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In recent years, there has been an exponential increase in the quest for development of non-invasive drug delivery systems. This is due to the various disadvantages generally associated with the conventional drug delivery systems. The main reasons being patient incompliance (associated with the injectables) and acid and/or enzymatic degradation in the gastro-intestinal region (associated with the oral delivery systems). Various bioactive agents (e.g. XXX) have to be repeatedly injected due to their short residence time in patients. This procedure requires constant medical supervision of the patients. The above disadvantages have forced the scientists to look for alternative routes for the administration of these bioactive agents . Various organs with mucosal linings (viz. nasal, buccal, rectal and vaginal) have shown great promises for improving the bioavailability of a large number of drugs when the drugs are administered locally. The improvement in the bioavailability of the administered drug may be attributed to the improved residence time of the drug delivery system at the site of absorption [XX]. Of these routes of administration, nasal drug delivery is gaining importance due to the large surface area, ease of accessibility and easy administration of the drug without any help of a medical professional . These factors have helped in improving the patient compliance thereby leading to the better therapeutic efficacy of the treatment. Nasal delivery of the drugs has been used in various indications which include pain, diabetes insipidus, prostate cancer and endometriosis . Nasal mucosal surface provide a highly permeable mucosa as compared to gastrointestinal, buccal and vaginal mucosa. It is also highly vascularized. The combined effect of the permeability and vascularization results in the rapid absorption of the drug in the systemic circulation and at the same time help in bypassing the first pass metabolism, which in turn results in the improved bioavailability of the drug [1, 44]. The improvement in the bioavailability of other bioactive agents like peptides and proteins has also been reported ..Various mucoadhesive polymers have been tried successfully to devise microspheres, liposomes, proliposomes, niosomes and patches for nasal drug delivery . Nasal-associated lymphoid tissues have been reported to assist in the uptake of microparticles, when administered intra-nasally [XX]. Amongst several mucoadhesive polymers, chitosan based nasal drug delivery has gained much attention in the recent past.
In the past decade, chitosan has received a great attention in pharmaceutical sector for the development of controlled delivery systems. This has been greatly influenced by the favorable biological properties exhibited by chitosan. It is a non-toxic (LD50= 16 g/Kg in rats) biodegradable natural polymer which has the ability to facilitate the paracellular transport of the macromolecules, viz. peptides and proteins, across the nasal mucosal layer . With the recent developments in the field of materials science, specially polymer science/ chemistry, it has been able to develop chitosan products which show different solubility profiles at different pHs. This has allowed developing drug-chitosan complexes with various physic-chemical properties. In the current review, an attempt will be made to study the recent advancements on the applications of the chitosan microparticles in nasasl drug delivery.
Nasal Anatomy & Physiology
Before go into details of the chitosan- based nasal delivery systems, it would be wise to discuss about the anatomy and physiology of the nasal cavity so as to have a bigger understanding in the mechanism of action of the delivery vehicles. The nasal cavity is primarily engaged in respiration and olfaction. It is also engaged in cleaning, heating and humidification of the inhaled air, to resonate the sounds produced and mucociliary clearance [XX]. The nasal vestibule is covered with hairs, which helps entrapping the particulate maters (e.g. dust and microorganisms) and thereby helping in filtering out of these particulate maters. In addition to this, the mucosal layer aids in the metabolizing the endogeneous materials, which can be easily eliminated from the body. In the present section, the anatomy and physiology of the nasal cavity will be discussed in brief.
The total nasal cavity volume in human is 15-20 ml. The nasal cavity is longitudinally divided into two halves by the nasal septum. These cavities are further divided into nasal vestibule, olfactory region and respiratory region . The areas within the nostrils are categorized as vestibule and have got an area of 0.6 cm2. On the roof of the nasal cavities lie olfactory region and is spread out in an area of 15-16 cm2 (approx.). The respiratory region has got an area of 136 cm2 (approx.) . The respiratory region can be further divided into three nasal turbinates, viz. superior, middle and inferior. These turbunates help in inducing turbulent flow of the inhaled air, which ensures more contact amongst the inhaled air and the mucosal surface. The anterior nasal cavity is having a lining of squamous epithelium. As we move towards the posterior end, the type of the cells change to pseudo stratified columnar epithelium, constituting respiratory epithelium. Respiratory epithelium (thickness of 100 Î¼m approx.) is main site for the absorption of the drugs . This may be attributed to the highly vascularized structure of the respiratory epithelium. Also, most of the cells in this region are non-ciliated which has been associated with the high metabolic activity and transport of the fluid. The lower turbinate area has 20 % (approx.) of ciliated cells, which helps in the transportation of the mucus toward nasopharynx. Both the ciliated and non-ciliated cells contain 300 (approx.) microvilli per cell in this region .
