Vitamin E enhances Ca(2+)-mediated vulnerability of immature cerebellar granule cells to ischemia

The effects of vitamin E on lipid peroxidation, intracellular free Ca2+ concentration ([Ca2+]i), and cell death were investigated in the postischemic immature cerebellum. Deprivation of oxygen and glucose for 10-min in a suspension of freshly dissociated granule cells from the cerebellum of 9-day-old male rat pups resulted in a recovery-induced consumption of cell nonenzymatic antioxidants (ascorbic acid, glutathione, and alpha-tocopherol) and development of membrane lipid peroxidation as measured by the thiobarbituric acid method. The rate of lipid peroxidation of the postischemic cells was stimulated, not reduced, by treatment of the cells with vitamin E (5-30 microM alpha-tocopherol phosphate). In flow-cytometric studies a 10-min period of ischemia resulted in a small increase in intracellular calcium concentration, lipid peroxidation products and cell death, but in the presence of alpha-tocopherol the same treatment caused a dramatic increase in cell death, accompanied by a large increase in [Ca2+]i and lipid peroxidation products. Pretreatment of the cells with a mixture of three antioxidants (vitamin C/rutin/ubiquinol-10, 10/5/1) or nickel (Ni2+) reduced the alpha-tocopherol-induced increases in [Ca2+]i, and cell death. Hydrogen peroxide (1 mM) and the water-soluble analogue of vitamin E, trolox (50 microM), mimicked the effect of vitamin E on lipid peroxidation in the postischemic cells. Pretreatment of the cells with the intracellular Ca2+ chelator BAPTA-AM, reduced both the alpha-tocopherol-induced increase in [Ca2+]i and cell death. The effect of vitamin E on [Ca2+]i was age dependent and decreased abruptly during maturation of the cerebellum between the first and second weeks of life. Results of in vitro treatment of the immature cerebellar cells with the water-soluble form of vitamin E (alpha-tocopherol phosphate) suggest that, after consumption of cellular co-antioxidants, vitamin E may be converted to an alpha-tocopheroxyl radical, which act as a toxic prooxidant as cellular bioenergetics deteriorate.

Differential effects of lead and cAMP on development and activities of Th1- and Th2-lymphocytes

Lead (Pb) is known to have detrimental effects on the central nervous, hematopoietic, renal, and immune systems. Herein, it is demonstrated that Pb can skew T cell reactivities by preferentially enhancing the development of Th2 cells and inhibiting the development of Th1 cells. When naive splenic CD4+ T cells from DO11.10 ovalbumin-specific transgenic (OVA-tg) mice or OVA-tg/RAG2-/- mice were developed in vitro in the presence of Pb, preferential skewing toward Th2 cells was evident. The Pb-driven skewing toward Th2 was blocked significantly in the presence of exogenous IL-12 or anti-IL-4 mAbs. Although Pb and dibutyryl cAMP (dbcAMP) appear to have similar effects on the development and reactivity of Th1 cells, unlike Pb, dbcAMP did not enhance Th2 development/activity. Further evidence of Pb's differential T cell effects was observed, in that regardless of the activation stimuli (Ag/APC; anti-CD3; PMA + ionomycin), the addition of PbCl2 consistently resulted in significant inhibition of IFN gamma production by a Th1 clone and in increased IL-4 production by a Th2 clone. In vitro addition of IL-12 overcame Pb's inhibition of Th1 cells. Th1 cells treated with a phosphodiesterase inhibitor had significantly elevated [cAMP]i levels following anti-CD3 activation in the presence of Pb, suggesting that Pb may inhibit Th1 development by enhancing adenylate cyclase activity and elevating the [cAMP]i level. Similar to Pb, a low concentration (10 microM) of dbcAMP inhibited IFN gamma production by Th1, which was prevented by IL-12; however, inhibition of protein kinase A activity by KT5720 did not reverse these effects. These results indicate that the environmental toxicant Pb can modify immune reactivities by significantly altering the differentiation of precursor or naive Th cells as well as by directly inhibiting Th1 cells and stimulating Th2 cells.

Lead potentiates cytokine- and glutamate-mediated increases in permeability of the blood-brain barrier

We have measured the transendothelial electrical resistance across the blood-brain barrier (BBB) with a microelectrode technique and determined the effects of subcutaneous injections (five injections over ten days) of lipopolysaccharide (LPS, 100 ng/g), recombinant mouse interleukin-6 (IL-6, 5 ng/g), and/or inorganic lead (lead, 2.5 5 micrograms/g) on the ion permeability of arterioles in the temporoparietal cortex of anaesthetized mice between 10 and 40 days of age. In controls the electrical resistance increased with age. It was decreased in animals treated with IL-6, but unaffected by lead at the different ages studied. In IL-6 treated mice, repeated neonatal exposure to lead (five injections between 2 and 10 days after birth) caused a delay in the increase in arteriole resistance with age. LPS injections caused a 36% increase in ion permeability of the BBB in twenty-day-old mice, and lead potentiated this effect of LPS. Intra-arterial injections of glutamate did not alter vascular resistance, but topical applications of glutamate on the cerebrum caused a reversible decrease in the resistance in mice not treated with lead, and an irreversible decrease in mice treated with lead. Injections of glutamate in the lumen of arterial vessels in the parietal and temporoparietal brain areas of mice pretreated with lead and LPS, plus a topical application of glutamate, caused depolarization of neurons in the temporoparietal cortex. These results suggest that disruption of the BBB can allow serum glutamate to penetrate the brain, causing further disruption of the BBB, and that lead irreversibly potentiates this cascade of harmful events.

Lipopolysaccharide and interleukin-6 enhance lead entry into cerebellar neurons: application of a new and sensitive flow cytometric technique to measure intracellular lead and calcium concentrations

The distribution of intracellular ionized lead (Pb) and calcium in dissociated cerebellar cells of ten-day-old mice was measured by flow cytometry. There are no fluorescent probes specific for lead, whereas commonly used fluorescent calcium indicators bind heavy metals with greater affinity than they do calcium, which impedes discrimination of lead- and calcium-induced fluorescence changes. Therefore, we developed a method to determine [Pb2+]i and [Ca2+]i by employing a combination of the calcium indicator fluo-3 and the heavy-metal chelator TPEN. Using these methods, we studied the effects of multiple in vivo exposure (five subcutaneous injections over 10 days) to lipopolysaccharide (LPS, 100 ng/g), recombinant mouse interleukin-6 (IL-6, 5 ng/g) and/or inorganic lead (lead, 2.5 micrograms/g) on lead and calcium concentrations. Control cells had [Cai] of 112 nM. Lead exposure alone had little effect on [Ca2+]i and resulted in a mean [Pb2+]i of about 7 pM, and did not alter cell volume. A significant fraction of cells (about 44% of living cells) from animals treated with lead plus LPS were swollen, as determined by analysis of the light scattering pattern, and there was a small increase in the number of dead cells, identified with the nucleic acid stain, 7-aminoactinomycin. While [Ca2+]i was not significantly increased in animals treated with either only LPS or IL-6, lead and calcium concentrations were increased in animals exposed to lead and LPS or IL-6 in both the non-swollen and swollen cells, with a mean value of (Pb2+)i of 32 pM and (Ca2+)i of 155 nM in cells not swollen. Electrophysiological analysis showed that LPS injections caused decreases in the membrane potential of endothelial cells of the blood-brain barrier (BBB) and lead potentiated the effect of LPS. IL-6 mimicked the effects of LPS, but was less potent. Thus these experiments indicate a synergistic interaction between lead and cytokines on biophysical properties of both neurons and endothelial cells of the BBB.

Plasminogen activator inhibitor-1 contains a cryptic high affinity binding site for the low density lipoprotein receptor-related protein

Much of the controversy surrounding the binding of plasminogen activator inhibitor-1 (PAI-1) to the low density lipoprotein receptor-related protein (LRP) may be due to the labile structure of PAI-1 and the distinct conformations that it can adopt. To examine this possibility and to test the hypothesis that PAI-1 contains a specific high affinity binding site for LRP, a sensitive and quantitative assay for PAI-1 binding to LRP was developed. This assay utilizes a unique PAI-1 mutant that was constructed with a hexapeptide tag at the NH2 terminus, which is recognized by the protein kinase, heart muscle kinase and can be specifically labeled with 32P. Our results show that only 32P-PAI-1 in complex with a proteinase binds LRP with high affinity and is efficiently endocytosed by cells, indicating that a high affinity site for LRP is generated on PAI-1 only when in complex with a proteinase. In addition, PAI-1 in complex with different proteinases is shown to cross-compete for LRP binding, demonstrating that the binding site is independent of the proteinase and therefore must reside on the PAI-1 portion of the complex. Finally, mutagenesis of PAI-1 results in loss of LRP binding, confirming that the high affinity binding site is located on PAI-1 and suggesting that the LRP binding site lays within a region of PAI-1 previously shown to contain the heparin binding domain.

