Testosterone and phosphodiesterase type-5 inhibitors: new strategy for preventing endothelial damage in internal and sexual medicine?

Abstract

Normal vascular endothelium is essential for the synthesis and release of substances affecting vascular tone (e.g. nitric oxide; NO), cell adhesion (e.g. endothelins, interleukins), and the homeostasis of clotting and fibrinolysis (e.g. plasminogen inhibitors, von Willebrand factor). The degeneration of endothelial integrity promotes adverse events (AEs) leading to increased atherogenesis and to the development of vascular systemic and penile end-organ disease. Testosterone (T) is an important player in the regulation of vascular tone through non-genomic actions exerted via blockade of extracellular-calcium entry or activation of potassium channels; also, adequate T concentrations are paramount for the regulation of phosphodiesterase type-5 (PDE5) expression and finally, for the actions exerted by hydrogen sulphide, a gas involved in the alternative pathway controlling vasodilator responses in penile tissue. It is known that an age-related decline of serum T is reported in approximately 20 to 30% of men whereas T deficiency is reported in up to 50% of men with metabolic syndrome or diabetes. A number of laboratory and human studies have shown the combination of T and other treatments for erectile dysfunction (ED), such as PDE5 inhibitors, to be more beneficial in patients with ED and hypogonadism, who fail monotherapy for sexual disturbances.The aim of this review is to show evidence on the role of T and PDE5 inhibitors, alone or in combination, as potential boosters of endothelial function in internal medicine diseases associated with reduced T or NO bioavailability, i.e. metabolic syndrome, obesity, diabetes, coronary artery disease, hyperhomocysteinemia, that share common risk factors with ED. Furthermore, the possibility of such a strategy to prevent endothelial dysfunction in men at increased cardiovascular risk is discussed.

Full text

Page 1

http://tau.sagepub.com
Therapeutic Advances in Urology
DOI: 10.1177/1756287209344992
2009; 1; 179 originally published online Sep 2, 2009; Therapeutic Advances in Urology
Antonio Aversa, Roberto Bruzziches, Davide Francomano, Marco Natali and Andrea Lenzi

damage in internal and sexual medicine?
Testosterone and phosphodiesterase type-5 inhibitors: new strategy for preventing endothelial
http://tau.sagepub.com/cgi/content/abstract/1/4/179

The online version of this article can be found at:

Published by:
http://www.sagepublications.com

can be found at:
Therapeutic Advances in Urology
Additional services and information for

http://tau.sagepub.com/cgi/alerts
Email Alerts:

http://tau.sagepub.com/subscriptions
Subscriptions:

http://www.sagepub.com/journalsReprints.nav
Reprints:

http://www.sagepub.co.uk/journalsPermissions.nav
Permissions:
http://tau.sagepub.com/cgi/content/refs/1/4/179
Citations
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.comDownloaded from

Page 2

Testosterone and phosphodiesterase
type-5 inhibitors: new strategy for
preventing endothelial damage in internal
and sexual medicine?
Antonio Aversa, Roberto Bruzziches, Davide Francomano, Marco Natali and Andrea Lenzi
Abstract: Normal vascular endothelium is essential for the synthesis and release of
substances affecting vascular tone (e.g. nitric oxide; NO), cell adhesion (e.g. endothelins,
interleukins), and the homeostasis of clotting and fibrinolysis (e.g. plasminogen inhibitors,
von Willebrand factor). The degeneration of endothelial integrity promotes adverse events
(AEs) leading to increased atherogenesis and to the development of vascular systemic and
penile end-organ disease. Testosterone (T) is an important player in the regulation of
vascular tone through non-genomic actions exerted via blockade of extracellular-calcium
entry or activation of potassium channels; also, adequate T concentrations are paramount
for the regulation of phosphodiesterase type-5 (PDE5) expression and finally, for the actions
exerted by hydrogen sulphide, a gas involved in the alternative pathway controlling vasodilator
responses in penile tissue. It is known that an age-related decline of serum T is reported in
approximately 20 to 30% of men whereas T deficiency is reported in up to 50% of men with
metabolic syndrome or diabetes. A number of laboratory and human studies have shown the
combination of T and other treatments for erectile dysfunction (ED), such as PDE5 inhibitors, to
be more beneficial in patients with ED and hypogonadism, who fail monotherapy for sexual
disturbances.
The aim of this review is to show evidence on the role of T and PDE5 inhibitors, alone or
in combination, as potential boosters of endothelial function in internal medicine diseases
associated with reduced T or NO bioavailability, i.e. metabolic syndrome, obesity, diabetes,
coronary artery disease, hyperhomocysteinemia, that share common risk factors with ED.
Furthermore, the possibility of such a strategy to prevent endothelial dysfunction in men at
increased cardiovascular risk is discussed.
Keywords: endothelial dysfunction, erectile dysfunction, phosphodiesterase type-5 inhibitors,
testosterone, cardiovascular disease, hydrogen sulphide, adenosine diphosphate
Introduction
The endothelium is the single layer of cells that
line the luminal surface of blood vessels. Over the
past few years, it has become increasingly appar-
ent that it is far more than just a structural lining
and has a range of important physiological func-
tions. The vascular endothelium is an active,
dynamic tissue that controls many important
functions on the vasculature, including regulation
of vascular tone, local hemostasis, proliferative
process, and maintenance of blood circulation,
fluidity, coagulation,andinflammatory
responses. Through these multiple functions,
the endothelium is primarily responsible for
enabling the arterial system to deliver sufficient
tissue perfusion [Haller, 1997; Vane et al. 1990].
Endothelial
increasing notoriety as a key player in the patho-
genesis of atherosclerosis [Ross, 1990]. As ather-
osclerosisisthemost
vasculogenic erectile dysfunction (ED) in older
men, the recognition of ED as a warning sign of
silent vascular disease has led to the concept that
dysfunction(EDys)hasgained
commoncause of
http://tau.sagepub.com179
Therapeutic Advances in UrologyReview
Ther Adv Urol
(2009) 1(4) 179?197
DOI: 10.1177/
1756287209344992
! The Author(s), 2009.
Reprints and permissions:
http://www.sagepub.co.uk/
journalsPermissions.nav
Correspondence to:
Antonio Aversa, MD, PhD
Dip.to Fisiopatologia
Medica, Room 37, Viale
Policlinico 155, 00161
Rome, Italy
antonio.aversa@
uniroma1.it
Roberto Bruzziches
Davide Francomano
Marco Natali
Andrea Lenzi
Department of Medical
Pathophysiology, Sapienza
University of Rome, Rome,
Italy
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.com Downloaded from

