Citrinin produces acute adverse changes in renal function and ultrastructure in pentobarbital-anesthetized dogs without concomitant reductions in [potassium]plasma.

Citrinin's nephrotoxicity was examined in pentobarbital-anesthetized dogs under conditions that minimized or avoided significant changes in a number of its actions that could indirectly and adversely affect renal function and ultrastructure, such as, (i) major acute reductions in blood pressure and renal blood flow and, (ii) emesis and diarrhea that could lead to dehydration and electrolyte imbalances, especially hypokalemia. Slow intravenous injection of 20 mumol citrinin/kg to pentobarbital-anesthetized dogs did not induce any alterations in renal tissue ultrastructure or in any of the 23 whole blood, plasma or renal function parameters that were monitored over a 6-h post-citrinin period. On the other hand, 80 mumol citrinin/kg produced significant increases in the hematocrit and in the renal excretion rates of protein and glucose; modest reductions were noted in CIN, RBF and excretion rate of inorganic phosphorus. In addition, 80 mumol citrinin/kg induced ultrastructural lesions in the cells of the S2 proximal tubular segment, the thick ascending limb, the distal convoluted tubule and the collecting ducts. The glomeruli, S1 and S3 cells of the proximal tubule and the thin descending and ascending limbs of Henle's loop were unaffected by both citrinin doses. The location and nature of the adverse ultrastructural lesions were most likely the result of the direct actions of citrinin (or a citrinin metabolite) since the effects of citrinin that could lead to indirect adverse renal effects were totally avoided or greatly minimized.

4-Maleimidohippuric acid--a tailor-made, direct, site-specific nephrotoxin: effects on renal function and ultrastructure in pentobarbital-anesthetized dogs.

A model has been proposed to explain at least one of the possible pathways through which a xenobiotic might produce proximal tubule necrosis. The model is formulated on the idea that a compound must possess two structural features: (i) a carboxyl or amino acid moiety that would allow for selective uptake into proximal tubule cells via the strategically located antiluminal membrane-bound organic anion transport system or the luminal membrane-bound amino acid transport system(s), respectively, and (ii) a highly reactive moiety that can directly alkylate proximal tubular components, or a moiety that can be biotransformed within proximal tubular cells to such a substance. In an attempt to validate the proposed structural features as prerequisites for xenobiotic induction of proximal tubular necrosis, a novel compound, 4-maleimidohippuric acid (4-MHA), was synthesized which possesses an anionic group and a reactive moiety. Following the administration of 4-MHA directly into the renal artery of pentobarbital-anesthetized dogs, specific unilateral ultrastructural damage was noted only in the S1 and S2 cell types of the proximal tubule; the most notable renal function changes included proteinuria and glucosuria. Anionic, but non-alkylating, relatives of 4-MHA failed to alter renal function or ultrastructure. The specific proximal tubular toxicity of 4-MHA validates the proposed structural requirements for induction of proximal tubular necrosis.

S-(1,2-dichlorovinyl)-3-mercaptopropionic acid effects on renal function and ultrastructure in pentobarbital-anesthetized dogs: site-specific toxicity and evidence for its toxification via the pathway responsible for beta-oxidation of fatty acids.

S-(1,2-dichlorovinyl)-3-mercaptopropionic acid (DCV-3-MPA) was equally nephrotoxic to spontaneously-respiring and mechanically-ventilated, pentobarbital-anesthetized dogs. Its nephrotoxicity was expressed as dose-dependent changes in key renal function parameters, in proximal tubular S1, S2 and S3 cellular architecture and in the ability of the kidneys to respond maximally to ethacrynic acid, an efficacious loop diuretic. The nephrotoxicity associated with DCV-3-MPA was not the result of extrarenal actions such as hypoxemia and subsequent renal tissue hypoxia because mechanical ventilation was not protective. Four lines of evidence suggested that DCV-3-MPA was taken-up by renal proximal tubular cells like a fatty acid and metabolized by the mitochondrial beta-oxidation pathway to a reactive nephrotoxic intermediate: (i) probenecid pretreatment, which reduces the renal uptake of many organic anions but fails to do so with anions of fatty acids, failed to modify the nephrotoxicity of DCV-3-MPA; (ii) the next higher and lower homologues of DCV-3-MPA (i.e., S-(1,2-dichlorovinyl)-4-mercaptobutanoic acid (DCV-4-MBA) and S-(1,2-dichlorovinyl)-mercaptoacetic acid (DCV-MAA)) cannot yield the same reactive intermediate as DCV-3-MPA upon beta-oxidation and neither was nephrotoxic; (iii) DCV-MAA was found in plasma and urine following administration of DCV-4-MBA and (iv) the renal mitochondria were reproducibly damaged by DCV-3-MPA whereas the peroxisomes, which are also capable of performing beta-oxidation of certain fatty acids, were unscathed.

