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Pharmacological potential of tocotrienols: A review

  • King Abdullah International Medical Research Center, Al Ahsa, Saudi Arabia

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Tocotrienols, members of the vitamin E family, are natural compounds found in a number of vegetable oils, wheat germ, barley, and certain types of nuts and grains. Like tocopherols, tocotrienols are also of four types viz. alpha, beta, gamma and delta. Unlike tocopherols, tocotrienols are unsaturated and possess an isoprenoid side chain. Tocopherols are lipophilic in nature and are found in association with lipoproteins, fat deposits and cellular membranes and protect the polyunsaturated fatty acids from peroxidation reactions. The unsaturated chain of tocotrienol allows an efficient penetration into tissues that have saturated fatty layers such as the brain and liver. Recent mechanistic studies indicate that other forms of vitamin E, such as γ-tocopherol, δ-tocopherol, and γ-tocotrienol, have unique antioxidant and anti-inflammatory properties that are superior to those of α-tocopherol against chronic diseases. These forms scavenge reactive nitrogen species, inhibit cyclooxygenase- and 5-lipoxygenase-catalyzed eicosanoids and suppress proinflammatory signalling, such as NF-κB and STAT. The animal and human studies show tocotrienols may be useful against inflammation-associated diseases. Many of the functions of tocotrienols are related to its antioxidant properties and its varied effects are due to it behaving as a signalling molecule. Tocotrienols exhibit biological activities that are also exhibited by tocopherols, such as neuroprotective, anti-cancer, anti-inflammatory and cholesterol lowering properties. Hence, effort has been made to compile the different functions and properties of tocotrienols in experimental model systems and humans. This article constitutes an in-depth review of the pharmacology, metabolism, toxicology and biosafety aspects of tocotrienols. Tocotrienols are detectable at appreciable levels in the plasma after supplementations. However, there is inadequate data on the plasma concentrations of tocotrienols that are sufficient to demonstrate significant physiological effect and biodistribution studies show their accumulation in vital organs of the body. Considering the wide range of benefits that tocotrienols possesses against some common human ailments and having a promising potential, the experimental analysis accounts for about a small fraction of all vitamin E research. The current state of knowledge deserves further investigation into this lesser known form of vitamin E.
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R E V I E W Open Access
Pharmacological potential of tocotrienols: a review
Haseeb Ahsan
, Amjid Ahad
, Jahangir Iqbal
and Waseem A Siddiqui
Tocotrienols, members of the vitamin E family, are natural compounds found in a number of vegetable oils, wheat
germ, barley, and certain types of nuts and grains. Like tocopherols, tocotrienols are also of four types viz. alpha,
beta, gamma and delta. Unlike tocopherols, tocotrienols are unsaturated and possess an isoprenoid side chain.
Tocopherols are lipophilic in nature and are found in association with lipoproteins, fat deposits and cellular
membranes and protect the polyunsaturated fatty acids from peroxidation reactions. The unsaturated chain of
tocotrienol allows an efficient penetration into tissues that have saturated fatty layers such as the brain and liver. Recent
mechanistic studies indicate that other forms of vitamin E, such as γ-tocopherol, δ-tocopherol, and γ-tocotrienol, have
unique antioxidant and anti-inflammatory properties that are superior to those of α-tocopherol against chronic diseases.
These forms scavenge reactive nitrogen species, inhibit cyclooxygenase- and 5-lipoxygenase-catalyzed eicosanoids and
suppress proinflammatory signalling, such as NF-κB and STAT. The animal and human studies show tocotrienols may
be useful against inflammation-associated diseases. Many of the functions of tocotrienols are related to its antioxidant
properties and its varied effects are due to it behaving as a signalling molecule. Tocotrienols exhibit biological activities
that are also exhibited by tocopherols, such as neuroprotective, anti-cancer, anti-inflammatory and cholesterol lowering
properties. Hence, effort has been made to compile the different functions and properties of tocotrienols in experimental
model systems and humans. This article constitutes an in-depth review of the pharmacology, metabolism,
toxicology and biosafety aspects of tocotrienols. Tocotrienols are detectable at appreciable levels in the
plasma after supplementations. However, there is inadequate data on the plasma concentrations of tocotrienols that
are sufficient to demonstrate significant physiological effect and biodistribution studies show their accumulation in vital
organs of the body. Considering the wide range of benefits that tocotrienols possesses against some common human
ailments and having a promising potential, the experimental analysis accounts for about a small fraction of all vitamin E
research. The current state of knowledge deserves further investigation into this lesser known form of vitamin E.
Keywords: Dietary tocotrienols, Pharmacology, Antioxidant, Anti-inflammatory, Hypolipidemic, Hypoglycaemic,
Anti-cancer, Cardioprotective
Evans and Bishop, in 1922, discovered that dietary sup-
plements with alfalfa leaves (rich in vitamin E) prevent
placental hemorrhage and reverse dietary sterility in
rats [1]. Evans and his associates [2] isolated the com-
pounds of vitamin E family and named them tocopherols
(Greek: Tocos-child birth; pheros- to bear; ol-alcohol).
While alpha-tocopherol was the first vitamin E isomer to
be recognized, eight chemically distinct isomers are now
known, consisting of alpha (α), beta (β), gamma (γ)and
delta (δ)-tocopherols and α,β,γand δ-tocotrienols (T3),
all of them are referred to as vitamin E. The tocopherols
are saturated forms of vitamin E, whereas the tocotrienols
are unsaturated and possess an isoprenoid side chain
(Table 1). The name tocotrienolwas first suggested by
Dr. Banyan, for the isomers of vitamin E, with isoprenoid
side chain present in nature, when isolated from the latex
of the rubber plant, Havea brasiliensis [3]. Tocotrienols
attracted no real attention until the 1980s and 1990s
when their cholesterol-lowering potential [4] and antican-
cer effects were described [5,6]. This review article will
take a closer look at the various functions of tocotrienol
by providing numerous potential evidences on how it may
be protective against these chronic diseases. Tocotrienols
are found in certain cereals and vegetables such as palm
oil, rice bran oil, coconut oil, barley germ, wheat germ and
* Correspondence:
Department of Biochemistry, Jamia Hamdard (Hamdard University), New
Delhi 110062, India
Full list of author information is available at the end of the article
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unless otherwise stated.
Ahsan et al. Nutrition & Metabolism 2014, 11:52
annatto [7,8]. Palm oil and rice bran oil contain particu-
larly higher amounts of tocotrienols (940 mg/kg and
465 mg/kg, respectively) [9]. Other sources of tocotrienols
include grape fruit seed oil, oats, hazelnuts, maize, olive
oil, Buckthorn berry, rye, flax seed oil, poppy seed oil and
sunflower oil.
Tocotrienols possess powerful neuroprotective, anti-
oxidant, anti-cancer and cholesterol lowering properties
that often differ from the properties of tocopherols [10].
Micromolar amounts of tocotrienol suppress the activity
of HMG-CoA reductase, the hepatic enzyme responsible
for the synthesis of cholesterol [11,12]. Tocotrienols
are thought to have more potent antioxidant proper-
ties than α-tocopherol [13,14]. The unsaturated side
chain of tocotrienol allows for more efficient penetration
into tissues that have saturated fatty layers such as the
brain and liver [15]. Experimental research examining the
antioxidant, free radical scavenging, effects of tocopherol
and tocotrienols have found that tocotrienols appear su-
perior due to their better distribution in the lipid layers of
the cell membrane [16]. One major conclusion often used
to undermine tocotrienol research is the relative inferiority
of the bioavailability of orally taken tocotrienols as com-
pared to that of α-tocopherol. The hepatic α-tocopherol
transfer protein (α-TTP), together with the tocopherol-
associated proteins (TAP) is responsible for the endogen-
ous accumulation of natural α-tocopherol.
Tocotrienols are absorbed, in the same way as other
vitamin E compounds, alongwith fat, in the small intes-
tine, after being cleaved by the enzyme esterase, located
in the stomach lining. Bile salts are necessary for the ab-
sorption. It is then packaged into chylomicrons and then
transported in the lymphatic system. The α-tocotrienol
appears to be better absorbed than the other forms of
tocotrienol. In the bloodstream, tocotrienols are exposed
to the oxidative free radicals and therefore perform most
of their antioxidant activity. Tissue uptake takes place
either with the help of lipoprotein lipases, digesting the
lipoprotein constituents, or by receptor mediated endo-
cytosis of lipoprotein. Lipoprotein lipase degrades lipo-
proteins to remnant particles which are then taken up
by liver or peripheral tissues by receptor mediated endo-
cytosis. Tocotrienols enter a variety of different tissue
types, with adipose and adrenal gland having the highest
levels. Vitamins can be stored in the tissue for long pe-
riods of time because of their exceedingly slow turnover
rate. Vitamin E is oxidized after it has performed its
antioxidant function. It is converted to its hydroquinone
form in a P450 dependent manner before being elimi-
nated from the body through faeces. Hydroquinone form
binds with glucuronic acid and mixes with bile for
removal through faeces. Despite the promising potential
of tocotrienol, the experimental analysis accounts for
only a small fraction of all vitamin E research. However,
Table 1 Structures of various homologs of tocotrienols
Type R1 R2 R3 Structure
alpha(α)-Tocotrienol Me Me Me
beta(β)-Tocotrienol Me H Me
gamma(γ)-Tocotrienol H Me Me
delta(δ)-Tocotrienol H H Me
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 2 of 22
biologists are increasingly realizing the importance of
this minor and unique vitamin E isomer [16].
Various minerals and vitamins are present in a variety
of food products and available as dietary supplements.
Selenium (Se) is an essential micronutrient that occurs pre-
dominantly as selenomethionine (SeMet), whereas vitamin
E (or a-tocopherol) is a fat-soluble physiological antioxi-
dant, both of which are required for normal health [17-19].
The Se and vitamin E are essential components of the
human diet and have been studied as antioxidants and
potential therapeutic agents for a variety of human dis-
eases. Various formulations of Se and vitamin E have
been shown to possess a therapeutic and preventive effect
against prostate cancer (PCa) cells [20].
