Zinc and protein metabolism in chronic liver diseases

Journal Pre-proof Zinc and protein metabolism in chronic liver diseases

Kazuhiro Katayama PII:

S0271-5317(19)30726-2

DOI:

https://doi.org/10.1016/j.nutres.2019.11.009

Reference:

NTR 8074

To appear in:

Nutrition Research

Received date:

31 July 2019

Revised date:

6 October 2019

Accepted date:

26 November 2019

Please cite this article as: K. Katayama, Zinc and protein metabolism in chronic liver diseases, Nutrition Research(2019), https://doi.org/10.1016/j.nutres.2019.11.009

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2019 Published by Elsevier.

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Zinc and Protein Metabolism in Chronic Liver Diseases

Kazuhiro Katayama, M.D. Department of Hepato-Biliary and Pancreatic Oncology, Osaka International

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Cancer Institute, Osaka, Japan.

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Corresponding author: Kazuhiro Katayama

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Department of Hepato-biliary and Pancreatic Oncology Osaka International Cancer Institute

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Tel: +81-6-6945-1181

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Address: 3-1-69, Otemae, Chuo-ku, Osaka 541-8567, Japan

Fax: +81-6-6945-1834

E-mail: [email protected], [email protected]

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Abbreviations BCAA; branched-chain amino acid AAA; aromatic amino acid FR; Fisher ratio

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BTR; BCAA/tyrosine ratio

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BCKA; branched-chain keto acid

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KG; alpha-ketoglutarate

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Abstract The capacity to metabolize proteins is closely related to the hepatic functional reserve in patients with chronic liver disease, and hypoalbuminemia and hyperammonemia develop along with hepatic disease progression. Zinc

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deficiency, which is frequently observed in patients with chronic liver disease,

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significantly affects protein metabolism. Ornithine transcarbamylase is a zinc

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enzyme involved in the urea cycle. Its activity decreases because of zinc

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deficiency, thereby reducing hepatic capacity to metabolize ammonia. Because the glutamine-synthesizing system in skeletal muscles compensates for the

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decrease in ammonia metabolism, hyperammonemia does not develop in the

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early stages of chronic liver disease. However, branched-chain amino acids (BCAAs) are consumed with the increase in glutamine-synthesizing system reactions, leading to a decreased capacity to synthesize proteins, including albumin, due to amino acid imbalance. Upon further disease progression, skeletal muscle mass decreases because of nutritional deficiency, as well as the further decreased capacity to metabolize ammonia in the liver, whereby the capacity to detoxify ammonia reduces as a whole, resulting in hyperammonemia. BCAA supplementation therapy for nutritional deficiency in liver cirrhosis

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improves survival by correcting amino acid imbalance via recovery of the capacity to synthesize albumin, while zinc supplementation therapy improves the capacity to metabolize ammonia in the liver. Here, the efficacy of a combination of BCAA and zinc preparation for nutritional deficiency in liver

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cirrhosis, as well as its theoretical background, were reviewed.

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Key words; Branched-chain amino acid; urea cycle; liver cirrhosis; albumin;

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ammonia.

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1. Introduction Liver cirrhosis is a late stage of chronic liver disease, and results in various complications due to decreased hepatic function and portal hypertension; it is

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also associated with a high likelihood of developing liver cancer. Since the liver

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is the principal organ responsible for metabolizing nutrients, liver cirrhosis results

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in defective nutrient metabolism, leading to complications or poor prognosis [1-3].

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The clinical significance of defective nutrient metabolism can be confirmed by reports of improvement of prognosis or mitigation of complications in patients

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with liver cirrhosis upon nutritional intervention, such as branched-chain amino

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acid (BCAA) supplementation [4-7]. Among protein, fats, and carbohydrates, the three major nutrient categories, protein metabolism has a significant role in albumin and prothrombin synthesis, as well as in ammonia detoxification. These processes are related to the hepatic functional reserve and development of hepatic encephalopathy and are targeted in nutrition therapy for liver cirrhosis. The significance of zinc, a trace metal, in chronic liver disease has also been recently recognized. Zinc plays important roles in the activation and structural maintenance of as many as 300 proteins and enzymes in the body, contributing

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to various internal processes such as growth, antioxidant effects, immune response, apoptosis, aging, and carcinogenesis [8-13]. In addition, zinc deficiency may be involved in many of the symptoms of liver cirrhosis [14-16]. Here, the efficacy of combination of BCAA and zinc preparation for nutritional

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2. Zinc metabolism in liver cirrhosis

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deficiency in liver cirrhosis and its theoretical background were reviewed.

