Correction to: Tryptophan depletion under conditions that imitate insulin resistance enhances fatty acid oxidation and induces endothelial dysfunction through reactive oxygen species-dependent and independent pathways.

In the original publication of the article, last author's name was misspelt. The correct name is given here.

Uric acid increases cellular and humoral alloimmunity in primary human peripheral blood mononuclear cells.

AIM: Hyperuricaemia is common among kidney transplant recipients and has been associated with worse graft outcome. Since episodes of acute cellular rejection and chronic humoral rejection contribute to decreased graft survival, in this study the effect of uric acid on cellular and humoral alloimmunity was evaluated. METHODS: Cellular alloimmunity was assessed by cell proliferation in two-way mixed lymphocyte reaction (MLR) with human peripheral blood mononuclear cells (PBMC). For assessing humoral alloimmunity we developed a method in which humoral alloimmunity was induced in one-way MLR. Then the de novo production of alloantibodies was measured with an antibody-mediated complement-dependent cytotoxicity assay, in which supernatants from the above MRLs were used against resting PBMC similar to the stimulator cells of the above MLRs. RESULTS: Uric acid at a concentration above its crystallization threshold increased cellular proliferation in two-way MLRs. Supernatants from one-way MLRs performed in the presence of uric acid were more cytotoxic against PBMC from individuals that had conferred the stimulator cells for the above MLRs. CONCLUSIONS: Uric acid increases both cellular and humoral alloimmunity in human PBMC. These results offer a possible pathogenetic mechanism for the observed relation between hyperuricaemia and worse kidney allograft survival.

Tryptophan depletion under conditions that imitate insulin resistance enhances fatty acid oxidation and induces endothelial dysfunction through reactive oxygen species-dependent and independent pathways.

In atherosclerosis-associated pathologic entities characterized by malnutrition and inflammation, L-tryptophan (TRP) levels are low. Insulin resistance is an independent cardiovascular risk factor and induces endothelial dysfunction by increasing fatty acid oxidation. It is also associated with inflammation and low TRP levels. Low TRP levels have been related to worse cardiovascular outcome. This study evaluated the effect of TRP depletion on endothelial dysfunction under conditions that imitate insulin resistance. Fatty acid oxidation, harmful pathways due to increased fatty acid oxidation, and endothelial dysfunction were assessed in primary human aortic endothelial cells cultured under normal glucose, low insulin conditions in the presence or absence of TRP. TRP depletion activated general control non-derepressible 2 kinase and inhibited aryl hydrocarbon receptor. It increased fatty acid oxidation by increasing expression and activity of carnitine palmitoyltransferase 1. Elevated fatty acid oxidation increased the formation of reactive oxygen species (ROS) triggering the polyol and hexosamine pathways, and enhancing protein kinase C activity and methylglyoxal production. TRP absence inhibited nitric oxide synthase activity in a ROS-dependent way, whereas it increased the expression of ICAM-1 and VCAM-1 in a ROS independent and possibly p53-dependent manner. Thus, TRP depletion, an amino acid whose low levels have been related to worse cardiovascular outcome and to inflammatory atherosclerosis-associated pathologic entities, under conditions that imitate insulin resistance enhances fatty acid oxidation and induces endothelial dysfunction through ROS-dependent and independent pathways. These findings may offer new insights at the molecular mechanisms involved in accelerated atherosclerosis that frequently accompanies malnutrition and inflammation.

Indoleamine 2,3-dioxygenase depletes tryptophan, activates general control non-derepressible 2 kinase and down-regulates key enzymes involved in fatty acid synthesis in primary human CD4+ T cells.

