Email updates

Keep up to date with the latest news and content from BMC Public Health and BioMed Central.

Open Access Research article

The relationship of air pollution and surrogate markers of endothelial dysfunction in a population-based sample of children

Parinaz Poursafa1, Roya Kelishadi2*, Ahmadreza Lahijanzadeh3, Mohammadreza Modaresi4, Shaghayegh Haghjouy Javanmard5, Raheleh Assari6, Mohammad Mehdi Amin7, Faramarz Moattar1, Abbasgholi Amini4 and Babak Sadeghian3

Author Affiliations

1 Faculty of Environment and Energy, Science and Research Branch, Islamic Azad University, Tehran, Iran

2 Pediatrics Department, Child Health Promotion Research Center, Isfahan University of Medical Sciences, Isfahan, Iran

3 Environmental Protection Department, Isfahan, Iran

4 Pediatrics Department, Pediatric Prevention Research Center, Isfahan University of Medical Sciences, Isfahan, Iran

5 Department of Physiology, Applied Physiology Research Center, Isfahan University of Medical Sciences, Isfahan, Iran

6 Pediatrics Department, School of Medicine, Pediatric Prevention Research Center, Isfahan University of Medical Sciences, Isfahan, Iran

7 Department of Environmental Health Engineering, Environment Research Center, Isfahan University of Medical Sciences, Isfahan, Iran

For all author emails, please log on.

BMC Public Health 2011, 11:115  doi:10.1186/1471-2458-11-115

The electronic version of this article is the complete one and can be found online at: http://www.biomedcentral.com/1471-2458/11/115


Received:8 September 2010
Accepted:18 February 2011
Published:18 February 2011

© 2011 Poursafa et al; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

This study aimed to assess the relationship of air pollution and plasma surrogate markers of endothelial dysfunction in the pediatric age group.

Methods

This cross-sectional study was conducted in 2009-2010 among 125 participants aged 10-18 years. They were randomly selected from different areas of Isfahan city, the second large and air-polluted city in Iran. The association of air pollutants' levels with serum thrombomodulin (TM) and tissue factor (TF) was determined after adjustment for age, gender, anthropometric measures, dietary and physical activity habits.

Results

Data of 118 participants was complete and was analyzed. The mean age was 12.79 (2.35) years. The mean pollution standards index (PSI) value was at moderate level, the mean particular matter measuring up to 10 μm (PM10) was more than twice the normal level. Multiple linear regression analysis showed that TF had significant relationship with all air pollutants except than carbon monoxide, and TM had significant inverse relationship with ozone. The odds ratio of elevated TF was significantly higher in the upper vs. the lowest quartiles of PM10, ozone and PSI. The corresponding figures were in opposite direction for TM.

Conclusions

The relationship of air pollutants with endothelial dysfunction and pro-coagulant state can be an important factor in the development of atherosclerosis from early life. This finding should be confirmed in future longitudinal studies. Concerns about the harmful effects of air pollution on children's health should be considered a top priority for public health policy; it should be underscored in primordial and primary prevention of chronic diseases.

Background

Today, air pollution is one of the major health threats both in developing and developed countries [1]. Children are more sensitive than adults to health effects of air pollutants; this might be because of the developmental changes in their respiratory system and their higher number of breaths per minute than adults. Moreover, compared to adults they may spend more time outdoors, and their activity level is higher [2,3].

The harmful effects of air pollution on cardiovascular system are well-documented, but the underlying mechanisms remain to be determined. A recent experimental study showed for the first time that pulmonary exposure to the particulate matter (PM) within diesel exhaust enhances atherogenesis [4]. The human blood vessel endothelium is a sensitive target for air pollutants [5]. The interactions of the inflammation and coagulation systems are of the main mechanisms involved in impairment of endothelial function and eventually cardiovascular diseases [6].

The effect of air pollution on inflammation, oxidative stress and cardiovascular risk factors has been demonstrated not only in older adults [7,8], but also in young adults [9] as well as in children and adolescents [10,11].

The inflammation process stimulates the coagulation system, and result in increased secretion of tissue factor (TF). Endothelial function has key roles in anticoagulant and fibrinolytic systems. In vitro studies have demonstrated significant decrease in endogenous anticoagulation activity, thrombomodulin (TM), endothelial protein C receptor antigen and culture of endothelial cells during the inflammation process [12-14].

