The presence of concanavalin-A(Con-A)-like molecules on natural-killer (NK)-sensitive target cells: their possible role in swainsonine-augmented human NK cytotoxicity

The immunomodulatory effects of Ipomoea carnea in rats vary depending on life stage

Ipomoea carnea Jacq. ssp. fistulosa (Mart. Ex Choisy; Convolvulaceae; I. carnea) possesses a toxic component: an indolizidine alkaloid swainsonine (SW) that has immunomodulatory effects due to its inhibition of glycoprotein metabolism. It is also known that SW is excreted into both the amniotic fluid and milk of female rats exposed to I. carnea. Thus, the aim of this study was to determine whether SW exposure, either in utero or from the milk of dams treated with I. carnea, modulates offspring immune function into adulthood. In addition, adult (70 days old) and juvenile rats (21 days old) were exposed to I. carnea in order to evaluate several other immune parameters: lymphoid organs relative weight and cellularity, humoral and cellular immune responses. Offspring exposed to I. carnea during lactation developed rheumatoid arthritis (RA) in adulthood after an immunogenic challenge. In addition, both adult and juvenile rats exposed to I. carnea showed discrepancies in several immune parameters, but did not exhibit any decrease in humoral immune response, which was enhanced at both ages. These findings indicate that SW modulates immune function in adult rats exposed to SW during lactation and in juvenile and adult rats exposed to SW as juveniles and adults, respectively.

A role for SHPS-1/SIRPalpha in Concanavalin A-dependent production of MMP-9

SHPS-1/SIRPalpha1 is a transmembrane glycoprotein that belongs to the immunoglobulin (Ig) super family. In the present study, we show that SHPS-1 strongly associates with Concanavalin A (Con A), a plant lectin obtained from jack beans. Further studies with SHPS-1 mutants reveal that the extracellular domain of SHPS-1 containing the Ig sequence is responsible for its association with Con A. Con A treatment induces cross-linking and multimerization of the SHPS-1 protein in the plasma membrane, accompanied by its tyrosine phosphorylation and recruitment of SHP-2. In contrast, Ricinus communis agglutinin (RCA), another lectin obtained from castor bean, does not bind or activate tyrosine phosphorylation of SHPS-1. Moreover, Con A activates Akt in a SHP-2-dependent manner. Treatment of mouse embryonic fibroblasts (MEFs) with Con A induces secretion of matrix metalloproteinase (MMP)-9, a phenomenon that is inhibited in cells expressing YF mutant of SHPS-1, a dominant negative form of Akt or in cells pre-treated with an Akt inhibitor, LY294002 or extracellular-signal regulated kinase (Erk) inhibitor, U0126. In addition, expression of the YF mutant of SHPS-1 inhibits Con A-dependent activation of Akt and Erk kinases. Taken together, our results suggest that SHPS-1 is a receptor for Con A that mediates Con A-dependent MMP-9 secretion through SHP-2-promoted activation of both Akt and Erk pathways.

Inhibition of the growth of human gastric carcinoma in vivo and in vitro by swainsonine

In Europe, swainsonine has been studied widely for prevention of metastasis and cancer therapy. In order to investigate the effects and mechanisms of swainsonine on the human gastric carcinoma SGC-7901 cell, we carried out in vivo and in vitro experiments. After treatment with swainsonine, an effective dose and IC50 value of swainsonine for SGC-7901 cells were examined by MTT assay. Cell-cycle distribution and apoptotic rates were analyzed using FCM, and [Ca2+]i was measured using LSCM. The expression of p53, c-myc and Bcl-2 were determined using an immunocytochemical method. Simultaneously, 50 mice were divided randomly into five groups. Three groups were administrated swainsonine at dose of 3, 6 and 12 mg/kg body wt., two control groups were administrated N.S. 20 ml/kg body wt. and 5-Fu 20 mg/kg body wt., respectively, by intraperitoneal injection. The inhibition rate was calculated and pathological sections were observed. The growth of SGC-7901 cell is inhibited by swainsonine in vitro, with an IC50 value at 24 h of 0.84 microg/ml, and complete inhibition concentration is 6.2 microg/ml. After treatment with swainsonine at the concentrations of 0.5, 1.5 and 4.5 microg/ml for 24 h, the expression of apoptosis inhibiting gene p53 and bcl-2 decreases, and the apoptotic trigger gene c-myc increases markedly (p<0.05), as well as [Ca2+]i overloading, SGC-7901 cell is induced to apoptosis in the end. It is also found that the percentages of S phase are 38.8%, 39.7% and 29.6%, respectively (20.0% in control group and 23.2% in 5-Fu group). The rates of inhibition were 13.2%, 28.9%, 27.3%, respectively, when the nude mice were administered swainsonine (p<0.05 or 0.01). The structure of the tumor showed hemorrhage, necrosis and inflammatory cell infiltration. We therefore conclude that swainsonine could inhibit cell proliferation in vitro and the growth of human gastric carcinoma in vivo. The mechanisms of swainsonine-induced apoptosis may relate to [Ca2+]i overloading and the expression of apoptosis-related genes.

