Avaliação da via alternativa do sistema renina-angiotensina na encefalopatia hepática experimental

Abstract

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome resulting from acute or chronic liver failure, characterized by a broad spectrum of cognitive and motor alterations that are potentially reversible but may progress to coma and death. In addition to hyperammonemia, neuroinflammation, neurotransmitter alterations, and oxidative stress, the pathogenesis of HE is known to be complex, involving poorly elucidated cellular and molecular mechanisms. Thus, with the discovery of components of the Renin-Angiotensin System (RAS) at the local level in the central nervous system (CNS), efforts have been made to understand its role in the development and exacerbation of HE-related alterations. This system has demonstrated a dual role: the classical pathway, mediated by angiotensin II (Ang II) acting on AT1 receptors, is associated with exacerbated inflammatory responses, leading to tissue damage. On the other hand, the alternative pathway, mediated by angiotensin-(1-7) (Ang-(1-7)) acting on the Mas receptor, exhibits anti-inflammatory and neuroprotective properties, as well as the potential to modulate mediators associated with oxidative stress. Therefore, the objective of this study was to evaluate the inhibition of the classical axis and activation of the alternative axis of the RAS. To assess the participation of both axes, ten-to-eleven-week-old female C57BL/6 mice with HE induced by thioacetamide (TAA) at a dose of 600 mg/kg were selected. The classical pathway was inhibited using the AT1 receptor competitive antagonist telmisartan at 10 mg/kg. To evaluate the alternative pathway, transgenic K18-hACE2 C57BL/6 mice with overexpression of angiotensin-converting enzyme 2 (ACE2) and C57BL/6 mice treated with liposoluble Ang-(1-7) at doses of 1.5 mg/kg and 3 mg/kg were used. Behavioral evaluations were conducted through the Open Field test, as well as hematological and histopathological analyses of the liver and central nervous system 24 hours after HE induction. Mice with TAA-induced HE exhibited locomotor deficits characterized by reduced total distance traveled and velocity in the Open Field test. However, inhibition of the classical pathway through telmisartan at a dose of 10 mg/kg was not sufficient to reverse the observed pattern. In contrast, increased ACE2 expression, although not completely reversing motor deficits, attenuated locomotor impairment, a result also observed with the use of Ang-(1-7) at a dose of 3 mg/kg. Treatment with Ang-(1-7) at a dose of 1.5 mg/kg fully reversed locomotor impairment, with treated HE animals displaying patterns similar to their respective controls. Regarding hematological evaluation, the combination of telmisartan at 10 mg/kg with TAA at 600 mg/kg led to significant thrombocytopenia and leukopenia. Mice with ACE2 overexpression and TAA induction showed an increase in the proportion of neutrophils and lymphocytes, while treatment with Ang-(1-7) at 3 mg/kg, along with TAA induction, affected leukocyte volume. Liver histopathology confirmed TAA-induced injury, demonstrated by areas of necrosis and inflammatory infiltration, with patterns and intensities similar across the different treatment groups. Thus, based on these findings, activation of the alternative RAS pathway demonstrated neuroprotective potential in HE induced by acute liver injury in mice.