What is gut microbiota? What is the influence of diet on the proper functioning of our gut microbiota? How does the gut-brain axis (GBA) influence the emotional and cognitive centers of the brain? Tune into this webinar to find out more about this timely topic.
Learning Objectives:
List the neurological and physiological connections that enable the bidirectional communication between the gut and the brain
Identify lifestyle, dietary, and microbial influences on the flow and function of signaling molecules along the gut-microbiota-brain axis
Implement dietary regimens that target the gut and gastrointestinal microbiota to improve or maintain optimal physical and mental health
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3. Dr. Hannah Holscher, PhD, RD
Assistant Professor in the Department of Food Science and
Human Nutrition at the University of Illinois.
The long-range goal of her research is to develop targeted
dietary interventions for disease prevention and treatment
by identifying key foods and/or nutrients that can be utilized
for modulation of the human gastrointestinal microbiome
for health benefit.
Current clinical research in her laboratory, the Nutrition and
Human Microbiome Laboratory, includes controlled feeding
studies investigating the impact of specific whole foods and
beverages, including, avocados, broccoli, walnuts, almonds,
whole grains, and kefir on the human gastrointestinal
microbiome, metabolic health, and the gut-microbiota-brain
axis.
Today’s Presenter
3
4. The Gut-Microbiota-Brain Axis
Hannah D. Holscher, PhD, RD
Assistant Professor
Department of Food Science and Human Nutrition
Division of Nutritional Sciences
University of Illinois
5. List the neurological and physiological connections that
enable the bidirectional communication between the gut
and the brain
Identify lifestyle, dietary, and microbial influences on the
flow and function of signaling molecules along the gut-
microbiota-brain axis
Implement dietary regimens that target the gut and
gastrointestinal microbiota to improve or maintain optimal
physical and mental health
Learning Objectives
5
6. Microbiome - a collection of microbial genomes
Microbiota – a collection of microbes
As many bacteria as host
cells in human body
150x more bacterial
genes than our human
genome
Microbiome
Disease
Health
6
9. Flint, H. J. et al. (2012) Nat. Rev. Gastroenterol. Hepatol.
Microbiota Functions
9
10. Gut-Microbiota-
Brain
Communication
Cryan, John F., and Timothy G. Dinan. "Mind-altering microorganisms: the impact of the gut
microbiota on brain and behaviour." Nature reviews neuroscience 13.10 (2012): 701-712. 10
11. Bidirectional communication
Central nervous system (brain and spinal cord)
Autonomic nervous system (sympathetic and
parasympathetic)
Enteric nervous system (intrinsic nervous system
of GI tract)
Hypothalamic pituitary adrenal axis (HPA)
Microbiome (collection of microorganisms and
their genomes in the gut)
Clarkea, Gerard, Ted Dinanb, and John Cryanc. "Microbiome–Gut–Brain Axis." (2013).
Gut-Microbiota-Brain Communication
11
12. Major nerve of the parasympathetic division of the autonomic
nervous system
Important pathway for bidirectional communication between the
gut microbes and the brain
Preclinical/animal studies demonstrate that probiotic effects on
brain are dependent on vagal afferent signals
Lactobacillus rhamnosus directly activates vagal neurons
Induces region-dependent alterations in GABA receptor
expression in the brain and reduced stress-induced
corticosterone and anxiety- and depression-like symptoms via
vagus nerve signaling in mice
Vagotomized mice do not exhibit this effect
Bravo, Javier A., et al. Proceedings of the National Academy of Sciences 108.38 (2011): 16050-16055.