The motivation for the use of vitamin E and Se for the
prevention of PCa comes from clinical trial data. Vitamin
E was shown to be a promising candidate for PCa preven-
tion in the α-Tocopherol β-Carotene Cancer Prevention
Study, a controlled smoking trial where α-tocopherol
reduced PCa incidence by 32% and mortality by 41%
[21]. The SUpplementation en VItamines et Mineraux
AntioXidants (SUVIMAX) study found a significant re-
duction in PCa rates among men receiving a multivitamin
containing 30 mg vitamin E, although the protective effect
could not be attributed to any specific micronutrient [22].
In contrast, the Heart Outcomes Prevention Evaluation
(HOPE) trial, the Heart Protection Study, the NIH-AARP
Diet and Health Study and the Cancer Prevention Study II
Nutrition Cohort donot support a general protective
effect of α-tocopherol supplement use for PCa pre-
vention [23-26].
Therefore, the Selenium and Vitamin E Cancer Pre-
vention Trial (SELECT), was designed to test a prostate
cancer chemoprevention hypothesis using oral Se and
vitamin E supplementation in disease-free volunteers.
Initiated in 2001, the SELECT was a phase III, randomized,
placebo-controlled human trial to investigate the PCa che-
mopreventive effects of Se, vitamin E or their combination
[27]. SELECT was among the largest clinical chemopre-
vention trials ever, with an enrollment of more than 35,000
men and an intended follow-up of up to 12 years [27].
SELECT was predicated on basic and clinical research in-
cluding secondary endpoint data from cancer prevention
studies that implied Se and vitamin E supplements
could be useful in reducing PCa risk. However, the trial
was prematurely terminated in 2008, 18 months before
its intended minimum follow-up length. The Se and
vitamin E doses and formulations used in SELECT were
found to be ineffective, and concern was raised about a
possible trend in developing type 2 diabetes mellitus
among the study participants taking Se [27]. Further,
a statistically nonsignificant increased risk of PCa was
also seen in the vitamin E group participants. Un-
fortunately, despite the perceived suitability of PCa for
chemoprevention and the considerable evidence suggest-
ing the usefulness of Se and vitamin E for PCa prevention,
SELECT failed to show a positive effect. Hence, the
SELECT trial was terminated early because of the safety
concerns and negative data for the formulations and doses
given [28].
The biological activity of vitamin E has generally been
associated with its well-defined antioxidant property,
specifically against lipid peroxidation in biological mem-
branes. In the vitamin E group, a-tocopherol is consid-
ered to be the most active form. Moreover, tocotrienol
has been shown to possess novel hypocholesterolemic
effects together with an ability to reduce the atherogenic
apolipoprotein B and lipoprotein(a) plasma levels. In ad-
dition, tocotrienol has been suggested to have an anti-
thrombotic and anti-tumor effect indicating that tocotrienol
may serve as an effective agent in the prevention and/or
treatment of cardiovascular disease and cancer. The phy-
siological activity of tocotrienol suggests it to be superior
than a-tocopherol in many pathophysiological conditions.
Hence, the role of tocotrienol in the prevention of cardio-
vascular disease and cancer may have significant clinical
implications. Additional studies on its mechanism of ac-
tion, as well as, long-term intervention studies from the
pharmacological point-of-view are required to elucidate
its function [29].
Biochemical functions
Vitamin E is not a single agent but is at least eight
vitamers,named tocochromanols and can be either
tocopherolsor tocotrienols. They are further assigned
Greek letter prefixes by degree of methyl substitution, that
is, α-tocopherol (with three chiral centers) exists naturally
as the (2R,4R,8R) stereoisomer and is synthesized as all-
racemic or (2RS,4RS,8RS) product [30]. In 1943, Joffe
and Harris demonstrated varying potencies of the eight
forms of vitamins [31]. It is known that α-tocopherol is
taken up in the human liver by hepatic transfer proteins
and some tocopherol stereoisomers penetrate cell mem-
branes more easily [31,32]. The 2R isomers of α-tocopherol
are putatively used to establish the vitamin E requirement
[33]. As commercial dietary supplements, both natural
(RRR) and synthetic (all-rac) α-tocopheryl esters (acetate
or succinate) are available and extensively used. Lee et al.
[34] showed that vitamin E succinate has a distinct
anti-prostaglandin effect in human lung epithelial cells.
Vitamin E is relatively safe for consumption even at high
dosages, since a 3,200-IU dose was well tolerated by adults
in short-term studies [35].
One of the most significant differences between αT
and other forms of vitamin E is that in contrast to αT,
which is mostly retained in tissues because of preferential
binding by α-TTP, large quantities of other forms of
vitamin E are readily metabolized by CYP4F2-initiated
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 3 of 22
ω-oxidation of the side chain to generate carboxychroma-
nols and conjugated counterparts. Short-chain carboxy-
chromanols such as CEHCs are excreted in the urine and
γ-CEHC has been shown to have natriuretic activities [36].
Long-chain carboxychromanols, especially 13-COOHs,
are found in tissues and faeces in animals supplemented
with γT, δT, and γTE [37-40]. The discovery of potent
anti-inflammatory [41,42] and anticancer [43] effects of
long-chain carboxychromanols represents an exciting
research direction and provides new insights into the
physiological roles of less tissue-preserved forms of vita-
min E [44].
α-tocopherol, the commonly studied isomer of vitamin
E, has been shown to possess an anti-cancer effect [45-47].
However, the researchers have also started evaluating γ-
tocopherol for its chemopreventive efficacy [45-51]. Inter-
estingly, γ-tocopherol is being increasingly appreciated to
have a better potential than α-tocopherol [52]. Studies
have shown that the in vitro products of γ-tocopherol
antioxidant reactions differ from those of α-tocopherol,
with the latter alone forming nitrosating agents when ex-
posed to NO
[52]. Christen et al. [53] showed that γ-
tocopherol may be required to complement the activity
of α-tocopherol, suggesting that supplementation of
α-tocopherol alone may suppress γ-tocopherol levels.
The majority of available experimental data on vitamin E
for suppressing PCa has been obtained with α-tocopherol,
leaving the possibility that other vitamin E isomers may
possess better chemopreventive or anticancer potential
against PCa, but which needs to be explored further [28].
All tocopherols and tocotrienols are potent antioxi-
dants with lipoperoxyl radical-scavenging activities. Only
until recently, most research on vitamin E has primarily
focused on αT [54], because αT is the predominant form
of vitamin E in tissues and low intake of this form
results in vitamin E deficiency-associated ataxia [55].
However, many human and animal studies on αT sup-
plementation have yielded disappointing outcomes re-
garding its protective role in prevention or treatment of
chronic diseases including cardiovascular diseases and
cancer [56,57]. On the other hand, recent mechanistic
studies combined with preclinical animal models have
indicated that compared with αT, other forms of vitamin
E appear to have different and superior biological prop-
erties that may be useful for prevention and therapy
against chronic diseases. Furthermore, emerging evidence
suggests that some long-chain vitamin E metabolites
have even stronger anti-inflammatory effects than their
vitamin precursors. These metabolites may be novel anti-
inflammatory agents and may contribute to beneficial
effects of vitamin E forms in vivo. Here we discuss
recent developments in the field of non-αT forms of vita-
min E with respect to their metabolism and antioxidant
and anti-inflammatory effects [44].
Most of the functions of tocotrienols are related to its
antioxidant property in animals. It prevents the non-
enzymatic oxidations of various cell components (e.g.
unsaturated fatty acids) by molecular oxygen and free
radicals such as superoxide (O
) and hydrogen peroxide
). The various biochemical functions of tocotrienols
are related either directly or indirectly to its antioxidant
property. They are essential for membrane structure and
integrity of the cell [58]. Tocotrienols prevent the pero-
xidation of polyunsaturated fatty acids in various tissues
and membranes and protects the red blood cells from
hemolysis by oxidizing agents [59]. It increases the syn-
thesis of heme by enhancing the activity of enzymes
δ-aminolevulinic acid (ALA) synthase and ALA dehydra-
tase. It is required for cellular respiration through electron
transport chain and is believed to stabilize coenzyme Q. It
prevents the oxidation of vitamin A and carotenes and
also LDL and thus may be helpful in the prevention of
some chronic diseases [9,59]. Tocotrienols also protects
the liver from being damaged by toxic compounds such
as CCL
Pharmacological properties
Tocotrienols have a very broad range of medicinal
properties and are used as antioxidant, analgesic, anti-
inflammatory, antibacterial, antipyretic, antithrombotic,
anticancer, cardioprotective, hepatoprotective, hypogly-
cemic, and nephroprotective, as discussed below. The
pharmacological potential of tocotrienols has also been
summarized in Table 2.
Anti-cancer effects
The anticancer properties of tocotrienols are well known
and documented [60-76]. Tocotrienols not only sup-
press cancer-cell proliferation, but also induces apop-
tosis in cancer cells. It has been reported that γ-and
δ-tocotrienols exhibit greater anticancer activity than
α-orβ-tocotrienols [76-78]. The mechanism of anti-
cancer effects of tocotrienols has been worked out
[5,79,80]. They exert anti-cancer activity on cancer cells by
cell cycle arrest through induction of cell cycle inhibitory
protein and decreased expression of cyclin dependent
kinase [64,65,79]. Tocotrienols also work as an anti-
cancer agent by inhibiting angiogenesis [81,82] or by en-
hancing immunity and inhibiting tumor cell migration [71].
