Acetaminophen hepatotoxicity and HIF-1α induction in acetaminophen toxicity in mice occurs without hypoxia

LDH and the MELD-LDH in Severe Acute Liver Injury and Acute Liver Failure: Preliminary Confirmation of a Novel Prognostic Score for Risk Stratification

BACKGROUND

Acute liver failure (ALF) is a devastating condition with high mortality. Currently, liver transplantation is the only life-saving treatment, but the decision to transplant is difficult due to the rapid progression of ALF and persistent shortage of donor organs. Biomarkers that predict death better than current prognostics could help. To our surprise, proteomics recently revealed that lactate dehydrogenase (LDH) is prognostic in ALF by itself and in a novel form of the model for end-stage liver disease (MELD) score called the MELD-LDH. The purpose of this study was to confirm our proteomics results in a larger population.

METHODS

We reviewed laboratory data from 238 patients admitted to the University of Arkansas for Medical Sciences Medical Center with a diagnosis of ALF and biochemical evidence of acute liver failure over a 12-year period, as well as subset of 170 patients with encephalopathy.

RESULTS

LDH was strikingly elevated in the nonsurvivors at the time of peak injury. Receiver operating characteristic (ROC) curve analyses revealed that LDH by itself could discriminate between survivors and nonsurvivors on the first day of hospitalization, although not as well as the MELD and MELD-LDH scores that performed alike. Importantly, however, LDH by itself performed similarly to the MELD at the time of peak injury and the MELD-LDH score moderately outperformed both. The MELD-LDH score also had greater sensitivity and negative predictive value than the MELD and the King's College Criteria.

CONCLUSIONS

The results support our prior finding that LDH and the MELD-LDH score predict death and therefore transplant need in ALF patients.

Hepatoprotective effect of β-myrcene pretreatment against acetaminophen-induced liver injury

Objective

In the present study, the hepatoprotective effects of β-myrcene (MYR) on acetaminophen-induced hepatotoxicity were investigated.

Materials and Methods

A total of 40 Balb/c mice were randomly divided into five groups as follows: 1) Normal control group which received only carboxymethylcellulose (CMC), the vehicle used to dissolve acetaminophen (N-acetyl-p-aminophenol, APAP, paracetamol) and MYR; 2) APAP group which received a single dose of acetaminophen (250 mg/kg) orally on day 7; 3) Silymarin group which received 200 mg/kg/day of silymarin; and 4 and 5) pretreatment groups in which, mice were treated with 100 or 200 mg/kg/day of MYR. Liver and blood samples were collected to analyze serum aminotransferases, inflammatory response, oxidative stress markers, and histopathological insults.

Results

Our results showed that MYR pretreatment attenuated liver damage and restored liver cells function and integrity as it decreased the leakage of serum aminotransferases (alanine and aspartate aminotransferases (ALT and AST, respectively)) into the blood (p<0.01). MYR treatment also reduced levels of myeloperoxidase (MPO) activity and nitric oxide (NO) (p<0.001). In addition, MYR pretreatment demonstrated significant antioxidant activity by decreasing malondialdehyde (MDA), reactive oxygen species (ROS), and reduced glutathione (GSH) levels (p<0.001). Furthermore, it restored the hepatic level of superoxide dismutase (SOD), catalase (CAT), and oxidized glutathione (GSSG) (p<0.001).

Conclusion

For the first time, our results showed that MYR treatment significantly improved liver function by reducing oxidative stress and the inflammatory response induced by APAP.

microRNA-21, via the HIF-1α/VEGF signaling pathway, is involved in arsenite-induced hepatic fibrosis through aberrant cross-talk of hepatocytes and hepatic stellate cells

