Iron-dependent activation of NF-kappaB in Kupffer cells: a priming mechanism for alcoholic liver disease

Chronic ethanol-mediated decrease in cAMP primes macrophages to enhanced LPS-inducible NF-kappaB activity and TNF expression: relevance to alcoholic liver disease

Increased plasma and hepatic TNF-alpha activity has been implicated in the pathogenesis of alcoholic liver disease (ALD). We previously reported that monocytes from alcoholic patients show enhanced constitutive as well as LPS-inducible NF-kappaB activation and TNF-alpha production. Studies in monocytes have shown that cAMP plays an important role in regulating TNF-alpha expression, and elevation of cellular cAMP suppresses TNF-alpha production. The effects of chronic ethanol exposure on the cellular levels of cAMP as well as TNF expression in monocytes were examined in vitro and in rat primary hepatic Kupffer cells obtained from a clinically relevant enteral alcohol feeding model of ALD. Chronic ethanol exposure significantly decreased cellular cAMP levels in both LPS-stimulated and unstimulated monocytes. Consistent with the decrease in cAMP levels, ethanol led to an increase in LPS-inducible TNF-alpha production by affecting NF-kappaB activation and induction of TNF mRNA expression, without any change in TNF mRNA stability. Enhancement of cellular cAMP with dibutyryl cAMP abrogated LPS-mediated TNF-alpha expression in ethanol-treated cells. Importantly, cAMP did not affect LPS-inducible NF-kappaB activation but significantly decreased its transcriptional activity. Together, these data strongly suggest that ethanol can synergize with LPS to upregulate the induction of TNF gene expression and consequent TNF overproduction by decreasing the cellular cAMP levels in monocytes/macrophages. Furthermore, these data also support the notion that cAMP-elevating agents could constitute an effective therapeutic approach in attenuating or preventing the progression of liver disease in alcoholic patients.

Pathophysiological basis for antioxidant therapy in chronic liver disease

Oxidative stress is a common pathogenetic mechanism contributing to initiation and progression of hepatic damage in a variety of liver disorders. Cell damage occurs when there is an excess of reactive species derived from oxygen and nitrogen, or a defect of antioxidant molecules. Experimental research on the delicately regulated molecular strategies whereby cells control the balance between oxidant and antioxidant molecules has progressed in recent years. On the basis of this evidence, antioxidants represent a logical therapeutic strategy for the treatment of chronic liver disease. Clinical studies with large numbers of patients have not yet been performed. However, results from several pilot trials support this concept and indicate that it may be worth performing multicentre studies, particularly combining antioxidants with anti-inflammatory and/or antiviral therapy. Oxidative stress plays a pathogenetic role in liver diseases such as alcoholic liver disease, chronic viral hepatitis, autoimmune liver diseases and non-alcoholic steatohepatitis. The use of antioxidants (e.g. S-adenosylmethionine [SAMe; ademetionine], tocopherol [vitamin E], polyenylphosphatidylcholine or silymarin) has already shown promising results in some of these pathologies.

Iron accumulation in alcoholic liver diseases

Increased hepatic iron is one of the important key factors which contribute alcohol toxicity of liver due to the production of reactive oxygen species. In patients with alcoholic liver diseases (ALD), liver iron is increased and the resulted lipid metabolite 4-hydroxynonenal-protein adduct was also increased. In general, iron is deposited in both parenchymal cells and and Kupffer cells in ALD. However, in patients with mild ALD, the parenchymal iron deposition is dominant rather than reticuloendothelial iron deposition, while the latter iron deposition is domimant in severe ALD, possibly due to endotoxemia and overproduction of inflammatory cytokines. We speculated that a parenchymal iron deposition in mild ALD is an important factor to trigger hepatocytes injury by ethanol, and the possible cause of parencynal iron deposition may be an increase of cellular iron uptake via serum transferrin in hepatocytes after ethanol exposure. By immuno-histochemical study of biopsied liver samples, the expression of transferrin receptor 1 (TfR1), which mediates cellular iron uptake by serum transferrin was increased. This increase of TfR1 by ethanol is confirmed by in vitro experiment using HepG2 cells and primary rat hepatocytes culture. Fe-labeled transferrin incorporation (but not transferrin non-bound iron (NTBI)) into the cells is also increased, suggesting that the increased TfR1 is functional. The increase of TfR1 expression is partially due to the increased activity of iron regulatory protein (IRP) by oxidative stress of ethanol metabolism. Thus, the post-transcriptional regulation of iron uptake by ethanol is involved in the hepatocyte iron accumulation. Another possibility is an increase of intestinal iron absorption. Our recent finding regarding the increase of pro-hepcidin serum in alcoholic patients with high serum ferritin support this assumption.

