3.1 The basic properties of CS

CS is a nontoxic natural polymer that is the only basic polysaccharide found in nature. It has good physical and chemical properties. CS has many advantages, such as widely available, nontoxic, biocompatible, biodegradable, and structure modifiable, and its derivatives also have some unique properties. CS has been widely used in environmental engineering, textile industry, papermaking, food industry, cosmetics, medicine, biotechnology, pharmacy, and also many other fields [29, 30]. In recent years, with the rapid development of the advanced DDS, CS and its derivatives have received extensive attention as drug carrier materials, especially for sustained and controlled drug release, and they have become popular research topics in this field [31, 32].

As a drug carrier, CS has the following advantages compared with other materials. (1) CS contains a large amount of amino groups, which easily become positively charged via combination with the H+ in solution. Thus, CS has a strong adsorption effect on carrying drugs with different characteristics [33, 34]. (2) The polysaccharide chain of the CS and the lipopolysaccharide (LPS) structure can be recognized by the macrophages, thereby activating and triggering local immune responses and enhancing the targeting effect to specific tissues or cells [35]. (3) CS and its derivatives have good antibacterial activity and can inhibit the growth and reproduction of some fungi, bacteria, and viruses [36]. (4) CS is a polycation, which can easily interact with the negatively charged groups on the cell membrane surface, thereby changing the fluidity and permeability of the cell membrane [37]. (5) CS is especially suitable for local administration because of its good adhesion property and histocompatibility, which can particularly meet the requirements for drug

Applications of Chitosan in Pulmonary Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.87932

The particles of sizes 0.5–1.0 μm are deposited on the respiratory bronchioles and alveolar walls. The particles of sizes <0.5 μm will be discharged out with airflow due to the Brownian motion, and typically 80% of them will be expelled out of the respiratory tract. Therefore, the particles with a size range of 1.0–5.0 μm have the highest deposition rate in the bronchioles and alveoli, and they are generally selected as the main components of the pulmonary inhalation preparations. Studies have shown that the pulmonary absorption of the drugs is a passive process, a small molecular weight contributes to fast drug absorption, and the absorption of the macromolecular drug is relatively slow [16]. The drugs with molecular weight below 1000 Da present short absorption half-life and good bioavailability. As the alveolar wall is very thin, macromolecular drugs can also be absorbed through the large gap between the cells or be swallowed into the lymphatic system by the macrophages in alveoli, before finally entering the blood circulation [27].

Role of Novel Drug Delivery Vehicles in Nanobiomedicine

In recent years, with the development of biomaterial science, biotechnology, and medical technology, the research of new PDDS for drug-loading has focused on polymer-based microspheres, liposomes, and NPs, which can be inhaled into the lung and deposited in the lung mucosa through atomization and in the form of dry powder or other forms [28]. Compared with the atomized injections currently used in clinic, the pulmonary administration preparations based on new PDDS have the advantages of convenience, sustained or controlled drug release, prolonged drug action time, enhanced bioavailability, and improved therapeutic efficiency. PDDS with better efficacy will be designed with the development of new materials and the advancement of pharmaceutical preparation technologies. Pulmonary administra-

tion will have broad prospects for disease treatment in the medical field.

CS is a nontoxic natural polymer that is the only basic polysaccharide found in nature. It has good physical and chemical properties. CS has many advantages, such as widely available, nontoxic, biocompatible, biodegradable, and structure modifiable, and its derivatives also have some unique properties. CS has been widely used in environmental engineering, textile industry, papermaking, food industry, cosmetics, medicine, biotechnology, pharmacy, and also many other fields [29, 30]. In recent years, with the rapid development of the advanced DDS, CS and its derivatives have received extensive attention as drug carrier materials, especially for sustained and controlled drug release, and they have become popular research

As a drug carrier, CS has the following advantages compared with other materials. (1) CS contains a large amount of amino groups, which easily become positively charged via combination with the H+ in solution. Thus, CS has a strong adsorption effect on carrying drugs with different characteristics [33, 34]. (2) The polysaccharide chain of the CS and the lipopolysaccharide (LPS) structure can be recognized by the macrophages, thereby activating and triggering local immune responses and enhancing the targeting effect to specific tissues or cells [35]. (3) CS and its derivatives have good antibacterial activity and can inhibit the growth and reproduction of some fungi, bacteria, and viruses [36]. (4) CS is a polycation, which can easily interact with the negatively charged groups on the cell membrane surface, thereby changing the fluidity and permeability of the cell membrane [37]. (5) CS is especially suitable for local administration because of its good adhesion property and histocompatibility, which can particularly meet the requirements for drug

3. The applications of CS in PDDS

3.1 The basic properties of CS

topics in this field [31, 32].

