A-FABP and Oxidative Stress Underlie the Impairment of Endothelium-Dependent Relaxations to Serotonin and the Intima-Medial Thickening in the Porcine Coronary Artery with Regenerated Endothelium

Abstract

Experiments were designed to determine the cause of the selective dysfunction of G i proteins, characterized by a reduced endothelium-dependent relaxation to serotonin (5-hydroxytryptamine), in coronary arteries lined with regenerated endothelial cells. Part of the endothelium of the left anterior descending coronary artery of female pigs was removed in vivo to induce regeneration. The animals were treated chronically with vehicle (control), apocynin (antioxidant), or BMS309403 (A-FABP inhibitor) for 28 days before functional examination and histological analysis of segments of coronary arteries with native or regenerated endothelium of the same hearts. Isometric tension was recorded in organ chambers and cumulative concentrationrelaxation curves obtained in response to endothelium-dependent [serotonin (G i protein mediated activation of eNOS) and bradykinin (G q protein mediated activation of eNOS)] and independent [detaNONOate (cGMP-mediated), isoproterenol (cAMP-mediated)] vasodilators. The two inhibitors tested did not acutely affect relaxations of preparations with either native or regenerated endothelium. In the chronically treated groups, however, both apocynin and BMS309403 abolished the reduction in relaxation to serotonin in segments covered with regenerated endothelium and prevented the intima-medial thickening caused by endothelial regeneration, without affecting responses to bradykinin or endothelium-independent agonists (detaNONOate and isoproterenol). Thus, inhibition of either oxidative stress or A-FABP likely prevents both the selective dysfunction of G i protein mediated relaxation to serotonin and the neointimal thickening resulting from endothelial regeneration.

Regenerated Endothelium and Its Senescent Response to Aggregating Platelets

“…9 ) VANHOUTTE PM selective reduction in endothelium-dependent responses to serotonin, as well as the intimal thickening caused by endothelial regeneration in vivo, without affecting relaxation responses to either bradykinin or the exogenous NO-donor sodium nitroprusside; a similar protection was obtained with chronic administration of the antioxidant apocynin (Figure 7). 59 These observations strongly support the conclusion that the overexpression of A-FABP, the subsequent increase in oxidative stress, and hence the resulting presence of oxidized LDL in the regenerated endothelial cells underlie their dysfunction. At the present time, our findings do not permit us to speculate further as to the molecular link between an increased expression/presence of A-FABP and augmentation in the production of oxygen-derived free radicals.…”

Protective effects of histamine on Gq-mediated relaxation in regenerated endothelium

“…This further enhances the importance of this pathway in the hypertensive subjects. Coronary arteries with regenerated endothelium maintain a normal responsiveness to bradykinin, implying that G q protein coupling is unaltered by the regeneration process (6,25,26). The current results demonstrate a major reduction in the relaxations to this peptide in rings with regenerated but not native endothelium of animals treated chronically with the H 1 antagonist pyrilamine.…”

“…They were kept at 21 Ϯ 1°C in a 12-h:12-h light-dark cycle. Under anesthesia (isoflurane, 2%) mixed with breathing gases, the endothelium of ϳ2 cm of the left anterior descending artery (immediately distal to the first branch) was removed by balloon angioplasty, as described (6,25) An angiogram was taken to ensure that no immediate vasospasm occurred in the denuded region. The animals were then given antibiotics and analgesics and observed until they recovered from the anesthesia.…”

“…The intimamedial layer was identified as the region between the lumen and the basal membrane outside of the medial layer. The mage was captured at ϫ2 using a microscope (Olympus, Hong Kong) and analyzed with a computer package (Olympus) (6).…”

“…Therefore, the present experiments were designed to test the hypothesis that chronic in vivo treatment with pyrilamine (H 1 receptor antagonist) prevents the dysfunction, as well as the resulting thickening of the intima-medial layer, associated with endothelial regeneration in the porcine coronary artery. The experiments were performed in parallel with another study (6) of which the untreated control group was used for statistical comparison with the present results obtained in pyrilaminetreated pigs.…”