Inflammatory bowel disease

Question 1

What are the 2 different inflammatory bowel diseases?

Answer 1

• Crohn’s disease (CD)
• Ulcerative Colitis (UC)

Question 2

Define the chronic characteristic of Inflammatory bowel diseases.

Answer 2

• Follows an unpredictable relapsing and remitting course, varying severity
  (during the relapse they have quite bad chronic inflammation (active inflammation), then patients can recover and feel well for a while.)
• Extra-gastrointestinal manifestations (e.g. cytokines, T cells etc)

Question 3

What is Crohn’s disease

Answer 3

• Can affect any part of the GI tract from the mouth to the anus/rectum
• Inflammation extends through all layers of the gut wall - severe
• Inflammation is patchy in distribution

Question 4

What is Ulcerative Colitis?

Answer 4

• Affects the colon and rectum ONLY - LARGE INTESTINE
• Only affects the mucosa (and submucosa)
• Inflammation diffuses in distribution - starts at the rectum and works its way around the colon.

Question 5

What is the aetiology/cause for IBD?

Answer 5

Factors thought to have a role:

ENVIRONMENTAL - may exacerbate
1. Diet
Many patients are able to identify foods that aggravate or exacerbate their symptoms e.g. cows milk or spicy food - Milk:- This is because when theres inflammation the lactase enzyme is not working properly hence the lactose is not broken down and get symptoms of diarrhoea. Spicy food:- Irritates the gut

2. Smoking
   Worsens the clinical course of the disease + increases the risk of relapse and need for surgery. Smoking may help prevent the onset of UC - Chemicals (Nitric Oxide) affects colon smooth muscle
3. Infection
   Some evidence that exposure to Mycobacterium Paractuberculosis can cause CD, probably a secondary pathogen to something else that is involved.
   UC can occur after episodes of infective diarrhoea.
   May be associated with measles and mumps infection.
   ENTERIC MICROFLORA - it usually grows in the gut but in IBD patient they may lose immunological tolerance to intestinal microflora (body starts rejecting)
4. Drugs
   - NSAIDs can exacerbate IBD (by inhibiting synthesis of cytoprotective prostaglandins)

• Antibiotics can change enteric microflora - less good bacteria (precipitate a relapse)
• Oral contraceptive pill (increases risk of developing CD + possibly causes by vascular changes)
• Isotretinoin - Vitamin A for acne (possible risk factor)

5. Appendectomy (surgical removal of appendix)
   - Has a protective effect in CD and UC
6. Stress
   - Can trigger a relapse in IBD
   - Activates inflammatory mediators at enteric nerve endings in gut wall.

GENETIC - if you have specific genes you are more susceptible to these disease.

• Good evidence
• Occurs when genes are changed or mutated and this cause:
  1. Disruption of the epithelial barrier integrity (can get immune cells through, leakage, reactions against microflora)
  2. You can get deficits in autophagy (cell eats itself - form of cell death) which is important for tissue destruction which is important in wound healing and resolving inflammation.
  3. Deficiencies in innate pattern recognition receptors - these recognise bacteria and foreign organisms and mounts an immune response
  4. Problems with lymphocytes - Production of lots of T cells etc.

OVERALL YOU GET EXCESS INFLAMMATION AND YOU CANT SWITCH IT OFF

• There is mutations of the gene CARD15/NOD2 - which is a intracellular pattern recognition receptor and its involved in inflammation of peripheral blood lymphocytes and hence its an inflammatory receptor
• 70% of UC patients have anti-neutrophil cytoplasmic antibodies (p-ANCA) - common in lots of autoimmune components

Question 6

What is the pathophysiology of IBD (general)?

Answer 6

IBD is a severe, prolonged and inappropriate inflammatory response to trigger factors.
(It alters the normal architecture of the GI tract- can breakdown mucosal barrier, allows lots of inflammatory cells in, causes swelling etc.)

