Inhibitory effect of mizoribine on matrix metalloproteinase-1 production in synovial fibroblasts and THP-1 macrophages

The immunosuppressive agent mizoribine monophosphate is an inhibitor of the human RNA capping enzyme

Mizoribine monophosphate (MZP) is a specific inhibitor of the cellular inosine-5′-monophosphate dehydrogenase (IMPDH), the enzyme catalyzing the rate-limiting step of de novo guanine nucleotide biosynthesis. MZP is a highly potent antagonistic inhibitor of IMPDH that blocks the proliferation of T and B lymphocytes that use the de novo pathway of guanine nucleotide synthesis almost exclusively. In the present study, we investigated the ability of MZP to directly inhibit the human RNA capping enzyme (HCE), a protein harboring both RNA 5′-triphosphatase and RNA guanylyltransferase activities. HCE is involved in the synthesis of the cap structure found at the 5′ end of eukaryotic mRNAs, which is critical for the splicing of the cap-proximal intron, the transport of mRNAs from the nucleus to the cytoplasm, and for both the stability and translation of mRNAs. Our biochemical studies provide the first insight that MZP can inhibit the formation of the RNA cap structure catalyzed by HCE. In the presence of MZP, the RNA 5′-triphosphatase activity appears to be relatively unaffected while the RNA guanylyltransferase activity is inhibited, indicating that the RNA guanylyltransferase activity is the main target of MZP inhibition. Kinetic studies reveal that MZP is a non-competitive inhibitor that likely targets an allosteric site on HCE. Mizoribine also impairs mRNA capping in living cells, which could account for the global mechanism of action of this therapeutic agent. Together, our study clearly demonstrates that mizoribine monophosphate inhibits the human RNA guanylyltransferase in vitro and impair mRNA capping in cellulo.

Mizoribine may suppress bone erosion in patients with rheumatoid arthritis by inhibiting osteoclastogenesis

Mizoribine is a disease-modifying anti-rheumatic drug (DMARD) that is used in the treatment of rheumatoid arthritis. However, clinical use of the drug is restricted to a few Asian countries due to a lack of comprehensive evidence on its effectiveness. The inhibitory effect of the drug on human osteoclastogenesis was investigated in the hopes of providing some clear evidence. Mizoribine was found to inhibit in vitro osteoclastogenesis in a dose-dependent manner. In addition, the size of the pit area was closely related to the number of osteoclasts in a bone resorption assay. However, mizoribine did not affect the phosphorylation of MAP kinase (p38, JNK, ERK), the degradation of IkappaBalpha, or receptor activator of NF-kappaB ligand (RANKL) expression in fibroblast-like synoviocytes stimulated with IL-1beta. These results suggested that mizoribine may partially suppress osteoclastogenesis, leading to progressive bone erosion by inhibiting the growth or the signaling pathway of precursor cells to form osteoclasts rather than fibroblast-like synoviocytes.

Use of mizoribine as a rescue drug for steroid-resistant pediatric IgA nephropathy

Recent clinical trials have shown a beneficial effect of mizoribine (Miz), an immunosuppressive drug, in the treatment of new-onset pediatric IgA nephropathy (IgAN). In this study, we evaluated the efficacy of Miz treatment in three children with established steroid-resistant IgAN. The patients had IgAN featuring persistent proteinuria and diffuse mesangial proliferation and had failed to respond to 2 years of treatment with prednisolone. Based upon the second biopsy results, patients were given methylprednisolone (mPSL) pulse therapy that induced a transient reduction in proteinuria, which was reversed when the mPSL dose was tapered. Miz therapy was then instigated in place of pulse mPSL. All three patients showed a substantial reduction in proteinuria and resolution of hematuria within 5 months. A follow-up biopsy in two of the patients showed a substantial reduction in the severity of glomerular lesions and a decrease in the number of activated macrophages. In conclusion, Miz therapy was found to be a safe and effective therapy in three cases of steroid-resistant pediatric IgAN. The ability of Miz to reduce the number of activated macrophages may be an important mechanism by which this drug ameliorated renal disease in these patients.

Auranofin inhibits overproduction of pro-inflammatory cytokines, cyclooxygenase expression and PGE2 production in macrophages

Auranofin (AF), a gold compound, is an orally active therapeutic agent used to treat rheumatoid arthritis (RA), a self-perpetuating inflammatory disease. RA is characterized by autoimmune-mediated proliferation of synovial cells that leads to inflammation, pain, and swelling in most major joints: However, the mechanism as to how AF relieves RA symptoms has not been fully elucidated. The object of this study was to examine the ability of AF to immunomodulate macrophages as antigen presenting cells (APCs). Macrophages are recognized as playing an important role in the pathogenesis of RA, in that there is a relative abundance of macrophage-derived cytokines, such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) in rheumatoid synovium. In this work, we tested whether AF (2.5-20 mM) could inhibit inflammatory activity in the macrophage cell line RAW 264.7. AF decreased production of nitric oxide (NO) and the pro-inflammatory cytokines, TNF-alpha, IL-1beta and IL-6 in macrophages. Furthermore, AF inhibited cyclooxygenase-2 (COX-2)-dependent prostaglandin E2 (PGE2) production in a concentration-dependent manner. In conclusion, these findings may provide an explanation for the clinical effects of AF in patients with RA.