Development of 3D melanoma cultures on a hyaluronic acid-based scaffold with synthetic self-assembling peptides: Electroporation enhancement

Electrochemotherapy (ECT) with bleomycin is an effective antitumor treatment. Still, researchers are investigating new drugs and electroporation conditions to improve its efficacy. To this aim, in vivo assays are accurate but expensive and ethically questionable. Conversely, in vitro assays, although cheaper and straightforward, do not reflect the architecture of the biological tissue because they lack a tridimensional (3D) structure (as in the case of two-dimensional [2D] in vitro assays) or do not include all the extracellular matrix components (as in the case of 3D in vitro scaffolds). To address this issue, 3D in vitro models have been proposed, including spheroids and hydrogel-based cultures, which require a suitable low-conductive medium to allow cell membrane electroporation. In this study, a synthetic scaffold based on hyaluronic acid (HA) and self-assembling peptides (SAPs; EAbuK), condensed with a Laminin-derived adhesive sequence (IKVAV), is proposed as a reliable alternative. We compare SKMEL28 cells cultured in the HA-EAbuK-IKVAV scaffold to the control (HA only scaffold). Three days after seeding, the culture on the HA-EAbuK-IKVAV scaffold showed collagen production. SKMEL28 cells cultured on the HA-EAbuK-IKVAV scaffold started to be electroporated at 400 V/cm, whereas, at the same electric field intensity, those cultured on HA were not. As a reference, 2D experiments showed that electroporation of SKMEL28 cells starts at 600 V/cm using an electroporation buffer and at 800 V/cm in a culture medium, but with very low efficiency (<50 % of cells electroporated). 3D cultures on HA-EAbuK-IKVAV allowed the simulation of a more reliable microenvironment and may represent a valuable tool for studying electroporation conditions. Using Finite Element Analysis (FEA) to compute the transmembrane potential, we detected the influence of inhomogeneity of the extracellular matrix on electroporation effect. Our 3D cell culture electroporation simulations showed that the transmembrane potential increased when collagen surrounded the cells. Of note, in the collagen-enriched HA-EAbuK-IKVAV scaffold, EP was already improved at lower electric field intensities. This study shows the influence of the extracellular matrix on electric conductivity and electric field distribution on cell membrane electroporation and supports the adoption of more reliable 3D scaffolds in experimental electroporation studies.

Development and preclinical evaluation of bioactive nerve conduits for peripheral nerve regeneration: A comparative study

In severe peripheral nerve injuries, nerve conduits (NCs) are good alternatives to autografts/allografts; however, the results the available devices guarantee for are still not fully satisfactory. Herein, differently bioactivated NCs based on the new polymer oxidized polyvinyl alcohol (OxPVA) are compared in a rat model of sciatic nerve neurotmesis (gap: 5 mm; end point: 6 weeks). Thirty Sprague Dawley rats are randomized to 6 groups: Reverse Autograft (RA); Reaxon®; OxPVA; OxPVA + EAK (self-assembling peptide, mechanical incorporation); OxPVA + EAK-YIGSR (mechanical incorporation); OxPVA + Nerve Growth Factor (NGF) (adsorption). Preliminarily, all OxPVA-based devices are comparable with Reaxon® in Sciatic Functional Index score and gait analysis; moreover, all conduits sustain nerve regeneration (S100, β-tubulin) without showing substantial inflammation (CD3, F4/80) evidences. Following morphometric analyses, OxPVA confirms its potential in PNI repair (comparable with Reaxon®) whereas OxPVA + EAK-YIGSR stands out for its myelinated axons total number and density, revealing promising in injury recovery and for future application in clinical practice.

Finite Element Evaluation of the Electric Field Distribution in a Non-Homogeneous Environment

Finite element analysis is used in this study to investigate the effect of media inhomogeneity on the electric field distribution in a sample composed of cells and their extracellular matrix. The sample is supposed to be subjected to very high pulsed electric field. Numerically computed electric field distribution and transmembrane potential at the cell membrane in electroporation conditions are considered in order to study cell behavior at different degrees of inhomogeneity. The different inhomogeneity grade is locally obtained using a representative model of fixed volume with cell-cell distance varying in the range of 1-283 um. The conductivity of the extracellular medium was varied between plain collagen and a gel-like myxoid matrix through combinations of the two, i.e., collagen and myxoid. An increase in the transmembrane potential was shown in the case of higher aggregate. The results obtained in this study show the effect of the presence of the cell aggregates and collagen on the transmembrane potential. In particular, by increasing the cell aggregation in the two cases, the transmembrane potential increased. Finally, the simulation results were compared to experimental data obtained by culturing HCC1954 cells in a hyaluronic acid-based scaffold. The experimental validation confirmed the behavior of the transmembrane potential in presence of the collagen: an increase in electroporation at a lower electric field intensity was found for the cells cultured in the scaffolds where there is the formation of collagen areas.

Strategies for the Covalent Anchoring of a BMP-2-Mimetic Peptide to PEEK Surface for Bone Tissue Engineering

Researchers in the field of tissue engineering are always searching for new scaffolds for bone repair. Polyetheretherketone (PEEK) is a chemically inert polymer that is insoluble in conventional solvents. PEEK's great potential in tissue engineering applications arises from its ability to not induce adverse reactions when in contact with biological tissues and its mechanical properties, which are similar to those of human bone. These exceptional features are limited by the bio-inertness of PEEK, which causes poor osteogenesis on the implant surface. Here, we demonstrated that the covalent grafting of the sequence (48-69) mapped on the BMP-2 growth factor (GBMP1α) significantly enhances the mineralization and gene expression of human osteoblasts. Different chemical methods were employed for covalently grafting the peptide onto 3D-printed PEEK disks: (a) the reaction between PEEK carbonyls and amino-oxy groups inserted in the peptides' N-terminal sites (oxime chemistry) and (b) the photoactivation of azido groups present in the peptides' N-terminal sites, which produces nitrene radicals able to react with PEEK surface. The peptide-induced PEEK surface modification was assessed using X-ray photoelectron measurements, while the superficial properties of the functionalized material were analyzed by means of atomic force microscopy and force spectroscopy. Live and dead assays and SEM measurements showed greater cell cover on functionalized samples than the control, without any cytotoxicity induction. Moreover, functionalization improved the rate of cell proliferation and the amount of calcium deposits, as demonstrated by the AlamarBlue™ and alizarin red results, respectively. The effects of GBMP1α on h-osteoblast gene expression were assayed using quantitative real-time polymerase chain reaction.

