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Phytochemistry Reviews
Fundamentals and Perspectives of
Natural Products Research
ISSN 1568-7767
Volume 12
Number 4
Phytochem Rev (2013) 12:581-602
DOI 10.1007/s11101-013-9323-3
Aloe barbadensis: how a miraculous plant
becomes reality
Nuria Chinchilla, Ceferino Carrera,
Alexandra G.Durán, Mariola Macías,
Ascensión Torres & Francisco A.Macías
1 23
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Aloe barbadensis: how a miraculous plant becomes reality
Nuria Chinchilla •Ceferino Carrera •
Alexandra G. Dura
´n•Mariola Macı
´as •
Ascensio
´n Torres •Francisco A. Macı
´as
Received: 1 July 2013 / Accepted: 28 August 2013 / Published online: 11 September 2013
ÓSpringer Science+Business Media Dordrecht 2013
Abstract Aloe barbadensis Miller is a plant that is
native to North and East Africa and has accompanied
man for over 5,000 years. The aloe vera plant has been
endowed with digestive, dermatological, culinary and
cosmetic virtues. On this basis, aloe provides a range
of possibilities for fascinating studies from several
points of view, including the analysis of chemical
composition, the biochemistry involved in various
activities and its application in pharmacology, as well
as from horticultural and economic standpoints. The
use of aloe vera as a medicinal plant is mentioned in
numerous ancient texts such as the Bible. This
multitude of medicinal uses has been described and
discussed for centuries, thus transforming this miracle
plant into reality. A summary of the historical uses,
chemical composition and biological activities of this
species is presented in this review. The latest clinical
studies involved in vivo and in vitro assays conducted
with aloe vera gel or its metabolites and the results of
these studies are reviewed.
Keywords Aloe vera Phytochemistry
Acemannan Bioactivity
Introduction
The genus Aloe is a plant that has always been
included in the Asfodelaceas and lily families. How-
ever, in view of their specific and individual charac-
teristics, Aloe has been introduced into a new botanical
family named Aloaceas. This family consists of more
than 350 species of Aloes registered throughout the
world, and new families are discovered each year:
from the small Aloe rockery stemless, measuring a few
centimeters, to the Aloe arborescent, which can
measure several tens of meters (Bassetti and Sala
2001). However, not all of these species are medicinal.
The best known Aloes are Aloe vera (Aloe barbadensis
Miller), Aloe Socotra Island (Aloe soccotrina Gar-
sault), Cape Aloe (Aloe ferox Miller), Aloe maculate
Forssk (Aloe saponaria), Aloe chinensis Steud. ex
Baker and Aloe arborescens Miller, all of which have
steely barbed characteristics. The most commonly
used examples in medicine are the species A.
N. Chinchilla C. Carrera A. G. Dura
´n
A. Torres F. A. Macı
´as (&)
Grupo de Alelopatı
´a, Departamento de Quı
´mica Orga
´nica,
Facultad de Ciencias, Instituto de Biomole
´culas (INBIO),
Universidad de Ca
´diz, Campus de Excelencia
Internacional Agroalimentario (ceiA3), C/Repu
´blica
Saharaui, s/n, 11510 Puerto Real, Ca
´diz, Spain
e-mail: famacias@uca.es
M. Macı
´as
Departamento de Biomedicina, Biotecnologı
´a y Salud
Pu
´blica (Inmunologı
´a) y Unidad de Investigacio
´n del
Hospital Universitario de Puerto Real, Servicio Central de
Investigacio
´n en Ciencias de la Salud, Instituto de
Biomole
´culas (INBIO), Edificio Andre
´s Segovia,
C/Dr. Maran
˜o
´n 3, 11002 Ca
´diz, Ca
´diz, Spain
123
Phytochem Rev (2013) 12:581–602
DOI 10.1007/s11101-013-9323-3
Author's personal copy
barbadensis Miller, from which aloe gel and the bitter
yellow exudates are obtained, and A. ferox Miller,
which provides a bitter yellow juice.
All Aloe species are perennial, leaf-succulent
xerophytes (Newton 2001). Xerophytes are plants
adapted to survive in areas of low or erratic precip-
itation and the adaptations may include structural and
physiological features. Aloes have thick and fleshy
leaves that are enlarged to accommodate the aqueous
tissue. The leaf cuticle is thick and is covered with a
layer of wax. Most species have groups of cells
associated with the vascular bundles, variously called
aloin or aloitic cells, which store and perhaps secrete a
mixture of compounds with medicinal value. The
composition of these secretions varies in different
species. This substance appears as an exudate, which
is usually yellow, when leaves are broken or cut.
Leaves of a few species, such as Aloe fibrosa Lavranos
and Newton, have fibers in place of the aloitic cells
(Reynolds 2004).
The exact origin of Aloe vera is uncertain, but it
seems likely that it is from the Arabian Peninsula,
home of the closely related, and possibly conspecific,
Aloe officinalis Forssk. The majority of Aloe species
occur naturally on mainland Africa in tropical and
subtropical latitudes. The genus is found almost
throughout the African continent south of the Sahara
Desert, except for the moist lowland forest zones and
the western end of West Africa. The majority of
species occur in southern Africa and on the eastern
side of the continent. Many other species are found on
the Arabian Peninsula and on Madagascar and a few,
mostly formerly in the genus Lomatophyllum, are
known on some of the smaller Indian Ocean islands.
The Arabian species have clear relationships with the
species of northeast Africa. Madagascan species do
not appear to be closely related to those of mainland
Africa and so active speciation seems to have occurred
since the separation of these two land masses.
Likewise, the former Lomatophyllum species form a
group that is not represented on the African mainland.
Some species are very widespread in terms of
distribution. Reynolds cites Aloe buettneri A.Berger
as the most widespread species, with a range of at least
5,600 km from Mali to Zambia, and the species has
since been recorded in Namibia (Reynolds 1966).
However, Carter regards this as a West African species
only, with two related species in the rest of the range
reported by Reynolds (Carter 1994). Another very
widespread species is Aloe myriacantha Haw., with a
range of about 4,800 km from Kenya and Uganda to
the Republic of South Africa. Most other widespread
species have more modest distribution ranges,
amounting to only hundreds of kilometers. Many
countries have some endemic species. The highest rate
of endemism is in Madagascar and isolated Indian
Ocean islands. Naturally, it is to be expected that very
large countries, such as South Africa and isolated
islands, such as Madagascar, would have many
endemic species. The actual species’ distribution has
been suggested to be the result of human cultivation
(Fig. 1) (DiscoverLife 2013).
Aloe barbadensis is native to Africa and spread to
America after expeditions by Columbus and Vespucci
owing to maritime trade with the Caribbean. The hot
and humid climate of Central America greatly favors
the good diffusion of this species, especially in the
Caribbean islands, from which its present name
barbadensis arises since it originates from Barbados.
The correct name is now accepted to be Aloe vera (L.)
