Platelet-associated NAD(P)H oxidase contributes to the thrombogenic phenotype induced by hypercholesterolemia

Abstract

Elevated cholesterol levels promote pro-inflammatory and prothrombogenic responses in venules and impaired endothelium-dependent arteriolar dilation. Although NAD(P)H oxidase-derived superoxide has been implicated in the altered vascular responses to hypercholesterolemia, it remains unclear whether this oxidative pathway mediates the associated arteriolar dysfunction and platelet adhesion in venules. Platelet and leukocyte adhesion in cremasteric postcapillary venules, and arteriolar dilation responses to acetylcholine were monitored in wild-type (WT), Cu,Zn-superoxide dismutase transgenic (SOD-TgN) and NAD(P)H oxidase-knockout (gp91 phox-/-) mice placed on normal (ND) or high cholesterol (HC) diet for 2 wk. HC elicited increased platelet and leukocyte adhesion in WT mice, versus ND. Cytosolic subunits of NAD(P)H oxidase (p47phox and p67phox) were expressed in platelets. This was not altered by hypercholesterolemia, however platelets and leukocytes from HC mice exhibited elevated generation of reactive oxygen species when compared to ND mice. Hypercholesterolemia-induced leukocyte recruitment was attenuated in SOD-TgN-HC and gp91 phox-/--HC mice. Recruitment of platelets derived from WT-HC mice in venules of SODTgN-HC or gp91 phox-/--HC recipients was comparable to ND levels. Adhesion of SOD-TgN-HC platelets paralleled the leukocyte response and was attenuated in SOD-TgN-HC recipients, but not in WT-HC recipients. However, gp91 phox-/--HC platelets exhibited low levels of adhesion comparable to WT-ND in both hypercholesterolemic gp91 phox-/-and WT recipients. Arteriolar dysfunction was evident in WT-HC mice, compared to WT-ND. Overexpression of SOD or, to a lesser extent, gp91 phox deficiency, restored arteriolar vasorelaxation responses towards WT-ND levels. These findings reveal a novel role for platelet-associated NAD(P)H oxidase in producing the thrombogenic phenotype in hypercholesterolemia and demonstrate that NAD(P)H oxidase-derived superoxide mediates the HC-induced arteriolar dysfunction.

T-Cell–Derived Interferon-γ Contributes to Arteriolar Dysfunction During Acute Hypercholesterolemia

“…27 It has been suggested that the increased NO release in arterial rings exposed to IFN-␥ leads to desensitization of the smooth muscle cell to NO, thereby impairing endothelium-dependent vasodilation. 11 Alternatively, the ability of IFN-␥ to induce NAD(P)H oxidase, 14,15 a superoxide-generating enzyme that contributes to hypercholesterolemia-induced arteriolar dysfunction, 24 may explain the actions of the cytokine in our model. IFN-␥ may also be acting indirectly by inducing the expression of or acting in concert with other cytokines such as TNF-␣ to alter NO bioavailability or oxygen free radical generation.…”

“…Reduced nitric oxide (NO) bioavailability and enhanced NAD(P)H oxidasederived superoxide generation have both been implicated in the impaired dilation. 10,23,24 Because IFN-␥ is a potent stimulator of NAD(P)H oxidase, 14,15 it is plausible that T-lymphocytes, acting through release of this cytokine, may contribute to this arteriolar dysfunction. Using lymphocytedeficient mice, we have obtained evidence that strongly implicates T-cells in the impaired endothelium-dependent vasodilation in arterioles of hypercholesterolemic mice.…”

Oxidative Stress and Platelets

“…57 In patients with hypercholesterolemia, platelet-associated NAD(P)H oxidase produces a thrombogenic phenotype and mediates the arteriolar dysfunction. 20 Platelet superoxide production in patients with hypertension alone and in patients with coexistent diabetes mellitus has been examined. It was shown that eNOS can reside in the uncoupled state in patients with hypertension and, to a greater extent, in patients with coexisting hypertension and diabetes, and that this contributes significantly to increased superoxide production in these disease states.…”

CD40/CD40L contributes to hypercholesterolemia-induced microvascular inflammation

“…These results implicate CD40/CD40L interactions between circulating cells and the vascular wall in both the arteriolar and venular dysfunction elicited by hypercholesterolemia and identify T-cell-associated CD40L as a key mediator of these responses. T lymphocytes; platelets; oxidative stress; arteriolar vasodilation; leukocyte adhesion HYPERCHOLESTEROLEMIA IS A well-characterized cardiovascular risk factor that is known to initiate inflammatory and thrombogenic responses in the microvasculature (34,35,41,42). These vascular reactions reflect a systemic low-level inflammatory phenotype that appears to predispose the microvasculature to larger injury responses following an exposure to other inflammatory stimuli, such as ischemia-reperfusion (14, 17).…”

“…T lymphocytes; platelets; oxidative stress; arteriolar vasodilation; leukocyte adhesion HYPERCHOLESTEROLEMIA IS A well-characterized cardiovascular risk factor that is known to initiate inflammatory and thrombogenic responses in the microvasculature (34,35,41,42). These vascular reactions reflect a systemic low-level inflammatory phenotype that appears to predispose the microvasculature to larger injury responses following an exposure to other inflammatory stimuli, such as ischemia-reperfusion (14,17).…”