patients including low CD4 T-cell counts. Thus, we aimed to further study the immunosuppression affecting the thymus in this clinically relevant model. Principle component analysis following RNA-sequencing of thymi from naïve and glioma-bearing mice revealed unbiased separation of the groups suggesting that the thymus is directly affected by a brain tumor. To determine the extent to which thymic involution was caused by a soluble factor we employed parabiosis. We demonstrated that thymic involution was transferable from glioma-bearing to non-tumor-bearing parabionts. Similarly, serum taken from GL261 glioma-bearing mice potently inhibited proliferation of T-cells in vitro. Together our data demonstrate that CNS-specific insults, regardless of nature, cause immunosuppression by prompting thymic involution through circulating factors. This accounts at least partially for immune deficiencies observed following neurological injuries. Identification of this suppressive factor is crucial in designing future therapeutics for GBM patients, and patients with other acute and chronic neurological trauma.

Ventriculostomy and Risk of Upward Herniation in Patients with Obstructive Hydrocephalus from Posterior Fossa Mass Lesions

BACKGROUND

Patients with posterior fossa lesions causing obstructive hydrocephalus present a unique clinical challenge, as relief of hydrocephalus can improve symptoms, but the perceived risk of upward herniation must also be weighed against the risk of worsening or continued hydrocephalus and its consequences. The aim of our study was to evaluate for clinically relevant upward herniation following external ventricular drainage (EVD) in patients with obstructive hydrocephalus due to posterior fossa lesions.

METHODS

We performed a retrospective review of patients undergoing urgent/emergent EVD placement at our institution between 2007 and 2014, evaluating the radiographic and clinical changes following treatment of obstructive hydrocephalus.

RESULTS

Even prior to EVD placement, radiographic upward herniation was present in 22 of 25 (88%) patients. The average Glasgow Coma Scale of patients before and after EVD placement was 10 and 11, respectively. Radiographic worsening of upward herniation occurred in two patients, and upward herniation in general persisted in 21 patients. Clinical worsening occurred in two patients (8%), though in all others the clinical examination remained stable (44%) or improved (48%) following EVD placement. Of the patients who had a worsening clinical exam, other variables likely also contributed to their decline, and cerebrospinal fluid diversion was likely not the main factor that prompted the clinical change.

CONCLUSIONS

Radiographic presence of upward herniation was often present prior to EVD placement. Clinically relevant upward herniation was rare, with only two patients worsening after the procedure, in the presence of other clinical confounders that likely contributed as well.

Insurance correlates with improved access to care and outcome among glioblastoma patients

Background

The current standard of care for glioblastoma (GBM) constitutes maximal safe surgical resection, followed by fractionated radiation and temozolomide. This treatment regimen is logistically burdensome, and in a health care system in which access to care is variable, there may be patients with worsened outcomes due to inadequate access to optimal treatment.

Methods

The National Cancer Database was queried for patients with diagnoses of GBM in 2006-2014. Patients were grouped according to insurance status: private insurance, Medicare, Medicaid, or uninsured. Treatments provided (surgery, radiation, and chemotherapy) were compared between groups in univariate and multivariable logistic regression analysis.

Results

A total of 61614 patients were analyzed. Compared with private insurance, the odds of surgery for Medicaid and uninsured patients were 0.72 (95% CI: 0.66-0.79) and 0.77 (95% CI: 0.69-0.87), respectively (P < 0.001). The multivariable odds of receiving radiotherapy were 0.91 (95% CI: 0.86-0.96), 0.62 (95% CI: 0.57-0.68), and 0.47 (95% CI: 0.43-0.52) for Medicare, Medicaid, and uninsured patients, respectively (all P < 0.001). In addition, the odds of receiving chemotherapy were 0.94 (95% CI: 0.89-0.99), 0.53 (95% CI: 0.49-0.57), and 0.41 (95% CI: 0.38-0.46) for Medicare, Medicaid, and uninsured patients, respectively (all P < 0.001).

Conclusion

Insurance status and type of insurance coverage appear to impact treatments rendered for GBM, independently of other variables. Furthermore, we find that such differential access to care significantly impacts survival. Ensuring adequate access to care for all patients with diagnoses of glioblastoma is critical to optimize survival, especially as therapies continue to advance.

The 100 Most-Cited Articles About Convection-Enhanced Delivery to the Brain: A Bibliometric Analysis

BACKGROUND

Convection-enhanced delivery (CED) overcomes the blood-brain barrier to deliver therapy within the central nervous system. Our aim was to evaluate citation and other bibliometric characteristics of the 100 most-cited articles about CED to the brain to better understand the state of research efforts in the field.

METHODS

Elsevier's Scopus database was searched for the 100 most-cited articles that focused on CED to the brain. Articles were dichotomized as either primarily basic science (BSc) or clinical (CL) articles. Various bibliometric parameters were summarized, and BSc and CL articles were compared.

