Abhängigkeit der Lipidperoxidation von der Pigmentierung porkiner Iris

Zusammenfassung

Hintergrund Lipidperoxidationsstudien haben gezeigt, dass Melanin antioxidativ wirkt. Wir haben nun die Abhängigkeit der Lipidperoxidation von der stromalen Pigmentierung in isoliertem porkinen Irisgewebe untersucht.

Material und Methoden Die gleiche Anzahl gering (weißlich) und stark pigmentierter Irisen (dunkelbraun; visuell ausgewählt) wurde in Puffer homogenisiert (50 mmol/l Na₂HPO₄, 50 mmol/l NaH₂PO₄ und 4 mmol/l Natriumazid; 1 : 20 w/v). Jeweils 500 μl Homogenisat wurden bei 37 °C für 5, 10, 20 und 40 min in Ab- und Anwesenheit von Fe²⁺, einem Induktor der Lipidperoxidation, inkubiert. Das Ausmaß an Lipidperoxidation wurde mit Hilfe des Thiobarbitursäure-(TBA)-Tests ermittelt. Die Ergebnisse wurden in nmol TBA-reaktives Material (TBAR)/mg Protein umgerechnet. Die Fe²⁺-Konzentration der Inkubationslösung wurde spektrophotometrisch mit Phenanthrolin bestimmt.

Ergebnisse 70 μmol/l, 180 μmol/l und 360 μmol/l Fe²⁺ induzierten Lipidperoxidation. Nach 20 min wurde ein Plateau erreicht. Es zeigte sich, dass sich die Lipidperoxidation in porkinen Irisen in Abhängigkeit von der stromalen Pigmentierung um den Faktor 2,8 unterschied. In Gegenwart von 180 μmol/l Fe²⁺ wurden nach einer Inkubationszeit von 10 min in gering pigmentiertem Irisgewebe 1,373 ± 0,138 nmol TBAR/mg Protein induziert, in stark pigmentiertem Irisgewebe dagegen nur 0,491 ± 0,125 nmol TBAR/mg Protein (p < 0,0001, n=4). Andererseits unterschied sich der Gehalt an Fe²⁺ in der Inkubationslösung nicht signifikant.

Schlussfolgerungen Die Lipidperoxidation wurde in gering pigmentiertem porkinen Irisgewebe stärker induziert als in stark pigmentiertem Irisgewebe. Dieser Effekt ist vermutlich auf den unterschiedlichen Gehalt an Melanin und dessen Antioxidansaktivität zurückzuführen.

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 μl homogenate were incubated at 37 ^oC 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 μmol/l, 180 μmol/l and 360 μmol/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 μmol/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.

Lipidperoxidation - oxidativer Stress - Iris - Pigmentierung - altersabhängige Makuladegeneration

Lipid peroxidation - oxidative stress - iris - pigmentation - age-related macular degeneration

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