von Hippel-Lindau gene mutations in N-nitrosodimethylamine-induced rat renal epithelial tumors

Evaluating the mutagenicity of N-nitrosodimethylamine in 2D and 3D HepaRG cell cultures using error-corrected next generation sequencing

Human liver-derived metabolically competent HepaRG cells have been successfully employed in both two-dimensional (2D) and 3D spheroid formats for performing the comet assay and micronucleus (MN) assay. In the present study, we have investigated expanding the genotoxicity endpoints evaluated in HepaRG cells by detecting mutagenesis using two error-corrected next generation sequencing (ecNGS) technologies, Duplex Sequencing (DS) and High-Fidelity (HiFi) Sequencing. Both HepaRG 2D cells and 3D spheroids were exposed for 72 h to N-nitrosodimethylamine (NDMA), followed by an additional incubation for the fixation of induced mutations. NDMA-induced DNA damage, chromosomal damage, and mutagenesis were determined using the comet assay, MN assay, and ecNGS, respectively. The 72-h treatment with NDMA resulted in concentration-dependent increases in cytotoxicity, DNA damage, MN formation, and mutation frequency in both 2D and 3D cultures, with greater responses observed in the 3D spheroids compared to 2D cells. The mutational spectrum analysis showed that NDMA induced predominantly A:T → G:C transitions, along with a lower frequency of G:C → A:T transitions, and exhibited a different trinucleotide signature relative to the negative control. These results demonstrate that the HepaRG 2D cells and 3D spheroid models can be used for mutagenesis assessment using both DS and HiFi Sequencing, with the caveat that severe cytotoxic concentrations should be avoided when conducting DS. With further validation, the HepaRG 2D/3D system may become a powerful human-based metabolically competent platform for genotoxicity testing.

Application of HepaRG cells for genotoxicity assessment: a review

There has been growing interest in the use of human-derived metabolically competent cells for genotoxicity testing. The HepaRG cell line is considered one of the most promising cell models because it is TP53-proficient and retains many characteristics of primary human hepatocytes. In recent years, HepaRG cells, cultured in both a traditional two-dimensional (2D) format and as more advanced in-vivo-like 3D spheroids, have been employed in assays that measure different types of genetic toxicity endpoints, including DNA damage, mutations, and chromosomal damage. This review summarizes published studies that have used HepaRG cells for genotoxicity assessment, including cell model evaluation studies and risk assessment for various compounds. Both 2D and 3D HepaRG models can be adapted to several high-throughput genotoxicity assays, generating a large number of data points that facilitate quantitative benchmark concentration modeling. With further validation, HepaRG cells could serve as a unique, human-based new alternative methodology for in vitro genotoxicity testing.

Renal hypoxia-HIF-PHD-EPO signaling in transition metal nephrotoxicity: friend or foe?

The kidney is the main organ that senses changes in systemic oxygen tension, but it is also the key detoxification, transit and excretion site of transition metals (TMs). Pivotal to oxygen sensing are prolyl-hydroxylases (PHDs), which hydroxylate specific residues in hypoxia-inducible factors (HIFs), key transcription factors that orchestrate responses to hypoxia, such as induction of erythropoietin (EPO). The essential TM ion Fe is a key component and regulator of the hypoxia–PHD–HIF–EPO (HPHE) signaling axis, which governs erythropoiesis, angiogenesis, anaerobic metabolism, adaptation, survival and proliferation, and hence cell and body homeostasis. However, inadequate concentrations of essential TMs or entry of non-essential TMs in organisms cause toxicity and disrupt health. Non-essential TMs are toxic because they enter cells and displace essential TMs by ionic and molecular mimicry, e. g. in metalloproteins. Here, we review the molecular mechanisms of HPHE interactions with TMs (Fe, Co, Ni, Cd, Cr, and Pt) as well as their implications in renal physiology, pathophysiology and toxicology. Some TMs, such as Fe and Co, may activate renal HPHE signaling, which may be beneficial under some circumstances, for example, by mitigating renal injuries from other causes, but may also promote pathologies, such as renal cancer development and metastasis. Yet some other TMs appear to disrupt renal HPHE signaling, contributing to the complex picture of TM (nephro-)toxicity. Strikingly, despite a wealth of literature on the topic, current knowledge lacks a deeper molecular understanding of TM interaction with HPHE signaling, in particular in the kidney. This precludes rationale preventive and therapeutic approaches to TM nephrotoxicity, although recently activators of HPHE signaling have become available for therapy.

