Isolated perfused rat kidney as a tool in the investigation of renal handling and effects of nonsteroidal antiinflammatory drugs

Iron chelators do not reduce cold-induced cell injury in the isolated perfused rat kidney model

BACKGROUND

In vitro, cold-induced injury is an important contributor to renal tubular cell damage. It is mediated by iron-dependent formation of reactive oxygen species and can be prevented by iron chelation. We studied whether iron chelators can prevent cold-induced damage in the isolated perfused rat kidney (IPK) model both after cold perfusion (CP) and after cold storage (CS). We hypothesized that in the CP model iron-dependent cold-induced injury is more pronounced, since oxygen is constantly provided.

METHODS

The IPK was either flushed with University of Wisconsin (UW) solution and stored for 4, 18 or 24 h at 4 degrees C or perfused during 4 h at 4 degrees C with UW for machine perfusion. The iron chelators 2,2'-dipyridyl or desferal, or the negative control 4,4'-dipyridyl were added during the cold perfusion. Kidney function was measured during 2 h reperfusion at 37.5 degrees C and compared to a control group (without cold preservation).

RESULTS

Compared to control perfusion, kidney function was decreased in all experimental protocols. glomerular filtration rate and FR(H2O) were significantly decreased, while FE(gluc) and FE(Na) were higher after 4 h CS and CP. After 4 h CP, also renal vascular resistance was increased. Addition of 2,2'-dipyridyl did not improve kidney function after either CS or CP. Prolonged periods of CS worsened kidney function. The addition of 2,2'-dipyridyl or desferal did not improve kidney function after longer periods of CS.

CONCLUSIONS

Addition of an iron chelator to the preservation solution UW did not improve kidney function after both CS and CP. Iron chelation is not able to prevent cold-induced damage in the isolated perfused rat kidney.

Impaired Renal Secretion of Substrates for the Multidrug Resistance Protein 2 in Mutant Transport–Deficient (TR−) Rats

ABSTRACT. Previous studies with mutant transport–deficient rats (TR−), in which the multidrug resistance protein 2 (Mrp2) is lacking, have emphasized the importance of this transport protein in the biliary excretion of a wide variety of glutathione conjugates, glucuronides, and other organic anions. Mrp2 is also present in the luminal membrane of proximal tubule cells of the kidney, but little information is available on its role in the renal excretion of xenobiotics. The authors compared renal transport of the fluorescent Mrp2 substrates calcein, fluo-3, and lucifer yellow (LY) between perfused kidneys isolated from Wistar Hannover (WH) and TR− rats. Isolated rat kidneys were perfused with 100 nM of the nonfluorescent calcein-AM or 500 nM fluo3-AM, which enter the tubular cells by diffusion and are hydrolyzed intracellularly into the fluorescent anion. The urinary excretion rates of calcein and fluo-3 were 3 to 4 times lower in perfused kidneys from TR− rats compared with WH rats. In contrast, the renal excretion of LY (10 μM, free anion) was somewhat delayed but appeared unimpaired in TR− rats. Membrane vesicles from Sf9 cells expressing human MRP2 or human MRP4 indicated that MRP2 exhibits a preferential affinity for calcein and fluo-3, whereas LY is a better substrate for MRP4. We conclude that the renal clearance of the Mrp2 substrates calcein and fluo-3 is significantly reduced in TR− rat; for LY, the absence of the transporter may be compensated for by (an)other organic anion transporter(s). E-mail: R.Masereeuw@ncmls.kun.nl

Anionic and cationic drug secretion in the isolated perfused rat kidney after neonatal surgical induction of ureteric obstruction

OBJECTIVE

To study the pathophysiological changes of renal tubular drug transport mechanisms in congenital renal obstruction, by developing a model for perfusing the isolated kidney (IPK) after neonatal surgical induction of partial ureteric obstruction in Hanover Wistar rats.