Physiology of nasal cavity:
The nasal epithelium is covered with a thin layer of a mucosal layer. This layer help in exchanging nutrients, water, gases, odorants, hormones and gametes but do not allow the permeation of most particulate matters including microbes . It also helps in removal of particulates by the process of mucocilliary clearance and humidification of the inspired air
(b) Humidification of inspired air to aid in heat transfer by holding water. Goblet cells, which cover 10% of the mucosa in the turbinate area, contain numerous secretory granules. The flow rate of human nasal mucus is in the order of 5 mm /min, renewing the mucus layer every 15-20 min.
Physiological Factors Limiting Nasal Absorption:
The absorption rate from the nasal cavity for most of the compounds is very rapid; therefore physiological factors such as rate of nasal secretion, ciliary movement and metabolism play a very important role
The nasal secretion aa well as the ciliary movement varies from person to person and they depend on the individual health condition. The bioavailability is smaller when the rate of nasal secretion is greatest and the ciliary movement is faster. Formulation approaches such as the utilization of non-irritating water miscible gels and the addition of small amounts of anesthetic to the formulation can minimize the effect of above physiological factors.
Nasal mucociliary clearance:
The mucociliary clearance system is an efficient defence system of human which protects the respiratory system against inhaled bacteria, irritants and particles. Such agents are transported (sticking to the viscous mucus) backwards in the nose and down to the throat. This transport of mucus is closely correlated to the beat of the cilia present on the respiratory epithelial cells.
It severely limits the time allowed for drug absorption to occur and effectively rules out sustained nasal drug administration. This occurs in the case of drugs that are not easily absorbed across the nasal membrane. Under normal condition both inhaion,liquid and powder formulations, are cleared in 15-20 min . However, bioadhesive polymers can be used to increase the nasal residence time, thus allowing longer absorption times to achieve a more intimate contact with the nasal mucosa, which results in a higher concentration gradient subsequently increasing absorption .
Low permeability of the nasal mucosa for the drugs:
Low membrane permeability is the most important factor limiting the nasal absorption of polar drugs and especially large molecular weight polar drugs such as peptides and proteins. Drugs cross the epithelial cell membrane by transcellular route exploiting simple concentration gradients, receptor mediated and vesicular transport mechanisms or by the paracellular route through the tight junctions between the cells. The monolayers Caco-2 cells were used to study this mechanism of drug transport through the nasal mucosa .
It seems to be necessary to consider an absorption enhancement mechanism for co-administration of drugs with either mucoadhesive polymers or penetration enhancers or combination of the two for an effective nasal delivery .In vitro cell models using monolayers from nasal epithelium have been studied in order to understand the transport and metabolism of proteins across the mucosal surface .
Metabolism of drugs in the nasal cavity
Enzymes exist in the nasal tissues but do not appear to have a significant effect on the extent of absorption of most compounds except peptides. For example, the bioavailibility is 100% for drugs like progesterone, testosterone, estradiol, naloxone, butorphanol when administered intranasally to that of their intravenous administration. The oral bioavailability of the above mentioned drugs ranges from 20-30% for propranolol and 0% for the other drugs. The extensive metabolism of the compounds in the gastrointestinal tract accounts for this low oral bioavailability. Thus one can attribute the above observations to one of the following reasons .
1. The absorption rate is very fast, making the exposure time of the drug to the enzyme very short;
2. The enzymes level in the nasal tissue (mg/g) is very low and can be easily saturated with the drug.
4. Blood supply and neuronal regulation
The presence of venous sinusoids and arteriovenous anastomosis gives the nasal mucosa the distinction of being a highly permeable site. Nasal cycles of congestion (increased blood supply resulting from parasympathetic stimulation and relaxation (decreased supply resulting from sympathetic stimulation regulate the rise and fall in the amounts of drug permeated, respectively.
Physicochemical Factors Affecting the Nasal Absorption:
The compounds that have been used for nasal delivery range from highly lipophilic compounds such as steroids to extremely hydrophilic drugs such as clofilium, sodium cromoglycate as well as peptides and proteins.
The rate and extent of nasal drug absorption may depend on a number of physicochemical factors, like the molecular weight.