Tocotrienol induces cell-cycle arrest and mitochondria-
mediated apoptosis in human pancreatic cancer cells
[68,70,75,83]. It has also been shown to inhibit the
tumor cell growth by suppressing HMG-CoA reductase
activity [84]. It has been shown to induce apoptosis in
stomach cancer cells through down-regulation of the Raf-
ERK signaling pathway [69]. Tocotrienol significantly acti-
vated caspase-dependent programmed cell death in skin
and pancreatic cells [73,76]. γ-andδ-tocotrienols derived
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 4 of 22
Table 2 Biological properties of tocotrienols
S.No. Protective activity Tocotrienol type Proposed mechanism of action References
1. Anti-cancer γ-T
Inhibition of NF-κB, TGF-βand P38 signalling
Induction and potentiation of apoptosis [20,22,31,144,145]
Activation of caspases [31,34,61,145,146]
Down-regulation of Bcl-2 and cyclin D [61]
Suppression of HMGR activity [44]
TRF from palm oil Induction of DNA fragmentation [18]
Inhibition of angiogenesis [55]
Inhibition of cell proliferation through
cell cycle arrest
Down-regulation of Raf/Erk pathway [27]
2. Anti-diabetic TRF from palm oil and rice bran oil Prevents the formation of advanced
glycationendproducts in diabetic rats
Reduces hyperglycemia and hyperlipidemia
in diabetic rats
Inhibition of NF-κB signalling pathway [75]
Inhibition of oxidative-nitrosative stress [120]
Inhibition of TNF-α, IL-1β, TGF-β1 and
caspase-3 activity
TRF from palm oil and rice bran oil Reduction of glucose-insulin index [79,80]
Increase in insulin sensitivity [59,81,83]
3. Anti-inflammatory α-T
Suppression of NF-κB, TNF-α, IL-1, IL-6,
IL-8 and iNOS
Suppression of cyclooxygenase-2 activity [51,57]
Suppression of STAT-3 signalling pathway [29,45]
4. Antioxidant α-T
Increase in the activity of antioxidant enzymes [59,60,62,65,148]
TRF from palm oil and rice bran oil,
Quenching and scavenging of free radicals [63,69,70,79]
Inhibition of lipid peroxidation [64,66,68]
5. Immuno-stimulatory α-T
Induction of antibody production [99,101]
Induction of IFN-γ, IL-4, IL-1βproduction [99,102]
Suppression of TNF-α[102]
6. Cardio-protective α-T
Inhibition of HMG-CoA reductase activity [10,86,104]
Inhibition of expression of cell adhesion molecules [105]
Reduction in the levels of blood cholesterol [106,107]
TRF from palm oil and rice bran oil, δ-T
Inhibition of lipid peroxidation [41,80]
Downregulation of c-Src expression [102]
Upregulation of phosphorylation of Akt [102]
TRF from palm oil Reduction in the production of apolipoprotein B,
platelet derived factor-4, thromboxane B2
TRF from palm oil and rice bran oil Downregulation of TGF-β[80]
7. Neuro-protective α-T
Inhibition of PP 60 (c-Src) kinase activity and
phosphorylation of Erk
Inhibition of 12-lipoxygenase activity [115,116]
Reduction of oxidative stress [77]
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 5 of 22
from palm oil exhibited strong activity against tumor
promotion by inhibiting EpsteinBarr virus (EBV) early
antigen expression in EBV-genome-carrying human lym-
phoblastoid cells induced by phorbol ester [9]. Tocotrie-
nols suppressed DMBA-induced mammary tumors and
hypercholesterolemia in murine model [85]. It induced
apoptosis in human fibroblast cells through TGF-beta
FasJNK-signaling pathways [47]. Gamma-Tocotrienol in-
duced poly (ADP-ribose) polymerase (PARP) cleavage and
stimulated a rise in caspase-3, caspase-8 and caspase-9 ac-
tivities in human hepatoma Hep3B cells [68]. The antipro-
liferative activity of tocotrienols are mediated through
modulation of growth factors such as vascular endothelial
growth factor (VEGF) [82], basic fibroblast growth factor
(bFGF) [86] and transforming growth factor-beta (TGF-β)
[62], HER2/neu [87], and interleukin-6 (IL-6) [88]. Cyclin-
dependent kinases (CDK2, CDK4, CDK6) and their inhibi-
tors, such as p21, p27 and p53 [60,64] and downregulation
of Rb phosphorylation [65,66] also mediate the growth-
suppressive effects of this agent. Downregulation of
the telomerase, c-myc, and rafERK signaling pathways
has been linked to tocotrienols ability to inhibit cell
survival [69,89].
Pancreatic cancer is a leading cause of cancer mortality
with less than 5% of patients surviving 5 years after diag-
nosis [90]. Several studies have combined natural com-
pounds that inhibit NF-kB, such as genistein, curcumin,
fisetin, and green tea, to investigate synergy in treating
pancreatic cancer [91-94]. However, translation of these
studies to the clinic has been challenging due to the
low bioavailability of some of these natural compounds in
humans. Tocotrienols, a group of 4 (α-, β-, δ-, and γ-
tocotrienol) unsaturated naturally occurring vitamin E
compounds have received increasing attention for their
potential as nontoxic dietary anticancer agents [95,96].
Husain et al. [97] has shown that oral administration of
100 mg/kg/d of d-tocotrienol to mice resulted in levels
that were 10 times higher in pancreas than in subcutane-
ously implanted tumor tissue, suggesting that these com-
pounds will have reasonable bioavailability for pancreatic
tumor intervention [97]. In another study, they inves-
tigated the potential of the natural tocotrienols to in-
hibit pancreatic cancer and NF-kB activation in vitro
and in vivo. In addition, they also investigated the
potential of the most bioactive tocotrienol to augment
gemcitabine activity in vitro and in vivo [98]. Their
results show that d- and g-tocotrienol inhibited NF-kB
activity, cell growth, cell survival, and tumor growth in
nude mice. It was shown by them that d-tocotrienol
augmented gemcitabine activity in vitro and in vivo.
The results suggest that inhibition of NF-kB signaling
by d-tocotrienol may be an effective approach for the
prevention and treatment of pancreatic cancer. Our
findings suggest evaluation of NF-kB signaling com-
pounds as an endpoint biomarker in the ongoing phase
I trial of d-tocotrienol in patients with pancreatic tu-
mors [98].
Breast cancer is the second most frequent cancer
affecting women worldwide after lung cancer. The toxicity
associated with chemical drugs has turned the attention
toward natural compounds as anticancer agents. Vitamin
E derivatives consisting of tocopherols and their analogs
namely tocotrienols have been extensively studied due to
their remarkable biological properties. While tocopherols
have failed to offer protection, tocotrienols, in particular,
a-, d-, and c-tocotrienols alone and in combination have
demonstrated anticancer properties. The antiangiogenic,
antiproliferative, and apoptotic effect of tocotrienols not
only suggests that they are potent antitumor agents but
also reinforces the notion that tocotrienols are indeed
more than antioxidants [99].
Nesaretnam et al. [100] conducted a double-blinded,
placebo-controlled pilot trial to test the effectiveness of ad-
juvant tocotrienol therapy in combination with tamoxifen
for 5 years in women with early breast cancer. Two-
hundred forty women, aged between 40 and 60 years, with
either tumor node metastases (TNM) breast cancer and es-
trogen receptor (ER)-positive tumors were non-randomly
assigned to two groups. The intervention group received
tocotrienol-rich fraction (TRF) plus tamoxifen, whereas
the control group received placebo plus tamoxifen, for
5 years. From the study, it was found that there is no asso-
ciation between adjuvant tocotrienol therapy and breast
cancer-specific survival in women with early breast cancer.
Hence, results from the study were not sufficient to indi-
cate a significant association between adjuvant tocotrienol
Table 2 Biological properties of tocotrienols (Continued)
8. Hepato-protective α-T
Inhibition of lipid peroxidation
and oxidative damage
Induction of the expression of CYP450,
UGT1A1 nad MDR-protein 1
TRF from palm oil and rice bran oil,
Induction of hepatic antioxidant status [59,137,138]
9. Nephro-protective TRF from rice bran oil, α-T
Inhibition of oxidative-nitrosative stress [12,136,141]
TRF from palm oil and rice bran oil, α-T
Downregulating the expression of NF-κB,
TGF-β, TNF-αand caspase-3
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 6 of 22
therapy and breast cancer survival in women with early
breast cancer. However, evidence suggested that tocotrie-
nols have anticancer effects and tamoxifen and tocotrienol
in vitro demonstrate synergy. Although a 60% lower mor-
tality occurred in the intervention group, this result was
not statistically significant. Hence, a large randomized trial
is certainly warranted in the near future to establish
whether tocotrienol adjuvant therapy can significantly im-
prove recurrence or mortality or both [100].
Nesaretnam et al. [99] have demonstrated a mechanism
for tocotrienol activity that involves estrogen receptor
(ER) signaling. In silico simulations and in vitro binding
analyses indicate a high affinity of specific forms of toco-
trienols for ERb, but not for ERa. Moreover, they found
that specific tocotrienols increase ERb translocation into
the nucleus which, in turn, activates the expression of es-
trogen responsive genes (MIC-1, EGR-1 and Cathepsin D)
in breast cancer cells only expressing ERb cells (MDA-MB-
231) and in cells expressing both ER isoforms (MCF-7).
The binding of specific tocotrienol forms to ERb is asso-
ciated with the alteration of cell morphology, caspase-3
activation, DNA fragmentation, and apoptosis. Further-
more, some clinical trials seem to suggest that tocotrienols
in combination may have the potential to extend breast
cancer-specific survival.
Advances in chemopreventive approaches would be an
immense breakthrough in lowering the mortality rate as-
sociated with breast cancer in women. Supplementation
or treatment with palm tocotrienols has shown encour-
aging results mainly from in vitro and in vivo studies.
Hence, tThe studies conducted by Nesaretnam et al. [99]
demonstrated that tocotrienols have convincing poten-
tial in suppressing and inhibiting the growth of mam-
mary tumor cells. Combined treatment with statins,
celecoxib, and tamoxifen resulted in a significantly enhan-
ced synergistic response compared with high doses of
treatment with individual compounds. Interestingly, this
effect was observed using lower doses of the anticancer
agent in combination with tocotrienols, suggesting that
the toxicity factor related to these drugs may be avoided.
The recent clinical trial, even though is reported as a null
study, displayed promising reduction in the risk and recur-
rence free survival in women with early breast cancer.
Nevertheless, tocotrienols exhibit potential as anticancer
agents to be used in combination treatment as well as
to enhance therapeutic responsiveness in breast cancer
patients [99].
Anti-inflammatory activity
Tocotrienols have been extensively studied for their
anti-inflammatory property and very promising scientific
evidences have been brought up. The activation of the
transcription factor NF-κB has been closely linked with
inflammation [101,102]. Tocotrienols have been shown
to suppress the expression of TNF-α[101,103], IL-1
[104], IL-6 [105], IL-8 [106], inducible nitric oxide syn-
thase [107], and cyclo-oxygenase 2 [41,103], all of which
mediate inflammation. Tocotrienols have also been shown
to suppress STAT3 cell-signaling pathway, also involved in
inflammation [71,85]. Hypoxia-induced factor-1 is another
pathway that has been linked with inflammation and is
modulated by tocotrienols [106]. Treatment of streptozo-
tocin-induced diabetic rats with tocotrienols (25 mg/kg,
50 mg/kg and 100 mg/kg body weight) for 10 weeks, sig-
nificantly prevented behavioral, biochemical and molecu-
lar changes associated with diabetes through suppression
of activation of the NF-κB signaling pathway [103]. Non-
toxic concentrations of tocotrienol attenuated the tumour
necrosis factor-α(TNF)-induced nuclear transcription
factor (NF-κB) activation in human chronic myeloid
leukemia cells (KBM-5), which are the key steps in the
development of inflammation [101].
