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PubMed1991

Phase I study of thiotepa in combination with the glutathione transferase inhibitor ethacrynic acid.

The glutathione transferases comprise a family of isoenzymes, one or more of which are involved in the conjugation of alkylating agents to glutathione (GSH). Increased GSH transferase activity has been shown to underlie acquired resistance to several alkylating agents. Ethacrynic acid inhibits the isoenzymes of GSH transferase with 50% inhibitory concentration values ranging from 0.3 to 6.0 microM and has been shown to restore sensitivity to alkylating agents in drug-resistant animal tumor models. We entered 27 previously treated patients with advanced cancer on a study of ethacrynic acid (25 to 75 mg/m2 p.o. every 6 h for 3 doses) and thiotepa (30 to 55 mg/m2 i.v. 1 h after the second dose of ethacrynic acid). The major toxicity of ethacrynic acid was diuresis, which was observed at every dose level; in addition, severe metabolic abnormalities occurred at 75 mg/m2. At 50 mg/m2, the diuretic effects were manageable. Myelosuppression was the most important effect of the combination. Two of seven courses of ethacrynic acid, 50 mg/m2, and thiotepa, 55 mg/m2, were associated with grade 3 or 4 neutropenia and/or thrombocytopenia. Nausea/vomiting greater than or equal to grade 2 was observed in 16% of courses. GSH transferase activity was assayed spectrophotometrically in the peripheral mononuclear cells of all patients. At each dose level, activity decreased following ethacrynic acid administration, with recovery by 6 h. Administration of ethacrynic acid, 50 mg/m2, resulted in a mean nadir of transferase activity of 37% of control. The pharmacokinetics of thiotepa and its principal metabolite TEPA were studied in 23 patients. The plasma disappearance of thiotepa fit a two-compartment open model with a terminal half-life of approximately 2 h. Plasma TEPA levels peaked at a mean of 2.16 h following thiotepa administration. The harmonic mean terminal half-life of TEPA was 10.4 h, and the TEPA area under the curve (AUC) did not increase with increasing thiotepa dose. The AUC of thiotepa was approximately twice, and the clearance about one-half, of the values obtained in a previous study of single agent thiotepa. The AUC of TEPA was lower than that previously observed. The data suggest that ethacrynic acid inhibits enzymes involved in the metabolic disposition of thiotepa, including its oxidative desulfuration to TEPA. The severity of the platelet toxicity was correlated with the AUC of thiotepa, but not with that of TEPA. This combination of thiotepa and ethacrynic acid will be tested further in Phase II trials.

Adult↗
PubMed1991

A gene coding for 3-deoxy-D-manno-octulosonic-acid transferase in Escherichia coli. Identification, mapping, cloning, and sequencing.

An autoradiographic assay applicable to colonies immobilized on filter paper was developed for obtaining temperature-sensitive mutants of Escherichia coli defective in the transfer of 3-deoxy-D-manno-octulosonic acid (KDO) from CMP-KDO to a tetraacyldisaccharide 1,4'-bisphosphate precursor of lipid A, designated lipid IVA. Cell-free extracts from two mutants found in a population of 30,000 mutagen-treated cells showed normal KDO transferase activity when assayed at 30 degrees C, but almost no activity at 42 degrees C. The mutation was mapped by mating one of the mutants with different Hfr strains and analyzing genetic linkage of KDO transferase activity to selectable markers. The lesion was located to a position between 80 and 84 min on the E. coli chromosome. A plasmid from the Clarke and Carbon collection (Clarke, L., and Carbon, J. (1976) Cell 9, 91-99), pLC17-24, known to contain genes from the rfa region (81 min), was shown to overexpress KDO transferase activity 4-5 times and to correct the mutation when the plasmid was conjugated into the mutant strains. The KDO transferase gene, designated kdtA, was subcloned from pLC17-24 into a multicopy vector. The resulting plasmid, pCL3, overproduced transferase activity approximately 100-fold. The kdtA gene was shown to code for a 43-kDa polypeptide, as judged by radiolabeling of minicells. Its DNA sequence was determined. The results demonstrate that overexpression of this single gene product greatly stimulates the incorporation of two stereochemically distinct KDO residues during lipopolysaccharide biosynthesis in extracts of E. coli.

