Lung surfactant dysfunction in tuberculosis: effect of mycobacterial tubercular lipids on dipalmitoylphosphatidylcholine surface activity

Mouse Models for Mycobacterium tuberculosis Pathogenesis: Show and Do Not Tell

Science has been taking profit from animal models since the first translational experiments back in ancient Greece. From there, and across all history, several remarkable findings have been obtained using animal models. One of the most popular models, especially for research in infectious diseases, is the mouse. Regarding research in tuberculosis, the mouse has provided useful information about host and bacterial traits related to susceptibility to the infection. The effect of aging, sexual dimorphisms, the route of infection, genetic differences between mice lineages and unbalanced immunity scenarios upon Mycobacterium tuberculosis infection and tuberculosis development has helped, helps and will help biomedical researchers in the design of new tools for diagnosis, treatment and prevention of tuberculosis, despite various discrepancies and the lack of deep study in some areas of these traits.

Roles for phthiocerol dimycocerosate lipids in Mycobacterium tuberculosis pathogenesis

The success of Mycobacterium tuberculosis as a pathogen is well established: tuberculosis is the leading cause of death by a single infectious agent worldwide. The threat of multi- and extensively drug-resistant bacteria has renewed global concerns about this pathogen and understanding its virulence strategies will be essential in the fight against tuberculosis. The current review will focus on phthiocerol dimycocerosates (PDIMs), a long-known and well-studied group of complex lipids found in the M. tuberculosis cell envelope. Numerous studies show a role for PDIMs in several key steps of M. tuberculosis pathogenesis, with recent studies highlighting its involvement in bacterial virulence, in association with the ESX-1 secretion system. Yet, the mechanisms by which PDIMs help M. tuberculosis to control macrophage phagocytosis, inhibit phagosome acidification and modulate host innate immunity, remain to be fully elucidated.

Drug Conjugation Induced Modulation of Structural and Membrane Interaction Features of Cationic Cell-Permeable Peptides

Cell-penetrating peptides might have great potential for enhancing the therapeutic effect of drug molecules against such dangerous pathogens as Mycobacterium tuberculosis (Mtb), which causes a major health problem worldwide. A set of cationic cell-penetration peptides with various hydrophobicity were selected and synthesized as drug carrier of isoniazid (INH), a first-line antibacterial agent against tuberculosis. Molecular interactions between the peptides and their INH-conjugates with cell-membrane-forming lipid layers composed of DPPC and mycolic acid (a characteristic component of Mtb cell wall) were evaluated, using the Langmuir balance technique. Secondary structure of the INH conjugates was analyzed and compared to that of the native peptides by circular dichroism spectroscopic experiments performed in aqueous and membrane mimetic environment. A correlation was found between the conjugation induced conformational and membrane affinity changes of the INH-peptide conjugates. The degree and mode of interaction were also characterized by AFM imaging of penetrated lipid layers. In vitro biological evaluation was performed with Penetratin and Transportan conjugates. Results showed similar internalization rate into EBC-1 human squamous cell carcinoma, but markedly different subcellular localization and activity on intracellular Mtb.

Mycobacteria Clumping Increase Their Capacity to Damage Macrophages

The rough morphotypes of non-tuberculous mycobacteria have been associated with the most severe illnesses in humans. This idea is consistent with the fact that Mycobacterium tuberculosis presents a stable rough morphotype. Unlike smooth morphotypes, the bacilli of rough morphotypes grow close together, leaving no spaces among them and forming large aggregates (clumps). Currently, the initial interaction of macrophages with clumps remains unclear. Thus, we infected J774 macrophages with bacterial suspensions of rough morphotypes of M. abscessus containing clumps and suspensions of smooth morphotypes, primarily containing isolated bacilli. Using confocal laser scanning microscopy and electron microscopy, we observed clumps of at least five rough-morphotype bacilli inside the phagocytic vesicles of macrophages at 3 h post-infection. These clumps grew within the phagocytic vesicles, killing 100% of the macrophages at 72 h post-infection, whereas the proliferation of macrophages infected with smooth morphotypes remained unaltered at 96 h post-infection. Thus, macrophages phagocytose large clumps, exceeding the bactericidal capacities of these cells. Furthermore, proinflammatory cytokines and granuloma-like structures were only produced by macrophages infected with rough morphotypes. Thus, the present study provides a foundation for further studies that consider mycobacterial clumps as virulence factors.

