Current Pharmaceutical Biotechnology - Volume 14, Issue 1, 2013

Cardiovascular diseases, including myocardial infarction and heart failure, are the main causes of death worldwide. Classical pharmacological treatment may halt, but cannot reverse the underlying disease process. Cellular cardiomyoplasty has the potential to reconstruct myocardium in situ; yet, it is hampered by poor cell survival, engraftment, and differentiation. Tissue engineering has emerged as an alternative cell-based approach, aiming at partial or full replacement of damaged organs with in vitro generated tissue equivalents. However, limited availability of therapeutic cardiomyocytes poses a major challenge on cell-based and in particular tissue engineering-based therapies. Rapidly evolving stem cell technologies, enabling mass cultures may overcome this limitation. Translating available experimental concepts into clinical reality will be the ultimate challenge. This review discusses potentially therapeutic cells for cardiac repair, current stem cell-based myocardial tissue engineering strategies, and the requirements for a translation of myocardial tissue engineering into clinical practice.

Chronic ischemic heart disease remains a major cause of morbidity and mortality worldwide. Although revascularisation strategies and pharmaceutical therapy are able to delay ventricular remodelling, until today no therapeutic strategy is available that might prevent or even reverse this process of remodelling and consequent ventricular failure. In the recent past, experimental and clinical studies have demonstrated the capacity of bone marrow stem cells in cardiac repair and regeneration of compromised heart muscle. Several clinical trials showed the safety and efficacy of autologous bone marrow stem cell transplantation in the patients with acute myocardial infarction or chronic ischemic heart disease. Today the therapeutic strategy of cell administration during cardiac surgery or coronary artery intervention is entering the clinical practice. In the following Review we will highlight biological as well as methodological backgrounds, indications and clinical results of cardiac stem cell therapy for the treatment of acute myocardial infarction and chronic ischemic heart disease.

In spite of increasing numbers of publications about cell replacement therapies in various neurodegenerative diseases, reports on therapeutic benefits are still rare due to the huge array of parameters affecting the clinically relevant outcome. Limiting conditions can be attributed to origin and number of cells used for transplantation, their in vitro storage, propagation and/or predifferentiation. In addition, the ability of these cells for a site directed differentiation and functional integration in sufficient numbers is known to depend on extrinsic factors including intracerebral position of graft(s). Thus, obstacles to the use of cells in replacement therapies of neurological disorders reflect the molecular as well as cellular complexity of affected functional systems. This review will highlight central aspects of cell replacement strategies that are currently regarded as the most limiting issues in respect to survival, cell identity and site directed differentiation as well as functional integration of grafts. Special attention will be paid to neural stem cells, derived from either fetal or adult central nervous tissue. Unravelling the molecular biology of these proliferating cells in combination with instructive environmental cues for their site directed differentiation will pave the way to high reproducibility in collection, propagation, and predifferentiation of transplantable cells in vitro. In addition, this knowledge of intrinsic and extrinsic cues for a site directed neural differentiation during development will broaden the perspective for any pluripotent stem cell, namely embryonic stem and induced pluripotent stem cells, as an alternate source for a cell based therapy of neurodegenerative diseases.

Radial glial cells represent a subpopulation of secondary neural precursor cells that differentiate from neuroepithelial progenitors and are transiently found in the developing CNS of mammals. There is ample evidence for a temporal and spatial arrangement of increasingly committed radial glial cells that is of critical importance for the organisation and specification of different brain regions. For the human ganglionic eminence, recent findings have shown an early molecular specification of this cell type by the CD15 carbohydrate epitope, beginning already at the end of the first trimester. Here we further characterise the CD15+ radial glia cells as bFGF/EGF responsive progenitors allowing its propagation in vitro. By magnet activated cell sorting, its trilineage differentiation potential can be shown by differentiation into (PSANCAM ß3 tubulin immunoreactive) neurones, GFAP expressing cells of astrocytic morphology, and O4 positive oligodendrocytes. Subcloning experiments under proliferation conditions reveal ongoing CD15 expression by dividing cells. Although the relative number of CD15+ progenitor cells is found to decrease in favour of CD15- precursor cells during continuous passaging, cell sorting experiments allow the repetitive purification of high numbers of positively selected precursor cells for up to 12 weeks. In conclusion, expression of the cell adhesion molecule CD15 by a subpopulation of proliferative cells from the lateral ganglionic eminence allows easy and reproducible purification of progenitor cells by cell sorting, enabling the generation of a compartment-specific cell pool as a prerequisite for a safe and standardised therapy of neurodegenerative basal forebrain diseases.

