title: Synthetic modifications of the immunomodulating peptide thymopentin to confer anti-mycobacterial activity.
abstract: Effective global control of tuberculosis (TB) is increasingly threatened by the convergence of multidrug-resistant TB and the human immunodeficiency virus (HIV) infection. TB/HIV coinfections exert a tremendous burden on the host's immune system, and this has prompted the clinical use of immunomodulators to enhance host defences as an alternative therapeutic strategy. In this study, we modified the clinically used synthetic immunomodulatory pentapeptide, thymopentin (TP-5, RKDVY), with six arginine residues (RR-6, RRRRRR) at the N- and C-termini to obtain the cationic peptides, RR-11 (RKDVYRRRRRR-NH2) and RY-11 (RRRRRRRKDVY-NH2), respectively. The arginine residues conferred anti-mycobacterial activity to TP-5 in the peptides as shown by effective minimum inhibitory concentrations of 125 mg/L and killing efficiencies of >99.99% against both rifampicin-susceptible and -resistant Mycobacterium smegmatis. The immunomodulatory action of the peptides remained unaffected as shown by their ability to stimulate TNF-α production in RAW 264.7 mouse macrophage cells. A distinct change in surface morphology after peptide treatment was observed in scanning electron micrographs, while confocal microscopy and dye leakage studies suggested bacterial membrane disruption by the modified peptides. The modified peptides were non-toxic and did not cause hemolysis of rat red blood cells up to a concentration of 2000 mg/L. Moreover, RY-11 showed synergism with rifampicin and reduced the effective concentration of rifampicin, while preventing the induction of rifampicin resistance. The synthetic peptides may have a potential application in both immunocompetent and immunocompromised TB patients.
authors.affiliation: Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 138669, Singapore.
authors.forename: Xi-Yu
authors.initials: XY
authors.lastname: Ke
authors.affiliation: Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore.
authors.forename: Jasmeet S
authors.initials: JS
authors.lastname: Khara
authors.affiliation: Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore.
authors.forename: Priti
authors.initials: P
authors.lastname: Bahety
authors.affiliation: Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 138669, Singapore.
authors.forename: Shaoqiong
authors.initials: S
authors.lastname: Liu
authors.affiliation: Department of Paediatrics, Yong Loo Lin School of Medicine, National University of Singapore, 5 Lower Kent Ridge Rd, Singapore 119074, Singapore.
authors.forename: See Voon
authors.initials: SV
authors.lastname: Seow
authors.affiliation: Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 138669, Singapore. Electronic address: yyyang@ibn.a-star.edu.sg.
authors.forename: Yi Yan
authors.initials: YY
authors.lastname: Yang
authors.affiliation: Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore. Electronic address: phaeplr@nus.edu.sg.
authors.forename: Pui Lai Rachel
authors.initials: PL
authors.lastname: Ee
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D024881:Drug Resistance, Bacterial / Q000187:drug effects; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D007155:Immunologic Factors / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008826:Microbial Sensitivity Tests; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D020102:Mycobacterium smegmatis / Q000187:drug effects* / Q000254:growth & development / Q000648:ultrastructure; D010455:Peptides / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology*; D051381:Rats; D012293:Rifampin / Q000494:pharmacology; D016305:Thymopentin / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
chemical_list: D000900:Anti-Bacterial Agents; D007155:Immunologic Factors; D010455:Peptides; D014409:Tumor Necrosis Factor-alpha; D016305:Thymopentin; D012293:Rifampin
keywords: Cationic peptides; Drug resistance; Immunotherapeutics; Mycobacterium smegmatis; Synergy; Thymopentin