Regulatory functions of the coronary endothelium

Hemodialysis removes uremic toxins that alter the biological actions of endothelial cells

Chronic kidney disease is linked to systemic inflammation and to an increased risk of ischemic heart disease and atherosclerosis. Endothelial dysfunction associates with hypertension and vascular disease in the presence of chronic kidney disease but the mechanisms that regulate the activation of the endothelium at the early stages of the disease, before systemic inflammation is established remain obscure. In the present study we investigated the effect of serum derived from patients with chronic kidney disease either before or after hemodialysis on the activation of human endothelial cells in vitro, as an attempt to define the overall effect of uremic toxins at the early stages of endothelial dysfunction. Our results argue that uremic toxins alter the biological actions of endothelial cells and the remodelling of the extracellular matrix before signs of systemic inflammatory responses are observed. This study further elucidates the early events of endothelial dysfunction during toxic uremia conditions allowing more complete understanding of the molecular events as well as their sequence during progressive renal failure.

Paradoxical effects of hypoxia-mimicking divalent cobalt ions in human endothelial cells in vitro

Divalent cobalt ions (Co2+) induce the expression of hypoxia responsive genes and are often used in cell biology to mimic hypoxia. In this in vitro study we compared the effects of hypoxia and Co2+ on human endothelial cells and examined processes that are stimulated in hypoxia in vivo (proliferation and angiogenesis). We analyzed the expression of the hypoxia-inducible factor-1alpha (HIF-1alpha) under different hypoxic conditions (3% and nearly 0% O2) and Co2+ -concentrations (0.01-0.7 mM). As in hypoxia, the amount of HIF-1alpha protein was enhanced by exposure to Co2+ (did not correlate with mRNA amount). however, contrary to the results of hypoxia, in vitro-angiogenesis was inhibited after exposure to even low Co2+-concentrations (> or =0.01 mM). This led to the conclusion that although hypoxia signaling after Co2+ -exposure took place, further yet unknown Co2+ -induced event(s) must have occurred.

Impaired coronary endothelial function in a rat model of spontaneous albuminuria

BACKGROUND

Albuminuria is an independent risk factor of coronary artery disease and has been proposed to reflect a general endothelial disorder. The Munich Wistar Frömter (MWF) rat strain develops spontaneous albuminuria and, therefore, may be an interesting experimental model to study alterations of endothelial function under conditions of increased albuminuria. Our aim was to investigate if the MWF strain shows generalized endothelial dysfunction or endothelial dysfunction localized to the coronary vascular bed, and if so, determine which endothelial dilative mediators are involved.

METHODS

Coronary and mesenteric arteries were investigated for endothelium-dependent relaxation and the contribution of prostacyclin, nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) in MWF rats compared to normal Wistar rats. In addition, as MWF rats show increased blood pressure, spontaneously hypertensive rats (SHR) with similar hypertension but without increased albuminuria also were studied.

RESULTS

Maximal total endothelium-dependent relaxation of coronary arteries was strongly impaired in MWF rats (55 +/- 3%) compared to Wistar (89 +/- 5%) and SHR (89 +/- 2%) P < 0.05, respectively. The NO-mediated relaxation as well as the relaxation mediated by EDH were significantly lower in coronary arteries from MWF compared to Wistar. In mesenteric arteries of MWF the endothelium-dependent relaxation was intact.

CONCLUSIONS

The strong impairment of coronary endothelium-dependent relaxation in the MWF model of spontaneous albuminuria may be due to defects in production or activity of NO and EDH. The intact mesenteric endothelium-dependent relaxation suggests that increased albuminuria may not be related to generalized endothelial vasodilator dysfunction in this model. Selective impairment of coronary endothelial function in a setting of spontaneous albuminuria may be a feature of the MWF that may be employed to further study cause-effect relations between albuminuria and coronary artery disease.

Thiopental inhibits nitric oxide production in rat aorta

We studied whether thiopental affects endothelial nitric oxide dependent vasodilator responses and nitrite production (an indicator of nitric oxide production) elicited by acetylcholine, histamine, and A23187 in rat aorta (artery in which nitric oxide is the main endothelial relaxant factor). In addition, we evaluated the barbiturate effect on nitric oxide synthase (NOS) activity in both rat aorta and kidney homogenates. Thiopental (10-100 µg/mL) reversibly inhibited the endothelium-dependent relaxation elicited by acetylcholine, histamine, and A23187. On the contrary, this anesthetic did not modify the endothelium-independent but cGMP-dependent relaxation elicited by sodium nitroprusside (1 nM - 1 µM) and nitroglycerin (1 nM - 1 µM), thus excluding an effect of thiopental on guanylate cyclase of vascular smooth muscle. Thiopental (100 µg/mL) inhibited both basal (87.8 ± 14.3%) and acetylcholine- or A23187-stimulated (78.6 ± 3.9 and 39.7 ± 5.6%, respectively) production of nitrites in aortic rings. In addition the barbiturate inhibited (100 µg/mL) the NOS (45 ± 4 and 42.8 ± 9%) in aortic and kidney homogenates, respectively (measured as 14C-labeled citrulline production). In conclusion, thiopental inhibition of endothelium-dependent relaxation and nitrite production in aortic rings strongly suggests an inhibitory effect on NOS. Thiopental inhibition of the NOS provides further support to this contention.Key words: thiopental, rat aorta, endothelium-dependent relaxation, nitric oxide synthesis.

Cold ischemia-induced damage to vascular endothelium results in permeability alterations in transplanted lungs

Despite suggestions of a connection between endothelial damage and permeability alterations after ischemia and reperfusion in pulmonary tissue undergoing transplantation, no direct correlation between vascular endothelial discontinuity and parenchymal edema has yet been shown.

METHODS

Forty-two rat lungs were harvested and stored for 48 or 72 hours under hypothermic and ischemic conditions. Stored pulmonary tissue was studied before transplantation and 5 minutes or 24 hours after transplantation by light microscopy and scanning electron microscopy of arterial vascular endothelium.

RESULTS

Stored lungs not subjected to revascularization showed moderate perivascular edema, with small intercellular gaps in endothelial monolayers. Five minutes after transplantation, pulmonary tissue appeared congested, with perivascular and alveolar edema. Examination of vascular endothelium by scanning electron microscopy showed detachment of endothelial cells. Twenty-four hours after transplantation, edema, hemorrhage, and vascular congestion were found in all specimens. Arterial vascular endothelium showed weak intercellular connections, numerous intercellular gaps, and widespread cell detachment. Bronchial epithelial cells appeared damaged after storage, with loss of cilia, blebbing of apical cytoplasm, and cellular rounding. These changes were maintained 5 minutes after transplantation but appeared totally reversed after 24 hours in specimens stored 48 hours, whereas bronchial denudation was observed in 72-hour stored lungs. Statistically significant positive correlations (Kendall p < 0.001) between revascularization time and alveolar edema and hemorrhage were found for both storage periods.

CONCLUSION

The results from this study demonstrate correlation between loss of endothelial monolayer continuity and histologic evidence of vascular permeability increases in pulmonary tissue before and after lung transplantation.