Accelerated suicidal erythrocyte death in Klotho-deficient mice

Association between vitamin D status and eryptosis-results from the German National Cohort Study

Vitamin D, besides its classical effect on mineral homeostasis and bone remodeling, can also modulate apoptosis. A special form of apoptosis termed eryptosis appears in erythrocytes. Eryptosis is characterized by cell shrinkage, membrane blebbing, and cell membrane phospholipid disorganization and associated with diseases such as sepsis, malaria or iron deficiency, and impaired microcirculation. To our knowledge, this is the first study that linked vitamin D with eryptosis in humans. This exploratory cross-sectional trial investigated the association between the vitamin D status assessed by the concentration of plasma 25-hydroxyvitamin D (25(OH)D) and eryptosis. Plasma 25(OH)D was analyzed by LC-MS/MS, and eryptosis was estimated from annexin V-FITC-binding erythrocytes by FACS analysis in 2074 blood samples from participants of the German National Cohort Study. We observed a weak but clear correlation between low vitamin D status and increased eryptosis (r =  - 0.15; 95% CI [- 0.19, - 0.10]). There were no differences in plasma concentrations of 25(OH)D and eryptosis between male and female subjects. This finding raises questions of the importance of vitamin D status for eryptosis in terms of increased risk for anemia or cardiovascular events.

Molecular Mechanisms and Pathophysiological Significance of Eryptosis

Despite lacking the central apoptotic machinery, senescent or damaged RBCs can undergo an unusual apoptosis-like cell death, termed eryptosis. This premature death can be caused by, or a symptom of, a wide range of diseases. However, various adverse conditions, xenobiotics, and endogenous mediators have also been recognized as triggers and inhibitors of eryptosis. Eukaryotic RBCs are unique among their cell membrane distribution of phospholipids. The change in the RBC membrane composition of the outer leaflet occurs in a variety of diseases, including sickle cell disease, renal diseases, leukemia, Parkinson’s disease, and diabetes. Eryptotic erythrocytes exhibit various morphological alterations such as shrinkage, swelling, and increased granulation. Biochemical changes include cytosolic Ca2+ increase, oxidative stress, stimulation of caspases, metabolic exhaustion, and ceramide accumulation. Eryptosis is an effective mechanism for the elimination of dysfunctional erythrocytes due to senescence, infection, or injury to prevent hemolysis. Nevertheless, excessive eryptosis is associated with multiple pathologies, most notably anemia, abnormal microcirculation, and prothrombotic risk; all of which contribute to the pathogenesis of several diseases. In this review, we provide an overview of the molecular mechanisms, physiological and pathophysiological relevance of eryptosis, as well as the potential role of natural and synthetic compounds in modulating RBC survival and death.

Monthly Continuous Erythropoietin Receptor Activator Versus Weekly Epoetin-Beta, Similar Hemoglobinization but Different Anisocytosis Degree in Hemodialysis Patients: A Randomized Controlled Trial

Background

The monthly continuous erythropoietin receptor activator (CERA) utilization maintains stable hemoglobin (Hb) after conversion from weekly epoetin-β (EB); however, how the different pharmacologic properties affect the red blood cell (RBC) size determined by RBC distribution width (RDW) has not been evaluated yet. We assess the potential differences in iron metabolism, plasma erythropoietin (EPO), hepcidin, and soluble α-Klotho (α-Klotho) levels as an emergent hematopoiesis factor.

Methods

Thirty-seven chronic hemodialysis patients were included from January 2010 to November 2011 and randomized (1:1) to continue with EB or to convert to monthly CERA. Primary outcome was the mean change in Hb between groups at months 0, 3 and 6, and the percentage of patients who maintained stable Hb (Hb ± 1 g/dL from baseline level to month 6). Secondary outcomes were the influence on the erythropoietic process and iron metabolism markers. Thirty-one patients completed the study (CERA: n = 15, EB: n = 16).

