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

Cornelia Huth, Simon Beuerle, Astrid Zierer, Margit Heier, Christian Herder, Thorsten Kaiser, Wolfgang Koenig, Florian Kronenberg, Konrad Oexle, Wolfgang Rathmann, Michael Roden, Sigrid Schwab, Jochen Seissler, Doris Stöckl, Christa Meisinger, Annette Peters, and Barbara Thorand

Objective

Iron has been suggested to play a role in the etiology of type 2 diabetes mellitus (T2DM). Except for ferritin, evidence is sparse for other markers of iron metabolism that are regulated differently and might act through independent pathways. We therefore investigated the associations of serum ferritin, transferrin, soluble transferrin receptor (sTfR), transferrin saturation (TSAT), sTfR-to-log10ferritin (sTfR-F) index, and iron with impaired glucose metabolism (IGM/‘prediabetes’), T2DM, and four continuous glucose and insulin traits.

Design and methods

Data from 2893 participants of the population-based Cooperative Health Research in the Region of Augsburg (KORA) F4 study (Germany) was investigated through regression analysis. The results were adjusted for socio-demographic, life-style, and obesity measures as well as metabolic, inflammatory, and other iron biomarkers following a step-wise approach. Non-linearity was tested by adding a non-linear spline component to the model.

Results

Ferritin and transferrin were positively associated with IGM (fourth vs first sex-specific quartile: ferritin odds ratio (OR)=2.08 (95% CI 1.43–3.04) and transferrin OR=1.89 (95% CI 1.32–2.70)), T2DM (ferritin OR=1.98 (95% CI 1.22–3.22) and transferrin OR=2.42 (95% CI 1.54–3.81)), and fasting as well as 2-h glucose. TSAT (OR=0.55 (95% CI 0.34–0.88)) and iron (OR=0.61 (95% CI 0.38–0.97)) were inversely associated with T2DM, sTfR-F-index was inversely associated with IGM (OR=0.67 (95% CI 0.48–0.95)). There was no strong evidence for non-linear relationships.

Conclusions

The observed associations of several markers of iron metabolism with hyperglycemia and insulin resistance suggest that iron stores as well as iron-related metabolic pathways contribute to the pathogenesis of IGM and T2DM. Moreover, TSAT levels are decreased in T2DM patients.

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Adiponectin, markers of subclinical inflammation and nerve conduction in individuals with recently diagnosed type 1 and type 2 diabetes

Imke Schamarek, Christian Herder, Bettina Nowotny, Maren Carstensen-Kirberg, Klaus Straßburger, Peter Nowotny, Alexander Strom, Sonja Püttgen, Karsten Müssig, Julia Szendroedi, Michael Roden, Dan Ziegler, and on behalf of the German Diabetes Study Group

Objective

Subclinical inflammation has been implicated in the development of diabetic sensorimotor polyneuropathy (DSPN), but studies using electrophysiological assessment as outcomes are scarce. Therefore, we aimed to investigate associations of biomarkers reflecting different aspects of subclinical inflammation with motor and sensory nerve conduction velocity (NCV) in individuals with diabetes.

Design and methods

Motor and sensory NCV was assessed in individuals with recently diagnosed type 2 (n=352) or type 1 diabetes (n=161) from the baseline cohort of the observational German Diabetes Study. NCV sum scores were calculated for median, ulnar and peroneal motor as well as median, ulnar and sural sensory nerves. Associations between inflammation-related biomarkers, DSPN and NCV sum scores were estimated using multiple regression models.

Results

In type 2 diabetes, high serum interleukin (IL)-6 was associated with the presence of DSPN and reduced motor NCV. Moreover, higher levels of high-molecular weight (HMW) adiponectin, total adiponectin and their ratio were associated with prevalent DSPN and both diminished motor and sensory NCV, whereas no consistent associations were observed for C-reactive protein, IL18, soluble intercellular adhesion molecule-1 and E-selectin. In type 1 diabetes, only HMW and total adiponectin showed positive associations with motor NCV.

Conclusions

Our results point to a link between IL6 and both DSPN and slowed motor NCV in recently diagnosed type 2 diabetes. The reverse associations between adiponectin and NCV in type 1 and type 2 diabetes are intriguing, and further studies should explore whether they may reflect differences in the pathogenesis of DSPN in both diabetes types.

Free access

The multi-ligand somatostatin analogue SOM230 inhibits ACTH secretion by cultured human corticotroph adenomas via somatostatin receptor type 5

Leo J Hofland, Joost van der Hoek, Richard Feelders, Maarten O van Aken, Peter M van Koetsveld, Marlijn Waaijers, Diana Sprij-Mooij, Christian Bruns, Gisbert Weckbecker, Wouter W de Herder, Albert Beckers, and Steven W J Lamberts

Objective: Currently, there is no effective medical treatment for patients with pituitary-dependent Cushing’s disease. A novel somatostatin (SS) analogue, named SOM230, with high binding affinity to SS receptor subtypes sst1, sst2, sst3 and sst5 was recently introduced. We compared the in vitro effects of the sst2-preferring SS analogue octreotide (OCT) and the multi-ligand SOM230 on ACTH release by human and mouse corticotroph tumour cells.

Methods: By quantitative RT-PCR the sst subtype expression level was determined in human corticotroph adenomas. In vitro, the inhibitory effect of OCT and SOM230 on ACTH release by dispersed human corticotroph adenoma cells and mouse AtT20 corticotroph adenoma cells was determined. In addition, the influence of dexamethasone on the responsiveness to OCT and SOM230 was studied.

Results: Corticotroph adenomas expressed predominantly sst5 mRNA (six out of six adenomas), whereas sst2 mRNA expression was detected at significantly lower levels. In a 72 h incubation with 10 nmol/l SOM230, ACTH release was inhibited in three out of five cultures (range −30 to −40%). Ten nmol/l OCT slightly inhibited ACTH release in only one of five cultures (− 28%). In AtT20 cells, expressing sst2, sst3 and sst5, SOM230 inhibited ACTH secretion with high potency (IC50 0.2 nmol/l). Dexamethasone (10 nmol/l) pre-treatment did not influence the sensitivity of the cells to the inhibitory effect of SOM230, suggesting that sst5 is relatively resistant to negative control by glucocorticoids.

Conclusions: The selective expression of sst5 receptors in corticotroph adenomas and the preferential inhibition of ACTH release by human corticotroph adenoma cells by SOM230 in vitro, suggest that SOM230 may have potential in the treatment of patients with pituitary-dependent Cushing’s disease.