Reviews pubs.acs.org/jpr
Effects of Motor Vehicle Exhaust on Male Reproductive Function and Associated Proteins Deivendran Rengaraj, Woo-Sung Kwon, and Myung-Geol Pang* Department of Animal Science & Technology, Chung-Ang University, Anseong, Gyeonggi-do 456-756, Republic of Korea ABSTRACT: Air pollution is consistently associated with various diseases and subsequent death among children, adult, and elderly people worldwide. Motor vehicle exhaust contributes to a large proportion of the air pollution present. The motor vehicle exhaust systems emit a variety of toxic components, including carbon monoxide, nitrogen oxides, volatile organic compounds, ozone, particulate matter, and polycyclic aromatic hydrocarbons. Several epidemiological studies and laboratory studies have demonstrated that these components are potentially mutagenic, carcinogenic, and endocrine disrupting agents. However, their impact on male reproductive function and associated proteins is not very clear. Therefore, a comprehensive review on the effects of motor vehicle exhaust on male reproductive function and associated proteins is needed to better understand the risks of exhaust exposure for men. We found that motor vehicle exhaust can cause harmful effects on male reproductive functions by altering organ weights, reducing the spermatozoa qualities, and inducing oxidative stress. Remarkably, motor vehicle exhaust exposure causes significant changes in the expression patterns of proteins that are key components involved in spermatogenesis and testosterone synthesis. In conclusion, this review helps to describe the risks of vehicle exhaust exposure and its relationship to potential adverse effects on the male reproduction system. KEYWORDS: motor vehicle exhaust, toxic components, male reproduction, proteins
1. INTRODUCTION Current levels of air pollution are consistently associated with various diseases and an increase in death rates among children, adult, and elderly people. Motor vehicles emit various components because of the combustion of fuels such as gasoline, diesel, and liquefied or compressed natural gas. It has been reported that motor vehicle exhaust is the primary source of mobile pollutants and contributes in large proportion to the air pollution levels found in metropolitan areas.1 The motor vehicle exhaust consists of various nontoxic and toxic components and particulates. Nontoxic components include nitrogen (N2), water vapor (H2O), and carbon dioxide (CO2). However, CO2 is considered a greenhouse gas that contributes to global warming. The major toxic components of motor vehicle exhaust include carbon monoxide (CO), nitrogen oxides (NOx), volatile organic compounds (VOCs), ozone (O3), particulate matter (PM), and polycyclic aromatic hydrocarbons (PAHs).1−6 Multiple epidemiological studies and laboratory studies in humans and animals have demonstrated that high exposure to these types of toxic components causes a variety of serious diseases, ranging from allergic inflammation to cancer. A number of these components are potentially mutagenic, carcinogenic, and endocrinedisrupting chemicals.7 From a public health perspective, CO poisoning may cause more than 50% of the deadly inhalation poisonings observed in many countries.8 Exogenous CO preferentially binds with © 2014 American Chemical Society
hemoglobin to produce carboxyhemoglobin; this causes a significant reduction in tissue oxygenation.9 Motor vehicle exhaust is the major source of atmospheric NOx. Primarily, nitrogen monoxide (NO) is emitted, which is oxidized to nitrogen dioxide (NO2).2 Among the nitrogen oxides, NO2 has the strongest association with mortality.10 It can be transported deep into the lungs, reaching the alveoli and causing lung disease and pulmonary vasodilation in humans.2 The major VOCs of motor vehicle exhaust are benzene, toluene, ethylbenzene, and xylene, all considered significantly toxic agents.1 VOCs have been found to cause a variety of toxic effects, including cancer, neurological, behavioral, ophthalmic, and renal toxicities.1,11 Motor vehicle exhaust is also a key source for the formation of ground-level O3. O3 is not emitted directly but is formed by photochemical reactions of VOCs and NOx.5 Increased cases of patients with allergic inflammation, asthma, and decreased lung function have been reported after high exposure to O3.12 Vehicle exhaust PM consists of minute particles suspended in the atmosphere. On the basis of the aerodynamic diameter, PM can be classified into PM10 or PM2.5. The aerodynamic diameter of toxic PM is
