Cell delivery to the central nervous system

Boron Delivery to Brain Cells via Cerebrospinal Fluid (CSF) Circulation in BNCT of Brain-Tumor-Model Rats—Ex Vivo Imaging of BPA Using MALDI Mass Spectrometry Imaging

The blood–brain barrier (BBB) is likely to be intact during the early stages of brain metastatic melanoma development, and thereby inhibits sufficient drug delivery into the metastatic lesions. Our laboratory has been developing a system for boron drug delivery to brain cells via cerebrospinal fluid (CSF) as a viable pathway to circumvent the BBB in boron neutron capture therapy (BNCT). BNCT is a cell-selective cancer treatment based on the use of boron-containing drugs and neutron irradiation. Selective tumor targeting by boron with minimal normal tissue toxicity is required for effective BNCT. Boronophenylalanine (BPA) is widely used as a boron drug for BNCT. In our previous study, we demonstrated that application of the CSF administration method results in high BPA accumulation in the brain tumor even with a low dose of BPA. In this study, we evaluate BPA biodistribution in the brain following application of the CSF method in brain-tumor-model rats (melanoma) utilizing matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI). We observed increased BPA penetration to the tumor tissue, where the color contrast on mass images indicates the border of BPA accumulation between tumor and normal cells. Our approach could be useful as drug delivery to different types of brain tumor, including brain metastases of melanoma.

MRI Guided Focused Ultrasound-Mediated Delivery of Therapeutic Cells to the Brain: A Review of the State-of-the-Art Methodology and Future Applications

Stem cell and immune cell therapies are being investigated as a potential therapeutic modality for CNS disorders, performing functions such as targeted drug or growth factor delivery, tumor cell destruction, or inflammatory regulation. Despite promising preclinical studies, delivery routes for maximizing cell engraftment, such as stereotactic or intrathecal injection, are invasive and carry risks of hemorrhage and infection. Recent developments in MRI-guided focused ultrasound (MRgFUS) technology have significant implications for treating focal CNS pathologies including neurodegenerative, vascular and malignant processes. MRgFUS is currently employed in the clinic for treating essential tremor and Parkinson's Disease by producing precise, incisionless, transcranial lesions. This non-invasive technology can also be modified for non-destructive applications to safely and transiently open the blood-brain barrier (BBB) to deliver a range of therapeutics, including cells. This review is meant to familiarize the neuro-interventionalist with this topic and discusses the use of MRgFUS for facilitating cellular delivery to the brain. A detailed and comprehensive description is provided on routes of cell administration, imaging strategies for targeting and tracking cellular delivery and engraftment, biophysical mechanisms of BBB enhanced permeability, supportive proof-of-concept studies, and potential for clinical translation.

Use of Super Paramagnetic Iron Oxide Nanoparticles as Drug Carriers in Brain and Ear: State of the Art and Challenges

Drug delivery and distribution in the central nervous system (CNS) and the inner ear represent a challenge for the medical and scientific world, especially because of the blood-brain and the blood-perilymph barriers. Solutions are being studied to circumvent or to facilitate drug diffusion across these structures. Using superparamagnetic iron oxide nanoparticles (SPIONs), which can be coated to change their properties and ensure biocompatibility, represents a promising tool as a drug carrier. They can act as nanocarriers and can be driven with precision by magnetic forces. The aim of this study was to systematically review the use of SPIONs in the CNS and the inner ear. A systematic PubMed search between 1999 and 2019 yielded 97 studies. In this review, we describe the applications of the SPIONS, their design, their administration, their pharmacokinetic, their toxicity and the methods used for targeted delivery of drugs into the ear and the CNS.

Personalized Needles for Microinjections in the Rodent Brain

Microinjections have been used for a long time for the delivery of drugs or toxins within specific brain areas and, more recently, they have been used to deliver gene or cell therapy products. Unfortunately, current microinjection techniques use steel or glass needles that are suboptimal for multiple reasons: in particular, steel needles may cause tissue damage, and glass needles may bend when lowered deeply into the brain, missing the target region. In this article, we describe a protocol to prepare and use quartz needles that combine a number of useful features. These needles do not produce detectable tissue damage and, being very rigid, ensure reliable delivery in the desired brain region even when using deep coordinates. Moreover, it is possible to personalize the design of the needle by making multiple holes of the desired diameter. Multiple holes facilitate the injection of large amounts of solution within a larger area, whereas large holes facilitate the injection of cells. In addition, these quartz needles can be cleaned and re-used, such that the procedure becomes cost-effective.

Neuroprotective Effects of Encapsulated CNTF-Producing Cells in a Rodent Model of Huntington's Disease are Dependent on the Proximity of the Implant to the Lesioned Striatum

Huntington's disease (HD) is a devastating genetic disorder with no effective treatments for preventing or lessening the underlying neuronal degeneration. Intracerebral delivery of CNTF in animal models of HD has shown considerable promise as a means of protecting striatal neurons that would otherwise be destined to die. The present study examines whether the neuroprotective effects of CNTF require that the delivery be immediately proximal to the lesion site or whether protective effects can be exerted when the delivery site is more distal to the site of injury. Encapsulated CNTF-producing cells were implanted into the lateral ventricle either ipsilateral or contralateral to an intrastriatal quinolinic acid (QA) injection. A robust neuroprotective effect was observed only in those animals receiving CNTF implants ipsilateral to the QA injection. In these animals, the loss of striatal ChAT and GAD activity as well as the behavioral impairments that resulted from QA were completely prevented. In contrast, no neurochemical or behavioral benefits were produced by implants of CNTF-producing cells in the contralateral ventricle. These data continue to support the use of cellular delivery of CNTF for HD but caution that delivery directly to the striatum may be needed if any clinical benefits are to be seen.