Proteolytically Resistant Bioactive Peptide-Grafted Sr/Mg-Doped Hardystonite Foams: Comparison of Two Covalent Functionalization Strategies

Hardystonite-based (HT) bioceramic foams were easily obtained via thermal treatment of silicone resins and reactive oxide fillers in air. By using a commercial silicone, incorporating strontium oxide and magnesium oxide precursors (as well as CaO and ZnO), and treating it at 1100 °C, a complex solid solution (Ca_1.4Sr_0.6Zn_0.85Mg_0.15Si₂O₇) that has superior biocompatibility and bioactivity properties compared to pure hardystonite (Ca₂ZnSi₂O₇) can be obtained. Proteolytic-resistant adhesive peptide mapped on vitronectin (D2HVP), was selectively grafted to Sr/Mg-doped HT foams using two different strategies. Unfortunately, the first method (via protected peptide) was unsuitable for acid-sensitive materials such as Sr/Mg-doped HT, resulting in the release of cytotoxic levels of Zinc over time, with consequent negative cellular response. To overcome this unexpected result, a novel functionalization strategy requiring aqueous solution and mild conditions was designed. Sr/Mg-doped HT functionalized with this second strategy (via aldehyde peptide) showed a dramatic increase in human osteoblast proliferation at 6 days compared to only silanized or non-functionalized samples. Furthermore, we demonstrated that the functionalization treatment does not induce any cytotoxicity. Functionalized foams enhanced mRNA-specific transcript levels coding IBSP, VTN, RUNX2, and SPP1 at 2 days post-seeding. In conclusion, the second functionalization strategy proved to be appropriate for this specific biomaterial and was effective at enhancing the material's bioactivity.

SARS-CoV-2 S Mutations: A Lesson from the Viral World to Understand How Human Furin Works

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the etiological agent responsible for the worldwide pandemic and has now claimed millions of lives. The virus combines several unusual characteristics and an extraordinary ability to spread among humans. In particular, the dependence of the maturation of the envelope glycoprotein S from Furin enables the invasion and replication of the virus virtually within the entire body, since this cellular protease is ubiquitously expressed. Here, we analyzed the naturally occurring variation of the amino acids sequence around the cleavage site of S. We found that the virus grossly mutates preferentially at P positions, resulting in single residue replacements that associate with gain-of-function phenotypes in specific conditions. Interestingly, some combinations of amino acids are absent, despite the evidence supporting some cleavability of the respective synthetic surrogates. In any case, the polybasic signature is maintained and, as a consequence, Furin dependence is preserved. Thus, no escape variants to Furin are observed in the population. Overall, the SARS-CoV-2 system per se represents an outstanding example of the evolution of substrate-enzyme interaction, demonstrating a fast-tracked optimization of a protein stretch towards the Furin catalytic pocket. Ultimately, these data disclose important information for the development of drugs targeting Furin and Furin-dependent pathogens.

Bioactive PEEK: Surface Enrichment of Vitronectin-Derived Adhesive Peptides

Polyetheretherketone (PEEK) is a thermoplastic polymer that has been recently employed for bone tissue engineering as a result of its biocompatibility and mechanical properties being comparable to human bone. PEEK, however, is a bio-inert material and, when implanted, does not interact with the host tissues, resulting in poor integration. In this work, the surfaces of 3D-printed PEEK disks were functionalized with: (i) an adhesive peptide reproducing [351-359] h-Vitronectin sequence (HVP) and (ii) HVP retro-inverted dimer (D2HVP), that combines the bioactivity of the native sequence (HVP) with the stability toward proteolytic degradation. Both sequences were designed to be anchored to the polymer surface through specific covalent bonds via oxime chemistry. All functionalized PEEK samples were characterized by Water Contact Angle (WCA) measurements, Atomic Force Microscopy (AFM), and X-ray Photoelectron Spectroscopy (XPS) to confirm the peptide enrichment. The biological results showed that both peptides were able to increase cell proliferation at 3 and 21 days. D2HVP functionalized PEEK resulted in an enhanced proliferation across all time points investigated with higher calcium deposition and more elongated cell morphology.

DAR 16-II Primes Endothelial Cells for Angiogenesis Improving Bone Ingrowth in 3D-Printed BCP Scaffolds and Regeneration of Critically Sized Bone Defects

Bone is a highly vascularized tissue and relies on the angiogenesis and response of cells in the immediate environmental niche at the defect site for regeneration. Hence, the ability to control angiogenesis and cellular responses during osteogenesis has important implications in tissue-engineered strategies. Self-assembling ionic-complementary peptides have received much interest as they mimic the natural extracellular matrix. Three-dimensional (3D)-printed biphasic calcium phosphate (BCP) scaffolds coated with self-assembling DAR 16-II peptide provide a support template with the ability to recruit and enhance the adhesion of cells. In vitro studies demonstrated prompt the adhesion of both human umbilical vein endothelial cells (HUVEC) and human mesenchymal stem cells (hMSC), favoring endothelial cell activation toward an angiogenic phenotype. The SEM-EDS and protein micro bicinchoninic acid (BCA) assays demonstrated the efficacy of the coating. Whole proteomic analysis of DAR 16-II-treated HUVECs demonstrated the upregulation of proteins involved in cell adhesion (HABP2), migration (AMOTL1), cytoskeletal re-arrangement (SHC1, TMOD2), immuno-modulation (AMBP, MIF), and morphogenesis (COL4A1). In vivo studies using DAR-16-II-coated scaffolds provided an architectural template, promoting cell colonization, osteogenesis, and angiogenesis. In conclusion, DAR 16-II acts as a proactive angiogenic factor when adsorbed onto BCP scaffolds and provides a simple and effective functionalization step to facilitate the translation of tailored 3D-printed BCP scaffolds for clinical applications.

