Effects of oxygen free radical scavengers, xanthine oxidase inhibition and calcium entry-blockers on leakage of albumin after ischaemia. An experimental study in rabbit kidneys

The effect of mannitol on oxidation-reduction potential in patients undergoing deceased donor renal transplantation-A randomized controlled trial

BACKGROUND

Mannitol, an osmotic diuretic, is proposed to be an oxygen radical scavenger. Mannitol is often used in renal transplantation to attenuate oxidative stress and thus to protect renal graft function. We tested the hypothesis that mannitol reduces overall oxidative stress during deceased donor renal transplantation.

METHODS

We randomly assigned 34 patients undergoing deceased donor renal transplantation to receive a solution of mannitol or placebo shortly before graft reperfusion until the end of surgery. We evaluated oxidative stress by measuring the static oxidative-reduction potential (sORP) and the capacity of the oxidative-reduction potential (cORP). sORP and cORP were measured pre-operatively, before and within 10 minutes after graft reperfusion, and post-operatively.

RESULTS

Seventeen patients were enrolled in the mannitol group and 17 patients were enrolled in the placebo group. Mannitol had no significant effect on sORP (148.5 mV [136.2; 160.2]) as compared to placebo (143.6 mV [135.8; 163.2], P = .99). There was also no significant difference in cORP between the mannitol (0.22 µC [0.16; 0.36]) and the placebo group (0.22 µC [0.17; 0.38], P = .76).

CONCLUSION

Mannitol showed no systemic redox scavenging effects during deceased donor renal transplantation. To evaluate the direct effect of mannitol on the renal graft further studies are needed.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02705573.

Fluids for Prevention and Management of Acute Kidney Injury

Fluids are the only known method of attenuating renal injury. Furthermore, whether for hydration, resuscitation or renal replacement therapy, fluid prescriptions must be tailored to the fluid and electrolyte, cardiovascular status and residual renal function of the patient. Different fluids have significantly different effects both on volume expansion as well as on the electrolyte and acid-base balance; while controversial, different fluids may even influence renal function differently. This systematic review focuses on fluids for prevention and management of acute kidney injury. We have reviewed the available evidence and have made recommendations for clinical practice and future studies.

Perioperative fluid management in renal transplantation: a narrative review of the literature

Adequate volume maintenance is essential to prevent acute renal failure during major surgery or to ensure graft function after renal transplantation. The various recommendations on the optimum fluid therapy are based, at best, on sparse evidence only from observational studies. This article reviews the literature on perioperative fluid management in renal transplantation. Crystalloid solutions not exerting any specific side-effects are the first choice for volume replacement in kidney transplantation. The use of colloids should be restricted to patients with severe intravascular volume deficits necessitating high volume restoration. The routine application of albumin, dopamine, and high dose diuretics is no longer warranted. Mannitol given immediately before removal of the vessel clamps reduces the requirement of post-transplant dialysis, but has no effects on graft function in the long term. There is insufficient evidence on the best use of dialysis, but it seems peritoneal dialysis pretransplant is associated with less delayed graft function, whereas the preference of dialysis post-transplant is not yet well-founded. This review article should provide better guidance for fluid management in kidney transplantation until best-evidence guidelines can be established based upon more research.

Clinical review: Treatment of heat stroke: should dantrolene be considered?

Rapid and efficient cooling is the most important therapeutic objective in patients with heat stroke (HS). This article reviews the mechanism of action and rationale for the use of dantrolene as a potential supportive cooling method in the treatment of HS. Relevant studies were included to support discussion of the role of dantrolene for the treatment of HS. In some studies dantrolene was shown to accelerate cooling rate when administered after the development of exertional HS. Dantrolene was also found to be effective in reducing the extent of HS signs when given as pretreatment in an animal model. Accumulated data do not support the routine use of dantrolene as an adjuvant cooling technique in HS, but administration of this drug in severe cases, or in which no improvement is observed, appears rational. Further trials are needed in order to assess the true effectiveness of dantrolene in HS.