The blood-brain barrier and nasal drug delivery to the central nervous system

BACKGROUND

The blood-brain barrier (BBB) is a highly efficient system that separates the central nervous system (CNS) from general circulation and promotes selective transport of molecules that are essential for brain function. However, it also limits the distribution of systemically administered therapeutics to the brain; therefore, there is a restricted number of drugs available for the treatment of brain disorders. Several drug-targeting strategies have been developed to attempt to bypass the BBB, but none has proved sufficiently effective in reaching the brain.

METHODS

The objective of this study is to generally review these strategies of drug administration to the CNS.

RESULTS

Noninvasive methods of drug delivery, such as chemical and biologic transport systems, do not represent a feasible platform, whereas for most drugs, it is still not possible to achieve therapeutic levels within the brain tissue after intravenous or oral administration, and the use of higher potency or more concentrated doses may cause serious toxic side effects. Direct intrathecal drug delivery through a catheter into the CNS also presents several problems. Intranasal drug delivery is a potential alternative method due to the direct transport into the cerebrospinal fluid (CSF) compartment along the olfactory pathway, but the study's conclusions are controversial. An endoscopic intranasal surgical procedure using established skull base surgery reconstruction techniques based on the use of a nasal mucosa surgical flap as the only obstacle between the nose and the subarachnoid space has appeared as a potential solution to increase the absorption of intranasal drugs to the CNS.

CONCLUSION

Despite extensive efforts to develop new techniques to cross the BBB, none has proved sufficiently effective in reaching the brain, whereas minimizing adverse effects and the endoscopic mucosal grafting technique offers new potential promise.

Fluorination of an antiepileptic drug: A self supporting transporter by oxygen enrichment mechanism

Drug therapy of seizures involves producing high levels of antiepileptic drugs in the blood. Drug must enter the brain by crossing from the blood into the brain tissue, called a transvascular route (TVR). Even before the drug can reach the brain tissue, factors such as systemic toxicity, macrophage phagocytises and reduction in oxygen content limit the success of this TVR. Encapsulating the drug within a nano scale delivering system, synthesising drugs with low molecular weight are the best mechanisms to deliver the drug to the brain. But through this article, we have explored a possibility of attaching a molecule 4-(trifluoromethyl) benzoic acid (TFMBA), that possess more number of fluorine atom, to benzodiazepine (BDZ) resulting in an ionic salt (S)-(+)-2,3-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine5,11(10H,11aH)-dione with 4-(trifluoromethyl)benzoic acid. By this way, reducing the toxicity of BDZ than the conventional anti-epileptic drugs (AEDs), increasing the solubility, reducing the melting point, enriching the TVR with excess oxygen content with the support of fluorine. With all these important prerequisites fulfilled, the drug along with the attached molecule is expected to travel more comfortably through the TVR without any external support than any other conventional AEDs. FTIR, (1)H NMR, (13)C NMR, HRMS spectroscopy, HRTEM and In vitro cytotoxicity analysis supports this study.

Construction of a novel inducing system with multi-layered alginate microcapsules to regulate differentiation of neural precursor cells from bone mesenchymal stem cells

Neural precursor cells (NPCs) are a promising cell source for the treatment of nervous system diseases; however, they are limited in their applications due to source-related ethical considerations or legislations. Therefore, a novel approach is necessary to obtain sufficient NPCs. Recently, the usage of bone marrow-derived mesenchymal stem cells (BMSCs) differentiated into neural cells has become a potential method to obtain NPCs. Moreover, growth factors (GFs) are emerging as inducers to evoke the differentiation of BMSCs into NPCs. For example, GFs may activate various signaling pathways related to neural differentiation, such as phosphatidylinositol 3 kinase/protein kinase B, cyclic adenosine monophosphate/protein kinase A, and Janus kinase/signal transducer activator of transcription. However, the utilization of growth factors still has some limitations such as high costs and low rates of neural differentiation. Neuroblastoma cells have been characterized as a potential pool for growth factors. Additionally, basic fibroblast growth factor (bFGF), a type of growth factor, has been demonstrated to be able to increase the differentiation and survival rate of NPCs. For better use of neuroblastoma cells and bFGF, we established a novel system involving multi-layered alginate-polylysine-alginate (APA) microcapsules to encapsulate neuroblastoma cells and bFGF, which may not only provide sufficient growth factors in a sustained manner but also avoid the carcinogenicity caused by neuroblastoma cells. Above all, we hypothesized that neuroblastoma cells and bFGF encapsulated in multilayered alginate microcapsules may efficiently induce the differentiation of BMSCs into NPCs.