Indoleamine 2,3-dioxygenase (IDO) is expressed in antigen-presenting cells and exerts immunosuppressive effects on CD4(+) T cells. One mechanism is through the inhibition of aerobic glycolysis. Another prerequisite for T-cell proliferation and differentiation into effector cells is increased fatty acid (FA) synthesis. The effect of IDO on enzymes involved in FA synthesis was evaluated in primary human cells both in mixed lymphocyte reactions in the presence or not of the IDO inhibitor 1-dl-methyl-tryptophan, and in stimulated CD4(+) T cells in the presence or not of the general control non-derepressible 2 (GCN2) kinase activator tryptophanol (TRP). IDO or TRP inhibited cell proliferation. By assessing the level of GCN2 kinase or mammalian target of rapamycin complex 1 substrates along with a kynurenine free system we showed that IDO exerts its effect mainly through activation of GCN2 kinase. IDO or TRP down-regulated ATP-citrate lyase and acetyl coenzyme A carboxylase 1, key enzymes involved in FA synthesis. Also, IDO or TRP altered the expression of enzymes that control the availability of carbon atoms for FA synthesis, such as lactate dehydrogenase-A, pyruvate dehydrogenase, glutaminase 1 and glutaminase 2, in a way that inhibits FA synthesis. In conclusion, IDO through GCN2 kinase activation inhibits CD4(+) T-cell proliferation and down-regulates key enzymes that directly or indirectly promote FA synthesis, a prerequisite for CD4(+) T-cell proliferation and differentiation into effector cell lineages.

Indoleamine 2,3-dioxygenase increases p53 levels in alloreactive human T cells, and both indoleamine 2,3-dioxygenase and p53 suppress glucose uptake, glycolysis and proliferation.

Indoleamine 2,3-dioxygenase (IDO) suppresses adaptive immunity by inhibiting T-cell proliferation and altering glucose metabolism. The tumor suppressor p53 also alters these cellular processes with similar results. The effect of IDO on p53 and on glucose metabolism was evaluated in alloreactive T cells. Mixed-lymphocyte reactions (MLRs) were performed in the presence or not of the IDO inhibitor, 1-dl-methyl-tryptophan (1-MT) and/or the p53 inhibitor, pifithrin-α (PFT). Cell proliferation, glucose consumption and lactate production were assessed. 1-MT increased cell proliferation, glucose influx and lactate production, whereas PFT enhanced cell proliferation and glucose influx, leaving lactate production unaffected. In MLR-derived T cells, protein analysis revealed that IDO activated general control non-derepressible 2 kinase and induced p53, p-p53 (p53 phosphorylated at serine 15) and p21. In addition, both IDO and p53 decreased glucose transporter 1 and TP53-induced glycolysis and apoptosis regulator and increased synthesis of cytochrome c oxidase 2. IDO also reduced lactate dehydrogenase-A and glutaminase 2 levels, whereas p53 left them unaffected. Neither 1-MT nor PFT affected glucose-6-phosphate dehydrogenase. In conclusion, in alloreactive T cells, IDO increases p53 levels, and both IDO and p53 inhibit cell proliferation, glucose consumption and glycolysis. Lactate production and glutaminolysis are also suppressed by IDO, but not by p53.

Increased visfatin in hemodialysis patients is associated with decreased demands for recombinant human erythropoietin.

BACKGROUND: Studies detected an association between visfatin and markers of iron metabolism in patients with insulin resistance. In this study, such a relation was evaluated in hemodialysis (HD) patients. Also relations between visfatin and hepcidin, demands for recombinant human erythropoietin (rHuEpo), inflammation, and situations characterized by insulin resistance were evaluated. METHODS: After a four-week washout period from iron treatment, 33 HD patients and 20 healthy volunteers enrolled in the study. Serum visfatin, hepcidin, and interleukin-6 (IL-6) were assessed by means of enzyme-linked immunosorbent assay. Hemoglobin, serum iron, ferritin, and transferrin saturation (TSAT) were also measured. RESULTS: Visfatin was markedly increased in HD patients. Visfatin levels did not differ between diabetics and non-diabetics. No relation was detected between visfatin and body mass index or IL-6 in HD patients. From the markers of iron metabolism, the hepcidin included, visfatin was related only to TSAT. A strong positive relation was revealed between visfatin and hemoglobin, whereas visfatin was inversely related to rHuEpo dose. Resistance to rHuEpo index was inversely and independently of TSAT related to visfatin. CONCLUSION: Visfatin is increased in HD patients and it is associated with decreased demands for rHuEpo.

The renal endothelium in diabetic nephropathy.