Page 3

a man with ED and no cardiac symptoms is a
cardiac (or vascular) patient until proven other-
wise [Solomon et al. 2003]. Vasculogenic ED
results from impairment of endothelial-depen-
dent or -independent smooth muscle relaxation
(functional vascular ED, initial stages), occlusion
of the cavernosal arteries by atherosclerosis
(structural vascular ED, late stages), or a combi-
nation of these. The association between ED and
clinical atherosclerosis has been documented
[Guay, 2007]. Furthermore, there is a high inci-
dence of cardiovascular disease (CVD) in men
with ED, and data suggest that ED may be an
early manifestation of EDys in the presence or
absence of cardiovascular risk factors (CRFs)
[Gazzaruso et al. 2008]. The presence of tradi-
tional CRFs, such as aging, smoking, hyperten-
sion, dyslipidemia, diabetes and obesity, and
some less-traditionalrisk
inflammation,hypoxia,
homocysteinemia, are known to cause EDys
[Brunner et al. 2005]. EDys frequently occurs
in acute coronary syndromes [Gonzalez and
Selwyn, 2003], heart failure, reperfusion injury,
renal failure, systemic inflammatory disorders
[Vlachopoulos et al. 2007] and ED [Bonetti
et al. 2003]. EDys is the key event in the patho-
physiology of ED and, importantly, men with
penile vascular damage may have EDys in other
vascular beds, as well [Kaiser et al. 2004].
Therefore, men with ED may be at increased
risk for cardiovascular adverse events (AEs)
and ED may be considered as a sentinel symp-
tom in patients with occult CVD [Thompsom
et al. 2005].
factors,
oxidative
including
stress and
The age-related testosterone (T) decline may
affect either arterial reactivity or sexual function
[Allan and McLachlan, 2004]. Hypogonadism
and ED in aging men are common disorders
found in patients presenting to andrology clinics.
Increasing evidence indicates that both disorders
have important associations with the metabolic
syndrome (MeS), diabetes and CVD, all condi-
tions with an increased morbidity and mortality
[Jones, 2007]. A low T-level is positively asso-
ciated with the presence and severity of athero-
sclerosis and a reduction in plasma T might
contribute to increased arterial stiffness, which
in turn has been associated with increased cardio-
vascular risk [Hougaku et al. 2006]. The early
recognition of these clinical conditions is impor-
tant to allow treatment and hence reduce cardio-
vascular risk. The increased incidence of CVD in
aging mencomparedwith premenopausal
women suggests an unfavourable effect of male
sex hormone T on the cardiovascular system.
However, numerous epidemiological and inter-
ventional studies reported a controversial rela-
tionship between T and CVD. T inversely
correlates with the severity of atherosclerosis
and has beneficial effects upon vascular reactivity,
inflammatorycytokine,
insulin resistance, serum lipids, and hemostatic
factors [Fukui et al. 2007]. Interestingly, men
with established coronary heart disease display
reduced circulating T levels [Rosano et al.
2007] that are often associated with a certain
degree of EDys independently of other vascular
risk factors (VRFs), suggesting a protective role
of endogenous T on the endothelium [Akishita
et al. 2007]. Thus, a modern approach to ED
should be geared not only towards ameliorating
the symptom of erectile inadequacy, but also
towards modifying the burden of any concomi-
tant medical conditions in which EDys plays a
pivotal role in worsening the course of disease
and thus contributing to the severity of ED
[Aversa et al. 2008a]. In this article, we shall dis-
cuss the role of T and PDE5-inhibitors to
improve endothelial and erectile functions and
their possible untoward effects on systemic
endothelial function/dysfunction deriving from
chronic exposure to these substances.
adhesionmolecules,
Endothelial function and dysfunction
In a normal physiologic state, healthy endothe-
lium serves as an anticoagulant membrane, exert-
ing predominantly fibrinolytic, anticoagulant and
anti-aggregatory effects. These effects occur
through the expression of anti-thrombin III (inhi-
biting fibrinogen to fibrin conversion), heparin-
like molecules (which enhance anti-thrombin III
activity), tissue factor pathway inhibitor (which
inactivates the extrinsic pathway)[Kharbanda
and Deanfield, 2001] and tissue-type plasmino-
gen activator (tPA) from intact endothelial cells
(ECs). Additionally, ECs bind thrombin, leading
to protein-C activation and eventually inactiva-
tion of plasminogen activator inhibitor-1 (PAI-1)
[Kharbanda and Deanfield, 2001]. In a haemo-
static response, ECs produce key components of
platelet activation and aggregation, including
von Willebrand factor (vWf), fibronectin and
thrombospondin, ultimately leading to the initia-
tion of the coagulation cascade [Sagripanti and
Carpi, 2000]. These dynamic thrombotic func-
tions are important, as thrombus formation is a
key element in atherosclerosis progression.
Therapeutic Advances in Urology 1 (4)
180 http://tau.sagepub.com
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.comDownloaded from

Page 4

The endothelium regulates transmigration of cir-
culating cells through a complex interplay of
trans-signaling molecules. ECs recruit inflamma-
tory cells via expression of cell adhesion molecules
(CAMs) such as selectin and immunoglobulin
superfamily adhesion molecules, and by respond-
ing to pro-adhesion signals from circulating cyto-
kines [Panes et al. 1999]. Platelets also have a
range of endothelial signalling abilities, including
the release of vasodilating agents (such as
adenosine diphosphate and serotonin), as well as
vasoconstricting and procoagulant factors (such
as endothelin-1 and vWf). The effects of these
circulating cell signals can further be attenuated
by some endothelially-derived substances such as
nitric oxide (NO) and prostacyclin [Kharbanda
and Deanfield, 2001]. The vascular endothelium
also playsan obligatoryrole invasodilation.These
effects are mediated in large part by the action of
endothelial derived nitric NO which has vasodila-
tory properties. NO is also known to inhibit
platelet activation/aggregation, vascular smooth
muscle proliferation, leukocyte adherence, and
low density lipoprotein oxidation, all of which
areknown tocontribute
Endothelial nitric oxide synthase (eNOS), one of
three nitric oxide synthase (NOS) isoforms, is
responsible for the majority of endothelium
derived production of NO from the substrate
L-arginine [Vane et al. 1990]. Bioavailable NO
can be increased by enhancing its production or
reducing its inactivation. As a freely diffusible gas,
NO acts not only within the lumen but also on
the surrounding smooth muscle cells where it
increasescyclicguanosine
(cGMP)-mediated vasodilation [Kharbanda and
Deanfield, 2001]. In contrast, the endothelium
also produces vasoconstricting hormones known
as the endothelins [Maas et al. 2002]. A number
ofnovelplasmamarkershavebeenassociatedwith
atherosclerosis and EDys, and the latter can be
tested in vivo using several techniques that rely
principally on measuring change in arterial diam-
eter or flow in response to stimuli, and in vitro
using circulating biomarkers, such as high-
sensitivity C-reactive protein, P-selectin, CAMs
and endothelial progenitor cells (EPCs) in clinical
studies [Farouqueand
Longitudinal observations confirmed that EDys
of the coronary and peripheral circulation is pre-
dictiveofcardiovascular events,thesensitivityand
specificity being greater for coronary artery EDys
than for peripheral dysfunction [Vita and Keaney,
2002].
toCVDstates.
monophosphate
Meredith,2001].
The mechanism underlying EDys induced by
CRFs, such as diabetes, hypertension, smoking
and dyslipidemia, involves two processes: the
inhibition of dimethylarginine dimethylaminohy-
drolase, which catalyses the hydrolysis of asym-
metric dimethyl arginine (ADMA), an inhibitor
of eNOS [Boger, 2003]; and the uncoupling of
eNOS activity [Watts et al. 2007]. Down-regula-
tion of eNOS with these diseases results in
reduced bioavailability of NO which determines
EDys. The guanidino dimethyl arginine deriva-
tives ? symmetric (SDMA) and ADMA are
derived from degradation of methylated proteins
and are found in plasma [Krzyzanowska et al.
2008]. ADMA, in contrast to SDMA, has been
shown to inhibit NOS, reduce NO levels and to
beassociatedwith
[Valkonen et al. 2001]. ADMA levels are ten
times higher inside ECs [Elesber et al. 2006].
Both processes increase oxidative stress in the
ECs [Cooke, 2005]. This increase in oxidative
stress leads to further oxidative catabolism of
NO, formation of peroxynitrite, and activation
of the proinflammatory nuclear factor kappa B,
which in turn induces cellular inflammation and
adhesion molecule production [Cooke and Dzau,
1997]. One potent free radical, superoxide anion,
inactivates NO resulting in the production of per-
oxynitrite ? a potent oxidant that stimulates the
production of vasoconstrictor prostanoids. NO
production is also reduced in the presence of
free radicals. Oxidative stress leads to the up-
regulation of anti-oxidation enzymes, such as
superoxide-dismutase, producing hydrogen per-
oxide [Browne et al. 2003]. These mechanisms,
andthe reductionin
endothelial progenitor cells (EPCs), could under-
pin a common pathogenesis for both ED and
EDys [Baumha ¨kel et al. 2006]. In individuals
with established ED, an elevated ADMA level
has been shown to correlate with the severity of
comorbidities, such as in patients with renal dis-
ease [Kielstein et al. 2001], insulin resistance and
diabetes [Schiel et al. 2003], and CAD [Browne
et al. 2003; Lu et al. 2003], indicating the
impactthatADMA
endothelial function [Wierzbicki et al. 2006].
cardiovascularevents
bone-marrow-derived
levels could haveon
EDys is an important component of the meta-
bolic or insulin resistance syndrome, as demon-
stratedby inadequate
paradoxical vasoconstriction in coronary and
peripheral arteries in response to stimuli that
release NO [Cersosimo and DeFronzo, 2006].
Other distinct non-metabolic
vasodilation and/or
branchesof
A Aversa, R Bruzziches et al.
http://tau.sagepub.com 181
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.comDownloaded from

