A monkey model of acetaminophen-induced hepatotoxicity; phenotypic similarity to human

Preclinical safety assessment of JNJ-10450232 (NTM-006), a structural analog of acetaminophen, that does not cause hepatotoxicity at supratherapeutic doses

JNJ-10450232 (NTM-006) is a new molecular entity that is structurally related to acetaminophen. A comprehensive non-clinical safety program was conducted to support first-in-human and clinical efficacy studies based on preclinical data suggesting that the compound has comparable or enhanced antinociceptive and antipyretic efficacy without causing hepatotoxicity at supratherapeutic doses. No hepatic toxicity was noted in a mouse model sensitive to acetaminophen hepatotoxicity or in rats, dogs, and non-human primates in 28-day repeat dose toxicity studies at and above doses/exposures at which acetaminophen is known to cause hepatotoxicity. In the 28-day toxicity studies, all treatment-related findings were monitorable and reversible. Methemoglobinemia, which was observed in dogs and to a lesser extent in rats, is also observed with acetaminophen. This finding is considered not relevant to humans due to species differences in metabolism. Thyroid hypertrophy and hyperplasia were also observed in dogs and were shown to be a consequence of a species-specific UGT induction also demonstrated with increased thyroid hormone metabolism. Indirect bilirubin elevation was observed in rats as a result of UGT1A1 Inhibition. JNJ-10450232 (NTM-006) had no toxicologically relevant findings in safety pharmacology or genotoxicity studies. Together, these data supported progressing into safety and efficacy studies in humans.

Iron loading exerts synergistic action via a different mechanistic pathway from that of acetaminophen-induced hepatic injury in mice

Acetaminophen (APAP) overdose is a major cause of drug-induced acute liver failure. In such cases, free iron is released from lysosomes and is transported to mitochondria where it plays a pivotal role in APAP-induced liver injury. We previously reported that ascorbic acid (Asc) markedly mitigates APAP-induced hepatic damage in aldehyde reductase (Akr1a)-knockout (KO) mice that produce about 10% Asc as wild-type (WT) mice. However, the issue of the protective mechanism of Asc in association with the status of iron remains ambiguous. To gain additional insights into this issue, we examined effects of APAP (500 mg/kg) on female KO mice under conditions of iron loading. While the KO mice without AsA supplementation were more sensitive to APAP toxicity than the WT mice, FeSO₄ loading (25 mg/kg) to WT mice aggravated the hepatic injury, which was a similar extent to that of the KO mice. Supplementation of Asc (1.5 mg/ml in the drinking water) ameliorated KO mice irrespective of iron status but did not change the iron-mediated increase in the lethality in the WT mice. Hepatic cysteine and glutathione levels declined to similar extents in all mouse groups at 3 h irrespective of the iron status and largely recovered at 18 h after the APAP treatment when liver damage was evident. Asc prominently mitigated APAP toxicity in KO mice irrespective of the iron status but had no effect on the synergistic action of iron and APAP in the WT mice, suggesting that the mechanism for the deteriorating action of loaded iron is different from that of APAP toxicity.

MiR-122 and other microRNAs as potential circulating biomarkers of drug-induced liver injury

INTRODUCTION

Drug-induced liver injury (DILI) is a severe adverse drug reaction which is of major concern to patients, clinicians and the pharmaceutical industry. Accurate and rapid detection of DILI is important for patient stratification and treatment in the clinic and benefits preclinical drug design and risk assessment. MicroRNAs (miRNAs) offer a potential new and improved class of circulating biomarkers of DILI over the current gold standard biomarkers. Areas covered: This review highlights the shortcomings of the currently used panel of biomarkers and how miRNAs, primarily miR-122, show an improved level of specificity and sensitivity in the prediction of DILI. Furthermore, the use of miRNAs as potential markers of progression of DILI and specific zonated damage within the liver is discussed. Expert commentary: MiRNAs offer more sensitive and specific markers over the current biomarkers for DILI. Combinations of different miRNAs may be able to relay the location of DILI and the progression of disease. More studies using different hepatotoxins apart from acetaminophen will ultimately strengthen the case for the clinical introduction of miRNAs as biomarkers of DILI.

