Effect of acrylamide on brain and hepatic mixed-function oxidases and glutathione-S-transferase in rats

Effect of acrylamide on rat hepatic and brain mixed-function oxidases and glutathione-S-transferase was investigated. Administration of acrylamide (25 mg/kg) for 7, 14, 21, and 28 days showed no significant effect on hepatic and brain mixed-function oxidases at 7 days whereas a slight increase in the activity of hepatic glutathione-S-transferase was observed. Brain glutathione-S-transferase remained unaffected at this treatment schedule. At 14 days of acrylamide exposure, all the hepatic mixed-function oxidases with the exception of aminopyrine-N-demethylase and brain aryl hydrocarbon hydroxylase showed a decrease, and by 21 days all the hepatic and brain mixed-function oxidases were significantly decreased. The decrease in enzyme activities was also evident at 28 days of acrylamide treatment. Hepatic glutathione-S-transferase returned to normal level at 14 days of acrylamide exposure. Both hepatic and brain GST showed a significant decrease at 21 and 28 days of acrylamide treatment. Administration of acrylamide at 50 mg/kg for 3, 6, and 10 days produced no changes in hepatic and brain glutathione-S-transferase activity at early time periods (3 and 6 days). A significant decrease in glutathione-S-transferase activity of both tissues was seen at 10 days of acrylamide exposure. Hepatic mixed-function oxidases showed no change at 3 days but significant decrease at 6 and 10 days of acrylamide exposure. Brain mixed-function monooxygenase activity at this dose was inhibited even after 3 days of acrylamide treatment. The results suggest that acrylamide interferes with xenobiotic metabolism in both liver and brain.     

Sublethal effects of pesticide mixtures on selected biomarkers of Carassius auratus

In the present study, the in vivo effects of commercial propoxur alone and in combination with isoprocarb and chlorpyrifos on acetylcholinesterase and glutathione S-transferases activities in goldfish (Carassius auratus) were investigated. Brain and muscle AChE activity was significantly inhibited (88% and 85% at most, respectively) by propoxur after 5 d of exposure at concentrations between 141 and 2263 μg/L, bell-shaped concentration–response curves were obtained. In most cases, time dependence was apparent. Under insecticide mixture exposure (binary mixture propoxur/isoprocarb and ternary mixture propoxur/isoprocarb/chlorpyrifos), the inhibition of AChE activity was significant in all cases and linear concentration–response relationships were observed. Propoxur (alone and in combination) significantly inhibited gill GST activity, and both mixtures also induced significant inhibition of liver GST activity. However, concentration and time dependence were not apparent. AChE is likely to be more informative than GST and seems to be a good biomarker to diagnose exposure to anticholinesterase pesticides in wild populations of this species.     

Interaction of acrylamide with glutathione in rat erythrocytes

Evidence is presented for an enzyme-catalyzed conjugation of acrylamide (ACR) in rat erythrocytes. Daily exposure of rats to ACR for a period of 7, 14 and 21 days resulted in a time-dependent decrease in glutathione content. In vitro incubation of ACR with rat erythrocytes suspension caused a concentration-dependent decrease in glutathione levels. Red blood cell (RBC) enzyme-catalyzed conjugation of ACR with glutathione increased with protein concentration and was dependent on pH and time of incubation. Glutathione-S-transferase (GST) activity using acrylamide and 1-chloro 2,4-dinitrobenzene (CDNB) as substrates followed the order: liver > kidney > brain > erythrocytes. Glutathione peroxidase activity of RBCs was inhibited by the in vitro addition of ACR to erythrocytes. These results suggest that rat erythrocytes are equipped with the mechanism which can inactivate toxic electrophilic chemicals, such as acrylamide.     

The toxicology and metabolism of chlorothalonil in fish. III. Metabolism,enzymatics and detoxication in Salmo spp. and Galaxias spp.

