Mechanisms of free radical production in the vascular wall

The Effects of Toradol on Postoperative Intimal Hyperplasia in a Rat Carotid Endarterectomy Model: Laboratory Research

Carotid endarterectomy (CEA) and more recently carotid artery stenting are the treatments of choice for atherosclerotic disease of the extracranial carotid arteries; however, early restenosis caused by neointimal hyperplasia confounds surgical therapy. Oxidative stress has been implicated in the progression of intimal hyperplasia. The authors hypothesized that ketorolac tromethamine (Toradol), a nonsteroidal antiinflammatory drug that is a potent cyclooxygenase inhibitor, would decrease oxidative stress and thereby reduce intimal hyperplasia in a rat CEA model. Twenty-nine male Sprague-Dawley rats underwent CEA and were divided into 3 treatment groups as follows: (1) control (placebo), (2) 7.5 mg/kg Toradol, and (3) 10 mg/kg Toradol. Toradol treatment began 2 days before CEA and continued for 2 weeks. Two weeks after endarterectomy, carotid arteries were fixed, harvested, and examined for platelet activity (platelet reactive units), oxidative stress (malondialdehyde and glutathione), and intimal hyperplasia (measured as percentage of luminal stenosis). Platelet activity, malondialdehyde and glutathione, and intimal hyperplasia were all significantly lowered in both 7.5- and 10-mg/kg doses of Toradol versus control. Toradol given daily beginning 2 days before CEA and ending 2 weeks after the procedure was effective at significantly reducing platelet activity, oxidative stress, and intimal hyperplasia development in the rat without any increase in bleeding. Although the mechanism of action of this reduction is not completely understood, one possible explanation may be through the inhibition of reactive oxygen species production.

FoxO4 inhibits atherosclerosis through its function in bone marrow derived cells

OBJECTIVES

FoxO proteins are transcription factors involved in varieties of cellular processes, including immune cell homeostasis, cytokine production, anti-oxidative stress, and cell proliferation and differentiation. Although these processes are implicated in the development of atherosclerosis, very little is known about the role of FoxO proteins in the context of atherosclerosis. Our objectives were to determine whether and how inactivation of Foxo4, a member of the FoxO family, in vivo promotes atherosclerosis.

METHODS AND RESULTS

Apolipoprotein E-deficient (apoE(-/-)) mice were crossbred with animals lacking Foxo4 (Foxo4(-/-)). After 10 weeks on a high fat diet (HFD), Foxo4(-/-)apoE(-/-) mice showed elevated atherosclerosis and increased amount of macrophages and T cells in the plaque compared to apoE(-/-) mice. Bone marrow transplantations of chimeric C57B/6 mice reconstituted with either wild-type or Foxo4(-/-) bone marrows indicate that Foxo4-deficiency in bone marrow derived cells sufficiently promoted atherosclerosis. Foxo4-null macrophages produced elevated inflammatory cytokine IL-6 and levels of reactive oxygen species (ROS) in response to lipopolysaccharides in vitro. Serum levels of IL-6 were upregulated in HFD-fed Foxo4(-/-)apoE(-/-) mice compared to those of apoE(-/-) mice.

CONCLUSIONS

FoxO4 inhibits atherosclerosis through bone marrow derived cells, possibly by inhibition of ROS and inflammatory cytokines that promote monocyte recruitment and/or retention.

Shear-induced reactive nitrogen species inhibit mitochondrial respiratory complex activities in cultured vascular endothelial cells

There is evidence that nitric oxide (NO), superoxide (O(2)(*-)), and their associated reactive nitrogen species (RNS) produced by vascular endothelial cells (ECs) in response to hemodynamic forces play a role in cell signaling. NO is known to impair mitochondrial respiration. We sought to determine whether exposure of human umbilical vein ECs (HUVECs) to steady laminar shear stress and the resultant NO production modulate electron transport chain (ETC) enzymatic activities. The activities of respiratory complexes I, II/III, and IV were dependent on the presence of serum and growth factor supplement in the medium. EC exposure to steady laminar shear stress (10 dyn/cm(2)) resulted in a gradual inhibition of each of the complexes starting as early as 5 min from the flow onset and lasting up to 16 h. Ramp flow resulted in inhibition of the complexes similar to that of step flow. When ECs were sheared in the presence of the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 100 microM), the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO; 100 microM), or the peroxynitrite (ONOO(-)) scavenger uric acid (UA; 50 microM), the flow-inhibitory effect on mitochondrial complexes was attenuated. In particular, L-NAME and UA abolished the flow effect on complex IV. Increased tyrosine nitration was observed in the mitochondria of sheared ECs, and UA blocked the shear-induced nitrotyrosine staining. In summary, shear stress induces mitochondrial RNS formation that inhibits the electron flux of the ETC at multiple sites. This may be a critical mechanism by which shear stress modulates EC signaling and function.

NAD(P)H oxidase in paraventricular nucleus contributes to the effect of angiotensin II on cardiac sympathetic afferent reflex

We previously reported that reactive oxygen species (ROS) in paraventricular nucleus (PVN) modulated cardiac sympathetic afferent reflex (CSAR) and mediated the effect of angiotensin II (Ang II) in the PVN on the CSAR. In the present study, we investigated whether the NAD(P)H oxidase in the PVN was a key source of ROS which modulated the CSAR and contributed to the effect of Ang II on the CSAR. In anesthetized rats with sinoaortic denervation and vagotomy, renal sympathetic nerve activity (RSNA) and arterial pressure were recorded. The CSAR was evaluated by the RSNA response to epicardial application of bradykinin (BK). The NAD(P)H oxidase activity in the PVN was measured with lucigenin-enhanced chemiluminescent method. Microinjection of the NAD(P)H oxidase inhibitor, either apocynin (1.0 nmol) or phenylarsine oxide (PAO, 1.0 nmol), into the PVN significantly inhibited the CSAR. Microinjection of Ang II (0.3 nmol) into the PVN significantly augmented the CSAR. The effects of Ang II were not only abolished by pretreatment with either apocynin or PAO in the PVN but also partially inhibited by xanthine oxidase inhibitor allopurinol. Either epicardial application of BK or microinjection of Ang II into the PVN significantly increased NAD(P)H oxidase activity in the PVN. The effect of Ang II on NAD(P)H oxidase activity was abolished by pretreatment with AT(1) receptor antagonist losartan in the PVN. These findings suggested that NAD(P)H oxidase in the PVN was a major source of the ROS in modulating the CSAR, and the NAD(P)H oxidase contributes to the effect of Ang II on the CSAR.