Vascular Biology of Nitric Oxide

Carmen Cheung, Rebecca Sabovich, Valeria Sula, Lester Yuen

Tuesday September 22, 2015

PHM142 Fall 2015 Instructor: Dr. Jeffrey Henderson

• Odourless gas

• Free radical

• Short lifespan (6-7 seconds)

• Won Molecule of the Year 1992

• The discovery of “Nitric Oxide as a Signaling Molecule in the Cardiovascular System” awarded Nobel Prize in 1998

Introduction: Nitric Oxide (NO)1, 2, 3

https://en.wikipedia.org/wiki/Nitric_oxide#/media/File:Nitric-oxide-3D-vdW.png

Introduction: Significance of Nitric Oxide4

• Important signaling messenger molecule that regulates:o Nervous system

o Cardiovascular system

• Other physiological implicationso Respiratory regulation

o Tissue injury repair

o Substance addiction

o Irregular production in tumours

Synthesis of Nitric Oxide5,6

Two-step reaction1) Hydroxylation of the guanidine nitrogen 2) Oxidation of Hydroxyarginine

Nitric Oxide Synthases (NOS)4

• Catalyzes the synthesis of NO via NADPH

• Functional enzyme is a homodimer of two NOS proteins

• Reductase domain o cofactors FAD, FMN

• Oxidase domaino BH4, Calmodulin, Heme groups

http://www.rcsb.org/pdb/explore/explore.do?structureId=2NSE

Nitric Oxide Synthases (NOS)4

• Three forms based on tissue/cell typeo Neuronal/ NOS Io Inducible/ NOS IIo Endothelial/ NOS III

Effects of NO7

1. Vascular tone2. Platelet adhesion, aggregation, and recruitment3. Vascular smooth muscle proliferation4. Antioxidant and oxidant effects5. Endothelial cell apoptosis and proliferation6. Leukocyte adhesion

Implications: diseases (heart disease, hypertension)

1. Vascular Tone7

• NO regulates constriction and dilation of the blood vessels

• NO deficiency causes hypertension• Dose-dependent manner:o Low [NO] causes vasodilationo High [NO] may lead to septic shock, hypotension

http://www.rosacea-treatment-clinic.com.au/Images/Vasodilation.gif

1. Vascular Tone - Mechanism7

2. Platelet Adhesion, Aggregation & Recruitment8

• Adhesion to vascular wall causes vascular problems• NO produced by platelets inhibits recruitment of more platelets to growing clot

http://naturalbloodthinners.org/

3. Vascular Smooth Muscle Proliferation7

• NO inhibits the proliferation of VSMCo cGMP-independent and -dependent mechanisms

• Proliferation of VSMC -> atherosclerosis• Dose-dependent manner:

o low [NO] by eNOS protects against atherosclerosis

o high [NO] by iNOS promotes atherosclerosis

http://www.univie.ac.at/pharmakognosie/I3MO/background.htmhttp://www.pharmaceutical-networking.com/merck-mk-0524b-treatment-of-atherosclerosis/

4. Antioxidant & Oxidant Effects7

• 3 redox forms of NO:o Nitrosonium, NO ⁺o Nitroxyl anion NO⁻o Free radical NO˙

NO• + O₂˙ -> ONOO⁻ ⁻• cardiovascular pathology

• Dose-dependent manner:o low [NO] by eNOS reduces the presence of ROS extracellular SOD heme-oxygenase I and ferritino high [NO] by iNOS may promote oxidative damage

5. Endothelial Cell Apoptosis & Proliferation7

• NO helps modulate vascular cell apoptosis• Dose-dependent manner:o low [NO] protects against apoptosis

cGMP-dependent and -independent mechanismso high [NO] can induce apoptosis

independent of cGMP

• NO also promotes angiogenesis and endothelial cell migration

o angiostatin

6. Leukocyte Adhesion7

• NO inhibits leukocyte recruitment and adhesion to the vascular endothelium

• Inhibits NFkB

PC: http://philschatz.com/anatomy-book/contents/m46701.html

Drugs9, 10, 11

• Nitroglycerines (e.g. Nitroderm)

o Metabolized into NO to increase vasodilation

• Statins (e.g. Lipitor)

o Ameliorate bioavailability of NO by enhanced activation and increased expression of eNOS

