Iron and clinical outcomes in dialysis and non-dialysis-dependent chronic kidney disease patients

Association of iron deficiency with kidney outcome and all-cause mortality in chronic kidney disease patients without anemia

BACKGROUND

Iron deficiency is prevalent in patients with chronic kidney disease (CKD), even in those without anemia. However, the effects of iron deficiency on CKD progression and all-cause mortality in non-dialysis-dependent CKD (NDD-CKD) patients without anemia remain incompletely understood.

METHODS

This multicenter retrospective nationwide cohort study included adult patients with non-anemia NDD-CKD from 24 hospitals across China. The study investigated the associations between serum ferritin or transferrin saturation (TSAT) levels and the risks of CKD progression and all-cause mortality.

RESULTS

Among 18,878 patients with NDD-CKD, 9,989 patients were included in the kidney outcome analysis, and 18,481 patients in the all-cause mortality analysis. Of the patients with the measurement, 2,450 (27.2%) had ferritin levels ≤ 100ng/mL and 2,440 (13.1%) had a TSAT level ≤ 20%. Compared with patients with TSAT level of > 20%, those with TSAT level of ≤ 20% had significantly higher risks of CKD progression (adjusted hazard ratio [aHR]: 1.66, 95% confidence intervals [CI]: 1.16-2.37; P = 0.005) and all-cause mortality (aHR: 2.21, 95% CI: 1.36-3.57; P = 0.001). The robustness of results was supported by subgroup analyses. However, there was no significant association found between ferritin levels and the risk of CKD progression or all-cause mortality (P > 0.05).

CONCLUSION

Iron deficiency was prevalent in NDD-CKD patients without anemia, and TSAT could be a modifiable risk factor of CKD progression and all-cause mortality. The screening of iron biomarkers, especially TSAT, in the early stage of NDD-CKD is important to assess and improve prognosis.

Roxadustat regulates iron metabolism in dialysis-dependent and non-dialysis-dependent chronic kidney disease patients: A meta-analysis

BACKGROUND/PURPOSE

The effect of roxadustat on iron homeostasis in patients with chronic kidney disease (CKD) is unclear. This study aimed to evaluate the efficacy of roxadustat for the treatment of iron metabolism disorders in dialysis-dependent (DD) and non-dialysis-dependent (NDD) CKD patients.

METHODS

We searched the PubMed, Embase, China National Knowledge Internet and Web of Science databases for randomized controlled trials (RCTs). The primary outcomes were changes in serum iron, total iron binding capacity (TIBC), transferrin saturation (TSAT), ferritin, transferrin, and hepcidin. The secondary outcomes included the changes in hemoglobin (Hb) and the incidences of adverse events (AEs) and severe adverse events (SAEs).

RESULTS

Twelve RCTs comprising 4976 participants were included. Compared to the control group, increases in the serum iron (SMD = 0.21, 95% CI: 0.15 to 0.27, P < 0.00001), TIBC (SMD = 1.02, 95% CI: 0.82 to 1.22, P < 0.00001) and transferrin levels (WMD = 0.55, 95% CI: 0.41 to 0.69, P < 0.00001) were found in the roxadustat group. Compared to the control group, decreases in the ferritin levels (WMD = -37.82, 95% CI: -59.89 to -15.74, P = 0.0008) and hepcidin levels (WMD = -24.04, 95% CI: -36.28 to -11.79, P = 0.0001) were observed in the roxadustat group. The meta-analysis showed that roxadustat significantly increases Hb levels (WMD = 0.77, 95% CI: 0.42 to 1.12, P < 0.0001). The incidences of AEs and SAEs in the roxadustat group was significantly higher than that in the control group (RR = 1.03, 95% CI: 1.00 to 1.07, P = 0.04; RR = 1.08, 95% CI: 1.00 to 1.15, P = 0.04).

CONCLUSION

Our findings suggest that roxadustat could effectively improve iron metabolism in patients with CKD.

