IDENTIFICATION OF DIGITALIS-LIKE COMPOUNDS IN HUMAN CATARACTOUS LENSES

Human cataractous lens nuclei extract inhibited, in a dose-dependent f ashion, [H-3]ouabain binding to rat brain synaptosomes and microsomal Na+- and K+-dependent adenosine triphosphate (Na+, K+-ATPase) activity and interacted with anti-digoxin antibodies. The compounds responsibl e for these activities, termed digitalis-like compounds (DLC), were al so detected in bovine, rat, cat and rabbit, normal, transparent lenses , but the levels were only 0.7-5.4% of the average levels in the catar actous human lenses. DLC from the human cataractous lenses were purifi ed by a procedure consisting of organic extractions and batch chromato graphy followed by filtration through a 3000 Da cut-off filter and sub sequent separations using reverse-phase high-performance liquid chroma tography. The presence of DLC in the different fractions obtained in t he chromatograms was monitored by their ability to inhibit [H-3]ouabai n binding and Na+, K+-ATPase activity. Based on chemical ionization ma ss spectrometry together with ultraviolet spectrometry and biological characterization, it is suggested that new bufodienolides, 19-norbufal in and 19-norbufalin peptide derivatives are responsible for the endog enous DLC activity. It is proposed that these compounds may regulate N a+, K+-ATPase activity in the lens under some physiological and pathol ogical conditions.