Autoradiography↗
PubMedDate not supplied

[Dietary protein as a modulator of the activity of enzymes metabolizing xenobiotics. UDP glucuronosyltransferase and glutathione transferase].

Activity of microsomal UDP-glucuronosyl transferase and cytosol glutathione transferase was studied in the liver and small intestine mucosa of rats which received rations with 5.18 and 33% of protein, during 2 months. Activity of UDP-glucuronosyl transferase GT1-isoform both in native and in detergent-activated microsomes of the liver increased with protein deficiency in the ration, while GT2-isoform activity and that of three glutathione transferase forms decreased. Excess of protein in the ration led to a growth of conjugation enzyme activity in the liver. The food protein level influenced the degree of GT1 and GT2 induction by benzyl but it did not change the capacity for induction of glutathione transferase. Activity of conjugation enzymes in the small intestine mucosa of rats to a lesser degree depended on the protein level in the ration.

Animals↗
PubMed1990

Human glutathione S-transferase deficiency as a marker of susceptibility to epoxide-induced cytogenetic damage.

The identification of genetic traits that predispose individuals to environmentally induced cancers is one of the most important problems in cancer risk assessment. Genetic deficiency in the mu-isozyme of the glutathione (GSH) S-transferases (EC 2.5.1.18) has recently been associated with increased lung cancer risk. To test whether this association could arise from a metabolically mediated sensitivity to mutagenic substrates, cytogenetic damage in lymphocytes from 21 isozyme-deficient and 24 nondeficient individuals was induced. Cells were treated with trans-stilbene oxide, an excellent substrate for GSH S-transferase mu, or cis-stilbene oxide, a poor substrate for the isozyme. Sister chromatid exchange induction was measured as an indicator of cytogenetic damage. A trimodal distribution of trans-stilbene oxide-induced sister chromatid exchanges was observed in the population, including resistant, moderate, and highly sensitive groups. Glutathione S-transferase mu deficiency was associated with both moderate and high sensitivity to trans-stilbene oxide-induced damage but had no effect on cis-stilbene oxide-induced sister chromatid exchange. The results indicate that GSH S-transferase mu, a proposed marker of cancer susceptibility, is also a marker of susceptibility to the induction of cytogenetic damage by a certain class of mutagens. The differential effects of the cis- and trans-isomers of stilbene oxide illustrate that the stereoselectivity of GSH S-transferase mu toward various alkene epoxide substrates can be an important factor affecting individual sensitivity to DNA-damaging epoxides.

Adult↗
PubMed1989

Immunocytochemical localization of the major glutathione S-transferases in adult Schistosoma mansoni.

Indirect immunofluorescence was used to investigate the tissue distribution of the major isoenzymes of Schistosoma mansoni glutathione S-transferase (GSH S-transferase). When polyclonal rabbit antisera against GSH S-transferase isoenzymes SmGST-1, -02, and -3 were applied to cryostat or plastic-embedded sections of fixed adult worms, a punctate pattern of enzyme distribution was observed that was restricted to the parenchyma. Labeling was much more pronounced in males than females, consistent with the biochemically determined distribution of these enzymes between the sexes. Intense immunolabeling was noted within the subectocytoplasmic core tissue of the tubercles of the male that appeared to be connected to deep parenchymal cells by immunoreactive cell processes. Immunofluorescence could be blocked completely by prior incubation of antisera with affinity-purified enzyme. Although schistosome GSH S-transferases have been reported to be protective antigens, no immunoreactivity was detected within or on the tegument, including the dorsal spines of the male. The lack of tegumental immunoreactivity was confirmed by immunoblotting of tegumental membrane preparations following SDS-PAGE. Muscle fibers, vitelline cells, and cecal epithelium also failed to react. The fact that the GSH S-transferases were not uniformly distributed among all parenchymal cells suggests the existence of subpopulations of parenchymal cells that are preferentially involved in the conjugation of electrophiles with glutathione.

Animals↗
PubMed1986

Rat glutathione S-transferases supergene family. Characterization of an anionic Yb subunit cDNA clone.