Could be due to:
- Increased activity of effector lymphocytes and pro-inflammatory cytokines that override normal control mechanisms and T-lymphocytes/regulatory cells that usually help stop this/knock it down and they’re not working properly.

• Primary failure of regulatory lymphocytes and cytokines
• In CD, T cells are resistant to apoptosis after inactivation - so they don’t kill themselves and still ongoing they’re causing too much inflammation

Question 7

What is the pathophysiology of CD?

Answer 7

1. Affects any part of the gut:
   - Involving one area or multiple areas
   - Usually the terminal ileum and ascending colon
   - Discontinuous
2. Affected areas are thickened (with inflammatory cells and fluid inside), oedematous and narrow (swelling is narrowing the lumen of the gut)
   - Deep ulcers can appear
   - Mucous membranes between fissures has a cobblestone appearance
   - Can progress to deep fissuring ulcers, fibrosis and strictures
3. Can lead to bowel obstructions, abscesses and gut perforations (hole)
4. Microscopically:
   - Non-specific granulomatous inflammation
   - Inflammation extends throughout all layers of the bowel (transmural)
   - Inflammatory cells are seen throughout - Lymphocytes and plasma cells
   - Th1-associated
5. Chronic inflammation leads to an increased risk of cancer - hence monitored and picked up early

Question 8

What is the pathophysiology of Ulcerative colitis?

Answer 8

• Starts in the rectum (proctitis), then can extend to the small intestine (left-sided) and carried to the large intestine (universal) etc. - Diffused
• Only the mucosa and submucosa are affected
• Continuous - starting in the rectum
• Formation of crypt abscesses and mucosal ulceration
• Mucosa looks red, inflamed and bleeds easily - LOTS OF BLOOD (seen in stools)

Microscopically:
- Inflammatory cells infiltrate the lamina propria and crypts
- Th2 associated
- Dysplasia (pre-cancerous) can be seen from biopsies (can progress to carcinomas)

Question 9

What are the symptoms for IBD? (general)

Answer 9

IBD- depends on site, extent and severity of active disease

Symptoms of both diseases:
- Diarrhoea
- Fever
- Abdominal pain
- Nausea and vomiting (more common in CD)
- Malaise (not feeling well)
- Lethargy (tiredness)
- Weight loss (more common in CD)
- Malabsorption
- Growth retardation in children

Question 10

What are the clinical features/symptoms in CD?

Answer 10

• Tends to be more disabling that UC
• Onset can be acute or insidious

Other symptoms:
- Pain
- Anaemia
- Palpable masses
- Small bowel obstructions
- Abscesses
- Fistulas
- Gut perforation

Question 11

What are the clinical features/symptoms in UC?

Answer 11

Symptoms:
- MAIN - Diarrhoea - possible with blood/mucus
- Abdominal pain (cramps) with fever
- Constipation (due to narrowing cause of swelling)

Severe attacks can be life-threatening

Question 12

Distinguishing features of CD vs UC

Answer 12

1. Skip areas (patchy) - Common in CD | Never in UC
2. Cobble mucosa - Common in CD | Rare in UC
3. Transmural (across the entire wall) involvement - Common in CD | Occasional in UC
4. Rectal sparing (no inflammation) - Common in CD | Never in UC
5. Perianal involvement - Common in CD | Never in UC
6. Fistulas - Common in CD | Never in UC
7. Strictures - Common in CD | Occasional in UC
8. Granulomas - Common in CD | Occasional in UC

Question 13

What are the complications of IBD?

Answer 13

Some of the inflammation can spill over into other tissues - Skin, Bone, Eyes and Liver - so can get problems with any of these areas.

1. Joint and Bones
   - Arthropathies and Osteopenia
2. Skin
   - Erythema nodosum (tender, hot, red nodules - subside over few days to leave brown skin discolouration)

• Pyoderma gangrenous (Pustule - develops into an ulcer)

3. Ocular
   - Episcleritis (intense burning and itching of blood vessels involved)

• Uveitis (Headache, burning red eye, blurred vision)

4. Sclerosing Cholangitis
   - Chronic inflammation on the biliary tree
   - Leads to progressive fibrosis and biliary strictures (narrowing)

Question 14

What are the morbidity factors in IBD?

