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		Thursday, February 09, 2012

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Air Pollution & Oxidative Stress

As we evolve from a developing to a developed nation, we have an occasion to celebrate. Definitely, there is change in the air! But each gift has a price tag. Raised standard of l iving and l i fes tyle changes associated with this transition are taking a toll on our health. This 'development' is showing a significantly adverse impact on our overall health status.

We are enjoying modern age luxuries- at the cost of basic necessities- most importantly the air we breathe to survive. Air is the fundamental need of life and the most important natural resource. Today, we have put it in the front line- for abuse- environmental pollution is overpowering! Increasing concern exists over the adverse effects of air pollution on human health. The rapid rise in pollution related disorders over the past few decades in developing and developed countries have been attributed to various factors- lead by altered lifestyle and abnormal environmental changes. There are more vehicles on the road now than ever before and the industrial growth is unmatched. But is this really a comfort? Industrialization and motorization associated with this modernization are spouting deathly pollution.

Culprits of Air Pollution

Gases and particles that reduce the quality of the air cause it to become polluted. Nitrogen dioxide, Ozone, Sulfur dioxide, Benzene, Carbon monoxide, Environmental tobacco smoke etc. are responsible for air pollution and can cause various health hazards. Each pollutant inflicts damage on the human body in a unique way.

Nitrogen dioxide generated by traffic, cooking with gas appliances and cigarette smoke can damage the lungs.

Though ozone in the atmosphere is protective, ground-level ozone is the major part of air pollution in most cities. Ozone is a highly reactive gas and a major constituent of photochemical smog. Breathing only slightly increased concentrations of ozone can result in a range of respiratory symptoms in the healthy population.

Environmental tobacco smoke is likely to be the most important indoor pollutant that is harmful for human health. Tobacco smoke contains more than 4,000 chemical substances, many of which are irritating, toxic or cancerous. Health hazards due to smoking were also found in passive smokers (people who are around those who smoke). Even fetus can be exposed to this deadly pollutant- either by the mother's active smoking or by her exposure to environmental tobacco smoke (during pregnancy). The problem is that most people who are exposed to passive smoking can't do anything about it. In addition to these gases ambient particles, which contain a large number of soluble metals, also are important contributors in creating pollution. Organic components carried on the particle surface play an important mediating role in producing the toxic effects.

Health Impacts of Air Pollution

The harmful effects of air pollution, sometimes, could be of a transient nature i.e. as soon as the air quality is improved the health can be restored back to its previous state. The symptoms could be marked by difficulty in breathing, wheezing, tightness in chest, irritation of eyes, etc.

However, if the exposure is persistent or an individual is very sensitive to the pollutants, it can lead to chronic diseases. People who already are suffering from pollution related diseases are usually at more risk of developing more disorders caused by air pollution.

Various studies have proved that environmental pollution primarily may be responsible for following disorders

Respiratory disorders

Cardiovascular disorders (Heart diseases)

Blood disorders

Air pollution and Respiratory diseases

The pr imar y function of the respiratory system i s to provide pure oxygen to the human body. This it does by sourc ing the oxygen from the surrounding environment. To source out this pure oxygen the respiratory system needs to be in direct touch (continuously) with the surrounding air.

Due to this direct and uninterrupted exposure to the environment, the respiratory system is highly prone to the disorders caused by air pollution as the health of the entire respiratory system is affected by the quality of the air we breathe. As the respiratory tissues are rich in
enzymes, they tend to transform all the organic pollutants into reactive substances that may cause lung injury.

Pollutants can cause damage of various types to respiratory organs. Let's see some as given below:

Nasal irritation and sinusitis

The pollutants that accumulate in the nose can cause problems in the nose and sinuses. Usually the symptoms are transient but sometimes it can lead to chronic allergic disorders or sinusitis.

Lung fibrosis

Pollutants can cause significant damage like scarring of the lung tissue- called fibrosis- and abnormal thickening of the tissue.