Burm. f. (Vinson et al. 2005). However, the plant has
been known under various names such as Aloe vera,
sa
´bila, Curacao Aloe, A. barbadensis Miller or collo-
quially as Aloe (Reynolds 2004). The first important
plantations date from 1870 but it was not until 1920 that
this plant was used on a larger scale. Since then this
species exploded on a small scale for the extraction of
leaf exudates. A. barbadensis is currently the most
widely used type of Aloe and it is known worldwide.
This is mainly due to the high efficiency of the leaves,
to its robustness and ease of pulping for drinks or gels
for external use. In fact, the active ingredients in this
famous strain cannot be compared, in quantitative
terms, to other smaller varieties that are rare and have
hardly been exploited from an industrial viewpoint.
Currently the high demand for natural products has
triggered a boom in the ‘biological’ properties and
around it a growing industry seeks to sell all manner of
low cholesterol, low fat, low calorie, high fiber,
omegas, vitamins, etc. The current desire for healthy
products has created a new language in which the word
‘bio’ has flooded the market. As a consequence, prior
to the proliferation of products that employ this term in
a misleading manner, the authorities forced the
removal the word ‘bio’, which can only be applied
when the production is carried out in a completely
ecological manner. Aloe vera has not escaped this
phenomenon as the number of companies involved in
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the sale of products derived from this plant has
increased markedly and many other completely unre-
lated companies have taken advantage of this demand
to offer yogurts, ice creams, perfumes, mattresses,
t-shirts, and even acrylic paint with aloe vera.
Regardless of the consumerist frenzy that inevitably
unleashes all fads, the aim of this review is to unravel
what is true and false about this plant, which some
people consider to be almost miraculous, because if it
is true that all fashions are passing, it is not a
coincidence that all the great ancient cultures knew
and used the healing properties of aloe vera.
Historical aspects and traditional uses
Long known for its mysterious beauty, wild elegance
and legendary therapeutic properties, aloe vera was
considered as a god in some civilizations. In ancient
Egypt, aloe was the plant whose ‘blood’ offered
beauty, health and eternal life. Aloe was part of the
ritual of embalming and accompanied the Pharaoh on
his journey to the other world. For mythical emperors
of China, aloe’s healing thorns personified the sacred
nails of Divinity. For the Indians of the New World,
aloe was one of the 16 sacred plants worshiped as
gods. In Africa, the camel-herding nomads called it the
‘lily of the desert’, the Americans ‘the silent healer’ or
‘Doctor Aloe’, and Russians the ‘elixir of life’,
amongst others.
The name Aloe vera is derived from the Arabic
word alloeh, which means ‘shining bitter substance’,
while vera in latin means ‘truth’. The first credible
human testimony concerning aloe was found in Egypt,
from about 3000 BC, and this consists of pictorial
representations adorning tombs and funerary monu-
ments. The oldest epigraphic document concerning the
medicinal use of aloe vera appears on baked clay
tablets from Sumeria, and these were written before
2100 BC and they describe in cuneiform the laxative
properties of the plant. Despite the fact that aloe has
been cited in previous texts, such as the codices of
Emperor Shon-Nung (about 1800 BC) or Babylonian
tablets from the same era, the Ebers papyrus or
Egyptian Book Remedies (1550 BC) are considered to
be the first medical compendium to contain formulas
for making elixirs with aloe juice (Swanson 1995).
Aloe also had the reputation of being able to
preserve beauty and women’s splendor in ancient
Egypt. The Pharaohs considered it to be an elixir of
long life. Tradition demanded that a staff of aloe was
carried as a symbol of rebirth as a present during
funeral ceremonies. Aloe was planted around the
pyramids and along the roads leading to the Valley of
the Kings and it accompanied the Pharaoh in his transit
to the afterlife in order to care for and feed him during
Fig. 1 Global distribution of A. barbadensis and A. ferox
Phytochem Rev (2013) 12:581–602 583
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his journey. When aloe bloomed, it was taken as a sign
that the deceased had happily reached the ‘other shore’
(Schweizer 1994).
Moreover, aloe was a symbol of beauty, patience,
luck and health for the Greeks. Hippocrates described
some medicinal properties of aloe, including the
ability to promote hair growth, as a cure for tumors
and for the relief of dysentery and stomach-ache. For
the Egyptians, aloe was considered as the plant of
immortality and today it is still considered to be an
emblem of happiness and protection and is often found
in the inside of houses to absorb negative energies.
Recent studies have shown that the aloe plant is
capable of removing more than 94 % of formaldehyde
in a closed space in just 4 days and it also shows
excellent absorption power against volatile organic
compounds, which are major components of environ-
mental pollution (Yau et al. 2011).
It is believed that, around 330 BC, Alexander the
Great was shot with an enemy arrow in the siege of
Gaza (Palestine). He saw how his wound became
infected during the conquering advance through Egypt
and the Libyan Desert. A priest sent by the celebrated
Aristotle (his tutor and mentor), smeared the wound
with an oil made from aloe that came from the island
of Socrota. His injury was cured. It seems that
Alexander the Great undertook a naval expedition to
take over Socrota’s Island and its aloe plantations with
the encouragement of Aristotle. Indeed, it was even
claimed that the juice of this plant made warriors
invulnerable (Evans 1989).
Since the earliest times, in the Middle East and
Africa, the Bedouin people from the Arabian Penin-
sula and the Tuareg warriors from the Sahara called
aloe the ‘Desert Lily’. In order to protect their homes,
the inhabitants of Mesopotamia decorated their doors
with aloe leaves. In case of an epidemic or famine,
Parsees and the Scythians had the custom of feeding
on aloe pulp.
It was not until the middle Ages and the Renais-
sance when Christian warriors discovered the proper-
ties of aloe during the Crusades as it was considered to
be a panacea for their Muslim adversaries. Arabs
introduced aloe into Andalusia during their conquests
in Europe. The Muslim name for aloe is saber and this
signifies patience, a term that refers to the period
between burial and resurrection (Grieve 1998).
The use of aloe pulp enabled Spanish sailors to be
partially protected from diseases and malnutrition.
These properties led Christopher Columbus to call it
the ‘potted doctor’. Consequently, the Spanish always
transported aloe aboard their ships. Paracelsus, the
great physician of the Renaissance period, discovered
the merits of aloe in Salerno and this reputation was
later exported to Spain and Portugal. Paracelsus sent a
letter in which he refered to aloe in veiled words such
as ‘mysterious and secret aloe whose golden aloe juice
cures burns and blood poisoning’. In particular,
Portuguese and Spanish Jesuits, following in the
footsteps of the early explorers, cultivated aloe in all
of the colonies of America, Africa and the Far East as a
plant that had known curative properties.
