Activity of cathelicidin peptides against Chlamydia spp.

Abstract number: 1133_213

Cevenini R., Donati M., Di Leo K., Benincasa M., Cavrini F., Accardo S., Moroni A., Gennaro R.

Objectives:  

To study the in vitro activity of six cathelicidin-derived peptides (Bac7, BMAP-28, SMAP-29, LL-37, PG-1, BMAP-27) against purified elementary bodies (EBs) of 25 Chlamydia strains.

Methods:  

Chlamydial strains were grown in LLC-KM2 cells and EBs purified by sucrose gradients. The cathelicidin peptides were synthesized by the solid phase method using Fmoc chemistry. After purification by reversed-phase HPLC the peptides were lyophilized and stored at 4°C. Peptides were twofold diluted in test tubes containing PBS and a total volume of 0.15 ml of a suspension of purified EBs in SPG medium was added to the tube. The suspensions were incubated at room temperature for 2 hours and inoculated onto LLC-MK2 cells. After incubation cell cultures were fixed and stained with fluorescein-conjugated monoclonal antibody reactive with the chlamydial specific genus antigen.

Results:  

A different sensitivity of chlamydiae to cathelicidin peptides was observed. C. trachomatis was the most sensitive of chlamydiae and SMAP-29 was the most active peptide. The treatment of C. trachomatis EBs with SMAP-29 reduced by over 50% the inclusion number of all the 10 strains tested, at a concentration of 10 mg/ml. BMAP-27, BMAP-28 and Bac7 displayed a similar activity at a concentration of 80 mg/ml. In contrast, LL-37 did not exert any inhibitory activity and PG-1 was only active against serotypes D,H and LGV2. C. pneumoniae strains ( n° tested = 5) were sensitive only to SMAP-29 at a concentration of 10 mg/ml. Chlamydia strains of animal origin ( n° tested = 10) were not susceptible to cathelicidins, with the exception of four strains of C. felis. Electron microscopy analysis of C. pneumoniae EBs treated with SMAP-29 showed striking morphological changes of EBs with the loss of their integrity, the appearance of amorphous and membranous material and empty vescicles.

Conclusions:  

Previous studies and the present one suggest that cathelicidin peptides have substantial in vitro activity against several microorganisms. Much remains to be done to evaluate their in vivo efficacy and safety, in particular with respect to their interaction with constituents of biological fluids. Therefore, studies in animal models of chlamydial infection are needed to prove whether they will parallel in vitro results.