Anti-myelin associated glycoprotein (MAG) neuropathy patients exhibit high levels of monoclonal IgM autoantibodies against the carbohydrate epitope HNK-1 (human natural killer-1). This glycoepitope is abundantly presented on the adhesion molecule MAG as well as on other glycoconjugates of the peripheral nervous system. Binding of the autoantibodies results in demyelination of the peripheral nerves causing severe sensorimotor deficits in anti-MAG neuropathy patients, including paresthesias and sensory ataxia. We have previously reported the effective neutralization and removal of anti-HNK-1 IgM autoantibodies in an immunological mouse model with the glycopolymer PPSGG (poly-l-lysine400 loaded with phenyl disodium 3-O-sulfo-ß-d-glucopyranuronate)-(1 → 3)-ß-D-galactopyranoside). Here, we further explore its physicochemical characteristics and its mode of action. The linear glycopolymer PPSGG is highly negatively charged, with an approximate length of 100 nm, and is readily taken up by liver and spleen resident macrophages through scavenger receptors. No aggregate formation or immune complex deposition in these or other organs is observed and despite fast and extensive uptake of PPSGG into Kupffer cells of the liver, it does not exhibit hepatotoxic effects ex vivo. In the presence of the anti-HNK-1 IgM antibodies, it preferentially forms complexes in a 1:1 or 1:2 binding stoichiometry (PPSGG/anti-HNK-1 IgM), however, without leading to aggregate formation though crosslinking of the multivalent binding partners in vitro. The complexes are actively taken up by murine macrophages in vivo and in human macrophages in vitro. PPSGG is designed to selectively and quickly remove disease-causing anti-HNK-1 IgM antibodies from circulation. Here, we demonstrate the unique mode of action of PPSGG and its therapeutic potential as the first antigen-specific treatment for anti-MAG neuropathy.

Front cover: Auditory hair cell degeneration underlies hearing loss, and finding effective treatment has been a holy grail quest of hearing research. So far, a combination of antioxidants and other protective substances have proven successful to a limited extent. Our findings show that the combination of nuclear factor of activated T‐cells (NFAT) inhibitor and N‐acetylcysteine provides full protection from gentamicin damage in hair cells. The main advantage is that hair cell protection can be achieved using lower concentrations of each component, and thus decreasing their potential side effects. This approach could be beneficial as treatment not just in aminoglycoside‐induced ototoxicity, but in all cases of ROS‐induced cochlear damage, with noise‐induced hearing loss being one of them.

Anti-myelin-associated glycoprotein (MAG) neuropathy is a disabling autoimmune peripheral neuropathy that is caused by circulating monoclonal IgM autoantibodies directed against the human natural killer-1 (HNK-1) epitope. This carbohydrate epitope is highly expressed on adhesion molecules such as MAG, a glycoprotein present in myelinated nerves. We previously showed the therapeutic potential of the glycopolymer poly(phenyl disodium 3-O-sulfo-beta-d-glucopyranuronate)-(1 -> 3)-beta-d-galactopyranoside (PPSGG) in selectively neutralizing anti-MAG IgM antibodies in an immunological mouse model and ex vivo with sera from anti-MAG neuropathy patients. PPSGG is composed of a biodegradable backbone that multivalently presents a mimetic of the HNK-1 epitope. In this study, we further explored the pharmacodynamic properties of the glycopolymer and its ability to inhibit the binding of anti-MAG IgM to peripheral nerves. The polymer selectively bound anti-MAG IgM autoantibodies and prevented the binding of patients' anti-MAG IgM antibodies to myelin of non-human primate sciatic nerves. Upon PPSGG treatment, neither activation nor inhibition of human and murine peripheral blood mononuclear cells nor alteration of systemic inflammatory markers was observed in mice or ex vivo in human peripheral blood mononuclear cells. Intravenous injections of PPSGG to mice immunized against the HNK-1 epitope removed anti-MAG IgM antibodies within less than 1 hr, indicating a fast and efficient mechanism of action as compared to a B-cell depletion with anti-CD20. In conclusion, these observations corroborate the therapeutic potential of PPSGG for an antigen-specific treatment of anti-MAG neuropathy.

Anti-MAG (myelin-associated glycoprotein) neuropathy is a disabling autoimmune peripheral neuropathy caused by monoclonal IgM autoantibodies that recognize the carbohydrate epitope HNK-1 (human natural killer-1). This glycoepitope is highly expressed on adhesion molecules, such as MAG, present in myelinated nerve fibers. Because the pathogenicity and demyelinating properties of anti-MAG autoantibodies are well established, current treatments are aimed at reducing autoantibody levels. However, current therapies are primarily immunosuppressive and lack selectivity and efficacy. We therefore hypothesized that a significant improvement in the disease condition could be achieved by selectively neutralizing the pathogenic anti-MAG antibodies with carbohydrate-based ligands mimicking the natural HNK-1 glycoepitope 1. In an inhibition assay, a mimetic (2, mimHNK-1) of the natural HNK-1 epitope blocked the interaction of MAG with pathogenic IgM antibodies from patient sera but with only micromolar affinity. Therefore, considering the multivalent nature of the MAG-IgM interaction, polylysine polymers of different sizes were substituted with mimetic 2. With the most promising polylysine glycopolymer PL84(mimHNK-1)45 the inhibitory effect on patient sera could be improved by a factor of up to 230,000 per epitope, consequently leading to a low-nanomolar inhibitory potency. Because clinical studies indicate a correlation between the reduction of anti-MAG IgM levels and clinical improvement, an immunological surrogate mouse model for anti-MAG neuropathy producing high levels of anti-MAG IgM was developed. The observed efficient removal of these antibodies with the glycopolymer PL84(mimHNK-1)45 represents an important step toward an antigen-specific therapy for anti-MAG neuropathy.