The invention relates to a composition comprising a pharmaceutically active agent and a bioadhesive delivery system that provides for the oral delivery of a vaccine to animals, particularly aquatic animals.

Description of the Invention

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a composition comprising a pharmaceutically active agent, such as, but not limited to, an immunogenic agent (e.g., a vaccine), and a bioadhesive delivery system, that allows the oral administration and delivery of the pharmaceutically active agent essentially unaltered to the intestinal mucosa.

2. Background of Related Art

Orally delivered pharmaceutically active agents present a significant problem in transiting an animal's stomach, an organ whose contents represent a harsh digestive environment consisting of low pH and enzymes specifically designed to denature proteins. As a consequence, orally delivered bacterin or subunit vaccines have not been proven to be efficacious since the antigens are generally modified by the stomach prior to presentation to the immuno-responsive cells of the gut mucosa. A number of approaches have been tested to provide an oral delivery vehicle that would transit the stomach but most have been unsuccessful at the commercial scale. One approach involves the transient changing of the stomach pH, neutralizing gastric enzymes and stimulating the mucosal immune response.

In 2003 about 200 million fish were vaccinated in Chile, primarily for Yersiniosis, Salmonid Ricketsial Septicaemia, and Invectious Pancreatic Necrosis (Bravo, 2007). Of the more than 20 vaccines for aquacultured fish were brought to the Chilean market from 1999-2003, none were orally delivered vaccines.

Salmon Rickettsial Septicaemia (SRS) is a pathology of salmonid fish caused by the intracellular bacterium Piscrickettsia salmonis and is a major infectious disease in the Chilean salmon industry with annual losses exceeding 20%. Unlike other bacterial diseases, the anti-SRS vaccination is not as effective in preventing the disease or in reducing the need for post-infection medication. This is because of a gradual diminishing of the SRS immunogenicity in the vaccinated fish. Boostering the vaccine at a later stage should allow the continued protection of the animals throughout the entire commercial growing period. However, it is extremely difficult and economically impractical to provide parenteral vaccine boosters to large animals in the grow-out net pens.

Almost all existing vaccines are delivered to aquatic animals by injection, which is traumatic, inconvenient, time consuming, expensive, has a number of side effects, and may fail to induce an appropriate immunogenic response in mucosal tissues. Thus, a method and system for delivery that avoids these disadvantages would be advantageous.

Perhaps the most well known antigen delivery systems are those derived from the linear polymeric esters of lactic acid and glycolic acid (i.e., poly DL-lactide-co-glycolide, PLGA, reviewed by Wu (Wu, 2004). In such systems, immunogenic subunit vaccine components have been captured in poly-acrylate and poly-glycolide/lactide beads or liposome-like vesicles through processes utilizing volatile organic solvents such as dichloromethane or chloroform. The solvents are used to form emulsions of polymer solutions or dried lipid films. Encapsulation of antigens into PLGA microcapsules affords a number of advantages including rapid degradation by hydrolysis and subsequent penetration of the Peyer's Patches (concentrated sites of lymphocytic tissue in the intestinal mucosa of higher vertebrates but not in fish). A major disadvantage of PLGA microcapsules is the requisite use of organic solvents. Contact with organic solvents can inactivate or reduce the efficacy of the vaccine by altering the immunogenicity of surface proteins critical to induction of humoral or cellular immune responses. Additionally, Poly-acrylate and poly-glycolide/lactide processes typically result in microbeads with extremely low immunogen or antigen capture efficiency.

Polymer microspheres and lamellar particles (e.g., liposomes) have been employed for the improved parenteral and mucosal administration of antigens. Because vaccines themselves may not be efficiently recognized and taken up by mucosal lymphocytes, they typically need to be co-administered with penetration enhancers or adjuvants. Different classes of polymer mixtures are known for potential use as Mucoadhesives (Malik et al., 2007). These include synthetic polymers such as poly (acrylic acid) (PAA), hydroxypropyl methylcellulose and poly(methylacrylate) derivatives, as well as naturally occurring polymers such as hyaluronic acid and chitosan.