Vagus Nerve
12
14. Neurotransmitter Released By Function
GABA Central Nervous
System (CNS)
Relaxes lower esophageal sphincter
Norepinephrine CNS, spinal cord,
sympathetic nerves
Decreases motility, increased contraction
of sphincters, inhibits secretions
Acetylcholine CNS, autonomic
system, other tissues
Increases motility, relaxes sphincters,
stimulates secretion
Serotonin GI tract, spinal cord Facilitates secretion and peristalsis
Neurotransmitters & GI Function
14
16. Biogenic amine that functions as a neurotransmitter
Tryptophan is precursor
Involved in GI secretion
Gut motility
Pain perception
Maintenance of mood and cognition
95% of serotonin is contained in the gut in the mucosa and
nerve terminals of the enteric nervous system
Alterations in serotonin transmission may underlie
pathological symptoms
Selective serotonin reuptake inhibitors are known to modulate psychiatric
and GI disorders (e.g., IBS)
O’Mahony, S. M., et al. Behavioural brain research 277 (2015): 32-48.
Serotonin
16
17. Holzer, Peter, Florian Reichmann, and Aitak Farzi. "Neuropeptide Y, peptide YY and pancreatic polypeptide in
the gut–brain axis." Neuropeptides 46.6 (2012): 261-274.
Gut Hormones and Neuropeptides
17
20. Gut can communicate with the brain via hormonal
signaling: gut peptides from enteroendocrine cells can
act directly on the brain.
Ghrelin
Gastrin
Orexin
Cholecystokinin
Leptin
Neuropeptide Y
Feeding Behavior
Energy
Homeostasis
Circadian Rhythm
Arousal
Anxiety
Forsythe, Paul, and Wolfgang A. Kunze. Cellular and molecular life sciences 70.1 (2013): 55-69.
Cameron, Jameason, and Eric Doucet. Applied Physiology, Nutrition, and Metabolism32.2 (2007): 177-189.
Schéle, Erik, et al. Endocrinology 154.10 (2013): 3643-3651.
Germ-free studies suggest that the gut microbiota
mediates and regulates the release of gut peptides
Gut Hormones and Neuropeptides
20
21. Under the anaerobic conditions of the large intestine, undigested
carbohydrates are fermented mainly to SCFAs
Acetate
Propionate
Butyrate
Gases (H2, CO2, CH4, and H2S).
SCFAs have multiple effects on the host
Energy sources for the host
Butyrate being consumed mainly by the colonic epithelium
Acetate becomes available systemically
Circulating SCFAs can be carried by across the blood–brain barrier
Short-Chain Fatty Acids (SCFAs)
Pomare, E. W., W. J. Branch, and J. H. Cummings. Journal of Clinical Investigation 75.5 (1985): 1448.
Maurer, Martin H., et al. Neuroscience letters 355.1 (2004): 105-108.
Microbiota-Derived Signaling
21
22. Evans, James M., Laura S. Morris, and Julian R. Marchesi. Journal of Endocrinology 218.3 (2013): R37-R47.
Anti-CancerEffects
Peptide YY
GLP-1
Enteroendocrine
Serotonin
secretion
SCFAs
Appetite Control
Inflammatory
GutMotility
Energy Expenditure
Anti-Cancer
Microbiota-Derived Signaling
22
23. Intricate neurological and physiological factors enable the
bidirectional communication between the gut and the brain
Bidirectional communication with afferent and efferent
signals
Vagus nerve
Neuropeptides
Microbiota can influence behavior, neurophysiology, and
neurochemistry
SCFAs represent set of bacterial metabolites with potentially
widespread health benefits
Importance of dietary fiber intake
Microbial-based therapeutics remain topic of further
investigation
Summary
23
24. List the neurological and physiological
connections that enable the bidirectional
communication between the gut and the brain
Objective 1 Review
24
25. List the neurological and physiological
connections that enable the bidirectional
communication between the gut and the brain
Central nervous system: brain and spinal cord
Autonomic nervous system: vagal nerve
Enteric nervous system: GI nerves
Microbes and their metabolites
SCFAs: acetate, propionate, & butyrate
Neurotransmitters: serotonin and GABA
Gut Hormones: PYY
Neuropeptides: NPY
Objective 1: Answers
25
27. Fecal communities clustered into enterotypes
distinguished by levels of Bacteroides and Prevotella.