RESULTS

Of the 100 most-cited articles, 64 (64%) were BSc and 36 (36%) were CL. The most common indications reported were brain tumors (59%) and Parkinson disease (5%). Overall median values were as follows: citation count, 102 (range, 70-933); citation rate per year, 9.0 (range, 3.7-49.4); number of authors, 5 (range, 1-25); and publication year, 2006 (range, 1994-2015). Articles were published in a total of 48 different journals, and predominately originated in the United States (n = 78, 78%). BSc and CL articles were statistically comparable in terms of bibliometric parameters.

CONCLUSIONS

In the 100 most-cited articles about CED to the brain, there were more BSc articles compared with CL articles; however, they were comparable with respect to the reported bibliometric parameters. Given that the peak year of publication of these articles was more than a decade ago, we anticipate that the field will shift toward more CL articles once effective therapies to be delivered via CED are discovered.

Recurrent papillary craniopharyngioma with BRAF V600E mutation treated with dabrafenib: case report

The authors present the case of a man with a papillary craniopharyngioma, first diagnosed at 47 years of age, who experienced multiple recurrences. Review of the pathologic specimen from his first resection demonstrated the BRAF V600E mutation. With his most recent recurrence following previous surgery and radiotherapy, at 52 years of age, the decision was made to initiate treatment with the BRAF V600E inhibitor dabrafenib. Imaging following initiation of dabrafenib demonstrated reduction in tumor size. He remained on dabrafenib therapy for approximately 1 year and continued to demonstrate a good clinical result. At that time the decision was made to discontinue dabrafenib therapy and follow up with serial imaging. After more than 1 year of follow-up since stopping dabrafenib, the patient has continued to do well with no radiographic evidence of tumor progression and continues to be monitored with frequent interval imaging.

Treatment Strategies in Diffuse Midline Gliomas With the H3K27M Mutation: The Role of Convection-Enhanced Delivery in Overcoming Anatomic Challenges

Diffuse midline gliomas harboring the H3 K27M mutation—including the previously named diffuse intrinsic pontine glioma (DIPG)—are lethal high-grade pediatric brain tumors that are inoperable and without cure. Despite numerous clinical trials, the prognosis remains poor, with a median survival of ~1 year from diagnosis. Systemic administration of chemotherapeutic agents is often hindered by the blood brain barrier (BBB), and even drugs that successfully cross the barrier may suffer from unpredictable distributions. The challenge in treating this deadly disease relies on effective delivery of a therapeutic agent to the bulk tumor as well as infiltrating cells. Therefore, methods that can enhance drug delivery to the brain are of great interest. Convection-enhanced delivery (CED) is a strategy that bypasses the BBB entirely and enhances drug distribution by applying hydraulic pressure to deliver agents directly and evenly into a target region. This technique reliably distributes infusate homogenously through the interstitial space of the target region and achieves high local drug concentrations in the brain. Moreover, recent studies have also shown that continuous delivery of drug over an extended period of time is safe, feasible, and more efficacious than standard single session CED. Therefore, CED represents a promising technique for treating midline tumors with the H3K27M mutation.

Resection of an extensive thoracic arachnoid cyst via less-invasive targeted laminoplasties

OBJECTIVE

Spinal arachnoid cysts are a known cause of spinal cord compression. When symptomatic, treatment of choice entails laminectomies over the length of the cyst in order to achieve complete cyst removal and fenestration.

METHODS

A 60-year-old woman presented with a one-year history of progressive pain between the shoulder blades, exacerbated by sitting up or standing, and relieved by lying supine. MRI imaging revealed a T3-T7 dorsal intradural arachnoid cyst. Due to extant spinal deformity and medical comorbidity, the decision was made to proceed with selective laminoplasties at the superior and inferior limits of the cyst.

RESULTS

After the dura was opened to reveal the margins, the cyst was sharply fenestrated and drained. Irrigation was passed through the cyst to ensure open communication, and a lumbar drain catheter was passed from the inferior to superior margin. The catheter was removed before closure. Postoperatively, MRI of the thoracic spine revealed decompression of the spinal cord and the patient noticed improvement in her symptoms. At 7-month follow-up, the patient remained free of symptoms and MRI demonstrated near-complete resolution of the cyst.

CONCLUSION

Although open exposure and complete resection are considered the treatment of choice for spinal arachnoid cysts, cyst fenestration through selective bony windows at the margins of the cyst represents a viable, less invasive alternative approach to effective cyst decompression, and can be considered in patients in whom a full exposure would be prohibitive.

Cranial Tumor Surgical Outcomes at a High-Volume Academic Referral Center

OBJECTIVE

To determine adverse event rates for adult cranial neuro-oncologic surgeries performed at a high-volume quaternary academic center and assess the impact of resident participation on perioperative complication rates.

