Single nucleotide polymorphisms of ABCC2 modulate renal secretion of endogenous organic anions

The ATP-binding cassette family transporter MRP2 (multidrug resistance-associated protein 2), encoded by the ABCC2 gene, is involved in the renal excretion of numerous xenobiotics and it is likely that it also transports many endogenous molecules arising from not only normal essential metabolic processes but also from environmental toxins or food intake. We used a targeted gas chromatography-mass spectrometry metabolomics analysis to study whether endogenous organic anions are differentially excreted in urines of healthy volunteers according to their genotype for three functional single nucleotide polymorphisms (SNPs) in ABCC2. This was the case for 35 of the 108 metabolites analyzed. Eight of them are most likely substrates of MRP2 since they are the most contributive to the difference between carriers of a decreasing function allele vs those carrying an increasing function one. Seven out of 8 metabolites are fatty acids (dodecanoic acid; 3-hydroxypropanoic acid) or metabolites of polyphenols (caffeine; resorcinol; caffeic acid; 2-(3,4-dihydroxyphenyl) acetic acid; and 4-hydroxyhippuric acid). Most of them were structurally similar to a series of substances previously shown to interact with MRP2 function in vitro. Interestingly, coproporphyrin isomer I, a prototypical substrate of MRP2, also belonged to our final list although it was not significantly discriminant on its own. This suggests that the simultaneous measurement of a set of endogenous metabolites in urine, rather than that of unique metabolites, has the potential to provide a phenotypic measure of MRP2 function in vivo. This would represent an innovative tool to study the variability of the transport activity of MRP2 under a physiological or pathological condition, especially in pharmacokinetic studies of its substrates.