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.
Oxidative stress has been implicated in the pathogenesis of human immunodeficiency virus (HIV) infection. We examined the effect of highly active antiretroviral therapy (HAART) on plasma levels of several antioxidants and intracellular glutathione-redox status in CD4+ T cells, in 20 HIV-infected patients. HAART was accompanied by both an improvement of glutathione-redox status and an increase in levels of antioxidant vitamins, without full normalization. Glutathione supplementation in vitro increases T cell proliferation and suppresses the spontaneous release of tumor necrosis factor-α from peripheral blood mononuclear cells, in HIV-infected patients receiving HAART. Our findings suggest that therapeutic intervention aimed at normalization of oxidative disturbances in HIV infection could be of interest, in addition to HAART.
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.
We administered reduced L-homocysteine perorally (67 mumol/kg of body wt) to 12 healthy subjects and injected the same dose into one person, and determined the kinetics of the alterations in reduced, oxidized, and protein-bound concentrations of homocysteine, cysteine, and cysteinylglycine. After oral intake, reduced homocysteine increased rapidly (tmax < or = 15 min), reaching concentrations [3.97 (SD 2.99) mumol/L] 20-fold above fasting values, and then declined towards the normal concentration within 2 h. There was a similar increase in reduced cysteine and a moderate increase in reduced cysteinylglycine. During this response, we observed a positive correlation between the reduced/total ratio for homocysteine and cysteine. When homocysteine was injected, the increase in reduced homocysteine preceded the increase in reduced cysteine by about 3 min. After oral loading, oxidized homocysteine showed a transient increase (tmax = 30 min) that lagged behind the increase of reduced homocysteine. Oxidized cysteine and cysteinylglycine were stable or decreased slightly. Protein-bound homocysteine increased the least rapidly after homocysteine administration (tmax = 1-2 h), and returned to normal values slowly. Changes in protein-bound homocysteine essentially mirrored a concurrent decrease in protein-bound cysteine, suggesting displacement of bound cysteine. These data show that plasma homocysteine has a pronounced, direct effect on the redox status and protein binding of other plasma thiol components. Such effects should be recognized when studying the mechanisms behind the atherogenic effect of increased plasma homocysteine.
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.
Seafood is assumed to be beneficial for cardiovascular health, mainly based on plasma lipid lowering and anti-inflammatory effects of n-3 polyunsaturated fatty acids. However, other plasma risk factors linked to cardiovascular disease are less studied. This study aimed to penetrate the effect of a phospholipid-protein complex (PPC) from Antarctic krill on one-carbon metabolism and production of trimethylamine-N-oxide (TMAO) in rats. Male Wistar rats were fed isoenergetic control, 6%, or 11% PPC diets for four weeks. Rats fed PPC had reduced total homocysteine plasma level and increased levels of choline, dimethylglycine and cysteine, whereas the plasma level of methionine was unchanged compared to control. PPC feeding increased the plasma level of TMAO, carnitine, its precursors trimethyllysine and γ-butyrobetaine. There was a close correlation between plasma TMAO and carnitine, trimethyllysine, and γ-butyrobetaine, but not between TMAO and choline. The present data suggest that PPC has a homocysteine lowering effect and is associated with altered plasma concentrations of metabolites related to one-carbon metabolism and B-vitamin status in rats. Moreover, the present study reveals a non-obligatory role of gut microbiota in the increased plasma TMAO level as it can be explained by the PPC’s content of TMAO. The increased level of carnitine and carnitine precursors is interpreted to reflect increased carnitine biosynthesis.
