Modes of cell death in rat liver after monocrotaline exposure

Combined Hepatotoxicity and Toxicity Mechanism of Intermedine and Lycopsamine

Pyrrolizidine alkaloids (PAs) are common constituents of plants and have serious hepatotoxicity. Intermedine (Im) and lycopsamine (La) are two monoesters of PAs that frequently coexist in the PA-containing plants (e.g., comfrey and tea). The present study aimed to explore the combined hepatotoxicity and toxicity mechanism of the Im and La mixture. In vitro, the combined cytotoxicity of the Im and La mixture on human hepatocytes (HepD) was examined by CCK-8, colony formation, wound healing, and Annexin V/PI staining assays. The combination of Im and La inhibited the ability of HepD cells to proliferate, colonize, and migrate and induced hepatocytes apoptosis in a dose-dependent manner. In addition to significantly causing a burst of intracellular reactive oxygen species (ROS), mitochondrial apoptosis, and endoplasmic reticulum (ER) stress, the Im and La mixture can also cause an increase in intracellular Ca2+, triggering the PERK/eIF2α/ATF4/CHOP apoptosis pathway. This study provided the first direct evidence that the combined PAs induced hepatotoxicity through ER-mediated apoptosis. These results supplemented the basic toxicity data for the combined PAs and provided a new perspective for the risk assessment of combined PA toxicity.

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.

Pyrrolizidine Alkaloids Induce Cell Death in Human HepaRG Cells in a Structure-Dependent Manner

Pyrrolizidine alkaloids (PAs) are a group of secondary metabolites produced in various plant species as a defense mechanism against herbivores. PAs consist of a necine base, which is esterified with one or two necine acids. Humans are exposed to PAs by consumption of contaminated food. PA intoxication in humans causes acute and chronic hepatotoxicity. It is considered that enzymatic PA toxification in hepatocytes is structure-dependent. In this study, we aimed to elucidate the induction of PA-induced cell death associated with apoptosis activation. Therefore, 22 structurally different PAs were analyzed concerning the disturbance of cell viability in the metabolically competent human hepatoma cell line HepaRG. The chosen PAs represent the main necine base structures and the different esterification types. Open-chained and cyclic heliotridine- and retronecine-type diesters induced strong cytotoxic effects, while treatment of HepaRG with monoesters did not affect cell viability. For more detailed investigation of apoptosis induction, comprising caspase activation and gene expression analysis, 14 PA representatives were selected. The proapoptotic effects were in line with the potency observed in cell viability studies. In vitro data point towards a strong structure–activity relationship whose effectiveness needs to be investigated in vivo and can then be the basis for a structure-associated risk assessment.

Preventive treatment with ginsenoside Rb1 ameliorates monocrotaline-induced pulmonary arterial hypertension in rats and involves store-operated calcium entry inhibition

CONTEXT

Ginsenoside Rb1, the main active ingredient of ginseng, exhibits ex vivo depression of store-operated calcium entry (SOCE) and related vasoconstriction in pulmonary arteries derived from pulmonary hypertension (PH) rats. However, the in vivo effects of ginsenoside Rb1 on PH remain unclear.

OBJECTIVE

This study explored the possibility of using ginsenoside Rb1 as an in vivo preventive medication for type I PH, i.e., pulmonary arterial hypertension (PAH), and potential mechanisms involving SOCE.

MATERIALS AND METHODS

Male Sprague-Dawley rats (170-180 g) were randomly divided into Control, MCT, and MCT + Rb1 groups (n = 20). Control rats received only saline injection. Rats in the MCT + Rb1 and MCT groups were intraperitoneally administered single doses of 50 mg/kg monocrotaline (MCT) combined with 30 mg/kg/day ginsenoside Rb1 or equivalent volumes of saline for 21 consecutive days. Subsequently, comprehensive parameters related to SOCE, vascular tone, histological changes and hemodynamics were measured.

RESULTS

Ginsenoside Rb1 reduced MCT-induced STIM1, TRPC1, and TRPC4 expression by 35.00, 31.96, and 32.24%, respectively, at the protein level. SOCE-related calcium entry and pulmonary artery contraction decreased by 162.6 nM and 71.72%. The mean pulmonary artery pressure, right ventricle systolic pressure, and right ventricular mass index decreased by 19.5 mmHg, 21.6 mmHg, and 39.50%. The wall thickness/radius ratios decreased by 14.67 and 17.65%, and the lumen area/total area ratios increased by 18.55 and 15.60% in intrapulmonary vessels with 51-100 and 101-150 μm o.d.

CONCLUSION

Ginsenoside Rb1, a promising candidate for PH prevention, inhibited SOCE and related pulmonary vasoconstriction, and relieved MCT-induced PAH in rats.

Protein cross-linking in primary cultured mouse hepatocytes by dehydropyrrolizidine alkaloids: Structure-toxicity relationship

Pyrrolizidine alkaloids (PAs) are natural toxins found in about 3%-5% of flowering plants. Dehydropyrrolizidine alkaloids contain a double bond in 1, 2-position of the necine bases, including retronecine type PAs (RET-PAs) and their N-oxides (RET N-oxide-PAs), and otonecine type PAs (OTO-PAs), and are known for their significant hepatotoxicity. Most dehydropyrrolizidine alkaloids are metabolically activated by cytochrome P450 (CYP450) enzymes to generate active pyrroles, which further bind to proteins to form pyrrole-protein adducts (PPAs). Methods for predicting PA-induced liver injury are generally performed on in vitro models with extremely low activities of CYP450 enzymes, which is different from the situation in vivo. In this regard, primary cultured mouse hepatocytes, which showed comparable CYP450 activity with the in vivo models, were applied to illustrate the structure-toxicity relationship of 13 dehydropyrrolizidine alkaloids, namely, eight RET-PAs, three RET N-oxide-PAs, and two OTO-PAs. PA-induced cytotoxicity and PA-generated PPAs were analyzed in primary mouse hepatocytes treated with different PAs. Results showed that PA-induced toxicity was correlated with the amount of PA-generated PPAs. RET-PAs and OTO-PAs were generally more toxic than RET N-oxide-PAs and generated higher amount of PPAs. PPAs were utilized to evaluate the efficiency of metabolic activation and predict the toxic potencies of dehydropyrrolizidine alkaloids. The proposed model could be a new approach for toxicity evaluation and risk control of exposure to PAs.