MATERIAL AND METHODS

Moderately severe obstruction of the right kidney of male rats was created by burying a segment of the right ureter under the psoas fascia at 5-7 days after birth. Different fluorescent substrates for renal organic anion and cation drug transport systems were added to the IPK, and the concentration of these substances with time analysed in perfusate and urine.

RESULTS

The reproducibility in all groups of the glomerular filtration rate (GFR) and drug excretion was remarkably good. GFR was significantly lower in obstructed kidneys than in unobstructed kidneys. 123Rhodamine, a marker for organic cation and P-glycoprotein transport, had a significantly lower maximum excretion rate in the obstructed than in unobstructed kidneys. Renal fractional clearance (123rhodamine clearance corrected for diminished GFR) was also significantly lower in obstructed kidneys. There was no significant difference in maximum excretion (absolute and corrected GFR) for Lucifer Yellow, a marker for sodium-dependent organic anion transport. The maximum excretion rate of calcein, a marker for sodium-independent organic anion transport, was significantly lower in the obstructed than in the unobstructed kidneys, but significantly higher after correcting for reduced GFR.

CONCLUSION

The IPK is a good model for studying the effect of neonatal renal obstruction on tubular drug transport. These results show that organic anion and cation transport mechanisms are affected differently by obstruction.

Sulphonylurea drugs reduce hypoxic damage in the isolated perfused rat kidney

Sulphonylurea drugs have been shown to protect against hypoxic damage in isolated proximal tubules of the kidney. In the present study we investigated whether these drugs can protect against hypoxic damage in a whole kidney preparation. Tolbutamide (200 microM) and glibenclamide (10 microM) were applied to the isolated perfused rat kidney prior to changing the gassing from oxygen to nitrogen for 30 min. Hypoxic perfusions resulted in an increased fractional excretion of glucose (FE % glucose 14.3+/-1.5 for hypoxic perfusions vs 4.9+/-1.6 for normoxic perfusions, mean +/- s.e. mean, P<0.05), which could be completely restored by 200 microM tolbutamide (5.7+/-0.4 for tolbutamide vs 14.3+/-1.5 for untreated hypoxic kidneys, P<0.01). Furthermore, tolbutamide reduced the total amount of LDH excreted in the urine (220+/-100 mU for tolbutamide vs. 1220+/-160 mU for untreated hypoxic kidneys, P<0.01). Comparable results were obtained with glibenclamide (10 microM). In agreement with the effect on functional parameters, ultrastructural analysis of proximal tubules showed increased brush border preservation in tolbutamide treated kidneys compared to untreated hypoxic kidneys. We conclude that glibenclamide and tolbutamide are both able to reduce hypoxic damage to proximal tubules in the isolated perfused rat kidney when applied in the appropriate concentrations.

Pretransplantation assessment of renal viability with NADH fluorimetry

BACKGROUND

A pathophysiologic feature possibly involved in ischemic injury in transplant kidneys is mitochondrial dysfunction caused by disintegration of oxidative metabolic pathways. Because the ability to synthesize ATP by respiratory activity determines the organ's capacity to recover from ischemic injury, an assessment of respiratory activity may provide information related to graft viability.

METHODS

NADH fluorimetry can be used to monitor kidney cortex metabolism noninvasively. During perfusion with (an)-aerobic perfusate, NADH fluorescence images were recorded. We evaluated the NADH oxidation kinetics of 20 rat kidneys, which were divided over four experimental groups. For six minimally damaged kidneys and six kidneys that had been stored for one hour at 37 degrees C, perfusion was followed by transplantation. We related the kinetic parameters of these kidneys with their post-transplantation function and histology. The transplant function was monitored by serum creatinine and urea levels.

RESULTS

Storage of transplant kidneys for one hour at 37 degrees C significantly reduced the post-transplantation function. Isolated perfusion of grafts, however, was not detrimental for renal function. The rate of NADH oxidation decreased with decreasing graft quality, and a good correlation between NADH oxidation kinetics and post-transplantation function was found.

