[Neoplastic and preneoplastic lesions in rats after oral administration of a single dose of N-nitrosomorpholine (author's transl)]

Heading Towards a Possible Rebirth of the Induced Renal Cell Carcinoma Models?

Introduction: Animal models are interesting tools to improve our knowledge of the pathophysiological processes underlying kidney cancer development. Recent advances have been made in the understanding of the genetic founding events underlying clear cell renal carcinoma. The aim of this paper was to review and discuss the characteristics of all the induced animal models of renal carcinogenesis that have been described in the scientific literature to date and to see if and how they could regain some use in the light of the latest discoveries. Methods: The authors reviewed all the papers available in PubMed regarding induced animal models of renal carcinogenesis. From this perspective, the keywords “induced”, “animal model”, and “renal cancer” were used in PubMed’s search engine. Another search was done using the keywords “induced”, “animal model”, and “kidney cancer”. PRISMA recommendations were used to develop the literature review. Results: Seventy-eight studies were included in this review. Results were presented depending on the mechanisms used to induce carcinogenesis in each model: induction by carcinogens, hormones, viral induction, or induction by other agents. Discussion focused on the possibility to rethink these different induced animal models and use them to answer new research questions. Conclusion: Many induced animal models have been developed in the past to study renal cancer. While these models seemed unable to yield new knowledge, the latest advances in the understanding of the genetics behind renal carcinogenesis could well bring the models back to the forefront.

Continuous flow synthesis of amine oxides by oxidation of tertiary amines

An efficient, safe and scalable continuous flow process for the synthesis of amine oxides with hydrogen peroxide is described.

Promoting Effect of Metal Compounds on Rat Renal Tumorigenesis

Five metal compounds, zinc chloride (ZnCl2), mercury chloride (HgCl2), chromium chloride (CrCl3) hexahydrate, cadmium chloride (CdCl2) hemidihydrate, and nickel chloride (NiCl2) hexahydrate, were selected and tested for potential modifying influence on renal tumorigenesis. Six groups, each consisting of 15 male F344 rats, were given N-ethyl-N-hydroxyethylnitrosamine (EHEN) at a concentration of 500 ppm in their drinking water for the first 2 weeks as the initiation of carcinogenesis. Thereafter, the rats were treated orally for 25 weeks with ZnCl2, HgCl2, CrCl3, CdCl2, and NiCl2, respectively, at concentrations of 450, 40, 600, 100, and 600 ppm in the drinking water. The control group was given unsupplemented distilled water (DW) after EHEN initiation. Renal neoplastic lesions were classified histologically into dysplastic foci (DF) and renal cell tumors (RCT). As a result, statistically significant increases were found in the mean numbers of DF per cm2 in rats treated with the five metal compounds. On the other hand, the incidence of RCT was significantly higher only in rats treated with NiCl2. It is concluded that NiCl2 exerted a potential for promotion of renal tumorigenesis under the conditions of this study.

PI3K/AKT/mTOR pathway plays a major pathogenetic role in glycogen accumulation and tumor development in renal distal tubules of rats and men

Activation of the PI3K/AKT/mTOR pathway is a crucial molecular event in human clear cell renal cell carcinoma (ccRCC), and is also upregulated in diabetic nephropathy. In diabetic rats metabolic changes affect the renal distal tubular epithelium and lead to glycogen-storing Armanni-Ebstein lesions (AEL), precursor lesions of RCC in the diabetes induced nephrocarcinogenesis model. These lesions resemble human sporadic clear cell tubules (CCT) and tumor cells of human ccRCC.

Human sporadic CCT were examined in a collection of 324 nephrectomy specimen, in terms of morphologic, metabolic and molecular alterations, and compared to preneoplastic CCT and RCC developed in the rat following streptozotocin-induced diabetes or N-Nitrosomorpholine administration. Diabetic and non-diabetic rats were subjected to the dual PI3K/mTOR inhibitor, NVP/BEZ235.

Human sporadic CCT could be detected in 17.3% of kidney specimens. Human and rat renal CCT display a strong induction of the PI3K/AKT/mTOR pathway and related metabolic alterations. Proteins involved in glycolysis and de novo lipogenesis were upregulated. In in vivo experiments, dual inhibition of PI3K and mTOR resulted in a reduction of proliferation of rat diabetes related CCT and increased autophagic activity.

The present data indicate that human sporadic CCT exhibit a pattern of morphologic and metabolic alterations similar to preneoplastic lesions in the rat model. Activation of the PI3K/AKT/mTOR pathway in glycogenotic tubuli is a remarkable molecular event and suggests a preneoplastic character of these lesions also in humans.

