Renal excretion of pyruvate, lactate and alpha-ketoglutarate in kidney donors before and after nephrectomy and in patients with terminal uremia

The excretional patterns of lactate, pyruvate and alpha-ketoglutarate in renal transplants

The excretional patterns of lactate, pyruvate and alpha-ketoglutarate were investigated after renal transplantation in 36 patients. Fourteen patients had received a living-donor kidney with short ischemia time and good initial graft function, 22 had a cadaver transplant with an initial 125iothalamate clearance of more than 6 ml/min. The excretion of lactate and pyruvate did not vary significantly from that seen in normal controls or patients with uremia. In six patients with cadaver transplants, clearance values of alpha-ketoglutarate exceeded that of the glomerular filtration rate, indicating a net tubular secretion of this substance. During acute rejection episodes in 5 patients, no changes were seen in the excretional patterns of lactate, pyruvate and alpha-ketoglutarate.

Decreased renal organic anion secretion and plasma accumulation of endogenous organic anions in OAT1 knock-out mice

The "classical" organic anion secretory pathway of the renal proximal tubule is critical for the renal excretion of the prototypic organic anion, para-aminohippurate, as well as of a large number of commonly prescribed drugs among other significant substrates. Organic anion transporter 1 (OAT1), originally identified as NKT (Lopez-Nieto, C. E., You, G., Bush, K. T., Barros, E. J. G., Beier, D. R., and Nigam, S. K. (1997) J. Biol. Chem. 272, 6471-6478), has physiological properties consistent with a role in this pathway. However, several other transporters (e.g. OAT2, OAT3, and MRP1) have also been proposed as important PAH transporters on the basis of in vitro studies; therefore, the relative contribution of OAT1 has remained unclear. We have now generated a colony of OAT1 knock-out mice, permitting elucidation of the role of OAT1 in the context of these other potentially functionally redundant transporters. We find that the knock-out mice manifest a profound loss of organic anion transport (e.g. para-aminohippurate) both ex vivo (in isolated renal slices) as well as in vivo (as indicated by loss of renal secretion). In the case of the organic anion, furosemide, loss of renal secretion in the knock-out results in impaired diuretic responsiveness to this drug. These results indicate a critical role for OAT1 in the functioning of the classical pathway. In addition, we have determined the levels of approximately 60 endogenous organic anions in the plasma and urine of wild-type and knock-out mice. This has led to identification of several compounds with significantly higher plasma concentrations and/or lower urinary concentrations in knock-out mice, suggesting the involvement of OAT1 in their renal secretion. We have also demonstrated in xenopus oocytes that some of these compounds interact with OAT1 in vitro. Thus, these latter compounds might represent physiological substrates of OAT1.