Expression of salt and urea transporters in rat kidney during cisplatin-induced polyuria

BACKGROUND

Cisplatin (CP) induced polyuria in rats is associated with a reduction in medullary hypertonicity, normally generated by the thick ascending limb (TAL) salt transporters, and the collecting duct urea transporters (UT). To investigate the molecular basis of this abnormality, we determined the protein abundance of major salt and UT isoforms in rat kidney during CP-induced polyuria.

METHODS

Male Sprague-Dawley rats received either a single injection of CP (5 mg/kg, N = 6) or saline (N = 6) intraperitoneally five days before sacrifice. Urine, blood, and kidneys were collected and analyzed.

RESULTS

CP-treated rats developed polyuric acute renal failure as assessed by increased blood urea nitrogen (BUN), urine volume and decreased urine osmolality. Western analysis of kidney homogenates revealed a marked reduction in band density of the bumetanide-sensitive Na-K-2Cl cotransporter in cortex (60% of control values, P < 0.05), but not in outer medulla (OM) (106% of control values). There were no differences in band densities for the renal outer medullary potassium channel (ROMK), the type III Na-H exchanger (NHE3), the alpha-subunit of Na,K-ATPase in the OM; or for UT-A1, UT-A2 or UT-A4 in outer or inner medulla. However, the band pattern of UT-A2 and UT-A4 proteins in the OM of CP-treated rats was different from the control rats, suggesting a qualitative modification of these proteins.

CONCLUSIONS

Changes in the abundance of outer or inner medullary salt or urea transporters are unlikely to play a role in the CP-induced reduction in medullary hypertonicity. However, qualitative changes in UT proteins may affect their functionality and thus may have a role.

Expression of renal aquaporins 1, 2, and 3 in a rat model of cisplatin-induced polyuria

BACKGROUND

Cisplatin (CP)-induced polyuria in rats is attributed to decreased medullary hypertonicity and/or an end-organ resistance to vasopressin. However, the roles of renal aquaporins (AQPs) have not yet been explored.

METHODS

Male Sprague-Dawley rats (230 to 245 g) received either a single injection of CP (5 mg/kg, N = 4) or saline (N = 4) intraperitoneally five days before sacrifice. Urine, blood, and kidney samples were analyzed.

RESULTS

Platinum accumulated in the cortex and outer medulla of CP-treated rats (39.05 +/- 7.50 and 36.48 +/- 12.44 microg/g vs. 2.52 +/- 0.43 and 1.87 +/- 0.84 microg/g dry tissue in controls, respectively). Histologically, tubular damage and decreased AQP1 immunolabeling were detected in the S3 segment of proximal tubules. CP treatment caused 4.4- and 4.8-fold increases, respectively, in blood urea nitrogen and urine volume, and a 4. 4-fold decrease in urine osmolality. Immunoblots showed that AQP2 and AQP3 were significantly reduced to 33 +/- 10% (P < 0.001) and 69 +/- 11% (P < 0.05), respectively, in the inner medulla of CP-treated rats. Immunocytochemical analysis showed a decrease in AQP2 labeling in the inner medulla of CP-treated rats. Northern hybridization revealed a 33 +/- 11% (P < 0.002) decrease in AQP2 mRNA expression in the inner medulla of CP-treated rats. AQP1 protein expression levels were modestly (67 +/- 7%, P = 0.057) and significantly (53 +/- 13%, P < 0.007) decreased in outer and inner medullae, respectively, of CP-treated rats.

CONCLUSIONS

CP-induced polyuria in rats is associated with a significant decrease in the expression of collecting duct (AQP2 and AQP3) and proximal nephron and microvascular (AQP1) water channels in the inner medulla.

