Rat liver theta-class glutathione S-transferases T1-1 and T2-2: their chromatographic, electrophoretic, immunochemical, and functional properties

Impact of polyphenol metabolites produced by colonic microbiota on expression of COX-2 and GSTT2 in human colon cells (LT97)

Polyphenols may play an important role in colon cancer prevention. After entering the colon, they are subjected to metabolism by the human gut microbiota. The objective of the present study was to analyze the impact of selected intestinal metabolites on modulation of enzymes involved in detoxification and inflammation in human adenoma cells LT97. LT97 cells were incubated with 3,4-dihydroxyphenylacetic acid (ES) and 3-(3,4-dihydroxyphenyl)-propionic acid (PS), metabolites of quercetin and chlorogenic acid/caffeic acid, respectively. The effect on cell number was analyzed using 4'- 6-diamino-2-phenylindole-dihydrochloride (DAPI)-staining. Modulation of glutathione S-transferase T2 (GSTT2) and cyclooxygenase-2 (COX-2) was measured by real-time PCR and Western blot. Comet assay was performed to assess the impact on DNA damage caused by the GSTT2 substrate cumene hydroperoxide (CumOOH). Polyphenol metabolites did not affect cell number but significantly upregulated GSTT2 expression and decreased COX-2. The latter was confirmed via Western blot. CumOOH-induced DNA damage was significantly reduced compared to the control. An upregulation of GSTT2 and downregulation of COX-2 could possibly contribute to the chemopreventive potential of polyphenols after degradation in the gut. Working with polyphenol metabolites is an important prerequisite to better understand the in vivo effects of pure polyphenols.

Impact of apple polyphenols on GSTT2 gene expression, subsequent protection of DNA and modulation of proliferation using LT97 human colon adenoma cells

Apple extract (AE) enhances expression of glutathione S-transferases (e.g., GSTT2) in human colon cells (LT97). Therefore, aim of the present study was to identify functional consequences of GSTT2 induction by AE and to determine the relation of AE effects to isolated compounds. Polyphenol composition of AE was analyzed. LT97 cells were treated with AE or synthetic polyphenol mixture (SPM) under conditions that induced GSTT2, and challenged with GSTT2-2 substrate cumene hydroperoxide (CumOOH) to determine DNA damage using comet assay. Modulation of GSTT2 expression (real-time PCR) was reassessed, and the influence on cell proliferation and pro-oxidative potential of AE and SPM were assessed to understand additional mechanisms. Induction of GSTT2 by AE was accompanied by protection of LT97 cells from CumOOH-induced genotoxicity. Although SPM was unable to reflect AE-specific bioactivity related to GSTT2 modulation and anti-genotoxicity, inhibition of LT97 cell proliferation by SPM was comparable. Storage of AE caused changes in phenolic composition along with loss of activity regarding GSTT2 induction and amplified growth inhibition. At the applied concentrations, no H(2)O(2) formation was detectable with any of the substances. AE can protect against oxidatively induced DNA damage. Nevertheless, chemopreventive effects of AE strongly depend on the specific composition, which is modified by storage.

Gene expression profiles in human peripheral blood mononuclear cells as biomarkers for nutritional in vitro and in vivo investigations

Identification of chemopreventive substances may be achieved by measuring biological endpoints in human cells in vitro. Since generally only tumour cells are available for such investigations, our aim was to test the applicability of peripheral blood mononuclear cells (PBMC) as an in vitro primary cell model since they mimic the human in vivo situation and are relatively easily available. Cell culture conditions were refined, and the basal variation of gene expression related to drug metabolism and stress response was determined. Results were compared with profiles of an established human colon cell line (HT29) as standard. For biomarker development of nutritional effects, PBMC and HT29 cells were treated with potentially chemopreventive substances (chrysin and butyrate), and gene expression was determined. Key results were that relevant stress response genes, such as glutathione S-transferase T2 (GSTT2) and GSTM2, were modulated by butyrate in PBMC as in HT29 cells, but the blood cells were less sensitive and responded with high individual differences. We conclude that these cells may serve as a surrogate tissue in dietary investigations and the identified differentially expressed genes have the potential to become marker genes for population studies on biological effects.

