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Biomedical subjects

P Aebischer

Publications and source records attributed to P Aebischer.

At least 73 records · Page 4Linked to original sources
PubMed1998

Synergistic but transient rescue effects of BDNF and GDNF on axotomized neonatal motoneurons.

Brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF), members of distinct families of polypeptide growth factors, have been shown to support motoneurons under various in vitro and in vivo conditions. We used a model of motoneuron cell death induced by sciatic nerve section in newborn rats and compared the efficacy of BDNF and GDNF administered alone or simultaneously in order to determine whether combinations of neurotrophic proteins can produce more potent motoneuron rescue than individual factors. The factors were administered by different methods, including (i) a single dose on to the transected nerve, (ii) continuous delivery from implanted slow-release polymer rods (BDNF) or encapsulated cells (GDNF), and (iii) repeated systemic injections (BDNF). Irrespective of the method of administration, either factor alone produced rescue effects which dramatically declined at two weeks as compared to one week post-lesion. In contrast, this decrease was significantly reduced when BDNF and GDNF were used simultaneously provided that one factor was applied on to the nerve while the other was continuously released from the rods or capsules. Other combinations in which GDNF was replaced by ciliary neurotrophic factor or axokine-1 failed to reproduce such additive activity. Two conclusions can be made from these experiments. First, when BDNF and GDNF are administered simultaneously but by distinct routes of delivery, their survival-promoting effects on the injured developing motoneurons are potentiated; second, even continuous delivery of each of these trophic factors alone cannot completely abrogate the time-dependent decline in rescue effects in this model of motoneuron cell death.

Animals↗
PubMed1998

Continuous delivery of human and mouse erythropoietin in mice by genetically engineered polymer encapsulated myoblasts.

The transplantation of polymer encapsulated myoblasts genetically engineered to secrete erythropoietin (Epo) may obviate the need for repeated parenteral administration of recombinant Epo as a treatment for chronic renal failure, cancer or AIDS-associated anemia. To explore this possibility, the human and mouse Epo cDNAs under the control of the housekeeping mouse PGK-1 promoter were transfected into mouse C2C12 myoblasts, which can be terminally differentiated upon exposure to low serum-containing media. Pools releasing 150 IU human Epo per 10(6) cells per day and 390 IU mouse Epo per 10(6) cells per day were selected. Polyether-sulfone (PES) capsules loaded with approximately 200,000 transfected myoblasts from these pools were implanted on the dorsal flank of DBA/2J, C3H and C57BL/6 mice. With human Epo secreting capsules, only a transient increase in the hematocrit occurred in DBA/2J mice, whereas no significant response was detected in C3H or C57BL/6 mice. On the contrary, all mice implanted with capsules releasing mouse Epo increased their hematocrit over 85% as early as 7 days after implantation and sustained these levels for at least 80 days. All retrieved implants released Epo and contained well preserved myoblasts. Moreover most capsules were surrounded by a neovascularization. Mice transplanted with nonencapsulated C2C12 cells releasing mouse Epo showed only a transitory elevation of their hematocrit reflecting the poor engraftment of injected myoblasts. These results indicate that polymer encapsulation of genetically engineered myoblasts is a promising approach for the long-term delivery of bioactive molecules, allowing the resolution of the shortcomings of free myoblast transfer.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Attenuation of 6-OHDA-induced neurotoxicity in glutathione peroxidase transgenic mice.

Normal cellular metabolism produces oxidants which are neutralized within cells by antioxidant enzymes and other antioxidants. An imbalance between oxidants and antioxidants has been postulated to lead to the degeneration of specific populations of neurons in neurodegenerative diseases, e.g. Parkinson's disease. The present study investigates whether overexpression of glutathione peroxidase, the enzyme which metabolizes hydrogen peroxide to water, can prevent or slow down neuronal injury in an animal model of Parkinson's disease. Transgenic mice overexpressing the human glutathione peroxidase gene under the control of the mouse hydroxymethylglutaryl-coenzyme A promoter and genetically matched control mice were injected intracerebroventricularly with the dopaminergic neurotoxin 6-hydroxydopamine. Seven days after injection, the number of tyrosine hydroxylase-positive nigral dopaminergic neurons was decreased by 52.4% and 20.5% in 6-hydroxydopamine-injected control and glutathione peroxidase transgenic mice, respectively. Similarly, 3 days after injection of the neurotoxin, striatal dopamine was decreased by 71.2% and 56.5%, respectively. Overexpression of glutathione peroxidase therefore partially protects dopaminergic neurons against 6-hydroxydopamine-induced toxicity.

