Prostaglandin I2 attenuates ischemic acute renal failure in the rat

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.

Iloprost for prevention of contrast-mediated nephropathy in high-risk patients undergoing a coronary procedure. Results of a randomized pilot study

OBJECTIVE

The prevention of contrast-mediated nephropathy (CMN), which accounts for considerable morbidity and mortality, remains a vexing problem. Contrast induced renal vasoconstriction is believed to play a pivotal role in the CMN mechanism. The aim of this pilot study was to examine the safety and efficacy of two doses of the prostacyclin analogue iloprost in preventing CMN in high-risk patients undergoing a coronary procedure.

METHODS

Forty-five patients undergoing coronary angiography and/or intervention who had a serum creatinine concentration >or=1.4 mg/dL were randomized to receive iloprost at 1 or 2 ng/kg/min or placebo, beginning 30-90 minutes before and terminating 4 hours after the procedure. CMN was defined by an absolute increase of serum creatinine >or=0.5 mg/dL or a relative increase of >or=25% measured 2 to 5 days after the procedure. Study drug infusion was discontinued in 2 patients in the low-dose iloprost group due to flush/nausea and in 5 patients in the high-dose group due to severe hypotension.

RESULTS

The mean creatinine concentration change in the placebo group (0.02 mg/dL) was unfavorable compared to that in the low-dose iloprost group (-0.11 mg/dL; p=0.08) and high-dose iloprost group (-0.23 mg/dL; p=0.048). The difference between the absolute changes in creatinine clearance was favorable compared to placebo for both the low (mean difference 6.1 mL/min, 95%CI -0.5 to 12.8 mL/min, p=0.07) and the high-dose iloprost group (11.8 mL/min, 95%CI 4.7 to 18.8 mL/min, p=0.002). Three cases of CMN were recorded; all in the placebo group (p=0.032).

CONCLUSIONS

The results of this pilot study suggest that prophylactic administration of iloprost may effectively prevent CMN, but higher dosages are connected with substantial tolerability issues.

Efficacy of prostaglandin I2 analog on liver grafts subjected to 30 minutes of warm ischemia

Due to the fact that no effective conditioning agent for hemodynamically unstable donors exists, the number of suitable donors is limited. The efficacy of OP-41483, a stable analog of prostaglandin I2, as a conditioning agent of the liver was investigated in this study using pigs. OP-41483 was administered via the portal tributary for 10 min before 30 min of warm ischemia. Graft livers were procured after perfusion with OP-41483 in cold normal saline, then flushed with OP-41483 in Euro-Collins solution and placed in cold storage prior to orthotopic transplantation. OP-41483 was also administered intraportally for 120 min after reperfusion. Biochemical and histological studies, and survival rates were compared with a control group not given OP-41483 in an otherwise similar experimental protocol. The graft function recovered better in the OP group than in the control group, shown by the lactate values and lactate-to-pyruvate ratios. The marked congestion noted in the parenchyma of the control group livers was minimal in the OP group, verifying the microcirculatory effect of prostaglandin I2 by its vasodilatory and antithrombotic actions. These findings suggest that OP-41483 has some protective effect as a conditioning agent in liver transplantation, with timing of administration being crucial.

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)

Vasodilating prostaglandins attenuate ischemic renal injury only if thromboxane is inhibited

Ischemia-induced renal injury is prevented by inhibition of thromboxane (Tx) synthesis. This protection was believed to be secondary to a high prostaglandin (PG)/TxA2 ratio. This study tests whether increasing the PG/Tx ratio by administration of vasodilating PGs protects the reperfused ischemic kidney. Anesthetized rats underwent right nephrectomy and 45 minutes of left renal pedicle clamping. Beginning 10 minutes before clamp release, animals were treated intravenously with the following: saline placebo (n = 10); the cyclooxygenase inhibitor ibuprofen (Ibu), 12.5 mg/Kg in a bolus (n = 8); a stable analogue of prostacyclin (PGI2), 500 ng/kg/minute for 2 hours (n = 9); PGE1, 400 ng/kg/minute for 2 hours (n = 8); the combination Ibu and PGI2 (n = 8) or PGE1 (n = 8). In saline treated ischemic controls, 5 minutes after reperfusion plasma, thromboxane (TxB2) and 6-keto-PGF1 levels were 2537 and 317 pg/ml, respectively--higher than the TxB2 and 6-keto-PGF1 levels of 750 and 80 pg/ml, respectively, in nephrectomized but nonischemic sham controls (n = 7) (p less than 0.05). In ischemic control animals at 24 hours, creatinine levels were 4.6 mg/dl, relative to 0.9 ml/dl in sham animals (p less than 0.05); the weight of the left (L) ischemic kidney relative to the right (R) normal kidney was 118%, compared with 99% in sham animals (p less than 0.05); and renal histology of ischemic control animals at 24 hours showed acute tubular necrosis (ATN) relative to normal findings in sham animals. Pretreatment with Ibu led to: TxB2 and 6-keto-PGF1 levels of 116 and 40 pg/ml, lower than those of sham animals (p less than 0.05); creatinine levels of 4.6 mg/dl, L/R renal weight of 119%; and ATN similar to that of ischemic controls. Treatment with a PGI2 analogue or PGE1 was not protective and led to increases in TxB2, 6-keto-PGF1, creatinine, L/R renal weight, and ATN similar to that of ischemic controls. The combination of Ibu and either PGI2 or PGE1 led to: reduced levels of TxB2 and 6-keto-PGF1 (p less than 0.05); attenuated increases in creatinine to 2.2 and 2.3 mg/dl, respectively (p less than 0.05); and limited ATN (p less than 0.05). These data indicate that the vasodilating PG protect the ischemic reperfused kidney only when Tx is inhibited.

Effects of a stable prostacyclin analog on experimental ischemic acute renal failure

The effect of OP-41483, a stable prostacyclin (PGI2) analog, on ischemic acute renal failure (ARF) was investigated in dogs. Administration of OP-41483 for three days after ischemia significantly increased renal cortical blood flow (RCBF) when compared with dogs treated with the saline vehicle. In the OP-41483-treated group, serum creatinine levels remained relatively low during postoperative days 1-3 and mean survival time was prolonged. Injection of a silicone rubber vascular casting compound (Microfil) revealed increased numbers of visible renal cortical glomeruli and microvessels compared to the saline vehicle group. Histologic sections showed only very limited tubular necrosis, whereas sections of kidneys treated with saline showed extensive tubular necrosis. In conclusion, this stable prostacyclin analog provided a significant degree of protection for the kidneys from ischemic injury and may be useful in a clinical setting.

Renal effects of the inhibitor of thromboxane A2-synthetase OKY-046

Acute renal failure (ARF) was associated with increased urinary thromboxane (TXA2) excretion and lessened excretion of sodium (UNaV) and fractional excretion of sodium (FENa%). The inhibitor of thromboxane A2-synthetase OKY-046 enhanced sodium excretion and fractional excretion of sodium in normal and saline loaded animals whereas it partially prevented the reduction in sodium excretion and creatinine clearance and significantly increased fractional excretion of sodium in glycerol treated rats suggesting a partial protection against the development of acute renal failure.