Alexey Y. Kolyada

Comparative analysis of urinary biomarkers for early detection of acute kidney injury following cardiopulmonary bypass

The purpose of this study was to compare the performance of six candidate urinary biomarkers, kidney injury molecule (KIM)-1, N-acetyl-β-D-glucosaminidase (NAG), neutrophil gelatinase-associated lipocalin (NGAL), interleukin (IL)-18, cystatin C and α-1 microglobulin, measured 2 h following cardiopulmonary bypass (CPB) for the early detection of acute kidney injury (AKI) in a prospective cohort of patients undergoing cardiac surgery. A total of 103 subjects were enrolled; AKI developed in 13%. Urinary KIM-1 achieved the highest area under-the-receiver-operator-characteristic curve (AUC 0.78, 95% confidence interval 0.64–0.91), followed by IL-18 and NAG. Only urinary KIM-1 remained independently associated with AKI after adjustment for a preoperative AKI prediction score (Cleveland Clinic Foundation score; p = 0.02), or CPB perfusion time (p = 0.006). In this small pilot cohort, KIM-1 performed best as an early biomarker for AKI. Larger studies are needed to explore further the role of biomarkers for early detection of AKI following cardiac surgery.

Interleukin-8 and Acute Kidney Injury following Cardiopulmonary Bypass: A Prospective Cohort Study

Background: Cardiopulmonary bypass (CPB) elicits an inflammatory response mediated partly by neutrophils, which are activated and recruited by interleukin-8 (IL-8). We hypothesized that acute kidney injury (AKI) following CPB might be mediated by IL-8 and examined the association of perioperative plasma IL-8 levels with AKI in a prospective cohort. Methods: Plasma IL-8 was measured before, and 2, 24 and 48 h following CPB. Two AKI definitions, a serum creatinine increase of ≥0.3 mg/dl or 50% (AKI Network [AKIN] stage-1) or ≥50% alone (AKI-50%), within the first 72 h, were used. Area under the receiver operator characteristic curves (AUCs) were generated and multivariable logistic regression analyses performed. Results: A total of 143 patients were enrolled. The baseline mean serum creatinine was 1.1 mg/ dl (SD = 0.3), the CPB perfusion time was 112 min (SD = 43). Twenty-nine percent of the patients developed AKIN stage-1 and 13% AKI-50%. The plasma IL-8 level 2 h after CPB was higher in AKIN stage-1 (p = 0.03) and AKI-50% (p < 0.01), and predicted AKIN stage-1 (AUC = 0.62; p = 0.02) and AKI-50% (AUC = 0.72; p < 0.01). On multivariable analysis, the 2-hour plasma IL-8 level was associated with 1.36- and 1.59-fold higher odds for AKIN stage-1 and AKI-50%, respectively (p = 0.05). Conclusion: Plasma IL-8 predicts the development of AKI following CPB, supporting a potential involvement for this chemokine in the pathogenesis of AKI.

A genetic variant of hypoxia-inducible factor-1α is associated with adverse outcomes in acute kidney injury

Hypoxia-inducible factor-1alpha (HIF-1alpha) is a transcription factor that mediates many cellular responses to tissue hypoxia, a common feature of acute kidney injury (AKI). Here we studied 241 patients with AKI and determined the relationship to adverse outcome of a non-synonymous polymorphism in the coding region of the HIF-1alpha gene where a C to T substitution occurs at position +85 in exon 12, a change known to enhance transactivation. The baseline characteristics of the patients were not different among genotype groups except for a significantly higher prevalence of shock and number of failed organs in T-allele carriers. A significant genotype-phenotype association was found for plasma levels of vascular endothelial growth factor-A but not angiopoietin-2, two downstream targets of HIF-1alpha. Compared to the CC genotype, T-allele carriers had significantly higher adjusted odds for dialysis requirement or in-hospital death; assisted mechanical ventilation or dialysis requirement; and the composite of assisted mechanical ventilation, dialysis requirement or in-hospital death. The trend for higher plasma angiopoietin-2 levels was associated with significantly higher adjusted odds for in-hospital death; dialysis requirement or in-hospital death; and the composite outcome of assisted mechanical ventilation, dialysis, or in-hospital death. Despite the limited cohort size, our study found this particular HIF-1alpha genetic variant to be associated with disease severity and adverse outcomes in AKI. Larger studies are needed to confirm these relationships.

