Effects of thiamine and benfotiamine on intracellular glucose metabolism and relevance in the prevention of diabetic complications

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DOI: 10.1007/s00592-008-0042-y · Source: PubMed
Abstract
Thiamine (vitamin B1) is an essential cofactor in most organisms and is required at several stages of anabolic and catabolic intermediary metabolism, such as intracellular glucose metabolism, and is also a modulator of neuronal and neuro-muscular transmission. Lack of thiamine or defects in its intracellular transport can cause a number of severe disorders. Thiamine acts as a coenzyme for transketolase (TK) and for the pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase complexes, enzymes which play a fundamental role for intracellular glucose metabolism. In particular, TK is able to shift excess fructose-6-phosphate and glycerhaldeyde-3-phosphate from glycolysis into the pentose-phosphate shunt, thus eliminating these potentially damaging metabolites from the cytosol. Diabetes might be considered a thiamine-deficient state, if not in absolute terms at least relative to the increased requirements deriving from accelerated and amplified glucose metabolism in non-insulin dependent tissues that, like the vessel wall, are prone to complications. A thiamine/TK activity deficiency has been described in diabetic patients, the correction of which by thiamine and/or its lipophilic derivative, benfotiamine, has been demonstrated in vitro to counteract the damaging effects of hyperglycaemia on vascular cells. Little is known, however, on the positive effects of thiamine/benfotiamine administration in diabetic patients, apart from the possible amelioration of neuropathic symptoms. Clinical trials on diabetic patients would be necessary to test this vitamin as a potential and inexpensive approach to the prevention and/or treatment of diabetic vascular complications.
REVIEW ARTICLE
Effects of thiamine and benfotiamine on intracellular glucose
metabolism and relevance in the prevention of diabetic
complications
Elena Beltramo Æ Elena Berrone Æ Sonia Tarallo Æ
Massimo Porta
Received: 27 March 2008 / Accepted: 30 May 2008 / Published online: 26 June 2008
Ó Springer-Verlag 2008
Abstract Thiamine (vitamin B1) is an essential cofactor
in most organisms and is required at several stages of
anabolic and catabolic intermediary metabolism, such as
intracellular glucose metabolism, and is also a modulator of
neuronal and neuro-muscular transmission. Lack of thia-
mine or defects in its intracellular transport can cause a
number of severe disorders. Thiamine acts as a coenzyme
for transketolase (TK) and for the pyruvate dehydrogenase
and a-ketoglutarate dehydrogenase complexes, enzymes
which play a fundamental role for intracellular glucose
metabolism. In particular, TK is able to shift excess fruc-
tose-6-phosphate and glycerhaldeyde-3-phosphate from
glycolysis into the pentose-phosphate shunt, thus eliminat-
ing these potentially damaging metabolites from the
cytosol. Diabetes might be considered a thiamine-deficient
state, if not in absolute terms at least relative to the
increased requirements deriving from accelerated and
amplified glucose metabolism in non-insulin dependent
tissues that, like the vessel wall, are prone to complications.
A thiamine/TK activity deficiency has been described in
diabetic patients, the correction of which by thiamine and/or
its lipophilic derivative, benfotiamine, has been demon-
strated in vitro to counteract the damaging effects of
hyperglycaemia on vascular cells. Little is known, however,
on the positive effects of thiamine/benfotiamine adminis-
tration in diabetic patients, apart from the possible
amelioration of neuropathic symptoms. Clinical trials on
diabetic patients would be necessary to test this vitamin as a
potential and inexpensive approach to the prevention and/or
treatment of diabetic vascular complications.
Keywords Thiamine Benfotiamine Diabetes
Diabetic complications High glucose
Introduction
Thiamine (vitamin B1) was the first vitamin of the B group
to be identified in 1926 by Jansen et al. [1]. It is an essential
cofactor in most organisms and has probably played a role
in the earliest stages of the evolution of life [2]. Its active
form, thiamine diphosphate (TDP) is required at several
stages of anabolic and catabolic intermediary metabolism,
such as the intracellular glucose metabolism (glycolysis,
Krebs cycle, pentose-phosphate cycle) [2], and is also a
modulator of neuronal and neuro-muscular transmission,
probably through its activation of a ionic channel for
chlorine [3].