Mn-Containing Bioactive Glass-Ceramics: BMP-2-Mimetic Peptide Covalent Grafting Boosts Human-Osteoblast Proliferation and Mineral Deposition

The addition of Mn in bioceramic formulation is gaining interest in the field of bone implants. Mn activates human osteoblast (h-osteoblast) integrins, enhancing cell proliferation with a dose-dependent effect, whereas Mn-enriched glasses induce inhibition of Gram-negative or Gram-positive bacteria and fungi. In an effort to further optimize Mn-containing scaffolds' beneficial interaction with h-osteoblasts, a selective and specific covalent functionalization with a bioactive peptide was carried out. The anchoring of a peptide, mapped on the BMP-2 wrist epitope, to the scaffold was performed by a reaction between an aldehyde group of the peptide and the aminic groups of silanized Mn-containing bioceramic. SEM-EDX, FT-IR, and Raman studies confirmed the presence of the peptide grafted onto the scaffold. In in vitro assays, a significant improvement in h-osteoblast proliferation, gene expression, and calcium salt deposition after 7 days was detected in the functionalized Mn-containing bioceramic compared to the controls.

Electrospun Chitosan Functionalized with C12, C14 or C16 Tails for Blood-Contacting Medical Devices

Medical applications stimulate the need for materials with broad potential. Chitosan, the partially deacetylated derivative of chitin, offers many interesting characteristics, such as biocompatibility and chemical derivatization possibility. In the present study, porous scaffolds composed of electrospun interwoven nanometric fibers are produced using chitosan or chitosan functionalized with aliphatic chains of twelve, fourteen or sixteen methylene groups. The scaffolds were thoroughly characterized by SEM and XPS. The length of the aliphatic tail influenced the physico-chemical and dynamic mechanical properties of the functionalized chitosan. The electrospun membranes revealed no interaction of Gram+ or Gram− bacteria, resulting in neither antibacterial nor bactericidal, but constitutively sterile. The electrospun scaffolds demonstrated the absence of cytotoxicity, inflammation response, and eryptosis. These results open the door to their application for blood purification devices, hemodialysis membranes, and vascular grafts.

Biofunctionalization of bioactive ceramic scaffolds to increase the cell response for bone regeneration

Biofunctionalization was investigated for polymers and metals considering their scarce integration ability. On the contrary few studies dealt with ceramic biofunctionalization because the bioactive and bioresorbable surfaces of ceramics are able to positively interact with biological environment. In this study the cell-response improvement on biofunctionalized wollastonite and diopside-based scaffolds was demonstrated. The ceramics were first obtained by heat treatment of a silicone embedding reactive oxide fillers and then biofunctionalized with adhesive peptides mapped on vitronectin. The most promisingin vitroresults, in terms of h-osteoblast proliferation and bone-related gene expression, were reached anchoring selectively a peptide stable toward proteolytic degradation induced by serum-enriched medium. Inin vivoassays the anchoring of this protease-stable adhesive peptide was combined with self-assembling peptides, for increasing cell viability and angiogenesis. The results demonstrated external and internal cell colonization of biofunctionalized scaffolds with formation of new blood vessels (neoangiogenesis) and stimulation of ectopic mineralization.

From nanoaggregates to mesoscale ribbons: the multistep self-organization of amphiphilic peptides

This paper reports atomic force microscopy results and molecular dynamics simulations of the striking differences of long-term self-organization structures of negatively charged (AcA₄)₂KD (double tail) and AcA₄D (single tail) peptides, respectively, forming micrometer-long, linearly ordered ribbon-like structures and nanometer-sized, unstructured, round-shaped aggregates. The subsequent formation steps of the long-range nanoribbons, experimentally observed only for the "double tail" (AcA₄)₂KD peptide, are analyzed in detail, showing that the initial "primary" unstructured round-shaped aggregates progressively evolve into longer nanofilaments and into micrometer-long, network-forming nanoribbon moieties. In particular, the long-range self-organization of the "double tail" peptides appears to be closely related to electrostatically driven diffusional motions of the primary aggregates and nanofilaments. The diffusional freedom degrees are prompted by the formation of a dynamic ternary air/liquid/substrate interface, due to the water evaporation process from the ultrathin films of the peptide solution cast onto a solid mica substrate. Overall, the initial aggregation of unstructured round-shaped moieties, for both the peptides, can be seen as an entropy-driven process, involving the intra- and intermolecular interactions of hydrophobic parts of the peptides, while the further formation of long nanoribbons, only for "double tail" peptides, can be viewed in terms of an enthalpy-driven process, mainly due to the predominant electrostatic interactions between the charged heads of the interacting peptides. The role of the solid-liquid interface, as the locus of the enthalpy-driven linear organization, is also highlighted.

Covalent functionalization of decellularized tissues accelerates endothelialization

In the field of tissue regeneration, the lack of a stable endothelial lining may affect the hemocompatibility of both synthetic and biological replacements. These drawbacks might be prevented by specific biomaterial functionalization to induce selective endothelial cell (EC) adhesion. Decellularized bovine pericardia and porcine aortas were selectively functionalized with a REDV tetrapeptide at 10⁻⁵ M and 10⁻⁶ M working concentrations. The scaffold-bound peptide was quantified and REDV potential EC adhesion enhancement was evaluated in vitro by static seeding of human umbilical vein ECs. The viable cells and MTS production were statistically higher in functionalized tissues than in control. Scaffold histoarchitecture, geometrical features, and mechanical properties were unaffected by peptide anchoring. The selective immobilization of REDV was effective in accelerating ECs adhesion while promoting proliferation in functionalized decellularized tissues intended for blood-contacting applications.

•

Covalent functionalization of the decellularized tissues with REDV peptide accelerates endothelialization.

•

New covalent grafting method not inducing collagen cross-linking.

•

Measurements through two photon miscroscopy allow the quantification of biological matrix bound peptide.

•

The decellularized tissues can be changed by chemical procedures to promote specific cellular behaviour with ECM preservation.

