Ergogenic effects of caffeine are mediated by myokines

TYPE Mini Review

PUBLISHED 08 December 2022

DOI 10.3389/fspor.2022.969623

OPEN ACCESS

EDITED BY

Takeshi Hashimoto,

Ritsumeikan University, Japan

REVIEWED BY

Ming Cai,

Shanghai University of Medicine and

Health Sciences, China

*CORRESPONDENCE

Shingo Takada

[email protected];

[email protected]

Shintaro Kinugawa

[email protected]

SPECIALTY SECTION

This article was submitted to

Sport and Exercise Nutrition,

a section of the journal

Frontiers in Sports and Active Living

RECEIVED 15 June 2022

ACCEPTED 31 October 2022

PUBLISHED 08 December 2022

CITATION

Takada S, Fumoto Y and Kinugawa S

(2022) Ergogenic eects of caeine

are mediated by myokines.

Front. Sports Act. Living 4:969623.

doi: 10.3389/fspor.2022.969623

Kinugawa. This is an open-access

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. The use, distribution

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not comply with these terms.

Ergogenic eects of caeine are

mediated by myokines

Shingo Takada

1,2

, Yoshizuki Fumoto

and

Shintaro Kinugawa

3,4

Department of Lifelong Sport, School of Sports Education, Hokusho University, Ebetsu, Japan,

Department of Molecular Biology, Hokkaido University Graduate School of Medicine, Sapporo,

Japan,

Department of Cardiovascular Medicine, Faculty of Medical Sciences, Kyushu University,

Fukuoka, Japan,

Division of Cardiovascular Medicine, Research Institute of Angiocardiology,

Faculty of Medical Sciences, Kyushu University, Fukuoka, Japan

Exercise has long been known to eectively improve and enhance skeletal

muscle function and performance. The favorable eects of exercise on

remote organs other than skeletal muscle are well known, but the underlying

mechanism has remained elusive. Recent studies have indicated that skeletal

muscle not only enables body movement, but also contributes to body

homeostasis and the systemic stress response via the expression and/or

secretion of cytokines (so-called myokines). Not only the induction of muscle

contraction itself, but also changes in intracellular calcium concentration

([Ca

]i) have been suggested to be involved in myokine production and

secretion. Caeine is widely known as a Ca

ionophore, which improves

skeletal muscle function and exercise performance (i.e., an “ergogenic aid”).

Interestingly, some studies reported that caeine or an increase in [Ca

enhances the expression and/or secretion of myokines. In this review,

we discuss the association between caeine as an ergogenic aid and

myokine regulation.

KEYWORDS

myokine, exercise mimetic, mitochondria, ergogenic aid, calcium ion (Ca)

, Ca

induced Ca

release, skeletal muscle, BDNF

Introduction

Exercise training has been demonstrated to have positive eﬀects on skeletal muscle

function and systemic exercise performance (

1, 2). The favorable eﬀects of exercise on

remote organs other than skeletal muscle are well known (

3, 4), but the underlying

mechanism remains unclear. Recent studies have indicated that skeletal muscle not only

enables body movement, but also contributes to body homeostasis and the systemic

stress response via the secretion of soluble proteins (

3, 4). It has been suggested that

these proteins, which are cytokines and other peptides that are produced, expressed, and

secreted by muscle ﬁbers, and exert paracrine, autocrine, or endocrine eﬀects, should

be classiﬁed as “myokines” (

5). Not only the induction of muscle contraction itself, but

also changes in intracellular calcium concentration ([Ca

]i) have been suggested to be

involved in myokine production and secretion (

6–10) (Figure 1). It is also known that

myokine secretion is promoted by the activation of 5

′

-AMP-activated protein kinase

(AMPK) signaling (

11, 12) (Figure 1).

Frontiers in Sports and Active Living 01 frontiersin.org

Takada et al. 10.3389/fspor.2022.969623

FIGURE 1

Ergogenic eects of caeine are mediated by myokines.

Caﬀeine is widely known as a Ca

ionophore and/or

AMPK activator that improves skeletal muscle function

and exercise performance (i.e., an “ergogenic aid”) (

13–16)

(

Figure 1). Some studies reported that caﬀeine, an increase in

[Ca

]i, and AMPK agonists enhance the secretion of myokines,

leading to positive eﬀects on skeletal muscle (e.g., increased

fatty acid or glucose oxidation and mitochondrial biosynthesis)

and exercise performance. (

7–9, 11, 12, 17). In this review, we

discuss the association between caﬀeine as an ergogenic aid and

myokine regulation.

Evidence of the ergogenic eects of

caeine

Short-term or long-term administration of caﬀeine has

ergogenic eﬀects, including enhancing fatty acid or glucose

oxidation, mitochondrial biogenesis, and muscle hypertrophy

signaling in cultured skeletal muscle cells and increasing

skeletal muscle mass in rodents (18–20). Similarly, caﬀeine

was identiﬁed as an ergogenic aid for exercise performance,

including aerobic endurance, mus cle strength, and muscle

endurance in humans by meta-analyses (

14). Thus, evidence

of the ergogenic eﬀects of caﬀeine on exercise performance is

well-established (14, 15, 18–22).

