Acetaminophen hepatotoxicity: studies on the mechanism of cysteamine protection

Inhibition of the cytochrome P-450-dependent formation of the acetaminophen-reactive metabolite was investigated as a possible mechanism for cysteamine protection against acetaminophen hepatotoxicity. Studies in isolated hamster hepatocytes indicated that cysteamine competitively inhibited the cytochrome P-450 enzyme system as represented by formation of the acetaminophen-glutathione conjugate. However, cysteamine was not a potent inhibitor of glutathione conjugate formation (Ki = 1.17 mM). Cysteamine also weakly inhibited the glucuronidation of acetaminophen (Ki = 2.44 mM). In vivo studies were in agreement with the results obtained in isolated hepatocytes; cysteamine moderately inhibited both glucuronidation and the cytochrome P-450-dependent formation of acetaminophen mercapturate. The overall elimination rate constant (beta) for acetaminophen was correspondingly decreased. Since cysteamine decreased both beta and the apparent rate constant for mercapturate formation (K'MA), the proportion of the dose of acetaminophen which is converted to the toxic metabolite (K'MA/beta) was not significantly decreased in the presence of cysteamine. Apparently, cysteamine does inhibit the cytochrome P-450-dependent formation of the acetaminophen-reactive metabolite, but this effect is not sufficient to explain antidotal protection.     

Potentiation of hepatotoxicity by ethanol in galactosamine-induced hepatitis in rats: role of propylthiouracil protection

Chronic ingestion of ethanol (5 g/kg/day) for 6 weeks increased the hepatotoxicity of a single injection of D-galactosamine (330 mg/kg) in rats. Plasma transaminases, alkaline phosphatase, gamma glutamyl transpeptidase and sulphobromophthalein retention were consistently high in alcohol-fed rats compared to sucrose-fed controls, 25 hours after galactosamine administration. Liver histology in sucrose-fed rats revealed typical inflammatory changes and cytoplasmic vacuolation without cell necrosis was seen. Propylthiouracil treatment had no beneficial or protective effect in alcohol-fed rats in this animal model of hepatitis.     

Amnesia induced by short-term treatment with ethanol: attenuation by pretest oxotremorine

CD-1 mice were administered a series of tones paired with footshock in the closed arm of a Y maze. On a test session 8 days later the animals were tested for retention of the conditioned emotional response (CER). On the 2-min test session, the three arms of the maze were open and the number of entries into the arms was counted. Retention of the CER was measured by the decrease in the number of entries in comparison with animals trained with no footshock. Starting 24 hr after training, and continuing for the 7 days between training and testing, the animals in different groups received a daily IP injection of saline, 3.6 g/kg of ethanol, 150 micrograms/kg of the cholinergic muscarinic agonist oxotremorine, or ethanol plus oxotremorine. Retention was evaluated 24 hr after the last injection. Ethanol reduced retention of the conditioned emotional response. This effect was attenuated by oxotremorine (150 micrograms/kg) given IP 6 min prior to testing, but not by the same dose of oxotremorine given daily together with the ethanol treatment. Oxotremorine injections administered prior to the retention test also enhanced the retention performance of the control group. Daily oxotremorine administration had no effect. These findings suggest that ethanol weakened retention of the conditioned emotional response, that this effect was unrelated to acquisition or consolidation, and that the deleterious effect of the ethanol treatment can be attenuated by oxotremorine administered prior to the retention test.     

Selenite-induced protection of bromobenzene hepatotoxicity in male rats

Acute treatment with sodium selenite effectively reduces bromobenzene hepatotoxicity in male, Sprague-Dawley rats. Hepatocellular damage was ameliorated as shown by marked decreases in plasma alanine and aspartate aminotransferase (ALT and AST) activities. A single dose of selenite (12.5 or 30 μmol Se/kg, ip) was administered to rats at 4, 24, 48, or 72 hr before injection of bromobenzene (7.5 mmol/kg, ip). Plasma ALT and AST activities and hepatic glutathione (GSH) content were measured 24 hr after bromobenzene treatment. As the length of time of selenite pretreatment increased, the extent of reduction of bromobenzene-induced elevation in plasma enzyme activities by selenite was enhanced, and generally, in a dose-related manner with optimal protection occurring in rats pretreated 72 hr prior with selenite. However, depletion of liver GSH by bromobenzene was not affected by selenite treatment. Hepatic GSH levels and GSH detoxication enzyme activities were measured at various intervals in rats treated with selenite alone. Selenite increased hepatic GSH content 20 to 25% at both 24 and 48 hr after injection, with a return to GSH control levels at 72 hr. Selenite treatment produced slight decreases in GSH peroxidase activity but did not alter GSH S-transferase activity. These studies suggest that the reduction of bromobenzene hepatotoxicity by selenite does not involve alterations in the activity of hepatic GSH detoxication enzymes; however, the data suggest that factors in addition to selenite-induced changes in hepatic glutathione levels are also involved.     

