Quantitative Profiling of Human Renal UDP-glucuronosyltransferases and Glucuronidation Activity: A Comparison of Normal and Tumoral Kidney Tissues

Abstract

Renal metabolism by UDP-glucuronosyltransferase (UGT) enzymes is central to the clearance of many drugs. However, significant discrepancies about the relative abundance and activity of individual UGT enzymes in the normal kidney prevail among reports, whereas glucuronidation in tumoral kidney has not been examined. In this study, we performed an extensive profiling of glucuronidation metabolism in normal (n = 12) and tumor (n = 14) kidneys using targeted mass spectrometry quantification of human UGTs. We then correlated UGT protein concentrations with mRNA levels assessed by quantitative polymerase chain reaction and with conjugation activity for the major renal UGTs. Beyond the wide interindividual variability in expression levels observed among kidney samples, UGT1A9, UGT2B7, and UGT1A6 are the most abundant renal UGTs in both normal and tumoral tissues based on protein quantification. In normal kidney tissues, only UGT1A9 protein levels correlated with mRNA levels, whereas UGT1A6, UGT1A9, and UGT2B7 quantification correlated significantly with their mRNA levels in tumor kidneys. Data support that posttranscriptional regulation of UGT2B7 and UGT1A6 expression is modulating glucuronidation in the kidney. Importantly, our study reveals a significant decreased glucuronidation capacity of neoplastic kidneys versus normal kidneys that is paralleled by drastically reduced UGT1A9 and UGT2B7 mRNA and protein expression. UGT2B7 activity is the most repressed in tumors relative to normal tissues, with a 96-fold decrease in zidovudine metabolism, whereas propofol and sorafenib glucuronidation is decreased by 7.6-and 5.2-fold, respectively. Findings demonstrate that renal drug metabolism is predominantly mediated by UGT1A9 and UGT2B7 and is greatly reduced in kidney tumors.

Quantitative profiling of the UGT transcriptome in human drug-metabolizing tissues

“…In tumors derived from the intestine and colon, this was characterized by a globally reduced overall UGT expression whereas in kidney tumors, we observed a considerably enhanced relative expression of alternative variants compared to normal kidney tissues. While these preliminary data are well in line with the reduced UGT1A and UGT2B protein expression and glucuronidation recently reported in tumor kidneys and colons, 3,18,20,24 they also suggest a preferential and regulated expression of alternative variants. These results raise the possibility of a physiological contribution of AS to pathogenic states such as cancer.…”

“…25,26 We also reported a switch in alternative splicing at the UGT2B7 locus toward functional enzyme upon maturation in the kidney and reversal of this process in kidney tumors, considerably modifying tissular glucuronidation of drug. 20,24 This supports the notion that variation in the expression levels of UGT genes induced by changes in alternative splicing has the potential to affect drug response.…”

“…17 Still, expression data are consistent with lower expression of UGTs in kidney and colon tissues as previously reported using other approaches, at the mRNA and protein levels. [18][19][20][21][22] Our preliminary observations also suggest a shift in the transcript profiles in kidney and intestine/colon tumors that requires additional investigations using a larger set of well-characterized tumor samples.…”

Key to Opening Kidney for In Vitro–In Vivo Extrapolation Entrance in Health and Disease: Part I: In Vitro Systems and Physiological Data

“…These findings are in agreement with the majority of quantitative abundance data from commercially available pooled human kidney microsomes, acquired using targeted LC-MS/MS proteomic methods (14,92). Large variability in both mRNA (72-85% CV, n = 11) and protein abundance (76-159% CV, n = 10) has been noted for UGT1A6, 1A9 and 2B7 in kidney homogenates prepared from unspecified regions of healthy kidney (93). Lower expression and abundances were observed in tumoral kidney homogenates, although variability reported was comparable to those in healthy kidney (93).…”

“…Large variability in both mRNA (72-85% CV, n = 11) and protein abundance (76-159% CV, n = 10) has been noted for UGT1A6, 1A9 and 2B7 in kidney homogenates prepared from unspecified regions of healthy kidney (93). Lower expression and abundances were observed in tumoral kidney homogenates, although variability reported was comparable to those in healthy kidney (93). In contrast to homogenates, lower variability in UGT1A6, 1A9 and 2B7 abundance was reported in microsomes from human kidney cortex (48-61% CV, n = 5), mixed kidney (32-44% CV, n = 5) and kidney medulla (15).…”