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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 InstituteJohns Hopkins Medicine
Baltimore, Maryland
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
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
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
Nitric Oxide: A Factor in ErectileTissue 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, 1990.
2. Rajfer J et al. N Engl J Med 326:90-4, 1992.
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
17 July 1992, Volume 257, pp. 401-403 Science
Nitric Oxide Synthase is Localized to the Autonomic Innervation of the
Human Penis
Burnett AL, et al. J Urol 150:73-6, 1993.
Nitric Oxide Synthase Knockout Mice
Developed to investigate the involvement of nitric oxide in various biological functions1
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, 2004
2. Burnett AL, et al. J Androl 23, 92-97, 2002
Neuronal NOS Knockouts eNOS-dependent mechanisms are retained1
Lack nNOS (which encodes exon 2) but preserve nNOS splice variants2
nNOS β is expressed and is physiologically relevant3
1. Burnett AL, et al. Molec Med 2, 288-296 (1996)2. Gonzalez-Cadavid NF, et al. Biol Reprod 63, 704-714 (2000)3. Hurt KJ, et al. Proc Natl Acad Sci 103, 3440-3443 (2006)
Endothelial NOS Knockouts
Display supra-normal erections to electrophysiologic stimulation1
Display attenuated erections to pharmacologic stimulation2
1. Burnett AL, et al. J Androl 23, 92-97 (2002)
2. Hurt KJ, et al. PNAS 99, 4061-4066 (2002)
www.pnas.org/cgi/doi/10.1073/pnas.052712499 PNAS I March 19, 2002 I vol. 99 I no. 6 I 4061-4066
NO/eNOS Amplification System
Towards Better Penile Health:Hypothesis
Vasoactive Therapy
Erectile Tissue Relaxation
Intrapenile Blood Flow Stimulation
Activation of Endothelial NOS
Penile Vascular Repair and Restoration
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 102:1661-66, 2005.
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
Interim Summary:Hypothesis
Sickle Cell Disease PDE5 Inhibitor Therapy
eNOS
eNOS
PDE5
PDE5
Priapism Restore Normal Penile Vascular Homeostasis
PenileVasculature Endothelial-NO
Endothelial-NO
?ROS ?
pre-CNS post-CNS0
4
8
12 *n=7
WT+sildSSSS+sild
*
****
WT
X Labels
pre-CNSpost-CNS
WTY SEM0.600.95
0.50180.6037
WT+sildY SEM0.761.15
0.64390.9517
SSY SEM
5.209.67
1.9671.724
SS+sildY SEM2.644.33
0.73490.9434
Freq
uenc
y(e
rect
ions
/hr)
Effect of Chronic PDE5 Inhibitor Therapyon Erectile Responses in Wild Type
and Transgenic Sickle Cell Mice
WT Sickle Sickle + sildenafil0
5
10
15
20
25ICS
*n=6
**
AUC
Pos
t IC
S (c
m2 )
WT
3 Week Sildenafil Treatment
Hemi Sickle+
Sildenafil
WTWT + Sildenafil (100 mg/kg day)SickleSickle + Sildenafil (100 mg/kg day)
Role of NO and cGMP in Erections
PDE5 inhibitor
Sexualstimulation
Smoothmusclerelaxation
Erection
Corpus cavernosum
NO
--
NANC
cGMP=cyclic guanosine monophosphate. GTP=guanosine triphosphate. NANC=nonadrenergic, noncholinergic neurons. NO=nitric oxide. PDE5=phosphodiesterase type 5.
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), 16624-9
NOS Roles in Penile Biology
Function Isoform
Erection Mediation
Initiator nNOS α/β, eNOS
Facilitator P-nNOS, P-eNOS
Erectile Tissue Preservation
Vasculoprotector P-eNOS
Anti-fibrosis agent iNOS
Homeostasis
Biochemical Modulator eNOS