**2. Experimental models in COPD**

Experimental models represent an important tool, since they enable the broadening of knowledge about COPD physiopathology, besides allowing the application of new therapeutic approaches.

The methodology of papain intratracheal instillation, proposed by Gross and coworkers in 1965, represented an original model for pulmonary emphysema induction. Starting from the proposition of this pioneer methodology, a series of studies were conducted, which led to the development of the models of induced pulmonary emphysema by the instillation of other proteases. (Pushpakom *et al*., 1970; Fusco *et al.*, 2002).

The use of proteolytic enzymes, chiefly of porcine pancreatic elastase (PPE) for the generation of DPOC in an animal model is a widely employed methodology for the conduction of experimental studies, since it is mainly a simple and fast method and produces physiopathological effects similar to the human disease (March, 2000; Shapiro, 2000). The experimental models of pulmonary emphysema induced by proteases instillation have not reproduced precisely the mechanisms of alveolar destruction ensuing the inhaling of smoke and other toxic particles, and, therefore, they do not mimic exactly the sequence of pathological events that occur in the disease in humans (Cendron, 1007).

The use of animal models of cigarette-smoke-induced emphysema means seeking an accuracy in experimental models to match the human, chiefly with respect to the

pulmonary emphysema (Ribeiro-Paes et al., 2009). The cigarette smoke in their gas and particle stages has a significant quantity of oxidant substances. A high number of particles and oxidant agents are contained in cigarette smoke. Oxidant agents are capable of reducing the effect of the anti-protease system through the oxidation of the active site of those enzymes and leading to a direct injury to the extracellular matrix (Barnes 2000; Barnes et al.,

The Global Initiative for Chronic Obstructive Lung Disease (GOLD, 2009) has pointed out COPD as a serious public health issue. The pathology is considered the fifth largest cause of death worldwide, and has 210 million patients, with 80 million already in the moderate and/or serious stage of the disease. Estimates put it at the third ranking of cause of death in 2020 (GOLD, 2009; WHO, 2008). Moreover, faced with the ageing of world population, the economic burden of COPD should represent a significant parcel of the future global

Several clinical strategies, associated with the pulmonary rehabilitation techniques have contributed to the extension and improvement of the quality of life of emphysema patients. Notwithstanding the significant advances resulting from the introduction of new therapeutic approaches and rehabilitation, there has not been any efficient form of treatment up to now, other than the one in the palliative scope. The surgery treatment entails highly complex procedures and, in the specific case of lung transplant, a shortage of donors. By taking these aspects into account, experimental models have been proposed, in order to advance the knowledge about the physiopathological processes and new therapeutic approaches to the pulmonary emphysema (Gross et al., 1965; Hele, 2002; Mahadeva &

Experimental models represent an important tool, since they enable the broadening of knowledge about COPD physiopathology, besides allowing the application of new

The methodology of papain intratracheal instillation, proposed by Gross and coworkers in 1965, represented an original model for pulmonary emphysema induction. Starting from the proposition of this pioneer methodology, a series of studies were conducted, which led to the development of the models of induced pulmonary emphysema by the instillation of

The use of proteolytic enzymes, chiefly of porcine pancreatic elastase (PPE) for the generation of DPOC in an animal model is a widely employed methodology for the conduction of experimental studies, since it is mainly a simple and fast method and produces physiopathological effects similar to the human disease (March, 2000; Shapiro, 2000). The experimental models of pulmonary emphysema induced by proteases instillation have not reproduced precisely the mechanisms of alveolar destruction ensuing the inhaling of smoke and other toxic particles, and, therefore, they do not mimic exactly the sequence of

The use of animal models of cigarette-smoke-induced emphysema means seeking an accuracy in experimental models to match the human, chiefly with respect to the

Shapiro, 2002; Martorana et al., 1989; Nikula et al., 2000; Ribeiro-Paes et al., 2009).

2003; Bast et al., 1991; Rufino & Lapa e Silva, 2006).

investments in health (Mannino & Buist, 2007).

**2. Experimental models in COPD** 

other proteases. (Pushpakom *et al*., 1970; Fusco *et al.*, 2002).

pathological events that occur in the disease in humans (Cendron, 1007).

therapeutic approaches.

physiopathological mechanisms involved in the formation of the emphysema. Up to the beginning of the 80's decade, the studies involving induced pulmonary emphysema in animals by exposure to cigarette smoke were scarce and their reliability questioned (March, 2000). In 1981, Huber and coworkers proposed a study based on the model of induced emphysema through exposure to cigarette smoke. Some achieved results in the study, with respect to morphometric and physiological aspects provided the basis for the ensuing research. According to the report from the First Siena International Conference on Animal Models of COPD held at the University of Siena in 2001, the induced lesions with the use of this model are similar to those observed in emphysematous humans, highlighting the importance of the stimulus through cigarette smoke in COPD experimental models. (Hele, 2001).

At our laboratory, a new apparatus (Figure 1) for induced emphysema through exposure to cigarette smoke is under test. The present device has a series of innovations when compared to the already existing inhaling models, such as the fact that the animals are contained inside acrylic containers making up the device, while in other cages the animals stay freed. Another important aspect worth highlighting relates to the smoke, which is pumped inside the box. In the device created by our team, the smoke pumped into the box interior comes from puffing on the cigarette; therefore, the situation of an active smoking human is mimicked. This apparatus is expected to lead to a model which mimics, as close as possible, the human pathology and, accordingly, which can be applied to research projects oriented to the analysis of physiopathological processes and to the development of new therapies in chronic degenerative pulmonary diseases.

