Acetaminophen hepatotoxicity in aging rats

Weaning Mice and Adult Mice Exhibit Differential Carbon Tetrachloride-Induced Acute Hepatotoxicity

Age is a risk factor for drug-induced liver injury (DILI). However, there is a limited understanding of pediatric DILI. Here, 2-week-old weaning and 8-week-old adult male ICR mice were intraperitoneally injected with CCl₄ (0.1 mmol/kg equal to 15.4 mg/kg) to comparatively evaluate the time-dependent liver damage and cellular events. CCl₄ significantly enhanced the serum alanine aminotransferase/aspartate aminotransferase levels and hepatic centrilobular necrosis in the weaning mice, whereas it induced mild liver injury in the adult mice. CCl₄-treated weaning mice exhibited higher hepatic levels of pro-apoptotic proteins (Bax, cleaved caspase-3, -7, and -9), activated MAPKs (p-JNK and p-Erk), and endoplasmic reticulum stress indicators (ATF6 and CHOP) and lower hepatic anti-apoptotic Bcl-2 levels than the adult mice. The weaning mice exhibited enhanced basal hepatic glutathione (GSH) levels due to high glutamate cysteine ligase (GCL) and low anti-cysteine dioxygenase (CDO) enzyme levels. However, CCl₄ markedly reduced the hepatic GSH levels only in the weaning mice. Furthermore, higher hepatic levels of oxidative stress-induced malondialdehyde, 4-hydroxynonenal, nitrotyrosine-protein adducts, and oxidized proteins were observed in CCl₄-treated weaning mice than in CCl₄-treated adult mice. The enhanced levels of hepatic cytochrome P450 (CYP) 2E1 and CYP3A, and decreased hepatic GSH S-transferase (GST)-π and GSH reductase (GR) levels in the weaning mice may contribute to their enhanced susceptibility to liver damage.

Drug-Induced Liver Injury in Children: Clinical Observations, Animal Models, and Regulatory Status

Drug-induced liver injury in children (cDILI) accounts for about 1% of all reported adverse drug reactions throughout all age groups, less than 10% of all clinical DILI cases, and around 20% of all acute liver failure cases in children. The overall DILI susceptibility in children has been assumed to be lower than in adults. Nevertheless, controversial evidence is emerging about children's sensitivity to DILI, with children's relative susceptibility to DILI appearing to be highly drug-specific. The culprit drugs in cDILI are similar but not identical to DILI in adults (aDILI). This is demonstrated by recent findings that a drug frequently associated with aDILI (amoxicillin/clavulanate) was rarely associated with cDILI and that the drug basiliximab caused only cDILI but not aDILI. The fatality in reported cDILI studies ranged from 4% to 31%. According to the US Food and Drug Administration-approved drugs labels, valproic acid, dactinomycin, and ampicillin appear more likely to cause cDILI. In contrast, deferasirox, isoniazid, dantrolene, and levofloxacin appear more likely to cause aDILI. Animal models have been explored to mimic children's increased susceptibility to valproic acid hepatotoxicity or decreased susceptibility to acetaminophen or halothane hepatotoxicity. However, for most drugs, animal models are not readily available, and the underlying mechanisms for the differential reactions to DILI between children and adults remain highly hypothetical. Diagnosis tools for cDILI are not yet available. A critical need exists to fill the knowledge gaps in cDILI. This review article provides an overview of cDILI and specific drugs associated with cDILI.

N-Acetyl cysteine does not prevent liver toxicity from chronic low-dose plus subacute high-dose paracetamol exposure in young or old mice