Approximately 20% to 80% of zinc from food is absorbed in the duodenum and

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upper small intestine. Unabsorbed zinc, as well as zinc secreted into the

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gastrointestinal tract, is excreted in the feces. Approximately 2% of ingested zinc is excreted in the urine. Thus, homeostasis of zinc in the body is mediated mainly by absorption in and excretion from the gastrointestinal tract [15,17]. Transporters, which play a significant role in absorption, excretion, and transport of zinc [18, 19], are categorized into two major families: the ZnT transporters, involved in the transport of zinc from the inside to the outside of the cell or from the inside of the cytoplasm into intracellular vesicles; the Zip transporters, involved in the transport of zinc from the outside to the inside of the cell or from

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intracellular vesicles into the cytoplasm. The expression of these transporters, which regulate the concentration of zinc, is organ-specific. Zip4, the main Zip transporter, as well as Zip5, Zip14, ZnT1, ZnT2, and ZnT4-7, are expressed in the gastrointestinal tract and pancreas and are involved in the absorption and

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secretion of zinc [18, 19]. However, the mechanisms by which these transporters

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contribute to zinc metabolism in patients with liver disease remain to be

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elucidated.

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Many studies have noted zinc deficiency in chronic liver disease, especially in liver cirrhosis [14-17]. Decreased zinc absorption in the gastrointestinal tract,

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increased zinc excretion in the urine, nutritional deficiency, hypoalbuminemia,

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portosystemic shunt, and decreased hepatic extraction have been reported as the reasons for zinc deficiency in liver cirrhosis. Decreased intake of zinc-containing foods due to aversion to taste, small-intestinal mucosal disorder possibly due to portal hypertension, and decreased secretion of picolinic acid from the pancreas are also associated with decreased zinc absorption in the gastrointestinal tract [14-17]. The majority of zinc in the blood binds to albumin, and part of it binds to alpha 2-macroglobulin or amino acids. In hypoalbuminemia due to liver disease, zinc in the blood that is unbound to albumin binds instead to

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amino acids, making it likely to be excreted in the urine [14]. The use of diuretics is also known to increase zinc excretion in the urine by a mechanism in which diuretics inhibit renal tubular reabsorption of zinc [14, 20]. These are the plausible mechanisms of zinc deficiency in disease stages in which liver cirrhosis

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has already developed. However, zinc deficiency also occurs in the early stages

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of liver cirrhosis, as described hereinafter; therefore, there may be additional

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mechanisms of zinc deficiency other than those mentioned above.

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Hormones such as insulin, glucagon, and glucocorticoids, bacterial endotoxins, and proinflammatory cytokines affect the kinetics of zinc [14,15,17]. It is also

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known that zinc transporters are regulated in various ways; for example, the

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expression of Zip14 in the gastrointestinal tract is increased in proinflammatory conditions [18, 19]. Since proinflammatory conditions are found in patients with liver cirrhosis, the kinetics of hormones and proinflammatory cytokines may partly contribute to zinc deficiency via the expression of these transporters. However, the details have not been clarified and remain to be studied.

3. Disorders of nitrogen metabolism and zinc in liver cirrhosis 3.1 Decreased capacity to synthesize proteins and its effects in liver cirrhosis

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A decrease in the capacity to synthesize albumin, which constitutes approximately 60% of total protein in the blood, is a useful predictor of poor prognosis in liver cirrhosis. A major cause of decreased capacity to synthesize albumin in liver cirrhosis is BCAA deficiency [7, 21]. BCAAs

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are essential amino acids and key components in protein synthesis.

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BCAAs also play a role in transmitting signals for protein synthesis into

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cells via mTOR, a second messenger [7]. This means that deficiency in

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BCAAs, essential amino acids, leads to a lack of components for protein synthesis as well as an attenuation of the signals necessary for protein

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synthesis, two major factors needed for albumin synthesis. While a

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deficiency in BCAAs is found in liver cirrhosis, no deficiency in tyrosine or phenylalanine, which are aromatic amino acids (AAAs), is found. Ratios of these amino acids, such as the Fisher ratio (FR) or BCAA/tyrosine ratio (BTR), are thus measured in clinical practice to determine the presence of BCAA deficiency [21]. Since there is a significant correlation between BTR and blood albumin concentration, a decrease in BTR reflects a decrease in the capacity to synthesize albumin thereafter in patients with chronic liver disease [21]. In addition, a decrease in BTR is observed

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even in the chronic stage of hepatitis [22]. This shows that BCAA deficiency occurs as early as in the chronic stage of hepatitis prior to the development of liver cirrhosis, causing a decrease in albumin synthesis in liver cirrhosis thereafter. As discussed below, these findings are

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supported by the fact that hypoalbuminemia in liver cirrhosis can be

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improved by the supplementation of BCAAs.

