Does 4-methylimidazole have tumor preventive activity in the rat?
ABSTRACT 4-Methylimidazole (4-MEI) is found in a wide array of food products. The National Toxicology Program (NTP) recently conducted a two-year feeding cancer bioassay of 4-MEI in B6C3F(1) mice and F344/N rats. In rats, NTP found "equivocal evidence of carcinogenic activity" in females based on increased incidences of mononuclear cell leukemia and "no evidence of carcinogenic activity" in males. However, dose-related, statistically significant decreases in multiple tumors were observed in both male and female rats exposed to 4-MEI in the NTP bioassay. For example, 4-MEI was associated with a 25-fold decrease in the incidence of mammary tumors among high dose females. NTP noted briefly that the decreases in certain tumors, including mammary tumors, were greater than could be attributed to body weight alone. The present paper provides a more detailed evaluation of the evidence that 4-MEI exhibits tumor preventive activity in the rat based upon the results of the NTP bioassay. Reduced body weight offers a partial explanation for the reduction in tumors, but does not appear to be the primary cause of the decreased tumor incidences, indicating that 4-MEI itself may possess an ability to prevent tumor formation.
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ABSTRACT: Rapid qualitative and quantitative analysis of 4-methylimidazole (4-MEI) in caramel and beverage samples is demonstrated using the paper spray form of ambient ionization mass spectrometry. The minimum level of pure 4-MEI detectable using multiple reaction monitoring (MRM) in a triple quadrupole instrument was 3 pg μL(-1) in neat solvent and 5 pg μL(-1) in a matrix containing caramel. This method was used to analyze 11 caramel samples for 4-MEI. After implementing effective quality control protocols, average relative standard deviations for paper spray triple quadrupole MS were less than 15% and the linear dynamic range was three orders of magnitude. Results obtained on three different days by two different analyst groups agreed closely. An ion trap tandem MS method of approximate quantitative analysis is also described and it gave similar precision to the triple quadrupole experiment when fluctuations in ion currents were cancelled by simultaneously isolating the analyte and internal standard and fragmenting both in an ion trap simultaneous MRM experiment. As another alternative, a rapid qualitative screening method based on the use of high-resolution measurements instead of tandem mass spectrometry using an Orbitrap was also tested and found to give a detection limit of 100 pg μL(-1).The Analyst 06/2013; DOI:10.1039/c3an00888f · 3.91 Impact Factor
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ABSTRACT: The potential carcinogenicity of 4-methylimidazole (4-MEI) was evaluated in a National Toxicology Program (NTP) rodent cancer bioassay in Fischer 344 rats and B6C3F1 mice (NTP, 2007; Chan et. al, 2008). The NTP concluded that there was "clear evidence of carcinogenic activity" in male and female mice, based on an increased incidence of lung tumors. The "category of evidence" that the NTP assigns to a rodent cancer bioassay outcome can have significant regulatory implications. This is especially important for 4-MEI, which forms in caramel colorings and other foods during cooking, with potential widespread human exposure in a broad spectrum of food and beverage products. A detailed analysis of all NTP mouse-lung-tumor-only carcinogens reveals that the proper call for lung tumors in the 4-MEI study should have been "some evidence" rather than "clear evidence" of carcinogenic activity for both male and female mice in order to be consistent with the NTP's interpretation of other mouse lung carcinogens showing a similar strength of response. Suggestions are given as to measures the NTP should consider in the preparation of some or all future Technical Reports in order to enhance consistency of interpretation of experimental results.Regulatory Toxicology and Pharmacology 03/2013; DOI:10.1016/j.yrtph.2013.03.009 · 2.14 Impact Factor
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ABSTRACT: 2- and 4-methylimidazoles (2-MI and 4-MI) are undesired byproducts produced during the manufacture of caramel color used to darken food products such as carbonated beverages. The Office of Environmental Health Hazard Assessment in California listed 4-MI as carcinogen in January 2011 with a proposed no significant risk level at 29 μg per person per day. Thus, a quantitative analytical measurement for 2-MI and 4-MI is desired for reliable risk assessments for exposure. An ultra-performance liquid chromatography (UPLC) coupled tandem mass spectrometric (MS/MS) method was developed for the quantification of 4-MI in beverage samples. Chromatographic separation of 2-MI and 4-MI were achieved by using a PFP reversed-phase column and a stepwise gradient of methanol and distilled water containing 0.1 % formic acid. Identification and quantification of 2-MI and 4-MI were performed using electrospray ionization-tandem mass monitoring the precursor to product ion transitions for 2-MI at m/z 83.1 → 42.2 and 4-MI at m/z 83.1 → 56.1 with melamine at m/z 127.1 → 85.1 as the internal standard. The performance of the method was evaluated against validation parameters such as specificity, carryover, linearity and calibration, correlation of determination (r(2)), detection limit, precision, accuracy, and recovery. Calibration curves at 10-400 ng/mL were constructed by plotting concentration versus peak-area ratio (analyte/internal standard) and fitting the data with a weighted 1/x. The accuracy of the assay ranged from 93.58 to 110.53 % for all analytes. Intra-assay precision for 2-MI and 4-MI were below 7.28 (relative standard deviation/RSD %) at QC samples. Here we present a new and improved method using UPLC-MS/MS to significantly simplify sample preparation and decrease chromatographic run time. This method allows accurate and reproducible quantification of 4-MI in carbonated beverages as low as sub ng/mL (ppb) levels.Archives of Pharmacal Research 10/2014; DOI:10.1007/s12272-014-0508-0 · 1.75 Impact Factor