Release of Enzymes by Ricin from Macrophages and Chinese Hamster Ovary Cells in Culture

Misincorporation of free m-tyrosine into cellular proteins: a potential cytotoxic mechanism for oxidized amino acids

In vitro studies demonstrate that the hydroxyl radical converts L-phenylalanine into m-tyrosine, an unnatural isomer of L-tyrosine. Quantification of m-tyrosine has been widely used as an index of oxidative damage in tissue proteins. However, the possibility that m-tyrosine might be generated oxidatively from free L-phenylalanine that could subsequently be incorporated into proteins as an L-tyrosine analogue has received little attention. In the present study, we demonstrate that free m-tyrosine is toxic to cultured CHO (Chinese-hamster ovary) cells. We readily detected radiolabelled material in proteins isolated from CHO cells that had been incubated with m-[14C]tyrosine, suggesting that the oxygenated amino acid was taken up and incorporated into cellular proteins. m-Tyrosine was detected by co-elution with authentic material on HPLC and by tandem mass spectrometric analysis in acid hydrolysates of proteins isolated from CHO cells exposed to m-tyrosine, indicating that free m-tyrosine was incorporated intact rather than being metabolized to other products that were subsequently incorporated into proteins. Incorporation of m-tyrosine into cellular proteins was sensitive to inhibition by cycloheximide, suggesting that protein synthesis was involved. Protein synthesis using a cell-free transcription/translation system showed that m-tyrosine was incorporated into proteins in vitro by a mechanism that may involve L-phenylalanine-tRNA synthetase. Collectively, these observations indicate that m-tyrosine is toxic to cells by a pathway that may involve incorporation of the oxidized amino acid into proteins. Thus misincorporation of free oxidized amino acids during protein synthesis may represent an alternative mechanism for oxidative stress and tissue injury during aging and disease.

Activation of A431 human carcinoma cell motility by extracellular high-mobility group box 1 protein and epidermal growth factor stimuli

HMGB1 (high-mobility group box 1) protein, a pleiotropic cytokine released by several cell types under physiological and pathological conditions, has been identified as a signal molecule active on A431 cells. Although extracellular HMGB1 itself does not trigger any detectable signalling effect on these cells, it induces an increased susceptibility to EGF (epidermal growth factor) stimulation. Specifically, at concentrations of EGF which promote undetectable or limited cell responses, the addition of sub-nanomolar concentrations of HMGB1 potentiates the effect of EGF by specifically activating a downstream pathway that leads to enhanced cell motility through an increase in Ca2+ influx, activation of extracellular-signal-regulated kinase 1/2 and remodelling of the actin cytoskeleton. These results, which identify extracellular HMGB1 as an activator of human tumour cell migration operating in concert with EGF, have important implications in the search for novel strategies to control tumour progression and metastatic invasion.

Effects of superoxide dismutase and polyclonal tumor necrosis factor-alpha antibodies on chloroacetate-induced cellular death and superoxide anion production by J774.A1 macrophages

Dichloroacetate (DCA) and trichloroacetate (TCA) are by-products that are formed during the process of water chlorination and have been previously shown to induce superoxide anion (SA) production and cellular death when added to J774.A1 macrophage cultures. In this study, the effects of superoxide dismutase (SOD) and polyclonal tumor necrosis factor-alpha (TNF-alpha) antibodies on DCA- and TCA-induced SA production and cellular death have been tested on the J774.A1 macrophage cultures. TCA and DCA were added to different cultures either alone, each at a concentration of 16 mM, or in combination with SOD (2-12 units/ml), or with TNF-alpha antibodies (10 and 25 units/ml). Cells were incubated for 48 h, after which cellular death/viability, lactate dehydrognase (LDH) leakage by the cells, and SA production by the cells were determined. While TCA and DCA caused significant cellular toxicity, indicated by reduction in cellular viability and increases in LDH leakage and SA production, SOD addition resulted in significant reduction of the effects induced by the compounds. On the other hand, addition of TNF-alpha antibodies to the DCA- and TCA-treated cultures resulted in significant reduction of DCA- but not TCA-induced cellular death and SA production by the cells. Although these results suggest a significant role for SA in DCA- and TCA-induced cellular death, they may also suggest two different mechanisms for the chloroacetate-induced SA production by the cells.

