Acute kidney injury: an intensivist's perspective

Synergistic effect of apoptosis and necroptosis inhibitors in cisplatin-induced nephrotoxicity

Necroptosis is a nonapoptotic cell death pathway. We aim to study the effect of necrostatin-1 (a specific necroptosis inhibitor) in cisplatin-induced injury. We analyzed the effect of the combined use of inhibitors of apoptosis (z-vad) and necroptosis (necrostatin-1) in acute kidney injury by cisplatin in human proximal tubule cells. Our results showed moderate effectiveness in cytoprotection after treatment with z-vad. But the concomitant use of inhibitors (z-vad and necrostatin-1) presented synergistic and additive protection. The present study analyzed the caspase-3 activity and we observed a significant decrease in the group treated with z-vad and cisplatin. However we did not observe changes in the group treated with both inhibitors (z-vad and necrostatin-1) and cisplatin. Thus, demonstrating that necroptosis is a caspase-independent mechanism. We also analyzed the effect of necrostatin-1 in vivo model. C57BL/6 mice were treated with cisplatin and/or inhibitors. The concomitant use of inhibitors (z-vad and necrostatin-1) recovered renal function and decreased levels of urinary Ngal. Additionally, we analyzed the expression of RIP-1, a specific marker for necroptosis. In animals treated with cisplatin and z-VAD levels of RIP-1 were higher. This result reinforces that necroptosis occurs only in conditions where apoptosis was blocked. However, the use of both inhibitors (z-vad and necrostatin-1) provided additional protection. In conclusion, our study has a significant potential to show in vitro and in vivo protection obtained by necrostatin-1. Therefore, our results suggest that necroptosis may be an important mechanism of cell death after kidney injury.

Hypernatremia is a significant risk factor for acute kidney injury after subarachnoid hemorrhage: a retrospective analysis

BACKGROUND

Hypertonic saline therapy is often used in critically ill subarachnoid hemorrhage (SAH) patients for indications ranging from control of intracranial hypertension to managing symptomatic hyponatremia. The risk factors for developing acute kidney injury (AKI) in this patient population are not well defined.

SPECIFIC AIM

To study the role of serum sodium in developing AKI (based on the AKIN definition) in the SAH population admitted to a large academic neurocritical care unit.

METHODS

This is an IRB-approved, retrospective cohort study of patients admitted to a tertiary neuro intensive care unit. We included adult (age ≥ 18 years) SAH patients admitted to the neuro intensive care unit for at least 72 h. Development of AKI after admission to the ICU was defined using the AKIN serum creatinine criteria between 72 h and 14 days following admission. A Cox proportional hazards survival model with multiple time varying covariates was developed to evaluate the effect of maximum sodium exposure on the risk of AKI. Sodium exposure was captured as the running maximum of daily maximum serum sodium concentration (mEq/L). Sodium exposure was used as a surrogate for hypertonic saline therapy.

RESULTS

The final cohort of patients included 736 patients admitted to the neuro intensive care unit between 2006 and 2012. The number of patients who developed AKI was 64 (9 %). These patients had an increased length of stay (15.6 ± 9.4 vs. 12.5 ± 8.7 days). The odds of death were more than two fold greater among patients who developed AKI (odds ratio 2.33 95 % CI 1.27, 4.3). Sodium exposure was significantly associated with the hazard of developing AKI, adjusting for age, sex, preexisting renal disease, diabetes mellitus, radiocontrast exposure, number of days on mechanical ventilation, and admission Glasgow Coma Scale score. For each 1 mEq/L increase in the running maximum daily serum sodium, the hazard of developing AKI was increased by 5.4 % (95 % CI 1.4, 9.7).

CONCLUSION

The maximum daily sodium is a significant risk factor for developing AKI in patients with SAH.

Cell Therapy Using Human Induced Pluripotent Stem Cell-Derived Renal Progenitors Ameliorates Acute Kidney Injury in Mice

Acute kidney injury (AKI) is defined as a rapid loss of renal function resulting from various etiologies, with a mortality rate exceeding 60% among intensive care patients. Because conventional treatments have failed to alleviate this condition, the development of regenerative therapies using human induced pluripotent stem cells (hiPSCs) presents a promising new therapeutic option for AKI. We describe our methodology for generating renal progenitors from hiPSCs that show potential in ameliorating AKI. We established a multistep differentiation protocol for inducing hiPSCs into OSR1+SIX2+ renal progenitors capable of reconstituting three-dimensional proximal renal tubule-like structures in vitro and in vivo. Moreover, we found that renal subcapsular transplantation of hiPSC-derived renal progenitors ameliorated the AKI in mice induced by ischemia/reperfusion injury, significantly suppressing the elevation of blood urea nitrogen and serum creatinine levels and attenuating histopathological changes, such as tubular necrosis, tubule dilatation with casts, and interstitial fibrosis. To our knowledge, few reports demonstrating the therapeutic efficacy of cell therapy with renal lineage cells generated from hiPSCs have been published. Our results suggest that regenerative medicine strategies for kidney diseases could be developed using hiPSC-derived renal cells.

SIGNIFICANCE

This report is the first to demonstrate that the transplantation of renal progenitor cells differentiated from human induced pluripotent stem (iPS) cells has therapeutic effectiveness in mouse models of acute kidney injury induced by ischemia/reperfusion injury. In addition, this report clearly demonstrates that the therapeutic benefits come from trophic effects by the renal progenitor cells, and it identifies the renoprotective factors secreted by the progenitors. The results of this study indicate the feasibility of developing regenerative medicine strategy using iPS cells against renal diseases.

Renal angina: concept and development of pretest probability assessment in acute kidney injury

The context of a diagnostic test is a critical component for the interpretation of its result. This context defines the pretest probability of the diagnosis and forms the basis for the interpretation and value of adding the diagnostic test. In the field of acute kidney injury, a multitude of early diagnostic biomarkers have been developed, but utilization in the appropriate context is less well understood and has not been codified until recently. In order to better operationalize the context and pretest probability assessment for acute kidney injury diagnosis, the renal angina concept was proposed in 2010 for use in both children and adults. Renal angina has been assessed in approximately 1,000 subjects. However, renal angina as a concept is still unfamiliar to most clinicians and the rationale for introducing the term is not obvious. We therefore review the concept and development of renal angina, and the currently available data validating it. We discuss the various arguments for and against this construct. Future research testing the performance of renal angina with acute kidney injury biomarkers is warranted.