Absorption via nasal route drops off sharply for drugs with a molecular weight over 1000 Da. There is a linear correlation between the log (% drug absorbed) and the log (molecular weight) for water soluble compounds. The intranasal bioavailability of high molecular weight peptides and even small proteins can be improved with the use of permeation enhancers. Hydrophilic drugs administered nasally generally are of low molecular-weight (<1000 Da) , and their transport across the mucosal membrane is relatively efficient compared to larger lipophilic drugs. Molecular weight is a very important determinant of the rate and degree of transport and finally the rate of absorption for polar drugs transported via the paracellular route. Nasal epithelial cells are inter-connected on the apical side by a series of narrow belt-like structures called the junctional complexes, including tight junctions (TJs), which form a dynamic, regulatable, semi-permeable diffusion barrier between the epithelial cells .
The pH of a formulation has been shown to affect the solubility, partition behavior and/or stability of many drugs, especially peptides and proteins .
For nasal mucosal membranes, a range of studies evaluating the effect of pH on nasal absorption of small molecular weight drugs has been performed in the rat model. The authors found out that the pH of the formulation as well as the membrane surface pH can affect a drug's absorption. Apart from these, nasal absorption of weak electrolytes such as salicylic acid and aminopyrine in rats was highly dependent on the degree of ionization. Studies reported that largest absorption of the drugs occurred when they were in their non-ionized state, in which drugs have a higher apparent partition coefficient, i.e., are more lipophilic .
Similarly, the effect of pH on the nasal absorption of benzoic acid (pKa = 4.19) was studied. The results showed that as the pH of the solution was increased from 2 to 7.19, the amount absorbed decreased from 44% (pH 2.5) to 13%.This was probably due to ionization of the drug. In another study conducted by the same group, reported that the absorption of L-tyrosine was pH independent in the range of 4 to 7.4 .
pKa and the partition coefficient of drug:
According to the pH partition theory, unionized species are absorbed better compared with ionized species and the same holds true in the case of nasal absorption. A study was conducted by to find out the quantitative relationship between the physicochemical properties of drugs and their nasal absorption, using drugs like diltiazem hydrochloride and paracetamol as model. Results showed that a quantitative relationship existed between the partition coefficient and the nasal absorption.
Studies indicate that drug concentrations in the cerebrospinal fluid (CSF) rise with an
increase in lipophilicity or the partition coefficient of the drugs. The nasal absorption of weak electrolytes such as salicylic acid and aminopyrine was found to be highly
dependent on their degree of ionization. Authors suggested that aminopyrine could be absorbed through the nasal mucosa passively .The absorption increased linearly with an increase in partition transport of its un-ionized portion. For salicylic acid, absorption rates decrease with pH and a substantial deviation of the experimental data from the theoretical profile was observed. nasal transport of decanoic, octanoic, and hexanoic acids is greatest at pH 4.5, which is near the pKa values at which the compounds are âˆ¼50% ionized. A likely explanation is that these acids may have poor water solubility below this pH value.
Chemical and physical stability:
Many drugs are susceptible to some form of chemical or physical instability such as degradation by hydrolysis or oxidation, isomerizsation, photochemical decomposition, or polymerization. These processes can lead to the loss of drug potency or change in the physical appearance of the formulation such as discoloration (e.g., due to the degradation product possessing a different color). In general, peptides and protein drugs have greater fragility compared to low-molecular-weight pharmaceuticals.
Hydroxyl groups of catechol moiety in Apomorphine, a drug candidate for IN delivery is susceptible to oxidation to the quinone in aqueous solution, causing a color change and thus possessing a delivery challenge. Addition of appropriate antioxidant systems is an approach to mitigate degradation in the aqueous IN formulation .Another approach is to deliver the drug in the powder form because reaction rates are typically lower in the solid compared with the aqueous state .
Effect of osmolarity:
The effect of osmolarity on the nasal epithelium was studied by perfusing Sodium chloride solutions with osmolarity ranging from 0 to 600 mOsm/kg H20 through the rat nasal passage. The perfusion volume changed during perfusion due to the varying osmolarities of the solutions, because of water uptake by (or release from) the rat
nasal cavity depending on the osmolarity of the solution. 
The amount of LDH release from the rat nasal mucosa at the end of 105 min perfusion has been studied as a function of osmolarity of solution. The figure below shows that when the formulation osmolarity is getting reduced from 600 to null point, the release profile of lactate dehydrogenase reaches its maximum of value.
