Effects of dexamethasone and transient malnutrition on rabbits infected with aerosolized Mycobacterium tuberculosis CDC1551

Effect of Low Doses of Dexamethasone on Experimental Pulmonary Tuberculosis

Tuberculosis (TB) is the deadliest disease caused by a bacterial agent. Glucocorticoids (GCs) have a typical anti-inflammatory effect, but recently it has been shown that they can present proinflammatory activity, mainly by increasing molecules from innate immunity. In the current study, we evaluated the effect of low doses of dexamethasone on Mycobacterium tuberculosis in vivo and in vitro. We used an established mice model of progressing tuberculosis (TB) in the in vivo studies. Intratracheal or intranasal dexamethasone therapy administered with conventional antibiotics in the late stage of the disease decreased the lung bacilli load and lung pneumonia, and increased the survival of the animals. Finally, the treatment decreased the inflammatory response in the SNC and, therefore, sickness behavior and neurological abnormalities in the infected animals. In the in vitro experiments, we used a cell line of murine alveolar macrophages infected with Mtb. Low-dose dexamethasone treatment increased the clearance capacity of Mtb by MHS macrophages, MIP-1α, and TLR2 expression, decreased proinflammatory and anti-inflammatory cytokines, and induced apoptosis, a molecular process that contributes to the control of the mycobacteria. In conclusion, the administration of low doses of dexamethasone represents a promising adjuvant treatment for pulmonary TB.

Therapeutic host-directed strategies to improve outcome in tuberculosis

Bacille Calmette-Guérin (BCG) is the only licenced tuberculosis (TB) vaccine, but has limited efficacy against pulmonary TB disease development and modest protection against extrapulmonary TB. Preventative antibiotic treatment for Mycobacterium tuberculosis (Mtb) infections in high-prevalence settings is unfeasible due to unclear treatment durability, drug toxicity, logistical constraints related to directly observed treatment strategy (DOTS) and the lengthy treatment protocols. Together, these factors promote non-adherence, contributing to relapse and establishment of drug-resistant Mtb strains. Although antibiotic treatment of drug-susceptible Mtb is generally effective, drug-resistant TB has a treatment efficacy below 50% and can, in a proportion, develop into progressive, untreatable disease. Other immune compromising co-infections and/or co-morbidities require more complex prevention/treatment approaches, posing huge financial burdens to national health services. Novel TB treatment strategies, such as host-directed therapeutics, are required to complement pathogen-targeted approaches. Pre-clinical studies have highlighted promising candidates that enhance endogenous pathways and/or limit destructive host responses. This review discusses promising pre-clinical candidates and forerunning compounds at advanced stages of clinical investigation in TB host-directed therapeutic (HDT) efficacy trials. Such approaches are rationalized to improve outcome in TB and shorten treatment strategies.

Interferon γ and interleukin 10 responses in immunocompetent and immunosuppressed New Zealand White rabbits naturally infected with Encephalitozoon cuniculi

Levels of interferon (IFN)-γ and interleukin (IL)-10 were measured in the serum of immunocompetent and immunosuppressed New Zealand White rabbits naturally infected with Encephalitozoon cuniculi. IFN-γ levels were elevated in infected rabbits, and a synergic effect was observed in animals treated with the immunosuppressive agent dexamethasone (Dex). The role of IL-10 in infected rabbits remains unclear, as IL-10 levels were similar to those of negative controls. Dex appeared to exhibit a proinflammatory effect, as IFN-γ levels were elevated in infected immunosuppressed rabbits. Similarly, Dex exhibited a synergic effect in infected immunosuppressed rabbits, as evidenced by the elevation in IFN-γ production. These data indicate that the immune response to this glucocorticoid should be considered in the design of future animal model studies of immunosuppression.

