Synergistic hepatotoxicity from coexposure to bacterial endotoxin and the pyrrolizidine alkaloid monocrotaline

Diagnosis, toxicological mechanism, and detoxification for hepatotoxicity induced by pyrrolizidine alkaloids from herbal medicines or other plants

Pyrrolizidine alkaloids (PAs) are one type of phytotoxins distributed in various plants, including many medicinal herbs. Many organs might suffer injuries from the intake of PAs, and the liver is the most susceptible one. The diagnosis, toxicological mechanism, and detoxification of PAs-induced hepatotoxicity have been studied for several decades, which is of great significance for its prevention, diagnosis, and therapy. When the liver was exposed to PAs, liver sinusoidal endothelial cells (LSECs) loss, hemorrhage, liver parenchymal cells death, nodular regeneration, Kupffer cells activation, and fibrogenesis occurred. These pathological changes classified the PAs-induced liver injury as acute, sub-acute, and chronic type. PAs metabolic activation, mitochondria injury, glutathione (GSH) depletion, inflammation, and LSECs damage-induced activation of the coagulation system were well recognized to play critical roles in the pathological process of PAs-induced hepatotoxicity. A lot of natural compounds like glycyrrhizic acid, (-)-epicatechin, quercetin, baicalein, chlorogenic acid, and so on were demonstrated to be effective in alleviating PAs-induced liver injury, which rendered them huge potential to be developed into therapeutic drugs for PAs poisoning in clinics. This review presents updated information about the diagnosis, toxicological mechanism, and detoxification studies on PAs-induced hepatotoxicity.

The effect of lipopolysaccharide on liver homeostasis and diseases based on the mutual interaction of macrophages, autophagy, and damage-associated molecular patterns in male F344/DuCrlCrlj rats

Lipopolysaccharide (LPS) has dose-dependent biphasic functions (cell protective versus cell toxic). To clarify the different effects of LPS on liver homeostasis or liver diseases, comparisons were made between low and high doses of LPS, in terms of the mutual relation of hepatic macrophages, autophagy, and damage-associated molecular patterns (DAMPs) in male F344/DuCrlCrlj rats. Rats injected with low dose (0.1 mg/kg) or high dose (2.0 mg/kg) of LPS were examined at 6, 10, and 24 hours following single injections. Histologically, focal hepatocellular necrosis was occasionally present in high-dose animals, whereas there were no significant changes in low-dose animals. In low-dose animals, Kupffer cells reacting to CD163 and CD204 were hypertrophic and regarded as M2 macrophages, which promote resolution of inflammation and tissue repair, whereas in high-dose animals, infiltration of M1 macrophages expressing CD68 and major histocompatibility complex class II, which enhance cell injury, was seen. Hepatocytes with high-mobility-group box-1 (HMGB1) (one of DAMPs)-positive cytoplasmic granules appeared more frequently in high-dose animals than in low-dose animals, indicating the translocation of nuclear HMGB1 into the cytoplasm. However, although light-chain 3 beta-positive autophagosomes in hepatocytes increased in both doses, abnormally vacuolated autophagosomes were only seen in injured hepatocytes in the high-dose group, indicating possible extracellular release of HMGB1, which might result in cell injury and inflammation. These findings suggested that low-dose LPS induced a favorable mutual relationship among hepatic macrophages, autophagy, and DAMPs leading to cytoprotection of hepatocytes, whereas failures of the relationship in high-dose LPS caused hepatocyte injury.

Tricyclic antidepressants induce liver inflammation by targeting NLRP3 inflammasome activation

BACKGROUND

Idiosyncratic drug-induced liver injury (IDILI) is common in hepatology practices and, in some cases, lethal. Increasing evidence show that tricyclic antidepressants (TCAs) can induce IDILI in clinical applications but the underlying mechanisms are still poorly understood.

METHODS

We assessed the specificity of several TCAs for NLRP3 inflammasome via MCC950 (a selective NLRP3 inhibitor) pretreatment and Nlrp3 knockout (Nlrp3^-/-) BMDMs. Meanwhile, the role of NLRP3 inflammasome in the TCA nortriptyline-induced hepatotoxicity was demonstrated in Nlrp3^-/- mice.

RESULTS

We reported here that nortriptyline, a common TCA, induced idiosyncratic hepatotoxicity in a NLRP3 inflammasome-dependent manner in mildly inflammatory states. In parallel in vitro studies, nortriptyline triggered the inflammasome activation, which was completely blocked by Nlrp3 deficiency or MCC950 pretreatment. Furthermore, nortriptyline treatment led to mitochondrial damage and subsequent mitochondrial reactive oxygen species (mtROS) production resulting in aberrant activation of the NLRP3 inflammasome; a selective mitochondrial ROS inhibitor pretreatment dramatically abrogated nortriptyline-triggered the NLRP3 inflammasome activation. Notably, exposure to other TCAs also induced aberrant activation of the NLRP3 inflammasome by triggering upstream signaling events.

CONCLUSION

Collectively, our findings revealed that the NLRP3 inflammasome may act as a crucial target for TCA agents and suggested that the core structures of TCAs may contribute to the aberrant activation of NLRP3 inflammasome induced by them, an important factor involved in the pathogenesis of TCA-induced liver injury. Video Abstract.

Regulatory Perspectives of Pyrrolizidine Alkaloid Contamination in Herbal Medicinal Products

The toxicity of plants containing certain pyrrolizidine alkaloids has long been recognized in grazing animals and humans. Genotoxicity and carcinogenicity data from in vitro and in vivo (animal) studies were published over the last few decades for some of the 1,2-unsaturated pyrrolizidine alkaloids, leading to regulatory action on herbal medicinal products with pyrrolizidine alkaloid-containing plants more than 30 years ago. In recent years, it has become evident that in addition to herbal medicinal products containing pyrrolizidine alkaloid-containing plants, these products may also contain pyrrolizidine alkaloids without actually including pyrrolizidine alkaloid-containing plants. This is explained by contamination by accessory herbs (weeds). The national competent authorities of the European member states and the European Medicines Agency, in this case, the Committee on Herbal Medicinal Products, reacted to these findings by setting limits for all herbal medicinal products. This review article will briefly discuss the data leading to the establishment of thresholds and the regulatory developments and consequences, as well as the current discussions and research in this area.

Clinical application of pyrrole-hemoglobin adducts as a biomarker of pyrrolizidine alkaloid exposure in humans

Pyrrolizidine alkaloids (PAs) are naturally occurring hepatotoxins widely present in hundreds of plant species and also known to contaminate many foodstuffs, such as grain, honey, and tea. The formation of pyrrole-protein adducts via metabolic activation of PAs has been suggested as a primary trigger initiating hepatotoxicity. The present study for the first time tested the suitability of pyrrole-hemoglobin adducts as a novel and specific biomarker of PA exposure in humans. The level and elimination kinetics of pyrrole-hemoglobin adducts were systematically investigated in the blood samples of 43 PA-induced liver injury (PA-ILI) patients. The results revealed significantly higher concentrations (84.50 ± 78.38 nM) and longer persistence (~ 4 months) of pyrrole-hemoglobin adducts than that (concentration: 9.53 ± 10.72 nM; persistence: ~ 2 months) of pyrrole-plasma protein adducts, our previously developed PA exposure biomarker. Our findings confirmed that pyrrole-hemoglobin adducts with higher level and longer persistence should serve as a more applicable PA exposure biomarker for future clinical diagnosis of PA-ILI in drug/herb-induced liver injury patients.

