Biomarkers of iron metabolism are independently associated with impaired glucose metabolism and type 2 diabetes: the KORA F4 study

The complementary roles of iron and estrogen in menopausal differences in cardiometabolic outcomes

Biological hormonal changes are frequently cited as an explanatory factor of sex and menopause differences in cardiometabolic diseases (CMD) and its associated risk factors. However, iron metabolism which varies between sexes and among women of different reproductive stages could also play a role. Recent evidence suggest that iron may contribute to CMD risk by modulating oxidative stress pathways and inflammatory responses, offering insights into the mechanistic interplay between iron and CMD development. In the current review, we provide a critical appraisal of the existing evidence on sex and menopausal differences in CMD, discuss the pitfall of current estrogen hypothesis as sole explanation, and the emerging role of iron in CMD as complementary pathway. Prior to menopause, body iron stores are lower in females as compared to males, but the increase during and after menopause, is tandem with an increased CMD risk. Importantly, basic science experiments show that an increased iron status is related to the development of type 2 diabetes (T2D), and different cardiovascular diseases (CVD). While epidemiological studies have consistently reported associations between heme iron intake and some iron biomarkers such as ferritin and transferrin saturation with the risk of T2D, the evidence regarding their connection to CVD remains controversial. We delve into the factors contributing to this inconsistency, and the limitation of relying on observational evidence, as it does not necessarily imply causation. In conclusion, we provide recommendations for future studies on evaluating the potential role of iron in elucidating the sex and menopausal differences observed in CMD.

The Modulation of Euglycemic Endocrine and Exocrine Pancreatic Secretions in Iron Deficiency

OBJECTIVES

The contribution of pancreatic secretions in iron metabolism has been elucidated, but the clinical outcomes of iron deficiency on pancreatic function are debatable. This study aimed to investigate the modulation of euglycemic endocrine and exocrine pancreatic excretions in response to variations in iron availability.

SUBJECTS AND METHODS

Serum levels of insulin, glucagon, insulin-to-glucagon ratio (IGR), and amylase were determined in 170 adult subjects with variable levels of serum iron.

RESULTS

Control (n = 46) and iron-deficient (n = 124) subjects had significant differences (p < 0.001) in their average levels of insulin (68.7 ± 0.5 vs. 100.0 ± 2.0 pmol/dL), glucagon (17.9 ± 0.6 vs. 10.8 ± 0.8 pmol/dL), IGR (4.0 ± 0.1 vs. 19.5 ± 2.1), and amylase (29.7 ± 0.9 vs. 17.5 ± 0.2). The upregulation of serum insulin levels increases proportionally and gradually to the extent of iron deficiency as compared to an abrupt downregulation of serum levels of glucagon and amylase. A significant association was observed between serum iron and IGR (r = -0.645, p < 0.001) and amylase levels (r = 0.653, p < 0.001). The receiver operating characteristic curve analysis defines an excellent predictivity of the reduced serum iron level to discriminate subjects with upregulated IGR and amylase levels with area under curves of 0.938 and 0.905, respectively.

CONCLUSION

Iron deficiency is associated with an adaptive modulation of euglycemic endocrine and exocrine secretions that is consistent with a status of insulin resistance.

Dual nature of ferritin for hematologic, liver functional, and metabolic parameters in older diabetic patients

This study explored the association between ferritin with hematologic, liver functional, and metabolic parameters in older diabetic patients. A total of 210 diabetic patients aged 65 or older were classified into four groups according to the reference range of serum ferritin. Demographic variables and health-related lifestyle factors were obtained through the utilization of a standardized questionnaire. Anthropometric measures, blood pressure, hematology test, and biochemical assessment were also performed. Among all patients, 29.5% had anemia. The percentage of anemia in groups low ferritin (< 40 μg/L), lower side within the reference range (40-120 μg/L), higher side within the reference range (121-200 μg/L), and high ferritin levels (> 200 μg/L) were 50.0, 27.7, 20.5, and 24.2% (P = 0.025), respectively. Low ferritin levels had a higher risk of anemia and a high red blood cell distribution width (RDW). High ferritin levels were associated with a higher risk of high glutamate pyruvate transaminase, obesity, high fasting blood glucose (FBG), and high postprandial blood glucose. The higher side within the reference range of ferritin also showed a higher risk of high FBG and high glycated hemoglobin. Nevertheless, there was no significant association between ferritin and inflammation marker, serum lipids or blood pressure. Overall, ferritin demonstrates a dual nature in older diabetic patients: low ferritin levels are linked to anemia or elevated RDW, while high levels are linked to obesity, increased liver enzymes, and worse glycemia control.

Metabolomic biomarkers of habitual B vitamin intakes unveil novel differentially methylated positions in the human epigenome

BACKGROUND

B vitamins such as folate (B9), B6, and B12 are key in one carbon metabolism, which generates methyl donors for DNA methylation. Several studies have linked differential methylation to self-reported intakes of folate and B12, but these estimates can be imprecise, while metabolomic biomarkers can offer an objective assessment of dietary intakes. We explored blood metabolomic biomarkers of folate and vitamins B6 and B12, to carry out epigenome-wide analyses across up to three European cohorts. Associations between self-reported habitual daily B vitamin intakes and 756 metabolites (Metabolon Inc.) were assessed in serum samples from 1064 UK participants from the TwinsUK cohort. The identified B vitamin metabolomic biomarkers were then used in epigenome-wide association tests with fasting blood DNA methylation levels at 430,768 sites from the Infinium HumanMethylation450 BeadChip in blood samples from 2182 European participants from the TwinsUK and KORA cohorts. Candidate signals were explored for metabolite associations with gene expression levels in a subset of the TwinsUK sample (n = 297). Metabolomic biomarker epigenetic associations were also compared with epigenetic associations of self-reported habitual B vitamin intakes in samples from 2294 European participants.

RESULTS

Eighteen metabolites were associated with B vitamin intakes after correction for multiple testing (Bonferroni-adj. p < 0.05), of which 7 metabolites were available in both cohorts and tested for epigenome-wide association. Three metabolites - pipecolate (metabolomic biomarker of B6 and folate intakes), pyridoxate (marker of B6 and folate) and docosahexaenoate (DHA, marker of B6) - were associated with 10, 3 and 1 differentially methylated positions (DMPs), respectively. The strongest association was observed between DHA and DMP cg03440556 in the SCD gene (effect = 0.093 ± 0.016, p = 4.07E-09). Pyridoxate, a catabolic product of vitamin B6, was inversely associated with CpG methylation near the SLC1A5 gene promoter region (cg02711608 and cg22304262) and with SLC7A11 (cg06690548), but not with corresponding changes in gene expression levels. The self-reported intake of folate and vitamin B6 had consistent but non-significant associations with the epigenetic signals.

CONCLUSION

Metabolomic biomarkers are a valuable approach to investigate the effects of dietary B vitamin intake on the human epigenome.

Beta Cell Dysfunction in Youth- and Adult-Onset Type 2 Diabetes: An Extensive Narrative Review with a Special Focus on the Role of Nutrients

Traditionally a disease of adults, type 2 diabetes (T2D) has been increasingly diagnosed in youth, particularly among adolescents and young adults of minority ethnic groups. Especially, during the recent COVID-19 pandemic, obesity and prediabetes have surged not only in minority ethnic groups but also in the general population, further raising T2D risk. Regarding its pathogenesis, a gradually increasing insulin resistance due to central adiposity combined with a progressively defective β-cell function are the main culprits. Especially in youth-onset T2D, a rapid β-cell activity decline has been observed, leading to higher treatment failure rates, and early complications. In addition, it is well established that both the quantity and quality of food ingested by individuals play a key role in T2D pathogenesis. A chronic imbalance between caloric intake and expenditure together with impaired micronutrient intake can lead to obesity and insulin resistance on one hand, and β-cell failure and defective insulin production on the other. This review summarizes our evolving understanding of the pathophysiological mechanisms involved in defective insulin secretion by the pancreatic islets in youth- and adult-onset T2D and, further, of the role various micronutrients play in these pathomechanisms. This knowledge is essential if we are to curtail the serious long-term complications of T2D both in pediatric and adult populations.

Association of Body Iron Metabolism with Type 2 Diabetes Mellitus in Chinese Women of Childbearing Age: Results from the China Adult Chronic Disease and Nutrition Surveillance (2015)

High iron stores have been reported to be associated with type 2 diabetes mellitus (T2DM). However, evidence for the associations of iron metabolism with T2DM is inconsistent, and whether there is a threshold effect remains controversial. In the present study, we aimed to examine the associations between various iron biomarkers and the risk of T2DM as well as impaired glucose metabolism (IGM) and hyperglycemia in Chinese women of childbearing age. A total of 1145 women were divided into three groups (normal blood glucose metabolism group; IGM group; T2DM group). Biomarkers of iron metabolism (serum ferritin (SF), transferrin, soluble transferrin receptor (sTfR), transferrin saturation, serum iron, total body iron, and sTfR-to-lgferritin index) were measured. After adjusting for various confounding risk factors, SF and sTfR were positively associated with the risk of IGM (fourth vs. first quartile: SF odds ratio (OR) = 1.93 (95% CI 1.17-3.20) and sTfR OR = 3.08 (95% CI 1.84-5.14)) and T2DM (SF OR = 2.39 (95% CI 1.40-4.06) and sTfR OR = 3.84 (95% CI 2.53-5.83)). There was a nonlinear relationship between SF and risk of T2DM and hyperglycemia (p for nonlinearity < 0.01). Our findings suggested that SF and sTfR could be independent predictors of T2DM risk.