Eryptosis - the Neglected Cause of Anemia in End Stage Renal Disease

End stage renal disease (ESRD) invariably leads to anemia which has been mainly attributed to compromised release of erythropoietin from the defective kidneys with subsequent impairment of erythropoiesis. However, erythropoietin replacement only partially reverses anemia pointing to the involvement of additional mechanisms. As shown more recently, anemia of ESRD is indeed in large part a result of accelerated erythrocyte loss due to suicidal erythrocyte death or eryptosis, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the cell surface. Phosphatidylserine exposing erythrocytes are bound to and engulfed by macrophages and are thus rapidly cleared from circulating blood. If the loss of erythrocytes cannot be fully compensated by enhanced erythropoiesis, stimulation of eryptosis leads to anemia. Eryptotic erythrocytes may further adhere to the vascular wall and thus impair microcirculation. Stimulators of eryptosis include complement, hyperosmotic shock, energy depletion, oxidative stress, and a wide variety of xenobiotics. Signaling involved in the stimulation of eryptosis includes increase of cytosolic Ca2+ activity, ceramide, caspases, calpain, p38 kinase, protein kinase C, Janus-activated kinase 3, casein kinase 1α, and cyclin-dependent kinase 4. Eryptosis is inhibited by AMP-activated kinase, p21-activated kinase 2, cGMP-dependent protein kinase, mitogen- and stress-activated kinase MSK1/2, and some illdefined tyrosine kinases. In ESRD eryptosis is stimulated at least in part by a plasma component, as it is triggered by exposure of erythrocytes from healthy individuals to plasma from ESRD patients. Several eryptosis-stimulating uremic toxins have been identified, such as vanadate, acrolein, methylglyoxal, indoxyl sulfate, indole-3-acetic acid and phosphate. Attempts to fully reverse anemia in ESRD with excessive stimulation of erythropoiesis enhances the number of circulating suicidal erythrocytes and bears the risk of interference with micocirculation, At least in theory, anemia in ESRD could preferably be treated with replacement of erythropoietin and additional inhibition of eryptosis thus avoiding eryptosis-induced impairment of microcirculation. A variety of eryptosis inhibitors have been identified, their efficacy in ESRD remains, however, to be shown.

Triggers, inhibitors, mechanisms, and significance of eryptosis: the suicidal erythrocyte death

Suicidal erythrocyte death or eryptosis is characterized by erythrocyte shrinkage, cell membrane blebbing, and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Triggers of eryptosis include Ca(2+) entry, ceramide formation, stimulation of caspases, calpain activation, energy depletion, oxidative stress, and dysregulation of several kinases. Eryptosis is triggered by a wide variety of xenobiotics. It is inhibited by several xenobiotics and endogenous molecules including NO and erythropoietin. The susceptibility of erythrocytes to eryptosis increases with erythrocyte age. Phosphatidylserine exposing erythrocytes adhere to the vascular wall by binding to endothelial CXC-Motiv-Chemokin-16/Scavenger-receptor for phosphatidylserine and oxidized low density lipoprotein (CXCL16). Phosphatidylserine exposing erythrocytes are further engulfed by phagocytosing cells and are thus rapidly cleared from circulating blood. Eryptosis eliminates infected or defective erythrocytes thus counteracting parasitemia in malaria and preventing detrimental hemolysis of defective cells. Excessive eryptosis, however, may lead to anemia and may interfere with microcirculation. Enhanced eryptosis contributes to the pathophysiology of several clinical disorders including metabolic syndrome and diabetes, malignancy, cardiac and renal insufficiency, hemolytic uremic syndrome, sepsis, mycoplasma infection, malaria, iron deficiency, sickle cell anemia, thalassemia, glucose 6-phosphate dehydrogenase deficiency, and Wilson's disease. Facilitating or inhibiting eryptosis may be a therapeutic option in those disorders.

Oxidative stress and suicidal erythrocyte death

SIGNIFICANCE

Eryptosis, the suicidal erythrocyte death, is characterized by cell shrinkage, membrane blebbing, and phosphatidylserine translocation to the outer membrane leaflet. Phosphatidylserine at the erythrocyte surface binds endothelial CXCL16/SR-PSOX (CXC-Motiv-Chemokin-16/Scavenger-receptor-for-phosphatidylserine-and-oxidized-low-density-lipoprotein) and fosters engulfment of affected erythrocytes by phagocytosing cells. Eryptosis serves to eliminate infected or defective erythrocytes, but excessive eryptosis may lead to anemia and may interfere with microcirculation. Clinical conditions with excessive eryptosis include diabetes, chronic renal failure, hemolytic uremic syndrome, sepsis, malaria, iron deficiency, sickle cell anemia, thalassemia, glucose 6-phosphate dehydrogenase deficiency, glutamate cysteine ligase modulator deficiency, and Wilson's disease.

