Glutathione depletion and resynthesis in laboratory animals

Growth hormone secretagogue peptide-6 enhances oreochromicins transcription and antimicrobial activity in tilapia (Oreochromis sp.)

Growth Hormone-Releasing Peptide 6 (GHRP-6) (His-(D-Trp)-Ala-Trp-(D-Phe)-Lys-NH2) is an agonist of the growth hormone secretagogue receptor. GHRP-6 mimics the effect of ghrelin. The present study focuses on the immunomodulatory effects of GHRP-6 in tilapia with and without the presence of Pseudomonas aeruginosa infection. GHRP-6 up-regulated the transcription levels of three piscidin-like antimicrobial peptides (Oreochromicins I, II, and III) and granzyme in a tissue-dependent manner. Antimicrobial activity stimulation in serum (lysozyme and anti-protease activity) was also confirmed. Besides, GHRP-6 enhanced the in vitro antimicrobial activity against P. aeruginosa in tilapia gills mucus and serum samples and decreased the bacterial load in vivo after infection with this Gram-negative bacterium. Our results evidenced, for the first time, a direct link between a growth hormone secretagogue ghrelin mimetic in fish and the enhancement of antimicrobial peptides transcription, which suggests that this secretagogue is capable to lead the activation of microbicidal activity in tilapia. Thus, these results open new possibilities for GHRP-6 application in aquaculture to stimulate the teleost immune system as an alternative treatment against opportunistic bacteria.

Osmolyte Signatures for the Protection of Aspergillus sydowii Cells under Halophilic Conditions and Osmotic Shock

Aspergillus sydowii is a moderate halophile fungus extensively studied for its biotechnological potential and halophile responses, which has also been reported as a coral reef pathogen. In a recent publication, the transcriptomic analysis of this fungus, when growing on wheat straw, showed that genes related to cell wall modification and cation transporters were upregulated under hypersaline conditions but not under 0.5 M NaCl, the optimal salinity for growth in this strain. This led us to study osmolyte accumulation as a mechanism to withstand moderate salinity. In this work, we show that A. sydowii accumulates trehalose, arabitol, mannitol, and glycerol with different temporal dynamics, which depend on whether the fungus is exposed to hypo- or hyperosmotic stress. The transcripts coding for enzymes responsible for polyalcohol synthesis were regulated in a stress-dependent manner. Interestingly, A. sydowii contains three homologs (Hog1, Hog2 and MpkC) of the Hog1 MAPK, the master regulator of hyperosmotic stress response in S. cerevisiae and other fungi. We show a differential regulation of these MAPKs under different salinity conditions, including sustained basal Hog1/Hog2 phosphorylation levels in the absence of NaCl or in the presence of 2.0 M NaCl, in contrast to what is observed in S. cerevisiae. These findings indicate that halophilic fungi such as A. sydowii utilize different osmoadaptation mechanisms to hypersaline conditions.

Haloadaptative Responses of Aspergillus sydowii to Extreme Water Deprivation: Morphology, Compatible Solutes, and Oxidative Stress at NaCl Saturation

Water activity (a_w) is critical for microbial growth, as it is severely restricted at a_w < 0.90. Saturating NaCl concentrations (~5.0 M) induce extreme water deprivation (a_w ≅ 0.75) and cellular stress responses. Halophilic fungi have cellular adaptations that enable osmotic balance and ionic/oxidative stress prevention to grow at high salinity. Here we studied the morphology, osmolyte synthesis, and oxidative stress defenses of the halophile Aspergillus sydowii EXF-12860 at 1.0 M and 5.13 M NaCl. Colony growth, pigmentation, exudate, and spore production were inhibited at NaCl-saturated media. Additionally, hyphae showed unpolarized growth, lower diameter, and increased septation, multicellularity and branching compared to optimal NaCl concentration. Trehalose, mannitol, arabitol, erythritol, and glycerol were produced in the presence of both 1.0 M and 5.13 M NaCl. Exposing A. sydowii cells to 5.13 M NaCl resulted in oxidative stress evidenced by an increase in antioxidant enzymes and lipid peroxidation biomarkers. Also, genes involved in cellular antioxidant defense systems were upregulated. This is the most comprehensive study that investigates the micromorphology and the adaptative cellular response of different non-enzymatic and enzymatic oxidative stress biomarkers in halophilic filamentous fungi.

