Protective effect of prostacyclin on postischemic acute renal failure in the rat

Treprostinil, a prostacyclin analog, ameliorates renal ischemia-reperfusion injury: preclinical studies in a rat model of acute kidney injury

BACKGROUND

Renal ischemia-reperfusion injury (IRI) is a major factor causing acute kidney injury (AKI). No pharmacological treatments for prevention or amelioration of I/R-induced renal injury are available. Here we investigate the protective effects of treprostinil, a prostacyclin analog, against renal IRI in vivo.

METHODS

Male Sprague Dawley rats were subjected to bilateral renal ischemia (45 min) followed by reperfusion for 1-168 h. Treprostinil (100 ng/kg/min) or placebo was administered subcutaneously for 18-24 h before ischemia.

RESULTS

Treatment with treprostinil both significantly reduced peak elevation and accelerated the return to baseline levels for serum creatinine and blood urea nitrogen versus I/R-placebo animals following IRI. I/R-treprostinil animals exhibited reduced histopathological features of tubular epithelial injury versus I/R-placebo animals. IRI resulted in a marked induction of messenger RNA coding for kidney injury biomarkers, kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin and for pro-inflammatory cytokines chemokine (C-C motif) ligand 2, interleukin 1β, interleukin 6 and intracellular adhesion molecular 1 in animals treated with placebo only relative to sham controls. Upregulation of expression of all these genes was significantly suppressed by treprostinil. Treprostinil significantly suppressed the elevation in renal lipid peroxidation found in the I/R-placebo group at 1-h post-reperfusion. In addition, renal protein expression of cleaved poly(ADP-ribose) polymerase 1 and caspase-3, -8 and -9 in I/R-placebo animals was significantly inhibited by treprostinil.

CONCLUSIONS

This study demonstrates the efficacy of treprostinil in ameliorating I/R-induced AKI in rats by significantly improving renal function early post-reperfusion and by inhibiting renal inflammation and tubular epithelial apoptosis. Importantly, these data suggest that treprostinil has the potential to serve as a therapeutic agent to protect the kidney against IRI in vivo.

Endothelial prostacyclin protects the kidney from ischemia-reperfusion injury

Prostacyclin, or PGI₂, is a product of PGI synthase (PGIS), down-stream of cyclooxygenase pathway. PGI₂ has been demonstrated to play an important role in maintaining renal blood flow. Non-steroidal anti-inflammatory drugs (NSAIDs) that inhibit cyclooxygenase are reported to increase the susceptibility of patients to acute kidney injury (AKI). This study explores the role of endothelium-derived prostacyclin in ischemia-reperfusion injury (I/RI). The renal PGIS expression and PGI₂ production markedly increased following I/RI. Loss of one allele of PGIS gene or selective endothelial PGIS deletion (TEK-CRE PGIS^fl/fl mice) caused more severe renal damage following I/RI than control mice. Iloprost, a PGI₂ analog, administered 30 min before the I/R surgery, markedly attenuated the renal damage in both control mice and TEK-CRE PGIS^fl/fl mice. Renal p-PKA expression significantly increased after I/RI in wild-type mice but not in the PGIS deletion mice, consistent with IP receptor mediating the protective effect. Further studies showed that PGIS deficiency was associated with reduced fluorescence microsphere accumulation in the kidney following I/R. Folic acid also induced marked kidney injury; however, endothelial PGIS deletion did not worsen kidney injury compared with wild-type mice. These studies indicate that PGIS-derived PGI₂ can protect the kidney from acute injury caused by ischemia and reperfusion and PGIS/PGI₂ is a potential intervention target for AKI.

