Hindawi Publishing Corporation
Critical Care Research and Practice
Volume 2012, Article ID 290805, 12 pages
Stimulators andActivators of SolubleGuanylate Cyclase:
Reviewand Potential TherapeuticIndications
Bobby Nossaman,1,2EdwardPankey,2and PhilipKadowitz2
1Critical Care Medicine Section, Department of Anesthesiology, Ochsner Medical Center, 1514 Jefferson Highway, New Orleans,
LA 70121, USA
2Department of Pharmacology, SL83, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA 70112-2699, USA
Correspondence should be addressed to Philip Kadowitz, firstname.lastname@example.org
Received 31 July 2011; Revised 18 November 2011; Accepted 19 November 2011
Academic Editor: Hector R. Wong
Copyright © 2012 Bobby Nossaman et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
Theheme-protein soluble guanylyl cyclase (sGC)is the intracellular receptor for nitricoxide (NO).sGC is a heterodimeric enzyme
with α and β subunits and contains a heme moiety essential for binding of NO and activation of the enzyme. Stimulation of sGC
mediates physiologic responses including smooth muscle relaxation, inhibition of inflammation, and thrombosis. In pathophysio-
logic states, NO formation and bioavailability can be impaired by oxidative stress and that tolerance to NO donors develops with
continuous use. Two classes of compounds have been developed that can directly activate sGC and increase cGMP formation in
pathophysiologic conditions when NO formation and bioavailability are impaired or when NO tolerance has developed. In this
report, we review current information on the pharmacology of heme-dependent stimulators and heme-independent activators of
sGC in animal and in early clinical studies and the potential role these compounds may have in the management of cardiovascular
Guanylyl cyclase (GC) is an enzyme that catalyzes the forma-
tion of guanosine 3?,5?-monophosphate (cGMP) from gua-
nosine triphosphate (GTP) and is found in tissues through-
out the animal kingdom [1, 2]. Soluble GC (sGC) is the re-
ceptor for nitric oxide (NO) in vascular smooth muscle [3,
4]. In the cardiovascular system, NO is endogenously gen-
erated by endothelial NO synthase (eNOS) from L-arginine
and activates sGC in adjacent vascular smooth muscle cells
to increase cGMP levels and induce relaxation (Figure 1).
NO plays a major role in the regulation of vascular tone and
blood pressure [5, 6]. When released from the endothelium
in response to physiologic stimuli such as shear stress, NO
binds to the normally reduced heme moiety of sGC and
increases the formation of cGMP from GTP leading to a dec-
rease in intracellular calcium and vasodilation [7–10]. More-
over, the NO-sGC-cGMP pathway is essential for the control
of a number of physiologic processes, including neuronal
vascular and platelet homeostasis [11–18].
Initial investigations into the role of NO were conducted
showing that nitrogen-containing compounds such as sod-
ium azide (NaN3), sodium nitrite (NaNO2), hydroxylamine
(NH2OH), nitroglycerin (C3H5N3O9), and sodium nitro-
23] (Figure 2). When tissues were homogenized and sepa-
rated by centrifugation, GC activity was detected in partic-
ulate and soluble fractions [19, 23–31]. As NO was shown
to rapidly activate GC , it was hypothesized that GC
activation may be due to the effect of NO or another sub-
stance that activated the enzyme . Moreover, these nitro-
gen-containing compounds were able to activate sGC, caus-
ing an increase in cGMP, and vascular relaxation [13, 21, 32,
Reduced bioavailability and/or responsiveness to endoge-
nous NO have been implicated in the pathogenesis of many
2Critical Care Research and Practice
Figure 1: Simplified role of NO (nitric oxide) stimulating soluble guanylyl cyclase smooth muscle relaxation. PKB (protein kinase B), NOS
(nitric oxide synthase).
• Inhibition of platelet aggregation
• Anti-inflammatory effect
Figure 2: Role of NO (nitric oxide), inhaled NO, and sGC (soluble
guanylyl cyclase) stimulators in stimulating the reduced heme of
sGC and the role of sGC activators in stimulated oxidized sGC to
gation and an anti-inflammatory effect in the vascular bed.
disease processes [34–36]. NO was originally described as
an endothelial-derived relaxing factor and is a vasodilator in
the pulmonary and systemic circulations [37–40]. The signi-
ficance of NO in the regulation of vasomotor tone has
been demonstrated in experimental animals and in hu-
man subjects by the use of NOS inhibitors [41–48]. Given
the importance of the NO-sGC-cGMP pathway in cardio-
pulmonary diseases, there have been enormous efforts to
improve NO therapy [36, 49–53].
3.1. Nitrates. Although glyceryl trinitrate (GTN) and amyl
heart failure for over 140 years [54, 55], the most commonly
used agents at the present include isosorbide dinitrate,
isosorbide-5-mononitrate, and GTN which are effective in
reducing ventricular preload by increasing peripheral venous
capacitance [56–59]. It is generally believed that the thera-
peutic effect of these drugs involves the release of NO from
nitrite anion, the activation of sGC, and relaxation of capaci-
tance blood vessels [54, 60–63]. These drugs can also dec-
rease pulmonary and systemic vascular resistances but re-
quire higher doses than needed for increasing venous capac-
itance [64–69]. These agents can reduce ventricular filling
pressure, wall stress, and myocardial oxygen consumption
 and may also improve systolic and diastolic ventricu-
lar function by improving coronary flow in patients with
ischemic cardiomyopathy. However, there is as yet no con-
vincing evidence that organic nitrates improve mortality in
patients with acute myocardial infarction [71, 72]. The lim-
itations of this class of agents are well known and include
adverse hemodynamic effects, including tolerance, lack of
selectivity, and limited bioavailability .
Studies in the literature provide evidence that vasore-
laxant responses to GTN are mediated by the formation of
NO or aclosely related S-nitroso molecule [13, 33, 73, 74].
However, the mechanism of this vasorelaxant response to
GTN is uncertain. Although studies in the literature indicate
Critical Care Research and Practice3
that NO contributes to the activation of sGC and vascular
smooth muscle relaxation [75, 76], other studies suggest that
vasorelaxant responses to GTN may be independent of NO
release and cGMP formation .
Studies have shown that the bioactivation of GTN re-
quires the presence of thiols or sulfhydryl-containing com-
pounds and that NO or NO-like compounds are believed
to be the biologically active species [3, 74, 78, 79]. Inter-
actions with GTN and sulfhydryl-containing molecules are
ated administration of GTN produces sulfhydryl depletion
and the development of tolerance [79–81]. Subsequent stud-
ies have demonstrated the release of NO following the de-
composition of an intermediate S-nitrosothiol . Addi-
tional studies suggest that an enzymatic mechanism may be
responsible for the bioactivation of GTN. However, these
enzymatic systems could not catalyze the selective formation
of 1,2-glyceryl dinitrate and nitrite from GTN, and more-
over, no association between the development of enzymatic
over, the discovery (1) that mitochondrial aldehyde dehy-
drogenase (mtALDH) generates 1,2-glyceryl dinitrate and
nitrite from GTN , (2) that this reaction requires a redu-
cing thiol cofactor [60, 90, 91], and (3) that the activity of
this enzyme is reduced in GTN tolerance [53, 61] suggests
that this pathway is responsible for GTN bioactivation in
vascular smooth muscle [53, 77, 89]. However, one difficulty
with these studies has been an inability to detect NO as a
byproduct of GTN metabolism . Moreover, the genera-
tion of NO was observed when the concentrations of GTN
been proposed that once GTN is bioactivated within the
mitochondria, nitrite or an additional action of mtALDH
generates the vasodilatory NO bioactivity . One sugges-
ted mechanism for this vasodilatory activity is that S-nitro-
soglutathione is formed by the reaction of reduced gluta-
thione and nitrite [99, 100]. This molecule subsequently un-
dergoes biotransformation to S-nitrosocysteine [89, 101]
that can release NO . However, excessive amounts of
GTN or S-nitrosothiols can dysregulate protein S-nitrosyla-
Chronic GTN administration has been shown to result in
acetylcholine-induced coronaryvasoconstriction ratherthan
relaxation [104, 105] and induce endothelial dysfunction
. An early event in the development of atherosclerosis
is the impairment of endothelial function or endothelial dys-
function that develops before structural changes and intimal
hyperplasia or lipid deposition occur . Moreover, redu-
ced oxidation of NO occurs through altered endothelial NOS
formation and activity , which can be evidenced by ab-
109]. Therefore, NO deficiency is linked to cardiopulmonary
disease processes and provides justification for the use of
effective NO replacement therapy.
