Nitric Oxide in the Penis: Scientific Discoveries and Clinical Applications

Transcription

1 Nitric Oxide in the Penis: Scientific Discoveries and Clinical Applications Arthur L. (Bud) Burnett, M.D., M.B.A., F.A.C.S. Patrick C. Walsh Professor of Urology The James Buchanan Brady Urological Institute Johns Hopkins Medicine Baltimore, Maryland

2 Disclosure Statement: In accordance with the ACCME policy on relevant financial disclosure, I disclose financial relationships with the following entities: American Medical Systems, Auxilium Inc, Coloplast, Endo Pharmaceuticals, National Institutes of Health, Pfizer Inc, Reflexonic LLC

3 Acknowledgments Urology Biljana Musicki, Trinity Bivalacqua, Thomas Chang Neuroscience Solomon Snyder, David Bredt, K. Joseph Hurt Cardiology Charles Lowenstein, Hunter Champion, David Kass Hematology James Casella, Samuel Charache, Lewis Hsu Reproductive Biology Barry Zirkin, Terry Brown

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6 Overview Multiple actions of nitric oxide in the penis Physiologic penile erection Penile vascular health Homeostasis and interaction with other signaling molecules Therapeutic relevance Erectile dysfunction Recurrent ischemic priapism Penile fibrosis

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9 A New Observation Leads to a New Question and to a New Discovery

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11 Nitric Oxide: A Factor in Erectile Tissue Relaxation Direct application of nitric oxide relaxes isolated muscle strips from the corpus cavernosum similar to nerve stimulation In vitro tissue relaxation effects are blocked by inhibitors of nitric oxide synthesis Neurotransmitter identity doubt proof needed that nitric oxide is released from neurons 1. Ignarro LJ et al. BBRC 170:843-50, Rajfer J et al. N Engl J Med 326:90-4, 1992.

12 Nitric Oxide: A Physiologic Mediator of Penile Erection Arthur L. Burnett, Charles J. Lowenstein, David S. Bredt, Thomas S. K. Chang, Solomon H. Snyder* Nitric oxide (NO) is a cytotoxic agent of macrophages, a messenger molecule of neurons, and a vasodilator produced by endothelial cells. NO synthase, the synthetic enzyme for NO, was localized to rat penile neurons innervating the corpora cavernosa and to neuronal plexuses in the adventitial layer of penile arteries. Small doses of NO synthase inhibitors abolished electrophysiologically induced penile erections. These results establish NO as a physiologic mediator of erectile function. Reprint Series Science 17 July 1992, Volume 257, pp

13 Nitric Oxide Synthase is Localized to the Autonomic Innervation of the Human Penis Burnett AL, et al. J Urol 150:73-6, 1993.

14 Control of Trabecular Smooth Muscle Contractility

15 Clinical Therapeutics: Target Sites Burnett AL. J Androl 2002; 23:S20-6.

16 A New Observation Leads to a New Question and to a New Discovery

17 Nitric Oxide Synthase Knockout Mice Developed to investigate the involvement of nitric oxide in various biological functions 1 Focus on nnos, enos, double NOS mutant mice in sexual physiology research Challenge: these mice preserve copulatory ability! 2 - Why, if this regulatory pathway is essential? - Do alternative mechanisms permit sexual function? 1. Huang PL. Semin Perinatol 24, 87-90, Burnett AL, et al. J Androl 23, 92-97, 2002

18 Neuronal NOS Knockouts enos-dependent mechanisms are retained 1 Lack nnos (which encodes exon 2) but preserve nnos splice variants 2 nnos β is expressed and is physiologically relevant 3 1. Burnett AL, et al. Molec Med 2, (1996) 2. Gonzalez-Cadavid NF, et al. Biol Reprod 63, (2000) 3. Hurt KJ, et al. Proc Natl Acad Sci 103, (2006)

19 Endothelial NOS Knockouts Display supra-normal erections to electrophysiologic stimulation 1 Display attenuated erections to pharmacologic stimulation 2 1. Burnett AL, et al. J Androl 23, (2002) 2. Hurt KJ, et al. PNAS 99, (2002)

20 NO/eNOS Amplification System PNAS I March 19, 2002 I vol. 99 I no. 6 I

21 Molecular Mechanisms that Underlie Penile Erection

22 Regulation of enos is the Key to Penile Vascular Health

23 Towards Better Penile Health: Hypothesis Vasoactive Therapy Erectile Tissue Relaxation Intrapenile Blood Flow Stimulation Activation of Endothelial NOS Penile Vascular Repair and Restoration

24 A New Observation Leads to a New Question and to a New Discovery

25 Erection Excess in enos-/- Mice Burnett AL, et al. J Androl 23:92-7, 2002

26 PDE5 Dysregulation In Penile Erectile Tissue: Mechanism Of Priapism NOS3 -/- mice had enhanced erectile response to CNS. enos gene transfer to the NOS3-/- mouse penis resulted in neurogenic-mediated erectile responses similar to WT mice via an elevation of PDE5A expression/activity. Thus, properly regulated PDE5 function under physiologically relevant NO signaling preserves normal erection physiology. Therefore, if penile PDE5 expression is dysregulated priapism occurs. Champion HC et al PNAS 102: , 2005.

27 Biochemical Activity Measurements in Sickle Cell Mouse Penes SS-/- mice show a priapic phenotype, and this is associated with reductions of both NOS and PDE5A activities

28 A Reversed Nitrate Tolerance Mechanism?

29 Mechanism of Priapism

30 Sickle Cell Disease Interim Summary: Hypothesis PDE5 Inhibitor Therapy Penile Vasculature enos Endothelial-NO ROS? PDE5 enos? PDE5 Endothelial-NO Priapism Restore Normal Penile Vascular Homeostasis

31 Effect of Chronic PDE5 Inhibitor Therapy on Erectile Responses in Wild Type and Transgenic Sickle Cell Mice Frequency (erections/hr) WT WT+sild + Sildenafil T (100 mg/kg day) SSickle SS+sild Sickle + Sildenafil (100 mg/kg day) 12 * n=7 8 4 WT * W ** ** AUC Post ICS (cm 2 ) n=6 ICS * ** 0 X Labels pre-cns post-cns pre-cns WT Y SEM WT+sild Y SEM post-cns SS Y SEM SS+sild Y SEM WT Hemi Sickle Sickle Sickle + sildenafil + Sildenafil 3 Week Sildenafil Treatment

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33 A New Observation Leads to a New Question and to a New Discovery

34 Role of NO and cgmp in Erections Sexual stimulation Corpus cavernosum Erection NO NANC Smooth muscle relaxation -- PDE5 inhibitor cgmp=cyclic guanosine monophosphate. GTP=guanosine triphosphate. NANC=nonadrenergic, noncholinergic neurons. NO=nitric oxide. PDE5=phosphodiesterase type 5.

35 I Sustained phosphorylation of nnos-s1412 after electrical stimulation of rat MPG. Intracavernous pressure increases with intrapenile injection of forskolin in wild-type but not nnos-/-mice or wild-type after L-NAME pretreatment. PNAS 109(2012),

36 Integrative Model of nnos and enos Regulation of Initiation and Maintenance of Erectile Function

37 NOS Roles in Penile Biology Function Erection Mediation Initiator Facilitator Erectile Tissue Preservation Vasculoprotector Anti-fibrosis agent Homeostasis Biochemical Modulator Isoform nnos α/β, enos P-nNOS, P-eNOS P-eNOS inos enos

38 Gladly I think of the days when all my members were limber, all except one Those days are certainly gone, now all my members are stiff, all except one -Goethe