Paracetamol is an analgesic commonly used by people of all ages, which is well documented to cause severe hepatotoxicity with acute overexposures. The risk of hepatotoxicity from nonacute paracetamol exposures is less extensively studied, and this is the exposure most common in older adults. Evidence on the effectiveness of N-acetyl cysteine (NAC) for nonacute paracetamol exposures, in any age group, is lacking. This study aimed to examine the effect of long-term exposure to therapeutic doses of paracetamol and subacute paracetamol overexposure, in young and old mice, and to investigate whether NAC was effective at preventing paracetamol hepatotoxicity induced by these exposures. Young and old male C57BL/6 mice were fed a paracetamol-containing (1.33 g/kg food) or control diet for 6 weeks. Mice were then dosed orally eight times over 3 days with additional paracetamol (250 mg/kg) or saline, followed by either one or two doses of oral NAC (1200 mg/kg) or saline. Chronic low-dose paracetamol exposure did not cause hepatotoxicity in young or old mice, measured by serum alanine aminotransferase (ALT) elevation, and confirmed by histology and a DNA fragmentation assay. Subacute paracetamol exposure caused significant hepatotoxicity in young and old mice, measured by biochemistry (ALT) and histology. Neither a single nor double dose of NAC protected against this toxicity from subacute paracetamol in young or old mice. This finding has important clinical implications for treating toxicity due to different paracetamol exposure types in patients of all ages, and implies a need to develop new treatments for subacute paracetamol toxicity.

Acetaminophen hepatotoxicity in mice: Effect of age, frailty and exposure type

Acetaminophen is a commonly used analgesic that can cause severe hepatotoxicity in overdose. Despite old age and frailty being associated with extensive and long-term utilization of acetaminophen and a high prevalence of adverse drug reactions, there is limited information on the risks of toxicity from acetaminophen in old age and frailty. This study aimed to assess changes in the risk and mechanisms of hepatotoxicity from acute, chronic and sub-acute acetaminophen exposure with old age and frailty in mice. Young and old male C57BL/6 mice were exposed to either acute (300 mg/kg via oral gavage), chronic (100 mg/kg/day in diet for six weeks) or sub-acute (250 mg/kg, t.i.d., for three days) acetaminophen, or saline control. Pre-dosing mice were scored for the mouse clinical frailty index, and after dosing serum and liver tissue were collected for assessment of toxicity and mechanisms. There were no differences with old age or frailty in the degree of hepatotoxicity induced by acute, chronic or subacute acetaminophen exposure as assessed by serum liver enzymes and histology. Age-related changes in the acetaminophen toxicity pathways included increased liver GSH concentrations, increased NQO1 activity and an increased pro- and anti-inflammatory response to acetaminophen in old age. Frailty-related changes included a negative correlation between frailty index and serum protein, albumin and ALP concentrations for some mouse groups. In conclusion, although there were changes in some pathways that would be expected to influence susceptibility to acetaminophen toxicity, there was no overall increase in acetaminophen hepatotoxicity with old age or frailty in mice.

Drug-induced liver injury in older adults

Drug-induced liver injury (DILI) is an important cause of hospitalisation and of medication deregistration. In old age, susceptibility to DILI is affected by changes in physiology and increased interindividual variability, compounded by an increased prevalence of disease and the frailty syndrome. While dose-related or predictable DILI reactions are often detected in preclinical trials, the occurrence of rare hypersensitivity or idiosyncratic reactions cannot be reliably predicted from preclinical studies or even by clinical trials. The limited participation of older adults in clinical trials means that the susceptibility of this population to DILI is largely unknown. Vigilance during clinical trials and postmarketing surveillance must be universally practised. A systematic approach should be taken to determine not only which medicines are hepatotoxic and should be removed from the market, but also the hepatotoxicity risks from marketed drugs to consumers with different characteristics, many of whom are older people.

Preliminary evaluation of Diopatra neapolitana regenerative capacity as a biomarker for paracetamol exposure

An increasing number of studies established unequivocal relationships between exposure to pharmaceutical drugs and toxicity in wildlife. However, few studies investigated physiological alterations caused by such compounds in polychaetes. Thus, in this study, the effects of increasing concentrations of paracetamol were studied in the polychaete Diopatra neapolitana using tissue regenerative capacity as a biomarker. The obtained results revealed that individuals exposed to ecologically relevant concentrations (namely, 25 μg/L) of paracetamol exhibited significantly lower capacity to regenerate their body in comparison with control organisms. This study evidenced that paracetamol can induce significant physiological alterations in D. neapolitana resulting in an overall diminished regenerative capacity, which is of significance to a species with high ecological and economic relevance. Additionally, this study indicates the promise of D. neapolitana as a test organism in laboratory-based bioassays, but also as an adequate sentinel species to pharmaceutical drugs.