Lack of thiamine or defects in its intracellular trans-
port can cause a number of severe disorders. Beriberi,a
neurological and cardiovascular disease, first described in
1630 by a Dutch physician who worked in Java and so-
called because its symptoms cause walking like sheep
(beri-beri in the local dialect), is due to a dietary
deficiency of thiamine. This leads to damage of the
peripheral nervous system, with pain in the limbs,
weakness of the musculature and distorted skin sensation;
the heart may be enlarged and cardiac output inadequate
[4] and, if not adequately cured, the consequence may be
death [1]. The disease is particularly common in Far
Eastern countries, because of the low content of thiamine
in rice, especially polished one because only the outer
layer contains an appreciable amount of the vitamin, but
E. Beltramo (&) E. Berrone S. Tarallo M. Porta
Department of Internal Medicine, University of Turin,
Corso AM Dogliotti, 14, 10126 Turin, Italy
e-mail: elena.beltramo@unito.it
123
Acta Diabetol (2008) 45:131–141
DOI 10.1007/s00592-008-0042-y
can occasionally be seen in severely malnourished alco-
holics [4].
Absence or severe lack of thiamine in the diet can also
cause the Wernicke–Korsakoff syndrome, or cerebral beri-
beri, a striking neuro-psychiatric disorder characterized by
paralysis of eye movements, abnormal stance and gait, and
markedly deranged mental function [4, 5].
Finally, an inborn defect in the intracellular transport of
thiamine could be the cause of the TRMA syndrome
(Thiamine-Responsive Megaloblastic Anemia), an autoso-
mal recessive disorder characterized by megaloblastic
anemia with ringed sieroblasts, diabetes and progressive
sensorineural deafness [6].
Thiamine levels are often reduced in alcoholics, mainly
due to their diet rich in carbohydrates, the impairment of
thiamine absorption for the effects of chronic alcohol
intake on the gut’s absorptive mechanisms and the accu-
mulation of acetaldehyde, which interferes with thiamine
utilization. Thiamine deficiency in alcoholics usually is not
resolved by thiamine supplementation [7]. A deficit in
thiamine is often described also in patients with diabetic
neuropathy [8, 9].
Biochemistry and mechanisms of action
The chemical structure of thiamine consists in a five-
membered thiazolium ring and a six-membered amino-
pyrimidine ring joined together by a methyl group
(Fig. 1a). The active form (TDP) has a diphosphate-ter-
minated side-chain (Fig. 1b).
Thiamine is present in free form and very low concen-
trations in the intestinal lumen; absorption takes place
mainly in the proximal part of the small intestine, through
two different mechanisms [1012]: at concentrations lower
than 1 lmol/l, thiamine is transported mainly by an active,
carrier-mediated system, which involves the phosphoryla-
tion of the vitamin [13]; at higher concentrations, passive
diffusion is the main mechanism. Thiamine uptake is
enhanced by thiamine deficiency [14] and reduced by
thyroid hormone and insulin [15], which cannot control
thiamine uptake directly [16], but can modify its absorption
by influencing intestinal tissue.
In the early 1960s, a group of lipid-soluble thiamine
derivatives, called allithiamine because they can be found
in nature in vegetables of the Allium family, was discov-
ered [17, 18]. These derivatives have much higher
absorption and bioavailability than water-soluble thiamine
salts, reaching higher concentrations in blood and tissues
and maintaining them longer [18, 19]. Water-soluble thia-
mine, as a matter of fact, is not stored in the body, but
rapidly excreted in the urine and must be replenished every
5–6 h [20].
Among lipid-soluble derivatives, benfotiamine, which
was developed to improve bioavailability for pharmaco-
logical administration [20, 21], seems to be the most
effective [22]. It contains an open thiazole ring (Fig. 1c),
which, subsequently to the passage through the mucous
membranes, is closed through a reduction reaction,
resolving with the production of biologically active thia-
mine [19], which is then converted in the active form, TDP.
TDP acts as a coenzyme for transketolase (TK) and for
the pyruvate dehydrogenase and a-ketoglutarate dehydro-
genase complexes, enzymes which play a fundamental role
for the intracellular glucose metabolism (Fig. 2). TK,
which contains a tightly bound TDP as its prosthetic group,
is able to shift excess fructose-6-phosphate and glycer-
haldeyde-3-phosphate (G3P) from glycolysis into the
pentose-phosphate shunt, thus eliminating from the cytosol
the excess of these damaging metabolites (Fig. 3). G3P is
one of the most effective agents of advanced-glycation
end-products (AGE) formation into the cytoplasm [23] and
also an end-product of the non-oxidative branch of the
pentose phosphate pathway and can be produced by TK.
Since the in vivo concentration of transketolase metabolites
is ten-fold lower than the K
M
of the enzyme, the net flux
and the direction of the reaction are dependent on substrate
and product concentration and on NADP
+
/NADPH ratio
[24]. TK expression has been shown to be activated by
high-dose thiamine and benfotiamine in the renal glomeruli
of diabetic rats [25], as well as human red blood cells [26],
bovine aortic endothelial cells and retinas of diabetic rats
[27]. TK activity in erythrocytes is often used as a marker
of a deficit in thiamine [28].
