Anin vitro study on the cytotoxicity of chlorhexidine digluconate to human gingival cells

Chlorhexidine digluconate is the active ingredient in mouthrinses used to prevent dental plaque and gingivitis. Thein vitro cytotoxicity of chlorhexidine was evaluated with the Smulow-Glickman (S-G) gingival epithelial cell line. The potency of chlorhexidine was dependent on the length of exposure and composition of the exposure medium. The midpoint cytotoxicity values for 1-, 24-, and 72-h exposures were 0.106, 0.011, and 0.0045 mmol/L, respectively. S-G cells exposed for 2 h to chlorhexidine and then maintained for 48 h in chlorhexidine-free medium were unable to recover from the initial insult. The adverse effects of chlorhexidine on the plasma membrane were suggested by the leakage of lactic acid dehydrogenase from chlorhexidine-treated S-G cells and by the increased permeability of chlorhexidine-treated liposomes to Ca²⁺. The toxicity of a 24-h exposure to chlorhexidine to the S-G cells was progressively lessened as the content of fetal bovine serum (FBS) in the exposure medium was increased from 2% to 8%. The potency of a 1-h exposure to chlorhexidine was reduced in medium amended with albumin, lecithin, and heat-killedEscherichia coli. These reductions in toxicity were presumably due to the binding of the cat onic chlorhexidine to the negatively charged chemical moieties of the components of FBS and of albumin and lecithin and of sites on the surfaces of bacteria. Combinations of chlorhexidine and carbamide peroxide were additive in their cytotoxicities.Abbreviations ANOVA analysis of variance - [Ca²⁺]i calcium concentration in internal medium of liposomes - DMEM Dulbecco's modified Eagle medium - EDTA ethylenediamine tetraacetic acid - FBS fetal bovine serum - Hepes N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid - HGF-1 human gingival fibroblast cell line - HSD honestly significant differences - KB cell line derived from a human epidermoid carcinoma in the mouth - LDH lactic acid dehydrogenase - NADH nicotinamide adenine dinucleotide, reduced form - NR neutral red - NR₅₀ concentration inhibiting neutral red uptake by 50% - PBS phosphate-buffered saline - SEM standard error of the mean - S-G Smulow-Glickman human gingival epithelial cell line     

Biocompatibility testing of an experimental fluoride releasing resin using human gingival epithelial cells in vitro

Summary Cell culture is a valuable method of evaluating the biocompatibility of new dental materials. The purpose of this study was to compare the in vitro biocompatibility of an experimental fluoride composite resin with fluoride and non-fluoride-releasing materials currently available. The dental materials tested were: MQ Silicate (silicate cement), KETAC-CEM and FUJI (type II glass ionomer cements), VISIO DISPERS (a light-cured, nonfluoridated, microfilled composite resin), and FR-17 (an experimental fluoride-releasing composite resin). The Smulow-Glickman (S-G) human, gingival epithelial cell line, which exhibits semidifferentiated characteristics, was used in the study as a test system. Biocompatibility was quantified by counting the viable cells per unit area remaining after 24 and 48 h at two radial distances from cured specimens immersed in the cell culture medium. The test materials were observed to be most toxic to cells nearest the materials. A Time-Distance Cytotoxicity Index (TDCI) was calculated to relate the percentage of dead cells to viable cells at each diffusion distance for each exposure time compared to a nontoxic control. The relative toxicity ranking of the materials tested based on the TDCI was VISIO DISPERS (91%), FUJI (82%), FR-17 (30%), MQ Silicate (23%), and KETAC-CEM (10%), which exhibited the least toxicity. The cytotoxicity of the experimental resin FR-17 was within the range of cytotoxicity of currently accepted restorative materials. this study was supported in part by grant R01-DE04749 from the National Institutes of Health, Bethesda, MD, to H. R. R., and by grant no. S07-RR05704-13 from the Biomedical Research Grant Program, Division of Research Resources, National Institutes of Health, awarded to the Louisiana State University School of Dentistry.     