Answer 14

• Quality of life generally lower in CD vs UC especially because of recurrences after surgery
• Increased risk of peritonitis (redness and swelling (inflammation) of the lining of your belly or abdomen)
• Malnutrition and chronic anaemia common in long-standing CD

Question 15

What is needed for the diagnosis of IBD?

Answer 15

Diagnosis is confirmed by clinical evaluation and a combination of investigations:
- Biochemical
- Endoscopic
- Radiological
- Histological
- Nuclear medicine based

Question 16

What is needed to obtain full history of the disease?

Answer 16

Full history including:
- Recent travel
- Medication
- Smoking
- Family history

Details of symptoms including:
- Stool frequency and consistency
- Urgency
- Rectal bleeding
- Abdominal pain
- Fever

Question 17

What physical signs can be examined for the diagnosis of IBD?

Answer 17

Physical signs:
- General well-being
- Pulse
- Blood pressure
- Temperature
- Weight loss
- Abdomen tenderness or distension
- Anus

Question 18

What initial investigations are done for the diagnosis of IBD?

Answer 18

1. Blood tests
2. Microbiological testing for infectious diarrhoea
3. Serological tests (presence of antibodies in the blood)
4. Abdominal Radiography
   - Excludes colonic dilatation
   - Helps assess disease extent in UC
   - Identifies proximal constipation
   - Gives an impression of right iliac fossa mass in CD
   - Can show evidence of small bowel dilation

Question 19

What is a Sigmoidoscopy?

Answer 19

• Internal examination of the colon (lower third) using a sigmoidoscope
• Used for all patients presenting with diarrhoea
• Used to confirm diagnosis of UC

Question 20

What is a rectal biopsy?

Answer 20

A biopsy is a procedure to remove a piece of tissue or a sample of cells from your body so that it can be tested in a laboratory.

Detects non-specific histological changes in the mucosa.

Question 21

What is a colonoscopy?

Answer 21

Internal examination of the colon (entire length) using a colonoscope.

Used for mild or moderate disease to assess extent of disease.

Biopsy can be performed as well

Question 22

What 3 components need to work together to maintain the gut healthy?

Answer 22

1. Microbes in the gut lumen
2. Epithelium (layer/barrier)
3. Immune cells (immune cells)

Question 23

What happens in the gut immune system when we have IBD?

Answer 23

• Disruption of the mucus layer
• Disregulation of epithelial tight junctions
• Increased intestinal permeability
• Increased bacterial adherence to epithelial cells

In IBD innate cells produce increased levels of TNFa, IL-6, IL-12, IL-23 and other chemokines. There is marked expansion of immune cells in the laminar propria and increased levels of CD4 T-cells especially the pro-inflammatory T cells. These also secrete increased levels of cytokines and chemokines. Increased levels of chemokines results in recruitment of additional leukocytes resulting in a cycle of inflammation.

Question 24

What are the 5 IBD drugs?

Answer 24

1. Corticosteroids
2. Azathioprine
3. 5- aminosalicylates
4. Ciclosporin
5. Methotrexate

Question 25

What are corticosteroids used for and what is the mechanism of action?

Answer 25

Corticosteroids are used for both CD and UC.

The glucocorticoid receptor complex can inactive pro-inflammatory factors such as NFkB and activator protein 1 (AP1).

Doing so will prevent them from activating inflammatory mediators such as IL-6 and leukotrienes.

Glucocorticoid are potent inhibitors of T cell activation and pro-inflammatory cytokines and are highly effective treatment for active IBD.

