Liver I/R injury is improved by the arginase inhibitor, N^ω-hydroxy-nor-l-arginine (nor-NOHA)

Abstract

Liver ischemia-reperfusion (I/R) injury is associated with profound arginine depletion due to arginase release from injured hepatocytes. The purpose of this study was to determine whether arginase inhibition with N -hydroxy-nor-L-arginine (nor-NOHA) would increase circulating arginine levels and decrease hepatic damage during liver I/R injury. The effects of nor-NOHA were initially tested in normal animals to determine in vivo toxicity. In the second series of experiments, orthotopic syngeneic liver transplantation (OLT) was performed after 18 h of cold ischemia time in Lewis rats. Animals were given nor-NOHA (100 mg/kg) or saline before and after graft reperfusion. In normal animals treated with nor-NOHA, there were no histopathological changes to organs, liver enzymes, serum creatinine, or body weight. In the OLT model, animals treated with saline exhibited markedly elevated serum transaminases and circulating arginase protein levels. Nor-NOHA administration blunted the increase in serum arginase activity by 80% and preserved serum arginine levels at 3 h after OLT. Nor-NOHA treatment reduced post-OLT serum liver enzyme release by 50%. Liver histology (degree of necrosis) in nor-NOHA-treated animals was markedly improved compared with the saline-treated group. Furthermore, use of the arginase inhibitor nor-NOHA did not influence polyamine synthesis owing to the decrease in ornithine levels. Arginase blockade represents a potentially novel strategy to combat hepatic I/R injury associated with liver transplantation. liver transplantation; arginine; nitric oxide; preservation injury ISCHEMIA-REPERFUSION (I/R) injury is a pathophysiological process whereby hypoxic organ damage is accentuated following return of blood flow and oxygen delivery to the compromised tissue. Transient episodes of hepatic ischemia occur during solid organ transplantation, trauma, hypovolemic shock, and elective liver resection, when inflow occlusion or total vascular exclusion is used to minimize blood loss. The pathophysiology of liver I/R injury includes both direct cellular damage as the result of the ischemic insult as well as delayed dysfunction and damage resulting from activation of inflammatory pathways (3,6,8,21,26,29). The injury that results from I/R after liver transplantation contributes to primary nonfunction in ϳ5-10% of liver grafts and delayed graft function in 15-30% of cases (9, 30).Nitric oxide (NO) is known to have an important role in regulating liver physiology and blood flow. NO and citrulline are produced by the family of nitric oxide synthases (NOS) from the substrate L-arginine (32). NO has been shown to exert protective effects in the liver by improving blood flow, antagonizing neutrophil activation and adhesion, neutralizing free radical injury, and eliciting antiapoptotic effects (19, 23). The beneficial effects of the L-arginine-NO pathway have also been reported in liver transplantation models. Experiments using arginine supplementation and NO donors have shown that NO serves to improve liver ischemia injury...

Arginase blockade protects against hepatic damage in warm ischemia-reperfusion

“…Measuring serum levels of nitrite and other more direct markers of nitric oxide production would be useful in determining whether the increased arginine following nor-NOHA protects via an NO-dependent mechanism. It is noteworthy that nor-NOHA treatment also restored the depleted levels of circulating arginine levels in a rodent model of liver transplantation, and improved liver graft injury [19]. Furthermore, some therapeutic interventions that may be beneficial in the cold I/R setting have not been proven to apply in warm hepatic I/R models.…”

“…Our selection of dosing regimen was based on previous testing of nor-NOHA in normal animals where doses up to 200 mg/kg IV × 2 resulted in no changes AST, ALT, or creatinine. Doses up to 400 mg/kg IV × 2 resulted in minimal increases in AST and ALT with no increase in creatinine [19]. Therefore the dose used in the current study (100 mg/kg I.V.…”

L-arginine in the ischemic phase protects against liver ischemia-reperfusion injury

“…Hepatoprotection via the LG-NOS pathway has been previously established in animal models of IRI 18,19 . Given that the LG-NOS pathway has been reported to play critical roles during inflammation, our data support the hypothesis that the administration of LG during the ischemic phase is beneficial by attenuating liver injury in a model of warm hepatic IRI.…”

“…Collectively, these observations suggest a balance between the local NO concentration and the time of NO exposure in determining the outcome of liver IRI 8 . Irrespective of the precise mechanisms involved, increased inflammation and cytotoxicity are key components in hepatocellular dysfunction during the pathogenesis of liver IRI [16][17][18][19][20] .…”

“…The LG-NOS pathway has been critically implicated in liver IRI, and most studies have suggested that intravenous LG infusion increases NO levels and protects the liver against damage due to IRI [8][9][10][11][12][13][14][15][16][17][18][19][20] .…”