Coffee intake and trace element blood concentrations in association with renal cell cancer among smokers

PURPOSE

To determine whether higher coffee intake may reduce the risk of renal cell cancer (RCC) associated with lead (Pb) and other heavy metals with known renal toxicity.

METHODS

We conducted a nested case-control study of male smokers (136 RCC cases and 304 controls) within the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study. Cases diagnosed with RCC at 5 or more years following cohort enrollment were matched to controls on age (± 7 years) and whole blood draw date (± 30 days). Conditional logistic regression (using two-sided tests) was used to test for main effects and additive models of effect modification.

RESULTS

After a mean follow-up of 16.3 years, coffee consumption was not significantly associated with renal cell cancer risk, when adjusting for blood concentrations of Cd, Hg, and Pb and RCC risk factors (age, smoking, BMI, and systolic blood pressure) (p-trend, 0.134). The association with above median blood Pb and RCC (HR = 1.69, 95% CI 1.06, 2.85) appeared to be modified by coffee consumption, such that RCC risk among individuals with both increased coffee intake and higher blood lead concentration were more than threefold higher RCC risk (HR = 3.40, 95% CI 1.62, 7.13; p-trend, 0.003).

CONCLUSION

Contrary to our initial hypothesis, this study suggests that heavy coffee consumption may increase the previously identified association between higher circulating lead (Pb) concentrations and increased RCC risk. Improved assessment of exposure, including potential trace element contaminants in coffee, is needed.

Mechanisms of Rodent Renal Carcinogenesis Revisited

The important renal tumors that can be induced by exposure of rats to chemical carcinogens are renal tubule tumors (RTTs) derived from tubule epithelium; renal pelvic carcinoma derived from the urothelial lining of the pelvis; renal mesenchymal tumors (RMTs) derived from the interstitial connective tissue; and nephroblastoma derived from the metanephric primordia. However, almost all of our knowledge concerning mechanisms of renal carcinogenesis in the rodent pertains to the adenomas and carcinomas originating from renal tubule epithelium. Currently, nine mechanistic pathways can be identified in either the rat or mouse following chemical exposure. These include direct DNA reactivity, indirect DNA reactivity through free radical formation, multiphase bioactivation involving glutathione conjugation, mitotic disruption, sustained cell proliferation from direct cytotoxicity, sustained cell proliferation by disruption of a physiologic process (alpha 2u-globulin nephropathy), exaggerated pharmacologic response, species-dominant metabolic pathway, and chemical exacerbation of chronic progressive nephropathy. Spontaneous occurrence of RTTs in the rat will be included since one example is a confounder for interpreting kidney tumor results in chemical carcinogenicity studies in rats.

Epidemiology of Renal Cell Carcinoma

The increasing incidence of RCC in most populations may in part be due to increasing numbers of incidentally detected cancers with new imaging methods. Further, the increase is not only limited to small local tumours but also includes more advanced tumours, which may to some part explain the still high mortality rates. The variation in incidence between populations may have several other explanations. Traditionally the starting point has included thoughts of environmental exposures, which so far have only in part explained the causes of RCC, by means of cigarette smoking and obesity, which may account for approximately 40% of cases in high-risk countries (Table 2). Further, the genetic variations may be of importance as a cause of the difference between populations. Continued research in RCC is needed with the knowledge that nearly 50% of patients die within 5 years after diagnosis. The further search for environmental exposures should take in account the knowledge that RCC consists of different types with specific genetic molecular characteristics. These genetic alterations have in some cases been suggested to be associated with specific exposures. Furthermore, there might exist a modulating effect of genetic polymorphisms among metabolic activation and detoxification enzymes. Hence, a further understanding of the genetic and molecular processes involved in RCC will hopefully give us a better knowledge how to analyse and interpret exposure associations that have importance for both initiation and progression of RCC.