Normalization of hyperglycaemia by oral vanadyl sulfate does not reverse diabetes-induced protection against cisplatin nephrotoxicity in streptozotocin-diabetic rats

Streptozotocin- and galactose-induced diabetic rats are protected against nephrotoxic effects of cisplatin. While the mechanism remains to be defined, protection is associated with a decrease in the accumulation of platinum in renal cortical tissues of streptozotocin-diabetic versus non-diabetic rats. A physiological abnormality common to streptozotocin and galactosemic models of diabetes is hyperglycaemia, suggesting that elevated sugars are involved in mediating protection of diabetic kidney against cisplatin nephrotoxicity. The current study focused on the effect of normalization of hyperglycaemia by vanadyl sulfate trihydrate on the initiation of protection and accumulation of platinum in kidneys of streptozotocin-diabetic rats. Streptozotocin-diabetic rats were treated with 0.75 mg/ml of vanadyl sulfate trihydrate in drinking water to normalize streptozotocin-induced hyperglycaemia. Vanadyl sulfate treatment normalized plasma glucose and glycosylated haemoglobin levels in streptozotocin-diabetic rats to values observed for non-diabetic rats. Intraperitoneal administration of cisplatin (5 mg/kg body weight) increased blood urea nitrogen by a factor >2.5 over baseline in both untreated and vanadyl-treated non-diabetic groups. Cisplatin-induced increases in blood urea nitrogen were 1.6 times baseline in both untreated and vanadyl-treated streptozotocin-diabetic rats. Renal platinum accumulation was significantly lower in streptozotocin-diabetic versus non-diabetic rats regardless of vanadyl sulfate treatment. Renal vanadium levels in all groups of diabetic rats were not significantly different from each other. These results indicate that normalization of plasma glucose levels with vanadyl sulfate in streptozotocin-diabetic rats did not reverse protection of streptozotocin-diabetic kidney against cisplatin nephrotoxicity.

High performance liquid chromatographic assay of amprolium and ethopabate in chicken feed using solid-phase extraction

A method for the assay of mixtures of amprolium and ethopabate in chicken feed was developed utilizing reversed-phase high-performance liquid chromatography (HPLC) after sample clean-up of a methanolic extract by solid-phase extraction using CN cartridges. HPLC was done with benzocaine as internal standard on a C-8 column with methanol-water 40:60, containing octanesulfonic acid, triethylamine and acetic acid, as mobile phase. Eluate was monitored at 274 nm. Baseline separation was achieved with retention times of approximately 7.5, 9.4, and 10.4 min, for amprolium, benzocaine, and ethopabate respectively. Feed constituents did not give peaks after 6.5 min. Peak area ratios were linear over 10-180 ng of amprolium, and 2-18 ng of ethopabate injected. Limits of quantitation at AUFS 0.05 were 0.5 and 0.3 ng respectively. Recovery studies from spiked feed (n = 9), covering +/- 30% of usual doses in feed, gave percent recoveries (+/- SD) of 99.4 +/- 1.4% for amprolium and 100.5 +/- 2.6% for ethopabate. Applying the method to two different batches of commercial feed gave results which were comparable to those obtained by the AOAC spectrofluorometric methods.

Effect of route of administration and dose on diabetes-induced protection against cisplatin nephrotoxicity

The kidneys of diabetic rats exhibit resistance to the actions of a variety of nephrotoxic chemicals. Using the streptozotocin (STZ) diabetic rat as a model, the experiments in this study examined the effect of the diabetic state on bioavailability, renal accumulation and renal toxicity following intraperitoneal (i.p.) and intravenous (i.v.) injection of cisplatin at various doses. Comparison of the areas under the plasma concentration versus time curves up to 220 min after cisplatin injection (5 mg/kg body wt) demonstrated that bioavailability of cisplatin was significantly impaired in STZ diabetic versus nondiabetic rats after the i.p. route of administration, but not after the i.v. route. Regardless of the route of cisplatin injection, both renal cortex platinum level and renal toxicity as quantified by blood urea nitrogen (BUN) increase, were significantly lower in STZ diabetic versus nondiabetic rats. Thus, while decreased bioavailability probably plays a role in the protection seen after i.p. injection, renal mechanisms must also be involved since protection was also noted after i.v. injection despite equal bioavailability. To determine whether the protection can be overcome by increasing the dose of cisplatin, renal platinum and BUN levels in STZ diabetics and nondiabetics were compared after i.p. and i.v. cisplatin injections at 2.5, 5, 7.5, and 10 mg/kg body wt. The results demonstrate that the diabetes-induced renal protection can be partially reversed by increased cisplatin dose, but only by the i.v. route. Reversal was accompanied by increased renal platinum accumulation. These results suggest that STZ diabetes alters the tubular cells in a manner that confers protection that more closely resembles tolerance than absolute inherent resistance to the nephrotoxic actions of cisplatin.