Hepatic glutathione S-transferase (GST) activity towards chlorothalonil, tetrachloroisophthalonitrile (TCIN), was established for the five fish species: Salmo gairdneri, S. trutta, Galaxias maculatus, G. truttaceus and G. auratus. Molecular weights and hepatic activity toward 1-chloro-2,4-dinitrobenzene (CDNB) of GST were determined in all species. Low level exposure to TCIN was found to induce higher GST activity in G. maculatus, G. truttaceus and S. gairdneri. Other properties of GST enzymes investigated in these fish included TCIN binding, reaction order and the effect of acephate on activity. The effect of TCIN exposure on liver thiol and glutathione (GSH) levels in S. gairdneri and G. truttaceus was investigated. Significant decreases occurred in liver thiol levels of fish when exposed to varying concentrations of TCIN for 96 h without feeding. Liver GSH levels increased in S. gairdneri exposed to 10 μg/l over 96 h with feeding. A marked increase in GST activity was observed during 96 h exposure to 10 μg/l. No significant changes in the activity of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) were observed during exposure to 10 μg/l TCIN in vivo. A transient decrease in activity was observed during exposure to 30 μg/l TCIN. The previously reported in vitro inhibition of GAPDH by TCIN was studied in the context of liver cytosolic levels of GAPDH and GSH. Hepatic GSH and GST activity levels toward ¹⁴C-TCIN and CDNB were compared in S. gairdneri, G. maculatus and G. auratus. The order of asymptotic LC₅₀ values for the three species agreed with that for total hepatic GST activity toward ¹⁴C-TCIN consistent with a detoxication role for GSH-TCIN conjugation. A proposal for a screening process for Australian freshwater fish based on detoxication enzyme activity is discussed.     

In vitro inhibition of alcohol dehydrogenase by acrylamide: interaction with enzyme-sh groups

Acrylamide, a reactive electrophile, caused a concentration-dependent inhibition of alcohol dehydrogenase (ADH) activity (purified) which was reversed by prior addition of glutathione. Reaction of thiol groups of this enzyme with or/Aophthalaldehyde (OPT), a fluorescent reagent, exhibited characteristic fluorescence maxima at 330 nm excitation and 420 nm emission. Addition of acrylamide to the enzyme resulted in a concentration-dependent (acrylamide and protein) quenching of fluorescence of thiol groups when compared with fluorescence quenching caused by N-ethylmaleimide (NEM), a known thiol ligand. The results demonstrate that acrylamide-induced inhibition of purified ADH activity is mediated through its specific interaction with -SH groups in the enzyme molecule.     

Interaction of chlorophenoxyalkyl acid herbicides with rat-liver glutathione S-transferases

The in vitro interaction of four chlorophenoxyalkyl (CPA) acid herbicides with rat-liver glutathione S-transferase (GST) was studied using reduced glutathione and 1-chloro-2,4-dinitrobenzene as substrates. Inhibition of GST activity by the CPA acids in crude extracts was dose dependent. Ring substitution and side-chain length were shown to be of importance in determining the extent of GST inhibition. While GST AA, an isoenzyme of GST, was stimulated by two CPA acids, each of the other GST isoenzymes (A, B, C, E and M) was inhibited, to different degrees. Kinetic studies revealed a mixed type inhibition of the isoenzymes. Conjugates of CPA acids with glutathione were not formed. These results indicate that CPA acids interact with GST by binding directly to these proteins, possibly at a different locus from that of the substrate. The binding of CPA acids to GST may, therefore, have a protective function against these herbicides.     