Association between systemic iron status and β-cell function and insulin sensitivity in patients with newly diagnosed type 2 diabetes

OBJECTIVE

Abnormal iron metabolism is related to the risk of diabetes, but the underlying mechanism of this association remains uncertain. This study was conducted to evaluate the contributions of systemic iron status to β-cell function and insulin sensitivity of patients with newly diagnosed T2DM.

METHODS

A total of 162 patients with newly diagnosed T2DM and 162 healthy controls were enrolled in the study. Basic characteristics, biochemical indicators, and iron metabolism biomarkers, including serum iron (SI), ferritin (SF), transferrin (Trf), and transferrin saturation (TS), were collected. All patients underwent a 75 g oral glucose tolerance test. A series of parameters for assessing β-cell function and insulin sensitivity were calculated. The multivariate stepwise linear regression model was used to investigate the contributions of iron metabolism to β-cell function and insulin sensitivity.

RESULTS

Compared with healthy controls, patients with newly diagnosed T2DM had significantly higher levels of SF. Among the diabetic patients, the SI and TS levels were higher, and the percentage of Trf levels below normal values was lower in men than in women. In all diabetic patients, SF was the independent risk factor associated with impaired β-cell function. Further stratification analysis showed that Trf was an independent protective factor for β-cell function in male patients, while SF was an independent risk factor for impaired β-cell function in female patients. However, systemic iron status did not affect insulin sensitivity.

CONCLUSION

Elevated SF levels and decreased Trf levels had a profound effect on impaired β-cell function in Chinese patients with newly diagnosed T2DM.

Association of Serum Antioxidant Minerals and Type 2 Diabetes Mellitus in Chinese Urban Residents

Antioxidant minerals including zinc, copper and selenium play critical roles in the maintenance of the redox balance in the body. However, their influences on type 2 diabetes mellitus (T2DM) are still inconclusive in Chinese populations. To elucidate the relationship between antioxidant minerals and T2DM, serum zinc, copper and selenium concentrations were measured in 1443 Chinese urban residents using a 1:2 matched case-control study. Conditional logistic regression models (CLR) were used to obtain the odds ratios (ORs) and 95% confidence intervals (CIs), and restricted cubic splines (RCS) were used to examine their dose−response associations. Serum zinc (OR = 0.52 [0.35, 0.77]) and copper concentrations (OR = 0.25 [0.17, 0.37]) were negatively associated with T2DM in a fully adjusted model. An L-shaped zinc-T2DM association (Poverall association = 0.003, and Pnonlinearity = 0.005) and a negative linear copper-T2DM association (Poverall association < 0.0001, and Pnonlinearity = 0.395) were observed. No association was found between serum selenium and T2DM in fully adjusted CLR or RCS models. In addition, joint associations with T2DM were identified between serum zinc and copper and between serum selenium and copper. In conclusion, our study emphasizes the importance of an adequate intake of antioxidant minerals for T2DM prevention in the Chinese population.

The role of iron metabolism in chronic diseases related to obesity

Obesity is one of the major public health problems threatening the world, as well as a potential risk factor for chronic metabolic diseases. There is growing evidence that iron metabolism is altered in obese people, however, the highly refined regulation of iron metabolism in obesity and obesity-related complications is still being investigated. Iron accumulation can affect the body’s sensitivity to insulin, Type 2 diabetes, liver disease and cardiovascular disease. This review summarized the changes and potential mechanisms of iron metabolism in several chronic diseases related to obesity, providing new clues for future research.

Repression of the iron exporter ferroportin may contribute to hepatocyte iron overload in individuals with type 2 diabetes

OBJECTIVE

Hyperferremia and hyperferritinemia are observed in patients and disease models of type 2 diabetes mellitus (T2DM). Likewise, patients with genetic iron overload diseases develop diabetes, suggesting a tight link between iron metabolism and diabetes. The liver controls systemic iron homeostasis and is a central organ for T2DM. Here, we investigate how the control of iron metabolism in hepatocytes is affected by T2DM.

METHODS

Perls Prussian blue staining was applied to analyze iron distribution in liver biopsies of T2DM patients. To identify molecular mechanisms underlying hepatocyte iron accumulation we established cellular models of insulin resistance by treatment with palmitate and insulin.

RESULTS

We show that a subset of T2DM patients accumulates iron in hepatocytes, a finding mirrored in a hepatocyte model of insulin resistance. Iron accumulation can be explained by the repression of the iron exporter ferroportin upon palmitate and/or insulin treatment. While during palmitate treatment the activation of the iron regulatory hormone hepcidin may contribute to reducing ferroportin protein levels in a cell-autonomous manner, insulin treatment decreases ferroportin transcription via the PI3K/AKT and Ras/Raf/MEK/ERK signaling pathways.

CONCLUSION

Repression of ferroportin at the transcriptional and post-transcriptional level may contribute to iron accumulation in hepatocytes observed in a subset of patients with T2DM.

Correlations Between Iron Status and Body Composition in Patients With Type 2 Diabetes Mellitus

Background

Our study aimed to investigate the association between iron metabolism and body composition in patients with type 2 diabetes mellitus (T2DM).

Methods

A total of 824 patients with T2DM were enrolled. Measurements of body composition were obtained by dual-energy X-ray absorptiometry. Patients were stratified into three groups according to their sex-specific ferritin levels. Basic information, laboratory results, and body composition were collected.

Results

Serum iron and transferrin saturation (TSAT) were increased significantly with increased serum ferritin (all p < 0.05). Total iron-binding capacity (TIBC) was decreased significantly with increased serum ferritin (p < 0.05). Visceral fat mass (VF), android fat/total body fat mass, android-to-gynoid fat ratio (A/G ratio), and high-sensitivity C-reactive protein were all increased significantly with increased serum ferritin (all p < 0.05). Patients with a high A/G ratio (A/G ratio ≧ 1) had significantly higher serum iron, ferritin, and TSAT, but significantly lower TIBC. In the model adjusted for age and gender, higher ferritin levels were associated with a higher VF (all p < 0.05). Serum iron was positively correlated with the occurrence of a high A/G ratio (A/G ratio ≧ 1) after the adjustment of confounding factors [an odds ratio (OR = 1.09, 95% CI, 1.02–1.19, p = 0.02)]. With receiver operating curve analysis, the cutoff value of serum iron for a high A/G ratio was 18.56, and the area under the curve was 0.771 (sensitivity 88.9%and specificity 63.9%, p = 0.01).

Conclusion

Higher serum iron and ferritin concentrations were positively associated with a higher VF. Higher serum iron concentrations were positively correlated with a high A/G ratio. This study indicates the potential relationship between iron overload and the body composition in patients with T2DM.

Association between hepatic iron overload assessed by magnetic resonance imaging and glucose intolerance states in the general population

BACKGROUND AND AIM

While there is evidence that iron overload disorders are associated with type 2 diabetes, the relationship between hepatic iron overload and prediabetes remains unclear. We aimed to investigate the association between hepatic iron overload, as assessed by magnetic resonance imaging (MRI), and different glucose intolerance states in the population-based Study.

METHODS AND RESULTS

We included data from 1622 individuals with MRI data, who did not have known type 2 diabetes (T2DM). Using an oral glucose tolerance testing, participants were classified as having isolated impaired fasting glucose (i-IFG), isolated impaired glucose tolerance (i-IGT), combined IFG and IGT (IFG + IGT) or previously unknown T2DM. Hepatic iron and fat contents were assessed through quantitative MRI. We undertook linear and multinomial logistic regression models adjusted for potential confounders and MRI-assessed hepatic fat content to examine the association of hepatic iron overload with different glucose intolerance states or continuous markers of glucose metabolism. MRI-assessed hepatic iron overload was positively associated only with both 2-h plasma glucose (β = 0.32; 95%CI 0.04-0.60) and the combined IFG + IGT category (relative risk ratio = 1.87; 95%CI 1.15-3.06). No significant associations were found between hepatic iron overload and other glucose intolerance states or biomarkers of glucose metabolism, independently of potential confounders.

CONCLUSIONS

MRI-assessed hepatic iron overload was associated with higher 2-h glucose concentrations and the combined IFG + IGT category, but not with other glucose intolerance states. Our findings suggest a weak adverse impact of hepatic iron overload on glucose metabolism, but further studies are needed to confirm these findings.

