Isoflavones : A Natural Substitute for Postmenopausal Management
By - 02/01/2006
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Prof. S. Saraf
Phytohormones have proven to be a better alternative for many kinds of diseases.
Isoflavones, represents the most active group of phyto-oestrogens which has
served as an important remedy for the treatment of various complex situations
such as post menopausal complications (PMC) 1-3.
The nature of complication is more psychological than pathological. The main
problem associated with PMC is the change in the psychological status of the
patient and the modern day medication recommends synthetic drugs, which are
associated with several serious side effects. On the basis of various epidemiological
and experimental studies, beneficial effect of isoflavones has been demonstrated.
Role of isoflavones in the steroid metabolism and synthesis is the key mechanism
explaining its role in hormonal disorders. Isoflavones, being natural source
of estrogenic supplement suffice its applicability as safer and effective option
for treatment of PMC and other related conditions.
Introduction
Isoflavones belongs to the group of flavonoids, which are low molecular weight
polyphenolic compounds present in all vascular plants. Isoflavones, along with
coumestans and lignans form an important class of non - steroidal phyto-oestrogens.
Isoflavones consist of phenyl benzopyrone skeleton (C6-C3-C6). Isoflavones occur
as unconjugated (aglycone) or conjugated to sugars (glucosidic forms) 4.
The aglycone forms of isoflavones are biologically active forms. Phtoestrogens
are naturally found in many foods of plant origin5 such as rice,
wheat, oats, barley, pomegranate apples, garlic, coffee, fennel, liquorice,
parsley, cherries, yeast. potatoes, soyabeans6-14 and even in alcoholic
beverages15-18 but, isoflavones occurs principally in legumes such
as soyabeans. 5,7,19-21.
These are also present in herbs Red clover flower (Trifolium pratense) and broomtops (Cystisus scoparius).
These contain the aglycone forms and thus readily enter bloodstream.22 Dietary intake of soyabean provides the plant precursors of isoflavones as biochaninA and
formononetin.23,24 On removing the sugar residue due to fermentation by the intestinal bacteria,19-21,23-27 these are converted to the active isoflavones genistein and daidzein.21,31,32.
So the principal types of isoflavones present are formononetin,its demethylated product daidzein,biochanin and its demethylated product ,genistein and glycetein 28
Table1: major soya sources of isoflavones25
| SOYA FOOD | DAIDZEIN*(mg/100gm) | GENISTEIN*(mg/100gm) |
| Soyabean | 84 | 111 |
| Soyabean (roasted) | 56 | 87 |
| Soya flour | 23 | 81 |
* Active ingredients of isoflavones
In soya, isoflavones exist naturally as 12 different isomers wich are Genistein,
Genistin, 6”--acetylgenistin, 6”-- malonylgnistin, Daidzein,
Daidzin, 6”--acetyldaidzin, 6”--malonyldaidzin, Glycetein, Glycetin,
6”--acetylglycetin, 6”-- lonylglycetin32. The two
most important isoflavones are Daidzein and Genistein 2,5,30,66 as
the concentrations of these two are the highest in soyabeans i.e upto 3 mg/g.7,
30. Of the two principle isoflavones, genistein is the most abundant,
and most active.8, 27 Better effect of genistein is due to its ability
to bind to Erβ31, 32 almost similar to estrogen33.
“Menopause” a complete cessation of menstrual bleeding is the measured change
in the female’s physiological system after the age of 35 years. This condition
is associated with the vicarious complex symptoms known as “menopausal complications”
or post menopausal complication (PMC) which is manifested as a result of estrogens
depletion leading to heart diseases, backache, brittle bones, hot flushes, mood
changes, vaginal dryness i.e. Post Menopausal complications begin to appear.
Estrogens and Progesterone are given in the form of hormonal replacement therapy
(HRT). HRT suffers with serious drawbacks such as it requires critical supervision
of medical personal in case of persons suffering from heart diseases, hypertension,
diabetes, liver diseases, migraine, epilepsy and associated severe side effects.
Isoflavones being natural sources of estrogenic supplement are the safer option
and promotes a sense of well being in post menopausal women’s. 34,35
Pharacodynamics
Isoflavones are chemically similar to naturally occurring estrogens, but much weaker. They are 10,000 to 1,40,000 times less potent than estradiol - 17β. The relative potency, however, varies depending on many factors such as target tissue, species and age of subject, route of delivery, dose, length of exposure and metabolism5, 8,36. Genistein is the most potent isoflavone. The difference between genistein and daidzein’s potency is due to the presence of 5- hydroxyl group in genistein32, 38,39.
