Balance between cytokine production by peripheral blood mononuclear cells and reactive oxygen species production by monocytes in patients with chronic kidney disease

Chronic Kidney Disease Is Characterized by Expansion of a Distinct Proinflammatory Intermediate Monocyte Subtype and by Increased Monocyte Adhesion to Endothelial Cells

SIGNIFICANCE STATEMENT

CKD is accompanied by abnormal inflammation, which contributes to progressive loss of functional renal tissue and accelerated cardiovascular disease. Although studies have documented that dysregulation of monocyte maturation and function is associated with CKD and its complications, it is not well characterized. This study reveals that a distinctive human monocyte subtype with high propensity for releasing proinflammatory mediators and activating endothelial cells is increased in adults with CKD compared with adults with high cardiovascular risk and normal kidney function. It also demonstrates that human monocyte adhesion to endothelial layers and responses to specific inflammatory migration signals are enhanced in CKD. These findings offer insights into the mechanisms of CKD-associated intravascular and localized inflammation and may suggest potential targets for therapeutic interventions.

BACKGROUND

Cardiovascular disease (CVD) in patients with CKD is associated with increased circulating intermediate monocytes (IMs). Dysregulation of monocyte maturation and function is associated with CKD and its complications, but it is incompletely characterized.

METHODS

To explore monocyte repertoire abnormalities in CKD, we studied properties of monocyte subpopulations, including IM subpopulations distinguished by HLA-DR expression level, in individuals with or without CKD. Using flow cytometry, we profiled monocyte populations in blood samples from adults with CKD, healthy volunteers (HVs), and patient controls (PCs) with high CVD risk. Monocyte subpopulations were also derived from single-cell RNA-sequencing profiles of paired blood and biopsy samples from kidney transplant recipients. We quantified intracellular cytokine production, migration, and endothelial adhesion in ex vivo assays of PBMCs.

RESULTS

Of four predefined blood monocyte subpopulations, only HLA-DR hi IMs were increased in individuals with CKD compared with HVs and PCs. In HVs and patients with CKD, LPS-stimulated HLA-DR hi IMs isolated from blood produced higher amounts of TNF and IL-1 β than other monocyte populations. Single-cell analysis revealed four monocyte clusters common to blood and kidneys, including an HLA-DR hi IM-like cluster that was enriched in kidneys versus blood. Migration toward CCL5 and CX3CL1 and adhesion to primary endothelial cell layers were increased in monocyte subpopulations in individuals with CKD compared with HVs. Monocyte adhesion to endothelial cells was partly dependent on CX3CR1/CX3CL1 interaction.

CONCLUSIONS

CKD is associated with an increased number of a distinctive proinflammatory IM subpopulation and abnormalities of monocyte migration and endothelial adhesion. Dysregulated monocyte maturation and function may represent targetable factors contributing to accelerated CVD in CKD.

Monocytes in Uremia

Monocytes play an important role in both innate immunity and antigen presentation for specific cellular immune defense. In patients with chronic renal failure, as well as those treated with maintenance hemodialysis, these cells are largely dysregulated. There is a large body of literature on monocyte alterations in such patients. However, most of the publications report on small series, there is a vast spectrum of different methods and the heterogeneity of the data prevents any meta-analytic approach. Thus, a narrative review was performed to describe the current knowledge. Monocytes from patients with chronic renal failure differ from those of healthy individuals in the pattern of surface molecule expression, cytokine and mediator production, and function. If these findings can be summarized at all, they might be subsumed as showing chronic inflammation in resting cells together with limited activation upon immunologic challenge. The picture is complicated by the fact that monocytes fall into morphologically and functionally different populations and population shifts interact heavily with dysregulation of the individual cells. Severe complications of chronic renal failure such as impaired immune defense, inflammation, and atherosclerosis can be related to several aspects of monocyte dysfunction. Therefore, this review aims to provide an overview about the impairment and activation of monocytes by uremia and the resulting clinical consequences for renal failure patients.

Mitochondria in monocytes and macrophages-implications for translational and basic research

The mitochondrion plays a crucial role in the immune system particularly in regulating the responses of monocytes and macrophages to tissue injury, pathogens, and inflammation. In systemic diseases such as atherosclerosis and chronic kidney disease (CKD), it has been established that disruption of monocyte and macrophage function can lead to chronic inflammation. Polarization of macrophages into the pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes results in distinct metabolic reprograming which corresponds to the progression and resolution of inflammation. In this review, we will discuss the role of the mitochondrion in monocyte and macrophage function and how these cells specifically influence the pathophysiology of atherosclerosis and CKD. We propose that assessing monocyte bioenergetics in different disease states could (1) enhance our understanding of the energetic perturbations occurring in systemic inflammatory conditions and (2) aid in identifying therapeutic interventions to mitigate these disorders in patients.