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3.2 Causes of BCAA deficiency in liver cirrhosis BCAA deficiency found in patients with liver cirrhosis is mainly caused by

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increased ammonia metabolism in the skeletal muscles [21]. In healthy

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people, approximately half of the ammonia is metabolized in the urea cycle in the liver, while the other half is metabolized in the glutamine-synthesizing

system

(the

system

in

which

glutamate

incorporates ammonia to form glutamine) in skeletal muscles [23] (Fig. 1A). In patients with liver cirrhosis, the capacity to detoxify ammonia produced from nitrogen metabolism is reduced because of hepatocellular dysfunction, portosystemic shunt, decreased hepatocyte levels, and other causes [21]. Ammonia that has not been metabolized by the liver is

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consequently metabolized by the glutamine-synthesizing system in skeletal muscles (Fig. 1B). In skeletal muscles, glutamate and branched-chain keto acids (BCKAs) are synthesized from BCAAs and alpha-ketoglutarate (αKG) in the BCAA aminotransferase reaction, and

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glutamate is used in the glutamine-synthesizing system to synthesize

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glutamine through a reaction with ammonia (Fig. 2B). Therefore, the

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glutamine-synthesizing system in skeletal muscles is stressed, and

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consumption of BCAAs is increased, resulting in decreased BCAAs in the serum. BCKAs are converted into BCAAs in each organ; thus, BCAAs

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can be supplied consequently. However, conversion of BCKAs to BCAAs

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is inhibited, either because BCKA dehydrogenase is activated by cytokines and cortisol or because reamination of BCKAs is impaired by liver cirrhosis, contributing to a decrease in BCAA levels [21, 24].

3.3 Causes of decreased urea cycle function in liver cirrhosis Ammonia is detoxified via the urea cycle and glutamine synthesis in the liver, with the urea cycle playing the main role. In patients with liver cirrhosis, the capacity to detoxify ammonia is reduced because of

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reduced urea cycle function, owing to zinc deficiency [25, 26]. Ornithine transcarbamylase, which plays an essential role in the urea cycle, is a zinc enzyme (Fig. 2A). Thus, its enzymatic activity decreases with zinc deficiency, causing a reduction in urea cycle function [26]. As mentioned

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above, zinc deficiency occurs in liver cirrhosis, leading to reduced urea

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cycle function. In fact, improvements in the capacity to detoxify ammonia

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by the recovery of urea cycle function through zinc supplementation have

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been reported in patients with liver cirrhosis and in animal models of liver cirrhosis [26-28]. Another study, however, demonstrated that some

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patients did not fully recover their urea cycle function solely through zinc

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supplementation; carnitine administration was also effective in reducing hyperammonemia in liver cirrhosis [29], indicating that factors other than zinc deficiency are involved in ammonia metabolism. These findings demonstrate

that

zinc

deficiency

is

an

important

cause

of

hypoalbuminemia in liver cirrhosis (Fig. 3).

3.4 Disease progression from chronic hepatitis to liver cirrhosis and metabolism of amino acids and ammonia

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As the disease progresses from chronic hepatitis to liver cirrhosis, changes in the intestinal flora occur [30, 31]. The intestinal flora is believed to play a significant role in ammonia production; however, recently, it was found that ammonia produced through metabolism of

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blood glutamine has a significant effect [21]. Nevertheless, there is no

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doubt that the intestinal flora has an important role in producing blood

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ammonia, given that the administration of antibacterial agents could

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decrease the blood levels of ammonia [32]. Zhang et al. noted in a study of the intestinal flora [31] that Streptococcus salivarius with urease activity,

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which was not found in healthy subjects, is present in patients with liver

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cirrhosis, suggesting that intestinal ammonia production may be increased in patients with liver cirrhosis. The function of detoxifying ammonia in the body works for intestinal ammonia production, i.e., the urea cycle in the liver and the glutamine-synthesizing system in skeletal muscles, in each of which approximately half of the ammonia in the body is metabolized in healthy people, as described above [23]. In patients with liver disease, while the liver function is nearly normal in the chronic stage of hepatitis, approximately 50% of ammonia is considered to be

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metabolized in each system in the same manner as in healthy people. Even when liver function has deteriorated and the capacity to detoxify ammonia in the liver is reduced with disease progression from chronic hepatitis to liver cirrhosis, blood ammonia concentrations do not increase

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in the early stages because of a compensatory increase in ammonia

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detoxification in skeletal muscles (the glutamine-synthesizing system).

