Transforming growth factor beta-3 crystals as reservoirs for slow release of active TGF-beta3

Biotechnological applications of amyloid fibrils

Protein aggregates and amyloid fibrils have special qualities and are used in a variety of biotechnological applications. They are extensively employed in bioremediation, biomaterials, and biocatalysis. Because of their capacity to encapsulate and release pharmaceuticals and their sensitivity to certain molecules, respectively, they are also used in drug delivery and biosensor applications. They have also demonstrated potential in the domains of food and bioremediation. Additionally, amyloid peptides have drawn interest in biological applications, especially in the investigation of illnesses like Parkinson's and Alzheimer's. The unique characteristics of amyloid fibrils, namely their mechanical strength and β-sheet structure, make them adaptable to a wide range of biotechnological uses. Even with their promise, one important factor to keep in mind before widely using modified amyloid materials is their potential toxicity. Thus, current research aims to overcome safety concerns while maximizing their potential.

New perspectives in macromolecular powder diffraction using single-photon-counting strip detectors: high-resolution structure of the pharmaceutical peptide octreotide

Advances in instrumentation, as well as the development of powerful crystallographic software have significantly facilitated the collection of high-resolution diffraction data and have made X-ray powder diffraction (XRPD) particularly useful for the extraction of structural information; this is true even for complex molecules, especially when combined with synchrotron radiation. In this study, in-line with past instrumental profile studies, an improved data collection strategy exploiting the MYTHEN II detector system together with significant beam focusing and tailored data collection options was introduced and optimized for protein samples at the Material Science beamline at the Swiss Light Source. Polycrystalline precipitates of octreotide, a somatostatin analog of particular pharmaceutical interest, were examined with this novel approach. XRPD experiments resulted in high angular and d-spacing (1.87 Å) resolution data, from which electron-density maps of enhanced quality were extracted, revealing the molecule's structural properties. Since microcrystalline precipitates represent a viable alternative for administration of therapeutic macromolecules, XRPD has been acknowledged as the most applicable tool for examining a wide spectrum of physicochemical properties of such materials and performing studies ranging from phase identification to complete structural characterization.

Fractal self-assembly and aggregation of human amylin

Human amylin is an intrinsically disordered protein believed to have a central role in Type-II diabetes mellitus (T2DM). The formation of intermediate oligomers is a seminal event in the eventual self-assembled fibril structures of amylin. However, the recent experimental investigations have shown the presence of different self-assembled (oligomers, protofilaments, and fibrils) and aggregated structures (amorphous aggregates) of amylin formed during its aggregation. Here, we show that amylin under diffusion-limited conditions leads to fractal self-assembly. The pH and solvent sensitive fractal self-assemblies of amylin were observed using an optical microscope. Confocal microscopy and scanning electron microscopy (SEM) with energy dispersion X-ray analysis (EDAX) were used to confirm the fractal self-assembly of amylin in water and PBS buffer, respectively. The fractal characteristics of the self-assemblies and the aggregates formed during the aggregation of amylin under different pH conditions were investigated using laser light scattering. The hydropathy and the docking study indicated the interactions between the anisotropically distributed hydrophobic residues and polar/ionic residues on the solvent-accessible surface of the protein as the crucial interaction hot-spots for driving the self-assembly and aggregation of human amylin. The simultaneous presence of various self-assemblies of human amylin was observed through different microscopy techniques. The present study may help in designing different fractal-like nanomaterials with potential applications in drug delivery, sensing, and tissue engineering.

Protein Nanofibrils as Storage Forms of Peptide Drugs and Hormones

Amyloids are highly organized cross β-sheet protein nanofibrils that are associated with both diseases and functions. Thermodynamically amyloids are stable structures as they represent the lowest free energy state that proteins can attain. However, recent studies suggest that amyloid fibrils can be dissociated by a change in environmental parameters such as pH and ionic strength. This reversibility of amyloids can not only be associated with disease, but function as well. In disease-associated amyloids, fibrils can act as reservoirs of cytotoxic oligomers. Recently, in higher organisms such as mammals, hormones were found to be stored in amyloid-like state, where these were reported to act as a reservoir of functional monomers. These hormone amyloids can dissociate to monomers upon release from the secretory granules, and subsequently bind to their respective receptors and perform their functions. In this book chapter, we describe in detail how these protein nanofibrils represent the densest possible peptide packing and are suitable for long-term storage. Thus, mimicking the feature of amyloids to release functional monomers, it is possible to formulate amyloid-based peptide/protein drugs, which can be used for sustained release.