A novel GH secretagogue, A233, exhibits enhanced growth activity and innate immune system stimulation in teleosts fish

In teleosts fish, secretion of GH is regulated by several hypothalamic factors that are influenced by the physiological state of the animal. There is an interaction between immune and endocrine systems through hormones and cytokines. GH in fish is involved in many physiological processes that are not overtly growth related, such as saltwater osmoregulation, antifreeze synthesis, and the regulation of sexual maturation and immune functions. This study was conducted to characterize a decapeptide compound A233 (GKFDLSPEHQ) designed by molecular modeling to evaluate its function as a GH secretagogue (GHS). In pituitary cell culture, the peptide A233 induces GH secretion and it is also able to increase superoxide production in tilapia head-kidney leukocyte cultures. This effect is blocked by preincubation with the GHS receptor antagonist [d-Lys(3)]-GHRP6. Immunoneutralization of GH by addition of anti-tilapia GH monoclonal antibody blocked the stimulatory effect of A233 on superoxide production. These experiments propose a GH-mediated mechanism for the action of A233. The in vivo biological action of the decapeptide was also demonstrated for growth stimulation in goldfish and tilapia larvae (P<0.001). Superoxide dismutase levels, antiprotease activity, and lectin titer were enhanced in tilapia larvae treated with this novel molecule. The decapeptide A233 designed by molecular modeling is able to function as a GHS in teleosts and enhance parameters of the innate immune system in the fish larvae.

Reactivity of 99mTc(V) ''3+1''mixed-ligand complexes towards glutathione

The stability and reactivity of mixed-ligand 99mTc complexes of the general formula [99mTcOL1L2], where L1H2 is either an N-substituted bis-(2-mercaptoethyl)amine [SNMeS] or 3-thiapentane-1,5-dithiol [SSS] and L2H is a monodentate thiol [RS], were investigated. The complexes undergo transchelation reactions with glutathione and other SH-group containing blood constituents. The reactions are reversible and can be inhibited by addition of diethylmaleate. Challenge experiments were performed with a broad set of 99mTc mixed-ligand complexes to investigate the influence of both the tridentate ligand and the monodentate ligand on the stability of this type of complex. The occurrence of ligand exchange reactions with glutathione depends on the donor set of the tridentate ligands as well as the structure of the monodentate ligands. Especially the stability of complexes containing a monodentate ligand with an amine nitrogen in the side chain can be increased by lengthening the carbon chain between the sulfhydryl group and the nitrogen. Thus, it might be possible to improve their in-vivo performance.

Novel function of recombinant pituitary adenylate cyclase-activating polypeptide as stimulator of innate immunity in African catfish (Clarias gariepinus) fry

There are several studies that clearly indicate a close bidirectional communication between the neuroendocrine and immune systems. In this sense, hypothalamic releasing hormones, besides their neuroendocrine role, have been shown to influence immune functions. Despite studies developed in mammals, there is, as yet, no information available about the role of the pituitary adenylate cyclase-activating polypeptide (PACAP) and PACAP-related peptide (PRP) in the fish innate immune system. The present study has evaluated the effect of PACAP and PRP administered by bath immersion, on important parameters of innate immunity and antioxidant defenses in African catfish (Clarias gariepinus) fry. We have shown, for the first time, that administration of recombinant C. gariepinus PACAP not only promotes growth but also increases lysozyme, nitric oxide synthase-derived metabolites and antioxidant defenses in treated fry. From our results, PACAP appears to act as a regulator of the teleostean immune system, in addition to its physiological role in controlling growth of fish.

Consequences of abrupt glutathione depletion in murine Clara cells: ultrastructural and biochemical investigations into the role of glutathione loss in naphthalene cytotoxicity

