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Alloantigen-specific immunosuppression in nerve allograft regeneration
P 70
Otolaryngology Head and Neck Surgery
Scientific Sessions- - Monday
8:30 AM
Ischemic Neuropraxla: Preservation of Neural Function by DFMO and Blockade of Preservation by Exogenous Putrescine ALBERTO D. FERNANDEZ, MD (presenter), NEWTON J, COKER, MD, and CHARLES M. HENLEY, PhD, Houston, Tex.
Several studies have implicated a role for the polyamines in mediating ischemic injury in the central nervous system, peripheral nerves, and in other tissues, ot-Difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase and putrescine biosynthesis, has been shown to reduce the size of cortical infarcts resulting from ischemia. The purpose of this study was to determine if DFMO preserves function in neuropraxic facial nerves and if the neuroprotective effects could be reversed by exogenously administered putrescine. New Zealand rabbits (n = 60) were assigned to three groups: group I, DFMO or saline solution; group II, DFMO and putrescine or saline solution and putrescine; and group III, sham-operated. Groups I and II were treated with saline solution, DFMO, and/or putrescine 1 hour before surgery. An ischemic compressive injury of the facial nerve was induced with a balloon-clamp apparatus for 4 hours at 80 mm Hg. Electroneuronography specifically evaluating the myogenic compound action potential (MCAP) was used to gauge the neuropraxic status of the nerve preoperatively, after dissection, compression, and 4 and 12 hours after clamp removal (reperfusion). MCAP amplitudes decreased significantly in animals treated with saline solution immediately following 4 hours of ischemic compression injury and remained depressed up to 12 hours after reperfusion. In contrast, MCAPs did not significantly decrease in the group treated with DFMO. The neuroprotective effects of DFMO on facial nerve function was reversed by systemic administration of putrescine (8 mg/kg SC), suggesting that polyamine metabolism may play an integral role in mediating neural damage caused by ischemic injury. DFMO may ultimately serve as a means of ameliorating nerve palsy related to edema secondary to infection, trauma or surgical intervention.
August 1996
2 around a femoral vascular pedicle in a rat. The significance of the vascular pedicle, marrow cells, and BMP-2 in the prefabrication of these grafts is also investigated. Material and methods: Five by seven millimeter cylindrical silastic chambers were implanted in the medial thigh of 48 male Lewis rats. The femoral vascular pedicle was mobilized and placed as a flow-through pedicle within the silastic chambers. Bone marrow was harvested from 50 syngeneic Lewis rats, and 1 x 108 cells were placed in each chamber. Twenty micrograms of rhBMP-2 were also placed in the chamber. Forty-eight animals were divided into four groups. Group 1 contained marrow cells and BMP only; group 2 contained marrow cells and vascular pedicle only; group 3 contained BMP and vascular pedicle only; and group 4 contained marrow cells, BMP, and vascular pedicle. Animals in each group were killed at 2, 4, and 6 weeks. The chamber contents were examined and vascular pedicle checked for patency. The contents were processed and 5 micron sections were stained with von Kossa's mineral stain, Goldner's Trichrome, and hematoxylin and eosin for histologic analysis. Results: Chambers with BMP and vascular pedicle only (group 3) did not produce any bone. Chambers containing marrow cells and vascular pedicle formed minimal bone at the periphery and only at 6 weeks (group 2). The chambers with marrow cells, BMP, and vascular pedicle (group 4) formed copious osteoid and woven bone as early as 2 weeks. At 4 weeks, woven and lamellar bone extended to the periphery of the chamber and the graft assumed a precise shape. At 6 weeks, central islands of bone had substantially reabsorbed and only thin lamellar bone remained in the periphery. Conclusions: We have demonstrated that vascularized bone grafts can be prefabricated in very precise shapes using rhBMP-2, marrow osteoprogenitor cells, and a femoral vascular pedicle. Early woven bone formation was seen at 2 weeks time. Remodeling to lamellar bone was completed by 4 weeks. Central resorption of the vascularized bone graft may be due to a lack of mechanical stress during its formation. The role of osteoprogenitor cells and BMP in bone graft formation is discussed. 9:00 AM
8:45 AM
Transmural Heparln to Prevent Mlcrovascular Thrombosis
Prefabrication of Vascularlzed Bone Grafts Using Bone Morphogenetlc Protein and Marrow Osteoprogenltor
LISA A. ORLOFF, MD (presenter), VINEETA PRASAD, BA, ABRAHAM J, DOMB, PhD, and D, EUGENE STRANDNESS, Jr., MD, San Diego, Calif., Jerusalem, Israel, and Seattle, Wash.
Cells JOHN I. SONG, MD (presenter), THOMAS C. CALCATERRA, MD, and NElL FORD JONES, MD, Los Angeles, Calif.
Introduction: The use of vascularized bone grafts in maxillofacial and mandibular reconstruction has greatly expanded reconstructive options. Vascularized fibular and lilac crest bone grafts are the most widely used. A prefabricated vascularized bone graft would allow precise shaping of grafts to fit specific defects and obviate the need for any donor site dissection. The purpose of this study was to fabricate a vascularized bone graft from osteoprogenitor cells and BMP-
Prevention of anastomotic complications is the most important determinant of success in microvascular surgery. Vascular thrombosis is the most significant complication, with catastrophic results that include total flap or tissue necrosis from ischemia or congestion. Thrombosis accounts for up to 20% of m i c r o v a s c u l a r anastomotic failures. An ideal antithrombotic system has yet to be identified. We have developed a promising form of antithrombotic therapy and prophylaxis in the form of controlled release of heparin by transmural delivery from a biodegradable polymer. We have
Otolaryngology Head and Neck Surgery
Scientific Sessions- - Monday
8:30 AM
Ischemic Neuropraxla: Preservation of Neural Function by DFMO and Blockade of Preservation by Exogenous Putrescine ALBERTO D. FERNANDEZ, MD (presenter), NEWTON J, COKER, MD, and CHARLES M. HENLEY, PhD, Houston, Tex.
