7
Chapter 2
REVIEW OF LITERATURE
Aegle marmelos (L.) Correa belonging to family Rutaceae is a medium sized
deciduous tree indigenous to the Indian subcontinent. It is also found in
Myanmar, Pakistan, Bangladesh, Burma, Nepal, Vietnam, Laos and
Cambodia. It grows mainly within the sub-Himalayan region (Kala, 2006).
The tree has religious importance as well and is known as “Shivadume”
(Jagetia et al., 2004). It has been studied for various medicinal properties
including diabetes mellitus (Ponnachan et al., 1993; Kamalakkannan and
Prince, 2003; Kar et al., 2003), analgesic, anti-inflammatory and antipyretic
activities (Arul et al., 2005), antifungal (Chakthong et al., 2012), antibacterial
(Gautam et al., 2013) and antiproliferative (Lampronti et al., 2008).
Auraptene present in the extracts of Aegle marmelos has been proposed to
inhibit the deleterious effects of ischemia in isolated cardiomyocytes by
decreasing calcium overload (Kakiuchi et al., 1991). The plant has also been
proposed to inhibit free radical mediated oxidative injury by altering the
biotransformation enzyme systems in rats (Singh et al., 2000). The plant is
also documented to have antifertility effect in male rats (Chauhan and
Agarwal, 2008).The young leaves of Aegle are used in ethno-medicine as
astringent, laxative, febrifuge and expectorant (Nandkarni, 1976).
2.1 TAXONOMIC CLASSIFICATION OF AEGLE MARMELOS
Kingdom : Plantae
Division : Magnoliophyta
Class : Magnoliopsida
Subclass : Rosidae
Order : Sapindales
Family : Rutaceae
Genus : Aegle
Species : marmelos
Fig. 1 Aegle marmelos tree and leaves
8
9
Synonyms: Bel, belbaum, bela, bael, sripal, bilwa, wood apple, stone apple,
golden apple, Bengal quince (Nandkarni, 1976)
The bael tree is the only species in the genus Aegle. It is a medium sized
deciduous plant which grows to a height of about 18 m indigenous to India
and Southeast Asia. In India, it is distributed in the Himalayas and South
Indian plateau. The tree is grown mainly for its fruit. It bears thorns and has
fragrant flowers. It bears fruits which are globose with smooth, hard, aromatic
rind and is about 5-15 cm in diameter. The fruit bears numerous seeds which
are covered with dense fibrous hairs embedded in a thick aromatic pulp. The
leaves are trifoliate with a terminal leaflet (Kesari et al., 2006). The
monographs of the fruits and roots are included in Ayurvedic pharmacopoeia
of India (1999). The plant is mostly used in multicomponent formulations in
Ayurvedic medicines. All the parts of the plant have been reported to have
medicinal properties and more than 100 bioactive principles have been
isolated from the plant (Maity et al., 2009). These include aegeline,
imperatorin, skimmianine, psoralen, auraptene, lupeol, eugenol, marmin etc.
which are reported to have diverse pharmacological actions such as anticancer,
gastroprotective, antidiarrhoeal, cardioprotective, antidiabetic etc. (Maity et
al., 2009).
2.2 CHEMICAL CONSTITUENTS OF AEGLE MARMELOS
More than 30 compounds from the leaves of Aegle marmelos (AM) have been
identified. The leaves of the plant have been reported to contain aegeline (1)
and few alkaloids (2-4) of aegeline type (Manandhar et al., 1978;
Govindachari et al., 1983).The major constituents of the root bark of the plant
have been identified to be coumarins, alkaloids, sterols, decursinol (5) and
haplopine (6). The essential oil has been reported to contain p-cymene,
caryophyllene, cineole, citral, citronellal, cinnamaldehyde, d-limonene and
eugenol (Kaur et al., 2006). Other constituents include alkaloids, triterpenoids,
flavonoids and coumarins (Basu and Sen, 1974). Sterols and triterpenoids such
as lupeol and β-sitosterol, α and β-amyrin, flavonoids such as rutin and
coumarins have been isolated from the root and stem-bark of the plant
(Chatterjee et al., 1978). Purified exudate gum from the plant has been
reported to contain D-galactose, L-rhamnose, L-arabinose and D-glucuronic
acid (Mandal and Mukherjee, 1980). Other phytoconstituents include
marmenol (7), praealtin D (8), rutaretin (9), montanine (10), transcinnamic
acid (11), valencic acid (12), N-p-cis-coumaroyltyramine (13) and N-p-trans-
coumaroyltyramine (14) (Ali and Pervez, 2004). Valencic acid (12) from
Aegle marmelos has been shown to possess neuroprotective effect (Epifano et
al., 2008).
10
11
Phuwapraisirisan et al. (2008) have isolated a series of phenylethyl
cinnamides from the leaves of the plant with α- glucosidase inhibitory activity
(15-17).