Breast Cancer Cell Cultures on Electrospun Poly(ε-Caprolactone) as a Potential Tool for Preclinical Studies on Anticancer Treatments

During anticancer drug development, most compounds selected by in vitro screening are ineffective in in vivo studies and clinical trials due to the unreliability of two-dimensional (2D) in vitro cultures that are unable to mimic the cancer microenvironment. Herein, HCC1954 cell cultures on electrospun polycaprolactone (PCL) were characterized by morphological analysis, cell viability assays, histochemical staining, immunofluorescence, and RT-PCR. Our data showed that electrospun PCL allows the in vitro formation of cultures characterized by mucopolysaccharide production and increased cancer stem cell population. Moreover, PCL-based cultures were less sensitive to doxorubicin and electroporation/bleomycin than those grown on polystyrene plates. Collectively, our data indicate that PCL-based cultures may be promising tools for preclinical studies.

Breast cancer cells grown on hyaluronic acid-based scaffolds as 3D in vitro model for electroporation

Nowadays, electroporation (EP) represents a promising method for the intracellular delivery of anticancer drugs. To setting up the process, the EP efficiency is usually evaluated by using cell suspension and adherent cell cultures that are not representative of the in vivo conditions. Indeed, cells are surrounded by extracellular matrix (ECM) whose composition and physical characteristics are different for each tissue. So, various three-dimensional (3D) in vitro models, such as spheroids and hydrogel-based cultures, have been proposed to mimic the tumour microenvironment. Herein, a 3D breast cancer in vitro model has been proposed. HCC1954 cells were seeded on crosslinked and lyophilized matrices composed of hyaluronic acid (HA) and ionic complementary self-assembling peptides (SAPs) already known to provide a fibrous structure mimicking collagen network. Herein, SAPs were functionalized with laminin derived IKVAV adhesion motif. Cultures were characterized by spheroids surrounded by ECM produced by cancer cells as demonstrated by collagen1a1 and laminin B1 transcripts. EP was carried out on both 2D and 3D cultures: a sequence of 8 voltage pulses at 5 kHz with different amplitude was applied using a plate electrode. Cell sensitivity to EP seemed to be modulated by the presence of ECM and the different cell organization. Indeed, cells cultured on HA-IKVAV were more sensitive than those treated in 2D and HA cultures, in terms of both cell membrane permeabilization and viability. Collectively, our results suggest that HA-IKVAV cultures may represent an interesting model for EP studies. Further studies will be needed to elucidate the influence of ECM composition on EP efficiency.

Hydroxyapatite Surfaces Functionalized with a Self-Assembling Peptide: XPS, RAIRS and NEXAFS Study

Hydroxyapatite (HAP) coatings can improve the biocompatibility and bioactivity of titanium alloys, such as Ti6Al4V, commonly used as material for orthopedic prostheses. In this framework, we have studied the surface of HAP coatings enriched with Mg and either Si or Ti deposited by RF magnetron sputtering on Ti6Al4V. HAP coatings have been furtherly functionalized by adsorption of a self-assembling peptide (SAP) on the HAP surface, with the aim of increasing the material bioactivity. The selected SAP (peptide sequence AbuEAbuEAbuKAbuKAbuEAbuEAbuKAbuK) is a self-complementary oligopeptide able to generate extended ordered structures by self-assembling in watery solutions. Samples were prepared by incubation of the HAP coatings in SAP solutions and subsequently analyzed by X-Ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared (FTIR) and Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopies, in order to determine the amount of adsorbed peptide, the peptide stability and the structure of the peptide overlayer on the HAP coatings as a function of the HAP substrate and of the pH of the mother SAP solution. Experimental data yielded evidence of SAP adsorption on the HAP surface, and peptide overlayers showed ordered structure and molecular orientation. The thickness of the SAP overlayer depends on the composition of the HAP coating.

The Efficiency of Gene Electrotransfer in Breast-Cancer Cell Lines Cultured on a Novel Collagen-Free 3D Scaffold

Gene Electro-Transfer (GET) is a powerful method of DNA delivery with great potential for medical applications. Although GET has been extensively studied in vitro and in vivo, the optimal parameters remain controversial. 2D cell cultures have been widely used to investigate GET protocols, but have intrinsic limitations, whereas 3D cultures may represent a more reliable model thanks to the capacity of reproducing the tumor architecture. Here we applied two GET protocols, using a plate or linear electrode, on 3D-cultured HCC1954 and MDA-MB231 breast cancer cell lines grown on a novel collagen-free 3D scaffold and compared results with conventional 2D cultures. To evaluate the electrotransfer efficiency, we used the plasmid pEGFP-C3 encoding the enhanced green fluorescent protein (EGFP) reporter gene. The novel 3D scaffold promoted extracellular matrix deposition, which particularly influences cell behavior in both in vitro cell cultures and in vivo tumor tissue. While the transfection efficiency was similar in the 2D-cultures, we observed significant differences in the 3D-model. The transfection efficiency in the 3D vs 2D model was 44% versus 15% (p < 0.01) and 24% versus 17% (p < 0.01) in HCC1954 and MDA-MB231 cell cultures, respectively. These findings suggest that the novel 3D scaffold allows reproducing, at least partially, the peculiar morphology of the original tumor tissues, thus allowing us to detect meaningful differences between the two cell lines. Following GET with plate electrodes, cell viability was higher in 3D-cultured HCC1954 (66%) and MDA-MB231 (96%) cell lines compared to their 2D counterpart (53% and 63%, respectively, p < 0.001). Based on these results, we propose the novel 3D scaffold as a reliable support for the preparation of cell cultures in GET studies. It may increase the reliability of in vitro assays and allow the optimization of GET parameters of in vivo protocols.

