Cell biology and molecular mechanisms of injury in ischemic acute renal failure

Prevention of kidney ischemia/reperfusion-induced functional injury, MAPK and MAPK kinase activation, and inflammation by remote transient ureteral obstruction

Protection against ischemic kidney injury is afforded by 24 h of ureteral obstruction (UO) applied 6 or 8 days prior to the ischemia. Uremia or humoral factors are not responsible for the protection, since unilateral UO confers protection on that kidney but not the contralateral kidney. Prior UO results in reduced postischemic outer medullary congestion and leukocyte infiltration. Prior UO results in reduced postischemic phosphorylation of c-Jun N-terminal stress-activated protein kinase 1/2 (JNK1/2), p38, mitogen-activated protein kinase (MAPK) kinase 4 (MKK4), and MKK3/6. Very few cells stain positively for proliferating cell nuclear antigen after obstruction, indicating that subsequent protection against ischemia is not related to proliferation with increased numbers of newly formed daughter cells more resistant to injury. UO increases the expression of heat shock protein (HSP)-25 and HSP-72. The increased HSP-25 expression persists for 6 or 8 days, whereas HSP-72 does not. HSP-25 expression is increased in the proximal tubule cells in the outer stripe of the outer medulla postobstruction, prior to, and 24 h after ischemia. In LLC-PK(1) renal epithelial cells, adenovirus-expressed human HSP-27 confers resistance to chemical anoxia and oxidative stress. Increased HSP-27 expression in LLC-PK(1) cells results in reduced H(2)O(2)-induced phosphorylation of JNK1/2 and p38. In conclusion, prior transient UO renders the kidney resistant to ischemia. This resistance to functional consequences of ischemia is associated with reduced postischemic activation of JNK, p38 MAP kinases, and their upstream MAPK kinases. The persistent increase in HSP-25 that occurs as a result of UO may contribute to the reduction in phosphorylation of MAPKs that have been implicated in adhesion molecule up-regulation and cell death.

Characteristics of EYFP-actin and visualization of actin dynamics during ATP depletion and repletion

Disruption of the actin cytoskeleton in proximal tubule cells is a key pathophysiological factor in acute renal failure. To investigate dynamic alterations of the actin cytoskeleton in live proximal tubule cells, LLC-PK(10) cells were transfected with an enhanced yellow fluorescence protein (EYFP)-actin construct, and a clone with stable EYFP-actin expression was established. Confluent live cells were studied by confocal microscopy under physiological conditions or during ATP depletion of up to 60 min. Immunoblots of stable transfected LLC-PK(10) cells confirmed the presence of EYFP-actin, accounting for 5% of total actin. EYFP-actin predominantly incorporated in stress fibers, i.e., cortical and microvillar actin as shown by excellent colocalization with Texas red phalloidin. Homogeneous cytosolic distribution of EYFP-actin indicated colocalization with G-actin as well. Beyond previous findings, we observed differential subcellular disassembly of F-actin structures: stress fibers tagged with EYFP-actin underwent rapid and complete disruption, whereas cortical and microvillar actin disassembled at slower rates. In parallel, ATP depletion induced the formation of perinuclear EYFP-actin aggregates that colocalized with F-actin. During ATP depletion the G-actin fraction of EYFP-actin substantially decreased while endogenous and EYFP-F-actin increased. During intracellular ATP repletion, after 30 min of ATP depletion, there was a high degree of agreement between F-actin formation from EYFP-actin and endogenous actin. Our data indicate that EYFP-actin did not alter the characteristics of the endogenous actin cytoskeleton or the morphology of LLC-PK(10) cells. Furthermore, EYFP-actin is a suitable probe to study the spatial and temporal dynamics of actin cytoskeleton alterations in live proximal tubule cells during ATP depletion and ATP repletion.

Interleukin-10 inhibits ischemic and cisplatin-induced acute renal injury

BACKGROUND

Acute renal failure (ARF) is caused by ischemic and nephrotoxic insults acting alone or in combination. Anti-inflammatory agents have been shown to decrease renal ischemia-reperfusion and cisplatin-induced injury and leukocyte infiltration. Interleukin-10 (IL-10) is a potent anti-inflammatory cytokine that inhibits inflammatory and cytotoxic pathways implicated in acute renal injury. Therefore, we sought to determine if IL-10 inhibits acute renal injury.

