2. Objectives
• Review the basics of gut microbiome and its
relationship to health.
• Understand how influences of microbiome are
being investigated with increasing number of
diseases.
• Review current understanding of microbiome
in relation to obesity.
• Discuss two recent papers regarding
microbiome and NAFLD.
3. Definitions
• Microbiota: microbial community.
• Microbiome: can refer to microbiota but can also
refer to collective genomes and gene products of
microbes living within and on humans.
• Metagenome: collection of genomes within
complex microbial communities and human DNA,
some also include RNA and proteins and other
metabolites.
• Biodiversity is a measure of the complexity of a
community. Includes number of taxa (richness) and
their range of abundance (evenness).
Johnson, Pediatrics, 2012
Weinstock, Nature, 2012
4. The human gut metagenome has at
least 100 times as many genes as “us.”
There are 10 to 100 trillion microbes in
our GI tract, most in the distal gut.
Two phyla (Bacteroidetes and
Firmicutes) make up >90% in adults.
Gill, Science, 2006
In 2007, the NIH Human Microbiome
Project was formed.
9. Early Influences on Microbiota
• Gestational age
• Mode of birth (vaginal vs.
c-section)
• Maternal microbiome
• Exposure to environment
(city vs. farm)
• Diet including breast milk
vs. formula
• Hospitalization and use of
antibiotics
KOALA Birth Cohort Study
• C/S infants have lower
bifidobacteria and
baceteroides and more
C difficile.
• Bifido and bacteroides may
be protective against
obesity.
Reinhardt, JPGN, 2009
10.
11. Breast milk vs. formula fed
• Human milk oligosaccharides
stimulate growth of
bifidobacterium and
selectively alter microbial
composition.
• Microbiomes of BF babies
have higher bifidobacterium
and lactobacillus.
• Formula fed babies have
higher clostridium.
• Possible protection against
allergies, neonatal diarrhea,
NEC, obesity, DM2.
Johnson, Pediatrics, 2012
Thompson, Am J Human Bio, 2012
15. Gut microbiome may alter obesity.
• Mice and human microbiotas have Firmicutes and
Bacteroidetes dominating.
• Transplantation of an “obese microbiota” to germ
free mice results in increased adiposity compared
to transplantation of a lean microbiota.
• Mice fed high calorie Western diet for 8 weeks
increased levels of Firmicutes and decreased
Bacteroidetes; this has been seen in humans as
well.
Reinhardt, JPGN, 2009
Ferrer, Env Micro, 2012
22. Methods
• 3 pediatric groups (n=63 total)
– NASH defined by biopsy (Kleiner’s criteria: hepatic fat
infiltration, inflammation, and fibrosis)
– Obese (BMI>95% with normal LFTs)
– Normal (BMI<85%)
• Microbiome assessed using stool sample via 16S
rRNA sequencing
• Blood sample taken for serum alcohol
concentration
• Dietary assessments
23.
24. Health status is a major impact factor
for the phylogenetic composition of
fecal samples.
25.
26.
27. Is gut microbiota enriched in alcohol producing bacteria
like E. coli supplying a constant source of reactive oxygen
species (alcohol metabolism) to the liver, thus causing
liver inflammation?
28. Conclusions
• NASH microbiome is distinct from normal and
obese microbiomes.
• Some statistically significant differences:
– Bifidobacterium: NASH<obese <normal
– Prevotella: NASH>obese>>>normal
– Escherichia: NASH>>obese>normal
• Escherichia is abundant in NASH microbiome
compared to obese.
• The fact that Escherichia are ethanol producers
may provide a mechanism.
29. Questions
• Liver ultrasound indicated that some obese patients
had fatty liver.
• Conflicting microbiomes compared to prior studies in
mice and humans.
• What other mechanisms might contribute to NAFLD
besides alcohol production? Absorption of
nutrients/digestion? Immune mediated? Gut
hormones?
• Does fatty liver lead to microbiome changes?
(chicken/egg)
• Why would Escherichia be increased in NASH patients?
31. Methods
• Double blind, placebo controlled pilot study.
• Recruit obese children, ALT>40 at least 3 months, US
diagnosed fatty liver.
• Exclude: other causes of liver disease were ruled out,
on antibiotics, past pharmacologic treatment for
obesity.
• Randomized to placebo vs. Lactobacillus GG (12 billion
CFU/day) x 8 weeks.
• Primary outcome: ALT improvement or normalization.
• Secondary outcome: changes in liver echogenicity,
TNFalpha, H2BT, PG-PS ab.
34. Conclusions
• Short course of probiotic treatment improved
ALT value independent of weight changes.
• Differences in bacterial overgrowth as
measured by breath test vs. PG-PS IgA are
inconsistent. Mechanism is unclear.
• Lactobacillus rhamnosus strain GG could be a
potential therapeutic tool for pediatric NAFLD.
35. Questions
• What about biopsy proven NAFLD? How about
NASH patients? Patients with fibrosis?
• Larger RCT looking at microbiome?
• What about other end points? Histology?
Ultrasound findings?
• Is SIBO in NAFLD patients the culprit?
36. Take home points
• Microbiome is increasingly being investigated
for potential contribution to many diseases.
• Individual microbiomes are influenced by
many factors starting from birth.
• Microbiome, through a variety of possible
mechanisms, may influence obesity.
• Pro and prebiotics are being investigated as
treatment options for NAFLD.
37. References
• Clemente, et al, “The impact of the gut microbiota on human health: an integrative view,” Cell, 2012.
• De Filippo, et al, “Impact of diet in shaping gut microbiota revealed by a comparative study in children
from Europe and rural Africa,” PNAS, 2010.
• Ferrer, et al, “Microbiota from the distal guts of lean and obese adolescents exhibit partial functional
redundancy besides clear differences in community structure,” Env Microbiology, 2012.
• Gill, et al, “Metagenomic analysis of the human distal gut microbiome,” Science, 206.
• Harris, et al, “Is the gut microbiota a new factor contributing to obesity and its metabolic disorders?”
J Obesity, 2012.
• Johnson, et al, “The human microbiome and its potential importance to pediatrics,” Pediatrics, 2012.
• Kallus, et al, “The intestinal microbiota and obesity,” J Clin Gastro, 2012.
• Moschen, et al, “Dietary factors: major regulartors of the gut’s microbiota,” Gut and Liver, 2012.
• O’Hara, et al, “The gut as a forgotten organ,” EMBO Reports, 2006.
• Reinhardt, et al, “Intestinal microbiota during infancy and its implications for obesity,” JPGN, 2009.
• Tehrani, “Obesity and its associated disease: a role for microbiota?” Neurogastroenterol Motil, 2012.
• Thompson, “Developmental origins of obesity,” Am J Human Bio, 2012.
• Vajro, et al, “Effects of lactobacillus rhamnosus strain GG in pediatric obesity-related liver disease,”
JPGN, 2011.
• Weinstock, “Genomic approaches to studying the human microbiota,” Nature, 2012.
• Zhu, et al, “Characterization of the gut microbiome in non-alcoholic steatohepatitis (NASH) patients: a
connection between endogenous alcohol and NASH,” Hepatology, 2012.
