Enhanced hepatotoxicity of endotoxin by hypoxia

Live imaging of alterations in cellular morphology and organelles during cornification using an epidermal equivalent model

The stratum corneum plays a crucial role in epidermal barrier function. Various changes occur in granular cells at the uppermost stratum granulosum during cornification. To understand the temporal details of this process, we visualized the cell shape and organelles of cornifying keratinocytes in a living human epidermal equivalent model. Three-dimensional time-lapse imaging with a two-photon microscope revealed that the granular cells did not simply flatten but first temporarily expanded in thickness just before flattening during cornification. Moreover, before expansion, intracellular vesicles abruptly stopped moving, and mitochondria were depolarized. When mitochondrial morphology and quantity were assessed, granular cells with fewer, mostly punctate mitochondria tended to transition to corneocytes. Several minutes after flattening, DNA leakage from the nucleus was visualized. We also observed extension of the cell-flattening time induced by the suppression of filaggrin expression. Overall, we successfully visualized the time-course of cornification, which describes temporal relationships between alterations in the transition from granular cells to corneocytes.

Inflammatory stress and idiosyncratic hepatotoxicity: hints from animal models

Adverse drug reactions (ADRs) present a serious human health problem. They are major contributors to hospitalization and mortality throughout the world (Lazarou et al., 1998; Pirmohamed et al., 2004). A small fraction (less than 5%) of ADRs can be classified as "idiosyncratic." Idiosyncratic ADRs (IADRs) are caused by drugs with diverse pharmacological effects and occur at various times during drug therapy. Although IADRs affect a number of organs, liver toxicity occurs frequently and is the primary focus of this review. Because of the inconsistency of clinical data and the lack of experimental animal models, how IADRs arise is largely undefined. Generation of toxic drug metabolites and induction of specific immunity are frequently cited as causes of IADRs, but definitive evidence supporting either mechanism is lacking for most drugs. Among the more recent hypotheses for causation of IADRs is that inflammatory stress induced by exogenous or endogenous inflammagens is a susceptibility factor. In this review, we give a brief overview of idiosyncratic hepatotoxicity and the inflammatory response induced by bacterial lipopolysaccharide. We discuss the inflammatory stress hypothesis and use as examples two drugs that have caused IADRs in human patients: ranitidine and diclofenac. The review focuses on experimental animal models that support the inflammatory stress hypothesis and on the mechanisms of hepatotoxic response in these models. The need for design of epidemiological studies and the potential for implementation of inflammation interaction studies in preclinical toxicity screening are also discussed briefly.

The emerging role of the gut in chronic heart failure

PURPOSE OF REVIEW

Chronic heart failure is a multisystem disease with increased sympathetic tone, an anabolic/catabolic dysbalance, and chronic inflammation. Recent studies suggest an altered morphology, permeability, and absorption of the digestive tract in chronic heart failure. Due to nonocclusive mesenterial ischaemia and disturbed intestinal microcirculation, bacterial endotoxin is thought to enter the bloodstream through the hypoperfused, oedematous gut wall, thereby triggering an inflammatory response. Circulating cytokines act as cardiosuppressors. Their plasma levels predict increased mortality in chronic heart failure.

RECENT FINDINGS

The present article focuses on specific alterations of the gastric, small intestinal, and large intestinal region in chronic heart failure. It describes the leaky intestinal barrier with an augmented bacterial biofilm that may contribute to chronic inflammation and malnutrition. Furthermore, we review methods for bowel perfusion measurement and potential therapeutic approaches.

SUMMARY

It remains unclear whether increased adherent bacteria in patients with chronic heart failure are a primary or secondary event and whether they contribute to systemic inflammation. Both lack of mucosal integrity with consecutive local and systemic inflammation and dysfunction of transport proteins may worsen the clinical symptoms of chronic heart failure. Therefore, future studies need to address the pathophysiology of the intestinal barrier whose reactivity seems to be crucial for heart function.

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.

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.

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.

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.