Seneciphylline, a main pyrrolizidine alkaloid in Gynura japonica, induces hepatotoxicity in mice and primary hepatocytes via activating mitochondria-mediated apoptosis

Herbal drug-induced liver injury has been reported worldwide and gained global attention. Thousands of hepatic sinusoidal obstruction syndrome (HSOS) cases have been reported after consumption of herbal medicines and preparations containing pyrrolizidine alkaloids (PAs), which are natural phytotoxins globally distributed. And herbal medicines, such as Gynura japonica, are the current leading cause of PA-induced HSOS. The present study aimed to reveal the mechanism underlying the hepatotoxicity of seneciphylline (Seph), a main PA in G. japonica. Results showed that Seph induced severe liver injury through apoptosis in mice (70 mg/kg Seph, orally) and primary mouse and human hepatocytes (5-50 μM Seph). Further research uncovered that Seph induced apoptosis by disrupting mitochondrial homeostasis, inducing mitochondrial depolarization, mitochondrial membrane potential (MMP) loss, and cytochrome c (Cyt c) release and activating c-Jun N-terminal kinase (JNK). The Seph-induced apoptosis in hepatocytes could be alleviated by Mdivi-1 (50 μM, a dynamin-related protein 1 inhibitor), as well as SP600125 (25 μM, a specific JNK inhibitor) and ZVAD-fmk (50 μM, a general caspase inhibitor). Moreover, the Seph-induced MMP loss in hepatocytes was also rescued by Mdivi-1. In conclusion, Seph induced liver toxicity via activating mitochondrial-mediated apoptosis in mice and primary hepatocytes. Our results provide further information on Seph detoxification and herbal medicines containing Seph such as G. japonica.

Monocrotaline-induced liver toxicity in rat predicted by a combined in vitro physiologically based kinetic modeling approach

The aim of the present study was to use an in vitro–in silico approach to predict the in vivo acute liver toxicity of monocrotaline and to characterize the influence of its metabolism on its relative toxic potency compared to lasiocarpine and riddelliine. In the absence of data on acute liver toxicity of monocrotaline upon oral exposure, the predicted dose–response curve for acute liver toxicity in rats and the resulting benchmark dose lower and upper confidence limits for 10% effect (BMDL₁₀ and BMDU₁₀) were compared to data obtained in studies with intraperitoneal or subcutaneous dosing regimens. This indicated the predicted BMDL₁₀ value to be in line with the no-observed-adverse-effect levels (NOAELs) derived from availabe in vivo studies. The predicted BMDL₁₀–BMDU₁₀ of 1.1–4.9 mg/kg bw/day also matched the oral dose range of 1–3 mg PA/kg bw/day at which adverse effects in human are reported. A comparison to the oral toxicity of the related pyrrolizidine alkaloids (PAs) lasiocarpine and riddelliine revealed that, although in the rat hepatocytes monocrotaline was less toxic than lasiocarpine and riddelliine, due to its relatively inefficient clearance, its in vivo acute liver toxicity was predicted to be comparable. It is concluded that the combined in vitro-PBK modeling approach can provide insight in monocrotaline-induced acute liver toxicity in rats, thereby filling existing gaps in the database on PA toxicity. Furthermore, the results reveal that the kinetic and metabolic properties of PAs can vary substantially and should be taken into account when considering differences in relative potency between different PAs.

The pyrrolizidine alkaloid senecionine induces CYP-dependent destruction of sinusoidal endothelial cells and cholestasis in mice

Pyrrolizidine alkaloids (PAs) are widely occurring phytotoxins which can induce severe liver damage in humans and other mammalian species by mechanisms that are not fully understood. Therefore, we investigated the development of PA hepatotoxicity in vivo, using an acutely toxic dose of the PA senecionine in mice, in combination with intravital two-photon microscopy, histology, clinical chemistry, and in vitro experiments with primary mouse hepatocytes and liver sinusoidal endothelial cells (LSECs). We observed pericentral LSEC necrosis together with elevated sinusoidal marker proteins in the serum of senecionine-treated mice and increased sinusoidal platelet aggregation in the damaged tissue regions. In vitro experiments showed no cytotoxicity to freshly isolated LSECs up to 500 µM senecionine. However, metabolic activation of senecionine by preincubation with primary mouse hepatocytes increased the cytotoxicity to cultivated LSECs with an EC50 of approximately 22 µM. The cytochrome P450 (CYP)-dependency of senecionine bioactivation was confirmed in CYP reductase-deficient mice where no PA-induced hepatotoxicity was observed. Therefore, toxic metabolites of senecionine are generated by hepatic CYPs, and may be partially released from hepatocytes leading to destruction of LSECs in the pericentral region of the liver lobules. Analysis of hepatic bile salt transport by intravital two-photon imaging revealed a delayed uptake of a fluorescent bile salt analogue from the hepatic sinusoids into hepatocytes and delayed elimination. This was accompanied by transcriptional deregulation of hepatic bile salt transporters like Abcb11 or Abcc1. In conclusion, senecionine destroys LSECs although the toxic metabolite is formed in a CYP-dependent manner in the adjacent pericentral hepatocytes.

Human CYP3A4-mediated toxification of the pyrrolizidine alkaloid lasiocarpine

Pyrrolizidine alkaloids (PA) are widely distributed phytotoxins contaminating food and feed. Hepatic enzymes are considered to bioactivate PA. Previous studies showed differences in the metabolism rate in liver homogenates of different species. Thus, uncertainty remains with respect to the relevance of human metabolism. Our study aimed to analyze whether the PA representative lasiocarpine is toxified by human cytochrome P450 (CYP) enzymes. We compared the metabolic elimination of lasiocarpine in the presence of rat and human S9 fractions and liver microsomes. Experiments with the potent CYP3A/Cyp3a inhibitor ketoconazole and supersomes containing individual human and rat CYPs revealed that enzymes of the CYP3A/Cyp3a family of both species are of major relevance for lasiocarpine metabolism. To assess if metabolism by human CYP3A4 results in a toxification of lasiocarpine we performed experiments with V79 cells. γH2AX and micronucleus formation were analyzed as endpoints for genotoxicity. No effects were observed in the wildtype cells, which lack CYP activity. By contrast, a V79 clone engineered for expression of human CYP3A4 showed concentration-dependent γH2AX and micronucleus formation. Concluding, our results showed the CYP3A4-dependent formation of genotoxic metabolites of lasiocarpine. The results confirm previous data indicating the need to include metabolism of PA for human risk assessment.

