In vivo study of the mechanism of protective effects of ascorbic acid and reduced glutathione in paraquat poisoning

Pulmonary protective effects of curcumin against paraquat toxicity

An early feature of paraquat (PQ) toxicity is the influx of inflammatory cells, releasing proteolytic enzymes and oxygen free radicals, which can destroy the lung epithelium and result in pulmonary fibrosis. Therefore, the ability to suppress early lung injury seems to be an appropriate therapy of pulmonary damage before the development of irreversible fibrosis. Here I show curcumin confers remarkable protection against PQ lung injury. A single intraperitoneal injection of PQ (50 mg/kg) resulted in a significant rise in the levels of protein, angiotensin converting enzyme (ACE), alkaline phosphatase (AKP), N-acetyl-beta-D-glucosaminidase (NAG) and thiobarbituric acid reactive substances (TBARS), and neutrophils in the bronchoalveolar lavage fluid (BALF), while a decrease in glutathione levels. In paraquat rats bronchoalveolar lavage (BAL) cell TBARS concentration was increased with a simultaneous decrease in glutathione content. In addition, the data also demonstrated that PQ caused a decrease in ACE and glutathione levels and an increase in levels of TBARS and myeloperoxidase (MPO) activity in the lung. Interestingly, curcumin prevented the general toxicity and mortality induced by PQ and blocked the rise in BALF protein, ACE, AKP, NAG TBARS and neutrophils. Similarly, curcumin prevented the rise in TBARS content in both BAL cell and lung tissue and MPO activity of the lung. In addition, PQ induced reduction in lung ACE and BAL cell and lung glutathione levels was abolished by curcumin treatment. These findings indicate that curcumin has important therapeutic implications in facilitating the early suppression of PQ lung injury.

Biochemical studies on the toxicity of 1, 1'-dimethyl-4, 4'-bipyridylium dichloride in the rat

The effect of intraperitoneal administration of lethal dose (50 mg/kg) of paraquat on the microsomal cysteine levels in the plasma, liver and lung of adult male Wistar rats has been investigated using Rank Chromaspek amino acid analyzer. The microsomal alanine levels were also determined to help in assessing the extent of paraquat interference with cellular protein. DL-Buthionine-[S,R]-Sulfoximine (BSO) and Diethyl maleate (DEM) were used to potentiate the toxic effect of the bipyridyl. The microsomal cysteine levels were significantly (P < or = 0.05) depressed in the plasma, liver and lung of the paraquat-treated rats compared with the saline-injected group but the alanine levels were not similarly affected. Probably, paraquat poisoning interferes specifically with the cellular cysteine content in the rat. These findings could provide a valuable information on the biochemical mechanism of paraquat intoxication.

Liposomal alpha-tocopherol alleviates the progression of paraquat-induced lung damage

The present study was carried out to investigate the efficacy of liposome-associated alpha-tocopherol in treating pulmonary damage caused by paraquat exposure. alpha-Tocopherol liposomes (8 mg alpha-tocopherol/kg body weight) or plain liposomes were intratracheally instilled into the lungs of rats 24 h after paraquat treatment (20 mg/kg, ip); treated animals were killed 8, 24 or 48 h after administration of the liposomal preparations. Lungs of animals exposed to paraquat were extensively damaged as evidenced by an increase in lung weight and decreases in pulmonary angiotensin converting enzyme and alkaline phosphatase activities. Also, paraquat treatment resulted in a significant reduction in glutathione (GSH) concentration in the lung and an elevation in microsomal lipid peroxidation levels, as measured by the formation of diene conjugates. Treatment of paraquat-injected rats with plain liposomes did not significantly alter paraquat-induced changes of all parameters examined. On the other hand, treatment of rats with alpha-tocopherol liposomes, 24 h after paraquat administration, resulted in a significant increase in pulmonary alpha-tocopherol concentrations as well as a reduction in paraquat-induced changes in lipid peroxidation, GSH concentration, and lung angiotensin converting enzyme and alkaline phosphatase activities. The results of the present study suggest that alpha-tocopherol, administered directly to the lung in a liposomal form, may serve as a potentially effective pharmacological agent in the treatment of paraquat-induced lung injury.