Acyl Coenzyme A↗
PubMed1997

A gene therapy approach to regulated delivery of erythropoietin as a function of oxygen tension.

Current therapy for several forms of anemia involves a weekly regime of multiple subcutaneous injections of recombinant human erythropoietin (hEpo). In an effort to provide a physiologically regulated administration of erythropoietin, we are developing cell lines genetically engineered to release hEpo as a function of oxygen tension. C2C12 cells were transfected using a vector containing the hEpo cDNA driven by the hypoxia-responsive promoter to the murine phosphoglycerate kinase gene. In vitro, these cells showed a threefold increase in hEpo secretion as oxygen levels were shifted from 21% to 1.3% oxygen. To test in vivo response, C2C12-hEpo cells were encapsulated in a microporous membrane and implanted subcutaneously on the dorsal flank of DBA/2J mice. On average, serum hEpo levels in animals exposed to 7% oxygen were two-fold higher than values seen in their control counterparts kept at 21% oxygen. Similar studies employing rats confirmed that hEpo delivery is regulated as a function of oxygen tension. These results suggest the feasibility of developing an oxygen-regulated, encapsulated cell-based system for hEpo delivery.

Anemia↗
PubMed1997

GDNF reduces drug-induced rotational behavior after medial forebrain bundle transection by a mechanism not involving striatal dopamine.

Parkinson's disease (PD) is characterized by the progressive loss of the substantia nigra (SN) dopaminergic neurons projecting to the striatum. Neurotrophic factors may have the potential to prevent or slow down the degenerative process occurring in PD. To that end, we examined whether low amounts of glial cell line-derived neurotrophic factor (GDNF) continuously released from polymer-encapsulated genetically engineered cells are able to prevent the loss of tyrosine hydroxylase immunoreactivity (TH-IR) in SN neurons and ameliorate the amphetamine-induced rotational asymmetry in rats that have been subjected to a unilateral medial forebrain bundle (MFB) axotomy. Baby hamster kidney (BHK) cells transfected with the cDNA for GDNF were encapsulated in a polymer fiber and implanted unilaterally at a location lateral to the MFB and rostral to the SN. ELISA assays before implantation show that the capsules release approximately 5 ng of GDNF/capsule per day. One week later, the MFB was axotomized unilaterally ipsilateral to the capsule placement. Seven days later, the animals were tested for amphetamine-induced rotational asymmetry and killed. The striatum was excised and analyzed either for catecholamine content or TH-IR, while the SN was immunostained for the presence of TH-IR. GDNF did not prevent the loss of dopamine in the striatum. However, GDNF significantly rescued TH-IR neurons in the SN pars compacta. Furthermore, GDNF also significantly reduced the number of turns per minute ipsilateral to the lesion under the influence of amphetamine. Improvement of rotational behavior in the absence of dopaminergic striatal reinnervation may reflect neuronal plasticity in the SN, as suggested by the dendritic sprouting observed in animals receiving GDNF. These results illustrate that the continuous release of low levels of GDNF close to the SN is capable of protecting the nigral dopaminergic neurons from an axotomy-induced lesion and significantly improving pharmacological rotational behavior by a mechanism other than dopaminergic striatal reinnervation.

Animals↗
PubMed1997

Transplant of polymer-encapsulated cells genetically engineered to release nerve growth factor allows a normal functional development of the visual cortex in dark-reared rats.

