Dr Paris Tavakoli, Longitudinal course of IBDs on 12 months of follow up, JGENCA July 2017

Feature article
Part one:
Longitudinal course of
inflammatory bowel disease —
12-month follow-up of disease phase
activity and factors contributing to its
manifestation and severity
Paris Tavakoli
E. Paris858@gmail.com
Supervisors
Professor Michael Grimm
Associate Professor Ute Volmer-Conna
Abstract
Existing data points to possible links between factors such
as psychological state, autonomic influences, microbiome
composition and immune modulation with inflammatory
bowel disease (IBD) symptom manifestation and severity
over time (Andrews, 2014). These factors, however, have
never been assessed longitudinally, and simultaneously,
in a cohort of IBD patients. A broader conceptual and
longitudinal framework of neuropsychological integration,
neurovisceral incorporation, core microbiome analysis and
immune reactivation assessment can be useful to document
and characterise the possible temporal relationship between
these factors.
UNSW, together with St Vincent Hospital and St
George hospital, conducted the “Longitudinal course of
inflammatory bowel disease — LIMBO” study in 2016, which
is a novel investigation and the first to document whether
IBD neuropsychiatric morbidity is mainly associated with
local or systemic measure of immune activation. This study
also brings a distinct and plausible insight into the temporal
sequences of sub-clinical events as potential ground for
neuropsychiatric disturbances and disease severity in IBD.
Keywords and abbreviations
Inflammatory bowel disease (IBD), interleukin (IL), tumour
necrosis factor α (TNF-α), autonomic nervous system (ANS).
Introduction
Inflammatory bowel diseases and factors contributing in its
symptoms severity
Inflammatory bowel diseases (IBDs) are characterised
by chronic inflammation of the GI tract and comprise two
idiopathic gastrointestinal disorders that share similarities:
ulcerative colitis (UC) and Crohn’s disease (CD). Despite
intense research efforts, the disease aetiology is still
unknown. It appears, however, that both genetic and
environmental factors are involved in IBD, affecting the
interaction between the intestinal mucosa and luminal
bacteria, with a breakdown in the regulatory constraints of
mucosal immune responses to enteric bacteria — in other
words, an immune (inflammatory) response that is too easily
triggered and/or needlessly prolonged. Both UC and CD are
chronic disorders of a remitting and relapsing kind. Just as
the cause of the first onset of IBD is unknown, what leads to
remission and relapse is also uncertain (Xavier & Podolsky,
2007).
The incidence of IBDs is about 8 per 100,000 per year,
although this varies across different ethnic groups
(Molodecky et al., 2012). In developed countries, up to 360
in every 100,000 individuals have IBD (Knowles & Mikocka-
Walus, 2015). The highest reported prevalence values for
IBD were in Europe and North America. Australia has one of
the highest prevalence rates worldwide. Estimates suggest
more than 61,000 Australians have IBD — approximately
28,000 have CD and 33,000 have UC (Gastroenterological
Society of Australia — GESA, 2013). The peak of the disease
is in adolescents and young adults, with a second peak in
middle age.
UC is characterised by chronic inflammation of the large
intestine, with abnormal activation of the immune system
and affects the innermost layer of the colon and rectum
(Podolsky, 1991). Crohn’s disease can affect any level of the
intestinal tract from the mouth to the anus and across all
layers of the bowel wall, but mostly affects the lower small
intestine (Ileum) and colon. The most common symptoms
of IBD include diarrhoea, rectal bleeding and abdominal
pain (Baumgart & Sandborn, 2007). The symptoms are
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due to intestinal damage resulting from the exaggerated
inflammatory response. Complications from these immunemediated
diseases include anaemia, malnutrition, bowel
obstruction, fistula, infection and an increased risk of colon
cancer. Extraintestinal manifestations may also develop,
such as joint problems (arthralgia, arthritis, and ankylosing
spondylitis), rashes and skin conditions (erythema nodosum),
chronic liver disease (primary sclerosing cholangitis) and
eye conditions (such as uveitis).
There is an accumulating body of research exploring
potential factors thought to contribute to the aetiology and
pathophysiology of IBD. These include genetics, microbiome,
dietary, environmental and psychosocial factors.
The genetics of IBD highlight considerable heterogeneity
between, and within, UC and CD, with some genes
common to both and some separate. More than 200 gene
polymorphisms have been identified that are associated with
IBD (Liu et al., 2015). Many of these genes increase the risk
of the development of disease by only a very small amount.
One-third of loci described confer susceptibility to both CD
and UC (Lees et al., 2011). In twin studies of CD and UC, a
strong familial aggregation has been observed (Brant, 2011).
Recent population-based sibling risk is 26-fold greater for
CD and 9-fold greater for UC (Bengtson, 2009). Many risk
alleles are associated with host responses to bacteria,
innate and adaptive immunity, autophagy, phagocytosis and
mucosal barrier function (Xavier & Podolsky, 2007).
