Endovascular treatment of experimental aneurysms with use of fibroblast transfected with replication-deficient adenovirus containing bone morphogenetic protein-13 gene

BACKGROUND AND PURPOSE

Modified coils have failed to improve long-term recanalization of aneurysms. This study examined whether ex vivo transduction of replication-deficient adenovirus containing the bone morphogenetic protein-13 gene (Ad-BMP-13) in fibroblast allografts would improve angiographic results via increased collagen synthesis, compared with fibroblast-coated platinum coils (FBC) and bare platinum coils (PA).

MATERIALS AND METHODS

Aneurysms were embolized with Ad-BMP-13-coated coils (n = 20). Rabbits were sacrificed at 14 days and at 1, 3, and 6 months after implantation. Digital subtraction angiography (DSA) evaluated stability after embolization. Histologic specimens were examined with a qualitative grading system. Masson trichrome evaluated collagen deposition. Findings were compared with previously reported controls for PA and FBC in the same model and time points.

RESULTS

The grading system showed a greater total score (P = .0002) in Ad-BMP-13 (6.8 +/- 1.6) and FBC (6.3 +/- 2.4) compared with PA (4.7 +/- 2.4). A group main effects test showed that aneurysm neck tissue coverage in Ad-BMP-13 (2.5 +/- 1.1) was higher (P = .0007) than both FBC (1.6 +/- 1.4) and PA (0.9 +/- 1.1). Ad-BMP-13 had more (P < .0001) collagen deposition than the FBC and PA. One- and 3-month Ad-BMP-13 collagen depositions increased (P < .05) over the FBC and PA. Finally, Ad-BMP-13 showed radiographic stability in 15 (75%) cases, coil compaction in 4 (20%) cases, and progressive occlusion in 1 (5%) case. There were no differences in angiographic results (P = .6522).

CONCLUSION

The Ad-BMP-13-coated coils can improve neck coverage and dome fibrosis in the rabbit model, even in the absence of observed differences in angiographic outcome.

Local immunomodulation with CD4 and CD8 antibodies, but not cyclosporine A, improves osteogenesis induced by ADhBMP9 gene therapy

This study was designed to see if immunosuppression achieved using local application of cyclosporine A (Cs. A) or CD4 and CD8 antibodies would improve bone formation following intramuscular injections of human BMP-4 and BMP-9 adenoviral vectors (ADhBMP4 and ADhBMP9) in Sprague-Dawley rats. Cs. A was injected into the thigh muscle. After 2 days, ADhBMP4, ADhBMP9, and the antibodies were separately injected into the left and right rear legs. At this time, the number of CD4+/CD3+ cells was significantly lower and the number of CD8+/CD3+ cells higher in the Cs. A group than in the control group (P < 0.01). The total number of white blood cells 3 days following injection of CD4 and CD8 antibodies was significantly lower than that before the injection (P < 0.01). At 4 weeks after the viral and antibody injections, mean bone volumes at the ADhBMP9 treatment sites were 0.29 +/- 0.01 cm3 in the viral control group, 0.17 +/- 0.03 cm3 in the Cs. A-ADhBMPs group, and 0.59 +/- 0.07 cm3 in the antibodies-ADhBMPs group. ADhBMP4 did not induce new bone formation in any group. This study demonstrates that local immunomodulation may improve the osteogenic potential of bone morphogenetic protein gene therapy in the clinical setting.

Attenuation of cerebral vasospasm by systemic administration of an endothelin-A receptor antagonist, TBC 11251, in a rabbit model of subarachnoid hemorrhage

Cerebral vasospasm is a major complication of subarachnoid hemorrhage (SAH) after the rupture of an intracranial aneurysm. Although the cause of cerebral vasospasm has not been fully established, several lines of evidence suggest that the vasoconstrictor peptide endothelin (ET) may play a crucial role. In the present study the potential of TBC 11251 (TBC), a newly developed ET(A) receptor antagonist, to prevent and/or reverse cerebral vasospasm was examined in a well-established rabbit model of SAH. Sixty-five New Zealand White rabbits were assigned to one of six groups. Experimental SAH was induced in rabbits comprising five of the groups by injecting autologous arterial blood into the cisterna magna. The treatment groups were as follows: 1) control (no SAH); 2) SAH only; 3) SAH + placebo at 24 and 36 hours (24/36); 4) SAH + TBC (24/36); 5) SAH + placebo twice daily (BID); and 6) SAH + TBC BID. All drug-treated animals received an intravenous dosage of 5 mg/kg TBC. After 48 hours, the animals were killed by intracardiac perfusion with fixative. The brainstems were removed and the basilar arteries (BAs) were prepared for histological examination. The cross-sectional area of each BA was measured using computer-assisted videomicroscopy by an investigator blind to the group from which it came. A one-way analysis of variance and paired group mean comparisons with the post-hoc Fisher least significant difference test were used for analysis of BA diameters and physiological parameters. The model provided reliable vasospasm, with the mean BA cross-sectional area constricting from 0.388 mm2 in the control group to 0.106 mm2 (27.4% of control) in the SAH only group. Treatment with TBC (24/36) after SAH (reversal protocol) produced a mean BA area of 0.175 mm2 (44.2% of control) which, although larger than the placebo group value of 0.135 mm2 (39.9% of control), was not statistically significant. However, treatment with TBC BID (prevention protocol) produced a mean BA area of 0.303 mm2 (78.1% of control) compared with the placebo BID value of 0.134 mm2 (34.6% of control); this effect was statistically significant (p < 0.01). There were no side effects noted and no differences in the mean arterial pressures between drug and placebo groups. These findings demonstrate that systemic administration of the ET(A) receptor antagonist TBC significantly attenuates cerebral vasospasm after SAH when given as a preventative therapy, and they provide additional support for the role of ET in the establishment of vasospasm.

Osteogenic potential of five different recombinant human bone morphogenetic protein adenoviral vectors in the rat

Bone morphogenetic protein (BMP) adenoviral vectors for the induction of osteogenesis are being developed for the treatment of bone pathology. However, it is still unknown which BMP adenoviral vector has the highest potential to stimulate bone formation in vivo. In this study, the osteogenic activities of recombinant human BMP-2, BMP-4, BMP-6, BMP-7, and BMP-9 adenoviruses were compared in vitro, in athymic nude rats, and in Sprague-Dawley rats. In vitro osteogenic activity was assessed by measuring the alkaline phosphatase activity in C2C12 cells transduced by the various BMP vectors. The alkaline phosphatase activity induced by 2 x 10(5) PFU/well of BMP viral vector was 4890 x 10(-12) U/well for ADCMVBMP-9, 302 x 10(-12) U/well for ADCMVBMP-4, 220 x 10(-12) U/well for ADCMVBMP-6, 45 x 10(-12) U/well for ADCMVBMP-2, and 0.43 x 10(-12) U/well for ADCMVBMP-7. The average volume of new bone induced by 10(7) PFU of BMP vector in athymic nude rats was 0.37+/-0.03 cm(3) for ADCMVBMP-2, 0.89+/-0.07 cm(3) for ADCMVBMP-4, 1.02+/-0.07 cm(3) for ADCMVBMP-6, 0.24+/-0.05 cm(3) for ADCMVBMP-7, and 0.63+/-0.07 cm(3) for ADCMVBMP-9. In immunocompetent Sprague-Dawley rats, no bone formation was demonstrated in the ADCMVBMP-2, ADCMVBMP-4, and ADCMVBMP-7 groups. ADCMVBMP-6 at a viral dose of 10(8) PFU induced 0.10+/-0.03 cm(3) of new bone, whereas ADCMVBMP-9 at a lower viral dose of 10(7) PFU induced more bone, with an average volume of 0.29+/-0.01 cm(3).

A horseradish peroxidase-light and electron microscopic study of immunoliposomes utilized for intracellular delivery to the rat striatum

Liposomes can deliver plasmid DNA, viruses, antisense oligonucleotides, and pharmacological agents to the central nervous system. Conjugation of antibodies to liposomes increases delivery specificity. Immunoliposomes created with Thy 1.1 antibody have previously been shown to be effective for neuronal delivery. The intracellular delivery of these immunoliposomes is evaluated by light and electron microscopy. Thy 1.1 conjugated liposomes were loaded with horseradish peroxidase and stereotactically injected into rat striatum. On light microscopy, immunoliposomes were concentrated within 0.2 mm of the injection site 8 h following delivery but, 24 h post-operatively, had diffused more than 0.5 mm from the injection site. With transmission electron microscopy, immunoliposomes were observed entering numerous neurons and some astrocytes in a process distinct from the clathrin-coated pit mechanism. These findings suggest that Thy 1.1 immunoliposomes are effective for intracellular delivery in vivo and their endocytosis occurs independently of a coated pit process. The research has helped to elucidate alternative mechanisms for immunoliposomal delivery. A more fundamental understanding of these attributes is needed to achieve the therapeutic potential of immunoliposomes.