Contemporary epidemiology of renal cell cancer

We analyzed renal cell cancer incidence patterns in the United States and reviewed recent epidemiologic evidence with regard to environmental and host genetic determinants of renal cell cancer risk. Renal cell cancer incidence rates continued to rise among all racial/ethnic groups in the United States, across all age groups, and for all tumor sizes, with the most rapid increases for localized stage disease and small tumors. Recent cohort studies confirmed the association of smoking, excess body weight, and hypertension with an elevated risk of renal cell cancer, and suggested that these factors can be modified to reduce the risk. There is increasing evidence for an inverse association between renal cell cancer risk and physical activity and moderate intake of alcohol. Occupational exposure to trichloroethylene has been positively associated with renal cell cancer risk in several recent studies, but its link with somatic mutations of the von Hippel-Lindau gene has not been confirmed. Studies of genetic polymorphisms in relation to renal cell cancer risk have produced mixed results, but genome-wide association studies with larger sample size and a more comprehensive approach are underway. Few epidemiologic studies have evaluated risk factors by subtypes of renal cell cancer defined by somatic mutations and other tumor markers.

Genetic signature for human risk assessment: lessons from trichloroethylene

Trichloroethylene (TCE), an organic solvent commonly used for metal degreasing and as a chemical additive, is a significant environmental contaminant that poses health concerns in humans. The US Environmental Protection Agency (EPA) is currently revising the 2001 TCE human risk assessment draft. The next draft is expected to be ready in 2008. TCE metabolites are detectable in humans and carry varying potencies for induction of cancers in animals. Genomic mechanisms have been explored in animals and humans to link TCE to carcinogenesis. DNA analysis provides an opportunity for detection of unique genetic alterations representing a signature of TCE exposure. These alterations can arise from genotoxic and nongenotoxic pathways at multiple points throughout tumorigenesis. Although fixation of alterations may require several stages of selection and modification, the spectra can be specific to TCE. Only a fraction of these alterations eventually lead to tumor formation and some contribute to tumor progression. Genetic events in two major TCE target organs are reviewed, including the VHL gene in kidney, and the Ras gene and genome-wide hypomethylation in liver. Attempts to identify a genetic signature of TCE exposure are challenged by inconsistent findings, lack of evidence of promutagenic lesions, biological relevance of specific genomic changes, and likelihood of coexposures. For human risk assessment, genome-wide screening is useful and is possible with the development of new DNA-sequencing technologies. Genetic screening for preneoplastic and tumor tissues from high-risk population is proposed to exclude the noise of passenger mutations and genetic polymorphisms.

Cigarette smoking, von Hippel-Lindau gene mutations and sporadic renal cell carcinoma

We investigated whether smoking is associated with mutations in the Von Hippel–Lindau (VHL) gene in 337 cases of sporadic renal cell carcinoma (RCC) among 120 852 people followed for 11.3 years; the findings suggest that smoking causes RCC independently of VHL gene mutations.

Prevalence of von Hippel-Lindau gene mutations in sporadic renal cell carcinoma: results from The Netherlands cohort study

BACKGROUND

Biallelic von Hippel-Lindau (VHL) gene defects, a rate-limiting event in the carcinogenesis, occur in approximately 75% of sporadic clear-cell Renal Cell Carcinoma (RCC). We studied the VHL mutation status in a large population-based case group.

METHODS

Cases were identified within the Netherlands cohort study on diet and cancer, which includes 120,852 men and women. After 11.3 years of follow-up, 337 incident cases with histologically confirmed epithelial cancers were identified. DNA was isolated from paraffin material collected from 51 pathology laboratories and revised by one pathologist, leaving material from 235 cases. VHL mutational status was assessed by SSCP followed by direct sequencing, after testing SSCP as a screening tool in a subsample.

RESULTS

The number of mutations was significantly higher for clear-cell RCC compared to other histological types. We observed 131 mutations in 114 out of 187 patients (61%) with clear-cell RCC. The majority of mutations were truncating mutations (47%). The mean tumor size was 72.7 mm for mutated tumors compared to 65.3 mm for wildtype tumors (p = 0.06). No statistically significant differences were observed for nuclear grade, TNM distribution or stage. In other histological types, we observed 8 mutations in 7 out of 48 patients (15%), 1 mutation in 1 of 6 oncocytoma, 3 mutations in 2 of 7 chromophobe RCC, 2 mutations in 2 of 30 papillary RCC, no mutations in 1 collecting duct carcinoma and 2 mutations in 2 of 4 unclassified RCC.

CONCLUSION

VHL mutations were detected in 61% of sporadic clear-cell RCC. VHL mutated and wildtype clear-cell RCC did not differ with respect to most parameters.

