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Human Gut Microbiota andHuman Gut Microbiota and Health
D R H l thD R H l thDr. R. Hemalatha, Dr. R. Hemalatha, MD, Scientist ‘D’MD, Scientist ‘D’Dr. B. Sesikeran, Dr. B. Sesikeran, MD, FAMSMD, FAMS
DirectorDirectorDirector Director National Institute of Nutrition National Institute of Nutrition (Indian Council of Medical Research)(Indian Council of Medical Research)
HyderabadHyderabad –– 500 604500 604
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Hyderabad Hyderabad 500 604500 604INDIAINDIA
Gut Bacteria
At birth -digestive tract of humans is sterileAt birth -digestive tract of humans is sterile.
Colonised by microbes within the first fewd f lifdays of life
At first, predominantly bifidobacteria (breast, p y (fed infants)
With the introduction of other foods a diverseWith the introduction of other foods, a diversemicrobial population develops in thegastrointestinal tract.
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MAIN FUNCTIONS OF GUT FLORA
Metabolic & Trophic functions
Immunomodulatory
Protective barrier function & Anti-diarrhealProtective barrier function & Anti-diarrheal
Antidiabetic ?
Anticarcinogenic ?
Hypocholesterolemic ?
Ob it t b li d ?
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Obesity, metabolic syndrome, cancer?
METABOLIC FUNCTIONS
Fermentation
Saccharolytic Proteolytic fermentation fermentation
SCFA PhenolicSCFA Phenoliccompounds
Energy for colonocytesCarbohydrate and lipid metabolismControl of the colonic pHMaintain integrity of colonic mucosa
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Intestinal motility and nutrient absorption.
SACCHAROLYTIC FERMENTATION
Short chain fatty acids
Acetic acid- used by muscle
Butyric acid – absorption of fluids, stimulation ofproliferation in normal cells
Propionic acid – decreases production of inflammatorymediators & helps ATP production in liver
Succinic acid – break- down of acetaldehyde (generatesNAD), anti inflammatory action
SCFA induce lipogenesis
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PROTEOLYTIC FERMENTATION
Phytochemicals undergo microbial fermentation –Phytochemicals undergo microbial fermentation
polyphenols, phenolic acids etc.
anti-inflammatory
anti oxidativeanti-oxidative
anti-aging
cancer preventive
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NUTRITIONAL EFFECTS OF COMMENSAL BACTERIA
1. Recycling: non absorbed nutrients, intestinalsecretions, mucus.secretions, mucus.
(It could account for 10% of total daily energy)
2. Favouring mineral absorption
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TROPHIC FUNCTIONS
Butyrate will affect proliferation in the smallintestines and colonintestines and colon.
Intracolonic butyrate may enhance intestinalgrowth during infancy (J Nutr 137:916 922 Aprilgrowth during infancy. (J. Nutr. 137:916-922, April2007)
Butyrate inhibits cell proliferation and stimulatescells differentiation in cell lines of neoplasticoriginorigin.
Butyrate promotes reversion of cells froml i l i h
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neoplastic to non-neoplastic phenotypes.
Commensal Bacteria Prevent Infection
Competition for attachment sites
Commensal Bacteria Prevent Infection
p
Competition for nutrient availability
Growth inhibition by productions of antimicrobialGrowth inhibition by productions of antimicrobialsubstances
Influence on mucosal barrierInfluence on mucosal barrier
- mucus production
epithelial gro th- epithelial growth
Influence on immune function
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Mucosal immune systemMucosal immune system
2 d Li f D f1st line of Defense-Mucosal surface integrityIgA
2nd Line of DefenseCell-mediated Immunity –
TH1 ActivationIgA
Intestinal permeability
Glycosaminoglycans(mucus!)
TH1 Activation
Delayed HyperSensitivity
Macrophage/Phagocytosis
Production of IgA at mucosalsurface
Humoral Immunity –
TH2 Activation
All i RAllergic Response
Antibody Formation
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Gut Microbiota and Mucosal Immune Function
