Macrophage activation through phagocytosis of muramyl dipeptide encapsulated in gelatin microspheres

Biodegradable Polymers for Microencapsulation Systems

Environmentally friendly alternatives have become sought after upon the development of scientific research and industrial processes. Recent trends suggest biodegradable polymers as the most promising solution for synthetic microcapsule systems. Safety, efficiency, biocompatibility, and biodegradability are some of the properties that biodegradable systems in microencapsulation can provide for a broad spectrum of applications. The controlled release of encapsulated active agents is a research field that, over the years, has been constantly innovating due to the promising applications in the areas of pharmaceutical, cosmetic, textile industry, among others. This article presents an overview of different polymers with potential for microcapsule synthesis, namely, biodegradable polymers. First, natural polymers are discussed, which are divided into two categories: polysaccharide-based polymers (cellulose, starch, chitosan, and alginate) and protein polymers (gelatin). Second, synthetic polymers are described, where biodegradable polymers such as polyesters, polyamides, among others appear as examples. For each polymer, this review presents its origin, relevant properties, applications, and examples found in the literature regarding its use in biodegradable microencapsulation systems.

Chitosan as an Underrated Polymer in Modern Tissue Engineering

Chitosan is one of the most well-known and characterized materials applied in tissue engineering. Due to its unique chemical, biological and physical properties chitosan is frequently used as the main component in a variety of biomaterials such as membranes, scaffolds, drug carriers, hydrogels and, lastly, as a component of bio-ink dedicated to medical applications. Chitosan's chemical structure and presence of active chemical groups allow for modification for tailoring material to meet specific requirements according to intended use such as adequate endurance, mechanical properties or biodegradability time. Chitosan can be blended with natural (gelatin, hyaluronic acid, collagen, silk, alginate, agarose, starch, cellulose, carbon nanotubes, natural rubber latex, κ-carrageenan) and synthetic (PVA, PEO, PVP, PNIPPAm PCL, PLA, PLLA, PAA) polymers as well as with other promising materials such as aloe vera, silica, MMt and many more. Chitosan has several derivates: carboxymethylated, acylated, quaternary ammonium, thiolated, and grafted chitosan. Its versatility and comprehensiveness are confirming by further chitosan utilization as a leading constituent of innovative bio-inks applied for tissue engineering. This review examines all the aspects described above, as well as is focusing on a novel application of chitosan and its modifications, including the 3D bioprinting technique which shows great potential among other techniques applied to biomaterials fabrication.

Enhanced full-thickness wound healing via Sophora gibbosa extract delivery based on a chitosan/gelatin dressing incorporating microemulsion

There are many synthetic drugs in literature have been utilized in healing of the wounds although the natural product specially antioxidants can offer similar if not better biological activity in that regard. Genus Sophora is well known to contain flavonoids and phenolic compounds which have antioxidant and inflammatory effects. So, the aim of the current study was to develop and evaluate chitosan/gelatin based Sophora gibbosa extract-loaded microemulsion as wound dressing. Sophora gibbosa extract (SGE) contained 16 major compounds which have reasonable antioxidant activity. The developed microemulsion showed that Tween 80 produced significant (p < 0.05) lower particle size than Pluronic F127 at the same SGE concentration whereas high concentration of extract results in large particle size. Thermodynamic stability studies showed that using higher concentration of the extract produced less stable formulations. The selected formulation was impregnated in the dressing base (chitosan/gelatin; 2:1 w/w ratio) which exhibited more water absorption. In vivo evaluation revealed that the dressing displayed superior wound repair compared to the control in terms histological examination and determination of alpha smooth muscle actin (α-SMA) and proliferating cell nuclear antigen (PCNA). Thus, SGE-loaded microemulsion-impregnated gelatin/chitosan could be a potential candidate for the wound healing.

Interaction of Activated Leukocytes with Polymeric Microspheres

Three types of polymeric particles with different surface wettabilities, i.e., poly(methylmethacrylate) (PMMA), poly(methylmethacrylate-hydroxyethylmethacrylate) (P(MMA/HEMA)) and poly(methylmethacrylate)/poly(vinyl alcohol) PMMA/PVAL with a diameter of 1.5 μm were produced in this study. These particles were incubated with blood samples obtained both from three patients undergoing cardiopulmonary bypass. In the blood samples taken before the bypass operations, there was considerable phagocytosis and/or adhesion of the PMMA particles, i.e., 14±4 particles per monocyte and 11±3 particles per neutrophil. While there was almost no phagocytosis and/or adhesion of the P(MMA/HEMA) and PMMA/PVAL particles. In the blood samples which were taken during bypass operations, phagocytosis and/or adhesion of PMMA microspheres increased significantly. The P(MMA/HEMA) and/or PMMA/PVAL particles adhered, or were even phagocytosed by the activated leukocytes in this case. Leukocytes activated during the bypass operations gradually returned to normal in about 24 h.

Preparation of a nitric oxide imaging agent from gelatin derivative micelles

INTRODUCTION

Nitric oxide (NO) is an intracellular and intercellular messenger that plays an important role in cellular events in physiological and pathophysiological processes. NO is one of the inflammation markers and macrophages of an inflammatory cell produce a large amount of NO compared with other cells. Non-invasive detection system of NO is highly required to realize an early therapeutic treatment considering the process of pathophysiological changes. The objective of this study is to develop an imaging agent of nitric oxide (NO).

METHODS

A water-insoluble DAR-4M of fluorescent dye for NO was solubilized in water through the micelle formation with gelatin grafted with l-α-phosphatidylethanolamine distearoyl (DAR-4M micelles). Physicochemical and biological properties of DAR-4M micelles were investigated by using cultured cells and animals.

