Alkyl galactofuranosides strongly interact with Leishmania donovani membrane and provide antileishmanial activity

6-Deoxy-6-fluoro galactofuranosides: regioselective glycosylation, unexpected reactivity, and anti-leishmanial activity

Selective glycosylation of the C-6 fluorinated galactofuranosyl acceptor 2 was studied with four galactofuranosyl donors. It was highlighted that this electron-withdrawing atom strongly impacted the behavior of the acceptor, thus leading to unprecedented glycosylation pathways. Competition between expected glycosylation of 2, ring expansion of this acceptor and furanosylation, and intermolecular aglycon transfer was observed. Further investigation of the fluorinated synthetic compounds showed that the presence of fluorine atom contributed to increase the inhibition of the growth of Leishmania tarentolae, a non-pathogenic strain of Leishmania.

In vitro and in vivo immunomodulatory properties of octyl-β-D-galactofuranoside during Leishmania donovani infection

BACKGROUND

The chemotherapeutic arsenal available to treat visceral leishmaniasis is currently limited, in view of many drawbacks such as high cost, toxicity or emerging resistance. New therapeutic strategies are particularly needed to improve the management and the outcome in immunosuppressed patients. The combination of an immunomodulatory drug to a conventional anti-Leishmania treatment is an emerging concept to reverse the immune bias from Th2 to Th1 response to boost healing and prevent relapses.

METHODS

Here, immunostimulating and leishmanicidal properties of octyl-β-D-galactofuranose (Galf) were assessed in human monocyte-derived macrophages (HM) and in a murine model, after challenge with Leishmania donovani promastigotes. We recorded parasite loads and expression of various cytokines and immune effectors in HM and mouse organs (liver, spleen, bone marrow), following treatment with free (Galf) and liposomal (L-Galf) formulations.

RESULTS

Both treatments significantly reduced parasite proliferation in HM, as well as liver parasite burden in vivo (Galf, P < 0.05). Consistent with in vitro results, we showed that Galf- and L-Galf-treated mice displayed an enhanced Th1 immune response, particularly in the spleen where pro-inflammatory cytokines TNF-α, IL-1β and IL-12 were significantly overexpressed compared to control group. The hepatic recruitment of myeloid cells was also favored by L-Galf treatment as evidenced by the five-fold increase of myeloperoxidase (MPO) induction, which was associated with a higher number of MPO-positive cells within granulomas. By contrast, the systemic level of various cytokines such as IL-1β, IL-6, IL-17A or IL-27 was drastically reduced at the end of treatment.

CONCLUSIONS

Overall, these results suggest that Galf could be tested as an adjuvant in combination with current anti-parasitic drugs, to restore an efficient immune response against infection in a model of immunosuppressed mice.

Improvement of the versatility of an arabinofuranosidase against galactofuranose for the synthesis of galactofuranoconjugates

A new performant biocatalyst was developed for the synthesis ofO-,S- and acyl-galactofuranoconjugates.

Synthesis and biological properties of galactofuranosyl-containing fluorescent dyes

Two fluorescent galactofuranosides were synthesized and their biological activities evaluated on non-infected and Leishmania infected macrophages. Both tagged scaffolds were able to penetrate macrophages. Compared to the activity of the parent octyl galactofuranoside used as a reference, the fluorescein-conjugate showed altered biological properties while the rhodamine 6G one synergistically acted with the lipid chain to significantly increase antiparasitic activity.

Leishmania cell wall as a potent target for antiparasitic drugs. A focus on the glycoconjugates

Although leishmaniasis has been studied for over a century, the fight against cutaneous, mucocutaneous and visceral forms of the disease remains a hot topic. This review refers to the parasitic cell wall and more particularly to the constitutive glycoconjugates. The structures of the main glycolipids and glycoproteins, which are species-dependent, are described. The focus is on the disturbance of the lipid membrane by existing drugs and possible new ones, in order to develop future therapeutic agents.

Biocatalyzed synthesis of difuranosides and their ability to trigger production of TNF-α

Transglycosylation reactions biocatalyzed by the native arabinofuranosidase Araf51 and using d-galactosyl, d-fucosyl and 6-deoxy-6-fluoro-D-galactosyl derivatives as donors and acceptors provided di-to pentahexofuranosides. The immunostimulatory potency of these compounds, and more especially their ability to induce production of TNF-α, was evaluated on the murine macrophage cell line, Raw 264.7. The results obtained showed concentration-dependent and most importantly, structure-dependent responses. Interestingly, oligoarabinofuranosides belonging to the oligopentafuranoside family displayed concentration-, chain length and aglycon-dependent bioactivities irrespective of their fine chemical variations. Thus, neo-oligofuranosides in D-Galf series, as well as their D-Fucf and 6-fluorinated counterparts are indeed potential sources of immunostimulating agents.

Analysis of Toxic Amyloid Fibril Interactions at Natively Derived Membranes by Ellipsometry

There is an ongoing debate regarding the culprits of cytotoxicity associated with amyloid disorders. Although small pre-fibrillar amyloid oligomers have been implicated as the primary toxic species, the fibrillar amyloid material itself can also induce cytotoxicity. To investigate membrane disruption and cytotoxic effects associated with intact and fragmented fibrils, the novel in situ spectroscopic technique of Total Internal Reflection Ellipsometry (TIRE) was used. Fibril lipid interactions were monitored using natively derived whole cell membranes as a model of the in vivo environment. We show that fragmented fibrils have an increased ability to disrupt these natively derived membranes by causing a loss of material from the deposited surface when compared with unfragmented fibrils. This effect was corroborated by observations of membrane disruption in live cells, and by dye release assay using synthetic liposomes. Through these studies we demonstrate the use of TIRE for the analysis of protein-lipid interactions on natively derived lipid surfaces, and provide an explanation on how amyloid fibrils can cause a toxic gain of function, while entangled amyloid plaques exert minimal biological activity.

Galactofuranose Biosynthesis: Discovery, Mechanisms and Therapeutic Relevance

Galactofuranose, the atypical and thermodynamically disfavored form of d-galactose, has in reality a very old history in chemistry and biochemistry. The purpose of this book chapter is to give an overview on the fundamental aspects of the galactofuranose biosynthesis, from the biological occurrence to the search of inhibitors.

Synthesis and evaluation of 1,2-trans alkyl galactofuranoside mimetics as mycobacteriostatic agents

The strong interaction of an octyl chain with M. smegmatis cells was paired with high specificity of the galactofuranose ring against mycobacteria growth.