Long-term exposure to arsenic, a widely distributed environmental toxicant, may result in damage to various organs, including the liver. Mice exposed chronically to arsenite developed hepatic damage, inflammation, and fibrosis, as well as increased levels of microRNA-21 (miR-21) and hypoxia-inducible factor (HIF)-1α. The levels of miR-21 and HIF-1α were also enhanced in primary hepatocytes and L-02 cells exposed to arsenite. The culture media from these cells induced the activation of hepatic stellate cells (HSCs), as demonstrated by up-regulation of the protein levels of α-smooth muscle actin (α-SMA) and collagen1A2 (COL1A2) and by increased activity in gel contractility assays. For L-02 cells, knockdown of miR-21 blocked the arsenite-induced up-regulation of HIF-1α and vascular endothelial growth factor (VEGF), which prevented the activation of LX-2 cells induced by medium from arsenite-exposed L-02 cells. However, these effects were reversed by down-regulation of von Hippel Lindau protein (pVHL). In arsenite-treated L-02 cells, miR-21 knockdown elevated the levels of ubiquitination and accelerated the degradation of HIF-1α via pVHL. In the livers of miR-21^-/- mice exposed chronically to arsenite, there were less hepatic damage, lower fibrosis, lower levels of HIF-1α and VEGF, and higher levels of pVHL than for wild-type mice. In summary, we propose that miR-21, acting via the HIF-1α/VEGF signaling pathway, is involved in arsenite-induced hepatic fibrosis through mediating aberrant cross-talk of hepatocytes and HSCs. The findings provide evidence relating to the pathogenesis of hepatic fibrosis induced by exposure to arsenic.

Insights into the modulatory role of cyclosporine A and its research advances in acute inflammation

Cyclosporine A(CsA), a classic immunosuppressant, is mainly applied for solid organ transplantation and some autoimmune diseases by suppressing T lymphocytes. Early studies showed that the application of CsA is primarily focused on chronic but not acute inflammation, nevertheless, increasing evidence supporting a role for CsA in acute inflammation, although most of proofs come from experimental models. It has long been known to us that the nuclear factor of activated T cells (NFAT) is the target of CsA to regulate T lymphocytes. However, NFAT also contributes to the regulation of innate immune cells, thus, CsA can not only target lymphocytes but also innate immune cells such as monocytes/macrophages, dendritic cells and neutrophils, which provides a basis for CsA to act on acute inflammation. Moreover, some other pathophysiological events in acute inflammation such as decreased vascular activity, mitochondrial dysfunction and endogenous cell apoptosis can also be alleviated by CsA. There being a moderate successes in the application of CsA for experimental acute inflammation such as sepsis, trauma/hemorrhagic shock and ischemic/reperfusion injury, yet data of the clinical treatment is not clear. In this review, we will critically analyze the existing hypotheses, summarize the application of CsA and its possible mechanisms in various acute inflammation over the past few decades, hope to provide some clues for the clinical treatment of acute inflammation.

Hypoxia upregulates Cxcl12 in hepatocytes by a complex mechanism involving hypoxia-inducible factors and transforming growth factor-β

INTRODUCTION

Cxcl12, or stromal-derived factor-1, is a chemokine produced by several hepatic cell types, including hepatocytes, after liver injury and surgical resection. Studies have revealed that Cxcl12 is important for regeneration of the liver after surgical resection and for development of liver fibrosis during chronic liver injury. While the function of Cxcl12 in the liver is well established, the mechanism by which Cxcl12 is upregulated is not fully understood. Because regions of hypoxia develop in the liver following injury, we tested the hypothesis that hypoxia upregulates Cxcl12 in hepatocytes by a hypoxia-inducible factor (HIF)-dependent mechanism.

METHODS

To test this hypothesis, primary mouse hepatocytes were isolated from the livers of HIF-1α-deficient mice or HIF-1β-deficient mice and exposed to 1% oxygen. Cxcl12 expression was increased following exposure of primary mouse hepatocytes to 1% oxygen. Previously we have shown, that in addition to HIFs, transforming growth factor-β is required for upregulation of a subset of genes in hypoxic hepatocytes. To examine the role of TGF-β in regulation of Cxcl12 during hypoxia, hepatocytes were pretreated with the TGF-β receptor I inhibitor, SB431542.

RESULTS

Upregulation of Cxcl12 by hypoxia was partially prevented in hepatocytes from HIF-1α-deficient mice and completely prevented in hepatocytes from HIF-1β-deficient hepatocytes. This suggests that under hypoxic conditions, both HIF-1α and HIF-2α regulate Cxcl12 in hepatocytes. Pretreatment of hepatocytes with SB431542 completely prevented upregulation Cxcl12 by hypoxia. Further, treatment of hepatocytes with recombinant TGF-β1 upregulated Cxcl12 in hepatocytes cultured in room air.