RESULTS

The DAR-4M micelles responded to NO secreted from a NO donors, in contrast to the same concentration of free DAR-4M. When RAW264.7 of a macrophage cell line was stimulated by lipopolysaccharide (LPS) to allow them to generate NO, the DAR-4M micelles could detect NO of the cells to a significant great extent compared with free DAR-4M. After the intravenous injection of DAR-4M micelles or free DAR-4M to a mouse model of aristolochic acid (AA) induced acute interstitial nephritis, the DAR-4M micelles enhanced the fluorescence intensity from the kidneys to a significant great extent compared with the free DAR-4M injection. In case of DAR-4M micelles injection into normal mice, such an enhanced kidney fluorescence was not observed. A body distribution experiment demonstrated that the kidney accumulation of DAR-4M micelles was not modified by the AA-induced inflammation. After the AA injection, the number of CD11b-positive cells increased with time, indicating the increased number of inflammatory macrophages.

CONCLUSION

DAR-4M micelles are effective in imaging NO generated from macrophages accompanied with inflammation.

Development of bioresorbable bilayered systems for application as affordable wound dressings

The objective of this work was the preparation and evaluation of a bioresorbable bilayered system for application in the treatment of dermal lesions. The system was based on a polyesterurethane as the external layer and a gelatin membrane as the internal layer. The polyesterurethane was synthesized from poly(ε-caprolactone), polyethylene glycol of 1 or 10 kDa as a hydrophilic component or Pluronic F127 as an amphiphilic component and l-lysine ethyl ester diisocyanate as an urethane precursor. Gelatin membrane was obtained by crosslinking with the naturally occurring crosslinker genipin. Three important points were addressed in this study: the physicochemical characterization of the system, the in vitro behaviour and the in vivo performance on a full-thickness wound defect of rat. The polyesterurethane containing polyethylene glycol of 10 kDa presented the optimum properties for the designed application as to be tested in animal experiments. The in vivo results showed good healing of the lesion with the formation of epidermis similar to normal rat skin. These promising results suggest the potential of this system to be used as an affordable wound dressing in the treatment of different dermal lesions.

Investigation of Surface Properties of Biodegradable Albumin Microspheres via Phagocytosis Phenomena

The phagocytosis of biodegradable albumin (Alb) microspheres by peripheral blood cells (neutrophils and monocytes) and mouse macrophage cells (peritoneal and lung macrophages) as a carrier matrix in drug targeting applications was investigated. Glutaraldehyde crosslinking was used to produce albumin microspheres with different sizes. Plain (nonmodified) microspheres with diameters of1, 2, and 4 mm were cultured with cells and their uptake was determined as 8, 5, and 1 particles/cell, respectively. Albumin microspheres (2 mm diameter) were also modified with various opsonization and passivation agents, such as fibronectin (Fn), amicasine, and poly(ethylene glycol) (PEG). Plain, Alb-PEG, Alb-Fn, and Alb-amicasine microspheres were phagocytized by monocytes and neutrophils and the number of particles taken up by each cell significantly increased for Alb-Fn microspheres with respect to the plain microspheres. No significant phagocytosis was observed for Alb-PEG microspheres. The number of particles taken up by each cell was less than the plain and amikacin modified albumin microspheres. Almost zero uptake was obtained for the phagocytosis of Alb-PEG microspheres with lung and peritoneal macrophages. For phagocytosis of plain and other modified particles by the macrophages, although the number of particles taken up by each cell increased with respect to those with neutrophils and monocytes, similar tendencies were also obtained.

Gelatin Microgel Incorporated Poly(ethylene glycol)-Based Bioadhesive with Enhanced Adhesive Property and Bioactivity

Up to 7.5 wt % of chemically cross-linked gelatin microgel was incorporated into dopamine-modified poly(ethylene glycol) (PEGDM) adhesive to simultaneously improve the material property and bioactivity of the PEG-based bioadhesive. Incorporation of gelatin microgel reduced cure time while it increased the elastic modulus and cross-linking density of the adhesive network. Most notably, the loss modulus values for microgel-containing adhesive were an order of magnitude higher when compared to microgel-free control. This drastic increase in the viscous dissipation ability of the adhesive is attributed to the introduction of reversible physical bonds into the adhesive network with the incorporation of the gelatin microgel. Additionally, incorporation of the microgel increased the adhesive properties of PEGDM by 1.5- to 2-fold. From in vitro cell culture studies, the composite adhesive is noncytotoxic and the incorporation of microgels provided binding site for promoting fibroblast attachment and viability. The subcutaneous implantation study indicated that the microgel-containing PEGDM adhesive is biocompatible and the incorporated microgels provided pockets for rapid cellular infiltration. Gelatin microgel incorporation was demonstrated to be a facile method to simultaneously enhance the adhesive property and the bioactivity of PEG-based adhesive.