Second Sphere Interactions in Amyloidogenic Diseases

Amyloids are protein aggregates bearing a highly ordered cross β structural motif, which may be functional but are mostly pathogenic. Their formation, deposition in tissues and consequent organ dysfunction is the central event in amyloidogenic diseases. Such protein aggregation may be brought about by conformational changes, and much attention has been directed toward factors like metal binding, post-translational modifications, mutations of protein etc., which eventually affect the reactivity and cytotoxicity of the associated proteins. Over the past decade, a global effort from different groups working on these misfolded/unfolded proteins/peptides has revealed that the amino acid residues in the second coordination sphere of the active sites of amyloidogenic proteins/peptides cause changes in H-bonding pattern or protein-protein interactions, which dramatically alter the structure and reactivity of these proteins/peptides. These second sphere effects not only determine the binding of transition metals and cofactors, which define the pathology of some of these diseases, but also change the mechanism of redox reactions catalyzed by these proteins/peptides and form the basis of oxidative damage associated with these amyloidogenic diseases. The present review seeks to discuss such second sphere modifications and their ramifications in the etiopathology of some representative amyloidogenic diseases like Alzheimer's disease (AD), type 2 diabetes mellitus (T2Dm), Parkinson's disease (PD), Huntington's disease (HD), and prion diseases.

Iron Overload and the Risk of Diabetes in the General Population: Results of the Chinese Health and Nutrition Survey Cohort Study

BACKGROUND

Recent studies have found that there are significant associations between body iron status and the development of diabetes. In the present study, we aimed to analyze the association among iron overload (IO), insulin resistance (IR), and diabetes in Chinese adults, and to explore the sex difference.

METHODS

Men and women (age >19 years) who participated in the Chinese Health and Nutrition Survey and did not have diabetes at baseline were followed between 2009 and 2015 (n=5,779). Over a mean of 6 years, 75 participants were diagnosed with incident diabetes. Logistic regression was used to assess the risk factors associated with IO. Cox proportional hazard regression was used to estimate the risk of incident diabetes and to determine whether the risk differed among subgroups. Causal mediation analysis (CMA) was used to explore the mechanism linking IO and diabetes.

RESULTS

According to sex-stratified multivariable-adjusted Cox proportional hazards regression, IO increased the risk of incident diabetes. Women with IO had a higher risk of diabetes than men. Subgroup analysis with respect to age showed that the association between IO and diabetes was stronger in older women and younger men (P<0.001). CMA showed that liver injury (alanine transaminase) and lipid metabolism abnormalities (triglyceride, apolipoprotein B) contributed to the association between IO and diabetes.

CONCLUSION

IO is associated with diabetes and this association is sex-specific. IO may indirectly induce IR via liver injury and lipid metabolism abnormalities, resulting in diabetes.

Renal outcomes and prognostic factors in patients with type-2 diabetes and chronic kidney disease confirmed by renal biopsy

Aim

To evaluate the renal outcomes and prognostic factors among patients with type-2 diabetes (T2D) and biopsy-confirmed diabetic nephropathy (DN), non-diabetic renal disease (NDRD) and DN mixed with NDRD (MIX).

Design and Methods

Patients with both T2D and chronic kidney disease (CKD) who underwent renal biopsy between January 2014 and December 2016 were recruited in this prospective observational study. Participants were divided into DN group, NDRD group, or MIX group according to the baseline pathological diagnosis. The primary endpoint was a composite renal event of end-stage renal disease (ESRD) or ⩾ 40% reduction in estimated glomerular filtration rate (eGFR).

Results

Among the 292 participants included, 153 (52.4%) belonged to the DN group, 30 (10.3%) belonged to the NDRD group, and 109 (37.3%) belonged to the MIX group. During the median follow-up of 27 months, the adverse renal events occurred in 132 (44.2%) patients. Compared with NDRD group, the multiple adjusted hazard ratios (HRs) for renal events in patients with DN and MIX groups were 3.900 (95% confidence interval [CI]: 1.103-13.788) and 2.691 (95% CI: 0.662-10.936), respectively. Baseline lower eGFR (HR: 1.159, 95% CI: 1.060-1.266), severe proteinuria (HR: 2.047, 95% CI: 1.227-3.416), lower hemoglobin (HR: 1.170, 95% CI: 1.008-1.267), and a family history of diabetes (HR: 1.138, 95% CI: 1.008-2.285) were independent predictors for adverse renal outcomes in patients with DN.

Conclusion

In patients with T2D and CKD, pure DN and MIX group displayed a worse renal prognosis than NDRD group. Worse renal function, severe proteinuria, lower hemoglobin, and a family history of diabetes may be associated with adverse renal outcomes in patients with DN.

Hepatic steatosis and hepatic iron overload modify the association of iron markers with glucose metabolism disorders and metabolic syndrome

BACKGROUND

Iron status has been linked with impaired glucose metabolism (IGM), type 2 diabetes mellitus (T2DM) and the metabolic syndrome (MetS), but the role of hepatic steatosis or iron overload on these associations remains uncertain.

METHODS

We analysed data from 2310 participants without known T2DM of the population-based Study of Health in Pomerania (SHIP-TREND, Germany) through logistic regression models. We tested additive and multiplicative interactions between ferritin and hepatic steatosis or iron overload.

RESULTS

Serum ferritin was positively associated with IGM (OR per 100 µg/L: 1.11 [1.01, 1.23]), T2DM (OR per 100 µg/L: 1.20 [1.06, 1.36]) and MetS (OR per 100 µg/L: 1.11 [1.02, 1.20]) in the total population as well as in participants without hepatic iron overload. However, the synergistic effect of higher ferritin concentrations and hepatic iron overload showed stronger associations with IGM and T2DM. Similarly, while ferritin was positively associated with T2DM and MetS even in the absence of hepatic steatosis, the synergistic effect of higher ferritin concentrations and hepatic steatosis showed stronger associations with IGM, T2DM and MetS. Transferrin was associated with isolated impaired glucose tolerance but not with T2DM and MetS.

CONCLUSIONS

Our study suggests that ferritin may be associated with glucose metabolism disorders and MetS even in people without hepatic steatosis or iron overload. However, in individuals with higher ferritin concentrations, the presence of hepatic steatosis may indicate stronger risk for glucose metabolism disorders and MetS, while the presence of hepatic iron overload may indicate stronger risk only for glucose metabolism disorders.

Serum Level of Transferrin Unique Peptide Is Decreased in Patients With Acute Ischemic Stroke

Objectives: Free irons are transported into brain tissues by transferrin and play an important role in neuronal/glial cell damage. Lower serum levels of transferrin have been found in patients with ischemic stroke, compared with healthy subjects. In present study, we investigated whether transferrin unique peptide (TF-UP) could be employed as a serum biomarker for brain tissue damage in acute ischemic stroke. Methods: The venous blood samples of 94 ischemic stroke patients and 35 brain tumor-stroke mimics (BT-SM) patients were collected within the first 72 h (Median time 23.25, Interquartile range 60.75) of acute onset in the emergency room. Total TF-UP and total albumin unique peptide (Alb-UP) were identified with liquid chromatography/mass spectrometry (LC-MS/MS) and quantified by multiple reaction monitoring (MRM) method using labeled reference peptide (LRP) for further analysis. Results: Median ratio of total TF-UP/LRP was 0.85 (Interquartile range, 0.21) in the brain tumor-stroke mimics (BT-SM) group, and 0.45 (0.14) in the ischemic stroke group; median Alb-UP/LRP ratio was 0.66 (0.16) in the BT-SM group, and 0.55 (0.20) in the ischemic stroke group. The overall trend from low to high levels was statistically significant for TF-UP/LRP (P < 0.0001), but not for Alb-UP/LRP (P = 0.1667). According to the receiver operating characteristic (ROC) curve, the area under the curve (AUC) was 0.9565 and the optimal cutoff value of serum TF-UP was 0.6317, which yielded a sensitivity of 91.49% and a specificity of 88.57%. The odds ratio (95% confidence intervals) of serum TF-UP/LRP was 83.31 (23.43, 296.22, P < 0.0001). Conclusions: Serum TF-UP/LRP level is decreased in patients with acute ischemic stroke in comparison with brain tumor, and it may serve as a serum biomarker for the neuronal/glial cell damage in cerebral infarction.

Multiplatform Approach for Plasma Proteomics: Complementarity of Olink Proximity Extension Assay Technology to Mass Spectrometry-Based Protein Profiling

The plasma proteome is the ultimate target for biomarker discovery. It stores an endless amount of information on the pathophysiological status of a living organism, which is, however, still difficult to comprehensively access. The high complexity of the plasma proteome can be addressed by either a system-wide and unbiased tool such as mass spectrometry (LC-MS/MS) or a highly sensitive targeted immunoassay such as the proximity extension assay (PEA). To address relevant differences and important shared characteristics, we tested the performance of LC-MS/MS in the data-dependent and data-independent acquisition modes and Olink PEA to measure circulating plasma proteins in 173 human plasma samples from a Southern German population-based cohort. We demonstrated the measurement of more than 300 proteins with both LC-MS/MS approaches applied, mainly including high-abundance plasma proteins. By the use of the PEA technology, we measured 728 plasma proteins, covering a broad dynamic range with high sensitivity down to pg/mL concentrations. Then, we quantified 35 overlapping proteins with all three analytical platforms, verifying the reproducibility of data distributions, measurement correlation, and gender-based differential expression. Our work highlights the limitations and the advantages of both targeted and untargeted approaches and proves their complementary strengths. We demonstrated a significant gain in proteome coverage depth and subsequent biological insight by a combination of platforms-a promising approach for future biomarker and mechanistic studies.

