Reliability of serum assays of iron status in postmenopausal women

Role of iron biomarkers and iron intakes in lung cancer risk: A systematic review and meta-analysis

BACKGROUND

The role of iron biomarkers and iron intake in the susceptibility to lung cancer is unclear. The purpose of this study was to conduct a systematic review and meta-analysis, to assess the relationship between iron levels in the body or iron intake and the risk of lung cancer.

METHOD

This review is registered with PROSPERO (number CRD 42020199776). PubMed, Web of Science, Scopus, Embase and Cochrane were used to search for studies assessing the relationship between iron and lung cancer, up to July 15, 2021. Qualitative and quantitative analysis was carried out to determine if there was a correlation between iron biomarkers/intakes and the risk of lung cancer.

RESULT

Twenty articles were included. Pooled analyses demonstrated that serum ferritin concentrations and transferrin saturation (TSAT) were significantly higher in patients with lung cancer than in healthy controls (ferritin: standardized mean differences [SMD], 0.235, 95% confidence interval [CI], 0.129, 0.341, I² = 32.1 %; TSAT: SMD, 0.07, 95 % CI, 0.018, 0.121, I² = 0 %). In contrast, serum transferrin concentrations were significantly lower in patients with lung cancer than in healthy controls (SMD, -0.591, 95 % CI, -1.18, -0.003, I² = 87.7 %). No significant effects of serum iron, lung tissue iron, bronchoalveolar lavage fluid (BALF) ferritin, or iron intake (total iron, dietary iron, heme iron, or non-heme iron) were found on lung cancer incidence.

CONCLUSION

Among the different iron biomarkers analyzed, a trend in association was only detected with serum ferritin, TSAT and transferrin concentration and no associations were found between iron intakes and the risk of lung cancer. However, more prospective studies are needed to strengthen the current evidence.

The role of disrupted iron homeostasis in the development and progression of arthropathy

Arthropathy or joint disease leads to significant pain and disability irrespective of etiology. Clinical and experimental evidence point to the presence of considerable links between arthropathy and iron overload. Previous work has suggested that iron accumulation in the joints is often associated with increased oxidative stress, disrupted matrix metabolism, and cartilage degeneration. However, key issues regarding the role of iron overload in the pathogenesis of arthropathy remain ambiguous. For example, significant gaps in our knowledge of the primary cellular targets of iron overload-induced damage and the exact molecular mechanism through which disrupted iron homeostasis leads to joint damage still exist. The exact signaling pathway that links iron metabolism and cellular damage in arthropathy also remains largely unmapped. In this review, we focus on the relationship between iron overload and arthropathy with special emphasis on the adversarial relationship between iron that accumulates in the joints over time and cartilage homeostasis. A better understanding of the mechanisms and pathways underlying iron-induced cartilage degeneration may help in defining new prognostic markers and therapeutic targets in arthropathy.

Red meat consumption and risk of cardiovascular diseases-is increased iron load a possible link?

Background

High iron load and red meat consumption could increase the risk of cardiovascular diseases (CVDs). As red meat is the main source of heme iron, which is in turn a major determinant of increased iron load, adverse cardiometabolic effects of meat consumption could be mediated by increased iron load.

Objective

The object of the study was to assess whether associations between red meat consumption and CVD risk are mediated by iron load in a population-based human study.

Design

We evaluated relations between red meat consumption, iron load (plasma ferritin), and risk of CVD in the prospective EPIC-Heidelberg Study using a case-cohort sample including a random subcohort (n = 2738) and incident cases of myocardial infarction (MI, n = 555), stroke (n = 513), and CVD mortality (n = 381). Following a 4-step mediation analysis, associations between red meat consumption and iron load, red meat consumption and CVD risk, and iron load and CVD risk were assessed by multivariable regression models before finally testing to which degree associations between red meat consumption and CVD risk were attenuated by adjustment for iron status.

Results

Red meat consumption was significantly positively associated with ferritin concentrations and MI risk [HR per 50 g daily intake: 1.18 (95% CI: 1.05, 1.33)], but no significant associations with stroke risk and CVD mortality were observed. While direct associations between ferritin concentrations and MI risk as well as CVD mortality were significant in age- and sex-adjusted Cox regression models, these associations were substantially attenuated and no longer significant after multivariable adjustment for classical CVD risk factors. Strikingly, ferritin concentrations were positively associated with a majority of classical CVD risk factors (age, male sex, alcohol intake, obesity, inflammation, and lower education).

Conclusion

Increased ferritin concentrations may be a marker of an overall unfavorable risk factor profile rather than a mediator of greater CVD risk due to meat consumption.