Amyloids Are Novel Cell-Adhesive Matrices

Amyloids are highly ordered peptide/protein aggregates traditionally associated with multiple human diseases including neurodegenerative disorders. However, recent studies suggest that amyloids can also perform several biological functions in organisms varying from bacteria to mammals. In many lower organisms, amyloid fibrils function as adhesives due to their unique surface topography. Recently, amyloid fibrils have been shown to support attachment and spreading of mammalian cells by interacting with the cell membrane and by cell adhesion machinery activation. Moreover, similar to cellular responses on natural extracellular matrices (ECMs), mammalian cells on amyloid surfaces also use integrin machinery for spreading, migration, and differentiation. This has led to the development of biocompatible and implantable amyloid-based hydrogels that could induce lineage-specific differentiation of stem cells. In this chapter, based on adhesion of both lower organisms and mammalian cells on amyloid nanofibrils, we posit that amyloids could have functioned as a primitive extracellular matrix in primordial earth.

Characterization and suitability of therapeutic antibody dense phases for subcutaneous delivery

Subcutaneous antibody dosing formulations comprising solid suspensions have the potential to reduce dosage viscosity and injection volume. Gel beads of three therapeutic antibodies were prepared to determine the feasibility of such formulations. The beads were formed directly from aqueous solution within 0.1-4 days upon addition of biocompatible precipitating agents under conditions compatible with the use of stabilizing excipients. The phase behavior of antibody gel beads and their mechanical characteristics were measured. Gel beads were characterized by reduced elastic moduli of 0.4-1.0 MPa, as measured by atomic force microscopy, and completely redissolved within 10-20 min under physiologic conditions, in vitro. Crystalline particles could also be prepared in some cases and were found to have reduced elastic moduli 3 orders of magnitude greater than those for the gel beads. Both crystalline and gel particles had protein concentrations of 100-180 mg/mL within the dense phase. Protein stored within the dense phase was recoverable after 40 days of incubation at room temperature or 4 °C.

Reversible crystallization of argatroban after subcutaneous application in pigs

Argatroban is a thrombin inhibitor used as anticoagulant in patients with heparin-induced thrombocytopenia. It is usually administered as an intravenous bolus followed by infusion. Nevertheless, its pharmacokinetics after subcutaneous administration is unknown. The aim of this study was to assess the pharmacokinetics of two different formulations of argatroban in pigs after subcutaneous administration. Antithrombotic activity in plasma was determined by ecarin chromogenic assay. To visualize the formation of crystals, argatroban was administered to rats into the subcutaneous tissue exposed after removing the skin, and the injection site was photographed at different times. After subcutaneous administration of a sorbitol/ethanol formulation of argatroban in pigs was observed a slow absorption phase was followed by long-lasting levels of this inhibitor. C(max) and AUC((0-24)) showed dose-dependent increases, while elimination half-life and t(max) value did not change significantly with dose. In contrast, saline-dissolved argatroban showed a faster absorption phase followed by a shorter elimination half-life. Argatroban dissolved in sorbitol/ethanol leads to long-lasting plasma levels due to the formation and permanent dissolution of a crystalline depot at the injection place. This represents a simple way to deliver argatroban continuously over an extended period which can be beneficial for prophylaxis or treatment of chronic coagulations disorders.

