The growth of nontransformed (Cl 8) and malignant (Cl 16) C3H/10T1/2 mouse embryo fibroblasts was inhibited by 3-deazaadenosine (c3Ado) (LD50 = 195 microM for Cl 8 and 30 microM for Cl 16 cells) and 3-deazaaristeromycin (c3Ari) (LD50 about 36 microM for Cl 8 and 9 microM for Cl 16 cells). Both compounds inhibited in a dose-dependent manner S-adenosylhomocysteine (AdoHcy) catabolism and homocysteine production, measured as homocysteine egress, and c3Ari was most potent in this respect. c3Ado gave rise to its congener, 3-deazaadenosylhomocysteine (c3AdoHcy). Addition of homocysteine thiolactone (Hcy-tl) to the medium enhanced AdoHcy (and c3AdoHcy) accumulation but did not affect the cell growth at concentrations of inhibitor less than 10 microM. At high concentrations (30-300 microM) both compounds were cytotoxic and decreased cell count when added during midexponential growth. When Hcy-tl was supplemented under these conditions it partly rescued the malignant cells exposed to c3Ari, did not affect the cytotoxicity of this agent towards the nontransformed cells, but greatly potentiated the cytotoxicity of c3Ado against both cell types. Differential metabolic effects were also observed in that high concentrations of c3Ado, but not c3Ari, induced build-up of c3AdoHcy and modulated cellular glutathione level. Growing cells contained the highest amount of glutathione, and in such cells c3Ado induced a significant increase in glutathione whereas the cytotoxic combination of c3Ado plus Hcy-tl decreased the amount of the reduced form. Quiescent confluent cells, which were less sensitive to the toxic effect of c3Ado, contained low glutathione, and under these conditions neither c3Ado alone nor in combination with Hcy-tl affected cellular glutathione. Remarkably, Hcy-tl alone induced an increase in glutathione in nondividing cells. These data suggest that homocysteine or some agents affecting homocysteine metabolism may modulate glutathione metabolism, but differently in dividing and nondividing cells.
Several thiols, including homocysteine and cysteamine, have been shown to increase glutathione levels in C3H/10T1/2 Cl 8 cells [Biochem. Pharmacol. 39:421-429 (1990)]. The present paper shows that cysteamine also increases homocysteine export from these cells. Cellular glutathione content and export of glutathione and homocysteine increased with increasing doses of cysteamine. Twenty-four hours after addition, 300 microM cysteamine increased both glutathione content and homocysteine export 3-4-fold. No change in the ratio between reduced and oxidized glutathione could be detected, suggesting that the cysteamine effect was not due to reduction of pools of oxidized glutathione. The elevation of glutathione occurred rapidly but declined between 24 and 48 hr after addition of cysteamine, whereas the homocysteine export increased momentarily after cysteamine exposure and then proceeded at a rate similar to that from untreated control cells. The cysteamine-induced increase in glutathione was completely prevented by the gamma-glutamylcysteine synthetase inhibitor buthionine sulfoximine but was not affected by inhibition of homocysteine formation by 3-deazaaristeromycin. Buthionine sulfoximine did not prevent the increase in homocysteine export by cysteamine, and only a small increase in homocysteine export was observed when the cells were exposed to 3-deazaaristeromycin before treatment with cysteamine. Two major conclusions were drawn. 1) Increase of glutathione content and homocysteine export by cysteamine were independent events, indicating that glutathione status and homocysteine formation are regulated by independent mechanisms in C3H/10T1/2 Cl 8 cells. 2) S-Adenosylhomocysteine catabolism was the main source of the homocysteine export induced by cysteamine.