A growing body of evidence suggests that the effects of air pollution on the inflammation and the coagulation systems may have a role in endothelial dysfunction and in turn in the progression of cardiovascular diseases [15-17]. Findings of experimental studies suggest that exposure to air pollution may result in increase in TF and decrease in TM [18,19].

Atherogenesis starts from the fetal life through interrelations of traditional risk factors with inflammatory, immune, and endothelial biomarkers [20]. Air pollution has various harmful effects on this process from early life [21-23]. Studying the effects of environmental factors on early stages of atherosclerosis in early life can help identify the underlying mechanisms.

To the best of our knowledge, no previous human study had determined the association of air pollutants with TF and TM in the pediatric age group. In the current study, we aimed to determine the relationship of air pollution with TS and TM, as surrogate markers of endothelial dysfunction, in a population-based sample of children and adolescents.

Methods

This cross-sectional study was conducted from November 2009 to February 2010 in Isfahan, which is the second large and air-polluted city in Iran. The study was approved in the Research Council &Ethics Committee of the School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran. It was conducted according to the Declaration of Helsinki. After providing detailed oral information, we obtained written informed consent from the parents and oral assent from participants.

Participants

Those children and adolescents were eligible who were aged 10 to 18 years, lived for at least 6 months in areas of the city which had air pollution measurement stations, and their homes and schools were located less than 1 kilometer far from these stations. Those individuals who had a history of active or passive smoking, chronic disease, long-term medication use, or a history of acute infectious diseases in the past two weeks were not included in the study.

By considering a power of 95% and the statistical significance of 5%, the sample size was calculated as 110, but because of possible attrition of participants, the study was conducted on 125 students. To avoid socioeconomic bias, they were selected by multistage-random cluster sampling, with consideration to the proportion of the different types of schools (public/private).

Study area

Isfahan is an industrial city with a population of near 1894382, located in the center of Iranian plateau, with an average altitude of 1500 m from the sea level bounded by NW-SE mountain range of 3000 m. The average monthly temperature is 16°C with maximum 29°C in July and minimum 3°C in December with mild winds from west and south. Also the air of the city of Isfahan is predominantly affected by industrial emissions and motor traffic which can lead to a buildup of elevated concentrations during stagnant conditions [24,25].

Clinical study and laboratory methods

After inviting the selected students to a health center, a trained nurse completed a questionnaire on demographic data, and physical examination was done by the same trained general practitioner and under the supervision of the same pediatrician. Subcutaneous fat of the biceps and triceps muscles were measured with a skinfold caliper (Mojtahedi, Iran), the percent body fat was determined by bio-electrical impedence using a Body Fat Monitor (Omron HBF-300, Japan).

For assessment of dietary habits, the Healthy Eating Index (HEI) was computed as described before [10]. Physical activity level was assessed by the international Physical Activity Questionnaire for Children [26], previously validated in Iranian children [27].

While one of parents accompanied his or her child, blood samples were taken from the ante-cubital vein. Serums were obtained after centrifuging blood samples, and were kept frozen at -70°C until assayed and analyzed in the laboratory of the Applied Physiology Research Center affiliated to Isfahan University of Medical Sciences. Enzyme-linked immunosorbent assay (ELISA) kits from Abcam Company (UK) with code Ab46508 were used for measurement of TM, and TF ELISA kits R&D Company (UK) with code DCF300 for laboratory examinations.

Air pollution data

The mean daily temperature, sunlight duration, humidity and wind speed were recorded. Data from 5 air pollution measurement stations in Isfahan city were recorded daily for the 7 days prior to blood sampling. Daily data pertaining to main air pollutants, i.e. sulfur dioxide (SO2), Ozone (O3), PM10, Nitrogen dioxide (NO2) and carbon monoxide (CO) as well as the Pollutant Standards Index (PSI) were recorded. The mean values of seven 24-hour means of air pollutants and PSI were considered for statistical analysis.

