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12 Mini-Reviews in Medicinal Chemistry, 2016, 16, 12-18
Creatine and the Liver: Metabolism and Possible Interactions
R.P. Barcelos1,2, S.T. Stefanello1, J.L. Mauriz2, J. González-Gallego2 and F.A.A. Soares1*
1Departamento de Bioquímica e Biologia Molecular, Centro de Ciências Naturais e Exatas (CCNE),
Universidade Federal de Santa Maria, Santa Maria (UFSM), Rio Grande do Sul, Brasil; 2Institute of
Biomedicine (IBIOMED) and CIBERehd, University of León, León, Spain
Abstract: The process of creatine synthesis occurs in two steps, catalyzed by L-arginine:glycine
amidinotransferase (AGAT) and guanidinoacetate N-methyltransferase (GAMT), which take place
mainly in kidney and liver, respectively. This molecule plays an important energy/pH buffer function
in tissues, and to guarantee the maintenance of its total body pool, the lost creatine must be replaced
from diet or de novo synthesis. Creatine administration is known to decrease the consumption of S-
adenosyl methionine and also reduce the homocysteine production in liver, diminishing fat
accumulation and resulting in beneficial effects in fatty liver and non-alcoholic liver disease. Different studies have shown
that creatine supplementation could supply brain energy, presenting neuroprotective effects against the encephalopathy
induced by hyperammonemia in acute liver failure. Creatine is also taken by many athletes for its ergogenic properties.
However, little is known about the adverse effects of creatine supplementation, which are barely described in the
literature, with reports of mainly hypothetical effects arising from a small number of scientific publications. Antioxidant
effects have been found in several studies, although one of the theories regarding the potential for toxicity from creatine
supplementation is that it can increase oxidative stress and potentially form carcinogenic compounds.
Keywords: Creatine, damage, exercise, kidney, liver.
1. THE LIVER ROLE IN THE SYNTHESIS OF
CREATINE
Creatine occurs naturally in food, especially in meat and
fish [1], although humans on a typical Western diet obtain
about one-half of their creatine by synthesis and one-half
from the diet [2, 3]. However, vegetarians obtain very little
dietary creatine, and the endogenous synthesis is their major
source [4]. Creatine plays an important energy/pH buffer
function in tissues, which continuously require a replacement
of creatine stores through the dietary or body synthesis [5].
The need to synthesize creatine arises from the fact that
in a young 70-kg male, under physiological conditions, there
is a loss of 1-2 g of creatine per day by the spontaneously
and irreversible conversion to creatinine [1, 6], which is
subsequently lost to the urine. Therefore, to guarantee the
maintenance of the total body pool of creatine, the lost
creatine must be replaced from diet or de novo synthesis [2].
The process of creatine biosynthesis occur in two steps
(Fig. 1) that require three amino acids, arginine, glycine
and methionine, and the enzymes L-arginine:glycine
amidinotransferase (AGAT, EC 2.1.4.1) and guanidinoacetate
N-methyltransferase (GAMT, EC 2.1.1.2) [7]. During the
first step, the amidino group from arginine is transferred to
the amino group of glycine, yielding ornithine and
*Address correspondence to this author at the Departamento de Bioquímica
e Biologia Molecular, Centro de Ciências Naturais e Exatas, Universidade
Federal de Santa Maria, Santa Maria, Rio Grande do Sul, Brazil; Tel: +55
55 32209522; Fax: +55 55 3220 8978; E-mail: felix@ufsm.br
guanidinoacetic acid (GAA), reaction catalyzed by the
enzyme AGAT [2, 5, 8]. In the second step, GAMT induces
the GAA methylation, on the original glycine nitrogen, using
S-adenosylmethionine (SAM) as the methyl donor to form S-
adenosylhomocysteine (SAH) and creatine [2, 5, 8]. It has
been suggested that AGAT is a critical control step in the
creatine biosynthesis, and creatine supplementation could
downregulate its expression [2, 9].
