Closing the gap on drug-induced liver injury

Drug-induced liver injury (DILI) limits the development and application of many therapeutic compounds and presents major challenges to the pharmaceutical industry and clinical medicine. Acetaminophen-containing compounds are among the most frequently prescribed drugs and are also the most common cause of DILI. Here we describe a pharmacological strategy that targets gap junction communication to prevent amplification of fulminant hepatic failure and acetaminophen-induced hepatotoxicity. We demonstrate that connexin 32 (Cx32), a key hepatic gap junction protein, is an essential mediator of DILI by showing that mice deficient in Cx32 are protected against liver damage, acute inflammation and death caused by liver-toxic drugs. We identify a small-molecule inhibitor of Cx32 that protects against liver failure and death in wild-type mice when co-administered with known hepatotoxic drugs. These findings indicate that gap junction inhibition could provide a pharmaceutical strategy to limit DILI and improve drug safety. (HEPATOLOGY 2012;).     

Thioacetamide-induced liver regeneration involves the expression of cyclooxygenase 2 and nitric oxide synthase 2 in hepatocytes

BACKGROUND/AIMS: A regeneration process intended to restore organ function follows liver hepatotoxicity induced by a necrogenic dose of thioacetamide (TAM). METHODS: The expression of genes related to inflammation such as nitric oxide synthase-2 (NOS-2) and cyclooxygenase-2 (COX-2) has been analyzed in the course of the regenerative response, using NOS-2 KO mice or animals treated with selective inhibitors of COX-2. RESULTS: All animals lacking both activities survived to the hepatotoxic administration. However, animals deficient for NOS-2 exhibited more severe organ damage in view of the levels of hepatic serum markers of function, as well as an attenuated activation of NF-kappaB. The levels of C/EBPs were determined as markers of hepatocyte de-differentiation and regeneration, and the expression of COX-2 in TAM treated animals was concomitant with a decrease in C/EBP-alpha level. Analysis of cyclin D1, E and PCNA correlated with hepatocytes entering into the S phase of cell cycle by the effect of TAM. CONCLUSIONS: These data indicate that hepatocytes from TAM-treated mice express NOS-2 and COX-2 proteins and initiate the regeneration process that follows acute liver injury. However, the absence of NO delays hepatocyte regeneration, whereas COX-2-inhibition appears to decrease liver damage.     

Activation of autophagy protects against acetaminophen-induced hepatotoxicity

Autophagy can selectively remove damaged organelles, including mitochondria, and, in turn, protect against mitochondria-damage-induced cell death. Acetaminophen (APAP) overdose can cause liver injury in animals and humans by inducing mitochondria damage and subsequent necrosis in hepatocytes. Although many detrimental mechanisms have been reported to be responsible for APAP-induced hepatotoxicity, it is not known whether APAP can modulate autophagy to regulate hepatotoxicity in hepatocytes. To test the hypothesis that autophagy may play a critical protective role against APAP-induced hepatotoxicity, primary cultured mouse hepatocytes and green fluorescent protein/light chain 3 transgenic mice were treated with APAP. By using a series of morphological and biochemical autophagic flux assays, we found that APAP induced autophagy both in the in vivo mouse liver and in primary cultured hepatocytes. We also found that APAP treatment might suppress mammalian target of rapamycin in hepatocytes and that APAP-induced autophagy was suppressed by N-acetylcysteine, suggesting APAP mitochondrial protein binding and the subsequent production of reactive oxygen species may play an important role in APAP-induced autophagy. Pharmacological inhibition of autophagy by 3-methyladenine or chloroquine further exacerbated APAP-induced hepatotoxicity. In contrast, induction of autophagy by rapamycin inhibited APAP-induced hepatotoxicity. CONCLUSION: APAP overdose induces autophagy, which attenuates APAP-induced liver cell death by removing damaged mitochondria.     

