Issue: 62 Page: 49-56
The Functions of Tomato Lycopene and Its Role in Human Health
by Joseph Levy, Yoav Sharoni
HerbalGram. 2004; 62:49-56 American Botanical Council
The Functions of Tomato Lycopene and Its Role in Human Health
Introduction
Carotenoids,
compounds found in fruits and vegetables, benefit human health by playing an important
role in cell function. The dietary necessity of the carotenoid beta-carotene,
the precursor of vitamin A, has been recognized for many decades. More recently,
lycopene has attracted substantial interest among carotenoid and medical researchers.
Lycopene is the red carotenoid found predominantly in tomatoes and in a few other
fruits and vegetables. Claims have been made that lycopene may be beneficial in
diseases such as cancer and coronary heart disease as well as other chronic conditions.
These claims have been studied extensively, through epidemiological studies, biochemical
investigations of lycopene’s properties, and thorough examination of lycopene’s
bioavailability from tomato-based diets. This article summarizes the current state
of knowledge of the properties of lycopene, its possible role in human health,
and areas for future lycopene research.
Lycopene’s function
in the human body
Although not considered an essential nutrient, research has
shown that lycopene may have various benefits for human health. As a major
carotenoid in human blood, lycopene protects against oxidative damage to
lipids, proteins, and DNA. Lycopene is a potent quencher of singlet oxygen (a
reactive form of oxygen), which suggests that it may have comparatively
stronger antioxidant properties than other major plasma carotenoids.1
Lycopene has been found to be a potent and specific inhibitor of cancer cell
proliferation,2, 3 which is regulated by an elaborated cellular
process called “cell cycle.” Rapid and uncontrolled cell division is a hallmark
of cancer cell metabolism; lycopene’s activity in retarding cell cycle
progression may explain its demonstrated activity in retarding the spread of
certain types of cancer. Lycopene may prevent malignant transformation (the
cellular process which describes the transformation of a normal cell into a
cancer cell). Contact inhibition is one of the mechanisms that controls excessive
cell division. By this mechanism, a cell, in crowded surroundings, will stop
multiplying. Special structures in the cell membrane, termed a “gap-junction,”
function as communication channels between cells. Normal cells are both
contact-inhibited and have a functional gap-junction whereas most tumor cells
exhibit fewer of these structures. Lycopene was found to induce the formation
of the protein connexin 43, one of the major building blocks of these channels,
and thereby to restore gap junctions.4 Lycopene induces Phase II
enzymes which help to eliminate carcinogens and toxins from the body. The
change of the levels of so many regulatory proteins is related to lycopene’s
ability to modulate various transcription factors which are key players in the
process of new cellular protein synthesis.5, 6
Structure, intake absorption, and transport
Lycopene is defined chemically as an acyclic carotene with 11 conjugated
double bonds, normally in the all-trans configuration (Fig. 1). The double bonds
are subject to isomerization, and various cis isomers (mainly 5, 9, 13, or 15)
are found in plants and also in blood plasma. Since the human body is unable to
synthesize carotenoids from endogenously produced biochemicals, the body is totally
dependent on dietary sourced (exogenous) carotenoids. In general, tomato fruit
and tomato-based food products provide at least 85% of dietary lycopene in humans.
The remaining 15% are usually obtained from watermelon, pink grapefruit, guava,
and papaya—all fruits that are dietary sources of lycopene, although at much lower
levels than tomatoes (Table 1).
Table 1: Lycopene content of common foods
Food Type
|
Amount mg per 100 gr. |
References |
Guava Fresh, pink |
5.4 |
7 |
Tomatoes Fresh, red |
3.1-7.7 |
8 |
Tomato Juice |
7.83 |
8 |
Tomato Paste |
30.07 8 |
8 |
Grapefruit Fresh, pink |
3.36 |
8 |
Watermelon Fresh, red |
4.1 |
7 |
Ketchup |
16.6 |
7 |
Pizza sauce |
32.9 |
8 |
Spaghetti sauce |
17.5 |
9 |
Papaya Fresh, red |
2.0-5.3 |
10 |
Tomato juice, tomato soup, ketchup, pizza, and spaghetti
sauce are the major contributing tomato products in the diet. Uptake of
carotenoids from the diet has been studied for many years. The bioavailability
of dietary lycopene appears to be dependent upon several factors. It is
absorbed better from lipid-rich diets and from cooked, rather than raw foods.11
Once ingested, lycopene appears in plasma, initially in the chylomicrons (microscopic
emulsified fat particles found in the blood serum and lymph that result from
fat digestion) and VLDL (very low-density lipoprotein) fractions and later in
LDL (low-density lipoproteins, the so-called “bad” cholesterol) and HDL
(high-density lipoproteins, often called “good” cholesterol). The highest
levels are found in LDL. Serum concentrations vary markedly from about 20 to
500 mcg/liter of serum with large interpersonal variations.
