Potential involvement of renal transport mechanisms in nephrotoxicity

Drug-induced acute kidney injury

PURPOSE OF REVIEW

The purpose of this review is to describe the most prevalent mechanisms of drug-induced acute kidney injury, to define the risk factors for nephrotoxicity, and to analyze the available evidence for preventive measures.

RECENT FINDINGS

Drug toxicity remains an important cause of acute kidney injury that, in many circumstances, can be prevented or at least minimized by vigilance and early intervention. Recent studies have resulted in increased insight into the subcellular mechanisms of drug nephrotoxicity. Further improvement is to be expected from the identification of early markers of nephrotoxicity and an increasing involvement of a clinical pharmacist.

SUMMARY

The main mechanisms of nephrotoxicity are vasoconstriction, altered intraglomerular hemodynamics, tubular cell toxicity, interstitial nephritis, crystal deposition, thrombotic microangiopathy, and osmotic nephrosis. Before prescribing a potentially nephrotoxic drug, the risk-to-benefit ratio and the availability of alternative drugs should be considered. Modifiable risk factors should be corrected. The correct drug dosage should be prescribed. Patients should be pre-hydrated and the glomerular filtration rate should be frequently monitored during the administration of a potentially nephrotoxic drug. Studies are needed to further elucidate the mechanisms of nephrotoxicity to design more-rational prevention and treatment strategies. Computer-based prescriber-order entry and an appropriately trained intensive care unit pharmacist are particularly helpful to minimize medication errors and adverse drug events.

Acute renal failure in experimental envenomation with Africanized bee venom

Human victims of multiple bee or wasp stings have been reported and develop severe clinical signs and symptoms. Acute renal failure (ARF), usually due to acute tubular necrosis (ATN) was a frequent complication. The pathogenetic mechanisms of ATN occurring in these accidents are still unclear. In the present study, female Wistar rats weighing 150-200 g were injected intravenously with Africanized bee venom at a dose of 0.4 microL/100 g body weight, and the kidney was observed under light and transmission electron microscopy and in immunohistochemical studies. The animals were divided into two groups: an Early group studied 3 to 8 hours after inoculation, and a Late group studied 24 to 30 hours after inoculation. The animals showed ATN mainly in the cortex and outer medulla with cast formation. After 24 hours, frequent mitotic figures were found in the tubular epithelium. Immunohistochemical studies revealed the presence of myoglobin and muscle actin in the tubular casts. Under electron microscopy, proximal tubule segments showed increasing intracytoplasmic vacuoles and attenuation of the brush border and of the basolateral infolding. This segment and the thick ascending limb of Henle's loop showed hydropic degeneration. Dead cells with apoptosis or necrosis due to cellular disintegration resulted in tubular basement membrane denudation. In the Late group, figures of intracytoplasmic myelin could be observed, some of them containing mitochondrial fragments. These changes are likely to be due to interactive effects of venom components, mainly mellitin and enzymes such as phospholipases, both acting on biological membranes. The ATN found was probably due to multiple causes, mainly a direct action of the venom on tubular cells, myoglobinuria, and perhaps ischemic mechanisms.

Renal handling of drugs and amino acids after impairment of kidney or liver function--influences of maturity and protective treatment

