Impairment of beta-adrenergic signaling in healthy peripheral blood mononuclear cells exposed to serum from patients with septic shock: involvement of the inhibitory pathway of adenylyl cyclase stimulation.

Abstract

The objective of this study was to determine whether the serum of patients with sepsis could alter the capability of healthy human peripheral blood mononuclear cells (PBMC) to synthesize cAMP in response to beta-adrenergic stimulation and to evaluate the involvement of the inhibitory pathway (Gi) of adenylyl cyclase in the sepsis-induced alteration of beta-adrenergic signaling. First, PBMC from a healthy donor were incubated for 24 h in serum-containing medium according to three culture conditions: serum alone, serum with pertussis toxin, and serum with propranolol. Second, PBMC were stimulated with 10(-5) M isoproterenol or 10(-6) M forskolin, and measurement of cyclic adenosine monophosphate (cAMP) intracellular accumulation was performed. Serum samples were obtained from three groups of subjects: 14 patients with severe sepsis, 21 patients with septic shock, and 10 healthy control subjects. Basal and forskolin-stimulated cAMP levels were similar in PBMC cultured in control or in septic serum. Isoproterenol-stimulated accumulation was reduced in PBMC preincubated in septic serum. The lowest cAMP levels were found after exposure to serum from patients with septic shock. The addition of pertussis toxin in the incubation medium constantly increased cAMP response to isoproterenol, but more significantly in PBMC exposed to septic serum. Incubation in the presence of propranolol had no significant effect. The serum of patients with sepsis contained soluble depressant substances that inhibited adenylyl cyclase activation by beta-adrenergic agonists. Septic shock serum exhibited the most potent inhibitory effect. Hyperactivation of the Gi pathway of adenylyl cyclase was mainly responsible for the altered transmembrane beta-adrenergic signaling.