Elastase-induced saccular aneurysms in rabbits: comparison of geometric features with those of human aneurysms

BACKGROUND AND PURPOSE

The development of more effective intracranial aneurysm therapy depends on the ability to test various intravascular occlusion devices and techniques in preclinical animal models. This requires the creation of experimental aneurysms, which, ideally, should mimic the size and geometric features of human intracranial aneurysms. The purpose of this study was to characterize the morphologic features of elastase-induced saccular aneurysms in rabbits to determine whether the morphology of such aneurysms mimics that of human intracranial aneurysms.

METHODS

Elastase-induced saccular aneurysms were created in 40 New Zealand white rabbits. Intravenous digital subtraction angiography was performed 14 days after surgery. Relative to an external sizing device, the following dimensions were determined: aneurysm dome (height and width), aneurysm neck diameter, and parent artery diameter. Based on maximal diameter, aneurysms were categorized as small (2.0-4.9 mm), medium-sized (5.0-9.9 mm), or large (10-16 mm), and as narrow-necked (<4.0 mm neck width) or wide-necked (>4.0 mm neck width). Mean dome-neck ratio was calculated and compared with that of human aneurysms.

RESULTS

All aneurysm cavities were angiographically patent. Widths of the cavities ranged from 2.5 to 7.1 mm (mean, 4.1 +/- 1.2 mm); heights ranged from 3.0 to 15.6 mm (mean, 8.8 +/- 2.6 mm). Three (7.5%) of 40 aneurysms were small, 20 (50%) were medium-sized, and 17 (42.5%) were large. Twenty-two (55%) of 40 aneurysms were small-necked, and 18 (45%) were wide-necked. Mean dome-neck ratio was 1.13 +/- 0.54. Mean parent artery diameter was 4.3 +/- 1.4 mm.

CONCLUSION

Saccular aneurysms of sizes similar to that of human intracranial aneurysms were reliably created using a simple method of vessel ligation and elastase injury. Neck sizes varied with both large and small-necked aneurysms created.

Transforming growth factor beta-coated platinum coils for endovascular treatment of aneurysms: an animal study

OBJECTIVE

To test the hypothesis that coating platinum coils with transforming growth factor beta (TGFbeta) would improve the cellular proliferation within experimental aneurysms relative to uncoated coils.

MATERIALS AND METHODS

Elastase-induced saccular aneurysms were created in 12 New Zealand White rabbits. These aneurysms were embolized with platinum coils, either "control" (unmodified) coils or "test" (coated with TGFbeta) coils. Subjects were killed either 2 weeks (n = 3, control; n = 3, test) or 6 weeks (n = 3, control; n = 3, test) after embolization. Aneurysm tissue was embedded in plastic, sectioned, and stained with hematoxylin and eosin. The thickness of tissue covering the coils at the coil-lumen interface was measured by use of a digital microscope, and was compared between groups by use of the Student's t test (P < or = 0.05).

RESULTS

Two-week implantation samples demonstrated mean thickness of tissue overlying TGFbeta-coated coils of 36+/-15 microm and mean thickness of overlying control coils of 3+/-5 microm, indicating significantly thicker tissue growth covering test versus control coils (P = 0.02). Six-week implantation samples demonstrated mean thickness of tissue overlying TGFbeta-coated coils of 86+/-74 microm versus mean thickness overlying control coils of 37+/-6 mu; this difference did not reach statistical significance (P = 0.30). Thickness of tissue covering TGFbeta-coated coils did not change significantly from 2 to 6 weeks (P = 0.31). Tissue thickness over control coils increased significantly between 2 and 6 weeks (P = 0.002).

CONCLUSION

TGFbeta-coated platinum coils undergo earlier cellular coverage than standard platinum coils, but differences in coverage between coated and control coils are no longer present at later time points. These data suggest that improvements in intra-aneurysmal cellular proliferation resulting from coil modifications, although significant in the early postembolization phase, may dissipate over time.

A light and electron microscopic study of ectopic tendon and ligament formation induced by bone morphogenetic protein-13 adenoviral gene therapy

OBJECT

Bone morphogenetic proteins (BMPs) are involved in the growth and development of many tissues, but it is their role in skeletal development and their unique ability to induce ectopic and orthotopic osteogenesis that have attracted the greatest interest. Expression of the BMP-13 gene is predominantly localized to hypertrophic chondrocytes in regions of endochondral bone formation during development, as well as in mature articular cartilage in the adult. In addition, the application of BMP-13 on a collagen carrier induces neotendon/neoligament formation when delivered subcutaneously or intramuscularly in rodents. The aim of the present study was to determine the histological and ultrastructural changes that occur after the intramuscular injection of a first-generation BMP-13 adenoviral vector.

METHODS

Athymic nude rats were injected with 3.75 x 10(10) plaque-forming units of adenovirus (Ad)-BMP-13 or Ad-beta-galactosidase in the thigh musculature, and the region was examined using light and electron microscopy at various time points between 2 days and 100 days postinjection. As early as 2 days after injection of Ad-BMP-13, progenitor cells were observed infiltrating between the transduced muscle fibers. These cells subsequently proliferated, differentiated, and secreted large amounts of collagenous extracellular matrix. By 100 days postinjection, the treated tissue displayed the histological and ultrastructural appearance of neotendon/neoligament, which was clearly demarcated from the surrounding muscle. Small foci of bone and fibrocartilage were also seen within the treated tissue. A short-term bromodeoxyuridine study also demonstrated rapid mesenchymal cell proliferation at the Ad-BMP-13 injection site as early as 48 hours postinjection. At all time points, the control AD-beta-gal injection sites were found to contain only normal muscle, without evidence of inflammation or mesenchymal cell proliferation.

CONCLUSIONS

The results of this study indicate that in the future the use of the BMP-13 gene may have therapeutic utility for the healing of tendon and ligament tears and avulsion injuries.

Bone graft substitutes for the promotion of spinal arthrodesis

In the prototypical method for inducing spinal fusion, autologous bone graft is harvested from the iliac crest or local bone removed during the spinal decompression. Although autologous bone remains the "gold standard" for stimulating bone repair and regeneration, modern molecular biology and bioengineering techniques have produced unique materials that have potent osteogenic activities. Recombinant human osteogenic growth factors, such as bone morphogenetic proteins, transforming growth factor-beta, and platelet-derived growth factor are now produced in highly concentrated and pure forms and have been shown to be extremely potent bone-inducing agents when delivered in vivo in rats, dogs, primates, and humans. The delivery of pluripotent mesenchymal stem cells (MSCs) to regions requiring bone formation is also compelling, and it has been shown to be successful in inducing osteogenesis in numerous preclinical studies in rats and dogs. Finally, the identification of biological and non-biological scaffolding materials is a crucial component of future bone graft substitutes, not only as a delivery vehicle for bone growth factors and MSCs but also as an osteoconductive matrix to stimulate bone deposition directly. In this paper, the currently available bone graft substitutes will be reviewed and the authors will discuss the novel therapeutic approaches that are currently being developed for use in the clinical setting.

Gene-based therapies for the induction of spinal fusion

Numerous mesenchymal growth factors with osteogenic properties have now been identified. Although many of these proteins can induce bone formation when delivered on a carrier matrix, these approaches have not been fully developed in the laboratory or clinic. The expression of osteogenic proteins via direct or ex vivo gene therapy techniques is also compelling because high-level, long-term gene expression can now be achieved using novel viral and nonviral vectors. In this brief review the authors will highlight recent advances in genetic therapies for the induction of osteogenesis, as well as their potential use for the promotion of spinal arthrodesis.

