Renal Excretion and Accumulation Kinetics of 2-Methylbenzoylglycine in the Isolated Perfused Rat Kidney

Abstract

The effect of protein binding on kidney function has been studied by investigating the renal accumulation and secretion of the hippurate analogue 2-methylbenzoylglycine in the isolated perfused rat kidney in the absence and presence of bovine serum albumin (BSA), Experiments were performed with either 2-5% pluronic or a combination of 2-2% pluronic and 2% BSA as oncotic agents; a wide concentration range (1-190 fig inL~1) of 2-methylbenzoylglycine was studied. Tubular secretion appeared to be a function of the amount of unbound drug in the perfusate and was best described by a model consisting of a high and low affinity Michaelis-Menten term. Parameters obtained after the analysis^of renal excretion data were maximum transport velocity for the high affinity site (TM iH ) -3 -0 db 2-8 fig min" , Michaelis-Menten constant for tubular transport for the high affinity site (KTfH ) = 0-5 ± 0-8 fig mL , maximum transport velocity for the low affinity site ^, 0 -2503:36 ¿¿g_min~ , and Michaelis-Menten constant for tubular transport for the low affinity site ( K T(l ) = 62 ±17 fig mL-1 . The compound accumulated extensively in kidney tissue, ratios up to 175 times the perfusate concentration were reached. Accumulation data were best analysed by a two-site model similar to the model used to describe renal excretion. Calculated parameters were theoretical maximum capacity of the high affinity site (Rm,h) = 26 ± 23 f i g g~\ affinity constant for renal accumulation at the high affinity site (KaiH ) = 0*2±04 ¿¿gmL" 1, theoretical maximum capacity of the low affinity site (RM<) = 1640± 1100 jug g and affinity constant for renal accumulation at the low affinity site (K a ,l) = 60± 58 fig mL-1 .TThe very high accumulation in kidney tissue could be explained by active tubular uptake, mediated by the secretory mechanisms involved, and dependent on the amount of free drug in the perfusate. This study shows that anionic drugs, subject to active secretion, may reach high concentrations in tubular cells even at low plasma concentrations.

Disposition of 4-Methylbenzoylglycine in Rat Isolated Perfused Kidney and Effects of Hippurates on Renal Mitochondrial Metabolism

“…In the current study 4-methylbenzoylglycine did not affect mitochondrial oxygen consumption, which is a good indication that the compound does not interfere with mitochondrial metabolism. 2-Methylbenzoylglycine affected mitochondrial oxygen consumption slightly, but not significantly, which is in agreement with its moderate effect on kidney function (Masereeuw et al 1996a). p-Aminohippurate, however, significantly inhibited both state 2 and state 3 of succinatestimulated respiration.…”

Uremic Toxins Inhibit Transport by Breast Cancer Resistance Protein and Multidrug Resistance Protein 4 at Clinically Relevant Concentrations

“…Since MRP4 and BCRP are located at the apical membrane of proximal tubule cells, transport activity depends on the intracellular levels of substrates rather than substrate concentrations in the blood. Previously, Masereeuw et al demonstrated that methyl hippuric acids accumulate during secretory transport in the isolated perfused rat kidney [20], [21]. Furthermore, they showed that 2-methyl hippuric acid levels were 175-times higher in kidney tissue compared to the perfusate and 4-methyl hippuric acid concentrations were even 600-times higher.…”

Saturable Accumulation and Diuretic Activity of Hydrochlorothiazide in the Isolated Perfused Rat Kidney

“…where C1R = renal clearance (ml/min); R r = renal excretion rate (pg/min); Qgf = glomerular filtration rate (ml/min); Cp = drug concentration in perfusate (pg/ml); Tm = maximum tubular transport velocity (pg/min); Kr = Michaelis-Menten constant of secretion (pg/ml): and FPr = fraction of excreted drug reab sorbed passively [14,15].…”

“…where Rm = maximum capacity of renal accumulation (pg/g); Ka = affinity constant of renal accumulation (pg/ml); and a = ratio CT/CP due to passive transport [15].…”