Ergogenic eects of caeine are

mediated by myokine secretion due

to increased [Ca

]i and/or AMPK

activation

One mechanism of the above-mentioned ergogenic eﬀects

of caﬀeine involves calcium-induced calcium release from

the sarcoplasmic reticulum, which increases [Ca

]i (

23–25).

Increased [Ca

]i is involved not only in protein expression

and/or modiﬁcation by enhancing the calcium signaling,

including the AMPK pathway, but also in the extracellular

secretion of proteins (

6, 7, 11, 26, 27).

Myokine production is thought to occur in response

to muscle contraction (

5, 28), but the detailed mechanism

remains unclear. Interestingly, it has been shown that myokine

secretion during acute electrical stimulation depends more on

intracellular calcium ﬂux than on skeletal muscle contr action

itself (9). Moreover, increased [Ca

]i has the potential to

promote myokine expression in skeletal muscle (

7, 8, 29). On

the other hand, caﬀeine is a well-known activator of AMPK

(

30, 31), and AMPK activation is involved in myokine regulation

(

11, 12). Next, we will focus on represent ative myokines

that can be regulated by increasing [Ca

]i and/or AMPK

activation, which have recently been shown to be involved in

Frontiers in Sports and Active Living 02 frontiersin.org

Takada et al. 10.3389/fspor.2022.969623

the function of skeletal muscle and other organs, as well as

exercise performance.

Caeine regulates the secretion of

interleukin-6 as a myokine

Exercise was found to increase the levels of circulating

and muscle interleukin (IL)-6, which is the most well-known

myokine, in humans (

5). Similarly, caﬀeine was found to

increase circulating and skeletal muscle IL-6 protein levels in

mice (

17). A23187, another Ca

ionophore, also increased IL-

6 mRNA expression in the skeletal muscle of mice and C2C12

myotubes (

32). Moreover, it is well known that IL-6 promotes

fatty acid and glucose oxidation in humans and in tissue culture

(

5, 33–35). Although the results are controversial, IL-6 also is

involved in muscle hypertrophy and m yogenesis (

28, 36).

In general, mM levels of caﬀeine have been shown to

promote Ca

release from the sarcoplasmic reticulum (SR) by

acting directly on the r yanodine receptor (RyR) (

6, 37). Ducreux

et al. showed that upon activation of the RyR by the RyR agonist

4-chloro-m-cresol, myotubes released IL-6; this was dependent

on de novo protein synthesis and was blocked by dantrolene

(a substance that speciﬁcally closes calcium channels, thereby

blocking calcium release from the SR) and cyclosporine (a

substance that blocks calcium-dependent calcineurin activation

by nuclear factor of activated T-cells) (

6). Moreover, in an

experiment in which caﬀeine was added to C2C12 skeletal

muscle cultured cells, Fang et al. observed that mM-level caﬀeine

secreted IL-6 in the culture supernatant (

17). However, this

report did not conﬁrm whether caﬀeine administration aﬀects

[Ca

]i. In addition, it has not been conﬁrmed whether the

caﬀeine-induced IL-6 secretion is suppressed by decreasing

[Ca

]i. On the other hand, in an experiment in which IL-6 was

secreted by the contraction of C2C12 cultured skeletal muscle

cells induced by electrical stimulation, it was reported that the

increase in [Ca

]i was more important than the contraction

of the cells themselves (

9). Therefore, an increase in [Ca

is considered to be important for the secretion of IL-6. These

results suggest that caﬀeine can regulate the secretion of IL-6

through an increase in [Ca

]i. In addition, both physiologic al

concentrations and µM levels of caﬀeine also act directly on

skeletal muscle to bring about an ergogenic eﬀect, and it is

thought that the mobilization of intracellular calcium is also

involved in this eﬀect (

38). Conversely, caﬀeine did not aﬀect

(i.e., did not induce) IL-6 vesicle secretion even after 70 min

of intravenous administration to mice at the highest possible

dose (85 mg/kg) (

11). In this study, confocal imaging was

used to visualize the endogenous IL-6 protein in glycolytic f ast

ﬁbers of the tibialis anterior muscle of mice. Moreover, 2 h of

incubation of either the extensor digitorum longus (EDL) or

soleus muscle from mice with the Ca

ionophore ionomycin

in the medium did not signiﬁcantly increase IL-6 levels (39).

However, ionomycin stimulation showed a tendency of an

increase in IL-6 release from skeletal muscle, particularly from

soleus m uscle. On the other hand, caﬀeine induced the rele ase

of IL-6 from human myotubular cells, and its maximum release

occurred 4 to 6 h after the addition of caﬀeine (

6). Similarly,

incubation of isolated rat soleus muscle with ionomycin for

60 min in the incub ation media increased protein levels of IL-6

of (

40). A possible explanation of the discrepancy among these

previous studies regarding the secretion of IL-6 from skeletal

muscle could be owing t o diﬀerences in ﬁber type ( glycolytic vs.

oxidative) or animal species (rats vs. mice) used in each study.