Visual experience is necessary for the normal development of the visual system. Dark-reared mammals show abnormal vision when reintroduced into a normal environment. The absence of visual experience during the critical period results in reduced and/or inappropriate neural responses in visual cortical neurons. The change in electrical activity induced by dark rearing is probably reflected by the modulation of specific unknown molecules. Neurotrophins are present in the developing visual cortex and their production depends on visually driven electrical activity. Recent findings support the possibility that an important link between electrical activity in the visual pathway and correct development of visual properties is represented by neurotrophins. We advance the hypothesis that the visual abnormalities present in dark-reared animals could be due to a decreased production of a neurotrophin secondary to the lack of visual stimulation. We report that some properties of visual cortical response such as receptive field size, orientation selectivity, adaptation to repeated stimulation, response latency and visual acuity are virtually normal in dark-reared rats transplanted with polymer-encapsulated baby hamster kidney cells genetically engineered to release nerve growth factor.

Adaptation, Ocular↗
PubMed1997

The copper chelator d-penicillamine delays onset of disease and extends survival in a transgenic mouse model of familial amyotrophic lateral sclerosis.

A subpopulation of familial cases of amyotrophic lateral sclerosis has been linked to mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). There is in vitro evidence that certain SOD1 mutants, in addition to their normal dismutation function, show increased ability of the enzyme to act as a peroxidase. This reaction is sensitive to inhibition by copper chelators. To test this hypothesis in vivo, we administered the copper chelator d-penicillamine to a transgenic mouse model of familial amyotrophic lateral sclerosis overexpressing a mutated form of human SOD1. We demonstrate that oral administration of d-penicillamine is able to delay the onset of the disease and extend the survival of these mice. Histological studies also showed a decreased loss of facial motor neurons in d-penicillamine-treated transgenic mice, corroborating the slower evolution of the disease in these animals. These results suggest that copper chelators may benefit patients with familial amyotrophic lateral sclerosis linked to mutations in the SOD1 gene.

Amyotrophic Lateral Sclerosis↗
PubMed1997

Neuronal GDNF expression in the adult rat nervous system identified by in situ hybridization.

Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor which has been purified on the basis of its ability to promote the survival of dopaminergic neurons in vitro. GDNF has subsequently been cloned and its sequence shown to be distantly related to transforming growth factor-beta (TGF-beta). To identify GDNF expressing cells in the adult rat brain, in situ hybridization using a digoxygenin (DIG)-labelled riboprobe has been performed. Our results show that GDNF mRNA is mainly expressed in neurons and that its synthesis is not restricted to dopaminergic areas. It is widely expressed in the cortex, the hippocampus, the striatum, the substantia nigra, the thalamus, the cerebellum and the spinal cord. Neuronal GDNF expression varies among brain regions as determined by the intensity of the in situ signal. Double labelling of the substantia nigra using tyrosine hydroxylase immunohistochemistry, associated with GDNF in situ hybridization, show that the majority of dopaminergic neurons express GDNF. The widespread expression of GDNF throughout the adult brain suggests that its administration in Parkinson's disease should be restricted to the altered structures, in order to avoid possible deleterious side effects.

Animals↗
PubMed1996

Central nervous system delivery of recombinant ciliary neurotrophic factor by polymer encapsulated differentiated C2C12 myoblasts.

Neurotrophic factors hold promise for the treatment of neurodegenerative diseases. Intrathecal transplantation of polymer encapsulated cell lines genetically engineered to release neurotrophic factors provides a means to deliver them continuously behind the blood-brain barrier. Long-term delivery, however, may benefit from the use of conditionally mitotic cells to avoid the overgrowth observed with continuously dividing cell lines. Myoblast lines have all the advantages of dividing cell lines, i.e., unlimited availability, possibility for in vitro screening for the presence of pathogens, suitability for stable gene transfer and clonal selection. Furthermore they can be differentiated into a nonmitotic stage upon exposure to low-serum-containing medium. In this study, mouse C2C12 myoblasts were transfected with a pNUT expression vector containing the human ciliary neurotrophic factor (CNTF) gene. hCNTF expression and bioactivity were demonstrated by Northern blot, ELISA assay, and measurement of choline acetyltransferase (ChAT) activity in embryonic spinal cord motor neuron cultures. One C2C12 clone was found to secrete 200 ng of CNTF/10(6) cells per day. The rate of secretion of hCNTF was not altered upon differentiation of C2C12 myoblasts. A bromodeoxyuridine (BrdU) proliferation assay indicated that approximately 12% of the myoblasts continue to divide after 4 days in low-serum-containing medium. The presence of the herpes simplex thymidine kinase gene (HSV-tk) in the expression vector, however, provides a way to eliminate these dividing myoblasts upon exposure to ganciclovir, therefore increasing the safety of the encapsulation technology using established cell lines. Encapsulated hCNTF-C2C12 cells can partially rescue motor neurons from axotomy-induced cell death. In adult rats, intrathecal implantation of encapsulated hCNTF-C2C12 cells or control C2C12 confirmed the long-term survival of these cells and their potential use as a source of neurotophic factors for the treatment of neurodegenerative diseases.