Association between Habitual Dietary Iron Intake and Glucose Metabolism in Individuals after Acute Pancreatitis

Dietary intake of iron is known to be associated with impaired glucose metabolism. However, its involvement in derangements of glucose metabolism after acute pancreatitis (AP) is not completely understood. The aim was to investigate the association between dietary iron intake and markers of glucose metabolism in individuals after an attack of AP. Fasting blood samples were collected to analyse markers of glucose metabolism (fasting plasma glucose (FPG) and haemoglobin A1c (HbA1c)). The EPIC-Norfolk food frequency questionnaire was used to determine the habitual intake of dietary iron (total, haem, and non-haem). Multivariable linear regression analyses were conducted and six statistical models were built to adjust for covariates. A total of 109 individuals after AP were studied in a cross-sectional fashion. Total iron (β (95% confidence interval) = -0.19 (-0.35, -0.05); p = 0.01 in the most adjusted model) and non-haem iron (β (95% confidence interval) = -0.19 (-0.33, -0.04); p = 0.03 in the most adjusted model) were significantly associated with FPG, consistently in all adjusted model. Total iron and non-haem iron did not have consistent significant associations with HbA1c. Dietary haem iron intake was not associated with either FPG or HbA1c. Habitual intake of dietary iron is inversely associated with FPG in individuals after an attack of AP and may be involved in the pathogenesis of new-onset diabetes after pancreatitis. Prospective longitudinal studies are now warranted to unveil the specific mechanism underlying the involvement of dietary iron.

Serum Transferrin Predicts New-Onset Type 2 Diabetes in Koreans: A 4-Year Retrospective Longitudinal Study

BACKGROUND

It is well known that high serum ferritin, a marker of iron storage, predicts incident type 2 diabetes. Limited information is available on the association between transferrin, another marker of iron metabolism, and type 2 diabetes. Thus, we investigated the association between transferrin and incident type 2 diabetes.

METHODS

Total 31,717 participants (mean age, 40.4±7.2 years) in a health screening program in 2005 were assessed via cross-sectional analysis. We included 30,699 subjects who underwent medical check-up in 2005 and 2009 and did not have type 2 diabetes at baseline in this retrospective longitudinal analysis.

RESULTS

The serum transferrin level was higher in the type 2 diabetes group than in the non-type 2 diabetes group (58.32±7.74 μmol/L vs. 56.17±7.96 μmol/L, P&lt;0.001). Transferrin correlated with fasting serum glucose and glycosylated hemoglobin in the correlational analysis (r=0.062, P&lt;0.001 and r=0.077, P&lt;0.001, respectively) after full adjustment for covariates. Transferrin was more closely related to homeostasis model assessment of insulin resistance than to homeostasis model assessment of β cell function (r=0.042, P&lt;0.001 and r=-0.019, P=0.004, respectively) after full adjustment. Transferrin predicted incident type 2 diabetes in non-type 2 diabetic subjects in a multivariate linear regression analysis; the odds ratio (95% confidence interval [CI]) of the 3rd tertile compared to that in the 1st tertile of transferrin for incident diabetes was 1.319 (95% CI, 1.082 to 1.607) after full adjustment (P=0.006).

CONCLUSION

Transferrin is positively associated with incident type 2 diabetes in Koreans.

Purification of pancreatic endocrine subsets reveals increased iron metabolism in beta cells

Objectives

The main endocrine cell types in pancreatic islets are alpha, beta, and delta cells. Although these cell types have distinct roles in the regulation of glucose homeostasis, inadequate purification methods preclude the study of cell type-specific effects. We developed a reliable approach that enables simultaneous sorting of live alpha, beta, and delta cells from mouse islets for downstream analyses.

Methods

We developed an antibody panel against cell surface antigens to enable isolation of highly purified endocrine subsets from mouse islets based on the specific differential expression of CD71 on beta cells and CD24 on delta cells. We rigorously demonstrated the reliability and validity of our approach using bulk and single cell qPCR, immunocytochemistry, reporter mice, and transcriptomics.

Results

Pancreatic alpha, beta, and delta cells can be separated based on beta cell-specific CD71 surface expression and high expression of CD24 on delta cells. We applied our new sorting strategy to demonstrate that CD71, which is the transferrin receptor mediating the uptake of transferrin-bound iron, is upregulated in beta cells during early postnatal weeks. We found that beta cells express higher levels of several other genes implicated in iron metabolism and iron deprivation significantly impaired beta cell function. In human beta cells, CD71 is similarly required for iron uptake and CD71 surface expression is regulated in a glucose-dependent manner.

Conclusions

This study provides a novel and efficient purification method for murine alpha, beta, and delta cells, identifies for the first time CD71 as a postnatal beta cell-specific marker, and demonstrates a central role of iron metabolism in beta cell function.

•

CD71 is a marker that is highly expressed in murine pancreatic beta-cells.

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CD71 and CD24 can be used to purify live murine alpha-, beta-, and delta-cells.

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Iron metabolism in murine beta-cells is increased compared to that in alpha-, and delta-cells.

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Human beta-cells regulate CD71 surface expression in a glucose-dependent manner.

Relationship between iron status markers and insulin resistance: an exploratory study in subjects with excess body weight

Background

Controversy exists on the relationship between iron metabolism and cardiometabolic risk. The aim of this study was to determine if there is a link between dysmetabolic iron and cardiometabolic markers in subjects with excess body weight.

Methods

Cross-sectional study with fifty participants presenting overweight or obesity and at least another metabolic syndrome factor. Determinations: anthropometry, body composition, blood pressure, lipids, glucose, insulin, leptin, areas under the curve (AUC) for glucose and insulin after an oral glucose tolerance test, hs-C reactive protein (hs-CRP), blood count, ferritin, transferrin, transferrin saturation (TSAT), soluble transferrin receptor (sTfR). Gender-adjusted linear correlations and two independent samples t tests were used.

Results

Ferritin was positively correlated with insulin-AUC (r = 0.547, p = 0.008) and TSAT was negatively correlated with waist-hip ratio (r =  − 0.385, p = 0.008), insulin (r =  − 0.551, p < 0.001), and insulin resistance (HOMA-IR, r =  − 0.586, p < 0.001). Subjects with TSAT ≤ 20% had higher insulin (p = 0.012) and HOMA-IR (p = 0.003) compared to those with TSAT > 20%. In conclusion, the observed results suggest that iron transport and storage are altered in subjects with overweight/obesity, at the same time that they exhibit the characteristic features of insulin resistance. Nevertheless, this occurs without iron overload or deficiency. These results should be validated in wider cohorts since they suggest that iron transport and storage should be assessed when performing the clinical evaluation of subjects with excess body weight.

Association of endothelial dysfunction with incident prediabetes, type 2 diabetes and related traits: the KORA F4/FF4 study

INTRODUCTION

Peripheral arterial tonometry (PAT) is an operator-independent and non-invasive measurement method to assess microvascular endothelial function in the fingertips. PAT-derived measures of endothelial function were associated with type 2 diabetes in cross-sectional studies. However, longitudinal studies are lacking. The study aims to investigate the association of two PAT-derived endothelial function parameters reactive hyperemia index (RHI) and mean baseline amplitude (MBA) with follow-up glucose and insulin parameters and the development of (pre)diabetes and type 2 diabetes.

RESEARCH DESIGN AND METHODS

The study included 673 participants initially without diabetes (328 men and 345 women) aged 52-71 years from the prospective population-based Cooperative Health Research in the Region of Augsburg F4/FF4 cohort study conducted in Southern Germany (baseline examination F4: 2006-2008; follow-up FF4: 2013-2014). An oral glucose tolerance test was performed at baseline and follow-up to define type 2 diabetes, prediabetes, fasting glucose, fasting insulin, 2-hour glucose, homeostasis model assessment of insulin resistance (HOMA-IR), homeostasis model assessment of beta-cell function and hemoglobin A1c.

RESULTS

In multivariable adjusted logistic/linear regression models, a 1 SD increase in baseline RHI was inversely associated with incident type 2 diabetes (OR 0.69 (95% CI 0.48 to 0.97)) as well as with fasting insulin (β -0.069 (95% CI -0.131 to -0.007)) and HOMA-IR (β -0.072 (95% CI -0.133 to -0.010)) at follow-up in participants with initial normoglycemia. A 1 SD increase in baseline MBA was positively associated with incident (pre)diabetes (OR 1.62 (95% CI 1.25 to 2.11)) and fasting glucose (β 0.096 (95% CI 0.047 to 0.146)) at follow-up in participants with initial normoglycemia.

CONCLUSIONS

Microvascular endothelial dysfunction seems to be involved in the development of early derangements in glucose metabolism and insulin resistance and could thereby trigger the development of prediabetes and type 2 diabetes.

Iron metabolism and type 2 diabetes mellitus: A meta-analysis and systematic review

AIMS/INTRODUCTION

Iron metabolism can directly or indirectly affect the occurrence and development of type 2 diabetes. This meta-analysis and systematic review aimed to analyze the association between serum iron metabolism indicators and type 2 diabetes.