CONCLUSION

Collectively, these studies demonstrate that hypoxia upregulates Cxcl12 in primary mouse hepatocytes by a mechanism that involves HIFs and TGF-β.

Probiotic Bacillus Spores Protect Against Acetaminophen Induced Acute Liver Injury in Rats

Acetaminophen (APAP) is one of the most used analgesics and antipyretic agents in the world. Intoxication with APAP is the main cause of acute liver toxicity in both the US and Europe. Spore-forming probiotic bacteria have the ability to resist harsh gastric and intestinal conditions. The aim of this study was to investigate the possible protective effect of Bacillus (B) species (sp) spores (B. licheniformis, B. indicus, B. subtilis, B. clausii, B. coagulans) against hepatotoxicity induced by APAP in rats. A total of 35 rats were randomly divided into seven groups: group I served as control; group II received silymarin; group III received MegaSporeBiotic^TM (MSB); group IV received APAP and served as the model of hepatotoxicity; group V received APAP and silymarin; group VI received APAP and MSB; group VII received APAP, silymarin and MSB. The livers for histopathological examination and blood samples were collected on the last day of the experiment. We determined aspartate aminotransferase (AST), alanine aminotransferase (ALT) and total antioxidant capacity (TAC) levels and zonula occludens (ZO-1), tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β) expression. APAP overdose increased AST and ALT. It slowly decreased TAC compared to the control group, but pretreatment with silymarin and MSB increased TAC levels. Elevated plasma concentrations were identified for ZO-1 in groups treated with APAP overdose compared with those without APAP or receiving APAP in combination with silymarin, MSB or both. The changes were positively correlated with the levels of other proinflammatory cytokines (TNF-α, IL-1β). In addition, histopathological hepatic injury was improved by preadministration of MSB or silymarin versus the disease model group. Bacillus sp spores had a protective effect on acute hepatic injury induced by APAP. Pretreatment with MSB resulted in a significant reduction in serum AST, ALT, TNF-α, IL-1β, ZO-1, TAC and also hepatocyte necrosis, similar to the well-known hepatoprotective agent—silymarin.

Hepatic hypoxia-inducible factors inhibit PPARα expression to exacerbate acetaminophen induced oxidative stress and hepatotoxicity

Oxidative stress has a critical role in the pathogenesis of acetaminophen (APAP) induced hepatocellular necrosis, and the identification of novel approaches to attenuate oxidative stress is essential to prevent/revert the disease. This study investigated the role of both HIF-1 and HIF-2 in the pathogenesis of APAP-induced oxidative stress, as well as the underlying mechanisms. In the present study, we initially found that knockout of HIF-1α or HIF-2α reduced APAP toxicity, and double knockout afforded the best protection. APAP treatment led to stabilization of both HIF-1α and HIF-2α in mouse livers. Moreover, the protective effects of HIF deficiency were related to the attenuated oxidative stress. Further experiments proved that PPARα, a master regulator in cellular metabolism accounted for the HIF deficiency-caused protective impact on APAP toxicity. Inactivation of HIFs promoted the expression of peroxisome proliferator-activated receptor α (PPARα) in the liver, which in turn activated nuclear factor erythroid 2-related factor 2 (Nrf2). Knockdown of PPARα or Nrf2 negated the hepatoprotection afforded by HIF deficiency. At last，examination of the PPARα promoter identified a HIF-binding site and HIF-dependent repression of PPARα in hepatocytes by luciferase reporter and EMSA study. Taken together， Our results demonstrate that HIFs are key suppressors of PPARα in the liver, thereby compromising the adaptive defense mechanisms against oxidative stress when confronted with APAP. These findings are important to the etiology and therapeutics of APAP hepatotoxicity. The functional link between HIFs and PPARα may have more implications in liver physiology and other pathologic conditions than APAP injury.

Trifluoperazine inhibits acetaminophen-induced hepatotoxicity and hepatic reactive nitrogen formation in mice and in freshly isolated hepatocytes

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Increased reactive nitrogen and oxygen species formation leads to APAP hepatoxicity.

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TFP is known to block nNOS both in vivo as well as in vitro.

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The nNOS inhibitor TFP blocks toxicity and the increased RNS/ROS formation.

