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Biomedical subjects

S R Winn

Publications and source records attributed to S R Winn.

52 records · Page 3Linked to original sources
PubMed1990

Polymer encapsulated dopaminergic cell lines as "alternative neural grafts".

Our preliminary findings (Jaeger et al., 1988; Aebischer et al., 1989; Tresco et al., 1989) and the studies in progress show that encapsulated dopaminergic cell lines survive enclosure within a semi-permeable membrane. The encapsulated cells remained viable for extended time periods when maintained in vitro. Moreover, encapsulated PC12 and T28 cells have the potential to survive following their implantation into the forebrain of rats. Cell lines are essentially "immortal" because they continue to divide indefinitely. This property allows perpetual "self-renewal" of a given cell population. However, the capacity of continuous uncontrolled cell division may also lead to tumor formation. This in fact is the case for unencapsulated PC12 cell implants placed into the brain of young Sprague Dawley rats (Jaeger, 1985). Cell line encapsulation has the potential to prevent tumor growth (Jaeger et al., 1988). Survival for 6 months in vitro suggests that encapsulation does not preclude long-term maintenance of an homogeneous cell line like PC12 cells. The presence of mitotic figures in the capsules further supports the likelihood of propagation and self renewal of the encapsulated population. Another significant property of cell lines is that they consist of a single, genetically homogeneous cell type. They do not require specific synaptic interactions for their survival. In the case of PC12 and T28 lines, the cells synthesize and release neurotransmitters. Our data show that PC12 and T28 cells continue to release dopamine spontaneously and to express specific transmitters and enzymes following encapsulation. Thus, cell lines such as these may constitute relatively simple "neural implants" exerting their function via humoral release.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Gland Neoplasms↗
PubMed1989

Brain tissue reaction to permselective polymer capsules.

The brain tissue reaction to permselective polymer capsules implanted in rats was evaluated for 1 to 54 weeks. The polymer capsules were well tolerated in all animals and no recognizable neurological or behavioral deficits were associated with the implants. Necrosis at the brain/polymer interface, as assessed with Nissl stain, was not observed. Foreign body giant cells were consistently absent. Immunocytochemically identified reactive neuroglial cells showed a remarkably low-grade tissue response to the synthetic material beyond the first 2 weeks of observation. Immunolabeled cortical neurons revealed conserved columnar arrays around the implants. Transmission electron microscopy showed a minimal degree of collagen deposition compared to implants in peripheral sites, and normal synapses within a few micrometers from the brain/polymer interface, supporting the prospect of biocompatible, immunoisolated xenografts in the central nervous system.

Acrylic Resins↗
PubMed1989

Basic fibroblast growth factor released from synthetic guidance channels facilitates peripheral nerve regeneration across long nerve gaps.

Basic fibroblast growth factor (b-FGF) has been shown to enhance the in vitro survival and neurite extension of various types of neurons including dorsal root ganglia (DRG) cells. Alpha-1 glycoprotein (alpha 1-GP), an acute phase reactant, has been reported to enhance the in vitro neuritic extensions of chick DRG cells. In the present study, we investigated the ability of synthetic nerve guidance channels, which release sustained controlled amounts of b-FGF and/or alpha 1-GP, to support the regeneration of a transected peripheral nerve over a 15 mm long gap, a distance that does not permit regeneration in conventional polymeric tubes. Tubes releasing bovine serum albumin (BSA), cytochrome C, BSA and b-FGF, BSA and denatured b-FGF, BSA and alpha 1-GP, or BSA, b-FGF, and alpha 1-GP were fabricated by a dip-molding technique. In vitro kinetic studies of protein release from these channels showed an initial burst during the 1st day, followed by a linear release for at least 2 weeks thereafter. In vitro studies indicated that the b-FGF released from the polymer was biologically active as assessed by the ability of channels releasing b-FGF to induce neurite extensions in PC12 cells. For in vivo studies, the various types of tubes were used as nerve guidance channels for the repair of a 15 mm nerve gap in the sciatic nerve of rats. Four weeks postimplantation, only the tubes releasing b-FGF or b-FGF and alpha 1-GP displayed regenerated cables bridging both nerve stumps, which contained nerve fascicles with myelinated and unmyelinated axons.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

An encapsulated dopamine-releasing polymer alleviates experimental parkinsonism in rats.