Table 2: Relative potency of Principal isoflavones as compared with
estrogens.5, 8,19,36-38.
Estrogen / Isoflavone | Potency |
Estradiol -17β | 100 |
Estrone | 50 |
Genistein | 0.084 |
Equol* | 0.061 |
Daidein | 0.013 |
* Breakdown product of daidzein
(i) Effect on menstrual cycle: Isoflavones lengthens the follicular
phase of menstrual cycle, but does not affect the luteal phase.23, 39-43
Furthermore isoflavones delay ovulation by lengthening the duration of menstrual
cycle41, 42 The prolongation of menstrual cycle with isoflavones
are associated with suppression of midcycle surges of FSH and LH.19, 30
As result, of isoflavones treatment the menstrual cycle lengthens by 2.5
days primarily by increase in the follicular phase. However, there is lesser
exposure to estrogen due to decreased circulating estrogen levels (20-30%).
(ii) Effect on heart
Isoflavones reduce total and the detrimental low density lipoprotein (LDL), cholesterol concentrations.29, 34. Since isoflavones are both hydrophobic and simultaneously hydrophihic, it shows their incorporation into LDL. 44 The various mechanisms of action where by isoflavones reduce cholesterol are
(i) Inhibition of cholesterol synthesis: less cholesterol available for circulation in LDL.20, 35,45.
(ii) Reducing lipoprotein a [Lp (a)] levels: Isoflavones uniquely reduce Lp (a) (in LDL) due to resemblance of genistein / daidzein to LDL particle. It is otherwise increasingly difficult to reduce the Lp (a) concentrations.21
(iii)Up regulation of LDL receptors in liver 26 increased removal of cholesterol from LDL molecules, which return to liver.
(iv)Increased bile acid synthesis: enhanced cholesterol excretion since bile acids are responsible for making cholesterol dissolve in bile.45, 46
Atherosclerosis:
Tyrosine kinase, an enzyme present within cells is responsible for the associated symptoms in atherosclerosis 47 and inflammatory response of the arterial lining in response to injury.48 Tyrosine kinase is directly responsible for causing smooth muscle cells to multiply which causes the initial obstruction of cardiac arteries, precipitating clot formation at the affected site .Tyrosine kinase is also responsible for platelet clumping (aggregation) by activating the platelets.49 Genistein is a well- known inhibitor of tyrosine kinase,50 as a result isoflavones are responsible for reduction in platelet derived growth factor (PDGF)50 which induces multiplication of smooth muscle cells. Genistein prevents platelet activation in response to stimulants like collagen, thromboxane A2, Thrombin and adenosine diphosphate (ADP),51 Diminishes platelet activation and prevents platelet aggregation.19,21 In fact, genistein and daidzein inhibit platelet aggregation by preventing thromboxane A2 from binding with its receptor 21 Also via inhibition of tyrosine kinase, genisten suppresses the activation of GPIIb/ III a receptors present on platelets which bind with fibrinogen, 52 and inhibits monocyte adhesion. Sticking of blood monocytes to arterial lining causes their migration into the arterial wall and their subsequent conversion into macrophages. Macrophages take up the cholesterol from LDL and deposit the same into the arterial wall to cause atherosclerosis.
