Glutathione transferase activities in renal carcinomas and adjacent normal renal tissues: factors influencing renal carcinogenesis induced by xenobiotics

Comparison of in vitro test systems using bacterial and mammalian cells for genotoxicity assessment within the "health-related indication value (HRIV) concept

In numerous cases, the German health-related indication value (HRIV) concept has proved its practicability for the assessment of drinking water relevant trace substances (Umweltbundesamt 2003). The HRIV is based on the toxicological profile of a substance. An open point of the HRIV concept has been the assignment of standardized test procedures to be used for the assessment. The level of the HRIV is at its lowest as soon as the genotoxicity of the substance is detected. As a single test on its own, it is not sufficient enough to assess the human toxicological relevance of a genotoxic effect or exclude it in the case of a negative result; a reasonable test battery was required, technically oriented towards the already harmonized international, hierarchical evaluation for toxicological assessment of chemicals. Therefore, an important aim of this project was to define a strategy for the genotoxicological assessment of anthropogenic trace substances. The basic test battery for genotoxicity of micropollutants in drinking water needs to fulfill several requirements. Although quick test results are needed for the determination of HRIV, a high degree of transferability to human genotoxicity should be ensured. Therefore, an in vitro genotoxicity test battery consisting of the Ames fluctuation test with two tester strains (ISO 11350), the umu test and the micronucleus test, or from the Ames test with five tester strains (OECD 471) and the micronucleus test is proposed. On the basis of selected test substances, it could be shown that the test battery leads to positive, indifferent, and negative results. Given indifferent results, the health authority and the water supplier must assume that it is a genotoxic substance. Genetically modified tester strains are being sensitive to different chemical classes by expression of selected mammalian key enzymes for example nitroreductase, acetyltransferase, and glutathione-S-transferase. These strains may provide valuable additional information and may give a first indication of the mechanism of action. To check this hypothesis, various additional strains expressing specific human-relevant enzymes were investigated. It could be shown that the additional use of genetically modified tester strains can enhance the detectable substance spectrum with the bacterial genotoxicological standard procedures or increase the sensitivity. The additional use provides orienting information at this level as a lot of data can be obtained quite quickly and with little effort. These indications of the mechanism of action should be however verified with a test system that uses mammalian cells, better human cells, to check their actual relevance. The selection of appropriate additional tester strains has to be defined from case to case depending on the molecular structure and also still requires some major expertise.

Re-assessment of the influence of polymorphisms of phase-II metabolic enzymes on renal cell cancer risk of trichloroethylene-exposed workers

PROBLEM

Individual differences in susceptibility to trichloroethylene-induced nephrocarcinogenicity may be conferred by genetic polymorphisms of glutathione S-transferases (GST), because enzymes of this group are pivotal for the metabolic activation of trichloroethylene. Because of a potential involvement of N-acetylation in the detoxication of reactive trichloroethylene metabolite(s) to N-acetyl-cysteine derivatives, polymorphisms of the NAT2 gene may also be relevant.

METHODS

The primary collective used for a re-investigation of these questions was that of a hospital-based case-control study by Brüning et al. (Am J Ind Med 43:274-285, 2003) of 134 renal cell cancer cases (20 cases exposed to trichloroethylene) and 401 matched controls. Genetic polymorphisms of GSTT1, GSTM1, GSTP1 and NAT2 were studied. Additional control collectives of non-diseased persons were used for comparison of allele frequencies.

RESULTS

No genetic influences on the development of renal cancer due to trichloroethylene were apparent, related to the deletion polymorphisms of GSTT1 and GSTM1, as well as to the NAT2 rapid/slow acetylator states. However, renal cell cancer cases displayed a somewhat higher proportion of the homozygous GSTP1 313A wild type (GSTP1*A), although this was not statistically significant (chi(2) test: P=0.1071, when using only the original controls of Brüning et al. (2003); P=0.0781 with inclusion of the additional controls).

CONCLUSION

The re-investigation does not confirm the working hypothesis of an influence of the deletion polymorphisms of the glutathione S-transferases GSTT1 and GSTM1 on renal cell cancer development due to high occupational exposures to trichloroethylene.

Identification of a glutathione S-transferase without affinity for glutathione sepharose in human kidney

To identify kidney glutathione S-transferase (GST) isoenzyme, which does not bind to glutathione affinity column, biochemical characterization was performed by using an array of substrates and by measuring sensitivity to inhibitors. Immunological characterization was done by immunoblotting. Affinity flow-through GST exhibited activity towards 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole and cumene hydroperoxide, typical class alpha substrates and high sensitivity towards hematin, an alpha class inhibitor. It cross-reacted with antibodies against alpha class GST. Affinity flow-through GST in human kidney is an alpha class member.