Development of a two-layer transwell co-culture model for the in vitro investigation of pyrrolizidine alkaloid-induced hepatic sinusoidal damage

Pyrrolizidine alkaloids (PAs) are hepatotoxic and specifically damage hepatic sinusoidal endothelial cells (HSECs) via cytochrome P450 enzymes (CYPs)-mediated metabolic activation. Due to the lack of CYPs in HSECs, currently there is no suitable cell model for investigating PA-induced HSEC injury. This study aimed to establish a two-layer transwell co-culture model that mimics hepatic environment by including HepaRG hepatocytes and HSECs to evaluate cytotoxicity of PAs on their major target HSECs. In this model, PAs were metabolically activated by CYPs in HepaRG hepatocytes to generate reactive pyrrolic metabolites, which react with co-cultured HSECs leading to HSEC damage. Three representative PAs, namely retrorsine, monocrotaline, and clivorine, induced significant concentration-dependent cytotoxicity in HSECs in the co-culture model, but did no cause obvious cytotoxicity directly in HSECs. Using the developed co-cultured model, further mechanism studies of retrorsine-induced HSEC damage demonstrated that the reactive pyrrolic metabolite generated by CYP-mediated bioactivation in HepaRG hepatocytes caused formation of pyrrole-protein adducts, reduction of GSH content, and generation of reactive oxygen species in HSECs, leading to cell apoptosis. The established co-culture model is reliable and applicable for cytotoxic assessment of PA-induced HSEC damage and offers a novel platform for screening toxicity of different PAs on their target cells.

Sensitization of Human Liver Cells Toward Fas-Mediated Apoptosis by the Metabolically Activated Pyrrolizidine Alkaloid Lasiocarpine

SCOPE

Pyrrolizidine alkaloids (PAs) are common phytotoxins. Intoxication can lead to liver damage. Previous studies showed PA-induced apoptosis in liver cells. However, the exact role of the extrinsic apoptotic pathway has not been investigated yet. This study aims to analyze whether the PA representative lasiocarpine sensitizes human liver cells toward extrinsic Fas-mediated apoptosis.

METHODS AND RESULTS

HepG2 cells with limited xenobiotic metabolic activity are used to analyze metabolism-dependent effects. External in vitro metabolism is simulated using rat or human liver enzymes. Additionally, metabolically competent HepaRG cells are used to confirm the observed effects in a human liver cell system with internal xenobiotic metabolism. Metabolized lasiocarpine decreases cell viability and induces Fas receptor gene expression in both cell lines. Increased Fas receptor protein expression on the cell surface is demonstrated by flow cytometry. The addition of a Fas ligand-simulating antibody induces apoptosis. Induction of extrinsic Fas-mediated apoptosis is verified by Western blotting for cleaved caspase 8, the initiator caspase of extrinsic apoptosis. All effects are dependent on lasiocarpine metabolism.

CONCLUSION

The results demonstrate that metabolically metabolized lasiocarpine sensitizes human liver cells toward Fas-mediated apoptosis. They broaden our knowledge on the hepatotoxic molecular mechanisms of PA as widely distributed food contaminants.

Structure-dependent induction of apoptosis by hepatotoxic pyrrolizidine alkaloids in the human hepatoma cell line HepaRG: Single versus repeated exposure

Pyrrolizidine alkaloids (PA) are secondary plant compounds. PA intoxication in humans causes severe acute and chronic hepatotoxicity. However, the molecular mechanisms of PA hepatotoxicity in humans are not well understood yet. Therefore, we investigated cell death parameters in human HepaRG cells following either single (24 h) or repeated dose treatment (14 d) with structurally different PA of the retronecine (echimidine, senecionine), heliotridine (heliotrine), and otonecine type (senkirkine). After 24 h of exposure only retronecine-type PA were cytotoxic in HepaRG cells and induced apoptosis indicated by a loss of membrane asymmetry, disruption of the mitochondrial membrane potential, and increased pro-caspase and PARP cleavage. In contrast, after 14 d all four PA exerted the aforementioned effects. Furthermore, the apoptotic events caspase 3, 8 and 9 activation as well as nuclear condensation and DNA fragmentation were only detected for the retronecine-type PA after single exposure (6 h). Overall, our studies revealed a time- and structure-dependent apoptosis after PA exposure, suggesting that retronecine-type PA seem to be more potent apoptosis inducers than heliotridine- or otonecine-type PA. Furthermore, our results suggest that PA-induced apoptosis in HepaRG cells occur most probably by involving both, the extrinsic death receptor pathway as well as the intrinsic mitochondrial pathway.

Differential induction of apoptosis and autophagy by pyrrolizidine alkaloid clivorine in human hepatoma Huh-7.5 cells and its toxic implication

Growing evidence suggests that the pyrrolizidine alkaloids (PAs)-induced hepatotoxicity is mediated by multiple cell death/defence modalities. However, the detailed mechanisms are still lacking. In this study, the hepatotoxic effects of four PAs including three retronecine-type ones (senecionine, seneciphylline and monocrotaline) and one otonecine-type (clivorine) on the proliferation of Huh-7.5 cells and the possible mechanisms were investigated. The results showed that all the PAs could inhibit cell proliferation and induce apoptosis in a concentration-dependent manner. Among them clivorine was the most significant one. In addition to its effect on apoptosis, clivorine treatment could promote autophagy in Huh-7.5 cells, as evidenced by the accumulation of autophagosomes, the enhancement of LC3B expression at the concentrations close to its IC0 value, and the increased conversion of LC3B-I to LC3B-II in the presence of lysosomal inhibitor (chloroquine) and decreased formation of green fluorescent protein (GFP)-LC3 positive puncta in the presence of autophagic sequestration inhibitor (3-methyladenine). Among the other tested PAs, senecionine and seneciphylline also activated autophagy at the same concentrations used for clivorine but monocrotaline did not. Furthermore, our study demonstrated that suppression or enhancement of autophagy resulted in the remarkable enhancement or suppression of senecionine, seneciphylline and clivorine-induced apoptosis at the concentration close to the IC10 for clivorine, respectively, indicating a protective role of autophagy against the PA-induced apoptosis at the low level of exposure. Collectively, our data suggest that PAs in different structures may exert different toxic disturbances on the liver cells. Apoptosis may be one of the most common models of the PA-induced cytotoxicity, while autophagy may be a structure-dependent defence model in the early stage of PA intoxication. Differential induction of apoptosis and autophagy probably depending on the concentration is essential for the cytotoxic potency of clivorine.

