Distribution of phosphatic metabolites in the porcine cornea using phosphorus-31 nuclear magnetic resonance

This study describes the phosphatic metabolite contribution of the porcine corneal stroma [by phosphorus-31 nuclear magnetic resonance (P-31 NMR)] and the corneal epithelium (by difference calculation) to the total phosphatic metabolic profile of the intact (i.e. whole, undissected) cornea. In order to provide such a regional analysis, the epithelium and endothelium were surgically removed from three sets of 12 corneas. Three additional sets of 12 intact corneas were used as controls. Histological examination of two randomly selected stromata from each set of corneas were analyzed to verify that epithelium and endothelium were removed. Perchloric acid extracts were prepared from the 10 remaining stromata for P-31 NMR analysis. Twenty phosphatic metabolites were measured including six unidentified (unknown) signals. Components with diminished relative concentrations in the stromal profile compared to that of the intact cornea profile are: the triose and hexose phosphates associated with glycolysis (including alpha-glycerophosphate), choline phosphate, ATP, uridine diphosphohexoses and the unknown compound resonating at 0.93 delta. The relative level of inorganic phosphate in the stroma is nearly doubled. The remaining measured phosphates are not significantly changed relative to the total extractable phosphorus content. Consistent with previous biochemical findings, phosphates associated with energy metabolism are found primarily in the epithelial fraction. The metabolic status of the endothelial monolayer cannot be assessed because of low tissue mass and the relatively low sensitivity of P-31 NMR spectroscopy. This study serves as baseline data for the interpretation of experimental and clinical phosphorus NMR data from intact cornea by providing the contribution to the whole corneal spectrum of metabolites of the individual corneal layers.