4.Activationof sGCby NO-Like Compounds
The activation of sGC enhances the conversion of GTP to
muscle relaxation and inhibition of platelet aggregation
[13–18]. However, little is known about sGC regulation by
substances other than NO-donors. The recent discovery of
a benzylindazole derivative, YC-1, that was shown to inhibit
platelet aggregation and increase by sixfold intracellular con-
regulation [110, 111]. Subsequent studies found that acti-
vation of sGC by YC-1 was NO-independent and was inde-
pendent of biotransformation [112, 113]. In contrast, orga-
nic nitrates appear to require biotransformation with inter-
mediates (nitrites, nitrosothiols, and organic thionitrates)
liberating NO [91, 114]. These findings with YC-1 as well as
other stimulators of sGC suggest that non-NO compounds
may also activate or modulate sGC activity [115–118]. Cur-
rent NO-donor drugs induce tolerance [34–36, 79–81].
However by increasing the responsiveness of sGC to endoge-
nous NO, YC-1 or YC-1-like compounds may represent a
novel class of drugs that cansensitize the sGC enzyme to res-
pond to NO. In disease states with dysfunctional sGC, it may
be possible to increase the effect of endogenously produced
dent stimulators for sGC have been developed for use in
pathophysiologic conditions when NO formation and bio-
availability are impaired or when NO tolerance has devel-
4.1. sGC Stimulators
4.1.1. Preclinical Studies. Compounds have been developed
that can directly stimulate sGC and increase cGMP forma-
bioavailability are impaired or when NO tolerance has devel-
oped [34–36] (Figure 2). The pyrazolopyridine compound,
BAY 41-8543, is an NO-independent stimulator of sGC that
has been shown to reduce systemic and pulmonary arterial
pressure, and relax isolated vessels from a variety of organ
systems [35, 119, 120]. BAY 41-2272 is closely related to BAY
nificant pulmonary vasodilator activity in a variety of species
[119, 121–125]. BAY 41-2272 has been shown to reduce right
in a chronic hypoxia-induced model of pulmonary hyper-
tension . It has been reported that when either BAY
41-2272 or BAY 41-8543 was administered by inhalation to
awake lambs, the pyrazolopyridine compounds had selec-
tive pulmonary vasodilator activity and BAY 41-8543 could
enhance the magnitude and prolong the duration of the
vasodilator response to inhaled NO [122, 125].
In an intact chest rat model, administration of BAY
41-8543 under control or baseline tone conditions produ-
ced small decreases in pulmonary arterial pressure, larger
dose-dependent decreases in systemic arterial pressure, and
increases in cardiac output . However, under elevated
nist, U46619, BAY 41-8543 produced larger dose-dependent
decreases in pulmonary arterial pressure when tone in the
pulmonary vascular bed was increased . Analyses of
the percent decreases in pulmonary and systemic arterial
pressures in response to BAY 41-8543 under elevated tone
4 Critical Care Research and Practice
conditions induced with U46619-infused animals were not
different, suggesting that the sGC stimulator had similar
vasodilator activity in the pulmonary and systemic vascular
beds in the intact chest rat .
The effect of NOS inhibition with L-NAME on vasodila-
tor responses to BAY 41-8543 was investigated in the intact
chest rat model, and following administration of the NOS
inhibitor, decreases in pulmonary and systemic arterial pres-
sures in response to BAY 41-8543 were reduced when com-
of responses to BAY 41-8543 at the same level of pulmonary
pressure in response to the sGC stimulator are reduced by
more than 50% in L-NAME-treated animals . These
results are consistent with the concept that responses to the
sGC stimulator are NO-independent; however, in the ab-
sence of endogenous NO formation, vasodilator responses to
the sGC stimulator were markedly attenuated. It has been
reported that stimulators of sGC have a dual role of action
in that they directly stimulate the native form of the enzyme
and render it more sensitive to endogenously produced NO
128]. The results in the intact chest rat model are consistent
with these findings [125, 128] that show that vasodilator res-
ponses to BAY 41-8543 are attenuated when endogenous NO
formation is inhibited.
examined in the intact chest model with the NO donor, sod-
ium nitroprusside (SNP). Although separate administration
of BAY 41-8543 and SNP produced significant decreases in
pulmonary and systemic arterial pressures, coadministration
that were significantly greater than the sum of responses to
either agent when administered alone . These results
suggest that BAY 41-8543 synergizes with NO in mediating
vasodilator responses to the sGC stimulator in the pulmo-
nary and systemic vascular beds in the intact rat.
BAY 41-8543 and BAY 41-2272 were synthesized based
upon analysis of the structure of YC-1 [36, 110, 129]. These
pyrazolopyridine stimulators activate sGC in a manner inde-
pendent of NO [35, 36, 121]. These compounds activate
purified sGC and strongly synergize with NO, reflecting sta-
bilization of the nitrosyl-heme complex of the enzyme .
Both BAY 41-8543 and BAY 41-2272 relax vascular smooth
muscle and have vasodilator activity in the pulmonary and
systemic vascular beds [34, 119, 121, 122, 128, 131].
Although BAY 41-8543 had beneficial effects in experi-
mental models of pulmonary hypertension, this agent does
not have favorable pharmacokinetic properties and cannot
be used in clinical trials . In contrast, BAY 63-2521
(Riociguat; Bayer Healthcare AG, Wuppertal, Germany),
a heme-dependent sGC stimulator closely related to BAY 41-
8543, has a better pharmacokinetic profile and has been used
in clinical studies . In respect to interesting similarities
and differences between the actions of BAY 41-8543 and
ted that BAY 41-2272, which is chemically similar to BAY
41-8543, produced greater decreases in pulmonary than
systemic arterial pressure and that pulmonary vasodilator
responses were not attenuated by L-NAME . In the pre-
sent study, BAY 41-8543 produced similar decreases in pul-
monary and systemic arterial pressures in U46619-infused
animals and decreases in both pulmonary and systemic arte-
rial pressures attenuated by L-NAME treatment. In an ovine
fetal model of pulmonary hypertension, chronic infusion of
BAY 41-2272 produced potent sustained decreases in pulmo-
nary arterial pressure that were not attenuated by a NOS
inhibitor, L-NA, and when infused at higher rates, systemic
response to stimulators of sGC in the awake sheep, the ovine
fetal circulation, and intact chest rat are the relative differ-
ences in vasodilator activity in the pulmonary and systemic
vascular beds and the role of endogenously produced NO in
modulating these responses [124, 125]. The reason for the
differences in results in the different experimental models
may involve differences in species, experimental design and
preparation, the BAY compound studied, or more impor-
the present study, BAY 41-8543 had similar vasodilator acti-
vity in the preconstricted pulmonary vascular bed and the
systemic vascular bed and vasodilator responses in both beds
were attenuated when NOS was inhibited with L-NAME.
These data suggest that the role of endogenous NO in the
activation of sGC is similar in both circulations in the
intact chest rat model and may differ from SGC activation
mechanisms in the pulmonary and systemic vascular beds in
the awake sheep and ovine fetal preparation [124, 125].
mulator, BAY 41-2272, was not dependent on the formation
of endogenous NO in the awake sheep model, the response
strongly synergized with inhaled NO . Therefore, the
was, in some respects, similar in the awake sheep and intact
rat models, although the synergism was much greater in the
The present results are consistent with the concept that sGC
NO-donor to produce maximum pulmonary vasodilation
4.1.2. Clinical Investigations. The first sGC simulator to
undergo clinical study was BAY 41-8543 . However,
although systemic blood pressure decreased as expected fol-
macokinetic issues occurred that lead to the development
of additional sGC compounds . Subsequently BAY 63-
2521 was developed, and when administered in 58 healthy
male volunteers as a single oral dose (0.25–5mg), no serious
adverse events were observed . Although both mean
arterial and diastolic pressures were decreased, systolic pres-
sure was not significantly affected. A dose-related increase in
heart rate up to ∼11bpm was observed with the 5-mg
dose; however, this dose was not well tolerated, due to an
increased number of adverse events, including headache,
nasal congestion, flushing, feeling hot, orthostatic hypoten-
sion, and palpitations. Increased levels in the vasoactive hor-
mones, norepinephrine, and plasma renin, but not plasma
Critical Care Research and Practice5
aldosterone or angiotensin II, were observed . Follow-
ing these encouraging findings, a clinical study was per-
formed to evaluate the short-term safety profile of BAY 63-
2561 (Riociguat) to determine the tolerability and efficacy in
patients with moderate to severe pulmonary hypertension
(PH) due to pulmonary arterial hypertension, distal chronic
thromboembolic PH, or PH with mild to moderate intersti-
tial lung disease . Safety and tolerability studies were
performed in 19 subjects with single doses ≤2.5mg. The
administration of the sGC stimulator significantly improved
in patients with PH in a dose-dependent manner, to a
greater extent than following administration of inhaled NO.
