Mycophenolic acid downregulates inducible nitric oxide synthase induction in astrocytes

Microglia-Dependent and Independent Brain Cytoprotective Effects of Mycophenolate Mofetil During Neuronal Damage

Acute lesions of the central nervous system often lead to permanent limiting deficits. In addition to the initial primary damage, accompanying neuroinflammation is responsible for progression of damage. Mycophenolate mofetil (MMF) as a selective inhibitor of inosine 5-monophosphate dehydrogenase (IMPDH) was shown to modulate the inflammatory response and promote neuronal survival when applied in specific time windows after neuronal injury. The application of brain cytoprotective therapeutics early after neuronal damage is a fundamental requirement for a successful immunomodulation approach. This study was designed to evaluate whether MMF can still mediate brain cytoprotection when applied in predefined short time intervals following CNS injury. Furthermore, the role of microglia and changes in IMPDH2 protein expression were assessed. Organotypic hippocampal slice cultures (OHSC) were used as an in vitro model and excitotoxically lesioned with N-methyl-aspartate (NMDA). Clodronate (Clo) was used to deplete microglia and analyze MMF mediated microglia independent effects. The temporal expression of IMPDH2 was studied in primary glial cell cultures treated with lipopolysaccharide (LPS). In excitotoxically lesioned OHSC a significant brain cytoprotective effect was observed between 8 and 36 h but not within 8 and 24 h after the NMDA damage. MMF mediated effects were mainly microglia dependent at 24, 36, 48 h after injury. However, further targets like astrocytes seem to be involved in protective effects 72 h post-injury. IMPDH2 expression was detected in primary microglia and astrocyte cell cultures. Our data indicate that MMF treatment in OHSC should still be started no later than 8–12 h after injury and should continue at least until 36 h post-injury. Microglia seem to be an essential mediator of the observed brain cytoprotective effects. However, a microglia-independent effect was also found, indicating involvement of astrocytes.

The effect of ribavirin on reactive astrogliosis in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an animal model of CNS inflammatory and demyelinating disease multiple sclerosis. Microglia and astrocytes represent two related cell types involved in the brain pathology in EAE. Accumulations of hypertrophic reactive astrocytes, intensely stained with glial fibrillary acidic protein (GFAP), which also expressed vimentin, are prominent features of EAE lesions. Recent studies from our laboratory reported that ribavirin attenuated the disease process in EAE by reducing clinical and histological manifestations. EAE was induced in genetically susceptible Dark Agouti rats with syngeneic spinal cord homogenate in complete Freund's adjuvant. Real time PCR and immunohistochemistry were used for determination of GFAP and vimentin gene and tissue expression. We have observed the increased gene and tissue expression of GFAP and vimentin in EAE rats. Ribavirin treatment significantly decreased the number of reactive astrocytes at the peak of disease. At the end of the disease, we have observed reactive GFAP(+) and vimentin(+) astrocytes in both immunized and ribavirin-treated groups, accompanied by increased level of GFAP mRNA. The present study indicates that ribavirin may have the ability to attenuate astrocyte proliferation and glial scaring at the peak of the disease and modulate the astroglial response to EAE during the time-course of the disease.

Immunosuppression after traumatic or ischemic CNS damage: it is neuroprotective and illuminates the role of microglial cells

Acute traumatic and ischemic events in the central nervous system (CNS) invariably result in activation of microglial cells as local representatives of the immune system. It is still under debate whether activated microglia promote neuronal survival, or whether they exacerbate the original extent of neuronal damage. Protagonists of the view that microglial cells cause secondary damage have proposed that inhibition of microglial activation by immunosuppression is beneficial after acute CNS damage. It is the aim of this review to analyse the effects of immunosuppressants on isolated microglial cells and neurons, and to scrutinize the effects of immunosuppression in different in vivo models of acute CNS trauma or ischemia. It is found that the immunosuppressants cytosine-arabinoside, different steroids, cyclosporin A, FK506, rapamycin, mycophenolate mofetil, and minocycline all have direct inhibitory effects on microglial cells. These effects are mainly exerted by inhibiting microglial proliferation or microglial secretion of neurotoxic substances such as proinflammatory cytokines and nitric oxide. Furthermore, immunosuppression after acute CNS trauma or ischemia results in improved structure preservation and, mostly, in enhanced function. However, all investigated immunosuppressants also have direct effects on neurons, and some immunosuppressants affect other glial cells such as astrocytes. In summary, it is safe to conclude that immunosuppression after acute CNS trauma or ischemia is neuroprotective. Furthermore, circumferential evidence indicates that microglial activation after traumatic or ischemic CNS damage is not beneficial to adjacent neurons in the immediate aftermath of such acute lesions. Further experiments with more specific agents or genetic approaches that specifically inhibit microglial cells are needed in order to fully answer the question of whether microglial activation is "good or bad".