Pathophysiology of acute kidney injury

Acute kidney injury (AKI) is the leading cause of nephrology consultation and is associated with high mortality rates. The primary causes of AKI include ischemia, hypoxia, or nephrotoxicity. An underlying feature is a rapid decline in glomerular filtration rate (GFR) usually associated with decreases in renal blood flow. Inflammation represents an important additional component of AKI leading to the extension phase of injury, which may be associated with insensitivity to vasodilator therapy. It is suggested that targeting the extension phase represents an area potential of treatment with the greatest possible impact. The underlying basis of renal injury appears to be impaired energetics of the highly metabolically active nephron segments (i.e., proximal tubules and thick ascending limb) in the renal outer medulla, which can trigger conversion from transient hypoxia to intrinsic renal failure. Injury to kidney cells can be lethal or sublethal. Sublethal injury represents an important component in AKI, as it may profoundly influence GFR and renal blood flow. The nature of the recovery response is mediated by the degree to which sublethal cells can restore normal function and promote regeneration. The successful recovery from AKI depends on the degree to which these repair processes ensue and these may be compromised in elderly or chronic kidney disease (CKD) patients. Recent data suggest that AKI represents a potential link to CKD in surviving patients. Finally, earlier diagnosis of AKI represents an important area in treating patients with AKI that has spawned increased awareness of the potential that biomarkers of AKI may play in the future.

The kallikrein-kinin system in health and in diseases of the kidney

Since kallikrein was discovered as a vasodilatory substance in human urine, the kallikrein-kinin system (KKS) has been considered to play a physiological role in controlling blood pressure. Gene targeting experiments in mice in which the KKS has been inactivated to varying degrees have, however, questioned this role, because basal blood pressures are not altered. Rather, these experiments have shown that the KKS has a different and important role in preventing changes associated with normal senescence in mice, and in reducing the nephropathy and accelerated senescence-associated phenotypes induced in mice by diabetes. Other experiments have shown that the KKS suppresses mitochondrial respiration, partly by nitric oxide and prostaglandins, and that this suppression may be a key to understanding how the KKS influences senescence-related diseases. Here we review the logical progression and experimental data leading to these conclusions, and discuss their relevance to human conditions.

Delayed graft function in kidney transplantation

Delayed graft function is a form of acute renal failure resulting in post-transplantation oliguria, increased allograft immunogenicity and risk of acute rejection episodes, and decreased long-term survival. Factors related to the donor and prerenal, renal, or postrenal transplant factors related to the recipient can contribute to this condition. From experimental studies, we have learnt that both ischaemia and reinstitution of blood flow in ischaemically damaged kidneys after hypothermic preservation activate a complex sequence of events that sustain renal injury and play a pivotal part in the development of delayed graft function. Elucidation of the pathophysiology of renal ischaemia and reperfusion injury has contributed to the development of strategies to decrease the rate of delayed graft function, focusing on donor management, organ procurement and preservation techniques, recipient fluid management, and pharmacological agents (vasodilators, antioxidants, anti-inflammatory agents). Several new drugs show promise in animal studies in preventing or ameliorating ischaemia-reperfusion injury and possibly delayed graft function, but definitive clinical trials are lacking. The goal of monotherapy for the prevention or treatment of is perhaps unattainable, and multidrug approaches or single drug targeting multiple signals will be the next step to reduce post-transplantation injury and delayed graft function.

Low-dose prostacyclin preserves renal function in high-risk patients after coronary bypass surgery

OBJECTIVE

Renal failure after bypass is still a threatening problem prolonging hospital care and reducing overall survival. The following pilot study was aimed to analyze whether perioperative low-dose prostacyclin infusion is able to preserve renal function in a selected group of patients who according to a poor cardiac function were stratified as high risk for the development of renal failure after bypass.

DESIGN

Prospective randomized study.

SETTING

Tertiary care university medical center.

PATIENTS

Thirty-four patients scheduled for primary cardiac bypass surgery were included in the study (prostacyclin n = 17, control n = 17). Inclusion criteria were normal renal function before surgery and a cardiac ejection fraction <40%.