Although riociguat had significant systemic blood pressure
effects and demonstrated no selectivity for the pulmonary
circulation, however, mean systolic blood pressure remained
be superior to inhaled NO in the response of the pulmonary
circulation . In a 12-week, phase II study, 75 patients
hypertension or pulmonary arterial hypertension) received
oralriociguat in 0.5mg increments in 2-week intervals from
1mg to a maximum of 2.5mg three times a day that was
titrated to systemic systolic blood pressure (SBP) . The
dose of the sGC stimulator was increased if systemic blood
pressure was greater than 100mmHg, was maintained once
SBP was stable in a range of 90–100mmHg, and decreased if
SBP was less than 90mmHg or with symptoms such as syn-
cope or dizziness. The primary endpoints studied were safety
and tolerability of the sGC stimulator with changes in phar-
macodynamics as the secondary endpoints. Riociguat was
well tolerated, and that asymptomatic hypotension (SBP less
than 90mmHg) occurred in 11/75 (15%) patients, but blood
pressure could be normalized with dose alteration in 2 pa-
tients and without dose alteration in 9 patients . Pul-
monary vascular resistance was significantly reduced. A sig-
nificant improvement in the median 6-minute walking dis-
tance was observed in patients with diagnosis of chronic
thromboembolic pulmonary hypertension (greater than 55
meters; P < 0.0001) and in patients with pulmonary arterial
hypertension (PAH) (greater than 57 meters; P < 0.0001).
Moreover, similar improvements were also observed in pa-
tients on chronic bosentan therapy . The most frequent
observed adverse events were dyspepsia, headache, and
strated a favorable safety profile with significant improve-
ments in pulmonary hemodynamics, and in exercise capac-
ity, but with a high through mild to moderate incidence of
patient symptoms .
4.2. sGC Activators
4.2.1. Preclinical Studies. The oxidation of the heme iron on
sGC decreases the responsiveness of the enzyme to NO and
pounds with a different mode of sGC activation have been
developed and have been shown to target NO receptor
proteins when the heme iron on sGC is in an oxidized (Fe3+
instead of Fe2+) state, or when the heme group is lost [36,
131, 137, 138] (Figure 2). These compounds activate the oxi-
dized or heme-deficient sGC enzyme that is not responsive
to NO . Oxidation of sGC results in loss of activation of
the enzyme [139–142]. Moreover, purified sGC also results
in marked to complete loss of enzyme responsiveness to NO-
donors [143, 144]. However, responsiveness was restored by
the addition of hematin, hemoglobin, or a heat-inactivated
catalase in the presence of a reducing agent [143, 144]. Orga-
development of tolerance limits their therapeutic value [53,
60, 145–147]. The development of compounds that over-
come this limitation that are able to stimulate sGC indepen-
studies indicates that these NO-independent receptors exist
and may become more abundant under pathological condi-
tions associated with oxidative stress [148–150].
Activation of the NO-sGC-cGMP pathway can induce
potent pulmonary and systemic vasodilatation [40, 151–
155]. Two classes of novel drugs have been developed that
can modulate sGC-cGMP signal transduction in an NO-
independent manner. Although stimulators of sGC can en-
hance the sensitivity of reduced sGC to NO , activators
of sGC can increase sGC enzyme activity even when the
52, 156]. In the intact chest rat, intravenous administration
of the sGC activator, BAY 60-2770, produced dose-related
decreases in systemic arterial pressure, increases in cardiac
cardiovascular responses were slow in onset and long in
duration . These observations are comparable to the
findings in the anesthetized dog following administration of
another sGC activator, BAY 41-2272 . These findings
suggest that sGC activators can increase sGC enzyme activity
in vascular beds from different species [123, 157].
Following a preclinical study in rats demonstrating that
Cinaciquat was able to reduce oxidative stress, improve car-
diac performance, and improve impaired cardiac relaxation
in experimentally induced myocardial infarction in rats
, the role of the sGC activator in ischemia-reperfusion
injury was investigated in a canine model of cardioplegic
arrest and extracorporeal circulation . Preconditioning
with the sGC activator improved left- and right-ventricular
contractility and led to a higher coronary blood flow. More-
was improved. These findings suggest that preconditioning
with Cinaciguat could improve myocardial and endothelial
function following cardiopulmonary bypass and could be a
novel therapeutic option in the protection against ischemia-
reperfusion injury in cardiac surgery .
Vasodilator responses to this novel class of drugs have
been studied in experimental models under conditions of
acute pulmonary hypertension (PH) induced with the stable
endoperoxide analogue, U46619 [122, 128]. In the intact
chest rat under elevated pulmonary arterial tone conditions
induced with U46619, administration of BAY 60-2770 pro-
duced significant decreases in both pulmonary and systemic
arterial pressure . Intravenous infusion of the sGC
6 Critical Care Research and Practice
stimulator, BAY 41-2272, or inhalation of the sGC activator,
BAY 58-2667, was able to reduce mean pulmonary arterial
pressure and pulmonary vascular resistance in awake lambs
sure changes observed following administration of the sGC
activator, BAY 58-2667, in the awake lamb , significant
decreases in systemic arterial pressure were observed follow-
ing administration of the sGC activator, BAY 60-2770, in the
intact chest rat model . The differences in results could
be due to the type of sGC activator administered, experi-
mental conditions, or species studied.
4.2.2. Clinical Studies. The development of heart failure due
to a number of etiologies is a common final stage in cardio-
vascular disease that is associated with high morbidity and
development of tolerance, due to the prosthetic heme group
of sGC existing in an oxidized or heme-free state, limits their
clinical effectiveness [161, 162]. BAY 58-2667 (Cinaciguat;
Bayer Healthcare AG, Wuppertal, Germany) has been shown
to preferentially activate sGC when the prostetic heme group
is in an oxidized or heme-free state . As a result,
Cinaciguat induces cGMP generation and vasodilation pref-
tial to induce vasodilation and increase cardiac output in
patients with HF. In the first clinical study with this sGC
macodynamics were analyzed in 76 healthy volunteers .
An intravenous infusion of Cinaciguat in a range of 50 to
250mcg/h was administered for up to 4 hours. During the
infusion period, the sGC activator decreased diastolic blood
pressure and increased heart rate without significantly
reducing systolic blood pressure. No serious adverse events
were observed. However, at the higher infusion rates (150–
250mcg/h), a decrease in mean arterial pressure and an in-
crease in plasma cGMP levels were observed. The findings
both preload and after load suggested that further investiga-
tion should occur in patients with HF . In a multicenter
phase II study, patients with a diagnosis of acute decompen-
sated heart failure received 6-hour intravenous infusions of
Cinaciguat which produced significant reductions in pul-
monary capillary wedge pressure, mean right atrial pressure,
mean pulmonary artery pressure, pulmonary vascular resis-
tance, and systemic vascular resistance, and cardiac output
by 1.7L/min while only increasing heart rates by 4bpm
. Cinaciguat was well tolerated in these patients, with
approximately one-fourth of the patients reporting adverse
events of mild to moderate intensity, with hypotension as
the most common adverse event . These results clearly
demonstrate the clinical efficacy of the sCG activator.
As sGC stimulators have been shown to stimulate sGC in-
dependently of NO donors, this class of agonists could have
increase in pulmonary vascular tone can occur during sym-
pathetic overstimulation following major surgery that would
be refractory to conventional NO-donor therapy, such as in
patients who develop ARDS and are refractory to inhaled
NO (iNO). The application of sGC stimulators would then
make iNO therapy more effective in the treatment of acute
pulmonary hypertension and possibly decease the incidence
of associated right ventricular heart failure.
In contrast to the benefits from sGC stimulators, the ap-
therapeutic management of chronic-diseased blood vessels
with extended periods of efficacy such as seen in systemic
hypertension, atherosclerosis, diabetes mellitus, angina, and
heart failure. Moreover, the use of this class of drugs may
reduce the development of oxidative stress from NO-donor
therapy and may reduce the common side effects from NO-
donor therapy such as headache that would improve patient
Research has shown that heme-dependent drugs are effective
effects are diminished under pathological conditions associ-
ated with increased oxidative stress and the development of
pendent compounds has been shown to higher affinities for
the oxidized form of sGC, and they are being developed
for the treatment of acute decompensated heart failure and
pulmonary hypertension. These two classes of drugs, sGC
stimulators and sGC activators, have been studied in animal
studies. These compounds are now undergoing preliminary
clinical trials and may be available for clinical use within the
 J. G. Hardman and E. W. Sutherland, “Guanyl cyclase, an
enzyme catalyzing the formation of guanosine 3’,5’-mono-
phosphate from guanosine trihosphate,” Journal of Biological
Chemistry, vol. 244, no. 23, pp. 6363–6370, 1969.
