Corneal absorption of glycerylphosphorylcholine.

This study documents the absorption of glycerylphosphorylcholine (GPC) into corneas ex vivo. Corneas in quadruplicate were incubated in preservation medium containing 30 mM GPC, which is used as a reference marker. The GPC reference marker is used to calibrate P nuclear magnetic resonance (NMR) spectral chemical-shift positions for identification of phosphatic metabolites and to calculate intracorneal pH in intact tissues ex vivo. Following baseline NMR ex vivo analysis, corneas were stored in eye bank chambers in preservation medium containing 30 mM GPC at 4 °C overnight for 8 h. After returning to room temperature, NMR analysis was repeated on the same corneas in fresh GPC-free preservation medium. NMR analysis also was performed on the 30 mM GPC preservation medium alone from the eye bank chambers for detection of the GPC signal. The elevated GPC signal unexpectedly persisted in corneas incubated at 4 °C overnight even though GPC was not present in the fresh GPC-free preservation medium. In fact, the concentration of GPC in the intact cornea was many times higher than that found in the cornea endogenously. The levels of phosphatic metabolites and the energy modulus, after subtracting the spectral contribution of the 30 mM exogenous GPC, as well as the intracorneal pH remained unchanged from pre-refrigeration analyses. Corneas also retained transparency through the time-course of this study irrespective of temperature or change in temperature. The GPC signal in the NMR analysis of the preservation medium from the eye bank chambers was nearly undetectable. GPC was unexpectedly absorbed into the corneal tissue without detectable metabolic or physical toxicity. The intracorneal uptake of GPC at reduced temperatures parallels the increase in GPC that occurs naturally in muscle tissue in animals during wintering periods and the very high concentration of GPC in sperm, a cryogenically compatible cell, suggestive of a potential role for GPC in cryopreservation.