FARMACIA, 2009, Vol. 57, 2
131
THE ROLE OF NITRIC OXIDE (NO) AND
STATINS IN ENDOTHELIAL DYSFUNCTION
AND ATHEROSCLEROSIS
MARIA SUCIU
University of Medicine and Pharmacy “Victor Babes“, Faculty of
Pharmacy, Department of Pharmacology and Clinical Pharmacy, P-ta
Eftimie Murgu, No. 2, 300041, Timişoara, Romania
*
corresponding author: [email protected]
Abstract
Vascular endothelium plays an essential role in the regulation of the vascular tone,
contributing to maintaining the balance between vasodilatation – vasoconstriction, owing to the
production of endogenous nitric oxide (NO) under the action of different endogenous and
exogenous factors. The loss of the functional integrity of the vascular endothelium, called
endothelial dysfunction, in different hearth diseases, is associated with the damage of NO
production. Atherosclerosis, an inflammatory chronic disease, is characterised from the
beginning through leukocytes adhesion to the vascular endothelium, the first step of endothelial
dysfunction in atherosclerosis. Statins, recently introduced in the therapy for lowering the
cholesterol level, through this effect and also the pleiotropic effects, improve the endothelial
dysfunction through the increase of endogenous production of NO in different pathways.
Rezumat
Endoteliul vascular joacă un rol cheie în reglarea tonusului vascular contribuind
la menţinerea unui echilibru între vasodilataţie – vasoconstricţie, datorită producţiei
endogene de oxid nitric (NO) sub acţiunea diferiţilor factori endogeni şi exogeni. Pierderea
integrităţii funcţionale a endoteliului vascular, denumită disfuncţie endotelială, în diferite
boli cardiovasculare, este asociată cu pierderea capacităţii de producţie a NO.
Ateroscleroza, afecţiune inflamatorie cronică, se caracterizează de la început prin adeziunea
leucocitelor de endoteliul vascular, prim pas al disfuncţiei endoteliale în ateroscleroză.
Statinele, recent introduse în terapia hipercolesterolemiei, atât prin efectul de scădere a
concentraţiei colesterolului, cât şi prin aşa numitele efecte pleiotrope ale lor, îmbunătăţesc
disfuncţia endotelială prin creşterea producţiei endogene de NO prin diferite mecanisme.
Keywords: nitric oxide, statins, endothelial dysfunction, atherosclerosis
The role of nitric oxide in endothelial dysfunction and atherosclerosis
Until 1980 vascular endothelium was considered a passive, semi
permeable barrier with role in bidirectional changes between blood and
tissue gases, ions, endogenous and exogenous substances with a small
molecular weight. In 1980, this perception was modified with the studies of
Furchgott and Zawadzki, who established the necessity of an intact vascular
endothelium in order to obtain a vasodilatation induced by acetylcholine.
From this moment, vascular endothelium demonstrated to have an active
132
FARMACIA, 2009, Vol. 57, 2
role in the vascular homeostasis regulation. Later, these scientists pointed
out an endothelial relaxation factor EDHF (endothelium derived
hyperpolarizing factor) liberated by acetylcholine in the presence of an
intact endothelium. When the endothelium is impaired, acetylcholine
produces constriction as a result of the vasoconstrictor effects on the smooth
muscle, which aren’t counteracted [1]. This was identified as the nitric
oxide, because both have similar chemical and biological properties [2, 3].
In the vascular endothelial cells (figure 1), NO is formed from the
terminal guanidino nitrogen of the amino acid L-arginine during the
conversion to L-citrulline. This reaction is catalysed by the endothelial
isoform of NO syntase (eNOS), which is constitutive expressed, activated
and regulated by calcium and calmoduline [5].
