Changes in endocannabinoid and palmitoylethanolamide levels in eye tissues of patients with diabetic retinopathy and age-related macular degeneration

Cannabinoid receptors and the endocannabinoids (anandamide (N-arachidonoylethanolamine—AEA) and 2-arachidonoylglycerol (2-AG)), as well as the AEA congener, palmitoylethanolamide (PEA), are involved in ocular physiology. We measured endocannabinoid and PEA levels by isotope-dilution liquid chromatography-mass spectrometric analysis in post-mortem eye tissues of patients with diabetic retinopathy (DR) or age-related macular degeneration (AMD). In eyes with DR, significantly enhanced levels of AEA were found in the retina (∼1.8-fold), ciliary body (∼1.5-fold) and, to a lesser extent, cornea (∼1.3-fold). Surprisingly, 2-AG levels were significantly higher (∼3-fold) only in the iris, whereas PEA levels only slightly increased (∼1.3-fold) in the ciliary body. In eyes with AMD, significantly enhanced levels of AEA were found in the choroid (∼1.3-fold), ciliary body (∼1.4-fold) and cornea (∼1.4-fold), whereas in the retina only a trend towards an increase (∼1.5-fold) was observed. The tissue- and disease-selective nature of the changes observed suggests that the compounds analyzed here may play different roles in the control of eye function under different pathological conditions.