Susceptibility of Chlamydia trachomatis to the Excipient Hydroxyethyl Cellulose: pH and Concentration Dependence of Antimicrobial Activity

Abstract

Hydroxyethyl cellulose (HEC) is used as a neutral excipient in microbicides used against sexually transmitted pathogens. However, HEC inhibits the infection of cervical epithelial cells by Chlamydia trachomatis at pH 5 in a concentration-dependent manner. At pH 7, infection is inversely dependent on the concentration of HEC, possibly due to pH-dependent calcium sequestration.Chlamydia trachomatis causes pelvic inflammatory disease, ectopic pregnancy, and reproductive disability and is the most common bacterial sexually transmitted infection in the world (4). However, chlamydial infection is asymptomatic in most men and women infected with the pathogen (9). Since new preventative antimicrobials could prevent chlamydial infection, there is much effort to develop microbicides and related compounds (7,20). Recently, a number of reports have highlighted the in vitro antichlamydial properties of polysaccharide-based chemotherapeutics and excipients (2,8,10,19). Studies on the basis of the antimicrobial properties of polysaccharides highlight the need for the use of excipient-only controls when the effectiveness of new antimicrobials is tested and contribute to our understanding of the molecular mechanism of chlamydial adhesion to polysaccharides or glycoproteins on the surface of host cells. The studies reported here were designed to interrogate the potential antichlamydial effects of the common polysaccharide-based excipient hydroxyethyl cellulose (HEC) as a function of both concentration and pH.Excipients are an inherent part of drug delivery systems used for both topical vaginal medications and contraceptives and fall into four principal classes: antioxidants, preservatives, acidifying agents, and gelling agents (8). Gelling agents are frequently polysaccharides, which are also adhesins through which bacterial pathogens bind to host cells. As such, these molecules can have competitive inhibitory effects on bacterial adhesion. However, it is possible that these excipients can play a more complex role in host-pathogen interactions. Although a number of potential host cell adhesins have been proposed to play a role in the initial stages of mammalian infection by C. trachomatis (3,14,18), it appears possible that membranelocalized calcium concentrations could also play a role in promoting infection.In the current study, three experimental parameters were adjusted to determine the effects of a commonly used excipient, HEC, upon infection of cervical epithelial cells (HeLa cells) by the lymphogranuloma (LGV/L2) serovar of C. trachomatis. HeLa 229 cells were chosen as a model host system, since they are immortalized cervical epithelial cells and are germane to in vitro modeling of vaginal infection by C. trachomatis. The effects of the HEC concentration, the average molecular mass, and pH were explored in order to test the hypothesis that the HEC monomer concentration is the primary determinant of antimicrobial potency. Both HeLa 229 cells and the LGV/L2 serovar strain of C. trachomatis were obtained from American Type Cu...

Vaginal Gel Component Hydroxyethyl Cellulose Significantly Enhances the Infectivity of Chlamydia trachomatis Serovars D and E

“…Interestingly, our results differ from those of Sater et al (13), who used the lymphogranuloma venereum strain C. trachomatis L2 and showed concentration-and pH-dependent inhibitory effects of HEC on chlamydial growth in vitro. However, there are important differences between the two studies, including the fact that we used a complex buffer that may better mimic the physicochemical properties of the vaginal fluid than the phosphate and acetate buffers used by Sater et al Moreover, we observed the growthenhancing effect at 0.75% to 1.5% wt/vol (7,500 -15,000 g/ml) HEC concentrations, which are common in the vaginal gels (7,14), whereas Sater et al used significantly lower HEC concentrations (2-200 g/ml).…”

An Automated Image-Based Method for Rapid Analysis of Chlamydia Infection as a Tool for Screening Antichlamydial Agents

“…1B). This proportionality between the concentration and the inhibitory effect supports a previously suggested mechanism for HEC inhibition, that HEC may act as a competitive inhibitor by competing with the host cell for the recognition site on the chlamydial surface (20).…”

“…Although excipients are typically used as delivery vehicles and are expected to be pharmacologically inactive, a 90-kDa HEC has been shown to have an inhibitory effect on C. trachomatis infection, purportedly as a competitive inhibitor for adhesion (20). When EBs were treated with HEC, the inhibitory effect of HEC was directly proportional to its concentration in the range of 0.175% to 0.7% and reached complete inhibition at 1.4% (Fig.…”

“…The accuracy and expediency of the automated method were compared to those of the conventional visual inspection in a 96-well format. For evaluating the efficacy and potential of iBAChIE to measure antichlamydial compounds, C. trachomatis infections were measured following treatment with four anti-Chlamydia molecules (tetracycline, polymyxin B, hydroxyethyl cellulose, and anti-C. trachomatis polyclonal antibody) that have contrasting mechanisms of inhibitory activity toward C. trachomatis (4,7,11,12,20,23,26).…”

Influence of chemical compounds and cellautonomous immunity on the replication of sexually transmitted pathogens

“…2-methoxystipandron (8) did not show any antiviral effect at the non-toxic concentration of 6.25 µM (data not shown). In vitro and in vivo monitoring of the effect of hydroxyethyl cellulose a major gelling agent of vaginal gels on C. trachomatis growth.Interestingly, our results are different from those of Sater et al[147], who used the lymphogranuloma venereum strain C. trachomatis L2 and showed a concentration-and pHdependent inhibitory effect of HEC on chlamydial growth in vitro. However, there are important differences between the two studies, including the fact that we used a complex buffer which may mimic better the physicochemical properties of the vaginal fluid than the phosphate and acetate buffers used by Sater et al.…”