12
Narender et al. (2007) have reported the antihyperglycemic and
antidyslipidemic agent from the alcoholic leaf extract of A.marmelos to be
aegeline (1) and proposed it to possess β-adrenergic receptor agonist using
predictive pharmacophoric hypothesis and 3D-QSAR model. Skimmianine,
lupeol and eugenol have also ben documented to be present in the plant (Maity
et al., 2009).
Skimmianine (18) Lupeol (19) Eugenol (20)
Maity et al. (2009) has reviewed the various phytoconstituents present in the
leaves of Aegle marmelos. Sharma et al. (1980) have reviewed the
phytoconstituents present in the fruits, Singh and Malik (2000) have reviewed
the phytochemical constituents in the seeds and Shoeb et al. (1973) have
reported the chemical constituents reported in the roots of the plant (Table 1).
Maity et al. (2009) have reviewed the pharmacological activities for these
phytoconstituents as presented in the Fig. 2-5. Skimmianine has been proposed
to have antimalarial, antipyretic, analgesic, anticancer and anticonvulsant
activities (Maity et al., 2009; Das and Das, 1995). Aegeline is reported to have
antihyperglycemic, antihyperlipidemic and cardioprotective actions (Narender
et al., 2007). Lupeol has been reported to be cardioactive and eugenol to have
antioxidative, antiulcer and antibacterial activities (Maity et al., 2009).
13
14
Table 1 Phytoconstituents reported in various parts of Aegle marmelos
Plant Part Phytoconstituent Reference
Leaf Tannins Maity et al., 2009
Limonene Maity et al., 2009
Aegelin Maity et al., 2009
O-(3,3-dimethylallyl)-halfordinol Manandhar et al., 1978
p- Cymene Maity et al., 2009
Phellandrene Maity et al., 2009
Cineole Maity et al., 2009
Marmelosin Nandkarni, 1976
Marmesinin Sharma et al., 1980
Rutin Sharma et al., 1980
Skimmianine Maity et al., 2009
Umbelliferone Arul et al., 2004
β- Sitosterol-D-glucoside Sharma et al., 1980
Fruit Alloimperatorin Sharma et al., 1980
Auraptene Kakiuchi et al., 1991
Calcium compounds Maity et al., 2009
Imperatorin Sharma et al., 1981
Glutamic acid Barthakur and Arnold, 1989
Glycine Barthakur and Arnold, 1989
Linoleic acid Maity et al., 2009
Lysine Barthakur and Arnold, 1989
Magnesium compounds Barthakur and Arnold, 1989
Marmelosine Badam et al., 2002
Marmeline Sharma et al., 1980
15
Phenylalanine Barthakur and Arnold, 1989
Proline Barthakur and Arnold, 1989
Psoralen Chakthong et al., 2012
Scoparone Sharma et al., 1980
Scopoletin Sharma et al., 1980
Skimmin Sharma et al., 1980
Umbelliferone Sharma et al., 1980
Xanthotoxol Sharma et al., 1980
Stem Bark Fagarine Chatterjee and Mitra, 1949
Marmin Chatterjee and Mitra, 1949
Seed Anthraquinones Mishra et al., 2010 b
Linoleic acid Singh and Malik, 2000
Linolenic acid Singh and Malik, 2000
Palmitic acid Singh and Malik, 2000
Stearic acid Singh and Malik, 2000
Root Α- Methyl scopoletin Shoeb et al., 1973
Psoralen Basu and Sen, 1974
Skimmin Shoeb et al., 1973
Scopoletin Shoeb et al., 1973
Timbamine Shoeb et al., 1973
Umbelliferone Basu and Sen, 1974
Xanthotoxin Basu and Sen, 1974
16
Skimmianine
Fig. 2 Pharmacological activities of Skimmianine
Antipyretic Anticancer Antimalarial
Analgesic Anticonvulsant
Aegeline
Antidyslipidemic Hypoglycemic
Cardioactive
Fig. 3 Pharmacological activities of Aegeline.
Antiinflammatory Cardioactive
Lupeol
Fig. 4 Pharmacological activities of Lupeol.
17
Eugenol
Antioxidative Antiulcer
Antiulcer
Fig. 5 Pharmacological activities of Eugenol.
18
2.3 PHARMACOLOGICAL ACTIVITIES OF AEGLE MARMELOS
Aegle marmelos has been studied for various pharmacological activities
including antiproliferative, antimicrobial, antidiabetic etc. which are discussed
in detail as under.
2.3.1 ANTICANCER AND ANTIPROLIFERATIVE ACTIVITY
Studies have revealed extracts of AM to have significant antiproliferative
activity (Lambole et al., 2010). Intraperitoneal administration of ethanol
extract of AM leaves has been found to have a strong inhibitory effect on
Dalton’s lymphoma ascites bearing mice (Chockalingam et al., 2012).
