Inflammation and exercise: Inhibition of monocytic intracellular TNF production by acute exercise via β2-adrenergic activation

Regular exercise is shown to exert anti-inflammatory effects, yet the effects of acute exercise on cellular inflammatory responses and its mechanisms remain unclear. We tested the hypothesis that sympathoad-renergic activation during a single bout of exercise has a suppressive effect on monocytic cytokine production mediated by beta(2) adrenergic receptors (AR). We investigated the effects of 20-min moderate (65-70% VO2 peak) exercise-induced catecholamine production on LPS-stimulated TNF production by monocytes in 47 healthy volunteers and determined AR subtypes involved. We also examined the effects of beta-agonist isoproterenol and endogenous beta-and alpha-agonists epinephrine and norepinephrine, and receptor-subtype-specific beta-and alpha-antagonists on TNF production in a series of in vitro investigations. LPS-stimulated TNF production by peripheral blood monocytes was determined intracellularly by flow cytometry, using an intracellular protein transport inhibitor. Percent TNF-producing monocytes and per-cell TNF production with and without LPS was suppressed by exercise with moderate to large effects, which was reversed by a beta(2)-AR antagonist in spite that plasma TNF levels did not change. This inhibitory response in TNF production by exercise was mirrored by beta-AR agonists in an agonist-specific and dose-dependent manner in vitro: similar isoproterenol (EC50 = 2.1-4.7 x 10(-10) M) and epinephrine (EC50 = 4.4-10 x 10(-10) M) potency and higher norepinephrine concentrations (EC50 = 2.6-4.3 x 10(-8) M) needed for the effects. Importantly, epinephrine levels observed during acute exercise in vivo significantly inhibited TNF production in vitro. The inhibitory effect of the AR agonists was abolished by beta(2)-, but not by beta(1)- or alpha-AR blockers. We conclude that the downregulation of monocytic TNF production during acute exercise is mediated by elevated epinephrine levels through beta(2)-ARs. Decreased inflammatory responses during acute exercise may protect against chronic conditions with low-grade inflammation. (C) 2016 Elsevier Inc. All rights reserved.