PATIENTS AND METHODS

All adult patients undergoing neurosurgical intervention for an intracranial neoplastic lesion between January 1, 2009, and December 31, 2013, were included. Cases were categorized as biopsy, extra-axial/skull base, intra-axial, or transsphenoidal. Complications were categorized as neurologic, medical, wound, mortality, or none and compared for patients managed by a chief resident vs a consultant neurosurgeon.

RESULTS

A total of 6277 neurosurgical procedures for intracranial neoplasms were performed. After excluding radiosurgical procedures and pediatric patients, 4151 adult patients who underwent 4423 procedures were available for analysis. Complications were infrequent, with overall rates of 9.8% (435 of 4423 procedures), 1.7% (73 of 4423), and 1.4% (63 of 4423) for neurologic, medical, and wound complications, respectively. The rate of perioperative mortality was 0.3% (14 of 4423 procedures). Case performance and management by a chief resident did not negatively impact outcome.

CONCLUSION

In our large-volume brain tumor practice, rates of complications were low, and management of cases by chief residents in a semiautonomous manner did not negatively impact surgical outcomes.

Delayed compression of the common peroneal nerve following rotational lateral gastrocnemius flap: case report

The authors present a case of delayed peroneal neuropathy following a lateral gastrocnemius rotational flap reconstruction. The patient presented 1.5 years after surgery with a new partial foot drop, which progressed over 3 years. At operation, a fascial band on the deep side of the gastrocnemius flap was compressing the common peroneal nerve proximal to the fibular head, correlating with preoperative imaging. Release of this fascial band and selective muscle resection led to immediate improvement in symptoms postoperatively.

Contemporary analysis of the intraoperative and perioperative complications of neurosurgical procedures performed in the sitting position

OBJECTIVE Historically, performing neurosurgery with the patient in the sitting position offered advantages such as improved visualization and gravity-assisted retraction. However, this position fell out of favor at many centers due to the perceived risk of venous air embolism (VAE) and other position-related complications. Some neurosurgical centers continue to perform sitting-position cases in select patients, often using modern monitoring techniques that may improve procedural safety. Therefore, this paper reports the risks associated with neurosurgical procedures performed in the sitting position in a modern series. METHODS The authors reviewed the anesthesia records for instances of clinically significant VAE and other complications for all neurosurgical procedures performed in the sitting position between January 1, 2000, and October 8, 2013. In addition, a prospectively maintained morbidity and mortality log of these procedures was reviewed for instances of subdural or intracerebral hemorrhage, tension pneumocephalus, and quadriplegia. Both overall and specific complication rates were calculated in relation to the specific type of procedure. RESULTS In a series of 1792 procedures, the overall complication rate related to the sitting position was 1.45%, which included clinically significant VAE, tension pneumocephalus, and subdural hemorrhage. The rate of any detected VAE was 4.7%, but the rate of VAE requiring clinical intervention was 1.06%. The risk of clinically significant VAE was highest in patients undergoing suboccipital craniotomy/craniectomy with a rate of 2.7% and an odds ratio (OR) of 2.8 relative to deep brain stimulator cases (95% confidence interval [CI] 1.2-70, p = 0.04). Sitting cervical spine cases had a comparatively lower complication rate of 0.7% and an OR of 0.28 as compared with all cranial procedures (95% CI 0.12-0.67, p < 0.01). Sitting cervical cases were further subdivided into extradural and intradural procedures. The rate of complications in intradural cases was significantly higher (OR 7.3, 95% CI 1.4-39, p = 0.02) than for extradural cases. The risk of VAE in intradural spine procedures did not differ significantly from sitting suboccipital craniotomy/craniectomy cases (OR 0.69, 95% CI 0.09-5.4, p = 0.7). Two cases (0.1%) had to be aborted intraoperatively due to complications. There were no instances of intraoperative deaths, although there was a single death within 30 days of surgery. CONCLUSIONS In this large, modern series of cases performed in the sitting position, the complication rate was low. Suboccipital craniotomy/craniectomy was associated with the highest risk of complications. When appropriately used with modern anesthesia techniques, the sitting position provides a safe means of surgical access.

Transplants of cells genetically modified to express neurotrophin-3 rescue axotomized Clarke's nucleus neurons after spinal cord hemisection in adult rats

To test the idea that genetically engineered cells can rescue axotomized neurons, we transplanted fibroblasts and immortalized neural stem cells (NSCs) modified to express neurotrophic factors into the injured spinal cord. The neurotrophin-3 (NT-3) or nerve growth factor (NGF) transgene was introduced into these cells using recombinant retroviral vectors containing an internal ribosome entry site (IRES) sequence and the beta-galactosidase or alkaline phosphatase reporter gene. Bioassay confirmed biological activity of the secreted neurotrophic factors. Clarke's nucleus (CN) axons, which project to the rostral spinal cord and cerebellum, were cut unilaterally in adult rats by T8 hemisection. Rats received transplants of fibroblasts or NSCs genetically modified to express NT-3 or NGF and a reporter gene, only a reporter gene, or no transplant. Two months postoperatively, grafted cells survived at the hemisection site. Grafted fibroblasts and NSCs expressed a reporter gene and immunoreactivity for the NGF or NT-3 transgene. Rats receiving no transplant or a transplant expressing only a reporter gene showed a 30% loss of CN neurons in the L1 segment on the lesioned side. NGF-expressing transplants produced partial rescue compared with hemisection alone. There was no significant neuron loss in rats receiving grafts of either fibroblasts or NSCs engineered to express NT-3. We postulate that NT-3 mediates survival of CN neurons through interaction with trkC receptors, which are expressed on CN neurons. These results support the idea that NT-3 contributes to long-term survival of axotomized CN neurons and show that genetically modified cells rescue axotomized neurons as efficiently as fetal CNS transplants.