Diabetic nephropathy is the leading cause of end-stage renal disease. Diabetes mellitus is characterized by generalized endothelial dysfunction. However, recent data also emphasizes the role of local renal endothelium dysfunction in the pathogenesis of diabetic nephropathy. Hyperglycemia triggers a complex network of signal-transduction molecules, transcription factors, and mediators that culminate in endothelial dysfunction. In the glomerulus, vascular endothelial growth factor-A (VEGF)-induced neoangiogenesis may contribute to the initial hyperfiltration and microalbuminuria due to increased filtration area and immaturity of the neovessels, respectively. However, subsequent decrease in podocytes number decreases VEGF production resulting in capillary rarefaction and decreased glomerular filtration rate (GFR). Decreased nitric oxide availability also plays a significant role in the development of advanced lesions of diabetic nephropathy through disruption of glomerular autoregulation, uncontrolled VEGF action, release of prothrombotic substances by endothelial cells and angiotensin-II-independent aldosterone production. In addition, disturbances in endothelial glycocalyx contribute to decreased permselectivity and microalbuminuria; whereas there are recent evidences that reduced glomerular fenestral endothelium leads to decreased GFR levels. Endothelial repair mechanisms are also impaired in diabetes, since circulating endothelial progenitor cells number is decreased in diabetic patients with microalbuminuria. Finally, in the context of elevated profibrotic cytokine transforming growth factor-ß levels, endothelial cells also confer to the deteriorating process of fibrosis in advanced diabetic nephropathy through endothelial to mesenchymal transition.

The indoleamine 2,3-dioxygenase inhibitor 1-methyl-tryptophan suppresses mitochondrial function, induces aerobic glycolysis and decreases interleukin-10 production in human lymphocytes.

BACKGROUND: Indoleamine 2,3-dioxygenase (IDO) suppresses adaptive immunity. It is known that IDO induces T-cell differentiation to regulatory T-cells (Treg) through tryptophan depletion and/or kynurenine pathway products. CD4+ effector T-cells require distinct metabolic programs in order to support their function as compared to Treg cells. Furthermore, glucose metabolism is also known to affect B-cell survival and function. The effect of IDO on glucose metabolism of lymphocytes was evaluated by using its inhibitor 1-methyl-DL-tryptophan (1-MT). METHODS: Ten healthy volunteers vaccinated against tetanus. Peripheral blood mononuclear cells (PBMC) were cultured with or without tetanus toxoid and/or 1-MT. Cell proliferation was assessed by optical microscopy, glucose uptake by measuring its concentration in the supernatant, aerobic glycolysis by assessing lactate concentration in the supernatant, mitochondrial function by XTT assay, and finally production of Tregs' signature cytokine IL-10 by means of ELISA. RESULTS: Primarily, IDO decreases glucose uptake by stimulated lymphocytes. Secondly, IDO increases mitochondrial function in stimulated lymphocytes. In addition, IDO decreases aerobic glycolysis in stimulated lymphocytes. Finally, IDO induces the production of the immunosuppressive cytokine IL-10 by stimulated lymphocytes. CONCLUSION: Considering that cell metabolism plays a significant role in lymphocyte differentiation and function, IDO may exert its immunomodulatory effect by interfering with cell metabolism.

Plasma indoleamine 2,3-dioxygenase concentration is increased in hemodialysis patients and may contribute to the pathogenesis of coronary heart disease.

INTRODUCTION: Coronary heart disease (CHD) is the leading cause of death in hemodialysis (HD) patients. Inflammation contributes to the pathogenesis of atherosclerosis in this population. Indoleamine 2,3-dioxygenase (IDO), an enzyme with immunomodulatory properties, was evaluated in HD patients with or without CHD. METHODS: Of the total of 66 HD patients, 22 of them with CHD were confirmed by coronary angiography and 24 healthy volunteers were enrolled in the study. Plasma IDO was assessed by means of enzyme-linked immunosorbent assay. Serum interleukin-6 (IL-6) and C-reactive protein (CRP) were also measured. RESULTS: Compared with healthy volunteers, plasma IDO concentration was markedly increased in HD patients (median 8.04 ng/mL vs. 48.9 ng/mL). Serum IL-6 and CRP were also significantly increased in HD patients. Compared with HD patients without CHD, plasma IDO concentration was significantly increased in HD patients with CHD (median 38.6 ng/mL vs. 74.5 ng/mL). Neither IL-6 nor CRP differed between the last two groups. IDO was negatively correlated with IL-6 and CRP. CONCLUSION: IDO concentration is increased in HD patients and is increased further in HD patients with CHD. It remains to be elucidated if increased IDO plays a direct role in the pathogenesis of atherosclerosis or if it affects atherosclerosis indirectly by curtailing chronic inflammation or both.

