Georgia Antoniadi

Disturbances of acquired immunity in hemodialysis patients

Acquired immunity disturbances in hemodialysis (HD) patients are many and diverse. They are caused by uremia per se, the HD procedure, chronic renal failure complications, and therapeutic interventions for their treatment. Current data suggest that acquired immunity disturbances in HD patients concern mainly the T‐lymphocyte and the antigen‐presenting cell (APC). The T‐lymphocyte‐dependent immune response is deficient, predisposing to infections and inadequate response to vaccinations. In addition, APCs are preactivated, which seems to be responsible for the malnutrition–inflammation–atherosclerosis syndrome, and also affects T‐lymphocyte function. At the molecular level it is assumed that the interaction between the APC and the T‐lymphocyte is impaired. This disturbance is likely to concern the signal that results from the interaction between the major histocompatibility complex:peptide complex on APC surfaces and T‐cell receptors on T‐lymphocyte surfaces, or the signal that results from the interaction among the co‐receptors of these two cells. The aim of the present review was to collect and classify the available clinical and experimental data in this area. Although many pieces are still missing from the puzzle, a better understanding of the responsible molecular mechanisms, will potentially lead to increased survival and a better quality of life in HD patients.

Basic Science and Dialysis: Disturbances of Acquired Immunity in Hemodialysis Patients

Acquired immunity disturbances in hemodialysis (HD) patients are many and diverse. They are caused by uremia per se, the HD procedure, chronic renal failure complications, and therapeutic interventions for their treatment. Current data suggest that acquired immunity disturbances in HD patients concern mainly the T‐lymphocyte and the antigen‐presenting cell (APC). The T‐lymphocyte‐dependent immune response is deficient, predisposing to infections and inadequate response to vaccinations. In addition, APCs are preactivated, which seems to be responsible for the malnutrition–inflammation–atherosclerosis syndrome, and also affects T‐lymphocyte function. At the molecular level it is assumed that the interaction between the APC and the T‐lymphocyte is impaired. This disturbance is likely to concern the signal that results from the interaction between the major histocompatibility complex:peptide complex on APC surfaces and T‐cell receptors on T‐lymphocyte surfaces, or the signal that results from the interaction among the co‐receptors of these two cells. The aim of the present review was to collect and classify the available clinical and experimental data in this area. Although many pieces are still missing from the puzzle, a better understanding of the responsible molecular mechanisms, will potentially lead to increased survival and a better quality of life in HD patients.

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.

Does Hepcidin Affect Erythropoiesis in Hemodialysis Patients

Introduction: Prohepcidin is the precursor of hepcidin, a liver-derived peptide involved in iron metabolism by blocking its intestinal absorption and its release by the reticuloendothelial system. Iron overload and inflammation increase hepcidin expression, whereas anemia and hypoxia suppress it. In the present study prohepcidin levels were determined in the serum of hemodialysis (HD) patients and its correlations with iron metabolism markers, C-reactive protein (CRP) and hematocrit (Hct) were assessed. Patients and Methods: Forty-sixHD patients and 22 healthy volunteers were enrolled in the study. Hct, serum prohepcidin, CRP, iron, ferritin, transferrin saturation and transferrin receptors were measured. The weekly erythropoietin dose, last-month intravenous iron dose and the patients’ demographics were recorded. Results: In comparison to the healthy volunteers, the HD patients had higher serum ferritin, transferrin receptors and CRP, lower serum iron and similar transferrin saturation and prohepcidin levels. In the patient group prohepcidin levels were negatively correlated with Hct but not with any other of the examined parameters. Multiple linear regression analysis considering age, inflammation, iron adequacy, erythropoietin dose and prohepcidin levels revealed that prohepcidin was the predominant determinant of Hct. Conclusions: Taking into account the low Hct levels in the HD patients of our study, it seems plausible that the prohepcidin levels assessed in this group are inappropriately high. These functionally high prohepcidin levels may be associated with the factors that inhibit erythropoiesis in HD patients. On the other hand, the absence of other expected correlations indicates that further studies are needed in order to definitely clarify this aspect.