Stress renders T cell blasts sensitive to killing by activated syngeneic NK cells

Exposure of primary T cell blasts to stress in the forms of heat, hydrogen peroxide, or high-density growth conditions resulted in a state of enhanced susceptibility to killing by syngeneic IL-2-activated NK cells or lymphokine-activated killer cells, but not to killing by CTL. Cytotoxicity was perforin mediated and was not due to decreased target expression of total MHC class I. The levels of stress used had little effect on cell viability. For thermal stress, sensitization increased with temperature, required a minimum exposure time, and disappeared when cells were given a long enough recovery time. Our data support a model that predicts that activated NK cells play a role in the immunosurveillance of nontransformed stressed cells in normal animals.

Suppressive effects of swainsonine and N-butyldeoxynojirimycin on human bone marrow neutrophil maturation

The effects of the N-linked oligosaccharide inhibitors swainsonine and N-butyldeoxynojirimycin (NB-DNJ) on granulopoiesis was investigated using human bone marrow cells in in vitro liquid and agar cultures. The addition of the inhibitors into cultures containing granulocyte colony-stimulating factor (G-CSF) suppressed maturation from myelocytes into mature neutrophils. Swainsonine did not induce apoptosis, but NB-DNJ induced considerable apoptosis, especially in the presence of G-CSF. This result indicated that the decrease of mature neutrophils by swainsonine was not because of cell degeneration. In the case of NB-DNJ, it was thought to be because of both maturation suppression and apoptosis. In a colony-forming unit-granuloid (CFU-G) colony assay, the number of colonies was increased in the presence of the inhibitors, but the morphology of colonies was predominantly compact, or immature. The inhibitors also suppressed the expressions of mRNAs of CCAAT/enhancer binding protein epsilon (C/EBPepsilon) and G-CSF receptor as markers of terminal neutrophil maturation. These findings suggested that the incompleteness of N-linked oligosaccharide leads to the suppression of terminal neutrophil maturation.

Development and viability of bovine preplacentation embryos treated with swainsonine in vitro

This study investigated the effects of swainsonine (a locoweed toxin) on bovine preplacentation embryo development using in vitro procedures. We examined and confirmed the viability and developmental potential of swainsonine-treated embryos by transfer to synchronized recipient heifers. Oocytes (n = 6338) were aspirated from ovaries collected from the abattoir and subjected to in vitro maturation (IVM), in vitro fertilization (IVF) and in vitro culture (IVC). Swainsonine was added to IVM, IVF, IVC media spatially and IVM/IVF/IVC continuously, at 0 ng/ml (TRTI, control), 200 ng/ml (TRT2), 400 ng/ml (TRT3), and 800 ng/ml (TRT4). Embryo development was evaluated with respect to oocyte cleavage rate and the rates of morula and blastocyst formation. There was no difference (P > 0.05) among treatments. The average number of nuclei per blastocyst at Day 7.5 of culture (Day 0 = IVF) was 85.9 +/- 4.3 (n = 47) and 89.3 +/- 4.4 (n = 44) for swainsonine-treated embryos (800 ng/ml) and control embryos, respectively. Pregnancy rate as determined by ultrasonography on day 35 to 40 post embryo transfer was 43.8% and 38.3% for swainsonine-treated (800 ng/ml) and control embryos, respectively. Nine (9.4%) healthy calves were delivered from heifers receiving swainsonine-exposed and nine (9.6%) from control embryos. No difference (P > 0.05) was detected in number of calves developing from TRT and control embryos. We conclude that swainsonine does not have an adverse effect on the development and viability of preplacentation bovine embryos.