Icariside Ⅱ, a main compound in Epimedii Folium, induces idiosyncratic hepatotoxicity by enhancing NLRP3 inflammasome activation

Idiosyncratic drug-induced liver injury (IDILI) is an infrequent but potentially serious disease that develops the main reason for post-marketing safety warnings and withdrawals of drugs. Epimedii Folium (EF), the widely used herbal medicine, has shown to cause idiosyncratic liver injury, but the underlying mechanisms are poorly understood. Increasing evidence has indicated that most cases of IDILI are immune mediated. Here, we report that icariside Ⅱ (ICS Ⅱ), the major active and metabolic constituent of EF, causes idiosyncratic liver injury by promoting NLRP3 inflammasome activation. ICS Ⅱ exacerbates NLRP3 inflammasome activation triggered by adenosine triphosphate (ATP) and nigericin, but not silicon dioxide (SiO₂), monosodium urate (MSU) crystal or cytosolic lipopolysaccharide (LPS). Additionally, the activation of NLRC4 and AIM2 inflammasomes is not affected by ICS Ⅱ. Mechanistically, synergistic induction of mitochondrial reactive oxygen species (mtROS) is a crucial contributor to the enhancing effect of ICS Ⅱ on ATP- or nigericin-induced NLRP3 inflammasome activation. Importantly, in vivo data show that a combination of non-hepatotoxic doses of LPS and ICS Ⅱ causes the increase of aminotransferase activity, hepatic inflammation and pyroptosis, which is attenuated by Nlrp3 deficiency or pretreatment with MCC950 (a specific NLRP3 inflammasome inhibitor). In conclusion, these findings demonstrate that ICS Ⅱ causes idiosyncratic liver injury through enhancing NLRP3 inflammasome activation and suggest that ICS Ⅱ may be a risk factor and responsible for EF-induced liver injury.

Hepatotoxicity Induced by Isoniazid-Lipopolysaccharide through Endoplasmic Reticulum Stress, Autophagy, and Apoptosis Pathways in Zebrafish

Isoniazid (INH) is a first-line antituberculosis drug. The incidence of adverse reactions accompanied by inflammation in the liver during drug administration to tuberculosis patients is high and severely affects clinical treatment. To better understand the mechanism of hepatotoxicity induced by INH under the inflammatory state, we compared the differences in levels of hepatotoxicity from INH between normal zebrafish and zebrafish in an inflammatory state to elucidate the hepatotoxic mechanism using different endpoints such as mortality, malformation, inflammatory effects, liver morphology, histological changes, transaminase analysis, and expression levels of certain genes. The results showed that the toxic effect of INH in zebrafish in an inflammatory state was more obvious than that in normal zebrafish, that liver size was significantly decreased as measured by liver fatty acid binding protein (LFABP) reporter fluorescence and intensity, and that alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were significantly increased. Hematoxylin and eosin (HE) staining and electron microscopy showed that hepatocyte injury was more obvious in the inflammatory state. In the inflammatory state, INH significantly increased the expression levels of endoplasmic reticulum stress (ERS)-related factors (GRP78, ATF6, PERK, IRE1, XBP1s, GRP94, and CHOP), autophagy-related factors (beclin 1, LC3, Atg3, and Atg12), and apoptosis-related factors (caspase-3, caspase-8, caspase-9, Bax, p53, and Cyt) in larvae. Correlational analyses indicated that the transcription levels of the inflammatory factors interleukin-1b (IL-1b), tumor necrosis factor beta (TNF-β), cyclooxygenase 2 (COX-2), and TNF-ɑ were strongly positively correlated with ALT and AST. Furthermore, the ERS inhibitor sodium 4-phenylbutyrate (4-PBA) could ameliorate the hepatotoxicity of INH-lipopolysaccharide (LPS) in zebrafish larvae. These results indicated that INH hepatotoxicity was enhanced in the inflammatory state. ERS and its mediated autophagy and apoptosis pathways might be involved in INH-induced liver injury promoted by inflammation.

Macrophage Populations and Expression of Regulatory Inflammatory Factors in Hepatic Macrophage-depleted Rat Livers under Lipopolysaccharide (LPS) Treatment

To investigate the significance of the appearance of hepatic macrophages and expression of inflammatory factors in normal and macrophage-depleted livers, hepatic macrophages were depleted with liposome (Lipo)-encapsulated clodronate (CLD; 50 mg/kg, i.v.) followed by lipopolysaccharide (LPS) administration (0.1 mg/kg, i.p.) in F344 rats (CLD + LPS). Vehicle control rats (Lipo + LPS) received empty-Lipo before LPS. The low dose of LPS did not result in microscopic changes in the liver in either treatment group but did modulate M1 and M2 macrophage activity in Lipo + LPS rats without altering repopulating hepatic macrophages in CLD + LPS rats. LPS treatment in Lipo + LPS rats dramatically increased the M1 (IL-1β, IL-6, TNF-α, and MCP-1) but not M2 macrophage-related factors (IL-4 and CSF-1) compared to CLD + LPS rats. In the CLD + LPS rats, the M2 macrophage-related factors IL-4 and CSF-1 were elevated. In conclusion, low-dose LPS activated hepatic macrophages in rat livers without causing liver injury or stimulating repopulating hepatic macrophages. These data suggest that LPS may alter the liver microenvironment by modulating M1 or M2 macrophage-related inflammatory mediators and macrophage-based hepatotoxicity.

Pyrrolizidine Alkaloids: Chemistry, Pharmacology, Toxicology and Food Safety

Pyrrolizidine alkaloids (PA) are widely distributed in plants throughout the world, frequently in species relevant for human consumption. Apart from the toxicity that these molecules can cause in humans and livestock, PA are also known for their wide range of pharmacological properties, which can be exploited in drug discovery programs. In this work we review the current body of knowledge regarding the chemistry, toxicology, pharmacology and food safety of PA.

Dexamethasone Pretreatment Alleviates Isoniazid/Lipopolysaccharide Hepatotoxicity: Inhibition of Inflammatory and Oxidative Stress

Isoniazid (INH) remains a cornerstone key constitute of the current tuberculosis management strategy, but its hepatotoxic potentiality remains a significant clinical problem. Our previous findings succeed to establish a rat model of INH hepatotoxicity employing the inflammatory stress theory in which non-injurious doses of inflammatory-mediating agent bacterial lipopolysaccharides (LPS) augmented the toxicity of INH that assist to uncover the mechanisms behind INH hepatotoxicity. Following LPS exposure, several inflammatory cells are activated and it is likely that the consequences of this activation rather than direct hepatocellular effects of LPS underlie the ability of LPS to augment toxic responses. In this study, we investigated the potential protective role of the anti-inflammatory agent dexamethasone (DEX), a potent synthetic glucocorticoid, in INH/LPS hepatotoxic rat model. DEX pre-treatment successfully eliminates the components of the inflammatory stress as shown through analysis of blood biochemistry and liver histopathology. DEX potentiated hepatic anti-oxidant mechanisms while serum and hepatic lipid profiles were reduced. However, DEX administration was not able to revoke the principal effects of cytochrome P450 2E1 (CYP2E1) in INH/LPS-induced liver damage. In conclusion, this study illustrated the DEX-preventive capabilities on INH/LPS-induced hepatotoxicity model through DEX-induced potent anti-inflammatory activity whereas the partial toxicity seen in the model could be attributed to the expression of hepatic CYP2E1. These findings potentiate the clinical applications of DEX co-administration with INH therapy in order to reduce the potential incidences of hepatotoxicity.

Regulation of bacterial lipopolysaccharide in liver toxicity caused by chlorpromazine and Z24 in Sprague-Dawley rats

LPS-induced inflammatory response could be used to establish screening models for ILT and provides a new way to reduce liver toxicity of Z24.