Results

The mean (95% confidence interval (CI)) Hb difference between groups was 0.28 g/dL (-0.36 to 0.93). There was no difference between the percentages of patients with stable Hb levels. In the CERA group RDW values increased progressively (interaction erythropoietin-stimulating agent (ESA) type and time on RDW values, F (1.57, 45.60) = 17.17, P < 0.01, partial η² = 0.37) and the mean corpuscular volume changed at the different time points, (F (2, 28) = 29.12, P = 0.03, partial η² = 0.23). During the evaluation period, in the CERA group, EPO was higher, and hepcidin and ferritin decreased significantly. α-Klotho decreased in both groups and correlated negatively with the changes on the RDW and positively with transferrin and serum iron. The number of serious adverse events was higher at the CERA group.

Conclusions

Monthly CERA maintained Hb concentrations; however, it showed a significant effect on RDW, probably due to its impact on the EPO and hepcidin levels. α-Klotho decreased significantly in both groups, and its changes correlated with the changes in iron metabolism. Whether the RDW evolution was associated with the serious adverse events (SAEs) is a feasible hypothesis that needs to be confirmed in large studies.

Administration of α-Klotho Does Not Rescue Renal Anemia in Mice

Renal anemia is a common complication in chronic kidney disease (CKD), associated with decreased production of erythropoietin (EPO) due to loss of kidney function, and subsequent decreased red blood cell (RBC) production. However, many other factors play a critical role in the development of renal anemia, such as iron deficiency, inflammation, and elevated fibroblast growth factor 23 (FGF23) levels. We previously reported that inhibition of FGF23 signaling rescues anemia in mice with CKD. In the present study we sought to investigate whether α-Klotho deficiency present in CKD also contributes to the development of renal anemia. To address this, we administered α-Klotho to mice with CKD induced by an adenine-rich diet. Mice were sacrificed 24 h after α-Klotho injection, and blood and organs were collected immediately post-mortem. Our data show that α-Klotho administration had no beneficial effect in mice with CKD-associated anemia as it did not increase RBC numbers and hemoglobin levels, and it did not stimulate EPO secretion. Moreover, α-Klotho did not improve iron deficiency and inflammation in CKD as it had no effect on iron levels or inflammatory markers. Interestingly, Klotho supplementation significantly reduced the number of erythroid progenitors in the bone marrow and downregulated renal Epo and Hif2α mRNA in mice fed control diet resulting in reduced circulating EPO levels in these mice. In addition, Klotho significantly decreased intestinal absorption of iron in control mice leading to reduced serum iron and transferrin saturation levels. Our findings demonstrate that α-Klotho does not have a direct role in renal anemia and that FGF23 suppresses erythropoiesis in CKD via a Klotho-independent mechanism. However, in physiological conditions α-Klotho appears to have an inhibitory effect on erythropoiesis and iron regulation.

Non-oxidative band-3 clustering agents cause the externalization of phosphatidylserine on erythrocyte surfaces by a calcium-independent mechanism

Aging of red blood cells (RBCs) is associated with alteration in a wide range of RBC features, occurring each on its own timescale. A number of these changes are interrelated and initiate a cascade of biochemical and structural transformations, including band-3 clustering and phosphatidylserine (PS) externalization. Using specific band-3 clustering agents (acridine orange (AO) and ZnCl₂), we examined whether treatment of RBCs with these agents may affects PS externalization and whether this process is Ca²⁺-dependent. RBCs were isolated from the blood of eight healthy donors upon obtaining their informed consent. The suspension was supplemented with increasing concentrations of AO or ZnCl₂ (from 0.5 to 2.0 mM) and incubated at 25 °C for 60 min. To detect PS at the RBC surface, we used allophycocyanin-conjugated recombinant human Annexin V. We demonstrated, that treatment of RBCs with both clustering agents caused an elevation in the percent of cells positively labeled by Annexin-V (RBC^PS), and that this value was not dependent on the presence of calcium in the buffer: RBCs treated with AO in the presence of either EDTA, EGTA or calcium exhibited similar percentage of RBC^PS. Moreover, the active influx of Zn²⁺ into RBCs induced by their co-incubation with both ZnCl₂ and A23187 did not increase the percent of RBC^PS as compared to RBCs incubated with ZnCl₂ alone. Taken together, these results demonstrate that the band-3 clustering agents (AO or ZnCl₂) induce PS externalization in a Ca²⁺ independent manner, and we hereby suggest a possible scenario for this phenomenon.