The pyruvate dehydrogenase complex is responsible for
the oxidative decarboxylation of pyruvate, the final product
Fig. 1 Chemical structures of thiamine (a), its activated form,
thiamine diphosphate (TDP)(b) and the lipophilic derivative
benfotiamine (c)
132 Acta Diabetol (2008) 45:131–141
123
of glycolysis, in the formation of acetyl-CoA, which then
enters the Krebs’ cycle; a deficit in thiamine is known to
decrease oxidation of pyruvate, with the subsequent accu-
mulation of pyruvate and lactate [29]; similarly, the a-
ketoglutarate dehydrogenase complex is responsible for the
oxidative decarboxylation of a-ketoglutarate into succinyl-
CoA inside the Krebs’ cycle: thiamine deficiency thwarts
the correct functioning of this enzyme, thus not decreasing
the metabolic flux inside the cycle [30].
Mechanisms of glucose-induced toxicity in diabetic
complications
Diabetic microangiopathy is a major cause of blindness,
renal failure and nerve damage, while, in large vessels,
diabetes accelerates atherosclerosis, leading to increased
risk of myocardial infarction, stroke and limb amputation.
The severity of microvascular complications in both type 1
and 2 diabetes has been clearly associated with the duration
and degree of hyperglycaemia. Diabetic patients with a
lifetime of poor glycaemic control have a high frequency of
tissue complications and definitive proof of the ‘glucose
hypothesis’ was provided by two large prospective clinical
trials [31, 32], which demonstrated the strong relationship
linking hyperglycaemia and diabetic complications in type
1 and, respectively, type 2 diabetes.
The majority of cell types is able to down-regulate
glucose transport in the presence of high ambient glucose,
in order to keep intracellular glucose concentration con-
stant. On the contrary, vascular endothelial and mesangial
cells, which are among the first targets of glucose toxicity,
are characteristically unable to reduce glucose transport in
hyperglycaemic conditions [33, 34], leading to glucose
accumulation inside the cell and overproduction of reactive
oxygen species (ROS) by the mitochondrial electron
transport chain: therefore high intracellular glucose levels
are among the major factors responsible for diabetic tissue
damage [35]. Mechanisms involved in glucose-mediated
damage can be divided into two groups: one causing acute
metabolic changes which are reversible when normal
glycaemia is restored, the other determining cumulative
impairments, that remain, or sometimes even worsen, when
euglycaemia is restored [36].
Several reports in the literature show a high sensitivity
of vascular cells to direct exposure to high glucose con-
centrations [3739]. Early apoptosis has been demonstrated
in both human umbilical vein endothelial cells and bovine
retinal pericytes, following 2-day incubation in high glu-
cose [39]. Glucose-induced apoptosis has also been
demonstrated in podocytes, mesangial cells, dorsal root
ganglion cells, cardiac myocytes and renal tubular epithe-
lial cells [4044]. Increased expression of the pro-apoptotic
Bax proteins in vivo and in vitro [38] and activation of NF-
jB in vitro [45] have been associated with vascular cell
apoptosis.
Rapid glucose depletion was shown to enhance apop-
tosis in retinal pericytes by modulating the expression of
the Bcl-2 family genes [46, 47], while a ROS—mediated
cellular ‘memory’ of vascular stress after glucose
normalization has been demonstrated in HUVECs and
ARPE-19 retinal cells [48]. Increased expression of type
IV-collagen and fibronectin long after normalization of the
glucose levels have been demonstrated in endothelial cells
previously grown in high glucose concentrations [49, 50].
Intermittent exposure to high glucose has been described to
increase apoptosis related to oxidative stress in human
umbilical vein endothelial cells, possibly through over-
production of mitochondrial superoxide [48,
5153].
Fig. 2 TDP acts as a coenzyme for transketolase (A) in the glycolytic
pathway, and for the pyruvate dehydrogenase (B) and a-ketoglutarate
dehydrogenase complexes (C) in the Krebs cycle, enzymes which
play a fundamental role for the intracellular glucose metabolism
Fig. 3 Transketolase (TK), which contains a tightly bound TDP as its
prosthetic group, is able to shift excess fructose-6-phosphate and
glycerhaldeyde-3-phosphate from glycolysis into the pentose-phos-
phate shunt, thus eliminating from the cytosol the excess of these
damaging metabolites. TALDO transaldolase
Acta Diabetol (2008) 45:131–141 133
123
Reinstitution of good metabolic control after 6-month hy-
perglycaemia was shown to elevate oxidative stress and
nitric oxide production in the kidney of diabetic rats [54].
