Effects of oxygen pressure and medium volume on the toxicity of paraquat in rat and human type II pneumocytes

Abstract

<jats:p> The herbicide, paraquat is highly toxic for mammals, with the lungs being the main target organ, because of the active accumulation of the compound in this organ. The cellular toxicity of paraquat has been shown to be an O<jats:sub>2</jats:sub>-driven process and hyperoxia is known to increase the lethality of paraquat. In this study we have examined the effect of various O<jats:sub>2</jats:sub> concentrations on the toxicity of paraquat in rat and human type II pneumocytes in culture, and we have tested whether the thickness of the liquid layer above the cells would influence the toxicity of paraquat. Type II pneumocytes were isolated from rat or human lung tissue using trypsin digestion, Percoll density gradient centrifu gation and differential attachment. Adherent cells (day 2) were incubated for 20 h in different volumes of culture medium (thickness of liquid layer), whether or not in the presence of paraquat, in the presence of different O<jats:sub>2</jats:sub> tensions. The viability of the cells was assessed by the release of LDH in the culture medium. In both rat and human type II pneumocytes the toxicity of paraquat was independent of the thickness of the liquid layer (2.5 to 10 mm height). The toxicity of paraquat in rat type II pneumocytes decreased from a TC<jats:sub>50</jats:sub> value of 28 μM paraquat at 21% O<jats:sub>2</jats:sub> to 107 μM at 10% O<jats:sub>2</jats:sub> and increased to 12 μM and 8 μM at 60% and 85% O<jats:sub>2</jats:sub>, respectively. For human type II pneumocytes the TC<jats:sub>50</jats:sub> values were 7 μM; 25 μM and &gt; 1000 μM paraquat at 60%, 21% and 10% O<jats:sub>2</jats:sub>, respectively. In this study we have shown that the diffusion of O<jats:sub>2</jats:sub> through a liquid layer does not limit the toxicity of paraquat and that, as in vivo, increasing O<jats:sub>2</jats:sub> partial pressure enhances the toxicity of paraquat. </jats:p>

Predictors of acute kidney injury after paraquat intoxication

“…Finally, all patients received normal inspired oxygen therapy (FiO 2 21%) throughout their hospitalization. The rationale for normal inspired oxygen therapy was that an increased FiO 2 could increase oxidative stress, and the production of free radicals and superoxide might worsen the acute lung injury and systemic toxicity [ 46 ].…”

Medical management of paraquat ingestion

“…Tachypnoea and/or hypoxia may be due to metabolic acidosis, aspiration and/or acute alveolitis and a blood gas and chest radiograph may help make the correct diagnosis. However, mild to moderate hypoxia should not be routinely treated with oxygen as it will worsen oxidative stress [64] and it greatly increases lethality in animal models [65].…”

Effects of 1,3,5-Trinitrobenzene on Cytotoxicity and Metabolic Activity of Type I Astrocytes of Rats

“…Decreasing medium volumes in individual culture chamber wells should allow for greater oxygen saturation of the medium and oxygen availability for radical formation (Hoet, Demedts, and Nemery 1997) Medium was not changed during the experiments. Cellular metabolic activity was assessed in astrocytes with the CellTiter 96 Aqueous One Solution Cell Proliferation Assay kit as described previously.…”

“…Higher oxygen tension favors the reaction of the nitro radical with molecular oxygen, which is usually faster than the ability of the enzyme to add a second electron, leading to production of superoxide radicals and the regeneration of the parent nitro compound (Mason 1990). Previous studies have demonstrated that decreasing medium depth in culture wells does not result in increased toxicity to type II pneumocytes from the superoxide generating compound paraquat (Hoet et al 1997). However, others have observed increased toxicity to Hep G2 cells from paraquat by decreasing the culture well medium depth (Qualls et al 2000).…”