Quercetin inhibits intestinal non-haem iron absorption by regulating iron metabolism genes in the tissues.

PURPOSE: There is general agreement that some dietary polyphenols block non-haem iron uptake, but the mechanisms by which they achieve this action are poorly understood. Since the polyphenol quercetin is ingested daily in significant amounts, we have investigated the effect of quercetin on duodenal non-haem iron absorption in vivo, as well as its effect on factors known to be involved in systemic iron metabolism. METHODS: Rats were subject to gastric gavage and systemic quercetin administration. Treatments were followed with uptake studies using radiolabeled iron, serum iron and transferrin saturation measurements, LC-MS/MS analysis of quercetin metabolites in serum, determination of tissue non-haem iron content and analysis of gene expression of iron-related proteins. RESULTS: Both oral and intraperitoneal (IP) quercetin caused serum and tissue iron depletion by two means, first by increasing mucosal iron uptake and inhibiting iron efflux from duodenal mucosa, and second by decreasing levels of duodenal DMT1, Dcytb and FPN. Additionally, IP quercetin induced highly significant increased liver expression of hepcidin, a hormone known to inhibit intestinal iron uptake. CONCLUSIONS: Oral quercetin significantly inhibited iron absorption, while IP quercetin significantly affected iron-related genes. These results could lead to development of new effective ways of preventing and treating iron deficiency anaemia, the most widespread nutritional disorder in the world.

A disease-causing mutation K240E disrupts ferroportin trafficking by SUMO (ferroportin SUMOylation).

Ferroportin (Fpn/IREG1/MTP1) is the only known transporter mediating iron efflux from epithelial cells and macrophages, and thus regulates how much iron is released into the circulation. Consequently, Fpn mutations are associated with haemochromatosis. Fpn itself is post-translationally regulated by hepcidin (Hepc) which induces its redistribution and degradation in a ubiquitin-dependent process. Together, the two proteins appear to be the nexus for iron homeostasis. Here we show that a rare gain-of-function mutation (K240E) that is associated with iron overload, impedes Fpn binding and subcellular trafficking by the small ubiquitin-like modifier (SUMO). Whereas wild-type Fpn is ensconced within vesicular bodies, the FpnK240E mutant appeared diffused within the cell when co-expressed with SUMO. Furthermore, compared with wild type Fpn, the sumoylation-defective mutant was constitutively-active, resulting in a lower intracellular labile iron pool than the former. These findings suggest that SUMO may regulate iron homeostasis by controlling Fpn trafficking.

Extensive Anti-CoA Immunostaining in Alzheimer's Disease and Covalent Modification of Tau by a Key Cellular Metabolite Coenzyme A.

Alzheimer's disease (AD) is a neurodegenerative disorder, accounting for at least two-thirds of dementia cases. A combination of genetic, epigenetic and environmental triggers is widely accepted to be responsible for the onset and development of AD. Accumulating evidence shows that oxidative stress and dysregulation of energy metabolism play an important role in AD pathogenesis, leading to neuronal dysfunction and death. Redox-induced protein modifications have been reported in the brain of AD patients, indicating excessive oxidative damage. Coenzyme A (CoA) is essential for diverse metabolic pathways, regulation of gene expression and biosynthesis of neurotransmitters. Dysregulation of CoA biosynthesis in animal models and inborn mutations in human genes involved in the CoA biosynthetic pathway have been associated with neurodegeneration. Recent studies have uncovered the antioxidant function of CoA, involving covalent protein modification by this cofactor (CoAlation) in cellular response to oxidative or metabolic stress. Protein CoAlation has been shown to both modulate the activity of modified proteins and protect cysteine residues from irreversible overoxidation. In this study, immunohistochemistry analysis with highly specific anti-CoA monoclonal antibody was used to reveal protein CoAlation across numerous neurodegenerative diseases, which appeared particularly frequent in AD. Furthermore, protein CoAlation consistently co-localized with tau-positive neurofibrillary tangles, underpinning one of the key pathological hallmarks of AD. Double immunihistochemical staining with tau and CoA antibodies in AD brain tissue revealed co-localization of the two immunoreactive signals. Further, recombinant 2N3R and 2N4R tau isoforms were found to be CoAlated in vitro and the site of CoAlation mapped by mass spectrometry to conserved cysteine 322, located in the microtubule binding region. We also report the reversible H2O2-induced dimerization of recombinant 2N3R, which is inhibited by CoAlation. Moreover, CoAlation of transiently expressed 2N4R tau was observed in diamide-treated HEK293/Pank1ß cells. Taken together, this study demonstrates for the first time extensive anti-CoA immunoreactivity in AD brain samples, which occurs in structures resembling neurofibrillary tangles and neuropil threads. Covalent modification of recombinant tau at cysteine 322 suggests that CoAlation may play an important role in protecting redox-sensitive tau cysteine from irreversible overoxidation and may modulate its acetyltransferase activity and functional interactions.

