© Whole Foods
July 1997


                       Cruciferous Vegetables and Indoles: An Interview with Dr. Merrill Andrus


                                                        Richard A. Passwater, Ph.D.



Dr. G. Merrill Andrus received his Ph. D. in chemistry from the University of Washington in 1957  and he has experience in wood chemistry and ion exchange techniques among other things , as well as biochemistry.  In 1994, he became interested in indole-3-carbinol (I3C).  Dr. Andrus is the Vice President of Designed Nutritional Products in Orem, Utah.


Passwater:  Dr. Andrus, several researchers are studying indole-3-carbinol (I3C) and there many publications describing the benefits of I3C in the prevention and even treatment of cancer and a number of other diseases.  Why are you studying I3C and how long have you been researching I3C?


Andrus:  I have been researching I3C for about 2 2 years because there are many benefits from eating I3C either as it occurs in digested food or as it occurs in a dietary supplement.  There are many paths that have yet to be explored with this compound that can be so very important to our health.


Passwater:  Let=s go back to the very beginning.  Why were cruciferous vegetables selected for anti-cancer study?


Andrus:  Epidemiological studies have associated the consumption of lots of cabbage, broccoli, Brussels sprouts, and other members of the cruciferous family of vegetables with lower rates of cancer.  I guess the most dramatic occurred during World War 2 when Europeans didn=t have much meat available so they had to eat a lot of vegetables.  During that time, the rate of breast cancer dropped dramatically among European women.  Since that time various people have picked up and conducted hundreds of animal studies and now clinical studies are underway with women, both with material from vegetables and with the isolated I3C and its metabolites.  There are a number of research centers working on various aspects of this relationship. 


Passwater: I had the pleasure of attending a lecture by Dr. Paul Talalay in 1992.  He had established that the sulforaphane in crucifers was a potent inducer of the Phase II enzymes that detoxify xenobiotics (compounds foreign to the body).  Does I3C also stimulate Phase II enzymes?


Andrus: Yes, I3C stimulates Phase II enzymes including glutathione-S-transferase, quinone reductase, and UDP-glucuronsyltransferase.  Dr. Talalay published his findings at about the same time as some other folks were studying I3C.  As a matter of fact, some of the first suggestions of the importance of vegetable phytochemicals were made by Dr. Lee Wattenberg 20 to 25 years ago.


Passwater:  Since they seem to have a common origin, are the chemical structures of I3C and  sulforaphane similar?


Andrus:  Not really.  Their relationship is that both sulforaphane and I3C are derived from glucosinolates, which are complex molecules occurring in cruciferous vegetables such as cabbage, broccoli, and Brussels sprouts.  Glucosinolates consist of a sulfur- containing group and a sugar group plus one other identifying group.  Sulforaphane is derived from one glucosinolate, while I3C is derived from another.  The glucosinolate which gives rise to I3C is glucobrassicin, while sulforaphane comes from glucoraphanin


Passwater:  You mentioned Dr. Wattenberg.  I remember his research on how xenobiotics stimulated P-450, a phase I enzyme.  In 1968, Dr. Dan Niebert, a colleague of mine who was at the NICHED at NIH were using a fairly new technique invented by Dr. Britton Chance called dual wavelength spectrophotometry to study P-450.  Dr. Niebert was a leader in

P-450 research and we became friends perhaps due to the fact that we had very similar interests and that I had an Aminco-Chance Dual Wavelength Spectrophotometer in my lab and he didn=t.  In 1970, Dr. Niebert and I applied for an Investigative New Drug Application to study the synergism of antioxidants in slowing the aging process in humans. Dr. Wattenberg=s research was of great interest to us.  That seems like a lifetime ago, but I am glad that the research has continued.

The name P-450 was given to these enzymes because their maximum peak of absorbed energy was at 450 nanometers, and even though we didn=t know what their chemical structures were, we could monitor them with a spectrophotometer and observe their reactions.  At first, it was thought that the P-450 peak was due to a single enzyme.  We learned this absorption maximum was common to members of a system of mixed oxidases.


I remember the implications that arose from finding that the compound that we believed was a carcinogen was really not a direct carcinogen, but its epoxide was the true carcinogen.  Dr. Niebert first hypothesized that those who produced more mixed enzymes in their livers might be at greater risk to develop cancer, because they would produce more of the epoxide carcinogen from the benzopyrene in cigarette smoke.  Smokers absorbing benzopyrene from cigarette smoke were not in danger until the carcinogen epoxide was formed by the P-450 enzymes.  Dr. Niebert wondered if we could measure the level of P-450 enzymes in people, could we predict their cancer risk?  As more research showed, this was only half of the story.  Would you please review for our readers how Phase I and Phase II enzymes work together to detoxify potentially harmful compounds?


