Characterization of DNA-hyaluronan matrix for sustained gene transfer

Star polymer-based nanolayers with immobilized complexes of polycationic stars and DNA for deposition gene delivery and recovery of intact transfected cells

We designed a novel thermoresponsive system of nanolayers composed of star poly[oligo(ethylene glycol) methacrylate]s (S-POEGMA) covalently bonded to a solid support and covered with polyplexes of cationic star polymers and plasmid DNA (pDNA). S-POEGMA stars were attached to the solid support via a UV-mediated "grafting to" method. To the best of our knowledge, for the first time, the conformational changes of obtained star nanolayers, occurring with changes in temperature, were studied using a quartz crystal microbalance technique. Next, the polyplexes of star poly[N,N'-dimethylaminoethyl methacrylate-ran-di(ethylene glycol) methacrylate] (S-P(DMAEMA-DEGMA)) with pDNA, exhibiting a phase transition temperature (T_CP) in culture medium DMEM, were deposited on S-POEGMA layers when the temperature increased above the T_CP of polyplex. The thermoresponsivity of the system was then the main mechanism for controlling the adhesion, proliferation, transfection and detachment of HT-1080 cells. The nanolayers promoted the effective cell culture and delivered nucleic acids into cells, with a transfection efficiency several times higher than that of the control. The detachment of the transfected cells was regulated only by the change of temperature. The studies demonstrated that we obtained a novel and effective system, based on a star polymer architecture, useful for gene delivery and tissue engineering applications.

Non-viral strategies for ocular gene delivery

The success of gene therapy relies on efficient gene transfer and stable transgene expression. The in vivo efficiency is determined by the delivery vector, route of administration, therapeutic gene, and target cells. While some requirements are common to several strategies, others depend on the target disease and transgene product. Consequently, it is unlikely that a single system is suitable for all applications. This review examines current gene therapy strategies, focusing on non-viral approaches and the use of natural polymers with the eye, and particularly the retina, as their gene delivery target.

Gene delivery from polymer scaffolds for tissue engineering

The combination of gene therapy with tissue engineering offers the potential to direct progenitor cell proliferation and differentiation into functional tissue replacements. Many approaches to engineering tissue replacements feature a polymer scaffold to create and maintain a space, support cell adhesion, and organize tissue formation. Polymer scaffolds, either natural, synthetic, or a combination of the two, have also been adapted to serve as delivery vehicles for viral and nonviral vectors, which can induce the expression of tissue inductive factors. Gene delivery is a versatile approach, capable of targeting any cellular process through localized expression of tissue inductive factors. The design and application of tissue engineering scaffolds for localized gene transfer are reviewed. Scaffolds are designed either to release the vector into the local tissue environment or maintain the vector at the polymer surface, which is regulated by the effective affinity of the vector for the polymer. Polymeric delivery can enhance gene transfer locally, promote and extend transgene expression, avoid vector distribution to distant tissues, and reduce the immune response to the vector. Scaffolds capable of controlled DNA delivery can provide a fundamental tool for directing progenitor cell function, which has applications with the engineering of numerous types of tissue. The utility of this approach will increase with the development of design parameters that correlate release and transgene expression, and with continued research into the biology of tissue formation.

Design of magnetic polyplexes taken up efficiently by dendritic cell for enhanced DNA vaccine delivery

Dendritic cells (DC) targeting vaccines require high efficiency for uptake, followed by DC activation and maturation. We used magnetic vectors comprising polyethylenimine (PEI)-coated superparamagnetic iron oxide nanoparticles, with hyaluronic acid (HA) of different molecular weights (<10 and 900 kDa) to reduce cytotoxicity and to facilitate endocytosis of particles into DCs via specific surface receptors. DNA encoding Plasmodium yoelii merozoite surface protein 1-19 and a plasmid encoding yellow fluorescent gene were added to the magnetic complexes with various % charge ratios of HA: PEI. The presence of magnetic fields significantly enhanced DC transfection and maturation. Vectors containing a high-molecular-weight HA with 100% charge ratio of HA: PEI yielded a better transfection efficiency than others. This phenomenon was attributed to their longer molecular chains and higher mucoadhesive properties aiding DNA condensation and stability. Insights gained should improve the design of more effective DNA vaccine delivery systems.

