Yukiko Hasuike

Determinants of Hepcidin in Patients on Maintenance Hemodialysis: Role of Inflammation

Background/Aim: Hepcidin could be one of the most important regulators for iron metabolism in patients on maintenance hemodialysis (MHD). The factors affecting serum hepcidin levels were evaluated among indexes of anemia, iron metabolism, or inflammation, as well as the dose of erythropoietin. Methods: 198 MHD patients treated with recombinant human erythropoietin were recruited and serum hepcidin-25 levels were specifically measured by liquid chromatography tandem mass spectrometry. Results: In multivariate analysis, only transferrin and ferritin were selected as significant predictors of hepcidin in all patients. In the selected patients with highly sensitive C-reactive protein of >0.3 mg/dl, however, ferritin as well as the IL-6 level were found to be significant predictors for serum hepcidin. The serum ferritin/hepcidin ratio was very similar among MHD and healthy volunteers, suggesting that uremic conditions do not affect the ratio. Serum hepcidin levels decreased by only 27% after a single hemodialysis session, but returned to basal levels 1 h after and remained so until the next hemodialysis session. Conclusions: In the absence of apparent inflammation, the serum hepcidin level could be exclusively associated with ferritin in MHD patients and was independent of inflammatory cytokines. Only in the presence of microinflammation, however, might IL-6 also affect hepcidin expression.

Tumor Necrosis Factor-α–Induced Iron Sequestration and Oxidative Stress in Human Endothelial Cells

Objective—Tumor necrosis factor (TNF)-&agr;–induced endothelial injury, which is associated with atherosclerosis, is mediated by intracellular reactive oxygen species. Iron is essential for the amplification of oxidative stress. We tested whether TNF-&agr; accelerated iron accumulation in vascular endothelium, favoring synthesis of hydroxyl radical. Methods and Results—Diverse iron transporters, including iron import proteins (transferrin receptor [TfR] and divalent metal transporter 1 [DMT1]) and an iron export protein (ferroportin 1 [FP1]) coexist in human umbilical endothelial cells (HUVECs). TNF-&agr; caused upregulation of TfR and DMT1 and downregulation of FP1, which were demonstrated in mRNA as well as protein levels. These changes in iron transporters were accompanied by accumulation of iron that was both transferrin-dependent and transferrin-independent. Modifications of these mRNAs were regulated post-transcriptionally, and were coordinated with activation of binding activity of iron regulatory protein 1 to the iron responsive element on transporter mRNAs. Using a salicylate trap method, we observed that only simultaneous exposure of endothelial cells to iron and TNF-&agr; accelerated hydroxyl radical production. Conclusions—TNF-&agr; could cause intracellular iron sequestration, which may participate importantly in the pathophysiology of atherosclerosis and cardiovascular disease.

Hepcidin as well as TNF-α are significant predictors of arterial stiffness in patients on maintenance hemodialysis

BACKGROUND Dysregulated iron metabolism has been suspected to be linked to anemia of chronic disease and to cardiovascular disease (CVD). For the purpose of clarifying the factors affecting arterial stiffness, we evaluated the relationship between iron metabolism, brachial-ankle (ba)-pulse wave velocity (PWV) and several risk factors for CVD in maintenance hemodialysis (MHD) patients. METHODS A total of 168 MHD patients were recruited, and the levels of iron parameters, hepcidin, CVD risk factors and ba-PWV were evaluated. The level of serum hepcidin-25 was specifically measured by liquid chromatography-tandem mass spectrometry. RESULTS Serum levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and hepcidin were higher in MHD patients, which was consistent with results from our previous study. ba-PWV significantly correlated with age (P < 0.01, R = 0.34), total cholesterol (T-CHO; P = 0.02, R = 0.21), TNF-α (P < 0.01, R = 0.24) and hepcidin (P < 0.01, R = 0.25) but not with other iron parameters and CVD risk factors. According to multiple regression analysis, age (β = 0.30), T-CHO (β = 0.24) TNF-α (β = 0.19) and hepcidin (β = 0.23) were selected as the significant predictors of ba-PWV in MHD patients. CONCLUSION Serum levels of both hepcidin and TNF-α are independently associated with arterial stiffness in MHD patients, suggesting that microinflammation and iron metabolism might affect the integrity of arterial walls.

