Lipoic Acid as a Possible Pharmacological Source of Hydrogen Sulfide/Sulfane Sulfur.

The aim of the present study was to verify whether lipoic acid (LA) itself is a source of H2S and sulfane sulfur. It was investigated in vitro non-enzymatically and enzymatically (in the presence of rat tissue homogenate). The results indicate that both H2S and sulfane sulfur are formed from LA non-enzymatically in the presence of environmental light. These results suggest that H2S is the first product of non-enzymatic light-dependent decomposition of LA that is, probably, next oxidized to sulfane sulfur-containing compound(s). The study performed in the presence of rat liver and kidney homogenate revealed an increase of H2S level in samples containing LA and its reduced form dihydrolipoic acid (DHLA). It was accompanied by a decrease in sulfane sulfur level. It seems that, in these conditions, DHLA acts as a reducing agent that releases H2S from an endogenous pool of sulfane sulfur compounds present in tissues. Simultaneously, it means that exogenous LA cannot be a direct donor of H2S/sulfane sulfur in animal tissues. The present study is an initial approach to the question whether LA itself is a donor of H2S/sulfane sulfur.

INACTIVATION OF ALDEHYDE DEHYDROGENASE BY NITROGLYCERIN IN THE PRESENCE AND ABSENCE OF LIPOIC ACID AND DIHYDROLIPOIC ACID. IMPLICATIONS FOR THE PROBLEM OF DIFFERENTIAL EFFECTS OF LIPOIC ACID IN VITRO AND IN VIVO.

Lipoic acid (LA-(SS), LA) and its reduced form - dihydrolipoic acid DHLA-(SH)2, DHLA) are synthesized mainly in the mammalian liver. In this study, we investigated in viti the inactivation of yeast aldehyde dehydrogenase (ALDH) by nitroglycerin (GTN) in the presence and absence of LA and DHLA. In vivo studies were performed to answer the question whether LA administered jointly with GTN for 8 days will affect the ALDH activity in the rat liver. The results indicated that in vito both LA and DHLA restored and protected ALDH activity against GTN-induced inactivation, while treatment of rats with LA and GTN in combination did not provide any protection against GTN-induced ALDH inhibition. In summary, the obtained results seem to confirm earlier reports indicating the differential effects of LA in vitio and in vivo.

The effect of lipoic acid administration on the urinary excretion of thiocyanate in rats exposed to potassium cyanide.

The oxidation of cyanide (CN-) to a much less toxic thiocyanate (SCN-) is the main in vivo biochemical pathway for CN- detoxification. SCN- is excreted mainly in urine. This study was performed to investigate the effect of lipoic acid (LA) on the urinary excretion of thiocyanate (SCN-; rhodanate) in rats. Groups of the animals were treated intraperitoneally (i.p.) as follows: group 1: potassium cyanide (KCN) (1 mg/kg); group 2: KCN (1 mg/kg) + LA (100 mg/kg). Urine was collected for 24 h and the pooled samples were examined for SCN- levels. The obtained results indicated that the treatment of animals with potassium cyanide and LA in combination significantly increased the urinary excretion of SCN- in comparison with the respective values in the KCN-alone-treated group. It indicates that LA increased the rate of CN- detoxification in rats.

In vivo anti-inflammatory activity of lipoic acid derivatives in mice.