Morphologic analysis of BMP-9 gene therapy-induced osteogenesis

The present study was performed to determine the histological, ultrastructural, and radiographic changes that occur over time at intramuscular BMP-9 gene therapy treatment sites. Several members of the bone morphogenetic protein (BMP) family have the potential to induce osteochondrogenesis when the protein is delivered to rodents, canines, rabbits, and nonhuman primates. Previous studies have also demonstrated that BMP gene therapy utilizing adenoviral vectors can also stimulate orthotopic and heterotopic bone formation in rodents and rabbits. Athymic nude and Sprague-Dawley rats were injected with Ad-BMP-9 or Ad-beta-Gal (3.75 x 10(9) particles) in their thigh musculature and light microscopic, electron microscopic, and computerized tomography analysis was performed 3, 6, 9, 12, 15, 18, 21, and 100 days later. To assess early mesenchymal cell proliferation, a bromodeoxyuridine (BrdU) immunohistochemical analysis was also performed 48, 60, and 72 hr postinjection in athymic nude rats. All animals demonstrated extensive endochondral bone formation at the Ad-BMP-9 treatment sites within 3 weeks. The Sprague-Dawley rats also exhibited a massive, acute inflammatory infiltrate during the first week. Proliferating mesenchymal stem cells were clearly evident as early as 2 days after treatment, which differentiated into small or hypertrophied chondrocytes during the next week. During the third week, the cartilaginous matrix mineralized and formed woven bone, which converted to lamellar bone by 3 months. No evidence of bone formation was demonstrated at the Ad-beta-Gal injection sites in the athymic nude or Sprague-Dawley rats. In addition, no cellular proliferation was seen at the Ad-beta-Gal treatment sites in the athymic nude animals as assessed by light microscopy and BrdU immunohistochemistry. The extensive bone formation induced by Ad-BMP-9 suggests that BMP gene therapy may have potential utility in the treatment of degenerative, rheumatic, or traumatic bone pathology.

Acquired lumbar spinal stenosis

Based on the individual clinical presentation and radiographic findings, an operation that completely decompresses the neural elements in the spinal canal and neural foramina followed by posterior, posterolateral, or interbody fusion, with or without instrumentation should be the procedure of choice in the future. The introduction of pharmacological agents to decrease scarring around the decompressed nerve roots will also increase the number of successful procedures. It must be stressed, however, that any new operative technique must be tested in a rigorous fashion, ideally with a prospective randomized clinical trial.

Endovascular treatment of experimental aneurysms by use of biologically modified embolic devices: coil-mediated intraaneurysmal delivery of fibroblast tissue allografts

BACKGROUND AND PURPOSE

Our long-term goal is to improve intraaneurysmal fibrosis after aneurysm embolization, by implanting exogenous fibroblasts, using platinum coils. For the current project, we tested two hypotheses: 1) that exogenous, fluorescence-labeled rabbit fibroblast allografts remained viable and proliferated within rabbit carotid arteries, and 2) that these fibroblast allografts could be reliably implanted into experimental aneurysms by use of platinum coils.

METHODS

Part 1. New Zealand White rabbit synovial fibroblasts obtained from a commercial vender were labeled with a fluorescent membrane marker. The common carotid arteries of New Zealand White rabbits were surgically exposed, ligated proximally and distally, and entered with 22-g angiocatheters. Through the angiocatheter we injected either phosphate-buffered saline-containing fluorescence-labeled fibroblasts (treatment vessels) or saline only (control vessels). The wounds were closed, and the subjects were kept alive for various time points up to 2 weeks. After sacrifice, the carotid artery segments were resected, processed for frozen-section histologic examination, and evaluated using epifluorescent microscopy and hematoxylin and eosin staining. Cell viability and proliferation were determined by comparing the treatment versus control vessels. Part 2. A) Fluorescence-labeled cells were grown in culture on platinum coils, which were then exposed to systemic arterial flow in the rabbit thoracic aorta for various lengths of time up to 40 minutes. The coil segments were then examined using fluorescent microscopy and the presence and relative amount of cells remaining on the coil were documented. B) Experimental aneurysms in rabbits were embolized with control platinum coils (n = 9) and platinum coils bearing rabbit synovial fibroblasts that were grown onto the coils in culture prior to implantation (n = 9). Subjects were sacrificed 3, 7, and 14 days after coil implantation. Histologic samples were studied to assess the presence or absence of nucleated cells within and around coil winds in order to determine whether fibroblasts had been successfully implanted into aneurysms. Data were evaluated using the chi-square test for statistical significance.

RESULTS

Part 1. Fluorescence-labeled cells were examined in the treatment carotid artery segments and results were recorded at all time intervals. The treatment vessel segments showed evidence of progressive cellular proliferation, leading to complete vessel fibrosis at 2 weeks. Conversely, control vessel segments were filled predominately with unorganized thrombus at each time interval. Part 2. A) Numerous labeled fibroblasts remained adherent to the coil despite prolonged exposure to systemic arterial flow. B) Fibroblasts were seen adjacent to or within the central lumen of coils in eight (88%) of nine aneurysms treated with cell-bearing coils. Nucleated cells were not present in any of the nine control coil subjects. This represented a statistically significant difference (P < .001).

CONCLUSION

Fibroblast allografts remain viable and proliferate in the vascular space in rabbits. Furthermore, these same fibroblasts, after seeding onto platinum coils in culture, remain protected within the lumen of the coils and are retained within the coil lumen even after prolonged exposure to arterial blood flow. Coils can be used to deliver viable fibroblasts directly into experimental aneurysms successfully. These findings indicate that coil-mediated cell implantation is feasible and may be a potential method of increasing the biological activity of embolic coils.

Gene therapy for skull base tumors

During the last 10 years, gene therapy has certainly risen to the forefront of basic science and clinical medicine. Designing more efficient gene delivery systems is currently the "holy grail" of genetic therapeutics, because even the most efficient viral vectors do not transfect all cells at the treatment site, which leads to local recurrence in the case of most brain tumors. The use of oncolytic viruses that propagate through tumors may have the best potential for treating skull base lesions in the future. Because many skull base tumors are histologically benign, gene therapy approaches for these tumors may be an excellent first step, as partial killing leading to local control with minimal morbidity and mortality may soon be possible. The accessibility of these tumors by endovascular approaches is also currently feasible, which could lead to high vector concentrations within the tumor bed, although limiting vector administration and gene expression in the adjacent brain. With advances in vector development, limiting gene expression to tumor cells with transcriptional or transductional targeting, and the application of more toxic gene therapy paradigms, the treatment of many skull base tumors may soon be possible.

Bone morphogenetic proteins and bone morphogenetic protein gene therapy in neurological surgery: a review

OBJECTIVE

To review the uses of bone morphogenetic proteins (BMPs) and BMP gene therapy for the treatment of neurosurgical disorders.

METHODS

Literature review.

RESULTS

BMPs are members of the transforming growth factor beta superfamily, and they play an important role in the growth and development of numerous tissues, including bone, brain, and spinal cord. Although the majority of previous studies have focused on the regulatory functions of BMPs in the normal growth and differentiation of the skeletal system, BMPs also seem to be exquisitely involved in the regulation of cellular proliferation, survival, differentiation, apoptosis, and lineage commitment in the central nervous system. When specific BMPs are delivered on biological matrices, they have the capacity to induce bone, cartilage, ligament, and tendon at both heterotopic and orthotopic sites, suggesting that they may play a major role in the future treatment of spinal and craniofacial pathology. For example, recent studies have clearly demonstrated the usefulness of BMPs and BMP gene therapy for the induction of spinal arthrodesis in several animal models. In addition, several BMPs have been shown to have a neuroprotective effect in animal models of head injury, cerebral ischemia, and Parkinson's disease and may therefore have direct clinical applications for the treatment of central nervous system disorders.

CONCLUSION

As the physiological activity of BMPs in the development and pathology of the central nervous system and spine are more fully elucidated, BMP therapeutics and gene therapy will probably have numerous applications in neurological surgery.

Use of bone morphogenetic protein-9 gene therapy to induce spinal arthrodesis in the rodent

OBJECT

Bone morphogenetic proteins (BMPs) have been shown to have significant osteoinductive activity in numerous in vitro and in vivo assay systems, and BMP-2 and BMP-7 are currently being evaluated in human clinical studies. In the spinal region, BMPs have been shown to promote spinal arthrodesis at a higher rate than autologous bone alone. The delivery of BMPs via direct or ex vivo gene therapy techniques is also currently being evaluated and has shown promise in several mammalian models. The present study was designed to evaluate the efficacy of the use of direct, percutaneous BMP-9 adenoviral gene therapy to promote spinal fusion in the rodent.