Characterization and intraspinal grafting of EGF/bFGF-dependent neurospheres derived from embryonic rat spinal cord

Recent advances in the isolation and characterization of neural precursor cells suggest that they have properties that would make them useful transplants for the treatment of central nervous system disorders. We demonstrate here that spinal cord cells isolated from embryonic day 14 Sprague-Dawley and Fischer 344 rats possess characteristics of precursor cells. They proliferate as undifferentiated neurospheres in the presence of EGF and bFGF and can be maintained in vitro or frozen, expanded and induced to differentiate into both neurons and glia. Exposure of these cells to serum in the absence of EGF and bFGF promotes differentiation into astrocytes; treatment with retinoic acid promotes differentiation into neurons. Spinal cord cells labeled with a nuclear dye or a recombinant adenovirus vector carrying the lacZ gene survive grafting into the injured spinal cord of immunosuppressed Sprague-Dawley rats and non-immunosuppressed Fischer 344 rats for up to 4 months following transplantation. In the presence of exogenously supplied BDNF, the grafted cells differentiate into both neurons and glia. These spinal cord cell grafts are permissive for growth by several populations of host axons, especially when combined with exogenous BDNF administration, as demonstrated by penetration into the graft of axons immunopositive for 5-HT and CGRP. Thus, precursor cells isolated from the embryonic spinal cord of rats, expanded in culture and genetically modified, are a promising type of transplant for repair of the injured spinal cord.

Axonal transport of microtubule-associated protein 1B (MAP1B) in the sciatic nerve of adult rat: distinct transport rates of different isoforms

Cytoskeletal proteins are axonally transported with slow components a and b (SCa and SCb). In peripheral nerves, the transport velocity of SCa, which includes neurofilaments and tubulin, is 1-2 mm/d, whereas SCb, which includes actin, tubulin, and numerous soluble proteins, moves as a heterogeneous wave at 2-4 mm/d. We have shown that two isoforms of microtubule-associated protein 1B (MAP1B), which can be separated on SDS polyacrylamide gels on the basis of differences in their phosphorylation states (band I and band II), were transported at two different rates. All of band I MAP1B moved as a coherent wave at a velocity of 7-9 mm/d, distinct from slow axonal transport components SCa and SCb. Several other proteins were detected within the component that moved at the velocity of 7-9 mm/d, including the leading wave of tubulin and actin. The properties of this component define a distinct fraction of the slow axonal transport that we suggest to term slow component c (SCc). The relatively fast transport of the phosphorylated MAP1B isoform at 7-9 mm/d may account for the high concentration of phosphorylated MAP1B in the distal end of growing axons. In contrast to band I MAP1B, the transport profile of band II was complex and contained components moving with SCa and SCb and a leading edge at SCc. Thus, MAP1B isoforms in different phosphorylation states move with distinct components of slow axonal transport, possibly because of differences in their abilities to associate with other proteins.

Intraspinal delivery of neurotrophin-3 using neural stem cells genetically modified by recombinant retrovirus

Neural stem cells have been shown to participate in the repair of experimental CNS disorders. To examine their potential in spinal cord repair, we used retroviral vectors to genetically modify a clone of neural stem cells, C17, to overproduce neurotrophin-3 (NT-3). The cells were infected with a retrovirus construct containing the NT-3.IRES.lacZ/neo sequence and cloned by limiting dilution and selection for lacZ expression. We studied the characteristics of the modified neural stem cells in vitro and after transplantation into the intact spinal cord of immunosuppressed adult rats. Our results show that: (i) most of the genetically modified cells express both NT-3 and lacZ genes with a high coexpression ratio in vitro and after transplantation; and (ii) large numbers of the xenografted cells survive in the spinal cord of adult rats for at least 2 months, differentiate into neuronal and glial phenotypes, and migrate for long distances. We conclude that genetically modified neural stem cells, acting as a source of neurotrophic factors, have the potential to participate in spinal cord repair.