Inhibition of Drp1 protects against senecionine-induced mitochondria-mediated apoptosis in primary hepatocytes and in mice

Pyrrolizidine alkaloids (PAs) are a group of compounds found in various plants and some of them are widely consumed in the world as herbal medicines and food supplements. PAs are potent hepatotoxins that cause irreversible liver injury in animals and humans. However, the mechanisms by which PAs induce liver injury are not clear. In the present study, we determined the hepatotoxicity and molecular mechanisms of senecionine, one of the most common toxic PAs, in primary cultured mouse and human hepatocytes as well as in mice. We found that senecionine administration increased serum alanine aminotransferase levels in mice. H&E and TUNEL staining of liver tissues revealed increased hemorrhage and hepatocyte apoptosis in liver zone 2 areas. Mechanistically, senecionine induced loss of mitochondrial membrane potential, release of mitochondrial cytochrome c as well as mitochondrial JNK translocation and activation prior to the increased DNA fragmentation and caspase-3 activation in primary cultured mouse and human hepatocytes. SP600125, a specific JNK inhibitor, and ZVAD-fmk, a general caspase inhibitor, alleviated senecionine-induced apoptosis in primary hepatocytes. Interestingly, senecionine also caused marked mitochondria fragmentation in hepatocytes. Pharmacological inhibition of dynamin-related protein1 (Drp1), a protein that is critical to regulate mitochondrial fission, blocked senecionine-induced mitochondrial fragmentation and mitochondrial release of cytochrome c and apoptosis. More importantly, hepatocyte-specific Drp1 knockout mice were resistant to senecionine-induced liver injury due to decreased mitochondrial damage and apoptosis. In conclusion, our results uncovered a novel mechanism of Drp1-mediated mitochondrial fragmentation in senecionine-induced liver injury. Targeting Drp1-mediated mitochondrial fragmentation and apoptosis may be a potential avenue to prevent and treat hepatotoxicity induced by PAs.

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Senecionine induces apoptosis in primary mouse and human hepatocytes as well as in mouse livers.

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Senecionine induces mitochondrial Drp1 translocation, mitochondrial fragmentation, loss of mitochondrial membrane potential and release of mitochondrial cytochrome c in hepatocytes.

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Pharmacological inhibition or genetic deletion of Drp1 protects against senecionine-induced hepatotoxicity.

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Targeting Drp1-mediated mitochondrial fragmentation and apoptosis may be a potential avenue to prevent and treat hepatotoxicity induced by Pyrrolizidine alkaloids.

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.

Assessment of pyrrolizidine alkaloid-induced toxicity in an in vitro screening model

ETHNOPHARMACOLOGICAL RELEVANCE

Pyrrolizidine alkaloids (PAs) are a group of heterocyclic phytotoxins present in a wide range of plants. The consumption of PA-containing medicinal herbs or PA-contaminated foodstuffs has long been reported to cause human hepatotoxicity. However, the degrees of hepatotoxicity of different PAs are unknown, which makes it difficult to determine a universal threshold of toxic dose of individual PAs for safe regulation of PA-containing natural products. The aim of the present study is to develop a simple and convenient in vitro model to assess the hepatotoxicity of different PAs.

MATERIAL AND METHODS

Six common cytotoxicity assays were used to evaluate the hepatotoxicity of different PAs in human hepatocellular carcinoma HepG2 cells.

RESULTS

The combination of MTT and bromodeoxyuridine incorporation (BrdU) assays demonstrated to be a suitable method to evaluate the toxic potencies of various PAs in HepG2 cells, and the results indicated that otonecine-type PA (clivorine: IC₂₀=0.013 ± 0.004 mM (MTT), 0.066 ± 0.031 mM (BrdU)) exhibited significantly higher cytotoxic and anti-proliferative effects than retronecine-type PA (retrorsine: IC₂₀=0.27 ± 0.07 mM (MTT), 0.19 ± 0.03 mM (BrdU)). While as expected, the known less toxic platyphylline-type PA (platyphylline: IC₂₀=0.85 ± 0.11 mM (MTT), 1.01 ± 0.40 mM (BrdU)) exhibited significantly less toxicity. The different cytotoxic and anti-proliferative potencies of various PAs in the same retronecine-type could also be discriminated by using the combined MTT and BrdU assays. In addition, the developed assays were further utilized to test alkaloid extract of Gynura segetum, a senecionine and seneciphylline-containing herb, the overall cytotoxicity of two PAs in the extract was comparable to that of these two PAs tested individually.

CONCLUSION

Using the developed in vitro model, the cytotoxicity of different PAs and the extract of a PA-containing herb were investigated in parallel in one system, and their different hepatotoxic potencies were determined and directly compared for the first time. The results suggested that the developed model has a great potential to be applied for the quick screening of the toxicity of PAs and PA-containing natural products.

Potentiation of the hepatic toxicity of carbon disulfide by chlordane

Objectives:

In this study, we investigated whether cytochrome P450s (CYPs) induced by a typical chlorinated hydrocarbon insecticide chlordane (CLD) potentiate hepatic toxicity of carbon disulfide (CS₂).

Materials and Methods:

Male Sprague-Dawley rats were treated with CLD (25 mg/kg, intraperitoneally (i.p.)) daily for 4 days, and 24 h after the final injection the rats were treated with CS₂ (380 mg/kg, i.p.) in corn oil; while controls received the vehicle alone. The rats were then sacrificed at 3, 6, and 24 h following the CS₂ treatment.

Results:

It was found that at 3 h post-treatment, total hepatic glutathione (GSH) decreased modestly, but lipid peroxidation increased markedly, while all CLD-inducible CYPs (1A1, 2B1, 2E1, and 3A2) were inhibited by CS₂ variably but significantly. On the other hand, samples taken at 24 h following the CS2 treatment showed a significant increase in relative liver weights, hepatic GSH and lipid peroxidation, microsomal reactive oxygen species (ROS), and serum alanine transaminase (ALT) level. Activity of the CYPs was also increased, but remained significantly depressed, especially that of CYP2B1. Livers removed at 3 and 6 h after CS₂ treatment showed subtle to distinct apoptotic changes, while a severe lesion of hydropic degeneration of the centrilobular cells with apoptosis was microscopically distinguishable in samples taken at 24 h.

Conclusions:

These results suggest that the metabolism of CS₂ by CLD-induced CYPs and the generation of lipid peroxides may have in concert contributed to the distinct hepatocellular damage.

Roles of the hemostatic system and neutrophils in liver injury from co-exposure to amiodarone and lipopolysaccharide

It has been demonstrated that co-treatment of rats with amiodarone (AMD) and bacterial lipopolysaccharide (LPS) produces idiosyncrasy-like liver injury. In this study, the hypothesis that the hemostatic system and neutrophils contribute to AMD/LPS-induced liver injury was explored. Rats were treated with AMD (400 mg/kg, ip) or vehicle and 16 h later with LPS (1.6×10⁶ endotoxin units/kg, iv) or saline (Sal). AMD did not affect the hemostatic system by itself but significantly potentiated LPS-induced coagulation activation and fibrinolysis impairment. Increased hepatic fibrin deposition and subsequent hypoxia were observed only in AMD/LPS-treated animals, starting before the onset of liver injury. Administration of anticoagulant heparin abolished AMD/LPS-induced hepatic fibrin deposition and reduced AMD/LPS-induced liver damage. Polymorphonuclear neutrophils (PMNs) accumulated in liver after treatment with LPS or AMD/LPS, but PMN activation was only observed in AMD/LPS-treated rats. Rabbit anti-rat PMN serum, which reduced accumulation of PMNs in liver, prevented PMN activation and attenuated AMD/LPS-induced liver injury in rats. PMN depletion did not affect hepatic fibrin deposition. Anticoagulation prevented PMN activation without affecting PMN accumulation. In summary, both the hemostatic system alteration and PMN activation contributed to AMD/LPS-induced liver injury in rats, in which fibrin deposition was critical for the activation of PMNs.