Monocytes-derived macrophages mediated stable expression of human brain-derived neurotrophic factor, a novel therapeutic strategy for neuroAIDS

HIV-1 associated dementia remains a significant public health burden. Clinical and experimental research has shown that reduced levels of brain-derived neurotrophic factor (BDNF) may be a risk factor for neurological complications associated with HIV-1 infection. We are actively testing genetically modified macrophages for their possible use as the cell-based gene delivery vehicle for the central nervous system (CNS). It can be an advantage to use the natural homing/migratory properties of monocyte-derived macrophages to deliver potentially neuroprotective BDNF into the CNS, as a non-invasive manner. Lentiviral-mediated gene transfer of human (h)BDNF plasmid was constructed and characterized. Defective lentiviral stocks were generated by transient transfection of 293T cells with lentiviral transfer plasmid together with packaging and envelope plasmids. High titer lentiviral vector stocks were harvested and used to transduce human neuronal cell lines, primary cultures of human peripheral mononocyte-derived macrophages (hMDM) and murine myeloid monocyte-derived macrophages (mMDM). These transduced cells were tested for hBDNF expression, stability, and neuroprotective activity. The GenomeLab GeXP Genetic Analysis System was used to evaluate transduced cells for any adverse effects by assessing gene profiles of 24 reference genes. High titer vectors were prepared for efficient transduction of neuronal cell lines, hMDM, and mMDM. Stable secretion of high levels of hBDNF was detected in supernatants of transduced cells using western blot and ELISA. The conditioned media containing hBDNF were shown to be protective to neuronal and monocytic cell lines from TNF-α and HIV-1 Tat mediated cytotoxicity. Lentiviral vector-mediated gene transduction of hMDM and mMDM resulted in high-level, stable expression of the neuroprotective factorBDNF in vitro. These findings form the basis for future research on the potential use of BDNF as a novel therapy for neuroAIDS.

Covalent layer-by-layer assembly of hyperbranched polymers on alginate microcapsulesto impart stability and permselectivity

The microencapsulation of cells has shown promise as a therapeutic vehicle for the treatment of a wide variety of diseases. While alginate microcapsules provide an ideal cell encapsulation material, polycations coatings are commonly employed to enhance stability and impart permselectivity. In this study, functionalized hyperbranched alginate and dendrimer polymers were used to generate discreet nanoscale coatings onto alginate microbeads via covalent layer-by-layer assembly. The bioorthogonal Staudinger ligation scheme was used to chemoselectively crosslink azide functionalized hyperbranched alginate (alginate-hN₃) to methyl-2-diphenylphosphino-terephthalate (MDT) linked PAMAM dendrimer (PAMAM-MDT). Covalent layer-by-layer deposition of PAMAM-MDT/alginate-hN₃ coatings onto alginate microbeads resulted in highly stable coatings, even after the inner alginate gel was liquefied to form microcapsules. The permselectivity of the coated microcapsules could be manipulated via the charge density of the PAMAM, the number of layers deposited, and the length of the functional arms. The cytocompatibility of the resulting PAMAM-MDT/alginate-hN₃ coating was evaluated using a beta cell line, with no significant detrimental response observed. The biocompatibility of the coatings in vivo was also found comparable to uncoated alginate beads. The remarkable stability and versatile nature of these coatings provides an appealing option for bioencapsulation and the release of therapeutic agents.

Co-administration of dual-targeting nanoparticles with penetration enhancement peptide for antiglioblastoma therapy

Chemotherapy is an indispensable auxiliary treatment for glioma but highly limited by the existence of both blood-brain barrier (BBB) and blood-brain tumor barrier (BBTB). The dysfunctional brain tumor blood vessels and high interstitial pressure in glioma also greatly hindered the accumulation and deep penetration of chemotherapeutics into the glioma. Lactoferrin (Lf), with its receptor overexpressed on both the brain endothelial cells and glioma cells, was here functionalized to the surface of poly(ethylene glycol)-poly(lactic acid) nanoparticles to mediate BBB/BBTB and glioma cell dual targeting. tLyP-1, a tumor-homing peptide, which contains a C-end Rule sequence that can mediate tissue penetration through the neuropilin-1-dependent internalization pathway, was coadministrated with Lf-functionalized nanoparticles (Lf-NP) to enhance its accumulation and deep penetration into the glioma parenchyma. Enhanced cellular association in both BCEC and C6 cells, increased cytotoxicity of the loaded paclitaxel, and deep penetration in the 3D glioma spheroids was achieved by Lf-NP. Following coadministration with tLyP-1, the functionalized nanoparticles obtained improved tumor targeting, glioma vascular extravasation, and antiglioma efficacy. The findings here suggested that the strategy by coadministrating BBB/BBTB and glioma cells dual-targeting nanocarriers with a tumor penetration enhancement peptide represent a promising platform for antiglioma drug delivery.

Cell transplantation for Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the degeneration of the dopamine producing neurons projecting from the substantia nigra into the corpus striatum. Current medical therapy is limited and cannot stop or reverse the degeneration. Over the past 30 years, attempts were made to change the course of the disease by replacing the lost neurons with grafts from various sources. Recent controlled clinical trials of fetal cell transplantation for PD have had disappointing results. These events present an opportunity to examine the past developments and future direction of cell transplantation for PD.

