Eliminating carcinogenic acetaldehyde by cysteine from saliva during smoking

Tobacco smoking is one of the strongest risk factors not only for lung cancer but also for cancers of the upper gastrointestinal tract. Acetaldehyde has been shown to dissolve into the saliva during smoking and to be a local carcinogen in the human upper digestive tract. Cysteine can bind to acetaldehyde and eliminate its toxicity. We developed a tablet that releases cysteine into the oral cavity during smoking and could therefore be a potential chemopreventive agent against toxicity of tobacco smoke. In this study, the efficacy of l-cysteine-containing tablets to reduce the carcinogenic acetaldehyde in the saliva during tobacco smoking was examined. Seven volunteers smoked five cigarettes. During every smoking period, each volunteer sucked a blinded tablet containing 0, 1.25, 2.5, 5, or 10 mg of l-cysteine. Acetaldehyde was analyzed from salivary samples gas chromatographically at 0, 5, and 10 minutes from the beginning of the smoking. All tablets containing l-cysteine reduced highly significantly the salivary acetaldehyde; 5 mg of l-cysteine was the minimum concentration to totally eliminate the acetaldehyde from saliva. The mean salivary acetaldehyde concentrations in samples collected immediately after smoking with 0, 1.25, 2.5, 5, or 10 mg of l-cysteine were 228+/-115 micromol/L, 85+/-42 micromol/L (P=0.007), 9+/-7 micromol/L, 0.09+/- 0.2 micromol/L, 0+/- 0 micromol/L (P<0.001), respectively. In conclusion, carcinogenic acetaldehyde could be totally inactivated in the saliva during smoking by sucking tablet containing 5 mg of l-cysteine. Even a small reduction of the carcinogenicity of cigarette smoke could gain benefit at the population level. Hence, this finding warrants for further clinical trials for l-cysteine tablet in the prevention of upper digestive tract cancers in smokers.