|Alpha-carotenes and Other Carotenoids |
|Interview with © Dr. Michiaki Murakoshi|
as Interviewed By© Richard A. Passwater PhD
Dr. Michiaki Murakoshi is a researcher in the Department of biochemistry
at the Kyoto Prefectural University of Medicine (Japan) and Research Manager
of the Oleochemistry Research Center of the Lion Corporation in Tokyo.
I have read most of Dr. Murakoshi's thirty-four research articles of
which I am aware of him publishing during the past ten years. One was in
French and with a couple of others I was limited to only having the article
abstracts. His research primarily deals with the structure of cells, especially
cancer cells, changes in normal cells that lead to them becoming cancer
cells, free radicals and lipid peroxidation, how the immune system fights
against cancer and the role of carotenoids in preventing cancers.
I had the pleasure of meeting Dr. Murakoshi in February 1993, and I had
the honor of introducing him from the podium during my NNFA lecture on Carotenoids
in July 1993. I thought that you might like to know more about his research.
Passwater: Dr. Murakoshi, what led you to this line of research?
Murakoshi: The interesting research of Dr. Hoyoku Nishino, Associate
Professor of the Department of Biochemistry at the Kyoto Prefectural University
of Medicine, who is the director of our project.
Passwater: Dr. Nishino has published hundreds of scientific articles.
What particularly caught your interest?
Murakoshi: His exploration of cancer chemo-prevention by minor dietary
constituents such as carotenoids, terpenes, flavones, tannins, curcumin,
and so forth.
Passwater: All of those compounds are interesting. I find that carotenoids
and bioflavonoids are particularly interesting, and that carotenoids are
particularly beautiful. As was pointed out last month, carotenoids are pigments
that give us most of the yellows, oranges and red colors of birds, fish,
crustaceans, flowers, vegetables and fruits. But there is much more to appreciate
about carotenoids when it comes to beauty. For without carotenoids, not
only would there be less color in our world, we wouldn't be able to see
anything at all. Without carotenoids, there would be no vitamin A and thus
gathering pigments in the eye.
Carotenoids and vitamin A both absorb light. The chemical name for vitamin
A and its family are "retinol" and "retinoids," respectfully,
which express their relationship to the retina of the eye. In the rods,
11-cis retinal combines with opsin to form the red pigment, rhodopsin, which
is the primary light sensor in the eye. In the cones, retinal forms the
Dr. Murakoshi, you, too, seem to favor the carotenoids over the other compounds
that Dr. Nishino was investigating. What brought your interest to carotenoids
other than beta-carotene?
Murakoshi: When Dr. Nishino and I wished to expand our knowledge
of the anti-cancer activity of beta-carotene, it became apparent to us that
there was little information available on the anti-cancer activity of the
other carotenoids. We were interested in all of the carotenoid constituents
of human blood. Since beta-carotene represents less than thirty percent
of all of the carotenoids in the blood, we needed to know the effects of
the others, which include alpha-carotene, lycopene, and lutein, among others.
I developed the technology to purify alpha-carotene from
the carotenoid mixtures. Palm fruit is especially rich in alpha-carotene
as well as beta-carotene, so we compared the anti-cancer activity of alpha-carotene
and beta-carotene in vitro and found that alpha-carotene had a stronger
anti-cancer activity than beta-carotene in the test system.
Passwater: Other carotenoids have anti-cancer action. At one time,
we thought that the anti-cancer action of the carotenoids was related to
their ability to make vitamin A in the body, and that vitamin A prevented
cancer by maintaining the health of mucous membranes, controlling the maturation
of cells, and of course, acting as a weak antioxidant. This reasoning was
supported by the fact that vitamin A and beta-carotene both reversed
oral pre-cancers called leukoplakia, whereas canthaxanthin, which does not
have provitamin A activity does not reverse leukoplakia.
However, beta-carotene and canthaxanthin both inhibit ultraviolet-induced
skin cancer, whereas chemically-induced skin cancer was inhibited
by beta-carotene, but not by canthaxanthin. This could imply that
protection against chemically-induced skin cancer required beta-carotene
to be converted into vitamin A, but ultraviolet-induced skin cancer protection
did not depend on conversion to vitamin A.