Long-term killing of natural killer-resistant target cells by interferon-alpha-, interferon-gamma-, and interleukin-2-activated natural killer cells

The sensitivity of target cells to natural killer (NK) cell-mediated cytotoxicity was investigated. Five target cell lines were examined for susceptibility to killing by activated NK cells in a 4-hour cytotoxicity assay: one of them (K562) was highly sensitive, while the other four were resistant. However, the four NK-resistant target cell lines were fully susceptible to lysis when the assay was extended to 24 h. The cytotoxic cells that killed the NK-resistant target cells in a 24-hour assay were plastic- and nylon wool-nonadherent human peripheral blood mononuclear cells (PBMC) and their cytotoxicity was increased by interferon-alpha, interferon-gamma, and interleukin-2. Further, the cytotoxic activity of PBMC in the long-term assay was associated with large granular lymphocytes purified on a Percoll gradient, that killed the NK-sensitive cell line K562 in a 4-hour assay. All of the above are general criteria to qualify the cytotoxic cells as NK cells. Thus, the NK-resistant phenotype may not reflect absolute immunity to NK-mediated lysis, but it may reflect the different rates at which various target cell lines can be killed.     

Protein precipitation In Vitro as a measure of chemical-induced cytotoxicity: an EDIT sub-programme

As a priority area of the Evaluation-Guided Development of In Vitro Toxicity and Toxicokinetic Tests (EDIT) programme, an in vitro protein precipitation (PP) assay was used on the 50 reference chemicals of the Multicentre Evaluation of In Vitro Cytotoxicity (MEIC) project, to confirm and extend the MEIC results. Dose-response curves were generated for only 30 of the chemicals, and the concentrations causing 10% (EC10) and 50% (EC50) protein precipitation versus the positive control were chosen as endpoints. The number of chemicals with a positive response increased to 46 when a new endpoint, the minimum effect concentration (MEC) that induces protein precipitation with respect to the negative control, was used. When the results were correlated with in vitro cytotoxicity in human cell lines, a similarly good correlation was found between the various endpoints of the PP assay at 5 hours and the 24-hour IC50 average cytotoxicity in human cell lines, even though the number of chemicals included in the correlation was larger for the MEC. Using the prediction error, the endpoint that gave the best correlation between the PP assay and human cell cytotoxicity was once more found to be the 5-hour MEC, and this was chosen for the PP assay. The sensitivity of the PP assay is lower than that of the in vitro cell-line cytotoxicity assay, possibly due to its shorter exposure period and because precipitation is the ultimate event in the sequence of a protein disturbance. It is expected that earlier denaturation steps would give better sensitivity. However, this simple, inexpensive and rapid assay could be useful in the early stages of testing chemicals.     

In vitro cytotoxicity of crustacean immunostimulants for lobster (Homarus gammarus) granulocytes demonstrated using the neutral red uptake assay

The neutral red uptake (NRU) cell viability assay was adapted for use with lobster Homarus gammarus (Linnaeus, 1758) granulocytes cultured in vitro. The assay was more sensitive than the conventional trypan blue exclusion assay and facilitated a higher sample throughput than subjective microscope-based assessments of cell viability. The NRU assay was demonstrated to have a linear response from 470 to at least 126000 cells cm(-2). It was used to investigate the acute cytotoxicity of three commercial and two candidate crustacean aquaculture immunostimulants on lobster granulocytes. All five stimulants had a cytotoxic action on the granulocytes and the toxic dose for some of these stimulants was found to be below their commercially prescribed dose. The long term energetic cost of the use of these stimulants and the concomitant potential for a reduction in growth rate of cultured decapod crustaceans, which is fundamental to the success of commercial aquaculture, is identified and discussed.     

The effects of antibodies and complement in macrophage-mediated cytotoxicity on metacercariae of the lung fluke, Paragonimus westermani