Extrarenal and direct renal actions of atractyloside contribute to its acute nephrotoxicity in pentobarbital-anesthetized dogs.

Acute extrarenal and renal changes were noted following the intravenous administration of atractyloside (ATR) (12.97 and 32.40 mumol/kg) to spontaneously-respiring, pentobarbital-anesthetized dogs. Severe hypoglycemia, respiratory depression and hypoxemia developed within 2 h. These extrarenal changes were accompanied by adverse changes in renal function, ultrastructural damage to S1, S2 and S3 cells of the proximal tubule and to thick ascending limb cells and an impaired ability of the kidneys to respond to a known diuretic--ethacrynic acid (EA). Mechanical ventilation of ATR-treated pentobarbital-anesthetized dogs circumvented the development of hypoxemia and all but eliminated the toxicity to S3 and thick ascending limb cells, thereby establishing that ATR's extrarenal actions contributed to its nephrotoxicity. On the other hand, direct renal actions of ATR were evident following its administration into the renal artery; certain important extrarenal effects were minimized, while adverse changes in renal function and ultrastructure of S1 and S2 cells were noted primarily in the ipsilateral kidney. The high degree of variability associated with ATR's systemic toxicity was confirmed and a similar degree of variability in its renal toxicity was established. Our results emphasize the importance of evaluating the extrarenal effects produced by any toxicant when determining its nephrotoxic potential.

Acute effects of a gamma-glutamylated derivative of S-(1,2-dichlorovinyl)-L-cysteine on renal function and ultrastructure in pentobarbital-anesthetized dogs: site-specific toxicity involving S1 and S2 cells of the proximal tubule.

It has been established that L-gamma-glutamylated derivatives of alpha-amino acids are delivered more efficiently to the kidneys than are the parent alpha-amino acids. Therefore, we synthesized L-gamma-glutamyl-S-(1,2-dichlorovinyl)-L-cysteine (L-gamma-glutamyl-L-DCVC), the simplest L-gamma-glutamylated derivative of the nephrotoxic alpha-amino acid S-(1,2-dichlorovinyl)-L-cysteine (L-DCVC), and investigated its effects on renal function and ultrastructure in pentobarbital-anesthetized dogs. Intravenous doses of 23.15 and 92.60 mumol of L-gamma-glutamyl-L-DCVC/kg of body weight induced significant increases in urinary protein output and significant decreases in the clearance of inulin during the 6-hour post-injection period. Changes were not observed in any of the other 13 renal function variables or in the 11 plasma and blood variables that were monitored throughout the same period. Both doses of L-gamma-glutamyl-L-DCVC induced renal ultrastructural lesions in the S1 and S2 cells of the canine proximal tubule; the remaining 8 cell types downstream and the glomeruli were not damaged. The onset and magnitude of renal function changes and the cell types affected by L-gamma-glutamyl-L-DCVC were virtually identical to those observed previously following IV administration of equivalent doses of L-DCVC to pentobarbital-anesthetized dogs. Rapid removal of the L-gamma-glutamyl group from L-gamma-glutamyl-L-DCVC (ie, deglutamylation) resulting in formation of the parent alpha-amino acid, L-DCVC, can best explain the extreme similarity in the nephrotoxic profiles of these 2 toxicants.

Acute effects of carboxyatractyloside and stevioside, inhibitors of mitochondrial ADP/ATP translocation, on renal function and ultrastructure in pentobarbital-anesthetized dogs.

