Some of the latest research on
apple polyphenols comes from
Cornell University and
Chang.Y. Lee, Cornell professor of food science at
the university's New York State Agricultural Experiment Station in Geneva,
N.Y. Lee is responsible for some of the latest research on
and colon cancer, and current studies on the benefits of
extracts in Alzheimer's Disease.
As you read
through the impressive research from Cornell, keep in mind that although
most of the studies conclude that people should eat more apples,
the materials actually used in the studies are
apple polyphenol extracts, not whole apples.
The use of standardized
apple polyphenol extracts
makes sense in terms of laboratory testing, but using the
extracts may also make sense for people wanting to realize the
reported health benefits, for the following reasons:
are the actual compounds showing the results in many of the studies.
apple peel powder extracts
may be higher than from whole apples, which must be digested to extract
The concentration of
extracts makes it possible to consume higher doses. (Many studies
you will read report dose-dependent effects, with higher dosages providing
The quantity of
varies greatly between apple varieties, fruit
maturity, and length of cold storage time.
The most thorough review of the available research on
apple polyphenols was
published in May 2004 in Nutrition Journal, under the title "Apple
phytochemicals and their health benefits." This is a superb collection
of the research on apple polyphenols and phytochemicals and their
emerging role in
human health. This review study receives our highest recommendation, and is
the best place to start for an overview of the science behind these
disease-fighting compounds. It is available to you in both
of Food Science Symposium, May 22-24 2005
Cardioprotective potentials of apple
phytochemicals in LDL oxidation and LDL receptor expression
Yi-Fang Chu and Rui Hai Liu, Cornell
Cardiovascular disease is the
leading cause of death in most industrialized countries. Both
elevated blood LDL cholesterol level and LDL oxidation lead to an enhanced
atherogenicity. Therapeutic strategies have been developed based on
targeting the pathogenesis; one is to prevent LDL oxidation by increasing
antioxidant levels, and another, as employed by statin drugs, is to lower
levels of plasma LDL cholesterol by increasing LDL uptake by hepatocytes
through LDL receptors and subsequent sterol excretion through bile acids.
Our objectives were to determine: 1) the effect of
apple extracts on
human LDL oxidation; 2) if apple
extracts affected hepatic LDL receptor expression and the level
of intracellular cholesterol in HepG2 hepatocytes; 3) if
affected the expression of sterol regulatory-element binding proteins (SREBPs).
were extracted using 80% acetone. LDL was isolated from human plasma by
sequential ultracentrifugation. Prevention of human LDL oxidation was
studied using a LDL Oxidation Model for Antioxidant Capacity (LOMAC) assay.
The expression of LDL receptors and SREBPs in HepG2 hepatocytes was
quantified by western blotting. Intracellular cholesterol was measured by
gas chromatography. Apple
extracts had potent antioxidant capacity against human LDL oxidationand increased delay and
suppression of LDL oxidation in a dose-dependent manner.
Apple extracts also significantly
induced expression of hepatic LDL receptors in a dose-dependent
manner (p<0.05) and increased intracellular uptake of cholesterol by HepG2
hepatocytes (p<0.05). These results suggest that
apple phytochemicals could lower
plasma LDL cholesterol by enhancing uptake of LDL in liver and
increase subsequent sterol excretion as bile acids. The attenuated level of
active SREBP expression by apple
phytochemicals indicates a decrease in intracellular lipogenesis
and cholesterol synthesis,
similar to the results caused by statin drugs such as Lipitor.
Apple phytochemicals can potentially improve human cardiovascular health by
both lowering blood LDL
cholesterol and preventing LDL
J Food Sci.
November/December 2004, Vol 69, No 9
Apple Phenolics Protect in Vitro Oxidative Stress-induced
Neuronal Cell Death
Heo HJ, Kim DO, Choi SJ, Shin DH, Lee CY. 2004. Apple Phenolics Protect in
Vitro Oxidative Stress-induced Neuronal Cell Death. J Food Sci
69(9):S357-60. ABSTRACT: Oxidative stress induced by reactive oxygen species may be
linked to neurodegenerative diseases.