Permeabilization of the blood-brain barrier via mucosal engrafting: implications for drug delivery to the brain

Utilization of neuropharmaceuticals for central nervous system(CNS) disease is highly limited due to the blood-brain barrier(BBB) which restricts molecules larger than 500Da from reaching the CNS. The development of a reliable method to bypass the BBB would represent an enormous advance in neuropharmacology enabling the use of many potential disease modifying therapies. Previous attempts such as transcranial catheter implantation have proven to be temporary and associated with multiple complications. Here we describe a novel method of creating a semipermeable window in the BBB using purely autologous tissues to allow for high molecular weight(HMW) drug delivery to the CNS. This approach is inspired by recent advances in human endoscopic transnasal skull base surgical techniques and involves engrafting semipermeable nasal mucosa within a surgical defect in the BBB. The mucosal graft thereby creates a permanent transmucosal conduit for drugs to access the CNS. The main objective of this study was to develop a murine model of this technique and use it to evaluate transmucosal permeability for the purpose of direct drug delivery to the brain. Using this model we demonstrate that mucosal grafts allow for the transport of molecules up to 500 kDa directly to the brain in both a time and molecular weight dependent fashion. Markers up to 40 kDa were found within the striatum suggesting a potential role for this technique in the treatment of Parkinson’s disease. This proof of principle study demonstrates that mucosal engrafting represents the first permanent and stable method of bypassing the BBB thereby providing a pathway for HMW therapeutics directly into the CNS.

Characterization of hyaluronan-methylcellulose hydrogels for cell delivery to the injured spinal cord

No effective clinical treatment currently exists for traumatic spinal cord injury. Cell replacement therapy holds promise for attaining functional repair. Cells may be delivered directly or near the injury site; however, this strategy requires a delivery vehicle to maintain cell viability. We have identified an injectable, biocompatible, and biodegradable hydrogel scaffold composed of hyaluronan (HA) and methylcellulose (MC) that may be an effective scaffold for therapeutic cell delivery. The purpose of the present study was to determine the effects of polymer concentration on HAMC mechanical strength, gelation time, and cell viability. The yield stress of HAMC, a measure of mechanical stiffness, was tunable via manipulation of MC and HA content. Measurement of the elastic and storage moduli as functions of time revealed that HAMC gels in less than 5 min at physiological temperatures. Human umbilical tissue-derived cells encapsulated in HAMC were homogenously and stably distributed over 3 days in culture and extended processes into the scaffold. Cell viability was stable over this period in all but the most concentrated HAMC formulation. Because of its strength-tunability, rapid gelation, and ability to maintain cell viability, HAMC is a promising vehicle for cell delivery and is being tested in ongoing in vivo studies.

Microcapsules with intrinsic barium radiopacity for immunoprotection and X-ray/CT imaging of pancreatic islet cells

Microencapsulation is a commonly used technique for immunoprotection of engrafted therapeutic cells. We investigated a library of capsule formulations to determine the most optimal formulation for pancreatic beta islet cell transplantation, using barium as the gelating ion and clinical-grade protamine sulfate (PS) as a new cationic capsule cross-linker. Barium-gelated alginate/PS/alginate microcapsules (APSA, diameter = 444 ± 21 μm) proved to be mechanically stronger and supported a higher cell viability as compared to conventional alginate/poly-l-lysine/alginate (APLLA) capsules. Human pancreatic islets encapsulated inside APSA capsules, gelated with 20 mm barium as optimal concentration, exhibited a sustained morphological integrity, viability, and functionality for at least 3-4 weeks in vitro, with secreted human C-peptide levels of 0.2-160 pg/ml/islet. Unlike APLLA capsules that are gelled with calcium, barium-APSA capsules are intrinsically radiopaque and, when engrafted into mice, could be readily imaged in vivo with micro-computed tomography (CT). Without the need of adding contrast agents, these capsules offer a clinically applicable alternative for simultaneous immunoprotection and real-time, non-invasive X-ray/CT monitoring of engrafted cells during and after in vivo administration.

Microencapsulation of islets within alginate/poly(ethylene glycol) gels cross-linked via Staudinger ligation

Functionalized alginate and poly(ethylene glycol) (PEG) polymers were used to generate covalently linked alginate-PEG (XAlgPEG) microbeads of high stability. The cell-compatible Staudinger ligation scheme was used to cross-link phosphine-terminated PEG chemoselectively to azide-functionalized alginate, resulting in XAlgPEG hydrogels. XAlgPEG microbeads were formed by co-incubation of the two polymers, followed by ionic cross-linking of the alginate using barium ions. The enhanced stability and gel properties of the resulting XAlgPEG microbeads, as well as the compatibility of these polymers for the encapsulation of islets and beta cells lines, were investigated. The data show that XAlgPEG microbeads exhibit superior resistance to osmotic swelling compared with traditional barium cross-linked alginate (Ba-Alg) beads, with a five-fold reduction in observed swelling, as well as resistance to dissolution via chelation solution. Diffusion and porosity studies found XAlgPEG beads to exhibit properties comparable with standard Ba-Alg. XAlgPEG microbeads were found to be highly cell compatible with insulinoma cell lines, as well as rat and human pancreatic islets, where the viability and functional assessment of cells within XAlgPEG are comparable with Ba-Alg controls. The remarkable improved stability, as well as demonstrated cellular compatibility, of XAlgPEG hydrogels makes them an appealing option for a wide variety of tissue engineering applications.

Intrathecal implantation of microencapsulated PC12 cells reduces cold allodynia in a rat model of neuropathic pain

The transplantation of cells into the central nervous system provides a constant and replenishable source of analgesic substances for the alleviation of chronic pain. In the present study, PC12 cells were microencapsulated in a semipermeable membrane that protected the cells from the host's immune system. A chronic neuropathic pain model was induced by chronic constriction injury (CCI) of the sciatic nerve in rats. Thirty Sprague-Dawley rats with CCI were divided randomly into two groups: the cell-loaded group received microencapsulated PC12 cells (n = 15) and the control group received empty capsules (n = 15). The microcapsules were implanted into the lumbar subarachnoid space. After implantation, a significant reduction of cold allodynia was observed in the rats of the cell-loaded group at 7, 14, 21, and 28 days compared to the control group with the empty capsules (P < 0.05). Furthermore, the levels of catecholamines and met-enkephalin in the cerebrospinal fluid of rats in the cell-loaded group were higher than the levels in the controls (P < 0.05). These results suggest that intrathecal microencapsulated PC12 cells could be a useful method for chronic neuropathic pain management.