BACKGROUND: In mammals lipoic acid (LA) and its reduced form dihydrolipoic acid (DHLA) function as cofactors for multienzymatic complexes catalyzing the decarboxylation of α-ketoacids. Moreover, LA is used as a drug in a variety of diseases including inflammatory diseases. The aim of the study was to examine anti-inflammatory properties of LA metabolites. MATERIAL/METHODS: The present paper reports the chemical synthesis of 2,4-bismethylthio-butanoic acid (BMTBA) and tetranor-dihydrolipoic acid (tetranor-DHLA). BMTBA is one of the biotransformation products of LA, while tetranor-DHLA is an analogue of DHLA. Structural identity of these compounds was confirmed by 1H NMR. These compounds were assessed for their anti-inflammatory activity in mice. For this purpose, the zymosan-induced peritonitis and the carrageenan-induced hind paw edema animal models were applied. RESULTS/CONCLUSIONS: The obtained results indicated that the early vascular permeability measured at 30 min of zymosan-induced peritonitis was significantly inhibited in groups receiving BMTBA (10, 30, 50 mg/kg). The early infiltration of neutrophils measured at 4 hours of zymosan-induced peritonitis was inhibited in the group receiving BMTBA (50 mg/kg) and tetranor-DHLA (50 mg/kg). The results indicated that the increase in paw edema was significantly inhibited in the groups receiving BMTBA (50, 100 mg/kg) and tetranor-DHLA (30, 50 mg/kg). In summary, the present studies clearly demonstrated that both BMTBA and tetranor-DHLA were able to act as anti-inflammatory agents. This is the first study examining in vivo the anti-inflammatory properties of LA metabolites.

Acceleration of anaerobic cysteine transformations to sulfane sulfur consequent to γ-glutamyl transpeptidase inhibition.

Toxicity of drugs and radiation in the cells is largely dependent on the level of thiols. In the present studies, an attempt has been made to inhibit γ-glutamyl transpeptidase (γGT) activity in EAT-bearing animals tissue. We have expected that administration of γGT inhibitors: acivicin and 1,2,3,4-tetrahydroisoquinoline (TIQ) may influence GSH/γ-glutamyl transpeptidase (γGT) system in the regulation of cysteine concentration and anaerobic cysteine metabolism in normal and cancer cells. Development of Ehrlich ascites tumor in mice enhances peroxidative processes, diminishes levels of nonprotein thiols (NPSH) and sulfane sulfur, and lowers activities of enzymes involved in its formation and transfer in the liver and kidney. Although γGT inhibitors further decrease NPSH level, they increase cysteine and sulfane sulfur levels. This means that upon γGT inhibition, cysteine can be efficiently acquired by normal liver and kidney cells via another pathway, that is so productive that sulfane sulfur level and intensity of anaerobic cysteine metabolism even rise.

The effect of the uremic toxin cyanate (CNO⁻) on anaerobic cysteine metabolism and oxidative processes in the rat liver: a protective effect of lipoate.

Chronic renal failure (CRF) patients have an increased plasma level of urea, which can be a source of cyanate. This compound can cause protein carbamoylation thereby changing biological activity of proteins. Therefore, in renal failure patients, cyanate can disturb metabolism and functioning of the liver. This work presents studies demonstrating that the treatment of rats with cyanate alone causes the following changes in the liver: (1) inhibition of rhodanese (TST), cystathionase (CST) and 3-mercaptopyruvate sulfotransferase (MPST) activities, (2) decrease in sulfane sulfur level (S*), (3) lowering of nonprotein sulfhydryl groups (NPSH) group level, and (4) enhancement of prooxidant processes (rise in reactive oxygen species (ROS) and malondialdehyde (MDA) level). This indicates that cyanate inhibits anaerobic cysteine metabolism and shows prooxidant action in the liver. Out of the above-mentioned changes, lipoate administered with cyanate jointly was able to correct MDA, ROS and NPSH levels, and TST activity. It had no significant effect on MPST and CST activities. It indicates that lipoate can prevent prooxidant cyanate action and cyanate-induced TST inhibition. These observations can be promising for CRF patients since lipoate can play a dual role in these patients as an efficient antioxidant defense and a protection against cyanate and cyanide toxicity.

The effects of modulation of gamma-glutamyl transpeptidase activity in HepG2 cells on thiol homeostasis and caspase-3-activity.

