Hepatoprotective phenylpropanoids from Scrophularia buergeriana roots against CCl(4)-induced toxicity: action mechanism and structure-activity relationship

Phenylpropanoids isolated from the roots of Scrophularia buergeriana MIQ. (Scrophulariaceae) protected primary cultures of rat hepatocytes from toxicity induced by carbon tetrachloride (CCl(4) ). In this report, we show that two of these phenylpropanoids, 4-O-E- p-methoxycinnamoyl-alpha-L-rhamnopyranoside ester ( 1) and p-methoxycinnamic acid ( 3) have significant hepatoprotective activity; another phenylpropanoid used for comparison, isoferulic acid ( 11), was equally active. To determine the mechanism(s) by which these three phenylpropanoids exerted their hepatoprotective activity, we measured activities of enzymes involved in the glutathione (GSH) redox system and assayed the level of hepatic mitochondrial GSH. The GSH levels in primary cultures of rat hepatocytes were significantly reduced with CCl(4) insult, but were significantly preserved by the treatment with these three phenylpropanoids. The activities of glutathione disulfide reductase and glutathione-S-transferase which normally decrease in CCl(4) -injured rat hepatocytes were significantly preserved by the treatment with these three phenylpropanoids. In addition, in CCl(4) -injured rat hepatocytes, the increased formation of malondialdehyde, a byproduct of lipid peroxidation, was reduced by the treatment with these phenylpropanoids. We determined the essential structural moiety within these three phenylpropanoids needed to exert hepatoprotective activity. The alpha,beta-unsaturated ester moiety seemed to be essential for exerting hepatoprotective activity.     

A novel cerebroside from lycii fructus preserves the hepatic glutathione redox system in primary cultures of rat hepatocytes.

We previously reported the isolation of a novel cerebroside (1-O-(beta-D-glucopyranosyl)-(2S,3R,4E,8Z)-2-N-palmityloc tadecasphinga-4,8-diene; LCC) from the fruits of Lycium chinense MILL. (Solanaceae) which protected primary cultured rat hepatocytes from the toxicity induced by carbon tetrachloride (CCl4). The present study was conducted to determine the mechanism(s) by which LCC might exert its hepatoprotective activity. To determine the effect of LCC on the glutathione (GSH) redox system, we measured the activities of enzymes involved in the system as well as the levels of hepatic mitochondrial GSH and malondialdehyde (MDA). The hepatotoxicant, CCl4, routinely decreased levels of total and reduced GSH. The levels of these compounds were significantly maintained at the levels of the control cultures following treatment with LCC. The decreased activities of glutathione reductase and glutathione peroxidase in CCl4-injured rat hepatocytes were significantly increased by the treatment of LCC. Furthermore, the elevated levels of MDA seen in CCl4-injured rat hepatocytes were reduced after treatment with LCC in a concentration dependent manner over a range of 1-10 microM. From these results, we postulate that LCC may preserve the hepatic mitochondrial level of GSH by scavenging reactive oxygen species produced during CCl4-induced toxicity and thereby reduce lipid peroxidation and cellular damage.     

Antioxidant lignans from Machilus thunbergii protect CCl4-injured primary cultures of rat hepatocytes

Eleven lignans (1-11) were isolated from the CH2Cl2 fraction of the bark of Machilus thunbergii Sieb. et Zucc. (Lauraceae). These were identified as (-)-acuminatin (1), (-)-isoguaiacin (2), meso-dihydroguaiaretic acid (3), (+)-galbacin (4), (-)-sesamin (5), (+)-galbelgin (6), machilin A (7), machilin G (8), licarin A (9), and nectandrin A (10) and B (11). Primary cultures of rat hepatocytes were co-incubated for 90 min with the hepatotoxin CCl4 and each of the 11 lignans (50 microM). Hepatoprotective activity was determined by measuring the level of glutamic pyruvic transaminase released into the medium from the primary cultures of rat hepatocytes. (-)-Acuminatin, (-)-isoguaiacin and meso-dihydroguaiaretic acid all significantly reduced the level of glutamic pyruvic transaminase released. Further investigation revealed that these three compounds significantly preserved the levels and the activities of glutathione, superoxide dismutase, glutathione peroxidase and catalase. (-)-Acuminatin, (-)-isoguaiacin and meso-dihydroguaiaretic acid also ameliorated lipid peroxidation as demonstrated by a reduction of malondialdehyde production. These results suggest that (-)-acuminatin, (-)-isoguaiacin and meso-dihydroguaiaretic acid exert diverse hepatoprotective activities, perhaps by serving as potent antioxidants.     