Glucocorticoids passively enter the cell and bind to an intracellular glucocorticoid receptor (GR). GR is held in the cytoplasm due to being bound to heat-shock protein complex which has 2 chaperone molecules hsp90 and hsp70 and immunophillin FKBP59. When the glucocorticoid lingand binds to GRa it becomes activated. This allows the formation of a homodimer of two activated Gas which is transported into the nucleus of the target cell. This the inhibits the promotor regions of genes such as NFkB and AP-1 which are potent transcription factors for many pro inflammatory cytokines and adhesion genes.

Central to the anti-inflammatory action of glucocorticoids Is the induction of IkBa which bind to and inhibits NFkB from entering the nucleus and into the cytoplasm (holds it back).

Question 26

What are azathioprines used for and what is the mechanism of action?

Answer 26

Azathioprine works by inhibiting de novo purine synthesis and acts as an anti proliferative agent by interfering with protein, DNA and RNA synthesis and promoting apoptosis.

MOA
1. Azathioprine is an immunosuppressive antimetabolite.

2. Azathioprine is metabolised into 6-mercaptopurine (6-MP)
3. Activation of 6-mercaptopurine occurs via HGPRT and a series of multi-enzymatic processes involving kinases i.e. Thiopurine S-methyltransferease (TPMT) to form 6-thioguanine nucleotides (6-TGNs) as major metabolites. The cytotoxicity of azathioprine is due to the incorporation of 6-TGN into DNA.

Another inactivation pathway is oxidation, which is catalysed by xanthine oxidase (XO) to form 6-thiouric acid.

Azathiopurine and its metabolites play a role in the control of T cell apoptosis by modulation of Rac1 activation upon CD28 co-stimulation:

1. Specific blockade of Rac1 activation is achieved by azathioprine-generated 6-Thio-GTP that binds to Rac1 instead of GTP.
2. Consequently, the activation of Rac1 target genes such as MEK, NFkB and bcl-xL is suppressed by azathioprine, leading to a mitochondrial pathways of apoptosis.
3. Azathioprine thus converts a costimulatory signal into an apoptotic signal by modulating Rac 1 activity.
4. Inhibiting the production of bcl-xl as theres inhibition of STAT3 and NFkB activation. Meaning theres no antiapoptopic signal.

Question 27

What are 5-aminosalicylates used for and what is the mechanism of action?

Answer 27

5-aminosalicylates (5-ASA) are administered orally, rectally via a suppository or enema.

5-ASA has effects on the prostaglandin synthesis/cyclooxygenase pathway:

Prostaglandin synthesis occurs through a pathways involving cyclooxyrgenase enzymes. This pathway is unregulated during inflammation. It causes cell proliferation and increased cell survival as well as modulating immune cell differentiation and gut epithelial stem cell function. INCREASED CELL GROWTH AND SURVIVAL.

1. The 5-ASA drug MESALAZINE has a similar molecular structure to aspirin. Its molecular targets are similar to other NSAIDs inhibiting cell proliferation through inhibiting COX and reducing prostaglandins synthesis and suppressing of pro inflammatory cytokine production.
2. 5-ASA also affects the COX-independant pathway: Reduces neutrophil chemotaxis to site of inflammation and inhibit the survival of immune cells through NFkB signalling and inhibits TNF-mediated effects on epithelial proliferation.
3. 5-ASA effects of reactive oxygen metabolites (ROM): There is an increased number of neutrophils and activated monocytes in IBD gut tissue; These cells are a source of reactive oxygen metabolites (ROM). ROM are produced during acute and chronic stages of inflammation causing DNA and collateral tissue damage and oxidative products have been detected in the gut lumen of IBD patients.
4. 5-ASA can scavenge free radicals during superoxide anion generation in neutrophils i.e. inhibit ROM generation so inhibiting oxidative DNA damage.

Question 28

What is Ciclosporin used for and what is the mechanism of action?

Answer 28

Ciclosporin modulates pro-inflammatory cytokine production and T-cell survival. Normally used in UC but NOT IN CD PATIENTS. Can induce remission in UC.