Engineering vaccines and niches for immune modulation

Controlled modulation of immune response, especially the balance between immunostimulatory and immunosuppressive responses, is critical for a variety of clinical applications, including immunotherapies against cancer and infectious diseases, treatment of autoimmune disorders, transplant surgeries, regenerative medicine, prosthetic implants, etc. Our ability to precisely modify both innate and adaptive immune responses could provide new therapeutic directions in a variety of diseases. In the context of vaccines and immunotherapies, the interplay between antigen-presenting cells (e.g. dendritic cells and macrophages), B cells, T helper and killer subtypes, and regulatory T- and B-cell responses is critical for generating effective immunity against cancer, infectious diseases and autoimmune diseases. In recent years, immunoengineering has emerged as a new field that uses quantitative engineering tools to understand molecular-, cellular- and system-level interactions of the immune system and to develop design-driven approaches to control and modulate immune responses. Biomaterials are an integral part of this engineering toolbox and can exploit the intrinsic biological and mechanical cues of the immune system to directly modulate and train immune cells and direct their response to a particular phenotype. A large body of literature exists on strategies to evade or suppress the immune response in implants, transplantation and regenerative medicine. This review specifically focuses on the use of biomaterials for immunostimulation and controlled modulation, especially in the context of vaccines and immunotherapies against cancer, infectious diseases and autoimmune disorders. Bioengineering smart systems that can simultaneously deliver multiple bioactive agents in a controlled manner or can work as a niche for in situ priming and modulation of the immune system could significantly enhance the efficacy of next-generation immunotherapeutics. In this review, we describe our perspective on the important design aspects for the development of biomaterials that can actively modulate immune responses by stimulating receptor complexes and cells, and delivering multiple immunomodulatory biomolecules.

Altering colloidal surface functionalization using DNA encapsulated inside monodisperse gelatin microsphere templates

Soluble oligonucleotides are typically introduced to bulk solution to promote hybridization activity on DNA-functionalized surfaces. Here, an alternative approach is explored by encapsulating secondary target strands inside semipermeable colloidal satellite assemblies, then triggering their release at 37 °C for subsequent surface hybridization activity. To prepare DNA-loaded satellite assemblies, uniform gelatin microspheres are fabricated using microfluidics, loaded with 15 base-long secondary DNA targets, capped with a polyelectrolyte bilayer, and finally coated with a monolayer of polystyrene microspheres functionalized with duplexes comprised of immobilized probes and soluble, 13 base-long hybridization partner strands. Once warmed to 37 °C, secondary DNA targets are released from the gelatin template and then competitively displace the shorter, original hybridization partners on the polystyrene microspheres.

Gelatin microspheres: correlation between embolic effect/degradability and cross-linkage/particle size

PURPOSE

To evaluate the embolic effect and degradability of gelatin microspheres (GMS) using various degrees of cross-linkage and particle sizes in rabbit renal artery embolization.

METHODS

Four types of GMS were used, as follows: 2 types of cross-linkage and 2 types of particle size. Twenty-four rabbits (6 in each group) were used for the renal artery embolization. Renal angiography was performed before and after embolization of right renal artery. Follow-up renal angiography was performed 2 days (n = 2), 5 days (n = 2), and 15 days (n = 2) after embolization in each group, and then kidneys were removed for histopathological evaluation. Vascular areas of the angiography were measured by Image J software, and the reperfusion rate was calculated. In renal specimens, residual GMS were checked and the degree of degradation was classified according to a 4-point scale.

RESULTS

The mean amounts of large- and small-particle-size GMS injected were 15.0 and 34.3 mg, respectively. Tissue necrosis was confirmed in each group; however, no difference was observed among groups. Renal reperfusion was observed more with small GMS than with large GMS. Renal reperfusion was also observed more with low cross-linked GMS than with high cross-linked GMS. In histopathological specimens, large GMS were confirmed in lobar artery, and small GMS were confirmed in lobular artery. Low cross-linked GMS completely degraded 15 days after embolization. In contrast, high cross-linked GMS were persistent 15 days after embolization.

CONCLUSION

Degree of cross-linkage and particle size affected degradability and reperfusion.

Inhaled therapies for tuberculosis and the relevance of activation of lung macrophages by particulate drug-delivery systems

Pathogenic strains of Mycobacterium tuberculosis (Mtb) induce ‘alternative activation’ of lung macrophages that they colonize, in order to create conditions that promote the establishment and progression of infection. There is some evidence to indicate that such macrophages may be rescued from alternative activation by inhalable microparticles containing a variety of drugs. This review summarizes the experience of various groups of researchers, relating to observations of induction of a number of classical macrophage activation pathways. Restoration of a ‘respiratory burst’ and upregulation of reactive oxygen species and nitrogen intermediates through the phagocyte oxidase and nitric oxide synthetase enzyme systems; induction of proinflammatory macrophage cytokines; and finally induction of apoptosis rather than necrosis of the infected macrophage are discussed. It is suggested that there is scope to co-opt host responses in the management of tuberculosis, through the route of pulmonary drug delivery.

Fabrication and characterization of chitosan-gelatin blend nanofibers for skin tissue engineering

Tissue engineering scaffolds produced by electrospinning feature a structural similarity to the natural extracellular matrix. Polymer blending is one of the effective methods to provide new and desirable biocomposites for tissue engineering applications. In this study chitosan was blended with gelatin and the effect of processing parameters of electrospinning and the solution properties of the polymer on the morphology of the fibers obtained were investigated. The morphology of the electrospun chitosan, gelatin and the chitosan-gelatin blend were characterized using a scanning electron microscope (SEM). The miscibility of the blend was determined using a SEM, and differential scanning calorimetry (DSC) Fourier transform Infrared spectrometer (FTIR). Further the tensile properties of the blend nanofibers were studied and compared with chitosan and gelatin fibers. In this study we have been able to electrospin defect-free chitosan, gelatin and chitosan-gelatin blend nanofibers with smooth morphology and diameter ranging from 120 to 200 nm, 100 to 150 nm, and 120-220 nm, respectively by optimizing the process and solution parameters. Chitosan and gelatin formed completely miscible blends as evidenced from DSC and FTIR measurements. The tensile strength of the chitosan-gelatin blend nanofibers (37.91 +/- 4.42 MPa) was significantly higher than the gelatin nanofibers (7.23 +/- 1.15 MPa) (p < 0.05) and comparable with that of normal human skin. Thus the novel chitosan-gelatin blend nanofiber system has potential application in skin regeneration.