Anti-oxidant activity
It is now well established that generation of free radicals
and OH
) from the incomplete reduction of
molecular oxygen during aerobic respiration is closely
related to cellular damage. Regulation of the balance
between production of reactive oxygen species (ROS) by
cellular processes and its removal by antioxidant defense
system maintains normal physiological processes. The
antioxidant activities of tocotrienols are mediated through
induction of antioxidant enzymes such as superoxide dis-
mutase [108,109], NADPH: quinoneoxidoreductase [110],
and glutathione peroxidase [111], which quench free radi-
cals such as superoxide radicals [112]. Effects of toco-
trienols on antioxidant defense system in various animal
models have been studied from time to time. lntragastric
administration of tocotrienol for 30 days caused a signifi-
cant elevation in different components of hepatic antioxi-
dant defence and reduction in serum enzymes of hepatic
damage in rats fed with 2-acetylaminofluorene (AAF)
[113]. Shamaan et al. [114] investigated the effect of
tocotrienol on the activities of glutathione S-transferases
(GSTs), glutathione reductase (GR) and glutathione perox-
idase (GPx) in rats given 2-acetylaminofluorene (AAF)
over a 20 week period. Liver and kidney GST and liver GR
activities were significantly increased after AAF adminis-
tration. Kidney GPx activities were significantly affected.
In another experiment, alpha-tocopherol (αT) and gamma-
tocotrienol (γT) were supplemented continuously for
8 weeks in the diets of normal rats and rats chemically
induced with cancer using diethylnitrosamine (DEN),
2-acetylaminofluorene (AAF) and partial hepatectomy.
Hepatocarcinogenesis was followed by determining the
plasma gamma-glutamyl-transpeptidase (GGT) and al-
kaline phosphatase (ALP) activities as well as placental
glutathione S-transferase (PGST) and GGT activities
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 7 of 22
histochemically, at 4-week intervals. Male rats (Rattus
norvegicus) were supplemented αTand γT at two different
doses of 30 and 300 mg/kg diet. Elevation of plasma GGT
activities and formation of PGST and GGT positive foci
were attenuated significantly (P < 0.05) when αTandγT
were supplemented simultaneously with cancer induction
[115]. Ong et al. [116] investigated the effect of tocotrienol
and tocopherol on glutathione S-transferase (GST) and
gamma-glutamyltranspeptidase (GGT) activities in cul-
tured rat hepatocytes. Tocotrienol and tocopherol signifi-
cantly decreased GGT activities at 5 days in culture but
tocotrienol also significantly decreased GGT activities at
12 days. Tocotrienol and tocopherol treatment sig-
nificantly decreased GST activities at 3 days compared to
the control but tocotrienol also decreased GST activities
at 13 days. Tocotrienol showed a more pronounced
effect at a dosage of greater than 50 microM tocotrienol
at 13 days in culture compared to the control.
Another group of researchers investigated the effects
of tocotrienol-rich fraction (TRF) on exercise endurance
and oxidative stress in forced swimming rats. The results
showed that the TRF-treated animals (268.0 ± 24.1 min
for TRF-25 and 332.5 ± 24.3 min for TRF-50) swam sig-
nificantly longer than the control (135.5 ± 32.9 min) and
T-25-treated (154.1 ± 36.4 min) animals, whereas there
was no difference in the performance between the T-25
and control groups [116]. The TRF-treated rats also showed
significantly higher concentrations superoxide dismutase
(SOD), catalase (CAT), and glutathione peroxidase (GPx),
but lower levels in blood lactate, plasma and liver TBARS,
and liver and muscle protein carbonyl. Their results sug-
gested that TRF was able to improve the physiological
condition and reduce the exercise-induced oxidative stress
in forced swimming rats [117,118].
Anti-diabetic activity
For centuries, dietary antioxidants are well-known for
the management of diabetes and some of them have
been experimentally evaluated. However search for new
anti-diabetic drugs continues. α-Tocotrienol (0.1 g/kg)
significantly prevented oxidative damage in streptozotocin
(STZ)-induced diabetic Osteogenic Disorder Shionogi
(ODS) rat [119]. The TRF at a dose of 1 g/kg bodyweight
significantly reduced streptozotocin induced diabetes in
SpragueDawley rats [120]. It also effectively prevented
increase in serum advanced glycosylation end-products
(AGE) and malondialdehyde (MDA), and caused decrease
in blood glucose and glycatedhemoglobin in diabetic
rats. Intragastric administration of TRF from palm oil
(200 mg/kg) significantly reduced the blood glucose level,
oxidative stress markers and improved dyslipidemia in dia-
betic rats [121]. Diabetes is associated with a number of
secondary complications such as neuropathy, retinopathy,
nephropathy, lower limb amputations, etc. Kuhad et al.
[122] evaluated the impact of tocotrienol on cognitive
function and neuroinflammatory cascade in streptozotocin-
induced diabetes. Streptozotocin-induced diabetic rats were
treated with tocotrienol for 10 weeks. After 10 weeks of
streptozotocin injection, the rats produced significant in-
crease in transfer latency which was coupled with enhanced
acetylcholinesterase activity, increased oxidative-nitrosative
stress, TNF-alpha, IL-1beta, caspase-3 activity and active
p65 subunit of NF-κB in different regions of diabetic rat
brain. Co-administration of tocotrienol significantly preven-
ted behavioural, biochemical and molecular changes asso-
ciated with diabetes. Moreover, diabetic rats treated with
insulin-tocotrienol combination produced more pronounced
effect on molecular parameters as compared to their per
se groups. Tocotrienol also prevented diabetic neuropathy
in rat models [123,124]. Oral administration of tocotrienol
also significantly reduced the fasting serum glucose level
in STZ induced diabetic rats by increased glucose metab-
olism and partly by hypotriglyceridemic effect of the plant
extract. The extract also possessed oxidative stress redu-
cing property in diabetic rats, which is believed to be a
pathogenic factor in the development of diabetic com-
plications [102,123,125-127]. The TRF from palm oil and
rice bran oil was able to cause a significant reduction of
elevated glucose-insulin index, signifying a potential insu-
lin sensitizing effect in streptozotocin induced diabetic
rats [127]. Oral administration of tocotrienol decreased
the HbA1c, plasma glucose, lipids, peroxylipid (malo-
nedialdehyde, MDA), albuminuria, proteinemia and
uremia, and also improved the insulin sensitivity in
various animal models [128-130]. It also prevents the
incidence of long term complication in diabetic nephropa-
thy [103,119,126,127].
Antihyperlipidemic activity
Hyperlipidaemia is a group of disorders in which a person
has increased levels of lipids in the bloodstream. These
lipids consist of cholesterol, phospholipids, triglycerides
and cholestryl esters. Since lipids are insoluble in aqueous
medium, they are usually carried in body fluids as soluble
protein complexes called as lipoproteins. Hyperlipidaemia
can lead to a number of metabolic diseases like cardiovas-
cular dysfunction and atherosclerosis. Hyperlipidemia may
also result from diseases such as diabetes, thyroid disease,
renal disorders, obesity, alcohol consumption and liver
disorders. Oxidative stress is regarded as an important risk
factor for hyperlipidemia. Tocotrienols, because of their
antioxidant activity, have long been used for reducing
blood lipid levels. Tocotrienols from barley, oats, palm
and rice bran have been demonstrated to lower choles-
terol levels in animals and humans [59,131-139], and that
this effect has been reported to be mediated by suppressing
HMG-CoA reductase activity through a post-translational
mechanism [12,134]. Magosso et al. [140] conducted a first
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 8 of 22
clinical trial that demonstrated mixed palm tocotrienols
exhibited significant hepatoprotective effects in hypercho-
lesterolemic adults with non-alcoholic fatty liver disease,
and this effect was proposed to be mediated by attenuating
triglyceride accumulation via regulation of fatty acid
synthase and carnitine palmitoyl transferase leading to a
reduction of hepatic inflammation and ER stress [141,142].
Furthermore, the study showed that tocotrienols sig-
nificantly reduced serum levels of total cholesterol (TC),
low density lipoproteins (LDL) and triglycerides (TG)
compared to baseline. In patients with hyperlipidemia and
carotid stenosis, long term treatment with palm oil (a rich
source of tocotrienols) resulted in attenuation of oxidative
modification of LDL and significantly prevented the initi-
ation and propagation of atherosclerosis [143]. In two
open clinical studies, tocotrienol (75 mg/day) supplemen-
tation for 2 months significantly reduced fasting blood
lipid levels. TC levels dropped 13% and LDL-C dropped
9-15%, whereas high density lipoprotein-cholesterol
(HDL-C) increased by 4-7%. In addition, δ-tocotrienol
promoted metabolic health, where TG levels dropped
20-30% [144].
Immunomodulatory activity
Tocotrienols virtues as an immune enhancer are only
beginning to receive recognition in medicine. Tocotrie-
nol enhanced both antigen specific (observed against
humoral as well as Cell-mediated immune response) and
nonspecific responses. Tocotrienols have been shown to
induce favourable effects on the human immune system.