Administration of AM extract has been found to inhibit micronuclei
frequencies in the bone marrow cells of cyclophosphamide treated mice in a
dose dependent manner (Gupta et al., 2011). Extracts from AM have been
documented to have antiproliferative activity against MCF-7 and MDA-MB-
231 breast cancer cell lines at higher doses (Lambertini et al., 2004). Studies
have revealed the plant extract to inhibit the proliferation of Ehrlich Ascites
carcinoma transplanted into mice (Jagetia et al., 2005).
The plant is documented to be used in Bangladeshi folk medicine for the
treatment of cancer (Costa-Lotufo et al., 2005). Bark extract of AM has been
postulated to have an inhibitory effect on proliferation of various human
tumour cell lines including leukemia, lymphoma, colon and breast cancer cell
lines in vitro and phytochemicals such as butyl-p-tolyl sufide, 6-methyl-4-
chromanon and butylated hydroxyl anisole have been identified in these
extracts (Lampronti et al., 2006; Khan et al., 2002). Imperatorin, a linear
furanocoumarin isolated from the fruit of AM has been documented to inhibit
the proliferation of human leukemia cell lines (Pae et al., 2002).
2.3.2 ANTIHYPERGLYCEMIC ACTIVITY
Diabetes mellitus is a global epidemic. The number of people afflicted with
diabetes has increased manifolds. The progress of the ailment is marked by a
high rate of morbidity due to the complications including diabetic retinopathy,
neuropathy, nephropathy and cardiomyopathy. Plant extracts have emerged as
useful sources of nutraceuticals due to the rich diversity of the
19
phytoconstituents present in these extracts. Extract of green leaves of the plant
has been shown to have hypoglycaemic activity in diabetic animals
(Chakarbarty et al., 1960; Rao et al., 1995). Studies have revealed that a 75 %
methanol extract of AM decreases the blood glucose levels in alloxan induced
diabetic rats when administered at a dose of 100 mg Kg-1 (Sabu and Kuttan,
2004). AM extract has also been found to increase the levels of reduced
glutathione in the erythrocytes and decreases the levels of malondialdehyde in
alloxan induced diabetic rats (Upadhya et al., 2004). Studies have revealed
significant improvement in the glucose tolerance in rats administered the
aqueous decoctions of the plant (Karunanayaka et al., 1984). Administration
of ethanol extract of the plant for a period of two weeks has been reported to
have a hypoglycemic effect in diabetic rats (Kar et al., 2003). Sachdewa et al.
(2001) have reported glucose lowering effect of AM on one week
administration of extract in diabetic rats. The AM extract has been
documented to have maximal antihyperglycemic effect at the end of second
week of administration in a four week study (Upadhya et al., 2004). AM
leaves have been investigated to have hypoglycemic effect in normoglycemic
rats as well (Sharma et al., 1996).
Numerous mechanisms have been reported for the hypoglycemic effect of the
plant in diabetic conditions. These include regeneration of the damaged
pancreatic beta cells (Das et al., 1995), increase in the concentration of insulin
secreted by the beta cells (Kamalakkannan and Prince, 2003; Nammi et al.,
2001; Rao et al., 1995; Sachdewa et al., 2001; Sharma et al., 1996), inhibition
of glucose absorption from the gastrointestinal tract (Rao et al., 1995),
increase in sensitivity of the peripheral tissues to glucose (Sachdewa et al.,
2001) and restoration of the liver and renal vasculature damaged due to
diabetes (Das et al., 1996). Treatment with AM extract is also postulated to
reverse the muscarinic M1 receptor gene expression which is decreased in
diabetic rats and subsequently increase the vagal nerve stimulation and insulin
secretion thereby having a regulatory effect on glucose homeostasis in
diabetes (Gireesh et al., 2008). Studies have revealed AM to have stimulatory
action on PPAR-γ in vitro (Anandharajan et al., 2006) and in vivo (Sharma et
al., 2011).
20
2.3.3 CARDIOPROTECTIVE ACTIVITY
Hyperlipidemia characterized by an increase in blood cholesterol, low density
lipoproteins cholesterol and triglycerides and decreased high density
lipoprotein cholesterol leads to a number of chronic cardiac ailments. The
incidence and prevalence of cardiovascular disorders has increased
tremendously over the last few decades and plants have emerged as attractive
targets for finding pharmacologically active molecules with improved
therapeutic profile. The aqueous and alcohol extract of the leaves of AM has
been shown to reduce the pulse rate and increase the amplitude and tone of
contractions in isolated frog heart (Haravey, 1968). The plant extract has also
been found to attenuate the deleterious effects of calcium overload in frogs
(Haravey, 1968). The methanol extract of the root bark of the plant is reported
to contain auraptene which decreases the calcium paradox induced ischemic
injury and spontaneous beating in isolated myocardial cells (Kakiuchi et al.,
1991).
