nitric oxide and its utility
TRANSCRIPT
Nitric Oxide and Its
UtilityBy
Dr Ketan Asawalle
JR1
Dept of Pharmacology
SVNGMC Yavatmal
Formula: NO
IUPAC ID: Nitric oxide
Molar mass: 30.01 g/mol
Density: 1.34 kg/m³
Boiling point: -152 °C
Soluble in: Water
Nitric Oxide (NO) is a novel mediator with diverse function
It is generated from L-argenine by nitric oxide synthase(NOS)
NOS occurs in endothelial, neuronal and inducible isoforms
Nitric oxide is a FREE RADICAL gas that forms during lightening storms
NO
NO
NO
NO
NO
NONO
NO
NO NO
NO
It was suspected that NO is produced in human body when cultures of MACROPHAGES were subjected to INFLAMMATORY mediators like
VASCULAR STUDIES also indicated towards the same
Mediators like acetylcholine were known to relax blood vessels
But this was seen only when LUMINAL ENDOTHELIAL CELLS near SMOOTH MUSCLES were preserved
They secreted EDRF
The physiological function
of NO was discovered
in the vasculature when
it was shown that the
endothelium derived
relaxing factor was
NOFURCHGOTT
ZAWADZKI
In the human body NO is formed by an enzymatic catalysed reaction between oxygen and L
Key role as a signalling molecule in
• CARDIOVASCULA SYSTEM
• NERVOUS SYSTEM
Also has a role in HOST DEFENCE
NO is endogenous activator of Guanylyl cyclase
Activates cGMP
Secondary Messenger
Nerves, smooth muscles, monocytes and platelets
Nitrogen and oxygen are neighbours in periodic table
so they have a few similar properties
For instance
HAEM
This is important for activation of guanylyl cyclase as it has a haem group
Similar mechanism acts in inactivation of NO by Haemoglobin
BIOSYNTHESIS OF NITRIC OXIDE
NITRIC OXIDE SYNTHASE
Enzyme in central control of Nitric Oxide biosynthesis
iNOS
NOS-II
nNOS
NOS-I
eNOS
NOS-III
i = Inducible n = Neuronale = Endothelial
iNOS
NOS-II
nNOS
NOS-I
eNOS
NOS-III
•Macrophages
•Kupffer cells
•Neutrophills
•Fibroblasts
•Vascular
smooth muscles
•Endothelium
•Cardiac myosites
•Osteoblasts
•Osteoclasts
•Neurons
PHYSIOLOGICAL
CONSTITUTIVE FORMS
PATHOLOGICAL
The activity of constitutive isoforms of NOS is controlled by
CALCIUM CALMODULIN
by TWO ways
Endothelium dependent Agonists like
Acetycholine,bradykinin,Substance P
Cytoplasmic Calcium ions
Calcium Calmodulin
Activates eNOS and nNOS
In the absence of any change in calcium ion concentration
Phosphorylation of specific resides on eNOS
Controls Calcium-Calmodulin concentration
The most important stimulus controlling endothelial NO synthesis is
SHEAR STRESS
Shear stress is sensed by mechanoreceptors and transduced via SERINE-THREONINE protein kinase channel Akt
cAMP
eNOS
Protein
Kinase A-
mediated
phosphorylation
e.g. ß2 agonists
Protein C kinase
eNOS
Phosphorylation
of residues in
calmodulin
binding domain
INSULIN
eNOS
Tyrosine Kinase
Activation
Unlike constitutive NOS, iNOS does not depend on Calcium for activation
iNOS is activated by
• Bacterial Lipopolysaccharides
• Cytokines synthesised in response to Lipopolysaccharides
Tumour Necrosis factor alpha
Interlukin-1
Involved in induction of iNOS
But Not Alone
INTERFERON GAMMA
DEGRADATION OF NITRIC OXIDE
2NO + O2 ——> N2O4
N2O4 + H2O ——> NO3- + NO2- + 2H+
NO2- + HbO ——> NO3- + Hb
Nitric Oxide is inactivated by
• Combination with haem of haemoglobin
• Oxidation to Nitrite or Nitrate
Excreted through
MAJOR ROUTE
NO is unstable and combine reversibly with CYSTINE residues
NO + Cystine residues of Albumin and Globulin
Stable Nitrosothiols
They act as circulation O2 sensitive NO carriers
REDUCTIVE reactions with a variety of oxides of nitrogen that can nitrosylate thiols and nitrate tyrosine
NO + PEROXISIDES ––> PEROXYNITRATE(ONOO-)
• DNA damage
• Nitration of tyrosine
• Oxidation of Cystine
EFFECTS OF
NITRIC OXIDE
Nitric Oxide is a volatile gas and it reacts with various metals, thiols and oxygen
One of the most important function of NO is activation of soluble Gyanylyl Cyclase which activates cGMP
NO activates enzymes by combining with haem group which is important for many physiological functions
BIOCHEMICAL AND CELLULAR ASPECTS
Pharmacological properties of NO can be studied with NO gas dissolved in deoxygenated salt solution
Various donors od NO can also be used to study the same e.g.