Morphology and proliferation kinetics of early tumor stages induced by dimethylnitrosamine in rat kidneys

A total of 49 dimethylnitrosamine (DMN)-induced rat renal cell tumors were analyzed and classified cytomorphologically at an early stage of development. Of these, 17 were basophilic-tubular tumors, two of which showed a direct transition to proximal tubules of the P3-segment; 21 lesions were vacuolated and contained glycogen; these were defined cytomorphologically as a separate tumor type the histogenetic derivation of which from the collecting duct system was established by documentation of a direct transition. Morphological similarities point to the lipid-storing variant of the basophilic tumor, but a carcinoma of the ducts of Bellini is another possible human equivalent of this tumor type. Another seven lesions were clear and granular cell tumors. In two of these a direct transition from the collecting duct system was found, thus confirming that this only recently established origin of experimentally induced rat renal clear cell tumors also applies to lesions induced by DMN. The proliferation kinetics of DMN-induced lesions were studied in autoradiograms after pulse-labeling with tritiated thymidine. The basal proliferation of these early tumor stages displayed a marked proliferative advantage over the normal parenchyma. The lesions were still subject to physiological growth stimulation as determined by 3H-TdR-continuous-labeling with osmotic mini-pumps following unilateral nephrectomy. However, compared with normal kidney parenchyma, the 3H-TdR-labeling index of the lesions was even higher indicating a response modification during early neoplasia.

Preneoplastic lesions in rodent kidney induced spontaneously or by non-genotoxic agents: predictive nature and comparison to lesions induced by genotoxic carcinogens

The current literature on non-genotoxic renal carcinogens and the associated neoplastic and preneoplastic lesions has been reviewed in order to determine their occurrence and predictive nature with regard to tumor formation. In addition the mechanisms involved in the genesis of renal tumors are discussed. A more generalized classification of preneoplastic and neoplastic renal lesions was introduced, based on studies conducted with genotoxic and non-genotoxic renal carcinogens. Reports on preneoplastic lesions were found in the literature for control animals as well as animals treated with non-genotoxic carcinogens. Due to the paucity of data regarding preneoplastic lesions in control animals and animals treated with non-genotoxic carcinogens, new data were also generated by rereading kidney slides of control animals of a randomly selected NTP study and kidney slides of male rats treated with the highest dose of ochratoxin A, one of the most potent non-genotoxic renal carcinogens known. The control slides and the slides from the ochratoxin A study indicated that the cytologic and morphologic types of preneoplastic lesions characteristically observed in bioassays using genotoxic carcinogens are also present in control animals and animals treated with non-genotoxic carcinogens. The incidence of preneoplastic lesions was low in control animals and higher in animals treated with non-genotoxic carcinogens. The diverse classifications used in the literature did not allow a direct comparison of lesions and corresponding incidences with those of the newly generated data. However, three major tendencies were observed: (a) whenever a high incidence of preneoplastic lesions was reported, renal neoplasms were also found, (b) the larger the size and the further a lesion had progressed, the higher was the probability of tumor formation, and (c) not all preneoplastic lesions are irreversible, but reversibility seemed to decrease with increasing lesion size and progression. It must be emphasized that the data available for these conclusions are limited. This is not due to the lack of adequate numbers of bioassays with non-genotoxic carcinogens, but rather to the lack of consistent reporting of data. A generalized and more widely used classification which incorporates early lesions would certainly improve the current data base on renal lesions and provide future improvements in the predictive nature of these lesions.

[Classification of renal cell carcinoma/tumors and their relationship to the nephron-collecting tubules system]

After a controversial phase of nomenclature (including--among others--the terms "hypernephroma" and "hypernephroid carcinoma") a cytomorphologically defined subtyping of renal cell tumours (adenomas, carcinomas, oncocytomas) is offered, based on new electron microscopical and histochemical observations. These data are in part supported by cytogenetical findings reported in the literature. Phenotypical/histogenetical relations to different parts or cell types, respectively, of the nephron-collecting duct system could be demonstrated. Chromophobe cell carcinoma and oncocytoma exhibit features of the intercalated cells.