Figure 1
Synthesis of NO-derived endothelium (Richard E. Klabunde, Cardiovascular Physiology Concepts)
(GC – guanylyl cyclase; cGMP- 3,5,-cyclic guanosine monophosphate, iNOS- inducible isoform of nitric oxide synthase)
Figure 2
Mechanism of action of NO derived endothelium in the regulation of the vascular tone
(Exerc. Sport Sci. Rev., 2004)
(eNOS- endothelial isoform of nitric oxide synthase; ecSOD- extracellular superoxide dismutase)
FARMACIA, 2009, Vol. 57, 2
133
Once it was synthesized, NO diffuses from the endothelial cell to
the vascular smooth muscle cell, where it activates the enzyme guanylat
cyclase (GC) which catalyses the transformation of GTP into cGMP (figures
1 and 2). The increase of cGMP activates a protein kinase GMP-dependent
which induces the kinase phosphorylation of the slight chain of myosin and
has as result the stabilization of the inactive form of myosin [5]. The result
of this action is the consecutive vasodilatation.
Recent studies have shown that beside the role in the control of the
vascular tone, NO endothelial derived (EDNO) has other roles in the
prophylaxis of atherosclerosis: regulation of the platelet function (platelet
aggregation and adhesion), vascular increasing and remodelling (inhibits
the proliferation and migration of the vascular and myocardial smooth
muscle cells), role in the adhesion of the inflammatory cells on the
endothelial surface, role in the modulation of the oxidative stress and
oxidation of LDL and also regulation of the apoptosis in atherosclerosis [6].
The sum-up of two factors: the loss of the vascular relaxation
directly dependent of the endothelium (flow – dependent) and the NO
dependent are the main reason for endothelial dysfunction and play a very
important role in the pathogenesis of heart failure. Endothelial dysfunction
on vascular peripheral levels contributes to the increased peripheral
resistance in patients with heart failure [7]. Endothelial dysfunction, as a
pathophysiology disorder, is early present in the initiation of the
atherosclerotic process. It represents an important risk factor for
atherosclerosis, as well as for other vascular diseases.
The bound between atherosclerosis and the impairment of EDNO was
first shown by Ludmer and his colleagues, who demonstrated that intracoronary
perfusion with acetylcholine produces vasoconstriction in the epicardic
coronary arteries in patients with angiographic evidence of atherosclerosis [8].
Otherwise the response of these patients to infusion with nitro-glycerine is
vasodilatation, which demonstrates that the vascular endothelium has kept its
capacity of response to exogenous NO; it only lost the capacity to generate
EDNO, endogenous NO. The injury of EDNO activity seems to appear early in
the atherosclerotic process, which is proved by the impaired coronary
vasodilatation response to perfusion with acetylcholine at a lot of patients with
hypertension [9], hypercholesterolemia [10], diabetes [11] or smokers [12],
before the appearance of the angiographic signs of atherosclerosis. In addition
to the early role in the initiation of the atherosclerotic process, the generation of
the atheromatous plaque in stable coronary diseases, the injury of EDNO
activity plays an important role itself or with the consequences it produces, and
in the splitting of the plaque, contributing then to the pathogenesis of acute
134
FARMACIA, 2009, Vol. 57, 2
coronary syndromes, which is demonstrated by the fact that the loss of NOdependent vasodilatation leads to increasing shear stress [13] from the vessels,
which can increase the risk for plaque rupture.
Mechanisms (figure 3) which are essential for the impairment of EDNO
activity, respectively for the appearance of endothelial dysfunction [14, 15] are:
• dysfunctional signal transduction receptor – endothelial cell;
• decreased bioavailability of the substrate L- arginine;
• altered expression of gene NOS3 and stability of mARN;
polymorphism NOS3;
• altered eNOS activity;
• increased destruction of NO;
• changes in the balance between NO derived endothelium and the
hyperpolarizing factor (EDHF);
• decreased sensitivity of atherosclerotic smooth muscle to NO.