Indeed, it has been known that rat soleus muscle contains more

oxidative ﬁbers than mouse soleus muscle (

41). As IL-6 secretion

from the soleus muscle of rats is gre ater than that from the soleus

muscle of mice, diﬀerences in skeletal muscle ﬁber types in each

animal species may explain the diﬀerences in responsiveness of

IL-6 secretion to an increase in intracellular calcium by caﬀeine

and other Ca

ionophores.

On the other hand, it has been reported that intravenous

acute AICAR stimulation (within 100 min) decreases the

number of IL-6-vesicles in mouse skeletal myocytes, suggesting

that AMPK activation can be involved in myokine secretion

(

11). In addition, incubation of cultured human myotubes

with AICAR within 4 to 24 h incre ases levels of IL-6 mRNA

(

42). These results suggest t hat AMPK signaling, one of the

mechanisms of the ergogenic eﬀects of caﬀeine reported to date,

may regulate myokine expression and release.

Caeine could regulate the secretion of

brain-derived neurotrophic factor as a

myokine

Exercise incre ases circulating and muscle brain-derived

neurotrophic factor (BDNF), which is a myokine, in humans

and mice (

43). BDNF promotes f atty acid oxidation and

mitochondrial biogenesis in cultured skeletal muscle cells and

the skeletal muscle of mice (

43–45). We also found that

blood BDNF levels in healthy subjects and patients with heart

failure (HF) are closely positively correlated with whole-body

exercise capacity (peak oxygen uptake) by univariate analysis

and was identiﬁed as independent determinants of peak oxygen

uptake by multivariate analysis (

46). The administration of

recombinant human BDNF (rhBDNF), as well as exercise

training, improved whole-body exercise performance in normal

mice (

45).

BDNF has been shown to be secreted by the electrical

stimulation of skeletal muscle (

43). However, whether BDNF

secretion from skeletal muscle is re gulated by caﬀeine or

ionomycin remains unknown. The central eﬀects of caﬀeine are

thought to depend on the release of various neurotransmitters

Frontiers in Sports and Active Living 03 frontiersin.org

Takada et al. 10.3389/fspor.2022.969623

by the inhibition of the adenosine receptors A1 and A2a (37).

Caﬀeine also has t he eﬀect of reducing skeletal muscle pain

during exercise, which is thought to be associated with its

inhibition of adenosine receptor A1 (

37). Thus, the central

eﬀects of caﬀeine and its eﬀects on skeletal muscle are considered

to be similar. It is known that the addition of caﬀeine increases

BDNF secretion in cultured hippocampal neurons, which is due

to the increase in [Ca

]i via the ryanodine receptor (47). It has

not yet been clariﬁed whet her caﬀeine induces BDNF secretion

in skeletal muscle cells. However, given the similarities between

the central and peripheral eﬀects of caﬀeine, BDNF could se crete

as a myokine via the caﬀeine-induced increase in [Ca

]i.

Caeine could regulate the secretion of

musclin as a myokine

Musclin is expressed speciﬁcally in skeletal muscle (

29), and

is considered to be a myokine be cause exercise increases skeletal

muscle levels of musclin protein and mRNA, and circulating

levels of musclin (

8). The genetic disruption of musclin causes

a decrease in physical endurance and mitochondrial content,

including the signaling of mitochondrial biogenesis (

8). In

contrast, skeletal muscle-speciﬁc musclin overexpression using

adeno-associated virus 6 also increases circulating musclin (

29).

This suggests that skeletal muscle musclin can be secreted

into the circulation. On the other hand, mRNA expression

levels of mus clin have also been reported to increase in

a [Ca

]i (addition of an ionophore and calcium itself)-

dependent manner in cultured murine and human primary

myoblasts (

8). Alt hough it has not yet been conﬁrmed, caﬀeine

administration could have the potential to induce musclin

secretion by increasing the expression level of musclin.

Activation of AMPK regulates IL-15 as a

myokine

IL-15 is predominantly expressed in skeletal muscle (

12),

and is considered to be a myokine because exercise increases

skeletal muscle levels of both IL-15 protein and mRNA, and

circulating levels of the IL-15 protein (

12, 48). Similarly, AICAR,

an activator of AMPK, was found to increase skeletal muscle

IL-15 mR NA levels in mice (

12). Moreover, it is well known

that IL-15 promotes fatty acid and glucose oxidation, and

mitochondrial oxidative function with supercomplex formation

of the electron transport chain in muscle tissue (

49–53).

IL-15 also inhibit skeletal muscle degradation and muscle

nuclear apoptosis (

54–56), and increase muscle grip strength

(

12). Moreover, circulating IL-15 and skeletal mus cle IL-15Ra

expression correlated with protein synthesis after resistance

exercise (57). Furthermore, mice overexpressing IL-15 in skeletal

muscle on a low-fat/low-energy diet and a high-fat/high-energy

diet had increased lean body mass, including skeletal muscle

(58). As described above, IL-15 is considered to be a myokine

that has a generally positive eﬀect on skelet al muscle, but

whether its expression and secretion can be regulated by caﬀeine

is a subject for future research.

Association of myokines with acute

and chronic eects of caeine

stimulation in vitro

The eﬀects of exercise can be acute or chronic (1, 59).