Page 5

insulin-signaling pathways regulate secretion of
the vasoconstrictor endothelin-1 in endothelium.
Metabolic insulin resistance is characterized by
pathway-specific impairment in phosphatidylino-
sitol 3-kinase-dependent signaling, which in
endothelium may cause imbalance between pro-
duction of NO and secretion of endothelin-1,
leading to decreased blood flow, which worsens
insulin resistance [Kim et al. 2006]. Deficiency
of endothelial-derived NO is believed to be the
primary defect that links insulin resistance and
EDys. NO deficiency results from decreased syn-
thesis and/or release, in combination with exag-
gerated consumption in tissues by high levels of
reactive oxygen (ROS) and nitrogen (RNS) spe-
cies, which are produced by cellular disturbances
in glucose and lipid metabolism. EDys contri-
butes to impaired insulin action, by altering the
transcapillary passage of insulin to target tissues.
Reduced expansion of the capillary network, with
attenuation of microcirculatory blood flow to
metabolically active tissues, contributes to the
impairment of insulin-stimulated glucose and
lipid metabolism. This establishes a reverberating
negative feedback cycle in which progressive
EDys and disturbances in glucose and lipid
metabolism develop secondary to the insulin
resistance [Kim et al. 2006].
The recent discovery that circulating endothelial
microparticles (EMPs) are a hallmark of EDys
[Brodsky et al. 2004] and that circulating EPCs
of bone marrow origin contribute to the regener-
ation of damaged endothelium has opened up
exciting avenuesof research
Clermont et al. 2005]. EPCs play a key role in
promoting endothelial repair processes after dif-
ferent injuries and their circulating levels are inti-
mately correlated with the degree of vascular
response to vasoconstrictor stimuli; in other
words, the higher the EPCs, the better the vaso-
dilator arterial response to shear stress. A low
number of circulating EPCs is supposed to be an
independentriskfactorforcoronaryheartdisease.
Recent studies demonstrated a reduction of
EPCs in patients with chronic heart failure
[Valgimigli et al.2004] orendothelial dysfunction
[LinksHeiss et al. 2004]. In subjects with the
MeS,circulatingEPCs
decreased by clustering components of the syn-
drome [Fadini et al. 2006], and their levels nega-
tively correlate with the homeostasis model
assessment value, a measure of insulin resistance.
Virtually all risk factors for atherosclerosis have
been associatedwith
[Goldschmidt-
aresynergistically
decreasedlevels of
circulating EPCs, while absent or insufficient
EPCs in patients with endothelial-cell injury
may affect the progression of cardiovascular dis-
ease, with EPCs as an independent predictor of
cardiovascular outcomes [Werner et al. 2007].
The finding that men with ED of any origin have
reduced number of EPCs and that men with type-
2 diabetes [Esposito et al. 2007] or who are over-
weight [Esposito et al.2009] haveincreased levels
of EMPs which are independently involved in the
pathogenesis of ED, opens a new scenario for the
application of these potential novel markers in
the early detection of ED. However, there is still
a matter of debate as to whether any reliable sur-
rogate marker of EDys in cardiovascular medicine
may be applied [Braunwald, 2008]. We can con-
clude that endothelial integrity has a paramount
role in preserving a man from cardiovascular and
genital organ injuries.
Hyperhomocysteinemia (HHcy) is considered
one of the most important CRFs increasing con-
siderably the risk of stroke and myocardial infarc-
tion. With respect to endothelial function, direct
effects of HHcy on vascular endothelial cells have
been demonstrated through the reduction of
endothelial NO production. Also, the presence
of mild elevations of plasma total homocysteine
has been identified as an independent risk factor
for early atherosclerotic vascular disease [Nyga ˚rd
et al. 1997]. Mild HHcy has a complex etiology,
including insufficient intake of vitamins B6 and
B12 and folate and genetic factors, of which an
homozygote mutation of 5-methylenetetrahydro-
folatereductase(MTHFR)thermolabilevariantis
probably the most important one (See Figure 1).
The mechanism of premature CVD or ED in this
context is not precisely known [Lombardo et al.
2004], but may be related to increased vulnerabil-
ity to lipid toxicity, vascular smooth muscle-cell
growth-factor properties
endothelial damage, or vasomotor dysfunction
or to disorders of platelet aggregation and coagu-
lation [Bellamy and McDowel, 1997].
ofhomocysteine,
Testosterone and endothelium
The cerebral vasculature is a target tissue for sex
steroid hormones. Estrogens, androgens, and
progestins modulate the function and pathophy-
siology of cerebral circulation [Krause et al.
2006]. Hypogonadism related-ED represents
the link between internal medicine and sexual
medicine, so far. T circulating-levels are determi-
nant for correct endothelial function, and tend
to a stepward decrease with aging and with
Therapeutic Advances in Urology 1 (4)
182http://tau.sagepub.com
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.com Downloaded from

Page 6

the
[Travison et al. 2007]. T plays a key role in coor-
dinating and facilitating the delicate balance
between the effect of endogenous vasoconstric-
tors and vasorelaxing agents of vascular tone
[Aversa et al. 2005; Thompson and Khalil,
2003]. This process is supported by the fact
that androgen receptors (ARs) have been loca-
lized within vascular endothelium and smooth
muscle-cells. Thus, arterial functions may be
directly subject to T influence and, most likely,
two independent pathways of T-induced effects
within the vessel wall can be assumed (i.e., geno-
mic and nongenomic) [Orshal and Khalil, 2004;
Wynne and Khalil, 2003]. The classic pathway of
androgen action involves steroid binding to the
AR,a ligand-activated
acting on the genome [Heinlein and Chang,
2002a; Kallio et al. 1996; Chang et al. 1995].
The genomic action of AR is modulated by a
large variety of coregulators, which are proteins
that fine-tune target gene expression by enhan-
cing (coactivators) or restraining (corepressors)
transcription [Lee and Chang, 2003; Heinlein
and Chang, 2002a]. Although T circulates
throughout the body, the factors responsible
forvariation intissue
remain to be further clarified. Intensity of
presenceofnumerouscomorbidities
transcriptionfactor
androgen sensitivity
expression of the single human AR [Kang et al.
2003; Lutz et al. 2003] partly defines androgen
sensitivity,butAR is
expressed to some degree in tissues. Further bio-
logic determinants of tissue androgen sensitivity,
including the functional AR polymorphisms as
well as tissue distribution and regulation of AR
coregulators, androgen metabolic enzymes, and
nongenomic mechanisms, remain to be better
defined so that their net integrated effects can
be more fully understood.
almost ubiquitously
Androgen sensitivity could be modulated by a
functional polymorphism of the AR that influ-
ences the strength of the genomic signal trans-
duced from its interaction with an androgen as a
bound ligand. One such functional AR poly-
morphism is the exon 1 triplet CAG (polygluta-
mine), whereby the repeat length is directly
correlated with T levels [Heinlein and Chang,
2002b]. There is now considerable evidence for
rapid, non-genomic effects of steroid, including
androgens [Cho et al. 2003]. Non-genomic ster-
oid action is distinguished from classic genomic
effects by rapid onset (seconds to minutes)
that is faster than genomic mechanisms; insensi-
tivity to inhibition of RNA and protein synthesis;
effects produced by steroids unstable to access
TESTOSTERONE
RegenerationApoptosis
Endothelial
progenitor cells
microparticles
PDE5 inhibitors
Genomic effect
Non genomic effect
Nos 1/2/3
PDE 5
Figure 1. Schematic representation of different pathways related to penile erection in humans controlled by
testosterone and phosphodiesterase type 5-inhibitors.
A Aversa, R Bruzziches et al.
http://tau.sagepub.com183
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.com Downloaded from