High serum iron is associated with increased cancer risk

Epidemiologic studies linking high serum iron with cancer risks are limited and inconclusive, despite evidence implicating body iron in human carcinogenesis. A cohort of 309,443 adults in Taiwan who had no history of cancer had serum iron levels tested at the time of recruitment (1997-2008). Initially measured iron levels were associated with subsequent cancer risk by linking individuals with the National Cancer Registry and National Death File. HRs were calculated by the Cox model. One third of males (35%) and one fifth of females (18%) had high serum iron (≥120 μg/dL), which was associated with a 25% increase in risk for incidence of all cancers [HR, 1.25; 95% confidence interval (CI), 1.16-1.35] and with a 39% increase in risk for mortality from all cancers (HR, 1.39; 95% CI, 1.23-1.57). The relationship between serum iron and cancer risk was a J-shaped one, with higher cancer risk at both ends, either at lower than 60 μg/dL or higher than 120 μg/dL. At the higher end, cancer risk increased by 4% for every 10 μg/dL increment above 80 μg/dL, showing a dose-response relationship, with 60 to 79 μg/dL as a reference level. In a sensitivity analysis, the increases in risk were still observed after the first 5 years of cancer cases were excluded. Liver cancer risk was increased in HBV (-) non-hepatitis B carrier (3-fold) and HBV (+) hepatitis B carrier (24-fold). Lifestyle risks such as smoking, drinking, or inactivity interacted synergistically with high serum iron and significantly increased the cancer risks. The liver (HR, 2.49; 95% CI, 1.97-3.16) and the breast (HR, 1.31; 95% CI, 1.01-1.70) were the two major cancer sites where significant cancer risks were observed for serum iron either ≥120 μg/dL or ≥140 μg/dL, respectively. This study reveals that high serum iron is both a common disorder and a marker of increased risk for several cancers.

Age-dependent ferritin elevations and HFE C282Y mutation as risk factors for symptomatic knee osteoarthritis in males: a longitudinal cohort study

Background

Age, gender and genetic predisposition are major intrinsic risk factors for osteoarthritis (OA). Iron increases are associated with age and gene mutation. In the present study, we examined whether serum ferritin, an indicator of total body iron stores, correlates with clinical features in patients with OA, and whether the hemochromatosis Fe (HFE) gene mutation plays a role.

Methods

In a 2-year longitudinal observational study, 127 patients with knee OA and 20 healthy individuals (controls) were enrolled. All patients underwent standardized weight-bearing fixed-flexion posteroanterior knee radiographs. Peripheral blood samples were analyzed for serum ferritin, and genotyped for HFE using allelic discrimination methods.

Results

Higher levels of serum ferritin were found in patients older than 56 years (P =0.0186) and males (P =0.0006), with a trend toward higher ferritin in patients with OA. HFE gene mutation carriers were more prevalent among patients with OA than among healthy controls. When stratified further by gender, we found that male patients with OA had higher levels of serum ferritin than male control subjects [odds ratio = 4.18 (limits of 95% confidence interval: 0.86–27.69, P = 0.048)]. Analyses of radiographic data indicated that higher ferritin was associated with narrower joint space width at baseline (P = 0.032) in male patients. Additionally, among men, risk prediction of radiographic severity [Kellgren-Lawrence (KL) grade >2)] in the higher ferritin group was almost five times that of the lower ferritin group (odds ratio = 4.74, P = 0.023).

Conclusion

Our data suggest that increased ferritin levels are associated with symptomatic knee OA in males. This finding needs to be validated in a larger cohort of patients.

17β-Estradiol inhibits iron hormone hepcidin through an estrogen responsive element half-site

Interaction of estrogen with iron at the systemic level is long suspected, but direct evidence linking the two is limited. In the present study, we examined the effects of 17β-estradiol (E2) on hepcidin, a key negative regulator of iron absorption from the liver. We found that transcription of hepcidin was suppressed by E2 treatment in human liver HuH7 and HepG2 cells, and this down-regulation was blocked by E2 antagonist ICI 182780. Chromatin immunoprecipitation, deletion, and EMSA detected a functional estrogen responsive element half-site that is located between -2474 and -2462 upstream from the start of transcription of the hepcidin gene. After cloning the human hepcidin promoter into the pGL3Luc-Reporter vector, luciferase activity was also down-regulated by E2 treatment in HepG2 cells. E2 reduced hepcidin mRNA in wild-type mice as well as in hemochromatosis Fe gene knockout mice. In summary, our data suggest that hepcidin inhibition by E2 is to increase iron uptake, a mechanism to compensate iron loss during menstruation. This mechanism may also contribute to increased iron stores in oral contraceptive users.

Circulating biomarkers of iron storage and clearance of incident human papillomavirus infection

BACKGROUND

Iron is an essential mineral for both cellular and pathogen survival and is essential for viral replication. In turn, iron metabolism has been shown to be altered by several viral infections. However, little is known about the association between iron status and human papillomavirus (HPV) natural history. We hypothesize iron to be an HPV cofactor that is associated with longer duration of infection.