Several studies have implicated a role for the polyamines in mediating ischemic injury in the central nervous system, peripheral nerves, and in other tissues, ot-Difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase and putrescine biosynthesis, has been shown to reduce the size of cortical infarcts resulting from ischemia. The purpose of this study was to determine if DFMO preserves function in neuropraxic facial nerves and if the neuroprotective effects could be reversed by exogenously administered putrescine. New Zealand rabbits (n = 60) were assigned to three groups: group I, DFMO or saline solution; group II, DFMO and putrescine or saline solution and putrescine; and group III, sham-operated. Groups I and II were treated with saline solution, DFMO, and/or putrescine 1 hour before surgery. An ischemic compressive injury of the facial nerve was induced with a balloon-clamp apparatus for 4 hours at 80 mm Hg. Electroneuronography specifically evaluating the myogenic compound action potential (MCAP) was used to gauge the neuropraxic status of the nerve preoperatively, after dissection, compression, and 4 and 12 hours after clamp removal (reperfusion). MCAP amplitudes decreased significantly in animals treated with saline solution immediately following 4 hours of ischemic compression injury and remained depressed up to 12 hours after reperfusion. In contrast, MCAPs did not significantly decrease in the group treated with DFMO. The neuroprotective effects of DFMO on facial nerve function was reversed by systemic administration of putrescine (8 mg/kg SC), suggesting that polyamine metabolism may play an integral role in mediating neural damage caused by ischemic injury. DFMO may ultimately serve as a means of ameliorating nerve palsy related to edema secondary to infection, trauma or surgical intervention.
August 1996
2 around a femoral vascular pedicle in a rat. The significance of the vascular pedicle, marrow cells, and BMP-2 in the prefabrication of these grafts is also investigated. Material and methods: Five by seven millimeter cylindrical silastic chambers were implanted in the medial thigh of 48 male Lewis rats. The femoral vascular pedicle was mobilized and placed as a flow-through pedicle within the silastic chambers. Bone marrow was harvested from 50 syngeneic Lewis rats, and 1 x 108 cells were placed in each chamber. Twenty micrograms of rhBMP-2 were also placed in the chamber. Forty-eight animals were divided into four groups. Group 1 contained marrow cells and BMP only; group 2 contained marrow cells and vascular pedicle only; group 3 contained BMP and vascular pedicle only; and group 4 contained marrow cells, BMP, and vascular pedicle. Animals in each group were killed at 2, 4, and 6 weeks. The chamber contents were examined and vascular pedicle checked for patency. The contents were processed and 5 micron sections were stained with von Kossa's mineral stain, Goldner's Trichrome, and hematoxylin and eosin for histologic analysis. Results: Chambers with BMP and vascular pedicle only (group 3) did not produce any bone. Chambers containing marrow cells and vascular pedicle formed minimal bone at the periphery and only at 6 weeks (group 2). The chambers with marrow cells, BMP, and vascular pedicle (group 4) formed copious osteoid and woven bone as early as 2 weeks. At 4 weeks, woven and lamellar bone extended to the periphery of the chamber and the graft assumed a precise shape. At 6 weeks, central islands of bone had substantially reabsorbed and only thin lamellar bone remained in the periphery. Conclusions: We have demonstrated that vascularized bone grafts can be prefabricated in very precise shapes using rhBMP-2, marrow osteoprogenitor cells, and a femoral vascular pedicle. Early woven bone formation was seen at 2 weeks time. Remodeling to lamellar bone was completed by 4 weeks. Central resorption of the vascularized bone graft may be due to a lack of mechanical stress during its formation. The role of osteoprogenitor cells and BMP in bone graft formation is discussed. 9:00 AM
8:45 AM
Transmural Heparln to Prevent Mlcrovascular Thrombosis
Prefabrication of Vascularlzed Bone Grafts Using Bone Morphogenetlc Protein and Marrow Osteoprogenltor
LISA A. ORLOFF, MD (presenter), VINEETA PRASAD, BA, ABRAHAM J, DOMB, PhD, and D, EUGENE STRANDNESS, Jr., MD, San Diego, Calif., Jerusalem, Israel, and Seattle, Wash.
Cells JOHN I. SONG, MD (presenter), THOMAS C. CALCATERRA, MD, and NElL FORD JONES, MD, Los Angeles, Calif.
Introduction: The use of vascularized bone grafts in maxillofacial and mandibular reconstruction has greatly expanded reconstructive options. Vascularized fibular and lilac crest bone grafts are the most widely used. A prefabricated vascularized bone graft would allow precise shaping of grafts to fit specific defects and obviate the need for any donor site dissection. The purpose of this study was to fabricate a vascularized bone graft from osteoprogenitor cells and BMP-
Prevention of anastomotic complications is the most important determinant of success in microvascular surgery. Vascular thrombosis is the most significant complication, with catastrophic results that include total flap or tissue necrosis from ischemia or congestion. Thrombosis accounts for up to 20% of m i c r o v a s c u l a r anastomotic failures. An ideal antithrombotic system has yet to be identified. We have developed a promising form of antithrombotic therapy and prophylaxis in the form of controlled release of heparin by transmural delivery from a biodegradable polymer. We have