The present studies aimed to elucidate how the modulation of gamma-glutamyl transpeptidase (gammaGT) activity in human hepatoma (HepG2) cell line influences H(2)O(2) production, caspase 3 activity, protein S-thiolation by glutathione (GSH), cysteinyl-glycine (Cys-Gly) and cysteine (Cys), and the level of other redox forms of these thiols. The experiments showed that 1-h stimulation of gammaGT elevated H(2)O(2) production, leading to prooxidant conditions. After 24-h stimulation, H(2)O(2) concentration was at the control level, while Cys-Gly-, Cys- and GSH-dependent S-thiolation was markedly increased, which was accompanied by a drop in caspase-3 activity. The inhibition of gammaGT activity by acivicin led to H(2)O(2) decrease after 1-h incubation which still persisted after 24 h. The inhibition of gammaGT activity in HepG2 cells was also connected with the lowering of S-thiolation with Cys and Cys-Gly and with increasing of caspase-3 activity. The results of our studies indicate that the modulation of gammaGT activity can be used to change cellular redox status, and can affect Cys- and Cys-Gly-dependent S-thiolation and caspase-3 activity. We suggest that the role of high gammaGT activity in HepG2 cells can be connected with production of reactive oxygen species and with S-thiolation with Cys and Cys-Gly that can influence activity of caspase 3.

The role of lipoic acid in prevention of nitroglycerin tolerance.

Besides other organic nitrates, nitroglycerin (glyceryl trinitrate; GTN) has been used to treat acute heart failure particularly due to ischemic heart disease. However, one of serious clinical problems of the GTN therapy, particularly a long-standing medication, is hemodynamic tolerance to GTN, manifested by the decreased therapeutic efficacy of the drug. The most recent studies have suggested that mitochondrial lipoate/dihydrolipoate system-dependent aldehyde dehydrogenase-2 plays a key role in nitric oxide release from GTN. The aldehyde dehydrogenase-2 performs three enzymatic activities of dehydrogenase, esterase and reductase. The reductase activity is responsible for bioactivation of organic nitrates, such as GTN yielding nitrite and dinitrate (1,2-GDN/1,3-GDN, approximately 8:1). In view of a large contribution of dihydrolipoic acid to stabilization and regeneration of thiol groups, necessary for the reductase activity of aldehyde dehydrogenase-2, we conducted studies aimed to determine whether lipoic acid administration to rats is able to prevent GTN tolerance. The studies were conducted on 4 groups of animals: control saline-treated, model GTN-tolerant, GTN + lipoic acid-treated, lipoic acid alone-administered groups. On the 9th day of experiment animals were given i.v. therapeutic dose of GTN. We measured in all animals systolic and diastolic blood pressure before injection of therapeutic dose of GTN into the cadual vein and during 20 min thereafter. Levels of nitric oxide and reactive oxygen species and activities of glutathione peroxidase and superoxide dismutase were assayed in the aorta, plasma and heart of all animals. In addition, levels of malondialdehyde, and non-protein thiols, and activities of glutathione S-transferase and gamma-glutamyl transpeptidase were evaluated in the heart and plasma. The obtained results indicate that treatment of rats with a combination of lipoic acid and GTN can efficiently counteract GTN tolerance.

Biological actions of lipoic acid associated with sulfane sulfur metabolism.

This work aimed to investigate the effect of lipoic acid (LA) on sulfane sulfur (S(*)) level and rhodanese activity in rat tissues. In vitro studies conduced so far have indicated that dihydrolipoic acid serves as an S(*) acceptor in the rhodanese-catalyzed S(*) transfer. This study revealed a significant increase in S(*) level and rhodanese activity in the heart, liver and kidney homogenates from rats that had previously been treated intraperitoneally with LA. It demonstrated for the first time in vivo that biological activity of lipoate might be connected with anaerobic cysteine metabolism to S(*) and with rhodanese activity.

Selective effects of diallyl disulfide, a sulfane sulfur precursor, in the liver and Ehrlich ascites tumor cells.