Blood Pyrrole-Protein Adducts--A Biomarker of Pyrrolizidine Alkaloid-Induced Liver Injury in Humans

Pyrrolizidine alkaloids (PAs) induce liver injury (PA-ILI) and is very likely to contribute significantly to drug-induced liver injury (DILI). In this study we used a newly developed ultra-high performance liquid chromatography-triple quadrupole-mass spectrometry (UHPLC-MS)-based method to detect and quantitate blood pyrrole-protein adducts in DILI patients. Among the 46 suspected DILI patients, 15 were identified as PA-ILI by the identification of PA-containing herbs exposed. Blood pyrrole-protein adducts were detected in all PA-ILI patients (100%). These results confirm that PA-ILI is one of the major causes of DILI and that blood pyrrole-protein adducts quantitated by the newly developed UHPLC-MS method can serve as a specific biomarker of PA-ILI.

Pyrrolizidine Alkaloids: Potential Role in the Etiology of Cancers, Pulmonary Hypertension, Congenital Anomalies, and Liver Disease

Large outbreaks of acute food-related poisoning, characterized by hepatic sinusoidal obstruction syndrome, hemorrhagic necrosis, and rapid liver failure, occur on a regular basis in some countries. They are caused by 1,2-dehydropyrrolizidine alkaloids contaminating locally grown grain. Similar acute poisoning can also result from deliberate or accidental consumption of 1,2-dehydropyrrolizidine alkaloid-containing herbal medicines, teas, and spices. In recent years, it has been confirmed that there is also significant, low-level dietary exposure to 1,2-dehydropyrrolizidine alkaloids in many countries due to consumption of common foods such as honey, milk, eggs, salads, and meat. The level of 1,2-dehydropyrrolizidine alkaloids in these foods is generally too low and too intermittent to cause acute toxicity. However, these alkaloids are genotoxic and can cause slowly developing chronic diseases such as pulmonary arterial hypertension, cancers, cirrhosis, and congenital anomalies, conditions unlikely to be easily linked with dietary exposure to 1,2-dehydropyrrolizidine alkaloids, especially if clinicians are unaware that such dietary exposure is occurring. This Perspective provides a comprehensive review of the acute and chronic toxicity of 1,2-dehydropyrrolizidine alkaloids and their potential to initiate certain chronic diseases, and suggests some associative considerations or indicators to assist in recognizing specific cases of diseases that may have resulted from dietary exposure to these hazardous natural substances. If it can be established that low-level dietary exposure to 1,2-dehydropyrrolizidine alkaloids is a significant cause of some of these costly and debilitating diseases, then this should lead to initiatives to reduce the level of these alkaloids in the food chain.

Impact of inflammation on chlorpromazine-induced cytotoxicity and cholestatic features in HepaRG cells

Several factors are thought to be implicated in the occurrence of idiosyncratic adverse drug reactions. The present work aimed to question as to whether inflammation is a determinant factor in hepatic lesions induced by chlorpromazine (CPZ) using the human HepaRG cell line. An inflammation state was induced by a 24-hour exposure to proinflammatory cytokines interleukin-6 (IL-6) and IL-1β; then the cells were simultaneously treated with CPZ and/or cytokine for 24 hours or daily for 5 days. The inflammatory response was assessed by induction of C-reactive protein and IL-8 transcripts and proteins as well as inhibition of CPZ metabolism and down-regulation of cytochrome 3A4 (CYP3A4) and CYP1A2 transcripts, two major cytochrome P450 (P450) enzymes involved in its metabolism. Most effects of cotreatments with cytokines and CPZ were amplified or only observed after five daily treatments; they mainly included increased cytotoxicity and overexpression of oxidative stress-related genes, decreased Na(+)-taurocholate cotransporting polypeptide mRNA levels and activity, a key transporter involved in bile acids uptake, and deregulation of several other transporters. However, CPZ-induced inhibition of taurocholic acid efflux and pericanalicular F-actin distribution were not affected. In addition, a time-dependent induction of phospholipidosis was noticed in CPZ-treated cells, without obvious influence of the inflammatory stress. In summary, our results show that an inflammatory state induced by proinflammatory cytokines increased cytotoxicity and enhanced some cholestatic features induced by the idiosyncratic drug CPZ in HepaRG cells. These changes, together with inhibition of P450 activities, could have important consequences if extrapolated to the in vivo situation.

Lipopolysaccharide exposure augments isoniazide-induced liver injury

Isoniazide (INH) is a classic antituberculosis drug associated with clinical idiosyncratic drug-induced liver injury. It has been hypothesized that the interaction between a drug and modest inflammation results in a decreased threshold for drug toxicity. In this study, we tested the hypothesis that INH causes liver injury in rats when coadministered with lipopolysaccharide (LPS). Neither INH nor LPS alone caused liver injury. The coadministration of INH and LPS was associated with increases in serum and histopathological markers of liver injury. Tumour necrosis factor-α expression was significantly increased in the coadministered group. The downregulation of the bile acid transporter, bile salt export pump, and multidrug resistance protein 2 at both mRNA and protein levels was observed. Furthermore, the level of Farnesoid X receptor, which regulates the bile salt export pump and multidrug resistance protein 2, were clearly decreased. These results indicate that the coadministration of nontoxic doses of LPS and INH causes liver injury; the disruption of biliary excretion is considered the primary inflammation-related characteristic of INH-induced hepatotoxicity.

Senecio scandens Buch.-Ham.: a review on its ethnopharmacology, phytochemistry, pharmacology, and toxicity

ETHNOPHARMACOLOGICAL RELEVANCE

The aerial parts of Senecio scandens Buch.-Ham. (family Asteraceae) have a long history in traditional Chinese medicine as a treatment for various ailments, such as bacterial diarrhea, enteritis, conjunctivitis, and respiratory tract infections.

MATERIALS AND METHODS

A bibliographic investigation of Senecio scandens was accomplished by analyzing secondary sources, including the Chinese Medicinal plantal Classics, the Internet (Google Scholar and Baidu Scholar), and scientific databases accepted worldwide (Pubmed, Scopus, Web of Science, SciFinder, and CNKI). These sources were scrutinized for available information about the uses of Senecio scandens in traditional Chinese medicine, phytochemistry, pharmacology, and toxicology.

RESULTS

Senecio scandens is a medicinal plant with a climbing woody stem. Phytochemical studies have shown the presence of numerous valuable compounds, such as flavonoids, alkaloids, phenolic acids, terpenes, volatile oils, carotenoids, and trace elements. Among them, PAs are the characteristic constituents, adonifoline is one of the index ingredients of Senecio scandens. Studies in modern pharmacology have demonstrated that extracts and compounds isolated from Senecio scandens show a wide spectrum of pharmacological activities, including anti-inflammatory, antimicrobial, anti-leptospirosis, hepatoprotective, anti-infusorial, antioxidant, antiviral, antitumoral, analgesic, mutagenic, and toxicological activities.

CONCLUSIONS

Phytochemical and pharmacological studies have demonstrated that the extracts of the plant possess various pharmacological activities that can be attributed to the presence of various flavonoids, phenolic acids, and alkaloids. Newer technologies for qualitative and quantitative methods of PAs need to be developed to obtain better accuracy and sensitivity. Due to the toxicity of PAs present in this medicinal plant, the regulations on PAs of Senecio scandens were varied among different countries and regions. In China, the PAs toxicity of Senecio scandens ranking criteria is not well defined in the Chinese Pharmacopoeia 2010, and there is no strict uniform requirement on the PAs in western countries. We propose that the use of Senecio scandens should be reevaluated based on a set of criteria, which includes risk-benefit analysis and severity of the toxic effects, clinical and preclinical data to ensure safe use while continuing to satisfy the need for access to the medicinal plant.