Active and passive smoking and risk of renal cell carcinoma in Canada

This study aimed to assess the role of active and passive smoking in the development of renal cell carcinoma (RCC). Mailed questionnaires were completed by 1279 incident RCC cases and 5370 population controls between 1994 and 1997 in eight Canadian provinces. Data were collected on socio-economic status, smoking habits, diet and passive smoking status, as well as residential and occupational history. The study found an increased risk of RCC associated with active smoking. Elevated risk of RCC was also observed with passive smoking; compared with those never exposed to either passive or active smoking, men and women with 43 or more years of passive residential and/or occupational exposure had respective adjusted Odds Ratios (ORs) of 3.9 (95% Confidence Interval (CI) 1.4-10.6) and 1.8 (95% CI 1.0-3.3) (P=0.001 and P=0.09, respectively). Both active and passive smoking might play a role in the aetiology of RCC.

VHL down-regulation and differential localization as mechanisms in tumorigenesis

BACKGROUND

The von Hippel-Lindau (VHL) gene has been widely analyzed in many tumors. Early studies in animal tumors suggest that changes in VHL protein level and localization may be also important in tumorigenesis. In this study, we determined the role of VHL protein in human renal cell carcinomas.

METHODS

Seventy-five human renal cell carcinomas, predominantly of clear cell type (60 of 75), were examined for VHL protein by immunohistochemistry. The level and pattern of protein expression were then compared to VHL mutations and tumor characteristics.

RESULTS

An apparent decline of VHL level (positive in <50% of tumor cells) was observed in 49 (65%) tumors, a change more frequent than VHL mutations (28 of 75) (37%). In tumors, VHL was localized to the cytoplasm and/or the cell membrane. The occurrence of a predominantly membranous signal was significantly associated with missense mutations (9 of 14 tumors with missense mutations versus 14 of 61 tumors with no or nonmissense mutations, P = 0.0025) and tumor stage (23 of 60 tumors with stage TI versus 0 of 15 tumors with TII and TIII, P = 0.0034).

CONCLUSION

This study provides the first evidence of the role of VHL protein level and intracellular localization in tumorigenesis in humans.

Mutations in the VHL gene from potassium bromate-induced rat clear cell renal tumors

Potassium bromate (KBrO(3)) is a rat renal carcinogen and a major drinking water disinfection by-product in water disinfected with ozone. Clear cell renal tumors, the most common form of human renal epithelial neoplasm, are rare in animals but are inducible by KBrO(3) in F344 rats. Detection of cytoplasmic periodic acid-Schiff-positive granules in clear cell tumors, indicative of glycogen accumulation, provides evidence of their biochemical similarity to human counterparts. Mutation in the coding region of the von Hippel-Lindau (VHL) gene is frequently detected in human clear cell renal carcinomas. Detection of VHL mutations in KBrO(3)-induced rat renal tumors could enhance the relevancy of these rat renal tumors for human health risk assessment. Formalin-fixed paraffin-embedded control tissues and renal tumors from male F344 rats exposed to KBrO(3) in the drinking water for 2 years were examined microscopically and were microdissected for DNA extraction. The coding sequence and a promoter region of the VHL gene were examined by polymerase chain reaction-single strand conformation polymorphism and/or DNA sequencing. Two of nine clear cell renal tumors carried the same C to T mutation at the core region of the Sp1 transcription factor binding motif in the VHL promoter and one of four untreated animals had C to T mutation outside the highly conserved core region. Mutation in the VHL coding sequence was only detected in one tumor. No VHL mutations were observed in three chromophilic tumors. KBrO(3)-induced rat renal tumors are morphologically similar to their human counterpart but the genetic basis of tumorigenesis is different.

Use of the spontaneous Tsc2 knockout (Eker) rat model of hereditary renal cell carcinoma for the study of renal carcinogens

The kidney is a frequent site for chemically induced cancers in rodents and among the 10 most frequent sites for cancer in human patients. Renal cell carcinoma (RCC) is the most frequent upper urinary tract cancer in humans and accounts for 80-85% of malignant renal tumors. Hereditary RCC occurs in Eker rats that are heterozygous for an insertion mutation in the Tsc2 tumor suppressor gene. The germline mutation renders heterozygous mutants highly susceptible to renal carcinogens. The utility of this model in studying potential renal carcinogens is due to an ordered progression of proliferative renal lesions that can be identified and counted microscopically. The quantitative nature of the model allows for the production of statistically powerful data to understand the relative degree and potency of chemical effects and allow analysis of genetic alterations that may be chemical specific.

