Leucine Enriched Essential Amino Acid Mixture to Reverse Muscle Loss in Cirrhosis

Loss of skeletal muscle mass or sarcopenia is the most common and potentially reversible
complication in cirrhosis that increases morbidity and mortality before, during and after
liver transplantation. No proven treatments exist for the prevention or reversal of
sarcopenia in cirrhosis, primarily because the mechanisms responsible for this are unknown.
Based on compelling preliminary studies and those of the co investigator, investigators
hypothesize that the mechanism of reduced skeletal muscle mass in cirrhosis is due to a
myostatin mediated impaired mTOR (mechanistic target of rapamycin) signaling resulting in
reduced protein synthesis and increased autophagy. Investigators further postulate that
leucine, a direct stimulant of mTOR, will reverse the impaired mTOR phosphorylation in the
skeletal muscle of cirrhotics. The consequent increase in protein synthesis reduced autophagy
will result in an increase in skeletal muscle mass. Investigators will test these hypotheses
by quantifying the response to acute and long term (3 month) administration of leucine
enriched essential amino acid (EAA/LEU) compared with an isonitrogenous isocaloric
non-essential balanced amino acid mixture (does not stimulate protein synthesis) in cirrhotic
patients. Fractional protein synthesis rate (FSR) in skeletal muscle, responses of the
molecular regulatory pathways of skeletal muscle protein synthesis, and autophagy flux will
be quantified in the acute and long term protocols. Tracer studies using L-[D5]-phenylalanine
(Phe) as a primed constant infusion (prime 2µmol.kg-1.hr-1; constant 0.05 µmol.kg-1.hr-1)
with and L [ring-D2] tyrosine, forearm plethysmography, and sequential skeletal muscle
biopsies (total of 3 per study subject) will be used to quantify these outcomes.
Anthropometric, clinical and body composition measures will be additional outcome measures
for the long term intervention. Expression of regulatory signaling proteins, myostatin, IGF-1
(insulin like growth factor) , phospho-Akt, phospho-AMPK (activated protein kinase),
phospho-mTOR and phospho-p70s6k will be quantified by Western immunoblots. Autophagy flux
will be measured by quantifying expression of the autophagosome proteins.