The effect of sustained intrastriatal release of dopamine (DA) from polymer matrices on apomorphine-induced turning behavior in a 6-hydroxydopamine (6-OHDA) unilaterally lesioned rat model was analyzed. A biocompatible semipermeable tube was placed in a denervated striatum as a receptacle for DA-releasing polymer rods. In vitro kinetics showed sustained release of DA from a polymeric rod for 15 days. Implantation of a DA-releasing rod within the striatal receptacle significantly decreased apomorphine-induced rotational behaviour in lesioned animals. Upon removal of the DA-releasing system from the receptacle, rotational behaviour increased within 2 weeks and approached preimplant control values 4 weeks later. Acute microdialysis revealed that DA appeared in the extracellular space within 20 min after the implantation of a DA-releasing rod into a denervated striatum. Significant DA amounts were still measurable 7 days postimplantation, indicating sustained DA release from the polymer rod. Dopamine released from a polymer matrix through a semipermeable receptacle alleviates experimental parkinsonism in rats, suggesting that controlled intrastriatal release of DA from a polymer matrix may provide an alternative method for the treatment of Parkinson's disease.

Acrylic Resins↗
PubMed1988

Blind-ended semipermeable guidance channels support peripheral nerve regeneration in the absence of a distal nerve stump.

The presence of a distal nerve segment is considered to be essential for peripheral nerve regeneration through impermeable synthetic guidance channels. The use of a perm-selective material may provide a more appropriate regenerating environment by allowing solute exchange across the wall of the channel. We compared perm-selective acrylic copolymer (AC) channels with impermeable silicone elastomer (SE) channels in terms of regeneration in the absence of a distal nerve stump. Cohorts of 6 animals received AC and SE channels for either 4 or 8 weeks, with the distal end of the polymer tube left open in half of the animals, and plugged with the same polymer ('capped') in the other half. Capped and uncapped AC channels contained regenerated nerve cables which extended fully to the distal end of the channel, whereas capped SE channels contained only 1 mm long granulomatous tissue cables, and uncapped SE channels showed small cables with only a few myelinated axons. The nerve cables regenerated in uncapped AC channels were smaller and contained fewer myelinated axons than those observed in capped AC channels. Capped AC channels sleeved with a tight-fitting silicone tube to render them impermeable, showed no regenerated tissue within their lumen. The use of a perm-selective channel may have allowed the influx of nutrients and growth factors from the external environment while concentrating factors released by the proximal nerve stump.

Acrylic Resins↗
PubMed1988

Transplantation of neural tissue in polymer capsules.

Neural tissue reaction to permselective polymer capsules and the feasibility of encapsulated neural tissue transplantation were evaluated in a rat model for a period of 1-12 weeks. Polymer implants in the central nervous system were generally well tolerated. The brain reaction to the synthetic material was minimal and did not disturb normal brain architectonics. Embryonic mouse mesencephalon enclosed in a polymer capsule remained morphologically intact for at least 12 weeks in the parietal cortex of rats. We conclude that the immunoprotection provided by a permselective polymer membrane encapsulating neural tissue is compatible with diffusional exchange of nutrients and metabolites. Polymer encapsulation may provide an alternative for the problem of immunorejection in transplantation of neural tissues.

Animals↗
PubMed1987

Collagen- and laminin-containing gels impede peripheral nerve regeneration through semipermeable nerve guidance channels.

Semipermeable guidance channels were filled with saline, collagen-, or laminin-containing gels and used to repair a 4-mm sciatic nerve gap in mice. After 12 weeks, nerve cables regenerated in gel-filled channels displayed fewer myelinated axons than saline-filled channels. Remnants of the exogenous substrates were still in evidence, in amounts related to the initial collagen or laminin gel concentration. The impairment of nerve regeneration by collagen or laminin-containing gels suggests that the regenerative environment created within semipermeable channels is not improved by the addition of growth substrates in a gel form.

Animals↗
PubMedDate not supplied

Microencapsulated bovine chromaffin cells in vitro: effect of density and coseeding with a NGF-releasing cell line.