 J. G. Hardman, J. W. Davis, and E. W. Sutherland, “Effects of
some hormonal and other factors on the excretion of guano-
sine 3’,5’-monophosphate and adenosine 3’,5’-monophos-
phate in rat urine,” Journal of Biological Chemistry, vol. 244,
no. 23, pp. 6354–6362, 1969.
 W. P. Arnold, C. K. Mittal, S. Katsuki, and F. Murad, “Nitric
oxide activates guanylate cyclase and increases guanosine
3’:5’-cyclic monophosphate levels in various tissue prepara-
tions,” Proceedings of the National Academy of Sciences of the
United States of America, vol. 74, no. 8, pp. 3203–3207, 1977.
 D. B. McNamara, P. J. Kadowitz, A. L. Hyman, and L. J.
Ignarro, “Adenosine 3’, 5’-monophosphate formation by pre-
parations of rat liver soluble guanylate cyclase activated with
nitric oxide, nitrosyl ferroheme, S-nitrosothiols, and other
nitroso compounds,” Canadian Journal of Physiology and
Pharmacology, vol. 58, no. 12, pp. 1446–1456, 1980.
 S. Moncada, R. M. J. Palmer, and E. A. Higgs, “The discovery
of nitric oxide as the endogenous nitrovasodilator,” Hyper-
tension, vol. 12, no. 4, pp. 365–372, 1988.
Critical Care Research and Practice7
 S. Moncada and E. A. Higgs, “Nitric oxide and the vascular
endothelium,” Handbook of Experimental Pharmacology, no.
176, pp. 213–254, 2006.
 J. R. Stone and M. A. Marletta, “Spectral and kinetic studies
on the activation of soluble guanylate cyclase by nitric oxide,”
Biochemistry, vol. 35, no. 4, pp. 1093–1099, 1996.
 B. Wedel, P. Humbert, C. Harteneck et al., “Mutation of His-
105 in the β1 subunit yields a nitric oxide-insensitive form of
of Sciences of the United States of America, vol. 91, no. 7, pp.
 L. J. Ignarro, J. N. Degnan, W. H. Baricos, P. J. Kadowitz,
and M. S. Wolin, “Activation of purified guanylate cyclase
by nitric oxide requires heme comparison of heme-deficient,
heme-reconstituted and heme-containing forms of soluble
718, no. 1, pp. 49–59, 1982.
 P. A. Craven and F. R. DeRubertis, “Requirement for heme in
the activation of purified guanylate cyclase by nitric oxide,”
Biochimica et Biophysica Acta, vol. 745, no. 3, pp. 310–321,
Progress in Neurobiology, vol. 90, no. 2, pp. 246–255, 2010.
 K. Domek-Łopaci´ nska and J. B. Strosznajder, “Cyclic GMP
metabolism and its role in brain physiology,” Journal of Phys-
iology and Pharmacology, vol. 56, supplement 2, pp. 15–34,
Ignarro, and P. J. Kadowitz, “Relaxation of bovine coronary
nitric oxide, nitroprusside and a carcinogenic nitrosoamine,”
Journal of Cyclic Nucleotide Research, vol. 5, no. 3, pp. 211–
 L. J. Ignarro, R. G. Harbison, K. S. Wood, and P. J. Kadowitz,
“Dissimilarities between methylene blue and cyanide on
relaxation and cyclic GMP formation in endothelium-intact
intrapulmonary artery caused by nitrogen oxide-containing
vasodilators and acetylcholine,” Journal of Pharmacology and
Experimental Therapeutics, vol. 236, no. 1, pp. 30–36, 1986.
 R. Busse, A. Luckhoff, and E. Bassenge, “Endothelium-
derived relaxant factor inhibits platelet activation,” Naunyn-
Schmiedeberg’s Archives of Pharmacology, vol. 336, no. 5, pp.
 A. J. Barber, “Cyclic nucleotides and platelet aggregation:
metabolizing enzymes,” Biochimica et Biophysica Acta, vol.
444, no. 2, pp. 579–595, 1976.
 B. T. Mellion, L. J. Ignarro, C. B. Myers et al., “Inhibition of
human platelet aggregation by S-nitrosothiols: heme-depen-
dent activation of soluble guanylate cyclase and stimulation
of cyclic GMP accumulation,” Molecular Pharmacology, vol.
23, no. 3, pp. 653–664, 1983.
 B. T. Mellion, L. J. Ignarro, E. H. Ohlstein, E. G. Pontecorvo,
A. L. Hyman, and P. J. Kadowitz, “Evidence for the inhibitory
role of guanosine 3’,5’-monophosphate in ADP-induced hu-
man platelet aggregation in the presence of nitric oxide and
related vasodilators,” Blood, vol. 57, no. 5, pp. 946–955, 1981.
 S. Katsuki, W. Arnold, C. Mittal, and F. Murad, “Stimulation
of guanylate cyclase by sodium nitroprusside, nitroglycerin
and nitric oxide in various tissue preparations and compari-
son to the effects of sodium azide and hydroxylamine,” Jour-
 H. Kimura, C. K. Mittal, and F. Murad, “Activation of gua-
nylate cyclase from rat liver and other tissues by sodium
azide,” Journal of Biological Chemistry, vol. 250, no. 20, pp.
 C. K. Mittal, H. Kimura, and F. Murad, “Requirement for a
macromolecular factor for sodium azide activation of guany-
late cyclase,” Journal of Cyclic Nucleotide Research, vol. 1, no.
5, pp. 261–269, 1975.
 S. Katsuki, W. P. Arnold, and F. Murad, “Effects of sodium
nitroprusside, nitroglycerin, and sodium azide on levels of
cyclic nucleotides and mechanical activity of various tissues,”
Journal of Cyclic Nucleotide Research, vol. 3, no. 4, pp. 239–
 W. E. Criss, F. Murad, and H. Kimura, “Properties of guany-
late cyclase from rat kidney cortex and transplantable kidney
tumors,” Journal of Cyclic Nucleotide Research, vol. 2, no. 1,
pp. 11–19, 1976.
 T. Deguchi, “Endogenous activating factor for guanylate cyc-
lase in synaptosomal-soluble fraction of rat brain,” Journal of
Biological Chemistry, vol. 252, no. 21, pp. 7617–7619, 1977.
 D. L. Garbers, J. L. Suddath, and J. G. Hardman, “Enzymatic
formation of inosine 3’,5’ monophosphate and of 2’ deoxy-
guanosine 3’,5’ monophosphate: inosinate and deoxyguany-
late cyclase activity,” Biochimica et Biophysica Acta, vol. 377,
no. 1, pp. 174–185, 1975.
 H. Kimura and F. Murad, “Localization of particulate guany-
late cyclase in plasma membranes and microsomes of rat
liver,” Journal of Biological Chemistry, vol. 250, no. 12, pp.
 E. Busse, “Proof of guanylate cyclase activity in the coronary
artery of cattle,” Acta Biologica et Medica Germanica, vol. 35,
no. 12, pp. 1595–1601, 1976.
 T. Deguchi, E. Amano, and M. Nakane, “Subcellular distri-
bution and activation by non ionic detergents of guanylate
cyclase in cerebral cortex of rat,” Journal of Neurochemistry,
vol. 27, no. 5, pp. 1027–1034, 1976.
of rat by hydroxylamine,” Journal of Biological Chemistry, vol.
252, no. 2, pp. 596–601, 1977.
 D. D. Mahaffee and D. A. Ontjes, “Properties of adenylate
cyclase solubilized from rat adrenal membranes: effects of
ACTH and other stimulators on solubilization,” Journal of
Cyclic Nucleotide Research, vol. 3, no. 5, pp. 325–334, 1977.
 K. B. Nilsson and G. G. Andersson, “Effects of carbachol and
calcium on the cyclic guanosine 3’,5’ monophosphate (cyc-
lic GMP) metabolism in intestinal smooth muscle,” Acta
Physiologica Scandinavica, vol. 99, no. 2, pp. 246–253, 1977.
 S. Katsuki and F. Murad, “Regulation of adenosine cyclic 3’,5’
monophosphate and guanosine cyclic 3’,5’ monophosphate
levels and contractility in bovine tracheal smooth muscle,”
Molecular Pharmacology, vol. 13, no. 2, pp. 330–341, 1977.