Down-regulation of von Hippel-Lindau protein in N-nitroso compound-induced rat non-clear cell renal tumors

Non-clear cell rat kidney tumors, inducible by N-nitroso compounds but lacking mutations in the von Hippel--Lindau (VHL) coding sequence, were examined for other VHL alterations. Neither mutations nor DNA methylation was detected in a putative promoter region. By immunohistochemistry, however, VHL protein level was evidently reduced in six of the eight eosinophilic renal epithelial tumors and in all the ten nephroblastomas. Immunoblotting of normal kidney detected two VHL proteins of 20 and 22kDa in a 16-day-old fetal rat but only 20kDa protein in an adult rat. This is the first demonstration of VHL alteration at the protein level.

Renal cancer: molecular mechanisms and newer therapeutic options

Renal cell carcinomas account for 80-85% of all primary renal neoplasms. Recent identification of VHL, c-met and TSC as candidate genes mutated in various types of renal carcinomas has greatly enhanced our understanding of the pathogenesis of renal carcinomas and has provided novel therapeutic options for patients with renal cancer. Furthermore, developments in angiogenesis and in tumor immunology have given us additional treatment modalities for cancer patients, especially those with renal cancer. This review highlights the genetic abnormalities seen in renal cell carcinomas and reviews current and future therapeutic options.

Heterozygous inactivation of TGF-beta1 increases the susceptibility to chemically induced mouse lung tumorigenesis independently of mutational activation of K-ras

Mice heterozygous for deletion of the transforming growth factor beta1 (TGF-beta1) gene show an enhanced rate of lung tumorigenesis following carcinogen treatment. Since the growth inhibitory activity of TGF-beta1 in epithelial cells is associated with K-ras p21, and K-ras mutations commonly occur in chemically-induced mouse lung tumors, we postulated that tumors in heterozygous TGF-beta1 mice might be more likely to have K-ras mutations compared with tumors in wildtype TGF-beta1 mice. Urethane-induced lung tumors in AJBL6 TGF-beta1 +/- and +/+ mice were examined for K-ras mutations by polymerase chain reaction/single strand conformation polymorphism analysis and sequencing. Mutation frequencies were similar in both genotypes: 12/18 +/- tumors (67%) and 10/16 +/+ tumors (62%). Mutations occurred in 80% +/- and 75% +/+ carcinomas, but in only 50% of the adenomas of both TGF-beta1 genotypes. Codon 61 A-->G transition mutations were predominant, occurring in 61% +/- and 44% +/+ tumors. Three +/- (17%) and three +/+ (19%) tumors showed codon 12 mutations, mostly G-->A transitions. Two +/- tumors had both codon 61 and codon 12 mutations. Interestingly, carcinomas with mutations in codon 61 were larger than those with codon 12 changes. It appears that the mechanism of enhanced susceptibility of TGF-beta1+/- mice to urethane-induced lung carcinogenesis does not involve selective development of tumors with K-ras mutations.

VHL gene alterations in renal cell carcinoma patients: novel hotspot or founder mutations and linkage disequilibrium

Mutations in the von Hippel-Lindau (VHL) gene are frequently detected in human sporadic renal cell carcinoma (RCC). We analysed 102 Swedish RCCs for VHL mutations by PCR-SSCP and sequencing. In 47 patients (46.1%), 70 different mutations were found, and most of them represented novel variations of the VHL gene. Mutations in the VHL gene were found in 54% of clear cell renal cell carcinomas (CCRCC) and in 18% of chromophilic cancers but in no chromophobe cancers or oncocytomas (P=0.016). Three novel hotspot or founder mutations were detected in our study: four CCRCCs carried a missense mutation (glutamic acid to lysine) at codon 160 which is critical in the stabilization of the H1 helix of the alpha domain and the alpha-beta domain interface in the VHL protein. Five CCRCCs and one chromophilic RCC harbored a 15-nucleotide in-frame deletion (codons 41-45) at a duplex tandem repeat sequence site. Moreover, this deletion was in linkage disequilibrium with a C-->T transition in the promoter region. The frequency of linkage was 17 times more common than chance. Five patients with this linked mutation resided in the same hospital district and at least three of them showed the two sequence variants in the tumor-adjacent tissue. In 5/6 patients the wild-type allele was lost in the tumor samples, suggesting a causal role for the mutations in RCC. These linked mutations might be novel polymorphisms maintained in a relative isolated population. Multiple mutations in VHL were found in 17 tumors out of 47 tumors with the VHL mutation. A higher multiple mutation detected rate (33%) was observed in grade 3 CCRCCs than those in grade 1 (22%) and grade 2 (9%) (P=0.04). This is evidence on the association between VHL mutation and extent of nuclear atypia.