Enterotypes were associated with long-term diets:
Bacteroides: protein and animal fat
Prevotella: carbohydrates
Wu et al., 2011; Science
Bacte ro ide s
Pre vo te lla
Enterotypes associated with habitual diet
27
28. Fiber:
Plant Based: 25 g per 1000 kcal
Animal Based: 0 g per 1000 kcal
Fat:
Plant: 20 % kcal
Animal: 70% kcal
Protein:
Plant: 10%
Animal: 30%
David et al. Nature 2014
Diet can rapidly impact microbiotaDiet can rapidly impact microbiota
6 male + 4 females; 21-33 years of age
BMI 19-32 kg/m2
Cross-over design: ad libitum 5-day consumption of diets
composed entirely of animal or plant products
Diet Composition
28
30. Plant Based Diet Animal Based Diet
David et al. Nature 2014
Diet can rapidly impact microbiota
30
31. • Plant-based: increased short-chain
fatty acids, acetate and butyrate
• Animal-based: increased branch-
chain fatty acids, isovalerate and
isobutyrate
David et al. Nature 2014
Bile acids tended
to increase on
animal-based diet
P<0.1
P>0.1
Diet can rapidly impact microbiota
31
32. Fiber: “Non-digestible soluble and insoluble carbohydrates
( > 3 monomeric units), and lignin that are intrinsic and
intact in plants; isolated or synthetic non-digestible
carbohydrates (> 3 or more monomeric units) determined
by FDA to have physiological effects that are beneficial to
human health.”
Different types of fibers in different types of plants
Supplemental fibers in a range of foods
Different botanical origins and chemical structure
Cellulose
B-glucans
Inulin
Polydextrose
Soluble Corn Fiber
Dietary Fiber
Food and Drug Administration 2016 32
33. Prebiotic – a substrate that is selectively utilized by host
microorganisms conferring a health benefit1
Probiotic– live microorganisms that when administered
in adequate amounts confer a benefit to the host2
Synbiotic: Product that contains both probiotics and
prebiotics
Pro-, Pre- & Syn-biotics
1. Gibson GR et al (2017) Nature Reviews Gastro Hept; 2. World Health Organization (2010) 33
35. Randomized, double-blind, placebo-controlled
crossover trial with three 21-day treatment periods
Healthy adult men (n = 21)
Daily food and GI tolerance records
3 fecal specimens were collected on days 16 - 21
Holscher et al. Am J Clin Nutr 2015
Study Design: PDX & SCF
35
36. a b b
a ab
p<0.01
Holscher et al. Am J Clin Nutr 2015
PDX & SCF shifted Bacteroidetes:Firmicutes Ratio
36
38. Randomized, double-blind, placebo-controlled
crossover trial with three 21-day treatment periods
Healthy adults (n=30)
Daily food and GI tolerance records
3 fecal specimens were collected on days 16 - 20
Holscher, H.D. et al., Food & Function, 2014
Design: Agave Inulin
38
39. Holscher, H.D. et al., J. Nutr 2015
Treatment (Agave inulin g/day)
b
a
c
a a
b
Increased Bifidobacterium & decreased Desulfovibrio
39
40. Holscher, H.D. et al., J. Nutr 2015
Agave inulin: phenotypic responses
40
41. Identify dietary and microbial influences on
the the gut-microbiota-brain axis
True or False? Habitual diet and rapid changes
in diet can influence microbial composition and
microbial metabolites
Objective 2: Review
41
42. Identify dietary and microbial influences on
the the gut-microbiota-brain axis
True
Both habitual diet and rapid changes in diet have
been shown to influence microbial composition
and microbial metabolites in adults
Objective 2: Answer
42
43. Identify dietary and microbial influences on
the the gut-microbiota-brain axis
Matching
1)Prebiotic
2)Probiotic
3)Synbiotic
Objective 2: Review
A. Microorganisms + substrates
B. Energy substrate for microbes
C. Microorganisms
43
44. Identify dietary and microbial influences on
the the gut-microbiota-brain axis
1. Prebiotic (B)– a substrate that is selectively
utilized by host microorganisms conferring a
health benefit
2. Probiotic (C)– live microorganisms that when
administered in adequate amounts confer a
benefit to the host
3. Synbiotic (A): product that contains both
probiotics and prebiotics