Protection of rat hepatocytes exposed to CCl4 in-vitro by cynandione A, a biacetophenone from Cynanchum wilfordii

To identify hepatoprotective agents from plant sources we use primary cultures of rat hepatocytes injured by CCl4. The hepatoprotective agents are the compounds that mitigate the injury caused by CCl4. Using this system we have investigated the biochemical mechanisms involved in the hepatoprotective activity of cynandione A, a biacetopherone, isolated from the roots of Cynanchum wilfordii Hemsley (Asclepiadaceae). Cynandione A (50 microM) significantly reduced (approximately 50%) the release into the culture medium of glutamic pyruvic transaminase and sorbitol dehydrogenase from the primary cultures of rat hepatocytes exposed to CCl4. Glutathione, superoxide dismutase, catalase and glutathione reductase play important roles in the cellular defence against oxidative stress. Cynandione A appeared to protect primary cultured rat hepatocytes exposed to CCl4 from significant drops in the levels of each of these four specific markers. Cynandione A also ameliorated lipid peroxidation by up to 50% as demonstrated by a reduction in the production of malondialdehyde. These results suggest that cynandione A protected the hepatocytes from CCl4-injury by maintaining the level of glutathione and by inhibiting the production of malondialdehyde, due to its radical scavenging properties.     

虎杖苷对CCl_4损伤原代培养大鼠肝细胞的保护作用

目的研究虎杖苷（ＰＤ）对ＣＣｌ４损伤原代培养大鼠肝细胞的保护作用。方法原位灌流法分离大鼠肝细胞，培养２４ｈ后加入ＰＤ，同时造成ＣＣｌ４损伤，分别于损伤后６，１２，２４和４８ｈ测培养液中谷丙转氨酶（ＡＬＴ）、丙二醛（ＭＤＡ）和还原型谷胱甘肽（ＧＳＨ）活性，４８ｈ后用ＭＴＴ比色法测肝细胞存活率。结果ＰＤ１×１０－７～１×１０－４ｍｏｌ·Ｌ－１能不同程度地抑制ＡＬＴ和ＭＤＡ的上升，提高ＧＳＨ水平，显著提高细胞存活率，以１×１０－５ｍｏｌ·Ｌ－１效果最好。结论ＰＤ１×１０－７～１×１０－４ｍｏｌ·Ｌ－１能有效保护ＣＣｌ４造成的原代培养大鼠肝细胞损伤     

Sauchinone, a lignan from Saururus chinensis, attenuates CCl4-induced toxicity in primary cultures of rat hepatocytes

We used primary cultures of rat hepatocytes injured by the hepatotoxin, carbon tetrachloride (CCl4), as a test system to screen for hepatoprotective compounds from natural products. Sauchinone was isolated from the aerial parts of Saururus chinensis (Saururaceae) by this method. At a concentration of 50 microM, sauchinone significantly reduced the release into the culture medium of glutamic pyruvic transaminase from CCl4-damaged cultures of rat hepatocytes. It has been determined that glutathione, superoxide dismutase and glutathione peroxidase all play important roles in the cellular defense against oxidative stress. Sauchinone appeared to protect primary cultured rat hepatocytes exposed to CCl4 from significant drops in the levels of each of these three specific markers, respectively. Sauchinone also seemed to ameliorate lipid peroxidation as demonstrated by a reduction in the production of the oxidized lipid byproduct, malondialdehyde. These results suggest that sauchinone may exert hepatoprotective activity through antioxidant activity.     

Efficient amelioration of carbon tetrachloride induced toxicity in isolated rat hepatocytes by Syzygium cumini Skeels extract.

Syzygiumcumini, Indian black plum or Java plum, is a rich source for anthocyanins (230mg/100g DW) showing high antioxidant activity in vitro. In the following study it is further demonstrated that S. cumini peel extract rich in anthocyanins (SCA) offers considerable protection against carbon tetrachloride (CCl(4))-induced damage in rat hepatocytes. SCA itself being non-toxic to primary rat hepatocytes at concentrations ranging from 50 to 500ppm, was found to suppress CCl(4)-induced LDH leakage by 54% at 50ppm, thereby improving the cell viability by 39%. The SCA significantly reversed the CCl(4) induced changes in cellular glutathione (GSH) level, lipid peroxidation and activity of the antioxidant enzyme glutathione peroxidase. Exposure of hepatocytes to SCA after CCl(4) treatment was found to elevate GSH and GPx activities by 2-folds, whereas the activities of catalase and superoxide dismutase were not significantly affected. The fruit pulp extract (SPE) was less effective in offering protection to rat hepatocytes, particularly in terms of total GSH content and a consequent increase in lipid peroxidation although the higher GPx activity suggests the probable involvement of GSH as a substrate for GPx. These observations suggest that the fruit peel extract of S. cumini, is largely responsible for the reversal of CCl(4)-induced oxidative damage in rat hepatocytes. Both peel and pulp extract appear to offer protection to rat hepatocytes through GPx along with other biological pathways independent of catalase and superoxide dismutase.     

