Systemic redox biomarkers and their relationship to prognostic risk markers in autosomal dominant polycystic kidney disease and IgA nephropathy

Modified Zhenwu Tang delays chronic renal failure progression by modulating oxidative stress and hypoxic responses in renal proximal tubular epithelial cells

Background

Tubulointerstitial fibrosis (TIF) is a critical pathological feature of chronic renal failure (CRF), with oxidative stress (OS) and hypoxic responses in renal proximal tubular epithelial cells playing pivotal roles in disease progression. This study explores the effects of Modified Zhenwu Tang (MZWT) on these processes, aiming to uncover its potential mechanisms in slowing CRF progression.

Methods

We used adenine (Ade) to induce CRF in rats, which were then treated with benazepril hydrochloride (Lotensin) and MZWT for 8 weeks. Assessments included liver and renal function, electrolytes, blood lipids, renal tissue pathology, OS levels, the hypoxia-inducible factor (HIF) pathway, inflammatory markers, and other relevant indicators. In vitro, human renal cortical proximal tubular epithelial cells were subjected to hypoxia and lipopolysaccharide for 72 h, with concurrent treatment using MZWT, FM19G11, and N-acetyl-l-cysteine. Measurements taken included reactive oxygen species (ROS), HIF pathway activity, inflammatory markers, and other relevant indicators.

Results

Ade treatment induced significant disruptions in renal function, blood lipids, electrolytes, and tubulointerstitial architecture, alongside heightened OS, HIF pathway activation, and inflammatory responses in rats. In vivo, MZWT effectively ameliorated proteinuria, renal dysfunction, lipid and electrolyte imbalances, and renal tissue damage; it also suppressed OS, HIF pathway activation, epithelial-mesenchymal transition (EMT) in proximal tubular epithelial cells, and reduced the production of inflammatory cytokines and collagen fibers. In vitro findings demonstrated that MZWT decreased apoptosis, reduced ROS production, curbed OS, HIF pathway activation, and EMT in proximal tubular epithelial cells, and diminished the output of inflammatory cytokines and collagen.

Conclusion

OS and hypoxic responses significantly contribute to TIF development. MZWT mitigates these responses in renal proximal tubular epithelial cells, thereby delaying the progression of CRF.

Emerging significance and therapeutic targets of ferroptosis: a potential avenue for human kidney diseases

Kidney diseases remain one of the leading causes of human death and have placed a heavy burden on the medical system. Regulated cell death contributes to the pathology of a plethora of renal diseases. Recently, with in-depth studies into kidney diseases and cell death, a new iron-dependent cell death modality, known as ferroptosis, has been identified and has attracted considerable attention among researchers in the pathogenesis of kidney diseases and therapeutics to treat them. The majority of studies suggest that ferroptosis plays an important role in the pathologies of multiple kidney diseases, such as acute kidney injury (AKI), chronic kidney disease, and renal cell carcinoma. In this review, we summarize recently identified regulatory molecular mechanisms of ferroptosis, discuss ferroptosis pathways and mechanisms of action in various kidney diseases, and describe the protective effect of ferroptosis inhibitors against kidney diseases, especially AKI. By summarizing the prominent roles of ferroptosis in different kidney diseases and the progress made in studying ferroptosis, we provide new directions and strategies for future research on kidney diseases. In summary, ferroptotic factors are potential targets for therapeutic intervention to alleviate different kidney diseases, and targeting them may lead to new treatments for patients with kidney diseases.

Association of redox and inflammation-related biomarkers with prognosis in IgA nephropathy: A prospective observational study

BACKGROUND

IgA nephropathy (IGAN) has a variable prognosis. Risk stratification tools are usually based on clinical parameters combined with histologic Oxford-MEST-C score. Circulating redox- and inflammation-related biomarkers may be related to histological changes in IGAN. Therefore, we studied the performance of these biomarkers in predicting the rate of GFR-loss in IGAN.

METHODS

This was an observational prospective study. Fifty-seven stable patients with IGAN were examined at baseline and after a mean observational time of 5.9 ± 1.1 years. The main outcome measure was eGFR-loss per year with predefined groups, stable (<1.5 ml/min/1,73 m²/year, intermediate (between 1.5 and 2.5), and progressive (>2.5).