 C. A. Gruetter, P. J. Kadowitz, and L. J. Ignarro, “Methylene
blue inhibits coronary arterial relaxation and guanylate cyc-
lase activation by nitroglycerin, sodium nitrite, and amyl nit-
rite,” Canadian Journal of Physiology and Pharmacology, vol.
59, no. 2, pp. 150–156, 1981.
 J. P. Stasch and A. J. Hobbs, “NO-independent, haem-depen-
dent soluble guanylate cyclase stimulators,” Handbook of Ex-
perimental Pharmacology, vol. 191, pp. 277–308, 2009.
 A. Straub, J. P. Stasch, C. Alonso-Alija et al., “NO-indepen-
dent stimulators of soluble guanylate cyclase,” Bioorganic and
8 Critical Care Research and Practice
 O. V. Evgenov, P. Pacher, P. M. Schmidt, G. Hask´ o, H. H. H.
W. Schmidt, and J. P. Stasch, “NO-independent stimulators
and activators of soluble guanylate cyclase: discovery and
therapeutic potential,” Nature Reviews Drug Discovery, vol.
5, no. 9, pp. 755–768, 2006.
 R. F. Furchgott and J. V. Zawadzki, “The obligatory role of
endothelial cells in the relaxation of arterial smooth muscle
by acetylcholine,” Nature, vol. 288, no. 5789, pp. 373–376,
 L. J. Ignarro, “Endothelium-derived nitric oxide: pharmacol-
ogy and relationship to the actions of organic nitrate esters,”
Pharmaceutical Research, vol. 6, no. 8, pp. 651–659, 1989.
thelium-derived relaxing factor from pulmonary artery and
vein possesses pharmacologic and chemical properties iden-
61, no. 6, pp. 866–879, 1987.
 L. J. Ignarro, R. G. Harbison, K. S. Wood, and P. J.
endothelium-derived relaxing factor from intrapulmonary
artery andvein: stimulationby acetylcholine, bradykinin and
arachidonic acid,” Journal of Pharmacology and Experimental
Therapeutics, vol. 237, no. 3, pp. 893–900, 1986.
 T. J. McMahon, J. S. Hood, and P. J. Kadowitz, “Pulmonary
nitro-L-arginine methyl ester in the cat,” Circulation Rese-
arch, vol. 70, no. 2, pp. 364–369, 1992.
 B. Hauser, H. Bracht, M. Matejovic, P. Radermacher, and B.
Venkatesh, “Nitric oxide synthase inhibition in sepsis? Les-
gesia, vol. 101, no. 2, pp. 488–498, 2005.
 M. L. Blitzer, E. Loh, M. A. Roddy, J. S. Stamler, and M.
A. Creager, “Endothelium-derived nitric oxide regulates sys-
temic and pulmonary vascular resistance during acute hypo-
xia in humans,” Journal of the American College of Cardiology,
vol. 28, no. 3, pp. 591–596, 1996.
 J. A. Bellan, R. K. Minkes, D. B. McNamara, and P. J. Kad-
responses to acetylcholine and bradykinin in cats,” American
Journal of Physiology, vol. 260, no. 3, pp. H1025–H1029,
 T. J. McMahon, J. S. Hood, J. A. Bellan, and P. J. Kadowitz,
“N(ω)-nitro-L-arginine methyl ester selectively inhibits pul-
monary vasodilator responses to acetylcholine and brady-
kinin,” Journal of Applied Physiology, vol. 71, no. 5, pp. 2026–
 J. A. Panza, P. R. Casino, C. M. Kilcoyne, and A. A. Quyyumi,
“Role of endothelium-derived nitric oxide in the abnormal
endothelium- dependent vascular relaxation of patients with
essential hypertension,” Circulation, vol. 87, no. 5, pp. 1468–
 T. Lauer, M. Preik, T. Rassaf et al., “Plasma nitrite rather
activity but lacks intrinsic vasodilator action,” Proceedings
of the National Academy of Sciences of the United States of
America, vol. 98, no. 22, pp. 12814–12819, 2001.
Panza, and R. O. Cannon III, “Contribution of nitric oxide to
metabolic coronary vasodilation in the human heart,” Circu-
lation, vol. 92, no. 3, pp. 320–326, 1995.
 T. F. Luscher, “Endogenous and exogenous nitrates and their
role in myocardial ischaemia,” British Journal of Clinical
Pharmacology, vol. 34, supplement 1, pp. 29S–35S, 1992.
 G. R. J. Thatcher, A. C. Nicolescu, B. M. Bennett, and V.
Toader, “Nitrates and NO release: contemporary aspects in
biological and medicinal chemistry,” Free Radical Biology and
Medicine, vol. 37, no. 8, pp. 1122–1143, 2004.
 H. H. H. W. Schmidt, P. M. Schmidt, and J. P. Stasch, “NO-
and haem-independent soluble guanylate cyclase activators,”
Handbook of Experimental Pharmacology, vol. 191, pp. 309–
 F. B. M. Priviero and R. C. Webb, “Heme-dependent and
independent soluble guanylate cyclase activators and vasodi-
lation,” Journal of Cardiovascular Pharmacology, vol. 56, no.
3, pp. 229–233, 2010.
tivation and nitrate tolerance: news, views and troubles,”
British Journal of Pharmacology, vol. 155, no. 2, pp. 170–184,
 W. Murrell, “Nitro-Glycerine in angina pectoris,” The Lancet,
vol. 1, pp. 80–81, 1879.
 T. L. Brunton, “On the use of nitrite of amyl in angina pec-
toris,” The Lancet, vol. 90, no. 2291, pp. 97–98, 1867.
 M.G.Bogaert,“Organic nitratesinanginapectoris,” Archives
Internationales de Pharmacodynamie et de Therapie, vol. 196,
supplement 196, p. 125, 1972.
 D. J. Battock, P. W. Levitt, and P. P. Steele, “Effects of
isosorbide dinitrate and nitroglycerin on central circulatory
dynamics in coronary artery disease,” American Heart Jour-
nal, vol. 92, no. 4, pp. 455–458, 1976.
 S. Silber, “Nitrates: why and how should they be used today?
Current status of the clinical usefulness of nitroglycerin,
isosorbide dinitrate and isosorbide-5-mononitrate,” Euro-
pean Journal of Clinical Pharmacology, vol. 38, supplement
1, pp. S35–S51, 1990.
 J. A. Parker, “Organic nitrates: new formulations and their
clinical advantages,” American Journal of Cardiology, vol. 77,
no. 13, pp. 38C–40C, 1996.
 J. D. Artz, B. Schmidt, J. L. McCracken, and M. A. Marletta,
“Effects of nitroglycerin on soluble guanylate cyclase: impli-
cations for nitrate tolerance,” Journal of Biological Chemistry,
vol. 277, no. 21, pp. 18253–18256, 2002.
 M. Beretta, K. Gruber, A. Kollau et al., “Bioactivation of
nitroglycerin by purified mitochondrial and cytosolic alde-
hyde dehydrogenases,” Journal of Biological Chemistry, vol.
283, no. 26, pp. 17873–17880, 2008.
 D.B.Casey,A.M.BadejoJr.,J.S.Dhaliwal etal.,“Pulmonary
vasodilator responses to sodium nitrite are mediated by
an allopurinol-sensitive mechanism in the rat,” American
Journal of Physiology, vol. 296, no. 2, pp. H524–H533, 2009.
 L. J. Ignarro, C. Napoli, and J. Loscalzo, “Nitric oxide donors
and cardiovascular agents modulating the bioactivity of nit-
ric oxide: an overview,” Circulation Research, vol. 90, no. 1,
pp. 21–28, 2002.
 J. B. Johnson, A. Fairley, and C. Carter, “Effects of sublingual
nitroglycerin on pulmonary arterial pressure in patients with
left ventricular failure,” Annals of Internal Medicine, vol. 50,
no. 1, pp. 34–42, 1959.
 R. E. Fremont, “The actions of organic nitrates on the car-
diopulmonary and peripheral circulations,” Angiology, vol.
12, pp. 391–400, 1961.
 E. Mikulic, J. A. Franciosa, and J. N. Cohn, “Comparative
hemodynamic effects of chewable isosorbide dinitrate and
nitroglycerin inpatients withcongestive heartfailure,”Circu-
lation, vol. 52, no. 3, pp. 477–482, 1975.
Critical Care Research and Practice9
 Y. Charuzi, “Use of nitroglycerin ointment in acute pulmo-
nary edema and hypertension,” Chest, vol. 82, no. 6, p. 800,
 H. I. Palevsky and A. P. Fishman, “Vasodilator therapy for
primary pulmonary hypertension,” Annual Review of Medi-
cine, vol. 36, pp. 563–578, 1985.
