Drug Metabolism and Disposition 1996-08-01

Biotransformation of the aerosol propellant 1,1,1,2,3,3,3-heptafluoropropane (HFA-227): lack of protein binding of the metabolite hexafluoroacetone.

U Köster, D Mayer, H M Deger, W DeKant

Index: Drug Metab. Dispos. 24(8) , 906-10, (1996)

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Abstract

The biotransformation of the aerosol propellant 1,1,1,2,3,3,3-heptafluoropropane (HFA-227) was investigated in rats in vivo and in rat and human liver microsomes. In the urine of rats exposed to 5000 ppm HFA-227 for 6 hr, very small amounts of hexafluoroacetone trihydrate were identified as an HFA-227 metabolite by 19F-NMR. Fluoride concentrations in the urine samples (0-48 hr after the end of the exposure) from exposed animals were not significantly different from those found in samples from nonexposed rats. In rat and human liver microsomes, fluoride and hexafluoroacetone trihydrate formation from HFA-227 was detected in very low levels only in liver microsomes from pyridine-treated rats and in two of eight human liver microsome samples, which exhibited the highest cytochrome P4502E1 activities. Because some aldehydes may covalently bind to proteins and the formation of fluorinated protein adducts has been implicated in immune-mediated hepatitis induced by halothane, the binding of hexafluoroacetone trihydrate to proteins was also investigated. Hexafluoroacetone trihydrate also gave only a very small resonance in fluorine NMR experiments when binding to human serum albumin was studied in comparison with the acylating agent S-ethyltrifluoroacetate. Moreover, no fluorine-containing products were formed by the reaction of hexafluoroacetone trihydrate with N alpha-acetyl-L-lysine, and hexafluoroacetone trihydrate was not metabolized to fluorine-containing metabolites or inorganic fluoride in rats. Comparative studies in human liver microsomes demonstrated that a halothane metabolite may covalently bind to proteins; in contrast, metabolism and covalent binding of HFA-227 could not be demonstrated. In summary, these data indicate that HFA-227 is biotransformed at very low rates to hexafluoroacetone trihydrate but irreversible binding of hexafluoroacetone trihydrate cannot be demonstrated, even with the application of very sensitive methods, and is considered unlikely, based on the combination of the results obtained.