RESULTS

Fifteen patients were in the progressive, 11 in the intermediate, and 31 in the stable groups. Positive relationships were detected between eGFR-loss per year and baseline nitrate, oxidized free cysteine, parathyroid hormone, APRIL, TNFR1, CD30, chitinase 3, and LIF-5. The progressive group had elevated concentrations of these markers plus AOPP and osteopontin. Through ROC analysis, it was observed that AOPP, oxidized free cysteine, TNFR1, osteopontin, and LIF-5 had the best ability to identify progressive vs. non-progressive diseases. The combination of urinary albumin/creatinine ratio with AOPP and TNFR1 significantly improved the ability to identify progressive eGFR decline with ROC AUC 95% (adjusted 85%).

CONCLUSIONS

We found prognostic biomarkers related to the rate of eGFR-loss in IGAN. These biomarkers may help identify patients at risk of progressive disease. AOPP, oxidized free cysteine, TNFR1, and osteopontin are promising prognostic biomarkers in IGAN, however, further validation studies are needed.

Targeting Enrichment and Correlation Studies of Glutathione and Homocysteine in IgAVN Patient Urine Based on a Core-Shell Zr-Based Metal-Organic Framework

Aminothiols are closely related to chronic kidney disease, but little is known regarding levels of related aminothiols in the urine of immunoglobulin A vasculitis with nephritis (IgAVN) patients. Herein, a well-defined core-shell Zr-based metal-organic framework (Zr-MOF) composite SiO₂@50Benz-Cys was constructed as a mercury ion affinity material via a solvent-assisted ligand exchange strategy for the selective extraction and enrichment of low-concentration aminothiols in IgAVN patient urine. SiO₂@50Benz-Cys was competent to enrich the total glutathione (GSH) and total homocysteine (Hcy) in virtue of the excellent affinity after chelation with mercury ions. The extraction efficiencies were closely related to the pH, dithiothreitol amount, and the dose of functional Zr-MOF. Coupled with HPLC-MS/MS in optimized conditions, GSH and Hcy were determined with low detection limits of 0.5 and 1 nmol L^-1, respectively. The recoveries of GSH and Hcy for the urine sample at three spiked levels were in the range of 85.3-105% and 79.5-103%, which showed good precision and accuracy. Benefiting from the matrix interference elimination in the process of extraction, the simultaneous detection of aminothiols in the urine of the healthy group and immunoglobulin A vasculitis (IgAV) and IgAVN patients was successfully carried out, suggesting that the Zr-MOF and the robust method together provided a potential application in the analysis of urinary biomolecules. The analysis of variance (ANOVA) showed that the levels of GSH and Hcy had significant differences between the patients and the control. This work is very valuable as it provides a better understanding of concentration alterations of GSH and Hcy in urine involved with IgAVN for clinical research.

Markers of endothelial dysfunction and arterial stiffness in patients with early-stage autosomal dominant polycystic kidney disease: A meta-analysis

OBJECTIVES

Autosomal dominant polycystic kidney disease (ADPKD) is characterised by increased rates of cardiovascular complications leading to significant morbidity and mortality. This meta-analysis aims to evaluate whether the disease is linked to endothelial dysfunction and arterial stiffness during its early stages.

METHODS

Medline, Scopus, CENTRAL, Web of Science, Clinicaltrials.gov and Google Scholar databases comparing ADPKD patients with preserved renal function to healthy controls were included. The outcomes of interest were brachial flow-mediated dilatation, carotid-femoral pulse wave velocity, augmentation index, carotid intima-media thickness and central systolic blood pressure, plasma ADMA or homocysteine levels. Standardised mean differences (SMDs) were estimated by a random-effects model in R-3.6.3.

