Dextran efflux from McCarey-Kaufman-stored corneas as measured by nuclear magnetic resonance

Dextran, a high molecular weight polymer of glucose, is used as an osmotic agent in McCarey-Kaufman (MK) (corneal storage) medium. It has been proposed that Dextran may cause deleterious effects on living cells either by high molecular weight toxicity or by the induction of an immunological reaction against transplanted tissues. Prolonged retention of Dextran in transplanted corneas, therefore, may produce deleterious side effects. The efflux of Dextran from MK-stored human corneas was monitored by transferring corneas to 2 ml of fresh Krebs Ringer bicarbonate solution (BSS) containing 5.5 mM 1-13C-labeled glucose at approximately 1 h intervals for 1-24 h. Chemical shifts of 98.7, 74.5, 72.5, 71.2, 70.6, and 66.5 ppm were found for the naturally abundant 13C NMR spectrum of 40,000 molecular weight Dextran. Peak heights for the 70.6 ppm Dextran chemical shift were measured and plotted against total wash time to determine the slope for Dextran efflux from each cornea. The results of this study suggest that all of the Dextran absorbed into human corneas stored for up to 2 weeks in MK medium is eluted in about 19 h and that the rate of Dextran efflux is unaffected by donor age, time of storage in MK, or corneal viability.