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Toxicity occurs with increased 3- nitro tyrosine both in vivo as well as in vitro.

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NNOS inhibition by TFP leads to decreasing 3-nitro tyrosine in vivo as well as in vitro.

The hepatotoxicity of acetaminophen (APAP) occurs by initial metabolism to N-acetyl-p-benzoquinone imine which depletes GSH and forms APAP-protein adducts. Subsequently, the reactive nitrogen species peroxynitrite is formed from nitric oxide (NO) and superoxide leading to 3-nitrotyrosine in proteins. Toxicity occurs with inhibited mitochondrial function. We previously reported that in hepatocytes the nNOS (NOS1) inhibitor NANT inhibited APAP toxicity, reactive nitrogen and oxygen species formation, and mitochondrial dysfunction. In this work we examined the effect of trifluoperazine (TFP), a calmodulin antagonist that inhibits calcium induced nNOS activation, on APAP hepatotoxicity and reactive nitrogen formation in murine hepatocytes and in vivo. In freshly isolated hepatocytes TFP inhibited APAP induced toxicity, reactive nitrogen formation (NO, GSNO, and 3-nitrotyrosine in protein), reactive oxygen formation (superoxide), loss of mitochondrial membrane potential, decreased ATP production, decreased oxygen consumption rate, and increased NADH accumulation. TFP did not alter APAP induced GSH depletion in the hepatocytes or the formation of APAP protein adducts which indicated that reactive metabolite formation was not inhibited. Since we previously reported that TFP inhibits the hepatotoxicity of APAP in mice without altering hepatic APAP-protein adduct formation, we examined the APAP treated mouse livers for evidence of reactive nitrogen formation. 3-Nitrotyrosine in hepatic proteins and GSNO were significantly increased in APAP treated mouse livers and decreased in the livers of mice treated with APAP plus TFP. These data are consistent with a hypothesis that APAP hepatotoxicity occurs with altered calcium metabolism, activation of nNOS leading to increased reactive nitrogen formation, and mitochondrial dysfunction.

Role of Hypoxia-Inducible Factors in the Development of Liver Fibrosis

Liver fibrosis remains a significant clinical problem in the United States and throughout the world. Although important advances in the understanding of this disease have been made, no effective pharmacologic agents have been developed that directly prevent or reverse the fibrotic process. Many of the successes in liver fibrosis treatment have been targeted toward treating the cause of fibrosis, such as the development of new antivirals that eradicate hepatitis virus. For many patients, however, this is not feasible, so a liver transplant remains the only viable option. Thus, there is a critical need to identify new therapeutic targets that will slow or reverse the progression of fibrosis in such patients. Research over the last 16 years has identified hypoxia-inducible factors (HIFs) as key transcription factors that drive many aspects of liver fibrosis, making them potential targets of therapy. In this review, we discuss the latest work on HIFs and liver fibrosis, including the cell-specific functions of these transcription factors in the development of liver fibrosis.

Comparison of Bile Acids and Acetaminophen Protein Adducts in Children and Adolescents with Acetaminophen Toxicity

Metabolomics approaches have enabled the study of new mechanisms of liver injury in experimental models of drug toxicity. Disruption of bile acid homeostasis is a known mechanism of drug induced liver injury. The relationship of individual bile acids to indicators of oxidative drug metabolism (acetaminophen protein adducts) and liver injury was examined in children with acetaminophen overdose, hospitalized children with low dose exposure to acetaminophen, and children with no recent exposure to acetaminophen. Nine bile acids were quantified through targeted metabolomic analysis in the serum samples of the three groups. Bile acids were compared to serum levels of acetaminophen protein adducts and alanine aminotransferase. Glycodeoxycholic acid, taurodeoxycholic acid, and glycochenodeoxycholic acid were significantly increased in children with acetaminophen overdose compared to healthy controls. Among patients with acetaminophen overdose, bile acids were higher in subjects with acetaminophen protein adduct values > 1.0 nmol/mL and modest correlations were noted for three bile acids and acetaminophen protein adducts as follows: taurodeoxycholic acid (R=0.604; p<0.001), glycodeoxycholic acid (R=0.581; p<0.001), and glycochenodeoxycholic acid (R=0.571; p<0.001). Variability in bile acids was greater among hospitalized children receiving low doses of acetaminophen than in healthy children with no recent acetaminophen exposure. Compared to bile acids, acetaminophen protein adducts more accurately discriminated among children with acetaminophen overdose, children with low dose exposure to acetaminophen, and healthy control subjects. In children with acetaminophen overdose, elevations of conjugated bile acids were associated with specific indicators of acetaminophen metabolism and non-specific indicators of liver injury.

