Immunomodulatory effects of azithromycin on the establishment of lipopolysaccharide tolerance in mice

Azithromycin preserves adult hippocampal neurogenesis and behavior in a mouse model of sepsis

The mammalian hippocampus can generate new neurons throughout life. Known as adult hippocampal neurogenesis (AHN), this process participates in learning, memory, mood regulation, and forgetting. The continuous incorporation of new neurons enhances the plasticity of the hippocampus and contributes to the cognitive reserve in aged individuals. However, the integrity of AHN is targeted by numerous pathological conditions, including neurodegenerative diseases and sustained inflammation. In this regard, the latter causes cognitive decline, mood alterations, and multiple AHN impairments. In fact, the systemic administration of Lipopolysaccharide (LPS) from E. coli to mice (a model of sepsis) triggers depression-like behavior, impairs pattern separation, and decreases the survival, maturation, and synaptic integration of adult-born hippocampal dentate granule cells. Here we tested the capacity of the macrolide antibiotic azithromycin to neutralize the deleterious consequences of LPS administration in female C57BL6J mice. This antibiotic exerted potent neuroprotective effects. It reversed the increased immobility time during the Porsolt test, hippocampal secretion of pro-inflammatory cytokines, and AHN impairments. Moreover, azithromycin promoted the synaptic integration of adult-born neurons and functionally remodeled the gut microbiome. Therefore, our data point to azithromycin as a clinically relevant drug with the putative capacity to ameliorate the negative consequences of chronic inflammation by modulating AHN and hippocampal-related behaviors.

Synthesis, Characterization, and in vivo Distribution of Intracellular Delivered Macrolide Short-Chain Fatty Acid Derivatives

Short-chain fatty acids (SCFAs) have a range of effects in metabolism and immune regulation. We have observed that delivery of SCFAs to lysosomes has potent immune regulatory effects, possibly as a surrogate signal for the presence of anaerobic organisms. To better understand the pharmacology of lysosomal SCFA donors, we investigated the distribution and metabolism of propionate and butyrate donors. Each analog (1 a and 2 a) can donate three SCFA equivalents via ester hydrolysis through six intermediate metabolites. The compounds are stabilized by low pH, and stability in cells is usually higher than in medium, but is cell-type specific. Butyrate derivatives were found to be more stable than propionates. Tri-esters were more stable than di- or mono-esters. The donors were surprisingly stable in vivo, and hydrolysis of each position was organ specific. Jejunum and liver caused rapid loss of 4'' esters. The gut metabolite pattern by i. v. differed from that of p.o. application, suggesting luminal and apical enzyme effects in the gut epithelium. Central organs could de-esterify the 11-position. Levels in lung relative to other organs were higher by p.o. than via i. v., suggesting that delivery route can influence the observed pharmacology and that gut metabolites distribute differently. The donors were largely eliminated by 24 h, following near linear decline in organs. The observed levels and distribution were found to be consistent with pharmacodynamic effects, particularly in the gut.

Immunomodulation by macrolides: therapeutic potential for critical care

Critical illness is associated with immune dysregulation, characterised by concurrent hyperinflammation and immune suppression. Hyperinflammation can result in collateral tissue damage and organ failure, whereas immune suppression has been implicated in susceptibility to secondary infections and reactivation of latent viruses. Macrolides are a class of bacteriostatic antibiotics that are used in the intensive care unit to control infections or to alleviate gastrointestinal dysmotility. Yet macrolides also have potent and wide-ranging immunomodulatory properties, which might have the potential to correct immune dysregulation in patients who are critically ill without affecting crucial antimicrobial defences. In this Review, we provide an overview of preclinical and clinical studies that point to the beneficial effects of macrolides in acute diseases relevant to critical care, and we discuss the possible underlying mechanisms of their immunomodulatory effects. Further studies are needed to explore the therapeutic potential of macrolides in critical illness, to identify subgroups of patients who might benefit from treatment, and to develop novel non-antibiotic macrolide derivatives with improved immunomodulatory properties.

Synergistic Antimicrobial Activity of Colistin in Combination with Rifampin and Azithromycin against Escherichia coli Producing MCR-1

