The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying lesions observed in the urinary tract of rats and mice. The standardized nomenclature of urinary tract lesions presented in this document is also available electronically on the Internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous developmental and aging lesions as well as those induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for urinary tract lesions in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

CPN (chronic progressive nephropathy) is a spontaneous age-related disease that occurs in high incidence in the strains of rat commonly used in preclinical toxicology studies, exhibiting a male predisposition. Although increasing in incidence and severity with age, evidence indicates that CPN should be regarded as a specific disease entity and not just a manifestation of the aging process. A number of factors, mainly dietary manipulations, have been shown to modify the expression of CPN. Amongst these, restriction of caloric intake is the most effective for inhibiting the disease process. The precise etiology of CPN and the mechanism(s) underlying its pathogenesis remain unknown, but the long-standing assumption that glomerular dysfunction is the primary basis is challenged in the light of contemporary developments in understanding filtration and postglomerular cellular processing of albumin. CPN is not only a degenerative disease, but also has regenerative aspects with a high cell proliferative rate in affected tubules. Accordingly, evidence is emerging that advanced, particularly end-stage CPN, is a risk factor for a marginal increase in the background incidence of renal tubule tumors. Many chemicals are known to exacerbate the severity of CPN to an advanced stage, and this interaction between chemical and CPN can result in a small increase in the incidence of renal adenomas in 2-year carcinogenicity bioassays. Review of the pathological entities associated with chronic renal failure in man emphasizes that this rodent condition has no strict human counterpart. Because CPN is a rodent-specific entity, the finding of a small, statistically significant increase in renal tubule tumors, linked to exacerbation of CPN by a test chemical in a preclinical study for carcinogenicity, can be regarded as having no relevance for extrapolation in human risk assessment.

The incidence of renal tubule carcinogenesis in male and female rats or mice with 69 chemicals from the 513 bioassays conducted to date by the NCI/NTP has been collated, the chemicals categorized, and the relationship between carcinogenesis and renal tubule hyperplasia and exacerbation of the spontaneous, age-related rodent disease chronic progressive nephropathy (CPN) examined. Where information on mechanism or mode of action exists, the chemicals have been categorized based on their ability to directly or indirectly interact with renal DNA, or on their activity via epigenetic pathways involving either direct or indirect cytotoxicity with regenerative hyperplasia, or exacerbation of CPN. Nine chemicals were identified as directly interacting with DNA, with six of these producing renal tubule tumors at high incidence in rats of both sexes, and in some cases also in mice. Ochratoxin A was the most potent compound in this group, producing a high tumor incidence at very low doses, often with metastasis. Three chemicals were discussed in the context of indirect DNA damage mediated by an oxidative free radical mechanism, one of these being from the NTP database. A third category included four chemicals that had the potential to cause DNA damage following conjugation with glutathione and subsequent enzymatic activation to a reactive species, usually a thiol-containing entity. Two chemicals were allocated into the category involving a direct cytotoxic action on the renal tubule followed by sustained compensatory cell proliferation, while nine were included in a group where the cell loss and sustained increase in renal tubule cell turnover were dependent on lysosomal accumulation of the male rat-specific protein, alpha2mu-globulin. In a sixth category, morphologic evidence on two chemicals indicated that the renal tumors were a consequence of exacerbated CPN. For the remaining chemicals, there were no pertinent data enabling assignment to a mechanistic category. Accordingly, these chemicals, acting through an as yet unknown mechanism, were grouped as either being associated with an enhancement of CPN (category 7, 16 chemicals), or not associated with enhanced CPN (category 8, 4 chemicals). A ninth category dealt with 11 chemicals that were regarded as producing increases in renal tubule tumors that did not reach statistical significance. A 10th category discussed 6 chemicals that induced renal tumors in mice but not in rats, plus 8 chemicals that produced a low incidence of renal tubule tumors in mice that did not reach statistical significance. As more mechanistic data are generated, some chemicals will inevitably be placed in different groups, particularly those from categories 7 and 8. A large number of chemicals in the series exacerbated CPN, but those in category 7 especially may be candidates for inclusion in category 6 when further information is gleaned from the relevant NTP studies. Also, new data on specific chemicals will probably expand category 5 as cytotoxicity and cell regeneration are identified as obliga...