Organic cation transporter 1 mediates the uptake of monocrotaline and plays an important role in its hepatotoxicity

Monocrotaline (MCT) is a kind of toxic retronecine-type pyrrolizidine alkaloids (PAs) from plants of Crotalaria, which can be bio-activated by cytochrome P450 (CYP) enzymes in liver and then induce hepatotoxicity. Since CYPs are localized in the endoplasmic reticulum, the influx of MCT to the liver is the key step for its hepatotoxicity. The objective of the present study was to investigate the role of organic cation transporter 1 (OCT1), a transporter mainly expressed in liver, in the uptake of MCT and in hepatotoxicity induced by MCT. The results revealed that MCT markedly inhibited the uptake of 1-methyl-4-phenylpyridinium (MPP(+)), an OCT1 substrate, in Madin-Darby canine kidney (MDCK) cells stably expressing human OCT1 (MDCK-hOCT1) with the IC50 of 5.52±0.56μM. The uptake of MCT was significantly higher in MDCK-hOCT1 cells than in MDCK-mock cells, and MCT uptake in MDCK-hOCT1 cells followed Michaelis-Menten kinetics with the Km and Vmax values of 25.0±6.7μM and 266±64pmol/mg protein/min, respectively. Moreover, the OCT1 inhibitors, such as quinidine, d-tetrahydropalmatine (d-THP), obviously inhibited the uptake of MCT in MDCK-hOCT1 cells and isolated rat primary hepatocytes, and attenuated the viability reduction and LDH release of the primary cultured rat hepatocytes caused by MCT. In conclusion, OCT1 mediates the hepatic uptake of MCT and may play an important role in MCT induced-hepatotoxicity.

Hypoxia-inducible factor activation in myeloid cells contributes to the development of liver fibrosis in cholestatic mice

Macrophages play an integral role in the development of liver fibrosis by releasing mediators, such as platelet-derived growth factor-B (PDGF-B) and transforming growth factor-β1, which stimulate hepatic stellate cell proliferation, chemotaxis, and collagen production. However, the mechanism by which chronic liver injury stimulates macrophages to release these mediators is not completely understood. We tested the hypothesis that chronic liver injury activates hypoxia-inducible factor (HIF) transcription factors in macrophages that regulate the production of mediators that promote fibrosis. To test this hypothesis, Cre/lox technology was used to generate myeloid cell-specific HIF-1α or HIF-1β knockout mice. When these mice were subjected to bile duct ligation (BDL), levels of α-smooth muscle actin and type I collagen in the liver were reduced compared with those of mice with normal levels of HIFs. The deficiency of HIFs in macrophages did not affect liver injury or inflammation after BDL but reduced PDGF-B mRNA and protein, suggesting that HIF activation in macrophages may promote fibrosis by regulating the production of PDGF-B. Consistent with a role for HIFs in liver fibrosis in cholestatic liver disease, nuclear HIF-1α protein was present in macrophages, hepatocytes, and fibroblasts in the livers from patients with primary biliary cirrhosis and primary sclerosing cholangitis. These studies demonstrate that HIFs are important regulators of profibrotic mediator production by macrophages during the development of liver fibrosis and suggest that HIFs may be a novel therapeutic target for the treatment of chronic liver disease in patients.

The monocrotaline model of pulmonary hypertension in perspective

Severe forms of pulmonary arterial hypertension (PAH) are characterized by various degrees of remodeling of the pulmonary arterial vessels, which increases the pulmonary vascular resistance and right ventricular afterload, thus contributing to the development of right ventricle dysfunction and failure. Recent years have seen advances in the understanding of the pathobiology of PAH; however, many important questions remain unanswered. Elucidating the pathobiology of PAH continues to be critical to design new effective therapeutic strategies, and appropriate animal models of PAH are necessary to achieve the task. Although the monocrotaline rat model of PAH has contributed to a better understanding of vascular remodeling in pulmonary hypertension, we question the validity of this model as a preclinically relevant model of severe plexogenic PAH. Here we review pertinent publications that either have been forgotten or ignored, and we reexamine the monocrotaline model in the context of human forms of PAH.

Cytotoxicity of monocrotaline in isolated rat hepatocytes: effects of dithiothreitol and fructose

Monocrotaline (MCT) is a pyrrolizidine alkaloid present in plants of the Crotalaria species that 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 (DHM). In previous studies using isolated rat liver mitochondria, we observed that DHM, but not MCT, inhibited the activity of respiratory chain complex I and stimulated the mitochondrial permeability transition with the consequent release of cytochrome c. In this study, we evaluated the effects of MCT and DHM on isolated rat hepatocytes. DHM, but not MCT, caused inhibition of the NADH-linked mitochondrial respiration. When hepatocytes of rats pre-treated with dexamethasone were incubated with MCT (5 mM), they showed ALT leakage, impaired ATP production and decreased levels of intracellular reduced glutathione and protein thiols. In addition, MCT caused cellular death by apoptosis. The addition of fructose or dithiotreitol to the isolated rat hepatocyte suspension containing MCT prevented the ATP depletion and/or glutathione or thiol oxidation and decreased the ALT leakage and apoptosis. These results suggest that the toxic effect of MCT on hepatocytes may be caused by metabolite-induced mitochondrial energetic impairment, together with a decrease of cellular glutathione and protein thiols.