However, epidemiological evidence implies that diets rich in total carotenoids
-- not just the carotenoids that possess pro-vitamin A activity -- were
very protective against many types of cancers, although high vitamin A intake
itself does not appear to be related to decreased risk of cancer.
Moreover, lycopene -- which is not a vitamin A precursor -- was associated
with a reduced risk of lung cancer, and canthaxanthin -- which also has
no pro-vitamin A activity -- inhibited chemically-induced cancer
in animals where vitamin A was not effective.
In cell culture studies, Dr. John Bertram of the University of Hawaii has
found that not only alpha-carotene and beta-carotene -- both of which are
vitamin A precursors -- but also lutein, lycopene and canthaxanthin -- which
are not vitamin A precursors --all inhibit transformation
to cancer cells.
Thus, the preponderance of evidence suggests that the antitumor effect of
carotenoids is independent of vitamin A. The effects may be due to various
actions of the carotenoids in various cancer systems.
Dr. Murakoshi, does your research shed any light on the mechanism of the
various carotenoids? Is it their antioxidant action, antiradical action,
singlet oxygen quenching, gap-junction communication or what?
Murakoshi: We found that not only beta-carotene, but alpha-carotene,
gamma-carotene, lycopene and lutein have anti-cancer activity. We have also
investigated the inhibitory effect of various carotenoids on the proliferation
of human malignant tumor cells, and found that fucoxanthin, from the brown
algae which is common in Japanese food, and halocynthiaxanthin, from sea
squirt, and cryptoxanthin have anti-cancer activity on the growth of human
neuroblastoma GOTO cells.
Although some carotenoids are more effective than others against certain
types of cancer depending on the mechanism of cancer initiation and the
molecular structure of the carotenoid, we cannot explain this relationship
at this time. The structure does determine how efficient the carotenoid
is as an antioxidant, antiradical, singlet oxygen quencher or gap-junction
communication enhancer, but more research is required to properly understand
just how changes in chemical structure and electron cloud distribution of
the carotenoid affects the cancer process.
Table 1 shows how the carotenoids that we tested compare in anti-cancer
activity and Table 2 shows the relative singlet oxygen quenching capability
of some antioxidants as were determined by Dr. Helmut Sies of the University
of Dusseldorf in Germany.
Passwater: In Cancer Research (52:6583-7, 1992) I believe that you
found that alpha-carotene was very protective against spontaneous liver
cancer and two-stage lung cancer in mice, and more importantly, protective
against proliferation of human malignant tumor cells, whereas beta-carotene
was not protective (compared to controls).  How do you interpret these
findings? Is beta-carotene more protective against some cancers and alpha-carotene
more effective against others? Or is alpha-carotene always more protective?
Murakoshi: We also believe that beta-carotene is a key cancer preventive
agent, since it is abundant in green and yellow vegetables and has the highest
pro-vitamin A activity. In fact, previous reports showed both beta-carotene
and vitamin A have cancer preventive and anti-cancer activity in-vivo
or in-vitro. However, it should also be noted that beta-carotene
is often associated with other types of natural carotenoids, such as alpha-carotene,
lycopene, lutein, etc. in vegetables and daily food stuffs, and these carotenoids
are detectable in human blood and various tissues.
It is of interest that the qualitative patterns -- the carotenoids present
-- in the different tissues are generally not similar. We believe that each
of the carotenoids has each function -- antioxidant, antiradical, singlet
oxygen quencher, gap-junction communication enhancement -- but with varying
degrees of strength of each function.
In one case, beta-carotene shows stronger cancer control activity, in another
case, alpha-carotene or another carotenoid shows stronger cancer control
activity than beta-carotene.
Passwater: In Oncology (49:492-7, 1992) you describe your research
showing that mixed carotenoids was protective against intestinal cancer.
 Did that research involve a different mechanism of cancer promotion?
Murakoshi: In the ENNG-induced mouse duodenal carcinogenesis model,
bile acid (glycocholic acid) is considered to be the tumor promoter. Bile
acid can cause induction of ornithine decarboxylase (ODC) activity. We found
that palm carotenoids have an inhibitory effect on ODC. This ability may
be attributed to anti-tumor promoting activity of palm carotenoids. The
chief carotenoids of palm are alpha-carotene, beta-carotene and lycopene.
