Every-other-week methotrexate in patients with rheumatoid arthritis. A double-blind, placebo-controlled prospective study

OBJECTIVE

To determine if patients with rheumatoid arthritis (RA) that is stable with weekly methotrexate (MTX) therapy could be switched to an every-other-week regimen of MTX.

METHODS

Forty-seven patients with classic or definite RA who had received MTX for at least 8 months were studied. Clinical measurements consisted of the number of tender and swollen joints, physician and patient global evaluation of disease activity on a 5-point scale, grip strength, patient evaluation of pain, morning stiffness, and the interval to onset of fatigue from time of awakening. Laboratory measures included the erythrocyte sedimentation rate (ESR), rheumatoid factor, C-reactive protein (CRP), and baseline serum folate levels. Uptake of MTX was measured with tritiated thymidine from peripheral blood mononuclear cells (PBMC) from patients ex vivo. Serum measures of interleukin-1 beta (IL-1 beta), IL-6, and tumor necrosis factor alpha (TNF alpha) were performed in sera, and TNF alpha was also measured on PBMC supernatants.

RESULTS

Twelve of the 23 patients receiving every-other-week MTX (52%) were able to complete 6 months of this treatment without experiencing a disease flare. Eleven of the 23 patients receiving every-other-week MTX (48%) withdrew from the study before completing 6 months of treatment, because of a flare. No significant differences in clinical or laboratory parameters were seen when the 24 patients receiving weekly MTX were compared with the 12 patients in the every-other-week MTX group who successfully completed 6 months of the study. None of the changes in serum cytokine levels were significantly different between the patients receiving MTX weekly versus those receiving it every other week, and changes in ESR and CRP did not differ between groups. Age, sex, RA disease duration, MTX weekly dose or duration, baseline joint counts, or serum folate status did not predict a flare. Tritiated MTX uptake did not differ between groups.

CONCLUSION

Some patients with RA that is stable on weekly dosing are able to change to every-other-week dosing without experiencing a flare in their disease activity.

Identification of tissue-type plasminogen activator-specific plasminogen activator inhibitor-1 mutants. Evidence that second sites of interaction contribute to target specificity

Plasminogen activator inhibitor-1 (PAI-1) is the primary inhibitor of the plasminogen activators (PAs), tissue-type plasminogen activator (tPA), and urokinase-type plasminogen activator (uPA). A library of PAI-1 mutants containing substitutions at the P1 and P1' positions was screened for functional activity against tPA and thrombin. Several PAI-1 variants that were inactive against uPA in a previous study (Sherman, P. M., Lawrence, D. A., Yang, A. Y., Vandenberg, E. T., Paielli, D., Olson, S. T., Shore, J. D., and Ginsburg, D. (1992) J. Biol. Chem. 267, 7588-7595) had significant inhibitory activity toward tPA. This set of tPA-specific PAI-1 mutants contained a wide range of amino acid substitutions at P1 including Asn, Gln, His, Ser, Thr, Leu, Met, and all the aromatic amino acids. This group of mutants also demonstrated a spectrum of substitutions at P1'. Kinetic analyses of selected variants identified P1Tyr and P1His as the most efficient tPA-specific inhibitors, with second-order rate constants (ki) of 4.0 x 10(5) M-1s-1 and 3.6 x 10(5) M-1s-1, respectively. Additional PA-specific PAI-1 variants containing substitutions at P3 through P1' were constructed. P3Tyr-P2Ser-P1Lys-P1'Trp and P3Tyr-P2Ser-P1Tyr-P1'Met had ki values of 1.7 x 10(6) M-1s-1 and 2.5 x 10(6) M-1s-1 against tPA, respectively, but both were inactive against uPA. In contrast, P2Arg-P1Lys-P1'Ala inhibited uPA 74-fold more rapidly than tPA. The mutant PAI-1 library was also screened for inhibitory activity toward thrombin in the presence and absence of the cofactor heparin. While wild-type PAI-1 and several P1Arg variants inhibited thrombin in the absence of heparin, a number of variants were thrombin inhibitors only in the presence of heparin. These results demonstrate the importance of the reactive center residues in determining PAI-1 target specificity and suggest that second sites of interaction between inhibitors and proteases can also contribute to target specificity. Finally, the PA-specific mutants described here should provide novel reagents for dissecting the physiological role of PAI-1 both in vitro and in vivo.

Phospholipid metabolism of lymphocytes with inhibited glutathione synthesis using L-buthionine-S,R-sulfoximine

The potential role of phospholipid metabolism in restricting lymphocyte proliferation under conditions of oxidative stress was investigated using [1-14C]-arachidonic acid (14C-AA) and 32P-orthophosphoric acid. Human peripheral blood lymphocytes (PBL) and PBL depleted of glutathione with L-buthionine-S,R-sulfoximine (BSO-PBL) were compared. The relative uniformity of glutathione depletion in the PBL population was assessed by flow cytometry. BSO-PBL were 40 to 90% depleted of glutathione 1 to 3 days after activation, respectively, and the BSO-PBL had unimpaired early activation events based on 32P-phosphatidylinositol levels. However, unlike stimulated PBL, which showed a progressive decrease in radioactivity incorporated into phosphatidylcholine and a corresponding increase into phosphatidylethanolamine, no significant differences occurred with BSO-PBL. Prelabeled BSO-PBL showed considerably more 14C radioactivity in the supernatant following 72-120 h stimulation with anti-CD3 than control PBL, which was mostly in the form of unmetabolized 14C-AA. Higher levels of leukotriene B4, 5-hydroxyeicosatetraenoate and 12-hydroxy-5,8,10-heptadecatrienoate also were observed with L-buthionine-S,R-sulfoximine treatment, which could explain the impaired proliferation obtained with a depletion of cellular glutathione. Both lysophosphatidylcholine and liberated free 14C-AA increased with L-buthionine-S,R-sulfoximine treatment following 72 h stimulation, suggesting functional impairment in the reacylating enzymes. The increased release of 14C-AA by BSO-PBL also may contribute to the imparied proliferation that occurs with loss of glutathione.

A fluorescent probe study of plasminogen activator inhibitor-1. Evidence for reactive center loop insertion and its role in the inhibitory mechanism

A mutant recombinant plasminogen activator inhibitor 1 (PAI-1) was created (Ser-338-->Cys) in which cysteine was placed at the P9 position of the reactive center loop. Labeling this mutant with N,N'-dimethyl-N-(acetyl)-N'-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) ethylene diamine (NBD) provided a molecule with a fluorescent probe at that position. The NBD-labeled mutant was almost as reactive as wild type but was considerably more stable. Complex formation with tissue or urokinase type plasminogen activator (tPA or uPA), and cleavage between P3 and P4 with a catalytic concentration of elastase, all resulted in identical 13-nm blue shifts of the peak fluorescence emission wavelength and 6.2-fold fluorescence enhancements. Formation of latent PAI showed the same 13-nm spectral shift with a 6.7-fold fluorescence emission increase, indicating that the NBD probe is in a slightly more hydrophobic milieu. These changes can be attributed to insertion of the reactive center loop into the beta sheet A of the inhibitor in a manner that exposes the NBD probe to a more hydrophobic milieu. The rate of loop insertion due to tPA complexation was followed using stopped flow fluorimetry. This rate showed a hyperbolic dependence on tPA concentration, with a half-saturation concentration of 0.96 microM and a maximum rate constant of 3.4 s-1. These results demonstrate experimentally that complexation with proteases is presumably associated with loop insertion. The identical fluorescence changes obtained with tPa.PAI-1 and uPA.PAI-1 complexes and elastase-cleaved PAI-1 strongly suggest that in the stable protease-PAI-1 complex the reactive center loop is cleaved and inserted into beta sheet A and that this process is central to the inhibition mechanism.