In Japan aloe is known as a ‘queen plant’. Tens of
species are cultivated for multiple uses. The plant
extracts are made into drinks and food due to the
medicinal properties of the plant in all its forms. In
ancient times, the samurai body was smeared with the
pulp of aloe before a battle in order to expel demons
and to make the warriors immortal. Nowadays, A.
saponaria pulp is used to make soaps and cosmetics.
Likewise, A. ferox,Aloe thraskii Baker and Aloe
marlothii A.Berger are used as components in numer-
ous pharmaceutical and cosmetics preparations.
Aloe is used in a wide range of forms in China. The
Chinese pharmacopoeia of Li Shih-Shen (1518–1593)
cites aloe amongst the plants with the highest thera-
peutic properties and it was called the ‘harmony
remedy’.
This multipurpose plant has been used since time
immemorial and today it is still used extensively
worldwide and has become a popular household
remedy, exhibiting a range of beneficial health-
promoting properties. The traditional use of natural
ingredients, which was largely based on empirical
evidence and folk medicine recipes, has been com-
pletely updated and scientifically validated by recent
bench and clinical research. An increasing body of
scientific data now supports the use of aloe in various
clinical settings and new indications are continuously
emerging. All of these findings may help to provide a
foundation for further studies and the development of
more controlled processing and applications for this
widely accepted medicinal plant.
A review of historical aspects and traditional uses
of this coveted ethnomedicinally and pharmacology
important species is presented along with a discussion
of the chemical composition and biological properties.
These ‘new naturals’ are expanding our choices for the
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management and treatment of different disorders on an
ongoing basis, with new and emerging usage and
research data supporting their strong reputation as safe
and effective options.
Chemical composition
The aloe plant has elongated and pointed leaves. Each
leaf consists of two parts, an outer green rind and an
inner clear pulp. The pulp is the major part of the leaf
by volume and it appears to be clear and mucilaginous.
It is this part of plant that has been most widely used
for therapeutic purposes. Acemannan Immunostimu-
lan
tk
, a pulp extract rich in mannan, has been licensed
for the treatment of fibrosarcoma in cats and dogs. The
pulp has been described using several other terms,
including inner gel, mucilaginous gel, mucilaginous
jelly and leaf parenchyma. A range of biological
activities, including anti-viral, anti-bacterial, laxative,
protection against radiation, anti-inflammatory and
immunostimulation have been attributed to this
plant—particularly its polysaccharides.
When the leaves of most species of Aloe are cut a
more or less copious exudate appears, which is yellow
at first but rapidly darkens to brown or, in a few
species, dark red. These exudates contain phenolic
compounds that can be distinguished chromatograph-
ically. Most of the exudate compounds identified to
date are chromone, anthraquinone or anthrone deriv-
atives. Some compounds are widespread in the genus
and some are confined to a few species and are
therefore of potential chemotaxonomic value. These
phenolics do not occur in the parenchyma cells within
the leaf, where polysaccharides and glycoproteins are
characteristic. The exudate has a high content of aloin
([28 % wet basis), which is a C-glucoside of aloe-
emodin anthrone (Reynolds 2004). This substance has
pharmaceutical uses as a laxative (Ramachandra and
Srinivasa Rao 2008).
Gel structure and composition
Ni et al. showed that the two distinct parts of the leaf,
i.e. the outer green rind and inner clear pulp, were
clearly visible. Vascular bundles are tubular structures
located in the pulp and these are adjacent to the green
rind. The number of these bundles varied depending
on the size of leaves (Fig. 2). The majority of the pulp
consists of water, with the dry matter only accounting
for 0.9 % (w/w, SD =0.33). Examination of sections
(2–3 mm) of fresh leaves showed that the pulp consists
of large clear mesophyll cells with a hexagonal or
elongated hexagonal shape. The aforementioned cells
are very large and some are more than 1,000 lm (or
1 mm) long. The walls of these cells are transparent.
The cell walls could be clearly seen under higher
magnification. Electron microscopy revealed that, in
addition to cell walls, only the cell membranes and a
very limited number of cellular organelles are present
in the pulp. Intact cellular organelles such as nuclei,
chloroplasts and mitochondria were only observed in
the green rind and vascular bundles. Thus, these
mesophyll cells in the pulp appeared to be non-living
cells and they probably play a role in water storage (Ni
et al. 2004).
The carbohydrate composition of the pulp has been
described in numerous reports. Various polysaccha-
rides have been detected or isolated from the pulp,
including mannan (Segal et al. 1968; Yagi et al. 1977,
1986; Waller et al. 1978; Gowda et al. 1979; Radjabi-
Nassab et al. 1984; ‘T Hart et al. 1989), galactan
(Mandal and Das 1980b), arabinan (Mandal and Das
1980a), arabinorhamnogalactan (Mabusela et al.
1990), pectic substance (Rowe and Parks 1941;
Ovodova et al. 1975; Mandal and Das 1980a,b) and
glucuronic acid-containing polysaccharide (Hrani-
savljevic-Jakovljevic and Miljkovic-Stojanovic
1981; Wozniewski et al. 1990). However, significant
variations in the pulp polysaccharide species were
found in some studies. For example, in several studies
mannan was identified as the major polysaccharide in
the pulp, whereas in other studies, in the absence of
Fig. 2 Gross view of Aloe vera leaf sections: athe rind, bthe
pulp and cthe vascular bundle
Phytochem Rev (2013) 12:581–602 585
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mannan, a pectic substance was identified as the
primary polysaccharide (Rowe and Parks 1941; Ovo-
dova et al. 1975; Mandal and Das 1980a,b; Mabusela
et al. 1990). The reason for such discrepancies was not
understood but was largely attributed to seasonal
changes and/or different geographic locations (Man-
dal and Das 1980b; Grindlay and Reynolds 1986b).
Mannan is the most widely studied polysaccharide
from A. barbadensis. This compound consists of b1-4-
linked mannose residues (Yagi et al. 1977,1984;
Paulsen et al. 1978; Gowda et al. 1979; Mandal and
Das 1980b; Radjabi-Nassab et al. 1984; Vilkas and
Radjabi-Nassab 1986; Manna and McAnalley 1993).
Mannan is partially acetylated at the C-2 and C-3
positions and thus the term acemannan was coined
(Manna and McAnalley 1993). Mannan also contains
some side chains—mainly galactose—attached to C-6
(Fig. 3).
The b-(1 ?4)-glycosidic bond configuration of
acemannan is an important consideration in terms of
the therapeutic effects of aloe vera gel, since humans
lack the ability to enzymatically break down these
bonds (Boudreau and Beland 2006). The acemannan
found in aloe is structurally unique and this makes it a
characteristic compound of aloe species amongst other
well-known plant mannans (which have distinct side-
chains or are not acetylated and are insoluble) (Ian and
Yawei 2004).