The present in vivo studies demonstrated that diallyl disulfide (DADS), occurring in garlic, elevated hepatic sulfane sulfur level and activities of gamma-cystathionase and 3-mercaptopyruvate sulfotransferase in healthy mice but did not affect the hepatic glutathione level. DADS efficiently corrected the concentrations of glutathione and sulfane sulfur, and ameliorated gamma-cystathionase activity that had been lowered in the livers of Ehrlich ascites tumor-bearing mice. In Ehrlich ascites tumor cells, diallyl disulfide did not alter bound sulfane sulfur level, sulfotransferases activity or glutathione level. These data indicate that this compound is capable of acting efficiently and selectively only in the liver and can be used for hepatoprotection during chemotherapy.

The effect of modulation of gamma-glutamyl transpeptidase and nitric oxide synthase activity on GSH homeostasis in HepG2 cells.

High glutathione (GSH) level and elevated gamma-glutamyl transpeptidase (gammaGT) activity are hallmarks of tumor cells. Toxicity of drugs and radiation to the cells is largely dependent on the level of thiols. In the present studies, we attempted to inhibit gammaGT activity in human hepatoblastoma (HepG2) cells to examine whether the administration of gammaGT inhibitors, acivicin (AC) and 1,2,3,4-tetrahydroisoquinoline (TIQ) influences cell proliferation and enhances cytostatic action of doxorubicin (DOX) and cisplatin (CP) on HepG2 cells. The effects of these inhibitors were determined by 1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT), BrdU and lactate dehydrogenase (LDH) tests and by estimation of GSH level. Additionally, we investigated the changes in caspase-3 activity, which is a marker of apoptosis. The obtained results showed that the gammaGT inhibitors introduced to the medium alone elicited cytotoxic effect, which was accompanied by an increase in GSH level in the cells. TIQ concomitantly increased caspase-3 activity. Doxorubicin and CP proved to be cytotoxic, and both inhibitors augmented this effect. As well DOX as CP radically decreased GSH levels, whereas gammaGT inhibitors had diverse effects. Therefore, the obtained results confirm that gammaGT inhibitors can enhance pharmacological action of DOX and CP, which may permit clinicians to decrease their doses thereby alleviating side effects. Aminoguanidine (nitric oxide synthase inhibitor) given alone was little cytotoxic to HepG2 cells, while its introduction to the medium together with DOX and CP significantly increased their cytotoxicity. Aminoguanidine on its own did not show any effect on GSH level in HepG2 cells, but markedly and significantly elevated its concentration when added in combination with CP but not with DOX. This indicates that when CP was used as a cytostatic, GSH level rose after treatment with its combination with both AC and aminoguanidine.

Nephroprotective effect of cystathionine is due to its diverse action on the kidney and Ehrlich ascites tumor cells.

Tumor cells, unlike normal cells, are characterized by trace cystathionase (CST) activity and sulfane sulfur levels. The present studies aimed to established whether cystathionine (CT), a substrate of cystathionase, can selectively influence the thiol-dependent antioxidant power of the kidney and Ehrlich ascites tumor (EAT). CT treatment reversed the changes in renal concentrations of non-protein thiols (NPSH), reactive oxygen species (ROS), sulfane sulfur and activities of rhodanese, cystathionase and glutathione S-transferase (GST) in tumor-bearing mice, which returned to the level observed in healthy animals. The results demonstrated that CT corrected all harmful changes in the mouse kidney induced by EAT. In contrast, CT did not elicit such effect in EAT cells, in which it only increased ROS level. It indicates that CT can selectively protect the kidney of tumor-bearing mice against nephrotoxicity of drugs as well as restore biological function of sulfane sulfur. On the other hand, cisplatin (CP) did not affect any of the parameters under study in the kidney of tumor-bearing mice. Interestingly, cisplatin markedly lowered glutathione S-transferase activity and increased sulfane sulfur level and rhodanese activity in tumor cells. It is also worth noting that CP doses devoid of nephrotoxic effect in tumor-bearing mice could enhance cystathionine action on the kidney, causing an additional increase in NPSH and CST and rhodanese activity.

[The different aspects of the biological role of glutathione]. / Rózne oblicza biologicznej roli glutationu.

