Apoptosis of human polymorphonuclear neutrophils accelerated by dialysis membranes via the activation of the complement system

Cell-free DNA as a marker for the outcome of end-stage renal disease patients on haemodialysis

Background

DNA damage and inflammation are common in end-stage renal disease (ESRD). Our aim was to evaluate the levels of circulating cell-free DNA (cfDNA) and the relationship with inflammation, anaemia, oxidative stress and haemostatic disturbances in ESRD patients on dialysis. By performing a 1-year follow-up study, we also aimed to evaluate the predictive value of cfDNA for the outcome of ESRD patients.

Methods

A total of 289 ESRD patients on dialysis were enrolled in the study: we evaluated cfDNA, haemogram, serum iron, hepcidin, inflammatory and oxidative stress markers, and haemostasis. Events and causes of deaths were recorded throughout the follow-up period.

Results

ESRD patients, as compared with controls, presented significantly higher levels of cfDNA, hepcidin, and inflammatory and oxidative stress markers, and significantly lower values of iron and anaemia-related haemogram parameters. The all-cause mortality rate was 9.7%; compared with alive patients, deceased patients (n = 28) were older and presented significantly higher values of inflammatory markers and of cfDNA, which was almost 2-fold higher. Furthermore, cfDNA was the best predictor of all-cause mortality and cardiovascular mortality in ESRD patients, in both unadjusted and adjusted models for basic confounding factors in dialysis.

Conclusions

Our data show cfDNA to be a valuable predictive marker of prognosis in ESRD patients on dialysis treatment; high levels of cfDNA were associated with a poor outcome.

Cytochrome c as a Potentially Clinical Useful Marker of Mitochondrial and Cellular Damage

Mitochondria are evolutionary endosymbionts derived from bacteria. Thus, they bear molecules, such as mitochondrial DNA (mtDNA) that contains CpG DNA repeats and N-formyl peptides (FPs), found in bacteria. Upon cell necrosis or apoptosis, these molecules are released into the interstitial space and the circulation and recognized by the immune cells through the same receptors that recognize pathogen-associated molecular patterns, leading to inflammation. Other mitochondrial molecules are not of bacterial origin, but they may serve as danger-associated molecular patterns (DAMPs) when due to cell injury are translocated into inappropriate compartments. There they are recognized by pattern recognition receptors of the immune cells. Cytochrome c is such a molecule. In this review, experimental and clinical data are presented that confirms cytochrome c release into the extracellular space in pathological conditions characterized by cell death. This indicates that serum cytochrome c, which can be easily measured, may be a clinically useful marker for diagnosing and assessing the severity of such pathological entities. Reasonably, detection of high cytochrome c level into the circulation means release of various other molecules that serves as DAMPs when found extracellularly, the mtDNA and FPs included. Finally, because the release of this universally found compound into the extracellular space makes cytochrome c an ideal molecule to play the role of a DAMP per se, the available experimental and clinical data that support such a role are provided.

Damage-associated molecular patterns derived from mitochondria may contribute to the hemodialysis-associated inflammation

PURPOSE

Inflammation is common in hemodialysis (HD) patients. Mitochondrial damage-associated molecular patterns (DAMPs) are released during cell necrosis or apoptosis and induce inflammation. Cell apoptosis is increased in HD patients. The mitochondrial protein cytochrome c, as a marker of released mitochondrial DAMPs, and interleukin-6 (IL-6), as a marker of inflammation, were evaluated in HD patients.

METHODS

Thirty-four HD patients and 20 controls were enrolled in the study. Serum cytochrome c and IL-6 were measured by means of enzyme-linked immunosorbent assay.

RESULTS

Compared to controls, cytochrome c was markedly increased in HD patients (1392.88 ± 905.24 pg/mL vs. 212.95 ± 91.71 pg/mL). IL-6 was also significantly increased in HD patients (50.32 ± 35.89 pg/mL vs. 14.27 ± 6.83 pg/mL). In HD patients serum IL-6 was positively related to serum cytochrome c (r = 0.458).

CONCLUSION

Both circulating cytochrome c and IL-6 are markedly increased in HD patients. Cytochrome c is positively related to IL-6.

Elevated serum interleukin-10 at time of hospital admission is predictive of mortality in patients with Staphylococcus aureus bacteremia

BACKGROUND

Staphylococcus aureus bacteremia (SaB) carries considerable morbidity and mortality. We examined the predictive value of serum concentrations of interleukin (IL)-10, proinflammatory cytokines, and terminal complement on patient survival and SaB duration.