METHODS

The effects of IL-10 were studied in mice following cisplatin administration and bilateral renal ischemia-reperfusion, in a rat model of renal transplantation, and in cultured mouse cortical tubule cells.

RESULTS

IL-10 significantly decreased renal injury following cisplatin administration and following renal ischemia/reperfusion. Delay of IL-10 treatment for one hour after cisplatin also significantly inhibited renal damage. IL-10 and alpha-melanocyte stimulating hormone (alpha-MSH) increased recovery following transplantation of a kidney subjected to warm ischemia. To explore the mechanism of action of IL-10, its effects were measured on mediators of leukocyte trafficking and inducible nitric oxide synthase (NOS-II). IL-10 inhibited cisplatin and ischemia-induced increases in mRNA for tumor necrosis factor-alpha (TNF-alpha), intercellular adhesion molecule-1 (ICAM-1), and NOS-II. IL-10 also inhibited staining for markers of apoptosis and cell cycle activity following cisplatin administration, and nitric oxide production in cultured mouse cortical tubules.

CONCLUSIONS

IL-10 protects against renal ischemic and cisplatin-induced injury. IL-10 may act, in part, by inhibiting the maladaptive activation of genes that cause leukocyte activation and adhesion, and induction of iNOS.

Anti-B7-1 blocks mononuclear cell adherence in vasa recta after ischemia

BACKGROUND

Blocking the costimulatory pathway by CTLA-4 Ig, reactive with both B7-1 and B7-2 costimulatory molecules, protects the kidney during acute ischemia/reperfusion injury. This study investigated whether and how B7-1 and/or B7-2 proteins are involved in renal ischemia/reperfusion injury (IRI).

METHODS

Uninephrectomized rats were submitted to warm renal ischemia (30 min) and received control monoclonal antibody (mAb; 17E3), anti-B7-1 (3H5), anti-B7-2 (24F), a combination of anti-B7-1/B7-2, or CTLA-4 Ig. Renal function, morphology, and the kinetics of inflammatory cells were studied for a ten-day period. Binding sites of the injected antibodies were detected by secondary staining with anti-mouse Ab.

RESULTS

Compared with controls, acute renal failure (ARF) in the anti-B7-1 group was attenuated both functionally and morphologically. Anti-B7-1/B7-2 and CTLA-4 Ig also were protective in IRI. ARF was not altered by anti-B7-2 treatment. Two hours after reperfusion, B7-1 was expressed along the endothelial cells of the ascending vasa recta. Expression of B7-1 increased over time during the first 24 hours and decreased thereafter. Two hours after reperfusion, adherence/accumulation of T cells and monocytes/macrophages was found in the vasa recta of the ischemic kidney. Anti-B7-1-treated animals had fewer T cells and monocytes/macrophages in the vasa recta compared with controls. Leukocyte accumulation in these vessels after anti-B7-2 treatment was not different from IRI controls.

CONCLUSION

These observations strongly support the key role of the B7-1 protein in the protection of renal IRI through inhibition of T cell and monocyte adherence at the level of the ascending vasa recta.

Postoperative renal insufficiency

The poor clinical outcomes associated with postoperative HARI necessitate increased vigilance for HARI detection and intervention to minimize the progression to dialysis dependency. Patient survival significantly worsens if HARI requires the initiation of dialysis. Postoperative changes, including intravascular volume expansion, SIRS, and reduced lean body mass, frequently confound the detection of HARI. Serum creatinine levels frequently do not reflect the decreased renal function because creatinine production rate is decreased with reduced lean body mass, and the serum creatinine concentration is reduced by increased intravascular volume expansion and increased volume of distribution associated with anasarca. Additional indices of renal function must be used postoperatively, including urine output, net volume status, urinalysis with microscopic examination of the spun pellet, and corrected estimations of creatinine clearance. Few therapeutic interventions currently exist to reverse HARI other than optimization of renal perfusion and limitation of nephrotoxin exposure. Dialysis remains a cornerstone of maintenance therapy for refractory and severe HARI. Selection of dialysis modality continues to be based on modality availability and patient stability.

