Bench-to-bedside review: Beta-adrenergic modulation in sepsis

Abstract

Sepsis, despite recent therapeutic progress, still carries unacceptably high mortality rates. The adrenergic system, a key modulator of organ function and cardiovascular homeostasis, could be an interesting new therapeutic target for septic shock. Beta-adrenergic regulation of the immune function in sepsis is complex and is time dependent. However, beta2 activation as well as beta1 blockade seems to downregulate proinflammatory response by modulating the cytokine production profile. beta1 blockade improves cardiovascular homeostasis in septic animals, by lowering myocardial oxygen consumption without altering organ perfusion, and perhaps by restoring normal cardiovascular variability. Beta-blockers could also be of interest in the systemic catabolic response to sepsis, as they oppose epinephrine which is known to promote hyperglycemia, lipid and protein catabolism. The role of beta-blockers in coagulation is less clear cut. They could have a favorable role in the septic pro-coagulant state, as beta1 blockade may reduce platelet aggregation and normalize the depressed fibrinolytic status induced by adrenergic stimulation. Therefore, beta1 blockade as well as beta2 activation improves sepsis-induced immune, cardiovascular and coagulation dysfunctions. Beta2 blocking, however, seems beneficial in the metabolic field. Enough evidence has been accumulated in the literature to propose beta-adrenergic modulation, beta1 blockade and beta2 activation in particular, as new promising therapeutic targets for septic dyshomeostasis, modulating favorably immune, cardiovascular, metabolic and coagulation systems.

Figure 1

T-helper type 1 and T-helper type 2 balance and the adrenergic system. Naive CD4⁺, T-helper type 0 (Th0) cells are bipotential and are precursors of T-helper type 1 (Th1) cells and T-helper type 2 (Th2) cells. IL-12, produced by antigen-presenting cells, is the major inducer of Th1 differentiation. Th1 and Th2 responses are mutually inhibitory. IL-12 and IFNγ therefore inhibit Th2 cell activity, while IL-4 and IL-10 inhibit the Th1 response. The stimulation of β-adrenergic receptors potently inhibits the production of IL-12 by antigen-presenting cells, and thus inhibits the development of Th1 cells while promoting Th2 cells.