It is common that drugs are administered to the nasal mucosa as a molecularly dispersed form, e.g., in solution. The volume of solution for IN administration is relatively low, and therefore drugs with low aqueous solubility and/or requiring high doses may possess a big problem. When a drug is administered as a powder formulation to the nasal cavity, a dissolution process will precede the absorption process. The uptake was size dependent (e.g., the smaller the size the higher the uptake), as well as highly dependent on the surface characteristics of the particles . The mechanism of transport was suggested to be an uptake into the nasal-associated lymphoid tissue, in particular into the cells similar to the M-cells in the gut. Due to the anatomy and size of the nasal cavity, only a relatively low volume of a liquid formulation can be administered, i.e., about 100-150 µL in each nostril. Although some exceptions exist (e.g., FluMist® nasal spray for influenza is âˆ¼1mL volume), these cases may represent a substantial amount of the drug dose being swallowed. Therefore, it is sometimes necessary to increase the solubility of the drug in order to allow for delivery of a therapeutically relevant dose. There are several approaches that may increase the solubility of poorly soluble compounds for nasal administration, some of which are:
(i) The use of pro-drugs;
(ii) Addition of co-solvents,
(iii) Use of cyclodextrins as solubilizing excipients, and
(iv) Choice of salt form.
Approaches based on non dissolving particulate systems for nasal delivery, such as nanoparticles, have been reported recently in the literature. It is believed that nanoparticles (and perhaps even microparticles) can be transported across the nasal cavity into the bloodstream without prior dissolution. Authors have described a system in the form of chitosan solutioncontaining insulin. The study was done in order to evaluate the effect of chitosan concentration on the absorption across the rabbit nasal mucosa .
Use of cyclodextrins as solubilizing excipients:
Many lipophilic drugs are poorly soluble in water and large hydrophilic drugs like peptides and proteins show an insufficient nasal absorption. Cyclodextrins, especially methylated Î²-cyclodextrins, have proven to be excellent solubilizers and absorption enhancers in nasal drug delivery of insulin .
Salts of chitosan are soluble in water; the solubility of which depends on the factors like degree of deacetylation and the pH of solution. Those with low degree of deacetylation (< 40%) are soluble up to a pH of 9, whereas highly deacetylated chitosans (>85%) are soluble only up to a pH of 6.5. the solubility of chitosans is interfered by addition of salts to the solution. The solubility is inversely dependant on the ionic strength, as charge neutralization occurs by increasing the concentration of counterions. Increasing the degree of deacetylation increases the viscosity .
Pharmaceutical approaches for intra nasal administration:
When administered through IN route corticosteroids and antihistamines have minimal potential for systemic adverse effects (as opposed to oral therapy), primarily due to the fact that relatively low doses are effective comparing when administered topically. For instance, the recommended therapeutic dosage of IN antihistamines does not cause significant sedation or impairment of psychomotor function, whereas these effects may be seen upon oral dosing (for which a much larger dose is required). Such factors make IN delivery of antihistamines and corticosteroids an attractive and typically preferred route of administration, particularly if rapid symptom relief is required.
IN route is the route of choice for drug delivery in local (or topical) treatment for examples decongestants for nasal cold symptoms, and antihistamines and corticosteroids for allergic rhinitis. Examples of nasal products with widespread use in this area and a include the histamine H1-antagonist levocabastine , the anti-cholinergic agent ipratropium bromide , and steroidal anti-inflammatory agents such as budesonide, mometasone furoate , triamcinolone , and beclomethasone.Many of the drugs are currently in the market and some are under investigations in patients or volunteers for example desmopressin, vasopressin, oxytocin, buserelin, nafarelin,calcitonin, insulin, glucagon, human growth hormone, butorphanol, dihydroergotamine, midazolam, nicotine, steroid hormones .
Studies have reported that nasal delivery of PCL nanospheres are efficient systems to vaccinate animals against infections as humoral, cellular and mucosal immune responses, were induced noticeably that are important for the defence after bacterial pathogens such as S. equi invades the host via the mucosal surface.
AUC for Nasal route has been shown to be more compared to that of oral for metoprolol in rats .
Microspheres as Nasal Drug Delivery:
Technology of microparticles has been applied now a day in designing formulations for nasal drug delivery. The primary rationale is to provide a better chance for drug absorption by allowing a more intimate and prolonged contact between the drug and the mucosal membrane .
"Microparticles" are particles with a diameter of 1-1000mm, irrespective of their interior or exterior structure. Within the broad category of microparticles, "microspheres" refers to spherical microparticles and the class of "microcapsules" applies to microparticles which have a core surrounded by a material distinctly different from that of the core. The core may be solid, liquid, or even gas. A formulation described as a microparticle is usually comprised of a fairly homogeneous mixture of polymer and active agent, whereas microcapsules have at least one discrete domain of active agent and sometimes more.