The effect of aging on acetaminophen pharmacokinetics, toxicity and Nrf2 in Fischer 344 rats

We investigated the effect of aging on hepatic pharmacokinetics and the degree of hepatotoxicity following a toxic dose of acetaminophen. Young and old male Fischer 344 rats were treated with 800 mg/kg acetaminophen (young n = 8, old n = 5) or saline (young n = 9, old n = 9). Serum measurements showed old rats treated with acetaminophen had significantly lower serum alanine aminotransferase and higher acetaminophen and acetaminophen glucuronide levels and creatinine, compared with acetaminophen treated young rats (p < .05). Immunoblotting and activity assays showed old saline-treated rats had twofold lower cytochrome P450 2E1 activity and threefold higher NAD(P)H quinone oxireductase 1 protein expression and activity than young saline-treated rats (p < .05), although Nrf2, glutathione cysteine ligase-modulatory subunit, glutathione cysteine ligase-catalytic subunit, and cytochrome P450 2E1 protein expressions were unchanged. Primary hepatocytes isolated from young rats treated with 10 mM acetaminophen had lower survival than those from old rats (52.4% ± 5.8%, young; 83.6% ± 1.7%, old, p < .05). The pharmacokinetic changes described may decrease susceptibility to acetaminophen-induced hepatotoxicity but may increase risk of nephrotoxicity in old age.

Age-related changes in the hepatic pharmacology and toxicology of paracetamol

Optimal pharmacotherapy is determined when the pharmacokinetics and pharmacodynamics of the drug are understood. However, the age-related changes in pharmacokinetics and pharmacodynamics, as well as the increased interindividual variation mean optimal dose selection are a challenge for prescribing in older adults. Poor understanding of how hepatic clearance and toxicity are different with age results in suboptimal dose selection, poor efficacy, and/or increased toxicity. Of particular concern is the analgesic paracetamol which has been in use for more than 50 years and is consumed by a large proportion of older adults. Paracetamol is considered to be a relatively safe drug; however, caution must be taken because of its potential for toxicity. Paracetamol-induced liver injury from accidental overdose accounts for up to 55% of cases in older adults. Better understanding of how age affects the hepatic clearance and toxicity of drugs will contribute to evidence-based prescribing for older people, leading to fewer adverse drug reactions without loss of benefit.

Age-related pseudocapillarization of the liver sinusoidal endothelium impairs the hepatic clearance of acetaminophen in rats

We investigated the effect of age-related pseudocapillarization of the liver sinusoidal endothelium on the hepatic disposition of acetaminophen. The multiple indicator dilution technique assessed the hepatic disposition of tracer (14)C-acetaminophen and reference markers in isolated perfused livers of young (n = 11) and old (n = 12) rats. Electron microscopy confirmed defenestration of the sinusoidal endothelium in old rats compared with young rats. Acetaminophen recovery following a single pass through the liver was significantly increased in old rats (0.64 ± 0.04, old; 0.59 ± 0.05, young; p < .05). In old age, there was significant reduction of the intercompartmental rate constant k(1) (0.34 ± 0.10 s(-1), old; 0.61 ± 0.38 s(-1), young; p < .05) and the permeability-surface area product for the transfer of acetaminophen across the sinusoidal endothelium (0.034 ± 0.006 mL/s/g, old; 0.048 ± 0.014 mL/s/g, young; p < .005). There was no difference in k(3), the measure of sequestration of acetaminophen that reflects enzyme activity. Age-related pseudocapillarization of the liver sinusoid resulted in increased acetaminophen recovery and decreased transfer of acetaminophen into the liver.

Clinical pharmacology in the geriatric patient

Geriatric patients are a subset of older people with multiple comorbidities that usually have significant functional implications. Geriatric patients have impaired homeostasis and wide inter-individual variability. Comprehensive geriatric assessment captures the complexity of the problems that characterize frail older patients and can be used to guide management, including prescribing. Prescribing for geriatric patients requires an understanding of the efficacy of the medication in frail older people, assessment of the risk of adverse drug events, discussion of the harm:benefit ratio with the patient, a decision about the dose regime and careful monitoring of the patient's response. This requires evaluation of evidence from clinical trials, application of the evidence to frail older people through an understanding of changes in pharmacokinetics and pharmacodynamics, and attention to medication management issues. Given that most disease occurs in older people, and that older people are the major recipients of drug therapy in the Western world, increased research and a better evidence base is essential to guide clinicians who manage geriatric patients.

