The Impacts of Cigarette Smoking on Rat’s Trachea: A Histologic Study A

The present study was conducted to examine the effects of cigarette smoking on trachea. The experimental study was carried out on 16 male albino rats which were randomly assigned into two groups (N=8), control group and smoking group. A digital smoking machine was developed to carry smoking experiment, so that 1 cigarette/rat/ day for 30 consecutive days was followed. A further period of one-month non-exposure (cessation) to smoking was followed as a recovery stage from the effects of cigarette and waterpipe smoking. Following each period, histological studies were performed. Results showed that control sections had shown healthy ciliated pseudostratified columnar epithelium, and all other layers normally seen in tracheal tissue. The tracheal mucosa of smoking group was adversely affected; showing an increase in the number of epithelial cells, amalgamation of cilia, presence of inclusion bodies, and heavy lymphocytic infiltration among the epithelial layer was observed. Recovery of cigarette smoking induced some improvements through reducing the level of inflammation and restoring the changes in columnar cells, cilia, and goblet cells with a slight separation in the respiratory epithelium. Taken together, cigarette smoking is associated with adverse health effects on trachea. It was found that in most of changes detected, quitting smoking was essential to revert most changes.


Introduction
There are many chemicals which are characterized by being harmful for the human health included in cigarette smoke [1].
Cigarette smoke has been categorized as a human carcinogen that makes a health threat for smokers and passive smokers [2]. It has been reported by several studies that the smoke of cigarette as an aerosol which includes two phases containing gases and particles. In general terms, cigarette smoke can be considered as a complicated mixture of oxidants and toxic substances. These studies have identified 4,800 substances to be included in tobacco smoke among which are 69 recognized carcinogens as well as a great number of toxic substances [3]. Smoking is thought to mainly affect lungs and participate in inducing several diseases such as respiratory diseases (lung cancer, chronic obstructive pulmonary diseases), cancer of the breast, brain, stomach, leukemia, lymphomas, coronary heart and peripheral vascular diseases, inflammation of the arteries, progressive narrowing of the vascular lumen, risk of developing myocardial infarction, etc., [3].
The Trachea is a tube that transports air from the upper respiratory tract to the lower respiratory tract [4]. The cervical trachea and the thoracic trachea are the two parts of the trachea.

ARTICLE INFO ABSTRACT
The present study was conducted to examine the effects of cigarette smoking on trachea. The experimental study was carried out on 16 male albino rats which were randomly assigned into two groups (N=8), control group and smoking group. A digital smoking machine was developed to carry smoking experiment, so that 1 cigarette/rat/ day for 30 consecutive days was followed. A further period of one-month non-exposure (cessation) to smoking was followed as a recovery stage from the effects of cigarette and waterpipe smoking. Following each period, histological studies were performed. Results showed that control sections had shown healthy ciliated pseudostratified columnar epithelium, and all other layers normally seen in tracheal tissue. The tracheal mucosa of smoking group was adversely affected; showing an increase in the number of epithelial cells, amalgamation of cilia, presence of inclusion bodies, and heavy lymphocytic infiltration among the epithelial layer was observed. Recovery of cigarette smoking induced some improvements through reducing the level of inflammation and restoring the changes in columnar cells, cilia, and goblet cells with a slight separation in the respiratory epithelium. Taken together, cigarette smoking is associated with adverse health effects on trachea. It was found that in most of changes detected, quitting smoking was essential to revert most changes.
The trachea is made up of 15-20 hyaline cartilage rings [5]. A layer of pseudostratified columnar epithelium ciliated with goblet cells lines the trachea. Mucins are produced by goblet cells, which are unicellular glands that moisturize and protect the airways. Mucus coats the ciliated cells of the trachea, allowing the cilia to detect inhaled foreign particles and propel them to the larynx and finally the pharynx, where they are either ingested or ejected as phlegm.
Mucociliary clearing is the name given to this mechanism. The ciliated cell has roughly 300 cilia, each with numerous mitochondria beneath them to supply energy. Brush cells, which have multiple microvilli connected to their apical surface, are another type of columnar cell [6].

Objectives
The main objective of the present study is to explore the pathologic changes associated with cigarette smoking on rat's trachea.

Methodology
Rats were randomly assigned into two groups (n= 8 per group), group 1 was negative control exposed only to fresh air, group 2 exposed to smoking (red LM cigarettes) as 1 cigarette/rat/day for 30 consecutive days. A further period of one-month non-exposure (cessation) to smoking was followed as a recovery stage from the effects of cigarette and waterpipe smoking. Following each period, histological studies were performed. The groups which were exposed to cigarette smoke were divided as follow: Group (2): was exposed to red LM cigarette for one month followed by a recovery period for one month.

The Digital Smoking Machine
A digital smoking apparatus was designed that have a special smoking topography, suitable for the exposure of rats to cigarette smoke [7]. The smoking machine is composed of the following components as illustrated in (Figure 1

c)
Finally, rats were allowed to breath normal fresh air for 30 seconds.

Cigarette Smoke-Exposed and After Cessation Period Groups
The tracheal mucosa of this group was adversely affected; showing an increase in the number of epithelial cells, amalgamation

Discussion
The exposure to smoking has been associated with adverse mucosal effects in the trachea. These changes included proliferation of epithelial cells, amalgamation of cilia, presence of inclusion bodies, and lymphocytic infiltration within the epithelial layers.
structural Changes in columnar cells were also observed as well as in goblet cells. Following smoking cessation most of changes were reversible. These findings are consistent with other studies. In his study, Liao, et al. [8] showed that passive exposure to cigarette smoking in rats induced inflammatory conditions in trachea. The study of Shraideh, et al. [7] reported similar findings in which the exposure of albino rats for 3 months to cigarette smoke induced drastic histological changes in the tracheal epithelium such as epithelial cells proliferation, disruption of cilia, and presence of inclusion bodies.

Conclusion
Cigarette smoking is associated with adverse health effects.
Smoking effects were histologically studied on trachea. It was found that in most of changes detected, quitting smoking was essential to revert most changes.