Malolyl glucans
Three malic acid acylated carbohydrates were isolated
from aloe vera gel and these were characterized
as veracylglucan A (6-O-(1-L-maloyl)-a-,b-D-Glcp),
veracylglucan B (a-d-Glcp-(1 ?4)-6-O-(1-L-maloyl)
-a-,b-D-Glcp) and veracylglucan C (a-D-Glcp-(1 ?4)
-tetra-[6-O-(1-L-maloyl)-a-D-Glcp-(1 ?4)]-6-O-(1-
L-maloyl)-a-,b-D-Glcp)(Fig.4).
Chromones
Most of the chromones described to date from aloe leaf
exudates are derivatives of 8-C-glucosyl-7-hydroxy-
5-methyl-2-propyl-4-chromone. The variations arise
from the degree of oxidation in the propyl side-chain,
methylation of the hydroxyl group on C7 and ester-
ification of the glucose moiety.
Aloesone was reported as a minor component of
aloe vera (Holdsworth 1972). Aloesin, which could be
regarded as the parent compound of the aloe chro-
mones, was described first (Haynes et al. 1970) and is
widespread throughout the genus, occurring in 35 %
(Reynolds 1985) or 46 % (Rauwald and Niyonzima
1991) of species examined and often in a significant
quantity. A variant with the C-glucosyl residue in the
furanose form has been described as neoAloesin A
(Park et al. 1996). Esterification of the glucose moiety
has been observed with cinnamic acid (Fig. 5).
Reduction of the keto group on carbon 10 gives rise
conceptually to another series of compounds that are
derivatives of aloesol (Okamura et al. 1997a), some of
which have been recognized in A. barbadensis. The
8-C-glucoside of the 2-methyl derivative has also been
found and the structure is shown in Fig. 6(Okamura
et al. 1996,1998; Lv et al. 2008).
The reduction of the hydroxyl group at position 10
generates another family of skeletons and the com-
pounds that have been isolated include aloeresin G
(Xiao et al. 2000) and C-20-decoumaroyl-aloeresin G.
The latter product, along with allo-aloeresin D,
showed activity against the enzyme b-secretase
(BACE 1), which has been recognized as a valuable
target for the treatment of Alzheimer’s disease (Lv
et al. 2008). Recently, two new chromones have been
isolated (Wu et al. 2012) with a new skeleton (Fig. 7).
Furthermore, oxidation of the propyl side-chain to
give a propanediol structure was observed in aloe
compounds.
Anthraquinones
Anthraquinones are tricyclic aromatic quinones that
are yellow, orange or red in color (Lee et al. 2012).
Several anthraquinones have been isolated from the
dried latex of the leaves of aloe vera. Some of these
compounds, such as aloe-emodin, physcion,
O
OO
HO
AcO OH
AcO OH
HO
H
HH
OH
HO
OO
AcO OH
AcO OH
HO
H
HH
OH
HO
OOH
AcO OH
AcO OH
HO
H
HH
OH
H
Fig. 3 Acemannan
structure
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crysophanol, emodin and rhein, among others, are
shown below (Meng et al. 2004; Ashnagar et al. 2006;
Hsu and Chung 2012) (Fig. 8).
Tetrahydroanthracenones
Compounds in which the C-ring is reduced are named
tetrahydroanthracenones. Two compounds have been
isolated from aloe vera (Fig. 9): aloechrysone (iso-
lated from the fresh sap of the leaves) and aloebar-
bendol (isolated from roots) (Saleen et al. 1997). In
addition, 4-O-glucosides of aloesaponols III and IV
have been isolated from the callus tissue of A.
barbadensis (Yagi et al. 1998). It has been demon-
strated that these compounds are usually found in the
roots along with some anthraquinones (Reynolds
2004).
Anthrones
Anthranoids, in particular diastereomic anthrone
C-glycosides, are characteristic secondary products
in the genus Aloe. They occur in the leaf exudates of
more than 60 % of the examined species (Sigler and
Rauwald 1994). One of the main phytoconstituents of
aloe vera is aloin (Fig. 10). This compound occurs
naturally as a mixture of diastereomers and is a
C-glucoside of aloe-emodin anthrone found in the outer
rind of the aloe plant. Both compounds are widely used
for their cathartic properties and as bittering agents in
alcoholic beverages.
This glycoside has a yellow fluorescence and plays
an important part in the defense mechanisms against
herbivores. The levels of aloin in leaves are highly
variable and they depend on the part of the leaf, age
and growing conditions. The aloin content is higher in
young leaves that in older leaves. On the other hand,
aloin has been reported to constitute up to 30 % dried
leaf exudates of the aloe plant (Patel et al. 2012).
Other anthrone C-glycosides obtained from the
bitter yellow juice of aloe leaves are shown in Fig. 11
(Rauwald 1990; Okamura et al. 1997b; Park et al.
1998; Saccu et al. 2001; Fanali et al. 2010; Lee et al.
2012; Wu et al. 2013).
Fig. 4 Malolyl glucans
isolated from A. barbadensis
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A diglycoside of O-methoxy-nataloe-emodin-8-
methyl ether from aloe vera has been described and
is named homonataloside B, which was isolated from
the leaf exudate (Viljoen et al. 2002) (Fig. 12). Two
other anthraquinone dimers have also been isolated
from ethanolic extracts of aloe vera (Conner et al.
1990; Yang et al. 2010).
Phenolic compounds
Phenolic compounds are widespread in plants and are
responsible for a multitude of biological activities.
The following compounds have been identified in the
skin of the leaves: sinapic acid, quercitrin, kaempferol,
apigenin, gallic acid, protocatechuic acid, catechin,
vanillic acid, epicatechin, syringic acid, chlorogenic
acid, gentisic acid, caffeic acid, coumaric acid, ferulic
acid, rutin, miricetin and quercetin. With the exception
of quercetin, all of these compounds have also been
identified in the flowers of the plant (Lopez et al.
2013). Leaf skin extracts were characterized by the
abundance of catechin, sinapic acid and quercitrin.
Gentisic acid, epicatechin and quercitrin were the
most prominent phenolic compounds in the flowers.
Another dimeric compound isolated from the roots
of aloe vera consisted of two 4-hydroxy-6-methox-
ybenzopyran moieties (Fig. 13) joined by a C–C bond
(Saleem et al. 1997) and this is distantly related to the
chromones. Feralolide, isolated as a minor component
of Cape aloes, was shown to be a dimer with a
methylene bridge of 2,4-dihydroxyacetophenone and
6,8-dihydroxyisocoumarin (Speranza et al. 1993).
This compound was subsequently found in aloe vera
(Choi et al. 1996).
Sterols
The common plant sterol b-sitosterol was found in
whole aloe vera leaves and it was accompanied by
smaller amounts of cholesterol, ampestrol and lupeol
(Waller et al. 1978). Sitosterol glucoside and its
palmitic acid ester were subsequently found in whole
leaves of aloe vera, once again in conjunction with
lupeol (Kinoshita et al. 1996). A later study also
showed b-sitosterol and a variety of n-alkanes in the
gel of aloe vera with n-octadecane predominating
along with fatty acids and their methyl esters
(Yamaguchi et al. 1993) (Fig. 14). Recently five
Fig. 5 Aloesone and its
derivatives
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phytosterols have been identified and these were
isolated from the fresh leaf gel in a CHCl
3
/MeOH
extract (Tanaka et al. 2006).