Objective 2: Answers
44
45. Identify dietary and microbial influences on
the the gut-microbiota-brain axis
True or False? All fibers and prebiotics change
the composition of the microbiome in the same
way
Objective 2: Review
45
46. Identify dietary and microbial influences on
the the gut-microbiota-brain axis
False
Fibers and prebiotics differentially change the
composition of the microbiome. For example,
SCF & PDX increased the abundances
Bacteroidetes, while agave inulin increased
Bifidobacterium
Objective 2: Answer
46
49. Foods
Oatmeal
Barley
Onions
Greens
Berries
Bananas
Legumes
Sources of Prebiotics
Supplements
Tablets
Powders
Prebiotic – a substrate that is selectively utilized by
host microorganisms conferring a health benefit
49
50. Supplements
Capsule
Powder
Tablets
Foods
Yogurt
Fermented milk drinks
Kefir
Infant formula
Cheese
Cereal
Sources of Probiotics
Probiotic– live microorganisms that when administered
in adequate amounts confer a benefit to the host
50
51. Galactooligosaccharies (GOS) 5.5 g/day
Reduced waking salivary cortisol
Suppression of the neuroendocrine stress response
Increased attentional vigilance in the processing of positive
versus negative
interpreted as showing an early anxiolytic-like profile, where
threatening stimuli are less likely to be attended to
Reduction of anxiety like behavior and dampening of
fight-or-flight response
Schmidt, K et al., Psychopharmacology (2015) 232:1793–1801
Gut-Brain Axis: Prebiotics
51
52. 4-week intake of a 250 g of fermented milk by healthy
women affected activity of brain regions that control
central processing of emotion and sensation
Bifidobacterium animalis subsp. lactis (2.5 x 1010
CFU/day)
Streptococcus thermophiles (2.4 x 109
CFU/day)
Lactobacillus bulgaricus (2.4 x 109
CFU/day)
Lactococcus lactis subsp. lactis
Beneficial effect on general signs of anxiety and
depression, reduced cortisol
L. helveticus and B. longum (3 x 109
CFU/day)
Tillisch et al., Gastroenterology 2013;144:1394 –1401
Messaoudi et al., British Journal of Nutrition (2011);105: 755–764
Gut-Brain Axis: Probiotics
52
53. Neurological and physiological connections that enable the
bidirectional communication between the gut and the brain
Dietary fiber, prebiotics, and probiotics impact human
health and the microbiota
Much interest in understanding the complex relationships
among diet, the microbiome, and health—identifying and
utilizing key foods, nutrients, and microbes to modulate
the microbiota for health benefit
Summary
53
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Need picture of GI Tract
~ 1:1 ratio bacteria:human cells
~ 50% of colonic content, feces
&gt; 1000 species
Varies along GI tract, from lumen to mucosa
The microbiome has a profound influence on human physiology and nutrition. GI microbes contribute to energy harvest from food
Protective Functions
Colonization resistance
Nutrient competition
Secretion of antimicrobials
Immune development
Structural Functions
Mucus layer
Tight junctions
Intestinal villi and crypts
Secretory IgA production
Pathways involved in bidirectional communication between the gut microbiota and the brain.
Multiple potential direct and indirect pathways exist through which the gut microbiota can modulate the gut–brain axis. They include endocrine (cortisol), immune (cytokines) and neural (vagus and enteric nervous system) pathways. The brain recruits these same mechanisms to influence the composition of the gut microbiota, for example, under conditions of stress.
The hypothalamus–pituitary– adrenal axis regulates cortisol secretion, and cortisol can affect immune cells (including cytokine secretion) both locally in the gut and systemically. Cortisol can also alter gut permeability and barrier function, and change gut microbiota composition.
Conversely, the gut microbiota and probiotic agents can alter the levels of circulating cytokines, and this can have a marked effect on brain function.
