Hepatotoxicity and metabolism of acetaminophen in male and female rats

The oral administration of Lacticaseibacillus casei Shirota alleviates acetaminophen-induced liver injury through accelerated acetaminophen metabolism via the liver-gut axis in mice

Acetaminophen is a widely used antipyretic and analgesic drug, and its overdose is the leading cause of drug-induced acute liver failure. This study aimed to investigate the effect and mechanism of Lacticaseibacillus casei Shirota (LcS), an extensively used and highly studied probiotic, on acetaminophen-induced acute liver injury. C57BL/6 mice were gavaged with LcS suspension or saline once daily for 7 days before acute liver injury was induced via intraperitoneal injection of 300 mg/kg acetaminophen. The results showed that LcS significantly decreased acetaminophen-induced liver and ileum injury, as demonstrated by reductions in the increases in aspartate aminotransferase, total bile acids, total bilirubin, indirect bilirubin, and hepatic cell necrosis. Moreover, LcS alleviated acetaminophen-induced intestinal mucosal permeability, decreased serum IL-1α and lipopolysaccharide levels, and elevated serum eosinophil chemokine (eotaxin) and hepatic glutathione levels. Furthermore, analysis of the gut microbiota and metabolome showed that LcS reduced the acetaminophen-enriched levels of Cyanobacteria, Oxyphotobacteria, long-chain fatty acids, cholesterol, and sugars in the gut. Additionally, the transcriptomic and proteomic results showed that LcS mitigated the decrease in metabolic and immune pathways as well as glutathione formation during acetaminophen-induced acute liver injury. This is the first study showing that pretreatment with LcS alleviates acetaminophen-enriched acute liver injury, and it provides a reference for the application of LcS.IMPORTANCEAcetaminophen is the most frequently used antipyretic analgesic worldwide. As a result, overdoses easily occur and lead to drug-induced acute liver injury, which quickly progresses to liver failure with a mortality of 60%-80% if not corrected in time. The current emergency treatment for overused acetaminophen needs to be administered within 8 hours to avoid liver injury or even liver failure. Therefore, developing preventive strategies for liver injury during planned acetaminophen medication is particularly important, preferably nonpharmacological methods. Lacticaseibacillus casei Shirota (LcS) is a famous probiotic that has been used for many years. Our study found that LcS significantly alleviated acetaminophen-induced acute liver injury, especially acetaminophen-induced liver injury toward fulminant hepatic failure. Here, we elucidated the function and potential mechanisms of LcS in alleviating acetaminophen-induced acute liver injury, hoping it will provide preventive strategies to people during acetaminophen treatment.

Interleukin-1β-induced inflammation and acetaminophen during infancy: Distinct and interactive effects on social-emotional and repetitive behavior in C57BL/6J mice

Acetaminophen (APAP) exposure early in life has been associated with increased risk of neurodevelopmental disorders in epidemiological studies. In rodent models, early-life APAP has similarly been shown to produce long-term changes in brain and behavior, including altered activity levels and social behavior. Most rodent studies to date have, nevertheless, attempted to model early-life APAP without considering that most APAP exposure occurs in a context of immune activation and/or fever. To mimic the repeated infections common during infancy, we employed the cytokine interleukin-1β (IL-1β) to induce immune activation three times during early postnatal development (i.e., day 5, 8, and 11). On these days, C57BL/6J pups were administered either IL-1β (0.2 μg/kg) or saline vehicle followed, after 45 min, by either APAP (103.9 mg/kg) or vehicle. Mice were subsequently administered a battery of tests of social-emotional and repetitive behavior. A number of distinct long-term effects of IL-1β and APAP treatments were found, including sex-specific shifts in repetitive behavior and emotional hyperthermia following early-life IL-1β and increased social caution in males following early-life APAP. We also observed significant interaction between IL-1β and APAP: as adults, 'two-hit' IL-1β + APAP females displayed greater anxiety-related thigmotaxis across a number of tests, including an open field. 'Two hit' males, in turn, showed elevated levels of avoidance of an unfamiliar social partner during a social interaction test. Our results highlight that IL-1β-induced inflammation and APAP have both distinct effects and significant interactions during early life, with enduring sex-specific effects on phenotypes relevant to neurodevelopmental disorders.

