The expression of a phenol uridine diphosphate glucuronosyltransferase (UGT) was investigated in rat brain homogenate and in primary cultures of astrocytes and neurons, by means of model substrates (1-naphthol and 4-methylumbelliferone) assays, Western blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) experiments. Glucuronidation of these substances occurred in cerebral cell or brain homogenates, although to different extents. The specific activity was the highest in astrocytes, with values more than 10- and 100-fold those found in neurons or total brain, respectively. Using antibodies able to recognize several rat liver UGT isoforms, only one protein with an apparent molecular mass of 54 kDa was detected in astrocyte and neuron homogenates and brain microsomes. RT-PCR experiments run with primers specifically designed for the rat liver UGT1A6 revealed amplificons of the expected sizes in accordance with the presence of UGT1A6 mRNA. The nucleotide sequence of the 330-base pair product was 100% homologous to that of exon 1 of rat liver isoform UGT1A6. In conclusion, this work allowed us to identify for the first time a constitutive cerebral UGT isoform identical to rat liver UGT1A6, which glucuronidates planar phenolic substances in cultured astrocytes, neurons, and the entire brain.
Copyright 1998 Academic Press.