Synergistic effects of pyrrolizidine alkaloids and lipopolysaccharide on preterm delivery and intrauterine fetal death in mice

Preterm birth is the leading cause of death for newborn infants, and lipopolysaccharide (LPS) is commonly used to induce preterm delivery in experimental animals. Pyrrolizidine alkaloids (PAs) are widespread and occur in foods, herbs, and other plants. This study was to investigate the synergistic effects of LPS and two representative PAs, retrorsine (RTS) and monocrotaline (MCT), on preterm delivery and fetal death. Pregnant Kunming mice were divided into seven groups: control, RTS, MCT, LPS, RTS+LPS and two MCT+LPS groups. Animals in PAs and PAs+LPS groups were dosed intragastrically with RTS (10mg/kg) or MCT (20 mg/kg or 60 mg/kg) from gestational day (GD) 9 to GD16; mice given LPS were injected intraperitoneally with 150 μg/kg on GD15.5. Latencies to delivery, numbers of pups live and dead at birth were recorded, and livers of live neonates were collected. The incidence of LPS-induced preterm birth was enhanced in dams pretreated with MCT, and combination of PAs and LPS increased fetal mortality from PAs. The enhancement of LPS-induced preterm delivery and fetal demise in animals exposed chronically to PAs and other substances found in foods and beverages consumed widely by humans merits further focused investigation.

Retrospective study of cattle poisonings in California: recognition, diagnosis, and treatment

In this retrospective study all suspect bovine intoxications submitted to the California Animal Health and Food Safety Laboratory between January 1, 2000 and December 31, 2011 were reviewed. A total of 1199 cases were submitted, but a diagnosis of intoxication was only established in 13.5% of cases. In these cases, overexposures to minerals, metals, and poisonous plants were determined as the most commonly diagnosed poisonings in cattle in California. Nitrate/nitrite poisoning was the most commonly diagnosed plant-associated intoxication, followed by gossypol and oleander. This study details the diagnostic challenges and treatment options for the most commonly diagnosed intoxications. To ensure proper treatment and prevention of new cases, accurate diagnosis is necessary, and therefore this review provides an essential tool for the food animal practitioner. Available toxicological analyses are offered at select laboratories, which can be time consuming and expensive, yet the potential for residues in consumed animal products and implications for human health necessitate testing and consultation. Any potential exposure to a toxicant in cattle should be reviewed to determine whether a residue hazard exists. Therapy focuses on immediate removal of the toxicant from the environment and from the gastrointestinal tract. With few antidotes available, most are cost prohibitive to treat numerous affected cattle. In addition, most antidotes will require extra-label drug use and establishment of meat and milk withdrawal times.

Lead hepatotoxicology: a study in an animal model

The increasing use of lead (Pb) for industrial purposes has resulted in the significant increase in environmental contamination of our planet especially in concern to water and food. In this study using the electron scanning microscopy (SEM), the authors showed the effects of this metal as a result of a chronic and cumulative process. As a primary method of detection of Pb in situ, SEM was chosen, coupled with a detection system Noran Voyager of basic microanalysis X-ray (SEM-XRM), with detection system energy dispersive spectrometry. Mice BALB/c was used as a study model. An animal model of inflammation was used, that consisted in the formation of a subcutaneous pocket of air. It was observed that 75% of Pb stock was captured by the liver, the main target organ in the capture of the metal, the kidney was the second organ to capture the Pb stock and the third was the spleen. It was verified that a low deposition of Pb was found in the lungs and the brain. The main results of this study showed how Pb is captured by different organs. We also demonstrated the vulnerability to inflammation of this metal.

Plants containing pyrrolizidine alkaloids: toxicity and problems

Pyrrolizidine alkaloids (PA) are toxic for human and livestock. They undergo a metabolic toxication process in the liver which is the first target organ for PA poisoning. Worldwide many episodes of human PA intoxications are well reported. In many cases the reason for these intoxications has been PA contamination in food. The main tools for analysing food and fodder on PA content are based on GC and HPLC separation, followed by MS(-MS) detection. Actual incidents with toxic PA are the 'Jacobaea vulgaris (syn. Senecio jacobaea) problem' in Europe and the 'Ageratum conyzoides problem' in Ethiopia.

Pyrrolizidine alkaloids in food: a spectrum of potential health consequences

Contamination of grain with 1,2-dehydropyrrolizidine ester alkaloids (dehydroPAs) and their N-oxides is responsible for large incidents of acute and subacute food poisoning, with high morbidity and mortality, in Africa and in central and south Asia. Herbal medicines and teas containing dehydroPAs have also caused fatalities in both developed and developing countries. There is now increasing recognition that some staple and widely consumed foods are sometimes contaminated by dehydroPAs and their N-oxides at levels that, while insufficient to cause acute poisoning, greatly exceed maximum tolerable daily intakes and/or maximum levels determined by a number of independent risk assessment authorities. This suggests that there may have been cases of disease in the past not recognised as resulting from dietary exposure to dehydroPAs. A review of the literature shows that there are a number of reports of liver disease where either exposure to dehydroPAs was suspected but no source was identified or a dehydroPA-aetiology was not considered but the symptoms and pathology suggests their involvement. DehydroPAs also cause progressive, chronic diseases such as cancer and pulmonary arterial hypertension but proof of their involvement in human cases of these chronic diseases, including sources of exposure to dehydroPAs, has generally been lacking. Growing recognition of hazardous levels of dehydroPAs in a range of common foods suggests that physicians and clinicians need to be alert to the possibility that these contaminants may, in some cases, be a possible cause of chronic diseases such as cirrhosis, pulmonary hypertension and cancer in humans.

Silencing of tissue factor by antisense deoxyoligonucleotide prevents monocrotaline/LPS renal injury in mice

Tissue factor (TF) is involved in monocrotaline (MCT)/lipopolysaccharide (LPS) hepatotoxicity. It is not known whether MCT/LPS can cause renal toxicity and whether TF is involved in this toxicity. Thus, the present study was undertaken to investigate the potential renal toxicity after MCT/LPS co-treatment and the involvement of TF in this toxicity. MCT was delivered to ND4 male mice (200 mg/kg) per os followed 4 h later by treatment with LPS ip (6 mg/kg) to investigate its effect on kidney. We injected TF antisense oligonucleotide (TF-AS) intravenously (i.v) in mice prior to LPS treatment, to block TF, and measured their blood urea nitrogen (BUN), creatinine (CRE), alkaline phosphatase (ALP), and potassium. In MCT/LPS co-treated group, fibrin was detected on the glomerular capillary lumina, distal tubules of renal cortex, and the necrotic tubules of renal medulla. An elevation of BUN, creatinine, and the BUN/creatinine ratio was seen in mice with MCT/LPS co-treatment, compared to animals receiving LPS or MCT alone. Simultaneously, an aggressive tubular necrosis was seen in the medullary tubules in the same group which may account for the oliguria observed in these animals. Fourfold inductions in the plasma TF level was detected at 10 h after MCT/LPS co-treatment which increased to 18-fold at 24 h. Increased blood level of leptin, interleukin-6 (IL-6) and downregulation of tubular chemokine (C-X-C motif) ligand 16 (CXCL16) are characteristic features in MCT/LPS co-treated animal. On the other hand, mice injected with TF-AS in the presence of MCT/LPS co-treatment showed no elevation of the blood BUN, creatinine, potassium, and normal levels of the proinflammatory molecules. TF-AS injection significantly prevented glomerular and tubular fibrin deposition, tubular necrosis, and improvement of the animal survivability. Renal toxicity involving TF can be prevented successfully by the use of TF-AS.