Gene expression profile in liver of differing ages of rats after single oral administration of acetaminophen

In order to verify the influence of the rat age on hepatotoxicity, male Sprague-Dawley rats of 6 (young) and 12 (adult) weeks of age were orally administered acetaminophen (APAP), isoniazid (INH), or carbon tetrachloride (CCl4). Liver samples were obtained in a time-course manner, and changes in gene expression examined by an Affymetrix GeneChip. APAP caused more prominent hepatic injury with respect to pathology and blood biochemistry in adults than in young rats, whereas no obvious age-related differences were observed in INH- or CCl4-treated rats. Comparing gene expression in control rats, CYP3A13 was higher and GSTY2c was lower in adults, suggesting that production of the active metabolite of APAP is higher and its detoxification is lower in adults. The total amount of glutathione and total SH in rat liver was found to be higher in adult rats whereas the extent of its reduction by APAP was larger in adults. A detailed analysis of genes showing age-related differences revealed that some of them were different not in their extent but in their time course, i.e., the stress responses occurred earlier in the young than in the adult, resulting in a difference at 24 hr after dosing. These results suggest that the age-related difference in toxicity would be attributed to a higher expression of CYP3A13, producing the active metabolite of APAP as well as the lower expression of the detoxification enzyme, GSTY2c, in adult rats. Furthermore, these differences affect the time course of APAP toxicity. The present study clearly depicts the advantage of the multi-time, multi-dose protocol employed in our project for analyzing the mechanism of toxicity by gene expression profiling.

Tolerance of aged Fischer 344 rats against chlordecone-amplified carbon tetrachloride toxicity

We have investigated the effects of chlordecone 1(CD)+CCl4 combination in adult (3 months), middle aged (14 months), and old aged (24 months) male Fischer 344 (F344) rats. After a non-toxic dietary regimen of CD (10 ppm) or normal powdered diet for 15 days, rats received a single non-toxic dose of CCl4 (100 microl/kg, i.p., 1:4 in corn oil) or corn oil (500 microl/kg, i.p.) alone on day 16. Liver injury was assessed by plasma ALT, AST, and histopathology during a time course of 0-96 h. Liver tissue repair was measured by [3H-CH3]-thymidine (3H-T) incorporation into hepatic nuclear DNA and proliferating cell nuclear antigen (PCNA) immunohistochemistry. Hepatomicrosomal CYP2E1 protein, enzyme activity, and covalent binding of 14CCl4-derived radiolabel were measured in normal and CD fed rats. Exposure to CCl4 alone caused modest liver injury only in 14- and 24-month-old rats but neither progression of injury nor mortality. The CD+CCl4 combination led to 100% mortality in 3-month-old rats by 72 h, whereas none of the 14- and 24-month-old rats died. Both 3- and 14-month-old rats exposed to CD+Cl4 had identical liver injury up to 36 h indicating that bioactivation-mediated CCl4 injury was the same in the two age groups. Thereafter, liver injury escalated only in 3-month-old while it declined in 14-month-old rats. In 24-month-old rats initial liver injury at 6 h was similar to the 3- and 14-month-old rats and thereafter did not develop to the level of the other two age groups, recovering from injury by 96 h as in the 14-month-old rats. Neither hepatomicrosomal CYP2E1 protein nor the associated p-nitrophenol hydroxylase activity or covalent binding of 14CCl4-derived radiolabel to liver tissue differed between the age groups or diet regimens 2 h after the administration of 14CCl4. Compensatory liver tissue repair (3H-T, PCNA) was prompt and robust soon after CCl4 liver injury in the 14- and 24-month-old rats. In stark contrast, in the 3-month-old rats it failed allowing unabated progression of liver injury. These findings suggest that stimulation of early onset and robust liver tissue repair rescue the 14- and 24-month-old F344 rats from the lethal effect of the CD+CCl4 combination.

