Current Pharmaceutical Design - Volume 23, Issue 26, 2017

The foundation of tissue engineering for either therapeutic or diagnostic applications is the ability to exploit living cells. Tissue engineering utilizes living cells as engineering materials implanted, seeded or bioplotted into an artificial structure capable of supporting three-dimensional tissue formation. These structures, typically called scaffolds, are critical, both ex vivo and in vivo, to influence their own microenvironments. Scaffolds can serve the following purposes: allow cell attachment and migration, deliver and retain cells and biochemical factors, enable diffusion of vital cell nutrients or expressed products, exert certain mechanical and biological influences to modify the behaviour of the cell phase. Traditional tissue engineering strategies typically employ a “top-down” approach, in which cells are seeded on a biodegradable three dimensional monolithic polymeric scaffold. More recently they have been updated by a “bottom- up” approach, also known as modular tissue engineering; it is aimed to address the challenge of recreating bio-mimetic structures by designing structural micro-features to build modular tissues, used as building blocks to re-create larger ones. These two different approaches will require scaffolds with given characteristics obtainable by choosing different fabrication technologies. Conventional and innovative supercritical technologies for monolithic scaffold production or biopolymer micro/nano devices will be discussed in this chapter. Some examples of bone and cartilage tissue engineering produced by using modular scaffold will be also discussed, as well as the fabrication of artificial extracellular matrix for spatio-temporally delivery of biological and mechanical signal to address cell fate.

β-Amino acids are being increasingly used in the design of bioactive ligands and more recently in the generation of novel biomaterials. Peptides containing either individual β-amino acid substitutions or peptides comprised entirely of β-amino acids, display unique properties in terms of their structural and/or chemical characteristics. β-Peptides form well-defined secondary structures that exhibit different geometries compared to the corresponding α-peptides. β-Peptides, including α-peptides containing only one or two β-amino acids, can be easily modified with different functional groups and are metabolically stable and, together with the predictable side chain topography, have led to the design of a growing number of bioactive β-peptides with a range of biological targets and therapeutic applications. More recently, our understanding of the folding and self-assembly of β-peptides has resulted in the generation of novel biomaterials. The focus of this review is to examine how the structural and chemical properties of β-peptides have been exploited in the design of bioactive peptides and selfassembled nanomaterials.

Hydroxyapatite (HAp) is a complicated ceramic material that varies between the way it appears in biological systems and how it is synthesized as various calcium phosphates. HAp varies in chemical composition of substituting atoms, crystallinity, grain size and electrical polarization. HAp can form solid to macro-, micro- and nanoporous structures. Also, particulate HAp can have highly porous structure. HAp can be used as coatings for metal implants in thicknesses from hundreds of microns down to hundreds of nanometers. Cotton wool-like HAp fibers can be electrospun compounded with polymers (or without) for tissue engineering (TE) scaffolds. This review describes the features of HAp that may be utilized further in developing novel applications. As a nanomaterial HAp has been applied for drug delivery. The adsorption of proteins and other compounds can be adjusted by modifying HAp composition, electrical polarization and wettability. Of special interest are the bisphosphonates that bind to HAp and thereby can be used to treat bone loss and also couple other drugs to the mineral. A new area for HAp constructs may appear in treating metallosis. HAp coating may function as a scavenger for the ions release from metal implants and thereby inhibit the adverse effects of the ion burden for the body. So far HAp is considered as safe biomaterial but nano HAp may insidiously possess adverse effects especially when ingested by cells and eliciting excess intracellular calcium. Thereby critical approach also for HAp biomaterials is of utmost importance.

This review article provides an overview of hybrid and nanocomposite materials used as biomaterials in nanomedicine, focusing on applications in controlled drug delivery, tissue engineering, biosensors and theranostic systems. Special emphasis is placed on the importance of tuning the properties of nanocomposites, which can be achieved by choosing appropriate synthetic methods and seeking synergy among different types of materials, particularly exploiting their nanoscale nature. The challenges in fabrication for the nanocomposites are highlighted by classifying them as those comprising solely inorganic phases (inorganic/inorganic hybrids), organic phases (organic/organic hybrids) and both types of phases (organic/inorganic hybrids). A variety of examples are given for applications from the recent literature, from which one may infer that significant developments for effective use of hybrid materials require a delicate balance among structure, biocompatibility, and stability.

