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The role of Branched Chain Amino Acids in the treatment of hepatic Encephalopathy

      The relationship between intake of nutrients and Hepatic Encephalopathy (HE) dates back to the historical roots of experimental hepatology. Branched-Chain Amino Acids (BCAA; Isoleucine, leucine and valine) have attracted particular interest and in 1956 Müting described the amino acid pattern in patients with cirrhosis. The abnormal plasma pattern has been characterized by the ratio between BCAA and aromatic amino acids in plasma, the so called 'Fischer´s ratio'. This ratio has been associated with the grade of HE. Under normal conditions, ammonia detoxification predominantly takes place in the liver. When the liver fails, the homeostasis is altered and muscle tissue becomes the main alternative organ for at least temporary detoxification of ammonia. BCAA are believed to support this muscle ammonia detoxification and the ammonia lowering effect of BCAA has been intensely investigated. In this review the effect of BCAA on muscle ammonia metabolism and the protein sparing and anabolic effects of BCAA are discussed. A Cochrane metaanalysis showed that BCAA had beneficial effects on HE with a number needed to treat of 5 patients (RR 0.73, 95% CI 0.61 to 0.88). The combined evidence suggests that although the pathophysiology is poorly understood, there is evidence to support clinical benefits of BCAA. BCAAs enhance muscle mass and exert anabolic effects via stimulation of protein synthesis. The beneficial long-term effects of BCAA on HE could be related to these effects and not only related to Branched-Chain Amino Acid increased ammonia metabolism.

      Abbreviations:

      HE (Hepatic Encephalopathy), BCCA (Branched-Chain Amino Acid)

      Keywords

      The relationship between intake of nutrients and Hepatic Encephalopathy (HE) dates back to the historical roots of experimental hepatology. In Saint Petersburg in 1893, behavioral scientists Pavlov and colleagues described how dogs with a portacaval shunt (Eck’s fistula) developed ataxia and coma when being fed with meat.
      • Hahn M.
      • Massen O.
      • Nencki M.
      • et al.
      Die Eck’sche Fistel zwischen der unteren Hohlvene und er pfortader und ihre Folgen fur den Organismus.
      They found that the behavioral changes reversed when the dogs were switched to dairy products, which we now know contain a high level of the Branched-Chain Amino Acids (BCAA) valine, isoleucine and leucine. In 1956 Müting found that cirrhosis was associated with low BCAA levels in plasma.
      • Muting D.
      • Wortmann V.
      Amino acid metabolism in liver diseases.
      The decreased BCAA concentrations combined with elevated concentrations of the aromatic amino acids (AAA) tyrosine and phenylalanine) were later confirmed in several other publications. The abnormal plasma amino acid pattern has been characterized by the ratio between BCAA and AAA in plasma, the so called ‘Fischer´s ratio’. This ratio has been associated with the grade of HE.
      • Fischer J.E.
      • Rosen H.M.
      • Ebeid A.M.
      • et al.
      The effect of normalization of plasma amino acids on hepatic encephalopathy in man.
      Both groups of amino acids compete for entry across the blood–brain barrier by the same transporter leading to an increased concentration of aromatic neurotransmitter precursors. These precursors were believed to cause an inefficient (‘false’) dopaminergic neurotransmission and inhibition of dopamine synthesis resulting in the neuro-depression seen in HE.
      • Gluud L.L.
      • Dam G.
      • Les I.
      • Marchesini G.
      • Borre M.
      • Aagaard N.K.
      • Vilstrup H.
      Branched-chain amino acids for people with hepatic encephalopathy.
      Although subsequent studies were unable to confirm this theory, BCAAs were continuously used as a pharmacological nutrient for patients with chronic liver disease. However, increasing evidence now suggests that BCAA is beneficial in HE but the mechanism of action seems to be different than primarily assumed. It is now believed that the beneficial effect of BCAA is associated with ammonia detoxification outside the liver, predominantly in muscles.