1. Commensal microbes have regulatory effects on mucosal immuneresponse.
2. Host immune response to commensals is species/ strain specific.
3. Commensal bacteria have a developmental role in the priming ofimmune response.
Modulation of the immune response by commensal bacteria
Stimulation of mucosal immunity
Suppression of mucosalimmunityimmunity
• Better oral vaccine responses
immunity
• Reduce allergy
• Reduce inflammation
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• Control infectionsReduce inflammation
Gut Microbiota and Mucosal Immune Regulation
Oral Tolerance:Bacteria can influence tolerance of Gut immune system toAntigens once ingested.g gThis can ↓ the hyperactive immune system in allergies,autoimmune disorders,etc
Preventing Allergy:Composition of gut flora varies in patients with/withoutallergiesallergies.Helpful gut flora stimulate the immune system and ‘train’ it torespond properly to AgL k f th b t i i l lif i d t l t i dLack of these bacteria in early life→inadequately trainedimmune system which overreacts with the Ag.In allergy: ↓Bacteroides,Bifidobacteria
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↑S.aureus, C.difficile
Preventing rotaviral and Antibiotic associated diarrhoea(AAD):(AAD):
Antibiotic can cause AAD by1. irritating the bowel directly1. irritating the bowel directly2. changing gut flora levels3. allowing pathogenic bacteria to grow4. or by increasing antibiotic resistant organisms.
The mechanism of diarrhoea can be:1. Inadequate fermentation of CHO or metabolism of
bile acidsbile acids2. CHO not broken down, absorb much water causing
diarrhoea
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3. - Lack of SCFA can also cause diarrhoea
Potential Mechanisms of anti-neoplastic action
Angiogenesis
InflammationButyrateApoptosis
P lif ti ImmunosurveillanceProliferation Immunosurveillance
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E. A. Williams et al. Proceedings of the Nutrition Society (2003), 62, 107–115
G t b t i d Li id l i ff tGut bacteria and Lipid lowering effect:Hyperlipidemic subjects- effects are primarily dueto reductions in cholesterol.Normal lipidemic subjects - effects on serumtriglycerides are dominant.
Gut bacteria are different in obese andnon obesenon obeseFirmicutes linked with obesity.Bifidobacterium and bacteroidetes normals
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Bifidobacterium and bacteroidetes –normals
Gut Microbes and ObesityYoung, conventionally reared mice have a higher bodyfat content (42%) than germ free strains, though theyconsumed 29% lesser food.
Microbiota were transferred to these germ free mice,then these mice experienced a 60% increase in body fatin 2 wks without any change in food consumption orin 2 wks without any change in food consumption orenergy expenditure.
Obese mice- More end products of fermentation, andObese ce o e e d p oducts o e e tat o , a dfewer calories in feces led to speculations that gutmicrobiota in mice help harvest additional calories fromingested food.ingested food.
In children from birth to age 7- analyzed stool samplescollected at 6 monthly intervals. differences in gut flora
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precede overweight-obesity
Do Microbial proportions matter?
Bacteroidetes constituted only 5% of the obese people’s gutflora but 20% in the lean subjects’flora, but 20% in the lean subjects .
After a year of either a carbohydrate- or fat-restricted dietAfter a year of either a carbohydrate- or fat-restricted diet,the obese lost weight and the ratio of Firmicutes toBacteroidetes shifted towards that of their leancounterparts. In the end, Bacteroidetes made up about 15%of their gut flora.
These changes are irrespective of diet and were proportional
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to the amount of wt lost.
SATURATED- FATOBESITY
Decreased Beneficial bacteria Increased Bad bacteria
Pathogenic bacteria ??????????
↑ ↓↑ Sphingomyelinases → ↓ Ceramide
Intestinal permeability ↑
Plasma LPS i.e. metabolic endotoxemia
B d i ht d f t d l t ↑ P i fl t t ki ↑
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Body weight and fat mass development ↑ Pro-inflammatory cytokines ↑macrophages infiltration↑ oxidative stress ↑ Glucose intolerance ↑ Diabetes ↑
High fat feeding induced Metabolic endotoxemia and changed intestinal bacteria
Patrice D.Canietal Diabetes,57, 2008
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CD14 mice are protected against LPS induced inflammation
• To demonstrate the causal link between LPS and obesity/Diabetes,CD14 mutant mice were studied.
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CD14 null mutation prevents the effect of LPS induced obesity and diabetes
• Body wt gain visceral and• Body wt gain, visceral andsubcutaneous adipose depotwts were increased in WT(Wild type), but unchanged inCD14 mutants(5a,b)
• Fasted and glucose stimulatedglycaemias were augmentedin WT-LPS compared to WT-C(5c)
• The area under the curve was• The area under the curve wasinc in response to LPSinfusion in WT only(5c inset)
• Plasma insulin conc weresimilar in basal and glucoseti l t d diti f llstimulated conditions for all
groups(5d)• Chr LPS infusions increased
liver wt of WT mice only(5e)T i l id i d• Triglycerides were increasedby 30% in WT-LPS mice’s liveronly, but were not statisticallysignificant(5f)
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Bifidobacterium Decreases Endotoxemia (LPS)
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Multiple correlation analysis between major Gram +ve and Gram-ve bacteria in thecaecal contents of mice was done to identify whether one specific group of gut bacteriawas involved in the determination of endotoxemia.