Protective Effect of Erythropoietin against Radiocontrast-Induced Renal Tubular Epithelial Cell Injury

Background/Aims: Recombinant human erythropoietin (rhEpo) has been shown to reduce tissue injury following ischemia-reperfusion. We examined whether rhEpo protects in vitro renal tubular epithelial cells against radiocontrast media-induced injury. Methods: LLC-PK1 renal tubular epithelial cells were exposed to non-ionic radiocontrast agent iohexol (low-osmolar) or iodixanol (iso-osmolar), with or without rhEpo (200 U/ml). Following a 6-hour exposure, cells were incubated for 24 h in radiocontrast-free culture medium. Cell viability was then assessed by the MTT assay. We also assessed cell apoptosis by the TUNEL assay, and activities of caspase-3, caspase-8, and caspase-9 were determined by a luminescence assay. Results: rhEpo improved viability of iohexol-treated LLC-PK1 cells by 27 ± 6% (88.1 ± 1.5 vs. 70.8 ± 3.3%, p = 0.008). Similarly, rhEpo improved the viability of iodixanol-treated LLC-PK1 cells by 26 ± 4% (82.5 ± 2.1vs. 65.7 ± 1.7%, p = 0.028). rhEpo also decreased apoptosis rates of iohexol-treated LLC-PK1 cells (6.4 ± 0.9/1,000 cells vs. 14.8 ± 2.4/1,000 cells, p = 0.028), and iodixanol-treated LLC-PK1 cells (8.0 ± 1.2/1,000 cells vs. 13.5 ± 1.9/1,000 cells, p = 0.028). In iohexol-treated LLC-PK1 cells, rhEpo attenuated activation of caspase-3 (p = 0.003), caspase-8 (p = 0.033) and caspase-9 (p = 0.055). Conclusion: rhEpo attenuates in vitro renal tubular epithelial cell injury induced by low- and iso-osmolar radiocontrast media, possibly by reduction of caspases activation and apoptosis rates.

Phenylethanolamine N-methyltransferase gene polymorphisms and adverse outcomes in acute kidney injury.

Background/Aims: The catecholaminergic pathway is important in the physical stress response; however, its role is not well understood in acute kidney injury (AKI). We studied single nucleotide polymorphisms (SNPs) of phenylethanolamine N-methyltransferase (PNMT), the terminal enzyme of the catecholaminergic pathway, and their association with adverse outcomes in AKI. Methods: We performed a case-control study of 961 Caucasian subjects (194 with AKI and 767 controls). The PNMT promoter G–161A (rs876493) and coding A+1543G (rs5638) SNPs were genotyped and haplotypes generated. The outcomes of interest were the development of AKI, in-hospital mortality, dialysis requirement, oliguria, and hemodynamic shock. Urine catecholamines were measured in cases to explore genotype-phenotype correlations. Results: The PNMT +1543 G allele was associated with AKI [odds ratio (OR) 2.19, 95% confidence interval (CI): 1.04–4.60]. For AKI cases, each PNMT –161 A allele was associated with lower mortality (OR 0.58, 95% CI: 0.35–0.99) and hemodynamic shock (OR 0.63, 95% CI: 0.40–1.00). The PNMT +1543 G allele was associated with oliguria (OR 3.35, 95% CI: 1.13–9.95). Urine adrenaline was associated with increased hemodynamic shock and mortality, but was lowest in PNMT –161 A/A carriers. Conclusion: In Caucasians, PNMT SNPs are associated with the development of AKI, disease severity, and in-hospital mortality. The adrenergic pathway provides another area of focus in the study of AKI.