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Beneficial biological effects and the underlying mechanisms of molecular hydrogen - comprehensive review of 321 original articles

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Therapeutic effects of molecular hydrogen for a wide range of disease models and human diseases have been investigated since 2007. A total of 321 original articles have been published from 2007 to June 2015. Most studies have been conducted in Japan, China, and the USA. About three-quarters of the articles show the effects in mice and rats. The number of clinical trials is increasing every year. In most diseases, the effect of hydrogen has been reported with hydrogen water or hydrogen gas, which was followed by confirmation of the effect with hydrogen-rich saline. Hydrogen water is mostly given ad libitum. Hydrogen gas of less than 4 % is given by inhalation. The effects have been reported in essentially all organs covering 31 disease categories that can be subdivided into 166 disease models, human diseases, treatment-associated pathologies, and pathophysiological conditions of plants with a predominance of oxidative stress-mediated diseases and inflammatory diseases. Specific extinctions of hydroxyl radical and peroxynitrite were initially presented, but the radical-scavenging effect of hydrogen cannot be held solely accountable for its drastic effects. We and others have shown that the effects can be mediated by modulating activities and expressions of various molecules such as Lyn, ERK, p38, JNK, ASK1, Akt, GTP-Rac1, iNOS, Nox1, NF-κB p65, IκBα, STAT3, NFATc1, c-Fos, and ghrelin. Master regulator(s) that drive these modifications, however, remain to be elucidated and are currently being extensively investigated.
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R E V I E W Open Access
Beneficial biological effects and the underlying
mechanisms of molecular hydrogen -
comprehensive review of 321 original articles -
Masatoshi Ichihara
1
, Sayaka Sobue
1
, Mikako Ito
2
, Masafumi Ito
3
, Masaaki Hirayama
4
and Kinji Ohno
2*
Abstract
Therapeutic effects of molecular hydrogen for a wide range of disease models and human diseases have been
investigated since 2007. A total of 321 original articles have been published from 2007 to June 2015. Most studies
have been conducted in Japan, China, and the USA. About three-quarters of the articles show the effects in mice
and rats. The number of clinical trials is increasing every year. In most diseases, the effect of hydrogen has been
reported with hydrogen water or hydrogen gas, which was followed by confirmation of the effect with hydrogen-rich
saline. Hydrogen water is mostly given ad libitum. Hydrogen gas of less than 4 % is given by inhalation. The effects
have been reported in essentially all organs covering 31 disease categories that can be subdivided into 166 disease
models, human diseases, treatment-associated pathologies, and pathophysiological conditions of plants with a
predominance of oxidative stress-mediated diseases and inflammatory diseases. Specific extinctions of hydroxyl radical
and peroxynitrite were initially presented, but the radical-scavenging effect of hydrogen cannot be held solely
accountable for its drastic effects. We and others have shown that the effects can be mediated by modulating activities
and expressions of various molecules such as Lyn, ERK, p38, JNK, ASK1, Akt, GTP-Rac1, iNOS, Nox1, NF-κBp65,IκBα,
STAT3, NFATc1, c-Fos, and ghrelin. Master regulator(s) that drive these modifications, however, remain to be elucidated
and are currently being extensively investigated.
Keywords: Molecular hydrogen, Ischemia-reperfusion injury, Inflammatory diseases
Introduction
It has been 8 years since Ohsawa and colleagues re-
ported the astonishing therapeutic effects of molecular
hydrogen on a rat model of cerebral infarction in Nature
Medicine in 2007 [1]. Inhalation of 14 % hydrogen gas
markedly reduced the sizes of cerebral infarction in rats.
They also demonstrated that hydrogen specifically scav-
enges hydroxyl radical and peroxynitrite but not hydro-
gen peroxide or superoxide. Their paper ignited interest
in the effect of molecular hydrogen in various diseases
and has been cited 533 times as of July 2015. Similarly,
the number of original articles demonstrating the effect
of molecular hydrogen adds up to more than 300. This
review summarizes research articles published in these
past 8 years and addresses possible molecular mecha-
nisms underlying the effects of hydrogen.
Molecular hydrogen research before 2007
Even before the publication by Ohsawa and colleagues
in 2007 [1], biological effects of molecular hydrogen had
been investigated in a small scale, as shown below. Dole
and colleagues first reported the hydrogen effect in Science
in 1975 [2]. They placed nude mice carrying squamous
cell carcinoma in a chamber with 2.5 % oxygen and 97.5 %
hydrogen under 8-atmospheric pressure and observed
prominent reduction in the size of the tumors. A similar
effect of hyperbaric hydrogen on leukemia was reported in
1978 [3]. Hydreliox, which contained 49 % hydrogen, 50 %
helium, and 1 % oxygen, was reported to be effective to
prevent decompression sickness and nitrogen narcosis for
divers working below 500 meters under sea level [4]. An
anti-inflammatory effect of hyperbaric hydrogen on a
mouse model of schistosomiasis-associated chronic liver
* Correspondence: ohnok@med.nagoya-u.ac.jp
2
Division of Neurogenetics, Center for Neurological Diseases and Cancer,
Nagoya University Graduate School of Medicine, 65 TsurumaiShowa-ku,
Nagoya 466-8550, Japan
Full list of author information is available at the end of the article
MEDICAL GAS
RESEARCH
© 2015 Ichihara et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Ichihara et al. Medical Gas Research (2015) 5:12
DOI 10.1186/s13618-015-0035-1
inflammation was also reported in 2001 [5]. Hyperbaric
hydrogen may be effective for some diseases, but only a
limited number of studies have been published. The differ-
ence between hyperbaric and normobaric hydrogen has
not been directly compared to date.
