Found in Translation: Reasons for Optimism in the Pursuit to Prevent Chronic Kidney Disease After Acute Kidney Injury

Selecting the right therapeutic target for kidney disease

Kidney disease is a complex disease with several different etiologies and underlying associated pathophysiology. This is reflected by the lack of effective treatment therapies in chronic kidney disease (CKD) that stop disease progression. However, novel strategies, recent scientific breakthroughs, and technological advances have revealed new possibilities for finding novel disease drivers in CKD. This review describes some of the latest advances in the field and brings them together in a more holistic framework as applied to identification and validation of disease drivers in CKD. It uses high-resolution 'patient-centric' omics data sets, advanced in silico tools (systems biology, connectivity mapping, and machine learning) and 'state-of-the-art' experimental systems (complex 3D systems in vitro, CRISPR gene editing, and various model biological systems in vivo). Application of such a framework is expected to increase the likelihood of successful identification of novel drug candidates based on strong human target validation and a better scientific understanding of underlying mechanisms.

F4/80hi Resident Macrophages Contribute to Cisplatin-Induced Renal Fibrosis

Background

Cisplatin-induced kidney injury remains a major obstacle in utilizing cisplatin as a chemotherapeutic for solid-organ cancers. Thirty percent of patients treated with cisplatin develop acute kidney injury (AKI), and even patients who do not develop AKI are at risk for long-term declines in kidney function and development of chronic kidney disease (CKD). Modeling cisplatin-induced kidney injury in mice has revealed that repeated low doses of cisplatin lead to development of kidney fibrosis. This model can be used to examine AKI-to-CKD transition processes. Macrophages play a role in some of these processes, including immune response, wound healing, and tissue remodeling. Depleting macrophage populations in the kidney reduced fibrosis development in other models of renal fibrosis.

Methods

We used either C57BL/6 mice with a Ccr2 genetic knockout or liposome encapsulated clodronate (Clodrosome) to deplete macrophage populations during repeated 9 mg/kg cisplatin treatments. We assessed how immune cell populations were altered in the blood and kidney of these mice and how these alterations affected development of renal fibrosis and kidney injury.

Results

We found that Clodrosome treatment decreased collagen deposition, myofibroblast accumulation, and inflammatory cytokine production, whereas Ccr2 genetic knockout had no effect on these markers after cisplatin treatment. Additionally, Ccr2-/- mice had decreased levels of F4/80lo infiltrating macrophages in the kidney after cisplatin treatments, but Clodrosome treatment depleted F4/80hi resident and CD206+ M2 macrophages.

Conclusions

These data suggest that Clodrosome depletion of F4/80hi and M2 macrophages in the kidney attenuates development of renal fibrosis after repeated low doses of cisplatin.

Sub-chronic oral exposure of tungsten induces markers of kidney injury

Tungsten is a naturally occurring transition element used in a broad range of applications. As a result of its extensive use, we are increasingly exposed to tungsten from our environment, including potable water, since tungsten can become bioaccessible in ground sources. The kidneys are particularly susceptible to tungsten exposure as this is the main site for tungsten excretion. In this study, we investigated the prolonged effects of tungsten on the kidneys and how this may impact injury and function. When mice were exposed to tungsten in their drinking water for 1-month, kidney function had not significantly changed. Following 3-month exposure, mice were presented with deterioration in kidney function as determined by serum and urine creatinine levels. During 3-months of tungsten exposure, murine kidneys demonstrated significant increases in the myofibroblast marker ⍺SMA, and extracellular matrix products: fibronectin, collagen, and matricellular proteins. In addition, Masson's trichrome and H&E staining revealed an increase in fibrotic tissue and vacuolization of tubular epithelial cells, respectively, from kidneys of tungsten-treated mice, indicative of renal injury. In vitro treatment of kidney fibroblasts with tungsten led to increased proliferation and upregulation of Transforming Growth Factor Beta 1 (TGFβ1), which was consistent with the appearance of fibroblast-to-myofibroblast transition (FMT) markers. Our data suggest that continuous exposure to tungsten impairs kidney function that may lead to the development of chronic kidney disease (CKD).

Incidence of Serum Creatinine Monitoring and Outpatient Visit Follow-Up among Acute Kidney Injury Survivors after Discharge: A Population-Based Cohort Study

INTRODUCTION

Acute kidney injury (AKI) affects 20% of hospitalized patients and worsens outcomes. To limit complications, post-discharge follow-up and kidney function testing are advised. The objective of this study was to evaluate the frequency of follow-up after discharge among AKI survivors.

METHODS

This was a population-based cohort study of adult Olmsted County residents hospitalized with an episode of stage II or III AKI between 2006 and 2014. Those dismissed from the hospital on dialysis, hospice, or who died within 30 days after discharge were excluded. The frequency and predictors of follow-up, defined as an outpatient serum creatinine (SCr) level or an in-person healthcare visit after discharge were described.

RESULTS

In the 627 included AKI survivors, the 30-day cumulative incidence of a follow-up outpatient SCr was 80% (95% confidence interval [CI]: 76% and 83%), a healthcare visit was 82% (95% CI: 79 and 85%), or both was 70% (95% CI: 66 and 73%). At 90 days and 1 year after discharge, the cumulative incidences of meeting both follow-up criteria rose to 82 and 91%, respectively. Independent predictors of receiving both an outpatient SCr assessment and healthcare visit within 30 days included lower estimated glomerular filtration rate at discharge, higher comorbidity burden, longer length of hospitalization, and greater maximum AKI severity. Age, sex, race/ethnicity, education level, and socioeconomic status did not predict follow-up.

CONCLUSIONS

Among patients with moderate to severe AKI, 30% did not have follow-up with a SCr and healthcare visit in the 30-day post-discharge interval. Follow-up was associated with higher acuity of illness rather than demographic or socioeconomic factors.