Passwater: In the Journal of the National Cancer Institute, you stated
that alpha-carotene was ten times more protective against cancer than beta-carotene.
 Was that just against proliferation of neuroblasts or for all cancer?
Murakoshi: Alpha-carotene shows the strongest anti-tumor activity
on human neuroblastoma GOTO cells. Alpha-carotene also shows stronger anti-proliferative
activity than that of beta-carotene on other human malignant cancer cells;
pancreatic cancer (PANC-1), glioblastoma (A172), and gastric cancer (HGC-27).
Passwater: What accounts for this difference? Beta-carotene has two
beta-ionone rings and thus our bodies, with the help of dioxygenase can
split a molecule of beta-carotene into two retinol (vitamin A) molecules.
Alpha-carotene is a very similar structure containing the same number of
carbon atoms (40), the same nine conjugated double bonds backbone, the same
number of ring structures (2), but one ring is a beta-ionone and the other
is slightly different in that the double bond is moved one carbon atom.
A molecule of alpha-carotene yields only one molecule of vitamin A. Why
is alpha-carotene more protective against some cancers than beta-carotene?
Murakoshi: Researchers trying to explain the anti-cancer activity
of carotenoids have focused on the carotenoids' properties as singlet oxygen
scavengers and antioxidant activities. Dr. P. D. Mascio and his group have
reported that the singlet oxygen quenching ability of alpha-carotene is
higher than that of beta-carotene.  Dr. Lester Packer's group reports
that the higher the carotenoid content, the higher the resistance of liver
homogenates to in-vitro induced lipid peroxidation, and the values
for correlation coefficients for inhibition of lipid peroxidation in the
order of alpha-carotene to beta-carotene.  Thus, it is possible that
the chemopreventive activities of these carotenes remains to be further
Passwater: When we eat fruits and vegetables, we get a mixture of
carotenoids. In natural foods, do we usually find alpha-carotene along with
Murakoshi: Yes. Some foods are particularly rich in alpha-carotene.
They have plenty of beta-carotene as well. As examples, in carrots, alpha-carotene
makes up 33 percent of all the carotenoids, and in pumpkins, alpha-carotene
makes up 42 percent of the total carotenes.
Passwater: Would this be a valid reason for selecting a supplement
that contains both alpha-carotene and beta-carotene ... and even other carotenoids
... as opposed to taking only beta-carotene?
Murakoshi: Many epidemiological studies have demonstrated that increased
dietary intake of both total carotenoids or fruits and vegetables, as well
as elevated blood levels of beta-carotene are consistently associated with
reduced cancer risk. Since beta-carotene has been considered a key constituent
of fruits and vegetables, much of the attention has been focused on beta-carotene.
However, beta-carotene is only one of several major dietary carotenoids,
and represents less than 30 percent of the total amount of carotenoids circulating
in the blood.
In a recent report, Dr. L. L. Marchand and his colleagues suggested that
total vegetable intake was more predictive of reduced risk of lung cancer
in Hawaii than was the amount of beta-carotene estimated to be in those
Dr. Regina Zeigler's group point out that other carotenoids, other constituents
of fruits and vegetables, and dietary patterns closely associated with fruit
and vegetable intake need to be explored further as alternatives to the
beta-carotene hypothesis.  In this context, it is interesting that Dr.
N. V. Hicks and colleagues report a protective association of alpha-carotene
intake against lung cancer that supports our results.  Further investigation
of the biological activity, not only of beta-carotene, but also of alpha-carotene
and other carotenoids in daily foods, could be important for cancer control.
Passwater: Did you find that a mixture of carotenoids was more effective
that either alpha-carotene or beta-carotene alone?
Murakoshi: Palm carotenoids were more effective than either alpha-carotene
or beta-carotene alone. This activity may be attributed to either the synergism
of the mixture of carotenoids or to the additional activity of the minor
carotenoid components such as lycopene and/or gamma-carotene.
Passwater: What is the next step in your research?