Glutathione monoethyl ester protects against glutathione deficiencies due to aging and acetaminophen in mice

Our previous results indicated that glutathione (GSH) and/or cysteine (Cys) deficiency occurs in many aging tissues and also after acetaminophen (APAP) administration. The aim of this study was to investigate whether GSH monoethyl ester (GSH-OEt) can correct these deficiencies. Mice of different ages (3-31 months) through the life span were sacrificed 2 h after i.p. injection of GSH-OEt (10 mmol/kg). In separate experiments, old mice (30-31 months) received the same dose of ester 30 min before the administration of APAP (375 mg/kg) or buthionine sulfoximine (BSO, 4 mmol/kg), an inhibitor of GSH synthesis. Liver and kidney samples were analyzed for GSH and Cys by HPLC. The hepatic GSH and renal cortical GSH and Cys concentrations were about 30% lower in old mice (30-31 months) compared to mature mice (12 months). GSH-OEt corrected these aging-related decreases. APAP decreased both hepatic and renal cortical GSH and Cys concentrations in old mice, but GSH-OEt prevented these decreases. GSH-OEt also prevented the BSO-induced decreases in hepatic and renal GSH concentrations. The results demonstrated that GSH-OEt protected against GSH deficiency due to biological aging as well as APAP-induced decreases in old mice.

Age-related susceptibility to hepatotoxicants

Limited information is available regarding age-associated events that lead to differences in vulnerability to chemicals that injure the liver. For some agents, such as allyl alcohol, alterations in metabolic activation, by liver biotransformation enzymes, are responsible for age-associated changes in severity of liver damage. For other toxicants, such as carbon tetrachloride, there appears to be no relation between changes in activation/detoxification processes and the effects of aging on the extent of liver injury. With diquat, a rise in iron content seems to explain the increased toxicity observed in hepatocytes of old rats compared with those of young-adult rats. Additional research is needed to identify the mechanisms responsible for age-dependent differences in sensitivity to environmental chemicals.

Age-associated increase in ferritin content of male rat liver: implication for diquat-mediated oxidative injury

Our previous studies in rat hepatocytes demonstrated an age-dependent increase in sensitivity to diquat-induced cytotoxicity, possibly as a result of increased iron availability. The present study was conducted to determine whether quantitative or qualitative changes in hepatic ferritin occur as a consequence of aging and whether diquat-mediated oxidation is intensified by elevated ferritin concentrations. Hepatic ferritins were isolated from male Fischer 344 rats ages 5, 15, and 25 months. Age-associated increases were observed in amounts of ferritin protein and ferritin iron per gram of liver, but there were no differences in proportions of H to L subunits or in rates of diquat-mediated iron release. The consequences of a threefold increase in ferritin content for diquat-mediated lipid peroxidation and protein carbonyl formation were examined in microsomal incubation systems. The addition of isolated rat liver ferritin augmented diquat-mediated oxidative damage in a time- and concentration-dependent manner, and the inclusion of deferoxamine completely inhibited the stimulation by ferritin. The results indicate that availability of ferritin iron is an important determinant of diquat-mediated oxidative injury and support the hypothesis that elevated hepatic ferritin content is responsible, at least in part, for the age-associated enhancement of diquat-induced toxicity.

Sex-dependent differences in the effects of aging on antioxidant defense mechanisms of rat liver

Information about age-related factors that influence sensitivity to hepatotoxic injury is important to geriatric medicine and environmental health. The purpose of the present study was to determine whether age-associated changes occur in hepatic antioxidant defense mechanisms of male and female Fischer 344 rats. Liver homogenates and post-mitochondrial supernatant fractions from rats aged 4, 14, 24 and 29 months were analyzed for antioxidant enzyme activities and for vitamin E and malondialdehyde content. Age-associated changes in catalase and glutathione reductase activities were observed that could be described as sex-determined differences that disappeared in old age. Cytosolic superoxide dismutase and glutathione peroxidase activities displayed sex-dependent variations in activity but were unaffected by aging. Hepatic vitamin E concentrations were lower in male rats than in female malondialdehyde concentrations also were lower in males than in females; malondialdehyde content increased in old males and decreased in old females. The results indicate that age-associated changes in enzymatic and nonenzymatic antioxidant defense mechanisms of rat liver are sex-dependent. In addition, comparison with findings from other studies in rats suggests that the effects of aging may also depend on the strain of rat.