Both the vagus nerve and modulation of systemic tryptophan levels are strongly implicated in relaying the influence of the gut microbiota to the brain.
In addition, short-chain fatty acids (SCFAs) are neuroactive bacterial metabolites of dietary fibres that can also modulate brain and behaviour. Other potential mechanisms by which microbiota affect the brain are described in BOX 1. ACTH, adrenocorticotropic hormone; CRF, corticotropin-releasing factor.
So far we have highlighted the complexity in micorbiota
A bidirectional communication network between the brain and the gastrointestinal tract that includes the central nervous system (brain and spinal cord), the sympathetic (fight or flight response) and parasympathetic (rest and digest) arms of the autonomic nervous system, the neuroendocrine and neuroimmune systems, the enteric nervous system, and the collection of microorganisms and their genomes in the gut habitat.
Neurotransmitters, also known as chemical messengers, are endogenous chemicals that enable neurotransmission. They transmit signals across a chemical synapse, such as a neuromuscular junction, from one neuron (nerve cell) to another &quot;target&quot; neuron, muscle cell, or gland cell.
Neurotransmitters are released from synaptic vesicles in synapses into the synaptic cleft, where they are received by receptors on the target cells. Many neurotransmitters are synthesized from simple and plentiful precursors such as amino acids, which are readily available from the diet and only require a small number of biosynthetic steps for conversion. Neurotransmitters play a major role in shaping everyday life and functions. Their exact numbers are unknown, but more than 100 chemical messengers have been uniquely identified.
Figure 1. Pathways involved in bidirectional communication between the gut microbiota and the brain.
There are many potential direct and indirect pathways through which the gut microbiota can modulate the gut–brain axis. They include endocrine (cortisol), immune (cytokines), and neural (vagus and enteric nervous system) pathways. The gut microbiota and probiotic agents can alter the levels of circulating cytokines, and this can have a marked effect on brain function. Both the vagus nerve and modulation of systemic tryptophan levels are strongly implicated in relaying the influence of the gut microbiota to the brain. Stress at the level of the CNS can also impact on gut function and lead to perturbations of the microbiota. In addition, short-chain fatty acids (SCFAs) are neuroactive bacterial metabolites of dietary fibers that can also modulate brain and behavior. Harnessing such pathways may provide a novel approach to treat various brain disorders. Neurotransmitters: serotonin, dopamine, norepinephrine, GABA.
Adapted from Cryan and Dinan (2015).
Serotonin is perhaps the best known neurotransmitter.
Alterations in serotonin transmission may underlie the pathological symptoms of both GI and some psychiatric disorders, and may explain their high comorbidity.
Actually, selective serotonin reuptake inhibitors and tricyclic antidepressants modulating serotonergic neurotransmission, have been shown to be effective in the treatment of both affective and GI disorders such as irritable bowel syndrome (IBS)
The bidirectional gut–brain axis. Four communication pathways (sensory neurons, cytokines, gut hormones and microbial factors) signal from the gut to the brain where they can modify cerebral function and behaviour. Two pathways (autonomic and neuroendocrine outputs) signal from the brain to the gut. EC, M and L denote different populations of endocrine cells in the gastrointestinal mucosa.
The NPY-Y receptor system in the gut–brain axis. The graph shows the major sources of NPY, PYY and PP along the gut–brain axis and the Y receptor subtypes which mediate the effects of these peptides at the different levels of the gut–brain axis. The arrow symbols denote stimulation, the tack symbols denote inhibition.
The bidirectional gut–brain axis. Four communication pathways (sensory neurons, cytokines, gut hormones and microbial factors) signal from the gut to the brain where they can modify cerebral function and behaviour. Two pathways (autonomic and neuroendocrine outputs) signal from the brain to the gut. EC, M and L denote different populations of endocrine cells in the gastrointestinal mucosa.
The NPY-Y receptor system in the gut–brain axis. The graph shows the major sources of NPY, PYY and PP along the gut–brain axis and the Y receptor subtypes which mediate the effects of these peptides at the different levels of the gut–brain axis. The arrow symbols denote stimulation, the tack symbols denote inhibition.