Mycophenolate mofetil for non-renal manifestations of systemic lupus erythematosus: a systematic review

OBJECTIVE

To summarize the evidence for the use of mycophenolate mofetil (MMF) in non-renal manifestations of systemic lupus erythematosus (SLE).

METHODS

Treatment trials in human SLE from 1990 to 2006 that have been published in the English literature were searched by Medline using the keywords 'lupus', 'mycophenolate', 'neuropsychiatric', 'neurological', 'hematological', 'dermatological', 'cutaneous', 'skin', 'hemolytic' and 'thrombocytopenia'. Laboratory studies were excluded.

RESULTS

Twenty relevant studies were summarized. All were case series or open-labelled trials. The main indications for MMF were refractory haematological and dermatological lupus. Data regarding MMF in neuropsychiatric SLE were scant. Favourable results were reported with haematological disease. Evidence regarding the efficacy of MMF in refractory lupus skin lesions was conflicting. The efficacy of MMF in neuropsychiatric lupus was only modest and could not be separated from that of concomitant therapies. In one uncontrolled study, MMF was reported to be effective in preventing clinical flares in patients with persistently active serological markers. MMF was well tolerated in these reports.

CONCLUSIONS

Limited evidence suggests that MMF may be effective in refractory haematological and dermatological manifestations of SLE. Because of the possibility of publication bias, the efficacy of MMF in these manifestations has to be confirmed with controlled trials. The efficacy of MMF in neuropsychiatric SLE is unproven and should be restricted to those patients who are refractory and intolerant to, or reluctant for, cyclophosphamide. Finally, the current level of evidence does not support treating serology alone in SLE by MMF.

5-Aza-2'-deoxycytidine stimulates inducible nitric oxide synthase induction in C6 astrocytoma cells

The influence of a nucleoside analog 5-aza-2'-deoxycytidine (5-AzadC) on inducible nitric oxide synthase (iNOS)-dependent nitric oxide (NO) production in various rat cell types was investigated. In C6 astrocytoma cell line and primary astrocytes, 5-AzadC enhanced proinflammatory cytokine (IFN-gamma, TNF-alpha, IL-1)-triggered NO synthesis in a time- and dose-dependent manner. In contrast, 5-AzadC did not potentiate NO production in IFN-gamma-stimulated macrophages, fibroblasts, or endothelial cells. Blockade of transcription or translation in C6 cells abolished the observed effect, suggesting the iNOS gene expression, rather than its catalytic activity, as a target for the drug action. Accordingly, 5-AzadC upregulated IFN-gamma-induced expression of iNOS mRNA in C6 astrocytes. The effect of 5-AzadC on astrocyte NO release was blocked by the inhibitor of p44/42 mitogen activated protein kinase-dependent signaling. Finally, the observed stimulatory effect of 5-AzadC on iNOS expression was apparently independent of DNA demethylation, as DNA digestion with methylation-sensitive restriction enzyme HpaII showed that 5-AzadC failed to demethylate cellular DNA in conditions used for iNOS induction.