Similarly, the eﬀects of acute and chronic muscle contraction

are diﬀerent (

10), but whether there is a diﬀerence in myokine

secretion is unclear. In this paper, we hypothesized and

discussed t hat the ergogenic eﬀects of caﬀeine are mediated

by myokine secretion. Long-term (i.e., chronic) as well

as single, short-term (i.e., acute) administration of caﬀeine

produces ergogenic eﬀects via intracellular calcium increases

and AMPK signaling (

Figure 1) (10). This is thought to

mimic the eﬀects of acute and chronic exercise (

1, 59). From

the viewpoint of intracellular calcium increase and AMPK

signaling, myokine secretion is thought to play an important

role in the eﬀects of caﬀeine. However, at present, IL-6 is

the only myokine that has been shown to be directly secreted

from skeletal muscle upon short-term caﬀeine s timulation

(

6). Therefore, comprehensive investigation of the types of

myokines that are secreted by caﬀeine stimulation is an

important research topic. In addition, research on myokine

secretion by chronic caﬀeine stimulation is also an unresolved

issue. It is well known that chronic caﬀeine administration

to skeletal muscle enhances glucose and lipid oxidation, and

mitochondrial biogenesis, which can be explained by the eﬀects

of BDNF (

44, 45).

Indirect eects of myokines on other

organs

Caﬀeine intake markedly increases IL-6 levels in the skeletal

muscle and blood, but not in the liver of mice. Furthermore,

caﬀeine-stimulated skeletal muscle IL-6 production alleviated

nonalcoholic fatty liver disease (NAFLD) in a rodent model

(17). On the other hand, the overexpression of musclin

in skeletal muscle was found to attenuate left ventricular

dysfunction and myocardial ﬁbrosis in mice with HF induced

by long-term pressure overload (

29). These results suggest

that caﬀeine ameliorates myocardial remodeling via inducing

crosstalk between the muscle and liver or heart. On the

other hand, mice overexpressing IL-15 in skeletal muscle

have reduced fat mass and show anti-obesity eﬀects (

52, 58).

Frontiers in Sports and Active Living 04 frontiersin.org

Takada et al. 10.3389/fspor.2022.969623

FIGURE 2

Increased myokines in skeletal muscle may improve heart failure, NAFLD, and obesity.

Therefore, increased myokine levels in the skeletal muscle

and circulation owing to exercise and/or the intake of

caﬀeine as an ergogenic aid may prevent or improve spe ciﬁc

pathologies, such as myocardial remodeling in HF, NAFLD, and

obesity (

Figure 2).

Future directions and perspectives

Why do the health beneﬁts of exercise extend beyond

the skeletal muscles to the whole body? Although the

full mechanism still remains unclear (

1), the discovery of

molecules that are the key to the systemic eﬀects of exercise,

namely myokines, has greatly advanced the ﬁeld of exercise

physiology (

3, 28). Through the discovery of myokines,

which are speciﬁc molecules that have physiological activity

and can be secreted into the blood, it has been shown

that exercise and caﬀeine, an exercise mimetic, have eﬀects

not only on skeletal muscle itself, but also on remote

organs via skeletal muscle (

4, 29, 60). In addition, many

mechanisms underlying the association between intracellular

calcium dynamics and intracellular transport and secretion

resulting from caﬀeine stimulation have been elucidated (

26,

27), and because intracellular calcium also demonstrates

characteristic dynamics during muscle contraction, it can be

speculated that myokine secretion into the blood is regulated by

exercise (

5, 28).

However, it should be reiterated that the intracellular events

reproduced by caﬀeine stimulation reﬂect some mechanisms

of some modes of exercise within the larger framework of

exercise. Indeed, it has been reported that the composition of

proteins in the blood changes with the intensity and type of

exercise performed (61), and hence attention should be paid

to what type of exercise is reproduced by caﬀeine. Caﬀeine

has the potential to increase our understanding of exercise-

induced myokine s ecretion and its systemic eﬀects, which is

an interdisciplinary ﬁeld between exercise physiology and cell

biology. Furthermore, clarifying the mechanism of myokine

secretion induced by exercise may help to resolve the eﬀects

of physical inactivity in older people and enhance the eﬃcacy

of post-injury rehabilitation. This is because some myokines

have already been found to be clinically signiﬁcant (

46, 62, 63).

In addition, not surprisingly, patients facing clinical challenges

often have diﬃculty exercising on their own, so the systemic

eﬀects of myokines induced by caﬀeine stimulation as an

exercise mimetic have great promise (

4, 64).

In this review, we conne cted “(1) the positive eﬀects of

myokines on skeletal muscle” with “(2) the secretion of these

myokines by caﬀeine and their eﬀects on skeletal muscle”

to form the hypotheses shown in Figure 1. The results of

(1) and (2) are from separate studies, and it hence remains

Frontiers in Sports and Active Living 05 frontiersin.org

Takada et al. 10.3389/fspor.2022.969623

unclear whether caﬀeine has acute or chronic eﬀects on

skeletal muscle via myokines, and whether caﬀeine improves

exercise performance.

Conclusion

The ergogenic eﬀects of caﬀeine are mediated thr ough

myokine regulation. Clarifying the underlying mechanisms will

require elucidation of not only the ergogenic eﬀects of caﬀeine,

but also the mechanisms of the eﬀects of exercise and myokines.