Cathepsin K Contributes to Cavitation and Collagen Turnover in Pulmonary Tuberculosis

Cavitation in tuberculosis enables highly efficient person-to-person aerosol transmission. We performed transcriptomics in the rabbit cavitary tuberculosis model. Among 17 318 transcripts, we identified 22 upregulated proteases. Five type I collagenases were overrepresented: cathepsin K (CTSK), mast cell chymase-1 (CMA1), matrix metalloproteinase 1 (MMP-1), MMP-13, and MMP-14. Studies of collagen turnover markers, specifically, collagen type I C-terminal propeptide (CICP), urinary deoxypyridinoline (DPD), and urinary helical peptide, revealed that cavitation in tuberculosis leads to both type I collagen destruction and synthesis and that proteases other than MMP-1, MMP-13, and MMP-14 are involved, suggesting a key role for CTSK. We confirmed the importance of CTSK upregulation in human lung specimens, using immunohistochemical analysis, which revealed perigranulomatous staining for CTSK, and we showed that CTSK levels were increased in the serum of patients with tuberculosis, compared with those in controls (3.3 vs 0.3 ng/mL; P = .005).

Pharmacokinetics and efficacy of Bioerodible Dexamethasone implant in Concanavalin A-induced uveitic cataract rabbit model

PURPOSE

To advance therapy for the treatment of concurrent uveitis and post-cataract surgical inflammation; we evaluated pharmacokinetics and pharmacodynamics of Bioerodible Dexamethasone Implant (BDI) containing 0.3 mg of dexamethasone (DXM) in Concanavalin A (Con A) induced uveitis followed by phacoemulsification in New Zealand White (NZW) rabbits.

METHODS

The BDI was implanted in the inferior fornix of the capsular bag after intravitreal injection of Con A and ensuing phacoemulsification in NZW rabbits; standard-of-care topical 0.1% dexamethasone drops served as control. DXM was quantified by liquid chromatography-tandem mass spectrometry and pharmacokinetics of DXM in disease vs. healthy eyes was compared. All eyes were assessed clinically using slit lamp biomicroscopy and Draize scoring scale. Retinal thickness and histological analyses were performed to evaluate retinal edema, inflammation and implant biocompatibility respectively.

RESULTS

In Con A-induced inflammatory uveitic cataract model the BDI controlled anterior and posterior segment inflammation as well as retinal thickening more effectively than topical drops. The exposure (AUC0-t) of DXM with BDI is superior in all ocular tissues, while topical drops did not achieve therapeutic posterior segment levels and did not control inflammation nor prevent retinal edema and architectural disruption.

CONCLUSIONS

Our results demonstrate the superiority of the BDI in suppressing Con A-induced inflammation and retinal edema in NZW rabbits and highlight the need for sustained bidirectional delivery of potent anti-inflammatory agents for 5 to 6 weeks to optimize clinical outcomes.

Penitentiary or penthouse condo: the tuberculous granuloma from the microbe's point of view

Granuloma formation represents a pivotal point during human infection with Mycobacterium tuberculosis, for this structure may limit mycobacterial spread and prevent active disease, while at the same time allow for the survival and persistence of viable mycobacteria within the host. The current therapeutic regimens for treating tuberculosis disease have proven effective in developing countries. However, in countries with large populations, limited access to health care, and high incidence of HIV co-infection, tuberculosis disease continues to represent a major global health emergency. Particularly, the emergence of extensively and multi-drug-resistant forms of tuberculosis underscores the need develop new treatment strategies. Recent mechanistic studies have identified bacterial virulence mechanisms that subvert host responses and lead to an inappropriate upregulation of host factors such as tumour necrosis factor-alpha (TNF-alpha) and matrix metalloproteinases (MMPs). Paradoxically, then, part of the mycobacterial virulence programme may be to promote granuloma development and maturation. These observations suggest that together with appropriate anti-microbials host-based therapeutics directed at TNF-alpha and MMP inhibition may counteract the microbial subterfuge, reduce the pro-granulomatous response, and offer an enhanced therapeutic effect. Host-directed therapy that alters the immune response may offer an alternative approach towards reducing treatment duration, the risk of anti-microbial resistance and improving patient outcome.