Differential production of interleukin-6 in the brain and spleen of mice treated with lipopolysaccharide in the presence and absence of lead

The heavy metal lead (Pb) markedly augments the lethality of endotoxin in laboratory animals. Much of the tissue injury produced by endotoxin is thought to be mediated by cytokines. Thus, the effects of Pb on the regulation of interleukin-6 (IL-6), a proinflammatory cytokine that shows high correlation with symptoms of endotoxic shock, and the levels of corticosterone, a hormone produced to prepare the body to cope with stress, upon lipopolysaccharide (LPS; endotoxin) administration were investigated. After intravenous administration of LPS, the kinetics of IL-6 gene expression by Northern blot analysis revealed a rapid increase of IL-6 mRNA, which peaked by 2 h in the spleens and 3 h in the brains of B6C3F1 female mice, with or without Pb exposure. Peak production of IL-6 protein after LPS challenge was observed at 2 h in the spleens and 3 h in the sera regardless of Pb-treatment. However, Pb-exposed mice showed an altered kinetic profile of IL-6 appearance in the brain, in that the levels of IL-6 in the brains peaked at 4 h rather than 3 h, the peak for the control mice. Moreover, at two time points, the amounts of IL-6 were found to be higher in the brains of Pb-treated mice. Increases in IL-6 were detected in multiple areas of the brain, but Pb did not significantly enhance this level in any area. The observation of both IL-6 transcripts and protein in the brains of mice upon peripheral LPS administration is indicative of local de novo synthesis of IL-6 in the brain. IL-6 production in the brain may contribute to the centrally mediated effects of IL-6, since IL-6 in the brain is known to activate the hypothalamus-pituitary-adrenal (HPA) axis. Upon LPS challenge, corticosterone levels peaked at the 2-h time point and stayed elevated for 6 h regardless of Pb exposure. The increases in brain IL-6 and its extended expression by Pb do not appear to have significantly altered the HPA axis on the basis of the corticosterone level, but brain IL-6 is known to affect multiple brain functions such as long-term potentiation.

Neuroserpin, a brain-associated inhibitor of tissue plasminogen activator is localized primarily in neurons. Implications for the regulation of motor learning and neuronal survival

A cDNA clone for the serine proteinase inhibitor (serpin), neuroserpin, was isolated from a human whole brain cDNA library, and recombinant protein was expressed in insect cells. The purified protein is an efficient inhibitor of tissue type plasminogen activator (tPA), having an apparent second-order rate constant of 6. 2 x 10(5) M-1 s-1 for the two-chain form. However, unlike other known plasminogen activator inhibitors, neuroserpin is a more effective inactivator of tPA than of urokinase-type plasminogen activator. Neuroserpin also effectively inhibited trypsin and nerve growth factor-gamma but reacted only slowly with plasmin and thrombin. Northern blot analysis showed a 1.8 kilobase messenger RNA expressed predominantly in adult human brain and spinal cord, and immunohistochemical studies of normal mouse tissue detected strong staining primarily in neuronal cells with occasionally positive microglial cells. Staining was most prominent in the ependymal cells of the choroid plexus, Purkinje cells of the cerebellum, select neurons of the hypothalamus and hippocampus, and in the myelinated axons of the commissura. Expression of tPA within these regions is reported to be high and has previously been correlated with both motor learning and neuronal survival. Taken together, these data suggest that neuroserpin is likely to be a critical regulator of tPA activity in the central nervous system, and as such may play an important role in neuronal plasticity and/or maintenance.

Interleukin-12 promotes enhanced resistance to Listeria monocytogenes infection of lead-exposed mice

The heavy metal lead (Pb) has been shown to downregulate various parameters of cell-mediated immune (CMI) responses. This inhibition of CMI responses by Pb is exemplified by a higher mortality rate upon infections with sublethal doses of a variety of pathogens. Unlike Pb, which lowers host resistance, interleukin-12 (IL-12) exerts a substantial stimulatory influence on the host response to intracellular bacteria such as Listeria monocytogenes. To explore the influence of IL-12 in mice rendered susceptible to Listerial infection by oral exposure to Pb, we determined bacterial burdens and production of interferon gamma (IFN-gamma). As expected, Pb-exposed mice had increased morbidity due to higher Listerial titers as compared to control mice. However, administration of exogenous IL-12 reversed the Pb-induced inhibition of host defense and boosted the resistance of the non-Pb-treated mice. The enhanced CMI responses observed in both IL-12-treated groups were accompanied with elevations of IFN-gamma in the sera and spleens. Significant reduction in the number of viable Listeria in Pb-exposed mice upon IL-12 administration suggests that the processes downstream of IL-12 production were intact in the Pb-exposed mice and that the inhibition by Pb was due to the lack of functional IL-12. Alternatively, the exogenous IL-12 may have overcome a downstream effect by enhancing an secondary pathway. Support for the former hypothesis is based on the observation that Pb induced elevated levels of p40 splenic messenger RNA since increased p40 expression would result from lack of IL-12 formation. Contrary to the IFN-gamma levels, significantly higher levels of IL-6 and corticosterone were observed in the sera and spleens of Pb-exposed mice upon infection, suggesting heightened stress in the absence of IL-12. Overall, the results suggest that an environmental pollutant such as Pb can enhance the stress response, which naturally occurs during an infection, and can further compromise health by lowering host resistance by altering cytokine levels.

Long-term exposure to methotrexate induces immunophenotypic changes, decreased methotrexate uptake and increased dihydrofolate gene copy number in Jurkat T cells

Methotrexate (MTX) treatment of rheumatoid arthritis may require increasing doses to maintain clinical efficacy. An overall plateau of clinical response is reached after only six months of treatment. To study the immunologic, biochemical and genetic effects of MTX on T cells, the Jurkat T cell line was made MTX-resistant by serial addition of methotrexate sodium into culture medium. Cells proliferated and divided successfully in MTX concentrations ranging to 15 microM. MTX resistance of Jurkat T cells in vitro was accompanied by significantly (P < 0.05) decreased expression of CD2, CD3, CD4, CD28, and CD69, IL-2 production, and MTX uptake assessed by cell association or disassociation of 3[H]-MTX or fluoresceinated MTX (FMTX), respectively. In addition, there was DHFR gene amplification and increased levels of DHFR in all resistant cell lines. Both permanent and transient phenotypic changes developed in resultant cell lines exposed to increasing concentrations of MTX in vitro. Expression of CD4 and CD25 and sensitivity to MTX returned to near-parental levels after removal of MTX from culture medium, whereas expression of CD26 and MTX uptake were significantly increased. Expression of CD2, CD3, CD69 and IL-2 production as well as the DHFR levels did not return to the parental phenotype after removal from MTX. We conclude that MTX-cultured cells express depressed levels of cell-surface markers vital for T cell function and activation. The return of enhancement of these cell-surface markers critical to T cell activation suggests a possible mechanism for the severe flares experienced by rheumatoid arthritis patients when drug treatment is discontinued.

Flow cytometric measurements of neuronal death triggered by PCBs

We have examined the effects of several individual polychlorinated biphenyl (PCB) congeners and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on viability and intracellular calcium concentration in acutely dissociated cerebellar granule cell neurons obtained from 7-14 day old rat pups, using a flow cytometer. Cell death was determined using the fluorescent dye, 7-aminoactinomycin-D (7-AAD), while intracellular calcium concentration was determined using Fluo-3-AM. When acutely isolated neurons were exposed to 2,4,4' trichlorobiphenyl (2,4,4', there was a dose- and time-dependent loss of viability beginning within 5 min. At a concentration of 100 microM, 80% of neurons were dead within 45 min. Loss of viability was preceded by an apparent increase in cell granularity. No significant cell death was observed upon exposure to the highly dioxin-like coplanar PCB, 3,4,5,3',4', at a concentration of 100 microM or by TCDD at a concentration of 0.1 microM. A slight loss of viability was seen with the ortho 2,6,2',6' and the coplanar 3,4,3',4', but for both it was small. All of the PCB congeners caused an early, transient increase in intracellular free calcium concentration, although TCDD did not. A small, late increase in intracellular free calcium was seen with 2,4,4', probably reflecting events leading to loss of viability. We conclude that at least one PCB congener, 2,4,4', is very neurotoxic and can cause rapid death of cerebellar granule cells.