Oral administration of the aqueous leaf extract of AM has been studied to
prevent isoprenaline induced myocardial infarction in rats (Prince and
Rajadurai, 2005). AM extract treatment for a period of 35 days has been
postulated to reduce the levels of creatine kinase, lactate dehydrogenase,
Na+/K+ ATPase in isoproterinol treated rats and hence confer cardioprotective
effect (Prince and Rajadurai, 2005). Kamalakkannan and Prince (2003) have
proposed AM extract to have a marked hypolipidemic effect in diabetic rats.
Ethanol extract of AM leaves is documented to inhibit the increase in serum
cholesterol and triglycerides and increase high density lipoproteins in triton
and diet induced hyperlipidemic rats (Vijaya et al., 2009).
A polyherbal preparation containing AM and five other plant extracts has been
documented to decrease the rise in serum lipids, cholesterol and triglycerides
significantly in experimental model of hyperlipidemia in rats (Ansarullah et
al., 2012). Periplogenin, a cardenolide obtained from the leaves of AM has
been reported to have a protective effect against doxorubicin induced
cardiotoxicity and lipid peroxidation in rats (Panda and Kar, 2006). Oral
administration of methanol extract of the leaves of AM has been proposed to
21
have significant hypolipidemic effect in streptozotocin induced diabetic rats
(Juvekar and Bandawane, 2009). Lupeol obtained from the leaves of AM has
been studied to have antidyslipidemic activity in streptozotocin diabetic rats
(Papi Reddy et al., 2009). Unripe fruit extract has been documented to be used
in cardiac ailments (Dhankar et al., 2011). AM has been proposed to have
therapeutic potential in cardiovascular disorders due to inhibition of apoptosis
induced by ischemia-reperfusion induced myocardial injury (Ahmad et al.,
2010).
Padma-28, a polyherbal Tibetian preparation containing AM has been reported
of have beneficial effect on patients suffering from peripheral arterial disease
in a meta- analysis study (Melzer and Saller, 2010). Aegeline, an alkaloidal-
amide isolated from the leaves of AM has been found to have antidyslipidemic
effect in streptozocin induced diabetic rats (Narendra et al., 2007).
Pharmacophoric and 3D QSAR studies have suggested that aegline may have
a β3 adrenergic agonistic activity (Narendra et al., 2007). Studies have
suggested fresh juice of AM to be better tolerated and less toxic cardiotonic in
isolated frog hearts as compared to digoxin (Dama et al., 2010).
2.3.4 ANTIMICROBIAL ACTIVITY
Consumer preferences to naturally derived antimicrobial agents have increased
and plant medicines are being explored for their antimicrobial activities.
Several studies have revealed the antibacterial activity of AM (Dey and De,
2012; Gautam et al., 2013; Prasannabalaji et al., 2012). Petroleum ether
extract obtained from callus culture of AM has been documented to have an
inhibitory effect on the growth of Salmonella typhi in in vitro studies
(Thangavel et al., 2008). Shahidine, a highly labile oxazoline obtained from
AM, has been reported to have antibacterial activity against Gram positive
bacteria (Faizi et al., 2009). Aqueous and ethanol extracts of AM have been
postulated to have strong inhibitory effect on the growth of some bacteria
causing common human diseases including Staphylococcus aureus,
Pseudomnas aerugenosa and Escherichia coli (Chattopadhyay et al., 2009).
Maity et al. (2009) have suggested AM to have therapeutic potential for
developing novel antimicrobials. Hot aqueous decoction of unripe fruits of
22
AM has been demonstrated to have cidal activity against Giardia and rota
virus in comparison to limited activity against bacteria such as E. coli (Brijesh
et al., 2009). Studies have hypothesized AM to have a broad spectrum
antibacterial activity that includes both the Gram positive and Gram negative
bacteria, while certain bacterial strains such as Bacillus subtilis are resistant to
the action of the plant extracts (SaradhaJyoti and SubbaRao, 2010).
Plant extracts of AM and Andrographis paniculata have been reported to have
synergistic antibacterial action (Rasi and Daniel, 2011). The bael plant has a
long history of use in ethnomedicine for its antibacterial property (Baliga et
al., 2011). The chloroform extract of the leaves of AM has been reported to
have a higher activity against Proteus mirabilis and Klebsiella pneumoniae
whereas the methanol extract has been studied to have a better action against
Salmonella typhi (Kothari et al., 2011). Aqueous and ethanol extract of the
leaves of AM have shown significant activity against multi drug resistant
strains of uropathogenic bacteria including Acinetobactor baumannii,
Citrobactor freundii, Klebsiella oxytoca, Proteus mirabilis, Proteus vulgaris
and Pseudomonas aeruginosa (Rath et al., 2012).
Chakthong et al. (2012) have isolated alkaloids and coumarins from the
acetone extract of green fruits of AM and investigated the antibacterial activity
of these compounds. The aqueous and ethanol extracts of AM have been
shown to have significant antimicrobial activity against ten species of multi
drug resistant strains of enteropathogenic bacteria (Rath and Padhy, 2012).