High multiplicity of GSH S-transferases (GST) with overlapping substrate specificities may be essential to their multiple roles in xenobiotics metabolism, drug biotransformation, and protection against peroxidative damage. Subunit composition analysis of rat liver GSH S-transferases indicated that heterodimer associations were not random, limiting the generation of GST isozyme multiplicity. We have analyzed a Yb subunit cDNA clone, pGTR187, that may correspond to an anionic Yb subunit sequence. Comparison with other GSH S-transferase cDNA sequences and blot hybridization results indicates that the multiple Yb subunits are encoded by a multigene family. This Yb subunit sequence has very limited homology to Ya and Yc subunit cDNAs, but slightly more sequence homology to the Yp subunit cDNA. More consistent sequence homology is found at the amino acid level with 28% conservation throughout the coding sequences. These results and results published from other laboratories clearly indicate that rat GSH S-transferases are products of at least four different gene families that constitute a supergene family. Conceptually, the supergene family may encode GSH S-transferases of very different structures that are essential to metabolize a multitude of xenobiotics in addition to serving other physiologically important functions.

Amino Acid Sequence↗
PubMed1988

Expression of an enzymatically active Yb3 glutathione S-transferase in Escherichia coli and identification of its natural form in rat brain.

Glutathione S-transferases containing Yb3 subunits are relatively uncommon forms that are expressed in a tissue-specific manner and have not been identified unequivocally or characterized. A cDNA clone containing the entire coding sequence of Yb3 glutathione S-transferase mRNA was incorporated into a pIN-III expression vector used to transform Escherichia coli. A fusion Yb3-protein containing 14 additional amino acid residues at its N terminus was purified to homogeneity. Recombinant Yb3 was enzymatically active with both 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene as substrates but lacked glutathione peroxidase activity. Substrate specificity patterns of recombinant Yb3 were more limited than those of glutathione S-transferase isoenzymes containing Yb1- or Yb2-type subunits. Peptides corresponding to unique amino acid sequences of Yb3 as well as a peptide from a region of homology with Yb1 and Yb2 subunits were synthesized. These synthetic peptides were used to raise antibodies specific to Yb3 and others that cross-reacted with all Yb forms. Immunoblotting was utilized to identify the natural counterpart of recombinant Yb3 among rat glutathione transferases. Brain and testis glutathione S-transferases were rich in Yb3 subunits, but very little was found in liver or kidney. Physical properties, substrate specificities, and binding patterns of the recombinant protein paralleled properties of the natural isoenzyme isolated from brain.

Amino Acid Sequence↗
PubMed1987

Selective expression of a unique glutathione S-transferase Yb3 gene in rat brain.

A cDNA clone from a rat brain lambda gt11 expression vector library contained the entire open reading frame, the 3' untranslated sequence, and 18 nucleotides of the 5' untranslated region of a Yb-type glutathione S-transferase that was clearly distinct from previously characterized liver forms. This form was designated as Yb3. Primer extension analysis indicated that the mRNA for Yb3 extends 118 nucleotides upstream of the translation initiation codon, and its total length of 1308 nucleotides is substantially larger than the transcripts of any of the liver glutathione S-transferases described thus far. The open reading frame of 654 nucleotides of Yb3 is the same as that of liver Yb1 and Yb2, with greater than 80% sequence homology. The amino acid sequence derived for Yb3 had regions conserved in all forms of Yb glutathione S-transferase, some other amino acid residues common to either Yb1 or Yb2, and 28 substitutions unique to Yb3. The 533 nucleotides in the 3' untranslated region of Yb3 were longer and not homologous to the 3' noncoding ends of the previously described glutathione S-transferases. A second clone from the brain library was virtually identical to that of the gene encoding the liver Yb1 form of the enzyme. Northern blot analyses of rat brain poly(A)+ RNA with specific Yb1 and Yb3 probes showed that the Yb3 form hybridized with a 1300-nucleotide mRNA, Yb1 with a separate 1100-nucleotide component, and that the two probes did not cross-hybridize. Moreover, while Yb3 is a minor component in liver, testis, and heart with even lesser amounts in spleen, lung, and kidney, it is a major glutathione S-transferase transcript in rat brain.

Amino Acid Sequence↗
PubMed1982

Benzo(a)pyrene metabolism by rat liver microsomes: effects of adding purified glutathione S-transferases A, B, and C.