In utero management of hydrops fetalis caused by critical aortic stenosis

Hydrops fetalis is rarely associated with congestive heart failure caused by obstructive left-sided heart lesions. There are rare cases of live born neonates with critical congenital valvar aortic stenosis and hydrops reported in the literature, all with fatal outcomes. This report describes, to the best of our knowledge, the first two newborns who were diagnosed prenatally to have hydrops fetalis caused by critical valvar aortic stenosis, who were treated prenatally with digoxin and who postnatally had successful percutaneous balloon aortic valvuloplasty. Both patients had not only left but right ventricular dysfunction. We speculate that right ventricular dysfunction was a contributing factor in the development of hydrops in these patients and in utero medical therapy with digoxin is associated with resolution of the hydrops before delivery.

In vivo the environmental pollutants lead and mercury induce oligoclonal T cell responses skewed toward type-2 reactivities

An oligoclonal utilization of Vbetas has been reported for pathogenesis of several autoimmune diseases, anti-tumorigenic activity, and superantigen-regulation of thymic T cell development. Altered ratios of Th1 and Th2 cells also are observed in immunodysregulations, leading to impaired cell-mediated immunity with an increased incidence of infectious disease or cancer and/or aberrant immunity that could culminate with an autoimmune disease. Lead (Pb) and mercury (Hg) are known pollutants with immunodisrupting activities; Hg is known to cause autoimmune glomerulonephritis. Both metals are known to suppress host resistance to pathogens. To further evaluate the manner by which these metals cause in vivo immunomodulation, their in vivo effects on Vbeta expression were evaluated along with the Th1 and Th2 frequency. Exposure of BALB/c mice to PbCl2 or HgCl2 induced an oligoclonal response with increases of Vbeta 5+, Vbeta 7+, and Vbeta 13+ CD4+ splenic, but not thymic, T cells. A significantly skewed frequency of Pb-induced splenic Th2 cells expressing Vbeta 7 or Vbeta 13 over Th1 cells was determined by limiting dilution analysis, but this Th2 predominance was not observed with CD4+ T cells expressing Vbeta 8. DO11.10 transgenic mouse exposed to Pb and antigen also demonstrated a skewed type-2 response evidenced by significantly increased IgE levels, lowered IFN-gamma levels, and increased IgG1 and lowered IgG2a anti-OVA levels. Even in the absence of specific T cell responses to a Pb-induced antigen, due to the restricted T cell specificity in the transgenic mouse model, Pb still was able to skew the response toward type-2 reactivity. However, this skewing occurred only in the presence of antigen. Therefore, the Pb-induced oligoclonal T cell response in BALB/c mice which must be initiated by self-antigens and was predominately type-2 may be responsible for autoantibody production and the detrimental health effects associated with Pb exposure.

Transforming growth factor-beta1 enhances the lethal effects of DNA-damaging agents in a human lung-cancer cell line

In tissue culture conditions, exogeneous active transforming growth factor-beta1 (TGF-beta1) enhances the lethal effect of DNA-damaging agents (UV-C, gamma rays, cisplatin, methotrexate and 5-fluorouracil) toward human A549 cells and mink Mv1Lu cells, as detected by the loss of their capacity to give rise to colonies; both these cell lines harbor a wild-type p53, as determined by immunoprecipitation. Contrastingly, the sole effect of the cytokine used alone is to inhibit reversibly the multiplication of the same cells without further impairing, once withdrawn from their environment, their capacity to divide and give rise to colonies. The lethal synergy between TGF-beta1 and UV-C was studied on mink and human cell lines, and the biomodulation by TGF-beta1 of cell killing by cisplatin, gamma rays, 5-fluorouracil or methotrexate was tested only on human cells. As investigated with UV-C-irradiated human A549 cells, TGF-beta1 appears to enhance apoptosis rather than to disturb the repair of DNA photolesions (mainly pyrimidine dimers) by the nucleotidic excision repair pathway according to results of nucleosomal ladder and comet tests. Our data raise the possibility that, in vivo, TGF-beta1 might affect the curative and/or undesirable secondary side effects of cancer therapy.

Assessment of immunotoxicity by multiparameter flow cytometry

Flow cytometry is a unique technology useful in the examination of effects of immunotoxic agents on target cells of the immune system. The purpose of this workshop was to provide an overview of the use of flow cytometry in new and established models of immunotoxicity, with emphasis on the potential applications, assay validation, and potential pitfalls. This overview begins with a discussion of methods useful in the assessment of Ca2+-dependent mechanisms of lymphoid cell activation in surface marker-defined human B cells, T cells, and monocytes. A discussion of the use of flow cytometry in analysis of apoptosis is also presented in this paper. The second paper presents data on the development and use of flow cytometry as an alternative to a Cr51 release assay for an assessment of cytotoxic T cell activation. The use of surface markers for characterizing and distinguishing the effects of chemical irritants from sensitizers is next presented, followed by an overview of the use of fluorescent probes to assess cell thiol status and overall oxidant-induced injury to lymphoid cells. Finally, an interlaboratory study designed to compare and evaluate the use of flow cytometry procedures in rat splenic cell subtyping is presented. Overall, these studies demonstrate the utility of flow cytometry assays in immunotoxicologic research, but further efforts are needed in the validation of many of these assays for routine use in immunotoxicologic testing.

Modulation of T-helper cell populations: potential mechanisms of respiratory hypersensitivity and immune suppression

Information presented at this symposium indicates that modulation of Th cell responses is one means by which xenobiotics may cause immunotoxicity. A shift from Th1 to Th2 responses can enhance both infectious and allergic disease. Hence, in some cases, a common mechanism may be responsible for effects that are generally considered to be very different. Because cytokines produced in the inflammatory process play a role in modulation of Th cell responses, there is a mechanism by which agents that appear to have only local effects at the portal of entry may, in fact, affect immune responses systemically. An understanding of conditions which trigger certain cytokine responses may be useful not only in understanding inflammation but also in predicting certain kinds of immunosuppressive and allergic responses. Future studies in this area are likely to provide insights into many areas of immunotoxicology.

Serpin conformational change in ovalbumin. Enhanced reactive center loop insertion through hinge region mutations

Ovalbumin is a noninhibitory member of the serpin superfamily that does not spontaneously undergo the loop-to-sheet conformational change upon cleavage of its reactive center that is characteristic of inhibitory serpins. We tested the hypothesis that ovalbumin could be turned into a proteinase inhibitor by increasing the rate of loop insertion through hinge region mutations alone. We found that none of the three variants examined showed any detectable proteinase inhibitory properties. However, replacement of the P14 arginine residue of ovalbumin by serine, either alone or in combination with changes of P12-P10 to alanine, resulted in a large increase in the rate of loop insertion into beta-sheet A following cleavage at the P1-P1' bond by porcine pancreatic elastase (PPE), as shown by the spontaneous formation of a loop-inserted form upon cleavage that has increased the thermal stability. From the magnitude of the increase in stability of the cleaved, loop-inserted forms of the P14 ovalbumin variants, as well as the accessibility of the P1-P1'-cleaved reactive center loop to further proteolysis at P8-P7, we concluded that the reactive center loop can only partially insert into beta-sheet A and therefore that ovalbumin is also defective in the ability of beta-sheet A to expand to fully accommodate the whole of the reactive center loop. This defect, through its effect on the extent and/or rate of loop insertion, is likely to be a principal reason for ovalbumin not being a proteinase inhibitor.

Characterization of the binding of different conformational forms of plasminogen activator inhibitor-1 to vitronectin. Implications for the regulation of pericellular proteolysis

Plasminogen activator inhibitor type 1 (PAI-1), the primary physiologic inhibitor of plasminogen activation, is associated with the adhesive glycoprotein vitronectin (Vn) in plasma and the extracellular matrix. In this study we examined the binding of different conformational forms of PAI-1 to both native and urea-purified vitronectin using a solid-phase binding assay. These results demonstrate that active PAI-1 binds to urea-purified Vn with approximately 6-fold higher affinity than to native Vn. In contrast, inactive forms of PAI-1 (latent, elastase-cleaved, synthetic reactive center loop peptide-annealed, or complexed to plasminogen activators) display greatly reduced affinities for both forms of adsorbed Vn, with relative affinities reduced by more than 2 orders of magnitude. Structurally, these inactive conformations all differ from active PAI-1 by insertion of an additional strand into beta-sheet A, suggesting that it is the rearrangement of sheet A that results in reduced Vn affinity. This is supported by the observation that PAI-1 associated with beta-anhydrotrypsin, which does not undergo rearrangement of beta-sheet A, shows no such decrease in affinity, whereas PAI-1 complexed to beta-trypsin, which does undergo sheet A rearrangement, displays reduced affinity for Vn similar to PAI-1.plasminogen activator complexes. Together these data demonstrate that the interaction between PAI-1 and Vn depends on the conformational state of both proteins and suggest that the Vn binding site on PAI-1 is sensitive to structural changes associated with loss of inhibitory activity.