Perinatal exposure to paracetamol: Dose and sex-dependent effects in behaviour and brain's oxidative stress markers in progeny

Paracetamol (PAR) has been employed worldwide for pain and fever treatment during pregnancy and lactation. Epidemiologic studies have shown that exposure to PAR can increase the risk for developmental disorders, such as attention-deficit hyperactive disorder and autism spectrum disorder. This study aimed to investigate if gestational and lactational exposure to human-relevant doses of PAR could alter behavioural and brain oxidative stress parameters in the rat`s offspring. Wistar dams were gavaged daily with water or PAR (35 mg/kg/ or 350 mg/kg) during gestational day 6 to weaning (postnatal day 21). Behavioural assessments occurred at post-natal days 10 (nest seeking test), 27 (behavioural stereotypy) and 28 (three chamber sociability test and open field). Concentration of advanced oxidation protein products (AOPP), reduced glutathione (GSH), lipid hydroperoxides (LOOH) and activity of superoxide dismutase (SOD) were estimate in prefrontal cortex, hippocampus, striatum and cerebellum of 22-day-old rats. Compared to CON animals, males exposed to PAR during pregnancy and lactation augmented apomorphine-induced stereotyped behaviour (350 mg/kg) and ambulation in open-field test (35 mg/kg). Reduced exploratory behaviour in three chamber sociability test was observed in pups exposed to PAR at 350 mg/kg in both sexes. PAR treatment decreased hippocampal GSH level and striatal SOD activity in males exposed to 35 mg/kg, suggesting the vulnerability of these areas in PAR-induced developmental neurotoxicity. Findings suggest PAR use during pregnancy and lactation as a potential risk factor for neurodevelopmental disorders with males being more susceptible.

Genetic Association of Single Nucleotide Polymorphisms with Acetaminophen-Induced Hepatotoxicity

Acetaminophen is commonly used to reduce pain and fever. Unfortunately, overdose of acetaminophen is a leading cause of acute liver injury and failure in many developed countries. The majority of acetaminophen is safely metabolized in the liver and excreted in the urine; however, a small percentage is converted to the highly reactive N-acetyl-p-benzoquinone imine (NAPQI). At therapeutic doses, NAPQI is inactivated by glutathione S-transferases, but at toxic levels, excess NAPQI forms reactive protein adducts that lead to hepatotoxicity. Individual variability in the response to both therapeutic and toxic levels of acetaminophen suggests a genetic component is involved in acetaminophen metabolism. In this review, we evaluate the genetic association studies that have identified 147 single nucleotide polymorphisms linked to acetaminophen-induced hepatotoxicity. The identification of novel genetic markers for acetaminophen-induced hepatotoxicity provides a rich resource for further evaluation and may lead to improved prognosis, prevention, and treatment.

Sex Differences in Human and Animal Toxicology

Sex, the states of being female or male, potentially interacts with all xenobiotic exposures, both inadvertent and deliberate, and influences their toxicokinetics (TK), toxicodynamics, and outcomes. Sex differences occur in behavior, exposure, anatomy, physiology, biochemistry, and genetics, accounting for female-male differences in responses to environmental chemicals, diet, and pharmaceuticals, including adverse drug reactions (ADRs). Often viewed as an annoying confounder, researchers have studied only one sex, adjusted for sex, or ignored it. Occupational epidemiology, the basis for understanding many toxic effects in humans, usually excluded women. Likewise, Food and Drug Administration rules excluded women of childbearing age from drug studies for many years. Aside from sex-specific organs, sex differences and sex × age interactions occur for a wide range of disease states as well as hormone-influenced conditions and drug distribution. Women have more ADRs than men; the classic sex hormone paradigm (gonadectomy and replacement) reveals significant interaction of sex and TK including absorption, distribution, metabolisms, and elimination. Studies should be designed to detect sex differences, describe the mechanisms, and interpret these in a broad social, clinical, and evolutionary context with phenomena that do not differ. Sex matters, but how much of a difference is needed to matter remains challenging.