Activated macrophages induce hepcidin expression in HuH7 hepatoma cells.

BACKGROUND: Hepcidin is an iron regulatory peptide produced by the liver in response to inflammation and elevated systemic iron. Recent studies suggest that circulating monocytes and resident liver macrophages--Küpffer cells--may influence both basal and inflammatory expression of hepcidin. DESIGN AND METHODS: We used an in vitro co-culture model to investigate hepatocyte hepcidin regulation in the presence of activated THP1 macrophages. HuH7 hepatoma cells were co-cultured with differentiated THP1 macrophages for 24 h prior to the measurement of HuH7 hepcidin (HAMP) mRNA expression using quantitative polymerase chain reaction, and HAMP promoter activity using a luciferase reporter assay. Luciferase assays were performed using the wild type HAMP promoter, and constructs containing mutations in BMP/SMAD4, STAT3, C/EBP and E-BOX response elements. Neutralizing antibodies against interleukin-6, interleukin-1beta , and the bone morphogenetic protein inhibitor noggin were used to identify the macrophage-derived cytokines involved in the regulation of HAMP expression. RESULTS: Co-culturing HuH7 cells with differentiated THP1 cells induced HAMP promoter activity and endogenous HAMP mRNA expression maximally after 24 h. This induction was fully neutralized in the presence of an interleukin-1beta antibody, and fully attenuated by mutations of the proximal C/EBP or BMP/SMAD4 response elements. CONCLUSIONS: Our data suggest that the interleukin-1beta and bone morphogenetic protein signaling pathways are central to the regulation of HAMP expression by macrophages in this co-culture model.

Hepcidin decreases iron transporter expression in vivo in mouse duodenum and spleen and in vitro in THP-1 macrophages and intestinal Caco-2 cells.

Hepcidin is thought to control iron metabolism by interacting with the iron efflux transporter ferroportin. In macrophages, there is compelling evidence that hepcidin directly regulates ferroportin protein expression. However, the effects of hepcidin on intestinal ferroportin levels are less conclusive. In this study, we compared the effects of hepcidin on iron transporter expression in the spleen and duodenum of mice treated with hepcidin over a 24- to 72-h period and observed a marked decrease in the expression of ferroportin in both duodenal enterocytes and splenic macrophages following treatment. Changes in transporter protein expression were associated with significant decreases in duodenal iron transport and serum iron. In THP-1 macrophages, ferroportin protein levels were decreased by 300 and 1000 nmol/L hepcidin. In contrast, ferroportin protein expression was unaltered in intestinal Caco-2 cells following exposure to hepcidin. However, iron efflux from Caco-2 cells was significantly inhibited in the presence of hepcidin, suggesting that the peptide could block ferroportin function in these cells. We conclude that hepcidin regulates the release of iron from both enterocytes and macrophages. However, taken together with our previous work, it is apparent that macrophages are more sensitive than enterocytes to a hepcidin challenge.

Effects of marginal iron overload on iron homeostasis and immune function in alveolar macrophages isolated from pregnant and normal rats.

The effects of changes in macrophage iron status, induced by single or multiple iron injections, iron depletion or pregnancy, on both immune function and mRNA expression of genes involved in iron influx and egress have been evaluated. Macrophages isolated from iron deficient rats, or pregnant rats at day 21 of gestation, either supplemented with a single dose of iron dextran, 10 mg, at the commencement of pregnancy, or not, showed significant increases of macrophage ferroportin mRNA expression, which was paralleled by significant decreases in hepatic Hamp mRNA expression. IRP activity in macrophages was not significantly altered by iron status or the inducement of pregnancy +/- a single iron supplement. Macrophage immune function was significantly altered by iron supplementation and pregnancy. Iron supplementation, alone or combined with pregnancy, increased the activities of both NADPH oxidase and nuclear factor kappa B (NFkappaB). In contrast, the imposition of pregnancy reduced the ability of these parameters to respond to an inflammatory stimuli. Increasing iron status, if only marginally, will reduce the ability of macrophages to mount a sustained response to inflammation as well as altering iron homeostatic mechanisms.

Bariatric surgery can correct iron depletion in morbidly obese women: a link with chronic inflammation.