Plasma indoleamine 2,3-dioxygenase and arginase type I may contribute to decreased blood T-cell count in hemodialysis patients.

BACKGROUND: Acquired immunity is impaired in hemodialysis (HD) patients, and decreased T-cell number may contribute. Indoleamine 2,3-dioxygenase (IDO) and arginase type I (ARG) catabolize tryptophane and arginine, respectively, and exert proapoptotic and antiproliferative effects on T-cells. Plasma levels of IDO and ARG and their relation to blood T-cell number were evaluated in HD patients. METHODS: Thirty-two HD patients and 20 healthy controls participated in the study. Plasma IDO and ARG were measured by means of enzyme-linked immunosorbent assay. T-cell number was assessed by means of flow cytometry. RESULTS: IDO concentration was significantly higher in HD patients than in healthy volunteers (44.30 ± 31.83 ng/mL vs. 21.28 ± 26.21 ng/mL, p = 0.009). There was a trend for higher ARG concentration in HD patients (13.43 ± 11.91 ng/mL) than in healthy volunteers (9.56 ± 4.03 ng/mL), which, however, did not reach statistic significance (p = 0.099). Absolute T-cell count was significantly lower in HD patients than in healthy controls (1176.99 ± 567.71 cells/mm3 vs. 1519.85 ± 594.96 cells/mm3, p = 0.040). Absolute blood T-cell number was inversely related to plasma IDO (r = -0.490, p = 0.004) and to plasma ARG (r = -0.387, p = 0.029) concentrations. CONCLUSIONS: Plasma IDO and ARG may contribute to decreased blood T-cell count in HD patients.

Vitamin D receptor activators and response to injury in kidney diseases.

Clinical studies have confirmed that administration of vitamin D receptor (VDR) activators offers a survival benefit in hemodialysis patients and may help in preservation of renal function in predialysis patients. Accumulated clinical and mainly experimental data support that in the context of kidney disease, VDR activators exert their beneficial effect not only due to their action on calcium and phosphorus homeostasis, but also through modulation of the response to injury. They attenuate systemic and renal inflammation, and they affect the tissue repair process, reducing renal fibrosis. This aspect of the functions of VDR activators in kidney disease is reviewed in the present manuscript.

Urate crystals trigger B-cell receptor signal transduction and induce B-cell proliferation.

Background Urate in its crystal form is a known danger-associated molecular pattern, which after its internalization activates cells of the innate immune system. However, by inducing lipid raft sequestration and clustering of membrane-bound proteins with immunoreceptor tyrosine-based activation motifs, urate crystals can also activate cells of the innate immune system without previous internalization. Also, urate crystals trigger T-cell receptor signal transduction and induce T-cell proliferation. In this study, we evaluated whether urate crystals can also initiate B-cell receptor (BCR) signal transduction and promote B-cell proliferation. Methods B cells were isolated from the blood of 10 individuals and cultured with or without urate at a concentration of 10 mg/dL, at which crystallization occurs. Phosphorylated Igα (CD79A) and c-Myc were assessed by Western blotting and B-cell proliferation with BrdU assay. Results Urate increased the level of phosphorylated Igα, a component of the BCR complex. Phosphorylation of Igα is the very proximal event in BCR signal transduction. Also, urate increased the expression of c-Myc, an essential transcription factor for BCR-induced B-cell proliferation. Finally, urate induces B-cell proliferation. Conclusions Urate crystals trigger BCR signal transduction and induce B-cell proliferation. The clinical significance of urate-induced B-cell activation remains to be elucidated.

The role of hepcidin in iron homeostasis and anemia in hemodialysis patients.