Toxicity and excretion of cisplatin in the avian kidney

Cisplatin is a widely applied antineoplastic drug with significant nephrotoxic potential. The purpose of this study was to define the toxic effect and excretion of cisplatin in the chicken, a species widely applied to the study of tubular transport mechanisms but little used for toxicology studies. Toxicity was assessed by the relative effect of cisplatin on renal clearances of the standard reference substrates inulin and p-aminohippurate (PAH) and by morphologic assessment of the kidneys of cisplatin-treated chickens. The data clearly support close similarities in the pattern of tubular cell damage produced in the chicken versus that reported for rats and human patients. It was further demonstrated that administration of an organic cation reduced Pt accumulation in the kidney and mitigated the toxicity as has been reported for rats. Excretion studies were carried out during unilateral renal portal infusion of cisplatin, and the results indicated that cisplatin does not undergo net tubular secretion as occurs in the rat and human. It can be concluded that, while the pattern of cisplatin-induced nephrotoxicity closely parallels that seen in mammals, the avian kidney exhibits a different pattern of urinary Pt excretion than does the mammalian kidney after cisplatin administration.

Reduced renal accumulation and toxicity of cisplatin in experimental galactosemia

The kidneys of streptozotocin (STZ)-diabetic rats are resistant to certain toxic effects of the antineoplastic drug cisplatin. The mechanism is unknown. This study used the galactosemic rat model to test the hypothesis that the apparent diabetes-induced protection is due to changes in the kidney secondary to chronically elevated hexose concentrations. Galactosemic rats are normoinsulinemic and are free from many of the multiple biochemical abnormalities seen in STZ diabetics. The experiments compared renal cortical platinum (Pt) and blood urea nitrogen (BUN) levels after intraperitoneal injection of 5 mg/kg of cisplatin in galactosemic, STZ-diabetic, and age-matched nondiabetic Sprague-Dawley rats. Nephrotoxicity was defined as a BUN concentration ratio (after to before cisplatin) > 2.5. The results demonstrate that the kidneys of both galactosemic and STZ-diabetic rats became resistant to cisplatin-induced elevation of BUN and, further, that the development of the protection was related to the duration of the diabetic state. Although the protective effect developed more slowly in the galactosemic rats, the attenuation of the rise in BUN was ultimately comparable to that seen in STZ diabetics. Renal cortex [Pt] after cisplatin injection was significantly lower in galactosemics and STZ diabetics compared with age-matched nondiabetics, with the order nondiabetics > galactosemics > STZ diabetics. It was noted, however, that renal Pt accumulation was maximally depressed within 4 weeks of experimental diabetes, whereas the BUN ratio continued to decline with increasing duration of both galactosemia and STZ diabetes. Thus, reduced renal Pt accumulation cannot by itself explain the progressive attenuation of the toxicity. The results support the hypothesis and suggest that the galactosemic rat will be a useful model for mechanistic study of diabetes-induced protection from cisplatin nephrotoxicity.

Synthesis and renal excretion of technetium-99m-labeled organic cations

Organic cations are excreted more efficiently than organic anions in uremia suggesting superiority as renal imaging agents. In this study, three 99mTc-labeled cationic cyclam complexes were synthesized and their renal clearance quantified in rats. The complexes are cleared at a rate of about 2.5-3 times that of inulin and about 60% that of p-amino-hipurate. Inhibition of 99Tc-cyclam excretion by quinine indicates transport by the organic cation process. Comparative in vivo imaging experiments demonstrated that in normal rats 99mTc-cyclam reached peak renal activity 1.8 +/- 0.6 min after injection, a value intermediate between that for [131I]OIH (1.0 +/- 0) and 99mTc-MAG3 (2.8 +/- 0.6). In rats injected with the acute nephrotoxin cisplatin, the times to peak were lengthened with the relative order being 99mTc-cyclam > 99mTc-MAG3 > [131I]OIH. The results demonstrate that cationic complexes may be useful for renal imaging diagnostic applications.

