Mechanisms of action of mycophenolate mofetil in preventing chronic rejection.
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Cell Division↗
Biomedical subjects
A C Allison
Publications and source records attributed to A C Allison.
Celastrol, a potent antioxidant and anti-inflammatory drug, as a possible treatment for Alzheimer's disease.
In the brains of patients with Alzheimer's disease (AD) signs of neuronal degeneration are accompanied by markers of microglial activation, inflammation, and oxidant damage. The presence of nitrotyrosine in the cell bodies of neurons in AD suggests that peroxynitrite contributes to the pathogenesis of the disease. A drug with antioxidant and anti-inflammatory activity may prevent neuronal degeneration in AD. Celastrol, a plant-derived triterpene, has these effects. In low nanomolar concentrations celastrol was found to suppress the production by human monocytes and macrophages of the pro-inflammatory cytokines TNF-alpha and IL-1beta. Celastrol also decreased the induced expression of class II MHC molecules by microglia. In macrophage lineage cells and endothelial cells celastrol decreased induced but not constitutive NO production. Celastrol suppressed adjuvant arthritis in the rat, demonstrating in vivo anti-inflammatory activity. Low doses of celastrol administered to rats significantly improved their performance in memory, learning and psychomotor activity tests. The potent antioxidant and anti-inflammatory activities of celastrol, and its effects on cognitive functions, suggest that the drug may be useful to treat neurodegenerative diseases accompanied by inflammation, such as AD.
Alzheimer Disease↗
The possible role of vitamin K deficiency in the pathogenesis of Alzheimer's disease and in augmenting brain damage associated with cardiovascular disease.
The incidence of Alzheimer's disease (AD) increases with age and in carriers of the apolipoprotein E4 genotype. A relative deficiency of vitamin K, affecting the extrahepatic functions of the vitamin, is common in ageing men and women. The concentration of vitamin K is lower in the circulating blood of APOE4 carriers than in that of persons with other APOE genotypes. Evidence is accumulating that vitamin K has important functions in the brain, including the regulation of sulfotransferase activity and the activity of a growth factor/tyrosine kinase receptor (Gas 6/Axl). The hypothesis is now proposed that vitamin K deficiency contributes to the pathogenesis of AD and that vitamin K supplementation may have a beneficial effect in preventing or treating the disease. Vitamin K may also reduce neuronal damage associated with cardiovascular disease.
Alzheimer Disease↗
Immunosuppressive drugs: the first 50 years and a glance forward.
During the past 50 years, many immunosuppressive drugs have been described. Often their mechanisms of action were established long after their discovery. Eventually these mechanisms were found to fall into five groups: (i) regulators of gene expression; (ii) alkylating agents; (iii) inhibitors of de novo purine synthesis; (iv) inhibitors of de novo pyrimidine synthesis; and (v) inhibitors of kinases and phosphatases. Glucocorticoids exert immunosuppressive and anti-inflammatory activity mainly by inhibiting the expression of genes for interleukin-2 and other mediators. Cyclophosphamide metabolites alkylate DNA bases and preferentially suppress immune responses mediated by B-lymphocytes. Methotrexate and its polyglutamate derivatives suppress inflammatory responses through release of adenosine; they suppress immune responses by inducing the apoptosis of activated T-lymphocytes and inhibiting the synthesis of both purines and pyrimidines. Azathioprine metabolites inhibit several enzymes of purine synthesis. Mycophenolic acid and mizoribine inhibit inosine monophosphate dehydrogenase, thereby depleting guanosine nucleotides. Mycophenolic acid induces apoptosis of activated T-lymphocytes. A leflunomide metabolite and Brequinar inhibit dihydroorotate dehydrogenase, thereby suppressing pyrimidine nucleotide synthesis. Cyclosporine and FK-506 (Tacrolimus) inhibit the phosphatase activity of calcineurin, thereby suppressing the production of IL-2 and other cytokines. In addition, these compounds have recently been found to block the JNK and p38 signaling pathways triggered by antigen recognition in T-cells. In contrast, rapamycin inhibits kinases required for cell cycling and responses to IL-2. Rapamycin also induces apoptosis of activated T-lymphocytes. Immunosuppressive and anti-inflammatory compounds in development include inhibitors of p38 kinase and of the type IV isoform of cyclic AMP phosphodiesterase which is expressed in lymphocytes and monocytes.A promising future application of immunosuppressive drugs is their use in a regime to induce tolerance to allografts. The role of leukocytes in grafts, and the induction of apoptosis of clones of responding T-lymphocytes, is discussed.
