ZOO 4753 Final Exam

where are mediators from?

cells or plasma proteins

cell-derived mediators

sequestered in granules, released via exocytosis (histamine) or synthesized de novo (cytokines)

plasma-derived mediators

produced mainly in liver as inactive precursors (i.e. complement, kinins)

what types of cells can contain mediators?

platelets, macrophages, neutrophils, monocytes, mast cells, most epithelial cells, mesenchymal cells

activation of mediators

produced in response to various stimuli (microbial products, necrotic cells)

mediators of inflammation

-one mediator can stimulate release of other mediators
-vary in range of cellular targets
-short lived

vasoactive amines

histamine and serotonin

what types of mediators are among the first to be activated?

vasoactive amines

what are vasoactive amines?

amino-acid derived mediators that act on blood vessels

source of vasoactive amines

mast cells, basophils, and platelets

histamine

-induces HCl production in stomach via H2 receptors (targets parietal cells
-causes dilation of arterioles, increases permeability of venules (binds H1 receptors on microvascular endothelial cells and produces interendothelial gaps

serotonin

-similar effects to histamine (vasodilation and increased vascular permeability
-lowest in morning (hungry) and release large amounts into digestive tract which increases peristalsis and can cause vomiting and diarrhea

what amino acid are histamine and serotonin derived from?

tryptophan

what triggers histamine release?

physical injury (trauma, cold, hot), binding of antibodies to mast cells, anaphylatoxins (fragments of C3a and C5a, proteins derived from leukocytes, neuropeptides, and cytokines

H1 receptor antagonists (anti-histamines)

block effects of histamine binding (constricted airways, fluid secretion in airways, vasodilation); block H1 receptors in brain (decreased alertness)

what anti-histamines lead to drowsiness?

Benadryl and Dramamine

what anti-histamines don't lead to drowsiness and why?

Claritin and Allegra; can't cross blood-brain barrier

H2 receptor antagonists

Tagamet and Zantac

what happens when histamine binds to H2 receptors?

causes acid secretion in gastric lining (i.e. scombroid fish poisoning)

scombroid fish poisoning

-bacteria in fish (i.e. tuna and mackerel) convert histadine into histamine
-occurs when caught fish are improperly chilled
-large amounts of histamine enters systematically (rapidness, 10-30 min, helps differentiate from food poisoning)

arachidonic metabolites

prostaglandins, leukotrienes, lipoxins

arachidonic acid

20C polyunsaturated fatty acid esterified in plasma membrane (not free in cells)

how is arachidonic acid derived?

from dietary sources (i.e. chicken) or conversion of linoleic acid (found in sunflower oil)

what stimuli causes release of arachidonic acid?

complement and trauma activate phospholipases (mainly A2)

eicosanoids

arachidonic acid turns into this after release by two enzyme classes:
-cyclooxygenases -> prostaglandins
-lipoxygenases -> leukotrienes and lipoxins
-can bind to GPCR on many cell types and mediate virtually every inflammation step

eicosanoids causing vasodilation

PGI2 (prostacyclin), PGE1, PGE2, PGD2

eicosanoids causing vasoconstriction

thromboxane A2, leukotrienes C4, D4, and E4

eicosanoids causing increased vascular permeability

leukotrienes C4, D4, and E4

eicosanoids causing chemotaxis and leukocyte adhesion

leukotriene B4, HETE

what enzymes produce prostaglandins?

COX-1 and COX-2

where are prostaglandins produced?

mast cells, macrophages, endothelial cells

prostaglandins (PGs)

-involved in vascular and systemic reactions of inflammation
-each derived by action of specific enzyme on pathway intermediate (some enzymes have restricted tissue distribution)

COX-1

constitutive (active), constitutively expressed in all cells and likely helps maintain homeostatic balance of electrolytes, cytoprotection in GI tract

COX-2

inducible, activated due to tissue damage/infection and responsible for pain and fever

which prostaglandins are most important for inflammation?