Intrahepatic microcirculatory disorder, parenchymal hypoxia and NOX4 upregulation result in zonal differences in hepatocyte apoptosis following lipopolysaccharide- and D-galactosamine-induced acute liver failure in rats

Although the mechanisms responsible for acute liver failure (ALF) have not yet been fully elucidated, studies have indicated that intrahepatic macrophage activation plays an important role in the pathogenesis of ALF through intrahepatic microcirculatory disorder and consequent parenchymal cell death. Intrahepatic microcirculatory disorder has been demonstrated in animal models using intravital microscopy; however, the limitations of this method include simultaneously evaluating blood flow and the surrounding pathological changes. Therefore, in this study, we devised a novel method involving tetramethylrhodamine isothiocyanate (TRITC)-dextran administration for the pathological assessment of hepatic microcirculation. In addition, we aimed to elucidate the mechanisms through which intrahepatic microcirculatory disorder progresses with relation to activated macrophages. ALF was induced in Wistar rats by exposure to lipopolysaccharide and D-galactosamine. Intrahepatic microcirculation and microcirculatory disorder in zone 3 (pericentral zone) of the livers of rats with ALF was observed. Immunohistochemical examinations in conjunction with TRITC-dextran images revealed that the macrophages were mainly distributed in zone 2 (intermediate zone), while cleaved caspase-3-positive hepatocytes, pimonidazole and hypoxia-inducible factor 1-α were abundant in zone 3. We also found that 4-hydroxy-2-nonenal and nicotinamide adenine dinucleotide phosphate oxidase (NOX)4-positive cells were predominantly located in the zone 3 parenchyma. The majority of apoptotic hepatocytes in zone 3 were co-localized with NOX4. Our results revealed that the apoptotic cells in zone 3 were a result of hypoxic conditions induced by intrahepatic microcirculatory disorder, and were not induced by activated macrophages. The increased levels of oxidative stress in zone 3 may contribute to the progression of hepatocyte apoptosis.

Acylcarnitine profiles in acetaminophen toxicity in the mouse: comparison to toxicity, metabolism and hepatocyte regeneration

High doses of acetaminophen (APAP) result in hepatotoxicity that involves metabolic activation of the parent compound, covalent binding of the reactive intermediate N-acetyl-p-benzoquinone imine (NAPQI) to liver proteins, and depletion of hepatic glutathione. Impaired fatty acid β-oxidation has been implicated in previous studies of APAP-induced hepatotoxicity. To better understand relationships between toxicity and fatty acid β-oxidation in the liver in APAP toxicity, metabolomic assays for long chain acylcarnitines were examined in relationship to established markers of liver toxicity, oxidative metabolism, and liver regeneration in a time course study in mice. Male B6C3F1 mice were treated with APAP (200 mg/kg IP) or saline and sacrificed at 1, 2, 4, 8, 24 or 48 h after APAP. At 1 h, hepatic glutathione was depleted and APAP protein adducts were markedly increased. Alanine aminotransferase (ALT) levels were elevated at 4 and 8 h, while proliferating cell nuclear antigen (PCNA) expression, indicative of hepatocyte regeneration, was apparent at 24 h and 48 h. Elevations of palmitoyl, oleoyl and myristoyl carnitine were apparent by 2–4 h, concurrent with the onset of Oil Red O staining in liver sections. By 8 h, acylcarnitine levels were below baseline levels and remained low at 24 and 48 h. A partial least squares (PLS) model suggested a direct association of acylcarnitine accumulation in serum to APAP protein adduct and hepatic glutathione levels in mice. Overall, the kinetics of serum acylcarnitines in APAP toxicity in mice followed a biphasic pattern involving early elevation after the metabolism phases of toxicity and later depletion of acylcarnitines.

