Antibacterial activity of human neutrophil peptide-1 against Mycobacteriumtuberculosis H37RV: in vitro and ex vivo study

The aim of the study was to investigate the activity of human neutrophil pe ptide (HNP)-1 to kill Mycobacterium tuberculosis H(37)Rv in vitro and ex vi vo in the murine macrophage cell line J744A.1 on the basis of colony formin g units. Macromolecular biosynthesis was studied by monitoring the incorporation of radioactive precursors into different macromolecules. The binding and local ization studies were carried out with radioiodinated HNP-1 whereas the cyto toxicity of HNP-1 to macrophages was determined by trypan blue exclusion as say. A concentration dependent inhibition in the growth of M. tuberculosis H(37) Rv was observed in the presence of HNP-1, The minimum inhibitory concentrat ion and median inhibitory concentration of HNP-1 were found to be 2.5 mu g. mL(-1) and 0.8 mu g.mL(-1). Treatment of both in vitro grown and phagocytos ed mycobacterial cells with HNP-1 resulted in generalized inhibition in the macromolecular biosynthesis with maximum inhibition in deoxyribonucleic ac id and lipid biosynthesis. HNP-1 exhibited equilibrium binding with respect to time and two-thirds of bound radioactivity was shown to be present insi de the macrophages. Approximately 50% and 98% killing of intracellular myco bacteria was observed after 3 days of treatment,vith 5 mu g.mL(-1) and 40 m u g.mL(-1) of HNP-1, respectively. HNP-1 exhibited low cytotoxicity towards the macrophage cell line at the bactericidal concentration to mycobacteria . From the results of this study, it is concluded that human neutrophil pepti de-1 possesses potent bactericidal activity against virulent mycobacteria i n vitro as well as mycobacteria replicating within macrophages.