Kidney Histopathology and Prediction of Kidney Failure: A Retrospective Cohort Study

Association of pulse pressure with incident end-stage kidney disease according to histopathological kidney findings in patients with diabetic nephropathy

Diabetic patients as well as the elderly are known to have high pulse pressure (PP), but there are few studies on how microangiopathy and macroangiopathy are involved in its mechanism. In this study, we examined the association between PP and atherosclerotic lesions by vessel size in kidney biopsy tissue and examined how PP is associated with kidney prognosis. This retrospective observational study included 408 patients with biopsy-proven diabetic nephropathy at Nara Medical University Hospital. Exposure of interest was PP measured at kidney biopsy. Outcome variable was kidney failure with replacement therapy (KFRT). Cox proportional hazards and competing risk regression models with all-cause mortality as a competing event were used to examine these associations. A total of 408 patients were divided into tertiles based on PP (mmHg): Tertile 1 (reference), <51; Tertile 2, 51-64; and Tertile 3, >64. Among the 408 patients, 99 developed KFRT during a median follow-up period of 6.7 years. Higher PP was independently associated with higher incidences of KFRT (hazard ratio [95% confidence interval] for Tertile 3 vs. Tertile 1; 2.07 [1.05-4.09]. In histological lesions, PP was strongly associated with glomerular lesions, tubulointerstitial lesions, and arteriolar hyalinosis (all ps for trend <0.001), but not with intimal thickening (p for trend = 0.714). PP was significantly associated with diabetic glomerular/tubulointerstitial lesions and arteriolar hyalinosis but not with intimal thickening at the time of kidney biopsy and was also significantly associated with subsequent KFRT in patients with diabetic nephropathy.

Inflammation primes the murine kidney for recovery by activating AZIN1 adenosine-to-inosine editing

The progression of kidney disease varies among individuals, but a general methodology to quantify disease timelines is lacking. Particularly challenging is the task of determining the potential for recovery from acute kidney injury following various insults. Here, we report that quantitation of post-transcriptional adenosine-to-inosine (A-to-I) RNA editing offers a distinct genome-wide signature, enabling the delineation of disease trajectories in the kidney. A well-defined murine model of endotoxemia permitted the identification of the origin and extent of A-to-I editing, along with temporally discrete signatures of double-stranded RNA stress and adenosine deaminase isoform switching. We found that A-to-I editing of antizyme inhibitor 1 (AZIN1), a positive regulator of polyamine biosynthesis, serves as a particularly useful temporal landmark during endotoxemia. Our data indicate that AZIN1 A-to-I editing, triggered by preceding inflammation, primes the kidney and activates endogenous recovery mechanisms. By comparing genetically modified human cell lines and mice locked in either A-to-I-edited or uneditable states, we uncovered that AZIN1 A-to-I editing not only enhances polyamine biosynthesis but also engages glycolysis and nicotinamide biosynthesis to drive the recovery phenotype. Our findings implicate that quantifying AZIN1 A-to-I editing could potentially identify individuals who have transitioned to an endogenous recovery phase. This phase would reflect their past inflammation and indicate their potential for future recovery.

The role of kidney biopsy in deciphering diabetic versus non-diabetic origin of kidney disease among patients with type 2 diabetes mellitus and nephrotic range proteinuria: A retrospective study

Background

Diabetes mellitus (DM) is tightly associated with the increased prevalence of diabetic kidney disease (DKD). Nonetheless, severe renal function impairment and/or nephrotic range-proteinuria could also result from non-diabetic renal disease (non-DRD) among patients with DM. The 'Gold standard' for the differential diagnosis between DKD and non-DRD is kidney biopsy, although no real consensus exists. Thus, this study intends to associate the clinical and biochemical profile of patients with DM and renal disease with the histopathological data of kidney biopsy.In addition, we aimed to evaluate the role of kidney biopsy, especially when other causes, other than DM, are highly suspected among patients with DM and kidney disease.

Methods

Thirty two patients with T2DM and nephrotic range levels of proteinuria or with co-existing factors pointing towards a non-diabetic origin of kidney disease were studied, retrospectively. All 32 patients underwent kidney biopsy and were classified according to histopathological findings into 3 groups: a) isolated diabetic kidney disease (DKD), b) non-diabetic kidney disease (NDKD) and c) mixed kidney disease (MKD).

Results

Fifteen out of the 32 patients had findings of an isolated DKD, while 17 out of 32 patients suffered from NDKD (13 patients) or MKD (4 patients). DKD patients were younger (p = 0.016) and had a higher HbA1c value (p = 0.069, borderline statistical significance), while the NDKD patients had significantly shorter disease duration (p = 0.04). Furthermore, the incidence of diabetic retinopathy (DR) was lower among the NDKD patients (p < 0.001), who had also significantly less interstitial fibrosis (p = 0.02). Finally, the presence of DR, higher levels of interstitial fibrosis and longer T2DM duration were recognized as factors, which were positively associated with DKD.

Conclusion

This study advocates the usefulness of kidney biopsy in patients with T2DM and nephrotic range levels of proteinuria, especially when DR is absent and shorter disease duration is observed.

Validation of histopathological chronicity scores in native kidney biopsies using light microscopy and digital morphometry for predicting renal outcome

Quantitative assessment of chronicity changes in native kidney biopsies offer valuable insights in to disease prognosis, despite the strength of qualitative information. Yet, standardization and reproducibility remain challenging. The present study aims to assess and compare the prognostic utility and reproducibility of two chronicity scoring systems based on light microscopy and whole slide imaging with morphometry and also to evaluate the prognostic utility of structural measurements: cortical non-sclerotic glomerular (NSG) density and NSG area/volume. We designed a retrospective longitudinal study involving 101 adult and paediatric patients who underwent native kidney biopsies. Chronicity scoring was performed using two semi-quantitative methods: Method 1 (method proposed in PMID: 28314581) and Method 2 (method proposed in PMID: 32516862), under light microscopy as well as on whole-slide scanned images, and assessed for prognostic utility. Kidney-Failure-Risk-Equation (KFRE) was employed in combination with chronicity-scoring-methods and assessed for predictive capability. Interobserver reproducibility for the two chronicity methods was studied among three renal pathologists. Structural measurements were performed on whole-slide- scanned-images. Both the chronicity scoring methods significantly predicted decline in estimated glomerular filtration rate (eGFR) and persistent need for renal replacement therapy in follow-up. Method 1 combined with KFRE, outperformed Method 2 in predicting renal survival. Method 2 however showed higher interobserver reproducibility. Combined KFRE plus histopathological scoring methods showed better predictive accuracy. The study validates the precision of chronicity scoring using whole slide scanned images. The morphometric structural measurements showed significant correlations with follow-up eGFR, thereby providing supplementary prognostic information.

Kidney Volume and Risk of Incident Kidney Outcomes

BACKGROUND

Low total kidney volume (TKV) is a risk factor for chronic kidney disease (CKD). However, evaluations of nonlinear relationships, incident events, causal inference, and prognostic utility beyond traditional biomarkers are lacking.

METHODS

TKV, height-adjusted TKV, and body surface area-adjusted TKV (BSA-TKV) of 34,595 White British ancestry participants were derived from the UK Biobank. Association with incident CKD, acute kidney injury (AKI), and cardiovascular events were assessed with Cox proportional hazard models. Prognostic thresholds for CKD risk stratification were identified using a modified Mazumdar method with bootstrap resampling. Two-sample Mendelian randomization was performed to assess the bidirectional association of genetically predicted TKV with kidney and cardiovascular traits.

RESULTS

Adjusted for eGFR and albuminuria, a lower TKV of 10 mL was associated with a 6% higher risk of incident CKD (hazard ratio [HR] 1.06, 95% confidence interval [CI] 1.03 to 1.08, P = 5.8 x 10-6) in contrast to no association with incident AKI (HR 1.00, 95% CI 0.98 to 1.02, P = 0.66). Comparison of nested models demonstrated improved accuracy over the CKD Prognosis Consortium Incident CKD Risk Score with the addition of BSA-TKV or prognostic thresholds at 119 (10th percentile) and 145 mL/m2 (50th percentile). In Mendelian randomization, a lower genetically predicted TKV by 10 mL was associated with 10% higher CKD risk (odds ratio [OR] 1.10, 95% CI 1.06 to 1.14, P = 1.3 x 10-7). Reciprocally, an elevated risk of genetically predicted CKD by 2-fold was associated with a lower TKV by 7.88 mL (95% CI -9.81 to -5.95, P = 1.2 x 10-15). There were no significant observational or Mendelian randomization associations of TKV with cardiovascular complications.