Statistical analysis

SPSS for Windows (version 15:0, SPSS Inc., Chicago, IL) was used for data analysis. Analyses were initially stratified by gender, but as the differences were not significant, results are presented for girls and boys combined. We used log-transformed concentrations of variables to achieve normal distributions. The relationships of air pollutants with serum TM and TF were determined by Pearson correlation test. The associations between air pollutants and markers of endothelial dysfunction were assessed by multiple linear regression after adjustment for age, gender, body mass index, waist circumference, healthy eating index and physical activity level. The concentrations of biomarkers and air pollutants were categorized to quartiles, and the upper quartile was considered as elevated value. As there is no cutoff value to determine the high and low levels of TM and TF in the pediatric age group, we considered their lowest quartiles as low, and their highest quartiles as high levels. Then, we examined the association of the dichotomized concentrations of these biomarkers (upper quartile vs. lower quartile) across the quartiles of air pollutants by using logistic regression analysis after adjustment for the abovementioned confounders. The significance level was set at p < 0.05.

Results

Data of 118 out of the125 students studied was complete and included in the statistical analysis. The study participants consisted of 57 (48.3%) boys and 61 (51.7%) girls with a mean age of 12.79 ± 2.35 years.

The mean (SD) of anthropometric and biochemical variables of the study participants is presented in Table 1. TF had a mean level of 64.77 ± 17.35 pg/mL, with the following quartile (Q) ranges: Q1: 27.11-63.79; Q2:63.80-78.84; Q3:78.85-89.17; Q4: 89.18-102.74. The corresponding figures for TM were 5.64 ± 3.27 ng/mL, Q1: 2.18-5.14; Q2: 5.15-9.27; Q3: 9.28-14.25; Q4:14.26-15.71, respectively.

Table 1. Characteristics of study participants

The environmental characteristics are presented in Table 2. It shows moderate levels of mean PSI, i.e. an inappropriate level for sensitive groups. Mean levels of O3, NO2 and SO2 were higher than acceptable values; the mean PM10 level was remarkably high, reaching more than twice the normal level (120.48 vs. 50 μg/m3).

Table 2. Environmental characteristics during the study period

Results of the Pearson correlation analyses of air pollutants level with serum markers showed that PSI and PM10 had significant correlation with TF (r = 0.3, p = 0.001) and non-significant inverse correlation with TM. CO had weak but significant correlation with TM and TF (r = 0.25, p = 0.01).

Multiple linear regression analysis showed that after adjustment for confounding factors, serum TF level had significant relationship with PSI. This relationship existed more or less with air pollutants, notably PM10 (Table 3).

Table 3. Regression coefficients* for the relation of air pollutants and Pollutant Standards Index with serum concentrations of biomarkers

The odds ratio (OR) of elevated TF increased as the quartiles of PM10, O3 and PSI increased; however these associations reached to significant level only in the highest quartile of PM10 and PSI. The corresponding figures for TM were in opposite direction, i.e. the OR was lower in the highest vs. lowest quartiles of PM10, O3 and PSI (Table 4).

Table 4. Associatio n* of the quartiles of air pollutants and Pollutant Standards Index with upper quartile of tissue factor and thrombomodulin

Discussion

This study, which to the best of our knowledge is the first of its kind in the pediatric age group, revealed significant association of air pollutants (notably PM10 and O3 ) and PSI with surrogate markers of endothelial dysfunction in early life. Increased levels of PM10, O3 and PSI increased the OR of elevated TF and reduced TM.

Findings of different studies, mostly of experimental type, have linked air pollution with various predisposing factors of cardiovascular diseases, i.e. the progression of atherosclerosis, endothelial dysfunction, vasoconstriction, high blood pressure, changes in coagulation system, inflammation, oxidative stress, autonomic imbalance and arrhythmias [28].The latest statement of the American Heart Association provides growing body of evidence about a causal relationship between ultrafine PM (PM2.5) exposure and cardiovascular morbidity and mortality [29].

Our findings provide confirmatory evidence for the health effects of PM, however similar to our previous study in the pediatric age group [10]; we found associations between larger particulate matter (PM10) and factors associated with atherosclerotic cardiovascular disease. This might suggest the higher susceptibility to the threats of air pollutants in the cardiovascular system of children than adults.

Whatever the underlying pathophysiological mechanisms, acute and chronic exposures to air pollutants, notably PM, have been linked to a wide spectrum of cardiovascular disorders characterized by endothelial dysfunction [30]. Episodic exposure to PM 2.5 induces vascular injury, reflected in part by depletion of circulating endothelial progenitor cell [31]. Adverse vascular effects of diesel exhaust inhalation occur over different running conditions [32], e.g. PM 2.5 may be an important environmental risk factor for increased arterial blood pressure [33]. A double-blind study on fifteen healthy men exposed to diesel exhaust (PM concentration 300 μg/m3) showed a selective and persistent impairment of endothelium-dependent vasodilatation that occurs in the presence of mild systemic inflammation [34]. A study among seniors showed that increases in black carbon and PM2.5 were associated with increases in blood pressure, heart rate, endothelin-1, vascular endothelial growth factor and oxidative stress, along with a decrease in brachial artery diameter [35]. The vascular effects of air pollution are also confirmed in young adults [36] and in children [11] as well.