Effects of ethanol consumption on bioactivation and hepatotoxicity of N-nitrosodimethylamine in rats

To study the effects of ethanol on the hepatotoxicity of N-nitrosodimethylamine (NDMA), 5 mg NDMA/kg body weight was injected intraperitoneally 3 times a week for 6 weeks into rats pair-fed liquid diets containing 36% of energy either as ethanol or as additional carbohydrates. Another group of rats was pair-fed with the same diets but injected with saline instead of NDMA. Co-administration of ethanol and NDMA produced much higher elevations of serum alanine and aspartate aminotransferase and glutamic dehydrogenase activities than the administration of either agent alone. The combined treatment also slightly increased focal necrosis, whereas other liver lesions (steatosis and fibrosis) and the functional impairment of mitochondrial respiration were not affected significantly. Microsomal low Km NDMA demethylation, as well as NDMA denitrosation, were inhibited markedly by incubation with an antibody against P450IIE1, suggesting the involvement of this alcohol-inducible P450 in both NDMA bioactivation reactions. The addition of ethanol inhibited P450-dependent demethylation and denitrosation of NDMA in liver microsomes, whereas both activities were enhanced markedly by chronic ethanol administration. At ethanol concentrations similar to those prevailing in the blood of alcohol-fed animals at the time of NDMA administration, hepatic microsomal demethylation and denitrosation remained significantly higher in ethanol-fed rats given NDMA than in controls. Our results suggest that bioactivation plays a critical role in the hepatotoxicity of NDMA and its aggravation by chronic alcohol consumption.     

Potentiation of aflatoxin B1 induced hepatotoxicity in male Wistar rats with ethanol pretreatment

The interaction of ethanol and aflatoxin B1 (AFB1)-induced hepatotoxicity was studied in male Wistar rats using the activity of plasma GOT and GPT, liver triglyceride and histopathologic changes of liver necrosis as indices. Pretreatment of four oral doses of ethanol (4.0 g/kg BW each) at 48, 45, 24 and 21 hrs prior to AFB1 (0.5 to 2.0 mg/kg BW) single i.p. administration caused a significant increase in the activity of PGOT (6 folds) and PGPT (5 folds), liver triglycerides (2 folds) and severity of liver necrosis at 48 hrs after AFB1 administration. Ethanol pretreatment potentiated AFB1-induced hepatotoxicity by increasing MFO enzymes, aniline hydroxylase and p-nitroanisole-O-demethylase activity and lipid peroxidation, and decreasing in cytochrome b5, epoxide hydrolase activity and hepatic glutathione content. However, it did not cause any significant change in the activity of NADPH-cytochrome c reductase and glutathione-S-transferase and cytochrome P-450. These results suggest that potentiation of ethanol pretreatment on AFB1-induced hepatotoxicity may be due to an increase in the metabolic formation of AFB1-2, 3-oxide and subsequent binding to DNA.     

