cyclic-gmp and Chagas-Cardiomyopathy

Circulating antibodies from human and murine chagasic sera are able to interact with myocardium-activating neurotransmitter receptors. Here we reported the presence of autoantibodies against the second extracellular loop of the human heart muscarinic acetylcholine receptors (mAChR) in patients with Chagas' disease by using a synthetic 24-mer peptide in immunoblotting and enzyme immunoassay. Affinity-purified antipeptide IgG from chagasic patients, similar to monoclonal antihuman M2 mAChR, recognized bands with a molecular weight corresponding to the cardiac mAChR. The binding was inhibited by the peptide, assessing the specificity of the interaction. The antipeptide autoantibody also displayed an "agonist-like" activity modifying the intracellular events associated with mAChR activation, i.e., decreased contractility, increased cGMP, and decreased cAMP production. All of these effects on rat atria by chagasic antipeptide autoantibodies resemble the effects of the authentic agonist and those of the total polyclonal chagasic IgG, being selectively blunted by atropine and neutralized by the synthetic peptide corresponding in aminoacid sequence to the second extracellular loop of the human M2 mAChR. A clinical relevance of these findings is demonstrated by a strong association between the existence of circulating antipeptide autoantibodies in chagasic patients and the presence of dysautonomic symptoms, making these autoantibodies a proper early marker of heart autonomic dysfunction.

Topics: Acetylcholine; Adult; Amino Acid Sequence; Animals; Antibodies, Protozoan; Antigens, Protozoan; Autoantibodies; Autonomic Nervous System Diseases; Biomarkers; Chagas Cardiomyopathy; Cross Reactions; Cyclic AMP; Cyclic GMP; Enzyme-Linked Immunosorbent Assay; Heart Atria; Humans; Immunoblotting; Immunoglobulin G; Male; Middle Aged; Molecular Sequence Data; Myocardial Contraction; Rats; Receptors, Muscarinic; Trypanosoma cruzi

Circulating antibodies from human and murine chagasic sera are able to interact with myocardium, activating neurotransmitter receptors. Here, we studied the effects of a monoclonal antibody (MAb CAK20.12), which recognizes a 150 kilodalton antigen of Trypanosoma cruzi and reacts with normal human and murine striated muscles and with cardiac tissue. The MAb CAK20.12 binds to purified cardiac membranes and interferes with the binding of beta-adrenergic receptor radioligand ([125I]CYP) and muscarinic cholinergic receptor (mAChR) radioligand ([3H]QNB) in a noncompetitive way. As a consequence of this interaction, beta-adrenergic receptor and mAChR were activated, leading to increased intracellular levels of cyclic AMP as a result of beta-adrenergic receptor-coupled adenylate cyclase triggering. When its sympathetic action was abrogated, it also induced an mAChR-mediated increase in cyclic GMP. Furthermore, cardiac physiology was modified by MAb CAK20.12, as it was able to increase cardiac contractility through beta-adrenoceptor activation and to decrease atrial frequency as a result of mAChR activation. The fact that this MAb modulates and modifies the mechanical and biochemical activity of normal murine heart established an important basis for future research and understanding of how the host's humoral immune response acts on the course and development of the chronic chagasic myocardiopathy.

Topics: Animals; Antibodies, Monoclonal; Antibodies, Protozoan; Chagas Cardiomyopathy; Cyclic AMP; Cyclic GMP; Heart; Humans; In Vitro Techniques; Iodocyanopindolol; Mice; Mice, Inbred BALB C; Muscarinic Antagonists; Myocardial Contraction; Myocardium; Pindolol; Quinuclidinyl Benzilate; Trypanosoma cruzi

The interaction of the IgG from Trypanosoma cruzi-infected mice (chagasic IgG) with cardiac cholinergic receptors by means of specific radioligand binding and by production of cholinergic-mediated cellular transmembrane signals was characterized. Chagasic IgG inhibited, in a noncompetitive manner, the binding of [3H]quinuclidinyl benzilate to the cardiac membrane. Moreover, chagasic IgG could modify all of the muscarinic cholinergic effects mediated by a G regulatory protein, i.e., decrement of atria contractility, inhibition of cAMP, or activation of the turnover of phosphoinositides via phospholipase C. The cGMP production was also increased by the antibody. The data demonstrated that chagasic IgG interacting with cardiac muscarinic cholinergic receptor triggers the biological effects associated with cholinergic-mediated cellular transmembrane signals. The implications of the results in the pathogenesis of Chagas' myocarditis are discussed.

Topics: Animals; Antibodies; Binding, Competitive; Chagas Cardiomyopathy; Cyclic AMP; Cyclic GMP; Heart Atria; Immunoglobulin Fab Fragments; Immunoglobulin G; Male; Mice; Mice, Inbred BALB C; Myocardium; Receptors, Muscarinic; Type C Phospholipases