Chitosan has been used for a variety of applications as a biomaterial for tissue engineering, wound healing, and as an excipient for drug delivery (Chopra et al., 2006; Dang and Leong, 2006). Chitosan has occasionally been tested as an adjuvant for mucosal application (Kim et al., 2007), but it is typically applied directly to a mucosal surface such as intranasal application in order to obtain IgA response in the nasopharyngeal mucosa of terrestrial animals (Kang et al., 2007). However, the use of chitosan in vaccine delivery remains very limited due to poor physicochemical characteristics such as a high transition temperature and interfacial free energy, resulting in a suboptimal interaction with mucosal surfaces and loose interpenetration and interdiffusion of the polymer. This problem is further compounded when used for poikilotheric lower vertebrates like salmonid fish. Chitosan also has the additional disadvantage of a low mechanical strength and solubility.

Thus, there remains a need for effective systems and processes for microencapsulation of immunogenic substances with polymers having superior adhesive and cohesive properties.

SUMMARY OF THE INVENTION

The present invention overcomes the shortcomings of the above-discussed encapsulation systems, wherein the present invention discloses a composition designed for an oral delivery of a primary and or booster vaccination that can be used for animals housed in the not only in hatchery but also grow-out pens. The exceptional mucoadhesive properties of compositions of the present invention provide a successful method of transmucosal drug delivery, especially for lower vertebrates with less developed digestive system and no Peyer's Patches such as fish.

One aspect of the present invention provides for a bioadhesive delivery system comprising a composition including a cationic polysaccharide, a neutral polysaccharide in combination with a pharmaceutically active agent, such as an immunogenic agent. Surprisingly, the immunogenic agent when administered with the cationic polysaccharide and neutral polysaccharide results in a similar or better immunologic induction than parenteral administration of the pharmaceutically active agent.

Another aspect of the present invention provides for a composition comprising a cationic polysaccharide, a neutral polysaccharide in combination with a pharmaceutically active agent, wherein the cationic polysaccharide is chitosan and the neutral polysaccharide is a fructan, and more preferably, an inulin or fragments thereof.

A further aspect of the present invention provides for oral delivery of a pharmaceutically active agent, such as an antigen, wherein the pharmaceutically active agent is released at the site of action (i.e., the Gut Associated Lymphoid Tissue; GALT) along the foregut and hindgut of the animal. Importantly, the delivery vehicle comprising a cationic polysaccharide, a neutral polysaccharide in combination with the pharmaceutically active agent, further provides protection of the antigen during transit through the stomach of the animal and then provides a gradual dissolution, corresponding to the hindgut transit time of about 2 hours, and permits reproducible release of the antigen therein.

A still further aspect of the present invention provides for a method of producing a bioadhesive delivery vehicle for vaccination of animals, such as aquatic animals, wherein the delivery vehicle is in a form of dry microparticles comprising an immunogenic agent embedded or impregnated in a composite matrix of cross-linked chitosan, oligosaccharides, saccharides. Any applicable oligosaccharides may be used in the composition. Common oligosaccharides include fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), and inulins. In a preferred embodiment of the invention, the method comprises producing a bioadhesive delivery vehicle containing an SRS vaccine for use in salmonid fish.

Another aspect of the present invention provides for a feed regime wherein animals are fed a bioadhesive delivery vehicle comprising a cationic polysaccharide, a neutral polysaccharide in combination with a pharmaceutically active agent, for the oral vaccination of animals. In a preferred embodiment, the vaccinated animal is a fish and, in a more preferred embodiment the fish are salmonids and the oral vaccination, or booster, is to prevent the disease known as SRS.

A still further aspect of the present invention provides for a composition for stablilizing and delivery of a pharmaceutically active agent to the gut, the composition comprising chitosan and inulin in combination with an emulsifier/sugar complex, wherein the emulsifier/sugar complex comprises lecithin and is in an amount sufficient to mediate the interaction between inulin and the hydrophobic amine residues of chitosan.

