Aspalathin a unique phytochemical from the South African rooibos plant (Aspalathus linearis): A mini Review

Abstract

Aspalathus linearis (rooibos) is a plant which grows in a limited habitat in South Africa. The plant is mainly renowned for the beverage (herbal tea) which is made from its aerial parts. The popularity of the herbal tea is not confined to South Africa as significant amounts of the tea are exported to many countries worldwide. Rooibos reportedly has several health benefits which have been attributed to its constituent phytochemicals. One of the major phytochemicals in rooibos is aspalathin. Aspalathin makes up between 4-12% of the plant. Aspalathin is a dihydrochalcone glycoside which has thus far only been isolated from Aspalathus linearis. Aspalathin has been shown to possess biological activity which imparts it with multiple health beneficial effects. This mini review highlights the recent findings on the biological properties of aspalathin. These include antioxidant, antidiabetic, cardioprotective, antihypertensive and antimutagenic effects. Given its multiplicity of biological effects, aspalathin is a natural phytochemical which has potential to be incorporated into current medical therapeutic regimes in light of recent preferences for the use of natural medicines.

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J. Afr. Ass. Physiol. Sci 5 (1): 1-6, July 2017
Journal of African Association of Physiological Sciences
Official Publication of the African Association of Physiological Sciences
http://www.jaaps.aapsnet.org
Minireview
Aspalathin a unique phytochemical from the South African
rooibos plant (Aspalathus linearis): A mini Review
K.H. Erlwanger1* and K.G. Ibrahim1,2
1School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown 2193,
Johannesburg, South Africa and 2Department of Physiology, College of Health Sciences, Usmanu Danfodiyo
University, P.M.B. 2254, Sokoto, Nigeria
Keywords:
Rooibos, Aspalathus
linearis, aspalathin,
flavonoid, biological
activity, antioxidant,
antidiabetic,
cardioprotection.
ABSTRACT
Aspalathus linearis (rooibos) is a plant which grows in a limited habitat in South Africa. The
plant is mainly renowned for the beverage (herbal tea) which is made from its aerial parts. The
popularity of the herbal tea is not confined to South Africa as significant amounts of the tea are
exported to many countries worldwide. Rooibos reportedly has several health benefits which
have been attributed to its constituent phytochemicals. One of the major phytochemicals in
rooibos is aspalathin. Aspalathin makes up between 4-12% of the plant. Aspalathin is a
dihydrochalcone glycoside which has thus far only been isolated from Aspalathus linearis.
Aspalathin has been shown to possess biological activity which imparts it with multiple health
beneficial effects. This mini review highlights the recent findings on the biological properties
of aspalathin. These include antioxidant, antidiabetic, cardioprotective, antihypertensive and
antimutagenic effects. Given its multiplicity of biological effects, aspalathin is a natural
phytochemical which has potential to be incorporated into current medical therapeutic regimes
in light of recent preferences for the use of natural medicines.
INTRODUCTION
Aspalathus linearis
The legume Aspalathus linearis is confined to the
north-western to western region of the Fynbos biome in
the Cape Floristic Region of South Africa (Hawkins et
al., 2011; Lötter and le Maitre, 2014). ‘Rooibos’ is a
term used when making reference to the plant or to the
herbal beverage (tea) made from the plant (Hawkins,
Malgas and Biénabe, 2011). Whilst there is limited
harvesting of wild uncultivated rooibos, it is also
cultivated and grown commercially. Hawkins et al.,
(2011) have described in detail the ecotypes and
ecology of the plant. Apart from the beverage which is
made from rooibos, it has found use in several other
products such as soaps, cosmetics and skin lotions
(Chuarienthong et al., 2010).
There are several reports on the health benefits of
rooibos. The earliest reports of its use are from the late
1700s when the local Khoi-Khoi people were observed
using the plant medicinally (Gadow et al., 1997).