Andrus:  Basically, Phase I enzymes such as cytochrome P-450 oxidize, hydrogenate, reduce or hydrolyze xenobiotics.  The Phase II enzymes then pick up where the Phase I enzymes left off by conjugating (adding atoms to) the xenobiotics with glucoronides, sulfates, or even glutathione.  Then the xenobiotics can easily be passed out of the body in the urine or feces.  The conjugation of sulfhydryl and methyl groups acts to make the toxin intermediate easier to bind and more water soluble so that it can be removed from the body.


Passwater:  This is a good one-two punch against toxins and carcinogens.  Does I3C affect Phase I enzymes?


Andrus:  P-450 enzymes are induced by eating I3C.  It=s particularly interesting that some of these, in turn, affect the metabolism of estradiol.  Normally, when estradiol, an estrogen or female sex hormone, is metabolized, it can be oxidized into several metabolites.  Two of these metabolic processes can be described as C-2 oxidation and C-16a oxidation.  The C-16a oxidation products acts a lot like a fully reactive estrogen, increasing the rate of cell division.  This process is essential in beginning cancer propagation.  It has been shown that women with breast cancer have higher levels of C-16a metabolites and lower levels of C-2 metabolites.  Higher levels of C-16a metabolites can be considered a biomarker of breast cancer.  This subject has been reviewed by Dr. Jon J. Michnovicz of the Institute for Hormone Research and Dr. H. Leon Bradlow of the Strang Cancer Prevention Center (both of New York City). 1


In studies by Dr. Bradlow and others, both vegetables and I3C have been shown to give increased C-2 oxidation, resulting in a decrease of the production of active estrogen metabolites.  In such studies, it has been shown that a proportional amount of I3C can provide as much protection as whole cruciferous vegetables.  Further, induced cancers in the mammary glands, forestomachs, livers, and tongues of laboratory animals have been inhibited by prior I3C feeding.  This concept has been extended to show that I3C inhibits endometrial cancer in female rats. 2


Currently, studies using humans are being conducted by several cancer research groups.  Then again, there are the epidemiological studies which I mentioned earlier of the breast cancer rates in the European women who ate lots of cruciferous vegetables.


Passwater:  Does I3C affect estrogen or testosterone metabolism


Andrus:  Yes, I3C does induce the enzymes which make 6a, 16a and 16b hydroxytestosterone.3


Passwater:  Has I3C been shown to directly block tumor formation?


Andrus:  That has been shown in several animal studies where laboratory rats or mice were fed I3C before or concurrently with exposure to a directly acting carcinogen.  The test animals showed significantly lower appearances of tumors compared to controls.  Incidently, recent reports from the University of Hawaii show that colon cancer biomarkers are significantly inhibited by feeding I3C to rats. 4,5


Passwater:  What do we know about I3C and prostate cancer?  Didn=t an animal study show that I3C inhibited the implantation of prostate cancer?


Andrus:  Not much is known formally.  One dietary supplement company has combined I3C with saw palmetto extract in a product for men.  There aren=t any clinical trials to back up the assumption that this combination is beneficial, but I expect that it is.


Passwater:  What do we know about I3C and cervical cancer?


Andrus:  We know that cervical cancer is encouraged by the C-16a form of estradiol oxidation and that I3C reverses, or at least limits this course of metabolism.  Therefore, cervical cancer is diminished by the feeding of I3C according to a substantial number of animal studies. 6


Passwater:  What do we know about I3C and uterine cancer?


Andrus:  About ten years ago, it was observed that the estradiol oxidation to give either the 2-hydroxyestrone or the 16a-hydroxyestrone could be used as a marker in post-menopausal endometrial cancer.  Recently, Japanese researchers have demonstrated that I3C can inhibit the formation of endometrial cancer in rats.2

 Passwater:  What do we know about I3C and warts?


Andrus:  We do know that a certain small population has a problem with warts on their larynx; it is called recurring respiratory papillomatosis (RRP).  It is a papillomas virus that causes a wart on the vocal cord and, roughly speaking, there are just maybe less than 10,000 people suffering from RRP in the United States, and just a few hundred have it in a severe form.  The most severe form is when the wart grows rapidly to fill the airway or go down into the lungs.  In one dramatic case, a whole lung was filled with wart tissue and the patient died at about age 18.  Over 60 percent of the people having this condition and who take I3C find that they don=t have to have surgical procedures so often.  When people have this laryngeal papillomatosis, the major surgical procedure is laser surgery on their vocal chords.  You can imagine how traumatic that might be to a little child, and many of the patients are children.  People who have this laser surgery maybe once or twice a month are very much relieved when they can take I3C as a capsule and have the frequency of their surgery cut back to once a year or less.

