Asbestos is a name given for a group of six naturally occurring silicate minerals chrysotile,
amosite,
crocidolite,
tremolite,
anthophyllite,
and actinolite.
Asbestos crystals according to the form of fibers are divided into two groups:
- Serpentine has curly fibers and is the most hazardous form,
as its fibets can easily reach terminal airways and alveoli.
Chrysotile is the only crystal in this group and is the most commonly used worldwide.
- Amphibole is a wider group of crystals that have needle shaped fibers.
Asbestos is durable,
strong and flexible material that was widely used in 19th-20th centuries due to its resistance to heat,
electricity and chemicals.
Not only having been popular in different types of industry and construction,
it was also used for manufacturing many commercial and household appliances such as coffee pots,
hairdryers,
toasters and even toys or cosmetic talcum powder.
The historical uses mean that not only occupational,
but also household exposure is possible. Family members of workers who are exposed to asbestos are at a higher risk too,
as asbestos dusts can be brought home on clothes,
shoes and other items.
Asbestos can also be found in old buildings where asbestos was used in constructions or for insulation when those materials start to deteriorate and small asbestos particles enter the air.
Nowadays asbestos is known as hazardous and very cancerogenous material that can cause mesothelioma,
lung cancer and some other forms of neoplasms.
In addition to malignancy,
it can cause another debilitating lung disease - asbestosis.
Benign pleural thickening,
pleural plaques and pleural effusion are benign diseases caused by asbestos.
Due to toxic properties asbestos is banned in Europe,
Australia,
Canada part of South America,
China and some other countries.
The usage is also regulated and restricted in the United States.
Asbestos related diseases are still widely spread worldwide despite all restrictions due to long latency period (15-60 years).
Due to this people with known asbestos exposure have to be followed up.
Lung function tests,
different imaging modalities,
cytology,
histology and various biomarkers are used for screening and differential diagnosis.
Asbestos fibers present in the air can be inhaled.
Serpentine fibers are more dangerous,
because they are more capable to reach alveoli.
Mucociliary clearance can remove asbestos dusts from the upper respiratory tract,
but the fibers cannot be eliminated once they reach the terminal airways and alveoli.
When settled in the lung,
asbestos fibers activate local immune response (macrophage phagocytosis),
cause chronic inflammatory reaction,
fibroblast activation and reduced tumour immunity due to various cytokines/chemokines release and immune changes.
Iron is a compound of asbestos crystals and is thought to be responsible for the release of reactive oxygen species (ROS) and reactive nitrogen species (RNS) which cause DNA damage to surrounding tissue cells and are related with cancerogenesis.
Asbestos is also known to be related with telomere shortening of mesothelial cells.
After apoptosis of the macrophages,
asbestos particles are released,
causing a repetition of the same immune response,
thus causing progressing inflammatory changes and pulmonary fibrosis.
Macrophages with phagocytosed asbestos particles can also be eliminated from airways through lymphatic system to the regional lymph nodes.
As a result,
fibers can be found everywhere along the lymphatic pathways,
including pleural spaces.