α-klotho and anemia in patients with chronic kidney disease patients: A new perspective

Normocytic normochromic anemia is a common complication of chronic kidney disease (CKD) and is associated with numerous adverse consequences. Certain symptoms previously attributed to CKD are now known to be a consequence of anemia. Anemia contributes to an increased cardiac output, and the development of left ventricular hypertrophy, angina and congestive heart failure, leading to high morbidity and mortality in patients with CKD. The multifunctional α-klotho (KL) protein, which is predominantly expressed in the kidneys, is associated with the occurrence of anemia in patients with CKD. The present review presents current evidence on the potential role of α-KL in renal anemia. Low expression of α-KL appears to improve anemia in patients with CKD, and has been hypothesized to be a compensatory mechanism to attenuate the effects of anemia in patients with CKD. Further understanding of the role of α-KL in renal anemia may offer novel insights into the treatment of patients with CKD complicated with anemia.

Eryptosis in health and disease: A paradigm shift towards understanding the (patho)physiological implications of programmed cell death of erythrocytes

During the course of their natural ageing and upon injury, anucleate erythrocytes can undergo an unconventional apoptosis-like cell death, termed eryptosis. Eryptotic erythrocytes display a plethora of morphological alterations including volume reduction, membrane blebbing and breakdown of the membrane phospholipid asymmetry resulting in phosphatidylserine externalization which, in turn, mediates their phagocytic recognition and clearance from the circulation. Overall, the eryptosis machinery is tightly orchestrated by a wide array of endogenous mediators, ion channels, membrane receptors, and a host of intracellular signaling proteins. Enhanced eryptosis shortens the lifespan of circulating erythrocytes and confers a procoagulant phenotype; this phenomenon has been tangibly implicated in the pathogenesis of anemia, deranged microcirculation, and increased prothrombotic risk associated with a multitude of clinical conditions. Herein, we reviewed the molecular mechanisms dictating eryptosis and erythrophagocytosis and critically analyzed the current evidence leading to the pathophysiological ramifications of eryptotic cell death in the context of human disease.

Ceramide in the regulation of eryptosis, the suicidal erythrocyte death

Similar to apoptosis of nucleated cells, erythrocytes may undergo eryptosis, a suicidal death characterized by cell shrinkage and phospholipid scrambling of the cell membrane leading to phosphatidylserine exposure at the cell surface. As eryptotic erythrocytes are rapidly cleared from circulating blood, excessive eryptosis may lead to anemia. Moreover, eryptotic erythrocytes may adhere to the vascular wall and thus impede microcirculation. Stimulators of eryptosis include osmotic shock, oxidative stress and energy depletion. Mechanisms involved in the stimulation eryptosis include ceramide formation which may result from phospholipase A2 dependent formation of platelet activating factor (PAF) with PAF dependent stimulation of sphingomyelinases. Enhanced erythrocytic ceramide formation is observed in fever, sepsis, HUS, uremia, hepatic failure, and Wilson's disease. Enhanced eryptosis is further observed in iron deficiency, phosphate depletion, dehydration, malignancy, malaria, sickle-cell anemia, beta-thalassemia and glucose-6-phosphate dehydrogenase-deficiency. Moreover, eryptosis is triggered by osmotic shock and a wide variety of xenobiotics, which are again partially effective by enhancing ceramide abundance. Ceramide formation is inhibited by high concentrations of urea. As shown in Wilson's disease, pharmacological interference with ceramide formation may be a therapeutic option in the treatment of eryptosis inducing clinical disorders.

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.

Mechanisms and pathophysiological significance of eryptosis, the suicidal erythrocyte death

Eryptosis, the suicidal erythrocyte death characterized by cell shrinkage and cell membrane scrambling, is stimulated by Ca(2+) entry through Ca(2+)-permeable, PGE2-activated cation channels, by ceramide, caspases, calpain, complement, hyperosmotic shock, energy depletion, oxidative stress, and deranged activity of several kinases (e.g. AMPK, GK, PAK2, CK1α, JAK3, PKC, p38-MAPK). Eryptosis is triggered by intoxication, malignancy, hepatic failure, diabetes, chronic renal insufficiency, hemolytic uremic syndrome, dehydration, phosphate depletion, fever, sepsis, mycoplasma infection, malaria, iron deficiency, sickle cell anemia, thalassemia, glucose 6-phosphate dehydrogenase deficiency, and Wilson's disease. Eryptosis may precede and protect against hemolysis but by the same token result in anemia and deranged microcirculation.