• Nitroprusside
• S-nitrosoacetylpenicillamine(SNAP)
• S-nitroglutathine(SNOG)
BIOCHEMICAL AND CELLULAR ASPECTS
NO can activate Gyanylyl Cyclase in the same cell that produces it
AUTOCRINE EFFECTS
e.g. Barrier function of endothelium
BIOCHEMICAL AND CELLULAR ASPECTS
NO can diffuse away from site of synthesis and activate Guanylyl Cyclase
This affects protein G, cyclic nucleotide phosphodiesterase, ion channels, etc.
INHIBITS calcium induced smooth muscle contraction and platelet aggregation
ANTIATHEROSCLEROTIC
BIOCHEMICAL AND CELLULAR ASPECTS
Inhibits
Smooth muscle
and
Fibroblast
proliferation
Migration
adhesion and
aggregation of
platelets
Monocyte
adhesion
BIOCHEMICAL AND CELLULAR ASPECTS
NMDA receptors when stimulated excessively produce NOS
Nitric Oxide
HOST
DEFENCE
NEURONAL
DESTRUCTION
Through
DIRECT EFFECT
PEROXYNITRATE ANIONS
VASCULAR EFFECTS
Argenine/NO pathway is tonically active in resistance vessels
The continuous release of NO keeps vasodilation in resistance vessels thus maintaining Blood Pressure
It is Anti-Atherosclerotic
Anti-Thrombotic
NEURONAL EFFECTS
Cholinergic mediators in many tissues like upper airway, GIT, Penis(errection)
Important for neuronal development
Helps in synaptic Plasticity
HOST DEFENCE
NO has Cytotoxic/Cytostatic effects
This has been proved experimentally in mice
Mice without iNOS were susceptible to Leishmania major
SEPTIC SHOCK
Systemic inflammatory response
Endotoxins
TNF-alpha
Cytokines
Macrophages
Neutrophils
T cells
Hepatocytes
Smooth muscle cells
Endothelial cells
Fibroblasts NO
HYPOTENSION
Actions of NO
Actions of NO
THERAPEUTIC
APPLICATIONS
NITRIC OXIDE
Inhalation of large quantities of nitric oxide causes
• ACUTE PULMONARY OEDEMA
• METHAEMOGLOBINEMIA
NO between 5 - 300 ppm has bronchodilatory action in guinea pigs
MAIN ACTION
PULMONARY VASODILATATION
Inspired NO preferentially acts on VENTILATED ALVEOLI
ARDS
ARDS is caused by different reasons causing shunting of arterial blood to venous blood
NO acts on arteries of PERFUSED areas and causing VASODILATION
ETHYL NITRIC gas is being used to reduce toxicity
NITRIC OXIDE DONORS/PRECURSORS
• GLYCERYL TRINITRATE(GTN)
• S-NITROSOGLUTATHIONE(SNOG)
• S-NITROSOACETYLPENICILLAMINE(SNAP)
• NITROPRUSIDE
The common mode of action of these drugs is
DONATION of NO
GTN is more potent on VASCULAR SMOOTH MUSCLES
SNOG selectively INHIBITS PLATELET FUNCTION
Dietary Nitrates (Beetroot) lowers arterial BP parallel to rise in plasma Nitrate concentration
SALIVARY conversion od Nitrate to Nitrite causes lowering of nitrites in body leading to rise in BP and abolishe
Rapidly acting Consistantly acting
Sodium Nitropruside
Brief duration of action - 2 to 5 minutes
Dose can be TITRATED
Relaxes both RESISTANCE and CAPACITANCE vessels
REDUCES both TOTAL PERIPHERAL RESISTANCE and CARDIAC OUTPUT
Myocardial work Reduced
Sodium Nitropruside
Sodium Nitropruside
Endothelial cells RBCs
Na Nitropruside
NITRIC OXIDE
EnzymaticallyNon
Enzymatically
50mg in 500 ml of 5% Dextrose
Slow IV
The bottle is covered with dark cloth to avoid oxidation of NO
USES
• Hypertensive emergencies
• Maintenance of patients with hypertension
• CONTROLLED HYPOTENSION in REFRACTORY CCF, Pump failure in MI and Acute MR