Transplants of fibroblasts genetically modified to express BDNF promote regeneration of adult rat rubrospinal axons and recovery of forelimb function

Adult mammalian CNS neurons do not normally regenerate their severed axons. This failure has been attributed to scar tissue and inhibitory molecules at the injury site that block the regenerating axons, a lack of trophic support for the axotomized neurons, and intrinsic neuronal changes that follow axotomy, including cell atrophy and death. We studied whether transplants of fibroblasts genetically engineered to produce brain-derived neurotrophic factor (BDNF) would promote rubrospinal tract (RST) regeneration in adult rats. Primary fibroblasts were modified by retroviral-mediated transfer of a DNA construct encoding the human BDNF gene, an internal ribosomal entry site, and a fusion gene of lacZ and neomycin resistance genes. The modified fibroblasts produce biologically active BDNF in vitro. These cells were grafted into a partial cervical hemisection cavity that completely interrupted one RST. One and two months after lesion and transplantation, RST regeneration was demonstrated with retrograde and anterograde tracing techniques. Retrograde tracing with fluorogold showed that approximately 7% of RST neurons regenerated axons at least three to four segments caudal to the transplants. Anterograde tracing with biotinylated dextran amine revealed that the RST axons regenerated through and around the transplants, grew for long distances within white matter caudal to the transplant, and terminated in spinal cord gray matter regions that are the normal targets of RST axons. Transplants of unmodified primary fibroblasts or Gelfoam alone did not elicit regeneration. Behavioral tests demonstrated that recipients of BDNF-producing fibroblasts showed significant recovery of forelimb usage, which was abolished by a second lesion that transected the regenerated axons.

Intraspinal grafting of fibroblasts genetically modified by recombinant adenoviruses

Intracerebral or intraspinal grafting of genetically modified primary fibroblasts has been shown to enhance functional recovery in several models of CNS disease, including spinal cord injury. Most of these studies utilized retrovirus vectors. In this report, we describe in vitro conditions for genetically modifying primary fibroblasts with recombinant adenovirus vectors carrying the lacZ or green fluorescent protein (GFP) genes. As intraspinal allografts in animals immunosuppressed by cyclosporin A, the genetically modified cells survived and expressed the transgenes for at least 2 months. We conclude that recombinant adenovirus vectors are efficient and convenient tools for ex vivo gene therapy in the CNS.

Critical interval for rescue of axotomized neurons by transplants

To determine whether embryonic spinal cord transplants retained the ability to prevent retrograde death of Clarke's nucleus (CN) neurons if supplied after a delay, we hemisected adult rats at the T8 spinal cord segment and placed transplants of fetal tissue into the hemisection cavity immediately or up to 14 days later. Transplants provided in the first 7 days after injury prevented virtually all of the 30% loss of CN neurons at L1 ipsilateral to hemisection that occurs without a transplant. Transplants supplied at 14 days post-hemisection were ineffective. Because prevention of retrograde neuron death is one mechanism by which transplants may contribute to locomotor recovery after spinal cord injury, this window of effectiveness should be considered in the design of clinical trials.

Neurotrophin-3 prevents death of axotomized Clarke's nucleus neurons in adult rat

In the present investigation, we studied whether neurotrophin-3 (NT-3) contributes to the rescue of axotomized Clarke's nucleus (CN) neurons in adult rats. A significant (24%) loss of CN neurons occurred at L-1 ipsilateral to T-8 hemisection by 14 days, which reached 31% at 2 months and then stabilized. Axotomized CN neurons had also atrophied by 14 days, but mean cell size did not decrease further. Animals that received gelfoam soaked in nerve growth factor, brain derived neurotrophic factor, or ciliary neurotrophic factor at the lesion site also showed a 30% neuron loss at 2 months, and a 40% reduction in average cell area. Rats receiving NT-3 showed a 15% neuron loss, which was not improved by additional neurotrophins in combination with NT-3. None of the treatments prevented neuron atrophy. Bioassay of the gelfoam showed that NT-3 bioactivity remained at 5 days after surgery but not at 14 days. Additional rats with hemisections that received NT-3 continuously via mini-pump for 2 months showed a 15% neuron loss, the same as with NT-3 given via gelfoam. These results indicate that even limited exposure of axotomized CN neurons to NT-3 produces permanent rescue of 50% of the neurons. The virtually complete rescue that we had previously observed with transplants of fetal central nervous system (CNS) tissues may, therefore, be due at least in part to NT-3, but the exogenous administration of a single neurotrophic factor or a combination of neurotrophic factors is less effective than transplants in producing long-term survival of axotomized CNS neurons.

Application of recombinant adenovirus for in vivo gene delivery to spinal cord

One strategy for treating spinal cord injury is to supply damaged neurons with the appropriate neurotrophins either by direct delivery or by transfer of the corresponding genes using viral vectors. Here we report the feasibility of using recombinant adenovirus for in vivo gene transfer in spinal cord. After injection of a recombinant adenovirus carrying a beta-galactosidase (beta-gal) reporter gene into the mid-thoracic spinal cord of adult rats, transgene expression occurred not only in several types of cells around the injection site but also in neurons whose axons project to this region from rostral or caudal to the injection site. Among labeled neurons were those of the red nucleus, the vestibular nuclei, reticular formation, locus coeruleus, and Clarke's nucleus. A non-specific immune reaction, which could be blocked by immunosuppression with Cyclosporin A, reduced the number of transduced cells surviving at the injection site by 1 month. In neurons away from the injection site, where the immune response was minimal, transgene expression lasted for at least 2 months. These results support the idea that recombinant adenovirus can be used in the spinal cord for in vivo delivery of therapeutic genes important for supporting neuron survival and axon regeneration.

