Background and purpose Cerebral aneurysm (CA) affects 3% of the population and is associated with hemodynamic stress and inflammation. Myeloperoxidase (MPO), a major oxidative enzyme associated with inflammation, is increased in CA patients, but whether MPO contributes to CA is not known. We tested the hypotheses that MPO is increased within human CA and is critical for formation and rupture of CA in mice. Methods Blood was drawn from the lumen of CAs and femoral arteries of 25 patients who underwent endovascular coiling of CA, and plasma MPO concentrations were measured with ELISA. Effects of endogenous MPO on CA formation and rupture were studied in MPO knockout (KO) mice and wild-type (WT) mice using an angiotensin II-elastase induction model of CA. In addition, effects of MPO on inflammatory gene expression in endothelial cells were analyzed. Results Plasma concentrations of MPO were 2.7-fold higher within CA than in femoral arterial blood in CA patients. MPO-positive cells were increased in aneurysm tissue compared with superficial temporal artery of CA patients. Incidence of aneurysms and subarachnoid hemorrhage was significantly lower in MPO KO than in WT mice. In cerebral arteries, proinflammatory molecules including TNFα, COX2, CXCL1, MMP8, CD68 and MMP13, and leukocytes were increased, and α-smooth muscle actin was decreased, in WT but not in MPO KO mice after induction of CA. MPO per se increased expression of VCAM1 and ICAM1 in endothelial cells. Conclusions These findings suggest that MPO may contribute importantly to formation and rupture of CA.

We determined if local increases in brachial artery shear during repetitive muscle contractions induce changes in protein expression of endothelial nitric oxide synthase (eNOS) and/or phosphorylated (p-)eNOS at Ser, the primary activation site on eNOS, in endothelial cells (ECs) of humans. Seven young male subjects (25 ± 1 yr) performed 20 separate bouts (3 min each) of rhythmic forearm exercise at 20% of maximum over a 2-h period. Each bout of exercise was separated by 3 min of rest. An additional six male subjects (24 ± 1 yr) served as time controls (no exercise). ECs were freshly isolated from the brachial artery using sterile J-wires through an arterial catheter at baseline and again after the 2-h exercise or time control period. Expression of eNOS or p-eNOS Ser in ECs was determined via immunofluorescence. Brachial artery mean shear rate was elevated compared with baseline and the time control group throughout the 2-h exercise protocol ( < 0.001). p-eNOS Ser expression was increased 57% in ECs in the exercise group [0.06 ± 0.01 vs. 0.10 ± 0.02 arbitrary units (au), = 0.02] but not in the time control group (0.08 ± 0.01 vs. 0.07 ± 0.01 au, = 0.72). In contrast, total eNOS expression did not change in either the exercise (0.13 ± 0.04 vs. 0.12 ± 0.03 au) or time control (0.12 ± 0.03 vs. 0.11 ± 0.03 au) group ( > 0.05 for both). Our novel results suggest that elevations in brachial artery shear increase eNOS Ser phosphorylation in the absence of changes in total eNOS in ECs of young healthy male subjects, suggesting that this model is sufficient to alter posttranslational modification of eNOS activity in vivo in humans. Elevations in brachial artery shear in response to forearm exercise increased endothelial nitric oxide synthase Ser phosphorylation in brachial artery endothelial cells of healthy humans. Our present study provides the first evidence in humans that muscle contraction-induced increases in conduit arterial shear lead to in vivo posttranslational modification of endothelial nitric oxide synthase activity in endothelial cells.

Inflammation plays a key role in formation and rupture of intracranial aneurysms. Because hepatocyte growth factor (HGF) protects against vascular inflammation, we sought to assess the role of endogenous HGF in the pathogenesis of intracranial aneurysms. Circulating HGF concentrations in blood samples drawn from the lumen of human intracranial aneurysms or femoral arteries were compared in 16 patients. Tissue from superficial temporal arteries (STA), and ruptured or unruptured intracranial aneurysms collected from patients undergoing clipping (n=10) were immunostained with antibodies to HGF and its receptor c-Met. Intracranial aneurysms were induced in mice treated with PF-04217903 (a c-Met antagonist) or vehicle. Expression of inflammatory molecules was also measured in cultured human endothelial, smooth muscle cells and monocytes treated with LPS in presence or absence of HGF and PF-04217903. We found that HGF concentrations were significantly higher in blood collected from human intracranial aneurysms (1076 ± 656 pg/ml) than in femoral arteries (196 ± 436 pg/ml, p<0.001). HGF and c-Met were detected by immunostaining in STA, and in both ruptured and unruptured human intracranial aneurysms. A c-Met antagonist did not alter the formation of intracranial aneurysms (P>0.05), but significantly increased the prevalence of subarachnoid hemorrhage and decreased survival in mice (P<0.05). HGF attenuated expression of VCAM-1 (P<0.05) and E-Selectin (P<0.05) in human aortic endothelial cells. In conclusion, plasma HGF concentrations are elevated in intracranial aneurysms. HGF and c-Met are expressed in STA and in intracranial aneurysms. HGF signaling through c-Met may decrease inflammation in endothelial cells and protect against intracranial aneurysm rupture.