engleski

Development of cataract caused by diabetes mellitus ; Raman study

Diabetes mellitus succeeded by diabetic cataract was induced to experimental animals (Wistar rats) by applying an Alloxan injection. Eye properties deterioration were monitored from clinical standpoint and using Raman and infrared spectroscopies. All cases of developed cataract were followed by important changes in vibrational spectra, but Raman spectroscopy proved to be more useful because of larger number of resolved bands. Each k-th Raman spectrum of diseased lens (in our notation k denotes disease age and cataract degree as described in chapter Alloxan diabetes) can be expressed as a sum of the Raman spectrum of healthy lens, IR, multiplied by a suitable constant ck, and the fluorescent background spectrum, IFB. We introduce the ratio of integrated intensities IFB and ck*IR as a physical parameter called fluorescent background index FFB. It turns out that FFB grows as cataract progresses and has its maximum at approx. 4, whence it decreases. FFB values are larger for 200 - 1800 cm-1 spectral interval than for 2500-4000 cm-1 interval. In the same manner another quantity called water band index FW is defined for each Raman spectrum of diseased lens in the 2800 - 3730 cm-1 interval. It is the ratio of the integrated intensity from 3100 to 3730 cm-1 (water band interval) divided by the integrated intensity of the 2800 - 3100 cm-1 interval (C-H stretching region). FW increases monotonously with cataract progression with maximum at the end of monitored period (5 months). These two indices helped us to formulate a model describing disease development from the earliest molecular changes to its macroscopic manifestation. As glucose and other small saccharide molecules enter the lens tissue, they bind to crystallin and other proteins via O- and S- glycosidic linkages which occur probably at tyrosine and cystein sites. In Raman spectrum this corresponds to broad bands at 540 and 1100 cm-1 which grow together with the fluorescent background, because both contributions orriginate in nonenzimatically glycated proteins. The maximum of possible binding ends after approximately four months (cataract degree 4), but the water continues to enter the tissue and resides in water agglomerates. The lens impairing caused by fluorescent light scattering on aberrant glycoproteins and other fluorescent centers appears first and is usually associated with the ageing cataract, while deterioration of lens properties caused by increased binding of water steadily rises with glucose and is characteristic of diabetic cataract. This interpretation is in agreement with electron microscopy results of other groups and with our preliminary findings obtained with light microscopy.

diabetes; eye-lens; cataract; raman spectroscopy

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