CONCLUSIONS

Kidney volume was associated with incident CKD independent of traditional risk factors including baseline eGFR and albuminuria. Mendelian randomization demonstrated a bidirectional relationship between kidney volume and CKD.

Associations of Kidney Functional Magnetic Resonance Imaging Biomarkers with Markers of Inflammation in Individuals with CKD

Key Points

Lower baseline apparent diffusion coefficient, indicative of greater cortical fibrosis, correlated with higher baseline concentrations of serum markers of inflammation. No association between baseline cortical R2* and baseline serum markers of inflammation were found. Baseline kidney functional magnetic resonance imaging biomarkers of fibrosis and oxygenation were not associated with changes in inflammatory markers over time, which may be due to small changes in kidney function in the study.

Background

Greater fibrosis and decreased oxygenation may amplify systemic inflammation, but data on the associations of kidney functional magnetic resonance imaging (fMRI) measurements of fibrosis (apparent diffusion coefficient [ADC]) and oxygenation (relaxation rate [R2*]) with systemic markers of inflammation are limited.

Methods

We evaluated associations of baseline kidney fMRI-derived ADC and R2* with baseline and follow-up serum IL-6 and C-reactive protein (CRP) in 127 participants from the CKD Optimal Management with Binders and NicotinamidE trial, a randomized, 12-month trial of nicotinamide and lanthanum carbonate versus placebo in individuals with CKD stages 3–4. Cross-sectional analyses of baseline kidney fMRI biomarkers and markers of inflammation used multivariable linear regression. Longitudinal analyses of baseline kidney fMRI biomarkers and change in markers of inflammation over time used linear mixed-effects models.

Results

Mean±SD eGFR, ADC, and R2* were 32.2±8.7 ml/min per 1.73 m2, 1.46±0.17×10−3 mm2/s, and 20.3±3.1 s−1, respectively. Median (interquartile range) IL-6 and CRP were 3.7 (2.4–4.9) pg/ml and 2.8 (1.2–6.3) mg/L, respectively. After multivariable adjustment, IL-6 and CRP were 13.1% and 27.3% higher per 1 SD decrease in baseline cortical ADC, respectively. Baseline cortical R2* did not have a significant association with IL-6 or CRP. Mean annual IL-6 and CRP slopes were 0.98 pg/ml per year and 0.91 mg/L per year, respectively. Baseline cortical ADC and R2* did not have significant associations with change in IL-6 or CRP over time.

Conclusions

Lower cortical ADC, suggestive of greater fibrosis, was associated with higher systemic inflammation. Baseline kidney fMRI biomarkers did not associate with changes in systemic markers of inflammation over time.

Management and Clinical Outcomes of Membranous Nephropathy, IgA Nephropathy, and Minimal Change Disease Two Years Post-Kidney Biopsy

INTRODUCTION

This study evaluated the phenotypic and pathology characteristics of patients undergoing kidney biopsy at a single center, while also determining the frequency and factors associated with clinical outcomes.

METHODS

The incidence and distribution of biopsy-proven kidney diseases in 2000-2019 were surveyed. Consecutive individuals diagnosed with membranous nephropathy (MN), immunoglobulin A nephropathy (IgAN), and minimal change disease (MCD) between August 2015 and December 2019 were enrolled in the prospective 2-year follow-up study. Outcomes included remission of proteinuria and kidney disease progression events. Multivariable-adjusted Cox proportional hazards model was applied.

RESULTS

4,550 kidney biopsies were performed in 2000-2019, showing a noticeable increase in the proportion of MN. 426 patients were enrolled in the follow-up cohort. 346 (81.2%) achieved remission of proteinuria, 39 (9.2%) suffered kidney disease progression and 51.3% of them were diagnosed with IgAN. Kidney pathological diagnosis (MN vs. MCD: hazard ratio [HR], 0.42; 95% confidence interval [95% CI], 0.31-0.57; IgAN vs. MCD: 0.58; 0.39-0.85), levels of 24-h urine protein at biopsy (1.04; 1.00-1.08) and presence of nodular mesangial sclerosis (0.70; 0.49-0.99) were significantly correlated with remission of proteinuria after adjusting for baseline variables. 24-h urine protein levels at biopsy (1.14; 1.04-1.25) and the presence of crescents (2.30; 1.06-4.95) were the independent risk factors for kidney disease progression events after adjusting for baseline variables.

CONCLUSION

The increasing frequency of MN has been affirmed over the past 2 decades. The therapeutic status, clinical outcomes, and factors influencing these outcomes were presented in this single-center study for the three primary glomerular diseases.

DP1, a multifaceted synthetic peptide: Mechanism of action, activity and clinical potential

AIMS

Microbial infections remain a leading cause of mortality worldwide, with Staphylococcus aureus (S. aureus) being a prominent etiological agent, responsible for causing persistent bacterial infections in humans. It is a nosocomial, opportunistic pathogen, capable to propagate within the bloodstream and withstand therapeutic interventions. In the current study, a novel, indigenously designed synthetic antimicrobial peptide (sAMP) has been evaluated for its antimicrobial potential to inhibit the growth and proliferation of S. aureus.

MAIN METHODS

The sAMP, designed peptide (DP1) was evaluated for its minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against a panel of pathogenic bacterial strains. Membrane mechanistic studies were performed by measuring membrane conductivity via dielectric spectroscopy and visualizing changes in bacterial membrane structure through field emission scanning electron microscopy (FE-SEM). Further, DP1 was tested for its in vivo antimicrobial potential in an S. aureus-induced systemic infection model.

KEY FINDINGS

The results indicated that DP1 has the potential to inhibit the growth and proliferation of a broad spectrum of Gram-positive, Gram-negative and multidrug-resistant (MDR) bacterial strains. Strong bactericidal effect attributed to change in electrical conductivity of the bacterial cells leading to membrane disruption was observed through dielectric spectroscopy and FE-SEM micrographs. Further, in the in vivo murine systemic infection study, 50 % reduction in S. aureus bioburden was observed within 1 day of the administration of DP1.

SIGNIFICANCE

The results indicate that DP1 is a multifaceted peptide with potent bactericidal, antioxidant and therapeutic properties. It holds significance as a novel drug candidate to effectively combat S. aureus-mediated systemic infections.

Urinary Vacuolar Casts Are a Unique Type of Casts in Advanced Proteinuric Glomerulopathies

Key Points

Vacuolar casts are a distinct type of casts identifiable by urinary sediment microscopy. Identification of urinary vacuolar casts is associated with the presence of an advanced and severe form of a proteinuric glomerular disease.

Background

Identification of casts by urinary sediment microscopy is a valuable diagnostic clinical tool for the evaluation of kidney disease. Vacuolar casts are an unrecognized unique type of casts characterized by the presence of nonpolarizable, clear vesicles of various sizes contained within a cast matrix, different from lipid casts, erythrocyte casts, or any other casts. We aimed to gain better understanding of the clinical relevance of these casts by establishing a multinational collaborative group to search for cases in which vacuolar casts were identified.

Methods

Leveraging an educational social media platform, we conducted a multinational observational study extracting cases of patients who presented with urinary vacuolar casts during evaluation for impaired kidney function. Parameters assessed included degree of proteinuria and kidney dysfunction, clinical and histopathological diagnosis, and severity of renal parenchymal scarring on biopsy. A control group of patients without vacuolar casts was included for comparison.

Results

Forty-six patients with urinary vacuolar casts were compiled from six countries. Nephrotic range proteinuria (82%), glomerular etiology (98%), and advanced CKD stage (62% 3B-5) were salient features. Histopathological diagnosis was available in 26 (57%) patients. Combining clinical and pathological diagnoses, diabetic nephropathy (48%), arterionephrosclerosis (30%), podocytopathies (15%), and proliferative glomerulonephritides (15%) accounted for most patients. Vacuolization of tubules or podocytes was present in 61% of the specimens. When compared with patients with histopathological diagnoses in which vacuolar casts were not found (n =186), patients with vacuolar casts more frequently had a glomerular etiology (100% versus 71%, P = 0.002), had greater proteinuria (median urine protein-to-creatinine 10.3 versus 2.2 g/g, P < 0.001), and had greater proportion of patients with ≥30% glomerular obsolescence (46% versus 20%, P = 0.003).

Conclusions

Thus, urinary vacuolar casts are strongly associated with advanced glomerulopathies with severe proteinuria. Future studies should examine their origin, composition, and prognostic value.