The human chromophobe cell renal carcinoma: its probable relation to intercalated cells of the collecting duct

In the present study we have examined ten cases of the chromophobe type renal cell carcinoma. This type of tumor is distinguished from the other carcinomas of the kidney with light cytoplasm (formerly called "hypernephroid") by (a) a positive Hale's iron colloid stain of the cytoplasm, (b) the occurrence of numerous invaginated vesicles within the cytoplasm that resemble the invaginated vesicles of intercalated cells of the collecting duct system, and (c) a positive immunoreaction of both the plasma membrane and the cytoplasm with antibodies to the epithelial membrane antigen (EMA) and carbonic anhydrase C (CAC), respectively. Unlike oncocytomas, which also express CAC and EMA, the chromophobe renal cell carcinoma does not express the erythrocyte anion exchanger band 3. These findings strongly indicate that chromophobe renal cell carcinomas as well as oncocytomas of the kidney are histogenetically related to the two populations of intercalated cells of the collecting duct system. Thus, both tumors represent examples of renal tumors which disprove the broadly accepted hypothesis that all epithelial tumors of the kidney are histogenetically related to the proximal tubule.

Experimental induction of renal tumors

Renal tumors have been reported to be induced by natural products, chemical carcinogens, viruses, or radiation. Species or strain specificity and sex also appear to play significant roles in their development. In man, it is also likely that the heredity existence of other diseases, smoking, food habits, and irradiation may be etiological factors. It also appears that hormonal, chemical, and other environmental factors can play a role. Nephrotoxin modifies two-stage chemical carcinogenesis in rat kidney. Some nephrotoxins without carcinogenicity promote the development of renal tumors in rats pretreated with subcarcinogenic doses of chemical carcinogens. The importance of nephrotoxin in development of renal adenocarcinomas needs elucidation. Preneoplastic lesions in the kidneys can be recognized by histochemical methods with specific antibodies. It is hoped that further research will be continued, so that data obtained from experimental work will provide a better understanding of the etiology and induction of renal cancer in man.

Correlative histochemical studies on preneoplastic and neoplastic lesions in the kidney of rats treated with nitrosamines

Renal tubular lesions induced in male rats by two different carcinogens, N-nitrosomorpholine (NNM) and N-ethyl-N-hydroxyethylnitrosamine (EHEN), using a limited exposure "stop" protocol were investigated histochemically to demonstrate phenotypic cellular changes. The parameters measured included basophilia, glycogen content and the activity of the enzymes glucose-6-phosphatase (G6PASE), glycogen synthetase (SYN), glycogen phosphorylase (PHO), glucose-6-phosphate dehydrogenase (G6PDH), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), succinate dehydrogenase (SDH), alkaline phosphatase (ALP), acid phosphatase (ACP) and gamma-glutamyl transpeptidase (gamma-GT). The lesions observed were predominantly of either basophilic or oncocytic types. In each case, tubular lesions (altered tubules) appeared to give rise to epithelial tumors (epitheliomas) with the same cellular phenotype. Basophilic tubules and epitheliomas proved to be strongly positive for GAPDH and G6PDH while demonstrating a reduction or loss of G6PASE, ALP, ACP, gamma-GT, and SDH compared with controls and the surrounding proximal or distal tubules. In addition, large basophilic epitheliomas demonstrated an increase in both SYN and PHO activities. In contrast, most oncocytic tubules and oncocytomas characterized by abundant densely granular cytoplasm showed a reduction in the activity of G6PDH, but were intensely positive for SDH. However, a few oncocytic lesions demonstrated a decrease in both SDH and G6PDH activity. Rarely, decreased SDH and elevated G6PDH activities were observed in altered tubules resembling oncocytic tubules. It remains to be clarified whether these tubules represent a variation of the oncocytic lesions or, perhaps, another type of tubular lesion. The results indicate that basophilic and oncocytic epithelial tumors differ in their cytochemical pattern and histogenesis. In line with earlier suggestions, the basophilic tumors apparently originate from the proximal renal tubules, while the oncocytomas develop from the distal parts of the nephron. The basophilic tumors are characterized by an increased pentose phosphate pathway and glycolysis, with a corresponding reduction in mitochondrial respiration. However, the majority of the oncocytomas show an increased activity of the mitochondrial enzyme SDH, and a marked decrease in the activity of the key enzyme of the pentose phosphate pathway.

Histopathology and classification of renal cell tumors (adenomas, oncocytomas and carcinomas). The basic cytological and histopathological elements and their use for diagnostics

The term renal cell tumors (adenomas and carcinomas) subsumes the tumors deriving from the uriniferous tubule epithelium of the kidney. Precise analysis shows that the renal cell tumors display different cell types which build up the individual tumor alone or in combination with each other. Three categories of basic elements are distinguished in the characterization of renal cell tumors: Cytological elements = tumor cell types: Clear, chromophobe, chromophilic (basophilic, eosinophilic), oncocytic, spindle-shaped/pleomorphic. Histological elements = growth patterns: Compact, acinar (nest-like), tubulopapillary (tubular, papillary), cystic. Cytological grading of malignancy: G I, G II, G III; mainly based on the degrees of nuclear atypia. The cytological features are given priority compared to the histological growth forms for classification of renal cell tumors. However, the latter are not to be neglected in the overall evaluation of a tumor. A classification of renal cell tumors is suggested and the result of its application in 510 renal cell carcinomas and oncocytomas is presented. On this basis and in connection with the cytological grading, a more precise prognostic evaluation of the renal cell carcinomas is expected.

