Soluble TNF binding proteins modulate the negative inotropic properties of TNF-α in vitro

Soluble tumor necrosis factor (TNF) binding proteins (TNF-BPs) were characterized with respect to their capacity to modulate the negative inotropic properties of TNF-α in isolated contracting cardiac myocytes. Three TNF-BPs were evaluated: two natural monomeric human TNF monomeric binding proteins, TNF-BP1 and TNF-BP2, and sTNFR:Fc, a dimer of two molecules of human TNF-BP2 linked by the Fc portion of the human immunoglobulin G1 molecule. When TNF-α (25 pM) was allowed to form TNF-BP-TNF-α complexes, the negative inotropic effects of TNF-α were completely prevented by 'neutralizing concentrations' of TNF-BPs, whereas lesser concentrations of TNF-BPs only partially attenuated the negative inotropic effects of TNF-α. The dimeric binding protein sTNFR:Fc was more effective on a molar basis than either of the monomeric binding proteins (TNF-BP1 or TNF-BP2) with respect to blocking the negative inotropic effects of TNF-α. When cardiac myocytes that had been treated with TNF-α (25 pM) were exposed to neutralizing concentrations of TNF-BP1, TNF-BP2, and sTNFR:Fc, the negative inotropic effects were completely reversed within 30 min. Thus these studies show for the first time that TNF-BPs are sufficient to prevent, as well as reverse, the negative inotropic properties of TNF-α in vitro.