It is well documented that any chronic disease is associated
with a greater burden of psychological stress, depression
and anxiety (Knowles & Mikocka-Walus, 2015). IBD follows
the same model of neuropsychiatric co-morbidities, which
are more prevalent with active disease when the disease
is difficult to control (Mikocka-Walus et al., 2007). It could
be projected that illness leads to psychological problems
through a unidirectional effect on patients’ wellbeing and
quality of life. A bidirectional interplay, however, between
disease factors including inflammatory activities in the
body (systemically) and/or in the gut (locally), and the
brain is more likely. Psychological state can influence
patients’ behaviour and their perception of disease. The
role of stress — conceptualised both as an environmental/
psychosocial challenge, as well as an internal stressor such
as an evolving illness, has been substantially investigated
in the course of IBD. It has been shown that stress can
aggravate physiological, psychological and environmental
vulnerabilities, leading to emotional distress and potentially
the onset of mental and physical disorders (Knowles &
Mikocka-Walus, 2015).
In the middle of the nineteenth century, the discovery of
the “enteric nervous system — ENS” was considered a
scientific breakthrough in understanding the interaction
between the nervous system and the digestive system
(Furness, 2006). Even before that, though, and for centuries,
psychologists and physiologists had recognised the
significance of interactions between the brain and the body,
here the digestive system. Early investigators have reported
top-down (brain to gastrointestinal function) modulation,
as well as bottom-up signalling via visceral afferents to the
brain and the gastrointestinal regulatory control by emotion/
stress. The sympathetic innervations in the gastrointestinal
tract modulate GI function and its immune regulation by
their close proximity to immune cells such as dendritic cells,
B-lymphocytes and mast cells (Lyte, Vulchanova & Brown,
2011). The parasympathetic innervations of the GI tract
(vagal and sacral parasympathetic divisions) are thought
to have an anti-inflammatory modulatory role (Knowles
& Mikocka-Walus, 2015). Extensive modification in the
autonomic nervous system and its dysfunction (perhaps
related to stress, anxiety and depression), alters autonomic
output to the gut and is likely to affect brain-gut signalling,
gut function and its immune regulation (Knowles & Mikocka-
Walus, 2015).
There is no cure for IBD, so the aim of treatment is to control
the symptoms, to maintain mucosal integrity and promote
healing. A recent breakthrough in controlling the disease has
been achieved using biologic therapies that target specific
components of the immune system, for example, by using
anti-tumour necrosis factor (anti-TNF) to suppress the
exaggerated immune response. The aim is to keep patients
in remission and asymptomatic, with a primary aim of
reducing inflammation during relapse and a secondary aim
of prolonging the time spent in remission (Shanahan, 2000).
Intestinal microbiome
Immediately after birth, environmentally exposed surfaces
such as skin, respiratory tract, mouth, vagina and gut are
introduced to and colonised by foreign microorganisms
(Ley, Peterson & Gordon, 2006). A large and dynamic
community of different bacteria is considered a natural
inhabitant of the human gut with well-documented effects
on human physiology and pathology arising from the
interaction between resident bacteria and the mucosal
immune system. However, the nature of this mutualisation
is not very well understood. The human intestine’s immune
system coexists and interacts with more than 400 different
species of bacteria (mostly in the large intestine), almost 10 14
bacteria/g faeces or 10 times more than the number of body
cells (Turnbaugh et al., 2007). This microbiota portfolio can
be affected by factors such as genetics, birth route, diet,
hygiene, psychological distress, infections and medications,
including antibiotics. The gut microflora are important in
inducing tolerance towards this natural habitat and they
are thought to out-compete pathogens. Important roles of
intestinal microorganisms in the colon’s physiology include
their influence on epithelial cell differentiation (Guarner &
Melagelada, 2003).
Gut-bacteria metabolism accounts for the conversion of
many substances into metabolites. These metabolites can
be absorbed and used by the host for processes such
as vitamin synthesis (Guarner & Melagelada, 2003), and
absorption of calcium, magnesium and iron (Miyazawa,
Iwabuchi & Yoshida, 1996). In the large intestine, anaerobic
bacteria ferment undigested carbohydrates to short-chain
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Feature article
fatty acids (SCFAs) including butyrate and acetate as well
as gases (such as hydrogen, carbon dioxide, methane,
and hydrogen sulphate — Flint et al., 2012). Butyrate and
acetate as well as other SCFAs are negatively charged
radicals (anions) in the colon and are a major source of
energy for colonocytes. Butyrate is mainly consumed by
colonic epithelial cells and acetate presented systemically
(Flint et al., 2012). The role of these SCFAs and their signal
to gut receptors, their influence on appetite control and
food intake (Sleeth et al., 2010) as well as their anti-cancer
(especially for butyrate) and anti-inflammatory properties
(Hamer et al., 2008), have been an extremely rapidly growing
area of research. There are several factors that control the
prevalence of bacteria in different parts of the GI tract;
such as pH, peristalsis, redox potential, bacterial adhesion,
bacterial cooperation, mucin secretion, nutrient availability,
diet, and bacterial antagonism (Hao & Lee, 2004). The
increasing promotion of probiotics and prebiotics to assist
human health shows recognition of a role for microbial flora
in the prevention/control of disease processes (Shanahan,
2000), although data supporting their role in health are scant
(Shanahan, 2000).
