Iron has emerged as a significant cause of neurotoxicity in several neurodegenerative conditions, including Alzheimer's disease (AD), Parkinson's disease (PD), sporadic Creutzfeldt-Jakob disease (sCJD), and others. In some cases, the underlying cause of iron mis-metabolism is known, while in others, our understanding is, at best, incomplete. Recent evidence implicating key proteins involved in the pathogenesis of AD, PD, and sCJD in cellular iron metabolism suggests that imbalance of brain iron homeostasis associated with these disorders is a direct consequence of disease pathogenesis. A complete understanding of the molecular events leading to this phenotype is lacking partly because of the complex regulation of iron homeostasis within the brain. Since systemic organs and the brain share several iron regulatory mechanisms and iron-modulating proteins, dysfunction of a specific pathway or selective absence of iron-modulating protein(s) in systemic organs has provided important insights into the maintenance of iron homeostasis within the brain. Here, we review recent information on the regulation of iron uptake and utilization in systemic organs and within the complex environment of the brain, with particular emphasis on the underlying mechanisms leading to brain iron mismetabolism in specific neurodegenerative conditions. Mouse models that have been instrumental in understanding systemic and brain disorders associated with iron mis-metabolism are also described, followed by current therapeutic strategies which are aimed at restoring brain iron homeostasis in different neurodegenerative conditions. We conclude by highlighting important gaps in our understanding of brain iron metabolism and mis-metabolism, particularly in the context of neurodegenerative disorders. Antioxid. Redox Signal. 20, 1324Signal. 20, -1363
Prion protein (PrPC) is implicated in the pathogenesis of prion disorders, but its normal function is unclear. We demonstrate that PrPC is a ferrireductase (FR), and its absence causes systemic iron deficiency in PrP knock-out mice (PrP−/−). When exposed to non-transferrin-bound (NTB) radioactive-iron (59FeCl3) by gastric-gavage, PrP−/− mice absorb significantly more 59Fe from the intestinal lumen relative to controls, indicating appropriate systemic response to the iron deficiency. Chronic exposure to excess dietary iron corrects this deficiency, but unlike wild-type (PrP+/+) controls that remain iron over-loaded, PrP−/− mice revert back to the iron deficient phenotype after 5 months of chase on normal diet. Bone marrow (BM) preparations of PrP−/− mice on normal diet show relatively less stainable iron, and this phenotype is only partially corrected by intraperitoneal administration of excess iron-dextran. Cultured PrP−/− BM-macrophages incorporate significantly less NTB-59Fe in the absence or presence of excess extracellular iron, indicating reduced uptake and/or storage of available iron in the absence of PrPC. When expressed in neuroblastoma cells, PrPC exhibits NAD(P)H-dependent cell-surface and intracellular FR activity that requires the copper-binding octa-peptide-repeat region and linkage to the plasma membrane for optimal function. Incorporation of NTB-59Fe by neuroblastoma cells correlates with FR activity of PrPC, implicating PrPC in cellular iron uptake and metabolism. These observations explain the correlation between PrPC expression and cellular iron levels, and the cause of iron imbalance in sporadic-Creutzfeldt-Jakob-disease brains where PrPC accumulates as insoluble aggregates.
Background Specific treatment for COVID-19 is still an unmet need. Outcomes of clinical trials on repurposed drugs have not been yielding success. Therefore, it is necessary to include complementary approaches of medicine against COVID-19. Purpose This study was designed to evaluate the impact of traditional Indian Ayurvedic treatment regime on asymptomatic patients with COVID-19 infection. Study design It is a placebo controlled randomized double-blind pilot clinical trial. Methods The study was registered with Clinical Trial Registry-India (vide Registration No. CTRI/2020/05/025273) and conducted at the Department of Medicine in National Institute of Medical Sciences and Research, Jaipur, India. 1 g of Giloy Ghanvati ( Tinospora cordifolia ) and 2 g of Swasari Ras (traditional herbo-mineral formulation) and 0.5 g each of Ashwagandha ( Withania somnifera ) and Tulsi Ghanvati ( Ocimum sanctum ) were given orally to the patients in treatment group twice per day for 7 days. Medicines were given in the form of tablets and each tablet weighed 500 mg. While, Swasari Ras was administered in powdered form, 30 min before breakfasts and dinners, rest were scheduled for 30 min post-meals. Patients in the treatment group also received 4 drops of Anu taila (traditional nasal drop) in each nostril every day 1 h before breakfast. Patients in the placebo group received identical-looking tablets and drops, post randomization and double blinded assortments. RT-qPCR test was used for the detection of viral load in the nasopharyngeal and oropharyngeal swab samples of study participants during the study. Chemiluminescent immunometric assay was used to quantify serum levels of interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α) and high sensitivity C-reactive protein (hs-CRP) on day 1 and day 7 of the study. Results By day 3, 71.1 % and 50.0 % patients recovered in the treatment and placebo groups, respectively. Treatment group witnessed 100% recovery by day 7, while it was 60.0 % in the placebo group. Average fold changes in serum levels of hs-CRP, IL-6 and TNF-α in treatment group were respectively, 12.4, 2.5 and 20 times lesser than those in the placebo group at day 7. There was 40% absolute reduction in the risk of delayed recovery from infection in the treatment group. Conclusions Ayurvedic treatment can expedite virological clearance, help in faster recovery and concomitantly reduce the risk of viral dissemination. Reduced inflammation markers suggested less severity of SARS-CoV-2 infection in the treatment group. Moreover, there was no adverse effect observed to be associated with this treatment.
Excess circulating iron is stored in the liver, and requires reduction of non-Tf-bound-iron (NTBI) and transferrin (Tf)-iron at the plasma membrane and endosomes respectively by ferrireductase (FR) proteins for transport across biological membranes through divalent metal transporters. Here, we report that prion-protein (PrPC), a ubiquitously expressed glycoprotein most abundant on neuronal cells, functions as a FR partner for divalent-metal transporter-1 (DMT1) and ZIP14. Thus, absence of PrPC in PrP-knock-out (PrP−/−) mice resulted in markedly reduced liver iron stores, a deficiency that was not corrected by chronic or acute administration of iron by the oral or intra-peritoneal routes. Likewise, preferential radiolabeling of circulating NTBI with 59Fe revealed significantly reduced uptake and storage of NTBI by the liver of PrP−/− mice relative to matched PrP+/+ controls. However, uptake, storage, and utilization of ferritin-bound iron that does not require reduction for uptake was increased in PrP−/− mice, indicating a compensatory response to the iron-deficiency. Expression of exogenous PrPC in HepG2-cells increased uptake and storage of ferric-iron (Fe3+), not ferrous-iron (Fe2+) from the medium, supporting the function of PrPC as a plasma membrane FR. Co-expression of PrPC with ZIP14 and DMT1 in HepG2 cells increased uptake of Fe3+ significantly, and surprisingly, increased the ratio of N-terminally truncated PrPC forms lacking the FR domain relative to full-length PrPC. Together, these observations indicate that PrPC promotes, and possibly regulates the uptake of NTBI through DMT1 and Zip14 via its FR activity. Implications of these observations for neuronal iron homeostasis under physiological and pathological conditions are discussed.
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