Fetal spinal cord transplants rescue some axotomized rubrospinal neurons from retrograde cell death in adult rats

Intraspinal transplants of fetal spinal cord may contribute to recovery after spinal cord injury by keeping axotomized neurons alive. In this study we examined whether transplants rescued axotomized red nucleus (RN) neurons from retrograde cell death in adult rats. RN neurons were labeled by retrograde transport of Fluorogold (FG); 1 week later right-sided RN neurons were axotomized by left-sided hemisection at C3-4 vertebral level, and Embryonic Day 14 spinal cord or gelfoam was introduced into the cavity. Additional rats received hemisection and a transplant of fetal spinal cord or gelfoam without FG injection. At 2 and 4 months, the number of neurons in the magnocellular portion of the RN contralateral to the hemisection decreased 35-40% in rats that received gelfoam; mean soma area of surviving neurons decreased 40%. RN cell loss was reduced to 20% in rats that received fetal spinal cord transplants, but the decrease in mean soma area was unchanged. Transplants therefore rescued about half of the axotomized RN neurons that otherwise would have died but did not prevent perikaryal atrophy. Anterograde transport of WGA-HRP injected into RN 2 months after transplantation showed that rubrospinal axons reached the site of injury but rarely entered transplants; FG injections caudal to transplants showed that axons of transplant neurons extended at least two segments into host spinal cord. Fetal spinal cord transplants may therefore contribute to locomotor recovery in adults with spinal cord injuries both by preventing retrograde cell death and by establishing novel circuits across the site of injury.

Grafts of fetal central nervous system tissue rescue axotomized Clarke's nucleus neurons in adult and neonatal operates

Many conditions are thought to contribute to neuron death after axotomy, including immaturity of the cell at the time of injury, inability to reestablish or maintain target contact, and dependence on trophic factors produced by targets. Exogenous application of neurotrophic factors and transplants of peripheral nerve and embryonic central nervous system (CNS) tissue temporarily rescue axotomized CNS neurons, but permanent rescue may require transplants that are normal targets of the injured neurons. We examined the requirements for survival of axotomized Clarke's nucleus (CN) neurons. Two months after hemisection of the spinal cord at the T8 segment, there was an ipsilateral 30% loss of neurons at the L1 segment in adult operates and a 40% loss in neonates. Transplants of embryonic spinal cord, cerebellum, and neocortex inserted into the T8 segment at the time of hemisection prevented virtually all of the cell death in both adults and neonates, but transplants of embryonic striatum were ineffective. None of the grafts prevented the somal atrophy of CN neurons caused by axotomy. Retrograde transport of fluoro-gold from the cerebellum demonstrated that 33% of all CN neurons at L1 project to the cerebellum, 50% of these died following a T8 hemisection, but all these projection neurons were rescued by a transplant of embryonic spinal cord. These results suggest that the rescue of axotomized CN neurons is relatively specific for the normal target areas of these neurons, but this specificity is not absolute and may depend on the distribution and synthesis of particular neurotrophic agents.

Death of some dorsal root ganglion neurons and plasticity of others following sciatic nerve section in adult and neonatal rats

Newborn animals recover from neurological injury to a greater extent than adults in spite of the greater vulnerability of developing neurons to retrograde or transneuronal degeneration (Kennard, '42; Goldman, '74; Prendergast and Stelzner, '76; Bregman and Goldberger, '82, '83). The cellular mechanisms underlying this "infant lesion effect" are incompletely understood (Bregman and Goldberger, '82). The dorsal root ganglion (DRG) is an excellent model in which to compare the developing and adult nervous system with respect to the effects of axotomy on cell survival and cellular function. We studied the survival of L5 DRG neurons after section-ligation of the sciatic nerve of adult and neonatal rats and used qualitative and quantitative immunocytochemical methods to examine changes in intraspinal substance P immunoreactivity (SPIR). Retrograde transport of wheatgerm agglutinin-horseradish (WGA-HRP) peroxidase applied to the sciatic nerve of adult or neonatal rats demonstrated that 70% of the neurons in the normal L5 DRG project into the sciatic nerve at the site of transection. In adults 20% of all L5 DRG neurons died between 10 and 60 days postoperative; in newborns 50% of the neurons died between 5 and 10 days. These results indicate that 30% of axotomized neurons in adults and 75% in neonates die after sciatic nerve section and that neuron loss is both more rapid and more extensive in neonates. No cell death was observed in the L5 DRG of neonates after dorsal rhizotomy, thus suggesting that at this stage of development the survival of DRG neurons depends on the peripheral but not the central process. SPIR in laminae I and II of both adult and newborn operates decreased and then recovered, but the time course and extent of the recovery differ. In adults SPIR was depleted in the medial portion of the L5 segment ipsilateral to surgery by 10 days postoperative and remained depleted for at least 2 months. By 1 year partial recovery occurred, but remained incomplete even at the longest survival time studied (15 months). SPIR, which is present in the dorsal horn at birth, was diminished in ipsilateral laminae I and II by 4 days after nerve section on the day of birth. Between 30 days and 60 days, the density of SPIR in the dorsal horn ipsilateral to surgery became virtually indistinguishable from that on the contralateral, intact side, suggesting a more rapid and complete recovery than in adults.(ABSTRACT TRUNCATED AT 400 WORDS)