RECENT ADVANCES

Eryptosis is triggered by a wide variety of xenobiotics and other injuries such as oxidative stress. Signaling of eryptosis includes prostaglandin E₂ formation with subsequent activation of Ca(2+)-permeable cation channels, Ca(2+) entry, activation of Ca(2+)-sensitive K(+) channels, and cell membrane scrambling, as well as phospholipase A2 stimulation with release of platelet-activating factor, sphingomyelinase activation, and ceramide formation. Eryptosis may involve stimulation of caspases and calpain with subsequent degradation of the cytoskeleton. It is regulated by AMP-activated kinase, cGMP-dependent protein kinase, Janus-activated kinase 3, casein kinase 1α, p38 kinase, and p21-activated kinase 2. It is inhibited by erythropoietin, antioxidants, and further small molecules.

CRITICAL ISSUES

It remains uncertain for most disorders whether eryptosis is rather beneficial because it precedes and thus prevents hemolysis or whether it is harmful because of induction of anemia and impairment of microcirculation.

FUTURE DIRECTIONS

This will address the significance of eryptosis, further mechanisms underlying eryptosis, and additional pharmacological tools fostering or inhibiting eryptosis.

Suicidal erythrocyte death in end-stage renal disease

Anemia in end-stage renal disease (ESRD) results mainly from erythropoietin and iron deficiency. Anemia could be confounded, however, by accelerated clearance of circulating erythrocytes because of premature suicidal erythrocyte death or eryptosis characterized by phosphatidylserine exposure at the erythrocyte surface. Triggers of eryptosis include increased cytosolic Ca(2+) concentration ([Ca(2+)]i), oxidative stress, and ceramide. The present study explored whether and how ESRD influences eryptosis. Blood was drawn from healthy volunteers (n = 20) as well as ESRD patients (n = 20) prior to and after hemodialysis. Phosphatidylserine exposure was estimated from annexin V binding, [Ca(2+)]i from Fluo3-fluorescence, reactive oxygen species (ROS) from 2',7'dichlorodihydrofluorescein fluorescence, and ceramide from fluorescein-isothiocyanate-conjugated antibody binding in flow cytometry. Measurements were made in erythrocytes from freshly drawn blood and in erythrocytes from healthy volunteers exposed in vitro for 24 h to plasma from healthy volunteers or ESRD patients prior to and following dialysis. The patients suffered from anemia (hemoglobin 10.1 ± 0.5 g/100 ml) despite 1.96 ± 0.34 % reticulocytes. The percentage of phosphatidylserine-exposing erythrocytes was significantly higher in ESRD patients (0.84 ± 0.09 %) than in healthy volunteers (0.43 ± 0.04 %) and was significantly increased immediately after dialysis (1.35 ± 0.13 %). The increase in phosphatidylserine exposure was paralleled by increase in [Ca(2+)]i, oxidative stress, and ceramide abundance. As compared to addition of plasma from healthy individuals, addition of predialytic but not of postdialytic plasma from ESRD patients increased phosphatidylserine exposure, [Ca(2+)]i, ROS, and ceramide abundance. In conclusion, both, dialyzable components of uremic plasma and dialysis procedure, trigger eryptosis at least in part by increasing erythrocyte [Ca(2+)]i, ROS, and ceramide formation.

KEY MESSAGES

Anemia in uremia results in part from eryptosis, the suicidal erythrocyte death. Eryptosis in uremia is triggered in part by a dialyzable plasma component. Eryptosis in uremia is further triggered by dialysis procedure. Eryptosis in uremia is in part due to increased cytosolic Ca(2+) concentration. Eryptosis in uremia is further due to oxidative stress and ceramide formation.