Volatile oil obtained from the leaves of plant has been documented to have
potent antifungal activity against various strains of fungi (Rana et al., 1997).
2.3.5 HEPATOPROTECTIVE ACTIVITY
Traditional systems of medicines have been widely practiced through
generations to cure various hepatic ailments. The chloroform, alcohol and
aqueous extracts of AM leaf have been documented to decrease the blood
levels of serum glutamate pyruvate, serum glutamate oxaloacetate
transaminase, alkaline phosphatase and bilirubin in ethanol induced
hepatotoxicity in rats (Modi et al., 2012). The aqueous fruit extract of the plant
23
has also been documented to have a protective action in paracetamol induced
hepatotoxicity in rats (Sastry et al., 2011). Administration of the dried leaf
powder of AM for a period of 14 days has been reported to have a
hepatoprotective effect in carbon tetrachloride induced hepatotoxicity in rats
(Jayachandra and Sivaraman, 2011). Furthermore, the hepatoprotective effect
of the dried leaf powder of the plant was comparable to that of the standard
drug Liv 52 (Jayachandra and Sivaraman, 2011).
2.3.6 ACTIVITY IN ULCERATIVE COLITIS
Ulcerative colitis is a highly debilitating ailment and therapeutic interventions
available are only a few. Plants have emerged as useful sources of drugs to
mitigate a number of chronic ailments such as ulcerative colitis. AM has been
reported to be used for gastroprotective effect in ethnomedicine (Romano et
al., 2012). Oral administration of the extract of unripe fruit of AM at different
concentrations, once daily, has been reported to have a significant protective
effect on acetic acid and indomethacin induced ulcerative colitis in rats
(Behera et al., 2012). The extract was found to decrease mast cell
degranulation, disease activity index, macroscopic and microscopic scores of
disease severity in both the models significantly (Behera et al., 2012). AM
treatment has also been postulated to have protective effect on 2,4-
dinitrobenzene sulfonic acid induced colitis in rats (Gandhi et al., 2009).
2.3.7 ANTIFERTILITY EFFECT
Aegle marmelos has been used in ethno medicine for antifertlity effect (Jain et
al., 2004). Studies have revealed that the various parts of AM including the
stems, fruits, seeds and leave have antifertility effect in male animals
(Agrawal et al., 2012; Gnanasam et al., 2002). The bark extract of AM
contains marmin and fagarine, which are postulated to reduce male fertility in
rats (Agrawal et al., 2012). Treatment of male rats with methanol extract of
AM caused dose dependent decrease in sperm density, motility, viability and
acrosomal integrity by decreasing the serum testosterone levels and the weight
of the reproductive organs in male animals. These observations suggest that it
may be used as a male contraceptive (Agrawal et al., 2012).
24
Administration of the aqueous leaf extract of AM has been associated with
reversible loss of fertility without affecting the vital parameters in rats
(Chauhan et al., 2009). Alkaloids, phenolics and triterpenoids present in the
aqueous extract of the leaves of AM have been reported to decrease the
vitality of human sperms in in vitro studies (Mohanraj et al., 2009). A dose of
300 mgKg-1 of 50% ethanol extract of AM is documented to produce a
complete inhibition of fertility in rats (Chauhan and Agarwal, 2007, 2008).
2.3.8 ANTIDIARRHEAL ACTIVITY
Aegle marmelos is used by the tribal populations in West Bengal and Assam
for its antidiarrheal action (Dry and De, 2012; Sharma et al., 2012). Methanol
extract of the unripe fruit of AM is documented to have protective effect on
castor oil induced diarrhea (Maity et al, 2009; Shoba and Thomas, 2001). AM
is documented to have a protective action against gastric mucosal damage and
diarrhea induced by various agents including hypothermia restraint, absolute
ethanol, indomethacin and castor oil and study reported AM to decrease the
intestinal fluid accumulation and gastric mucosal damage significantly (Shoba
and Thomas, 2001). Mebarid, an Ayurvedic polyherbal formulation containing
AM as one of the components, has been documented to have potent
antidiarrheal, antimotility and antiulcer activities in rats (Bafna and
Bodhankar, 2003). Studies have revealed that intracaecal administration of
methanol extract of AM is more effective than oral dose in protection against
experimentally induced diarrhea (Shoba and Thomas, 2003).
It has been postulated that free radical scavenging activity of AM plays a
significant role in protection against experimentally induced ulcers and
diarrhea in rats (Rao et al., 2003). The chloroform extract of the root of AM
has also been suggested to have in vitro and in vivo antidiarrheal activity
(Mazumdar et al., 2006). Hot water decoction of the dried unripe fruit of AM
is documented to prevent infective diarrhea caused by micro-organisms such
as Giardia and rota virus both of which are highly virulent (Brijesh et al.,
2009).