Author contributions

All authors listed have made a substantial, direct, and

intellectual contribution to the work and approved it for

publication.

Funding

This work was supported in part by Grants-in- Aid

for Scientiﬁc Research (Grant Nos. JP17H04758 to ST

and 21H03360 to SK) and Grants-in-Aid for Challenging

Exploratory Research (Grant No. 19K22791 to ST) from the

Japan Society for the Promotion of Science, grants from the

Akiyama Life Science Foundation (to ST), the Suhara Memorial

Foundation (to ST), and the Japan Foundation for Applied

Enzymology (to ST).

Acknowledgments

The authors thank H.A. Popiel for her critical reading of

the manuscript.

Conﬂict of interest

The authors declare that the research was conducted in the

absence of any commercial or ﬁnancial relationships that could

be construed as a potential conﬂict of interest.

Publisher’s note

All claims expressed in this article are solely those of the

authors and do not necessarily represent those of their aﬃliated

organizations, or those of t he publisher, the editors and the

reviewers. Any product that may be evaluated in this article, or

claim that may be made by its manufacturer, is not guaranteed

or endorsed by the publisher.

References

1. Egan B, Zierath JR. Exercise metabolism and the molecular

regulation of skeletal muscle adaptation. Cell Metab. (2013) 17:162–

84. doi: 10.1016/j.cmet.2012.12.012

2. Thyfault JP, Bergouignan A. Exercise and met abolic health: beyond skeletal

muscle. Diabetologia. (2020) 63:1464–74. doi: 10.1007/s00125-020-05177-6

3. Bay ML, Pedersen BK. Muscle-organ crosstalk: focus on immunometabolism.

Front Physiol. (2020) 11:567881. doi: 10.3389/fphys.2020.567881

4. Takada S, Sabe H, Kinugawa S. Abnormalities of skeletal muscle, adipocyte

tissue, and lipid metabolism in heart failure: practical therapeutic targets. Front

Cardiovasc Med. (2020) 7:79. doi: 10.3389/fcvm.2020.00079

5. Pedersen BK, Febbraio MA. Muscle as an endocrine organ:

focus on muscle-derived interleukin-6. Physiol Rev. (2008) 88:1379–

406. doi: 10.1152/physrev.90100.2007

6. Ducreux S, Zorzato F, Muller C, Sewry C, Muntoni F, Quinlivan R, et al. Eﬀect

of ryanodine receptor mutations on interleukin-6 release and intracellular calcium

homeostasis in human myotubes from malignant hyperthermia-susceptible

individuals and patients aﬀected by central core disease. J Biol Chem. (2004)

279:43838–46. doi: 10.1074/jbc.M403612200

7. Seldin MM, Peterson JM, Byerly MS, Wei Z, Wong GW. Myonectin

(CTRP15), a novel myokine that links skeletal muscle to systemic lipid

homeostasis. J Biol Chem. (2012) 287:11968–80. doi: 10.1074/jbc.M111.

336834

8. Subbotina E, Sierra A, Zhu Z, Gao Z, Koganti SR, Reyes S, et al. Musclin is an

activity-stimulated myokine that enhances physical endurance. Proc Natl Acad Sci

U S A. (2015) 112:16042–7. doi: 10.1073/pnas.1514250112

9. Furuichi Y, Manabe Y, Takagi M, Aoki M, Fujii NL. Evidence for acute

contraction-induced myokine se cretion by C2C12 myotubes. PLoS ONE. (2018)

13:e0206146. doi: 10.1371/journal.pone.0206146

10. Carter S, Solomon TPJ. In vitro experimental models for examining t he

skeletal muscle cell biology of exercise: the possibilities, challenges and future

developments. Pﬂugers Arch. (2019) 471:413–29. doi: 10.1007/s00424-018-2210-4

11. Lauritzen HP, Brandauer J, Schjerling P, Koh HJ, Treebak JT, Hirshman MF,

et al. Contraction and AICAR stimulate IL-6 vesicle depletion from skeletal muscle

ﬁbers in v i vo. Diabetes. (2013) 62:3081–92. doi: 10.2337/db12-1261

12. Crane JD, Macneil LG, Lally JS, Ford RJ, Bujak AL, Brar IK, et al. Exercise-

stimulated interleukin-15 is controlled by AMPK and regulates skin metabolism

and aging. Aging Cell. (2015) 14:625–34. doi: 10.1111/acel.12341

13. Davis JK, Green JM. Caﬀeine and anaerobic performance:

ergogenic value and mechanisms of action. Sports Med. (2009)

39:813–32. doi: 10.2165/11317770-000000000-00000

14. Grgic J, Grgic I, Pickering C, Schoenfeld BJ, Bishop DJ, Pedisic Z. Wake

up and smell the coﬀee: caﬀeine supplementation and exercise performance-an

umbrella review of 21 published meta-analyses. Br J Sports Med. (2020) 54:681–

8. doi: 10.1136/bjsports-2018-100278

15. Martins GL, Guilherme J, Ferreira LHB, De Souza-Junior TP, Lancha AHJr.

Caﬀeine and exercise performance: possible directions for deﬁnitive ﬁndings. Front

Sports Act Living. (2020) 2:574854. doi: 10.3389/fspor.2020.574854

16. Kreutzer A, Graybeal AJ, Moss K, Braun-Trocchio R, Shah M. Caﬀeine

supplementation strategies among endurance athletes. Front Sports Act Living.

