Mechanism of protection of alveolar type II cells against paraquat-induced cytotoxicity by deferoxamine.

Paraquat toxicity has been associated with the generation of free radicals in alveolar epithelial cells in which paraquat specifically accumulates via a polyamine uptake system. In the present study we investigated whether deferoxamine (DF), an iron chelator that has antioxidant capacity and that also has a polyamine-like structure, could protect alveolar type II cells (ATTC) against injury by paraquat. Radiolabeled [3H]adenine ATTC were incubated in a medium containing 75 microM paraquat in the absence or presence of DF (500 microM). After 3 hr of incubation paraquat-mediated cytotoxicity of ATTC, as measured by [3H]adenine release, was significantly (P less than 0.005) decreased by addition of DF (26.6 +/- 2.6% vs 7.4 +/- 1.7%). Accumulation of radiolabeled [14C]paraquat at a concentration of 75 microM was also decreased (70%) by 500 microM DF from 94.8 +/- 2.1 to 28.9 +/- 6.7 nmoles paraquat/2.5 x 10(5) ATTC. This effect of DF was dose dependent and comparable with the protective effect of equimolar concentrations of putrescine. However, per cent uptake of paraquat at a concentration of 500 microM was not significantly inhibited by DF (1 mM), whereas paraquat-induced injury was still markedly reduced (36.2 +/- 2.5% vs 2.6 +/- 4.2%). This indicated that the protective effect of DF could not be explained by its competition with paraquat on uptake alone. In the same series of experiments using another iron chelator, pyridoxal benzoyl hydrazone (PBH), which has antioxidant properties similar to DF but does not show its polyamine-like structure, ATTC lysis was also prevented although paraquat uptake was not reduced. These in vitro data indicate that the mechanism of protection by DF against paraquat toxicity in lung epithelial type II cells is two-fold: inhibition of paraquat uptake through its compliance with the structural requirements necessary for transport, and inhibition of paraquat-induced iron-catalysed free radical generation.

A rapid and sensitive micro-assay to determine the capacity of quinones to undergo redox cycling.

Using a series of aziridinyl-benzoquinones it is shown that the conversion of oxyhemoglobin to methemoglobin in sheep erythrocytes is correlated with the capacity of each quinone to undergo redox cycling. Based on these findings a semiquantitative assay is developed for the rapid screening of redox cycling quinones.

Effect of iron chelators on paraquat toxicity in rats and alveolar type II cells.

There is general agreement that the lung damage seen in paraquat poisoning is due to the generation of free radicals in alveolar epithelial cells. We have recently shown that the iron chelator and antioxidant deferoxamine (DF) reduces the mortality caused by paraquat in vitamin-E-deficient rats. In the present study we investigated the effect of DF and the lipid soluble iron chelator compound 51 (CP51) of the hydroxypyridin-4-one family on paraquat poisoning in rats with a normal vitamin E status and on isolated alveolar type II cells (ATTC). Adult rats were intravenously injected with a lethal dose of paraquat (40 mg/kg) while concurrent treatment with a continuous intravenous infusion of DF or CP51 was started. Survival of rats receiving DF at 25 and 50 mg/kg/24 h was not significantly increased compared with PBS-treated control animals. CP51, however, significantly (p less than 0.01) reduced the mortality caused by paraquat. When rats were treated with 25 mg/kg/24 h, eight of 15 rats survived the study period of 35 days compared with three in the PBS-treated control group (n = 27). In ancillary in vitro studies radiolabeled [51Cr]ATTC were incubated in a medium containing 100 microM paraquat in the absence or presence of DF and CP51. Paraquat-induced ATTC lysis increased to approximately 25% after 7 h of incubation. At the highest tested concentration (500 microM) of chelator, injury decreased markedly (80%), whereas at the lowest tested concentration (50 microM) cytotoxicity was not prevented.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuous intravenous infusion of deferoxamine reduces mortality by paraquat in vitamin E-deficient rats.

Paraquat, an oxygen radical-generating agent, is a widely used agrochemical that is also toxic for humans, in whom it may cause respiratory failure. In the present study, we investigated the effect of deferoxamine (DF), an iron chelator with antioxidant capacity, on paraquat toxicity in vitamin E-deficient rats. After the administration of paraquat at a dose of 20 mg/kg the animals were treated with a continuous intravenous infusion of DF for 14 days. In a dose-response study, four of six animals receiving 100 mg DF/kg/24 h survived the study period of 14 days compared with none in the saline-treated control group (n = 6), and three and two animals in the groups receiving 50 (n = 6) and 200 mg DF/kg/24 h (n = 6), respectively. In another series of experiments, animals were monitored for a total period of 35 days, at which time any survivors were killed, and lung histologic examination was carried out. Deferoxamine treatment was started simultaneously (n = 21), 6 h (n = 18), and 16 h (n = 18) after paraquat poisoning. Percent survival in the various time-point groups was 47.7 (p less than 0.01), 38.9 (p less than 0.02), and 22.2 (not significant), respectively, compared with 7.1 (n = 14) in the control group. The presence of lung damage was seen only in those of the surviving rats where DF was started at the 16 h time point after paraquat administration. In ancillary in vitro studies, where Escherichia coli was used as a source of enzymic activity for the redox-cycling of paraquat, DF completely inhibited the formation of hydroxyl radical (.OH).(ABSTRACT TRUNCATED AT 250 WORDS)