A team of Malaysian scientists evaluated the effects of a
tocotrienol compound on immune function, recruiting
108 healthy non-smoking women, ages 18 and 25 years,
for a two-month long study. One group received 400 mg
of tocotrienol compound per day, while the other group
received placebo (400 mg/day soy oil) for the study
period. Blood samples were analyzed at the start of the
study, and again after 28 and 56 days. After 28 days of
supplementation, all subjects received a single shot of
tetanus toxoid (TT) vaccine. The team observed signifi-
cant increases in levels of the anti-TT antibody, interferon
(IFN)-gamma and interleukin (IL)-4 in the tocotrienol
group, as compared with the placebo group. The resear-
chers concluded that tocotrienols have immunostimu-
latory effects and potential clinical benefits to enhance
immune response [145]. A study was conducted to deter-
mine the effect of dietary supplementation of tocotrienols
on immune response of young and old C57BL/6 mice
using a wide range of immune indices. The study demon-
strated that dietary supplementation with T3 resulted in
enhanced T cell proliferation [146]. In another study, the
immunoregulatory effects of dietary α-tocopherol (Toc)
and tocotrienols (T3) on humoral and cell-mediated
immunity and cytokine productions were examined in
Brown Norway rats. It was found that the IgA and IgG
productivity of spleen and mesenteric lymph node (MLN)
lymphocytes was significantly enhanced in the rats fed on
Toc or T3, irrespective of concanavalin A (Con A) stimu-
lation of the lymphocytes. On the contrary, the IgE prod-
uctivity of lymphocytes from the rats fed on Toc or T-3
was less without ConA stimulation, but was greater in the
presence of Con A, especially in the T3 group. Toc or T3
feeding significantly decreased the proportion of CD4
cells and the ratio of CD4
in both spleen and MLN
lymphocytes of the rats fed on Toc or T3. The interferon-
γproductivity of MLN lymphocytes was higher in the rats
fed on Toc or T3 than in those fed on a control diet in the
presence of Con A, while that of spleen lymphocytes was
lower in the rats fed on Toc or T3. In addition, T3 feeding
decreased the productivity of tumor necrosis factor-αof
spleen lymphocytes, while it enhanced the productivity of
MLN lymphocytes. The results suggested that oral admin-
istration of Toc and T3 affected the proliferation and
function of spleen and MLN lymphocytes [147]. The TRF
was found to enhance immune response to tetanus toxoid
(TT) immunisation in BALB/c mice. The production of
anti-TT antibodies was augmented (P < 0.05) in mice that
were fed with δ-T3 or TRF. The production of IFN-γand
IL-4 by splenocytes from the TRF treated mice was signifi-
cantly (P < 0.05) higher. Production of TNF-αwas also
suppressed in the vitamin E supplemented mice [148]. All
these findings suggest that tocotrienol could be a useful
natural complementfor immune boasting.
Protection against cardiovascular disease
Cardiovascular disorder is the one of the most potent
causes of death throughout the world and the role of toco-
trienols in its prevention may have significant clinical
implications. Out of a minimum of four different isoforms
of tocotrienols, a- and c-tocotrienols are considered as the
effective isoforms which possess the cardioprotective abil-
ities. A number of studies have determined the cardiopro-
tective abilities of tocotrienols and have been shown to
possess novel hypocholesterolemic effects together with
an ability to reduce the atherogenic apolipoprotein and
lipoprotein plasma levels. In addition, tocotrienol has been
suggested to have an antioxidant, anti-thrombotic, and
antitumor effect indicating that tocotrienol may serve as
an effective agent in the prevention and/or treatment of
cardiovascular disease and cancer. The bioactivity exhib-
ited is due to the structural characteristics of tocotrienols.
Rich sources of tocotrienols which include rice bran, palm
oil, and other edible oils exhibit protective effect against
cardiovascular disorders [149].
Diseases that involve the heart and blood vessels
remain the biggest cause of deaths worldwide. Coronary
heart disease, cardiomyopathy, ischemic heart disease,
heart failure, hypertensive heart disease, inflammatory
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 9 of 22
heart disease and valvular heart disease are some of
cardiovascular complications. Tocotrienol has long been
used for various cardiac complications. Tocotrienols
cardioprotective effects are mediated through their anti-
oxidant mechanisms and their ability to suppress inflam-
mation, and inhibit HMG-CoA reductase, a rate-limiting
enzyme in cholesterol biosynthesis [11,12,150], and reduce
the expression of adhesion molecules and monocyte
endothelial cell adhesion [151]. Tocotrienols were found
to be more effective than α-tocopherol in depressing age-
related increases in systolic blood pressure of spon-
taneously hypertensive rats [152]. TRF from rice bran oil
improved lipid abnormalities, reduced the atherogenic
index and suppressed the hyperinsulinemic response in
rats with streptozotocin/nicotinamide-induced type 2 dia-
betes mellitus [153]. Tocotrienol significantly alleviated
atherosclerotic iliac artery stenosis induced by both the
endothelialization and high cholesterol diet. It also signi-
ficantly lowered aortic contents of malondialdehyde and
intimal thickening as well as preserved the internal elastic
lamina in rabbits [154]. The tocotrienols also significantly
alleviated the ischemia-reperfusion injury, and reduced
infarct size in the ischemic region of myocardial tissue,
through the downmodulation of c-Src and upregula-
tion of phosphorylation of Akt, thus generating a survival
signal [155]. Treatment of tocotrienols orally to pigs
expressing hereditary hypercholesterolemia significantly
reduced serum total cholesterol, LDL-cholesterol, apoli-
poprotein B, platelet factor 4, thromboxane B(2), glucose,
triglycerides, and glucagon. The tocotrienols also lowered
the hepatic HMG-CoA reductase activity and cholesterol
and fatty acid levels in various tissues [156].
In one study, the effects of red palm oil on the myo-
cardial nitric oxide-cGMP signaling pathway, associated
with myocardial protection against ischemia, were investi-
gated [157]. Treatment with red palm oil increased aortic
output and increased levels of cGMP and polyunsaturated
fatty acid in rat hearts suggesting that dietary red palm
oil protects via the nitric oxidecGMP pathway and/or
changes in polyunsaturated fatty acid composition during
ischemia/reperfusion. Newaz et al. [109] determined the
effects of γ-tocotrienol on lipid peroxidation and total
antioxidant status of spontaneously hypertensive rats. The
γ-tocotrienol exhibited a dose dependent hypotensive ef-
fect on the systolic blood pressure of spontaneously hyper-
sensitive rats. It also caused a significant drop in the mean
arterial pressure in a dose dependent manner, decreased
lipid peroxidation and increased the activity of antioxidant
enzymes in hearts of rats. Myocardial ischemic injury
results from severe impairment of coronary blood supply
and produces a spectrum of clinical syndromes. In a study,
γ-tocotrienol significantly reduced coronary perfusion
pressure and heart rate. It exerted protection against
myocardial injury by mitigating cardiac dysfunction and
oxidative injury in rats and also by the differential inter-
action of MAPK with caveolin 1/3 in conjunction with
proteasome stabilization, possibly by altering the availabil-
ity of prosurvival and antisurvival proteins [158]. Diabetes
mellitus is always accompanied by dyslipidemia, which is
an important factor in the pathogenesis of diabetic com-
plications, such as cardiovascular diseases and diabetic
nephropathy. The TRF from palm oil and rice bran oil has
been shown to decrease the serum lipid profile in type-1
and type-2 diabetic Wistar rats [127,130]. It has also been
reported to decrease the dyslipidemia induced diabetic
nephropathy through the downregulation of the TGF-β
expression [127].
Neuroprotective effects
Various reports suggest that tocotrienols are neuropro-
tective [159-166]. Tocotrienols also have activity against
Parkinson disease [167]. In one study, HT4 hippocampal
neuronal cells were studied to compare the efficacy of
tocopherols and tocotrienol to protect against glutamate-
induced death. Tocotrienols were more effective than
alpha-tocopherol in preventing glutamate-induced death.
It was suggested that tocotrienols may have protected cells
by an antioxidant-independent mechanism. Examination
of signal transduction pathways revealed that protein tyro-
sine phosphorylation processes played a central role in the
execution of death. Activation of pp60(c-Src) kinase and
phosphorylation of ERK were observed in response to glu-
tamate treatment. Nanomolar amounts of α-tocotrienol,
but not α-tocopherol, blocked glutamate-induced death
by suppressing glutamate-induced early activation of c-Src
kinase. Overexpression of kinase-active c-Src sensitized
cells to glutamate-induced death. Tocotrienol treatment
prevented death of Src-overexpressing cells treated with
glutamate [159].
A growing body of research supports that members of
the vitamin E family are not redundant with respect to
their biological function. Palm oil derived from Elaeis
guineensis represents the richest source of the lesser
characterized vitamin E, α-tocotrienol. One of 8 natur-
ally occurring and chemically distinct vitamin E analogs,
α-tocotrienol possesses unique biological activity that is
independent of its potent antioxidant capacity. Current
developments in α-tocotrienol research demonstrate
neuroprotective properties for the lipid-soluble vitamin in
brain tissue rich in polyunsaturated fatty acids (PUFAs).
Arachidonic acid (AA), one of the most abundant PUFAs
of the central nervous system, is highly susceptible to oxi-
dative metabolism under pathologic conditions. Cleaved
from the membrane phospholipid bilayer by cytosolic
phospholipase A2, AA is metabolized by both enzymatic
and nonenzymatic pathways. A number of neurodegener-
ative conditions in the human brain are associated with
disturbed PUFA metabolism of AA, including acute
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 10 of 22
ischemic stroke. Palm oilderived α-tocotrienol at nano-
molar concentrations has been shown to attenuate both
enzymatic and nonenzymatic mediators of AA meta-
bolism and neurodegeneration. On a concentration basis,
this represents the most potent of all biological functions
exhibited by any natural vitamin E molecule. Despite such
therapeutic potential, the scientific literature on tocotrie-
nols accounts for roughly 1% of the total literature on vita-
min E, thus warranting further investigation [168].
A growing body of literature has begun to delineate the
unique and potent biological properties of the natural vita-
min E, αTCT [169]. To date, the neuroprotective qualities
of αTCT in neurodegenerative disorders of the CNS are
well characterized, with specific molecular targets (cPLA2,
12-LOX, and c-Src) and mechanisms of action identified.
Beyond the CNS, αTCT has also demonstrated thera-
peutic promise in the treatment cancer and hypercho-
lesterolemia. As a dietary source in humans, the oil palm
represents the richest source of αTCT known today.