Metals
In addition to the organic compounds discussed above,
several studies have been carried out to determine the
inorganic components of the aloe plant. The most
important study concerns the determination of metals
in the plant, with the same three parts considered: skin,
filet and gel. The gel was obtained when the filets were
extruded and the remaining fibrous fraction was
discarded. Ca, K, Na and Mg were the predominant
mineral elements in all the aloe fractions. In particular,
Ca was the main mineral element in all fractions
except in the gel, in which Na and K were detected in
higher quantities (Femenia et al. 1999). Robson et al.
pointed out that the presence of K in different
concentrations may regulate the healing properties of
aloe vera. Other elements, such as Fe, Cu, Zn and P,
were detected in minor amounts (Robson et al. 1982).
Germanium is one of the trace elements present in
aloe vera and this warrants further mention due to its
many health benefits. Germanium is found in revital-
izing plants such as ginseng and ginger. Carboxyeth-
ylgermanium sesquioxide (Ge-132) or organic
germanium (Fig. 15) has various biological activities
and is indicated for many diseases. The mode of action
of this chemical is an increase in lymphocyte produc-
tion NKlo, which causes activation of the immune
system and destroys all cells and tumor malfunctions.
Fig. 6 Aloesol and its derivatives
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Aloe leaves have a total concentration of germanium
of 1219.50 ng/g, of which 98.99 % is organic germa-
nium (McMahon et al. 2006).
Bioactivity studies
As mentioned above, the aloe plant has been used as a
popular therapeutic resource since ancient times.
These uses are reflected in the main areas of study
that concern aloe vera. Almost 80 % of the publica-
tions are in the area of medicine and pharmacology,
followed by agriculture, biochemistry and chemistry.
The interest in the scientific community for Aloe and
its many properties has increased in recent years—as
can be seen in Fig. 16, which shows how the number
of publications in which aloe vera is mentioned has
increased in recent years (Scopus 2013). This review
provides an overview of the multiple biological
activities that have been described for this plant.
Antitumoral activity
Over 4,000 studies have been performed on the
effectiveness of aloe vera in medical treatment and
some of these addressed its role in recovery from
diagnosed cancer. Basic research over the past couple
of decades has started to reveal the extent of aloe’s
Fig. 7 Other chromones from A. barbadensis
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pharmaceutical potential, particularly against neoplas-
tic disease (Harlev et al. 2012). Aloe plants exhibit
anticancer activity in vitro and in vivo. The antineo-
plastic properties are due to at least three different
mechanisms based on antiproliferative, immunostim-
ulatory and antioxidant effects. The antiproliferative
action is determined by anthracenic and anthraqui-
nonic molecules such as aloe-emodin, aloesin and
aloin, which are present in the gel of the aloe vera leaf,
while the immunostimulating activity is mainly due to
acemannan, a mucopolysaccharide of aloe vera gel
that displays antitumor activities in vitro through the
activation of immune responses (Zhang and Tizard
1996).
The majority of the studies conducted to date have
focused on acemannan, which is attributed to various
biological activities including immunomodulatory
and antitumor (Tizard and Ramamoorthy 2004). The
anticancer biological mechanism of acemannan may
be exerted through pluripotent effector cells, such as
macrophages, as aloe extracts are known to induce
macrophage activity (Zhang and Tizard 1996).
Fig. 8 Anthraquinones
isolated from A. barbadensis
OOHOMe
OH
Aloechrysone
O
OH
Aloebarbendol
HO
OH
OH OH O
OH
O
O
HO
OH
HO
OH
4-O-glucoside aloesaponol III
OH OH O
O
O
O
HO
OH
HO
OH
4-O-glucoside aloesaponol IV
Fig. 9 Tetrahydroanthracenones isolated from aloe vera
Fig. 10 Aloin isolated from the leaf exudates
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Clinical studies have even been carried out on dogs
and cats with spontaneous tumors and the animals
were treated with acemannan by intraperitoneal and
intralesional routes of administration (Harris et al.
1991). Similar studies have also been conducted on
humans. The study included 50 patients suffering from
lung cancer, gastrointestinal tract tumors, breast
cancer or brain glioblastoma. The patients were
treated with melatonin (MLT) alone or melatonin plus
aloe vera tincture. This preliminary work suggested
Fig. 11 Anthrone C-glycosides isolated from the bitter exudate of aloe leaves
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that natural cancer therapy with MLT plus aloe vera
extracts may produce therapeutic benefits, at least in
terms of stabilization of the disease and survival, in
patients with advanced solid tumors for whom no
other standard effective therapy is available (Grindlay
and Reynolds 1986a).
The antiproliferative and cytotoxic potential of the
natural anthracycline aloin from aloe vera was tested
on human uterine carcinoma HeLaS3 cells. Aloin
showed a pronounced antiproliferative effect at phys-
iological concentration, caused cell cycle arrest in the
S phase, and markedly increased HeLaS3 cell apop-
tosis. These results indicate that aloin, due to its less
undesirable side effects and anti-metastatic potential,
may be the agent of choice for clinical protocols for
the treatment of human cervical carcinoma in the
future (Niciforovic et al. 2007).
The aglycone of aloin, aloe-emodin, also has
antitumor activities (Acevedo-Duncan et al. 2004).
There are numerous studies on aloe-emodin in vitro,
in vivo and in clinical studies. The anticancer effect
of aloe-emodin in vitro was tested on two human
colon carcinoma cell lines, DLD-1 and WiDr (Lin
and Uen 2010). This compound induced cell death
in a dose-dependent and time-dependent manner.
Notably, the WiDr cells were more sensitive to aloe-
emodin than the DLD-1 cells. Aloe-emodin affected
the release of apoptosis-inducing factor and cyto-
chrome c(cyt. c) from mitochondria, followed by
activation of caspase-3, leading to DNA fragmenta-
tion, nuclear shrinkage, and apoptosis. The exposure
of colon carcinoma cells to aloe-emodin suppressed
the casein kinase II activity in a time-dependent
manner, and this was accompanied by a reduced
phosphorylation of Bid, a downstream substrate of
casein kinase II and a proapoptotic molecule. These
findings indicate that the inhibition of casein kinase
II activity, the release of apoptosis-inducing factor
and cyt. cand caspase-3 activation are involved in
O
O
O
O
OH
OH
O
HO
OH O OH
OH
bis-benzopyran Feralolide
Ac
Fig. 13 Phenolic compounds from aloe vera
Fig. 12 Homonataloside B and glycosylated anthraquinones obtained from aloe vera
HO
R
HO
Lupeol
R= C2H5 b-Sitosterol
R= H Cholesterol
R=CH3 Campesterol
HO
R
HO
R
R= H Lophenol
R=CH3 24-methyl-lophenol
R= C2H5 24-ethyl-lophenol
R= H Cycloartanol
R= =CH2 24-methylene-cycloartanol
Fig. 14 Sterols from aloe vera
HO Ge OGe
OOH
O
O O
Ge-132
Fig. 15 Carboxyethylgermanium sesquioxide (Ge-132)
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aloe-emodin-mediated apoptosis in colon carcinoma
cells.
