Synthetic Arabinomannan Heptasaccharide Glycolipids Inhibit Biofilm Growth and Augment Isoniazid Effects in Mycobacterium smegmatis

Abstract

Biofilm formation, involving attachment to an adherent surface, is a critical survival strategy of mycobacterial colonies in hostile environmental conditions. Here we report the synthesis of heptasaccharide glycolipids based on mannopyranoside units anchored on to a branched arabinofuranoside core. Two types of glycolipids-2,3-branched and 2,5-branched-were synthesized and evaluated for their efficacies in inhibiting biofilm growth by the non-pathogenic mycobacterium variant Mycobacterium smegmatis. Biofilm formation was inhibited at a minimum biofilm growth inhibition concentration (MBIC) of 100 μg mL in the case of the 2,5-branched heptasaccharide glycolipid. Further, we were able to ascertain that a combination of the drug isoniazid with the branched heptasaccharide glycolipid (50 μg mL ) potentiates the drug, making it three times more effective, with an improved MBIC of 30 μg mL . These studies establish that synthetic glycolipids not only act as inhibitors of biofilm growth, but also provide a synergistic effect when combined with significantly lowered concentrations of isoniazid to disrupt the biofilm structures of the mycobacteria.

Mannopyranoside Glycolipids Inhibit Mycobacterial and Biofilm Growth and Potentiate Isoniazid Inhibition Activities in M. smegmatis

“…Scheme shows the synthetic route to prepare the mannose disaccharide containing glycolipid. p ‐Tolylthio‐2,3,4‐ tri ‐ O ‐benzoyl‐α‐ d ‐mannopyranoside ( 11 ) was used as an acceptor to react with trichloroacetimidate donor 9 , under Lewis acid catalyzed glycosylation conditions, to afford thioglycoside disaccharide 12 . The reaction of donor 12 with hydroxyl moiety tethered lipid derivative 10 , with the aid of AgOTf as a promoter, afforded the protected form of glycolipid 2 .…”

“…The glycolipids are composed of lipidic and mannan portions, which qualitatively follow the pattern of components present in mycobacterial cell wall bound lipomannans. Our earlier studies on a series of synthetic oligoarabinan and oligoarabinomannan glycolipids demonstrated a reduction in mycobacterial growth upon treatment with these glycolipids . A pertinent query in these studies is the role of glycolipids composed of individual sugar moieties, as opposed to mixed oligoarabinomannan glycolipids.…”

“…From a series of studies, we previously identified that synthetic arabinomannan‐containing glycolipids exhibited potent inhibitory effects against M. smegmatis in its growth and biofilm phases. A strong inhibitory effect against mycobacterial sliding motility was also observed . Further chromatographic and mass spectroscopic analysis of the lipid profile suggested a regulatory effect in the presence of glycolipids .…”

“…Lipodomics profiling studies show that the biosynthesis of epoxy‐ and ketomycolic acids and phosphatidylinositol mannosides are downregulated in the presence of these glycolipids. Furthermore, oligosaccharide glycolipids consisting of an arabinofuranosyl core and mannopyranosyl caps supplement the antibiotic activity of the cocktail drug isoniazid against M. smegmatis , in addition to inhibiting biofilm growth on their own …”

“…smegmatis . We also recently identified that synthetic glycolipids supplemented the inhibition activities of the drug isoniazid on biofilm‐grown mycobacterium; thus suggesting the role of glycolipids on the drug involved in the inhibition of cell wall biosynthesis . A study on lipomannans, which are devoid of the arabinan portion, becomes pertinent to identify the effects of the arabinomannan glycolipids arising from mannan moieties alone.…”