Taurine supplementation induces multidrug resistance protein 2 and bile salt export pump expression in rats and prevents endotoxin-induced cholestasis

The effect of oral taurine supplementation on endotoxin-induced cholestasis was investigated in rat liver. At 12h following lipopolysaccharide (LPS) injection (4mg/kg body weight i.p.) bile flow and bromosulfophthalein (BSP) and taurocholate (TC) excretion were determined in the perfused liver and the expression of the canalicular transporters multidrug resistance protein 2 (Mrp2) and bile salt export pump (Bsep) was analyzed. Injection of LPS induced a significant decrease of bile flow ( 2.2+/-0.2 microl/g liver wet weight/min vs 3.3+/-0.1 microl/g liver wet weight in controls), biliary BSP excretion (10.8+/-2.2 nmol/g/min vs 21.0+/-3.8 nmol/g/min), and biliary TC excretion (114+/-23 nmol/g/min vs 228+/-8 nmol/g/min). These effects were due to transporter retrieval from the canalicular membrane and downregulation of Mrp2 and Bsep expression. In taurine-supplemented rats bile flow was 30% higher than that in untreated rats and the expression of Mrp2 and Bsep protein was increased two- to threefold. In taurine-supplemented rats there was no significant reduction of bile flow or of BSP and TC excretion at 12h following LPS injection. This protective effect of taurine was due to higher Mrp2 and Bsep protein levels compared to nonsupplemented LPS-treated rats, whereas relative Mrp2 retrieval from the canalicular membrane induced by LPS was not significantly different. LPS-induced tumor necrosis factor alpha and interleukin-1beta release were lower in taurine-fed rats; however, downregulation of Mrp2 and Bsep expression by LPS was delayed but not prevented. The data show that oral supplementation of taurine induces Mrp2 and Bsep expression and may prevent LPS-induced cholestasis.     

Oxidative stress and Mrp2 internalization

Oxidative stress in the liver is sometimes accompanied by cholestasis. We have described the internalization of multidrug resistance-associated protein 2/ATP-binding cassette transporter family 2 (Mrp2/Abcc2), a biliary transporter involved in bile-salt-independent bile flow, under ethacrynic acid (EA)-induced acute oxidative stress in rat liver. However, the signaling pathway and regulatory molecules have not been investigated. In the present study, we investigated the mechanism of EA-induced Mrp2 internalization using isolated rat hepatocyte couplets (IRCHs). The Mrp2 index, defined as the ratio of Mrp2-positive canalicular membrane staining in IRCHs per number of cell nuclei, was significantly reduced by treatment with EA. This reduction was abolished by a nonspecific protein kinase C (PKC) inhibitor Gö6850, a Ca²⁺ chelator, EGTA, but not by a protein kinase A (PKA)-selective inhibitor, a Ca²⁺-dependent conventional PKC (cPKC) inhibitor Gö6976, or a protein kinase G (PKG) inhibitor (1 μM). Moreover, an increase in the intracellular Ca²⁺ level and NO release into medium were observed shortly after the EA treatment. Both of these increases, as well as Mrp2 internalization, were completely blocked by EGTA. In conclusion, EA produced a reduction in GSH, Ca²⁺ elevation, NO production, and nPKC activation in a sequential manner, finally leading to Mrp2 internalization.     

Mrp2 is involved in benzylpenicillin-induced choleresis

Benzylpenicillin (PCG; 180 micromol/kg), a classic beta-lactam antibiotic, was intravenously given to Sprague-Dawley (SD) rats and multidrug resistance-associated protein 2 (Mrp2)-deficient Eisai hyperbilirubinemic rats (EHBR). A percentage of the [(3)H]PCG was excreted into the bile of the rats within 60 min (SD rats: 31.7% and EHBR: 4.3%). Remarkably, a transient increase in the bile flow ( approximately 2-fold) and a slight increase in the total biliary bilirubin excretion were observed in SD rats but not in the EHBR after PCG administration. This suggests that the biliary excretion of PCG and its choleretic effect are Mrp2-dependent. Positive correlations were observed between the biliary excretion rate of PCG and bile flow (r(2) = 0.768) and more remarkably between the biliary excretion rate of GSH and bile flow (r(2) = 0.968). No ATP-dependent uptake of [(3)H]PCG was observed in Mrp2-expressing Sf9 membrane vesicles, whereas other forms of Mrp2-substrate transport were stimulated in the presence of PCG. GSH efflux mediated by human MRP2 expressed in Madin-Darby canine kidney II cells was enhanced in the presence of PCG in a concentration-dependent manner. In conclusion, the choleretic effect of PCG is caused by the stimulation of biliary GSH efflux as well as the concentrative biliary excretion of PCG itself, both of which were Mrp2 dependent.     