INTERVENTIONS

Low-dose prostacyclin (2 ng/kg/min) was added to the standard anesthetic protocol. Infusion was started immediately before surgery and was continued for a maximum of 48

MEASUREMENTS AND MAIN RESULTS

Significant differences in the endogenous creatinine clearance were found between the prostacyclin and the control group. Whereas there was a significant drop in the creatinine clearance at 6 hrs after surgery in the control group with a prolonged recovery period, values in the prostacyclin group remained stable. Creatinine clearance before intervention was 100 +/- 22 mL/min in the control group and 91 +/- 22 mL/min in the prostacyclin group, values at 24 hr were 68 +/- 34 mL/min vs. 103 +/- 37 mL/min, respectively (p < .01). Significant findings in favor for the prostacyclin group were also found for urine output and the fractional excretion rate of sodium.

CONCLUSION

This first pilot study indicates that low-dose prostacyclin may be of substantial value for preserving renal function in high-risk patients after coronary bypass surgery.

Purinergic receptors mediate cell proliferation and enhanced recovery from renal ischemia by adenosine triphosphate

Kidney dysfunction after ischemia can be improved by either limiting the initial injury or by enhancing the subsequent proliferative repair process. Adenosine triphosphate (ATP) favorably affects kidney function when it is given shortly after ischemia. We tested whether ATP promotes the proliferative repair response. Rats were subjected to occlusion of the left renal artery for 40 minutes and received an infusion of ATP, 12.5 micromol intravenously over 30 minutes, beginning at reperfusion. Control animals received saline solution or the hydroxyl radical scavenger dimethylthiourea (DMTU). Despite comparable functional protection by DMTU and ATP, only ATP specifically increased DNA synthesis (renal incorporation of tritiated thymidine) to an extent greater than that produced by ischemia alone. In other animals, ribonucleic acid was extracted from kidneys for Northern analysis. Expression of the proto-oncogenes c-fos and c-jun was enhanced in ATP-treated animals as compared with controls. Expression of a histone protein gene (H2b) and thymidine kinase was increased by ischemia but was not additionally affected by ATP. In vitro studies of primary cultures of renal proximal tubule epithelial cells confirmed the ability of ATP to stimulate cellular proliferation as a consequence of stimulation of purinergic P2 receptors, possibly of the P2x subclass. In summary, ATP given after ischemia increased new DNA synthesis and augmented expression of genes critical to cellular proliferation. These beneficial effects were not merely a consequence of limiting initial cellular damage, and they suggest a novel mechanism of action for ATP and other purinergic receptor agonists in renal ischemia.

Delayed graft function in renal transplantation: etiology, management and long-term significance

PURPOSE

In cadaveric renal transplantation a period of delayed graft function postoperatively is not uncommon and often associated with a poor outcome. We reviewed the biology of reperfusion injury and delayed graft function in renal transplantation, as well as its prevention, management and long-term effects.

MATERIALS AND METHODS

The medical literature covering acute tubular necrosis, delayed graft function in renal transplantation and immunology of ischemia reperfusion injury was reviewed.

RESULTS

Delayed graft function is clearly associated with poor allograft survival, and is caused by an interaction of ischemic and immunological factors. Technical and pharmacological maneuvers can improve early function rates. The response to ischemic injury is complex, and may increase graft immunogenicity and promote the chronic proliferative changes seen in chronic allograft nephropathy.

CONCLUSIONS

Improvement in early renal function should be a primary goal in renal transplantation to enhance early and long-term results. Basic research into the injury response may yield insights into renal pathophysiology.

Role of thromboxane A2 and prostacyclin in uninephrectomy-induced attenuation of ischemic renal injury