Metal-induced modulation of nitric oxide production in vitro by murine macrophages: lead, nickel, and cobalt utilize different mechanisms

Macrophages (M phi) can be induced to produce nitric oxide (NO), which has been suggested to be important for macrophages to exercise various functions. We have previously reported that an environmental toxicant, lead (Pb), can significantly inhibit NO production by murine splenic M phis. Herein, eight additional metal ions, gold (Au), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), and zinc (Zn), were assessed. In addition to Pb, Hg and Cd significantly suppressed NO production by cytokine (interferon-gamma and tumor necrosis factor-alpha)-stimulated murine M phis. Au and Cu also were inhibitory, but less than Pb, Hg, and Cd. In contrast, Cr and Zn were not modulatory, and Ni and Co significantly enhanced NO production by cytokine-stimulated M phis. The enhancement by Ni and Co was inhibited by the arginine analog N-monomethylarginine. The metals showed different activating/inhibiting profiles when added to a cell-free (activated M phi lysate) NO-producing-system in which inducible NO synthase (iNOS) is already expressed. Cr, Cu, Pb, and Zn moderately suppressed iNOS, which suggests that they may directly modify enzyme or cofactor activity. Cd, Hg, Mg, Ni, or Co did not produce any significant effect on NO production by the cell-free system. Inhibition of NO production by Pb-exposed M phis was not due to decreased expression of iNOS nor limited to its modest direct inhibition of iNOS; thus, other mechanism(s) must be accountable for the efficient Pb-induced inhibition of NO production by M phi. Ni or Co did induce a substantial increase of iNOS protein. Overall, these observations provide additional insight into the means by which metals via inhibition or enhancement of NO production may be pathogenic, by suppression of defense mechanisms or induction of hypersensitivity, respectively.

Surface thiols of human lymphocytes and their changes after in vitro and in vivo activation

Cellular thiols have long been known to play a role in cell activation and proliferation; however, the differential expression of surface thiols on the lymphoid subsets had not been described. Neither was it known whether alteration of surface thiols occurs after exposure to mitogens or infectious agents. Herein, an impermeant thiol-specific fluorescent probe was employed for flow cytometric analysis of surface thiols. Quantification of surface thiols on resting lymphocytes revealed that some subsets expressed different concentrations of surface thiols (CD19+ > CD8+ > CD4+). Furthermore, surface thiols increased on all subsets by 8 h after mitogenic activation. This increase was blocked by cycloheximide or monensin but not by actinomycin D or inhibition of glutathione synthesis by buthionine sulfoximine. In addition, bacitracin, an inhibitor of protein disulfide isomerase, inhibited the increase in surface thiols and DNA synthesis. Lymphocytes from HIV-infected individuals displayed increased surface thiols on CD19+ and CD4+ cells but not CD8+ cells. Although cellular thiols in general have been believed to play a role in protection against oxidants, signaling associated with cell growth, and apoptosis, there is now evidence that changes in exofacial thiols appear to be involved in some of these critical cell reactivities. Thus, quantitative and possibly qualitative differences in surface thiols correlate with membrane differences between lymphoid subsets and with their differential sensitivities to oxidative stress, which suggests that the mechanisms by which surface thiols are maintained and modified after activation are important cellular functions that need to be further evaluated.

The serpin PAI-1 inhibits cell migration by blocking integrin alpha V beta 3 binding to vitronectin

During wound healing, migrating cells increase expression of both the vitronectin receptor (VNR) integrins and plasminogen activators. Here we report that vitronectin significantly enhances the migration of smooth muscle cells (SMCs), and that the specific VNR alpha V beta 3 is required for cell motility. We also show that the alpha V beta 3 attachment site on vitronectin overlaps with the binding site for plasminogen activator inhibitor (PAI)-1, and that the active conformation of PAI-1 blocks SMC migration. This effect requires high-affinity binding to vitronectin, and is not dependent on the ability of PAI-1 to inhibit plasminogen activators. Formation of a complex between PAI-1 and plasminogen activators results in loss of PAI-1 affinity for vitronectin and restores cell migration. These data demonstrate a direct link between plasminogen activators and integrin-mediated cell migration, and show that PAI-1 can control cell-matrix interactions by regulating the accessibility of specific cell-attachment sites. This indicates that the localization of plasminogen activators at sites of focal contact does not initiate a proteolytic cascade leading to generalized matrix destruction, but instead is required to expose cryptic cell-attachment sites necessary for SMC migration.

Differential in vitro effects of physiological and atmospheric oxygen tension on normal human peripheral blood mononuclear cell proliferation, cytokine and immunoglobulin production

Since the early work of Mischell & Dutton (Science 153, 1004-1008, 1966), it has been recognized that certain lymphocyte cultures are exquisitely sensitive to the harsh effects of atmospheric oxygen tension. The influence of oxygen partial pressure (pO2) on normal human peripheral blood mononuclear cell (PBMC) phenotype, proliferative ability, cytokine, immunoglobulin production, and redox status was examined by culturing PBMC under ambient oxygen (high pO2) or a more physiological pO2 (5% O2; low pO2). Low pO2 conditions promoted a significant increase in overall viable PBMC number and enhanced Concanavalin A (Con A)- or pokeweed mitogen (PWM)-stimulated PBMC proliferation by approximately 30% and 50%, respectively. No differential pO2 effects were apparent on phytohemagglutinin (PHA)- or staphylococcal enterotoxin B (SEB)-induced proliferation. Both resting and Con A-stimulated lymphocytes incubated for 24 h under high pO2 had a greater baseline carboxy-2',7'-dichlorofluorescin (C-DCF) fluorescence, and were less able to quench the effect of H2O2 treatment compared to lymphocytes cultured under low pO2 conditions. Supernatant gamma-IFN, IL-2, and IL-4 concentrations were elevated 50-65% when PBMC were stimulated with Con A for 24 h under low pO2; however, lipopolysaccharide (LPS)-stimulated IL-1 beta production was reduced by over 75%. PWM-stimulated IgM production by PBMC was significantly reduced in day 7 cultures incubated under low pO2, whereas IgG and IgA production remained relatively unaltered. Immunophenotyping analyses did not reveal any significant alterations in cell subset or marker distribution at the time points examined; however, an interesting trend of increased CD69 expression was observed for Con A-stimulated PBMC incubated under low pO2. These results demonstrate that O2 is a critical parameter for the in vitro culture of lymphocytes, and suggests that varying pO2 may differentially alter PBMC functionality.

Hydroquinone resistance in a murine myeloblastic leukemia cell line. Involvement of quinone reductase and glutathione-dependent detoxification in nonclassical multidrug resistance

A hydroquinone-resistant derivative of the M1 cell line, designated M1HQ, was generated and used to evaluate the biochemical mechanism responsible for resistance to oxidative stress-inducing agents. The hydroquinone concentrations that were cytotoxic to 50 and 90% of the parental M1 cell line in 48 hr were 25 and 90 microM, respectively, whereas exposure to 500 microM hydroquinone did not decrease M1HQ viability significantly. M1HQ cells grew slower than M1 cells and exhibited significantly higher resistance to colchicine, doxorubicin, hydrogen peroxide, 4-hydroperoxycyclophosphamide, and 1,3-bis (2-chloroethyl)-1-nitrosourea but not to benzoquinone, vinblastine, or gamma-radiation. M1HQ cells possessed significantly higher levels of total thiols, glutathione, glutathione peroxidase, glutathione reductase, quinone reductase, and gamma-glutamyl transpeptidase than the parental M1 cell line. Steady-state gamma-glutamylcysteine synthetase mRNA expression also was 1.6-fold higher in M1HQ cells. P-glycoprotein transcripts were detectable in both M1 and M1HQ cells, but were 2-fold higher in M1HQ. Multidrug resistance-associated protein transcripts were not detectable in either M1 or M1HQ. Hydroquinone resistance in M1HQ cells was partially reversible with a combination of inhibitors of quinone reductase, gamma-glutamylcysteine synthetase, glutathione peroxidase, and the multidrug resistance-associated protein, but not with inhibitors of P-glycoprotein, gamma-glutamyl transpeptidase, or glutathione-S-transferase. When treated with [14C]hydroquinone, M1HQ cells did not generate significant hydroquinone-protein adducts but did release an adduct similar to N-acetylcysteinyl-benzoquinone. In contrast, numerous [14C]hydroquinone-protein adducts were produced in M1 cells, while the N-acetylcysteinyl-benzoquinone-like molecule was undetectable. Thus, hydroquinone resistance in M1HQ cells appeared to result from a glutathione-dependent detoxification and export mechanism.