Gelatin microspheres: initial clinical experience for the transcatheter arterial embolization

PURPOSE

The purpose of this study is to evaluate the embolization effects of gelatin microspheres (GMSs) when used as an embolic material for transcatheter arterial embolization (TAE) for several organs.

MATERIALS AND METHODS

We prepared GMSs that dissolves in 5 days in extravasuclar tissue. GMSs were used in five cases in total, four cases with multiple liver tumors and one case with a pelvic bone tumor.

RESULTS

In all five cases, it was possible to treat the targeted tumors by TAE with GMSs. In the contrast-enhanced CT performed 2-4 weeks later, the embolized tumors did not show an enhancement effect. Passage of GMSs in the microcatheter was excellent.

CONCLUSION

GMSs showed sufficient potential to be used as an embolic material.

Microparticle-based technologies for vaccines

Microparticles have been effectively used for many years as delivery systems for drugs and therapeutic proteins. Their application to the delivery of vaccines is not as extensive, but is growing. Utility has been demonstrated for the delivery of various types of vaccines (e.g., recombinant proteins, plasmid DNA, and peptides) and other vaccine components (e.g., immune potentiators). With respect to delivery of immune potentiators, synergistic effects are often observed whereby much more potent immune responses are induced with a combination than with either component alone. Hence, the prospects for broad application of microparticle-based delivery systems for vaccines are excellent.

Intravenous injection of phagocytes transfected ex vivo with FGF4 DNA/biodegradable gelatin complex promotes angiogenesis in a rat myocardial ischemia/reperfusion injury model

Conventional gene therapies still present difficulties due to poor tissue-targeting, invasiveness of delivery, method, or the use of viral vectors. To establish the feasibility of using non-virally ex vivo transfected phagocytes to promote angiogenesis in ischemic myocardium, gene-transfection into isolated phagocytes was performed by culture with positively charged gelatin impregnated with plasmid DNA. A high rate of gene transfection was achieved in rat macrophages and human monocytes, but not in mouse fibroblasts. The efficiency was 68 +/- 11% in rat macrophages and 78 +/- 8% in human monocytes. Intravenously injected phagocytes accumulated predominantly in ischemic tissue (13 +/- 8%) and spleen (84 +/- 6%), but negligibly in other organs in rodents. The efficiency of accumulation in the target ischemic tissue reached more than 86% on direct local tissue injection. In a rat model of myocardial ischemia-reperfusion, intravenous injection of fibroblast growth factor 4 (FGF4)-gene-transfected macrophages significantly increased regional blood flow in the ischemic myocardium (78 +/- 7.1 % in terms of flow ratio of ischemic/non-ischemic myocardium) compared with intravenous administration of saline (36 +/- 11%) or nontransfected macrophages (42 +/- 12 %), or intramuscular administration of naked DNA encoding FGF4 (75 +/- 18 %). Enhanced angiogenesis in the ischemic tissue we confirmed histologically. Similarly, intravenous injection of FGF4-gene-transfected monocytes enhanced regional blood flow in an ischemic hindlimb model in mice (93 +/- 22 %), being superior to the three other treatments described above (38 +/- 12, 39 +/- 15, and 55 +/- 12%, respectively). Phagocytes transfected ex vivo with FGF4 DNA/gelatin promoted angiogenesis. This approach might have potential for non-viral angiogenic gene therapy.

Adrenomedullin: angiogenesis and gene therapy

Adrenomedullin (AM) is a potent, long-lasting vasodilator peptide that was originally isolated from human pheochromocytoma. AM signaling is of particular significance in endothelial cell biology since the peptide protects cells from apoptosis, promotes angiogenesis, and affects vascular tone and permeability. The angiogenic effect of AM is mediated by activation of Akt, mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2, and focal adhesion kinase in endothelial cells. Both AM and its receptor, calcitonin receptor-like receptor, are upregulated through a hypoxia-inducible factor-1-dependent pathway under hypoxic conditions. Thus AM signaling plays an important role in the regulation of angiogenesis in hypoxic conditions. Recently, we have developed a nonviral vector, gelatin. Positively charged gelatin holds negatively charged plasmid DNA in its lattice structure. DNA-gelatin complexes can delay gene degradation, leading to efficient gene transfer. Administration of AM DNA-gelatin complexes induces potent angiogenic effects in a rabbit model of hindlimb ischemia. Thus gelatin-mediated AM gene transfer may be a new therapeutic strategy for the treatment of tissue ischemia. Endothelial progenitor cells (EPCs) play an important role in endothelial regeneration. Interestingly, EPCs phagocytose ionically linked DNA-gelatin complexes in coculture, which allows nonviral gene transfer into EPCs. AM gene transfer into EPCs inhibits cell apoptosis and induces proliferation and migration, suggesting that AM gene transfer strengthens the therapeutic potential of EPCs. Intravenous administration of AM gene-modified EPCs regenerate pulmonary endothelium, resulting in improvement of pulmonary hypertension. These results suggest that in vivo and in vitro transfer of AM gene using gelatin may be applicable for intractable cardiovascular disease.

