Lovastatin, but not pravastatin, limits in vitro infection due to Coxiella burnetii

Treatment of persistent focalized Q fever: time has come for an international randomized controlled trial

Q fever is a worldwide zoonosis due to Coxiella burnetii, responsible for endocarditis and endovascular infections. Since the 1990s, the combination hydroxychloroquine + doxycycline has constituted the curative and prophylactic treatment in persistent focalized Q fever. This combination appears to have significantly reduced the treatment's duration (from 60 to 26 months), yet substantial evidence of effectiveness remains lacking. Data are mostly based on in vitro and observational studies. We conducted a literature review to assess the effectiveness of this therapy, along with potential alternatives. The proposed in vitro mechanism of action describes the inhibition of Coxiella replication by doxycycline through the restoration of its bactericidal activity (inhibited in acidic environment) by alkalinization of phagolysosome-like vacuoles with hydroxychloroquine. So far, the rarity and heterogeneous presentation of cases have made it challenging to design prospective studies with statistical power. The main studies supporting this treatment are retrospective cohorts, dating back to the 1990s-2000s. Retrospective studies from the large Dutch outbreak of Q fever (>4000 cases between 2007 and 2010) did not corroborate a clear benefit of this combination, notably in comparison with other regimens. Thus, there is still no consensus among the medical community on this issue. However insufficient the evidence, today the doxycycline + hydroxychloroquine combination remains the regimen with the largest clinical experience in the treatment of 'chronic' Q fever. Reinforcing the guidelines' level of evidence is critical. We herein propose the creation of an extensive international registry, followed by a prospective cohort or ideally a randomized controlled trial.

Atorvastatin Potentially Reduces Mycobacterial Severity through Its Action on Lipoarabinomannan and Drug Permeability in Granulomas

The majority of preclinical research has shown that Mycobacterium tuberculosis can modify host lipids in various ways. To boost its intramacrophage survival, M. tuberculosis causes host lipids to build up, resulting in the development of lipid-laden foam cells. M. tuberculosis binds to and enters the macrophage via the cell membrane cholesterol. Aggregation of cholesterol in the cell wall of M. tuberculosis and an increase in vascularity at the granuloma site reduce the permeability of rifampicin and isoniazid concentrations. However, very few studies have assessed the effect of statins on drug penetration. Here, we used atorvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, to observe its effect on the bacterial burden by increasing the drug concentration at the infection site. We looked into how atorvastatin could be used in conjunction with first-line drugs to promote drug permeation. In this study, we detected an accumulation of drugs at the peripheral sites of the lungs and impaired drug distribution to the diseased sites. The efficacy of antituberculosis drugs, with atorvastatin as an adjunct, on the viability of M. tuberculosis cells was demonstrated. A nontoxic statin dosage established phenotypic and normal granuloma vasculature and showed an additive effect with rifampicin and isoniazid. Our data show that statins help to reduce the tuberculosis bacterial burden. Our findings reveal that the bacterial load is connected with impaired drug permeability resulting from lipid accumulation in the bacterial cell wall. Statin therapy combined with antituberculosis medications have the potential to improve treatment in tuberculosis patients. IMPORTANCE Mycobacterium tuberculosis binds to and enters the macrophage via the cell membrane cholesterol. M. tuberculosis limits phagosomal maturation and activation without engaging in phagocytosis. Aggregation of cholesterol in the cell wall of M. tuberculosis and an increase in the vascularity at the granuloma site reduce the permeability of rifampicin and isoniazid concentrations. However, very few studies have assessed the effect of statins on drug penetration, which can be increased through a reduction in cholesterol and vascularity. Herein, we used atorvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, to observe its effect on bacterial burden through increasing the drug concentration at the infection site. Our main research goal is to diminish mycobacterial dissemination and attenuate bacterial growth by increasing drug permeability.

