Systemic infections can decrease the threshold of statin-induced muscle injury

Innovations in Evaluating Statin Benefit and Efficacy in Staphylococcus aureus Intracellular Infection Management

An emerging therapeutic approach in the treatment of infectious disease is to augment the host response through repurposing of well-tolerated, non-antibiotic, host-directed therapeutics. Earlier retrospective studies identify a positive association between statin use and a decreased risk of death due to sepsis or bacteremia. However, more recent randomized control trials fail to detect a therapeutic benefit in these complex infection settings. It is postulated that unrecognized biases in certain observational studies may have led to an overestimation of benefit and that statin use is instead a marker for health status, wealth, and demographic characteristics which may separately affect death due to infection. What remains unresolved is that in vitro and in vivo evidence reproducibly indicates that statin pharmacology limits infection and augments immunomodulatory responses, suggesting that therapeutic benefits may be attainable in certain infection settings, such as intracellular infection by S. aureus. Carefully considering the biological mechanisms capable of driving the relationship between statins and infections and constructing a methodology to avoid potential biases in observational studies would enable the examination of protective effects against infection and limit the risk of underestimating statin efficacy. Such an approach would rely on the examination of statin use in defined infection settings based on an underlying mode-of-action and pharmacology, where the inhibition of HMG-CoA-reductase at the rate-limiting step in cholesterol biosynthesis diminishes not only cholesterol levels but also isoprenoid intermediates central to host cell invasion by S. aureus. Therapeutic benefit in such settings, if existent, may be of clinical importance.

Pleiotropic Effects of Statins: New Therapeutic Approaches to Chronic, Recurrent Infection by Staphylococcus aureus

An emergent approach to bacterial infection is the use of host rather than bacterial-directed strategies. This approach has the potential to improve efficacy in especially challenging infection settings, including chronic, recurrent infection due to intracellular pathogens. For nearly two decades, the pleiotropic effects of statin drugs have been examined for therapeutic usefulness beyond the treatment of hypercholesterolemia. Interest originated after retrospective studies reported decreases in the risk of death due to bacteremia or sepsis for those on a statin regimen. Although subsequent clinical trials have yielded mixed results and earlier findings have been questioned for biased study design, in vitro and in vivo studies have provided clear evidence of protective mechanisms that include immunomodulatory effects and the inhibition of host cell invasion. Ultimately, the benefits of statins in an infection setting appear to require attention to the underlying host response and to the timing of the dosage. From this examination of statin efficacy, additional novel host-directed strategies may produce adjunctive therapeutic approaches for the treatment of infection where traditional antimicrobial therapy continues to yield poor outcomes. This review focuses on the opportunistic pathogen, Staphylococcus aureus, as a proof of principle in examining the promise and limitations of statins in recalcitrant infection.

Simvastatin is protective during Staphylococcus aureus pneumonia

Epidemiologic studies suggest that the incidence and severity of sepsis are ameliorated in patients on statins (3- hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) for cholesterol lowering indications. We sought to understand the mechanism underlying such protection and hypothesized that simvastatin would be protective in mice against acute infection with Staphylococcus aureus, the primary etiologic agent in sepsis. Mice were treated with simvastatin or buffer for two weeks and were subsequently challenged with S. aureus intratracheally or intravenously. Relative to buffer-treated mice, bacterial killing was enhanced 4-fold (p=0.02), systemic dissemination was reduced, and lethality was decreased (hazard ratio 8.8, 95% CI 2.5 to 31.3, p=0.001) in mice that were pretreated with simvastatin for two weeks. Systemic inflammatory response was abrogated and the local elaboration of inflammatory mediators was diminished. Serum concentrations of pro-fibrinolytic protein C were elevated (p=0.034), while the concentration of pro-coagulant tissue factor in bronchoalveolar lavage fluids was attenuated (reduced 25%), p=0.001, in simvastatin-treated mice. Taken together, these data indicate that extended treatment with simvastatin is protective during infection with S. aureus through enhanced bacterial clearance, anti-inflammatory, and anti-coagulant activities. These studies provide insights into the mechanism by which statins confer protection in acute infection, support the notion that statins may be effective adjuncts in the treatment of sepsis, and provide a rationale for randomized control trials in patients that are at a high risk for infection characterized by coagulopathy.

Simvastatin inhibits Staphylococcus aureus host cell invasion through modulation of isoprenoid intermediates

Patients on a statin regimen have a decreased risk of death due to bacterial sepsis. We have found that protection by simvastatin includes the inhibition of host cell invasion by Staphylococcus aureus, the most common etiologic agent of sepsis. Inhibition was due in part to depletion of isoprenoid intermediates within the cholesterol biosynthesis pathway and led to the cytosolic accumulation of the small GTPases CDC42, Rac, and RhoB. Actin stress fiber disassembly required for host invasion was attenuated by simvastatin and by the inhibition of phosphoinositide 3-kinase (PI3K) activity. PI3K relies on coupling to prenylated proteins, such as this subset of small GTPases, for access to membrane-bound phosphoinositide to mediate stress fiber disassembly. Therefore, we examined whether simvastatin restricts PI3K cellular localization. In response to simvastatin, the PI3K isoform p85, coupled to these small-GTPases, was sequestered within the cytosol. From these findings, we propose a mechanism whereby simvastatin restricts p85 localization, inhibiting the actin dynamics required for bacterial endocytosis. This approach may provide the basis for protection at the level of the host in invasive infections by S. aureus.