The effect of ascorbic acid and ferric ammonium citrate on iron uptake and storage in lens epithelial cells

Silencing of lipocalin-2 improves cardiomyocyte viability under iron overload conditions via decreasing mitochondrial dysfunction and apoptosis

This study aimed to investigate the mechanistic roles of LCN-2 and LCN-2 receptors (LCN-2R) as iron transporters in cardiomyocytes under iron overload condition. H9c2 cardiomyocytes were treated with either LCN-2 small interfering RNA (siRNA) or LCN-2R siRNA or L-type or T-type calcium channel (LTCC or TTCC) blockers, or iron chelator deferiprone (DFP). After the treatments, the cells were exposed to Fe³⁺ or Fe²⁺ , after that biological parameters were determined. Silencing of lipocalin-2 or its receptor improved cardiomyocyte viability via decreasing iron uptake, mitochondrial fission, mitophagy and cleaved caspase-3 only in the Fe³⁺ overload condition. In contrast, treatments with LTCC blocker and TTCC blocker showed beneficial effects on those parameters only in conditions of Fe²⁺ overload. Treatment with DFP has been shown beneficial effects both in Fe²⁺ and Fe³⁺ overload condition. All of these findings suggested that LTCC and TTCC play crucial roles in the Fe²⁺ uptake, whereas LCN-2 and LCN-2R were essential for Fe³⁺ uptake into the cardiomyocytes under iron overload conditions.

Targeting autophagy enhances the anticancer effect of artemisinin and its derivatives

Artemisinin and its derivatives, with their outstanding clinical efficacy and safety, represent the most effective and impactful antimalarial drugs. Apart from its antimalarial effect, artemisinin has also been shown to exhibit selective anticancer properties against multiple cancer types both in vitro and in vivo. Specifically, our previous studies highlighted the therapeutic effects of artemisinin on autophagy regulation. Autophagy is a well-conserved degradative process that recycles cytoplasmic contents and organelles in lysosomes to maintain cellular homeostasis. The deregulation of autophagy is often observed in cancer cells, where it contributes to tumor adaptation to nutrient-deficient tumor microenvironments. This review discusses recent advances in the anticancer properties of artemisinin and its derivatives via their regulation of autophagy, mitophagy, and ferritinophagy. In particular, we will discuss the mechanisms of artemisinin activation in cancer and novel findings regarding the role of artemisinin in regulating autophagy, which involves changes in multiple signaling pathways. More importantly, with increasing failure rates and the high cost of the development of novel anticancer drugs, the strategy of repurposing traditional therapeutic Chinese medicinal agents such as artemisinin to treat cancer provides a more attractive alternative. We believe that the topics covered here will be important in demonstrating the potential of artemisinin and its derivatives as safe and potent anticancer agents.

Time-Dependent Transcriptional Changes in Axenic Giardia duodenalis Trophozoites

Giardia duodenalis is the most common gastrointestinal protozoan parasite of humans and a significant contributor to the global burden of both diarrheal disease and post-infectious chronic disorders. Although G. duodenalis can be cultured axenically, significant gaps exist in our understanding of the molecular biology and metabolism of this pathogen. The present study employed RNA sequencing to characterize the mRNA transcriptome of G. duodenalis trophozoites in axenic culture, at log (48 h of growth), stationary (60 h), and declining (96 h) growth phases. Using ~400-times coverage of the transcriptome, we identified 754 differentially transcribed genes (DTGs), mainly representing two large DTG groups: 438 that were down-regulated in the declining phase relative to log and stationary phases, and 281 that were up-regulated. Differential transcription of prominent antioxidant and glycolytic enzymes implicated oxygen tension as a key factor influencing the transcriptional program of axenic trophozoites. Systematic bioinformatic characterization of numerous DTGs encoding hypothetical proteins of unknown function was achieved using structural homology searching. This powerful approach greatly informed the differential transcription analysis and revealed putative novel antioxidant-coding genes, and the presence of a near-complete two-component-like signaling system that may link cytosolic redox or metabolite sensing to the observed transcriptional changes. Motif searching applied to promoter regions of the two large DTG groups identified different putative transcription factor-binding motifs that may underpin global transcriptional regulation. This study provides new insights into the drivers and potential mediators of transcriptional variation in axenic G. duodenalis and provides context for static transcriptional studies.