Subsequent research has confirmed the health benefits
of rooibos. It has been shown to have antidiabetic and
hypoglycaemic effects (Jin et al., 2013; Kamakura et
al., 2015; Van Der Merwe et al., 2015; Mahmood et
al., 2016), antioxidant (Canda et al., 2014) as well as
anti-HIV effects in vitro (Nakano et al., 1997). In
addition, rooibos also has demonstrated anti-
inflammatory effects (Baba et al., 2009), it has been
shown to reduce colitis and modulate immune function
in vitro (Hendricks and Pool, 2010) as well as in vivo
where it has been shown to promote antigen-specific
antibody production through augmentation of
interleukin-2 production (Kunishiro et al., 2001). The
bronchodilatory effects of rooibos have been attributed
to the phytochemical chrysoeriol which also has
antispasmodic, antiviral and antimicrobial effects
(Khan and Gilani, 2006). The chemoprotective effects
of rooibos have been demonstrated in rat liver using the
cancer initiator diethylnitrosamine (Marnewick et al.,
2009). Rooibos is further reported to have
anticarcinogenic and antiallergic activities (Standley et
© Copyright 2017 African Association of Physiological Sciences -ISSN: 2315-9987; e-ISSN: 2449-108X All rights reserved
*Address for correspondence:
E-mail: Kennedy.Erlwanger@wits.ac.za

Aspalathin: A unique phytochemical from Aspalathus linearis
2 J. Afr. Ass. Physiol. Sci. 5 (1): July, 2017 Erlwanger and Ibrahim
Fig.1. Chemical structure of aspalathin.
Source: Pubchem. Weblink https://pubchem.ncbi.nlm.nih.gov/compound/11282394#section=Top
al., 2001; Marnewick, 2010). The multiplicity of effects
of rooibos is attributed to its constituent
phytochemicals.
Phytochemicals in rooibos
The plant contains several biologically active
phytochemicals which include polyphenols and
flavonoids (McKay and Blumberg, 2007).
Phytochemicals isolated from rooibos include
isoorientin, orientin, chryoseriol, isovitexin, nothofagin,
rutin, isoquercetin and hyperoside (McKay and
Blumberg, 2007). There are several recent studies
which provide further detail on the phytochemicals in
rooibos (Ligor et al., 2008; Breiter et al., 2011; Joubert
and de Beer, 2011). It is important to note that
processing the rooibos eg fermentation significantly
reduces the content of some of the phytochemicals
including aspalathin. It has been reported that
fermentation oxidizes over 90% of the aspalathin
mainly to dihydro-iso-orientin (Perold, 2009).
Unfermented rooibos is called green rooibos whilst the
fermented form is called red rooibos.
There are numerous studies on the health benefits of
crude and purified extracts of rooibos however the
focus of this review will be specifically on aspalathin, a
flavonoid which is uniquely found in rooibos (Van Der
Merwe et al., 2015). Aspalathin constitutes about 4-
12% of the dry rooibos plant material (Gadow et al.,
1997; Kreuz et al., 2008).
Aspalathin
Structurally aspalathin is a C-linked dihydrochalcone
glycoside. The molecular formula for aspalathin is
C21H24O11. The biochemical structure is shown in figure
1 above.
Gastrointestinal and skin absorption of aspalathin
A study using pigs, showed that aspalathin was
absorbed as a C-glycoside (Kreuz et al., 2008). Liquid
chromatography-mass spectrometry identified in urine,
metabolites of aspalathin which were “methylated
aspalathin, glucuronidated and methylated aspalathin, a
glucuronidated aglycone of aspalathin, as well as a
metabolite of eriodictyol” (Kreuz et al., 2008).
In vitro studies with intestinal epithelial Caco-2 (human
epithelial colorectal adenocarcinoma) cells showed that
absorption was dose dependant (Huang et al., 2008).
However, percutaneous studies using human abdominal
skin cells showed that less than 0.01% of the initial
dose was transported across the skin (Huang et al.,
2008). Thus the cutaneous absorption is significantly
lower than absorption from the gastrointestinal tract.