Expression and function of the stromal cell-derived factor-1 (SDF-1) and CXC chemokine receptor 4 (CXCR4) in the swine ovarian follicle

The most characterized stromal cell-derived factor-1 (SDF-1) variants are the isoform α, which is the predominant one but undergoes rapid proteolysis, and the β isoform, which is more resistant. Through the interaction with a specific chemokine receptor called CXCR4, SDF-1 is able to regulate different physiological processes. The aim of this study was to verify the expression and potential functional role of SDF-1 and CXCR4 in the porcine ovary. Firstly, the expression of SDF-1 and its receptor in different ovarian districts was verified for the first time. Thereafter, the effect of SDF-1 β isoform (51-72) fragment on functional parameters, such as proliferation, metabolic activity, redox status, nitric oxide production, and steroidogenic activity, was assessed on granulosa cells collected from follicles. In addition, the potential effect of this protein in vascular events was verified through investigations on porcine aortic (AOC) endothelial cells, such as the production of nitric oxide and viability tests. The proliferation and metabolic activity were not affected by treatment with the cytokine. As regard to steroidogenesis, the peptide stimulated both estrogen (P = 0.049) and progesterone production (P = 0.039). Redox status was affected by the examined substance since superoxide anion was inhibited (P = 0.001), while antioxidant power (P = 0.034), as well as nitric oxide generation, were stimulated (P = 0.034). Tests performed on AOCs showed significant stimulation of nitric oxide production (P = 0.004) by the examined peptide, while cell viability was unaffected. Therefore, the potential role of cytokine in the mechanisms involved in the regulation of follicular function can be hypothesized.

Cysteine-Modified Self-Assembling Peptides on Gold: The Role of the Head and Tail

Molecular self-assembly consists of the spontaneous aggregation of molecules into a well-defined structure guided by noncovalent bonds. The self-assembly strategy is ubiquitous in nature and recently has been proposed as a nature-mimetic strategy in polymer science and biomaterial engineering. In this context, we aim at designing and testing innovative but simple chemical strategies to efficiently modify surfaces by exploiting minor modifications in the bioactive molecule functionalities, for example, introducing cysteine (Cys) as a terminal residue in self-assembling peptides (SAPs). In this work, we report the attenuated total reflection-Fourier transform infrared spectroscopy, synchrotron radiation-induced X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and time-of-flight secondary ion mass spectrometry investigation of self-assembled layers of oligopeptides anchored onto gold surfaces through cysteine residues, opportunely inserted in an SAP (EAK16-II) main chain in three different positions: at the amine end group, at the carboxyl end group, and at both terminal groups (i.e., a bidentate SAP). This study, which allowed us to individuate in the bidentate SAP the best candidate for the controlled production of ordered SAP layers on the gold substrate surface, is envisaged to open wide perspectives for efficient chemical modification of surfaces with biomolecules, leading to obtaining innovative bioactive materials for applications in the field of tissue engineering.

Biofunctionalization of TiO2 Surfaces with Self-Assembling Layers of Oligopeptides Covalently Grafted to Chitosan

In the field of tissue engineering, a promising approach to obtain a bioactive, biomimetic, and antibiotic implant is the functionalization of a "classical" biocompatible material, for example, titanium, with appropriate biomolecules. For this purpose, we propose preparing self-assembling films of multiple components, allowing the mixing of different biofunctionalities "on demand". Self-assembling peptides (SAPs) are synthetic materials characterized by the ability to self-organize in nanostructures both in aqueous solution and as thin or thick films. Moreover, ordered layers of SAPs adhere on titanium surface as a scaffold coating to mimic the extracellular matrix. Chitosan is a versatile hydrophilic polysaccharide derived from chitin, with a broad antimicrobial spectrum to which Gram-negative and Gram-positive bacteria and fungi are highly susceptible, and is already known in the literature for the ability of its derivatives to firmly graft titanium alloys and show protective effects against some bacterial species, either alone or in combination with other antimicrobial substances such as antibiotics or antimicrobial peptides. In this context, we functionalized titanium surfaces with chitosan grafted to EAK16-II (a SAP), obtaining layer-by-layer structures of different degrees of order, depending on the preparative stoichiometry and path. The chemical composition, molecular structure, and arrangement of the obtained biofunctionalized surfaces were investigated by surface-sensitive techniques such as reflection-absorption infrared spectroscopy (RAIRS) and state-of-the-art synchrotron radiation-induced spectroscopies as X-ray photoemission spectroscopy (SR-XPS), and near-edge X-ray absorption fine structure (NEXAFS). Furthermore, was demonstrated that surfaces coated with EAK and Chit-EAK can support hNPs cell attachment and growth.

3D Synthetic Peptide-based Architectures for the Engineering of the Enteric Nervous System

Damage of enteric neurons and partial or total loss of selective neuronal populations are reported in intestinal disorders including inflammatory bowel diseases and necrotizing enterocolitis. To develop three-dimensional scaffolds for enteric neurons we propose the decoration of ionic-complementary self-assembling peptide (SAP) hydrogels, namely EAK or EAbuK, with bioactive motives. Our results showed the ability of EAK in supporting neuronal cell attachment and neurite development. Therefore, EAK was covalently conjugated to: RGD, (GRGDSP)₄K (fibronectin), FRHRNRKGY (h-vitronectin, named HVP), IKVAV (laminin), and type 1 Insulin-like Growth Factor (IGF-1). Chemoselective ligation was applied for the SAP conjugation with IGF-1 and the other longer sequences. Freshly isolated murine enteric neurons attached and grew on all functionalized EAK but IGF-1. Cell-cell contact was evident on hydrogels enriched with (GRGDSP)₄K and HVP. Moreover (GRGDSP)₄K significantly increased mRNA expression of neurotrophin-3 and nerve growth factor, two trophic factors supporting neuronal survival and differentiation, whereas IKVAV decoration specifically increased mRNA expression of acetylcholinesterase and choline acetyltransferase, genes involved in synaptic communication between cholinergic neurons. Thus, decorated hydrogels are proposed as injectable scaffolds to support in loco survival of enteric neurons, foster synaptic communication, or drive the differentiation of neuronal subtypes.