Characterization of bile acid transport mediated by multidrug resistance associated protein 2 and bile salt export pump

Biliary excretion of certain bile acids is mediated by multidrug resistance associated protein 2 (Mrp2) and the bile salt export pump (Bsep). In the present study, the transport properties of several bile acids were characterized in canalicular membrane vesicles (CMVs) isolated from Sprague--Dawley (SD) rats and Eisai hyperbilirubinemic rats (EHBR) whose Mrp2 function is hereditarily defective and in membrane vesicles isolated from Sf9 cells infected with recombinant baculovirus containing cDNAs encoding Mrp2 and Bsep. ATP-dependent uptake of [(3)H]taurochenodeoxycholate sulfate (TCDC-S) (K(m)=8.8 microM) and [(3)H]taurolithocholate sulfate (TLC-S) (K(m)=1.5 microM) was observed in CMVs from SD rats, but not from EHBR. In addition, ATP-dependent uptake of [(3)H]TLC-S (K(m)=3.9 microM) and [(3)H]taurocholate (TC) (K(m)=7.5 microM) was also observed in Mrp2- and Bsep-expressing Sf9 membrane vesicles, respectively. TCDC-S and TLC-S inhibited the ATP-dependent TC uptake into CMVs from SD rats with IC(50) values of 4.6 microM and 1.2 microM, respectively. In contrast, the corresponding values for Sf9 cells expressing Bsep were 59 and 62 microM, respectively, which were similar to those determined in CMVs from EHBR (68 and 33 microM, respectively). By co-expressing Mrp2 with Bsep in Sf9 cells, IC(50) values for membrane vesicles from these cells shifted to values comparable with those in CMVs from SD rats (4.6 and 1.2 microM). Moreover, in membrane vesicles where both Mrp2 and Bsep are co-expressed, preincubation with the sulfated bile acids potentiated their inhibitory effect on Bsep-mediated TC transport. These results can be accounted for by assuming that the sulfated bile acids trans-inhibit the Bsep-mediated transport of TC.     

The multidrug resistance protein 1 (Mrp1), but not Mrp5, mediates export of glutathione and glutathione disulfide from brain astrocytes

Astrocytes play an important role in the glutathione (GSH) metabolism of the brain. To test for an involvement of multidrug resistance protein (Mrp) 1 and 5 in the release of GSH and glutathione disulfide (GSSG) from astrocytes, we used astrocyte cultures from wild-type, Mrp1-deficient [Mrp1(-/-)] and Mrp5-deficient [Mrp5(-/-)] mice. During incubation of wild-type or Mrp5(-/-) astrocytes, GSH accumulated in the medium at a rate of about 3 nmol/(h.mg), whereas the export of GSH from Mrp1(-/-) astrocytes was only one-third of that. In addition, Mrp1(-/-) astrocytes had a 50% higher specific GSH content than wild-type or Mrp5(-/-) cells. The presence of 50 microm of the Mrp inhibitor MK571 inhibited the rate of GSH release from wild-type and Mrp5(-/-) astrocytes by 60%, but stimulated at the low concentration of 1 microm GSH release by 40%. In contrast, both concentrations of MK571 did not affect GSH export from Mrp1(-/-) astrocytes. Moreover, in contrast to wild-type and Mrp5(-/-) cells, GSSG export during H(2)O(2) stress was not observed for Mrp1(-/-) astrocytes. These data demonstrate that in astrocytes Mrp1 mediates 60% of the GSH export, that Mrp1 is exclusively responsible for GSSG export and that Mrp5 does not contribute to these transport processes.     

