Lipoprotein-associated phospholipase A2 (Lp-PLA2) as a therapeutic target to prevent retinal vasopermeability during diabetes

Paul Canning; Bridget-Ann Kenny; Vivien Prise; Josephine Glenn; Mosharraf H. Sarker; Natalie Hudson; Martin Brandt; Francisco J. Lopez; David Gale; Philip J. Luthert; Peter Adamson; Patric Turowski; Alan W. Stitt

doi:10.1073/pnas.1514213113

New Research In

Edited by Jian-xing Ma, University of Oklahoma Health Science Center, Oklahoma City, OK, and accepted by Editorial Board Member Jeremy Nathans May 6, 2016 (received for review July 22, 2015)

Significance

Breakdown of the blood–retinal barrier (BRB) is central to diabetic macular edema (DME). Here, we demonstrate that lipoprotein-associated phospholipase A₂ (Lp-PLA₂) plays a critical role in diabetes-related retinal vasopermeability, a response that is mediated by lysophosphatidylcholine (LPC). Because neutralization of VEGF is the current gold-standard treatment for DME, we assessed suboptimal systemic treatment of an Lp-PLA₂ inhibitor alongside a suboptimal intravitreal injection with a rat-specific VEGF antibody and demonstrated that protection against diabetes-mediated retinal vasopermeability was additive. We have also shown a coalescence of the LPC and VEGF pathways in retinal vascular endothelium via a common VEGF receptor 2-mediated mechanism. Alongside currently administered anti-VEGF agents, Lp-PLA₂ may be a useful therapeutic target for DME.

Abstract

Lipoprotein-associated phospholipase A₂ (Lp-PLA₂) hydrolyses oxidized low-density lipoproteins into proinflammatory products, which can have detrimental effects on vascular function. As a specific inhibitor of Lp-PLA₂, darapladib has been shown to be protective against atherogenesis and vascular leakage in diabetic and hypercholesterolemic animal models. This study has investigated whether Lp-PLA₂ and its major enzymatic product, lysophosphatidylcholine (LPC), are involved in blood–retinal barrier (BRB) damage during diabetic retinopathy. We assessed BRB protection in diabetic rats through use of species-specific analogs of darapladib. Systemic Lp-PLA₂ inhibition using SB-435495 at 10 mg/kg (i.p.) effectively suppressed BRB breakdown in streptozotocin-diabetic Brown Norway rats. This inhibitory effect was comparable to intravitreal VEGF neutralization, and the protection against BRB dysfunction was additive when both targets were inhibited simultaneously. Mechanistic studies in primary brain and retinal microvascular endothelial cells, as well as occluded rat pial microvessels, showed that luminal but not abluminal LPC potently induced permeability, and that this required signaling by the VEGF receptor 2 (VEGFR2). Taken together, this study demonstrates that Lp-PLA₂ inhibition can effectively prevent diabetes-mediated BRB dysfunction and that LPC impacts on the retinal vascular endothelium to induce vasopermeability via VEGFR2. Thus, Lp-PLA₂ may be a useful therapeutic target for patients with diabetic macular edema (DME), perhaps in combination with currently administered anti-VEGF agents.

Footnotes

↵¹P.T. and A.W.S. contributed equally to this work.
↵²To whom correspondence may be addressed. Email: a.stitt{at}qub.ac.uk or p.turowski{at}ucl.ac.uk.

Author contributions: F.J.L., P.A., P.T., and A.W.S. designed research; P.C., B.-A.K., V.P., J.G., M.H.S., N.H., M.B., D.G., P.J.L., P.T., and A.W.S. performed research; F.J.L. contributed new reagents/analytic tools; P.C., B.-A.K., J.G., D.G., and P.T. analyzed data; and P.C., P.A., P.T., and A.W.S. wrote the paper.
Conflict of interest statement: The authors M.B., F.J.L., D.G., and P.A. are (or have been) employed by GlaxoSmithKline. The funding of this research has been through a grant provided by GlaxoSmithKline.
This article is a PNAS Direct Submission. J.-x.M. is a guest editor invited by the Editorial Board.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1514213113/-/DCSupplemental.

Freely available online through the PNAS open access option.

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