Role of endogenous cytokines in endotoxin- and interleukin-1-induced pulmonary inflammatory response and oxygen tolerance

Endotoxin lipopolysaccharide and the cytokines, tumor necrosis factor (TNF) and interleukin-1 (IL-1), are known to protect adult rats against O2 toxicity. However, whether the effect of endotoxin is mediated by these cytokines is not clear. We have previously demonstrated that depletion of 84% rat alveolar macrophages (AM), which reduced lipopolysaccharide (LPS)-induced release of TNF by 86%, had no effect on LPS-induced O2 tolerance. In this study, we demonstrated that coinsufflation of LPS with anti-TNF antibody and IL-1 receptor antagonist (IL-1ra), which completely inhibited LPS-induced TNF and IL-1 activities, had no effect on LPS-induced alveolar inflammatory response and O2 tolerance. Likewise, coinsufflation of IL-1 and anti-TNF antibody, which completely neutralized IL-1-induced TNF activity, had no effect on IL-1-induced alveolar inflammatory response and O2 tolerance. In contrast, IL-1ra completely abolished IL-1-induced inflammatory response and markedly inhibited IL-1-induced O2 tolerance. These results suggest that LPS-induced alveolar inflammatory response and O2 tolerance are not mediated by endogenous TNF and IL-1. Similarly, endogenous TNF does not mediate IL-1-induced alveolar inflammatory response and O2 tolerance.

Activated T cells enhance nitric oxide production by murine splenic macrophages through gp39 and LFA-1

Macrophages can be stimulated to produce a relatively large amount of nitric oxide, which is an important component in macrophage-mediated defense mechanisms and regulation of T cell activities. It has been known that T helper (Th) cell activation requires intimate physical interaction between T helper cells and macrophages and that cytokines from activated Th cells regulate macrophage activities including nitric oxide production. The current study indicates that surface molecules on activated Th cells also can synergize with cytokines to substantially enhance nitric oxide production by macrophages through cell-cell contact. The CD40 ligand (gp39) and LFA-1 appear to be two major contributors for T cell dependent nitric oxide production.

Serpin reactive center loop mobility is required for inhibitor function but not for enzyme recognition

One feature that distinguishes all of the inhibitory members of the serpin gene family is the presence of a small uncharged residue at the P14 position of the reactive center loop. In this report we examine the effects of mutations at this position, in the serpin, plasminogen activator inhibitor type 1 (PAI-1). Replacement of the native P14 Thr-333 residue by an Arg (Thr-333-->Arg) resulted in complete loss of inhibitory activity toward tissue-type plasminogen activator and urokinase-type plasminogen activator. Comparison of the binding of the mutant inhibitor and wild type PAI-1 (WTPAI-1) to anhydrotrypsin indicated that the initial interaction of the two inhibitors with proteases was identical. However, whereas WTPAI-1 forms SDS-stable complexes with both plasminogen activators, the mutant PAI-1 was efficiently cleaved as a substrate. Amino-terminal sequence analysis indicated that cleavage of the mutant PAI-1 occurred at its reactive center P1-P1' Arg-Met bond. Thermal denaturation studies of native and cleaved PAIs indicated that native Thr-333-->Arg mutant had a thermal stability identical to active WTPAI-1 and that both proteins became significantly more stable following cleavage by elastase (cleaved at the P4-P3 bond). Finally, the function of recombinant PAI-1 variants containing 15 of the possible 19 amino acid substitutions at P14 were analyzed. While residue size appeared to have little effect on inhibitory activity, the presence of either a positive or a negative charge at P14, converted PAI-1 to a substrate. Taken together, these results suggest that while insertion of the reactive center loop is not essential for protease binding, it is a necessary second step required for inhibitor function. The presence of a charged residue at P14 can retard this insertion, resulting in conversion of the serpin to a substrate.

In vitro effects of hydroquinone, benzoquinone, and doxorubicin on mouse and human bone marrow cells at physiological oxygen partial pressure

A comparative study was undertaken in order to assess the hematotoxic effects of hydroquinone (HQ), 1,4-benzoquinone (BQ), and doxorubicin (DX) on mouse and human bone marrow (BM) cells. Initial experiments indicated that the inhibitory effects of near-ambient pO2 and HQ on granulocyte/macrophage colony-stimulating factor (GM-CSF)-induced colony formation were additive. Thus, subsequent experiments were done under conditions of continuous toxicant exposure in complete medium at physiological temperature and O2 partial pressure. Viability was measured 24 hr after exposure, and at the concentrations tested, HQ was less cytotoxic than BQ. DX did not exhibit significant cytotoxicity at the concentrations used. Both HQ and BQ were slightly more cytotoxic to mouse BM cells than to human BM cells. Dose-response analyses of HQ, BQ, or DX inhibition of GM-CSF-induced proliferative and colony-forming responses indicated that murine GM progenitors were significantly less sensitive to HQ than to the majority of myeloid BM cells that proliferated in response to GM-CSF. This preferential resistance of GM progenitors to HQ was not observed when human BM cells were used. HQ was somewhat more inhibitory to human than to mouse GM-CSF responses. Inhibition of GM-CSF-induced responses by BQ correlated closely with cytotoxicity, and DX was 1000-fold more inhibitory to GM-CSF-induced proliferative and colony-forming responses than either HQ or BQ. Again, DX appeared to be slightly more inhibitory to human BM cells than to mouse BM cells. Purified human hematopoietic progenitor cells (HPCs) were also used in the dose-response analyses of HQ, BQ, or DX inhibition of GM-CSF-induced proliferative and colony-forming responses. Inhibition of GM-CSF-induced HPC responses by HQ, BQ, and DX was very similar to that obtained when BM mononuclear cells were used, suggesting that the human HPC is a target for the direct effects of HQ, BQ, and DX.

Regions involved in binding of urokinase-type-1 inhibitor complex and pro-urokinase to the endocytic alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein. Evidence that the urokinase receptor protects pro-urokinase against binding to the endocytic receptor

The alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein (alpha 2MR/LRP) binds several ligands, including complex between the two chain urokinase-type plasminogen activator (uPA) and type-1 plasminogen activator inhibitor (PAI-1), and the single chain zymogen pro-urokinase (pro-uPA). We have used truncated variants of uPA and PAI-1 as well as Fab fragments of monoclonal antibodies with known epitopes to identify regions in the uPA.PAI-1 complex and in pro-uPA involved in binding to alpha 2MR/LRP.uPA.PAI-1 complex bound with high affinity (EC50 about 0.4 nM) via contacts in the PAI-1 moiety as well as the uPA serine proteinase domain and the uPAA chain. Pro-uPA bound with lower affinity (EC50 about 10 nM), and efficient binding to alpha 2MR/LRP was dependent on contact with both the A chain and the serine proteinase domain. We analyzed the effect of complex formation with the urokinase receptor since this is the primary target for binding of uPA.PAI-1 and pro-uPA at the cell surface, and since it has been demonstrated that urokinase receptor-bound uPA.PAI-1 complex is internalized following interaction with alpha 2 MR/LRP (Nykjaer, A., Petersen, C. M., Møller, B., Jensen, P.H., Moestrup, S.K., Holtet, T.L., Etzerodt M., Thøgersen, H.C., Munch, M., Andreasen, P.A., and Gliemann, J. (1992) J. Biol. Chem. 267, 14543-14546). Soluble recombinant urokinase receptor blocked the binding of pro-uPA to alpha 2MR/LRP but caused only a slight reduction in the affinity for binding of uPA.PAI-1. Moreover, pro-uPA bound to the urokinase receptor at the cell surface was not internalized and degraded unless activated to uPA and complexed with PAI-1. We conclude that pro-uPA is protected against degradation via alpha 2MR/LRP when bound to uPAR due to shielding of a binding contact in the A chain, whereas the affinity of uPAR-bound uPA.PAI-1 complex for binding to alpha 2MR/LRP remains sufficient to allow rapid internalization and degradation.

Localization of vitronectin binding domain in plasminogen activator inhibitor-1

Plasminogen activator inhibitor type 1 (PAI-1) is the rapid physiologic inhibitor of tissue-type plasminogen activator and urokinase-type plasminogen activator (uPA). In plasma and the extracellular matrix, PAI-1 is associated with the adhesive glycoprotein vitronectin. In order to characterize the PAI-1 structural domain responsible for binding to vitronectin, the segment of the PAI-1 cDNA encoding amino acids 13-147 (nucleotides 248-650) was randomly mutagenized and subcloned into a bacterial expression vector containing the mature PAI-1 coding sequence. Recombinant PAI-1 mutants were expressed in Escherichia coli and bacterial lysates assayed in duplicate for uPA inhibitory activity and vitronectin binding. Of 190 clones screened, six consistently demonstrated decreased vitronectin binding relative to uPA inhibitory activity. DNA sequence analysis of four of these clones identified 10 unique missense mutations, all located between base pairs 298 and 641, with each clone containing between one and four substitutions. Each substitution was expressed independently by site-directed mutagenesis and again analyzed for uPA inhibitory activity and vitronectin binding. Five point mutations that selectively disrupt vitronectin binding were identified. All 5 residues are located on the exterior of the PAI-1 structure. These findings appear to define a complex binding surface that bridges alpha-helices C and E to beta-strand 1A and includes amino acids 55, 109, 110, 116, and 123. These results suggest that vitronectin binding may stabilize the active conformation of PAI-1 by restricting the movement of beta-sheet A and thereby preventing insertion of the reactive center loop.