The active role of vitamin C in mammalian iron metabolism: much more than just enhanced iron absorption!

Ascorbate is a cofactor in numerous metabolic reactions. Humans cannot synthesize ascorbate owing to inactivation of the gene encoding the enzyme l-gulono-γ-lactone oxidase, which is essential for ascorbate synthesis. Accumulating evidence strongly suggests that in addition to the known ability of dietary ascorbate to enhance nonheme iron absorption in the gut, ascorbate within mammalian systems can regulate cellular iron uptake and metabolism. Ascorbate modulates iron metabolism by stimulating ferritin synthesis, inhibiting lysosomal ferritin degradation, and decreasing cellular iron efflux. Furthermore, ascorbate cycling across the plasma membrane is responsible for ascorbate-stimulated iron uptake from low-molecular-weight iron-citrate complexes, which are prominent in the plasma of individuals with iron-overload disorders. Importantly, this iron-uptake pathway is of particular relevance to astrocyte brain iron metabolism and tissue iron loading in disorders such as hereditary hemochromatosis and β-thalassemia. Recent evidence also indicates that ascorbate is a novel modulator of the classical transferrin-iron uptake pathway, which provides almost all iron for cellular demands and erythropoiesis under physiological conditions. Ascorbate acts to stimulate transferrin-dependent iron uptake by an intracellular reductive mechanism, strongly suggesting that it may act to stimulate iron mobilization from the endosome. The ability of ascorbate to regulate transferrin iron uptake could help explain the metabolic defect that contributes to ascorbate-deficiency-induced anemia.

Hypoxia induced changes in expression of proteins involved in iron uptake and storage in cultured lens epithelial cells

Hypoxia inducible factor (HIF) regulates expression of over 60 genes by binding to hypoxia response elements (HRE) located upstream of the transcriptional start sites. Many genes encoding proteins involved in iron transport and homeostasis are regulated by HIF. Expression of iron handling proteins can also be translationally regulated by binding of iron regulatory protein (IRP) to iron responsive elements (IREs) on the mRNA of ferritin chains and transferrin receptor (TfR). Lens epithelial cells (LEC) function in a low oxygen environment. This increases the risk of iron catalyzed formation of reactive oxygen species (ROS) and oxidative cell damage. We examined changes in expression of ferritin (iron storage protein) and Tf/TfR1 (iron uptake proteins) in LEC cultured under hypoxic conditions. Ferritin consists of 24 subunits of two types, heavy (H-chain) and light (L-chain) assembled in a cell specific ratio. Real-time PCR showed that 24 h exposure to hypoxia lowered transcription of both ferritin chains by over 50% when compared with normoxic LEC. However it increased the level of ferritin chain proteins (20% average). We previously found that 6 h exposure of LEC to hypoxia increased the concentration of cytosolic iron which would stimulate translation of ferritin chains. This elevated ferritin concentration increased the iron storage capacity of LEC. Hypoxic LEC labeled with 59FeTf incorporated 70% more iron into ferritin after 6 h as compared to normoxic LEC. Exposure of LEC to hypoxia for 24 h reduced the concentration of TfR1 in cell lysates. As a result, hypoxic LEC internalized less Tf at this later time point. Incorporation of 59Fe into ferritin of hypoxic LEC after 24 h did not differ from that of normoxic LEC due to lower 59FeTf uptake. This study showed that hypoxia acutely increased iron storage capacity and lowered iron uptake due to changes in expression of iron handling proteins. These changes may better protect LEC against oxidative stress by limiting iron-catalyzed ROS formation in the low oxygen environment in which the lens resides.

