Neutrophils in acidotic haemodialysed patients have lower intracellular pH and inflamed state

Immune System Dysfunction and Inflammation in Hemodialysis Patients: Two Sides of the Same Coin

Biocompatibility in hemodialysis (HD) has considerably improved in recent decades, but remains an open issue to be solved, appearing essential to reduce systemic inflammation and enhance patients’ clinical outcomes. Clotting prevention, reduction in complement and leukocyte activation, and improvement of antioxidant effect represent the main goals. This review aims to analyze the different pathways involved in HD patients, leading to immune system dysfunction and inflammation. In particular, we mostly review the evidence about thrombogenicity, which probably represents the most important characteristic of bio-incompatibility. Platelet activation is one of the first steps occurring in HD patients, determining several events causing chronic sub-clinical inflammation and immune dysfunction involvement. Moreover, oxidative stress processes, resulting from a loss of balance between pro-oxidant factors and antioxidant mechanisms, have been described, highlighting the link with inflammation. We updated both innate and acquired immune system dysfunctions and their close link with uremic toxins occurring in HD patients, with several consequences leading to increased mortality. The elucidation of the role of immune dysfunction and inflammation in HD patients would enhance not only the understanding of disease physiopathology, but also has the potential to provide new insights into the development of therapeutic strategies.

Immune Dysfunction in Uremia 2020

Cardiovascular disease and infections are major causes for the high incidence of morbidity and mortality of patients with chronic kidney disease. Both complications are directly or indirectly associated with disturbed functions or altered apoptotic rates of polymorphonuclear leukocytes, monocytes, lymphocytes, and dendritic cells. Normal responses of immune cells can be reduced, leading to infectious diseases or pre-activated/primed, giving rise to inflammation and subsequently to cardiovascular disease. This review summarizes the impact of kidney dysfunction on the immune system. Renal failure results in disturbed renal metabolic activities with reduced renin, erythropoietin, and vitamin D production, which adversely affects the immune system. Decreased kidney function also leads to reduced glomerular filtration and the retention of uremic toxins. A large number of uremic toxins with detrimental effects on immune cells have been identified. Besides small water-soluble and protein-bound compounds originating from the intestinal microbiome, several molecules in the middle molecular range, e.g., immunoglobulin light chains, retinol-binding protein, the neuropeptides Met-enkephalin and neuropeptide Y, endothelin-1, and the adipokines leptin and resistin, adversely affect immune cells. Posttranslational modifications such as carbamoylation, advanced glycation products, and oxidative modifications contribute to uremic toxicity. Furthermore, high-density lipoprotein from uremic patients has an altered protein profile and thereby loses its anti-inflammatory properties.

Sepsis Induces a Dysregulated Neutrophil Phenotype That Is Associated with Increased Mortality

Background

Neutrophil dysfunction in sepsis has been implicated in the pathogenesis of multiorgan failure; however, the role of neutrophil extracellular traps (NETs) remains uncertain. We aimed to determine the sequential changes in ex vivo NETosis and its relationship with mortality in patients with sepsis and severe sepsis.

Methods

This was a prospective observational cohort study enrolling 21 healthy age-matched controls and 39 sepsis and 60 severe sepsis patients from acute admissions to two UK hospitals. Patients had sequential bloods for the ex vivo assessment of NETosis in response to phorbol-myristate acetate (PMA) using a fluorometric technique and chemotaxis using time-lapse video microscopy. Continuous data was tested for normality, with appropriate parametric and nonparametric tests, whilst categorical data was analysed using a chi-squared test. Correlations were performed using Spearman's rho.

Results

Ex vivo NETosis was reduced in patients with severe sepsis, compared to patients with sepsis and controls (p = 0.002). PMA NETosis from patients with septic shock was reduced further (p < 0.001) compared to controls. The degree of metabolic acidosis correlated with reduced NETosis (p < 0.001), and this was replicated when neutrophils from healthy donors were incubated in acidotic media. Reduced NETosis at baseline was associated with an increased 30-day (p = 0.002) and 90-day mortality (p = 0.014) in sepsis patients. These findings were accompanied by defects in neutrophil migration and delayed apoptosis. Resolution of sepsis was not associated with the return to baseline levels of NETosis or migration.

Conclusions

Sepsis induces significant changes in neutrophil function with the degree of dysfunction corresponding to the severity of the septic insult which persists beyond physiological recovery from sepsis. The changes induced lead to the failure to effectively contain and eliminate the invading pathogens and contribute to sepsis-induced immunosuppression. For the first time, we demonstrate that reduced ex vivo NETosis is associated with poorer outcomes from sepsis.