Should we reconsider iron administration based on prevailing ferritin and hepcidin concentrations

The results of recent randomized, controlled trials in patients with chronic kidney disease and anemia have suggested that hyporesponsiveness to erythropoiesis stimulating agents (ESA) is a significant predictor of poor patient outcomes. Functional iron deficiency (FID) is the most common cause of suboptimal ESA response, and intravenous iron administration (IVFe) efficiently raises hemoglobin (Hb) concentrations even under the condition of FID. Consequently, renal anemia correction has conceptually shifted from ‘higher Hb values with high ESA doses’ to ‘prevention of ESA hyporesponsiveness with IVFe’. The discovery of hepcidin has profoundly changed our understanding of the place of FID in renal anemia therapy. Hepcidin reduces the abundance of iron transport proteins which facilitate iron absorption from the gut and iron mobilization from macrophages. Serum hepcidin is mainly modulated by iron stores, as is serum ferritin. High hepcidin or ferritin levels block intestinal iron absorption and iron recycling in macrophages and decrease iron availability for erythropoiesis, leading to FID. Iron administration, especially IVFe, increases hepcidin levels and concomitantly inhibits iron supply to erythroid cells. This in turn could lead to a vicious circle, exacerbating FID and increasing iron demand. Therefore, physicians should be cautious with unrestricted IVFe to chronic kidney disease patients with FID.

Aldosterone Requires Vasopressin V1a Receptors on Intercalated Cells to Mediate Acid-Base Homeostasis

Both aldosterone and luminal vasopressin may contribute to the maintenance of acid-base homeostasis, but the functional relationship between these hormones is not well understood. The effects of luminal vasopressin likely result from its interaction with V1a receptors on the luminal membranes of intercalated cells in the collecting duct. Here, we found that mice lacking the V1a receptor exhibit type 4 renal tubular acidosis. The administration of the mineralocorticoid agonist fludrocortisone ameliorated the acidosis by restoring excretion of urinary ammonium via increased expression of Rhcg and H-K-ATPase and decreased expression of H-ATPase. In a cell line of intercalated cells established from transgenic rats expressing the mineralocorticoid and V1a receptors, but not V2 receptors, knockdown of the V1a receptor gene abrogated the effects of aldosterone on H-K-ATPase, Rhcg, and H-ATPase expression. These data suggest that defects in the vasopressin V1a receptor in intercalated cells can cause type 4 renal tubular acidosis and that the tubular effects of aldosterone depend on a functional V1a receptor in the intercalated cells.

Importance of Ferritin for Optimizing Anemia Therapy in Chronic Kidney Disease

The clinical significance of serum ferritin in monitoring the iron status of patients on maintenance hemodialysis (MHD) has become suspected. In this review, we reassess the interpretation of high serum ferritin values in such patients, with the goal of treating their anemia in a safe way. From the observations that (1) H-ferritin gene transcription is predominantly active in inflammatory conditions, whereas L-ferritin is induced only after exposure to very high iron concentrations and is preferentially secreted to plasma from hepatocytes; (2) the expression of both types of ferritin proteins are exclusively dependent on intracellular free iron, which is often sequestered by LPS or cytokines in several cell types, and (3) splenic iron is depleted and serum ferritin does not increase in the combined conditions of both inflammation and iron deficiency, it is deduced that elevated serum ferritin levels are caused by the accumulation of intracellular iron, especially reticuloendothelial cells or macrophages, hepatocytes, and other cells, while cytokines or inflammation might modulate the relative ratio of ferritin to body iron storage. Therefore, high levels of serum ferritin in patients on MHD can be used to indicate iron deposition in most cells, including vascular and immunocompetent cells, and is still a reliable indicator of the need to withhold iron administration.

Interleukin-6 Is a Predictor of Mortality in Stable Hemodialysis Patients

Background/Aims: Mortality in end-stage renal disease patients with dialysis remains high. A high percentage of dialysis patients display signs of chronic microinflammation. To clarify whether microinflammation is involved in the high incidence of poor prognosis in dialysis patients, we investigated the association of inflammatory markers with mortality in a prospective observational cohort study. Methods: 120 patients undergoing hemodialysis were enrolled. Baseline cross-sectional analysis of the relationship between inflammatory markers [interleukin-6 (IL-6), tumor necrosis factor-α and high-sensitivity C-reactive protein] and other factors, along with a survival analysis for death, were performed. All subjects were divided into 2 groups according to the median value of IL-6. Results: The mortality rate was significantly higher in the high (20.0%) compared with the low IL-6 group (3.3%, p = 0.0046). Receiver-operating characteristic curves indicated high mortality to be closely associated with a high IL-6 level rather than tumor necrosis factor-α. In stepwise multiple regression analyses, age, phosphorus and high-sensitivity C-reactive protein were independent predictors of IL-6 (R2 = 0.466, p < 0.0001). Conclusions: These data clearly show that plasma IL-6 is a powerful predictor of all-cause mortality in dialysis patients.