Transforming growth factor-beta: a general review

Three isoforms of Transforming Growth Factor-beta (TGF-beta 1, beta 2 and beta 3) exist in mammals. They play critical roles in growth regulation and development. Each isoform is encoded by a unique gene on different chromosomes. All three of these growth factors are secreted by most cell types, generally in a latent form, requiring activation before they can exert biological activity. This activation of latent TGF-beta, which may involve plasmin, thrombospondin and possibly acidic microenvironments, appears to be a crucial regulatory step in controlling their effects. The TGF-betas possess three major activities: they inhibit proliferation of most cells, but can stimulate the growth of some mesenchymal cells; they exert immunosuppressive effects; and they enhance the formation of extracellular matrix. Two types of membrane receptors (type I and type II) possessing a serine/threonine kinase activity within their cytoplasmic domains are involved in signal transduction. Inhibition of growth by the TGF-betas stems from a blockage of the cell cycle in late G1 phase. Among the molecular participants concerned in G1-arrest are the Retinoblastoma (Rb) protein and members of the Cyclin/Cyclin-dependent kinase/Cyclin dependent kinase inhibitor families. In the intact organism the TGF-betas are involved in wound repair processes and in starting inflammatory reactions and then in their resolution. The latter effects of the TGF-betas derive in part from their chemotactic attraction of inflammatory cells and of fibroblasts. From gene knockout and from overexpression studies it has been shown that precise regulation of each isoform is essential for survival, at least in the long term. Several clinical applications for certain isoforms have already shown their efficacy and they have been implicated in numerous other pathological situations.

Inhibition of human T lymphoblast proliferation by hydroquinone

Hydroquinone (HQ) is a major metabolite of benzene and is present in large quantities in cigarette tar as a result of the combustion of tobacco leaf pigments. We hypothesize that the immunosuppressive effects of cigarette smoking are due, in part, to the deposition of large quantities of HQ in the lungs. Exposure of primary human T lymphoblasts (HTL) in vitro to 50 microM HQ blocked IL-2-dependent proliferation by > 90% with no loss in viability. Inhibition of DNA synthesis was observed immediately after the addition of HQ to the cells. However, this effect could be reversed up to 6 hr later by simply washing the cells and reculturing them in the absence of HQ. HQ did not significantly alter intracellular glutathione levels up to 24 hr later, and the presence of 50 microM 2-mercaptoethanol or 500 microM dithiothreitol during the treatment did not prevent inhibition of DNA synthesis. HQ did not block binding of 125I-IL-2 to the cells, but inhibited the IL-2-dependent progression of HTL through S phase of the cell cycle. These observations demonstrate that HQ, in concentrations comparable to those found in cigarette tar, is a potent inhibitor of IL-2-dependent T cell proliferation and may therefore help to explain the potent immunosuppressive effects of cigarette smoke on lung T lymphocytes.

Regulation of HLA-DR and invariant chain expression by human peripheral blood mononuclear cells with lead, interferon-gamma, or interleukin-4

It has been reported that the expression of major histocompatibility complex (MHC) class II can be regulated by lead (Pb) in murine cells. In both human and mouse, the expression of MHC class II and invariant chain (Ii) can be regulated by cytokines, including interferon-gamma (IFN-gamma) and interleukin-4 (IL-4). Herein we report that in humans, as with IL-4, Pb enhanced MHC class II antigen DR (HLA-DR) surface expression by monocytes and B cells; Ii surface expression by monocytes and B cells was not affected by Pb while it was enhanced by IL-4. IFN-gamma increased HLA-DR and Ii surface expression by monocytes but it decreased HLA-DR and Ii surface expression by B cells. Total cellular HLA-DR expression by peripheral blood mononuclear cells (PBMC) was increased by Pb, IFN-gamma, or IL-4. Total cellular Ii (p33 and p35) expression by PRMC was not affected by Pb or IFN-gamma while it was increased by IL-4. In PBMC, the steady-state mRNA levels of HLA-DR alpha and Ii were not affected by Pb; IFN-gamma increased HLA-DR alpha mRNA expression but not Ii; IL-4 increased both mRNA levels of HLA-DR alpha and Ii. Furthermore, Pb, IFN-gamma, or IL-4 significantly increased the total cellular level of HLA-DR:Ii complexes in PBMC while they had no effect on cell surface HLA-DR:Ii complex expression. Overall, these results suggest that, in vitro, Pb, IFN-gamma, and IL-4 differentially modulate HLA-DR and Ii expression by human PBMC.

The heavy metal lead modulates the expression of both TNF-alpha and TNF-alpha receptors in lipopolysaccharide-activated human peripheral blood mononuclear cells

It has been shown that lead (Pb) potentiates lipopolysaccharide (LPS) lethality in animals by increasing the secretion and uptake or reactivity of tumor necrosis factor-alpha (TNF-alpha). Herein we report that PbCl2 increased TNF-alpha secretion from LPS-treated human peripheral blood mononuclear cells (PBMC) in a concentration- and time-dependent manner. PbCl2 also increased total cellular TNF-alpha levels but had no effect on the steady-state levels of TNF-alpha mRNA. PbCl2 decreased membrane-associated TNF-alpha (mTNF-alpha) on LPS-treated monocytes, whereas PbCl2 increased TNF-alpha receptor (TNF-R) p55 surface expression, and had no effect on TNF-R p75 surface expression by LPS-treated monocytes. Overall, the results suggest that PbCl2 increases TNF-alpha expression by posttranscriptional mechanisms in human PBMC, and enhances the reactivity and uptake of TNF-alpha by increasing the surface expression of TNF-R p55.

Mercury (Hg 2+) enhances the depressant effect of kainate on Ca-inactivated potassium current in telencephalic cells derived from chick embryos

The effect of HgCl2 on kainate (KA)-induced depression of voltage-gated potassium (K+) current in chick embryo telencephalic cells was studied using conventional and nystatin-perforated whole-cell patch-clamp recordings, fluorescence imaging, and flow cytometry techniques. Hg2+ (1 microM) alone did not effect the 4-aminopyridine-(4-AP)-sensitive transient K+ current in immature cells (Embryonic Day 5), but irreversibly potentiated the depressant effect of KA on this K+ current. A 50% potentiation of KA-induced depression of the K+ current was produced by an application of 0.19 microM Hg2+. Application of ionomycin (5 microM) or calcium ionophore A23187 (2 microM) suppressed the K+ current. To test the possibility that the 4-AP-sensitive transient K+ current is a Ca-inactivated current, the effect of intracellular Ca2+ concentration ([Ca2+]i) in the range of 30 nM to 2 microM was determined. The amplitude of the K+ current was sensitive to [Ca2+]i with half-maximal inactivation at 370 nm at +60 mV. The concentration-response curve of the K+ current inhibition by [Ca2+]i was shifted to lower [Ca2+]i and the slope of the curve was reduced in the presence of KA. Hg2+ potentiated these effects of KA. The Ca-dependence of the K+ current was maximal at the 5th embryonic day, declined to the 9th embryonic day, and was absent at the 11th embryonic day. Application of Hg2+ (0.1-1 microM) had no effect on the basal [Ca2+]i of freshly dissociated cells (10th day in ovo) and cells in culture (the 4-day cultures from the telencephalon of 5-day-old embryos), but potentiated KA-induced increase of [Ca2+]i in a Ca-free-EGTA solution in a concentration-dependent manner. Moreover 1 microM Hg2+ delayed and reduced the recovery to basal [Ca2+]i after washout of KA. Exposure to 5-30 microM H2+ caused an irreversible decline of membrane resistance, an increased cell size, and reduced cell granularity and complexity. Intracellular recording of spontaneous neuronal activity and immunocytochemical identification showed that the KA/Hg2+-sensitive Ca-inactivated K+ current exists in early differentiating telencephalic neurons. Because depression of the K+ current by KA and Hg2+ decreases the interspike interval and irreversibly perturbs the frequency code of information in the nervous system, the expression of this current during early neuroembryogenesis may be one of the reasons for the developmental toxicity of inorganic mercury.

