Toxicologic Evaluation of Humectants Added to Cigarette Tobacco: 13-Week Smoke Inhalation Study of Glycerin and Propylene Glycol in Fischer 344 Rats

Abstract

Glycerin (CAS no. 56-81-5) and propylene glycol (CAS no. 57-55-6) are commonly used as humectant ingredients in manufactured cigarettes to control and maintain the moisture content of the cut tobacco filler. The potential of these added humectants to affect the toxicity of cigarette smoke was investigated in a subchronic nose-only smoke inhalation study in rats. Filtered test cigarettes were prepared from an American-style tobacco blend containing either glycerin added at 5.1% w/w tobacco, propylene glycol at 2.2% w/w tobacco, or combinations of these humectants totaling 2.3%, 3.9%, and 7.2% w/w tobacco. Other groups of animals were exposed similarly to the smoke of reference cigarettes without added humectants, or to filtered air (sham control). Smoke exposures were conducted for 1 h/day, 5 days/wk for 13 wk, at target smoke particulate concentrations of 350 mg/m(3). All smoke-exposed groups had equivalent increases in blood carboxyhemoglobin, serum nicotine, and serum cotinine relative to the air controls. Smoke-associated reductions in body weights and occasional increases in heart and lung weights were generally similar among the various exposure conditions at necropsy. Increases in serum alkaline phosphatase and decreases in serum glucose and cholesterol were observed among smoke-exposed females relative to air controls. However, no significant differences in these parameters were evident between the humectant-containing and reference cigarette smoke exposure groups. Assessments of respiration conducted after 3, 6, 9, and 12 wk of smoke exposure indicated an initial smoke-related but not humectant-related decrease in respiratory rate, tidal volume, and minute volume during the first 20 min of each smoke exposure. Respiratory-tract histopathology was consistent across sexes and smoke groups, comprising (1) diffuse and focal alveolar pigmented macrophages and chronic interstitial inflammation in the lung, (2) laryngeal epithelial hyperplasia, squamous metaplasia, and scab formation, and (3) epithelial hyperplasia in the anterior nose. Smoke-related histopathology resolved substantially during a 6-wk postexposure recovery period. Addition of the tested humectants to cigarettes, singly or in combination, had no meaningful effect on the site, occurrence, or severity of respiratory-tract changes or on the measured indices of pulmonary function. It was concluded that the addition of glycerin and propylene glycol to cigarettes does not significantly affect the biological activity of inhaled cigarette smoke in this rat model.

Influence of Additives on Cigarette Related Health Risks

“…An increase of mainstream smoke toxicity due to the use of 1,2-propylene glycol was not seen. Examining the effects of the humectants, glycerol and 1,2-propylene glycol added to tobacco, on mainstream cigarette smoke in a subchronic 13-week nose-only inhalation study with rats (described above in more detail), HECK et al (397) found no significant difference between the animal groups exposed to smoke from cigarettes with and without added humectants. Comparable results were obtained by BAKER et al (239) in their evaluation of the effects of tobacco additives on cigarette mainstream smoke toxicity using test cigarettes containing up to 8.3% 1,2-propylene glycol applied on tobacco in a casing mixture.…”

“…HECK et al (397) examined cigarettes spiked with glycerol and 1,2-propylene glycol (singly and in combination) and found that the addition of these humectants to cigarettes did not significantly affect the biological activity of inhaled cigarette smoke in rats. GAWORSKI et al (406), in the study mentioned before, subjected the smoke of test cigarettes with target levels of 4, 7 and 10% 1,2-propylene glycol added to tobacco to chemical analysis (41 analytes), toxicological in vitro assays (bacterial mutagenicity and cytotoxicity using neutral red uptake) and a sub-chronic inhalation study.…”

“…They also studied the effects of this humectant on toxicity in several in vitro and in vivo assays. The studies presented above (231,232,239,397) had applied 1,2-propylene glycol to cigarette tobacco in a casing formula or in combination with glycerol. Therefore, overlapping effects with other additives could have influenced the results.…”

“…• (397) investigated the effects of glycerol and 1,2-propylene glycol in cigarettes on mainstream smoke in a subchronic inhalation study. Fischer 344 rats were exposed nose-only for 13 weeks.…”

O impacto dos aditivos do tabaco na toxicidade da fumaça do cigarro: uma avaliação crítica dos estudos patrocinados pela indústria do fumo

“…Nr-COH; neutral red uptake cytoxicity assay with COH cells; SCE-COH: sister chromatid exchange assay in Chinese hamster ovary cells. Table 2 shows that the impact of tobacco additives on cigarette mainstream smoke toxicity was investigated through in vitro mutagenicity (Ames test) and mammalian cytotoxicity (Neutral red uptake) assays 29,30,31 , and in vivo sub-chronic (90 day) inhalation toxicity studies with rats 31,32,33,34 . In addition to these investigations (Table 2), a sub-chronic toxicity (26-week) study tested smoke condensates from cigarettes with and without tobacco additives for tumor promoting activity in the two-stage carcinogenicity test on mouse back skin 35 .…”