(2022) 4:821750. doi: 10.3389/fspor.2022.821750

17. Fang C, Cai X, Hayashi S, Hao S, Sakiyama H, Wang X, et al.

Caﬀeine-stimulated muscle IL-6 mediates alleviation of n on-alcoholic fatty

liver disease. Biochim Biophys Acta Mol Cell Biol Lipids. (2019) 1864:271–

80. doi: 10.1016/j.bbalip.2018.12.003

18. Mcconell GK, Ng GP, Phillips M, Ruan Z, Macaulay SL, Wadley

GD. Central role of nitric oxide synthase in AICAR and caﬀeine-induced

Frontiers in Sports and Active Living 06 frontiersin.org

Takada et al. 10.3389/fspor.2022.969623

mitochondrial biogenesis in L6 myocytes. J Appl Physiol. (2010) 108:589–

95. doi: 10.1152/japplphysiol.00377.2009

19. Lally JSV, Jain SS, Han XX, Snook LA, Glatz JFC, Luiken J, et al. Caﬀeine-

stimulated fatty acid oxidation is blunted in CD36 null mice. Acta Physiol. (2012)

205:71–81. doi: 10.1111/j.1748-1716.2012.02396.x

20. Moore TM, Mortensen XM, Ashby CK, Harris AM, Kump KJ, Laird DW,

et al. The eﬀect of c aﬀeine on skelet al muscle anabolic signaling and hypertrophy.

Appl Physiol Nutr Metab. (2017) 42:621–9. doi: 10.1139/apnm-2016-0547

21. Talanian JL, Spriet LL. Low and moderate doses of caﬀeine late in exercise

improve performance in trained cyclists. Appl Physiol Nutr Metab. (2016) 41:850–

5. doi: 10.1139/apnm-2016-0053

22. Ramirez-Maldonado M, Jurado-Fasoli L, Del Coso J, Ruiz JR, Amaro-

Gahete FJ. Caﬀeine increases maximal fat oxidation during a graded

exercise test: is there a diurnal variation? J Int Soc Sports Nutr. (2021)

18:5. doi: 10.1186/s12970-020-00400-6

23. Endo M. Calcium release from the sarcoplasmic reticulum. Physiol Rev.

(1977) 57:71–108. doi: 10.1152/physrev.1977.57.1.71

24. Endo M. Calci um-induced calcium release in skeletal muscle. Physiol Re v.

(2009) 89:1153–76. doi: 10.1152/physrev.00040.2008

25. Maurya SK, Herrera JL, Sahoo SK, Reis FCG, Vega RB, Kelly DP, et al.

Sarcolipin signaling promotes mitochondrial biogenesis and oxidative metabolism

in skeletal muscle. Cell Rep. (2018) 24:2919–31. doi: 10.1016/j.celrep.2018.08.036

26. Olson EN, Williams RS. Calcineurin signaling and muscle remodeling. Cell.

(2000) 101:689–92. doi: 10.1016/S0092-8674(00)80880-6

27. Stojilkovic SS. Ca2+-regulated exocytosis and SNARE function. Trends

Endocrinol Metab. (2005) 16:81–3. doi: 10.1016/j.tem.2005.0 2.002

28. Pedersen BK, Febbraio MA. Muscles, exercise and obesity: skeletal muscle as a

secretory organ. Nat Rev Endocrinol. (2012) 8:457–65. doi: 10.1038/nrendo.2012.49

29. Szaroszyk M, Kattih B, Martin-Garrido A, Trogisch FA, Dittrich GM, Grund

A, et al. Skeletal muscle derived Musclin protects t he heart during pathological

overload. Nat Commun. (2022) 13:149. doi: 10.1038/s41467-021-27634-5

30. Egawa T, Hamada T, Ma X, Karaike K, Kameda N, Masuda

S, et al. Caﬀeine activates preferentially alpha1-isoform of 5’AMP-

activated protein kinase in rat skeletal muscle. Acta Physiol. (2011)

201:227–38. doi: 10.1111/j.1748-1716.2010.02169.x

31. Mathew TS, Ferris RK, Downs RM, Kinsey ST, Baumgarner BL. Caﬀeine

promotes autophagy in skeletal muscle cells by increasing the calcium-dependent

activation of AMP-activated protein kinase. Biochem Biophys Res Commun. (2014)

453:411–8. doi: 10.1016/j.bbrc.2014.09.094

32. Allen DL, Uyenishi JJ, Cleary AS, Mehan RS, Linds ay SF, Reed JM.

Calcineurin activates interleukin-6 transcription in mouse skeletal muscle i n vivo

and in C2C12 myotubes in vitro. Am J Physiol Regul Integr Comp Physiol. (2010)

298:R198–210. doi: 10.1152/ajpregu.00325.2009

33. Petersen EW, Carey AL, Sacchetti M, Steinberg GR, Macaulay SL, Febbraio

MA, et al. Acute IL-6 treatment increases fatty acid turnover in elderly humans

in vivo and in tissue culture in vitro. Am J Physiol Endocrinol Metab. (2005)

288:E155–162. doi: 10.1152/ajpendo.00257.2004

34. Carey AL, Steinberg GR, Macaulay SL, Thomas WG, Holmes AG, Ramm G,

et al. Interleukin-6 increases insulin-stimulated glucose disposal in humans and

glucose uptake and fatty acid oxidation in vitro via AMP-activated protein kinase.