The results of several studies in vivo show that aloe-
emodin selectively inhibits human neuroectodermal
tumor cell growth in tissue cultures and in animal
models. In these cases, aloe-emodin was shown to be
selectively toxic against neuroectodermal tumors and
to inhibit human neuroectodermal tumor growth in an
animal model with no evidence of acute or chronic
toxicity. The lack of toxicity in combination with
significant antitumor activity results in a favorable
therapeutic index (Pecere et al. 2000).
The activity of mixtures of extracts and compounds
has also been evaluated. An extract of A. barbadensis
was examined for its cellular toxicity on HepG2 cells.
The results show that aloe vera extracts induce HepG2
apoptosis by ATP depletion-related impairment of
mitochondria, which is caspase-independent (Kim and
Kwon 2006). The potential anticancer properties and
modulatory effect of selected aloe vera active com-
pounds on antioxidant enzyme activities were tested.
Thus, three anthraquinones, aloesin, aloe-emodin and
aloin, were extracted from aloe vera leaves. These three
compounds, along with an N-terminal octapeptide
derived from verectin (a biologically active 14 kDa
glycoprotein present in aloe vera), were tested for their
relative antitumor efficacyin vivo. It was found that the
active compounds exhibited significant prolongation of
the life span of tumor-transplanted animals in the
following order: barbaloin (aloin) [octapep-
tide [aloesin [aloe-emodin (El-Shemy et al. 2010).
Anti-inflammatory effects
The anti-inflammatory effect of aloe vera is certainly
the most widely observed (Davis et al. 1989; Adler
et al. 1995; Vazquez et al. 1996; Reynolds and Dweck
1999; Bassetti and Sala 2001). Inflammation is a
complex reaction of the body and it involves various
metabolic pathways and various agents. The mecha-
nisms by which aloe extracts exert anti-inflammatory
effects are multiple, and several distinct pathways
have been described. For example, some evidence
suggests that the activity is due to gibberellins. Thus,
the anti-inflammatory activities of aloe vera and
gibberellin were measured in streptozotocin-induced
diabetic mice by measuring the inhibition of poly-
morphonuclear leukocyte infiltration into a site of
gelatin-induced inflammation (Davis and Maro 1989).
Both aloe and gibberellin inhibited inflammation to a
similar extent in a dose–response manner. These data
were interpreted as suggesting that gibberellin or a
gibberellin-like substance is an active anti-inflamma-
tory component in aloe vera.
A second possible mechanism may involve com-
plement depletion. Thus, an aqueous extract of aloe
vera gel was fractionated into high (h-Mr) and low
(l-Mr) molecular weight fractions by dialysis. Sub-
sequent fractionation generated two fractions with
molecular weights of 320 and 200 kDa. Preincubation
of human pooled serum with these fractions resulted in
a depletion of classical and alternative pathway
complement activity. The inhibition appeared to be
Fig. 16 Evolution of the
number of publications per
year
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due to alternative pathway activation, resulting in
consumption of C3 (‘T Hart et al. 1989,1990). The
active fractions were mannose-rich polysaccharides.
A third possible mechanism may involve neutrophil
emigration into inflamed tissues (Bowden 1995). The
effect of some anti-inflammatory agents such as
dexamethasone is related to a greater inhibition of
neutrophil migration. The mode of action of these
agents is related to the inhibitory action on the
arachidonic acid pathway. An aqueous extract of aloe
vera inhibited in vitro the conversion of arachidonic
acid to prostaglandin E
2
(PGE2), which suggests that
the extract has cyclooxygenase inhibitory properties
(Vazquez et al. 1996).
Numerous more recent studies in vivo have high-
lighted anti-inflammatory properties. For example,
aloe vera extracts showed an inhibitory effect on the
activity of partially purified lipoxygenase from the rat
lung cytosol fraction. This antilipoxygenase activity
could explain the anti-inflammatory properties, espe-
cially in applications for the healing of minor burns
and skin ulcers (Bezakova et al. 2005).
Oral administration of A. barbadensis gel over
21 days significantly decreased the level of homocys-
teine and the level of folic acid was significantly
elevated when compared to diabetic control in rats
with alloxan-induced diabetes. The results suggest
potent anti-inflammatory potential of A. barbadensis
gel in experimental diabetes, meaning that aloe vera
can be used as an alternative remedy for the treatment
of diabetes mellitus and its complications (Vanitha
et al. 2013). A chronic inflammatory state is a major
pathogenesis of type 2 diabetes mellitus (Haffner
2006).
Effect on the skin and wounds
Besides the anti-inflammatory effect, the topical use of
pure gel promotes healing and regeneration of the
skin. Aloe vera gel act on fibroblasts, macrophages
and epidermal cell activity, and it stimulates the
formation of epidermal tissue, increases collagen
synthesis and remodels and enhances tensile stress
(Chithra et al. 1998).
Recent studies in vivo indicate that topical appli-
cation of aloe vera leads to significantly faster wound
healing and an increased amount of tissue repair. Such
compounds can be applied as a topical treatment to
accelerate the healing of surgically induced wounds in
rats in comparison with other topical applications,
such as thyroid hormone or silver sulfadiazine (Tara-
meshloo et al. 2012a,b).
Burning mouth syndrome (BMS) is manifested as a
subjective burning sensation of the tongue, lips or
entire oral cavity, but it does not show any visible
lesions and there are no laboratory tests capable of
accounting for the discomfort (Scala et al. 2003). In a
clinical trial conducted on 75 patients diagnosed with
this syndrome, the efficacy of aloe vera was evaluated
in combination with a tongue protector and compar-
ison was made with a placebo. The chronic nature and
high prevalence of BMS meant that the condition was
not resolved in the trial but the patients with severe
pain passed to moderate pain, thus demonstrating a
clinical improvement (Lopez-Jornet et al. 2013).
In an effort to exploit the beneficial properties of
this plant on the skin, recent studies have focused on
the feasibility of creating membranes for use as
dressings for wounds (Khoshgozaran-Abras et al.
2012; Silva et al. 2013).
Antibacterial activity
The antibacterial activity of A. barbadensis was tested
on several pathogens and the results showed that aloe
vera could be recommended for the treatment of
various bacterial diseases in the future. The leaf of this
plant can be divided into gel and peel. These biological
and toxicological effects have been widely studied in
aloe vera gel while there is still little information on
the uses of the peel, which is usually discarded as
waste in the aloe industry (Kwon et al. 2011).
