Quasi vitamins, flavonoids

Quasi-vitamins:
Flavonoids
Domina Petric, MD

28.4.2018. 2Combs GF. The Vitamins. Fundamental Aspects
in Nutrition and Health. Elsevier Inc. 2008.

Flavonols
These derivatives (R3
hydroxy, R4 keto) include
quercetin, kaempferol,
isorhamnetic and myricetin.
Flavonols are the most
abundant flavonoids in
human diets.

Flavonols
Flavonols are found in a variety of fruits and
vegetables, often as glycosides.
Relatively high amounts (15-40 mg/100 g) are
found in broccoli, kale, leeks and onions.
Flavanols are also found in red wine, tea and
fruit juices.

Flavanols
These derivatives (R3 hydroxy) include
catechin, epicatechin, epigallocatechin
and their gallate derivatives.
Flavanols are found in apples, apricots
and red grapes (2-20 mg/100 g).
Green tea and dark chocolate are rich
in catechins (40-65 mg/100 g).

Flavones
• This group of some 300 compounds
retains the basic flavane nucleus
structure.
• Flavones include apigenin and luteolin
in very high concentrations (>600 mg/100 g)
in parsley, and in lower but significant
amounts in cereal grains, celery and
citrus rinds (which contain
polymethoxylated forms).

Proanthocyanidins
These derivatives are polymeric
flavanols, also called condensed tannins.
Proanthocyanidins are present in all
plants.
These polyphenols have strong
antioxidant properties in vitro.

Anthocyanins
• These derivatives (R3 and R4 reduced)
exist as glycosides, their aglycone
chromophores being referred to as
anthocyanidins.
• The most common anthocyanins are
cyanidin, delphinidin, malvinidin,
pelargonidin, peonidin, petunidin and
malvidin.
• Most are red or blue pigments.

Anthocyanins
• The richest sources (600 mg/100 g)
are raspberries, black berries
and blue berries.
• Cherries, radishes, red cabbage,
red skinned potato, red onions,
and red wine are also good
sources (50-150 mg/100 g).

Anthocyanins
Anthocyanins have antioxidant
properties.
Unlike other flavonoids, anthocyanins
are relatively unstable to cooking and
high-temperature food processing.

Flavanones
• These derivatives (R4 keto, C ring
otherwise reduced) are found primarily
in citrus fruit (15-50 mg/100 g) where
they are also present as O- and C-
glycosides and methoxylated
derivatives.
• Flavanones include eriocitrin,
neoericitrin, hesperidin, neohesperidin,
naringin, narirutin, didymin and poncirin.

Isoflavones
• These derivatives (B aromatic
ring linked at R3) are contained only in
legumes, mostly as glycosides.
• Isoflavones include daidzein, genistein,
and glycitein, which are also referred to
as phytoestrogens due to the affinities of
their 7- and 4′-hydroxyl groups to binding
mammalian estrogen receptors.
• Soy products can contain 25-200 mg/100 g.

Flavonoid utilization
The hydroxyl groups of these
polyphenols enable them to form
glycosidic linkages with sugars.
Most flavonoids occur
naturally as glycosides.

• Flavonoid glycosides appear to be
hydrolyzed by glycosidases in saliva, the
brush border of the intestines and the
intestinal microflora.
• Hindgut bacteria can also degrade the
flavanoid by cleaving the heterocyclic
ring, leading to the formation of various
phenolic acids and their lactones, some of
which may be absorbed from the colon.
28.4.2018. Combs GF. The Vitamins. Fundamental Aspects
14

Upon absorption, flavonoids
are conjugated as
glucuronides or sulfates in the
liver and are degraded to a
variety of phenolic compounds
that are rapidly excreted.
15

HEALTH EFFECTS
16

Antioxidant activity
• Flavonoids are able to chelate divalent
metal cations (Cu2+, Fe2+), thus serving
antioxidant functions by removing those
catalysts of lipid peroxidation reactions.
• The flavonol quercetin (multiple phenolic
hydroxyl groups, carbonyl group at C-4,
free C-3 and C-5 hydroxyl groups) can
scavenge superoxide radical ions, hydroxyl
radicals and fatty acyl peroxyl radicals.
17

Antioxidant activity
• Flavonols and some
proanthocyanins have been shown
to inhibit macrophage-mediated
LDL oxidation in vitro, probably by
protecting LDL-α-tocopherol from
oxidation or by reacting with the
tocopheroxyl radical to regenerate
α-tocopherol.
18

Enzyme modulation
19

Enzyme modulation
20

Enzyme modulation
21

Tea flavanols:
Inhibit redox-sensitive transcription factors: NFkB, AP-1.
Inhibit prooxidative enzymes: lipooxygenases,
cyclooxygenases, nitric oxide synthase, xanthine oxidase.
Induce phase II enzymes.
Induce antioxidant enzymes: glutathione S-transferases,
superoxide dismutases.
22

Enzyme modulation
Flavanones have been shown to induce
phase II enzymes and to exert anti-
inflammatory effects.
Naringin has been implicated in the
effect of grapefruit juice in inhibiting
cytrochrome P450-dependent drug
metabolism.
23

Chronic diseases
• Some epidemiologic studies have
demonstrated associations of diets
high in flavonoids (mainly
quercetin) with reduced risks of
cardiovascular diseases (21-53%
reductions in prevalence) and
cancers of the lung and rectum
(44-47% reductions in prevalence).
24

Chronic diseases
Cardioprotective effects have been
attributed to:
• vasodilatory effects and blood pressure
reduction
• antioxidant protection of LDLs against
lipid peroxidation
• inhibition of platelet aggregation
• reduced inflammation
25

Chronic diseases
Quercetin has been found to inhibit
the activation of c-Jun N-terminal
kinase in the modulation of
angiotensin-induced hypertrophy of
vascular smooth muscle cells.
Various proanthocyanins have been
shown to inhibit platelet activation
and expression of interleukin-2, to
lower serum levels of glucose,
triglyceride and cholesterol.
26

Chronic diseases
• Various flavones have been found to inhibit
cell proliferation and angiogenesis in vitro
and to inhibit phorbol ester-induced skin
cancer in the mouse model.
• These effects may involve inhibition of
protein kinase C, stimulation of DNA repair
mechanisms and altered carcinogen
metabolism.
• Some proanthocyanins have been shown to
induce apoptosis.
27

Antiestrogenic effects of soy isoflavones
• Isoflavones bind to estrogen
receptors α and ß, thus
affecting the estrogen-
synthetic activity of 17ß-steroid
oxidoreductase, as well as
estrogen-dependent signal
transduction pathways.
28

Antiestrogenic effects of soy isoflavones
The consumption of soy isoflavones
has been associated with higher bone
mineral density in a limited number of
epidemiological studies.
Soy isoflavones might be useful in
improving bone mineralization for
the prevention of osteoporosis.
29

Literature
• Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
28.4.2018. 30

Quasi vitamins, flavonoids

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