Biomedical subjects

Lonneke M Bevers

Publications and source records attributed to Lonneke M Bevers.

3 recordsLinked to original sources

PubMed2006

Low albumin levels increase endothelial NO production and decrease vascular NO sensitivity.

BACKGROUND: Hypoalbuminaemia is associated with increased risk of cardiovascular disease. It is unclear whether endothelial dysfunction is a direct result of low albumin or whether it is caused by factors like chronic inflammation or dyslipidaemia. In this study, the effect of low albumin concentrations on endothelial nitric oxide synthase (eNOS)-dependent NO production was determined in vitro and ex vivo. METHODS: eNOS activity, assessed by arginine-citrulline conversion, and NO production, determined by 4,5-diaminofluorescein diacetate, electron paramagnetic resonance and Griess colorimetry, were measured in cultured endothelial cells expressing high levels of eNOS (bEnd.3) after exposure to albumin concentrations ranging from 0.5 mmol/l (33 g/l) to 0 mmol/l. Analbuminaemic and control rat plasma NO metabolites and aortic eNOS protein mass were determined, and aortic endothelium-independent and endothelium-dependent vasodilator tone were measured ex vivo under albumin-free conditions. RESULTS: In vitro, eNOS activity was significantly increased in the absence of albumin (75 +/- 2 vs 26 +/- 6 pmol/min/mg protein; P < 0.01). Low albumin levels consistently increased NO production in endothelial cells. Plasma NO metabolites were increased (18.2 +/- 1.9 vs 12.5 +/- 0.8 micromol/l; P < 0.05) and endothelium-independent relaxation was markedly blunted in analbuminaemic rats, resulting in a considerably higher ED50 (80 +/- 2 vs 1.1 +/- 0.2 nmol/l, P < 0.01), while endothelium-dependent dilatation was slightly, but significantly, increased. Aortic eNOS protein mass was not affected. This implies that in vivo hypoalbuminaemia reduces vascular NO sensitivity. CONCLUSION: We show that low albumin as such seems to enhance, rather than diminish, eNOS-mediated endothelial NO production.

Albumins↗

PubMed2006

Reduction enhances yields of nitric oxide trapping by iron-diethyldithiocarbamate complex in biological systems.

The mechanism of NO trapping by iron-diethylthiocarbamate complexes was investigated in cultured cells and animal and plant tissues. Contrary to common belief, the NO radicals are trapped by iron-diethylthiocarbamates not only in ferrous but in ferric state also in the biosystems. When DETC was excess over endogenous iron ligands like citrate, ferric DETC complexes were directly observed with EPR spectroscopy at g=4.3. This was the case when isolated spinach leaves, endothelial cultured cells were incubated in the medium with 2.5mM DETC or mouse liver was perfused with 100mM DETC solution. After trapping NO, the nitrosylated Fe-DETC adducts are mostly in diamagnetic ferric state, with only a minor fraction having been reduced to paramagnetic ferrous state by endogenous biological reductants. In actual in vivo trapping experiments with mice, the condition of excess DETC was not met. The substantial quantities of iron in animal tissues were bound to ligands other than DETC, in particular citrate. These non-DETC complexes appear as roughly equal mixtures of ferric and ferrous iron. The presence of NO favors the replacement of non-DETC ligands by DETC. In all biological systems considered here, the nitrosylated Fe-DETC adducts appear as mixture of diamagnetic and paramagnetic states. The diamagnetic ferric nitrosyl complexes may be reduced ex vivo to paramagnetic form by exogenous reductants like dithionite. The trapping yields are significantly enhanced upon exogenous reduction, as proven by NO trapping experiments in plants, cell cultures and mice.

Animals↗

PubMed2005

Tetrahydrobiopterin, but not L-arginine, decreases NO synthase uncoupling in cells expressing high levels of endothelial NO synthase.

Endothelial NO synthase (eNOS) produces superoxide when depleted of (6R)-5,6,7,8-tetrahydro-L-biopterin (BH4) and L-arginine by uncoupling the electron flow from NO production. High expression of eNOS has been reported to have beneficial effects in atherosclerotic arteries after relatively short periods of time. However, sustained high expression of eNOS may have disadvantageous vascular effects because of uncoupling. We investigated NO and reactive oxygen species (ROS) production in a microvascular endothelial cell line (bEnd.3) with sustained high eNOS expression and absent inducible NOS and neuronal NOS expression using 4,5-diaminofluorescein diacetate and diacetyldichlorofluorescein as probes, respectively. Unstimulated cells produced both NO and ROS. After stimulation with vascular endothelial growth factor (VEGF), NO and ROS production increased. VEGF-induced ROS production was even further increased by the addition of extra L-arginine. Nomega-nitro-L-arginine methyl ester decreased ROS production. These findings strongly suggest that eNOS is a source of ROS in these cells. Although BH4 levels were increased as compared with another endothelial cell line, eNOS levels were >2 orders of magnitude higher. The addition of BH4 resulted in increased NO production and decreased generation of ROS, indicating that bEnd.3 cells produce ROS through eNOS uncoupling because of relative BH4 deficiency. Nevertheless, eNOS-dependent ROS production was not completely abolished by the addition of BH4, suggesting intrinsic superoxide production by eNOS. This study indicates that potentially beneficial sustained increases in eNOS expression and activity could lead to eNOS uncoupling and superoxide production as a consequence. Therefore, sustained increases of eNOS or VEGF activity should be accompanied by concomitant supplementation of BH4.

Antioxidants↗