Following a small number of studies with hyperbaric
hydrogen, the effect of electrolytically alkaline water has
been reported. Shirahata and colleagues hypothesized
that the hydrogen atom, which they called active hydro-
gen, is generated in electrolysis and proposed that active
hydrogen scavenges reactive oxygen species (ROS) [6].
Although it is unlikely that atomic hydrogen is able to
exist for a substantial time in our bodies, molecular
hydrogen does exist in electrolyzed water and the effects
of electrolyzed water have been reported thereafter. Li
and colleagues reported that electrolyzed water scav-
enged ROS and protected a hamster pancreatic beta cell
line from alloxan-induced cell damage [7]. Similarly, re-
duced hemodialysis solution produced by an electrolysis
device (Nihon Trim Co. Ltd.) ameliorated oxidative
stress in hemodialysis patients [8]. In 2005, researchers
in Tohoku University Graduate School of Medicine and
Nihon Trim started cooperative clinical studies and
established the Association of Electrolyzed Water-
Hemodialysis Study Group in 2008. According to per-
sonal communications with this group, they now believe
that the effects of electrolyzed water are likely due to
dissolved hydrogen molecules.
In 2005, Yanagihara and colleagues at Miz Co. Ltd. re-
ported that hydrogen-rich neutral water that was pro-
duced with their unique electrolysis device reduced
oxidative stress in rats [9]. This was a pioneering work,
because they explicitly proved that molecular hydrogen
but not alkaline in the electrolyzed alkaline water exerts
therapeutic effects.
Molecular hydrogen research in and after year 2007
As stated in the introduction, the Nature Medicine paper
in 2007 [1] spurred interest in hydrogen research.
Figure 1 shows 321 original articles up to June 2015 in
the MEDLINE database, which demonstrate the effects
of molecular hydrogen on disease models, human
diseases, treatment-associated pathologies, and patho-
physiological conditions of plants. Most studies were
conducted in Japan, China, and the USA, with a pre-
dominance of China since 2010 (Fig. 1A). About three-
quarters of the articles show the effects in mice and rats
(Fig. 1B), but the number of human studies is increasing
every year (1 article each in 20082009; 2 in 2010; 3 in
2011; 5 in 2012; 9 in 2013; 6 in 2014; and 6 in 2015). In
addition, the effects of hydrogen have been reported in
plants in 13 articles, which suggest a wide range of ef-
fects over various species not restricted to mammals.
The effects of molecular hydrogen on plants may
warrant application of hydrogen to increase agricultural
production. Modalities of hydrogen administration are
shown in Fig. 1C. Hydrogen-rich saline, which is almost
exclusively used in China, dominates over the others.
Hydrogenized saline is administered either by intraperi-
toneal injection or drip infusion. Hydrogen water is
mostly given ad libitum. Hydrogen gas is usually given
by inhaling 14 % hydrogen gas, which is below the ex-
plosion level (4 %). There is a single report, in which
hydrogen gas was injected intraperitoneally [10].
Among the various routes of hydrogen administration
shown in Fig. 1C, the best method still remains uncer-
tain. This is partly because only a few reports have ad-
dressed the difference of effects among administration
A
B
C
Fig. 1 Profiles of 321 original articles up to June 2015 showing
therapeutic effects of molecular hydrogen. aTemporal profile of
countries where the studies are reported from 2007 to June 2015.
bBiological species used in the studies. cModalities of hydrogen
administration to model animals, humans, and plants
Ichihara et al. Medical Gas Research (2015) 5:12 Page 2 of 21
methods. We previously showed that drinking hydrogen
water, but not continuous hydrogen gas exposure, pre-
vented development of 6-hydorxydopamine-induced
Parkinsons disease in rats [11]. In addition, we recently
showed that continuous exposure to hydrogen gas and
ad libitum per os administration of hydrogen water
modulated signaling pathways and gene expressions in
different manners in mice [12]. We demonstrated that
hydrogen-responsive genes are divided into four groups:
genes that respond favorably to hydrogen gas, those that
respond exclusively to hydrogen water, those that re-
spond to both hydrogen gas and water, and those that
respond only to the simultaneous administration of gas
and water (Fig. 2). As hydrogen gas and water increase
the hydrogen concentrations in the rodent body to a
similar level [12], the difference in the organs exposed to
a high concentration of hydrogen, the rise time of
hydrogen concentration, and/or the area under the curve
of hydrogen concentration may account for the differ-
ence in the modulated genes. On the other hand, a colla-
tion of hydrogen reports indicate that a similar degree of
effects can be observed with different modalities of ad-
ministration. For example, the marked effect of hydro-
gen on a mouse model of LPS-induced acute lung injury
has been reported by four different groups with three
different modalities: hydrogen gas [13, 14], hydrogen
water [15], and hydrogen-rich saline [14, 16]. Similarly,
the dramatic effect of hydrogen on animal models of
acute myocardial infarction has been reported by eight
different groups with two different modalities: hydrogen
gas [1720] and hydrogen-rich saline [2124]. To clarify
the difference of hydrogens effects with different modal-
ities of administration, each research group should
scrutinize the difference of the effects between hydrogen
gas, hydrogen water, and hydrogen-rich saline. This
would uncover the best modality for each disease model,
if any, and also the optimal hydrogen dose.
