Binding of piperine to mycobacterial RNA polymerase improves the efficacy of rifampicin activity against Mycobacterium leprae and nontuberculous mycobacteria

Abstract

Piperine (PPN) is a known inhibitor of efflux pumps in Mycobacterium tuberculosis and in vitro synergism with rifampicin (RIF) has been proven. The current study evaluates the activity of PPN and synergism with RIF in rapidly and slowly growing nontuberculous mycobacteria (NTM). Also, to propose a possible mechanism of interaction of PPN with M. leprae (Mlp) RNA polymerase (RNAp). Minimal inhibitory concentration and drug combination assay was determined by resazurin microtiter assay and resazurin drug combination assay, respectively. In silico evaluation of PPN binding was performed by molecular docking and molecular dynamics (MD). PPN showed higher antimicrobial activity against rapidly growing NTM (32-128 mg/L) rather than for slowly growing NTM (≥ 256 mg/L). Further, 77.8% of NTM tested exhibited FICI ≤ 0.5 when exposed to PPN and RIF combination, regardless of growth speed. Docking and MD simulations showed a possible PPN binding site at the interface between β and β’ subunits of RNAp, in close proximity to the trigger-helix and bridge-helix elements. MD results indicated that PPN binding hindered the mobility of these elements, which are essential for RNA transcription. We hypothesize that PPN binding might affect mycobacterial RNAp activity, and, possibly, RIF activity and that this mechanism is partially responsible for synergic behaviors with RIF reported in vitro.

Communicated by Ramaswamy H. Sarma

Keywords:

• Nontuberculous mycobacteria
• mycobacterium leprae
• piperine
• molecular docking
• RNA polymerase

Acknowledgments

The authors acknowledge the National Laboratory for Scientific Computing (LNCC/MCTI, Brazil) for providing HPC resources of the SDumont supercomputer, which have contributed to the research results reported within this paper. URL: http://sdumont.lncc.br.

Disclosure statement

The authors report there are no competing interests to declare.

Additional information

Funding

This work was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES) [finance code 001], Fundação Araucária (grants 40/16 and 53/2019), and Conselho Nacional de Desenvolvimento Científico e Tecnológico – Brasil (CNPq).