Normal endothelial functions include control of platelet adhesion, mediation of coagulation and immune function, and control of volume and electrolyte content of body components.1) Endothelial dysfunction is a pathophysiological condition of abnormal process carried out by the endothelium. It is thought to be a key initial step in the development of atherosclerosis and can be used as a prognostic marker in predicting cardiovascular events including stroke and heart attacks.2)3) Endothelial dysfunction can be resulted from disease processes including hypertension, dyslipidemia, and diabetes as well as from environmental factors such as smoking.1)

Endothelial dysfunction can be characterized as the inability of arteries to dilate fully in response to appropriated stimuli. This can be detected by flow-mediated dilatation (FMD) using temporary arterial occlusion by inflating a blood pressure cuff to high pressures.4) Flow-mediated changes in conduit artery diameter are caused by shear-stress induced generation of endothelia derived vasoactive mediators including nitric oxides.5)6)

Cilostazol (Otsuka Pharmaceutical Co. Tokushima, Japan), 6-[4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quinolinone, is a 2-oxo-quinoline derivative with anti-thrombotic, vasodilator, antimitogenic and cardiotonic properties.7) The compound is a potent inhibitor of phosphodiesterase (PDE)-3. It may be useful for treating chronic arterial occlusive diseases and symptoms of intermittent claudication.8) Cilostazol inhibits platelet aggregation and has considerable antithrombotic effects in vivo. Also, this compound relaxes vascular smooth muscle and inhibits mitogenesis and migration of vascular smooth muscle cells. In the heart, it has positive inotropic and chronotropic effects.7)8)

This present study investigated the effects of cilostazol that could improve the endothelial dysfunction, especially in young male smokers.

There was no significant difference in the clinical characteristics including age, body mass index, blood pressure, serum cholesterol profile, high sensitive C-reactive protein, and serum glucose level between two groups (Table 1). There was no significant side-effect associated with use of oral cilostazol except headache. Though majority subjects with headache were well controlled with oral analgesics, two of 20 smokers dropped out because of uncontrolled severe headache.

Baseline EDD was significantly higher in the control group than in the smoker group (12.0 ± 4.5 in the control group vs. 8.0 ± 2.1% in the smoker group, p = 0.002, Fig. 1A). Baseline EID was similar in two groups (13.6 ± 4.5% in the control group vs. 11.9 ± 4.9% in the smoker group, p = 0.681, Fig. 1B). After two weeks of oral cilostazol treatment, follow-up EDD values were significantly increased in both groups (control group: 12.0 ± 4.5 to 16.1 ± 3.7%, p = 0.041, Fig. 2A; smoker group: 8.0 ± 2.1 to 12.2 ± 5.1%, p = 0.003, Fig. 2B). Follow-up EDD in the control group showed higher value than that of control group (16.1 ± 3.7 in the control group vs. 12.2 ± 5.1% in the smoker group, p = 0.018).

However, follow up EID value was not significantly increased compared with baseline value in both groups. (13.6 ± 4.5% to 16.1 ± 3.7%, p = 0.182 in the control group, Fig. 3A; 11.9 ± 4.9% to 13.7 ± 4.3%, p = 0.430 in the smoker group, Fig. 3B).

In this FMD study with oral cilostazol, we demonstrated decreased baseline EDD level in the smoker group and significant improvement of EDD with administration of oral cilostazol in this group. However, cilostazol did not change the EID in this group.

Nitric oxide (NO), also known as the endothelium-derived Nitric oxide (NO), also known as the endothelium-derived relaxing factor (EDRF), is a chemical compound which is an important signaling molecule in the mammalian bodies. It is biosynthesized endogenously from L-arginine and oxygen by various nitric oxide synthase (NOS).10) It contributes to vessel homeostasis by inhibiting platelet aggregation, vascular smooth muscle contraction and growth, and leukocyte adhesion to the endothelium.10) FMD is one of methods to exam endothelial function. Increased shear stress in the arterial wall, usually caused by occlusion of the artery, can open specialized ion channels in the endothelium and influxed calcium ions through these channels stimulate endothelial nitric oxide synthase (eNOS). Increased eNOS activity enhanced NO synthesis and elevated NO evokes vasodilation.3) The vasodilatory effect of NO, EDRF, on the vessel (vasodilation) can be assessed by FMD. Arterial distensibility after reactive hyperemia is influenced by variable factors. FMD can be influenced by a single high-fat meal,11) mental stress,12) cigarette smoking,13) hyperglycemia,14) and changes in electrolytes (sodium and calcium).15) Also, EDD can be decreased by theophylline (adrenoreceptor agonist) or ibuprofen (prostaglandin synthesis inhibitor).16)

