Acute and subacute inhalation toxicity assessment of WS-23 in Sprague-Dawley rats

2-isopropyl-N,2,3-trimethylbutyramide (WS-23) is a well-known artificial synthesis cooling agent widely used in foods, medicines, and tobaccos. As a commonly cooling agent in e-cigarette liquids, WS-23 has led to concerns about the inhalation toxicity with the prosperous of e-cigarettes in recent years. Thus, the aim of this study is to assess the acute and subacute inhalation toxicity of WS-23 in Sprague-Dawley (SD) rats according to the Organization for Economic Cooperation and Development (OECD) guidelines. In the acute toxicity study, there was no mortality and behavioral signs of toxicity at the limit test dose level (340.0 mg/m(3)) in the exposure period and the following 14-day observation period. In the subacute inhalation toxicity study, there was no significant difference observed in the body weights, feed consumption, and relative organ weights. Haematological, serum biochemical, urine, and bronchoalveolar lavage fluid (BALF) analysis revealed the non-adverse effects after 28-day repeated WS-23 inhalation (342.85 mg/m(3)), accompanied by slight changes in few parameters which returned to normal during the 28-day recovery period. The histopathologic examination also did not show any differences in vital organs. In conclusion, the maximum tolerated dose for WS-23 acute inhalation is not less than 340.0 mg/m(3), and the No Observed Adverse Effect Level (NOAEL) of WS-23 subacute inhalation was determined to be over 342.85 mg/m(3).