Mucosal adjuvants and delivery systems for protein-, DNA- and RNA-based vaccines

Almost all vaccinations today are delivered through parenteral routes. Mucosal vaccination offers several benefits over parenteral routes of vaccination, including ease of administration, the possibility of self-administration, elimination of the chance of injection with infected needles, and induction of mucosal as well as systemic immunity. However, mucosal vaccines have to overcome several formidable barriers in the form of significant dilution and dispersion; competition with a myriad of various live replicating bacteria, viruses, inert food and dust particles; enzymatic degradation; and low pH before reaching the target immune cells. It has long been known that vaccination through mucosal membranes requires potent adjuvants to enhance immunogenicity, as well as delivery systems to decrease the rate of dilution and degradation and to target the vaccine to the site of immune function. This review is a summary of current approaches to mucosal vaccination, and it primarily focuses on adjuvants as immunopotentiators and vaccine delivery systems for mucosal vaccines based on protein, DNA or RNA. In this context, we define adjuvants as protein or oligonucleotides with immunopotentiating properties co-administered with pathogen-derived antigens, and vaccine delivery systems as chemical formulations that are more inert and have less immunomodulatory effects than adjuvants, and that protect and deliver the vaccine through the site of administration. Although vaccines can be quite diverse in their composition, including inactivated virus, virus-like particles and inactivated bacteria (which are inert), protein-like vaccines, and non-replicating viral vectors such as poxvirus and adenovirus (which can serve as DNA delivery systems), this review will focus primarily on recombinant protein antigens, plasmid DNA, and alphavirus-based replicon RNA vaccines and delivery systems. This review is not an exhaustive list of all available protein, DNA and RNA vaccines, with related adjuvants and delivery systems, but rather is an attempt to highlight many of the currently available approaches in immunopotentiation of mucosal vaccines.

Enhancement of vaccine potency through improved delivery

The need for more potent, safe and well-characterised vaccines has necessitated the discovery and development of new vaccine technologies. These include adjuvants to target the innate immune system to provide a stimulus that potentiates the development of an antigen-specific immune response, and delivery systems to ensure that the antigen and adjuvant are localised to the appropriate immune compartments. Several such technologies are being tested in human clinical trials and a few have been licensed for limited use in human vaccines. This review will highlight some of the promising technologies that may have an impact on how vaccines are administered.

Adrenomedullin gene transfer induces therapeutic angiogenesis in a rabbit model of chronic hind limb ischemia: benefits of a novel nonviral vector, gelatin

BACKGROUND

Earlier studies have shown that adrenomedullin (AM), a potent vasodilator peptide, has a variety of cardiovascular effects. However, whether AM has angiogenic potential remains unknown. This study investigated whether AM gene transfer induces therapeutic angiogenesis in chronic hind limb ischemia.

METHODS AND RESULTS

Ischemia was induced in the hind limb of 21 Japanese White rabbits. Positively charged biodegradable gelatin was used to produce ionically linked DNA-gelatin complexes that could delay DNA degradation. Human AM DNA (naked AM group), AM DNA-gelatin complex (AM-gelatin group), or gelatin alone (control group) was injected into the ischemic thigh muscles. Four weeks after gene transfer, significant improvements in collateral formation and hind limb perfusion were observed in the naked AM group and AM-gelatin group compared with the control group (calf blood pressure ratio: 0.60+/-0.02, 0.72+/-0.03, 0.42+/-0.06, respectively). Interestingly, hind limb perfusion and capillary density of ischemic muscles were highest in the AM-gelatin group, which revealed the highest content of AM in the muscles among the three groups. As a result, necrosis of lower hind limb and thigh muscles was minimal in the AM-gelatin group.

CONCLUSIONS

AM gene transfer induced therapeutic angiogenesis in a rabbit model of chronic hind limb ischemia. Furthermore, the use of biodegradable gelatin as a nonviral vector augmented AM expression and thereby enhanced the therapeutic effects of AM gene transfer. Thus, gelatin-mediated AM gene transfer may be a new therapeutic strategy for the treatment of peripheral vascular diseases.

Hybrid cell-gene therapy for pulmonary hypertension based on phagocytosing action of endothelial progenitor cells

BACKGROUND

Circulating endothelial progenitor cells (EPCs) migrate to injured vascular endothelium and differentiate into mature endothelial cells. We investigated whether transplantation of vasodilator gene-transduced EPCs ameliorates monocrotaline (MCT)-induced pulmonary hypertension in rats.

METHODS AND RESULTS

We obtained EPCs from cultured human umbilical cord blood mononuclear cells and constructed plasmid DNA of adrenomedullin (AM), a potent vasodilator peptide. We used cationic gelatin to produce ionically linked DNA-gelatin complexes. Interestingly, EPCs phagocytosed plasmid DNA-gelatin complexes, which allowed nonviral, highly efficient gene transfer into EPCs. Intravenously administered EPCs were incorporated into the pulmonary vasculature of immunodeficient nude rats given MCT. Transplantation of EPCs alone modestly attenuated MCT-induced pulmonary hypertension (16% decrease in pulmonary vascular resistance). Furthermore, transplantation of AM DNA-transduced EPCs markedly ameliorated pulmonary hypertension in MCT rats (39% decrease in pulmonary vascular resistance). MCT rats transplanted with AM-expressing EPCs had a significantly higher survival rate than those given culture medium or EPCs alone.

CONCLUSIONS

Umbilical cord blood-derived EPCs had a phagocytosing action that allowed nonviral, highly efficient gene transfer into EPCs. Transplantation of AM gene-transduced EPCs caused significantly greater improvement in pulmonary hypertension in MCT rats than transplantation of EPCs alone. Thus, a novel hybrid cell-gene therapy based on the phagocytosing action of EPCs may be a new therapeutic strategy for the treatment of pulmonary hypertension.

