Samenvatting
Summary of case 1 - 6 (midterm)
- Instelling
- Maastricht University (UM)
Complete summary of cases 1 to 6, notes made during the turtorials are in red. I received a 8 for the midterm of this course, so the summary is complete!
[Meer zien]Voorbeeld 4 van de 68 pagina's
Voorbeeld 4 van de 68 pagina's
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Door: patrick98joosten • 3 jaar geleden
Voorbeeld van de inhoud
Case 1 – pre and probioticsIntestinal microbiome
= Collection of microbes; bacteria, viruses, archaea, protists and funghi.
- Major function is the fermentation of undigested food components into short-chain fatty
acids (SCFAs)
- Operates as a barrier that prevents harmful bacteria from invading the GI tract.
- Prevents overgrowth of harmful bacteria.
- Plays a role in immune system
- chemokines, cytokines, t-cell regulation
Bacterial cells in the intestine account for ± 90% of the total cells in the body. The amount of bacteria
in the body is 10 times higher than the body cells.
- Number of bacteria in total: 1012 bacteria per gram content
o CFU (colony forming unit) = expression microbes
o 1 colony: amount deriving from 1 bacterium.
- Proximal colon: contains most microorganism
- 10% of caloric production comes from the microbiota.
Developing microbiome during birth process:
- C-section → less exposure to bacteria
- Normal birth → more exposure to different bacteria which eventually leads to a greater
diversity of the microbiome
- Breast feeding (mostly bifido) → leads to more diversity of microbiome
The microbiome definition in biology refers to the microorganisms and their genes whereas the
microbiota only refers to the microbes themselves.
Enterotypes= a classification of living organisms based on its bacteriological ecosystem in the human
gut microbiome not dictated by age, gender, body weight, or national divisions.
Most common species (300 known, probably 1000 existing):
- Bacteroides
- Firmicutes
- Bifidobacterium
The microbiota is different for every person. When a prebiotic enters the gut, not all bacteria will be
able to transport and metabolize that prebiotic. And when they can, they also have to outcompete
other autochthonous members of the microbiota to actually utilize the prebiotic compounds and
potentially expand its population. SCFA’s are produced when fermenting prebiotics.
Therefore, eating combinations of prebiotics increases the response of more bacteria, leading to a
more diverse microbiome. This is considered to be important for a functional gut ecosystem.
- This leads to improvement in insulin sensitivity and is associated with successful treatments
for C. difficile infections.
- Eubacteria, Faecalibacter, Akkermansia, Ruminococcus, and Roseburia, are known to
respond to prebiotics
,Cross-feeding = the metabolism product of a certain bacterium which is stimulated by SCFA might
stimulate growth of other members of the microbiota, releasing metabolites that in turn stimulate
butyrate production by other microorganisms.
Reabsorption minerals
Probiotics decrease the pH by the production of acids/protons, the acid environment makes it
difficult for pathogens to survive but also makes minerals (such as calcium) more soluble and
therefore they can me more easily absorbed.
Prebiotics
= A non-digestible food ingredient that beneficially affects the host by selectively stimulating the
growth and/or modifying the metabolic activity of one or a limited number of bacterial species
already established in the colon that have the potential to improve host health.
= A substrate that is selectively utilized by host microorganisms conferring a health benefit’.
- Categorized by their genus, followed by their species, strain.
- Will be fermented into acetate, propionate, butyrate
Key criteria to classify food as prebiotic:
1. Must not be hydrolyzed or absorbed in the upper part of the GI tract so that it reaches the
colon in significant amounts
2. Resists gastric acidity
3. Must be a selective substrate for one or more beneficial bacteria that are stimulated to grow
4. Induce local (in the colon) or systemic effects through bacterial fermentation products that
are beneficial to host health.
Application: Dairy products, table spreads, baked goods and breads, breakfast cereals and bars, salad
dressings, meat products and some confectionery items.