Renal metallothionein and platinum levels in diabetic and nondiabetic rats injected with cisplatin

This study was designed to investigate the relationship between the attenuation of cisplatin-induced nephrotoxicity in experimental diabetes and the increased level of renal metallothionein (MT) reported to occur in this condition. Two groups of male Sprague-Dawley rats were used: 42-day streptozotocin diabetics and age-matched nondiabetics. Half of each group was injected with a nephrotoxic dose of cisplatin (5 mg/kg, ip) and half with vehicle. Four hours after injection, renal MT and platinum (Pt) content were quantified. Mean renal MT concentration in vehicle-injected diabetics was about triple that found in nondiabetics. Comparison of renal MT concentrations in cisplatin-injected diabetics and nondiabetics with their vehicle-injected counterparts suggested an inducing effect of the drug. In contrast to the marked elevations of MT in diabetic kidney, mean renal Pt concentration in the cisplatin-injected diabetic group was only about one-fourth that of the nondiabetic group. No difference was evident in the intracellular distribution Pt between cytosolic and particulate fractions from diabetic and nondiabetic kidneys. It was concluded that: (i) Sequestration of Pt by MT cannot account for the resistance of diabetic kidney to cisplatin toxicity. (ii) Rather, the resistance is due to a significant decrease in renal uptake/retention of cisplatin or derivatives during the critical first few hours after injection.

Concentrative uptake of digoxin by slices of chicken renal cortex

The purpose of this investigation was to define, under controlled in vitro conditions, the processes contributing to the uptake and accumulation of [3H]digoxin by incubated slices of chicken renal cortex. Progressive uptake was evident in time-course experiments with the slice-to-medium concentration ratio (S/M) reaching 5.25 after 120 min. No metabolism was evident. Increasing the ratio of unlabeled to labeled digoxin resulted in a concentration-dependent decrease in relative uptake of the label, suggesting saturability. Incubation under conditions of metabolic inhibition reduced digoxin S/M by about 50%, indicating that both energy-requiring and passive mechanisms contribute to the overall accumulation process. The structural nature of the uptake process was explored by incubating digoxin in the presence of potential inhibitors of transport. The organic cation quinine and the non-glycosidic steroids digoxigenin and spironolactone were without effect even at greater than 1000-fold excess compared to digoxin. Similarly, the sugar digitoxose had no inhibitory activity on digoxin accumulation by the slices. On the other hand, the glycosides digitoxin, digoxigenin-bis-digitoxoside and digoxigenin-mono-digitoxoside inhibited dogoxin uptake in a concentration-dependent manner. These results indicate a structural preference for an intact glycoside rather than for either the steroidal or sugar portion of the molecule alone. An inhibitory effect of ouabain and a stimulatory effect of reduced medium potassium concentration suggest a possible role for Na+,K(+)-ATPase in the uptake of digoxin by the renal cortex.

Accumulation of aluminum by rabbit renal cortex

Aluminum is a ubiquitous metal with significant toxic potential for humans. It is eliminated principally by the kidney, however the mechanisms involved remain obscure. The purpose of this study was to define and quantify the uptake process for aluminum by incubated slices of rabbit kidney cortex. Time-course experiments demonstrated that aluminum uptake was progressive and substantial, with a slice-to-medium ratio (S/M) exceeding 20 after four hours of incubation of slices in the presence of 0.01 mM aluminum (as the lactate). Concentration-dependent uptake studies suggested that the process was of limited capacity with maximal tissue uptake of approximately 24 micrograms/gm wet wt. Incubation of slices with aluminum in the presence of metabolic inhibitors (NaCN, 2,4-DNP) demonstrated that about 20-35% of the uptake could be attributed to an energy-dependent component. The calcium channel blockers verapamil, diltiazem and lanthanum decreased S/M aluminum by 65-73% compared to control, suggesting that a calcium dependent process plays a role in aluminum accumulation in renal cortex. Aluminum was not acutely toxic to the renal tubular cells even at a medium concentration of 1.0 mM.