25
2.3.9 ANTIVIRAL ACTIVITY
Viral infections are one of the most severe microbial infections and lead to a
high incidence of morbidity and mortality globally. Infections such as HIV,
dengue, hepatitis B and C, and influenza are among the most notorious viral
infections. Due to high toxicity of the existing antiviral drugs, natural products
are being explored for potential antiviral activity. Studies have revealed the
bark, fruit and root of Aegle marmelos to have activity against human
coxsackie viruses and marmelide has been isolated as the antiviral
phytoconstituent (Badam et al., 2002). Marmelide is reported to interfere with
the early stages of viral replication. The fruit extract of AM has been
postulated to have an action similar to interferons (Babbar et al., 1968). The
ethanol extract of bael fruit has been documented to inhibit the Ranikhet
disease virus (Dhar et al., 1968).
2.3.10 MISCELLANEOUS ACTIONS
Arul et al. (2005) have investigated the extracts of leaves of AM in various
solvents including petroleum ether, chloroform and ethanol for analgesic and
anti-inflammatory activities. The results of the study revealed marked
analgesic and anti-inflammatory activities of the extracts. Ethanol extract of
AM has been shown to have most significant analgesic activity on oral
administration (Muruganandan et al., 2000). Methanol extract of AM has been
reported to decrease acetic acid induced writhing and thermal hyperalgesia in
mice (Shankarananth et al., 2007). Ethanol extract of AM leaves has been
postulated to produce relaxant effect in histamine induced contractions in
isolated ileum and tracheal chain from guinea pigs (Arul et al., 2004). AM is
used in indigenous medicine for the treatment of asthma (Prasad et al., 2009).
Studies have revealed the fruit extract of the plant to have immunomodulatory
activity (Patel et al., 2010).
Water extract of AM leaves has been shown to inhibit the levels of thyroid
hormones in rats when administered at a dose of 1 g Kg-1 (Panda and Kar,
2006). The decrease in serum T3 and T4 levels has been postulated to be due
to antiperoxidative action of AM (Kar et al., 2003). PHF, a polyherbal
preparation containing seven herbs including AM has been documented to
have prokinetic effect in mice and rats (Srinivasan et al., 2005).
Aqueous extract of the fruits of AM has been reported to lower the intraocular
pressure in water loading and steroid induced models of raised intraocular
pressure in New Zealand white rabbits when applied topically (Agarwal et al.,
2009). Studies have revealed the ointment containing aqueous and methanol
extracts of bael seeds to increase the percentage wound contraction, tensile
strength and decrease the period of epithelialization of excision and incision
wound models in rats (Sharma et al., 2011). Toxicological studies have
revealed LD50 of AM leaves to be relatively high when given orally and
intraperitoneally in a single dose as well as on chronic administration for 14
days (Veerappan et al., 2007).
The number of papers on Aegle marmelos published in the last ten years and
the journals where these have been published are given in Fig. 6 and Fig. 7
respectively.
0
50
100
150
200
250
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
Years
No.
of P
ublic
atio
ns
Fig. 6 Evolution of published work on Aegle marmelos
[Retrieved from SCOPUS database]
26
0 5 10 15 20 25 30 35
Indian Drugs
J. App. Pharma. Sci.
American Eurasian J. Sustainable Agri.
Pharmaceutical Biology
Indian J. Pharmacol.
BMC Complementary Alter. Med.
Int. J. Pharma Bio Sci.
Evidence Based Complementary & Alternat. Med.
Int. J. Pharma. Sci. Review Res.
Asian Pacific J. Tropical Disease
Food Chemical Toxicol.
Pharmacologyonline
Asian Pacific J. Tropical Biomedicine
Int. J. Pharmacy Pharmaceut. Sci.
Journal of Ethnopharmacol.
Fig. 7 Journals publishing research articles on Aegle marmelos from year 2007-2012 [Retrieved from SCOPUS database]
2.4 COUMARINS IN PLANTS
Coumarins are synthesized as secondary metabolites in plants and are
benzopyrone derivatives. Coumarins contain α-pyrone group where as
flavonoids, which are structurally close to coumarins have γ-pyrone moiety.
Linear furanocoumarins are typical to the families Rutaceae, Apiaceae,
Leguminosae and Moraceae (Berenbaum et al., 1991). In their natural form,
coumarins may be linked with sugars and may be present as glycosides. The
furanocoumarins have a five membered furan ring attached to the coumarin
nucleus and are synthesized via shikimic acid pathway in plants (Berenbaum
et al., 1991). In plants coumarins act as phytoalexins which are formed in
response to injury to the plant and are abundantly present in leaves, fruits and
seeds of the plants (Berenbaum et al., 1991).