Combining the cell-encapsulation technique and axon guidance for cell transplantation therapy

In cell transplantation therapy for the treatment of neurodegenerative disorders, encapsulation of implanted cells in a semipermeable membrane is a promising approach to protect the implanted cells from host immune rejection and inhibit the invasion of tumor into surrounding tissue if the implanted cells form a tumor after transplantation. However, implanted neurons isolated by capsules could not build connections with host neurons, preventing the implanted neurons from responding to stimuli from host neurons. In the present study, we focused on the passage of neurites and axons navigated by axon guidance molecules through membrane pores to enable encapsulated neurons and host neurons to form connections. The type of matrix coated on membranes and the pore size of the membranes greatly affected the successful passage of PC12 neurites through membrane pores. PC12 neurites preferably passed through collagen-coated membranes with pores greater than 0.8 μm in diameter, but the neurites did not pass through albumin- or fibronectin-coated membranes or membranes with pores less than 0.1 μm in diameter. We could navigate the direction of commissural neural axon extensions by utilizing the axon guidance molecules secreted from floor plate and make guided axons pass through the membrane pores. These results suggest the feasibility of building connections between encapsulated neurons and host neurons by encapsulating the implanted neurons and axon guidance molecules, which attract the axons of host neurons into the capsule, in the porous membranes with suitable pore size and matrix coating.

Progress technology in microencapsulation methods for cell therapy

Cell encapsulation in microcapsules allows the in situ delivery of secreted proteins to treat different pathological conditions. Spherical microcapsules offer optimal surface-to-volume ratio for protein and nutrient diffusion, and thus, cell viability. This technology permits cell survival along with protein secretion activity upon appropriate host stimuli without the deleterious effects of immunosuppressant drugs. Microcapsules can be classified in 3 categories: matrix-core/shell microcapsules, liquid-core/shell microcapsules, and cells-core/shell microcapsules (or conformal coating). Many preparation techniques using natural or synthetic polymers as well as inorganic compounds have been reported. Matrix-core/shell microcapsules in which cells are hydrogel-embedded, exemplified by alginates capsule, is by far the most studied method. Numerous refinement of the technique have been proposed over the years such as better material characterization and purification, improvements in microbead generation methods, and new microbeads coating techniques. Other approaches, based on liquid-core capsules showed improved protein production and increased cell survival. But aside those more traditional techniques, new techniques are emerging in response to shortcomings of existing methods. More recently, direct cell aggregate coating have been proposed to minimize membrane thickness and implants size. Microcapsule performances are largely dictated by the physicochemical properties of the materials and the preparation techniques employed. Despite numerous promising pre-clinical results, at the present time each methods proposed need further improvements before reaching the clinical phase.

Impact of Orally Administered Microcapsules on Gastrointestinal Microbial Flora: In-Vitro Investigation Using Computer Controlled Dynamic Human Gastrointestinal Model

Oral administration of artificial cell microcapsules has been proposed for various therapy procedures using biologically active materials. Recently we have designed novel APPPA microcapsules using alginate, poly-L-lysine, pectin, poly-L-lysine and alginate that have shown superior oral delivery features. This article investigates, in-vitro using a computer controlled dynamic gastrointestinal (GI) model, effects of APPPA microcapsules on health of gastrointestinal (GI) microbial flora. The impact of APPPA microcapsules on GI bacterial population, total anaerobes, total aerobes, Escherichia coli, Lactobacillus sp. and Staphylococcus sp. has been analyzed. In addition, the effects of microcapsules on GI microbial extracellular enzymatic activities have been investigated. Result shows the altered activities of microbial flora and enzymes due to the use of APPPA microcapsule. The most disparity is observed in the colon ascendans microbial activities. This study would have significant impact on future microcapsule design. However, further in-vivo studies are required.

Non-viral delivery of the gene for glial cell line-derived neurotrophic factor to mesenchymal stem cells in vitro via a collagen scaffold

Recent advances in tissue engineering that combine an extracellular matrix-like scaffold with therapeutic molecules, cells, DNA encoding therapeutic proteins, or a combination of the three hold promise for treating defects in the brain resulting from a penetrating injury or tumor resection. The purpose of this study was to investigate a porous sponge-like collagen scaffold for non-viral delivery of a plasmid encoding for glial cell line-derived neurotrophic factor (pGDNF) to rat marrow stromal stem cells (also referred to as mesenchymal stem cells, MSCs). The effects of the following parameters on GDNF synthesis in the three-dimensional (3D) constructs were evaluated and compared with results in monolayer culture: initial plasmid load (2-50 microg pGDNF), ratio of a lipid transfection reagent to plasmid (5:10), culture environment during the transfection (static and dynamic), and cell density. The level of gene expression in the collagen scaffolds achieved therapeutic levels that had previously been found to support survival of dopaminergic and trigeminal neurons in vitro. For the highest loading of plasmid (50 microg), the level of GDNF protein remained six to seven times above the control level after 2 weeks, a significant difference. Cell density in the scaffold was of importance for an early increase in GDNF production, with accumulated GDNF being approximately 60% greater after 9 days of culture when scaffolds were initially seeded with 2 million rat MSCs compared to 500,000 cells. Application of orbital shaking during the 4 h of transfection had a positive effect on the production of GDNF on 3D constructs but not of the same magnitude as reported in monolayer studies. Overall, these results demonstrate that the combination of tissue engineering and non-viral transfection of MSCs for the over-expression of GDNF is a promising approach for the long-term production of GDNF and probably for neurotrophic factors in general.