Table 1 summarizes disease categories for which the
effects of hydrogen have been reported. Ohsawa and col-
leagues reported the hydrogen effect in cerebral infarc-
tion [1] and many subsequent studies also showed its
effect in ischemia-reperfusion injuries including organ
transplantations. Following the initial report by Ohsawa
and colleagues, the specific hydroxyl radical scavenging
effect of hydrogen has been repeatedly proposed in oxi-
dative stress-mediated diseases including inflammatory
diseases and metabolic diseases.
Table 2 shows the details of organs and diseases for
which the effects of hydrogen have been reported.
Table 2 is an update of our previous review article in
2012 [25]. We have now classified the organs and dis-
eases into 31 categories and showed the effects in 166
A
C
B
D
Fig. 2 Four groups of genes that show different responses to hydrogen gas and/or water [12] . aBcl6 responds to hydrogen gas more than
hydrogen water. bG6pc responds only to hydrogen water. cWee1 responds to both hydrogen water and gas. dEgr1 responds only to
simultaneous administration of hydrogen gas and water
Ichihara et al. Medical Gas Research (2015) 5:12 Page 3 of 21
disease models, human diseases, treatment-associated
pathologies, and pathophysiological conditions of plants.
Hydrogen is effective in essentially all organs, as well as
in plants.
Molecular mechanisms of the effects of hydrogen
Collation of the 321 original articles reveals that most
communications address the anti-oxidative stress, anti-
inflammatory, and anti-apoptotic effects. Specific scav-
enging activities of hydroxyl radical and peroxynitrite,
however, cannot fully explain the anti-inflammatory and
anti-apoptotic effects, which should involve a number of
fine-tuned signaling pathways. We have shown that
hydrogen suppresses signaling pathways in allergies [26]
and inflammation [27] without directly scavenging react-
ive oxygen/nitrogen species. Signaling molecules that are
modulated by hydrogen include Lyn [26, 28], Ras [29],
MEK [29, 30], ERK [12, 24, 2937], p38 [12, 16, 24, 27,
30, 32, 33, 3541], JNK [13, 24, 27, 30, 32, 33, 3538, 40,
4247], ASK1 [27, 46], Akt [12, 29, 36, 37, 48, 49], GTP-
Rac1 [36], iNOS [27, 34, 36, 5052], Nox1 [36], NF-κB
p65 or NF-κB [12, 14, 27, 3538, 40, 41, 43, 49, 5375],
IκBα[27, 40, 41, 54, 60, 62, 69, 73, 76], STAT3 [65, 77,
78], NFATc1 [12, 36, 78], c-Fos [36], GSK-3β[48, 79],
ROCK [80]. Activities and expressions of these mole-
cules are modified by hydrogen. Master regulator(s) that
drive these modifications remain to be elucidated.
The anti-oxidative stress effect of hydrogen was first
reported to be conferred by direct elimination of hy-
droxyl radical and peroxynitrite. Subsequent studies in-
dicate that hydrogen activates the Nrf2-Keap1 system.
Hydrogen activates Nrf2 [36, 8187] and its downstream
heme oxygenase-1 (HO-1) [36, 51, 52, 65, 71, 81, 82,
8493]. Kawamura and colleagues reported that hydro-
gen did not mitigate hyperoxic lung injury in Nrf2-
knockout mice [82]. Similarly, Ohsawa and colleagues
reported that hydrogen enhanced mitochondrial func-
tions and induced nuclear translocation of Nrf2 at the
Symposium of Medical Molecular Hydrogen in 2012 and
2013. They proposed that hydrogen induces an adaptive
response against oxidative stress, which is also known as
a hormesis effect. These studies indicate that the effect
of hydrogen is mediated by Nrf2, but the mechanisms of
how Nrf2 is activated by hydrogen remain to be solved.
Another interesting mechanism is that hydrogen mod-
ulates miRNA expressions [64, 94]. Hydrogen regulates
expressions of miR-9, miR-21, and miR-199, and modi-
fies expressions of IKK-β, NF-κB, and PDCD4 in LPS-
activated retinal microglia cells [64]. Similarly, analysis
of miRNA profiles of hippocampal neurons during I/R
injury revealed that hydrogen inhibits I/R-induced ex-
pression of the miR-200 family by reducing ROS produc-
tion, which has led to suppression of cell death [94].
However, modulation of miRNA expression cannot
solely explain all the biological effects mediated by
hydrogen. In addition, mechanisms underlying modu-
lated miRNA expressions remain to be elucidated.