METHODS

Each animal was injected with 7.5x10(8) pfu of a BMP-9 adenoviral vector in the lumbar paraspinal musculature and allowed to survive 16 weeks. Computerized tomography studies and histological analysis demonstrated massive bone induction at the injection sites, clearly leading to solid spinal arthrodesis, without evidence of pseudarthroses, nerve root compression, or systemic side effects.

CONCLUSIONS

The results of this study strongly support the advancement of BMP gene therapy techniques toward clinical use.

Cerebral ischemia-reperfusion injury: a novel therapeutic approach with TAK-218

The goal of the present study was to evaluate the potential neuroprotective effect of TAK-218 in an in vivo rat focal cerebral ischemia/reperfusion model. TAK-218 is a novel compound with multiple antiischemic properties, including suppression of aberrant dopamine release, modulation of sodium channels, and inhibition of lipid peroxidation. The study was a blinded, randomized, placebo-controlled study of TAK-218 in a three-vessel focal ischemic rat model. A total of 22 rats were randomly assigned to the treatment or placebo group. Animals were injected intrapertoneally with either a 2 mg/kg dose of drug or saline at 2 hours after reperfusion. Infarction volume was measured with use of 2,3,5-triphenyltetrazolium chloride. Total adjusted infarction volume in treated animals decreased by 10%. With use of a statistical analysis requiring 80% power with a 20% reduction desired effect, there was no statistically significant difference in the end-point of infarction volume between drug and placebo treatment groups. In light of the proven efficacy of thrombolytic therapy for acute stroke, it is now desirable to test neuroprotective agents during the 3-hour therapeutic window after ischemia. Further research is necessary to discern if a therapeutic agent with multiple antiischemic properties may provide a more robust neuroprotective effect than an agent with a single neuroprotective action.

Bovine type I collagen as an endovascular stent-graft material: biocompatibility study in rabbits

PURPOSE

To study the biocompatibility of a bovine type I collagen preparation as a material for small-vessel stent-grafts in rabbits.

MATERIALS AND METHODS

A composite nitinol-collagen endovascular stent-graft with a 4-mm inner diameter was deployed in the abdominal aorta in nine rabbits. Angiography was performed, and the rabbits were sacrificed at 1, 2, and 7 days and at 1 and 3 months. The portion of the aorta containing the stent-graft was excised and was histologically evaluated.

RESULTS

All stent-grafts were patent at all time points. On days 1, 2, and 7 after implantation, scattered red and white blood cells adhered to the stent-graft. At 1 month, the stent-graft was endothelialized and was infiltrated with fibroblasts that deposited collagen within the interstices of the implanted collagen material. At 3 months, there was additional collagen deposition within the interstices of the stent-graft that did not narrow the lumen of the stent-grafts.

CONCLUSION

Type I collagen as a intravascular stent-graft material is biocompatible for at least 3 months in rabbits. It is rapidly endothelialized and does not cause reactive stenosis. As a versatile and biocompatible polymer, collagen is potentially useful in the construction of endovascular stent-grafts for use in human arteries.

1999 ARRS Executive Council Award. Creation of saccular aneurysms in the rabbit: a model suitable for testing endovascular devices. American Roentgen Ray Society

OBJECTIVE

This study developed an animal model of intracranial aneurysms suitable for evaluating emerging endovascular devices for aneurysmal therapy. We characterized the short-, medium-, and long-term attributes of this endovascular technique for saccular aneurysmal creation in the rabbit.

MATERIALS AND METHODS

The right common carotid artery was surgically exposed in nine New Zealand white rabbits. Using endovascular techniques, we occluded the origin of the right common carotid artery with a pliable balloon. Elastase was incubated endoluminally in the proximal common carotid artery above the balloon. The common carotid artery was ligated distally. Animals were studied angiographically and sacrificed at 2 weeks (n = 3), 10 weeks (n = 3), and 24 weeks (n = 3) after aneurysm creation. Histology was obtained.

RESULTS

Saccular aneurysms formed in eight of the nine rabbits. The aneurysm projected from the apex of an approximately 90 degree curve of the parent vessel, the brachiocephalic artery. Mean aneurysm diameter was 4.5 mm (SD, 1.2 mm), and mean height was 7.5 mm (SD, 1.6 mm). All samples showed thinned elastic lamina and no evidence of inflammation. In four of eight aneurysms, unorganized thrombus was present in the dome of the aneurysm.

CONCLUSION

Arterial aneurysms with intact endothelium and deficient elastic lamina were reliably created in an area of high shear stress in New Zealand white rabbits. Three of these aneurysms remained patent for at least 6 months. We found a simple procedure that can be readily applied to the testing of new endovascular devices for a reliable creation of aneurysms in rabbits.

The use of bone morphogenetic protein gene therapy in craniofacial bone repair

Bone morphogenetic proteins (BMPs) are capable of inducing endochondral bone formation when applied on biologic carriers in numerous mammalian in vivo assay systems. Bone morphogenetic protein gene therapy is also currently being developed to promote osteogenesis for clinical indications such as spinal fusions, craniofacial bone loss, and osteoporosis. In this study, critical-sized mandibular defects were treated with a control adenoviral vector (Ad-beta-gal), a BMP-2 adenoviral vector (Ad-BMP-2), or a BMP-9 adenoviral vector (Ad-BMP-9). Gross tissue examination, radiographic analysis, and histologic analysis demonstrated significant bony healing in the BMP treated groups compared to controls. Osteogenesis was limited to the bony defect, without extension into the surrounding soft tissues. The study suggests that with further development, BMP gene therapy may be potentially useful for repair of bony defects in the craniofacial region.

Endovascular creation of an in vivo bifurcation aneurysm model in rabbits

PURPOSE

To develop a rabbit model of an intracranial bifurcation aneurysm to test new endovascular therapies.

MATERIALS AND METHODS

An experimental aneurysm model was created in rabbits by means of endovascular balloon occlusion of the left common carotid artery, which created an aneurysm at the bifurcation formed by the aortic arch and the brachiocephalic trunk. A total of 18 aneurysms were created. In eight rabbits, the aneurysms were incubated with intraluminal elastase to induce degeneration of the elastic laminae. The animals were followed up with angiography for as long as 3 months. The animals were sacrificed at various times, and histologic evaluation of the aneurysm was performed.

RESULTS

Ten aneurysms created without elastase infusion were all very small or completely closed at 1-3 months. Six aneurysms created with elastase infusion had long-term patency (two were patent at 1 month and four, at 3 months). The elastase aneurysms had a mean width of 3 mm (range, 2-3.5 mm) and a mean length of 5 mm (range, 3-7 mm). Histologic evaluation revealed destruction of the normal elastin layers, which allowed the artery to become aneurysmal.

CONCLUSION

This aneurysm model re-created the hemodynamic forces and size of human cerebral bifurcation aneurysms and maintained the integrity of the endothelium. The creation of the aneurysms was rapid, reliable, and reproducible.

Histologic evaluation of platinum coil embolization in an aneurysm model in rabbits

PURPOSE

To characterize the histologic response to platinum coil embolization by using a rabbit aneurysm model.

MATERIALS AND METHODS

Saccular aneurysms were created in New Zealand White rabbits by using vessel ligation with intraluminal elastase incubation. Aneurysms were subsequently embolized by using platinum coils. Subjects were sacrificed at various intervals up to 12 weeks following coil embolization. The aneurysm cavities and adjacent vessels were embedded in methylmethacrylate, were sectioned, and were stained for histologic examination.

RESULTS

Two weeks following coil implantation, aneurysms were filled predominantly with unorganized thrombus. Six weeks following coil implantation, histologic features included complete filling of the aneurysm lumen with either prominent laminated but unorganized thrombus or areas of unorganized thrombus interspersed among areas of cellular infiltration. At 12 weeks following coil implantation, aneurysms were filled with the loosely packed, disordered cells contained within the extracellular matrix. Fibrosis or smooth muscle cell infiltration was not present in any of the 6- or 12-week samples.

CONCLUSION

Platinum coils placed into experimental saccular aneurysms in New Zealand White rabbits failed to elicit a fibrotic response. This model can be used for the testing of biologic modifications of platinum coils aimed at increasing intra-aneurysmal fibrosis.

