Decreased Expression and Uncoupling of Endothelial Nitric Oxide Synthase in the Cerebral Cortex of Rats with Thioacetamide-Induced Acute Liver Failure.

Krzysztof Milewski,Jan Albrecht,Magdalena Zielińska,Anna Maria Czarnecka

doi:10.3390/ijms22136662

Abstract

Acute liver failure (ALF) is associated with deregulated nitric oxide (NO) signaling in the brain, which is one of the key molecular abnormalities leading to the neuropsychiatric disorder called hepatic encephalopathy (HE). This study focuses on the effect of ALF on the relatively unexplored endothelial NOS isoform (eNOS). The cerebral prefrontal cortices of rats with thioacetamide (TAA)-induced ALF showed decreased eNOS expression, which resulted in an overall reduction of NOS activity. ALF also decreased the content of the NOS cofactor, tetrahydro-L-biopterin (BH4), and evoked eNOS uncoupling (reduction of the eNOS dimer/monomer ratio). The addition of the NO precursor L-arginine in the absence of BH4 potentiated ROS accumulation, whereas nonspecific NOS inhibitor L-NAME or EDTA attenuated ROS increase. The ALF-induced decrease of eNOS content and its uncoupling concurred with, and was likely causally related to, both increased brain content of reactive oxidative species (ROS) and decreased cerebral cortical blood flow (CBF) in the same model.

Highlights

Hepatic encephalopathy (HE) is a neuropsychiatric disorder associated with acute (ALF) or chronic liver failure
The key observation of the present study is that Acute liver failure (ALF) significantly impairs brain endothelial nitric oxide synthases (NOSs) isoform (eNOS) function as a consequence of both eNOS protein loss and its uncoupling, as reflected by a drop in the ratio of the active dimer to the inactive monomer
L-arginine-evoked enhancement of reactive oxygen species (ROS) generation was abolished by Ca2+ ions chelation, a maneuver abrogating eNOS activity

Summary

Introduction

Hepatic encephalopathy (HE) is a neuropsychiatric disorder associated with acute (ALF) or chronic liver failure. Brain edema and impaired cerebral blood flow (CBF) are the two major manifestations of HE [1,2,3]. These two interrelated impairments are associated with the induction of oxidative and nitrosative stress (ONS) triggered by different stimuli. While N-methyl-D-aspartate (NMDA) receptor-mediated accumulation of intracellular calcium and neuroinflammation clearly appear to induce ONS in HE [5,6,7], ROS generation is associated with the excessive production of superoxide anion (O2 − ), resulting from the p47phox subunit of the NADPH oxidase enzyme, as shown in cultured rat astrocytes and cortical mouse brain slices [8]. Additional questions addressed in this study are whether and to what degree ALF-induced changes affect NO production and CBF in the whole brain

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Conclusion