Expression of the HumanUGT1Locus in Transgenic Mice by 4-Chloro-6-(2,3-xylidino)-2-pyrimidinylthioacetic Acid (WY-14643) and Implications on Drug Metabolism through Peroxisome Proliferator-Activated Receptor α Activation

Abstract

The UDP-glucuronosyltransferase (UGT) 1A genes in humans have been shown to be differentially regulated in a tissue-specific fashion. Transgenic mice carrying the human UGT1 locus (Tg-UGT1) were recently created, demonstrating that expression of the nine UGT1A genes closely resembles the patterns of expression observed in human tissues. In the present study, UGT1A1, UGT1A3, UGT1A4, and UGT1A6 have been identified as targets of the peroxisome proliferator-activated receptor (PPAR) alpha in human hepatocytes and Tg-UGT1 mice. Oral administration of the PPARalpha agonist 4-chloro-6-(2,3-xylidino)-2-pyrimidinylthioacetic acid (pirinixic acid, WY-14643) to Tg-UGT1 mice led to induction of these proteins in either the liver, gastrointestinal tract, or kidney. The levels of induced UGT1A3 gene transcripts in liver and UGT1A4 protein in small intestine correlated with induced lamotrigine glucuronidation activity in these tissues. With UGT1A3 previously identified as the major human enzyme involved in human C24-glucuronidation of lithocholic acid (LCA), the dramatic induction of liver UGT1A3 RNA in Tg-UGT1 mice was consistent with the formation of LCA-24G in plasma. Furthermore, PPAR-responsive elements (PPREs) were identified flanking the UGT1A1, UGT1A3, and UGT1A6 genes by a combination of site-directed mutagenesis, specific binding to PPARalpha and retinoic acid X receptor alpha, and functional response of the concatenated PPREs in HepG2 cells overexpressing PPARalpha. In conclusion, these results suggest that oral fibrate treatment in humans will induce the UGT1A family of proteins in the gastrointestinal tract and liver, influencing bile acid glucuronidation and first-pass metabolism of other drugs that are taken concurrently with hypolipidemic therapy.

Intestinal glucuronidation protects against chemotherapy-induced toxicity by irinotecan (CPT-11)

“…If tumor Ugt1a gene expression is impaired, induction of gene activity in nondiseased normal tissue may protect the surrounding epithelial cells from SN-38 damage by increasing glucuronidation capacity and improving drug tolerance. For example, UGT1A1, the primary UGT involved in SN-38 glucuronidation (15), can be regulated by induction of the human UGT1A1 gene after activation of XNRs PXR (39,40), CAR (15), and PPARα (41). One could envision that potential therapeutics could be developed to target induction of the UGT1A1 gene in healthy tissue, thus providing an added level of protection toward the toxicity inherent in the accumulation of SN-38.…”

From differential induction of UDP-glucuronosyltransferases in rat liver to characterization of responsible ligand-activated transcription factors, and their multilevel crosstalk in humans

“…CYP4 family members were the first fibrate-induced XME target genes shown to be involved in omega-hydroxylation of fatty acids [5]. PPARα is involved in regulation of all phases of the XME system including regulation of many UGTs (UGT1A1, 1A3, 1A4 [51], 1A9 [52], 2B4 [53]). PPARα-induced hepatic UGTs are possibly involved in detoxification of eicosanoids, as discussed in section 4.4.…”

“…It is tempting to speculate that evolution of the gtPBREM cluster of binding sites for a number of LATFs in the promoter of UGT1A1 [46,47] may be related to the need for perinatal UGT1A1 induction in primates. This cluster contains binding sites for CAR and PXR [47], AhR [33], Nrf2 [76], PPARα [51] and for the glucocorticoid receptor [47]. It is obvious that perinatal induction represents a stressful condition.…”

“…Multiple HETEs have been characterized as PPARα agonists [11,48]. They are also substrates of UGT1A1,1A3,1A4,1A6,1A9 [51], and UGT2B4, 2B7 and 2B10 [87]. Interestingly, a stepwise increase in LOX metabolites such as 12-and 15-HETE characterizes the progression from normal liver to nonalcoholic fatty liver disease and steatohepatitis [63].…”

UGT genomic diversity: beyond gene duplication

“…Thus, it is clear that the alternative usage of duplicated first exons is the basis of UGT1A function and expression diversities. Besides, all this tissue-specific expression is well orchestrated by the cooperative interaction between transcription factors and the transcription initiation complex (for review see (Mackenzie et al, 2003;Owens, Basu, & Banerjee, 2005;Strassburg, Kalthoff, & Ehmer, 2008;Tukey & Strassburg, 2001) (Gardner-Stephen & Mackenzie, 2008) Studies concerning UGT1A promoter-interacting factors have revealed the binding of some important activators, such as HNF-1, cdx2, Nrf2, PXR, XRE (AhR) and CAR (Aueviriyavit, Furihata, Morimoto, Kobayashi, & Chiba, 2007;Bonzo, Belanger, & Tukey, 2007;Buckley & Klaassen, 2009;Gregory, Lewinsky, Gardner-Stephen, & Mackenzie, 2004;Senekeo-Effenberger et al, 2007;Sugatani, Sueyoshi, Negishi, & Miwa, 2005;Verreault et al, 2006;Yuan, Li, & Yang, 2007). Transcriptional regulation of the UGT1A gene by transcription factors is more specifically addressed in some following chapters.…”