Hyaluronan and synovial joint: function, distribution and healing

Synovial fluid is a viscous solution found in the cavities of synovial joints. The principal role of synovial fluid is to reduce friction between the articular cartilages of synovial joints during movement. The presence of high molar mass hyaluronan (HA) in this fluid gives it the required viscosity for its function as lubricant solution. Inflammation oxidation stress enhances normal degradation of hyaluronan causing several diseases related to joints. This review describes hyaluronan properties and distribution, applications and its function in synovial joints, with short review for using thiol compounds as antioxidants preventing HA degradations under inflammation conditions.

Polysaccharide-based nucleic acid nanoformulations

Therapeutic application of nucleic acids requires their encapsulation in nanosized carriers that enable safe and efficient intracellular delivery. Before the desired site of action is reached, drug-loaded nanoparticles (nanomedicines) encounter numerous extra- and intracellular barriers. Judicious nanocarrier design is highly needed to stimulate nucleic acid delivery across these barriers and maximize the therapeutic benefit. Natural polysaccharides are widely used for biomedical and pharmaceutical applications due to their inherent biocompatibility. At present, there is a growing interest in applying these biopolymers for the development of nanomedicines. This review highlights various polysaccharides and their derivatives, currently employed in the design of nucleic acid nanocarriers. In particular, recent progress made in polysaccharide-assisted nucleic acid delivery is summarized and the specific benefits that polysaccharides might offer to improve the delivery process are critically discussed.

Targeted therapy of gastrointestinal tumors using hyaluronic acid drug carriers

Hyaluronic acid (HA) is a natural, linear, high molecular weight mucopolysaccharide with good biocompatibility and biodegradability. Recently, HA receptor has been found on the surface of tumor cells. Therefore, sustained-release and tumor-targeting drug carriers with hyaluronic acid and its derivatives have been fabricated, because they can bind specifically to the HA receptor on the surface of tumor cells and are biodegradable. Now, the research on targeted therapy using hyaluronic acid drug carriers is focused on the therapy of prostatic cancer, pulmonary cancer and head and neck neoplasms. Colon tumors are the only type of gastrointestinal tumors in which hyaluronic acid drug carriers were studied. In this paper, we introduce the design and characteristics of hyaluronic acid drug carriers and review recent progress and future prospects of targeted treatment of gastrointestinal tumors using hyaluronic acid drug carriers.

Development and characterization of local anti-inflammatory implantation for the controlled release of the hexane extract of the flower-heads of Euryops pectinatus L. (Cass.)

A hexane extract of the flower-heads of Euryops pectinatus L. (Cass.) was formulated into local anti-inflammatory implantation patches with controlled release. Cross-linked sodium hyaluronate patches (F1-F3) and chitosan patches (F4-F6) were prepared by a casting/solvent evaporation technique. Morphological and mechanical characterizations including the components ratio, surfactant and the loaded amount of the hexane extract (50, 100, and 200 mg/kg b.wt.) were investigated. Release studies were performed during 24 h using a diffusion cell. Films with optimum in vitro release rate have been investigated for testing the anti-inflammatory activity and the sustaining effect of the formulations. The sustained anti-inflammatory effect of the hexane extract of E. pectinatus flower-heads from the selected films was studied by inducing paw edema in rats with 1% (w/v) carrageenan solution. The results indicated the compatibility of hexane extract with both sodium hyaluronate and chitosan patches forming yellowish transparent films. Based on variations in drug release profiles throughout the 24-h among the formulations (F1-F6) studies, F3 and F6 were selected for further investigation. When the films were applied 1 h before the subplantar injection of carrageenan in the hind paw of male Albino rats, formulation (F3) provided its maximum inhibition of paw edema in rats (91.3%) 4 h after edema induction whereas, formulation (F6) showed less inhibition after 4 h (70.6%). The previous two formulations (F3 and F6) produced potent results (95.3 and 89.5%, respectively) after 24 h when compared with a local market preparation containing 25% β-sitosterol used as positive control. Histophathological investigation was conducted for 1, 4, and 12 weeks to study the tissue response for the two formulations (F3 and F6) at the implantation site. Chemical investigation of the hexane extract was achieved for both unsaponifiable matter (USM) and fatty acid methyl esters (FAME) using gas liquid chromatography (GLC). The USM was dominated by n-pentacosane (14.40%), phytosterols (Cholesterol, Campesterol, Stigmasterol, β-sitosterol, α-amyrin) reached 33.44% and the FAME was dominated by Linoleinic (49.97%). Quality control of the local implantation was evaluated by GLC using cholesterol as an analytical marker and phytosterols as an active marker compared to the plain extract.

