3-nitrotyrosine and Iron-Overload

The hypothesis of this study was that alterations in Fe distribution triggered by lipopolysaccharide (LPS) administration were affected in vivo by Fe overload. Lipopolysaccharide treatment by itself significantly decreased Fe content in serum and increased the blood NO-hemoglobin (NO-Hb) EPR signal and nitrotyrosine protein content in liver, as compared to values in control animals. Fe overload (produced by Fe-dextran ip administration) caused an increase, as compared to values in control animals, in Fe content in serum, and a significant enhancement in ferritin (Ft) content, Fe content in Ft, the labile Fe pool (LIP), and the protein carbonyl content in the liver. The simultaneous administration of LPS and Fe-dextran lead to a significant increase in the Fe content in serum, blood NO-Hb EPR signal, the content of Fe, Fe in Ft, LIP, protein carbonyl, and nitrotyrosine protein in liver, as compared to values in control animals. The data reported here indicate that the protective strategy against endotoxemia of sequestering serum Fe content is not fully operative under Fe overload conditions. However, the oxidative condition of the liver does not seem to be being affected, since endogenous mechanisms were able to regulate the amount of catalytically active Fe to the same levels observed after Fe-dextran administration, even in the presence of LPS, over the initial six-hour period.

Topics: Analysis of Variance; Animals; Endotoxemia; Ferritins; Hemoglobins; Iron; Iron Overload; Iron-Dextran Complex; Lipopolysaccharides; Liver; Male; Nitric Oxide; Protein Carbonylation; Rats; Rats, Wistar; Tyrosine

Iron overload can contribute to oxidative stress in many tissues. We studied the effects of pretreatment with iron dextran on RGC loss in a calibrated partial optic nerve crush (PONC) model in rats, along with the protection offered by tempol (4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl, a membrane-permeable superoxide dismutase mimetic and free-radical scavenger), in the same experimental paradigm. A total of 40 rats in 6 groups of 5-8 animals each underwent PONC in one eye and sham crush in the other. Animals were pretreated with a single iron dextran load 24 h prior to PONC, and treated with tempol 6 h before and then once daily after PONC. Control animals were treated with PBS. RGC were retrogradely labeled with a fluorescent marker; all data are expressed in percent of the RGC count in the respective sham-treated eye. Immunohistochemistry was performed to visualize 3-nitrotyrosine, a marker of nitroxidative stress. PONC without iron pretreatment resulted in the survival of only 31.4% of labeled RGC after 7 days. Even fewer RGC (12.7%) survived after PONC with iron pretreatment. However, tempol in doses of 20 mg/kg of body weight (BW) significantly attenuated this effect when given as described above; in the group without iron pretreatment the number of surviving RGC doubled from 31.4% to 62.1%. In the group with iron pretreatment the survival rate of RGC increased even more pronouncedly, from 12.7% without tempol to 46.2% with tempol. Tempol in doses of 1 mg/kg BW and 5 mg/kg BW showed no significant rescue of RGC. Immunostaining showed nitrotyrosine-positive RGCs in PONC but not in sham-treated eyes and an increase in positive cells after iron load. Tempol treatment reduced nitrotyrosine staining in both the iron and non-iron groups. Our results demonstrate that PONC results in significantly greater RGC damage when iron pretreatment is performed, and that the compound tempol may provide additional protection for RGC in cases of neuronal damage both with and without prior iron treatment.

Topics: Animals; Antioxidants; Cell Count; Cell Survival; Cyclic N-Oxides; Disease Models, Animal; Dose-Response Relationship, Drug; Hematinics; Immunoenzyme Techniques; Iron Overload; Iron-Dextran Complex; Neuroprotective Agents; Optic Nerve Injuries; Oxidative Stress; Rats; Rats, Inbred BN; Retinal Degeneration; Retinal Ganglion Cells; Spin Labels; Tyrosine