The results of this study clearly demonstrate that levels of 3-HPMA are higher in smokers than non-smokers and that they decrease significantly on abstinence from smoking. These results show therefore that urinary 3-HPMA, formed from the toxic cigarette smoke constituent acrolein, is a smoking-related biomarker.
Our results are consistent with previous studies and with the amount of acrolein in mainstream cigarette smoke. Mascher et al reported a method similar to ours and found levels of acrolein in smokers and non-smokers similar to those reported here (12
). In a recent study, Scherer et al found that when smokers switched from cigarettes containing cellulose acetate filters to charcoal filters, there was a small reduction of 3-HPMA, of borderline significance (14
). The levels of 3-HPMA in urine are quite consistent with the measured levels in cigarette smoke. If the average mainstream delivery of acrolein were 50 µg per cigarette (6
), then a smoker of 1 pack per day would excrete a maximum of about 4 mg per day of 3-HPMA. The average amount of 3-HPMA in our smokers was 1095 ng/ml, which amounts to about 1.7 - 2 mg per day (assuming urine volume of ~1.6 L – 2.0 L per day), consistent with the assumption that 3-HPMA is a major metabolite of acrolein, as it is in the rat (11
All subjects in our study had 3-HPMA in their urine, independent of smoking status. Acrolein is a common product of combustion and air pollutant, occurring in gasoline and diesel engine exhaust, aircraft emissions, and industrial emissions (7
). It is formed in high temperature cooking and may contribute to lung cancer in women who perform wok cooking (15
). It is also found in a wide variety of foods (7
), and occurs endogenously as a lipid peroxidation product (16
). However, it is clear from the cessation study that cigarette smoking represents a major source of acrolein exposure and 3-HPMA in urine.
The relationship between levels of 3-HPMA in urine to adducts 3 and 4 in lung could be complex. At a given level of exposure to acrolein, individuals with more efficient glutathione detoxification capacity would be expected to have higher levels of urinary 3-HPMA, and this could contribute to lower adduct levels by scavenging acrolein. However, adduct levels could also be affected by repair and cell turnover. Furthermore, 3-HPMA may reflect predominantly hepatic detoxification of acrolein while our adduct measurements were in lung. Nevertheless, we did observe a negative correlation between urinary 3-HPMA and adduct 3, but no relationship with adduct 4 or total adduct levels. These results were based on only 14 subjects for whom we had both urine and lung tissue and require further investigation.
The potential role of acrolein as a cause of lung cancer in smokers needs further research. The data reported here, together with the results of Feng et al demonstrating that it causes DNA damage at mutational hot spots in the p53
), suggest involvement. Furthermore, adduct 3
has been shown to be mutagenic in human cells, causing G to T transversions (17
), and we have shown that this adduct is present in human lung (8
). However, levels of adducts 3
in human lung were unrelated to smoking status in our study, although the number of subjects was small. Considering the results of the present study, the relationship of levels of adducts 3
in human lung to acrolein exposure from cigarette smoking requires further investigation. Arguing against a role of acrolein in smoking induced lung cancer is its weak carcinogenic activity (7
). A working group of the International Agency for Research on Cancer concluded that there is inadequate evidence in experimental animals for the carcinogenicity of acrolein (7
). Acrolein did not induce tumors in several studies in mice and rats and, when administered by inhalation to hamsters, did not enhance the carcinogenicity of either benzo[a
]pyrene or N
). It did however produce bladder tumors in rats when given as a tumor initiator, followed by promotion with dietary uracil (18
). The potential role of acrolein in cigarette smoke induced lung cancer requires further research.
In summary, the results of this study demonstrate that levels of 3-HPMA in human urine are related to cigarette smoking. The source of the higher levels in smokers is acrolein in cigarette smoke. While this paper was under review, two studies were published, one in which 3-HPMA levels were compared in smokers and non-smokers (19
), and a second in which smokers abstained (20
). The results were similar to those reported here. As acrolein is a highly toxic compound that could also be involved in tobacco smoke carcinogenesis, 3-HPMA should be incorporated as a standard urinary biomarker in investigations of cigarette smoke induced disease.