There are high activities of AGAT in the kidneys and of
GAMT in the livers of various species [10]. Such tissue
enrichment has suggested that creatine synthesis is an
interorgan process [11]. On the basis mostly of these latter
findings and of the fact that the rate of creatine biosynthesis
is considerably reduced in nephrectomized animals [12-14],
it was postulated, and is still largely accep ted, that the main
route of creatine biosynthesis in mammals involves
formation of GAA, produced by the kidney, released into the
circulation for transportation through the blood and then
methylated to creatine in the liver [11] (Fig. 2).
However, both AGAT and GAMT occur in tissues other
than kidney and liver. In particular, it is known that brain can
synthesize creatine [8]. Since it is known that the blood-brain
barrier is poorly permeable to creatine, the central nervous
system can be considered an autonomous tissue in creatine
synthesis [15]. In mammals, pancreas contains high levels of
both enzymes, whereas livers contain high amounts of
GAMT. On the other way, kidneys of all the species tested
so far express high amounts of AGAT but relatively lower
levels of GAMT. Although livers of cow, pig, monkey, and
F.A.A. Soares
1875-5607/16 $58.00+.00 © 2016 Bentham Science Publishers
Creatine and Liver Mini-Reviews in Medicinal Chemistry, 2016, Vol. 16, No. 1 13
Fig. (1). Creatine biosynthesis pathway. In the first step, L-arginine:glycine amidinotransferase (AGAT) transferes an amidino group from
arginine to the amino group of glycine, yielding ornithine and guanidinoacetic acid (GAA). In the second step, GAA is methylated by
the enzyme guanidinoacetate methyltransferase (GAMT), using S-adenosylmethionine (SAM) as the methyl donor, to form
S-adenosylhomocyestine (SAH) and creatine.
Fig. (2). Creatine biosynthesis as an interorgan process. Guanidinoacetic acid (GAA) synthetized in kidney is released into circulation and
transported to the liver where it is methylated to produce creatine. Synthetized creatine is distributed via bloodstream to the organs of usage
(mainly muscle and brain).
Arginine + Glycine
GAA
Ornithine
LIVER
KIDNEY BLOOD
AGAT
GAA GAA
SAM
SAH
Creatine Creatine
(to other
organs and
tissues)
14 Mini-Reviews in Medicinal Chemistry, 2016, Vol. 16, No. 1 Barcelos et al.
human also have high amounts of AGAT, livers of common
laboratory mammals such as the rat, mouse, dog, cat, and
rabbit are reported to lack AGAT activity [16]. However, the
renal production of GAA in humans appears to represent
only 20% of the daily loss of creatinine, suggesting that
GAA must be synthesized in other tissues [2].
It has been suggested that the entire creatine synthetic
pathway can be formed in the liver, in a situation where
arginine could be acted upon by either arginase to form urea
or by AGAT to form GAA. Ornithine would be formed and
metabolized via the urea cycle enzyme ornithine
transcarbamoylase [17]. Some studies reported an AGAT
mRNA expression in human liver [18]. In support of this
hypothesis, immunohistochemical evidence for the AGAT
protein in the cytosol of rat hepatocytes was found [19].
However, some past failures to measure AGAT activity
under standard assay conditions in rat liver are also reported
in literature [2].
Finally, the creatine-requiring tissues, via a specific
transporter, can take up creatine released from the liver into
circulation [11]. Creatine transporters have been described in
muscle, brain, kidney, and intestine [20, 21]. These are Na+-
and Cl--dependent active transporters, which concentrate
creatine intracellularly [22]. However, such transporters
seem inappropriate for the liver.
AGAT is the critical control step in creatine synthesis.