Immunologic detection of the cellular receptor for urokinase plasminogen activator

The cellular receptor for urokinase plasminogen activator (uPA-R) is a monomeric phosphatidylinositol-linked glycoprotein (gp40-65) that may contribute to the invasive capacity of tumor and inflammatory cells by focusing the activity of urokinase (uPA) in converting plasminogen to plasmin, a serine protease capable of degrading extracellular matrix proteins. The further characterization of uPA-R has been facilitated by our recent development of a monoclonal antibody, anti-Mo3f, specific for uPA-R. This mAb bound to uPA-R expressed by phorbol myristate acetate-stimulated U-937 cells and by NIH-3T3 cells permanently transfected with uPA-R cDNA. In competitive binding assays, anti-Mo3f inhibited the binding of fluorescein-conjugated uPA ligand to uPA-R expressed by U-937 cells and uPA-R transfectants; conversely, preexposure of cells to saturating quantities of exogenous uPA partially blocked the subsequent binding of anti-Mo3f mAb to uPA-R. Anti-Mo3f mAb was employed as the capture reagent in an ELISA for the quantitation of soluble forms of uPA-R (derived from U-937 cells and recombinant uPA-R) which had a sensitivity of approximately 4-12 ng/ml. Anti-Mo3f mAb was also applied as a serologic probe for the detection of uPA-R expressed by human tumor tissues. By immunoperoxidase staining, anti-Mo3f demonstrated positive tumor cell staining in 4 of 16 breast and 7 of 31 prostate carcinomas in formalin-fixed, paraffin-embedded specimens. These data indicate that the anti-Mo3f mAb detects an epitope proximate to or within the ligand binding domain (domain 1) of uPA-R and may be useful as a tool for the serologic detection of uPA-R in soluble form or associated with human tumors.

Engineering plasminogen activator inhibitor 1 mutants with increased functional stability

Plasminogen activator inhibitor 1 (PAI-1), a member of the serine protease inhibitor (Serpin) superfamily, is the primary inhibitor of the plasminogen activators tPA and uPA. PAI-1 is produced in an active form but converts to an inactive or latent form with a half-life of approximately 1 h at pH 7.5, 37 degrees C. This study describes the construction, expression, and characterization of PAI-1 mutants with increased functional stability. Three mutations that disrupt an ion pair, present in latent PAI-1, between Arg-30 and Glu-350 (P4'), were introduced into recombinant PAI-1. All three mutant proteins maintained normal functional activity against both uPA and tPA. However, the half-life of each purified PAI-1 mutant was extended compared to the 1.1 h observed for wild-type PAI-1 (wtPAI-1) (1.2 h for Glu-350-->Arg, 2.0 h for Glu-350-->Pro, and 2.1 h for the Arg-30-->Glu mutation). An additional PAI-1 variant containing a second mutation designed to potentially reconstitute the ion pair (Arg-30-->Glu, Glu-350-->Arg) failed to restore the wild-type half-life. Circular dichroism spectra analysis indicated that the active and latent forms of wtPAI-1 and all four mutants contained similar secondary structural elements. Thermal stability determinations showed that latent wtPAI-1 was much more structurally stable than the active conformation. However, the latent form for all four mutants was significantly less stable than the corresponding wtPAI-1 conformer. This is the first report of PAI-1 mutants which have been specifically engineered to produce enhanced functional stability.

The urokinase receptor is expressed in invasive breast cancer but not in normal breast tissue

We have studied expression of the urokinase receptor (u-PAR) in paraffin-embedded breast tissues at various stages of malignant progression. Forty-nine of 59 invasive cancers studied showed varying degrees of reactivity with our polyclonal antibody. The staining pattern was variable from case to case, although strong surface staining of tumor-associated macrophages was evident in most of these sections. In several cases, blood vessels in selected tumor areas were stained, as confirmed by treatment of adjacent sections with an anti-factor VIII antibody. These could represent regions of recent angiogenesis. Staining of tumor cells was observed in 21 of 59 cases and was extensive in 5 cases but confined to a small percentage of cells in the remaining 16 samples. In contrast with the cancer sections, all normal breast tissue (12 cases) was negative, as well as all fibroadenomas (4 cases), papillomas (5 cases), and hyperplasia with atypia (2 cases) studied. Seven carcinomas in situ examined were also negative for u-PAR, with the exception of few macrophages in two cases, suggesting that u-PAR expression may be associated with invasive tumor. The presence of u-PAR in human breast cancer and its absence from nonmalignant breast tissue supports the idea that plasminogen activation plays an important role in the process of cancer invasion. Expression of u-PAR on macrophages, endothelial cells, and cancer cells suggests the existence of complex paracrine interactions between tumor cells and stroma.

Transforming growth factor-beta 1 enhances serum-induced dephosphorylation of the P53 protein in cell lines growth-inhibited by this factor

A 24 hr TGF-beta 1 treatment (4 ng/ml) of SV40-transformed WI38 embryonic fibroblasts (VA13 cells) causes a moderate but reproducible inhibition of their serum-stimulated growth. By immunoprecipitation with the PAb122 antibody, we show that serum stimulation of previously serum-deprived cells causes a dephosphorylation of the wild type P53 protein, which is accentuated by the TGF-beta 1 treatment. The TGF-beta 1-enhanced dephosphorylation effect is also observed in two other cell lines growth-inhibited by TGF-beta 1, but which do not contain Large T (mink lung CCL64 and human KHOS cells). On the contrary, TGF-beta 1 treatment of the untransformed WI38 fibroblasts stimulates their growth, without affecting the phosphorylation of P53. Such treatment did not affect the expression of the corresponding mRNA nor the level of synthesis of the protein. The results suggest that the P53 protein could be a downstream target of TGF-beta 1 action on those cells growth-inhibited by the factor.

Immunomodulation by metals

A symposium entitled Immunomodulation by Metals was held at the 32nd Annual Meeting of the Society of Toxicology (SOT) in New Orleans, Louisiana. The symposium was co-sponsored by the Immunotoxicology and Metals Specialty Sections of SOT and was designed to describe the types of adverse immunological reactions which occur in response to environmental and/or occupational exposure to metals. Epidemiological evidence and underlying mechanisms responsible for the observed alterations were also discussed. The following is a summary of each of the individual presentations.

Kinetics of inactivation of alpha-thrombin by plasminogen activator inhibitor-1. Comparison of the effects of native and urea-treated forms of vitronectin

Kinetic studies are presented which show that native human vitronectin, but not urea-treated vitronectin, accelerates the inactivation of human alpha-thrombin by human plasminogen activator inhibitor-1 (PAI-1). We demonstrate that although urea-treated vitronectin binds PAI-1 with an affinity greater than that of native vitronectin, it does not accelerate the rate of inactivation of alpha-thrombin by PAI-1. We present evidence to suggest that the inability of urea-treated vitronectin to accelerate the reaction between alpha-thrombin and PAI-1 results at least in part from the inability of urea-treated vitronectin to bind to alpha-thrombin. The accelerated reaction between PAI-1 and alpha-thrombin can be accounted for by the formation of a tight complex between native vitronectin and PAI-1 that reacts in a saturable manner (Kd = 75 nM) with alpha-thrombin. The second-order rate constant (kI/Kd) for the reaction of the native vitronectin-PAI-1 complex with alpha-thrombin (1.64 x 10(5) M(-)-1 s-1) is 270-fold greater than the second-order rate constant for the reaction in the absence of vitronectin (610 m-1 s-1). The increase in the second-order rate constant is largely due to an increase in the affinity of alpha-thrombin for the native vitronectin-PAI-1 complex, as reflected by a greater than 25-fold reduction in the dissociation constant (Kd) observed for the vitronectin-PAI-1 complex relative to that of uncomplexed PAI-1.

