Abstract
Although cancer is traditionally considered a genetic disease, the epigenetic abnormalities, including DNA hypermethylation, histone deacetylation, and/or microRNA dysregulation, have been demonstrated as a hallmark of cancer. Compared with gene mutations, aberrant epigenetic changes occur more frequently, and cellular epigenome is more susceptible to change by environmental factors. Excess cancer risks are positively associated with exposure to occupational and environmental chemical carcinogens, including those from gasoline combustion exhausted in vehicles. Of note, previous studies proposed particulate matter index (PMI) as a measure for gasoline sooting tendency, and showed that, compared with the other molecules in gasoline, 1,2,4–Trimethylbenzene, 2–methylnaphthalene and toluene significantly contribute to PMI of the gasoline blends. Mechanistically, both epigenome and genome are important in carcinogenicity, and the genotoxicity of chemical agents has been thoroughly studied. However, less effort has been put into studying the epigenotoxicity. Moreover, as the blending of ethanol into gasoline substitutes for carcinogens, like benzene, toluene, xylene, butadiene, and polycyclic aromatic hydrocarbons, etc., a reduction of secondary aromatics has been achieved in the atmosphere. This may lead to diminished cancer initiation and progression through altered cellular epigenetic landscape. The present review summarizes the most important findings in the literature on the association between exposures to carcinogens from gasoline combustion, cancer epigenetics and the potential epigenetic impacts of biofuels.
Highlights
Air pollution, containing harmful or poisonous substances, is a worldwide threat to human health, even at low doses
Ethanol volumetrically dilutes multiple harmful gasoline compounds [68]; (4) Previous studies [69] revealed that an increase in the ethanol content in the fuel blends reduces the emissions of some regulated gases, carbon monoxide (CO) and total hydrocarbons (THC); and (5) emerging evidence suggests that by blending ethanol into the gasoline, all PHAs are decreased with more reductions when ethanol blending is higher [70]
Another benefit of biofuels is the reduction of COVID-19 infection, because recent studies and analysis [71,72,73] showed that exposure to particulate matter (PM) could increase the susceptibility and severity of COVID-19 patient symptoms, for example, an increase of only 1 μg/m3 in PM2.5 is associated with an 8% increase in the COVID-19 death rate, and there is a positive correlation between exposure to PM and COVID-19 virus spread [74,75]
Summary
Air pollution, containing harmful or poisonous substances, is a worldwide threat to human health, even at low doses. The chemical mixture emitting from gasoline combustion that constitutes the main carcinogenic concerns consists of benzene, toluene, xylene, butadiene, 1,2,4–Trimethylbenzene, 2–methylnaphthalene, acetaldehyde, and many PAHs (Table 1). Limited studies in a population-based investigation showed that occupational exposure to one or more of these agents (butadiene, toluene, xylene) may be associated with lung cancer, higher risks of overall prostate cancer and an increased risk of hematological malignancies [16,18,19]. Based on the Agency for Toxic Substances and Disease Registry (ATSDR), there is no direct evidence in humans that naphthalene and 2–methylnaphthalene can induce cancerous transformation, some studies showed that exposure to 2–methylnaphthalene leads to pulmonary alveolar proteinosis but does not possess unequivocal carcinogenic potential in B6C3Fj mice [67]. Conditions of exposure to xylene in animal and human studies, both occupational and experimental, are usually different
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