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Published on: December 12, 2014
[Dependence of lipid peroxidation on pigmentation of the porcine iris]
K Nau-Staudt1, W M Nau, I O Haefliger
1Universitäts-Augenklinik, Labor für okuläre Pharmakologie und Physiologie, Mittlere Strasse 91, CH-4056 Basel. kerstin.nau@unibas.ch
Purpose:
Melanin has been shown to act as antioxidant in lipid peroxidation studies. We have now investigated lipid peroxidation in dependence on stromal pigmentation in isolated porcine irises.
Methods:
The same number of lightly pigmented and heavily pigmented porcine irises (visual selection) were homogenized in buffer (50 mmol/l Na2HPO4, 50 mmol/l NaH2PO4 and 4 mmol/l sodium azide; 1:20 w/v). 500 microliters homogenate were incubated at 37 degrees C for 5, 10, 20 and 40 min in absence and presence of Fe2+ as inducer of lipid peroxidation. Lipid peroxidation was assayed by the thiobarbituric acid (TBA) test. Results are expressed as nmol of TBA reactive material produced (TBAR) per mg protein. Fe2+ concentration of the supernatant was determined spectrophotometrically with phenanthroline.
Results:
70 mumol/l, 180 mumol/l and 360 mumol/l Fe2+ induced lipid peroxidation. A plateau region was reached after 20 min. Lipid peroxidation differed in dependence on stromal pigmentation in porcine irises by a factor of 2.8. 180 mumol/l Fe2+ induced 1.373 +/- 0.138 nmol TBAR/mg protein in lightly pigmented irises compared to 0.491 +/- 0.125 nmol TBAR/mg protein in heavily pigmented irises after 10 min incubation (p < 0.0001, n = 4). On the other hand, the content of Fe2+ in the supernatant was the same within error.
Conclusions:
There was a stronger induction of lipid peroxidation in lightly pigmented porcine irises compared to heavily pigmented porcine irises. This effect may be related to the difference in stromal melanin content and its antioxidant activity.