Molecular fabrications of smart nanobiomaterials and applications in personalized medicine

Recent advances in nanotechnology adequately address many of the current challenges in biomedicine. However, to advance medicine we need personalized treatments which require the combination of nanotechnological progress with genetics, molecular biology, gene sequencing, and computational design. This paper reviews the literature of nanoscale biomaterials described to be totally biocompatible, non-toxic, non-immunogenic, and biodegradable and furthermore, have been used or have the potential to be used in personalized biomedical applications such as drug delivery, tissue regeneration, and diagnostics. The nanobiomaterial architecture is discussed as basis for fabrication of novel integrated systems involving cells, growth factors, proteins, cytokines, drug molecules, and other biomolecules with the purpose of creating a universal, all purpose nanobiomedical device for personalized therapies. Nanofabrication strategies toward the development of a platform for the implementation of nanotechnology in personalized medicine are also presented. In addition, there is a discussion on the challenges faced for designing versatile, smart nanobiomaterials and the requirements for choosing a material with tailor made specifications to address the needs of a specific patient.

Preparation of hyaluronan-DNA matrices and films

Natural carbohydrate is a class of underexplored polymers for gene delivery. The noninflammatory and nonimmunogenic properties of hyaluronan (hyaluronic acid, HA) are important in clinical situations. It has a role in wound repair and has great lubricating ability. Moreover, the presence of hyaluronidase in vivo enables any vehicle fabricated from HA to be degraded by enzyme-mediated erosion. When DNA is entrapped in a cross-linked HA vehicle, HA-DNA fragments are released on digestion by hyaluronidase. These fragments could serve both as microcarriers of DNA and its protective mechanism. This protocol describes preparation of water-insoluble HA-DNA matrices and films designed for clinical applications, and assays for verification of their bioactivities. Plasmid DNA (pDNA) encoding platelet-derived growth factor (PDGF) is coupled to the matrices that could be implanted into chronic wounds to accelerate their healing. pDNA encoding hyaluronan synthase 2 (HAS2) is coupled to the film that could initially serve as a physical barrier and subsequently a pDNA reservoir for sustaining HAS2 transfection. This would lead to continual HA production for preventing postsurgical adhesion.

Hyaluronic acid: evaluation as a potential delivery vehicle for vitronectin:growth factor complexes in wound healing applications

We have previously reported that novel vitronectin:growth factor (VN:GF) complexes significantly increase re-epithelialization in a porcine deep dermal partial-thickness burn model. However, the potential exists to further enhance the healing response through combination with an appropriate delivery vehicle which facilitates sustained local release and reduced doses of VN:GF complexes. Hyaluronic acid (HA), an abundant constituent of the interstitium, is known to function as a reservoir for growth factors and other bioactive species. The physicochemical properties of HA confer it with an ability to sustain elevated pericellular concentrations of these species. This has been proposed to arise via HA prolonging interactions of the bioactive species with cell surface receptors and/or protecting them from degradation. In view of this, the potential of HA to facilitate the topical delivery of VN:GF complexes was evaluated. Two-dimensional (2D) monolayer cell cultures and 3D de-epidermised dermis (DED) human skin equivalent (HSE) models were used to test skin cell responses to HA and VN:GF complexes. Our 2D studies revealed that VN:GF complexes and HA stimulate the proliferation of human fibroblasts but not keratinocytes. Experiments in our 3D DED-HSE models showed that VN:GF complexes, both alone and in conjunction with HA, led to enhanced development of both the proliferative and differentiating layers in the DED-HSE models. However, there was no significant difference between the thicknesses of the epidermis treated with VN:GF complexes alone and VN:GF complexes together with HA. While the addition of HA did not enhance all the cellular responses to VN:GF complexes examined, it was not inhibitory, and may confer other advantages related to enhanced absorption and transport that could be beneficial in delivery of the VN:GF complexes to wounds.