Strand-selective repair of DNA damage in the yeast GAL7 gene requires RNA polymerase II

We examined the role of transcription in directing repair of DNA damage in active genes by comparing the repair of thymine glycols produced by H2O2 and of UV-induced pyrimidine dimers on each strand of the GAL7 gene of Saccharomyces cerevisiae. Repair of both thymine glycols and pyrimidine dimers on the transcribed strand of the gene occurs two to three times faster than on its nontranscribed strand or in the genome overall. When the gene is inactive, no preferential or strand-selective repair is observed. Using a yeast strain containing a temperature-sensitive mutation in one of the subunits of RNA polymerase II, we find that inactivating RNA polymerase II by shifting the cells to the nonpermissive temperature during repair eliminates the strand selectivity of repair under conditions where repair on the nontranscribed strand of the gene and in the genome overall are only slightly affected. Our observation of strand-selective repair of thymine glycols in the GAL7 gene is the first evidence that this repair process occurs for a nonbulky lesion. In addition, we demonstrate that the transcriptional complex plays a critical role in directing repair to the transcribed strand of active genes.

Effects of 2-mercaptoethanol and buthionine sulfoximine on cystine metabolism by and proliferation of mitogen-stimulated human and mouse lymphocytes

Cysteine is an essential amino acid for lymphocytes and its anabolic products are intimately involved in lymphocyte activation. The purpose of this study was to assess the uptake and subsequent utilization of cyst(e)ine by mitogen-stimulated human peripheral blood mononuclear cells (PBMC), to evaluate the effect of an exogenous thiol, 2-mercaptoethanol (2ME), on these processes, and to compare human and mouse lymphocyte reactivities. Unlike mouse lymphocytes, the proliferation of human T-cells was inhibited by addition of 2ME although 2ME enhanced cystine uptake. Optimal responses to T-cell mitogens (Con A and PHA) were obtained with a cystine concentration of greater than or equal to 25 and 200 microM for human and mouse cells, respectively, and 2ME enhanced DNA synthesis of Con A-stimulated mouse cells regardless of the cystine dose; however, 2ME enhanced the response of human cells only in the presence of suboptimal doses of cystine. To assess whether 2ME's inability to enhance human PBMC responses was related to their glutathione (GSH) content, the human PBMC were pretreated with buthionine sulfoximine (BSO, an inhibitor of GSH synthesis). Even when the initial intracellular GSH concentration was lowered to below that of mouse lymphocytes, 2ME still inhibited proliferation. In contrast, addition of 2ME to human PBMC maintained in the presence of BSO enhanced the proliferative response suggesting that a critical level of thiols is needed for proliferation. The ability of 2ME to enhance proliferative responses in cystine deficient medium supports this contention. Consistent with thiol involvement in activation, Con A increased [35S]cystine uptake 2-fold within 4 h of incubation and enhanced subsequent conversion of cystine into cysteine and GSH. Interestingly, BSO treatment only slightly inhibited Con A-induced protein synthesis (5%), but it significantly suppressed conversion of cystine into cysteine or GSH (80-95%) and blocked DNA synthesis (90%). Overall, the results indicate that various differential thiol characteristics must exist between human and mouse lymphocytes and that a reducing equivalent is necessary for DNA synthesis but not lymphocyte activation.

Saturation mutagenesis of the plasminogen activator inhibitor-1 reactive center

Plasminogen activator inhibitor-1 (PAI-1) is a specific inhibitor of the serine proteases tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA). To systematically investigate the roles of the reactive center P1 and P1' residues in PAI-1 function, saturation mutagenesis was utilized to construct a library of PAI-1 variants. Examination of 177 unique recombinant proteins indicated that a basic residue was required at P1 for significant inhibitory activity toward uPA, whereas all substitutions except proline were tolerated at P1'. P1Lys variants exhibited lower inhibition rate constants and greater sensitivity to P1' substitutions than P1Arg variants. Alterations at either P1 or P1' generally had a larger effect on the inhibition of tPA. A number of variants that were relatively specific for either uPA or tPA were identified. P1Lys-P1'Ala reacted 40-fold more rapidly with uPA than tPA, whereas P1Lys-P1'Trp showed a 6.5-fold preference for tPA. P1-P1' variants containing additional mutations near the reactive center demonstrated only minor changes in activity, suggesting that specific amino acids in this region do not contribute significantly to PAI-1 function. These findings have important implications for the role of reactive center residues in determining serine protease inhibitor (serpin) function and target specificity.

TGF-beta-like activity produced during regression of exacerbations in multiple sclerosis

Samples representative of different stages of disease from a longitudinal study of multiple sclerosis patients were tested in the anchorage-independent growth assay for TGF-beta and an increased activity was detected in the supernatants from 2-day blood cell cultures from patients with active disease compared to patients without active disease and healthy donors. Within the group of patients with active disease, the TGF-beta like activity was significantly increased in the subgroup of patients tested during the period of regression of the symptoms where it appeared in 86.9% of the samples. These results suggest that TGF-beta or a TGF-beta like factor may play a role in regeneration processes in multiple sclerosis.

Lead, a major environmental pollutant, is immunomodulatory by its differential effects on CD4+ T cells subsets

Studies were undertaken to address the necessity of B-T cell contact for the enhancement of B cell differentiation caused by the heavy metal lead (Pb). Membrane segregated cultures were used so that the influences of direct B-T cell contact and T cell factors on B cell differentiation could be independently evaluated. B-T cell contact was not absolutely required for Pb's enhancement of B cell maturation to antibody forming cells (AFCs); however, enhancement of the AFC response by Pb was optimal when B-T cell interactions were allowed. These results were corroborated by use of anti-L3T4 (mouse CD4) to block CD4+ T cell-B cell interaction. Blockade of B-T cell contact with anti-L3T4 did not inhibit the enhancement of the AFC response by Pb. Additional experimentation showed that Pb enhanced the AFC response and Ig production in the presence of antigen-specific T cell help, suggesting that Pb enhances B cell differentiation by augmenting cognate help rather than by inducing a response to Pb-altered-self. In studies employing antigen-specific T cell clones, Pb was found to differentially modulate antigen presentation to TH1 versus TH2 T cell clones, in that TH1 activation was inhibited and TH2 activation was enhanced by Pb.

The oxidative inactivation of plasminogen activator inhibitor type 1 results from a conformational change in the molecule and does not require the involvement of the P1' methionine

Plasminogen activator inhibitor 1 (PAI-1) is sensitive to oxidative inactivation, and it has been suggested that specific oxidation of a methionine residue, Met347, situated in the P1' position of the reactive center may be the cause of the inactivation. To test this hypothesis we have purified and biochemically characterized mutant proteins of PAI-1 in which Met347 and either of two other methionines, Met266 or Met354, has been replaced with oxidation-resistant valine residues. The mutant proteins were found to be equally sensitive to oxidation as wild-type PAI-1, suggesting that a specific oxidation of the P1' Met347 is not responsible for the inactivation. When PAI-1 was oxidized, circular dichroism analysis revealed a rapid conformational change that correlated to the loss of inhibitory activity. The oxidation sensitivity of PAI-1 was enhanced dramatically in the presence of 0.001% sodium dodecyl sulfate, and the circular dichroism spectrum was significantly different from that of untreated PAI-1, suggesting that the increased sensitivity to oxidation may be caused by a conformational change in the inhibitor molecule. Taken together, our data suggest that the oxidative inactivation of PAI-1 is not caused by the specific oxidation of the P1' methionine but results from a conformational change in the protein structure.

Preferential repair of DNA damage on the transcribed strand of the human metallothionein genes requires RNA polymerase II

To examine the possible role of transcription in directing repair of DNA damage in active genes, we compared repair of UV- and aflatoxin B1-induced damage on each strand of the human metallothionein (hMT) genes. Repair on the transcribed strand of an active hMT gene occurs at least 3 times faster than that on its nontranscribed strand. Both strands of inactive genes and both strands of a regulatory region 5' to an active gene are not repaired at this faster rate. Inducing higher levels of transcription with dexamethasone selectively increased the rate of repair on only the transcribed strand of the induced gene, while treatment of cells with alpha-amanitin eliminated the strand-selective repair. These results demonstrate that repair on the transcribed strand of a gene is independent of repair on the nontranscribed strand and that the transcriptional complex plays a role in directing repair to the transcribed strand of active genes.

