Associations between erythrocyte and ciliary epithelium phosphatidylcholine concentrations in healthy humans

Abstract

Purpose: The pathogenesis of primary open angle glaucoma (POAG) with elevated IOP lies in trabeculum. We have shown previously that red blood cell concentrations of several phosphatidylcholines, namely PC(18:0/22:6), PC(18:1/22:6), and PC(22:6/22:6), are reduced in patients with POAG (Acar et al Exp Eye Res 2009;89:840-853). As red blood cells lipid composition is considered as a good marker of the lipid profile of peripheral tissues, the aim of this work was to check whether the erythrocyte concentrations of PC(18:0/22:6), PC(18:1/22:6), and PC(22:6/22:6) are associated with that of phosphatidylcholines in the ciliary epithelium, the ocular structure responsible for aqueous humor production.

Methods: Red blood cells and ciliary epitheliums were collected from seven healthy human donors. Following lipid extraction, individual species of phosphatidylcholines were identified and quantified by HPLC-ESI-MS/MS on a triple quadrupole MS instrument. Spearman correlations were estimated for each compound to determine plausible associations between circulating and tissue concentrations.

Results: Whereas the red blood cell levels of PC(18:0/22:6) and PC(22:6/22:6) did not show any relevant association with any phosphatidylcholine species in ciliary epithelium, the erythrocyte concentration of PC(18:1/22:6) was strongly and positively associated with that of PC(18:0/22:6) (rSpearman=0.828, p<0.05), PC(18:0/22:5) (rSpearman=0.882, p<0.05), PC(20:0/22:6) (rSpearman=0.882, p<0.05), PC(22:6/22:6) (rSpearman=0.936, p<0.05), and total phosphatidylcholines (rSpearman=0.954, p<0.05) in ciliary epithelium.

Conclusions: According to our data, PC(18:0/22:6) represents the best candidate for seeking correlations between peripheral blood and ciliary epithelium. Further studies in POAG globes are mandatory to confirm these observations.