Glutathione plays many critical roles within the cell, including offering protection from reactive chemicals. The bioactivated toxicant naphthalene forms chemically reactive intermediates that can deplete glutathione and covalently bind to cellular proteins. Naphthalene selectively injures the nonciliated epithelial cells of the intrapulmonary airways (i.e., Clara cells). This study attempted to define what role glutathione loss plays in naphthalene cytotoxicity by comparing Swiss-Webster mice treated with naphthalene with those treated with the glutathione depletor diethylmaleate. High-resolution imaging techniques were used to evaluate acute changes in Clara cell ultrastructure, membrane permeability, and cytoskeleton structure. A single dose of either diethylmaleate (1000 mg/kg) or naphthalene (200 mg/kg) caused similar glutathione losses in intrapulmonary airways (< 20% of control). Diethylmaleate did not increase membrane permeability, disrupt mitochondria, or lead to cell death--hallmark features of naphthalene cytotoxicity. However, diethylmaleate treatment did cause Clara cell swelling, plasma membrane blebs, and actin cytoskeleton disruptions similar to naphthalene treatment. Structural changes in mitochondria and Golgi bodies also were noted. Changes in ATP levels were measured as an indication of overall cell function, in isolated airway explants incubated with diethylmaleate, naphthalene, or naphthalene metabolites in vitro. Only the reactive metabolites of naphthalene caused significant ATP losses. Unlike the lethal injury caused by naphthalene, the disruptive cellular changes associated with glutathione loss from diethylmaleate seemed to be reversible after recovery of glutathione levels. This suggests that glutathione depletion may be responsible for some aspects of naphthalene cytotoxicity, but it is not sufficient to cause cell death without further stresses.

Protection against 3,4-methylenedioxymethamphetamine-induced neurodegeneration produced by glutathione depletion in rats is mediated by attenuation of hyperthermia

3,4-Methylenedioxymethamphetamine (MDMA) administration produces neurotoxic degeneration of serotonin terminals in rat brain. These effects occur only after systemic administration and not after central injection, suggesting that peripheral metabolism, possibly hepatic, is required for toxicity. Glutathione is one of the principal cellular defence mechanisms, but conjugation with glutathione can, on some occasions, increase the reactivity of certain molecules. Previous studies have shown that central administration of glutathione adducts of a MDMA metabolite produces a neurotoxicity profile similar to that of systemic MDMA. In the present study, depletion of peripheral (hepatic) glutathione by 43% with dl-buthionine-(S,R)-sulfoximine (an inhibitor of glutathione synthesis) did not attenuate MDMA-induced neurotoxicity as indicated by the 34% loss of [(3) H]paroxetine binding to the serotonin uptake sites in Dark Agouti rats treated with the inhibitor. However, a more profound depletion (92%) of glutathione by diethylmaleate (direct conjugation) administration significantly reduced the serotonergic neurotoxicity produced by MDMA. This depletion protocol also attenuated the hyperthermic response to MDMA. A combination protocol utilising both buthionine-(S,R)-sulfoximine and diethylmaleate that did not alter the hyperthermic response of the rats given MDMA also failed to attenuate the neurotoxicity. These findings indicate that glutathione depletion does not offer specific protection against MDMA-induced serotonin neurotoxicity in Dark Agouti rats.

Ozone oxidative preconditioning: a protection against cellular damage by free radicals

There is some anecdotal evidence that oxygen-ozone therapy may be beneficial in some human diseases. However so far only a few biochemical and pharmacodynamic mechanisms have been elucidated. On the basis of preliminary data we postulated that controlled ozone administration would promote an oxidative preconditioning preventing the hepatocellular damage mediated by free radicals. Six groups of rats were classified as follows: (1) negative control, using intraperitoneal sunflower oil; (2) positive control using carbon tetrachloride (CCl4) as an oxidative challenge; (3) oxygen-ozone, pretreatment via rectal insufflation (15 sessions) and after it, CCl4; (4) oxygen, as group 3 but using oxygen only; (5) control oxygen-ozone, as group 3, but without CCl4; group (6) control oxygen, as group 5, but using oxygen only. We have evaluated critical biochemical parameters such as levels of transaminase, cholinesterase, superoxide dismutase, catalase, phospholipase A, calcium dependent ATPase, reduced glutathione, glucose 6 phosphate dehydrogenase and lipid peroxidation. Interestingly, in spite of CCl4 administration, group 3 did not differ from group 1, while groups 2 and 4 showed significant differences from groups 1 and 3 and displayed hepatic damage. To our knowledge these are the first experimental results showing that repeated administration of ozone in atoxic doses is able to induce an adaptation to oxidative stress thus enabling the animals to maintain hepatocellular integrity after CCl4 poisoning.