Although the interaction of coagulation, inflammation and endothelial dysfunction is well documented, but different effects of air pollutants have been documented on these systems, and the mechanisms underlying the associations of air pollutants with endothelial function are unclear. The interaction between the inflammation and coagulation systems is reciprocal, with protein C and TF playing a key role in this process [37,38]. We found significant association between PSI and TF, and among air pollutants the highest correlation was documented for PM10 and TF. This finding is consistent with various experimental studies that showed exposure to ultrafine PM increase TF expression in atherosclerotic lesions [39-41]. Study on cultured human smooth muscle cells and monocytes documented dose-dependent increases in TF in response to in vivo and in vitro exposure to ambient PM2.5 [42]. Some studies support potential pro-coagulant and thrombotic effects of PM [40], not only its ultrafine particles but also PM10 [43].

Findings of a study on 37 workers in a steel production plant revealed that short-term PM exposure is weakly associated with TM, but it did not show any effect on coagulation system [44]. On the other hand, an experimental study suggested that exposure to the soluble organic fraction of PM and diesel exhaust induced oxidative stress and reduced the PAI-1 production of endothelial cells, but it did not affect the TM production [45]. It is suggested that PM activates circulating monocytes directly or indirectly; it might stimulate other cells as pulmonary endothelial cells and might induce pulmonary and/or systemic inflammation [46]. However in an experimental study, ultrafine PM was associated with prothrombotic changes on the endothelial surface but did not trigger an inflammatory reaction and did not induce microvascular tissue injury [47].

A longitudinal study in the US found significant association between black carbon and markers of endothelial function and inflammation, with larger effect in obese individuals [48]. In the current study, similar to our previous experience among children adolescents [10], the association of air pollutants with biochemical markers remained significant even after adjustment for anthropometric measures. This difference might be because of the cross-sectional nature of our studies and the higher susceptibility of the pediatric age group in our study than older age group in the abovementioned study. Moreover, the genetic differences related to oxidative defense and stress response gene expression [41,48] should be considered as well.

Harmful effects of air pollution are mostly attributed to its PM content [29], however exposure to other air pollutants might have various health consequences [49]. Different air pollutants can have independent and possibly synergistic or opposed effects with each other and with PM; and the health impact of exposure to combinations of air pollutants remains to be determined [29].

In an experimental study, asbestos and mineral fibers affected TM level in human umbilical vein endothelial cells [50]. Furthermore, it is documented that a single O3 exposure might induce significant biological response in TM level, inflammatory and pro-coagulant reactions in the lungs of mice [18]. Consistent with this study, we found that O3 level was significantly associated with TF and TM. Although the only significant relationships of TM with air pollutants were its inverse associations with O3 followed by CO, but in higher quartiles of PSI, PM10 and O3, the OR of elevated TM decreased, and vice versa was documented for TF. This finding may have implications for understanding the systemic effects and possible pro-coagulant state induced by air pollutants; additional studies in this regard seem warranted.

Isfahan is the second most polluted industrial city in Iran, where the number of factories, cars and motorcycles is rapidly increasing [24,25]. Although during the time period of the current study, the urban air had a moderate level of PSI in general, but air pollutants had independent association with surrogate markers of endothelial dysfunction. This association might be because of the vulnerability of children to environmental threats, and/or due to considerably high level of PM10, being more than twice as high as standard. Furthermore, this association might be the result of the long-term exposure of the children studied to improper air quality year-round. In addition to the effects of air pollution on coronary artery diseases in the elderly and mortality [51,52] as the main focus of many statements, the impact of air pollutants on children's health should be also considered as a public health priority.