2-取代胺甲基-5(6)-(E)-取代亚甲基环戊(己)酮盐酸盐类化合物的设计、合成及其抗肿瘤活性

目的设计合成20个2,5(6)-双取代环戊(己)酮类化合物,进行抗肿瘤活性研究。方法以WB852为先导化合物,设计合成了20个2-取代胺甲基-5(6)-(E)-取代亚甲基环戊(己)酮盐酸盐类化合物。利用MTT法对其中17个化合物进行了体外细胞毒活性筛选,所用肿瘤细胞株为人乳腺癌细胞T47D、MCF-7、MCF-7/Adr;通过Habig的酶动力学方法,测试了部分目标化合物细胞外对GSTπ活性的影响。结果与结论合成了20个2-取代胺甲基-5(6)-(E)-取代亚甲基环戊(己)酮盐酸盐类化合物,其中16个为未见文献报道的新化合物,其结构均经1H-NMR、MS和IR确证。体外抗肿瘤活性筛选结果,17个化合物对3种肿瘤细胞均有不同程度的生长抑制活性,A-16、A-17、A-18、A-19等4个化合物活性显著,值得进行深入研究。9个化合物均有不同程度地抑制GSTπ的活性,其中A-4、8、9、11和15等5个化合物对GSTπ的抑制作用强于WB852。取代胺甲基部分、取代亚甲基侧链的改变以及环的大小对抗肿瘤活性和选择性影响不大,但显著影响对GSTπ的抑制作用。A-16、A-17、A-18、A-19对MCF-7/Adr的生长抑制作用与WB852相当,但均低于对MCF-7细胞的活性,对耐药细胞的活性与GSTπ抑制无关。     

Sublethal effects of pesticide mixtures on selected biomarkers of Carassius auratus

In the present study, the in vivo effects of commercial propoxur alone and in combination with isoprocarb and chlorpyrifos on acetylcholinesterase and glutathione S-transferases activities in goldfish (Carassius auratus) were investigated. Brain and muscle AChE activity was significantly inhibited (88% and 85% at most, respectively) by propoxur after 5 d of exposure at concentrations between 141 and 2263 μg/L, bell-shaped concentration–response curves were obtained. In most cases, time dependence was apparent. Under insecticide mixture exposure (binary mixture propoxur/isoprocarb and ternary mixture propoxur/isoprocarb/chlorpyrifos), the inhibition of AChE activity was significant in all cases and linear concentration–response relationships were observed. Propoxur (alone and in combination) significantly inhibited gill GST activity, and both mixtures also induced significant inhibition of liver GST activity. However, concentration and time dependence were not apparent. AChE is likely to be more informative than GST and seems to be a good biomarker to diagnose exposure to anticholinesterase pesticides in wild populations of this species.     

Responses of AChE and GST activities to insecticide coexposure in Carassius auratus

Organophosphates and carbamates are widely used pesticides and play an important role in global agriculture. The misuse of these compounds has caused environmental problems and has had a negative impact on wildlife. In this study, the in vivo effects of commercial chlorpyrifos and isoprocarb on acetylcholinesterase (AChE) and glutathione S‐transferase (GST) activities in goldfish (Carassius auratus) were investigated. Muscle and brain AChE activity was significantly inhibited by chlorpyrifos and isoprocarb (alone and in combination) after 2, 5, 10, and 15 days of exposure, and obvious concentration‐response and time‐response relationships were obtained. Gill GST activity was significantly inhibited by chlorpyrifos and isoprocarb (single compounds and in combination), however, concentration dependence and time dependence were not apparent. The joint effect of chlorpyrifos/isoprocarb was additive with regard to AChE activity inhibition and was antagonistic with regard to GST activity inhibition. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2012.     

Role of Calcium Fluxes in the Action of Glucagon on Cytosolic Glutathione S-Transferase Activity in Rat Liver Slices *

Abstract: In a previous study we demonstrated that the administration of 20 μg/kg b.wt. of glucagon to rats caused a significant diminution of hepatic cytosolic glutathione S-transferase (GST) activity. This inhibition was non-competitive and reversible. We suggested that the effect would be mediated by cytosolic effectors. The present work was performed to characterize the mechanism involved in this inhibition. Liver tissue slices (170 to 200 mg) were incubated during different periods of time (0, 5, 10, 15, 20 and 30 min.) with several concentrations of glucagon (10^-5M, 10^-8M and 10^-10M), dibutiryl cyclic AMP (10^-4M, 10^-6M and 10^-9M), divalent cation ionophore A23187 (10^-4M, 10^-6M and 10^-9M) or vasopressin (10^-7M, 5×10^-7M and 10^-8M). The incubation was done with or without calcium in the medium. In all cases the cytosolic GST activity were determined in liver slices. The percentage of inhibition of GST activity was directly related to the increase of concentration of the test substances. An inhibition between 40% to 45% after 10 min. of incubation with the highest concentrations was observed (except vasopressin which caused 10% of inhibition). 10^-10M glucagon did not produce a decrease of GST activity. The inhibition disappeared in calcium-free incubated slices, but direct relationship between plasma-membrane calcium influx and inhibition of GST activity (r=0.950, P<0.001, n=24) could be obtained. By using calmodulin antagonists, we conclude that the inhibition process of the enzyme was mediated by calmodulin. In summary, we propose that plasma-membrane calcium influx induced by high concentrations of glucagon activates calmodulin, which promotes a modification (actually a methylation, according to other authors) on GST, thereby causing a decrease in its activity.     