Viscoelastic Oxidized Alginates with Reversible Imine Type Crosslinks: Self-Healing, Injectable, and Bioprintable Hydrogels

Bioprinting techniques allow for the recreation of 3D tissue-like structures. By deposition of hydrogels combined with cells (bioinks) in a spatially controlled way, one can create complex and multiscale structures. Despite this promise, the ability to deposit customizable cell-laden structures for soft tissues is still limited. Traditionally, bioprinting relies on hydrogels comprised of covalent or mostly static crosslinks. Yet, soft tissues and the extracellular matrix (ECM) possess viscoelastic properties, which can be more appropriately mimicked with hydrogels containing reversible crosslinks. In this study, we have investigated aldehyde containing oxidized alginate (ox-alg), combined with different cross-linkers, to develop a small library of viscoelastic, self-healing, and bioprintable hydrogels. By using distinctly different imine-type dynamic covalent chemistries (DCvC), (oxime, semicarbazone, and hydrazone), rational tuning of rheological and mechanical properties was possible. While all materials showed biocompatibility, we observed that the nature of imine type crosslink had a marked influence on hydrogel stiffness, viscoelasticity, self-healing, cell morphology, and printability. The semicarbazone and hydrazone crosslinks were found to be viscoelastic, self-healing, and printable-without the need for additional Ca2+ crosslinking-while also promoting the adhesion and spreading of fibroblasts. In contrast, the oxime cross-linked gels were found to be mostly elastic and showed neither self-healing, suitable printability, nor fibroblast spreading. The semicarbazone and hydrazone gels hold great potential as dynamic 3D cell culture systems, for therapeutics and cell delivery, and a newer generation of smart bioinks.

Biofunctionalization of TiO2 surfaces with self-assembling oligopeptides in different pH and Ionic Strength conditions: Charge effects and molecular organization

Self-assembling peptides (SAPs) were investigated by means of XPS and Angular Dependent NEXAFS spectroscopies, with the aim to probe the influence of pH and Ionic Strength conditions on the chemical structure and molecular organization of SAPs anchored on titania surfaces. XPS at the C1s, N1s, O1s core levels allowed to study surfaces and biomolecule/substrate interfaces. NEXAFS data allowed ascertaining that SAPs molecular structure is preserved upon grafting to the titania surface. Angular Dependent NEXAFS was used to investigate the influence of environmental conditions on the molecular organization behaviour. The objective of our study was to establish a set of methodologies for obtaining arrangements of well-organized biomolecules on scaffolds surfaces as a basic technology to develop and optimize cells adhesion and proliferation for tissue engineering applications.

Enhancement of peri-implant bone osteogenic activity induced by a peptidomimetic functionalization of titanium

Osteoblast cell adhesion to the extracellular matrix is established through two main pathways: one is mediated by the binding between integrin and a minimal adhesion sequence (RGD) on the extracellular protein, the other is based on the interactions between transmembrane proteoglycans and heparin-binding sequences found in many matrix proteins. The aim of this study is the evaluation in an in vivo endosseous implant model of the early osteogenic response of the peri-implant bone to a biomimetic titanium surface functionalized with the retro-inverso 2DHVP peptide, an analogue of Vitronectin heparin binding site. The experimental plan is based on a bilateral study design of Control and 2DHVP implants inserted respectively in the right and left femur distal metaphysis of adult male Wistar rats (n=16) weighing about 300grams and evaluated after 15days. Fluorochromic bone vital markers were given in a specific time frame, in order to monitor the dynamic of new bone deposition. The effect inducted by the peptidomimetic coating on the surrounding bone were qualitatively and quantitatively evaluated by means of static and dynamic histomorphometric analyses performed within three concentric and subsequent circular Regions of Interest (ROI) of equivalent thickness (220μm), ROI1 adjacent to the interface, ROI2, the middle, and ROI3 the farthest. The data indicated that these functionalized implants stimulated a higher bone apposition rate (p<0,01) and larger and rapid osteoblast activation in terms of mineralizing surface within ROI1 compared to the control (p<0,01). These higher osteoblast recruitment and activation leads to a greater bone-to-implant contact reached for DHVP samples (p<0,5). This represents an initial stimulus of the osteogenic activity that might results in a faster and better osteointegration process.

Smart biomaterials: Surfaces functionalized with proteolytically stable osteoblast-adhesive peptides

Engineered scaffolds for bone tissue regeneration are designed to promote cell adhesion, growth, proliferation and differentiation. Recently, covalent and selective functionalization of glass and titanium surfaces with an adhesive peptide (HVP) mapped on [351-359] sequence of human Vitronectin allowed to selectively increase osteoblast attachment and adhesion strength in in vitro assays, and to promote osseointegration in in vivo studies. For the first time to our knowledge, in this study we investigated the resistance of adhesion sequences to proteolytic digestion: HVP was completely cleaved after 5 h. In order to overcome the enzymatic degradation of the native peptide under physiological conditions we synthetized three analogues of HVP sequence. A retro-inverted peptide D-2HVP, composed of D amino acids, was completely stable in serum-containing medium. In addition, glass surfaces functionalized with D-2HVP increased human osteoblast adhesion as compared to the native peptide and maintained deposition of calcium. Interestingly, D-2HVP increased expression of IBSP, VTN and SPP1 genes as compared to HVP functionalized surfaces. Total internal reflection fluorescence microscope analysis showed cells with numerous filopodia spread on D-2HVP-functionalized surfaces. Therefore, the D-2HVP sequence is proposed as new osteoblast adhesive peptide with increased bioactivity and high proteolytic resistance.

Design of Decorated Self-Assembling Peptide Hydrogels as Architecture for Mesenchymal Stem Cells

Hydrogels from self-assembling ionic complementary peptides have been receiving a lot of interest from the scientific community as mimetic of the extracellular matrix that can offer three-dimensional supports for cell growth or can become vehicles for the delivery of stem cells, drugs or bioactive proteins. In order to develop a 3D “architecture” for mesenchymal stem cells, we propose the introduction in the hydrogel of conjugates obtained by chemoselective ligation between a ionic-complementary self-assembling peptide (called EAK) and three different bioactive molecules: an adhesive sequence with 4 Glycine-Arginine-Glycine-Aspartic Acid-Serine-Proline (GRGDSP) motifs per chain, an adhesive peptide mapped on h-Vitronectin and the growth factor Insulin-like Growth Factor-1 (IGF-1). The mesenchymal stem cell adhesion assays showed a significant increase in adhesion and proliferation for the hydrogels decorated with each of the synthesized conjugates; moreover, such functionalized 3D hydrogels support cell spreading and elongation, validating the use of this class of self-assembly peptides-based material as very promising 3D model scaffolds for cell cultures, at variance of the less realistic 2D ones. Furthermore, small amplitude oscillatory shear tests showed that the presence of IGF-1-conjugate did not alter significantly the viscoelastic properties of the hydrogels even though differences were observed in the nanoscale structure of the scaffolds obtained by changing their composition, ranging from long, well-defined fibers for conjugates with adhesion sequences to the compact and dense film for the IGF-1-conjugate.