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However, since BCAA consumption increases as activity of the

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glutamine-synthesizing system increases, BCAA deficiency (a decrease in FR or BTR) occurs [21]. As the disease progresses, the deficiency in

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BCAAs, i.e., essential amino acids, results in a lack of components for

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protein synthesis and reduced signaling function, leading to decreased capacity to synthesize albumin [7, 21]. With further disease progression, the capacity to detoxify ammonia in the liver decreases further, while skeletal muscle mass also decreases because of nutritional deficiency (sarcopenia). At this stage, capacities in the liver and skeletal muscles are not sufficient to detoxify the total amount of ammonia in the body, and blood ammonia concentrations start to increase (Fig. 4). The early stage of liver cirrhosis, in which decreased capacity to detoxify ammonia in the

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liver is compensated by skeletal muscles, is considered the period of compensated liver cirrhosis, as no symptoms such as hypoalbuminemia or hyperammonemia are observed. Thereafter, when the capacity to detoxify ammonia cannot be compensated by skeletal muscles, and

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hypoalbuminemia or hyperammonemia develops, it is considered the

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period of decompensated liver cirrhosis. This hypothesis is supported by

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the following two articles. Nardelli et al. and Hanai et al. investigated, in

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patients with liver cirrhosis, the relationship between sarcopenia and hepatic encephalopathy (minimal and overt), and found that sarcopenia

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was associated with hepatic encephalopathy, probably because the

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reduced capacity of handling ammonia by muscles [33, 34].

4. Treatment for disorders of nitrogen metabolism in liver cirrhosis 4.1 BCAA supplementation therapy Since BCAA deficiency occurs in liver cirrhosis [21], and BCAAs are believed to have effects in promoting albumin synthesis, improving immune

function,

and

inhibiting

carcinogenesis

[7],

BCAA

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supplementation is expected to improve pathologic conditions in patients with liver cirrhosis. In fact, a randomized controlled trial in which BCAA was administered to patients with liver cirrhosis revealed that it was effective in reducing complications of liver cirrhosis and improving the

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quality of life of patients [4]. Its sub-analyses demonstrated that the high

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incidence of liver cancer in liver cirrhosis patients with obesity (body mass

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index ≥ 25 kg/m2) decreased following BCAA administration [35].

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Kawaguchi et al. conducted a cohort study in 299 patients with liver cirrhosis, demonstrating a significant decrease in both the incidence of

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liver cancer and mortality in patients who received BCAAs [5]. As a

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mechanism of hepatocarcinogenesis inhibition by BCAA, Kawaguchi et al. suggests that BCAA plays a role in improving insulin resistance, immunity, and oxidative stress [7]. Cha et al. reported that BCAA administration in mouse models of hepatocarcinogenesis inhibited hepatic fibrosis and tumor angiogenesis, showing its inhibitory effect on hepatocarcinogenesis [36].

Although

the

details

of

the

mechanism

underlying

hepatocarcinogenesis inhibition by BCAA remain to be elucidated, BCAA administration is a useful treatment in patients with early-stage liver

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cirrhosis who do not exhibit protein intolerance.

4.2 Limitations of BCAA supplementation therapy As described above, BCAA administration is an effective treatment for

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disorders of nitrogen metabolism in liver cirrhosis. However, since BCAAs

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contain nitrogen, BCAA administration in patients in advanced stages of

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liver cirrhosis leads to increased blood ammonia concentrations [21, 24].

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Holecek noted in a review that, in terms of the effects of BCAA administration in liver cirrhosis, blood ammonia concentrations increased

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in some patients but not in others [21]. This difference may be due to

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differences in the stages of liver cirrhosis or BCAA doses in the patients studied. Since BCAAs are involved in ammonia detoxification in the glutamine-synthesizing system in skeletal muscles, BCAA administration reduces blood ammonia concentrations. However, the produced glutamine is then metabolized in the gastrointestinal tract and other parts of the body, producing ammonia. Thus, when BCAAs are administered in patients with decreased capacity to detoxify ammonia in the liver (the impaired function of urea cycle), BCAAs are consumed in glutamine

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synthesis, an ammonia metabolism reaction in skeletal muscles; the produced glutamine is thereby metabolized in the gastrointestinal tract, producing ammonia [21, 24]. Therefore, even if ammonia in skeletal muscles is reduced, ammonia is produced in the gastrointestinal tract

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consequently, meaning that ammonia can be transferred safely between

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organs; however, the total amount in the body cannot be reduced. Rather,

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the more nitrogen is administered, the more the ammonia concentration

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increases. Holecek terms this series of reactions a vicious cycle [21, 24]. To reduce the ammonia in the body, ammonia should be converted into

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urea in the urea cycle in the liver and then removed from the body through

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the kidneys. In addition, if glutamine can be effectively removed, glutamine metabolism and subsequent ammonia production can be reduced, implying that ammonia production due to BCAA administration can be reduced.

