Tobacco-specific nitrosamines
Encyclopedia
Tobacco-specific nitrosamines comprise one of the most important groups of carcinogen
s in tobacco
products, particularly cigarettes and American style (fermented) dipping snuff.
carcinogens are formed from nicotine
and related compounds by a nitrosation
reaction that occurs during the curing and processing of tobacco. They are called tobacco-specific nitrosamines because they are found only in tobacco products (and possibly in some other nicotine-containing products). Thus the tobacco-specific nitrosamines are present in both "smokeless" tobacco products such as dipping tobacco
and in cigarette
smoke. They are present to a significantly less degree in snus
, a Swedish style snuff that is not fermented and is pasteurized. They have been detected in American style "smokeless" tobacco products, but Health New Zealand concluded, in their study, that carcinogens and toxicants were present only below harmful levels. They are among the most important carcinogens in cigarette smoke, along with combustion products and other carcinogens.
Among the tobacco-specific nitrosamines, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) are the most carcinogenic. NNK and its metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) are potent systemic lung carcinogens in rats. Tumors of the nasal cavity, liver, and pancreas are also observed in NNK- or NNAL-treated rats. NNN is an effective esophageal carcinogen in the rat, and induces respiratory tract tumors in mice, hamsters, and mink. A mixture of NNK and NNN caused oral tumors when swabbed in the rat oral cavity. Thus, considerable evidence supports the role of tobacco-specific nitrosamines as important causative factors for cancers of the lung
, pancreas
, esophagus
, and oral cavity
in people who use tobacco products.
Metabolism and chemical binding to DNA (adduct
formation) are critical in cancer induction by NNK and NNN.
Human metabolism of NNK and NNN varies widely from individual to individual, and current research is attempting to identify those individuals who are particularly sensitive to the carcinogenic effects of these compounds. Such individuals would be at higher risk for cancer when they use tobacco products or are exposed to secondhand smoke. Identification of high-risk individuals could lead to improved methods of prevention of tobacco-related cancer, and improved risk valuation for insurers.
A new study shows that tobacco-specific nitrosamines can be formed from third-hand smoke, the residue that clings to surfaces after a cigarette is extinguished, especially in an environment with unvented gas appliances which produce nitrous acid.
Carcinogen
A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...
s in tobacco
Tobacco
Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...
products, particularly cigarettes and American style (fermented) dipping snuff.
Background
These nitrosamineNitrosamine
Nitrosamines are chemical compounds of the chemical structure R1N-N=O, some of which are carcinogenic.-Usages:Nitrosamines are used in manufacture of some cosmetics, pesticides, and in most rubber products. -Occurrences:...
carcinogens are formed from nicotine
Nicotine
Nicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...
and related compounds by a nitrosation
Nitrosation
Nitrosation is a process of converting organic compounds into nitroso derivatives, i.e. compounds containing the R-NO functionality.-C-Nitroso compounds:C-Nitroso compounds, such as nitrosobenzene, are typically prepared by oxidation of hydroxylamines:...
reaction that occurs during the curing and processing of tobacco. They are called tobacco-specific nitrosamines because they are found only in tobacco products (and possibly in some other nicotine-containing products). Thus the tobacco-specific nitrosamines are present in both "smokeless" tobacco products such as dipping tobacco
Dipping tobacco
Dipping tobacco, traditionally referred to as moist snuff, is a type of finely ground or shredded, moistened smokeless tobacco product. It is commonly and idiomatically known by various terms – most often as dip and sometimes rub or chew...
and in cigarette
Cigarette
A cigarette is a small roll of finely cut tobacco leaves wrapped in a cylinder of thin paper for smoking. The cigarette is ignited at one end and allowed to smoulder; its smoke is inhaled from the other end, which is held in or to the mouth and in some cases a cigarette holder may be used as well...
smoke. They are present to a significantly less degree in snus
Snus
Snus , or Swedish snuff, is a moist powder tobacco product originated from a variant of dry snuff in the early 19th century in Sweden, consumed by placing it under the lip for extended periods of time. The precursor of snus, the dry form of snuff inhaled through the nose, was introduced in Europe...
, a Swedish style snuff that is not fermented and is pasteurized. They have been detected in American style "smokeless" tobacco products, but Health New Zealand concluded, in their study, that carcinogens and toxicants were present only below harmful levels. They are among the most important carcinogens in cigarette smoke, along with combustion products and other carcinogens.
Among the tobacco-specific nitrosamines, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) are the most carcinogenic. NNK and its metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) are potent systemic lung carcinogens in rats. Tumors of the nasal cavity, liver, and pancreas are also observed in NNK- or NNAL-treated rats. NNN is an effective esophageal carcinogen in the rat, and induces respiratory tract tumors in mice, hamsters, and mink. A mixture of NNK and NNN caused oral tumors when swabbed in the rat oral cavity. Thus, considerable evidence supports the role of tobacco-specific nitrosamines as important causative factors for cancers of the lung
Lung cancer
Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue and, eventually, into other parts of the body. Most cancers that start in lung, known as primary...
, pancreas
Pancreatic cancer
Pancreatic cancer refers to a malignant neoplasm of the pancreas. The most common type of pancreatic cancer, accounting for 95% of these tumors is adenocarcinoma, which arises within the exocrine component of the pancreas. A minority arises from the islet cells and is classified as a...
, esophagus
Esophageal cancer
Esophageal cancer is malignancy of the esophagus. There are various subtypes, primarily squamous cell cancer and adenocarcinoma . Squamous cell cancer arises from the cells that line the upper part of the esophagus...
, and oral cavity
Oral cancer
Oral cancer is a subtype of head and neck cancer, is any cancerous tissue growth located in the oral cavity. It may arise as a primary lesion originating in any of the oral tissues, by metastasis from a distant site of origin, or by extension from a neighboring anatomic structure, such as the...
in people who use tobacco products.
Metabolism and chemical binding to DNA (adduct
DNA adduct
In molecular genetics, a DNA adduct is a piece of DNA covalently bonded to a chemical. This process could be the start of a cancerous cell, or carcinogenesis. DNA adducts in scientific experiments are used as biomarkers of exposure and as such are themselves measured to reflect quantitatively,...
formation) are critical in cancer induction by NNK and NNN.
Human metabolism of NNK and NNN varies widely from individual to individual, and current research is attempting to identify those individuals who are particularly sensitive to the carcinogenic effects of these compounds. Such individuals would be at higher risk for cancer when they use tobacco products or are exposed to secondhand smoke. Identification of high-risk individuals could lead to improved methods of prevention of tobacco-related cancer, and improved risk valuation for insurers.
A new study shows that tobacco-specific nitrosamines can be formed from third-hand smoke, the residue that clings to surfaces after a cigarette is extinguished, especially in an environment with unvented gas appliances which produce nitrous acid.
External links
- http://www.cancer.gov/researchandfunding/MERIT/Hecht
- This article is based on public domain text taken from an article on the website of the National Cancer Institute, a U.S. Federal Government agency