Lead differentially modifies cytokine production in vitro and in vivo

An imbalance between helper T cell type 1 (Th1) and helper T cell type 2 (Th2) activation can result in immunodysregulations leading to impaired cell-mediated immunity with an increased incidence of infectious disease or cancer and/or aberrant humoral immunity that may culminate with an autoimmune disease. Mercury, a heavy-metal toxicant, is known to induce renal autoimmunity characterized by a predominant Th2 response. Lead, another metal toxicant, causes enhanced B cell activities and impairs host resistance to several bacterial and viral infections. In addition, Pb was reported to enhance Th2 proliferation and inhibit Th1 proliferation. The differential effects of Pb on Th subset activation have been further investigated. In vitro IL-4 production by a Th2 clone was significantly increased by the addition of PbCl2, whereas IFN gamma production by a Th1 clone was decreased by the addition of PbCl2. When BALB/c mice were subcutaneously exposed to PbCl2, ex vivo Il-4 production by anti-CD3-stimulated splenic T cells was enhanced, but IFN gamma production was inhibited. Additionally, the plasma IL-4 and IgE levels of Pb-exposed mice were increased, and the plasma IFN gamma levels were significantly lowered in the absence of any additional exogenous antigen. In vitro, ex vivo, and in vivo treatment with HgCl2 produced similar findings. This study is the first report of the preferential activation of a Th2 response by Pb in vivo and suggests that PB, like Hg, may induce autoimmune responses by upsetting the balance between Th1- and Th2-like cells, which could enhance production of antibodies to self antigens.

Plasminogen activator inhibitor-1 and vitronectin promote the cellular clearance of thrombin by low density lipoprotein receptor-related proteins 1 and 2

Thrombin is a multifunctional protein that has both proteinase and growth factor-like activities. Its regulation is largely mediated by interaction with a host of inhibitors including antithrombin III (ATIII), heparin cofactor II (HCII), alpha2-macroglobulin (alpha2-M), protease nexin I, and plasminogen activator inhibitor-1 (PAI-1). ATIII, HCII, and alpha2-M are all abundant in blood and can inactivate blood-borne thrombin leading to rapid hepatic clearance of the thrombin-inhibitor complex. PAI-1 alone, a poor solution phase inhibitor of thrombin, can efficiently inhibit thrombin in the presence of native vitronectin (VN). In this study, active thrombin was found to be efficiently endocytosed and degraded by cultured pre-type II pneumocyte cells, and both processes could be blocked by polyclonal antibodies to PAI-1. When the relative efficiency of cellular endocytosis of thrombin in complex with a number of inhibitors was examined, 125I-thrombin-PAI-1 complexes were most efficiently cleared compared to 125I-thrombin in complex with the serpins ATIII, HCII, alpha1-proteinase inhibitor, or d-phenylalanyl-l-prolyl-l-arginine chloromethyl ketone. Low density lipoprotein receptor-related proteins 1 (LRP) and 2 (gp330/megalin) mediate the endocytosis of thrombin-PAI-1, since antagonists of receptor function such as LRP-1 and LRP-2 antibodies and the 39-kDa receptor-associated protein blocked 125I-thrombin-PAI-1 endocytosis and degradation. The LRP-mediated clearance of exogenously added 125I-thrombin by cultured cells was found to be enhanced 5-fold by inclusion of wild-type PAI-1 but by only 2-fold when a mutant form of PAI-1 that is unable to bind VN was included. This wild-type PAI-1 enhancement of 125I-thrombin clearance was found to occur only in the presence of native VN and not with its conformationally altered form. The results highlight a novel mechanism for cellular clearance of thrombin involving native VN promoting the interaction of thrombin and PAI-1 and the subsequent endocytosis of the complex by LRP-1 or LRP-2. This pathway is potentially important for the regulation of the potent biological activities of thrombin, particularly at sites of vascular injury.

Influence of oxygen partial pressure on human and mouse myeloid cell line characteristics

Mouse and human cells have been reported to have different thiol characteristics (J. M. Messina and D. A. Lawrence, 1992, Int. J. Immunopharmacol. 14, 1221-1234). In addition, when cells are undergoing active growth, they usually have an increased thiol content. In an attempt to determine whether a mouse and a human cell line with similar characteristics can be induced to change their phenotype simply by being cultured at a lower oxygen partial pressure (pO2), the human KG-1 and mouse M1 myeloid cell lines were cultured at 5 and 20% oxygen. It is important to note that 5% O2 is close to the physiological pO2, whereas the percentage of O2 usually employed for most in vitro methods is atmospheric pO2. After long-term culturing at 5% (L cell lines) versus 20% O2 (H cell lines), the thiol content of the original (H) cell lines significantly changed. The amount of total and surface thiols was lower in both L cell lines, but only significantly different on the M1 lines, whereas the glutathione content was significantly lower in the L cell lines of KG-1 and M1. The mouse lines showed the greatest sensitivity to pO2 changes; however, the mouse cell lines were not more sensitive to hydrogen peroxide than the human cell lines even though they possess significantly less total thiols and glutathione. Interestingly, cell lines maintained at lower pO2 (physiological pO2) were more sensitive to hydrogen peroxide than their parental counterparts that were maintained at atmospheric oxygen levels.

Genetic mapping of GLCLC, the human gene encoding the catalytic subunit of gamma-glutamyl-cysteine synthetase, to chromosome band 6p12 and characterization of a polymorphic trinucleotide repeat within its 5' untranslated region

The first and rate-limiting step in the formation of glutathione is catalyzed by gamma-glutamylcysteine synthetase (glutamate-cysteine ligase, E.C. 6.3.2.2). Herein, we describe a trinucleotide repeat polymorphism located in the 5' untranslated region of the human gene, GLCLC, that encodes the catalytic subunit of this enzyme, and we genetically map GLCLC to band 6p12, 1.6 cM distal to D6S295.

Role of the catalytic serine in the interactions of serine proteinases with protein inhibitors of the serpin family. Contribution of a covalent interaction to the binding energy of serpin-proteinase complexes

The contribution of a covalent bond to the stability of complexes of serine proteinases with inhibitors of the serpin family was evaluated by comparing the affinities of beta-trypsin and the catalytic serine-modified derivative, beta-anhydrotrypsin, for several serpin and non-serpin (Kunitz) inhibitors. Kinetic analyses showed that anhydrotrypsin had little or no ability to compete with trypsin for binding to alpha 1-proteinase inhibitor (alpha 1PI), plasminogen activator inhibitor 1 (PAI-1), antithrombin (AT), or AT-heparin complex when present at up to a 100-fold molar excess over trypsin. By contrast, equimolar levels of anhydrotrypsin blocked trypsin binding to non-serpin inhibitors. Equilibrium binding studies of inhibitor-enzyme interactions monitored by inhibitor displacement of the fluorescence probe, p-aminobenzamidine, from the enzyme active site, confirmed that the binding of serpins to anhydrotrypsin was undetectable in the case of alpha 1PI or AT (KI > 10(-5) M), of low affinity in the case of AT-heparin complex (KI 7-9 x 10(-6) M), and of moderate affinity in the case of PAI-1 (KI 2 x 10(-7) M). This contrasted with the stoichiometric high affinity binding of the serpins to trypsin as well as of the non-serpin inhibitors to both trypsin and anhydrotrypsin. Maximal KI values for serpin-trypsin interactions of 1 to 8 x 10(-11) M, obtained from kinetic analyses of association and dissociation rate constants, indicated that the affinity of serpins for trypsin was minimally 4 to 6 orders of magnitude greater than that of anhydrotrypsin. Anhydrotrypsin, unlike trypsin, failed to induce the characteristic fluorescence changes in a P9 Ser-->Cys PAI-1 variant labeled with a nitrobenzofuran fluorescent probe (NBD) which were shown previously to report the serpin conformational change associated with active enzyme binding. These results demonstrate that a covalent interaction involving the proteinase catalytic serine contributes a major fraction of the binding energy to serpin-trypsin interactions and is essential for inducing the serpin conformational change involved in the trapping of enzyme in stable complexes.