There are studies going on at three universities that I know of to show that I3C is effective for patients having laryngeal papillomatosis.  An extension of this idea is that general warts, which afflict 25 to 40 million Americans, come from a similar kind of papillomas virus.  Researchers are beginning to look at I3C as a way of treating those problems.


Passwater:  The reason that I asked that question, is that I recently had a grandson who had prolonged laryngitis.  His CT scan (computerized tomography, often called a CAT scan) suggested that he possibly had a growth on his vocal chords.  As it turned out he didn=t have a growth, but an accumulation of debris from a bacterial infection.  When I did a literature search  on laryngeal warts, I was relieved to find that I3C was available to control such things rather than having surgery every few months.


The control of laryngeal warts seems to involve a different mechanism than stimulation of phase II enzymes to detoxify xenobiotics.  What is the mechanism here?  Here we have a virus involved rather than a xenobiotic.  Before we were talking about prevention and now we are talking about warts that already exist.  What is going on here?


Andrus:  There is a relationship between C-16a oxidation of estradiol and the proliferation of warts caused by papillomas virus.7  Our bodies prevent cancer by utilizing tumor-suppressing proteins. One theory is that this virus can make proteins that block the action of the tumor-suppressing proteins.  Unfortunately, the virus may be much more able to do this when the C-16a metabolite binds covalently to a receptor on the body=s soft-tissue cells.  This causes a complex chain of events with the end result being that the virus is Aturned on.@  Because the C-2 metabolite doesn=t bind covalently to the cell=s receptors, the virus is not Aturned on.@


Passwater:  Earlier, we discussed that I3C and sulforaphane were similar in plant origin.  Would you please discuss their chemical origins and structures?


Andrus:  Sulforaphane and I3C both come from the same kind of plants.  These are cruciferous vegetables which include many common foods such as cabbage, broccoli, Brussels sprouts, radishes, turnips, mustard, rapeseed from which we get canola oil, collards, kale, kohlrabi, and a host of other plants.  In cruciferous vegetables is a set of compounds called glucosinolates, which contain one molecule of glucose bound to the sulfur in a N=C=S chain.  Another identifying group which varies from one glucosinolate to another is bound to the carbon in this chain.  Much of the flavor of these vegetables comes from the glucosinolates.


There are more than a dozen of the major glucosinolates spread throughout these cruciferous plants and many more minor glucosinolates.  Each variety of crucifer will usually contain six or eight glucosinolates.  I3C comes from a glucosinolate called glucobrassicin.  Sulforaphane comes from glucoraphanin.


In the case of sulforaphane, the N=C=S chain remains as an isothiocyanate associated with the characteristic group which distinguishes glucoraphanin.  Its primary action in human metabolism is an inducer of Phase II detoxification enzymes.


            In the case with I3C, the essential indole ring structure and the carbinol group at the 3-position makes it very reactive.  I3C and/or its combination products have been shown to be inducers of both Phase I and Phase II enzymes.


Passwater:  Many readers may fear that “indole@ is a Achemical.@  Indole may be a new word for them, and thus, they may not feel that it is a natural composition of food that has health benefits C just as ascorbic acid (vitamin C) and bioflavonoids.  As we identify more and more of the beneficial compounds in food, we have to use their technical names because no common names have had a chance to develop.


Andrus:  That=s correct.  Each of the vitamins has a chemical name which is often cumbersome in normal conversation, so letters have been applied to most of the vitamins (vitamin A, vitamin C, vitamin E, etc.).  As you know, indoles have characteristic odors which are used in small amounts in perfumes and colognes.


Passwater:  Really!  I always think of them as stinky compounds.  I am a firm believer that some of the stinkiest compounds are very important nutrients.  That=s why I like the sulfur compounds like NAC.


Andrus:  Yes, indoles are Astinky@ in larger quantities than used in perfumes.  They are also major constituents of waste material.  They occur in many foods and the body makes some indoles.  This is how they get into body wastes.  Indoles are in many foods, and indeed, they do good for both plants and animals.


Passwater:  How does I3C get liberated from glucobrassicin so that it can stimulate these enzymes?


