Aspirin damage in the rat kidney in the intact animal and after unilateral nephrectomy

Mitochondrial glutathione in toxicology and disease of the kidneys

The tripeptide glutathione (GSH), comprised of the amino acids l-cysteine, glycine, and l-glutamate, is found in all cells of aerobic organisms and plays numerous, critical roles as an antioxidant and nucleophile in regulating cellular homeostasis and drug metabolism. GSH is synthesized exclusively in the cytoplasm of most cells by two ATP-dependent reactions. Despite this compartmentation, GSH is found in other subcellular compartments, including mitochondria. As the GSH molecule has a net negative charge at physiological pH, it cannot cross cellular membranes by diffusion. Rather, GSH is a substrate for a variety of anion and amino acid transporters. Two organic anion carriers in the inner membrane of renal mitochondria, the dicarboxylate carrier (DIC; Slc25a10) and the 2-oxoglutarate carrier (OGC; Slc25a11), are responsible for most of the transport of GSH from cytoplasm into mitochondrial matrix. Genetic manipulation of DIC and/or OGC expression in renal cell lines demonstrated the ability to produce sustained increases in mitochondrial GSH content, which then protected these cells from cytotoxicity due to several oxidants and mitochondrial toxicants. Several diseases and pathological states are associated with mitochondrial dysfunction and oxidative stress, suggesting that the mitochondrial GSH pool may be a therapeutic target. One such disease that is of particular concern for public health is diabetic nephropathy. Another chronic, pathological state that is associated with bioenergetic and redox changes is compensatory renal hypertrophy that results from reductions in functional renal mass. This review summarizes pathways of mitochondrial GSH transport and discusses studies on its manipulation in toxicological and pathological states.

Influence of renal compensatory hypertrophy on mitochondrial energetics and redox status

A reduction in functional renal mass is common in numerous renal diseases and aging. The remaining functional renal tissue undergoes compensatory growth primarily due to hypertrophy. This is associated with a series of physiological, morphological and biochemical changes similar to those observed after uninephrectomy. Previous work showed that compensatory renal cellular hypertrophy resulted in an increase in susceptibility to several drugs and environmental chemicals and appeared to be associated with oxidative stress. Compensatory renal cellular hypertrophy was also associated with increases in mitochondrial metabolic activity, uptake of glutathione (GSH) across renal plasma and mitochondrial inner membranes, and intracellular GSH concentrations. Based on these observations, we hypothesize that the morphological, physiological and biochemical changes in the hypertrophied kidney are associated with marked alterations in renal cellular energetics, redox status and renal function in vivo. In this study, we used a uninephrectomized (NPX) rat model to induce compensatory renal growth. Our results show alterations in renal physiological parameters consistent with modest renal injury, altered renal cellular energetics, upregulation of certain renal plasma membrane transporters, including some that have been observed to transport GSH, and evidence of increased oxidative stress in mitochondria from the remnant kidney of NPX rats. These studies provide additional insight into the molecular changes that occur in compensatory renal hypertrophy and should help in the development of novel therapeutic approaches for patients with reduced renal mass.

Origin and types of calcium oxalate monohydrate papillary renal calculi

OBJECTIVES

Subepithelial hydroxyapatite calcification of renal papilla is thought to be involved in the formation of calcium oxalate monohydrate (COM) papillary calculi. To assess the mechanism of formation, we sought to correlate the fine structure of papillary renal calculi with specific pathophysiologic conditions and urinary alterations.

METHODS

The study included 831 COM papillary renal calculi with established fine inner structures. A total of 24 patients with chronic stone formation were randomly selected, and their urine was collected and analyzed. The case history and lifestyle habits of these patients were obtained.

RESULTS

The 831 papillary calculi could be classified into 1 of 4 main groups. Type I included small calculi in which COM columnar crystals begin to develop in the concave zone in close contact with papillary tissue. Type II calculi contained a hydroxyapatite core located in or near the concave zone. Type III consisted of calculi that developed on the tip of the papillae and in the concave zone, containing hydroxyapatite, calcified tissue, and calcified tubules. Type IV consisted of papillary calculi in which the core, which is situated near, but not in, the concave zone, is formed by intergrown COM crystals and organic matter. Many factors, including urinary alterations (eg, hyperoxaluria), associated diseases (eg, hypertension, diabetes), and consumption or exposure to cytotoxic substances (eg, analgesic abuse) were associated with these types of calculi.

CONCLUSIONS

Our findings have indicated that injury is the first cause of papillary COM calculus formation, with the location of the injury determining the morphology of the resulting calculus.