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-β levels, endothelial cells also confer to the deteriorating process of fibrosis in advanced diabetic nephropathy through endothelial to mesenchymal transition.

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. ζ-Chain phosphorylation is an early and central event in the process that follows antigen recognition by the T cell antigen receptor (TCR). T cell ζ-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 ζ-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 ζ-chain-positive T cells, as well as T cell ζ-chain mean fluorescence intensity (MFI) were evaluated with flow cytometry. The inflammatory markers C-reactive protein, interleukin-6 and tumor necrosis factor-α 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 ζ-chain MFI was decreased. CD3-Ε MFI did not differ between the two groups indicating that among the TCR complex constituents, ζ-chain is selectively downregulated. Conclusions: HD is a state of chronic inflammation. Like in other pathological chronic inflammatory conditions, T cell ζ-chain is downregulated in HD patients. Since ζ-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.

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.

Effect of One-year Oral α-Tocopherol Administration on the Antioxidant Defense System in Hemodialysis Patients

Abstract:  Oxidative stress is increased in hemodialysis (HD) patients and contributes to the increased morbidity and mortality in this population. Vitamin E is an antioxidant agent. In the present study the effect of prolonged oral α‐tocopherol administration on the antioxidant defense system was evaluated. The antioxidant factors plasma total antioxidant status (TAS), red blood cell superoxide dismutase (SOD) activity and glutathione peroxidase (GPX) activity were evaluated with spectrometry in 27 HD patients. Measurements were performed before and after oral administration of α‐tocopherol at a dose of 500 mg/d for a one‐year period. Twenty HD patients received a placebo and 22 healthy volunteers served as controls. TAS was increased in HD patients. No difference was detected in SOD and GPX activity between HD patients and healthy volunteers. Tocopherol administration induced a significant decrease in TAS and SOD activity. Levels of GPX activity remained unaffected. All the evaluated factors remained stable in the HD patients receiving a placebo. Prolonged oral α‐tocopherol administration in HD patients induces a decrease in some components of the antioxidant defense system, raising the possibility for a pro‐oxidative role of vitamin E. Vitamin E is an antioxidant agent, but it is also known to have pro‐oxidant action under special conditions that can be encountered 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-α 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.

Dichloroacetate at therapeutic concentration alters glucose metabolism and induces regulatory T-cell differentiation in alloreactive human lymphocytes

Abstract Background: Most cancer cells rely on aerobic glycolysis. Dichloroacetate (DCA) inhibits aerobic glycolysis and is a promising relatively nontoxic anticancer compound. However, rapidly proliferating effector T-cells also rely on aerobic glycolysis, whereas regulatory T-cells (Treg) do not. The effect of DCA on glucose metabolism and Treg differentiation was evaluated in alloreactive lymphocytes. Methods: Peripheral blood mononuclear cells from healthy volunteers were used in a two-way mixed lymphocyte reaction. Lymphocyte proliferation was assessed by cell counting; DCA cytotoxicity, by lactate dehydrogenase release assay; and glucose uptake and aerobic glycolysis, by measuring in the supernatants the correspondent glucose and lactate concentrations. Interleukin-10 (IL-10) was measured in the supernatants, whereas the Treg signature transcription factor forkhead box P3 (FOXP3) was measured in cell lysates by means of enzyme-linked immunosorbent assay. Results: DCA had a minor effect on lymphocyte proliferation and cytotoxicity. However, DCA decreased glucose uptake and inhibited aerobic glycolysis. Finally, DCA markedly increased the production of IL-10 and the expression of FOXP3. Conclusions: DCA inhibits aerobic glycolysis and induces Treg differentiation in human alloreactive lymphocytes. This could result in decreased immunosurveillance in case of its use as an anticancer drug. However, DCA could play a role as an immunosuppressant in the fields of transplantation and autoimmunity.