Free radical scavengers and diaphragm injury following inspiratory resistive loading

Three groups of NZW rabbits were studied to examine the role of free radical scavengers in preventing diaphragm injury produced by inspiratory resistive load (IRL): control, IRL, and scavenger groups. An IRL (Pao: 45-55 cm H2O) was applied to the IRL and the scavenger groups on Day 1. Free radical scavengers (polyethylene glycol superoxide dismutase, N-acetylcysteine, and mannitol) were given (intravenously) to the scavenger group both before and after the IRL. All rabbits were killed on Day 3 to collect diaphragms. Point counting H&E-stained diaphragm x-sections indicated that abnormal diaphragm muscle in the IRL group was significantly greater than control (p < 0.01). However, it was significantly lower in the scavenger group than the IRL group (p < 0.05) and it did not differ from control. In vitro diaphragm physiological studies found that the twitch tension (p < 0.05) and maximal tension (p < 0.01) in the IRL group were significantly lower than control. The maximal tensions (p < 0.05) in the scavenger group were lower than control. After the fatigue protocol, diaphragmatic contractility in the scavenger group was similar to control and was better maintained compared with the IRL group. We conclude that free radical scavengers can prevent the development of diaphragm injury as evidenced by histology but the protection of diaphragm function is limited.

Genetic responses to free radicals. Homeostasis and gene control

Gene regulation mechanisms have evolved allowing cells to finetune the level of "endogenous" oxidative stress and to cope with increased free radicals from external sources. Levels of H2O2 are tightly controlled in E. coli by OxyR, which is activated by H2O2 to increase scavenging activities and limit H2O2 generation by the respiratory chain. Sub-micromolar levels of H2O2 are maintained in mammalian tissues, though the regulatory systems that govern this control are unknown. Excess superoxide triggers the soxRS system in E. coli, which is controlled by the oxidant-sensitive iron-sulfur centers of the SoxR protein. Nitric oxide activates SoxR by a different modification of the iron-sulfur centers. The soxRS regulon mobilizes diverse functions to scavenge free radicals and repair oxidative damage in macromolecules, and other mechanisms that exclude many environmental agents from the cell. Mammalian cells also sense and respond to sub-toxic levels of nitric oxide, activating expression of heme oxygenase 1 through stabilization of its mRNA. These inductions give rise to adaptive resistance to nitric oxide in neuronal and other cell types.

Lipid peroxidation and changes in cytochrome c oxidase and xanthine oxidase activity in organophosphorus anticholinesterase induced myopathy

A possible role of radical oxygen species (ROS) initiated lipid peroxidation in diisopropylphosphorofluoridate (DFP)-induced muscle necrosis was investigated by quantifying muscle changes in F2-isoprostanes, novel and extremely accurate markers of lipid peroxidation in vivo. A significant increase in F2-isoprostanes of 56% was found in the diaphragm of rats 60 min after DFP-induced fasciculations. As possible source of ROS initiating lipid peroxidation, the cytocrome-c oxidase (Cyt-ox) and xanthine dehydrogenase-xanthine oxidase (XD-XO) systems were investigated. Within 30 min of onset of fasciculations Cyt-ox activity was reduced by 50% from 0.526 to 0.263 mumol/mg prot/min and XO activity increased from 0.242 to 0.541 mumol/mg prot/min. Total XD-XO activity was unchanged, indicating a conversion from XD into XO. In rats pretreatment with the neuromuscular blocking agent d-tubocurarine, prevented DFP-induced fasciculations, increases in F2-isoprostanes and changes in Cyt-ox or XD-XO. The decrease in Cyt-ox and increase in XO suggest that ROS are produced during DFP induced muscle fasciculations initiating lipid peroxidation and subsequent myopathy.

Nitrendipine and superoxide dismutase in ischemic renal injury

The effect of the Ca entry blocker nitrendipine, the antioxidant superoxide dismutase (SOD), and a combination of nitrendipine and superoxide dismutase on postischemic renal function was studied in four groups (n = 24) of rats. The rats in group 1 (n = 6) were the ischemic control and received 10 mL of 0.9% NaCl. Group II (n = 6) received SOD 7.0 mg/kg. Group III (n = 6) received nitrendipine 1 mg/kg. Group IV (n = 6) received nitrendipine 1 mg/kg and SOD 7 mg/kg. After administration, both kidneys were rendered ischemic by cross-clamping the renal vessels for 60 min. Comparison of 24-h creatinine clearance (CCr) for 3 days after reversal of ischemia revealed: (a) nitrendipine alone was the most effective in preserving renal function (p < .05); (b) SOD provided some degree of improvement, but only on day 3 (p < .05); (c) a similar result was detected using a combination of nitrendipine and SOD (p < .05); (d) there was no significant difference between SOD and nitrendipine nor between SOD and the combination of nitrendipine/SOD; (e) there was a significant improvement with nitrendipine when compared to the combination of nitrendipine/SOD (p < .05).

