CD1 Mouse Retina Is Shielded From Iron Overload Caused by a High Iron Diet.

PURPOSE: High RPE iron levels have been associated with age-related macular degeneration. Mutation of the ferroxidase ceruloplasmin leads to RPE iron accumulation and degeneration in patients with aceruloplasminemia; mice lacking ceruloplasmin and its homolog hephaestin have a similar RPE degeneration. To determine whether a high iron diet (HID) could cause RPE iron accumulation, possibly contributing to RPE oxidative stress in AMD, we tested the effect of dietary iron on mouse RPE iron. METHODS: Male CD1 strain mice were fed either a standard iron diet (SID) or the same diet with extra iron added (HID) for either 3 months or 10 months. Mice were analyzed with immunofluorescence and Perls' histochemical iron stain to assess iron levels. Levels of ferritin, transferrin receptor, and oxidative stress gene mRNAs were measured by quantitative PCR (qPCR) in neural retina (NR) and isolated RPE. Morphology was assessed in plastic sections. RESULTS: Ferritin immunoreactivity demonstrated a modest increase in the RPE in 10-month HID mice. Analysis by qPCR showed changes in mRNA levels of iron-responsive genes, indicating moderately increased iron in the RPE of 10-month HID mice. However, even by age 18 months, there was no Perls' signal in the retina or RPE and no retinal degeneration. CONCLUSIONS: These findings indicate that iron absorbed from the diet can modestly increase the level of iron deposition in the wild-type mouse RPE without causing RPE or retinal degeneration. This suggests regulation of retinal iron uptake at the blood-retinal barriers.

A high serum iron level causes mouse retinal iron accumulation despite an intact blood-retinal barrier.

The retina can be shielded by the blood-retinal barrier. Because photoreceptors are damaged by excess iron, it is important to understand whether the blood-retinal barrier protects against high serum iron levels. Bone morphogenic protein 6 (Bmp6) knockout mice have serum iron overload. Herein, we tested whether the previously documented retinal iron accumulation in Bmp6 knockout mice might result from the high serum iron levels or, alternatively, low levels of retinal hepcidin, an iron regulatory hormone whose transcription can be up-regulated by Bmp6. Furthermore, to determine whether increases in serum iron can elevate retinal iron levels, we i.v. injected iron into wild-type mice. Retinas were analyzed by real-time quantitative PCR and immunofluorescence to assess the levels of iron-regulated genes/proteins and oxidative stress. Retinal hepcidin mRNA levels in Bmp6 knockout retinas were the same as, or greater than, those in age-matched wild-type retinas, indicating that Bmp6 knockout does not cause retinal hepcidin deficiency. Changes in mRNA levels of L ferritin and transferrin receptor indicated increased retinal iron levels in i.v. iron-injected wild-type mice. Oxidative stress markers were elevated in photoreceptors of mice receiving i.v. iron. These findings suggest that elevated serum iron levels can overwhelm local retinal iron regulatory mechanisms.

Bayesian probability of malignancy with BI-RADS sonographic features.

OBJECTIVES: The purpose of this study was to develop a quantitative approach for combining individual American College of Radiology Breast Imaging Reporting and Data System (BI-RADS) sonographic features of breast masses for assessing the overall probability of malignancy. METHODS: Sonograms of solid breast masses were analyzed by 2 observers blinded to patient age, mammographic features, and lesion pathologic findings. BI-RADS sonographic features were determined by using American College of Radiology criteria. A naïve Bayes model was used to determine the probability of malignancy of all the sonographic features together and with age and BI-RADS mammographic features. The diagnostic performance for various combinations was evaluated by using the area under the receiver operating curve (Az). RESULTS: Sonographic features had high positive and negative predictive values. The Az values for BI-RADS sonographic features for the 2 observers ranged from 0.772 to 0.884, which increased to 0.866 to 0.924 when used with patient age and BI-RADS mammographic features. The benefit of adding age and mammographic information was more marked for the observer with lower initial diagnostic performance. Age-specific analysis showed that diagnostic performance varied with age, with higher performance for patients aged 45 years and younger and patients older than 60 years compared to those aged 46 to 60 years. In 85% of cases, the diagnosis of the observers matched. When the consensus between the observers was used for diagnostic decisions, a high level of diagnostic performance (Az, 0.954) was achieved. CONCLUSIONS: A naïve Bayes model provides a systematic approach for combining sonographic features and other patient characteristics for assessing the probability of malignancy to differentiate malignant and benign breast masses.

Dexras1, a small GTPase, is required for glutamate-NMDA neurotoxicity.

Dexras1, a small G-protein localized predominantly to the brain, is transcriptionally upregulated by the synthetic glucocorticoid dexamethasone. It has close homology to the Ras subfamily but differs in that Dexras1 contains an extended 7 kDa C-terminal tail. Previous studies in our laboratory showed that NMDA receptor activation, via NO and Dexras1, physiologically stimulates DMT1, the major iron importer. A membrane-permeable iron chelator substantially reduces NMDA excitotoxicity, suggesting that Dexras1-mediated iron influx plays a crucial role in NMDA/NO-mediated cell death. We here report that iron influx is elicited by nitric oxide but not by other proapoptotic stimuli, such as H2O2 or staurosporine. Deletion of Dexras1 in mice attenuates NO-mediated cell death in dissociated primary cortical neurons and retinal ganglion cells in vivo. Thus, Dexras1 appears to mediate NMDA-elicited neurotoxicity via NO and iron influx.

