Mycobactericidal activity of some micro-encapsulated synthetic Host Defense Peptides (HDP) by expediting the permeation of antibiotic: A new paradigm of drug delivery for tuberculosis.

Resistance to anti-Tuberculosis (anti-TB) drugs is primarily due to unique intrinsic resistance mechanisms that mycobacterium possess. The most important determinant of resistance is a peculiar hydrophobic and multi-layered mycobacterial cell-wall structure with mycolic-acid and wax-D, which restricts permeability of both hydrophobic and hydrophilic drugs into bacteria. In this study, it was supposed that Host Defense peptides (HDP) which are known to permeabilize bacterial membranes may, therefore, help anti-TB antibiotics to target internal sites in bacteria. To test this hypothesis, we examined the effect of suboptimal concentration (10 µg/ml) of selected microencapsulated-HDP (Ub2-MS, K4-MS, and Aurein1.2-MS) with a standard anti-TB drug (Isoniazid, INH, 3 µg/ml). We also examined the combined effect of different concentrations of HDP-MS with a suboptimal concentration of anti-TB drug (INH, 1.5 µg/ml) which showed additive efficacy. A number of cationic HDP were encapsulated in inhalable microspheres (HDP-MS) and characterized for physicochemical and aerodynamic properties. These peptides were further evaluated for molecular mass by MALDI-TOF and random coil in its secondary structure as determined by circular dichroism. The anti-mycobacterial kinetics of selected HDP-MS (Ub2-MS, K4-MS, and Aurein1.2-MS) was evaluated against virulent Mycobacterium tuberculosis (Mtb), both alone and in conjunction with anti-TB drug (INH). HDP-MS exhibited up to ∼3.02 and ∼3.41-log decrease in CFU as compared to blank-MS (drug free) and untreated control group in 96 h. The combination of HDP-MS with a suboptimal concentration of INH (1.5 µg/ml) showed superior antibiotic activity against Mtb. Our findings show that the enhanced efficacy is due to augmentation of membrane permeation by HDP which expedited the entry of TB drug into apparently the impermeant mycobacterial membrane which further enhances the effective efficacy of the drug. This phenomenon can reduce the need for high dosages and represents a novel paradigm for potential clinical applications.