Starch microspheres of insulin increased the absorption of insulin through the nasal mucosa of rats. Absorption enhancers have also shown great results. Surfactants and bile salts were the first to be used as an absorption enhancer . Microspheres of insulin prepared using hyaluronic acid produced a large and significant increase in the nasal drug absorption in sheep. Starch microspheres of desmopressin along with and without absorption promoter LPC 1-alpha lysophosphatidylcholine were studied .Results showed increased absorption of the microsphere delivery system in the sheep model. DEAE-dextran absorbed water and formed a gel-like layer, which was cleared slowly from the nasal cavity and thus can be applied for controlled drug delivery system.
Microspheres of different materials like albumin, starch and DEAE-dextran have been evaluated in vivo as nasal drug delivery systems. These polymers have increased the absorption of drugs like gentamicin, growth hormone, metoclopramide, desmopressin and insulin Monolayers of Caco-2 cells has yielded a good deal of relevant information for the mechanism of drug absorption by microspheres.
Studies on improved absolute biovailability of gentamicin in rats and sheep from 1% when in solution formulation,to 50% by incorporating the drug into microspheres have been reported.
Mechanism of common mucosal immune system (CMIS):
A mucosal response after intranasal (i.n.) administration of polymeric particles is induced in lymphoid tissues regardless of the target site, and the response is paralleled by the appearance of antibodies in secretions of glands distant from the site of immunization due to the role of the common mucosal immune system (CMIS), which highlights the immunoadjuvant properties of these carriers. Some studies have also that when chitosan microparticles and mutant diphtheria toxin was nasally administered it enhanced both systemic and local immune responses .
Factors influencing transport through mucus:
Particulate transport through the mucus is rather complex and is controlled by the
- Mucus layer
- Size and charge
- surface wettability of the particles.
Importance of Muco/Bioadhesion:
Mucoadhesive systems are designed to adhere to the mucosal surface of the biological tissues. Adhesion of the drug delivery system offers various advantages such as:
(i) Longer residence time of the dosage form on mucosal tissues thus increasing the drug's bioavailability.
(ii) Higher drug concentration at the site of adhesion-absorption will create a driving force for the paracellular passive uptake .
To explain the mechanism of polymer-mucus interactions which lead to mucoadhesion. Several theories have been put forward. The sequential events that occur during bioadhesion starts with an intimate contact between the bioadhesive polymer and
the biological tissue, due to proper wetting of the bioadhesive surface and swelling of the bioadhesive penetration of the bioadhesive into the tissue crevices, interpenetration between the mucoadhesive polymer chains and those of the mucus follows this step.
Subsequently low chemical bonds can become operative. The intimacy of contact between the mucoadhesive and the biological tissue improves as the surface of that tissue becomes rough. There are six major theories which account for the bioadhesion are the adsorption , electronic ,wetting, diffusion, mechanical and fracture theories. According to the adsorption theory of bioadhesion adhesion of a polymer to a biological tissue results majorly from:
Primary and secondary chemical bonds of the covalent and noncovalent (which involve van der Waals, hydrogen, hydrophobic and electrostatic forces) are formed between the mucoadhesive polymer and the mucus at initial contact.
The primary chemical bonds are somewhat permanent and therefore undesirable in bioadhesion and most of the initial interactions are attributed to the non-covalent forces. The secondary bonds are highly dependent on the properties of polymer .
The electronic theory proposes the existence of an electrical charge double layer at the
interface between the adhesive and biological tissue due to the difference in their electric charge.
Chitosans as mucoadhesive drug delivery:
Chitosan is a polymer obtained from the deacetylation of, a naturally-occurring structural polymer chitin abundant in exoskeleton of crabs, shrimp shells (crustaceans) and also some fungi. Chitin is the second most abundant polysaccharides in nature, cellulose being the most abundant. Chitosan is a cationic polysaccharide with linear chain containing Î²-(1, 4)-linked 2-acetamido-2-deoxy-Î²-D-glucopyranose (GlcNAc) and 2-amino-2-deoxy-Î²-D-glucopyranose (GlcN). Through inter and intramolecular hydrogen bonding chitosan forms a rigid crystalline structure. Because chitosan has favorable biological properties such as biodegradability, biocompatibility and low toxicity it has attracted a lot of attention in pharmaceutical and medical fields .
Molecular weight and the degree of deacetylation of chitosan influences both the physicochemical and biological parameters. Chitosan refers to a large number of polymers, which differ in their degree of N- deacetylation (40-98%) and molecular weight (50,000-2,000,000 Da). Chitosan is a weak base. pKa value of its D-glucosamine residue is about 6.2-7.0 and, therefore, is insoluble at neutral and alkaline pH values, however it forms salts with inorganic and organic acids such as acetic acid, glutamic acid, hydrochloric acid, and lactic acid. In acidic medium, the amine groups of the polymer are protonated that results in a soluble, positively charged polysaccharide having a high charge density (one charge for each D-glucosamine unit). Interaction with different types of divalent and polyvalent anions leads to the formation of gels .