Neutrophil depletion protects against murine acetaminophen hepatotoxicity

We previously reported that liver natural killer (NK) and NKT cells play a critical role in mouse model of acetaminophen (APAP)-induced liver injury by producing interferon gamma (IFN-gamma) and modulating chemokine production and subsequent recruitment of neutrophils into the liver. In this report, we examined the role of neutrophils in the progression of APAP hepatotoxicity. C57BL/6 mice were given an intraperitoneal toxic dose of APAP (500 mg/kg), which caused severe acute liver injury characterized by significant elevation of serum ALT, centrilobular hepatic necrosis, and increased hepatic inflammatory cell accumulation. Flow cytometric analysis of isolated hepatic leukocytes demonstrated that the major fraction of increased hepatic leukocytes at 6 and 24 hours after APAP was neutrophils (Mac-1+ Gr-1+). Depletion of neutrophils by in vivo treatment with anti-Gr-1 antibody (RB6-8C5) significantly protected mice against APAP-induced liver injury, as evidenced by markedly reduced serum ALT levels, centrilobular hepatic necrosis, and improved mouse survival. The protection was associated with decreased FasL-expressing cells, cytotoxicity against hepatocytes, and respiratory burst in hepatic leukocytes. In intracellular adhesion molecule (ICAM)-1-deficient mice, APAP caused markedly reduced liver injury when compared with wild-type mice. The marked protection in ICAM-1-deficient mice was associated with decreased accumulation of neutrophils in the liver. Hepatic GSH depletion and APAP-adducts showed no differences among the antibody-treated, ICAM-1-deficient, and normal mice. In conclusion, accumulated neutrophils in the liver contribute to the progression and severity of APAP-induced liver injury.     

Role of nuclear receptor CAR in carbon tetrachloride-induced hepatotoxicity

AIM: To investigate the precise roles of CAR in CCI4-induced acute hepatotoxicity. METHODS: To prepare an acute liver injury model,CCI4 was intraperitonealiy injected in CAR+/+ and CAR-/- mice, RESULTS: Elevation of serum alanine aminotransferase and extension of centrilobular necrosis were slightly inhibited in CAR-/- mice compared to CAR+/+ mice without PB. Administration of a CAR inducer, PB, revealed that CCl4-induced liver toxicity was partially inhibited in CAR-/-mice compared with CAR+/+ mice. On the other hand, androstanol, an inverse agonist ligand, inhibited hepatotoxicity in CAR+/+ but not in CAR-/- mice. Thus, CAR activation caused CCI4 hepatotoxicity while CAR inhibition resulted in partial protection against CCl4-induced hepatotoxicity.There were no differences in the expression of CYP2E1, the main metabolizing enzyme for CCl4, between CAR+/+ and CAR-/- mice. However, the expression of other CCI4-metabolizing enzymes, such as CYP2B10 and 3A11, was induced by PB in CAR+/+ but not in CAR-/1 mice. Although the main pathway of CCI4-induced acute liver injury is mediated by CYP2E1, CAR modulates its pathway via induction of CYP2B10 and 3A11 in the presence of activator or inhibitor. CONCLUSION: The nuclear receptor CAR modulates CCl4-induced liver injury via induction of CCI4-metabolizing enzymes in the presence of an activator. Our results suggest that drugs interacting with nuclear receptors such as PB might play critical roles in drug-induced liver injury or drug-drug interaction even though such drugs themselves are not hepatotoxic.     

Selective elimination of hepatic natural killer T cells with concanavalin A improves liver regeneration in mice.

BACKGROUND: Although concanavalin A (Con A) as a T cell stimulant can cause natural killer T (NKT) cell-mediated liver injury in mice and a nonhepatotoxic dose of Con A can trigger innate immune cells including NKT cells to prevent tumor metastasis in the liver, little is known about the role of Con A-primed NKT cells in liver repair. In this study, we aimed to investigate the effect of pretreatment with a nontoxic dose of Con A on subsequent liver regeneration in mice. METHODS: A nontoxic dose of Con A was injected intravenously 24 h before partial hepatectomy (PHx), which was used as a model of liver regeneration. Ratios of remnant liver mass to body weight, bromodeoxyuridine (BrdU) incorporation and proliferating cell nuclear antigen (PCNA) labeling were used to assess liver regeneration. RESULTS: Hepatic mononuclear cells were isolated and analyzed by flow cytometry. After PHx, the ratios of liver weight to body weight, PCNA-positive hepatocytes and BrdU-positive hepatocytes in Con A-pretreated mice were significantly higher than that of phosphate-buffered saline-treated mice, indicating that Con A pretreatment can accelerate liver regeneration. Flow cytometric analysis showed that NKT cells were significantly activated and selectively eliminated after the Con A administration. Moreover, NKT cells expressed more apoptosis-related molecules, Fas and Annexin V. CONCLUSIONS: Taken together, Con A accelerates liver regeneration in mice by eliminating hepatic NKT cells via activation-induced cell death.     