Adjunctive Host-Directed Therapy With Statins Improves Tuberculosis-Related Outcomes in Mice

BACKGROUND

Tuberculosis (TB) treatment is lengthy and complicated and patients often develop chronic lung disease. Recent attention has focused on host-directed therapies aimed at optimizing immune responses to Mycobacterium tuberculosis (Mtb), as adjunctive treatment given with antitubercular drugs. In addition to their cholesterol-lowering properties, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have broad anti-inflammatory and immunomodulatory activities.

METHODS

In the current study, we screened 8 commercially available statins for cytotoxic effect, anti-TB activity, synergy with first-line drugs in macrophages, pharmacokinetics and adjunctive bactericidal activity, and, in 2 different mouse models, as adjunctive therapy to first-line TB drugs.

RESULTS

Pravastatin showed the least toxicity in THP-1 and Vero cells. At nontoxic doses, atorvastatin and mevastatin were unable to inhibit Mtb growth in THP-1 cells. Simvastatin, fluvastatin, and pravastatin showed the most favorable therapeutic index and enhanced the antitubercular activity of the first-line drugs isoniazid, rifampin, and pyrazinamide in THP-1 cells. Pravastatin modulated phagosomal maturation characteristics in macrophages, phenocopying macrophage activation, and exhibited potent adjunctive activity in the standard mouse model of TB chemotherapy and in a mouse model of human-like necrotic TB lung granulomas.

CONCLUSIONS

These data provide compelling evidence for clinical evaluation of pravastatin as adjunctive, host-directed therapy for TB.

Statins: a viable candidate for host-directed therapy against infectious diseases

Statins were first identified over 40 years ago as lipid-lowering drugs and have been remarkably effective in treating cardiovascular diseases. As research advanced, the protective effects of statins were additionally attributed to their anti-inflammatory, antioxidative, anti-thrombotic and immunomodulatory functions rather than lipid-lowering abilities alone. By promoting host defence mechanisms and inhibiting pathological inflammation, statins increase survival in human infectious diseases. At the cellular level, statins inhibit the intermediates of the host mevalonate pathway, thus compromising the immune evasion strategies of pathogens and their survival. Here, we discuss the potential use of statins as an inexpensive and practical alternative or adjunctive host-directed therapy for infectious diseases caused by intracellular pathogens, such as viruses, protozoa, fungi and bacteria.

Roles of the Mevalonate Pathway and Cholesterol Trafficking in Pulmonary Host Defense

The mevalonic acid synthesis pathway, cholesterol, and lipoproteins play fundamental roles in lung physiology and the innate immune response. Recent literature investigating roles for cholesterol synthesis and trafficking in host defense against respiratory infection was critically reviewed. The innate immune response and the cholesterol biosynthesis/trafficking network regulate one another, with important implications for pathogen invasion and host defense in the lung. The activation of pathogen recognition receptors and downstream cellular host defense functions are critically sensitive to cellular cholesterol. Conversely, microorganisms can co-opt the sterol/lipoprotein network in order to facilitate replication and evade immunity. Emerging literature suggests the potential for harnessing these insights towards therapeutic development. Given that >50% of adults in the U.S. have serum cholesterol abnormalities and pneumonia remains a leading cause of death, the potential impact of cholesterol on pulmonary host defense is of tremendous public health significance and warrants further mechanistic and translational investigation.

From Q Fever to Coxiella burnetii Infection: a Paradigm Change

Coxiella burnetii is the agent of Q fever, or "query fever," a zoonosis first described in Australia in 1937. Since this first description, knowledge about this pathogen and its associated infections has increased dramatically. We review here all the progress made over the last 20 years on this topic. C. burnetii is classically a strict intracellular, Gram-negative bacterium. However, a major step in the characterization of this pathogen was achieved by the establishment of its axenic culture. C. burnetii infects a wide range of animals, from arthropods to humans. The genetic determinants of virulence are now better known, thanks to the achievement of determining the genome sequences of several strains of this species and comparative genomic analyses. Q fever can be found worldwide, but the epidemiological features of this disease vary according to the geographic area considered, including situations where it is endemic or hyperendemic, and the occurrence of large epidemic outbreaks. In recent years, a major breakthrough in the understanding of the natural history of human infection with C. burnetii was the breaking of the old dichotomy between "acute" and "chronic" Q fever. The clinical presentation of C. burnetii infection depends on both the virulence of the infecting C. burnetii strain and specific risks factors in the infected patient. Moreover, no persistent infection can exist without a focus of infection. This paradigm change should allow better diagnosis and management of primary infection and long-term complications in patients with C. burnetii infection.