Mesenchymal stem cells (MSCs) have become one of the most important cell sources for regenerative medicine. However, some mechanisms of MSC-based therapy are still not fully understood. The clinical outcome may be restricted by some MSC-related obstacles such as the low survival rate, differentiation into undesired lineages and malignant transformation. In recent years, with the emergence of nanotechnology, various types of multifunctional nanoparticles (NPs) have been designed, prepared and explored for bio-related applications. There is high potential of NPs in biomedical applications, attributed to the high capacity of cellular internalization in MSCs and their multiple functionalities. They can be used either as labeling agent to track MSCs for mechanism study or as gene/drug delivery carriers to regulate the cellular behavior and functions of MSCs. However, the application of NPs may be accompanied by some undesirable effects, as some NPs can induce cell death, inhibit cell proliferation or influence the differentiation of MSCs. Aiming to provide a comprehensive understanding of the interaction between NPs and MSCs, recent progress in the design and preparation of multifunctional NPs is summarized in this review, mechanisms of cellular internalization of the NPs are discussed, the main applications of multifunctional NPs in MSCs are highlighted and overview about cellular response of MSCs to different NPs is given. Future studies aiming on design and development of NPs with multifunctionality may open a new field of applying nanotechnology in stem cell-based therapy.

Increasing numbers of requests for transplantable organs and their scarcity has led to a pressing need to find alternative solutions to standard transplantation. An appealing but challenging proposal came from the fields of tissue engineering and regenerative medicine, the purpose of which is to build tissues/organs from scratch in the laboratory and use them as either permanent substitutes for direct implantation into the patient’s body, or as temporary substitutes to bridge patients until organ regeneration or transplantation. Using bioartificial constructs requires administration of immunosuppressant therapies to prevent rejection by the recipient. Microencapsulation has been identified as promising technology for immunoisolating biological materials from immune system attacks by the patient. It is based on entrapping cellular material within a spherical semipermeable polymeric scaffold. This latter defines the boundary between the internal native-like environment and the external “aggressive” one. The scaffold thus acts like a selective filter that makes possible an appropriate supply of nutrients and oxygen to the cellular constructs, while blocking the passage for adverse molecules. Alginate, which is a natural polymer, is the main biomaterial used in this context. Its excellent properties and mild gelation ability provide suitable conditions for supporting viability and preserving the functionalities of the cellular- engineered constructs over long periods. Although much remains to be done before bringing microencapsulated constructs into clinical practice, an increasing number of applications for alginate-based microencapsulation in numerous medical areas confirm the considerable potential for this technology in providing a cure for transplant in patients that excludes immunosuppressive therapies.

Facing the problems of limited renal regeneration capacity and the persistent shortage of donor kidneys, dialysis remains the only treatment option for many end-stage renal disease patients. Unfortunately, dialysis is only a medium-term solution because large and protein-bound uremic solutes are not efficiently cleared from the body and lead to disease progression over time. Current strategies for improved renal replacement therapies (RRTs) range from whole organ engineering to biofabrication of renal assist devices and biological injectables for in vivo regeneration. Notably, all approaches coincide with the incorporation of cellular components and biomimetic micro-environments. Concerning the latter, hydrogels form promising materials as scaffolds and cell carrier systems due to the demonstrated biocompatibility of most natural hydrogels, tunable biochemical and mechanical properties, and various application possibilities. In this review, the potential of hydrogel-based cell therapies for kidney regeneration is discussed. First, we provide an overview of current trends in the development of RRTs and in vivo regeneration options, before examining the possible roles of hydrogels within these fields. We discuss major application-specific hydrogel design criteria and, subsequently, assess the potential of emergent biofabrication technologies, such as micromolding, microfluidics and electrodeposition for the development of new RRTs and injectable stem cell therapies.