In vivo endochondral bone formation using a bone morphogenetic protein 2 adenoviral vector

Bone morphogenetic proteins (BMPs) are polypeptides that induce ectopic bone formation in standard rat in vivo assay systems. Previous studies have demonstrated the clinical utility of these proteins in spinal fusion, fracture healing, and prosthetic joint stabilization. Gene therapy is also a theoretically attractive technique to express BMPs clinically, since long-term, regulatable gene expression and systemic delivery with tissue-specific expression may be possible in future. This study was performed to determine whether an adenoviral vector containing the BMP-2 gene can be used to express BMP-2 in vitro and promote endochondral bone formation in vivo. In vitro, U87 MG cells transduced per cell with 20 MOI of an adenoviral construct containing the BMP-2 gene under the control of the universal CMV promoter (Ad-BMP-2) showed positive antibody staining for the BMP-2 protein at posttransfection day 2. The synthesis and secretion of active BMP-2 into the conditioned medium of Ad-BMP-2-transduced 293 cells were confirmed by Western blot analysis and the induction of alkaline phosphatase activity in a W-20 stromal cell assay. In vivo, Sprague-Dawley rats and athymic nude rats were injected with Ad-BMP-2 in the thigh musculature and were sacrificed on day 3, 6, 9, 12, 16, 21, 60, and 110 for histological analysis. The Sprague-Dawley rats showed evidence of acute inflammation, without ectopic bone formation, at the injection sites. In the athymic nude rats, BMP-2 gene therapy induced mesenchymal stem cell chemotaxis and proliferation, with subsequent differentiation to chondrocytes. The chondrocytes secreted a cartilaginous matrix, which then mineralized and was replaced by mature bone. This study demonstrates that a BMP-2 adenoviral vector can be utilized to produce BMP-2 by striated muscle cells in athymic nude rats, leading to endochondral bone formation. However, in immunocompetent animals the endochondral response is attenuated, secondary to the massive immune response elicited by the first-generation adenoviral construct.

Percutaneous spinal fusion using bone morphogenetic protein-2 gene therapy

OBJECT

Gene therapy has many potential applications in neurosurgery. One application involves bone morphogenetic protein-2 (BMP-2), a low-molecular-weight glycoprotein that induces bone formation in vivo. Numerous studies have demonstrated that the BMP-2 protein can enhance spinal fusion. This study was undertaken to determine whether direct injection of an adenoviral construct containing the BMP-2 gene can be used for spinal fusion.

METHODS

Twelve athymic nude rats were used in this study. Recombinant, replication-defective type 5 adenovirus with the cytomegalovirus (CMV) promoter and BMP-2 gene (Ad-BMP-2) was used. A second adenovirus constructed with the CMV promoter and beta-galactosidase (beta-gal) gene (Ad-beta-gal) was used as a control. In three groups (four rats each) 7.5 microl of virus (5x10(8) particles/microl) was injected percutaneously and paraspinally at the lumbosacral junction: Group 1 received Ad-BMP-2 bilaterally; Group 2 received Ad-BMP-2 on the right, Ad-beta-gal on the left; and Group 3 received Ad-beta-gal bilaterally. Computerized tomography (CT) scans of the lumbosacral spine were obtained at 3, 5, 8, and 12 weeks. At 12 weeks, the animals were killed and underwent histological inspection. Ectopic bone formation was observed both on three-dimensionally reconstructed CT scans and histological examination in all rats at sites treated with Ad-BMP-2. Histological analysis demonstrated bone at different stages of maturity adjacent to the spinous processes, laminae, and transverse processes.

CONCLUSIONS

Results of this study clearly demonstrated that it is possible to produce in vivo endochondral bone formation by using direct adenoviral construct injection into the paraspinal musculature, which suggests that gene therapy may be useful for spinal fusion in the future.

Systemic administration of the endothelin-A receptor antagonist TBC 11251 attenuates cerebral vasospasm after experimental subarachnoid hemorrhage: dose study and review of endothelin-based therapies in the literature on cerebral vasospasm

OBJECTIVE

Increasing evidence implicates endothelin (ET)-1 in the pathophysiological development of cerebral vasospasm. This study examined the ability of TBC 11251 (TBC), a new ETA receptor antagonist, to prevent vasospasm in a rabbit model of subarachnoid hemorrhage (SAH).

METHODS

Eighty-five New Zealand White rabbits were assigned to 1 of 10 groups. SAH was induced by injecting autologous blood into the cisterna magna. The treatment groups were as follows: 1) control (no SAH), 2) SAH alone, 3) SAH plus vehicle every 12 hours (BID), 4) SAH plus 5 mg/kg TBC BID, 5) SAH plus 10 mg/kg TBC BID, 6) SAH plus 20 mg/kg TBC BID, 7) SAH plus vehicle at 24 and 36 hours after SAH (24/36), 8) SAH plus 5 mg/kg TBC 24/36, 9) SAH plus 10 mg/kg TBC 24/36, and 10) SAH plus 20 mg/kg TBC 24/36. Animals were killed 48 hours after SAH, by perfusion-fixation, and then basilar arteries were histologically prepared and their cross-sectional areas were measured.

RESULTS

The mean basilar artery cross-sectional area was constricted from 0.332 mm2 in the control group to 0.131 mm2 in the SAH alone group, 0.132 in the vehicle 24/36 group, and 0.125 in the vehicle BID group. All groups treated with TBC showed an increase in cross-sectional luminal basilar artery area, relative to the vehicle-treated groups. The 5 mg/kg TBC BID group exhibited a mean basilar artery area of 0.217 mm2, and the 10 mg/kg TBC BID group showed a mean basilar artery area of 0.240 mm2; both groups were statistically improved, compared with the vehicle-treated groups (P < 0.05). No side effects were seen, and there were no differences in the mean arterial pressures between drug- and vehicle-treated groups.

CONCLUSION

These findings demonstrate that systemic administration of the ETA receptor antagonist TBC significantly attenuates cerebral vasospasm after SAH, thus providing additional support for the role of ET-1 in vasospasm.

Practice parameters in adults with suspected or known supratentorial nonoptic pathway low-grade glioma

Gene therapy has many potential applications in neurosurgery. One application involves bone morphogenetic protein-2 (BMP-2), a low-molecular-weight glycoprotein that induces bone formation in vivo. Numerous studies have demonstrated that the BMP-2 protein can enhance spinal fusion. This study was undertaken to determine whether direct injection of an adenoviral construct containing the BMP-2 gene can be used for spinal fusion. Twelve athymic nude rats were used in this study. Recombinant, replication-defective type-5 adenovirus with a universal promoter and BMP-2 gene (Ad-BMP-2) was used. A second adenovirus constructed with a universal promoter and beta-galactosidase (beta-gal) gene (Ad-beta-gal) was used as a control. Seven and one-half microliters of virus was injected percutaneously and paraspinally at the lumbosacral junction in three groups (four animals each): 1) Ad-BMP-2 bilaterally, 2) Ad-BMP-2 on the right, Ad-beta-gal on the left, and 3) Ad-beta-gal bilaterally. Computerized tomography (CT) scans of the lumbosacral spine were obtained at 3, 5, and 12 weeks. At 12 weeks, the animals were killed for histological inspection. Ectopic bone formation was seen both on three-dimensional CT reconstruction and histologically in all rats at sites treated with Ad-BMP-2. Histological analysis revealed bone at different stages of maturity adjacent to the spinous processes, laminae, and transverse processes. This study clearly demonstrated that it is possible to produce in vivo endochondral bone formation by using direct adenoviral construct injection into the paraspinal musculature, which suggests that gene therapy may be useful for spinal fusion in the future.

Platinum coil-mediated implantation of growth factor-secreting endovascular tissue grafts: an in vivo study

PURPOSE

To demonstrate in vivo that platinum embolic coils can be used to deliver genetically modified, growth factor-secreting fibroblast grafts into the endovascular space with the long-term goal of improving fibrosis within coil-embolized cerebral aneurysms.

MATERIALS AND METHODS

Murine fibroblasts that contained multiple inserts of the DNA for human basic fibroblast growth factor were grown in culture onto 10-mm-long segments of Guglielmi detachable coils. Control (n = 4) and fibroblast-bearing (n = 4) coils were implanted into the common carotid artery in nude rats. The arterial segments that contained the coil were harvested after 14 or 35 days. Cellular content and collagen formation in the treated vessels were assessed histologically.