The induction of oxidative stress and cellular death by the drinking water disinfection by-products, dichloroacetate and trichloroacetate in J774.A1 cells

The in vitro toxicity of the drinking water disinfection by products dichloroacetate (DCA) and trichloroacetate (TCA) were studied using the J774A.1 macrophage cell line. DCA and TCA were added to cell cultures at concentrations ranging between 8-32 mM and incubated for 24, 36 and 60 h. DCA and TCA effects on cellular viability, lactate dehydrogenase (LDH) release and superoxide anion (SA) production by the cells, as well as superoxide dismutase (SOD) activities of the cells were determined. DCA and TCA caused time- and concentration-dependent increases in cellular death, in LDH release and production of SA by the cells. The compounds also caused modulations in SOD activities of the cells, with increases observed at the lower concentrations and/or shorter periods of incubations and suppression with the higher concentrations and/or longer periods of incubation. The results of the study indicate that DCA and TCA induce macrophage activation and that the activation is associated with cellular toxicity. Also, DCA and TCA are found to be equitoxic to J774.A1 cells.

Prediction of in vivo hepatic clearance from in vitro data using cryopreserved human hepatocytes

1. Cryopreserved human hepatocytes were used to predict in vivo hepatic clearance (CL(hepatic)) from estimates of in vitro intrinsic clearance (CL' int). 2. (CL' int) was estimated for phenytoin, valproic acid, carbamazepine, theophylline, quinidine and procainamide after their addition to hepatocytes suspended either in human serum or in serum-free media. (CL' int)was estimated from in vitro concentration versus time data fitted to a monoexponential decay model. (CL' int) was estimated from concentrations measured at four time points and from just two-point measures, namely the initial concentration (C(0)) and the final concentration measurement (C(last)). 3. Predicted CL(hepatic) was within twofold of reported in vivo values of CL(hepatic) for all substrates. Moreover, predictions were not significantly different whether derived from hepatocytes suspended in serum or in serum-free medium. 4. Two-point estimates of (CL' int) were just as accurate in predicting CL(hepatic) as were multipoint estimates of (CL' int). 5. Although the data set was limited, the findings suggest that the measurement of the disappearance of xenobiotics from serum or serum-free media in which primary human hepatocytes have been suspended provides a physiologically relevant estimate of hepatic clearance that can be employed early in the drug development process to eliminate xenobiotics with unacceptable clearances.

Time- and concentration-dependent production of superoxide anion, nitric oxide, DNA damage and cellular death by ricin in the J774A.1 macrophage cells

The time- and concentration-dependent effects of ricin on some biomarkers of cellular toxicity, including production of superoxide anion (O2-), nitric oxide (NO), and DNA single strand breaks (SSB), as well as cellular death, have been examined in the J774A.1 macrophage cell cultures. Various concentrations of ricin have been added to various cell cultures, and the cells were incubated for 12, 24, 36, and 48 hours. Following 12 hour incubation, ricin did not cause significant increases in any of those biomarkers. However, time- and concentration-dependent increases were observed in the induction of all the biomarkers after incubation for 24-48 hours. Approximately twofold increases in the production of O2- were observed after incubation with 1 and 10 ng/mL of ricin for 24 and 36-48 hours, respectively. The concentrations of ricin that caused approximately twofold increases in the rate of DNA-SSB are 10 and 1-10 ng/mL after 24 and 36-48 hours incubation, respectively. Approximately twofold increases in NO production were only observed after incubation of the cultures with 1-10 ng/mL of ricin for 36-48 hours. Fifty percent reductions in cellular viability were also observed with ricin concentrations of 10-100, 10, and 1-10 ng/mL, after incubation for 24, 36, and 48 hours, respectively.

Ricin-induced toxicity in the macrophage J744A.1 cells: the role of TNF-alpha and the modulation effects of TNF-alpha polyclonal antibody

Ricin is a natural toxin of the castor beans (Ricinus communus). We studied the time- and concentration-dependent effects of ricin on the release of TNF-alpha and lactate dehydrogenase (LDH), as well as the modulation of the ricin-induced effects by TNF-alpha antibody in the J774A.1 cells. When added at concentrations ranging from 0 to 1000 ng/mL, ricin caused concentration-dependent increases in the release of TNF-alpha after incubation for 12 to 24 hours. Concentration-dependent increases in the leakage of LDH were also observed after incubation of the cells with those concentrations of ricin for 24 to 48 hours. Addition of 5 units/mL of rabbit anti-mouse TNF-alpha polyclonal antibody (TNF-alpha antibody) 2 hours prior to the addition of ricin resulted in a decrease in the ricin-induced toxicity, indicated by the release of LDH by the cells. However, when added at concentrations higher than 5 units/mL, the antibody resulted in either no effect or an increase in the ricin-induced LDH leakage. These results suggest that secretion of TNF-alpha by the macrophages in response to ricin plays a significant role in the toxicity of ricin and that TNF-alpha antibody can antagonize the effects of ricin in this cell line when added at relatively low concentrations.