Soluble α-klotho as a novel biomarker in the early stage of nephropathy in patients with type 2 diabetes

Objective

Although α-klotho is known as an anti-aging, antioxidant, and cardio-renal protective protein, the clinical implications of soluble α-klotho levels in patients with diabetes have not been evaluated. Therefore, this study evaluated whether plasma and urinary α-klotho levels are associated with albuminuria in kidney disease in diabetes.

Research Design and Methods

A total of 147 patients with type 2 diabetes and 25 healthy control subjects were enrolled. The plasma and urine concentrations of α-klotho were analyzed by enzyme-linked immunosorbent assay.

Results

Plasma α-klotho (572.4 pg/mL [95% CI, 541.9–604.6 pg/mL] vs. 476.9 pg/mL [95% CI, 416.9–545.5 pg/mL]) and urinary α-klotho levels (59.8 pg/mg creatinine [95% CI, 43.6–82.0 pg/mg creatinine] vs. 21.0 pg/mg creatinine [95% CI, 9.7–45.6 pg/mg creatinine]) were significantly higher in diabetic patients than non-diabetic controls. Among diabetic patients, plasma α-klotho concentration was inversely associated with albuminuria stages (normoalbuminuria, 612.6 pg/mL [95% CI, 568.9–659.6 pg/mL], microalbuminuria, 551.8 pg/mL [95% CI, 500.5–608.3 pg/mL], and macroalbuminuria, 505.7 pg/mL [95% CI, 439.7–581.7 pg/mL] (p for trend  = 0.0081), while urinary α-klotho levels were remained constantly high with increasing urinary albumin excretion.

Conclusions

Soluble α-klotho levels in plasma and urine may be novel and useful early markers of diabetic renal injury.

Sensitization of erythrocytes to suicidal erythrocyte death following water deprivation

BACKGROUND/AIMS

Klotho deficiency results in excessive formation of 1,25(OH)2D3, accelerated ageing and early death. Moreover, klotho deficiency enhances eryptosis, the suicidal erythrocyte death characterized by phosphatidylserine exposure at the erythrocyte surface. Triggers of eryptosis include increase of cytosolic Ca(2+)-activity ([Ca(2+)]i), glucose depletion, hyperosmotic shock and oxidative stress. Klotho expression is decreased and 1,25(OH)2D3-formation enhanced by dehydration. The present study thus explored whether dehydration influences eryptosis.

METHODS

Blood was drawn from hydrated or 36h dehydrated mice. Plasma osmolarity was determined by vapour pressure method, plasma 1,25(OH)2D3 and aldosterone concentrations using ELISA, and plasma Ca(2+)-concentration utilizing photometry. Erythrocytes were exposed to Ca(2+)-ionophore ionomycin (1 µM, 30 min), energy depletion (12 h glucose removal), hyperosmotic shock (500 mM sucrose added, 2 h) and oxidative stress (100 µM tert-butyl-hydroperoxide, 30 min) and phosphatidylserine exposure at the erythrocyte surface estimated from annexin V binding.

RESULTS

Dehydration increased plasma osmolarity and plasma 1,25(OH)2D3 and aldosterone concentrations. Dehydration did not significantly modify phosphatidylserine-exposure of freshly drawn erythrocytes but significantly enhanced the increase of phosphatidylserine-exposure under control conditions and following treatment with ionomycin, glucose-deprivation, hyperosmolarity or tert-butyl-hydroperoxide.

CONCLUSIONS

Dehydration sensitizes the erythrocytes to spontaneous eryptosis and to the triggering of eryptosis by excessive Ca(2+)-entry, energy depletion, hyperosmotic shock and oxidative stress.