Stimulation of suicidal erythrocyte death by increased extracellular phosphate concentrations

BACKGROUND/AIM

Anemia in renal insufficiency results in part from impaired erythrocyte formation due to erythropoietin and iron deficiency. Beyond that, renal insufficiency enhances eryptosis, the suicidal erythrocyte death characterized by phosphatidylserine-exposure at the erythrocyte surface. Eryptosis may be stimulated by increase of cytosolic Ca(2+)-activity ([Ca(2+)]i). Several uremic toxins have previously been shown to stimulate eryptosis. Renal insufficiency is further paralleled by increase of plasma phosphate concentration. The present study thus explored the effect of phosphate on erythrocyte death.

METHODS

Cell volume was estimated from forward scatter, phosphatidylserine-exposure from annexin V binding, and [Ca(2+)]i from Fluo3-fluorescence.

RESULTS

Following a 48 hours incubation, the percentage of phosphatidylserine exposing erythrocytes markedly increased as a function of extracellular phosphate concentration (from 0-5 mM). The exposure to 2 mM or 5 mM phosphate was followed by slight but significant hemolysis. [Ca(2+)]i did not change significantly up to 2 mM phosphate but significantly decreased at 5 mM phosphate. The effect of 2 mM phosphate on phosphatidylserine exposure was significantly augmented by increase of extracellular Ca(2+) to 1.7 mM, and significantly blunted by nominal absence of extracellular Ca(2+), by additional presence of pyrophosphate as well as by presence of p38 inhibitor SB203580.

CONCLUSION

Increasing phosphate concentration stimulates erythrocyte membrane scrambling, an effect depending on extracellular but not intracellular Ca(2+) concentration. It is hypothesized that suicidal erythrocyte death is triggered by complexed CaHPO4.

Triggering of suicidal erythrocyte death by uremic toxin indoxyl sulfate

Background

Anemia in end stage renal disease is attributed to impaired erythrocyte formation due to erythropoietin and iron deficiency. On the other hand, end stage renal disease enhances eryptosis, the suicidal erythrocyte death characterized by cell shrinkage and phosphatidylserine-exposure at the erythrocyte surface. Eryptosis may be triggered by increase of cytosolic Ca²⁺-activity ([Ca²⁺]_i) and by ceramide, which sensitizes erythrocytes to [Ca²⁺]_i. Mechanisms triggering eryptosis in endstage renal disease remained enigmatic. The present study explored the effect of indoxyl sulfate, an uremic toxin accumulated in blood of patients with chronic kidney disease.

Methods

Cell volume was estimated from forward scatter, phosphatidylserine-exposure from annexin V binding, ceramide abundance by specific antibodies, hemolysis from hemoglobin release, and [Ca²⁺]_i from Fluo3-fluorescence.

Results

A 48 hours exposure to indoxyl sulfate significantly increased [Ca²⁺]_i (≥ 300 μM), significantly decreased forward scatter (≥ 300 μM) and significantly increased annexin-V-binding (≥ 50 μM). Indoxyl sulfate (150 μM) induced annexin-V-binding was virtually abolished in the nominal absence of extracellular Ca²⁺. Indoxyl sulfate (150 μM) further enhanced ceramide abundance.

Conclusion

Indoxyl sulfate stimulates suicidal erythrocyte death or eryptosis, an effect in large part due to stimulation of extracellular Ca²⁺entry with subsequent stimulation of cell shrinkage and cell membrane scrambling.

Stable hemoglobin in hemodialysis patients: forest for the trees--a 12-week pilot observational study

Background

Hemoglobin (Hb) variability is a common occurrence in hemodialysis patients treated with erythropoiesis-stimulating agents. High amplitude fluctuations have been associated with greater risk of morbidity and mortality.

Methods

This prospective, single centre pilot observational study was conducted over a 3-month period in daily practice patterns, to assess per-dialysis events and inter-dialysis complications that could interfere with erythropoiesis in patients undergoing hemodialysis.

Results

Mean Hb levels remained stable in the 78 evaluable patients, as did darbepoetin alfa (DA) doses, including in patients suffering from diabetes or cardiac affections. In total, an average of 7.7 events / patient / month occurred, but no significant relationship with Hb excursions was shown.