Literature strongly suggests that the regulation of creatine
biosynthesis is usually through this enzyme [5]. While the
growth hormone upregulates AGAT expression [23, 24], an
increase in serum levels of creatine results in a decrease in
AGAT enzyme activity, enzyme level, and mRNA
expression in rat kidney [25], whereas creatine ingestion by
humans lowers plasma GAA levels, which is consistent with
the downregulation of AGAT activity [26]. However,
GAMT isolated from pig or rat liver is not inhibited by
creatine but is competitively inhibited by SAH, as well as the
other methyltransferases [27, 28]. Moreover, GAMT should
maintain the low levels of GAA, since it has been
demonstrated that high GAA levels result in neurotoxicity
[29]. Creatine supplementation is also known to modulate
methylation demand and decrease the plasma homocysteine
concentration [11, 30], brought about by the downregulation
of renal AGAT enzyme activity. Deminici et al. have shown
that creatine supplementation also prevents the decrease in
liver SAM concentration seen in high fat-fed rats [1].
2. HEPATIC INJURY AND CREATINE
Liver is a central organ involved in the regulation of
multimetabolic functions as well as detoxification of
xenobiotic, drugs, chemicals and infectious organism [31].
Therefore, several epidemiological studies have been
conducted to elucidate the main causes and consequences of
hepatic injury generation [32].
The development of liver injury was related to various
risk factors such as age, sex, alcohol, nutritional status, viral
infections, genetic factors, as well as the association of toxic
chemicals, fatty liver, nonalcoholic steatohepatitis (NASH),
drug induced liver injury (DILI), cirrhosis and liver cancer,
which could compromise the whole organism functionality
[33]. Among the myriad of metabolic problems resulting
from hepatic injury, the creatine endogenous synthesis is
also compromised [34]. In addition, a profound depletion of
brain creatine is intimately associated with severe
neurological symptoms that include mental retardation,
speech delay, and epileptic seizures [35].
Moreover, creatine exerts many of its functions by
increasing phosphocreatine levels, thereby permitting very
rapid regeneration of ATP after a burst of ATP utilization,
i.e. exercise conditions [35], and developing a spectrum of
therapeutic effects in both animals models and human
diseases [3, 36].
2.1. Possible Toxic Effects of Creatine Supplementation
in the Liver
After conducting studies that corroborated creatine
supplementation with ergogenic effects, this product has
become widely used for athletes and bodybuilders to
increase physical performance [37]. However, there are some
controversial studies about the ideal creatine dose which can
produce benefits without side effects [38, 39].
Research has revealed that creatine supplementation is
related to a reduction in the endogenous creatine formation,
down-regulation of renal AGAT activity [11], and
impairment of homocysteine (Hcy) production [30, 40].
Addition ally, Hcy reduction has been considered as one
mechanism of creatine neurological beneficial properties,
given the fact that high levels of Hcy increase the risk of
hypertension, neural tube defects, Alzheimer’s disease,
dementia, loss of cognitive function, and renal and liver
disease [7]. Thus, several researches showed that creatine
supplementation at “recommended” doses did not produce
toxic effects in the liver [41]. However, other authors have
reported that creatine supplementation leads to hepatocyte
injury as well as significant hepatic inflammatory lesions due
to direct toxic stress or intracellular creatine accumulation
[42]. Additionally, creatine accumulation may contribute to
the formation of cytotoxic substances, i.e. formaldehyde and
methylamine, due to the lower metabolic hepatocyte capacity
to convert creatine into creatinine and the enzymatic
capability of accomplishing methylation processes [43-45].