BACKGROUND: Obesity is associated with a chronic and low-grade inflammation which may cause hypoferremia as seen in patients with chronic inflammatory diseases. The aim of the present study was to investigate the relationship between iron status and markers of inflammation in morbidly obese women and the effect of bariatric surgery. METHODS: Our cohort of patients consisted of 178 morbidly obese females selected for bariatric surgery. Clinical and biochemical data were recorded before surgery, and histopathological studies were carried out on preoperative liver biopsy samples. Fifty-five patients have been followed up after bariatric surgery. RESULTS: A high prevalence of iron depletion was present in this cohort, with 53% having a transferrin saturation ratio below 0.20. Iron depletion was significantly correlated with raised levels of indices of inflammation, C-reactive protein (CRP), orosomucoid and haptoglobin), and with the white blood cell count. In multivariate analysis, orosomucoid and CRP were independently associated with iron depletion. Moreover, 6 months after bariatric surgery, inflammation level decreased, which was inversely correlated with the increase in transferrin saturation. CONCLUSIONS: Iron depletion is common in morbidly obese women. Low-grade chronic inflammation associated with obesity could be a modulator of iron uptake and utilization. Bariatric surgery may reduce chronic inflammation and improve iron status.

Publisher Correction: Tubular iron deposition and iron handling proteins in human healthy kidney and chronic kidney disease.

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Tubular iron deposition and iron handling proteins in human healthy kidney and chronic kidney disease.

Iron is suggested to play a detrimental role in the progression of chronic kidney disease (CKD). The kidney recycles iron back into the circulation. However, the localization of proteins relevant for physiological tubular iron handling and their potential role in CKD remain unclear. We examined associations between iron deposition, expression of iron handling proteins and tubular injury in kidney biopsies from CKD patients and healthy controls using immunohistochemistry. Iron was deposited in proximal (PT) and distal tubules (DT) in 33% of CKD biopsies, predominantly in pathologies with glomerular dysfunction, but absent in controls. In healthy kidney, PT contained proteins required for iron recycling including putative iron importers ZIP8, ZIP14, DMT1, iron storage proteins L- and H-ferritin and iron exporter ferroportin, while DT only contained ZIP8, ZIP14, and DMT1. In CKD, iron deposition associated with increased intensity of iron importers (ZIP14, ZIP8), storage proteins (L-, H-ferritin), and/or decreased ferroportin abundance. This demonstrates that tubular iron accumulation may result from increased iron uptake and/or inadequate iron export. Iron deposition associated with oxidative injury as indicated by heme oxygenase-1 abundance. In conclusion, iron deposition is relatively common in CKD, and may result from altered molecular iron handling and may contribute to renal injury.

Molecular mechanisms involved in intestinal iron absorption.

Iron is an essential trace metal in the human diet due to its obligate role in a number of metabolic processes. In the diet, iron is present in a number of different forms, generally described as haem (from haemoglobin and myoglobin in animal tissue) and non-haem iron (including ferric oxides and salts, ferritin and lactoferrin). This review describes the molecular mechanisms that co-ordinate the absorption of iron from the diet and its release into the circulation. While many components of the iron transport pathway have been elucidated, a number of key issues still remain to be resolved. Future work in this area will provide a clearer picture regarding the transcellular flux of iron and its regulation by dietary and humoral factors.

Effects of copper on the expression of metal transporters in human intestinal Caco-2 cells.

Copper is an essential dietary trace metal, however the mechanisms involved in intestinal copper uptake are unclear. Two putative copper transporters are expressed in Caco-2 cells, the divalent metal transporter (DMT1) and copper transporter (Ctr1). Our data demonstrate that copper could compete with iron for uptake via DMT1 and that DMT1 protein and mRNA expression were decreased following exposure (24 h) to high copper. Expression of Ctr1, which acts as a copper transporter in transfected cell lines, was unaffected by copper treatment. Interestingly, exposure to copper increased iron efflux from Caco-2 cells and up regulated IREG1 (iron-regulated mRNA) expression.

Tumour necrosis factor alpha regulates iron transport and transporter expression in human intestinal epithelial cells.

TNFalpha has dramatic effects on iron metabolism contributing to the generation of hypoferraemia in the anaemia of chronic disease. Interestingly, TNFalpha is also synthesised and released within the intestinal mucosa, suggesting that this pro-inflammatory cytokine may play a role in regulating dietary iron absorption. To investigate this possibility, we stimulated intestinal Caco-2 cells with TNFalpha (10 ng/ml). In TNFalpha-treated cells, apical iron uptake was significantly decreased and this was accompanied by a reduction in divalent metal transporter protein and mRNA expression. Our data suggest that TNFalpha could regulate dietary iron absorption and that the apical transport machinery is the target for these actions.