The influence of very low doses of N-nitrosodimethylamine (NDMA) on the apoptosis of rat neutrophils in vivo. The role of reactive oxygen species

N-nitrosodimethylamine (NDMA) causes the apoptosis of neutrophils in vitro experiments. This compound also has the ability to stimulate neutrophils for the production of reactive oxygen species. It has been decided to examine more closely whether the apoptosis of neutrophils by NDMA is caused by the influence of the radicals produced by these cells and whether the stimulation to undergo apoptosis of neutrophils is caused by NDMA in either the original form or by its metabolites. The experiment was conducted on rats. The animals were administered a one-time dose of NDMA intragastrically, 1.5 mg/kg. The research was conducted 1,2,4,12 h consecutively following NDMA administration. The concentration of NDMA in blood was evaluated by means of the gas chromatography method. The neutrophils were isolated from blood by means of differential centrifugation. Respiratory burst was assessed in cells, by means of the cytochrome c reduction method. The percentage of cells revealing morphological properties of apoptosis was determined under the fluorescent microscope. It has been observed that the activation of the respiratory burst is caused mainly by non-metabolised NDMA. Probably the non-metabolised molecules of this compound also have a decisive role in the initiation of apoptosis of neutrophils. It can be assumed that the main factor responsible for the apoptosis of neutrophil rats following a one-time NDMA administration is the induction of respiratory burst in neutrophils by this compound.

K-ras mutations in mouse lung tumors of extreme age: independent of paternal preconceptional exposure to chromium(III) but significantly more frequent in carcinomas than adenomas

Preconceptional exposure of male NIH Swiss mice to chromium(III) chloride resulted in increased incidence of neoplastic and non-neoplastic changes in their progeny, including lung tumors in females [Toxicol. Appl. Pharmacol. 158 (1999) 161-176]. Since mutations in the K-ras protooncogene are frequent, early changes in mouse lung tumors, we investigated possible mutational activation of this gene as a mechanism for preconceptional carcinogenesis by chromium(III). These offspring had lived until natural death at advanced ages (average 816+/-175 days for controls, 904+/-164 for progeny of chromium-treated fathers). Mutations of K-ras, analyzed by single-strand conformation polymorphism and sequencing, were, in codon 12, wild type GGT (glycine), to GAT (aspartic acid); to GTT (valine); and to CGT (arginine); and in codon 61, wild-type CAA (glutamine), to CGA (arginine). K-ras mutation frequencies in lung tumors were very similar in control progeny (4/14) and in progeny of chromium-treated fathers (5/15). Thus, germline mutation or tendency to spontaneous mutation in K-ras does not seem to be part of the mechanism of preconceptional carcinogenesis here. However, an additional interesting observation was that K-ras mutations were much more frequent in lung carcinomas (8/16) than in adenomas (1/13) (P=0.02), for all progeny combined. This was not related to age of the tumor-bearing mice or the size of the tumors. K-ras mutations may contribute to malignant tumor progression during aging, of possible relevance to the putative association of such mutations with poor prognosis of human lung adenocarcinomas.

Renal toxicity and carcinogenicity of trichloroethylene: key results, mechanisms, and controversies