Anti-HIV-1 Activity of CD4 Synthetic Oligopeptides Representative of the Putative gp120 Binding Site

Two CD4 oligopeptides, corresponding to residues (37–53) and (37–55) of the V1 domain of CD4, which recent structural studies propose as the most likely binding site of HIV-1 gp120, have been chemically synthesized by solid-phase techniques, modified by the addition of two side-chain protected cysteines at both termini and purified by HPLC. Their ability to inhibit the infectivity of human immunodeficiency virus type 1 (HIV-1) (HTLV-IIIB, RF and GB8 strains) in different cell lines was monitored by the production of progeny virus, p24 and reverse transcriptase activity in the culture supernatants and by electron microscopy. The results indicated that the peptides inhibited HIV-1 infectivity in a dose-dependent fashion without any detectable cytotoxicity.

Electrospun Scaffolds for Osteoblast Cells: Peptide-Induced Concentration-Dependent Improvements of Polycaprolactone

The design of hybrid poly-ε-caprolactone (PCL)-self-assembling peptides (SAPs) matrices represents a simple method for the surface functionalization of synthetic scaffolds, which is essential for cell compatibility. This study investigates the influence of increasing concentrations (2.5%, 5%, 10% and 15% w/w SAP compared to PCL) of three different SAPs on the physico-chemical/mechanical and biological properties of PCL fibers. We demonstrated that physico-chemical surface characteristics were slightly improved at increasing SAP concentrations: the fiber diameter increased; surface wettability increased with the first SAP addition (2.5%) and slightly less for the following ones; SAP-surface density increased but no change in the conformation was registered. These results could allow engineering matrices with structural characteristics and desired wettability according to the needs and the cell system used. The biological and mechanical characteristics of these scaffolds showed a particular trend at increasing SAP concentrations suggesting a prevailing correlation between cell behavior and mechanical features of the matrices. As compared with bare PCL, SAP enrichment increased the number of metabolic active h-osteoblast cells, fostered the expression of specific osteoblast-related mRNA transcripts, and guided calcium deposition, revealing the potential application of PCL-SAP scaffolds for the maintenance of osteoblast phenotype.

Mechanisms underlying the attachment and spreading of human osteoblasts: from transient interactions to focal adhesions on vitronectin-grafted bioactive surfaces

The features of implant devices and the reactions of bone-derived cells to foreign surfaces determine implant success during osseointegration. In an attempt to better understand the mechanisms underlying osteoblasts attachment and spreading, in this study adhesive peptides containing the fibronectin sequence motif for integrin binding (Arg-Gly-Asp, RGD) or mapping the human vitronectin protein (HVP) were grafted on glass and titanium surfaces with or without chemically induced controlled immobilization. As shown by total internal reflection fluorescence microscopy, human osteoblasts develop adhesion patches only on specifically immobilized peptides. Indeed, cells quickly develop focal adhesions on RGD-grafted surfaces, while HVP peptide promotes filopodia, structures involved in cellular spreading. As indicated by immunocytochemistry and quantitative polymerase chain reaction, focal adhesions kinase activation is delayed on HVP peptides with respect to RGD while an osteogenic phenotypic response appears within 24h on osteoblasts cultured on both peptides. Cellular pathways underlying osteoblasts attachment are, however, different. As demonstrated by adhesion blocking assays, integrins are mainly involved in osteoblast adhesion to RGD peptide, while HVP selects osteoblasts for attachment through proteoglycan-mediated interactions. Thus an interfacial layer of an endosseous device grafted with specifically immobilized HVP peptide not only selects the attachment and supports differentiation of osteoblasts but also promotes cellular migration.

Self-assembling peptide-enriched electrospun polycaprolactone scaffolds promote the h-osteoblast adhesion and modulate differentiation-associated gene expression

Electrospun polycaprolactone (PCL) is able to support the adhesion and growth of h-osteoblasts and to delay their degradation rate to a greater extent with respect to other polyesters. The drawbacks linked to its employment in regenerative medicine arise from its hydrophobic nature and the lack of biochemical signals linked to it. This work reports on the attempt to add five different self-assembling (SA) peptides to PCL solutions before electrospinning. The hybrid scaffolds obtained had regular fibers (SEM analysis) whose diameters were similar to those of the extracellular matrix, more stable hydrophilic (contact angle measurement) surfaces, and an amorphous phase constrained by peptides (DSC analysis). They appeared to have a notable capacity to promote the h-osteoblast adhesion and differentiation process by increasing the gene expression of alkaline phosphatase, bone sialoprotein, and osteopontin. Adding an Arg-Gly-Asp (RGD) motif to a self-assembling sequence was found to enhance cell adhesion, while the same motif condensed with a scrambled sequence did not, indicating that there is a cooperative effect between RGD and 3D architecture created by the self-assembling peptides. The study demonstrates that self-assembling peptide scaffolds are still able to promote beneficial effects on h-osteoblasts even after they have been included in electrospun polycaprolactone. The possibility of linking biochemical messages to self-assembling peptides could lead the way to a 3D decoration of fibrous scaffolds.

In vitro biological activity of bovine milk ribonuclease-4

Several members of the ribonuclease superfamily possess a variety of interesting biological properties, including ribonucleolytic, angiogenic, antiproliferative, cytotoxic, embryotoxic, aspermatogenic and antitumoral activity. In this study, we report the purification from bovine milk of a protein with structural and enzymatic properties very similar to those of ribonuclease-4 (RNase-4), which is normally present in the liver and lungs, and examined its functional properties, biological activity and cytotoxic effects. RNase-4, at physiological concentrations, had a positive effect on the vitality and proliferation of human umbilical vein endothelial cells. Moreover, it induced an increase in cellular migration and the formation of in vitro capillary-like structures. We also evaluated the effect of RNase-4 in vitro on human breast, colorectal and cervical carcinoma cell lines. The protein was revealed to have a cytotoxic effect similar to that of RNase-A. We suggest that the positive effects of RNase-4 on normal cells were due to its particularly close interaction with RNase inhibitor, while good conformational stability and resistance to proteolytic degradation potentially favour ribonuclease cytotoxicity.