These phytoconstituents have been studied for a wide variety of biological
activities including facilitating skin pigmentation in vitiligo and psoriasis
(Dewick, 2009), cytotoxic activity against cancer cell lines (Um et al., 2010),
cardioprotective activity (Vimal and Devaki, 2004). Imperatorin is a linear
furanocoumarin isolated from the fruit extract of AM (Kamalakkanan and
Prince, 2003). Studies have revealed that imperatorin inhibits the action of γ-
27
28
aminobutyric acid (GABA)-transaminase, the enzyme that causes degradation
of the neurotransmitter GABA (Choi et al., 2005). Imperatorin has been
documented to ameliorate electro-shock induced convulsions in rats (Luszczki
et al., 2009).
2.5 PEROXISOME PROLIFERATOR-ACTIVATED RECEPTORS
Peroxisome Proliferator-Activated Receptors (PPARs) are a family of nuclear
receptors discovered in 1990 (Issemenn and Green, 1990). They are members
of steroid hormone receptor superfamily (Youssef and Badr, 2011). Three
types of PPARs have been identified. These include PPAR-α, PPAR-β/δ and
PPAR-γ, which differ in their tissue distribution, and the ligand specificity
(Berger and Moller, 2002). These receptors form heterodimers with the
retinoid X receptor (RXR) to which the ligands bind (Fig. 8). The complex
then translocates into the nucleus where it binds to specific PPAR response
elements in the DNA in specific promoter regions and brings about a cascade
of complex events involving the influx of co-activators and release of co-
repressors, and finally culminating into transcription (Youssef and Badr,
2011).
PPARs are mainly involved in fatty acid mobilisation and utilization, insulin
sensitivity, lipid storage in liver and lipid mobilization (Jungbauer and
Medjakovic, 2012). PPARs have emerged as interesting and promising targets
for developing new drugs to treat disorders such as cancer, diabetes mellitus,
obesity etc. PPARs have also been postulated to be present in the central
nervous system where they may be involved in various neurological processes
regulating the brain function (Heneka and Landreth, 2007). Studies have
indicated a role of PPARs in H.pylori infection (Lee et al., 2012). The PPARs
are characterized by the presence of six structural regions with four functional
domains. Out of these the A/B region is ligand-independent transactivation
domain, the C region is the region for DNA binding, E/F is the ligand binding
domain that has co-activator/co-repressor binding regions (Jungbauer and
Medjakovic, 2012).
Fig. 8 Mechanism of PPAR signalling.
2.5.1 PPARs IN CANCER
Studies have revealed that the PPARs may be involved in the pathogenesis of
various types of tumors (Panigrahy et al., 2008). It has been reported that
PPAR-γ agonists have an inhibitory effect on the growth of brain tumor cells
(Grommes et al., 2006). Pioglitazone, a PPAR-γ agonist, has been found to
reduce the proliferation of glioblastoma (Papi et al., 2009). Treatment with
L16504, a PPAR-β/δ agonist, has been shown to inhibit lung carcinoma cells
(Fukumoto et al., 2005). It has been postulated that decreased expression of
PPAR-γ is associated with poor prognosis in the patients suffering from lung
cancer (Sasaki et al., 2002). PPAR-γ receptor has been postulated to be
involved in the antiproliferative effect of prostacyclin (Nemenoff et al., 2008).
PPAR-γ has also been linked to decrease in the proliferation of colonocytes
(Matthiessen et al., 2005).
It has been documented that PPAR-γ is expressed in the urinary tract and is
associated with decreased incidence of tumour proliferation (Myloma et al.,
2009). PPAR-γ agonists have also been associated with decreased incidence of
29
30
hematological cancers (Garcia-Bates et al., 2008). The molecular mechanisms
of inhibition of tumours include promoting apoptosis in the tumor cells,
alteration in membrane permeability and, up-regulation of anti-apoptotic
proteins in normal cells (Youssef and Badr, 2011). In clinical studies,
rosiglitazone treatment has been found to have a significant inhibitory effect
on pancreatic cancer (Youssef and Badr, 2011). The synergistic effect of
PPAR ligands with radiation therapy and chemotherapy of cancers has been
shown both in vitro and in vivo (Shimizu and Moriwaki, 2008).
2.5.2 PPARs IN DIABETIC NEPHROPATHY AND CARDIOMYOPATHY
Diabetes mellitus is now prevalent in epidemic proportions world wide. The
availability of numerous options for controlling blood glucose levels has
increased the life expectancy of diabetic patients and this increase in life span
of the patients has led to a higher incidence of the complications due to
diabetes such as diabetic neuropathy, diabetic nephropathy (DN) and diabetic
cardiomyopathy (DCM). These complications are a major cause of concern in
the diabetic patients and cause a very high morbidity, and mortality. It is
estimated that by the year 2030 more than 360 million patients suffering from
type II diabetes mellitus will be at a high risk of DN and DCM
(Kouromichakis et al., 2012). The pathogenesis of these syndromes is
complex and multifactorial. The therapeutic options currently available in the
treatment of these complications are insufficient. Inflammatory process is now
believed to be involved in the pathogenesis of chronic ailments including
diabetes mellitus (Jungbauer and Medjakovic, 2012). PPARs have been
postulated to play a vital role in controlling inflammation (Chinetti et al.,
2000). Various chemical mediators are involved in the inflammatory process,
including, interleukins, tumour necrosis factor, interferons, leukotrienes,
prostanglandins, endoperoxides etc. (Fain, 2006).
