Identification of risk factors associated with acute kidney injury in patients admitted to acute medical units

In 2009, the National Confidential Enquiry into Patient Outcome and Death (NCEPOD) report identified significant deficiencies in the management of acute kidney injury (AKI) in hospitals in the UK. Many errors arose from failure to recognise patients with AKI and those at risk of developing AKI. Currently, there is no universally accepted risk factor assessment for identifying such patients on admission to acute medical units (AMUs). A multicentre prospective observational study was performed in the AMUs of 10 hospitals in England and Scotland to define the risk factors associated with AKI and to assess quality of care. Data were collected on consecutive acute medical admissions over two separate 24-h periods. Acute kidney injury was present in 55/316 (17.7%) patients, with sepsis, hypovolaemia, chronic kidney disease (CKD) and diabetes mellitus identified as the major risk factors. Deficiencies in patient care were identified, reinforcing the continuing need to improve the management of AKI.

Potent activation of multiple signalling pathways by C-peptide in opossum kidney proximal tubular cells

AIMS/HYPOTHESIS

Proinsulin C-peptide is generally believed to be inert without any appreciable biological functions. However, it has been shown to modulate a variety of cellular processes important in the pathophysiology of diabetic complications. We therefore investigated the ability of C-peptide to stimulate intracellular signalling pathways in kidney proximal tubular cells, the altered activation of which may possibly be related to the development of diabetic nephropathy.

METHODS

Extracellular signal-regulated kinase (ERK) and Akt phosphorylation were evaluated by western blotting. ERK activity was measured by in vitro kinase assay. Intracellular Ca(2+) was evaluated by confocal imaging. The membrane and cytosol-associated fractions of protein kinase C (PKC) isoforms were evaluated by western blotting. Proliferation was assessed by thymidine incorporation assay.

RESULTS

Using the opossum proximal tubular kidney cell line as a model, we demonstrated that at high picomolar to low nanomolar concentrations, C-peptide stimulates extracellular signal-regulated mitogen-activated kinase (3.3+/-0.1-fold over basal at 3 minutes) and phosphatidylinositol 3-kinase (4.1+/-0.05-fold over basal at 5 minutes). ERK activation was attenuated by pre-treatment with a PKC inhibitor and abolished by pertussis toxin. Elevations of intracellular [Ca(2+)] are seen in response to 5 nmol/l C-peptide with consequent activation of PKC-alpha. Pre-treatment with pertussis toxin abolished PKC-alpha. C-peptide is also a functional mitogen in this cell type, stimulating significantly increased cell proliferation. Proliferation was attenuated by wortmannin and pertussis toxin pre-treatments. None of these effects is reproduced by scrambled C-peptide.

CONCLUSIONS/INTERPRETATION

This study provides evidence that C-peptide, within physiological concentration ranges, stimulates many signalling pathways in opossum kidney cells.

Inhibition of poly(ADP-ribose) polymerase attenuates ischemic renal injury in rats

The enzyme, poly(ADP-ribose) polymerase (PARP), effects repair of DNA after ischemia-reperfusion (I/R) injury to cells in nerve and muscle tissue. However, its activation in severely damaged cells can lead to ATP depletion and death. We show that PARP expression is enhanced in damaged renal proximal tubules beginning at 6-12 h after I/R injury. Intraperitoneal administration of PARP inhibitors, benzamide or 3-amino benzamide, after I/R injury accelerates the recovery of normal renal function, as assessed by monitoring the levels of plasma creatinine and blood urea nitrogen during 6 days postischemia. PARP inhibition leads to increased cell proliferation at 1 day postinjury as assessed by proliferating cell nuclear antigen and improves the histopathological appearance of kidneys examined at 7 days postinjury. Furthermore, inhibition of PARP increases levels of ATP measured at 24 h postischemia compared with those in vehicle-treated animals. Our data indicate that PARP activation is a part of the cascade of molecular events that occurs after I/R injury in the kidney. Although caution is advised, transient inhibition of PARP postischemia may constitute a novel therapy for acute renal failure.

