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L Kessel, S Kalinin, M Larsen, L-Å Johansson; Time-resolved and Steady-state Fluorescence Spectroscopic Studies of the Human Lens . Invest. Ophthalmol. Vis. Sci. 2002;43(13):470.
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Purpose: The blue-green fluorescence of the human lens increases with age and in the presence of diabetes. Several fluorophores have been identified, mainly advanced glycation end products. The present study was performed to characterize the time-resolved and steady-state fluorescence spectroscopic properties of the human lens. Fluorescence emission spectra were studied at different excitations to examine whether more than one fluorophore contributes to the fluorescence. To identify the origin of fluorescence, human lens fluorescence was compared to two glycation products, argpyrimidine and pentosidine, and a photooxidative derivative of tryptophan, 3-OH-kynurenine. Methods: Six human lenses, extracted post mortem from donors aged 28 to 73 years, were studied. Time-resolved fluorescence was recorded at excitation 330 and 404 nm. Emission spectra were measured after excitation at 280, 335, 350, 360, and 400 nm and excitation spectra were obtained with a fixed emission set at 420 nm. Similar measurements were carried out for argpyrimidine, pentosidine and 3-OH-kynurenine. Results: The shape of the emission spectra and average fluorescence lifetimes did not change with age. Excitation spectra demonstrated an accumulation of fluorophores with age, while no evidence was found for the formation of new fluorophores. At least two fluorophores contributed to the observed fluorescence. The spectral shape of the dominant fluorophore (excitation 339 nm, emission 420 nm) was compatible to a protonated form of argpyrimidine with a life-time of less than 1 ns. Pentosidine may provide minor contributions to the total fluorescence whereas that of 3-OH-kynurenine is negligible. Conclusion: The present work demonstrates that at least two distinct fluorophores contribute to the blue fluorescence of the human lens. A single fluorophore, argpyrimidine, dominated and as argpyrimidine is an advanced glycation end product the study confirms the well-established relation between lens autofluorescence and diabetes.
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