The regional distribution and molecular interactions of phospholipids and glucose in mammalian vitreous humors.

Abstract

The vitreous humor (VH) is located in between the lens and the retina. It is composed of 98% water, hyaluronan (HA), collagen, proteins, phospholipids (PLs), and other metabolites. With aging, the VH undergoes liquefaction, a process that causes the gel-like structure of the VH to turn into a liquid and can lead to serious ocular diseases, including retinal detachment, vitreal detachment, and macular hole formation. The liquefaction process is expedited in diabetic VHs. This project focuses on understanding the molecular changes that lead to liquefaction and the reasons for which this process is accelerated with diabetes. Matrix-assisted laser desorption ionization/mass spectrometry (MALDI/MS) and nuclear magnetic resonance (NMR) spectroscopy were applied for in vitro, ex situ, and model studies of VHs to identify and quantify several components of the VH network and explore their interactions. In-vitro and ex-situ methods were optimized and conducted on porcine and human VHs. The mammalian species produced similar compositional trends. MALDI/MS showed that PLs were most abundant in the posterior region (closest to the retina) followed by the anterior (closest to the lens) and then the central regions. Diabetic and non-diabetic VHs regional distribution of glucose was compared. Glucose was vi present in significant higher levels (three-fold) in diabetic VHs compared to non-diabetic ones of similar age. The levels of glucose in the diabetic VH were highest in the posterior followed by the anterior and central regions. This trend follows that observed for the PLs. Model studies were performed to explore the interaction(s) of vitreal components and hyaluronan (HA) using MALDI/MS and NMR. The studies indicate interactions between both the headgroups of PLs and the carboxylate groups of HA as well as that between the acyl tails on PC with the hydrophobic regions of HA. Such interactions are proposed to disrupt the H-bonding network of HA and contribute to liquefaction of the VH. Future studies will focus on age-dependent studies of human VHs as well as the analysis of fresh human VHs following vitrectomy surgery. vii