The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings have not been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of the NTP or the U.S. Government.
1-Butyl-1-methylpyrrolidinium chloride is a cyclic quaternary amine and is classified as an "ionic liquid" (Knudsen et al., 2009). Ionic liquids (ILs) are salts of organic cations with melting points generally below 100°C (Landry et al., 2005). They typically consist of nitrogen-containing organic cations and inorganic anions. ILs are being widely investigated in industrial and laboratory processes as replacements for volatile organic solvents in catalysis, synthesis, and separation processes (Landry et al., 2005; Sipes, et al., 2008). They have gained attention within the green chemistry community because they are distinguished by a range of useful properties such as negligible vapor pressure, thermal stability, nonflammability, high ionic conductivity, and remarkable solubility properties. Three ILs, 1-butyl-3-methylimidazolium chloride, BMPY, and N-butylpyridinium chloride, were nominated to the NTP by the Center for Green Manufacturing, University of Alabama, for toxicological testing based on the increasingly widespread interest in these compounds. Limited toxicity studies have evaluated the cytotoxicity of ILs in vitro in mammalian cell lines and in ecotoxicity studies using a variety of organisms. There is currently no available information regarding the potential contact hypersensitivity effects following dermal exposure to BMPY. However, a recent NTP study (NTP, 2010) has indicated that BMIM, an ionic liquid with similar chemical structure to BMPY, at concentrations of 6.25%-25% (w/v) increased ear swelling when compared to the 4:1 acetone:olive oil vehicle in female BALB/c mice after 3 consecutive days of dermal application. In the same study, BMIM exhibited overt toxicity when applied to the ear at 25% (w/v) and when applied to the back at 12.5% (w/v).
The objective of this study was to determine the sensitization potential of BMPY when applied dermally to female BALB/c mice. The Local Lymph Node Assay was initially performed to measure the sensitization potential of BMPY at the concentrations of 1.65%, 3.12%, 6.25%, and 12.5% (w/v) in vehicle dimethylformamide. However, BMPY was found to cause overt toxicity in the LLNA at 12.5% (w/v), which manifested as either morbidity or moribundity. Therefore, evaluation of the contact hypersensitivity potential of BMPY was conducted at lower concentrations (0.825-6.25%). BMPY increased the draining lymph node cell proliferation in all LLNA studies when administered at 6.25% (w/v), however the increase did not reach the level of 3-fold enhancement over the vehicle control in any of the studies. This 3-fold enhancement criterion is used to classify a compound as a sensitizer by the Interagency Coordinating Committee on the Validation of Alternative Methods.
The irritant potential of BMPY was examined using the irritancy assay. There were no significant increases in percent ear swelling at 24 hr following the last exposure in animals treated with BMPY at concentrations of 0.825-6.25%.
The Mouse Ear Swelling Test was performed to further investigate the potential contact hypersensitivity effects of BMPY. The MEST was initially conducted using 3.12% and 6.25% (w/v) BMPY in the vehicle DMF for the sensitization phase and 6.25% BMPY for the challenge phase. However, BMPY was found to cause overt toxicity in the MEST at 6.25% (w/v), which manifested as either morbidity or moribundity. Therefore, evaluation of the contact hypersensitivity potential of BMPY could only be performed at lower concentrations. In the sensitization phase, two concentrations of BMPY (1.56% and 3.12%) were used, and a concentration of 3.12% was applied during the challenge phase. BMPY had no effect on the ear thickness at either 24 hr post-challenge or 48 hr post-challenge when compared to the vehicle irritancy control group. In addition, there were no significant differences in percent ear swelling between the VHIC group and the vehicle control group at both 24 hr and 48 hr post-challenge, which was consistent with the negative findings from the IRR assay.
In summary, the results from these studies have demonstrated that BMPY at concentrations of 0.825-6.25% (w/v) had minimal effects on lymph node cell proliferation in the LLNA assay, which was consistent with the negative findings in the MEST. Additionally, BMPY was not an irritant at the concentrations tested.
Knudsen G.A., Cheng Y., Kuester R.K., Hooth M.J., & Sipes I.G. (2009). Effects of dose and route on the disposition and kinetics of 1-butyl-1-methylpyrrolidinium chloride in male F-344 rats. Drug Metabolism and disposition 37 (11): 2171-2177.
Landry T.D., Brooks K., Poche D., & Woolhiser M. (2005). Acute toxicity profile of 1-Butyl-3-Methylimidazolium Chloride. Bull. Environ. Conm. Toxicol. 74: 559-565.
Sipes I.G., Knudsen G.A., & Kuester R.K. (2008). The effects of dose and route on the toxicokinetics and disposition of 1-Butyl-3-Methylimidazolium Chloride in male F-344 and Female B6C3F1 mice. Drug metabolism and disposition 36: 284-293.
NTP. (2010). Final Report: Assessment of contact hypersensitivity to 1-butyl-3-methylimidazolium chloride in female BALB/c mice.