Oxidized low-density lipoprotein and tissue factor are involved in monocrotaline/lipopolysaccharide-induced hepatotoxicity

These studies were aimed at characterizing an animal model of inflammation-induced hepatotoxicity that would mimic features of idiosyncratic liver toxicity observed in humans. An attempt was made to identify oxidative damage and the involvement of coagulation system in liver after monocrotaline (MCT) administration under the modest inflammatory condition induced by lipopolysaccharide (LPS) exposure. Mice were given MCT (200 mg/kg) or an equivalent volume of sterile saline (Veh.) po followed 4 h later by ip injection of LPS (6 mg/kg) or vehicle. Mice co-treated with MCT and LPS showed increased plasma alanine aminotransferase (ALT), decrease in platelet number, and a reduction in hematocrit. Accumulation of oxidized low-density lipoprotein (ox-LDL) was remarkably higher in the liver sections of mice co-treated with MCT and LPS compared to those given MCT or LPS alone. A similar trend was observed in the expression of CXCL16 receptor in the same liver sections. Elevated expression of tissue factor (TF) and fibrinogen was also observed in the liver sections of MCT/LPS co-treated mice. The in vitro results showed that incubation of HepG2 cells with CXCL16 antibody strongly diminished uptake of ox-LDL. Expression of ox-LDL, CXCL16, and TF represents an early event in the onset of hepatotoxicity induced by MCT/LPS; thus, it may contribute to our understanding of idiosyncratic liver injury and points to potential targets for protection or intervention.

Acute exposure to ozone exacerbates acetaminophen-induced liver injury in mice

Ozone (O(3)), an oxidant air pollutant in photochemical smog, principally targets epithelial cells lining the respiratory tract. However, changes in gene expression have also been reported in livers of O(3)-exposed mice. The principal aim of the present study was to determine if acute exposure to environmentally relevant concentrations of O(3) could cause exacerbation of drug-induced liver injury in mice. Overdose with acetaminophen (APAP) is the most common cause of drug-induced liver injury in developed countries. In the present study, we examined the hepatic effects of acute O(3) exposure in mice pretreated with a hepatotoxic dose of APAP. C57BL/6 male mice were fasted overnight and then given APAP (300 mg/kg ip) or saline vehicle (0 mg/kg APAP). Two hours later, mice were exposed to 0, 0.25, or 0.5 ppm O(3) for 6 h and then sacrificed 9 or 32 h after APAP administration (1 or 24 h after O(3) exposure, respectively). Animals euthanized at 32 h were given 5-bromo-2-deoxyuridine 2 h before sacrifice to identify hepatocytes undergoing reparative DNA synthesis. Saline-treated mice exposed to either air or O(3) had no liver injury. All APAP-treated mice developed marked centrilobular hepatocellular necrosis that increased in severity with time after APAP exposure. O(3) exposure increased the severity of APAP-induced liver injury as indicated by an increase in necrotic hepatic tissue and plasma alanine aminotransferase activity. O(3) also caused an increase in neutrophil accumulation in livers of APAP-treated animals. APAP induced a 10-fold increase in the number of bromodeoxyuridine-labeled hepatocytes that was markedly attenuated by O(3) exposure. Gene expression analysis 9 h after APAP revealed differential expression of genes involved in inflammation, oxidative stress, and cellular regeneration in mice treated with APAP and O(3) compared to APAP or O(3) alone, providing some indications of the mechanisms behind the APAP and O(3) potentiation. These results suggest that acute exposure to near ambient concentrations of this oxidant air pollutant may exacerbate drug-induced liver injury by delaying hepatic repair.

Hepatotoxic herbs: will injury mechanisms guide treatment strategies?

Harmful and fatal outcomes related to specific herbal therapies are reported with increasing regularity. However, US physicians remain inadequately informed about potential toxicities. The purpose of this focused review is to highlight past and more recently recognized herbal therapies or complementary and alternative medicine (CAM) that are shown to cause hepatotoxicity. Where available, the proposed mechanisms for toxicity are discussed. An aggressive approach for more stringent regulation of CAM is needed, in addition to a systematic and scientific study of causality and underlying toxic mechanisms, to provide reliable information about the safety of CAM and enable practitioners to deliver effective remedies when toxicities occur.

Different bacteria species lipopolysaccharide co-exposure with Pseudomonas exotoxin A on multiple organ injury induction

The present study investigated the effect of different bacterial species lipopolysaccharide plus Pseudomonas exotoxin A (LPS/PEA) on the induction of multiple organ injury (MOI). Rats were injected with various LPS from Salmonella (SAE, SAT), E. coli (EB4, EB5), or P. aeruginosa (PAL) and PEA showed a greater mortality in the SAE/PEA and SAT/PEA groups. Histological alterations, serum enzymes, and cytokines changes were severer in the SAE/PEA group than the EB4/PEA or PAL/PEA group. EB4/PEA and PAL/PEA failed to induce MOI, even at the LPS doses increased up to 2-4- and 4-8-fold, respectively. Rats co-treated with Salmonella lipid A/PEA developed severer MOI than the E. coli lipid A/PEA. The results indicated the critical roles of MOI induction, which were related to LPS derived from appropriate bacterial species.

Mercury Alters Endotoxin-Induced Inflammatory Cytokine Expression in Liver: Differential Roles of P38 and Extracellular Signal-Regulated Mitogen-Activated Protein Kinases

Mercury is a widespread metal in the environment and consequently large populations are currently exposed to low levels of mercury. Endotoxin, a component of the Gram-negative bacteria, promotes inflammatory responses. We recently reported that mercury modulates the production of nitric oxide and various inflammatory cytokines induced by endotoxin in a macrophage cell line (Nitric Oxide 2002, 7:67). The present study was designed to determine the impact of mercury on endotoxin-induced inflammatory cytokine expression and corresponding signal transduction in mouse liver. Male BALB/c mice were exposed continuously to 0, 0.3, 1.5, 7.5, or 37.5 ppm of mercury in drinking water for 14 days and at the end of the treatment period lipopolysaccharide (LPS, 0.5 mg/kg) was injected intraperitoneally 2 hr prior to euthanasia. The doses of mercury and LPS did not cause hepatotoxicity as indicated by unaltered circulating alanine aminotransferase and aspartate aminotransferase levels. Mercury decreased liver glutathione (GSH) and with LPS additively decreased GSH. Mercury activated p38 mitogen-activated protein kinase (MAPK) and additively increased LPS-induced p38 MAPK phosphorylation. In contrast, mercury alone had no effect on activation of extracellular signal-regulated kinase (ERK) but inhibited LPS-induced ERK activation. Mercury increased the expression of tumor necrosis factor alpha (TNFalpha) and further potentiated LPS-induced TNFalpha expression. Mercury did not affect LPS-induced interleukin (IL)-1beta expression but decreased LPS-induced IL-6 expression. Results indicated that low levels of mercury augment LPS-induced TNFalpha expression by altering GSH and p38 MAPK. Mercury modulates LPS-induced p38 and ERK activation and downstream TNFalpha and IL-6 expression in mouse liver.

Managing symptomatic drug-induced liver injury in HIV-hepatitis C virus-coinfected patients: a role for interferon

BACKGROUND

Human immunodeficiency virus (HIV)-infected patients with hepatitis C virus (HCV) coinfection are at increased risk for drug-induced liver injury (DILI) compared with patients with HIV infection alone. The mechanism underlying this observation is unknown. We hypothesized that interferon (IFN) would induce biochemical improvement through its anti-inflammatory properties and thereby facilitate the reintroduction of antiretroviral therapy (ART) in patients with DILI.

METHODS

Patients with symptomatic DILI were referred for evaluation; biopsy of a liver sample was performed for all patients, except 1 with clinical cirrhosis.

RESULTS

Twelve patients with acquired immunodeficiency syndrome and symptomatic grade 3/4 hepatotoxicity received treatment with IFN and ribavirin (RBV). Seven of these patients had a history of recurrent DILI. The mean baseline CD4(+) T cell counts and HIV RNA levels were 124 cells/mm(3) and 115,369 copies/mL, respectively. Biopsies of liver samples demonstrated significant necroinflammation (mean grade, 10.3) and fibrosis (mean stage, 2.9). Three patients continued to receive ART when they began treatment with IFN-RBV; 9 reinitiated ART within an average of 12 weeks (range, 4-20 weeks) of HCV treatment initiation. All patients attained marked improvement in aminotransferases and continued to receive ART treatment during a mean follow-up regimen of 26.5 months, with subsequent virologic suppression and immunologic reconstitution (mean CD4(+) cell count increase, 251/mm(3)). However, only 1 patient maintained HCV suppression after completion of treatment with IFN-RBV.

