Critical role of acidic sphingomyelinase in murine hepatic ischemia-reperfusion injury

Abstract

The molecular mechanisms of hepatic ischemia/reperfusion (I/R) damage are incompletely understood. We investigated the role of ceramide in a murine model of warm hepatic I/R injury. This sphingolipid induces cell death and participates in tumor necrosis factor (TNF) signaling. Hepatic ceramide levels transiently increased after the reperfusion phase of the ischemic liver in mice, because of an early activation of acidic sphingomyelinase (ASMase) followed by acid ceramidase stimulation. In vivo administration of an ASMase inhibitor, imipramine, or ASMase knockdown by siRNA decreased ceramide generation during I/R, and attenuated serum ALT levels, hepatocellular necrosis, cytochrome c release, and caspase-3 activation. ASMase-induced ceramide generation activated JNK resulting in Bim L phosphorylation and translocation to mitochondria, as the inhibition of ASMase by imipramine prevented these events. In contrast, blockade of ceramide catabolism by N-oleyolethanolamine (NOE), a ceramidase inhibitor, enhanced ceramide levels and potentiated I/R injury compared with vehicle-treated mice. Pentoxifylline treatment prevented TNF upregulation and ASMase activation. Furthermore, 9 of 11 mice treated with imipramine survived 7 days after total liver ischemia, compared with 4 of 12 vehicle-treated mice, whereas 8 of 8 NOE-treated mice died within 2 days of total liver ischemia. In conclusion, ceramide generated from ASMase plays a key role in I/R-induced liver damage, and its modulation may be of therapeutic relevance.

Targeting cholesterol at different levels in the mevalonate pathway protects fatty liver against ischemia–reperfusion injury

“…After a midline laparotomy, hepatic inflow to the median and left lobes was occluded by application of a micro-vascular clamp (Biemer clip, 0.29-0.39 N) for 60-90 min as described previously [12,13] to prevent hepatic blood flow for 90 minutes. Mesenteric venous congestion was prevented by portal decompression through the right and caudate lobes.…”

“…Mesenteric venous congestion was prevented by portal decompression through the right and caudate lobes. Blood samples and liver biopsies were taken at different periods after reperfusion for further evaluation, typically 4-6 hours postreperfusion when massive liver injur is observed [12,13]. Control animals were sham operated.…”

“…Serum ALT levels were measured by the Centro de Diagnóstico Medico (Hospital Clinic, Barcelona, Spain). Lipid peroxidation in liver samples was determined after the production of malondialdehyde (MDA) using the thiobarbituric acid (TBA) method as described previously [13].…”

Cytolytic T cells induce ceramide-rich platforms in target cell membranes to initiate graft-versus-host disease

“…Hepatocytes were chosen as target cells in this assay because they are classic target cells for GVHD and use the sphingomyelin pathway for apoptosis. 20,21,43 Coincubation with 0 to 2 ϫ 10 6 alloactive splenic T cells increased hepatocyte apoptosis from 4.7% (Ϯ 0.7%) to 33.8% (Ϯ 1.9%) by 16 hours, detected by nuclear morphologic changes ( Figure 4A). In contrast, syngeneic LP hepatocytes did not undergo significant apoptosis above baseline (not shown).…”

“…16,17 Recent studies have indicated that the sphingomyelin pathway and its second messenger ceramide regulate TNF superfamily receptor-induced apoptosis in some systems, 18,19 as well as apoptosis in select liver and gastrointestinal (GI) stress responses in vivo. Ceramide generation occurs rapidly in hepatic ischemiareperfusion injury, 20 TNF-induced hepatitis/cirrhosis, 21 and radiation-induced GI toxicity. 22 Genetic or pharmacologic inhibition of acid sphingomyelinase (ASMase)-mediated ceramide generation markedly attenuates pathogenesis of these syndromes.…”