Carbohydrate polymers for nonviral nucleic acid delivery

Carbohydrates have been investigated and developed as delivery vehicles for shuttling nucleic acids into cells. In this review, we present the state of the art in carbohydrate-based polymeric vehicles for nucleic acid delivery, with the focus on the recent successes in preclinical models, both in vitro and in vivo. Polymeric scaffolds based on the natural polysaccharides chitosan, hyaluronan, pullulan, dextran, and schizophyllan each have unique properties and potential for modification, and these results are discussed with the focus on facile synthetic routes and favorable performance in biological systems. Many of these carbohydrates have been used to develop alternative types of biomaterials for nucleic acid delivery to typical polyplexes, and these novel materials are discussed. Also presented are polymeric vehicles that incorporate copolymerized carbohydrates into polymer backbones based on polyethylenimine and polylysine and their effect on transfection and biocompatibility. Unique scaffolds, such as clusters and polymers based on cyclodextrin (CD), are also discussed, with the focus on recent successes in vivo and in the clinic. These results are presented with the emphasis on the role of carbohydrate and charge on transfection. Use of carbohydrates as molecular recognition ligands for cell-type specific delivery is also briefly reviewed. We contend that carbohydrates have contributed significantly to progress in the field of non-viral DNA delivery, and these new discoveries are impactful for developing new vehicles and materials for treatment of human disease.

Target specific and long-acting delivery of protein, peptide, and nucleotide therapeutics using hyaluronic acid derivatives

Hyaluronic acid (HA) is a biodegradable, biocompatible, non-toxic, non-immunogenic and non-inflammatory linear polysaccharide, which has been used for various medical applications such as arthritis treatment, ocular surgery, tissue augmentation, and so on. In this review, the effect of chemical modification of HA on its distribution throughout the body was reported for target specific and long-acting delivery applications of protein, peptide, and nucleotide therapeutics. According to the real-time bio-imaging of HA derivatives using quantum dots (QDot), HA-QDot conjugates with 35mol% HA modification maintaining enough binding sites for HA receptors were mainly accumulated in the liver, while those with 68mol% HA modification losing much of HA characteristics were evenly distributed to the tissues in the body. The results are well matched with the fact that HA receptors are abundantly present in the liver with a high specificity to HA molecules. Accordingly, slightly modified HA derivatives were used for target specific intracellular delivery of nucleotide therapeutics and highly modified HA derivatives were used for long-acting conjugation of peptide and protein therapeutics. HA has been also used as a novel depot system in the forms of physically and chemically crosslinked hydrogels for various protein drug delivery. This review will give you a peer overview on novel HA derivatives and the latest advances in HA-based drug delivery systems of various biopharmaceuticals for further clinical development.

Delivery of nucleic acids via disulfide-based carrier systems

Nucleic acids are not only expected to assume a pivotal position as "drugs" in the treatment of genetic and acquired diseases, but could also act as molecular cues to control the microenvironment during tissue regeneration. Despite this promise, the efficient delivery of nucleic acids to their side of action is still the major hurdle. One among many prerequisites for a successful carrier system for nucleic acids is high stability in the extracellular environment, accompanied by an efficient release of the cargo in the intracellular compartment. A promising strategy to create such an interactive delivery system is to exploit the redox gradient between the extra- and intracellular compartments. In this review, emphasis is placed on the biological rationale for the synthesis of redox sensitive, disulfide-based carrier systems, as well as the extra- and intracellular processing of macromolecules containing disulfide bonds. Moreover, the basic synthetic approaches for introducing disulfide bonds into carrier molecules, together with examples that demonstrate the benefit of disulfides at the individual stages of nucleic acid delivery, will be presented.

Prevention of cerebral vasospasm by local delivery of cromakalim with a biodegradable controlled-release system in a rat model of subarachnoid hemorrhage

OBJECT

One mechanism that contributes to cerebral vasospasm is the impairment of potassium channels in vascular smooth muscles. Adenosine triphosphate-sensitive potassium channel openers (PCOs) appear to be particularly effective for dilating cerebral arteries in experimental models of subarachnoid hemorrhage (SAH). A mode of safe administration that provides timed release of PCO drugs is still a subject of investigation. The authors tested the efficacy of locally delivered intrathecal cromakalim, a PCO, incorporated into a controlled-release system to prevent cerebral vasospasm in a rat model of SAH.