Animals↗
PubMed1996

Gene therapy for amyotrophic lateral sclerosis (ALS) using a polymer encapsulated xenogenic cell line engineered to secrete hCNTF.

The gene therapy approach presented in this protocol employs a polymer encapsulated, xenogenic, transfected cell line to release human ciliary neurotrophic factor (hCNTF) for the treatment of Amyotrophic Lateral Sclerosis (ALS). A tethered device, containing around 10(6) genetically modified cells surrounded by a semipermeable membrane, is implanted intrathecally; it provides for slow continuous release of hCNTF at a rate of 0.25 to 1.0 micrograms/24 hours. The semipermeable membrane prevents immunologic rejection of the cells and interposes a physical, virally impermeable barrier between cells and host. Moreover, the device and the cells it contains may be retrieved in the event of side effects. A vector containing the human CNTF gene was transfected into a line of baby hamster kidney cells (BHK) with calcium phosphate using a dihydrofolate reductase-based selection vector with a SV40 promoter and contains a HSV-tk killer gene. hCNTF is a potent neurotrophic factor which may have utility for the treatment of ALS. Systemic delivery of hCNTF in humans has been frustrated by peripheral side effects, the molecule's short half life, and its inability to cross the blood-brain barrier. The gene therapy approach described in this protocol is expected to mitigate such difficulties by local intrathecal delivery of a known quantity of continuously-synthesized hCNTF from a retrievable implant.

Amyotrophic Lateral Sclerosis↗
PubMed1996

Combined effects of GDNF, BDNF, and CNTF on motoneuron differentiation in vitro.

We have previously shown that glial cell line-derived neurotrophic factor (GDNF), in addition to promoting the survival of dopaminergic neurons in cultures from embryonic rat ventral mesencephalon,also increases the activity of choline acetyltransferase (ChAT) in the cranial motoneurons present in these cultures (Zurn et al.: Neuroreport 6:113-118, 1994). By using the intermediate filament protein peripherin as a motoneuron marker, we report here that GDNF increases the number of motoneurons as well as the length of their neurites. Brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor (CNTF) also promote ChAT activity, motoneuron survival, and neurite outgrowth in these cultures, but to varying degrees. Although these three molecules have similar effects on cultured motoneurons, we provide evidence for a distinct mode of action of GDNF, BDNF, and CNTF, since combinations of GDNF and BDNF, GDNF and CNTF, and BDNF and CNTF have either additive or synergistic effects on ChAT activity and motoneuron number. In addition to the previously described motoneuron-specific neurotrophic factors BDNF and CNTF, GDNF combined with the latter two factors may provide an important tool for the treatment of human motoneuron diseases such as amyotrophic lateral sclerosis and spinal muscular atrophy, both by increasing efficiency of treatment, and by decreasing the likelihood of deleterious side-effects.

Animals↗
PubMed1996

GDNF slows loss of motoneurons but not axonal degeneration or premature death of pmn/pmn mice.

Glial cell line-derived neurotrophic factor (GDNF), a member of the TG F-beta superfamily, has been shown to be a highly potent neurotrophic factor that enhances survival of various neuronal cell types including motoneurons. To assess its therapeutic potential in treating neurodegenerative diseases such as amyotrophic lateral sclerosis, we treated mutant mice displaying motoneuron degeneration (progressive motor neuropathy; pmn) with encapsulated GDNF-secreting cells. Effects of GDNF treatment on pmn/pmn mice were compared with previous results obtained with ciliary neurotrophic factor (CNTF) [Sagot Y, Tan SA, Baetge E, Schmalbruch H, Kato AC, Aebischer P (1995) Eur J Neurosci 7:1313-1322]. In contrast to CNTF, GDNF did not increase the lifespan of pmn/pmn mice. However, GDNF significantly reduced the loss of facial motoneurons by 50%, a value similar to what was observed when CNTF was administered to the pmn/pmn mice. Surprisingly, myelinated axon counts revealed that GDNF had no effect on nerve degeneration. Therefore, despite its potential in rescuing motoneuron cell bodies, the inability of GDNF to prevent nerve degeneration in pmn/pmn mice suggests that its usefulness in the treatment of motor neuron diseases may be restricted to cotreatment with other factors that act on the nerve process.