• Sildenafil a.k.a. Viagra

o Prevents cGMP from degradation allowing NO to vasodilate corpus cavernosum

Summary

Actions of NO Low [NO] High [NO]Vascular tone Vasodilation against

hypertensionToo much hypotension → septic shock

Platelet aggregation & recruitment

inhibits the recruitment of more platelets in a clot

n/a

Vascular smooth muscle proliferation

Inhibits VSM proliferation against atherosclerosis

Promotes atherosclerosis

Antioxidant & oxidant effects

Reduces the presence of ROS

Promotes oxidative damage

Endothelial cell apoptosis & proliferation

Protects against apoptosis Can induce apoptosis

Leukocyte adhesion Limits leukocyte adhesion n/a

Drugs: nitroglycerines, statins, sildenafil

References

1) Gunay, YA. et al. Vascular Pharmacology. 45, 268-276 (2006)

2) Culotta, Elizabeth and Koshland, Daniel E. Jr (1992). "NO news is good news".Science 258 (5090): 1862–1864

3) Physiology or Medicine for 1998 - Press Release". Nobelprize.org. Nobel Media AB 2014. Web. 22 Sep 2015. <http://www.nobelprize.org/nobel_prizes/medicine/laureates/1998/press.html>

4) Hirst, DG., Robson, T. Methods in Molecular Biology 704, 1-13 (2010)

5) Sessa, W. et al. European Heart Journal 33, 829-837 (2012)

6) Marletta, MA. et al. Current Opinion in Chemical Biology 2, 656-663 (1998)

7) Walford, G. Journal of Thrombosis and Haemostasis. 1, 2112-2118 (2003)

8) Riddell, DR. Owen JS. Vitamins and Hormones 57, 25-48 (1999).

9) Chen, Z. et al. Proceedings of the National Academy of Sciences of the United States of America 102, 12159–12164 (2005)

10) Waslter, G.H. et al. Seminars in Vascular Medicine. 4, 385-393 (2004)

11) Webb, D.J. et al. American Journal of Cardiology. 83, 21C–28C (1999)

References

“Antiproliferative and antimigratory activity of I3MO”. univie.ac.at. Department of Pharmacognosy 2011. Web. 19. Sep. 2015. http://www.univie.ac.at/pharmakognosie/I3MO/background.htm.

Chen, Z; Foster, MW; Zhang, J; Mao, L; Rockman, HA; Kawamoto, T; Kitagawa, K; Nakayama, KI et al. "An essential role for mitochondrial aldehyde dehydrogenase in nitroglycerin bioactivation". Proc. Natl. Acad. Sci. USA 102 (34): 12159–12164 (2005).

“Physiology or Medicine for 1998 – Press Release”. Nobelprize.org. Nobel Media AB 2014. Web. 22. Sep. 2015. www.nobelprize.org/nobel_prizes/medicine/laureates/1998/press.html.

“Treatment of Atherosclerosis”. Pharmaceutical-Networking.com. Saffron Networking Ltd 2014. Web. 20. Sep. 2015. http://www.pharmaceutical-networking.com/merck-mk-0524b-treatment-of-atherosclerosis/.

Walford G, Loscalzo J. Nitric oxide and vascular biology. J Thromb Haemost 2003; 1: 2112-2118. Culotta, Elizabeth and Koshland, Daniel E. Jr (1992). "NO news is good news".Science 258 (5090): 1862–1864

Waslter, G.H.; Dimmeler, S; Zeiher, A.M. . “Effects of statins on endothelium and endothelial progenitor cell recruitment”. Semin. Vasc. Med. 4 (4): 385-393 (November, 2004).

Webb, D.J.; Freestone, S.; Allen, M.J.; Muirhead, G.J. . "Sildenafil citrate and blood-pressure-lowering drugs: results of drug interaction studies with an organic nitrate and a calcium antagonist". Am. J. Cardiol. 83 (5A): 21C–28C (March 4, 1999).