Authors using the in vitro model, reported that the structural properties of chitosans such as the degree of acetylation and molecular weight, are very important for the absorption enhancement of hydrophilic drugs . Results showed that to increase the epithelial permeability of chitosan a low degree of acetylation i.e. high percent deacetylation with greater charge density or a high molecular weight are necessary. This charge distribution gives rise to strong elelctrostatic interaction with the negatively charged mucosal surface which provides longer contact time for drug transport across the nasal membrane Toxicity of chitosan also depends on its high charge density but appears to be less affected by the molecular weight.
In vivo absorption studies in animals have been carried out to evaluate the nasal absorption promoting the activity of chitosan using insulin as a model peptide. In both in vitro and in vivo models chitosan has shown to enhance the nasal absorption of hydrophilic drugs such as peptides, hormones. In recent years,chitosan derivatives are used to improve its solubility at different pH values and to improve the permeability of anionic drugs thus avoiding precipitation of drug - polymer complexes.
The corticosteroid beclometasone dipropionate (BDP) is a common anti-inflammatory drug used in the treatment of asthma and chronic obstructive pulmonary disease .By incorporating BDP into a spray-dried formulation containing a hydrophobic polymer (chitosan) and an aerosolisation enhancer (leucine),highly modified spray dried powders have been produced. Spray drying is a one-step constructive process that provides
greater control over particle size, particle morphology and powder density. Spray-dried powders were also produced from 30% (v/v) aqueous ethanol formulations that contained hydrophilic (terbutaline sulphate) and hydrophobic (beclometasone dipropionate) as model drugs, chitosan and leucine as aerosolisation enhancer. In both the cases chitosan was used as a release modifier .
Chitosan in peptide delivery:
Microspheres of chitosan are being used to provide the controlled release of many drugs and to improve the bioavailability of highly degradable substances such as protein, as well as to enhance the uptake of hydrophilic substances across the epithelial layers. Chitosan microparticles or nanoparticles loaded with macromolecules also enhance the absorption of these molecules at mucosal sites.
The mechanism of action of chitosan behind the improval of transport of polar drugs across the epithelial membrane is believed to be a combination of bioadhesion and transient opening of the tight junctions in the cell membrane to enable the passage of polar drugs.
chitosan as a nasal delivery system for insulin in rats and sheep was investigated by llium etal in 1994. The optimum concentration of chitosan for maximal absorption of insulin in rats and sheep was found to be 0.2% and 0.5% respectively. The AUC for chitosan and insulin solution in sheep was found to be 7 times greater than the AUC for insulin alone. This increase in absorption of insulin was attributed to the mucoadhesive properties of the chitosan .
A powder dosage form containing chitosan and HPMC to deliver oxymetazoline nasally was developed. This pharmaceutical composition has improved adhesion characteristics and provided a high bioavailability of the active ingredient.
Chitosan in vaccination:
Vaccination is the most effective medical intervention introduced in human history. Human papillomavirus vaccine (consisting of a major viral capsid protein) was the first FDA approved for cervical cancer prevention. The field of vaccine development is expanding towards the treatment of diseases without a pathogen but with a strong immunological component (e.g. Alzheimer and Parkinsons disease) .
Due to high permeability, low enzymatic activity and the presence of an important number of immunocompetent cells, the nasal delivery has gained special attraction. The use of polymeric materials especially chitosan solutions have already shown potential for the delivery of variety of antigens in different animal models, promoting satisfactory immune responses.
Studies have reported that Low-molecular-weight chitosan nanoparticles prepared by an ionic cross linking method containing tetanus toxoid could induce long-lasting immune responses after the nasal administration in mice .
Chitosan significantly enhances the immune response of nasally administered vaccines e.g., influenza , pertussis and diphtheria vaccines via induction of serum IgG responses similar to secretory IgA levels and superior to that induced by parenteral administration of the vaccine.
Soluble chitosan based formulation admixed with trivalent influenza vaccine has been tested recently in a human trial, the results showed increased serum haemagglutination inhibiting antibodies production were detected as compared to the nasal administration of the conventional aqueous influenza vaccine (which is normally administered intramuscularly) .
DNA vaccination also called as genetic immunization have shown to be a good strategy becuse both humoral and the cell mediated response are induced .The principle is the usage the host cell as protein factories for plasmid encoded antigen .