Cytotoxicity evaluation of gelatin sponges prepared with different cross-linking agents

Gelatin is a natural polymer used in pharmaceutical and medical applications, especially in the production of biocompatible and biodegradable wound dressings and drug delivery systems. Gelatin granules hydrate, swell and solubilize in water, and rapidly degrade in vivo. The durability of these materials could, however, be prolonged by cross-linking by aldehydes, carbodiimides, and aldose sugars, but the biocompatibility of collagenous biomaterials is profoundly influenced by the nature and extent of cross-linking. In this study, gelatin sponges were prepared by using various cross-linkers such as glutaraldehyde (GA), 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDAC), and D-fructose. The effects of the type and the amount of cross-linker on thermal and mechanical properties, stability, and cytotoxicity were investigated. The mechanical analysis data showed that an increase in the amount of GA in the sponge structures caused a slight increase in the modulus of elasticity but had almost no effect on the tensile strength. Increase in the EDAC concentration produced a maximum in the modulus of elasticity and tensile strength values. The stability of the sponges and the time required for complete degradation in aqueous media increased in parallel with the cross-linker content. In vitro studies carried out with fibroblast cells demonstrated a higher cell viability for the samples cross-linked with low concentrations of GA than for those cross-linked with EDAC.

Study on gelatin-containing artificial skin IV: A comparative study on the effect of antibiotic and EGF on cell proliferation during epidermal healing

Gelatin-hyaluronate sponge with and without antibiotic and epidermal growth factor (EGF) were prepared and compared. Four types of sponges were applied on the full-thickness dorsal skin defect of Wistar rat. The effects of antibiotic and EGF in gelatin-hyaluronate sponge on wound healing were investigated by light microscopy and image analyzer at postoperative days of 5, 12 and 21. An immunohistochemical technique, employing PC10, a monoclonal antibody against proliferating cell nuclear antigen (PCNA) was applied to wounded tissue sections. The number of PC10-positive cells was very high for the sponge with EGF at postoperative day 5, then gradually decreased with time. Also we found that antibiotics restrained the cell proliferation during the migratory phase. The sponge with both antibiotic and EGF showed good wound healing performances on the whole for a healing period. The epithelium was regenerated fast with EGF-impregnated sponges at day 5, but each sample had nearly the same length of regenerated epithelium at day 12.

Evaluation of gelatin hydrogel crosslinked with various crosslinking agents as bioadhesives: in vitro study

Bioadhesives are used for tissue adhesion and hemostasis in surgery. A gelatin-resorcinol mixture crosslinked with formaldehyde (GRF glue) and/or glutaraldehyde (GRG) is used for this purpose. Although the bonding strength of the GRF glue to tissue is satisfactory, concerns about the cytotoxicity of formaldehyde are reported in the literature. It was suggested that the cytotoxicity problem of the GRF glue may be overcome by changing its crosslinking method. The study was therefore undertaken to assess the feasibility of using an epoxy compound (GRE glue), a water-soluble carbodiimide (GAC glue), or genipin (GG glue) to crosslink with a gelatin hydrogel as new bioadhesives. GRF glue and GRG glue were used as controls. The results of our cytotoxicity study suggested that the cellular compatibility of the GAC and GG glues was superior to the GRF, GRG, and GRE glues. The gelation time for the GG glue was relatively longer than the GRF and GRG glues, while no gelation time could be determined for the GAC glue. Additionally, it took approximately 17 h for the GRE glue to become adhesive. The GRF and GRG glues had the greatest bonding strengths to tissue among all test adhesives, while the bonding strengths of the GAC and GG glues were comparable. In contrast, there was almost no bonding strength to tissue for the GRE glue. However, the GRF and GRG glues were less flexible than the GAC and GG glues. Subsequent to the bonding strength measurement, each test adhesive was found to adhere firmly to the tissue surface and underwent cohesive failure during the bond breaking. In conclusion, the GRF and GRG glues may be used as tissue adhesives when their ability to bind tissue rapidly and tightly is required; the GAC and GG glues are preferable when the adhesive action must be accompanied with minimal cytotoxicity and stiffness; and the GRE glue is not suitable for bioadhesion in clinical applications.

Protein-loaded poly(epsilon-caprolactone) microparticles. II. Muramyl dipeptide for oral controlled release of adjuvant

This work investigated the means for the efficient encapsulation of muramyl dipeptide (MDP) in poly(epsilon-caprolactone) (PCL) microparticles (MP) by a solvent evaporation method in order to optimize the effect of the adjuvant for oral immunization. Therefore, the influence of MDP concentration in the inner aqueous phase was evaluated on MP characteristics such as size, morphology, drug entrapment, entrapment efficiency and the eventual interactions of MDP with co-entrapped model antigen, bovine serum albumin (BSA). The process of manufacturing produced a high entrapment efficiency of MDP (63.58 +/- 0.40%) without altering its integrity, as shown by chromatogram peaks analysis of a and beta anomers. The crystallinity of the polymer was dramatically increased (+24.6%) either with or without MDP loading but the entrapment of BSA reduced this crystallinity suggesting BSA-PCL interaction. These MP were resistant to simulated gastric fluid and exhibited a continuous BSA release. Moreover, their average diameter (<10 microm) combined with their high hydrophobicity make of this delivery system an exciting alternative for enhanced oral immunization.