Page 7

the
membrane-impermeable macromolecules or in
cells lacking a nucleus); and not usually blocked
by classic antagonists resulting from different
steroidal specificity from classic cognate nuclear
receptors. As for other steroids, non-genomic
androgen effects characteristically involve the
rapid induction of conventional second-messen-
gersignal transduction
increases in cytosolic calcium and activation of
protein kinase A, protein kinase C, and MAP-
kinase, leading to diverse cellular effects, includ-
ingsmooth muscle relaxation,neuromuscular and
junctional signal transmission, and neuronal plas-
ticity [Aversa et al. 2005]. Most non-genomic
effects involve a membrane receptor, and puta-
tive-binding sites are described for all major
classes of steroids, including androgens [Herve,
2002; Gerdes et al. 2000]. No membrane AR
has been characterized, but preliminary evidence
of a low-affinity microsomal membrane-binding
site for alkylated androgens [Chirino et al. 1989]
and an endothelial cell plasma membrane dehy-
droepiandrosterone(DHEA)-binding
[Williams et al. 2002] still require functional
proof of specific receptor status. A plasma mem-
brane sex harmone binding globuline (SHBG)
receptor capable of modulating androgen action
at the level of plasma membranes and initiating
intracellular cyclic 3’-5’ adenosine monopho-
sphate (cAMP) signaling has been described in
humans. The SHBG receptor remains to be fully
characterized, anditis notclear whether ithas any
physiological role in species like rodents that lack
circulating SHBG [Rosner et al. 1999].
nucleus (eithercovalentlylinkedto
cascades,including
site
Recent animal and in vitro studies have further
documented that T up-regulates the expression
of arterial AR mRNA and is associated with an
inhibitory effect on neo-intimal plaque formation
[Hanke et al. 2001]. Additionally, positive acute
hemodynamic effects of T on coronary vasomo-
tion and stress-test induced ischemia were
reported [Rosano et al. 1999]. Vascular ARs
may mediate these effects of T on the arterial
wall, and T has been shown to produce coronary,
aortic, and brachial vasculature dilatation by acti-
vation of both endothelial-dependent and -inde-
pendent mechanisms
Endothelium-dependent effects of T are likely
mediated, at least in part, through NO produc-
tion, whereasmechanisms
independent effects involve one or more types
of smooth muscle ion conductance channels
[Littleton-Kearneyand
[Chou
et al. 1996].
ofendothelium-
Hurn,2004]. The
interaction of Twith its specific nuclear receptors
may trigger not only long-term genomic effects,
but also acute non-genomic vasodilator responses
[Wynne and Khalil, 2003]. T may activate the
endothelium and stimulate the NO-cGMP and/
or the hyperpolarization-mediated vascular relax-
ation pathway and may thus represent potential
beneficial effects of T against coronary artery
atherosclerosis. Additional
pendent effects of T may involve inhibition of
the signaling mechanism of vascular smooth
muscle contraction such as intracellular concen-
tration [Ca2+] and protein kinase C, whereas a
significant portion of the vasorelaxing effect of T
appears to be endothelium independent because
no significant difference is observed between the
relaxing effect of the hormone in isolated vessels
with or without endothelium [Crews and Khalil,
1999]. Also, inhibition of NO-synthase, prosta-
glandin synthase, and guanylate cyclase do not
appear to affect the vasorelaxing effect of T, sug-
gesting that the T-induced vascular relaxation
may involve inhibition of the mechanism of vas-
cular smooth muscle contraction [Murphy and
Khalil, 1999; Yue et al. 1995]. Several studies
have shown that acute administration of T
induces a rapid relaxation in vascular tissues of
different species including humans [Costarella
et al. 1996; Perusquia et al. 1996], suggesting a
non-genomic effect of this hormone on vascular
reactivity[English
et al.
mechanisms have been proposed to explain
T-induced vasodilatation [Tep-Areenan et al.
2002] but it remains a matter of debate which
is the effective mechanisms and which are the
mediators involved of the T-induced vasorelaxa-
tion. T might induce relaxation in human iso-
lated corpora cavernosa strips by activation of
smooth muscle adenosine triphosphate-sensitive
K(+)channels. This finding suggests that T, in
addition to its known endothelial action, might
regulate erectile function locally by its action on
the smooth muscle of the human corpus caver-
nosum [Yildiz et al. 2009]. By contrast, contrac-
tile studies suggested that T may enhance
thromboaxane A2 (TXA2)-induced coronary
vasoconstriction in guinea pigs [Schro ¨r et al.
1994]. Androgens may also regulate the expres-
sion and density of TXA2 receptors in cultured
rat aortic and guinea pig coronary smooth-
muscle cells [Higashiura et al. 1997]. TXA2
acts through membrane surface receptors to
aggregate platelets by both constricting or mod-
ulating the proliferation vascular smooth-muscle
cells [Aiayi et al. 1995]. Any systemic vascular
endothelium-inde-
2002].Different
Therapeutic Advances in Urology 1 (4)
184 http://tau.sagepub.com
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.comDownloaded from

Page 8

effect of T, therefore, is likely to be a balance of
vasodilatation by endothelial and non-endothelial
effects and vasoconstriction resulting from TXA2
andpossiblyother mediators[Hondaet al.1999].
Recently, hydrogen sulphide (H2S) has been
shown to act as gaseous modulator on rat vascu-
lar system both in vivo [Zhao et al. 2003] and in
vitro [Hosoki et al. 1997]. H2S is an endogenous
gas produced in mammals from L-cysteine by
two different enzymes: cystathionine ?-synthe-
tase (CBS), predominantly present in the central
nervoussystem,and
(CSE), predominantly localized in the cardiovas-
cular network [Levonen et al. 2000; Yap et al.
2000; Van der Molen et al. 1978]. The finding
that activation of K-channels is involved in
T-induced vasodilatation [Deenadayalu et al.
2001; Ding and Stallone, 2001] led to the
hypothesis of a possible involvement of H2S as
a mediator involved, since drugs that block
KATP channels, such as glibenclamide, have
been shown to block the relaxant effect caused
by exogenous H2S [Cheng et al. 2004; Zhao
et al. 2001]. In a recent study, Bucci et al. ele-
gantly suggested that the T non-genomic vascular
effect might involve the L-cysteine/H2S pathway.
In particular, the data presented demonstrated
that, in rat aorta, the non-genomic effect of T is
linked to a positive modulation of CSE/CBS
activity. The H2S produced acts on KATPchan-
nels, contributing to the vasodilator effect of T.
Thus, H2S involvement in the vascular activity of
T may help to explain the beneficial effects of T
on the cardiovascular system [Bucci et al. 2008].
On this basis, preliminary animal studies have
suggested the involvement of H2S in facilitating
erectile function [Srilatha et al. 2007, 2006].
However, the involvement of a functionally
intact L-Cys/H2S pathway in human penile erec-
tion has not yet been demonstrated. In a recent
work, by using human corpora obtained by a
standardized surgical procedure, it has been
demonstrated that human penile tissue expresses
both CBS and CSE, and tissue homogenates effi-
ciently convert L-Cys to H2S. Functional studies,
performed in vitro, confirm that the L-Cys/H2S
pathway plays a functional role in human tissue.
Indeed, either sodium hydrogen sulfide (NaHS),
an exogenous source of H2S, or L-Cys, the
substrate for CBS/CSE, relaxed HCC strips in a
concentration-related manner. Pharmacological
modulation of CBS and CSE by using a CSE
inhibitor and/or a CBS inhibitor confirmed the
involvement of the L-Cys/H2S pathway both in
cystathionine
?-lyase
vitro and in vivo in rats. Collectively, these obser-
vations indicate that a functional L-Cys/H2S
pathway may be involved in mediating penile
erectionin humans
[D’Emmanuele di Villa Bianca et al. 2009].
(see Figure 1).
andother mammals
Moreover, the recent finding that hypotestoster-
onemia is associated with a low number of
circulating EPCs in young hypogonadotropic
hypogonadal patients [Foresta et al. 2006] and
that T replacement is able to revert EPC reduced
counts through a direct stimulatory effect on the
bone marrow, [Foresta et al. 2008] clearly sug-
gests a new potential field of application for T
replacement therapy. Pilot studies suggest that
T may have a role as an antiatherogenic therapy,
by preserving endothelial and smooth-muscle cell
integrity; also, recent evidence demonstrated that
androgen deprivation for prostate cancer may
reduce insulin sensitivity, thus suggesting a key
role for T in the development of insulin resis-
tance/MeS also [Smith et al. 2006].
PDE5-inhibitors and endothelium
The PDE5-inhibitors (PDE5-i) have revolutio-
nized the management of ED since they appeared
toofferadvantages
approaches in terms of ease of administration
and costs, and oral drug treatment with PDE5-i
is now widely advocated as first-line therapy.
These agents act by potentiating the action of
intracavernosal NO, thereby leading to a more
sustained erection.Sildenafil
PDE5-i to be released and has been studied
extensively. Subsequently two other agents ? var-
denafil and tadalafil ? have been introduced. All
of these drugs have been shown to be effective
across a wide range of ED etiologies and have
been shown to improve erectile function, pene-
tration and maintenance of erection, resulting in
more successful intercourse. Their effects are
greater at higher doses [Lugg et al. 1995].
Sildenafil and vardenafil are short-acting agents,
while tadalafil is a long-acting agent thus allowing
the user more flexibility in planning sexual activ-
ity [Aversa et al. 2006]. Although the various
classes of PDE5-i differ with respect to selectivity
and pharmacokinetic profiles, their efficacy and
safety are almost comparable in broad popula-
tions of men with ED. PDE5-i have no effect
on the penis in the absence of sexual stimulation.
The ability of a drug to select the target tissue
(penis) while bypassing other tissues (vascular
system) depends upon the fact that human
over othermedical
wasthefirst
A Aversa, R Bruzziches et al.
http://tau.sagepub.com185
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.comDownloaded from