Sodium Nitropruside
SIDE EFFECTS
Palpitations
Nervousness
Vomiting
Perspiration
Abdominal pain
Disorientation
Weakness
Lacti acidosis
Sodium Nitropruside
GTN
It a VOLATILE LIQUID
SUBLINGUAL route of administration is preferred
Acts in 1 - 2 minutes and peaks in 3 - 6 minutes
T1/2 is 2 minutes
Duration of action depends on the amount of time the drug is in contact with the sublingual surface
GTN
GTN
GTN is readily absorbed from skin
OINTMENT produces hemodynamic effects in 4
TRANSDERMAL PATCH produces effect in 60 minutes
IV administration produces stable titrable effects
GTN
ISOSORBIDE DINITRATE
SUBLINGUAL route gives peak in5 - 6 minutes
ORALY T1/2 is 40 minutes but sustained release can give effect up to 8 hours
ISOSORBIDE MOMONITRATE
Active metabolite of Isosorbide dinitrate
USES
• Angina Pectoris
• Acute Coronary Syndrome
• MI
• CHF with acute LVH
• Biliary colic
• Esophagial spasm
• Cyanide poisoning
CYANIDE POISONING
Haemoglobin
Methaemoglobin
CYANIDE
Cyanomethhemoglobin
Methaemoglobin + Na Thiocynate
SODIUM
NITRITE
AMYL
NITRITE
SODIUM
THIOSULPHATE
INHIBITORS OF
NITRIC OXIDE
SYNTHESIS
N-MONOMETHYL-L-ARGENINE(L-NMMA)
NITRO-L-ARGENINE METHYL ESTER(L-NAME)
ASSYMETRIC DIMETHYL GLYCERENE
NON SELECTIVE
NMMA when infused slowly in brachial artery causes LOCAL VASOCONSTRICTION
L-NMMA acts through nNOS
When Given IV
Vasoconstriction of Renal, Mesenteric and Cerebral vessels
Sustained muscle resistance and increased BP
SELECTIVE
• iNOS - N-iminomethyl-L-lysine
•nNOS - 7-nitroindazole
S-methyl-L-thiocitruline
POTENTIATORS OF NITRIC OXIDE
SELECTIVE NO DONORS
GTN
SNOG
SNAP
DIETARY SUPPLIMENTS
BEETROOT
ANTIOXIDNTS
Reduce free oxygen radicals and stabilise NO
ACE inhibitors, Statins, Insulins, Oestrogens
RESTORE ENDOTHELIUM FUNCTION
ß2 AGONISTS
Activate L-Argenine/NO Pathway
PHOSPHODIESTERASE V INHIBITORS
Sildenafil, Tadanafil, Vardenafil
PHOSPHODIESTERASE V INHIBITORS
Used in treatment of ERECTILE DYSFUNCTION
SILDENAFIL
TADANAFIL
VARDENAFIL
NOGenerates cGMP
Dephosphorylates
MLCK
PD-5SILDENAFIL
TADANAFIL
VARDENAFIL
5-GMP
SILDENAFIL
Selective PD-5 Inhibitor
Enhances NO activity in CORPORA CAVERNOSA
Oral bioavailability is about 40%
Peak blood levels attained in about 1 - 2 hours
Metabolised by CYP3A4
SILDENAFIL
SIDE EFFECTS
Headache
Nasal congestion
Dizziness
Facial flushing
Fall in BP
Pulmonary HTN
TADANAFIL
Faster onset of action
Longer lasting
T1/2 18 hours
Duration of action 24-36 hours
Peak Plasma levels in 80 - 120 minutes
UTILITY OF NITRIC OXIDE
HYPERTENSION
Nitroprusside
Maintenance
Emegencies
Na Nitroprusside
GTN
Isosorbide
UTILITY OF NITRIC OXIDE
ERECTILE DYSFUNCTION
Sildenafil
Tadanafil
Vardenafil
UTILITY OF NITRIC OXIDE
PULMONARY HTN and GASTRIC STASIS
NO is under investigaton
ADULT and NEONATAL RESPIRATORY DISTRESS SYNDROME
INHALED NO and ETHYL NITRIC GAS
UTILITY OF NITRIC OXIDE
NO inhibitors are under investigation for conditions where there is excess NO production e.g. INFLAMMATION, SEPSIS, NEURODEGE
THANK
YOU
References1. Rang and Dale’s Pharmacology 6th edition
2. Basic and Clinical Pharmacology; Katzung 12th
edition
3. Essential of Medical Pharmacology; K D Tripathi
7th edition