Heat stress prior to diving has been shown to confer protection against endothelial damage due to decompression sickness. Several lines of evidence indicate a relation between such protection and the heat shock protein (HSP)70 and HSP90 and the major cellular red-ox determinant, glutathione (GSH). The present study has used human endothelial cells as a model system to investigate how heat stress and simulated diving affect these central cellular defense molecules. The results demonstrated for the first time that a simulated dive at 2.6 MPa (26 bar) had a potentiating effect on the heat-induced expression of HSP70, increasing the HSP70 concentration on average 54 times above control level. In contrast, a simulated dive had no significant potentiating effect on the HSP90 level, which might be due to the higher baseline level of HSP90. Both 2 and 24-h dive had similar effects on the HSP70 and HSP90, suggesting that the observed effects were independent of duration of the dive. The rapid HSP response following a 2-h dive with a decompression time of 5 min might suggest that the effects were due to compression or pressure per se rather than decompression and may involve posttranslational processing of HSP. The exposure order seemed to be critical for the HSP70 response supporting the suggestion that the potentiating effect of dive was not due to de novo synthesis of HSP70. Neither heat shock nor a simulated dive had any significant effect on the intracellular GSH level while a heat shock and a subsequent dive increased the total GSH level approximately 62%. Neither of these conditions seemed to have any effect on the GSH red-ox status.
Clinical studies on cancer and psoriasis patients have shown that plasma and urinary homocysteine (Hcy) responds to methotrexate (MTX) therapy, indicating that Hcy in extracellular fluids may be an indicator of the antifolate effect. However, the clinical data indicate that the burden of proliferating cells, cytotoxicity and the folate status are also determinants of extracellular Hcy. To evaluate this further, we investigated the modulation of cellular Hcy egress by MTX, rescue agents, cell proliferation and cytotoxicity. Nontransformed and chemically transformed fibroblasts and murine lymphoma cells, which are characterized by different growth behavior and MTX response, were used. The Hcy export rate was correlated positively with the proliferation rate in all cell types. 5-Formyltetrahydrofolate or 5-methyltetrahydrofolate added to fibroblasts not exposed to MTX reduced the Hcy export rate, whereas the export from the lymphoma cells was not affected. All cells types exposed to MTX were rescued by thymidine + hypoxanthine, and this allowed the assessment of Hcy export during MTX exposure without interference from cytotoxicity. In the fibroblasts, MTX with thymidine + hypoxanthine rescue induced a marked increase in Hcy export, and the dose-response paralleled the cytotoxicity curves obtained for MTX without rescue. Nontoxic concentrations of MTX without rescue enhanced the Hcy export. When MTX concentration was increased further, Hcy export was stimulated initially, and then declined rapidly as cell death ensued. MTX did not enhance the Hcy export from the lymphoma cells and, in the absence of rescue, the Hcy export from these cells declined in proportion to inhibition of cell growth.(ABSTRACT TRUNCATED AT 250 WORDS)
Fumigation is a process that is carried out to prevent deterioration of goods by pests and spread of unwanted organisms for example during long-distance carriage by sea. Several intoxications due to use of pesticides on bulk cargo ships have been indicated, but for some of these incidents the documentation are questionable. The objective of the present study was therefore to examine the extent of the problem by collecting available information of incidents or intoxications due to use of pesticides on bulk cargo ships. Information sources such as PubMed, Google Scholar, Gard (marine insurance company), Marine Accident Investigation Branch, United Kingdom, and Professional Mariner (a magazine) were searched using similar search phrases. The results indicate that the present practice of fumigation with pesticides of cargo holds on bulk ships represents a serious health risk to both seafarers and port workers. A thorough search for information in both scientific and non-scientific sources revealed a number of intoxications including several fatalities. According to the available documentation, phosphine seems to be used more or less exclusively as fumigant on bulk cargo ships today. Phosphine has a high acute toxicity, and recent findings suggest long-term effects. Several of the reported incidents point to lack of knowledge and neglecting of recommended procedures as key elements in this respect. The problem is likely underestimated due to lack of available documentation of several incidents. Preventive actions should be implemented that focus on documentation of incidents, increase knowledge of pesticide health hazard and implementation of safety procedures that are mandatory to perform when fumigated cargo is to be handled on bulk ships.