Current research in neural tissue-engineering is focused on the development of advanced biomaterials for the creation of sophisticated neuro-tissue analogues, showing that mimicking the in vivo tissue disposition and functions is a useful tool for the study of brain-related issues in normal and pathological states. In addition, the most common approach for developing new drug therapies is to carry out in vitro investigation before in vivo test, thus, it is increasingly important to develop valuable models that can predict the results of in vivo studies. This review presents the recent state of the art concerning the multifunctional role of biohybrid membrane systems in neuronal tissue engineering as innovative in vitro platforms with a well-controlled microenvironment, that enhance nervous system repair by guiding neuronal growth and differentiation. In vitro membrane-based models of brain tissue, created by combining neurons, membranes and therapeutic molecules, were described highlighting the innovative approaches directed to investigate specific biological phenomena as well as for testing biopharmaceutical compounds in neurodegenerative diseases, and drug delivery to the CNS. Furthermore, several examples of in vivo application of membrane-based stem cell delivery approaches for nerve regeneration were summarized.

Transport systems are hydrophobic proteins localized in cell membranes where they mediate transmembrane flow of nutrients, ions and any other compounds essential for cell metabolism. More than 400 transporters of the SoLuteCarrier (SLC) group are present in human cells. Transporters take contacts also with xenobiotics, thus mediating absorption and/or interaction with these exogenous compounds. Since drugs belong to xenobiotics, transporters gained interest also in drug discovery. Transporters differentially expressed in pathological conditions are exploited as drug targets. Among the methodologies for defining drug interactions, in silico ligand screening and intact cell transport assay were the most diffused, so far. The first is a predictive methodology based on docking chemicals to transporters. It presents limitations due to the small number of human transporter 3D structures that have to be constructed by homology modeling. Intact cells are used for testing effects of drugs and for validating predictions. The challenges of handling this very complex experimental system, are the interferences caused by other transporters and/or intracellular enzymes. Thus, methodologies with lower complexity are welcome. One of the most updated is the proteoliposome nanotechnology consisting in a cell mimicking phospholipid membrane in which a purified transporter is inserted. In this system, drug-transporter interaction can be studied defining kinetics and mechanisms. Several data have been obtained by proteoliposome nanotechnology. An overview of data obtained on the organic cation transporters OCTN1, OCTN2 and on the amino acid transporters ASCT2 and B0AT1 will be presented. Standardized procedures, expected to be pointed out, will enlarge the assay to High Throughput Screenings.

Background: Ischemia-reperfusion (I/R) injury causes the dysfunctions of different major organs, leading to morbidity and mortality on the global scale. Among a battery of therapeutic targets, the heme oxygenase- 1 (HO-1)/carbon monoxide (CO) system has been evaluated for the development of new therapies against I/R injury. The enzyme HO-1 catalyzes the degradation of heme into three biologically active end products, namely biliverdin/bilirubin, CO and ferrous ion. Interestingly, CO is one of a few bioactive gaseous molecules with the capability of regulating inflammation, cell survival and growth. In fact, several CO-releasing compounds have been developed for directly reprogramming the intracellular apoptotic, inflammatory and proliferative signaling networks. In parallel, chemical and genetic approaches have also been evaluated for up-regulating HO-1 expression as an endogenous mechanism to ameliorate I/R injury and heal wounds. Methods: In this review, we discussed the recent studies on the therapeutic potential of HO-1/CO system in the treatment of I/R injury in the heart, brain, liver, kidney, lung, intestine and retina. We focused on the activities and underlying mechanisms of various therapeutic strategies to regulate HO-1/CO system against I/R injury. Results: A large number of studies have demonstrated that HO-1/CO system exhibits potent anti-oxidative, antiapoptotic, anti-inflammatory and cytoprotective activities against I/R injury. The regulation of HO-1/CO expression has been achieved either by genetic overexpression of HO-1 cDNA or pharmacological induction with drugs including curcumin and resveratrol. Conclusion: The HO-1/CO system is a potential target for treating I/R injury. Further studies should be directed to in vivo efficacy and clinical application of HO-1/CO system in the therapy of I/R injury.

Brain injury constitutes a disabling health condition of several etiologies. One of the major causes of brain injury is hypoxia-ischemia. Until recently, pharmacological treatments were solely focused on neurons. In the last decades, glial cells started to be considered as alternative targets for neuroprotection. Novel treatments for hypoxia-ischemia intend to modulate reactive forms of glial cells, and/or potentiate their recovery response. In this review, we summarize these neuroprotective strategies in hypoxia-ischemia and discuss their mechanisms of action.