Although tocotrienols are present in edible products such
as palm oil, it remains questionable whether a dietary
source alone could provide sufficient amounts of αTCT to
humans [169], which is particularly relevant in diets that
are typically devoid of palm oil and other natural sources
of αTCT. Enrichment of αTCT from crude palm oil for
dietary supplementation is achievable, and to date repre-
sents the most cost effective and readily available source
of natural αTCT [168].
a-Tocotrienol (TCT) represents the most potent neu-
roprotective form of natural vitamin E that is generally
recognized as a safe certified by the U.S. Food and Drug
Administration. The recent work of Park et al. [170]
addresses a novel molecular mechanism by which a-TCT
may be protective against stroke in vivo. Elevation of in-
tracellular oxidized glutathione (GSSG) triggers neural cell
death. Multidrug resistance-associated protein 1 (MRP1),
a key mediator of intracellular oxidized glutathione efflux
from neural cells, may therefore possess neuroprotective
functions. Stroke-dependent brain tissue damage was
studied in MRP1-deficient mice and a-TCT-supplemented
mice. Elevated MRP1 expression was observed in glu-
tamate-challenged primary cortical neuronal cells and
in stroke-affected brain tissue. MRP1-deficient mice
displayed larger stroke-induced lesions, recognizing a
protective role of MRP1. In vitro, protection against
glutamate-induced neurotoxicity by a-TCT was attenu-
ated under conditions of MRP1 knockdown; this suggests
the role of MRP1 in a-TCT-dependent neuroprotection.
In vivo studies demonstrated that oral supplementation of
a-TCT protected against murine stroke. MRP1 expression
was elevated in the stroke-affected cortical tissue of
a-TCT-supplemented mice. Efforts to elucidate the
underlying mechanism identified MRP1 as a target of a
microRNA (miRNA). In a-TCT-supplemented mice, the
miRNA was downregulated in stroke-affected brain tissue
[170]. The work of Park et al. [170] recognizes MRP1 as a
protective factor against stroke. Furthermore, findings of
this study add a new dimension to the current under-
standing of the molecular bases of a-TCT neuroprotection
in 2 ways: by identifying MRP1 as a a-TCT-sensitive target
and by unveiling the general prospect that oral a-TCT
may regulate miRNA expression in stroke-affected brain
tissue [170]. Hence, the findings of their study add a new
dimension to the current understanding of the molecular
bases of a-TCT neuroprotection in 2 ways: by identifying
MRP1 as a-TCT-sensitive target and by unveiling the gen-
eral prospect that oral a-TCT may regulate microRNA ex-
pression in stroke-affected brain tissue. Neuroprotective,
as well as hypocholesterolemic, properties of a-TCT make
it a good candidate for nutrition based intervention in
people at high risk for stroke. Transient ischemic attack,
or mini-stroke, serves as a sentinel warning sign for high-
risk stroke patients. Prophylactic stroke therapy therefore
provides an opportunity for intervention in patients tran-
sient ischemic attack before a major stroke event. Out-
comes of the current study warrant clinical assessment of
a-TCT in transient ischemic attack patients. Furthermore,
a-TCT is a nutrient that is certified by the U.S. Food and
Drug Administration to be generally recognized as safe
and is not a drug with potential side effects. Thus, a-TCT
may be considered as a preventive nutritional counter-
measure for people at high risk for stroke.
In order to determine whether the neuroprotective
activity of alpha-tocotrienol is antioxidant-independent
or -dependent, Khanna et al. [162] conducted a study
using two different triggers of neurotoxicity, homocys-
teic acid (HCA) and linoleic acid. Both HCA and linoleic
acid caused neurotoxicity with comparable features,
such as increased ratio of oxidized to reduced glutathione
GSSG/GSH, raised intracellular calcium concentration and
compromised mitochondrial membrane potential. Mecha-
nisms underlying HCA-induced neurodegeneration were
comparable to those in the path implicated in glutamate-
induced neurotoxicity. Inducible activation of c-Src and
12-lipoxygenase (12-Lox) represented early events in
that pathway. Overexpression of active c-Src or 12-
Lox sensitized cells to HCA-induced death. Nanomo-
lar α-tocotrienol was protective. Knock-down of c-Src
or 12-Lox attenuated HCA-induced neurotoxicity. Oxida-
tive stress represented a late event in HCA-induced death.
The observation that micromolar, but not nanomolar,
α-tocotrienol functions as an antioxidant was verified
in a model involving linoleic acid-induced oxidative stress
and cell death. Oral supplementation of alpha-tocotrienol
to humans results in a peak plasma concentration of
3mM.Thus,oralα-tocotrienol may be neuroprotective by
antioxidant-independent as well as antioxidant-dependent
mechanisms [162]. In another study, Khanna et al. [164]
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 11 of 22
tested the hypothesis that phospholipase A2 (PLA2) activ-
ity is sensitive to glutamate and mobilizes arachidonic acid
(AA), a substrate for 12-lipoxygenase. Furthermore, the
researchers examined whether α-tocotrienol (TCT) regu-
lates glutamate-inducible PLA2 activity in neural cells.
Glutamate challenge induced the release of [
H]AA from
HT4 neural cells. Such response was attenuated by
calcium chelators, ethylene glycol tetraacetic acid (EGTA)
and 1,2-bis(o-aminophenoxy)ethane- N,N,N',N'-tetraacetic
acid (BAPTA), cytosolic PLA2 (cPLA2)-specific inhibitor
arachidonyltrifluoromethyl ketone (AACOCF3) as well as
TCT at 250 nM. Glutamate also caused the elevation of
free polyunsaturated fatty acid (AA and docosahexaenoic
acid) levels and disappearance of phospholipid-esterified
AA in neural cells. Furthermore, glutamate induced a
time-dependent translocation and enhanced serine phos-
phorylation of cPLA2 in the cells. These effects of glutam-
ate on fatty acid levels and on cPLA2 were significantly
attenuated by TCT. The observations that AACOCF3,
transient knock-down of cPLA2 as well as TCT signi-
ficantly protected against the glutamate-induced death
of neural cells implicate cPLA2 as a TCT-sensitive mediator
of glutamate induced neural cell death. The study suggested
that TCT provided neuroprotection through glutamate-
induced changes in cPLA2. Tocotrienols have also been
found to possess neuroprotective activity in animal models
of diabetic neuropathy [103,122,124,170] and alcoholic neu-
ropathy [171,172]. Tocotrienols have been reported to
suppress the proinflammatory pathways in diabetes and
chronic alcoholism, which in turn prevented the ani-
mals from cognitive impairment and oxidative-nitrosative
Positive effects on bone metabolism
Bone is a specialised connective tissue hardened by min-
eralisation with calcium phosphate in the form hydroxy-
apatite ([Ca
). Bone has well recognised
mechanical functions: it provides rigidity and shape,
protection and support for body structures, and aids
locomotion. The rate of bone turnover, collagen matrix,
size, structure, geometry and density all combine to deter-
mine the bones overall mechanical properties. Defects in
these parameters will result in diseases such as osteopor-
osis, Pagets disease of bone, osteoporosis and osteogenesis
imperfecta. In order for the strength of the bone to be
maintained, the process of bone turnover must be care-
fully regulated. Vitamin E and its various forms have been
reported to help in the maintenance of bone metabolism
[104,105,173-182]. Vitamin E supplements reversed nico-
tine-induced bone loss and stimulated bone formation
[173,174]. Tocotrienols are slightly superior to tocopherols
in attenuating the effects of tobacco; γ-tocotrienol espe-
cially may have therapeutic potential to repair bone dam-
age caused by chronic smoking. Other studies have shown
that tocotrienols can reverse glucocorticoid-induced
or free radical-induced bone loss in adrenalectomized
rats [105,175,177] and improve normal bone structure
[175,177,178] possibly through its antioxidant activity
in bone [177,182]. Ima-Nirwana et al. [180] showed that
treatment with γ-tocotrienol (60 mg/kg body weight/day)
reduced body fat mass and increased fourth lumbar ver-
tebra bone calcium content in rats, while a-tocopherol
was ineffective. Therefore, palm-oil derived γ-tocotrienol
has the potential to be utilized as a prophylactic agent in
prevention of the skeletal side effects of long-term gluco-
corticoid and tobacco use (Figure 1).
Gastroprotective effects
Azlina et al. compared the impacts of tocopherols and
tocotrienols on gastric acidity, gastric tissue content of
parameters such as malondialdehyde and prostaglandin
E2, and serum levels of gastrin and glucagon-like peptide-1
in rats exposed to restraint stress. They found that toco-
trienol-treated animals, both stressed and non-stressed,
had comparable gastric acidity and gastrin levels [183].
Both tocopherols and tocotrienols had gastroprotective
effects against damage by free radicals generated in stress
conditions, but only tocotrienols had the ability to block
stress induced changes in gastric acidity and gastrin level.
Another group showed that tocotrienols can prevent
aspirin-induced gastric lesions through their ability to limit
lipid peroxidation [184].
Hepatoprotective activity
Liver the largest glandular organ of the body and the key
organ of metabolism has a pivotal and immense task of
detoxification of xenobiotics, environmental pollutants
and chemotherapeutic agents. Hence this organ is sub-
jected to a variety of diseases and disorders. In the absence
of reliable hepatoprotective drugs in the allopathic (mod-
ern) medicinal system and the wide range of hepatic disor-
ders, dietary antioxidants play an important role in the
management of liver disorders.
Tocotrienol has been extensively studied for its efficacy
against hepatic toxicity. Oral administration of tocotrienols
offered a significant protection against 2-acetylaminofluor-
ene (AAF) induced hepatotoxicity as assessed in terms of
biochemical and histological parameters [113,114]. Toco-
trienols completely normalized the 2-acetylaminofluorene
(AAF) induced increase in the levels of plasma and liver
microsomal gamma-glutamyltranspeptidase (GGT) and
liver microsomal UDP-glucuronyltransferase (UDP-GT)
confirming in vivohepatoprotective activity of toco-
trienols against AAF induced toxicity. Tocopherol and
γ-tocotrienol have been shown to prevent the nitrofur-
antoin induced damage in rat liver when administered
for 10 weeks. The extract characteristically inhibited hep-
atic lipid peroxidation [111]. Tocotrienol also significantly
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 12 of 22
increased the percent viability of cultured rat hepatocytes
prepared from rats treated with diethylnitrosamine (DEN)
and 2-acetylaminofluorene (AAF). Tocotrienol significantly
decreased levels of glutathione S-transferase (GST) and
gamma-glutamyltranspeptidase (GGT) activities in cul-
tured rat hepatocytes at 13 days [116,185]. In addition
to their antioxidant activity, tocotrienols are found to
increase the expression of drug metabolising enzymes
such as cytochrome P450 enzyme (CYP450), UDP-glucuro-
nosyltransferase 1A1 (UGT1A1) and multidrug resistance
protein-1 (MDR1) via the activation of the pregnane-X-
receptor (PXR) and steroid and xenobiotic receptor (SXR),
which are the nuclear receptors that regulate drug clear-
ance in the liver and intestine via induction of genes in-
volved in drug and xenobiotic metabolism, thus increasing
the activity of liver to metabolize the xenobiotics [186,187].