MOA:

1. Interaction of antigen with a T-helper (Th) cell recpetor results in increased intracellular Ca2+
2. Stimulation of Calcineurin
3. Activation of various transcription factors that initiate IL-2 expression.
4. CICLOSPORIN BINDS TO CYCLOPHILIN, and ciclosporin is a specific competitive inhibitor of calcineruin calcium and caladium-dependent phosphatase. Calcineurin normally acts in opposition to the many protein kinases involved in signal transduction.
5. Ciclosporin inhibits translocation of NF-AT transcription factors and reduced transcription of cytokine genes for IL-2, TNF-a, IL-3, IL-4 etc.
6. REDUCTION IN IL-2 CYTOKINE SYNTHESIS CAUSES DECREASED CLONAL PROLIFERATION OF T LYMPHOCYTES AND DECREASES EXPRESSION OF IL-2 RECEPTORS.

Question 29

What is methotrexte used for and what is the mechanism of action?

Answer 29

• Folates are actively taken up into cells and then converted to polyglutamates (Fglu).
• Folates are essential for the synthesis of purine nucleotides and thymidylate
• The dihydrofolate reductase enzyme (DHF R) is involved in thymidylate synthesis and is important for transforming an inactive form of folic acid into the active form, which is NECESSARY to make some of the building blocks needed for DNA production.
• The 2 step reaction is catalysed by DHFR which converts the substrate first to dihydrofolate FH2 and then FH4.
• FH4 function is an essential co-factor carrying the methyl groups necessary for the transformation of DUMP to DTMP required for the synthesis of DNA and purines.

MOA:

1. MTX is an antimetabolite of folic acid. It interferes with the normal metabolic activity of folic acid and inhibits the DHFR enzyme. FH4 is then depleted.
2. MTX prevents de novo DNA and purine synthesis, inhibiting proliferation of lymphocytes involved in the inflammation
3. MTX blocked the survival of T cells by blocking proliferation and inducing apoptosis through the elevation of ROS
4. Supresses production of proinflammatory cytokines IL6, IL3, TNFa and IFNy
5. Blocks leukocyte-endothelial adhesion molecules e.g. E-selectin, ICAM-1 and platelet adhesion molecules PECAM-1 and VCAM-1 expression.

Question 30

What are the types of treatment available for IBD?

Answer 30

• Anti-TNF therapy
• T cell homing/trafficking therapy
• Janus kinase inhibitors

Question 31

How are Anti-TNF therapies used in the treatment of IBD?

Answer 31

• TNF is elevated in the serum of IBD patients.
• Immune cells isolated from gut biopsies spontaneously produced increased amounts of TNF which correlated with the degree of mucosal inflammation in the tissue.
• TNF is also produced by immune cells in the inflamed gut mucosa of IBD e.g. macrophages, T cells, dendritic cells and non-immune such as fibroblasts and is ONLY PRESENT IN PANETH CELLS DURING IBD
• EFFECTS OF TNF: Activates macrophages to produce pro inflammatory cytokines, increases apoptosis of gut epithelial cells, regulates T cell apoptosis, causes Paneth cell death via NECROPTOSIS (unprogrammed inflammatory cell death)

Desired effect of blocking TNF:
- To induce T cell and inflammatory cell apoptosis.
- Reduce inflammatory cytokine production
- Reduce Paneth cell necroptosis
- Reduce epithelial cell apoptosis
- Elevate regulatory macrophages
- Reduce MMP-induced tissue destruction

EXAMPLES:
Infliximab, Golimumab (UC only) and Adalimumab are used in IBD

They are human monoclonal antibodies that bind to both the soluble and transmembrane bioactive forms of human TNFa. This interaction prevents the binding of TNFa to its receptors, thereby inhibiting the biological activity of TNFa.

• About 50% of patients initially respond to anti-TNF therapy but then lose their response following continued treatment due to the production of anti-drug antibodies.

Question 32

How are T cell homing and retention therapies used in the treatment of IBD?