Functional and toxicological characteristics of isolated renal mitochondria: impact of compensatory renal growth

Mitochondria were isolated from renal cortical homogenates from control rats and rats that had undergone uninephrectomy and compensatory renal growth (NPX rats). Activities of selected mitochondrial processes, including key enzymes of intermediary metabolism, glutathione-dependent enzymes, and glutathione transport, were measured, and the effects of three mitochondrial toxicants were assessed to test the hypothesis that compensatory renal growth is accompanied by increases in mitochondrial metabolism and that this is associated with increased susceptibility to injury from oxidants or other mitochondrial toxicants. Activities of malic and succinic dehydrogenases were significantly higher in mitochondria from NPX rats than in mitochondria from control rats. Although the rates of state 3 respiration were significantly higher in mitochondria from NPX rats, the rates of state 4 respiration and respiratory control ratios were not different between mitochondria from control and NPX rats. Activities of glutathione redox cycle enzymes did not differ significantly between mitochondria from control and NPX rats. However, the rates of uptake of glutathione into mitochondria were approximately 2.5-fold higher in tissue from NPX rats than in tissue from control rats. Incubation of mitochondria from NPX rats with three mitochondrial toxicants [tert-butyl hydroperoxide, methyl vinyl ketone, and S-(1,2-dichlorovinyl)-L-cysteine] caused greater inhibition of state 3 respiration and larger increases in malondialdehyde formation than similar incubations of mitochondria from control rats. These results indicate that mitochondria from hypertrophied renal cells are more sensitive to oxidants or mitochondrial toxicants. Baseline levels of malondialdehyde were also significantly higher in mitochondria from NPX rats, suggesting that a basal oxidant stress exists in mitochondria from hypertrophied cells.

Renal papillary necrosis--40 years on

Analgesics and nonsteroidal anti-inflammatory drugs (NSAIDs) are well recognized as a major class of therapeutic agent that causes renal papillary necrosis (RPN). Over the last decade a broad spectrum of other therapeutic agents and many chemicals have also been reported that have the potential to cause this lesion in animals and man. There is consensus that RPN is the primary lesion that can progress to cortical degeneration; and it is only at this stage that the lesion is easily diagnosed. In the absence of sensitive and selective noninvasive biomarkers of RPN there is still no clear indication of which compound, under what circumstances, has the greatest potential to cause this lesion in man. Attempts to mimic RPN in rodents using analgesics and NSAIDs have not provided robust models of the lesion. Thus, much of the research has concentrated on those compounds that cause an acute or subacute RPN as the basis by which to study the pathogenesis of the lesion. Based on the mechanistic understanding gleaned from these model compounds it has been possible to transpose an understanding of the underlying processes to the analgesics and NSAIDs. The mechanism of RPN is still controversial. There are data that support microvascular changes and local ischemic injury as the underlying cause. Alternatively, several model papillotoxins, some analgesics, and NSAIDs target selectively for the medullary interstitial cells, which is the earliest reported aberration, after which there are a series of degenerative processes affecting other renal cell types. Many papillotoxins have the potential to undergo prostaglandin hydroperoxidase-mediated metabolic activation, specifically in the renal medullary interstitial cells. These reactive intermediates, in the presence of large quantities of polyunsaturated lipid droplets, result in localized and selective injury of the medullary interstitial cells. These highly differentiated cells do not repair, and it is generally accepted that continuing insult to these cells will result in their progressive erosion. The loss of these cells is thought to be central to the degenerative cascade that affects the cortex. There is still a need to understand better the primary mechanism and the secondary consequences of RPN so that the risk of chemical agents in use and novel molecules can be fully assessed.

Normal ultrastructure of the kidney and lower urinary tract

The mammalian urinary tract includes the kidneys, ureters, urinary bladder, and urethra. The renal parenchyma is composed of the glomeruli and a heterogeneous array of tubule segments that are specialized in both function and structure and are arranged in a specific spatial distribution. The ultrastructure of the glomeruli and renal tubule epithelia have been well characterized and the relationship between the cellular structure and the function of the various components of the kidney have been the subject of intense study by many investigators. The lower urinary tract, the ureters, urinary bladder, and urethra, which are histologically similar throughout, are composed of a mucosal layer lined by transitional epithelium, a tunica muscularis, and a tunica serosa or adventitia. The present manuscript reviews the normal ultrastructural morphology of the kidney and the lower urinary tract. The normal ultrastructure is illustrated using transmission electron microscopy of normal rat kidney and urinary bladder preserved by in vivo perfusion with glutaraldehyde fixative and processed in epoxy resin.