Interleukin-1beta induction of NFkappaB is partially regulated by H2O2-mediated activation of NFkappaB-inducing kinase

Reactive oxygen species (ROS) have been demonstrated to act as second messengers in a number of signal transduction pathways, including NFkappaB. However, the mechanism(s) by which ROS regulate NFkappaB remain unclear and controversial. In the present report, we describe a mechanism whereby interleukin-1beta (IL-1beta) stimulation of NFkappaB is partially regulated by H2O2-mediated activation of NIK and subsequent NIK-mediated phosphorylation of IKKalpha. IL-1beta induced H2O2 production in MCF-7 cells and clearance of this ROS through the expression of GPx-1 reduced NFkappaB transcriptional activation by inhibiting NIK-mediated phosphorylation of IKKalpha. Although IKKalpha and IKKbeta were both involved in IL-1beta-mediated activation of NFkappaB, only the IKKalpha-dependent component was modulated by changes in H2O2 levels. Interestingly, in vitro reconstitution experiments demonstrated that NIK was activated by a very narrow range of H2O2 (1-10 microM), whereas higher concentrations (100 microM to 1 mM) inhibited NIK activity. Treatment of cells with the general Ser/Thr phosphatase inhibitor (okadaic acid) lead to activation of NFkappaB and enhanced NIK activity as a IKKalpha kinase, suggesting that ROS may directly regulate NIK through the inhibition of phosphatases. Recruitment of NIK to TRAF6 following IL-1beta stimulation was inhibited by H2O2 clearance and Rac1 siRNA, suggesting that Rac-dependent NADPH oxidase may be a source of ROS required for NIK activation. In summary, our studies have demonstrated that redox regulation of NIK by H2O2 is mechanistically important in IL-1beta induction of NFkappaB activation.

Propofol: an immunomodulating agent

Propofol (2,6-diisopropylphenol) is a potent intravenous hypnotic agent widely administered for induction and maintenance of anesthesia and for sedation in the intensive care unit. Propofol is insoluble in water and therefore is formulated in a lipid emulsion. In addition, a preservative (ethylenediaminetetraacetic acid [EDTA] or sodium metabisulfite) is added to retard bacterial growth. Propofol has antiinflammatory properties, decreasing production of proinflammatory cytokines, altering expression of nitric oxide, and inhibiting neutrophil function. Propofol also is a potent antioxidant. The added preservatives have biologic activity; EDTA has antiinflammatory properties, whereas metabisulfite may cause lipid peroxidation. The antiinflammatory and antioxidant properties of propofol may have beneficial effects in patients with sepsis and systemic inflammatory response syndrome.

Antisense gene delivered by an adenoassociated viral vector inhibits iron uptake in human intestinal cells: Potential application in hemochromatosis

Hereditary hemochromatosis (HH) is a condition in which intestinal iron absorption is greatly elevated. Present treatment is weekly phlebotomy, affecting quality of life and leading to recurrent infections. The iron transporter divalent metal transporter-1 (DMT-1) of enterocytes is responsible for iron uptake from the intestinal lumen; iron is further extruded into the blood by the basolateral transporter ferroportin-1. A therapeutic approach for HH could start with a long-term reduction of iron transport by reduction of DMT-1 levels. We designed an AAV vector coding for a short antisense RNA (AAV-DMT-1-AS) against DMT-1, which reduced iron uptake by 50-60% in human intestinal cells (Caco-2). At low infection levels, DMT-1 mRNA virtually disappeared, suggesting RNAi-like and/or RNase H antisense effects. DMT-1 mRNA levels returned to normal at higher infection levels, indicating that an additional mechanism of mRNA occupation, able to block DMT-1 translation and to avoid feedback regulation by iron responsive elements (IRE), also exists. Cell morphology was normal in all cases and no increases in the interferon-related responses, measured by (a) 2'-5' A oligo synthetase (b) IFITM1 and (c) ISGF3gamma mRNA levels, were observed. Studies presented herein indicate that enterocyte targeting with a gene coding for a short antisense against iron transport blocks enterocyte iron uptake, which may have therapeutic value.