 H. Bundgaard, S. Boesgaard, S. A. Mortensen, H. Arendrup,
and J. Aldershvile, “Effect of nitroglycerin in patients with
increased pulmonary vascular resistance undergoing cardiac
transplantation,” Scandinavian Cardiovascular Journal, vol.
31, no. 6, pp. 339–342, 1997.
 A. S. Pearlman, R. L. Engler, R. A. Goldstein, K. M. Kent,
and S. E. Epstein, “Relative effects of nitroglycerin and nitro-
prusside during experimental acute myocardial ischemia,”
European Journal of Cardiology, vol. 11, no. 4, pp. 295–313,
 GISSI-3 Investigators, “GISSI-3: effects of lisinopril and
transdermal glyceryl binitrate singly and together on 6-week
mortality and ventricular function after acute myocardial
nell’infarto Miocardico,” The Lancet, vol. 343, no. 8906, pp.
 B. I. Jugdutt, “Nitrates in myocardial infarction,” Cardiovas-
cular Drugs and Therapy, vol. 8, no. 4, pp. 635–646, 1994.
 H. L. Lippton, C. A. Gruetter, L. J. Ignarro, R. L. Meyer, and
pounds,” Canadian Journal of Physiology and Pharmacology,
vol. 60, no. 1, pp. 68–75, 1982.
 L. J. Ignarro, H. Lippton, J. C. Edwards et al., “Mechanism of
vascular smooth muscle relaxation by organic nitrates, nit-
rites, nitroprusside and nitric oxide: evidence for the involve-
ment of S-Nitrosothiols as active intermediates,” Journal of
Pharmacology and Experimental Therapeutics, vol. 218, no. 3,
pp. 739–749, 1981.
 L. J. Ignarro and C. A. Gruetter, “Requirement of thiols for
activation of coronary arterial guanylate cyclase by glyceryl
trinitrate and sodium nitrite: possible involvement of S-nit-
rosothiols,” Biochimica et Biophysica Acta, vol. 631, no. 2, pp.
 G. Kojda, M. Patzner, A. Hacker, and E. Noack, “Nitric oxide
inhibits vascular bioactivation of glyceryl trinitrate: a novel
mechanism to explain preferential venodilation of organic
nitrates,” Molecular Pharmacology, vol. 53, no. 3, pp. 547–
 Z. Chen, J. Zhang, and J. S. Stamler, “Identification of the
enzymatic mechanism of nitroglycerin bioactivation,” Pro-
ceedings of the National Academy of Sciences of the United
States of America, vol. 99, no. 12, pp. 8306–8311, 2002.
 F. Murad, C. K. Mittal, W. P. Arnold, S. Katsuki, and H.
Kimura, “Guanylate cyclase: activation by azide, nitro com-
pounds, nitric oxide, and hydroxyl radical and inhibition by
hemoglobin and myoglobin,” Advances in Cyclic Nucleotide
Research, vol. 9, pp. 145–158, 1978.
 P. Needleman, B. Jakschik, and E. M. Johnson Jr., “Sulfhydryl
requirement for relaxation of vascular smooth muscle,” Jour-
nal of Pharmacology and Experimental Therapeutics, vol. 187,
no. 2, pp. 324–331, 1973.
 P. Needleman, “Organic nitrate metabolism,” Annual Review
of Pharmacology and Toxicology, vol. 16, pp. 81–93, 1976.
 P. Needleman and E. M. Johnson Jr., “Mechanism of toler-
ance development to organic nitrates,” Journal of Pharmacol-
ogy and Experimental Therapeutics, vol. 184, no. 3, pp. 709–
 S. Tsuchida, T. Maki, and K. Sato, “Purification and charac-
terization of glutathione transferases with an activity toward
human class Mu forms,” Journal of Biological Chemistry, vol.
265, no. 13, pp. 7150–7157, 1990.
 R. A. Yeates, M. Schmid, and M. Leitold, “Antagonism
of glycerol trinitrate activity by an inhibitor of glutathione
S-transferase,” Biochemical Pharmacology, vol. 38, no. 11, pp.
 T. M. Millar, C. R. Stevens, N. Benjamin, R. Eisenthal, R.
Harrison, and D. R. Blake, “Xanthine oxidoreductase catal-
yses the reduction of nitrates and nitrite to nitric oxide under
hypoxic conditions,” FEBS Letters, vol. 427, no. 2, pp. 225–
 B. J. McDonald and B. M. Bennett, “Cytochrome P-450 med-
iated biotransformation of organic nitrates,” Canadian Jour-
nal of Physiology and Pharmacology, vol. 68, no. 12, pp. 1552–
 B. J. McDonald and B. M. Bennett, “Biotransformation of
glyceryl trinitrate by rat aortic cytochrome P450,” Biochemi-
cal Pharmacology, vol. 45, no. 1, pp. 268–270, 1993.
 P. Seth and H. L. Fung, “Biochemical characterization of a
membrane-bound enzyme responsible for generating nitric
oxide from nitroglycerin in vascular smooth muscle cells,”
Biochemical Pharmacology, vol. 46, no. 8, pp. 1481–1486,
 J. J. McGuire, D. J. Anderson, B. J. McDonald, R.
Narayanasami, and B. M. Bennett, “Inhibition of NADPH-
cytochrome P450 reductase and glyceryl trinitrate biotrans-
formation by diphenyleneiodonium sulfate,” Biochemical
Pharmacology, vol. 56, no. 7, pp. 881–893, 1998.
 Z. Chen, M. W. Foster, J. Zhang et al., “An essential role
for mitochondrial aldehyde dehydrogenase in nitroglycerin
bioactivation,” Proceedings of the National Academy of Sci-
ences of the United States of America, vol. 102, no. 34, pp.
 M. Packer, W. H. Lee, P. D. Kessler, S. S. Gottlieb, N. Medina,
and M. Yushak, “Prevention and reversal of nitrate tolerance
in patients with congestive heart failure,” The New England
Journal of Medicine, vol. 317, no. 13, pp. 799–804, 1987.
 E. Noack and M. Feelisch, “Molecular mechanisms of nitro-
vasodilator bioactivation,” Basic Research in Cardiology, vol.
86, supplement 2, pp. 37–50, 1991.
 C. N´ u˜ nez, V. M. V´ ıctor, R. Tur et al., “Discrepancies between
nitroglycerin and NO-releasing drugs on mitochondrial oxy-
lation Research, vol. 97, no. 10, pp. 1063–1069, 2005.
 M. Feelisch and M. Kelm, “Biotransformation of organic
nitrates to nitric oxide by vascular smooth muscle and endo-
cations, vol. 180, no. 1, pp. 286–293, 1991.
 K. Schror, S. Forster, and I. Woditsch, “On-line measurement
nary circulation,” Naunyn-Schmiedeberg’s Archives of Phar-
macology, vol. 344, no. 2, pp. 240–246, 1991.
 G. S. Marks, B. E. McLaughlin, K. Nakatsu, and J. F. Brien,
“Direct evidence for nitric oxide formation from glyceryl
trinitrate during incubation with intact bovine pulmonary
artery,” Canadian Journal of Physiology and Pharmacology,
vol. 70, no. 2, pp. 308–311, 1992.
 S. J. Chung and H. L. Fung, “Relationship between nitro-
glycerin-induced vascular relaxation and nitric oxide pro-
duction: probes with inhibitors and tolerance development,”
Biochemical Pharmacology, vol. 45, no. 1, pp. 157–163, 1993.
10Critical Care Research and Practice
 M. Feelisch, F. Brands, and M. Kelm, “Human endothelial
cells bioactivate organic nitrates to nitric oxide. Implications
for the reinforcement of endothelial defence mechanisms,”
European Journal of Clinical Investigation, vol. 25, no. 10, pp.
 A. Mulsch, A. Bara, P. Mordvintcev, A. Vanin, and R. Busse,
“Specificity of different organic nitrates to elicit NO forma-
tion in rabbit vascular tissues and organs in vivo,” British
 W. N. Kuo, J. M. Kocis, M. J. Robinson, J. Nibbs, and R.
Nayar, “Further study on s-nitrosation by nitrite,” Frontiers
in Bioscience, vol. 8, pp. a143–a147, 2003.
 D. J. Meyer, H. Kramer, and B. Ketterer, “Human glutathione
transferase catalysis of the formation of S-nitrosoglutathione
no. 3, pp. 427–428, 1994.