RESULTS

At both 14 and 35 days, samples with control coils showed primarily involuting blood elements with minimal fibroblast proliferation or collagen formation. At 14 days, samples with fibroblast-bearing coils showed extensive fibroblast proliferation. At 35 days, samples with fibroblast-bearing coils showed marked interval fibroblast proliferation and collagen formation.

CONCLUSION

Platinum coils can be used as a cell delivery device. Direct intravascular implantation of growth factor-secreting fibroblast grafts leads to improved intravascular scar formation, therefore theoretically reducing the potential for aneurysm regrowth or coil compaction.

Transforming growth factor-Beta binds reversibly in vitro to guglielmi detachable coils

SUMMARY

We determined the propensity for and reversibility of transforming growth factor-beta(TGFbeta) binding to uncoated Guglielmi Detachable Coils (GDC) and to GDC coated with extracellular matrix (ECM) proteins. Three 1.0 centimetre samples each of uncoated GDC-18 and of GDC-18 coated with either poly-L-lysine, laminin, type I collagen, type IV collagen, fibronectin, or poly-L-lysine and laminin were prepared. These samples were immersed briefly in a solution containing I(125)-labelled TGFbeta at a concentration of 0.225 mug/ml with initial specific activity of 123.3 mCi/mg (DuPont-NEN, Billerica, MA), and were counted using a scintillation counter. Each sample was then placed in a vial containing saline, shaken for 60 seconds, and counted again. Selected samples were immersed for varying periods within the TGFbeta solution and counted before and after saline rinse. Samples were rinsed one week after initial rinsing and counted again. The amount of binding between coil types was compared using the Student t test. For all samples initial binding of TGFbeta was in the order of 60-120 pg/cm. For the pre-rinse data there were no statistically significant differences between the amount bound to any single coil coating type relative to other coatings. Compared to the initial accumulations, the amount remaining after rinsing ranged from 40% (poly-L-lysine) to 63% (poly-L-lysine with laminin), with a mean of 55% among the seven coil types. After rinsing there was more growth factor remaining on uncoated coils than on poly-L-lysine-coated coils (p=0.05), fibronectin-coated coils (p=0.01), and type IV collagen-coated coils (p=0.04). There was a trend toward greater residual growth factor on coils coated with poly-L-lysine and laminin compared to coils coated with poly-L-lysine alone (p=0.10). Delayed, second rinsing of the samples one week after initial testing demonstrated only minor incremental loss of TGFbeta from the coil surfaces. After five minutes of immersion, accumulation was approximately 200% greater than that noted with brief submersion, but immersions lasting over five minutes did not yield increasing levels of TGFbeta binding. TGFbeta binds to GDC coils. Binding is not improved with ECM protein-coated coils compared to uncoated coils. The absolute amount of TGFbeta bound to the coil will likely result in local concentrations of growth factor in the order of those required for biological activity in vivo.

In vitro proliferation and adhesion of basic fibroblast growth factor-producing fibroblasts on platinum coils

PURPOSE

To evaluate the growth and adhesion characteristics in vitro of genetically modified, basic fibroblast growth factor-producing fibroblasts on platinum detachable coils.

MATERIALS AND METHODS

Coils of two sizes were coated with laminin, poly-L-lysine, fibronectin, and type I and type IV collagen and were cultured with basic fibroblast growth factor-secreting fibroblasts. Type I collagen strands were inserted in the lumen of some coils. Cellular proliferation and adherence during passage of coils through microcatheters were studied with both light and scanning electron microscopy. Growth factor concentration in the culture medium was measured.

RESULTS

Rapid cellular proliferation was noted on all coated coils except those coated with type IV collagen. Proliferation on uncoated coils was slightly slower than on most coated coils, although confluent cell layers were present on uncoated larger-diameter coils within 48 hours. Cells had a marked propensity to grow between the primary coil windings into the coil lumen, except in coils that contained collagen filaments. Passage through microcatheters caused widespread stripping of cells from the outer surface of coils, especially the uncoated samples. Viable cells remained in the coil lumen. Supernatant contained high concentrations of growth factor.

CONCLUSION

Platinum embolic coils are a promising mechanism of cell delivery for stimulation of scar formation or other desirable biologic effects.

Routine angiography after surgery for ruptured intracranial aneurysms: a cost versus benefit analysis

PURPOSE

To assess the cost versus the benefit of routine cerebral angiography after surgery for ruptured aneurysms.

METHODS

Decision tree and Markov analyses that used cohort simulation were conducted to determine the incremental cost:benefit ratio of routine postsurgical angiography. Input data for unexpected partially clipped and unclipped cerebral aneurysms were estimated from the literature for the following variables: frequency; annual rate of subsequent hemorrhage; morbidity and mortality rates of subsequent hemorrhage; efficacy and morbidity and mortality rates of subsequent surgery; and costs of subsequent surgery, angiography, subsequent hemorrhage of aneurysm, and rehabilitation. RESULTS; Baseline input variables resulted in an acceptable cost:benefit ratio for routine postsurgical angiography. However, essentially all of the benefit was derived from intervening in cases of unexpected unclipped aneurysms rather than partially clipped aneurysms. Isolated instances of angiography and subsequent surgery for unexpected partially clipped aneurysms yielded unacceptable cost:benefit ratios. Surgical costs had minimal effect on the analysis.

CONCLUSIONS

When routine postsurgical angiography was performed primarily to diagnose and to subsequently operate on unexpected partially clipped aneurysms, the cost:benefit ratio was unacceptable. However, even low frequencies of unexpected unclipped aneurysms resulted in favorable cost:benefit ratios.

Acquired lumbar stenosis: topic review and a case series

Stenosis of the central and lateral lumbar vertebral canal can be congenital or acquired; the latter is most often caused by a degenerative process. The associated neurogenic claudication and/or radiculopathic symptom complexes are thought to result from compression of the cauda equina and lumbosacral nerve roots by hypertrophy of or encroachment by any combination of the following: canal walls, ligamenta flava, intervertebral discs, posterior longitudinal ligament, or epidural fat. The authors' technique for the treatment of lumbar stenosis involves extensive unilateral decompression with undercutting of the spinous process and obviates the need for instrumentation by using a contralateral autologous bone fusion. The results in a series of 29 patients in whom the procedure was performed suggest that this decompression method safely and successfully treats not only the radicular symptoms caused by lateral stenosis but also the neurogenic claudication symptoms associated with central stenosis. In addition, the procedure can preserve spinal stability without instrumentation by using contralateral autologous bone fusion along the laminae and spinous processes.

Partial pediculectomy in the treatment of lumbar spinal stenosis: technical note

OBJECTIVE

We note an additional pathological condition associated with lumbar spinal stenosis that may be responsible for significant postoperative pain. Recognizing that nerve roots are stretched around hypertrophic pedicles in some cases of spinal stenosis, we have altered our surgical management of these cases to address what may be a previously unrecognized but significant anatomic pathological finding.

SURGICAL TECHNIQUE

After ipsilateral posterior bony decompression of the spinal canal, the nerve root is examined as it courses around the pedicle. If the root appears stretched, the medial part of the pedicle is removed using first a diamond bit and then a curet. The nerve root is retracted and protected during this procedure.

RESULTS

Inspection of the root after partial pediculectomy frequently reveals lateral movement of the root into space previously occupied by the pedicle. Anatomically, the nerve is better decompressed and free of obstruction. This technique adds little time to the overall duration of the operation.

CONCLUSION

Anatomic evidence obtained through intraoperative examination and preoperative imaging techniques indicates that partial pediculectomy may play a role in the treatment of some cases of lumbar stenosis.

MPP+ induced apoptotic cell death in SH-SY5Y neuroblastoma cells: an electron microscope study

PD is a common, late-onset neurodegenerative disorder that results in part from the gradual loss of dopaminergic neurons in the substantia nigra pars compacta. The neurotoxin MPTP can induce PD-like clinical symptomatology and neuropathological destruction and, thus, has been used as a PD model. The human neuroblastoma cell line SH-SY5Y possesses many of the qualities of human neurons and, as such, has served as a model for them. Apoptosis is the mode of cell death induced in SH-SY5Y cells by MPTP, and this was confirmed with nick end labeling and bisbenzimide staining. Transmission electron microscopic analysis of the ultrastructural changes occurring in neurotoxin exposed SH-SY5Ys revealed many morphological characteristics consistent with apoptosis. These changes included plasmalemmal blebbing, altered cytosolic density, nuclear condensation and fragmentation, pronounced vacuole formation, ribosomal dispersion, and the disappearance of the golgi complex, microtubules, and smooth endoplasmic reticulum. Limited amounts of rough endoplasmic reticulum and mitochondria exhibited normal morphology throughout the apoptotic changes but then were disrupted during secondary necrotic changes. The in vitro induction of apoptosis by a parkinsonism neurotoxin might be reflective of the mechanisms of in vivo nigral degeneration occurring during PD.