Coordinate effects of P2X7 and extracellular acidification in microglial cells

Extracellular adenosine 5′-triphosphate (ATP) is a damage-associated molecular pattern and contributes to inflammation associated diseases including cancer. Extracellular acidosis is a novel danger signal in the inflammatory sites, where it can modulate inflammation, immunity and tumor growth. Extracellular acidification was shown to inhibit P2X7-mediated channel currents, while it remains unknown how acidification and P2X7 together affect cellular responses. Here, we treated BV-2 microglial cells with ATP in a short period (<15 min) or a sustained acidified condition. For short acidification we compared the actions of neutralized ATP and acidic ATP in a condition with pH buffering. For sustained acidification, we treated cells with neutralized ATP in acidic medium or acidic ATP in medium without pH buffering. In the short acidified condition, neutralized ATP induced higher responses than acidic ATP to increase intracellular calcium and reactive oxygen species, decrease intracellular potassium and induce cell death. In contrast, these cellular responses and mitochondrial fission caused by neutralized ATP were enhanced by pH 6.0 and pH 4.5 media. P2X7 activation can also rapidly block mitochondrial ATP turnover and respiration capacity, both of which were mimicked by nigericin and enhanced by acidity. Taken together P2X7-mediated ionic fluxes and reactive oxygen species production are attenuated under short acidification, while sustained acidification itself can induce mitochondrial toxicity which deteriorates the mitochondrial function under P2X7 activation.

Low Serum Neutrophil Gelatinase-associated Lipocalin Level as a Marker of Malnutrition in Maintenance Hemodialysis Patients

Background

Neutrophil gelatinase-associated lipocalin (NGAL or LCN2) is an iron-transporting factor which possesses various activities such as amelioration of kidney injury and host defense against pathogens. Its circulating concentrations are elevated in acute and chronic kidney diseases and show a positive correlation with poor renal outcome and mortality, but its clinical significance in maintenance hemodialysis (HD) patients remains elusive.

Methods

Serum NGAL levels were determined by enzyme-linked immunosorbent assay in out-patient, Japanese HD subjects. Their correlation to laboratory findings and morbidity (as development of severe infection or serum albumin reduction) was investigated using linear regression analysis and χ² test.

Results

Pre-dialysis serum NGAL levels in HD patients were elevated by 13-fold compared to healthy subjects (n=8, P<0.001). In a cross-sectional study of 139 cases, serum NGAL concentrations were determined independently by % creatinine generation rate (an indicator of muscle mass, standardized coefficient β=0.40, P<0.001), peripheral blood neutrophil count (β=0.38, P<0.001) and anion gap (which likely reflects dietary protein intake, β=0.16, P<0.05). Iron administration to anemic HD patients caused marked elevation of peripheral blood hemoglobin, serum ferritin and iron-regulatory hormone hepcidin-25 levels, but NGAL levels were not affected. In a prospective study of 87 cases, increase in serum albumin levels a year later was positively associated to baseline NGAL levels by univariate analysis (r=0.36, P<0.01). Furthermore, within a year, patients with the lowest NGAL tertile showed significantly increased risk for marked decline in serum albumin levels (≥0.4 g/dl; odds ratio 5.5, 95% confidence interval 1.5–20.3, P<0.05) and tendency of increased occurrence of severe infection requiring admission (odds ratio 3.1, not significant) compared to the middle and highest tertiles.

Conclusion

Low serum NGAL levels appear to be associated with current malnutrition and also its progressive worsening in maintenance HD patients.

Cytokine secretion and markers of inflammation in relation to acidosis among chronic hemodialysis patients

BACKGROUND

Various cytokines are increased in hemodialysis (HD) patients, and are considered prognostic markers. Metabolic acidosis is common among chronic HD patients and is associated with survival. The relationship between acidosis and cytokines in HD patients has not been fully explored. The study aim was to measure pro- and anti-inflammatory cytokines in HD patients, with relation to bicarbonate levels.

METHODS

Forty-seven stable HD patients were included (male/female 28/19, mean age 70.4 ± 14.5 years). Blood tests were taken before a midweek dialysis session. Cytokine secretion from peripheral blood mononuclear cells was measured.