Early ultrastructural lesions of diphenylamine-induced renal papillary necrosis in Syrian hamsters

The ultrastructural lesions of diphenylamine-induced renal papillary necrosis in Syrian hamsters were characterized by transmission electron microscopy. Twenty-four male Syrian hamsters were orally administered 600 mg diphenylamine/kg body weight as a single dose. At 30 minutes and at 1, 2, 4, 8, 16 and 24 hours after administration of diphenylamine, three hamsters were anesthetized with pentobarbital, perfused via the left ventricle with half-strength KARNOVSKY's fixative, and the renal papilla and outer medulla collected. Three hamsters administered 0.5 ml peanut oil/kg body weight (vehicle controls) were anesthetized at 24 hours, perfused, and the renal papilla and outer medulla collected. Initial ultrastructural lesions were observed in the endothelial cells of the ascending vasa recta in the proximal portion of the renal papilla at 1 hour after diphenylamine administration. The endothelial cell basal plasma membrane was elevated from the basal lamina, forming large subendothelial vacuoles. Alterations in inner medullary interstitial cells, endothelial cells of the descending vasa recta, and the epithelial cells of the thin limbs of Henle and the medullary collecting tubules were observed subsequent to the lesion in the ascending vasa recta. It was concluded that the endothelial cell of the ascending vasa recta is the target cell in diphenylamine-induced renal papillary necrosis in Syrian hamsters.

Renal metallothionein metabolism after a reduction of renal mass. I. Effect of unilateral nephrectomy and compensatory renal growth on basal and metal-induced renal metallothionein metabolism

The effects of unilateral nephrectomy and compensatory renal growth on renal metallothionein metabolism were evaluated in the present study. In rats, the renal content of metallothionein increased in proportion to the increase in renal mass after unilateral nephrectomy and compensatory renal growth. However, when zinc was used to induce the synthesis of renal metallothionein, the remnant kidney in uninephrectomized (NPX) rats produced significantly greater amounts of metallothionein on a per gram kidney basis than a normal kidney in sham-operated (SO) rats. In both NPX and SO rats, zinc pretreatment caused metallothionein synthesis to increase primarily in the renal cortex and renal outer stripe of the outer medulla. Zinc pretreatment also changed the pattern for the intrarenal accumulation of inorganic mercury in NPX rats. After pretreatment with zinc, the accumulation of inorganic mercury predominated in the renal cortex rather than in the outer stripe of the outer medulla in the NPX rats. In addition, both NPX and SO rats were afforded complete protection against the nephrotoxic effects of a low, toxic dose of inorganic mercury when they were pretreated with inorganic zinc. The protection is postulated to be related to the alteration in the pattern of renal accumulation of inorganic mercury. In conclusion, the capacity to synthesize metallothionein increases significantly in rats after they have undergone unilateral nephrectomy and compensatory renal growth. The increased capacity of the remnant kidney to synthesize metallothionein may involve adaptive changes both in transcriptional and/or translational controls of metallothionein synthesis.

The role of apoptosis in the development of renal cortical tubular atrophy associated with healed experimental renal papillary necrosis

An animal model of chronic analgesic nephropathy, in which renal papillary necrosis was induced by the administration of a single injection of bromoethylamine 2-hydrobromide in male Sprague-Dawley rats, was used to investigate the pathogenesis of the atrophy of tubules that leads to cortical atrophy or 'scarring' in analgesic nephropathy. One of the major objectives was documentation of the participation of apoptosis, a distinctive mode of cell death, in the process of cortical tubular atrophy. Control and treated groups of animals were studied at 2 wks, and at subsequent monthly intervals up to 4 mths. At each time, light microscopy and ultrastructure were used to relate changes in cellular pathology to alterations in renal mass. Apoptosis was quantitated in paraffin sections, and autoradiographic identification of cells showing tritiated thymidine uptake was used as an indication of cell proliferation. In animals with total renal papillary necrosis (RPN), focal or diffuse cortical atrophy developed, the extent of which appeared to be proportional to the extent of the RPN. Renal mass was reduced only in those kidneys that developed extensive, diffuse lesions. Compensatory renal growth occurred in the areas of healthy tissue adjacent to the foci of atrophy, with both cellular hyperplasia and hypertrophy playing roles in its development. One of the prominent cellular events was the appearance of apoptotic cells and bodies, with invading intraepithelial macrophages involved in their phagocytosis and degradation. We propose that this form of cell death plays an important role in the pathogenesis of cortical atrophy. Current descriptions of the cortical lesions that occur in analgesic nephropathy refer to the changes as 'scars'. Although the focal lesions have a macroscopic appearance that resembles scars, the results of the present study indicate that usage of this terminology may be misleading, since scarring is often described after severe tissue injury or necrosis, which was not identified in the present study.

Renal and urinary lipid changes associated with an acutely induced renal papillary necrosis in rats

A single dose of 2-bromoethanamine hydrobromide (BEA; 100 mg/kg body weight) given ip to male Wistar rats causes an acute renal papillary necrosis in 24 hr. Oil Red O (ORO) lipid staining is normally confined to the polyunsaturated lipid droplets of the medullary interstitial cells, but ORO-positive material was present in the endothelial cells of the vasa recta 7 hr after BEA treatment. At 24 hr (by which time papillary necrosis had developed), there were also markedly increased quantities of lipid in the cells of the collecting ducts and covering epithelia. At 48 hr totally necrosed areas stained heavily with ORO, and lipid deposits were particularly numerous in the hyperplastic urothelia adjacent to the necrosed region. Epithelial and endothelial accumulation of lipid material also extended into areas of the juxtamedulla and cortex, which appeared normal by routine haematoxylin and eosin staining. Lipid staining is more selective and sensitive for identifying papillary necrosis than routine histology, because neither hexachlorobutadiene-, aminoglycoside-, cis-platin- nor polybrene-induced lesions produce similar histochemical changes. This suggests that the capillary and epithelial deposits of lipid material are pathognomonic for the development of renal papillary necrosis. An increase in urinary triglycerides following BEA treatment supports the biochemical basis of these ORO changes as a neutral lipid accumulation.