Another aspect of the present invention provides for a method of preparing a composition for oral delivery of a pharmaceutically active ingredient comprising: a) preparing an acidic aqueous solution comprising at least one bioadhesive polymer, wherein the bioadhesive polymer is chitosan and the acidic solution has a pH low enough to gelatinize the chitosan; b) combining an oligosaccharide, such as inulin, into the solution with the gelatinized chitosan to form a inulin-chitosan solution; c) combining an emulsifier with a sugar, wherein the sugar and emulsifer form a sugar/emulsifier complex; d) introducing the sugar/emulsifier complex into the inulin-chitosan solution to form a smooth emulsion while maintaining the acidic pH of the solution; e) adding a pharmaceutically active agent into the smooth emulsion; and f) precipitating the emulsion into a phosphate containing cross-linking solution.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an improved immunogenic substance for oral delivery. The invention is based on the discovery of unexpected synergetic properties of a complex mixture of chitosan and a fructan.

Fructans or fructosans are oligosaccharides or polysaccharides comprising a sequence of anhydrofructose units optionally combined with one [lacuna] more different saccharide residues of the fructose. Fructans can be linear or branched. Fructans can be products obtained directly from a plant or microbial source or else products with a chain length which has been modified (increased or reduced) by splitting, synthesis or hydrolysis, in particular of the enzymatic variety. Fructans generally have a degree of polymerization from 2 to approximately 1 000 and preferably from 3 to approximately 60.

The fructan is preferably used in an amount of between 0.01 and 20% by weight with respect to the total weight of the composition. More preferably, this amount is between 0.05 and 15% by weight with respect to the total weight of the composition and more preferably between 1 and 10% by weight.

The preferred fructans are inulins. Inulins refer to a group of naturally-occurring fructose-containing oligosaccharides. Because inulin fiber is resistant to digestion in the upper gastrointestinal tract (i.e., the stomach), it reaches the large intestine essentially intact, where it can be digested by indigenous bacteria. Inulins generally consist of chains of polyfructose in which the fructose units are connected to each other mostly or exclusively by .beta.-(2-1) linkages. Inulin occurs in nature, in general, as a polydisperse mixture of polyfructose chains, most of which terminate in one glucosyl unit. They are derived from the roots of chicory (Cichorium intybus), the dahlia and Jerusalem artichokes. Additonally, inulin can be obtained from bacterial syntheses or can be made in vitro by enzymatic synthesis starting from sucrose. It has been shown that inulin stimulates mucosal immunity and seems to improve efficacy of a Salmonella vaccine in mice (Benyacoub et al., 2008). Although the mechanism of action is unclear, several studies have proposed that inulin may induce changes in colonic epithelium by stimulating proliferation in the crypts, increasing the concentration of polyamines, changing the profile of mucins, and/or modulating endocrine as well as immune functions (Roberfroid, 2005). The average degree of polymerisation of inulins marketed as nutritional supplements is 10 to 12. Inulins stimulate the growth of Bifidobacterium species in the large intestine.

Fructooligosaccharides or FOS typically refer to short-chain oligosaccharides comprised of D-fructose and D-glucose, containing from three to five monosaccharide units. FOS, also called neosugar and short-chain FOS, are produced on a commercial scale from sucrose using a fungal fructosyltransferase enzyme. FOS are resistant to digestion in the upper gastrointestinal tract. They act to stimulate the growth of Bifidobacterium species in the large intestine.