CONCLUSIONS

In patients with symptomatic DILI, treatment with IFN-ribavirin (RBV) led to decreases in aminotransferase levels, which enabled the reinitiation of ART. The beneficial effects of IFN-based therapy may be modulated through the suppression of proinflammatory cytokines, even in virologic nonresponders. Herein, we propose a novel mechanism for DILI, whereby HCV- and HIV-associated inflammatory mediators induce liver injury synergistically.

Dehydromonocrotaline inhibits mitochondrial complex I. A potential mechanism accounting for hepatotoxicity of monocrotaline

Monocrotaline is a pyrrolizidine alkaloid present in plants of the Crotalaria species, which causes cytotoxicity and genotoxicity, including hepatotoxicity in animals and humans. It is metabolized by cytochrome P-450 in the liver to the alkylating agent dehydromonocrotaline. We evaluated the effects of monocrotaline and its metabolite on respiration, membrane potential and ATP levels in isolated rat liver mitochondria, and on respiratory chain complex I NADH oxidase activity in submitochondrial particles. Dehydromonocrotaline, but not the parent compound, showed a concentration-dependent inhibition of glutamate/malate-supported state 3 respiration (respiratory chain complex I), but did not affect succinate-supported respiration (complex II). Only dehydromonocrotaline dissipated mitochondrial membrane potential, depleted ATP, and inhibited complex I NADH oxidase activity (IC50=62.06 microM) through a non-competitive type of inhibition (K(I)=8.1 microM). Therefore, dehydromonocrotaline is an inhibitor of the activity of respiratory chain complex I NADH oxidase, an action potentially accounting for the well-documented monocrotaline's hepatotoxicity to animals and humans. The mechanism probably involves change of the complex I conformation resulting from modification of cysteine thiol groups by the metabolite.

Investigations toward enhanced understanding of hepatic idiosyncratic drug reactions

Idiosyncratic drug reactions (IDRs) of a hepatic origin are a major health concern and a notoriously difficult challenge for the pharmaceutical industry. These types of adverse events are rare, with a typical occurrence of 1 in 100 to 1 in 100,000 patients. Typical adverse outcomes are most likely statistically impossible to predict in traditional preclinical safety studies or clinical trials. Unfortunately, these reactions can pose a significant risk to the public health, resulting in devastating consequences such as irreversible liver injury, liver transplantation and fatality. This review provides many examples of experimental efforts that are underway for a better understanding of molecular events that may be responsible for IDRs. A list of existing hypotheses for IDRs is also provided, each with current literature examples or supporting evidence. The possibilities for developing suitable animal models for the prediction and characterisation of IDRs are elaborated, especially for a drug-inflammation interaction rat model of hepatic IDR. The need for predictive biomarkers of IDR is addressed, with the exploration of some possible candidates. Finally, the use of primary human hepatocyte culture systems is explored as an in vitro system, with application for providing an increased mechanistic knowledge of IDR. Several examples of informative studies on the nature of IDRs that employ toxicogenomic and proteomic technologies are summarised.

Modeling inflammation-drug interactions in vitro: a rat Kupffer cell-hepatocyte coculture system

Xenobiotic-inflammation interactions lead to hepatotoxicity in vivo. Selected xenobiotic agents (acetaminophen, APAP; chlorpromazine, CPZ; allyl alcohol, AlOH; monocrotaline, MCT) for which this occurs were evaluated for ability to elicit the release of Kupffer cell (KC)-derived inflammatory mediators and to modulate lipopolysaccharide (LPS)-stimulated release of these mediators. Using KCs and hepatocytes (HPCs) isolated from rat, KC/HPC cocultures were treated with either LPS, xenobiotic, vehicle or a combination. Six hours later, the release of inflammatory mediators was assessed. LPS alone caused a concentration-dependent increase in TNF-alpha release but had no significant effect on the release of PGE(2). APAP by itself did not alter release of TNF-alpha, PGE(2), IL-10, Gro/KC or IFN-gamma; however, in the presence of LPS, APAP enhanced LPS-induced TNF-alpha and Gro/KC release. APAP also attenuated LPS-induced increases in IL-10 and MCP-1. CPZ alone caused a concentration-dependent increase in TNF-alpha release, which was approximately additive in the presence of LPS. AlOH alone did not affect TNF-alpha release, but decreased TNF-alpha production in the presence of LPS. AlOH increased PGE(2) production, and this effect was potentiated in the presence of LPS. MCT by itself did not affect release of TNF-alpha but increased the response to LPS. Neither MCT, LPS, nor the combination affected production of PGE(2). These results demonstrate that KC/HPC cocultures can be used to evaluate interactions of xenobiotics with LPS. Furthermore, data from these studies qualitatively mirror reported data from whole animal studies, suggesting that this model could be useful for predicting aspects of xenobiotic-inflammation interactions in vivo.

Metabonomic evaluation of idiosyncrasy-like liver injury in rats cotreated with ranitidine and lipopolysaccharide

Idiosyncratic liver injury occurs in a small fraction of people on certain drug regimens. The cause of idiosyncratic hepatotoxicity is not known; however, it has been proposed that environmental factors such as concurrent inflammation initiated by bacterial lipopolysaccharide (LPS) increase an individual's susceptibility to drug toxicity. Ranitidine (RAN), a histamine-2 receptor antagonist, causes idiosyncratic liver injury in humans. In a previous report, idiosyncrasy-like liver toxicity was created in rats by cotreating them with LPS and RAN. In the present study, the ability of metabonomic techniques to distinguish animals cotreated with LPS and RAN from those treated with each agent individually was investigated. Rats were treated with LPS or its vehicle and with RAN or its vehicle, and urine was collected for nuclear magnetic resonance (NMR)- and mass spectroscopy-based metabonomic analyses. Blood and liver samples were also collected to compare metabonomic results with clinical chemistry and histopathology. NMR metabonomic analysis indicated changes in the pattern of metabolites consistent with liver damage that occurred only in the LPS/RAN cotreated group. Principal component analysis of urine spectra by either NMR or mass spectroscopy produced a clear separation of the rats treated with LPS/RAN from the other three groups. Clinical chemistry (serum alanine aminotransferase and aspartate aminotransferase activities) and histopathology corroborated these results. These findings support the potential use of a noninvasive metabonomic approach to identify drug candidates with potential to cause idiosyncratic liver toxicity with inflammagen coexposure.

Cyanobacterial lipopolysaccharides and human health - a review

Cyanobacterial lipopolysaccharide/s (LPS) are frequently cited in the cyanobacteria literature as toxins responsible for a variety of heath effects in humans, from skin rashes to gastrointestinal, respiratory and allergic reactions. The attribution of toxic properties to cyanobacterial LPS dates from the 1970s, when it was thought that lipid A, the toxic moiety of LPS, was structurally and functionally conserved across all Gram-negative bacteria. However, more recent research has shown that this is not the case, and lipid A structures are now known to be very different, expressing properties ranging from LPS agonists, through weak endotoxicity to LPS antagonists. Although cyanobacterial LPS is widely cited as a putative toxin, most of the small number of formal research reports describe cyanobacterial LPS as weakly toxic compared to LPS from the Enterobacteriaceae. We systematically reviewed the literature on cyanobacterial LPS, and also examined the much lager body of literature relating to heterotrophic bacterial LPS and the atypical lipid A structures of some photosynthetic bacteria. While the literature on the biological activity of heterotrophic bacterial LPS is overwhelmingly large and therefore difficult to review for the purposes of exclusion, we were unable to find a convincing body of evidence to suggest that heterotrophic bacterial LPS, in the absence of other virulence factors, is responsible for acute gastrointestinal, dermatological or allergic reactions via natural exposure routes in humans. There is a danger that initial speculation about cyanobacterial LPS may evolve into orthodoxy without basis in research findings. No cyanobacterial lipid A structures have been described and published to date, so a recommendation is made that cyanobacteriologists should not continue to attribute such a diverse range of clinical symptoms to cyanobacterial LPS without research confirmation.