Syntheses, antiinflammatory, and analgesic activities of arylbiurets

A number of arylbiurets were prepared and evaluated as antiinflammatory and analgesic agents by using the carrageenan paw edema and acetic acid stretching tests. Among them, the antiinflammatory activity of 1,3-dimethyl-5-phenylbiuret (7), 1-ethyl-3-methyl-5-phenylbiuret (11), and 1,1,3-trimethyl-5-phenylbiuret (13) were found to be more potent than phenylbutazone. The analgesic activity of 7 and of 5-(4-chlorophenyl)-1,1,3-trimethylphenylbiuret (16) is higher than that of aminopyrine.

High resolution light microscopic morphological and microvascular changes in an acutely induced renal papillary necrosis

Morphological changes were followed in semi-thin glycolmethacrylate sections, after treating male Wistar rats with a single ip dose of 2-bromoethanamine (BEA) hydrobromide (100 mg/kg) to induce renal papillary necrosis. Medullary interstitial cells had irregular nuclei at 4 hr and focal necrosis by 8 hr which spread from the papilla tip to the cortico-medullary junction from 12 hr. Increased mucopolysaccharide staining was observed in the papilla tip at 4 hr, and was lost from those regions where necrosis had developed by 48 hr. Endothelial platelet adhesion, first seen at 8 hr, was very marked at 18 hr, but affected capillaries in necrotic regions only, up to 144 hr. The absence of extravasated Monastral Blue B demonstrated the integrity of the medullary microvascular endothelia. The distal nephron showed degenerative changes at 12 hr and cell exfoliation at 18 hr. Cortical changes were confined to PAS-positive casts in the collecting duct and loop of Henle from 8 hr and dilatation of distal and proximal tubules at 8 and 72 hr, respectively. There was active repair at the junction between viable and necrotic tissue in the papilla from 24 hr with mitoses in the collecting ducts and loops of Henle. Normally the urothelium is less than 3-4 cells thick, but upper urothelial proliferation followed BEA administration. Hyperplasia was especially marked at the mouth of the ureter and in the pelvis opposite the region of necrosis (7-8 cells thick at 18 hr) and had only partially resolved by 144 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Enzyme histochemical changes in an acutely induced renal papillary necrosis

Enzyme histochemistry was assessed in semi-thin glycolmethacrylate sections after 100 mg/kg 2-bromoethanamine (BEA) hydrobromide had been given ip to male Wistar rats to induce renal papillary necrosis. Changes in the proximal tubular marker enzymes alkaline phosphatase (Alk Phos), gamma-glutamytranspeptidase (GGT) and adenosine triphosphatase (ATPase) were not apparent before 8 hr, but there was a progressive loss up to 144 hr. The proteinaceous PAS-positive casts in the loops of Henle and the collecting ducts stained for Alk Phos and GGT (from 12 hr) and for ATPase (from 18 hr). Acid phosphatase (Acid Phos) staining was increased in the proximal tubule lysosomes from 18 hr. There was a marked increase in Alk Phos in all hyperplastic upper urothelial cells from 8 to 24 hr, and a mosaic of staining remained in the pelvis adjacent to the necrosed papilla at 144 hr. At 12 hr, there was an increase in the staining of the pelvic, ureter and bladder vascular endothelial ATPase, the intensity and area of which increased progressively from 18 hr and almost occluded the capillary lumens in the worst affected areas by 144 hr. These data show several distinct series of pathological changes after the administration of BEA. The subtle degenerative changes in the proximal tubule followed the papillary lesion, but exfoliated brush border and proximal tubular cells were important components of the protein casts in the distal nephron. Similarly, the intense Alk Phos staining in the hyperplastic regions of the upper urothelium and the increased pelvic, ureteric and bladder endothelial ATPase staining suggested they develop as a consequence of the papillary lesion.