National Toxicology Program nomenclature for hepatoproliferative lesions of rats

Diagnostic criteria for hepatoproliferative lesions of Fischer 344 rats are presented to permit more complete categorization of the spectrum of lesions observed in two-year chemical carcinogenicity studies. A nomenclature recently adopted by the National Toxicology Program differs from previous classification schemes in that hepatocellular hyperplasia and hepatocellular adenoma are to be used for lesions which were previously combined under the diagnosis of neoplastic nodule. The term hyperplasia is reserved for proliferative lesions that are perceived to be secondary, nonneoplastic responses to degenerative changes in the liver. Foci of cellular alteration, hepatocellular adenoma, and hepatocellular carcinoma are believed to represent a spectrum of changes that comprise the natural history of neoplasia. This change in nomenclature was made subsequent to a peer review of representative hepatoproliferative lesions from two-year carcinogenicity studies. The revised nomenclature is consistent with traditional pathologic diagnoses for proliferative lesions in other epithelial tissues and should facilitate the interpretation of conventional toxicity and carcinogenicity studies in rats. Morphologic features of other selected rat liver lesions are also presented.

Aberrant regulation of carbohydrate metabolism and metamorphosis during renal carcinogenesis

Systematic studies of the sequence of cellular changes during renal carcinogenesis induced in rats by stop experiments with N-nitrosomorpholine or streptozotocin and of human renal cell carcinomas led to the following main results and conclusions: All types of epithelial kidney tumors known from human pathology, namely clear-cell, acidophilic (granular), basophilic, chromophobic and oncocytic tumors, can be induced by the chemicals. Phenotypically altered epithelia resembling those in the tumors appear in single or multiple tubules long before unequivocal tumors develop. The progression from the preneoplastic tubular lesions to the tumors is an autogenous process which is independent of the further action of the carcinogen. At least three different types of tubular lesions can be distinguished: (a) Clear cell tubules storing glycogen in excess, (b) chromophobic or basophilic tubules frequently accumulating acid mucopolysaccharides (glycosaminoglycans, proteoglycans), and (c) oncocytic tubules accumulating atypical mitochondria. Whereas the precise site of origin of the clear cell tubules within the nephron remains unclear, the fine structural and cytochemical findings suggest that the chromophobic and basophilic tubules originate from the proximal and the oncocytic tubules from the distal nephron. Each type of tubular lesion is apparently the precursor of a cytologically specific tumor type. The well-known aberration in carbohydrate metabolism in renal tumors might occur in response to a carcinogen-induced metabolic derangement which is frequently associated with excessive storage of polysaccharides or lipids persisting for weeks and months until fast-growing tumors appear. Whereas the primary biochemical lesion leading to the persisting storage phenomena is most probably fixed at the genetic level, epigenetic changes, namely an adaptation of cellular enzymes gradually activating alternative metabolic pathways, might be responsible for the ultimate neoplastic transformation of the cell.

Carcinogenicity and modification of the carcinogenic response by BHA, BHT, and other antioxidants

Carcinogenicity tests showed that addition of the antioxidant BHA to the diet of F344 rats induced high incidences of papilloma and squamous cell carcinoma of the forestomach of both sexes. Male hamsters given BHA for 24 weeks also developed papilloma showing downward growth into the submucosa of the forestomach. These results indicate that BHA should be classified in the category of "sufficient evidence of carcinogenicity" as judged by IARC criteria. The 3-tert isomer of BHA seemed to be responsible for the carcinogenicity of crude BHA in the forestomach of rats. BHT was not found to be carcinogenic in rats or mice. In two-stage carcinogenesis in rats after appropriate initiation, BHA enhanced carcinogenesis in the forestomach and urinary bladder of rats, but inhibited carcinogenesis in the liver. BHT enhanced the induction of urinary bladder tumors and inhibited that of liver tumors, but had no effect on carcinogenesis in the forestomach. BHT could be a promoter of thyroid carcinogenesis. Sodium L-ascorbate enhanced forestomach and urinary bladder carcinogenesis. Ethoxyquin enhanced kidney and urinary bladder carcinogenesis, but inhibited liver carcinogenesis. Thus, these antioxidants modify two-stage chemical carcinogenesis in the forestomach, liver, kidney, urinary bladder, and thyroid, but show organ-specific differences in effects.