Chitosan is a linear cationic polysaccharide which is gelled or crosslinked in the presence of anions, such as citrate, phosphate or sulfate. Chitosan has also been shown to possess useful properties such as non-toxicity, high biocompatibility and non-antigenicity. While chitosan is itself largely insoluble in water, solubility markedly increases if the pH is shifted towards the acid condition. To obtain an appreciable polymer concentration, it is therefore necessary to prepare the solution or dispersion with simultaneous use of an acid. To be able to more easily remove this acid from the composition later, it turned out that the acid should have a low boiling point, namely preferably maximally 140.degree. C., in particular maximally 120.degree. C., especially preferred maximally 100.degree. C., and most preferably maximally 80.degree. C., such as hydrogen chloride, hydrogen bromide, trifluoracetic acid, formic acid and acetic acid. Other suitable are also acids forming a lower-boiling binary azeotrope with water, such as acetic acid or propionic acid.

Chitosan can be obtained through the deacetylation of chitin, the major compound of exoskeletons in crustaceans. Chitosan [a-(1.about.4)-2-amino-2-deoxy-.beta.-D-glucan], a mucopolysaccharide closely related to cellulose, exhibits chemical properties that are determined by the molecular weight, degree of deacetylation, and viscosity. Chitosan can form microparticles and nanoparticles that can encapsulate large amounts of antigens (van der Lubben et al., 2001; Davis, 2006). In the acidic environment of the stomach, chitosan retains its positive charges that hold the particle together. It has been shown that ovalbumin loaded chitosan microparticles can be taken up by the Peyer's Patches of the gut associated lymphoid tissue of higher vertebrates. Additionally, after co-administering chitosan with antigens in nasal vaccination studies in a strong enhancement of both mucosal and systemic immune responses in mice was observed (van der Lubben et al., 2001).

Preparation of the Bioadhesive Delivery System specific to gut mucosa: An aqueous solution or suspension of a pharmaceutically active agent (e.g., an immunogenic agent, including, but not limited to vaccines) and, if desired, an adjuvant including, but not limited to beta glucan, lipopolysaccharide, aluminium salts, squalene and/or virosomes, is dissolved or suspended in an aqueous solution of a suitable mucoadhesive polymer such as, but not limited to, chitosan and a suitable oligosaccharide such as, but not limited to, inulin. The resulting solution/suspension is then dispersed directly or by atomization into an aqueous cross-linking solution containing water-soluble phosphate salts. Upon contact, a salt exchange reaction (cross-linking) takes place, resulting in the formation of beads or capsules in which the pharmaceutically active agent is retained. The resulting suspension of microparticles containing the encased pharmaceutically active agent is then collected, dried, and milled if necessary to form particles having a size range from 10-1000 micron. Details of the preparation are set out in the series of steps described below:

Step (a): Preparation of complex mucoadhesive hydrogel. A mucoadhesive polymer such as chitosan, at a concentration of 1 to 10% (w/w), is dispersed in 1-5 N acetic acid solution at a temperature range of 20 to 65.degree. C. until all polymer granules are fully dissolved. Preferably, the chitosan is at least 85% deacetylated. Additionally it is preferred that the pH is of the acidic aqueous solution is from about 2 to about 4. The gelatinization of the polymer granules is required in order to prepare a microparticle possessing the immunogenic property.

In embodiments of the invention, indigestible short chain oligosaccharide components are also be added at a concentration of from about 1 to 30% (w/w) to improve protection of the antigen from stomach acidity, bile acids and proteases and increase the intestinal adsorption of the antigen. Examples of applicable materials include, but not limited to, chitosan oligosaccharide (COS), inulin, fructooligosaccharides (FOS), and dextrin. These absorption-increasing components may dissolve more readily in intestinal juices than other matrix materials. Consequently, permeability and biodegradability of the matrix polymer can be increased, resulting in an improved release of the pharmaceutically active agent at the desired location in the GALT of the intestinal mucosa.