Influences of glutathione status on different cytocidal responses of monolayer rat hepatocytes exposed to aflatoxin B1 or acetaminophen

In short-term primary monolayer cultures of rat hepatocytes, aflatoxin B1 (AFB1) causes a characteristic prelethal cytomorphological response in which peripheral attached cytoplasm contracts segmentally to form finger-like blebs. This response precedes lethal injury as detected by release of lactate dehydrogenase (LDH) into culture medium. We compared the influences of various modifiers of cellular glutathione (GSH) status on cytocidal responses of Fischer 344 rats hepatocytes exposed to AFB1 or acetaminophen (AAP), a hepatotoxin which does not produce segmental cytoplasmic contraction. N-Acetylcysteine (4 mM) reduced the degree of LDH release by AAP (4 to 16 mM) but was not protective against cell killing by AFB1, although it slightly reduced the percentage of hepatocytes with segmental cytoplasmic contraction at 6 hr. BCNU (1,3-bis(2-chloroethyl)-1-nitrosourea) at 40 microM markedly inhibited glutathione reductase and also strongly potentiated cell killing by AAP but did not significantly influence segmental cytoplasmic contraction or LDH release in response to AFB1. Diethylmaleate (40 to 160 microM), a depletor of hepatocellular GSH, and buthionine-D,L-sulfoximine (4 mM), an inhibitor of GSH synthesis, each did not alter hepatocyte killing by AFB1 but were strong potentiators of toxicity of AAP. AAP inhibited glutathione reductase but AFB1 did not. Total GSH concentrations at 6 and 18 hr were reduced by AAP and to a lesser extent by AFB1 in comparison with control cultures. These findings demonstrate that, in contrast to AAP toxicity, the characteristic mode of hepatocyte killing by AFB1 in monolayer cultures is substantially independent of induced alterations in GSH. These results indicate that GSH-dependent detoxification mechanisms do not play a major role in removing necrogenic metabolites of AFB1 in Fischer 344 rat hepatocytes. They further suggest that prelethal responses of AFB1-injured hepatocytes are not affected by GSH-dependent cytoprotective mechanisms.     

Neuroprotective dibenzylbutyrolactone lignans of Torreya nucifera

The methanolic extract of the bark of Torreya nucifera Sieb. et Zucc. (Taxaceae) significantly protected primary cultures of rat cortical cells exposed to the excitotoxic amino acid, L-glutamate. (-)-Arctigenin (1), (-)-traxillagenin (2), arctiin (4), traxillaside (5), and a newly-reported compound 3 (-)-4'-demethyltraxillagenin [(2R,3R)-2-(4'-hydroxy-3'-methoxybenzyl)-3-(4'-hydroxy-3',5'-dimethoxybenzyl)-butyrolactone] were isolated by bioactivity-guided fractionation and further separation using chromatographic techniques. These lignans and their glycosides had significant neuroprotective activities against glutamate-induced toxicity in primary cultures of rat cortical cells at concentrations ranging from 0.01 microM to 10.0 microM.     

Studies on the mechanism of coumarin-induced toxicity in rat hepatocytes: comparison with dihydrocoumarin and other coumarin metabolites