Podcast

This article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/K360/2024_01_26_KID0000000000000346.mp3

The chromatin landscape of healthy and injured cell types in the human kidney

There is a need to define regions of gene activation or repression that control human kidney cells in states of health, injury, and repair to understand the molecular pathogenesis of kidney disease and design therapeutic strategies. Comprehensive integration of gene expression with epigenetic features that define regulatory elements remains a significant challenge. We measure dual single nucleus RNA expression and chromatin accessibility, DNA methylation, and H3K27ac, H3K4me1, H3K4me3, and H3K27me3 histone modifications to decipher the chromatin landscape and gene regulation of the kidney in reference and adaptive injury states. We establish a spatially-anchored epigenomic atlas to define the kidney's active, silent, and regulatory accessible chromatin regions across the genome. Using this atlas, we note distinct control of adaptive injury in different epithelial cell types. A proximal tubule cell transcription factor network of ELF3, KLF6, and KLF10 regulates the transition between health and injury, while in thick ascending limb cells this transition is regulated by NR2F1. Further, combined perturbation of ELF3, KLF6, and KLF10 distinguishes two adaptive proximal tubular cell subtypes, one of which manifested a repair trajectory after knockout. This atlas will serve as a foundation to facilitate targeted cell-specific therapeutics by reprogramming gene regulatory networks.

Impact of pancreas transplantation alone on kidney function: A multicenter clinical cohort study

Pancreas transplantation alone (PTA) is a β cell replacement option for selected patients with type 1 diabetes mellitus; concerns have been raised regarding deterioration in kidney function (KF) after PTA. This retrospective multicenter study assessed actual impact of transplantation and immunosuppression on KF in PTA recipients at three Transplant Centers. The primary composite endpoint 10 years after PTA was >50% eGFR decline, eGFR < 30 mL/min/1.73 m2 , and/or receiving a kidney transplant (KT). Overall, 822 PTA recipients met eligibility. Median baseline and 10-year eGFR (mL/min/1.73 m2 ) were 76.3 (58.1-100.8) and 51.3 (35.3-65.9), respectively. Primary composite endpoint occurred in 98 patients (53.5%) with 45 experiencing a >50% decrease in eGFR by 10 years post-transplant, 38 eGFR < 30 mL/min/1.73 m2 and 49 requiring KT. KF declined most significantly within 6 months post-PTA, more often in females and patients with better preserved GFR up to 5 years with 11.6% kidney failure at 10 years. Patient survival and death-censored graft survival were both 68% at 10 years with overall graft thrombosis rate 8%. KF declined initially after PTA but stabilized with further slow progression. In conclusion, prospective intervention studies are needed to test renal sparing interventions while gathering more granular data.

Clinical Outcomes of Monoclonal Gammopathy of Renal Significance Without Detectable Clones

Introduction

Monoclonal gammopathy of renal significance (MGRS) is characterized by monoclonal immunoglobulin deposition in kidneys. However, monoclonal immunoglobulin and responsible clone(s) are not always detectable. Treatment response and kidney outcome of MGRS without detectable clones remain unclear.

Methods

In this single-center, retrospective cohort study, we identified MGRS without detectable clones from our biopsy repository between 2010 and 2022. We investigated the correlations between treatment regimens and kidney outcomes defined by proteinuria and estimated glomerular filtration rate (eGFR), and the impact of repeat kidney biopsy.

Results

Our study cohort included 29 cases (27 native kidney and 2 transplant allograft biopsies) of MGRS without detectable clones. At diagnosis, median serum creatinine was 1.8 mg/dl (interquartile range [IQR] 1.3-2.7), with proteinuria 4.6 g/gCr (IQR 2.3-7.9). Treatment regimens were variable: 6 (21%) received conservative therapy, 13 (45%) received plasma cell clone-directed therapy, 8 (28%) received lymphocytic clone-directed therapy, and 2 (7%) received nonclone-directed immunosuppressive therapy. Of 24 patients with proteinuria >0.5 g/gCr at diagnosis, 9 (38%) and 6 (25%) achieved complete response (CR) and partial response (PR), respectively. If interstitial fibrosis and tubular atrophy (IFTA) was >50% at the initial biopsy, less proportion of patients achieved CR. Six of 7 repeat biopsies showed progression of chronic changes (e.g., IFTA) but provided limited information on treatment response.

Conclusion

Treatment regimens and outcomes of MGRS without detectable clones were extremely variable. Repeat biopsy provided limited information to assess disease activity or the need for additional treatment. More sensitive tools are needed to detect clones and to assess treatment response.

Cumulative smoking dose is associated with subclinical renal injury: a pathological study in individuals without chronic kidney disease

BACKGROUND

Epidemiological studies have identified smoking as an independent risk factor for development of chronic kidney disease. However, the early renal pathological lesions have not been clearly elucidated.

METHODS

We investigated time-zero biopsy specimens from 547 living kidney donors and evaluated the relationships between smoking and renal histological changes, including arteriolar hyalinization, intimal thickening of small-medium arteries, global glomerulosclerosis, and interstitial fibrosis and tubular atrophy (IF/TA).

RESULTS

A total of 199 subjects (36.4%) had smoking history; 92 (16.8%) and 107 (19.6%) subjects had <20 pack-years and ≥20 pack-years of smoking, respectively. Cumulative smoking dose was significantly associated with prevalence of arteriolar hyalinization: the multivariable-adjusted odds ratio (OR) per 20 pack-year increase was 1.50 (95% confidence interval 1.15-1.97). The ORs for smokers with <20 pack-years and ≥20 pack-years versus never-smokers were 1.76 (1.01-3.09) and 2.56 (1.48-4.44), respectively. Smoking was also associated with prevalence of >10% global glomerulosclerosis: the OR per 20 pack-year increase was 1.24 (0.96-1.59). The ORs for smokers with <20 pack-years and ≥20 pack-years versus never-smokers were 1.50 (0.98-2.78) and 2.11 (1.18-3.79), respectively. The ORs for these pathological changes increased significantly depending on cumulative smoking dose. Intimal thickening of small-medium arteries and IF/TA were not associated with smoking status. The prevalence of arteriolar hyalinization remained higher in patients with ≥10 years since smoking cessation than in never-smokers [OR 2.23 (1.03-4.83)].

CONCLUSIONS

Subclinical pathological injury caused by smoking is potentially associated with renal arteriolar hyalinization and glomerular ischaemia.

[Non-Classical Clinical Types and Pathological Changes of Diabetic Kidney Disease: A Review]

Diabetic kidney disease (DKD) is a common complication of diabetes mellitus and approximately 1/3 of diabetic patients may progress to DKD. A typical early clinical manifestation of DKD is microalbuminuria and patients may present with macroproteinuria accompanied by a decrease in renal function condition as the disease progresses. It is generally believed that the likelihood of a reversal of the disease is reduced after the development of macroproteinuria in patients with DKD, and that eventually some patients' condition may develop into end-stage renal disease (ESRD). Moreover, the thickening of the glomerular basement membrane, mesangial matrix expansion, Kimmelstiel-Wilson (K-W) nodules, and glomerulosclerosis in end-stage diabetes mellitus are typical pathologic changes of DKD. However, some DKD patients, especially those with type 2 diabetes mellitus (T2DM) combined with DKD, may have diverse clinical manifestations, showing variations in disease progression and regression, and manifesting as non-classical types of DKD, such as normoalbuminuric DKD, proteinuria-reduced DKD, and DKD with rapid decline in renal function. In addition, the formation of crescents, a special pathological change, is observed in renal biopsy. However, this issue is currently under-recognized by clinicians and therefore deserves more attention. In order to improve clinicians' understanding of the presentations and pathological changes of non-classical DKD and the level of DKD prevention and treatment in China, we present a preliminary introduction to the clinical phenotypes and pathological changes of non-classical types of DKD in this paper by summarizing the findings of our prior studies as well as domestic and international literature.

The AKI-to-CKD Transition: The Role of Uremic Toxins

After acute kidney injury (AKI), renal function continues to deteriorate in some patients. In a pro-inflammatory and profibrotic environment, the proximal tubules are subject to maladaptive repair. In the AKI-to-CKD transition, impaired recovery from AKI reduces tubular and glomerular filtration and leads to chronic kidney disease (CKD). Reduced kidney secretion capacity is characterized by the plasma accumulation of biologically active molecules, referred to as uremic toxins (UTs). These toxins have a role in the development of neurological, cardiovascular, bone, and renal complications of CKD. However, UTs might also cause CKD as well as be the consequence. Recent studies have shown that these molecules accumulate early in AKI and contribute to the establishment of this pro-inflammatory and profibrotic environment in the kidney. The objective of the present work was to review the mechanisms of UT toxicity that potentially contribute to the AKI-to-CKD transition in each renal compartment.