METHODS

Cromakalim was coupled to a viscous carrier, hyaluronan, 15% by weight. In vitro release kinetics studies showed a steady release of cromakalim over days. Fifty adult male Sprague-Dawley rats weighing 350-400 g each were divided into 10 groups and treated with various doses of cromakalim or cromakalim/hyaluronan in a rat double SAH model. Treatment was started 30 minutes after the second SAH induction. Animals were killed 3 days after treatment, and the basilar arteries were processed for morphometric measurements and histological analysis.

RESULTS

Controlled release of cromakalim from the cromakalim/hyaluronan implant at a dose of 0.055 mg/kg significantly increased lumen patency in a dose-dependent manner up to 94 +/- 8% (mean +/- standard error of the mean) of the basilar arteries of the sham group compared with the empty polymer group (p = 0.006). Results in the empty polymer group were not different from those in the SAH-only group, with a lumen patency of 65 +/- 12%. Lumen patencies of the cromakalim-only groups did not differ in statistical significance at low (64 +/- 9%) or high (66 +/- 7%) doses compared to the SAH-only group.

CONCLUSIONS

Treatment of SAH with a controlled-release cromakalim/hyaluronan implant prevented experimental cerebral vasospasm in this rat double hemorrhage model; this inhibition was dose-dependent. The authors' results confirm that sustained delivery of cromakalim perivascularly to cerebral vessels could be an effective therapeutic strategy in the treatment of cerebral vasospasm after SAH.

Design of novel polysaccharidic nanostructures for gene delivery

The goal of the present work was to develop a new synthetic nanosystem for gene delivery. For this purpose, we chose two polysaccharides, hyaluronic acid (HA) and chitosan (CS), as the main components of the nanocarrier. Nanoparticles with different hyaluronate:chitosan (HA:CS) mass ratios (0.5:1 and 1:1) and different polymer molecular weights (hyaluronate 170 (HA) or <10 kDa (HAO) and chitosan 125 (CS) or 10-12 (CSO) kDa) could be obtained using an ionic crosslinking method. These nanoparticles were loaded with pDNA and characterized for their size, zeta potential and pDNA association efficiency. Moreover, their toxicity and ability to transfect the model plasmid pEGFP-C1 were evaluated in the cell line HEK 293, as well as their intracellular fate. The results showed that HA:CS nanoparticles have a small size in the range of 110-230 nm, a positive zeta potential of +10 to +32 mV and a very high pDNA association efficiency of 87-99% (w/w). On the other hand, nanoparticles exhibited low cell toxicity and transfection levels up to 25% GFP expressing HEK 293 cells, lasting for the whole observation period of 10 days. We also provide basic information about the role of both polymers, HA and CS, and the effect of their molecular weight on the effectiveness of the resulting DNA nanocarrier, being the highest transfection levels observed with HAO:CSO 1:1 nanoparticles. In conclusion, HA:CS nanoparticles are promising carriers for gene delivery.

Human hepatoblast phenotype maintained by hyaluronan hydrogels

Human hepatoblasts and hepatic stem cells, pluripotent hepatic progenitors that give rise to hepatocytes and biliary cells, were isolated from fetal livers and found to express hyaluronan receptors (CD44) in both the freshly isolated cells and after culture. This implicates an in vivo connection to hyaluronan (HA), an embryonic matrix component, as a candidate 3-dimensional (3-D) scaffold for hepatic progenitor cell expansion and/or differentiation. To assess HAs as scaffolds, hepatoblasts and hepatic stem cells were seeded into HA hydrogels with a serum-free, hormonally defined medium tailored for expansion of hepatic progenitors. Cell aggregates formed within the HA hydrogels and remained viable, proliferative, and demonstrated a stable phenotype intermediate between that of hepatic stem cells and hepatoblasts throughout more than 4 weeks of culturing, with little evidence of lineage restriction towards either hepatocytic or biliary pathways. The phenotype consisted of stable co-expression of both hepatocytic and biliary markers such as biliary-specific cytokeratin, CK19, low levels of expression of albumin, and urea synthesis. HA hydrogels are ideal as 3-D scaffolds for pluripotent hepatic progenitors and should be useful for generating cells to be used in bioartificial livers or tissue engineered liver grafts.