“Pincer movement”: Reversing cisplatin resistance based on simultaneous glutathione depletion and glutathione S-transferases inhibition by redox-responsive degradable organosilica hybrid nanoparticles

The therapeutic efficacy of cisplatin has been restricted by drug resistance of cancers. Intracellular glutathione (GSH) detoxification of cisplatin under the catalysis of glutathione S-transferases (GST) plays important roles in the development of cisplatin resistance. Herein, a strategy of “pincer movement” based on simultaneous GSH depletion and GST inhibition is proposed to enhance cisplatin-based chemotherapy. Specifically, a redox-responsive nanomedicine based on disulfide-bridged degradable organosilica hybrid nanoparticles is developed and loaded with cisplatin and ethacrynic acid (EA), a GST inhibitor. Responding to high level of intracellular GSH, the hybrid nanoparticles can be gradually degraded due to the break of disulfide bonds, which further promotes drug release. Meanwhile, the disulfide-mediated GSH depletion and EA-induced GST inhibition cooperatively prevent cellular detoxification of cisplatin and reverse drug resistance. Moreover, the nanomedicine is integrated into microneedles for intralesional drug delivery against cisplatin-resistant melanoma. The in vivo results show that the nanomedicine-loaded microneedles can achieve significant GSH depletion, GST inhibition, and consequent tumor growth suppression. Overall, this research provides a promising strategy for the construction of new-type nanomedicines to overcome cisplatin resistance, which extends the biomedical application of organosilica hybrid nanomaterials and enables more efficient chemotherapy against drug-resistant cancers.     

Ligustrazine derivate DLJ14 reduces multidrug resistance of K562/A02 cells by modulating GSTπ activity

Multidrug resistance (MDR) of tumor cells is a major obstacle in chemotherapeutic cancer treatment. Over-expression of glutathione S-transferase π (GSTπ) is one of the mechanisms contributing to MDR. In this study, we investigated the reversal of MDR by DLJ14, a ligustrazine derivate, in adriamycin (Adr) resistant human myelogenous leukemia (K562/A02) cells by modulating the expression of GSTπ and the activity of GST-related enzymes. In the MTT test, DLJ14 showed a weak inhibition on proliferation of both K562/A02 and K562 cells, while verapamil at the same concentration showed a much stronger inhibition. The sensitivity of K562/A02 cells to cytotoxic killing by Adr was enhanced by incubation with DLJ14 as a result of the increased intracellular accumulation of Adr. The accumulation of Adr induced by DLJ14 may due to down regulation of GST-related enzyme activity. Western blot analysis and RT-PCR showed that DLJ14 was able to inhibit the protein expression and mRNA expression of GSTπ in K562/A02 cells. Moreover, DLJ14 increased the expression of cellular c-Jun NH₂-terminal kinase (JNK) in K562/A02 cells exposure to Adr. This is consistent with the inhibition of GSTπ. These results demonstrate that DLJ14 may be an attractive new agent for the chemosensitization of cancer cells.     

Glutathione sulfotransferase inhibition activity of a self-fermented beverage,Kanji

Context: Kanji, a liquid preparation of roots of Daucus carota L. ssp. sativus (Hoffm.) Arcang. var. vavilovii Mazk. (Apiaceae), may inhibit glutathione sulfotransferase (GST) activity due to ferulic acid content.