Inflammation primes the kidney for recovery by activating AZIN1 A-to-I editing

The progression of kidney disease varies among individuals, but a general methodology to quantify disease timelines is lacking. Particularly challenging is the task of determining the potential for recovery from acute kidney injury following various insults. Here, we report that quantitation of post-transcriptional adenosine-to-inosine (A-to-I) RNA editing offers a distinct genome-wide signature, enabling the delineation of disease trajectories in the kidney. A well-defined murine model of endotoxemia permitted the identification of the origin and extent of A-to-I editing, along with temporally discrete signatures of double-stranded RNA stress and Adenosine Deaminase isoform switching. We found that A-to-I editing of Antizyme Inhibitor 1 (AZIN1), a positive regulator of polyamine biosynthesis, serves as a particularly useful temporal landmark during endotoxemia. Our data indicate that AZIN1 A-to-I editing, triggered by preceding inflammation, primes the kidney and activates endogenous recovery mechanisms. By comparing genetically modified human cell lines and mice locked in either A-to-I edited or uneditable states, we uncovered that AZIN1 A-to-I editing not only enhances polyamine biosynthesis but also engages glycolysis and nicotinamide biosynthesis to drive the recovery phenotype. Our findings implicate that quantifying AZIN1 A-to-I editing could potentially identify individuals who have transitioned to an endogenous recovery phase. This phase would reflect their past inflammation and indicate their potential for future recovery.

Defining the molecular correlate of arteriolar hyalinosis in kidney disease progression by integration of single cell transcriptomic analysis and pathology scoring

Arteriolar hyalinosis in kidneys is an independent predictor of cardiovascular disease, the main cause of mortality in chronic kidney disease (CKD). The underlying molecular mechanisms of protein accumulation in the subendothelial space are not well understood. Using single cell transcriptomic data and whole slide images from kidney biopsies of patients with CKD and acute kidney injury in the Kidney Precision Medicine Project, the molecular signals associated with arteriolar hyalinosis were evaluated. Co-expression network analysis of the endothelial genes yielded three gene set modules as significantly associated with arteriolar hyalinosis. Pathway analysis of these modules showed enrichment of transforming growth factor beta / bone morphogenetic protein (TGFβ / BMP) and vascular endothelial growth factor (VEGF) signaling pathways in the endothelial cell signatures. Ligand-receptor analysis identified multiple integrins and cell adhesion receptors as over-expressed in arteriolar hyalinosis, suggesting a potential role of integrin-mediated TGFβ signaling. Further analysis of arteriolar hyalinosis associated endothelial module genes identified focal segmental glomerular sclerosis as an enriched term. On validation in gene expression profiles from the Nephrotic Syndrome Study Network cohort, one of the three modules was significantly associated with the composite endpoint (> 40% reduction in estimated glomerular filtration rate (eGFR) or kidney failure) independent of age, sex, race, and baseline eGFR, suggesting poor prognosis with elevated expression of genes in this module. Thus, integration of structural and single cell molecular features yielded biologically relevant gene sets, signaling pathways and ligand-receptor interactions, underlying arteriolar hyalinosis and putative targets for therapeutic intervention.

A spatially anchored transcriptomic atlas of the human kidney papilla identifies significant immune injury in patients with stone disease

Kidney stone disease causes significant morbidity and increases health care utilization. In this work, we decipher the cellular and molecular niche of the human renal papilla in patients with calcium oxalate (CaOx) stone disease and healthy subjects. In addition to identifying cell types important in papillary physiology, we characterize collecting duct cell subtypes and an undifferentiated epithelial cell type that was more prevalent in stone patients. Despite the focal nature of mineral deposition in nephrolithiasis, we uncover a global injury signature characterized by immune activation, oxidative stress and extracellular matrix remodeling. We also identify the association of MMP7 and MMP9 expression with stone disease and mineral deposition, respectively. MMP7 and MMP9 are significantly increased in the urine of patients with CaOx stone disease, and their levels correlate with disease activity. Our results define the spatial molecular landscape and specific pathways contributing to stone-mediated injury in the human papilla and identify associated urinary biomarkers.

An atlas of healthy and injured cell states and niches in the human kidney

Understanding kidney disease relies on defining the complexity of cell types and states, their associated molecular profiles and interactions within tissue neighbourhoods1. Here we applied multiple single-cell and single-nucleus assays (>400,000 nuclei or cells) and spatial imaging technologies to a broad spectrum of healthy reference kidneys (45 donors) and diseased kidneys (48 patients). This has provided a high-resolution cellular atlas of 51 main cell types, which include rare and previously undescribed cell populations. The multi-omic approach provides detailed transcriptomic profiles, regulatory factors and spatial localizations spanning the entire kidney. We also define 28 cellular states across nephron segments and interstitium that were altered in kidney injury, encompassing cycling, adaptive (successful or maladaptive repair), transitioning and degenerative states. Molecular signatures permitted the localization of these states within injury neighbourhoods using spatial transcriptomics, while large-scale 3D imaging analysis (around 1.2 million neighbourhoods) provided corresponding linkages to active immune responses. These analyses defined biological pathways that are relevant to injury time-course and niches, including signatures underlying epithelial repair that predicted maladaptive states associated with a decline in kidney function. This integrated multimodal spatial cell atlas of healthy and diseased human kidneys represents a comprehensive benchmark of cellular states, neighbourhoods, outcome-associated signatures and publicly available interactive visualizations.

The chromatin landscape of healthy and injured cell types in the human kidney

There is a need to define regions of gene activation or repression that control human kidney cells in states of health, injury, and repair to understand the molecular pathogenesis of kidney disease and design therapeutic strategies. However, comprehensive integration of gene expression with epigenetic features that define regulatory elements remains a significant challenge. We measured dual single nucleus RNA expression and chromatin accessibility, DNA methylation, and H3K27ac, H3K4me1, H3K4me3, and H3K27me3 histone modifications to decipher the chromatin landscape and gene regulation of the kidney in reference and adaptive injury states. We established a comprehensive and spatially-anchored epigenomic atlas to define the kidney's active, silent, and regulatory accessible chromatin regions across the genome. Using this atlas, we noted distinct control of adaptive injury in different epithelial cell types. A proximal tubule cell transcription factor network of ELF3 , KLF6 , and KLF10 regulated the transition between health and injury, while in thick ascending limb cells this transition was regulated by NR2F1 . Further, combined perturbation of ELF3 , KLF6 , and KLF10 distinguished two adaptive proximal tubular cell subtypes, one of which manifested a repair trajectory after knockout. This atlas will serve as a foundation to facilitate targeted cell-specific therapeutics by reprogramming gene regulatory networks.

Use of Histologic Parameters to Predict Glomerular Disease Progression: Findings From the China Kidney Biopsy Cohort Study

RATIONALE & OBJECTIVE

Challenges in achieving valid risk prediction and stratification impede treatment decisions and clinical research design for patients with glomerular diseases. This study evaluated whether chronic histologic changes, when complementing other clinical data, improved the prediction of disease outcomes across a diverse group of glomerular diseases.

STUDY DESIGN

Multicenter retrospective cohort study.

SETTING & PARTICIPANTS

4,982 patients with biopsy-proven glomerular disease who underwent native biopsy at 8 tertiary care hospitals across China in 2004-2020.

NEW PREDICTORS & ESTABLISHED PREDICTORS

Chronicity scores depicted as 4 categories of histological chronic change, as well as baseline clinical and demographic variables.

OUTCOME

Progression of glomerular disease defined as a composite of kidney failure or a ≥40% decrease in estimated glomerular filtration rate from the measurement at the time of biopsy.

ANALYTICAL APPROACH

Multivariable Cox proportional hazard models. The performance of predictive models was evaluated by C statistic, time-dependent area under the receiver operating characteristic curve (AUROC), net reclassification index, integrated discrimination index, and calibration plots.

RESULTS

The derivation and validation cohorts included 3,488 and 1,494 patients, respectively. During a median of 31 months of follow-up, a total of 444 (8.9%) patients had disease progression in the 2 cohorts. For prediction of the 2-year risk of disease progression, the AUROC of the model combining chronicity score and the Kidney Failure Risk Equation (KFRE) in the validation cohort was 0.76 (95% CI, 0.65-0.87); in comparison with the KFRE model (AUROC, 0.68 [95% CI, 0.56-0.79]), the combined model was significantly better (P = 0.04). The combined model also had a better fit, with a lower Akaike information criterion and a significant improvement in reclassification as assessed by the integrated discrimination improvements and net reclassification improvements. Similar improvements in predictive performance were observed in subgroup and sensitivity analyses.

LIMITATIONS

Selection bias, relatively short follow-up, lack of external validation.

CONCLUSIONS

Adding histologic chronicity scores to the KFRE model improved the prediction of kidney disease progression at the time of kidney biopsy in patients with glomerular diseases.