Utilization of type I collagen gel, demineralized bone matrix, and bone morphogenetic protein-2 to enhance autologous bone lumbar spinal fusion

Autologous bone grafts are currently considered "gold standard" material for achieving long-term spinal arthrodesis. The present study was performed to determine whether demineralized bone matrix (DBM), type I collagen gels, or bone morphogenetic protein-2 (BMP-2) can improve autologous bone spinal fusions. Using a unilateral decompression-contralateral fusion technique in dogs, each of these materials was added to an autologous bone graft. Volumetric analysis, histological analysis, and biomechanical testing were performed to assess the effectiveness of each material. The DBM had an inhibitory effect on solid bone fusion of the spine, whereas the type I collagen gels improved the bony interface between the graft and the host spine. The BMP-2 strongly enhanced the amount of bone deposition at the fusion site and increased the number of intervertebral levels that were solidly fused. This study strongly supports the use of BMP-2 as an additive to autologous bone grafts in spine stabilization.

Molecular methods of enhancing lumbar spine fusion

OBJECTIVE

An optimal method for spinal fusion would induce rapid growth of bone via an osteoconductive and osteoinductive implant. This study examines the spinal fusion enhancement potential of some osteoconductive and osteoinductive biomaterials.

METHODS

Four similar canines received unilateral posterolateral fusions on the left side at T13-L1 and L4-L5 and on the right side at L2-L3 and L6-L7. The experiments were grouped as follows: Group A, autogenous bone harvested from the iliac crest; Group B, autogenous bone and collagen; Group C, no implant; and Group D, autogenous bone, collagen, and recombinant human bone morphogenetic protein-2. Radiographic assessment, three-dimensional computed tomographic volumetric analysis, and biomechanical testing were performed at each level.

RESULTS

For Groups A and B, the fusions demonstrated moderate bone formation at 6 and 12 weeks postoperatively. Group D fusions exhibited earlier and more dramatic increases in volume and radiodensity and eventually were comparable in size to the vertebral bodies. Average fusion volumes computed from three-dimensional computed tomographic analysis were: Group A = 1.243 cc, Group B = 0.900 cc, Group C = 0.000 cc, and Group D = 6.668 cc (P = 0.003 compared to Group A). Group D exhibited flexion and extension biomechanical properties much greater than controls. The addition of recombinant human bone morphogenetic protein-2 consistently yielded the strongest fused segments and, on average, enhanced extension stiffness by 626% and flexion stiffness by 1120% over controls.

CONCLUSION

The most advantageous spinal fusion implant matrix consisted of recombinant human bone morphogenetic protein-2, autogenous bone, and collagen. Future investigators, however, need to examine the appropriate quantities of the individual components and clarify the efficacy of the matrix for the various types of spinal fusion approaches.

Treatment of lumbar spinal stenosis by extensive unilateral decompression and contralateral autologous bone fusion: operative technique and results

A new surgical technique for the treatment of lumbar spinal stenosis features extensive unilateral decompression with undercutting of the spinous process and, to preserve stability, uses contralateral autologous bone fusion of the spinous processes, laminae, and facets. The operation was performed in 29 patients over a 19-month period ending in December of 1991. All individuals had been unresponsive to conservative treatment and presented with low-back pain in addition to signs and symptoms consistent with neurogenic claudication or radiculopathy. Nine had undergone previous lumbar decompressive surgery. The minimum and mean postoperative follow-up times were 2 and 2 1/2 years, respectively. The mean patient age was 64 years; only two patients were younger than 50 years of age. Of the patients with neurogenic claudication, 69% reported complete pain relief at follow-up review. Of those with radicular symptoms, 41% had complete relief and 23% had mild residual pain that was rated 3 or less on a pain-functionality scale of 0 to 10. For the entire sample, this surgery decreased pain from 9.2 to 3.3 (p < 0.0001) on the scale. Sixty-nine percent of patients were satisfied with surgery. Low-back pain was significantly relieved in 62% of all patients (p < 0.0001). Low-back pain relief correlated negatively with number of levels decompressed (p < 0.05). To assess fusion, follow-up flexion/extension radiographs were obtained, and no motion was detected at the surgically treated levels in any patient. The results suggest that this decompression procedure safely and successfully treats not only the radicular symptoms caused by lateral stenosis but also the neurogenic claudication symptoms associated with central stenosis. In addition, the procedure, by using contralateral autologous bone fusion along the laminae and spinous processes, can preserve stability without instrumentation.

The accessory optic system in the frog, Rana Pipiens: an electron microscopic study of the retinal afferents utilizing the anterograde tracer biocytin

The retinal afferents to the basal optic nucleus in the frog, Rana Pipiens, were labeled anterogradely with biocytin and subsequently studied at the electron microscopic level. Labeled synaptic terminals in the nucleus varied in size from 0.5 microns to 2.0 microns and made symmetric synaptic contacts with large and small dendrites, although very rare axospinous and axosomatic contacts were also demonstrated.

Magnetic resonance imaging of neuronal grafts in the primate

This preliminary study demonstrates the vital role that magnetic resonance imaging plays in the study of neuronal grafts in a nonhuman primate model of Huntington's disease. MRI scans were used to accurately locate and stereotactically lesion the anterior putamen of an adult rhesus monkey, thereby mimicking the anatomical and biochemical changes in Huntington's disease. Follow-up scans were utilized to confirm correct placement of the lesion and to stereotactically implant primate fetal neuronal tissue precisely into the lesion. Additionally, MRI appeared capable of imaging the fetal striatal grafts in rhesus monkeys. While the precise cellular composition of growing grafts was not identifiable on MRI scans, differentiation between normal, lesioned, and engrafted tissue was possible. Correlation of the magnetic resonance images of the grafted regions with actual graft tissue in perfused sections of the brain was shown. The use of magnetic resonance imaging, as indicated in these neuronal implantation studies, allows for a wide variety of future research possibilities where noninvasive and precise localization of the graft is mandated.

Carotid artery revascularization following Crutchfield clamp placement. Report of two cases

Several types of adjustable clamp have been widely utilized to gradually occlude the carotid artery for the treatment of various intracranial vascular lesions. A fairly large number of patients, many of whom have not been adequately followed, have these clamps still in place. The authors report two patients, initially treated with a Crutchfield clamp for an intracranial aneurysm, in whom carotid artery system revascularization occurred through the clamp many years later, leading to continued filling of the aneurysm. Recommendations are given on monitoring patients with Crutchfield clamps in order to minimize long-term complications.

Degeneration of long-term fetal neostriatal allografts in the rhesus monkey: an electron microscopic study

Primate fetal neostriatal neurons were implanted into the ibotenic acid-lesioned primate striatum and the animals were allowed to survive for 8 months. Light microscopic examination of the transplanted tissue demonstrated that the grafts were between 1.0 and 1.5 mm in diameter. The transplants were highly gliotic, but contained both normal appearing and degenerating neurons. At the electron microscopic level, the transplanted neurons displayed ultrastructural features identical to those of medium spiny, medium aspiny, and large aspiny striatal neurons. However, the majority of the grafted neurons showed evidence of degeneration. The grafts' neuropil demonstrated numerous glial processes, as well as mature axodendritic and axospinous synapses. Although this study was limited to only two graft recipients, the degenerative changes seen in the long-term primate allografts suggest that extension of these techniques into the clinical setting may be premature at the present time.

A method for utilizing biocytin to study retinofugal pathways at the light and electron microscopic levels

Numerous methods have been utilized in the past to study the retinofugal pathway at both the light and electron microscopic levels. However, many of these techniques have technical drawbacks that make them difficult to use in electron microscopic studies. We present herein a method for utilizing the anterograde tracer biocytin to study the retinal pathways at both the light and electron microscopic levels. Biocytin is an especially useful tracer since it clearly labels very small axons and boutons in addition to the larger fibers. In addition, the synaptic ultrastructure is left intact and the technique can be utilized in numerous double-labeling neuroanatomical studies.

