Nitrate Respiration Protects Hypoxic Mycobacterium tuberculosis Against Acid- and Reactive Nitrogen Species Stresses

In high enough concentrations, such as produced by inducible nitric oxide synthase (iNOS), reactive nitrogen species (RNS) can kill Mycobacterium tuberculosis (Mtb). Lesional macrophages in macaques and humans with tuberculosis express iNOS, and mice need iNOS to avoid succumbing rapidly to tuberculosis. However, Mtb's own ability to produce RNS is rarely considered, perhaps because nitrate reduction to nitrite is only prominent in axenic Mtb cultures at oxygen tensions ≤1%. Here we found that cultures of Mtbinfected human macrophages cultured at physiologic oxygen tensions produced copious nitrite. Surprisingly, the nitrite arose from the Mtb, not the macrophages. Mtb responded to nitrite by ceasing growth; elevating levels of ATP through reduced consumption; and altering the expression of 120 genes associated with adaptation to acid, hypoxia, nitric oxide, oxidative stress, and iron deprivation. The transcriptomic effect of endogenous nitrite was distinct from that of nitric oxide. Thus, whether or not Mtb is hypoxic, the host expresses iNOS, or hypoxia impairs the action of iNOS, Mtb in vivo is likely to encounter RNS by producing nitrite. Endogenous nitrite may slow Mtb's growth and prepare it to resist host stresses while the pathogen waits for immunopathology to promote its transmission.

Section: Mtb Respires Nitrate In Human Macrophages Cultured At Nonhypsupporting

confidence: 89%

Section: Mtb Respires Nitrate In Human Macrophages Cultured At Nonhypmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Nitrite produced byMycobacterium tuberculosisin human macrophages in physiologic oxygen impacts bacterial ATP consumption and gene expression

Cunningham‐Bussel¹,

Zhang

Nathan³

2013

“…RNIs are produced by human macrophages in tuberculous lesions (35). In granulomas, hypoxia may limit RNI production by host enzymes, but O 2 -starved Mtb respires nitrate (which is abundant in body fluids) and produces its own nitrite (36,37). Mild acid converted OPB to a form that was active against R Mtb as well as NR Mtb, and RNIs accelerated the conversion.…”

Section: Discussionmentioning

confidence: 99%

Nonsteroidal anti-inflammatory drug sensitizes Mycobacterium tuberculosis to endogenous and exogenous antimicrobials

Gold¹,

Pingle²,

Brickner³

et al. 2012

101

159

Existing drugs are slow to eradicate Mycobacterium tuberculosis (Mtb) in patients and have failed to control tuberculosis globally. One reason may be that host conditions impair Mtb's replication, reducing its sensitivity to most antiinfectives. We devised a highthroughput screen for compounds that kill Mtb when its replication has been halted by reactive nitrogen intermediates (RNIs), acid, hypoxia, and a fatty acid carbon source. At concentrations routinely achieved in human blood, oxyphenbutazone (OPB), an inexpensive anti-inflammatory drug, was selectively mycobactericidal to nonreplicating (NR) Mtb. Its cidal activity depended on mild acid and was augmented by RNIs and fatty acid. Acid and RNIs fostered OPB's 4-hydroxylation. The resultant 4-butyl-4-hydroxy-1-(4-hydroxyphenyl)-2-phenylpyrazolidine-3,5-dione (4-OH-OPB) killed both replicating and NR Mtb, including Mtb resistant to standard drugs. 4-OH-OPB depleted flavins and formed covalent adducts with N-acetyl-cysteine and mycothiol. 4-OH-OPB killed Mtb synergistically with oxidants and several antituberculosis drugs. Thus, conditions that block Mtb's replication modify OPB and enhance its cidal action. Modified OPB kills both replicating and NR Mtb and sensitizes both to host-derived and medicinal antimycobacterial agents.

“…The specific biochemical conditions encountered by M. tuberculosis in the host are complex and heterogeneous (3, 4, 7, 9, 10). Nitrate is a natural component of human body fluids that arises in part from dietary sources and in part as a terminal autooxidation product of the nitric oxide produced by the three isoforms of nitric oxide synthase in diverse cells, including immune-activated smooth muscle, epithelial cells, and hematopoietic cells, such as macrophages infected with M. tuberculosis (11,15,(43)(44)(45). Both nitric oxide and hypoxia increase M. tuberculosis nitrate reductase activity at the whole cell level.…”

Section: Metabolic Essentiality Of Succinate Dehydrogenase Activity Inmentioning

confidence: 99%

Multifunctional essentiality of succinate metabolism in adaptation to hypoxia in Mycobacterium tuberculosis

Eoh

Rhee

2013

255

330

Mycobacterium tuberculosis is a chronic, facultative intracellular pathogen that spends the majority of its decades-long life cycle in a non-or slowly replicating state. However, the bacterium remains poised to resume replicating so that it can transmit itself to a new host. Knowledge of the metabolic adaptations used to facilitate entry into and exit from nonreplicative states remains incomplete. Here, we apply 13 C-based metabolomic profiling to characterize the activity of M. tuberculosis tricarboxylic acid cycle during adaptation to and recovery from hypoxia, a physiologically relevant condition associated with nonreplication. We show that, as M. tuberculosis adapts to hypoxia, it slows and remodels its tricarboxylic acid cycle to increase production of succinate, which is used to flexibly sustain membrane potential, ATP synthesis, and anaplerosis, in response to varying degrees of O 2 limitation and the presence or absence of the alternate electron acceptor nitrate. This remodeling is mediated by the bifunctional enzyme isocitrate lyase acting in a noncanonical role distinct from fatty acid catabolism. Isocitrate lyase-dependent production of succinate affords M. tuberculosis with a unique and bioenergetically efficient metabolic means of entry into and exit from hypoxia-induced quiescence. Q uiescence, or exit from cell cycle, is a physiologic prerogative of all cells, executed irreversibly by some upon terminal differentiation and reversibly by others as they adapt to changing conditions (1). For Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), quiescence has emerged as a hallmark of its pathogenicity. M. tuberculosis infects approximately one in every three people worldwide and is the leading bacterial cause of death. Following infection, M. tuberculosis enters a clinically asymptomatic state of non-or slowly replicating physiology that often lasts decades, if not the lifetime, of the infected host, and exhibits a form of nonheritable resistance to nearly all TB drugs that has hindered mass eradication strategies (2). Clinical TB arises when M. tuberculosis reenters cell cycle and provokes an inflammatory response that inflicts host tissue damage and enables it to transmit itself to a new host. However, some of the M. tuberculosis in active TB is nonreplicating. This is thought to impose the need for chemotherapies that are longer and more complex than for virtually any other bacterial infection (2-7). However, biochemical knowledge of quiescent M. tuberculosis remains highly incomplete.Relieved of the requirement to double biomass, quiescent cells have generally been perceived to have minimal metabolic activity. However, quiescent cells often occupy ecological niches that are highly dynamic and face the challenge of preserving both their viability and their ability to reenter cell cycle. Fibroblasts induced into quiescence by contact inhibition metabolized glucose through all branches of central carbon metabolism at a rate similar to those of proliferating cells (8). Such studies ha...