ATP-dependent GSH and glutathione S-conjugate transport in skate liver: role of an Mrp functional homologue

Multidrug resistance-associated proteins 1 and 2 (Mrp1 and Mrp2) are thought to mediate low-affinity ATP-dependent transport of reduced glutathione (GSH), but there is as yet no direct evidence for this hypothesis. The present study examined whether livers from the little skate (Raja erinacea) express an Mrp2 homologue and whether skate liver membrane vesicles exhibit ATP-dependent GSH transport activity. Antibodies directed against mammalian Mrp2-specific epitopes labeled a 180-kDa protein band in skate liver plasma membranes and stained canaliculi by immunofluorescence, indicating that skate livers express a homologous protein. Functional assays of Mrp transport activity were carried out using (3)H-labeled S-dinitrophenyl-glutathione (DNP-SG). DNP-SG was accumulated in skate liver membrane vesicles by both ATP-dependent and ATP-independent mechanisms. ATP-dependent DNP-SG uptake was of relatively high affinity [Michaelis-Menten constant (K(m)) = 32 +/- 9 microM] and was cis-inhibited by known substrates of Mrp2 and by GSH. Interestingly, ATP-dependent transport of (3)H-labeled S-ethylglutathione and (3)H-labeled GSH was also detected in the vesicles. ATP-dependent GSH transport was mediated by a low-affinity pathway (K(m) = 12 +/- 2 mM) that was cis-inhibited by substrates of the Mrp2 transporter but was not affected by membrane potential or pH gradient uncouplers. These results provide the first direct evidence for ATP-dependent transport of GSH in liver membrane vesicles and support the hypothesis that GSH efflux from mammalian cells is mediated by members of the Mrp family of proteins.     

Depletion of liver glutathione induced by iodobenzene poisoning and its relation to lipid peroxidation and necrosis

The mechanisms underlying iodobenzene hepatotoxicity were investigated in Albino mice in which the hepatic glutathione (GSH) content had been decreased by nearly 50% by starvation for 16 h before poisoning. After iodobenzene administration (9 mmol/Kg, p.o.) the hepatic GSH content decreased progressively and liver necrosis, as measured by the plasma transaminase (GPT, GOT) levels, occurred in many animals at 12 and 16 h. A clear cut necrosis was evident only when the hepatic GSH depletion reached a threshold value (3.5-2.5 nmol/mg protein). The same threshold value was evident for the occurrence of lipid peroxidation (measured as both carbonyl functions and conjugated dienes in liver phospholipids). The highly significant correlation found between lipid peroxidation and liver necrosis supports the possibility of a cause-effect relationship between the two phenomena.     

Retrieval of the mrp2 gene encoded conjugate export pump from the canalicular membrane contributes to cholestasis induced by tert-butyl hydroperoxide and chloro-dinitrobenzene

Oxidative stress is known to induce cholestasis, but the underlying mechanisms are poorly understood. In this study we have characterized the short-term effects of tert-butyl hydroperoxide (t-BOOH)- and 1-chloro-2,4-dinitrobenzene (CDNB) on the mrp2 gene encoded canalicular export pump (Mrp2). The effects of t-BOOH and CDNB on bile formation, tissue GSH levels and subcellular Mrp2 localization were studied in perfused rat liver. Both, t-BOOH (0.5 mM) and CDNB (0.1 mM) induced within 60 min a decrease of hepatic GSH levels by more than 90% and an almost complete cessation of bile flow. As revealed by confocal laser scanning microscopy, this cholestasis was accompanied by a loss of immunoreactive MRP2 from the canalicular membrane and its appearance inside the hepatocytes in putative intracellular vesicles. On the other hand, the intracellular distribution of dipeptidyl peptidase IV (DPPIV), another canalicular protein, and of zonula occludens associated polypeptide (ZO-1) remained unaffected, indicating selectivity of the Mrp2 retrieval pattern. Both, t-BOOH and CDNB induced a rapid net K+ efflux from the liver and a significant decrease of liver cell hydration. We conclude that severe glutathione depletion induces cholestasis by a retrieval of Mrp2, but not of DPPIV from the canalicular membrane. The underlying mechanism is unclear; however, a decrease in liver cell hydration, which occurs under these conditions, may contribute to this effect.     

