Cardioprotective potency of the radical scavenger S-2-(3 aminopropylamino) ethylphosphorothioic acid in the post-ischaemic rat heart

Protective effects of amifostine on ischemia-reperfusion injury of rat kidneys

Objectives:

Amifostine is a drug which can eliminate free oxygen radicals that appear in the body after radiation or chemotherapeutic agent exposure. It is used to decrease the renal toxicity of cisplatin. The aim of this study was to determine the role of amifostine in warm ischemia kidney model for prevention of ischemia/reperfusion injury and also to find out the mechanism for prevention from ischemia/reperfusion injury if such an effect does exist.

Materials and Methods:

Adult female rats (n = 40) that used in our study were divided into three groups. Group 1: Control (n = 8), group 2: Ischemia-control (n = 16), group 3: Amifostine treated (n = 16). The effect of amifostine on ischemia/reperfusion injury investigated in rat kidneys.

Results:

At the 7^th day, blood urea nitrogen level was statistically significantly higher in ischemia-control group than all groups (P = 0.001) and mean serum creatinine levels were found to be the highest in ischemia-control group (P = 0.091). Mean malondialdehyde levels in left kidneys removed on the 7^th day were not significantly different (P = 0.105) at all three groups. Between ischemia-control group and amifostine group, there was a significant difference in reduced glutathione (GSH) levels (P = 0.001). In amifostine group, grade 4 necrosis was not detected neither on 7^th day nor day 0.

Conclusion:

Amifostine could decrease the degree and severity of necrosis after reperfusion. Amifostine could not prevent membrane lipid peroxidation caused by superoxide anion radicals in kidney but they could protect tissues from the harmful effects of ischemia/reperfusion injury by increasing the level of reduced GSH which is a well-known oxygen radical eliminator.

Use of diethyl(2-methylpyrrolidin-2-yl)phosphonate as a highly sensitive extra- and intracellular 31P NMR pH indicator in isolated organs. Direct NMR evidence of acidic compartments in the ischemic and reperfused rat liver

The novel phosphorylated pyrrolidine diethyl(2-methylpyrrolidin-2-yl)phosphonate (DEPMPH) was evaluated as a (31)P NMR probe of the pH changes associated with ischemia/reperfusion of rat isolated hearts and livers. In vitro titration curves indicated that DEPMPH exhibited a 4-fold larger amplitude of chemical shift variation than inorganic phosphate yielding an enhanced NMR sensitivity in the pH range of 5.0-7.5 that allowed us to assess pH variations of less than 0.1 pH units. At the non-toxic concentration of 5 mm, DEPMPH distributed into external and cytosolic compartments in both normoxic organs, as assessed by the appearance of two resonance peaks. An additional peak was observed in normoxic and ischemic livers, assigned to DEPMPH in acidic vesicles (pH 5.3-5.6). During severe myocardial ischemia, a third peak corresponding to DEPMPH located in ventricular and atrial cavities appeared (pH 6.9). Mass spectrometry and NMR analyses of perchloric extracts showed that no significant metabolism of DEPMPH occurred in the ischemic liver. Reperfusion with plain buffer resulted in a rapid washout of DEPMPH from both organs. It was concluded that the highly pH-sensitive DEPMPH could be of great interest in noninvasive ex vivo studies of pH gradients that may be involved in many pathological processes.

Free radicals and reactive oxygen species in programmed cell death

Oxidative stress, originating from reactive oxygen species and free radicals provides a constant challenge to eukaryotic cell survival. While implicated in a number of degenerative diseases, some associated with aging and with aging itself, the manner and extent to which oxidative stress contributes to the initiation or implementation of programmed-cell death is problematic. If oxidative stress is an important modulator of programmed-cell death, any ability intentionally to augment or inhibit it might ameliorate diseases in which the process is abnormally underactive or overactive.

Cytoprotection in the treatment of pediatric cancer: review of current strategies in adults and their application to children

BACKGROUND

The protection of patients from the acute and/or chronic toxicity of antineoplastic therapy has become a major concern of oncology centers around the world. However, most of the effort has been directed toward the adult population, and limited studies have been performed in the group that may gain the most from such strategies, namely, children.

PROCEDURES

The MedLine and CancerLit databases were surveyed, and the relevant biomedical literature on cytoprotection during antineoplastic treatment was analyzed.

RESULTS

Cytotoxicity from antineoplastic therapy customarily is addressed by altering dosing schedules, a technique that can seriously impact the efficacy of the therapy. Colony stimulating factors have been used posttherapy to stimulate recovery from neutropenia, and various agents have been proposed as pretherapy cytoprotectors. Trials in adults have produced mixed results, and, to date, only amifostine and dexrazoxane have been approved as cytoprotectors for very narrow indications. Few trials have been performed in children, although these patients often can look forward to long-term remission.

CONCLUSIONS

To prevent permanent toxicities from antineoplastic therapies that impact long-term pediatric survivors, the experience gained in adults should be extended more aggressively to children, and formal, randomized trials should be performed to determine the type of protection most suitable for the pediatric population.

