The brain tissue response to biodegradable poly(methylidene malonate 2.1.2)-based microspheres in the rat

Local Delivery Strategies for Peptides and Proteins into the CNS: Status Quo, Challenges, and Future Perspectives

Over the past decades, peptides and proteins have been increasingly important in the treatment of various human diseases and conditions owing to their specificity, potency, and minimized off-target toxicity. However, the existence of the practically impermeable blood brain barrier (BBB) limits the entry of macromolecular therapeutics into the central nervous systems (CNS). Consequently, clinical translation of peptide/protein therapeutics for the treatment of CNS diseases has been limited. Over the past decades, developing effective delivery strategies for peptides and proteins has gained extensive attention, in particular with localized delivery strategies, due to the fact that they are capable of circumventing the physiological barrier to directly introduce macromolecular therapeutics into the CNS to improve therapeutic effects and reduce systemic side effects. Here, we discuss various local administration and formulation strategies that have shown successes in the treatment of CNS diseases using peptide/protein therapeutics. Lastly, we discuss challenges and future perspectives of these approaches.

Recent advances in nanocarrier-loaded gels: Which drug delivery technologies against which diseases?

The combination of pharmaceutical technologies can be a wise choice for developing innovative therapeutic strategies. The association of nanocarriers and gels provides new therapeutic possibilities due to the combined properties of the two technologies. Gels support the nanocarriers, localize their administration to the target tissue, and sustain their release. In addition to the properties afforded by the gel, nanocarriers can provide additional drug sustained release or different pharmacokinetic and biodistribution profiles than those from nanocarriers administered by the conventional route to improve the drug therapeutic index. This review focuses on recent (over the last ten years) in vivo data showing the advances and advantages of using nanocarrier-loaded gels. Liposomes, micelles, liquid and solid lipid nanocapsules, polymeric nanoparticles, dendrimers, and fullerenes are all nanotechnologies which have been recently assessed for medical applications, such as cancer therapy, the treatment of cutaneous and infectious diseases, anesthesia, the administration of antidepressants, and the treatment of unexpected diseases, such as alopecia.

The neurotoxicity of gene vectors and its amelioration by packaging with collagen hollow spheres

Over the last twenty years there have been several reports on the use of nonviral vectors to facilitate gene transfer in the mammalian brain. Whilst a large emphasis has been placed on vector transfection efficiency, the study of the adverse effects upon the brain, caused by the vectors themselves, remains completely overshadowed. To this end, a study was undertaken to study the tissue response to three commercially available transfection agents in the brain of adult Sprague Dawley rats. The response to these transfection agents was compared to adeno-associated viral vector (AAV), PBS and naked DNA. Furthermore, the use of a collagen hollow sphere (CHS) sustained delivery system was analysed for its ability to reduce striatal toxicity of the most predominantly studied polymer vector, polyethyleneimine (PEI). The size of the gross tissue loss at the injection site was analysed after immunohistochemical staining and was used as an indication of acute toxicity. Polymeric vectors showed similar levels of acute brain toxicity as seen with AAV, and CHS were able to significantly reduce the toxicity of the PEI vector. In addition; the host response to the vectors was measured in terms of reactive astrocytes and microglial cell recruitment. To understand whether this gross tissue loss was caused by the direct toxicity of the vectors themselves an in vitro study on primary astrocytes was conducted. All vectors reduced the viability of the cells which is brought about by direct necrosis and apoptosis. The CHS delivery system reduced cell necrosis in the early stages of post administration. In conclusion, whilst polymeric gene vectors cause acute necrosis, administration in the brain causes adverse effects no worse than that of an AAV vector. Furthermore, packaging the PEI vector with CHS reduces surface charge and direct toxicity without elevating the host response.

Building biocompatible hydrogels for tissue engineering of the brain and spinal cord

Tissue engineering strategies employing biomaterials have made great progress in the last few decades. However, the tissues of the brain and spinal cord pose unique challenges due to a separate immune system and their nature as soft tissue. Because of this, neural tissue engineering for the brain and spinal cord may require re-establishing biocompatibility and functionality of biomaterials that have previously been successful for tissue engineering in the body. The goal of this review is to briefly describe the distinctive properties of the central nervous system, specifically the neuroimmune response, and to describe the factors which contribute to building polymer hydrogels compatible with this tissue. These factors include polymer chemistry, polymerization and degradation, and the physical and mechanical properties of the hydrogel. By understanding the necessities in making hydrogels biocompatible with tissue of the brain and spinal cord, tissue engineers can then functionalize these materials for repairing and replacing tissue in the central nervous system.