Expression of microRNA-150 targeting vascular endothelial growth factor-A is downregulated under hypoxia during liver regeneration

Vascular endothelial growth factor (VEGF) is a factor that stimulates the proliferation of sinusoidal endothelial cells and hepatocytes during liver regeneration (LR). The present study aimed to screen and validate a microRNA (miRNA) that targets VEGF-A with relative specificity and to elucidate the potential association between hypoxia-inducible factor-1α (HIF‑1α) and miRNA expression in the early phase of LR. Changes in the expression of miRNAs, which were predicted to target VEGF-A using online databases, were detected at 12, 24 and 48 h following a 70% partial hepatectomy (PHx) using quantitative PCR (qPCR). An inhibitor of the most downregulated miRNA was transfected into the primary hepatocytes in order to observe changes in the expression of the VEGF-A gene. The expression of HIF-1α protein in the regenerating liver was investigated using western blot analysis. The expression levels of HIF-1α mRNA (messenger RNA), the selected miRNA and VEGF-A mRNA in an anoxic model of hepatocytes was examined with qPCR. Of seven putative miRNAs, the expression of miR-150 exhibited the sharpest downregulation from 12-48 h. The micrOFF™ miR-150 inhibitor significantly elevated the expression levels of VEGF-A mRNA and protein 48 h after transfection. Thus, VEGF-A may be a downstream target of miR-150 during LR. Furthermore, HIF-1α protein expression increased to its highest level 24 h following PHx. miR-150 expression was inhibited and the expression of VEGF-A mRNA increased accordingly in the hypoxia-induced hepatocytes. Our results suggest that miR-150 expression is subject to negative regulation by HIF-1α.

Effect of trifluoperazine on toxicity, HIF-1α induction and hepatocyte regeneration in acetaminophen toxicity in mice

Oxidative stress and mitochondrial permeability transition (MPT) are important mechanisms in acetaminophen (APAP) toxicity. The MPT inhibitor trifluoperazine (TFP) reduced MPT, oxidative stress, and toxicity in freshly isolated hepatocytes treated with APAP. Since hypoxia inducible factor-one alpha (HIF-1α) is induced very early in APAP toxicity, a role for oxidative stress in the induction has been postulated. In the present study, the effect of TFP on toxicity and HIF-1α induction in B6C3F1 male mice treated with APAP was examined. Mice received TFP (10mg/kg, oral gavage) prior to APAP (200mg/kg IP) and at 7 and 36h after APAP. Measures of metabolism (hepatic glutathione and APAP protein adducts) were comparable in the two groups of mice. Toxicity was decreased in the APAP/TFP mice at 2, 4, and 8h, compared to the APAP mice. At 24 and 48h, there were no significant differences in toxicity between the two groups. TFP lowered HIF-1α induction but also reduced the expression of proliferating cell nuclear antigen, a marker of hepatocyte regeneration. TFP can also inhibit phospholipase A(2), and cytosolic and secretory PLA(2) activity levels were reduced in the APAP/TFP mice compared to the APAP mice. TFP also lowered prostaglandin E(2) expression, a known mechanism of cytoprotection. In summary, the MPT inhibitor TFP delayed the onset of toxicity and lowered HIF-1α induction in APAP treated mice. TFP also reduced PGE(2) expression and hepatocyte regeneration, likely through a mechanism involving PLA(2).

Acute acetaminophen intoxication leads to hepatic iron loading by decreased hepcidin synthesis

Acetaminophen (APAP), a major cause of acute liver injury in the Western world, is mediated by metabolism and oxidative stress. Recent studies have suggested a role for iron in potentiating APAP-induced liver injury although its regulatory mechanism is not completely understood. The current study was designed to unravel the iron-regulating pathways in mice after APAP-induced hepatotoxicity. Mice with severe injury showed a significant increase in liver iron concentration and oxidative stress. Concurrently, the plasma concentration of hepcidin, the key regulator in iron metabolism, and hepatic hepcidin antimicrobial peptide (Hamp) mRNA expression levels were significantly reduced. We showed that hepcidin transcription was inhibited via several hepcidin-regulating factors, including the bone morphogenetic protein/small mother against decapentaplegic (BMP/SMAD) pathway, CCAAT/enhancer-binding protein α (C/EBPα), and possibly also via erythropoietin (EPO). Downregulation of the BMP/SMAD signaling pathway was most likely caused by hypoxia-inducible factor 1α (HIF-1α), which was increased in mice with severe APAP-induced liver injury. HIF-1α stimulates cleaving of hemojuvelin, the cofactor of the BMP receptor, thereby blocking BMP-induced signaling. In addition, gene expression levels of C/ebpα were significantly reduced, and Epo mRNA expression levels were significantly increased after APAP intoxication. These factors are regulated through HIF-1α during oxidative stress and suggest that HIF-1α is a key modulator in reduced hepcidin transcription after APAP-induced hepatotoxicity. In conclusion, acute APAP-induced liver injury leads to activation of HIF-1α, which results in a downregulation in hepcidin expression through a BMP/SMAD signaling pathway and through C/EBPα inhibition. Eventually, this leads to hepatic iron loading associated with APAP cytotoxicity.