Detection of chemically induced renal injury: the cascade of degenerative morphological and functional changes that follow the primary nephrotoxic insult and evaluation of these changes by in-vitro methods

A diversity of chemicals cause discrete lesions in the kidney by a number of different mechanisms, and similar types of chemicals may give rise to more than one target cell injury. Screening for these lesions in vivo may be unreliable if a single noninvasive or invasive criterion is used. Instead, evidence of nephrotoxicity must be based on an array of tests, applied over a period of time. These should include biochemical, pathological and histochemical tests conducted in tandem. A primary toxic injury to the kidney may give rise to recovery, to permanently altered functional reserve or to a clinically identifiable effect, such as acute or chronic renal failure or malignancy. These clinical effects occur as a result of a cascade of degenerative changes which are a consequence of a primary lesion but also affect other parts of the kidney. A number of factors can modulate the progression of the primary insult to the end-effect. In-vitro nephrotoxicity screening is also difficult, but a rational approach can be based on current understanding of how chemicals target for and damage cells in anatomically well-defined regions of the kidney. In-vitro techniques can provide answers to specific questions about the mechanisms by which chemicals damage these discrete cell types. It is essential that a number of different in-vitro systems be developed in parallel to address the mechanistic aspects and screening of nephrotoxicity properly. Data generated in vitro must be related to the situation in vivo and used to devise reliable noninvasive tests for assessing nephrotoxicity in man.

Nephrotoxicity of uranyl fluoride in uninephrectomized and sham-operated rats

The aim of the present study was to determine whether the nephrotoxicity of the uranium-containing compound uranyl fluoride (UO2F2) is enhanced after unilateral nephrectomy. Unilaterally nephrectomized (NPX) and sham-operated (SO) rats were given single intravenous injections of UO2F2 at doses delivering 100 or 250 micrograms U/kg 16 days after surgery. Between the second and third day after the administration of either dose of UO2F2, the urinary excretion of the cellular enzymes lactate dehydrogenase (LDH) and aspartate aminotransferase (AST) and the plasma solute albumin began to increase significantly in both the NPX and SO rats. The urinary excretion of the plasma solute glucose did not begin to increase significantly in the NPX and SO rats until 4 days after the administration of either dose of UO2F2. During the fifth day following the administration of either dose of UO2F2 (which was also the last day that urinary data were collected) the urinary excretion of LDH, AST, and glucose in the NPX and SO rats was greater than that during any previous day. The urinary excretion of these three compounds during this fifth day was greater in the SO rats than in the NPX rats. Also during the fifth day following the injection of either dose of UO2F2, the fractional excretion of glucose was higher in the SO rats than in the NPX rats. By the end of the fifth day, the level of histologically demonstrable cellular necrosis in the pars recta of proximal tubules in the renal cortex and outer medulla of the NPX and SO rats was statistically similar. Therefore, the nephropathy in rats induced by UO2F2 is not made more severe as a result of unilateral nephrectomy.

Mercuric chloride-induced nephrotoxicity in the rat following unilateral nephrectomy and compensatory renal growth

The nephropathy induced by mercuric chloride was assessed in unilaterally nephrectomized (NPX) and sham-operated (SO) rats using histological and urinalysis techniques. This assessment was carried out in order to test whether or not rats are more susceptible to the nephrotoxic effects of mercuric chloride after unilateral nephrectomy and a period allowing for compensatory renal growth. Twelve days after surgery both NPX and SO rats were given a single 1.5, 2.0 or 2.5 mumol/kg dose of mercuric chloride (i.v.). Twenty-four hours after the 1.5 or 2.0 mumol/kg dose of mercuric chloride was administered, cellular and tubular necrosis in the pars recta segments of proximal tubules in the outer medulla was more severe in NPX rats than in SO rats. Moreover, the urinary excretion of a number of cellular enzymes (e.g. lactate dehydrogenase) and plasma solutes (e.g. albumin) was greater in NPX rats than in SO rats. At the 2.5 mumol/kg dose of mercuric chloride, renal tubular damage was quite extensive in both groups of rats; to such an extent that possible differences in renal tubular damage between the NPX and SO rats could not be determined histologically. However, the urinary excretion of alanine aminopeptidase was greater in the NPX rats than in the SO rats. Therefore, based on the aforementioned findings, rats that have undergone and adapted to a reduction in renal mass (i.e. unilateral nephrectomy) appear to be more vulnerable to the nephrotoxic effects of mercuric chloride than rats with two normal kidneys.

Enhanced accumulation of injected inorganic mercury in renal outer medulla after unilateral nephrectomy

The effects of unilateral nephrectomy on renal accumulation and intrarenal distribution of mercury following a single injection of mercuric chloride (HgCl2, 0.5 mumol Hg/kg body wt, ip) were evaluated in the rat. In rats injected with HgCl2 immediately after nephrectomy or 10, 28, or 43 days after nephrectomy, the accumulation of mercury in the renal outer medulla was significantly greater than in respective sham-operated control rats. The increased accumulation of mercury in renal outer medulla was evident at 24 hr after injection of HgCl2 and persisted for at least 72 hr. The effect appeared to be a phenomenon associated specifically with the renal outer medulla in that elevated concentrations of mercury in the outer medulla were observed in the absence of similar elevations in the renal cortex, inner medulla, liver, and blood or in the whole body mercury content. Urinary excretion of mercury was unaffected by nephrectomy. Thus, associated with unilateral nephrectomy are changes in the renal accumulation and intrarenal distribution of systemically administered inorganic mercury that persist long after the rapid phase of compensatory renal growth (0-7 days) is completed.

