Diannexin, a novel annexin V homodimer, provides prolonged protection against hepatic ischemia-reperfusion injury in mice.

BACKGROUND AND AIMS: Ischemia-reperfusion injury (IRI) remains an important cause of liver failure after hepatic surgery or transplantation. The mechanism seems to originate within the hepatic sinusoid, with damage to endothelial cells, an early, reproducible finding. Sinusoidal endothelial cells (SECs), damaged during reperfusion, activate and recruit inflammatory cells and platelets. We hypothesized that a recombinant human annexin V homodimer, Diannexin, would protect SECs from reperfusion injury. METHODS: We tested this proposal in a well-characterized in vivo murine partial hepatic IRI model. RESULTS: Whether administered 5 minutes or 24 hours before or 1 hour after ischemia-reperfusion, Diannexin (100-1000 microg/kg) almost completely protected against liver injury. The protective efficacy conferred by Diannexin was highly visible at the microcirculatory level. Thus, although IR in this model is associated with early swelling and gap formation in SECs, Diannexin ameliorated these effects as shown by >80% reduction in alanine aminotransferase values during the early phase of reperfusion injury (2 hours) and near normalization of liver necrosis and inflammation in the late phase of inflammatory recruitment (24 hours). Consistent with the proposed role of SEC injury in hepatic IRI, Diannexin also decreased hepatic expression of proinflammatory molecules (MIP-2, ICAM-1, VCAM), abolished leukocyte and platelet adherence to damaged SECs, and, by in vivo microscopy, Diannexin preserved microcirculatory blood flow and hepatocyte integrity during reperfusion. CONCLUSIONS: Diannexin is an apparently safe therapeutic protein that provides prolonged protection against hepatic IRI via cytoprotection of SECs, thereby interrupting secondary microcirculatory inflammation and coagulation.

Interleukin-6 is a key mediator of the hepatoprotective and pro-proliferative effects of ischaemic preconditioning in mice.

BACKGROUND/AIMS: The biological effects of ischaemic preconditioning include NF-kappaB activation, increased TNF synthesis, stimulation of cell cycle entry and hepatoprotection against ischaemia-reperfusion (IR) injury. Low dose TNF initiates the priming phase of liver regeneration via NF-kappaB and IL-6. To determine whether (1) IL-6 is released during preconditioning and confers protection against hepatic IR injury, and (2) IL-6 could mediate the biological effects of preconditioning. METHODS: Wildtype (wt) and TNF-/- C57BL6 mice were subjected to 90 min partial hepatic ischaemia and 2-44 h reperfusion with or without prior 10 min ischaemic preconditioning. To restitute liver injury, TNF-/- mice were administered murine TNF 5 microg/kg iv 1 min prior to IR. Murine recombinant IL-6 (500 ng/kg iv) was administered 30 min prior to IR, either to wt mice or to TNF-/--repleted mice; in the latter case, 1 min before preconditioning. RESULTS: In wt mice, IL-6 attenuated hepatic IR injury and stimulated cell cycle entry. IR injury in TNF-repleted TNF-/- mice was not ameliorated by preconditioning. However, prior IL-6 administration conferred hepatoprotection (IL-6/preconditioned: 349+/-169 U/L vs vehicle/preconditioned: 1250+/-608 U/L, P<0.01). CONCLUSIONS: IL-6 is one likely mediator of the hepatoprotective and pro-proliferative effects of ischaemic preconditioning.

NF-kappaB activation, rather than TNF, mediates hepatic inflammation in a murine dietary model of steatohepatitis.