Rapid regulation of divalent metal transporter (DMT1) protein but not mRNA expression by non-haem iron in human intestinal Caco-2 cells.

A divalent metal transporter, DMT1, located on the apical membrane of intestinal enterocytes is the major pathway for the absorption of dietary non-haem iron. Using human intestinal Caco-2 TC7 cells, we have shown that iron uptake and DMT1 protein in the plasma membrane were significantly decreased by exposure to high iron for 24 h, in a concentration-dependent manner, whereas whole cell DMT1 protein abundance was unaltered. This suggests that part of the response to high iron involved redistribution of DMT1 between the cytosol and cell membrane. These events preceded changes in DMT1 mRNA, which was only decreased following 72 h exposure to high iron.

The effects of inhibition of haem biosynthesis by griseofulvin on intestinal iron absorption.

The relationship between haem biosynthesis and intestinal iron absorption in mice was investigated by ascertaining the effect of the haem synthesis inhibitor, griseofulvin, on duodenal iron absorption using both in vivo and in vitro measurements. Urinary 5-aminolaevulinic acid levels were increased within 24 hr of feeding mice with griseofulvin diet (2.5% w/w), with more marked increases seen after 3-7 days. Urinary porphobilinogen levels also showed a similar trend. In vivo intestinal iron absorption was significantly reduced (P<0.05) in experimental mice, mainly due to reduction in the transfer of 59Fe from the enterocytes to the portal circulation. In vitro studies using isolated duodenal fragments also exhibited marked decreases in both iron uptake and Fe (III) reduction. Changes in mucosal Divalent Metal Transporter 1 (DMT-1), Dcytb and Ireg1 (iron regulated protein 1) mRNA levels paralleled the changes in iron absorption. The reduction in iron absorption after griseofulvin treatment was normalised when mice were simultaneously injected with haem-arginate. These data support the hypothesis that intermediates in haem biosynthesis, particularly 5-aminolaevulinic acid, regulate intestinal iron absorption.

Effect of high dose thiamine on the levels of urinary protein biomarkers in diabetes mellitus type 2.

The proteomics is known to be a valuable field of study and has become one of the most attractive sub-disciplines in clinical proteomics for human diseases. In the present research work, the levels of urinary protein biomarkers of diabetes mellitus type 2 using proteomic technology have been identified and characterized. Effect of high dose thiamine has also been observed on the levels of these marker proteins. Above 100 type 2 diabetic patients, and 50 same age and sex-matched normal healthy controls were recruited from the Sheikh Zayed Hospital, Lahore, Pakistan and 40 diabetic and 20 control have completed the trial. The urine samples from control and diabetic groups before or after thiamine therapy were further analyzed and identified by 2-D liquid chromatographic system (HPLC) and mass spectrometry MALDI-TOF/TOF and microTOF analysis. All the samples belonging to the control and diabetic groups were then analyzed by ELISA and estimated the levels of some proteins which were found to vary. In the urine samples, the levels of transthyretin, AMBP, haptoglobin precursor were found to decrease while albumin, zinc α 2 glycoprotein, RBP4 and E cadherin were found to increase in the diabetic patients as compared to the controls. The level of albumin in the urine samples of diabetic patients only decreased by 34% after thiamine therapy as compared to the controls and the placebo, while other urinary protein markers did not show a significant change after the therapy. Assessment of the levels of these biomarkers will be helpful in the diagnosis and treatment of diabetes mellitus type 2.

Proteomic identification of human urinary biomarkers in diabetes mellitus type 2.

BACKGROUND: During the proteomic era, one of the most rapidly growing areas in biomedical research is biomarker discovery, particularly using proteomic technologies. The urinary proteome is known to be a valuable field of study and has become one of the most attractive subdisciplines in clinical proteomics for human diseases. We have described the levels of protein biomarkers specific to diabetes mellitus type 2 in the Pakistani population using proteomic technology. METHODS: One hundred type 2 diabetes patients with 50 age- and sex-matched normal healthy controls were recruited from Sheikh Zayed Hospital, Lahore, Pakistan. Urinary proteins were analyzed by two-dimensional liquid chromatography, using chromatofocusing in the first dimension and reverse-phase chromatography in the second, followed by mass spectrometric analysis. Levels of the proteins, which were found to vary in the diabetes type 2 patients compared to the controls, were then determined by enzyme-linked immunosorbent assay in all the samples. RESULTS: Levels of transthyretin, α-1-microglobulin/bikunin precursor, and haptoglobin precursor decreased by 30.8%, 55.2%, and 81.45%, whereas levels of albumin, zinc α2 glycoprotein, retinol binding protein 4, and E-cadherin increased by 486.5%, 29.23%, 100%, and 693%, respectively, in the diabetes patients compared to the controls. CONCLUSIONS: Variation in the levels of these identified protein biomarkers have been reported in other pathological states. Assessment of the levels of these biomarkers will be helpful not only in early diagnosis but also in prognosis of diabetes mellitus type 2.

