Leukotriene B4 pathway activation and atherosclerosis in obstructive sleep apnea

Abstract

Leukotriene B(4) (LTB(4)) production increases in obstructive sleep apnea syndrome (OSA) and is linked to early vascular remodeling, the mechanism of which is unknown. The objective of this study was to to determine the molecular mechanisms of LTB(4) pathway activation in polymorphonuclear cells (PMNs) and early vascular remodeling in OSA and the specific contribution of intermittent hypoxia (IH). PMNs were isolated from 120 OSA patients and 33 healthy subjects and used for measurements of LTB(4) production, determination of mRNA and protein expression levels, or exposed for four cycles of in vitro IH. PMNs derived from OSA patients exhibited increased LTB(4) production, for which apnea-hypopnea index was an independent predictor (P=0.042). 5-Lipoxygenase-activating protein (FLAP) mRNA and protein increased significantly in PMNs from OSA patients versus controls and were associated with carotid luminal diameter and intima-media thickness. LTB(4) (10 ng/ml) increased IL-6 (P=0.006) and MCP-1 (P=0.002) production in OSA patient monocytes. In vitro exposure of PMNs from controls to IH enhanced FLAP mRNA levels (P= 0.027) and induced a 2.7-fold increase (P=0.028) in LTB(4) secretion compared with PMNs exposed to normoxia. In conclusion, upregulation of FLAP in PMNs in response to IH may participate in early vascular remodeling in OSA patients, suggesting FLAP as a potential therapeutic target for the cardiovascular morbidity associated with OSA.

Trial registration: ClinicalTrials.gov NCT01089257.

Figures

Fig. 1.

Flow chart detailing patient inclusion in the different experiments.

Fig. 2.

Representative typical LC-MS/MS chromatogram of LTB4, 6 trans-LTB4 and 6-trans-12-epi LTB4 obtained from PMNs stimulated with A23187 10 µM.

Fig. 3.

A: mRNA levels of FLAP, 5-LO, and LTA4H in PMNs from OSA patients. B: membrane FLAP and cytosolic LTA4H protein expression in PMNs derived from controls and OSA patients.

Fig. 4.

A/mRNA levels of 5-LO, FLAP, and LTA4H in PMNs from healthy subjects exposed in vitro to intermittent hypoxia (IH) or normoxia (NX). (results were calculated as 2- D CT, and expressed as fold change compared with NX) B/A23187-mediated LTB4 production by PMNs exposed to in vitro IH or NX.

Fig. 5.

Cytokine production in monocytes from OSA patients in response to LTB4 challenge 10 ng/ml (+) or vehicle (+).