Figure 3
Mechanisms of NO-related vascular endothelial dysfunction in atherosclerosis and
hypercholesterolemia [14]
(THB- tetrahydrobiopterin; EDHF- endothelium-derived hyperpolarizing factor; ADMA- asymmetric
dimethylarginine; DDAH- dimethylarginine dimethyaminohydrolase; AT1- angiotensin II subtype 1 receptor)
The role of the statins in endothelial dysfunction and atherosclerosis
Atherosclerosis, considered a long time as a passive process of
cholesterol accumulation in the arteries walls, is now identified to be an
inflammatory chronic process, where the inflammation is present in all its
steps, from the initiation, progression and splitting of the plaque to the
thrombosis complications of the atherosclerosis [16]. During the
atherosclerosis process the normal functional homeostasis of the vascular
FARMACIA, 2009, Vol. 57, 2
135
endothelium is affected as a response to any kind of aggression to the
endothelium, leukocyte adhesion to the impaired endothelial cells
representing the first step of this inflammatory process [17].
The discovery of the statins represents an important progress in the
treatment of atherosclerosis through its direct action on the cholesterol
through competitive inhibition of 3-hydroxy-3-methylglutaryl coenzyme A
reductase (HMG-CoA reductase), which has as result the decrease of
endogenous cholesterol synthesis in the liver and the increase of the LDL
cholesterol catabolism ( it results the decrease of the cholesterol level in the
organism) and also through the pleiotropic effects (figure 4) which interfere
with a lot of atherosclerotic components, like cell migration, endothelial
function, splitting of the plaque, tendency to thrombosis, etc [18].
The role of statins related to lowering of cholesterol
Mechanisms, which contribute to the lowering of cholesterol,
increased in atherosclerosis, are [19]:
• inhibition of HMG CoA reductase, the enzyme that converts HMGCoA into mevalonic acid, a cholesterol endogenous precursor;
• direct effects of HMG CoA reductase inhibition, inhibiting liverwort
the synthesis of apolipoprotein B-100, determining a reduction of the
synthesis and secretion of triglyceride rich lipoproteins;
• reduction of LDL susceptibility towards oxidation;
• inhibition of the expression of type A scavenger receptor in THP -1
cells and human monocytes, which decreases the receptor-mediated
degradation of oxidised LDL.
Figure 4
Immunomodulatory mechanisms of statins [20]
(SMC- smooth muscle cells; IFNγ- interferon γ; LFA-1- leukocyte function antigen-1;
ICAM-1- intercellular adhesion molecule 1)
136
FARMACIA, 2009, Vol. 57, 2
Pleiotropic effects of statins
Beside the effects on the cholesterol, the statins present a lot of
other actions, known as the pleiotropic effects of the statins. These are
defined to be the effects other than those due to lowering LDL levels and
independent of the LDL level, like:
• improved endothelial function
• diminish vascular inflammation
• improve ventricular function of heart failure
• antithrombotic effect
• reduce the rate of vascular events
• antioxidant effect
but also other effects: reduction in blood pressure, reduced incidence of type
II diabetes, reduction of allograft organ rejection, regression of tumour cells,
reduced incidence of dementia, reduction in osteoporosis and risks of
fracture, all of them contributing to a better quality life of the patient.
The role of the statins on the endothelial function
Vascular Endothelium
The essential role in the regulation of the vascular homeostasis
belongs to the vascular endothelium, which in conditions of a good
functionality is responsible to maintain a balance between vasodilatation –
vasoconstriction, between inhibition – stimulation of proliferation and
migration of smooth muscle cells, between thrombosis – fibrinolysis [22,
23]. Thus, a dysfunction of the vascular endothelium is considered a first
sign in the atherosclerotic process, before angiographic or ultrasonic
changes, which show the atheromatous plaque [22]. Therefore is relieved
the interest for the role of statins in lowering the cholesterol (directly and
indirectly) improving the endothelial function. Statins improve endothelial
function through the following mechanisms (figure 5):
• enhanced endothelial NO production by decrease of cholesterol, by
up regulating posttranscriptional mRNA of eNOS [24] and by
antioxidative effects (reduction of reactive oxygen species, increase
of super oxide elimination and decrease of oxidized LDL) [25];
• reduced production of endothelin-1, endothelial vasoconstrictor
factor [26];
• diminish the affinity for AT1 receptors [26];
• stimulation of angiogenesis through proliferation, migration and
surviving of the circulating endothelial progenitor cells in part by
enhancing vascular endothelial growth factor production (VEGF)
[27, 28].