Fresh Red Delicious
having 232.9 mg/100 g vitamin C equivalent antioxidant capacity,
protected the rat pheochromocytoma
neuronal (PC-12) cells from H2O2-induced
oxidative toxicity in vitro in a dose-dependent manner. MTT
(3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) reduction
assay showed significant increase in
cell viability when PC-12 cells were treated with apple extracts.
This indicates that the apple
phenolics protected oxidative stress-induced neurotoxicity. Because
oxidative stress is also known to increase neuronal cell membrane breakdown,
we further investigated by lactate dehydrogenase and trypan blue exclusion
assays. Apple phenolics inhibited
oxidative stress-induced membrane damage in neuronal cells.
Therefore, these results may suggest that naturally occurring antioxidants,
such as phenolic phytochemicals in
fresh apples, may reduce the risk of neurodegenerative disorders. KEYWORDS: apple, oxidative stress, neurodegeneration, phenolic phytochemicals, reactive oxygen species Submitted 5/13/04, Revised 6/23/04, Accepted 7/7/04, Published on Web
10/28/2004 Authors Heo, Kim, and Lee are with Dept. of Food Science and Technology, Cornell
Univ., Geneva, NY 14456. Authors Choi and Shin are with Graduate School of
Biotechnology, Korea Univ., Seoul, Korea.
Direct inquiries to author Lee (E-mail: CYL1@cornell.edu).
J Agric Food
Chem. 2004 Nov 3;52(22):6818-23
Novel low-density lipoprotein (LDL) oxidation model: antioxidant
capacity for the inhibition of LDL oxidation.
Chu YF, Liu RH.
Department of Food Science and Institute of Comparative and Environmental
Toxicology, Cornell University, Ithaca, New York 14853, USA.
A novel model of peroxyl radical initiated low-density lipoprotein (LDL)
oxidation (LDL oxidation model for antioxidant capacity, or LOMAC) was
developed to assess the free radical scavenging capacity of antioxidants and
the extracts of natural products. A water-soluble free radical initiator,
2,2'-azobis(amidinopropane) dihydrochloride, was used at physiological
temperature (37 degrees C) to generate peroxyl radicals to catalyze lipid
oxidation of LDL isolated from human plasma samples. Headspace hexanal, a
major decomposition product of LDL oxidation, was measured by a headspace
gas chromatograph as an indicator of antioxidant capacity of different
concentrations of pure antioxidants (vitamins C and E) and the extracts of
natural products (fresh apple phytochemical extracts). All vitamin C and E andapple
extract concentrations tested resulted in increasing partial suppression and
delay of LDL oxidation. On the basis of the median effective dose
(EC(50)) calculated for each compound or
extract tested, the LOMAC
value of 100 g of apple against LDL
oxidation was equivalent to 1470 mg of vitamin E or to 402 mg of vitamin C.
This study shows that the LOMAC assay can be routinely used to analyze or
screen antioxidants or phytochemical
extracts against LDL oxidation to prevent cardiovascular disease. The
food-specific LOMAC values will be very useful as a new alternative
biomarker for future epidemiological studies of cardiovascular disease.
PMID: 15506821 [PubMed - in process]
American Journal of
Clinical Nutrition, Vol. 78, No. 3, 517S-520S, September 2003
Health benefits of fruit and vegetables are
from additive and synergistic combinations of phytochemicals1,2,3,4
Rui Hai Liu
1 From the Department of Food Science and the Institute of Comparative and Environmental Toxicology,
Cornell University, Ithaca, NY.
Cardiovascular disease and cancer are ranked as the first
andsecond leading causes of death in the United States and in
Regular consumption of fruit and
vegetablesis associated with reduced risks of cancer,
cardiovascular disease,stroke, Alzheimer disease, cataracts, and
some of the functionaldeclines associated with aging.
Prevention is a more effectivestrategy than is treatment of
chronic diseases. Functional foodsthat contain significant
amounts of bioactive components mayprovide desirable health
benefits beyond basic nutrition andplay important roles in the
prevention of chronic diseases.The key question is whether a
purified phytochemical has thesame health benefit as does the
whole food or mixture of foodsin which the phytochemical is
present. Our group found, forexample, that the vitamin C
with skin accounts foronly 0.4% of the total antioxidant
activity, suggesting thatmost of the antioxidant activity of
fruit and vegetables maycome from phenolics and flavonoids in
We propose thatthe additive and synergistic effects of
phytochemicals in fruitand vegetables are responsible for their
anticancer activities, and that the benefit of a diet rich
in fruit and vegetables is attributed to the complex mixtureof
phytochemicals present in whole foods.