These findings are consistent with the clinical observation
that daily fluctuations in plasma glucose concentrations,
which occur in diabetic patients, are correlated to increases
in cardiovascular disease [55] and microvascular compli-
cations [56]. On the other hand, diabetic retinopathy was
demonstrated to accelerate after restoration of normal
blood glucose levels, in particular if improvement in gly-
caemic control is achieved rapidly [5760].
Among the possible mechanisms of glucose-induced
vascular damage, four hypotheses have been widely
entertained and clinical trials established to study specific
inhibitors: (1) increased flux through the polyol pathway;
(2) increased formation of AGE; (3) PKC activation; (4)
increased flux through the hexosamine pathway (Fig. 4a).
1. The key-enzyme of polyol pathway is aldose reductase
(AR), which normally reduces toxic aldehydes to
inactive alcohols, but, in the case of excess intracel-
lular glucose, reduces it to sorbitol, while consuming
the cofactor NADPH, with consequent hyperglycaemic
pseudohypoxia [61] and increased susceptibility to
intracellular oxidative stress [62, 63]. It has been
demonstrated, among other effects, that treating dia-
betic dogs with an AR inhibitor prevents diabetes-
induced damage to nerve conduction velocity [64].
2. High glucose inside the cell initially reacts with
proteins, amino acids and nucleic acids via Schiff
base condensation with amino groups, followed by
irreversible rearrangement into an Amadori product.
Further Maillard reactions slowly produce advanced
glycation end products, or AGEs, which can also
derive from the earlier glycation products (Schiff base
and Amadori intermediates) through glycoxidation
reactions or from reactive dicarbonyl fragments gen-
erated from free glucose [65]. AGEs, in turn, can
modify intracellular proteins, including some involved
in the regulation of gene transcription [66], while
diffusing out of the cell can modify extracellular
matrix [67], leading to reduced cell-to-cell adhesion
and vascular dysfunction [68, 69], and circulating
blood proteins, leading to activation of AGE receptors
and production of inflammatory cytokines and growth
factors [7072]. Inhibition of AGE by aminoguanidine
prevents structural changes in experimental diabetic
retinopathy [73].
3. Intracellular high glucose increases the de novo
synthesis of the lipid second messenger diacylglycerol
(DAG), which in turn activates PKC synthesis [74],
causing a number of negative effects inside the cell,
such as decreased synthesis of endothelial nitric oxide
synthase (eNOS) or increased synthesis of endothelin-
1, transforming growth factor b, plasminogen activator
inhibitor-1 [75] and NF-jB[36, 76]. Inhibition of PKC
prevents vascular dysfunction in diabetic retina and
kidney [77, 78].
4. Excess fructose-6-phosphate derived from high avail-
ability of intracellular glucose can be transformed to
glucosamine-6-phosphate and then to UDP N-acetyl-
glucosamine, which acts on serine and threonine
residues of transcription factors, resulting in patholog-
ical changes in gene expression [79, 80].
Brownlee et al. [76] have hypothesized that the possible
common denominator (‘‘unifying mechanism’’) of these
apparently independent biochemical pathways is high-
glucose-induced excess production of ROS by the mito-
chondrial electron transport chain inside the endothelium,
as a result of increased flux through the Krebs’ cycle.
Inhibition of high glucose-induced superoxide production
by superoxide dismutase (SOD) prevents diabetic
nephropathy in the db/db diabetic mouse [81]. ROS,
causing strand breaks in nuclear DNA, activate the poly-
(ADP-ribose)-polymerase (PARP), which in turn inhibit
glyceraldehyde phosphate dehydrogenase (GAPDH)
activity [82], therefore pushing metabolites from glycolysis
in the upstream pathways mentioned above (Fig. 4a).
Metabolic effects of thiamine and benfotiamine in
preventing diabetic complications: in vitro
and in vivo studies
High glucose concentrations cause a number of patholog-
ical changes in small and large vessels, the mechanisms of
which are not yet fully understood, as stated above.
Potentially, thiamine can prevent cell damage induced by
hyperglycaemia, both by removing excess G3P from the
cytoplasm, as described above (‘Biochemistry and mech-
anisms of action’) and, through activation of a-
ketoglutarate dehydrogenase, by facilitating the utilization,
in the Krebs’ cycle, of acetyl-CoA derived from acceler-
ated glycolysis [83]. Addition of thiamine was shown in
1996 to normalize cell replication, lactate production and
AGE formation in endothelial cells from human umbilical
veins and bovine retinas, cultured in high glucose con-
centrations, by re-directing the glycolytic flux towards
alternative pathways, whereas it had no stimulatory or
inhibitory effects if added to physiological glucose con-
centrations [83].