Page 9

corporeal smooth muscle is known to be rich in
PDE5, which is abundant in the aorta and in
some part of the peripheral vascular smooth
muscle [Mercapide et al. 1999]. Experimental
findings support the fact that chronic administra-
tion of PDE5-i may regulate the transduction
pathway leading to the activation of endothelial-
NOS but has no effect on NO bioavailability or
on the cGMP pathway, thereby eliminating a
possible concernfor
Roussel et al. 2005].Since PDE5-i are widely
used in treating male ED, it has been recently
hypothesized that they may exert also important
systemic effects, at the endothelial level, as well
[Reffelmann and Kloner, 2006].
tachyphylaxis [Behr-
Recent research focused on PDE5-i has proven to
be of great impact in the treatment of numerous
human extra-sexual diseases [Aversa, 2008b].
In fact, specific inhibitors of members of the
PDE super family are currently being investigated
for the treatment of asthma, acute ischemic
stroke,cancer,systemicinflammation,pulmonary
hypertension,andmanyotherconditionsandthey
have been approved for clinical use in the treat-
ment of claudicatio intermittens, congestive heart
failure, chronic obstructive pulmonary disease
[Lin, 2003]. The distribution of PDE activity
has been determined with anti-PDE1 and anti-
PDE5 antibodies in the human cardiac ventricle
and saphenous vein, and in vitro studies were per-
formed on the isolated human cardiac ventricle,
corpora cavernosa, saphenous vein, and mesen-
tericarteryaswellasonrabbitaorta,dogcoronary
artery, dog trabecular tissue, and rabbit and
human platelets. In fact, sildenafil selectively
increases cGMP levels in coronary vascular
smooth muscle tissue but produces no change in
cyclic adenosine monophosphate (cAMP) levels,
which is consistent with the drug’s selectivity for
PDE5[Walliset al.1999].Aninterestingstudyby
Turko et al. showed that sildenafil stimulates
cGMP binding to the allosteric sites of PDE5 by
interacting at the catalytic site of this enzyme, but
the drug does not compete with cGMP for bind-
ing at the allosteric sites. In that study, it was con-
cludedthattheselectivityandpotencyofsildenafil
was likely to be provided by a non-conserved res-
idue or residues of specific aminoacids in the
PDE5 catalytic domain [Turko et al. 1999].
As already outlined above, the event that triggers
EDys is represented by the reduction of the over-
all antioxidant pool [Parodi et al. 2007] with the
consequent reduced response to oxidative stress
and the activation of several pro-atherogenic pro-
cesses: reduction of NO bioavailability; increased
levels of circulating free fatty acids, with subse-
quent sub-endothelial storage of lipid depots and
increased smooth-muscle cell proliferation of the
media layer of the vascular wall [Marks et al.
1995]. Pro-inflammatory and -infective processes
may in turn contribute to activate and amplify the
acute endothelial injury thus perpetuating such a
vicious circle. In early atherogenic lesions, EDys
causes adhesion and migration of monocytes and
T-lymphocytes in the vascular inner layer in
response to increased endothelial production of
intercellular molecules, i.e. selectin, VCAM-1
and ICAM-1 that may quench NO [Basta et al.
2004]. This process may concur to determine
impaired arterial inflow to the penis, thus contri-
buting to persistent ED.
Growing evidence indicates that PDE5-i have a
beneficial effect on inflammatory activation and
surrogate markers of EDys. Although exact
mechanisms are not fully known, the basis for
these anti-inflammatory effects is the increased
activity of the NO-cyclic guanosine monopho-
sphate (NO-cGMP) axis [Vlachopoulos et al.
2005]. Through their up-regulation of nicotina-
mideadenine dinucleotide
(NADPH)-oxidase, cytokines not only increase
formation of superoxide, but they also up-regu-
late the expression of PDE5. PDE5-i antagonize
these inflammatory effects by enhancing the NO-
cGMP pathway, which, apart from augmenting
smooth-muscle-cell relaxation, inhibits NADPH-
oxidase expression/activity [Hotston et al. 2007].
Beneficial acute and chronic effects of sildenafil
on arterial function in men with ED are well
known [Desouza et al. 2002]. Given the unfa-
vourable effect of inflammation on arterial func-
tion, this effect could be partly attributed to a
robust anti-inflammatory action of daily sildenafil
[Aversa et al. 2008c]. In a pilot study, a 4-week
treatment with tadalafil every other day produced
a favourable effect on endothelium-dependent
vasodilatation of cavernous arteries compared
with an on-demand dosage in men with ED of
any origin. In that study, positive effects on mar-
kers of endothelial function and inflammation,
including VCAM and ICAM, ET-1, and high-
sensitivity C-reactive protein, as well as on insulin
were also found [Aversa et al. 2007a]. Daily
tadalafil also significantly decreased hypoxia-
induced up-regulation of tumor-necrosis factor
alpha (TNF-a) and interleukin-1 beta (IL-1ß)
expression in pulmonary arteries and improved
phosphate
Therapeutic Advances in Urology 1 (4)
186http://tau.sagepub.com
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.comDownloaded from

Page 10

erectile function in diabetic men, representing a
preferred dosing option when compared with on-
demand administration [Buvat et al. 2006].
Thus, an emerging role in the management of
ED patients seems to be the possible use of
daily dosing with a threefold purpose: First,
recovery of non-responders to on-demand ther-
apy; second, rehabilitation of erectile function
which means endothelial rehabilitation; and
third, modification of hormonal patterns, thus
adding clinical evidence to the possibility of alter-
native regimens producing multiple systemic
benefits [Bruzziches et al. 2008]. There is grow-
ing evidence that patients presenting with ED
should be investigated for CVD, including dia-
betes, even if they have no symptoms. HHcy,
known to be an important risk factor for EDys,
seems to be an important determinant in ED
especially in diabetic
et al. 2008]. The relationship between HHcy
and low arterial blood supply to penile arteries
in patients with ED [Demir et al. 2006] suggests
that adopting strategies to reduce HHcy may
offer the potential of improving the functioning
of the entire vascular system thus turning out a
men who is a PDE5-i non-responder into a
responder [Lombardo et al. 2004]. On the basis
of currently available evidence, it is possible to
hypothesize that EDys and systemic cardiovascu-
lar pathology may be modulated by daily PDE5
inhibition, resulting in improved erectile function
owing to effects upon both local and systemic
targets. Unlike pulmonary hypertension, for
which sildenafil may provide a net cost saving
compared with inhaled or intravenous medica-
tions [Vida et al. 2007], daily PDE5-i use may
be actually limited by high costs, given the aver-
age course frequency of five to six times per
month. Should lower-dose daily administration
confirm attractive efficacy and safety profiles
compared with on-demand use, and equivalent
net monthly cost approach, once-a-day PDE5-i
use will become an important treatment option
especially in complicated patients [Aversa et al.
2007b].
patients[Al-Hunayan
The endothelium links internal to sexual
medicine
Since the metabolic aspect of ED is rather
neglected or not sufficiently treated, it is our
opinion that ED should mark the starting point
for the evaluation and prevention of significant
severe diseases (such as diabetes, dyslipidemia,
atherosclerosis, hypertension,
pathy, etc.) hitherto unknown by the patients
CAD,neuro-
[Foresta et al. 2009], all of which contribute to
CVD and are associated with EDys. These
abnormalities frequently cluster in individuals,
and the term MeS is now widely used to define
this cluster. On the other hand, many established
therapies for CVD, such as ?-blockers, angioten-
sin converting enzyme inhibitors (ACE-i), and
statins, have been investigated for their impacts
on the process of atherosclerosis and EDys
[Shindel
et al. 2008].
demonstrated that statin treatment increases the
number of EPCs and improves EPC function.
[Llevadot et al. 2001]. Moreover, statin therapy
is able to promote vascular repair after balloon
injury mediated by EPC [Walter et al. 2002].
By contrast, it has been reported that the statin
dose during chronic and continuous treatment
independently predicts reduced numbers of cir-
culating as well as isolated EPCs in patients with
CAD [Hristov et al. 2007]. A significant effect of
statins in lowering total T and SHBG levels in a
population of men with type-2 diabetes has been
recently demonstrated [Stanworth et al, 2009].
These findings have important implications for
the diagnosis of hypogonadism not only in dia-
betic men receiving statin treatment but also
other drugs that are able to directly inhibit T
synthesis, i.e. antiandrogens, antifungals. There
is growing evidence that ED can be considered
as a useful surrogate marker for CAD, with stu-
dies showing that a large proportion of men
develop the problem before cardiac symptoms
become evident [Aversa and Bruzziches, 2007].
One study showed that ED symptoms occurred
before symptoms of CAD in 67% of men in a
consecutive series presenting with chest pain
and angiographically documented CAD. Of par-
ticular note, all patients with type-1 diabetes and
ED developed sexual dysfunction before CAD
onset [Montorsi et al. 2003a]. Gazzaruso et al.
also evaluated the presence of ED in 133 uncom-
plicated type-2 diabetic men with angiographi-
cally verified silent CAD and in 127 type-2
diabetic men without myocardial infarction at
exercise ECG, 48-h ambulatory ECG and stress
echocardiography. The findings showed a strong,
independent association between ED and silent
CAD in apparently uncomplicated type-2 dia-
betic patients [Gazzaruso et al. 2004]. The
obvious reason why ED may present before
other signs of CVD is because penile artery
diameter is smaller (1?2mm) than the coronary
artery (3?4mm) or carotid artery (5?7mm), so
the symptoms associated with atherosclerosis
occur sooner (the ‘artery size’ hypothesis).
Recentstudies have
A Aversa, R Bruzziches et al.
http://tau.sagepub.com187
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.com Downloaded from