Single doses of coumarin (125 mg/kg, ip) produced a depletion of hepatic nonprotein sulfhydryl groups (mainly reduced glutathione; GSH) in young male Sprague-Dawley rats after 2 hr and increased liver weight and produced hepatic centrilobular necrosis after 24 hr. Coumarin also produced time- and dose-dependent toxic effects in primary rat hepatocyte cultures. A marked reduction of GSH levels was also observed in vitro and this was not due either to the formation of oxidized glutathione (GSSG) or to the leakage of GSH and/or GSSG from the hepatocytes. Coumarin-induced toxicity in rat hepatocytes could be inhibited by the cytochrome P450 inhibitors ellipticine and metyrapone and potentiated by depleting hepatocyte GSH levels with diethyl maleate. In contrast to coumarin, dihydrocoumarin--which lacks the 3,4-double bond--produced little toxicity in rat hepatocytes either in vivo (127 and 254 mg/kg, ip) or in vitro. Similarly, coumarin was more toxic to rat hepatocytes than a number of known coumarin metabolites including 3- and 7-hydroxycoumarin and o-hydroxyphenylacetic acid. The results of these studies demonstrate a good in vivo/in vitro correlation for the effects of coumarin and dihydrocoumarin in rat hepatocytes. Furthermore, the data suggest that coumarin hepatoxicity in the rat is due to coumarin bioactivation by cytochrome P450-dependent enzymes to a toxic metabolite(s), which may be a coumarin 3,4-epoxide intermediate. GSH appears to protect against coumarin-induced toxicity possibly by the formation of conjugates with the toxic coumarin metabolite(s).     

Antiviral,Cyototoxic And Antimicrobial Activities Of Anthraquinones Isolated From The Roots Of Morinda Elliptica

Two enantiomers of schisandrin B (Sch B), an active ingredient isolated from the fruit of Schisandra chinensis, were chirally separated. Pretreating mice with (+)Sch B or (-)Sch B at a daily oral dose of 1 mmol/kg for 3 days protected against carbon tetrachloride (CCl 4) hepatotoxicity, as evidenced by highly significant decreases in plasma alanine aminotransferases activity and hepatic malondialdehyde level. The hepatoprotection afforded by pretreatment with the enantiomers was associated with increases in hepatic glutathione S-transferases and glutathione reductase (GRD) activities as well as mitochondrial reduced glutathione (GSH) level. However, only the (+)Sch B pretreated animals showed a reduction in the extent of CCl 4 -induced inhibition of hepatic Se-glutathione peroxidase activity. In addition, (+)Sch B pretreatment produced a more potent stimulatory effect on hepatic GRD activity and mitochondrial GSH level in CCl 4 -treated mice. The differential ability between (+)Sch B and (-)Sch B in enhancing hepatic glutathione antioxidant system in CCl 4 -intoxicated mice may implicate the presence of a chiral-/stereo-specific intracellular target for mediating the antioxidant action of Sch B.     

Evaluation of the effect of culture configuration on morphology, survival time, antioxidant status and metabolic capacities of cultured rat hepatocytes.

We evaluated the antioxidant status, namely cellular lipid peroxidation, by measuring thiobarbituric acid reactive substances (TBARS), cellular reduced glutathione (GSH) content, glutathione reductase (GSSG-R), glutathione transferase (GST), glutathione peroxidase (GSH-Px) and catalase activities in rat liver, hepatocytes immediately after isolation and in two-dimensional (2D) culture (on non-coated or collagen-coated dishes, as collagen-collagen or collagen-Matrigel sandwich cultures) or three-dimensional (3D) culture on Matrigel-coated dishes. Microsomal cytochrome P450 (CYP)- and UDP-glucuronosyl transferase (UGT)- dependent activities were also assessed in rat livers and hepatocyte cultures. The overall antioxidant status of rat hepatocytes immediately after isolation was not significantly different from that of rat livers. During culture, GSH was increased in 2D but not in 3D cultures in accordance with morphological observations; that is that matrix-cell interactions involving GSH, important in 2D, are minimal in 3D cultures. While UGT- and GST-dependent activities were equivalent in cultured hepatocytes and in rat livers, both catalase and GSH-Px activities decreased with time in all culture configurations. Constitutive CYP-dependent activities were drastically decreased in hepatocytes after isolation and attachment and did not recover in any culture configuration tested. Our results highlight that, although 2D sandwich cultures and 3D cultures on Matrigel allow longevity of rat hepatocyte cultures and optimal induction of CYPs, an imbalance in phase I/phase II detoxication processes in cultured rat hepatocytes occurs, whatever the culture configuration.     

