Air Pollution: A Major Culprit of Asthma

 

Bharti Ahirwar1*, Alpana Ram1, Dheeraj Ahirwar2

1SLT Institute of Pharmaceutical Sciences, Guru Ghasidas University, Bilaspur (CG) 495 009

2School of Pharmacy, Chouksey Engg. College, Bilaspur (CG) 495 007

 

ABSTRACT

The prevalence of allergic disease and asthma has increased dramatically over the past decades. Allergic disease arises as a result of aberrant immune responsiveness against innocuous environmental proteins (antigen). The most important determinant for the development of allergy and asthma is also genetic predisposition, environmental factors, such as exposure to allergens, infections, and air pollution plays an important role in the development of allergic and asthmatic inflammatory responses.

 

Keywords:  Asthma, allergy, environmental factors.

 

 

INTRODUCTION:

Asthma has become the most common chronic disease in the world and the epidemiological studies suggested that its prevalence, severity and mortality rate are on the rise due to the increased exposure to allergens and atmospheric pollutants 1.It is evident that the prevalence of allergic disease is increasing especially in industrialized countries2. Asthma remains one of the commonest breathing problems across the world. Despite advancement in the management of asthma there is worsening of morbidity and mortality in asthma and chronic obstructive pulmonary disease. Asthma patient give a history of intermittent wheezing, labored breathing, cough which was at night or early in the morning. Factors such as environmental pollutants and allergens, modern urban living, domestic pets, coloring and flavoring agents, chemical and physical stimuli are held responsible for the fast growth of the disease and also for the hyper responsiveness which also precipitate bronchoconstriction and late response in vast majority of asthmatic patients. It results from the narrowing of the airway smooth muscles within lungs due to constrictions and mucosal edema. Although asthma affect all ages but is usually thought the disease of young children’s. Asthmatic subjects also display a state of bronchial hyper responsiveness which is an exaggerated response of the airways to inhale environmental allergens and non specific stimuli such as strong odor, cold air and histamine and many suspected mediator of asthma include increased prostanoids, leukotrienes, and platelets, activating factors, acetylcholine and substrate P. The cellular participants include mast cells, autonomic and sensory nerves and infiltrating inflammatory elements include the airway walls 2-8.

 

World Status:

Around the globe between 100 to 150 million people suffer from asthma. The most worrying aspect of these statistics is that the numbers are on the increase worldwide and the deaths from this condition have reached over 180,000 annually. India has an estimated 15-20 million asthmatics. Genetic predisposition is one of the factors in children for the increased prevalence. Other factor like urbanization, air pollution and environmental tobacco smoke contribute more significantly. Hospital based study on 20,000 children under the age of 18 years from 1997, 1984, 1989, 1994, and 1999 in the city of Bangalore showed a prevalence of 9%, 10.5%, 18.5%, 24.5% and 29.5%respectively9-11.

 

Bronchial Asthma:

Bronchial asthma is one of the most common chronic illness9, 10.  Although asthma is non-contagious, it affects million of people in the whole world11.  It may appear in childhood and those who are so affected may suffer


throughout their lives or they may overcome this disease in their adolescence. The second cases are those people who show no symptoms of asthma in their childhood or youth, but suddenly develop asthmatic symptom later in life. Chronic asthma has been considered as an inflammatory disease.12

 

Two major classes of asthma are extrinsic asthma and intrinsic asthma

 

Atopic extrinsic asthmatics have generally in their blood and organs the antibody called regain. It is known as IgE, a type of gamma globulin. When antigen reacts with IgE i.e. allergic reaction and they cause allergic manifestations like spasm of the muscles of the airway of the lung in asthma, rhinitis and eczema13.

 

Intrinsic asthma generally occurs in adulthood in which case, allergic factors may not be demonstrated. A variety of stimuli like emotional state, exposure to cold air or inert dust may induce the episode of intrinsic asthma 14.

 

The effect of Atmospheric Pollution:

The root factor of allergic illnesses and asthma in particular, are of two kinds, genetic and environmental, with important interaction existing between the two. Identification and modification of genes responsible for the immune-pathology of asthma could not constitute a coherent explanation for the increase in asthma prevalence observed in last twenty years. Environmental factors appear, therefore are in the forefront as possible culprits.

 

On the physio- pathological level, asthma is characterized by an inflammation of the bronchial mucous membrane. This inflammation is continuous, more or less significant, according to the degree of illness. Many studies have characterized this bronchial inflammation and studied the factor that could induce and/ aggravate it. Among this factor, air borne allergens and different toxins appear to be the major factors. Many atmospheric pollutants could interact with air borne allergens, magnifying the response vis-a- vis by an aero-allergens. This interaction could be linked to the fact that a pollutants could be a co-factor of the allergic reactions (immunotoxicity); or to the fact that it can induce a bronchial inflammation that would add to the inflammation which is itself produced by inhalation of the allergens (pro-inflammatory effects).

