Pyruvate Kinase M2: A Novel Biomarker for the Early Detection of Acute Kidney Injury

Abstract

The identification of biomarkers for the early detection of acute kidney injury (AKI) is clinically important. Acute kidney injury (AKI) in critically ill patients is closely associated with increased morbidity and mortality. Conventional biomarkers, such as serum creatinine (SCr) and blood urea nitrogen (BUN), are frequently used to diagnose AKI. However, these biomarkers increase only after significant structural damage has occurred. Recent efforts have focused on identification and validation of new noninvasive biomarkers for the early detection of AKI, prior to extensive structural damage. Furthermore, AKI biomarkers can provide valuable insight into the molecular mechanisms of this complex and heterogeneous disease. Our previous study suggested that pyruvate kinase M2 (PKM2), which is excreted in the urine, is a sensitive biomarker for nephrotoxicity. To appropriately and optimally utilize PKM2 as a biomarker for AKI requires its complete characterization. This review highlights the major studies that have addressed the diagnostic and prognostic predictive power of biomarkers for AKI and assesses the potential usage of PKM2 as an early biomarker for AKI. We summarize the current state of knowledge regarding the role of biomarkers and the molecular and cellular mechanisms of AKI. This review will elucidate the biological basis of specific biomarkers that will contribute to improving the early detection and diagnosis of AKI.

Keywords: Acute kidney injury; Biomarker; Pyruvate kinase M2.

Fig. 1

The cellular mechanisms involved in acute kidney injury and its urinary biomarkers. Biomarkers are renal or non-renal derived molecules that report the functional status of kidney filtration and tubule injury. Markers may be non-renal molecules that are filtered, secreted or reabsorbed, molecules that are constitutively expressed, or molecules that are up-regulated by inflammation-mediated immune cells.

Fig. 2

Fold change in metabolites observed in conditioned media from HK-2 cells treated with cisplatin (10 μM). Fold changes were calculated as the ratio of cisplatin-treated groups and control groups (cisplatin-treated/control) of a given metabolite at each time point. Data are representative of 3 independent experiments. Concentrations of metabolites were detected by [¹H]NMR in conditioned media of HK-2 cells after cisplatin-treatment. Data were then calibrated to TSP-d₄ at δ 0.00 ppm. Spectral assignment was performed by Chenomx NMR Suite 7.1 software (Chenomx Inc., Edmonton, Canada) and compared with published data. After processing, data were reduced into 920 spectral integral regions corresponding to a chemical shift range of δ 0.2ppm-10ppm using the Chenomx NMR Suite.

Fig. 3

Fold change of metabolites observed in the lysates of HK-2 cells treated with cisplatin (10 μM). Fold changes were calculated as the ratio of cisplatin-treated groups and control groups (cisplatin-treated/control) of a given metabolite at each time point. Data are representative of 3 independent experiments. Concentrations of metabolites were detected by [¹H]NMR in lysates of HK-2 cells after cisplatin-treatment. Data were then normalized to TSP-d₄ at δ 0.00 ppm. Spectral assignment was performed by Chenomx NMR Suite 7.1 software (Chenomx Inc., Edmonton, Canada) and compared with published data. After processing, data were reduced into 920 spectral integral regions corresponding to a chemical shift range of δ 0.2 ppm-10 ppm using the Chenomx NMR Suite.

Fig. 4

Schematic illustrating glucose metabolism during acute kidney damage. Pyruvate kinase M2 (PKM2) catalyzes the rate-limiting step of glycolysis, controlling the conversion of phosphoenolpyruvate (PEP) to pyruvate, and thus ATP generation. PKM2, a cytosolic protein, is highly expressed in the tubular cells because of pro-apoptotic stimuli in the early stage of AKI. Finally, PKM2 may be released into the urine by leakage through the damaged cell membranes in cell death-inducing conditions. (A) Increased levels of PKM2 were detected in cisplatin-treated rats. Urine samples of rats treated with cisplatin were subjected to immunoblot analysis for PKM2. Data are representative of 3 independent experiments. (B) The fold changes of lactate detected by [¹H]NMR in the urine of Sprague-Dawley rats are indicated. Male Sprague-Dawley rats were administered saline (control) or cisplatin (10mg/kg), and urine samples were collected at the indicated time points. The analysis of lactate in urine samples was carried out with a Varian analyzer (Varian Inc., Palo Alto, CA) with a working frequency of 600.167MHz at a temperature of 299.1 K.