Paragonimus westermani is a tissue migrating parasite in the early stage until arriving at lung, and most of the parasites spend their life spans there. Considerable immune responses including activation of macrophages are taken place during the residence of parasites in the host. However, concerning the immunologic defense mechanisms of the host against this parasite, only a few document is available so far. In this study, the cytotoxic effect of peritoneal macrophages under the presence of antibody and/or complement against metacercariae of P. westermani was investigated in vitro. Metacercariae were collected from the crayfish, Cambaroides similis and hatched out in Tyrode solution (pH 7.4). Plastic adherent cells from normal or infected rat (Wistar) peritoneal exudates were used as experimental macrophages. Polyclonal antibodies were obtained from infected rats and a cat. Cat IgG was fractioned with ion exchange chromatography. Fresh rabbit complement was used according to experimental scheme. Various combinations of peritoneal macrophages, normal or infected rat serum, complement and cat IgG were incubated at 36 degrees C in 5% CO2 incubator for 6, 14, 24 and 48 hours. The results obtained were as follows: 1. P. westermani infection activated peritoneal macrophages non-specifically and this activation induced increases of cell adherence and cytotoxicity on metacercariae. 2. In the presence of infected rat serum the antibody-dependent cell-mediated cytotoxicity of peritoneal macrophages on metacercariae was significantly increased and showed a peak at 6-hour incubation. But the cytotoxic effect was markedly reduced after inactivation of complement and heat-labile IgE antibody by the heating of infected serum at 56 degrees C for 30 minutes. 3. The highest cytotoxic effect (100%) of concomitant incubation with IgG and complement showed 24 hours after incubation, although cell adherence was relatively low at 6-hour incubation and 0% at 24-hour incubation. 4. Coordinative functions of complement with serum and IgG were effective in cell adherence and in cytotoxicity, but it is not clear the independent role of complement on the macrophage-mediated cytotoxicity in this study. With these results it is assumed that P. westermani infection can induce the non-specific activation of peritoneal macrophages, and serum antibodies including IgE antibody might enhance the cytotoxicity by macrophages.     

Forms of Selenium Affect its Transport, Uptake and Glutathione Peroxidase Activity in the Caco-2 Cell Model

The aim of this study was to investigate the possible time- and dose-dependent cytotoxic effects of cobalt chloride on Vero cells. The cultured cells were incubated with different concentrations of cobalt chloride ranging from 0.5 to 1,000 μM, and cytotoxicity was determined by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) and resazurin assays. Possible protective effects of vitamin E, coenzyme Q(10), and zinc chloride were also tested in this system. A gradual decrease in cell proliferation was observed at concentrations ~≥ 200 μM in incubation periods of 24, 48, 72, and 96 h with MTT assay. Exposure of cells to 500 and 1,000 μM cobalt chloride caused significant decrease in cell survival. A biphasic survival profile of cells was observed at 1-25 μM concentration range following 96 h of incubation. With resazurin assay, cytotoxicity profile of CoCl(2) was found comparable to the results of MTT assay, particularly at high concentrations and long incubation periods. Dose-dependent cytotoxicity was noted following exposure of cells to ≥ 250 μM of CoCl(2) for 24 h and ≥ 100 μM concentrations of CoCl(2) for 48-96 h. Pretreatment of cells with ZnCl(2) for 4 or 24 h provided significant protection against cobalt chloride-induced cytotoxicity when measured with MTT assay. However, vitamin E or coenzyme Q(10) was not protective. CoCl(2) had dose- and time-dependent cytotoxic effects in Vero cells. Preventive effect of ZnCl(2) against CoCl(2)-induced cytotoxicity should be considered in detail to define exact mechanism of toxicity in Vero cells.     

Poly(sebacic acid-co-ricinoleic acid) biodegradable injectable in situ gelling polymer

The investigated polymers, poly(sebacic acid-co-ricinoleic acid) containing > or =70% ricinoleic acid, may be injected via a 22 gauge needle and become gel upon contact with aqueous medium, both in vitro and in vivo. Various properties of the polymers including viscosity, thermal analysis, and in vivo behavior, before and after exposure to aqueous medium, were determined. These polymers were observed using scanning electron microscopy (SEM) at dry and wet states. It was found that the viscosity and melting temperature of P(SA:RA) increased after exposure to buffer. The viscosity at 37 degrees C of P(SA:RA)3:7 had the highest increase: from 4200 cP before to 8940 cP after exposure to buffer; in the case of P(SA:RA)25:75 before exposure to buffer the viscosity was 1150 cP while after it raised to 3200 cP. The viscosity of P(SA:RA)2:8 also increased from 400 cP before exposure to buffer to 1000 cP after. On the other hand polymer without sebacic acid, (poly(ricinoleic acid)), did not show gelation properties. Thermal analysis also showed an increase in the melting point of the polymers exposed to the aqueous medium during the first 24 h of incubation. Images obtained by SEM showed formation of a three-dimensional network in polymers exposed to buffers. When injected into animals, P(SA:RA) forms a solid implant in the injection site already at 8 h postinjection.     

