PROJECT SUMMARY:
It has been well recognized that individuals with type 2 diabetes (T2DM) are increasingly
susceptible to Mycobacterium tuberculosis (Mtb) infection. The tripeptide, glutathione (GSH)
protects all cells against oxidizing agents, free radicals and reactive oxygen intermediates
(ROI), either directly or through enzymatic action of GSH peroxidases and GSH-transferases.
Interestingly, mycobacteria do not synthesize GSH. Rather, they produce mycothiol in millimolar
amounts. We observed that the virulent laboratory strain of Mtb, H37Rv is sensitive to
physiological concentrations of GSH (5mM) when grown in vitro. We also found that
enhancing the levels of GSH in human macrophages resulted in inhibition in the growth of
intracellular Mtb. Thus, GSH has direct antimycobacterial activity, functioning as an effector
molecule in innate defense against Mtb infection. These results unfold a novel and potentially
important innate defense mechanism adopted by human macrophages to control Mtb infection.
We also reported that GSH in combination with cytokines such as IL-2 and IL-12 enhances the
functional activity of natural killer cells to inhibit the growth of Mtb inside human monocytes. We
then demonstrated that GSH activates the functions of T lymphocytes to control Mtb infection
inside human monocytes. These results indicate that GSH inhibits the growth of Mtb by both
direct antimycobacterial effects as well as by enhancing the functions of immune cells. Finally,
we demonstrated that the levels of GSH are significantly compromised in the plasma,
monocytes and red blood cells (RBCs) derived from individuals with T2DM and this
decrease is due diminished levels of GSH de novo synthesis enzymes and due to
increased production of free radicals. These results led us to hypothesize that GSH-
deficiency in the lung parenchyma can impair the formation of granuloma and dampen
the granulomatous effector responses against Mtb infection, thereby favoring bacterial
replication and pathogenesis. We will test our hypothesis by performing in vivo infection
studies in GSH-deficient diabetic mice (db/db) and in glutamate cysteine ligase modifier
subunit knock-out (GCLM-/-) mice.
SPECFIC AIMS:
SPCIFIC AIM 1: To determine the effects of GSH deficiency in the lung parenchyma in altering
the innate and adaptive immune responses against Mtb infection.
SPCIFIC AIM 2: To assess the effects of GSH restoration in enhancing the granulomatous
responses against Mtb infection.
SPCIFIC AIM 3: To determine the synergistic effects of liposomal GSH in conjunction with
suboptimal concentration of Rifampicin in clearing Mtb infection.
Studies proposed in this application will enable us to characterize the underlying mechanisms
by which GSH deficiency in the lung parenchyma leads to altered immune responses in the
granulomas resulting in increased susceptibility to Mtb infection and tap the potential use of
GSH as a possible immunomodulatory agent. The proposed research will therefore provide
compelling evidence on whether appropriate GSH-enhancing agents can be used to prevent the
development of active TB in individuals with T2DM.