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Biomedical subjects

C Y Lau

Publications and source records attributed to C Y Lau.

At least 37 records · Page 2Linked to original sources
PubMed1996

The NF-kappa B inhibitor, tepoxalin, suppresses surface expression of the cell adhesion molecules CD62E, CD11b/CD18 and CD106.

Tepoxalin, a dual enzyme inhibitor of cyclooxygenase and 5-lipoxygenase has been shown to inhibit T-cell activation. Its immunosuppressive property is distinct from cyclosporin because only tepoxalin, but not cyclosporin, suppresses NF-kappa B activation. Here we report that tepoxalin selectively inhibits intercellular adhesion molecule-1 (ICAM-1, CD54)/MAC-1 (CD11b/CD18) dependent adhesion of polymorphonuclear cells to IL-1 activated human umbilical vein endothelial cells. The mechanism of inhibition is related to the surface expression of several cell adhesion molecules. Flow cytometry analyses on cultured cells that were treated with tepoxalin or antisense oligonucleotides to the P65/p50 subunit of NF-kappa B, and then stimulated with PMA, revealed a reduced expression of CD11b/CD18 on monocytic HL60 cells, and endothelial adhesion molecule-1 (CD62E) and vascular adhesion molecule-1 (CD106) on human umbilical vein endothelial cells. Expression of other adhesion molecules such as lymphocyte function associated-antigen-1 (CD11a/CD18) and CD54 were unaffected. Tepoxalin also inhibited the secretion of a NF-kappa B regulated chemokine, IL-8, a known inducer of CD11b/CD18 expression. Thus the suppression of CD11b/CD18 expression by tepoxalin may involve IL-8. Our results suggest that by inhibiting NF-kappa B activation, surface expression of several adhesion molecules can be modulated and that tepoxalin may be useful in treating selected adhesion mediated events such as leukocyte migration or atherosclerotic plaque formation.

Antibodies, Blocking↗
PubMed1995

Tepoxalin, a novel immunomodulatory compound, synergizes with CsA in suppression of graft-versus-host reaction and allogeneic skin graft rejection.

Tepoxalin, a dual 5-lipoxygenase and cyclooxygenase inhibitor with nonsteroidal antiinflammatory effects, has recently been shown to suppress NF kappa B transactivation and inhibit T cell proliferation via a mechanism very different from cyclosporine (CsA). In this report, we demonstrate that this novel immunosuppressive effect of tepoxalin is manifested in in vivo transplantation models. Tepoxalin suppressed murine spleen cell proliferation in a mixed lymphocyte reaction (MLR) with an IC50 of 1.3 microM. Coadministration of tepoxalin and CsA in MLR cultures showed an additive inhibitory effect. Oral administration of tepoxalin at 12 mg/kg/day to mice suppressed local graft-versus-host (GVH) responses by about 40% (n = 10). Combination of tepoxalin and CsA at suboptimal doses synergized their immunosuppressive effects on GVH responses (n = 20). In skin transplantation, the median survival time of allogeneic BALB/cByJ (H-2d) mouse skin grafted onto C3H/HeJ (H-2 kappa) mice was 10.5 days (n = 8), and was prolonged to 15.0 days (n = 9) for recipient mice administered tepoxalin at 50 mg/kg/day. Coadministration of suboptimal doses of tepoxalin (12.5 mg/kg/day) and CsA (50 mg/kg/day) prolonged skin graft rejections dramatically (55% of the grafts survived for more than 40 days, n = 9). Taken together, these results demonstrate that tepoxalin is a potent immunomodulatory compound that, when combined with CsA, provides synergistic immunosuppressive activity. The fact that tepoxalin and CsA act on different transcription factors, NF kappa B and NFAT respectively, might explain the synergistic suppressive effects when both compounds were used. Tepoxalin could be an important addition to the cohort of immunosuppressive therapies currently used in solid organ and bone marrow transplantations.

Animals↗
PubMed1995

Tepoxalin, a novel dual inhibitor of the prostaglandin-H synthase cyclooxygenase and peroxidase activities.

