Correlation of redox fluorometry and analytical measurements of pyridine nucleotide

Pyridine nucleotide levels in the corneal epithelium were measured using redox fluorometry, a noninvasive method for monitoring the metabolic status of corneal tissue, and a sensitive bioluminescent assay and an improved extraction procedure that allows the simultaneous extraction and measurement of both NADH and NAD. The same corneas were measured using each of the two methods to enable comparison of the results. The NADH/(NADH + NAD) fraction in the normal epithelium measured by the bioluminescent assay was 0.14 +/- 0.06. Incubation of corneas in 1 mM potassium cyanide (KCN) to mimic the anoxic state increased the NADH/(NADH + NAD) fraction significantly to 0.24 +/- 0.03 (P less than 0.001). The autofluorescence from reduced pyridine nucleotide measured by redox fluorometry also increased with KCN from 2840 +/- 605 to 5147 +/- 738 (P less than 0.0001). A plot of the fluorescence and analytical data for each cornea showed a positive correlation between the two methods, with a correlation coefficient (r value) of 0.80. The correlation was improved but was not dependent on the high values of the KCN treated corneas; an r value of 0.73 was obtained for the non-KCN treated corneas alone. Additional measurements of the temperature dependence of the fluorescence intensity of an NADH solution and the cornea gave a decrease in intensity of 17% from 25 degrees C to 35 degrees C for the NADH solution and 11% (P = 0.0004) for the reduced pyridine nucleotide fluorescence in the cornea over the same temperature range.