Naproxen-induced oxidative stress in the isolated perfused rat liver

We previously showed that naproxen induced the oxidative stress in the liver microsomes and the isolated hepatocytes of rats. In this study, the in situ effect of naproxen on the rat liver tissue was investigated, using the isolated perfused liver from the view-point of the naproxen-induced hepatotoxicity. The leakage of glutamic-oxaloacetic transaminase (GOT) from the perfused liver and appearance of thiobarbituric acid reactive substances (TBARS) in the perfusate increased with the progress of perfusion after a lag time of about 1h. The naproxen-perfusion of the liver decreased the biliary excretion of glutathione (GSH) and oxidized glutathione, glutathione disulfide (GSSG) prior to TBARS production and GOT leakage. GSSG content in the naproxen-perfused liver was significantly higher than in the control. TBARS appeared in the perfusate of the naproxen-perfused liver for 30 min, but not in the control. The biliary excretion clearance (CL(bile)) of indocyanine green (ICG), a reagent for testing the liver function, in the liver perfused with naproxen decreased to a half of that in the liver perfused without naproxen. Thus, the naproxen-induced oxidative stress in the liver was shown to affect the physiological function of liver through the impairment of biliary excretion, which is recognized as a detoxification system.     

Determination of phase I metabolic enzyme activities in liver microsomes of Mrp2 deficient TR- and EHBR rats

The canalicular multispecific organic anion transporter/multidrug resistance protein 2 (cMOAT/Mrp2) plays a major role in the transport of anionic xenobiotics across the bile canalicular membrane. Transport deficient rats (TR-) and Eisai-hyperbilirubinemic rats (EHBR), defective in Mrp2, are mutants of Wistar and Sprague Dawley (SD) rats, respectively. In this study, Phase I metabolic enzyme activities in liver microsomes prepared from these mutant male and female rats were compared to their corresponding non-mutant rats. The total cytochrome P450 contents and NADPH-cytochrome P450 reductase activity in male and female TR- rats were significantly higher than in Wistar rats. In male TR- rats, ethoxyresorufin O-deethylation (EROD), pentoxyresorufin O-deethylation (PROD), testosterone 2alpha, 7alpha and 16 alpha-hydroxylase activities were higher, but testosterone 6beta-hydroxylase activity and the rate of androstenedione formation were lower than in Wistar rats. Female TR- rats had higher 7alpha-hydroxylase activity, but EROD activity was lower in female Wistar rats. Similar studies conducted in EHBR versus SD rats demonstrated increased total cytochrome P450 content in male and female EHBR rats; NADPH-cytochrome P450 reductase activity was not significantly affected. Decreased PROD activity and the rate of androstenedione formation were observed in male and female EHBR rats. Furthermore, testosterone 6beta-hydroxylase activity was lower in male EHBR rats than in male SD rats while testosterone 7alpha-hydroxylase activity was significantly higher in male and female EHBR rats. Thus, in addition to Mrp2 deficiency, differential expression of CYP isoforms and their potential impact on the metabolism and pharmacokinetics of compounds should be considered when interpreting data from these rat strains.     

Chelerythrine stimulates GSH transport by rat Mrp2 (Abcc2) expressed in canine kidney cells

Rat multidrug resistant protein 2 (Mrp2; Abcc2), an ATP-driven pump located on the canalicular domain of hepatocytes, exports glutathione S-conjugates (GS-X) and GSH among its wide variety of substrates. Previous studies have shown that chelerythrine (CHEL), a quaternary benzophenanthridine cation, reacts with GSH to form a reversible adduct under physiological conditions. Here we report that CHEL can strongly stimulate GSH efflux by Mrp2, when it is constitutively expressed in polarized canine kidney cells, thereby leading to the depletion of cellular GSH. Transepithelial transport experiments indicate that Mrp2 transports GSH and CHEL with a 1:1 stoichiometry, which can be readily inhibited by GS-bimane, a GS-X substrate for Mrp2. Moreover, CHEL can block Mrp2-mediated leukotriene C4 uptake by membrane vesicles with an IC50 approximately 100 microM in the presence of GSH, but not S-methyl GSH or ophthalmic acid. Thus the thiol group of GSH is required for inhibition of Mrp2 in the presence of CHEL. Our results suggest that CHEL stimulates GSH efflux by forming a reversible GS-CHEL adduct, which is transported by Mrp2 and dissociates extracellularly.     