Lesions of the renal papilla induced by paracetamol

The acute nephrotoxic effects of paracetamol in the uninephrectomized homozygous Gunn rat are different from those of aspirin. Both compounds induce renal papillary necrosis but paracetamol produces accumulation of non-cellular material in the interstitial space, less damage to interstitial cells, more damage to tubular epithelium, and more severe necrosis of proximal convoluted tubules. In both cortex and papilla only a small fraction of the cells at risk are affected. It is concluded that the findings are consistent with a synergistic nephrotoxic effect between the two compounds, but that the lesions are not sufficiently severe for the natural history of analgesic nephropathy to be wholly explicable by such synergism.

The effect of long-term administration of aspirin and sodium saccharin on the rat kidney

In a study primarily designed to evaluate the inhibitory effects of aspirin on N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT)-initiated and saccharin-promoted bladder carcinogenesis, significant renal lesions were observed. Thus, administration in the diet of aspirin and sodium saccharin to F344 male rats for 68 weeks resulted in significant lesions of the renal papilla. In contrast to the bladder, aspirin enhanced the frequency and severity of the proliferative action of sodium saccharin on the epithelium of the renal papilla (p less than 0.05 compared to rats treated with either compound alone). The majority of rats administered the two chemicals together demonstrated moderate to severe urothelial hyperplasia of the renal papilla. Columnar metaplasia of the papillary epithelium also occurred frequently in rats fed the combination of chemicals. The rats treated with a combination of sodium saccharin and aspirin had a high incidence of renal papillary necrosis which was also present to a lesser extent among rats treated with aspirin only. Papillary calcification was also frequently observed in the rats fed the combination of aspirin and sodium saccharin. Sodium saccharin or aspirin alone reduced the light microscopic incidence and severity of rat nephropathy, a common finding in aging rats. It would appear that the hyperplastic and renal papillary toxic effects of aspirin and sodium saccharin are independent responses, and that the administration of the two chemicals together greatly accentuates these responses.

Chemically induced renal papillary necrosis and upper urothelial carcinoma. Part 1

In the past, renal papillary necrosis (RPN) has been commonly associated with long-term abusive analgesic intake, but over recent years a wide variety of industrially and therapeutically used chemicals have been shown to induce this lesion experimentally or in man. Destruction of the renal papilla may result in: (1) secondary degenerative cortical changes which precede chronic renal failure or (2) a rapidly metastasizing upper urothelial carcinoma, which has a very poor prognosis. This article will briefly review the published data on the morphology, function, and biochemistry of the normal renal medulla and the pathology associated with RPN, together with the secondary changes which give rise to cortical degeneration or epithelial carcinoma. It will then examine in detail those chemicals which have been reported to cause RPN in an attempt to delineate structure-activity relationships. Finally, the many different theories that have been proposed to explain the pathophysiology of RPN will be examined and an hypothesis will be put forward to explain the primary pathogenesis of the lesion and its secondary consequences.

Chemically induced renal papillary necrosis and upper urothelial carcinoma. Part 2

In the past, renal papillary necrosis (RPN) has been commonly associated with long-term abusive analgesic intake, but over recent years a wide variety of industrially and therapeutically used chemicals have been shown to induce this lesion experimentally or in man. Destruction of the renal papilla may result in: (1) secondary degenerative cortical changes which precede chronic renal failure or (2) a rapidly metastasizing upper urothelial carcinoma, which has a very poor prognosis. This article will briefly review the published data on the morphology, function, and biochemistry of the normal renal medulla and the pathology associated with RPN, together with the secondary changes which give rise to cortical degeneration or epithelial carcinoma. It will then examine in detail those chemicals which have been reported to cause RPN in an attempt to delineate structure-activity relationships. Finally, the many different theories that have been proposed to explain the pathophysiology of RPN will be examined and an hypothesis will be put forward to explain the primary pathogenesis of the lesion and its secondary consequences.

