Hepcidin levels in diabetes mellitus and polycystic ovary syndrome.

AIM: Increased body iron is associated with insulin resistance. Hepcidin is the key hormone that negatively regulates iron homeostasis. We hypothesized that individuals with insulin resistance have inadequate hepcidin levels for their iron load. METHODS: Serum concentrations of the active form of hepcidin (hepcidin-25) and hepcidin:ferritin ratio were evaluated in participants with Type 2 diabetes (n = 33, control subjects matched for age, gender and BMI, n = 33) and participants with polycystic ovary syndrome (n = 27, control subjects matched for age and BMI, n = 16). To investigate whether any changes observed were associated with insulin resistance rather than insulin deficiency or hyperglycaemia per se, the same measurements were made in participants with Type 1 diabetes (n = 28, control subjects matched for age, gender and BMI, n = 30). Finally, the relationship between homeostasis model assessment of insulin resistance and serum hepcidin:ferritin ratio was explored in overweight or obese participants without diabetes (n = 16). RESULTS: Participants with Type 2 diabetes had significantly lower hepcidin and hepcidin:ferritin ratio than control subjects (P < 0.05 and P < 0.01, respectively). Participants with polycystic ovary syndrome had a significantly lower hepcidin:ferritin ratio than control subjects (P < 0.05). There was no significant difference in hepcidin or hepcidin:ferritin ratio between participants with Type 1 diabetes and control subjects (P = 0.88 and P = 0.94). Serum hepcidin:ferritin ratio inversely correlated with homeostasis model assessment of insulin resistance (r = -0.59, P < 0.05). CONCLUSION: Insulin resistance, but not insulin deficiency or hyperglycaemia per se, is associated with inadequate hepcidin levels. Reduced hepcidin concentrations may cause increased body iron stores in insulin-resistant states.

Development of a novel immunoassay for the iron regulatory peptide hepcidin.

To date there have been few published immunoassays for the important iron regulator hepcidin. This study describes a novel competitive radioimmunoassay (RIA) for the bioactive hepcidin peptide. A rabbit anti-hepcidin polyclonal antibody was produced using synthetic hepcidin radiolabelled with 125I to produce a competitive RIA. Normal patient (n=47) samples were collected and assayed for hepcidin to determine a reference range. Other patient groups collected were ulcerative colitis (UC; n=40), iron deficiency anaemia (IDA; n=15), chronic kidney disease not requiring dialysis (CKD; n=45) and chronic kidney disease requiring dialysis (HCKD; n=94). Detection limit of the assay was determined as 0.6 ng/mL. Intra-assay precision was 5 ng/mL (7.2%) and 50 ng/mL (5.8%), interassay precision was 5 ng/mL (7.6%) and 50 ng/mL (6.7%). Analytical recovery was 98% (5 ng/mL), 94% (10 ng/mL) and 97% (50 ng/mL). The assay was linear up to 200 ng/mL. No demonstrable cross-reactivity with human insulin, glucagon I, angiotensinogen I, beta-defensin 1-4, alpha-defensin-1 and plectasin was observed. There was significant correlation (r=0.96, P < or = 0.0001) between the hepcidin RIA and an established hepcidin SELDI-TOF-MS method. Analysis of the normal human samples gave a reference range of 1.1-55 ng/mL for hepcidin. Further statistical evaluation revealed a significant difference between male and female hepcidin levels. There was significant correlation between hepcidin and ferritin in the control group (r=0.6, P < or = 0.0001). There was also a significant difference between the normal and disease groups (P < or = 0.0001). Healthy volunteers (n=10) showed a diurnal increase in plasma hepcidin at 4.00 pm compared to 8.00 am. A robust and optimised immunoassay for bioactive hepcidin has been produced and the patient sample results obtained further validates the important role of hepcidin in iron regulation, and will allow further investigation of this important peptide and its role in iron homeostasis.

Alarin stimulates food intake and gonadotrophin release in male rats.

BACKGROUND AND PURPOSE: Alarin is a recently discovered member of the galanin peptide family encoded by a splice variant of galanin-like peptide (GALP) mRNA. Galanin and GALP regulate energy homeostasis and reproduction. We therefore investigated the effects of alarin on food intake and gonadotrophin release. EXPERIMENTAL APPROACH: Alarin was administered into the third cerebral ventricle (i.c.v.) of rats, and food intake or circulating hormone levels were measured. The effect of alarin on the hypothalamo-pituitary-gonadal axis was investigated in vitro using hypothalamic and anterior pituitary explants, and immortalized cell lines. Receptor binding assays were used to determine whether alarin binds to galanin receptors. KEY RESULTS: The i.c.v. administration of alarin (30 nmol) to ad libitum fed male rats significantly increased acute food intake to 500%, and plasma luteinizing hormone (LH) levels to 170% of responses to saline. In vitro, 100 nM alarin stimulated neuropeptide Y (NPY) and gonadotrophin-releasing hormone (GnRH) release from hypothalamic explants from male rats, and 1000 nM alarin increased GnRH release from GT1-7 cells. In vivo, pretreatment with the GnRH receptor antagonist cetrorelix prevented the increase in plasma LH levels observed following i.c.v. alarin administration. Receptor binding studies confirmed alarin did not bind to any known galanin receptor, or compete with radiolabelled galanin for hypothalamic binding sites. CONCLUSIONS AND IMPLICATIONS: These results suggest alarin is a novel orexigenic peptide, and that it increases circulating LH levels via hypothalamic GnRH. Further work is required to identify the receptor(s) mediating the biological effects of alarin.