Modulation of glutathione conjugation in vivo: how to decrease glutathione conjugation in vivo or in intact cellular systems in vitro

Glutathione conjugation is involved in detoxification and toxification of a variety of electrophilic substrates. Thus it plays a major role in protection against reactive intermediates. At the same time this conjugation may cause resistance of tumor cells against certain cytostatics. In this review the methods available to decrease glutathione conjugation in vivo are discussed. So far the only in vivo active inhibitors of glutathione S-transferases are ethacrynic acid and a number of glutathione-derived structures; the latter seem very promising for further development. For (chronic) glutathione-depletion, buthionine sulfoximine is most effective, and surprisingly safe in clinical studies. Diethylmaleate can be used for acute depletion. Inhibition of glutathione transferases offers advantages over glutathione depletion as a method of decreasing glutathione conjugation since inhibition may be accomplished without changing the activities of other glutathione-dependent reactions in the cell. However, clinically safe, in vivo effective and isoenzyme-selective glutathione S-transferase inhibitors have not yet been developed.

Protective antioxidant mechanisms in rat and guinea pig tissues challenged by acute exposure to cigarette smoke

Cellular damage from reactive intermediates formed during xenobiotic biotransformation is prevented by the presence of adequate levels of antioxidant chemicals in the tissues. Equally important for cell protection is the rate at which these chemicals are replaced if tissue stores are depleted. The present experiments, using adult male Sprague-Dawley rats and Hartley guinea pigs, were conducted to ascertain what effects mainstream (MS) and sidestream (SS) tobacco smoke would have on the water-soluble, cytoplasmic antioxidants, ascorbic acid (AA) and reduced glutathione (GSH). The animals were exposed by nose-only inhalation to varying doses (40, 120, 240 puffs) of a 1:5 dilution of a 35-ml volume of freshly generated MS from cigarettes made from different types of tobacco and delivered by a B.-A.T-Mason inhalation apparatus. The animals were euthanized either immediately following exposure or at 3 and 6 h. The blood, lungs, liver, kidneys, heart and bladder were removed for the quantitation of AA and GSH following homogenization and deproteinization. Immediately following exposure to MS, dose-dependent decreases in pulmonary and renal GSH were observed in rats whereas, in guinea pigs, reductions in pulmonary, hepatic and renal GSH were observed only at the highest level of exposure. No reductions in tissue AA were observed in either species at any exposure level. In both species, blood levels of GSH and AA remained unchanged following exposure. Mainstream smoke (240 puffs) from flue-cured or dark, air-cured tobaccos elicited a significant, immediate reduction in pulmonary and renal GSH, but MS from low tar, filter cigarettes was without effect. Within 3 h of exposure, GSH in all tissues has returned to pre-exposure levels. Whole-body, chamber exposure to concentrated SS, generated from smouldering cigarettes, caused a dose-dependent reduction in rat pulmonary, hepatic, renal, cardiac and bladder muscle GSH but only affected pulmonary GSH in the guinea pig. Lesser effects were observed in tissues of rats exposed to diluted SS. In the rat, a comparison of the results of diethylmaleate- and smoke-induced depletion of tissue GSH suggested that, even at exceptionally high levels of exposure, there was a significant store of GSH in tissues that did not interact with tobacco smoke.

Spin-trapping studies of hepatic free radicals formed following the acute administration of ethanol to rats: in vivo detection of 1-hydroxyethyl radicals with PBN

The generation of free radicals in rat liver following the acute oral administration of ethanol was studied with the spin-trapping method, using a deuterated derivative of phenyl-N-tert-butylnitrone (PBN-d14) as the spin-trapping agent. After administration of ethanol and PBN-d14 to rats, organic extracts of the liver were prepared and subjected to ESR spectroscopy. In the case of ethanol-treated rats, the ESR spectra indicated that mixtures of radicals had been trapped, while spectra from control rats were essentially negative. The predominant spin adduct detected after ethanol treatment is proposed to be from a carbon-centered, primary alkyl radical, based on gamma-hydrogen hyperfine splitting patterns observed with PBN-d14. Oxygen-centered radicals also contributed to the ESR spectra. Liver extracts also contained low concentrations of the 1-hydroxyethyl radical spin adduct, which was indicated by weak spectral lines corresponding to those of the 1-13C-ethanol adduct. These data confirm previous suggestions that ethanol is metabolized to a free radical metabolite in rat liver. In addition, some information on types of lipid radicals generated during alcohol intoxication has been obtained.

