Nimbidin–induced downregulation of TNF-α mRNA in human monocytes infected with Mycobacterium tuberculosis

Tuberculosis (TB) is spiraling out of control at an alarming rate where reports implicate TNF-α to proliferate MTB 85B in infected host during early stage of infection. Reactive oxygen species plays an important role augmenting TNF-α, which in turn proliferates MTB 85B in bacilli-infected monocytes. Thus, in view of the above, an attempt was made to probe the antioxidant, anti-inflammatory and antimicrobial effects of phytochemicals from plants having medicinal value in combating TB. Thus, we employed nimbidin, a mixture of tetranortriterpenes including nimbin and nimbinin from Azadirachta indica (Neem) to probe its antioxidant, antimicrobial and anti-inflammatory in MTB-infected human monocytes. Various techniques like ‘real time’ RT-PCR, cell culture, ELISA and enzyme assays were employed in the present study. We show the augmented expression of TNF-α mRNA in 24 h cultures of MTB-infected monocytes was suppressed by nimbidin in a dose dependent manner. The nimbidin -induced up-regulation of glutathione with simultaneous decrease in TNF-α expression supports the anti-inflammatory property of nimbidin. This suppression was mediated via inhibition of GPx activity and NF-κB pathway, because TNF-α mRNA was suppressed when glutathione or its precursor NAC as well as SN50, a known inhibitor of NF-κB, was present in cultures. The doses of nimbidin employed were non-toxic to host cells as revealed by RT-PCR of human housekeeping gene R18 as well as MTT cell viability assay. Thus, nimbidin may act as a potential adjunct in management of tuberculosis and inflammatory diseases.