Direct chemiluminescent imaging detection of Cu/Zn-superoxidase dismutase, glutathione peroxidase, carbonic anhydrase-III, and catalase in rat liver cytosol separated by native porous gradient polyacrylamide gel electrophoresis

The cytosolic enzymes extracted from rat hepatocytes were separated by native porous gradient-PAGE (PG-PAGE) and were detected with a sensitive and fast chemiluminescence (CL) imaging method. Several peroxidases including glutathione peroxidase, Cu/Zn-superoxidase dismutase, and some other metallo-enzymes such as catalase, carbonic anhydrase-III (CA-III) present in the cytosol of rat hepatocytes have been selectively and sensitively detected by the direct CL imaging method using the luminol-H(2)O(2) chemiluminescent reagents. All detections after PG-PAGE were completed within 9 min. The linear range for the typical metallo-enzyme, e.g., CA-III is 0.75-4.9 microg/mL, with a detection limit of 0.25 microg/mL. In comparison with the traditional CBB-R250 staining method, the detection period decreased about 70 times and the detection sensitivity improved over ten times. Furthermore, two enzymes present in rat liver cytosol were identified employing MALDI-MS analysis of the tryptic digest after PG-PAGE.

Characterisation of a Zeta Class Glutathione Transferase from Arabidopsis thaliana with a Putative Role in Tyrosine Catabolism

A glutathione transferase (GST) similar to zeta GSTs in animals and fungi has been cloned from Arabidopsis thaliana using RT-PCR. The Arabidopsis zeta GST (AtGSTZ1) was expressed in Escherichia coli as his-tagged polypeptides, which associated together to form the 50-kDa AtGSTZ1-1 homodimer. Following purification, AtGSTZ1-1 was assayed for a range of activities and compared with other purified recombinant plant GSTs from the phi, tau, and theta classes. AtGSTZ1-1 differed from the other GSTs in showing no glutathione conjugating activity toward xenobiotics and no glutathione peroxidase activity toward organic hydroperoxides. Uniquely among the plant GSTs, AtGSTZ1-1 showed activity as a maleylacetone isomerase (MAI). This glutathione-dependent reaction is analogous to the cis-trans isomerization of maleylacetoacetate to fumarylacetoacetate, which occurs in the course of tyrosine catabolism to acetoacetate and fumarate. Thus, rather than functioning as a conventional GST, AtGSTZ1-1 appears to be involved in tyrosine degradation. In addition to the MAI activity, the AtGSTZ1-1 also catalyzed the glutathione-dependent dehalogenation of dichloroacetic acid to glyoxylic acid. This latter activity was used to demonstrate the presence of functional AtGSTZ1-1 inplanta.

Marked expression of glutathione S-transferase A4-4 detoxifying 4-hydroxy-2(E)-nonenal in the skin of rats irradiated by ultraviolet B-band light (UVB)

Enzyme, Western blot, and immunohistochemical analyses indicated that rat skin cytosol contained no detectable level of the homodimeric, alpha-class glutathione S-transferase (rGST) A4-4 which catalyzes the GSH conjugation of the toxic product, 4-hydroxy-2(E)-nonenal (HNE), nonenzymatically formed from n-6 polyunsaturated fatty acid residues of lipids by lipid peroxidation. Rats irradiated by single doses (4000-24,000 mJ/cm(2)) of ultraviolet B-band light (UVB, 200 mJ/cm(2)/min) markedly expressed rGSTA4-4 in the skin at a level one-fifth that of the liver in apparent specific activity toward HNE at a single dose of 24,000 mJ/cm(2). Skin rGSTA4-4 was isolated, purified to homogeneity, and identified with hepatic rGSTA4-4 by reverse-phase partition HPLC and by amino acid sequence analysis of its CNBr fission peptides. Immunohistochemistry with polyclonal antibody raised against rGSTA4-4 demonstrated the selective expression of rGSTA4-4 in epidermis and sebaceous glands localized in dermis after UVB irradiation.

Comparison of cytogenetic effects of 3,4-epoxy-1-butene and 1,2:3, 4-diepoxybutane in mouse, rat and human lymphocytes following in vitro G0 exposures

To understand better the species differences in carcinogenicity caused by 1,3-butadiene (BD), we exposed G0 lymphocytes (either splenic or peripheral blood) from rats, mice and humans to 3, 4-epoxy-1-butene (EB) (20 to 931 microM) or 1,2:3,4-diepoxybutane (DEB) (2.5 to 320 uM), two of the suspected active metabolites of BD. Short EB exposures induced little measurable cytogenetic damage in either rat, mouse, or human G0 lymphocytes as measured by either sister chromatid exchange (SCE) or chromosome aberration (CA) analyses. However, DEB was a potent inducer of both SCEs and CAs in G0 splenic and peripheral blood lymphocytes. A comparison of the responses among species showed that the rat and mouse were approximately equisensitive to the cytogenetic damaging effects of DEB, but the situation for the human subjects was more complex. The presence of the GSTT1-1 gene (expressed in the erythrocytes) reduced the relative sensitivity of the lymphocytes to the SCE-inducing effects of DEB. However, additional factors also appear to influence the genotoxic response of humans to DEB. This study is the first direct comparison of the genotoxicity of EB and DEB in the cells from all three species.