Acetaminophen-induced liver oxidative stress and hepatotoxicity: influence of Kupffer cell activity assessed in the isolated perfused rat liver

Summary

The influence of acetaminophen (APAP) treatment (400 mg/kg) on Kupffer cell function was studied in the isolated perfused liver by colloidal carbon infusion, concomitantly with parameters related to oxidative stress (thiobarbituric acid reactants (TBARS) formation and glutathione (GSH) content) and tissue injury (sinusoidal efflux of lactate dehydrogenase (LDH)). APAP led to increased rates of hepatic TBARS formation, GSH depletion, and higher sinusoidal LDH efflux compared to control values, without changes in the basal rate of O₂ consumption. In addition, APAP significantly enhanced the rate of carbon uptake by perfused livers and the associated carbon-induced O₂ consumption, with carbon-induced LDH effluxes being increased by 411% over control values or by 124% compared to basal LDH release in APAP-treated rats. APAP-induced changes in liver TBARS formation and GSH levels were attenuated by gadolinium chloride (GdCl₃) pretreatment, whereas those in carbon uptake, carbon-induced respiration, and LDH efflux were abolished. GdCl₃ pretreatment decreased liver O₂ consumption irrespectively of APAP treatment, an effect that seems to be due to depression of mitochondrial respiration. It is concluded that APAP intoxication enhances Kupffer cell function as assessed in the intact liver, which may represent an important source of reactive O₂ species and chemical mediators conditioning the increased oxidative stress status and the tissue injury which developed.     

An in vivo role of Mrp2 in the rat hepatocytes by immunocytochemistry for amoxicillin using the transporter-deficient EHBR

An in vivo role of the multidrug resistant-associated protein (Mrp2) in rat hepatocytes was examined by immunocytochemistry (ICC) for amoxicillin (AMPC) by the use of the transporter-deficient Eisai hyperbilirubinemic rats (EHBR). The ICC revealed that in the liver of EHBR at 3-h post-administration, amoxicillin accumulated in the cytoplasmic pools and nuclei of the hepatocytes in a characteristic granular morphology on the bile capillaries. However, no amoxicillin was observed on the surface of the lumina ranging from the bile capillaries to the interlobular bile ducts. The drug persisted at least for 6-h after administration. In contrast, in the control rat liver at 3-h post-administration, AMPC-adsorption occurred on such luminal surface, while AMPC accumulated to a less level in both the cytoplasm and nuclei of the hepatocytes. The drug completely disappeared in the hepatocytes at 6-h post-administration. These results strongly suggest that AMPC taken up into the cytoplasm of the hepatocytes excretes via Mrp2 into the bile flow. Furthermore, electron microscopy demonstrated that the lower electron density areas in large sizes, corresponding to the cytoplasmic pools in ICC for AMPC, occurred in the cytoplasm peripheral to the nuclei of the hepatocytes in EHBR at 3-h post-administration, and then disappeared 24 h after administration.     

The effects of nimodipine and L-NAME on coronary flow and oxidative stress parameters in isolated rat heart

The aim of this study was to assess the effects of Ca2+ channel antagonist nimodipine (in concentration which competitive inhibited phosphodiesterase 1--PDE1) on oxidative stress alone or under inhibition of nitric oxide synthase by L-NAME in isolated rat heart. The hearts from male Wistar albino rats (n=18, BM about 200 g, age 8 weeks) were retrograde perfused according to the Langendorff technique at gradually increased constant perfusion pressure conditions (CPP, 40-120 cm H2O). The experiments were performed under control conditions, in the presence of Nimodipine (2 microM) or Nimodipine (2 microM) plus L-NAME (30 microM). Coronary flow (CF) varied in the autoregulatory range from 3.7 +/- 0.4 ml/min/g wt at 50 cm H2O to 4.35 +/- 0.79 at 90 cm H2O. Basal nitrite outflow, index of lipid peroxidation (measured as TBARS release) and superoxide anion release (O2-) (at 60 cm H2O) were 0.64 +/- 0.18 nmol/min/g wt, 0.55 +/- 0.13 micromol/min/g wt and 19.72 +/- 3.70 nmol/min/g wt, respectively. Nimodipine induced significant vasodilation at all values of CPP (from 26% at 40 cm H2O to 36% at 120 cm H2O) accompanied with significant decrease of nitrite outflow (from 59% at 40 cm H2O to 40% at 120 cm H2O), significant increase of TBARS above autoregulatory range (about 40%) and significant increase of O2- release (from 186% at 40 cm H2O to 117% at 120 cm H2O). However, perfusion with L-NAME completely reversed the effects of Nimodipine. Nimodipine-induced flow changes were decreased under L-NAME (from 3% at 40 cm H2O to 11% at 120 cm H2O) without changes in the autoregulatory range, accompanied with significantly increased nitrite outflow (from 69% at 40 cm H2O to 36% at 120 cm H2O) and TBARS release (almost 50%), as well as significantly decreased O2- release (from 50% at 40 cm H2O to 43% at 120 cm H20). Our findings show that effect of nimodipine on coronary flow should be significantly influenced by NO, TBARS and O2- release in isolated rat heart.     