The acid stabilization of plasminogen activator inhibitor-1 depends on protonation of a single group that affects loop insertion into beta-sheet A

The serpin plasminogen activator inhibitor-1 (PAI-1) spontaneously adopts an inactive or latent conformation by inserting the N-terminal part of the reactive center loop as strand 4 into the major beta-sheet (sheet A). To examine factors that may regulate reactive loop insertion in PAI-1, we determined the inactivation rate of the inhibitor in the pH range 4.5-13. Below pH 9, inactivation led primarily to latent PAI-1, and one predominant effect of pH on the corresponding rate constant could be observed. Protonation of a group exhibiting a pKa of 7.6 (25 degrees C, ionic strength = 0.15 M) reduced the rate of formation of latent PAI-1 by a factor of 35, from 0.17 h-1 at pH 9 to about 0.005 h-1 below pH 6. The ionization with a pKa 7.6 was found to have no effect on the rate by which PAI-1 inhibits trypsin and is therefore unlikely to change the flexibility of the loop or the orientation of the reactive center. The peptides Ac-TEASSSTA and Ac-TVASSSTA (cf. P14-P7 in the reactive loop of PAI-1) formed stable complexes with PAI-1 and converted the inhibitor to a substrate for tissue type plasminogen activator. We found that peptide binding and formation of latent PAI-1 are mutually exclusive events, similarly affected by the pKa 7.6 ionization. This is direct evidence that external peptides can substitute for strand 4 in beta-sheet A of PAI-1 and that the pKa 7.6 ionization regulates insertion of complementary, internal or external, strands into this position. A model that accounts for the observed pH effects is presented, and the identity of the ionizing group is discussed based on the structure of latent PAI-1. The group is tentatively identified as His-143 in helix F, located on top of sheet A.

The effects of interleukin-1 beta and tumor necrosis factor-alpha on in vitro colony formation by human hematopoietic progenitor cells exposed to doxorubicin or hydroquinone

Previous studies have shown that treatment of bone marrow (BM) cells with interleukin-1 beta (IL-1 beta) or tumor necrosis factor-alpha (TNF-alpha) can protect hematopoietic progenitor cells (HPC) from the toxic effects of 4-hydroperoxycyclophosphamide (4HC) or gamma-irradiation. Since doxorubicin (DX) and hydroquinone (HQ) may inhibit hematopoiesis through mechanisms similar to 4HC and gamma-irradiation, it was of interest to determine whether IL-1 beta or TNF-alpha could protect HPC from DX and HQ as well. Bone marrow mononuclear cells (BMMNC) or purified HPC (pHPC) were exposed to 50 ng/mL IL-1 beta or 25 ng/mL TNF-alpha alone or in combination with DX or HQ for 22 hours at physiological O2 partial pressure and temperature. The cells were washed free of the cytokines and toxicants and plated in cytokine-containing semisolid medium. Under these concurrent cytokine +/- toxicant treatment conditions, neither IL-1 beta nor TNF-alpha significantly affected progenitor cell frequencies (assessed as CFU-C) or lineage commitment compared with the medium-treated controls. Treatment with either 100 nM DX or 30 microM HQ, however, reduced CFU-C frequencies by approximately 70%. When BMMNC were used, treatment with neither IL-1 beta nor TNF-alpha consistently protected CFU-C from either DX or HQ. In contrast, using pHPC, IL-1 beta or TNF-alpha treatment conferred nearly two-fold protection of CFU-C from DX in all donors tested. TNF-alpha protected CFU-C from HQ using pHPC from all but one donor, while IL-1 beta did not protect CFU-C from HQ. Using phPC, maximum protection of CFU-C from DX was reached at IL-1 beta or TNF-alpha concentrations above 10 ng/mL or 1 ng/mL, respectively. Treatment of pHPC with TNF-alpha for at least 8 hours was necessary before significant protection from DX could be detected. Therefore, we conclude that IL-1 beta and TNF-alpha can act directly on human HPC to protect them from the inhibitory effects of DX and that, to a lesser extent, TNF-alpha can directly protect HPC from HQ.

Serpin-protease complexes are trapped as stable acyl-enzyme intermediates

The serine protease inhibitors of the serpin family are an unusual group of proteins thought to have metastable native structures. Functionally, they are unique among polypeptide protease inhibitors, although their precise mechanism of action remains controversial. Conflicting results from previous studies have suggested that the stable serpin-protease complex is trapped in either a tight Michaelis-like structure, a tetrahedral intermediate, or an acyl-enzyme. In this report we show that, upon association with a target protease, the serpin reactive-center loop (RCL) is cleaved resulting in formation of an acyl-enzyme intermediate. This cleavage is coupled to rapid movement of the RCL into the body of the protein bringing the inhibitor closer to its lowest free energy state. From these data we suggest a model for serpin action in which the drive toward the lowest free energy state results in trapping of the protease-inhibitor complex as an acyl-enzyme intermediate.

Thrombin increases expression of urokinase receptor by activation of the thrombin receptor

PURPOSE

To investigate the effect of thrombin on the urokinase plasminogen activator receptor (u-PAR) in retinal pigment epithelial (RPE) cells.

METHODS

The authors analyzed u-PAR mRNA by Northern blot hybridization. Retinal pigment epithelial cell surface u-PAR was assayed by measuring the amount of functional urokinase plasminogen activator (u-PA) bound to cells at saturation. Retinal pigment epithelial cells were derived from fetal retinal tissue and established in primary cell culture.

RESULTS

Thrombin increased u-PAR mRNA 4-fold in RPE cells examined by Northern blot hybridization, whereas the amount of thrombin receptor mRNA was unchanged. Thrombin stimulated u-PA binding to RPE cells 2.5- to 5-fold in a time- and dose-dependent manner. Hirudin, a thrombin antagonist, completely blocked the effects of thrombin on u-PAR expression in RPE cells. Phosphatidylinositol phospholipase C treatment of RPE cells resulted in the abolition of thrombin-induced u-PA binding. Recombinant soluble u-PAR competitively inhibited two-chain u-PA binding to the surface of thrombin-treated RPE cells. A thrombin receptor agonist peptide (SFLLRNPNDKYEPF) also induced a 2.5-fold increase in binding of u-PA to the surface of RPE cells.

CONCLUSION

Thrombin increases u-PAR expression by RPE cells by a mechanism involving activation of the seven transmembrane thrombin receptor.

N-ras mRNA expression is unaffected in glutathione-depleted cells of hematopoietic origin

Glutathione (GSH) depletion in mitogen-stimulated T lymphocytes has been shown to markedly inhibit their proliferative response. This block in proliferation is associated with a significant reduction in total RNA and DNA synthesis; however, the specific mechanism involved in this inhibition of proliferation is unknown. Miller et al. have reported that lowering intracellular GSH levels by greater than 30%, in murine and human tumor cell lines of non-hematopoietic origin, leads to down-regulation of HA-, Ki- and N-ras oncogene expression [Miller. A.C., Gafner, J., Clark, E.P. and Samid, D. (1993) Mol. Cell Biol., 13, 4416-4422]. The reduction in ras transcript levels correlated with the extent of GSH depletion and was independent of the specific mode of oncogene activation. Since the activity of p21(ras) is thought to be involved in pathways of T cell activation, we set out to determine whether down-regulation of ras expression in T cells could be the mechanism by which T cell proliferation was inhibited in GSH-depleted T lymphocytes. Despite reducing the GSH level of concanavalin A-activated human peripheral blood mononuclear cells by 66%, no effect on ras mRNA expression was observed. Similarly, no reduction of ras transcript levels were detected in a human T cell line (Jurkat) or in a human monocytic cell line (THP-1) depleted of glutathione. Our results demonstrate that the mechanism by which GSH depletion inhibits T cell proliferation does not appear to involve a decrease in ras mRNA expression. In addition, our results suggest that differences in the regulation of ras mRNA expression may exist between lymphoid/monocytic cells of non-hematopoietic origin.

Effects of high-dose fish oil on rheumatoid arthritis after stopping nonsteroidal antiinflammatory drugs. Clinical and immune correlates

OBJECTIVE

To determine the following: 1) whether dietary supplementation with fish oil will allow the discontinuation of nonsteroidal antiinflammatory drugs (NSAIDs) in patients with rheumatoid arthritis (RA); 2) the clinical efficacy of high-dose dietary omega 3 fatty acid fish oil supplementation in RA patients; and 3) the effect of fish oil supplements on the production of multiple cytokines in this population.

METHODS

Sixty-six RA patients entered a double-blind, placebo-controlled, prospective study of fish oil supplementation while taking diclofenac (75 mg twice a day). Patients took either 130 mg/kg/day of omega 3 fatty acids or 9 capsules/day of corn oil. Placebo diclofenac was substituted at week 18 or 22, and fish oil supplements were continued for 8 weeks (to week 26 or 30). Serum levels of interleukin-1 beta (IL-1 beta), IL-2, IL-6, and IL-8 and tumor necrosis factor alpha were measured by enzyme-linked immunosorbent assay at baseline and during the study.