Effects of renal diseases on the regulation and expression of renal and hepatic drug-metabolizing enzymes: a review

1. The activity of drug-metabolizing enzymes (DMEs) in extrahepatic organs is highest in the kidneys. Generally, the kidneys contain most, if not all, of the DMEs found in the liver. Surprisingly, some of these DMEs show higher activity in the kidneys than in the liver. 2. Most of the renal DMEs are localized in the cortex of the kidneys, especially in the proximal tubules. DMEs are also found in the distal tubules and collecting ducts. 3. Renal diseases such as acute and chronic renal failure and renal cell carcinoma alter the regulation of both hepatic and extrahepatic phase I and II DMEs. Changes in the expression of these DMEs seem to be tissue and species specific. 4. Generally, there is significant down-regulation of most of the phase I and a few of phase II DMEs at the protein, mRNA and activity levels. Unfortunately, the mechanisms leading to the alteration in DMEs in renal diseases remain unclear, although many theories have been made. 5. The presence of some circulating factors such as cytokines, nitric oxide, parathyroid hormones and increased intracellular calcium play a role in the regulation of DMEs in renal diseases.

Changes in gene expression during chemical-induced nephrocarcinogenicity in the Eker rat

Hydroquinone (HQ) is a rodent carcinogen and a potential human carcinogen. Glutathione conjugation of HQ enhances its biological reactivity, and 2,3,5-tris-(glutathion-S-yl)hydroquinone (TGHQ) is a potent nephrotoxicant and nephrocarcinogen in the Eker rat. Moreover, a single exposure of primary epithelial cells derived from Eker rat kidneys to TGHQ transforms these cells into an immortalized phenotype (quinol-thioether transformed rat renal epithelial (QT-RRE) cells). The Eker rat bears a mutation in one allele of the tuberous sclerosis-2 (Tsc-2) tumor suppressor gene, which predisposes the animals to the development of spontaneous and chemical-induced renal cell carcinoma. Thus, the Eker rat provides a unique model for elucidating the mechanisms of renal tubular epithelial carcinogeneisis. cDNA microarray analysis of QT-RRE3 cells and of tumor tissue derived from the kidneys of Eker rats treated with TGHQ revealed alterations (by threefold or greater) in the expression of a total of 80 genes. Fifteen percent of these genes exhibited similar expression patterns in both QT-RRE cells and tumor tissue. The differentially expressed genes primarily participate in three major areas: (1) signal transduction or in the regulation of signal transduction (extracellular signal regulated kinase 2 (ERK2); protein kinase CK2; protein kinase B; c-jun; NF-kappaB; ras-related GTPases; annexins), (2) stress response, tissue remodeling, and DNA repair (glutathione-S-transferases; procollagen c proteinase enhancer; plasminogen activator; tissue inhibitor of metalloprotease 3; apurinic/apyrimidic endonuclease), and (3) electron transport and energy homeostasis (cytochrome c oxidase subunits). The changes in the expression of many of these genes was confirmed by reverse transcription (RT)-polymerase chain reactions (PCR) using primers specific for the differentially expressed genes. As an example, the annexin I and II genes, implicated in signal transduction, were highly induced in tumor tissue and also in dysplastic lesions isolated from the kidneys of rats treated chronically with TGHQ. The annexin I and II proteins were also upregulated in tumor tissue, which probably play an important role in TGHQ-induced nephrocarcinogenesis. Moreover, in the present study, a tumorigenicity assay using athymic nude mice revealed that QT-RRE cell lines formed tumors when injected in the subcutis of nude mice, providing evidence that the cells are malignantly transformed. Histopathological analysis further indicated that the tumors were composed of neoplastic cells, resembling renal carcinoma cells with varying degrees of atypia, with the presence of apoptotic and mitotic figures.