PGE2, PGD2, PGF2a, PGI2 (prostacyclin), and TxA2 (thromboxane)

platelets and PGs

contain thromboxane synthetase and TxA2 is major product

TxA2

platelet aggregator (helps with clotting) and vasoconstrictor

endothelium and PGs

no thromboxane synthetase but instead prostacyclin synthetase which produces PGI2

PGI2

vasodilator, inhibitor of platelet aggregation, potentiates chemotactic and permeability-enhancing effects of other mediators

PGE2

causes vasodilation and increased permeability, involved in fever and pain in inflammation (fever analgesic)

PGD2

causes vasodilation and increased permeability, chemoattractant for neutrophils

PGF2a

stimulates contraction of uterine and bronchial smooth muscle and small arterioles

what enzyme produces leukotrienes?

lipoxygenase

what secretes leukotrienes?

secreted mainly by leukocytes

leukotrienes

serve as leukocyte chemoattractants and some vascular effects, more potent than histamine (enhanced permeability and bronchospasms)

5-hydorxyeicosatetraenoic acid

serves as a chemoattractant for neutrophils and is precursor for leukotrienes

LTB4

chemotactic, activator of neutrophils (causes them to adhere to endothelium and release lysosomal granules)

LTC4, LTD4, LTE4

intense vasoconstriction, bronchospasm, and increased vascular permeability

how are lipoxins generated?

lipoxygenase pathway

lipoxins

inhibitors of inflammation, inhibit leukocyte recruitment and cellular components of inflammation, likely serve as endogenous negative regulators of inflammation

what two cells are needed to produce lipoxins?

neutrophils and platelets

Cox inhibitors

aspirin and other NSAIDs (non-steroidal anti-inflammatory drugs)

aspirin

irreversibly acetylates and inactivated cyclooxygenases (both 1 and 2)

COX-2 inhibitors

-only inhibit COX-2
-increases risk of heart attack and stroke in individual already prone to cardiovascular disease
-may inhibit prostacyclin production while leaving COX-1-mediated thromboxane A2 intact
-pro-inflammatory in early phase and anti-inflammatory in late phase (rodent models)

why don't COX-2 inhibitors damage stomach lining?

don't inhibit PGE2 production (PGE2 stimulates mucus production)

what are some examples of COX-2 inhibitors?

Celebrex (approved by FDA in 2018) and Vioxx (removed)

what does aspirin do at high doses (350mg)?

inhibits production of prostacyclin (this promotes clotting); inhibits production of PGE2 in stomach (causes gastric ulcers, stomach bleeding)

what does aspirin do at low doses (81mg)?

decreased production of thromboxane A2 (blocks clot formation), promotes production of resolvins and protectins)

resolvins

anti-inflammatory, inhibit ROS production by migration of leukocytes

protectins

protect cells from forming MAC (MAC punches holes in target cell membrane)
-ex CD59 aka MAC-inhibitory protein, inhibit leukocyte recruitment and upregulation of CCRs (mop-up pro-inflammatory cytokines)

lipoxygenase inhibitors

not affected by NSAIDs

what are some examples of lipoxygenase inhibitors?

-zilueton (zyflow) to inhibit leukotriene production
-montelukast (singulair) blocks leukotriene receptors

what are lipoxygenase inhibitors used in the tx of?

used in treatment of asthma (help relieve bronchospasm and increase mucus production)

corticosteroids

powerful anti-inflammatories that reduce transcription of genes for COX-2 and pro-inflammatory cytokines like TNF and IL-1
-gene blocked = lipocortin which blocks PG synthesis and leads to blocking leukotrienes and adhesion molecules

Are there any adverse consequences to corticosteroid use either locally or systemically?

administering systematically can be worried about immunosuppression (promotes apoptosis of WBCs, inhibits expression of B and T cells), triggers lipolysis (due to cortisol), and leads to hyperglycemia

fish oil

can't be converted into active inflammatory mediators by COX or lipoxygenase but can be converted into resolvins and protectins

what is fish oil commonly used to treat?

patients with arthritis to decrease the use of pain relievers

hydrocortizone cream

block way upstream of pro-inflammatory production, can cross plasma membrane directly (topical)

platelet-activating factor

-derived from phospholipids
-involved in oxidative burst and chemotaxis (increase adhesion via integrin expression)

where can platelet-activating factor be found?

platelets, macrophages, neutrophils, basophils, endothelial cells

What does platelet activating factor do at low concentrations?

vasodilation and vascular permeability

What does platelet activating factor do at high concentrations?

vaso- and bronchoconstriction

What role do ROS play in inflammation?