The effect of N-phenylanthranilic acid-induced renal papillary necrosis on urinary acidification and renal electrolyte handling

The oral administration of a suspension of N-phenylanthranilic acid (N-PAA), over the range of 0.5 to 2 mmol/kg for 14 consecutive days, caused a dose-related renal papillary necrosis (RPN), which involved no more than 30% of the medullary apex. This area of necrosis was no greater following daily doses of 3 and 5 mmol/kg of N-PAA for 14 days, but cortical degenerative changes were induced. The area of the necrotic lesion was greater in the left kidneys of individual rats than in the right kidneys. The apex-limited histopathological changes associated with the administration of low doses of N-PAA were not reflected by altered electrolyte or water homeostasis and only high doses of N-PAA caused significant changes. Urinary volume was significantly increased (in animals treated with 5 mmol/kg), whereas urinary osmolality (greater than 2 mmol/kg N-PAA), and Na+ (5 mmol/kg), K+ (5 mmol/kg), and Cl- (5 mmol/kg) excretion was decreased compared to controls. Blood urea nitrogen was increased at doses greater than 3 mmol/kg in association with cortical degenerative changes. When untreated rats were dosed orally with NH4Cl (400 mg/kg) there was a lag period between 0 and 2 hr (when no changes in H+ excretion occurred), but the urinary pH was depressed in the 2- to 4-hr collection period. Only those rats treated with the highest dose of N-PAA (5 mmol/kg) showed a significantly impaired urinary acidification after NH4Cl loading. There was, however, a statistically significant dose-related decrease in the excretion of Cl- following NH4Cl dosing, provided urine was sampled between 0 and 2 hr. These data highlight the failure of the commonly used renal function tests (such as urinary volume, osmolality, and electrolyte excretion) to reflect apex-limited RPN, unless cortical degenerative changes were also present. The dose-related depression of Cl- excretion in the 0- to 2-hr period following oral NH4Cl loading, suggests that appropriately timed sampling of this urinary anion could offer an improved criterion for the diagnosis of RPN.

The role of metabolic activation of analgesics and non-steroidal anti-inflammatory drugs in the development of renal papillary necrosis and upper urothelial carcinoma

There has been no cogent hypothesis to explain the molecular basis of analgesic and non-steroidal anti-inflammatory drug (NSAID) associated renal papillary necrosis (RPN) and upper urothelial carcinoma (UUC). The microsomal cytochrome P-450 enzyme system may generate reactive intermediates which promote pathophysiological effects in the lung, liver and renal cortex, but the absence of P-450 activity in the medulla suggests that it is unlikely that similar events lead to RPN and UUC. Other enzymes (eg. peroxidases) convert substituted aromatics into benzoquinoneimines (an intermediate that has previously been defined in P-450-mediated toxicity). The medulla is rich in fatty acid peroxidases involved in the metabolism of arachidonic acid. NSAID and analgesics interact with key enzymes in this pathway, which could lead to the co-oxygenation of exogenous and endogenous compounds via the peroxidase, lipoxygenase, or prostaglandin hydroperoxidase enzymes. The generation of reactive molecules in the medulla could explain both RPN and UUC via the alkylation of macromolecules. The formation of free radicals would give rise to extensive lipid peroxidation, (there are large quantities of free polyunsaturated fatty acids in the medullary interstitial cells), an event of major potential importance to local cell destruction and genotoxic effects. At present this proposed mechanism of co-oxygenation offers the most attractive working hypothesis to explain the molecular pathogenesis of both RPN and UUC.

Chronic renal lesions in the uninephrectomized Gunn rat after analgesic mixtures

Chronic cortical and medullary damage have been produced in uninephrectomized homozygous Gunn rats by single doses of the analgesics aspirin, paracetamol and phenazone, and by analgesic mixtures. The lesions are more severe than those of other experimental models of analgesic nephropathy, and the appearances of the cortical lesions suggest that they are ultimately due to the effects of papillary necrosis rather than to acute tubular necrosis observed in acute experiments with this model. The presence of an acute inflammatory reaction in both cortex and medulla in a number of animals one month after administration of analgesics indicates the possibility that the observed chronic renal damage may result from the intervention of additional complicating factors rather than from a single direct effect of analgesics.

Pattern of renal cortical scarring after experimental papillary necrosis

Three types of renal cortical damage were found in rats 2 mth after papillary necrosis had been induced by ethylenimine: (1) Circumscribed areas of interstitial nephritis affecting either deep or superficial nephrons. (2) Wedge-shaped or conical scars, extending from capsule to inner medulla. (3) Widespread tubular dilatation and cyst formation with a diffuse increase in interstitial tissue, usually associated with dense fibrous repair of the papillary remnant. The extent and character of the cortical changes did not appear to be determined by the severity of the papillary necrosis, and even the more severe cortical lesions were not accompanied by any major reduction in kidney size. Although these chronic experimental cortical lesions are the products of a less complex and less protracted natural history than end stage cortical damage in analgesic nephropathy, some of the factors influencing their evolution, such as infection, may also determine the natural history of the clinical lesion.

Ultrastructural appearances of acute renal papillary lesions induced by aspirin

Renal papillary necrosis develops 16 hr after intravenous administration of aspirin to the uninephrectomised homozygous Gunn rat. Ultrastructural studies show the papillary interstitial cells to be most severely affected, the first changes being visible at 1 hr. Changes in capillaries are late in onset, and this suggests that the lesions are due to a direct toxic effect rather than to ischaemia.