We have examined the effects of adding glutathione and isolated cytosolic glutathione S-transferases A, B, and C to rat liver microsomes metabolizing benzo(a)pyrene. Addition of glutathione alone resulted in the conjugation of 15 to 20% of the total metabolites of benzo(a)pyrene, and this conjugation could be inhibited almost entirely by bromosulfophthalein (an inhibitor of glutathione S-transferases), indicating that it is catalyzed by the glutathione S-transferase present in microsomes. Addition of purified cytosolic glutathione S-transferases A, B, and C yielded about 30 to 40% conjugate formation. Analysis of metabolites by high-pressure liquid chromatography demonstrated that the formation of 4,5-diol of benzo(a)pyrene was decreased by at least 80% by conjugation and that the 7,8-diol was also decreased significantly (40 to 60%). In addition, it was found that glutathione S-transferase B is capable of conjugating benzo(a)pyrene 1,6- and 3,6-quinones.

Animals↗
PubMed1984

Distinctions between the multiple cationic forms of rat liver glutathione S-transferase.

Three cationic glutathione S-transferase forms isolated from rat liver were characterized as dimers that originated from different combinations of two subunit types, Ya and Yc. The cationic forms were purified using lysyl glutathione affinity matrices and were chromatographically resolved from anionic glutathione S-transferases that contain Yb subunits. The three classes of cationic transferase exhibited similar specific activities with 1-chloro-2,4-dinitrobenzene as a substrate, all forms cross-reacted with antibodies to glutathione S-transferase B, and all had comparable secondary structures and tryptophan fluorescence properties. In spite of those similarities, the Yc-containing forms were clearly distinguishable from Ya forms on the basis of characteristic differences in circular dichroic patterns associated with their aromatic side chains. All cationic transferases bound bilirubin with stoichiometric ratios of 1 mol/dimeric protein molecule, but discrete differences in mode of binding were ascribed to forms containing Ya subunits as compared to Yc dimers. Binding to Yc forms was of lower affinity and may be associated with the catalytic region of the protein since glutathione effectively displaced bilirubin from the Yc component.

Animals↗
PubMed1981

Evolutionarily homologous alpha 2 beta 2 oligomeric structures in beta-ketoadipate succinyl-CoA transferases from Acinetobacter calcoaceticus and Pseudomonas putida.

Homogeneous beta-ketoadipate succinyl-CoA transferase (EC 2.8.3.6) preparations were obtained from extracts of Acinetobacter calcoaceticus and Pseudomonas putida. Gel filtration indicated that the respective transferases have similar molecular weights of 108,000 and 109,000; each transferase appears to have an alpha 2 beta 2 oligomeric structure formed by association of nonidentical subunits with a molecular weight of about 25,000. The subunits were separated by sodium dodecyl sulfate-gel electrophoresis, and differences in their primary structures were revealed by determination of the NH2-terminal amino acid sequences of the oligomers. The transferases cross-react immunologically and possess similar amino acid compositions. These are remarkably similar to the amino acid compositions of gamma-carboxymuconolactone decarboxylases (EC 4.1.1.44) and beta-ketoadipate enol-lactone hydrolases (EC 3.1.1.24), enzymes that mediate consecutive reactions preceding the transferase step in the beta-ketoadipate pathway.

Acinetobacter↗
PubMed1982

Isolation and identification of kahweol palmitate and cafestol palmitate as active constituents of green coffee beans that enhance glutathione S-transferase activity in the mouse.

Glutathione (GSH) S-transferase is a major detoxification enzyme system that catalyzes the binding of a variety of electrophiles, including reactive forms of chemical carcinogens, to GSH. Green coffee beans fed in the diet induced increased GSH S-transferase activity in the mucosa of the small intestine and in the liver of mice. A potent compound that induces increased GSH S-transferase activity was isolated from green coffee beans and identified as kahweol palmitate. The corresponding free alcohol, kahweol, and its synthetic monoacetate are also potent inducers of the activity of GSH S-transferase. A similar diterpene ester, cafestol palmitate, isolated from green coffee beans was active but less so than was kahweol palmitate. Likewise, the corresponding alcohol, cafestol, and its monoacetate showed moderate potency as inducers of increased GSH S-transferase activity. Kahweol palmitate and cafestol palmitate were extracted from green coffee beans into petroleum ether. The petroleum ether extract was fractionated by preparative normal-phase and reverse-phase liquid chromatographies successively. Final purification with silver nitrate-impregnated thin-layer chromatography yielded the pure palmitates of cafestol and kahweol. The structures were determined by examination of the spectroscopic data of the esters and their parent alcohols and by derivative comparison.

