Pyruvate Inhibits Hepatic Ischemia-Reperfusion (I/R) Injury

Abstract

1036 I/R injury remains an important limiting factor in liver transplantation. We have recently shown that the 3-carbon compound pyruvate (PY) inhibits intestinal I/R and preservation injury. This study aims to evaluate the protective effect of PY on hepatic I/R injury. Male ACI rats of 150-200g were used. Study animals were fed liquid diet containing 15mMol/day of PY while control animals received the same diet containing isoenergetic amount of polycose (placebo). In each group, rats were sacrificed following 60 min. of partial hepatic ischemia (obtained clamping the portal and arterial branches to left and median lobe) and after reperfusion (2, 6, 24 and 48 hours; n=6 each). For each time point serum AST, ALT and LDH were measured and liver biopsies were obtained and examined for morphology, DNA fragmentation (DNA Laddering) and evaluation of apoptosis (TUNEL). Data is expressed as mean±SD and statistical analyses were performed using Student's t test and Kaplan Meier survival curves. Survival rate 48 hours following I/R was 83% in the control group, while in the PY-treated group was 100% (p>0.05). Increased enzymatic levels, especially during the first 24 hours, confirmed the liver damage (control vs. PY respectively: AST 1252±176 vs. 578±54, p<0.002; ALT 728±232 vs. 260±46, p<0.03; LDH 4573±767 vs. 2869±630, p>0.05). Histologic alteration of the liver following I/R was observed as sinusoidal congestion and edema, vacuolization of hepatocytes, focal necrosis and leukocyte infiltration in the control animals. In PY-treated animals these findings were significantly attenuated. Completely different patterns of DNA fragmentation were observed in the two groups. In control rats, the apoptotic process was particularly enhanced after 1 hour of ischemia and peaked after 2 hours of reperfusion to decrease gradually 48h after reperfusion. In the PY-treated group DNA ladders concentrated mostly after 6h of reperfusion being still moderately evident after 24h and disappeared by 48h. Following 1h of ischemia the number of apoptotic nuclei was significantly increased in control livers (38.6±18.8) compared to normal pre-ischemic livers (6.8±1.6; p<0.01) while were significantly reduced by PY treatment (6.6±1.9; p<0.01). Following 2h of reperfusion the maximum number of apoptotic cells was observed (49.8±27.3) while PY significantly reduced such event (13.8±4.7; p<0.05). The number of apoptotic cells returned to baseline 48h after reperfusion in both groups (1.6±0.8 and 4.0±3.7). Apoptosis was delayed in PY treated livers to 6h post reperfusion, peaking at a significantly lower count compared to placebo treated controls (29.2±5.93; p<0.05). These data indicates that PY has a protective effect on I/R injury of the liver. This inhibitory effect of PY is mediated by reduced DNA fragmentation. The protective effect of PY in this model is accompanied by a delay and reduction of hepatocyte apoptosis.