Anemia is a common complication in hemodialysis (HD) patients. Despite the great success of recombinant human erythropoietin in clinical practice, resistance to this therapy is common. Additionally, nephrologists frequently witness a rapid and significant drop in their patients' hematocrit during the course of various acute events that regularly take place in this sensitive population. Hepcidin, a recently identified peptide, may mediate this development in many instances. Hepcidin production is regulated by hypoxia/anemia, iron status, and importantly, inflammation. This peptide can block iron absorption by the duodenum, iron release from both the liver (the main iron storage pool) and, more significantly, the macrophages interrupting iron recycling between senescent red cells and the reticuloendothelial system. The decreased availability of iron for erythropoiesis leads to the anemia of chronic disease or, in HD patients, aggravate an already existing anemia HD is now widely considered an inflammatory state probably accounting for the increased serum hepcidin levels that have been associated with it. The physiology of hepcidin and its possible contribution to the pathogenesis of anemia in HD patients are the subject of this review.

Decreased CD3+CD16+ natural killer-like T-cell percentage and zeta-chain expression accompany chronic inflammation in haemodialysis patients.

AIM: Clinical and experimental data indicate a deficient immune response in haemodialysis (HD) patients. Natural killer-like (NKL) T cells express on their surface both the T-cell antigen receptor (TCR) and a diverse set of NK-cell receptors (NKR) and share properties of both T cells and NK cells. zeta-Chain phosphorylation is an early event that follows TCR activation or some NKR activation. The zeta-chain of both T cell and NK cells is downregulated in many chronic inflammatory states, HD included. In the present study, NKL T-cell percentage and zeta-chain expression in HD patients were evaluated. METHODS: Thirty-three stable HD patients and 30 healthy volunteers were enrolled into the study. NKL T-cell percentage and NKL T-cell zeta-chain mean fluorescence intensity (MFI) were evaluated with flow cytometry. The inflammatory markers C-reactive protein, interleukin-6 and tumour necrosis factor-alpha were measured in the serum by means of enzyme-linked immunosorbent assay. RESULTS: All the evaluated markers of inflammation were increased in HD patients. In these patients, NKL T-cell percentage (1.71 +/- 1.69% vs 3.94 +/- 3.86%) and zeta-chain MFI (3.66 +/- 2.79 vs 7.03 +/- 7.91) were decreased. CONCLUSIONS: NKL T-cell percentage and zeta-chain expression is decreased in HD patients. Taking into consideration the continuously increasing age of the HD patients and that normally NKL T-cell numbers increase with age counteracting the impaired T-cell and NK-cell function accompanying advancing age, the above NKL T-cell disturbances could contribute to the impaired immune response in this population. Measures towards alleviating chronic inflammation could partially restore NKL T-cell impairment.

Indoleamine 2,3-dioxygenase suppresses humoral alloimmunity via pathways that different to those associated with its effects on T cells.

Chronic antibody-mediated rejection remains a major cause of late graft loss. Regarding cellular alloimmunity, the immunosuppressive properties of indoleamine 2,3-dioxygenase (IDO) have been well investigated; however, little is known of its effects on humoral alloimmunity. Therefore, the present study aimed to evaluate the effects of IDO on humoral alloimmunity. We developed a method for the induction of humoral alloimmunity in a one-way mixed lymphocyte reaction (MLR), which was measured with an antibody-mediated complement-dependent cytotoxicity assay using resting cells, which are similar to the stimulator cells of the aforementioned MLR. In parallel, cellular alloimmunity was assessed in two-way MLRs. The IDO inhibitor 1-methyl-DL-tryptophan was used for evaluating the role of IDO. In order to investigate whether the pathways known to serve a role in the effects of IDO on T cells are applied in humoral alloimmunity, the general control nonderepressible-2 (GCN-2) kinase activator tryptophanol and the aryl hydrocarbon receptor (AhR) inhibitor CH223191 were employed. The IDO inhibitor was revealed to increased cellular autoimmunity, but was decreased by the GCN-2 kinase activator. Unexpectedly, the AhR inhibitor decreased cellular alloimmunity. In addition, the IDO inhibitor was observed to suppress humoral alloimmunity, which may occur in manners independent of GCN-2 kinase AhR. The present study proposed that IDO may decrease humoral alloimmunity in primary human peripheral blood mononuclear cells via pathways that differ to those associated with its effect on T cells.