Oral administration of TRF on exercise endurance and
oxidative stress in forced swimming rats caused significant
increase in the concentrations of liver glycogen, SOD,
CAT, and GPx, as well as of muscle glycogen and SOD
than the control and lowered levels of blood lactate,
plasma and liver TBARS, and liver and muscle protein
carbonyl. Taken together, these results suggest that TRF is
able to improve the physiological condition and reduce
the exercise-induced oxidative stress in forced swimming
rats [108].
Organophosphorus insecticides (OPIs) may induce
oxidative stress leading to generation of free radicals and
alteration in antioxidant system of animals. Bhatti et al.
[188,189] conducted a study to investigate the possible
protective role of vitamin E on ethion-induced hepato-
toxicity in rats using qualitative, quantitative and bio-
chemical approaches. The result of their study shows
that in vivo administration of ethion caused a significant
induction of oxidative damage in liver tissue as evi-
denced by increased level of LPO and decreased GSH
content. Ethion toxicity also led to a significant increase
in the activities of SOD, CAT, GPx and GST in liver tissue.
In addition, decrease in GR activity was observed in ethion
administered rats compared to control. Histopathological
findings revealed that exposure to ethion caused damage in
liver tissue. However, simultaneous supplementation with
Figure 1 Mechanistic action of tocotrienols in bone protection. Tocotrienols prevent the increase in expression of TNF-αand nitric oxide
(NO) due to nicotine administration, oxidative stress and inflammation and thus prevent osteoclast formation. Tocotrienols also downregulate the
expression of Receptor activator of nuclear factor kappa-B (RANK) and Receptor activator of nuclear factor kappa-B ligand (RANKL). Osteoporosis
and glucocorticoids also decrease the calcium ion concentration in bone leading to bone desorption. Tocotrienols prevent the desorption of
calcium ions from bone, thus increasing the bone strength. Tocotrienols also increase the expression of interleukin-8 (IL-8), IL-17, granulocyte
colony stimulating factor (G-CSF) which in turn lead to the formation of bone osteoblasts.
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 13 of 22
vitamin E restored these parameters partially. The results
revealed that supplementation of vitamin E exhibited pro-
tective effect by inhibiting ethion-induced toxicity in liver
and erythrocytes. Patel et al. [190] conducted a study to de-
termine the concentrations of TE (200 mg mixed TE, b.i.
d.) and TCP (200 mg alpha-TCP, b.i.d.) in vital tissues and
organs of adults receiving oral supplementation. A total of
eighty participants were studied. Skin and blood vitamin E
concentrations were determined from healthy participants
following 12 wk of oral supplementation of TE or TCP.
Vital organ vitamin E levels were determined by HPLC in
adipose, brain, cardiac muscle, and liver of surgical patients
following oral TE or TCP supplementation (mean dura-
tion, 20 wk; range, 196 wk). Oral supplementation of TE
significantly increased the TE tissue concentrations in
blood, skin, adipose, brain, cardiac muscle, and liver over
time. The alpha-TE was delivered to human brain at a con-
centration reported to be neuroprotective in experimental
models of stroke. In prospective liver transplantation
patients, oral TE lowered the model for end-stage liver
disease (MELD) score in 50% of patients supplemented,
whereas only 20% of TCP-supplemented patients demon-
strated a reduction in MELD score. The results demon-
strated that orally supplemented TE are transported to
vital organs of adult humans. The findings of this study, in
the context of the current literature, lay the foundation for
Phase II clinical trials testing the efficacy of TE against
stroke and end-stage liver disease in humans. All these
findings are very promising and demand the attention
of the scientific community for further exploration and
evaluation of tocotrienols against hepatic toxicity.
Nephroprotective activity
The kidneys are organs that serve several essential regu-
latory roles in vertebrate animals. They are essential in
the urinary system and also serve homeostatic functions
such as the regulation of electrolytes, maintenance of
acidbase balance, and regulation of blood pressure (via
maintaining salt and water balance). They serve the body
as a natural filter of the blood, and remove wastes pro-
duced by metabolism in the form of urine. Just like liver,
kidneys are also susceptible to a variety of diseases and
disorders. Tocotrienols have been reported to possess
significant nephroprotective activity. In one study, the
effects of a long-term treatment with vitamin E (α-toco-
phenol), insulin, or their combination on renal damage
in STZ-induced diabetic rats fed a high cholesterol diet
was investigated. Increases in urinary albumin and lipid
peroxide (LPO) excretions were observed in these dia-
betic rats, when both urinary parameters were measured
at 8 and 15 weeks after STZ administration. Daily treat-
ment with α-tocophenol, insulin, or their combination
markedly suppressed the increase in the 24 h urinary albu-
min and lipid peroxide excretions. Furthermore, glycogen
degeneration of distal tubules, fatty degeneration of glom-
erular endothelium and hypertrophy of glomeruli and
mesangium were observed in the kidneys of the diabetic
animals when histopathological evaluation was perfor-
med at 4, 8, and 15 weeks (glomerular and mesangial
hypertrophy were observed only at 15 weeks). Combined
α-tocophenol (vitamin E) and insulin treatment was the
most effective at suppressing these renal histopathological
changes. Hence, the results indicated that combined vita-
min E and insulin treatment additively prevented the
development and progression of renal damage in diabetic
rats, possibly because of their antioxidant and hypolipid-
emic activity [191].
Tocotrienol (100 mg/kg) as well as TRF (200 mg/kg)
from palm oil and rice bran oil prevents the kidneys
from diabetic nephropathy in streptozotocin-induced
type-1 and high-fat diet/streptozotocin induced type-2
diabetic rats. Diabetic rats produced significant alteration
in renal function, increased oxidative-nitrosative stress,
TNF-alpha, TGF-beta1, caspase-3 activity in cytoplasmic
lysate and active p65 subunit of NF-κB in nuclear lysate of
kidney of diabetic rats. Interestingly, administration of
tocotrienol and TRF from rice bran oil and palm oil sig-
nificantly and dose-dependently prevented biochemical
and molecular changes associated with diabetes. Toco-
trienols modulated the release of profibrotic cytokines,
oxidative stress, ongoing chronic inflammation and
apoptosis and thus exerts a marked renoprotective effect
Tocotrienol also prevents the kidneys from ferric nitri-
lotriacetate (Fe-NTA) toxicity, a well-established nephro-
toxic agent. Pretreatment with tocotrienol (50 mg/kg/day)
for 7 days before Fe-NTA administration in rats signi-
ficantly reduced the serum creatinine and BUN levels,
reduced lipid peroxidation in a significant manner, and
restored levels of reduced glutathione and superoxide
dismutase. Tocotrienol pretreatment also attenuated the
serum tumor necrosis factor-alpha levels and restored
normal renal morphology [192]. TRF from palm oil
(200 mg/kg, bw, orally, once daily for 21 days) was
also found to prevent the kidneys in rats from potassium
dichromate and Fenitrothion (FNT) induced acute renal
toxicity [193,194]. Nowak et al. [195] conducted a study to
determine whether γ-tocotrienol (γT3) protects against
mitochondrial dysfunction and renal proximal tubular cell
(RPTC) injury caused by oxidants. Primary cultures of
RPTCs were injured by using tert-butyl hydroperoxide
(TBHP) in the absence and presence of γT3 or AT. ROS
production increased 300% in TBHP-injured RPTCs. State
3 respiration, oligomycin-sensitive respiration, and respi-
ratory control ratio (RCR) decreased 50, 63, and 47%,
respectively. The number of RPTCs with polarized mito-
chondria decreased 54%. F(0)F(1)-ATPase activity and
ATP content decreased 31 and 65%, respectively. Cell lysis
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 14 of 22
increased from 3% in controls to 26 and 52% at 4
and 24 h, respectively, after TBHP exposure. γT3 blocked
ROS production, ameliorated decreases in state 3 and
oligomycin-sensitive respirations and F(0)F(1)-ATPase ac-
tivity, and maintained RCR and mitochondrial membrane
potential (DeltaPsi(m)) in injured RPTCs. GT3 maintained
ATP content, blocked RPTC lysis at 4 h, and reduced it to
13% at 24 h after injury. Treatment with equivalent con-
centrations of AT did not block ROS production and cell
lysis and moderately improved mitochondrial respiration
and coupling. This is the first report demonstrating the
protective effects of GT3 against RPTC injury by: i) de-
creasing production of ROS, ii) improving mitochondrial
respiration, coupling, Delta-Psi (m), and F(0)F(1)-ATPase
function, iii) maintaining ATP levels, and iv) preventing
RPTC lysis. The data suggested that GT3 is superior to
AT in protecting RPTCs against oxidant injury and may
prove therapeutically valuable for preventing renal injury
associated with oxidative stress.
Radioprotective effects
Radiation-induced toxicity in various tissues is a manifest-
ation of free radicals, oxidative stress, DNA damage [196],
inflammation, [197] and apoptosis [198]. These different
signaling pathways are known to have deleterious effects
in various diseases such as hypertension, diabetes, and
cancer progression [197,199]. Various compounds such
as antioxidants, thiols, antiapoptotic molecules, cyto-
kines and growth factors have been tested against
acute radiation injury [200-202]. Ghosh et al. [203] have
shown that the prophylactic treatment with gamma-
tocotrienol (GT3), 24 h prior to irradiation protects
mice from radiation injury. Radioprotection by GT3 is
associated with reduction of radiation-induced DNA
damage [204] and inhibition of HMGCR-mediated-
nitrosative stress [205]. GT3 is also shown to increase
serum interleukin-6 (IL-6) and G-CSF levels which are
known to stimulate hematopoiesis. Induction of these
cytokines may contribute to radioprotective action of
GT3 [206].
The radioprotective effect of GT3 depends not only on
its antioxidative properties but also on its abilities to
concentrate in endothelial cells and inhibit the enzyme,
3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA)
reductase. HMG-CoA reductase inhibitors are commonly
used in the treatment of hyperlipidemia disorders but
in addition have a plethora of vasculoprotective, anti-
inflammatory and anti-fibrotic effects mediated by endo-
thelial nitric oxide synthase (eNOS, NOS3) [207,208].