Animals↗
PubMedDate not supplied

Problems in the diagnosis of transferase and galactokinase deficient galactosemia.

Galactose in serum and galactose-1-phosphate in erythrocytes were measured in six transferase deficient children to determine if these metabolites could be used in detecting transferase deficient galactosemia. In all six children the galactose levels were normal and the galactose-1-phosphate elevated. The galactose level depends on diet and the rate of metabolism to galactose-1-phosphate and, therefore, should not be used to predict transferase deficient galactosemia. The galactose-1-phosphate level was elevated in all the transferase deficient children because once formed it cannot be metabolized. Measurement of galactose-1-phosphate is difficult and is usually requested to determine whether or not the child is following the galactose restricted diet. In transferase deficient galactosemia, the enzyme hexose-1-phosphate uridylyltransferase is absent. The diagnosis should be determined by measurement of the activity of the enzyme hexose-1-phosphate uridylyltransferase in erythrocytes. In galactokinase deficient galactosemia, the enzyme galactokinase is absent. Galactose levels are elevated but the amount present depends on diet and how soon the blood was collected after the ingestion of galactose containing foods. The diagnosis of galactokinase deficient galactosemia is based on the measurement of the enzyme galactokinase in erythrocytes.

Adolescent↗
PubMed1994

Reaction of rat liver glutathione S-transferases and bacterial dichloromethane dehalogenase with dihalomethanes.

Dichloromethane dehalogenase from Methylophilus sp. DM11 is a glutathione S-transferase homolog that is specifically active with dihalomethane substrates. This bacterial enzyme and rat liver glutathione S-transferases were purified to investigate their relative reactivity with CH2Cl2 and related substrates. Rat liver alpha class glutathione transferases were inactive and mu class enzymes showed low activity (7-23 nmol/min/mg of protein) with CH2Cl2. theta class glutathione transferase 5-5 from rat liver and Methylophilus sp. dichloromethane dehalogenase showed specific activities of > or = 1 mumol/min/mg of protein. Apparent Kcat/Km were determined to be 3.3 x 10(4) and 6.0 x 10(4) L M-1 S-1 for the two enzymes, respectively. Dideutero-dichloromethane was processed to dideutereo-formaldehyde, consistent with a nucleophilic halide displacement mechanism. The possibility of a GSCH2X reaction intermediate (GS, glutathione; X, halide) was probed using CH2ClF to generate a more stable halomethylglutathione species (GSCH2F). The reaction of CH2ClF with dichloromethane dehalogenase produced a kinetically identifiable intermediate that decomposed to formaldehyde at a similar rate to synthetic HOCH2CH2SCH2F. 19F-NMR revealed the transient formation of an intermediate identified as GSCH2F by its chemical shift, its triplet resonance, and H-F coupling constant consistent with a fluoromethylthioether. Its decomposition was matched by a stoichiometric formation of fluoride. These studies indicated that the bacterial dichloromethane dehalogenase directs a nucleophilic attack of glutathione on CH2Cl2 to produce a halomethylthioether intermediate. This focuses attention on the mechanism used by theta class glutathione transferases to generate a halomethylthioeter from relatively unreactive dihalomethanes.

Animals↗
PubMed1977

The glutathione S-transferases of the small intestine in the rat.

Glutathione S-transferase activities have been identified in the small intestine of the rat. Thrree activities obtained with p-nitrobenzyl chloride (aralkyl), 1,2-epoxy-3(p-nitrophenoxy)propane (epoxide), and ethacrynic acid (alkene) as substrates were present in significant amounts. Gel filtration indicated an elution volume for the intestinal transferase activities that was similar to those activities in the liver and kidney. The induction of the intestinal transferases by polycyclic aromatic hydrocarbons and phenobarbital is similar to those effects observed previously for the hepatic and renal enzymes. The highest concentration of transferase activities occurs in the proximal small intestine; these activities are reduced upon fasting. Parallel observations have been reported for aryl hydrocarbon hydroxylases. Because only low or negligible levels of epoxide hydrases have been reported in the small intestine, the glutathione S-transferases may be the primary epoxide-detoxifying system in that organ.