Matsumoto and colleagues reported that oral intake of
hydrogen water increased gastric expression and secre-
tion of ghrelin and that the neuroprotective effect of
hydrogen water was abolished by the ghrelin receptor-
antagonist and by the ghrelin secretion-antagonist [95].
As stated above, we have shown that hydrogen water,
but not hydrogen gas, prevented development of Parkin-
sons disease in a rat model [11]. Prominent effect of oral
hydrogen intake rather than hydrogen gas inhalation
may be partly accounted for by gastric induction of
ghrelin.
Recently, Ohta and colleagues showed at the 5th Sym-
posium of Medical Molecular Hydrogen at Nagoya,
Japan in 2015 that hydrogen influences a free radical
chain reaction of unsaturated fatty acid on cell mem-
brane and modifies its lipid peroxidation process. Fur-
thermore, they demonstrated that air-oxidized
phospholipid that was produced either in the presence
or absence of hydrogen in vitro, gives rise to different
intracellular signaling and gene expression profiles when
added to the culture medium. They also showed that
this aberrant oxidization of phospholipid was observed
with a low concentration of hydrogen (at least 1.3 %),
suggesting that the biological effects of hydrogen could
be explained by the aberrant oxidation of phospholipid
under hydrogen exposure. Among the many molecules
that are altered by hydrogen, most are predicted to be
passengers (downstream regulators) that are modulated
secondarily to a change in a driver (master regulator).
The best way to identify the master regulator is to prove
the effect of hydrogen in an in vitro system. Although,
to our knowledge, the study on lipid peroxidation has
not yet been published, the free radical chain reaction
for lipid peroxidation might be the second master regu-
lator of hydrogen next to the radical scavenging effect.
We are also analyzing other novel molecules as possible
master regulators of hydrogen (in preparation). Taken
together, hydrogen is likely to have multiple master reg-
ulators, which drive a diverse array of downstream
Table 1 Disease categories for which hydrogen exhibited
beneficial effects
Pathophysiology No. of articles %
Oxidative stress 224 69.8
(I/R injury 80 24.9)
(Others 144 44.9)
Inflammation 66 20.6
Metabolism 20 6.2
Others 11 3.4
I/R ischemia/reperfusion
Ichihara et al. Medical Gas Research (2015) 5:12 Page 4 of 21
Table 2 Disease models, human diseases, treatment-associated pathologies, and pathophysiological conditions of plants (321
original articles published in English) for which the effects of hydrogen have been reported from 2007 to June 2015
Diseases and conditions References
Brain
Cerebrovascular diseases (CVD)
Cerebral I/R injury [1,10,56,83,94,99109]
Hypertensive stroke [110]
Brain injury secondary to intracerebral hemorrhage [28]
Subarachnoid hemorrhage [48,61,66,73,111113]
Brain injury other than CVD
Traumatic brain injury [114118]
Deep hypothermic circulatory arrest-induced brain damage [57]
Neurodegenerative diseases
Parkinsons disease [11,9597,119]
Alzheimers disease [43,120]
Others
Restraint-induced dementia [121]
Senile dementia in senescence-accelerated mice [122]
LPS-induced neuroinflammation [81,123]
Oxidative stress-induced neuronal cell damage [124,125]
Spinal Cord and peripheral nerve
Spinal cord I/R injury [126,127]
Spinal cord injury [77,128]
Neuropathic pain [39,92,129,130]
Hyperalgesia [79,131,132]
Eye
Retinal I/R injury [133,134]
Diabetic retinopathy [135,136]
Hyperoxia-induced retinopathy [137]
Light-induced retinopathy [138,139]
Glutamine-induced retinopathy [50]
S-nitroso-N-acetylpenicillamine-induced retinopathy [140]
Optic nerve crush [141]
Selenite-induced cataract [142]
Corneal alkali-burn [55]
Anti-inflammatory effects on LPS-activated retinal microglia cells [64]
Ear
Hearing loss [143148]
Cisplatin-induced ototoxicity [149,150]
Ouabain-induced ototoxicity [151]
Oral Cavity
Periodontitis [32]
Periodontal oxidative damage [152]
Lung
Lung I/R injury [153,154]
Oxygen-induced lung injury [82,155,156]
Ichihara et al. Medical Gas Research (2015) 5:12 Page 5 of 21
Table 2 Disease models, human diseases, treatment-associated pathologies, and pathophysiological conditions of plants (321
original articles published in English) for which the effects of hydrogen have been reported from 2007 to June 2015 (Continued)
Ventilation-induced lung injury [53,157]
LPS-induced acute lung injury [13,14,16,158]
Intestinal I/R-induced lung injury [159]
Burn-induced lung injury [160]
Paraquat-induced lung injury [161,162]
igarette smoking lung injury [163]
Smoke inhalation lung injury [74]
Pulmonary hypertension [78,164]
Heart
Myocardial infarction and I/R injury [1724,84]
Diabetic cardiomyopathy [40]
Sleep apnea-induced left ventricular remodeling [165,166]
Ventricular hypertrophy [167]
Stomach
Stress-induced gastric ulceration [38]