Animals↗
Mycophenolate mofetil and its mechanisms of action.
Mycophenolate mofetil (MMF, CellCept(R)) is a prodrug of mycophenolic acid (MPA), an inhibitor of inosine monophosphate dehydrogenase (IMPDH). This is the rate-limiting enzyme in de novo synthesis of guanosine nucleotides. T- and B-lymphocytes are more dependent on this pathway than other cell types are. Moreover, MPA is a fivefold more potent inhibitor of the type II isoform of IMPDH, which is expressed in activated lymphocytes, than of the type I isoform of IMPDH, which is expressed in most cell types. MPA has therefore a more potent cytostatic effect on lymphocytes than on other cell types. This is the principal mechanism by which MPA exerts immunosuppressive effects. Three other mechanisms may also contribute to the efficacy of MPA in preventing allograft rejection and other applications. First, MPA can induce apoptosis of activated T-lymphocytes, which may eliminate clones of cells responding to antigenic stimulation. Second, by depleting guanosine nucleotides, MPA suppresses glycosylation and the expression of some adhesion molecules, thereby decreasing the recruitment of lymphocytes and monocytes into sites of inflammation and graft rejection. Third, by depleting guanosine nucleotides MPA also depletes tetrahydrobiopterin, a co-factor for the inducible form of nitric oxide synthase (iNOS). MPA therefore suppresses the production by iNOS of NO, and consequent tissue damage mediated by peroxynitrite. CellCept(R) suppresses T-lymphocytic responses to allogeneic cells and other antigens. The drug also suppresses primary, but not secondary, antibody responses. The efficacy of regimes including CellCept(R) in preventing allograft rejection, and in the treatment of rejection, is now firmly established. CellCept(R) is also efficacious in several experimental animal models of chronic rejection, and it is hoped that the drug will have the same effect in humans.
Animals↗
Squalene and squalane emulsions as adjuvants.
Microfluidized squalene or squalane emulsions are efficient adjuvants, eliciting both humoral and cellular immune responses. Microfluidization stabilizes the emulsions and allows sterilization by terminal filtration. The emulsions are stable for years at ambient temperature and can be frozen. Antigens are added after emulsification so that conformational epitopes are not lost by denaturation and to facilitate manufacture. A Pluronic block copolymer can be added to the squalane or squalene emulsion. Soluble antigens administered in such emulsions generate cytotoxic T lymphocytes able to lyse target cells expressing the antigen in a genetically restricted fashion. Optionally a relatively nontoxic analog of muramyl dipeptide (MDP) or another immunomodulator can be added; however, the dose of MDP must be restricted to avoid systemic side effects in humans. Squalene or squalane emulsions without copolymers or MDP have very little toxicity and elicit potent antibody responses to several antigens in nonhuman primates. They could be used to improve a wide range of vaccines. Squalene or squalane emulsions have been administered in human cancer vaccines, with mild side effects and evidence of efficacy, in terms of both immune responses and antitumor activity.
Acetylmuramyl-Alanyl-Isoglutamine↗
Antioxidants inhibit the in vitro production of inflammatory cytokines in Crohn's disease and ulcerative colitis.