Metabolism of ethanol and associated hepatotoxicity

Over the last three decades, direct hepatotoxic effects of ethanol were established, some of which were linked to redox changes produced by NADH generated via the alcohol dehydrogenase (ADH) pathway and shown to affect the metabolism of lipids, carbohydrates, proteins, and purines. It was also determined that ethanol can be oxidized by a microsomal ethanol oxidizing system (MEOS) involving a specific cytochrome P-450; this newly discovered ethanol-inducible cytochrome P-450 (P-450 IIEi) contributes to ethanol metabolism, tolerance, energy wastage (with associated weight loss), and the selective hepatic perivenular toxicity of various xenobiotics. Their activation by P-450IIEi now provides an understanding of the increased susceptibility of the heavy drinker to the toxicity of industrial solvents, anaesthetic agents, commonly prescribed drugs, over-the-counter analgesics, and chemical carcinogens. P-450 induction also explains depletion (and toxicity) of nutritional factors such as vitamin A. As a consequence, treatment with vitamin A and other nutritional factors is beneficial, but must take into account a narrowed therapeutic window in alcoholics who have increased needs for nutrients and also display an enhanced susceptibility to some of their adverse effects. Acetaldehyde (the metabolite produced from ethanol by either ADH or MEOS) impairs hepatic oxygen utilization and forms protein adducts, resulting in antibody production, enzyme inactivation, and decreased DNA repair. It also stimulates collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts, and causes glutathione depletion. Supplementation with S-adenosyl-L-methionine partly corrects the depletion and associated mitochondrial injury, whereas administration of polyunsaturated lecithin opposes the fibrosis. Thus, at the cellular level, the classic dichotomy between the nutritional and toxic effects of ethanol has now been bridged. The understanding of how the ensuing injury eventually results in irreversible scarring or cirrhosis may provide us with improved modalities for treatment and prevention.     

Enhanced hepatotoxicity of carbon tetrachloride, thioacetamide, and dimethylnitrosamine by pretreatment of rats with ethanol and some comparisons with potentiation by isopropanol.

Elevated plasma glutamic-pyruvic transaminase (GPT) activity induced by carbon tetrachloride (CCl₄), thioacetamide, or dimethylnitrosamine in male rats was increased by pretreatment with four doses (each 5 ml/kg) of ethanol orally 48, 42, 24, and 18 hr before the hepatotoxic agent. The potentiated hepatotoxicity of CCl₄ was confirmed by histologic evaluation. During the pretreatment, blood ethanol concentrations fluctuated between 0 and 300 mg/100 ml, but were less than 5 mg/100 ml when a hepatotoxic agent was injected ip. Pretreatment with ethanol did not affect the hepatic concentrations of CCl₄ or its metabolite, chloroform (CHCl₃), at 1 hr after administration of CCl₄. The CCl₄-induced diene conjugation tended to increase after ethanol pretreatment and was significantly potentiated by pretreatment with isopropanol or pyrazole and a single dose of ethanol. In rats pretreated with ethanol, covalent binding of ¹⁴CCl₄ to liver protein and lipid in vivo was significantly greater at 6 and 24 hr, but not during the first 3 hr, than in control rats. The in vitro binding of ¹⁴CCl₄, ¹⁴CHCl₃, and ¹⁴CBrCl₃ to hepatic microsomal protein was increased by ethanol pretreatment. Ethanol pretreatment also doubled the in vitro rate of demethylation of dimethyl-nitrosamine by liver microsomes, but did not affect the amount of microsomal protein and cytochrome P-450, NADPH c reductase activity nor the rate of N-demethylation of ethylmorphine. The similarities in microsomal effects of pretreatment with isopropanol and pretreatment with four doses of ethanol suggest that similar mechanisms are involved in their potentiation of CCl₄-induced hepatotoxicity. The potentiation by pretreatment with ethanol, but not with isopropanol, of the hepatotoxicity of thioacetamide and dimethylnitrosamine suggests that ethanol pretreatment also activates some additional mechanisms.     

Potentiation of cocaine hepatotoxicity by ethanol in human hepatocytes

The hepatotoxic effects of cocaine on the human liver and the effect of ethanol on cocaine-induced hepatotoxicity have been examined in adult human hepatocytes cultured in chemically defined conditions. Cultures were exposed to concentrations of cocaine ranging from 10(-2) to 10(-5) M. Cytotoxicity was evaluated after 24 hr of continuous exposure to cocaine by measuring the leakage of intracellular LDH and the ability of cells to reduce MTT. According to these end-point parameters, half-maximal cytotoxic concentrations of cocaine for human hepatocytes (IC50) were 6.8 and 7.8 mM, respectively. Lower concentrations of cocaine, however, impaired basic metabolic functions of human hepatocytes. Exposure of cells to 2 mM cocaine for 24 hr resulted in a 50% decrease in hepatic glycogen, a 40% decrease in cellular glutathione content, and a 40% decrease in urea synthesis with respect to control values. For most of the metabolic parameters assayed, significant alterations were observed at 0.5 mM cocaine. Glycogen reloading of hepatocytes began to be inhibited in the presence of 0.60 mM cocaine (IC10). Ethanol greatly potentiated cocaine-induced hepatotoxicity. After a 48 hr pretreatment of human hepatocytes with 50 mM ethanol, low concentration of cocaine (0.25 mM) that had no effects on hepatocyte metabolism in the absence of ethanol caused a 20% inhibition of the urea synthesis rate, a 40% degradation of glycogen stores, and a 30% reduction in glutathione content. The results of our work show that ethanol increases the effects of cocaine on human hepatocytes by a factor of 10.     

