Anti-inflammatories Flashcards
What are NSAIDs?
they inhibit the production of inflammatory mediators such as prostaglandins and thromboxanes
- cyclooxygenases (COX) are enzymes which synthesis these paracrine mediators
- NSAIDs inhibit COX enzymes so inhibit the production of PGs and thromboxanes
- therefore they prevent paracrine signalling between cells at sites of inflammation
how are paracrine mediators produced?
arachidonic acid is produced from membrane phospholipids
- it acts as a second messenger and as a substrate for lipoxygenases and cyclooxygenases which leads to generation of paracrine mediators
- lipoxygenase pathway produces leukotrines
- cyclooxygenase pathway forms PGs and thromboxanes
what are prostaglandins?
- PGs are created by cells and act only in the surrounding area before they are broken down
- PGs control neighbourhood processes such as vasodilation (PGE2), aggregation of platelets during clotting (PGD), constriction of uterus during labour (PGF) and a hyperalgesic (makes you more sensitive to pain) (PGE2)
what is the role of PGs?
- deliver and strengthen pain signals to induce inflammation
- chemoattractants - recruit immune cells
what do NSAIDs result in?
- anti-inflammatory - modify the inflammatory reaction
- decrease vasodilation and in turn oedema
- effective against headaches as they reduce the vasodilator effect of PGs on cerebral tissue - analgesic - reduce pains
- decrease production of PGs in damaged and inflamed tissue which sensitises nociceptors to inflammatory mediators e.g. bradykinin, 5-HT - antipyretic - lowers raised temperature
- thermostat in hypothalamus is activated by IL-1 induced COX2 production of PGe
what is the structure of the COX enzyme?
- made up of 2 identical subunits, each with 2 catalytic sites
- 2 active sites are collectively termed as prostaglandin synthase:
- one side has a cyclooxygenase active site
- the other side has a peroxidase site which activates haem groups in
the COX reaction
- enzyme complex is a dimer of 2 subunits, so there are 2 cyclooxygenase sites and 2 peroxidase sites in close proximity
- each subunit has a carbon-rich knob which anchors the complex to the ER membrane
- cyclooxygenase active site is buried deep inside the protein which is accessible through a tunnel in the knob which acts as a funnel to guide arachidonic acid into the enzyme
what are the types of COX enzymes?
- COX1: constitutive expression
- important for platelets, stomach, kidney and colon - COX2: inducible expression
- most cells, especially inflammtory cells after stimulation with cytokines, growth factors or tumour promoters
- immediate-early response gene
3 COX3: in CNS, target for paracetamol?
what is the action of NSAIDs?
- COX1 and COX2 inhibitors prevent the cyclooxygenation reaction of arachidonic acid to prevent production of PGs
- aspirin inhibits expression of transcription factor NF-kappaB which has a key role in triggering gene transcription of inflammatory mediators
how are NSAIDs selective?
- COX1 contains isoleucine residue while COX2 contains valine residues, allowing the creation of NSAIDs which are selective to COX1 or COX2
- COX2 is inducible, so is only produced when there is tissue damage
- COX1 is constitutive so maintains homeostatic mechanisms e.g. PGs in the GI tract maintain the mucus layer to protect GI cells from acid
how may NSAIDs have unwanted side effects?
if PG production is inhibited by COX1-inhibitors, the mucus layer in the GI tract is reduced, so acid from the stomach may harm GI cells, leading to ulcers
what is the action of aspirin?
suicide inhibitor:
- aspirin is composed of an acetyl group which attaches to salicylic acid
- when aspirin attacks cyclooxygenase, its acetyl group covalently binds to the serine residue in COX to permanently deactivate the enzyme
- this prevents arachidonic acid from reaching the cyclooxygenase site through the tunnel
- aspirin therefore blocks the active site
what are the 2 isoforms of COX?
COX1: constitutive, expressed in most cells including platelets, has a housekeeping role in homeostasis
COX2: induced in inflammatory cells when activated and produces prostanoid mediators of inflammation
do NSAIDS show a lot of selectivity? how do types of NSAIDs differ?
no, they show little selectively.
main differences are in toxicity, duration of action and pain tolerence
what are the side effects of NSAIDs?