Objectives: GST inhibition activity and characterization of Kanji and methanol extract of D. carota roots, and oral absorption pattern of ferulic acid from Kanji in rats.

Materials and methods: GST inhibition activity of Kanji and methanol extract of D. carota roots in concentration range 0.001–100.00?mg/mL was determined using Sprague Dawley rat liver cytosolic fraction. Methanol extract upon column chromatography gave ferulic acid, which was used to characterize Kanji and determine its oral absorption pattern in Wistar rats.

Results: The GST inhibition activity of Kanji (100.00?μg/mL), methanol extract of D. carota roots (100.00?μg/mL) and tannic acid (10.00?μg/mL, positive control) was found to be 0.162?±?0.016, 0.106?±?0.013 and 0.073?±?0.004?μM/min/mg, respectively. Different Kanji samples and methanol extract contained ferulic acid (0.222–0.316?mg/g) and 0.77?mg/g, respectively. Ferulic acid did not appear in plasma after oral administration of Kanji.

Discussion: Kanji having solid contents 80.0?μg/mL, equivalent to 0.0025?μg/mL ferulic acid, does not inhibit the activity of GST. The oral administration of Kanji, in human equivalent dose (528?mg/kg, 16.67?μg ferulic acid), to rats indicated poor absorption of ferulic acid.

Conclusion: Kanji having solid contents 14–36?mg/mL does not inhibit GST activity, hence may not interfere with drugs that are the substrates of GST, if taken concomitantly.     

Inhibition of glutathione S-transferases by thonningianin A, isolated from the African medicinal herb, Thonningia sanguinea, in vitro.

There is evidence that increased expression of glutathione S-transferase (EC: 2.5.1.18, GST) is involved in resistance of tumor cells against chemotherapeutic agents. In this study we investigated the inhibitory effects of thonningianin A (Th A), a novel antioxidant isolated from the medicinal herb, Thonningia sanguinea on uncharacterized rat liver GST and human GST P1-1. Using 1-chloro-2,4-dinitrobenzene (CDNB) as substrate, rat liver cytosolic GST activity was inhibited by Th A in a concentration dependent manner with 50% inhibition concentration (IC50) of 1.1 microM. When Th A was compared with known potent GST inhibitors the order of inhibition was tannic acid>cibacron blue>hematin>Th A>ethacrynic acid with CDNB as substrate. Th A also exhibited non-competitive inhibition towards both CDNB and glutathione. Furthermore, using 1,2-dichloro-4-nitrobenzene, ethacrynic acid and 1,2-epoxy-3-(p-nitrophenoxy) propane as substrates Th A at 1.0 microM inhibited cytosolic GST by 2%, 12% and 36% respectively. Human GST P1-1 was also inhibited by Th A with an IC50 of 3.6 microM. While Th A showed competitive inhibition towards CDNB it exhibited non-competitive inhibition towards GSH of the human GST P1-1. These results suggest that Th A represents a new potent GST in vitro inhibitor.     

Relationship between cytocidal activity and glutathione-S-transferase inhibition using doxorubicin coupled to stereoisomers of glutathione with different substrate specificity.

To determine the cytotoxic mode of action of a glutathione (GSH)--doxorubicin (DXR) conjugate, which exhibited potent cytotoxicity against various multidrug-resistant as well as DXR-sensitive cell lines, the molecular interaction between covalent GSH--DXR conjugates and glutathione-S-transferase (GST), a possible molecular target of the conjugates, was investigated. The following four GSH molecules with stereoisomeric forms were prepared: L-Glu--L-Cys--Gly (LL-GSH), D-Glu--L-Cys--Gly (DL-GSH), L-Glu--D-Cys--Gly (LD-GSH) and D-Glu--D-Cys--Gly (DD-GSH). The enzymic activity of GST against each GSH stereoisomer was 88, 38, 8 and 4 nmol/mg/min, respectively, suggesting that the L-form cysteine residue in the molecule was an important substrate of GST. Addition of DXR conjugated with each isomer (10 microM) to a GSH-containing GST assay mixture inhibited the GST activity to 32% for LL-GSH--XR, 16% for DL-GSH-DXR and 61% for LD-GSH-DXR as compared with the solvent control. Moreover, IC50 values for these conjugates were 30, 20 and 250 nM, respectively. The cytocidal activity of each conjugate corresponded to the substrate specificity of GST activity for the GSH isomer. These conjugates bound to the GST molecule, and the binding ability was 0.746, 0.627 and 0.462 mol/mol of GST for LL-GSH--XR, DL-GSH-DXR and LD-GSH--XR, respectively. These findings suggested that GSH--DXR interacted with the substrate-binding site of the GST molecule and inhibition of GST activity exhibited potent cytotoxicity.     