PLAIN-LANGUAGE SUMMARY

Risk prediction and stratification remain big challenges for treatment decisions and clinical research design for patients with glomerular diseases. The extent of chronic changes is an important component of kidney biopsy evaluations in glomerular disease. In this large multicenter cohort including 4,982 Chinese adults undergoing native kidney biopsy, we evaluated whether histologic chronicity scores, when added to clinical data, could improve the prediction of disease prognosis for a diverse set of glomerular diseases. We observed that adding histologic chronicity scores to the kidney failure risk equation improved the prediction of kidney disease progression at the time of kidney biopsy in patients with glomerular diseases.

Spatially Aware Transformer Networks for Contextual Prediction of Diabetic Nephropathy Progression from Whole Slide Images

Diabetic nephropathy (DN) in the context of type 2 diabetes is the leading cause of end-stage renal disease (ESRD) in the United States. DN is graded based on glomerular morphology and has a spatially heterogeneous presentation in kidney biopsies that complicates pathologists' predictions of disease progression. Artificial intelligence and deep learning methods for pathology have shown promise for quantitative pathological evaluation and clinical trajectory estimation; but, they often fail to capture large-scale spatial anatomy and relationships found in whole slide images (WSIs). In this study, we present a transformer-based, multi-stage ESRD prediction framework built upon nonlinear dimensionality reduction, relative Euclidean pixel distance embeddings between every pair of observable glomeruli, and a corresponding spatial self-attention mechanism for a robust contextual representation. We developed a deep transformer network for encoding WSI and predicting future ESRD using a dataset of 56 kidney biopsy WSIs from DN patients at Seoul National University Hospital. Using a leave-one-out cross-validation scheme, our modified transformer framework outperformed RNNs, XGBoost, and logistic regression baseline models, and resulted in an area under the receiver operating characteristic curve (AUC) of 0.97 (95% CI: 0.90-1.00) for predicting two-year ESRD, compared with an AUC of 0.86 (95% CI: 0.66-0.99) without our relative distance embedding, and an AUC of 0.76 (95% CI: 0.59-0.92) without a denoising autoencoder module. While the variability and generalizability induced by smaller sample sizes are challenging, our distance-based embedding approach and overfitting mitigation techniques yielded results that sugest opportunities for future spatially aware WSI research using limited pathology datasets.

Protective Effect of Neutral Electrolyzed Saline on Gentamicin-Induced Nephrotoxicity: Evaluation of Histopathologic Parameters in a Murine Model

Background and Objectives: Gentamicin (GM) is a nephrotoxic aminoglycoside. Neutral electrolyzed saline (SES) is a compound with anti-inflammatory, antioxidant, and immunomodulatory properties. The objective of the present study was to evaluate whether kidney damage by GM can be prevented and/or reversed through the administration of SES. Materials and Methods: The study was carried out as a prospective, single-blind, five-arm, parallel-group, randomized, preclinical trial. The nephrotoxicity model was established in male BALB/c mice by administering GM at a dose of 100 mg/kg/day intraperitoneally for 30 days, concomitantly administering (+) SES or placebo (physiologic saline solution), and then administering SES for another 30 days after the initial 30 days of GM plus SES or placebo. At the end of the test, the mice were euthanized, and renal tissues were evaluated histopathologically. Results: The GM + placebo group showed significant tubular injury, interstitial fibrosis, and increased interstitial infiltrate of inflammatory cells compared with the group without GM. Tubular injury and interstitial fibrosis were lower in the groups that received concomitant GM + SES compared with the GM + placebo group. SES administration for 30 days after the GM administration periods (GM + placebo and GM + SES for 30 days) did not reduce nephrotoxicity. Conclusions: Intraperitoneal administration of SES prevents gentamicin-induced histologic nephrotoxicity when administered concomitantly, but it cannot reverse the damage when administered later.

Biopsy-proven CKD etiology and outcomes: the Chronic Kidney Disease Japan Cohort (CKD-JAC) study

BACKGROUND

The Kidney Disease: Improving Global Outcomes guidelines advocate the cause-glomerular filtration rate (GFR)-albuminuria (CGA) classification for predicting outcomes. However, there is a dearth of data supporting the use of the cause of chronic kidney disease. This study aimed to address how to incorporate a prior biopsy-proven diagnosis in outcome prediction.

METHODS

We examined the association of biopsy-proven kidney disease diagnoses with kidney failure with replacement therapy (KFRT) and all-cause death before KFRT in patients with various biopsy-proven diagnoses (n = 778, analysis A) and patients with diabetes mellitus labeled with biopsy-proven diabetic nephropathy (DN), other biopsy-proven diseases and no biopsy (n = 1117, analysis B).

RESULTS

In analysis A, adding biopsy-proven diagnoses to the GFR-albuminuria (GA) classification improved the prediction of 8-year incidence of KFRT and all-cause death significantly regarding integrated discrimination improvement and net reclassification index. Fine-Gray (FG) models with KFRT as a competing event showed significantly higher subdistribution hazard ratios (SHRs) for all-cause death in nephrosclerosis {4.12 [95% confidence interval (CI) 1.11-15.2)], focal segmental glomerulosclerosis [3.77 (95% CI 1.09-13.1)]} and membranous nephropathy (MN) [2.91 (95% CI 1.02-8.30)] than in immunoglobulin A nephropathy (IgAN), while the Cox model failed to show significant associations. Crescentic glomerulonephritis had the highest risk of all-cause death [SHR 5.90 (95% CI 2.05-17.0)]. MN had a significantly lower risk of KFRT than IgAN [SHR 0.45 (95% CI 0.24-0.84)]. In analysis B, other biopsy-proven diseases had a lower risk of KFRT than biopsy-proven DN in the FG model, with death as a competing event [SHR 0.62 (95% CI 0.39-0.97)].

CONCLUSIONS

The CGA classification is of greater value in predicting outcomes than the GA classification.

Evaluating the renal mild tubulointerstitial damage and renal function in IgAN patients: a comparative study based on diffusion kurtosis imaging and diffusion tensor imaging

OBJECTIVE

To compare the performance of 3.0 T magnetic resonance diffusion kurtosis imaging (DKI) and diffusion tensor imaging (DTI) in evaluation of the degree of tubulointerstitial damage and renal function in Immunoglobulin A Nephropathy (IgAN) patients.

METHODS

Both DKI and DTI were performed in 40 IgAN patients and 17 healthy volunteers. IgAN patients were divided into two groups according to tubulointerstitial lesion score: Mild injury group, n = 24; Moderate-severe injury group, n = 16. DKI characteristic parameters [mean kurtosis (MK), axial kurtosis (Ka), radial kurtosis (Kr)] and DTI parameters [fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (Da), radial diffusivity (Dr)] of renal cortex and medulla were measured and compared among different groups. Correlations between DKI, DTI parameters and clinicopathological characteristics were assessed. Diagnostic performance of DKI and DTI to evaluate tubulointerstitial damage of IgAN was compared.

RESULTS

Cortical MK, Kr, Da and parenchymal Ka significantly differed among three groups (P < 0.05). Cortical MK, Kr, Ka were negatively correlated with estimated glomerular filtration rate (eGFR) (MK: r = - 0.613; Kr: r = - 0.539; Ka: r = - 0.664) and positively correlated with tubulointerstitial lesion score (MK: r = 0.655; Kr: r = 0.577; Ka: r = 0.661) (all P < 0.001). Lower correlation coefficient was found among cortical FA, MD, Dr and eGFR, tubulointerstitial lesion score (all|r|< 0.350). The AUCs of DKI and DTI parameters for differentiating Mild injury group from control group were (cortical MK 0.822, cortical Ka 0.816; cortical FA 0.515, cortical MD 0.714) and for differentiating Mild injury group from Moderate-severe injury group were (cortical MK 0.813, cortical Ka 0.831; medulla FA 0.784, medulla MD 0.586).

CONCLUSION

Compared with DTI, DKI was more sensitive and accurate to probe the renal function and the tubulointerstitial damage of IgAN, especially the mild tubulointerstitial damage.