Conclusion

The observation of 7.7 events per patient per month suggests a careful monitoring of Hb and DA dosing every other week, in order to maintain Hb level within the target.

[Intravenous iron during predialysis period improves anemia management and cardiovascular parameters in incident hemodialysis patients]

Individualized use of iron therapy (IT) and erythropoiesis-stimulating agents (ESA) may effectively correct anemia and its symptoms in CKD patients (Pts). The aim of this retrospective study was to precise the anemia management (AM) in incident HD Pts, and to compare Pts treated by intravenous (i.v.) IT and ESA during predialysis to those treated by oral IT and ESA on AM and cardiovascular parameters during the first year of HD. One hundred and two Pts performed their first dialysis in the unit, mean age 58.5 (15.9) years, 70% males, 27% diabetes. Ninety Pts started with a native arteriovenous fistula. Charlson comorbidity index was 7.3 (3.5). Mortality rate was 3% at one year. Hb level was at start 10.6 (1.7) and at one year 11.7 (1.1) g/dL (P<0.0001). DA injected every 2weeks was at the beginning at 107 (56) μg and then at 61 (46) (P<0.0001). i.v. IT injected every week was at the dosage of 87 (23) mg and then at 57 (40mg) per injection (P<0.001). Out of 102 Pts, 33 received i.v. IT during predialysis. These Pts started dialysis with a better Hb level: 11.1 (1.3) versus 10.4 (1.55) g/dL (P<0.01), had a TSAT at 50.0 (19.2) versus 30.1 (15.2) % (P<0.001), received less ESA 0.58 (0.28) versus 0.82 (0.37) μg/kg per week (P<0.01). More important were the changes on the cardiovascular functions: left ventricular mass at 116 (34) versus 134 (39) g/m(2) (P<0.02), left ventricular ejection fraction at 64.7 (4.4) versus 61.4 (8.7) % (P<0.02) and mean arterial pressure at 104.7 (80) versus 109 (13.2) mmHg (P<0.02). These Pts were also less hospitalized. This study revealed the importance of i.v. IT during predialysis care not only on AM but also on cardiovascular status in HD Pts starting dialysis.

Trace minerals in patients with end-stage renal disease

The kidneys are famously responsible for maintaining external balance of prevalent minerals, such as sodium, chloride, and potassium. The kidney's role in handling trace minerals is more obscure to most nephrologists. Similarly, the impact of kidney failure on trace mineral metabolism is difficult to anticipate. The associated dietary modifications and dialysis create the potential for trace mineral deficiencies and intoxications. Indeed, there are numerous reports of dialysis-associated mishaps causing mineral intoxication, notable for the challenge of assigning causation. Equally challenging has been the recognition of mineral deficiency syndromes, amid what is often a cacophony of multiple comorbidities that vie for the attention of clinicians who care for patients with chronic kidney disease. In this paper, I review a variety of minerals, some of which are required for maintenance of normal human physiology (the U.S. Food and Drug Administration's list of essential minerals), and some that have attracted attention in the care of dialysis patients. For each mineral, I will discuss its role in normal physiology and will review reported deficiency and toxicity states. I will point out the interesting inter-relationships between several of the elements. Finally, I will address the special concerns of aluminum and magnesium as they pertain to the dialysis population.

Anemia in renal disease: diagnosis and management

Chronic kidney disease (CKD) is a widespread health problem in the world and anemia is a common complication. Anemia conveys significant risk for cardiovascular disease, faster progression of renal failure and decreased quality of life. Patients with CKD can have anemia for many reasons, including but not invariably their renal insufficiency. These patients require a thorough evaluation to identify and correct causes of anemia other than erythropoietin deficiency. The mainstay of treatment of anemia secondary to CKD has become erythropoiesis-stimulating agents (ESAs). The use of ESAs does carry risks and these agents need to be used judiciously. Iron deficiency often co-exists in this population and must be evaluated and treated. Correction of iron deficiency can improve anemia and reduce ESA requirements. Partial, but not complete, correction of anemia is associated with improved outcomes in patients with CKD.