Is There Potential for Repurposing Statins as Novel Antimicrobials?

Statins are members of a class of pharmaceutical widely used to reduce high levels of serum cholesterol. In addition, statins have so-called "pleiotropic effects," which include inflammation reduction, immunomodulation, and antimicrobial effects. An increasing number of studies are emerging which detail the attenuation of bacterial growth and in vitro and in vivo virulence by statin treatment. In this review, we describe the current information available concerning the effects of statins on bacterial infections and provide insight regarding the potential use of these compounds as antimicrobial therapeutic agents.

Are there any benefits from statin treatment for the septic patient?

Statins have become the most widely used drugs for lowering cholesterol levels worldwide. At least 20% of patients requiring admission to hospital are on established statin therapy, and this proportion is growing each year. Evidence from observational studies and basic science research suggests that statins might be associated with a reduced mortality in sepsis. Randomized trials are producing equivocal results but have not shown the marked improvement in outcome suggested by the observational studies. Continued use in current statin users appears a more fruitful area for future research than statin use de novo as an adjuvant therapy in sepsis. Statin use in patients with pneumonia, acute lung injury or early sepsis warrants further study. International practice of statin use in critically ill patients is variable, and potential toxicity mandates careful monitoring. Further studies are required to address fundamental issues such as efficacy, potential target patient populations, dose, class equivalence and safety.

Use of the plaque assay for testing the antibiotic susceptibility of intracellular bacteria

The plaque assay was first described for titration of bacterial inoculums and clonal isolation, and was later adapted for testing antibiotics susceptibility and to study virulence factors and motility of bacteria. Over time, the sensitivity and reproducibility of the technique has been improved. Usually, the number of plaques is counted; however, the recent development of informatics tools has stimulated interest in the quantification of plaque size. Owing to this new approach, the plaque assay has been used to characterize the host cell response when infected cells are treated with antimicrobial agents. It was found that statins prevented cell lesions following rickettsial infection; in other studies, some antibiotics were found to cause apoptosis of host cells, suggesting a toxic activity. Here, we present an overview of the plaque assay as it has been used to investigate intracellular bacteria.

Exploring Leishmania donovani 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) as a potential drug target by biochemical, biophysical and inhibition studies

3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase (HMGR), an NADPH dependant enzyme catalyzes the synthesis of mevalonic acid from HMG-CoA required for isoprenoid biosynthesis. The HMGR gene from Leishmania donovani was cloned and expressed. Genome analysis of L. donovani revealed that HMGR gene having an open reading frame of 1305 bp encodes a putative protein of 434 amino acids. LdHMGR showed optimal activity at pH 7.2 and temperature 37 °C. Kinetic analysis of this enzyme revealed Km values of 35.7 ± 2.5 μM for (R,S)-HMG-CoA and 70 ± 7.9 μM for the cofactor NADPH. On tryptophan fluorescence quenching, the Stern Volmer constant (Ksv), binding constant (Ka) and protein:cofactor stoichiometry for interaction of NADPH cofactor with the enzyme were found to be 6.0 ± 0.7 M(-1), 0.17 μM and 0.72 respectively. Polyclonal anti-rat HMGR antibody detected a band of ∼45 kDa in all phases of promastigote growth. Biophysical analysis of the secondary structure of LdHMGR confirmed the presence of 25.7 ± 0.35% alpha helicity. Thermal denaturation studies showed extreme stability of the enzyme with 60% helical structure retained at 90 °C. Statins (simvastatin and atorvastatin) and non-statin (resveratrol) effectively inhibited the growth of L. donovani promastigotes as well as the catalytic activity of the recombinant LdHMGR. Atorvastatin was found to be most potent antileishmanial inhibitor with an IC50 value of 19.4 ± 3.07 μM and a very lower concentration of 315.5 ± 2.1 nM was enough to cause 50% recombinant LdHMGR enzyme inhibition suggesting direct interaction with the rate limiting enzyme of the ergosterol biosynthetic pathway. Exogenous supplementation of ergosterol in case of atorvastatin and resveratrol treated cells caused complete reversal of growth inhibition whereas simvastatin was found to be ergosterol refractory. Cholesterol supplementation however, failed to overcome growth inhibition in all the cases. Overall our study emphasizes on exploring LdHMGR as a potential drug target for the development of novel antileishmanial agents.