Spatially Aware Transformer Networks for Contextual Prediction of Diabetic Nephropathy Progression from Whole Slide Images

Diabetic nephropathy (DN) in the context of type 2 diabetes is the leading cause of end-stage renal disease (ESRD) in the United States. DN is graded based on glomerular morphology and has a spatially heterogeneous presentation in kidney biopsies that complicates pathologists' predictions of disease progression. Artificial intelligence and deep learning methods for pathology have shown promise for quantitative pathological evaluation and clinical trajectory estimation; but, they often fail to capture large-scale spatial anatomy and relationships found in whole slide images (WSIs). In this study, we present a transformer-based, multi-stage ESRD prediction framework built upon nonlinear dimensionality reduction, relative Euclidean pixel distance embeddings between every pair of observable glomeruli, and a corresponding spatial self-attention mechanism for a robust contextual representation. We developed a deep transformer network for encoding WSI and predicting future ESRD using a dataset of 56 kidney biopsy WSIs from DN patients at Seoul National University Hospital. Using a leave-one-out cross-validation scheme, our modified transformer framework outperformed RNNs, XGBoost, and logistic regression baseline models, and resulted in an area under the receiver operating characteristic curve (AUC) of 0.97 (95% CI: 0.90-1.00) for predicting two-year ESRD, compared with an AUC of 0.86 (95% CI: 0.66-0.99) without our relative distance embedding, and an AUC of 0.76 (95% CI: 0.59-0.92) without a denoising autoencoder module. While the variability and generalizability induced by smaller sample sizes are challenging, our distance-based embedding approach and overfitting mitigation techniques yielded results that suggest opportunities for future spatially aware WSI research using limited pathology datasets.

Polymerized human cord hemoglobin assisted with ascorbic acid as a red blood cell substitute alleviating oxidative stress for blood transfusion

Introduction: Blood transfusion is widely used in clinical settings, where considerable efforts have been devoted to develop red blood cell substitutes to overcome blood shortage and safety concerns. Among the several kinds of artificial oxygen carriers, hemoglobin-based oxygen carriers are promising due to their inherent good oxygen-binding and -loading properties. However, difficulties in prone to oxidation, production of oxidative stress, and injury in organs limited their clinical utility. In this work, we report a red blood cell substitute composed of polymerized human cord hemoglobin (PolyCHb) assisted with ascorbic acid (AA) that alleviates oxidative stress for blood transfusion. Methods: In this study, the in vitro impacts of AA on the PolyCHb were evaluated by testing the circular dichroism, methemoglobin (MetHb) contents and oxygen binding affinity before and after the addition of AA. In the in vivo study, guinea pigs were subjected to a 50% exchange transfusion with PolyCHb and AA co-administration, followed by the collection of blood, urine, and kidney samples. The hemoglobin contents of the urine samples were analyzed, and histopathologic changes, lipid peroxidation, DNA peroxidation, and heme catabolic markers in the kidneys were evaluated. Results: After treating with AA, there was no effect on the secondary structure and oxygen binding affinity of the PolyCHb, while the MetHb content was kept at 55%, which was much lower than that without AA treating. Moreover, the reduction of PolyCHbFe3+ was significantly promoted, and the content of MetHb could be reduced from 100% to 51% within 3 h. In vivo study results showed that PolyCHb assisted with AA inhibited the formation of hemoglobinuria, upgraded the total antioxidant capacity and downgraded the superoxide dismutase activity of kidney tissue, and lowered the expression of biomarkers for oxidative stress, e.g., malondialdehyde (ET vs ET+AA: 4.03±0.26 μmol/mg vs 1.83±0.16 μmol/mg), 4-hydroxy-2-nonenal (ET vs ET+AA: 0.98±0.07 vs 0.57±0.04), 8-hydroxy 2 deoxyguanosine(ET vs ET+AA: 14.81±1.58 ng/ml vs 10.91±1.36 ng/ml), heme oxygenase 1 (ET vs ET+AA: 1.51±0.08 vs 1.18±0.05) and ferritin (ET vs ET+AA: 1.75±0.09 vs 1.32±0.04). The kidney histopathology results also demonstrated that kidney tissue damage was effectively alleviated. Conclusion: In conclusion, these comprehensive results provide evidence for the potential role of AA in controlling oxidative stress and organ injury in the kidneys induced by PolyCHb, and suggest that PolyCHb assisted with AA has promising application for blood transfusion.

Development and external validation of a diagnostic model for biopsy-proven acute interstitial nephritis using electronic health record data

BACKGROUND

Patients with acute interstitial nephritis (AIN) can present without typical clinical features, leading to a delay in diagnosis and treatment. We therefore developed and validated a diagnostic model to identify patients at risk of AIN using variables from the electronic health record.

METHODS

In patients who underwent a kidney biopsy at Yale University between 2013 and 2018, we tested the association of &gt;150 variables with AIN, including demographics, comorbidities, vital signs and laboratory tests (training set 70%). We used least absolute shrinkage and selection operator methodology to select prebiopsy features associated with AIN. We performed area under the receiver operating characteristics curve (AUC) analysis with internal (held-out test set 30%) and external validation (Biopsy Biobank Cohort of Indiana). We tested the change in model performance after the addition of urine biomarkers in the Yale AIN study.

RESULTS

We included 393 patients (AIN 22%) in the training set, 158 patients (AIN 27%) in the test set, 1118 patients (AIN 11%) in the validation set and 265 patients (AIN 11%) in the Yale AIN study. Variables in the selected model included serum creatinine {adjusted odds ratio [aOR] 2.31 [95% confidence interval (CI) 1.42-3.76]}, blood urea nitrogen:creatinine ratio [aOR 0.40 (95% CI 0.20-0.78)] and urine dipstick specific gravity [aOR 0.95 (95% CI 0.91-0.99)] and protein [aOR 0.39 (95% CI 0.23-0.68)]. This model showed an AUC of 0.73 (95% CI 0.64-0.81) in the test set, which was similar to the AUC in the external validation cohort [0.74 (95% CI 0.69-0.79)]. The AUC improved to 0.84 (95% CI 0.76-0.91) upon the addition of urine interleukin-9 and tumor necrosis factor-α.

CONCLUSIONS

We developed and validated a statistical model that showed a modest AUC for AIN diagnosis, which improved upon the addition of urine biomarkers. Future studies could evaluate this model and biomarkers to identify unrecognized cases of AIN.

Prognostic Implications of a Morphometric Evaluation for Chronic Changes on All Diagnostic Native Kidney Biopsies

BACKGROUND

Semiquantitative visual inspection for glomerulosclerosis, interstitial fibrosis, and arteriosclerosis is often used to assess chronic changes in native kidney biopsies. Morphometric evaluation of these and other chronic changes may improve the prognostic assessment.

METHODS

We studied a historical cohort of patients who underwent a native kidney biopsy between 1993 and 2015 and were followed through 2021 for ESKD and for progressive CKD (defined as experiencing 50% eGFR decline, temporary dialysis, or ESKD). Pathologist scores for the percentages of globally sclerosed glomeruli (GSG), interstitial fibrosis and tubular atrophy (IFTA), and arteriosclerosis (luminal stenosis) were available. We scanned biopsy sections into high-resolution images to trace microstructures. Morphometry measures were percentage of GSG; percentage of glomerulosclerosis (percentage of GSG, ischemic-appearing glomeruli, or segmentally sclerosed glomeruli); percentage of IFTA; IFTA foci density; percentage of artery luminal stenosis; arteriolar hyalinosis counts; and measures of nephron size. Models assessed risk of ESKD or progressive CKD with biopsy measures adjusted for age, hypertension, diabetes, body mass index, eGFR, and proteinuria.

RESULTS

Of 353 patients (followed for a median 7.5 years), 75 developed ESKD and 139 experienced progressive CKD events. Visually estimated scores by pathologists versus morphometry measures for percentages of GSG, IFTA, and luminal stenosis did not substantively differ in predicting outcomes. However, adding percentage of glomerulosclerosis, IFTA foci density, and arteriolar hyalinosis improved outcome prediction. A 10-point score using percentage of glomerulosclerosis, percentage of IFTA, IFTA foci density, and any arteriolar hyalinosis outperformed a 10-point score based on percentages of GSG, IFTA, and luminal stenosis >50% in discriminating risk of ESKD or progressive CKD.

CONCLUSION

Morphometric characterization of glomerulosclerosis, IFTA, and arteriolar hyalinosis on kidney biopsy improves prediction of long-term kidney outcomes.

Antifibrotic Agents for the Management of CKD: A Review

Kidney fibrosis is a hallmark of chronic kidney disease (CKD) and a potential therapeutic target. However, there are conceptual and practical challenges to directly targeting kidney fibrosis. Whether fibrosis is mainly a cause or a consequence of CKD progression has been disputed. It is unclear whether specifically targeting fibrosis is feasible in clinical practice because most drugs that decrease fibrosis in preclinical models target additional and often multiple pathogenic pathways (eg, renin-angiotensin-aldosterone system blockade). Moreover, tools to assess whole-kidney fibrosis in routine clinical practice are lacking. Pirfenidone, a drug used for idiopathic pulmonary fibrosis, is undergoing a phase 2 trial for kidney fibrosis. Other drugs in use or being tested for idiopathic pulmonary fibrosis (eg, nintedanib, PRM-151, epigallocatechin gallate) are also potential candidates to treat kidney fibrosis. Novel therapeutic approaches may include antagomirs (eg, lademirsen) or drugs targeting interleukin 11 or NKD2 (WNT signaling pathway inhibitor). Reversing the dysfunctional tubular cell metabolism that leads to kidney fibrosis offers additional therapeutic opportunities. However, any future drug targeting fibrosis of the kidneys should demonstrate added benefit to a standard of care that combines renin-angiotensin system with mineralocorticoid receptor (eg, finerenone) blockade or with sodium/glucose cotransporter 2 inhibitors.