4.3 Zinc supplementation therapy Zinc deficiency frequently observed in liver cirrhosis has been regarded as a cause of disorders of ammonia metabolism and hepatic

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encephalopathy. In view of this, since Reding et al. proved the efficacy of zinc supplementation for hepatic encephalopathy in liver cirrhosis [37], many studies have reported on the efficacy of zinc supplementation for hepatic encephalopathy or hyperammonemia in liver cirrhosis. Marchesini

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et al. demonstrated that zinc sulfate administration in patients with liver

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cirrhosis resulted in improved encephalopathy indicators, such as better

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scores on the number connection test to assess neurological functions,

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significantly decreased blood ammonia concentrations, and slightly improved FR [27]. They also measured the rate of metabolism of alanine

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to urea nitrogen and reported that the rate had dropped by approximately

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50% in patients with liver cirrhosis, but improved with zinc administration. A recent double-blinded, randomized, controlled study, which compared zinc preparation and placebo in a 3-month treatment regimen, showed that zinc supplementation significantly reduced hyperammonemia [28]. Based on these findings, it is clear that disorders of nitrogen metabolism, including ammonia, occur in patients with liver cirrhosis due to zinc deficiency, which can be improved through zinc supplementation therapy. Recently, Hosui et al. reported that long-term supplementation of zinc in

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patients with liver cirrhosis not only improved liver function, but also reduced the risk of hepatocarcinogenesis [38]. Although the pathogenetic relationship

between

zinc

deficiency

and

mechanisms

of

hepatocarcinogenesis has not been fully elucidated, there are several

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possibilities. Zinc plays a critical role in numerous biochemical and

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physiological processes. It acts as an essential component of

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DNA-binding of Zn-finger proteins, as well as of several proteins involved

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in DNA repair and also plays important roles in antioxidant defense and DNA repair [14, 15]. Further, zinc has important antioxidant properties and

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helps regulate the immune system. Zinc supplementation might prevent

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cancer induction by decreasing oxidative stress and improving the immune system function [15]. However, further studies are required to determine the precise mechanisms of zinc in hepatocarcinogenesis.

4.4 Treatment for disorders of nitrogen metabolism considering the progression of chronic liver disease and protein metabolism As the disease progresses from chronic hepatitis to liver cirrhosis, disorders of protein metabolism occur, such as BCAA deficiency,

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decreased

albumin

synthesis,

and

increased

blood

ammonia

concentrations (Fig. 4). As a treatment for disorders of nitrogen metabolism in patients with liver cirrhosis, BCAA administration is recommended for hypoalbuminemia, and administration of synthetic

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disaccharides and poorly absorbable antibacterial agents to reduce

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ammonia is recommended for hyperammonemia. Zinc supplementation

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therapy is also effective for hyperammonemia. As discussed above,

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hypoalbuminemia and BCAA deficiency may be caused by zinc deficiency, and it is thus recommended to start zinc supplementation therapy in the

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stages in which decreased FR or decreased capacity to synthesize

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albumin is observed; that is, before hyperammonemia develops. In other words,

using

a

zinc

preparation

in

combination

when

BCAA

administration is started may alleviate the impact of increased nitrogen in treatment and leads to more efficient use of BCAA.

4.5 Effects of combination therapy with BCAA and zinc BCAA supplementation therapy is useful for liver cirrhosis, in which amino acid balance and the capacity to synthesize albumin are improved, while

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complications and hepatocarcinogenesis are inhibited. However, as described above, decreased capacity to detoxify ammonia in the liver, i.e., decreased urea cycle function, significantly contributes to disorders of nitrogen metabolism in patients with liver cirrhosis. Therefore, to further

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enhance the effects of BCAA treatment, combination with a therapeutic

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strategy to restore urea cycle function is considered useful. In Japan, an

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indicator to start BCAA treatment in liver cirrhosis is blood albumin

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concentration ≤ 3.5 g/dL. A study with a large number of liver cirrhosis patients demonstrated that the incidence of zinc deficiency was as high

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as approximately 90% among liver cirrhosis patients with blood albumin

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concentrations ≤ 3.5 g/dL [16]. Thus, it is theoretically reasonable to use zinc in combination with BCAA administration in patients with liver cirrhosis.

Two studies in which a combination of BCAA and zinc preparation was administered to liver cirrhosis patients with hypoalbuminemia (≤ 3.5 g/dL) and zinc deficiency (≤ 70 μg/dL) were performed. In the first study, 40 patients with the above conditions were divided into two groups, one which was treated with BCAA monotherapy and one which was treated

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with combination therapy of BCAA and zinc preparation. The 6-month courses of treatment were compared between the two groups [39]. While blood ammonia concentrations increased as a whole in the BCAA monotherapy group, they decreased in the zinc combination group, with a

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significant difference in the rates of change between the groups. In

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addition, FR significantly improved in the zinc combination group. In the

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second study, 37 patients with type C liver cirrhosis were divided into two

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groups, one which was treated with BCAA monotherapy and one which was treated with zinc combination therapy. Courses of treatment in the

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two groups were observed with an average follow-up time of 3.2 years,

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and clinical characteristics were recorded such as cancer-free survival rates and blood test results [40]. In this study, significant positive cancer-free survival rates were observed in the group in which blood zinc concentrations of 80 μg/dL were maintained. The findings suggest that zinc supplementation therapy was able to not only improve nitrogen metabolism, but also inhibit carcinogenesis. Although both studies suggested the usefulness of combination therapy with BCAA and zinc preparation for liver cirrhosis, the number of patients in both studies was

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small and these studies were performed by our groups; thus, further studies with more patients are warranted.