We recently reported that
phytochemical extracts from
fruithave strong antioxidant and antiproliferative effects and
proposedthat the combination of phytochemicals in fruit and
vegetablesis critical to powerful antioxidant and anticancer
For example, the total antioxidant activity ofphytochemicals in
1 g of apples
with skin is equivalent to 83.3΅mol vitamin C equivalentsthat
is, the antioxidantvalue of 100 g apples is
equivalent to 1500 mg of vitamin C.This is much higher than the
total antioxidant activity of 0.057mg of vitamin C (the amount
of vitamin C in 1 g of apples withskin). In other words, vitamin C in apples
contributed only< 0.4% of total antioxidant activity (31).
Thus, most ofthe
antioxidant activity comes from phytochemicals, not vitaminC. The natural combination of phytochemicals in fruit and vegetablesis responsible for their potent antioxidant activity. Appleextracts also contain bioactive compounds that inhibit tumorcell growth in vitro. Phytochemicals in 50 mg apple with
skinper milliliter (on a wet basis)
inhibit tumor cell proliferationby 42%. Phytochemicals in 50 mg apple
without skin per milliliterinhibit tumor cell proliferation by
23%. The apple
extractswith skin significantly reduced the tumor cell
proliferationwhen compared with the apple
extracts without skin
Temple NJ. Antioxidants
and disease: more questions than answers. Nutr Res 2000;20:44959.
Willett WC. Diet and
health: what should we eat? Science 1994;254:53237.
Willett WC. Diet,
nutrition, and avoidable cancer. Environ Health Perspect
Doll R, Peto R.
Avoidable risks of cancer in the United States. J Nat Cancer Inst
National Academy of
Sciences, Committee on Diet, Nutrition, and Cancer, Assembly of Life
Sciences, National Research Council. Diet, nutrition, and cancer.
Washington, DC: National Academy Press, 1982.
National Academy of
Sciences, Committee on Diet and Health, National Research Council. Diet
and health: implications for reducing chronic disease risk. Washington,
DC: National Academy Press, 1989.
Shahidi F, Naczk M. Food
phenolics: an overview. In: Shahidi F, Naczk M, eds. Food phenolics:
sources, chemistry, effects, applications. Lancaster, PA: Technomic
Publishing Company Inc, 1995:15.
Ames BN, Gold LS.
Endogenous mutagens and the causes of aging and cancer. Mutat Res
Liu RH, Hotchkiss JH.
Potential genotoxicity of chronically elevated nitric oxide: a review.
Mutat Res 1995;339:7389.[Medline]
Ames BN, Shigenaga MK,
Gold LS. DNA lesions, inducible DNA repair, and cell division: the three
key factors in mutagenesis and carcinogenesis. Environ Health Perspect
Block G, Patterson B,
Subar A. Fruit, vegetables, and cancer prevention: a review of the
epidemiological evidence. Nutr Cancer 1992;18(1):129.[Medline]
Knekt P, Jarvinen R,
Seppanen R, et al. Dietary flavonoids and the risk of lung cancer and
other malignant neoplasms. Am J Epidemiol 1997;146:22330.[Abstract]
Le Marchand L, Murphy
SP, Hankin JH, Wilkens LR, Kolonel LN. Intake of flavonoids and lung
cancer. J Natl Cancer Inst 2000;92(2):15460.[Abstract/Free
Boyle SP, Dobson VL,
Duthie SJ, Kyle JAM, Collins AR. Absorption and DNA protective effects of
flavonoid glycosides from an onion meal. Eur J Nutr
Dragsted LO, Strube M,
Larsen JC. Cancer-protective factors in fruits and vegetables: biochemical
and biological background. Pharmacol Toxicol 1993;72:11635.