Incidence and Importance of Calcium Deposition in Kidney Biopsy Specimens

INTRODUCTION

Calcification on native kidney biopsy specimens is often noted by pathologists, but the consequence is unknown.

METHODS

We searched the pathology reports in the Biopsy Biobank Cohort of Indiana for native biopsy specimens with calcification.

RESULTS

Of the 4,364 specimens, 416 (9.8%) had calcification. We compared clinical and histopathology findings in those with calcification (n = 429) compared to those without calcification (n = 3,936). Patients with calcification were older, had more comorbidities, lower estimated glomerular filtration rates (eGFR), were more likely to have hyaline arteriosclerosis, interstitial fibrosis/tubular atrophy, and a primary pathologic diagnosis of acute tubular injury or acute tubular necrosis when compared to patients without calcification. Patients with calcium oxalate deposition alone, compared to calcium phosphate or mixed calcifications, had fewer comorbidities but were more likely to have a history of gastric bypass surgery or malabsorption and take vitamin D. In patients with two or more years of follow-up, multivariate analyses showed the presence of calcification (HR 0.59, 0.38-0.92, p = 0.02) and higher eGFR (HR 0.76, 0.73-0.79, p < 0.001), was associated with decreased likelihood of progressing to end-stage renal disease. The presence of calcification was also associated with a reduced slope/decline in eGFR compared to known biopsy and clinical risk factors for decline in kidney function. We hypothesized this was due to more recoverable acute kidney injury (AKI) and found more severe acute kidney injury network stage in patients with kidney calcification but also greater improvement over time.

DISCUSSION/CONCLUSION

In summary, we demonstrated that calcification on kidney biopsy specimens was associated with a better prognosis than those without calcification due to the association with recoverable AKI.

Alterations in Protein Translation and Carboxylic Acid Catabolic Processes in Diabetic Kidney Disease

Diabetic kidney disease (DKD) remains the leading cause of end-stage kidney disease despite decades of study. Alterations in the glomerulus and kidney tubules both contribute to the pathogenesis of DKD although the majority of investigative efforts have focused on the glomerulus. We sought to examine the differential expression signature of human DKD in the glomerulus and proximal tubule and corroborate our findings in the db/db mouse model of diabetes. A transcriptogram network analysis of RNAseq data from laser microdissected (LMD) human glomerulus and proximal tubule of DKD and reference nephrectomy samples revealed enriched pathways including rhodopsin-like receptors, olfactory signaling, and ribosome (protein translation) in the proximal tubule of human DKD biopsy samples. The translation pathway was also enriched in the glomerulus. Increased translation in diabetic kidneys was validated using polyribosomal profiling in the db/db mouse model of diabetes. Using single nuclear RNA sequencing (snRNAseq) of kidneys from db/db mice, we prioritized additional pathways identified in human DKD. The top overlapping pathway identified in the murine snRNAseq proximal tubule clusters and the human LMD proximal tubule compartment was carboxylic acid catabolism. Using ultra-performance liquid chromatography–mass spectrometry, the fatty acid catabolism pathway was also found to be dysregulated in the db/db mouse model. The Acetyl-CoA metabolite was down-regulated in db/db mice, aligning with the human differential expression of the genes ACOX1 and ACACB. In summary, our findings demonstrate that proximal tubular alterations in protein translation and carboxylic acid catabolism are key features in both human and murine DKD.

Label-free imaging of non-deparaffinized sections of the human kidney to determine tissue quality and signatures of disease

Label-free fluorescence imaging of kidney sections can provide important morphological information, but its utility has not been tested in a histology processing workflow. We tested the feasibility of label-free imaging of paraffin-embedded sections without deparaffinization and its potential usefulness in generating actionable data. Kidney tissue specimens were obtained during percutaneous nephrolithotomy or via diagnostic needle biopsy. Unstained non-deparaffinized sections were imaged using widefield fluorescence microscopy to capture endogenous fluorescence. Some samples were also imaged with confocal microscopy and multiphoton excitation to collect second harmonic generation (SHG) signal to obtain high-quality autofluorescence images with optical sectioning. To adjudicate the label-free signal, the samples or corresponding contiguous sections were subsequently deparaffinized and stained with Lillie's allochrome. Label-free imaging allowed the recognition of various kidney structures and enabled morphological qualification for adequacy. SHG and confocal imaging yielded quantifiable high-quality images for tissue collagens and revealed specific patterns in glomeruli and various tubules. Disease specimens from patients with diabetic kidney disease and focal segmental glomerulosclerosis showed distinctive signatures compared to specimens from healthy controls with normal kidney function. Quantitative cytometry could also be performed when DAPI is added in situ before imaging. These results show that label-free imaging of non-deparaffinized sections provides useful information about tissue quality that could be beneficial to nephropathologists by maximizing the use of scarce kidney tissue. This approach also provides quantifiable features that could inform on the biology of health and disease.

Transgelin-2 in Multiple Myeloma: A New Marker of Renal Impairment?

Transgelin is a 22-kDa protein involved in cytoskeletal organization and expressed in smooth muscle tissue. According to animal studies, it is a potential mediator of kidney injury and fibrosis, and moreover, its role in tumorigenesis is emerging in a variety of cancers. The study included 126 ambulatory patients with multiple myeloma (MM). Serum transgelin-2 concentrations were measured by enzyme-linked immunoassay. We evaluated associations between baseline transgelin and kidney function (serum creatinine, estimated glomerular filtration rate—eGFR, urinary markers of tubular injury: cystatin-C, neutrophil gelatinase associated lipocalin—NGAL monomer, cell cycle arrest biomarkers IGFBP-7 and TIMP-2) and markers of MM burden. Baseline serum transgelin was also evaluated as a predictor of kidney function after a follow-up of 27 months from the start of the study. Significant correlations were detected between serum transgelin-2 and serum creatinine (R = 0.29; p = 0.001) and eGFR (R = −0.25; p = 0.007). Transgelin significantly correlated with serum free light chains lambda (R = 0.18; p = 0.047) and serum periostin (R = −0.22; p = 0.013), after exclusion of smoldering MM patients. Patients with decreasing eGFR had higher transgelin levels (median 106.6 versus 83.9 ng/mL), although the difference was marginally significant (p = 0.05). However, baseline transgelin positively correlated with serum creatinine after the follow-up period (R = 0.37; p < 0.001) and negatively correlated with eGFR after the follow-up period (R = −0.33; p < 0.001). Moreover, higher baseline serum transgelin (beta = −0.11 ± 0.05; p = 0.032) significantly predicted lower eGFR values after the follow-up period, irrespective of baseline eGFR and follow-up duration. Our study shows for the first time that elevated serum transgelin is negatively associated with glomerular filtration in MM and predicts a decline in renal function over long-term follow-up.

Assessing and counteracting fibrosis is a cornerstone of the treatment of CKD secondary to systemic and renal limited autoimmune disorders

Chronic kidney disease (CKD) is an increasing cause of morbidity and mortality worldwide. Besides the higher prevalence of diabetes, hypertension and aging worldwide, immune mediated disorders remain an important cause of kidney disease and are especially prevalent in young adults. Regardless of the initial insult, final pathway to CKD and kidney failure is always the loss of normal tissue and fibrosis development, in which the dynamic equilibrium between extracellular matrix synthesis and degradation is disturbed, leading to excessive production and accumulation. During fibrosis, a multitude of cell types intervene at different levels, but myofibroblasts and inflammatory cells are considered critical in the process. They exert their effects through different molecular pathways, of which transforming growth factor β (TGF-β) has demonstrated to be of particular importance. Additionally, CKD itself promotes fibrosis due to the accumulation of toxins and hormonal changes, and proteinuria is simultaneously a manifestation of CKD and a specific driver of renal fibrosis. Pathways involved in renal fibrosis and CKD are closely interrelated, and although important advances have been made in our knowledge of them, it is still necessary to translate them into clinical practice. Given the complexity of this process, it is highly likely that its treatment will require a multi-target strategy to control the origin of the damage but also the mechanisms that perpetuate it. Fortunately, rapid technology development over the last years and new available drugs in the nephrologist's armamentarium give reasons for optimism that more personalized assistance for CKD and renal fibrosis will appear in the future.