- Gut - PGs normally inhibit acid secretion to protect mucosa, so NSAIDs prevent this
- causes diarrhoea, dyspepsia, nausea, vomiting, gastric bleeding and ulceration
- co-administration of misoprostal (PG analogue) helps
- can be relieved by use of COX2-selective drugs - Renal function: PGs maintain renal blood flow, so NSAIDs may cause issues with renal function, leading to renal failure
- liver damage: the metabolite of paracetamol in the phase 1 reaction is toxic to liver
- patients must be careful if cytochrome p450 is induced as an overdose may cause liver failure - bronchospasm/asthma attacks
- skin rashes
what is the risk of GI complications with NSAIDs?
35-45% users sustain some form of GI damage
what are the advantages of COX1/COX2-selective NSAIDs?
COX2-selective NSAIDS such as rofecoxib (Vioxx), valdecoxib, parecoxib and celecoxib can reduce burden of GI toxicity:
- analgesic and anti-inflammatory]
COX1-selective NSAIDs may be antithrombotic and can help prevent stroke (COX1 is involved in clot formation)
what are the disadvantages of COX1/COX2-selective NSAIDs?
COX2-selective drugs may cause increased arterial blood pressure, increased atherogenesis, or increased thrombotic tendency
- there is evidence for these NSAIDs to have cardiovascular toxicity if COX2 is consistently inhibited
- increased blood pressure and increased salt retention -> kidney failure
COX1-selective drugs are not suitable with someone with a bleeding disorder, as these drugs prevent clot formation
aspirin vs paracetamol:
aspirin:
- Anti-platelet action
- Reduced risk of colonic and rectal cancer
- Reduced risk of Alzheimer’s
- Weak acid, rapid and efficient absorption in the ileum
- Suicide inhibitor (irreversible)
paracetamol
- Analgesic-antipyretic due to CNS effects
- Weak anti-inflammatory
- Cox3/1 selective
- Well absorbed, metabolized in liver
- Less side-effects than aspirin with long term use, but large doses may increase kidney damage
- N-acetyl-p-benzoquinone imine is hepatotoxic in uncongugated form
- Competitive Inhibitor
what is ibuprofen?
same as aspirin except it is a competitive inhibitor
what are the clinical uses of NSAIDs?
- antithrombotic = aspirin (for patients with high risk of arterial thrombosis)
- analgesia:
short term: aspirin, paracetamol, ibuprofen,
long-term = naproxen (codeine) - anti-inflammatory = ibuprofen, aspirin and naproxen
- antipyretic (reduces fever) = paracetamol
what is rheumatoid arthritis?
- chronic inflammatory condition and autoimmune disease
- possibly genetic
- 3x more prevalent in women than in men
- affects joints, inflammation of synovium and erosion of cartilage and bone
- treated with DMARDs (reverse/halt the disease) and NSAIDs (alleviate symptoms)
- no cure
- smoking is a risk factor
what are the mediators involved in the pathogenesis of rheumatoid arthritis?
- T cells activate macrophages which release cytokines involved in driving the inflammatory response:
e.g. IL-1 and TNF-alpha
how can rheumatoid arthritis be treated?
- methotrexate: low doses have cytotoxic and immunosuppresant activity (high doses for chemotherapy)
- folic acid is the antagonist
- DMARDs: mixed group of drugs with different mechanisms of action
- clinical effects are slow, so NSAIDs are provided as cover during
induction phase
- clinical effects are slow, so NSAIDs are provided as cover during
give examples of some DMARDs:
- sulfasalazine: sulfa drug used for chronic inflammatory bowel disease
- bacteria in colon produce 5-aminosalicylic acid which acts as a free radical to decrease damage by neurtrophils - penicillamine (d-isoform): metabolite of penicillin, used as a heavy metal chelator in poisoning
- gold compounds e.g. auranofin: inhibits induction of IL-1 and TNF-alpha
what is the role of immunosuppressant drugs?
they inhibit the induction phase of the inflammatory response:
- cyclosporin and glucocorticoids inhibit transcription of pro-inflammatory cytokines such as IL-2
what is the mechanism of action of cyclosporin?
inhibits IL-2 synthesis to cause decrease in T cell proliferation:
1. cyclosporin binds to cyclophilin, a cytosolic immunophilin protein
2. the drug-immunophilin complex bind to and inhibit calcineurin to prevent activation/signalling via transcription factor NF-kappaB, which is regulated by calcium signalling in T cells
- calcineurin is a phosphatase regulated by calcium and targets NF-kappaB transcription factor to produce cytokines
3. inhibition of calcineurin means NF-kappaB can no longer drive the production and secretion of cytokines IL-2, IL-1 and TNF-alpha
what is the mechanism of action of glucocorticoids?
they act at the level of gene transcription by binding to DNA itself:
- they act as repressors of transcription of genes that make pro-inflammatory cytokines
- they affect IL-1, TNF-alpha and INF-gamma synthesis
- effective in induction and effector phases of the immune response
- they also inhibit NF-kappaB
how are biopharmaceuticals used as anti-inflammatory drugs?
