PCTH 400 LAST LECTURE Endothelial dysfunction and cardiovascular diseases. Classic Vascular pharmacology -chronic -systemic Local Vascular pharmacology -acute -targeted High blood pressure Blood pressure control Atherosclerosis Endothelial Injury Thrombus CABG PTCA Stent Drug eluting stents Patient burden Restenosis In-sent restenosis Lipid lowering drugs Platelet/SMC pharmacology Providence Heart + Lung Institute at St. Paul s Hospital University of British Columbia Blood vessel Endothelium Endothelium SMC Nitric Oxide Prostacyclin EDHF Superoxide
How was NO discovered How was NO discovered -In 1978, Furchgott discovered a substance in endothelial cells that relaxes blood vessels, calling it endothelium-derived relaxing factor (EDRF) ACh Endothelium Aortic rings in cascade Half-life of NO:? -Endothelium dependent vasorelaxation -inhibited by Hemoglobin 2 seconds How NO was discovered How was NO discovered -In 1977, Ferid Murad s group show that nitric oxide and various nitro compounds were shown to activate the cytosolic form of guanylate cyclase and to elevate cyclic GMP levels in various tissues. Nitroglycerin was one of those nitro compounds that he had studied and speculated that it might release nitric oxide which then activated guanylate cyclase. -In 1979, Lou Ignarro s group showed that gaseous NO causes profound vasorelaxation and that Murad s obervations on cgmp were induced by NO which causes relaxation using cgmp as a SMC messenger. -inhibited by Hemoglobin
How was NO discovered 1998 Nobel Prize -In the late 1970 s, Salvador Moncada showed that NO is released by the endothelium and that its synthesis is derived from L-arginine. Furchgott: -died Ignarro: -Herbalife controversy Murad: -U Virginia -Stanford -UTexas -Abbott Salvador Moncada Where is Salvador Moncada? -2001 University of Dundee PhD Honoris Causa It is widely recognised as a travesty of justice that Salvador Moncada did not share the Nobel Prize for Medicine that was awarded to Furchgott in 1998 for the discovery of nitric oxide. -L-NAME does not work in septic shock -Controversy: -Political manipulation of jury (Honduras) -No exception to the rule of 3 -L-Name controversy in septic shock A phase III trial of 546C88 enrolled 797 patients with septic shock.[94] Patients received either placebo or 546C88 0-20 mg/kg/hour. The trial was stopped early by an independent data safety monitoring board after it was determined that mortality was greater in patients treated with 546C88. Twenty-eight-day mortality was 49% in placebo recipients and 59% in those who received study drug (p<0.005). The results of this study prompted withdrawal of 546C88 from further clinical development. It is unlikely, due to the adverse effect profile of L-NAME and dismal clinical results from L-NMMA studies, that this compound will be assessed further.
What is NO? Why is NO so important? -Nitric Oxide or NO -Chemical formula : NO so it s a free radical - Reactivity! -In the presence of O 2, NO forms Nitrite and Nitrate -Gas, so you can buy cylinders of NO. -Highly diffusible -Most potent vasodilator, no matter what agonist is used for pre-constriction. -FREELY PENETRATES CELLS -Many roles: -Blood pressure -Heart diseases -Immune system -Digestion -Cancer -Inflammation -Wound healing -Pain Relief -Energy met. -Diabetes -Impotence -Fertility -Memory enhancement -Weight loss Endothelial derived-nitric Oxide How NO causes SMC relaxation L-arginine NO + L-citrulline enos L-Name inhibits enos Nitric Oxide Genetic evidence supporting the importance of endothelium derived NO in the cardiovascular system Endogenous vasodilator Increases vascular permeability Anti-atherosclerotic Prevents oxidative stress Necessary for angiogenesis stimulated by tissue ischemia. May be involved in stem cell mobilization cgmp-dependent activity (most of NO activity) cgmp-independent activity -Nitrosylation of cysteine residues
How NO causes vasorelaxation Endothelial Nitric oxide synthase Decreased activity PKG Increased phosphatase activity Prostacyclin or PGI 2 Prostacyclin or PGI 2 -Discovered in 1976 by John Vane -Nobel prize -Used in pulmonary hypertension -Flolan -Polish scientists: They reported striking and prolonged benefits following intra-arterial infusion of prostacyclin in five patients with advanced atherosclerotic lower-limb peripheral vascular disease. Rest pain disappeared, previously refractory ulcers healed, and muscle blood flow as measured by Xenon 133 clearance was significantly increased for at least 6 weeks after prostacyclin infusion. They later reported striking improvements in some of 55 patients with advanced peripheral artery disease of the lower extremities.