Study limitations& strengths

The findings of the current study should be considered with its limitations. As with all ecological studies, this study is limited by the lack of precise exposure estimates, and that the ambient pollution concentrations may not adequately reflect exposures of individual subjects. Because of the cross-sectional nature of the study, cause-effect relations cannot be inferred. We compared our findings in areas with different levels of air pollution, repeated measures design particularly capturing episodes of mild and severe pollution might provide more information. Noteworthy to mention that the existing equipment was unable to measure more specific particles such as PM2.5, although we found significant association of larger particle (PM10) with biomarkers studied, but studying ultrafine particle might result to stronger associations. Moreover, we measured systemic biomarkers, more localized investigation e.g. assessment of lung tissue inflammatory response in broncho-alveolar lavage may yield better results.

The strengths of this study are mainly its novelty in the pediatric age group and in assessment of potential confounding factors and controlling them in our analysis for studying the independent association of surrogate markers of endothelial dysfunction with air pollutants in a representative population-based sample of healthy children.

Conclusion

The independent association of air pollutants with surrogate markers of endothelial dysfunction and a possible pro-coagulant state is underscored. The presence of these associations with PM10, larger than PM2.5 usually considered as harmful, and in a moderate air quality, which is commonly considered with few or no health effect for the general population, highlights the need to re-examine environmental health policies and standards for the pediatric age group. Further studies on the effects of air pollution on the first stages of atherosclerosis in early life are needed. Concerns about the harmful effects of air pollution on children's health should be considered a top priority for public health policy; it should be underscored in primordial and primary prevention of chronic diseases.

Abbreviations

PSI: Pollutant Standards Index; PM: Particular matter; TF: Tissue factor;TM: Thrombomodulin; SO2: Sulfur dioxide; O3: Ozone; NO2: Nitrogen dioxide; CO: Carbon monoxide; ELISA: Enzyme-linked immunosorbent assay; SD: Standard deviation; OR: Odds ratio

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

PP participated in the design and conducting the study and helped to draft the manuscript. RK participated in the design and conducting the study and helped to draft and edit the manuscript. AL helped in conducting the study. MM participated in the design of the study and its conduction. SHJ participated in the design of the study and its conduction. RA participated in the design and conducting the study. MMA participated in the design of the study and helped to revise the manuscript. FM participated in the design of the study and helped to revise the manuscript. AA helped in conducting the study. BS participated in conducting the study. All authors read and approved the final manuscript.

Acknowledgements

This study was funded as a thesis by the Vice-chancellery for Research, Isfahan University of Medical Sciences, Isfahan, Iran.

References

  1. Deguen S, Zmirou-Navier D: Social inequalities resulting from health risks related to ambient air quality-A European review.

    Eur J Public Health 2010, 20:27-35. PubMed Abstract | Publisher Full Text OpenURL

  2. Irena B, Samuel K, Alvaro R, Osornio V: The effects of air pollution on the health of children.

    Peadiatr Child Health 2006, 11:513-516. OpenURL

  3. Kim JJ, American Academy of pediatrics, committee on Environmental health: Ambient air pollution: health hazards to children.

    Pediatrics 2004, 114:1699-1707. PubMed Abstract | Publisher Full Text OpenURL

  4. Miller MR, McLean SG, Duffin R, Shaw CA, Mills NL, Donaldson K, Newby DE, Hadoke PW: BAS/BSCR27 Diesel exhaust particles promote atherosclerosis in apolipoprotein E-deficient mice.

    Heart 2010, 96:e20. Publisher Full Text OpenURL

  5. Andersson H, Piras E, Demma J, Hellman B, Brittebo E: Low levels of the air pollutant 1-nitropyrene induce DNA damage, increased levels of reactive oxygen species and endoplasmic reticulum stress in human endothelial cells.

    Toxicology 2009, 262:57-64. PubMed Abstract | Publisher Full Text OpenURL

  6. Leroyer AS, Anfosso F, Lacroix R, Sabatier F, Simoncini S, Njock SM, et al.: Endothelial-derived microparticles: Biological conveyors at the crossroad of inflammation, thrombosis and angiogenesis.

    Thromb Haemost 2010, 104:456-463. PubMed Abstract | Publisher Full Text OpenURL

  7. Sun Q, Hong X, Wold LE: Cardiovascular effects of ambient particulate air pollution exposure.

    Circulation 2010, 121:2755-2765. PubMed Abstract | Publisher Full Text OpenURL

  8. Brook RD, Rajagopalan S: Particulate matter air pollution and atherosclerosis.

    Curr Atheroscler Rep 2010, 12:291-300. PubMed Abstract | Publisher Full Text OpenURL

  9. Chuang KJ, Chan CC, Su TC, Lee CT, Tang CS: The effect of urban air pollution on inflammation, oxidative stress, coagulation, and autonomic dysfunction in young adults.