4.6 Other treatments for hyperammonemia

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The efficacy of other treatments for hyperammonemia has been

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demonstrated, such as synthetic disaccharides and poorly absorbable

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antibacterial agents. In a recent study, a carnitine preparation was found

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to be effective for hyperammonemia in liver cirrhosis [29]. Further studies are warranted for the appropriate selection of these therapies for clinical

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practice, as well as for determining the efficacy of zinc preparation and

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combination therapy.

5. Unknown aspects and future research Although the pathogenetic relationship between zinc deficiency and mechanism of hepatocarcinogenesis is not fully elucidated, there are several possibilities. Zinc plays a critical role in numerous biochemical and physiological processes. Zinc act as an essential component of DNA-binding Zn-finger proteins, as well as of several proteins involved in DNA repair, and plays important roles in

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antioxidant defense and DNA repair. Further, zinc has important antioxidant properties, and plays an important role in the regulation of immune system. It is possible that zinc supplementation might prevent cancer induction by decreasing oxidative stress

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f

and improving immune system function. However, further study is required to

e-

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determine the precise mechanism of zinc in hepatocarcinogenesis.

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6. Conclusion

Decreased capacity to metabolize ammonia due to zinc deficiency significantly

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contributes to disorders of protein metabolism in patients with chronic liver

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disease, suggesting the efficacy of zinc supplementation therapy. Further research is warranted to elucidate the appropriate timing and treatment monitoring method of zinc supplementation therapy in patients with liver cirrhosis. Zinc also plays a significant role in hepatocarcinogenesis [14, 15, 38, 40], glucose metabolism [14, 41], and fat metabolism [42]. The contribution of zinc to pathologic conditions other than impaired nitrogen metabolism in patients with liver cirrhosis and possibilities for treatment also remain to be studied.

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Acknowledgment KK has received honoraria for lectures from Nobelpharma Co., Ltd.

This

research did not receive any specific grant from funding agencies in the public,

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e-

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or not-for-profit sectors.

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References 1. Alberino F, Gatta A, Amodio P, Merkel C, D. Pascoli L, Boffo G, et al. Nutrition

and

survival

in

patients

with

liver

cirrhosis.

Nutrition

oo

f

2001;17:445-50.

pr

2. Christensen E, Schlichting P, Fenerholdt I, Gluud C, Andersen PK, Juhl E, et

e-

al. Prognostic value of Child-Turcotte criteria in medically treated cirrhosis.

Pr

Hepatology 1984;4:430-5.

3. Tajika M, Kato M, Mohri H, Miwa Y, Kato T, Ohnishi H, et al. Prognostic value metabolism

patients

with

liver

cirrhosis.

Nutrition

Jo u

2002;18:229-34.

in

al

energy

rn

of

4. Muto Y, Seto S, Watanabe A, Moriwaki H, Suzuki K, Kato A, et al. Effects of oral branched-chain amino acid granules on event-free survival in patients with liver cirrhosis. Clin Gantroenterol Hepatol 2005;3:705-713. 5. Kawaguchi T, Shiraishi K, Ito T, Suzuki K, Koreeda C, Ohtake T, et al. Branched-chain amino acids prevent hepatocarcinogenesis and prolong survival

of

patients

with

cirrhosis.

Clin

Gastroenterol

Hepatol

2014;12:1012-1018.

27

Journal Pre-proof

6. Swart GR, Zillikans MC, van Vuure JK, van den Berg JW. Effects of a late evening meal on nitrogen balance in patients with cirrhosis of the liver. BMJ 1989;299:1202-1203. 7. Kawaguchi T, Izumi N, Charlton MR, Sata M. Branched-chain amino acids

oo

f

as pharmacological nutrients in chronic liver disease. Hepatology

pr

2011;54:1063-1070.

e-

8. Prasad AS. Zinc: an overview. Nutrition 1995;11:93-95.

Pr

9. Prasad AS. Zinc and immunity. Mol Cell Biochem 1998;188:63-69.

Rev 1993;73:79-118.

al

10. Vallee BI, Fulchuk KH. The biochemical basis of zinc physiology. Physiol

Jo u

rn

11. Leoni G, Rosato A, Perozzi G. Zinc proteome interaction network as a model to identify nutrient-affected pathways in human pathologies. Genes Nutr 2014;9:436. 12. Powell

SR.