Advanced molecular biologic techniques in toxicologic disease

The advancement of molecular biologic techniques and their capabilities to answer questions pertaining to mechanisms of pathophysiologic events have greatly expanded over the past few years. In particular, these opportunities have provided researchers and clinicians alike the framework from with which to answer clinical questions not amenable for elucidation using previous, more antiquated methods. Utilizing extremely small molecules, namely microRNA, DNA, protein, and nanoparticles, we discuss the background and utility of these approaches to the progressive, practicing physician. Finally, we consider the application of these tools employed as future bedside point of care tests, aiding in the ultimate goal of unsurpassed patient care.

Correlation of MRI findings to histology of acetaminophen toxicity in the mouse

Acetaminophen (APAP) toxicity is responsible for approximately half of all cases of acute liver failure in the United States. The mouse model of APAP toxicity is widely used to examine mechanisms of APAP toxicity. Noninvasive approaches would allow for serial measurements in a single animal to study the effects of experimental interventions on the development and resolution of hepatocellular necrosis. The following study examined the time course of hepatic necrosis using small animal magnetic resonance imaging (MRI) following the administration of 200 mg/kg ip APAP given to B6C3F1 male mice. Mice treated with saline served as controls (CON). Other mice received treatment with the clinical antidote N-acetylcysteine (APAP+NAC). Mouse liver pathology was characterized using T1- and T2-weighted sequences at 2, 4, 8 and 24 h following APAP administration. Standard assays for APAP toxicity [serum alanine aminotransaminase (ALT) levels and hematoxylin and eosin (H&E) staining of liver sections] were examined relative to MRI findings. Overall, T2 sequences had a greater sensitivity for necrosis and hemorrhage than T1 (FLASH) images. Liver injury severity scoring of MR images demonstrated increased scores in the APAP mice at 4, 8 and 24 h compared to the CON mice. APAP+NAC mice had MRI scores similar to the CON mice. Semiquantitative analysis of hepatic hemorrhage strongly correlated with serum ALT. Small animal MRI can be used to monitor the evolution of APAP toxicity over time and to evaluate the response to therapy.

Echinomycin decreases induction of vascular endothelial growth factor and hepatocyte regeneration in acetaminophen toxicity in mice

Up-regulation of vascular endothelial growth factor (VEGF) is important to hepatocyte regeneration in the late stages of acetaminophen (APAP) toxicity in the mouse. This study was conducted to examine the relationship of hypoxia-inducible factor 1α (HIF-1α) to VEGF and hepatocyte regeneration in APAP toxicity using an inhibitor of HIF-1α DNA-binding activity, echinomycin (EC). B6C3F1 male mice were treated with APAP (200 mg/kg IP), followed by EC (0.15 mg IP) and killed at 4 hr. Serum alanine aminotransferase (ALT), necrosis, hepatic glutathione (GSH) and APAP protein adducts were comparable in the APAP/EC and the APAP/veh mice at 4 hr. Additional studies showed that high dose EC (0.3 mg) reduced hepatic VEGF but also lowered hepatic GSH. Subsequent studies were performed using the 0.15-mg dose of EC. Although EC 0.15 mg had no effect on hepatic VEGF levels at 8 hr, by 24 hr VEGF levels were decreased by 40%. Toxicity (ALT and histopathology) was comparable in the APAP and APAP/EC groups at 24 and 48 hr. Proliferating cell nuclear antigen expression was reduced by both Western blot analysis and immunohistochemical staining in the APAP/EC mice at 48 hr. The data support the hypothesis that induction of HIF-1α, its binding to DNA and subsequent expression of VEGF are important factors in hepatocyte regeneration in APAP toxicity in the mouse.