AMYLOID: A NATURAL NANOMATERIAL

Amyloids are stable, β-sheet-rich protein/peptides aggregates with 2–15 nm diameter and few micrometers long. It is originally associated with many human diseases such as Alzheimer's, Parkinson's and prion diseases. Amyloids are resistant to enzyme degradation, temperature changes and wide ranges of pH. Although, amyloids are hard and their stiffness is comparable to steel, a constant recycling of monomer occur inside the amyloid fibrils. It grows in a nucleation dependent polymerization manner by recruiting native soluble protein and by converting them to amyloid. These extraordinary physical properties make amyloids attractive for nanotechnological applications. Some amyloid fibrils have also evolved to perform native biological functions (functional amyloid) of the host organism. Functional amyloids are present in mammals such as amyloids of pMel17 and pituitary hormones, where they help in skin pigmentation and hormone storage, respectively. Here, the progress of utilizing amyloid fibrils for nanobiotechnological applications with particular emphasis on the recent studies that amyloid could be utilized for the formulation of peptide/protein drugs depot and how secretory cells uses amyloid for hormone storage will be reviewed.

Nanomaterials: amyloids reflect their brighter side

Amyloid fibrils belong to the group of ordered nanostructures that are self-assembled from a wide range of polypeptides/proteins. Amyloids are highly rigid structures possessing a high mechanical strength. Although amyloids have been implicated in the pathogenesis of several human diseases, growing evidence indicates that amyloids may also perform native functions in host organisms. Discovery of such amyloids, referred to as functional amyloids, highlight their possible use in designing novel nanostructure materials. This review summarizes recent advances in the application of amyloids for the development of nanomaterials and prospective applications of such materials in nanotechnology and biomedicine.

Localized delivery of growth factors for periodontal tissue regeneration: role, strategies, and perspectives

Difficulties associated with achieving predictable periodontal regeneration, means that novel techniques need to be developed in order to regenerate the extensive soft and hard tissue destruction that results from periodontitis. Localized delivery of growth factors to the periodontium is an emerging and versatile therapeutic approach, with the potential to become a powerful tool in future regenerative periodontal therapy. Optimized delivery regimes and well-defined release kinetics appear to be logical prerequisites for safe and efficacious clinical application of growth factors and to avoid unwanted side effects and toxicity. While adequate concentrations of growth factor(s) need to be appropriately localized, delivery vehicles are also expected to possess properties such as protein protection, precision in controlled release, biocompatibility and biodegradability, self-regulated therapeutic activity, potential for multiple delivery, and good cell/tissue penetration. Here, current knowledge, recent advances, and future possibilities of growth factor delivery strategies are outlined for periodontal regeneration. First, the role of those growth factors that have been implicated in the periodontal healing/regeneration process, general requirements for their delivery, and the different material types available are described. A detailed discussion follows of current strategies for the selection of devices for localized growth factor delivery, with particular emphasis placed upon their advantages and disadvantages and future prospects for ongoing studies in reconstructing the tooth supporting apparatus.

Amyloid as a depot for the formulation of long-acting drugs

Amyloids are highly organized protein aggregates that are associated with both neurodegenerative diseases such as Alzheimer disease and benign functions like skin pigmentation. Amyloids self-polymerize in a nucleation-dependent manner by recruiting their soluble protein/peptide counterpart and are stable against harsh physical, chemical, and biochemical conditions. These extraordinary properties make amyloids attractive for applications in nanotechnology. Here, we suggest the use of amyloids in the formulation of long-acting drugs. It is our rationale that amyloids have the properties required of a long-acting drug because they are stable depots that guarantee a controlled release of the active peptide drug from the amyloid termini. This concept is tested with a family of short- and long-acting analogs of gonadotropin-releasing hormone (GnRH), and it is shown that amyloids thereof can act as a source for the sustained release of biologically active peptides.

Amyloids are highly organized protein aggregates that are associated with both neurodegenerative diseases such as Alzheimer disease and benign functions such as skin pigmentation. Amyloids self-polymerize by recruiting their soluble protein counterpart and remain stable against harsh physical, chemical, and biochemical conditions. These extraordinary properties make amyloids attractive for applications in nanotechnology. Here, we suggest the use of amyloids in the formulation of long-acting drugs, which are active over extended periods of days and weeks. Long-acting drugs have been designed to increase patient comfort, convenience, dosage accuracy, and assurance of patient compliance for drugs that have a low oral bioavailability. It is our rationale that amyloids have the properties required of a long-acting drug because they are stable depots that guarantee a controlled release of the active peptide drug from the amyloid termini. This concept is tested with a family of short- and long-acting analogs of gonadotropin-releasing hormone, and it is shown that amyloids thereof can act as a source for the sustained release of biologically active peptides.