Alcohol and the liver

PURPOSE OF REVIEW

To highlight salient recent discoveries and results of clinical trials in alcoholic liver disease (ALD). The burden of care for ALD patients is hefty and the prevalence of alcohol abuse may be increasing in both the developed and the underdeveloped world.

RECENT FINDINGS

Molecular mechanisms of alcoholism are being identified but not of the predisposition to alcoholic liver injury, except perhaps for polymorphism of a cytotoxic T-cell antigen. The Mayo End-stage Liver Disease (MELD) score performs well in assessing the prognosis of ALD; serological biomarkers for predicting ALD outcome are of uncertain value. Concomitant liver disease (e.g., obesity, hepatitis C, and iron overload) aggravates the severity of ALD; conversely, alcohol abuse may be a cryptic co-factor in some cases of non-alcoholic fatty liver. For alcoholic hepatitis, nutritional support is the mainstay of treatment; steroids are considered by some (but not all) as safe and effective therapy, whereas manipulations of tumor necrosis factor-alpha activity have been disappointing, or of unproven benefit at best. In liver transplantation for ALD, methods are being devised to monitor recidivism and to ameliorate its risk and that of co-morbid psychiatric conditions.

SUMMARY

Much of the pathogenesis of ALD has been identified and headway has been made in predicting its prognosis. However, much remains to be done to elucidate the molecular genetics of the risk of developing ALD and in formulating safe, effective therapies for alcoholic hepatitis.

Expression of NGF in hepatocellular carcinoma cells with its receptors in non-tumor cell components

Nerve growth factor (NGF) is suggested to have a role in tumor progression in addition to its role in differentiation and survival of neuronal cells. We investigated expression of NGF and its receptors, TrkA and p75NTR, in hepatocellular carcinomas (HCCs). Although hepatocytes and hepatic stellate cells (HSCs) showed respectively weak and intense NGF immunostaining in the background livers of patients suffering from liver cirrhosis (LC) or chronic hepatitis (CH), intense staining was demonstrated in HCC cells of 33 of 54 (61.1%) tumors. RT-PCR detected NGF mRNA in 7 freshly-isolated HCC samples, and in 2 of 4 cases, in which both background livers and tumors could be analyzed, NGF mRNA was more abundant in the tumors than the background livers. TrkA was detected in the smooth muscle cells of hepatic arteries, but it was negative in tumor cells as well as non-neoplastic hepatocytes. p75NTR and alpha-smooth muscle actin (alphaSMA) was expressed in HSCs in the background liver and fibroblast-like cells in stromal septa, whereas HSCs within the HCC tissues were mostly negative for p75NTR but positive for alphaSMA. This suggests that HSCs in HCC have a different property from those in background livers. Furthermore, the stromal septa contained abundant nerve fibers, which may be related to the increased NGF expression in HCC cells. NGF and its receptors are then thought to have a role in cellular interactions involving HCC cells, HSCs, arterial cells and nerve cells in HCC tissues.

Molecular aspects of alcohol metabolism: transcription factors involved in early ethanol-induced liver injury

Alcohol metabolism takes place primarily in the liver. Initial exposures to ethanol have a major impact on the hepatic redox state and intermediary metabolism as a consequence of ethanol metabolism via alcohol dehydrogenase. However, upon continued exposure to ethanol, the progression of liver injury involves ethanol metabolism via CYP2E1 and consequent oxidant stress, as well as potential direct effects of ethanol on membrane proteins that are independent of ethanol metabolism. Multiple organ systems contribute to liver injury, including the innate immune system and adipose tissue. In response to ethanol exposure, specific signal transduction pathways, including NFkappaB and the mitogen-activated protein kinase family members ERK1/2, JNK, and p38, are activated. These complex responses to ethanol exposure translate into activation of nuclear transcription factors and altered gene expression within the liver, leading to the development of steatosis and inflammation in the early stages of alcohol-induced liver injury.