      Ammonia

      Under normal physiological conditions the key part of ammonia detoxification takes place in the liver. The urea cycle runs in periportal hepatocytes and glutamine synthesis in the perivenous hepatocytes. In patients with advanced liver disease, ammonia reaches the systemic circulation due to diminished urea synthesis
      • Vilstrup H.
      Synthesis of urea after stimulation with amino acids: relation to liver function.
      and portosystemic shunting.
      • Syrota A.
      • Paraf A.
      • Gaudebout C.
      • et al.
      Significance of intra- and extrahepatic portasystemic shunting in survival of cirrhotic patients.
      HE is associated with increased blood ammonia concentrations
      • Keiding S.
      • Sørensen M.
      • Bender D.
      • et al.
      Brain metabolism of 13N-ammonia during acute hepatic encephalopathy in cirrhosis measured by positron emission tomography.
      and experimental studies suggest that ammonia is neurotoxic.
      • Norenberg M.D.
      • Rama Rao K.V.
      • Jayakumar A.R.
      Signaling factors in the mechanism of ammonia neurotoxicity.
      ,
      • Gorg B.
      • Morwinsky A.
      • Keitel V.
      • et al.
      Ammonia triggers exocytotic release of l-glutamate from cultured rat astrocytes.
      It is generally accepted that ammonia plays a key role in the pathogenesis of HE.
      • Lockwood A.H.
      • McDonald J.M.
      • Reiman R.E.
      • et al.
      The dynamics of ammonia metabolism in man. Effects of liver disease and hyperammonemia.
      • Ott P.
      • Larsen F.S.
      Blood-brain barrier permeability to ammonia in liver failure: a critical reappraisal.
      • Haussinger D.
      • FAU - Gorg B.
      • Gorg B.
      Interaction of oxidative stress, astrocyte swelling and cerebral ammonia toxicity.
      • Clemmesen J.O.
      • Larsen F.S.
      • Kondrup J.
      • et al.
      Cerebral herniation in patients with acute liver failure is correlated with arterial ammonia concentration.
      Most interventions for patients with HE is directed at reducing blood ammonia levels.