Application of high-throughput sequencing to circulating microRNAs reveals novel biomarkers for drug-induced liver injury

Drug-induced liver injury (DILI) is a leading cause of acute liver failure and the major reason for withdrawal of drugs from the market. Preclinical evaluation of drug candidates has failed to detect about 40% of potentially hepatotoxic compounds in humans. At the onset of liver injury in humans, currently used biomarkers have difficulty differentiating severe DILI from mild, and/or predict the outcome of injury for individual subjects. Therefore, new biomarker approaches for predicting and diagnosing DILI in humans are urgently needed. Recently, circulating microRNAs (miRNAs) such as miR-122 and miR-192 have emerged as promising biomarkers of liver injury in preclinical species and in DILI patients. In this study, we focused on examining global circulating miRNA profiles in serum samples from subjects with liver injury caused by accidental acetaminophen (APAP) overdose. Upon applying next generation high-throughput sequencing of small RNA libraries, we identified 36 miRNAs, including 3 novel miRNA-like small nuclear RNAs, which were enriched in the serum of APAP overdosed subjects. The set comprised miRNAs that are functionally associated with liver-specific biological processes and relevant to APAP toxic mechanisms. Although more patients need to be investigated, our study suggests that profiles of circulating miRNAs in human serum might provide additional biomarker candidates and possibly mechanistic information relevant to liver injury.

Effects of administration of subtoxic doses of acetaminophen on liver and blood levels of insulin-like growth factor-1 in rats

Acetaminophen (APAP) is widely used in the treatment of pain. Toxic doses of APAP cause acute liver failure, but therapeutic doses are believed to be safe. The purpose of this study is to investigate the effects of administration of subtoxic doses of APAP on liver and blood levels of insulin-like growth factor-1 (IGF-1) in rats. Low dose (100 mg/kg) and high dose (250 mg/kg) of APAP were intraperitoneally injected into Wistar albino rats. Following administration of therapeutic doses of APAP, there were no significant changes in serum transaminases and liver glutathione levels. Both doses of APAP induced a decrease in liver and blood levels of IGF-1 when compared with the controls. There was no significant difference in liver IGF-1 levels between the high-dose and low-dose APAP groups; however, there was a significant difference in blood IGF-1 levels between both the groups. The histological examination showed that low dose of APAP induced mild degree of structural change, while high dose of APAP induced severe structural damage. In conclusion, these results suggest that blood IGF-1 levels may have a value in predicting hepatic damage resulting from therapeutic doses of APAP.

Focused DNA microarray analysis for sex-dependent gene expression of drug metabolizing enzymes, transporters and nuclear receptors in rat livers and kidneys

Cytochrome P450(CYP)s are known to show a sexual dimorphic expression in rat livers. However, the comprehensive analysis for the sex-dependent gene expressions of drug metabolizing enzymes except for CYPs, transporters and nuclear receptors in rat livers and kidneys has not been investigated yet. The purpose of the present study was to identify the novel drug metabolizing and pharmacokinetics (DMPK)-related gene(s) which show the sex difference in the mRNA expressions in rat livers and kidneys. Total RNAs were prepared from livers and kidneys in both male and female rats (Crl:CD(SD) and Crlj:WI). A DNA microarray analysis using a "GeneSQUARE Multiple Assay DNA Microarray Drug Metabolism Gene Expression for Rat" was performed. DMPK-related genes which showed sex differences in the mRNA expression were identified in rat livers or kidneys. Especially, the female dominant expressions of UDP glucuronosyltransferase (UGT) s were seen in rat livers and kidneys. The sex difference of UGT expressions in rats might be one of the causal factors of the sex difference of the biological response to UGT substrates.

Sex-related differences in renal toxicodynamics in rodents

INTRODUCTION

An issue yet to be addressed, in the investigation of the xenobiotic toxicity, is a detailed characterization of the sex differences in toxicological responses. The 'sex issue' is particularly significant in nephrotoxicology as the kidney is a relevant target organ for xenobiotics and few studies have approached this subject in the past. There is a strong need to improve our understanding regarding the influence of sex in toxicology, given their increased requirement to establish the limits of exposure to chemicals in the environment and at work.

AREAS COVERED

In this review, the authors provide the reader with the current knowledge of sex differences in kidney toxicity for rats and mice. To make the review easier to consult, these studies have been organized according to the class of xenobiotic.

EXPERT OPINION

From the analysis of the present knowledge emerges a dramatic need for information on sex differences in xenobiotics toxicity. Although animals are reasonably good predictors of adverse renal effects in patients, there is need to identify alternative methods (e.g. in vitro/ex vivo) to better study sex differences in organ toxicity.