To assess the direct renal toxicity of carboxyatractyloside (CATR), it was administered in relatively low intravenous (i.v.) doses (6.5 and 13.0 mumol/kg) to pentobarbital-anesthetized dogs that were being mechanically ventilated in order to circumvent severe extrarenal effects, such as hypoxemia, that could contribute to its nephrotoxicity. Within 2 h post-CATR, site-specific renal damage was noted in S2 and S3 cells of the proximal tubules; characteristic lesions in both cell types included loss of brush border, condensation of mitochondria and proliferation of small vesicles. Other S2 cells exhibited intense staining and reduced cell height. In 3 of 14 CATR-treated dogs, extrarenal effects were of sufficient magnitude to induce cellular swelling and occlusion of tubular lumina in S3 and thick ascending limb segments. Stevioside (STEV), related to CATR in structure and actions on the mitochondrial ADP/ATP translocase, was totally devoid of acute extrarenal or direct renal effects during the 6-h period following intravenous administration of 2.5 times the higher dose of CATR. The ability of CATR to produce renal toxicity via its renal and extrarenal actions emphasizes the importance of minimizing the latter actions of any toxicant when attempting to ascertain the mechanism by which it adversely affects renal function and ultrastructure.

The acute effects of S-(1,2-dichlorovinyl)-L-cysteine and related chemicals on renal function and ultrastructure in the pentobarbital-anesthetized dog: structure-activity relationships, biotransformation, and unique site-specific nephrotoxicity.

S-(1,2-Dichlorovinyl)-L-cysteine (L-DCVC), a substrate for the renal cysteine conjugate beta-lyase, and other related chemicals were administered intravenously to pentobarbital-anesthetized dogs. Six pertinent findings emerged regarding their nephrotoxicity. (1) L-DCVC was acutely nephrotoxic in the dog. (2) The earliest indicator of L-DCVC-induced renal damage was an increase in the urinary excretion rate of protein. (3) Contrary to results from other species, L-DCVC induced renal ultrastructural lesions only in the S1 and S2 cells of the proximal tubule. (4) The toxicity of L-DCVC (23.15 mumol/kg, iv) to S1 and S2 cells resulted from a direct tubular insult and not from overlapping episodes of hypoxia or ischemia. (5) L-DCVC could be detected in plasma only during the first 30 min after its injection. In addition, no L-DCVC and only small amounts of N-acetyl-L-DCVC and S-(1,2-dichlorovinyl)mercaptoacetic acid (DCV-MAA) (1.5% and less than 1% of the administered dose, respectively) were detectable in urine during the 6 hr following L-DCVC administration. (6) DCV-MAA and chloroacetic acid as well as other compounds that are not substrates for the renal cysteine conjugate beta-lyase (i.e., S-allyl-L-cysteine, vinthionine, and S-(1,2-dichlorovinyl)-D,L-alpha-methylcysteine) were not acutely nephrotoxic. These findings provide indirect evidence for the involvement of beta-lyase in the toxification of L-DCVC in the dog.

Acute effects of the D-isomer of S-(1,2-dichlorovinyl)cysteine on renal function and ultrastructure in the pentobarbital-anesthetized dog: site-specific toxicity involving the S1 and S2 cells of the proximal tubule.

Intravenous doses of 92.6 and 185.2 mumol S-(1,2-dichlorovinyl)-D-cysteine (D-DCVC)/kg were acutely nephrotoxic in pentobarbital-anesthetized dogs. During the 6-h period following administration of either dose, renal arterial blood flow decreased modestly, urinary excretion rate of protein increased, and in contrast to findings in rabbits, ultrastructural lesions developed only in S1 and S2 cells of proximal tubules. The higher dose also induced significant increases in urine flow rate and urinary excretion rate of glucose. The adverse changes noted following the low dose of D-DCVC were due to its direct renal actions and not to extrarenal actions such as major changes in blood gases, total renal blood flow or mean arterial blood pressure that could have indirectly contributed to renal damage via induction of episodes of renal ischemia or hypoxia. In addition, there was a correlation between the proximal tubular cell types injured by D-DCVC and the location of D-amino acid oxidase (DAAO) in the canine nephron. Overall, the nephrotoxicity of D-DCVC was characterized by the same renal function and ultrastructure changes as noted previously with L-DCVC, but the D-isomer was slightly less potent. Our data suggested that the similarity in the toxicity of D- and L-DCVC might be related to DAAO-catalyzed conversion of D-DCVC to the corresponding alpha-ketoacid (DCV-O-MPA) and subsequent biotransformation of the latter to the same highly reactive fragment as generated from the L-isomer.

