The broad objective of the proposed research is to investigate the metabolism and toxicity of hydrofluorocarbons and hydrochlorofluorocarbons (H(C)FCs). H(C)FCs are being developed as replacements for ozone- depleting chlorofluorocarbons. To prevent migration to the stratosphere and depletion of ozone, H(C)FCs were developed because the presence of C-H bonds in H(C)FCs was expected to enhance tropospheric lability and thereby reduce migration to the stratosphere. The C-H bonds that impart tropospheric lability may also be expected to impart metabolic lability, and this hypothesis has been confirmed. Studies in past years of support and in other laboratories demonstrate that H(C)FCs undergo cytochrome P- 450-catalyzed oxygenation reactions to afford a range of products. These findings will be extended and expanded in the competitive renewal application. There are three Specific Aims:
Specific Aim 1 includes investigations of the metabolism and toxicity of H(C)FCs, including in vivo metabolic fate and gas-uptake pharmacokinetic experiments, in vitro biotransformation studies, and studies on the toxicity and cellular interactions of H(C)FCs and H(C)FC metabolites.
Specific Aim 2 includes a comparison of mammalian cytochrome P-450 2E1 and bacterial cytochrome P- 450 101 (P-450cam) as catalysts for the biotransformation of H(C)FCs and development of computational predictions of H(C)FC reactivity.
Specific Aim 3 will focus on synthetic, stereochemical, and analytical aspects of H(C)FCs. A major focus of this aim is to develop synthetic routes for the preparation of chiral H(C)FCs of high enantiomeric excess, which will allow, for the first time, investigation of the role of chirality in the metabolism and toxicity of H(C)FCs. The proposed research is significant because the commercial use of H(C)FCs will likely be accompanied by occupational, consumer, and general-population exposure to H(C)FCs. Although exposure concentrations may be low, the populations exposed may be large. Hence it is important to understand thoroughly the metabolism and toxicity of H(C)FCs. Moreover, some H(C)FCs (HCFC-123 and HFC-134a) induce benign tumor formation in experimental animals, indicating that H(C)FCs are not inert chemicals and that the interaction of H(C)FCs or H(C)FCs metabolites with cellular constituents may lead to toxicity.