Contralateral uninephrectomy attenuates unilateral renal ischemic injury. The present work was performed to elucidate whether the beneficial effect of uninephrectomy was mediated through the modification of the actions of thromboxane A2 (TxA2) or prostacyclin. Unilateral ischemic injury was provoked by a 60-minute left renal artery occlusion in right nephrectomized (Nx) and in sham-nephrectomized (Sham-Nx) rats. Inulin clearance (CIn) of left kidney 48 hours after ischemia was significantly higher in the Nx group than in the Sham-Nx group (0.11 +/- 0.07 vs. 0.00 +/- 0.00 ml/min/kidney, P < 0.05). Ischemia-induced tubular necrosis was also less in Nx animals. Proliferating cell nuclear antigen (PCNA) staining, a marker for cell proliferation, was found more markedly in Nx rats than in Sham-Nx animals. Forty-eight hours after ischemia, renal cortical TxB2 content was greater in Sham-Nx rats than in Nx rats (29.5 +/- 4.4 vs. 18.3 +/- 1.7 pg/mg protein, P < 0.05). No significant difference was found in the intrarenal content of 6-keto prostaglandin F1 alpha between two ischemia groups. A thromboxane synthetase inhibitor, OKY-046 (100 mg/kg/day, i.p.), significantly increased CIn 48 hours after ischemia (0.00 +/- 0.00 vs. 0.17 +/- 0.09 ml/min/kidney, P < 0.05) and attenuated ischemic tubular damage in Sham-Nx rats but not in Nx animals. Under OKY-046 treatment, no significant difference was found in postischemic CIn and ischemic tubular damage between the Nx and Sham-Nx groups. OKY-046 also increased PCNA expression in the cortex and outer stripe in Sham-Nx animals. These data suggest that less production of intrarenal TxB2 plays an important role for the uninephrectomy-induced attenuation of ischemic renal damage and for the facilitation of tubular recovery.

Improvement of postischemic kidney function by reperfusion with a specifically developed solution (BT01)

Reperfusion is a critical phase of organ preservation. The purpose of this study was to develop a solution specifically for postischemic kidney reperfusion. Unilateral left normothermic kidney ischemia was induced for 60 minutes in two groups of micropigs. In group 1 (control pigs, n = 6) the kidney was reperfused immediately with pure blood at systemic pressure by unclamping the renal artery. In group 2 (test animals, n = 6) the kidney was initially reperfused with an intracellular flush solution enriched with solution BT01 composed of cytoprotectors (natriuretic factor, PGI2), free radical chelating agents (allopurinol, mannitol), and substrates for the mitochondrial respiratory chain (aspartate, glutamate). This solution was mixed immediately before use with blood in a ration of 1:4 parts and injected into the left renal artery with a perfuser at a constant pressure of 60 mm Hg. After 20 minutes, the kidney was reperfused with systemic blood for 100 minutes. Glomerular filtration rate (GFR) was determined by measuring inulin clearance. Kidney blood flow was measured throughout the experiment. After 120 minutes of reperfusion, the kidneys were removed for histologic examination. In the control pigs (group 1) 50% of the animals were anuric. The ratio between GFR measured in the left kidney at the end of perfusion and at equilibrium in the remaining animals was 0.16 +/- 0.01. In test animals (group 2) all animals recovered diuresis. The ratio between GFR measured in the left kidney at the end of perfusion and equilibrium was 0.51 +/- 0.12 (p < 0.001, group 2 vs. group 1). In group 2 postperfusion kidney blood flow was higher than in group 1 (63.0 ml/min vs. 27.4 ml/min; p < 0.05) because of a decrease in renal vascular resistance. Light microscopic examination of kidneys form animals in group 1 revealed tubular necrosis that extended to the parenchyma, with exposure of tubular interstitium. In group 2 only degenerative lesions with edema of tubular cells and disappearance of brush borders were observed. Our findings indicate that flushing the kidneys with BT01 solution mixed with blood improves postischemic kidney function by reducing reperfusion damage.

Prostaglandins protect kidneys against ischemic and toxic injury by a cellular effect