Comparative methods for multiplex analysis of cytokine protein expression in plasma of lipopolysaccharide-treated mice

Changes in circulating cytokines might serve as predictors of compound-evoked inflammatory responses. CD-1 mice were treated with lipopolysaccharide (LPS; 0.2 ml of 0.25 mg/ml, intraperitoneal) for subsequent expression measurement of plasma cytokine protein expression at 24-h post-treatment using multiple antibody Western blot, and at both 2-h and 24-h post-treatment using antibody array and suspension bead array. Antibody array provided a semi-qualitative assessment and suggested significantly increased expression of GCSF at 2-h post-treatment and GCSF, IL-6, IL-12, MCP-1, MCP-5, RANTES and sTNFR1 at 24-h post-treatment. Densitometric analysis of multiple antibody Western blots provided a semi-quantitative assessment and indicated significantly increased expression of IL-6, IL-12, IL-17, GCSF, eotaxin, and MCP-2 at 24-h post-treatment. The suspension bead array yielded statistically significant cytokine protein expression increases for IL-6, IL-10, IFNgamma and TNFalpha at both 2-h and 24-h post-treatments, while significant expression at 24-h post-treatment only was noted for IL-1beta, IL-5, IL-12 and GM-CSF. Suspension bead array provided the greatest range of detection, revealing subtle increased expression of GM-CSF, IL-1beta, IL-5, IL-10, TNFalpha and IFNgamma at 24-h post-treatment, not detected by antibody array or multiple antibody Western blot. Suspension bead array proved to be the best method for detection of LPS-evoked changes in plasma cytokine levels.

Adverse hepatic drug reactions: inflammatory episodes as consequence and contributor

Susceptibility to drug toxicity is influenced by a variety of factors, both genetic and environmental. The focus of this article is the evidence addressing the hypothesis that inflammation is both a result of and a susceptibility factor for drug toxicity, with an emphasis on liver as a target organ. Results of studies suggesting a role for inflammatory mediators in the hepatotoxicity caused by acetaminophen or ethanol are discussed. For several drugs, the evidence from animal models that concurrent inflammation increases injury is presented. In addition, the occurrence of adverse drug reactions in people with preexisting inflammatory diseases is considered. The special case of idiosyncratic drug reactions is discussed and the potential raised for development of animal models for this type of drug toxicity. The conclusion is that inflammatory factors should be considered as determinants of sensitivity to adverse drug reactions.

Workshop Overview: Hepatotoxicity Assessment for Botanical Dietary Supplements

Botanical dietary supplements (herbal products) have flooded the market in the United States over the past decade, and studies show a significant percentage of Americans use them. With increasing frequency and duration of exposure, some serious adverse effects, though relatively uncommon, have been reported. Among the most troublesome is the association of some botanicals with serious hepatotoxicity. In some cases, hepatotoxicity has been linked to the consumption of botanicals with recognized hepatotoxic components (e.g., pyrrolizidine alkaloids). However, in other cases, the causative agent(s) is less clear and, overall, the mechanisms of hepatotoxicity are poorly understood. To help create a scientific basis for understanding botanical-induced hepatotoxicity and better tools for hepatotoxicity assessment and prediction, the National Center for Natural Product Research (NCNPR) hosted a workshop (September 8 and 9, 2003) in cooperation with the Center for Food Safety and Applied Nutrition (CFSAN) of the Food and Drug Administration (FDA). The workshop featured presentations by 22 experts and was attended by 65 individuals. The agenda can be found in the supplementary data at www.toxsci.oupjournals.org.

Ranitidine treatment during a modest inflammatory response precipitates idiosyncrasy-like liver injury in rats

Drug idiosyncrasy is an adverse event of unknown etiology that occurs in a small fraction of people taking a drug. Some idiosyncratic drug reactions may occur from episodic decreases in the threshold for drug hepatotoxicity. Previous studies in rats have shown that modest underlying inflammation triggered by bacterial lipopolysaccharide (LPS) can decrease the threshold for xenobiotic hepatotoxicity. The histamine-2 (H2)-receptor antagonist ranitidine (RAN) causes idiosyncratic reactions in people, with liver as a usual target. We tested the hypothesis that RAN could be rendered hepatotoxic in animals undergoing a modest inflammatory response. Male rats were treated with a nonhepatotoxic dose of LPS (44 x 10(6) endotoxin units/kg i.v.) or its vehicle and then 2 h later with a nonhepatotoxic dose of RAN (30 mg/kg i.v.) or its vehicle. Liver injury was evident only in animals treated with both RAN and LPS as estimated by increases in serum alanine aminotransferase, aspartate aminotransferase, and gamma-glutamyl transferase activities within 6 h after RAN administration. LPS/RAN cotreatment resulted in midzonal liver lesions characterized by acute necrosuppurative hepatitis. Famotidine (FAM) is an H2-antagonist for which the propensity for idiosyncratic reactions is far less than RAN. Rats given LPS and FAM at a dose pharmacologically equipotent to that of RAN did not develop liver injury. In vitro, RAN sensitized hepatocytes to killing by cytotoxic products from activated neutrophils, whereas FAM lacked this ability. The results indicate that a response resembling human RAN idiosyncrasy can be reproduced in animals by RAN exposure during modest inflammation.

Inflammation and drug idiosyncrasy--is there a connection?

"Drug idiosyncrasy" refers to untoward reactions to drugs that occur in a small fraction of patients and have no obvious relationship to dose or duration of therapy. The liver is a frequent target for toxicity. Much of the conventional thinking about mechanisms of drug idiosyncrasy has centered on hypotheses that the reactions have a metabolic basis involving drug metabolism polymorphisms or that they arise from a specific immune response to the drug or its metabolite(s). For very few drugs does convincing evidence exist for either of these mechanisms, however. The erratic temporal and dose relationships that characterize idiosyncratic drug responses suggest the possibility that some event during the course of therapy renders tissues peculiarly susceptible to toxic effects of the drug. For example, episodes of inflammation are commonplace in people, and results of numerous studies in animals indicate that a modest inflammatory response can enhance tissue sensitivity to a variety of toxic chemicals. These observations have led to the hypothesis that an episode of inflammation during drug therapy could decrease the threshold for drug toxicity and thereby render an individual susceptible to a toxic reaction that would not otherwise occur (i.e., an "idiosyncratic" response). This hypothesis can explain the features of drug idiosyncrasy using fundamental pharmacologic principles, and results of recent animal studies are supportive of this. Knowledge gaps that need to be filled before the hypothesis should be widely accepted are discussed.

The coagulation system contributes to synergistic liver injury from exposure to monocrotaline and bacterial lipopolysaccharide

Coexposure to a noninjurious dose of bacterial lipopolysaccharide (LPS; 7.4 x 106 EU/kg) and a nontoxic dose of the food-borne toxin monocrotaline (MCT; 100 mg/kg) leads to synergistic hepatotoxicity in Sprague-Dawley rats. Inflammatory factors, such as Kupffer cells (KCs), tumor necrosis factor-alpha (TNF)-alpha, and neutrophils (polymorphonuclear leukocytes; PMNs), are critical to the pathogenesis. Inasmuch as activation of the coagulation system and sinusoidal endothelial cell (SEC) injury precede hepatic parenchymal cell (HPC) injury, and since fibrin deposition occurs within liver lesions, the coagulation system might be a critical component of injury. In this study, this hypothesis is tested, and the interdependence of the coagulation system and inflammatory factors is explored. Administration of the anticoagulants heparin or warfarin to MCT/LPS-cotreated animals attenuated HPC and SEC injury. Morphometric analysis revealed that anticoagulant treatment significantly reduced the area of centrilobular and midzonal lesions. Heparin treatment also reduced fibrin deposition in these regions. Furthermore, anticoagulant treatment decreased hepatic PMN accumulation but did not affect plasma TNF-alpha concentration. Neither KC inactivation nor TNF-alpha depletion prevented activation of the coagulation system. PMN depletion, however, prevented coagulation system activation, suggesting that PMNs are needed for this response. These results provide evidence that the coagulation system and its interplay with PMNs are important in the pathogenesis of MCT/LPS-induced liver injury.