Several lines of
evidence suggest that oxidatively modified LDL is damaging to the arterial
wall, and that atherosclerosis can be attenuated by natural antioxidants. As
reported by Fuhrman et al., tomato lycopene, alone or in combination with other
natural antioxidants, inhibits LDL oxidation.12 Moreover, the same group
reported that dietary supplementation of tomato’s lycopene (60 mg/day) when
administered to 6 males for a 3-month period resulted in a significant
reduction in their plasma LDL cholesterol. This was in agreement with their in
vitro results showing that lycopene suppresses cholesterol synthesis and
augments LDL receptor activity in macrophages.13
Lycopene is found in most human tissues but is not
accumulated uniformly.14 There is preferential accumulation of
lycopene, particularly in the adrenals and testes. The confirmed ability to
increase lycopene levels in tissues is one prerequisite for using it as a
dietary supplement to improve health. Indeed, it has recently been reported
that supplementation of tomato lycopene oleoresin in volunteers undergoing
elective surgery produced a significant increase in carotenoids in plasma,
skin, and adipose tissues.15 Little is known about the metabolism or
degradation of lycopene in mammals. A number of oxygenated metabolites have
been found in plasma and tissues, but more studies are needed in order to
estimate their physiological roles, if any.
Clinical research
demonstrates that lycopene is absorbed more readily from heat processed tomato
products than from uncooked sources and absorption is improved by the presence
of oil.16
Lycopene benefits from synergistic relationship with other micronutrients
When reviewing data related to the chemoprevention of
various diseases, it becomes evident that the use of a single carotenoid, or
any other micronutrient which has been successful in in vitro and animal
models, does not prove as favorable in human intervention studies. That is,
there is no magic bullet. In fact, accumulating evidence suggests that a
concerted, synergistic action of various micronutrients is more likely to be
the basis of the disease-prevention activity of a diet rich in vegetables and
fruit. Indeed, the sources of lycopene used in most of the human studies
reviewed here were either prepared tomato products or tomato extracts
containing lycopene and other tomato micronutrients and carotenoids in various
proportions. Pure lycopene has not been tested as a single agent in human
prevention studies. On the other hand, many studies showing the beneficial
effect of lycopene in alleviating chronic conditions have been conducted in
which the subjects were provided with tomato-based foods, or tomato extracts,
but not with the pure compound. For example, the oleoresin preparation used in
many of these studies also contained other tomato carotenoids such as phytoene,
phytofluene, and beta-carotene (Fig 1). A critical view of these studies might
question whether compounds other than lycopene in tomato may be responsible for
the benefit; however, in vitro studies support synergistic action of the tomato
carotenoids and other antioxidants present in tomato.17-19
This approach was tested in a recent study20 that
compared the potency of freeze-dried whole tomatoes (tomato powder) or pure
lycopene in a rat model of prostate cancer. Rats were treated with the
carcinogen NMU (N-methyl-N-nitrosourea) combined with androgens to stimulate
prostate carcinogenesis, and the ability of these two preparations containing
lycopene to enhance survival was compared. Mortality with prostate cancer was
lower by 25% (P = 0.09) for rats fed the
tomato powder diet than for rats fed control feed. Prostate cancer mortality of
rats fed pure lycopene was similar to that of the control group. The authors
concluded that consumption of tomato powder but not pure lycopene inhibited
prostate carcinogenesis, suggesting that tomato products contain other
compounds, besides lycopene, that modify prostate carcinogenesis. In an
accompanying editorial, Gann et al.21 note that this study
contributes to the debate about whether cancer prevention is best achieved with
whole foods or with single compounds. They point out that carotenoids and other
secondary plant compounds have evolved as sets of interacting compounds, a
complexity that limits the usefulness of reductionist approaches seeking to
identify single protective compounds. Unfortunately, the ensuing coverage of
the results of this study in the media included headlines declaring that
lycopene was found to be ineffective in treating prostate cancer, while
ignoring the beneficial results from the tomato powder.
The protective role of lycopene in preventing degenerative diseases
A comprehensive review of
the epidemiological literature on the relation of tomato consumption and cancer
was published by Giovannucci.22 He found that among 72 studies, 57
reported inverse associations between tomato intake or blood lycopene level and
the risk of cancer at a defined anatomic site. Thirty-five out of 57 of these
inverse associations were statistically significant. None of the cited studies
indicated that higher tomato consumption or blood lycopene level significantly
increased the risk of cancer at any of the investigated sites. The evidence for
a benefit was strongest for cancers of the prostate, lung, and stomach. Data
were also suggestive of a benefit for cancers of the pancreas, colon and
rectum, esophagus, oral cavity, breast, and cervix. Giovannucci suggests that
lycopene may contribute to these beneficial effects of tomato containing foods,
but this has not been conclusively proven. In addition, as discussed above, the
anticancer properties can also be explained by interactions among multiple
components found in tomatoes. Cancer of the prostate continues to be the focus
of lycopene research and, following Giovannucci’s comprehensive review, several
new studies have appeared in the literature.