Improvement of therapeutic effect of human recombinant superoxide dismutase on ischemic acute renal failure in the rat via cationization and conjugation with polyethylene glycol

Therapeutic effect of superoxide dismutase (SOD) and three derivatives: a conjugate with polyethylene glycol (SOD-PEG2), a cationized derivative (cSOD), and a mannosylated derivative (Man-SOD), on acute renal failure induced by ischemia/reperfusion was studied in rats. SOD and derivatives were administered intravenously to the rat after nephrectomy of the right kidney and before and after 60 min occlusion of the left renal artery. At 48 hr after reperfusion, the renal function was evaluated by determining the urinary excretion rate of 14C-inulin injected intravenously. No therapeutic effect on the impaired renal function was shown in the case of low dose SOD (2600 unit/kg) treatment. In contrast, administration of cSOD which was shown to be taken up by the isolated perfused kidney from its capillary side and SOD-PEG2 which maintained high plasma concentration exhibited significant therapeutic effect, as did SOD at ten-fold higher dose (26,000 unit/kg). On the other hand, renal damage was promoted by Man-SOD. Thus, the present study demonstrated that chemical modification may improve the therapeutic effect of SOD on the ischemic acute renal failure and increased SOD concentration in the renal vascular space is an important factor for the improved effect.

Antioxidant enzyme status of ischemic and postischemic liver and ischemic kidney in rats

The specific activity of seven enzymes involved in protecting tissue from oxidative stress was determined in rat kidneys subjected to 0, 2, 4, or 8 h of normothermic ischemia and in isolated rat livers during control perfusion, after 2 h ischemia, and after 2 h ischemia plus 1 h of reperfusion. In general, none of the antioxidant enzymes measured showed any consistent variation throughout the ischemic period even though mitochondrial function was significantly decreased, indicating substantial cell injury. Glutathione peroxidase (Se-GSH-Px) activity remained constant during 8 h of ischemia, although a small (29%) increase above control activity was noted at 4 h of ischemia. Se-independent GSH-Px activity (non-Se-GSH-Px) and glutathione reductase (GSSG-Red) remained constant up to 8 h of ischemia, when we measured an increase of 158% above controls in non-Se-GSH-Px and a decrease of 35% relative to controls in GSSG-Red. In perfused livers, the only change in enzyme activity after 2 h of ischemia was an increased GSSG-Red activity of 21% above control. This increase persisted into the reperfusion phase (35% above control activity) and was accompanied by decreases in both forms of GSH-Px (28% Se-GSH-Px and 44% non-Se-GSH-Px).

Hydrogen peroxide metabolism and oxidative stress in cortical, medullary and papillary zones of rat kidney

The cortical, medullary and papillary regions of rat kidney were evaluated for a series of parameters related to hydrogen peroxide metabolism and oxidative stress. The rates of oxygen uptake, prostaglandin synthesis and malondialdehyde production by kidney slices were: 47, 0.003 and 0.051 mumol/h g wet wt., respectively, in cortex, 32, 0.023 and 0.035 in medulla and 22, 0.034 and 0.007 in papilla. The activities of superoxide dismutase, catalase and glutathione peroxidase were: 144 +/- 16 U/g wet wt., 880 +/- 100 pmol/g wet wt. and 177 +/- 16 U/g wet wt. in cortex; 97 +/- 9 U/g wet wt., 550 +/- 50 pmol/g wet wt. and 142 +/- 18 U/g wet wt. in medulla; and 23 +/- 2 U/g wet wt., 90 +/- 9 pmol/g wet wt. and 147 +/- 5 U/g wet wt. in papilla. Hydrogen peroxide steady-state concentrations were 0.09 +/- 0.01, 0.07 +/- 0.01 and 0.08 +/- 0.01 microM whereas alpha-tocopherol content was 21 +/- 2, 23 +/- 1 and 34 +/- 3 mumol/g wet wt. and hydroperoxide-initiated chemiluminescence was 22 +/- 2, 33 +/- 2 and 14 +/- 1 cpm. 10(-3)/mg prot for cortex, medulla and papilla, respectively. After 60 min ischemia-30 min reperfusion hydroperoxide-initiated chemiluminescence and hydrogen peroxide steady-state concentration increased by 30% and 60% in cortex and 80% and 60% in medulla, whereas alpha-tocopherol content decreased by 30%, 50% and 2% in cortex, medulla and papilla, respectively. The reperfusion/control ratio of hydroperoxide-initiated chemiluminescence and hydrogen peroxide steady-state concentrations in cortex and medulla indicate the occurrence of oxidative stress after ischemia-reperfusion. The lower sensitivity to oxidative stress found in papilla could be explained by the relatively high relationship of alpha-tocopherol content to hydrogen peroxide production rate in this sub-organ.

