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

A safety assessment of fixed combinations of acetaminophen and acetylsalicylic acid, coformulated with caffeine

Overuse and abuse of phenacetin-containing mixed analgesics has contributed to end-stage renal disease. Combination analgesics, especially those coformulated with caffeine, have been implicated as imparting a greater risk of analgesic-associated nephropathy (AAN) than single or coformulated analgesics without caffeine. This has led to a recommendation that the sale of "two plus caffeine" analgesic mixtures be reclassified from over-the-counter to prescription only availability. There is a rational basis for coformulating acetylsalicylic acid (ASA) and acetaminophen (paracetamol) as this reduces the dose of each, without altering efficacy. The coformulation of caffeine with these analgesics has a significant adjuvant effect and increases analgesic efficacy 1.4-1.6-fold. Currently available animal and human data do not support the notion that the nephrotoxic risk from coformulated ASA and acetaminophen is higher than the risk from either ASA or acetaminophen alone, in equivalent analgesic doses. There are no epidemiological data that implicate caffeine in AAN, and only limited evidence that links excessive acetaminophen usage to renal disease. There is no evidence that caffeine increases analgesics papillotoxicity directly. The presence of caffeine in mixtures of analgesics are no more addictive than other sources of caffeine. There is no evidence to suggest that adding caffeine to analgesic mixtures enhances the potential for promoting analgesic misuse in the general population. Thus distinct therapeutic benefits of ASA, acetaminophen and caffeine appear to outweigh any known risk. It is doubtful if preventing the availability of these products will significantly affect the role of analgesic abuse/overuse in end-stage renal disease. Better risk management would come from a focused educational program, developed in a close collaboration between industry, healthcare professionals and consumer organizations, such a program must warn against the potential dangers of analgesic and non-steroidal anti-inflammatory drug misuse.

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.

Investigation of regional glutathione levels in a model of chemically-induced renal papillary necrosis

The effect of diphenylamine on renal cortical, outer medullary and inner medullary glutathione (GSH) concentrations and the effect of GSH depletion on the nephrotoxicity of diphenylamine were investigated in male Syrian hamsters. A dose-dependent decrease in renal cortical GSH was observed within 1 hr of a single oral dose of diphenylamine (200, 400 or 600 mg/kg body weight), but statistically significant changes in outer medullary or papillary GSH were not observed. Reduction of renal papillary GSH to 29% of basal concentration [by prior treatment with L-buthionine sulfoxime (500 mg/kg body weight, ip)] did not increase the papillotoxicity of a non-toxic dose of diphenylamine (400 mg/kg) administered orally. The findings indicate that diphenylamine-induced renal papillary necrosis in the Syrian hamster is not associated with a decrease in renal papillary or outer medullary GSH nor mediated by oxidative cell injury.

Experimental models of kidney tumors

We here present in outline some outstanding results on the animal models of renal tumors submitted to the highest attention, which include two kinds of epithelial neoplasms: those developed from the epithelium lining each the renal tubules (renal cell tumors) and pelvis; the mesenchymal tumor of rat; and tumors with embryonal appearance: the nephroblastoma as well as the variant of it known as the estrogen-induced tumor in the hamster. The review deals with methods for tumor induction and the pathobiology of tumors, the latter mainly focused on the identification of the precise types of renal cells committed in tumor origin. The existence of closely related counterparts of these animal tumors in man is also emphasized, by representing a situation of great potentiality, already exploited, to improve understanding of both the nature and development of renal tumors in man.

Relevance of a rat model of papillary necrosis and upper urothelial carcinoma in understanding the role of ochratoxin A in Balkan endemic nephropathy and its associated carcinoma

Ochratoxin A is nephrotoxic and has been implicated in the genesis of Balkan endemic nephropathy (BEN), a condition that leads to end-stage renal disease and upper urothelial tumours. This compound induces renal parenchymal carcinoma in male mice only, and is not considered to be a potent carcinogen nor is there experimental evidence of its propensity to cause upper urothelial carcinoma. There is, however, evidence that exposure to more than one mycotoxin may be an important factor in the clinical spectrum of BEN. Analgesic nephropathy is clinically different, but is also associated with an upper urothelial carcinoma. The combination of urothelial initiation and an acute papillary necrosis in rats produces upper urothelial carcinoma. This two-stage experimental model offers the potential to assess the role of ochratoxin A in BEN-associated upper urothelial carcinoma under experimental conditions.

Irreversible damage to the medullary interstitium in experimental analgesic nephropathy in F344 rats

Renal papillary necrosis (RPN) and a decreased urinary concentrating ability developed during continuous long-term treatment with aspirin and paracetamol in female Fischer 344 rats. Renal structure and concentrating ability were examined after a recovery period of up to 18 weeks, when no analgesics were given, to investigate whether the analgesic-induced changes were reversible. There was no evidence of repair to the damaged medullary interstitial matrix, or proliferation of remaining undamaged type 1 medullary interstitial cells after the recovery period following analgesic treatment. The recovery of urinary concentrating ability was related to the length of analgesic treatment and the extent of the resulting inner medullary structural damage. During the early stages of analgesic treatment, the changes in urinary concentrating ability were reversible, but after prolonged analgesic treatment, maximum urinary concentrating ability failed to recover. This study shows that prolonged analgesic treatment in Fischer 344 rats causes progressive and irreversible damage to the interstitial matrix and type 1 interstitial cells leading to RPN. The associated urinary concentrating defect is reversible only during the early stages of structural damage to the inner medulla.