Protective effects of the thiophosphate amifostine (WR 2721) and a lazaroid (U83836E) on lipid peroxidation in endothelial cells during hypoxia/reoxygenation

Little is known about pharmacological interventions with thiophosphates or lazaroids in endothelial cells injured by hypoxia/reoxygenation with respect to membrane lipid peroxidation (LPO) caused by reactive oxygen species. Therefore, a cell line of bovine aortic endothelial cells was studied after 120-min hypoxia followed by 30-min reoxygenation, resulting in moderate and predominantly reversible injury (energy depression/cytosolic Ca2+-accumulation during hypoxia, which almost normalized during reoxygenation; membrane blebs, an increasing amount of lysosomes, vacuolization, lipofuscin formation, alterations in mitochondria size, some lyzed cells). 18.9 +/- 4.3% of the cells died. Radical-induced LPO measured as malondialdehyde continuously increased to 2.18 +/- 0.17 nmol/mg of protein after reoxygenation vs control (0.41 +/- 0.13, P < 0.05). Simultaneously, the content of 4-hydroxynonenal, a novel indicator of LPO, increased from 0.02 +/- 0.01 to 0.11 +/- 0.02 nmol/mg of protein (P < 0.01). The results support the assumption that reoxygenation injury is accompanied by an increase in membrane LPO, causing structural and functional disturbances in the monolayer. The thiophosphate WR 2721 [S-2-(3-aminopropylamino) ethylphosphorothioic acid] and the lazaroid U83836E [(-)-2-[[4-(2,6-di-1-pyrrolidinyl-4-pyrimidinyl)-1-piperazinyl] methyl]-3,4-dihydro-2,5,7,8-tetramethyl-2H-1-benzopyran-6-ol (dihydrochloride)] were effective scavengers of .OH, being more efficient than trolox C (6-hydroxy-2,5,7,8-tetramethylchroman-2-carbon acid) used as standard (EC50: 12, 5 and 15 microM, respectively, measured by electron spin resonance spectroscopy). One mM WR 2721, 10 microM U83836E, and 5 microM trolox C reduced formation of malondialdehyde during hypoxia/reoxygenation to 53 +/- 7, 51 +/- 10 and 48 +/- 6%, respectively (P < 0.05 each, versus control). In general, WR 2721 and U83836E prevent radical-induced membrane LPO in a model of endothelial cells injured by hypoxia/reoxygenation. The use of these two agents is a new approach to protect the endothelium against oxidative stress.

Gradual changes in permeability of inner mitochondrial membrane precede the mitochondrial permeability transition

Some compounds are known to induce solute-nonselective permeability of the inner mitochondrial membrane (IMM) in Ca2+-loaded mitochondria. Existing data suggest that this process, following the opening of a mitochondrial permeability transition pore, is preceded by different solute-selective permeable states of IMM. At pH 7, for instance, the K0.5 for Ca2+-induced pore opening is 16 microM, a value 80-fold above a therapeutically relevant shift of intracellular Ca2+ during ischemia in vivo. The present work shows that in the absence of Ca2+, phenylarsine oxide and tetraalkyl thiuram disulfides (TDs) are able to induce a complex sequence of IMM permeability changes. At first, these agents activated an electrogenic K+ influx into the mitochondria. This K+-specific pathway had K0.5 = 35 mM for K+ and was inhibited by bromsulfalein with Ki = 2.5 microM. The inhibitors of mitochondrial KATP channel, ATP and glibenclamide, did not inhibit K+ transport via this pathway. Moreover, 50 microM glibenclamide induced by itself K+ influx into the mitochondria. After the increase in K+ permeability of IMM, mitochondria become increasingly permeable to protons. Mechanisms of H+ leak and nonselective permeability increase could also be different depending on the type of mitochondrial permeability transition (MPT) inducer. Thus, permeabilization of mitochondria induced by phenylarsine oxide was fully prevented by ADP and/or cyclosporin A, whereas TD-induced membrane alterations were insensitive toward these inhibitors. It is suggested that MPT in vivo leading to irreversible apoptosis is irrelevant in reversible ischemia/reperfusion injury.

Uncoupling of mitochondrial oxidative phosphorylation alters lipid peroxidation-derived free radical production but not recovery of postischemic rat hearts and post-hypoxic endothelial cells

The contribution of mitochondrial free radical production towards the initiation of lipid peroxidation (LPO) and functional injury in the post-ischemic heart is unclear. Using the isolated rat heart model, the effects of the uncoupler of mitochondrial oxidative phosphorylation dinitrophenol (DNP, 50 microM final) on post-ischemic lipid peroxidation-derived free radical production and functional recovery were assessed. Hearts were subjected to 30 min total global ischemia followed by 15 min of reperfusion in the presence of DNP. As expected, DNP enhanced oxygen consumption before (11.3 +/- 0.9 mumol/min, p < 0.001) and during reperfusion (at 10 min: 7.9 +/- 0.7 mu umol/min), compared to the heart with control treatment (8.2 +/- 0.5 and 6.7 +/- 0.3, respectively). This effect was only associated with a higher incidence of ventricular tachycardia during reperfusion (80 vs. 50% for control treatment, p < 0.05). Electron spin resonance spectroscopy (ESR) and spin trapping with alpha-phenyl-tert-butylnitrone PBN-radical adducts (untreated: 6.4 +/- 1.0 nM, at 10 min) decreased in the presence of DNP (1.7 +/- 0.4 nM, p < 0.01). The radical concentration inversely correlated with myocardial oxygen consumption. Total liberation of free radical adducts during the initial 10 min of reperfusion was reduced by DNP (0.59 +/- 0.09 nmol, p < 0.01) compared to the respective control treatment (1.26 +/- 0.16 nmol). Similar effects, prevention of PBN adduct formation and unchanged viability in the presence of DNP, were obtained with endothelial cells during post-hypoxic reoxygenation. Since inhibition of mitochondrial phosphorylation can inhibit the formation of LPO-derived free radicals after an ischemic/hypoxic interval, mitochondria may represent an important source of free radicals capable of initiating lipid peroxidative injury during reperfusion/reoxygenation.