Efficient delivery and expression was obtained following Plasmid DNA encoding respiratory syncytial virus (RSV) antigens after intranasal administration in chitosan complexes, resulting in efficient production of specific antibodies (serum IgG, and nasal IgA), interpheron-gamma and also in the induction of cytotoxic T-cells .
Intranasal vaccine delivery against hepatitis B have also been applied using chitosan complexes with DNA.
Nasal Route for Centrally Acting Drugs:
Microparticulate system of carbamazepine (CBZ)based on chitosan glutamate were developed.The high CBZ microspheres based on chitosan glutamate, adhered on the mucosal surface and at the same time improve the dissolution of the drug in the aqueous environment of the mucosa so increased the absorption .
Atropine sulphate showed a better bioavailability by the nasal route due to use of chitosan in comparison with the intramuscular route .
Nasal Route for Local Effects:
Nasal drug formulations for local application are widely used as over-the-counter products for frequently occurring diseases like common cold and hayfever.
Nasal Route for Systemic Effects:
Chitosan/Î²-cyclodextrin theophylline microspheres had high yields (> 45%) and encapsulation efficiencies (about 90%). The microspheres were stable at stored conditions 4 °C, 25 °C,40 °C and 60 °C (RH 75%) for three months.and reduced the ciliotoxicity which was evaluated with in situ toad palate model . Mucoadhesive microspheres-based antiasthmatic drug delivery system for bronchial asthma can prolong the drug release thus reducing the frequency of dosing and providing safety for a whole day. One such approach was developd by formulating chitosan mucoadhesive microspheres of salbutamol. By controlling the particle size distribution, an aerosolized system was developed that adhered to the brochial mucosa releasing the salbutamol locally and constantly for 24 hr .
Nasal Route for Brain Targeting:
Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by a slow, progressive decline in cognitive function and behavior. An approach was developed for treating this disease by targeting the chitosan magnetic microparticles of tacrine in to brain using male wistar rat. The results indicated that magnetic chitosan microparticles transported the drug tacrine to the brain in comparison with the free drug. The developed formulations reduced the total dose required for the therapy with concurrent reduction in dose related toxicity .
The adenosine derivative N6-cyclopentyladenosine (CPA) formulated as CPA-Chitosan microparticles by spray-drying could be administered to the male wistar rat by nasal route using the single dose Monopowder P® and thus promising an effective antiischemic agent for targeting the brain.
The olfactory neuroepithelium is the only area of the body in which an extension of the central nervous system (CNS) comes in direct contact with the environment. The
olfactory receptor cells are bipolar neurons with swellings that are covered by hair like cilia which project into the nasal cavity. The axons from these cells collect into aggregates, enter the cranial cavity through the cribrifom plate, and form synapses with mitral cells in the olfactory bulb of the brain .Studies have reported this as a major route for the delivery of 17Î² - estradiol mucoadhsinve chitosan nanoparticles for Alzheimer's disease .
Chitosan in antibiotics delivery:
Mucoadhesive microspheres of hyaluronic acid and chitosan for nasal delivery of gentamicin sulfate were prepared and this had an added advantage in combining the mucoadhesive potential of HA with the permeation promoting effect of chitosan . Nasal delivery of other antibiotics such as vancomycin and tobramycin with chitosan has also been reported. Results have shown showed that the presence of chitosan salts at pH 5.5 and pH 7.4 slows down the release of vancomycin hydrochloride, thus guaranteeing a sustained release at acidic and alkaline pH of drug in the nasal cavity.
Mechanism of Mucoadhesion:
Mucin glycoproteins are the basic components of mucus which form an unstirred gel layer over the epithelial cells of the mucosa. For optimum mucoadhesion, there has to be an intimate contact between the adhesive and the substrate and interpenetration of
the polymer chains with the mucin glycoprotein network.
It has been reported that chitosan has mucoadhesive properties due to the ionic interaction between the positively charged amino groups in chitosan and the negatively charged sialic acid residues in mucus .
Preparation of Chitosan Microspheres:
Chitosan microspheres are prepared by reacting chitosan with controlled amounts of multivalent anion that results in cross-linking of chitosan molecules. Depending on the method employed the crosslinking is achieved in acidic, basic or the neutral pH. Chitosan microspheres can be prepared by various methods are cross-linking with anions, precipitation, complex-coacervation, modified emulsification and ionotropic gelation, precipitation-chemical cross-linking, glutaraldehyde cross-linking, thermal cross-linking, and more. The cross-linking of polymers affects the strength for mucoadhesionof the microspheres .