MATERIALS AND METHODS

The databases PubMed and Embase were searched for studies on the correlations between serum iron metabolism indicators (iron, ferritin, transferrin, hepcidin and soluble transferrin receptor) and type 2 diabetes since January 2006. Relevant data were extracted from the included studies, and meta-analysis was carried out.

RESULTS

A total of 12 case-control and cohort studies were analyzed. Of the 12 studies, 11 described the correlation between serum ferritin levels and type 2 diabetes. The median and high serum ferritin concentrations were significantly associated with the risks of type 2 diabetes (odds ratio [OR] 1.20, 95% confidence interval [CI] 1.08-1.33 and OR 1.43, 95% CI 1.29-1.59, respectively). However, the low concentration was not correlated with the risk of type 2 diabetes (OR 0.99, 95% CI 0.89-1.11). No significant association was observed between serum soluble transferrin receptor and type 2 diabetes, whereas the soluble transferrin receptor-to-ferritin ratio was significantly inversely related to the risk of type 2 diabetes in the median and high ratio subgroups (OR 0.71, 95% CI 0.51, 0.99 and OR 0.65, 95% CI 0.45-0.95).

CONCLUSIONS

The elevated serum ferritin was one of the risk factors for type 2 diabetes, and soluble transferrin receptor-to-ferritin ratio was inversely related to the risk of type 2 diabetes. A systematic review showed that serum transferrin and hepcidin might be directly or indirectly related to the development of diabetes.

Role of Minerals and Trace Elements in Diabetes and Insulin Resistance

Minerals and trace elements are micronutrients that are essential to the human body but present only in traceable amounts. Nonetheless, they exhibit well-defined biochemical functions. Deficiencies in these micronutrients are related to widespread human health problems. This review article is focused on some of these minerals and trace element deficiencies and their consequences in diabetes and insulin resistance. The levels of trace elements vary considerably among different populations, contingent on the composition of the diet. In several Asian countries, large proportions of the population are affected by a number of micronutrient deficiencies. Local differences in selenium, zinc, copper, iron, chromium and iodine in the diet occur in both developed and developing countries, largely due to malnutrition and dependence on indigenous nutrition. These overall deficiencies and, in a few cases, excess of essential trace elements may lead to imbalances in glucose homeostasis and insulin resistance. The most extensive problems affecting one billion people or more worldwide are associated with inadequate supply of a number of minerals and trace elements including iodine, selenium, zinc, calcium, chromium, cobalt, iron, boron and magnesium. This review comprises various randomized controlled trials, cohort and case-controlled studies, and observational and laboratory-based studies with substantial outcomes of micronutrient deficiencies on diabetes and insulin resistance in diverse racial inhabitants from parts of Asia, Africa, and North America. Changes in these micronutrient levels in the serum and urine of subjects may indicate the trajectory toward metabolic changes, oxidative stress and provide disease-relevant information.

Associations of iron markers with type 2 diabetes mellitus and metabolic syndrome: Results from the prospective SHIP study

AIMS

To assess the role of serum ferritin and transferrin with prevalent and incident type 2 diabetes mellitus (T2DM) and metabolic syndrome (MetS) and whether these associations are independent of inflammatory markers and hepatic enzymes.

METHODS

We analyzed data from 3,232 participants aged 20-81 years of the population-based Study of Health in Pomerania (SHIP) from Northeast Germany with a median follow-up time of 10.6 years. Logistic and Cox regression analyses were performed.

RESULTS

Serum ferritin concentrations were associated with a higher prevalence of T2DM (total population OR: 1.16 [95% CI: 1.07, 1.26]; men OR: 1.18 [95% CI: 1.08, 1.30) and MetS (total population OR: 1.27 [95% CI: 1.16, 1.38]; men OR: 1.26 [95% CI: 1.15, 1.38]) in the total population and men independently of inflammatory markers and hepatic enzymes. In longitudinal analyses, baseline ferritin concentrations were associated with a higher risk of incident T2DM in women (HR: 1.38 [95% CI: 1.10, 1.71]), but not in men or in the total population and also with a higher risk of incident MetS (HR: 1.09 [95% CI: 1.01, 1.17]) in the total population. These longitudinal associations attenuated considerably after adjustment for hepatic enzymes but not inflammatory markers. Transferrin was not associated with any of the outcomes.

CONCLUSIONS

Our results suggest a link between ferritin and T2DM and MetS, which might be partially explained by hepatic dysfunction.

Biomarker-defined pathways for incident type 2 diabetes and coronary heart disease-a comparison in the MONICA/KORA study

Background

Biomarkers may contribute to our understanding of the pathophysiology of various diseases. Type 2 diabetes (T2D) and coronary heart disease (CHD) share many clinical and lifestyle risk factors and several biomarkers are associated with both diseases. The current analysis aims to assess the relevance of biomarkers combined to pathway groups for the development of T2D and CHD in the same cohort.

Methods

Forty-seven serum biomarkers were measured in the MONICA/KORA case-cohort study using clinical chemistry assays and ultrasensitive molecular counting technology. The T2D (CHD) analyses included 689 (568) incident cases and 1850 (2004) non-cases from three population-based surveys. At baseline, the study participants were 35–74 years old. The median follow-up was 14 years. We computed Cox regression models for each biomarker, adjusted for age, sex, and survey. Additionally, we assigned the biomarkers to 19 etiological pathways based on information from literature. One age-, sex-, and survey-controlled average variable was built for each pathway. We used the R²_PM coefficient of determination to assess the explained disease risk.

Results

The associations of many biomarkers, such as several cytokines or the iron marker soluble transferrin receptor (sTfR), were similar in strength for T2D and CHD, but we also observed important differences. Lipoprotein (a) (Lp(a)) and N-terminal pro B-type natriuretic peptide (NT-proBNP) even demonstrated opposite effect directions. All pathway variables together explained 49% of the T2D risk and 21% of the CHD risk. The insulin-like growth factor binding protein 2 (IGFBP-2, IGF/IGFBP system pathway) best explained the T2D risk (about 9% explained risk, independent of all other pathway variables). For CHD, the myocardial-injury- and lipid-related-pathways were most important and both explained about 4% of the CHD risk.

Conclusions

The biomarker-derived pathway variables explained a higher proportion of the T2D risk compared to CHD. The ranking of the pathways differed between the two diseases, with the IGF/IGFBP-system-pathway being most strongly associated with T2D and the myocardial-injury- and lipid-related-pathways with CHD. Our results help to better understand the pathophysiology of the two diseases, with the ultimate goal of pointing out targets for lifestyle intervention and drug development to ideally prevent both T2D and CHD development.

Glucose and insulin levels are associated with arterial stiffness and concentric remodeling of the heart

BACKGROUND

Mortality attributable to heart failure remains high. The prevalence of heart failure in patients with diabetes mellitus ranges from 19 to 26%. It is estimated that up to 21.1 million adults in the United States have diagnosed diabetes mellitus and around 80.8 million have impaired fasting glucose. We investigated the associations of fasting glucose (FG) and fasting insulin (FI), the homeostasis model assessment-insulin resistance index (HOMA-IR) and 2-h postload glucose (2HG) and insulin (2HI) with parameters of left ventricular geometry and function and arterial stiffness determined by magnetic resonance imaging in individuals without diagnosed type 2 diabetes.

METHODS

Cross-sectional analyses of 1001 individuals (453 women, 45.3%), aged 21 to 80 years, from two independent population-based studies, the Study of Health in Pomerania (SHIP-TREND-0) and KORA FF4 Study. FG, FI, HOMA-IR, 2HG and 2HI, as well as glucose tolerance categories, were analyzed for associations with heart and arterial parameters using multivariable-adjusted linear regression models.

RESULTS

In total, 390 individuals (39%) had prediabetes (isolated impaired fasting glucose, isolated glucose tolerance or both), and 49 (4.9%) were found to have unknown type 2 diabetes. In the multivariable-adjusted analysis, positive linear associations of FG, FI, HOMA-IR, 2HG and 2HI with arterial stiffness index and left ventricular wall-thickness and concentricity and inverse linear associations with left ventricular end-diastolic volume were observed. A 1 mmol/l higher FG was associated with a 1.18 ml/m^2.7 (1.80 to 0.57; p < 0.001) lower left ventricular end-diastolic volume index, a 0.042 mm/m^2.7 (0.014 to 0.070) higher left ventricular wall-thickness index, a 0.12 mmHg m^2.7/ml (0.06 to 0.17; p < 0.001) greater arterial stiffness index and a 0.037 g/ml (0.018 to 0.056; p < 0.001) higher left ventricular concentricity.

CONCLUSIONS

Our findings suggest that higher glucose levels in the prediabetic range and insulin resistance might lead to higher arterial stiffness and concentric remodeling of the heart.

Sex-Specific Association of Circulating Ferritin Level and Risk of Type 2 Diabetes: A Dose-Response Meta-Analysis of Prospective Studies

CONTEXT

Although the role of iron in the development of type 2 diabetes (T2D) has long been a concern, prospective studies directly linking body iron stores to T2D risk in a sex-dependent context have been inconsistent.