      Ammonia detoxification in skeletal muscle and the potential role of BCAA

      Skeletal muscle contributes to the regulation of blood ammonia levels via absorption of ammonia from plasma, and release of glutamine.
      • Ganda O.P.
      • Ruderman N.B.
      Muscle nitrogen metabolism in chronic hepatic insufficiency.
      • Hod G.
      • Chaouat M.
      • Haskel Y.
      • et al.
      Ammonia uptake by skeletal muscle in the hyperammonaemic rat.
      • Chatauret N.
      • Desjardins P.
      • Zwingmann C.
      • et al.
      Direct molecular and spectroscopic evidence for increased ammonia removal capacity of skeletal muscle in acute liver failure.
      • Clemmesen J.O.
      • Kondrup J.
      • Ott P.
      1; Splanchnic and leg exchange of amino acids and ammonia in acute liver failure.
      In cirrhosis, the ammonia detoxification in the muscle may even remove more ammonia from the circulation than the liver.
      • Bernal W.
      • Auzinger G.
      • Sizer E.
      • et al.
      Variation in blood ammonia concentration with site of measurement and evidence of brain and muscle uptake in patients with acute liver failure.
      ,
      • Olde Damink S.W.
      • Jalan R.
      • Redhead D.N.
      • et al.
      Interorgan ammonia and amino acid metabolism in metabolically stable patients with cirrhosis and a TIPSS.
      Patients with cirrhosis have an increased whole-body clearance of BCAA compared to healthy subjects.
      • Yamato M.
      • Muto y
      • Yoshida T.
      • et al.
      This may reflect an increased metabolic demand of BCAA in skeletal muscle where the BCAA are primarily metabolized.
      • Wahren J.
      • Felig P.
      Influence of protein ingestion on the amino acid metabolism in diabetes mellitus.
      This is in contrast to the majority of amino acids which are metabolized mainly in the liver.
      The muscle arterial-venous uptake of BCAA increases with the arterial ammonia concentration in patients with decompensated cirrhosis, indicating that muscle BCAA metabolism plays a role for ammonia removal.
      • Hayashi M.
      • Ohnishi H.
      • Kawade Y.
      • et al.
      Augmented utilization of branched-chain amino acids by skeletal muscle in decompensated liver cirrhosis in special relation to ammonia detoxication.
      Ammonia given to healthy rats causes a decrease in muscle and blood BCAA concentrations and an increase in glutamine concentrations.
      • Leweling H.
      • Breitkreutz R.
      • Behne F.
      • et al.
      Hyperammonemia-induced depletion of glutamate and branched-chain amino acids in muscle and plasma.
      This suggests that hyperammonemia lowers the plasma levels of BCAA by increased muscle BCAA uptake and increased glutamine synthesis in muscle. In vitro experiments of muscle metabolism under control of effects of glucose, insulin and pH found that high levels of ammonia increase the oxidation of leucine and the release of glutamine.
      • Holecek M.
      • Kandar R.
      • Sispera L.
      • Kovarik M.
      Acute hyperammonemia activates branched-chain amino acid catabolism and decreases their extracellular concentrations: different sensitivity of red and white muscle.
      Thus, ammonia may lower the plasma levels of BCAA by increasing the intramuscular metabolism by diverting their carbon skeletons and amino-N towards glutamate synthesis and coupling with ammonia for carbamate N in glutamine (Figure 1). In this way, muscular metabolism of BCAA results in muscular export of twice the amount of N and hence removal of ammonia.
      Figure 1
      Figure 1BCAA supports ammonia detoxification in the TCA-cycle in muscle tissue.
      BCAA enhance ammonia detoxification in skeletal muscle and thereby reduce plasma ammonia concentration. This leads to the assumption that external replenishment of BCAA further enhances the detoxification of ammonia in muscle.
      In 2011 we studied ammonia and amino acid metabolism in muscle before and after ingestion of BCAA in patients with cirrhosis and healthy subjects.
      • Dam G.
      • Keiding S.
      • Munk O.L.
      • et al.
      Branched-chain amino acids increase arterial ammonia in spite of enhanced intrinsic muscle ammonia metabolism in patients with cirrhosis and healthy subjects.
      The net metabolism of ammonia across the leg was studied directly by arterial-venous differences and blood flow measurements. Such measurements reflect the combined metabolism of blood-borne (exogenous) ammonia and any contribution to ammonia metabolism from the leg itself (endogenous). To distinguish these effects, the uptake of blood borne ammonia was measured by dynamic 13N-ammonia-PET. We found that the ingestion of BCAA increased the uptake of ammonia by skeletal muscle in all persons, but also increased the blood ammonia concentration. This may reflect that BCAA exert their primary effect on ammonia by stimulation of the intramuscular ammonia metabolism rather than by increasing the metabolism of blood-supplied ammonia.
      The baseline muscle uptake of BCAA was similar in cirrhosis patients and healthy subjects. However, cirrhosis patients usually suffer from muscle wasting and the muscle BCAA uptake per kilo muscle was likely higher in the cirrhosis compared to healthy subject who did not have sarcopenia.
