Research ArticleRecombinant human manganese superoxide dismutase reduces liver fibrosis and portal pressure in CCl4-cirrhotic rats
Introduction
Increased intrahepatic vascular resistance is the primary factor in the development of portal hypertension, the main complication of cirrhosis, and it is the result of both structural changes in the liver that are inherent to cirrhosis and increased hepatic vascular tone [1], [2], [3]. Sinusoidal endothelial dysfunction, characterized by impaired endothelium-dependent vasodilatation, is a major pathogenic factor in the increased vascular tone and is mainly attributed to insufficient nitric oxide (NO) availability within the cirrhotic liver. The decreased liver NO is due to diminished NO synthase (eNOS) activity [4], [5], [6] and to NO scavenging by increased release of superoxide () [7].
We have previously shown that the increased content in cirrhotic livers is a consequence not only of increased production but also of decreased expression and activity of superoxide dismutase (SOD), the critical antioxidant enzyme in the liver [8]. Our group has clearly demonstrated that strategies which decrease intrahepatic levels enhance intrahepatic NO bioavailability and reduce portal pressure in portal hypertensive cirrhotic rats [9]. Two different experimental therapeutic strategies have previously been evaluated, adenoviral delivery of SOD [10] and intraportal administration of tempol (a SOD mimetic) [11]. However, the use of adenovirus-based gene therapies is highly controversial in humans, and although tempol administration is known to reduce portal pressure it may also have systemic effects.
Recently, a novel recombinant isoform of human manganese SOD (rMnSOD) has been developed. The particular property of this form of SOD is that after administration, it enters cells, due to its uncleaved terminal peptide sequence [12], [13], [14]. It has been shown to be very effective at scavenging intra and extracellular and at improving pathological conditions associated with increased oxidative stress [15], [16]. In addition, rMnSOD shows good biodistribution in the liver compared to other organs, suggesting that it is well suited for correcting hepatic oxidative stress [13]. The present study therefore aimed at investigating whether chronic administration of rMnSOD could be a new therapeutic strategy to reduce portal hypertension in cirrhosis.
Section snippets
Effects of rMnSOD on the increased hepatic levels promoted by NADPH oxidase
To confirm that rMnSOD (produced in the lab of Dr. Aldo Mancini, Istituto Nazionale dei Tumori di Napoli, Naples, Italy) [12], [13], [14], [15] is able to scavenge increased intrahepatic levels, control rats received a single dose of rMnSOD (15 μg/kg, i.p.) or vehicle (phosphate buffer saline, PBS) 2 h before the experiment. Afterwards, livers were isolated and perfused as described below, and oxidative stress was generated by adding nicotinamide adenine dinucleotide phosphate (NADPH; 1 mM;
Results
There were no deaths during treatment in neither CCl4- nor BDL-cirrhotic rats. There were no significant differences between CCl4-cirrhotic rats treated with vehicle or rMnSOD in terms of AST, ALT or albumin (Table 1).
Discussion
Increased intrahepatic resistance within the cirrhotic liver, the primary cause of portal hypertension, is mainly due to increased intrahepatic resistance, which results from structural changes inherent to progressive fibrosis and dynamic changes due to increased hepatic vascular tone [1], [2], [3]. Low NO bioavailability and exacerbated production of vasoconstrictors, that leads to the contraction of hepatic stellate cells, are considered the main factors responsible for endothelial
Financial support
Maeva Guillaume was supported by the Direction pour la Recherche Clinique et l’Innovation de Toulouse. This study was supported by grants from the Ministerio de Educación y Ciencia (SAF 2010/17043) and from the Instituto de Salud Carlos III (PS09/0126, ACI2009-0938 and FIS PI11/00235), Spain. J.G.-S. has a contract from the Programa Ramón y Cajal, Ministerio de Economía y Competitividad, Spain. CIBERehd is funded by the Instituto de Salud Carlos III. Part of this work was carried out at the
Conflict of interest
The authors who have taken part in this study declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.
Acknowledgements
Part of this work was carried out at the Esther Koplowitz Centre, Barcelona. The authors would like to thank Hector Garcia, Montse Monclús, Antonella Borrelli, Antonella Schiattarella and Roberto Mancini for their technical assistance.
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These authors contributed equally to this work and share first authorship.