Fig. 1. Apparatus created by the team of the Laboratory of Genetics and Cell Therapy – GenTe Cel to induce emphysema by cigarette smoke.

Notwithstanding the challenges involved in some parameters related to the cigarette-smokeinduced emphysema models, mainly with respect to the age of the animals, exposure time and reproducibility difficulty due to the required resources and time, this is a promising approach to turning animal models closer to the human, chiefly in relation to the physiopathological processes featured in the human pulmonary emphysema (March, 2000).

Cell Therapy in Chronic Obstructive Pulmonary Disease: State of the Art and Perspectives 459

disease. The use of these models affords the broadening of knowledge, especially related to the physiopathology. The achieved results in animal models may be the grounds for the development of new therapeutic alternatives with the ensuing impact on the survival and

The employment of cells for treating diseases is an ancient therapeutic practice, which dates back to the transfusion of whole blood or platelet concentrate in different acute or chronic clinical conditions. The first hematopoietic stem cells (HSC) transplantations were made according to the works of Till and Mculloch in 1961, on the response of mice with the bone marrow transplanted after lesion by ionizing radiation. Since then, new ranges and possibilities of use of other tissues according to the experimental model adopted by the

The potential of differentiation of stem cells (SC), i.e., the wide range of options of commitments available for the cell (Smith, 2006), has aroused a growing and great interest, bearing in view the employment in the therapy of several types of degenerative diseases and in tissue bioengineering (Atala, 2008). According to The National Institutes of Health (NIH), SC can be defined as cells able to divide for indefinite time *in vitro* and to give origin to specialized cells. Melton and Cowan (2004) proposed a working definition of SC: "a clonal self-renewable entity which is multipotent and can generate several types of differentiated cells." Notwithstanding the concept variation, SC have two basic characteristic aspects: selfrenewal, in order to maintain the pool of undifferentiated cells for tissue replacement, remodeling, and repair, as well as the differentiation into at least one mature cell type. These inherent properties for SC are afforded through particular asymmetric divisions, where undifferentiated cells are originated, or, alternatively, differentiation into specialized cells

Fig. 2. Assimetric SC division. An undifferentiated SC under microenvironment stimulation start assimetric divisions producing two distinct daughter cells. One cell, undifferentiated, maintain the SC pool. In contrast, the differentiated cell acquires a new mature and

**3. Stem cells and cell therapy: The rationale for use in the lung** 

improvement of the quality of life of COPD patients.

authors have arisen.

(Figure 2).

specialized phenotype.

Currently, the creation and use of genetic models is a very important tool for DPOC study, since the strains mimic a series of aspects related to the human disease, mainly with respect to the α1-antitrypsin deficiency (March, et al., 2000). At present, several mice strains are known to have natural or laboratory-induced mutations (gene targeting), which generate abnormal conditions in the animal development and are completed with the spontaneous arise of DPOC (March, 2000; Shapiro, 2000). Other methodological approaches to emphysema induction entail animal models with genetic modifications. Martorana *et al*. (1995), showed the installation and development of pulmonary emphysema in Tight skin transgenic mice, which show mutation in the fibrillin-1 gene, a protein related to the elastic fibers assembly making up the pulmonary tissue (Kietly, 1998).

The Table 1 shows some advantagens and disadvantages of the main animal models of induction of COPD.


Table 1. Comparison of the main experimental models of COPD.

Taking into account these aspects, is evident the great importance of experimental models of COPD, even though none of them entirely mimic all the features making up the human

Currently, the creation and use of genetic models is a very important tool for DPOC study, since the strains mimic a series of aspects related to the human disease, mainly with respect to the α1-antitrypsin deficiency (March, et al., 2000). At present, several mice strains are known to have natural or laboratory-induced mutations (gene targeting), which generate abnormal conditions in the animal development and are completed with the spontaneous arise of DPOC (March, 2000; Shapiro, 2000). Other methodological approaches to emphysema induction entail animal models with genetic modifications. Martorana *et al*. (1995), showed the installation and development of pulmonary emphysema in Tight skin transgenic mice, which show mutation in the fibrillin-1 gene, a protein related to the elastic

The Table 1 shows some advantagens and disadvantages of the main animal models of

**Advantages Disadvantages References** 







March *et al*. (2000)

Shapiro (2000)

Fujita and Nakanishi (2007)

> Zheng *et al.* (2009)

fibers assembly making up the pulmonary tissue (Kietly, 1998).







Taking into account these aspects, is evident the great importance of experimental models of COPD, even though none of them entirely mimic all the features making up the human

Table 1. Comparison of the main experimental models of COPD.

induction of COPD.

**Experimental model of COPD** 

Protease-induced Emphysema

Genetic models

Smoke cigarette

disease. The use of these models affords the broadening of knowledge, especially related to the physiopathology. The achieved results in animal models may be the grounds for the development of new therapeutic alternatives with the ensuing impact on the survival and improvement of the quality of life of COPD patients.
