Bilirubin From Heme Oxygenase-1 Attenuates Vascular Endothelial Activation and Dysfunction

Abstract

Objective-Heme oxygenase-1 (HO-1), the rate-limiting enzyme of heme degradation, has recently been considered to have protective roles against various pathophysiological conditions. Since we demonstrated that HO-1 overexpression inhibits atherosclerotic formation in animal models, we examined the effect of HO modulation on proinflammatory cytokine production, endothelial NO synthase (eNOS) expression, and endothelium-dependent vascular relaxation responses. Methods and Results-After HO-1 induction by heme arginate (HA), vascular endothelial cell cultures were exposed to oxidized low-density lipoprotein (oxLDL) or tumor necrosis factor-␣ (TNF-␣). HA pretreatment significantly attenuated the production of vascular cell adhesion molecule-1, monocyte chemotactic protein-1, and macrophage colonystimulating factor, suggesting that HO-1 induction attenuates proinflammatory responses. In addition, HO-1 overexpression also alleviated endothelial dysfunction as judged by restoration of attenuated eNOS expression after exposure to oxLDL and TNF-␣. Importantly, impaired endothelium-dependent vascular relaxation responses in thoracic aortic rings from high-fat-fed LDL receptor knockout mice were also improved. These effects were observed by treatment with bilirubin not by carbon monoxide. Key Words: heme oxygenase Ⅲ oxidized LDL Ⅲ endothelial nitric oxide synthase Ⅲ bilirubin Ⅲ carbon monoxide V ascular endothelial cell activation by oxidized LDL (oxLDL) and cytokines such as tumor necrosis factor-␣ (TNF-␣) is considered to play an essential role in the development of atherosclerotic lesions. 1 Activated endothelial cells produce adhesion molecules, chemokines, and growth factors such as vascular cell adhesion molecule-1 (VCAM-1), monocyte chemotactic protein-1 (MCP-1), and macrophage colony-stimulating factor (MCSF). [2][3][4] Numerous studies have shown that these molecules promote multiple steps in the formation of atherosclerotic lesion. 1,3,4 Endothelial dysfunction, which is associated with decreased bioavailability of NO from endothelial NO synthase (eNOS), is also considered to play an important role in atherogenesis. 1,5 NO formed by eNOS has been shown to contribute to vascular smooth muscle cell relaxation and inhibition of platelet aggregation. 1 Heme oxygenase (HO) catalyzes the rate-limiting step of heme degradation in mammals. 6 The products of the reaction are biliverdin, carbon monoxide (CO), and free iron. It has been suggested that biliverdin and CO have cytoprotective effects against various cellular stresses. [7][8][9] We demonstrated that the inducible form of HO (HO-1) is induced in cultured vascular endothelial cells, smooth muscle cells, and macrophages by oxidized low-density lipoprotein (oxLDL), and that high expression of HO-1 results in attenuation of monocyte chemotaxis by oxLDL. 9 In fact, HO-1 is expressed in atherosclerotic lesions. 10,11 We also demonstrated that overexpression of HO-1 inhibits the formation of atherosclerotic lesions by inhibiting lipid peroxidation and by affecting NO meta...

Serum Total Bilirubin Level and Prevalent Lower-Extremity Peripheral Arterial Disease

“…33,34 Several investigators have found that the vascular-protective effects of HO can be reproduced by the administration of bilirubin or biliverdin, suggesting that the production of bilirubin is a major component of the vascular protection offered by HO. 8,25,28 Our result is similar to the inverse relationship reported between bilirubin level and CAD. 12,35 Two studies in this area are particularly noteworthy.…”

“…Bilirubin inhibits inflammatory cytokine-induced endothelial cell expression of vascular cell adhesion molecule (VCAM)-1, 7 an initial step in atherosclerosis. 9 Bilirubin also inhibits monocyte transmigration, 25 prevents the formation of oxidized LDL, 26 inhibits endothelial inflammation and dysfunction, 8 inhibits vascular smooth muscle proliferation, 27 and prevents thrombus formation. 28 Human studies demonstrate that low bilirubin is associated with impaired endothelial function and increased carotid intima media thickness, 2 predictors of atherosclerosis, in healthy individuals free of cardiovascular risk factors.…”

“…6 Additionally, bilirubin exerts antiinflammatory effects on the vasculature. 7,8 Oxidative stress and inflammation are fundamental to the pathogenesis of atherosclerosis. 9 -11 The inverse association of serum total bilirubin with coronary artery disease (CAD) suggests that the antiinflammatory and antioxidant properties of bilirubin might offer protection from atherosclerosis.…”

Reduced Expression of Heme Oxygenase-1 in Patients with Coronary Atherosclerosis

“…HO-1, expressed in the endothelium (39,40) and monocytes/macrophages (41), is upregulated upon exposure to reactive oxygen species, or oxidized LDL (42), and it antagonizes the pro-atherosclerotic processes through the actions of its catalytic end-products, carbon monoxide and bilirubin. It is of note that heme, either endogenous in hemorrhagic atherosclerotic lesions or derived from the denatured hemoglobin within them, significantly contributes to the lesion formation and potently induces HO-1 (30).…”

Inverse Relation of Total Serum Bilirubin to Coronary Artery Calcification Score Detected by Multidetector Computed Tomography in Males

“…effects on vasculature. 4,5 Oxidative stress and inflammation are fundamental to the arteriopathy. 6 -8 Bilirubin was proven to act against plaque formation and subsequent atherosclerosis, 1 which was further confirmed by the studies revealing the relationships between bilirubin and peripheral artery disease (PAD) and carotid intima-media thickness (IMT).…”