Many previous studies using animal models have shown that a class of compounds known as isothiocyanates (ITCs) inhibit lung cancer. ITCs are found in cruciferous vegetables such as broccoli, cabbage, bok choy, and cauliflower. Epidemiologic studies have suggested that high intake of these vegetables reduces risk for lung cancer. However, there have been no studies performed where ITC levels were measured in relation to lung cancer risk to provide direct evidence that these, compounds as opposed to others in the diet, are responsible for the reduced risk.
GSTs are a family of enzymes known to detoxify many foreign substances in many species. GSTM1 detoxifies the carcinogenic metabolite of benzo[a]pyrene which is found in tobacco smoke. However, GSTs also metabolize ITC thus decreasing its beneficial effects. Some individuals lack the genes coding for GSTs suggesting that they metabolize ITCs slower which may have impacts on their risk for lung cancer. This study was performed to determine if the lung cancer preventive effects of ITCs might be heightened if the GSTs that eliminate them are missing. The research team included NIEHS grantees and intramural scientists.
ITC measurements were carried out on urine collected from a cohort of men in Shanghai, China. This group was followed for lung cancer incidence from 1986 to 1997 and included 232 men diagnosed with lung cancer and 710 matched controls. The technique for measuring ITC was developed by the researchers. Subjects with detectable levels of urine ITC had a 40% reduction in the risk for lung cancer. Among those subjects lacking the genes coding for GSTs, the risk for lung cancer was reduced by 64%.
This study demonstrates that ITCs reduce the risk of lung cancer in humans. The effect is stronger in people without the gene coding for GST who are predicted to metabolize ITCs slower. Other scientists are trying to determine which of the ITCs has the greatest potential for intervention treatments. These findings add significant human data to this effort.