Significance of the anti-aging protein Klotho

The Klotho gene was identified as an 'aging suppressor' in mice. Overexpression of the Klotho gene extends lifespan and defective Klotho results in rapid aging and early death. Both the membrane and secreted forms of Klotho have biological activity that include regulatory effects on general metabolism and a more specific effect on mineral metabolism that correlates with its effect on aging. Klotho serves as a co-receptor for fibroblast growth factor (FGF), but it also functions as a humoral factor that regulates cell survival and proliferation, vitamin D metabolism, and calcium and phosphate homeostasis and may serve as a potential tumor suppressor. Moreover, Klotho protects against several pathogenic processes in a FGF23-independent manner. These processes include cancer metastasis, vascular calcification, and renal fibrosis. This review covers the recent advances in Klotho research and discusses novel Klotho-dependent mechanisms that are clinically relevant in aging and age-related diseases.

Regulation of mineral metabolism by lithium

Lithium, an inhibitor of glycogen synthase kinase 3 (GSK3), is widely used for the treatment of mood disorders. Side effects of lithium include nephrogenic diabetes insipidus, leading to renal water loss. Dehydration has in turn been shown to downregulate Klotho, which is required as co-receptor for the downregulation of 1,25(OH)2D3 formation by fibroblast growth factor 23 (FGF23). FGF23 decreases and 1,25(OH)2D3 stimulates renal tubular phosphate reabsorption. The present study explored whether lithium influences renal Klotho expression, FGF23 serum levels, 1,25(OH)2D3 formation, and renal phosphate excretion. To this end, mice were analyzed after a 14-day period of sham treatment or of treatment with lithium (200 mg/kg/day subcutaneously). Serum antidiuretic hormone (ADH), FGF23, and 1,25(OH)2D3 concentrations were determined by ELISA or EIA, renal Klotho protein abundance and GSK3 phosphorylation were analyzed by Western blotting, and serum phosphate and calcium concentration by photometry. Lithium treatment significantly increased renal GSK3 phosphorylation, enhanced serum ADH and FGF23 concentrations, downregulated renal Klotho expression, stimulated renal calcium and phosphate excretion, and decreased serum 1,25(OH)2D3 and phosphate concentrations. In conclusion, lithium treatment upregulates FGF23 formation, an effect paralleled by substantial decrease of serum 1,25(OH)2D3, and phosphate concentrations and thus possibly affecting tissue calcification.

Klotho sensitivity of the hERG channel

Klotho, a hormone and enzyme, is a powerful regulator of ageing and life span. Klotho deficiency leads to cardiac arrythmia and sudden cardiac death. We thus explored whether klotho modifies cardiac K(+)-channel hERG. Current was determined utilizing dual electrode voltage clamp and hERG protein abundance utilizing immunohistochemistry and chemiluminescence in Xenopus oocytes expressing hERG with or without klotho. Coexpression of klotho increased cell membrane hERG-protein abundance and hERG current at any given voltage without significantly modifying the voltage required to activate the channel. The effect of klotho coexpression was mimicked by recombinant klotho protein and reversed by β-glucuronidase-inhibitor D-saccharic acid-1,4-lactone.

Adhesion of klotho-deficient eryptotic erythrocytes to endothelial cells

AIM

Suicidal erythrocyte death or eryptosis is characterized by cell shrinkage and phosphatidylserine exposure at the cell surface. Eryptotic erythrocytes may adhere to the vascular wall by binding of phosphatidylserine to endothelial CXC chemokine ligand 16 (CXCL16). Triggers of eryptosis include osmotic shock or energy depletion. Susceptibility to eryptosis is modified by Klotho, a protein with profound effect on ageing and lifespan. Klotho deficiency leads to accelerated ageing and early death. The percentage of eryptotic erythrocytes is significantly larger in klotho-deficient mice (klotho(-/-) ) than in their wild-type littermates (klotho(+/+) ). The present study explored whether the accelerated eryptosis of klotho-deficient mice is paralleled by enhanced adhesion.

METHODS

Phosphatidylserine-exposing erythrocytes were identified by measurement of annexin V binding and adhesion to human umbilical vein endothelial cells (HUVEC) from trapping of labelled erythrocytes in a flow chamber.