Significant antimicrobial activities have been reported
both in the inner gel and in the peel and further in vivo
and in vitro studies should be carried out in order to
enhance such properties of the gel and efforts should
be made to identify the compounds responsible for the
activity.
The antibacterial activity of aloe vera inner gel has
been tested in Gram-positive and Gram-negative
bacteria by several methods (Hamman 2008). In
recent studies, extracts in different solvents such us
hexane, chloroform, methanol and water of freeze-
dried gel aloe powder were evaluated against Gram-
positive (Staphylococcus aureus,Enterococcus bovis)
and Gram-negative (Shigella flexneri,Enterobacter
cloacae) bacteria. These experiments show lower MIC
(minimum inhibitory concentration) values for aloe
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vera gel than for the aqueous extract (Habeeb et al.
2007).
In another study, aloe vera gel has recently been
explored as an edible coating in order to reduce the
loss of post-harvest fruit quality in papaya. The
antimicrobial effects of aloe gel were compared with
those of the natural polysaccharide chitosan (an
established coating material with antifungal activity).
Fresh papaya fruits were coated with aloe gel, 50 %
aloe gel, papaya leaf extract (it is a potential antifungal
agent), papaya leaf extract with aloe gel (1:1) and with
2.5 % of chitosan. The coated and uncoated samples
were stored at 30 °C and 42–55 % relative humidity
for 15 days. These assays showed that the coated fruits
survived the storage period, while uncoated controls
decayed within 10 days. Moreover, the effectiveness
of the aloe gel coating was improved on incorporation
of papaya leaf extract (Marpudi et al. 2011). These
preservation technologies have been used for other
fruits such as table grapes (Valverde et al. 2005;
Serrano et al. 2006), mangoes (Dang et al. 2008),
nectarines (Ahmed et al. 2009), apples (Song et al.
2013) and kiwis (Benı
´tez et al. 2013).
Moreover, the antimicrobial activity was studied
for ethanol, methanol and acetone extracts of aloe vera
gel powder against four Gram-positive (Bacillus
cereus,Bacillus subtilis,S. aureus,Streptococcus
pyogenes) and Gram-negative (Escherichia coli,
Pseudomonas aeruginosa,Salmonella typhi,Klebsi-
ella pneumonia) bacteria using the agar well diffusion
method. The ethanol and methanol extracts showed
higher activity than the acetone extract against most of
the tested pathogens (the first two had an inhibition
zone between 12.66 and 23.33 mm and the maximum
value was obtained for B. cereus). Nevertheless, the
inhibition zone obtained on using the acetone extract
ranged from 6.00 (for E.coli) to 7.33 mm (for S.
pyogenes) and activity was not observed for P.
aeruginosa and S. typhi. Generally, these extracts
showed better activity against Gram-positive bacteria
(Lawrence et al. 2009).
Regarding the activity of aloe vera peel, Kwon et al.
evaluated the activity of the aqueous extract against
Gram-positive (S. aureus,Bacillus spp., Enterococcus
spp.) and Gram-negative (E. coli,Salmonella ty-
phimurium,Pseudonomas aeruginosa,Vibrio vulnif-
icus and Vibrio parahaemolyticus) bacteria. The best
antimicrobial activity was shown against E. coli and
Vibrio spp. Moreover, an in vivo study was carried out
on mice challenged with S. typhimurium DT104. Fecal
shedding of this bacteria significantly decreased and
intestinal Salmonella specific IgA and IgG titers
increased in mice fed with peel extracts (Kwon et al.
2011). In another study, aqueous, ethanolic and
acetone extracts of aloe peel were analyzed against
S. aureus,S. pyogenes,P. aeruginosa and E. coli. The
maximum antibacterial activity was observed in the
acetone extract and maximum growth suppression was
observed in S. pyogenes and P. aeruginosa. When
antifungal activity was evaluated against Aspergillus
flavus and Aspergillus niger, the best results were also
observed for the acetone extract (Arunkumar and
Muthuselvam 2009).
Analogously, Pandey et al. evaluated the antibac-
terial activity of aqueous and ethanolic extracts of aloe
peel against Gram-positive (E. bovis and S. aureus)
and Gram-negative (E. coli,Proteus vulgaris,Proteus
mirabilis,P. aeruginosa,Morganella morganii and
Klebsiella pneumoniae) bacteria. The ethanolic
extract showed great inhibitory effects for Gram-
positive bacteria E. bovis, while among Gram-nega-
tive bacteria the highest inhibitory effect was observed
in P. aeruginosa. However, minimum inhibition
concentrations were very low for both Gram-positive
and Gram-negative bacteria (Pandey and Mishra
2010).
Immunomodulatory activity
A number of studies indicated immunomodulating
activities of the polysaccharides in aloe vera gel and
suggested that these effects occur via activation of
macrophage cells to generate nitric oxide, secrete
cytokines and present cell surface markers (Zhang and
Tizard 1996; Chow et al. 2005; Im et al. 2005;
Farahnejad et al. 2011). Some immune reactions that
seem to be specific for acemannan as compared to
other polysaccharides include stimulation of the
antigenic response of human lymphocytes as well as
the formation of all types of leucocytes from both
spleen and bone marrow in irradiated mice. However,
some other immunomodulation effects were shown to
be linked to glycoproteins, namely lectins, found in
aloe gel (Reynolds and Dweck 1999).
In another study it was shown that relatively high
concentrations of acemannan are required to achieve
modest activation of macrophages compared to crude
aloe vera juice, which suggests that there is another
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component in the juice responsible for the macrophage
activation. Further investigations revealed that
although this component is present only in small
amounts, its potency in terms of macrophage stimu-
lation accounted fully for the activity obtained for the
crude aloe vera juice (Pugh et al. 2001).
Recent studies have shown the effect of aloe vera
gel extract and its isolated fractions on peritoneal
macrophages against Candida albicans infection
(Farahnejad et al. 2011). C. albicans is one of the
most frequent pathogens among the medically impor-
tant Candida species and it causes severe candidiasis
in immunocompromised patients (Garber 2001). The
results indicate that aloe vera gel extract induces
macrophage cell viability against C. albicans.This
study also indicated that the fraction that contains high
molecular weight components, which encompasses
acemannan (MW [100 kDa), is the most effective
fraction of aloe vera.
Furthermore, in this case the activity against human
immunodeficient virus type 1 (HIV-1) would be
remarkable. Aloe vera gel included in nutritional
supplements was used in a clinical trial with these
patients and it showed beneficial results (Pulse and
Uhlig 1990). Previous studies carried out with ac-
emannan showed a 71 % reduction in symptoms of
AIDS patients, probably due to stimulation of the
immune system (Reynolds and Dweck 1999).