In a recently published
meta-analysis, Etminan et al.23 tested the assumption that intake of
tomato products reduces the risk of prostate cancer. Researchers reviewed 21
studies involving the daily intake of one serving or more of tomatoes, tomato
products, or lycopene supplements. The results show that tomato products may
play a role in the prevention of prostate cancer. However, this effect is
modest (11% reduction in cancer risk) and restricted to high amounts of tomato
intake. Moreover, the preventive effect was slightly stronger for high intakes
of cooked tomato products than for high intakes of raw tomatoes, probably due
to the bioavailability of lycopene, which is increased with processing, heat,
and presence of fat.16, 24 It was previously reported that there is
low correlation between dietary lycopene intake and serum level,25
probably due to the saturation of absorption at higher lycopene intake levels.
Thus, stronger protective effect was observed in studies that directly measured
plasma lycopene as compared to those that estimated lycopene intake. The
authors concluded that further research is needed to determine the type and
quantity of tomato products and their role in preventing prostate cancer.
An ecologic (multi-country statistical) approach has also
found that tomatoes reduce the risk of prostate cancer, most likely due to the
action of lycopene.26 High lycopene intake was associated with lower
risk for gastric cancer.27 In an integrated series of studies in Italy,28 tomato consumption showed a consistent
inverse relationship to the risk of digestive tract neoplasm (abnormal new
tissue growth, tumor). Two small-scale, preliminary intervention studies on
prostate cancer patients were carried out with natural tomato preparations. In
one, Chen et al.29 showed that after dietary intervention, serum and
prostate lycopene concentrations were increased and oxidative DNA damage both in leukocytes and in prostate
tissue was significantly lower. Furthermore, serum levels of prostate-specific
antigen (PSA) decreased after the intervention. In the other study, Kucuk et
al.30 reported that supplementation with tomato extract in men with
prostate cancer modulates the grade and volume of prostate intraepithelial
neoplasia and tumor, the level of serum PSA, and the level of biomarkers of
cell growth and differentiation. High lycopene intake was associated with lower
risk for breast cancer in women.31, 32
Coronary heart disease
Coronary heart disease (CHD) is one of the primary causes of
death in the Western world. The emphasis of research so far has been on the
relationship between serum cholesterol levels and the risk of CHD. More
recently, oxidative stress induced by reactive oxygen species (ROS) is also
considered to play an important part in the etiology of this disease. Dietary
lycopene has been shown in in vitro studies
to prevent the formation of oxidized LDL, a key player in the pathogenesis of
atherosclerosis and CHD.12 The source of lycopene used in most of
these studies was either tomato food products or tomato-derived lycopene
extracts. Both of these sources contain various proportions of other
carotenoids in addition to lycopene; therefore, it is not possible to attribute
the demonstrated effects solely to lycopene.
The evidence in support of the role of lycopene in the
prevention of CHD stems primarily from the epidemiological observations of
normal and at-risk populations. The most impressive population-based evidence
comes from a multi-center case-control study (the EURAMIC study) in which
subjects from 10 European countries were evaluated for a relationship between
their antioxidant status and acute myocardial infarctions. After adjusting for
a range of dietary variables, only lycopene levels, not beta-carotene levels,
were found to be protective.33 These results were also confirmed by
another study (the Rotterdam Study).34
Serum lycopene concentration may play a role in the early
stages of atherosclerosis. Increased thickness of intima-media (the innermost
lining of a blood vessel, including the middle, muscular layer in the wall of
the blood vessel) has been shown to predict coronary events. A low serum
lycopene concentration, prevalent in eastern Finland, was associated with an
increased thickness of the intima-media.35, 36 In Lithuanian and
Swedish populations showing diverging mortality rates from CHD, lower blood
lycopene levels were found to be associated with increased risk and mortality
from CHD.37 Recently a prospective, nested, case-control study was
conducted by Harvard University researchers on 39,876 women. The study showed
that higher plasma lycopene concentrations are associated with a lower risk of
cardiovascular disease in middle-aged and elderly women.38 Moreover,
as noted previously by the same group,39 the possible inverse
associations with cardiovascular disease for higher levels of tomato-based
products (particularly tomato sauce and pizza), suggest that dietary lycopene
or other phytochemicals consumed as oil-based or oil-containing tomato products
confer cardiovascular benefits.
Skin protection
Oral sun protectants are probably more efficient than
topical ones, as most sun exposure is incidental to daily living and not
related to vacation time when topical sunscreens are commonly used.40
(This hypothesis has not been adequately investigated or confirmed.) Studies
are scarce, however, on the protective effect of oral carotenoid supplements
against skin responses to sun exposure. The protective effects are thought to
be related to the antioxidant properties of the carotenoids. During ultraviolet
(UV) irradiation, skin is exposed to photo-oxidative damage induced by the
formation of ROS. Photo-oxidative damage affects cellular lipids, proteins, and
DNA and is considered to be involved in the formation of erythema, premature
aging of the skin, photodermatoses, and skin cancer.