Detection of unknown toxic mycotoxins inAspergillus nidulans using a structure-activity approach

Mycotoxins are secondary metabolites of filamentous fungi that can cause various acute and chronic toxic effects in humans. Previous work by Büngeret al. exhibited that the cytotoxicityof Aspergillus nidulans, one of the most frequent toxigenic moulds in composting plants, could not be explained by its content of identified mycotoxins. The presence of additional mycotoxins or other toxic prinpiples was assumed, which may be detected by a structure-activity approach. An HPLC-diode array detector method was used to separate and characterize the components of theA. nidulans-extract within 50 minutes/analysis. Aliquots of the extract were chromatographed and nine 5-minutes-fractions were collected and lyophilized. Rechromatography of aliquots of the residues confirmed the accuracy of the 5-minutes-cuts. The cytotoxicity of these fractions was estimated in three cell lines (A-549, L-929 and Hep-G2) using the neutral red assay (NRU assay). Ethanol/dichloromethane (1:1, v/v) was proven to be a suitable solvent mixture with a low cytotoxicity. HPLC-fractions were dissolved in this mixture prior to the NRU assay. Three 5-minutes-fractions exhibited a strong cytotoxicity in this screening system and will be further analysed to identify the underlying unknown toxic principles. Presented at the 28^th Mykotoxin-Workshop, Bydgoszcz, Poland, May 29–31, 2006, and the 47^th spring meeting of the DGPT, Mainz, Germany, April 4–6, 2006 Financial support: Deutsche Forschungsgemeinschaft (Project MU 1716–2)     

Endocytosis in cultured rat alveolar type II cells: effect of lysosomotropic weak bases on the processes.

We investigated the uptake of Lucifer yellow and surfactant complexed with gold (S-G) by isolated alveolar Type II cells. The fluid phase marker Lucifer yellow did not reach lamellar bodies (LB) even after prolonged incubation time, whereas S-G was internalized and found in LB. Treatment of Type II cells with lysosomotropic weak bases (NH4Cl and chloroquine) resulted in dilation of endosomes, lysosomes, and LB. The effect of these agents on LB resulted in disappearance of their lamellar organization, as detected by polarized light and electron microscopy. After incubation in lysosomotropic agent-free medium, endocytosis of Lucifer yellow and S-G in treated cells was mainly directed towards large vacuoles resembling either multivesicular bodies (MVB) or lysosomes. The possible relationship between LB, MVB, and lysosomes in freshly isolated as well as cultured alveolar Type II cells is discussed.     

Cytotoxicity of the MEIC reference chemicals in antioxidant-enriched, rat hepatoma-derived Fa32 cells

Since vitamin E increases the antioxidant status of cells, its influence on cytotoxicity was investigated. The neutral red uptake (NRU) inhibition effects of 39 MEIC reference chemicals were measured after treatment of rat hepatoma-derived Fa32 cells in the presence of vitamin E for 30 minutes. The results were quantified in terms of the NI50, the concentration of test compound required to reduce the NRU by 50%. Sodium chloride was the only chemical that was more toxic in the presence of vitamin E. This effect was related to the concentration of vitamin E in the cell culture medium. A vitamin E dose-related response was also observed for the decreased toxicity of paracetamol and caffeine. Glutathione levels were slightly increased in the presence of vitamin E, which could contribute to the protective effect of vitamin E. Of the remaining chemicals, 50% were less toxic in the presence of vitamin E, but the correlation with the acute human toxicity data of the MEIC study was not improved. The results imply that reactive oxygen species interfere with the toxicity of a high proportion of toxic chemicals. The assay described provides a quick and easy method for checking whether reactive oxygen species contribute to the toxicity of a chemical.     