Surface tension in human pathophysiology and its application as a medical diagnostic tool

Introduction: Pathological features of disease appear to be quite different. Despite this diversity, the common feature of various disorders underlies physicochemical and biochemical factors such as surface tension. Human biological fluids comprise various proteins and phospholipids which are capable of adsorption at fluid interfaces and play a vital role in the physiological function of human organs. Surface tension of body fluids correlates directly to the development of pathological states.

Methods: In this review, the variety of human diseases mediated by the surface tension changes of biological phenomena and the failure of biological fluids to remain in their native state are discussed.

Results: Dynamic surface tension measurements of human biological fluids depend on various parameters such as sex, age and changes during pregnancy or certain disease. It is expected that studies of surface tension behavior of human biological fluids will provide additional information and might become useful in medical practice. Theoretical background on surface tension measurement and surface tension values of reference fluids obtained from healthy and sick patients are depicted.

Conclusion: It is well accepted that no single biomarker will be effective in clinical diagnosis. The surface tension measurement combined with routine lab tests may be a novel non-invasive method which can not only facilitate the discovery of diagnostic models for various diseases and its severity, but also be a useful tool for monitoring treatment efficacy. We therefore expect that studies of surface tension behavior of human biological fluids will provide additional useful information in medical practice.

Respirable nanocarriers as a promising strategy for antitubercular drug delivery

Tuberculosis is considered a fatal respiratory infectious disease that represents a global threat, which must be faced. Despite the availability of oral conventional anti-tuberculosis therapy, the disease is characterized by high progression. The leading causes are poor patient compliance and failure to adhere to the drug regimen primarily due to systemic toxicity. In this context, inhalation therapy as a non-invasive route of administration is capable of increasing local drug concentrations in lung tissues, the primary infection side, by passive targeting as well as reducing the risk of systemic toxicity and hence improving the patient compliance. Nanotechnology represents a promising strategy in the development of inhaled drug delivery systems. Nanocarriers can improve the drug effectiveness and decrease the expected side effects as consequences of their ability to target the drug to the infected area as well as sustain its release in a prolonged manner. The current review summarizes the state-of-the-art in the development of inhaled nanotechnological carriers confined currently available anti-tuberculosis drugs (anti TB) for local and targeting drug delivery specifically, polymeric nanoparticles, solid lipid nanoparticles, nanoliposomes and nanomicelles. Moreover, complexes and ion pairs are also reported. The impact and progress of nanotechnology on the therapeutic effectiveness and patient adherence to anti TB regimen are addressed.

In vitro evaluation of inhalable isoniazid-loaded surfactant liposomes as an adjunct therapy in pulmonary tuberculosis

In this study, exogenous pulmonary surfactant was evaluated as an inhalable drug carrier for antitubercular drug isoniazid (INH). Isoniazid-entrapped liposomes of dipalmitoylphosphatidylcholine (DPPC) (the most abundant lipid of lung surfactant and exogenous surfactant) were developed and evaluated for size, drug entrapment, release, in vitro alveolar deposition, biocompatibility, antimycobacterial activity, and pulmonary surfactant action. Isoniazid-entrapped DPPC liposomes were about 750 nm in diameter and had entrapment efficiency of 36.7% +/- 1.8%. Sustained release of INH from DPPC liposomes was observed over 24 h. In vitro alveolar deposition efficiency using the twin impinger exhibited approximately 25-27% INH deposition in the alveolar chamber upon one minute nebulization using a jet nebulizer. At 37 degrees C, the formulation had better pulmonary surfactant function with quicker reduction of surface tension on adsorption (36.7 +/- 0.4 mN/m) than DPPC liposomes (44.7 +/- 0.6 mN/m) and 87% airway patency was exhibited by the formulation in a capillary surfactometer. The formulation was biocompatible and had antimycobacterial activity. The isoniazid-entrapped DPPC liposomes could fulfill the dual purpose of pulmonary drug delivery and alveolar stabilization due to antiatelectatic effect of the surfactant action which can improve the reach of antitubercular drug INH to the alveoli.