Carotenoids, and especially lycopene, are efficient
scavengers of ROS.40 Several animal studies and in vitro experiments
provided evidence that carotenoids and tocopherols prevent UV light–induced
skin lesions and protect against skin cancer. Plasma and skin carotenoid
concentrations decrease with UV irradiation; however, it is interesting that
lycopene is lost preferentially over other carotenoids.41 Exposure
of a small area of the forearm skin to UV light resulted in a reduction in skin
lycopene. The same UV dose, however, did not result in significant changes in
skin beta-carotene concentration. The authors concluded that when skin is
subjected to UV light stress, more skin lycopene is destroyed as compared with
beta-carotene, suggesting that lycopene plays a role in mitigating oxidative
damage in tissues. However, other interpretations of these results are
possible.
In a recent study,40 the efficacy of a mixture of
carotenoids containing beta-carotene, lutein, and lycopene was compared to
beta-carotene alone for protection from UV induced skin erythema. Caucasian
volunteers were tested in a placebo-controlled, parallel study. The intake of
either beta-carotene or a mixture of carotenoids similarly increased total
carotenoids in skin from week 0 to week 12. No changes in total carotenoids in
skin occurred in the control group. The intensity of erythema 24 hours after
irradiation was diminished in both groups that received carotenoids and was
significantly lower than baseline after 12 weeks of supplementation. Long-term
supplementation for 12 weeks with 24 mg/day of a carotenoid mix supplying
similar amounts of beta-carotene, lutein, and lycopene ameliorates UV-induced
erythema in humans. The superior protection with mixtures may be due to
different absorption wavelengths of the various compounds, leading to a greater
absorption potential of the broader range of wavelengths. In another study, the
same research group demonstrated that supplementation with tomato, a natural
source for lycopene and other carotenoids (see Fig. 1), protects against
UV-induced skin erythema in humans.42
Mechanism of action
a. Antioxidant Activity
Oxidative stress is recognized as one of the major
contributors to the increased risk of cardiovascular disease and cancer. Among
the common carotenoids lycopene stands as the most potent antioxidant as
demonstrated by in vitro experimental systems.1 Based on this study
the antioxidant potency of carotenoids can be ranked as follows: lycopene > [is greater than]
alpha-tocopherol > alpha-carotene > beta-cryptoxanthin > zeaxanthin
> beta-carotene > lutein. Mixtures of carotenoids were more effective
than the single compounds.19 This synergistic effect was most
pronounced when lycopene or lutein was present. The superior protection of
mixtures may be related to the specific positioning of different carotenoids in
cell membranes.
Several studies of tomato consumption demonstrate the
antioxidant properties in humans. For example, recently it was found that daily
consumption of a tomato product containing 15 mg lycopene plus other tomato
phytonutrients significantly enhanced the protection of lipoproteins from ex
vivo oxidative stress.43 These results indicate that lycopene
absorbed from tomato products may act as an in vivo antioxidant.
b. Inhibition of cancer cell proliferation (cell cycle)
Lycopene has been found to inhibit proliferation of several
types of cancer cells, including those of breast, prostate, lung, and
endometrium. The inhibitory effects of lycopene on mammary and prostate cancer
cell growth were not accompanied by apoptotic (programmed) or necrotic
(resulting from injury or disease) cell death, a mechanism related to the
action of some drugs but not to micronutrients frequently consumed in the human
diet. This effect was accompanied by inhibition of cell cycle progression from
the G0/G1 to the S phase as measured by flow cytometry.3 The
inhibition of cell proliferation correlated with a decrease in cyclin D1
protein levels which is a key regulator of this process. It is well documented
that growth factors affect the cell cycle apparatus (primarily during G1 phase)
and that the main components acting as growth factor sensors are the D-type
cyclins.44 Moreover, cyclin D1 is known to act as an oncogene (a
gene whose dysregulation causes normal cells to become cancerous) and is found
to be over-expressed in many breast cancer cell lines as well as in primary
tumors.45 Thus, the decrease in cellular cyclin D1 level by lycopene
provides a mechanistic explanation for the anticancer activity of the
carotenoid.
c. Interference with growth factors stimulation of cancer
cell proliferation
The growth stimulation of mammary cancer cells by
insulin-like growth factor 1 (IGF-1) was markedly reduced by physiological
concentrations of lycopene in experimental in vitro studies.2, 46 The significance of this
finding for cancer prevention is related to independent epidemiological
findings that elevated IGF-1 levels increase lifetime risks of breast and
prostate cancer.47, 48 If lycopene interference with IGF-1
stimulation of tumor cell growth is confirmed in clinical studies, this would
provide a strong rationale for recommending increased intake of lycopene,
particularly via tomato-based food products, for cancer prevention.