Aspirin-induced gastric ulceration [168,169]
Intestine
Intestinal I/R injury [170,171]
Ulcerative colitis [172,173]
Colon inflammation [174]
Sepsis-induced intestinal injury [87]
Necrotizing enterocolitis [175]
Liver
Liver I/R injury [71,98,176178]
Chronic hepatitis B [179]
Nonalcoholic steatohepatitis [180]
Liver injury induced by massive hepatectomy [67,93,181]
Liver injury induced by obstructive jaundice [31]
Liver injury induced by endotoxin [35]
Liver injury induced by acetaminophen [47]
Liver injury induced by carbon tetrachloride [42]
Liver injury induced by concanavalin A [182]
Liver cirrhosis [183]
Liver fibrosis [184]
Pancreas
Acute pancreatitis [76,185187]
Peritoneum
Acute peritonitis [68]
Kidney
Renal I/R injury [188190]
Acute renal injury [37,72,191194]
Hypertensive renal injury [69]
Cisplatin-induced nephropathy [195197]
Gentamicin-induced nephrotoxicity [198]
Ichihara et al. Medical Gas Research (2015) 5:12 Page 6 of 21
Table 2 Disease models, human diseases, treatment-associated pathologies, and pathophysiological conditions of plants (321
original articles published in English) for which the effects of hydrogen have been reported from 2007 to June 2015 (Continued)
Inhibition of AGEs production [199]
Renal calcium deposition [200]
Bladder
Interstitial cystitis [201]
Reproductive organ
Testicular I/R injury [202,203]
Erectile dysfunction [204]
Nicotine-induced testicular oxidative stress [205]
Cigarette smoke-induced testicular damage [206]
Skin
I/R injury [46,207]
UV-induced skin injury [45,208211]
Acute erythematous skin disease [212]
Atopic dermatitis [213,214]
Psoriasis [215]
Pressure ulcer [216]
Burn [49,70]
Arsenic toxicity [217]
Bone and Joint
Rheumatoid arthritis [218,219]
Osteoporosis [36,62]
Bone loss induced by microgravity [34]
TNFα-induced osteoblast injury [220]
NO-induced cartilage toxicity [221]
Skeletal Muscle and soft tissue
I/R injury in skeletal muscle [222]
Inflammatory and mitochondrial myopathies [223]
Muscle fatigue [224]
Sports-related soft tissue injury [225]
Blood vessel
Atherosclerosis [58,59,85,226,227]
AGEs-induced blood vessel damage [228]
Neointimal hyperplasia [29]
Hyperplasia in arterialized vein graft [229]
Vascular dysfunction [60]
Vascular endothelial function [230]
Blood and Bone Marrow
Aplastic anemia [231]
Maintenance of multipotential stroma/mesenchymal stem cells [232]
Neutrophil function [233]
Inhibition of collagen-induced platelet aggregation [234]
Improvement of blood fluidity [235]
Metabolism
Diabetes mellitus [236241]
Ichihara et al. Medical Gas Research (2015) 5:12 Page 7 of 21
Table 2 Disease models, human diseases, treatment-associated pathologies, and pathophysiological conditions of plants (321
original articles published in English) for which the effects of hydrogen have been reported from 2007 to June 2015 (Continued)
Hyperlipidemia [44,242244]
Metabolic syndrome [245247]
Metabolic process-related gene expression [248]
Oxidized low density lipoprotein-induced cell toxicity [54]
Serum alkalinization [249]
Exercise-induced metabolic acidosis [250]
Inflammation/Allergy
Sepsis [41,86,251255]
LPS/IFNγ-induced NO production [27]
LPS-induced inflammatory response [90]
LPS-induced vascular permeability [80,256]
Zymosan-induced inflammation [257]
Carrageenan-induced paw edema [258]
Inflammatory response of cardiopulmonary bypass [259]
Type I allergy [26]
Asthma [63]
Perinatal Disorders
Neonatal cerebral hypoxia [260263]
LPS-induced fetal lung injury [15]
Preeclampsia [264,265]
Cancer
Growth of tongue carcinoma cells [266]
Fe-NTA-induced nephrotoxicity and tumor progression [65]
Radiation-induced thymic lymphoma [267]
Tumor angiogenesis [268]
Enhancement of 5-FU antitumor efficacy [269]
Radiation
Cardiac damage [270]
Lung damage [271]
Testicular damage [272]
Skin damage [273,274]
Germ, hematopoietic and other cell damage [275280]
Radiation-induced adverse effects [281]
Radiation-induced immune dysfunction [282]
Intoxication
Carbon monoxide [283286]
Sevoflurane [287,288]
Doxorubicin-induced heart failure [289]
Melamine-induced urinary stone [290]
Chlorpyrifos-induced neurotoxicity [291]
Transplantation
Heart [52,292294]
Lung [33,88,295299]
Kidney [30,51]
Ichihara et al. Medical Gas Research (2015) 5:12 Page 8 of 21
regulators and achieve beneficial biological effects
against oxidative stress, inflammation, apoptosis, and
dysmetabolism to name a few (Fig. 3).
These studies all point to the notion that hydrogen
modulates intracellular signal transduction systems and
regulates the downstream gene expressions to mitigate
disease processes. In general, biologically active sub-
stances that modulate signaling molecules have both
beneficial and noxious effects on our bodies. Hydrogen
may also have undisclosed toxic effects, although none
have been reported to date to the best of our knowledge.