Activation of General Control Nonderepressible-2 Kinase Ameliorates Glucotoxicity in Human Peritoneal Mesothelial Cells, Preserves Their Integrity, and Prevents Mesothelial to Mesenchymal Transition.

Along with infections, ultrafiltration failure due to the toxicity of glucose-containing peritoneal dialysis (PD) solutions is the Achilles' heel of PD method. Triggered by the protective effect of general control nonderepressible-2 (GCN-2) kinase activation against high-glucose conditions in other cell types, we evaluated whether the same occurs in human peritoneal mesothelial cells. We activated GCN-2 kinase with halofuginone or tryptophanol, and assessed the impact of this intervention on glucose transporter-1, glucose transporter-3, and sodium-glucose cotransporter-1, glucose influx, reactive oxygen species (ROS), and the events that result in glucotoxicity. These involve the inhibition of glyceraldehyde 3-phosphate dehydrogenase and the diversion of upstream glycolytic products to the aldose pathway (assessed by D-sorbitol), the lipid synthesis pathway (assessed by protein kinase C activity), the hexosamine pathway (determined by O-linked ß-N-acetyl glucosamine-modified proteins), and the advanced glycation end products generation pathway (assessed by methylglyoxal). Then, we examined the production of the profibrotic transforming growth factor-ß1 (TGF-ß1), the pro-inflammatory interleukin-8 (IL-8). Cell apoptosis was assessed by cleaved caspase-3, and mesothelial to mesenchymal transition (MMT) was evaluated by α-smooth muscle actin protein. High-glucose conditions increased glucose transporters, glucose influx, ROS, all the high-glucose-induced harmful pathways, TGF-ß1 and IL-8, cell apoptosis, and MMT. Halofuginone and tryptophanol inhibited all of the above high glucose-induced alterations, indicating that activation of GCN-2 kinase ameliorates glucotoxicity in human peritoneal mesothelial cells, preserves their integrity, and prevents MMT. Whether such a strategy could be applied in the clinic to avoid ultrafiltration failure in PD patients remains to be investigated.

Chronic inflammation and T cell zeta-chain downregulation in hemodialysis patients.

BACKGROUND: Clinical and experimental data indicate a deficient immune response in hemodialysis (HD) patients. zeta-Chain phosphorylation is an early and central event in the process that follows antigen recognition by the T cell antigen receptor (TCR). T cell zeta-chain is downregulated in many chronic inflammatory states, such as cancer, autoimmune disease and chronic infection. HD is also characterized as a chronic inflammatory state. The aim of the present study was to evaluate T cell zeta-chain expression in HD patients. PATIENTS AND METHODS: Thirty-three stable HD patients and 30 healthy volunteers were enrolled into the study. T cell count, the percentage of zeta-chain-positive T cells, as well as T cell zeta-chain mean fluorescence intensity (MFI) were evaluated with flow cytometry. The inflammatory markers C-reactive protein, interleukin-6 and tumor necrosis factor-alpha were measured in the serum by means of ELISA. RESULTS: All the evaluated markers of inflammation were increased in HD patients. In these patients, T cell zeta-chain MFI was decreased. CD3-epsilon MFI did not differ between the two groups indicating that among the TCR complex constituents, zeta-chain is selectively downregulated. CONCLUSIONS: HD is a state of chronic inflammation. Like in other pathological chronic inflammatory conditions, T cell zeta-chain is downregulated in HD patients. Since zeta-chain plays a key role in the transduction of the signal that follows antigen recognition by the TCR, its downregulation could be responsible for the deficient cellular immune response observed in HD patients.

Chronic inflammation and CD16+ natural killer cell zeta-chain downregulation in hemodialysis patients.