d. Cancer prevention by inducing phase II enzymes
Induction of phase II enzymes, which conjugate reactive
electrophiles (chemicals that are attracted to electrons or tend to accept
electrons from other chemicals) and act as indirect antioxidants, appears to be
an effective means for achieving protection against a variety of carcinogens in
animals and humans. Bhuvaneswari et al.49 associated the chemopreventive
(cancer-preventive) effect of lycopene on the incidence of DMBA-induced hamster
buccal (cheek, mouth) pouch tumors with a simultaneous rise in the level of
reduced glutathione, enzymes of the glutathione redox cycle, and glutathione
S-transferase (GST) in the buccal pouch mucosa. (Note: DMBA is a
9,10-dimethylbenz-a-anthracene, a potent tumor-initiating compound.) These
results suggest that the lycopene-induced increase in the levels of GSH and the
phase II enzyme GST inactivates carcinogens by forming conjugates (chemicals
formed by two or more compounds), products that are less toxic and readily
excreted.
e. Regulation of transcription
Transcription is the process whereby genetic information is
carried from the DNA molecule via the RNA molecule acting as a messenger. This
biochemical route leads to the formation of new proteins by the process called
translation. As discussed above, lycopene modulates the basic mechanisms of
cell proliferation, growth factor signaling, and gap junctional intercellular
communication.50 Additionally, lycopene produces changes in the
expression of many proteins participating in these processes, e.g., connexins,
cyclins, and phase II enzymes. Therefore, the question that arises is “By what
mechanisms does lycopene affect so many diverse cellular pathways?” The changes
in the expression of multiple proteins suggest that the initial effect of
lycopene involves modulation of transcription; this process is reviewed by
Sharoni et al. in a recent publication.51 This may be due to either
direct interaction of the carotenoid molecules or their derivatives with
transcription factors (e.g., with ligand-activated nuclear receptors52)
or indirect modification of transcriptional activity (e.g., via changes in
status of cellular redox, which affects redox-sensitive transcription systems53).
Safety of lycopene
The safety issue for carotenoids attracted much attention
after the publication of the beta-carotene supplementation trials, which
yielded negative results. It is interesting that in those studies an increased
risk for lung cancer was related to a 12- and 16-fold increase in beta-carotene
plasma levels due to supplementation (the CARET and ATBC studies,
respectively).54 In these studies beta-carotene plasma levels
increased from 0.32 µM before supplementation up to 3.9 and 5.9 µM,
respectively. (Note: One microMolar [µM] denotes a concentration of 1 x 10-6
gram-molecular weight of solute per liter of solution.) In a third study,
which showed no effect for beta-carotene supplementation (the Physicians’
Health Study),54 only a 5-fold increase in the carotenoid serum
level was achieved. Interestingly, the only study with positive results after
supplementation with beta-carotene was achieved in Linxian, a Chinese community
with very low carotenoid levels (0.11 µM) before the intervention.54
Although supplementation caused an 11-fold increase in beta-carotene level, the
final concentration of beta-carotene reached was a relatively low 1.5 mM. All these studies used synthetic
beta-carotene. Thus, keeping plasma levels of carotenoids in the upper range of
physiological level, but not higher, may be a good safety guide. Interestingly,
reviewing many studies which measured serum levels of beta-carotene and
lycopene after supplementation suggests that beta-carotene serum levels are
significantly higher than those found for lycopene. Serum levels reached for
beta-carotene are around 3 mM and may
exceed 5 mM after supplementation; on
the other hand lycopene levels above 1.2 mM
are rarely seen even after long-term application. Moreover, the serum level
achieved for lycopene was not directly correlated to the amount of the
supplemented carotenoid. For example, supplementation as high as 75 mg/day did
not increase lycopene serum levels more than 1 mM.55,
56 In conclusion, by some unknown mechanism, lycopene plasma levels after
supplementation remain relatively low, which may provide a safety valve.
Several safety studies on formulated synthetic lycopene
preparation were performed in rats and rabbits. The results of these
studies demonstrated the absence of any significant toxicological effects of
the tested materials in animals.57-59 However, the Scientific
Committee on Food of the European Commission found these synthetic preparations
to be unacceptable for use as food because of their high sensitivity to oxygen
and light, which form degradation products with mutagenic activity.60
A thorough safety review by an independent panel of toxicologists has resulted
in a GRAS (generally recognized as safe) self-affirmation for Lyc-O-Mato®
(LycoRed, Beer-Sheva, Israel), a branded tomato extract that has been the
subject for several of the studies evaluating the effects of tomato products in
dietary supplement form on a variety of disease parameters.61
Concluding remarks
The scientific research to date has demonstrated an array of
health benefits clearly associated with tomato products in the diet. A look at
the synergy between carotenoids has demonstrated that neither synthetic
lycopene nor tomato lycopene alone will act as a magic bullet. Effectiveness
and safety are married together in the whole tomato. Health benefits are
derived from the addition of tomato products to the diet, particularly cooked
tomato products containing oil, or from supplements of tomato extract suspended
in oil. The natural tomato oil increases the bioavailability of the tomato
phytonutrients. For maximum benefit, dietary supplement customers who have
opted for a nutritional approach should consider products containing a
standardized tomato extract that supplies many of the active phytonutients in
tomato.