Role of endotoxin in the hepatic microvascular inflammatory response to ethanol

Kupffer cells (KC) and gut-derived bacterial endotoxin have been implicated in the aetiology of alcoholic liver disease. Using in vivo microscopic methods, we have shown that ethanol ingestion in mice causes a dose dependent increase in leucocyte adhesion and endothelial cell swelling in hepatic sinusoids. Activation of KC is elicited at low doses while depression occurs at high doses and with chronic exposure. The responses are exacerbated in the presence of endotoxaemia or sepsis and are not seen in endotoxin-resistant animals, implicating a role for endotoxin in the ethanol-induced inflammatory response. In addition, the responses are abolished with anti-TNF alpha suggesting that TNF alpha is a primary mediator of these events. Nitric oxide (NO) initially appears to play an important role in these events by stabilizing the TNF alpha-mediated hepatic microvascular inflammatory response to acute ethanol ingestion, thereby helping to protect the liver from ischaemia and leucocyte induced oxidative injury. Finally, an ongoing clinical study has confirmed a mild systemic endotoxaemia in patients hospitalized for alcoholic liver disease. All of these results support important roles for endotoxin, cytokines, nitric oxide and sinusoidal lining cells in the pathophysiology of liver injury resulting from ethanol alone or in combination with infection.

Hepatic failure after partial hepatectomy due to synergism between endotoxaemia and congestion of the liver

To determine whether hepatic failure after partial hepatectomy is due to synergism between endotoxaemia and congestion of the liver, we examined endotoxin hepatotoxicity in partially hepatectomized rats with and without congestion of the liver. In partially hepatectomized rats without congestion of the liver, endotoxin administration induced slight elevation of the serum transaminase activity and mild or moderate hepatocellular necrosis in a few rats: these findings were not significantly different from those in sham operated rats treated with endotoxin. On the other hand, in partially hepatectomized rats with congestion of the liver, endotoxin administration induced marked elevation of serum transaminase activity and moderate or severe hepatocellular necrosis in almost all rats: these findings were significantly different from those in endotoxin-treated partially hepatectomized rats without congestion of the liver. These experimental data suggest that synergism between endotoxaemia and congestion of the liver may be a cause of hepatic failure after partial hepatectomy.

Endotoxin hepatotoxicity augmented by ethanol

To determine whether alcohol increases endotoxin hepatotoxicity, we administered ethanol (4.8 g/kg body wt in 4 ml of water) to rats through a gastric tube, then immediately injected endotoxin (2, 2.5, or 3 mg/kg body wt). In the rats pretreated with ethanol, the injection of 2 mg/kg body wt of endotoxin induced a slight rise of serum transaminase. However, when 2.5 mg/kg body wt of endotoxin was given, there were no significant histopathological or biochemical differences between the rats pretreated with ethanol and those pretreated with water. Moreover, there was no significant difference in mortality rates between the rats pretreated with ethanol and the controls when 3 mg/kg body wt (LD50) of endotoxin was injected. These results suggest that acute administration of alcohol enhances endotoxin hepatotoxicity when the dose of endotoxin is small, but that the effect of alcohol is masked when larger doses of endotoxin are given.

Role of endotoxaemia in the development of hepatic failure following hepatic artery occlusion

The present study was undertaken to examine whether endotoxemia relates to the development of hepatic failure following surgical ligation or embolization of the hepatic artery. A small amount of endotoxin was given immediately or 1 week after hepatic artery ligation in rats, and liver function tests and morphological examination of the liver were performed at 24 h after the administration. Hepatic artery ligation alone or endotoxin administration alone did not induce functional and morphological alteration of the liver. However, when endotoxin was given immediately after hepatic artery ligation, there was an increase in serum transaminase activity and focal hepatocellular necrosis developed. On the other hand, when endotoxin was given 1 week after hepatic artery ligation, the hepatic injury was not induced because of the development of hepatic arterial collaterals. These data suggest that endotoxaemia may be a cause of hepatic failure following hepatic artery occlusion, and that the risk may persist until the establishment of hepatic arterial collaterals.