“Pincer movement”: Reversing cisplatin resistance based on simultaneous glutathione depletion and glutathione S-transferases inhibition by redox-responsive degradable organosilica hybrid nanoparticles

The therapeutic efficacy of cisplatin has been restricted by drug resistance of cancers. Intracellular glutathione (GSH) detoxification of cisplatin under the catalysis of glutathione S-transferases (GST) plays important roles in the development of cisplatin resistance. Herein, a strategy of “pincer movement” based on simultaneous GSH depletion and GST inhibition is proposed to enhance cisplatin-based chemotherapy. Specifically, a redox-responsive nanomedicine based on disulfide-bridged degradable organosilica hybrid nanoparticles is developed and loaded with cisplatin and ethacrynic acid (EA), a GST inhibitor. Responding to high level of intracellular GSH, the hybrid nanoparticles can be gradually degraded due to the break of disulfide bonds, which further promotes drug release. Meanwhile, the disulfide-mediated GSH depletion and EA-induced GST inhibition cooperatively prevent cellular detoxification of cisplatin and reverse drug resistance. Moreover, the nanomedicine is integrated into microneedles for intralesional drug delivery against cisplatin-resistant melanoma. The in vivo results show that the nanomedicine-loaded microneedles can achieve significant GSH depletion, GST inhibition, and consequent tumor growth suppression. Overall, this research provides a promising strategy for the construction of new-type nanomedicines to overcome cisplatin resistance, which extends the biomedical application of organosilica hybrid nanomaterials and enables more efficient chemotherapy against drug-resistant cancers.KEY WORDS: Cancer therapy, Cisplatin, Drug resistance, Glutathione depletion, Glutathione S-transferases, Disulfide bonds, Organosilica hybrid nanoparticles, Ethacrynic acid     

In vitro interaction of dithiocarb with rat liver glutathione S-transferases

The in vitro interaction of dithiocarb (DTC) with rat liver glutathione S-transferase was studied, using reduced glutathione (GSH) and 1-chloro-2,4-dinitrobenzene (CDNB) as substrates. The inhibition of the GST activity by DTC was dose dependent, but not linear. The different GST isoenzymes were inhibited to different degrees. Kinetic studies revealed uncompetitive inhibition towards GSH for GST AA, and an intermediate kinetic pattern between uncompetitive and noncompetitive inhibition for the other GST isoenzymes. With respect to CDNB, mixed type inhibition was found for most GST isoenzymes, and nearly uncompetitive inhibition for GST AA and M. Titration of remaining GSH in appropriate incubation mixtures with DTC revealed no GST catalyzed conjugation of DTC with GSH. It is concluded that DTC interact with GST by direct binding to these proteins. This binding could have a protective function against DTC.     

Human glutathione transferases catalyzing the bioactivation of anticancer thiopurine prodrugs