RESULTS

Acidosis versus no acidosis (serum HCO3 – 21.5 ± 0.2 vs. 24.9 ± 0.3 mEq/l, p < 0.001) was associated with decreased secretion of the anti-inflammatory interleukin-10 (IL-10, 1.16 ± 0.11 vs. 1.71 ± 0.20 ng/ml, p = 0.023). Patients with acidosis had higher parathyroid hormone (PTH), calcium-phosphate product, protein intake and transferrin. Higher IL-10 was associated with increased IL-6 secretion, higher bicarbonate, younger age and lower PTH.

CONCLUSIONS

In stable chronic HD patients, a possible direct relation exists between metabolic acidosis and IL-10.

Efeito inibidor do soro urêmico sobre o metabolismo oxidativo dos neutrófilos de cães

Foi testada a hipótese de que, à semelhança do que ocorre em humanos, os componentes do soro urêmico inibem o metabolismo oxidativo dos neutrófilos de cães. Para isto, o sangue total de 10 cães foi incubado com soro homólogo urêmico e não urêmico e posteriormente comparado quanto à produção neutrofílica de superóxido estimada pelo método citoquímico de redução do tetrazólio nitroazul (NBT). A produção de superóxido gerada pelo metabolismo oxidativo dos neutrófilos tratados com soro urêmico apresentou significante redução (P<0,05) em relação aos tratados com plasma autólogo e homólogo com níveis normais de ureia. Concluiu-se que os componentes presentes no soro urêmico inibem ex vivo o metabolismo oxidativo dos neutrófilos de cães portadores de insuficiência renal e que, portanto, têm sua imunidade inata comprometida.

New insights into uremic toxicity

PURPOSE OF REVIEW

Our concept of uremia has expanded to encompass the illness patients begin to suffer as glomerular filtration rate declines long before the onset of end-stage renal disease (ESRD) not explained by known derangements in volume status or metabolic parameters. New insights into the accumulation of uremic toxins and the loss of function of hormones and enzymes provide important information on the etiology of uremia.

RECENT FINDINGS

New data are accumulating on the identity and toxicity of uremic toxins and the syndromes that encompass uremia. rho-Cresol sulfate and indoxyl sulfate are small, protein-bound molecules that are poorly cleared with dialysis. These molecules have been linked to cardiovascular disease and oxidative injury. Impaired immunity plays a central role in the morbidity of ESRD and may be both the result of uremic toxicity and a contributor to oxidative stress in ESRD. Uremic cachexia is an underrecognized uremic syndrome. New insights into disordered feeding circuits in ESRD may lead to novel therapies using hormone agonists.

SUMMARY

Mortality in ESRD remains unacceptably high. It is hoped that as knowledge emerges on the causes and consequences of uremia, we are embarking on an era not only of new insights but also new and effective treatments for patients with the ill effects of uremia.

Aspects of immune dysfunction in end-stage renal disease

End-stage renal disease (ESRD) is associated with significantly increased morbidity and mortality resulting from cardiovascular disease (CVD) and infections, accounting for 50% and 20%, respectively, of the total mortality in ESRD patients. It is possible that these two complications are linked to alterations in the immune system in ESRD, as uremia is associated with a state of immune dysfunction characterized by immunodepression that contributes to the high prevalence of infections among these patients, as well as by immunoactivation resulting in inflammation that may contribute to CVD. This review describes disorders of the innate and adaptive immune systems in ESRD, underlining the specific role of ESRD-associated disturbances of Toll-like receptors. Finally, based on the emerging links between the alterations of immune system, CVD, and infections in ESRD patients, it emphasizes the potential role of the immune dysfunction in ESRD as an underlying cause for the high mortality in this patient population and the need for more studies in this area.

Immune dysfunction in uremia

Kidney dysfunction leads to disturbed renal metabolic activities and to impaired glomerular filtration, resulting in the retention of toxic solutes affecting all organs of the body. Cardiovascular disease (CVD) and infections are the main causes for the increased occurrence of morbidity and mortality among patients with chronic kidney disease (CKD). Both complications are directly or indirectly linked to a compromised immune defense. The specific coordinated roles of polymorphonuclear leukocytes (PMNLs), monocytes/macrophages, lymphocytes and antigen-presenting cells (APCs) in maintaining an efficient immune response are affected. Their normal response can be impaired, giving rise to infectious diseases or pre-activated/primed, leading to inflammation and consequently to CVD. Whereas the coordinated removal via apoptosis of activated immune cells is crucial for the resolution of inflammation, inappropriately high apoptotic rates lead to a diminished immune response. In uremia, the balance between pro- and anti-inflammatory and between pro- and anti-apoptotic factors is disturbed. This review summarizes the interrelated parameters interfering with the immune response in uremia, with a special focus on the non-specific immune response and the role of uremic toxins.