RESULTS

Annexin V binding was higher in klotho(-/-) erythrocytes than in klotho(+/+) erythrocytes. Osmotic shock for 1 h (addition of 550 mm sucrose) and energy depletion (12-h glucose depletion) increased annexin V binding to values again significantly larger in klotho(-/-) erythrocytes than in klotho(+/+) erythrocytes. klotho(-/-) erythrocytes were particularly sensitive to osmotic shock. Both osmotic shock and energy depletion enhanced erythrocyte adhesion, an effect again more pronounced in klotho(-/-) erythrocytes than in klotho(+/+) erythrocytes. The adhesion was significantly decreased by coating of phospatidylserine with annexin V (5 μL mL(-1) ) or by coating of CXCL16 with neutralizing antibodies (4 μg mL(-1) ).

CONCLUSIONS

klotho(-/-) erythrocytes are particularly sensitive to osmotic shock, and enhanced eryptosis of klotho(-/-) erythrocytes is paralleled by enhanced adhesion to endothelial CXCL16.

Downregulation of NaPi-IIa and NaPi-IIb Na-coupled phosphate transporters by coexpression of Klotho

Klotho, a transmembrane protein, protease and hormone has been shown to exert a profound effect on phosphate metabolism. Klotho overexpression lowers and Klotho deficiency increases the plasma phosphate concentration, effects in part attributed to an inhibitory effect of Klotho on the formation of 1,25-dihydroxycholecalciferol (1,25(OH) (2)D(3)), the active form of Vitamin D. Beyond that Klotho has been shown to decrease renal tubular phosphate transport more directly. The influence of Klotho on the plasma phosphate concentration contributes to the profound effect of Klotho on ageing and life span. The present study explored whether Klotho influences the major renal tubular (NaPi-IIa) and the major intestinal (NaPi-IIb) phosphate transporters. For functional analysis NaPi-IIa or NaPi-IIb were expressed in Xenopus oocytes both, without or with additional coexpression of Klotho and electrogenic phosphate transport was estimated from the phosphate-induced current (Ip). According to RT-PCR Klotho is expressed in the murine kidney and intestine. Coexpression of Klotho decreased Ip in both NaPi-IIa- and NaPi-IIb-expressing oocytes. Klotho decreased the maximal Ip without appreciably affecting the concentration required for halfmaximal Ip. Treatment of NaPi-IIa- or NaPi-IIb-expressing oocytes with Klotho protein similarly decreased Ip. In conclusion, Klotho down regulates both, renal (NaPi-IIa) and intestinal (NaPi-IIb) phosphate transporters.

Downregulation of Klotho expression by dehydration

Klotho, a transmembrane protein, protease, and hormone mainly expressed in renal tissue counteracts aging. Overexpression of Klotho substantially prolongs the life span. Klotho deficiency leads to excessive formation of 1,25(OH)(2)D(3), growth deficit, accelerated aging, and early death. Aging is frequently paralleled by dehydration, which is considered to accelerate the development of age-related disorders. The present study explored the possibility that dehydration influences Klotho expression. Klotho transcript levels were determined by RT-PCR, and Klotho protein abundance was detected by Western blotting in renal tissue from hydrated and 36-h-dehydrated mice as well as in human embryonic kidney (HEK293) cells. Dehydration was followed by a significant decline of renal Klotho transcript levels and protein abundance, accompanied by an increase in plasma osmolarity as well as plasma ADH, aldosterone, and 1,25(OH)(2)D(3) levels. Antidiuretic hormone (ADH; 50 nM) and aldosterone (1 μM) significantly decreased Klotho transcription and protein expression in HEK293 cells. In conclusion, the present observations disclose a powerful effect of dehydration on Klotho expression, an effect at least partially mediated by enhanced release of ADH and aldosterone.

Association of serum phosphorus level with anemia in kidney transplant recipients

BACKGROUND

Anemia and mineral and bone disorders (MBD) are both important and common complications in kidney transplant recipients. Studies in patients with chronic kidney disease indicated a possible independent association of higher serum phosphorus with anemia, but similar associations have not been examined in kidney transplant recipients. We hypothesized that higher serum phosphorus is associated with anemia independent of other components of MBD.

METHODS

We examined the association of serum phosphorus with hemoglobin level and the prevalence of anemia in a prevalent cohort of 992 kidney transplant recipients in a single outpatient transplant center. Associations were examined in linear and logistic regression models with adjustment for demographic and comorbid conditions for various known risk factors of anemia, including measures of iron deficiency, inflammation, and components of MBD including serum levels of 25(OH) vitamin D, parathyroid hormone, and fibroblast growth factor 23.