Diabetes and hypertriglyceridemia modify the mode of acetaminophen-induced hepatotoxicity and nephrotoxicity in rats and mice

Certain disease conditions can modify drug-induced toxicities, which, in turn, may cause a medication-related health crisis. Therefore, preclinical investigations into the alterations in drug-induced toxicities using appropriate disease animal models are very important. This paper reviews the reported data related to the effects of diabetes and hypertriglyceridemia, common lifestyle-related diseases in a modern society, on acetaminophen (APAP)-induced hepatotoxicity and nephrotoxicity in rats and mice. It has generally been reported that diabetes protects rats and mice from APAP-induced hepatotoxicity and there are several reports that help to speculate on the effects of diabetes on APAP-induced nephrotoxicity. In fructose-induced hypertriglyceridemic rats, hepatotoxicity of APAP becomes apparently less severe, whereas nephrotoxicity of APAP becomes significantly more severe. The mechanisms of alteration of APAP-induced hepatorenal toxicity under diabetic and hypertriglyceridemic conditions are also discussed in this paper.

Effect of gender, dose, and time on 3-(3,5-dichlorophenyl)-2,4-thiazolidinedione (DCPT)-induced hepatotoxicity in Fischer 344 rats

1. The thiazolidinedione ring present in drugs available for type II diabetes can contribute to hepatic injury. Another thiazolidinedione ring-containing compound, 3-(3,5-dichlorophenyl)-2,4-thiazoli-dinedione (DCPT), produces liver damage in rats. Accordingly, the effects of gender, dose, and time on DCPT hepatotoxicity were therefore evaluated. 2. Male rats were more sensitive to DCPT (0.4-1.0 mmol kg(-1) by intraperitoneal administration) as shown by increased serum alanine aminotransferase levels and altered hepatic morphology 24 h post-dosing. Effects in both genders were dose dependent. In males, DCPT (0.6 mmol kg(-1)) produced elevations in alanine aminotransferases and changes in liver sections 3 h after dosing that progressively worsened up to 12 h. DCPT-induced renal effects were mild. 3. It is concluded that male rats are more susceptible to DCPT hepatotoxicity and that damage occurs rapidly. DCPT primarily affects the liver and can be a useful compound to investigate the role of the thiazolidinedione ring in hepatic injury. However, the gender dependency and rapid onset of DCPT hepatotoxicity require further investigation.

Overexpression of CYP3A aggravates endotoxin-induced liver injury in hypophysectomized female rats

AIM

CYP3A2 is a male-specific isoform of cytochrome P450 enzyme which is expressed abundantly in male rats but not in intact female rats. Having previously reported that hepatic CYP3A2 promotes lipopolysaccharide (LPS)-induced liver injury in male rats, we further examined the impact of CYP3A on LPS-induced liver injury by comparing intact and hypophysectomized female rats. In hypophysectomized female rats, phenobarbital (PB), a cytochrome P450 inducer, markedly increased the hepatic content and activity of CYP3A1/2, but did not do so in intact rats. CYP2B1 increased to similar levels in PB-treated hypophysectomized and intact rats.

METHODS

Rats were administered 10 mg/kg LPS intravenously and some were given PB for three days before LPS injection. Liver injury was analyzed 8 h after LPS injection.

RESULTS

PB-LPS increased plasma alanine aminotransferase significantly more in hypophysectomized female rats than in intact female rats. Ketoconazole, a CYP3A inhibitor, inhibited the increase of liver injury. Hepatic 8-hydroxydeoxyguanosine in nuclei and 4-hydroxy-2-nonenal-modified proteins, measured to evaluate oxidative stress by LPS treatment, increased markedly more in PB-treated, hypophysectomized female rats, than in intact female rats.

CONCLUSION

Overexpression of CYP3A aggravated LPS-induced liver injury in rats, apparently through the formation of reactive oxygen species.

Induction of Hepatic CYP2E1 by a Subtoxic Dose of Acetaminophen in Rats: Increase in Dichloromethane Metabolism and Carboxyhemoglobin Elevation