Page 11

These studies have demonstrated that cardiovas-
cular assessment of men with ED enables the
detection of CVD and has been showed that
ED presented well before angina symptoms of
CAD in two-thirds of men with a mean time
interval of almost 3 years [Kaiser et al. 2004;
Montorsi et al. 2003b]. Another study revealed
that 45% of men with ED had previously undiag-
nosed hyperlipidemia, 5% had undiagnosed dia-
betes and 7% had undiagnosed hypertension
[Billups and Friedrich, 2000]. Kaiser et al. also
looked at whether patients with vascular ED and
no other clinical CVD had structural and func-
tional abnormalities at other levels. The vascular
parameters of 30 patients with ED (and 27 age-
matched normalcontrols)
Results showed that patients with ED have a
peripheral vascular defect in endothelium-depen-
dent and -independent vasodilation that occurs
before the development of other overt functional
or structural systemic vascular disease and is
independent of other traditional risk factors
[Kaiser et al. 2004]. Detecting atherosclerosis
at this early stage could potentially prevent life-
threatening events by facilitating appropriate
intervention. This provides justification for inves-
tigating ED patients for other cardiovascular
symptoms. Preliminary diagnostic testing for
silent CAD by means of adenosine stress myocar-
dial perfusion scintigraphy in diabetic patients
with ED revealed that 45% of them had coronary
alterations in the presence of concomitant penile
artery damage as detected by penile ultrasound
[Corona et al. 2008]. However, for the future, it
will be important to perform studies in order to
assess the sensitivity, specificity and cost-effec-
tiveness of using ED as a marker for CVD
[Kirby et al. 2005]. Recent data suggest tadalafil
could exert prolonged beneficial effects on vascu-
larendothelialfunction
[Caretta et al. 2005]. In this view, once-a-day
dosing with tadalafil should be an attractive alter-
native especially for those ED patients with overt
EDys. We can speculate that precocious treat-
ment of these men with daily long-acting
PDE5-i, i.e. tadalafil, may represent a future
strategy for preventing or reducing the extent of
coronary dysfunction and/or myocardial infarc-
tion. A daily-based approach also may improve
organic ED at the level of vascular endothelial
function. Another possible explanation as to
why chronic PDE5-i may induce endothelial
rehabilitation comes from a recent study by
Ayala et al. [Ayala et al. 2007] that demonstrated
improvements in insulin action by chronic
weremeasured.
iftaken regularly
sildenafil in a murine model of diet-induced obe-
sity and insulin resistance. In their experiment,
this improvement occurred even in the absence
of an exogenous NO donor, suggesting that the
endogenous supply of NO in the high fat-fed
state did not limit the effect of sildenafil on insu-
lin action. Chronic PDE5 inhibition also resulted
in increased energy expenditure, suggesting that
improved energy balance and weight reduction
might be partially responsible for the enhanced
insulin action without any adverse effects on
cardiac morphology or blood pressure measured
in vivo, supporting human studies showing no
association between long-term use of sildenafil
and risk of ischemic events [Pegge et al. 2006].
These data have been confirmed with administra-
tionof chronic, short-acting
2008c] and long-acting PDE5-i tadalafil in men
with CRFs even in the absence of ED [Rosano
et al. 2005].A pilot
[McMahon, 2004] evaluated improvements in
response rates once non-responders to on-
demand tadalafil were shifted to daily dosing
and concluded that up to 30% of non-responders
may be ‘salvaged’ by daily dosing. Additional
data on endothelial response to chronic tadalafil
have been obtained in another pilot study invol-
ving men with ED and comorbidities. Results
suggest a beneficial effect on endothelial function
via decreasing plasma levels of surrogate markers
(i.e., endothelin-1, C-reactive protein, CAMs).
In this study, the authors added another possible
mechanismunderlying
improvement of morning erections, which may
provide better end-organ oxygenation, especially
in the diabetic population. This latter aspect was
confirmed in another study [Proietti et al. 2007]
carried out in male sclerodermic patients with
ED. Besides improvement in penile vascular cir-
culation, daily tadalafil
endothelin-1 plasma levels and increased morn-
ing erections after 12 weeks of treatment.
Moreover, in ED-patients with systemic sclerosis,
it was hypothesized that the reduction of adreno-
medullin levels obtained after daily tadalafil, was
responsible for the reduction of Raynaud’s phe-
nomenon number and severity of attacks over the
time [Rosato et al. 2009]. Although this appears
to be a fascinating hypothesis that opens new
treatmentperspectives,
needed in order to assess the possible clinical
implications of chronic therapy with PDE5-i for
cardioprotection and endothelial rehabilitation in
patients with comorbidities. Most notably, these
drugs are largely used for obstructive sleep
[Aversa
et al.
study by McMahon
penile rehabilitation:
markedlyreduced
largerstudies are
Therapeutic Advances in Urology 1 (4)
188 http://tau.sagepub.com
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.com Downloaded from

Page 12

apnea-induced ED. Because NO promotes upper
airway congestion, muscle relaxation, and pul-
monary vasodilation, it has been demonstrated
that a single 50mg dose of sildenafil at bedtime
may worsen respiratory and desaturation events
[Roizenblatt et al. 2006] so that caution is man-
datory in this group of patients.
The relationship between diabetes, the MeS and
T deficiency is complex. Male hypogonadism is
generally characterized by abnormally low serum
T-levels. Typical symptoms include change in
mood and cognitive function disorders [Kenny
et al. 2002], decreased bone mineral density
[Snyder et al. 1999], increased visceral adiposity
and body mass index (BMI) [Tan and Pu, 2002],
decreased muscle mass and strength [Kenny
et al. 2001], and sexual dysfunction [Morales
and Heaton, 2001]. Free T-levels begin to decline
at a rate of 1% per year after the age of 40 years.
It is estimated to affect between 19 and 34% of
men over the age of 60 [Kalyani and Dobs,
2007]. Cross-sectional studies have found that
between 20 and 64% of men with diabetes have
hypogonadism, with higher prevalence rates
found in the elderly. Hypogonadism can be a
risk factor for the development of diabetes and
the MeS through various mechanisms including
changes in body composition, androgen receptor
polymorphisms, glucose transport, and reduced
antioxidant effect. Conversely, diabetes and the
MeS can be risk factors for hypogonadism
throughsomesimilar
mechanisms, such as increased body weight and
leptin levels, decreased sex hormone binding
globulin levels, suppression of gonadotrophin
release or Leydig cell T production, cytokine-
mediated inhibition
production, and increased aromatase activity
contributing to relative
[Nieschlag et al. 2004]. Defects in the hypotha-
lamic-pituitary-gonadal axis may also result from
type-2 diabetes,visceral
strongly associated with
CAD and MeS and from treatments with a
wide range of medications [Kapoor et al. 2006].
Androgen deficiency can also occur at any time
during a man’s life, but occurs more frequently
with advancing age (LOH, late onset hypogonad-
ism). Short-term interventional studies have also
demonstrated that T replacement therapy pro-
duces an improvement in insulin sensitivity in
men. Thus, hypotestosteronemia may have a
role in the pathogenesis of insulin-resistant
states and androgen replacement therapy could
but mostly distinct
oftesticular steroid
estrogen excess
obesity
insulin
(which
resistance),
is
be a potential treatment that could be offered
for improvements in glycemic control, insulin
resistance, cholesterol and visceral adiposity and
reduction in cardiovascular risk, particularly in
diabetic men [Heinlein and Chang, 2002b].
Treatment of ED in men with diabetes has
been changed by the introduction of PDE5-i.
However, men with diabetes tend to respond
less positively to these agents, at least as currently
prescribed. This decreased responsiveness may
be related to the severity of EDys that usually
occurs in these patients. There has been much
recent interest in the potential relationship
between LOH and diabetes, but there is no evi-
dence of a causal relationship and the evidence in
favor of treating borderline hypogonadism in dia-
betes is limited.
Combination therapy in internal and sexual
medicine
The role of T salvage in the setting of ‘sub-clin-
ical’ hypogonadism of patients with ED has been
evaluated in the presence and absence of PDE5-i
effectiveness [Morelli et al. 2004]. Preclinical
investigations reported by Traish et al. [Traish
et al. 1999] provided convincing evidence that
PDE5-i are ineffective in improving erectile func-
tion in androgen-deficient animals and that the
re-administration of androgen facilitates PDE5-i
action. As already outlined, T may directly con-
trol the expression and activity of PDE5 in
humanpeniletissues
Androgen deficiency or hypogonadism reduce
the cavernosal expression of PDE5 mRNA, pro-
tein and enzyme activity, and T supplementation
restores PDE5 expression and activity which
represents the substrate for the inhibitory action
of PDE5-i. The effects of androgens on penile
tissues in experimental models demonstrated
that androgen deprivation induces: smooth-
muscle cell degeneration (apoptosis), adipose
tissue deposition with associated fibrosis of
corpus cavernosum [Traish and Guay, 2006];
reduction in the expression of eNOS and
nNOS; decrease of arterial inflow and increase
of venous out-flow in the corpus cavernosum;
enhanced response to mediators of vasoconstric-
tion and smooth muscle contraction such as
a-adrenergic agents; decrease of NO-mediated
smooth muscle relaxation during sexual stimuli;
and down-regulation of expression of PDE5
enzyme. This latter aspect seems to be crucial
in determining metabolic and structural imbal-
ance in the corpus cavernosum, resulting in
venous leakage and ED; this suggests a rationale
[Traish
et al.
2003].
A Aversa, R Bruzziches et al.
http://tau.sagepub.com189
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.com Downloaded from