Hepcidin: another culprit for complications in patients with chronic kidney disease?

Hepcidin has been established as a central regulator of iron metabolism. In most patients with chronic kidney disease (CKD), serum hepcidin levels are relatively high, favoring iron sequestration in several cell types and organs and thereby leading to iron-related complications. In the absence of overt inflammation, serum hepcidin has been found to be most closely associated with serum ferritin in healthy subjects and in CKD patients. Intestinal iron absorption is tightly regulated by both iron stores and hepcidin. The expression of the mammalian iron exporter, ferroportin (FPN), limits the growth of intracellular bacteria by depleting cytosolic iron. An upregulation of hepcidin could diminish FPN and favor bacterial growth. Of note, in patients with hyperferritinemia impaired hepcidin expression caused by a mutation in the hemochromatosis gene associates with an attenuation of atherosclerosis. Thus, hepcidin might accelerate atherosclerosis by preventing iron exit from macrophages or other cells in the arterial wall. High hepcidin levels have also been found to be linked to good erythropoiesis-stimulating agents (ESAs) response, in conjunction with the strong hepcidin-ferritin correlation. Finally, hepcidin may also play a significant role by itself in the pathogenesis of CKD complications associated with disturbed iron metabolism, i.e. unrelated to ESA hyporesponsiveness, such as bacterial infections and atherosclerosis.

Therapeutic efficacy of double filtration plasmapheresis in patients with anti-aquaporin-4 antibody-positive multiple sclerosis

Multiple sclerosis (MS) in Asian countries, including Japan, is classified into two types: conventional MS (C-MS), characterized mainly by cerebral lesions, and opticospinal MS (OS-MS) or neuromyelitis optica (NMO), characterized by selective involvement of the optic nerve and spinal cord. Recently, a serum immunoglobulin-G-antibody was discovered in patients with NMO that targets aquaporin-4 (AQP4). The existence of the anti-AQP4 antibody shows the pathogenetic role of humoral immune factors in OS-MS/NMO. We treated eight patients with anti-AQP4 antibody-positive MS with double filtration plasmapheresis (DFPP) to remove the antibody. Improvement of vision was observed in two patients. Motion improvement was seen in seven patients. Sensory improvement was observed in four patients. In total, six out of eight patients (75%) showed therapeutic improvement after DFPP treatment. We propose that DFPP might be an effective therapeutic option for patients with anti-AQP4 antibody-positive MS.

Carbamylated Hemoglobin as a Therapeutic Marker in Hemodialysis

Carbamylation requires isocyanic acid derived from urea. Carbamylation of hemoglobin (Hb) produces carbamylated Hb (carbHb), which could serve as a marker of posttranslational protein modification possibly associated with such uremic complications as atherosclerosis. Since relative carbHb levels are determined by mean urea concentration and duration of exposure, they could be used to assess the adequacy of a patient’s hemodialysis (HD) regimen. We therefore determined the relationship between carbHb and urea kinetics in patients with chronic renal failure (CRF) undergoing maintenance HD. In pre-HD determinations as well as in nondialyzed subjects including healthy subjects and CRF patients without dialysis, carbHb correlated well with blood urea nitrogen (BUN) concentrations, especially with BUN averaged for the preceding 1–3 months. In HD patients, carbHb correlated significantly with urea kinetics (time-averaged concentration of urea, or TACurea, Kt/V and urea reduction rate). The estimated mean urea concentration in HD patients calculated from the relationship between carbHb and averaged BUN over 3 months in the nondialyzed groups was lower than TACurea, suggesting that TACurea may be an overestimate. Pre-HD BUN is not a good nutritional index since detrimental decreases in urea elimination from the body can elevate pre-HD BUN independently of nutrition. We therefore devised a new nutritional index, BUN/carbHb, which correlated significantly with serum albumin as well as the normalized protein catabolic rate. These results demonstrate that carbHb accurately reflects uremic control and the BUN/carbHb ratio could serve as an index of nutritional state in HD patients.