Protective effect of liposome-associated alpha-tocopherol against paraquat-induced acute lung toxicity

The present study was undertaken to investigate whether alpha-tocopherol, entrapped in liposomes and delivered directly to the lung, could protect against paraquat-induced lung damage in the rat. Plain liposomes (composed of dipalmitoylphosphatidylcholine, DPPC) or DPPC/alpha-tocopherol liposomes were administered intratracheally to animals 24 hr prior to an intraperitoneal injection of paraquat (20 mg/kg); rats were killed 24 or 48 hr after paraquat treatment. Results of this study showed that lungs of animals treated with paraquat were damaged extensively as evidenced by an increase in lung weight and a significant reduction in lung angiotensin-converting enzyme (ACE) activity and cytochrome P450 concentration. Furthermore, paraquat treatment resulted in a significant decrease in reduced glutathione (GSH) concentrations and a marked elevation in microsomal lipid peroxidation levels as measured by the formation of diene conjugates. Pretreatment of rats with DPPC liposomes alone did not alter significantly the paraquat-induced changes of all parameters examined. On the other hand, pretreatment of rats with DPPC/alpha-tocopherol liposomes 24 hr prior to paraquat challenge resulted in a significant increase in pulmonary alpha-tocopherol concentrations and antagonized paraquat-induced changes in lipid peroxidation, GSH/GSSG ratio, lung ACE activity and cytochrome P450 concentrations. Results of this study suggested that alpha-tocopherol, delivered directly to the lung in a liposomal formulation 24 hr prior to paraquat administration, confers protection against paraquat-induced lung damage.

Oral glutathione increases tissue glutathione in vivo

Mice were given an oral dose of glutathione (GSH) (100 mg/kg) and concentrations of GSH were measured at 30, 45 and 60 min in blood plasma and after 1 h in liver, kidney, heart, lung, brain, small intestine and skin. In control mice, GSH concentrations in plasma increased from 30 microM to 75 microM within 30 min of oral GSH administration, consistent with a rapid flux of GSH from the intestinal lumen to plasma. Under these GSH-sufficient conditions, no increases over control values were obtained in GSH concentrations in most tissues except lung over the same time course. Mice pretreated for 5 days with the GSH synthesis inhibitor, L-buthionine-S,R-sulfoximine (BSO, 80 mumol/day) had substantially decreased tissue concentrations of GSH. Oral administration of GSH to these GSH-deficient animals gave statistically significant increases in GSH concentrations in kidney, heart, lung, brain, small intestine and skin but not in the liver. Administration of the equivalent amount of the constituent amino acids, glutamate, cysteine, and glycine, resulted in little change in GSH concentrations in all tissues in GSH-deficient animals. Thus, the results show that oral GSH can increase GSH concentrations in several tissues following GSH depletion, such as can occur in toxicological and pathological conditions in which GSH homeostasis is compromised.

An evaluation of the redox cycling potencies of paraquat and nitrofurantoin in microsomal and lung slice systems

The redox cycling abilities of the pulmonary toxins paraquat and nitrofurantoin have been compared with those of the potent redox cyclers, diquat and menadione in lung and liver microsomes by using the oxidation of NADPH and consumption of oxygen. The relative potencies of these compounds to undergo redox cycling were in the order: diquat approximately menadione much greater than paraquat congruent to nitrofurantoin. This was partly attributed to the much lower affinity (Km) of lung and liver microsomes for paraquat and nitrofurantoin than for diquat and menadione. The potential to redox cycle was assessed in an intact cellular system by determining the oxygen consumption of rat lung slices in the presence (10(-6), 10(-5) and 10(-4) M) or absence of each of the four substrates. At concentrations of paraquat (10(-5) M) known to be accumulated by lung slices, a small but significant stimulation of lung slice oxygen uptake was observed. Nitrofurantoin (10(-4)-10(-6) M) did not affect lung slice oxygen uptake in lung slices, an observation consistent with its being a poor redox cycling compound, which is not actively accumulated into lung cells. This data has important implications in assessing the risk of exposure to paraquat. Low levels of paraquat would not be expected to cause lung damage because insufficient compound is present in the lung to exert its toxicity by redox cycling (due to the high Km observed).