Effect of aflatoxin B1 treatment in vivo on the in vitro activity of hepatic and extrahepatic glutathione S-transferase

The effect of aflatoxin B1 (AFB1) on the glutathione S-transferase activity (GST) and on non-protein thiol levels of different tissues was studied in adult male Wistar rats. Animals received a single dose of the toxin (100 or 500 micrograms/kg body wt., p.o.), and were studied 6 or 24 h after administration. GST was determined in liver, renal cortex, duodenum, jejunum-ileum and distal ileum, using 3 substrates: 1-chloro-2,4-dinitrobenzene (CDNB), trans-4-phenyl-3-buten-2-one (PBO) and 1,2-epoxyethylbenzene (STOX). The non-protein thiol content of all tissues tested increased with the lowest dose at 6 h, returning to normal values at 24 h, while the higher dose produced a significant decrease in reduced thiol levels at 6 h, returning to normal values at 24 h. AFB1 administration induced, independently of dose and tissue, total GST (CDNB) and epoxide-transferase activity (STOX) while A--C-type transferases (PBO) were inhibited. Almost all activities returned to normal values at 24 h. In cases of enzyme induction there was in general an increase in Vmax and a decrease in apparent Km. The opposite was seen in cases of inhibition. In conclusion, the results provide evidence that extrahepatic GST could be important in the overall process of detoxification of AFB1. The behavior seen in hepatic and extrahepatic tissues revealed the functions of catalysis (B-type transferases) and covalent bond formation, as well as inactivation by probable AFB1 metabolites (A--C-type transferases).

Bioactivation of dapsone to a cytotoxic metabolite by human hepatic microsomal enzymes

1. Using human mononuclear leucocytes as target cells, we have investigated the bioactivation of dapsone (DDS) to a cytotoxic metabolite in the presence of microsomes from nine human livers. Values for NADPH dependent toxicity ranged from 8.8-27% (15.8 +/- 5.9%) and were similar to those for microsomes from control mice, 16-24% (19.0 +/- 4.8%). 2. Microsomes prepared from mice induced with either phenobarbitone or beta-naphthoflavone did not produce significantly more NADPH dependent toxicity than microsomes prepared from control mice. 3. Cytotoxicity was abolished not only by ascorbic acid, but also by sub-physiological concentrations of N-acetylcysteine and glutathione. 4. DDS was metabolised in vitro to a hydroxylamine (metabolic conversion 3.1 +/- 1.5%), which was oxidised further to a cytotoxic metabolite which also became irreversibly bound to protein.

Enhancement of murine phenytoin teratogenicity by the gamma-glutamylcysteine synthetase inhibitor L-buthionine-(S,R)-sulfoximine and by the glutathione depletor diethyl maleate

The teratogenicity of phenytoin may result from its enzymatic bioactivation to a reactive intermediate, which, if not detoxified, can interact with embryonic tissues and alter development. Glutathione (GSH) is an important cofactor/substrate for many physiological processes and for the detoxification of xenobiotic reactive intermediates. This study examined the effects of the GSH depletor diethyl maleate (DEM) and the GSH synthesis inhibitor L-buthionine-(S,R)-sulfoximine (BSO) on phenytoin embryopathy. Phenytoin, 55 mg/kg, was administered intraperitoneally (ip) to pregnant CD-1 mice at 0900 hr on gestational days 12 and 13. Pretreatment with DEM, 150 or 300 mg/kg ip, enhanced the incidence of phenytoin-induced cleft palates by 3.3-fold and 2.3-fold, respectively (P less than 0.05), without affecting the incidence of resorptions, postpartum death, or mean fetal weight. BSO, 1,800 mg/kg ip, given 0.5 hr prior to phenytoin, resulted in a 2.4-fold increase in postpartum lethality and a 5-fold increase in fetal weight loss (P less than 0.05), without altering the incidence of resorptions or cleft palates. In two subsequent studies, BSO, 680-1,018 mg/kg/day, was given in the drinking water on gestational days 9 to 13 in the first study and on days 10 to 14 in the second study. Phenytoin, 55 mg/kg ip, was given on days 11 and 12 and on days 11 to 13 in the respective studies. In the first drinking water study, BSO enhanced the incidence of phenytoin-induced fetal resorptions 3.8-fold and cleft palates 3.3-fold (P less than 0.05) but did not affect postpartum death. In the second study, BSO enhanced the incidence of resorptions, cleft palates, and postpartum death by 2-fold, 2.6-fold, and 1.7-fold, respectively (P less than 0.05). In both of the latter two studies, phenytoin-induced fetal weight loss was altered by BSO treatment (P less than 0.05). BSO alone had no embryopathic effects. These results suggest that GSH may be involved in the detoxification of a reactive intermediate of phenytoin and/or in fetal cytoprotection.