BACKGROUND: Modulation of cytokine secretion may be of interest in the treatment of Crohn's disease or ulcerative colitis. METHODS: The effect of three antioxidants - butylated hydroxyanisol, tetrahydropapaveroline and nordihydroguaiaretic acid - on the production of tumour necrosis factor (TNF), interleukin (IL) 1, IL-6 and IL-8 (measured by enzyme-linked immunosorbent assay) by peripheral mononuclear cells and biopsies of inflamed colonic mucosa from inflammatory bowel disease patients were studied. RESULTS: We observed a decrease in IL-1 and IL-6 production by peripheral mononuclear cells from inflammatory bowel disease patients (approximately 50% of control). The three drugs did not decrease IL-6 and IL-8 secretion by colonic biopsies, whereas they did inhibit IL-1 and, to some degree, TNF production. The cytokine-inhibitory effect of antioxidants seems to be more pronounced in ulcerative colitis than in Crohn's disease. CONCLUSION: Our results suggest that the studied antioxidants, or related compounds, may be of interest in inflammatory bowel disease treatment.
Adult↗
Rooperol tetraacetate decreases cytokine mRNA levels and binding capacity of transcription factors in U937 cells.
We have previously described inhibition of the synthesis of three acute-phase inflammatory cytokines in human and rat macrophages by acetate esters of rooperol, a dicatechol of plant origin. Analysing the mechanism of anticytokine activity of rooperol, we compared levels of TNFalpha, IL-1beta and IL-6 mRNAs in the human promonocytic U937 cell line pretreated with phorbol myristate acetate (PMA) and incubated with rooperol tetraacetate (RTA) alone or in combination with LPS (500 ng/ml). It was found that 10 microM RTA decreased the levels of cytokine mRNAs both in the presence and absence of LPS, suggesting pretranslational inhibition of cytokine synthesis. Electrophoretic mobility shift analysis (EMSA) showed that RTA may influence cytokine mRNA expression by decreasing the binding activity of transcription factors NF-kappaB and AP-1.
Anti-Inflammatory Agents, Non-Steroidal↗
The mode of action of immunological adjuvants.
Adjuvants augment immune responses to antigens and influence the balance between cell-mediated and humoral responses, as well as the isotypes of antibodies formed. New adjuvant formulations include antigen-carrying vehicles and small molecules with immunomodulating activity. Widely used two-phase vehicles comprise liposomes and microfluidized squalene or squalane emulsions. These are believed to target antigens to antigen-presenting cells, including dendritic cells (DC), follicular dendritic cells (FDC) and B-lymphocytes. Activation of complement generates C3d, which binds CR2 (CD21) on FDC and B-lymphocytes, thereby stimulating the proliferation of the latter and the generation of B-memory. Targeting of antigens to DC may favour cell-mediated immunity. Immunomodulating agents induce the production of cytokine cascades. In a primary cascade at injection sites TNF-alpha, GM-CSF and IL-1 are produced. TNF-alpha promotes migration of DC to lymphoid tissues, while GM-CSF and IL-1 accelerate the maturation of DC into efficient antigen-presenting cells for T-lymphocytes. In a secondary cytokine cascade in draining lymph nodes, DC produce IL-12, which induces Th1 responses with the production of IFN-gamma. The cytokines elicit cell-mediated immune responses and the formation of antibodies of protective isotypes, such as IgG2a in the mouse and IgG1 in humans. Antibodies of these isotypes activate complement and collaborate with antibody-dependent effector cells in protective immune responses.
Adjuvants, Immunologic↗
Inhibitory effect of di-catechol rooperol on VCAM-1 and iNOS expression in cytokine-stimulated endothelium.
Induced expression of vascular cell adhesion molecule-1 (VCAM-1) and of nitric oxide synthase (iNOS) is believed to play a role in the pathogenesis of atherosclerosis, asthma, as well as other inflammatory disorders. In the current study we examined the effect of the di-catechol rooperol [(E)-1,5-bis (3',4'-dihydroxyphenyl) pent-4-en-1-yne] on the process of microvascular endothelial cell (MME) activation by TNF-alpha and IFN-gamma. We show that rooperol decreases VCAM-1 and iNOS mRNA levels in cytokine-activated MME with subsequent inhibition of VCAM-1 membrane expression as measured by adhesion of P815 cells to MME monolayers, and NO production, as reflected in the nitrite concentration in culture medium. The properties of rooperol now described suggest that rooperol may be an anti-inflammatory agent useful in the treatment of several inflammatory disorders.