Joseph Levy, PhD and Yoav Sharoni, PhD are professors at the Department of Clinical Biochemistry,
Faculty of Health Sciences, Ben-Gurion University of the Negev and Soroka
Medical Center of Kupat Holim, Beer-Sheva, Israel.
References:
1. Di Mascio P, Kaiser S, Sies H. Lycopene as the most
efficient biological carotenoid singlet oxygen quencher. Arch Biochem
Biophys. 1989;274(2):532-538.
2. Levy J, Bosin E, Feldman B, et al. Lycopene is a more
potent inhibitor of human cancer cell proliferation than either a-carotene or b-carotene.
Nutr Cancer. 1995;24:257-267.
3. Nahum A, Hirsch K, Danilenko M, et al. Lycopene
inhibition of cell cycle progression in breast and endometrial cancer cells is
associated with reduction in cyclin D levels and retention of p27(Kip1) in the
cyclin E-cdk2 complexes. Oncogene. 2001;20(26):3428-3436.
4. Zhang LX, Cooney RV, Bertram JS. Carotenoids up-regulate
connexin-43 gene expression independent of their provitamin-A or antioxidant
properties. Cancer Res. 1992;52(20):5707-5712.
5. Ben-Dor A, Nahum A, Danilenko M, et al. Effects of
acyclo-retinoic acid and lycopene on activation of the retinoic acid receptor
and proliferation of mammary cancer cells. Arch Biochem Biophys. 2001;391(1):295–302.
6. Wang XD, Liu C, Bronson RT, Smith DE, Krinsky NI, Russell
M. Retinoid signaling and activator protein-1 expression in ferrets given
beta-carotene supplements and exposed to tobacco smoke. J Natl Cancer Inst. 1999;91(1):60-66.
7. USDA. 1998. USDA-NCI Carotenoid Database for U.S. Foods.
Nutrient Data Lab., Agric. Res. Service, U.S. Dept. of Agriculture, Beltsville
Human Nutrition Research Center, Riverdale, MD.
8. Nguyen ML, Schwartz SJ. Lycopene stability during food
processing. Proc Soc Exp Biol Med. Jun
1998;218(2):101-105.
9. Hadley CW, Miller EC, Schwartz SJ, Clinton SK. Tomatoes,
lycopene, and prostate cancer: progress and promise. Exp Biol Med (Maywood).
Nov 2002;227(10):869-880.
10. Mangels AR, Holden JM, Beecher GR, Forman MR, Lanza E.
Carotenoid content of fruits and vegetables: an evaluation of analytic data. J.
Am. Diet Assoc. 1993;93:284-296.
11. Bohm V, Bitsch R. Intestinal absorption of lycopene from
different matrices and interactions to other carotenoids, the lipid status, and
the antioxidant capacity of human plasma. Eur J Nutr. Jun 1999;38(3):118-125.
12. Fuhrman B, Ben-Yaish L, Attias J, Hayek T, Aviram M.
Tomato lycopene and beta-carotene inhibit low density lipoprotein oxidation and
this effect depends on lipoprotein vitamin E content. Nutr Metab Cardiovasc
Dis. 1997;7:433-443.
13. Fuhrman B, Elis A, Aviram M. Hypocholesterolemic effect
of lycopene and beta-carotene is related to suppression of cholesterol
synthesis and augmentation of LDL receptor activity in macrophages. Biochem
Biophys Res Commun. 1997;233(3):658-662.
14. Khachik F, Carvalho L, Bernstein PS, Muir GJ, Zhao DY,
Katz NB. Chemistry, distribution, and metabolism of tomato carotenoids and
their impact on human health. Exp Biol Med (Maywood). Nov 2002;227(10):845-851.
15. Walfisch Y, Walfisch S, Agbaria R, Levy J, Sharoni Y.
Lycopene in serum, skin and adipose tissues after tomato-oleoresin
supplementation in patients undergoing haemorrhoidectomy or peri-anal
fistulotomy. Br J Nutr. Oct
2003;90(4):759-766.
16. Stahl W, Sies H. Uptake of lycopene and its geometrical
isomers is greater from heat-processed than from unprocessed tomato juice in
humans. J Nutr. 1992;122(11):2161-2166.
17. Amir H, Karas M, Giat J, et al. Lycopene and
1,25-dihydroxyvitamin-D3 cooperate in the inhibition of cell cycle progression
and induction of differentiation in HL-60 leukemic cells. Nutr Cancer. 1999;33:105-112.
18. Pastori M, Pfander H, Boscoboinik D, Azzi A. Lycopene in
association with alpha-tocopherol inhibits at physiological concentrations
proliferation of prostate carcinoma cells. Biochem Biophys Res Commun. 1998;250(3):582-585.