The discussion on renal carcinogenicity of trichloroethylene addresses epidemiological, mechanistic, and metabolic aspects. After trichloroethylene exposure of rats, renal cell tumors were found increased in males, and an increased incidence of interstitial cell tumors of the testes was reported. Studies on the metabolism of trichloroethylene in rodents and in humans support the role of bioactivation reactions for the development of tumors following exposure to trichloroethylene. Epidemiological cohort studies addressing the carcinogenicity of trichloroethylene with respect to the renal or urothelial target sites have been conducted, and no clear evidence for an elevated renal or urinary tract cancer risk in trichloroethylene-exposed groups was visible in exposed populations. However, a cohort study of 169 male workers having been exposed to unusually high levels of trichloroethylene in Germany within the period between 1956 and 1975 supported a nephrocarcinogenic effect of trichloroethylene in humans. The results of this study were discussed in the literature with considerable reserve; criticism was based mainly on the choice of the study group, which had been recruited from personnel of a company in which a cluster of four renal tumors was observed previously. Hence, a further case-control study was conducted in the same region. This study confirmed the results of the previous cohort study, supporting the concept of involvement of prolonged and high-dose trichloroethylene exposures in the development of renal cell cancer. Further investigations on patients with renal cell carcinoma and with histories of high trichloroethylene exposures, on the basis of excretion of marker proteins in the urine, pointed to toxic damage to the proximal renal tubules by trichloroethylene. The hypothesis of implication of a glutathione transferase-dependent bioactivating pathway of trichloroethylene, established in experimental animals, seems at least also plausible for humans. Apparently, the occurrence of renal cell carcinomas in man follows high-dose exposures to trichloroethylene that are also accompanied by damage to tubular renal cells. Development of renal cell carcinomas has been related to mutations in the vonHippel-Lindau (VHL) tumor suppressor gene. Renal cell carcinoma tissues of persons with histories of prolonged high-dose exposure to trichloroethylene were investigated for the occurrence of mutations of the vonHippel-Lindau (VHL) tumor suppressor gene. VHL gene mutations were found in the majority of renal cell tumors associated with high-level exposure to trichloroethylene. A specific mutational hot spot at the VHL nucleotide 454 was addressed as a unique mutation pattern of the VHL tumor suppressor gene. A synopsis of all experimental, clinical, and epidemiological data suggests that reactive metabolites of trichloroethylene, with likely involvement of dichlorovinyl-cysteine (DCVC), exert a genotoxic effect on the proximal tubule of the human kidney. This constitutes a tumor-initiating process of genotoxic nature, the initial genotoxic effect apparently being linked with mutational changes in the VHL tumor suppressor gene. However, there is compelling evidence that the full development of a malignant tumor requires continued promotional stimuli. Repetitive episodes of high peak exposures to trichloroethylene over a prolonged period of time apparently led to nephrotoxicity, visualized by the excretion of tubular marker proteins in the urine. This critical process of development of tubular damage by trichloroethylene must follow a "conventional" dose-dependence, implying a practical threshold. This view is much corroborated by the fact that the occurrence of human renal cell cancer is obviously confined to cases of unusually high trichloroethylene exposures in the past, with special characteristics of very high and repetitive peak exposures. Current instruments of regulation should be adjusted to allow adequate consideration of su

Expression of the von Hippel-Lindau Tumor Suppressor Gene in Nonneoplastic and Neoplastic Lesions of the Thyroid

Alterations of the von Hippel-Lindau (VHL) gene, which is supposed to act as a tumor suppressor gene, can cause hereditary tumors associated with the VHL syndrome and are found in different sporadic cancers as well. While VHL protein is distinctly detectable in thyroid follicles, so far its expression in nonneoplastic and neoplastic lesions of the thyroid has not been investigated comprehensively. To illuminate the role of VHL for thyroid tumorigenesis, we investigated 12 follicular adenomas; 22 follicular carcinomas; 11 papillary carcinomas; 6 poorly differentiated carcinomas (PDTCs); 9 undifferentiated carcinomas (UTCs); 8 medullary carcinomas; 13 cases with nonneoplastic as well as normal thyroid tissue of 10 patients with antibodies against VHL, vascular endothelial growth factor (VEGF); and the proliferation marker MIB1 immunohistochemically; and selected cases by Western blot analysis. VHL was clearly expressed in nonneoplastic lesions and differentiated tumors derived from follicular epithelium, diminished in PDTCs and very weakly or not detectable in UTCs (p = 0.001), nonneoplastic, and neoplastic C-cells. Although slightly increased in certain differentiated tumors, VEGF was found to be reduced in UTCs as well. In summary, VHL is expressed differently in nonneoplastic and neoplastic lesions of the thyroid in proportion to the level of differentiation. VHL gene alterations appear to be a late event in tumorigenesis of the thyroid and a reduction in VHL protein expression is associated with a loss of differentiation and increased aggressiveness in thyroid tumors. There is no apparent inverse correlation between VHL and VEGF expression as described for other sporadic carcinomas. Therefore, the role of VHL for angiogenesis and the molecular basis of the inactivation of VHL in thyroid tumors remains to be elucidated.