Diabetes. (2006) 55:2688–97. doi: 10.2337/db05-1404

35. Glund S, Deshmukh A, Long YC, Moller T, Koistinen HA, Caidahl K,

et al. Interleukin-6 directly increases glucose metabolism in resting human skeletal

muscle. Diabetes. (2007) 56:1630–7. doi: 10.2337/db06-1733

36. Serrano AL, Baeza-Raja B, Perdiguero E, Jardi M, Munoz-Canoves P.

Interleukin-6 is an essential regulator of satellite cell-mediated skeletal muscle

hypertrophy. Cell Metab. (2008) 7:33–44. doi: 10.1016/j.cmet.2007.11.011

37. Mclellan TM, Caldwell JA, Lieberman HR. A review of caﬀeine’s eﬀects on

cognitive, physical and occupational performance. Neurosci Biobehav Rev. (2016)

71:294–312. doi: 10.1016/j.neubiorev.2016.09.001

38. Tallis J, Duncan MJ, James RS. What can isolated skelet al muscle experiments

tell us about the eﬀects of caﬀeine on exercise performance? Br J Pharmacol. (2015)

172:3703–13. doi: 10.1111/bph.13187

39. Glund S, Treebak JT, Long YC, Barres R, Viollet B, Wojtaszewski JF, et al.

Role of adenosine 5’-monophosphate-activated protein kinase in interleukin-6

release from isolated mouse skeletal muscle. Endocrinology. (2009) 150:600–

6. doi: 10.1210/en.2008-1204

40. Holmes AG, Watt MJ, Carey AL, Febbraio MA. Ionomycin,

but not physiologic doses of epinephrine, stimulates skeletal muscle

interleukin-6 mRNA expression and protein release. Metabolism. (2004)

53:1492–5. doi: 10.1016/j.metabol.2004.05.015

41. Gregorevic P, Meznarich NA, Blankinship MJ, Crawford RW, Chamberlain

JS. Fluorophore-labeled myosin-speciﬁc antibodies simplify muscle-ﬁber

phenotyping. Muscle Nerve. (2008) 37:104–6. doi: 10.1002/mus.20877

42. Weigert C, Dufer M, Simon P, Debre E, Runge H, Brodbeck K, et al.

Upregulation of IL-6 mRNA by IL-6 in skeletal muscle cells: role of IL-6 mRNA

stabilization and Ca2+-dependent mechanisms. Am J Physiol Cell Physiol. (2007)

293:C1139–1147. doi: 10.1152/ajpcell.00142.2007

43. Matthews VB, Astrom MB, Chan MH, Bruce CR, Krabbe KS, Prelovsek O,

et al. Brain-derived neurotrophic factor is produced by skeletal muscle cells in

response to contraction and enhances fat oxidation via activation of AMP-activated

protein kinase. Diabetologia. (2009) 52:1409–18. doi: 10.1007/s00125-009-1364-1

44. Matsumoto J, Takada S, Kinugawa S, Furihata T, Nambu H,

Kakutani N, et al. Brain-derived neurotrophic factor improves limited

exercise capacity in mice with heart failure. Circulation. (2018)

138:2064–6. doi: 10.1161/CIRCULATIONAHA.118.035212

45. Matsumoto J, Takada S, Furihata T, Nambu H, Kakutani N, Maekawa

S, et al. Brain-Derived neurotrophic factor improves impaired fatty

acid oxidation via the activation of adenosine monophosphate-activated

protein kinase-a - proliferator-activated receptor-r coactivator-1a sign aling

in skeletal muscle of mice with heart failure. Circ Heart Fail. (2021)

14:e005890. doi: 10.1161/CIRCHEARTFAILURE.119.005890

46. Fukushima A, Kinugawa S, Homma T, Masaki Y, Furihata T, Yokota T,

et al. Decreased serum brain-derived neurotrophic factor levels are correlated

with exercise intolerance in patients with heart failure. Int J Cardiol. (2013)

168:e142–144. doi: 10.1016/j.ijcard.2013.08.073

47. Lao-Peregrin C, Ballesteros JJ, Fernandez M, Zamora-Moratalla A, Saavedra

A, Gomez Lazaro M, et al. Caﬀeine-mediated BD NF release regulates long-

term synaptic plasticity through activation of IRS2 signaling. Addict Biol. (2017)

22:1706–18. doi: 10.1111/adb.12433

48. Yang H, Chang J, Chen W, Zhao L, Qu B, Tang C, et al. Treadmill exercise

promotes interleukin 15 expression in skeletal muscle and interleukin 15 receptor

alpha expression in adipose tissue of high-fat diet rats. Endocr i ne. (2013) 43:579–

85. doi: 10.1007/s12020-012-9809-6

49. Almendro V, Busquets S, Ametller E, Carbo N, Figueras M, Fuster G,

et al. Eﬀects of interleukin-15 on lipid oxidation: disposal of an oral [(14)C]-

triolein load. Biochim Biophys Acta. (2006) 1761:37–42. doi: 10.1016/j.bbalip.2005.