Understanding the exact molecular mechanisms of the
effects of hydrogen will elucidate its master regulator(s)
and clarify the pros and cons of hydrogen therapy, which
will also potentially lead to the development of another
therapeutic modality to modulate the master regula-
tor(s). We summarized in Table 3 original articles that
addressed biological effects and in vivo kinetics of
hydrogen, which were not directly relevant to disease
models or human diseases. It is essential to elucidate
detailed pharmacokinetics of hydrogen in vivo from the
viewpoint of clinical application of hydrogen, although
we have accumulated vast knowledge about the effects
and not the kinetics of hydrogen in disease models and
human diseases. Through these analyses, promising out-
comes are expected for more effective administration
regimen of hydrogen therapy.
Clinical studies of molecular hydrogen
As stated in the introduction, the number of clinical tri-
als has been increasing since 2011. About half of human
studies have been conducted in Japan. Dependable stud-
ies recruiting more than ten patients or employing
double-blind studies are summarized in Table 4.
Features shared in these clinical studies are that hydro-
gen exhibits statistically significant effects in patients but
the effects are usually not as conspicuous as those ob-
served in rodent models. These can be accounted for by
i) the difference in species, ii) technical difficulty in pre-
paring a high concentration of hydrogen water every day
Table 2 Disease models, human diseases, treatment-associated pathologies, and pathophysiological conditions of plants (321
original articles published in English) for which the effects of hydrogen have been reported from 2007 to June 2015 (Continued)
Intestine [89,300,301]
Pancreas [302]
Osteochondral grafts [303]
Acute GVHD [304,305]
Resuscitation
Cardiac arrest [306,307]
Hemorrhagic shock [75,308,309]
Dialysis
Hemodialysis [310313]
Peritoneal dialysis [314,315]
Others
Lifespan extension [316]
Sperm motility [317]
Decompression sickness [318]
Genotoxicity and mutagenicity [319]
Plant
Root organogenesis [91,320]
Salt tolerance [321,322]
Postharvest ripening [323]
Stomatal closure [324]
Radish sprout tolerance to UVA [325]
High light stress [326]
Phytohormone signaling and stress responses [327]
Tolerance to paraquat-induced oxidative stress [328]
Cadmium toxicity [329,330]
Mercury toxicity [331]
Ichihara et al. Medical Gas Research (2015) 5:12 Page 9 of 21
for the patients, and iii) the difference between acute
and chronic diseases. Further large-scale and long-term
clinical studies are expected to prove the effects of
hydrogen in humans.
Table 5 shows clinical studies currently registered in
Japan. Researchers in Juntendo University have started a
large-scale clinical trial of Parkinsons disease after they
have shown the effects of molecular hydrogen in a small
number of patients in a short duration [96]. Being
prompted by the prominent effects of hydrogen for
mouse models with ischemia reperfusion injuries, clin-
ical trials for acute post cardiac arrest syndrome and
myocardial infarction have started at Keio University.
Similarly, a clinical trial for cerebral infarction has
started at the National Defense Medical College.
Conclusions
The number of original articles showing the effects of
hydrogen are increasing yearly after 2007, and an
extensive review of these articles are getting more and
more difficult. Some of these articles, however, are a
repetition of previous studies with insignificant novel
findings. We suppose that almost all disease models and
almost all modalities by which hydrogen is administered
have been already examined. Large-scale controlled hu-
man studies and elucidation of molecular mechanisms
underlying the effects of hydrogen are the next steps
that must be pursued.
A doseresponse effect of hydrogen is observed in
drinking hydrogen-rich water [94, 97]. A similar dose
response effect is also observed in inhaled hydrogen gas
[1, 17, 98]. However, when hydrogen concentrations in
drinking water and in inhaled gas are compared, there is
no doseresponse effect. Hydrogen-rich water generally
shows a more prominent effect than hydrogen gas, al-
though the amount of hydrogen taken up by hydrogen
water is ~100 times less than that given by hydrogen gas
[11]. Gastric secretion of ghrelin may partly account for
Table 3 Original articles showing physiological effects and in vivo kinetics of hydrogen
Biological effects and in vivo kinetics of hydrogen References
Superoxide formation in brain slices in mice [332]
Gene expression profiles and signal transduction pathways evaluated by DNA microarray and RNA-seq in rodents [33]
a
,[12], [118]
a
,[248]
a
Comparison of intermittent and continuous administration of hydrogen gas in rats [11]
a
Safety of hydrogen inhalation in patients with cerebral ischemia [333]
A convenient method to estimate the concentration of hydrogen in water [334]
Hydrogen consumption in human body after hydrogen administration [335,336]
Ghrelin induction and secretion by hydrogen-dissolved water in mice [95]
a
Additive effects of hydrogen and NO [20,158]
a
In vivo kinetics of hydrogen after hydrogen administration in rodents [12,337]
Lack of reactivity of hydrogen with peroxynitrite [338]
Antioxidant activity of nano-bubble hydrogen-dissolved water [339]
Additive effects of hydrogen gas and hydrogen-rich water [12]
a
These articles are also listed in Table 2
Fig. 3 Schematic summary of molecular mechanisms of hydrogen
Ichihara et al. Medical Gas Research (2015) 5:12 Page 10 of 21
Table 4 Clinical trials published as of June, 2015
Authors/Year Disease Sample
size
Open-label (OL),
double-blind (DB), or
single-blind (SB)
Hydrogen
administration
Summary of the outcome
Kajiyama et al.