Biological activity of aspalathin
Antidiabetic effects
Aspalathin has shown potential for use as an
antidiabetic agent due to its glucose lowering effect
(Han et al., 2014). Aspalathin from green rooibos tea
was found to prevent postprandial hyperglycaemia by
suppressing glucose absorption and inhibiting
carbohydrate hydrolyzing enzymes (Mikami et al.,
2015). When KK-Ay type 2 diabetic mice were fed
with aspalathin rich green rooibos extract for five
weeks, it suppressed increases in plasma glucose
(Kamakura et al., 2015). An in vitro study by the same
investigators also showed green rooibos to increase
uptake of glucose and induce phosphorylation of 5Ꞌ
adenosine monophosphate protein kinase (AMPK) in
L6 myotubes (Kamakura et al., 2015). In mice with
impaired glucose tolerance, aspalathin improved

Aspalathin: A unique phytochemical from Aspalathus linearis
3 J. Afr. Ass. Physiol. Sci. 5 (1): July, 2017 Erlwanger and Ibrahim
glucose tolerance (Kawano et al., 2009). Aspalathin
was further shown to reduce hyperglycaemia induced
vascular inflammation in rats by reducing
hyperpermeability and expression of cell adhesion
molecules (Ku et al., 2014). In the same study
aspalathin was noted to decrease activation of nuclear
factor (NF)-κB in vivo (Ku et al., 2014).
Antioxidant effects
Aspalathin showed high antioxidant capacity when it
was compared with other flavonoids in rooibos using
ABTS [2,2′-Azino-bis(3-ethylbenzothiazoline-6-
sulfonic acid) diammonium salt] radical cation, metal
chelating and Fe (II)-induced microsomal lipid
peroxidation assays (Snijman et al., 2009). When
rooibos was administered to rats ad libitum, it
suppressed the accumulation of lipid peroxides in the
brain, which is usually associated with ageing (Inanami
et al., 1995). Rooibos tea also partially prevented
oxidative stress in streptozocin-induced diabetic rats
(Ulicna et al., 2006). Recently aspalathin rich tea was
shown to decrease oxidative stress induced by
immobilization of rats. Several mechanisms were
proposed including the restoration of stress induced
protein degradation, regulation of glutathione and
modulation of superoxide dismutase and catalase, both
of which are antioxidant enzymes (Hong et al., 2014).
However, a study in which aspalathin enriched green
roobios extracts were fed to rats for up to 90 days
showed that blood monitoring in the assessment of
biosafety of phytochemicals is not sensitive and
specific and hence there is need to use molecular
techniques e.g. Quantitative Real Time polymerase
chain reaction analysis, to investigate gene expression
and the activity of regulatory proteins (Van Der Merwe
et al., 2015). By these means the authors observed that
the aspalathin enriched green rooibos extracts caused
some oxidative stress and possibly biliary dysfunction
(Van Der Merwe et al., 2015). The implications of this
finding need further investigation.
Antihypertensive effects
In vitro, aspalathin-rich rooibos tea caused a significant
increase in the production of nitric oxide (Persson et
al., 2006) in human endothelial cells; however,
compared to green tea (Camillia sinensis) it was shown
to not have any effect on angiotensin converting
enzyme (ACE) in vitro, a finding which was attributed
to it lacking catechins (Persson et al., 2006).
Interestingly in vivo, in a randomized three-phase cross
over study, rooibos tea was shown to have a 6%
inhibitory activity (vs 16% for chronic enalpril) of
angiotensin converting enzyme in healthy volunteers
(Persson et al., 2010). The findings may be related to
the impact of NO on ACE. Further noteworthy
findings from the study were that there were
differences in responses to the interventions based on
ACE genotype whereby individuals with genotypes II
and ID showed a significant inhibition of ACE activity
following the drinking of rooibos tea with aspalathin,
whereas those with ACE genotype DD were less
responsive (Persson et al., 2010). Thus it is important
to note that genotypes may play a role in responses to
prophylactic and therapeutic interventions and hence
stresses the importance of the need for greater use of
personalized medicine which takes individual
variability into account in the provision of treatments
(Collins and Varmus, 2015).