Bifidobacterium Decreases Blood Glucose and Insulin Levels
• Fasted insulin andglycaemic responseglycaemic responsewere positivelycorrelated withplasma endotoxinl l (4 b)levels(4a,b)
• And negativelycorrelated withcorrelated withBifidbacteria(4 c,d)
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Bifidobacterium associated with low body weight and visceral fat
• Body weight and• Body weight andvisceral fat masscorrelatedpositively withplasma endotoxinplevels(5a,b)
• Correlatednegatively withg yBifidobacteria.(5c,d)
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Markers of metabolic syndrome
Glucose Intolerance
Fasted InsulinemiaIncrease with
Fasted Insulinemia
Inflammatory MarkersEndotoxemiaDecrease with
Adipose Tissue &
Body Weight Gain
Bifidobacteria
y g
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LPS leaks through epithelial barrier!
• Gut microbiome• Probiotics• Prebiotics
• Infection• High fat diet• Env./stress
• Otherbioactives
Systemic
Adipo-cytes Fatty
liver
Immune/inflammatory responseSystemic
inflammation& MS
Ins res
LP
Defence
Imbalance
BARRIER FUNCTIONBARRIER FUNCTION
Athero-sclerosis
Ins.res.T2DM
PS/endotoxaeImbalance
IBS,IBD,CD etc. NF-kBTLR’4
CVD etc
emia?
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Prebiotics Control High Fat Diet Induced Inflammation• IL-1α, IL-1β, and IL-
6 were increased inHF mice comparedto control
• HF-OFS hadHF OFS hadsignificantlynormalized IL-1αand IL-6 cytokinesplasma levelsplasma levelscompared with HFand decreased IL-1β
• HF Cell mice• HF –Cell miceshowedintermediary levels.
C- open barsHF-closed barsHF-Cell- hatched barsHF-OFS- grey bars
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Prebiotics Improve Glucose Tolerance and Restore Glucose Induced Insulin Secretion
• HF mice showed strongglucose intolerance( 3a,b)
• Fasted insulinemia wasi ifi tl i d isignificantly increased in
HF and HF-Cell micecompared to control(3c)
• Insulin secretionfollowing glucose loadwas almost absent in HFand HF-Cell mice(3c,d). Incontrast HF-OF miceshowed normal fastingplasma insulin levels andrestored glucose-insulinsecretion.
3a: C- closed squaresHF- closed circlesHFCell-open squares
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HF-OFS-open circles
Food Sources of PrebioticsFood Sources of Prebiotics
Chicory
Oatmeal
BarleyBarley
Whole grains
Onions garlicOnions, garlic
Greens (spinach, mustard green)
B i b h f iBerries, banana, other fruits
Legumes (lentils,kidney beans, chickpeas)
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Can Bifidobacteria help prevent development of metabolic syndrome?
Hi h f t di t High fat dietHigh fat diet High fat diet+ oligofructose
Endotoxaemia(plasma LPS
Caecal counts
Endotoxaemia(plasma LPS
Caecal countsCaecal counts- Gram positives- Bifidobacteria
Caecal counts- Gram positives- Bifidobacteria
Selective Increases ofBifidobacteria in Gut MicrofloraImprove High-Fat-Diet-InducedDiabetes in Mice Through aMechanism Associated with
Modifying the gut microbiota infavour of Bifidobacteria mayprevent deleterious effects of
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Mechanism Associated withEndotoxaemia
Cani PD et al. 2007,Diabetologia,
phigh-fat-diet-induced metabolicdiseases…
THE FUTUREStudies on gut microbiota interactions withmetabolic phenotypes (so-called functionalmetabolic phenotypes (so called functionalmetagenomics)
Understanding of microbiota diversity on aUnderstanding of microbiota diversity on apopulation level and across various cultural andethnic group.
To standardize the microbiota analysis methodology,sample collection, storage, analysis methods.
Correlating microbiota composition with diseaserisk, require large prospective epidemiological
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g gstudies.
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