Defining and designing polymers and hydrogels for neural tissue engineering

The use of biomaterials, such as hydrogels, as neural cell delivery devices is becoming more common in areas of research such as stroke, traumatic brain injury, and spinal cord injury. When reviewing the available research there is some ambiguity in the type of materials used and results are often at odds. This review aims to provide the neuroscience community who may not be familiar with fundamental concepts of hydrogel construction, with basic information that would pertain to neural tissue applications, and to describe the use of hydrogels as cell and drug delivery devices. We will illustrate some of the many tunable properties of hydrogels and the importance of these properties in obtaining reliable and consistent results. It is our hope that this review promotes creative ideas for ways that hydrogels could be adapted and employed for the treatment of a broad range of neurological disorders.

A methodology based on the "anterior chamber of rabbit eyes" model for noninvasively determining the biocompatibility of biomaterials in an immune privileged site

In this study, a novel methodology based on the anterior chamber of rabbit eyes model was developed to evaluate the in vivo biocompatibility of biomaterials in an immune privileged site. The 7-mm-diameter membrane implants made from either a biological tissue material (amniotic membrane, AM group) or a biomedical polymeric material (gelatin, GM group) were inserted in rabbit anterior chamber for 36 months and characterized by biomicroscopic examinations, intraocular pressure measurements, and corneal thickness measurements. The noninvasive ophthalmic parameters were scored to provide a quantitative grading system. In this animal model, both AM and GM implants were visible in an ocular immune privileged site during clinical observations. The implants of the AM group appeared as soft tissue patches and have undergone a slow dissolution process resulting in a partial reduction of their size. Additionally, the AM implants did not induce any foreign body reaction or change in ocular tissue response for the studied period. By contrast, in the GM groups, significant corneal edema, elevated intraocular pressure, and increased corneal thickness were noted in the early postoperative phase (within 3 days), but resolved rapidly with in vivo dissolution of the gelatin. The results from the ocular grading system showed that both implants had good long-term biocompatibility in an ocular immune privileged site for up to 3 years. It is concluded that the anterior chamber of rabbit eyes model is an efficient method for noninvasively determining the immune privileged tissue/biomaterial interactions.

Biocompatibility of polyhydroxybutyrate microspheres: in vitro and in vivo evaluation

Microspheres have been prepared from the resorbable linear polyester of beta-hydroxybutyric acid (polyhydroxybutyrate, PHB) by the solvent evaporation technique and investigated in vitro and in vivo. Biocompatibility of the microspheres has been proved in tests in the culture of mouse fibroblast cell line NIH 3T3 and in experiments on intramuscular implantation of the microspheres to Wistar rats for 3 months. Tissue response to the implantation of polymeric microspheres has been found to consist in a mild inflammatory reaction, pronounced macrophage infiltration that increases over time, involving mono- and poly-nuclear foreign body giant cells that resorb the polymeric matrix. No fibrous capsules were formed around polymeric microparticles; neither necrosis nor any other adverse morphological changes and tissue transformation in response to the implantation of the PHB microparticles were recorded. The results of the study suggest that polyhydroxybutyrate is a good candidate for fabricating prolonged-action drugs in the form of microparticles intended for intramuscular injection.

Biocompatibility of PEG-Based Hydrogels in Primate Brain

Degradable polymers have been used successfully in a wide variety of peripheral applications from tissue regeneration to drug delivery. These polymers induce little inflammatory response and appear to be well accepted by the host environment. Their use in the brain, for neural tissue reconstruction or drug delivery, also could be advantageous in treating neurodegenerative disorders. Because the brain has a unique immune response, a polymer that is compatible in the body may not be so in the brain. In the present study, polyethylene glycol (PEG)-based hydrogels were implanted into the striatum and cerebral cortex of nonhuman primates. Four months after implantation, brains were processed to evaluate the extent of astrogliosis and scaring, the presence of microglia/macrophages, and the extent of T-cell infiltration. Hydrogels with 20% w/v PEG implanted into the brain stimulated a slight increase in astrocytic and microglial/macrophage presence, as indicated by a small increase in glial fibrillary acidic protein (GFAP) and CD68 staining intensity. This increase was not substantially different from that found in the sham-implanted hemispheres of the brain. Staining for CD3+ T cells indicated no presence of peripheral T-cell infiltration. No gliotic scarring was seen in any implanted hemisphere. The combination of low density of GFAP-positive cells and CD68-positive cells, the absence of T cells, and the lack of gliotic scarring suggest that this level of immune response is not indicative of immunorejection and that the PEG-based hydrogel has potential to be used in the primate brain for local drug delivery or neural tissue regeneration.