Prostaglandin-H synthase-1, the rate-limiting enzyme in prostaglandin synthesis, has both cyclooxygenase (CO) and peroxidase (PO) activities. While most nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit only the CO activity, we describe an inhibitor, tepoxalin, that inhibits both the CO (IC50 = 0.1 microM) and the PO (IC50 = 4 microM) activities. Unlike many NSAIDs which are competitive inhibitors of CO, tepoxalin is a noncompetitive inhibitor of CO and its inhibitory effect on PO but not CO is reversed by excess heme. Moreover, inhibition of the PO activity by tepoxalin is not dependent on the enzymatic turnover of the CO activity. The hydroxamic acid of tepoxalin is responsible for the PO inhibition since a carboxylic acid derivative of tepoxalin retains full CO but not PO inhibition. We postulated that the hydroxamic group might confer the ability to inhibit PO on conventional CO inhibitors. This idea was supported by the observation that naproxen hydroxamic acid, but not naproxen showed PO inhibition. Furthermore, tepoxalin's carboxylic acid analogue and naproxen each competitively relieved PO inhibition by their respective hydroxamic acids. The intracellular activity of PO as monitored by the release of reactive oxygen species was also inhibited by both tepoxalin and naproxen hydroxamic acid. These observations suggest a strategy for design of novel compounds to inhibit prostaglandin synthase PO. The therapeutic implications of these novel PO inhibitors are discussed.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1995

Suppression of NF kappa B activation and NF kappa B-dependent gene expression by tepoxalin, a dual inhibitor of cyclooxygenase and 5-lipoxygenase.

Tepoxalin, a dual inhibitor of cyclooxygenase (CO) and 5-lipoxygenase (5LO) with cytokine modifying activity, is also a potent inhibitor of the transcription factor, nuclear factor kappa B (NF kappa B). NF kappa B is a pleiotropic activator that is involved in the regulation of many genes whose products participate in immune or inflammatory responses. Tepoxalin inhibited in a dose related manner NF kappa B activation by PMA + ionomycin or H2O2 in Jurkat and HeLa cells. TNF-alpha-induced NF kappa B was also inhibited by tepoxalin in HeLa cells, while relatively less marked inhibition was observed in Jurkat cells. Activation of NF kappa B in several monocytic cell lines was also suppressed by tepoxalin. However AP-1 stimulation under the same conditions was not affected by tepoxalin. Other CO, LO inhibitors such as naproxen or zileuton did not inhibit NF kappa B activities. This inhibitory activity of tepoxalin was further illustrated by its suppression of NF kappa B regulated genes such as IL-6 in PMA stimulated human PBL and c-myc in IL-2 dependent T cell lines. Tepoxalin also blocked PMA + ionomycin-induced I kappa B degradation in a time-dependent fashion. The possible mechanism of tepoxalin in NF kappa B activation and its potential clinical application are discussed.

Animals↗
PubMed1995

Intestinal T cells in CD8 alpha knockout mice and T cell receptor transgenic mice.

Intraepithelial lymphocytes (IEL) refer to the T cells located at the epithelium of the intestines. Unlike the T cells in other peripheral lymphoid organs, the majority of IEL express the CD8 cell surface protein. To study the role of CD8 in the ontogeny and the function of IEL, phenotypic analysis of IEL from CD8 alpha knockout mice and normal mice was performed. The CD8 alpha gene in CD8 alpha knockout mice was disrupted by homologous recombination. These mice are defective in thymic maturation of cytotoxic T cells. In normal mice, alpha beta T cells that were CD8 alpha alpha+ or CD4+ CD8 alpha alpha+, and gamma delta T cells that were CD8 alpha alpha+, were the distinct populations found only in IEL. In CD8 alpha knockout mice, the population size of IEL remained normal, but the majority of IEL were CD4- CD8- T cells expressing alpha beta or gamma delta T cell receptors. IEL from the H-Y transgenic mice2, which express the male H-Y antigen specific T cell receptor in a normal and in a CD8 alpha-null background, were also studied. In contrast to thymic derived T cells, CD8 alpha alpha+ IEL with the autoreactive transgenic T cell receptor were not deleted, but clonally expanded in the male transgenic mice. Interestingly, no pathological symptoms were observed in the intestines of these mice. In the absence of CD8 alpha expression, the H-Y specific autoreactive IEL did not accumulate in the intestines. The results suggest that CD8 alpha alpha+ IEL are derived extra-thymically and their responses towards antigens require the CD8 accessory molecule.