BACKGROUND & AIMS: We explored the roles of nuclear factor-kappaB (NF-kappaB) and tumor necrosis factor (TNF) alpha (TNF-alpha) as mediators of inflammation in a nutritional model of steatohepatitis. METHODS: Wild-type (wt), TNF null -/-, and TNF receptor (R)-1-/- mice were fed a methionine- and choline-deficient (MCD) diet for up to 5 weeks. Liver injury (serum alanine aminotransferase [ALT]), hepatic inflammation, triglycerides, and lipid peroxide levels were determined. Hepatic NF-kappaB activation and expression of TNF and intercellular adhesion molecule-1 (ICAM-1) were assayed. RESULTS: Irrespective of genotype, MCD diet-fed mice developed hepatic lipid peroxidation and serum ALT elevation; at day 10, livers from wt, TNF-/-, and TNFR-1-/- mice showed equivalent steatohepatitis. NF-kappaB/DNA binding was enhanced in hepatic nuclear fractions from MCD diet-fed wt mice compared with dietary controls; there were corresponding increases of ICAM-1 and TNF messenger RNA (mRNA). Likewise, NF-kappaB activation and ICAM-1 expression were enhanced by MCD dietary feeding in TNF-/- and TNFR-1-/- mice compared with respective controls. To establish whether NF-kappaB is a primary mediator of inflammation in experimental steatohepatitis, we over-expressed a mutant, nondegradable IkappaB (mIkappaB), delivered by adenovirus in vivo. As expected, hepatic mIkappaB expression reduced NF-kappaB/DNA binding induced by MCD dietary feeding, with resultant abrogation of ICAM-1 and TNF synthesis. Such blockade of NF-kappaB transcriptional activation substantially protected against development of steatohepatitis, with significant reductions in liver injury and hepatic inflammation. CONCLUSIONS: In the MCD dietary model of steatohepatitis, NF-kappaB is activated early and is an important proinflammatory mediator of lesion development, but steatohepatitis occurs independently of TNF synthesis and TNFR-1 activation.

Dual role of tumor necrosis factor-alpha in hepatic ischemia-reperfusion injury: studies in tumor necrosis factor-alpha gene knockout mice.

Although hepatic ischemia-reperfusion (IR) injury is partially mediated by tumor necrosis factor-alpha (TNF), we recently found that low-dose TNF before IR is hepatoprotective. We examined the seemingly conflicting roles of TNF in mediating liver injury in a partial hepatic IR model using TNF gene knockout (TNF ko) mice to allow TNF replacement at specified times. Compared with wild-type mice, TNF ko mice exhibit minimal alanine aminotransferase release and few hepatonecrotic lesions during the early (time, 2 hours) and late (time, 24 hours) phases of IR. TNF ko mice differed from wild-type mice in that TNF ko mice exhibited no activation or induction of nuclear factor-kappa B, p38, cyclin D1, or proliferating cell nuclear antigen after IR. A single low-dose TNF injection 1 minute before the onset of hepatic ischemia restored hepatic IR injury in TNF ko mice. To clarify the importance of TNF for hepatoprotection, preconditioning (10 minutes of ischemia and 10 minutes of reperfusion) was performed before the onset of IR for TNF ko mice whose capacity to undergo IR injury had been restored by TNF replacement. Ischemic preconditioning failed to protect these mice from TNF-augmented IR injury; however, following the administration of intravenous TNF (1 microg per kg body weight, which mimics the early increase in hepatic and plasma TNF levels that is mobilized by ischemic preconditioning), significant hepatoprotection against both the early and late phases of TNF-augmented IR injury was observed. In conclusion, TNF appears to mediate both the early and late phases of liver injury in hepatic IR, but it also is an essential mediator of hepatoprotective effects brought about by ischemic preconditioning.

Transgenic mouse models of human CYP3A4 gene regulation.

CYP3A4, the predominant but variably expressed cytochrome P450 of adult human liver, is subject to multifaceted constitutive regulation as well as transcriptional induction by a variety of structurally unrelated xenobiotics. Using transient transfections in HepG2 cells, we previously demonstrated the existence of a potent xenobiotic-responsive enhancer module located between - 7.2 and - 7.8 kilobases upstream of the CYP3A4 transcription start site. Induction is mediated by interaction of transcription factor binding sites in the XREM with the nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR). To determine the in vivo relevance of these findings and to establish a mouse model of human CYP3A4 regulation, we have generated transgenic mice carrying constructs comprising the upstream regulatory region of the human CYP3A4 gene linked to the lacZ reporter gene. Constitutive expression was observed in a developmental, tissue- and cell-specific fashion that mirrors the human situation. In addition, robust hepatic and intestinal induction with a range of reagents known to activate PXR and/or CAR (e.g., dexamethasone, pregnenolone 16alpha-carbonitrile, and phenobarbital) was observed. However, no expression or induction was apparent with a construct lacking upstream sequences beyond - 3.2 kilobases. Histochemical staining for beta-galactosidase activity revealed that dose-dependent increases in transgene levels were associated with a zonal expansion of lacZ expressing hepatocytes, suggesting that xenobiotic induction of CYP3A genes operates primarily through the recruitment of more cells committed to expression. In summary, CYP3A4/lacZ transgenic mice provide an in vivo model for the study of the molecular mechanisms involved in the regulation of a significant human drug metabolizing enzyme.