It also reduces LDL oxidation: Only oxidized LDL can give its cholesterol
content to the macrophage. Thus isoflavones decreases cholesterol accumulation
into arteries by reducing monocytes conversion to macrophages and also lessening
cholesterol uptake by protecting LDL. As a result of all these actions, lsoflavones
can prevent development of atherosclerosis.25
(iii) Effect on bone: Isoflavones increase the bone mineral content
(BMC) as well as the bone mineral density (BMD). Isoflavones facilitate bone-forming
action of osteoblasts by combining especially with ERβ. Isoflavones suppress
bone destroying osteoclasts by directly suppressing recruitment and functioning
of osteoclasts, it also indirectly suppresses osteoclasts by facilation of inhibitory
chemical mediators for osteoclasts by osteoblasts.25,39
iv) Estrogenic / antiestrogen effects: A protein called as estrogen receptor (ER) is present in cell membranes of estrogen responsive tissues like female reproductive organs, breast, pituitary and hypothalamus. Estrogen attaches to ER and this estrogen - protein complex then moves into nucleus wherein it docks at sites within selected genes. Depending upon whether the gene is switched on or off, specific messenger ribonucleic acid (mRNA) and certain specific proteins are synthesized. The ER in genital tissues is ER alpha (α). Another receptor ER-beta (β), which is also estrogen-responsive, is found in cardiovascular system, lung, bone, urinary bladder, and prostate.53, 54
Table 3: Distribution of estrogen receptors46
ERα ERβ ERα +ERβ |
Adrenal Bone Breast |
Kidney Brain Ovary |
Testis lung uterus |
Prostate Vascular |
Thymus |
Urinary Bladder |
Isoflavones, like estrogens, also act by binding to ERs.5, 29,31
At low doses, Isoflavones displaces endogenous estrogens from the binding site.
At such levels, since the isoflavones themselves behave as weak estrogens at
ERβ, the net effect is antiestrogenic.55 At mid-concentrations,
isoflavones displace enough endogenous estrogens. The higher concentrations
of isoflavones compensates for the displaced estrogens and thus higher doses
of isoflavones acts like the displaced endogenous estrogen itself. In this way
the isoflavones can act as either estrogens or as antiestrogens. Since the postmenopausal
women have low levels of estrogens, isoflavones, even in small quantities, act
like weak estrogens by binding to the unoccupied ERs. The weak estrogenic effects
of isoflavones is due to their diminished affinity and occupancy time at ERs
as compared to 17β-estradiol.25Amongst the isoflavones, genistein
is the most active estrogen with highest binding affinity for the estrogen receptor
32. If l7β-estradiol affinity is100% for ER, then for genestein
it is only 27%. However, isoflavones attain concentrations100-fold higher
than endogenous estrogens.56 Hence, less affinity of isoflavones
for ERs is compensated by the high levels: the net effect is thus insignificant.
Selective effect for ER: Isoflavones are selective for Erα 29, 33 and therefore exert more effects on the cardiovascular system, bone and urinary bladder.37 The reproductive tissues have 100-1000 fold greater number of ERs than bone: however, bones have more ERα than Erβ.39
Some other effects of Isoflavones includes Inhibition of enzymes, Isoflavones inhibit the enzymes like Tyrosine kinase23,57, Estrogen synthetase , Aromatase 19,21, Type 1 17 b- hydroxysteroid reductase61,Topoisomerases (Topo) I and II 58,59 and Ornithine decarboxylase21.Antioxidant action- Isoflavones also exerts an antioxidant effect both in aqueous as well as in lipid media compartments. Genistein is the most potent antioxidant27.
Pharmacokinetics:
Absorption: Following intake of soya product containing isoflavones, the intestinal bacteria convert the contents into active genistein and daidzein. 39,55 The latter are absorbed by the small intestine and colon. The absorption of genistein is around 40%. 44
Blood levels: For isoflavones to be effective, genistein levels of 25 mmol/L should be achieved in blood. when total isoflavones intake is 50 mg/day, the blood plasma concentrations achieved are 50-800 ng/ml for genistein+ daidzein + equol26. Generally after 6 weeks of isoflavones intake, detectable levels are achieved in blood.60The plasma
Half- life of genistein/ daidzein is 7.9 hours in adults.46
Table 4: Plasma levels following intake of 50 mg isoflavones per day60
PLASMA LEVELS (ng/ml) GENISTEIN DAIDZEIN |
week 6 105.10 117.62 |
Week l0 175.15 184.85 |
Distribution: All the isoflavones are basically fat - soluble molecules,
and hence follow the same path as followed by other lipid nutrients. After absorption,
the chylomicrons deliver isoflavones to the liver.5,25 Here the isoflavones
are conjugated by the liver enzymes: both the unconjugated (ftee and active)
and conjugated isoflavones circulate in blood5,56 Only free
isoflavones (<_1%) are biologically active since they can be taken up
by tissues. Since isoflavones are not able to bind with serum proteins, even
their minute quantities (as free isoflavones) are sufficient for effects62.
All tissues, which contain ERs, take up circulating isoflavones from blood.