Proliferation of hepatic lineage cells of normal C57BL and interleukin-6 knockout mice after cocaine-induced periportal injury

The cellular response to periportal liver injury, induced by phenobarbital feeding and cocaine injection, is used to compare the restitutive proliferation of hepatocytes, cholangiocytes, and oval cells in the livers of normal control to those of interleukin-6 (IL-6) knockout mice. After this injury hepatocytes in noninjured middle and central zones start to proliferate first, followed by proliferation of cholangiocytes and intraportal oval cells. Proliferation of all cell types peaks at 2 days, but oval cells continue to proliferate and differentiate through days 4 and 6 as they reconstitute the necrotic zone. By day 10, the injured zone is completely repaired, and no dividing cells remain. During the first 3 to 4 days after injury, the number of proliferating hepatocytes, cholangiocytes, and sinusoidal cells is lower in IL-6 knockout mice than in normal mice, whereas the number of dividing oval cells is higher. However, overall repair of the injury is accomplished in the same time period in both groups. During repair of the periportal zone, oval cells acquire differentiation markers of hepatocytes as they cross the zone of injury. In conclusion, the phenobarbital/cocaine injury model is useful to study restitutive proliferation of mouse liver cell lineages. The proliferative response in IL-6 knockout mice shows that IL-6 is not required for proliferation of liver cells; timely repair of liver injury occurs in both normal and IL-6 knockout mice. Increased proliferation of oval cells in IL-6 knockout mice may compensate for the lower proliferation of other liver cell types.     

Regulation of T cell-mediated hepatic inflammation by adiponectin and leptin

Concanavalin A-induced hepatotoxicity was compared in lipodystrophic aP2-nSREBP-1c transgenic mice (LD mice) lacking adipose tissue, obese leptin-deficient ob/ob mice, and lean wild-type (WT) mice. Serum leptin and adiponectin were low in LD mice, whereas ob/ob mice had undetectable leptin, but high adiponectin. Protection from hepatotoxicity was observed in ob/ob, but not in LD mice, despite low cytokine levels and reduced T cell activation and hepatic natural killer T cells in both groups. Administration of adiponectin protected LD mice from hepatotoxicity without altering cytokine levels. In contrast, administration of leptin heightened disease susceptibility by restoring cytokine production. Neutralization of TNF alpha protected LD mice from liver damage. Increased in vivo susceptibility to the hepatotoxic effect of TNF alpha was observed in LD mice. In vitro, adiponectin protected primary hepatocytes from TNF alpha-induced death, whereas leptin had no protective effect. In conclusion, although leptin increases susceptibility to hepatotoxicity by regulating cytokine production and T cell activation, adiponectin protects hepatocytes from TNF alpha-induced death.     

Melatonin alleviates cadmium‐induced liver injury by inhibiting the TXNIP‐NLRP3 inflammasome

Cadmium (Cd) is a persistent environmental and occupational contaminant that accumulates in the liver and induces oxidative stress and inflammation. Melatonin possesses potent hepatoprotective properties against the development and progression of acute and chronic liver injury. Nevertheless, the molecular mechanism underlying the protective effects of melatonin against Cd‐induced hepatotoxicity remains obscure. In this study, we aimed to investigate the effects of melatonin on Cd‐induced liver inflammation and hepatocyte death. Male C57BL/6 mice were intraperitoneally injected with melatonin (10 mg/kg) once a day for 3 days before exposure to CdCl₂ (2.0 mg/kg). We found that Cd induced hepatocellular damage and inflammatory infiltration as well as increased serum ALT/AST enzymes. In addition, we showed that Cd triggered an inflammatory cell death, which is mediated by the NOD‐like receptor pyrin domain containing 3 (NLRP3) inflammasome. Moreover, melatonin treatment significantly alleviated Cd‐induced liver injury by decreasing serum ALT/AST levels, suppressing pro‐inflammatory cytokine production, inhibiting NLRP3 inflammasome activation, ameliorating oxidative stress, and attenuating hepatocyte death. Most importantly, melatonin markedly abrogated Cd‐induced TXNIP overexpression and decreased the interaction between TXNIP and NLRP3 in vivo and in vitro. However, treatment with siRNA targeting TXNIP blocked the protective effects of melatonin in Cd‐treated primary hepatocytes. Collectively, our results suggest that melatonin confers protection against Cd‐induced liver inflammation and hepatocyte death via inhibition of the TXNIP‐NLRP3 inflammasome pathway.     