Prostacyclin or PGI 2 Prostacyclin or PGI 2 Protects the endothelium.. Exogenous and endogenous Site of synthesis: Heart, vascular endothelium Action: inhibits platelet and leukocyte aggregation decreases T-cell proliferation and lymphocyte migration and secretion of IL-1a and IL-2 induces vasodilation and production of camp through Prostacyclin I2 receptor on SMC Prostacyclin or PGI 2 Prostacyclin or PGI 2 Ibuprofen Inhibits cyclooxygenase -Prostacyclin acts chiefly to prevent platelet formation and clumping involved in blood clothing (thrombus formation). -It is also an effective vasodilator. -Inhibitor of PGI2 synthesis: V..
EDHF-Vessel tone EDHF -Tone is mostly determined by smooth muscle cell contractility. 1) cytochrome P-450 (CYP450) products, 2) K+ 3) H2O2. 4) Adenosine -Contractility is determined by cytosolic Calcium concentration. -Calcium enters SMC following depolarisation t-type and L-type Ca++ channels. EDHF diffuses to the vascular smooth muscle cells (VSMCs), activates KCa2+ channels, and causes endothelium-dependent hyperpolarization Endothelial dysfunction Hyperaemic response -Attenuation or absence of stimulated (ACh) or basal NO production is a hallmark of EC dysfunction. -Marker of: CHF Hypertension Atherogenesis Restenosis EndoPAT-2000 -Risk factors: Diabetes Hypercholesterolem. Smoking Hypertension AGING -Clinical use Providence Heart + Lung Institute at St. Paul s Hospital University of British Columbia Providence Heart + Lung Institute at St. Paul s Hospital University of British Columbia
Endothelial function in patients Endothelial function in patients Circulation. 1995; 91: 1981-1987 Endothelial dysfunction causes hypertension and vice-versa Oxidative stress Which one comes first? -General term used to describe the steady state level of oxidative damage in a cell, tissue, or organ, caused by reactive oxygen species (ROS). EC dysfunction Hypertension Atherosclerosis Arteriosclerosis
Oxidative stress Endothelial Nitric oxide synthase -There are many different sources by which the reactive oxygen species are generated. Most reactive oxygen species come from energy generation from mitochondria, xanthine oxidases, NADPH oxidase. -Direct damage to tissues (DNA, proteins, lipids) -Scavenges NO -Angiotensin II is the main mediator of oxidative stress -Also released by enos when uncoupled Endothelium Questions? Endothelium SMC Nitric Oxide Prostacyclin -What are the positive mediators of endothelial function -What is the negative regulator of endothelial function (Superoxide) -How is their synthesis regulated? -What is endothelial dysfunction? EDHF Superoxide
Endothelial dysfunction Endothelial dysfunction -Impairment of normal endothelial functions (all induce vasodilation). -Attenuation or absence of stimulated (ACh) or basal NO production is the hallmark of EC dysfunction. L-Arginine Vasodilation -Risk factors: Diabetes Hypercholesterolemia Hypertension Atherosclerosis Smoking AGING -Consequences: Hypertension ACS Stroke enos-ca 2+ -Hsp90 Calmodulin complex (active) NO sgc sgc sgc sgc sgc Smooth muscle NO (exogenous) However, vasodilatory responses to EC-independent exogenous NO (sodium nitroprusside for instance) are preserved. enos is regulated by post-translational modifications How was EDHF discovered? -In smaller arteries in which NO and PGI2 synthesis is blocked, some vessels can still relax following Ach stimulation. -enos KO and COX KO. -Endothelium dependent enos protein