 

From the 13th century, periodic efforts were made to forbid the burning of coal but on the whole, pupils have accepted a polluted atmosphere as a part of urban life. Power plant, steel mills, oil refineries, automobiles is virtually ubiquitous. All of these manifestations of modernize pollute the air, water and soil around them 19.

 

Health effects of air pollution:

Episode of high air pollution cause mortality and morbidity. Air pollutants enter the body predominantly through the lungs.  Out of the sources of air pollutants five pollutants account for nearly 98% of air pollutions. These are carbon monoxide, sulphur oxide, volatile organic compounds, particulate matter, and nitrogen oxide. A distinction often is made between two kinds of pollution the first is characterized by sulphur dioxide and smoke from incomplete combustion of coal and by conditions of fog and cool temperature. The second kind of pollution is characterized by hydrocarbons, oxide of nitrogen and photochemical oxidants 20. Sulfur dioxide gas is generated primarily by burning of fossil fuel that contains sulfur. SO2 is an upper airway irritant that can stimulate mucus secretion and bronchoconstriction. Long term expose to ozone may cause thickening of the terminal respiratory bronchioles. Nitrogen Dioxide like ozone is a deep lung irritant that is capable of causing pulmonary edema. Reactive oxygen species such as super oxide radicals, hydrogen peroxide and hydroxyl radicals are highly toxic to the cells. Severe oxidative stress can produce major disturbance on the cell metabolism that include DNA and RNA damage, raises in intracellular free ions and lipid per oxidation.

 

The lungs always expose to higher level of oxygen than most other tissues that leads to DNA damage by a free radical related mechanism. Most important active metabolites in human lungs include superoxide radical, hydrogen peroxide and hydoxy radicals, which are generated by multiple enzymatic reactions 21. The lung is an active metabolic organ22 and the normal human lung is efficiently protected and buffered against exogenous free radicals23. Toxic free radicals have been implicated as an important pathologic factor in pulmonary disorders. Oxidative stress arises when the balance between pro-oxidants and anti oxidants is shifted towards the pro –oxidants24. In normal individuals the level of lipid per oxidation in the lung is very low because of the powerful anti oxidant system, but under certain conditions the antioxidants the reverse can be depleted.

 

Many studies have shown that respiratory epithelial cells participate in an active way in the inflammatory reaction following penetration of air – borne allergen into lungs. Indeed, epithelial cells are capable of secreting many mediators and in particular, pro-inflammatory cytokines. Recent studies have shown that diesel particles could be phagocytosed by the bronchial and alveolar epithelial cells25. These diesel particles also induce a secretion of cytokines and GM-CSF particularly, by epithelial cells25.GS-CSF is the principal cytokines that is responsible for the recruitment and activation of langerhans cells in the epithelia of air passages. Interspersed between the epithelial cells, where they constitute a veritable network, langerhans cells of the air passages and dendritic cells associated with mucous membrane, are in an ideal position to exercise a supervisory function vis-avis air contaminants which penetrate the airways.

 

Langerhans cells represent the principal antigen-presenting cells of the air passages. It is therefore, very probable that they intervene in the physiopathology of immunoallergic illnesses.       Thus diesel emissions favor sensitivity to allergens in different ways; on the one hand by modifying pollen grains and facilitating pulmonary penetrating of allergens adsorb on diesel particles and on the other hand by acting on the immune system.

 

Pro inflammatory effect:

Many atmospheric pollutants are capable of inducing an inflammation at different levels of the airways. The farmer is at the route of a bronchial hyper reactivity that is to say an increased contraction of smooth bronchial muscles in response to various stimuli. These pollutants are responsible for bronchial irritation depending on different individual mechanisms which are often accompanied by a cytotoxic effect on the epithelial cells of the airways.

Epidemiological studies:

Two principal types of studies permit the analysis of short term or average effects of pollution:

Ecological studies, where the short of health is estimated from aggregate data of hospitalizations, cells to emergency departments, absenteeism, etc. these ecological studies , which are generally retrospective, allow for taking into account a certain number of confusing factor, such as influenza epidemics, meteorological factors, and long –term temporal variations.

 

Prospective study panels, where the state of health is evaluated from individuals data for example, focusing on healthy patients or asthmatic patients had the difficulties of having quite a long period of observation at one’s disposal, gathering and maintain a sufficient number of subjects throughout the study, taking into consideration numerous environmental factors linked to respiratory ailments and, finally, utilizing the appropriate techniques of analysis. 

 

The long term effects of a continued exposure to atmospheric polluted area, even if pollution levels are lower than standard levels, could increase bronchial hyperreactivity, independently of asthma, atrophy and level of pulmonary functioning26.

 

CONCLUSION:

The root factors of allergic illnesses, and asthma, in particular, are of two types, genetic and environmental, with important interaction existing between the two. Environmental factors therefore appear to be the most plausible explanation. Among these factors, air pollution and changes in life style on one hand, and the disappearance of resistance on the other, are in the forefront of possible culprits.

 

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Received on 12.06.2009

Accepted on 11.07.2009   

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Research J.  Science and Tech.  1(1): July-Aug. 2009: 01-03