METHODS

Clinical information on consecutive patients with SaB at a tertiary medical center were collected prospectively. Patient serum samples obtained at the day of clinical presentation were assayed for tumor necrosis factor-α, IL-1β, IL-10, and complement membrane attack complex C5b-9 concentrations using enzyme-linked immunoassay. Logistic regression identified predictors of mortality and duration of bacteremia.

RESULTS

In 59 patients with SaB, 14% died and 17% had prolonged bacteremia (>4 days). Elevated IL-10 serum concentrations (>7.8 pg/mL) identified all 8 patients who died, whereas there were no deaths in patients with normal IL-10 (P = .016). The lack of an IL-1β response (≤0.45 pg/mL) defined all patients with SaB >4 days. In multivariate analysis, patient age (odds ratio [OR], 1.16; P = .022), duration of bacteremia (OR, 1.16; P = .031), and serum IL-10 (OR, 1.05; P = .014) were identified as independent predictors of patient mortality.

CONCLUSIONS

SaB mortality was confined strictly to patients with elevated IL-10 concentrations. We recommend that future clinical trials of SaB stratify patients according to IL-10 and IL-1β serum concentrations in order to better evaluate the impact of therapeutic interventions on patient outcome.

Apoptotic cell-free DNA promotes inflammation in haemodialysis patients

BACKGROUND

A proinflammatory environment characterized by the continuous activation of the innate immune system is thought to contribute to the markedly elevated mortality in haemodialysis (HD) patients with end-stage renal disease (ESRD). The presence of circulating cell-free DNA (cfDNA) has been demonstrated as biomarker in many pathologies.

METHODS

We evaluated the occurrence of cfDNA in HD patients and its functional relevance for innate immunity and inflammation.

RESULTS

Here, we found that cfDNA was enhanced in the plasma of ESRD patients after HD compared to healthy controls. Functionally, cfDNA selectively stimulated the production of the proinflammatory cytokine interleukin (IL)-6 by human monocytes, whereas tumour necrosis factor-α or IL-10 was not induced. Conversely, plasma from HD patients, but not from healthy controls or DNase I-treated HD plasma, induced IL-6 production from monocytes.

CONCLUSION

We provide the first evidence that cfDNA has selective immunostimulatory effects on human monocytes. This process may contribute to the proinflammatory milieu observed in HD patients.

Heat shock proteins in children and young adults on chronic hemodialysis

Chronic inflammation, lipid and autoimmune disorders are hallmarks of atherogenesis, and hemodialysis per se may be an additional factor predisposing to accelerated atherosclerosis. Elevated levels of heat shock proteins (HSP) and antibodies against these HSP have been described in adults with atherosclerotic lesions and cardiovascular events, but to date there has been a scarcity of investigations on these parameters in adult and pediatric patients on hemodialysis (HD). We have investigated the HSP profile in hemodialyzed children and the impact of a single HD session on those proteins and their correlations with known risk factors for atherosclerosis. The study group consisted of 17 children and young adults undergoing HD with polysulfone membranes. The control group comprised 15 age-matched subjects with normal kidney function. The serum concentrations of Hsp60, Hsp90alpha, anti-Hsp60, anti-Hsp70, and sE-selectin were assessed by an enzyme-linked immunosorbent assay, and serum concentration of high-sensitivity-C-reactive protein was assayed by nephelometry. The serum lipid profile [total cholesterol (CHOL), high-density lipoprotein-CHOL, low-density lipoprotein-CHOL, triglycerides] was also estimated. Compared to the control values, the median values of Hsp60 before the HD session were lower, whereas those of Hsp90alpha and anti-Hsp60 were higher. A single HD session raised the median values of Hsp60 and Hsp90alpha and decreased the concentrations of anti-Hsp60 and anti-Hsp70. In addition, the concentrations of HSPs and the antibodies against them correlated with the lipid markers both before and after HD. The altered HSP and anti-HSP concentrations in HD children, which correlated with the lipid profile and the endothelial markers, suggest a dysfunctional HSP system in this population and the possibility of HSPs being classified as new markers of atherosclerosis.

The uraemic retention solute para-hydroxy-hippuric acid attenuates apoptosis of polymorphonuclear leukocytes from healthy subjects but not from haemodialysis patients

BACKGROUND

Disturbed polymorphonuclear leukocyte (PMNL) apoptosis contributes to the dysregulation of the non-specific immune system in uraemia. Intracellular Ca(2+) modulates PMNL apoptotic cell death. We investigated the effect of para-hydroxy-hippuric acid (PHA), an erythrocyte plasma membrane Ca(2+)-ATPase inhibitor accumulating in uraemic sera, and of cyclopiazonic acid (CPA), an inhibitor of the sarko/endoplasmatic Ca(2+)-ATPase, on PMNL apoptosis.