The ability of prostaglandins to protect the kidney against ischemic and toxic renal injury was evaluated by in vivo and in vitro models of renal ischemia. The prostaglandin E1 analogue, misoprostol, was found to provide significant protection against ischemia-induced renal dysfunction in rats subjected to 40 minutes of renal artery occlusion. Misoprostol-treated rats had glomerular filtration rates almost threefold greater than control animals, although renal blood flow and renal vascular resistance were not significantly different. Improved tubular function was reflected in a lower fractional excretion of sodium and a higher urine-to-plasma creatinine ratio. Misoprostol also provided similar protection in a model of toxic renal injury produced by mercuric chloride. In an in vitro model employing primary cultures of proximal tubule epithelial cells subjected to hypoxia and reoxygenation, misoprostol limited cell death. Posthypoxic cells had apical membrane disruption and loss of microvilli when examined by transmission electron microscopy. These changes were not seen in misoprostol-treated cells. The "cytoprotective" effect was also produced by prostaglandin E2 and prostacyclin. The ability of prostaglandin E to protect against toxic and ischemic renal injury did not appear to be due to an antioxidant effect because misoprostol did not limit lipid peroxidation in vivo and did not protect against oxidant injury by tert-butyl hydroperoxide in vitro. Although the exact mechanism of prostaglandin protection was not revealed, these studies demonstrate that prostaglandins protect renal tubule epithelial cells from hypoxic injury at the cellular level independent of hemodynamic factors or inflammatory responses. Such a "cytoprotective" effect of prostaglandins may be a generalized phenomenon since it has also been demonstrated in gastrointestinal epithelium.

Blood sample analysis and monitoring of hemodynamic parameters and renal function in the conscious rat

A method is described for chronic instrumentation of the rat with arterial and venous catheters. The technique minimizes the risk of catheter occlusion and damage, and reduces restraint of the animals during the evaluation. In the conscious animal, hemodynamic parameters and renal function can be monitored while substances are injected or blood samples withdrawn.

Prostanoids and hypothermic renal preservation injury

The effect of 48 hours of hypothermic renal ischemia utilizing Euro-Collins flush and short term reperfusion on renal prostaglandin synthesis was studied in dogs. Hypothermic ischemia followed by 60 minutes of reperfusion in-vivo resulted in significant elevations in renal Thromboxane B2 (TXB2) production in the outer cortex, inner cortex, and medulla, relative to non-ischemic kidneys. Prostaglandin E2 (PGE2) and 6-keto Prostaglandin F1 alpha (6-K PGF1 alpha) production were not significantly affected by ischemia and reperfusion. Enhanced TXB2 production was not seen with ischemia alone (without reperfusion) or with reperfusion with O2 saturated buffer, indicating a blood born source or stimuli. Early postreperfusion renal blood flow after hypothermic ischemia followed a biphasic pattern; blood flow increased for the first 10 minutes of reperfusion to achieve normal values, and then steadily declined over the next 20 minutes. This pattern was not altered by the cyclooxygenase inhibitors Idomethacin (5 mg/kg, P.O.) or Mefenamic acid (10 mg/kg, I.V.). Administration of the TXA2 synthesis inhibitor CGS-12970 (3 mg/kg, I.V.) or the TXA2/endoperoxide receptor antagonist SQ-29548 (80 micrograms/min, I.A.) significantly increased renal blood flow during reperfusion but neither agent altered the basic time dependent pattern observed in the control group. These data indicate that 48 hours of hypothermic renal ischemia results in dramatic changes in intrarenal TXA2 synthesis at the time of reperfusion. Enhanced TXA2 production is not dependent on reoxygenation per se, but rather requires reperfusion with blood suggesting a circulatory source.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnosis and management of acute tubular necrosis

The term acute tubular necrosis refers to those forms of acute renal failure that occur in association with ischemic or hypoxic injury or exposure to nephrotoxic substances. This article discusses the various alternative classifications that are based solely on the clinical setting in which the acute renal failure occurs, and the types of therapies used in the management of them.

Cyclosporin treatment alters prostanoid and thromboxane production by rat isolated kidney mitochondria