Anti-obesity effects
Aspalathin from rooibos showed potential as a weight
loss inductive agent with associated reduction in food
intake (Mahmood et al., 2016). Whilst boiled
fermented rooibos tea was shown to decrease leptin
secretion, inhibit adipogenesis and alter the metabolism
of adipocytes in vitro, the phytochemical profile
showed the extracts to contain mainly isoorientin,
orientin, quercetin-3-O-robinobioside and enolic
phenylpyruvic acid-2-O-β-d-glucoside (Sanderson et
al., 2014). Thus due to processing (fermentation) it is
likely that aspalathin was oxidized as described in an
earlier section of this review and thus unlikely to have
contributed to the anti-obesity effects noted.
Cardio-protective effects
Asapalathin has been shown to protect isolated
cardiomyocytes from hyperglycaemia-induced
metabolic substrate shifts and apopotosis (Dludla et al.,
2017). The possible mechanisms were elucidated using
an H9c2 cardiomyocyte model (Johnson et al., 2016).
Aspalathin modulated several key lipid metabolism
regulators and mechanistically it activated Adipoq
while modulating the expression of the glitazone
receptor peroxisome proliferator-activated receptor
gamma (PPARG and Srebf1/2. Inflammation was
decreased through the proinflammatory IL-6 cytokine
and Jak2 signaling pathway. In addition, the expression
of Bcl2 (aregulator proteins for cell death) was
increased thus preventing apoptosis of the myocardium
(Johnson et al., 2016).
Hypouricaemic effects
The hypouricaemic activity of aspalathin-rich fraction
and purified aspalathin from rooibos on mice was
investigated. These polyphenols significantly
suppressed increased plasma uric acid concentration in
a dose dependent manner (Kondo et al., 2013).
Antimutagenic effects
The antimutagenic effects of rooibos have been
explored and demonstrated in murine experimental
models. Using a Salmonella typhimurium mutagenicity
assay, it was shown that aspalathin showed mild

Aspalathin: A unique phytochemical from Aspalathus linearis
4 J. Afr. Ass. Physiol. Sci. 5 (1): July, 2017 Erlwanger and Ibrahim
antimutagenic activity (Snijman et al., 2007). Topical
application of aspalathin rich green rooibos tea extracts
significantly inhibited tumorigenesis in ICR mice
(Marnewick et al., 2005). Further investigations using
other tumours are necessary.
CONCLUSION
Rooibos is an important plant in the economy of South
Africa. Given the popularity of rooibos as a herbal tea,
and the increasing use of rooibos extracts in cosmetics,
it is important that more research be undertaken on its
long term effects. Aspalathin which is one of the major
phytochemicals in rooibos has been shown to have
multiple health benefits and impacts several organs.
Given its multiple targets, there is need to also explore
the potential adverse effects of aspalathin.
The developmental origins of health and disease have
now been well established wherein interventions and
events in early life (conception, gestation and neonatal
periods) can impact health outcomes later in life
(Gillman, 2005). Phytochemicals are increasingly
gaining prominence as prophylactics, and as therapeutic
interventions for many diseases. For example, a recent
study showed that resveratrol administered to lactating
mice attenuated hepatic lipid synthesis in the offspring
when they were adults (Tanaka et al., 2017). We have
also shown that neonatal administration of oleanolic
acid also prevented lipid accumulation in high fructose
diet-induced metabolic dysfunction (Nyakudya et al.,
2017). In light of the popularity of rooibos, there is
need to investigate whether consumption of aspalathin
during periods of developmental plasticity can induce
intergenerational health (or disease) outcomes through
epigenetic changes.
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