The aerosol rabbit model of TB latency, reactivation and immune reconstitution inflammatory syndrome

The large reservoir of human latent tuberculosis (TB) contributes to the global success of the pathogen, Mycobacterium tuberculosis (Mtb). We sought to test whether aerosol infection of rabbits with Mtb H37Rv could model paucibacillary human latent TB. The lung burden of infection peaked at 5 weeks after aerosol infection followed by host containment of infection that was achieved in all rabbits. One-third of rabbits had at least one caseous granuloma with culturable bacilli at 36 weeks after infection suggesting persistent paucibacillary infection. Corticosteroid-induced immunosuppression initiated after disease containment resulted in reactivation of disease. Seventy-two percent of rabbits had culturable bacilli in the right upper lung lobe homogenates compared to none of the untreated controls. Discontinuation of dexamethasone led to predictable lymphoid recovery, with a proportion of rabbits developing multicentric large caseous granuloma. The development and severity of the immune reconstitution inflammatory syndrome (IRIS) was dependent on the antigen load at the time of immunosuppression and subsequent bacillary replication during corticosteroid-induced immunosuppression. Clinically, many aspects were similar to IRIS in severely immunosuppressed HIV-infected patients who have functional restoration of T cells in response to effective (highly active) antiretroviral therapy. This corticosteroid model is the only animal model of the IRIS. Further study of the rabbit model of TB latency, reactivation and IRIS may be important in understanding the immunopathogenesis of these poorly modeled states as well as for improved diagnostics for specific stages of disease.

Dexamethasone-induced immunosuppression: a rabbit model

Rabbits are often used as animal models for experimental purposes; in many cases steroid-induced immunosuppression is necessary. The aim of this study was to characterise a model of immunosuppression in rabbits, based on changes in the lymphocyte subset distribution, changes in proliferative capacity of lymphocytes and activity of neutrophils 1, 3 and 7 days after the administration of 2mg/kg dexamethasone phosphate (DXP) three times at 6-h intervals. In peripheral blood, neutrophilia and lymphopenia together with eosinopenia, monocytopenia and basopenia in the absence of leukocytosis was detected. One day after DXP administration the absolute numbers of all lymphocyte subsets decreased in the blood, whereas in bone marrow, absolute numbers of all lymphocyte subsets increased significantly, except CD79alpha(+) cells that increased only in relative numbers. The effect of DXP on lymphocytes from the spleen, mesenteric and popliteal lymph nodes was less pronounced. In the thymus, DXP led to a marked reduction of the relative and absolute numbers of CD4(+)CD8(+) thymocytes. The proliferative capacity of lymphocytes after concanavalin A stimulation was lower in the peripheral blood and spleen only on day 1, no changes were detected in lymph nodes or in bone marrow. A marked increase in proliferative capacity was detected in the thymus. Spontaneous production of reactive oxygen metabolites by neutrophils was reduced on days 1 and 3 after DXP administration. The present results demonstrate clearly that this DXP application protocol is useful for the experimental induction of relatively short-lasting immunosuppression in rabbits.

Susceptibility to tuberculosis: composition of tuberculous granulomas in Thorbecke and outbred New Zealand White rabbits

We sought to characterize the lung cellular immune responses to inhaled Mycobacterium tuberculosis (Mtb) of the susceptible inbred Thorbecke rabbit (the genomically sequenced strain, now unavailable) and compare it to outbred, Mtb-resistant, New Zealand White rabbits. Using Mtb CDC1551, we confirmed that the inbred rabbits allowed establishment of infection with this low virulence strain, compared to poor establishment in outbred rabbits. With a more virulent strain, Mtb Erdman, that establishes infection well in both rabbit strains, we analyzed granulomas from rabbit lungs 5 weeks after aerosol infection. The lung granulomas of inbred rabbits had significantly higher frequencies of cells expressing MHC Class II and CD11b, and lower frequencies of CD8+ T cells than the outbred controls. Macrophage-sized cells expressing MHC Class II in inbred rabbit granulomas showed significantly decreased intensity of expression, suggesting impaired maturation. Although the inbred dermal tuberculin reactions were decreased, the in vitro IFN-gamma mRNA responses of hilar node lymphocytes to tuberculin were higher than those of outbred rabbits. Further delineation of the outbred rabbit's resistant immune response to Mtb infection is warranted.

Animal models of cavitation in pulmonary tuberculosis

Transmission of tuberculosis occurs with the highest frequency from patients with extensive, cavitary, pulmonary disease and positive sputum smear microscopy. In animal models of tuberculosis, the development of caseous necrosis is an important prerequisite for the formation of cavities although the immunological triggers for liquefaction are unknown. We review the relative merits and the information gleaned from the available animal models of pulmonary cavitation. Understanding the host-pathogen interaction important to the formation of cavities may lead to new strategies to prevent cavitation and thereby, block transmission.