Chronic exposure to high fatty acids impedes receptor agonist-induced nitric oxide production and increments of cytosolic Ca2+ levels in endothelial cells

Abstract

Dyslipidemia is a common metabolic disorder in diabetes. Nitric oxide (NO) production from endothelium plays the primary role in endothelium-mediated vascular relaxation and other endothelial functions. Therefore, we investigated the effects of elevated free fatty acids (FFA) on the stimulation of NO production by phospholipase C (PLC)-activating receptor agonists (potent physiological endothelium-dependent vasodilators) and defined the possible alterations of signaling pathways implicated in this scenario. Exposure of bovine aortic endothelial cells (BAECs) to high concentrations of a mixture of fatty acids (oleate and palmitate) for 5 or 10 days significantly reduced NO production evoked by receptor agonists (bradykinin or ATP) in a time-and dose-dependent manner. Such defects were not associated with alterations of either endothelial NO synthase mass or inositol phospholipid contents but were probably due to reduced elevations of intracellular free Ca 2C levels ([Ca 2C ] i ) under these conditions. Exposure of BAECs to FFA significantly attenuated agonist-induced [Ca 2C ] i increases by up to 54% in a dose-and time-dependent manner. Moreover, bradykinin receptor affinity on the cell surface was significantly decreased by high concentrations of FFA. The morphology of BAECs was altered after 10-day culture with high FFA. Co-culture with protein kinase C (PKC) inhibitors or antioxidants was able to reverse the impairments of receptor agonist-induced NO production and [Ca 2C ] i rises as well as the alteration of receptor affinity in BAECs exposed to FFA. These data indicate that chronic exposure to high FFA reduces NO generation in endothelial cells probably by impairing PLC-mediated Ca 2C signaling pathway through activation of PKC and excess generation of oxidants.

Store-Dependent Ca2+ Entry in Endothelial Progenitor Cells As a Perspective Tool to Enhance Cell-Based Therapy and Adverse Tumour Vascularization

“…gene modification of the Ca 2+ handling machinery might recorrect the well known EPC dysfunctions that occur in patients affected by cardiovascular pathologies and hamper autologous cell transplantation. For instance, SOCE is up-regulated in bovine aortic ECs exposed to high glucose levels [138], whereas it is significantly decreased in ECs cultured in the presence of high concentrations of a mixture of fatty acids (oleate and palmitate) [139]. EPCs isolated from either diabetic or obese patients display reduced proliferative potential and migratory function.…”

Lipotoxicity contributes to endothelial dysfunction: A focus on the contribution from ceramide

“…[24] Kim et al showed that each of these fatty acids impair basal and insulin-stimulated NO production in bovine aortic endothelial cells (BAECs), with palmitic acid exerting the greatest effect [25]. Elevated FFAs can promote de novo synthesis of diacylglycerol which activates certain protein kinase C (PKC) isoforms[7;16]. Tang and Li [16] reported that endothelial cells exposed to 5 or 10 days of palmitate treatment displayed impaired agonist-evoked (i.e., bradykinin, ATP) NO production that was secondary to blunted elevations of intracellular free Ca 2+ [Ca 2+ ]i. Co-culture of endothelial cells with PKC inhibitors neutralized the ability of palmitate to lower NO.…”

“…Elevated FFAs can promote de novo synthesis of diacylglycerol which activates certain protein kinase C (PKC) isoforms[7;16]. Tang and Li [16] reported that endothelial cells exposed to 5 or 10 days of palmitate treatment displayed impaired agonist-evoked (i.e., bradykinin, ATP) NO production that was secondary to blunted elevations of intracellular free Ca 2+ [Ca 2+ ]i. Co-culture of endothelial cells with PKC inhibitors neutralized the ability of palmitate to lower NO. This finding is consistent with observations that PKC activation selectively inhibits PI3K / Akt signaling in the vasculature [10;26] such that cGMP formation - an estimate of NO bioavailability – is impaired [27].…”

Mechanisms of Lipotoxicity in the Cardiovascular System

“…Excessive free fatty acids (FFAs) can promote de novo synthesis of diacylglycerol that activates classic and novel protein kinase C (PKC) isoforms [5, 6]. PKC activation inhibits insulin and Vascular endothelial growth factor (VEGF)-mediated activation of PI3K and Akt [7, 2••], which limits cGMP formation from nitric oxide (eNOS generated) activation of guanylate cyclase [8•].…”