Differentiation of substantia gelatinosa-like regions in intraspinal and intracerebral transplants of embryonic spinal cord tissue in the rat

The differentiation of intracerebral and intraspinal transplants of fetal (E14-E15) rat spinal cord was studied to determine the extent to which myelin-free zones in these embryonic grafts exhibit cytological features and immunocytochemical characteristics of the substantia gelatinosa (SG) of the normal spinal cord. Immunocytochemical staining with antiserum to myelin basic protein (MBP) revealed myelin-free areas of varying proportions within fetal spinal cord grafts. These regions were identified in both newborn and adult recipients regardless of whether donor tissue was grafted to heterotopic (intracerebral) or homotopic (intraspinal) sites. As in the SG of the intact spinal cord, the myelin-free regions consisted mainly of small (7-15 microns) diameter neurons. At the ultrastructural level, these cells were surrounded by a neuropil composed of numerous small caliber, unmyelinated axons and intermediate-sized dendrites. Synaptic terminals in these areas were primarily characterized by the presence of clear, round vesicles, although granular vesicles were occasionally found within these terminals. Immunocytochemical staining demonstrated met- and leu-enkephalin-, neurotensin-, substance P-, and somatostatin-like immunoreactive elements within these myelin-free areas. Thus, regions within embryonic spinal cord grafts undergo some topographical differentiation which parallels that of the normal superficial dorsal horn. The presence of SG-like regions illustrates the potential capacity of fetal spinal cord transplants for replacing some intraspinal neuronal populations at the site of a spinal cord injury in neonatal and adult animals. These graft regions may serve as a source of intersegmental projection neurons or establish an extensive intrinsic circuitry similar to that seen in the normal SG. In addition, the definition of these areas provides a useful model to study the innervation patterns of host axons that typically project to the substantia gelatinosa of the normal spinal cord.

Regeneration of adult dorsal root axons into transplants of embryonic spinal cord

Transplants of the embryonic rat spinal cord survive and differentiate in the spinal cords of adult and newborn host rats. Very little is known about the extent to which these homotopic transplants can provide an environment for regeneration of adult host axons that normally terminate in the spinal cord. We have used horseradish peroxidase injury filling and transganglionic transport methods to determine whether transected dorsal roots regenerate into fetal spinal cord tissue grafted into the spinal cords of adult rats. Additional transplants were examined for the presence of calcitonin gene-related peptide-like immunoreactivity, which in the normal dorsal horn is derived exclusively from primary afferent axons. Host animals had one side of the L4-5 spinal cord resected and replaced by a transplant of E14 or E15 spinal cord. Adjacent dorsal roots were sectioned and juxtaposed to the graft. The dorsal roots and their projections into the transplants were then labeled 2-9 months later. The tracing methods that used transport or diffusion of horseradish peroxidase demonstrated that severed host dorsal root axons had regenerated and grown into the transplants. In addition, some donor and host neurons had extended their axons into the periphery to at least the midthigh level as indicated by retrograde labeling following application of tracer to the sciatic nerve. Primary afferent axons immunoreactive for calcitonin gene-related peptide were among those that regenerated into transplants, and the projections shown by this immunocytochemical method exceeded those demonstrated by the horseradish peroxidase tracing techniques. Growth of the host dorsal roots into transplants indicates that fetal spinal cord tissue permits regeneration of adult axotomized neurons that would otherwise be aborted at the dorsal root/spinal cord junction. This transplantation model should therefore prove useful in studying the enhancement and specificity of the regrowth of axons that normally terminate in the spinal cord.