The lack of available antibiotics is a global public health problem due to the emergence of antimicrobial resistance. Effective therapeutic regimens are urgently needed against Escherichia coli strains that produce the colistin resistance gene mcr-1 and to inhibit the emergence of resistance. In this study, we assessed the antimicrobial activity of a series of concentrations of colistin-based combinations with rifampin and/or azithromycin against three strains of Escherichia coli, including colistin-resistant isolate MZ1501^R, isolate HE1704^R that produces MCR-1, and colistin-susceptible isolate MZ1509^S Experiments were conducted with a medium inoculum of ∼10⁷ CFU/ml over 48 h. Subsequently, the in vivo therapeutic effect was investigated using a neutropenic mouse thigh infection model. Almost all monotherapies showed unsatisfactory antibacterial activity against E. coli isolates producing MCR-1. In contrast, colistin in combination with rifampin or azithromycin resulted in an obvious decrease in the bacterial burden albeit with regrowth. More obviously, synergistic antimicrobial activity of colistin-based triple-combination therapy with rifampin and azithromycin was observed, resulting in a rapid and exhaustive antibacterial effect. In vivo treatments confirmed these findings, where mean decreases of 0.38 to 0.90 log₁₀ CFU and 1.27 to 1.78 log₁₀ CFU were noted after 24 h and 48 h of treatment, respectively, against colistin-resistant E. coli strains when 5 mg/kg of body weight of colistin was combined with rifampin and azithromycin. Colistin-based combinations with rifampin and azithromycin provide a more active therapeutic regimen than monotherapy or colistin-based double combinations against E. coli producing MCR-1.

Pentoxifylline, dexamethasone and azithromycin demonstrate distinct age-dependent and synergistic inhibition of TLR- and inflammasome-mediated cytokine production in human newborn and adult blood in vitro

Introduction

Neonatal inflammation, mediated in part through Toll-like receptor (TLR) and inflammasome signaling, contributes to adverse outcomes including organ injury. Pentoxifylline (PTX), a phosphodiesterase inhibitor which potently suppresses cytokine production in newborn cord blood, is a candidate neonatal anti-inflammatory agent. We hypothesized that combinations of PTX with other anti-inflammatory agents, the steroid dexamethasone (DEX) or the macrolide azithromycin (AZI), may exert broader, more profound and/or synergistic anti-inflammatory activity towards neonatal TLR- and inflammasome-mediated cytokine production.

Methods

Whole newborn and adult blood was treated with PTX (50–200 μM), DEX (10⁻¹⁰–10⁻⁷ M), or AZI (2.5–20 μM), alone or combined, and cultured with lipopolysaccharide (LPS) (TLR4 agonist), R848 (TLR7/8 agonist) or LPS/adenosine triphosphate (ATP) (inflammasome induction). Supernatant and intracellular cytokines, signaling molecules and mRNA were measured by multiplex assay, flow cytometry and real-time PCR. Drug interactions were assessed based on Loewe's additivity.

Results

PTX, DEX and AZI inhibited TLR- and/or inflammasome-mediated cytokine production in newborn and adult blood, whether added before, simultaneously or after TLR stimulation. PTX preferentially inhibited pro-inflammatory cytokines especially TNF. DEX inhibited IL-10 in newborn, and TNF, IL-1β, IL-6 and interferon-α in newborn and adult blood. AZI inhibited R848-induced TNF, IL-1β, IL-6 and IL-10, and LPS-induced IL-1β and IL-10. (PTX+DEX) synergistically decreased LPS- and LPS/ATP-induced TNF, IL-1β, and IL-6, and R848-induced IL-1β and interferon-α, while (PTX+AZI) synergistically decreased induction of TNF, IL-1β, and IL-6. Synergistic inhibition of TNF production by (PTX+DEX) was especially pronounced in newborn vs. adult blood and was accompanied by reduction of TNF mRNA and enhancement of IL10 mRNA.

Conclusions

Age, agent, and specific drug-drug combinations exert distinct anti-inflammatory effects towards TLR- and/or inflammasome-mediated cytokine production in human newborn blood in vitro. Synergistic combinations of PTX, DEX and AZI may offer benefit for prevention and/or treatment of neonatal inflammatory conditions while potentially limiting drug exposure and toxicity.

Update on the combination effect of macrolide antibiotics in community-acquired pneumonia

Community-acquired pneumonia (CAP) is a leading cause of death from an infectious cause worldwide. Guideline-concordant antibiotic therapy initiated in a timely manner is associated with improved treatment responses and patient outcomes. In the post-antibiotic era, much of the morbidity and mortality of CAP is as a result of the interaction between bacterial virulence factors and host immune responses. In patients with severe CAP, or who are critically ill, there is a lot of emerging observational evidence demonstrating improved survival rates when treatment using combination therapy with a β-lactam and a macrolide is initiated, as compared to other antibiotic regimes without a macrolide. Macrolides in combination with a β-lactam antibiotic provide broader coverage for the atypical organisms implicated in CAP, and may contribute to antibacterial synergism. However, it has been postulated that the documented immunomodulatory effects of macrolides are the primary mechanism for improved patient outcomes through attenuation of bacterial virulence factors and host systemic inflammatory responses. Despite concerns regarding the limitations of observational evidence and the lack of confirmatory randomized controlled trials, the potential magnitude of mortality benefits estimated at 20-50% cannot be overlooked. In light of recent data from a number of trials showing that combination treatment with a macrolide and a suitable second agent is justified in all patients with severe CAP, such treatment should be obligatory for those admitted to an intensive care setting.