Biomaterial-mediated retroviral gene transfer using self-assembled monolayers

Biomaterial-mediated gene delivery has recently emerged as a promising alternative to conventional gene transfer technologies that focus on direct delivery of viral vectors or DNA-polymer/matrix complexes. However, biomaterial-based strategies have primarily targeted transient gene expression vehicles, including plasmid DNA and adenovirus particles. This study expands on this work by characterizing biomaterial properties conducive to the surface immobilization of retroviral particles and subsequent transduction of mammalian cells at the cell-material interface. Self-assembled monolayers (SAMs) of functionally-terminated alkanethiols on gold were used to establish biomaterial surfaces of defined chemical composition. Gene transfer was observed to be greater than 90% on NH(2)-terminated surfaces, approximately 50% on COOH-functionalized surfaces, and undetectable on CH(3)-terminated SAMs, similar to controls of tissue culture-treated polystyrene. Gene delivery via the NH(2)-SAM was further characterized as a function of retrovirus coating time, virus concentration, and cell seeding density. Finally, SAM-mediated gene delivery was comparable to fibronectin- and poly-l-lysine-based methods for gene transfer. This work is significant to establishing safe and effective gene therapy strategies, developing efficient methods for gene delivery, and supporting recent progress in the field of biomaterial-mediated gene transfer.

Hyaluronan: pharmaceutical characterization and drug delivery

Hyaluronic acid (HA), is a polyanionic polysaccharide that consists of N-acetyl-D-glucosamine and beta-glucoronic acid. It is most frequently referred to as hyaluronan because it exists in vivo as a polyanion and not in the protonated acid form. HA is distributed widely in vertebrates and presents as a component of the cell coat of many strains of bacteria. Initially the main functions of HA were believed to be mechanical as it has a protective, structure stabilizing and shock-absorbing role in the body. However, more recently the role of HA in the mediation of physiological functions via interaction with binding proteins and cell surface receptors including morphogenesis, regeneration, wound healing, and tumor invasion, as well as in the dynamic regulation of such interactions on cell signaling and behavior has been documented. The unique viscoelastic nature of hyaluronan along with its biocompatibility and nonimmunogenicity has led to its use in a number of cosmetic, medical, and pharmaceutical applications. More recently, HA has been investigated as a drug delivery agent for ophthalmic, nasal, pulmonary, parenteral, and dermal routes. The purpose of our review is to describe the physical, chemical, and biological properties of native HA together with how it can be produced and assayed along with a detailed analysis of its medical and pharmaceutical applications.

Protective efficiency of dendrosomes as novel nano-sized adjuvants for DNA vaccination against birch pollen allergy

We evaluated the use of a novel gene porter (Den123--a nontoxic self-assembled dendritic spheroidal nanoparticle made of biodegradable monomers), aiming to enhance and improve the desired immune response in protection from allergy. Footpad DNA immunization in Balb/c mice was done three times using the Bet v 1a gene with or without Den123 with 2-week intervals followed by sensitization with rBetv1 (5 microg) in alum twice in a weekly interval. Different doses of pCMV-Betv1 were used (10 microg and 100 microg). The protective role of different formulations was evaluated by measuring the IgG1, IgG2a and IgE antibody production, cytokine release of isolated splenocytes and beta-hexosaminidase release from the RBL cells. Higher and increasing ratios of IgG2a/IgG1 were seen in mice which received plasmids in combination with Den123. Den123 and DNA vaccine synergistically enhanced the Interferon gamma released from splenocytes. In the presence of Den123, IgE inhibition was independent of the dose and type of the injected DNA. All DNA-pre-immunized mice demonstrated low basophil degranulation. It is therefore concluded that administration of the DNA entrapped in Den123 nanoparticles results in sustained release of plasmids, Th1/Th2 balanced immune response with promising IgE inhibition. Also higher amounts of DNA contributed to stronger Th1 response.