Systemic delivery of umbilical cord blood cells for stroke therapy: a review

PURPOSE

This review paper summarizes relevant studies, discusses potential mechanisms of transplanted cell-mediated neuroprotection, and builds a case for the need to establish outcome parameters that are critical for transplantation success. In particular, we outline the advantages and disadvantages of systemic delivery of human umbilical cord blood (HUCB) cells in the field of cellular transplantation for treating ischemic stroke.

METHODS

A MEDLINE/PubMed systematic search of published articles in peer-reviewed journals over the last 25 years was performed focusing on the theme of HUCB as donor graft source for transplantation therapy in neurological disorders with emphasis on stroke.

RESULTS

Ischemic stroke remains a leading cause of human death and disability. Although stroke survivors may gain spontaneous partial functional recovery, they often suffer from sensory-motor dysfunction, behavioral/neurological alterations, and various degrees of paralysis. Currently, limited clinical intervention is available to prevent ischemic damage and restore lost function in stroke victims. Stem cells from fetal tissues, bone marrow, and HUCB has emerged in the last few years as a potential cell transplant cell source for ischemic stroke, because of their capability to differentiate into multiple cell types and the possibility that they may provide trophic support for cell survival, tissue repair, and functional recovery.

CONCLUSION

A growing number of studies highlight the potential of systemic delivery of HUCB cells as a novel therapeutic approach for stroke. However, additional preclinical studies are warranted to reveal the optimal HUCB transplant regimen that is safe and efficacious prior to proceeding to large-scale clinical application of these cells for stroke therapy.

Preparation of hydrogel hollow particles for cell encapsulation by a method of polyester core degradation

Implantation of encapsulated cells in particles of less than 1 mm (micro-encapsulation) has been proposed as a cell synthesized bio-molecule delivery system. Encapsulation provides immuno-isolation, protecting foreign cells from host immune system while nutrients, oxygen and therapeutic products can diffuse freely across capsule walls. A new method is described for the synthesis of a new family of hollow microparticles for cell encapsulation. Unlike other micro-encapsulation methods, encapsulation in those devices will take place after capsule synthesis, by micro-injection. The microcapsules were prepared by a three-steps original procedure: first, synthesis of a core particle, followed by coating with a layer of epichlorohydrin cross-linked amylo-pectin gel and, finally, selective degradation of the core particle to create the cavity. Initial experiments make use of amylo-pectin cross-linked with trimetaphosphate as core particle material. However, selective degradation was difficult to achieve. In further essays, polyesters were used successfully for the preparation of core particles. Optimizations were carried out and the permeability and morphology of the hollow particles were investigated. The preliminary results show that the new method has the potential to become a standard procedure to obtain hydrogel hollow particles. Moreover, the permeability study seems to be in accordance with specifications for immuno-isolation.

Challenges and emerging technologies in the immunoisolation of cells and tissues

Protection of transplanted cells from the host immune system using immunoisolation technology will be important in realizing the full potential of cell-based therapeutics. Microencapsulation of cells and cell aggregates has been the most widely explored immunoisolation strategy, but widespread clinical application of this technology has been limited, in part, by inadequate transport of nutrients, deleterious innate inflammatory responses, and immune recognition of encapsulated cells via indirect antigen presentation pathways. To reduce mass transport limitations and decrease void volume, recent efforts have focused on developing conformal coatings of micron and submicron scale on individual cells or cell aggregates. Additionally, anti-inflammatory and immunomodulatory capabilities are being integrated into immunoisolation devices to generate bioactive barriers that locally modulate host responses to encapsulated cells. Continued exploration of emerging paradigms governed by the inherent challenges associated with immunoisolation will be critical to actualizing the clinical potential of cell-based therapeutics.

Nerve guidance channels as drug delivery vehicles

Nerve guidance channels (NGCs) have been shown to facilitate regeneration after transection injury to the peripheral nerve or spinal cord. Various therapeutic molecules, including neurotrophic factors, have improved regeneration and functional recovery after injury when combined with NGCs; however, their impact has not been maximized partly due to the lack of an appropriate drug delivery system. To address this limitation, nerve growth factor (NGF) was incorporated into NGCs of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate), P(HEMA-co-MMA). The NGCs were synthesized by a liquid-liquid centrifugal casting process and three different methods of protein incorporation were compared in terms of protein distribution and NGF release profile: (1) NGF was encapsulated (with BSA) in biodegradable poly(d,l-lactide-co-glycolide) 85/15 microspheres, which were combined with a PHEMA polymerization formulation and coated on the inside of pre-formed NGCs by a second liquid-liquid centrifugal casting technique; (2) pre-formed NGCs were imbibed with a solution of NGF/BSA and (3) NGF/BSA alone was combined with a PHEMA formulation and coated on the inside of pre-formed NGCs by a second liquid-liquid centrifugal casting technique. Using a fluorescently labelled model protein, the distribution of proteins in NGCs prepared with a coating of either protein-loaded microspheres or protein alone was found to be confined to the inner PHEMA layer. Sustained release of NGF was achieved from NGCs with either NGF-loaded microspheres or NGF alone incorporated into the inner layer, but not from channels imbibed with NGF. By day 28, NGCs with microspheres released a total of 220 pg NGF/cm of channel whereas those NGCs imbibed with NGF released 1040 pg/cm and those NGCs with NGF incorporated directly in a PHEMA layer released 8624 pg/cm. The release of NGF from NGCs with microspheres was limited by a slow-degrading microsphere formulation and by the maximum amount of microspheres that could be incorporated into the NGCs structure. Notwithstanding, the liquid-liquid centrifugal casting process is promising for localized and controlled release of multiple factors that are key to tissue regeneration.