Chronic bronchitis

Bronchus (plural: bronchi) is the branch of trachea (wind pipe) that acts as a passageway into the air spaces of the lungs. Inflammation (swelling, redness, pain, increased temperature) of the bronchi that persists for a long time is called as chronic bronchitis. Pollutants can cause chronic bronchitis and subsequent obstruction of the airway.

Bronchial asthma

Pollutants predispose individuals to Bronchial asthma. Spasm (contraction) and narrowing of the bronchi that leads to bronchial airway obstruction is called as bronchial asthma. Pollutants like groundlevel ozone have been shown to contribute to increased responsiveness to allergic substances, which aggravates the (existing) asthma. These pollutants may even develop asthmatic conditions in children. It is now well accepted that persons with asthma are more sensitive than persons without asthma to air pollutants such as cigarette smoke, traffic emissions and photochemical smog components.

Pneumoconiosis

Pneumoconiosis is the abnormal condition caused by the invasion of dust (asbestos, silica, glass, etc.) in the lungs. It is the permanent deposition of substantial amount of particulate matters in the lungs. It may be associated with inflammation or infection.

Lung Cancer

Exposure of the lungs to pollutants makes the lungs vulnerable to development of cancer.

Lung infection

Pollutants can impair the infection-fighting ability of white blood cells in the lung and therefore may increase the risk of lung infections.

Air pollution and Cardiovascular system

The cardiovascular system has two major components- the heart and a network of blood vessels. Though the cardiovascular system, like the respiratory system, is not directly in touch with the external environment, it still is significantly affected by air pollution.

The inhalation of air pollutants (inadvertently or knowingly) into the respiratory system eventually leads to their absorption into the bloodstream which are then (subsequently) transported to the heart. Upon exposure to pollutants, the lung cells also release a variety of potent chemical substances that may critically affect the functioning of other organs such as those in the cardiovascular system.

Various harmful substances so produced may interact directly with the cardiovascular system and cause grave structural changes. These pollutants might even affect the contractibility and rhythm patterns of the heart and predispose the inhaler to heart diseases. Through their actions on the nervous system and hormones, pollutants also indirectly produce cardiovascular damage.

Experiments conducted in Delhi have found that the prevalence of coronary heart diseases in urban Delhi, were strikingly higher than the prevalence rate observed in a rural population barely 50 km away from the city. An unhealthy diet combined with lack of physical activity and increased stress in urban population was one of the predictable culprits behind this difference.

But, according to the scientists it seems reasonable to argue that at least a part of the sharp and striking difference in heart disease incidence, as between urban Delhi and its immediate rural environs (barely 50 km outside the city), may be attributable to air pollution.

Air pollution and Blood

To collect the oxygen from the air and circulate it throughout the body, the lungs are provided with an extensive blood vessel network. Hence it's not a surprise that the pollutants that enter the lungs get an
easy access into the blood.

Red blood cells in the blood contain hemoglobin, a substance responsible for carrying oxygen. The oxygen absorbed from the lungs gets attached to hemoglobin and is transported to all the organs in the body. Carbon monoxide, a pollutant in the air, binds over 200 times more firmly to hemoglobin than oxygen greatly and gravely hampering the oxygen carrying capacity of the blood. Severe acute exposure to carbon monoxide can even result in death or permanent damage to the central nervous system.

When the association between pollution and increasing incidence of disorders was researched and studied in detail the world over, scientists were able to pinpoint a new culprit-

It is now proven that oxidative stress generated in the human body is an important contributory factor to the grave damage.

OXIDATIVE STRESS AND POLLUTION

To understand the role of oxidative stress it is essential to know about certain elements called as the free radicals. An atom has protons and neutrons at its center and electrons revolving around the center in orbits. In normal conditions, these electrons are found in pairs. If an electron revolving around the center is not paired, the species is called as a free radical. Free radicals are unstable and highly reactive. To achieve stability they 'rob' electrons from the surrounding molecules to produce an electron pair. Due to this, the molecule from which the electron is removed becomes unstable and turns into a free radical. This process of
'robbing' repeats with the new free radical and the chain progresses. In this way, a single radical is capable of producing a sequence of electron transfer reactions. The process of the removal of electron is called as
oxidation. And the stress thus generated by the free radicals is called as oxidative stress. These free radicals attack fatty acids and proteins in cell membranes and cause damage to it. Free radicals also damage the DNA.

