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BISC 438 > lecture 27: polyphenols > Flashcards

lecture 27: polyphenols Flashcards

1
Q

polyphenols

A

plant secondary metabolites

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2
Q

flavonoids

A

plant polyphenols with a basic chemical structure of 15C

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3
Q

flavanols

A

sub-family of polyphenols
catechin, epicatechin

most abundant is (-)-epicatechin

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4
Q

procyanidins

A

polymers/oligomers of flavanols
not degraded through gastric transit, found in intestine

conc in GI tract can be maintained or increased when consumed on a daily basis

local effects at GI tract

can prevent DCA-induced CRC, inhibit oxidant production and Ca2+ increases

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5
Q

catechin, epicatechin absorption and metabolism

A

absorption and metabolism influenced by stereochemical configuration

(-)-epicatechin best absorbed

after absorption, transformed into several methylated, sulfated, etc metabolites

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6
Q

how to flavanols and procyanidins prevent cholesterol and TAG absorption?

A

tea polyphenols inhibit pancreatic lipase activity

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7
Q

polyphenol inhibition of fat absorption

A

flavanols and procyanidins in tea inhibit TG absorption
tea polyphenols inhibit activity of pancreatic lipase (TG to FA)

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8
Q

NOX (NADPH Oxidase)

A

oxidizes NADPH and forms O2-
O2- and NO can form peroxynitrite, potent oxidant

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9
Q

polyphenol regulation of BP

A

OVERALL: flavanols improve NO bioavailability > decrease BP
epicatechin decrease NOX or increase eNOS

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10
Q

polyphenols and antioxidant effects

A

decreased oxidative stress, action of flavanols and procyanidins on cellular components > decreased level of tissue oxidants

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11
Q

if the concentration of flavonoids do not reach concentrations within the body to be effective metal chelators or free radical scavengers, how can they have antioxidant actions?

A

they must be effective modulators of specific protein targets

ex. flavanols inhibit NOX

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12
Q

2 measures of oxidative stress

A

GSH and MDA

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13
Q

glutathione (GSH)

A

antioxidant, preventing damage caused by ROS by serving as electron donor > dimeric form GSSG
ratio of GSH:GSSG is indicator of oxidative stress

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14
Q

malondialdehyde (MDA)

A

results from lipid perodixation of PUFAs

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15
Q

suggested effects of epicatechin

A

1) increase in eNOS activity
eNOS activation via PI3K/AKT or Ca2+/calmodulin pathway

2) diminished NOX activity

both increase NO bioavailability!

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16
Q

DCA (deoxycholic acid)

A

secondary bile acid for emulsification of fats
increase ROS production > oxidative stress

affects local conc of cholesterol and alters membrane lipid rafts

17
Q

lipid rafts

A

specialized areas of the plasma membrane characterized by high content of cholesterol

18
Q

MAPK/ERK Pathway

A

ligand binds to EGFR > phosphorylation cascade to activate ERK1/2, which activates transcription factors like NF-kB > activate TNFa

overactivation > tumor growth

19
Q

protein kinase C (PKC)

A

can be activated by DAG or Ca2+

overactivation > tumor growth

20
Q

NF-kB

A

transcription factor involved in inflammatory response

maintained in inhibited state by IkBa, activated/released upon phosphorylation of IkBa, NFkB enters nucleus

21
Q

TNFa

A

cell signaling protein (cytokine) involved in inflammation

triggers adipocyte activation of ERK1/2, JNK, p38, AP-1, NFkB

22
Q

AP-1

A

transcription factor, downstream target of ERK 1/2 and p38
activated by DCA

23
Q

procyanidins and DCA

A

blocks ERK 1/2, p38, Akt, AP1, NF-kB activation

24
Q

procyanidins and cholesterol

A

prevents redistribution/depletion of cholesterol from membrane (alter of lipid rafts)

25
Q

ER stress

A

oversupply of nutrients available, accumulation of misfolded proteins in ER > activate unfolded protein response (UPR)
linked with oxidative stress > insulin resistance

26
Q

main source of superoxide and hydrogen peroxide

A

NOX enzymes
high fructose/fat diet > increased expression of NOX

27
Q

UPR (unfolded protein response)

A

JNK and IKK activated, triggered by inflammation
IKK activates NFkB

28
Q

adiposity promotes…

A

secretion of proinflammatory cytokines such as TNFa > insulin resistance

29
Q

binding of TNFa to its receptor

A

causes activation of NADPH oxidase > increase in oxidant production

30
Q

PTP1B

A

negative regulator of the insulin signaling pathway
can dephosphorylate activated insulin receptor kinase

31
Q

PTP1B pathway

A

1) binding of insulin to receptor
2) phosphorylation of tyrosine residues in receptor
3) receptor generates binding sites for insulin receptor substrate
4) PTP1B inactivates the insulin receptor and substrate by dephosphorylation
5) diminished GLUT4 translocation > glucose in bloodstream

NFkB > increased PTP1B > inactivates insulin receptor > diminished GLUT4 translocation

32
Q

PPAR(y)

A

increases insulin sensitivity
downregulated by TNFa - this decreases insulin sensitivity

33
Q

NOX and insulin resistance

A

NOX inhibitor improves insulin sensitivity, epicatechin

34
Q

When considering the biological actions of polyphenols that are absorbed, what are two factors that should be considered?

A

1) Bioavailability: amount absorbed, structural modification into metabolites after absorption

2) Concentration at target tissue

35
Q

How does epicatechin increase nitric oxide bioavailability? What impact does this have on blood pressure?

A

inhibits NOX and enhances eNOS, increasing NO bioavailability > vasodilation

36
Q

Epicatechin and procyanidins are both capable of preventing the activation of NF-kB. However, their mechanism of action appears to be different. Explain how both forms of polyphenols accomplish this.

A

1) Epicatechin
monomer, can be absorbed
Inhibit NOX, activate eNOS > inhibit NF-kB
inhibits the degradation of IkBa, which maintains NF-kB in the inhibited state

2) Procyanidins
cannot be absorbed → acting on the GI tract
prevents lipid rafts disruption and cholesterol redistribution
block Akt and p38 activation - upstream to NF-kB activation

37
Q

We discussed epicatechin as a food molecule that can aid in increasing insulin sensitivity. How do high amounts of dietary sugar decrease insulin sensitivity? How is NADPH oxidase involved?

A

High dietary sugar > ER stress > oxidative stress > increase NOX > ROS, NF-kB, PTP1B

GLUT 4 translocation blocked > lack of glucose absorption
Promoting expression of TNFa, activate NFkB

38
Q

superoxide and peroxynitrite

A

NO can react with superoxide (O2-) to form peroxynitrite
superoxide production by NOX
therefore, NOX inhibition increases NO bioavailability

BISC 438 (28 decks)

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