Gelatin-derived bioadhesives for closing skin wounds: an in vivo study

Bioadhesives have been used in surgery as hemostatic and wound healing agents. GRF (gelatin + resorcinol + formaldehyde) glue, composed of a mixture of gelatin and resorcinol polymerized by the addition of formaldehyde, has been used for this purpose. Widespread acceptance of the GRF glue, however, has been limited by reports of cytotoxicity due to its release of formaldehyde upon degradation. It has been suggested by Wertzel et al. that the cytotoxicity problem of GRF glue may be overcome by changing its cross-linking method. The study was, therefore, undertaken to assess the feasibility of using a water-soluble carbodiimide or genipin to cross-link gelatin as new bioadhesives to close skin wound lesions in a rat model. Formaldehyde-cross-linked counterpart (GRF glue) and a resorbable suture were used as controls. It was noted that the tensile strength of the skin across each wound treated by either application of test glues or suture increased consistently with time during the healing process. Also, the wounds repaired by test glues or suture caused no calcification. The suture used in the study was completely resorbed at the wound area in about 6 days postoperatively. However, the durations required to completely resorb the carbodiimide- or genipin-cross-linked glues were approximately the same (9 days), while it took about 14 days to completely resorb the formaldehyde-cross-linked glue. The healing process for the suture wound repaired was more rapid than those treated by test glues. Of the test glues, the wounds treated by the carbodiimide- or genipin-cross-linked glues induced less inflammatory response and recovered sooner than that treated by the formaldehyde-cross-linked glue. This indicated that the biocompatibility of the carbodiimide- or genipin-cross-linked glues was superior to the formaldehyde-cross-linked glue. The results of this study may serve as a preliminary experimental model for the further investigation of both the carbodiimide- and genipin-cross-linked glues when applied to human skin closure.

Microencapsulation of chlorpheniramine maleate-resin particles with crosslinked chitosan for sustained release

Formulation and preparation parameters of drug/ion-exchange particles microencapsulated in cross-linked chitosan were evaluated for controlled release of the water-soluble drug chlorpheniramine maleate (CPM) in a suspension. An emulsion solvent evaporation method was used to produce CPM-resinates embedded in glutaraldehyde (GTA) crosslinked chitosan microspheres (MCSs). Crosslinking extent in the chitosan was monitored by swelling measurements. Controlled release was evaluated by dissolution tests in simulated gastric fluid without enzyme (SGF) and in simulated intestinal fluid without enzyme (SIF). CPM-resinates contained 62% (w/w) of drug. MCSs were spherical, ranging from 82 to 420 microns in diameter, and contained multiple resinates. The sizes of MCSs prepared with safflower oil and Span 80 were controlled by surfactant concentration, stirring speed, and duration of stirring. Maximum crosslinking was produced with 240 mg GTA per 250 mg of chitosan. Maximum drug release from free CPM-resinates was about 60% by 1 hr in SGF, and was about 100% by 3 hr in SIF. CPM release was slower from MCSs crosslinked with 120 mg of GTA compared to 5 mg GTA in both media. By 8.3 hr, the more crosslinked MCSs released about 30% CPM in SGF, and about 60% in SIF. Because of the apparent ceiling on release in SGF, the final experiments were conducted in SIF. Increasing the weight ratio of the chitosan coating to CPM-resinate ratio from 1:1 to 4:1 moderately decreased release profiles carried out to 33 hr. Increasing MCS diameters from 82 to 163 microns moderately decreased release profiles. Microencapsulation of CPM-resinates with crosslinked chitosan demonstrated controlled release of CPM in SGF and SIF without enzymes. The retardation effect increased when the crosslinking extent and chitosan to resin ratio increased.

Gelatin nanoencapsulation of protein/peptide drugs using an emulsifier-free emulsion method

The nanoencapsulation of a model protein drug, bovine serum albumin (BSA), using gelatin as the matrix material is reported. Nanoencapsulation was conducted using a modified water-in-oil (w/o) emulsion method, which is emulsifier-free and simple. The nanoencapsulation product, BSA-containing gelatin nanoparticles, is characterized in terms of nanoparticle morphology, size and size distribution, water content, and in vitro protein release. The BSA-containing gelatin nanoparticles obtained from this nanoencapsulation process are nearly spherical and have a log-normal size distribution. The average diameter of the BSA-containing gelatin nanoparticles is approximately 840 nm. They can absorb 51-72% of water. In vitro release experiments demonstrate that BSA has been successfully encapsulated in, and can be released from the gelatin nanoparticles. The release of BSA from the gelatin nanoparticulate matrix follows a diffusion-controlled release mechanism. It is found that temperature affects both the water content and the BSA release rate of the gelatin nanoparticles.

Preparation and characterization of agarose hydrogel nanoparticles for protein and peptide drug delivery

The purpose of this work was to develop and characterize a protein and peptide injectable drug delivery system in agarose hydrogel nanoparticles. The nanoparticles were prepared by using a new emulsion-converted-to-suspension in situ method. This is an emulsifier-free method that has advantages for protein and peptide drug encapsulations. Ovalbumin, used as a model protein drug, was successfully encapsulated into nearly spherical agarose hydrogel nanoparticles under mild conditions. The nanoparticles possessed a log-normal size distribution with an average size of 504 nm. They imbibed a large amount of water (66.85% to 84.33%) and the water content was a function of temperature; the water content increased with increase in temperature. Release studies of the ovalbumin from the agarose hydrogel nanoparticles revealed a diffusion-controlled release mechanism with a temperature dependence; the ovalbumin release rate was higher at 37 degrees C than that at room temperature. The great biocompatibility of agarose hydrogel, plus the mild conditions for drug encapsulation, make the agarose hydrogel nanoparticles a potential system for protein and peptide drug delivery.