Glutathione plays a key role in maintaining a physiological balance between prooxidants and antioxidants, crucial for the life and death of a cell. Glutathione occurs in the human body in several redox forms, of which reduced glutathione (GSH), oxidized glutathione (GSSG), S-nitrosoglutathione (GSNO), and mixed disulfides of glutathione with proteins are the most important. There is a clear relationship between the levels of different redox forms of glutathione and the regulation of cellular metabolism in a broad sense. Therefore, each of these forms of glutathione can be beneficial or harmful to the organism depending on the cell type and its metabolic status. In such a situation, elevation of GSH level can constitute a very important factor aiding treatment. A rise in GSH level is beneficial in all pathological states, accompanied by lowered GSH content, while a lowering of GSH level is an indication to induce short-term immunosuppression required in organ transplantation and in tumor cells to selectively increase their sensitivity to chemo- and radiotherapy. GSH itself cannot be used as a therapeutic since it is not transported through plasma membranes. Cysteine, an amino acid which limits glutathione biosynthesis, also cannot be used in therapy due to its high neurotoxicity. For this reason, there is currently an intensive search for possibilities of modulating cellular glutathione and cysteine levels, and this problem can be the subject of interdisciplinary studies combining such scientific fields as biology, pharmacology, toxicology, and clinical medicine.

[Glutatione transferases--structure and functions. beta-lyase-dependent bioactivation of cysteine S-conjugates]. / Tranferazy glutationowe--bioaktywacja S-koniugatów glutationu z udzialem beta-liazy.

Glutathione transferases (GSTs) catalyze nucleophilic attack of glutathione on electrophilic center of the second substrate, hydrophobic in character. It leads to the formation of glutathione S-conjugates (thioethers), which are subsequently eliminated from the organism as mercapturic acids. However, in some reactions, glutathione can also fulfills the role of a cofactor, facilitating transformation of a hydrophobic substrate molecule, and released after the structure has been changed. Glutathione transferases participate in the processes of conjugation, reduction, isomerization, synthesis of sex hormones, prostaglangins and leukotrienes, degradation of aromatic compounds and signal transduction. The role of these enzymes consists principally in increasing glutathione nucleophilicity by its appropriate positioning and binding in active center, and its following activation by catalytic amino acid residues. There are also so-called ligandins, i.e. glutathione transferases which can bind hydrophobic, non-substrate ligands, thereby contributing to their sequestration. GSTs play a dominating role in detoxification of xenobiotics eliminated from the body in the form of thioethers, which however, under certain conditions, can be bioactivated in beta-liase-catalyzed reaction to form compounds capable of forming tissue adducts. Inhibition of S-transferase activity can have therapeutic significance both when thioethers are activated by beta-liase and during carcinogenesis, which is often accompanied by overexpression of GSTs.

The selective effect of cystathionine on doxorubicin hepatotoxicity in tumor-bearing mice.

The aim of the present study was to examine the protective effect of cystathionine as a cysteine precursor on doxorubicin toxicity in the liver of Ehrlich ascites tumor (EAT)-bearing mice and in the EAT cells. Both compounds were injected intraperitoneally alone or in combination at the following doses: cystathionine at 10 mg and doxorubicin at 5 mg per kg of body weight. In the liver of EAT-bearing mice, glutathione (GSH), cysteine and sulfane sulfur levels as well as the activities of: glutathione S-transferase, gamma-glutamyl transpeptidase, rhodanese and gamma-cystathionase significantly dropped in comparison with healthy animals. Administration of cystathionine elevated GSH and cysteine levels in the livers of EAT-bearing mice and reduced lipid peroxidation. Furthermore, cystathionine increased gamma-glutamyl transpeptidase activity, thereby activating gamma-glutamyl cycle, responsible for proper glutathione metabolism in the cells. Cystationine did not influence sulfane sulfur level and rhodanese and gamma-cystathionase activity in the livers of EAT-bearing mice. It was next shown that cystathionine administered in combination with doxorubicin protected against the drug toxicity since it elevated thiol level, lowering reactive oxygen species content and suppressing lipid peroxidation. This means that, cystathionine in the liver of EAT-bearing mice can both correct harmful effects of carcinogenesis, and protect the liver from doxorubicin cytotoxicity. In contrast, in EAT cells, cystathionine lowered GSH and cysteine levels and did not alter reactive oxygen species level, lipid peroxidation, and gamma-glutamyl transpeptidase activity. All these data indicate that cystathionine action is selectively beneficial for normal cells because it corrects harmful effects induced by EAT development and protects the organism against doxorubicin cytotoxicity without impairing cytotoxicity of this drug to tumor cells.