Dichloromethane (DCM) is metabolically converted to carbon monoxide mostly by CYP2E1 in liver, resulting in elevation of blood carboxyhemoglobin (COHb) levels. We investigated the effects of a subtoxic dose of acetaminophen (APAP) on the metabolic elimination of DCM and COHb elevation in adult female rats. APAP, at 500 mg/kg i.p., was not hepatotoxic as measured by a lack of change in serum aspartate aminotransferase, alanine aminotransferase, and sorbitol dehydrogenase activities. In rats pretreated with APAP at this dose, the COHb elevation resulting from administration of DCM (3 mmol/kg i.p.) was enhanced significantly. Also blood DCM levels were reduced, and its disappearance from blood appeared to be increased. Hepatic CYP2E1-mediated activities measured with chlorzoxazone, p-nitrophenol, and p-nitroanisole as substrates were all induced markedly in microsomes of rats treated with APAP. Aminopyrine N-demethylase activity was also increased slightly, but significantly. Western blot analysis showed that APAP treatment induced the expression of CYP2E1 and CYP3A proteins. Neither hepatic glutathione contents nor glutathione S-transferase activity was changed by the dose of APAP used. The results indicate that, contrary to the well known hepatotoxic effects of this drug at large doses, a subtoxic dose of APAP may induce CYP2E1, and to a lesser degree, CYP3A expression. This is the first report that APAP can increase cytochrome P450 (P450)-mediated hepatic metabolism and the resulting toxicity of a xenobiotic in the whole animal. The pharmacological/toxicological significance of induction of P450s by a subtoxic dose of APAP is discussed.

Acetaminophen metabolism does not contribute to gender difference in its hepatotoxicity in mouse

Gender is an important factor in pharmacokinetics and pharmacodynamics. In the current study, gender difference in acetaminophen (APAP)-induced hepatotoxicity has been examined. Male and female mice were injected with a toxic dose of APAP (500 mg/kg, ip). Female mice were resistant to the hepatotoxic effects of APAP, depicted by serum alanine aminotransferase and sorbital dehydrogenase activities and histological analysis. Basal hepatic reduced glutathione (GSH) levels were lower in females than in males, suggesting that basal GSH level may not be a factor in determining the gender difference of APAP hepatotoxicity. APAP metabolism was slower in females than males, revealed by lower levels of glucuronidation and sulfation and higher amounts of free APAP in the livers of female mice. Lower basal Cyp1a2 mRNA levels and lower expression of Cyp1a2 and Cyp3a11 mRNAs after APAP dosing were also observed in females compared with males. However, there was no gender difference in N-acetyl-p-benzoquinone imine covalent binding 2 h after APAP administration, suggesting similar APAP bioactivation between genders. Moreover, liver Gst pi mRNA levels were significantly lower in females than males. This finding is consistent with a previous report, which showed that Gst pi knockout mice are protected from APAP-induced liver toxicity. In conclusion, gender difference of APAP-induced hepatotoxicity is not likely due to APAP metabolism. Perhaps, it is in part due to gender-dependent Gst pi expression. However, the mechanism underlying the association between reduction in Gst pi expression and hepatoprotective effect against APAP toxicity remains to be further explored.

Characterization and evaluation of detoxification functions of a nontumorigenic immortalized porcine hepatocyte cell line (HepLiu)

Primary porcine hepatocytes (PPH) are currently used in research and therapeutic applications as the biological component of extracorporeal liver assist devices to overcome the shortage of human hepatocytes. However, their finite life span and typically rapid loss of functions limit their utility. An immortalized, nontumorigenic, highly differentiated porcine hepatocyte cell line was developed in our laboratory to resolve these disadvantages. PPH were transfected with simian virus 40 (SV40) T antigen under the control of the SV40 early promoter. From the established 69 clones, 23 clones displaying hepatocyte-like morphology were screened for diazepam metabolism. One clone, HepLiu D63, has been maintained in culture for > 2 years, through more than 60 passages and 240 divisions. Albumin protein, present in early passages, was lost at later passages, but albumin transcript still was detectable in later passages. Carbamoyl phosphate synthetase, a gateway enzyme of the urea cycle, was consistently detectable in HepLiu cells. Cytokeratin 18, a characteristic marker of primary hepatocytes, was detected by both immunofluorescent staining and Western blot in HepLiu cells. Furthermore, maintenance of P450 functions in HepLiu cells was evidenced by diazepam and 7-ethoxycoumarin metabolites measured by HPLC. Phase II conjugative function was measured as acetaminophen glucuronidation. P450 dealkylase was demonstrated microscopically by the conversion of a nonfluorescent substrate to a fluorescent product. Both Northern blot analysis and immunofluorescent staining showed SV40 T antigen expression in the nuclei of HepLiu cells. No tumor formation occurred when HepLiu cells were injected into severe combined immunodeficient (SCID) mice nor was the TAI (a tumor marker) mRNA expressed, even in later passages. This immortalized, nontumorigenic, highly functional cell line may provide a valuable tool for drug/toxicological studies, liver biologic regulation studies, and artificial liver support systems.