PPAR ligands have emerged as molecules with pleiotropic actions and are
being explored for their value in treating these ailments (Kouromichakis et al.,
2012). DN is the leading cause of end stage renal disease in clinical settings.
Various factors such as altered lipid balance, proinflammatory mediators,
increased blood pressure, and oxidant stress etc. lead to DN (Levi, 2011).
31
Studies have revealed PPAR-α agonists to be of benefit in decreasing the
symptoms of DN in type II diabetic mice (T2DM) (Park et al., 2006). Patients
with mutations in PPAR-γ have been associated with increased severity of
insulin resistance and decrease in the onset time of hypertension, DN and
DCM (Lombard and Cowley, 2012).
Several studies have reported the protective effect of PPAR-γ agonists in DN
(Yoshioka et al., 1993; Levi, 2011). The glitazones which are PPAR-γ
agonists have been found to decrease the symptoms of DN such as
albuminuria, maintain glomerular filteration rate, prevent fibrosis in the
interstitium and glomerulosclerosis (Sarafidis et al., 2006). PPAR γ agonists
have been shown to have synergistic effects with PPAR-α agonists in
decreasing the severity of diabetic symptoms in animal studies (Cha et al.,
2007). In addition to the above effects, PPAR-γ agonists offer other
advantages including antifibrotic, anti-inflammatory and antiproliferative
effects through inhibition of activation of NFkB, free radical species and
infiltration of inflammatory cells like the macrophages (Wu et al., 2004).
Human type I and type II diabetes mellitus is associated with altered lipid
balance and fatty acid, and cholesterol deposition in the renal tissue as well
(Levi, 2011). The PPARs because they help in mobilising the fatty deposits
are receiving special attention in mitigating the renal complications of diabetes
(Yoshioka et al., 1993).
The vascular function has been found to be altered in patients with mutations
in PPAR- γ and impaired relaxant response of the blood vessels to
acetylcholine has been found in these patients (Lombard and Cowley, 2012).
Vascular effects of PPARs include direct effects mediated by PPARs in the
blood vessel wall and indirect effects which are caused by regulation of
glucose, and fatty acid metabolism (Wang et al., 2006). Also, activation of
PPAR-δ has anti-inflammatory effects and decrease in apoptosis in the blood
vessels (Katusic et al., 2012). The PPARs regulate fuel metabolism in the
heart. PPAR-γ is involved primarily with the differentiation of adipose cells
and fat storage. It is expressed in the myocardium as well although the extent
is lower (Madrazo and Kelly, 2008). Studies have revealed beneficial effects
32
of thiazolidinediones in the diabetic heart and this protection is due to anti-
inflammatory effect of the PPAR-γ ligands (Abdelrahman et al., 2005). The
PPAR ligands have diverse target sites to mediate the protective effects in
DCM such as anti-inflammatory action, antihypertensive effect, preserving the
endothelial function, suppression of renin-angiotensin system (RAS) etc
(Sugawara et al., 2010).
2.5.3 PPARs IN EPILEPSY
PPARs have been postulated to be present in the brain. PPAR-γ is the most
widely expressed PPAR in the brain (Fajas et al., 1998). Three splice variants
of PPAR-γ are known PPAR-γ1, PPAR-γ2 and PPAR-γ3 (Fajas et al., 1998).
PPAR-γ in brain is involved in many regulatory functions. The inhibition of
neuroinflammation is proposed to be involved in the inhibition of various
neuropsychiatric disorders such as depression, epilepsy etc as well as
neurodegenerative disorders including Alzheimer’s disease, Parkinson’s
disease, Huntington’s disease (Garcia-Bueno et al., 2008). Administration of
thiazolidinediones is documented to decrease the expression of inflammatory
mediators including tumour necrosis factor alpha and inducible nitric oxide
synthase (iNOS) in brain cells (Garcia-Bueno et al., 2008). Rosiglitazone has
been found to produce a dose dependently increase in the dendritic spine
density in rat neurons (Brodbeck et al., 2008). Modulation of bioenergetics in
the brains of stressed animals such as to inhibit excitotoxicity has been
documented with PPAR γ ligands (Garcia- Bueno et al., 2008). The methanol
extract of A. marmelos has been documented to promote glucose uptake by
activation of PPAR-γ in in vitro studies (Anandharajan et al., 2006). Recently,
the fruit extract of Aegle marmelos has been reported to increase the
expression of PPAR-γ diabetic rats (Sharma et al., 2011).
Top Related