Source-dependent intracellular distribution of iron in lens epithelial cells cultured under normoxic and hypoxic conditions

PURPOSE

Intracellular iron trafficking and the characteristics of iron distribution from different sources are poorly understood. We previously determined that the lens removes excess iron from fluids of inflamed eyes. In the current study, we examined uptake and intracellular distribution of ⁵⁹Fe from iron transport protein transferrin or ferric chloride (nontransferrin-bound iron [NTBI]) in cultured canine lens epithelial cells (LECs). Because lens tissue physiologically functions under low oxygen tension, we also tested effects of hypoxia on iron trafficking. Excess iron, not bound to proteins, can be damaging to cells due to its ability to catalyze formation of reactive oxygen species.

METHODS

LECs were labeled with ⁵⁹Fe-Tf or ⁵⁹FeCl₃ under normoxic or hypoxic conditions. Cell lysates were fractioned into mitochondria-rich, nuclei-rich, and cytosolic fractions. Iron uptake and its subcellular distribution were measured by gamma counting.

RESULTS

⁵⁹Fe accumulation into LECs labeled with ⁵⁹Fe-Tf was 55-fold lower as compared with that of ⁵⁹FeCl₃. Hypoxia (24 hours) decreased uptake of iron from transferrin but not from FeCl₃. More iron from ⁵⁹FeCl₃ was directed to the mitochondria-rich fraction (32.6%-47.7%) compared with ⁵⁹Fe from transferrin (10.6%-12.6%). The opposite was found for the cytosolic fraction (8.7%-18.3% and 54.2%-46.6 %, respectively). Hypoxia significantly decreased iron accumulation in the mitochondria-rich fraction of LECs labeled with ⁵⁹Fe-Tf .

CONCLUSIONS

There are source-dependent differences in iron uptake and trafficking. Uptake and distribution of NTBI are not as strictly regulated as that of iron from transferrin. Excessive exposure to NTBI, which could occur in pathological conditions, may oxidatively damage organelles, particularly mitochondria.

Transferrin iron uptake is stimulated by ascorbate via an intracellular reductive mechanism

Although ascorbate has long been known to stimulate dietary iron (Fe) absorption and non-transferrin Fe uptake, the role of ascorbate in transferrin Fe uptake is unknown. Transferrin is a serum Fe transport protein supplying almost all cellular Fe under physiological conditions. We sought to examine ascorbate's role in this process, particularly as cultured cells are typically ascorbate-deficient. At typical plasma concentrations, ascorbate significantly increased (59)Fe uptake from transferrin by 1.5-2-fold in a range of cells. Moreover, ascorbate enhanced ferritin expression and increased (59)Fe accumulation in ferritin. The lack of effect of cycloheximide or the cytosolic aconitase inhibitor, oxalomalate, on ascorbate-mediated (59)Fe uptake from transferrin indicate increased ferritin synthesis or cytosolic aconitase activity was not responsible for ascorbate's activity. Experiments with membrane-permeant and -impermeant ascorbate-oxidizing reagents indicate that while extracellular ascorbate is required for stimulation of (59)Fe uptake from (59)Fe-citrate, only intracellular ascorbate is needed for transferrin (59)Fe uptake. Additionally, experiments with l-ascorbate analogs indicate ascorbate's reducing ene-diol moiety is necessary for its stimulatory activity. Importantly, neither N-acetylcysteine nor buthionine sulfoximine, which increase or decrease intracellular glutathione, respectively, affected transferrin-dependent (59)Fe uptake. Thus, ascorbate's stimulatory effect is not due to a general increase in cellular reducing capacity. Ascorbate also did not affect expression of transferrin receptor 1 or (125)I-transferrin cellular flux. However, transferrin receptors, endocytosis, vacuolar-type ATPase activity and endosomal acidification were required for ascorbate's stimulatory activity. Therefore, ascorbate is a novel modulator of the classical transferrin Fe uptake pathway, acting via an intracellular reductive mechanism.