Disruption of thiol homeostasis in plasma of terminal renal failure patients.

BACKGROUND: The aim of the present studies was to investigate the changes in concentrations of different forms of thiols in plasma of terminal renal failure patients before and after hemodialysis. METHODS: Total concentrations of thiols, their free forms and the level of their mixed disulfides with proteins were determined with HPLC. RESULTS: In terminal renal failure patients before dialysis, total concentrations of cysteine, homocysteine and cysteinylglycine and their free and protein-bound fractions increased while level of all such forms of glutathione dropped. A single dialysis session caused short-lasting return of concentrations of all forms of thiols to the level equal or close to the control group. The changes observed in non-dialyzed patients were similar to those observed in dialyzed patients before single dialysis procedure. CONCLUSIONS: The obtained results showed severe disturbance of thiol homeostasis in plasma of terminal renal failure patients. The following changes have to be emphasized: (1) high level of free cysteine (cystine) fraction, (2) strong tendency of homocysteine to form mixed disulfides with proteins, (3) drop of glutathione level. These observations confirm a suggestion that atherogenic action of homocysteine can be a result of S-homocysteinylation and N-homocysteinylation reactions, whereas toxic action of cysteine can result from auto-oxidation reaction.

Oxidative hemolysis of erythrocytes.

This exercise for students will allow them to simultaneously observe lipid peroxidation and consequent hemolysis of rat erythrocytes and the effect of sodium azide, a catalase inhibitor, on these processes. It will also demonstrate a protective action of antioxidants, the therapeutically used N-acetylcysteine and albumins present in plasma.

Hypotensive effect of alpha-lipoic acid after a single administration in rats.

OBJECTIVE: The effect of alpha-lipoic acid on blood pressure was investigated many times in chronic studies, but there are no studies on the effect of this compound after a single administration. Alpha-lipoic acid is a drug used in diabetic neuropathy, often in obese patients, to treat hypertension. Therefore, knowledge of the potential antihypertensive effect of alpha-lipoic acid even after a single dose and possibly too much pressure reduction is interesting and useful. METHODS: The mechanism of the hypotensive effect of alpha-lipoic acid was examined in normotensive rats in vivo after a single intraperitoneal administration, blood pressure in the left carotid artery of the rats was measured prior to the administration of the compounds (alpha- lipoic acid and/or glibenclamide) and 80 min thereafter. RESULTS: Alpha-lipoic acid at a dosage of 50 mg/kg b.w. i.p. significantly decreased the blood pressure from the 50th min after drug administration. This cardiovascular effect of this compound was reversed by glibenclamide, a selective KATP blocker. Glibenclamide alone at this dose did not significantly affect the blood pressure. Statistical significance was evaluated using two-way ANOVA. CONCLUSION: This suggests that alpha-lipoic acid affects ATP-dependent potassium channels. It is possible that this is an indirect effect of hydrogen sulfide because alpha-lipoic acid can increase its concentration. The results obtained in this study are very important because the patients taking alpha-lipoic acid may be treated for co-existing hypertension. Therefore, the possibility of blood pressure lowering by alpha-lipoic acid should be taken into account, although it does not lead to excessive orthostatic hypotension.

Cysteine Metabolism and Oxidative Processes in the Rat Liver and Kidney after Acute and Repeated Cocaine Treatment.