DNA methylation is associated with altered gene expression in AMD.

PURPOSE: Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly. Evidence suggests oxidative stress plays a role in the disease. To assess the potential contribution of epigenetic regulation of antioxidant genes relevant to AMD pathogenesis, we evaluated DNA methylation, a tissue-specific genetic modulation that affects gene expression. METHODS: Using the Infinium HumanMethylation27 Illumina platform, we performed DNA bisulfite sequencing to compare the methylation status in postmortem retina pigment epithelium (RPE)/choroid between patients with AMD and age-matched controls. Gene expression was assessed with the Affymetrix Exon Array. TaqMan gene expression assays were used for relative quantification (RT-PCR) confirmation of the expression array results: Glutathione S-transferase isoform mu1 (GSTM1) and mu5 (GSTM5) promoter methylation was confirmed by CpG island bisulfite pyrosequencing. To assess protein levels and localization, we used Western analysis, immunohistochemistry, and immunofluorescence with murine and human samples. RESULTS: The mRNA levels of GSTM1 and GSTM5 were significantly reduced in AMD versus age-matched controls in RPE/choroid and neurosensory retina (NSR), which corresponded to hypermethylation of the GSTM1 promoter. mRNA and protein levels were decreased (RPE to a greater extent than NSR) in AMD postmortem samples, irrespective of age. Immunohistochemistry and immunofluorescence confirm the presence of the enzymes in the NSR and RPE. CONCLUSIONS: Comparison of DNA methylation, together with mRNA levels, revealed significant differences between AMD versus normal retinas. The evidence presented suggests that GSTM1 and GSTM5 undergo epigenetic repression in AMD RPE/choroid, which may increase susceptibility to oxidative stress in AMD retinas.

The Oral Iron Chelator Deferiprone Protects Against Retinal Degeneration Induced through Diverse Mechanisms.

PURPOSE: To investigate the effect of the iron chelator deferiprone (DFP) on sodium iodate (NaIO3)-induced retinal degeneration and on the hereditary retinal degeneration caused by the rd6 mutation. METHODS: Retinas from NaIO3-treated C57BL/6J mice, with or without DFP cotreatment, were analyzed by histology, immunofluorescence, and quantitative PCR to investigate the effect of DFP on retinal degeneration. To facilitate photoreceptor quantification, we developed a new function of MATLAB to perform this task in a semiautomated fashion. Additionally, rd6 mice treated with or without DFP were analyzed by histology to assess possible protection. RESULTS: In NaIO3-treated mice, DFP protected against retinal degeneration and significantly decreased expression of the oxidative stress-related gene heme oxygenase-1 and the complement gene C3. DFP treatment partially protected against NaIO3-induced reduction in the levels of mRNAs encoded by visual cycle genes rhodopsin (Rho) and retinal pigment epithelium-specific 65 kDa protein (Rpe65), consistent with the morphological data indicating preservation of photoreceptors and RPE, respectively. DFP treatment also protected photoreceptors in rd6 mice. CONCLUSIONS: The oral iron chelator DFP provides significant protection against retinal degeneration induced through different modalities. This suggests that iron chelation could be useful as a treatment for retinal degeneration even when the main etiology does not appear to be iron dysregulation. TRANSLATIONAL RELEVANCE: These data provide proof of principle that the oral iron chelator DFP can protect the retina against diverse insults. Further testing of DFP in additional animal retinal degeneration models at a range of doses is warranted.

The Oral Iron Chelator Deferiprone Protects Against Retinal Degeneration Induced through Diverse Mechanisms.

PURPOSE: To investigate the effect of the iron chelator deferiprone (DFP) on sodium iodate (NaIO3)-induced retinal degeneration and on the hereditary retinal degeneration caused by the rd6 mutation. METHODS: Retinas from NaIO3-treated C57BL/6J mice, with or without DFP cotreatment, were analyzed by histology, immunofluorescence, and quantitative PCR to investigate the effect of DFP on retinal degeneration. To facilitate photoreceptor quantification, we developed a new function of MATLAB to perform this task in a semiautomated fashion. Additionally, rd6 mice treated with or without DFP were analyzed by histology to assess possible protection. RESULTS: In NaIO3-treated mice, DFP protected against retinal degeneration and significantly decreased expression of the oxidative stress-related gene heme oxygenase-1 and the complement gene C3. DFP treatment partially protected against NaIO3-induced reduction in the levels of mRNAs encoded by visual cycle genes rhodopsin (Rho) and retinal pigment epithelium-specific 65 kDa protein (Rpe65), consistent with the morphological data indicating preservation of photoreceptors and RPE, respectively. DFP treatment also protected photoreceptors in rd6 mice. CONCLUSIONS: The oral iron chelator DFP provides significant protection against retinal degeneration induced through different modalities. This suggests that iron chelation could be useful as a treatment for retinal degeneration even when the main etiology does not appear to be iron dysregulation. TRANSLATIONAL RELEVANCE: These data provide proof of principle that the oral iron chelator DFP can protect the retina against diverse insults. Further testing of DFP in additional animal retinal degeneration models at a range of doses is warranted.