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Benzo[a]pyrene (BaP or B[a]P) is a polycyclic aromatic hydrocarbon and the result of incomplete combustion of organic matter at temperatures between 300 °C (572 °F) and 600 °C (1,112 °F). The ubiquitous compound can be found in coal tar, tobacco smoke and many foods, especially grilled meats. The substance with the formula C20H12 is one of the benzopyrenes, formed by a benzene ring fused to pyrene. Its diol epoxide metabolites, more commonly known as BPDE, react with and bind to DNA, resulting in mutations and eventually cancer. It is listed as a Group 1 carcinogen by the IARC. In the 18th century a scrotal cancer of chimney sweepers, the chimney sweeps' carcinoma, was already known to be connected to soot.




Description


Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon found in coal tar with the formula C20H12. The compound is one of the benzopyrenes, formed by a benzene ring fused to pyrene, and is the result of incomplete combustion at temperatures between 300 °C (572 °F) and 600 °C (1,112 °F).




Sources


The main source of atmospheric BaP is residential wood burning. It is also found in coal tar, in automobile exhaust fumes (especially from diesel engines), in all smoke resulting from the combustion of organic material (including cigarette smoke), and in charbroiled food.
A 2001 National Cancer Institute study found levels of BaP to be significantly higher in foods that were cooked well-done on the barbecue, particularly steaks, chicken with skin, and hamburgers: Cooked meat products have been shown to contain up to 4 ng/g of BaP, and up to 5.5 ng/g in fried chicken and 62.6 ng/g in overcooked charcoal barbecued beef.
BaP is discharged in wastewater by industries such as smelters, particularly iron and steel mills and aluminium smelters.




History


In the 18th century, young British chimney sweeps who climbed into chimneys suffered from chimney sweeps' carcinoma, a scrotal cancer peculiar to their profession, and this was connected to the effects of soot in 1775, in the first work of occupational cancer epidemiology and also the first connection of any chemical mixture to cancer formation. Frequent skin cancers were noted among fuel industry workers in the 19th century. In 1933, BaP was determined to be the compound responsible for these cases, and its carcinogenicity was demonstrated when skin tumors occurred in laboratory animals repeatedly painted with coal tar. BaP has since been identified as a prime carcinogen in cigarette smoke.




Toxicity






= Nervous system

=
Prenatal exposure of BaP in rats is known to affect learning and memory in rodent models. Pregnant rats eating BaP were shown to negatively affect the brain function in the late life of their offspring. At a time when synapses are first formed and adjusted in strength by activity, BaP diminished NMDA receptor-dependent nerve cell activity measured as mRNA expression of the NMDA NR2B receptor subunit.




= Immune system

=
BaP has an effect on the number of white blood cells, inhibiting some of them from differentiating into macrophages, the body's first line of defense to fight infections. In 2016, the molecular mechanism was uncovered as damage to the macrophage membrane's lipid raft integrity by decreasing membrane cholesterol at 25%. This means less immunoreceptors CD32 (a member of the Fc family of immunoreceptors) could bind to IgG and turn the white blood cell into a macrophage. Therefore, macrophage membranes become susceptible to bacterial infections.




= Reproductive system

=
In experiments with male rats, subchronic exposure to inhaled BaP has been shown to generally reduce the function of testicles and epididymis with lower sex steroid/testosterone production and sperm production.




= Carcinogenicity

=
BaP's metabolites are mutagenic and highly carcinogenic, and it is listed as a Group 1 carcinogen by the IARC. Chemical agents and related occupations, Volume 10, A review of Human Carcinogens, IARC Monographs, Lyon France 2009
In June 2016, BaP was added as benzo[def]chrysene to the REACH Candidate List of Substances of very high concern for Authorisation.
Numerous studies since the 1970s have documented links between BaP and cancers. It has been more difficult to link cancers to specific BaP sources, especially in humans, and difficult to quantify risks posed by various methods of exposure (inhalation or ingestion). A link between vitamin A deficiency and emphysema in smokers was described in 2005 to be due to BaP, which induces vitamin A deficiency in rats.
A 1996 study provided molecular evidence linking components in tobacco smoke to lung cancer. BaP was shown to cause genetic damage in lung cells that was identical to the damage observed in the DNA of most malignant lung tumours.
Regular consumption of cooked meats has been epidemiologically associated with increased levels of colon cancer (although this in itself does not prove carcinogenicity),
A 2005 NCI study found an increased risk of colorectal adenomas was associated with BaP intake, and more strongly with BaP intake from all foods.
The detoxification enzymes cytochrome P450 1A1 (CYP1A1) and cytochrome P450 1B1 (CYP1B1) are both protective and necessary for benzo[a]pyrene toxicity. Experiments with strains of mice engineered to remove (knockout) CYP1A1 and CYP1B1 reveal that CYP1A1 primarily acts to protect mammals from low doses of BaP, and that removing this protection accumulates large concentrations of BaP. Unless CYP1B1 is also knocked out, toxicity results from the bioactivation of BaP to benzo[a]pyrene -7,8-dihydrodiol-9,10-epoxide, the ultimate toxic compound.