The effect of paraquat lung on mononuclear cells

The mouse footpad swelling test was used to clarify the possibility of the induction of local cellular reaction with cell suspension of mouse lungs treated with paraquat in a syngeneous animal. Among the inbred strains used, the highest, statistically significant cellular reactivity was observed in C3H/He strain mice. These results suggest indirect evidence of macrophage activation in the lung toxicity of paraquat.

Selective inhibition of bipyridyl-stimulated NADPH oxidation by ascorbic acid

The effect of the bipyridyl herbicides, paraquat and diquat (0.01-1.0 mM), on NADPH oxidation was determined in vitro using rat lung microsomal preparations. Experiments were performed in the absence of mixed function oxidation (MFO) substrates, in the presence of substrates (ethylmorphine or benzphetamine), and also in the presence of ascorbic acid (0.1-10.0 mM). NADPH oxidation was stimulated by both herbicides in the absence or presence of either substrate in a concentration-dependent manner. When ascorbic acid was included in incubations along with either bipyridyl, the stimulated rate of NADPH oxidation decreased in the presence of benzphetamine but the stimulation was unaltered in the presence of ethylmorphine or in the absence of substrate. These studies indicate that ascorbic acid may offer some protection from bipyridyl-mediated NADPH oxidation in rat lung microsomal fractions, but that protection appears to be dependent upon the simultaneous presence of specific MFO substrates.

Pharmacological treatments of paraquat poisoning

A large number of pharmacological techniques aimed at modifying paraquat toxicity have been investigated. There is no convincing controlled evidence that any are unequivocally useful. Studies with an ascorbic acid and riboflavin combination appear effective in rats, and there is a suggestion that cyclophosphamide and dexamethasone may in some way alter paraquat toxicity in man and by pretreatment, but not concurrent treatment, also in the rat. Further controlled studies are required of these treatments in patients who are potentially salvageable. There is a need for a rapid paraquat assay for clinical use in order that patients in this category can be identified quickly and included in appropriate controlled studies.

The search for ideal antidote treatment in Gramoxone intoxication

The herbicide Gramoxone (the active ingredient is paraquat) actively accumulates in the lung in the mammalian organism, where it exerts its toxic effect through the generation of oxygen radicals. Efforts were made to counteract the toxic effect in experiments in mice. Its penetration into the cells was blocked with the diamines putrescine and cadaverine. The synthesis of the prostaglandins, which are supposed by responsible for the acute symptoms, was inhibited with Aspisol. Accumulation inhibition with biogenic amines is considered the most effective.

Effects of ascorbic acid in vivo on the fatty acid composition of the tissues of mice treated with Gramoxone

The effects of the simultaneous administration of ascorbic acid and the LD50 of paraquat (an ingredient of Gramoxone), and of ascorbic acid pretreatment followed by the LD50 of paraquat, were studied on the phospholipid and triglyceride fatty acid levels in homogenates of mouse lung, liver and kidney. Ascorbic acid treatment increases the content of polyunsaturated fatty acids in the lung considerably, i.e. the pulmonary membrane fluidity decreases significantly in response to ascorbic acid. In the liver homogenate, the membrane fluidity is significantly increased by ascorbic acid pretreatment, and significantly decreased by simultaneous ascorbic acid treatment. In the renal tissue, the result of ascorbic acid pretreatment exhibits a similar tendency to that of paraquat treatment, but a more significant one, while the administration of ascorbic acid together with paraquat does not cause a substantial change in the fluidity index compared to the control.

Effects of various thiols on paraquat toxicity

It was demonstrated that cysteine and D-penicillamine are able to replace reduced glutathione to some extent in the glutathione peroxidase reaction. An in vivo study was made of the role played by--SH compounds in the antioxidant enzyme system involved in the detoxication of the LD50 of paraquat (PQ), and hence of their role in the detoxication of PQ. The effectiveness was D-PA greater than GSH greater then Cys in the liver and GSH greater than Cys greater than D-PA in the lung.