cis-6-(2-Acetylvinylthio)purine (cAVTP) and trans-6-(2-acetylvinylthio)guanine (tAVTG) are thiopurine prodrugs provisionally inactivated by an α,β-unsaturated substituent on the sulfur of the parental thiopurines 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG). The active thiopurines are liberated intracellularly by glutathione (GSH) in reactions catalyzed by glutathione transferases (GSTs) (EC 2.5.1.18). Catalytic activities of 13 human GSTs representing seven distinct classes of soluble GSTs have been determined. The bioactivation of cAVTP and tAVTG occurs via a transient addition of GSH to the activated double bond of the S-substituent of the prodrug, followed by elimination of the thiopurine. The first of these consecutive reactions is rate-limiting for thiopurine release, but GST-activation of this first addition is shifting the rate limitation to the subsequent elimination. Highly active GSTs reveal the transient intermediate, which is detectable by UV spectroscopy and HPLC analysis. LC/MS analysis of the reaction products demonstrates that the primary GSH conjugate, 4-glutathionylbuten-2-one, can react with a second GSH molecule to form the 4-(bis-glutathionyl)butan-2-one. GST M1-1 and GST A4-4 were the most efficient enzymes with tAVTG, and GST M1-1 and GST M2-2 had highest activity with cAVTP. The highly efficient GST M1-1 is polymorphic and is absent in approximately half of the human population. GST P1-1, which is overexpressed in many cancer cells, had no detectable activity with cAVTP and only minor activity with tAVTG. Other GST-activated prodrugs have targeted GST P1-1-expressing cancer cells. Tumors expressing high levels of GST M1-1 or GST A4-4 can be predicted to be particularly vulnerable to chemotherapy with cAVTP or tAVTG.     

Protective effects of thiopronin against isoniazid-induced hepatotoxicity in rats

Isoniazid is a widely used drug for the treatment of tuberculosis, but hepatotoxicity is a major concern during treatment. Thiopronin contains an SH-group and is generally considered an antioxidant. The aim of the present study was to investigate the effects of thiopronin during liver injury and DNA damage induced by isoniazid. Rats were injected daily with isoniazid (100 mg/kg, i.p.) for 21 days with or without thiopronin co-administration (60 mg/kg, i.p.) from day 11 to day 21. The influence of thiopronin on isoniazid-induced DNA oxidative damage was analyzed in precision-cut rat liver slices by HPLC–MS/MS. Thiopronin prevented isoniazid-induced hepatotoxicity, indicated by both diagnostic indicators of liver damage (alanine aminotransferase and aspartate aminotransferase) and histopathological analysis. In vivo, thiopronin significantly inhibited isoniazid-induced CYP2E1 activity as assessed by both chlorzoxazone hydroxylase and aniline hydroxylase (p < 0.001). Thiopronin concentration-dependently inhibited CYP2E1-dependent aniline hydroxylation, and the Dixon plots suggest that thiopronin is a competitive inhibitor of CYP2E1. Thiopronin markedly attenuated isoniazid-induced inhibition of the detoxification system through cytosolic glutathione S-transferases (GSTs), including mu GST and alpha GST. In precision-cut liver slices, the free radical scavenging activity of thiopronin reduced the generation of DNA adducts induced by isoniazid (p < 0.05). Altogether, these results suggest that thiopronin exerts its hepatoprotective activity against isoniazid-induced hepatotoxicity by inhibiting the production of free radicals in addition to its role as a scavenger. Thiopronin may reduce free radical generation via inhibition of hepatic CYP2E1 and increase the removal of free radicals directly or through the induction of cytosolic GSTs.     

Purification and characterization of a new glutathioneS-transferase,class δ, from human erythrocytes

A new polymorphic form of glutathioneS-transferase (GST), metabolising monohalogenated methanes, ethylene oxide and dichloromethane, has been purified from human erythrocytes and characterized. Several characteristics, such as similar elution patterns on different chromatographic matrices, K_M-values and activity towards antibodies, confirm a previous assumption that this novel GST is a class δ enzyme. Although the presence or absence of the enzyme activity in human red blood cells is parallel with the polymorphism of the human GST T1 gene, the new GST δ in red blood cells may differ from the known GST T1-1 enzyme from other tissues in terms of substrate specificity, since established GST T1-1 substrates [1,2-epoxy-3-(p-nitro-phenoxy)propane andp-nitrobenzyl chloride] are not metabolized. The substrate specifity of the new enzyme in erythrocytes resembles more closely that of GST T2-2, most likely due to a commonN-terminal modification which modifies substrate binding. The new polymorphic GST-isoform in human red blood cells therefore may be considered to represent anN-terminally modified isoform of GST T1-1.