Effects of 3alpha- and 3beta-galactosylated alpha-galactosylceramides on the immune system

Synthesis of N-dialkylphosphoryl iminosugar derivatives and their immunosuppressive activities

Twelve novel N-dialkylphosphoryliminosugar derivatives were synthesized and their immunosuppressive activities were evaluated on the proliferation of the mouse splenocytes and the secretion of IFN-γ and IL-4. The experimental data demonstrated that the iminosugars with the double long alkyl chains exhibited better inhibitory effects than those with the single long alkyl chain, and the iminosugars with the 10-carbon linear alkyl chain exhibited the strongest immunosuppressive activities. The assay of the cytokine secretion showed that the introduction of dialkyl chains on iminosugars could regulate the polarization of immune inhibition by varying the length of the alkyl chains. The disclosure of the structure-activity relationships may benefit the structural modifications of iminosugars to find new types of immunosuppressive agents.

Alpha-c-galactosylceramides: synthesis and immunology

The immunostimulant activity of alpha-galactosylceramides provided the impetus for the research described here. The activity was first discovered via screening of extracts of a marine sponge. The active materials purified from the extracts were alpha-O-galactosylceramides. The work described herein focuses on syntheses of alpha-C-galactosylceramides. Crucial methodologies for the syntheses were (i) Ramberg-Bäcklund reaction, (ii) modified Julia olefination, (iii) olefin cross-metathesis, and (iv) Sharpless asymmetric epoxidation in four independent routes. The immunostimulant activity of the synthetic alpha-C-galactosylceramide far surpasses that of the O-galactosyl material. A discussion of the reasons for the difference in activity is presented.

Synthesis and human NKT cell stimulating properties of 3-O-sulfo-alpha/beta-galactosylceramides

Two novel hybrid molecules 3-O-sulfo-alpha/beta-galactosylceramide 3 and 4, which are derived from an immunostimulatory agent alpha-GalCer 1 and self-glycolipid ligand sulfatide 2, were designed and synthesized. Compound 3 was shown to efficiently stimulate human NKT cells to secret IL-4 and IFN-gamma, with activities similar to 1, suggesting that modification of the 3''-OH position of the galactose moiety with sulfate has no significant effect on NKT cell stimulation. As a comparison, the beta-isomer 4 has no affinity to NKT cells, which demonstrates that the alpha-glycosidic bond of galactosylceramide is crucial to the NKT cells activation.

Total enantioselective synthesis and in vivo biological evaluation of a novel fluorescent BODIPY alpha-galactosylceramide

Natural killer T (NKT) cells are a distinct subset of mature lymphocytes endowed with features of activated and regulatory T cells. alpha-Galactosylceramides (alpha-GalCers), the synthetic prototype of which is KRN7000, are the only natural reagents recognised by the T-cell receptor of NKT cells. The alpha-GalCer-activated NKT cells promptly release IFN gamma and IL-4 (IFN=interferon; IL=interleukin) and undergo apoptotic death within hours. In mice, activated NKT cells are responsible for antitumour activity and protection against autoimmune diseases. KRN7000 can thus be considered as the root of a family of novel immunoregulatory drugs. To get insights into the in vivo behaviour of alpha-galactosylceramides, an original fluorescent derivative has been prepared by following a convergent synthetic scheme. This strategy allows the introduction of different acyl chains, carbohydrate residues and various labels in the final steps of the synthesis. The fluorescent BODIPY probe derived from a versatile glycolipid precursor is as active as KRN7000 for inducing apoptosis of liver NKT cells. Fluorescence was detected in peritoneal macrophages and splenic antigen-presenting cells, in Kupffer-like cells in the liver, but not in lymphocytes.