The

antioxidant

properties

of

zinc.

J

Nutr

2000;130:S1447-S1454. 13. Kitamura H, Morikawa H, Kamon H, Iguchi M, Hojyo S, Fukada T, et al. Toll-like receptor-mediated regulation of zinc homeostasis influences dendritic cell function. Nature Immnology 2006;7:971-977.

28

Journal Pre-proof

14. Stamoulis I, Kouraklis G, Theocharis S. Zinc and the liver: An active interaction. Dig Dis Sci 2007;52:1595-1612. 15. Grungreiff K, Reinhold D, Wedemeyer H. The role of zinc in liver cirrhosis. Annals of Hepatology 2016;15:7-16.

oo

f

16. Katayama K, Kawaguchi T, Shiraishi K, Ito T, Suzuki K, Koreeda C, et al. The

pr

prevalence and implication of zinc deficiency in patients with chronic liver

e-

disease. J Clin Med Res 2018;10:437-444.

Pr

17. Walravens PA. Zinc metabolism and its implications in clinical medicine. West J Med 1979;130:133-142.

al

18. Cousins RJ. Gastrointestinal factors influencing zinc absorption and

Jo u

rn

homeostasis. Int J Vitam Nutr Res 2010;80:243-248. 19. Wang Z and Zhou B. Dietary zinc absorption: A play of Zips and ZnTs in the Gut. IUBUB Life 2010;62:176-182. 20. Chiba M, Katayama K, Takeda R, Morita R, Iwahashi K, Onishi Y, et al. Diuretics aggravate zinc deficiency in patients with liver cirrhosis by increasing zinc excretion in urine. Hepatol Res 2013;43:365-373. 21. Holecek M. Ammonia and amino acid profiles in liver cirrhosis: Effects of variable leading to hepatic encephalopathy. Nutrition 2015;31:14-20.

29

Journal Pre-proof

22. Suzuki K, Suzuki K, Koizumi K, Ichimura H, Oka S, Takada H, et al. Measurement of serum branched-chain amino acids to tyrosine ratio level is useful in a prediction of a change of serum albumin in chronic liver disease. Hepatol Res 2008;38:267-272.

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f

23. Lockwood AH, MacDonald JM, Reiman RE, Gelbard AS, Laughlin JS, Duffy

pr

TE, et al. The dynamics of ammonia metabolism in man. Effects of liver

e-

disease and hyperammonemia. J Clin Invest 1979;63:449-460.

Pr

24. Holecek M. Branched-chain amino acid supplementation in treatment of liver cirrhosis: Updated views on how to attenuate their harmful effects on

al

cataplerosis and ammonia formation. Nutrition 2017;41:80-85.

Jo u

rn

25. Katayama K. Ammonia metabolism and hepatic encephalopathy. Heptol Res 2004;30S:S71-S78.

26. Riggio O, Merli M, Capocaccia L, Caschera M, Zullo A, Pinto G, et al. Zinc supplementation reduces blood ammonia and increases liver ornithine transcarbamylase

activity

in

experimental

cirrhosis.

Hepatology

1992;16:785-789. 27. Marchesini G, Fabbri A, Bianchi G, Brizi M, Zoli M. Zinc supplementation and amino acid-nitrogen metabolism in patients with advanced cirrhosis.

30

Journal Pre-proof

Hepatology 1996;23:1084-1092. 28. Katayama K, Saito M, Kawaguchi T, Endo R, Sawara K, Nishiguchi S, et al. Effect of zinc on liver cirrhosis with hyperammonemia: A preliminary randomized,

placebo-controlled

double-blind

trial.

Nutrition

oo

f

2014;30:1409-1414.

pr

29. Malaguarnera M, Risino C, Cammalleri L, Malaguarnera L, Astuto M,

e-

Vecchio I, et al. Branched chain amino acids supplemented with

Pr

L-acetylcarnitine versus BCAA treatment in hepatic coma: a randomized and controlled double blind study. Eur J Gastroenterol Hepatol 2009;21:762-770.

al

30. Qin N, Yang F, Li A, Prifti E, Chen Y, Shao L et al. Alterations of the human

Jo u

rn

gut microbiome in liver cirrhosis. Nature 2014;513(7516):56-64. 31. Zhang Z, Zhai H, Geng J, Yu R, Ren H, Fan H, et al. Large-scale survey of gut microbiota associated with MHE Via 16S rRNA-based pyrosequencing. Am J Gastroenterol 2013;108:1601-1611. 32. Bass NM, Mullen KD, Sanyal A, Poordad F, Neff G, Leevy CB, et al. Rifaximin

treatment

in

hepatic

encephalopathy.