A new reproducible experimental model of analgesic nephropathy

The uninephrectomised homozygous Gunn rat is more sensitive than other experimental animals to the nephrotoxic effects of analgesics. Phenacetin derivatives produce severe necrosis of proximal convoluted tubules and aspirin and phenazone renal papillary necrosis. The observations suggest that the components of compound analgesic preparations have separate and complementary nephrotoxic effects, and this is a possible factor contributing to the association of analgesic nephropathy with abuse of such preparations.

The influence of metabolic variation on analgesic nephrotoxicity. Experiments with the Gunn rat

The analgesics aspirin and paracetamol administered as single I.V. doses produce renal lesions in the homozygous Gunn rat. The lesions affect both cortex and medulla but are less severe than the renal lesions of analgesic nephropathy. By contrast the reactive compounds p-aminophenol and 5-aminosalicylic acid which are known to cause renal damage in other less susceptible strains respectively produce cortical and medullary renal lesions in homozygous Gunn rats which are as extensive as those found in patients with analgesic nephropathy. The increased frequency of renal lesions from the analgesics aspirin and paracetamol as compared to heterozygous and albino rats and the increased severity of the lesions due to p-aminophenol and 5-aminosalicylic acid is considered to be at least partly due to impaired glucuronide formation and consequent delayed excretion of nephrotoxic substances.

Factors influencing the severity and progress of ethylenimine-induced papillary necrosis

The severity of the renal papillary necrosis produced in rats by ethylenimine is dependent both on dose and urinary concentration within the medulla. When this is reduced by diuresis, the severity of the lesion is effectively reduced. Increasing urinary concentration has a reverse effect, but of less magnitude. When the concentrating power of the renal medulla is impaired by a single dose of ethylenimine, insufficient to cause necrosis of the whole papilla, further doses of ethylenimine do not cause progressive damage to the papilla.

Clinical and pathological aspects of analgesic nephropathy

1 Analgesic nephropathy is part of the analgesic syndrome which has gastrointestinal, haematological, cardiovascular, psychological and psychiatric, and pregnancy and gonadal manifestations; premature ageing may also be a feature. 2 Analgesic nephropathy is a form of renal disease characterized by renal papillary necrosis, secondary chronic interstitial nephritis and renal failure with features of predominant tubulointerstitial dysfunction. 3 The percentage of patients with analgesic nephropathy who present with terminal renal failure is 12%. With appropriate management, 17% of analgesic nephropathy patients improve, 50% remain stable and 23% deteriorate. The 6 year cumulative survival is 70%. The major factors influencing deterioration are malignant hypertension, persistent proteinuria and small initial renal size. 4 The risk of renal papillary carcinoma in patients who regularly take analgesics is 8 per 100,000 patients per year. 5 Renal papillary necrosis is a consequence of the chronic toxicity of all non-steroidal anti-inflammatory drugs and results from medullary ischaemia secondary to suppression of prostaglandin E2 synthesis and from direct cellular toxicity. 6 Analgesic nephropathy is a preventable form of renal disease and renal failure. It can be prevented by limiting the abuse potential of analgesics rather than by making minor modifications in the composition of analgesic mixtures.

Pathology of analgesic nephropathy: Australian experience

Analgesic nephropathy was first studied in Switzerland and Scandinavia, and most observers thought that papillary necrosis, a feature of the pathology, was the result of chronic interstitial nephritis, the other principal feature. From 1962, reports indicated a high incidence of analgesic nephropathy in Australia and suggested that papillary changes preceded cortical damage. Later, associated uroepithelial carcinoma was noted. Early papillary lesions consist of necrosis of elements around groups of collecting ducts. Necrosis extends upward through the medulla from the papilla and gradually intensifies to total papillary destruction. Fat and calcium accumulation and changes in matrix mucopolysaccharide are markers of papillary injury. Cortical atrophy is dependent upon collecting duct obstruction and is proportional to the degree of obstruction. Infection may complicate late pathologic changes. It is suggested that in the early stages the disease represents an injury to "concentrating columns" in the medulla.

Experimental renal papillary necrosis

Review of experimental work indicates that renal papillary necrosis (RPN) is more readily induced by mixtures of analgesics which include phenacetin or paracetamol, than by either of the latter drugs alone. In an experiment in which moderate doses of analgesics were given to rats over a long period, it was shown that aspirin had a greater nephrotoxic effect than either phenacetin or paracetamol although less than in combination with either. In a study of the evolution of aspirin-induced damage, the earliest changes were shown to occur in the interstitial cells. There was also loss of medullary mucopolysaccharides. Occlusive lesions were demonstrated in the vasa recta. Using partial papillectomy, it was shown that the development of analgesic-induced cortical lesions did not depend on the presence of papillary necrosis. It was suggested that the early papillary changes might be due to ischemia, medullary blood flow being reduced as a result of aspirin's action as an inhibitor of prostagladin synthesis. The lesions in the vasa recta might cause ischemia at a late stage, leading to total RPN.