RESULTS

A total of 27 studies were included, comprising 1967 individuals. ADPKD was linked to significantly lower flow-mediated dilatation (SMD: -1.44, 95% CI: [-2.35, -0.53]) and higher pulse wave velocity (SMD: 1.44, 95% CI: [0.22, 2.66]) and carotid intima-media thickness (SMD: 1.02, 95% CI: [0.57, 1.47]). No significant associations were noted regarding augmentation index (SMD: 0.62, 95% CI: [-0.19, 1.43]) and central systolic blood pressure (SMD: 1.84, 95% CI: [-0.12, 3.80]). Plasma homocysteine was significantly higher in ADPKD (SMD: 0.81, 95% CI: [0.16, 1.45]), while no difference was calculated for ADMA levels (SMD: 1.14, 95% CI: [-0.25, 2.53]).

CONCLUSIONS

Early-stage ADPKD patients present increased vascular stiffness and endothelial dysfunction, as reflected by low flow-mediated dilatation and elevated values of pulse wave velocity, carotid intima-media thickness and plasma homocysteine. The exact effects of early arterial stiffness on long-term outcomes remain to be elucidated.

Lower serum bilirubin is associated with poor renal outcome in IgA nephropathy patients

Aims: IgA nephropathy (IgAN) is the most prevalent primary glomerulonephritis worldwide. We conducted this study to explore the relationship between serum bilirubin and renal outcome of patients with IgAN. Methods: A total of 1492 biopsy proven IgAN patients were recruited and divided into two groups according to their median serum bilirubin concentration: the low bilirubin group (serum bilirubin≤9.7umol/L, n=753) and high bilirubin group (serum bilirubin>9.7umol/L, n=739). Basic clinical characteristics were assessed at the time of renal biopsy and the relationships between serum bilirubin and the combined endpoints were analyzed. The combined endpoints were defined as a 50% decline in estimate glomerular filtration rate (e-GFR), end-stage kidney disease (ESKD), renal transplantation and/or death. In addition, propensity score matching (PSM) was then performed to improve balance and simulate randomization between patients in different groups. Kaplan-Meier survival analysis was applied to explore the role of serum bilirubin in the progression of IgAN. Three clinicopathological models of multivariate Cox regression analysis were established to evaluate the association of serum bilirubin and renal prognosis of IgAN. Results: During median 5-year follow-up period, significant differences were shown in Kaplan-Meier analysis. In the unmatched group, 189 (12.7%) patients progressed to the renal combined endpoints. Among this, 122 in 753 patients (16.2%) were in low bilirubin group and 67 in 739 patients (9.1%) were in high bilirubin group (p<0.001). After PSM, there were 134 (11.8%) patients reached the combined endpoints, which included 77 in 566 patients (14.6%) in low bilirubin group and 57 in 566 patients (10.1%) in high bilirubin group (p=0.039). The results of three models (including demographics, pathological, clinical indicators and serum bilirubin) demonstrated that a lower basic serum bilirubin level was significantly associated with a higher risk of reaching combined endpoints in IgAN patients both in unmatched and matched cohort. Conclusion: Serum bilirubin level may be negatively associated with the progression of IgAN.

Circulating inflammation-related factors are correlated with systemic redox status in IgA nephropathy; a case-control study

BACKGROUND

IgA nephropathy (IGAN) is characterized by oxidative stress and inflammation. In the present study, we explored the relationship of redox status vs. that of circulating inflammation-related factors with other biomarkers in patients with IGAN.

METHODS

This is a case-control study comparing patients with IGAN (Stage 1-4) to healthy controls. Forty patients and 40 controls were matched for age and sex. Two circulating dynamic redox parameters were analysed: oxidized free cysteine (Cys) and nitrate. Thirty-seven inflammation-related factors were measured in serum.

RESULTS

The patients had elevated levels of oxidized free Cys and nitrate, indicating the presence of oxidative stress. Nine circulating inflammation-related factors were higher in the serum of patients than in that of controls. The most important factors were APRIL, MMP-3, osteopontin, TNFR1 and TWEAK. Inflammation-related factors were positively correlated with oxidized free Cys, nitrate, creatinine and parathyroid hormone (PTH) in the patients. The correlation coefficients of Latent Inflammatory Factor vs. oxidized free Cys and nitrate were r = 0.43 (p = 0.007) and r = 0.51 (p = 0.001), respectively. This finding persisted after adjusting for the glomerular filtration rate.

