CRL-1072 enhances antimycobacterial activity of human macrophages through interleukin-8

The New Frontier of Host-Directed Therapies for Mycobacterium avium Complex

Mycobacterium avium complex (MAC) is an increasingly important cause of morbidity and mortality, and is responsible for pulmonary infection in patients with underlying lung disease and disseminated disease in patients with AIDS. MAC has evolved various virulence strategies to subvert immune responses and persist in the infected host. Current treatment for MAC is challenging, requiring a combination of multiple antibiotics given over a long time period (for at least 12 months after negative sputum culture conversion). Moreover, even after eradication of infection, many patients are left with residual lung dysfunction. In order to address similar challenges facing the management of patients with tuberculosis, recent attention has focused on the development of novel adjunctive, host-directed therapies (HDTs), with the goal of accelerating the clearance of mycobacteria by immune defenses and reducing or reversing mycobacterial-induced lung damage. In this review, we will summarize the evidence supporting specific adjunctive, HDTs for MAC, with a focus on the repurposing of existing immune-modulatory agents targeting a variety of different cellular pathways. We also highlight areas meriting further investigation.

Human and mouse macrophages collaborate with neutrophils to kill larval Strongyloides stercoralis

Macrophages are multifunctional cells that are active in TH1- and TH2-mediated responses. In this study, we demonstrate that human and mouse macrophages collaborate with neutrophils and complement to kill the parasite Strongyloides stercoralis in vitro. Infection of mice with worms resulted in the induction of alternatively activated macrophages (AAM) within the peritoneal cavity. These cells killed the worms in vivo and collaborated with neutrophils and complement during the in vitro killing process. AAM generated in vitro killed larvae more rapidly than naive macrophages, which killed larvae after a longer time period. In contrast, classically activated macrophages were unable to kill larvae either in vitro or in vivo. This study adds macrophages to the armamentarium of immune components that function in elimination of parasitic helminths and demonstrate a novel function by which AAM control large extracellular parasites.

When two is better than one: macrophages and neutrophils work in concert in innate immunity as complementary and cooperative partners of a myeloid phagocyte system

The antimicrobial effector activity of phagocytes is crucial in the host innate defense against infection, and the classic view is that the phagocytes operating against intracellular and extracellular microbial pathogens are,respectively, macrophages and neutrophils. As a result of the common origin of the two phagocytes, they share several functionalities, including avid phagocytosis,similar kinetic behavior under inflammatory/infectious conditions, and antimicrobial and immunomodulatory activities. However, consequent to specialization during their differentiation, macrophages and neutrophils acquire distinctive, complementary features that originate different levels of antimicrobial capacities and cytotoxicity and different tissue localization and lifespan.This review highlights data suggesting the perspective that the combination of overlapping and complementary characteristics of the two professional phagocytes promotes their cooperative participation as effectors and modulators in innate immunity against infection and as orchestrators of adaptive immunity. In the concerted activities operating in antimicrobial innate immunity, macrophages and neutrophils are not able to replace each other. The common and complementary developmental,kinetic, and functional properties of neutrophils and macrophages make them the effector arms of a myeloid phagocyte system that groups neutrophils with members of the old mononuclear phagocyte system. The use by mammals of a system with two dedicated phagocytic cells working cooperatively represents an advantageous innate immune attack strategy that allows the efficient and safe use of powerful but dangerous microbicidal molecules.This crucial strategy is a target of key virulence mechanisms of successful pathogens.

Stealth liposomes and long circulating nanoparticles: critical issues in pharmacokinetics, opsonization and protein-binding properties

This article critically examines and evaluates the likely mechanisms that contribute to prolonged circulation times of sterically protected nanoparticles and liposomes. It is generally assumed that the macrophage-resistant property of sterically protected particles is due to suppression in surface opsonization and protein adsorption. However, recent evidence shows that sterically stabilized particles are prone to opsonization particularly by the opsonic components of the complement system. We have evaluated these phenomena and discussed theories that reconcile complement activation and opsonization with prolonged circulation times. With respect to particle longevity, the physiological state of macrophages also plays a critical role. For example, stimulated or newly recruited macrophages can recognize and rapidly internalize sterically protected nanoparticles by opsonic-independent mechanisms. These concepts are also examined.

Therapeutic synthetic polymers: a game of Russian roulette?

Synthetic polymer-based drug-delivery systems have been applied in drug delivery for the past 50 years. So why are there so few examples of these macromolecules being used successfully in the clinic? It is our view that many products are failing because of a neglect of the fundamental science surrounding the architectural control of the molecules present, their behaviour following in vivo administration and host response. Adverse events following parenteral administration of approved synthetic polymer-based systems have resulted in unpredictable and fatal responses in a significant number of individuals. Acceptance of the importance of immunotoxicological factors in response to the presence of these macromolecules must be addressed if emergent technologies, such as polymer-based gene-delivery systems, are going to succeed.