Mechanism of protection by metallothionein against acetaminophen hepatotoxicity

Acetaminophen (APAP) overdose is the most frequent cause of drug-induced liver failure in the US. Metallothionein (MT) expression attenuates APAP-induced liver injury. However, the mechanism of this protection remains incompletely understood. To address this issue, C57BL/6 mice were treated with 100 μmol/kg ZnCl₂ for 3 days to induce MT. Twenty-four hours after the last dose of zinc, the animals received 300 mg/kg APAP. Liver injury (plasma ALT activities, area of necrosis), DNA fragmentation, peroxynitrite formation (nitrotyrosine staining), MT expression, hepatic glutathione (GSH), and glutathione disulfide (GSSG) levels were determined after 6 h. APAP alone caused severe liver injury with oxidant stress (increased GSSG levels), peroxynitrite formation, and DNA fragmentation, all of which were attenuated by zinc-induced MT expression. In contrast, MT knockout mice were not protected by zinc. Hydrogen peroxide-induced cell injury in primary hepatocytes was dependent only on the intracellular GSH levels but not on MT expression. Thus, the protective effect of MT in vivo was not due to the direct scavenging of reactive oxygen species. Zinc treatment had no effect on the early GSH depletion kinetics after APAP administration, which is an indicator of the metabolic activation of APAP to its reactive metabolite N-acetyl-p-benzoquinone imine (NAPQI). However, MT was able to effectively trap NAPQI by covalent binding. We conclude that MT scavenges some of the excess NAPQI after GSH depletion and prevents covalent binding to cellular proteins, which is the trigger for the propagation of the cell injury mechanisms through mitochondrial dysfunction and nuclear DNA damage.     

Effect of ethanol on hepatotoxicity and hepatic DNA-binding of aflatoxin B1 in rats

The hepatocarcinogen aflatoxin B1 is converted to reactive metabolites that bind covalently to cellular macromolecules. These metabolites may also react with glutathione, resulting in the formation of glutathione conjugates and detoxication of the reactive metabolite. When rats were pretreated with ethanol by gastric intubation at a dose of 100 mmol/kg, 6 hr (the time of maximal GSH depletion) before the administration of aflatoxin B1, the covalent binding of 8,9-epoxide-aflatoxin B1 to DNA in vivo was increased by 47% and the hepatotoxicity was also potentiated. However, the covalent binding was not increased by pretreatment with ethanol 18 hr (time with approximately normal GSH levels) before administration of the toxin, and no potentiation of hepatotoxicity was observed. Pretreatment with a non-toxic dose of ethanol had no effects on the activity of glutathione S-transferase and glutathione peroxidase. These results suggest that the depletion of GSH and the increased formation of DNA-adduct from the liver constitute an important mechanism for the potentiation of aflatoxin B1-induced hepatotoxicity by ethanol.     

Hepatoprotective effect of Stachys pilifera ethanol extract in carbon tetrachloride-induce hepatotoxicity in rats

Context: Stachys pilifera Benth (Lamiaceae) has long been used to treat infectious diseases, respiratory and rheumatoid disorders in Iranian folk medicine. Antitumor and antioxidant activity of the plant have been reported.

Objective: The study was designed to assess the hepatoprotective activity of ethanol extract of Stachys pilifera in carbon tetrachloride (CCl₄)-induced hepatotoxicity in rats.