CONCLUSIONS

A reduction of NADH oxidation rates as a consequence of warm ischemia supports the view that mitochondrial respiratory activity is impaired by ischemic injury. The correlation between NADH oxidation kinetics in perfused grafts and their post-transplantation function indicates that NADH fluorimetry may be useful in predicting the viability of preserved grafts prior to transplantation.

Increase by NO synthase inhibitor of lead-induced release of N-acetyl-beta-D-glucosaminidase from perfused rat kidney

Urinary N-acetyl-beta-D-glucosaminidase (NAG) had been shown to be a useful early marker of renal injury such as lead nephrotoxicity. This study investigated the effect of lead acetate on nephrotoxicity and its correlation with the nitric oxide (NO) system by determining the NAG release in perfused rat kidney. Lead acetate caused a time and concentration-dependent increase in enzymuria. The effect of concurrent perfusion with lead and L-arginine (L-arg) or L-N(G)-nitro arginine methyl ester (L-NAME) [substrate and inhibitor of NO synthase respectively] in the perfusion fluid was also studied by measuring NAG activity in the perfusate kidney rat. L-arg (2 mM) has significantly decreased the lead-induced NAG release (P < 0.001), and L-NAME (0.1 mM) has significantly increased the lead-induced enzyme release in a time-dependent manner (P < 0.001). Moreover, histological studies using light microscope showed that some of the epithelial cells of the proximal convoluted tubules are degenerated or necrotic and desquamated into the lumens in rat treated with lead acetate. This change occurs at 50 microg/dl of lead acetate and was increased by addition of L-NAME to lead acetate. However, addition of L-arg had no effect on histology of lead nephrotoxicity. This may suggest that lead may interfere with the NO system in rat kidney.

Disposition of 4-methylbenzoylglycine in rat isolated perfused kidney and effects of hippurates on renal mitochondrial metabolism

Hippurates tend to accumulate within proximal tubule cells during renal secretion. High intracellular concentrations can alter proximal tubular function or lead to tubular toxicity. In this study we examined the renal disposition of the hippurate 4-methylbenzoylglycine, a compound known for its high renal intrinsic clearance in-vivo. The effect of intracellular accumulation on mitochondrial respiration was also measured in-vitro and compared with that of the 2-methyl and 4-amino analogues. Experiments were performed with either 2.5% pluronic or a combination of 2.2% pluronic and 2% bovine serum albumin (BSA) as oncotic agents. Within the concentration range studied (1-200 microg mL(-1)) tubular secretion seemed to be a function of the amount of unbound drug in the perfusate. Renal excretion data were best fitted by a model in which a Michaelis-Menten term was used to describe active secretion. Parameters obtained after the analysis of renal excretion data were the maximum transport velocity (TM = 55+/-2 microg min(-1)) and the Michaelis-Menten constant for tubular transport (KT = 4.2+/-0.8 microg mL(-1)). The compound accumulated extensively in kidney tissue, ratios up to 600 times the perfusate concentration were reached. Accumulation could be explained by active tubular uptake and data were analysed best by a model similar to the model used to describe renal excretion. Calculated parameters were theoretical maximum capacity (RM =300+/-210 microg g(-1)) and affinity constant for renal accumulation (KA = 5.0+/-4.4 microg mL(-1)). The high intracellular concentrations of 4-methylbenzoylglycine had no effect on kidney function and mitochondrial oxygen consumption. The 2-methyl analogue reduced mitochondrial respiration slightly, but 4-aminobenzoylglycine (p-aminohippurate) caused a significant reduction. In conclusion, this study shows that renal accumulation of a hippurate is determined by the efficiency of its tubular secretion. Whether the high intracellular concentrations affect tubular cell functioning depends on the analogue involved.