Immobilization of discrete cell clusters within a partially crosslinked matrix prevents reaggregation of primary tissues and may provide a means for long-term maintenance of encapsulated cells. Dissociated bovine adrenal chromaffin (BAC) cells were suspended throughout crosslinked polyanionic microspheres previously shown to be selectively permeable. Microcapsules approximately 500 microns in diameter were seeded with: 1) three different densities of BAC cells; and 2) BAC cells suspended in Matrigel or coseeded with a genetically modified nerve growth factor (NGF)-releasing fibroblast cell line. Each group was analyzed in vitro at 1, 4 and 8 weeks for spontaneous and potassium-evoked release of catecholamines, and maintained in vitro for up to 12 weeks for morphological observations. Over time, release of norepinephrine (NE) and epinephrine (EPI) diminished, while dopamine (DA) remained constant from the monoseeded capsules. In the coseeded group, an increase in potassium-evoked release of DA was observed from 1 to 4 weeks, and remained at that level up to 8 weeks. Encapsulated chromaffin cells retained a rounded morphology typical of undifferentiated cells. Intact chromaffin cells with well preserved and abundant secretory granules were observed ultrastructurally after 4 weeks in vitro. Small neurites from the chromaffin cells in the coseeded group were observed at 4 weeks with light microscopy, and up to 12 weeks with electron microscopy. Under static incubation conditions, 1 mM D-amphetamine resulted in a significant increase in the output of NE and DA from the coseeded capsules 8 weeks post-implantation, as compared to microcapsules loaded with chromaffin cells alone. Encapsulation within an immobilization matrix allows manipulation of the internal environment, thereby providing the ability to pre-treat cells with various factors in a non-invasive manner, which may enhance long-term cellular viability.

Animals↗
PubMedDate not supplied

Polymer-encapsulated Schwannoma cells expressing human nerve growth factor promote the survival of cholinergic neurons after a fimbria-fornix transection.

Many investigators have recently used genetically modified primary fibroblasts of fibroblast cell lines (e.g., 3T3, 208F, or BHK cells) to deliver recombinant nerve growth factor (NGF) into the CNS. In the current study, SCT-1 cells, a Schwannoma cell line derived from a transgenic mouse, were transfected with a human NGF (hNGF) cDNA. After selection, these cells were encased within a polymer capsule and implanted into the ventricles of fimbria-fornix lesioned rats. Encapsulated, non-transfected cells served as controls. Results demonstrated that the hNGF transgene is expressed for at least 3 weeks after implantation. Moreover, the cells did not overgrow the capsule. Recombinant hNGF was able to save > 70% of lesioned cholinergic neurons, as assessed by NGF-receptor (NGFr) and choline acetyltransferase (ChAT) immunohistochemistry, from cell death. The number of cholinergic neurons in animals that received control capsules (i.e., nontransfected SCT-1 cells) was similar to lesion only animals (i.e., approximately 27% and approximately 33% for NGFr- and ChAT-positive neurons, respectively. These results show that SCT-1 cells can be used to deliver biologically active hNGF into the lesioned rat brain.

Animals↗
PubMedDate not supplied

Effects of intraventricular encapsulated hNGF-secreting fibroblasts in aged rats.

Exogenous NGF administered into the central nervous system (CNS) has been reported to improve cognitive function in aged rats. However, concerns have been expressed about the risks involved with supplying NGF to the CNS. In this study, baby hamster kidney cells (BHK) genetically modified to secrete human NGF (hNGF) were encapsulated in semipermeable membranes and implanted intraventricularly. ChAT/LNGFR-positive basal forebrain neurons were shown to atrophy and degenerate with age, especially in cognitively impaired rats. The encapsulated BHK-NGF cells produced less than 10% of doses previously reported to be effective, but this was sufficient to increase the size of ChAT/LNGFR-positive basal forebrain neurons in the aged and learning-impaired rats to the size of the neurons in young healthy rats. The hNGF from these encapsulated cells also improved performance in a repeated-acquisition version of the Morris water maze spatial learning task in learning-impaired 20.6- and 26.7-mo-old rats. Furthermore, there was no evidence that these doses of hNGF impaired Morris water maze performance in the youngest 3.3-5.4 mo rats, and analyses of mortality rates, body weights, somatosensory thresholds, potential hyperalgesia, and activity levels, suggested that these levels of exogenous hNGF are not toxic or harmful to aged rats. These results suggest that CNS-implanted semipermeable membranes, containing genetically modified xenogeneic cells continuously producing these levels of hNGF, attenuate age-related cognitive deficits in nonimmunosuppressed aged rats, and that both the surgical implantation procedure and long-term exposure to low doses of hNGF appear safe in aged rats.

Aging↗
PubMedDate not supplied

Continued presence of intrastriatal but not intraventricular polymer-encapsulated PC12 cells is required for alleviation of behavioral deficits in Parkinsonian rodents.