166

retention after mucosal administration [38]. Therefore, CS has a wide range of applications in drug delivery. It can increase the stability of the drug, prolong the drug action time, change the administration route, increase the targeting ability of the drug, control the drug release, improve the dissolution of drugs with poor solubility, and adjust the cell membrane permeability of the hydrophobic drugs. At the same time, the positively charged CS can be easily adsorbed on the mucosal surface and also hard to be removed by the cilium, thereby providing conditions for the drug to penetrate the cell membrane. Moreover, CS can open the tight junctions between the cells, which will promote drug transportation in the epithelial tissues and increase the drug absorption rate and bioavailability. Thus, CS is especially applicable for PDDS [39, 40]. CS also has inherent immunogenicity, which is absent in other polymers, and this enables its use as an adjuvant for vaccine delivery into the lung [5]. Therefore, research on the applications of the CS-based PDDS has attracted great attention all over the world.

#### 3.2 Novel PDDS based on CS and its derivatives

Traditional pulmonary administration preparations have drawbacks such as relatively short drug onset time, high frequency of administration, and poor patient compliance. In order to overcome these problems, research has been focused on the development of new PDDS with sustained or controlled drug release properties, also with active targeting abilities, for increasing the drug retention time in the lung, improving the drug concentration in treated areas, reducing the damage to normal tissues or cells, and enhancing the bioavailability of the drugs. The new formulations for PDDS in recent studies mainly include microspheres, polymeric NPs, liposomes, and active targeted systems [41]. In the following content, we will introduce the above-mentioned formulations one by one.

#### 3.2.1 CS-based microspheres

Microspheres are microparticulate disperse systems formed by drugs dispersed or adsorbed in the polymer matrix. Microspheres have some unique advantages as a DDS for pulmonary administration [42]. They can be deposited in the lung, delay the drug release, and protect biomacromolecules, such as proteins and peptides from hydrolysis by enzymes. By optimization of the preparation process, a microsphere with an aerodynamic diameter of 1–5 μm and with suitable shape and porosity can be obtained, for meeting the requirements of pulmonary administration. In addition, microspheres usually have good stability with high moisture resistance ability. These characteristics have determined the wide applications of microspheres in pulmonary administration formulations [43].

There are many kinds of carrier materials for preparing microspheres. At present, the use of biodegradable microsphere as controlled release carrier is popular in DDS research [44]. Poly(lactic-co-glycolic acid) copolymer (PLGA) and CS are the commonly used biodegradable materials for microsphere preparation [45]. The conventional methods for preparing CS microspheres include emulsion crosslinking, solvent evaporation, ion induction, and spray drying [46–49]. Among these, crosslinking is the most commonly used method in the preparation of drugloaded CS microspheres with controlled-release property. The reaction can be carried out under mild conditions, and it also can be industrially prepared easily [50]. Moreover, as CS is positively charged, it can combine with the negatively charged drugs by electrostatic binding interaction to form a complex, which can help to improve the drug loading capacity of the microspheres.

Weifen Zhang's group had developed a series of CS-based microspheres for pulmonary administration. They reported the preparation of CS and β-cyclodextrin microspheres as PDDS [51–55]. The microspheres were prepared by the spray drying method, and theophylline was loaded into the microspheres as a model drug. These microspheres possessed spherical shape with smooth or wrinkled surfaces, and had suitable aerodynamic diameters, which were suitable for inhalation. The microspheres had high drug entrapment and encapsulation efficiency. They can remain stable under storage conditions. The microspheres could also easily penetrate the membrane with a high permeation rate. The results showed that these microspheres had good potential as a sustained drug release carrier for pulmonary administration.