miRNA-122 Protects Mice and Human Hepatocytes from Acetaminophen Toxicity by Regulating Cytochrome P450 Family 1 Subfamily A Member 2 and Family 2 Subfamily E Member 1 Expression

Acetaminophen toxicity is a leading cause of acute liver failure (ALF). We found that miRNA-122 (miR-122) is down-regulated in liver biopsy specimens of patients with ALF and in acetaminophen-treated mice. A marked decrease in the primary miR-122 expression occurs in mice on acetaminophen overdose because of suppression of its key transactivators, hepatocyte nuclear factor (HNF)-4α and HNF6. More importantly, the mortality rates of male and female liver-specific miR-122 knockout (LKO) mice were significantly higher than control mice when injected i.p. with an acetaminophen dose not lethal to the control. LKO livers exhibited higher basal expression of cytochrome P450 family 2 subfamily E member 1 (CYP2E1) and cytochrome P450 family 1 subfamily A member 2 (CYP1A2) that convert acetaminophen to highly reactive N-acetyl-p-benzoquinone imine. Upregulation of Cyp1a2 primary transcript and mRNA in LKO mice correlated with the elevation of aryl hydrocarbon receptor (AHR) and mediator 1 (MED1), two transactivators of Cyp1a2. Analysis of ChIP-seq data in the ENCODE (Encyclopedia of DNA Element) database identified association of CCCTC-binding factor (CTCF) with Ahr promoter in mouse livers. Both MED1 and CTCF are validated conserved miR-122 targets. Furthermore, depletion of Ahr, Med1, or Ctcf in Mir122^-/- hepatocytes reduced Cyp1a2 expression. Pulse-chase studies found that CYP2E1 protein level is upregulated in LKO hepatocytes. Notably, miR-122 depletion sensitized differentiated human HepaRG cells to acetaminophen toxicity that correlated with upregulation of AHR, MED1, and CYP1A2 expression. Collectively, these results reveal a critical role of miR-122 in acetaminophen detoxification and implicate its therapeutic potential in patients with ALF.

Circulating liver-specific microRNAs in cynomolgus monkeys

Circulating microRNAs (miRNAs) can potentially be used as sensitive and specific biomarkers for tissue injury. However, the usefulness of circulating miRNAs as safety biomarkers in nonclinical toxicological studies using nonhuman primates is debatable owing to the limited information on organ-specific miRNAs. Therefore, a systematic investigation was performed to address this point. We identified organ-specific miRNAs from cynomolgus monkeys by next-generation sequencing analysis, which revealed that miR-122 was only abundant in the liver, whereas miR-192 was abundant in the liver, stomach, intestines, and kidney. The sequences of these miRNAs were identical to their human counterparts. Next, the absolute miR-122 and miR-192 levels were qualified by quantitative reverse transcription polymerase chain reaction (RT-qPCR) to determine the circulating levels of the miRNAs. No significant differences in the levels of circulating miRNAs between sexes were noted, and there was greater interindividual variation in miR-122 (20-fold variation) than in miR-192 (8-fold variation), based on their dynamic ranges. Finally, we evaluated the fluctuation in circulating liver-specific miRNAs in a monkey model of acetaminophen-induced hepatotoxicity. Acetaminophen with L-buthionine-(S,R)-sulfoximine induced hepatotoxicity in all the animals, which was characterized histopathologically by centrilobular necrosis and vacuolation of hepatocytes. Circulating miR-122 and miR-192 levels increased more than ALT levels after 24 h, indicating that circulating miR-122 and miR-192 may serve as sensitive biomarkers for the detection of hepatotoxicity in cynomolgus monkeys. This review describes the fundamental profiles of circulating liver-specific miRNAs in cynomolgus monkeys and focusses on their organ specificity, circulating levels, and fluctuations in drug-induced hepatotoxicity.