Nicole Duerrschmidt

NADPH Oxidase in Endothelial Cells: Impact on Atherosclerosis

An elevated vascular superoxide anion formation has been implicated in the initiation and progression of hypertension and atherosclerosis. In this review, we would like to discuss the generation of superoxide anions by an NADPH oxidase complex in vascular cells. Special focus is on the induction of endothelial NADPH oxidase by proatherosclerotic stimuli. We propose a proatherosclerotic vicious cycle of increased NADPH oxidase-dependent superoxide anion formation, augmented generation and uptake of oxidatively modified low-density lipoprotein, and further potentiation of oxidative stress by oxidized low-density lipoprotein itself, angiotensin II, and endothelin-1 in endothelial cells. Furthermore, novel homologues of NADPH oxidase subunit gp91(phox) are summarized. Future directions of research for a better understanding of the role of NADPH oxidase in the pathogenesis of atherosclerosis and clinical implications are discussed.

NO‐mediated regulation of NAD(P)H oxidase by laminar shear stress in human endothelial cells

The flowing blood generates shear stress at the endothelial cell surface. In endothelial cells, NAD(P)H oxidase complexes have been identified as major sources of superoxide anion (·O2−) formation. In this study, we analysed the effect of laminar shear stress on ·O2− formation by cytochrome c reduction assay and on NAD(P)H oxidase subunit expression by standard calibrated competitive reverse transcription‐polymerase chain reaction and Western blot in human endothelial cells. Primary cultures of human umbilical vein endothelial cells were exposed to laminar shear stress in a cone‐and‐plate viscometer for up to 24 h. Short‐term application of shear stress transiently induced ·O2− formation. This was inhibited by NAD(P)H oxidase inhibitor gp91ds‐tat, but NAD(P)H oxidase subunit expression was unchanged. Long‐term arterial laminar shear stress (30 dyne cm−2, 24 h) down‐regulated ·O2− formation, and mRNA and protein expression of NAD(P)H oxidase subunits Nox2/gp91phox and p47phox. In parallel, endothelial NO formation and eNOS, but not Cu/Zn SOD, protein expression was increased. Down‐regulation of ·O2− formation, gp91phox and p47phox expression by long‐term laminar shear stress was blocked by l‐NAME. NO donor DETA‐NO down‐regulates ·O2− formation, gp91phox and p47phox expression in static cultures. In conclusion, our data suggest a transient activation of ·O2− formation by short‐term shear stress, followed by a down‐regulation of endothelial NAD(P)H oxidase in response to long‐term laminar shear stress. NO‐mediated down‐regulation by shear stress preferentially affects the gp91phox/p47phox‐containing NAD(P)H oxidase complex. This mechanism might contribute to the regulation of endothelial NO/·O2− balance and the vasoprotective potential of physiological levels of laminar shear stress.

Augmented endothelial uptake of oxidized low-density lipoprotein in response to endothelin-1

Endothelin-1 (ET-1) may be involved in the development and progression of atherosclerosis. Furthermore, endothelin receptor blockade was shown to reduce the formation of atherosclerotic lesions in experimental studies. Another potent pro-atherosclerotic risk factor is oxidized low-density lipoprotein (oxLDL). Endothelial cells mediate the uptake of oxLDL by the recently identified lectin-like oxLDL receptor-1 (LOX-1), which accumulates in atherosclerotic lesions. In the present study, we analysed the effects of ET-1 on oxLDL uptake and LOX-1 expression in primary cultures of human umbilical vein endothelial cells (HUVEC). ET-1 stimulated uptake of oxLDL in HUVEC, which reached a maximum after 1 h. In further studies, we found a similar induction of LOX-1 mRNA and protein expression in response to ET-1. The augmented oxLDL uptake and the increased LOX-1 expression in response to ET-1 are mediated by the endothelin receptor B. Our data support a new pathophysiological mechanism by which locally and systemically increased ET-1 levels, e.g. in hypertensive patients, could promote LOX-1-mediated oxLDL uptake in human endothelial cells. This mechanism could promote the development and progression of endothelial dysfunction and atherosclerosis. In addition, endothelin receptor blockade could be considered as a new anti-atherosclerotic therapeutic principle.

Gender-Specific Remodeling in Atrial Fibrillation?

BACKGROUND The authors wanted to investigate whether the remodeling process in AF regarding gap junction proteins, collagen I, and amyloid may be gender dependent in humans. METHODS In total, 123 patients with sinus rhythm (SR, n = 41) or atrial fibrillation (AF, n = 82) suffering from mitral valve disease undergoing cardiac surgery were included. Of the 123 patients, 66 patients (SR: n = 17, AF: n = 49) were investigated biochemically for the expression of the atrial gap junction proteins connexin40 (Cx40), connexin43 (Cx43) and collagen I and 57 patients (SR: n = 24; AF: n = 33) using histochemical methods for possible amyloid depositions. RESULTS AF led to increased levels of Cx40, Cx43, and collagen I protein. Regarding Cx40 this upregulation was significantly higher in female than in male patients. For AF-induced changes in collagen or Cx43, there were no significant gender-dependent differences. Amyloid depositions were found with increasing age, but were not significantly related to AF or gender. CONCLUSIONS Remodeling in AF seems to be similar in men and women, with a tendency for women exhibiting somewhat stronger AF-induced changes in Cx40, which is probably a secondary effect because there is nothing known about hormone sensitivity of the Cx40 promoter, and a not significant tendency for higher Cx43 and collagen I.