Protective effect of (S)-bakuchiol from Psoralea corylifolia on rat liver injury in vitro and in vivo

The aim of this study was to investigate the protective effect of (S)-bakuchiol isolated from the seed of Psoralea corylifolia, on liver injury. Primary rat hepatocyte intoxication was induced by tert-butyl hydroperoxide (tBH), carbon tetrachloride (CCl4) or D-galactosamine (D-GalN). Liver injury was induced by either CCl4 or D-GalN in rats. In vitro, the cellular leakage of lactate dehydrogenase and cell viability following treatment with hepatotoxicants were significantly improved by bakuchiol treatment at a concentration range of 25-200 microM for tBH, 100-200 microM for CCl4 and 100-200 microM for D-GalN-induced hepatocyte injury. Treatment with bakuchiol significantly inhibited lipid peroxidation and intracellular glutathione depletion in hepatocytes induced by tBH, CCl4 or D-GalN. Treatment with bakuchiol (25 or 50 mg/kg, p.o.) at 1, 24 and 48 h after subcutaneous injection of CCl4 significantly reduced the levels of aspartate transaminase and alanine transaminase in serum. Histological observations revealed that fatty acid changes, hepatocyte necrosis and inflammatory cell infiltration in CCl4-injured liver was improved when treated with bakuchiol. Bakuchiol treatment (25 and 50 mg/kg, p.o.) also significantly reduced the levels of aspartate transaminase and alanine transaminase in an acute liver injury model induced by D-GalN. From these results, bakuchiol has a protective effect against tBH, CCl4 or D-GalN-induced hepatotoxicity in vitro or in vivo.     

Toxic interactions between carbon tetrachloride and chloroform in cultured rat hepatocytes

Primary cultures of adult rat hepatocytes were incubated (1.5-16 hr) with various concentrations of CCl4 (less than or equal to 0.5 mM) and/or CHCl3 (less than or equal to 2.5 mM). Agent-dependent alterations in hepatocyte functions were assessed by measuring (1) [3H]choline incorporation into phosphatidylcholine (endoplasmic reticulum), (2) MTT (tetrazolium salt) reduction (mitochondria), and (3) AST release into medium (plasma membrane). Cultured hepatocytes incubated with 0.5 mM CCl4 displayed a significant (p less than or equal to 0.001) and rapid (1.5 hr) reduction (40%) in endoplasmic reticulum function that preceded significant (p less than or equal to 0.001) alterations in mitochondria (6-16 hr) and plasma membrane (6-16 hr) functions. CCl4-dependent alterations in liver cell functions are a result of CCl4 bioactivation since metyrapone inhibits the CCl4-mediated changes in cell functions. Response surface methods (RSM) were used to determine the influence of combinations of CCl4 and CHCl3 on liver cell MTT reduction and [3H]choline incorporation. Regression coefficients were determined for CCl4, CHCl3, and CCl4-CHCl3. All results were significant (p less than 0.0001) and implied that CCl4 was a more potent hepatotoxin in vitro than CHCl3. The RSM analysis also suggested that combinations of CHCl3 and CCl4 have greater than additive effects on MTT reduction and [3H]choline incorporation. These effects of CCl4 and/or CHCl3 on liver cell functions in vitro are consistent with liver alterations observed in vivo. Therefore, primary cultures of adult rat hepatocytes may be an appropriate model in vitro to assess the hepatotoxic potential of agents alone or in combination.     

Oxidative stress potentiated by diallylsulfide, a selective CYP2E1 inhibitor, in isoniazid toxic effect on rat primary hepatocytes

Isoniazid (INH), one of the first-line antituberculosis drugs, has potential liver toxicity. Mechanisms reported by previous studies mainly focused on oxidative stress. In the present study, we investigated acute effects of diallylsulfide (DAS), a selective CYP2E1 inhibitor, on reduced glutathione (GSH) and reactive oxygen species (ROS) levels in rat primary hepatocytes treated with INH. In cultures treated with INH for 1, 4, 8h, significant loss of GSH content and decrease of ROS levels were observed. Moreover, when hepatocytes were co-treated with INH and 1mM DAS, accelerated GSH depletion and increased ROS production appeared. Further more, rat primary hepatocytes survival rates decreased significantly in cultures treated with INH together with DAS than in cultures treated with INH alone after 24h. In conclusion, DAS could potentiate INH toxic effect and this is the first study reporting the effect of DAS on oxidative stress in INH-induced hepatocytotoxicity.     