Animal model for theophylline--cimetidine drug interaction

Cimetidine (300 mg I.V.) and theophylline (15 mg/kg I.V.) were studied in Beagle dogs for possible drug interaction. The drugs were administered alone and in combination using a crossover design. Although none of the determined pharmacokinetic parameters for theophylline changed significantly in the presence of cimetidine, a trend towards significance was found for the terminal half-life, area under the curve, and mean residence time. The magnitude in changes found in Beagles is representative of the changes reported in man.

Uptake of trimethoprim by renal cortex

The purpose of this study was to examine the mechanisms involved in the uptake of the urinary antibacterial drug trimethoprim by incubated slices of rat renal cortex. Concentration-dependent studies of the uptake process demonstrated that a saturable component was involved. The results of inhibitor studies as well as the time-course pattern support the conclusion that at least two processes are involved in the uptake of trimethoprim. These include active transport via the organic cation system, accounting for about 40% of the total uptake, and a second component that continues to operate under conditions of inhibited cellular metabolism. Chromatographic examination of post-incubation bathing medium and slice extracts failed to demonstrate renal cortex metabolism of trimethoprim.

Accumulation of cimetidine by kidney cortex slices

The mechanisms involved in the excretion of the histamine H2-receptor antagonist cimetidine are as yet incompletely understood. The purpose of this study was to examine the interaction of cimetidine with incubated slices of dog kidney cortex. The results of time and concentration-dependent experiments by using 3H-labeled cimetidine demonstrated that the drug was accumulated without metabolism against a concentration gradient by a saturable process. Inhibition of uptake by cyanide and by incubation under a nitrogen atmosphere indicated energy dependence. Uptake of cimetidine by active cationic transport was likely inasmuch as both cyanine 863 and quinine blocked accumulation. However, a probenecid-sensitive component, accounting for about 20% of steady-state accumulation, also was identified. The lack of inhibitory action of p-aminohippuric acid and the cationic nature of the cimetidine molecule suggest the probenecid-sensitivity was not related to the renal organic anion mechanism. Further, probenecid inhibition was not due to a generalized cellular toxicity because maximally inhibitory concentrations of probenecid did not interfere with uptake of the cation tetraethylammonium.

Effect of co-trimoxazole and sulfamethoxazole on serum creatinine in normal subjects

Significant elevation of serum creatinine concentration and reduction in creatinine clearance have been reported following cotrimoxazole therapy in patients with normal and impaired renal function. Both components of co-trimoxazole, trimethoprim and sulfamethoxazole, have been proposed as the causative agent. Ten healthy male volunteers were treated for seven days with either sulfamethoxazole (5 subjects) or co-trimoxazole (5 subjects) in the usual recommended doses. After a one-week recovery period, the subjects were allocated to the alternate treatment regimen for another seven days. Cotrimoxazole caused a mean elevation in the serum creatinine concentration of 0.12 mg/dl over the base-line value (p less than 0.05). Sulfamethoxazole produced an insignificant fall in the serum creatinine level. The increase in the serum creatinine concentration induced by co-trimoxazole was reversed seven days after discontinuation of the drug. From this study, it can be concluded that either trimethoprim alone or an interaction between trimethoprim and sulfamethoxazole is responsible for the increase in serum creatinine observed following co-trimoxazole therapy and that sulfamethoxazole alone is not the causative agent.