In the same year, a high in vitro inhibition of antigenic
late (post-Amadori) AGE formation by TDP on bovine
serum albumin, ribonuclease A and human hemoglobin
was demonstrated, in contrast with the ‘classic’ AGE
134 Acta Diabetol (2008) 45:131–141
123
inhibitor aminoguanidine, which seems to inhibit the
initial phase of glycation and suggesting that the thera-
peutical potential of these inhibitors may be significantly
enhanced by co-administration of thiamine and amino-
guanidine [84].
Incubation of human red blood cells with normal and
high glucose in the presence of different concentrations of
thiamine, by increasing TK activity, led to a decrease in the
intracellular concentrations of triosephosphates, such as
G3P, and a subsequent increase of ribose-5-phosphate and
sedoheptuloxe-7-phosphate, together with decreased for-
mation of methylglyoxal, one of the most potent agent of
non-enzymatic glycation [85].
Benfotiamine was subsequently reported to be similar to
thiamine in correcting delayed replication and increased
AGE formation in human endothelial cells [86]: an addi-
tional explanation to this, apart from the shifting of toxic
intermediates of glycolysis towards alternative pathways,
was that thiamine/benfotiamine exert a protective effect
from high glucose damage by increasing the availability of
reduced glutathione [87], which in turn depends on the
recycling of oxidized glutathione through an NADPH-
requiring reaction. Since the pentose phosphate shunt is an
important source of NADPH and it is potentiated by thia-
mine [88], the latter has been suggested to act indirectly as
an anti-oxidant [86, 87].
Fig. 4 a Among the possible
mechanisms of glucose-induced
vascular damage, four
hypothesis has been widely
examined: (1) increased flux
through the polyol pathway; (2)
increased formation of AGE; (3)
PKC activation; (4) increased
flux through the hexosamine
pathway. The common
denominator of these apparently
independent biochemical
pathways (‘‘unifying
mechanism’’) seems to be high-
glucose-induced excess
production of ROS by the
mitochondrial electron transport
chain inside the endothelium, as
a result of increased flux
through the Krebs’ cycle
[36, 76]. ROS, causing strand
breaks in nuclear DNA, activate
the poly-(ADP-ribose)-
polymerase (PARP), which in
turn inhibit glyceraldehyde
phosphate dehydrogenase
(GAPDH) activity [82],
therefore pushing metabolites
from glycolysis in the upstream
pathways mentioned above.
b Thiamine/benfotiamine have
been shown to normalize
all the four branches in
hyperglycaemic conditions in
vascular cells and diabetic rats
[27, 90]
Acta Diabetol (2008) 45:131–141 135
123
Thiamine and benfotiamine were shown to be effective
in preventing two markers of apoptosis (increase of DNA
fragmentation and caspase-3 activity) due to exposure to
high ambient glucose in endothelial cells and pericytes,
possibly by protecting against the intracytoplasmic accu-
mulation of damaging metabolites and, consequently,
AGEs, though no effects on cell cycle traversal for both
high glucose and thiamine/benfotiamine were observed
[39].
High doses of thiamine and benfotiamine were also
shown to prevent incipient diabetic nephropathy in the
streptozotocin (STZ)-induced diabetic rat model of diabe-
tes with moderate insulin therapy, that were discovered in
this study to be thiamine deficient, due to increased urinary
excretion of the vitamin. Thiamine and benfotiamine were
demonstrated to inhibit the accumulation of triosephos-
phates through their conversion to ribose-5-phosphate,
increase TK expression in renal glomeruli, decrease PKC
activation, oxidative stress and protein glycation, and
finally inhibit the development of microalbuminuria; this
was achieved without changes of either plasma glucose
concentration or glycated hemoglobin [25].
Studies on the prevention of the early hallmarks of
diabetic retinopathy (pericyte loss and thickening of the
basement membrane) showed that thiamine is able, simi-
larly to aminoguanidine, to normalize bovine retinal
pericyte adhesion to extracellular matrix produced by
human endothelial cells in high glucose concentrations,
possibly through reduction of matrix protein glycation due
to highly glycating glucose intermediate metabolites [68];
as a matter of fact, as structural components of the extra-
cellular matrix, such as collagen, are the prime targets of
advanced glycation processes, cross-link formation
induced by AGE could cause stiffness of the basement
membrane and impair tissue remodeling [89]; in a sub-
sequent study [69], an indirect confirmation of these
findings was given by the finding that pericyte viability (i.e.
proliferation, cell cycle traversal and apoptosis) was not
affected by culturing them on high-glucose conditioned
extracellular matrices.