A role for complement C5 in organism containment and granulomatous response during murine tuberculosis

The molecular mechanisms underlying protective granuloma formation and control of bacterial growth during infection with Mycobacterium tuberculosis (MTB) are not yet completely understood. MTB-infected mice with natural deficiency in complement component C5 are unable to develop productive granulomatous responses, and are impaired in limiting organism growth within the lung. To address the molecular basis for this histologic dysfunction, congenic complement C5-sufficient (B10.D2-H2d H2-T18c Hcl/nSnJ) and complement C5-deficient strains (B10.D2-H2d H2-T18c Hco/oSnJ) congenic mice were infected with Mycobacterium tuberculosis, and cytokine and chemokine responses were examined. Twelve and 28 days after infection, lungs showed elevated messages for multiple inflammatory cytokines in both congenic strains. Interleukin (IL)-12(p40) mRNA was also induced during infection in C5-deficient mice, although levels were significantly decreased compared to C5-sufficient congenics. C5-deficient mice also demonstrated reduced KC, MIP-2, IP-10, and MCP-1 mRNA. The defect may directly involve C5-mediated effects on macrophage responses; C5-deficient bone marrow derived macrophages had significantly reduced secretion of KC, MIP-1 alpha and MIP-2 compared to C5-sufficient macrophages following in vitro infection. These findings indicate a role for C5 in mediation of chemotactic and activation events that are the basis for granulomatous responses during murine tuberculosis.

Effect of poloxamer CRL-1072 on drug uptake and nitric-oxide-mediated killing of Mycobacterium avium by macrophages

Mycobacterium avium-intracellulare complex (MAI) are common pathogens of opportunistic infections that are naturally resistant to most antibiotics and develop acquired resistance rapidly. An experimental drug, poloxamer CRL-1072, was found to have two unusual properties: it synergistically enhanced the activity of several antibiotics against MAI even though it had little activity as a single agent and it had greater activity against MAI in macrophage culture or in mice than in broth culture. Studies were undertaken to investigate the mechanisms of these effects. CRL-1072 was taken up by MAI and enhanced the uptake of fluorescent-labeled streptomycin and erythromycin in broth culture. The labeled antibiotics had reduced activity so the relevance for naive antibiotics must be inferred. In culture with human U937 monocytoid cells, CRL-1072 became localized in phagosomes and promoted uptake of streptomycin. Finally, CRL-1072 was found to induce production of mRNA for inducible nitric oxide synthase (iNOS) and nitric oxide (NO) by U937 cells. The antimycobacterial effect in macrophages was reversed by the iNOS inhibitor N-monomethyl L-arginine (NMMA), suggesting that CRL-1072 promotes killing of MAI by inducing NO. These effects were induced by noncytotoxic concentrations of CRL-1072. These data suggest that the antimycobacterial mechanisms of CRL-1072 include enhancing the delivery of antibiotic to targets within MAI and enhancement of the ability of macrophages to kill ingested organisms.

Identification of viable and non-viable Mycobacterium tuberculosis in mouse organs by directed RT-PCR for antigen 85B mRNA

Mycobacterium tuberculosis (MTB) the causative organism of tuberculosis can remain dormant as a non-culturable organism, reactivate and cause disease in man and animals. There is a need for proof of viability of such organisms in order to understand the process of reactivation. PCR for bacterial DNA cannot distinguish between viable and non-viable bacilli. We have tested a previously described two tube directed reverse transcriptase polymerase chain reaction (RT-PCR) for the detection of mRNA of antigen 85B (Ag85B) of MTB that can distinguish between viable and non-viable organisms. Using a set of external and internal primers for Ag85B, a cDNA amplified product (216 bp) was seen among simulated samples containing only viable cfus at a sensitivity of >10 and <100 cfu/ml. Eucaryotic DNA rich normal mouse lung homogenate did not interfere among these samples. The method amplified the 216 bp product also among cfu positive tissues of naturally infected mice. Finally, in a mouse model of dormancy, direct RT-PCR detected a signal among multiple tissues that were negative for cfus and hence non-culturable. Ag85B is abundantly secreted by MTB and hyper-expressed under stress conditions. Thus the method to identify its mRNA message may be useful to detect viable but dormant bacteria.

Activities of poloxamer CRL-1072 against Mycobacterium avium in macrophage culture and in mice

Earlier studies reported that certain large hydrophobic poloxamer surfactants were able to inhibit the growth of Mycobacterium avium-M. intracellulare complex (MAI) in broth and to produce synergistic enhancement of the activity of rifampin. CRL-1072 was synthesized to have an optimal structure for antimicrobic effects and greater purity. Its MIC for MAI in broth was greater than 100 microg/ml. Surprisingly, its MIC for MAI growing in human U937 monocytoid cells was much lower, 5 microg/ml. A still lower concentration, 0.1 microg/ml, produced synergistic enhancement of the activities of clarithromycin, rifampin, amikacin, streptomycin, and clindamycin, but not isoniazid, against MAI infecting monocytoid cells. Mice tolerated injection of doses of CRL-1072 as high as 125 mg/kg of body weight. Pharmacokinetic analysis revealed that the copolymer had an elimination half-life of 60 h and suggested dosing regimens that might produce therapeutic concentrations in tissue. In a mouse model of acute MAI infection, CRL-1072 significantly enhanced the bactericidal activities of clarithromycin and rifampin when it was administered at 1.0 mg/kg intravenously (i.v.) three times per week. CRL-1072 given i.v. or orally also enhanced the bactericidal activity of clindamycin against MAI.