      All in all, these studies on BCAA supplementation in cirrhosis show effects on blood concentrations of amino acids and ammonia indicating that muscles metabolize more ammonia when BCAA are supplied. The mechanism on the molecular signaling level is not clarified. Skeletal muscle hyperammonemia contributes to the sarcopenia observed in cirrhosis. One possibility is that ammonia affects the mTOR signaling system. Ammonia impairs mTOR signaling that decreases protein synthesis and increases autophagy. Thus, reactivation of mTOR is a potential target to reverse impaired muscle protein synthesis. Leucine in itself is a powerful activator of mTOR and may alleviate the detrimental effects of mTOR inhibition, possibly potentiated by the leucine induced fall in ammonia. This was confirmed by a muscle biopsy study of healthy controls and patients with cirrhosis given an oral leucine supplement. The study found that both the impaired mTOR signaling and the increased autophagy in the skeletal muscle of patients with alcoholic cirrhosis were reversed by Leucin.
      • Tsien C.
      • Davuluri G.
      • Singh D.
      • et al.
      Metabolic and molecular responses to leucine-enriched branched chain amino acid supplementation in the skeletal muscle of alcoholic cirrhosis.
      The first double-blind, placebo controlled clinical study evaluating BCAA for the treatment of patients with cirrhosis was published by Horst in 1984.
      • Horst D.
      • Grace N.D.
      • Conn H.O.
      • et al.
      Comparison of dietary protein with an oral, branched chain-enriched amino acid supplement in chronic portal-systemic encephalopathy: a randomized controlled trial.
      Thirty-seven hospitalized patients with protein intolerance were fed weekly with increasing amounts of 20 g of either dietary protein or BCAA until they attained an intake of 80 g/protein per day or until they developed grade 2 HE. The study found that BCAA decreased the occurrence of HE and that both groups improved their nitrogen balance.
      An Italian multicenter double-blinded, placebo-controlled and randomized trial with 15 centers was published in 2005.
      • Marchesini G.
      • Bianchi G.
      • Merli M.
      • et al.
      Nutritional supplementation with branched-chain amino acids in advanced cirrhosis: a double-blind, randomized trial.
      The study caompared: BCAA, lactoalbumin (isonitrogenous) and maltodextrin (isocaloric) administered to 174 patients. The duration of follow up was one year. The combined risk of HE, ascites formation and death, was significantly lower in the group who received BCAA.
      A Japanese multicenter, randomized, and calorie intake–controlled trial was published by Muto in 2005.
      • Muto Y.
      • Sato S.
      • Watanabe A.
      • Moriwaki H.
      • et al.
      Effects of oral branched-chain amino acid granules on event-free survival in patients with liver cirrhosis.
      The effects of orally administered BCAA 12 g/day for 2 years was compared to diet therapy with defined daily food intake (1.0–1.4 g protein/kg/day and 25–35 kcal/kg/day) in 646 patients with decompensated cirrhosis. 89 centers included patients. BCAA decreased the risk of HE, but the control arm was not isonitrogenous.
      Based on these trials, the European Society for Nutrition (ESPEN) recommended BCAA for the improvement of clinical outcome in advanced cirrhosis. The International Society for HE and Nitrogen metabolism (ISHEN) recommends that BCAA supplements may be of value in the occasional patient intolerant of dietary protein.
      • Gluud L.L.
      • Dam G.
      • Les I.
      • et al.
      Branched-chain amino acids for people with hepatic encephalopathy.
      In 2016 we updated a Cochrane meta-analysis on the effects of BCAA in cirrhosis.
      • Gluud L.L.
      • Dam G.
      • Les I.
      • Marchesini G.
      • Borre M.
      • Aagaard N.K.
      • Vilstrup H.
      Branched-chain amino acids for people with hepatic encephalopathy.
      We evaluated the beneficial and harmful effects of BCAA supplements versus no intervention, placebo or control diets on HE, mortality, nutritional status and adverse events for patients with HE. We found 16 randomized clinical trials comprising 827 participants with HE classed as overt (12 trials) or minimal (four trials). Eight trials assessed oral BCAA supplements and seven trials assessed intravenous BCAA. The control groups received placebo/no intervention (two trials), diets (10 trials), lactulose (two trials), or neomycin (two trials). In 15 trials, all participants had cirrhosis.
      BCAA had a beneficial effect on hepatic encephalopathy with a number needed to treat of 5 patients (RR 0.73, 95% CI 0.61 to 0.88; 827 participants; 16 trials). We confirmed the beneficial effect of BCAA in a sensitivity analysis that only included trials with a low risk of bias (RR 0.71, 95% CI 0.52 to 0.96). We found no effect on mortality, quality of life, or nutritional measures. Unfortunately, we have no head-to-head trials to compare the effect of BCAAs with the effects of non-absorbable disaccharides (lactulose), rifaximin, or other antibiotics.
      The combined evidence suggests that although the pathophysiology is poorly understood, there is evidence to support the clinical benefits of BCAA. BCAAs enhance muscle mass and exert anabolic effects via stimulation of protein synthesis. Furthermore, BCAAs are precursors for protein synthesis, but also stimulate insulin secretion and hepatocyte growth factor which may support both protein synthesis and the liver function. The beneficial long-term effects of BCAA on HE could therefore be related to these effects and not only related to an increase in ammonia metabolism. In our institution we use BCAA as an “add on” to correct lactulose treatment and nutrition if the patients nonetheless have minimal/covert HE, if they are protein intolerant or if they have recurrent HE.