RESULTS

In multivariable adjusted regression models, a 1 standard deviation (0.8 mg/dL) higher serum phosphorus level was associated with 0.26 g/dL lower blood hemoglobin concentration (95% confidence intervals -0.36 to -0.15, P<0.001) and with an odds ratio for anemia of 1.77 (95% confidence intervals 1.33-2.37, P<0.001). These associations were consistent across the entire spectrum of the physiologic serum phosphorus concentration and were more accentuated in patients with lower estimated glomerular filtration rate.

CONCLUSIONS

Higher serum phosphorus is independently associated with anemia in kidney transplant recipients.

Hyperaldosteronism in Klotho-deficient mice

Klotho is a membrane protein participating in the inhibitory effect of FGF23 on the formation of 1,25-dihydroxyvitamin-D(3) [1,25(OH)(2)D(3)]. It participates in the regulation of renal tubular phosphate reabsorption and stimulates renal tubular Ca(2+) reabsorption. Klotho hypomorphic mice (klotho(hm)) suffer from severe growth deficit, rapid aging, and early death, events largely reversed by a vitamin D-deficient diet. The present study explored the role of Klotho deficiency in mineral and electrolyte metabolism. To this end, klotho(hm) mice and wild-type mice (klotho(+/+)) were subjected to a normal (D(+)) or vitamin D-deficient (D(-)) diet or to a vitamin D-deficient diet for 4 wk and then to a normal diet (D(-/+)). At the age of 8 wk, body weight was significantly lower in klotho(hm)D(+) mice than in klotho(+/+)D(+) mice, klotho(hm)D(-) mice, and klotho(hm)D(-/+) mice. Plasma concentrations of 1,25(OH)(2)D(3,) adrenocorticotropic hormone (ACTH), antidiuretic hormone (ADH), and aldosterone were significantly higher in klotho(hm)D(+) mice than in klotho(+/+)D(+) mice. Plasma volume was significantly smaller in klotho(hm)D(-/+) mice, and plasma urea, Ca(2+), phosphate and Na(+), but not K(+) concentrations were significantly higher in klotho(hm)D(+) mice than in klotho(+/+)D(+) mice. The differences were partially abrogated by a vitamin D-deficient diet. Moreover, the hyperaldosteronism was partially reversed by Ca(2+)-deficient diet. Ussing chamber experiments revealed a marked increase in amiloride-sensitive current across the colonic epithelium, pointing to enhanced epithelial sodium channel (ENaC) activity. A salt-deficient diet tended to decrease and a salt-rich diet significantly increased the life span of klotho(hm)D(+) mice. In conclusion, the present observation disclose that the excessive formation of 1,25(OH)(2)D(3) in Klotho-deficient mice results in extracellular volume depletion, which significantly contributes to the shortening of life span.

Stimulation of ceramide formation and suicidal erythrocyte death by vitamin K(3) (menadione)

Vitamin K(3) is an essential micronutrient required for the activation of coagulation factors and thus hemostasis. Administration of vitamin K(3) analogues may cause anemia, which at least in theory could be due to stimulation of suicidal erythrocyte death or eryptosis characterized by cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane leading to exposure of phosphatidylserine at the erythrocyte surface. Eryptosis is triggered by an increase in the cytosolic Ca(2+) activity, by ceramide and by energy depletion (decrease of cytosolic ATP). The present experiments explored, whether vitamin K(3) may influence eryptosis. Hemolysis was estimated from the supernatant hemoglobin concentration, phosphatidylserine-exposing erythrocytes from annexin V-binding in fluorescence-activated cell sorter (FACS) analysis, erythrocyte volume from forward scatter in FACS analysis, ceramide formation from binding of fluorescent antibodies, and erythrocyte ATP content from a luciferin-luciferase assay. As a result, vitamin K(3) (> or =1microM) caused lysis of an only small fraction of erythrocytes, but significantly increased ceramide formation, significantly increased the percentage of annexin V-binding erythrocytes, significantly decreased forward scatter and, at higher concentrations, significantly decreased the cellular ATP content. In conclusion, vitamin K(3) stimulates suicidal erythrocyte death, an effect at least partially due to ceramide formation and ATP depletion.