Glutathione and lipid peroxide levels in rat liver following administration of methapyrilene and analogs

The possibility was examined that the induction of tumors in rat liver by feeding methapyrilene, which is not mutagenic, is related to effects on glutathione levels and lipid peroxidation. Fischer 344 rats were given single-dose and multiple-dose treatments with the anti-histamine methapyrilene (MP), which is carcinogenic in rats, and with two non-carcinogenic analogs, methafurylene (MF) and thenyldiamine (TD) and the effects on malonaldehyde (MDA) formation and glutathione (GSH) levels in the liver were investigated. After a single dose, MDA levels were increased at 6 h by MF and TD and at 24 h by MP. MDA levels returned to normal after 30 h with MP and MF, but not with TD. Levels of MDA (and other TBA-reactive products) after four daily treatments were most elevated by TD, less elevated by MP, and were lowered by MF. Forty-two hours following treatment with both MP and MF, MDA levels had returned to normal, but in TD-treated animals MDA remained high. GSH levels were highest after MF and MP, and remained high at 42 h, but TD induced only a small increase. There appears to be increased lipid peroxidation in the liver as a result of treatment of rats with MP, MF and TD. The greater response induced by TD, as well as the increased liver GSH levels after repeated administration of all three drugs indicate that lipid peroxidation in rat liver is not a particular effect related to the liver carcinogen methapyrilene.

The retention mechanism of technetium-99m-HM-PAO: intracellular reaction with glutathione

Preparations of d,l- and meso-hexamethylpropyleneamine oxime (HM-PAO) labeled with technetium-99m were added to rat brain homogenates diluted with phosphate buffer (1:10). The conversion of d,l-HM-PAO to hydrophilic forms took place with an initial rate constant of 0.12 min-1. Incubation of the brain homogenate with 2% diethyl maleate for 5 h decreased the homogenate's measured glutathione (GSH) concentration from 160 to 16 microM and decreased the conversion rate to 0.012 min-1. Buffered aqueous solutions of glutathione rapidly converted the HM-PAO tracers to hydrophilic forms having the same chromatographic characteristics as found in the brain homogenates. The rate constant for the conversion reaction of d,l-HM-PAO in GSH aqueous solution was 208 and 317 L/mol/min in two different assay systems and for meso-HM-PAO the values were 14.7 and 23.2 L/mol/min, respectively. Rat brain has a GSH concentration of about 2.3 mM and the conversion of the d,l-HM-PAO due to GSH alone should proceed with a rate constant of 0.48 to 0.73 min-1 and be correspondingly 14-fold slower for meso-HM-PAO. In human brain, the in vivo data of Lassen et al. show a conversion rate constant of 0.80 min-1. This correspondence of values supports the notion that GSH may be important for the in vivo conversion of 99mTc-labeled HM-PAO to hydrophilic forms and may be the mechanism of trapping in brain and other cells. A kinetic model for the trapping of d,l- and meso-HM-PAO in tissue is developed that is based on data of GSH concentration in various organs.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutathione depletion in the guinea pig and its effect on the acute cochlear toxicity of ethacrynic acid

