Endothelium-derived nitric oxide (NO) is synthesized in response to chemical and physical stimuli. Here, we investigated a possible role of the endothelial cell glycocalyx as a biomechanical sensor that triggers endothelial NO production by transmitting flow-related shear forces to the endothelial membrane. Isolated canine femoral arteries were perfused with a Krebs-Henseleit solution at a wide range of perfusion rates with and without pretreatment with hyaluronidase to degrade hyaluronic acid glycosaminoglycans within the glycocalyx layer. NO production rate was evaluated as the product of nitrite concentration in the perfusate and steady-state perfusion rate. The slope that correlates the linear relation between perfusion rate and NO production rate was taken as a measure for flow-induced NO production. Hyaluronidase treatment significantly decreased flow-induced NO production to 19 +/- 9% of control (mean +/- SD; P < 0.0001 vs. control; n = 11), whereas it did not affect acetylcholine-induced NO production (88 +/- 17% of pretreatment level, P = not significant; n = 10). We conclude that hyaluronic acid glycosaminoglycans within the glycocalyx play a pivotal role in detecting and amplifying the shear force of flowing blood that triggers endothelium-derived NO production in isolated canine femoral arteries.

Abstract-We investigated whether aliskiren, a direct renin inhibitor, improves NO bioavailability and protects against spontaneous atherosclerotic changes. We also examined the effects of cotreatment with aliskiren and valsartan, an angiotensin II receptor blocker, on the above-mentioned outcomes. Watanabe heritable hyperlipidemic rabbits were treated with vehicle (control), aliskiren, valsartan, or aliskiren plus valsartan for 8 weeks. Then, acetylcholine-induced NO production was measured as a surrogate index of endothelium protective function, and both superoxide and vascular peroxynitrite were measured. Tetrahydrobiopterin in aortic segments was assessed by high-performance liquid chromatography with fluorescence detection. Plaque area was quantified by histology. Increase in plasma NO concentration in response to intra-aortic acetylcholine infusion was significantly greater in all of the test groups than in controls. Aliskirenϩvalsartan cotreatment increased acetylcholine-induced NO by 6.2 nmol/L, which was significantly higher than that with either aliskiren or valsartan alone. Vascular superoxide and peroxynitrite levels were both significantly higher in controls and significantly lower in the aliskirenϩvalsartan group than in the aliskiren or valsartan group. The highest tetrahydrobiopterin levels were observed after aliskirenϩvalsartan cotreatment. Histology of the thoracic aorta revealed that the plaque area was significantly decreased with combination therapy compared with monotherapy. Treatment with a direct renin inhibitor has protective effects on endothelial function and atherosclerotic changes. Furthermore, cotreatment with a direct renin inhibitor and an angiotensin II receptor blocker has additive protective effects on both. T he renin-angiotensin system (RAS) activity may be a key factor in the pathophysiology and development of hypertension, atherosclerosis, heart failure, and renal disease in a substantial number of patients. 1,2 However, it remains unclear whether angiotensin-converting enzyme (ACE) inhibitors and angiotensin (Ang) II receptor blockers (ARBs) have fully delivered the expected reduction in cardiovascular risk. In fact, optimized RAS suppression is difficult to achieve with currently available antihypertensive agents, partly because ACE inhibitors and ARBs both activate compensatory feedback mechanisms that result in renin release and increase plasma renin activity (PRA). [3][4][5] In contrast, renin inhibitors neutralize any compensatory increase in PRA and prevent the formation of both Ang I and Ang II. 6 Aliskiren, the first in a new class of orally effective renin inhibitors for the treatment of hypertension, is a potent and specific inhibitor of human renin in vitro with an IC 50 value in the low nanomolar range. 7,8 Studies in healthy volunteers have shown that aliskiren treatment leads to dose-dependent reductions in PRA and Ang II levels. 9 Early clinical trials in hypertensive patients showed that this drug provided antihypertensive efficacy comparable to those of th...

The interaction between monocytes and endothelial cells is considered to play a major role in the early stage of atherosclerosis, and the involved endothelial cell micromechanics may provide us with important aspects of atherogenesis. In the present study, we evaluated (i) the endothelial cell-to-cell and cell-to-substrate gaps with the electric cell-substrate impedance sensing system, which can detect the nanometer order changes of cell-to-cell and cell-tosubstrate distances separately, and (ii) the endothelial cell micromechanical properties with an atomic force microscope after application of monocytes to endothelial cells. Application of monocytic THP-1 cells to IL-1␤-stimulated human umbilical vein endothelial cells immediately decreased the electrical resistance of the endothelial cell-to-substrate (increase of the cell-to-substrate gap), whereas the endothelial cell-to-cell resistance (cell-to-cell gap) did not change. The elastic modulus of the endothelial cells decreased after 2-h monocyte application, indicating an increase of endothelial cell deformability. In conclusion, the interaction of the monocytes to the endothelial cells reduced the adhesiveness to the substrate and increased the deformability of endothelial cells. These changes in the adhesiveness and the deformability may facilitate migration of monocytes, a key process of atherogenesis in the later stage.A t the early stage of atherosclerosis, an aggregation of lipid-rich macrophages that were derived from monocytes was observed in the intima (1). Adhesion of monocytes to the arterial endothelial cells and their migration into the arterial intima are the earliest key events in atherogenesis (1). Previous studies demonstrated that leukocytes could migrate throughout the endothelial monolayer via not only paracellular but also transcellular pathways in vivo and in vitro (2-5). The endothelial cell micromechanics that are involved in endothelial cell micromotion and the mechanical properties of endothelial cells may be key factors in these processes. Earlier studies reported the importance of adhesion molecules in the adhesion and migration of monocytes to endothelial cells (6, 7). We previously demonstrated that the adhesion of monocytes to human umbilical vein endothelial cells (HUVEC) induces the decrease in the amount of focal adhesion kinase (p125 FAK ) with reduction of the density of F-actin stress fibers in HUVEC (8). These results suggest that the adhesion of monocytes induces changes of the adhesiveness of endothelial cells to the substrate and the mechanical properties of endothelial cells. However, the accompanying micromechanics and micromotion of endothelial cells were little understood.For the micromotion measurement of the cultured cells, Giaever and Keese (9) developed a morphological biosensor, the electric cell-substrate impedance sensing (ECIS) system. The advantage of this system is that quantitative estimation of cell-to-cell and cell-to-substrate distances can be performed separately and in real time. Atomic force micros...

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