[236]/2008
Diabetes mellitus
type II
30 DB Water Improvement of fractions of low-density lipoprotein
(LDL)-cholesterol and a glucose tolerance test.
Nakao et al.
[245]/2010
Metabolic
syndrome
20 OL Water Improvement of urinary markers for oxidative stress such
as SOD and TBARS, and increase of high-density lipopro-
tein (HDL)-cholesterol.
Nakayama et al.
[311]/2010
Chronic renal failure 29 OL Dialysis Amelioration of hypertension and improvement of markers
for oxidative stress and inflammation.
Ito et al.
[223]/2011
Inflammatory and
mitochondrial
myopathies
31 OL/DB Water OL: Improvement of the serum lactate/pyruvate ratio in
mitochondrial myopathies and the serum matrix
metalloproteinse-3 level in polymyositis/dermatomyositis.
DB: Improvement of the serum lactate.
Kang et al.
[281]/2011
Radiation-induced
adverse effects for
liver tumors
49 OL Water Improvement of quality of life (QOL) scores during
radiotherapy.
Reduction of blood reactive oxygen metabolites and
maintenance of blood oxidation potential.
Ishibashi et al.
[218]/2012
Rheumatoid arthritis 20 OL Water Improvement of disease activity score for rheumatoid
arthritis (DAS28).
Decrease of urinary 8-OHdG.
Aoki et al.
[224]/2012
Muscle fatigue 10 DB Water Improvement of muscle fatigue in young athletes
Li et al.
[216]/2013
Pressure skin ulcer 22 OL Water Wound size reduction and early recovery from skin
pressure ulcer.
Matsumoto et al.
[201]/2013
Interstitial cystitis 30 DB Water No significant effect on symptoms.
Reduction of the bladder pain score in 11 % of patients.
Nagatani et al.
[106]/2013
Cerebral ischemia 38 OL Intravenous
infusion
Confirmation of safety of intravenous H
2
infusion.
Decrease of MDA-LDL, a serum marker for oxidative
stress, in a subset of patients.
Shin et al.
[45]/2013
UV-induced skin
injury
28 OL Gas Prevention and modulation of UV-induced skin
inflammation, intrinsic skin aging, and photo aging
process through reduction of MMP-1, IL-6, and IL-1b
mRNA expression.
Song et al.
[243]/2013
Hyperlipidemia 20 OL Water Decrease of total serum cholesterol, LDL-cholesterol,
apolipoprotein (apo) B100, and apoE
Xia et al.
[179]/2013
Chronic hepatitis B 60 DB Water Attenuation of oxidative stress
Yoritaka et al.
[96]/2013
Parkinson disease 17 DB Water Improvement of Total Unified Parkinsons Disease Rating
Scale (UPDRS) and exacerbation after termination of H
2
water.
Ishibashi et al.
[219]/2014
Rheumatoid arthritis 24 DB Intravenous
saline infusion
Improvement of DAS28.
Decrease of serum IL-6, MMP3, CRP, and urinary 8-OHdG.
Ostojic et al.
[225]/2014
Sports-related soft
tissue injury
36 SB H2-rich tablets
and topical H
2
packs
Decrease of plasma viscosity.
Faster recovery from soft tissue injury.
Ostojic et al.
[250]/2014
Exercise-induced
metabolic acidosis
52 DB Water Increased blood alkalinity in physically active men.
Sakai et al.
[230]/2014
Vascular endothelial
function.
34 DB Water Increased flow-mediated dilation of branchial artery,
suggesting that H
2
can serve as a modulator of
vasomotor function of vasculature.
Song et al.
[244]/2015
Hyperlipidemia 68 DB Water Down-regulation of plasma levels of total cholesterol, and
LDL-cholesterol, followed by increased plasma pre-β-HDL,
apoM, and decreased plasma oxidized-LDL, apoB100.
Ichihara et al. Medical Gas Research (2015) 5:12 Page 11 of 21
this difference [95]. Another factor that accounts for the
effects of hydrogen is the temporal profile of hydrogen
administration. Intermittent inhalation, but not continu-
ous inhalation, of hydrogen is protective against a rat
model of Parkinsons disease, which is against a dose-
responsiveness of hydrogen [11]. The prominent effects
of molecular hydrogen in a variety of disease models,
human diseases, treatment-associated pathologies, and
pathophysiological conditions of plants have been dis-
closed in these 8 years, but unsolved conundrums still
challenge us.
Competing interests
We have no competing interest to disclose.
Authorscontributions
MI
1
collated and scrutinized all hydrogen papers. SS, MI
2
,MI
3
, and MH made
critical comments on hydrogen papers. MI
1
and KO wrote the paper. All
authors read and approved the final manuscript.
Acknowledgements
Works done in our laboratories were supported by Grants-in-Aid from the
Ministry of Education, Culture, Sports, Science and Technology of Japan
(MEXT), the Ministry of Health, Labor and Welfare (MHLW) of Japan, the
Japan Agency for Medical Research and Development (AMED), and Chubu
University Grants A and B.