U5 monoclonal antibody identifies a novel lymphocyte surface antigen preferentially expressed in human circulating natural killer cells with high cytotoxic activity

U5 monoclonal antibody (mAb), developed against Japanese monkey lymphocytes, identified a glycoprotein of 32 000 MW that is expressed in a subset of human circulating natural killer (NK) cells. The distribution of U5 molecules was restricted among CD16+ cells, and U5 antigen was preferentially expressed in the CD38+ subset. U5+ CD16+ CD56+ cells were highly active on NK assay against K562 target cells. Variations in cytolytic activities and mRNA expression of perforin, granzyme B and Fas ligand (FasL) were observed in U5- CD16+ CD56+ cells depending on the donor. We found that in some donors, a phenotypically mature (CD16+ CD56+) but functionally immature subset was present in the peripheral circulation. The U5- CD16+ CD56+ cells of some donors exhibited negligible cytolytic activity with no detectable expression of the above mRNAs, whereas those of the other donors had a significant but lower cytolytic activity with a reduced expression of granzyme B mRNA as compared with those of U5+ CD16+ CD56+ cells. Concanavalin A (Con A) stimulation induced an expression of U5 antigen in U5- CD16+ CD56+ cells accompanied by an up-regulation of granzyme B mRNA expression. These findings suggest that U5 antigen may be a novel molecule involved in the maturation or differentiation of human circulating NK cells.

Inhibition of N-linked glycosylation by tunicamycin enhances sensitivity to cisplatin in human head-and-neck carcinoma cells

Tunicamycin (TM), a naturally occurring antibiotic, blocks the first step in the biosynthesis of N-linked oligosaccharides in cells. In this study, we investigated whether changes in N-linked glycosylation affect the sensitivity of head-and-neck carcinoma cell lines to cis-diaminedichloroplatinum(II) (cisplatin) in vitro and in vivo. In vitro treatment of the IMC-3 and KB cell lines with TM significantly decreased the 50% inhibitory concentration (IC50) of cisplatin, as determined by the MTT assay (24.15 to 10.97 microg/ml, p < 0.05). In addition, TM significantly decreased the IC50 of cisplatin against established cisplatin-resistant IMC-3/CR cells (>100 to 14.4 microg/ml, p < 0.05) to levels similar to those against parental IMC-3 cells. TM treatment decreased the number of Con A- and L-PHA-binding sites on the surface of tumor cells but had no effect on the intracellular platinum concentration. Induction of apoptosis in vitro by TM plus cisplatin in combination was increased compared with that by cisplatin alone. Furthermore, in vivo administration of TM plus cisplatin in combination significantly inhibited local tumor growth in the cisplatin-resistant in vivo C3H/He mouse model as compared with the control group (p < 0.05) and increased in vivo apoptosis of tumor cells. Our results suggest that the manipulation of glycosylation by TM in tumor cells might be a useful therapeutic strategy for successful chemotherapy using cisplatin against head-and-neck cancer.

Enhancement of cytolytic activity of human peripheral blood lymphocytes by sodium periodate (IO4) possible involvement of protein kinase C

Sodium periodate (IO4) exerts a number of biological effects including the enhancement of lymphocyte activation. In this study, we investigated its effects on cytotoxicity of human peripheral blood lymphocytes (PBL) and explored the mechanism whereby it exerted these effects. In vitro treatment of human PBL with IO4 augmented their cytotoxicity against K562 myelogenous leukemia cells. IO4 oxidative treatment increased the frequency of effector-to-target cell binding. It also increased cellular ATP levels in effector cells, suggesting that the post-binding cytolytic functions of these cells were also enhanced after treatment with IO4. Moreover, IO4 treatment significantly increased the protein kinase C (PKC) activity of effector cells and induced the translocation of activity in the membrane fraction from the cytosol. H-7, a potent PKC inhibitor, significantly reduced this enhancement of membrane-associated PKC activity at 10 microM and significantly reduced the enhanced cytotoxicity of PBL at the same concentration. These results indicated that IO4 enhanced the binding capacity and post-binding cytolytic functions of PBL and that PKC activation was one mechanism to explain the IO4-induced cellular activation.

Effects of Aroclor 1254 on the thyroid gland, immune function, and hepatic cytochrome P450 activity in mallards

Adult male mallards were exposed to 0, 4, 20, 100, 250, and 500 mg/kg Aroclor 1254 by gavage twice per week for 5 weeks. Immunotoxic effects, as measured by antibody titers to sheep erythrocytes, natural killer cell activity and lymphocyte mitogenesis to phytohemagglutinin, were not detected as a consequence of polychlorinated biphenyl (PCB) exposure. Hepatic cytochrome P450 activities were measured as microsomal dealkylations of ethoxyresorufin (EROD) and pentoxyresorufin (PROD). Significant elevations in EROD and PROD were noted at 20 mg/kg and peaked in birds treated with 100 mg/kg. Total P450 was induced beginning at 100 mg/kg and peaked at 250 mg/kg. Relative liver weights were dose-dependently increased following treatment with 100 mg/kg or more. Thyroid weights were significantly increased in PCB-treated birds treated with 100 mg/kg or greater, but no significant histological abnormalities were observed, except at the highest dose. Plasma total triiodothyronine (T3) was decreased in a dose-dependent manner, with a significant lowest-observed-adverse-effect level (LOAEL) of 20 mg/kg. T3 was decreased following 7 days treatment with 100 mg/kg. The no-observed-adverse-effect level (NOAEL) was 4 mg/kg for decreased T3. Plasma glucose levels were decreased on days 28 and 35 in mallards treated with 500 mg/kg, while other clinical plasma biochemistry parameters were unaltered by PCB treatment. Plasma corticosterone levels were unchanged by PCB treatment. These results indicate that thyroid hormone levels and P450 activity in mallards are sensitive to subchronic PCB exposure in the absence of gross toxic effects and immunotoxicity.

