Dissecting the Mechanism of Intracellular Mycobacterium smegmatis Growth Inhibition by Platelet Activating Factor C-16

Abstract

Mycobacterium tuberculosis (M.tb) infection results in approximately 1.3 million human deaths each year. M.tb resides primarily inside macrophages, and maintains persistent infection. In response to infection and inflammation, platelet activating factor C-16 (PAF C-16), a phospholipid compound, is released by various cells including neutophils and monocytes. We have recently shown that PAF C-16 can directly inhibit the growth of two representative non-pathogenic mycobacteria, Mycobacterium bovis BCG and Mycobacterium smegmatis (M. smegmatis), by damaging the bacterial cell membrane. Here, we have examined the effect of PAF C-16 on M. smegmatis residing within macrophages, and identified mechanisms involved in their growth inhibitory function. Our results demonstrated that exogenous PAF C-16 inhibited the growth of M. smegmatis inside phagocytic cells of monocytic cell line, THP-1; this effect was partially blocked by PAF receptor antagonists, suggesting the involvement of PAF receptor-mediated signaling pathways. Arachidonic acid, a downstream metabolite of PAF C-16 signaling pathway, directly inhibited the growth of M. smegmatis in vitro. Moreover, the inhibition of phospholipase C and phospholipase A 2 activities, involved in PAF C-16 signaling pathway, increased survival of intracellular M. smegmatis. Interestingly, we also observed that inhibition of inducible nitric oxide synthase (iNOS) enzyme and antibody-mediated neutralization of TNF-α partially mitigated the intracellular growth inhibitory effect of PAF C-16. Use of a number of PAF C-16 structural analogs, including Lyso-PAF, 2-O-methyl PAF, PAF C-18 and Hexanolamino PAF, revealed that the presence of acetyl group (CH 3 CO) at sn-2 position of the glycerol backbone of PAF is important for the intracellular growth inhibition activity against M. smegmatis. Taken together, these results suggest that exogenous PAF C-16 treatment inhibits intracellular M. smegmatis growth, at least partially, in a nitric oxide and TNF-α dependent manner.

Immunological aspects of host–pathogen crosstalk in the co-pathogenesis of diabetes and latent tuberculosis

“…To understand the crosstalk between intracellular mycobacteria and host macrophages, the THP-1 monocytic cell line was grown under hyperglycemic conditions and infected with latent as well as active cultures of M. tuberculosis for 3 h. Accordingly, mycobacterial phagocytosis by macrophages under high glucose conditions was studied. THP-1 cells were used as model phagocytic cells ( Ranaivomanana et al., 2018 ; Riaz et al., 2020 ). CFU enumeration at normal glucose conditions suggested that the dormant bacilli were better contained within the macrophages as compared to the active bacilli.…”

Cecal Metabolomic Fingerprint of Unscathed Rats: Does It Reflect the Good Response to a Provocative Decompression?

“…C18_lysoPAF may have direct or indirect inflammatory effects ( Dyer et al, 2010 ), but it is essentially a precursor of PAF, the Platelet Activation Factor that can be released by enterobacteria such as E. coli and which is a potent mediator of inflammatory diseases and septic shock or gastric ulceration ( Denizot et al, 1989 ). Its analog C_16 has similar properties with a broad spectrum of inflammatory actions, at the level of IL-1β or on the glutathione ratio per example ( Riaz et al, 2018 ; Riaz et al, 2020 ). Considering literature ( Lee and Polin, 2003 ; Welch et al, 2009 ; Dyer et al, 2010 ; Riaz et al, 2020 ), this result is of prime importance because it suggests that the modulation of the quantities of PAF is a non-negligible possibility after an hyperbaric exposure, including dive.…”

“…Its analog C_16 has similar properties with a broad spectrum of inflammatory actions, at the level of IL-1β or on the glutathione ratio per example ( Riaz et al, 2018 ; Riaz et al, 2020 ). Considering literature ( Lee and Polin, 2003 ; Welch et al, 2009 ; Dyer et al, 2010 ; Riaz et al, 2020 ), this result is of prime importance because it suggests that the modulation of the quantities of PAF is a non-negligible possibility after an hyperbaric exposure, including dive. Unfortunately, we do not measure PAF in this study, and the increased C18_LysoPAF can be read in many ways.…”