Descriptive morphology of developing fetal neostriatal allografts in the rhesus monkey: a correlated light and electron microscopic Golgi study

Primate fetal striatal neurons were transplanted into the ibotenic acid lesioned rhesus monkey striatum. Ten weeks after transplantation the monkeys were transcardially perfused and graft tissue was histologically stained. Golgi impregnated, and processed for electron microscopy. The monkeys received magnetic resonance imaging (MRI) scans before lesioning, after lesioning, and ten weeks after transplantation to noninvasively study the striatal grafts. The study demonstrated that fetal striatal grafts, measuring up to 0.4 x 0.8 cm, can survive for extended periods of time in the non-human primate. Hematoxylin-eosin stained sections of the transplant demonstrated that neuronal, glial, vascular, and lymphocytic cells were present in the graft. The majority of the neurons had somatic diameters between 8 and 20 microns and were characterized by nuclei containing multiple nucleoli. A few neurons within the graft had somatic diameters up to 40 microns. These larger neurons exhibited more mature cytoplasm containing a moderate amount of Nissl substance. Some of the blood vessels within the graft were surrounded by a large number of plasma cells, but there was no evidence of hemorrhage or necrosis. Bielschowsky staining and Golgi impregnation of the transplanted tissue demonstrated that there were neurons at various degrees of differentiation. Some of the neurons had varicose dendrites, growth cones, and filopodia, which are all characteristics of immature neurons, while others had a much more mature appearance, including a moderate number of dendritic spines. Some of these neurons had an appearance typical of differentiating "medium spiny" neurons of the normal striatum. Electron microscopic analysis of the transplanted tissue and individual Golgi-impregnated neurons within the transplant confirmed that there were developing neurons within the graft. These neurons had an increased nuclear-to-cytoplasmic ratio and had nuclei containing multiple nucleoli. The neuropil surrounding these neurons was loosely organized and contained large areas of extracellular space. The neuropil exhibited developing dendrites, numerous growth cones, and mature synapses. In summary, the study demonstrated that fetal striatal allografts can survive for up to three months in the rhesus monkey and undergo normal differentiation as assessed by Golgi impregnation and electron microscopy.

Choline acetyltransferase- and substance P-like immunoreactive elements in fetal striatal grafts in the rat: a correlated light and electron microscopic study

Fetal striatal neurons were transplanted into the ibotenic acid-lesioned rat striatum. Three months after transplantation, the graft tissue was processed for choline acetyltransferase- and substance P-like immunoreactivity and was subsequently examined at the light and electron microscopic levels. The study demonstrated that choline acetyltransferase- and substance P-like-immunoreactive neurons were homogenously present throughout fetal striatal grafts, although in decreased numbers compared with those in the normal rat striatum. The majority of the choline acetyltransferase-immunoreactive neurons had fusiform, oval, or polygonal somata with somatic diameters greater than 20 microns and contained deeply invaginated nuclei surrounded by copious cytoplasm. In addition, choline acetyltransferase-immunoreactive neurons with somatic diameters between 10 and 20 microns were also demonstrated. The grafts' substance P-like-immunoreactive neurons, which had somatic diameters between 10 and 25 microns and had oval or polygonal perikarya, could be classified into two types based on their ultrastructural characteristics. Type I neurons contained an unindented nucleus which was surrounded by a thin rim or moderate amount of cytoplasm, whereas Type II immunoreactive neurons contained an indented nucleus which was surrounded by copious cytoplasm. Choline acetyltransferase- and substance P-like-immunoreactive dendrites in the grafts' neuropil were contacted by multiple unlabeled axon terminals. In addition, choline acetyltransferase- and substance P-like-immunoreactive axon terminals forming symmetric contacts with unlabeled dendrites were present within the graft. The study demonstrated that many of the neuroanatomical features of choline acetyltransferase- and substance P-like-immunoreactive elements found in the normal rat striatum are present in mature fetal striatal grafts.

Development of D1 and D2 dopamine receptors and associated second messenger systems in fetal striatal transplants

Stereotactic implantation of fetal brain regional anlage into adult host brain ("brain transplantation") appears to be an increasingly viable strategy for therapy of neurodegenerative diseases. We have studied implantation of fetal striatum into adult striatum, previously lesioned by neurotoxic amino acid injection, as a model for transplantation therapy of Huntington's disease. The beginning of behavioral recovery to apomorphine is not apparent until 6.5 months after implantation. By 4 months after implantation cerebral blood flow through the implants appears equal to that in the intact contralateral striatum. At this time, cerebral glucose utilization is reduced in the implants but increases following apomorphine treatment. The development of D1 and D2 dopamine (DA) receptors is markedly deficient in the striatal grafts at both 4 and 6.5 months after implantation. Very little D2 radioligand binding was observed in the grafts at either time point; D1 receptors appeared in a patchy fashion by 6.5 months at densities approaching normal striatum. In situ hybridization of D2 dopamine receptor mRNA demonstrated robust hybridization signal in normal striatum and accumbens but no signal in 6.5-month-old striatal grafts. Adenylate cyclase (AC) activity, examined with high-affinity [3H]forskolin binding, also appeared in patches similar to D1 receptors at 6.5 months. In contrast, protein kinase C activity, labeled with [3H]phorbol ester, was very apparent in the grafts at both time points. Higher and generally homogenous densities of muscarinic cholinergic receptors, assessed with [3H]QNB binding, develop in the grafts, but there appear to be few functioning cholinergic terminals, as measured by [3H]hemicholinium binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal neostriatal transplants in the rat: a light and electron microscopic Golgi study

Fetal striatal neurons were transplanted into the ibotenic acid lesioned rat striatum. Three months after transplantation the grafted tissue was Golgi-impregnated and examined at the light microscopic level to determine the morphological characteristics of the transplanted neurons. Golgi-impregnated neurons were then gold-toned and examined at the electron microscopic level. The transplanted neurons were classified by both somatic size and somatic and dendritic morphology, which demonstrated that at least seven distinct cell types are present in striatal grafts. Type I large neurons had aspinous somata, sparsely spined dendrites, and indented nuclei, whereas type II large neurons displayed somatic spines, sparsely spined dendrites, and indented nuclei. Type I medium neurons exhibited aspinous somata and proximal dendrites, heavily spined distal dendrites, and unindented nuclei. Type II medium neurons had somatic spines, sparsely spined dendrites, and indented nuclei. Type III medium neurons had aspinous somata, poorly branched and sparsely spined dendrites, and indented nuclei, while type IV medium neurons had aspinous somata, highly branched and sparsely spined dendrites, and indented nuclei. Type V medium neurons displayed aspinous somata, varicose dendrites, and indented nuclei. These results demonstrate that transplanted fetal striatal neurons differentiate into morphologically and ultrastructurally distinct striatal cell types.

In vitro and in vivo transplantation of fetal rat brain cells following incubation with various anatomic tracing substances

Implantation of fetal brain regional anlage into host brains ('brain transplantation') holds promise as a plausible treatment for certain human neurodegenerative disorders. Improvements in experimental brain transplantation techniques include: (1) utilization of brain cells in tissue culture as opposed to freshly prepared cell suspensions as a transplantation source, (2) prelabeling of fetal brain cells with inert, non-toxic tracer substances to allow subsequent (a) unequivocal identification of those cells as being fetally derived, and (b) anatomical and immunohistochemical identification of transplanted neurons, and (3) development of in vitro models for transplantation to allow physiological studies of connections formed between fetal neurons and host brain tissue. We examined the ability of brain cell suspensions derived from rat fetuses 15-17 gestational days old to accumulate and retain anatomic tracing substances, including Phaseolus vulgaris leucoagglutinin (PHA-L), rhodamine-labeled latex microspheres (RLM) and fluorogold (FG). All tracers were rapidly accumulated by fetal brain cells, but only PHA-L and RLM were retained following implantation into adult hosts or in tissue culture in vitro. PHA-L-labeled fetal brain cells transplanted in vivo showed morphological characteristics similar to fetal neurons kept in tissue culture in vitro. RLM- or PHA-L-labeled fetal brain cells can be co-cultured with rat brain slices maintained in long-term roller culture. This in vitro system will allow identification and physiological or immunohistochemical study of interactions between fetally derived and host brain neurons.