The pentobarbital anesthetized dog: an animal model for assessing chemically induced changes in renal function and ultrastructure.

An experimental procedure was devised using the pentobarbital-anesthetized dog that could be used for the comprehensive evaluation of the renal effects of chemicals. After IV or renal arterial administration of 0.9% saline solution (vehicle), 12 renal function determinants were continuously monitored for periods of 2 and 6 hours. At the completion of the 2 or 6 hours of study, the kidneys of a number of dogs (usually between 1 and 7) in each vehicle-treated group were subjected to a modification of the intravascular perfusion-of-fixative technique to evaluate the ultrastructural status of the outer cortical, inner cortical, and outer medullary tissue. The remaining dogs (at least 3) in each vehicle-treated group were given a nonnephrotoxic, but maximally effective, diuretic dose of ethacrynic acid, which enabled an assessment of the functional integrity of the thick ascending limb of Henle's loop. Renal function and glomerular and tubular ultrastructure remained stable in the pentobarbital-anesthetized dog for up to 6 hours after administration of vehicle. Sustained infusion of inulin (included in the procedure to estimate glomerular filtration rate) throughout the duration of the experiments, and pentobarbital anesthesia of various durations did not alter the morphologic status of the canine nephron. The procedure used for the renal perfusion of fixative circumvented any manipulation of the kidneys before fixation and allowed for the acquisition of normal (unaltered) appearing tissue from all areas of the kidneys. The responses of pentobarbital-anesthetized dogs to ethacrynic acid administration were similar when given 2 and 6 hours after the vehicle administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute effects of alkylating agents on canine renal function and ultrastructure: high-dose ethacrynic acid vs. dihydroethacrynic acid and ticrynafen.

Ethacrynic acid (EA) is unique among diuretics in that it is both an avid alkylating agent and is actively secreted by renal proximal tubular cells. EA might therefore be expected to produce detrimental proximal tubular changes at elevated doses. Because of this possibility, we examined the renal effects of two relatively high doses of EA (i.e., 66 and 151 mumol/kg i.v.) and an equivalent high dose (i.e., 151 mumol/kg) of two nonalkylating relatives of EA [dihydro-EA (EA-H2) and ticrynafen]. Twelve renal function parameters were monitored in pentobarbital-anesthetized dogs for a period of 2 hr after administration of EA, EA-H2 and ticrynafen and renal tissue was acquired at the end of the 2 hr of study for light and electron microscopic evaluation. Both doses of EA produced a profound diuresis of similar magnitude. However, only the larger dose was associated with a concomitant reduction in the glomerular filtration rate, a downward trend in the renal blood flow, a proteinuric response in four of the seven dogs in the treatment group and a reproducible vacuolation of the initial portion of the proximal convoluted tubules (i.e., the S1 cells). EA-H2 induced a small, transient increase in the excretion rates of sodium, chloride and potassium, but failed to elicit a proteinuric response or alter proximal tubular ultrastructure. Ticrynafen, a far more efficacious diuretic agent than EA-H2, likewise failed to trigger a proteinuric response or changes in renal ultrastructure. The combination of acidic (anionic) and alkylating properties of EA is thought to be responsible for the proximal tubular effects observed in this study.

Acute effects of alkylating agents on canine renal function: specifically designed synthetic maleimides.

Maleimidohippurates and maleimidobenzoates were synthesized that possess a carboxy group for active uptake into renal proximal tubular cells and a reactive maleimide moiety to covalently bond with proximal tubular components. The reactivity of the maleimide moiety in each series was progressively reduced by substitution of methyl groups in place of the vinyl hydrogens. In contrast to N-ethylmaleimide (NEM), the resulting maleimidohippurates and maleimidobenzoates did not possess significant diuretic activity in the dog following renal arterial administration. However, as predicted, the nephrotoxicity of the maleimidohippurates paralleled their in vitro alkylating ability and was quite specifically located in the proximal portion of the canine renal tubule.