Lack of effect of antioxidant therapy during renal ischemia and reperfusion in dogs

Acute ischemic renal failure is of great clinical importance because of its frequent occurrence and the high mortality it causes. Recent observations indicate that reperfusion has its own dangers because of oxygen-derived free radicals. To study this problem, ischemia was evoked in dogs in one kidney, by clamping the left renal artery for 45 min. This was followed by a 90-min period of reperfusion when diuresis, GFR, PAH clearance and sodium and potassium excretion were studied. Besides a control group (n = 6), the following treatment groups were investigated. Allopurinol (n = 7): 50 mg/kg for two days p.o. and 50 mg/kg in physiological saline infusion during the experiment; a small dose of SOD (n = 6): 0.5 mg/kg in infusion, started 1 min before reperfusion and given continuously for 10 min; and a high dose of SOD (n = 7): 5 mg/kg as above. In the first 15 min following reperfusion, the renal functions significantly worsened in all groups. Later on, the renal functions gradually improved and in the last period after reperfusion, GFR in the ischemic kidney was 64%, cPAH 59%, diuresis 60% and sodium and potassium excretion were 65% and 76%, respectively, of the basal values in the control group. Treatment with free radical scavengers did not cause any considerable changes in the renal functions. In some respects, the worst results were observed with low-level SOD treatment (cPAH, diuresis, as well as sodium and potassium excretion). At the end of reperfusion, there was a significant drop in sodium excretion by the right (intact circulation) kidney of the treated animals.

Myocardial capillary permeability after regional ischemia and reperfusion in the in vivo canine heart. Effect of superoxide dismutase

This study assesses the effect of the superoxide anion scavenger superoxide dismutase on myocardial capillary permeability-surface area (PS) products for small hydrophilic molecules after ischemia and reperfusion. Open-chest dogs underwent a 20-minute occlusion of the left anterior descending coronary artery followed by 1 hour of reperfusion. Myocardial plasma flow rate and capillary extraction of chromium 51-labeled EDTA or technetium 99m-labeled diethylenetriaminepentaacetic acid were measured by the single-injection, residue-detection method before ischemia and 5 and 60 minutes after the start of reperfusion. In 13 dogs, no scavenger treatment was given (nonprotected control group), whereas eight dogs were treated systemically with 15,000 units/kg superoxide dismutase during 1 hour, starting 20 minutes before ischemia. In the control group, three dogs developed reperfusion ventricular fibrillation in contrast to none in the superoxide dismutase group. Before ischemia, plasma flow rate, myocardial capillary extraction fraction, and PS values were similar in the two groups. Five minutes after the start of reperfusion, plasma flow rate increased significantly (p less than 0.01) in both groups. In the control group, capillary extraction fraction increased by 12% (p = NS) in spite of the higher plasma flow; these increases in capillary extraction fraction and plasma flow induced a 69% increase in PS (p less than 0.01). In the superoxide dismutase-treated group, capillary extraction fraction decreased by 32% (p less than 0.05) in accordance with the increased plasma flow rate, resulting in an unchanged PS (p = NS). Sixty minutes after reperfusion, plasma flow rate, capillary extraction fraction, and PS returned to preocclusion values in both groups (p = NS). The increased capillary extraction fraction and PS values seen in the control group suggest an increased capillary permeability after ischemia and reperfusion. Superoxide anions seem to participate, directly or indirectly, in this response.

Protective effects of pretreatment with superoxide dismutase, catalase and oxypurinol on tubular damage caused by transient ischaemia

The effect of 60 min of ischaemia on glomerular and tubular functions (osmolar clearance, fractional Na+ excretion, K+ clearance, concentrating ability) after different periods of time was studied in New Zealand White rabbits. Pronounced changes in both glomerular and tubular functions were observed immediately on reperfusion and after 48 h. One week after ischaemia the functions appeared to be normalized. Mannitol is routinely used in clinical kidney transplantation due to its hyperosmolar effects and its ability to scavenge the hydroxyl radical. In the present study the possible additive protective effect against ischaemia-reperfusion damage of a combined pretreatment with mannitol and oxygen free radical scavengers or mannitol and a xanthine oxidase inhibitor was examined. Oxypurinol was chosen as the xanthine oxidase inhibitor due to its direct inhibitory effect. Concerning glomerular function, no protective effect of the combined pretreatment compared with mannitol alone was observed. However, concerning the tubular function tests combined pretreatment with either mannitol-superoxide dismutase-catalase or mannitol-oxypurinol turned out to be superior compared with that of mannitol alone.