Animals↗
PubMed1995

Cytokine-modulating activity of tepoxalin, a new potential antirheumatic.

Tepoxalin is a new dual cyclooxygenase/5-lipoxygenase anti-inflammatory compound currently under clinical investigation. It has been shown to possess anti-inflammatory activity in a variety of animal models and more recently to inhibit IL-2 induced signal transduction. The current study was conducted to evaluate the cytokine modulating activity of tepoxalin and the role of iron in these effects. In human peripheral blood mononuclear cells (PBMC) stimulated with OKT3/PMA, tepoxalin inhibited lymphocyte proliferation with an IC50 of 6 microM. Additionally, it inhibited the production of LTB4 (IC50 = 0.5 microM) and the cytokines IL-2, IL-6 and TNF alpha (IC50 = 10-12 microM). Cytotoxicity was not demonstrated at these concentrations. Add-back experiments with either cytokines (IL-2 or IL-6), LTB4 or conditioned media failed to restore the proliferative response in the presence of tepoxalin. However, the concurrent addition of iron (in the form of ferrous or ferric chloride and other iron salts) reversed the inhibition of proliferation caused by tepoxalin. Tepoxalin also inhibits the activation of NF kappa B, a transcription factor which acts on several cytokine genes. Tepoxalin's effect on NF kappa B is also reversed by the addition of iron salts. These data suggest that the action of tepoxalin to inhibit proliferation in PBMC may be at least in part due to its ability to reduce the amount of available iron resulting in decreased activation of NF kappa B and subsequent inhibition of cytokine production.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1995

Turning down the heat: new routes to inhibition of inflammatory signaling by prostaglandin H2 synthases.

Many nonsteroidal anti-inflammatory drugs act by inhibiting the cyclooxygenase activity of prostaglandin H2 synthase (PGHS), a key enzyme in the biosynthesis of prostaglandins. Gastric toxicity remains a serious problem with the current drugs, however. Recent advances in the understanding of PGHS now suggest two possible approaches to producing drugs with fewer side effects.

Animals↗
PubMed1994

Tepoxalin, a novel immunosuppressive agent with a different mechanism of action from cyclosporin A.

Tepoxalin, a compound previously identified as a dual cyclooxygenase/lipoxygenase (CO/LO) inhibitor, is a potent inhibitor of T cell proliferation. Comparing the suppressive effects of tepoxalin and cyclosporin A (CsA) on OKT3-, PMA-, IL-2-, and PMA+ionomycin-induced T cell proliferations revealed marked differences in the mechanism of action between the two compounds. Whereas CsA was most effective in suppressing OKT3-stimulated proliferation, tepoxalin was more potent in inhibiting PMA-, PMA+ionomycin-, and IL-2-induced proliferation. Quantitative PCR (QPCR) assays used to detect cytokine messages showed that tepoxalin blocked IL-2 mRNA transcription in PMA- and PMA+ionomycin-, but not OKT3-stimulated T cells whereas CsA was most potent in inhibiting OKT3-induced IL-2 mRNA induction in these cells. Both tepoxalin and CsA did not inhibit the expression of IL-2R; however, only tepoxalin, but not CsA, inhibited the proliferation of IL-2-dependent blasts and the transcription of IFN-gamma, an IL-2-dependent target gene. Moreover, addition of exogenous IL-2 restored OKT3-induced proliferation to CsA- but not tepoxalin-treated cells. These data suggest that tepoxalin, but not CsA, suppressed T cell proliferation by inhibiting IL-2-induced signal transduction. Consistent with these findings, tepoxalin, unlike CsA, which was most potent when added at the initiation of OKT3 stimulation, was equally active, regardless of whether it was added at the beginning or 48 h after culture initiation. The difference in mechanism of action between tepoxalin and CsA was confirmed further by the synergistic suppressive effects on T cell proliferation upon co-administration of the two compounds.

Base Sequence↗
PubMed1994

Reduced thymic maturation but normal effector function of CD8+ T cells in CD8 beta gene-targeted mice.