    Am J Respir Crit Care Med 2007, 176:370-376. PubMed Abstract | Publisher Full Text OpenURL

  10. Kelishadi R, Mirghaffari N, Poursafa P, Gidding SS: Lifestyle and environmental factors associated with inflammation, oxidative stress and insulin resistance in children.

    Atherosclerosis 2009, 203:311-319. PubMed Abstract | Publisher Full Text OpenURL

  11. Iannuzzi A, Verga MC, Renis M, Schiavo A, Salvatore V, Santoriello C, et al.: Air pollution and carotid arterial stiffness in children.

    Cardiol Young 2010, 20:186-190. PubMed Abstract | Publisher Full Text OpenURL

  12. Falati S, Liu Q, Gross P, Merrill-Skoloff G, Chou J, Vandendries E, et al.: Accumulation of tissue factor in to developing thrombi in vivo is dependent upon microparticle P- selection ligand 1 and platelet P- selection.

    J Exp Med 2003, 197:1585-1598. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  13. Levi M, ten Cate H, van der Poll T: Endothelium: interface between coagulation and inflammation.

    Crit Care Med 2002, 30:S220-224. PubMed Abstract | Publisher Full Text OpenURL

  14. Nan B, Lin P, Lumsden AB, Yao Q, Chen C: Effects of TNF-alpha and curcumin on the expression of thrombomodulin and endothelial protein C receptor in human endothelial cells.

    Thromb Res 2005, 115:417-426. PubMed Abstract | Publisher Full Text OpenURL

  15. Nogueira JB: Air pollution and cardiovascular disease.

    Rev Port Cardiol 2009, 28:715-733. PubMed Abstract OpenURL

  16. Kannan S, Misra DP, Dvonch JT, Krishnakumar A: Exposures to airborne particulate matter and adverse perinatal outcomes: a biologically plausible mechanistic framework for exploring potential.

    Cien Saude Colet 2007, 12:1591-1602. PubMed Abstract | Publisher Full Text OpenURL

  17. Inoue K, Takano H, Sakurai M, Oda T, Tamura H, Yanagisawa R, Shimada A, Yoshikawa T: Pulmonary exposure to diesel exhaust particles enhances coagulatory disturbance with endothelial damage and systemic inflammation related to lung inflammation.

    Exp Biol Med (Maywood) 2006, 231:1626-1632. PubMed Abstract | Publisher Full Text OpenURL

  18. Kooter IM, Frederix K, Spronk HM, Boere AJ, Leseman DL, van Steeg H, et al.: Lung inflammation and thrombogenic responses in a time course study of Csb mice exposed to ozone.

    J Appl Toxicol 2008, 28:779-787. PubMed Abstract | Publisher Full Text OpenURL

  19. Fredrix K, Kooter IM, van Oerle R, Fens D, Hamulyak K, Gerlofs-Nijland ME, et al.: A new method to determine tissue specific tissue factor thrombomodullin activities: endotoxin and particular air pollution induced disbalance.

    Thromb J 2008, 6:14-17. PubMed Abstract | BioMed Central Full Text | PubMed Central Full Text OpenURL

  20. Kelishadi R, Poursafa P: Air pollution and non-respiratory health hazards for children.

    Arch Med Sci 2010, 6:483-495. OpenURL

  21. Mc Mahan CA, Gill Hc MC, Gidding SS, Malcom GT, Newman WP, Tracy RE, Strong JP, Pathobiological determinants of atherosclerosis in youth (PDAY) research group : PDAY risk score predicts advanced coronary artery atherosclerosis in middle aged persons as well as youth.

    Atherosclerosis 2007, 190:370-377. PubMed Abstract | Publisher Full Text OpenURL

  22. Poursafa P, Kelishadi R: Air Pollution, Platelet Activation and Atherosclerosis.

    Inflamm Allergy Drug Targets 2010, in press. PubMed Abstract | Publisher Full Text OpenURL

  23. Kelishadi R: Inflammation-Induced Atherosclerosis as a Target for Prevention of Cardiovascular Diseases from Early Life.

    Open Cardiovasc Med J 2010, 4:24-29. OpenURL

  24. Talebi SM, Tavakoli T, Ghinani A: Levels of PM10 and its chemical composition in the atmosphere of the city of Isfahan.