FARMACIA, 2009, Vol. 57, 2
137
Figure 5
The direct and indirect role of statins by improving the endothelial function [29]
(ET-1- endothelin-1; Ang II- angiotensin II; oxLDL- oxidized LDL; VLDL- very low-density lipoprotein; TNFαtumor necrosis factor α, IGF-1- insulin-like growth factor-1; VCAM-1- vascular cell adhesion molecule;
ICAM-1- intracellular adhesion molecule)
•
•
•
•
Vascular swell
Statins decrease the swell of the vascular wall [26, 30] by:
decreasing the level of C - reactive protein,
decreasing the synthesis of proinflammatory cytokines (IL-1, IL-6,
IL-8, TNF α),
diminishing the leukocyte adhesion to endothelial cells,
inhibiting macrophage growth and smooth muscle cell migration and
proliferation.
Because of the aspects presented above, it can be supposed that
improve of the activity EDNO can reduce the endothelial dysfunction, the
risk of appearance of the atheromatous plaque or the splitting of one already
existent, thus reducing the risk of complications of vascular diseases. Also
the association of a treatment by reducing the cholesterol levels could
improve endothelial dependent vasodilatation at patients with high levels of
cholesterol, contributing to the primary/secondary prevention of
cardiovascular diseases (figure 6).
138
FARMACIA, 2009, Vol. 57, 2
Figure 6
Relationship NO-statins in endothelial dysfunction and atherosclerosis
as treatment basis in cardiovascular diseases [30]
(RhoA- Ras homolog gene family; MMPs- matrix metalloproteinases; TF- tissue factor; t-PA- tissue- type
plasminogen activator; PAI-1 – plasminogen activator inhibitor-1; TXA2- thromboxane A2)
1.
2.
3.
4.
5.
6.
7.
8.
References
Furchgott R.F., Zawadzki J.V., The obligatory role of endothelial cells in the
relaxation of arterial smooth muscle by acetylcholine, Nature, 1980, 288, 373-376
Ignarro L.J., Byrns R.E., Buga G.M., Wood K.S., Endothelium-derived relaxing
factor from pulmonary artery and vein possess pharmacologic and chemical
properties identical to those of nitric oxide radical, Circ Res, 1987, 61, 866-879
Palmer R.M., Ferrige A.G., Moncada S., Nitric oxide release accounts for the
biological activity of endothelium-derived relaxing factor, Nature, 1987, 327, 524526
Myers P.R., Minor R.L., Guerra R., Bates J.N., Harrison D.G., Vasorelaxant
properties of the endothelium-derived relaxing factor more closely resembles Snitrosocysteine than nitric oxide, Nature, 1990, 345, 161-163
Loscalzo J., Welch G., Nitric oxide and its role in the cardiovascular system,
Progr Cardiovasc Dis, 1995, 38, 87-104
Eberhardt R.T., Loscalzo J., Nitric Oxide in Atherosclerosis in Nitric Oxide and
Cardiovascular System, 2000, Humana Press, Totowa, New Jersey, 273- 295
Farre A.L., Casado S., Heart failure, redox alterations and endothelial dysfunction,
Hypertension, 2001, 38, 1400-1405
Ludmer P.L., Selwyn A.P., Shook T.L., Wayne R.R., Mudge G.H., Alexander
R.W. et al., Paradoxical vasoconstriction induced by acetylcholine in
atherosclerotic coronary arteries, N Engl J Med, 1986, 315, 1046 – 1051
FARMACIA, 2009, Vol. 57, 2
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
139
Treasure C.B., Manoukian S.V., Klein J.L., Vita J.A., Nabel E.G., Renwick G.H.,
et al., Epicardial coronary artery responses to acetylcholine are impaired in
hipertensive patients, Circ Res, 1992, 71, 776-781
