title: Caspase-Independent Apoptosis Induced by Reperfusion Following Ischemia without Bile Duct Occlusion in Rat Liver.
abstract: The contribution of caspases to hepatic ischemia/reperfusion (I/R)-induced apoptosis has not been completely understood yet. Several studies have demonstrated increased caspase activity during I/R and the protective effect of caspase inhibitors against I/R injuries. However, reports with opposing results also exist. Herein, we examined the contribution of caspases to the I/R-induced hepatic apoptosis in rats using caspase inhibitors and specific substrates of caspases. Hepatic I/R was induced via a 2-h occlusion of the portal vein and the hepatic artery, without conducting bile duct occlusion. DNA laddering and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP) nick end-labeling (TUNEL)-positive cells were increased at 3 h after reperfusion. Pretreatment with caspase inhibitors (Z-Asp-2,6-dichlorobenzoyloxymethylketone (Z-Asp-cmk) 2 or 10 mg/kg intravenously (i.v.), 20 mg/kg intraperitoneally (i.p.), Z-Val-Ala-Asp(OMe)-fluoromethylketone (Z-VAD-fmk) 3 mg/kg i.v.) failed to reduce apoptosis induced by I/R. Interestingly, apoptosis induced by the portal triad (hepatic artery, portal vein, and bile duct) occlusion/reperfusion could be marginally attenuated using Z-Asp-cmk (2 mg/kg i.v.). The cleavage activity for Ac-DEVD-α-(4-methylcoumaryl-7-amide) (MCA), a caspase-3/7/8/9 substrate, was significantly increased by I/R. Conversely, the cleavage activities for Ac-DNLD-MCA and MCA-VDQVDGW[K-DNP]-NH2, specific substrates for caspase-3 and -7 respectively, were decreased by I/R. Protein expression of the cellular inhibitor of apoptosis protein 2 (c-IAP2), an endogenous caspase inhibitor, was increased by ischemia. Nuclear translocation of the apoptosis-inducing factor (AIF), an initiator protein of caspase-independent apoptosis, was also increased during I/R. These results suggest that caspases are inhibited by c-IAP2 induced during ischemia and that AIF may be involved in initiation of apoptosis induced by hepatic I/R without bile duct occlusion.
authors.affiliation: Department of Pharmacology, Faculty of Pharmaceutical Sciences, Tokushima Bunri University.
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Matsui
authors.forename: Rie
authors.initials: R
authors.lastname: Yoshioka
authors.forename: Asako
authors.initials: A
authors.lastname: Nozawa
authors.forename: Naonobu
authors.initials: N
authors.lastname: Kobayashi
authors.forename: Yukari
authors.initials: Y
authors.lastname: Shichijo
authors.forename: Tadatoshi
authors.initials: T
authors.lastname: Yoshikawa
authors.forename: Masaaki
authors.initials: M
authors.lastname: Akagi
mesh_terms: D000818:Animals; D017209:Apoptosis; D051033:Apoptosis Inducing Factor / Q000378:metabolism; D001652:Bile Ducts; D061945:Caspase Inhibitors / Q000494:pharmacology; D020169:Caspases / Q000378:metabolism; D053938:DNA Fragmentation; D051034:Inhibitor of Apoptosis Proteins / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D017208:Rats, Wistar; D015427:Reperfusion Injury / Q000378:metabolism*
chemical_list: C494831:Aifm1 protein, rat; D051033:Apoptosis Inducing Factor; D061945:Caspase Inhibitors; D051034:Inhibitor of Apoptosis Proteins; D020169:Caspases