Rhodamine 123 accumulates extensively in the isolated perfused rat kidney and is secreted by the organic cation system

Rhodamine 123 has been shown to be a substrate for P-glycoprotein in multidrug resistant cells. In the present investigation the disposition of rhodamine 123 was studied in the isolated perfused rat kidney. After exposing the kidneys to perfusate concentrations ranging from 10 to 1000 ng/ml, the renal clearance was 4-1 times the clearance by glomerular filtration, respectively, indicating active and saturable secretion of rhodamine 123. The rate-limiting step in secretion was found to be membrane passage from cell to tubular lumen. Suprisingly, renal clearance was not influenced by the P-glycoprotein inhibitors cyclosporin A or digoxin. However, pretreatment of the kidneys with verapamil and quinidine (inhibitors of both P-glycoprotein and organic cation transport) or cimetidine (organic cation transport inhibitor) resulted in a significantly reduced rhodamine 123 clearance, indicating that the renal organic cation carrier may be involved in active secretion. Rhodamine 123 accumulated extensively in the isolated perfused rat kidney; tissue concentrations of 270-360 times the perfusate concentration were determined. Similar accumulation ratios at different perfusate concentrations were found, suggesting that the compound enters the tubular cells by (facilitated) diffusion. In conclusion, rhodamine 123 accumulated extensively in the isolated perfused rat kidney and active renal secretion appears to be preferentially mediated by the organic cation carrier and not by P-glycoprotein.

Glomerular filtration and saturable absorption of iohexol in the rat isolated perfused kidney

1. The renal handling of iohexol was examined in the rat isolated perfused kidney (IPK) over a perfusate concentration range of 5-20 micrograms ml-1. 2. At a concentration of 5 micrograms ml-1, a ratio of renal clearance over clearance by glomerular filtration (ClR/GF) of 0.63 +/- 0.06 could be determined. This ratio increased until 1.02 +/- 0.06 at 20 micrograms ml-1, indicating that a saturable mechanism is involved in the luminal disappearance of the drug. 3. Pretreatment of the kidneys with polylysine, probenecid or diatrizoate resulted in a significantly enhanced clearance of iohexol, probably due to inhibition of membrane binding. Renal clearance data were fitted to a kinetic model including filtration into the primary urine followed by saturable absorption at the luminal membrane. An absorption constant, KA, of 7.3 +/- 1.3 micrograms ml-1, and a maximum rate of absorption, VA,Max, of 1.4 +/- 0.1 micrograms min-1 were determined. 4. Iohexol accumulated in kidney tissue, reaching a concentration of 2 to 7.5 times the perfusate concentration. In freshly isolated proximal tubular cells and kidney cortex mitochondria, iohexol reduced the uncoupled respiratory rate at a concentration comparable to the highest tissue concentration found in the IPK. 5. In conclusion, iohexol is not only filtered by the kidney but also reabsorbed via a saturable mechanism, which results in tubular accumulation. Intracellularly sequestered iohexol may affect mitochondrial oxidative metabolism. Our results indicate that iohexol is not a true filtration marker.

Inhibition by lithium and rubidium of gentamicin-induced release of N-acetyl-beta-D-glucosaminidase from perfused rat kidney

N-acetyl-beta-D-glucosaminidase (NAG) is one of the sensitive hydrolytic lysosomal enzymes which is released after renal tubular damages. We studied gentamicin-induced nephrotoxicity by determining the NAG release in perfused rat kidney. 100 micrograms/ml of gentamicin caused a time-dependent increase in enzymuria, peaking at 90 min. At this time the released NAG is about sixfold more than the control. The effect of concurrent perfusion with 100 micrograms/ml gentamicin and with 0.5 mmol/l lithium chloride or 0.5 mmol/l rubidium chloride in the perfusion fluid was also studied by measuring NAG activity in the perfusate. Both cations decrease the gentamicin-induced NAG release. However, the inhibitory effect of lithium chloride may be due to interference of this ion with the polyphosphoinositide cycle in renal tubular lysosomal membranes. There is no obvious evidence for an inhibitory effect of rubidium chloride.