Carcinogen activation by sulfate conjugate formation

The foregoing pages presented a substantial body of data that established that sulfotransferase conjugation can transform many xenobiotics into agents that can modify cellular macromolecules. However, activation by sulfation is rarely the only metabolic pathway that is open to these compounds; other pathways can become more important in response to a variety of factors. This metabolic switching can be produced by substrate concentration, cofactor availability, kinetic factors that dictate the velocity of the various possible conjugation reactions, and, in some cases, competition between Phase-I and Phase-II metabolism. Also, it is important to realize that demonstration of activation by sulfate ester formation in vitro does not necessarily mean that a similar activation process will occur in vivo. Experience also teaches that argument by analogy can be very misleading in the case of sulfate activation. Small structural differences can upset the delicate balance between sulfate activation and the various other competing pathways. Nevertheless, sulfation is an important mechanism by which a number of chemicals are transformed to their activated forms.

Sulfation and glucuronidation of acetaminophen by cultured hepatocytes reproducing in vivo sex-differences in conjugation on Matrigel and type 1 collagen

The sulfate and glucuronide conjugation of acetaminophen (APAP) by hepatocytes cultured on Matrigel or type 1 collagen was compared to APAP metabolism in vivo. The metabolic fate of low (15 mg/kg), medium (125 mg/kg), and high (300 mg/kg) doses of APAP injected intraperitoneally were determined in male and female rats. Males excreted more APAP as the sulfate conjugate than females, which correlated with the twofold greater APAP sulfotransferase activity in the male vs. females (301 +/- 24 vs. 156 +/- 18 pmol.mg-1 protein.min-1). Also, as sulfate conjugation became saturated, there was a dose-related shift in APAP metabolism from sulfate to glucuronide conjugation in both sexes. After death, the livers of the same animals were perfused with collagenase and the hepatocytes cultured in modified Waymouth's medium on either Matrigel or rat-tail collagen, with various doses of APAP (0, 0.125, 0.25, 0.5, and 1.0 mM). Sex differences in APAP sulfation and glucuronidation persisted in culture for up to 4 days, with sulfation predominating in the male similar to in vivo. With increasing APAP concentration (dose), there was a saturation of sulfate conjugation and a shift to glucuronidation as observed in vivo. Sex differences in APAP sulfation and glucuronidation were no longer significant by Day 4 in culture. Sulfation, and to a lesser extent, glucuronidation, were more stable on Matrigel than collagen. We concluded that APAP metabolism of freshly isolated hepatocytes could replicate in vivo sex differences in conjugation, and that Matrigel was superior to collagen as substrate.

Sex differences in the cellular defence system against free radicals from oxygen or drug metabolites in rat

In this study, it was investigated whether sex-related differences in the protective mechanisms against oxygen radicals and free radical metabolites from drugs were present in rat liver, heart, and kidney. To that end, superoxide dismutase, catalase, the factors of the glutathione system and vitamin E were measured. In addition, NADPH-dependent cytochrome c-reductase activity was established, as this enzyme is involved in the formation of free radicals in the presence of many xenobiotics. The total capacity of the cellular systems that detoxify reactive oxygen species or free radical-drug metabolites seems to be higher in female liver as compared to male. No differences were found for heart and kidney tissue. It is hypothesized that female rats probably are less vulnerable for those drugs whose hepatotoxic action is induced by excessive formation of free radical species.

Effect of acetaminophen toxicity on erythrocyte osmotic fragility in the Fisher rat

The protective effect of propylthiouracil (PTU) pretreatment against acetaminophen-induced erythrocyte osmotic fragility was determined in the male Fisher rat. Hepatotoxicity was assessed for comparative purposes. PTU (0.15%) was fed in chow for a period of 12 days. Acetaminophen (1 g/kg body wt) was then administered orally by a stomach tube after an overnight fast. The rats were killed either 4 or 24 hr later. Erythrocyte osmotic fragility was determined by the extent of hemolysis in various concentrations of NaCl solutions. Hepatotoxicity was assessed by a rise in serum transaminases and by histological examination of hepatic tissue. PTU treatment when compared with control not only protected rats against acetaminophen-induced hepatotoxicity as reported before, but also protected against erythrocyte osmotic fragility. The time course of acetaminophen toxicity seems to be similar for liver and erythrocyte since both showed damage after 24 hr but not after 4 hr of acetaminophen administration. The data show that PTU pretreatment affords protection against acetaminophen-induced increased erythrocyte osmotic fragility even when their glutathione concentrations were not significantly different, suggesting that PTU per se has a protective effect.