Ceruloplasmin alters intracellular iron regulated proteins and pathways: ferritin, transferrin receptor, glutamate and hypoxia-inducible factor-1α

Ceruloplasmin (Cp) is a ferroxidase important to the regulation of both systemic and intracellular iron levels. Cp has a critical role in iron metabolism in the brain and retina as shown in patients with aceruloplasminemia and in Cp-/-hep-/y mice where iron accumulates and neural and retinal degeneration ensue. We have previously shown that cultured lens epithelial cells (LEC) secrete Cp. The purpose of the current study was to determine if cultured retinal pigmented epithelial cells (RPE) also secrete Cp. In addition, the effects of exogenously added Cp on iron regulated proteins and pathways, ferritin, transferrin receptor, glutamate secretion and levels of hypoxia-inducible factor-1α in the nucleus were determined. Like LEC, RPE secrete Cp. Cp was found diffusely distributed within both cultured LEC and RPE, but the cell membranes had more intense staining. Exogenously added Cp caused an increase in ferritin levels in both cell types and increased secretion of glutamate. The Cp-induced increase in glutamate secretion was inhibited by both the aconitase inhibitor oxalomalic acid as well as iron chelators. As predicted by the canonical view of the iron regulatory protein (IRP) as the predominant controller of cellular iron status these results indicate that there is an increase in available iron (called the labile iron pool (LIP)) in the cytoplasm. However, both transferrin receptor (TfR) and nuclear levels of HIF-1α were increased and these results point to a decrease in available iron. Such confounding results have been found in other systems and indicate that there is a much more complex regulation of intracellularly available iron (LIP) and its downstream effects on cell metabolism. Importantly, the Cp increased production and secretion of the neurotransmitter, glutamate, is a substantive finding of clinical relevance because of the neural and retinal degeneration found in aceruloplasminemia patients. This finding and Cp-induced nuclear translocation of the hypoxia-inducible factor-1 (HIF1) subunit HIF-1α adds novel information to the list of critical pathways impacted by Cp.

Altered ferritin subunit composition: change in iron metabolism in lens epithelial cells and downstream effects on glutathione levels and VEGF secretion

PURPOSE

The iron storage protein ferritin is necessary for the safe storage of iron and for protection against the production of iron-catalyzed oxidative damage. Ferritin is composed of 24 subunits of two types: heavy (H) and light (L). The ratio of these subunits is tissue specific, and alteration of this ratio can have profound effects on iron storage and availability. In the present study, siRNA for each of the chains was used to alter the ferritin H:L chain ratio and to determine the effect of these changes on ferritin synthesis, iron metabolism, and downstream effects on iron-responsive pathways in canine lens epithelial cells.

METHODS

Primary cultures of canine lens epithelial cells were used. The cells were transfected with custom-made siRNA for canine ferritin H- and L-chains. De novo ferritin synthesis was determined by labeling newly synthesized ferritin chains with 35S-methionine, immunoprecipitation, and separation by SDS-PAGE. Iron uptake into cells and incorporation into ferritin was measured by incubating the cells with 59Fe-labeled transferrin. Western blot analysis was used to determine the presence of transferrin receptor, and ELISA was used to determine total ferritin concentration. Ferritin localization in the cells was determined by immunofluorescence labeling. VEGF, glutathione secretion levels, and cystine uptake were measured.

RESULTS

FHsiRNA decreased ferritin H-chain synthesis, but doubled ferritin L-chain synthesis. FLsiRNA decreased both ferritin H- and L-chain synthesis. The degradation of ferritin H-chain was blocked by both siRNAs, whereas only FHsiRNA blocked the degradation of ferritin L-chain, which caused significant accumulation of ferritin L-chain in the cells. This excess ferritin L-chain was found in inclusion bodies, some of which were co-localized with lysosomes. Iron storage in ferritin was greatly reduced by FHsiRNA, resulting in increased iron availability, as noted by a decrease in transferrin receptor levels and iron uptake from transferrin. Increased iron availability also increased cystine uptake and glutathione concentration and decreased nuclear translocation of hypoxia-inducible factor 1-alpha and vascular endothelial growth factor (VEGF) accumulation in the cell-conditioned medium.