Stem cells possess great promise as therapeutic tools for neurological disorders such as neurodegenerative diseases (Parkinson's disease and Huntington's disease), cerebrovascular diseases (stroke), neurotraumata (spinal cord injury) and demyelinating diseases (multiple sclerosis). This aspiration is based on the cells` ability to maintain a status of self-renewal and to differentiate into the various cell types of an organism. The use of the cells ranges from in vitro to in vivo studies in animal models, ending with clinical applications in humans. The self-renewal and commitment of stem/progenitor cells to differentiate and mature involves complex events leading to the generation of different phenotypes via distinctive developmental programs. Small molecules provide a tool with which to influence these regulatory changes in a controlled manner and to help understand the underlying mechanisms. Furthermore, substantial progress in generating induced pluripotent stem cells has been made using small molecules to replace reprogramming factors and enhance the reprogramming efficiency and kinetics, thus generating cells more compatible with the requirements for cell replacement therapies. In this review we will present the recent progress on the use of small molecules in embryonic and induced pluripotent stem cell research. In the final section we will give a short summary of the clinical approaches using these cells.

Gene delivery has attracted increasing interest as a highly promising therapeutic method to treat various diseases, including both genetic and acquired disorders. Viral-vectors based gene delivery can achieve higher transduction efficiency and long-term gene expression, but they may be associated with some shortcomings, such as immunogenicity, carcinogenicity, poor target cell specificity, inability to transfer large size genes and high costs. Non-viral approaches show high potential due to advantages of relative safety, ability to transfer large size gene, less toxicity and easiness for preparation etc. However, the clinical application of non-viral methods is still restricted by some limitations including low transfection efficiency and poor transgene expression. In order to improve gene transfer efficacy, a lot of efforts have been made in the past years, and numerous gene carriers and techniques have been developed. In this review, we summarized the features, drawbacks and prospects of existing and emerging non-viral gene delivery methods.

Heart failure is a life threatening disorder in worldwide and many papers reported about myocardial regeneration through surgical method induced by LVAD, cellular cardiomyoplasty (cell injection), tissue cardiomyoplasty (bioengineered cardiac graft implantation), in situ engineering (scaffold implantation), and LV restrictive devices. Some of these innovated technologies have been introduced to clinical settings. This review article provides summary about recent basical and clinical advances about myocardial regeneration induced by bioengineered cardiac tissue.

Drug-eluting stents (DES) have revolutionized the treatment of coronary artery blockage by tremendously reducing the rate of in-stent restenosis and the necessity of repeat revascularization compared to bare-metal stents. They are also gaining increasing importance in other medical fields such as the treatment of certain localized tumors and in glaucoma therapy. DES generally contain most potent drugs, e.g. immunosuppressants or cytostatics, which are supposed to be released in a well controlled manner over time spans which are chosen according to disease progression. Typically, this means that fairly small amounts of drug are released over long periods of time. Therefore, quantification of in vivo plasma levels is often not feasible. Due to this limitation and the fact that tissue levels cannot be determined in humans, in vitro dissolution testing is one of the most powerful tools to gain insight into the release behaviour of DES. This article focuses on the methods for in vitro dissolution testing of DES which are available up to date and highlights the specific characteristics of drug release from stents arising from the composition and the in vivo localization of the dosage form.

Beyond their originally sole mechanical function, current drug-eluting stents (DES) implement the concept of local drug delivery for the re-opening of stenotic arterial vessels, and for prevention of in-stent restenosis as one of the major limitations of conventional bare metal stents (BMS). Current DES consist of a permanent metallic stent platform and an active agent being released from a drug-incorporated polymer coating or a porous stent surface. Although DES have impressively demonstrated their capability of reducing in-stent restenosis, their safety remains under debate due to potential risks, such as delayed healing, late thrombosis and hypersensitivity demanding further development. Current advancements in the stent design address the stent platform, the pharmacologically active substance and/or the drug carrier. For instance, novel biocompatible absorbable stent platforms and drug carriers are developed and novel drugs with a differential effect on vascular endothelial and smooth muscle cells, providing efficient inhibition of muscle cells without altering the endothelial cell function, are identified. Moreover, biofunctionalization of the stent’s surface with capture molecules for endothelial progenitor cells are under investigation in order to achieve an in situ endothelialization of the implant. In this context, this review paper discusses the current advances in coronary stent technology with a special focus on novel stent platforms, drugs and stent coatings for the prevention of restenosis and improvement of biocompatibility.