Inhibition of protein carbonyl formation and lipid peroxidation by glutathione in rat liver microsomes.

The peroxidation of rat liver microsomal lipids is stimulated in the presence of iron by the addition of NADPH or ascorbate and is inhibited by the addition of glutathione (GSH). The fate of GSH and the oxidative modification of proteins under these conditions have not been well studied. Rat liver microsomes were incubated at 37 degrees C under 95% O2:5% CO2 in the presence of 10 microM ferric chloride, 400 microM ADP, and either 450 microM ascorbic acid or 400 microM NADPH. Lipid peroxidation was assessed in the presence 0, 0.2, 0.5, 1, or 5 mM GSH by measuring thiobarbituric acid reactive substance (TBARS) and oxidative modification of proteins by measuring protein thiol and carbonyl groups. GSH inhibited TBARS and protein carbonyl group formation in both ascorbate and NADPH systems in a dose-dependent manner. Heat denaturing of microsomes or treatment with trypsin resulted in the loss of this protection. The formation of protein carbonyl groups could be duplicated by incubating microsomes with 4-hydroxynonenal. Ascorbate-dependent peroxidation caused a loss of protein thiol groups which was diminished by GSH only in fresh microsomes. Both boiling and trypsin treatment significantly decreased the basal protein thiol content of microsomes and enhanced ascorbate-stimulated lipid peroxidation. Protection against protein carbonyl group formation by GSH correlated with the inhibition of lipid peroxidation and appeared not to be due to the formation of the GSH conjugate of 4-hydroxynonenal as only trace amounts of this conjugate were detected. Ninety percent of the GSH lost after 60 min of peroxidation was recoverable as borohydride reducible material in the supernatant fraction. The remaining 10% could be accounted for as GSH-bound protein mixed disulfides. However, only 75% of the GSH lost during peroxidation appeared as glutathione disulfide, suggesting that some was converted to other soluble borohydride reducible forms. These data support a role for protein thiol groups in the GSH-mediated protection of microsomes against lipid peroxidation.     

Canalicular Mrp2 localization is reversibly regulated by the intracellular redox status

Oxidative stress is known to be a common feature of cholestatic syndrome. We have described the internalization of multidrug resistance-associated protein 2 (Mrp2), a biliary transporter involved in bile salt-independent bile flow, under acute oxidative stress, and a series of signaling pathways finally leading to the activation of novel protein kinase C were involved in this mechanism; however, it has been unclear whether the internalized Mrp2 localization was relocalized to the canalicular membrane when the intracellular redox status was recovered from oxidative stress. In this study, we demonstrated that decreased canalicular expression of Mrp2 induced by tertiary-butyl hydroperoxide (t-BHP) was recovered to the canalicular membrane by the replenishment of GSH by GSH-ethyl ester, a cell-permeable form of GSH. Moreover, pretreatment of isolated rat hepatocytes with colchicine and PKA inhibitor did not affect the t-BHP-induced Mrp2 internalization process but did prevent the Mrp2 recycling process induced by GSH replenishment. Moreover, intracellular cAMP concentration similarly changed with the change of intracellular GSH content. Taken together, our data clearly indicate that the redox-sensitive balance of PKA/PKC activation regulates the reversible Mrp2 localization in two different pathways, the microtubule-independent internalization pathway and -dependent recycling pathway of Mrp2.     