ABSTRAC~ in theLaboratory studies with classical renal carcinogens in the rat and mouse, as well as research investigation with some of the chemicals proving positive for the kidney in National Toxicology Program carcinogenicity bioassays, have demonstrated the existence of a range of diverse mechanisms underlying rodent kidney carcinogenesis. The classical carcinogens used as experimental models for studying renal tumor pathogenesis, such as the nitrosamines, are genotoxic and interact directly with DNA, forming DNA adducts with mutagenic potential. In contrast, potassium bromate and femc nitrilotriacetate (Fe-NTA), also effective renal carcinogens, appear to cause indirect damage to DNA mediated by oxidative stress. A number of nongenotoxic chemicals are associated with epigenetic renal tumor induction in rodents, and the activity of these tends to involve prolonged stimulation of cell proliferation throughout the duration of exposure. This mode of action reflects a sustained regenerative response, either due to dircct chemical toxicity to the tubule cells, as with chloroform, or to indirect cytotoxicity associated with lysosomal overload, as in a,,-globulin accumulation in male rats resulting from the administration of such chemicals as d-limonene and tetrachloroethylene. The histopathologic nature of hydroquinone renal carcinogenesis suggests that an additional epigenetic pathway to renal tubule tumor formation in rats may be through chemicalmediated exacerbation of, and interaction with, the age-related spontaneous renal disease, chronic progressive nephropathy. These various mechanistic pathways have implications for the nature of the induced cancer process with respect to tumor incidence, latency, malignancy, and sex predisposition.

The rates of cell proliferation and cell loss in conjunction with the differentiation status of a tissue are among the many factors contributing to carcinogenesis. Nongenotoxic (non-DNA reactive) chemicals may affect this balance by increasing proliferation through direct mitogenesis or through a regenerative response following loss of cells through cytotoxic (oncotic) or apoptotic necrosis. In a recent NTP study in Fischer rats and B6C3F(1) mice, the mycotoxin fumonisin B(1) caused renal carcinomas in male rats and liver cancer in female mice. In an earlier study in male BD-IX rats, fumonisin B(1) caused hepatic toxicity and hepatocellular carcinomas. An early effect of fumonisin B(1) exposure in these target organs is apoptosis. However, there is also some evidence of oncotic necrosis following fumonisin B(1) administration, especially in the liver. Induction of apoptosis may be a consequence of ceramide synthase inhibition and disruption of sphingolipid metabolism by fumonisin B(1). Fumonisin B(1) is not genotoxic in bacterial mutagenesis screens or in the rat liver unscheduled DNA-synthesis assay. Fumonisin B(1) may be the first example of an apparently nongenotoxic (non-DNA reactive) agent producing tumors through a mode of action involving apoptotic necrosis, atrophy, and consequent regeneration.

Ochratoxin A (OTA), a mycotoxin produced by several fungi of Aspergillus and Penicillium species, may contaminate agricultural products, resulting in chronic human exposure. In rats, OTA is a potent nephrotoxin, and repeated administration of OTA for 2 years to rats in doses up to 0.21 mg/kg of body wt resulted in high incidences of renal tumors arising from the proximal tubular epithelial cells. The mechanism of tumor formation by OTA in the kidney is not well-defined, and controversial results regarding mode of action have been published. The aim of this study was to characterize dose-dependent changes induced by OTA by application of clinical chemistry, biochemical markers, and toxicokinetics for a better conclusion on modes of action. Administration of OTA (0, 0.25, 0.5, 1, and 2 mg/kg of body wt) to male F344 rats (n = 3 per group) by oral gavage for 2 weeks resulted in a dose-dependent increase in OTA plasma concentrations and concentrations of OTA in both liver and kidney. Although oxidative stress has been implicated in OTA carcinogenicity, treatment with OTA did not induce overt lipid peroxidation or an increase in 8-oxo-7,8-dihydro-2'deoxyguanosine (8-OH-dG) in kidney. In the kidney, OTA-induced pathology was present at all dose levels administered, with a clear increase in severity related to dose. Pathology was restricted to the outer stripe of the outer medulla and consisted of disorganization of the tubule arrangement, frequent apoptotic cells, and abnormally enlarged nuclei scattered through the S3 tubules. Consistent with the histopathology, a dose-dependent increase in the expression of proliferating cell nuclear antigen (PCNA), indicative of cell proliferation, was observed in kidneys, but not in livers of treated animals. The most prominent change in the composition of urine induced by OTA analyzed by 1H NMR and principal component analysis consisted of a major increase in the excretion of trimethylamine N-oxide. However, typical changes observed with other proximal tubular toxins such as increased excretion of glucose were not observed at any of the doses administered. Similarly, treatment with OTA had no clear effects on clinical chemical parameters indicative of nephrotoxicity, although urinary volume was increased at the higher-dose groups. Taken together, the uncommon changes induced by OTA suggest that a unique mechanism may be involved in OTA nephrotoxicity and carcinogenicity.