In an attempt to enhance the radioprotective efficacy
of GT3, Kulkarni et al. [209] tested the effect of PTX, a
methyl derivative of xanthine, in combination with GT3.
They have shown that the increase in the radioprotective
efficacy of GT3 by combining it with pentoxifylline
(PTX) was due to PDE inhibition, an effect that was
reversed by calmodulin administration [209]. PTX has
similar antioxidant, vasculoprotective, anti-inflammatory
and anti-fibrotic properties and similarly increases eNOS
activity through an increase in intracellular cyclic adeno-
sine monophosphate (cAMP) [210-212].
PTX is an FDA-approved non-specific PDE inhibitor
used for intermittent claudication [213,214]. PTX has been
used alone and in combination with vitamin E (alpha-
tocopherol) in preclinical and clinical studies to reduce
long-term effects of radiation such as fibrosis [215-217].
Beneficial effects of PTX are contributed to its ability to
inhibit proinflammatory cytokine signaling such as tumor
necrosis factor-alpha (TNF-α) accumulation [218]. Accor-
ding to these studies, there was significant reduction in
TNF-αin presence of PTX in early (2 weeks) as well as
late (24 weeks) phase of radiation injury. It was recently
shown that combining PTX with GT3 increased the radio-
protective efficacy of GT3 in protecting mice from acute
radiation injury [218]. These studies indicated that even
though PTX increased the radioprotection in mice treated
with GT3, its mechanism of protection was independent
of endothelial nitric oxide synthase (eNOS). PTX was
shown to increase nitric oxide production [210] by in-
creasing cAMP levels.
Berbee et al. [219] examined the effects of GT3 in
combination with PTX on total body irradiation (TBI)-
induced acute hematopoietic, intestinal and vascular in-
jury and subsequent mortality. They used eNOS-deficient
mice to determine whether protection against lethality
from either drug alone or the combination required the
presence of eNOS. Combined therapy was significantly
more effective in improving postirradiation survival than
treatment with GT3 only, but the effect on postirradiation
lethality did not require the presence of eNOS. Moreover,
their data suggested that administration of GT3 together
with PTX may modulate the hematopoietic radiation
response by the induction of hematopoietic stimuli.
GT3 combined with PTX also reduced postirradiation
intestinal injury and vascular oxidative stress com-
pared to vehicle, but no additional benefit was observed
by the addition of PTX to GT3 compared to treatment
with GT3 alone [219].
Toxicity and dosage
To start with, quoting Paracelsus (14931541 Switzerland),
in all things there is a poison, and there is nothing without
a poison. It depends on only upon the dose whether a
poison is a poison or not. Under dietary considerations,
tocotrienol has been regarded as a safe biomolecule and
experimental studies have also supported this view. There
is no possible report of any adverse reactions caused by
tocotrienol, except that in a study done on experimental
animals in a 13-week oral toxicity study performed in
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 15 of 22
Fischer 344 rats of both sexes at dose levels of 0% (group
1), 0.19% (group 2), 0.75% (group 3) and 3% (group 4) of a
diet preparation in powdered form. On hematological
examination, significant decrease in mean corpuscular
volume (MCV) was observed in all treated males. Platelets
were significantly reduced in group 3 and 4 males. He-
moglobin concentration, MCV, mean corpuscular hemo-
globin and mean corpuscular hemoglobin concentration
were significantly decreased in group 3 and 4 females and
hematocrit in group 4 females. On biochemical examin-
ation, increase in the albumin/globulin ratio (A/G) and
alkaline phosphatase in all treated males, elevated alanine
transaminase in group 4 of both sexes and increases in as-
paragine transaminase and gamma-glutamyl transaminase
in group 4 females were observed. With regard to relative
organ weights, liver weights in group 4 of both sexes and
adrenal weights in all treated males demonstrated an
increase, and ovary and uterus weights in group 4 females
were reduced. A slight hepatocellular hypertrophy in
group 3 and 4 males, and reduction of cytoplasmic vacuol-
ation in the adrenal cortical region in group 4 males were
observed. Because of pathological changes in male liver
and hematological changes in females, the no-observed-
adverse-effect level (NOAEL) was concluded to be 0.19%
in the diet (120 mg/kg for male rats and 130 mg/kg body
weight/day for female rats) [220]. Since, most of the stud-
ies have been in favor of tocotrienols, however, it needs to
be replicated in human populations to evaluate the safety
and efficacy of tocotrienols as a therapeutic agent or drug.
There are convincing evidence that tocotrienols are
detectable at appreciable levels in the plasma after short
term and long term supplementations. However, there is
insufficient data on the range of plasma concentrations
of tocotrienols that are adequate to demonstrate signifi-
cant physiological effects. Although the pharmacokinetics
of tocotrienols are distinctly different from tocopherols
which are well studied and remained longer in blood cir-
culation, biodistribution study showed considerable accu-
mulation of tocotrienols in vital organs. In the perspective
of therapeutic efficacy, it is evident that the outcome of
clinical evaluations is not only affected by the bioavail-
ability of tocotrienols. In view of the limited understand-
ing, more studies on the mechanisms of absorption are
essential [221].
In an effort to determine the therapeutic window for
tocotrienols, a number of long term clinical studies have
been carried out using TRF and tocotrienol derivatives.
The majority of these trials were focused on lipid profile
as tocotrienols were found to inhibit HMG-CoA reductase
[76-78]. However, the optimum dosing regimen to induce
therapeutic effects remained unclear.
Although most studies were conducted in rodents and
animals, they serve as a basis for clinical evaluations to
establish their health benefits in humans. A number of
clinical trials were conducted to examine the multi-
faceted health benefits of tocotrienols in different popu-
lations. The bioavailability and efficacy of TRF may vary
in different populations. tocotrienols seem to respond
differently to a range of age groups but did not show
consistent efficacies in the target study populations.
Most of the studies conducted in patients with chronic
diseases had relatively small sample size. This demon-
strates the need to conduct randomized controlled trials
in larger population to confidently evaluate the thera-
peutic potentials of tocotrienols [221].
Patel et al. [190] have determined the concentrations
of TE (200 mg mixed TE, b.i.d.) and TCP [200 mg a-TCP,
b.i.d.)] in vital tissues and organs of adults receiving oral
supplementation. Skin and serum vitamin E concentra-
tions were determined from healthy participants following
12 wk of oral supplementation of TE or TCP. The vitamin
E levels in vital organ were determined by HPLC in adi-
pose, brain, cardiac muscle, and liver of surgical patients
following oral TE or TCP supplementation (mean dura-
tion, 20 wk; range, 196 wk). Oral supplementation of TE
significantly increased the TE tissue concentrations in
blood, skin, adipose, brain, cardiac muscle, and liver over
time. a-TE was delivered to human brain at a concen-
tration reported to be neuroprotective in experimental
models of stroke. The finding of the study is the foun-
dation for Phase II clinical trials testing the efficacy of TE
against stroke and end-stage liver disease in humans
[190]. Their work provides the first evidence on tissue
availability of TE in vital organs of adult humans following
oral supplementation to characterize multiple vital organ
concentration of TCP in adults. TE was delivered and
accumulated in vital human organs supports future stud-
ies to identify specific mechanisms of tissue delivery and
metabolism. The outcomes of this work provide clear
evidence that oral TE supplementation enriches its
concentration in whole blood, adipose, skin, brain, cardiac
muscle, and liver [190].
In recent years, the basic research on vitamin E has
expanded from primarily focusing on αT and its anti-
oxidant effects to investigation of different tocoph-
erols and tocotrienols, their metabolism, and their
non-antioxidant activities including anti-inflammatory
properties. Despite well-documented beneficial effects
[3,220], as well as negative association between αTintake
and chronic diseases, supplementation with αT has failed
to offer consistent benefits for the prevention of chronic
diseases, including cancer and cardiovascular diseases, in
many large clinical intervention studies [4,5,222,223]. αT
may be beneficial to individuals with deficiency of αTand/
or other micronutrients [220], that can be caused by low
dietary intake of this vitamin E or depletion of αTdueto
Ahsan et al. Nutrition & Metabolism 2014, 11:52 Page 16 of 22
pathological condition or malnutrition associated with
smoking, alcoholism, and malabsorption. Under these
subclinical conditions, αT supplementation is likely to be
beneficial, as indicated in the Linxian study in a popu-
lation with deficiencies of micronutrients [224] and the
ATBC study including heavy smokers [225]. On the other
hand, αT supplementation did not show beneficial effects
in people with adequate nutrient status [4,5].
In contrast to αT, despite no evidence that deficiency
of other vitamin E forms would result in obvious clinical
symptoms, accumulating evidence suggests that γT, δT,
and tocotrienols seem to have unique properties that are
superior to αT and relevant to prevention and therapy
against chronic diseases even under conditions with ad-
equate αT status. It is noteworthy that these bioactivities of
tocopherols and tocotrienols including anti-inflammatory
properties have been identified by mechanistic studies and
subsequently substantiated in some preclinical models as
well as clinical studies [44].
Hence, tocotrienols possess neuroprotective, antioxi-
dant, anti-cancer and cholesterol lowering properties.
Tocotrienols are thought to have more potent antioxidant
and free radical scavenging properties due to their better
distribution in the lipid layers of the cell membrane. In
spite of the promising potential, the experimental analysis
of tocotrienols accounts for only a small portion of vita-
min E research. However, recent studies have enforced a
serious reconsideration of this conventional perception
and this review article will go a long way in reiterating
research pursuit.
Competing interests
The authors declare that they have no competing interests.
HA drafted the script and collected literature on the subject. AA collected
and compiled the relevant information. JI contributed with critical
assessment on the subject based on published work in the area. WAS
participated in collection of data, manuscript preparation and final drafting.
All authors read and approved the final manuscript.
The authors wish to acknowledge the reviewers for their evaluation,
comments and suggestions for improving the manuscript
Author details
Department of Biochemistry, Faculty of Dentistry, Jamia Millia Islamia, New
Delhi 110025, India.
Department of Biochemistry, Jamia Hamdard (Hamdard
University), New Delhi 110062, India.
Department of Cell Biology and
Pediatrics, SUNY Downstate Medical Center, Brooklyn, NY 11203, USA.
Received: 4 June 2014 Accepted: 15 October 2014
Published: 12 November 2014
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Cite this article as: Ahsan et al.:Pharmacological potential of tocotrienols:
areview.Nutrition & Metabolism 2014 11:52.
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