    Ir J Chem Engin 2008, 3:62-67. OpenURL

  25. Modarres R, Khosravi Dehkordi A: Daily air pollution time series analysis of Isfahan city.

    Int J Environ Sci Technol 2005, 7:259-262. OpenURL

  26. Crocker PR, Bailey DA, Faulkner RA, Kowalski KC, McGrath R: Measuring general levels of physical activity: preliminary evidence for the physical activity questionnaire for older children.

    Med Sci Sports Exerc 1997, 29:1344-1349. PubMed Abstract | Publisher Full Text OpenURL

  27. Faghihimani Z, Nourian M, Nikkar AH, Farajzadegan Z, Khavariyan N, Ghatrehsamani S, et al.: Validation of the Child and Adolescent International physical activity questionnaires in Iranian children and adolescents.

    ARYA Atherosclerosis J 2010, 5:163-166. OpenURL

  28. Simkhovich BZ, Kleinman MT, Kloner RA: Particulate air pollution and coronary heart disease.

    Curr Opin Cardiol 2009, 24:604-609. PubMed Abstract | Publisher Full Text OpenURL

  29. Brook RD, Rajagopalan S, Pope CA, Brook JR, Bhatnagar A, Diez-Roux AV, American Heart Association Council on Epidemiology and Prevention, Council on the Kidney in Cardiovascular Disease, and Council on Nutrition, Physical Activity and Metabolism, et al.: Particulate matter air pollution and cardiovascular disease: An update to the scientific statement from the American Heart Association.

    Circulation 2010, 121:2331-2378. PubMed Abstract | Publisher Full Text OpenURL

  30. Chauhan V, Breznan D, Thomson E, Karthikeyan S, Vincent R: Effects of ambient air particles on the endothelin system in human pulmonary epithelial cells (A549).

    Cell Biol Toxicol 2005, 21:191-205. PubMed Abstract | Publisher Full Text OpenURL

  31. O'Toole TE, Hellmann J, Wheat L, Haberzettl P, Lee J, Conklin DJ, et al.: Episodic exposure to fine particulate air pollution decreases circulating levels of endothelial progenitor cells.

    Circ Res 2010, 107:200-203. PubMed Abstract | Publisher Full Text OpenURL

  32. Barath S, Mills NL, Lundbäck M, Törnqvist H, Lucking AJ, Langrish JP, et al.: Impaired vascular function after exposure to diesel exhaust generated at urban transient running conditions.

    Part Fibre Toxicol 2010, 7:19. PubMed Abstract | BioMed Central Full Text | PubMed Central Full Text OpenURL

  33. Brook RD, Rajagopalan S: Particulate matter, air pollution, and blood pressure.

    J Am Soc Hypertens 2009, 3:332-350. PubMed Abstract | Publisher Full Text OpenURL

  34. Törnqvist H, Mills NL, Gonzalez M, Miller MR, Robinson SD, Megson IL, et al.: Persistent endothelial dysfunction in humans after diesel exhaust inhalation.

    Am J Respir Crit Care Med 2007, 176:395-400. PubMed Abstract | Publisher Full Text OpenURL

  35. Liu L, Ruddy T, Dalipaj M, Poon R, Szyszkowicz M, You H, et al.: Effects of indoor, outdoor, and personal exposure to particulate air pollution on cardiovascular physiology and systemic mediators in seniors.

    J Occup Environ Med 2009, 51:1088-1098. PubMed Abstract | Publisher Full Text OpenURL

  36. Lenters V, Uiterwaal CS, Beelen R, Bots ML, Fischer P, Brunekreef B, Hoek G: Long-term exposure to air pollution and vascular damage in young adults.

    Epidemiology 2010, 21:512-520. PubMed Abstract | Publisher Full Text OpenURL

  37. Esmon CT: The interactions between inflammation and coagulation.

    Br J Haematol 2005, 131:417-430. PubMed Abstract | Publisher Full Text OpenURL

  38. Levi M, van der Poll T, Buller HR: Bidirectional relation between inflammation and coagulation.

    Circulation 2004, 109:2698-2704. PubMed Abstract | Publisher Full Text OpenURL

  39. Karoly ED, Li Z, Dailey LA, Hyseni X, Huang YC: Up-regulation of tissue factor in human pulmonary artery endothelial cells after ultrafine particle exposure.