RESULTS

In the group taking fish oil, there were significant decreases from baseline in the mean (+/- SEM) number of tender joints (5.3 +/- 0.835; P < 0.0001), duration of morning stiffness (-67.7 +/- 23.3 minutes; P = 0.008), physician's and patient's evaluation of global arthritis activity (-0.33 +/- 0.13; P = 0.017 and -0.38 +/- 0.17; P = 0.036, respectively), and physician's evaluation of pain (-0.38 +/- 0.12; P = 0.004). In patients taking corn oil, no clinical parameters improved from baseline. The decrease in the number of tender joints remained significant 8 weeks after discontinuing diclofenac in patients taking fish oil (-7.8 +/- 2.6; P = 0.011) and the decrease in the number of tender joints at this time was significant compared with that in patients receiving corn oil (P = 0.043). IL-1 beta decreased significantly from baseline through weeks 18 and 22 in patients consuming fish oil (-7.7 +/- 3.1; P = 0.026).

CONCLUSION

Patients taking dietary supplements of fish oil exhibit improvements in clinical parameters of disease activity from baseline, including the number of tender joints, and these improvements are associated with significant decreases in levels of IL-1 beta from baseline. Some patients who take fish oil are able to discontinue NSAIDs without experiencing a disease flare.

Glutathione depletion in human T lymphocytes: analysis of activation-associated gene expression and the stress response

Glutathione depletion achieved by continuous exposure of mitogen-activated human T lymphocytes to L-buthionine-(S,R)-sulfoximine, a specific inhibitor of gamma-glutamylcysteine synthetase, leads to a marked inhibition of the proliferative response. Concanavalin A-activated T cells treated with buthionine sulfoximine failed to exhibit the increase in glutathione content normally observed in activated T cells and were depleted of cellular glutathione over 4 days of culture. On Day 3 of culture, DNA synthesis was inhibited by greater than 75%. In addition, total RNA synthesis was dramatically reduced in the glutathione-depleted cells being inhibited by 26, 61, and 82% on Days 2, 3, and 4, respectively. Despite this global reduction in RNA synthesis, no specific effects on mRNA expression of a number of critical T cell genes required for activation and/or proliferation were detected. In contrast to a recent report of GSH depletion leading to down-regulation of ras mRNA expression in a number of transformed cell lines, glutathione depletion did not influence N-ras mRNA expression in T lymphocytes. No influence of glutathione depletion on the induction of histone mRNA expression was observed. However, consistent with previous studies on regulation of histone mRNA expression, histone transcript levels were reduced when DNA synthesis was markedly inhibited. A cellular stress response, characterized by an increase in mRNA levels of the two stress response genes, HSP70 and gadd 153, was evident in glutathione-depleted unstimulated cells. Additionally, in these cells at 48 hr, we observed a 3.5-fold increase in the steady-state level of mRNA encoding the catalytic subunit of gamma-glutamylcysteine synthetase, the enzyme inhibited by buthionine sulfoximine.

The spatial coding strategies of one-year-old infants in a locomotor search task

The ability of 1-year-old infants to remember the location of a nonvisible target was investigated in 3 experiments. Infants searched for a toy hidden in one of many possible locations within a circular bounded space. The presence, number, and spatial arrangement of local cues or "landmarks" within this space were varied. The results of Experiment 1 showed that search performance was highly successful when a landmark was coincident with the location of the toy ("direct"), but less successful when a landmark was adjacent to the target location ("indirect"). The results of Experiment 2 suggested that search with an indirect landmark may be more fragile than search with no landmarks at all. In Experiments 3a and 3b, 2 different configurations of indirect landmarks were employed; search performance was equally poor with both of these and was inferior to search with no landmarks. It is concluded that infants of this age are able to associate a nonvisible target with a direct landmark and are able to code the distance and direction of a target with respect to themselves or with respect to the larger framework. However, there was no evidence that they can code the distance and direction of a target relative to another object. The difficulty of coding with indirect landmarks is interpreted in terms of cognitive complexity and conflict between spatial strategies.

Molecular evolution of plasminogen activator inhibitor-1 functional stability

Plasminogen activator inhibitor-1 (PAI-1) is a member of the serine protease inhibitor (serpin) supergene family and a central regulatory protein in the blood coagulation system. PAI-1 is unique among serpins in exhibiting distinct active and inactive (latent) conformations in vivo. Though the structure of latent PAI-1 was recently solved, the structure of the short-lived, active form of PAI-1 is not known. In order to probe the structural basis for this unique conformational change, a randomly mutated recombinant PAI-1 expression library was constructed in bacteriophage and screened for increased functional stability. Fourteen unique clones were selected, and shown to exhibit functional half-lives (T1/2S) exceeding that of wild-type PAI-1 by up to 72-fold. The most stable variant (T1/2 = 145 h) contained four mutations. Detailed analysis of these four mutations, individually and in combination, demonstrated that the markedly enhanced functional stability of the parent compound mutant required contributions from all four substitutions, with no individual T1/2 exceeding 6.6 h. The functional stability of at least eight of the remaining 13 compound mutants also required interactions between two or more amino acid substitutions, with no single variant increasing the T1/2 by > 10-fold. The nature of the identified mutations implies that the unique instability of the PAI-1 active conformation evolved through global changes in protein packing and suggest a selective advantage for transient inhibitor function.

Nucleotide changes in oxidatively stressed lymphocytes

Similar to HIV-1-induced suppression of thymus-derived lymphocytes (T cells), oxidatively stressed T cells show inhibited DNA synthesis and proliferation. The influence of oxidative stress on nucleotide pools was explored using 3H-uridine addition to OKT3-stimulated peripheral blood lymphocytes. The cells were preincubated and stimulated in the presence of 1 mM buthionine sulfoximine to inhibit GSH synthesis. This treatment gave rise to a significant reduction in dUDP and TTP biosynthesis following 18-32 hours stimulation, indicating possible impairment of ribonucleotide reductase activity.

Peptide-mediated inactivation of recombinant and platelet plasminogen activator inhibitor-1 in vitro

Plasminogen activator inhibitor-1 (PAI-1), the primary inhibitor of tissue-type plasminogen activator (t-PA) and urokinase plasminogen activator, is an important regulator of the blood fibrinolytic system. Elevated plasma levels of PAI-1 are associated with thrombosis, and high levels of PAI-1 within platelet-rich clots contribute to their resistance to lysis by t-PA. Consequently, strategies aimed at inhibition of PAI-1 may prove clinically useful. This study was designed to test the hypothesis that a 14-amino acid peptide, corresponding to the PAI-1 reactive center loop (residues 333-346), can rapidly inhibit PAI-1 function. PAI-1 (0.7 microM) was incubated with peptide (55 microM) at 37 degrees C. At timed intervals, residual PAI-1 activity was determined by addition of reaction mixture samples to t-PA and chromogenic substrate. The T1/2 of PAI-1 activity in the presence of peptide was 4 +/- 3 min compared to a control T1/2 of 98 +/- 18 min. The peptide also inhibited complex formation between PAI-1 and t-PA as demonstrated by SDS-PAGE analysis. However, the capacity of the peptide to inhibit PAI-1 bound to vitronectin, a plasma protein that stabilizes PAI-1 activity, was markedly attenuated. Finally, the peptide significantly enhanced in vitro lysis of platelet-rich clots and platelet-poor clots containing recombinant PAI-1. These results indicate that a 14-amino acid peptide can rapidly inactivate PAI-1 and accelerate fibrinolysis in vitro. These studies also demonstrate that PAI-1 function can be directly attenuated in a physiologic setting and suggest a novel approach for augmenting fibrinolysis in vivo.

Lead inhibits nitric oxide production in vitro by murine splenic macrophages

The heavy metal lead is an environmental toxicant that can compromise host defense systems and induce pathophysiological changes in many organ systems. We report herein that low levels of lead can efficiently block nitric oxide production in vitro by murine splenic macrophages, which could contribute to lead's inhibition of pathogen killing by macrophages. We observed that lead was able to suppress nitric oxide production by concanavalin A-stimulated murine splenocyte cultures. Since splenocyte cultures contain macrophages, lymphocytes, and other cell types, we further delineated the target(s) of the inhibition. High- and low-dose interferon-gamma and tumor necrosis factor-alpha-induced nitric oxide production by macrophages was readily blocked by low levels of lead (ID50 = 0.35-0.95 microM or 0.07-0.19 ppm); however, activated T cell membrane-enhanced nitric oxide production by macrophages was less sensitive to inhibition by lead. Since lead has been reported to preferentially enhance the activation of T helper-2 cells, which produce interleukin-4, a regulator of macrophage activities, the role of interleukin-4 in the inhibition by lead also was assessed. Interleukin-4 did not mediate the inhibition; instead, interleukin-4 appeared to be an enhancing factor for nitric oxide production in vitro. The observed effects of lead on nitric oxide production may provide an explanation for some of the lead-induced abnormalities associated with host defense and organ systems in addition to the immune system.