The bioadhesive microspheres are also produced by the dissolution of a drug so as to incorporate it into the carrier, followed by lyophilisation or spray-drying. Though Spray drying has been used for the production of gentamicin microspheres with sufficient yield and encapsulation efficiency.Although spray drying is less expensive than lyophilisation, but both these methods still have associated disadvantages with respect to drug stability, solvent residues and the size range of the resulting particles. Another method would be to create interactive mixtures with a mucoadhesive carrier, if the mixtures are obtained in the appropriate size range .These mixtures are binary mixtures that are highly homogenous in which fine drug particles are adhered to coarse carrier particles to form interactive units .Some of the methods used by crosslinking are as follows.
Preparation of Microspheres by Thermal Cross-linking
Citric acid, is used as a cross-linking agent was added to an aqueous acetic acid solution of chitosan maintaining a constant molar ratio between chitosan and citric acid. The chitosan cross-linker solution was cooled to 0°C and then added to a fixed volume of sesame oil previously maintained at 0°C, with stirring for 10 minutes. This emulsion was then added to corn oil maintained at 120°C, and cross-linking was performed in a glass beaker under vigorous stirring (1000 rpm) for 40 minutes. The microspheres obtained were filtered and then washed with diethyl ether, dried, and sieved .
Preparation of Microspheres by Emulsification and Ionotropic Gelation by NaOH
The dispersed phase consisting of aqueous acetic acid and specified chitosan was added to the continuous phase consisting of hexane and Span 85 to form a w/o emulsion. After 20 minutes of mechanical stirring, sodium hydroxide solution was added at the rate of 5 mL per min at 15-minute intervals. Stirring speed of 2000 to 2200 rpm was continued for 2.5 hours. The microspheres were separated by filtration and subsequently washed with petroleum ether, followed by distilled water and then air dried.
Preparation of Microspheres by Tripolyphosphate:
The microspheres were formed by dropping the bubble-free aqueous solution of chitosan in 2%acetic acid through a 6 gauge needle driven by syringe pump onto a gently agitated (magnetic stirrer) 5% or 10% wt/vol aqueous TPP solution ,under a high electrostatic field.The chitosan microspheres were collected by centrifugation and rinsed with distilled water; then they were freeze dried .
Preparation by spray dry method:
In mice a high titres of anti-BSA antibodies were induced when BSA was
encapsulated in chitosan microspheres formulated using the spray-drying method.Inhalable protein loaded microparticles have also been prepared by this method using polymers like alginate, ovalbumin, Hydroxypropyl cellulose(HPC) .
7 times higher AUC
N-trimethyl chitosan chloride (TMC), a partially quaternized chitosan derivative, has a good water solubility over a wide pH range. This soluble TMC has mucoadhesive properties and excellent absorption enhancing effects even at neutral pH. Moreover, Studies have shown that it promotes the Caco-2 cell permeation by enhancing FD-4 .Thus TMC is an attractive alternative over chitosan for the design of protein loaded particles by ionic cross-linking .
Chitosan derivatives such as 5-Methylpyrrolidinone chitosan (MPC) in which the aminogroups of glucosamine units of the polysaccharide backbone are partially substituted at position 5 by methylpyrrolidinone (MP) by covalent bonding. It belongs to the class of the gel-forming reabsorbable biopolymeric substituted chitosans possessing significant biological properties like the promotion of oteoconduction in human dental surgery . This chitosan derivative combines the biocompatibility of chitosan and the hydrophilic characteristics of the pyrrolidinone moiety, particularly susceptible to the hydrolytic action of lysozyme .
Chitosan glutamate is able to enhance the in vitro transport of small hydrophilic compounds, e.g., 14C-mannitol.
A primary systemic immune response and considerably enhanced secondary immune responses were illlicted by both chitosan chloride and chitosan base microspheres .
Chitosan is an abundant natural polymer, obtained by alkaline N-deacetylation of chitin. The physical and chemical properties of chitosan, such as inter and intramolecular hydrogen bonding and the cationic charge in acidic medium, makes this polymer attractive for the development of conventional and novel pharmaceutical products.Its biodegradability and physicochemical compatibility makes it a remarkable polymer for IN delivery for any given drug, various facets of the drug's characteristics and intended use need to be considered. IN delivery of chitosan microspheres may be suitable for either topical or systemic delivery Another application for IN dosing using chitosan microspheres is for vaccine therapeutics. The chitosan microspheres can be applicable for high molecular-weight drugs such as peptides and proteins for example insulin delivery through nasal route is gaining attention , however, systemic bioavailability is dramatically dependent upon the presence of permeation enhancers.One major aspect of delivering mucoadhesive microspheres of chitosan is its degree of deacetylation which accounts for its solubility and thus its biocompatibility.