Leptin-specific mechanisms for impaired liver regeneration in ob/ob mice after toxic injury.

BACKGROUND & AIMS: Profound impairment of liver regeneration in rodents with dysfunctional leptin signaling has been attributed to non-alcohol-induced fatty liver disorders (NAFLD). Our aim was to establish whether defective liver regeneration in ob/ob mice is a direct consequence of leptin-dependent, intracellular signaling mechanisms controlling cell-cycle regulation in hepatocytes. METHODS: After exposure to a single hepatotoxic dose of (CCl(4)), the regenerative response to hepatic injury was studied in leptin-deficient ob/ob and control mice. The effects of leptin supplementation (100 microg x kg(-1) x day(-1)) were examined. We assessed entry into and progression through the cell cycle and activation of key signaling intermediates and transcriptional regulators. RESULTS: CCl(4)-induced liver injury was equally severe in ob/ob and control mice. In leptin-deficient mice, it was associated with exaggerated activation of NF-kappa B and STAT3 during the priming phase, abrogation of tumor necrosis factor (TNF) and interleukin (IL)-6 release at the time of G1/S transition, and failure of hepatocyte induction of cyclin D1 and cell cycle entry. Leptin replacement corrected these defects in ob/ob mice by restoring TNF and IL-6 release and inducing cyclin D1. Hepatocytes entered S phase and progressed, as in wild-type mice, to vigorous mitosis and normal hepatic regenerative response. In ob/ob mice, low doses of TNF before CCl(4) also were associated with restitution of TNF release and proliferative capabilities. CONCLUSIONS: Impaired liver regeneration in ob/ob mice is caused by leptin deficiency. We propose that altered cytokine production in ob/ob mice is part of the mechanisms responsible for impaired proliferation in response to hepatic injury.

How reversible is hepatic functional impairment in autoimmune hepatitis?

BACKGROUND AND AIMS: We quantifed the short-term effects of immunosuppressive therapy on hepatic metabolic function in autoimmune hepatitis to establish how long it takes to achieve maximum functional improvement. METHODS: We studied 14 newly diagnosed patients with autoimmune hepatitis (12 type 1, two type 2) by antipyrine clearance and conventional liver tests, then repeated studies at 3-6 month intervals during the first 18 months of immunosuppressive therapy. RESULTS: Low values for antipyrine clearance were found in 13 of 14 cases; serum albumin concentration was low in four, bilirubin raised in eight and prothrombin time prolonged in four. Following immunosuppressive treatment for 3 months, antipyrine clearance improved by 98% (standard error of the mean 24%), which was proportionally greater than for serum albumin, bilirubin or prothrombin time. Antipyrine clearance and serum albumin continued to improve after 6-12 months of immunosuppressive treatment in several cases, whereas there were no further improvements in alanine aminotransferase (ALT), bilirubin and prothrombin time. CONCLUSIONS: In the short term, immunosuppressive therapy for autoimmune hepatitis markedly improves hepatic metabolic function, which is particularly striking for the sensitive metabolic test antipyrine clearance, but may also be seen with serum albumin. However, it may take up to 12 months to achieve maximal functional recovery. Management guidelines on autoimmune hepatitis should be extended to emphasize that changes in hepatic metabolic function, as well as ALT and gamma-globulin levels, be taken into consideration in the definition of remission.