Mitochondrial protection by the JNK inhibitor leflunomide rescues mice from acetaminophen-induced liver injury

Acetaminophen (APAP) is a widely used analgesic and antipyretic drug that is safe at therapeutic doses but which can precipitate liver injury at high doses. We have previously found that the antirheumatic drug leflunomide is a potent inhibitor of APAP toxicity in cultured human hepatocytes, protecting them from mitochondria-mediated cell death by inhibiting the mitochondrial permeability transition. The purpose of this study was to explore whether leflunomide protects against APAP hepatotoxicity in vivo and to define the molecular pathways of cytoprotection. Male C57BL/6 mice were treated with a hepatotoxic dose of APAP (750 mg/kg, ip) followed by a single injection of leflunomide (30 mg/kg, ip). Leflunomide (4 hours after APAP dose) afforded significant protection from liver necrosis as assessed by serum ALT activity and histopathology after 8 and 24 hours. The mechanism of protection by leflunomide was not through inhibition of cytochrome P450 (CYP)-catalyzed APAP bioactivation or an apparent suppression of the innate immune system. Instead, leflunomide inhibited APAP-induced activation (phosphorylation) of c-jun NH2-terminal protein kinase (JNK), thus preventing downstream Bcl-2 and Bcl-XL inactivation and protecting from mitochondrial permeabilization and cytochrome c release. Furthermore, leflunomide inhibited the APAP-mediated increased expression of inducible nitric oxide synthase and prevented the formation of peroxynitrite, as judged from the absence of hepatic nitrotyrosine adducts. Even when given 8 hours after APAP dose, leflunomide still protected from massive liver necrosis. Conclusion: Leflunomide afforded protection against APAP-induced hepatotoxicity in mice through inhibition of JNK-mediated activation of mitochondrial permeabilization.     

Effect of Hepatic Stimulator Substance (HSS) on Cadmium-Induced Acute Hepatotoxicity in the Rat Liver

The hepatoprotective effect of HSS against cadmium-induced liver injury was investigated. Rats were intoxicated with a dose of cadmium (3.5 mg/kg b.w.). The rats were treated with normal saline (group I) or HSS (100 mg protein/kg b.w.; group II) 2 hr later and killed at different time points. Hematoxylin-eosin (HE) sections were assessed for necrosis, apoptosis, peliosis, mitoses, and inflammatory infiltration. Serum enzyme activities were assayed. Apoptosis was quantified by the Tunel technique. Thymidine kinase activity and the rate of [3H]thymidine incorporation into DNA were also assayed. Necrosis, hepatocyte apoptosis, and peliosis were minimized in HSS-treated rats (group II). Nonparenchymal cell apoptosis and liver regeneration were not quantitively altered in the HSS-treated group, though the time profile was different. HSS protects hepatocytes against cadmium-induced necrosis, apoptosis, and peliosis. Apoptosis was the major type of cell death for nonparenchymal liver cells and strongly correlated with the extent of peliosis. Interactions between hepatocytes and nonparenchymal liver cells seem to be important for the genesis of hepatic trauma in acute cadmium hepatotoxicity.     

Acute cholestasis following treatment with nimesulide and oral contraception: case report and review

Our case report of acute cholestatic liver injury highlights the potential hepatotoxicity of nimesulide treatment in combination with oral contraception. Rarely occuring histological findings of "pure" cholestasis without any inflammatory or necrotic changes with favourable outcome following ursodeoxycholic acid administration are described. It was not possible to distinguish the separate role of any of these two drugs on hepatotoxicity according to the available information. Based on the known similarities in hepatotoxic profile of nimesulide and oral contraceptives, it can be assumed that their interaction could increase the risk of liver damage, although the precise mechanisms are not ellucidated yet. Nimesulide toxicity however is often reported in cases taking several potentially hepatotoxic drugs. It is therefore prudent to reconsider any concommitant treatment and closely monitor liver function tests in patients requiring nimesulide treatment.     