Lovastatin protects against experimental plague in mice

BACKGROUND

Plague is an ectoparasite-borne deadly infection caused by Yersinia pestis, a bacterium classified among the group A bioterrorism agents. Thousands of deaths are reported every year in some African countries. Tetracyclines and cotrimoxazole are used in the secondary prophylaxis of plague in the case of potential exposure to Y. pestis, but cotrimoxazole-resistant isolates have been reported. There is a need for additional prophylactic measures. We aimed to study the effectiveness of lovastatin, a cholesterol-lowering drug known to alleviate the symptoms of sepsis, for plague prophylaxis in an experimental model.

METHODOLOGY

Lovastatin dissolved in Endolipide was intraperitoneally administered to mice (20 mg/kg) every day for 6 days prior to a Y. pestis Orientalis biotype challenge. Non-challenged, lovastatin-treated and challenged, untreated mice were also used as control groups in the study. Body weight, physical behavior and death were recorded both prior to infection and for 10 days post-infection. Samples of the blood, lungs and spleen were collected from dead mice for direct microbiological examination, histopathology and culture. The potential antibiotic effect of lovastatin was tested on blood agar plates.

CONCLUSIONS/SIGNIFICANCE

Lovastatin had no in-vitro antibiotic effect against Y. pestis. The difference in the mortality between control mice (11/15; 73.5%) and lovastatin-treated mice (3/15; 20%) was significant (P<0.004; Mantel-Haenszel test). Dead mice exhibited Y. pestis septicemia and inflammatory destruction of lung and spleen tissues not seen in lovastatin-treated surviving mice. These data suggest that lovastatin may help prevent the deadly effects of plague. Field observations are warranted to assess the role of lovastatin in the prophylaxis of human plague.

Atorvastatin is a promising partner for antimalarial drugs in treatment of Plasmodium falciparum malaria

Atorvastatin (AVA) is a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor. AVA exposure resulted in the reduced in vitro growth of 22 Plasmodium falciparum strains, with the 50% inhibitory concentrations (IC(50)s) ranging from 2.5 microM to 10.8 microM. A significant positive correlation was found between the strains' responses to AVA and mefloquine (r = 0.553; P = 0.008). We found no correlation between the responses to AVA and to chloroquine, quinine, monodesethylamodiaquine, lumefantrine, dihydroartemisinin, atovaquone, or doxycycline. These data could suggest that the mechanism of AVA uptake and/or the mode of action of AVA is different from those for other antimalarial drugs. The IC(50)s for AVA were unrelated to the occurrence of mutations in the transport protein genes involved in quinoline antimalarial drug resistance, such as the P. falciparum crt, mdr1, mrp, and nhe-1 genes. Therefore, AVA can be ruled out as a substrate for the transport proteins (CRT, Pgh1, and MRP) and is not subject to the pH modification induced by the P. falciparum NHE-1 protein. The absence of in vitro cross-resistance between AVA and chloroquine, quinine, mefloquine, monodesethylamodiaquine, lumefantrine, dihydroartemisinin, atovaquone, and doxycycline argues that these antimalarial drugs could potentially be paired with AVA as a treatment for malaria. In conclusion, the present observations suggest that AVA is a good candidate for further studies on the use of statins in association with drugs known to have activities against the malaria parasite.