OBJECTIVE

A systematic meta-analysis was conducted to explore the sex-specific association of circulating ferritin with T2D risk.

DATA SOURCES

We searched PubMed, Web of Science, and EMBASE databases to identify available prospective studies through 1 August 2018.

RESULTS

Fifteen prospective studies comprising 77,352 participants and 18,404 patients with T2D, aged 20 to 80 years, and with ∼3 to 17 years of follow-up were identified. For each 100-μg/L increment in ferritin levels of overall participants, T2D risk increased by 22% (RR, 1.22; 95% CI, 1.14 to 1.31). Of note, major heterogeneities by sex were identified, with increased ferritin level having an apparently greater effect on T2D risk in women (RR, 1.53; 95% CI, 1.29 to 1.82) than in men (RR, 1.21; 95% CI, 1.15 to 1.27) after exclusion of a study with high heterogeneity (41,512 men and 6974 women for sex-specific analyses; P = 0.020 for sex difference). Further nonlinear analysis between circulating ferritin and T2D risk also showed sex-dimorphic association in that the T2D risk of women was twice as strong in magnitude as that of men at the same ferritin level.

CONCLUSIONS

Greater circulating ferritin levels were independently associated with increased T2D risk, which appeared stronger among women than men. Our findings provide prospective evidence for further testing of the utility of ferritin levels in predicting T2D risk in a sex-specific manner.

Protein markers and risk of type 2 diabetes and prediabetes: a targeted proteomics approach in the KORA F4/FF4 study

The objective of the present study was to identify proteins that contribute to pathophysiology and allow prediction of incident type 2 diabetes or incident prediabetes. We quantified 14 candidate proteins using targeted mass spectrometry in plasma samples of the prospective, population-based German KORA F4/FF4 study (6.5-year follow-up). 892 participants aged 42–81 years were selected using a case-cohort design, including 123 persons with incident type 2 diabetes and 255 persons with incident WHO-defined prediabetes. Prospective associations between protein levels and diabetes, prediabetes as well as continuous fasting and 2 h glucose, fasting insulin and insulin resistance were investigated using regression models adjusted for established risk factors. The best predictive panel of proteins on top of a non-invasive risk factor model or on top of HbA1c, age, and sex was selected. Mannan-binding lectin serine peptidase (MASP) levels were positively associated with both incident type 2 diabetes and prediabetes. Adiponectin was inversely associated with incident type 2 diabetes. MASP, adiponectin, apolipoprotein A-IV, apolipoprotein C-II, C-reactive protein, and glycosylphosphatidylinositol specific phospholipase D1 were associated with individual continuous outcomes. The combination of MASP, apolipoprotein E (apoE) and adiponectin improved diabetes prediction on top of both reference models, while prediabetes prediction was improved by MASP plus CRP on top of the HbA1c model. In conclusion, our mass spectrometric approach revealed a novel association of MASP with incident type 2 diabetes and incident prediabetes. In combination, MASP, adiponectin and apoE improved type 2 diabetes prediction beyond non-invasive risk factors or HbA1c, age and sex.

No effects without causes: the Iron Dysregulation and Dormant Microbes hypothesis for chronic, inflammatory diseases

Since the successful conquest of many acute, communicable (infectious) diseases through the use of vaccines and antibiotics, the currently most prevalent diseases are chronic and progressive in nature, and are all accompanied by inflammation. These diseases include neurodegenerative (e.g. Alzheimer's, Parkinson's), vascular (e.g. atherosclerosis, pre-eclampsia, type 2 diabetes) and autoimmune (e.g. rheumatoid arthritis and multiple sclerosis) diseases that may appear to have little in common. In fact they all share significant features, in particular chronic inflammation and its attendant inflammatory cytokines. Such effects do not happen without underlying and initially 'external' causes, and it is of interest to seek these causes. Taking a systems approach, we argue that these causes include (i) stress-induced iron dysregulation, and (ii) its ability to awaken dormant, non-replicating microbes with which the host has become infected. Other external causes may be dietary. Such microbes are capable of shedding small, but functionally significant amounts of highly inflammagenic molecules such as lipopolysaccharide and lipoteichoic acid. Sequelae include significant coagulopathies, not least the recently discovered amyloidogenic clotting of blood, leading to cell death and the release of further inflammagens. The extensive evidence discussed here implies, as was found with ulcers, that almost all chronic, infectious diseases do in fact harbour a microbial component. What differs is simply the microbes and the anatomical location from and at which they exert damage. This analysis offers novel avenues for diagnosis and treatment.

The Study on the Correlation Between Six Kinds of Mineral Elements and Diabetes

The study aimed to explore the relationship of six kinds of mineral elements and diabetes among adults in northeast China. A cross-sectional survey was conducted in Jilin Province, northeast China. A total of 366 males and 204 females aged 18 ~ 77 years from Jingyu town, Dongliao town, and Changling town were included using a multistage stratified random cluster sampling design. Data was obtained from face to face interview, physical examination, and laboratory measurement. We defined the normal people (3.9 ~ 6.0 mmol/L), impaired fasting glucose (IFG) individuals (6.1 ~ 6.9 mmol/L), and diabetes mellitus (DM) (> 7.0 mmol/L) according to the WHO diagnostic criteria. Kruskal-Wallis test, Spearman rank correlation, as well as binary logistic regression were used to analyze influencing factors. lg(Cu/Zn)was correlated with DM (OR 8.390; 95% CI of OR 1.272-55.347). The specific mineral elements such as Zn, Ca, as well as Cu/Zn ratio may be the potential risk factors for diabetes. So, the supplement or reduction of these elements is supposed to be told to IFG to prevent or delay the occurrence of diabetes or DM to avoid its complication.

Insulin Sensitivity and Glucose Homeostasis Can Be Influenced by Metabolic Acid Load

Recent epidemiological findings suggest that high levels of dietary acid load can affect insulin sensitivity and glucose metabolism. Consumption of high protein diets results in the over-production of metabolic acids which has been associated with the development of chronic metabolic disturbances. Mild metabolic acidosis has been shown to impair peripheral insulin action and several epidemiological findings suggest that metabolic acid load markers are associated with insulin resistance and impaired glycemic control through an interference intracellular insulin signaling pathways and translocation. In addition, higher incidence of diabetes, insulin resistance, or impaired glucose control have been found in subjects with elevated metabolic acid load markers. Hence, lowering dietary acid load may be relevant for improving glucose homeostasis and prevention of type 2 diabetes development on a long-term basis. However, limitations related to patient acid load estimation, nutritional determinants, and metabolic status considerably flaws available findings, and the lack of solid data on the background physiopathology contributes to the questionability of results. Furthermore, evidence from interventional studies is very limited and the trials carried out report no beneficial results following alkali supplementation. Available literature suggests that poor acid load control may contribute to impaired insulin sensitivity and glucose homeostasis, but it is not sufficiently supportive to fully elucidate the issue and additional well-designed studies are clearly needed.

Elevated serum ferritin concentration is associated with incident type 2 diabetes mellitus in a Chinese population: A prospective cohort study

AIMS

We aimed to evaluate the association between serum ferritin levels and incident type 2 diabetes mellitus risk in a Chinese population.

METHODS

This cohort study assessed 2225 Chinese individuals aged 25-75 years. Diabetes mellitus was diagnosed using the 1999 World Health Organization definition with a median follow-up period of 20 months. Cox proportional hazard models were used to estimate adjusted hazard ratios and 95% confidence intervals (CI) for incident diabetes when serum ferritin concentrations increased by one standard deviation.

RESULTS

During the follow-up period, 112 cases (62 men and 50 women) of type 2 diabetes mellitus were identified. Baseline serum ferritin levels were higher in the diabetes than the non-diabetes group. After adjusting for age, body mass index, waist circumference, mean arterial pressure, fasting plasma glucose, fasting insulin, hemoglobin A1c, total cholesterol, high-density lipoprotein cholesterol, alanine transaminase and triglyceride levels, family history of diabetes mellitus, pork meat consumption, neutrophil/lymphocyte ratio, education, and annual household income, the hazard ratios for incident diabetes corresponding to one standard deviation increase in serum ferritin levels were 1.17 (95% CI 1.03, 1.34), 1.20 (95% CI 1.003, 1.43), and 1.03 (95% CI 0.82, 1.31) for the total population, men, and women, respectively.

CONCLUSIONS

High serum ferritin levels were associated with a higher risk of incident type 2 diabetes mellitus independent of traditional risk factors in the total population and men.

Prediabetes is associated with microalbuminuria, reduced kidney function and chronic kidney disease in the general population: The KORA (Cooperative Health Research in the Augsburg Region) F4-Study

BACKGROUND AND AIMS

We investigated the associations of serum fasting (FG) and 2-h postload (2HG) glucose from an oral glucose tolerance test (OGTT), glycated hemoglobin (HbA1c), fasting insulin and the homeostasis model assessment-insulin resistance index (HOMA-IR) with urinary albumin-to-creatinine ratio (ACR) and estimated glomerular filtration rate (eGFR).