A novel role of alkaline phosphatase in protection from immunological liver injury in mice

AIMS/BACKGROUND: Little is known about the role of alkaline phosphatase (AP) in liver diseases, except for its elevation in jaundice or cholestasis. Its substrate, endotoxin, is usually elevated in patients as well as animals with liver damage. This study aimed to provide evidence for its new role as protection against immunological liver damage. METHODS: Liver injury was induced in mice by delayed-type hypersensitivity to picryl chloride. AP activity was measured using a commercial kit. RESULTS: In acute liver injury, a significant decrease in AP activity in serum was observed but there was an increase in liver tissue. Single administration of cyclophosphamide before sensitization with picryl chloride exacerbated the liver injury, with more serious AP changes, while consecutive use after the sensitization alleviated the injury with a recovery from the changes. When liver injury proceeded for 1 week, both serum and liver showed decreased AP activity. Lipopolysaccharide facilitated alanine transaminase release from levamisole-pretreated but not non-treated hepatocytes from naive mice. However, the release was confirmed from liver slices of mice with liver injury proceeding for 1 week, even without levamisole pretreatment. CONCLUSION: The development of liver injury may lead to a dysfunction in AP synthesis and release. Levamisole may make normal hepatocytes, like the hepatocytes from liver-injured mice, highly sensitive to lipopolysaccharide through inhibiting AP synthesis. The findings obtained in this study suggest that AP may contribute to protection from injury by a mechanism involving neutralization of endotoxin.     

Protection against acetaminophen-induced liver injury and lethality by interleukin 10: role of inducible nitric oxide synthase

Mechanistic study of idiosyncratic drug-induced hepatitis (DIH) continues to be a challenging problem because of the lack of animal models. The inability to produce this type of hepatotoxicity in animals, and its relative rarity in humans, may be linked to the production of anti-inflammatory factors that prevent drug-protein adducts from causing liver injury by immune and nonimmune mechanisms. We tested this hypothesis by using a model of acetaminophen (APAP)-induced liver injury in mice. After APAP treatment, a significant increase was observed in serum levels of interleukin (IL)-4, IL-10, and IL-13, cytokines that regulate inflammatory mediator production and cell-mediated autoimmunity. When IL-10 knockout (KO) mice were treated with APAP, most of these mice died within 24 to 48 hours from liver injury. This increased susceptibility to APAP-induced liver injury appeared to correlate with an elevated expression of liver proinflammatory cytokines, tumor necrosis factor (TNF)-alpha, and IL-1, as well as inducible nitric oxide synthase (iNOS). In this regard, mice lacking both IL-10 and iNOS genes were protected from APAP-induced liver injury and lethality when compared with IL-10 KO mice. All strains, including wild-type animals, generated similar amounts of liver APAP-protein adducts, indicating that the increased susceptibility of IL-10 KO mice to APAP hepatotoxicity was not caused by an enhanced formation of APAP-protein adducts. In conclusion, these findings suggest that an important feature of the normal response to drug-induced liver injury may be the increased expression of anti-inflammatory factors such as IL-10. Certain polymorphisms of these factors may have a role in determining the susceptibility of individuals to idiosyncratic DIH.     

Taurochenodeoxycholic acid induced biphasic hepatotoxicity in isolated perfused rat liver: roles of Ca2+ and calpain

BACKGROUND/AIMS: We examined taurochenodeoxycholic acid-induced hepatotoxicity with reference to Ca2+ and calpain involvement, intracellular bile acid content, and zone specificity in isolated perfused rat liver. METHODOLOGY: Taurochenodeoxycholic acid or chenodeoxycholic acid was infused into the portal vein and lactate dehydrogenase release, a marker of hepatocyte injury, in the effluent and bile acid output were measured in the presence and absence of either nickel, a membranous Ca2+ channel blocker, or calpain inhibitor in isolated perfused rat liver. RESULTS: Taurochenodeoxycholic acid induced a significant and transient increase (first peak; 4 min) and subsequent time- and dose-dependent elevation in lactate dehydrogenase release which was proportional to accumulated bile acids in the liver. Although the first peak was significantly suppressed by pretreatment with nickel, the subsequent release was not reduced. Lactate dehydrogenase release at 15, 20, and 25 min was significantly suppressed by the calpain inhibitor. Numbers of damaged hepatocytes stained with trypan blue were significantly increased in the periportal region (zone 1) compared with the pericentral region (zone 3) and these cells were consistently stained with anti-calpain antibody. CONCLUSIONS: Taurochenodeoxycholic acid causes both transient damage and subsequent increasing hepatotoxicity which are respectively dependent on Ca2+ influx via membranous Ca2+ channels and calpain, with the periportal region being more susceptible.