Oxaloacetate Protects Rat Liver From Experimental Warm Ischemia/Reperfusion Injury by Improving Cellular Energy Metabolism

Abstract

Liver ischemia/reperfusion injury (IRI) is an important cause of liver damage especially early after liver transplantation, following liver resection, and in other clinical situations. Using rat experimental models, we identified oxaloacetate (OAA) as a key metabolite able to protect hepatocytes from hypoxia and IRI. In vitro screening of metabolic intermediates beneficial for hepatocyte survival under hypoxia was performed by measures of cell death and injury. In vivo, the effect of OAA was evaluated using the left portal vein ligation (LPVL) model of liver ischemia and a model of warm IRI. Liver injury was evaluated in vivo by serum transaminase levels, liver histology, and liver weight (edema). Levels and activity of caspase 3 were also measured. In vitro, the addition of OAA to hepatocytes kept in a hypoxic environment significantly improved cell viability (P < 0.01), decreased cell injury (P < 0.01), and improved energy metabolism (P < 0.01). Administration of OAA significantly reduced the extent of liver injury in the LPVL model with lower levels of alanine aminotransferase (ALT; P < 0.01), aspartate aminotransferase (AST; P < 0.01), and reduced liver necrosis (P < 0.05). When tested in a warm IRI model, OAA significantly decreased ALT (P < 0.001) and AST levels (P < 0.001), prevented liver edema (P < 0.001), significantly decreased caspase 3 expression (P < 0.01), as well as histological signs of cellular vesiculation and vacuolation (P < 0.05). This was associated with higher adenosine triphosphate (P < 0.05) and energy charge levels (P < 0.01). In conclusion, OAA can significantly improve survival of ischemic hepatocytes. The hepatoprotective effect of OAA was associated with increased levels of liver bioenergetics both in vitro and in vivo. These results suggest that it is possible to support mitochondrial activity despite the presence of ischemia and that OAA can effectively reduce ischemia‐induced injury in the liver.

L‐Lactate–Based Improvement of Energetic Charge and Protection of Rat Liver

“…Our experiments using lactate (sodium L-lactate) conclude that liver protection and improved energetic charge are also associated in a model of cold ischemia reperfusion injury of ex vivo livers that were isolated from rats fasted for 18 hours. Our experimental observation may complement those of Merlen et al, (1) drawing the attention to OAA and lactate as double-edged compounds for liver metabolism due to their capacity for dual commitment in both energy-expensive gluconeogenesis and mitochondrial energy-producing oxidations. Because the former and latter metabolic pathways may lead to depleting and feeding hepatocyte cell energetic status, respectively, the preservation/gain in energetic charge may attest to the preponderance of the latter over the former.…”

“…Lactate is a precursor of OAA, and its protective properties might be therefore attributed to those of OAA. (1) Interestingly, in contrast to lactate, load by OAA of cytosol may not induce NADH burst (OAA decreases versus increases NADH through cytosolic malate dehydrogenase reaction). This absence of a rise in cytoplasmic NADH/NAD+ ratio might prevent gluconeogenesis to proceed, making OAA available for mitochondrial Krebs cycle oxidation as described.…”

“…This absence of a rise in cytoplasmic NADH/NAD+ ratio might prevent gluconeogenesis to proceed, making OAA available for mitochondrial Krebs cycle oxidation as described. (1) By analogy, switch of lactate to mitochondrial oxidations versus gluconeogenesis might also require prevention or loss of the cytosolic NADH burst. This might be achieved by a mitochondrial lactate oxidation complex, which directly couples lactate-dependent NADH production to the mitochondrial electron chain (3) and not to gluconeogenesis.…”

“…To this purpose, the liver produces glucose by gluconeogenesis from metabolic precursors, some of which, in turn, may also be oxidized by liver mitochondria. This is the case for OAA, a substrate of both gluconeogenesis and mitochondrial Krebs' cycle oxidation, and which, in a recent issue of Liver Transplantation, (1) was shown to protect rat liver and energetic charge under warm ischemia/ reperfusion injury. Here, we document experimental lactate-based protection of injured ex vivo rat liver and energetic charge.…”

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Recently, Merlen et al (1) reported protection by oxaloacetate (OAA) of rat liver against warm ischemia/ reperfusion injury. On this occasion, improved energetic metabolism and charge was linked to protection.

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