FOS= fructo-oligosaccharides
GOS= galacto-oligosaccharides
Prebiotic will be fermented in SCFAs:
- These fermentation products are absorbed from the gut and can provide up to 10% of the
hosts daily energy requirements. SCFA also affect intestinal epithelial cell transport
processes, energy transduction in colonocytes, growth and cellular differentiation, hepatic
, control of lipid and carbohydrate metabolism, and provide energy to muscle, kidney, heart
and brain.
- 3 most important SCFA’s:
- Butyrate: most important SCFA for maintenance of colonic health, primarily by acting
as a direct source of energy for colonocytes. Found in small amount in peripheral
blood.
- Acetate: smaller role in colonic health. Used in cholesterol and fatty acid synthesis.
- Propionate: smaller role in colonic health. Substrate for gluconeogenesis,
lipogenesis, and protein synthesis.
→ Almost all butyrate will be used by colonocytes. Remaining of acetate and
propionate will be released by gut and processed by liver.
Mechanisms of action:
1. Increased production of SCFAs:
a. Energy source to colonocytes: mostly butyrate, less propionate and acetate
b. Increase blood flow in the colonic mucosa by exerting a dilatory effect on arteriolar
walls and increase oxygen uptake by colonocytes.
c. Bind to GPRs (located on colonocytes): suppressing the inflammatory response and
act as tumor suppressor:
i. GPR41: all SCFA’s have an even chance to bind. Expressed by
enteroendocrine L cells in the intestine, mast cells and leukocytes.
ii. GPR43: mostly propionate, medium butyrate and less acetate. Expressed by
enteroendocrine L cells in the intestine, mast cells and leukocytes.
iii. GPR109a: only for butyrate.
d. Inhibit histone deacetylases (HDACs) in colonocytes and mucosal immune cells:
especially butyrate, less propionate and not acetate.
i. Acetyl group remains on the histone → histones are unwinded →
transcription takes place → gene expression of MUC1, MUC2, MUC3 and
MUC4 → increased mucus synthesis → protect colonic epithelium from
external harm, such as caused by bacteria, reactive oxygen species, or
immune-modulating prostaglandins.
ii. HDACs probably cause that SCFA’s can modulate oxidative stress and
immune modulators → protects the colonic epithelium, the mucus layer →
reduces change on colorectal cancer and colonic inflammation.
iii. Promotes cell differentiation and inhibited cell migration in colon cancer cells
in vitro → reducing the invasiveness of carcinoma cells.
e. Lower intestinal pH
f. Stronger and healthier intestinal barrier by activation of 5’adenosine
monophosphate (AMP) kinase:
i. Enhances mucosal healing
ii. Reduces the chance of colonization and infection by gut bacteria
iii. Decreases the possibility of tumor invasion, cell migration, formation of
metastases, and inflammation.
g. Enhanced local oxygen consumption → stabilizing hypoxia inducible factor →
improving epithelial barrier function
2. Inhibition of a number of pathogenic species
3. FOS and several other prebiotics cause an increased count of lymphocytes and or leukocytes
in gut associated lymphoid tissues (GALTs) and in peripheral blood
4. Increased secretion of IgA by GALTs may stimulate the phagocytic function of intra-
inflammatory macrophages.
5. Increase in faecal water
, 6. Decrease in the toxicity of the luminal contents
7. Sometimes, laxative properties including softening of faeces
8. Stimulation of colonic mineral absorption (magnesium, calcium
Recognition pathogens:
1. Pathogen is recognized by PRRs (pattern recognition receptors) because the pathogen has a
PAMPs on its surface.
2. TLR-mediated pathogen recognition by innate cells (dendritic cells)
3. Recruitment and activation of innate cells (dendritic cells) and protein effectors
4. Dendritic cells link the innate immune system and adaptive immune system.
https://www.youtube.com/watch?v=fHzs9FcnkdE
Extra information:
Greater than 95% of SCFA are absorbed in the gut, amount that is produced with different prebiotics
cannot be readily measured in fecal material → therefore in vitro models to compare the
fermentability of different prebiotics.
Probiotic
= live microorganisms which when administered in adequate amounts confer a health benefit on the
host
Only transient in the intestinal tract and do not become part of the host's gut microflora, regular
consumption is necessary for maintenance of favourable effects.
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