In Weifen Zhang's another work, paclitaxel (PTX) and quercetin (QUE) were respectively loaded in the NPs, which were synthesized with the oleic acidconjugated CS (OA-CTS). And these drug-loaded NPs were further used in the preparation of polymeric microspheres (PMs) by the spray-drying method (Figure 1) [56]. The microspheres could help prolong the retention time of PTX in the presence of QUE, for bypassing the P-glycoprotein drug efflux pumps. The diameters of the PMs ranged from 1 to 5 μm, and they had a uniform size distribution. The PMs displayed slow-release characteristics at pH levels of 4.5 and 7.4. In vivo pharmacokinetic and biodistribution studies suggested that the PMs exhibited a prolonged circulation time and a markedly high accumulation in the lung. The PMs could serve as a promising PDDS for combined therapy using hydrophobic drugs.

Recently, Ludmylla Cunha et al. developed inhalable CS microparticles for simultaneous delivery of isoniazid and rifabutin in lung tuberculosis treatment [57]. Spray-dried CS microparticles were obtained with adequate flow properties for deep lung delivery (aerodynamic diameter of 4 μm) and high drug association efficiencies (93% for isoniazid and 99% for rifabutin). No cytotoxicity effect was found in human alveolar epithelial (A549) cells. The CS microparticles could activate macrophage-like cells, inducing cytokine secretion well above basal levels. Moreover, the uptake level of macrophages to internalize microparticles was over 90%. The microparticles also inhibited bacterial growth by 96%, demonstrating that the microencapsulation preserved drug antibacterial activity in vitro. The dual drug-loaded CS microparticles demonstrated to be potential candidates for inhalable therapy of pulmonary tuberculosis.

#### 3.2.2 CS-based NPs

As a potential DDS, NPs have been widely used in medicine and other fields, and it has already become a research hotspot for decades [58–60]. NPs can improve the solubility and stability of the drugs, prolong the half-life, and enhance the drug absorption rate. NPs can also help to realize sustained or controlled drug release, prolong drug acting time, reduce administration frequency, and improve patient compliance. Moreover, NPs can target the drugs to specific organs and cells by the passive or active targeting ability of the multiple functionalized NPs. The NPs can be modified to avoid the phagocytosis of the macrophages or the removal of mucosal cilia, thereby improving the bioavailability of the drugs.

Drug delivery by NPs is an effective approach for the pulmonary administration of insoluble drugs [61, 62]. The surface of the NPs can be modified to prolong the drug residence time in the lung and to achieve appropriate release property for improving the therapeutic effect. The pulmonary administration route for NPs is mostly by inhalation in the form of aerosolized colloidal solution. However, when the NPs are administered directly into the lung, some of them may be discharged out with the breath due to their small particle size, thereby resulting in low

deposition in the lung and discounted effect. Studies have shown that coating the surface of the NPs with biocompatible polymers, such as CS, can prolong the residence time of NPs in the lung [5]. Sometimes the surface energy of the NPs is

(A) The synthesis and preparation route of the PMs. (B and C) SEM image of the PMs with a scale bar of 5 and 2 μm. (D and E) The concentration of PTX and QUE accumulated in different organs measured by HPLC at

Figure 1.

169

0.5, 1, 3, and 6 h after pulmonary administration.

Applications of Chitosan in Pulmonary Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.87932

Applications of Chitosan in Pulmonary Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.87932

Weifen Zhang's group had developed a series of CS-based microspheres for pulmonary administration. They reported the preparation of CS and β-cyclodextrin microspheres as PDDS [51–55]. The microspheres were prepared by the spray drying method, and theophylline was loaded into the microspheres as a model drug. These microspheres possessed spherical shape with smooth or wrinkled surfaces, and had suitable aerodynamic diameters, which were suitable for inhalation. The microspheres had high drug entrapment and encapsulation efficiency. They can remain stable under storage conditions. The microspheres could also easily penetrate the membrane with a high permeation rate. The results showed that these microspheres had good potential as a sustained drug release carrier for pulmonary

Role of Novel Drug Delivery Vehicles in Nanobiomedicine

In Weifen Zhang's another work, paclitaxel (PTX) and quercetin (QUE) were

As a potential DDS, NPs have been widely used in medicine and other fields, and it has already become a research hotspot for decades [58–60]. NPs can improve the solubility and stability of the drugs, prolong the half-life, and enhance the drug absorption rate. NPs can also help to realize sustained or controlled drug release, prolong drug acting time, reduce administration frequency, and improve patient compliance. Moreover, NPs can target the drugs to specific organs and cells by the passive or active targeting ability of the multiple functionalized NPs. The NPs can be modified to avoid the phagocytosis of the macrophages or the removal of