Effects of induced hypo- and hyperthyroidism on immune function and plasma biochemistry in mallards (Anas platyrhynchos)

Hypo- or hyperthyroid states were induced in adult male mallards (Anas platyrhynchos) by subchronic exposure to daily injections of methimazole or a 9:1 ratio of thyroxine (T4): triiodothyronine (T3). The levels of T4 given were 0, 125, 250, or 500 micrograms/kg/day and for methimazole; 10 mg/kg/day for 22 or 21 days. Plasma T3 showed a lasting decrease with T4:T3 treatment, despite the attempt to maintain the normal T4:T3 ratio. Antibody formation to sheep red blood cells was decreased only at the 125 micrograms/kg/day dose of T4, and was unaffected by methimazole treatment. Natural killer cell activity to RP-9 tumor cells and macrophage phagocytosis of killed, opsonized Saccaromyces cereviseae were unaffected by treatment throughout the study. However, lectin-dependent cellular cytotoxic activity to RP-9 tumor cells was significantly decreased after 21 days of methimazole treatment, indicating that hypothyroidism may have an influence on cell-mediated immunity. Hypo- and hyperthyroid conditions had opposing effects on plasma cholesterol levels.

Stimulation of synthesis and release of swainosonine from transformed roots of Swainsona galegifolia

Transformed root cultures of Swainsona galegifolia were established for swainsonine production. Stimulation of production of swainsonine and its release into the culture medium was achieved using copper sulphate, reduction of medium pH and supply of swainsonine precursors. The yield of control cultures (0.3 g of roots grown in 15 ml medium for 30 days) was 79 micrograms swainsonine with only a trace of swainsonine in the medium. After treatment with 1 mM copper sulphate for two days before harvest on day 30, 155 micrograms of swainsonine was produced, of which 14.3 micrograms was in the medium. Reduction of medium pH from 5.7 to 2.7 for one day before harvest resulted in 159 micrograms of swainsonine (47 micrograms in the medium). Supplementation with 2 mM malonic acid for 12 days before harvest resulted in 187 micrograms total swainsonine (34 micrograms in the medium), while 2 mM pipecolic acid for six days before harvest gave the highest swainsonine yield (220 micrograms total, 43 micrograms in the medium). The increased yields were achieved through small increases in biomass, as well as increases in the level of swainsonine synthesis.

Application of chemical immunomodulators to the treatment of cancer and AIDS

A number of potential advantages, development of promising new agents, and the discovery of synergy with cytokines or cell products continue to spur research into the application of chemical immunomodulators for the treatment of cancer and AIDS. In preclinical in vitro and in vivo systems, chemical immunomodulators definitely modulate the immune system and have therapeutic efficacy. Although clinical trials have shown the ability of these agents to modulate the human immune system, thus far chemical immunomodulators have generally not fulfilled the therapeutic promise generated in animal models for the treatment of human diseases. While the discrepancy in results between animal models and human trials is obvious, the basis is not apparent. Species differences in elimination kinetics, presentation of active drug at the site of action, and the development of tachyphylaxis have been postulated as reasons for the minimal activity of these agents in humans. In addition, the use of investigational techniques established for cytotoxic agents may not be appropriate for immunomodulators. As with any immunomodulator, determining an optimal immunostimulatory dose and schedule and applying the therapy to patients with minimal tumor burden would perhaps be more appropriate than use of a maximally tolerated dose in patients with advanced disease. A dose-immunological effect relationship has recently been demonstrated for levamisole at doses higher than those used for many years in levamisole trials (99). While research and clinical investigation have identified several potentially useful chemical immunomodulators, the elementary understanding of the biochemical mechanisms involved in immunoregulation remains basic. Future research must elucidate these mechanisms, particularly in humans, to maximize the benefits of chemical immunomodulators as single agents or combined with cytotoxic chemotherapeutic agents, surgery, radiation therapy, other immunomodulators, and antiviral agents.