Animals↗
Immunological adjuvants and their modes of action.
New adjuvant formulations contain a vehicle, which carries antigens to antigen-presenting cells. Examples of vehicles are liposomes, immune-stimulating complexes and microfluidized squalene-in-water emulsions. Adjuvant formulations may contain immunomodulators, which augment cytokine production, such as a synthetic muramyl dipeptide analog or monophosphoryl lipid A. In a primary cascade of cytokine production at the site of antigen + adjuvant injection, TNF-alpha promotes the migration of dendritic cells (DC) to lymphoid tissues while GM-CSF accelerates the differentiation of DC into efficient presenters of antigens to T cells. Adjuvants also up-regulate a secondary cascade of cytokines in lymphoid tissues responding to antigenic stimulation: IL-12 augments the production of IFN-gamma, which favors the production of antibodies of protective isotypes (IgG2a in the mouse). Thus adjuvants can regulate immune responses qualitatively as well as quantitatively. Adjuvant formulations can also activate complement, generating C3d, which binds CD21 on follicular dendritic cells (FDC) and B cells. FDC targeting favors the generation of B lymphocyte memory, which is important for vaccination.
Acetylmuramyl-Alanyl-Isoglutamine↗
Cytokine production in human and rat macrophages and dicatechol rooperol and esters.
The ability of dicatechol rooperol and esters to inhibit the production of cytokines in endotoxin-stimulated human alveolar macrophages, human blood monocyte/macrophages, histiocytic cell line U937, and rat alveolar macrophages was examined in vitro. Rooperol derivatives inhibited the production of tumour necrosis factor-alpha, interleukin-1 beta and interleukin-6. Of the esters tested on human cells, rooperol diacetate and tetraacetate were more potent inhibitors of cytokine production (IC50 in the range of 10-20 microM) than rooperol disulphate (IC50 in the range of 25-75 microM). The acetate esters also inhibited cytokine production in rat alveolar macrophages, whereas the sulphate had little effect. Rooperol and acetate esters, in the same concentration range, decreased the production of nitric oxide by rat alveolar macrophages stimulated by endotoxin. These concentrations of rooperol had no effect on cell viability, as indicated by incorporation of 14C-labelled leucine into macrophage proteins and their content of lactate dehydrogenase. The results obtained suggest that rooperol esters are potentially useful antiinflammatory agents.
Animals↗
Fibrogenic and other biological effects of silica.
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Animals↗
Effect of in vitro passage of healthy human gingival fibroblasts on cellular morphology and cytokine expression.
Cytokines have been implicated in the regulation of antibody and inflammatory responses, but their role in periodontal diseases has not been elucidated. In the present study, cytokine production by human gingival fibroblasts (HGF) following in vitro passage was assessed in order to determine the basal levels of cytokine message and protein and to determine if the cellular morphology and the profile of cytokines produced differed with passage. The HGF cell line F-CL was established by explantation from non-inflamed gingival tissue, and cells from passages 1-10 were studied. The number of cells was determined in confluent cultures and cell morphology was examined by light microscopy. Fibroblasts from confluent cultures were examined for cytokine mRNA by reverse transcription-polymerase chain reaction and culture supernatants were assessed for cytokines by enzyme-linked immunosorbent assay. The morphology of F-CL fibroblasts in passages 1-4 was normal, while fibroblasts in passages 5-10 were larger. In general, the number of cells decreased from early to late passage. Fibroblasts from passages 1-10 contained message for interleukin-1 beta, -6 and -8, but not for interleukin-1 alpha or tumour necrosis factor-alpha. Interleukin-6 was detected in culture supernatants of F-CL fibroblasts by the enzyme immunoassay and its level decreased with increasing passage.
Cell Culture Techniques↗
Transforming growth factor beta1 induces angiogenesis in vivo with a threshold pattern.
