Electron spin resonance and high pressure liquid chromatographic analysis of melanin in posterior choroidal melanomas.

Electron spin resonance (ESR) and high pressure liquid chromatography (HPLC) were utilized to characterize the physical and biochemical characteristics of melanin in choroidal melanoma. ESR free radical signals indicative of eumelanin could be elicited from formalin-fixed paraffin-embedded tissues. Zinc ions (50 mM) increased the number of melanin-free radicals resulting in greater ESR sensitivity. Pyrole 2,3,6 tricarboxylic acid (PTCA) and amino hydroxy phenylalanine (AHP) were identified by HPLC after permanganate oxidation and hydroiodic acid hydrolysis, respectively, of a choroidal melanoma obtained at enucleation. The results indicate eumelanin is the primary melanin type in posterior choroidal melanomas. The feasibility of these techniques in the detection of metastatic disease from ocular melanomas is discussed.