Recent research has identified oxidative stress as one of the potential features underlyingthe toxic effect of air pollutants.

The lungs are the primary portal of entry for oxygen. Toxic compounds present in the air are very powerful pro-oxidants. It is therefore inevitable, that the metabolism of oxygen give rise to a number of highly reactive oxygen-derived free radicals.

Our bodies are superb defense machines- the lung lining fluid protects the lung from this oxidative challenge arising from air pollution. But, the pollution levels today make this protection dismally insufficient. Whenever there is an excess load of pollutants, the products of oxidation increase; it is possible that these transmit toxic signals to the underlying lung tissues. Sometimes the pollutants exhaust the defense of the lungs and damage the respiratory tissue.

The free radicals generated by the pollutants also damage the heart through their effects on lipoproteins. Cholesterol travels in the blood and all through the body in tiny clumps of fat and proteins called lipoproteins. Low-density lipoprotein cholesterol (LDL-C) is termed as bad cholesterol. An increase in the LDL-C level (in the blood) and the subsequent oxidation is responsible for the formation of plaque on blood vessels (this is called atherosclerosis).

Air pollutants are responsible for this oxidation of LDL-C.

Thus, air pollution indirectly leads to atherosclerosis and subsequent narrowing and hardening blood vessels. Ultimately it leads to heart diseases.

The production of free radicals in the heart tissues has also been associated with abnormal rhythms and heart cell death.

ANTIOXIDANTS AND AIR POLLUTION

We now have sufficient knowledge and facts to prove the contribution of free radicals and oxidative stress towards the development of pollution related health hazards. Hence, it is logical to say that any substance that can reduce the oxidative stress can offer protection to the body from environmental pollution- And antioxidants the substances are!

Antioxidants are substances whose presence, in relatively low concentrations, significantly inhibits the rate of oxidation. It is the counter to the process of oxidation. Antioxidants deal with the free radicals and control oxidative stress. Every person exposed to air pollution is bound to experience oxidative stress due to an excessive burden of free radicals. To neutralize this oxidative stress our body has a store of natural antioxidants. Antioxidants in the lung are the first line of defense against oxygen free radicals. In the body antioxidants are present in the form of various secretions such as Albumin, Bilirubin, Estrogen, etc. These are the Natural (physiological) antioxidants that our body uses to fight off the potential (damage) threat posed by oxidative stress. These natural antioxidants, which are synthesized in our bodies, may not be always sufficient to take care of the additional burden of free radicals generated due to exposure to air pollution. So,
we need to extract antioxidants from our diet. But our supposedly“modern”, and deviously unhealthy, food habits prevent the sufficient intake of the much-needed dietary antioxidants. This is the reason why we need additional supply of antioxidants, especially when we cannot avoid exposure to pollutants.

A research oriented interest in dietary antioxidants first arose in the area of lung disease in the 1980s, when retrospective observational studies suggested that individuals with low intakes of dietary antioxidants displayed decreased lung function. It was also observed that patients with asthma, obstructive lung diseases and cardiovascular diseases showed a marked antioxidant deficiency and were more susceptible to the effects of air pollution.

Dietary requirements with respect to some micronutrients and antioxidants are expected to be much higher in urban population groups subjected to higher air pollution levels as the heavy, deleterious pro-oxidant burden imposed by pollutants would lead to far greater demands for dietary antioxidants.

There is substantial evidence that air pollution exposure results in increased oxidative stress and that dietary supplementationmay play a modulating role on the acute effect of air pollutants. Any nutritional supplement that can offer sufficient antioxidant activity may offer a significantly protective role in prevention and management of air pollution related disorders.

References