Colloidal carriers and blood–brain barrier (BBB) translocation: A way to deliver drugs to the brain?

The major problem in drug delivery to the brain is the presence of the blood-brain barrier (BBB) which limits drug penetration even if in certain pathological situations the BBB is partly disrupted. Therefore, various strategies have been proposed to improve the delivery of drugs to this tissue. This review presents the status of the BBB in healthy patients and in pathologies like neurodegenerative, cerebrovascular and inflammatory diseases. The second part of this article aims to review the invasive and non-invasive strategies developed to circumvent the BBB and deliver drugs into the brain. The use of nanotechnologies (liposomes, nanoparticles) is especially discussed in the ultimate part of the review evidencing their potentiality as non-invasive technique in the brain delivery of drugs with the possibility to target specific brain tissue thanks to ligand linked to carrier surface.

Immunoisolated chromaffin cells implanted into the subarachnoid space of rats reduce cold allodynia in a model of neuropathic pain: a novel application of microencapsulation technology

Intrathecal transplants of adrenal medullary chromaffin cells relieve chronic pain by secreting catecholamines, opioids, and other neuroactive substances. Recently, macrocapsules with semipermeable membranes were used to isolate immunologically xenogenic chromaffin cells, but the poor viability in vivo of the encapsulated chromaffin cells limited the usefulness of this method. In this study, we used a novel method of encapsulation to increase the viability of chromaffin cells. We found that microencapsulated chromaffin cells that were implanted into the subarachnoid space of rats relieved cold allodynia in a model of neuropathic pain. Furthermore, microencapsulated chromaffin cells were morphologically normal and retained their functionality. These findings suggest that the intrathecal placement of microencapsulated chromaffin cells might be a useful method for treating chronic pain.

Delivery systems for small molecule drugs, proteins, and DNA: the neuroscience/biomaterial interface

Manipulation of cellular processes in vivo by the delivery of drugs, proteins or DNA is of paramount importance to neuroscience research. Methods for the presentation of these molecules vary widely, including direct injection (either systemic or stereotactic), osmotic pump-mediated chronic delivery, or even implantation of cells engineered to indefinitely secrete a factor of interest. Biomaterial-based delivery systems represent an alternative to more traditional approaches, with the possibility of increased efficacy. Drug-releasing biomaterials, either as injectable microspheres or as three-dimensional implants, can deliver a molecule of interest (including small molecule drugs, biologically active proteins, or DNA) over a more prolonged period of time than by standard bolus injection, avoiding the need for repeated administration. Furthermore, sustained-release systems can maintain therapeutic concentrations at a target site, thus reducing the chance for toxicity. This review summarizes applications of polymer-based delivery of small molecule drugs, proteins, and DNA specifically relevant to neuroscience research. We detail the fabrication procedures for the polymeric systems and their utility in various experimental models. The biomaterial field offers unique experimental tools with downstream clinical application for the study and treatment of neurologic disease.

Tissue-engineering approaches for axonal guidance

Owing to the profound impact of nervous system damage, extensive studies have been carried out aimed at facilitating axonal regeneration following injury. Tissue engineering, as an emerging and rapidly growing field, has received extensive attention for nervous system axonal guidance. Numerous engineered substrates containing oriented extracellular matrix molecules, cells or channels have displayed potential of supporting axonal regeneration and functional recovery. Most attempts are focused on seeking new biomaterials, new cell sources, as well as novel designs of tissue-engineered neuronal bridging devices, to generate safer and more efficacious neuronal tissue repairs.

A cell encapsulation device for studying soluble factor release from cells transplanted in the rat brain

The transplantation of a variety of naturally occurring and genetically modified cell types has been shown to be an effective experimental method to achieve sustained delivery of therapeutic molecules to specific target areas in the brain. To acquire a better understanding of dosing, implant mechanism of action, and how certain cell types affect remodeling of central nervous system (CNS) tissue, a refillable cell encapsulation device was developed for introducing cells into the brain while keeping them physically isolated from contact with brain tissue with a semipermeable membrane. The stereotactically placed device consists of a hollow fiber membrane (HFM), a polyurethane grommet with watertight cap that snaps into a precisely drilled hole in the rat skull, and a removable cell-containing insert. The cell-containing insert can be introduced or removed in a time-dependent manner to study the influence of soluble factors released from transplanted cells. The study describes the device design and validates its utility using a well-established cell transplantation model of Parkinson's disease.