Expression of CD44 in kidney after acute ischemic injury in rats

De novo CD44 and ligand expression at wound margins accompanies cellular proliferation and migration that effect repair of injured mucosal and vascular endothelial tissues. To determine whether CD44 could play a role in recovery from acute ischemic renal injury, we characterized its renal expression and those of two of its ligands, hyaluronic acid and osteopontin. Although no expression is detectable in nonischemic kidneys, several mRNAs for CD44 are present within 1 day after injury. CD44 mRNA is expressed in proximal tubules undergoing repair. CD44 peptide is present in basal and lateral cell membranes. Hyaluronic acid is normally expressed in the interstitium of the renal papilla only. By 1 day postischemia, hyaluronic acid can be detected, in addition, in the interstitium surrounding regenerating tubules. Osteopontin, not normally expressed in the renal proximal tubule, is expressed in regenerating tubules by 3 days after induction of acute ischemic injury. Immunoreactive osteopontin peptide continues to be localized in those tubules still undergoing repair for as long as 7 days after the injury. Our data are consistent with a role for CD44-ligand interactions in the regenerating proximal tubule participating in the process of recovery after ischemic injury.

Molecular mechanisms of cell death and regeneration in acute ischemic renal injury

Acute renal failure continues to have an unacceptably high mortality rate. Ischemic renal injury is the most common cause of acute renal failure. Understanding the molecular mechanisms of cell death and regeneration is important for designing future therapeutic strategies. Recent interest in our laboratory has focused on molecular response after ischemic renal injury and, in particular, genes that are important in cell death and repair after ischemia. The identification of genes that are differentially expressed after ischemia has led to new information regarding the identity of possible mediators of cell death and regeneration in renal tubular epithelial cells.

Expression of CD27 and ischemia/reperfusion-induced expression of its ligand Siva in rat kidneys

BACKGROUND

Studies identifying genes that are differentially expressed following induction of acute ischemic injury have been useful in delineating the pathophysiology of acute renal failure.

METHODS

A differential cDNA library screening technique was used to identify genes that are differentially expressed in rat kidney following induction of acute ischemic renal injury.

RESULTS

Levels of mRNA with a high homology to that coding for Siva, a human proapoptotic protein, were increased approximately 4.5-fold in kidneys obtained from rats within 12 hours following ischemia, compared to kidneys from sham-operated rats. A partial cDNA sequence for the rat protein (rat Siva) was determined that overlaps 92% of the human open reading frame. The cDNA sequence predicts a protein 177 amino acids in length with 76% homology to human Siva. Levels of rat Siva in kidneys were elevated at one, five and seven days post-ischemia were not different from those in kidneys from sham-operated controls. In situ hybridization demonstrated that rat Siva mRNA was expressed in cells lining damaged sections in the S3 segment of the proximal tubule at 12 hours and one day post-ischemia. At five and seven days, Siva mRNA was located in epithelial cells of regenerating tubules including in papillary proliferations. TdT-mediated dUTP-biotin nick end-labeling (TUNEL)-positive cells colocalized with cells containing Siva mRNA. CD27, the receptor for Siva was localized by immunohistochemistry to sloughed cells in the lumens of damaged S3 segments at 12 hours post-ischemia and to cells within papillary proliferations at five days post-injury.

CONCLUSIONS

Siva that is produced within the kidney could be a mediator of apoptosis post-ischemia via an interaction with CD27.

Induction of calcyclin after ischemic injury to rat kidney

Genes differentially expressed after acute renal ischemic injury were identified using differential display-polymerase chain reaction (DD-PCR). Messenger RNA for calcyclin, a member of the S100 family of calcium-binding proteins, is increased in kidneys by 6 h following ischemic injury to rats compared with sham surgery. The level of calcyclin mRNA is increased 10-fold by 1 day postinjury and declines thereafter. In situ hybridization demonstrates little calcyclin mRNA in kidneys of sham-operated rats. However, calcyclin protein is present in glomeruli and distal tubules (DT). Compared with kidneys from sham-operated controls, both calcyclin mRNA and protein expression are increased at 1-3 days following ischemic injury in the thick ascending limb of Henle, the DT, and in damaged regenerating segments of proximal tubules. By 7 days postischemia there is a reduction in mRNA and protein expression. Calcyclin could play a role in the regulation of renal cell proliferation and regeneration in the recovery process after acute ischemic injury.