CONCLUSIONS

Most of the effects of altering the ferritin H:L ratio with the specific siRNAs were due to changes in the availability of iron in a labile pool. They caused significant changes in iron uptake and storage, the rate of ferritin synthesis and degradation, the secretion of VEGF, and the levels of glutathione in cultured lens epithelial cells. These profound effects clearly demonstrate that maintenance of a specific H:L ratio is part of a basic cellular homeostatic mechanism.

Lens epithelial cells synthesize and secrete ceruloplasmin: effects of ceruloplasmin and transferrin on iron efflux and intracellular iron dynamics

Although an essential nutrient, iron can catalyze damaging free radical reactions. Therefore elaborate mechanisms have evolved to carefully regulate iron metabolism. Ceruloplasmin, a protein with ferroxidase activity, and transferrin, an iron binding protein have important roles in maintaining iron homeostasis in cells. Since oxidative damage is a hallmark of cataractogenesis, it is essential to determine iron's role in lenticular physiology and pathology. In the current study of lens epithelial cells, the effects of ceruloplasmin and transferrin on intracellular distribution and efflux of iron were determined. Both ceruloplasmin and transferrin increased iron efflux from these cells and their effects were additive. Ceruloplasmin had significant effects on extracellular iron distribution only in cases of iron overload. Surprisingly, both transferrin and ceruloplasmin had significant effects on intracellular iron distribution. Under physiological conditions, ceruloplasmin increased iron incorporation into the storage protein, ferritin. Under conditions of iron overload, it decreased iron incorporation into ferritin, which is consistent with increased efflux of iron. Measurements of an intracellular chelatable iron pool indicated that both transferrin and ceruloplasmin increased the size of this pool at 24 h, but these increases had different downstream effects. Finally, lens epithelial cells made and secreted transferrin and ceruloplasmin. These results indicate an important role for these proteins in iron metabolism in the lens.

Development of a fluorescent reporter to assess iron regulatory protein activity in living cells

Through the insertion of an iron responsive element (IRE) into a pd2ECFP vector, we demonstrate a noninvasive method for determining alterations in iron regulatory protein (IRP) activity that results in changes in protein translation in living cells. This construct takes advantage of the specifically iron-dependent interaction between IRPs that bind IREs on mRNAs to posttranscriptionally regulate protein expression in a manner similar to ferritin production. In this report, we demonstrate, using HEK-293 cells, that an IRE-driven fluorescent reporter can be used to observe changes in cellular iron status that are sufficient to alter protein synthesis. When iron availability was decreased, there was less cyan fluorescent protein (CFP) expression, suggesting that IRPs bind to the IRE and block protein translation. Conversely, exposing the cells to iron increased CFP fluorescence. This construct has advantages over traditionally used dyes and existing IRE driven constructs because it can be used to repeatedly study iron-influenced protein production over extended periods of time. The future applications of this construct include investigation of how mutations in cells may impact cellular iron metabolism and how various types of exogenously applied trophic, stress, and therapeutic agents may impact cellular iron metabolism.

Iron alters glutamate secretion by regulating cytosolic aconitase activity

Glutamate has many important physiological functions, including its role as a neurotransmitter in the retina and the central nervous system. We have made the novel observations that retinal pigment epithelial cells underlying and intimately interacting with the retina secrete glutamate and that this secretion is significantly affected by iron. In addition, iron increased secretion of glutamate in cultured lens and neuronal cells, indicating that this may be a common mechanism for the regulation of glutamate production in many cell types. The activity of the iron-dependent enzyme cytosolic aconitase (c-aconitase) is increased by iron. The conversion of citrate to isocitrate by c-aconitase is the first step in a three-step process leading to glutamate formation. In the present study, iron increased c-aconitase activity, and this increase was associated with an increase in glutamate secretion. Inhibition of c-aconitase by oxalomalate decreased glutamate secretion and completely inhibited the iron-induced increase in glutamate secretion. Derangements in both glutamate secretion and iron metabolism have been noted in neurological diseases and retinal degeneration. Our results are the first to provide a functional link between these two physiologically important substances by demonstrating a significant role for iron in the regulation of glutamate production and secretion in mammalian cells resulting from iron regulation of aconitase activity. Glutamatergic systems are found in many nonneuronal tissues. We provide the first evidence that, in addition to secreting glutamate, retinal pigment epithelial cells express the vesicular glutamate transporter VGLUT1 and that regulated vesicular release of glutamate from these cells can be inhibited by riluzole.