Increased bioactivation of dihaloalkanes in rat liver due to induction of class theta glutathione S-transferase T1-1

A characteristic feature of the class Theta glutathione S-transferase (GST) T1-1 is its ability to activate dichloromethane and dibromoethane by catalysing the formation of mutagenic conjugates. The level of the GSTT1 subunit within tissues is an important determinant of susceptibility to the carcinogenic effects of these dihaloalkanes. In the present study it is demonstrated that hepatic GST activity towards these compounds can be elevated significantly in female and male Fischer-344 rats by feeding these animals on diets supplemented with cancer chemopreventive agents. Immunoblotting experiments showed that increased activity towards the dihaloalkanes is associated with elevated levels of the GSTT1 subunit in rat liver. Sex-specific effects were observed in the induction of GSTT1 protein. Amongst the chemopreventive agents tested, indole-3-carbinol proved to be the most potent inducer of hepatic GSTT1 in male rats (6.2-fold), whereas coumarin was the most potent inducer of this subunit in the livers of female rats (3. 5-fold). Phenobarbital showed significant induction of GSTT1 only in male rat liver and had little effect in female rat liver. Western blotting showed that class Alpha, Mu and Pi GST subunits are not co-ordinately induced with GSTT1, indicating that the expression of GSTT1 is determined, at least in part, by mechanisms distinct from those that regulate levels of other transferases. The increase in amount of hepatic GSTT1 protein was also reflected by an increase in the steady-state level of mRNA in response to treatment with chemopreventive agents and model inducers. Immunohistochemical detection of GSTT1 in rat liver supported the Western blotting data, but showed, in addition to cytoplasmic staining, significant nuclear localization of the enzyme in hepatocytes from some treated animals, including those fed on an oltipraz-containing diet. Significantly, the hepatic level of cytochrome P-450 2E1, an enzyme which offers a detoxification pathway for dihaloalkanes, was unchanged by the various inducing agents studied. It is concluded that the induction of GSTT1 by dietary components and its localization within cells are important factors that should be considered when assessing the risk dihaloalkanes pose to human health.

Guinea pig liver Mu-class glutathione S-transferase M1-2 cross-reacts with antibodies to both rat Mu- and theta-class glutathione S-transferases

Two novel major heterodimeric Mu-class glutathione (GSH) S-transferases (GSTs), designated M1-2 and M1-3*, were isolated from guinea pig (gp) liver cytosol and purified to homogeneity together with a known major homodimeric Mu-class gpGSTM1-1 (reported as GST b by R. Oshino, K. Kamei, M. Nishioka, and M. Shin, 1990, J. Biochem. 107, 105-110). These three gpGSTs were quantitatively retained on an S-hexyl-GSH affinity column and separated as homogeneous proteins by chromatofocusing. Subunits of the heterodimers were inseparable on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but could be completely separated by reverse-phase partition high-performance liquid chromatography. A molecular cloning study demonstrated that the gpGST subunit M2 consisted of 217 amino acid residues with a calculated molecular mass of 25,562 and shared 84% identity in overall amino acid sequence with gpGSTM1-1. N-terminal amino acid sequences of peptides from the gpGST subunit M3* with a blocked N-terminus strongly suggested that it should belong to the Mu class. Western blot analysis using antisera raised against purified rat (r) GSTsA1-2 (Alpha), M1-1, P1-1 (Pi), and T2-2 (Theta) indicated that gpGSTsM1-1 and M1-3* cross-reacted only with anti-rGSTM1 antibody. However, gpGSTM1-2 cross-reacted intensely to almost the same extent with antibodies to both rGSTsM1-1 and T2-2. A homodimeric gpGSTM2-2, artificially constructed from native gpGSTM1-2 by treatment with guanidine hydrochloride followed by dialysis, intensely cross-reacted with antibodies to both the rat Mu- and Theta-class GSTs. Thus, the gpGST subunit M2 provided the first evidence for the double immuno-cross-reaction of a GST with polyclonal antibodies to two different classes of GSTs.