Jacqueline Field

Dual role of tumor necrosis factor-α in hepatic ischemia-reperfusion injury: Studies in tumor necrosis factor-α gene knockout mice

Although hepatic ischemia‐reperfusion (IR) injury is partially mediated by tumor necrosis factor‐α (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‐κ 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 μg 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. (HEPATOLOGY 2004;39:412–421.)

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.

Halothane‐induced liver injury in guinea‐pigs: Importance of cytochrome P450 enzyme activity and hepatic blood flow

The basis for susceptibility to halothane‐induced liver necrosis in guinea‐pigs was examined. In hepatic microsomes, the following were similar in susceptible and resistant animals: total cytochrome (CYP) P450 (P450), phenobarbital‐inducible pathways of mixed function oxidation (androstenedione 6β‐ and 16β‐hydroxylase activities) and the CYP2E1‐catalysed pathway of N‐nitrosodimethylamine N‐demethylase activity. Similarly, immunohistochemical staining of CYP2E1 protein was equivalent in livers from susceptible and resistant guinea‐pigs. Prior treatment with the P450‐inhibitors, metyrapone and SKF‐525A ameliorated halothane‐induced liver damage in susceptible animals. Conversely, in resistant guinea‐pigs, stimulation of hepatic CYP2E1 activity by treatment with 4‐methylpyrazole produced severe hepatotoxicity after re‐exposure to halothane. These results confirm the conclusions of others, that P450‐mediated metabolism produces halothane‐induced liver necrosis in the guinea‐pig model but, as in other work, the data fail to explain why no difference in activity of these enzymes could be found between susceptible and resistant guinea‐pigs. To establish whether a differential effect on hepatic blood flow between susceptible and resistant guinea‐pigs could explain this paradox, studies were performed using a radiolabelled microsphere technique. The effect of halothane on lowering cardiac output was identical in both groups of animals and halothane significantly reduced hepatic arterial but not portal blood flow. The effect on arterial blood flow was more profound in susceptible guinea‐pigs (0.67 ± 0.17% of injected microspheres) than in resistant animals (0.99 ± 0.13%; P< 0.005). It is concluded that P450‐catalysed metabolism and reduced hepatic blood flow are both necessary to produce halothane‐induced liver injury in susceptible guinea‐pigs, but it is the effect of halothane on hepatic arterial blood flow that differs between susceptible and resistant animals.

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.