maleic-acid and Reperfusion-Injury

Alpha-1-antitrypsin (AAT) is a hepatic stress protein with protease inhibitor activity. Recent evidence indicates that ischemic or toxic injury can evoke selective changes within kidney that resemble a hepatic phenotype. Hence, we tested the following: i) Does acute kidney injury (AKI) up-regulate the normally renal silent AAT gene? ii) Does rapid urinary AAT excretion result? And iii) Can AAT's anti-protease/anti-neutrophil elastase (NE) activity protect injured proximal tubule cells? CD-1 mice were subjected to ischemic or nephrotoxic (glycerol, maleate, cisplatin) AKI. Renal functional and biochemical assessments were made 4-72 hrs later. Rapidly following injury, 5-10 fold renal cortical and isolated proximal tubule AAT mRNA and protein increases occurred. These were paralleled by rapid (>100 fold) increases in urinary AAT excretion. AKI also induced marked increases in renal cortical/isolated proximal tubule NE mRNA. However, sharp NE protein levels declines resulted, which strikingly correlated (r, -0.94) with rising AAT protein levels (reflecting NE complexing by AAT/destruction). NE addition to HK-2 cells evoked ∼95% cell death. AAT completely blocked this NE toxicity, as well as Fe induced oxidant HK-2 cell attack. Translational relevance of experimental AAT gene induction was indicated by ∼100-1000 fold urinary AAT increases in 22 AKI patients (matching urine NGAL increases). We conclude: i) AKI rapidly up-regulates the renal cortical/proximal tubule AAT gene; ii) NE gene induction also results; iii) AAT can confer cytoprotection, potentially by blocking/reducing cytotoxic NE accumulation; and iv) marked increases in urinary AAT excretion in AKI patients implies clinical relevance of the AKI- AAT induction pathway.

Topics: Acute Kidney Injury; Acute-Phase Proteins; alpha 1-Antitrypsin; Animals; Azotemia; Cell Line; Cisplatin; Glycerol; Humans; Kidney; Kidney Cortex; Kidney Tubules; Kidney Tubules, Proximal; Leukocyte Elastase; Male; Maleates; Mice; Phenotype; Reperfusion Injury; Up-Regulation

This study evaluated the potential utility of albuminuria as a "biomarker" of acute kidney injury (AKI) and tested whether AKI induces renal expression of the normally silent albumin gene. Urine albumin concentrations were measured in mice with five different AKI models (maleate, ischemia-reperfusion, rhabdomyolysis, endotoxemia, ureteral obstruction). Albumin gene induction in renal cortex, and in antimycin A-injured cultured proximal tubular cells, was assessed (mRNA levels; RNA polymerase II binding to the albumin gene). Albumin's clinical performance as an AKI biomarker was also tested (29 APACHE II-matched intensive care unit patients with and without AKI). Results were contrasted to those obtained for neutrophil gelatinase-associated lipocalin (NGAL), an established "AKI biomarker" gene. The experimental and clinical assessments indicated albumin's equivalence to NGAL as an AKI biomarker (greater specificity in experimental AKI; slightly better receiver-operating curve in humans). Furthermore, experimental AKI markedly induced the albumin gene (mRNA/RNA polymerase II binding increases; comparable to those seen for NGAL). Albumin gene activation in patients with AKI was suggested by fivefold increases in RNA polymerase II binding to urinary fragments of the albumin gene (vs. AKI controls). Experimental AKI also increased renal cortical mRNA levels for α-fetoprotein (albumin's embryonic equivalent). A correlate in patients was increased urinary α-fetoprotein excretion. We conclude that AKI can unmask, in the kidney, the normally silent renal albumin and α-fetoprotein genes. In addition, the urinary protein data independently indicate that albuminuria, and perhaps α-fetoprotein, have substantial utility as biomarkers of acute tubular injury.

Topics: Acute Kidney Injury; Adult; Aged; Albumins; Albuminuria; Animals; Biomarkers; Cells, Cultured; Endotoxemia; Female; Glycerol; Humans; Kidney Cortex; Kidney Tubules, Proximal; Male; Maleates; Mice; Mice, Inbred Strains; Middle Aged; Models, Animal; Reperfusion Injury; Rhabdomyolysis; Severity of Illness Index; Ureteral Obstruction