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

HIF-1α is a nuclear factor important in the transcription of genes controlling angiogenesis including vascular endothelial growth factor (VEGF). Both hypoxia and oxidative stress are known mechanisms for the induction of HIF-1α. Oxidative stress and mitochondrial permeability transition (MPT) are mechanistically important in acetaminophen (APAP) toxicity in the mouse. MPT may occur as a result of oxidative stress and leads to a large increase in oxidative stress. We previously reported the induction of HIF-1α in mice with APAP toxicity and have shown that VEGF is important in hepatocyte regeneration following APAP toxicity. The following study was performed to examine the relative contribution of hypoxia versus oxidative stress to the induction of HIF-1α in APAP toxicity in the mouse. Time course studies using the hypoxia marker pimonidazole showed no staining for pimonidazole at 1 or 2h in B6C3F1 mice treated with APAP. Staining for pimonidazole was present in the midzonal to periportal regions at 4, 8, 24 and 48h and no staining was observed in centrilobular hepatocytes, the sites of the toxicity. Subsequent studies with the MPT inhibitor cyclosporine A showed that cyclosporine A (CYC; 10mg/kg) reduced HIF-1α induction in APAP treated mice at 1 and 4h and did not inhibit the metabolism of APAP (depletion of hepatic non-protein sulfhydryls and hepatic protein adduct levels). The data suggest that HIF-1α induction in the early stages of APAP toxicity is secondary to oxidative stress via a mechanism involving MPT. In addition, APAP toxicity is not mediated by a hypoxia mechanism.

Developing and Characterizing a Mouse Model of Hepatotoxicity Using Oral Pyrrolizidine Alkaloid (Monocrotaline) Administration, with Potentiation of the Liver Injury by Co-administration of LPS

Oral administration of xenobiotics is preferable for research in In Vivo models because it mimics the real life situation of human subjects. Therefore, oral (po) monocrotaline (MCT) (a common contaminant of dietary supplements)/intraperitoneal (ip) lipopolysaccharides (LPS)-induced liver injury possibly imitates idiosyncratic hepatotoxicity in humans. Cytokines, for example interleukin-1β (IL-1β) and transforming growth factor beta (TGF-β) are known to play a role in the development of toxicity and repair processes, respectively. The purpose of this study was to develop and characterize a model of po MCT/ip LPS hepatotoxicity which may elucidate the mechanisms of injury. ND4 male mice were given MCT (200 mg/kg) followed 4 h later by LPS (6 mg/kg). Blood samples were drawn for plasma chemistry and IL-1β. Animals were euthanized and livers were harvested at different time points. We have shown that MCT/LPS cotreatment results in significant elevation of plasma alanine aminotransferase (ALT), CRP, IL-1β and TGF-β. Histopathological evaluation revealed diffuse degenerative injury. In summary, we have established a reproducible in vivo model of hepatotoxicity by po MCT/ip LPS cotreatment that may closely mimic real life idiosyncratic hepatotoxicity.

Hepatic regeneration is decreased in a rat model of sinusoidal obstruction syndrome

BACKGROUND AND OBJECTIVES

Oxaliplatin is a chemotherapeutic drug for colorectal adenocarcinoma able to extend the indications for resection of colorectal liver metastases. However, the drug may severely injure hepatic sinusoids, inducing a sinusoidal obstruction syndrome in non-tumoral parenchyma with a risk of decreased regeneration in the remnant liver following partial hepatectomy.

METHODS

We then investigated the evolution of hepatic functions and liver regeneration following partial hepatectomy in rats with sinusoidal obstruction syndrome. The sinusoidal obstruction syndrome was induced with a single intragastric administration of monocrotaline (MCT).

RESULTS

MCT administration induced obstruction of the hepatic microcirculation and increased portal pressure, hepatic VEGF expression, and Ki67 positive hepatocytes. A mild cholestasis was present without modification of hepatic tests. Following a 70% hepatectomy, liver regeneration was significantly impaired by MCT administration and this impaired regeneration was associated with hepatocellular injury evidenced 1 week after hepatectomy.

CONCLUSIONS

The presence of sinusoidal obstruction syndrome impairs hepatic regeneration in this rat model of sinusoidal obstruction syndrome.

Dehydromonocrotaline induces cyclosporine A-insensitive mitochondrial permeability transition/cytochrome c release

Monocrotaline (MCT) is a pyrrolizidine alkaloid present in plants of the genus Crotalaria that causes cytotoxicity and genotoxicity in animals and humans. It is well established that the toxicity of MCT results from its hepatic bioactivation to dehydromonocrotaline (DHM), an alkylating agent, but the exact mechanism of action remains unknown. In a previous study, we demonstrated DHM's inhibition of mitochondrial NADH-dehydrogenase activity at micromolar concentrations, which is an effect associated with a significant reduction in ATP synthesis. As a follow-up study, we have evaluated the ability of DHM to induce mitochondrial permeability transition (MPT) and its associated processes in isolated rat liver mitochondria. In the presence of 10 microM Ca(2+), DHM (50-250 microM) elicited MPT in a concentration-dependent, but cyclosporine A-independent manner, as assessed by mitochondrial swelling, which is associated with mitochondrial Ca(2+) efflux and cytochrome c release. DHM (50-250 microM) did not cause hydrogen peroxide accumulation but did deplete endogenous glutathione and NAD(P)H, while oxidizing protein thiol groups. These results potentially indicate the involvement of mitochondria, via apoptosis, in the well-documented cytotoxicity of monocrotaline.

Hepatotoxic interaction of sulindac with lipopolysaccharide: role of the hemostatic system

Sulindac (SLD) is a nonsteroidal anti-inflammatory drug (NSAID) that has been associated with a greater incidence of idiosyncratic hepatotoxicity in human patients than other NSAIDs. One hypothesis regarding idiosyncratic adverse drug reactions is that interaction of a drug with a modest inflammatory episode precipitates liver injury. In this study, we tested the hypothesis that lipopolysaccharide (LPS) interacts with SLD to cause liver injury in rats. SLD (50 mg/kg) or its vehicle was administered to rats by gavage 15.5 h before LPS (8.3 x 10(5) endotoxin unit/kg) or its saline vehicle (i.v.). Thirty minutes after LPS treatment, SLD or vehicle administration was repeated. Rats were killed at various times after treatment, and serum, plasma, and liver samples were taken. Neither SLD nor LPS alone caused liver injury. Cotreatment with SLD/LPS led to increases in serum biomarkers of both hepatocellular injury and cholestasis. Histological evidence of liver damage was found only after SLD/LPS cotreatment. As a result of activation of hemostasis induced by SLD/LPS cotreatment, fibrin and hypoxia were present in liver tissue before the onset of hepatotoxicity. Heparin treatment reduced hepatic fibrin deposition and hypoxia and protected against liver injury induced by SLD/LPS cotreatment. These results indicate that cotreatment with nontoxic doses of LPS and SLD causes liver injury in rats, and this could serve as a model of human idiosyncratic liver injury. The hemostatic system is activated by SLD/LPS cotreatment and plays an important role in the development of SLD/LPS-induced liver injury.