Drug delivery by NPs is an effective approach for the pulmonary administration of insoluble drugs [61, 62]. The surface of the NPs can be modified to prolong the drug residence time in the lung and to achieve appropriate release property for improving the therapeutic effect. The pulmonary administration route for NPs is mostly by inhalation in the form of aerosolized colloidal solution. However, when the NPs are administered directly into the lung, some of them may be discharged out with the breath due to their small particle size, thereby resulting in low

mucosal cilia, thereby improving the bioavailability of the drugs.

respectively loaded in the NPs, which were synthesized with the oleic acidconjugated CS (OA-CTS). And these drug-loaded NPs were further used in the preparation of polymeric microspheres (PMs) by the spray-drying method (Figure 1) [56]. The microspheres could help prolong the retention time of PTX in the presence of QUE, for bypassing the P-glycoprotein drug efflux pumps. The diameters of the PMs ranged from 1 to 5 μm, and they had a uniform size distribution. The PMs displayed slow-release characteristics at pH levels of 4.5 and 7.4. In vivo pharmacokinetic and biodistribution studies suggested that the PMs exhibited a prolonged circulation time and a markedly high accumulation in the lung. The PMs could serve as a promising PDDS for combined therapy using hydrophobic drugs. Recently, Ludmylla Cunha et al. developed inhalable CS microparticles for simultaneous delivery of isoniazid and rifabutin in lung tuberculosis treatment [57]. Spray-dried CS microparticles were obtained with adequate flow properties for deep lung delivery (aerodynamic diameter of 4 μm) and high drug association efficiencies (93% for isoniazid and 99% for rifabutin). No cytotoxicity effect was found in human alveolar epithelial (A549) cells. The CS microparticles could activate macrophage-like cells, inducing cytokine secretion well above basal levels. Moreover, the uptake level of macrophages to internalize microparticles was over 90%. The microparticles also inhibited bacterial growth by 96%, demonstrating that the microencapsulation preserved drug antibacterial activity in vitro. The dual drug-loaded CS microparticles demonstrated to be potential candidates for

inhalable therapy of pulmonary tuberculosis.

3.2.2 CS-based NPs

168

administration.

Figure 1.

(A) The synthesis and preparation route of the PMs. (B and C) SEM image of the PMs with a scale bar of 5 and 2 μm. (D and E) The concentration of PTX and QUE accumulated in different organs measured by HPLC at 0.5, 1, 3, and 6 h after pulmonary administration.

deposition in the lung and discounted effect. Studies have shown that coating the surface of the NPs with biocompatible polymers, such as CS, can prolong the residence time of NPs in the lung [5]. Sometimes the surface energy of the NPs is relatively high, and the weak stability will lead to aggregations and interactions between the NPs. Thus, special surface modification will also be an effective way to improve the stability of the NPs.

Abdallah Makhlof et al. synthesized a thiomer derivative of glycol CS (GCS), which was coupled with thioglycolic acid (TGA) [65]. The NPs were prepared with GCS and GCS-TGA by ionic gelation for the pulmonary delivery of peptides. The NPs were positively charged and had sizes in the range of 230–330 nm. They also showed high calcitonin entrapment. After intratracheal administration, the mucoadhesion capacity of the GCS-TGA NPs was much better than that of

nonthiolated NPs in rats. The toxic effect of the NPs with lung tissue was confirmed with negligible epithelial damage and toxicity. The NPs could enhance the pulmonary absorption of the delivered peptides, and the calcitonin-loaded GCS and GCS-TGA NPs showed efficient hypocalcemic effect. The GCS and its thiomer derivative

