Lipid Composition of the Human Eye: Are Red Blood Cells a Good Mirror of Retinal and Optic Nerve Fatty Acids?

et al. (2012) Lipid Composition of the Human Eye: Are Red Blood Cells a Good Mirror of Retinal and Optic Nerve Fatty Acids? PLoS ONE 7(4): e35102. doi:10.1371/journal.pone.0035102 Lipid Composition of the Human Eye: Are Red Blood Cells a Good Mirror of Retinal and Optic Nerve Fatty Acids? Niyazi Acar 0 Olivier Berdeaux 0 Ste phane Gre goire 0 Ste phanie Cabaret 0 Lucy Martine 0 Philippe Gain 0 Gilles Thuret 0 Catherine P. Creuzot-Garcher 0 Alain M. Bron 0 Lionel Bretillon 0 Edward Chaum, University of Tennessee, United States of America 0 1 CNRS, UMR6265 Centre des Sciences du Gou t et de l'Alimentation , Dijon, France, 2 INRA , UMR1324 Centre des Sciences du Gou t et de l'Alimentation, Dijon, France, 3 Universite de Bourgogne, UMR Centre des Sciences du Gou t et de l'Alimentation, Dijon, France, 4 Biology, Imaging, and Engineering of Corneal Grafts, Faculty of Medicine, Department of Ophthalmology , Saint Etienne , France , 5 Department of Ophthalmology, University Hospital , Dijon , France Background: The assessment of blood lipids is very frequent in clinical research as it is assumed to reflect the lipid composition of peripheral tissues. Even well accepted such relationships have never been clearly established. This is particularly true in ophthalmology where the use of blood lipids has become very common following recent data linking lipid intake to ocular health and disease. In the present study, we wanted to determine in humans whether a lipidomic approach based on red blood cells could reveal associations between circulating and tissue lipid profiles. To check if the analytical sensitivity may be of importance in such analyses, we have used a double approach for lipidomics. Methodology and Principal Findings: Red blood cells, retinas and optic nerves were collected from 9 human donors. The lipidomic analyses on tissues consisted in gas chromatography and liquid chromatography coupled to an electrospray ionization source-mass spectrometer (LC-ESI-MS). Gas chromatography did not reveal any relevant association between circulating and ocular fatty acids except for arachidonic acid whose circulating amounts were positively associated with its levels in the retina and in the optic nerve. In contrast, several significant associations emerged from LC-ESI-MS analyses. Particularly, lipid entities in red blood cells were positively or negatively associated with representative pools of retinal docosahexaenoic acid (DHA), retinal very-long chain polyunsaturated fatty acids (VLC-PUFA) or optic nerve plasmalogens. Conclusions and Significance: LC-ESI-MS is more appropriate than gas chromatography for lipidomics on red blood cells, and further extrapolation to ocular lipids. The several individual lipid species we have identified are good candidates to represent circulating biomarkers of ocular lipids. However, further investigation is needed before considering them as indexes of disease risk and before using them in clinical studies on optic nerve neuropathies or retinal diseases displaying photoreceptors degeneration. - The nervous system is the organ with the second largest concentration of lipids, only exceeded by adipose tissue. Nervous tissues contain about 50 to 60% of their dry weight as lipids, and approximately 35 to 40% of these lipids are polyunsaturated fatty acids (PUFAs) [1,2,3,4]. These lipids almost exclusively consist in PUFA-rich-membrane phospholipids and in cholesterol playing a structural function without being related to energy metabolism [3]. As elements of the nervous system, ocular tissues such as the optic nerve and the neural retina display similar characteristics [5,6,7]. Phospholipids represent about two-thirds of total lipids in these structures and are characterized by species rich in PUFAs. Although docosahexaenoic acid (DHA; C22:6n-3) represents a small percentage of the fatty acids in most human tissues, it is the most abundant PUFA in the retina [7]. The highest level of DHA in the retina is observed in the outer part of photoreceptor cells where it plays important biophysical and biochemical functions in visual transduction [8], and protection against cell injury [9]. Since it is composed by myelinated axons of retinal ganglion cells, the optic nerve is characterized by its high content in particular phospholipids termed as plasmalogens, whose concentration is increased in myelin [3,5,10]. Ophthalmic diseases affecting the optic nerve and the retina result in alteration of specific cell types, and obviously of the tissue lipid molecular profile. The loss of DHA-rich photoreceptor cells in the retina is a characteristic feature of retinal degenerations such as age-related macular degeneration (AMD) _the leading cause of vision loss in people aged 65 years or more in western countries [11]_ or retinitis pigmentosa that is a group of hereditary retinal degenerations characterized by progressive night blindness [12]. Concerning the optic nerve, glaucomatous optic neuropathy or glaucoma is one of the most important degenerative disease in term of prevalence since it represents the second leading cause of blindness worldwide by affecting more than 60 million people in 2010 [13]. Glaucoma is characterized by structural changes in the optic nerve head and a reduction of the optic nerve diameter, due to a loss of either axons, myelin, or both [14,15]. Results from numerous epidemiological studies have suggested that lower dietary intakes and lower circulating concentrations of DHA are associated with higher risk of AMD [16,17,18,19,20,21]. Several works have also shown lower levels of DHA in plasma and erythrocytes of patients with retinitis pigmentosa [22,23,24,25]. These data led to dietary supplementation trials with DHA for both AMD and retinitis pigmentosa [26,27,28], and to the commercialization of DHA-rich dietary supplements in markets [29], the objective being to maintain or to increase retinal DHA in order to prevent these diseases. To our knowledge, only two studies have established potential relationships between circulating lipids and the pathogenesis of glaucoma. Both of them have demonstrated reduced levels of DHA in plasma and red blood cells of primary open angle glaucoma patients [30,31], together with an additional alteration of circulating levels of plasmalogens [31]. All of these human studies that aim to characterize either pathophysiological events occurring in the eye or the bioavailability/efficacy of dietary treatments need valuable circulating biomarkers in order to mirror retinal concentrations in lipids under pathological influence or in response to a dietary supplementation. Red blood cell membrane lipids are considered as an index of tissue lipid status because the fatty acids they contain are associated with structural membrane lipids [32]. Since red blood cell lipids are also less sensitive than plasma lipids to dietary fluctuations, another advantage is that they represent the longer-term fatty acid st (...truncated)