Waladkhani AR, Clemens
MR. Effect of dietary phytochemicals on cancer development. Int J Mol Med
Hertog MGL, Feskens EJM,
Hollman PCH, Katan MB, Kromhout D. Dietary antioxidant flavonoids and risk
of coronary heart disease: the Zutphen Elderly Study. Lancet
Knekt P, Jarvinen R,
Reunanen A, Maatela J. Flavonoid intake and coronary mortality in Finland:
a cohort study. Br Med J 1996;312(7027):47881.[Abstract/Free
Arai Y, Watanabe S,
Kimira M, Shimoi K, Mochizuki R, Kinae N. Dietary intakes of flavonols,
flavones and isoflavones by Japanese women and the inverse correlation
between quercetin intake and plasma LDL cholesterol concentration. J Nutr
Joshipura KJ, Hu FB,
Manson JE, et al. The effect of fruit and vegetable intake on risk for
coronary heart disease. Ann Intern Med 2001;134:110614.[Abstract/Free
Berliner J, Leitinger N,
Watson A, Huber J, Fogelman A, Navab M. Oxidized lipids in atherogenesis:
formation, destruction and action. Thromb Haemost 1997;78:1959.[Medline]
Witztum JL, Berliner JA.
Oxidized phospholipids and isoprostanes in atherosclerosis. Curr Opin
Jimenez-Escrig A, Saura-Calixto F. Study of low-density lipoprotein
oxidizability indexes to measure the antioxidant activity of dietary
polyphenols. Nutr Res 2000;20(7):94153.
Ridker PM, Rifai N, Rose
L, Buring JE, Cook NR. Comparison of C-reactive protein and low-density
lipoprotein cholesterol levels in the prediction of first cardiovascular
events. N Engl J Med 2002;347:155765.[Abstract/Free
Hennekens CH, Buring JE,
Manson JE, et al. Lack of effect of long-term supplementation with
ί-carotene on the incidence of malignant neoplasms and cardiovascular
disease. N Engl J Med 1996;334:114549.[Abstract/Free
Greenberg ER, Baron JA,
Stuckel TA, Stevens MM, Mandel JS. A clinical trial of ί-carotene to
prevent basal cell and squamous cell cancers of the skin. N Engl J Med
ί-carotene Cancer Prevention Study Group. The effect of vitamin E and
ί-carotene on the incidence of lung cancer and other cancers in male
smokers. N Engl J Med 1994;330:102035.
Omenn GS, Goodman GE,
Thornquist MD, et al. Effects of a combination of ί-carotene and vitamin A
on lung cancer and cardiovascular disease. N Engl J Med
Blot WJ, Li JY, Taylor
PR, et al. Nutrition intervention trials in Linxian, China:
supplementation with specific vitamin/mineral combinations, cancer
incidence, and disease-specific mortality in the general population. J
Natl Cancer Inst 1993;85(18):148392.[Abstract]
Salonen JT, Nyysonen K,
Salonen R, et al. Antioxidant Supplementation in Atherosclerosis
Prevention (ASAP) study: a randomized trial of the effect of vitamins E
and C on 3-year progression of carotid atherosclerosis. J Intern Med
Eberhardt MV, Lee CY,
Liu RH. Antioxidant activity of fresh apples.
Sun J, Chu Y-F, Wu X,
Liu RH. Antioxidant and antiproliferative activities of fruits. J Agric
Food Chem. 2002;50:744954.[Medline]
Chu Y-F, Sun J, Wu X,
Liu RH. Antioxidant and antiproliferative activities of vegetables. J
Agric Food Chem. 2002;50:691016.[Medline]
Council. Recommended Dietrary Allowance. 10th ed. Washington, DC: National
Academy Press, 1989.
Podmore ID, Griffiths
HR, Herbert KE, Mistry N, Mistry P, Lunec J. Vitamin C exhibits
pro-oxidant properties. Nature 1998;392:559.[Medline]
J Agric Food
Chem. 2003 Jan 29;51(3):609-14.
Antioxidant activity of
Wolfe K, Wu X, Liu RH.
Institute of Comparative and Environmental Toxicology and Department of Food
Science, Stocking Hall, Cornell University, Ithaca, New York 14853-7201,
Consumption of fruits and vegetables
has been shown to be effective in the prevention of chronic diseases.
These benefits are often attributed to the high antioxidant content of some
plant foods. Apples are commonly eaten and are large contributors of
phenolic compounds in European and North American diets.