Page 13

for combination therapy with PDE5-i combined
with T preparation for treating ED refractory to
monotherapy [Shabsigh et al. 2006]. These clin-
ical observations suggest a critical role for T in
human erectile function. Aversa and co-workers
were the very first to demonstrate that in the clin-
ical setting, men with ED and low free-T may
have an impaired relaxation of the penile
smooth muscle, thus providing clinical evidence
for the importance of androgen in regulating
erectile function [Aversa et al. 2000]. More
importantly, in all patients a strong direct corre-
lation between resistive index values and free-T
levels has been reported. Again, this relationship
was maintained also when adjusted for age,
SHBG, and estradiol. These results indicate
that in men with ED, low free-T may correlate
independently of age with the impaired relaxation
of the cavernous smooth muscle cells. In a sub-
sequent study, it has been shown that the treat-
ment with transdermal T-patch and sildenafil on-
demand, significantly increased scores in the
erectile function domain of the International
Index of Erectile Function (IIEF) [Aversa et al.
2003]. Other studies demonstrated that T ther-
apy is able to improve erectile function and the
response to PDE5-i in patients with ED and
hypogonadism and also in men with LOH symp-
toms [Shabsigh et al. 2004; Kalinchenko et al.
2003]. Administration of intramuscular T and
sildenafil was found to be efficacious in renal
transplant patients and in patients on renal dia-
lysis [Tas et al. 2006], and oral T has been
reported to reverse ED associated with type-2
diabetes in patients failing on sildenafil therapy
alone [Lin et al. 2001]. On the other hand,
few studies suggested that in ED-associated
hypogonadism, T alone may not be sufficient
for early restoration
[Shabsigh, 2003; Yassin et al. 2006] thus sug-
gesting that the combination with a PDE5-i is
initially recommended. In conclusion, T plus
PDE5-i combination
response to PDE5-i in patients previously not
responding to PDE5-i therapy alone and in
whom T levels at baseline are in the hypogonadal
or normal-low adult range, i.e. late-onset hypo-
gonadism, without any side effects on prostate
size and PSA values in the long-term [El-Sakka
et al. 2005]. Notewhorthy, T-induced remodel-
ling of penile tissue structure is a process that
may require a longer period of T administration,
as long as 4 weeks for expected results on
erection.
oferectile potency
therapyimproves the
Regarding the hypothesis on steroid hormone
changes induced by chronic treatments with
PDE5-i for sexual disturbances, several studies
indicate that resumption of sexual function with
different oral therapies is able to increase T levels
[Jannini et al. 1999]. It has been demonstrated as
a beneficial effect of the administration of sildena-
fil or tadalafil on steroid hormones, i.e. total- and
free-T that raised more significantly in those sub-
jects using tadalafil versus sildenafil probably
because of the more robust activation of the
hypothalamic-pituitary
number of sexual intercourses per month allowed
by the long-acting drug [Carosa et al. 2004].
Successive studies have demonstrated that due
to its indirect action, the raising effect on T is
transient and is lost twelve months after continua-
tive tadalafil assumption; T:estradiol ratio incre-
ased due to a significant reduction of estradiol
levels which may account for by tadalafil persis-
tent efficacy over the time [Greco et al. 2006a].
This study suggested for the first time a possible
direct inhibitory effect of tadalafil on aromatase
activity in humans independently from the body
mass index and the quantity of adipose tissue.
Preliminary studies from our laboratory aimed
to investigate whether tadalafil could directly
modulate aromatase expression in differentiated
human adipocytes in culture demonstrated that
it directly affect aromatase expression, hence it
could positively modulate the T:estradiol circulat-
ing ratio in vivo [data not published]. Thus, the
aromatase activity inhibition due to chronic expo-
sure of tadalafil might be responsible for tadalafil
sustained effectiveness in vivo during daily tadala-
fil low-dose treatment.
axis due tohigher
Conclusion
It is clear that the modification of reversible
causes,i.e.inadequatelifestyle,cigarettesmoking,
alcohol or recreational drug abuse [Aversa et al.
2008b], hyperglycemia and hypertension, must
represent the first approach to improve endothe-
lial function and to promote general well-being
and sexual health. Almost 20?30% of ED cases
may be attributed to subnormal T levels [Morelli
et al. 2005] and T deficiency is frequently asso-
ciated with chronic diseases, that are in turn asso-
ciated with increased deposition of visceral fat;
this latter serves as an endocrine organ, producing
inflammatorycytokinesandthuspromotingEDys
and concurring to determine vascular disease. In
fact, a considerable body of evidence exists sug-
gesting a link among reduced T plasma levels and
the presence of diabetes, MeS and systemic
Therapeutic Advances in Urology 1 (4)
190http://tau.sagepub.com
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.comDownloaded from

Page 14

vascular diseases. Adequate T concentrations are
alsocrucialfor theregulationofacorrectendothe-
lial function, for the expression of penile PDE5
isoenzyme [Greco et al. 2006b; Morelli et al.
2004] as well as for the adequate production of
H2S. Men with ED and low T levels are potential
candidates to benefit from combination therapies
if response to monotherapy is not sufficient
[Rosano, 2000]. However, if we consider overall
hormonal alterations of sex steroids in men com-
plaining ED, it is noteworthyto remember that up
to 41% of these men may present with alterations
of T:estradiol ratios [Aversa et al. 2006a]. The
beneficial effects of T supplementation along
with chronic PDE5-i administration on endothe-
lium in deficient men with or without ED appears
to be a promising therapy to boost the effects on
remodeling of vascular wall determined by single
vasoactive agents used to treat internal medicine
diseases [Aversa, 2008], and may represent a ‘sal-
vage’ therapy especially in difficult-to-treat ED.
Although the safety of this class of agents has
been indisputably established for the treatment
of ED on an on-demand basis, there remains a
paucity of controlled data on the long-term
endothelial effects and possible hormonal unto-
ward effects deriving from chronic use.
Conflict of interest statement
None declared.
References
Aiayi, A.A., Mathur, R. and Halushka, P.V. (1995)
Testosterone increases human platelet thromboxane
A2 receptor density and aggregation responses.
Circulation 91: 2742?2747.
Akishita, M., Hashimoto, M., Ohike, Y., Ogawa, S.,
Iijima, K., Eto, M. et al. (2007) Low testosterone level
is an independent determinant of EDys in men.
Hypertens Res 30: 1029?1034.
Al-Hunayan, A., Thalib, L., Kehinde, E.O. and Asfar,
S. (2008) Hyperhomocysteinemia is a risk factor for
erectile dysfunction in men with adult-onset diabetes
mellitus. Urology 71: 897?900.
Allan, C.A. and McLachlan, R.I. (2004) Age-related
changes in testosterone and the role of replacement
therapy in older men. Clin Endocrinol (Oxf)
60: 653?670.
Aversa, A., Isidori, A.M., De Martino, M.U., Caprio,
M., Fabbrini, E., Rocchietti-March, M. et al. (2000)
Androgens and penile erection: evidence for a direct
relationship between free testosterone and cavernous
vasodilation in men with erectile dysfunction. Clin
Endocrinol 53: 517?522.
Aversa, A., Isidori, A.M., Spera, G., Lenzi, A. and
Fabbri, A. (2003) Androgens improve cavernous
vasodilation and response to sildenafil in patients with
erectile dysfunction. Clin Endocrinol 58: 632?638.
Aversa, A., Bruzziches, R. and Spera, G. (2005) A
rationale for the use of testosterone salvage in
treatment of men with erectile dysfunction failing
phosphodiesterase inhibitors. The Endocrinologist
15: 99?105.
Aversa, A., Bruzziches, R., Pili, M. and Spera, G.
(2006) Phosphodiesterase 5 inhibitors in the treatment
of erectile dysfunction. Curr Pharm Des
12: 3467?3484.
Aversa, A., Bruzziches, R., Greco, E.A., Pili, M. and
Spera, G. (2006a) Possible involvement of gonadic
steroids in determining erectile response to pharma-
coerection test in men with erectile dysfunction. It J
Sex Reprod Med 13: 3?9.
Aversa, A., Greco, E., Bruzziches, R., Pili, M.,
Rosano, G. and Spera, G. (2007a) Relationship
between chronic tadalafil administration and
improvement of endothelial function in men with
erectile dysfunction: a pilot study. Int J Impot Res
19: 200?207.
Aversa, A., Bruzziches, R., Vitale, C., Marazzi, G.,
Francomano, D., Barbaro, G. et al. (2007b)
Chronic sildenafil in men with diabetes and
erectile dysfunction. Expert Opin Drug Metab Toxicol
3: 451?464.
Aversa, A. and Bruzziches, R. (2007)
Phosphodiesterase type 5 inhibitors and endothelial
function. Curr Sex Health Rep 4: 157?162.
Aversa, A. (2008) Drugs targeted to improve
endothelial function: clinical correlates between
sexual and internal medicine. Curr Pharm Des
14: 3698?3699.
Aversa, A., Caprio, M., Rosano, G.M. and Spera, G.
(2008a) Endothelial effects of drugs designed to
treat erectile dysfunction. Curr Pharm Des
14: 3768?3778.
Aversa, A., Rossi, F., Francomano, D., Bruzziches, R.,
Bertone, C., Santiemma, V. et al. (2008b) Early
endothelial dysfunction as a marker of vasculogenic
erectile dysfunction in young habitual cannabis users.
Int J Impot Res 20: 566?573.
Aversa, A., Vitale, C., Volterrani, M., Fabbri, A.,
Spera, G., Fini, M. et al. (2008c) Chronic adminis-
tration of sildenafil improves markers of endothelial
function in men with Type 2 diabetes. Diabet Med
25: 37?44.
Ayala, J.E., Bracy, D.P., Julien, B.M., Rottman, J.N.,
Fueger, P.T. and Wasserman, D.H. (2007) Chronic
treatment with sildenafil improves energy balance and
insulin action in high fat-fed conscious mice. Diabetes
56: 1025?1033.
Basta, G., Schmidt, A.M. and De Caterina, R. (2004)
Advanced glycation end products and vascular
A Aversa, R Bruzziches et al.
http://tau.sagepub.com191
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.comDownloaded from