Renal tubular cells are involved both in secretion and in reabsorption processes within the kidney. Normally, most xenobiotics are secreted into the urine at the basolateral membrane of the tubular cell, whereas amino acids are reabsorbed quantitatively at the luminal side. Under different pathological or experimental circumstances, these transport steps may be changed, e.g., they may be reduced by renal impairment (reduction of kidney mass, renal ischemia, administration of nephrotoxins) or they may be enhanced after stimulation of transport carriers. Furthermore, a distinct interrelationship exists between excretory functions of the kidney and the liver. That means liver injury can influence renal transport systems also (hepato-renal syndrome). In this review, the following aspects were included: based upon general information concerning different transport pathways for xenobiotics and amino acids within kidney cells and upon a brief characterization of methods for testing impairment of kidney function, the maturation of renal transport and its stimulation are described. Similarities and differences between the postnatal development of kidney function and the increase of renal transport capacity after suitable stimulatory treatment by, for example, various hormones or xenobiotics are reviewed. Especially, renal transport in acute renal failure is described for individuals of different ages. Depending upon the maturity of kidney function, age differences in susceptibility to kidney injury occur: if energy-requiring processes are involved in the transport of the respective substance, then adults, in general, are more susceptible to renal failure than young individuals, because in immature organisms, anaerobic energy production predominates within the kidney. On the other hand, adult animals can better compensate for the loss of renal tissue (partial nephrectomy). With respect to stimulation of renal transport capacity after repeated pretreatment with suitable substances, age differences also exist: most stimulatory schedules are more effective in young, developing individuals than in mature animals. Therefore, the consequences of the stimulation of renal transport can be different in animals of different ages and are discussed in detail. Furthermore, the extent of stimulation is different for the transporters located at the basolateral and at the luminal membranes: obviously the tubular secretion at the contraluminal membrane can be stimulated more effectively than reabsorption processes at the luminal side.

Glutathione status, lipid peroxidation and kidney function in streptozotocin diabetic rats

In adult female rats diabetic nephropathy was induced by i.v. administration of streptozotocin (6 mg/100 g b.w.). The animals survive for 3 weeks when very low daily doses of insulin (0.3 IU/animal) are administered. High blood urea concentrations and distinct proteinuria indicate the impairment of kidney function in streptozotocin diabetic rats. Streptozotocin induces mild polyuria and increased renal excretion of potassium; there is also an increase in renal excretion of administered p-aminohippurate. Three weeks after administration of streptozotocin the formation of lipid peroxides is increased in the kidney. At this time glutathione content (GSH, GSSG) is unchanged in liver and kidney of streptozotocin diabetic rats. Impairment of kidney function in streptozotocin diabetic rats can be prevented by daily supplementation with sufficient doses of insulin (about 3 IU/animal).

Acute renal toxicity of thiabendazole (TBZ) in ICR mice

The acute toxic effects of thiabendazole [2-(4'-thiazolyl)benzimidazole; TBZ] on the kidneys of ICR mice were investigated. The mice were given 0, 250, 500 or 1000 mg TBZ/kg body weight by gavage (using olive oil as a vehicle), and the kidneys were subjected to pathological examination at 1, 3, 5 or 24 hr after dosing. Gross findings were slight enlargement and the presence of whitish areas (white maculae) in kidneys of treated mice at 3, 5 or 24 hr after dosing. Histological findings were desquamation of degenerated cells in proximal tubules of treated mice at 1 hr. Dilation of proximal, distal and collecting tubules was apparent in treated mice at 3, 5 and 24 hr. TBZ-induced renal injury was reduced by pretreatment with inducers of the microsomal monooxygenase system (sodium phenobarbital, beta-naphthoflavone and 3-methylcholanthrene) and were enhanced by pretreatment with inhibitors of that system (2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride and piperonyl butoxide). The concentration of TBZ in blood at 1 or 5 hr after dosing was lower in mice pretreated with microsomal monooxygenase system inducers and was higher in those pretreated with the inhibitors, than in those given TBZ alone. These results suggest that TBZ-induced renal injury may be attributable to the parent compound rather than its metabolites. Measurement of organic ion uptake into renal slices revealed significant depression of [1-14C]tetraethylammonium bromide (TEA) uptake in treated mice at 1 or 5 hr, whereas uptake of p-[glycyl-2-3H]aminohippurate (PAH) was not depressed at 1 or 5 hr after dosing. The reduction in uptake of TEA is interpreted as the result of competitive suppression of the tubular transport of TEA by TBZ. TBZ-induced renal injury was reduced by organic cation transport inhibitors [N'-methylnicotinamide (NMN) or thiamine] but not by organic anion transport inhibitor [p-(dipropylsulphamyl)benzoic acid probenecid], suggesting that the reduction of TBZ-induced renal injury is the result of competitive suppression of the tubular transport of TBZ by NMN or thiamine.