Step (b): Complex formation of the mucoadhesive material and a short chain oligosaccharide. Without wishing to be bound by theory, it is believed that the processes described herein yield a novel complex composition mediated by an emulsifier/sugar complex and comprising polysaccharides and oligosaccharides in the form of a complex matrix having an insoluble microparticle nature. The emulsifier and sugar molecules mediate the interaction between hydroxyl residues of the short chain oligosaccharide and hydrophobic amine residues of the cationic polysaccharide. Generally, the emulsifiers can be, but are not limited to, any of monoglycerides, sorbitan esters, propylene glycol esters, lecithin, polysorbates and sucrose esters of medium and long chain saturated fatty acids, and the sugars will be any mono- or disaccharides such as, but not limited to glucose, fructose, or sucrose. A solution comprising an emulsifier/sugar mediating mixture (containing 0.5 to 12.5% w/w emulsifier and 5-30% w/w sugar) is added to the gelatinized mucoadhesive polysaccharide and short chain oligosaccharide solution at a temperature range of from 20 to 65.degree. C. and pH 3-5 until a smooth and stable emulsion has formed. This emulsion is stabilized by the interaction between positive charge of the cationic polysaccharide, the emulsifier and hydroxyl groups of the short chain oilgosaccharides. The increased hydrophobicity and elasticity of the mucoadhesive polysaccharide and emulsifier helps delay or prevent penetration of water or gastric juices into the matrix once formed into microparticles. The acidity of the product slurry is then gradually increased to pH 6.2 by the addition of base such as, but not limited to sodium hydroxide.

Step (c): Addition of immunogenic substance and cross-linking reaction. A solution comprising a pharmaceutically active agent. such as, but not limited to, an immunogen or immunogenic antigen is dissolved into the slurry described in Step (b) above, and the composition can be dried to produce a powder by a number of art-recognized methods including, but not limited to, low temperature spray drying, belt drying, freeze drying, drum drying or flash drying. In a preferred embodiment, the dispersion is passed through a tube or needle ranging from 10 um to 1,000 um in diameter to fall dropwise or in a continuous stream into a cross-linked solution containing 1-10% sodium triphosphate in water. Alternatively, the slurry can be spray-atomized into an aqueous solution containing 1-10% sodium triphosphate. Wet particles can be harvested from the cross-linking bath by any suitable means well known in the art (e.g., filtration, centrifugation, etc) and mixed with any acceptable thickening agent such as methylcellulose, pectin, alginate, xanthan gum, carboxymethyl cellulose, hydroxypropyl cellulose, and the like, and sprayed onto feed pellets (i.e., top-coated). Alternatively, the wet particles can be dried using conventional processes well known in the art such as, but not limited to, vacuum drying, spray drying, and tunnel drying, milled to the appropriate size class if necessary, and then mixed with fish oil or other edible oils prior to application to a standard commercially available feed by top-coating using methods known in the art.

Feeding strategy for oral vaccination: Juvenile fish having a mature immune system (for Atlantic Salmon generally at about 0.5 g) are ready to be orally vaccinated. However the instant invention provides a flexible strategy that also allows the vaccination of, or boosting the immunogenic response of larger fish and other animals. To effectively induce the immunogenic response, the fish or other animals should be orally fed in a single event at a similar or greater dose of immunogen that is usually provided by injection. To maximize the fish immunogencity and depending the on Immunogen type, fish size and responsiveness, this single feeding event may be repeated (e.g., every three days for up to ten feeding events).
 

Claim 1 of 11 Claims

1. A composition for oral administration to an animal for intestinal delivery of a pharmaceutically active agent, said composition comprising: a) at least one bioadhesive polymer selected from the group consisting of chitosan, hyaluronic acid, cationic guar, and combinations thereof; wherein the bioadhesive polymer is present at a concentration of between 1% and 10%; b) at least one oligosaccharide selected from the group consisting of inulin, fructooligosaccharide and dextrin, wherein the oligosaccharide is present at a concentration of between 1% and 50%; c) at least one mediating compound having both hydrophilic and lipophilic properties, wherein the mediating compound comprises an emulsifier/sugar complex containing 0.5 to 12.5% w/w emulsifier and 5-30% w/w sugar, and d) a pharmaceutically active agent.
 

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