Identification of flame retardants in polyurethane foam collected from baby products

With the phase-out of PentaBDE in 2004, alternative flame retardants are being used in polyurethane foam to meet flammability standards. However, insufficient information is available on the identity of the flame retardants currently in use. Baby products containing polyurethane foam must meet California state furniture flammability standards, which likely affects the use of flame retardants in baby products throughout the U.S. However, it is unclear which products contain flame retardants and at what concentrations. In this study we surveyed baby products containing polyurethane foam to investigate how often flame retardants were used in these products. Information on when the products were purchased and whether they contained a label indicating that the product meets requirements for a California flammability standard were recorded. When possible, we identified the flame retardants being used and their concentrations in the foam. Foam samples collected from 101 commonly used baby products were analyzed. Eighty samples contained an identifiable flame retardant additive, and all but one of these was either chlorinated or brominated. The most common flame retardant detected was tris(1,3-dichloroisopropyl) phosphate (TDCPP; detection frequency 36%), followed by components typically found in the Firemaster550 commercial mixture (detection frequency 17%). Five samples contained PBDE congeners commonly associated with PentaBDE, suggesting products with PentaBDE are still in-use. Two chlorinated organophosphate flame retardants (OPFRs) not previously documented in the environment were also identified, one of which is commercially sold as V6 (detection frequency 15%) and contains tris(2-chloroethyl) phosphate (TCEP) as an impurity. As an addition to this study, we used a portable X-ray fluorescence (XRF) analyzer to estimate the bromine and chlorine content of the foam and investigate whether XRF is a useful method for predicting the presence of halogenated flame retardant additives in these products. A significant correlation was observed for bromine; however, there was no significant relationship observed for chlorine. To the authors knowledge, this is the first study to report on flame retardants in baby products. In addition, we have identified two chlorinated OPFRs not previously documented in the environment or in consumer products. Based on exposure estimates conducted by the Consumer Product Safety Commission (CPSC), we predict that infants may receive greater exposure to TDCPP from these products compared to the average child or adult from upholstered furniture, all of which are higher than acceptable daily intake levels of TDCPP set by the CPSC. Future studies are therefore warranted to specifically measure infants exposure to these flame retardants from intimate contact with these products and to determine if there are any associated health concerns.

The role of hypoxia-inducible factor-1α in acetaminophen hepatotoxicity

Hypoxia-inducible factor-1α (HIF-1α) is a critical transcription factor that controls oxygen homeostasis in response to hypoxia, inflammation, and oxidative stress. HIF has been implicated in the pathogenesis of liver injury in which these events play a role, including acetaminophen (APAP) overdose, which is the leading cause of acute liver failure in the United States. APAP overdose has been reported to activate HIF-1α in mouse livers and isolated hepatocytes downstream of oxidative stress. HIF-1α signaling controls many factors that contribute to APAP hepatotoxicity, including mitochondrial cell death, inflammation, and hemostasis. Therefore, we tested the hypothesis that HIF-1α contributes to APAP hepatotoxicity. Conditional HIF-1α deletion was generated in mice using an inducible Cre-lox system. Control (HIF-1α-sufficient) mice developed severe liver injury 6 and 24 h after APAP overdose (400 mg/kg). HIF-1α-deficient mice were protected from APAP hepatotoxicity at 6 h, but developed severe liver injury by 24 h, suggesting that HIF-1α is involved in the early stage of APAP toxicity. In further studies, HIF-1α-deficient mice had attenuated thrombin generation and reduced plasminogen activator inhibitor-1 production compared with control mice, indicating that HIF-1α signaling contributes to hemostasis in APAP hepatotoxicity. Finally, HIF-1α-deficient animals had decreased hepatic neutrophil accumulation and plasma concentrations of interleukin-6, keratinocyte chemoattractant, and regulated upon activation normal T cell expressed and secreted compared with control mice, suggesting an altered inflammatory response. HIF-1α contributes to hemostasis, sterile inflammation, and early hepatocellular necrosis during the pathogenesis of APAP toxicity.