There is controversy as to whether or not the acute cochlear toxicity of ethacrynic acid (EA) is dependent upon its metabolic conversion to EA-cysteine via conjugation with glutathione. In order to investigate this we examined the acute effects of EA on cochlear potentials in guinea pigs in which glutathione levels were decreased by prior administration of (+/-)-buthionine sulphoximine (BSO), an inhibitor of glutamylcysteine synthetase. First, we determined the effects of BSO on hepatic and renal glutathione levels in the guinea pig. Guinea pigs (pigmented animals of both sexes or male albino animals) were killed at intervals up to 72 hr after i.p. administration of 1.6 g kg-1 BSO. Livers, and also kidneys in the case of pigmented guinea pigs, were removed and total glutathione (GSH + GSSG) measured. Glutathione levels reached a nadir in the liver at 24-48 hr (11% of control) and in the kidneys at 24 hr (14% of control) after administration of BSO. Hepatic but not renal levels approached control values by 72 hr. There were no sex or strain differences. Pigmented guinea pigs were anaesthetised and their endocochlear potential and a.c. cochlear potential in response to a 4 kHz tone were measured using an intracochlear microelectrode. The depression of these potentials by i.v. administration of 60 mg kg-1 EA was not affected by administration of 1.6 g kg-1 BSO 24 hr earlier, despite profound depletion of glutathione. Also prior p.o. administration of N-acetyl-L-cysteine did not affect hepatic glutathione levels nor modify the toxicity of EA. These results suggest that the acute cochlear toxicity of EA is not altered by glutathione depletion, a finding which argues against a role for the metabolic activation of EA in its ototoxicity.

Role of cutaneous GSH in 12-O-tetradecanoyl-phorbol 13-acetate-induced mouse skin tumor promotion

The role of glutathione (GSH) in skin tumor promotion was ascertained in the present study by investigating the effect of the GSH depletor, diethyl-maleate (DEM), on the tumor-promoting ability of TPA in DMBA-initiated mouse skin. DEM lowered the tumor yield and the tumor incidence by 80% (p less than 0.001) in the DMBA + TPA treated group. The rate of tumor formation was also found to be influenced by DEM. The results suggest that clonal expansion of tumor-initiated cells, stimulated by TPA, depends upon the availability of reduced GSH in the tissue. The mechanism by which depletion of reduced GSH could result in inhibition of skin tumor promotion is not known. However, inactivation of GSH and thus blockage of the physiological function of reduced GSH in the biochemical events obligatory to tumor-cell proliferation in mouse skin could be the possible mechanisms providing effective control over proliferation of tumor cells.

Depletion and resynthesis of tissue thiols by helenalin and tenulin

The depletion of tissue thiols by two anti-leukemic agents helenalin and tenulin was studied in mice. Helenalin (100 mg/kg) and tenulin (213 mg/kg) in dimethyl sulfoxide (DMSO) were administered orally, and the acid-soluble total thiol concentrations in the liver, kidney, stomach and small intestine were determined at 0.5, 1.0, 3.0, 6.0, 12.0 and 24.0 hr post-treatment. The lowest tissue thiol levels (42-84% of pretrial values) were observed within 0.5 - 1.0 hr following helenalin treatment. The tenulin treated mice exhibited the lowest values (46-80% of pretrial control values) at 3.0 hr post-treatment in all tissues except in the stomach, which reached its lowest value at 1.0 hr. The most dramatic effects were found in the stomach and small intestine where the mean thiol concentrations varied from 43% to 141% (at 1.0 and 24.0 hr) and from 76% to 169% (at 0.5 and 24.0 hr) of pretrial values, respectively, among helenalin treated mice. The tissue thiol levels in DMSO- and physiological saline (PSS)-treated mice fluctuated probably due to fasting and/or diurnal changes.

In vivo effects of 1,3-bis(2-chloroethyl)-1-nitrosourea and doxorubicin on the cardiac and hepatic glutathione systems

Doxorubicin and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) are anti-cancer drugs which have been used together in combination therapy of certain cancers. Each drug has been reported to affect intracellular glutathione stores and together, doxorubicin and BCNU have been shown to exert synergistic toxicity and to deplete completely the glutathione content of isolated hepatocytes. Cardiac and hepatic glutathione reductase activity was significantly inhibited following treatment in vivo with BCNU. Treatment of mice with both doxorubicin and BCNU resulted in increased mortality compared to either drug alone. There was, however, no depletion of hepatic or cardiac glutathione levels in vivo beyond that seen with either BCNU or doxorubicin alone. Diethyl maleate, a known glutathione depletor whose effects are enhanced by BCNU in vitro, also was unable to increase GSH depletion after BCNU in vivo. These discrepancies between in vivo and in vitro studies may be due to the presence of more effective compensatory mechanisms in the whole animal, or to differences in the metabolism and inactivation of these drugs.