The peels of apples, in particular,
are high in phenolics. During applesauce and canned apple
manufacture, the antioxidant-rich peels of apples are discarded. To
determine if a useful source of antioxidants is being wasted, the
phytochemical content, antioxidant activity, and antiproliferative activity
of the peels of four varieties of apples (Rome Beauty, Idared, Cortland, and
Golden Delicious) commonly used in applesauce production in New York state
were investigated. The values of the peels were compared to those of the
flesh and flesh + peel components of the apples. Within each variety, the
total phenolic and flavonoid contents were highest in the peels, followed by
the flesh + peel and the flesh. Idared and Rome Beauty apple peels had the
highest total phenolic contents (588.9 +/- 83.2 and 500.2 +/- 13.7 mg of
gallic acid equivalents/100 g of peels, respectively). Rome Beauty and
Idared peels were also highest in flavonoids (306.1 +/- 6.7 and 303.2 +/-
41.5 mg of catechin equivalents/100 g of peels, respectively). Of the four
varieties, Idared apple peels had the most anthocyanins, with 26.8 +/- 6.5
mg of cyanidin 3-glucoside equivalents/100 g of peels. The peels all had
significantly higher total antioxidant activities than the flesh + peel and
flesh of the apple varieties examined. Idared peels had the greatest
antioxidant activity (312.2 +/- 9.8 micromol of vitamin C equivalents/g of
peels). Apple peels were also shown to more effectively inhibit the growth
of HepG(2) human liver cancer cells than the other apple components. Rome
Beauty apple peels showed the most bioactivity, inhibiting cell
proliferation by 50% at the low concentration of 12.4 +/- 0.4 mg of peels/mL.
The high content of phenolic
compounds, antioxidant activity, and antiproliferative activity of apple
peels indicate that they may impart health benefits when consumed and should
be regarded as a valuable source of antioxidants.
PMID: 12537430 [PubMed - indexed for MEDLINE]
J Agric Food
Chem. 2003 Mar 12;51(6):1676-83.
Apple peels as a
value-added food ingredient.
Wolfe KL, Liu RH.
Institute of Comparative and Environmental Toxicology, Cornell University,
Ithaca, New York 14853-7201, USA.
There is some evidence that chronic diseases, such as cancer and
cardiovascular disease, may occur as a result of oxidative stress.
Apple peels have high concentrations
of phenolic compounds and may assist in the prevention of chronic diseases.
Millions of pounds of waste apple peels are generated in the production of
applesauce and canned apples in New York State each year.
We proposed that a valuable food
ingredient could be made using the peels of these apples if they could be
dried and ground to a powder without large losses of phytochemicals.
Rome Beauty apple peels were treated with citric acid dips, ascorbic acid
dips, and blanches before being oven-dried at 60 degrees C. Only blanching
treatments greatly preserved the phenolic compounds, and peels blanched for
10 s had the highest total phenolic content. Rome Beauty apple peels were
then blanched for 10 s and dried under various conditions (oven-dried at 40,
60, or 80 degrees C, air-dried, or freeze-dried). The air-dried and
freeze-dried apple peels had the highest total phenolic, flavonoid, and
anthocyanin contents. On a fresh
weight basis, the total phenolic and flavonoid contents of these samples
were similar to those of the fresh apple peels. Freeze-dried peels
had a lower water activity than air-dried peels on a fresh weight basis. The
optimal processing conditions for the ingredient were blanching for 10s and
freeze-drying. The process was scaled up, and the
ingredient was characterized. The total phenolic content was 3342 +/- 12 mg
gallic acid equivalents/100 g dried peels, the flavonoid content was 2299
+/- 52 mg catechin equivalents/100 g dried peels, and the anthocyanin
content was 169.7 +/- 1.6 mg cyanidin 3-glucoside equivalents/100 g dried
peels. These phytochemical contents
were a significantly higher than those of the fresh apple peels
if calculated on a fresh weight basis (p < 0.05). The
apple peel powderhad a total antioxidant activity of 1251 +/- 56 micromol vitamin C
equivalents/g, similar to fresh Rome Beauty peels on a fresh weight basis (p
> 0.05). One gram of powderhad an antioxidant activity equivalent to 220 mg
of vitamin C. The freeze-dried apple
peels also had a strong antiproliferative effect on HepG(2) liver cancer
cells with a median effective dose (EC(50)) of 1.88 +/- 0.01 mg/mL.