一些保肝药物对原代培养大鼠肝细胞糖原合成功能的影响

本文参照PO Seglen的方法并加以修改,建立了原代培养大鼠肝细胞糖原合成功能的测定体系。观察到联苯双酯既能使正常肝细胞合成糖原增加88%,又能保护肝细胞完全拮抗四氯化碳对其功能的损伤;银耳多糖能使四氯化碳对肝细胞糖原合成功能的损伤减轻57%;去甲斑蝥素10μg/ml能增加肝细胞糖原合成,浓度增加到100μg/ml时,此作用减弱,1000μg/ml则明显抑制糖原的合成,而且在10～100μg/ml浓度时,即能加强四氯化碳的损伤作用;100μg/ml CL₁₅₀₀和熊果酸二钠单独应用可增加肝细胞糖原合成,但与四氯化碳同时应用,反而加重对糖原合成的抑制作用。     

龙眼参多糖对四氯化碳诱导大鼠原代肝细胞损伤的保护作用

目的:研究龙眼参多糖(LYS)对大鼠原代肝细胞损伤的保护作用及其机制。方法:用四氯化碳(CCl4)体外诱导大鼠原代肝细胞损伤,检测培养上清液中天门冬氨酸转移酶(AST)和丙氨酸氨基转移酶(ALT)水平,测定肝细胞中丙二醛(MDA)和谷胱甘肽(GSH)含量,四甲基偶氮唑盐(MTT)法检测细胞活性。结果:与模型组比较,LYS组AST和ALT水平及肝细胞MDA含量明显降低,肝细胞存活率和GSH含量升高。结论:LYS对大鼠原代培养肝细胞损伤有直接保护作用,机制可能与其抗氧化作用有关。     

Metabolic activation of a pentafluorophenylethylamine derivative: formation of glutathione conjugates in vitro in the rat

The aim was to investigate the metabolic activation potential of a pentafluorophenylethylamine derivative (compound I) in vitro in the rat and to identify the cytochrome P450 (CYP) enzymes that catalyse these metabolic activation processes. Reduced glutathione (GSH) was fortified in rat hepatocytes and liver microsomes to trap possible reactive intermediates. Four glutathione conjugates (M1-4) were identified by LC-MS(n) following incubation of compound I in GSH-enriched rat hepatocytes and liver microsomes. Three of these conjugates (M2-4) have not been reported previously for pentafluorophenyl derivatives. Elemental composition analysis of these conjugates was obtained using high-resolution quadrupole time-of-flight mass spectrometry. The formation of GSH conjugate M1 was rationalized as a direct nucleophilic replacement of fluoride by glutathione, whereas the formation of the GSH conjugates M2-4 was proposed to occur by NADPH-dependent metabolic activation of the pentafluorophenyl ring via arene oxide, quinone and/or quinoneimine reactive intermediates. Formation of these conjugates was enhanced three- to five-fold in liver microsomes obtained from phenobarbital- and dexamethasone-treated rats. In incubations with pooled rat liver microsomes and recombinant rat CYP3A1 and CYP3A2, troleandomycin (TAO) reduced the formation of GSH conjugates M2-4 by 80-90%, but it had no effect on the formation of M1. Incubation of compound I with rat supersomes indicated that only CYP3A1 and CYP3A2 were capable of mediating these metabolic activation processes.     

Enalapril cytotoxicity in primary cultures of rat hepatocytes. II. Role of glutathione

The cytotoxicity of enalapril maleate (EN) in primary cultures of rat hepatocytes, at concentrations of 0.5 mM or greater, was measured by the release of lactate dehydrogenase (LDH) into the culture medium. Pretreatment of the hepatocytes with L-buthionine-(S,R)-sulfoximine (BSO) and diethyl maleate (DEM) potentiated the toxicity whereas N-acetyl-L-cysteine (NAC) provided protection. EN produced a dose-dependent reduction in intracellular glutathione (GSH) concentration. This was an early effect, apparent after only 1 h of exposure to the drug, whereas loss of cell viability occurred after 6-18 h. These results suggest that the mechanism of EN cytotoxicity involves a GSH-dependent detoxification pathway.     

Protective effect of S-adenosyl-L-methionine against CCl4-induced hepatotoxicity in cultured hepatocytes

Effect of S-adenosyl-L-methionine disulfate tosylate salt (SAMe-ST) and L-methionine (L-Met) on primary cultured rat hepatocytes were studied. In cultured hepatocytes treated with CCl4, SAMe-ST and L-Met suppressed the decrease in urea-nitrogen secretion as well as the leakages of GOT and GPT. The membrane-protective action of these two compounds was verified by the histological data. Failure of SAMe-ST to counteract CCl4-induced reduction of radioactive leucine incorporation into the trichloroacetic acid-insoluble materials in hepatocytes indicates that the observed effects of SAMe-ST or L-Met do not involve acceleration of protein synthesis. The present results indicate that SAMe-ST remarkably protects hepatocytes from CCl4-induced hepatotoxicity, probably by either changing the structure or compositions of membrane phospholipids or by modifying the interaction of CCl4 with the intracellular drug-metabolizing enzyme systems.