      Conflicts of interest

      The authors have none to declare.

      References

        • Hahn M.
        • Massen O.
        • Nencki M.
        • et al.
        Die Eck’sche Fistel zwischen der unteren Hohlvene und er pfortader und ihre Folgen fur den Organismus.
        Arch Exp Pathol Pharmakol. 1893; 32: 3161-3210
        • Muting D.
        • Wortmann V.
        Amino acid metabolism in liver diseases.
        Dtsch Med Wochenschr. 1956; 81: 1853-1856
        • Fischer J.E.
        • Rosen H.M.
        • Ebeid A.M.
        • et al.
        The effect of normalization of plasma amino acids on hepatic encephalopathy in man.
        Surgery. 1976; 80: 77-91
        • Gluud L.L.
        • Dam G.
        • Les I.
        • Marchesini G.
        • Borre M.
        • Aagaard N.K.
        • Vilstrup H.
        Branched-chain amino acids for people with hepatic encephalopathy.
        Cochrane Database Syst Rev. 2017 18; 5: CD001939
        • Vilstrup H.
        Synthesis of urea after stimulation with amino acids: relation to liver function.
        Gut. 1980; 21: 990-995
        • Syrota A.
        • Paraf A.
        • Gaudebout C.
        • et al.
        Significance of intra- and extrahepatic portasystemic shunting in survival of cirrhotic patients.
        Dig Dis Sci. 1981; 26: 878-885
        • Keiding S.
        • Sørensen M.
        • Bender D.
        • et al.
        Brain metabolism of 13N-ammonia during acute hepatic encephalopathy in cirrhosis measured by positron emission tomography.
        Hepatology. 2006; 43: 42-50
        • Norenberg M.D.
        • Rama Rao K.V.
        • Jayakumar A.R.
        Signaling factors in the mechanism of ammonia neurotoxicity.
        Metab Brain Dis. 2009; 24: 103-117
        • Gorg B.
        • Morwinsky A.
        • Keitel V.
        • et al.
        Ammonia triggers exocytotic release of l-glutamate from cultured rat astrocytes.
        Glia. 2009; 58: 691-705
        • Lockwood A.H.
        • McDonald J.M.
        • Reiman R.E.
        • et al.
        The dynamics of ammonia metabolism in man. Effects of liver disease and hyperammonemia.
        J Clin Invest. 1979; 63: 449-460
        • Ott P.
        • Larsen F.S.
        Blood-brain barrier permeability to ammonia in liver failure: a critical reappraisal.
        Neurochem Int. 2004; 44: 185-198
        • Haussinger D.
        • FAU - Gorg B.
        • Gorg B.
        Interaction of oxidative stress, astrocyte swelling and cerebral ammonia toxicity.
        Curr Opin Clin Nutr Metab Care. 2010; 13: 87-92
        • Clemmesen J.O.
        • Larsen F.S.
        • Kondrup J.
        • et al.
        Cerebral herniation in patients with acute liver failure is correlated with arterial ammonia concentration.
        Hepatology. 1999; 29: 648-653
        • Ganda O.P.
        • Ruderman N.B.
        Muscle nitrogen metabolism in chronic hepatic insufficiency.
        Metabolism. 1976; 25: 427-435
        • Hod G.
        • Chaouat M.
        • Haskel Y.
        • et al.
        Ammonia uptake by skeletal muscle in the hyperammonaemic rat.
        Eur J Clin Invest. 1982; 12: 445-450
        • Chatauret N.
        • Desjardins P.
        • Zwingmann C.
        • et al.
        Direct molecular and spectroscopic evidence for increased ammonia removal capacity of skeletal muscle in acute liver failure.
        J Hepatol. 2006; 44: 1083-1088
        • Clemmesen J.O.
        • Kondrup J.