Astrocyte-induced regulatory T cells mitigate CNS autoimmunity

Although astrocytes presumably participate in maintaining the immune privilege of the central nervous system (CNS), the mechanisms behind their immunoregulatory properties are still largely undefined. In this study, we describe the development of regulatory T cells upon contact with astrocytes. Rat T cells pre-incubated with astrocytes completely lost the ability to proliferate in response to mitogenic stimuli. The cells were blocked in G0/G1 phase of the cell cycle, expressed less IL-2R, and produced significantly lower amounts of interferon-gamma (IFN-gamma), but not interleukin-2 (IL-2), IL-10, or tumor necrosis factor (TNF). These anergic cells completely prevented mitogen-induced growth of normal T lymphocytes, as well as CNS antigen-driven proliferation of autoreactive T cells. The suppressive activity resided in both CD4+ and CD8+ T-cell compartments. Heat-sensitive soluble T-cell factors, not including transforming growth factor-beta (TGF-beta) or IL-10, were solely responsible for the observed suppression, as well as for the transfer of suppressive activity to normal T cells. The administration of astrocyte-induced regulatory T cells markedly alleviated CNS inflammation and clinical symptoms of CNS autoimmunity in rats with experimental allergic encephalomyelitis. Finally, the cells with suppressive properties were readily generated from human lymphocytes after contact with astrocytes. Taken together, these data indicate that astrocyte-induced regulatory T cells might represent an important mechanism for self-limitation of excessive inflammation in the brain.

The immunosuppressant mycophenolate mofetil attenuates neuronal damage after excitotoxic injury in hippocampal slice cultures

In this study we investigated whether treatment with the immunosuppressant mycophenolate mofetil (MMF) has beneficial effects on neuronal damage after excitotoxic injury. Organotypic hippocampal slice culture (OHSC), lesioned by the application of N-methyl-d-aspartate (NMDA) after 6 days in vitro, showed an improved preservation of the hippocampal cytoarchitecture after continuous treatment with MMF for 3 further days (10 or 100 micro g/mL). Treatment with NMDA and MMF (100 microg/mL) reduced the number of damaged propidium iodide (PI)+ neurons by 50.7% and the number of microglial cells by 52%. Continuous treatment of lesioned OHSCs with MMF for 3 days almost abrogated the glial proliferative response, reflected by the 91.5% reduction in the number of bromo-desoxy-uridine (BrdU)-labelled microglial cells and astrocytes. Microglial cells in MMF-treated OHSCs contained fragmented nuclei, indicating apoptotic cell death, an effect which was also found in isolated microglial cells treated with MMF. The beneficial effect of MMF on neuronal survival apparently does not reflect a direct antiexcitotoxic effect, as short-term treatment of OHSCs with NMDA and MMF for 4 h did not reduce the number of PI+ neurons. In conclusion, MMF inhibits proliferation and activation of microglia and astrocytes and protects neurons after excitotoxic injury.

Mycophenolic acid inhibits activation of inducible nitric oxide synthase in rodent fibroblasts

Mycophenolate mofetil (MMF) is an immunosuppressive drug that acts as a selective inhibitor of inosine monophosphate dehydrogenase (IMPDH). MMF has recently been shown to inhibit the enzymatic activity of inducible NO synthase (iNOS) and subsequent production of the cytotoxic free radical nitric oxide (NO) in endothelial cells. We here investigated the effect of bioactive MMF compound mycophenolic acid (MPA) on iNOS-mediated NO synthesis in fibroblasts, which are important source of NO in rheumatoid arthritis and during rejection of solid organ transplants. MPA exerted dose-dependent inhibition of NO synthesis, measured as nitrite accumulation, in IFN-gamma + LPS-stimulated L929 mouse fibroblast cell line and rat primary fibroblasts. The effect of MPA was not mediated through interference with IMPDH-dependent synthesis of iNOS co-factor BH4 and subsequent suppression of iNOS enzymatic activity, as direct BH4 precursor sepiapterin failed to block the action of the drug. MPA suppressed the IFN-gamma + LPS-induced expression of fibroblast iNOS protein, as well as mRNA for iNOS and its transcription factor IRF-1, as assessed by cell-based ELISA and semiquantitative RT-PCR, respectively. MPA suppression of fibroblast NO release, iNOS, and IRF-1 activation, was efficiently prevented by exogenous guanosine, indicating that the drug acted through reduction of IMPDH-dependent synthesis of guanosine nucleotides. These results suggest that MPA inhibits NO production in fibroblasts by blocking guanosine nucleotide-dependent expression of iNOS gene, through mechanisms that might involve the interference with the induction of iNOS transcription factor IRF-1.