2.2. Uses of Creatine in Fatty Liver and NASH
NASH is a clinical patholog ical state of patients with
absence of alcohol abuse characterized by a wide spectrum
of liver damage including steatosis, non-alcoholic
steatohepatitis, fibrosis and cirrhosis [46, 47]. In addition, fat
accumulation and NASH progression are intimately
associated with the insufficiency of methionine metabolism
in liver, presenting a diminished availability of SAM as well
as an elevation in Hcy levels and oxidative stress generation
[1]. Moreover, normally the creatine biosynthesis uses SAM
stores and also produces Hcy in liver [6]. In this sense,
creatine supplementation is known to decrease the
consumption of SAM and also reduce the Hcy production in
liver, diminishing fat accu mulation in liver [1]. Recently, it
Creatine and Liver Mini-Reviews in Medicinal Chemistry, 2016, Vol. 16, No. 1 15
has been indicated that creatine, but not structural analogs
such as guanidinoacetate, guanidinopropionic acid or or
methylguanidine, is able to reduce liv er triglycerides (TG)
synthesis and accumulation, thus increasing fatty acid
oxidation and TG secretion. These changes appear to be at
least partially mediated by the peroxisome proliferator of
activated receptor alpha (PPAR-α) pathway signaling and its
downstream targets [48].
2.3. Disorders by Creatine Supplementation and its
Utility in Acute Liver Failure Associated with ELA
Encephalopathy
Creatine, phosphocreatine and creatine kinase are
important in maintaining cellular energy homeostasis that
would prevent or impede the neurodegenerative process [49,
50]. Thus, creatine supplementation has been used in a
number of neurological and neurodegenerative diseases such
as Parkinson’s disease, Huntington’s disease, amyotrophic
lateral sclerosis, and Alzheimer’s disease [51-53]. Moreover,
several studies have associated different drugs, i.e.
acetaminophen, thioacetamide or carbon tetrachloride, with
acute liver failure and encephalopathy development [54, 55].
This encephalopathy is intimately linked with increased
ammonia levels in blood and brain, which can diminish the
energy in brain and decrease neuronal activity as well [56].
Different studies have shown that creatine supplementation
could supply brain energy, presenting neuroprotective effects
against the encephalopathy induced by hyperammonemia
[49, 56]. Curiously, the lack of energy caused by
hyperammonemia, which is involved with neuronal death,
seems to b e able to increase the creatin e uptake in brain
endothelial cells [49, 56, 57].
3. FINAL CONSIDERATIONS
Creatine, in the form of creatine monohydrate, is taken
by many athletes for its ergogenic properties [35] and
performance-enhancing potential [58-62], and some human
studies have demonstrated benefits in certain pathological
conditions [63-66]. On the other hand, little is known about
the adverse effects of creatine supplementation, which are
barely described in the literature [67, 68], with reports of
mainly hypothetical effects arising from a small number of
scientific publications.
In animals, the effects of creatine supplementation on
liver have not been well described and some of them are
conflicting. Whereas some studies did not observe any
alteration in renal and hepatic function [42, 69], others have
reported that creatine supplementation can accelerate renal
and hepatic disease progression [42, 70-72]. The potential
creatine toxicity is based on some anecdotal human case
reports [73, 74], one animal study in hypertensive rats [70],
and the fact that carcinogens can be formed if creatine and
sugars are heated to high temperatures [16, 75].
In humans, the most commonly recommended dose of
creatine supplementation is 5g/day [41, 58, 61], however, it
can range from 3 g/day to 20 g/day [59, 60, 62, 68].
Moreover, most of the studies that have examined the
potential for toxicity of creatine supplementation in humans,
have not found evidence of side effects when consumed at
recommended doses [41, 62, 76-81]. Little information on
liver metabolism changes induced by oral creatine
supplementation is available. There are studies reporting
some data on liver function while consuming creatine
supplements [82-84]. The results of these studies indicate no
or minimal changes on the level of serum urea and bilirubin,
alkaline phosphatase, aspartate aminotransferase, alanine
aminotransferase and ɣ -glutamyltransferase. The general
conclusion is that creatine supplementation induces no real
modification in liver metabolism in humans.
However, some isolated cases have been found in the
literature. For example, a case report identified a healthy
individual that had been using creatine supplementation
during 9 months accompanied by a supplementation of whey
protein on the last four months. The blood analysis of this
individual demonstrated high level of aminotransferases,
alkaline phosphate, bilirubin and creatinine. Symptoms
decreased gradually after the supplementation withdrawn.