Murakoshi: We have enough supporting evidence to justify clinical
trials in the chemoprevention of cancer, and that is just what we are going
Passwater: Thank you for sharing your research findings with us,
and please let us know how the clinical trials turn out.
Effect of various types of carotenoids on the growth of GOTO cells.
Carotenoid Concentration Inhibition
2 days 5 days
Beta-carotene ( 2 micromol) 0 2.8
(20 micromol) 1.2 47.8
Alpha-carotene ( 2 micromol) 15.2 52.4
(20 micromol) 100 100
Fucoxanthin ( 2 micromol) 3.9 8.9
(20 micromol) 49.8 80.2
Halocynthiaxanthin ( 2 micromol) 12.1 32.2
(20 micromol) 100 100
Cryptoxanthin ( 2 micromol) 3.1 6.2
(20 micromol) 39.9 70.2
After 2 days of the inoculation of GOTO cells, carotene or its vehicle was
added into culture medium. Viable cells were counted after 2 and 5 days.
Data are mean values of duplicate experiments, and expressed as % of inhibition.
From Reference # 9.
Singlet oxygen quenching constants and content in human tissues of various
carotenoids, xanthophylls, alpha-tocopherol, and bile pigments.
Compound kq(109M-1s-1) Content
Lycopene 31 0.5-1.0 micromol,plasma
Alpha-carotene 19 0.05-0.1 micromol,plasma
Beta-carotene 14 0.3-0.6 micromol,plasma
Zeaxanthin 10 43 ng/retina
Lutein 8 80 ng/retina(zeaxanthin and lutein,0.5 micromol, plasma)
Cryptoxanthin 6 0.3 micromol, plasma
Bilirubin 3.2 5-20 micromol, plasma
Alpha-tocopherol 0.3 15-31 micromol, plasma
Retinoic acid no quenching
Adapted from Reference # 4
All rights, including electronic and print media, to this article are copyrighted
by © Richard A. Passwater, Ph.D. and Whole Foods magazine (WFC Inc.).
1. Potent preventive action of alpha-carotene againstcarcinogenesis: Spontaneous
liver carcinogenesis andpromoting stage of lung and skin carcinogenesis
in mice aresuppressed more effectively by alpha-carotene than bybeta-carotene.Murakoshi,
M.; Nishino, H.; Satomi, Y.; et al.Cancer Res. 52:6583-7 (1992)
2. Palm carotene inhibits tumor-promoting activity of bile acidand intestinal
carcinogenesis.Okuzumi, J.; Nishino, H.; Murakoshi, M.; et al.Oncology 49:492-7
3. Inhibitory effects of alpha-carotene on proliferation of thehuman neuroblastoma
cell line GOTO.Murakoshi, M.; Takayasu, J.; Kimura, O.; et al.J. Natl. Cancer
Inst. 81:1649-52 (1989)
4. Lycopene as the most efficient biological carotenoid singletoxygen quencher.Mascio,
P. D.; Kaiser, S. and Sies, H.Archiv. Biochem. Biopsy. 274:532-8 (1989)
5. Distribution and antioxidant activity of a palm oil carotenefraction
in rats.Serbinova, E.; Choo, M. and Packer, L.Biochem. Int. (1993) (In Press)
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study in Hawaii.Marchand L. L.; Yoshizawa, C. N.; Kolonel, L. N.; et al.J.
Natl. Cancer Inst. 81:1158-64 (1989)
7. Does beta-carotene explain why reduced cancer risk isassociated with
vegetable and fruit intake?Ziegler, R. G.; Subar, A. F.; Craft, N. E.; et
al.Cancer Res. 52:2060s-2066s (1992)
8. The effect of specific carotenoids on lung cancer risk(Abstract).Hicks,
N. V.; Buffler, P. A.; Mackerras, D.; Burau, K. andChristensen, B. L.In:
Carotenoids in Human Health, San Diego, The New YorkAcademy of Sciences.
(Feb 6-9, 1993)
9. Anti-tumor and anti-tumor promoting activity of alpha- andbeta-carotene.Nishino,
H.; Murakoshi, M.; Kitano, H.; et al.Lipid-Soluble Antioxidants; Biochemistry
and ClinicalApplications. (1992) pp228-42.