CD8 is a cell surface glycoprotein on major histocompatibility complex class I-restricted T cells. Thymocytes and most peripheral T cells express CD8 as heterodimers of CD8 alpha and CD8 beta. The intestinal intraepithelial lymphocytes (IEL), which have been suggested to be generated extrathymically, express CD8 predominantly as homodimers of CD8 alpha. We have generated CD8 beta gene-targeted mice. CD8 alpha+ T cell population in the thymus and in most peripheral lymphoid organs was reduced to 20-30% of that in wild-type littermates. CD8 alpha expression on thymocytes and peripheral T cells also decreased to 44 and 53% of the normal levels, respectively. In contrast, neither the population size nor the CD8 alpha expression level of CD8 alpha+ IEL was reduced. This finding indicates that CD8 beta is important only for thymic-derived CD8+ T cells. The lack of CD8 beta reduces but does not completely abolish thymic maturation of CD8+ T cells. Our result also reveals the role of CD8 beta in regulating CD8 alpha expression on thymic derived T cells. Peripheral T cells in these mice were efficient in cytotoxic activity against lymphocytic choriomeningitis virus and vesicular stomatitis virus, suggesting that CD8 beta is not essential for the effector function of CD8+ T cells.

Animals↗
PubMed1994

Differential ligand binding specificities of recombinant CD11b/CD18 integrin I-domain.

The alpha subunits of leukocyte CD11/CD18 integrins contain an approximately 200-amino acid "inserted" domain (I-domain) that may be important for multivalent adhesive recognitions. A recombinant form of the I-domain of CD11b/CD18 was generated and analyzed directly for interaction with complementary integrin ligands. CD11b I-domain bound the activation-dependent monoclonal antibody 7E3, and the functionally blocking anti-CD11b monoclonal antibodies OKM9, 60.1, and LM2/1, but not OKM1 or M1/70. Fibrinogen or soluble intercellular adhesion molecule-1 associated with CD11b I-domain in a concentration-dependent manner. Binding of 125I-fibrinogen to recombinant CD11b I-domain was saturable, governed by a Kd of approximately 0.22 +/- 0.06 microM, and fully inhibited by molar excess of unlabeled fibrinogen, or by the P1 peptide (KY)GWTVFQKRLDGSV (IC50 approximately 2.5-5 microM), duplicating the fibrinogen gamma chain sequence Gly190-Val202. In contrast, 125I-factor X binding to CD11b I-domain was only partially inhibited (50-60%) by a molar excess of unlabeled factor X, and entirely unaffected by functionally blocking anti-CD11b monoclonal antibodies or by factor X-derived synthetic peptidyl antagonists. We conclude that the I-domain of CD11b participates in qualitative mechanisms of receptor activation and contains the binding site(s) for the CD11b/CD18 ligands fibrinogen and intercellular adhesion molecule-1, while it is only minimally implicated in the recognition of factor X.

Amino Acid Sequence↗
PubMed1994

A leukocyte lipid up-regulates the avidity of lymphocyte function-associated antigen-1.

An acidic lipid termed leukocyte adhesion lipid (LAL) was isolated from PMA stimulated lymphoid and myeloid cell lines HL60, Jurkat, K562 and U937 but not from unstimulated cells or PMA treated Cos7 cells. LAL treated peripheral blood leukocytes (PBL) adhered strongly to IL-1 beta activated human umbilical vein endothelial cells (HUVEC), and the interaction could be inhibited by antibodies to intercellular adhesion molecule (ICAM-1) or lymphocyte function-associated antigen-1 (LFA-1). Leukocytes treated with LAL maintained the high avidity state of LFA-1 for at least 1 hr whereas the avidity of LFA-1 in PMA treated cells declined after 30 min. LAL was stable to heat (100 degrees C, 10 min), alkaline phosphatase and proteinase K treatments. Chemical analysis suggested that LAL contained unsaturated lipids. Our findings provide evidence for the involvement of lipids in LFA-1 activation.

Cell Adhesion↗
PubMed1994

Use of a human skin-grafted nude mouse model for the evaluation of topical retinoic acid treatment.