= Interaction with DNA

=

Properly speaking, BaP is a procarcinogen, meaning that its mechanism of carcinogenesis depends on its enzymatic metabolism to BaP diol epoxide It intercalates in DNA, and the electrophilic epoxide is attacked by nucleophilic guanine bases, forming a bulky guanine adduct.

X-ray crystallographic and nuclear magnetic resonance structure studies have shown how this binding distorts the DNA by perturbing the double-helical DNA structure. This disrupts the normal process of copying DNA and induces mutations, which explains the occurrence of cancer after exposure. This mechanism of action is similar to that of aflatoxin which binds to the N7 position of guanine.
There are indications that benzo[a]pyrene diol epoxide specifically targets the protective p53 gene. This gene is a transcription factor that regulates the cell cycle and hence functions as a tumor suppressor. By inducing G (guanine) to T (thymidine) transversions in transversion hotspots within p53, there is a probability that benzo[a]pyrene diol epoxide inactivates the tumor suppression ability in certain cells, leading to cancer.
Benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide is the carcinogenic product of three enzymatic reactions:

Benzo[a]pyrene is first oxidized by cytochrome P450 1A1 to form a variety of products, including (+)benzo[a]pyrene-7,8-epoxide.
This product is metabolized by epoxide hydrolase, opening up the epoxide ring to yield (−)benzo[a]pyrene-7,8-dihydrodiol.
The ultimate carcinogen is formed after another reaction with cytochrome P450 1A1 to yield the (+)benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide. It is this diol epoxide that covalently binds to DNA.
BaP induces cytochrome P450 1A1 (CYP1A1) by binding to the AHR (aryl hydrocarbon receptor) in the cytosol. Upon binding the transformed receptor translocates to the nucleus where it dimerises with ARNT (aryl hydrocarbon receptor nuclear translocator) and then binds xenobiotic response elements (XREs) in DNA located upstream of certain genes. This process increases transcription of certain genes, notably CYP1A1, followed by increased CYP1A1 protein production. This process is similar to induction of CYP1A1 by certain polychlorinated biphenyls and dioxins. Seemingly, CYP1A1 activity in the intestinal mucosa prevents major amounts of ingested benzo[a]pyrene to enter portal blood and systemic circulation. Intestinal, but not hepatic, expression of CYP1A1 depends on TOLL-like receptor 2 (TLR2), which is a eukaryotic receptor for bacterial surface structures such as lipoteichoic acid.
Moreover, BaP has been found to activate a transposon, LINE1, in humans.




Nucleotide excision repair


As illustrated above, (+)benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE) forms bulky covalent DNA adducts with guanines. Most of these adducts can be efficiently eliminated from DNA by the process of nucleotide excision repair. Those adducts that are not removed can cause errors during DNA replication leading to carcinogenic mutations.




See also


Benzopyrene
Benzo[e]pyrene
Pyrene, a four-ring analogue
Toxification




References






External links


International Chemical Safety Card 0104
National Pollutant Inventory – Polycyclic Aromatic Hydrocarbon Fact Sheet
"Lung cancer as consequence by Benzopyrene in smokers". Lung Cancer. Archived from the original on April 14, 2005. Retrieved March 5, 2005.
"Levels of Benzopyrene in Burnt toasts". Guardian Unlimited, Special reports: Close encounters. Retrieved March 5, 2005.
Karle, I. L. (2004). "Crystal and molecular structure of a benzo[a]pyrene-7,8-diol-9,10-epoxide N2-deoxyguanosine adduct: Absolute configuration and conformation". Proceedings of the National Academy of Sciences. 101 (6): 1433–8. Bibcode:2004PNAS..101.1433K. doi:10.1073/pnas.0307305101. PMC 341736. PMID 14757823.