Differential induction of glucocorticoid-dependent apoptosis in murine lymphoid subpopulations in vivo following coexposure to lipopolysaccharide and vomitoxin (deoxynivalenol)

Lipopolysaccharide (LPS) and vomitoxin (VT) synergistically induce glucocorticoid- mediated apoptotic cell death in lymphoid tissues of the mouse. Based on the known effects of glucocorticoids, it was hypothesized that the combined exposure to LPS and VT targets immature lymphocyte populations. To test this hypothesis, we quantified the effects of VT and LPS on apoptosis induction in T lymphocyte subsets in thymus and B lymphocyte subsets in Peyer's patches and bone marrow. Flow cytometry revealed that a single dose of LPS (0.1 mg/kg body wt ip) together with VT (12.5 mg/kg body wt po) promoted apoptosis of immature (CD4(-)CD8(-), CD4(+)CD8(+)) and mature (CD4(-)CD8(+)) thymocytes at 12 h with a subsequent reduction of these populations being detectable at 24 h. RU 486, a glucocorticoid receptor antagonist, significantly abrogated apoptosis in CD4(-)CD8(-), CD4(+)CD8(+), and CD4(-)CD8(+) subsets and also prevented loss in cell numbers. In Peyer's patches, mature-B lymphocytes (B220(+)IgM(-)IgD(+)) underwent apoptosis and, in bone marrow, pro/pre-B lymphocytes (B220(+)IgM(-)IgD(-)) and mature-B lymphocytes (B220(+)IgM(-)IgD(+)) underwent apoptosis at 12 h after toxin co- exposure. RU 486 blocked LPS + VT-induced apoptosis of the aforementioned subsets in Peyer patches and bone marrow at 12 h. Taken together, these data suggest that LPS can interact with VT in mice to induce the glucocorticoid-driven apoptotic loss of immature thymocytes and cytotoxic T lymphocytes in thymus, mature-B lymphocytes in Peyer's patch, and pro/pre-B lymphocytes and mature-B lymphocytes in bone marrow in mice.

The temporal relationship between bacterial lipopolysaccharide and monocrotaline exposures influences toxicity: shift in response from hepatotoxicity to nitric oxide-dependent lethality

Liver injury from a variety of hepatotoxicants, including the food-borne phytotoxin monocrotaline (MCT), can be augmented by exposure to a noninjurious dose of the inflammagen bacterial lipopolysaccharide (LPS). In a previous study, a nontoxic dose of LPS given 4 h after MCT resulted in synergistic hepatotoxicity within 12-18 h. This study was designed to determine whether temporal differences in MCT and LPS exposure affect toxicity. When LPS (3.4 x 10(6) EU/kg; iv) was given one hour before MCT (100 mg/kg; ip), hepatotoxicity developed between 4 and 8 h after MCT administration, and mortality was much greater than when LPS was administered 4 h after MCT. To explore this difference, the temporal relationship between LPS and MCT exposure (7.4 x 10(6) EU/kg and 100 mg/kg, respectively) was altered. Twenty-four-hour survival was high in animals that received LPS 4 h before (86%) or after (88%) MCT, but it decreased markedly when LPS was administered 1 h before MCT (17%). Using this latter dosing regimen, animals became moribund as early as 4 h after MCT administration. Since liver injury was similar from regimens that differed greatly in mortality, death appeared to result from extrahepatic causes. To explore a role for nitric oxide (NO)-induced shock in this regimen, animals were treated with aminoguanidine (AG), an inhibitor of inducible NO synthase, prior to administration of LPS given an hour before MCT. In the cotreated animals, AG significantly attenuated mortality and decreased plasma nitrate/nitrite concentrations, markers of NO biosynthesis. Hence, the primary target of toxicity from MCT and LPS cotreatment appeared to shift from the liver to an extrahepatic site or sites as exposure to these agents occurred closer together temporally. NO appears to be causally involved in the deaths of animals treated with LPS 1 h before MCT.

Anticoagulants prevent monocrotaline-induced hepatic parenchymal cell injury but not endothelial cell injury in the rat

Monocrotaline (MCT) is a pyrrolizidine alkaloid plant toxin that produces hepatotoxicity in humans and animals. Human exposure to MCT occurs through consumption of contaminated grains and herbal medicines. Administration of MCT to rats stimulates activation of the coagulation system and fibrin deposition in the liver. Fibrin deposition occurs simultaneously with endothelial cell damage and prior to hepatic parenchymal cell injury. Accordingly, the hypothesis that activation of the coagulation system is required for MCT-induced liver injury was tested. Treatment of rats with either heparin or warfarin significantly reduced MCT-induced activation of the coagulation system and the increase in alanine aminotransferase activity in the plasma, a biomarker of hepatic parenchymal cell injury. Histopathological examination of liver sections revealed that heparin decreased parenchymal cell necrosis but did not affect central venular endothelial cell damage, congestion and dilation of the sinusoids, or hemorrhage in the liver. Morphometric analysis revealed that 28% of the area of livers from MCT-treated rats contained regions of coagulative necrosis, whereas less than 5% of the area of livers from rats treated with MCT and heparin contained these regions. By contrast, neither heparin nor warfarin prevented MCT-induced damage to endothelial cells in the liver as estimated by increased plasma hyaluronic acid concentration. These results suggest that activation of the coagulation system is required for MCT-induced parenchymal cell injury but not endothelial cell injury in the liver.

Underlying endotoxemia augments toxic responses to chlorpromazine: is there a relationship to drug idiosyncrasy?

Idiosyncratic reactions occur in a small fraction (typically <5%) of the population taking therapeutic drugs. Chlorpromazine (CPZ) is a phenothiazine, antipsychotic drug that has caused several idiosyncratic responses during its therapeutic use. Clinical evidence suggests that conditions associated with inflammation are risk factors for the appearance of these responses. Accordingly, we tested the hypothesis that an inflammatory stimulus, bacterial lipopolysaccharide (LPS), renders animals susceptible to CPZ-induced idiosyncratic reactions seen in humans. Male Sprague-Dawley rats (200-250 g) were fasted for 24 h. A small dose of LPS (7.4 x 10(6) EU/kg from Escherichia coli) or its vehicle (saline) was administered by tail vein 2 h before an intraperitoneal injection of CPZ (70 mg/kg) or its vehicle (saline). Cholestasis and hepatocellular necrosis were evaluated as increased concentrations of serum bile acids and bilirubin and increased activities of alkaline phosphatase, gamma-glutamyltransferase, alanine aminotransferase, and aspartate aminotransferase. With the exception of bile acids, these serum markers were elevated in animals treated with LPS/CPZ. Histopathological lesions in liver sections were consistent with these findings. Elevated serum creatine kinase activity, which is associated with human idiosyncratic responses to phenothiazines, was also found in animals treated with LPS/CPZ, but not with either LPS or CPZ alone. These results raise the possibility that concurrent, modest inflammation may underlie susceptibility of individuals to certain idiosyncratic reactions and may form the basis for an animal model with which to understand and predict drug idiosyncrasy.