Cultured human keratinocytes and artificial dermal equivalents maintained in vitro do not perfectly mimic the terminal differentiation patterns and response to drugs observed in intact human skin. We have made use of human skin grafted onto nude mice to demonstrate that such grafts maintain the pattern of pharmacologic responsiveness to all-trans retinoic acid previously reported in human subjects. The use of a quantitative polymerase chain reaction method to measure induction of a retinoic acid responsive gene, cytoplasmic retinoic acid binding protein II, has made it possible to generate objective data suitable for investigations of drug efficacy. This method of using grafted human skin has potential broad applicability for investigation of topical drugs in a number of therapeutic fields.

Administration, Topical↗
PubMed1993

Characterization of the gene for the human high affinity IgE receptor (Fc epsilon RI) alpha-chain.

The Fc epsilon RI couples the mast cell-surface binding of IgE and Ag to a complex series of intracellular events culminating in cell activation and degranulation. The alpha-chain of Fc epsilon RI constitutes the Ig-binding subunit of this heterotetrameric receptor, and is itself a member of the Ig gene superfamily. We have isolated a human genomic DNA clone containing the entire Fc epsilon RI alpha gene, and completely sequenced a region from 1257 bp 5' of the transcription start site, to 513 bp 3' of the last exon of the gene. As with the previously characterized rat and mouse genes, human Fc epsilon RI alpha consists of five exons and four introns, and spans 5889 bp of genomic DNA. The splice donor and acceptor sites deduced by comparison with the cDNA sequence corresponded exactly to the locations found in analogous rodent genes. By mapping the 5' end of Fc epsilon RI alpha transcripts we found three major transcription initiation sites 24, 27, and 29 bp upstream of the ATG translation initiation codon. As well, several longer minor transcripts were seen, with a maximum of 60 nt of 5'-untranslated sequence. About 650 bp of DNA upstream of the ATG translation initiation codon were compared among human, rat, and mouse Fc epsilon RI alpha sequences in search of common motifs that might mediate conserved regulatory interactions with DNA binding proteins. A 172-bp region of the human Fc epsilon RI alpha 5'-flanking sequence was highly conserved in both rodent species. Further studies will be required to determine whether these or other sequences are involved in Fc epsilon RI alpha gene regulation.

Base Sequence↗
PubMed1993

Loxoribine (7-allyl-8-oxoguanosine) activates natural killer cells and primes cytolytic precursor cells for activation by IL-2.

Guanine ribonucleosides that have been substituted at the C8 position with bromine or thiol groups have been shown previously to activate NK cells and to act as sparing agents for IL-2 in the generation of LAK cells. Herein, we examined a disubstituted guanosine, 7-allyl-8-oxoguanosine (loxoribine), for the ability to activate NK cells and to interact with IL-2 in the generation of LAK cells. Loxoribine enhanced the NK activity of murine spleen cells with optimal activity occurring after 10 h of culture at concentrations ranging from 50 to 150 microM. The response was, however, short lived, approaching baseline levels by 24 h of culture. In contrast, if spleen cells were cultured with a suboptimal concentration of IL-2 (10 U/ml) in combination with loxoribine, a prolonged and enhanced cytolytic activity was seen. The enhancement was greatest if the loxoribine and IL-2 were both added to the cultures at the beginning of the incubation period. Analysis of the expression of the alpha-chain of the IL-2 receptor after loxoribine stimulation indicated that gene transcription was enhanced within 4 h, and cell surface expression was observed on NK1.1+ Thy1+ and NK1.1+ Thy1- cell populations within 24 h of loxoribine treatment. The priming of LAK cell precursors by loxoribine did not appear to be mediated by IFN-alpha/beta, because anti-IFN antibodies did not block either the activation of cytolytic cells by IL-2 or the expression of IL-2 receptors after culture with loxoribine. These data suggest that one mechanism by which cytolytic precursor cells are primed by loxoribine to respond to IL-2 faster and with enhanced cytolytic activity may be through the expression of high affinity IL-2 receptors due to the up-regulation of the alpha-chain.

Animals↗
PubMed1993

In vivo activation of natural killer cells and priming of IL-2 responsive cytolytic cells by loxoribine (7-allyl-8-oxoguanosine).