        • Ott P.
        1; Splanchnic and leg exchange of amino acids and ammonia in acute liver failure.
        Gastroenterology. 2000; 118: 1131-1139
        • Bernal W.
        • Auzinger G.
        • Sizer E.
        • et al.
        Variation in blood ammonia concentration with site of measurement and evidence of brain and muscle uptake in patients with acute liver failure.
        Liver Int. 2008; 28: 415-417
        • Olde Damink S.W.
        • Jalan R.
        • Redhead D.N.
        • et al.
        Interorgan ammonia and amino acid metabolism in metabolically stable patients with cirrhosis and a TIPSS.
        Hepatology. 2002; 36: 1163-1171
        • Yamato M.
        • Muto y
        • Yoshida T.
        • et al.
        Clearance rate of plasma Branched-chain amino acids correlates significantly with blood ammonia level in patients with liver cirrhosis. 1995; 3: 91-96
        • Wahren J.
        • Felig P.
        Influence of protein ingestion on the amino acid metabolism in diabetes mellitus.
        J Annu Diabetol Hotel Dieu. 1976; : 7-20
        • Hayashi M.
        • Ohnishi H.
        • Kawade Y.
        • et al.
        Augmented utilization of branched-chain amino acids by skeletal muscle in decompensated liver cirrhosis in special relation to ammonia detoxication.
        Gastroenterol Jpn. 1981; 16: 64-70
        • Leweling H.
        • Breitkreutz R.
        • Behne F.
        • et al.
        Hyperammonemia-induced depletion of glutamate and branched-chain amino acids in muscle and plasma.
        J Hepatol. 1996; 25: 756-762
        • Holecek M.
        • Kandar R.
        • Sispera L.
        • Kovarik M.
        Acute hyperammonemia activates branched-chain amino acid catabolism and decreases their extracellular concentrations: different sensitivity of red and white muscle.
        Amino Acids. 2011; 40: 575-584
        • Dam G.
        • Keiding S.
        • Munk O.L.
        • et al.
        Branched-chain amino acids increase arterial ammonia in spite of enhanced intrinsic muscle ammonia metabolism in patients with cirrhosis and healthy subjects.
        Am J Physiol Gastrointest Liver Physiol. 2011; 301: 269-277
        • Tsien C.
        • Davuluri G.
        • Singh D.
        • et al.
        Metabolic and molecular responses to leucine-enriched branched chain amino acid supplementation in the skeletal muscle of alcoholic cirrhosis.
        Hepatology. 2015; 61: 2018-2029
        • Horst D.
        • Grace N.D.
        • Conn H.O.
        • et al.
        Comparison of dietary protein with an oral, branched chain-enriched amino acid supplement in chronic portal-systemic encephalopathy: a randomized controlled trial.
        Hepatology. 1984; 4: 279-287
        • Marchesini G.
        • Bianchi G.
        • Merli M.
        • et al.
        Nutritional supplementation with branched-chain amino acids in advanced cirrhosis: a double-blind, randomized trial.
        Gastroenterology. 2003; 124: 1792-1801
        • Muto Y.
        • Sato S.
        • Watanabe A.
        • Moriwaki H.
        • et al.
        Effects of oral branched-chain amino acid granules on event-free survival in patients with liver cirrhosis.
        Clin Gastroenterol Hepatol. 2005; 3: 705-713
        • Gluud L.L.
        • Dam G.
        • Les I.
        • et al.
        Branched-chain amino acids for people with hepatic encephalopathy.
        Cochrane Database Syst Rev. 2017 18; 5