Hammes et al. [27] showed how benfotiamine can
normalize the excess production of ROS inside the altered
endothelium, both in bovine aortic endothelial cells and
retinas from rats with nine months of diabetes, by inhibiting
the activation of the hexosamine and the diacylglycerol-
PKC pathways and AGE formation, thus leading to
normalization of 3 out of the four branches of the
‘unifying mechanism’ proposed to be at the basis of the
pathogenesis of diabetic vascular complications. In another
study [90], the fourth branch, the polyol pathway, was
shown to be normalized by the addition of either thiamine
or benfotiamine to high glucose in vascular cells, through
the decrease of aldose reductase activity, sorbitol and
intracellular glucose levels (Fig. 4b). Inhibition of hyper-
glycaemia-associated NF-jB activation in diabetic rat
retinas by benfotiamine treatment through TK activation
was also demonstrated [27]. In the same work, morpho-
logical studies on rat retinas showed that benfotiamine is
able to prevent the formation of acellular capillaries, thus
preventing experimental diabetic retinopathy.
Thiamine was also shown to improve endothelial cell
migration after endothelial injury, as well as revert
decreased cell migration and increased von Willebrand
factor secretion, a marker of endothelial cell damage, under
hyperglycaemic conditions, thus suggesting that thiamine
treatment may decrease endothelial cell dysfunction due to
high glucose and improve re-endothelialization after inti-
mal injury in diabetic and non-diabetic conditions [91].
More recently, benfotiamine was demonstrated to pre-
vent ischemia-induced toe necrosis, improve hind limb
perfusion and oxygenation and restore endothelium-
dependent vasodilatation in STZ-induced diabetic mice,
probably through protein kinase B (PKB)/Akt mediated
potentiation of angiogenesis and inhibition of apoptosis:
PKB/Akt are known to play a central role in the control of
angiogenesis and endothelial cell homeostasis [92].
Moreover, benfotiamine was able to prevent the accumu-
lation of AGEs and the induction of the pro-apoptotic
caspase-3 in ischemic muscles, while normalizing Nos3
and Akt expression [92]. In the same study, benfotiamine
supplementation was shown to stimulate proliferation and
inhibit apoptosis of endothelial progenitor cells (EPCs)
cultured in hyperglycaemic conditions, and to increase the
number of circulating EPCs in diabetic mice submitted to
limb ischemia.
The positive effect of benfotiamine on EPCs was con-
firmed by Marchetti et al. [93], who showed that
hyperglycaemia impairs EPC number, uptake and binding
of acLDL and lectin-1, together with EPC ability to dif-
ferentiate into mature endothelial cells and be involved in
de novo tube formation, when co-cultured with mature
endothelial cells on matrigel. Benfotiamine administration,
through the modulation of Akt/FoxO1 activity, improves
the expression of endothelial cell markers in EPCs, restores
eNOS levels and the ability of EPCs to take part to
angiogenesis.
Stracke et al. [94] described the beneficial effects of
benfotiamine, though not thiamine, on peripheral nerve
function (motor nerve conduction velocity) and the for-
mation of glycation products in nervous tissue of STZ-
induced diabetic rats. Total thiamine levels in blood and
nerve tissue were found to be much higher after adminis-
tration of benfotiamine compared with thiamine nitrate, so
that the amelioration of motor nerve conduction velocity
and decrease of glycation products may be attributed to the
higher tissue availability of benfotiamine. Moreover, early
136 Acta Diabetol (2008) 45:131–141
123
administration of benfotiamine (immediately after diabetes
induction) was proven to be more effective than later
administration (two months after diabetes induction).
Benfotiamine was demonstrated to alleviate oxidative
stress in STZ-induced diabetic mice both in cerebral cortex
tissue, through a mechanism independent of AGE, tissue
factor and TNF-a [9], and cardiomyocytes, in which it also
improved contractile function [95]. Failure of benfotiamine
in rescue AGE formation was, in these studies, probably
due to the short-time exposure (14 days) to the vitamin.
High-dose thiamine therapy (70 mg/kg) normalized
food intake and prevented diabetic-induced increases in
plasma cholesterol and triglycerides in STZ-induced dia-
betic rats, thus counteracting dyslipidaemia, but did not
reverse the decrease of HDL [96]. This was due to pre-
vention of thiamine depletion and decrease of TK activity
in rat liver, with a concomitant decrease in UDP-N-acet-
ylglucosamine and fatty acid synthase activity. However,
lower doses of thiamine (7 mg/kg) and benfotiamine
at both concentrations were ineffective [96], probably
because exogenous thiamine is able to increase hepatic
thiamine levels more effectively than benfotiamine in the
90-min postprandial period [97]. In the same study [96],
diuresis and glicosuria, but not plasma glucose concentra-
tion, of STZ diabetic rats were decreased by either
thiamine and benfotiamine.