Role of protein kinase C in basal and hydrogen peroxide-stimulated NF-kappa B activation in the murine macrophage J774A.1 cell line

In macrophages, hydrogen peroxide appears to be a physiological activator of the transcription factor, nuclear factor kappa B (NF-kappa B); however, the molecular basis of H2O2-stimulated NF-kappa B activation is not well defined. The observations that NF-kappa B can be activated in cells by phorbol 12-myristate 13-acetate and in vitro by addition of protein kinase C (PKC) are suggestive of a role of PKC in NF-kappa B activation, which was investigated in the J774A.1 murine macrophage cell line. Basal NF-kappa B DNA-binding activity and nuclear localization were decreased by PKC inhibitors. Although PKC activity was modified by H2O2 with a similar time course as H2O2 activation of NF-kappa B, the H2O2-stimulated increase in NF-kappa B DNA binding and translocation to the nucleus was unaffected by PKC inhibitors. Furthermore, PKC down-regulation (through preincubation with phorbol esters) also affected only baseline NF-kappa B DNA binding but not H2O2-stimulated NF-kappa B activation. Buffering of changes in intracellular free calcium concentration also had no effect upon H2O2-stimulated NF-kappa B activation. Thus, classical PKC activity may modulate basal NF-kappa B activity but does not participate in H2O2-stimulated NF-kappa B activation.

Transmembrane redox signaling activates NF-kappaB in macrophages

In macrophages, NF-kappaB can be activated by H2O2 generated by the respiratory burst or added exogenously. The mechanism of H2O2 signaling may involve changes in the cellular redox state or a redox reaction at the plasma membrane; however, the site of H2O2 action cannot be readily ascertained because of its membrane permeability. Ferricyanide, a nonpermeable redox active anion, activated NF-kappaB in the macrophage cell line, J774A.1. In contrast with exogenous H2O2, activation by ferricyanide did not correlate with net oxidation of NAD(P)H or glutathione, suggesting that a transplasma membrane redox reaction itself was the first signaling process in NF-kappaB activation.

Induction of apoptosis by ribosome-inactivating proteins and related immunotoxins

Immunotoxins have been prepared with 3 ribosome-inactivating proteins (RIPs), namely, momordin, pokeweed anti-viral protein from seeds (PAP-S) and saporin, linked to the Ber-H2 monoclonal antibody directed against the CD30 antigen of human lymphocytes. Either the RIPs or the immunotoxins induced apoptosis in the CD30+ L540 cell line, as shown by the morphological aspects of the cells, by the DNA fragmentation visible at the electrophoresis, and by the formation of DNA breaks evidenced by 2 cytofluorometric techniques (propidium-iodide staining and fluoresceine-isothiocyanate conjugate dUTP incorporation). The AC50 (concentration causing apoptosis in 50% of the cells) is in the range 10(-8) to 10(-7) M in the case of RIPs, and 10(-11) to 10(-10) M in the case of the immunotoxins.

Activation of NF kappa B by the respiratory burst of macrophages

H2O2 and other reduced oxygen species have been proposed as activators of the transcription factor, NF Kappa B. Stimulated macrophages produce superoxide and H2O2 (the respiratory burst). We tested the hypothesis that production of these species could serve as part of the NF Kappa B activation pathway in rat alveolar macrophages and the J774A.1 mouse monocyte/macrophage cell line. Phorbol myristate acetate (PMA) and ADP, which stimulate the respiratory burst, caused NF Kappa B activation in both cells. Catalase abolished NF kappa B activation, while superoxide dismutase produced little inhibition. Thus, H2O2 was the principal agent of respiratory burst-associated NF kappa B activation. Abolition of NF kappa B activation by catalase also suggested that intermediate signaling pathways, such as protein kinase C activation or intracellular free calcium elevation must not be involved. Exogenous H2O2 added as a bolus > or = 50 microM (> or = 50 nmol/10(6) macrophages) also activated NF kappa B in macrophages. Nevertheless, the maximum endogenous production of H2O2 by stimulated alveolar macrophages during a 30-min incubation was < or = 1.3 nmol H2O2/10(6) cells for PMA stimulation and < or = 0.2 nmol H2O2/10(6) cells for ADP stimulation. Thus, relatively little endogenous H2O2 generation was required to produce NF kappa B activation compared to the required amount of exogenous H2O2. As H2O2 rapidly diffuses and is consumed, these results suggest that the site of action for endogenously generated H2O2 is probably close to its origin, the plasma membrane.

