Inflammatory bowel disease Flashcards

Question

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

Answer 1

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).

Answer 2

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.

Answer 3

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.

Answer 4

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.

Answer 5

- 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.

Answer 6

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

Answer 7

- 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.