Hyaluronic acid: a unique topical vehicle for the localized delivery of drugs to the skin

Hyaluronic acid (HA) is a naturally occurring polyanionic, polysaccharide that consists of N-acetyl-D-glucosamine and beta-glucoronic acid. It is present in the intercellular matrix of most vertebrate connective tissues especially skin where it has a protective, structure stabilizing and shock-absorbing role. The unique viscoelastic nature of HA along with its biocompatibility and non-immunogenicity has led to its use in a number of clinical applications, which include: the supplementation of joint fluid in arthritis; as a surgical aid in eye surgery; and to facilitate the healing and regeneration of surgical wounds. More recently, HA has been investigated as a drug delivery agent for various routes of administration, including ophthalmic, nasal, pulmonary, parenteral and topical. In fact, regulatory approval in the USA, Canada and Europe was granted recently for 3% diclofenac in 2.5% HA gel, Solaraze, for the topical treatment of actinic keratoses, which is the third most common skin complaint in the USA. The gel is well tolerated, safe and efficacious and provides an attractive, cost-effective alternative to cryoablation, curettage or dermabrasion, or treatment with 5-fluorouracil. The purpose of this review is to describe briefly the physical, chemical and biological properties of HA together with some details of its medical and pharmaceutical uses with emphasis on this more recent topical application.

Delivery of a vector encoding mouse hyaluronan synthase 2 via a crosslinked hyaluronan film

We have developed a crosslinked hyaluronic acid (HA) film with DNA incorporated within its structure and have characterized this system for its efficacy in sustained transferring of a vector encoding mouse hyaluronan synthase 2 (Has2). Analysis of the DNA release kinetics indicated that the HA films degraded when treated with hyaluronidase and that they released DNA over a prolonged period of time. Gel electrophoresis revealed that this DNA was intact and immunohistochemical analysis verified the transfection capabilities of DNA release samples. The ability of released DNA encoding Has2 to promote HA synthesis was confirmed by quantifying the amount of HA produced by COS-1 cells that were transfected with release samples. The intended future application of the HA films is in prevention of post-operative peritoneal adhesions. In addition to serving as a physical barrier, the film would function as a vehicle for sustained delivery of DNA encoding Has2, which would promote the synthesis of HA in transfected tissues.

Hyaluronan microspheres for sustained gene delivery and site-specific targeting

Hyaluronan is a naturally occurring polymer that has enjoyed wide successes in biomedical and cosmetic applications as coatings, matrices, and hydrogels. For controlled delivery applications, formulating native hyaluronan into microspheres could be advantageous but has been difficult to process unless organic solvents are used or hyaluronan has been modified by etherification. Therefore, we present a novel method of preparing hyaluronan microspheres using adipic dihydrazide mediated crosslinking chemistry. To evaluate their potential for medical applications, hyaluronan microspheres are incorporated with DNA for gene delivery or conjugated with an antigen for cell-specific targeting. The results show that our method, originally developed for preparing hyaluronan hydrogels, generates robust microspheres with a size distribution of 5-20mum. The release of the encapsulated plasmid DNA can be sustained for months and is capable of transfection in vitro and in vivo. Hyaluronan microspheres, conjugated with monoclonal antibodies to E- and P-selectin, demonstrate selective binding to cells expressing these receptors. In conclusion, we have developed a novel microsphere preparation using native hyaluronan that delivers DNA at a controlled rate and adaptable for site-specific targeting.

Controlled release systems for DNA delivery

Adapting controlled release technologies to the delivery of DNA has the potential to overcome extracellular barriers that limit gene therapy. Controlled release systems can enhance gene delivery and increase the extent and duration of transgene expression relative to more traditional delivery methods (e.g., injection). These systems typically deliver vectors locally, which can avoid distribution to distant tissues, decrease toxicity to nontarget cells, and reduce the immune response to the vector. Delivery vehicles for controlled release are fabricated from natural and synthetic polymers, which function either by releasing the vector into the local tissue environment or by maintaining the vector at the polymer surface. Vector release or binding is regulated by the effective affinity of the vector for the polymer, which depends upon the strength of molecular interactions. These interactions occur through nonspecific binding based on vector and polymer composition or through the incorporation of complementary binding sites (e.g., biotin-avidin). This review examines the delivery of nonviral and viral vectors from natural and synthetic polymers and presents opportunities for continuing developments to increase their applicability.