Lipid peroxidation measured as thiobarbituric acid-reactive substances in tissue slices: characterization and comparison with homogenates and microsomes

Liver slices were used to measure lipid peroxidation induced by bromotrichloromethane, tert-butyl hydroperoxide (t-BOOH), or ferrous iron. The responses of liver homogenates and microsomes to oxidative conditions were compared with the response of tissue slices. Lipid peroxidation was evaluated by the production of thiobarbituric acid-reactive substances (TBARS). As was observed in homogenates and microsomes, TBARS production by liver slices depended upon the amount of tissue, the incubation time, inducer, the amount of inducer, and the presence of antioxidant. Control liver slices incubated at 37 degrees C for 2 h produced 19 nmol of TBARS per g of liver. When slices were incubated in the presence of 1 mM BrCCl3, 1 mM t-BOOH, or 50 microM ferrous iron, TBARS production increased 4.6-, 8.2-, or 6.7-fold over the control value, respectively. Comparable induction of TBARS by liver homogenates and microsomes was observed when these preparations were incubated with the same inducers. Addition of 5 microM butylated hydroxytoluene (BHT) prevented the induction of TBARS by 50 microM ferrous iron by liver slices. The results indicate the usefulness of tissue slices to measure lipid peroxidation. The usefulness of tissue slices is emphasized when a number of compounds or tissues are studied and tissue integrity is desired as in toxicological, pharmacological, and nutritional studies where reduced numbers of experimental animals is a relevant issue.     

Attenuation of the acute adriamycin-induced cardiac and hepatic oxidative toxicity by N-(2-mercaptopropionyl) glycine in rats

The protective effect of the synthetic aminothiol, N-(2-mercaptopropionyl) glycine (MPG) on adriamycin (ADR) induced acute cardiac and hepatic oxidative toxicity was evaluated in rats. ADR toxicity, induced by a single intraperitoneal injection (15 mg/kg), was indicated by an elevation in the level of serum glutamic pyruvic transaminase (GPT), glutamic oxaloacetic transaminase (GOT), creatine kinase isoenzyme (CK-MB), and lactic dehydrogenase (LDH). ADR produced significant elevation in thiobarbituric acid reactive substances (TBARS), indicating lipid peroxidation, and significantly inhibited the activity of superoxide dismutase (SOD) in heart and liver tissues. In contrast, a single injection of ADR did not affect the cardiac or hepatic glutathione (GSH) content and cardiac catalase (CAT) activity but elevated hepatic CAT. Pretreatment with MPG, (2.5 mg/kg) intragastrically, significantly reduced TBARS concentration in both heart and liver and ameliorated the inhibition of cardiac and hepatic SOD activity. In addition, MPG significantly decreased the serum level of GOT, GPT, CK-MB, and LDH of ADR treated rats. These results suggest that MPG exhibited antioxidative potentials that may protect heart and liver against ADR-induced acute oxidative toxicity. This protective effect might be mediated, at least in part, by the high redox potential of sulfhydryl groups that limit the activity of free radicals generated by ADR.     

Attenuation of the acute adriamycin-induced cardiac and hepatic oxidative toxicity by N-(2-mercaptopropionyl) glycine in rats

The protective effect of the synthetic aminothiol, N-(2-mercaptopropionyl) glycine (MPG) on adriamycin (ADR) induced acute cardiac and hepatic oxidative toxicity was evaluated in rats. ADR toxicity, induced by a single intraperitoneal injection (15 mg/kg), was indicated by an elevation in the level of serum glutamic pyruvic transaminase (GPT), glutamic oxaloacetic transaminase (GOT), creatine kinase isoenzyme (CK-MB), and lactic dehydrogenase (LDH). ADR produced significant elevation in thiobarbituric acid reactive substances (TBARS), indicating lipid peroxidation, and significantly inhibited the activity of superoxide dismutase (SOD) in heart and liver tissues. In contrast, a single injection of ADR did not affect the cardiac or hepatic glutathione (GSH) content and cardiac catalase (CAT) activity but elevated hepatic CAT. Pretreatment with MPG, (2.5 mg/kg) intragastrically, significantly reduced TBARS concentration in both heart and liver and ameliorated the inhibition of cardiac and hepatic SOD activity. In addition, MPG significantly decreased the serum level of GOT, GPT, CK-MB, and LDH of ADR treated rats. These results suggest that MPG exhibited antioxidative potentials that may protect heart and liver against ADR-induced acute oxidative toxicity. This protective effect might be mediated, at least in part, by the high redox potential of sulfhydryl groups that limit the activity of free radicals generated by ADR.