This study was designed to investigate the effects of chronic treatment with cyclosporin A (CSA) on the endogenous synthesis of prostanoids (PGs) and thromboxane (Tx) by renal isolated medullary and cortical mitochondria. The administration of CSA, dissolved in 10% ethanol in olive oil, to male Wistar rats (20 mg kg-1 day-1 i.p.) for 14 days resulted in alterations in mitochondrial biosynthesis of immunoreactive PGs. The endogenous synthesis of thromboxane by medullary and cortical mitochondria isolated from CSA-treated rats was significantly enhanced by 120 and 55%, respectively, whereas the synthesis of prostaglandin E2 by medullary mitochondria was reduced by 35%. The synthesis of prostaglandin F2 alpha and prostacyclin was not affected by CSA treatment. The conversion of exogenous arachidonic acid to PGs and Tx by cortical mitochondria isolated from CSA-treated rats was significantly increased. In addition, CSA treatment resulted in i) a reduced acylation of arachidonic acid into medullary phospholipids by 25% and into medullary and cortical triglycerides by 33 and 27%, respectively, and ii) an increase in cortical and medullary triglycerides. We suggest that the alterations in the endogenous mitochondrial production of PGs and Tx caused by CSA, may play a role in the impairment of membrane mediated functions.

Effects of pentoxifylline in experimental acute renal failure

The beneficial effects of post-insult administration of pentoxifylline, a novel hemorheologic agent experimentally studied in various ischemic diseases, were evaluated in two models of acute renal failure (ARF): direct nephrotoxicity (mercuric chloride 4 mg/kg via femoral vein) and hemoglobinuria (glycerol 10 ml/kg i.m.). Glomerular filtration rate (GFR) was estimated at baseline and following drug administration by creatinine clearances; tubular function was assessed by renal fractional and absolute electrolyte excretions. The incidence of mortality was decreased with a single dose of pentoxifylline 45 mg/kg (21.4%) compared to control rats (71.4%) 48 hours following induction of ARF with mercuric chloride. Although GFR and renal electrolyte excretion were significantly greater in rats given pentoxifylline compared to saline, the magnitude of difference was minimal. A return to baseline GFR was observed in the glycerol group administered a single i.p. dose of pentoxifylline 45 mg/kg (100.8 +/- 54.8%) compared to saline controls (45.6 +/- 22.7%; P less than 0.05). No differences in renal electrolyte excretion or mortality were observed in this model. Taken together, these data suggest that pentoxifylline, administered shortly after the initiation of ARF, exerts an ameliorative effect on the course and mortality of experimental ARF. The mechanism of amelioration most likely involves the stimulation of renal vasodilator prostaglandins as well as prevention of vascular congestion.

The role of eicosanoids in cyclosporine nephrotoxicity in the rat

Nephrotoxicity is the most troublesome complication of cyclosporine (CSA) therapy. The present study was designed to investigate the effects of chronic treatment with CSA on the 24-hr urinary excretion of prostanoids (PGs) and thromboxane (Tx) and on the renal function in the absence or presence of indomethacin. CSA administration to Wistar rats (20 mg/kg/day, i.p.) for 14 days caused a significant increase in plasma creatinine, blood urea nitrogen (BUN), urine osmolality, fractional excretion of sodium and potassium and a reduction in creatinine clearance (CCr) and urine volume. These changes were associated with a significant reduction in urinary excretion of PGE2 (21.1 +/- 3.3 vs 33.0 +/- 2.5 ng/24 hr) and PGF2 alpha (13.4 +/- 1.4 vs 27.9 +/- 3.8 ng/24 hr) and an increase in TxB2 (12.1 +/- 3.0 vs 4.6 +/- 0.5 ng/24 hr), and 6-keto PGF1 alpha (56.2 +/- 7.7 vs 27.7 +/- 1.9 ng/24 hr). However, the synthesis of TxB2 and 6-keto PGF1 alpha by renal medullary and cortical slices prepared from CSA treated rats was not different from values obtained for vehicle treatment. In contrast, PGE2 synthesis by cortical slices prepared from the CSA group was increased. A single injection of indomethacin (10 mg/kg) to vehicle and CSA treated rats resulted in a significant reduction in PGs and TxB2 excretion. This, was associated with a further reduction in CCr (0.81 +/- 0.06 vs 1.03 +/- 0.04 ml/min) and an increase in BUN (38.5 +/- 5.2 vs 28.2 +/- 1.4 mg%) only in the CSA group. We suggest that the vasodilating PGs attenuate the renal toxic effects induced by CSA.