To date, few studies have systematically evaluated the most appropriate location for grafting catecholaminergic cells as a potential treatment for Parkinson's disease (PD). The following study was conducted to determine 1) if placement of catecholamine-secreting encapsulated PC12 cells into the lateral ventricle of 6-OHDA-treated rats is as effective as intrastriatal implants on reducing apomorphine-induced rotational behavior, and 2) to determine if the survival of encapsulated PC12 cells is differentially affected by the implant site. Polymerencapsulated PC12 cells were implanted into either the striatum or lateral ventricle of unilateral 6-OHDA-lesioned rats. Animals were tested for apomorphine-induced rotations over a 6-wk period. Only those animals that received intrastriatal implants of encapsulated PC12 cells showed a reduction in rotation behavior. Moreover, removal of the devices from the striatum resulted in a return to preimplant rotation levels. Postexplant neurochemical analyses demonstrated that the potassium-evoked L-dopa device output increased in vivo while the potassium-evoked dopamine output from the devices decreased over time in vivo. The location of the implant significantly affected catecholamine output from the PC12 cell-loaded devices. The increase in potassium-evoked L-dopa output was greatest, as was the decrease in potassium-evoked dopamine output, from those devices implanted in the striatum. Basal output of dopamine and DOPAC was also significantly higher from devices explanted from the lateral ventricle. These results demonstrate that the continued presence of intrastriatal implants of encapsulated PC12 cells is required to maintain the behavioral effects in 6-OHDA-lesioned rats. In addition, the site of implantation appears to affect device output. These results provide additional support for intraparenchymal delivery of L-dopa and dopamine via polymer encapsulation as a possible treatment for PD.

Animals↗
PubMedDate not supplied

Polymer-encapsulated PC-12 cells demonstrate high-affinity uptake of dopamine in vitro and 18F-Dopa uptake and metabolism after intracerebral implantation in nonhuman primates.

Intracranial implantation of polymer-encapsulated PC-12 cells has been shown to improve motor behavioral performance in animal models of Parkinson's disease. The purpose of this blinded study was to examine whether such improvement is associated with the active uptake and metabolism of dopamine precursors by intracerebrally implanted polymer-encapsulated PC-12 cells. In an in vitro experiment we demonstrate that 3H-dopamine uptake by PC-12 cells was 10(8) fmol/min x 10(6) cells, and that this uptake can be specifically blocked 88% by the addition of 10nM of nomifensine. In the in vivo experiments, polymer-encapsulated PC-12 cells were implanted in four MPTP-treated monkeys into the left deep parietal white matter (R1) or left striatum (R2-4). A fifth MPTP-treated monkey (R5) served as a control and received left striatal implants of empty capsules. 18-F-Dopa Positron Emission Tomography (PET) imaging was performed on each monkey before and after implantation surgery by blinded investigators. PET images obtained 5-13 wk after implantation demonstrated well delineated focal areas of high 18F-dopa uptake in R1, R2, and R4. The focal area of high 18F-dopa uptake in R1 precisely coregistered on a brain magnetic resonance image to the site of implantation. R3 (in whom the polymer-encapsulated PC-12 cells demonstrated poor cell survival upon explantation) and R5 (empty capsules) failed to demonstrate any area of increased 18F-dopa uptake in their PET images. Histological examination of the host brain revealed no sprouting of dopaminergic nerve terminals around the implantation sites of the polymer-encapsulated PC-12 cells. These results indicate that the previously noted behavioral improvement after intrastriatal implantation of polymer encapsulated PC-12 cells is at least in part due to their highly specific uptake and metabolism of dopamine precursors. Furthermore, these data suggest that polymer-encapsulated PC-12 cells can store, reuptake, and functionally replenish dopamine and therefore, may be an effective treatment for Parkinson's disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMedDate not supplied

Polymer encapsulated neurotransmitter secreting cells. Potential treatment for Parkinson's disease.

Parkinson's disease, a neurologic disorder characterized by a dopamine deficit within the striatum, may be improved by transplantation of polymer encapsulated neurosecretory cells. Surrounding cells with a selectively permeable barrier offers several advantages, including preventing immune rejection and tumor formation while allowing functional efficacy. Bovine adrenal medullary chromaffin cells, or PC12 cells, a rat-derived pheochromocytoma cell line, were encapsulated within polyelectrolyte-based microcapsules or thermoplastic-based macrocapsules. Histologic and biochemical analyses revealed that both types of cells survived and that neurotransmitter release from capsules was sustained for several months in vitro, irrespective of the encapsulation method employed. Both of the encapsulation systems protected the enclosed cells from an immunologic challenge in vitro, and prevented immune rejection when cell containing capsules were implanted in an immunologically incompatible host. Chromaffin or PC12 cell containing capsules implanted into the dopamine (DA) depleted striatum of rats reduced the lesion associated functional deficit. These results suggest that encapsulated neurosecretory cell implants may be useful in treating various central nervous system (CNS) deficits, particularly in cases involving a specific neurochemical lesion.

Adrenal Medulla↗