N

Engl

J

Med

2010;362:1071-1081. 33. Nardelli S, Lattanzi B, Merli M, Farcomeni A, Gioia S, Ridola L, et al. Muscle

31

Journal Pre-proof

alterations are associated with minimal and overt hepatic encephalopathy in patients with liver cirrhosis. Hepatology 2019 Apr 30. [Epub ahead of print] 34. Hanai T, Shiraki M, Watanabe S, Kochi T, Imai K, Suetsugu A, et al. Sarcopenia predicts minimal hepatic encephalopathy in patient with liver

oo

f

cirrhosis. Hepatol Res 2017;47:1359-1367.

pr

35. Muto Y, Sato S, Watanabe A, Moriwaki H, Suzuki K, Kato A, et al.

e-

Overweight and obesity increase the risk of liver cancer in patients with liver

Pr

cirrhosis and long-term oral supplementation with branched-chain amino acid granules inhibits liver carcinogenesis in heavier patients with liver

al

cirrhosis. Hepatol Res 2006;35:204-214.

Jo u

rn

36. Cha JH, Bae SH, Kim HL, Park NR, Choi ES, Jung ES, et al. Branched-chain amino acids ameliorate fibrosis and suppress tumor growth in a rat model of hepatocellular carcinoma with liver cirrhosis. PLoS ONE 2013;8(11):e77899. 37. Reding P, Duchateau J, Bataille C. Oral zinc supplementation improves hepatic encephalopathy. Results of a randomized controlled trial. Lancet 1984;2:493-495. 38. Hosui A, Kimura E, Abe S, Tanimoto T, Onishi K, Kusumoto Y, et al. Long-term zinc supplementation improves liver function and decreases the

32

Journal Pre-proof

risk of developing hepatocellular carcinoma. Nutrients 2018;10:1955. Doi:10.3390/nu10121955. 39. Hayashi M, Ikezawa K, Ono A, Okabayashi S, Hayashi Y, Shimizu S, et al. Evaluation of the effects of combination therapy with branched-chain amino

oo

f

acid and zinc supplements on nitrogen metabolism in liver cirrhosis. Hepatol

pr

Res 2007;37:615-619.

e-

40. Katayama K, Sakakibara M, Imanaka K, Ohkawa K, Matsunaga T, Naito M,

Pr

et al. Effect of zinc supplementation in patients with type C liver cirrhosis. Open J Gastroenterology 2011;1:22-28.

al

41. Jayawardena R, Ranasinghe P, Galappatthy P, Malkanthi R, Constantine G,

Jo u

rn

Katulanda P. Effects of zinc supplementation on diabetes mellitus: A systematic review and meta-analysis. Diabetol Metab Syndr 2012;4(1):13. 42. Ranasinghe P, Wathurapatha WS, Ishara MH, Jayawardena R, Galappatthy P, Katulanda P, et al. Effects of zinc supplementation on serum lipids: A systematic review and meta-analysis. Nutr Metab (Lond). 2015;12:26.

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Figure captions Fig. 1 Schematic illustrating pathways of ammonia metabolism. Panel A. In normal individuals, ammonia produced in the gastrointestinal tract is detoxicated by the liver and skeletal muscles on a 1:1 ratio. Panel B. In patients with liver

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cirrhosis, because the ability of ammonia detoxication by the liver is impaired,

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the amount of ammonia detoxication by skeletal muscles is increased, as

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compensation.

Fig. 2 Mechanisms of ammonia detoxication. Panel A. Urea cycle. OTC promote

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the reaction of carbamoyl phosphate and ornithine to citruline. Panel B.

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Ammonia detoxication to glutamine by glutamine synthetase. This process is associated with branched-chain amino acid consumption. OTC, ornithine transcarbamylase

Fig. 3. Pathogenesis of decreased ability of albumin synthesis in patients with liver cirrhosis.

Fig. 4. Hypothetical concept of ammonia detoxication. As liver disease

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progresses from chronic hepatitis to decompensated liver cirrhosis, ammonia production (solid lined box with vertical streaks) increases. In chronic hepatitis, the ability of ammonia detoxication by the liver and muscles (dashed-lined boxes with gray color) is still able to cover the amount of ammonia. In compensated

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liver cirrhosis, although the ability of ammonia detoxication by the liver begins to

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decrease, glutamine synthesis increases ammonia detoxication as a form of

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compensation; thus, ammonia detoxication is maintained. However, as a result,

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BCAA consumption in glutamine synthesis increases, resulting in BCAA deficiency and hypoalbuminemia. In decompensated liver cirrhosis, because the

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ability of ammonia detoxication by the skeletal muscles also decreases, the

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capacity of ammonia detoxication by both the liver and muscles is unable to cover the amount of ammonia produced.

BCAA, branched-chain amino acid.

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Figure 1

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