Cigarette smoking is one of the well-known risk factors causing endothelial dysfunction and there are strong relationships between cigarette smoking, atherosclerotic burden, and ischemic heart disease.17-19) Cigarette smoking induces initial atherosclerosis and promotes cardiovascular disease through multiple mechanisms including vasomotor, neurohormonal, and hemoatologic dysfunction, and increased oxidative stress19)20) Endothelial dysfunction can be resulted from inhaled cigarette smoke. Smoking as few as 2 cigarettes a day doubles the number of damaged endothelial cells in the blood stream.19-21)

There are several drugs improve endothelial dysfunction including angiotensin converting enzyme inhibitors, angiotensin receptor blockers, and nifedipine in the hypertensive patients, statins, fibrates and omega-3 fatty acid in the dyslipidemic patients, metformin and rosiglitazone in the diabetic patients.22) Few studies have been reported in the improvement of endothelial dysfunction in the smokers. Smoking cessation is one of the well-known methods to restore endothelial dysfunction.23) Guthikonda et al.24) published their study that allopurinol reverses endothelial dysfunction in the heavy smokers. Oida et al.25) presented that oral cilostazol treatment can be associated with improvement of endothelial dysfunction.

Cilostazol, a selective PDE-3 inhibitor, increases cyclic adenosine mono-phosphate (cAMP) in the platelets and inhibits platelet aggregation. Moreover, increased cAMP in the vascular smooth muscle cells activates protein kinase A and decreases intracellular calcium concentration. These effects result in vasodilation.26) Yasuda et al.26) reported that two weeks treatment of oral cilostazol increased tissue blood flow through the pedal vessels through vasodilation in the patients with peripheral arterial occlusive disease. Cilostazol has been approved by the Food and Drug Administration (FDA) in the treatment of peripheral arterial occlusive disease since 1999.27) Recently, triple combination antiplatelet therapy, aspirin, clopidogrel and cilostazol, has been reported to reduce thrombotic complication and recurrence of restenosis after implantation of coronary stent, especially in the diabetic patients.28)

Additional effects of cilostazol on the vascular endothelium have been described. Cilostazol has been associated with increased NO production. Ikeda et al.29) published their study showing cilostazol increased NO production in cultured vascular smooth muscle cells via cAMP pathway. Nakamura et al.30) reported that cilostazol dilated thoracic aorta via released NO from aortic endothelium. Increased NO production with cilostazol treatment can be associated with increased EDD in our study. Our result is similar to that of the previously reported article by Oida et al.25) However, the mean age of the participants was younger (late twenties vs. late thirties) and treated dosage was higher (200 mg per day vs. 150 mg per day) in our study. Because of younger age and shorter duration of smoking, the EDD level in our study may be associated with higher value than that of study by Oida et al.25)

Cilostazol improved reactive hyperemia in these eighteen smokers. This effect can be resulted from the NO production and relaxation of smooth muscle cells in the vessel. Endothelial dysfunction can be resulted from smoking as a result of increased oxidative stresses such as oxygen free radical which disturb normal endothelial functions. Therefore, cilostazol can improve endothelial dysfunctions caused by cigarette smoking.

In this study, most of participants complained headache after cilostazol medication. Most normal participants complained severe headache despite of oral analgesic treatment. Moreover, two of 20 smokers dropped out due to severe headache.

In conclusion, the administration of cilostazol improves the vasodilatory response to reactive hyperemia in the smokers.