Inhibition of interleukin-2 production in the human T cell line JURKAT by nonpolar maleimides

The immunosuppressive properties of polar and nonpolar maleimides were studied by measuring their ability to inhibit mitogen-induced interleukin-2 (IL-2) production by JURKAT T cells. The nonpolar maleimides N-ethylmaleimide (NEM) and N-phenylmaleimide (NPM) inhibited IL-2 production by 85-99%, but only when added to JURKAT cells prior to the mitogen. The polar maleimides N-hydroxymaleimide (NHM) and 4-maleimidosalicylic acid (M84) did not suppress IL-2 production significantly, even though NHM reacted with more cellular thiols (12%) than did NPM (8%). Both NEM and NPM suppressed IL-2 production at doses that did not affect proliferation. NEM inhibited IL-2 production induced by PHA, anti-CD3 (alpha CD3) monoclonal antibodies or PMA, and A23187, but did not interfere with the binding of alpha CD3 to the cells. NEM inhibited IL-2 production at concentrations that did not interfere with the PHA-induced increase in intracellular free calcium [( Ca]i). Neither NPM nor NHM inhibited the rise in [Ca]i, even at the highest concentrations tested. Although JURKAT T cells require both PMA and A23187 to induce IL-2 production, we found that cells pretreated with PMA could respond to A23187 added 18 hr later. PMA-treated cells were not resistant to the immunosuppressive effects of NEM or NPM. However, PMA-pretreated cells became resistant to the inhibitory effects of NEM upon the addition of A23187, suggesting that nonpolar maleimides inhibit activation events induced by the rise in [Ca]i.

Residual activation events functional after irradiation of mouse splenic lymphocytes

The radioresistance of lymphocytes increases after mitogenic stimulation, suggesting that a radiosensitive activation event contributes to the overall radiosensitivity of lymphocytes. We have sought to identify this activation event by determining the extent of activation of mitogen-stimulated lymphocytes previously exposed to growth-inhibiting doses of radiation. Mouse splenic lymphocytes were exposed to 0-15 Gy 137Cs radiation, and structural and functional damage were assayed. Although damage to cellular thiols and nonprotein thiols was modest, there was a significant loss of viability by 6 h as determined by uptake of propidium iodide (PI). Since cells did not die immediately after irradiation, the activation events which remained were evaluated. Growth-inhibiting doses of radiation left cells partially responsive to mitogen, in that cells were able to exit G0 phase, but they could progress no further into the cell cycle than G1a phase. It is important to note that assessment of viability by uptake of PI indicated substantial cell death after 15 Gy (45%, 6 h; 90%, 24 h); however, cell cycle analysis at 24 h indicated no significant decrease in progression from G0 to G1a phase. The LPS-stimulated response of B cells was more radiosensitive than the Con A-stimulated response of T cells. Further analysis of the Con A response indicated that production of interleukin-2 (IL-2) was unaffected, but expression of the IL-2 receptor was inhibited. Inhibition of poly-ADP-ribosylation and damage to lipids did not prevent the lack of mitogen responsiveness, since neither the ADP-ribose transferase inhibitor 3-aminobenzamide nor lipid radical scavengers had restorative effects on the mitogenic response. Nor was Con A-stimulated incorporation of [3H]thymidine restored with inhibitors of prostaglandin or leukotriene synthesis, suggesting that inhibition was due to direct effects on the Con A responders, and not indirect effects mediated by arachidonate metabolites. These results indicate that growth-inhibiting doses of radiation trigger the process in lymphocytes that culminates in apoptosis, yet leave the cells partially responsive to mitogenic stimuli.

Lead influences translational or posttranslational regulation of Ia expression and increases invariant chain expression in mouse B cells

The molecular mechanisms governing the increased cell surface expression of major histocompatibility complex (MHC) class II molecules (Ia) on lead-treated mouse B cells was investigated. Lead has been shown to directly cause a selective, two-fold increase in the B cell's surface density of both products of the I region of the mouse MHC, I-A and I-E. In the present study, Western blot analysis showed that Pb increases the total cellular pool of I-A beta-chain by twofold. The increase in cellular I-A was not found to be due to increased messenger RNA (mRNA) for either the alpha- or the beta-chain of I-A. Biosynthetic labeling studies showed that Pb increases the translation or the stability of the Ia-associated invariant chain (Ii or gamma) and possibly the beta-chain of Ia. Collectively these results suggest that Pb increases the B cell's surface Ia by influencing translational or posttranslational regulation of Ia and/or Ia-associated chains.

Structure-function studies of the SERPIN plasminogen activator inhibitor type 1. Analysis of chimeric strained loop mutants

Three chimeric mutants of plasminogen activator inhibitor 1 (PAI-1) have been constructed where the strained loop of wild type PAI-1 (wtPAI-1) has been replaced with a 19-amino acid region from either plasminogen activator inhibitor 2 (PAI-2), antithrombin III, or with an artificial serine protease inhibitor superfamily consensus strained loop. The inhibitors were expressed in Escherichia coli, and the purified proteins had specific activities toward urokinase-type plasminogen activator (uPA) or the single- and two-chain forms of tissue type plasminogen activator (tPA) that were similar to wtPAI-1. Experiments suggest that the strained loop of PAI-1 is not responsible for the transition between the latent and the active conformations or for binding to vitronectin. Second-order rate constants for the interactions with uPA and single- or two-chain tPA were similar to those of wtPAI-1. Values range from a low of 1.8 x 10(5) M-1 s-1 for the interaction of the PAI-2 chimera with single-chain tPA to a high value of 1.6 x 10(7) M-1 s-1 for the consensus mutant with two-chain tPA. This former value is 200 times higher than the reported rate constant for the interaction between PAI-2 and single-chain tPA, suggesting that structures outside of the strained loop are responsible for the major differences in specificity between PAI-1 and PAI-2.

The heavy metal lead exhibits B cell-stimulatory factor activity by enhancing B cell Ia expression and differentiation

Lead (Pb) has been shown to enhance B cell differentiation and to induce T cell proliferation in vitro. Our work demonstrates a direct enhancing effect of Pb on IgM production by T cell depleted-, LPS-activated B cells. Pb also caused a significant, dose-dependent increase in the B cell surface density of both products from the I-region of the murine MHC, I-A and I-E, that was comparable to and within the same time frame as other conventional B cell activators. Pb did not alter B cell surface density of MHC class-I molecules, but it did modulate the levels of other relevant activation Ag such as sIgD and Fc epsilon R. The modulation of the B cell phenotype caused by Pb was not due to release of IL-4 from residual T cells or endotoxin contamination of any culture reagents. Hg also increased cell surface MHC class II molecule density; however, neither Ni, Zn, nor Cd modulated Ia, indicating that immunomodulatory metals have different mechanisms of action. These results suggest that the mechanism of Pb immunopotentiation might be due to increased B-Th cell collaboration and that Pb can act as a B cell stimulatory factor. In addition to the obvious environmental implications of these results, determining Pbs mechanism of action on B cells may yield important information relevant to B cell activation in general.

The heavy metal lead exhibits B cell-stimulatory factor activity by enhancing B cell Ia expression and differentiation

Lead (Pb) has been shown to enhance B cell differentiation and to induce T cell proliferation in vitro. Our work demonstrates a direct enhancing effect of Pb on IgM production by T cell depleted-, LPS-activated B cells. Pb also caused a significant, dose-dependent increase in the B cell surface density of both products from the I-region of the murine MHC, I-A and I-E, that was comparable to and within the same time frame as other conventional B cell activators. Pb did not alter B cell surface density of MHC class-I molecules, but it did modulate the levels of other relevant activation Ag such as sIgD and Fc epsilon R. The modulation of the B cell phenotype caused by Pb was not due to release of IL-4 from residual T cells or endotoxin contamination of any culture reagents. Hg also increased cell surface MHC class II molecule density; however, neither Ni, Zn, nor Cd modulated Ia, indicating that immunomodulatory metals have different mechanisms of action. These results suggest that the mechanism of Pb immunopotentiation might be due to increased B-Th cell collaboration and that Pb can act as a B cell stimulatory factor. In addition to the obvious environmental implications of these results, determining Pbs mechanism of action on B cells may yield important information relevant to B cell activation in general.

