Caspase-Independent Apoptosis Induced by Reperfusion Following Ischemia without Bile Duct Occlusion in Rat Liver

• Published in: Biological & pharmaceutical bulletin 2017/01/01, Vol.40(1), pp.104-107
• Main Authors: Matsui, Nobuaki, Yoshioka, Rie, Nozawa, Asako, Kobayashi, Naonobu, Shichijo, Yukari, Yoshikawa, Tadatoshi, Akagi, Masaaki
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis; Apoptosis Inducing Factor - metabolism; Apoptosis-inducing factor; Bile; Bile Ducts; Caspase; Caspase inhibitors; Caspase Inhibitors - pharmacology; Caspase-3; Caspases - metabolism; Cleavage; DNA Fragmentation; DNA nucleotidylexotransferase; Hepatic artery; Inhibitor of Apoptosis Proteins - metabolism; Inhibitors; Ischemia; ischemia/reperfusion; Liver; Liver - metabolism; Male; Nuclear transport; Occlusion; Portal vein; Pretreatment; Proteins; Rats, Wistar; Reperfusion; Reperfusion Injury - metabolism; Substrate inhibition; Substrates; Translocation
• ISSN: 0918-6158; 1347-5215
• DOI: 10.1248/bpb.b16-00587

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.