The role of cocaine in modulating the metabolism of sulfur-containing compounds in the peripheral tissues is poorly understood. In the present study we addressed the question about the effects of acute and repeated (5 days) cocaine (10 mg/kg i.p.) administration on the total cysteine (Cys) metabolism and on the oxidative processes in the rat liver and kidney. The whole pool of sulfane sulfur, its bound fraction and hydrogen sulfide (H2S) were considered as markers of anaerobic Cys metabolism while the sulfate as a measure of its aerobic metabolism. The total-, non-protein- and protein- SH group levels were assayed as indicators of the redox status of thiols. Additionally, the activities of enzymes involved in H2S formation (cystathionine γ-lyase, CSE; 3-mercaptopyruvate sulfurtransferase, 3-MST) and GSH metabolism (γ-glutamyl transpeptidase, γ-GT; glutathione S-transferase, GST) were determined. Finally, we assayed the concentrations of reactive oxygen species (ROS) and malondialdehyde (MDA) as markers of oxidative stress and lipid peroxidation, respectively. In the liver, acute cocaine treatment, did not change concentrations of the whole pool of sulfane sulfur, its bound fraction, H2S or sulfate but markedly decreased levels of non-protein SH groups (NPSH), ROS and GST activity while γ-GT was unaffected. In the kidney, acute cocaine significantly increased concentration of the whole pool of sulfane sulfur, reduced the content of its bound fraction but H2S, sulfate and NPSH levels were unchanged while ROS and activities of GST and γ-GT were reduced. Acute cocaine enhanced activity of the CSE and 3-MST in the liver and kidney, respectively. Repeatedly administered cocaine enhanced the whole pool of sulfane sulfur and reduced H2S level simultaneously increasing sulfate content both in the liver and kidney. After repeated cocaine, a significant decrease in ROS was still observed in the liver while in the kidney, despite unchanged ROS content, a marked increase in MDA level was visible. The repeated cocaine decreased 3-MST and increased γ-GT activities in both organs but reduced GST in the kidney. Our results show that cocaine administered at a relatively low dose shifts Cys metabolism towards the formation of sulfane sulfur compounds which possess antioxidant and redox regulatory properties and are a source of H2S which can support mitochondrial bioenergetics.

Treatment with 1,2,3,4-tetrahydroisoquinolone affects the levels of nitric oxide, S-nitrosothiols, glutathione and the enzymatic activity of gamma-glutamyl transpeptidase in the dopaminergic structures of rat brain.

Depletion of glutathione (GSH), nitrosative stress and chronic intoxication with some neurotoxins have been postulated to play a major role in the pathogenesis of Parkinson's disease. This study aimed to examine the effects of acute and chronic treatments with 1,2,3,4-tetrahydroisoquinoline (TIQ), an endo-/exogenous substance suspected of producing Parkinsonism in human, on the levels of nitric oxide (NO), S-nitrosothiols and glutathione (GSH) in the whole rat brain and in its dopaminergic structures. TIQ administered at a dose of 50 mg/kg i.p. significantly increased the tissue concentrations of NO and GSH in the substantia nigra (SN), striatum (STR) and cortex (CTX) of rats receiving this compound both acutely and chronically. Moreover, it decreased the level of oxidized glutathione (GSSG) and enhanced GSH:GSSG ratio affecting in this way the redox state of brain cells. TIQ also increased the level of S-nitrosothiols when measured in the whole rat brain and CTX, although it markedly decreased their level in the STR after both treatments. Inhibition of the constitutive NO synthase by l-NAME in the presence of TIQ caused decreases in GSH and S-nitrosothiol levels in the brain. The latter effect shows that the TIQ-mediated increases in GSH and S-nitrosothiol concentrations were dependent on the enhanced NO level. The above-described results suggest that TIQ can act as a modulator of GSH, NO and S-nitrosothiol levels but not as a parkinsonism-inducing agent in the rat brain.