Alpha lipoic acid changes iron uptake and storage in lens epithelial cells

Alpha lipoic acid (LA) is a cofactor in mitochondrial dehydrogenase complexes. Previous studies have shown that when administered exogenously LA has antioxidant properties, which include free radical scavenging, metal chelation and regeneration of other antioxidants. The cells convert LA into dihydroplipoic acid (DHLA), which in the presence of iron can act as a prooxidant. In vitro DHLA reduces Fe(+3) to Fe(+2) and removes iron from ferritin, increasing the risk of Fe catalyzed free radical formation. In the present study we examined the in vivo effects of lipoic acid treatment on Fe metabolism in cultured lens epithelial cells, and found that LA decreases Fe uptake from transferrin, increases Fe deposition into ferritin and increases the concentration of this protein. When administered together with ascorbic acid, lipoic acid changes the characteristic heavy to light chain ratio of ferritin makeup. The decreased Fe uptake and increased storage diminishes the size of the cytosolic highly reactive Fe pool (LIP). These changes are associated with increased cell resistance to H(2)O(2) challenge. Therefore, LA may reduce the risk of Fe induced oxidative damage and also might be useful as a treatment of Fe overload.

Multivalent metal-induced iron acquisition from transferrin and lactoferrin by myeloid cells

We previously described a unique, high-capacity, ATP-independent mechanism through which myeloid cells acquire Fe from low-m.w. chelates. The rate of this Fe acquisition is markedly increased by cellular exposure to multivalent metal cations. Because most Fe in vivo is bound to transferrin or lactoferrin, we examined whether this mechanism also contributes to myeloid cell acquisition of Fe from transferrin and/or lactoferrin. Using HL-60 cells as a model system, we show cellular acquisition of (59)Fe from both lactoferrin and transferrin that was unaffected by conditions that depleted the cells of ATP or disrupted their cytoskeleton. Fe acquisition was dramatically increased by cell exposure to various metals including Ga(3+), Gd(3+), Al(3+), Fe(3+), La(3+), Zr(4+), Sn(4+), Cu(2+), and Zn(2+) by a process that was reversible. Exposure to these same metals also increased binding of both transferrin and lactoferrin to the cell surface by a process that does not appear to involve the well-described plasma membrane receptor for transferrin. Approximately 60% of the Fe acquired by the cells from transferrin and lactoferrin remained cell associated 18 h later. HL-60 cells possess a high-capacity multivalent metal-inducible mechanism for Fe acquisition from transferrin and lactoferrin that bears many similarities to the process previously described that allows these and other cell types to acquire Fe from low-m.w. Fe chelates. The biologic importance of this mechanism may relate to its high Fe acquisition capacity and the speed with which it is able to rapidly adapt to the level of extracellular Fe.

Identification of choroidal ovotransferrin as a potential ocular growth regulator

PURPOSE

In an effort to identify choroidal factors potentially involved in the regulation of ocular growth, proteins released into culture medium of organ-cultured choroids were compared between control eyes and eyes recovering from form deprivation myopia.