Characterization of forms of immunoreactive somatostatin in sensory neuron and normal and deafferented spinal cord

In order to determine the contribution made by primary sensory afferents and supraspinal projections to the immunoreactive somatostatin (IRS) content of the spinal cord, measurements were made of the concentration of IRS in the dorsal and ventral halves of the cord in cats subjected to unilateral lumbosacral dorsal rhizotomy (L1-S3) alone or combined with spinal cord transection. The molecular forms of IRS (characterized by gel chromatography) in L7 lumbar spinal cord, L6-S1 dorsal roots, ventral roots and dorsal root ganglia, and sciatic nerve were also determined. S14 was the predominant form in all tissues examined, but two additional molecular forms corresponding to S28 and S11.5 kdalton were present in dorsal root ganglia and spinal cord; S28 but not S11.5 kdalton was detected in both dorsal roots and sciatic nerves. These results indicate that S14 and S28 are transported along the central and peripheral processes of dorsal root ganglia, but that spinal cord S11.5 kdalton originates in the central nervous system. IRS in the dorsal horn was reduced by ca. 40% following dorsal root section. Neither disruption of descending pathways by spinal transection nor surgical isolation of the lumbar segments lowered cord somatostatin content below that produced by dorsal root section, indicating that most of the somatostatin within the cord arises from the dorsal root and from neurons in local spinal segments. Although the total content of IRS in the dorsal horn was reduced by ca. 40% following dorsal rhizotomy, the pattern of molecular forms was not changed accordingly.(ABSTRACT TRUNCATED AT 250 WORDS)

Sciatic nerve transection produces death of dorsal root ganglion cells and reversible loss of substance P in spinal cord

Sciatic nerve section has been shown to reduce substance P (SP) in the dorsal horn of the spinal cord, but the mechanism which underlies the reduction is not understood. Whether SP levels subsequently recover as they do after dorsal rhizotomy has also been unknown. To test the hypothesis that transganglionic degeneration of primary afferents contributes to the reduction of SP, we have studied the changes in SP which result from section of the cat sciatic nerve and determined the extent of dorsal root ganglion (DRG) cell death. Sciatic nerve section resulted in DRG cell death, but the amount was variable and not seen in all animals. Reduction in dorsal horn and DRG SP was seen in all animals, and in the spinal cord it was followed by recovery. These sequelae resemble the changes which follow dorsal rhizotomy. After sciatic nerve section, the reduction in dorsal horn SP is smaller than after rhizotomy, the recovery more complete, and both the reduction and the recovery proceed more slowly. Evidence is presented that similar mechanisms may contribute to depletion of intraspinal SP after sciatic nerve section and after dorsal rhizotomy. The mechanisms contributing to recovery of spinal cord SP after sciatic nerve section may resemble known mechanisms of recovery that occur when the lesion is central.

Recovery of substance P but not somatostatin in the cat spinal cord after unilateral lumbosacral dorsal rhizotomy: a quantitative study

The dorsal horn of the cat spinal cord contains substance P and somatostatin within nerve endings which arise from cells located in dorsal root ganglia and from cells within the neuraxis. Previous studies from this laboratory have demonstrated that dorsal rhizotomy depletes both peptides from the dorsal horn. However, the changes in the two peptides differ. Substance P is at first severely depleted by dorsal rhizotomy and then recovers in part, whereas somatostatin is diminished less but does not recover. In the present experiments the validity of these conclusions which were based on anatomical observations has been evaluated quantitatively with the use of radioimmunoassay. After a 74% reduction at 10-14 days postoperative, substance P immunoreactivity in the deafferented dorsal horn shows a small, statistically significant recovery by 30 days to 60% of normal values. In contrast, somatostatin is reduced by 46% at 10-14 days but does not return significantly. As previously suggested by immunocytochemistry, dorsal rhizotomy produces no significant decline of either peptide in the ventral horn. The differing response of the two peptides is consistent with the hypothesis that intrinsic spinal substance P-containing neurons increase their projections (or their production of substance P) in the deafferented dorsal horn, but that somatostatin-containing neurons do not. Because synaptic number returns to normal in at least the deafferented lamina II of the cat yet substance P recovers only partially, it is likely that axons which contain transmitters other than substance P or somatostatin also increase the numbers of their terminals in response to dorsal rhizotomy.

Spinal neurons mediate return of substance P following deafferentation of cat spinal cord

Deafferentation of the cat dorsal horn by complete unilateral lumbosacral dorsal rhizotomy produces a loss and subsequent partial recovery of substance P (SP) immunoreactivity as visualized by the peroxidase-antiperoxidase technique. The present experiments aimed to determine whether this return of SP represents a generalized response of all fiber systems afferent to the denervated segments or a more selective response of a specific spinal system. Although a contribution from other sources cannot be excluded by this qualitative immunocytochemical technique, several observations indicate that the return of SP staining depends on interneurons which contain SP immunoreactivity: (1) the amount of SP staining in the chronically deafferented dorsal horn deprived of extrinsic fiber systems is comparable to that seen after deafferentation alone; (2) SP-containing neurons are present within the lumbar segments; and (3) destruction of lumbar neurons by the intraspinal injection of kainic acid abolishes SP staining from the chronically deafferented dorsal horn. From these observations it would appear that the anatomical plasticity of SP-containing fibers in the deafferented dorsal horn is due to the response of a particular system rather than to a generalized response of all systems which terminate there.