Controlled delivery of antigens and adjuvants in vaccine development

Advances in the understanding of the pathogenesis of infectious diseases and cancer immunology have inspired many new approaches to vaccine development. Many subunit antigens and peptides that are effective for vaccination have been discovered. These subunit antigens in tum stimulate synthesis of effective adjuvants to enhance their immunogenicity. Controlled-release technology offers the potential of further improving the efficacy of conventional vaccine formulations by optimizing the temporal and spatial presentation of the-antigens and adjuvants to the immune system. The combination of sustained release and depot effect may also reduce the amount of antigens or adjuvants needed and eliminate the booster shots that are necessary for the success of many vaccinations. This review examines the contribution controlled release technology can make in various areas of vaccination, with an emphasis on tumor vaccines.

A new biological glue from gelatin and poly (L-glutamic acid)

This study describes the potentiality of hydrogels composed of gelatin and poly(L-glutamic acid) (PLGA) as a biological glue for soft tissues and compares its effectiveness with that of a conventional fibrin glue. Water-soluble carbodiimides (WSC) were used to crosslink the aqueous mixture of gelatin and PLGA. The mixed aqueous solution of gelatin and PLGA set to a hydrogel by use of WSC as rapidly as BOLHEAL fibrin glue. An addition of PLGA to gelatin aqueous solution reduced not only its gelation time but also the WSC concentration necessary for hydrogel formation. The cured hydrogel exhibited firm adhesion to the mouse skin and other soft tissues with a higher bonding strength than BOLHEAL fibrin glue. Cohesive failure in the hydrogel was observed when the gel-tissue bond was broken, in contrast to BOLHEAL fibrin glue. The bonding strength of the gelatin-PLGA hydrogel became higher with the increasing PLGA concentration. The inflammatory reaction around the gelatin-PLGA hydrogel subcutaneously implanted in mice was mild, and the hydrogel was gradually absorbed with time in vivo. A toxicity test demonstrated that the concentration of WSC necessary as a biological glue was low enough not to induce its toxicity.

The formation of a crosslinked carboxyhemoglobin membrane at an organic-aqueous interface

A 30% carboxyhemoglobin solution was encapsulated with a membrane composed of crosslinked hemoglobin as a potential artificial red blood cell by adding a 25 microL droplet of 30% carboxyhemoglobin solution in phosphate buffer to a buffer-saturated toluene solution of a homobifunctional crosslinking agent. Disuccinimidyl glutarate, disuccinimidyl suberate, and terephthaldicarboxaldehyde proved successful in crosslinking hemoglobin at concentrations of 0.05%, 0.08%, and 4.3%, respectively (saturated levels in buffer-saturated toluene). Disuccinimidyl glutarate exhibited maximal crosslinking of 11.0% in approximately 30 minutes. Disuccinimidyl suberate and terephthaldicarboxaldehyde required at least 12 hours to form a viable sphere and crosslinked 39.4% and 37.8% of the hemoglobin in 18 hours. Membrane integrity was assessed by determining the permeability of uncrosslinked hemoglobin through the membrane as a function of time.

Phagocytosis of monosize polystyrene-based microspheres having different size and surface properties

In this study, nondegradable monosize polystyrene (PS) based polymeric microspheres with different size and surface chemistries were prepared by different polymerization techniques. Surfaces of the plain microspheres were further modified biologically by albumin (BSA) or fibronectin (Fn) preadsorption. Phagocytosis of these polymeric microspheres by leukocytes and macrophages were investigated. The phagocytic response of both leukocytes and macrophages decreased by increasing size of the particles. More hydrophilic particles phagocytosed less. Positive charges increased the uptake while negative charges oppositely reduced the uptake. BSA on the surface almost prevented the uptake, while Fn caused opsonization.

Interaction between fibronectin-bearing surfaces and Bacillus Calmette-Guérin (BCG) or gelatin microparticles

Gelatin, prepared commercially by degradation of animal collagen, was studied to see whether it had an affinity for fibronectin, which has a known affinity for collagen, and whether gelatin-based drugs could be used to target fibronectin-excreting tumours. Bacillus Calmette-Guérin (BCG) vaccine, an attenuated strain of Mycobacterium bovis, is currently the most effective treatment for superficial transitional cell carcinoma of the bladder. The living cells of the BCG vaccine associate with the fibronectin-bearing surfaces of the tumour. Using a multi-well culture plate technique, gelatin microparticles were shown to be adsorbed onto murine S180 sarcoma cells and this reaction was substantially inhibited by the addition of human plasma fibronectin. The avidities of various BCG substrains and gelatin microparticles for glass-bound fibronectin were measured and the association constants determined. The gelatin microparticles associated with the fibronectin with equal avidity as the BCG cells. The results suggest that this model system may allow the investigation of gelatin-based drug delivery devices capable of targeting fibronectin-bearing surfaces associated with some tumours.

In-vivo and in-vitro targeting of a murine sarcoma by gelatin microparticles loaded with a glycan (PS1)

PS1, a complex polysaccharide derived from Mycobacterium bovis (Bacillus Calmette-Guérin, BCG) with considerable antitumor activity in-vivo, was loaded onto gelatin microparticles (mean diam. 1.45 micron) at a level shown to not produce the burst effect often seen with drug-loaded microparticulate systems. In-vitro dissolution experiments had demonstrated a sustained-release behaviour, with a half-life of approximately 8 h for what is an extremely water-soluble material. These PS1/gelatin systems had no measurable cytotoxicity against an S180 murine sarcoma cell in-vitro although fibronectin-mediated targeting of the microparticles for the tumour cells could be demonstrated. Injection into mice, with the S180 cells, of PS1 solutions or suspensions of PS1-loaded gelatin microparticles resulted in almost identical dose-related suppression for the tumour cell growth. When injected at intervals following injection of the tumour cells, however, for a period of 24-48 h there was a relatively enhanced activity of the formulated PS1, compared with the aqueous solution, after which both formulated and unformulated material became progressively less effective.