Interactions between the cells of the immune and nervous system: neurotrophins as neuroprotection mediators in CNS injury

Inflammatory processes in the central nervous system (CNS) are considered neurotoxic, although recent studies suggest that they also can be beneficial and confer neuroprotection (neuroprotective autoimmunity). Cells from the immune system have been detected in CNS injury and found to produce and secrete a variety of neurotrophins such as NGF, BDNF, NT-3 and NT-4/5, and to express (similarly to neuronal cells), members of the tyrosine kinase (Trk) receptor family such as TrkA, TrkB and TrkC. Indeed, autocrine and paracrine interactions are observed at the site of CNS injury, resulting in a variety of homologic-heterologic modulations of immune and neuronal cell function. The end result of the inflammatory process, neurotoxicity and/or neuroprotection, is a function of the fine balance between the two cellular systems, i.e., of the complex signaling relationships between anti-inflammatory neuroprotective factors (neurotrophins and other chemical mediators) and proinflammatory neurotoxic factors (TNF, free radicals, certain cytokines, etc.). Autoimmune neuroprotection is a novel therapeutic approach aimed at shifting the balance between the immune and neuronal cells towards survival pathways in a variety of CNS injuries. This review focuses on data supporting this concept and its future therapeutical implications for optic nerve injury and multiple sclerosis.

Complications of a trophic xenotransplant approach in parkinsonian monkeys

Various restorative cell transplantation strategies have been investigated to substitute for lost dopamine (DA) neurons or to enhance DA synthesis in Parkinson's disease. Intracerebral implantation of engineered cells encapsulated in a semipermeable polymer membrane constitutes one way to deliver bioactive substances unable to cross the blood-brain barrier while avoiding the need for long-term immunosuppression. Glial cell line-derived neurotrophic factor (GDNF) has shown trophic effects on DA neurons but effective and sustained delivery within the brain parenchyma remains problematic. The long-term efficacy and late complications of a xenotransplant approach utilizing GDNF-expressing encapsulated baby hamster kidney (BHK) cells were examined. Each of five MPTP-lesioned parkinsonian cynomolgus monkeys received five devices containing active or inert cells grafted bilaterally in the striatum in a two-stage procedure 9 months apart and animals were sacrificed 4 months later for analyses. No definite motor benefit was observed, DA levels were comparable between GDNF- and control cell-implanted striata, and tyrosine hydroxylase (TH) immunoreactivity in the substantia nigra showed no consistent recovery. Cell viability and GDNF synthesis in the explanted devices were negligible. The brain tissue surrounding all implants showed an intense immune reaction with prominent "foreign body" inflammatory infiltrates. Membrane biophysics, the cell type used, and the extended period of time the devices remained in situ may have contributed to the negative outcome and should be addressed in future investigations using this approach.

The neurosurgeon as local oncologist: cellular and molecular neurosurgery in malignant glioma therapy

Malignant gliomas are among the most challenging of all cancers to treat successfully, being characterized not only by aggressive proliferation and expansion but also by inexorable tumor invasion into distant brain tissue. Although considerable progress has been made in the treatment of these tumors with combinations of surgery, radiotherapy, and chemotherapy, these efforts have not been curative. Neurosurgeons as oncologists have increasingly turned their attention to therapies on a molecular scale. Of particular interest to neurosurgeons is the ability to deliver therapy locally to the tumor site or to take advantage of existing immunological mediators, enhancing drug concentrations or therapeutic cell numbers while bypassing the blood-brain barrier to maximize efficacy and minimize systemic toxicity. Exciting local-therapy approaches have been proposed for these devastating tumors. In this review, we discuss the potential applications of bioreactors, neural stem cells, immunotherapies, biodegradable polymers, and convection-enhanced drug delivery in the treatment of malignant gliomas. These approaches are at different stages of readiness for application in clinical neurosurgery, and their eventual effects on the morbidity and mortality rates of gliomas among human patients are difficult to ascertain from successes in animal models. Nevertheless, we are entering an exciting era of "nanoneurosurgery," in which molecular therapies such as those discussed here may routinely complement existing surgical, radiological, and chemotherapeutic approaches to the treatment of neuro-oncological disease. The potential to deploy any of a number of eloquently devised molecular therapies may provide renewed hope for neurosurgeons treating malignant gliomas.

The potential of antisense as a CNS therapeutic

Antisense offers a precise and specific means of knocking down expression of a target gene, and is a major focus of research in neuroscience and other areas. It has application as a tool in gene function and target validation studies and is emerging as a therapeutic technology in its own right. It has become increasingly obvious, however, that there are a number of hurdles to overcome before antisense can be used effectively in the CNS, most notably finding suitable nucleic acid chemistries and an effective delivery vehicle to transport antisense oligonucleotides (AS-ODNs) across the blood-brain barrier (BBB) to their site of action. Despite these problems, a number of potential applications of AS-ODNs in CNS therapeutics have been validated in vitro and, in some cases, in vivo. Here the authors outline available nucleic acid chemistries and review progress in the development of non-invasive delivery vehicles that may be applicable to CNS therapeutics. Further to this, they discuss a number of experimental applications of AS-ODNs to CNS research and speculate on the development of antisense techniques to treat CNS disease.

Drug and gene delivery to the brain: the vascular route

Brain drug development of either small molecule or large molecule (recombinant proteins, gene medicines) neurotherapeutics has been limited, owing to the restrictive transport properties of the brain microvasculature, which forms the blood-brain barrier (BBB) in vivo. Widespread drug delivery to the brain, while not feasible via craniotomy and intracerebral injection, is possible if the drug is delivered to brain via the transvascular route through the BBB. Novel brain drug delivery and drug targeting strategies can be developed from an understanding of the molecular and cellular biology of the brain microvascular and BBB transport processes.