Decreased incidence of diphenylamine-induced renal papillary necrosis in Syrian hamsters given dimethylsulphoxide

The renal papillotoxicity of diphenylamine dissolved in dimethylsulphoxide (DMSO) was investigated in male Syrian hamsters, male Sprague-Dawley rats and female Mongolian gerbils. When diphenylamine in DMSO was administered orally to male Syrian hamsters (400, 600 or 800 mg/kg body weight/day for up to 9 days), the incidence of renal papillary necrosis was almost zero. Hamsters pretreated with DMSO (0.5 ml/100 g body weight/day) and 1 hr later given 400, 600 or 800 mg diphenylamine in peanut oil/kg body weight/day for 3 consecutive days had significantly reduced incidences of renal papillary necrosis (0/10, 0/10 and 1/10 in the low-, mid- and high-dose groups, respectively) when compared with hamsters given similar doses of diphenylamine but not pretreated with DMSO (5/10, 7/10 and 5/10 in the low-, mid- and high-dose groups, respectively). Focal, apex-limited renal papillary necrosis was observed in two Sprague-Dawley rats given 800 mg diphenylamine in DMSO/kg body weight/day orally for 9 days. Focal, intermediate renal papillary necrosis was observed in two additional rats administered 800 mg diphenylamine in DMSO/kg/day orally for 9 days. Renal papillary necrosis was not observed in any of the Mongolian gerbils. The results of these studies suggest that DMSO protects against diphenylamine-induced renal papillary necrosis in male Syrian hamsters.

Analgesic nephropathy in Fischer 344 rats: comparative effects of chronic treatment with either aspirin or paracetamol

This study has compared the relative nephrotoxicity of chronic treatment with aspirin or paracetamol in an animal model. Changes in renal structure and urinary concentrating ability were examined in female Fischer 344 rats after continuous treatment with either aspirin (120-230 mg/kg body wt/day), or paracetamol (140-210 mg/kg body wt/day), and were compared with age-matched untreated control rats. Renal morphological changes were examined after 40-83 weeks of analgesic treatment, using light and electron microscopy. Aspirin caused renal papillary necrosis and a decrease in urinary concentrating ability, whereas paracetamol alone did not cause significant renal damage. Aspirin produced damage to the interstitial cells and matrix, particularly in the mid-papillary region, followed by changes to the thin limbs of the loop of Henle and medullary capillary endothelium. These structural changes were similar to those described previously, when continuous treatment with combined aspirin and paracetamol was studied in the same animal model.

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.

The effect of acetaminophen on pig kidneys with a 2-bromoethanamine-induced papillary necrosis

Large White pigs were used to investigate the effects of acetaminophen (paracetamol) on normal kidneys or those with an existing renal papillary necrosis. Pairs of young female animals were treated with either a single iv dose of 50 mg/kg 2-bromoethanamine (BEA), 100 mg/kg/day acetaminophen po for 28 days, or a combination of BEA followed by the acetaminophen treatment. Two pigs served as untreated controls. Kidney length, diameter and parenchymal thickness were measured by ultrasound scans, and glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) assessed by 99mTc-DTPA and 131I-hippuran renography prior to treatment and on day 26. Acetaminophen only caused no renal pathology. Despite the lack of a gross RPN, hyperplasia of the pelvic and ureteric urothelia (with extensive vacuolation) was observed following BEA, but BEA followed by acetaminophen for 28 days did not enhance the lesion. The BEA and BEA-acetaminophen groups (but not acetaminophen only) showed an increased ERPF compared with age-matched controls, but there was no significant difference in the overall GFR between the groups.

Experimental analgesic nephropathy: changes in renal structure and urinary concentrating ability in Fischer 344 rats given continuous low doses of aspirin and paracetamol

Long-term treatment with aspirin and paracetamol produced renal papillary necrosis in female Fischer 344 rats. Aspirin (230 mg/kg body weight/day) and paracetamol (380 mg/kg body weight/day) were dissolved in drinking water and given continuously for up to 65 weeks. Renal morphological changes were examined between 21 weeks and 65 weeks of commencement of analgesic treatment using light and electron microscopy, and were compared with age-matched controls. Structural damage initially occurred in the mid-papillary region, and specifically involved the interstitial cells and interstitial matrix. Necrosis of the epithelium of the thin limbs of the loop of Henle was present only after interstitial changes were well established. Cortical interstitial fibrosis and tubular atrophy occurred after renal papillary changes were observed. There was no evidence of significant vascular damage. Urinary concentrating ability was measured sequentially during the period of analgesic treatment. A decrease in urine concentrating ability was present when early changes to the interstitial cells and matrix were observed, and concentrating ability continued to decrease in parallel with increasing morphological damage. This study describes an animal model of analgesic-induced nephropathy, enabling early morphological changes to be studied and correlated with renal functional changes.