METHODS

Ferritin and soluble transferrin receptor (sTfR) were measured in baseline serum samples from 327 women enrolled in the Ludwig-McGill cohort. Incident HPV clearance rates (any-type, oncogenic HPV, nononcogenic HPV, and HPV-16) over a 3 year time period were estimated from Cox proportional hazard models accounting for correlations between multiple infections.

RESULTS

Women with ferritin levels above the median were less likely to clear incident oncogenic HPV [adjusted hazard ratio (AHR), 0.73; 95% confidence interval (CI), 0.55-0.96] and HPV-16 infections (AHR, 0.29; 95% CI, 0.11-0.73). Using physiologic cutoff points, women with enriched iron stores (>120 μg/L) were less likely to clear incident oncogenic HPV infections than those with low levels of iron (<20 μg/L; AHR, 0.34; 95% CI, 0.15-0.81).

CONCLUSION

This study observed that women with the highest ferritin levels were less likely to clear incident oncogenic and HPV-16 infections than women with low ferritin. Rising iron stores may decrease probability of clearing new HPV infection, possibly by promoting viral activity and contributing to oxidative DNA damage.

IMPACT

This novel study suggests that elevated iron stores may put women at risk for persistent HPV infection, an early event in cervical carcinogenesis. Further examination of the association between iron status and HPV natural history is warranted.

Brain structure in healthy adults is related to serum transferrin and the H63D polymorphism in the HFE gene

Control of iron homeostasis is essential for healthy central nervous system function: iron deficiency is associated with cognitive impairment, yet iron overload is thought to promote neurodegenerative diseases. Specific genetic markers have been previously identified that influence levels of transferrin, the protein that transports iron throughout the body, in the blood and brain. Here, we discovered that transferrin levels are related to detectable differences in the macro- and microstructure of the living brain. We collected brain MRI scans from 615 healthy young adult twins and siblings, of whom 574 were also scanned with diffusion tensor imaging at 4 Tesla. Fiber integrity was assessed by using the diffusion tensor imaging-based measure of fractional anisotropy. In bivariate genetic models based on monozygotic and dizygotic twins, we discovered that partially overlapping additive genetic factors influenced transferrin levels and brain microstructure. We also examined common variants in genes associated with transferrin levels, TF and HFE, and found that a commonly carried polymorphism (H63D at rs1799945) in the hemochromatotic HFE gene was associated with white matter fiber integrity. This gene has a well documented association with iron overload. Our statistical maps reveal previously unknown influences of the same gene on brain microstructure and transferrin levels. This discovery may shed light on the neural mechanisms by which iron affects cognition, neurodevelopment, and neurodegeneration.

Inhibitory effects of iron on bone morphogenetic protein 2-induced osteoblastogenesis

Postmenopausal osteoporosis is characterized by an imbalance of bone resorption exceeding bone formation, resulting in a net loss of bone mineral density (BMD). Estrogen deficiency is known to promote bone resorption. However, the causative factors that impair bone formation have not been identified. Women after menopause experience not only estrogen deficiency but also iron accumulation as a result of cessation of menstruation. In this study we investigated whether increased iron plays a role in osteoporosis. By growing primary mouse osteoclast and osteoblast progenitor cells as well as immortalized cell lines in the presence of iron, we found that increased iron had minimal effects on osteoclast cell differentiation. Interestingly, iron, particularly in its inorganic form, and to a lesser extent ferritin and transferrin all suppressed alkaline phosphatase (ALP) activities in osteoblasts. Moreover, iron downregulated mRNA levels of several other osteoblastogenic markers such as Runx2, osterix, osteopontin, and osteocalcin. To further show that this in vitro finding is relevant to the in vivo condition, we demonstrated that iron-accumulated mice with intact ovaries exhibited a significant decrease in BMD. Although iron inhibited preosteoblast cell differentiation, it did enhance preosteoblast cell proliferation, as evidenced by increased cell growth and expression of cell cycle regulator genes such as CDK4, CDK6, cyclin D1, and cyclin D3 and G(2) /M phase cell population. Taken together, our results suggest that increased iron could be a factor that slows down bone formation in postmenopausal women.