HIF-1 regulates heritable variation and allele expression phenotypes of the macrophage immune response gene SLC11A1 from a Z-DNA forming microsatellite.

The Ity/Lsh/Bcg locus encodes the macrophage protein Slc11a1/Nramp1, which protects inbred mice against infection by diverse intracellular pathogens including Leishmania, Mycobacterium, and Salmonella. Human susceptibility to infectious and inflammatory diseases, including rheumatoid arthritis, inflammatory bowel disease, and tuberculosis, shows allelic association with a highly polymorphic regulatory, Z-DNA-forming microsatellite of (GT/AC)n dinucleotides within the proximal SLC11A1 promoter. We surmised that cis-acting allelic polymorphisms may underlie heritable differences in SLC11A1 expression and phenotypic variation in disease risk. However, it is unclear what may underlie such variation in SLC11A1 allele expression. Here we show that hypoxia-inducible Factor 1 (HIF-1) regulates allelic variation in SLC11A1 expression by binding directly to the microsatellite during macrophage activation by infection or inflammation. Targeted Hif-1alpha ablation in murine macrophages attenuated Slc11a11 expression and responsiveness to S typhimurium infection. Our data also showed that HIF-1 may be functionally linked to complex prototypical inflammatory diseases associated with certain SLC11A1 alleles. As these alleles are highly polymorphic, our finding suggests that HIF-1 may influence heritable variation in SLC11A1-dependent innate resistance to infection and inflammation within and between populations. This report also suggests that microsatellites may play critical roles in the directional evolution of complex heritable traits by regulating gene expression phenotypes.

Increased adipose tissue expression of hepcidin in severe obesity is independent from diabetes and NASH.

BACKGROUNDS & AIMS: Hepcidin is an acute-phase response peptide. We have investigated the possible involvement of hepcidin in massive obesity, a state of chronic low-grade inflammation. Three groups of severely obese patients with or without diabetes or nonalcoholic steatohepatitis were investigated. METHODS: Hepcidin expression was studied in liver and adipose tissue of these patients. Hepcidin regulation was investigated in vitro by adipose tissue explant stimulation studies. RESULTS: Hepcidin was expressed not only in the liver but also at the messenger RNA (mRNA) and the protein levels in adipose tissue. Moreover, mRNA expression was increased in adipose tissue of obese patients. The presence of diabetes or NASH did not modify the hepcidin expression levels in liver and adipose tissue. In adipose tissue, mRNA expression correlated with indexes of inflammation, interleukin-6, and C-reactive protein. Interleukin-6 also promoted in vitro hepcidin expression. A low transferrin saturation ratio was observed in 68% of the obese patients; moreover, 24% of these patients presented with anemia. The observed changes in iron status could be due to the role of hepcidin as a negative regulator of intestinal iron absorption and macrophage iron efflux. Interestingly, a feedback control mechanism on hepcidin expression related to low transferrin saturation occurred in the liver but not in the adipose tissue. CONCLUSIONS: Hepcidin is a proinflammatory adipokine and may play an important role in hypoferremia of inflammation in obese condition.

Inhibition of iron transport across human intestinal epithelial cells by hepcidin.

We investigated the effects of the iron regulatory peptide hepcidin on iron transport by the human intestinal epithelial Caco-2 cell line. Caco-2 cells were exposed to hepcidin for 24 hours prior to the measurement of both iron transport and transporter protein and mRNA expression. Incubation with hepcidin significantly decreased apical iron uptake by Caco-2 cells. This was accompanied by a decrease in both the protein and the mRNA expression of the iron-response element containing variant of the divalent metal transporter (DMT1[+IRE]). In contrast, iron efflux and iron-regulated gene1 (IREG1) expression were unaffected by hepcidin. Hepcidin interacts directly with a model intestinal epithelium. The primary effect of this regulatory peptide is to modulate the apical membrane uptake machinery, thereby controlling the amount of iron absorbed from the diet.