Obesity, cholesterol and anti-diabetic activity
Obesity is a condition in which an excess accumula-
tion of body fat is caused by an imbalance of energy
intake and expenditure, in addition to genetic back-
ground. Obesity, especially visceral fat obesity, is
strongly associated with the development of metabolic
syndrome, which includes insulin resistance, type 2
diabetes mellitus, hypertension, dyslipidemia and
cardiovascular disease (Alberti et al. 2005). The
prevalence of obesity is currently one of the most
serious health problems around the world (Misawa
et al. 2012). Aloe vera has been used as a folk remedy
in many cultures to treat diabetes (Vogler and Ernst
1999; Yeh et al. 2003). Several clinical and experi-
mental studies have demonstrated the hypoglycemic
effects of aloe vera (Fugh-Berman 2000; Low 2006;
Tapsell et al. 2006). Additionally, several reports on
aloe vera-derived extracts showed a preventive effect
against insulin resistance (Tundis et al. 2010) and a
lipid-lowering effect (Vogler and Ernst 1999). From
these observations, it is expected that aloe vera could
be beneficial for the prevention or improvement of
metabolic syndrome-related disorders.
The in vivo antidiabetic effects of the plant were
investigated using streptozotocin-induced type 2 dia-
betic model rats (Moniruzzaman et al. 2012) and the
hypolipedemic and antioxidant effects were also
assessed. The ethanolic skin extracts of aloe vera
were observed to contain the highest total phenolic and
flavonoid contents. Furthermore, these extracts exhib-
ited high DPPH scavenging activities and FRAP
values, indicating the potential of this plant to be used
as an antioxidant. Aloe vera extracts also have the
potential to be used as hypoglycemic agents, espe-
cially the skin extract. Additionally, although the
result is not statistically significant, the ethanol skin
extract exhibited potent hypolipedemic effects by
decreasing the serum cholesterol and LDL levels by 25
and 69 %, respectively, while the HDL levels also
increased.
In other tests related to diabetes, leaf extracts in
hexane, chloroform, acetone, methanol and water
were evaluated at a dose of 100 mg/kg during 15 days.
The results show that the aqueous extract of the leaves
of aloe vera has potential for its antidiabetic activity,
with the blood sugar levels in albino rats reduced by
48 % at the 15th day (Maithani et al. 2011).
The effects of the oral administration of lophenol
(Lo) and cycloartanol (Cy), two kinds of antidiabetic
phytosterol isolated from aloe vera, have also been
evaluated on glucose and lipid metabolism in Zucker
diabetic fatty (ZDF) rats (Misawa et al. 2012). It was
demonstrated that the administrations of Lo and Cy
suppressed random and fasting glucose levels and
reduced visceral fat weights significantly. It was also
observed that treatments with Lo and Cy decreased
serum and hepatic lipid concentrations (triglyceride,
nonesterified fatty acid and total cholesterol). Addi-
tionally, Lo and Cy treatments resulted in a tendency
for the reduction in the serum monocyte chemotactic
protein-1 (MCP-1) level and an elevation in serum
adiponectin level. Furthermore, the expression levels
of hepatic genes encoding gluconeogenic enzymes
(G6 Pase, PEPCK), lipogenic enzymes (ACC, FAS)
and SREBP-1 were decreased significantly by the
administration of aloe sterols. In contrast, Lo and Cy
administration increased mRNA levels of glycolysis
enzyme (GK) in the liver. It was also observed that the
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hepatic b-oxidation enzymes (ACO, CPT1) and
PPARaexpressions tended to increase in the livers
of the Lo- and Cy-treated rats compared with those in
ZDF-control rats. It was therefore concluded that
orally ingested aloe sterols altered the expressions of
genes related to glucose and lipid metabolism and
ameliorated obesity-associated metabolic disorders in
ZDF rats. These findings suggest that aloe sterols
could be beneficial in preventing and improving
metabolic disorders with obesity and diabetes in rats.
Laxative effects
Constipation is a highly prevalent and often chronic
functional gastrointestinal disorder affecting humans
irrespective of race and color, with victims exposed to
the risk of colorectal cancer. Although the traditional
use of aloe vera as a laxative is known, little scientific
evidence is available in the literature on the purgative
potential of this plant.
The laxative activity of aloe vera has mainly been
attributed to the anthraquinones (mainly aloin) present
in the yellow exudates of the leaves (Tan et al. 2012).
This anthraquinone, which is poorly absorbed from the
GIT, is cleaved by gut bacteria to produce aloe-
emodin, which is more readily absorbed and is
responsible for the purgative properties of aloe vera
(Steenkamp and Stewart 2007). The laxative effect is
believed to take place through water accumulation in
the intestine via active Na
?
transport (Ishi et al. 1990)
or by water secretion due to a prostaglandin-dependent
mechanism (Capasso et al. 1983).
There are studies in which the laxative effect of this
plant has been demonstrated in vivo. Thus, the laxative
potential of the ethanolic leaf extract of aloe vera has
been tested in Wistar rats with loperamide-induced
constipation (Ashafa et al. 2011). Treatment of the rats
with the extract at 50, 100 and 200 mg/kg body weight
for 7 days improved intestinal motility, increased
fecal volume and normalized body weight in the
constipated rats. There are indications of the laxative
properties of the herb, with a level of 200 mg/kg body
weight of the extract showing the best efficacy.
Conclusions
The beneficial effects of A. barbadensis are univer-
sally accepted nowadays. In this overview an in-depth
knowledge of the history, composition and action of
these plants was obtained from the recent literature. It
is worth emphasizing the number of historical refer-
ences concerning this plant. Throughout the centuries
Aloe vera has been considered to be a magic plant that
and has been capable of solving numerous human
infirmities. In recent decades, detailed investigations
have allowed us to summarize the characteristics of
this plant, which seems to hide its secrets behind
botanical and pharmacological mysteries and today
many more responses are being uncovered.
Many analyses have been carried out on aloes in
search of constituents that might be responsible for the
beneficial properties and various new organic com-
pounds, in addition to those described above, are
reported from time to time.
It is clear that these biological effects have been
widely studied in aloe vera gel but there is little
information on the exploitation of the peel, which is
usually discarded as waste in the aloe industry.
Significant activities have been reported and efforts
have been made to enhance the properties of the gel
and to identify the compounds responsible for the
activity. Numerous bioactivity studies have been
carried out on the application of extracts in water
and organic solvents from the gel and leaf peel, but it is
noteworthy that synergistic effects have barely been
investigated. Thus, a great deal of effort must be
invested in order to obtain further information on these
effects for different compounds.
At present almost 80 % of the publications on Aloe
vera are in the area of medicine and pharmacology,
followed by agriculture, biochemistry and chemistry.
These new natural compounds are expanding our
treatment choices for the management of different
disorders on an ongoing basis, with new and different
uses and research data supporting their prestige as safe
and effective options.
Acknowledgments This work was supported by the Consejerı
´a
de Innovacio
´n, Ciencia y Empresa, Junta de Andalucı
´a (Project
P10-AGR5822).
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