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.

Analgesic nephropathy

Analgesic nephropathy has been a recognized clinical problem for the past three decades. The association between chronic renal insufficiency and habitual analgesic consumption initially focused on combination analgesics containing phenacetin. Most recently, the increased popularity of nonsteroidal anti-inflammatory drugs has led to the recognition that these agents are capable of producing several distinct clinical syndromes. This review discusses both of these disorders from a clinical perspective.

Nephrotoxicity: a rational approach to target cell injury in vitro in the kidney

1. The kidney is a complex organ in which there is cellular heterogeneity. Many nephrotoxic chemicals target preferentially for discrete cell types, but adjacent, morphologically different cells are unaffected. This selectivity has made the assessment of nephrotoxicity in vivo (and the study of underlying mechanisms) difficult. Discrete renal injury can, however, be exploited in vitro, to study the interactions between the toxic compound and the target cell. 2. Several in vitro models have been used to study the potential interaction between the target cells and chemicals, including perfusion of the isolated kidney, renal slices, freshly isolated fragments, primary cultures and continuous cell lines. Where appropriate, isolated organelles and purified enzymes can also be used. 3. The target cell toxicity in vivo of adriamycin, 2-bromoethanamine and hexachlorobutadiene N-acetyl cysteine conjugate is selectively maintained towards glomerular epithelial, medullary interstitial and proximal tubular cells, respectively, in vitro, showing that the "in vivo-in vitro gap" can be bridged. Characteristics unique to each of these renal cell types, such as the selective uptake of a toxin, enzyme systems for generating biologically reactive intermediates, and the presence of lipid droplets (rich in polyunsaturated fatty acid) and peroxidase activity have been identified, and one or more of these may explain the mechanisms of selective injury in discrete regions of the kidney.

Analgesic-associated nephropathy

Although the question of whether or not analgesic abuse leads to a certain type of nephropathy has been investigated since 1953, no conclusive answer has been forthcoming. Epidemiologic investigations on the correlation between analgesic abuse and renal function as well as experimental animal studies have given contradictory results concerning the possibility of analgesic-associated kidney damage. However, studies on the correlation between analgesic abuse and papillary necrosis have demonstrated that this lesion coincides in 69% of the cases with an analgesic history. Follow-up studies of patients with analgesic nephropathy have shown that renal function deteriorates in 60% of the patients with continued abuse and that it stabilizes in 80% of the patients after cessation of abuse. Studies on the legislative restriction of phenacetin/acetaminophen, carried out mostly in Scandinavian countries since 1965, show a 50%-90% decline in signs of analgesic nephropathy (papillary necrosis) following a reduction in the sale of these drugs. The prevalence of analgesic abuse may be underestimated, since up to 80% of the abusers tend to deny their analgesic intake. Obviously, only a small percentage of analgesic abusers (approximately 1%) finally develop nephropathy. Even though the results of epidemiologic and experimental studies are contradictory, the results of investigations on papillary necrosis and on legislative prevention as well as of patient follow-ups tend to indicate a correlation between analgesic abuse and a well-defined type of nephropathy.

The mechanisms of target cell injury by nephrotoxins

Hexachlorobutadiene-N-acetylcysteine (HCBD-NAC), adriamycin and 2-bromoethanamine hydrobromide are three renal toxins that have shown in vivo a highly selective target cell toxicity--to the proximal tubules, the glomerular epithelial cells and the medullary interstitial cells, respectively. To study some aspects of the mechanisms of this selective toxicity, the three types of target cell were isolated from the kidneys of Wistar rats, and cultures of the cells or tissue fragments were exposed to various concentrations of the three toxins. Using fluorescence microscopy combined with enzyme and histochemical probes, the selective target-cell toxicity of the three compounds already established in vivo was demonstrated also in vitro. Moreover, the in vitro toxic effect of HCBD-NAC was ameliorated by probenecid, as is the case in vivo. Several functional characteristics specific to each of the target cells, such as the selective uptake of a toxin, the presence of lipid droplets and the level of peroxidative enzyme activity, have been identified as probable factors in the occurrence of the target cell necrosis.

A decision tree approach for the application of drug metabolism and kinetic studies to in vivo and in vitro toxicological and pharmacological testing

The integration of toxicological and other biological findings with information on drug metabolism and pharmacokinetics is often very important for rational decision making in safety evaluation programmes. This goal is unlikely to be achieved by conducting a routine package of inflexibly defined drug metabolism and pharmacokinetic test protocols for each new chemical. Rather, an intelligent selection of experiments based on the known properties of a chemical is required. A series of decision trees are proposed which serve as an aide memoire in the choice of appropriate drug metabolism and pharmacokinetic experiments. These decision trees cover the physicochemical properties of a chemical, data on animal and human pharmacology and toxicology, and environmental information relevant to possible contamination. In many cases, drug metabolism and pharmacokinetic factors are an important prerequisite to the design of in vitro tests that are relevant to the in vivo situation. A scheme is provided to assist the identification of appropriate conditions for the in vitro testing of individual chemicals.

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.