Finally, a protective effect of high-dose thiamine on
detrusor contractility and the progression of diabetic cyst-
opathy in STZ-diabetic rats was suggested [98].
Metabolic effects of thiamine and benfotiamine
in preventing diabetic complications: clinical studies
Beneficial effects of administration of thiamine and
derivatives have been demonstrated in thiamine-deficient
patients with chronic renal insufficiency, in whom benf-
otiamine administration led to higher TDP concentrations
in erythrocytes accompanied with a significant improve-
ment of the erythrocyte transketolase activity [99] and
alcoholic polyneuropathy, in which vibration perception
(measured at the tip of the great toe), as well as motor
function, improved after benfotiamine administration; a
tendency toward improvement was also evident for pain
and co-ordination [100].
Little is known, however, on the possible positive
effects of thiamine/benfotiamine administration in diabetic
patients. A significant improvement in neuropathy symp-
toms (nerve conduction velocity and vibration perception
threshold) and decrease in pain, together with the patients’
sensation of improved clinical conditions, were signaled in
diabetic subjects with polyneuropathy treated with either
thiamine [8] or benfotiamine [101, 102].
It was observed that diabetic subjects tend to have lower
blood thiamine concentrations than healthy controls,
together with a reduced erythrocyte transketolase activity
[103105] and an increased thiamine renal clearance [106],
while intestinal absorption and membrane transport of
thiamine may be decreased [15]. Although the intestinal
thiamine transporter is saturated by relatively low doses of
thiamine, there is slow passive diffusion of thiamine at
high concentrations [12].
However, since diabetic subjects usually do not manifest
the typical clinical markers of thiamine deficiency, this is
probably due to a specific pattern of vascular cells. Endo-
thelial cells and pericytes are unable to regulate glucose
transport, reaching high levels of intracellular glucose
concentrations [33], in the presence of hyperglycaemia.
Such high levels of glucose determine high production of
ROS, which could oxidize thiamine, with the production of
inactive compounds, such as thiochrome and oxydihydro-
thiochrome [107].
Benfotiamine was shown to completely prevent macro-
and microvascular endothelial dysfunction and oxidative
stress, as assessed by measurement of flow-mediated
dilatation and hyperemia, following an AGE-rich meal in
type 2 diabetic patients, possibly through reduction of
endogenous AGEs and dycarbonyl (metyl-glyoxal) pro-
duction, and suggesting a role for benfotiamine in
atherosclerosis prevention in diabetic patients [108]. A
similar effect was demonstrated for thiamine, the intra-
venous administration of 100 mg of which improved
endothelium-dependent vasodilatation in the presence of
hyperglycaemia [109]. Both studies showed that thiamine/
benfotiamine effects were not due to a glucose-lowering
mechanism as either compound had no effects in nor-
moglycemic conditions.
Conclusions
Diabetes might be considered a thiamine-deficient state, if
not in absolute terms at least relative to the increased
requirements deriving from accelerated and amplified
glucose metabolism in non-insulin dependent tissues that,
like the vessel wall, are prone to complications.
As shown in this review, thiamine and its derivatives
have been widely demonstrated to have the potential to
correct most of the known metabolic abnormalities
induced by high glucose in isolated cells and also to
prevent complications in animals with experimental
diabetes.
Surprisingly enough, however, the huge amount of lit-
erature on the beneficial effects of thiamine and
benfotiamine in cell and animal models has been followed
so far by very few clinical trials on diabetic patients, which
Acta Diabetol (2008) 45:131–141 137
123
would be necessary to test this vitamin as a potential and
inexpensive approach to the prevention and/or treatment of
diabetic vascular complications.
