Sildenafil inhibits the up-regulation of phosphodiesterase type 5 elicited with nicotine and tumour necrosis factor-alpha in cavernosal vascular smooth muscle cells: mediation by superoxide.
OBJECTIVE
To determine whether there is an association between vascular phosphodiesterase type 5 (PDE-5) and NADPH oxidase (NOX) in cavernosal vascular smooth muscle cells (CVSMCs), and to study the actions of the PDE-5 inhibitor sildenafil; the pro-erectile actions of nitric oxide (NO) are reduced by PDE-5 which hydrolyses cGMP to inactive GMP, thus an up-regulation of PDE-5 and over-production of O(2)(-) derived from NOX might promote erectile dysfunction (ED).


METHODS
To study the effects of nicotine and tumour necrosis factor-alpha (TNF-alpha) on superoxide (O(2)(-)) production and PDE-5 expression, CVSMCs from rabbit penis were incubated with nicotine or TNF-alpha, and superoxide dismutase (SOD), catalase, sildenafil citrate, or apocynin (NADPH inhibitor) for 16 h. The expression of PDE-5 and of glyceraldehyde-3-phosphate dehydrogenase (internal standard) was assessed using Western blotting. O(2)(-) was measured spectrophotometrically.


RESULTS
After a 16-h incubation, both nicotine (maximal at 10 microm) and TNF-alpha (10 ng/mL) significantly increased O(2)(-) formation in CVSMCs; this effect was blocked by co-incubating with SOD, catalase, and sildenafil (1 microm). Apocynin also inhibited O(2)(-) formation when added after 16-h incubation with nicotine (10 microm) or TNF-alpha. PDE-5 expression was also significantly increased in CVSMCs incubated with nicotine and TNF-alpha. This effect was negated by 16-h co-incubation with SOD, catalase, apocynin, and sildenafil.


CONCLUSIONS
Nicotine and TNF-alpha up-regulate PDE-5 expression in CVSMCs through an a priori up-regulation of NOX and formation of O(2)(-). As PDE-5 hydrolyses cGMP, this effect might 'blunt' the pro-erectile actions of NO. Sildenafil inhibits O(2)(-) formation, and 'normalizes' PDE-5 expression. This represents a novel pathogenic mechanism underlying ED, and a novel mechanism of action of sildenafil.
Hotston
Matthew R
MR
Department of Urology, Bristol Royal Infirmary, Bristol, Avon, UK. matthotston@hotmail.com
Jeremy
Jamie Y
JY
Bloor
Jonathan
J
Koupparis
Anthony
A
Persad
Raj
R
Shukla
Nilima
N
D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism*; D000818:Animals; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D018783:Impotence, Vasculogenic / Q000188:drug therapy; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000201:enzymology; D019255:NADPH Oxidases / Q000378:metabolism; D009538:Nicotine / Q000494:pharmacology*; D010413:Penis / Q000201:enzymology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology*; D011687:Purines / Q000494:pharmacology; D011817:Rabbits; D000068677:Sildenafil Citrate; D013450:Sulfones / Q000494:pharmacology*; D013481:Superoxides / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects
D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D014409:Tumor Necrosis Factor-alpha; D013481:Superoxides; D009538:Nicotine; D000068677:Sildenafil Citrate; D019255:NADPH Oxidases; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5