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MONOGASTRIC GI > 6.4 – Dietary Fibre Digestion and Fermentation to SCFA > Flashcards

6.4 – Dietary Fibre Digestion and Fermentation to SCFA Flashcards

1
Q

Dietary fiber:

A

-CHO that are not digested or are poorly digested by enzymes in SI
-non-starch polysaccharides

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2
Q

What are the non-starch polysaccharides (NSP) cell wall components:

A

-cellulose
-hemicellulose
-others (arabinoxylans, xyloglucans, arabinogalactnas, beta-glucans)

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3
Q

Cellulose:

A

-linear unbranched chain of glucose with beta-(1,4) linkages
-tightly packed

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4
Q

Hemicellulose:

A

-branched chain polysaccharides
>hexoses and pentoses
Ex. most common in grains is xylan

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5
Q

Xylan:

A

-xylose backbone with side chains composed of arabinose, mannonse, galactose and glucose

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6
Q

What are some examples of naturally occurring plant fibers that are insoluble?

A

-cellulose, hemicellulose
-lignin’s

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7
Q

What are the effects of lignins?

A

-adds bulk
-laxative

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8
Q

What are some examples of naturally occurring plant fibers that are soluble?

A

-beta-glucans:
-guar gum
-inuli
-pectins
-resistant starct

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9
Q

Beet pulp:

A

-combination of soluble and insoluble fibers

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10
Q

Solubility vs. fermentability:

A

-related, but not the SAME
-insoluble=never digested
-soluble=some fermented, but not ALWAYS

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11
Q

Fiber main effect on stomach and SI:

A

release of satiety hormones
>GLP-1
>PYY
>CCK

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12
Q

Fiber other effects on stomach and SI:

A

-promote satiety
>distension
>delay gastric emptying (increased viscosity)
>release of hormones
-reduced rate of nutrient absorption
-reduced postprandial glucose and cholesterol absorption

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13
Q

Fiber main effect on colon:

A

-fermentation
>altar gut microbial composition
>production of SCFA

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14
Q

Fiber other effects on colon:

A

-increased bacterial mass (stool mass)
*excess can cause GI intolerance (high intakes of rapidly fermentable)

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15
Q

Dietary fiber for dogs study?

A

-no effect of diet on insulin, PYY, GLP-1 or ghrelin post feeding
-butyrate didn’t change
-BCP went done
-no effect on fecal score
*more fermentable fiber=dramatic decrease in voluntary food intake

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16
Q

Fermentation in colon leads to:

A

-proliferation of colonic bacteria =increases stool mass
>decreased pH (affects bacterial metabolism and growth)
-formation of SCFAs

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17
Q

What are some SCFAs that are made from fermentation of fiber?

A

-acetate
-propionate
-butyrate

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18
Q

Acetate production:

A

-produced directly from 2 acetyl-CoA joining OR
-PREFERRED: Wood-Ljungdahl pathway using CO2
-methanogens use the H2 to produce methane

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19
Q

Butyrate:

A

-important energy source for colonocytes
>60-70% of their energy
-important for barrier function and gut integrity
-some will be taken up by liver and oxidized to acetyl-CoA

20
Q

Butyrate production:

A

-2 acetyl-CoA are condensed to form butyryl CoA then become butyric acid

21
Q

Propionate is taken up by liver and metabolized to:

A

-succinyl-CoA then to TCA intermediates or used for gluconeogenesis

22
Q

Propionate production:

A

-succinate decarboxylation to propionate
-lactate to propionate via acryl CoA

23
Q

What are some examples of bacteria that can do succinate decarboxylation to

A

proprionate?
-Selenomnas ruminantium (amylolytic)
-Bacteroides succinogens (amylolytic)

24
Q

How much fuel value can fermentable CHO give you?

A

-1.5-2.6 kcal/g (vs. 4 kcal/g from starch)

25
Q

Valerate comes from:

A

-fermentation OR diet

26
Q

What are branched chain SFA (iso-) derived from?

A

-fermentation of the branched chain AA (valine, leucine, and isoleucine)
Ex. iso-valerate is NOT from valerate

27
Q

What is the environment in the colon?

A

-anaerobic

28
Q

Fermentation first step:

A

-breakdown of fermentable poly- or oligosaccharides to monosaccharides by bacterial glycosidases

29
Q

What pathway do most intestinal bacteria use to derive energy from CHO?

A

-glycolytic pathway, but NO ETC!
>substrate level phosphorylation (not as efficiently)
*energy output is relatively low
*usually get pyruvate (or oxaloacetate)

30
Q

How are SCFAs absorbed?

A

-SCFA/HCO3- exchange
-various active transporters (ex. couple with Na or H OR straight diffusion)
-binding receptors (GPR)
-non-ionized=SCFAs are freely absorbed
*ionization depends on pKa and pH of colon

31
Q

What is the pKa of most SCFAs?

A

-4.6-4.8

32
Q

Where is acetate transported through?

A

-portal vein
>absorbed into liver and periphery
>form acetyl-CoA
*also used in FA synthesis

33
Q

Where is propionate transported through?

A

-portal vein
>metabolized by hepatocytes

34
Q

What is propionate and lactate ‘converted’ to?

A

-propionate: oxaloacetate then glucose
-lactate: pyruvate then glucose
*only SCFA that can form glucose

35
Q

What is butyrate transported/used for?

A

-primarily metabolized by colonic mucosa as an energy source
>beta-hydroxybutyrate (ketone body)

36
Q

Beta-hydroxybutyrate is used by colonocytes for:

A

-energy
*also provides initial C skeleton for FAs in milk

37
Q

What are some physiological effects of dietary fiber in the colon?

A

-production of SCFAs leads to activation of SCFA receptors
-alter gut microbial composition and activity
>may improve gut barrier/immune function

38
Q

What are some SCFA receptors that are expressed in the colon?

A

-FFAR2 and FFAR3 (GPCR)
>expressed by L-cells that secrete GLP-1 and PYY
>also in other tissues
-NLRP3

39
Q

What does NLRP3 receptors do?

A

-reduce inflammation
-improved barrier function
*how feeding fiber can effect the immune system

40
Q

‘prebiotic’:

A

-ability to increase growth of bifidobacterial and lactobacilli

41
Q

Tissue of colon: gradient of different molecules

A

-lots of acetate, butyrate, propionate

42
Q

Portal vein: gradient of different molecules

A

*not much butyrate

43
Q

Systemic circulation: gradient of different molecules

A

*not much propionate in systemic circulation as it was ‘used’ by the liver
-need to take samples from the colon itself!

44
Q

What is the role of SCFA as signalling molecules?

A

-gut-brain communication and brain function (directly or indirectly)
-intestinal barrier function and immunity
-hormone production
-systemic inflammation
-activate brown AT
-regulation of mitochondrial function
-increased insulin secretion
-whole body homeostasis
*can cross the BBB

45
Q

Highly fermentable fiber and swine dysentery (diarrhea):

A

*decreased clinical sigs even thought they were positive
>got the disease but didn’t get sick
*improved growth with only modest effects on feed intake
>increased efficiency

MONOGASTRIC GI (24 decks)

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