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    • "Specifically, benfotiamine was shown to induce leukemia cell growth inhibition as a result of cell cycle arrest and paraptosis cells death. Although the effects of benfotiamine on cell metabolism [6,23] may play a role in its antitumor activity, it is more likely that the antitumor effect is a unique property of this synthetic compound, presumably mediated by the compound's benzoyl group, which shares some features with benzaldehyde, an organic compound with reported antitumor effects against several solid tumors [24,25]. Moreover, because benfotiamine is an S-acyl thiamine derivative, it has been suggested that the spontaneous rearrangement of S-acyl cysteine derivatives into N-acyl cysteine derivatives may occur in vivo [26]. "
    [Show abstract] [Hide abstract] ABSTRACT: Benfotiamine is a synthetic thiamine analogue that stimulates transketolase, a cellular enzyme essential for glucose metabolism. Currently, benfotiamine is used to treat diabetic neuropathy. We recently reported that oral benfotiamine induced a temporary but remarkable recovery from acute myeloid leukemia in an elderly patient who was ineligible for standard chemotherapy due to dementia and renal failure. In the present study we present evidences that benfotiamine possess antitumor activity against leukemia cells. In a panel of nine myeloid leukemia cell lines benfotiamine impaired the viability of HL-60, NB4, K562 and KG1 cells and also inhibited the growing of primary leukemic blasts. The antitumor activity of benfotiamine is not mediated by apoptosis, necrosis or autophagy, but rather occurs though paraptosis cell death induction. Mechanistic studies revealed that benfotiamine inhibited the activity of constitutively active ERK1/2 and concomitantly increased the phosphorylation of JNK1/2 kinase in leukemic cells. In addition, benfotiamine induced the down regulation of the cell cycle regulator CDK3 which resulted in G1 cell cycle arrest in the sensitive leukemic cells. Moreover, combination index studies showed that benfotiamine enhanced the antiproliferative activities of cytarabine against leukemia cells. These findings suggest that benfotiamine has antitumor therapeutic potential.
    Full-text · Article · Apr 2015
    • "Meanwhile, it is reported that regular exercise increases the PDH activation in the model exposed to diabetes and improves carbohydrate metabolism [23]. It is observed that much supplement of thiamine is effective in improving diabetic complication24252627282930; it is also confirmed that the result is related to the PDH activation, as thiamine supplementation increases the PDH activation [31]. Therefore, the thiamine supplementation suggests that it would activate PDH at the same level of regular exercise, and it is required to verify how thiamine supplementation affects healthy person. "
    [Show abstract] [Hide abstract] ABSTRACT: The purpose of this study was to find the effect of endurance training and thiamine supplementation on anti-fatigue during the exercise. Each nine students from K Women's University went through three cross-over treatments: placebo treatment, training treatment and thiamine treatment. Training treatment was performed with bicycle ergometer exercise for four weeks (five days per week). Each exercise was performed for an hour with intensity set at 70% (50rpm) of maximal oxygen uptake. Thiamine treatment group was given 10mg of thiamine tetrahydrofurfuryl disulfide per one kilogram for four weeks. The bicycle ergometer exercise was performed at 70% of maximal oxygen uptake in exercise intensity which 60 minutes of exercise was performed at 50rpm . Lactate concentration was significantly decreased during 15 to 30 minutes of exercise for those with training treatment and 15 to 60 minutes of exercise for those with thiamine treatment compared to placebo treatment group. Ammonia concentration was significantly decreased during 15 to 60 minutes of exercise and 15 to 30 minutes of recovery for those with training and thiamine treatment compared to placebo treatment. Resting blood thiamine concentrations of placebo treatment were significantly lower than training treatment. 60 minutes after the exercise, plasma thiamine concentration was significantly increased in all treatment group. To sum up the previous, thiamine intake during exercise positively benefits carbohydrate metabolism in a way that will decrease lactate concentration, ammonia concentration, and anti- fatigue by reducing the RPE. Therefore, we can consider thiamine intake to be utilized as similar benefits as endurance training.
    Full-text · Article · Dec 2013
    • "Hence, glucose intolerance and diabetes might be the result of a thiamine‑deficient state. [1,31] This difference between our results and other reports could be due to differences in the type of study and individuals that had been investigated. Jeon et al. [32] found that the dietary intake of thiamin in obese individuals is higher than subjects without MS, while Bruscato et al. [24] found no association between thiamin intake and risk of MS as we have now found. "
    [Show abstract] [Hide abstract] ABSTRACT: Dietary micronutrients have been proposed to protect against oxidative damage and related clinical complications. We aimed to compare the micronutrient intake between individuals with and without metabolic syndrome (MS). This cross-sectional study included 3800 men and women who were aged between 35 and 65 years. The diagnosis of the MS was based on International Diabetes Federation criteria. Dietary intake of participants was assessed using a questionnaire for 24 h dietary recall. Student's t-test and Mann-Whitney U-tests were used for comparing the micronutrient intake of subjects with or without the MS and the odds ratio for the presence of the MS was calculated for each micronutrient by control for total energy intake adjusted by the residue method. The mean age of MS subjects and the control group was 48.8 ± 7.9 years and 47.6 ± 7.6 years, respectively. Energy-adjusted intake of vitamin E (P < 0.05), B2 (P < 0.01), and B12 (P < 0.05) was higher in normal women compared with women with MS. Energy-adjusted intake of vitamin B1 was significantly higher in women with MS. After logistic regression analysis, no significant association between micronutrient intake and MS was shown. We found no significant association between micronutrient intake and MS.
    Full-text · Article · Jun 2013
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