METHODS

The choroids were obtained from the posterior poles of control and recovering chick eyes, and placed into organ culture containing ( 35)S-methionine/(35)S-cysteine. Culture medium was collected after 24 hours and proteins were separated and identified by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), fluorography, immunoprecipitation, western blot analysis and by amino acid sequencing. Choroidal proteins were tested for their effect on scleral proteoglycan synthesis by measuring (35)SO( 4) incorporation into scleral glycosaminoglycans (GAG) in vitro. Choroidal thickness and axial elongation were measured in control and recovering eyes using high frequency A-scan ultrasound.

RESULTS

The synthesis of an 80 kD protein was greatly increased in the choroids of recovering eyes compared with those of control eyes. Amino acid sequencing and immunoprecipitation indicated that the newly synthesized 80 kD protein was ovotransferrin (transferrin, conalbumin). Ovotransferrin release into the culture medium by isolated recovering choroids was associated with a decrease in the rate of axial elongation in recovering eyes. When tested in vitro, ovotransferrin (500 ng/micro) inhibited scleral proteoglycan synthesis in the sclera by 62% in a dose-dependent manner.

CONCLUSIONS

Chick choroids of recovering eyes synthesize and release ovotransferrin during the recovery from form deprivation myopia. Ovotransferrin significantly inhibited proteoglycan synthesis by the sclera, indicating that ovotransferrin may play a role in slowing the rate of vitreous chamber elongation and facilitating the recovery from induced myopia.

The lens in hereditary hyperferritinaemia cataract syndrome contains crystalline deposits of L-ferritin

BACKGROUND/AIM

Hereditary hyperferritinaemia cataract syndrome (HHCS) is an autosomal dominant disorder characterised by elevated serum L-ferritin and bilateral cataracts. The ocular manifestations of this disorder are poorly studied. This study therefore sought to determine the origin of cataracts in HHCS.

METHODS

L-ferritin ELISA, immunohistochemical and ultrastructural analysis of a lens nucleus from an HHCS individual.

RESULTS

The HHCS lens L-ferritin content was 147 microg/g dry weight of lens compared with <16 microg/g for a non-HHCS control cataract lens. The cataract comprised discrete crystalline inclusions with positive staining with anti-L-ferritin but not anti-H-ferritin.

CONCLUSIONS

This unusual finding of crystalline opacities in the lens may be unique to HHCS and is likely to result from disturbed metabolism of L-ferritin within the lens or an abnormal interaction between L-ferritin and lens proteins.

The effects of Tempol on ferritin synthesis and Fe metabolism in lens epithelial cells

The nitroxide, Tempol, can protect tissue from oxidative damage by removing superoxide and by oxidizing Fe(II) to Fe(III), thus decreasing formation of the hydroxyl radical. However, long-term exposure to Tempol can damage cells. The oxidation of Fe could have profound effects on Fe metabolism in cells, yet this has not been previously studied. In the present investigation, the effects of Tempol on the synthesis of the Fe storage protein, ferritin, and its ability to store Fe were studied in cultured lens epithelial cells (LEC). In addition, the effects of short- and long-term Tempol treatment on the resistance of LEC to oxidative stress were determined. Tempol had a clear dose-dependent inhibitory effect on ferritin synthesis noted at 6 h. By 20 h, ferritin synthesis returned toward normal levels. However, Fe incorporation into ferritin was decreased by almost 90% by the highest dose of Tempol, even at the 20-h time point. The decrease in Fe incorporation into ferritin was accompanied by a significant increase in the LMW pool of Fe. After short-term (4 h) treatment with Tempol, LEC were protected against the toxic effects of tertiary butyl hydroperoxide. However, after longer term treatment (20 h), Tempol itself had a toxic effect and did not afford protection. Indeed, at the higher doses, Tempol significantly reduced the ability of the cells to withstand oxidative stress. The redistribution of Fe within the cell after 20 h of Tempol treatment appears to render the cells more vulnerable to oxidative stress. The deleterious effects of Tempol on LEC are likely due to its effects on Fe metabolism, perhaps by reducing the availability of Fe for incorporation into ferritin and Fe-dependent enzymes as well as enlarging a low molecular weight pool of Fe which may be capable of catalyzing damaging free radical reactions.