CONCLUSIONS

Patients with IGAN had disturbed redox status. Several circulating inflammation-related factors were elevated, suggesting activation of the non-canonical NF-kB pathway. There was a positive relationship between systemic redox status and the level of inflammation-related factors, partially independent of GFR. The present findings raise the question of whether circulating oxidized free Cys and/or nitrate may be employed as prognostic biomarkers for IGAN in the future.

Activation of NRF2 ameliorates oxidative stress and cystogenesis in autosomal dominant polycystic kidney disease

Oxidative stress is emerging as a crucial contributor to the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD), but the molecular mechanisms underlying the disturbed redox homeostasis in cystic cells remain elusive. Here, we identified the impaired activity of the NRF2 (nuclear factor erythroid 2–related factor 2) antioxidant pathway as a driver of oxidative damage and ADPKD progression. Using a quantitative proteomic approach, together with biochemical analyses, we found that increased degradation of NRF2 protein suppressed the NRF2 antioxidant pathway in ADPKD mouse kidneys. In a cohort of patients with ADPKD, reactive oxygen species (ROS) frequently accumulated, and their production correlated negatively with NRF2 abundance and positively with disease severity. In an orthologous ADPKD mouse model, genetic deletion of Nrf2 further increased ROS generation and promoted cyst growth, whereas pharmacological induction of NRF2 reduced ROS production and slowed cystogenesis and disease progression. Mechanistically, pharmacological induction of NRF2 remodeled enhancer landscapes and activated NRF2-bound enhancer-associated genes in ADPKD cells. The activation domain of NRF2 formed phase-separated condensates with MEDIATOR complex subunit MED16 in vitro, and optimal Mediator recruitment to genomic loci depended on NRF2 in vivo. Together, these findings indicate that NRF2 remodels enhancer landscapes and activates its target genes through a phase separation mechanism and that activation of NRF2 represents a promising strategy for restoring redox homeostasis and combatting ADPKD.

Role of oxygen and the HIF-pathway in polycystic kidney disease

Kidney cyst growth in ADPKD is associated with regional hypoxia, presumably due to a mismatch between enlarged cysts and the peritubular capillary blood supply and compression of peritubular capillaries in cyst walls. Regional hypoxia leads to activation of hypoxia-inducible transcription factors, with the two main HIF isoforms, HIF-1 and HIF-2 expressed in cyst epithelia and pericystic interstitial cells, respectively. While HIF-2 activation is linked to EPO production, mitigating the anemia that normally accompanies chronic kidney disease, HIF-1 promotes cyst growth. HIF-dependent cyst growth is primarily due to an increase in chloride-dependent fluid secretion into the cyst lumen. However, given the broad spectrum of HIF-target genes, additional HIF-mediated pathways may also contribute to cyst progression. Furthermore, hypoxia can influence cyst growth through the generation of reactive oxygen species. Since cyst expansion aggravates regional hypoxia, a feedforward loop is established that accelerates cyst expansion and disease progression. Inhibiting the HIF pathway and/or HIF target genes that are of particular relevance for HIF-dependent cyst fluid secretion may therefore represent novel therapeutic approaches to retard the progression of APDKD.

The role of DNA damage as a therapeutic target in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenic kidney disease and is caused by heterozygous germ-line mutations in either PKD1 (85%) or PKD2 (15%). It is characterised by the formation of numerous fluid-filled renal cysts and leads to adult-onset kidney failure in ~50% of patients by 60 years. Kidney cysts in ADPKD are focal and sporadic, arising from the clonal proliferation of collecting-duct principal cells, but in only 1-2% of nephrons for reasons that are not clear. Previous studies have demonstrated that further postnatal reductions in PKD1 (or PKD2) dose are required for kidney cyst formation, but the exact triggering factors are not clear. A growing body of evidence suggests that DNA damage, and activation of the DNA damage response pathway, are altered in ciliopathies. The aims of this review are to: (i) analyse the evidence linking DNA damage and renal cyst formation in ADPKD; (ii) evaluate the advantages and disadvantages of biomarkers to assess DNA damage in ADPKD and finally, (iii) evaluate the potential effects of current clinical treatments on modifying DNA damage in ADPKD. These studies will address the significance of DNA damage and may lead to a new therapeutic approach in ADPKD.