Materials and methods: The rats were randomly divided into six equal groups (n?=?7). Group I was treated with normal saline; Group II received CCl₄ (1?mL/kg. i.p., twice a week) for 60 consecutive days; Groups III, IV and V were given CCl₄ plus Stachys pilifera (100, 200 and 400?mg/kg/d,p.o.); Group VI received the extract (400?mg/kg/d, p.o.). Histopathological analysis and measurement of serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), malondialdehyde (MDA), total protein (TP) and albumin (ALB) were performed.

Results: CCl₄ caused a significant increase in the serum levels of AST, ALT, ALP and MDA as well as decreased ALB, and TP serum levels (p?4-elevated levels of ALT, AST, ALP and MDA (p?4 group (p4.

Discussion: The results revealed that the Stachys pilifera extract could provide considerable protection against CCl₄ hepatotoxicity in rats that may be related to its antioxidant properties.     

Exacerbation of acetaminophen hepatotoxicity by thalidomide and protection by nicotinic acid amide

• 1.1. The effects of racemic thalidomide (d[ + ]/l[ - ] α-phthalimido-glutarimide) on acetaminophen (AAP)-induced hepatitis were tested in male NMRI mice (n = 133) and quantified as serum activities of glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT).
• 2.2. A 2.1-fold increase of GOT and a 1.9-fold increase of GPT activities (P < 0.001) were observed in mice treated perorally with 500 mg/kg of AAP plus 150 mg/kg of thalidomide (Tha1). In the absence of AAP, Thal did not display any detectable hepatotoxic effects.
• 3.3. The Thal-induced exacerbation of AAP hepatotoxicity was completely inhibited by nicotinic acid amide, a selective inhibitor of poly(ADP-ribose) polymerase (PARP) (P < 0.0001), suggesting a possible influence of Thal on the hepatic metabolism of NAD-adenoribosylation.
• 4.4. We see the main application of nicotinic acid amide as for the combinational use in pharmaceutical preparations of AAP in order to avoid hepatic damage in patients treated with AAP and Thal.

     

Assessment of the hepatotoxicity of acute and short-term exposure to inhaled p-xylene in F-344 rats

Due to the ubiquitous presence of p-xylene in air and the existing uncertainty regarding its hepatotoxic potential, we examined the effect of acute and short-term exposure to inhaled p-xylene on the liver. Male F-344 rats were exposed to 0 or to 1600 ppm p-xylene, 6 h/d, for 1 or 3 d. Exposure to inhaled p-xylene caused no histopathological evidence of hepatic damage and had little or no effect on the serum levels of aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, ornithine carbamyl transferase, alkaline phosphatase, and total bilirubin. Exposure to p-xylene for 1 or 3 d resulted in an increase in relative liver weight on d 1 post-exposure. The concentration of hepatic cytochrome P-450 was increased by both p-xylene exposure regimens on d 1 postexposure and had returned to control levels by d 3 following the single p-xylene exposure and by d 2 following the 3-d exposure. These observations provide consistent evidence that acute and short-term exposure to 1600 ppm p-xylene by inhalation did not produce overt hepatotoxicity but resulted in a significant increase in the concentration of hepatic cytochrome P-450, the principal enzyme system involved in the metabolic biotransformation of xenobiotics.     

Protection against acetaminophen-induced hepatotoxicity by prior treatment with fenitrothion

This study was undertaken to determine if interactions of toxicologic importance might occur during simultaneous exposure of mice to acetaminophen and fenitrothion. Acetaminophen administration induced dose-dependent hepatic morphologic changes which were accompanied by leakage of sorbitol dehydrogenase (SDH) into plasma 18 hr after dosing. Glutathione (GSH) depletion was maximal 2 hr after acetaminophen even at doses below those required for hepatic necrosis. Pretreatments with fenitrothion (50 or 500 mg/kg, ip) decreased hepatic GSH concentration and inhibited microsomal aniline hydroxylase and paranitroanisole O-demethylase activities. Similar treatments in mice subsequently challenged with acetaminophen (400 or 600 mg/kg, po) prevented the elevations in plasma SDH activity and lethality. Massive necrosis and 70% lethality were observed after 800 mg acetaminophen/kg and these effects were prevented by earlier pretreatment with 50 mg fenitrothion/kg. This pretreatment also decreased the degree of hepatic GSH depletion detected at 2 hr after 800 mg of acetaminophen. This finding would suggest that production of acetaminophen electrophile had been deceased by the pretreatment. Thus, with respect to interaction with acetaminophen, these results suggest that fenitrothion inhibition of mixed function oxidases predominated over fenitrothion depletion of GSH. Thus, even though GSH stores were lowered, less acetaminophen electrophile was generated and critical macromolecules were spared.     

