IN-VITRO UPTAKE OF METHYL TERT-BUTYL ETHER IN MALE-RAT KIDNEY - USE OF A 2-COMPARTMENT MODEL TO DESCRIBE PROTEIN INTERACTIONS

Methyl tert-butyl ether (MTBE) is a gasoline additive that causes rena l tumors in male rats. In the process of measuring chemical specific p arameters necessary to develop a quantitative dosimetry model of MTBE in rats, the uptake of MTBE was found to be 5.5 times greater in male than in female F-344 rat kidney homogenate. The objectives of this stu dy were to characterize the factor(s) that influences the high uptake of MTBE into male rat kidney in vitro and to develop a system to evalu ate the interaction of MTBE with the male rat-specific protein, alpha 2u-globulin (alpha 2u). The uptake of MTBE in male, but not female, ra t kidney homogenate was found to be dependent on protein and chemical concentrations. When [C-14]MTBE was incubated with male rat kidney hom ogenate, radioactivity coeluted with the total protein fraction on a g el filtration column. An interaction between [C-14]MTBE and male rat k idney proteins was not found under conditions of dialysis or anion exc hange chromatography. A two-compartment vial equilibration model was u sed to assess the interaction between MTBE and alpha 2u. Using this sy stem, the dissociation constant for MTBE and alpha 2u was estimated to be 2.15 x 10(-4) M, which is in the range of other chemicals known to bind to alpha 2u and cause alpha 2u-mediated nephropathy, d-Limonene oxide was used to validate this two-compartment vial equilibration sys tem. These findings illustrate a technique useful in estimating the di ssociation constant for a volatile chemical and a protein, as well as explain the process that contributes to the uptake of MTBE into male r at kidney homogenate in vitro. A description of the weak interaction b etween MTBE and alpha 2u will be used to refine a physiologically base d pharmacokinetic model to describe the target tissue (kidney) concent rations of MTBE. (C) 1997 Academic Press.