Coffee and its chemopreventive components Kahweol and Cafestol increase the activity of O6-methylguanine-DNA methyltransferase in rat liver--comparison with phase II xenobiotic metabolism

A lower rate of colon cancer was observed in consumers of coffee with a high content of the diterpenes Kahweol and Cafestol (K/C). In animal models, K/C have been found to protect against the mutagenic/carcinogenic effects of compounds such as 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), aflatoxin B1, and 7,12-dimethylbenz[a]anthracene. Thus far, such chemoprotection by K/C has been attributed to modifications of xenobiotic metabolism, e.g. enhanced detoxification by UDP-glucuronosyltransferase (UDPGT) and/or glutathione transferase (GST). In the present study, we investigated the potential of several coffee-related treatments (K/C [1:1], Cafestol-alone, Turkish coffee) to modify the expression level of the DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT) which is involved in the reversal of the precarcinogenic DNA damage O(6)-alkylguanine induced by alkylating agents. The results show that, in the male F344 rat, K/C and Cafestol increase hepatic MGMT in a dose-dependent manner up to a maximum of 2.6-fold at 0.122% K/C in the feed. Turkish coffee led to enhancements of up to 16%, the more moderate increase being associated with the lower estimated K/C intake through the beverage. In the livers of the rats receiving Turkish coffee, we also found 10-30% increases in several GST-related parameters (overall GST, GST-pi, glutathione, gamma-glutamylcysteine-synthetase) and a two-fold increase in UDPGT activity. Dose-response studies with K/C revealed that MGMT increased in parallel with three of the four GST-related parameters whereas the dose-response curves of UDPGT and of GST-pi activity displayed a steeper slope. Increased expression level of MGMT may extend the antimutagenic/anticarcinogenic potential of coffee components to protection against DNA alkylating agents.

Purification and characterization of a novel glutathione S-transferase from Asaphis dichotoma

An isoenzyme of glutathione S-transferase (adGST) was purified from liver intestine of the seashell (Asaphis dichotoma) by GST-Sepharose 4B affinity chromatography followed by reverse-phase HPLC. The enzyme has a pI value of 4.6 and is composed of two subunits each with a molecular weight of 23kDa. It exhibits different catalytic activities toward the substrates 1-chloro-2,4-dinitrobenzene, 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole, ethacrynic acid, and p-nitrophenyl acetate and, fascinatingly, shows high activity toward CDNB. The amino acid composition of adGST was determined and found to be very similar to the Sloane squid GSTs. N-terminal analysis of the first 15 residues of adGST revealed that it has 73% sequence identity with the pig roundworm GSTs. The adGST shows characteristics similar to those of class sigma GSTs, as was indicated by its substrate specificity, N-terminal amino acid sequence, and amino acid composition.

Genetic susceptibility to environmental toxicants: the interface between human and experimental studies in the development of new toxicological concepts

The growing knowledge of the genetic polymorphisms of enzymes metabolising xenobiotics in humans and their connections with individual susceptibility towards toxicants has created new and important interfaces between human epidemiology and experimental toxicology. The results of molecular epidemiological studies may provide new hypotheses and concepts, which call for experimental verification, and experimental concepts may obtain further proof by molecular epidemiological studies. If applied diligently, these possibilities may be combined to lead to new strategies of human-oriented toxicological research. This overview will present some outstanding examples for such strategies taken from the practically very important field of occupational toxicology. The main focus is placed on the effects of enzyme polymorphisms of the xenobiotic metabolism in association with the induction of bladder cancer and renal cell cancer after exposure to occupational chemicals. Also, smoking and induction of head and neck squamous cell cancer are considered.

Application of the S-pyridylethylation reaction to the elucidation of the structures and functions of proteins

Cysteine (Cys) and cystine residues in proteins are unstable under conditions used for acid hydrolysis of peptide bonds. To overcome this problem, we proposed the use of the S-pyridylethylation reaction to stabilize Cys residues as pyridylethyl-cysteine (PEC) protein derivatives. This suggestion was based on our observation that two synthetic derivatives formed by pyridylethylation of the SH group of Cys with either 2-vinylpyridine (2-VP) or 4-vinylpyridine (4-VP), designated as S-beta-(2-pyridylethyl)-L-cysteine (2-PEC) and S-beta-(4-pyridylethyl)-L-cysteine (4-PEC), were stable under acid conditions used to hydrolyze proteins. This was also the case for protein-bound PEC groups. Since their discovery over 30 years ago, pyridylethylation reactions have been widely modified and automated for the analysis of many structurally different proteins at levels as low as 20 picomoles, to determine the primary structures of proteins and to define the influence of SH groups and disulfide bonds on the structures and functional, enzymatic, medical, nutritional, pharmacological, and toxic properties of proteins isolated from plant, microbial, marine, animal, and human sources. Pyridylethylation has been accepted as the best method for the modification of Cys residues in proteins for subsequent analysis and sequence determination. The reaction has also been proposed to measure D-Cys, homocysteine, glutathione, tryptophan, dehydroalanine, and furanthiol food flavors. This integrated overview of the diverse literature on these reactions emphasizes general concepts. It is intended to serve as a resource and guide for further progress based on the reported application of pyridylethylation reactions to more than 150 proteins.