PHA 316 Other Mediators Nitric Oxide Submit 2022 PDF

Other Peripheral Mediators Nitric Oxide as a mediator Nitric Oxide as a mediator Objectives Outline the nitric oxide biosynthesis pathway Describe the physiological role of nitric oxide as a mediator Describe the bio-signaling pathway for nitric oxide List key clinical conditions...

Other Peripheral Mediators Nitric Oxide as a mediator Nitric Oxide as a mediator Objectives Outline the nitric oxide biosynthesis pathway Describe the physiological role of nitric oxide as a mediator Describe the bio-signaling pathway for nitric oxide List key clinical conditions due to dysregulation of NO synthesis/signaling pathways Describe the pharmacological control of the above dysregulation  Nitric Oxide as a mediator Overview Nitric oxide has very many physiological activities in various tissues It’s a key signalling molecule in the CV, NS and has role in host defence These can serve as potential sites for dysregulation and subsequent pharmacological intervention Will review biosynthesis and signalling and then potential sites for pharmacological intervention Nitric Oxide Biosynthesis Endogenous NO synthesized from L- arginine by family of enzymes called Nitric oxide synthase (NOS) These intracellular enzymes are activated by calcium influx or by cytokines in the endothelial cells Differences between the three (3) isoforms of NOS enzymes and significance thereof (stimuli and rate) – 2 constitutive (eNOS/NOS3 and nNOS/NOS1) Present under physiological conditions in the endothelium and in neurons Generate relatively smaller amounts of NO – 1 Inducible (iNOS/NOS2) Expressed in macrophages, neutrophils, fibroblasts, vascular smooth muscles and endothelial cells in response to pathological stimuli Produces much greater amounts of NO  Nitric Oxide Biosynthesis Activity of enzymes as determinants for rate of production of NO – When can high dose L-Arginine be used to restore endothelial NO biosynthesis? Control of constitutive NOS activity by Calcium-calmodulin is exerted in 2 ways – Endothelium dependent agonists e.g Ach, bradykinin, substance P etc increase the cytoplasmic conc of Ca2+ with consequent increase in Ca2+-Calmodulin which increases activity of NOS1 and NOS3 – Phosphorylation of specific residues in NOS3 controls its sensitivity to Ca2+-Calmodulin. This can alter the activity of NO in the absence of increased Ca2+ In contrast activity of inducible NOS is independent of Ca2+ levels and can be fully activated even in case of low Ca2+ levels  Nitric Oxide Biosynthesis Following synthesis, NO diffuses to site of action in neighboring cells causing activation of guanylyl cyclase Nitric oxide is not stored in cells Effects of GC on conversion GTP to GMP Effects of cGMP on dephosphorylation and inactivation of myosin light chain resulting in relaxation of muscle cells Effects of cGMP are terminated by phosphodiesterase enzyme Physiological Effects of Nitric Oxide: Summary See table 21.1 Gaseous, unstable, not Relaxation of vascular stored in cells Half Life – smooth muscles - vasodilation less than 5-10 sec Cardiovascular Site of production versus Platelet Aggregation inhibition site of action – Ability to diffuse through Host defense Virus, bacteria etc cell membranes Other substances that Peripheral – GIT, penile stimulate endogenous erection, upper resp etc production of nitric oxide Nervous System Clinical conditions CNS - later associated with derangement  Effects of Nitric oxide Smooth muscles – Vasodilator – Role in erectile tissue function in which smooth muscle relaxation is required to bring about the influx of blood that causes erection Cell adhesion limitation Host defence – against viruses, bacteria, fungi, parasites Exercise: Refer to table 21.1 for postulated roles of endogenous nitric oxide – What is the physiological role of NO on CV system (vascular smooth muscles? – What is the pathological effect of excessive NO production on the vascular smooth muscles – What is the pathological effect of inadequate NO on vascular smooth muscles?  Common Pathological Condition Associated with Dysregulation of Nitric Oxide Over or under production – still area of immense research Over Activity – Hypotension – Neurodegenerative disorders – Septic shock Conditions associated with reduced NO activity – Atherosclerosis – Erectile dysfunction – Thrombosis – Hypercholesterimiae Nitric Oxide – Signaling Pathways and dysregulation  Nitric Oxide related Pharmacological intervention – Clinical Use NO Pharm Interventions NO – inhalation of low volumes for Nitric oxide NO replacement or Inhibition of nitric pulmonary donors/precursors - potentiation oxide vasodilation Dietary supplement Respiratory distress Nitroprusside, with L-arginine or syndrome inorganic nitrates Nitroglycerine, Isorsorbide dinitrate, PDE type 5 Inhibitors Isorsorbide - sildenafil mononitrate  High Level Pharmacological Intervention: Exogenous Nitric Oxide donors Why not NO direct? Nitric oxide is released from several important drugs including – Nitroprusside Occurs spontaneously in the blood in the presence of oxygen. Immediate reduction of BP in hypertensive crisis. – Nitrates Intracellular release and requires presence of thiol compounds. Tolerance may happen if endogenous thiol compounds are depleted – Nitrites Intracellular release and requires presence of thiol compounds. Tolerance may happen if endogenous thiol compounds are depleted Exercise: Read on use and misuse of amyl nitrite, type of products that contain amyl nitrite  High Level Pharmacological Intervention – Potentiation of nitric oxide Type 5 phosphodiesterase (PDE) Inhibitors e.g. Sildenafil, tadalafil – Potentiate the effect of NO and are used to treat erectile dysfunction – How? – See use in pulmonary hypertensions – Why is concurrent use of nitrates e.g. nitroglycerine and sildenafil contraindicated or require extra caution? What is the underlying mechanism for the interaction? Counseling of patients on sildenafil Potentiation of nitric oxide -Investigational – Dietary supplements Exercise: Investigate, use of L-Arginine supplements, Indications supported by literature, drug interactions that as a pharmacist you would need to be aware of – Antioxidants – Drugs that restore endothelial function in patients with metabolic risk factors L-Arginine preparations- Various