Table 5: Major target tissues for isoflavones
Reproductive tissue | Uterus, breast, prostate |
Cardiovascular tissue | Arteries, lipoproteins |
Skeletal tissue | Bone |
Metabolism: Genistein is broken down to p-ethyl-phenol and dihydrogenistein.39,52
Daidzein is converted to equol (which is biologically active) and O-demethylangolensin
(0-DMA).5,19 Equol is an active metabolite and is more estrogenic
than daidzein and 0-DMA.63
Excretion: Isoflavones are removed from the body via bile, urine, saliva, semen, faeces and breast milk. Since bile pours the isoflavones into the intestine, there is a re circulation of isoflavones and are once again absorbed (enterohepatic circulation). Biliary excretion and reabsorption continues till all the isoflavones are finally eliminated in urine.64, 65.
{mospagebreak title=Conclusion and References}
Conclusion:
Isoflavones a class of phytoestrogen are a natural and safe alternative for postmenopausal complications especially for such women who find it hard to tolerate the side effects of hormonal replacement therapy. Besides controlling the major symptoms of post menopause such as hot flushes, vaginal dryness etc., Isoflavones have positive effects in management of other symptoms such as headache. fatigue, depression, urinary frequency and it also shows antioxidant effect. They are also safe from risk of breast and uterus cancer.Moreover,psychological burden associated with the treatment regimen is also eliminated because patient is not subjected to any dosing as the dietary supplement of isoflavones is considered as safe alternative.
Although ample of experimental and epidemiological data is available supporting
the efficacy of isoflavones in PMC and related disorders.But ,still an elaborative
investigations regarding the dose response relationships and other aspects related
to human exposure is needed so that its protective role could be established
without any induced side effects.
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{mospagebreak title=About Authors}
About Authors
D.Singh, Manju Rawat, Swarnlata Saraf and S. Saraf*
Institute of Pharniacy, Pt. Ravishankar Shukla University,
Raipur 492 010 C.G.
Mr. Deependra Singh has nearly 6 years of research and teaching
experience. He is a hard working researcher . Mr . Singh did his masters degree
from Dept. of Pharmacy, Dr. H. S. Gour University, SAGAR., He has over 16 publications
to his credit published in international and national journals. He is an founder
secretary of IPA Chhattisgarh branch. His research interest extends from Noble
topical delivery systems, Delivery Systems for biologicals to Plant tissue culture.
Presently, he is working as a Lecturer at Institute of Pharmacy Pt. Ravishankar
Shukla University, Raipur, (C.G.)
Dr. (Mrs). Swarnlata Saraf has nearly 14 years of research
and teaching experience. She is a leading scientist and well-known in the field
of herbal cosmatics . Dr. Saraf did her doctoral research at the Dept. of Pharmacy,
Dr. H. S. Gour University, SAGAR. She has over 40 publications to her credit
published in international and national journals. She is an active member of
ipa ,apti and iste. Her research interest extends from Herbal Cosmetics to transdermal
drug delivery (specially Iontiphoresis), New Drug Delivery Systems for biological
therapeutic agents. She has Co-authored 1 books, in press. Presently, she is
working as a Reader at Institute of pharmacy Pt. Ravishankar Shukla University,
Raipur, (C.G.)
Prof. S. Saraf has nearly 17 years of research and teaching
experience at both U.G. and P.G. levels. He is a leading scientist and well-known
academician . Prof. Saraf did his doctoral research at the Dept. of Pharmacy,
Dr. H. S. Gour University, SAGAR. under the supervision of Prof. V. K. Dixit,
a renowned Pharmacognosist. He has over 50 research publications to his credit
published in international and national journals. He has delivered invited lectures
and chaired many sessions in several National Conferences and Symposia in India.
His research interest extends from Herbal Cosmetics to Herbal drug standardization
Modern analytical techniques, New Drug Delivery Systems with biotechnology bias.
He has authored 1 books, in press. Presently, he is Professor and Director Institute
of pharmacy and Dean, Faculty of Technology, Pt. Ravishankar Shukla University
, Raipur , (C.G.)
*Author for Correspondance
Ms. Manju Rawat has 3 years of research and teaching experience. She has been a bright student through out . Ms Rawat did her M.Pharm from Dept. of Pharmacy, Dr. H. S. Gour University, SAGAR. She has 04 publications to her credit published in international and national journals. Her research interest extends from Protein delivery to novel Drug Delivery. Presently, she is working as a Lecturer.