12.006

50. Busquets S, Figueras M, Almendro V, Lopez-Soriano FJ, Argiles

JM. Interleukin-15 increases glucose uptake in skeletal muscle. An

antidiabetogenic eﬀect of the cytokine. Biochim Biophys Acta. (2006)

1760:1613–7. doi: 10.1016/j.bbagen.2006.09.001

51. Krolopp JE, Thornton SM, Abbott MJ. IL-15 Activates the Jak3/STAT3

signaling pathway to mediate glucose uptake in skeletal muscle cells. Front Physiol.

(2016) 7:626. doi: 10.3389/fphys.2016.00626

52. Nadeau L, Aguer C. Interleukin-15 as a myokine: mechanistic insight into

its eﬀect on skeletal muscle metabolism. Appl Physiol Nutr Metab. (2019) 44:229–

38. doi: 10.1139/apnm-2018-0022

53. Nadeau L, Patten DA, Caron A, Garneau L, Pinault-Masson E, Foretz M,

et al. IL-15 improves skeletal muscle oxidative metabolism and glucose uptake

in association with increased respiratory chain supercomplex formation and

AMPK pathway activation. Biochim Biophys Acta Gen Subj. (2019) 1863:395–

407. doi: 10.1016/j.bbagen.2018.10.021

54. Carb o N, Lopez-Soriano J, Costelli P, Busquets S, Alvarez B, Baccino FM,

et al. Interleukin-15 antagonizes muscle protein waste in tumour-bearing rats. Br J

Cancer. (2000) 83:526–31. doi: 10.1054/bjoc.2000.1299

55. Quinn LS, Anderson BG, Drivdahl RH, Alvarez B, Argiles JM.

Overexpression of interleukin-15 induces skeletal muscle hypertrophy i n vitro:

implications for treatment of muscle wasting disorders. Exp Cell Res. (2002)

280:55–63. doi: 10.1006/excr.2002.5624

56. Busquets S, Figueras MT, Meijsing S, Carbo N, Quinn LS, Almendro V, et al.

Interleukin-15 decreases proteolysis in skeletal muscle: a direct eﬀect. Int J Mol

Med. (2005) 16:471–6. doi: 10.3892/ijmm.16.3.471

57. Perez-Lopez A, Mckendry J, Martin-Rincon M, Morales-Alamo D, Perez-

Kohler B, Valades D, et al. Skeletal muscle IL-15/IL-15Ralpha and myoﬁbrillar

protein synthesis after resistance exercise. Scand J M ed Sci Sports. (2018) 28:116–

25. doi: 10.1111/sms.12901

58. Quinn LS, Anderson BG, Strait-Bodey L, Stroud AM, Argiles JM.

Oversecretion of interleukin-15 from skeletal muscle reduces adiposity. Am

J Physiol Endocrinol Metab. (2009) 296:E191–202. doi: 10.1152/ajpendo.90506.

2008

59. Chow LS, Gerszten RE, Taylor JM, Pedersen BK, Van Praag

H, Trappe S, et al. Exerkines in health, resilience and disease.

Frontiers in Sports and Active Living 07 frontiersin.org

Takada et al. 10.3389/fspor.2022.969623

Nat Rev Endocrinol. (2022) 18:273–89. doi: 10.1038/s41574-022-

00641-2

60. Gubert C, Hannan AJ. Exercise mimetics: harnessing the

therapeutic eﬀects of physical activity. Nat Rev Drug Discov. (2021)

20:862–79. doi: 10.1038/s41573-021-00217-1

61. Morville T, Sahl RE, Moritz T, Helge JW, Clemmensen C. Plasma metabolome

proﬁling of resistance exercise and endurance exercise in humans. Cell Rep. (2020)

33:108554. doi: 10.1016/j.celrep.2020.108554

62. Fukushima A, Kinugawa S, Homma T, Masaki Y, Furihata T, Yokota

T, et al. Serum brain-derived neurotropic factor level predicts adverse

clinical outcomes i n patients with heart failure. J Card Fail. (2015) 21:300–

6. doi: 10.1016/j.cardfail.2015.01.003

63. Nakano I, Kinugawa S, Hori H, Fukushima A, Yokota T, Takada S, et al.

Serum brain-derived neurotrophic factor levels are associated with skeletal muscle

function but not wi th muscle mass in patients with heart failure. Int Heart J. (2020)

61:96–102. doi: 10.1536/ihj.19-400

64. Takada S, Sabe H, Kinugawa S. Treatments for skeletal muscle abnormalities

in heart failure: sodium-glucose transporter 2 and ketone bodies. Am J

Physiol Heart Circ Physiol. (2022) 322:H117–28. doi: 10.1152/ajpheart.00100.

2021

Frontiers in Sports and Active Living 08 frontiersin.org