Animals↗
PubMed1996

The problems of delivering neuroactive molecules to the CNS.

At present, the aetiologies of many neurological and neurodegenerative diseases are unknown. However, emergence of a better understanding of these diseases, at both cellular and molecular levels, opens up the possibility of replacement therapies. The presence of the blood-brain barrier complicates the delivery of molecules to the central nervous system. Numerous attempts have been made to bypass this barrier either by delivering the drugs directly into the brain or by transplanting cells to produce the missing molecules in situ. This review explores several methods for delivering bioactive molecules into the CNS, including the use of permeabilizers, osmotic pumps, slow polymer release systems and transplantation of cells with or without the use of the encapsulation technology.

Animals↗
PubMed1996

Intrathecal delivery of CNTF using encapsulated genetically modified xenogeneic cells in amyotrophic lateral sclerosis patients.

Neuronal growth factors hold promise for providing therapeutic benefits in various neurological disorders. As a means of ensuring adequate central nervous system delivery of growth factors and minimizing significant adverse side effects associated with systemic delivery methods, we have developed an ex vivo gene therapy approach for protein delivery using encapsulated genetically modified xenogeneic cells. Ciliary neurotrophic factor (CNTF) has been shown in various rodent models to reduce the motor neuron cell death similar to that seen in amyotrophic lateral sclerosis (ALS). The initial trials focusing on the systemic administration of CNTF for ALS have been discontinued as a result of major side effects, thus preventing determination of the potential efficacy of the molecule. In order to deliver CNTF directly to the nervous system, we conducted a phase I study in which six ALS patients were implanted with polymer capsules containing genetically engineered baby hamster kidney cells releasing approximately 0.5 microgram of human CNTF per day in vitro. The CNTF-releasing implants were surgically placed within the lumbar intrathecal space. Nanogram levels of CNTF were measured within the patients' cerebrospinal fluid (CSF) for at least 17 weeks post-transplantation, whereas it was undetectable before implantation. Intrathecal delivery of CNTF was not associated with the limiting side effects observed with systemic delivery. These results demonstrate that neurotrophic factors can be continuously delivered within the CSF of humans by an ex vivo gene therapy approach, opening new avenues for the treatment of neurological diseases.

Amyotrophic Lateral Sclerosis↗
PubMed1996

Immunoisolated xenogenic chromaffin cell therapy for chronic pain. Initial clinical experience.

BACKGROUND: Chromaffin cells from the adrenal gland secrete a mixture of compounds that have a strong analgesic effect, especially when administered intrathecally. Many studies in animal models have shown that discordant xenogeneic cell isolates, including chromaffin cells, can survive and have biologic effects when transplanted within a semipermeable membrane capsule. METHODS: To evaluate the clinical potential of encapsulated cell therapy, a human-scale implant containing bovine chromaffin cells was developed, characterized, and implanted in the subarachnoid space of seven patients with severe chronic pain not satisfactorily managed with conventional therapies. Patients received no pharmacologic immunosuppression. Cell devices were implanted during minimally invasive surgery, and device design allowed retrieval. All devices were recovered after implant periods of 41 to 176 days. RESULTS: Postexplant histologic analysis, immunostaining, and secretory function all confirmed survival and biochemical function of the encapsulated cells. Reductions in morphine intake and improvement in pain ratings were observed in several patients. CONCLUSIONS: This study represents the first successful trial of encapsulated xenogeneic cells in humans. The preliminary findings of pain reduction warrant the initiation of a randomized, double-blind phase II study to evaluate the potential efficacy of the procedure.

Adult↗