This was lower than the EC(50) exhibited by the fresh apple peels (p <
0.05). Apple peel powder may be used
in a various food products to add phytochemicals and promote good health.
PMID: 12617604 [PubMed - indexed for MEDLINE]
J Agric Food
Chem. 2003 Mar 12;51(6):1718-23
Antiproliferative activity of apples is not due to phenolic-induced
hydrogen peroxide formation.
Liu RH, Sun J.
Department of Food Science and
Institute of Comparative and Environmental Toxicology,
Cornell University, Ithaca, New York 14853-7201, USA. RL23@cornell.edu
screening of natural products using tumor cell lines has been
commonly used to identify anticancer drugs. Two highly significant
anticancer drugs, paclitaxel (Taxol) and camptothecin, were discovered using
tumor cell lines by the U.S. National Cancer Institute (NCI) screening
program of plants. It has been recently reported that the inhibition of
cancer cell proliferation by fruit extractswas indirectly caused by
phenolic-induced H(2)O(2) production in the cell culture media, suggesting
that many previously reported effects of flavonoids and phenolic compounds
on cultured cells might be from an artifact of H(2)O(2)-induced oxidative
stress. The objective of the present study was to determine if
extracts induced H(2)O(2) formation in common cell culture media and to
investigate if the antiproliferative activity of
apple extracts was due to phenolic-induced H(2)O(2) formation. It is reported here that
apple extracts did not induce
H(2)O(2) formation in WME, DMEM, or DMEM/Ham F12 media with the cell
culture conditions tested. These
same extracts inhibited proliferation of HepG(2) and Caco-2 cells.
activity of apple extracts was not due to the phenolic-induced
H(2)O(2) production in cell culture media. In addition, H(2)O(2) added to
the culture medium at 100 microM did not cause inhibition of cell
proliferation in either HepG(2) liver cancer cells or Caco-2 colon cancer
cells in vitro.
PMID: 12617611 [PubMed - indexed for MEDLINE]
J Agric Food
Chem. 2002 Dec 4;50(25):7449-54
Antioxidant and antiproliferative activities of common fruits.
Sun J, Chu YF, Wu X, Liu RH.
Department of Food Science, Cornell University, Ithaca, New York 14853-7201,
Consumption of fruits and vegetables
has been associated with reduced risk of chronic diseases such as
cardiovascular disease and cancer. Phytochemicals, especially phenolics, in
fruits and vegetables are suggested to be the major bioactive compounds for
the health benefits. However, the phenolic contents and their
antioxidant activities in fruits and vegetables were underestimated in the
literature, because bound phenolics were not included. This study was
designed to investigate the profiles of total phenolics, including both
soluble free and bound forms in common fruits, by applying solvent
extraction, base digestion, and solid-phase extraction methods.
Cranberry had the highest total
phenolic content, followed by apple, red grape, strawberry,
pineapple, banana, peach, lemon, orange, pear, and grapefruit. Total
antioxidant activity was measured using the TOSC assay. Cranberry had the
highest total antioxidant activity (177.0 +/- 4.3 micromol of vitamin C
equiv/g of fruit), followed by apple, red grape, strawberry, peach, lemon,
pear, banana, orange, grapefruit, and pineapple.
Antiproliferation activities were
also studied in vitro using HepG(2) human liver-cancer cells, and
cranberry showed the highest inhibitory effect with an EC(50) of 14.5 +/-
0.5 mg/mL, followed by lemon,
strawberry, red grape, banana, grapefruit, and peach. A bioactivity index
(BI) for dietary cancer prevention is proposed to provide a new alternative
biomarker for future epidemiological studies in dietary cancer prevention
and health promotion.
PMID: 12452674 [PubMed - indexed for MEDLINE]
J Agric Food
Chem. 2003 Oct 22;51(22):6516-20
Major phenolics in apple and their contribution to the total
Lee KW, Kim YJ, Kim DO, Lee HJ, Lee CY.
Department of Food Science and Technology, Cornell University, Geneva, NY
The contribution of each phytochemical to the total antioxidant capacity of
apples was determined. Major phenolicphytochemicalsof six
were identified and quantified, and their contributions to total antioxidant
activity of apples were determined using a
2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging
assay and expressed as vitamin C equivalent antioxidant capacity (VCEAC).