Guanine ribonucleosides which have been substituted at the N7 and/or C8 positions have been shown previously to activate natural killer (NK) cells and to act as sparing agents for interleukin-2 (IL-2) in the in vitro generation of lymphokine activated killer (LAK) cells. In this paper we examined a disubstituted guanosine, 7-allyl-8-oxoguanosine (loxoribine), for the ability to activate NK cells and to interact with IL-2 in the generation of LAK cells in vivo. Following iv administration, loxoribine enhanced murine splenic NK activity in a dose-related fashion, with optimal responses occurring at 3 mg/mouse. Enhanced lysis of YAC-1 cells was seen within 6 hr of injection and NK activity remained elevated for over 96 hr. Mature B and T cells were not required for NK activation since SCID mice responded to loxoribine within the same dose range as did the normal, immunocompetent mice. Both effector and precursor cells were eliminated by the administration of anti-asialo GM1 antibodies and NK activation was totally blocked in mice injected with anti-NK 1.1 antibodies. To test whether loxoribine would act as a sparing agent for IL-2 stimulated LAK activation, mice were injected with 2 mg loxoribine followed by twice daily administration of 10,000 units IL-2. In assays performed 48, 72, and 96 hr after injection of loxoribine, the cytolytic activity with the combination therapy exceeded the activity expected from the algebraic sum of the responses to the individual agents. Single injections of 2 mg loxoribine and 25,000 units IL-2 also stimulated NK/LAK activity, but the greatest enhancement was seen when loxoribine was administered 24 hr before the IL-2. Analysis of mRNA transcripts for the alpha chain of the IL-2 receptor indicated that gene transcription was enhanced within hours of loxoribine administration.

Animals↗
PubMed1992

In vivo enhancement of murine natural killer cell activity by 7-allyl-8-oxoguanosine (loxoribine).

7-Allyl-8-oxoguanosine (loxoribine) is a novel immunostimulatory compound which has been shown previously to enhance the antibody synthesis of antigen-stimulated B-lymphocytes. In this report, loxoribine was tested for the ability to activate murine natural killer (NK) cells. In studies in which mice were given a single subcutaneous (s.c.) or intravenous (i.v.) injection of loxoribine, splenic NK cell activity was increased in a dose-related manner with clear enhancement seen within 2 h of drug administration. The enhancement was optimal at 48 h but persisted for a minimum of 4 days. Slow and continuous administration of loxoribine via subcutaneously implanted infusion pumps successfully enhanced the NK activity for several days after all of the pump contents had been delivered. Peak NK responses were seen following s.c. or i.v. administration of 2-3 mg loxoribine per mouse in sesame oil, intralipid, or saline vehicles. Significant oral activity was seen after the administration of 8-10 mg/mouse in sesame oil or intralipid. The in vivo enhancement of NK activity was observed in spleen, blood, and bone marrow but was negligible in lymph nodes and thymus. Multiple injections of optimal concentrations of loxoribine did not tend to enhance the NK activity above that seen with a single injection, suggesting that the timing of injections was critical for optimal responsiveness.

Adjuvants, Immunologic↗
PubMed1986

Lymphocytotoxins in vasculitis. Correlation with clinical manifestations and laboratory variables.

Twenty-eight of 53 patients with various types of vasculitis were found to have cold reacting lymphocytotoxins (LCT). LCT were cytotoxic to both peripheral blood B and T cells as well as to OKT4 and OKT8 subpopulations. The interaction with the B cells was more pronounced than with the T cells as shown by reactivity with the former at higher serum dilutions than with the latter. Similar results were obtained with eluates from the unseparated lymphocytes and from B or from T cells. Partial purification of LCT demonstrated that they belong to the IgM class. LCT correlated with the level of circulating immune complexes as determined by the fluid phase C1q binding assay, but they did not correlate with the level of immunoglobulins, complement or antinuclear factors. The presence of LCT correlated significantly with the activity but not with the disease duration or the number of involved organs. Correlation of LCT with the activity of vasculitis implies that these cytotoxins may have a pathogenetic role and perhaps may serve as a marker for disease activity.

Antigen-Antibody Complex↗