Evaluation of antitubercular drug-loaded surfactants as inhalable drug-delivery systems for pulmonary tuberculosis

Pulmonary tuberculosis is associated with a year-long chemotherapy, poor alveolar drug levels, drug-related systemic toxicity, and patient noncompliance. In this study, exogenous pulmonary surfactant is proposed as a drug carrier for antitubercular drugs. Dipalmitoylphosphatidylcholine (DPPC), the major lung-surfactant lipid, has been combined with antitubercular drugs isoniazid (INH), rifampicin (RFM), and ethambutol (ETH) in 1:1 ratio by weight, in which drugs had a ratio of 1:2:3 by weight. At 37 degrees C, the formulation had better surfactant function with quicker reduction of surface tension on adsorption (32.71 +/- 0.65 mN/m) than DPPC liposomes (44.67 +/- 0.57 mN/m) and maintained 100% airway patency in a capillary surfactometer. Drug-loaded surfactant liposomes were about 2 microm and had entrapment efficiency of 30.04% +/- 2.05%, 18.85% +/- 2.92%, and 61.47% +/- 3.32% for INH, RFM, and ETH, respectively. Sustained release of the drugs from surfactants was observed over 24 h. In vitro alveolar deposition efficiency using the twin impinger showed 12.06% +/- 1.87% of INH, 43.30% +/- 0.87% of RFM, and 22.07% +/- 2.02% of ETH deposited in the alveolar chamber upon nebulization for a minute using a jet nebulizer. The formulation was biocompatible and stable with physicochemical properties being retained even after storage for a month at 4 degrees C. Antitubercular drug-loaded surfactants developed could serve dual purposes of alveolar stabilization due to surfactant action and better reach of these drugs to the alveoli due to antiatelectatic effect of the surfactant.

Transcriptional responses of Mycobacterium tuberculosis to lung surfactant

This study uses microarray analyses to examine gene expression profiles for Mycobacterium tuberculosis (Mtb) induced by exposure in vitro to bovine lung surfactant preparations that vary in apoprotein content: (i) whole lung surfactant (WLS) containing the complete mixture of endogenous lipids and surfactant proteins (SP)-A, -B, -C, and -D; (ii) extracted lung surfactant (CLSE) containing lipids plus SP-B and -C; (iii) column-purified surfactant lipids (PPL) containing no apoproteins, and (iv) purified human SP-A. Exposure to WLS evoked a multitude of transcriptional responses in Mtb, with 52 genes up-regulated and 23 genes down-regulated at 30min exposure, plus 146 genes up-regulated and 27 genes down-regulated at 2h. Notably, WLS rapidly induced several membrane-associated lipases that presumptively act on surfactant lipids as substrates, and a large number of genes involved in the synthesis of phthiocerol dimycocerosate (PDIM), a cell wall component known to be important in macrophage interactions and Mtb virulence. Exposure of Mtb to CLSE, PPL, or purified SP-A caused a substantially weaker transcriptional response ( Collapse

Key Words

• mycobacterium tuberculosis
• microarray
• transcriptional responses
• surfactant
• surfactant proteins

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MESH Headings

• Animals
• Cattle
• Gene Expression Profiling
• Humans
• Mycobacterium tuberculosis/drug effects
• Oligonucleotide Array Sequence Analysis
• Pulmonary Surfactants/metabolism
• Stress, Physiological

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Grants

• R01 HL055936 NHLBI NIH HHS
• R01 HL055936-08 NHLBI NIH HHS
• 5 R01 HL55936 NHLBI NIH HHS

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Affiliation(s)

Ute Schwab Department of Microbiology and Immunology, Cornell University College of Veterinary Medicine, Ithaca, NY 14853, USA.
Kyle H Rohde
Zhengdong Wang
Patricia R Chess
Robert H Notter
David G Russell

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Effect of mycolic acid on surface activity of binary surfactant lipid monolayers

In pulmonary tuberculosis, Mycobacterium tuberculosis lies in close physical proximity to alveolar surfactant. Cell walls of the mycobacteria contain loosely bound, detachable surface-active lipids. In this study, the effect of mycolic acid (MA), the most abundant mycobacterial cell wall lipid, on the surface activity of phospholipid mixtures from lung surfactant was investigated using Langmuir monolayers and atomic force microscopy (AFM). In the presence of mycolic acid, all the surfactant lipid mixtures attained high minimum surface tensions (between 20 and 40 mN/m) and decreased surface compressibility moduli <50 mN/m. AFM images showed that the smooth surface topography of surfactant lipid monolayers was altered with addition of MA. Aggregates with diverse heights of at least two layer thicknesses were found in the presence of mycolic acid. Mycolic acids could aggregate within surfactant lipid monolayers and result in disturbed monolayer surface activity. The extent of the effect of mycolic acid depended on the initial state of the monolayer, with fluid films of DPPC-POPC and DPPC-CHOL being least affected. The results imply inhibitory effects of mycolic acid toward lung surfactant lipids and could be a mechanism of lung surfactant dysfunction in pulmonary tuberculosis.