Similar compounds searching system by using the gene expression microarray database

Numbers of microarrays have been examined and several public and commercial databases have been developed. However, it is not easy to compare in-house microarray data with those in a database because of insufficient reproducibility due to differences in the experimental conditions. As one of the approach to use these databases, we developed the similar compounds searching system (SCSS) on a toxicogenomics database. The datasets of 55 compounds administered to rats in the Toxicogenomics Project (TGP) database in Japan were used in this study. Using the fold-change ranking method developed by Lamb et al. [Lamb, J., Crawford, E.D., Peck, D., Modell, J.W., Blat, I.C., Wrobel, M.J., Lerner, J., Brunet, J.P., Subramanian, A., Ross, K.N., Reich, M., Hieronymus, H., Wei, G., Armstrong, S.A., Haggarty, S.J., Clemons, P.A., Wei, R., Carr, S.A., Lander, E.S., Golub, T.R., 2006. The connectivity map: using gene-expression signatures to connect small molecules, genes, and disease. Science 313, 1929-1935] and criteria called hit ratio, the system let us compare in-house microarray data and those in the database. In-house generated data for clofibrate, phenobarbital, and a proprietary compound were tested to evaluate the performance of the SCSS method. Phenobarbital and clofibrate, which were included in the TGP database, scored highest by the SCSS method. Other high scoring compounds had effects similar to either phenobarbital (a cytochrome P450s inducer) or clofibrate (a peroxisome proliferator). Some of high scoring compounds identified using the proprietary compound-administered rats have been known to cause similar toxicological changes in different species. Our results suggest that the SCSS method could be used in drug discovery and development. Moreover, this method may be a powerful tool to understand the mechanisms by which biological systems respond to various chemical compounds and may also predict adverse effects of new compounds.

PERK eIF2 alpha kinase is required to regulate the viability of the exocrine pancreas in mice

Background

Deficiency of the PERK eIF2α kinase in humans and mice results in postnatal exocrine pancreatic atrophy as well as severe growth and metabolic anomalies in other organs and tissues. To determine if the exocrine pancreatic atrophy is due to a cell-autonomous defect, the Perk gene was specifically ablated in acinar cells of the exocrine pancreas in mice.

Results

We show that expression of PERK in the acinar cells is required to maintain their viability but is not required for normal protein synthesis and secretion. Exocrine pancreatic atrophy in PERK-deficient mice was previously attributed to uncontrolled ER-stress followed by apoptotic cell death based on studies in cultured fibroblasts. However, we have found no evidence for perturbations in the endoplasmic reticulum or ER-stress and show that acinar cells succumb to a non-apoptotic form of cell death, oncosis, which is associated with a pronounced inflammatory response and induction of the pancreatitis stress response genes. We also show that mice carrying a knockout mutation of PERK's downstream target, ATF4, exhibit pancreatic deficiency caused by developmental defects and that mice ablated for ATF4's transcriptional target CHOP have a normal exocrine pancreas.

Conclusion

We conclude that PERK modulates secretory capacity of the exocrine pancreas by regulating cell viability of acinar cells.

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.

Neutrophil interaction with the hemostatic system contributes to liver injury in rats cotreated with lipopolysaccharide and ranitidine

Cotreatment of rats with nontoxic doses of ranitidine (RAN) and lipopolysaccharide (LPS) causes liver injury, and this drug-inflammation interaction might be a model for idiosyncratic adverse drug responses in humans. Both polymorphonuclear neutrophils (PMNs) and the hemostatic system have been shown to be important in the injury. We tested the hypothesis that PMNs cause liver injury by interacting with the hemostatic system and producing subsequent hypoxia. In rats cotreated with LPS/RAN, PMN depletion by anti-PMN serum reduced fibrin deposition and hypoxia in the liver. PMN depletion also reduced the plasma concentration of active plasminogen activator inhibitor-1 (PAI-1), a major down-regulator of the fibrinolytic system. This suggests that PMNs promote fibrin deposition by increasing PAI-1 concentration. PMNs were activated in the livers of LPS/RAN-cotreated rats as evidenced by increased staining for hypochlorous acid-modified proteins generated by the myeloperoxidase-hydrogen peroxide-chloride system of activated phagocytes. Antiserum against the PMN adhesion molecule CD18 protected against LPS/RAN-induced liver injury. Because CD18 is important for PMN transmigration and activation, these results suggest that PMN activation is required for the liver injury. Furthermore, anti-CD18 serum reduced biomarkers of hemostasis and hypoxia, suggesting the necessity for PMN activation in the interaction between PMNs and the hemostatic system/hypoxia. Liver injury, liver fibrin, and plasma PAI-1 concentration were also reduced by eglin C, an inhibitor of proteases released by activated PMNs. In summary, PMNs are activated in LPS/RAN-cotreated rats and participate in the liver injury in part by contributing to hemostasis and hypoxia.

Hypoxia, drug therapy and toxicity

Hypoxia is defined as a decrease in available oxygen reaching the tissues of the body. It is linked to the pathology of cancer, cardiovascular disease, and stroke, the leading causes of death in the United States. Cells under hypoxic stress either induce an adaptive response that includes increasing the rates of glycolysis and angiogenesis or undergo cell death by promoting apoptosis or necrosis. The ability of cells to maintain a balance between adaptation and cell death is regulated by a family of transcription factors called the hypoxia inducible factors (HIF). HIF1, the most widely studied HIF, is essential for regulating the expression of a battery of hypoxia-responsive genes involved in the adaptive and cell death responses. The ability of HIF1 to balance these 2 responses likely lies in the regulation of HIF1alpha stability and transcriptional activity by post-translational hydroxylation and its ability to respond to other cellular factors including key metabolites and growth factors. Targeting HIF1 signaling for therapeutics, therefore, requires an understanding of how these various signals converge upon HIF1 and regulate its role in maintaining the balance between adaptation and cell death. In addition, one must understand how this balance can be perturbed during toxicant-induced tissue damage. This review will summarize our current understanding of hypoxia signaling as it applies to drug therapy and toxicity and describe how these processes can influence the HIF-mediated balance between adaptation and cell death.

