Aim: Calcineurin inhibitors are substrates for P-glycoprotein (P-gp), the expression of which is associated with ABCB1 C3435T polymorphism. Individual P-gp response to calcineurin inhibitor may be linked to nephrotoxicity or rejection. 99mTc-2-Methoxyisobutylisonitrile (99mTc-MIBI) is also a P-gp substrate. The aim of this study, therefore, was to determine 99mTc-MIBI organ kinetics and compare them with ABCB1 genotype with a view to replacing 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) with 99mTc-MIBI in renal transplant care.
Methods: Thirty prospective donors (13 male) were imaged for 20 min after administration of 99mTc-MIBI (400 MBq) intravenously. Posterior images of the abdomen were acquired at 30 and 120 min. Organ 30 min/peak count rate ratios and exponential two-point (30–120 min) rate constants (k, min−1) were calculated. Nineteen donors were genotyped for C3435T (exon 26), G2677T (exon 21), C1236T (exon 12), and G1199A (exon 11) ABCB1 polymorphisms using a PCR-based technique.
Results: 99mTc-MIBI and 99mTc-MAG3 gave similar perfusion images. Although their patterns of renal elimination were different, differential renal function was not significantly different. There was a negative trend between the hepatic 30 min/peak ratio and C3435T genotype (CC: 0.8374±0.0502; TC: 0.6806±0.1300; TT: 0.6919±0.1506; P=0.083). Renal k showed a negative trend with C3435T (CC: 0.0021±0.0020; TC: 0.0037±0.0013; TT: 0.0040±0.0012 min−1; P=0.087) but with no other genotypes. There were no significant sex-related differences in 99mTc-MIBI kinetics.
Conclusion: 99mTc-MIBI can replace 99mTc-MAG3 for pretransplant workup. The ABCB1 C3435T polymorphism may influence 99mTc-MIBI kinetics and thus have a role in renal transplant care. Further prospective trials are required to establish the full potential of 99mTc-MIBI in renal transplant management.