Toxicological assessment of kretek cigarettes Part 5: mechanistic investigations, inhalation toxicity

The biological effects of mainstream smoke (MS) from Indonesian-blended cigarettes with and without added cloves, cloves extracted with hot ethanol, and extracted cloves replenished with eugenol or clove oil were assessed in a 90-day inhalation study in rats. A separate 35-day inhalation study in rats was performed with MS from American-blended cigarettes with 0%, 2.5%, 5% or 10% added eugenol. Effects commonly seen in inhalation studies with MS were observed. These included histopathological changes indicative of irritation in the entire respiratory tract and inflammatory responses in the lung. Adding cloves to American- or Indonesian-blended cigarettes reduced the inflammatory response in the lung but with no difference between the two blend types. When the clove oil was extracted (∼ 75% reduction of eugenol achieved) from cloves, the inflammatory response in the lung was still reduced similarly to whole cloves but the severity of histopathological changes in the upper respiratory tract was less reduced. Add back of clove oil or pure eugenol reduced this response to a level similar to what was seen with whole cloves. When eugenol was added to American-blended cigarettes, similar findings of reduced lung inflammation and severity of histopathological changes in respiratory the tract was confirmed. These studies demonstrate a clear effect of cloves, and in particular eugenol, in explaining these findings.