Multi-targeted protection of acetaminophen-induced hepatotoxicity in mice by tannic acid

Tannic acid (TA) is the polyphenol that has beneficial health effects against oxidative stress. However, the hepatoprotective effects of TA are still relatively unknown. In the present study, we evaluated the effects of TA on an acetaminophen (APAP)-induced hepatotoxicity model, which was established by administration of 400 mg/kg of APAP. The levels of alanine transferase (ALT), aspartate transferase (AST), dendothelin-1 (ET-1), nitric oxide (NO) and malondialdehyde (MDA) in the APAP-induced hepatotoxicity mice were significantly increased (up to ~ 200%), while their levels were reduced by pretreatment with TA (25 and 50 mg/kg) (P < 0.05). The activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) in the APAP-induced hepatotoxicity mice were significantly reduced (lower to ~ 65%), while their activities were increased by pretreatment with TA (25 and 50 mg/kg) (P < 0.05). In addition, pretreatment with oral TA (25 and 50 mg/kg) for 3 days before the APAP administration dose-dependently ameliorated changes in hepatic histopathology, suppressed overexpression of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), c-fos, c-jun, NF-κB (p65) and caspase-3 (all P < 0.05), downregulated bax and upregulated bcl-2, nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) (all P < 0.05) in the liver. These results indicate that TA exhibits significant hepatoprotective effects against APAP-induced hepatotoxicity and suggest that the hepatoprotective mechanisms of TA may be related to anti-oxidation, anti-inflammation and anti-apoptosis.     

Suppression by ketamine and dextromethorphan of precipitated abstinence syndrome in rats

The development of physical dependence on opiates appears to involve an inhibition by opiates of L-asparaginase and glutaminase, and the blockade by opiates of aspartatergic (ASPergic)/glutamatergic (GLUergic) receptors. Ketamine (K) (0.5 or 1 mg/kg) or dextromethorphan (DM) (1 or 2 mg/kg), both of which are known to decrease the responsiveness of ASPergic/GLUergic receptors, were administered to the three morphine (M)-containing pellets implanted rats prior to 2 mg/kg naloxone (NL) injection. Whereas 0.5 mg/kg K showed no significant effect on abstinence syndrome signs, 1 mg/kg K and 1 mg/kg DM significantly attenuated some of the signs. The attenuation or prevention of all the signs were observed after 2 mg/kg DM administration. Almost complete prevention was seen from the second minute on during the ten-minute observation period. As ASP and GLU antagonists K and DM have this antagonizing effect on the precipitated abstinence syndrome signs, the manifestation of abstinence syndrome may mainly result from the normalization of ASP and GLU production because of the disinhibition by NL of the enzymes and the stronger stimulation of ASPergic/GLUergic receptors which have no opiate blockade after NL injection.     

A possible mechanism of protection by polyamines against gastric damage induced by acidified ethanol in rats: polyamine protection may depend on its antiperoxidative properties

The protective mechanism of polyamines against acidified ethanol-induced gastric damage was studied. Their oral administration prevented the formation of gastric mucosal lesions induced by 90% ethanol in 150 mM HCl in a dose-dependent manner, with the order of the protective potency being spermine greater than spermidine greater than putrescine. The acidified ethanol-induced lesions were accompanied by a concomitant increase in gastric mucosal lipid peroxide levels, but spermine in a protective dose could prevent the increment of lipid peroxides. Polyamines, in a concentration-dependent fashion, inhibited the reduction of nitroblue tetrazolium by superoxide anion radicals generated in vitro in the xanthine-xanthine oxidase system and the lipid peroxidation in vitro induced by ferrous ion in the porcine gastric mucosal homogenate. The order of the superoxide scavenging potency and the inhibitory potency of iron-induced lipid peroxidation by polyamines corresponded to the order to the protective potency against acidified ethanol-induced gastric lesions. The present results suggest that cytoprotection by polyamines may be responsible for their antiperoxidative activities.