    Environ Health Perspect 2007, 115:535-540. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  40. Cozzi E, Wingard CJ, Cascio WE, Devlin RB, Miles JJ, Bofferding AR, et al.: Effect of ambient particulate matter exposure on hemostasis.

    Transl Res 2007, 149:324-332. PubMed Abstract | Publisher Full Text OpenURL

  41. Li R, Ning Z, Majumdar R, Cui J, Takabe W, Jen N, Sioutas C, Hsiai T: Ultrafine particles from diesel vehicle emissions at different driving cycles induce differential vascular pro-inflammatory responses: implication of chemical components and NF-kappaB signaling.

    Part Fibre Toxicol 2010, 7:6. PubMed Abstract | BioMed Central Full Text | PubMed Central Full Text OpenURL

  42. Sun Q, Yue P, Kirk RI, Wang A, Moatti D, Jin X, et al.: Ambient air particulate matter exposure and tissue factor expression in atherosclerosis.

    Inhal Toxicol 2008, 20:127-137. PubMed Abstract | Publisher Full Text OpenURL

  43. Gilmour PS, Morrison ER, Vickers MA, Ford I, Ludlam CA, Greaves M, et al.: The procoagulant potential of environmental particles (PM10).

    Occup Environ Med 2005, 62:164-171. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  44. Bonzini M, Tripodi A, Artoni A, Tarantini L, Marinelli B, Bertazzi PA, et al.: Effects of inhalable particulate matter on blood coagulation.

    J Thromb Haemost 2010, 8:662-668. PubMed Abstract | Publisher Full Text OpenURL

  45. Furuyama A, Hirano S, Koike E, Kobayashi T: Induction of oxidative stress and inhibition of plasminogen activator inhibitor-1 production in endothelial cells following exposure to organic extracts of diesel exhaust particles and urban fine particles.

    Arch Toxicol 2006, 80:154-62. PubMed Abstract | Publisher Full Text OpenURL

  46. den Hartigh LJ, Lamé MW, Ham W, Kleeman MJ, Tablin F, Wilson DW: Endotoxin and polycyclic aromatic hydrocarbons in ambient fine particulate matter from Fresno, California initiate human monocyte inflammatory responses mediated by reactive oxygen species.

    Toxicol In Vitro 2010, in press. PubMed Abstract | Publisher Full Text OpenURL

  47. Khandoga A, Stampfl A, Takenaka S, Schulz H, Radykewicz R, Kreyling W, Krombach F: Ultrafine particles exert prothrombotic but not inflammatory effects on the hepatic microcirculation in healthy mice in vivo.

    Circulation 2004, 109:1320-1325. PubMed Abstract | Publisher Full Text OpenURL

  48. Madrigano J, Baccarelli A, Wright RO, Suh H, Sparrow D, Vokonas PS, Schwartz J: Air pollution, obesity, genes and cellular adhesion molecules.

    Occup Environ Med 2010, 67:312-317. PubMed Abstract | Publisher Full Text OpenURL

  49. Campen MJ, Lund AK, Doyle-Eisele ML, McDonald JD, Knuckles TL, Rohr AC, et al.: A comparison of vascular effects from complex and individual air pollutants indicates a role for monoxide gases and volatile hydrocarbons.

    Environ Health Perspect 2010, 118:921-927. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  50. Urano H, Gotoh S, Shirahata A, Higashi K, Karasaki Y: Increases of thrombomodulin activity and antigen level on human umbilical vein endothelial cells treated with asbestos and man-made mineral fibers.

    Ind Health 1997, 3:359-366. OpenURL

  51. Gerber Y, Myers V, Broday DM, Koton S, Steinberg DM, Drory Y: Cumulative exposure to air pollution and long term outcomes after first acute myocardial infarction: a population-based cohort study. Objectives and methodology.

    BMC Public Health 2010, 10:369. PubMed Abstract | BioMed Central Full Text | PubMed Central Full Text OpenURL

  52. Richardson E, Pearce J, Mitchell R, Day P, Kingham S: The association between green space and cause-specific mortality in urban New Zealand: an ecological analysis of green space utility.

    BMC Public Health 2010, 10:240. PubMed Abstract | BioMed Central Full Text | PubMed Central Full Text OpenURL

Pre-publication history

The pre-publication history for this paper can be accessed here:

http://www.biomedcentral.com/1471-2458/11/115/prepub