It has long been proposed that gut bacteria play an
important role in the pathogenesis of IBD through their direct
interaction with the intestinal mucosa. There is convincing
evidence from animal studies showing the involvement
of the enteric bacteria in the pathogenesis of IBD. Also it
has been observed that UC and CD closely mimic defined
intestinal infections, and occur in areas with the highest
luminal bacterial concentrations (Farrell & La Mont, 2002).
Older studies have convincingly shown that diversion of
faecal stream induces inflammatory remission and can
prevent recurrence of CD, while Infusion of intestinal
contents to the excluded ileal segments reactivates mucosal
lesions (Thompson-Chagoyan et al., 2005; D’Haens et al.,
1998). Animal model studies on mice, rats and guinea pigs
have shown increasing evidence that antigens derived from
communal bacteria regulate the immune response. The
absence of the normal flora in these studies is correlated
with non-appearance of the intestinal inflammation (Taurog
et al., 1994). Transgenic mice missing the T cell receptors
(TCRa) spontaneously develop colitis in response to normal
intestine microbiota (Mombaerts et al., 1993).
Immune reactivation and IBD
The make-up of the intestinal epithelium includes four cell
families that arise from pluripotent stem cell progenitors
(Yen & Wright, 2006). These cells are: absorptive enterocytes
(IECs); goblet cells that create and secrete mucus;
enteroendocrine cells that produce and secrete hormones;
and Paneth cells that release antimicrobial peptides or
lectins (Yen & Wright, 2006). Beneath the IECs, the lamina
propria is the home of stromal cells, T cells, dendritic cells,
macrophages, B cells (IgA producing plasma cells), and
intraepithelial lymphocytes. Dendritic cells of lamina propria
are capable to establish tight junction like structures with
epithelial cells, to have direct bacterial uptake from the
intestinal lumen (Rescigno et al., 2001). They are positioned
to reach out in the lumen and sample the luminal contents as
an important surveillance strategy (Niess, 2005). Activated
dendritic cells then can migrate to lymph nodes where they
can activate T cells.
The epithelial cells contain, and are coated with pattern
recognition receptors (PRRs, including Toll-like receptors
(TLR) and nucleotide-binding oligomerisation domainlike
receptors (NOD like receptors), which are the key
component of the innate immune system in the intestine
and can recognise common repetitive patterns preset
on Gram-positive and Gram-negative bacteria, viruses,
parasites, and fungi (Furrie et al., 2005). These receptors
are sensitive to pathogen associate-molecular patterns
(PAMPs), such as bacterial lipopolysaccharides (LPS —
Lotz et al., 2006), Gram-positive and mycobacterial PAMPs
(Takeuchi et al., 1999) bacterial lipopeptide (Aliprantis
et al., 1999), lipoteichoic acid (LTA) and peptidoglycan
(PGN — Schwandner et al., 1999), double-stranded viral
RNA and bacterial DNA (Hemmi et al., 2000), and reactive
oxygen species (ROS) induced by commensals (Kumar et
al., 2007). IECs’ Toll-like receptors (TLR 1-9) are expressed
in the small intestine and colon (Otte, Cario & Podolsky,
2004; Cario & Podolsky, 2000). Signalling from TLRs leads
to epithelial cell proliferation, safeguarding of the IECs tight
junctions, release of IgA and expression of antimicrobial
peptides, regulation of pro-inflammatory cascades through
signalling the lamina propria’s immune cells (Khan et al.,
2006), and production of inflammatory cytokines, in case
any products of the bacteria permeate the epithelial layer
and are sensed by these receptors (Lee, Gonzales-Navajas
& Raz, 2008). Nucleotide oligomerisation domain (Nod1 and
Nod2) are additional pattern recognition receptors that are
intracellular, and are required for defense against invasive
enteric pathogens (Abreu, Masayuki & Moshe, 2005).
Immune cells of the adaptive immune system are differentiated
in Peyers patches of the small intestine, lymphoid follicles
of the colon, or mesenteric lymph nodes. IBD is generally
believed to be driven by an increased population of effector
T cells and increased titres of pro-inflammatory cytokines
(such as TNF-α, IL-6, INF-γ). The balance between proinflammatory
and immunosuppressive forces can determine
the progression of inflammation (Teitelbaum & Walker, 2002).