19. Stahl W, Junghans A, deBoer B, Driomina ES, Briviba K,
Sies H. Carotenoid mixtures protect multilamellar liposomes against oxidative
damage: synergistic effects of lycopene and lutein. FEBS Lett. 1998;427(2):305-308.
20. Boileau TW, Liao Z, Kim S, Lemeshow S, Erdman JW Jr,
Clinton SK. Prostate carcinogenesis in N-methyl-N-nitrosourea
(NMU)-testosterone-treated rats fed tomato powder, lycopene, or
energy-restricted diets. J Natl Cancer Inst. Nov 5 2003;95(21):1578-1586.
21. Gann PH, Khachik F. Tomatoes or lycopene versus prostate
cancer: is evolution anti-reductionist? J Natl Cancer Inst. Nov 5 2003;95(21):1563-1565.
22. Giovannucci E. Tomatoes, tomato-based products,
lycopene, and cancer: review of the epidemiologic literature. J Natl Cancer
Inst. 1999;91:317-331.
23. Etminan M, Takkouche B, Caamano-Isorna F. The role of
tomato products and lycopene in the prevention of prostate cancer: a
meta-analysis of observational studies. Cancer Epidemiol Biomarkers Prev. Mar 2004;13(3):340-345.
24. Giovannucci E, Ascherio A, Rimm EB, Stampfer MJ, Colditz
GA, Willett WC. Intake of carotenoids and retinol in relation to risk of
prostate cancer. J Natl Canc Inst. 1995;87:1767-1776.
25. Freeman VL, Meydani M, Yong S, et al. Prostatic levels
of tocopherols, carotenoids, and retinol in relation to plasma levels and
self-reported usual dietary intake. Am J Epidemiol. Jan 15 2000;151(2):109-118.
26. Grant WB. An ecologic study of dietary links to prostate
cancer. Altern Med Rev. 1999;4(3):162-169.
27. Tsubono Y, Tsugane S, Gey KF. Plasma antioxidant
vitamins and carotenoids in five Japanese populations with varied mortality
from gastric cancer. Nutr Cancer. 1999;34(1):56-61.
28. La Vecchia C. Tomatoes, lycopene intake, and digestive
tract and female hormone-related neoplasms. Exp Biol Med (Maywood). Nov 2002;227(10):860-863.
29. Chen L, Stacewicz-Sapuntzakis M, Duncan C, et al.
Oxidative DNA damage in prostate cancer patients consuming tomato sauce-based
entrees as a whole-food intervention. J Natl Cancer Inst. 2001;93(24):1872-1879.
30. Kucuk O, Sarkar FH, Sakr W, et al. Phase II randomized
clinical trial of lycopene supplementation before radical prostatectomy. Cancer
Epidemiol Biomarkers Prev. 2001;10(8):861-868.
31. Ronco A, De Stefani E, Boffetta P, Deneo-Pellegrini H,
Mendilaharsu M, Leborgne F. Vegetables, fruits, and related nutrients and risk
of breast cancer: a case-control study in Uruguay. Nutr Cancer. 1999;35(2):111-119.
32. Hulten K, Van Kappel AL, Winkvist A, et al. Carotenoids,
alpha-tocopherols, and retinol in plasma and breast cancer risk in northern
Sweden. Cancer Causes Control. Aug
2001;12(6):529-537.
33. Kohlmeier L, Kark JD, GomezGracia E, et al. Lycopene and
myocardial infarction risk in the EURAMIC Study. Am J Epidemiol. 1997;146:618-626.
34. Klipstein-Grobusch K, Launer LJ, Geleijnse JM, Boeing H,
Hofman A, Witteman JC. Serum carotenoids and atherosclerosis. The Rotterdam
Study. Atherosclerosis. 2000;148(1):49-56.
35. Rissanen TH, Voutilainen S, Nyyssonen K, et al. Low
serum lycopene concentration is associated with an excess incidence of acute
coronary events and stroke: the Kuopio Ischaemic Heart Disease Risk Factor
Study. Br J Nutr. 2001;85(6):749-754.
36. Rissanen TH, Voutilainen S, Nyyssonen K, Salonen R,
Kaplan GA, Salonen JT. Serum lycopene concentrations and carotid
atherosclerosis: the Kuopio Ischaemic Heart Disease Risk Factor Study. Am J
Clin Nutr. Jan 2003;77(1):133-138.
37. Kristenson M, Zieden B, Kucinskiene Z, et al.
Antioxidant state and mortality from coronary heart disease in Lithuanian and
Swedish men: concomitant cross sectional study of men aged 50. BMJ. 1997;314(7081):629-633.
38. Sesso HD, Buring JE, Norkus EP, Gaziano JM. Plasma
lycopene, other carotenoids, and retinol and the risk of cardiovascular disease
in women. Am J Clin Nutr. Jan
2004;79(1):47-53.