Ochratoxin A (OTA) is nephrotoxic and a potent renal carcinogen. Male rats are most susceptible to OTA toxicity, and chronic administration of OTA (70 and 210 microg/kg bw) for 2 years has been shown to induce high incidences of adenomas and carcinomas arising from the straight segment of the proximal tubule epithelium. In contrast, treatment with a lower dose of 21 microg/kg bw did not result in increased tumor rates, suggesting a nonlinear dose response for renal tumor formation by OTA. Since the mechanism of OTA carcinogenicity is still largely unknown, this study was conducted to investigate early functional and pathological effects of OTA and to determine if sustained stimulation of renal cell proliferation plays a role. Male F344/N rats were treated with OTA for up to 13 weeks under conditions of the National Toxicology Program (NTP) bioassay. Cell proliferation in the renal cortex and outer stripe of the outer medulla (OSOM) was determined using bromodeoxyuridine incorporation and immunohistochemistry. Histopathological examination showed renal alterations in mid- and high-dose-treated animals involving single-cell death and prominent nuclear enlargement within the straight proximal tubules. Treatment with OTA at doses of 70 and 210 microg/kg bw led to a marked dose- and time-dependent increase in renal cell proliferation, extending from the medullary rays into the OSOM. No effects were evident in kidneys of low-dose-treated animals or in the liver, which is not a target for OTA carcinogenicity. A no observed effect level in this study was established at 21 microg/kg bw, correlating with the dose in the NTP 2-year bioassay that did not produce renal tumors. The apparent correlation between enhanced cell turnover and tumor formation induced by OTA indicates that stimulation of cell proliferation may play an important role in OTA carcinogenicity and provides further evidence for an epigenetic, thresholded mechanism.

This review paper examines the relationship between chemicals inducing ewessive accumulation of a2u-globulin (ai21g) (CIGA) in hyline droplets inmale rat kidneys and the subsequent development of nephoit and rnal tubule nopaia in the male rt. This dose-responsive hyaline droplet accumulation distinguishes CIGA carcinogens fromclssical renal carcinogens. CIGA carcinogens also do not appear to react with DNA and are generally negative in short-term tests for genotoxicity. CIGA or their metabolites bind specifically, but reversibly, tomale rat a2,-g The resulting complex appears to be more resistant to hydrolytic degradation in the proximaltubule than native, unbound a2,-g Singlecell necrosis of the tubule epithelium, with associated granular cast formation and papillary mineralization, is followed by sustained regenerative tubule cell prolifertin, foci oftubulehyerl a inthe aovoited pronal bules, and renal tubule tumor Although stnrcturally similar proteins have been detected in other species, including hu_ms, renal lesios characteristic Of a2,-g nephropathy have not been observed. Epidemiologic investigation has not specifically examined the CIGA hypothesis for humans. Based on cancer bioassays, hormone manipulation studies, investigations in an ae,-g-deficient strain of rat, and other laboratory data, an increased proliferative response caused by chemically induced cytotoxicity appears to play a role in the development ofrenal tubule tumors in male rats Thus, it is reasonable to suggest that the renal effects induced in male rats by chemicals causing a2.-g accumulation are unlikely to occur in humans. IntroductionFor most hazardous chemicals, adequate human data are not available, and risk analyses must rely on information from laboratory studies of rats or mice. The inference that the results ofanimal experiments can be applied to humans is a fundamental principle of all toxicologic research. This analysis deals with a specific case, however, where the male rat seems to respond in a manner different from other laboratory species. The possibility of a unique response in the rat among laboratory animals raises questions about the applicability of the rat data to other species, including humans. Our review evaluates the matter of human 'Medical Research Council relevance and describes the types of information needed for hazard assessment of such chemicals.A variety of organic chemicals have produced specific renal lesions in male rats in the form of a protein (hyaline) droplet nephropathy accompanied by accumulation of a2%-globulin (a2.-g) [reviewed in (1,2)]. Among the chemicals tested are paraffins (3,4), decalin (decahydronaphthalene) (5,6), petroleum-based and synthetic fuels (7), military aviation propellants (8), and 2,2,4-trimethylpentane (TMP) (9). As seen in Table 1, which lists a sampling ofchemicals that have been tested, many are of considerable regulatory and commercial interest. For example, isophorone is a chemical intermediate of major industrial importance. Aviation and automotive fuels fit i...