Hepatocellular glycogenosis and related pattern of enzymatic changes during hepatocarcinogenesis

Systematic studies of the sequence of cellular changes during hepatocarcinogenesis induced predominantly in rats by stop experiments with N-nitrosomorpholine (NNM) led to the following main results and conclusions: The development of hepatocellular tumors is preceded by a multifocal hepatic glycogen storage disease (glycogenosis). Cytomorphological and cytochemical findings suggest a sequence of focal changes leading from clear and acidophilic glycogen storage foci through mixed cell foci and neoplastic nodules to hepatocellular carcinomas. The clear and acidophilic glycogen storage cells persisting after withdrawal of the carcinogen apparently represent a preneoplastic cell population, the neoplastic transformation of which is accompanied by a gradual reduction of glycogen and a concomitant increase in ribosomes (basophilia). The first appearance and frequency of the different liver lesions investigated was shown to depend on the dose of carcinogen administered. With increasing dose of NNM, the number of focal lesions considerably increased, and this was accompanied by an earlier development of mixed and basophilic cell populations. There was no indication of any reversibility of pronounced focal lesions under the experimental conditions chosen. On the contrary, the foci became larger and acquired phenotypic markers closer to neoplasia independent of further action of the carcinogen. Enzyme histochemically, the majority of the pronounced glycogen storage foci showed a reduction in the activities of glycogen phosphorylase and glucose-6-phosphatase while the activity of glucose-6-phosphate dehydrogenase, a key enzyme for the pentose phosphate pathway, was increased. The mixed cell foci, neoplastic nodules and carcinomas which emerged at later stages were characterized by a progressive shift away from glycogen metabolism towards glycolysis and the pentose phosphate pathway. as indicated by an increase in glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphate dehydrogenase activities. These changes in enzyme pattern are in keeping with a developmental sequence leading from glycogen storage foci through mixed cell foci and neoplastic nodules to hepatocellular carcinomas. Biochemical microanalysis of dissected glycogen storage foci and mixed cell foci revealed that the foci composed exclusively of storage cells contained on an average 100% more glycogen than the normal liver tissue. The overall glycogen content of the mixed cell foci, which were composed of both glycogenotic and glycogen-poor basophilic cells, was not distinguishable from that of normal tissue.(ABSTRACT TRUNCATED AT 400 WORDS)

[Morphogenesis and micromorphology of epithelial tumors induced in the rat kidney by nitrosomorpholine. IV. Tubular lesions and basophilic tumors (author's transl)]

The genesis of basophilic cell kidney tumors was investigated stepwise by light and electron microscopy in rats treated with N-nitrosomorpholine for a limited time (stop experiment). Seven weeks after the beginning of the experiment the kidney tubules sometimes showed unusually large "chromophobic" and basophilic cells. After a lag period of 22-97 weeks more than 60% of the animals had developed these atypical tubules. Parallel to the appearance of chromophobic tubules 50% of the carcinogen-treated animals developed basophilic cell kidney tumors. All intermediate stages between chromophobic or basophilic cell tubules and tumors were found. During the neoplastic transformation chromophobic epithelia appeared to change into basophilic cells. Some of the chromophobic renal tubules and most of the renal tubules which consisted of chromophobic and basophilic epithelia stored acid mucopolysaccharides as demonstrated by histochemical methods. The fine structure of the basophilic epitheliomas was relatively uniform. The basophilia observed under the light microscope correlated with abundant membrane-bound and free ribosomes as seen under the electron microscope. The frequent appearance of brush borders and microbodies indicated the origin of the basophilic cell tumors from proximal renal tubules. In some tumor cells many mitochondria were found. These cells resembled oncocytes. However, in contrast to typical oncocytes the mitochondria of these cells were poor in cristae or showed tubular formations of the inner membrane. In some mitochondria homogeneous condensations could be detected in the intracristal space and tooth-like formations were seen on the surface of the cristae. In perpendicular sections these cristae resembled saw blades. Acute tubular lesions and cellular regeneration, as described earlier by other authors in early stages of the development of kidney tumors, were not found. It is suggested that the storage of acid mucopolysaccharides observed in many tubules and in some renal tumors indicates a disturbance of the cellular metabolism which plays an important role in tumor development.