Renal excretion and accumulation kinetics of 2-methylbenzoylglycine in the isolated perfused rat kidney

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 micrograms mL-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,H) = 3.0 +/- 2.8 micrograms min-1, Michaelis-Menten constant for tubular transport for the high affinity site (KT.H) = 0.5 +/- 0.8 microgram mL-1, maximum transport velocity for the low affinity site (TM,L) = 250 +/- 36 micrograms min-1, and Michaelis-Menten constant for tubular transport for the low affinity site (KT,L) = 62 +/- 17 micrograms 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 micrograms g-1, affinity constant for renal accumulation at the high affinity site (KA,H) = 0.2 +/- 0.4 microgram mL-1, theoretical maximum capacity of the low affinity site (RM,L) = 1640 +/- 1100 micrograms g-1 and affinity constant for renal accumulation at the low affinity site (KA,L) = 60 +/- 58 micrograms mL-1. The 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.

Renal handling and effects of S(+)-ibuprofen and R(-)-ibuprofen in the rat isolated perfused kidney

1. The renal handling and effects of S(+)- and R(-)-ibuprofen have been studied in the isolated perfused kidney (IPK) of the rat. 2. Both ibuprofen enantiomers were extensively reabsorbed and accumulated in the kidney in a concentration-dependent manner. No pharmacokinetic differences were observed between the two enantiomers. 3. S(+)-ibuprofen concentrations ranging from 0.25 to 25 micrograms ml-1 (1.2 to 120 microM) caused a decrease in urinary flow, glomerular filtration rate (GFR) and electrolyte excretion. Urinary pH and excretion of glucose were not influenced. R(-)-ibuprofen concentrations ranging from 2.5 to 25 micrograms ml-1 (12 to 120 microM) also decreased urinary flow and electrolyte excretion. This decrease, however, was less than observed with S(+)-ibuprofen. GFR, urinary pH and glucose excretion were not affected by R(-)-ibuprofen. Prostaglandin E2 (PGE2) concentrations of 133 ng ml-1 reversed the effects on renal function of both enantiomers. 4. Very high S(+)- and R(-)-ibuprofen concentrations (greater than 400 micrograms ml-1) resulted in an increase in urinary flow and fractional excretion of sodium, chloride, potassium, glucose and calcium. 5. It is concluded that the pharmacokinetic behaviour of ibuprofen in the kidney is not stereoselective. Relatively high concentrations of both enantiomers increased the urinary flow and electrolyte excretion in a nonstereoselective manner. Lower concentrations of S(+)-ibuprofen decreased urinary flow and electrolyte excretion. The pharmacologically inactive R(-)-ibuprofen was also able to affect renal function in a similar way, but at different concentrations. These effects on renal function are probably caused by inhibition of PGE2 synthesis.

Renal handling and effects of salicylic acid in the isolated perfused rat kidney

The renal handling of salicylic acid (SA) and its effects on renal function were studied in the isolated perfused rat kidney (IPK). The renal handling of SA is dominated by reabsorption and only a small fraction of the filtered SA is excreted into the urine. Reabsorption is a passive process and is dependent on urinary pH. Because of the extensive reabsorption, no decrease in perfusate concentration can be observed in the course of the IPK experiment. SA accumulated slightly in the IPK and this accumulation is concentration dependent. Small amounts of SA were converted to salicyluric acid (SU), the glycine conjugate of SA. SA concentrations higher than 100 micrograms/ml caused an immediate increase in urinary flow and in fractional excretion of sodium, potassium, chloride and calcium. Fractional excretion of glucose increased gradually. Glomerular filtration rate, renal perfusion flow, renal pressure and fractional excretion of magnesium were not affected by SA. The effects were dependent on the SA concentration. Although SA is a classical non-steroidal antiinflammatory drug (NSAID), its influence on renal function appears to be different from other NSAIDs which are usually associated with a reduction in urinary flow and salt excretion.