Author details
1
Department of Biomedical Sciences, College of Life and Health Sciences,
Chubu University, 1200 Matsumoto-cho, Kasugai 487-8501, Japan.
2
Division
of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya
University Graduate School of Medicine, 65 TsurumaiShowa-ku, Nagoya
466-8550, Japan.
3
Research Team for Mechanism of Aging, Tokyo
Metropolitan Institute of Gerontology, 35-2 Sakae-cho, Itabashi, Tokyo
173-0015, Japan.
4
Department of Pathophysiological Laboratory Sciences,
Nagoya University Graduate School of Medicine, 1-1-20 Daiko-Minami,
Higashi-ku, Nagoya 461-8673, Japan.
Received: 20 July 2015 Accepted: 9 October 2015
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Table 5 Clinical trials registered in Japan as of June, 2015
Date Disease Affiliation Status
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9/30/2011 Normal adults Faculty of Health Sciences, Kyorin Univ. Finished
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3/14/2012 Parkinsons disease Neurology, Juntendo Univ. Finished [96]
10/16/2012 Multiple system atrophy, Progressive
supranuclear palsy
Neurology, Juntendo Univ. Trial in progress
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5/1/2013 Chronic obstructive pulmonary disease Respiratory Medicine, Juntendo Univ. Trial in progress
5/20/2013 Hepatitis and liver cirrhosis Gastroenterology and Hepatology, Okayama Univ. In preparation
11/22/2013 Post cardiac arrest syndrome Emergency and Critical care medicine, Keio Univ. Calling for participants
2/22/2014 Eye disease Ophthalmology, Nippon Medical school Finished
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7/29/2014 Subarachnoid hemorrhage Neurosurgery, Self Defense Medical College Calling for participants [113]
8/1/2014 Lung transplantation General thoracic surgery, Osaka Univ. Calling for participants
10/27/2014 Retinal artery occlusion Ophthalmology, Nippon Medical school Calling for participants
7/3/2015 Type 2 diabetes mellitus Tokyo Metropolitan Institute of Gerontology Calling for participants
The department names are shown if they are available in the UMIN clinical trial database
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Ichihara et al. Medical Gas Research (2015) 5:12 Page 21 of 21
... Hydrogen molecules have been proven to be a safe and effective anti-inflammatory agent which can ameliorate ischemia-reperfusion injury and activate skin cells to promote wound healing [13][14][15][16][17][18][19][20][21] . Recently, a hydrogen-producing hydrogel dressing made of living Bacillus--Chlorella was developed to light-responsively produce hydrogen for accelerated diabetic wound healing, but the lifetimes of Bacillus and Chlorella in the dressing were limited (60 h) 22 . ...
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High-glucose microenvironment in the diabetic foot ulcer (DFU) causes excessive glycation and induces chronic inflammation, leading to the difficulty of DFU healing. Hydrogen-rich water bath can promote the healing of DFU in clinic by virtue of the anti-inflammatory effect of hydrogen molecules, but the long-term daily soaking counts against the formation of a scab and cannot change the high-glucose microenvironment, limiting the outcome of DFU therapy. In this work, photocatalytic therapy of diabetic wound is proposed for sustainable hydrogen generation and local glucose depletion by utilizing glucose in the high-glucose microenvironment as a sacrificial agent. Hydrogen-incorporated titanium oxide nanorods are developed to realize efficient visible light (VIS)-responsive photocatalysis for glucose depletion and hydrogen generation, achieving a high efficacy of diabetic wound healing. Mechanistically, local glucose depletion and hydrogen generation jointly attenuate the apoptosis of skin cells and promote their proliferation and migration by inhibiting the synthesis of advanced glycation end products and the expression of their receptors, respectively. The proposed VIS-photocatalytic strategy provides a solution for facile, safe and efficient treatment of DFU.
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Catalytic therapy can effectively kill tumor cells and inhibit tumor growth by producing highly toxic reactive oxygen species (ROS). However, the long-term catalysis of nanozymes easily lead to ROS breaking through the boundary in tumor tissues, resulting in spillover and injuring normal cells. Therefore, how to control the threshold of ROS production from nanozymes in tumor tissues is an unsolved problem. In this work, to prevent the boundary effect of the photosensitizer ([Ru(bpy)2(tip)]2+, RBT) during ROS generation, we used the sensitivity of RBT and PdH0.2-Ir with different wavelengths of near-infrared light (NIR) to generate ROS and H2, respectively. Therefore, an intelligent nanosystem PdH0.2-Ir@RBT(PIH@R) was constructed to precisely control ROS generation by adjusting the NIR laser wavelength. The palladium-iridium alloy (Pd-Ir) nanoparticles as the core can co-load hydrogen (H2) and RBT and show NIR-responsive behaviors. Under 808 nm laser irradiation, PIH@R produces ROS with the photocatalysis of RBT, while under 1064 nm laser irradiation PIH@R will quickly activate and release H2 to eliminate ROS. Interestingly, in vitro and in vivo experiments showed that PIH@R acted like a "Trojan horse": PIH@R can destroy