Peripheral cell wall lipids of Mycobacterium tuberculosis are inhibitory to surfactant function

The transmission of Mycobacterium tuberculosis (TB) requires extensive damage to the lungs to facilitate bacterial release into the airways, and it is therefore likely that the microorganism has evolved mechanisms to exacerbate its local pathology. This study examines the inhibitory effects of lipids extracted and purified chromatographically from TB on the surface-active function of lavaged bovine lung surfactant (LS) and a clinically relevant calf lung surfactant extract (CLSE). Total lipids from TB greatly inhibited the surface activity of LS and CLSE on the pulsating bubble surfactometer at physical conditions applicable for respiration in vivo (37 degrees C, 20 cycles/min, 50% area compression). Minimum surface tensions for LS (0.5 mg/ml) and CLSE (1 mg/ml) were raised from <1 mN/m to 15.7+/-1.2 and 18.7+/-1.3 mN/m after 5 min of bubble pulsation in the presence of total TB lipids (0.15 mg/ml). TB mixed waxes (0.15 mg/ml) and TB trehalose monomycolates (TMMs, 0.15 mg/ml) also significantly inhibited the surface activity of LS and CLSE (minimum surface tensions of 10-16 mN/m after 5 min of bubble pulsation), as did purified trehalose 6,6'-dimycolate (TDM, cord factor). Phosphatidylinositol mannosides (PIMs, 0.15 mg/ml) from TB had no inhibitory effect on the surface activity of LS or CLSE. Concentration dependence studies showed that LS was also inhibited significantly by total TB lipids at 0.075 mg/ml, with a smaller activity decrease apparent even at 0.00375 mg/ml. These findings document that TB contains multiple lipids that can directly impair the biophysical function of endogenous and exogenous lung surfactants. Direct inhibition by TB lipids could worsen surfactant dysfunction caused by plasma proteins or other endogenous substances induced by inflammatory injury in the infected lungs. TB lipids could also inhibit the effectiveness of exogenous surfactants used to treat severe acute respiratory failure in TB patients meeting criteria for clinical acute lung injury (ALI) or the acute respiratory distress syndrome (ARDS).

Mycobacterium fortuitum pneumonia in a cat and the role of lipid in the pathogenesis of atypical mycobacterial infections

Mycobacterium fortuitum is a saprophytic, fast-growing, nontuberculous, and nonlepromatous mycobacterium that can cause infections in animals and humans. In dogs and cats, it is one of the most common agents of ulcerative dermatitides and panniculitides caused by atypical mycobacteria. In humans, it is frequently found in lipoid pneumonias or contaminated surgical sites. We report a cat with granulomatous pneumonia caused by M fortuitum resembling lipoid pneumonia in humans. The similarity between the histopathology of the lung and skin lesions caused by this organism in dogs and cats is emphasized. We discuss the role of lipids in the pathogenesis of mycobacterioses and suggest an association between atypical mycobacteria and lipid-rich environments. We conclude that M fortuitum should be included as a differential in cases of lipid-rich pneumonias that do not respond to common antibiotics.

Trehalose 6,6'-dimycolate and lipid in the pathogenesis of caseating granulomas of tuberculosis in mice

Trehalose 6,6'-dimycolate (TDM) is the most abundant, most granulomagenic, and most toxic lipid extractable from the surface of virulent Mycobacterium tuberculosis (MTB). We further examined its toxicity, which requires activation by oily surfaces. Injections of MTB and/or TDM into sensitized mice induced caseating granulomas that centered on oil droplets. If large doses of MTB were injected in saline, caseating granulomas developed in adipose tissue, but MTB with surface TDM removed induced only acute inflammation that did not persist. Variations in protocols produced several variants of caseating granulomas, each with characteristics of human tuberculosis. In each instance, MTB were localized in fat cells or oil drops during initiation of caseating granulomas suggesting that necrosis was caused by activation of the toxicity of TDM toxicity. Evidence extending these findings to the lung was derived from the observation that in sensitized mice, as in humans, tuberculosis development stimulates accumulation of lipid selectively in alveoli. MTB preferentially associated with lipid droplets in developing necrotic foci in late-stage murine tuberculosis. This supports the hypothesis that pulmonary tuberculosis sequesters MTB in a protected environment that accumulates lipid until it is able to activate the toxicity of TDM and initiate necrosis that results in caseating granulomas.