Acute effects of alkylating agents on canine renal function: N-ethylmaleimide and some of its potential biotransformation products.

Changes in urine flow rate, glomerular filtration rate and sodium, potassium and chloride excretion rates were monitored after the i.v. and renal arterial administration of N-ethylmaleimide (NEM) to dogs. Intravenous administration of NEM (72.9 and 117 mumol/kg) failed to induce an increase in any of the parameters mentioned. Renal arterial injection of 36.5 mumol/kg of NEM appeared to be nephrotoxic, whereas doses of 8.00 and 0.80 mumol/kg were associated with rapid and sustained increases in urine flow rate and the excretion rates of sodium, potassium and chloride. No changes in renal function were noted when the renal arterial dose of NEM was reduced to 0.08 mumol/kg. Three potential biotransformation products of NEM [i.e., N-ethylmaleamic acid; the cysteine adduct of NEM (NEM-cysteine); and the glutathione adduct of NEM (NEM-glutathione)] failed to induce an increase in any of the functional parameters studied regardless of the route of administration. We conclude that NEM is diuretic in the dog, but only after injection directly into the renal artery. The observed diuresis appears to be: 1) induced by NEM itself rather than by one of its potential biotransformation products, 2) due to its relatively irreversible alkylating property and 3) either a manifestation of the renal toxicity elicited by this agent or an independent effect that simply occurs at doses similar to those that induce renal injury.

Acute effects of alkylating agents on canine renal function. 1. [4-(2-Bromoalkanoyl)phenoxy]acetic acids.

A group of [4-(2-bromoalkanoyl)phenoxy]acetic acids was studied to determine if there was an association between the alkylating ability and the diuretic activity of its members. Acute studies in dogs revealed that there is not a consistent correlation in the alkylating potential of these alpha-bromo ketones and their ability to induce a diuretic response. In addition, pretreatment of dogs with the various alpha-bromo ketones did not alter the diuretic activity normally observed with ethacrynic acid (EA). The role of chemical-induced renal tissue alkylation in the initiation of a diuresis or a nephrotoxic response is discussed.

Diuretic activity of Mannich base derivatives of ethacrynic acid and certain ethacrynic acid analogues.

Various Mannich base derivatives of selected phenoxyacetic acid type diuretics were synthesized and their diuretic potency was evaluated in dogs. It is concluded that the Mannich bases possess little, if any, diuretic activity of their own. Those Mannich bases that do possess diuretic activity undoubtedly do so as a consequence of an elimination reaction (a retro-Michael type reaction) which yields the corresponding pharmacologically active alpha,beta-unsaturated ketone.

Thiol adducts of ethacrynic acid: a correlation of the rate of liberation of ethacrynic acid with the onset and magnitude of the diuretic response.

It is thought that a derivative of ethacrynic acid (EA) must possess an intact alpha, beta-unsaturated ketone group in order to be capable of eliciting a diuretic response. The 2,3-dimercapto-1-propanol and the cysteine adducts of ethacrynic acid lack such a functional group and still have diuretic activity, especially the cysteine adduct. An in vitro study showed that various thiol adducts of EA liberate EA and the accompanying thiol at a rate that is primarily dependent on the nature of the functional groups present in the thiol portion of the adduct. When the thiol adducts of EA were injected into dogs, the cysteine and mercaptoethylamine hydrochloride adducts which rapidly release EA under specific in vitro conditions were as effective as EA in producing a diuretic response. The onset of action was also similar to that of EA. The thiosalicylic acid adduct of EA releases the accompanying thiol at an intermediate rate in vitro and was less effective than EA in a small dose (3.3 mumol/kg) and the peak response to it was slower to develop. Other adducts that release EA and the accompanying thiol slowly in vitro either produce a very weak response which takes considerable time to develop or are completely devoid of diuretic activity. Thus, the onset and magnitude of the diuretic response produced by various thiol adducts of EA (with the possible exception of the cysteine adduct) are governed primarily by the rate of in vivo release of EA.