Reliability of tumor markers, chemokines, and metastasis-related molecules in serum

There is a growing interest in the role that cancer biomarkers, metastasis-related molecules, and chemokines may play in the development and progression of various cancers. However, few studies have addressed the reliability of such biomarkers in healthy individuals over time. The objective of this study was to investigate the temporal reliability of multiple proteins in serum samples from healthy women who donated blood over successive years. Thirty five, postmenopausal women with two, repeated annual visits, and thirty, premenopausal women with three, repeated annual visits were randomly selected among eligible subjects from an existing, prospective cohort. Multiplexing Luminex xMAPTM technology was used to measure the levels of 55 serum proteins representing cancer antigens, chemokines, angiogenic and anti-angiogenic factors, proteases, adipokines, apoptotic molecules, and other markers in these women. The biomarkers with high detection rates (> 60%) and acceptable reliability (intraclass correlation coefficient, ICCs > or = 0.55) using xMAPTM method were: cancer antigens: AFP, CA 15-3, CEA, CA-125, SCC, SAA; growth factors/related molecules: ErbB2, IGFBP-1; proteases and adhesion molecules: MMP-1, 8, 9, sE-selectin, human kallikreins (KLK) 8,10, ICAM-1, VCAM-1, chemokines: fractalkine, MCP-1,2, RANTES, MIP-1alpha, MIP-1beta, Eotaxin, GRO-alpha, IP-10; inhibitors of angiogenesis: angiostatin and endostatin; adipokines leptin and resistin; apoptotic factor: Fas, and other proteins mesothelin, myeloperoxidase (MPO), and PAI-1. The rest of the biomarkers under investigation either had ICCs less than 0.55 or had low levels of detection (< 60%). These included cancer antigens: CA 19-9, CA 72-4, MICA, S100, TTR, ULBP1, ULBP2, ULBP3; proteases: MMP 2, 3, 7, 12, 13; chemokines: MCP-3, MIF, MIG; adipokines: leptin and resistin; apoptotic factors: FasL, DR5, Cyfra 21-1; and inhibitors of angiogenesis and other markers: thrombospondin and heat shock protein (HSP) 27. In conclusion, 34 out of the 55 biomarkers investigated were present in detectable levels in > 60% of the samples, and with an ICC > or = 0.55, indicating that a single serum measurement can be used in prospective epidemiological studies using the xMAPTM method.

Risk-benefit analysis of mineral intakes: case studies on copper and iron

Dietary reference values for essential trace elements are designed to meet requirements with minimal risk of deficiency and toxicity. Risk-benefit analysis requires data on habitual dietary intakes, an estimate of variation and effects of deficiency and excess on health. For some nutrients, the range between the upper and lower limits may be extremely narrow and even overlap, which creates difficulties when setting safety margins. A new approach for estimating optimal intakes, taking into account several health biomarkers, has been developed and applied to selenium, but at present there are insufficient data to extend this technique to other micronutrients. The existing methods for deriving reference values for Cu and Fe are described. For Cu, there are no sensitive biomarkers of status or health relating to marginal deficiency or toxicity, despite the well-characterised genetic disorders of Menkes and Wilson's disease which, if untreated, lead to lethal deficiency and overload, respectively. For Fe, the wide variation in bioavailability confounds the relationship between intake and status and complicates risk-benefit analysis. As with Cu, health effects associated with deficiency or toxicity are not easy to quantify, therefore status is the most accessible variable for risk-benefit analysis. Serum ferritin reflects Fe stores but is affected by infection/inflammation, and therefore additional biomarkers are generally employed to measure and assess Fe status. Characterising the relationship between health and dietary intake is problematic for both these trace elements due to the confounding effects of bioavailability, inadequate biomarkers of status and a lack of sensitive and specific biomarkers for health outcomes.

Serum prohepcidin is associated with soluble transferrin receptor-1 but not ferritin in healthy post-menopausal women

Hepcidin is a 25-amino-acid iron peptide hormone originated from its two precursors of prohepcidin (60-amino-acid) and preprohepcidin (84-amino-acid). Serum prohepcidin levels have been widely used to evaluate iron overload in clinical and preclinical studies. However, its usefulness is often questioned and its stepwise conversion mechanism remains largely unknown. Using New York University Women's Health Study subjects, we measured serum levels of prohepcidin with ELISA and hepcidin with mass spectrometry as well as ferritin and soluble transferrin receptor 1 (sTfR1) in 45 normal healthy post-menopausal women over a 1-year period with 2 samples per subject. We found that serum prohepcidin levels are correlated with the serum sTfR1 levels (r=0.45, p<0.01) but not to ferritin levels (r=0.08, p=0.60), suggesting that serum prohepcidin is not a biomarker of iron overload that was originally thought and designed for. Interestingly, serum hepcidin levels are associated with serum ferritin levels (r=0.64, p<0.0001) but not with sTfR1 levels (r=0.06, p=0.70), indicating that hepcidin is a measure of iron overload. Although hepcidin is a downstream product of prohepcidin, the amounts of hepcidin and prohepcidin are not related to each other (r=-0.007, p=0.90) under normal physiological conditions. The interrelationships between sTfR1 and prohepcidin or between ferritin and hepcidin suggest that ferritin- and sTfR1-sensed hepcidin conversion system exist in human body and maybe regulated at the post-translational level.