Humanised monoclonal antibodies:
- can bind to cytokines and prevent their inflammatory response
- high affinity and selectivity for target
- they neutralise the action of soluble or membrane-bound pro-inflammatory cytokines
- long half-life
- the antibodies are engineered with human sequences to prevent rejection
Soluble receptors:
- proteins engineered that mimic the binding site of a known cytokine receptor
- protein is injected into body and cytokine binds to it but has no downstream inflammatory activity
what are the issues with biopharmaceuticals’ use in anti-inflammatory drugs?
very expensive
what is COPD? How is it treated?
chronic obstructive pulmonary disease:
- disease driven by macrophages
- symptoms: breathlessness and eventually respiratory failure
- emphysema
- treatment: B2 agonists, muscarinic antagonists and corticosteroids
- cannot be cured
what is asthma?
- shortness of breath especially when exhaling
- symptoms: cough, wheezing, inflammation of airways, bronchial hyperactivity, reversible airway obstruction
how can asthma be treated?
- bronchodilators: salbutamol is a B2-adrenoreceptor agonist (GPCR via Gs and adenylyl cyclase) on airway smooth muscle to relax the airways
- polymorphisms in B2-adrenoreceptors cause reduced efficacy of bronchodilators
- anti-inflammatory agents: prednisolone and omalizumab reduce cytokine production
what are the types of respiratory allergies?
- allergic rhinitis (hayfever) - issue in upper airways
- allergen activates mast cells in the nasal mucosa
- nasal congestion, sneezing and allergic conjunctivitis - allergic asthma (atopic) - issue in lower airways
- allergen activates mast cells in lower respiratory tract
- early/immediate phase reactions are reversible airway obstructions
- bronchial hyperactivity - abnormal sensitivity to many stimuli, causing bronchoconstriction
- acute attacks are reversible but can progress to chronic state
- patients have an increased no. in mast cells in the bronchi
what is involved in the late phase reactions of asthma?
- cytokines and leukocyte infiltration (especially eosinophils), leading to inflammation
- some patients develop chronic asthma: chronic inflammation, tissue damage and airway remodelling
- 50% of asthma patients suffer with this
what causes asthma?
- associated with overactivity of T-helper cells as they drive the immune response and production of antibodes to the allergen
- antibody is bound to mast cells and eosinophils
- when receptors are activated from allergen binding to antibody, histamine is released and binds to smooth muscle receptors to cause constriction
- histamine drives production of PGs which also cause bronchoconstriction
what are mast cells and their role in asthma?
mediators of type 1 hypersensitivity reactions
- cause: smooth muscle contraction, increased vascular permeability, mucous secretion, platelet activation, stimulation of nerve endings and recruitment of eosinophils
- they secrete cytokines and chemokines during the immediate phase to set the scene for the late phase of an asthma attack
- IgE has natural role in allergic reaction
what is the pathology associated with chronic inflammation of the airways?
- clogged airways are full of mucus which restricts oxygen exchange
- thickening and growth of smooth muscle cells affects the stretchiness of airways, so future allergen responses are worse
- increase in mucus-producing cells
what are the unwanted side effects of prednisolone steroid use?
Cushing’s syndrome:
- hypertension
- moon face
- poor wound healing
- muscle wasting
- increased abdominal fat
what are the new therapies for treating asthma?
- humanised antibodies and soluble receptors to IgE (omalizumab), cytokines and chemokines (biopharmaceuticals)
- prostaglandin D2-R antagonists: PG D2 is synthesised in mast cells by PGD synthase
- PGD2 acts on DP1 receptors on vessels to mediate vasodilation, and
also on DP2 receptors to attract T-helper2 cells and eosinophils - therefore PGD2-R antagonists prevent the vasodilation and
recruitment
- PGD2 acts on DP1 receptors on vessels to mediate vasodilation, and
- antagonists of DP1 and DP2 receptors, and inhibitors of PGDs are in clinical development for asthma therapy