The bidirectional gut–brain axis. Four communication pathways (sensory neurons, cytokines, gut hormones and microbial factors) signal from the gut to the brain where they can modify cerebral function and behaviour. Two pathways (autonomic and neuroendocrine outputs) signal from the brain to the gut. EC, M and L denote different populations of endocrine cells in the gastrointestinal mucosa.
The NPY-Y receptor system in the gut–brain axis. The graph shows the major sources of NPY, PYY and PP along the gut–brain axis and the Y receptor subtypes which mediate the effects of these peptides at the different levels of the gut–brain axis. The arrow symbols denote stimulation, the tack symbols denote inhibition.
Need picture of brain.
Of course NPY is one of many gut peptides that are influenced by microbiota and may influence the brain. A large family hormones released by the gut are known to directly impact the brain and influence subconscious as well as conscious actions in the brain.
The gut can also communicate with the brain via hormonal signaling pathways that involve the release of gut peptides from enteroendocrine cells, which can act directly on the brain.
Gut peptides, such as ghrelin, gastrin, orexin, pancreatic polypeptide, cholecystokinin, and leptin, modulate feeding behavior, energy homeostasis, circadian rhythm, sexual behavior, arousal, and anxiety. This may have been an evolutionary adaptation to increase activity/movement in service of food seeking behavior.
Ghrelin which is released from the upper GI tract under conditions of hunger, reduces both anxiety-like and depression-related behavior (Lutter et al., 2008 and Schellekens et al., 2012).
Leptin receptors can be found in limbic structures, and chronic leptin treatment reverses stress-induced behavioral deficits (Lu, Kim, Frazer, & Zhang, 2006), suggesting a potential role for this hormone in emotional processes (Finger, Dinan, & Cryan, 2010).
The role of the gut hormonal response in the microbiota-gut-brain cross talk is clearly an area of research that demands more attention and may offer novel therapeutic targets for the brain-gut axis disorders.
For the final 2 slides for this presentation I would like to talk spend a few minutes talking about the importance of bacterial metabolites, particularly SCFAs and their role in the microbiota-gut-brain-axis.
SCFAs represent a potent dietary or broadly speaking a behavioral input that may have wide-ranging consequences from acute regulation of feeding behavior as is the case with appetite control and gut motility but chronic energy expenditure as well as anti-inflammatory agents that may prevent carcinogenesis.
This is an area of active research.
Correlation of diet and gut microbial taxa identified in the cross-sectional COMBO analysis. Columns correspond to bacterial taxa quantified using 16S rDNA tags; rows correspond to nutrients measured by dietary questionnaire. Red and blue denote positive and negative association, respectively. The intensity of the colors represents the degree of association between the taxa abundances and nutrients as measured by the Spearman’s correlations. Bacterial phyla are summarized by the color code on the bottom; lower-level taxonomic assignments specified are in fig. S1. The dots indicate the associations that are significant at an FDR of 25%. The FFQ data were used for this comparison (both FFQ and Recall dietary data are shown together in fig. S1). Columns and rows are clustered by Euclidean distance, with rows separated by the predominant
a, b, Faecal concentrations of SCFAs from carbohydrate (a) and amino acid (b) fermentation (*P &lt; 0.05, two-sided Mann–Whitney U test; n = 9–11 faecal samples per diet arm; Supplementary Table 11).
Median bulk bile acid concentrations are shown for all individuals on the plant-based (a) and animal-based (b) diets (error bars denote median absolute deviations). For detailed experimental protocols, see Methods. Bile acid levels did not significantly change on the plant-based diet relative to baseline levels (P &gt; 0.1, Mann–Whitney U test). However, bile acid levels trended upwards on the animal-based diet, rising from 1.48 μmol per 100 mg dry stool during the baseline period to 2.37 μmol per 100 mg dry stool (P &lt; 0.10, Mann–Whitney U test).
Any open source pictures of toolboxes available?
Any open source pictures available?
Any open source pictures available?
Any open source pictures available?
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