Andrus:  When crucifers are chewed, chopped, or ground up, in other words, when the cell walls are broken and the vegetable juice is created, an enzyme called myrosinase is released from those cell walls.  Myrosinase breaks glucosinolates into their three main components C glucose, isothiocyanate, and the variable component.  In the case of glucoraphanin, the isothiocyanate remains attached to the variable component to form sulforaphane.  There are eight to ten important glucosinolates found in various ratios in the family of cruciferous vegetables.


In glucobrassicin, the variable component is I3C, but the I3C does not get released unless myrosinase is present.  The release of myrosinase is not operative in powdered vegetables.  In other words, if you take powdered broccoli or powdered cabbage you will not in any event get any I3C out of it.  The glucobrassicin will not yield I3C because the myrosinase of course is deactivated by the drying process.  So there is a lot that goes on in your mouth (or the vegetable chopper or juicer) to get the I3C into the stomach.



Once in the stomach, I3C undergoes additional reactions, often reacting with itself.  The researchers who are studying this process have concluded that it is probably not the I3C itself that gets into the cells of the human body to give the enzyme-inducing action.  It is probably some derivatives from I3C that gives the observed response.  We have been doing a lot of study on the reactions of I3C with itself under various conditions.  One kind of treatment is with gastric juice or simulated gastric juice.  Simply warming I3C or exposing it to light will also bring about many of the same reactions that take place in the stomach.  Under such conditions, an array of twenty to forty major and minor products are formed.


One of these products of I3C reacting with itself is what might be called a dimer, since it has two indole rings joined by a methylene bridge.  This is called diindolyl methane, which some think to be the most bioreactive of the I3C products.  Another product is a carbazole identified by Professor Leonard F. Bjeldanes of the University of California.  This compound is another combination of two indole-3-carbinols, and it may be one of the most bioreactive of the many compounds which the human body makes from I3C.  There is a lot of chemistry going on in the mouth, in the stomach, in the intestines, and in the cells of the body where the derivatives of from I3C are utilized.  I3C is very bioreactive compared to most laboratory chemicals.


Passwater:  What do we know about the safety of I3C?  Could it be safer than eating more crucifers as an example?


Andrus:  We know that some people take up to 400 milligrams of I3C per day, which is equivalent to many pounds of cabbage, and they do this without serious adverse effects.


A number of reports have been published indicating that eating massive amounts of cruciferous vegetables resulted in excessive amounts of goiterin, another product of the glucosinolates.  Goiterin has been sometimes implicated in the incidence of goiters, a swelling of the thyroid glands. More recent studies on the effects of goiterin have emphasized that iodine deficiency is a cause of goiter development.


As with any of the indole materials, and cruciferous vegetables, if you eat massive amounts, you are going to have some intestinal symptoms.  Some people get diarrhea if they take large quantities (in excess of 500 milligrams per day) of I3C and materials derived from it.


Passwater:  What have the toxicological tests that were done in preparation for the clinical studies shown?


Andrus:  The toxicology is very good.  No untoward effects have been seen in rats until dosages over 100 milligrams per kilogram of body weight.  The  LDLo50 is 500 milligrams per kilogram, subcutaneous in rats.  So it isn=t very toxic at doses people would take.


Passwater:  How much I3C should be taken by healthy people as a prophylactic?


Andrus:  For people who have problems with laryngeal warts, the recommendation of the experts is that children should take between 100 and 200 milligrams per day, and that adults should take 200 to 400 milligrams per day.  This is kind of an upper end of dosage which people want to take.  For normal, healthy people who simply want I3C as a preventative, 25 to 50 milligrams per day should be ample.  It is difficult to equate a known amount of a given substance with the amount of equivalent vegetable.  Growing conditions and other factors make I3C in cruciferous vegetables highly variable.  Roughly speaking, 25 milligrams of I3C is equivalent to a pound of cabbage.


Passwater:  Should cancer patients take more?


Andrus:  We are not in a position to say that yet.  I don=t think that the results are really out there to show that they ought to take hundreds of milligrams per day.  I don=t know of any data showing that cancer patients benefit from I3C.  Most of the work applies to prevention rather than cure.


Passwater:  Yes, but I can=t help but wonder if some of the benefit to cancer patients found from the proper juicing of whole vegetables doesn=t come from I3C.


Thank you for sharing your knowledge of I3C with us.  It looks as if I3C may help our bodies get rid of carcinogens and other toxins, as well as improve the way in which sex hormones are metabolized. WF


© 1997 Whole Foods Magazine and Richard A. Passwater, Ph.D.

This article is copyrighted and may not be re-produced in any form (including electronic) without the written permission of the copyright owners.