Systematically applied chemicals that damage lung tissue

A large, and increasing number of drugs and chemicals have been found which are toxic to lung following systemic administration. These agents damage lung tissue specifically, or in addition to damage to other tissues. Mechanisms explaining the pulmonary damage produced by some lung toxins have been uncovered. These include concentration of the agent within lung, the absence of adequate pulmonary detoxication systems, and bioactivation to a toxic species within specific lung cells or at distant sites followed by transport to the lung. The basic biochemical lesions underlying lung damage, responses of individual lung cells and pulmonary repair processes to the toxic agent, and species and age differences in susceptibility to lung damage have not, however, been well defined for most lung toxins. This review describes the information available on pulmonary biochemical and pathological changes associated with some of these lung-toxic agents. In addition, mechanisms proposed to explain the lung damage are discussed. The agents covered include: paraquat, the thioureas, butylated hydroxytoluene, the trialkylphosphorothioates, various lung-toxic furans and antineoplastic agents, the pyrrolizidine alkaloids, metals and organometallic compounds, amphiphilic agents, hydrocarbons, oleic acid, 3-methylindole, and diabetogenic agents. Detailed reviews on the overall toxicity of many of these agents have been published elsewhere. This review concentrates on their pulmonary toxicity. Information is presented as an overview to illustrate both the extensive literature that is available and the important questions that remain to be answered about systemic chemicals that damage lung tissue.

Changes induced by Gramoxon in tissue phospholipids and phospholipid fatty acids in mouse and guinea-pig

Following administration of the LD50 or the LD100 of Gramoxon (PQ), the phospholipids (PL) of the lung, liver and kidney were separated and both the PLs and the fatty acids isolable from them were examined quantitatively. The different doses of PQ caused different changes of the saturated and unsaturated fatty acids in the various organs. The changes in the PL unsaturated fatty acids point to PQ-induced lipid peroxidation enhancement and membrane damage.

Studies on the in vitro interaction of mitomycin C, nitrofurantoin and paraquat with pulmonary microsomes. Stimulation of reactive oxygen-dependent lipid peroxidation

In vitro experiments were performed to evaluate the capacity of the redox cycling compounds mitomycin C (MC), nitrofurantoin (NF) and paraquat (PQ) to stimulate pulmonary microsomal lipid peroxidation. It was observed that the interaction of MC, NF or PQ with rat or mouse lung microsomes in the presence of an NADPH-generating system and an O2 atmosphere resulted in significant lipid peroxidation. All three compounds demonstrated similar concentration dependency, similar time courses and the ability to generate lipid peroxidation-associated chemiluminescence. The stimulation of lipid peroxidation by MC, NF or PQ was inhibited significantly by superoxide dismutase, glutathione, ascorbic acid, catalase and EDTA, agents which either scavenge reactive oxygen and/or prevent the generation of secondary reactive oxygen metabolites. In addition, the ability of MC or NF, but not PQ, to stimulate lipid peroxidation was reduced significantly following preincubation with microsomes and NADPH under N2 (15-20 min) prior to incubation under O2. During this period under N2. MC and NF underwent reductive metabolism of their quinone and nitro moieties respectively. Thus, it appears that under aerobic conditions the pulmonary microsomal-mediated redox cycling of MC, NF and PQ is accompanied by the stimulation of reactive oxygen-dependent lipid peroxidation.

Some new data to the toxicological effects of paraquat and the therapy

1. Substances previously tested therapeutically were studied to obtain evidence on the pathomechanism in mice of paraquat, the active ingredient of Gramoxon, connected with the radicals formed from molecular oxygen, and also to extend the therapeutic possibilities. 2. The effects of these substances were assessed on the basis of the 72-hr survival rate and the percentage ratio of the wet lung weight to the overall body weight. 3. Other toxicological parameters too were followed. 4. Our present investigations indicate that, in agreement with our earlier results, besides reduced glutathione and ascorbic acid, vitamin E and C-ase are of the greatest importance from the aspect of the protection against paraquat toxicity. 5. In addition to those listed, other materials too, e.g. antifibrotic substances, naturally possess considerable detoxicating properties too.