METHODS

Apoptosis of PMNLs from healthy subjects and from haemodialysis (HD) patients was assessed after incubation for 20 h by evaluating morphological features under the fluorescence microscope and by measuring the DNA content and caspase activities by flow cytometry. The intracellular calcium concentration ([Ca(2+)](i)) was determined by measurement of fura-2 fluorescence using the 340/ 380 nm dual wavelength excitation.

RESULTS

Spontaneous apoptosis of PMNLs from healthy subjects and from HD patients did not differ. PHA significantly attenuated, while CPA increased, the apoptotic cell death of PMNLs from healthy subjects. The PHA effect was not observed with PMNLs from HD patients, irrespective of whether the blood was drawn before or after HD treatment. Baseline [Ca(2+)](i) was increased in PMNLs obtained from HD patients before dialysis but reversed after dialysis. The PHA effects were not mediated via [Ca(2+)](i). The chemotactic peptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) induced a [Ca(2+)](i) increase and reduced PMNL survival. Extracellular Ca(2+) did not affect CPA- and fMLP-induced apoptosis.

CONCLUSIONS

PHA, without affecting [Ca(2+)](i), attenuates apoptosis of healthy but not of uraemic PMNLs. CPA and fMLP enhance PMNL apoptosis independently of Ca(2+) influx.

In vitro--transcriptional response of polymorphonuclear leukocytes following contact with different antigens

Background Human polymorphonuclear neutrophils (PMN) are activated and undergo apoptosis if brought into contact with cuprophane haemodialysis membranes, a phenomenon not observed if more 'biocompatible' polysulfone dialysers are used. It remains yet to be defined if this differential response is due to mechanisms regulated on a transcriptional or protein level. Furthermore, it is not clear if the contact of PMN with membranes ('frustrated' phagocytosis) activates the same response as phagocytosis of bacteria (complete phagocytosis). Materials and methods We performed a genome-wide differential gene expression study using cDNA microarrays to analyse the impact of different dialysis fibres on the transcriptional response of PMN of human healthy volunteers. These results were compared to transcriptional response of PMN during phagocytosis of Escherichia coli. Results We did not detect significant differences in gene expression between PMN stimulated with cuprophane or pulysulfone. Compared to unstimulated PMN the 'frustrated' phagocytosis of either dialysis membrane resulted in increased expression of 50 genes, with a marked up-regulation of FOS - and JUN - transcripts, but with only little activation of immune response genes, and virtually no activation of apoptosis related RNA transcripts. In contrast, phagocytosis of E.coli was associated with a striking up-regulation of 88 genes, most of them involved in pro- and antiapoptotic pathways, immune response and activation of nuclear factor kappa B and inhibitor of NF-kappa B. Conclusions Our results suggest that the response of PMN to artificial surfaces is not controlled on transcriptional level. Complete and 'frustrated' phagocytosis activate markedly distinct transcriptional regulatory pathways in PMN.

Neutrophils interact with adenovirus vectors via Fc receptors and complement receptor 1

Neutrophils are effectors of the innate immune response to adenovirus vectors. Following the systemic administration of Cy2-labeled AdLuc in mice, flow cytometry and PCR analysis of liver leukocytes revealed that 25% of recruited neutrophils interacted with adenovirus vectors. In vitro, flow cytometry of human neutrophils incubated with Cy2-labeled AdLuc also demonstrated a significant interaction with adenovirus vectors. Fluorescence and electron microscopy confirmed vector internalization by neutrophils. The AdLuc-neutrophil interaction reduced vector transduction efficiency by more than 50% in coincubation assays in epithelium-derived cells. Adenovirus vector uptake by neutrophils occurred independently of coxsackievirus adenovirus receptor (CAR) and capsid RGD motifs, since neutrophils do not express CAR and uptake of the RGD-deleted vector AdL.PB* was similar to that of AdLuc. Furthermore, both AdLuc and AdL.PB* activated neutrophils and induced similar degrees of L-selectin shedding. Neutrophil uptake of AdLuc was dependent on the presence of complement and antibodies, since the interaction between AdLuc and neutrophils was significantly reduced when they were incubated in immunoglobulin G-depleted or heat-inactivated human serum. Blocking of complement receptor 1 (CD35) but not complement receptor 3 (CD11b/CD18) significantly reduced neutrophil uptake of AdLuc. Blocking of Fc gammaRI (CD64), Fc gammaRII (CD32), and Fc gammaRIII (CD16) individually or together also reduced neutrophil uptake of AdLuc, although less than blocking of CD35 alone. Combined CR1 and Fc receptor blockade synergistically inhibited neutrophil-AdLuc interactions close to baseline. These results demonstrate opsonin-dependent adenovirus vector interactions with neutrophils and their corresponding receptors.