 H. Zeng, N. Y. Spencer, and N. Hogg, “Metabolism of S-nit-
rosoglutathione by endothelial cells,” American Journal of
Physiology, vol. 281, no. 1, pp. H432–H439, 2001.
 M. Sarr, I. Lobysheva, A. S. Diallo, J. C. Stoclet, V. B. Schini-
Kerth, and B. Muller, “Formation of releasable NO stores by
S-nitrosoglutathione in arteries exhibiting tolerance to gly-
ceryl-trinitrate,” European Journal of Pharmacology, vol. 513,
no. 1-2, pp. 119–123, 2005.
 M. W. Foster, T. J. McMahon, and J. S. Stamler, “S-nitro-
sylation in health and disease,” Trends in Molecular Medicine,
vol. 9, no. 4, pp. 160–168, 2003.
 P. R. A. Caramori, A. G. Adelman, E. R. Azevedo, G. E.
Newton, A. B. Parker, and J. D. Parker, “Therapy with nitro-
glycerin increases coronary vasoconstriction in response to
acetylcholine,” Journal of the American College of Cardiology,
vol. 32, no. 7, pp. 1969–1974, 1998.
 E. R. Azevedo, A. M. Schofield, S. Kelly, and J. D. Parker,
vasomotor response to acetylcholine,” Journal of the Ameri-
can College of Cardiology, vol. 37, no. 2, pp. 505–509, 2001.
 E. Schulz, N. Tsilimingas, R. Rinze et al., “Functional and
biochemical analysis of endothelial (Dys)function and NO/
cGMP signaling in human blood vessels with and without
nitroglycerin pretreatment,” Circulation, vol. 105, no. 10, pp.
 C. Napoli and L. J. Ignarro, “Nitric oxide and pathogenic
mechanisms involved in the development of vascular dis-
eases,” Archives of Pharmacal Research, vol. 32, no. 8, pp.
 G. Berkenboom, P. Unger, and J. Fontaine, “Atherosclerosis
and responses of human isolated coronary arteries to endo-
thelium-dependent and -independent vasodilators,” Journal
of Cardiovascular Pharmacology, vol. 14, supplement 11, pp.
nary arteries of cardiac transplant patients to acetylcholine,”
Journal of Clinical Investigation, vol. 81, no. 1, pp. 21–31,
a novel activator of platelet guanylate cyclase,” Blood, vol. 84,
no. 12, pp. 4226–4233, 1994.
 C. C. Wu, F. N. Ko, S. C. Kuo, F. Y. Lee, and C. M. Teng,
“YC-1 inhibited human platelet aggregation through NO-
independent activation of soluble guanylate cyclase,” British
 A. Friebe, G. Schultz, and D. Koesling, “Sensitizing soluble
guanylyl cyclase to become a highly CO-sensitive enzyme,”
The EMBO Journal, vol. 15, no. 24, pp. 6863–6868, 1996.
 M. Feelisch, P. Kotsonis, J. Siebe, B. Clement, and H. H.
H. W. Schmidt, “The soluble guanylyl cyclase inhibitor 1H-
[1,2,4]oxadiazolo-[4,3,-a]quinoxalin-1-one is a nonselective
heme protein inhibitor of nitric oxide synthase and other
cytochrome P-450 enzymes involved in nitric oxide donor
bioactivation,” Molecular Pharmacology, vol. 56, no. 2, pp.
 B. M. Bennett, B. J. McDonald, R. Nigam, and W. C. Simon,
“Biotransformation of organic nitrates and vascular smooth
muscle cell function,” Trendsin Pharmacological Sciences,vol.
15, no. 7, pp. 245–249, 1994.
 A. M¨ ulsch, J. Bauersachs, A. Sch¨ afer, J.-P. Stasch, R. Kast, and
R. Busse, “Effect of YC-1, an NO-independent, superoxide-
sensitive stimulator of soluble guanylyl cyclase, on smooth
Pharmacology, vol. 120, no. 4, pp. 681–689, 1997.
a nitric oxide-independent activator of soluble guanylate
cyclase, inhibits platelet-rich thrombosis in mice,” European
Journal of Pharmacology, vol. 320, no. 2-3, pp. 161–166,
 J. W. Wegener, I. Gath, U. F¨ orstermann, and H. Nawrath,
“Activation of soluble guanylyl cyclase by YC-1 in aortic
smooth muscle but not in ventricular myocardium from rat,”
British Journal of Pharmacology, vol. 122, no. 7, pp. 1523–
 C.-C. Wu, F.-N. Ko, and C.-M. Teng, “Inhibition of platelet
adhesion to collagen by cGMP-elevating agents,” Biochemical
and Biophysical Research Communications, vol. 231, no. 2, pp.
 A. Straub, J. Benet-Buckholz, R. Fr¨ ode et al., “Metabolites of
orally active NO-independent pyrazolopyridine stimulators
of soluble guanylate cyclase,” Bioorganic and Medicinal Che-
mistry, vol. 10, no. 6, pp. 1711–1717, 2002.
 J. P. Stasch, C. Alonso-Alija, H. Apeler et al., “Pharmaco-
logical actions of a novel NO-independent guanylyl cyclase
stimulator, BAY 41-8543: in vitro studies,” British Journal of
Pharmacology, vol. 135, no. 2, pp. 333–343, 2002.
 J. P. Stasch, E. M. Becker, C. Alonso-Alija et al., “NO-inde-
pendent regulatory site on soluble guanylate cyclase,” Nature,
vol. 410, no. 6825, pp. 212–215, 2001.
 O. V. Evgenov, D. S. Kohane, K. D. Bloch et al., “Inhaled ago-
nists of soluble guanylate cyclase induce selective pulmonary
vasodilation,” American Journal of Respiratory and Critical
Care Medicine, vol. 176, no. 11, pp. 1138–1145, 2007.
 C. F. Freitas, R. P. Morganti, J. M. Annichino-Bizzacchi, G.
De Nucci, and E. Antunes, “Effect of bay 41-2272 in the
pulmonary hypertension induced by heparin-protamine
complex in anaesthetized dogs,” Clinical and Experimental
Pharmacology and Physiology, vol. 34, no. 1-2, pp. 10–14,
 P. Deruelle, T. R. Grover, L. Storme, and S. H. Abman,
on pulmonary vascular reactivity in the ovine fetus,” Amer-
ican Journal of Physiology, vol. 288, no. 4, pp. L727–L733,
 P. Deruelle, T. R. Grover, and S. H. Abman, “Pulmonary
vascular effects of nitric oxide-cGMP augmentation in a
model of chronic pulmonary hypertension in fetal and neo-
natal sheep,” American Journal of Physiology, vol. 289, no. 5,
pp. L798–L806, 2005.
 P. Deruelle, V. Balasubramaniam, A. M. Kunig, G. J. See-
dorf, N. E. Markham, and S. H. Abman, “BAY 41-2272,
a direct activator of soluble guanylate cyclase, reduces right
Critical Care Research and Practice 11
ventricular hypertrophy and prevents pulmonary vascular
remodeling during chronic hypoxia in neonatal rats,” Biology
of the Neonate, vol. 90, no. 2, pp. 135–144, 2006.
lyl cyclase stimulator, BAY 41-8543, are modulated by nitric
oxide,” American Journal of Physiology, vol. 299, no. 4, pp.
 O. V. Evgenov, F. Ichinose, N. V. Evgenov et al., “Soluble
guanylate cyclase activator reverses acute pulmonary hyper-
tension and augments the pulmonary vasodilator response
to inhaled nitric oxide in awake lambs,” Circulation, vol. 110,
no. 15, pp. 2253–2259, 2004.
 S. A. Doggrell, “Clinical potential of nitric oxide-indepen-
dent soluble guanylate cyclase activators,” Current Opinion in
Investigational Drugs, vol. 6, no. 9, pp. 874–878, 2005.
 P. Schmidt, M. Schramm, H. Schr¨ oder, and J.-P. Stasch,
“Mechanisms of nitric oxide independent activation of solu-
ble guanylyl cyclase,” European Journal of Pharmacology, vol.
468, no. 3, pp. 167–174, 2003.
basis and cardiovascular implications of a new pharmacolog-
ical principle,” British Journal of Pharmacology, vol. 136, no.
5, pp. 773–783, 2002.
 J. Mittendorf, S. Weigand, C. Alonso-Alija et al., “Discovery
of riociguat (BAY 63-2521): a potent, oral stimulator of solu-
ble guanylate cyclase for the treatment of pulmonary hyper-
tension,” ChemMedChem, vol. 4, no. 5, pp. 853–865, 2009.