Average concentrations of major phenolics and vitamin C in six apple
cultivars were as follows (mg/100 g of fresh weight of apples): quercetin
glycosides, 13.20; procyanidin B(2), 9.35; chlorogenic acid, 9.02;
epicatechin, 8.65; phloretin glycosides, 5.59; vitamin C, 12.80. A highly
linear relationship (r (2) > 0.97) was attained between concentrations and
total antioxidant capacity of phenolics and vitamin C. Relative VCEAC values
of these compounds were in the order quercetin (3.06) > epicatechin (2.67) >
procyanidin B(2) (2.36) > phloretin (1.63) > vitamin C (1.00) > chlorogenic
acid (0.97). Therefore, the estimated contribution of major phenolics and
vitamin C to the total antioxidant capacity of 100 g of fresh apples is as
follows: quercetin (40.39 VCEAC) > epicatechin (23.10) > procyanidin B(2)
(22.07) > vitamin C (12.80) > phloretin (9.11) > chlorogenic acid (8.75).
These results indicate that
flavonoids such as quercetin, epicatechin, and procyanidin B(2) rather than
vitamin C contribute significantly to the total antioxidant activity of
PMID: 14558772 [PubMed - indexed for MEDLINE]
Carcinogenesis 1997; 18: 37-42. [Correspondence]
Preventive effects of vitamin C on carcinogenesis
dietary phenolic substances have stronger antioxidant and antiproliferative
effects than vitamin C, but vitamin C in fruits and vegetables is
still an important bioactive constituent. However, the mechanism for the
inhibitory effects of vitamin C on carcinogenesis has not yet been
discovered, except for its free-radical scavenging activity against
oxidative DNA damage.
We have noted
that vitamin C has preventive effects on inhibition of hydrogen peroxide (H2O2)-induced
gap-junction intercellular communication (GJIC). GJIC is essential for
maintaining the homoeostatic balance through modulation of cell
proliferation and differentiation in multicellular organisms. Inhibition of
GJIC is strongly related to the carcinogenic process, especially to tumour
promotion.1 H2O2, a tumour promoter,
induces inhibition of GJIC and hyperphosphorylation of connexin43 protein
(Cx43), which mainly modulates GJIC.1 We investigated the effects
of vitamin C on GJIC and phosphorylation pattern of connexin43 in rat liver
epithelial cells treated with H2O2, according to our
GJIC and hyperphosphorylation of connexin43 induced by H2O2
was prevented by pretreatment of the cells with 100 ΅mol/L vitamin C
(figure). By contrast, free-radical scavengers, such as propylgallate and
trolox did not prevent inhibition of GJIC by H2O2.1
Vitamin C might, therefore, have antitumour promoting effects through a
different mechanism, rather than the scavenging effects of free radicals on
carcinogenesis. Our results suggest that the mechanistic basis for cancer
preventive action of vitamin C might be related to the effects against the
inhibition of GJIC by free radicals.
In addition, we noted that quercetin, a phytochemical found in apples, has
stronger effects than vitamin C in this system (unpublished data).
Preventive effects of vitamin C on inhibition of GJIC and
hyperphosphorylation of Cx43 in rat liver epithelial cells
GJIC=mean number of communicating cells measured by scrape
loading dye transfer method: Cx43 analysed by western blot. A=untreated
control; B=H2O2 only; C=treated with 100 ΅mol/L
vitamin C. P0, P1, and P2=phosphorylation patterns of Cx43 in untreated
cells; P3=hyperphosphorylation pattern of Cx43 in cells treated with H2O2.
powerful weapon against cancer is prevention, and we postulate that
a diet rich in phytochemical will
reduce the risk of cancer. When considering cancer-preventive
strategies, inhibition of tumour promotion (a reversible and long-term
process) is more practical than that of tumour initiation (irreversible and
Lee, Hyong Joo Lee, Kyung-Sun Kang, *Chang Yong Lee
Departments of Food Science and Technology, and Veterinary Public
Health, Seoul National University,
Korea; and *Department of Food Science, Cornell
University, Geneva, NY 14456, USA (e-mail:firstname.lastname@example.org)