Background We have reported that the major outer membrane of C trachomatis is glycosylated and the glycan is a high mannose oligosaccharide. Cumulative studies have demonstrated that the glycan is important in attachment and infectivity through binding to the mannose receptor (MR). Glycan removal decreases infectivity in vitro and in vivo and simultaneous administration of mannan, a ligand of the MR, abrogates C trachomatis infection in a mouse model of pneumonitis. Thus, we are investigating the feasibility of an anti-adhesive therapy to prevent C trachomatis infection by identifying oligosaccharides that are effective in inhibiting infection in vitro and testing their efficacy in a mouse model of genital tract infection.
Methods HeLa 229 cell monolayers were pretreated with serial concentrations of oligosaccharides prior to infection with C trachomatis. Neutralisation of infectivity was scored as >50% inhibition. For animal experiments, 8-week-old Swiss Webster female mice were primed with subcutaneous injections of Depo-Provera 1 week prior to challenge. Subsequently, mice were inoculated intravaginally with carbohydrates or PBS (n=5 mice per group) 30 min prior to infection with C trachomatis. Vaginal swab samples were obtained at 24, 48, and 72 h. post-infection, at peak times of shedding. Statistical significance was determined by the Student's t test.
Results Carbohydrates have been tested in vitro in hapten inhibition experiments against three serovars (D, E, F) most frequently isolated from genital tract infection. At the highest concentration tested, 4-nitrophenyl-α-D-mannopyranoside inhibited infectivity by 91%–92%; α-D-mannose-PAA from 77 to 93%; hen ovalbumin by 85%–89%; mannan by 77%–83%; and the high mannose fraction prepared from ovalbumin by 59%–98%. To determine efficacy in vivo, Swiss Webster mice were inoculated with different concentrations of inhibitors. Of those tested thus far, shedding of organism was significantly decreased (p<0.05). The maximum inhibitions observed were: 4-nitrophenyl-α-D-mannopyranoside (86%), α-D-mannose-PAA (81%), mannan (93%), and the high mannose fraction from ovalbumin (94%).
Conclusions These preliminary studies suggest the potential feasibility for developing an “anti-adhesive therapy” as an alternate topical microbicide approach to prevent C trachomatis genital tract infection.
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