Monocrotaline promotes transplanted cell engraftment and advances liver repopulation in rats via liver conditioning

Disruption of the hepatic endothelial barrier or Kupffer cell function facilitates transplanted cell engraftment in the liver. To determine whether these mechanisms could be activated simultaneously, we studied the effects of monocrotaline, a pyrollizidine alkaloid, with reported toxicity in liver sinusoidal endothelial cells and Kupffer cells. The effects of monocrotaline in Fischer 344 rats were examined by tissue morphology, serum hyaluronic acid levels, and liver tests (endothelial and hepatocyte injury) or incorporation of carbon and (99m)Tc-sulfur colloid (Kupffer cell damage). To study changes in cell engraftment and liver repopulation, Fischer 344 rat hepatocytes were transplanted into syngeneic dipeptidyl peptidase IV-deficient rats followed by histological assays. We observed extensive endothelial injury without Kupffer cell or hepatocyte damage in monocrotaline-treated rats. Monocrotaline enhanced transplanted cell engraftment without changes in transplanted cell numbers or induction of proliferation in native hepatocytes over 3 months. In monocrotaline-treated rats, transplanted cells integrated into the liver parenchyma and survived in vascular spaces. To determine whether native hepatocytes suffered inapparent damage after monocrotaline, we introduced further liver injury with carbon tetrachloride subsequent to cell transplantation. Monocrotaline sensitized the liver to carbon tetrachloride-induced necrosis, which advanced transplanted cell proliferation, leading to significant liver repopulation. During this process, we observed proliferation of bile duct cells and small epithelial cells, although transplanted hepatocytes did not appear to reconstitute bile ducts. The studies showed that perturbation of multiple liver cell compartments by monocrotaline promoted transplanted cell engraftment and proliferation. In conclusion, development of drugs with monocrotaline-like effects will help advance liver cell therapy.

Pathways of myocyte death: implications for development of clinical laboratory biomarkers

The recognition that cardiac myocytes die by multiple mechanisms and thus substantially affect ventricular remodeling in diseased human hearts supports the concept of ongoing myocyte death in the progression of heart failure and constitutes the basis of this review. In addition, based on the pathophysiology of myocardial cell deaths, the present study emphasizes that currently methodologies, although with some inherent limitations, are available to recognize and measure quantitatively the contribution of myocyte cell death to the progression of the pathologic state of the heart. Our own studies show that application of such methodologies including modern microscopy techniques and the use of different molecular and immunohistochemical markers may generate the consensus that myocyte cell death is a quantifiable parameter in the normal and pathological human heart. The present study also demonstrates that myocyte cell death, apoptotic, oncotic or autophagic in nature, has to be regarded as an additional critical variable of the multifactorial events implicated in the alterations of cardiac anatomy and myocardial structure of the diseased human heart.

Coagulation-Mediated Hypoxia and Neutrophil-Dependent Hepatic Injury in Rats Given Lipopolysaccharide and Ranitidine

Idiosyncrasy-like liver injury occurs in rats cotreated with nonhepatotoxic doses of ranitidine (RAN) and bacterial lipopolysaccharide (LPS). Hepatocellular oncotic necrosis is accompanied by neutrophil (PMN) accumulation and fibrin deposition in LPS/RAN-treated rats, but the contribution of PMNs to injury has not been shown. We tested the hypothesis that PMNs are critical mediators of LPS/RAN-induced liver injury and explored the potential for interaction between PMNs and hemostasis-induced hypoxia. Rats were given either LPS (44.4 x 10(6) endotoxin units/kg) or its vehicle and then RAN (30 mg/kg) or its vehicle 2 h later. They were killed 3 or 6 h after RAN treatment, and hepatocellular injury was estimated from serum alanine aminotransferase activity and liver histopathology. Plasma PMN chemokine concentration and the number of PMNs in liver increased after LPS treatment at 3 h and were not markedly altered by RAN cotreatment. Depletion of circulating PMNs attenuated hepatic PMN accumulation and liver injury and had no effect on coagulation system activation. Anticoagulation with heparin attenuated liver fibrin deposition and injury in LPS/RAN-treated rats; however, heparin had little effect on liver PMN accumulation or plasma chemokine concentration. Liver hypoxia occurred in LPS/RAN-cotreated rats and was significantly reduced by heparin. In vitro, hypoxia enhanced the killing of rat hepatocytes by PMN elastase and shortened its onset, indicating a synergistic interaction between PMNs and hypoxia. The results suggest that PMNs are involved in the hepatocellular injury caused by LPS/RAN-cotreatment and that hemostasis increases sensitivity to PMN-induced hepatocellular injury by causing liver hypoxia.

Acute intoxication by Crotalaria retusa in sheep

Acute intoxication by seeding Crotalaria retusa occurred during the dry season, in a flock of 80 sheep, in the semi-arid region of the state of Paraiba, northeastern Brazil. Anorexia, severe depression, mild jaundice, incoordination and recumbence were observed in 16 sheep that died within 12 h. At necropsy the liver had a nutmeg appearance. Seeds of C. retusa were found in large amounts in the rumen of the dead animals. Histologic lesions of the liver were characterized by centrilobular necrosis. Seeds of C. retusa were given to six sheep at doses of 2.5 (two sheep), 5, 10, 20 and 40 g/kg bw (one sheep for each dose). Sheep ingesting 5-40 g/kg bw were killed when moribund, 38-120 h after the start of the administration. Clinical signs and gross and histologic lesions were similar to those observed in field outbreak. The seeds used in the experiment contained 1.4% of monocrotaline. It is concluded that hungry sheep can be affected spontaneously by acute monocrotaline intoxication when they ingest large amounts of C. retusa seeds in a short period of time.

Role of hepatic fibrin in idiosyncrasy-like liver injury from lipopolysaccharide-ranitidine coexposure in rats

Coadministration of nonhepatotoxic doses of the histamine 2-receptor antagonist ranitidine (RAN) and bacterial lipopolysaccharide (LPS) results in hepatocellular injury in rats, the onset of which occurs in 3 to 6 hours. This reaction resembles RAN idiosyncratic hepatotoxicity in humans. Early fibrin deposition occurs in livers of rats cotreated with LPS/RAN. Accordingly, we tested the hypothesis that the hemostatic system contributes to liver injury in LPS/RAN-treated rats. Rats were given either LPS (44.4 x 10(6) EU/kg) or its vehicle, then RAN (30 mg/kg) or its vehicle 2 hours later. They were killed 2, 3, 6, 12, or 24 hours after RAN treatment, and liver injury was estimated from serum alanine aminotransferase activity. A modest elevation in serum hyaluronic acid, which was most pronounced in LPS/RAN-cotreated rats, suggested altered sinusoidal endothelial cell function. A decrease in plasma fibrinogen and increases in thrombin-antithrombin dimers and in serum concentration of plasminogen activator inhibitor-1 occurred before the onset of liver injury. Hepatic fibrin deposition was observed in livers from LPS/RAN-cotreated rats 3 and 6 hours after RAN. Liver injury was abolished by the anticoagulant heparin and was significantly attenuated by the fibrinolytic agent streptokinase. Hypoxia, one potential consequence of sinusoidal fibrin deposition, was observed in livers of LPS/RAN-treated rats. In conclusion, the results suggest that the hemostatic system is activated after LPS/RAN cotreatment and that fibrin deposition in liver is important for the genesis of hepatic parenchymal cell injury in this model.

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.