METHODS AND RESULTS

We performed cross-sectional analyses of 2713 subjects (1429 women; 52.7%) without known type 2 diabetes, aged 31-82 years, from the KORA (Cooperative Health Research in the Augsburg Region) F4-Study. FG, 2HG, HbA1c, fasting insulin, HOMA-IR and glucose tolerance categories were analyzed for association with ACR and eGFR in multivariable adjusted linear and median regression models, and with isolated microalbuminuria (i-MA), isolated reduced kidney function (i-RKF) and chronic kidney disease (CKD, defined as MA and/or RKF) in multivariable adjusted logistic regression models. Among the 2713 study participants, 28% revealed prediabetes (isolated impaired fasting glucose [i-IFG], isolated glucose tolerance [i-IGT] or both by American Diabetes Association definition), 4.2% had unknown type 2 diabetes, 6.5% had i-MA, 3.1% i-RKF and 10.9% CKD. In multivariable adjusted analysis, all continuous variables (FG, 2HG, HbA1c, fasting insulin and HOMA-IR) were associated with i-MA, i-RKF and CKD. The odds ratios (ORs) for i-MA and CKD were 1.54 (95% confidence interval: 1.02-2.33) and 1.58 (1.10-2.25) for individuals with i-IFG. Moreover, the OR for i-RKF was 2.57 (1.31-5.06) for individuals with IFG + IGT.

CONCLUSION

Our findings suggest that prediabetes might have harmful effects on the kidney.

Iron reduction response and demographic differences between diabetics and non-diabetics with cardiovascular disease entered into a controlled clinical trial

Filings of elemental iron separated magnetically from a homogenate of breakfast cereal implicated in the risk of cardiovascular disease and diabetes.

Prediabetes is associated with lower brain gray matter volume in the general population. The Study of Health in Pomerania (SHIP)

BACKGROUND AND AIMS

We investigated the associations of fasting (FG) and 2-h postload (2HG) plasma glucose from oral glucose tolerance test (OGTT) with gray (GMV) and white (WMV) matter volume.

METHODS AND RESULTS

We analyzed data from 1330 subjects without known diabetes mellitus, aged 21 to 81, from the second cohort (SHIP-Trend-0) of the population-based Study of Health in Pomerania (SHIP). Following the OGTT, individuals were classified in five groups (according to the American Diabetes Association criteria): normal glucose tolerance (NGT), isolated impaired fasting glucose (i-IFG), isolated impaired glucose tolerance (i-IGT), combined IFG and IGT (IFG + IGT) and unknown type 2 diabetes mellitus (UDM). GMV and WMV were determined by magnetic resonance imaging. FG, 2HG and OGTT groups were associated with GMV and WMV by linear regression models adjusted for confounders. FG and 2HG were inversely associated with GMV. The adjusted mean GMV, when compared with the NGT group (584 ml [95% CI: 581 to 587]), was significantly lower in the groups i-IFG (578 ml [95% CI: 573 to 582]; p = 0.035) and UDM (562 ml [95% CI: 551 to 573]; p < 0.001), but not different in the i-IGT (586 ml [95% CI: 576 to 596]; p = 0.688) and IFG + IGT (579 ml [95% CI: 571 to 586]; p = 0.209) groups. There were no associations of FG, 2HG and OGTT parameters with WMV.

CONCLUSION

Our findings suggest that elevated FG levels, even within the prediabetic range, might already have some harmful effects on GMV.

Uncoupled iron homeostasis in type 2 diabetes mellitus

Diabetes mellitus is frequently associated with iron overload conditions, such as primary and secondary hemochromatosis. Conversely, patients affected by type 2 diabetes mellitus (T2DM) show elevated ferritin levels, a biomarker for increased body iron stores. Despite these documented associations between dysregulated iron metabolism and T2DM, the underlying mechanisms are poorly understood. Here, we show that T2DM patients have reduced serum levels of hepcidin, the iron-regulated hormone that maintains systemic iron homeostasis. Consistent with this finding, we also observed an increase in circulating iron and ferritin levels. Our analysis of db/db mice demonstrates that this model recapitulates the systemic alterations observed in patients. Interestingly, db/db mice show an overall hepatic iron deficiency despite unaltered expression of ferritin and the iron importer TfR1. In addition, the liver correctly senses increased circulating iron levels by activating the BMP/SMAD signaling pathway even though hepcidin expression is decreased. We show that increased AKT phosphorylation may override active BMP/SMAD signaling and decrease hepcidin expression in 10-week old db/db mice. We conclude that the metabolic alterations occurring in T2DM impact on the regulation of iron homeostasis on multiple levels. As a result, metabolic perturbations induce an "iron resistance" phenotype, whereby signals that translate increased circulating iron levels into hepcidin production, are dysregulated.

KEY MESSAGES

T2DM patients show increased circulating iron levels. T2DM is associated with inappropriately low hepcidin levels. Metabolic alterations in T2DM induce an "iron resistance" phenotype.

Soluble transferrin receptor and risk of type 2 diabetes in the obese and nonobese

BACKGROUND

Studies evaluating the relationship between soluble transferrin receptor (sTfR), a biomarker inversely related to body iron stores, and risk of type 2 diabetes mellitus (T2DM) are scarce and inconclusive. Furthermore, sTfR concentrations have been observed to be significantly higher in obese than in nonobese individuals. Therefore, the aim of this study was to assess the relationship between sTfR and the risk of T2DM in obese and nonobese subjects.

DESIGN

A nested case-control study of 153 cases of newly diagnosed diabetic subjects, 73 obese and 80 nonobese, and 306 individually matched controls, 138 obese and 166 nonobese, who did not develop T2DM for a median 6-year follow-up (interquartile range: 3·9-6·5) was conducted using data from the PREvention with MEDiterranean Diet (PREDIMED) cohort (http://www.controlled-trials.com/ISRCTN35739639). Cases and controls were matched for age (≤ 67 vs. > 67 years), gender, dietary intervention group and BMI (≤ 27 vs. > 27 kg/m² ).

RESULTS

Waist circumference is the main determinant of sTfR concentrations in the whole sample (β = 0·476, P < 0·001), in the obese (β = 0·802, P < 0·001) and the nonobese (β = 0·455, P = 0·003). Furthermore, sTfR is directly associated with the risk of T2DM in obese individuals (OR = 2·79; 95% CI: 1·35-5·77, P = 0·005) and inversely associated in nonobese individuals (OR = 0·40; 95% CI: 0·20-0·79, P = 0·015).

CONCLUSIONS

The association between sTfR levels and risk of T2DM in a population at high cardiovascular risk depend on the presence or absence of obesity. While in nonobese subjects elevated sTfR levels are associated with a decreased risk of developing T2DM, in obese subjects the risk increases. This suggests that obesity alters the relationship between sTfR and T2DM incidence.

Diabetes in HFE Hemochromatosis

Diabetes in whites of European descent with hemochromatosis was first attributed to pancreatic siderosis. Later observations revealed that the pathogenesis of diabetes in HFE hemochromatosis is multifactorial and its clinical manifestations are heterogeneous. Increased type 2 diabetes risk in HFE hemochromatosis is associated with one or more factors, including abnormal iron homeostasis and iron overload, decreased insulin secretion, cirrhosis, diabetes in first-degree relatives, increased body mass index, insulin resistance, and metabolic syndrome. In p.C282Y homozygotes, serum ferritin, usually elevated at hemochromatosis diagnosis, largely reflects body iron stores but not diabetes risk. In persons with diabetes type 2 without hemochromatosis diagnoses, serum ferritin levels are higher than those of persons without diabetes, but most values are within the reference range. Phlebotomy therapy to achieve iron depletion does not improve diabetes control in all persons with HFE hemochromatosis. The prevalence of type 2 diabetes diagnosed today in whites of European descent with and without HFE hemochromatosis is similar. Routine iron phenotyping or HFE genotyping of patients with type 2 diabetes is not recommended. Herein, we review diabetes in HFE hemochromatosis and the role of iron in diabetes pathogenesis in whites of European descent with and without HFE hemochromatosis.

Iron Profile and Glycaemic Control in Patients with Type 2 Diabetes Mellitus

Iron overload is increasingly being connected to insulin resistance in Type 2 Diabetes Mellitus (T2DM) patients. Free iron causes the assembly of reactive oxygen species that invariably steer the body’s homeostasis towards oxidative stress-mediated diabetic complications. This study aims to assess the serum iron, total iron binding capacity (TIBC), and percentage transferrin saturation (Tsat) of 150 subjects divided into three groups (I,II,III) of 50. Healthy individuals (controls) constituted Group I. Group II consisted of T2DM patients with optimal glycaemic control. T2DM patients with suboptimal glycaemic control formed group III. Mean serum free iron concentration was 105.34 ± 3.5, 107.33 ± 3.45, and 125.58 ± 3.45 μg/dL in Group I, Group II, and Group III, respectively. Mean serum TIBC concentration in Group I, Group II, and Group III was 311.39 ± 5.47, 309.63 ± 6.1, and 284.2 ± 3.18μg/dL, respectively. Mean serum transferrin saturation (%) in Group I, Group II, and Group III was 34.17 ± 1.21, 35.02 ± 1.2, and 44.39 ± 1.07, respectively. The difference between TIBC, mean serum free iron concentration, and transferrin saturation between Group I and Group III (for all, p values <0.001), as well as between Group II and Group III (p values 0.0012, 0.0015, and <0.0001, respectively) was statistically significant. The fasting plasma glucose values of Groups II and III were significantly higher than those of Group I, (p < 0.0001). Glycated haemoglobin (HbA1c) values were also shown to increase from Group I to II and then III, and the increase was highly significant (all p values <0.0001). Thus, decreased glycaemic control and an increase in the glycation of haemoglobin was the key to elevation in serum iron values and alterations in other parameters. However, a significant correlation was absent between serum iron and HbA1c (r = 0.05) and transferrin saturation (r = 0.0496) in Group III.