Comparative accumulation of uric acid and hypoxanthine by slices of avian renal cortex

The purpose of the study was to compare the concentrative uptake processes of the 14C-labeled purines uric acid (UA) and hypoxanthine (HX) by slices of chicken renal cortex. It was found that both purines were accumulated by the slices and that, while UA was unaltered metabolically, HX was partially oxidized to UA during the incubation. Inhibition of the oxidation of HX to UA by use of the enzyme inhibitor allopurinol did not alter accumulation indicating that metabolism of HX did not drive accumulation. UA accumulation was eliminated by the presence of low concentrations of the organic anion transport inhibitors probenecid and 4-acetamido-4'-isothiocyano-stilbene-2,2'-disulfonic acid. However, HX accumulation was unaffected by probenecid and significantly decreased by 4-acetamido-4'-isothiocyano-stilbene-2,2'-disulfonic acid only at concentrations considerably in excess of those needed to eliminate UA accumulation. The lack of effect of probenecid is in contrast to its reported inhibitory action on HX excretion by the chicken in vivo, a difference which may reflect lack of luminal transport by in vitro slices. Neither was HX accumulation sensitive to the presence of high concentrations of the organic cations quinine and tetraethylammonium. Despite the insensitivity of the HX accumulation process to organic anions or cations, the process was blocked by cyanide and an N2 atmosphere indicating energy dependence. The results suggest that both UA and HX are accumulated by separable transport processes indicating that the renal tubules possess more than one system capable of contributing to purine excretion.

Quantification of renal uric acid synthesis in the rat

The excretion of nephrogenic uric acid in the urine of Sprague-Dawley rats was estimated by use of the isotope-dilution technique. In nonfasted rats the urine-to-plasma specific activity ratio (SAR) of [14C]uric acid was 0.93, suggesting that a minimum of 7% of the uric acid excreted in the urine is synthesized in the kidney. During hypoxanthine infusion the SAR decreased in a dose-related fashion, indicating that the rat kidney is capable of synthesizing relatively large amounts of uric acid and that circulating precursor levels may in part regulate the renal synthesis of uric acid. During allopurinol infusion the SAR increased to 1.0, demonstrating that the SAR is a valid indicator of the contribution of nephrogenic uric acid excreted into the urine. Results of perfusion studies in isolated rat kidneys suggest that uric acid is the major end product of purine catabolism in the rat kidney and that some uric acid formed in the kidney may be absorbed directly into the circulation.

The excretion of coumarin and hydroxycoumarins by the avian kidney in vivo

The mechanics involved in the renal excretion of C14-labeled coumarin (C), 7-hydroxycoumarin (7HC) and 4-hydroxycoumarin (4HC) were studied in unanesthetized chickens by use of the Sperber technique. Analysis of urine collected during unilateral portal infusion of C, 4HC or 7HC indicated that the chicken excreted these coumarins almost entirely in conjugated form. Both 7HC and 4HC appeared in the urine only as the corresponding glucuronide. During C infusion, 84% of excreted radioactivity was identified as 7HC-glucuronide with only 8% appearing as a conjugate of open-ring metabolite o-hydroxyphenylacetic acid (HPAA). This demonstrated that, unlike other commonly-used laboratory animals, the chicken excretes C in a manner similar to man and suggests that this species is the most appropriate model for C pharmacodynamic studies applicable to humans. Comparative analysis of urines from the infused and control side kidneys indicated that neither C or 4HC undergoes net tubular secretion. In contrast 7HC was excreted by an active process which was significantly inhibited by simultaneous probenecid infusion. In addition it was demonstrated that the renal tubule cells conjugate 7HC as it crosses from blood to lumen suggesting that the kidney may contribute to the metabolism of C.

The metabolism and active excretion of the hypoxanthine by the renal tubules in the chicken

Infusion of [14C]hypoxanthine into one renal portal circulation of the chicken resulted in an excess of [14C]uric acid excreted into the urine from the infused side kidney. No [14C]hypoxanthine appeared in the urine from either kidney. When the renal metabolism of [14C]hypoxanthine was inhibited by xanthine dehydrogenase inhibitors, almost no excess 14C-label appeared in the urine of the infused side suggesting that formation of nephrogenic urate plays an important role in the tubular excretion of hypoxanthine. A comparison of the effects of inhibitors on the renal excretion of preformed urate and nephrogenic urate suggests the existence of a p-aminohippurate-independent transport step for purines at the luminal membrane of the renal tubular cell. Studies with transport inhibitors suggest that the active transport step is anionic in character.