Kata Kunci Pencarian:

• Sulforafana
• Roti panggang
• Tar (residu tembakau)
• Tumor
• Benzo(a)pyrene
• (+)-Benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide
• Benzopyrene
• Soil contamination
• Polycyclic aromatic hydrocarbon
• Carcinogen
• Benzo(e)pyrene
• Dibenzopyrenes
• Maté
• Pyrene

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• Benzo (a)pyrene - Wikipedia
• Benzo [a]pyrene | C20H12 | CID 2336 - PubChem
• Benzopyrene - Wikipedia
• Consumer Factsheet on: BENZO(A)PYREN - US EPA
• IRIS Toxicological Review of Benzo[A]Pyrene (Final Report) - US …
• BENZO[ a ]PYRENE - National Center for Biotechnology Information
• Benzo[ a ]pyrene—Environmental Occurrence, Human Exposure, …
• Benzo [a]pyrene (BaP) CASRN 50-32-8 | IRIS | US EPA, ORD
• Benz[a]pyrene | chemical compound | Britannica - Encyclopedia Britannica
• Benzo (a)pyrene - an overview | ScienceDirect Topics

Benzo (a)pyrene - Wikipedia

Benzo [a]pyrene (B a P) is a polycyclic aromatic hydrocarbon found in coal tar with the formula C 20 H 12. The compound is one of the benzopyrenes, formed by a benzene ring fused to pyrene, and is the result of incomplete combustion at temperatures …

Benzo [a]pyrene | C20H12 | CID 2336 - PubChem

Benzo(a)pyrene is a biomarker of polycyclic aromatic hydrocarbon (PAH) exposure as occurs in aluminum production and coal gasification, two processes which are carcinogenic to humans (urinary bladder and lung).

Benzopyrene - Wikipedia

Structurally speaking, the colorless isomers of benzopyrene are pentacyclic hydrocarbons and are fusion products of pyrene and a phenylene group. Two isomeric species of benzopyrene are benzo [a]pyrene and the less common benzo [e]pyrene. They belong to the chemical class of polycyclic aromatic hydrocarbons.

Consumer Factsheet on: BENZO(A)PYREN - US EPA

Short-term: EPA has found benzo(a)pyrene to potentially cause the following health effects when people are exposed to it at levels above the MCL for relatively short periods of time: red blood cell damage, leading to anemia; suppressed immune system.

IRIS Toxicological Review of Benzo[A]Pyrene (Final Report) - US …

EPA has finalized the Integrated Risk Information System (IRIS) assessment of benzo[a]pyrene. This assessment addresses the potential cancer and noncancer human health effects from long-term exposure to benzo[a]pyrene.

BENZO[ a ]PYRENE - National Center for Biotechnology Information

Benzo [a]pyrene and other polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants formed during incomplete combustion or pyrolysis of organic material. These substances are found in air, water, soils and sediments, generally at trace levels except near their sources.

Benzo[ a ]pyrene—Environmental Occurrence, Human Exposure, …

Benzo[a]pyrene (B[a]P) is the main representative of polycyclic aromatic hydrocarbons (PAHs), and has been repeatedly found in the air, surface water, soil, and sediments. It is present in cigarette smoke as well as in food products, especially when smoked and grilled.

Benzo [a]pyrene (BaP) CASRN 50-32-8 | IRIS | US EPA, ORD

Jan 19, 2017 · Under EPA’s Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005), benzo [a]pyrene is “carcinogenic to humans” based on strong and consistent evidence in animals and humans. This may be a synopsis of the full weight-of-evidence narrative.

Benz[a]pyrene | chemical compound | Britannica - Encyclopedia Britannica

Benzo[a]pyrene, an aromatic hydrocarbon produced in small amounts by the combustion of organic substances, contains five fused benzene rings. Like several other polycyclic aromatic hydrocarbons, it is carcinogenic.

Benzo (a)pyrene - an overview | ScienceDirect Topics

Jan 2, 2012 · Benzo[a]pyrene (B[a]P) is one of a large number of polycyclic aromatic hydrocarbons (PAHs) that are formed during the incomplete combustion of organic matter. It is the most well-studied PAH, a cancer-inducing substance for which toxicological data serve as quantitative benchmarks for the entire carcinogenic subgroup.