Effect of potassium depletion of Hep 2 cells on intracellular pH and on chloride uptake by anion antiport

The effect of K+ depletion of Hep 2 cells on ion fluxes, internal pH, cell volume, and membrane potential was studied. The cells were depleted of K+ by incubation in K+-free buffer with or without a preceding exposure to hypotonic medium. Efflux of K+ in cells not exposed to hypotonic medium was inhibited by furosemide or by incubation in Na+-free medium, indicating that in this case at least part of the K+ efflux occurs by Na+/K+/Cl- cotransport. After exposure to hypotonic medium, K+ efflux was not inhibited by furosemide, whereas it was partly inhibited by 4,4'-diisothiocyano-2,2'-stilbene-disulfonic acid (DIDS). Exposure to hypotonic medium induced acidification of the cytosol, apparently because of efflux of protons from intracellular acidic vesicles. When isotonicity was restored, a rebound alkalinization of the cytosol was induced, because of activation of the Na+/H+ antiporter. While hypotonic shock and a subsequent incubation in K+-free buffer rapidly depolarized the cells, depolarization occurred much more slowly when the K+ depletion was carried out by incubation in K+-free buffer alone. The cell volume was reduced in both cases. K+ depletion by either method strongly reduced the ability of the cells to accumulate 36Cl- by anion antiport, and K+-depleted cells were unable to increase the rate of 36Cl- uptake in response to alkalinization of the cytosol.     

The FRAME alternatives laboratory database. 1. In vitro basal cytotoxicity determined by the Kenacid blue total protein assay

A database of over 280 chemicals has been compiled by using a mouse 3T3-L1 fibroblast-like cell line in exponential growth, exposed to chemicals for 72 hours in a 96-well tissue culture plate format, and determining cell number via the Kenacid blue (KB) assay for total protein. Ranking the chemicals according to their basal cytotoxicity, expressed as the concentration (mM) that inhibits increase in total cellular protein over 72 hours by 50% (the ID50 value) shows a wide range of ID50 values, from 0.00003 mM to 10,096 mM. This information includes the results for MEIC chemicals 1-50, and we have now added basal cytotoxicity data for 23 of the next 25 MEIC chemicals. When the neutral red uptake (NRU) assay was performed with the same cell cultures, before the KB assay, very similar indications of basal cytotoxicity were obtained. Comparisons between the results with 3T3-L1 cells and with a human fibroblast-like cell line, BCL-D1 showed a significant difference in order of magnitude of the ID50 value for only 5 of 52 chemicals. However, there was a difference in ID50 value of more than one order of magnitude for 8 of 24 chemicals tested with an undifferentiated teratocarcinoma cell line, F9.     

Paraquat depresses the activity of angiotensin converting enzyme expressed by human umbilical vein endothelial cells in culture

The activity of angiotensin converting enzyme (ACE) in cell lysate of cultured human umbilical vein endothelial cells (HUVEC) after a 24-hour incubation with 10(-3) and 10(-4)M of paraquat (PQ) was decreased. However, LDH released into the culture medium of HUVEC during the 24-hour incubation with PQ was not increased. Many investigators show that the change in serum ACE activity reflects the impairment of vascular endothelial cells. We showed in this report that ACE was decreased even at an early stage of endothelial injury induced by PQ, when LDH release is not yet increased.     

Sensitization Potential of Dental Resins: 2-Hydroxyethyl Methacrylate and Its Water-Soluble Oligomers Have Immunostimulatory Effects

The immunostimulatory effects of the representative dental resin monomer 2-hydroxyethyl methacrylate (HEMA), a HEMA derivative that does not contain a double bond (2-hydroxyethyl isobutyrate, HEIB), and polymerized water-soluble oligomers of HEMA (PHEMA) were investigated. It is known that expression levels of either or both of CD54 and CD86 in THP-1 cells are increased by exposure to sensitizing substances. In this study, the expression levels of CD54 and CD86, the production of reactive oxygen species (ROS), and the viability of the cells were measured after 24 h of incubation with these materials at different concentrations. The concentrations of the materials that induced the expression of both CD54 and CD86 were low in the following order: NiSO₄, HEMA, and methyl methacrylate (MMA). These results indicate that these dental resin monomers have lower sensitizing potentials than NiSO₄. Although HEIB, which lacks a double bond, resulted in negligible ROS production and reduced cytotoxicity than HEMA, it induced the expression of CD54 and CD86. Comparison of the results for HEMA and HEIB indicates that dental resin monomer-induced sensitization may be related not only to the oxidative stress related to the methacryloyl group but also to the structures of these compounds. Of particular interest is the result that a water-soluble PHEMA oligomer with a relatively high-molecular weight also exhibited negligible cytotoxicity, whereas the expression level of CD54 increased after exposure to PHEMA at a high concentration. This result serves as a warning that polymerized substances also have the potential to induce sensitization. This study provides insight into the nature of allergic responses to dental resin materials in clinical use and may facilitate the development of more biocompatible restorative materials in the future.     

