Bile Acid Precursors Compete with very Long Chain Fatty Acids for Translocation into Peroxisomes

Abstract

AIM: To investigate steps of transport of bile acid intermediates across the peroxisomal membrane. METHODS: The uptake of bile acid precursors into highly purified hepatic peroxisomes and corresponding matrix fractions of wildtype mice and rats as well as of mice lacking adrenoleukodystrophy protein (ALDP), a transporter in the peroxisomal membrane, was studied. Import of these precursors was characterized by monitoring the formation of bile acid conjugates using electrospray ionisationtandem mass spectrometry (ESI-MS/MS). RESULTS: Conjugate biosynthesis was inhibited when organelles were pre-treated with protease or histone 2A indicating a participation of peroxisomal membrane proteins, depended on CoA-esterification of the intermediates, but was independent of ATP. Supplementing the incubation medium with activated very long chain fatty acids (VLCFA) also diminished conjugate production. Hence, bile acid intermediates and VLCFA are supposed to interfere with one another crossing the peroxisomal membrane. Importantly, translocation of the bile acid CoA-esters was hampered in peroxisomes isolated from mice lacking ALDP expression. CONCLUSION: Our study suggests that VLCFA- and bile acid-CoA esters make use of the same peroxisomal import route, with ALDP affecting this pathway.