Page 15

inflammation: implications for accelerated athero-
sclerosis in diabetes. Cardiovasc Res 63: 582?592.
Baumha ¨kel, M., Werner, N., Bo ¨hm, M. and Nickenig,
G. (2006) Circulating endothelial progenitor cells
correlate with erectile function in patients with
coronary heart disease. Eur Heart J 27: 2184?2188.
Behr-Roussel, D., Gorny, D., Mevel, K., Caisey, S.,
Bernabe, J., Burgess, G. et al. (2005) Chronic
sildenafil improves erectile function and endothelium-
dependent cavernosal relaxations in rats: lack of
tachyphylaxis. Eur Urol 47: 87?91.
Bellamy, M.F. and McDowell, I.F. (1997) Putative
mechanisms for vascular damage by homocysteine.
J Inherit Metab Dis 20: 307?315.
Billups, K. and Friedrich, S. (2000) Assessment
of fasting lipid profiles and Doppler ultrasound
testing in men presenting with ED and no other
medical problems. J Urol 163: 147.
Bonetti, P.O., Lerman, L.O. and Lerman, A. (2003)
Endothelial dysfunction: a marker of atherosclerotic
risk. Arterioscler Thromb Vasc Biol 23: 168?175.
Boger, R.H. (2003) The emerging role of asymmetric
dimethylarginine as a novel cardiovascular risk factor.
Cardiovasc Res 59: 824?833.
Braunwald, E. (2008) Biomarkers in heart failure.
N Engl J Med 358: 2148?2159.
Brodsky, S.V., Zhang, F., Nasjletti, A. and Goligorsky,
M.S. (2004) Endotheliumderived microparticles
impair endothelial function in vitro. Am J Physiol Circ
Heart Physiol 286: H1910?H1915.
Browne, D., Meeking, D., Shaw, K. and Cummings,
M. (2003) Endothelial dysfunction and presympto-
matic atherosclerosis in Type 1 diabetes -
pathogenesis and identification. Br J Diabetes Vasc Dis
3: 27?34.
Brunner, H., Cockcroft, J.R., Deanfield, J., Donald,
A., Ferrannini, E., Halcox, J. et al. (2005) Endothelial
function and dysfunction. Part II: association with
cardiovascular risk factors and diseases. A statement by
the Working Group on Endothelins and Endothelial
Factors of the European Society of Hypertension.
J Hypertens 23: 233?246.
Bruzziches, R., Greco, E.A., Pili, M., Francomano, D.,
Spera, G. and Aversa, A. (2008) Redefining the role of
long-acting phosphodiesterase inhibitor tadalafil in the
treatment of diabetic erectile dysfunction. Curr
Diabetes Rev 4: 24?30.
Bucci, M., Mirone, V., Di Lorenzo, A., Vellecco, V.,
Roviezzo, F., Brancaleone, V. et al. (2009) Hydrogen
sulphide is involved in testosterone vascular effect. Eur
Urol In press. May 22. 56: 378?383.
Buvat, J., Van Ahlen, H., Schmitt, H., Chan, M.,
Kuepfer, C. and Varanese, L. (2006) Efficacy and
safety of two dosing regimens of tadalafil and patterns
of sexual activity in men with diabetes mellitus and
erectile dysfunction: scheduled use vs. on-demand
regimen evaluation (SURE) study in 14 European
countries. J Sex Med 3: 512?520.
Caretta, N., Palego, P., Ferlin, A., Garolla, A., Bettella,
A., Selice, R. et al. (2005) Resumption of spontaneous
erections in selected patients affected by erectile dys-
function and various degrees of carotid wall alteration:
Role of tadalafil. Eur Urol 48: 326?332.
Carosa, E., Martini, P., Brandetti, F., Di Stasi, S.M.,
Lombardo, F., Lenzi, A. et al. (2004) Type 5
phosphodiesterase inhibitor treatments for erectile
dysfunction increase testosterone levels. Clin
Endocrinol 61: 382?386.
Cersosimo, E. and DeFronzo, R.A. (2006)
Insulin resistance and EDys: the road map to CVDs.
Diabetes Metab Res Rev 22: 423?436.
Chang, C., Saltzman, A., Yeh, S., Young, W., Keller,
E., Lee, H.J. et al. (1995) Androgen receptor: an
overview. Crit Rev Eukaryot Gene Expr 5: 97?125.
Cheng, Y., Ndisang, J.F., Tang, G., Cao, K. and
Wang, R. (2004) Hydrogen sulphide-induced
relaxation of resistance mesenteric artery beds of rats.
Am J Physiol Heart Circ Physiol 287: H2316?H2323.
Chirino, R., Lo ´pez, A., Navarro, D., Cabrera, J.J.,
Rivero, J.F., Dı ´az-Chico, B.N. et al. (1989) Steroid
induction of low-affinity glucocorticoid binding sites in
rat liver microsomes. J Steroid Biochem 34: 97?105.
Cho, J.J., Cadet, P., Salamon, E., Mantione, K. and
Stefano, G.B. (2003) The nongenomic protective
effects of estrogen on the male cardiovascular system:
clinical and therapeutic implications in aging men.
Med Sci Monit 9: RA63?RA68.
Chou, T.M., Sudhir, K., Hutchison, S.J., Ko, E.,
Amidon, T.M., Collins, P. et al. (1996) Testosterone
induces dilatation in canine coronary conductance
and resistance arteries in vivo. Circulation
94: 2614?2619.
Cooke, J.P. and Dzau, V.J. (1997) Nitric oxide
synthase: role in the genesis of vascular disease. Annu
Rev Med 48: 489?509.
Cooke, J.P. (2005) ADMA: its role in vascular disease.
Vasc Med 10: S11?S17.
Corona, G., Fagioli, G., Mannucci, E., Romeo, A.,
Rossi, M., Lotti, F. et al. (2008) Penile doppler
ultrasound in patients with erectile dysfunction (ED):
role of peak systolic velocity measured in the flaccid
state in predicting arteriogenic ED and silent coronary
artery disease. J Sex Med 5: 2623?2634.
Costarella, C.E., Stallone, J.N., Rutecki, G.W. and
Whittier, F.C. (1996) Testosterone causes direct
relaxation of rat thoracic aorta. J Pharm Exp Ther
277: 349.
Crews, J.K. and Khalil, R.A. (1999) Antagonistic
effect of 17 beta-oestradiol, progesterone and testos-
terone on Ca2+ entry mechanism of coronary vaso-
constriction. Arterioscler Thromb Vasc Biol
19: 1034?1040.
Therapeutic Advances in Urology 1 (4)
192http://tau.sagepub.com
at Dip Teoria Dello Stato on March 22, 2010 http://tau.sagepub.comDownloaded from