Induction of cytotoxic effector activity in the HL-60 promyelocytic cell line by incubation with phorbol myristate acetate: a model system of human spontaneous monocyte-mediated cytotoxicity

In an attempt to develop a constant and reproducible in vitro system for a detailed analysis of cytotoxic effector mechanisms of nonimmune mononuclear phagocytes, the HL-60 promyelocytic cell line was studied for its cytotoxic action on chicken erythrocyte target cells. HL-60 cells cultured in complete medium were found to be noncytotoxic for chicken erythrocytes in an 18-hr 51Cr-release assay. These cells have been shown to acquire several characteristics of mature macrophages upon incubation with phorbol myristate acetate (PMA), and when PMA was included in the medium during the assay, the HL-60 cells became strongly cytotoxic to the target cells in the absence of exogenous antibody, lectin, or serum complement. Freshly isolated peripheral blood monocytes also became cytotoxic in the presence of PMA, whereas peripheral blood lymphocytes and the U937 histiocytic cell line did not. Detectable target lysis was observed between 4 and 8 hr after HL-60 stimulation with PMA, and HL-60 cells prestimulated with PMA for 24 hr retained their cytotoxic activity following washing and assay in PMA-free medium. Cytotoxic HL-60 cells developed after exposure to 10(-6) to 10(-9) M PMA, and significant target cell lysis occurred at effector:target cell ratios as low as 0.5:1. The PMA-induced HL-60-mediated cytotoxic response was markedly inhibited by blockers of protein synthesis, inhibition of microfilament function, and depletion of cellular superoxide and hydrogen peroxide. Interestingly, cytotoxicity of HL-60 cells for chicken erythrocyte targets was modulated by the direct addition of certain simple saccharides to the assay in a fashion similar to that observed with spontaneously cytotoxic mononuclear cells from several vertebrate and invertebrate species. Thus, the cytolytic effector function induced in HL-60 cells by incubation with PMA presents a useful model for the study of cellular cytotoxic mechanisms as well as the mechanisms utilized by nonimmune cells in the recognition of non-self.     

Anticancer drug testing in vitro: Use of an activating system with the human tumor stem cell assay

The soft agar tumor colony assay has been adapted for measurement of cytotoxicity of drugs such as cyclophosphamide whose antitumor activity depends upon biotransformation to active metabolites. The S-9 fraction of rat liver, MgCl₂, KCl, glucose-6-phosphate and NADP in phosphate buffer was added to medium containing cells from various continuous human tumor cell lines in the presence and in the absence of drug. After incubation for 1 hour at 37°, cells were washed twice with medium, seeded into 0.3% agar, and plated onto 0.5% agar in petri dishes. Colonies were counted 7 to 21 days later under phase contrast microscopy. Incubation of cells from human lines with cyclophosphamide or heliotrine, an experimental antitumor agent, in the absence of complete activating system caused no or minimal inhibition of colony formation. Incubation of cell lines with cyclophosphamide or heliotrine in the presence of complete activating system markedly reduced colony formation. The cytotoxic effects of both drugs were NADP dependent. This simple technique extends the usefulness of the soft agar stem cell assay to drugs requiring microsomal activation.     

Role of extracellular matrix in the action of basic fibroblast growth factor: Matrix as a source of growth factor for long-term stimulation of plasminogen activator production and DNA synthesis

When bovine capillary endothelial (BCE) cells were treated with 10 ng/ml of basic fibroblast growth factor (bFGF) for 10 or 30 minutes at 37°C, washed extensively with phosphate-buffered saline (PBS) and incubated in bFGF-free medium, plasminogen activator (PA) production was stimulated to the same extent as in cells exposed continuously to bFGF. Three methods of removing bFGF from heparin-like binding sites in the extracellular matrix, but not from bFGF receptors, abolished this long-term effect of a brief exposure to bFGF. First, BCE cells exposed to bFGF for 30 minutes were washed with 2M NaCI and incubated in bFGF-free medium. Second, BCE cells were incubated with bFGF for 10 minutes in the presence of heparin, and cells were washed with PBS and incubated in bFGF-free medium. Third, BCE cell cultures were treated with heparinase and exposed to bFGF. Each of these treatments abolished the long-term (24-48 hours) stimulation of PA production normally observed after brief exposure to bFGF. In each of these experiments, incubation of cells in bFGF-containing medium after the treatments resulted in normal stimulation of PA production, demonstrating that the treatments did not harm the cells. Stimulation of DNA synthesis was observed when cells were exposed to bFGF for 2 hours at 4°C, incubated in bFGF-free medium for 24 hours at 37°C, and assayed for ³H-thymidine incorporation. However, no stimulation was observed if the 2 hours incubation at 4°C was carried out in the presence of heparin. Thus, long-term stimulation of PA activity and DNA synthesis after a brief exposure to bFGF seems to be a consequence of bFGF binding to the extracellular matrix. The extracellular matrixmay act as a physiologic buffer, binding bFGF when concentrations are high and releasing it later for interaction with its receptor. This interaction with matrix may be required for the in vivo action of bFGF.     