 R. Frey, W. M¨ uck, S. Unger, U. Artmeier-Brandt, G.
Weimann, and G. Wensing, “Single-dose pharmacokinetics,
pharmacodynamics, tolerability, and safety of the soluble
cology, vol. 48, no. 8, pp. 926–934, 2008.
 F. Grimminger, G. Weimann, R. Frey et al., “First acute hae-
ciguat in pulmonary hypertension,” European Respiratory
Journal, vol. 33, no. 4, pp. 785–792, 2009.
 H. A. Ghofrani, M. M. Hoeper, M. Halank et al., “Riociguat
for chronic thromboembolic pulmonary hypertension and
pulmonary arterial hypertension: a phase II study,” European
Respiratory Journal, vol. 36, no. 4, pp. 792–799, 2010.
 M. S. Wolin, “Reactive oxygen species and the control of
vascular function,” American Journal of Physiology, vol. 296,
no. 3, pp. H539–H549, 2009.
 P. M. Schmidt, M. Schramm, H. Schr¨ oder, F. Wunder, and
J. P. Stasch, “Identification of residues crucially involved in
the binding of the heme moiety of soluble guanylate cyclase,”
Journal of Biological Chemistry, vol. 279, no. 4, pp. 3025–
 U. Schindler, H. Strobel, K. Sch¨ onafinger et al., “Biochem-
istry and pharmacology of novel anthranilic acid derivatives
Pharmacology, vol. 69, no. 4, pp. 1260–1268, 2006.
 Y. Zhao, P. E. Brandish, M. DiValentin, J. P. M. Schelvis, G. T.
Babcock, and M. A. Marletta, “Inhibition of soluble guany-
late cyclase by ODQ,” Biochemistry, vol. 39, no. 35, pp.
 E. A. Dierks and J. N. Burstyn, “The deactivation of soluble
guanylyl cyclase by redox-active agents,” Archives of Biochem-
istry and Biophysics, vol. 351, no. 1, pp. 1–7, 1998.
 K. Schmidt, W. F. Graier, G. M. Kostner, B. Mayer, E. Bohme,
and W. R. Kukovetz, “Oxidized low-density lipoprotein anta-
gonizes the activation of purified soluble guanylate cyclase by
endothelium-derived relaxing factor but does not interfere
with its biosynthesis,” Cellular Signalling, vol. 3, no. 4, pp.
 J. Galle, A. Mulsch, R. Busse, and E. Bassenge, “Effects of
native and oxidized low density lipoproteins on formation
and inactivation of endothelium-derived relaxing factor,”
Arteriosclerosis and Thrombosis, vol. 11, no. 1, pp. 198–203,
 P. A. Craven and F. R. DeRubertis, “Restoration of the res-
ponsiveness of purified guanylate cyclase to nitrosoguani-
dine, nitric oxide, and related activators by heme and heme-
proteins: evidence for involvement of the paramagnetic
nitrosyl.heme complex in enzyme activation,” Journal of Bio-
logical Chemistry, vol. 253, no. 23, pp. 8433–8443, 1978.
resonance study of the role of nitrosyl-heme in the activation
of guanylate cyclase by nitrosoguanidine and related ago-
vol. 83, no. 1, pp. 158–167, 1978.
 U. Elkayam, A. Roth, A. Mehra et al., “Randomized study to
evaluate the relation between oral isosorbide dinitrate dosing
left ventricular filling pressure in patients with chronic heart
failure,” Circulation, vol. 84, no. 5, pp. 2040–2048, 1991.
 U. Elkayam, “Tolerance to organic nitrates: evidence, mech-
anisms, clinical relevance, and strategies for prevention,” An-
nals of Internal Medicine, vol. 114, no. 8, pp. 667–677, 1991.
 M. Schwemmer and E. Bassenge, “New approaches to over-
come tolerance to nitrates,” Cardiovascular Drugs and Ther-
apy, vol. 17, no. 2, pp. 159–173, 2003.
 R.Dumitrascu, N.Weissmann, H.A.Ghofrani etal., “Activa-
tion of soluble guanylate cyclase reverses experimental pul-
monary hypertension and vascular remodeling,” Circulation,
vol. 113, no. 2, pp. 286–295, 2006.
 J. P. Stasch, P. M. Schmidt, P. I. Nedvetsky et al., “Targeting
the heme-oxidized nitric oxide receptor for selective vasodi-
latation of diseased blood vessels,” Journal of Clinical Investi-
gation, vol. 116, no. 9, pp. 2552–2561, 2006.
 G. Boerrigter, L. C. Costello-Boerrigter, A. Cataliotti, H.
Lapp, J. P. Stasch, and J. C. Burnett Jr., “Targeting heme-oxi-
Hypertension, vol. 49, no. 5, pp. 1128–1133, 2007.
 S. Thom, A. Hughes, G. Martin, and P. S. Sever, “Endothe-
lium-dependent relaxation in isolated human arteries and
veins,” Clinical Science, vol. 73, no. 5, pp. 547–552, 1987.
 T. J. McMahon and P. J. Kadowitz, “Methylene blue inhibits
neurogenic cholinergic vasodilator responses in the pulmo-
nary vascular bed of the cat,” American Journal of Physiology,
vol. 263, no. 5, pp. L575–L584, 1992.
 D. B. Casey, A. M. Badejo Jr., J. S. Dhaliwal et al., “Analysis
of responses to the Rho-kinase inhibitor Y-27632 in the
pulmonary and systemic vascular bed of the rat,” American
Journal of Physiology, vol. 299, no. 1, pp. H184–H192,
 P. Vuorinen, I. Porsti, T. Metsa-Ketela, V. Manninen, H.
Vapaatalo, and K. E. Laustiola, “Modification of nitrova-
sodilator effects on vascular smooth muscle by exogenous
GTP and guanosine,” Journal of Cardiovascular Pharmacol-
ogy, vol. 18, no. 6, pp. 871–877, 1991.
12Critical Care Research and Practice
 C. J. Feng, D. Y. Cheng, A. D. Kaye, P. J. Kadowitz, and B. D.
 S. N. Murthy, B. D. Nossaman, and P. J. Kadowitz, “New
approaches to the treatment of pulmonary hypertension:
from bench to bedside,” Cardiology in Review, vol. 18, no. 2,
pp. 76–84, 2010.
 E. A. Pankey, M. Bhartiya, A. M. Badejo Jr. et al., “Pulmonary
and systemic vasodilator responses to the soluble guanylyl
nous nitric oxide or reduced heme,” American Journal of
Physiology, vol. 300, no. 3, pp. H792–H802, 2011.
 S. Korkmaz, T. Radovits, E. Barnucz et al., “Pharmacological
activation of soluble guanylate cyclase protects the heart
against ischemic injury,” Circulation, vol. 120, no. 8, pp. 677–
 T. Radovits, S. Korkmaz, C. Miesel-Gr¨ oschel et al., “Pre-
conditioning with the soluble guanylate cyclase activator
Cinaciguat reduces ischaemia-reperfusion injury after car-
diopulmonary bypass,” European Journal of Cardio-thoracic
Surgery, vol. 39, no. 2, pp. 248–255, 2011.
 G. Boerrigter, H. Lapp, and J. C. Burnett Jr., “Modulation of
cGMP in heart failure: a new therapeutic paradigm,” Hand-
book of Experimental Pharmacology, vol. 191, pp. 485–506,
 B. D. Nossaman, H. A. Akuly, G. F. Lasker, V. E. Nossaman, P.
A. Rothberg, and P. J. Kadowitz, “The reemergence of nitrite
as a beneficial agent in the treatment of ischemic cardiovas-
cular diseases,” Asian Journal of Experimental Biological Sci-
ences, vol. 1, no. 2, pp. 451–459, 2010.
 V. E. Nossaman, B. D. Nossaman, and P. J. Kadowitz, “Nitra-
tes and nitrites in the treatment of ischemic cardiac disease,”
Cardiology in Review, vol. 18, no. 4, pp. 190–197, 2010.
 R. Frey, W. M¨ uck, S. Unger, U. Artmeier-Brandt, G.
Weimann, and G. Wensing, “Pharmacokinetics, pharmaco-
dynamics, tolerability, and safety of the soluble guanylate
cyclase activator cinaciguat (BAY 58-2667) in healthy male
volunteers,” Journal of Clinical Pharmacology, vol. 48, no. 12,
pp. 1400–1410, 2008.
 H. Lapp, V. Mitrovic, N. Franz et al., “Cinaciguat (BAY 58-
2667) improves cardiopulmonary hemodynamics in patients
with acute decompensated heart failure,” Circulation, vol.
119, no. 21, pp. 2781–2788, 2009.