Animals↗
PubMed1993

A basis for differentiating among the multiple human Mu-glutathione S-transferases and molecular cloning of brain GSTM5.

Specific cDNA probes and antisera were employed to interpret genetic polymorphisms of human Mu-class glutathione S-transferases and to provide a basis for identifying individual forms in human tissues. A cDNA probe that cross-hybridized with various human and rodent Mu-glutathione S-transferase transcripts, hybridized with at least three discrete components by Northern analysis of RNA from human tissue. The smallest (1.3 kb) transcript was identified as the one that encodes GSTM3-3 subunits. A form designated GSTM5, was cloned from a human brain cDNA library and its sequence determined. The open reading frame of GSTM5 shared a high degree of homology with the sequences of other Mu-class glutathione S-transferases, but its 846-nucleotide 3'-noncoding region was unique and considerably larger than that of any of the other Mu forms. Specific synthetic peptide antigens were utilized to distinguish among Mu-class glutathione S-transferases in different tissues of representative individuals. The primary hepatic transcript was that encoding GSTM1-1 with much lesser amounts of GSTM3-3, but livers were devoid of GSTM2-2, and GSTM5-5. Immunoblots confirmed that null-phenotype individuals lacked the GSTM1 gene rather than its GSTM2 homologue that is nearly identical in its exon sequences. The null phenotype therefore was conspicuous in liver, where GSTM1-1 ordinarily was the predominant Mu transcript, but brain and testis contained all four forms. A general strategy was devised to distinguish among and assign primary structures to individual glutathione S-transferases from human tissue.

Adult↗
PubMed1988

Gamma glutamyl transferase activity in rat colon during experimental colonic carcinogenesis.

Colonic gamma glutamyl transferase activity is raised in colonic malignancy. This study was undertaken to determine how early and how extensively this raised activity occurs during carcinogenesis. Sixty rats were given weekly injections of dimethylhydrazine for 16 weeks, and 20 rats acted as controls. Groups of treated and control rats were sacrificed at regular intervals during the pre-cancerous phase of carcinogenesis, and gamma glutamyl transferase activity was measured at several sites in the colon. Gamma glutamyl transferase activity was raised as early as 4 weeks after the first injection of dimethylhydrazine (p less than 0.05), and the elevation persisted until the development of overt tumours. The raised gamma glutamyl transferase activity was observed throughout both the proximal and distal colon long before the appearance of macroscopic tumours. We conclude that an early and widespread elevation of colonic gamma glutamyl transferase activity occurs during carcinogenesis. This may have useful applications in the early detection of colonic malignancy.

1,2-Dimethylhydrazine↗
PubMed1993

Carnitine palmitoyl transferase deficiency in malignant hyperthermia.

The activity of carnitine palmitoyl transferase, an enzyme that catalyzes the transport of long-chain acylcarnitines into mitochondria, was quantitated in EB-virus-transformed lymphoblasts from 7 patients with susceptibility for malignant hyperthermia. Immunoreactive enzyme protein was also measured using an enzyme-linked immunosorbent assay. Cell lines derived from patients with carnitine palmitoyl transferase deficiency of muscle and from normal individuals were used as positive and negative controls, respectively. One patient with malignant hyperthermia had a deficiency in the enzyme activity which was comparable with that of the known carnitine palmitoyl transferase deficient patients. This individual's lymphoblasts were also deficient in immunoreactive enzyme protein. All of the remaining patients with malignant hyperthermia were deficient only when the backward assay for carnitine palmitoyl transferase was used for quantitation. It is likely that a subset of individuals with a malignant hyperthermia phenotype have a primary deficiency of carnitine palmitoyl transferase and that others have a milder enzyme deficiency secondary to the primary defect in malignant hyperthermia.

Carnitine O-Palmitoyltransferase↗