Exposure to low- vs iso-osmolar contrast agents reduces NADPH-dependent reactive oxygen species generation in a cellular model of renal injury

Contrast-induced nephropathy represents the third cause of hospital-acquired acute renal failure. This study investigated the effects of low- vs iso-osmolar contrast medium (CM) exposure on NADPH-dependent reactive oxygen species (ROS) generation by tubular cells. X-ray attenuation of iohexol, iopamidol, and iodixanol was assessed at equimolar iodine concentrations and their effects on human renal proximal tubular cells (PTCs) were evaluated with equally attenuating solutions of each CM. Cytotoxicity, apoptosis, and necrosis were investigated by trypan blue exclusion, MTT assay, and annexin V/propidium iodide assay, respectively. ROS production was assessed by DCF assay, NADPH oxidase activity by the lucigenin-enhanced chemiluminescence method, and Nox4 expression by immunoblot. Yielding the same X-ray attenuation, CM cytotoxicity was assessed in PTCs at equimolar iodine concentrations. More necrosis was present after incubation with iohexol and iopamidol than after incubation with equal concentrations of iodixanol. Iohexol and iodixanol at low iodine concentrations induced less cytotoxicity than iopamidol. Moreover, both iohexol and iopamidol induced more apoptosis than iodixanol, with a dose-dependent effect. ROS generation was significantly higher with iopamidol and iohexol compared to iodixanol. NADPH oxidase activity and Nox4 protein expression significantly increased after exposure to iopamidol and iohexol, with a dose-dependent effect, compared with iodixanol. CM-induced Nox4 expression and activity depended upon Src activation. In conclusion, at angiographic concentrations, iodixanol induces fewer cytotoxic effects on cultured tubular cells than iohexol and iopamidol along with a lower induction of Nox4-dependent ROS generation. This enzyme may, thus, represent a potential therapeutic target to prevent iodinated CM-related oxidative stress.     

A possible role of prostaglandins in the inhibition of natural and antibody-dependent cell-mediated cytotoxicity against tumor cells

We recently observed that certain tumor cell lines in tissue culture produced prostaglandins and that increased production occurred when the tumor cells were exposed to lymphocytes. The present experiments tested the effect of prostaglandins E₁ and E₂ on natural and antibody-dependent lymphocyte cytotoxicity against the same target cells in order to determine whether the production of prostaglandins by the tumor cells might influence the efficacy of the cellular immune response. Target cell lines T₂₄ and HCV₂₉ were labeled with ⁵¹Chromium and incubated at 37 °C for various times with lymphocytes prepared from venous blood of normal donors. Antiserum to T₂₄ and varying concentrations of prostaglandin E₁ or E₂ were added to the samples prior to incubation. In some experiments, lymphocytes or labeled target cells were preincubated with prostaglandins and then washed prior to their addition to the assay tubes. Cytotoxicity was determined by measuring the release of ⁵¹Chromium from the target cells after incubation. Both prostaglandins E₁ and E₂ inhibited natural and antibody-dependent lymphocyte cytotoxicity against the target cells. The effect appeared to represent a direct one on lymphocytes, and it was amplified by the presence of theophylline in the medium. Inhibition could be effected early on in lymphocyte/target cell interaction, and only a short exposure of lymphocytes to prostaglandins was required for the effect to be manifested. It thus appears that the production of prostaglandins by tumor cells may constitute a means by which the tumor cells subvert the effect of a cellular immune response that is directed against them.