Impaired nitric oxide-mediated vasodilation in transgenic sickle mouse

Abstract

Transgenic sickle mice expressing human beta(S)- and beta(S-Antilles)-globins show intravascular sickling, red blood cell adhesion, and attenuated arteriolar constriction in response to oxygen. We hypothesize that these abnormalities and the likely endothelial damage, also reported in sickle cell anemia, alter nitric oxide (NO)-mediated microvascular responses and hemodynamics in this mouse model. Transgenic mice showed a lower mean arterial pressure (MAP) compared with control groups (90 +/- 7 vs. 113 +/- 8 mmHg, P < 0.00001), accompanied by increased endothelial nitric oxide synthase (eNOS) expression. N(G)-nitro-L-arginine methyl ester (L-NAME), a nonselective inhibitor of NOS, caused an approximately 30% increase in MAP and approximately 40% decrease in the diameters of cremaster muscle arterioles (branching orders: A2 and A3) in both control and transgenic mice, confirming NOS activity; these changes were reversible after L-arginine administration. Aminoguanidine, an inhibitor of inducible NOS, had no effect. Transgenic mice showed a decreased (P < 0.02-0.01) arteriolar dilation in response to NO-mediated vasodilators, i.e., ACh and sodium nitroprusside (SNP). Indomethacin did not alter the responses to ACh and SNP. Forskolin, a cAMP-activating agent, caused a comparable dilation of A2 and A3 vessels ( approximately 44 and 70%) in both groups of mice. Thus in transgenic mice, an increased eNOS/NO activity results in lower blood pressure and diminished arteriolar responses to NO-mediated vasodilators. Although the increased NOS/NO activity may compensate for flow abnormalities, it may also cause pathophysiological alterations in vascular tone.

Sickle cell anemia is associated with reduced nitric oxide bioactivity in peripheral conduit and resistance vessels

“…In HbSS, additional effects of increased shear stress and tissue hypoxemia may further stimulate NOS expression and NO production. Transgenic murine models of sickle cell disease have shown greater basal NO production with a greater rise in blood pressure with NOS inhibition, although results regarding NOS expression are controversial [5,6]. In humans with HbSS, the contribution of NO to increased basal flow and reduced peripheral resistance is unclear [7].…”

“…Transgenic murine models of HbSS have shown diminished responses to endogenous and exogenous NO-mediated dilators [4][5][6]. However, in humans with HbSS, there is controversy regarding microvascular dysfunction of the resistance vessel of the forearm.…”

“…In experimental models, despite increased NO production and perhaps NOS (NO synthase) expression, the response to endothelium-dependent vasodilators is impaired in both micro-and macrocirculations [4][5][6]. In humans with HbSS, abnormalities of endothelium-dependent vasodilation in conduit vessels has been reported; however, uncertainty remains regarding resistance vessel response to NO-mediated vasodilators [7][8][9].…”

Endothelial nitric oxide synthase and nitric oxide regulate endothelial tissue factor expression in vivo in the sickle transgenic mouse

“…This can occur due to several events: enzyme oxidation [21]; deficiency of co-factor NADPH [22]; deficiency of arginine due to diet, release of arginase from red cells [23,24], or metabolic changes accompanying renal disease [25]; deficiency of tetrahydrobiopterin; presence of the elevated levels of the endogenous inhibitor asymmetric dimethylarginine [26]; and abnormal eNOS monomerization [27] caused by abnormal enzyme S-nitrosylation [28]. Notably, tetrahydrobiopterin can be relatively deficient in situations where amount of eNOS enzyme is increased, as may be the case in sickle mice [29]. This may differ among different tissues, and there has been no comprehensive survey of either eNOS enzyme amount or activity heterogeneity in sickle models.…”

Vasoactive factors in sickle cell disease: In vitro evidence for endothelin‐1‐mediated vasoconstriction

“…Although clinical manifestation of SCD displays a wide array of symptoms, a common clinical problem is recurrent acute vaso-occlusive episodes [2,3]. The interaction between sickle erythrocytes and endothelium may contribute to the vascular occlusion in SCD via several mechanisms including erythrocyte sickling, enhanced adhesion of sickle erythrocytes to endothelium and local vascular instability precipitated by the imbalance of local vasoconstrictors and vasodilators produced by endothelial cells in response to interaction with sickled erythrocytes [1,[3][4][5].…”