Chromium-induced production of reactive oxygen species, DNA single-strand breaks, nitric oxide production, and lactate dehydrogenase leakage in J774A.1 cell cultures

The involvement of oxidative stress in the toxicity of chromium (VI) and chromium (III) has been proposed. We have therefore examined the effects of these cations on the production of superoxide anion, nitric oxide (NO), and DNA single strand breaks (SSB) in J774A.1 macrophage cells in culture as well as the effects on lactate dehydrogenase (LDH) leakage and cell viability. Following a 48 hour incubation, over twofold increases in superoxide anion and NO production were observed at concentrations of approximately 0.30 and 50 microM for Cr (VI) and Cr (III), respectively. The patterns of cell viability and LDH leakage paralleled superoxide anion and NO production for Cr (VI) and Cr (III). A 50% decrease in viability was observed at approximately the concentrations that produced a twofold increase in superoxide and NO production. Concentration-dependent increases in DNA-SSB were observed after incubation with Cr (III) with maximum increases occurring at a concentration of approximately 60 microM. Cr (VI) had no effect on the incidence of DNA-SSB at any of the tested concentrations. The results indicate that Cr (VI) and Cr (III) are toxic to the J774A.1 cell line, and the toxicity may be due at least in part to an oxidative stress induced by the production of reactive oxygen species.

Protective effects of free radical scavengers and antioxidants against smokeless tobacco extract (STE)-induced oxidative stress in macrophage J774A.1 cell cultures

Previous studies have demonstrated that an aqueous smokeless tobacco extract (STE) administered in an acute oral dose to rats induces an enhanced induction of hepatic mitochondrial and microsomal lipid peroxidation, hepatic nuclear DNA single strand breaks, enhanced excretion of urinary lipid metabolites, including malondialdehyde, formaldehyde, acetaldehyde and acetone, and increased production of nitric oxide (NO) by peritoneal macrophage cells. These observations indicate that STE induces the production of oxygen free radicals. We have therefore examined the in vitro incubation of cultured J774A.1 macrophage cells with STE on the release of the enzyme lactate dehydrogenase (LDH) into the media as an indicator of cellular membrane damage and cytotoxicity. The amount of LDH released by STE was both concentration- and time-dependent. The cytotoxicity of STE to macrophage J774A.1 cells in culture was further determined from percent viability after various periods of incubation. The addition of 250 micrograms STE/ml to the cultured J774A.1 cells resulted in a 2.9-fold increase in the release of LDH. Individual coincubation with superoxide dismutase (SOD), catalase, mannitol, and allopurinol had no significant effect on the release of LDH into the culture medium, while a combination of the four free radical scavengers resulted in a 59% decrease in the STE-induced release of LDH. At 75 microM concentrations of viramine E and vitamin E succinate, approximately 28% and 41% inhibitions were observed in STE-induced LDH leakage, respectively. Taken together with previous studies, the results indicate that STE activates macrophage cells, resulting in the production of reactive oxygen species.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of vitamin E succinate on smokeless tobacco-induced production of nitric oxide by rat peritoneal macrophages and J774A.1 macrophage cells in culture

Previous studies have shown that an aqueous smokeless tobacco extract when administered in a single oral dose to rats results in an enhanced induction of hepatic lipid peroxidation, hepatic DNA single strand breaks, and a marked increase in the urinary excretion of the lipid metabolites malondialdehyde, formaldehyde, acetaldehyde, and acetone. These observations strongly suggest that STE induces the production of reactive oxygen species. We have therefore examined the effects of STE in vivo in rats on the production of nitric oxide (NO) by isolated peritoneal exudate (macrophage) cells and when incubated with cultured J774A.1 macrophage cells. In both cases, a significant increase in NO production was observed. When the antioxidant vitamin E succinate was preadministered to rats, a marked decrease in NO production in response to STE by isolated peritoneal macrophages was observed. Similar results were observed when J774A.1 macrophages were cultured in the presence of vitamin E succinate and STE. When vitamin E succinate alone was cultured with macrophages, an increase in NO production was observed. A similar increase was observed when the vitamin E succinate was administered to rats, and NO production by isolated peritoneal macrophages was assessed. The results demonstrated that the increase in NO production by macrophages in response to vitamin E succinate was due to a succinate moiety. Taken together with previous studies, the results indicate that STE activates macrophages, which result in the production of reactive oxygen species. These reactive oxygen species may be responsible for tissue damaging effects including lipid peroxidation and DNA damage, which may be associated with the cytotoxicity and mutagenicity of smokeless tobacco products.