Hemodialysis in acute renal failure: does the membrane matter?

Patients who develop hospital-acquired acute renal failure (ARF) that require dialytic support have high mortality rates. The potential impact of dialyzer membrane biocompatibility on clinical outcomes in ARF has been a subject of ongoing controversy. This article summarizes the clinical trials published to date that have examined the effect of dialyzer membrane biocompatibility on clinical outcomes of patients with ARF who require intermittent hemodialysis. A redirection of research endeavors in the field of dialysis in ARF is also argued.

Nuclear translocation of cytosolic phospholipase A2 is induced by ATP depletion

Phospholipase A(2) (PLA(2)) enzymes may play a role in cellular injury due to ATP depletion. Renal Madin-Darby canine kidney cells were subjected to ATP depletion to assess the effects of cellular energy metabolism on cytosolic PLA(2) (cPLA(2)) regulation. ATP depletion results in a decrease in soluble cPLA(2) activity and an increase in membrane-associated activity, which is reversed upon restoration of ATP levels by addition of dextrose. In ATP-depleted cells cPLA(2) mass shifts from cytosol to nuclear fractions. GFP-cPLA(2) is localized at the nuclear membrane of stably transfected ATP-depleted LLC-PK(1) cells under conditions where [Ca(2+)](i) is known to increase. cPLA(2) translocation does not occur if the increase in [Ca(2+)](i) increase is inhibited. If [Ca(2+)](i) is allowed to increase when ATP is depleted and the cells are then lysed, cPLA(2) remains associated with nuclear fractions even if the homogenate [Ca(2+)] is markedly reduced. In contrast, cPLA(2), which becomes associated with the nucleus when [Ca(2+)](i) is increased using ionophore, readily dissociates from the nuclear fractions of ATP-replete cells upon reduction of homogenate [Ca(2+)]. Okadaic acid inhibits the ATP depletion-induced association of cPLA(2) with nuclear fractions. Thus energy deprivation results in [Ca(2+)]-induced nuclear translocation, which is partially prevented by a phosphatase inhibitor.

Inhibiting the complement system does not reduce injury in renal ischemia reperfusion

The complex pathogenesis of ischemia reperfusion injury (IRI) includes endothelial expression of adhesion molecules, leukocyte recruitment and activation, reactive oxygen species production, and apoptotic and necrotic cell death. A role for complement in IRI of different organs, including kidney, has been proposed on the basis of results of experiments that used pharmacologic inhibitors as well as animals that were deficient in individual complement proteins. Here, renal IRI in mice was examined. Animals that were deficient in C3 had partial protection from IRI induced by 27.5 min of bilateral renal ischemia, followed by 20 h of reperfusion (blood urea nitrogen [BUN] values, 46.6 +/- 6.9 and 68.4 +/- 7.9 mg/dl in C3 -/- and C3 +/+ mice; n = 7 and 8, respectively; P = 0.033). Given the reduction in IRI in C3 -/- mice, it was investigated, by use of the rodent C3 convertase inhibitor CR1-related gene/protein y-Ig (Crry-Ig), whether exogenous administration of a complement inhibitor could lessen renal injury. Despite the use of Crry-Ig in high doses, there was no significant reduction of injury induced by 20 to 30 min of ischemia followed by up to 30 h of reperfusion. Histologic examination revealed acute tubular necrosis and neutrophilic infiltration, both of which correlated significantly with BUN values (P < 0.001). Of interest, C3 deposition around renal tubules was significantly less in animals with IRI, compared with that in unmanipulated controls (P < 0.001). In Crry-Ig-treated animals, C3 deposition was inversely proportional to BUN values (r = -0.63; P < 0.001), which presumably indicates that severe vascular IRI allowed access of the 160 kD Crry-Ig to the interstitium. Thus, renal IRI in mice may have a partial complement dependence, yet pharmacologic inhibition of the complement system does not seem to be effective, likely because of the presence of other mediator systems that operate in parallel.