Molecular organization of the non-bilayer phospholipid arrangements that induce an autoimmune disease resembling human lupus in mice

Abstract

Non-bilayer phospholipid arrangements are three-dimensional structures that can form when anionic phospholipids with an intermediate form of the tubular hexagonal phase II (H_II), such as phosphatidic acid, phosphatidylserine or cardiolipin, are present in a bilayer of lipids. The drugs chlorpromazine and procainamide, which trigger a lupus-like disease in humans, can induce the formation of non-bilayer phospholipid arrangements, and we have previously shown that liposomes with non-bilayer arrangements induced by these drugs cause an autoimmune disease resembling human lupus in mice. Here we show that liposomes with non-bilayer phospholipid arrangements induced by Mn²⁺ cause a similar disease in mice. We extensively characterize the physical properties and immunological reactivity of liposomes made of the zwitterionic lipid phosphatidylcholine and a H_II-preferring lipid, in the absence or presence of Mn²⁺, chlorpromazine or procainamide. We use an hapten inhibition assay to define the epitope recognized by sera of mice with the disease, and by a monoclonal antibody that binds specifically to non-bilayer phospholipid arrangements, and we report that phosphorylcholine and glycerolphosphorylcholine, which form part of the polar region of phosphatidylcholine, are the only haptens that block the binding of the tested antibodies to non-bilayer arrangements. We propose a model in which the negatively charged H_II-preferring lipids form an inverted micelle by electrostatic interactions with the positive charge of Mn²⁺, chlorpromazine or procainamide; the inverted micelle is inserted into the bilayer of phosphatidylcholine, whose polar regions are exposed and become targets for antibody production. This model may be relevant in the pathogenesis of human lupus.

Keywords::

• Non-bilayer phospholipid arrangements
• H_II-preferring lipids
• murine lupus-like disease

Acknowledgements

We thank Isabel Wong-Baeza for discussion and assistance in the preparation of the English manuscript.

Declaration of interest : This study was supported by grants from the National Polytechnic Institute, Mexico (SIP20101117 to I.B., SIP20101111 to C.W. and SIP20100416 to M.I.). I.B, M.I. and C.W. are listed as authors in the following patents: (1) Baeza I, Aguilar L, Wong C, Ibáñez M, Lara M. (2004). US Patent 6,777,193 B1. Methods for diagnostic and/or treatment of antiphospholipid antibodies-related diseases and devices. (2) Baeza I, Aguilar L, Wong C, Ibáñez M, Lara M. (2011). US Patent 7,867,723 B2. Methods for antiphospholipid syndrome. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.