BACKGROUND: Natural killer (NK) cell activity is decreased in hemodialysis (HD) patients. Zeta-chain phosphorylation is an early event that follows the triggering of some NK cell-activating receptors. NK cell zeta-chain is downregulated in patients with cancer due to chronic inflammation. HD is also a chronic inflammatory state. NK cell zeta-chain expression in HD was evaluated. PATIENTS AND METHODS: Thirty-three HD patients and 30 healthy volunteers were enrolled into the study. The CD3-CD16+ subpopulation was examined, since it corresponds to 90% of all NK cells and has the highest cytotoxicity.NK cell count and zeta-chain mean fluorescence intensity were evaluated with flow cytometry. The inflammatory markers C-reactive protein, IL-6 and tumor necrosis factor-alpha were measured with ELISA. RESULTS: The inflammatory markers were increased in HD patients. NK cell count did not differ between HD patients and healthy volunteers. NK cell zeta-chain mean fluorescence intensity was decreased in the patient group. CONCLUSIONS: Chronic inflammation could be responsible for the NK cell zeta- chain downregulation in HD patients, contributing to the decreased NK cell activity.

The impact of chronic inflammation on bone turnover in hemodialysis patients.

BACKGROUND: Renal osteodystrophy is very common in hemodialysis (HD) patients. HD is a chronic inflammatory state. Studies in other pathological entities have shown an impact of chronic inflammation on bone metabolism. In the present study, the impact of chronic inflammation on bone turnover in HD patients was evaluated. PATIENTS AND METHODS: Thirty-three anuric HD patients free of other pathological conditions or medications that affect immune system or bone metabolism and 30 healthy volunteers enrolled into the study. Intact parathyroid hormone (iPTH), the markers of inflammation IL-6 and CRP, as well as the markers of bone turnover osteocalcin (OCN) and beta-isomerized C-terminal cross-linked peptide of collagen type I (beta-CTx) were measured in the serum. RESULTS: All evaluated factors were increased in HD patients. In the HD group, the serum marker of osteoblastic activity OCN was related inversely to patients' age (r = -0.469, p = 0.006), CRP (rho = -0.460, p = 0.007), and IL-6 (r = -0.485, p = 0.004) but positively to iPTH (r = 0.707, p < 0.001). Similarly, the serum marker of osteoclastic activity beta-CTx was related inversely to patients' age (r = -0.383, p = -0.028), CRP (rho = -0.466, p = 0.006), and IL-6 (r = -0.460, p = 0.007) but positively to iPTH (r = 0.657, p < 0.001). Multiple linear regression analysis revealed that IL-6 affects bone turnover independently of PTH and to the opposite direction. CONCLUSION: Chronic inflammation has a negative impact on bone turnover in HD patients. Certainly, further research and large clinical trials are needed for definite conclusions and for clarifying the exact molecular mechanisms implicated in the interaction between the immune system and bone metabolism in HD patients.

Energy handling in renal tubular epithelial cells of the hamster, a native hibernator, under warm anoxia or reoxygenation.

Ischemia-reperfusion (I-R) injury causes several diseases, including acute kidney injury. Hibernating mammals survive periods of torpor with a marked drop in tissue perfusion, interspersed with periods of arousal, and consequently I-R injury. In the present study, sensitivity to anoxia and/or reoxygenation and alterations in cellular ATP and homeostasis of the two most energy consuming processes, protein translation and Na+-K+-ATPase function, were evaluated in renal proximal tubular epithelial cells of mouse or native hibernator hamster origin. Compared with the mouse cells, the hamster cells were less sensitive to anoxia and reoxygenation and ATP was preserved under anoxia. Anoxia triggered mechanisms that suppress protein translation in both species. However, under anoxia, the activity of ATPase, which is mostly attributed to Na+-K+-ATPase function, remained stable in the hamster cells but decreased in the mouse cells. In normoxia, ATPase activity in hamster cells was considerably lower than that in mouse cells. As the Na+-K+-ATPase pump preserves the ion gradient against passive leakage through ion channels, the lower energy demand for the function of this pump in hamster cells may indicate less ion leakage due to fewer ion channels. In accordance with this hypothesis, ouabain-treated hamster cells had a higher survival rate than mouse cells, indicating fewer ion channels and consequently slower deregulation of intracellular ion concentration and cell death due to Na+-K+-ATPase inhibition. Therefore, it is likely that the conserved energy from the suppression of protein translation is adequate enough to support the lower energy demand for Na+-K+-ATPase function and cell survival of hamster cells under anoxia. Clarifying how cells of a native hibernator manage energy under warm I-R may reveal novel and possible clinically applicable pathways for preventing I-R injury.