Drosophila cell extracts contain a TGF-beta-like activity

Extracts of the Drosophila cell line KCo contain a TGF-beta-like activity. This bioactivity, like mammalian TGF-beta, induces the anchorage-independent growth of rat NRK-49F cells in the presence of EGF, inhibits 3H-thymidine incorporation in the mink epithelial cell line CCL-64 and is acid and heat stable but destroyed by dithiothreitol. On a reverse phase column a single bioactive peak eluted at 37-40% acetonitrile. This TGF-beta-like activity in KCo cells inhibits the growth of the homotypic Drosophila cell line 14-11-23, whereas porcine TGF-beta 1 had no effect.

Dietary fish oil and olive oil supplementation in patients with rheumatoid arthritis. Clinical and immunologic effects

Forty-nine patients with active rheumatoid arthritis completed a 24-week, prospective, double-blind, randomized study of dietary supplementation with 2 different dosages of fish oil and 1 dosage of olive oil. Clinical evaluations were performed at baseline and every 6 weeks thereafter, and immunologic variables were measured at baseline and after 24 weeks of study. The 3 groups of patients were matched for age, sex, disease severity, and use of disease-modifying antirheumatic drugs (DMARDs). Subjects continued receiving DMARDs and other background medications without change during the study. Twenty patients consumed daily dietary supplements of n3 fatty acids containing 27 mg/kg eicosapentaenoic acid (EPA) and 18 mg/kg docosahexaenoic acid (DHA) (low dose), 17 patients ingested 54 mg/kg EPA and 36 mg/kg DHA (high dose), and 12 patients ingested olive oil capsules containing 6.8 gm of oleic acid. Significant improvements from baseline in the number of tender joints were noted in the low-dose group at week 24 (P = 0.05) and in the high-dose group at week 18 (P = 0.04) and 24 (P = 0.02). Significant decreases from baseline in the number of swollen joints were noted in the low-dose group at weeks 12 (P = 0.003), 18 (P = 0.002), and 24 (P = 0.001) and in the high-dose group at weeks 12 (P = 0.0001), 18 (P = 0.008), and 24 (P = 0.02). A total of 5 of 45 clinical measures were significantly changed from baseline in the olive oil group, 8 of 45 in the low-dose fish oil group, and 21 of 45 in the high-dose fish oil group during the study (P = 0.0002). Neutrophil leukotriene B4 production decreased by 19% from baseline in the low-dose fish oil group (P = 0.0003) and 20% in the high-dose group (P = 0.03), while macrophage interleukin-1 production decreased by 38.5% in the olive oil group (P not significant), 40.6% in the low-dose group (P = 0.06), and 54.7% in the high-dose group (P = 0.0005). Tritiated thymidine incorporation in peripheral blood mononuclear cells after stimulation with concanavalin A increased significantly in all 3 groups after 24 weeks, compared with baseline values. We conclude that the clinical benefits of dietary supplementation with omega-3 fatty acids are more commonly observed in patients consuming higher dosages of fish oil for time intervals that are longer than those previously studied. Dietary supplementation with olive oil is also associated with certain changes in immune function, which require further investigation.

Extracellular metallothionein effects on lymphocyte activities

Metal cation influences on the immune response have been reported in a wide variety of experimental systems. These influences can either result in the augmentation or suppression of immunological activities. In order to investigate possible mechanisms of these influences, we examined the role that a metal cation-induced protein, metallothionein (MT), might play. Our findings suggest that thioneins, either as apoproteins or when complexed as Cd,Zn-MT, Zn-MT, or Cd-MT, are capable of inducing lymphocyte proliferation. This level of induction is substantially reduced when Zn,Cd-MT is added to lymphocyte cultures in the presence of 50 microM 2-mercaptoethanol. Apoprotein, Zn,Cd-MT, Zn-MT and Cd-MT also augment LPS-induced proliferation of splenic lymphocytes. Only the Zn,Cd-MT preparation significantly augmented ConA-induced proliferation. Hg-MT and Cu-MT were inhibitory as additions in either LPS or ConA mitogen proliferation assays, and did not stimulate proliferation when added alone to lymphocyte cultures. The capacity to induce proliferation correlates with the measurable thiol level of the particular thionein. Interestingly, Zn,Cd-MT and apothionein had an equivalent number of accessible thiols. Although Zn, Pb, Hg and Cu lowered the number of these sites, the immunoreactivity of these MTs was not altered substantially except by Pb. These results suggest that some metal influences on lymphocytes might be through a thionein intermediary. Our results also demonstrate that thioneins complexed with certain metal cations are detrimental to the normal cellular activities of lymphocytes. At least in these circumstances, MT does not play a role as a protective agent.

Measurement of macrophage adherence and spreading with weak electric fields

A new method to monitor macrophage attachment on protein-coated surfaces and spreading in response to activating agents is described. Murine macrophages were cultured on small gold electrodes coated with protein, and attachment and spreading were detected as electrical impedance changes. The rate of attachment of cells to fibronectin-coated electrodes was measured to be significantly greater than to other proteins tested. Activation agents used included interferon-gamma, lipopolysaccharide and heat killed Listeria monocytogenes. Addition of each agent to macrophages on electrodes resulted in characteristic patterns in the impedance time course with impedance changes as large as 40%.

Oxidatively stressed lymphocytes remain in G0/G1a on mitogenic stimulation

Thiol modifiers and oxidants inhibit lymphocyte activation. To investigate which of the many cell functions sensitive to oxidation are critical in this inhibition, mouse splenic lymphocytes were treated with oxidants prior to exposure to mitogen, and progression into the cell cycle was assayed. Different treatments were used to chemically dissect different potential targets within the cell: copper phenanthroline (CuP), to oxidize surface sulfhydryls; N-ethyl maleimide (NEM), to alkylate extra- and intracellular thiols; and hydrogen peroxide, which generates the highly reactive hydroxyl radical within the cell. Progression into the cell cycle was assayed with acridine orange (AO) and assays of interleukin-2 (IL-2) production and IL-2 receptor (IL-2R) expression. The contribution of ADP-ribosylation to inhibition of mitogenesis was assessed using 3-aminobenzamide (3AB) to inhibit adenosine 5'-diphosphate (ADP)-ribose transferases. The results indicate that the CuP and NEM treatments both produce two independent inhibitory effects, that is, a failure in the production of and response to IL-2. Cells treated with these compounds were able to progress only through G1a upon mitogenic stimulation. H2O2 had more complex effects. Both ADP-ribosylation and modulations of cytosolic Ca2+ were involved in the inhibitory effects. With lower inhibitory doses of H2O2, lymphocytes were completely unresponsive to mitogen and failed to exit Go upon mitogenic stimulation. If intra- and extracellular Ca2+ were buffered before treatment with H2O2, higher concentrations were required, and under these conditions cells were able to enter G1a but could not progress into G1b. Under neither of these conditions could cells produce IL-2 or express IL-2R.

Cell cycle progression of glutathione-depleted human peripheral blood mononuclear cells is inhibited at S phase

Glutathione (GSH) the most abundant nonprotein thiol, is involved in the maintenance of the cellular redox state. In this capacity it may influence lymphocyte responsiveness to various stimuli. We have investigated the requirement of GSH during the activation and proliferation of PBMC. The intracellular GSH content of PBMC was altered by continuous culture or pretreatment with buthionine-S,R-sulfoximine (BSO), a specific and irreversible inhibitor of GSH synthesis. Initial experiments demonstrated that the addition of BSO at the initiation of culture, or shortly thereafter (6 hr), inhibited DNA synthesis and produced a simultaneous decrease in intracellular GSH. It was necessary that the BSO be present in the culture for at least 24 hr prior to the initiation of DNA synthesis for maximal inhibition. Cell cycle analysis revealed that BSO did not affect the entry and progression of PBMC through G1 of the cell cycle, however, entry into S-phase was inhibited in a dose-dependent fashion. These results were further substantiated by the inability of BSO to inhibit IL-2 production and expression of the IL-2R. In addition the timely expression of the transferrin receptor by BSO-treated cells indicated that the block occurred at the G1/S transition. The influence of GSH on early activation events was determined by BSO pretreatments. Lowering the intracellular GSH level of PBMC to less than 10% of the initial content prior to mitogenic stimulation did not impair the ability of these cells to produce IL-2 and express IL-2R, indicating that GSH may not be involved in the generation and response to early activation signals. Furthermore, the removal of BSO from these cultures rapidly reversed its inhibitory effects on DNA and GSH synthesis. In the course of these studies we also observed a modest (17%) albeit consistent increase during activation in the total thiol levels of GSH-depleted PBMC. These thiols may have a key role in the activation process. These data support our hypothesis that GSH is required for lymphocyte proliferation and that additional thiols are involved during the activation process.