SUMMARY: The true role of transforming growth factor beta1 (TGFbeta) on angiogenesis is in question. Several in vitro studies have shown inhibition of proliferation and migration of endothelial cells (EC). However, some investigators have observed that TGFbeta stimulates the formation of EC tubes in vitro. Fewer in vivo studies have been performed, but these also show discrepancies: some report angiogenic induction and at least one reports inhibition. We used the disc angiogenesis system (DAS) to measure the in vivo effect of TGFbeta. Discs containing 1 ng to 2000 ng of TGFbeta were placed subcutaneously in mice, removed after a growth period of 14 days, measured by three different techniques, and compared with spontaneous growth controls and with positive controls containing prostaglandin El. Tritiated thymidine was used to determine proliferation of EC. The discs were also examined morphologically for patterns of vessel and stromal proliferation. The contribution of native TGFbeta to the spontaneous angiogenesis of wound healing was tested using a monoclonal anti-TGFbeta antibody. The combined effect of TGFbeta and fibroblast growth factor (bFGF) was studied by using suboptimal doses of both (500 ng and 10 microg, respectively). Although TGFbeta doses of 1 ng to 500 ng failed to induce angiogenesis, 1000 ng induced a significant level of angiogenesis which was maintained at 2000 ng. This effect was the same regardless of the method of quantification: centripetal growth of the vessels, size of fibrovascular growth area, or amount of incorporation of tritiated thymidine. The anti-TGFbeta antibody decreased the spontaneous vascular growth below the level of controls containing irrelevant IgG. The combination of TGFbeta and bFGF at suboptimal doses did not increase or decrease the angiogenic response. Discs containing TGFbeta showed more collagen and greater accumulation of neutrophils than control discs or discs containing other cytokines. In conclusion, TGFbeta1 is angiogenic in vivo, when it reaches a threshold of 1 microg, but is not angiogenic at doses of 1 to 500 ng. Endogenous TGFbeta contributes to spontaneous (wound healing) angiogenesis. At the suboptimal doses of TGFbeta and bFGF used, there is no evidence of a combined angiogenic effect. The angiogenic effect of TGFbeta is probably indirect, requiring recruitment of leukocytes that secondarily release angiogenic substances. This secondary effect may explain some of the discrepancies between the in vitro and in vivo effects of TGFbeta.
Alprostadil↗
Purine metabolism and immunosuppressive effects of mycophenolate mofetil (MMF).
Mycophenolate mofetil (MMF) is a novel immunosuppressive drug that shows promise in preventing the rejection of organ allografts and in the treatment of ongoing rejection. Orally administered MMF is hydrolyzed by esterases in the intestine and blood to release mycophenolic acid (MPA), a potent, selective, noncompetitive inhibitor of the type 2 isoform of inosine monophosphate dehydroxygenase (IMPDH) expressed in activated human T and B lymphocytes. By inhibiting IMPDH, MPA depletes the pool of dGTP required for DNA synthesis. MPA has a more potent cytostatic effect on lymphocytes than on other cell types, and this is the principal mechanism by which immunosuppressive activity is exerted. MPA also depletes pools of GTP in human lymphocytes and monocytes, thereby inhibiting the synthesis of fucose- and mannose-containing saccharide components of membrane glycoproteins. These are recognized by the family of adhesion molecules termed selectins. By this mechanism, MPA could decrease the recruitment of lymphocytes and monocytes into sites of graft rejection. In addition to preventing allograft rejection, MMF suppresses graft-versus-host reactions in lethal and nonlethal murine models. MMF inhibits primary antibody responses more efficiently than secondary responses. MPA inhibits the proliferation of human B lymphocytes transformed by Epstein-Barr virus and is not mutagenic. Clinically attainable concentrations of MPA suppress the proliferation of human arterial smooth muscle cells. These two properties of MPA may decrease the risk of lymphoma development and proliferative arteriopathy in long-term recipients of MMF.
Animals↗
Co-ordinate inhibition of the production of TNF, IL-1, and IL-6 by small molecules.
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Animals↗