Amyloids have the properties required of a long-acting drug because they are stable depots that guarantee a controlled release of the active peptide drug from the amyloid termini.

Monomeric and dimeric GDF-5 show equal type I receptor binding and oligomerization capability and have the same biological activity

Growth and differentiation factor 5 (GDF-5) is a homodimeric protein stabilized by a single disulfide bridge between cysteine 465 in the respective monomers, as well as by three intramolecular cysteine bridges within each subunit. A mature recombinant human GDF-5 variant with cysteine 465 replaced by alanine (rhGDF-5 C465A) was expressed in E. coli, purified to homogeneity, and chemically renatured. Biochemical analysis showed that this procedure eliminated the sole interchain disulfide bond. Surprisingly, the monomeric variant of rhGDF-5 is as potent in vitro as the dimeric form. This could be confirmed by alkaline phosphatase assays and Smad reporter gene activation. Furthermore, dimeric and monomeric rhGDF-5 show comparable binding to their specific type I receptor, BRIb. Studies on living cells showed that both the dimeric and monomeric rhGDF-5 induce homomeric BRIb and heteromeric BRIb/BRII oligomers. Our results suggest that rhGDF-5 C465A has the same biological activity as rhGDF-5 with respect to binding to, oligomerization of and signaling through the BMP receptor type Ib.

Sustained delivery of bioactive cytokine using a dense collagen gel vehicle

OBJECTIVE

The use of cytokines as localized therapeutic agents is limited by the lack of a satisfactory delivery system. The aim of the current investigation was to determine the release kinetics and bioactivity of a simplified cytokine/collagen gel system designed to achieve extended, local delivery of bioactive cytokines at sites of premature cranial suture fusion (craniosynostosis).

DESIGN

Cytokine release was determined by ELISA measurements of Tgf-beta3 collected in media. Cytokine bioactivity was determined by measuring the effect of conditioned media, containing released Tgf-beta3, on mink lung epithelial cell proliferation and osteoblast alkaline phosphatase activity. Osteoblast response was evaluated by measuring proliferation of cells cultured on collagen gel containing Tgf-beta3 using an AlamarBlue assay.

RESULTS

Gels loaded with 100 and 500 ng of Tgf-beta3 produced a sustained release over 14 days with a pattern of initial large release followed by a gradual reduction in the amount released over the time. The reduced release over time was correlated to the amount initially loaded. Mink lung epithelial cell assay results indicated that Tgf-beta3 released from the collagen gel retained its bioactivity following incorporation into the collagen gel and release into the media. This bioactivity was further illustrated by a decreased alkaline phosphatase activity measured in osteoblasts cultured on the gels loaded with Tgf-beta3. Osteoblast proliferation assays demonstrated that the collagen gel has an inherent inhibitory effect on osteoblast cell number.

CONCLUSIONS

This collagen gel/cytokine delivery system can retain and release bioactive cytokine over a prolonged period. These results will allow for better optimization of future in vitro and in vivo studies directed at improving the treatment of craniosynostosis.

Localized delivery of growth factors for bone repair

Delivery of growth factors for tissue (e.g. bone, cartilage) or cell repair (e.g. nerves) is about to gain important potential as a future therapeutic tool. Depending on the targeted cell type and its state of differentiation, growth factors can activate or regulate a variety of cellular functions. Therefore, strictly localized delivery regimens at well-defined kinetics appear to be logical prerequisites to assure safe and efficacious therapeutic use of such factors and avoid unwanted side effects and toxicity, a major hurdle in the clinical development of growth factor therapies so far. This review summarizes various approaches for localized growth factor delivery as focused on bone repair. Similar considerations may apply to other growth factors and therapeutic indications. Considering the vast number of preclinical studies reported in the area of growth factor-assisted bone repair, it surprises though that only two medical products for bone repair have so far been commercialized, both consisting of a collagen matrix impregnated with a bone morphogenetic protein. The marked diversity of the reported growth factors, delivery concepts and not yet standardized animal models adds to the complexity to learn from past preclinical studies presented in the literature. Nonetheless, it is now firmly established from the available information that the type, dose and delivery kinetics of growth factors all play a decisive role for the therapeutic success of any such approach. Very likely, all of these parameters have to be adapted and optimized for each animal model or clinical case. In the future, systems for localized growth factor delivery thus need to be designed in such a way that their modular components are readily adaptable to the individual pathology. To make such customized systems feasible, close cooperative networks of biomedical and biomaterials engineers, pharmaceutical scientists, chemists, biologists and clinicians need to be established.