39. Sesso HD, Liu S, Gaziano JM, Buring JE. Dietary
lycopene, tomato-based food products and cardiovascular disease in women. J
Nutr. Jul 2003;133(7):2336-2341.
40. Heinrich U, Gartner C, Wiebusch M, et al.
Supplementation with beta-carotene or a similar amount of mixed carotenoids
protects humans from UV-induced erythema. J Nutr. Jan 2003;133(1):98-101.
41. Ribaya Mercado JD, Garmyn M, Gilchrest BA, Russell RM.
Skin lycopene is destroyed preferentially over beta-carotene during ultraviolet
irradiation in humans. J Nutr. 1995;125(7):1854-1859.
42. Stahl W, Heinrich U, Wiseman S, Eichler O, Sies H,
Tronnier H. Dietary tomato paste protects against ultraviolet light-induced
erythema in humans. J Nutr. May 2001;131(5):1449-1451.
43. Hadley CW, Clinton SK, Schwartz SJ. The consumption of
processed tomato products enhances plasma lycopene concentrations in
association with a reduced lipoprotein sensitivity to oxidative damage. J
Nutr. Mar 2003;133(3):727-732.
44. Sherr CJ. D-type cyclins. Trends Biochem Sci. 1995;20(5):187-190.
45. Buckley MF, Sweeney KJ, Hamilton JA, et al. Expression
and amplification of cyclin genes in human breast cancer. Oncogene. 1993;8(8):2127-2133.
46. Karas M, Amir H, Fishman D, et al. Lycopene interferes
with cell cycle progression and insulin-like growth factor I signaling in
mammary cancer cells. Nutr Cancer. 2000;36:101-111.
47. Chan JM, Stampfer MJ, Giovannucci E, et al. Plasma
insulin-like growth factor-I and prostate cancer risk: A prospective study. Science.
1998;279:563-566.
48. Hankinson SE, Willett WC, Colditz GA, et al. Circulating
concentrations of insulin-like growth factor I and risk of breast cancer. Lancet.
1998;351:1393-1396.
49. Bhuvaneswari V, Velmurugan B, Balasenthil S,
Ramachandran CR, Nagini S. Chemopreventive efficacy of lycopene on
7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis. Fitoterapia.
Dec 2001;72(8):865-874.
50. Aust O, Ale-Agha N, Zhang L, Wollersen H, Sies H, Stahl
W. Lycopene Oxidation Product Enhances Gap Junctional Communication. Food
Chem Toxicol. 2003;41(10):1399-1407.
51. Sharoni Y, Danilenko M, Dubi N, Ben-Dor A, Levy J.
Carotenoids and transcription. Arch. Biochem. Biophys. 2004;In press.
52. Stahl W, von Laar J, Martin HD, Emmerich T, Sies H.
Stimulation of gap junctional communication: comparison of acyclo- retinoic
acid and lycopene. Arch Biochem Biophys. 2000;373(1):271-274.
53. Levy J, Ben-Dor A, Dubi N, Danilenko M, Zick A, Sharoni
Y. Carotenoids activate the antioxidant response element (are) transcription
system. AACR Annual Meeting. 2004:Abstract
4035.
54. IARC Handbook of Cancer prevention. Vol 2 Carotenoids; 1998.
55. Agarwal S, Rao AV. Tomato lycopene and low density
lipoprotein oxidation: a human dietary intervention study. Lipids . 1998;33(10):981-984.
56. Paetau I, Khachik F, Brown ED, et al. Chronic ingestion
of lycopene-rich tomato juice or lycopene supplements significantly increases
plasma concentrations of lycopene and related tomato carotenoids in humans. Am
J Clin Nutr. Dec 1998;68(6):1187-1195.
57. Mellert W, Deckardt K, Gembardt C, Schulte S, Van
Ravenzwaay B, Slesinski R. Thirteen-week oral toxicity study of synthetic
lycopene products in rats. Food Chem Toxicol. Nov 2002;40(11):1581-1588.
58. Christian MS, Schulte S, Hellwig J. Developmental
(embryo-fetal toxicity/teratogenicity) toxicity studies of synthetic
crystalline lycopene in rats and rabbits. Food Chem Toxicol. Jun 2003;41(6):773-783.
59. Jonker D, Kuper CF, Fraile N, Estrella A, Rodriguez
Otero C. Ninety-day oral toxicity study of lycopene from Blakeslea trispora in
rats. Regul Toxicol Pharmacol. Jun
2003;37(3):396-406.
60. European C. Opinion on synthetic lycopene as a colouring
matter for use in foodstuffs. Annex V to the minutes of the 119th plenary
meeting of the European Scientific committee on food. 1999.
61. Burdock Group. Opinion of an Expert Panel on the
Generally Recognized as Safe (GRAS) status of Lyc-O-Mato ® oleoresin 6% as a
food ingredient. The Burdock Group, May 31, 2003.
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