Evidence for anti-inflammatory effects of exercise in CKD

CKD is associated with a complex state of immune dysfunction characterized by immune depression, predisposing patients to infections, and immune activation, resulting in inflammation that associates with higher risk of cardiovascular disease. Physical exercise may enhance immune function and exert anti-inflammatory effects, but such effects are unclear in CKD. We investigated the separate effects of acute and regular moderate-intensity aerobic exercise on neutrophil degranulation (elastase release), activation of T lymphocytes (CD69 expression) and monocytes (CD86 and HLA-DR expression), and plasma inflammatory markers (IL-6, IL-10, soluble TNF-receptors, and C-reactive protein) in patients with predialysis CKD. A single 30-minute (acute) bout of walking induced a normal pattern of leukocyte mobilization and had no effect on T-lymphocyte and monocyte activation but improved neutrophil responsiveness to a bacterial challenge in the postexercise period. Furthermore, acute exercise induced a systemic anti-inflammatory environment, evidenced by a marked increase in plasma IL-10 levels (peaked at 1 hour postexercise), that was most likely mediated by increased plasma IL-6 levels (peaked immediately postexercise). Six months of regular walking exercise (30 min/d for 5 times/wk) exerted anti-inflammatory effects (reduction in the ratio of plasma IL-6 to IL-10 levels) and a downregulation of T-lymphocyte and monocyte activation, but it had no effect on circulating immune cell numbers or neutrophil degranulation responses. Renal function, proteinuria, and BP were also unaffected. These findings provide compelling evidence that walking exercise is safe with regard to immune and inflammatory responses and has the potential to be an effective anti-inflammatory therapy in predialysis CKD.

Ascorbic acid reduces gentamicin-induced nephrotoxicity in rats through the control of reactive oxygen species

BACKGROUND & AIM

Oxidative stress has been implicated in the pathophysiology of many forms of acute renal failure. The aim was examine the effect of vitamin C on oxidative stress and its relationship with nitric oxide on gentamicin-induced nephrotoxicity in rats.

METHODS

We utilized 32 Wistar rats allocated in four groups of eight animals each: control (CTL), vitamin C (VIT C), gentamicin (GENTA), and GENTA + VIT C; all groups were treated during seven days.

RESULTS

Serum urea and creatinine, serum and renal tissue malondialdehyde, blood superoxide anion and hydrogen peroxide in GENTA were increased vs CTL and vs VIT C, and decreased in GENTA + VIT C vs GENTA (all P < 0.05). Serum nitric oxide increased in GENTA vs CTL and vs VIT C, and reduced in GENTA + VIT C vs GENTA (P < 0.001). Urinary nitric oxide was reduced in GENTA vs CTL and vs VIT C and increased in GENTA + VIT C vs GENTA (P < 0.001). Severe degeneration of proximal tubules was present in GENTA, but only mild lesions were observed in GENTA + VIT C.

CONCLUSION

This study suggests that VIT C is a valuable tool to protect against GENTA-induced nephrotoxicity, by reducing reactive oxygen species and increasing the nitric oxide.

Plasma B-type natriuretic peptide level predicts kidney prognosis in patients with predialysis chronic kidney disease

BACKGROUND

As a cardiorenal syndrome, there is a dynamic interplay between the heart and the kidney. We conducted a prospective study to evaluate the prognostic impact of plasma B-type natriuretic peptide (BNP) level, a cardiac biomarker, on the long-term kidney prognosis in chronic kidney disease (CKD) patients.

METHODS

We prospectively enrolled 508 patients with CKD Stages 3, 4 and 5 not on dialysis, from a single nephrology department between 2004 and 2010. The exclusion criteria were over 90 years of age, malignancy, active infection, low cardiac ejection fraction and rapid progressive glomerulonephritis. Relationships between BNP and kidney end point [defined as doubling of baseline serum creatinine and end-stage kidney disease (ESKD) requiring kidney replacement therapy] were measured using Cox models for case-mix and laboratory variables.

RESULTS

The final analysis covered 485 participants with no loss to follow-up. The median follow-up period was 3.2 years. Two hundred and twenty-eight of the 485 patients reached ESKD requiring dialysis, and baseline serum creatinine levels doubled in another 31. The kidney end point was significantly poorer among patients with plasma BNP levels above, compared with below a cut-off value of 86.1 pg/mL indicated from receiver operating characteristic analysis. Multivariable Cox regression analysis identified the common logarithm BNP as a predictor of kidney end point (adjusted hazard ratio 1.78, 95% CI: 1.28-2.46, P < 0.01).

CONCLUSIONS

Elevation of BNP level is associated with an increased risk for accelerated progression of CKD ultimately to ESKD. Monitoring the BNP level could be helpful in the management of combined heart and kidney disease.

Increased phagocytic nicotinamide adenine dinucleotide phosphate oxidase–dependent superoxide production in patients with early chronic kidney disease

BACKGROUND

Oxidative stress has been implicated in the pathogenesis of atherosclerosis that develops in patients with advanced chronic kidney disease (CKD). This study was designed to investigate whether a relationship exists between phagocytic nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-dependent superoxide anion (*O2-) production and subclinical atherosclerosis in patients with early CKD.

METHODS

Superoxide production was assayed by chemiluminescence under baseline and stimulated conditions on mononuclear cells obtained from asymptomatic patients with stage 1 to 2 CKD (N=22) and healthy controls (N=21). Ultrasonographic determination of carotid intima-media thickness (IMT) was used to assess the presence of atherosclerosis.

RESULTS

Although there were no differences in baseline *O2- production between controls and patients, the *O2- production in phorbol myristate acetate-stimulated mononuclear cells was increased (P<0.05) in patients compared with controls. The phorbol myristate acetate-induced *O2- production was completely abolished by apocynin, a specific inhibitor of NADPH oxidase. A direct correlation (r=0.441, P<0.05) was found between plasma insulin levels and NADPH oxidase-mediated *O2- production in patients. Carotid IMT was higher (P<0.005) in patients than in controls. Carotid IMT values above the upper normal limit in controls were found in 70% and 40% of patients with increased or normal NADPH oxidase-mediated *O2- production, respectively.

CONCLUSION

Generation of *O2- that is mainly dependent on NADPH oxidase is abnormally enhanced in patients with early CKD. It is suggested that this alteration could be related to the development of subclinical atherosclerosis in these patients.