Differential lymphocyte growth-modifying effects of oxidants: changes in cytosolic Ca+2

An increase in the concentration of cytosolic Ca+2 ([Ca-2]i) is among the earliest changes seen in mitogen-stimulated lymphocytes and is a consequence of signal transduction which usually results in the initiation of cell cycle progression. However, increased [Ca+2]i has also been correlated with cytotoxicity. We have determined whether modulations of [Ca+2]i are involved in the functional inactivation of cells observed with sublethal concentrations of oxidants. Specifically, [Ca+2]i was measured in mouse splenic lymphocytes that were treated with different oxidants in order to determine if oxidative stress interferes with mitogen-stimulated increases in [Ca+2]i, if oxidants themselves modulated [Ca+2]i, and, if so, whether such Ca+2 modulations by oxidants had stimulatory or inhibitory effects on the response of lymphocytes to mitogens. The oxidants employed were copper phenanthroline (CuP; surface thiol oxidizer), N-ethyl maleimide (NEM; permeant thiol alkylator), hydrogen peroxide (H2O2; generates hydroxyl radical within the cell), and radiation (Cs137; generates hydroxyl radical by radiolysis). Growth of all treated cells was equally inhibited upon stimulation with Con A or PMA/A23187, suggesting that all the oxidants inhibited cell functions required distal in activation to the transduction pathway utilized by Con A but bypassed by PMA/A23187. Doses of CuP, NEM, and radiation which fully inhibited Con A-stimulated proliferation had little effect on resting or mitogen-stimulated changes of [Ca+2]i, but H2O2 doses which fully inhibited proliferation increased [Ca+2]i in unstimulated cells and prevented the increase normally caused by Con A. Both intra- and extracellular Ca+2 contributed to the increased [Ca+2]i seen in unstimulated cells. An elevated [Ca+2]i was sufficient to reduce responsiveness, since pharmacologically increasing the [Ca+2]i with the ionophore A23187 rendered lymphocytes less responsive to Con A. Unlike A23187, H2O2 was unable to synergize with PMA, suggesting that the H2O2-induced increase of [Ca+2]i delivered predominantly negative signals to the cell. The results also suggest that [Ca+2]i utilization by Con A versus PMA-activated lymphocytes must be different. When cells were treated with H2O2 under conditions where intracellular and extracellular Ca+2 were chelated with BAPTA and EGTA, respectively, the response to Con A was restored. Under these conditions, higher concentrations of H2O2 were required to inhibit the response to Con A. Our results indicate that signal transduction may be compromised in cells treated with H2O2, but not in cells treated with CuP, NEM, or radiation.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell cycle progression of glutathione-depleted human peripheral blood mononuclear cells is inhibited at S phase

Glutathione (GSH) the most abundant nonprotein thiol, is involved in the maintenance of the cellular redox state. In this capacity it may influence lymphocyte responsiveness to various stimuli. We have investigated the requirement of GSH during the activation and proliferation of PBMC. The intracellular GSH content of PBMC was altered by continuous culture or pretreatment with buthionine-S,R-sulfoximine (BSO), a specific and irreversible inhibitor of GSH synthesis. Initial experiments demonstrated that the addition of BSO at the initiation of culture, or shortly thereafter (6 hr), inhibited DNA synthesis and produced a simultaneous decrease in intracellular GSH. It was necessary that the BSO be present in the culture for at least 24 hr prior to the initiation of DNA synthesis for maximal inhibition. Cell cycle analysis revealed that BSO did not affect the entry and progression of PBMC through G1 of the cell cycle, however, entry into S-phase was inhibited in a dose-dependent fashion. These results were further substantiated by the inability of BSO to inhibit IL-2 production and expression of the IL-2R. In addition the timely expression of the transferrin receptor by BSO-treated cells indicated that the block occurred at the G1/S transition. The influence of GSH on early activation events was determined by BSO pretreatments. Lowering the intracellular GSH level of PBMC to less than 10% of the initial content prior to mitogenic stimulation did not impair the ability of these cells to produce IL-2 and express IL-2R, indicating that GSH may not be involved in the generation and response to early activation signals. Furthermore, the removal of BSO from these cultures rapidly reversed its inhibitory effects on DNA and GSH synthesis. In the course of these studies we also observed a modest (17%) albeit consistent increase during activation in the total thiol levels of GSH-depleted PBMC. These thiols may have a key role in the activation process. These data support our hypothesis that GSH is required for lymphocyte proliferation and that additional thiols are involved during the activation process.

Acidic cellular environments: activation of latent TGF-beta and sensitization of cellular responses to TGF-beta and EGF

Transient (about 2 hr) acidification to approx. pH 5.0 of agar-gelled overlayers containing untransformed NRK-49F or KiMSV-transformed NRK-49F cells in the presence of fetal calf serum or crude 49F-cell conditioned medium, as sources of latent TGF-beta, elicited EGF-dependent colony formation of 49F cells and inhibited spontaneous growth of transformed cells. Pure, active TGF-beta (porcine, type I) had the same effects on these respective cell types, suggesting that the above results were due to activation of latent TGF-beta in the transiently acidic cellular environment. Similar acidifications in the absence of a source of latent TGF-beta enhanced the positive growth response of 49F and AKR-2B cells to EGF and active TGF-beta and also the negative growth response of KiMSV-transformed 49F cells to active TGF-beta. These results are compatible with the idea that acidic cellular environments, particularly in tumor tissues, are conducive to activation of latent TGF-beta, perhaps in conjunction with other activating mechanisms, and to an enhanced response to some growth factors. However, the heterogeneity of cell populations within tumoral masses presents an obstacle to a clear understanding of the consequences of such activation.

Evidence for a novel growth factor in Xenopus oocytes

Xenopus oocytes contain a novel growth factor, as determined by its effect on the anchorage-dependent and -independent growth of various rat cells and on a Xenopus cell line; it is destroyed by trypsin, acidification (pH 2.0), heating (100 degrees C, 3 min), 8 M urea but not by dithiothreitol. Gel filtration of this activity in nondissociating conditions suggests the existence of aggregates and the presence of a very high (approximately 2000 Kd) and a much lower (approximately 30 Kd) form.

Lead-induced alterations of in vitro bone marrow cell responses to colony stimulating factor-1

Bone marrow cell responsiveness to hematopoietic growth factors is an integral part of immune responsiveness. Since host resistance is often dependent on bone marrow cell responsiveness and Pb alters host resistance, the influence of Pb on bone marrow cell responsiveness to the hematopoietic growth factor CSF-1 was evaluated. Cell number, soft agar colony formation, cell cycle analysis, as well as 3H-thymidine incorporation were utilized to determine if CSF-1 driven bone marrow-derived macrophage (BMDM) proliferation in vitro is altered in the presence of PbCl2. Data obtained indicate that Pb potentiates the ability of CSF-1 to stimulate thymidine incorporation by BMDM; however, colony formation is inhibited reversibly, and the absolute number of cells in culture is adversely affected by Pb. Propagation of BMDM appears to be more sensitive to Pb (100 nM) than other immune parameters. The decrease in bone marrow cell responsiveness to CSF-1 in the presence of Pb observed in this system may contribute to the decrease in host resistance observed in Pb-exposed animals.

