Human endotoxemia: a model for mechanistic insight and therapeutic targeting

Abstract

The diversity of phenotypic manifestations, comorbidities, and therapeutic algorithms in patients with severe inflammation have confounded efforts to translate mechanistic insights from the bench top to the bedside. This dilemma has negatively impacted upon many therapeutic interventions that exhibited seemingly well-reasoned preclinical portfolios. Prudence urges the assessment of potent immunoregulatory therapies, wherever possible, in models that replicate the clinical phenotype absent overt manifestations of genetically or environmentally modified processes. The healthy human model of endotoxin administration (systemic or endobronchial) provides such an opportunity and has been used to great advantage for gaining insight into mechanisms of disease and for determination of therapeutic signal strength. When thoughtfully interpreted, the model may provide proof of principle as well as lessen the unpredictability of clinical responses. Although the broad characteristics of this model are well described in the literature, it is recognized that this model does not fully replicate the magnitude of initial inflammatory stress nor the latent spectrum of inflammation/sepsis-inducible organ system pathologies. Nevertheless, the similarities between the early, transient clinical phenotype, inducible physiochemical change, and biochemical pathway activation of this model to the early hyperdynamic phase of resuscitated injury and infection are striking. Rational testing of a therapeutic mechanism requires a quantifiable and reproducibly altered marker of the hypothetical mechanism. Given the modest nature of endotoxin induced insult, interventions that demonstrate target specific efficacy in conjunction with attenuated phenotype responses are more likely to exhibit efficacy within lower risk patient populations. By contrast, the model cannot predict clinical efficacy among higher risk patients nor in those who have endured extended periods of inflammatory stress.