**7. Acknowledgment**

The experiments performed in the authors' laboratories were or are supported by grants Intra-European Fellowship Marie Curie in Seventh Framework Programme (FP7-PEOPLE-2010-IEF number PIEF-GA-2010-272485), Excellency Project P06-CTS-01887 from Junta de Andalucia and PI07425 del Ministerio de Sanidad y Consumo from Spain, and from Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas del Instituto de salud Carlos III of the Ministry of Spanish Health. Ornithinephenlacetate has been provided by Ocera Therapeutics, San Diego, CA.