Modification of lipoprotein patterns and retardation of atherogenesis by a fish oil supplement to a hyperlipidemic diet for swine

We have studied the effect of addition of 30 ml cod liver oil (FO) daily to a highly atherogenic butter (BT) diet for swine on lesion development in the coronary arteries and aorta, plasma lipoprotein (LP) patterns, plasma levels of thiobarbituric acid-reactive substances (TBARS) and on tritiated thymidine-labeling indices ([3H]TdR LI) of smooth muscle cells (SMC) and monocyte/macrophages (M/M phi) in the atherosclerotic lesions. Seventeen male Yorkshire swine (11.1 +/- 0.4 kg) were divided into 3 groups: BT (n = 6), BT + FO (n = 6) and mash (n = 5). They were fed the respective diets for 4 months. Terminally, fasting plasma was obtained and cholesterol contents were determined in various fractions of lipoproteins separated by density gradient ultracentrifugation, Pevikon block electrophoresis and immunoelectrophoresis. Apoprotein (B, A-I, E and C) contents of the plasma and lipoprotein fractions were determined by polyacrylamide gel electrophoresis and densitometry of gels stained with Coomassie blue. Swine were injected intramuscularly with 0.5 mCi/kg of [3H]TdR 2 h before death. The aorta and coronary arteries were perfusion fixed in situ under anesthesia. Samples were obtained for microscopic morphometry, autoradiography and immunohistochemistry from distal abdominal aorta, thoracic aorta, and proximal coronary arteries; left main (LM), left anterior descending (LAD), left circumflex (LCX), right main (RM), and right coronary artery (RCA). On the BT diet without FO there was extensive atherosclerotic (AS) lesion development, which was drastically reduced by the addition of FO to the BT diet in all sites by from 71 to 94%. The overall plasma cholesterol (CH) levels were reduced only modestly by the FO (816 +/- 64 to 629 +/- 14 mg/dl) but the distribution of CH in the various lipoprotein classes was remarkably altered. The CH in the large lipoprotein molecules containing both B and E apoproteins was reduced from 488 +/- 84 to 204 +/- 17 mg/dl by the FO with an almost corresponding increase in the conventional LDL molecules containing apo B only (158 +/- 29 to 344 +/- 15 mg/dl). We offer the hypothesis that the large apo B,E containing molecules are much more atherogenic than the smaller apo B containing molecules. This hypothesis is supported by a highly significant correlation between extent of lesion development in all arterial sites and plasma levels of CH in apo B,E containing lipoproteins. Plasma TBARS were elevated by the BT + FO diet but seemed to have no significant effect on the lesions.(ABSTRACT TRUNCATED AT 400 WORDS)

The inhibitory effects of N-ethylmaleimide, colchicine and cytochalasins on human T-cell functions

The thiol-alkylating agent, N-ethylmaleimide (NEM), was found to inhibit the response of human peripheral blood mononuclear cells to the T-cell mitogen, concanavalin A (Con A). NEM (10 microM) blocked Con A-induced agglutination, production of interleukin-2 (IL-2) and expression of the IL-2 receptors (Tac) without toxicity. In order to determine whether the effects of NEM on lymphokine production were related to inhibition of agglutination, we compared the immunosuppressive effects of NEM with those of cytochalasin A, cytochalasin B and colchicine. NEM did not inhibit E-rosette (ER) formation, suggesting that it does not interfere with actin filaments. Low concentrations of NEM (4 microM) inhibited IL-2 production and Tac expression without inhibiting agglutination, while 6-10 microM NEM blocked agglutination and DNA synthesis as well. In contrast, 5-10 microM cytochalasin B (CB) inhibited ER formation, agglutination, Tac expression and DNA synthesis, but augmented IL-2 production by three- to ten-fold. Colchicine (0.1-10 microM) had no effect on ER formation or agglutination and augmented IL-2 production by as much as 18-fold. However, colchicine blocked Tac expression by greater than 40% and DNA synthesis by greater than 80%. Cytochalasin A (CA), which has the thiol-reactive properties of NEM, the actin filament-disrupting properties of CB, and the microtubule-disrupting properties of colchicine, exhibited the immunosuppressive effects of all three compounds. These studies suggest that the inhibitory effects of NEM on IL-2 production do not appear to be due to reactivity with the cytoskeleton, but are probably due to effects on signal transduction pathways leading to IL-2 production and expression of IL-2 receptors.

Immunomodulation of in vitro antigen presentation by cations

The ability of various cations to alter an antigen-specific (ovalbumin) T cell activation system in vitro has been assessed. This in vitro system includes analysis of antigen capture, processing, and presentation by antigen presenting cells (APC) (splenocytes, B cells or macrophages) in a major histocompatibility complex (MHC) restricted fashion and the evaluation of the activation of a T-cell hybridoma, DO-11.10, which is specific for "processed" ovalbumin in association with I-Ad. Activation is determined by production of IL2 which is quantitated in a bioassay with HT-2 cells. Numerous metals (10 and 100 microM) were screened in the coculture assay (APC and DO-11.10 plus ovalbumin). Metals with inhibitory effects were Cd greater than Cu greater than Pb greater than Zn. Co and Cr had no modulatory effect and Ni had an enhancing effect (increased IL2 production). The effects of the modulatory metals were further assessed for influences on the individual cellular components of this system. Cd was toxic to all cell types whereas Cu was toxic only to irradiated splenocytes and Do-11.10. Pb was the only metal which was not toxic to any cell type but still inhibited antigen presentation. To prevent influences of metals on DO-11.10 or carryover into the bioassay, APC were preincubated with metals and then assessed for presentation capability. After preincubation, only Cd, Pb, and Cu were inhibitory. The inhibition by Cd was due to toxicity. Cu inhibited only irradiated splenocyte presentation and this effect was due to toxicity. Pb inhibition was due to a mechanism other than toxicity and its biochemical influences on APC are discussed.

Bifunctional activity of transforming growth factor type beta on the growth of NRK-49F cells, normal and transformed by Kirsten murine sarcoma virus

Transformation of rat NRK-49F cells (49F) by Kirsten murine sarcoma virus (Ki-MSV) renders these cells (Ki-49F cells) capable of autonomous anchorage independent (AI) growth. As compared to nontransformed 49F cells, the transformation by Ki-MSV does not modify the cell response to transforming growth factor-beta (TGF-beta) in monolayer conditions, but alters it in A I growth conditions. The growth of nontransformed or Ki-MSV-transformed adherent 49F cells is slowed down by porcine TGF-beta, and this effect is reversed by epidermal growth factor (EGF). This decrease in the cell growth rate, induced by TGF-beta, does not affect the cloning efficiency of untransformed and transformed adherent 49F cells. Contrarily, porcine TGF-beta decreases the A I cloning efficiency of Ki-49F cells in agar-gelled medium; this effect is only partly reversed by EGF, which does not synergise with TGF-beta to enhance the A I growth as in the case of untransformed 49F cells. Media conditioned by 49F cells, Ki-49F cells, and chicken embryo fibroblasts contain a latent TGF-beta whose capacity to promote the A I growth of 49F cells and to inhibit that of Ki-49F cells is unmasked by acidification. The same situation exists concerning TGF-beta from human platelets. Neutral extracts are inefficient in both tests of promotion and inhibition of A I growth and contain an acid-activable component with an apparent molecular weight of 600 kd. In acid extracts, a 5-9 kd apparent molecular weight component is responsible for the A I growth enhancement of 49F cells and the A I growth inhibition of Ki-49F cells. Further purification by reverse phase chromatography shows that both activities strictly coelute at the same point (32%) of an acetonitrile gradient. These results indicate that TGF-beta is present in physiological conditions as a latent form which requires activation for inhibiting the A I growth of transformed cells as well as for enhancing that of 49F cells.

Effect of lead on macrophage function

Lead (Pb) has been shown to alter various parameters of immune function such as host resistance and antibody formation. In addition, various heavy metals have been implicated as inducers of autoimmunity. In these experiments, macrophages, isolated from the peritoneal cavity of mice exposed to various doses of lead in vivo as well as cells exposed in vitro were tested for the following immunologic parameters: phagocytosis, antigen presentation, interleukin 1 production, and their ability to stimulate the autologous mixed lymphocyte reaction (AMLR). The results obtained indicate that Pb appears to alter the ability of macrophages to present antigen by enhancing the AMLR while having no effect on phagocytosis or IL-1 production. These data suggest that Pb may interfere with antigen-specific interactions between macrophages and T cells.