The liver analysis showed findings similar to a drug-induced
cholestasis [85].
The possible side effects of creatine supplementation,
regarding liver and renal toxicity, or dysfunction are still
inconclusive [86]. It is speculated that creatine
supplementation can interfere on urea metabolism, which is
one of the metabolic products of creatine metabolism. Urea
is involved in the conversion of toxic compounds such as
methylamine and formaldehyde, and creatine supplementation
can also be expected to influence this conversion [44].
Another curious data found in literature is that creatine
supplementation decreased blood glucose level in mice,
possibly due to the fact that it leads to increased insulin
production [87]. This study supported data by Rooney et al.,
who reported that chronic supplementation of creatine leads
to higher secretion of insulin, which decreases the blood
glucose concentrations [88].
There also some contradictory theories regarding the
oxidant/antioxidant effect of creatine. Antioxidant effects
were found in several studies with creatine supplementation
[89], decreasing markers of oxidative stress in animal
models of neurodegenerative disease [90, 91]. In liver of
exercise rats, it has been reported that creatine
supplementation could improve the activity of some
antioxidant enzymes such as glutathione peroxidase and
catalase, but it was not effective in normalizing the increased
hydrogen peroxide (H2O2) concentrations induced by
exercise in rats [92]. Interestingly, other studies indicated
that creatine can produce antioxidant effects on liver
resistance-exercised rats, scavenging reactive oxygen species
but with no changes in th e activity of antioxidants enzymes
[93]. On the other way, one of the theories regarding the
potential for toxicity from creatine supplementation is that
creatine can increase oxidative stress and potentially form
carcinogenic compounds in vitro [16]. Tarnopolsky et al.
have shown that creatine supplementation in regular doses
results on a lymphocytic hepatitis in a mouse model of
oxidative stress [42]. It was postulated that either direct toxic
stress or osmotic changes after 40 days of creatine
supplementation in rats submitted to swimming training
result on increases in AST and GGT levels. This study,
suggests that creatine can promote substantial changes in
16 Mini-Reviews in Medicinal Chemistry, 2016, Vol. 16, No. 1 Barcelos et al.
liver and kidney metabolism and/or function, possibly
developing hepatic and renal disorders [94]. Moreover, other
studies confirmed that long-term creatine supplementation
(4-8 weeks) can also induce structural alterations, indicating
hepatic and renal damage, in sedentary rats [95].
However, in spite of the above commented cases, the
general conclusion about creatine supplementation toxicity is
the fact that the major risk for health is probably associated
with the purity of commercially available creatine [96].
Nevertheless, there is no conclusive evidence to affirm that
this supplementation may affect kidney and liver function in
healthy individuals [62, 76-81, 97-102].
LIST OF ABBREVIATIONS
AGAT = L-arginine:glycine amidinotransferase
DILI = Drug induced liver injury
GAA = Guanidinoacetic acid
GAMT = Guanidinoacetate N-methyltransferase
Hcy = Homocysteine
NASH = Nonalcoholic steatoshepatitis
PPARα = Peroxisome proliferator of activated receptor
alpha
SAH = S-adenosylhomocysteine
SAM = S-adenosylmethionine
TG = Triglycerides
CONFLICT OF INTEREST
The author(s) confirm that this article content has no
conflict of interest.
ACKNOWLEDGEMENTS
CIBERehd is funded by the Instituto de Salud Carlos III,
Spain. Coordenação de Aperfeiçoamento de Pessoal de Nível
Superior (CAPES) for providing fellowship to R.P.B. and
S.T.S. Conselho Nacional de Desenvolvimento Científico e
Tecnológico (CNPq) for providing fellowship to F.A.A.S.
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Received: January 20, 2015 Revised: March 21, 2015 Accepted: April 23, 2015