Computer assisted biofabrication of fully functional living tissue for regenerative medicine involves generation of complex three-dimensional constructs consisting of living cells and biomaterials. Laser BioPrinting (LaBP) based on laser-induced forward-transfer provides unique possibilities for the deposition of different living cells and biomaterials in a well-defined 3D structure. LaBP can be applied to generate scaffold-free 3D cell systems through a layer-by-layer technique by combining cell solutions with materials that are able to form stable gels. Also, it is used to precisely populate scaffolds with different cells and different cell densities. It was proven that printed cells are not affected by the laser printing procedure and that a differentiation of printed stem cells is not induced. Thus, LaBP is demonstrated as a promising tool for the ex vivo generation of tissue replacements.

Glaucoma is a common cause of blindness in industrialized countries and is the most frequent cause of irreversible blindness worldwide. Since raised intraocular pressure (IOP) has been implicated as the major risk factor, the main goal of all glaucoma treatment is to reduce IOP sufficiently to prevent continuous irreversible retinal ganglion cell damage and progression of visual field loss. Pharmacological reduction of IOP is first-line therapy, followed by laser treatment of the trabecular meshwork and filtering glaucoma surgery, and cyclophotocoagulation of the ciliary body or allogenic implants. The most important glaucoma implants are presented (MOLTENO, AHMED, BAERVELDT, KRUPIN) together with more recent developments (Ex-Press, Eyepass, iStent, Gold micro shunt). Drainage into the suprachoroidal space is a promising option, but is also limited by scarring of the new created outflow route due to proliferation and adhesion of fibroblasts. A deeper understanding of fibroblasts in the related eye compartments is required. Characterization of scleral, choroidal, and, as a reference, Tenon fibroblast subtypes, is possible based on gene expression patterns. Alongside mitomycin C and 5-fluorouracil, newer drugs to prevent fibrosis have been proposed, offering effects that are more specific and more physiological. Effectors involved in wound healing phases and signaling pathways are potential targets for pharmaceutical intervention. Downregulation of growth factors like TGF-ß and their downstream effectors may suppress proliferation and differentiation of fibroblasts, extracellular matrix deposition, wound contraction, and neovascularization. Furthermore, current approaches to local drug delivery in glaucoma implant technology are briefly summarized.

Cochlear implants have evolved to become the treatment of choice for severely hearing-impaired patients. Speech signals are picked up by a microphone, processed and then delivered to the stimulating electrodes (the current maximum number being 22) that are placed on an electrode array implanted into the scala tympani of the cochlea. The target cells of electrical stimulation, the spiral ganglion cells (SGCs), are located some distance away in the central axis of the cochlea. SGCs start to degenerate after the onset of deafness. Additionally, fibrous tissue is formed around the electrode array after implantation. If cochlear implants are to deliver sound that is closer to natural hearing, the number of independent stimulation channels has to be increased. Optimization of the interface between the electrode array and the surrounding tissue is, therefore, the focus of current research. Promising approaches relating to cells, micro- and nanosystems will be reviewed.

The use of botulinum neurotoxins (BoNTs) for therapeutic purposes in neuromuscular disorders and peripheral hypercholinergic conditions as well as in aesthetic medicine is widespread and common. BoNTs are also able to block the release of a wide range of transmitters from presynaptic boutons. Therefore, application of BoNTs directly in the central nervous system (CNS) is currently under study with respect to basic research and potentially as a new therapeutic strategy of neurological diseases. Investigations concentrate on effects of intracerebral and intraspinal application of BoNTs in rodents on the impact on spinal, nuclear, limbic and cortical neuronal circuits. In animal model first promising BoNTinduced therapeutical benefit has been shown in the treatment of pain, epilepsy, stroke and Parkinson's disease.