The Regulatory T cells (Tregs) regulate the level and function
of the proinflammatory cytokines derived from effector
T cells, to direct the immune responses (Thompson &
Powie, 2004). Tregs widely proliferate in an antigen-specific
manner and can respond to both self and foreign peptides.
Cytokines released by Tregs are very important to limit an
uncontrolled immune response at environmentally exposed
surfaces such as the gut. These special T cells play a key role
in the maintenance of self-tolerance, therefore preventing
autoimmune and inflammatory diseases (Thompson &
Powie, 2004). Regulatory T-cell deficiency results in an
effector T-cell response and IBD. This response is driven
by reactivity against microbial antigens. Tregs suppress
inflammation through diverse mechanisms, including release
of inhibitory cytokines such as IL-10 and transforming
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growth factor – β, and IL-35 (Vignali, Collison & Workman,
2008). IL-10 deficient mice develop spontaneous colitis
through IL-23 and TH-17 pathways. Genetically determined
deficiency of IL-10 activity could lead to severe early-onset
forms of IBD in humans.
Recently a new population of T cells known as T Helper
17 (TH-17) cells, which are responsible for production
and release of a specific proinflammatory cytokine (IL-17),
have been addressed in pathogenesis of human colitis
(Kobayashi et al., 2008). IL-23 is the cytokines that regulate
the maintenance and function of TH-17 immune cells. In
animal studies (mice), it has been shown that IL-6, TGF-β,
IL-1β, IL-23 and ATP that derives from commensal bacteria,
(such as segmented filamentous bacteria) are required for
TH-17 cells differentiation. Recent studies have directed
toward the intestinal immune modulation by the microbiota,
as it has been shown that germ-free animals have TH-17
cell development impairment and reduced level of IL-17
production in the colon (Ivanov et al., 2008) and Tregs in
these animals are not as effective as in conventionally
colonised animals (Ishikawa et al., 2008).
The human immune system plays a critical role in the
recognition, response and adaptation to countless self
and foreign molecules; so its integrity is very important in
maintaining and recovering health. The basic development
of human immune system function depends on its
interaction with the human microbiome (Macpherson &
Harris, 2004). The first line for mucosal defence is to prevent
the diffusion of foreign antigens from pathogenic bacteria
that penetrate the mucosal barrier. In all mammals, the
intestinal lumen is colonised by communities of bacteria that
result in biofilm production — the proteolytic cleavage of the
outer coating of mucus, which creates a barrier to infection.
Any challenge that alters the microbiota composition and
suppresses their regrowth can disturb the barrier, allowing
infection and disease to occur (Stecher et al., 2007). The
thickness of this mucus layer of the epithelium is correlated
to bacterial content of the intestine. It is thinner in the
proximal small intestine (containing 10 3 –10 5 organisms per
gram) and is thicker in the distal small and large intestine
(containing 10 10 –10 12 organisms per gram). Previous
studies have shown that both humans and mice normally
tolerate autologous microbiota and the breakdown of this
tolerance is associated with chronic intestinal inflammation
(Duchman et al., 1995). It is likely that potential pathological
responses to the component of intestinal flora, which are
restrained by immunoregulatory controls, do occur. When
this immune constraint is breached, it modulates the
inflammatory response (Garside, Mowat & Khoruts, 1999).
In addition, it is possible that alteration in the composition
of gut microbiota (dysbiosis), disturbs the interaction
between the immune system and microbiome and ultimately
leads to immune response alteration and may motivate
inflammatory disorders (Round & Mazmanian, 2009). IBD
patients respond to antibiotic therapy, faecal diversion and
have higher titres of antibodies against commensal bacteria,
compared to healthy individuals (Tannock, 2002). Clinically
and endoscopically, the distribution of the inflammatory
lesions of IBD is more pronounced in the areas of gut with
higher concentration of bacteria.
Conclusion
IBDs are chronic gastrointestinal inflammatory disorders.
The onset of disease is in adolescents and young adults
with the second peak in middle age (Andrews, 2014).
There are multiple genetic, environmental, psychological,
immune and microbiota factors contributing to the
manifestation and disease severity. The aetiology of IBDs
is not very well understood. Prevalence of IBD in Australia
is more than 61,000 cases diagnosed (Gastroenterology
Society of Australia, 2014). The national total hospital cost
of IBD in Australia is more than $100m per annum (PWC
Australia, March 2013). To characterise the risk factors
and vulnerabilities in remission and individual differences
and their interdependence, it is important to demonstrate
a longitudinal assessment of biological and psychological
factors and their temporal trajectory, including in relapse.
To be continued in the next GENCA Journal
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