Injectable controlled release formulations incorporating protein crystals

Development of ready-to-inject in situ formable controlled release gel systems for proteins is extremely challenging due to poor stability of proteins in the organic solvents typically used to fabricate these systems and because of the need of initial drying of proteins. The focus of the present study was to develop and characterize injectable controlled release systems composed of crystals of amylase, a model protein, suspended in solutions of polymeric and non-polymeric matrix materials in organic solvents. In this study, alpha-amylase derived from Aspergillus oryzae was crystallized and crystals were suspended in a poly(DL-lactide-co-glycolide) (PLGA) solution in acetonitrile (PLGA/acetonitrile), or in sucrose acetate isobutyrate (SAIB) plasticized with ethanol (SAIB/ethanol) systems. The results indicate that the protein crystals could be incorporated in these in situ formable gels without the need for initial drying. The crystals withstand organic solvents and water/organic solvent interfaces, and provide high protein loading (>30%) in these systems. Moreover, changing the morphology of the amylase crystals successfully modulated amylase release profiles. Study of long-term stability at 4 degrees C revealed a greater stability of crystalline protein compared to amorphous amylase. The above-mentioned data suggest that protein crystals might offer greater feasibility in developing sustained release injectable in situ formable protein depot systems.

Emerging technologies that overcome biological barriers for therapeutic protein delivery

In the past decade, genomic research and the nascent field of proteomics have exponentially increased the number of potential protein therapeutic molecules for treating medical needs that were previously unmet. To realise the full clinical potential of many of the novel protein drug entities arising from these intense research efforts, emerging protein delivery technologies may be required. Advanced delivery technologies may offer the ability to overcome biochemical and anatomical barriers to protein drug transport, without incurring adverse events, to deliver the agent(s) at a certain desired rate and duration, to protect therapeutic macromolecules from in situ or systemic degradation, as well as increase their therapeutic index by targeting the drug action to a specific site. This review will cover a myriad of novel and emerging technologies that are directed at bypassing biological barriers and that have shown promise in advancing the therapeutic potential of protein drugs.

Soft tissue reaction to microgrooved poly-L-lactic acid implants loaded with transforming growth factor beta(3)

In both normal and disturbed wound healing, the generation of large, contracting scars can raise serious functional and cosmetic problems. A possible strategy to minimize or avoid the generation of scar tissue surrounding an implant is to apply transforming growth factor-beta(3) (TGF-beta(3)) to the implant. TGF-beta(3) (0, 1, or 2.5 microg) was freeze-dried onto poly-L-lactic acid (PLA) microgrooved substrates (width, 10 microm; depth, 1 microm) and implanted subcutaneously on the backs of rats for 2 and 8 weeks. After sacrifice, implants and surrounding tissue were histologically processed. Light microscopic and histomorphometric evaluation of capsule thickness, capsule quality, and implant-tissue interface was performed. In addition, we stained for alpha-smooth muscle actin (SMA), collagen, and ED-1 (a monocyte-macrophage marker). All implants were surrounded by a fibrous capsule. Capsules of the implants loaded with 1 or 2.5 microg of TGF-beta(3) showed significantly higher capsule quality. This meant that capsules were more mature compared with implants without TGF-beta(3). However, no significant differences were found in terms of thickness of the capsules or quality of the interface. Finally, apparently significant differences were also found in the expression of alpha-SMA, when comparing the various growth factor concentrations at both implantation points. In conclusion, the use of microgrooved PLA substrates with TGF-beta(3) did not lead to an overall improvement of periimplant tissue healing.