Synthesis and chromatography-free purification of PNA-PEO conjugates for the functionalisation of gold sensors

Peptide Nucleic Acids (PNAs) linked to high molecular weight (MW) poly(ethylene oxide) (PEO) derivatives could be useful conjugates for the direct functionalisation of gold surfaces dedicated to Surface Plasmon Resonance (SPR)-based DNA sensing. However their use is hampered by the difficulty to obtain them through a convenient and economical route. In this work we compared three synthetic strategies to obtain PNA-high MW PEO conjugates composed of (a) a 15-mer PNA sequence as the probe complementary to genomic DNA of Mycobacterium tuberculosis, (b) a PEO moiety (2 or 5 KDa MW) and (c) a terminal trityl-protected thiol necessary (after acidic deprotection) for grafting to gold surfaces. The 15-mer PNA was obtained by solid-phase synthesis. Its amino terminal group was later condensed to bi-functional PEO derivatives (2 and 5 KDa MW) carrying a Trt-cysteine at one end and a carboxyl group at the other end. The reaction was carried out either in solution, using HATU or PyOxim as coupling agents, or through the solid-phase approach, with 49.6%, 100% and 5.2% yield, respectively. A differential solvent extraction strategy for product purification without the need for chromatography is described. The ability of the 5 KDa PEO conjugate to function as a probe for complementary DNA detection was demonstrated using a Grating-Coupling Surface Plasmon Resonance (GC-SPR) system. The optimized PEO conjugation and purification protocols are economical and simple enough to be reproduced also within laboratories that are not highly equipped for chemical synthesis.

Cardiomyocytes in vitro adhesion is actively influenced by biomimetic synthetic peptides for cardiac tissue engineering

Scaffolds for tissue engineering must be designed to direct desired events such as cell attachment, growth, and differentiation. The incorporation of extracellular matrix-derived peptides into biomaterials has been proposed to mimic biochemical signals. In this study, three synthetic fragments of fibronectin, vitronectin, and stromal-derived factor-1 were investigated for the first time as potential adhesive sequences for cardiomyocytes (CMs) compared to smooth muscle cells. CMs are responsive to all peptides to differing degrees, demonstrating the existence of diverse adhesion mechanisms. The pretreatment of nontissue culture well surfaces with the (Arginine-Glycine-Aspartic Acid) RGD sequence anticipated the appearance of CMs' contractility compared to the control (fibronectin-coated well) and doubled the length of cell viability. Future prospects are the inclusion of these sequences into biomaterial formulation with the improvement in cell adhesion that could play an important role in cell retention during dynamic cell seeding.

Chemoselective surface immobilization of proteins through a cleavable peptide

Surface immobilization of biomolecules is a fundamental step in several experimental techniques such as surface plasmon resonance analysis and microarrays. Oxime ligation allows reaching chemoselective protein immobilization with the retention of native-like conformation by proteins. Beside the need for chemoselective ligation of molecules to surface/particle, equally important is the controlled release of the immobilized molecules, even after a specific binding event. For this purpose, we have designed and assessed in an SPR experiment a peptide linker able to (i) anchor a given protein (enzymes, receptors, or antibodies) to a surface in a precise orientation and (ii) release the immobilized protein after selective enzymatic cleavage. These results open up the possibility to anchor to a surface a protein probe leaving bioactive sites free for interaction with substrates, ligands, antigens, or drugs and successively remove the probe-ligand complex by enzymatic cleavage. This peptide linker can be considered both an improvement of SPR analysis for macromolecular interaction and a novel strategy for drug delivery and biomaterial developments.

Self-assembling properties of ionic-complementary peptides

Self-complementary synthetic peptides, composed by 8 and 16 residues, were analyzed by CD, NMR and small angle neutron scattering (SANS) techniques in order to investigate the relevance of charge and hydrophobic interactions in determining their self-assembling properties. All the sequences are potentially able to form fibrils and membranes as they share, with the prototype EAK16, a strictly alternating arrangement of polar and nonpolar residues. We find that 16-mer peptides show higher self-assembling propensities than the 8-mer analogs and that the aggregation processes are favored by salts and neutral pH. Peptide hydrophobic character appears as the most relevant factor in determining self-assembling. Solution conformational analysis, diffusion and SANS measurements all together show that the sequences with a higher self-assemble propensity are distributed, in mild conditions, between light and heavy forms. For some of the systems, the light form is mostly constituted by monomers in a random conformation, while the heavy one is constituted by beta-aggregates. In our study we also verified that sequences designed to adopt extended conformation, when dissolved in alcohol-water mixtures, can easily fold in helix structures. In that media, the prototype of the series appears distributed between helical monomers and beta-aggregates. It is worth noticing that the structural conversion from helical monomer to beta-aggregates, mimics beta-amyloid peptide aggregation mechanisms.

Self-assembling peptides: sequence, secondary structure in solution and film formation

Peptides of alternating charge and hydrophobic amino acids have a tendency to adopt unusually stable beta-sheet structures that can form insoluble macroscopic aggregates under physiological conditions. In this study, analogues of a well-known self-assembling peptide, characterized by the same polar/nonpolar periodicity but with different residues, were designed to study the relationship between sequence, conformation in solution and film-forming capacity in saline solution. Peptide conformation, evaluated by circular dichroism, correlated with film forming capacity observed by inverted optical microscopy after addition of saline solution and subsequent drying. We found that polar/nonpolar periodicity of several analogues is not criterion enough to induce beta-sheet and thus film formation and that conformations different from beta-sheet also allow self-assemblage. Furthermore, addition of the short adhesive sequence RGD to a known self-assembling sequence was shown to not prevent the self-assembling process. This finding might prove useful for the design of biomimetic scaffolds.