-endothelial cell damage (induces endothelial cells to produce own ROS, serve as attractor of nearby leukocytes; when leukocytes turn on surrounding normal cells, leads to enhanced vascular permeability; die via necrosis)
-injury to parenchymal cells
-inactivation of antiproteases (i.e. emphysema = lose elastin fibers in lungs)

nitric oxide

promotes vasodilation, inhibits cellular components of inflammation (platelet aggregation and leukocyte recruitment), causes free radical damage to microbes

what does it mean when nitric oxide is paracrine?

locally active, doesn't need receptor to cross cell membrane

what two enzymes produce nitric oxide?

endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS)

endothelial nitric oxide synthase (eNOS)

produces NO in blood vessels, causes reduced adhesion of leukocytes and platelets which causes blood vessel relaxation and vasodilation

inducible nitric oxide synthase (iNOS)

produces NO in macrophage that is used in microbe killing

cytokines

proteins produced by many cell types (macrophages, endothelial cells) that modulate functions of other cell types

what are the two most important cytokines involved in inflammatory response?

TNF and IL-1

what produces IL-1

inflammasome

What role do caspases play in the inflammasome?

once assembled it activates caspases (especially caspase-1) which cleaves pro-IL-1 to active IL-1

What happens in the condition called Familial Mediterranean Fever?

-inherited disorder (autosomal recessive)
-disruption in pyrin (defect causes IL-1 overproduction)

How does TNF affect energy balance?

IL-1 causes increased TNF which works through leptin (major hormone of homeostasis)
-leptin suppresses appetite which leads to cachexia

complement system

20 proteins that function in both innate and adaptive immunity against microbes (most important = C3 and C5, active = C3a and C5a)

what is the function of the complement system?

increase vascular permeability, chemotaxis, and opsonization (opsonins), normal cells express regulatory proteins that remove bound complement to prevent healthy cells from being injured

alternative pathway

one pathway of complement activation involving direct recognition to bacterial component (i.e. LPS)

classical pathway

one pathway of complement activation involving antibodies (IgM/IgD) biding to antigens

lectin pathway

one pathway of complement activation involving lectin in plasma binding to manose (sugar in membrane of pathogen)

What are the potential outcomes of complement system activation in the body?

-C5a and C3a: inflammation, enhance phagocytosis, enhance chemotaxis
-C3b: phagocytosis
-MAC: lysis of microbe (released components can trigger complement)

what are the three possible outcomes of the acute inflammatory response?

chronic inflammation, fibrosis, and resolution

chronic inflammation

-can't remove injurious stimulus, derives from acute inflammation or de novo
-angiogenesis, mononuclear cell infiltrate (macrophages, lymphocytes, eosinophils, basophils), fibrosis, progressive tissue injury

fibrosis

collagen deposition (collagen replaces cells) leads to loss of funciton

resolution

clearance of injurious stimulus, clearance of mediators and acute inflammatory cells, replacement of injured cells, normal function (best case scenario)

morphologic patterns of acute inflammation

-vascular congestion and stasis: inflammation: RBCs packed inside vessels (stasis), slower flow, increased permeability
-leukocyte infiltration: extravasated (i.e. neutrophils enter lumen of alveoli)
vasodilation
-fluid in extracellular space

serous inflammation

effusion = serous fluid leaks into body cavities (i.e. blister)

mesothelioma

malignant transformation of mesothelial cells (specific in lungs)

fibrinous inflammation

-extravasated fibrin (clot formation) occurring with penetrating trauma
-caused because body can't clear fibrin in time and it becomes fixed, gets trapped in collagen (can impede tissue function)

suppurative inflammation

-aka purulent (pus = neutrophils)
-commonly encounter with abscess (pocket of pus), over time abscess may become walled off by leukocytes which can lead to scar tissue

ulcers

-either gastric or duodenal (10x more common)
-local excavation on surface of organ or tissue bed
-caused by shedding inflamed and necrotic tissue
-have chronic and acute components occurring simultaneously
-if left untreated can perforate