Effects of reserpine and L-cysteine and glutathione depletion on 2-bromoethylamine hydrobromide-induced tubular necrosis in Swiss ICR mice

Female Swiss ICR mice were injected ip with 100 or 300 mg 2-bromoethylamine hydrobromide (BEA)/kg body weight. Male Swiss ICR mice were subjected to water deprivation, or treated with 5% dextrose in water, dimethylsulphoxide, piperonyl butoxide, SKF-525A, sodium phenobarbital, beta-naphthoflavone, probenecid, reserpine, diethyl maleate, buthionine sulphoximine or L-cysteine. Urine collected sequentially from male Swiss ICR mice given 300 mg BEA/kg body weight was analysed for glucose, protein, pH and specific gravity. Female mice were less sensitive to BEA than were male mice. Diuresis, antidiuresis, treatment with cytochrome P-450 inducers and inhibitors, and the antioxidant dimethyl-sulphoxide had no effect on the incidence or severity of tubular necrosis (TN) induced by BEA. Probenecid and L-cysteine decreased the severity, but they had no effect on the incidence of TN. Glutathione depletion by diethyl maleate and inhibition of glutathione synthesis by buthionine sulphoximine decreased the dose of BEA necessary to cause TN; buthionine sulphoximine was more effective than diethyl maleate. Reserpine decreased both the incidence and severity of TN. Glycosuria, aciduria and decreased urinary specific gravity occurred before morphological changes were seen under the microscope, indicating that the functional changes precede the morphological changes. These data indicate that glutathione is important in protecting against BEA-induced TN, that BEA or a metabolite is concentrated in the tubule epithelium by way of anion transport, and that vasoconstriction contributes to the development of BEA-induced TN.

Environmentally related diseases of the urinary tract

Nephrotoxicity from exposure to therapeutic agents and chemicals in the environment and workplace results in a broad spectrum of clinical renal disease that may mimic disorders from other causes. Nephrotoxic agents may, in fact, be responsible for some fraction of renal disease of undetermined etiology. Specific diagnosis and treatment by removal from exposure to the toxic agent is more likely in the early phase of the disorder. Measurement and characterization of proteinuria provides the most sensitive and reliable method of early detection. Increased urinary excretion of serum proteins with molecular weight in excess of 50,000, such as albumin and transferrin, is an early indicator of glomerular injury. Low-molecular-weight proteinuria (beta 2-microglobulin or retinol-binding protein) and enzymuria, particularly excretion of NAG, are sensitive indicators of renal tubular cell injury. Tests that reflect hypersensitivity reactions are often indicative of immunologically mediated nephrotoxicity but are not specific for the kidney. Cancers of the kidney and urinary bladder appear to be increasing and are most common among the socially active and affluent. Susceptibility of the urinary tract to toxicity and carcinogenicity reflect contact of excreted toxins with the epithelial cells of nephrons and urinary bladder.

Renal proximal tubular cells in suspension or in primary culture as in vitro models to study nephrotoxicity

The kidney forms a frequent target for xenobiotic toxicity. The complex biochemical mechanisms underlying nephrotoxicity are best studied in vitro provided that reliable and relevant in vitro models are available. Since most nephrotoxicants affect primarily the cells of the proximal tubules (PTC), much effort has been directed towards the development of in vitro models of PTC. This review focuses on the preparation of PTC and the use of these cells. Discussed are important criteria such as the viability (survival time) of the cells and the parameters to assess toxicity. Recent studies have shown that isolated PTC in suspension are especially suitable for studies on the biochemical mechanisms of 'acute' nephrotoxicity, whereas PTC in primary culture may be used to investigate mechanisms of nephrotoxic damage at very low concentrations, upon prolonged exposure. PTC cultured on porous filter membranes provide new possibilities to study toxicity in relation to cell and transport polarity. Primary cell cultures of human PTC have been set up. Although a further characterization of these systems is needed, recent data indicate their usefulness.