Smooth Muscle (pt 4/4) Nitric Oxide Flashcards
What is the difference between N2O and NO2?
N2O = Nitrous Oxide (anesthetic gas)
NO2 = Toxic Pulmonary Irritant
What is Nitric Oxide?
-A highly reactive gaseous signaling molecule
-Readily diffuses across cell membranes
-Endogenous to the human body
-Potent Vasodilator
-Platelet Inhibitor
-Immune Regulator
-Neurotransmitter
-Exogenous NO and NO-releasing compounds used in pharmacology (Nitrates, nitrites, nitroprusside, nitroglycerin)
-A naturally occurring environmental pollutant
-The major bioactive component of Endothelial-Derived Relaxing Factor (EDRF)
-Acts on vascular smooth muscle → relaxation
A gas that can diffuse through cell membranes.
-Triggers biochemical reactions
-Dissipates rapidly
-Synthesized & released by normal endothelium
-Regulated by endothelial ICF Ca++
↑ cytosol Ca++ ⇒ NO production
-Synthesis induced by increased stress
Nitric Oxide
Increased cytosol Ca++ causes what?
Nitric Oxide Production
What substances lead to increased cytosol Ca++ (leading to increased Nitric Oxide)?
Ach
Bradykinin
Catecholamines
Substance P
ADP
What is the MOA of Nitric Oxide?
-Vasodilation via guanylyl cyclase activation (↑cGMP)
-Inhibits platelet aggregation (Anti-thrombotic effect)
-Inhibits platelet derived vasoconstrictive substances
-Produced in leukocytes, fibroblasts, & vascular smooth muscle
The synthesis of Nitric Oxide is made by 1 of 3 enzymes that are expressed in a wide variety of cell types. What are the 3 enzymes?
nNOS (NOS-1)
iNOS (NOS-2)
eNOS (NOS-3)
What is nNOS (NOS-1)?
nNOS (NOS-1) – neuronal
Triggered by ↑ intracellular Ca2+
What is iNOS (NOS-2)?
-inducible or macrophage
-Triggered by inflammatory mediators
-Has constitutive activity
What is eNOS (NOS-3)?
eNOS (NOS-3) – endothelial
Triggered by ↑ intracellular Ca2+
NO mediates its effects by ______ modification of proteins.
covalent
How does Nitric Oxide interact with metals (Metalloproteins)?
-NO interacts with metals especially Heme
-NO binds to the heme of sGC (primary target)
-Synthesizes GTP to cGMP to activate Protein Kinase G (PKG)
-Reduce Ca2+ levels in blood vessels
-Decreases vascular tone
-Decreases vascular smooth muscle contraction
-Mechanism contributes to cytotoxic effects r/t NO overproduction
-NO inhibits the heme of heme-containing CYP450 enzymes
-Major cause of inflammatory liver disease
How does Nitric Oxide overproduction contribute to inflammatory liver disease?
Nitric Oxide binds to heme, synthesizing GTP to cGMP and activating Protein Kinase G (PKG).
-NO Inhibits the heme of heme-containing CYP450 enzymes
-Major cause of inflammatory liver dz
How does Nitric Oxide interact with Thiols?
-Compounds containing a carbon bonded sulfur + hydrogen group
-NO + (-SH) = nitrosothiol
-Found endogenously in the amino acid cysteine
-Unknown physiologic role
What is Tyrosine Nitration?
-NO undergoes both oxidation and reduction reactions
-NO reacts very efficiently to superoxide
-Superoxide = O2- (a free radical; Synthesized by many cellular enzymes)
-NO + (O2-) = OONO- (Peroxynitrite – highly reactive oxidizing agent that causes DNA damage, Nitration of tyrosine, and Oxidation of cysteine to disulfides or sulfur oxides)
-Reaction is mitigated by glutathion
-NO synthesis is increased in many inflammatory and degenerative diseases (Shown by Increasing Peroxynitrite levels and Increased tyrosine nitration = irreversible protein modification (Activate or inhibit protein function) )
-(+) Detection of tyrosine in tissues is a sign of oxidative stress
-Accumulation of toxins, peroxides and free radicals
What is Superoxide (O2-)?
A free radical synthesized by many cellular enzymes.
Nitric Oxide + Superoxide (O2-) = ?
Peroxynitrite (OONO-): a very highly reactive oxidizing agent.
What are the effects of Peroxynitrite (OONO-)?
-DNA damage
-Nitration of tyrosine
-Oxidation of cysteine to disulfides or sulfur oxides
What mitigates the reaction of Nitric Oxide + Superoxide to Peroxynitrite?