Tejal Rawal et al. designed a NP-based dry powder formulation of rifampicin (RFM) for achieving local and sustained targeting of anti-tubercular drugs to reduce dose and frequency [67]. The drug-loaded NPs were formulated by the ionic gelation probe sonication method. The optimized formulation had a small particle size of 124.1 nm with an entrapment efficiency of 72%. No toxicity was found by in vitro and in vivo experiments. The pharmacokinetic assay verified that the NP formulation would serve a better alternative because it could minimize the frequent dosing schedule than conventional dry powder inhalation and market formulation. The RFM-loaded NPs open new avenues for developing therapeutic interventions

Liposomes are primarily used as PDDS for the treatment of respiratory distress syndrome and other lung diseases [68]. The drugs carried by liposomes mainly have stable physicochemical properties and strong lipophilicity. Liposome-based drug carrier has been one of the research hotspots in pharmaceutics [69, 70]. At present, drug-loaded liposome preparations, such as for amphotericin B, daunorubicin, doxorubicin, cytarabine, and morphine, have been successively developed [71]. The liposome preparations of these drugs have many unique advantages compared with their common preparations. Liposome-based pulmonary administration has the advantages of rapid absorption, little irritation, good tolerance, high safety, controllable drug release, and improved bioavailability [72]. The encapsulation of the drug in liposomes affects the pharmacokinetic property of the drug and prolongs drug half-life. Moreover, 85% of the components of the alveolar surface are phospholipids, which can facilitate the liposomes accumulate and enter the lung tissue. Liposome-loaded macromolecules with low lipophilicity can significantly improve bioavailability, and liposomes can also reduce the side effects of the toxic drugs to

Marco Zaru et al. prepared CS-coated liposomes and used them as drug carriers for pulmonary delivery by nebulization [73]. Rifampicin (RFM) was loaded in the CS-coated liposomes with different lipid compositions. By coating with CS, the encapsulation efficiency of the liposomes increased slightly, and after nebulization,

the stability also remarkably increased. The mucoadhesive capacity of the

In another work, Adriana Trapani et al. had prepared CS and GCS NPs containing Lipoid S100 for the systemic delivery of low molecular weight heparin (LMWH) by pulmonary administration [66]. The NPs were prepared by ionotropic gelation method. The NPs were positively charged and with nanoscale size. Efficient drug entrapment and good mucoadhesive property could be achieved by using these NPs. The LMWH was effectively delivered into the lung by the aerosolization of the drug-loaded NPs. These results revealed the promising characteristics of the

could be used as potential PDDS for delivering peptides.

Applications of Chitosan in Pulmonary Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.87932

CS-based NPs, which were highly applicable for PDDS.

for lung tuberculosis.

171

3.2.3 CS-modified liposomes

normal tissues by pulmonary administration.

Kenneth A. Howard et al. had developed CS-based siRNA-loaded NPs for pulmonary RNA interference therapy [63]. The negatively charged siRNA was complexed by the positively charged CS to form the polyelectrolyte complex NPs. The particle size ranged from 40 to 600 nm. These NPs showed a rapid uptake (1 h) into NIH 3T3 cells. The NPs could mediate efficient knockdown of endogenous enhanced green fluorescent protein (EGFP) in both H1299 human lung carcinoma cells and murine peritoneal macrophages in vitro. Moreover, effective in vivo RNA interference was also realized in the bronchiole epithelial cells of transgenic EGFP mice after nasal administration. The results indicated that this kind of CS-based complex NPs has great potential in RNA interference therapy for systemic and mucosal disease.

A series of CS/fucoidan (CS/F) NPs had been designed and prepared as PDDS for gentamicin (GM) in Yi-Cheng Huang's study (Figure 2) [64]. The NPs presented a biphasic release feature, with a zero-order release of GM for the first 10 h, followed by a sustained release of up to 72 h, and the cumulative release value reached 99%. The GM-loaded CS/F NPs exhibited multiple antimicrobial capabilities against Klebsiella pneumoniae. The intratracheal administration of the GMloaded CS/F NPs displayed a higher area under the curve (AUC) and lower minimum inhibitory concentration ratio than the free GM that was administrated by intravenous injection. These results had showed that the CS/F NPs had superior antimicrobial efficacy and lower risk of systemic toxicity, and this GM pulmonary delivery system has exhibited good potential for pneumonia treatment.

#### Figure 2.

(A) The preparation of the GM-loaded CS/F NPs. (B) TEM of the GM-C5F1 NPs. (C–E) Long-term stability of the series of CS/F NPs.
