Proximal tubular secretion of creatinine by organic cation transporter OCT2 in cancer patients

Abstract

Purpose: Knowledge of transporters responsible for the renal secretion of creatinine is key to a proper interpretation of serum creatinine and/or creatinine clearance as markers of renal function in cancer patients receiving chemotherapeutic agents.

Experimental design: Creatinine transport was studied in transfected HEK293 cells in vitro and in wild-type mice and age-matched organic cation transporter 1 and 2-deficient [Oct1/2(-/-)] mice ex vivo and in vivo. Clinical pharmacogenetic and transport inhibition studies were done in two separate cohorts of cancer patients.

Results: Compared with wild-type mice, creatinine clearance was significantly impaired in Oct1/2(-/-) mice. Furthermore, creatinine inhibited organic cation transport in freshly isolated proximal tubules from wild-type mice and humans, but not in those from Oct1/2(-/-) mice. In a genetic association analysis (n = 590), several polymorphisms around the OCT2/SLC22A2 gene locus, including rs2504954 (P = 0.000873), were significantly associated with age-adjusted creatinine levels. Furthermore, in cancer patients (n = 68), the OCT2 substrate cisplatin caused an acute elevation of serum creatinine (P = 0.0083), consistent with inhibition of an elimination pathway.

Conclusions: Collectively, this study shows that OCT2 plays a decisive role in the renal secretion of creatinine. This process can be inhibited by OCT2 substrates, which impair the usefulness of creatinine as a marker of renal function.

Figure 1

Accumulation of [¹⁴C]creatinine in HEK293 cells stably transfected with human (panel A) and murine (panel B) organic ion transporters. Data are presented as mean values ± SEM. The number of experiments for each group is 6. * indicates a statistical significant difference compared with control experiments with HEK293 cells transfected with null vector (P<0.05, unpaired two-tailed t-test).

Figure 2

Concentration-response curves for the inhibition of initial ASP⁺-uptake by creatinine in HEK 293 cells stably expressing hOCT2 (panel A). Values are means ± SEM expressed as % ASP⁺-uptake in the absence of creatinine with number of observation in parentheses. IC₅₀ value of ASP⁺-uptake inhibition by creatinine determined from this curve was 580 μM. Effect of 1 mM TEA⁺ (white columns) and 10 mM creatinine (black columns) on the uptake of ASP⁺ in freshly isolated S1 and S3 segments of proximal tubules from wild-type mice (panel B). The effects of these concentrations of TEA⁺ and creatinine on ASP⁺-uptake in S3 segments from Oct1/2(−/−) mice and from humans is also shown. Data are presented as mean values ± SEM. The number of mouse or human tubules for each group is indicated above the column. * indicates a statistical significant difference compared with control experiments in the presence of ASP⁺ only (P<0.05, unpaired two-tailed t-test).

Figure 3

Creatinine clearance (panel A) and accumulation of exogenous [¹⁴C]creatinine (panel B) in male wild-type and Oct1/2(−/−) mice. Data are presented as mean values ± SEM. The number of animals for each group is indicated above the column. * indicates a statistical significant difference compared with wild-type mice (P<0.05, unpaired two-tailed t-test).

Figure 4

Association of serum creatinine levels with single nucleotide polymorphisms (SNPs) located in or near the OCT2 gene, SLC22A2. Each SNP is individually plotted according to its chromosomal location versus the P-value of its association with serum creatinine levels. The SNP exhibiting the smallest P-value is shown as a diamond and labeled with its corresponding rs number (rs2504954) and P-value (P=0.000873). The remaining SNPs are indicated as boxes whose color intensities are in direct proportion to the degree of linkage disequilibrium (LD) between the corresponding SNP and rs2504954, relative to CEU/HapMap (release 21). The light blue lines represent the magnitude of the recombination rate observed along the indicated chromosomal stretch. The green arrows indicate RNA transcripts.

Figure 5

Changes in serum creatinine measured at baseline and after the first day of a 3-h i.v. infusion of cisplatin at a dose of 100 mg/m² in 68 adult cancer patients. Data are presented as mean values (bars) ± SEM (error bars).