Intranasal immunization with a vaccinia virus vaccine vector expressing pre-fusion stabilized SARS-CoV-2 spike fully protected mice against lethal challenge with the heavily mutated mouse-adapted SARS2-N501Y MA30 strain of SARS-CoV-2

The Omicron SARS-CoV-2 variant has been designated a variant of concern because its spike protein is heavily mutated. In particular, Omicron spike is mutated at 5 positions (K417, N440, E484, Q493 and N501) that have been associated with escape from neutralizing antibodies induced by either infection with or immunization against the early Washington strain of SARS-CoV-2. The mouse-adapted strain of SARS-CoV-2, SARS2-N501Y _MA30 , contains a spike that is also heavily mutated, with mutations at 4 of the 5 positions in Omicron spike associated with neutralizing antibody escape (K417, E484, Q493 and N501). In this manuscript we show that intranasal immunization with a pre-fusion stabilized Washington strain spike, expressed from a highly attenuated, replication-competent vaccinia virus construct, NYVAC-KC, fully protected mice against disease and death from SARS2-N501Y _MA30 . Similarly, immunization by scarification on the skin fully protected against death, but not from mild disease. This data demonstrates that Washington strain spike, when expressed from a highly attenuated, replication-competent poxvirus, administered without parenteral injection can fully protect against the heavily mutated mouse-adapted SARS2-N501Y _MA30 .

Renal Histologic Analysis Provides Complementary Information to Kidney Function Measurement for Patients with Early Diabetic or Hypertensive Disease

BACKGROUND

Patients with diabetic or hypertensive kidney disease rarely undergo kidney biopsy because nephrologists commonly believe that biopsy-related risk outweighs the potential benefits of obtaining histologic information to guide clinical decisions. Although kidney function is acutely regulated, histologic changes such as interstitial fibrosis, tubular atrophy, and glomerulosclerosis may represent chronic kidney damage, and thus might provide additional information about disease severity. However, whether histologic analysis provides information complementary to clinically used kidney function measurements, such as eGFR and proteinuria, is unclear.

METHODS

We performed a standardized semiquantitative histologic analysis of 859 nephrectomies obtained from individuals with or without diabetes mellitus or hypertension and varying degrees of kidney dysfunction. Changes in glomeruli, tubules, interstitium, and the vasculature were scored using 17 descriptive parameters in a standardized manner. We used multivariable linear and logistic regression analyses and unbiased, hierarchical clustering to assess associations between histologic alterations and clinical variables.

RESULTS

At CKD stages 3-5, eGFR correlates reasonably well with the degree of glomerulosclerosis and interstitial fibrosis and tubular atrophy (IFTA). In patients with CKD stages 1-2, the degree of histologic damage was highly variable and eGFR poorly estimated the degree of damage. Individuals with diabetes mellitus, hypertension, or Black race had significantly more glomerulosclerosis and IFTA, at the same eGFR level. Inclusion of glomerulosclerosis improved the kidney function decline estimation, even at early disease stages.

CONCLUSIONS

Histologic analysis is an important complementary method for kidney disease evaluation, especially at early disease stages. Some individuals present with relatively severe structural damage despite preserved eGFR.

Fibrosis, the Bad Actor in Cardiorenal Syndromes: Mechanisms Involved

Cardiorenal syndrome is a term that defines the complex bidirectional nature of the interaction between cardiac and renal disease. It is well established that patients with kidney disease have higher incidence of cardiovascular comorbidities and that renal dysfunction is a significant threat to the prognosis of patients with cardiac disease. Fibrosis is a common characteristic of organ injury progression that has been proposed not only as a marker but also as an important driver of the pathophysiology of cardiorenal syndromes. Due to the relevance of fibrosis, its study might give insight into the mechanisms and targets that could potentially be modulated to prevent fibrosis development. The aim of this review was to summarize some of the pathophysiological pathways involved in the fibrotic damage seen in cardiorenal syndromes, such as inflammation, oxidative stress and endoplasmic reticulum stress, which are known to be triggers and mediators of fibrosis.

Targeting the Pathobiology of Diabetic Kidney Disease

The pathobiology of diabetic kidney disease (DKD) involves an interplay between all the many different cell types that exist within the kidney and their shared and cumulative dysfunction in response to chronic hyperglycemia. DKD is characteriszed by morphological changes including tubular hypertrophy, podocyte dysfunction, mesangial expansion and mesangiolysis, endothelitis and capillary rarefaction, arteriolar hyalinosis, basement membrane thickening, and ultimately nephron dropout and tubulointerstitial fibrosis. These adaptive but ultimately maladaptive changes accelerate the progression of lesions in the diabetic kidney by increasing mechanical and oxidative stress, hypoxia, fibrogenesis, inflammation, senescence, and apoptosis. In particular, atrophy at the critical junction between Bowman's capsule and the proximal tubule likely represent the leading cause of nephron dropout and kidney function decline in DKD. Preventing, slowing, or reversing these changes should be the target of future "smart" therapies for patients with DKD, many of which are now under development.

Integration of spatial and single-cell transcriptomics localizes epithelial cell-immune cross-talk in kidney injury

Single-cell sequencing studies have characterized the transcriptomic signature of cell types within the kidney. However, the spatial distribution of acute kidney injury (AKI) is regional and affects cells heterogeneously. We first optimized coordination of spatial transcriptomics and single-nuclear sequencing data sets, mapping 30 dominant cell types to a human nephrectomy. The predicted cell-type spots corresponded with the underlying histopathology. To study the implications of AKI on transcript expression, we then characterized the spatial transcriptomic signature of 2 murine AKI models: ischemia/reperfusion injury (IRI) and cecal ligation puncture (CLP). Localized regions of reduced overall expression were associated with injury pathways. Using single-cell sequencing, we deconvoluted the signature of each spatial transcriptomic spot, identifying patterns of colocalization between immune and epithelial cells. Neutrophils infiltrated the renal medulla in the ischemia model. Atf3 was identified as a chemotactic factor in S3 proximal tubules. In the CLP model, infiltrating macrophages dominated the outer cortical signature, and Mdk was identified as a corresponding chemotactic factor. The regional distribution of these immune cells was validated with multiplexed CO-Detection by indEXing (CODEX) immunofluorescence. Spatial transcriptomic sequencing complemented single-cell sequencing by uncovering mechanisms driving immune cell infiltration and detection of relevant cell subpopulations.

Validation of a Histologic Scoring Index for C3 Glomerulopathy

RATIONALE & OBJECTIVE

A previous study that evaluated associations of kidney biopsy findings with disease progression in patients with C3 glomerulopathy (C3G) proposed a prognostic histologic index (C3G-HI) that has not yet been validated. Our objective was to validate the performance of the C3G-HI in a new patient population.

STUDY DESIGN

Multicenter, retrospective cohort study.

SETTING & PARTICIPANTS

111 patients fulfilling diagnostic criteria of C3G between January 1995 and December 2019, from 33 nephrology departments belonging to the Spanish Group for the Study of Glomerular Diseases (GLOSEN).

PREDICTORS

Demographic, clinical parameters, C3G-HI total activity score, and the C3G-HI total chronicity score.

OUTCOME

Time to kidney failure.

ANALYTICAL APPROACH

Intraclass correlation coefficients and κ statistic were used to summarize inter-rater reproducibility for assessment of histopathology in kidney biopsies. The nonlinear relationships of risk of kidney failure with the total activity score and total chronicity score were modeled using Cox proportional hazards analysis that incorporated cubic splines.

RESULTS

The study group included 93 patients with C3 glomerulonephritis and 18 with dense-deposit disease. Participants had an overall meanage of 35±22 (SD) years. Forty-eight patients (43%) developed kidney failure after a mean follow-up of 65±27 months. The overall inter-rater reproducibility was very good for the total activity score (intraclass correlation coefficient [ICC]=0.63) and excellent for total chronicity score (ICC=0.89). Baseline estimated glomerular filtration rate (eGFR), 24-hour proteinuria, and treatment with immunosuppression were the main determinants of kidney failure in a model with only clinical variables. Only tubular atrophy and interstitial fibrosis were identified as predictors in a model with histological variables. When the total activity score and total chronicity score were added to the model, only the latter was identified as an independent predictor of kidney failure.

LIMITATIONS

Only a subset of the kidney biopsies was centrally reviewed. Residual confounding.

CONCLUSIONS

We validated the performance of C3G-HI as a predictor of kidney failure in patients with C3G. The total chronicity score was the principal histologic correlate of kidney failure.