Iron and non-alcoholic fatty liver disease

The mechanisms that promote liver injury in non-alcoholic fatty liver disease (NAFLD) are yet to be thoroughly elucidated. As such, effective treatment strategies are lacking and novel therapeutic targets are required. Iron has been widely implicated in the pathogenesis of NAFLD and represents a potential target for treatment. Relationships between serum ferritin concentration and NAFLD are noted in a majority of studies, although serum ferritin is an imprecise measure of iron loading. Numerous mechanisms for a pathogenic role of hepatic iron in NAFLD have been demonstrated in animal and cell culture models. However, the human data linking hepatic iron to liver injury in NAFLD is less clear, with seemingly conflicting evidence, supporting either an effect of iron in hepatocytes or within reticulo-endothelial cells. Adipose tissue has emerged as a key site at which iron may have a pathogenic role in NAFLD. Evidence for this comes indirectly from studies that have evaluated the role of adipose tissue iron with respect to insulin resistance. Adding further complexity, multiple strands of evidence support an effect of NAFLD itself on iron metabolism. In this review, we summarise the human and basic science data that has evaluated the role of iron in NAFLD pathogenesis.

Soluble transferrin receptor levels are positively associated with insulin resistance but not with the metabolic syndrome or its individual components

The metabolic syndrome (MetS) is known to be associated with elevated serum ferritin levels. The possible association with other Fe markers has been less well studied. We aimed to investigate the cross-sectional association of soluble transferrin receptor (sTfR) and ferritin levels with the MetS components, insulin resistance and glycosylated Hb (HbA1C). The sample consisted of 725 adults, aged 19-93 years (284 men, 151 premenopausal and 290 postmenopausal women), from the Croatian island of Vis. Serum sTfR and ferritin levels were measured by immunoturbidimetry and electrochemiluminescence assays, respectively. The MetS was defined using modified international consensus criteria. Logistic and linear regression analyses were conducted to investigate the associations adjusting for age, fibrinogen, smoking status, alcohol consumption and BMI. Prevalence of the MetS was 48·7 %. Standardised values of ferritin were positively associated with all of the MetS components (except high blood pressure and waist circumference) in men (P0·05). sTfR levels could be spuriously elevated in subjects with insulin resistance and without association with the MetS or its components. We conclude that different markers of Fe metabolism are not consistently associated with cardiometabolic risk.

MASP1, THBS1, GPLD1 and ApoA-IV are novel biomarkers associated with prediabetes: the KORA F4 study

AIMS/HYPOTHESIS

Individuals at a high risk of type 2 diabetes demonstrate moderate impairments in glucose metabolism years before the clinical manifestation of type 2 diabetes, a state called 'prediabetes'. In order to elucidate the pathophysiological processes leading to type 2 diabetes, we aimed to identify protein biomarkers associated with prediabetes.

METHODS

In a proteomics study, we used targeted selected reaction monitoring (SRM)-MS to quantify 23 candidate proteins in the plasma of 439 randomly selected men and women aged 47-76 years from the population-based German KORA F4 study. Cross-sectional associations of protein levels with prediabetes (impaired fasting glucose and/or impaired glucose tolerance), type 2 diabetes, glucose levels in both the fasting state and 2 h after an OGTT, fasting insulin and insulin resistance were investigated using regression models adjusted for technical covariables, age, sex, BMI, smoking, alcohol intake, physical inactivity, actual hypertension, triacylglycerol levels, total cholesterol/HDL-cholesterol ratio, and high-sensitivity C-reactive protein levels.

RESULTS

Mannan-binding lectin serine peptidase 1 (MASP1; OR per SD 1.77 [95% CI 1.26, 2.47]), thrombospondin 1 (THBS1; OR per SD 1.55 [95% CI 1.16, 2.07]) and glycosylphosphatidylinositol-specific phospholipase D1 (GPLD1; OR per SD 1.40 [95% CI 1.01, 1.94]) were positively associated with prediabetes, and apolipoprotein A-IV (ApoA-IV; OR per SD 0.75 [95% CI 0.56, 1.00]) was inversely associated with prediabetes. MASP1 was positively associated with fasting and 2 h glucose levels. ApoA-IV was inversely and THBS1 was positively associated with 2 h glucose levels. MASP1 associations with prediabetes and fasting glucose resisted Bonferroni correction. Type 2 diabetes associations were partly influenced by glucose-lowering medication.

CONCLUSIONS/INTERPRETATION

We discovered novel and independent associations of prediabetes and related traits with MASP1, and some evidence for associations with THBS1, GPLD1 and ApoA-IV, suggesting a role for these proteins in the pathophysiology of type 2 diabetes.

Association of Multiple Biomarkers of Iron Metabolism and Type 2 Diabetes: The EPIC-InterAct Study

OBJECTIVE

Observational studies show an association between ferritin and type 2 diabetes (T2D), suggesting a role of high iron stores in T2D development. However, ferritin is influenced by factors other than iron stores, which is less the case for other biomarkers of iron metabolism. We investigated associations of ferritin, transferrin saturation (TSAT), serum iron, and transferrin with T2D incidence to clarify the role of iron in the pathogenesis of T2D.

RESEARCH DESIGN AND METHODS

The European Prospective Investigation into Cancer and Nutrition-InterAct study includes 12,403 incident T2D cases and a representative subcohort of 16,154 individuals from a European cohort with 3.99 million person-years of follow-up. We studied the prospective association of ferritin, TSAT, serum iron, and transferrin with incident T2D in 11,052 cases and a random subcohort of 15,182 individuals and assessed whether these associations differed by subgroups of the population.

RESULTS

Higher levels of ferritin and transferrin were associated with a higher risk of T2D (hazard ratio [HR] [95% CI] in men and women, respectively: 1.07 [1.01-1.12] and 1.12 [1.05-1.19] per 100 μg/L higher ferritin level; 1.11 [1.00-1.24] and 1.22 [1.12-1.33] per 0.5 g/L higher transferrin level) after adjustment for age, center, BMI, physical activity, smoking status, education, hs-CRP, alanine aminotransferase, and γ-glutamyl transferase. Elevated TSAT (≥45% vs. <45%) was associated with a lower risk of T2D in women (0.68 [0.54-0.86]) but was not statistically significantly associated in men (0.90 [0.75-1.08]). Serum iron was not associated with T2D. The association of ferritin with T2D was stronger among leaner individuals (Pinteraction < 0.01).

CONCLUSIONS

The pattern of association of TSAT and transferrin with T2D suggests that the underlying relationship between iron stores and T2D is more complex than the simple link suggested by the association of ferritin with T2D.

Risk Factors for Insulin Resistance, Metabolic Syndrome, and Diabetes in 248 HFE C282Y Homozygotes Identified by Population Screening in the HEIRS Study

BACKGROUND

We sought to identify risk factors for insulin resistance, metabolic syndrome (MetS), and diabetes mellitus in 248 non-Hispanic white HFE C282Y homozygotes identified by population screening.

METHODS

We analyzed observations obtained prospectively in a postscreening examination: age; sex; body mass index (BMI); systolic/diastolic blood pressure; metacarpophalangeal (MP) joint hypertrophy; hepatomegaly; complete blood counts; alanine/aspartate aminotransferase levels; elevated C-reactive protein (>0.5 mg/dL); transferrin saturation; serum ferritin; homeostasis model assessment-insulin resistance (HOMA-IR); and MetS.

RESULTS

Twenty-six participants (10.5%) had diabetes diagnoses. A significant trend across HOMA-IR quartiles was observed only for blood neutrophils. Logistic regression on HOMA-IR fourth quartile revealed positive associations: age (P = 0.0002); male sex (P = 0.0022); and BMI (P < 0.0001). HOMA-IR fourth quartile predicted MetS (P < 0.0001). Logistic regression on diabetes revealed positive associations: age (P = 0.0012); male sex (P = 0.0068); MP joint hypertrophy (P = 0.0167); neutrophils (P = 0.0342); and MetS (P = 0.0298). Serum ferritin did not predict HOMA-IR fourth quartile, MetS, or diabetes.

CONCLUSIONS

In screening C282Y homozygotes, age, male sex, and BMI predicted HOMA-IR fourth quartile. HOMA-IR fourth quartile alone predicted MetS. Diabetes was associated with greater age, male sex, MP joint hypertrophy, greater blood neutrophil counts, and MetS.