Glutathione
NO synthesis is ________ in many inflammatory and degenerative diseases.
Increased
Increased Nitric Oxide synthesis in inflammatory and degenerative diseases leads to ?
-Increasing Peroxynitrite levels
-Increased tyrosine nitration = irreversible protein modification (Activate or inhibit protein function).
What is a sign of oxidative stress?
(+) Detection of tyrosine in tissues
Accumulation of toxins, peroxides and free radicals
Endogenous vasodilators (Acetylcholine or bradykinen) activate NO synthesis in the luminal endothelial cells, leading to ?
Endogenous vasodilators (Acetylcholine or bradykinen) activate NO synthesis in the luminal endothelial cells, leading to calcium efflux from the endoplasmic reticulum into the cytoplasm
Increased Calcium into the cytoplasm causes Ca to bind to _____, which activates _______, resulting in ____ synthesis from _______.
Calcium binds to calmodulin (CaM), which activates NO synthase (eNOS), resulting in NO synthesis from L-arginine.
NO diffuses into smooth muscle cells, where it activates ________ and _____ synthesis from ______.
NO diffuses into smooth muscle cells where it activates soluble guanylyl cyclase and cGMP synthesis from guanosine triphosphate (GTP).
cGMP binds to and activates ______, resulting in an overall reduction in calcium influx and _______ of calcium-dependent muscle contraction.
cGMP binds to and activates protein kinase G (PKG), resulting in an overall reduction in calcium influx and inhibition of calcium-dependent muscle contraction.
PKG can also block _____ that lead to muscle contraction.
PKG can also block other pathways that lead to muscle contraction.
cGMP signaling is terminated by ______, which convert cGMP to ______.
cGMP signaling is terminated by phosphodiesterases, which convert cGMP to GMP.
What is the primary approach to decreasing Nitric Oxide generation in cells?
NOS Inhibitors.
What is the structure of NOS Inhibitors?
Structure = Arginine analogues
Bind to the NOS arginine-binding site
NOS’s are structurally _____, so most meds are non-selective.
NOS’s are structurally similar so most meds are non-selective
nNOS Inhibition is useful in what disorders?
nNOS Inhibition – useful in neurodegenerative disorders
iNOS inhibition is useful in what disorders?
iNOS Inhibition – useful in sepsis and inflammatory disorders
Concurrent eNOS inhibition impairs what?
Concurrent eNOS inhibition impairs hemostatic signaling.
-Vasoconstriction
-Ischemic damage
NOS selective drugs are ?
Under investigation.
What is the MOA of Nitric Oxide donors?
Metabolized to release Nitric Oxide and elicit smooth muscle relaxation.
Explain the effects of Organic Nitrates.
-Ex: Nitroglycerin is metabolized to NO, promoting venous dilation.
Arterial & venous dilation with less effects on platelet aggregation.
-Exhibit tolerance during continuous administration
Explain the effects of Organic Nitrites.
Arterial vasodilators but abused for euphoric effects.
-Require metabolic activation to elicit vasorelaxation
-Arterial vasodilators
-Do not exhibit tolerance
What is the example drug of the Organic Nitrites?
Ex: Inhaled Amyl Nitrite
What are the effects of Sodium Nitroprusside (Nipride)?
Arterial & venous dilation and used to rapidly reduce arterial HTN.
-Dilates arterioles and venules
-Used for rapid pressure reduction in arterial hypertension
-Breaks down to cyanide and NO in the presence of light and via chemical/enzymatic mechanisms
What are the effects of NO Inhalation?
Reduces PA pressures & improves perfusion of ventilated lung areas.
-Used in the Tx of: Pulmonary HTN, Acute Hypoxia, and CPR.
-Ex: Compressed Gas
What reaction can occur with the use of Compressed Gas for NO Inhalation?
-Can react with O2=NO2
-Pulmonary irritant = decreased lung function
-Can induce the formation of methemoglobin
What is the example drug of the PDE Inhibitors?
Sildenafil
What are the intended and adverse effects of the PDE Inhibitors?
Slows the degradation of cGMP & prolong NO effects.
-Risk for Hypotension, blindness with surgery & anesthesia (ischemic optic neuropathy)
Why should you give Newborns with hypoxic respiratory failure due to pulmonary hypertension Inhaled Nitric Oxide?
Because it dilates the pulmonary vessels.
↓ Peripheral Vascular Resistance
↓ PA Pressures
↓ V/Q Mismatch due to dilation of lung tissue with better ventilation
Does Extracorporeal membrane oxygenation (ECMO) effect pulmonary pressures?
No