Vita J.A., Treasure C.B., Nabel E.G., McLenachan J.M., Fish R.D., Yeung A.C.,
et al., Coronary vasomotor response to acetylcholine relates to risk factors for
coronary artery disease, Circulation, 1990, 81, 491-497
Nitenberg A., Valersi P., Sachs R., Dali M., Aptecar E., Attali J.R., Impairment of
coronary vascular reserve in and ACH-induced coronary vasodilatation in diabetic
patients with angiographically normal coronary arteries and normal left ventricular
systolic function, Diabetes, 1993, 42, 1017-1025
Nitenberg A., Antony I., Foult J.M., Acetylcholine-induced coronary
vasoconstriction in young, heavy smokers with normal coronary arteriographic
findings, Am J Med ,1993, 95, 71-77
Vita J.A., Treasure C.B., Ganz P., Cox D.A., Fish R.D., Selwyn A.P., Control of
shear stress in the epicardial coronary arteries of humans: impairment by
atherosclerosis, J Am Coll Cardiol, 1989, 14, 1193-1199
Guido R.Y. De Meyer, Herman A. G., Nitric Oxide and Vascular Endothelial
Dysfunction, in Nitric Oxide - Biology and Pathobiology, 2000, Elsevier Inc., 547560
Dillon G.A., Vita J.A., Nitric Oxide and Endothelial Dysfunction in Nitric Oxide
and Cardiovascular System, 2000, Humana Press, Totowa, New Jersey, 207 – 226
Libby P., Ridker P.M., Maseri A., Inflammation and Atherosclerosis, Circulation,
2002, 105, 1135-1143
Prescott S.M., McIntyre T.M., Zimmerman G.A., Stafforini D.M., Molecular
Events in Acute Inflammation, Arterioscler Thromb Vasc Biol, 2002, 22, 727-733
Vaughan C.J., Gotto A.M. Jr., Basson C.T., The Evolving Role of Statins in the
Management of Atherosclerosis, JACC, 2000, 35, 1–10
Stancu C., Sima A., Statins: mechanism of action and effects, J. Cell. Mol. Med.,
2001, 5(4), 378-387
Palinski W., Tsimikas S., Immunomodulatory Effects of Statins: Mechanisms and
Potential Impact on Arteriosclerosis, J Am Soc Nephrol, 2002, 13, 1673–1681
Futterman L.G., Lemberg L., Statin Pleiotropy: Fact or Fiction?, Am J Crit Care,
2004, 13(3), 244-249
Luscher T.F., Barton M., Biology of the endothelium, Clin Cardiol, 1997, 20
(suppl. II), II3-II10
Kinlay S., Libby P., Ganz P., Endothelial function and coronary artery disease,
Curr Opin Lipidol, 2001, 12, 383- 389
Laufs U., La Fata V., Plutzky J., Liao J.K., Upregulation of endothelial nitric
oxide synthase by HMG-CoA reductase inhibitors, Circulation, 1998, 97, 11291135
Diaz M.N., Frei B., Vita J.A., Keaney J.F. jr., Antioxidants and atherosclerotic
heart disease, N Engl J Med ,1997, 337, 408-416
Wolfrum S., Jensen K.S., Liao J.K., Endothelium-dependent effects of statins,
Arterioscler Thromb Vasc Biol, 2001, 21, 1712-1719
Llevadot J., Murasawa S., Kureishi Y., Uchida S., Masuda H., Kawamoto A. et al.,
HMG-CoA reductase inhibitor mobilizes bone marrow-derived endothelial
progenitor cells, J Clin Invest, 2001, 108, 399-405
140
FARMACIA, 2009, Vol. 57, 2
28. Matsuno H., Takei M., Hayashi H., Nakajima K., Ishisaki A., Kozawa O.,
Simvastatin enhances the regeneration of endothelial cells via VEGF secretion in
injured arteries, J. Cardiovasc. Pharmacol., 2004, 43, 333-340
29. Masaaki I.I., Losordo D.W., Statins and the endothelium, Vascular Pharmacology,
2007, 46, 1-9
30. Takemoto M., Liao J.K., Pleiotropic effects of 3-hydroxy-3-methylglutaryl
coenzyme A reductase inhibitors, Arterioscler Thromb Vasc Biol, 2001, 21, 17121719
Manuscript received: 10.09.2008