Interaction of human chagasic IgG with human colon muscarinic acetylcholine receptor: molecular and functional evidence

Abstract

Background and aims-Gastrointestinal disorders is one of the clinical manifestations of chronic Chagas' disease. The pathogenesis seems to be associated with autonomic dysfunction. Here, we consider the muscarinic cholinoceptor mediated alteration in distal colon function in chagasic megacolon. Patients-Patients were divided into four groups: group I, chronic chagasic patients with megacolon; group II, chronic chagasic patients without megacolon; group III, nonchagasic patients with megacolon; and group IV, normal healthy volunteers (control). Methods-Binding assay and immunoblot of cholinoceptors from human and rat colon and enzyme immunoassay (ELISA) using a synthetic 24mer peptide corresponding to the second extracellular loop of human M 2 muscarinic acetylcholine receptors (mAChR) were used to detect the presence of serum antibodies. The eVect of antibodies on basal tone and 3',5'-cyclic monophosphate (cAMP) production of human and rat distal colon strips were also tested. Results-Group I but not the other groups had circulating antibodies capable of interacting with human colon activating M 2 mAChR, as they competed with binding of specific radioligand to mAChR and interacted with the second extracellular loop of human M 2 mAChR. Moreover, aYnity purified anti-M 2 peptide IgG from group I, in common with monoclonal antihuman M 2 mAChR, recognised bands with a molecular weight corresponding to colon mAChR. This antibody also displayed an agonist-like activity, increasing basal tone and decreasing cAMP accumulation. Both eVects were blunted by AF-DX 116 and neutralised by the synthetic peptide. Conclusions-In chagasic patients with megacolon there are antibodies that can recognise and activate M 2 mAChR. The implications of these autoantibodies in the pathogenesis of chagasic megacolon is discussed. (Gut 2001;49:699-705)

The role of humoral autoimmunity in gastrointestinal neuromuscular diseases

“…Incubation of cardiac or GI smooth muscle with IgG revealed pertussis toxin-sensitive decreased tissue levels of cyclic adenosine monophosphate (cAMP) and an increase in cyclic guanosine monophosphate (cGMP). This is consistent with muscarinic receptor activation Goin et al 1999;Sterin-Borda et al 2001). …”

“…These autoantibodies have been detected in 84% of patients with chagasic achalasia versus 21% of those with Chagas' disease but no oesophageal sequalae and 28% in idiopathic achalasia (Goin et al 1999). Similarly, in those with chagasic colonic dysfunction, autoantibodies were detected in 87% compared to 24% of those without megacolon (Sterin-Borda et al 2001). However, using the same ELISA, these antibodies have been found in a high proportion of patients with other types of heart disease including 62% of patients with idiopathic cardiomyopathy, 46% with hypertensive heart disease and 48% with rheumatic valvular disease (Fu et al 1993;Zhang et al 2002).…”

“…In oesophageal and colonic muscle preparations, IgG produced concentration-dependent increases in basal tone which were sensitive to M 2 mAChR antagonism (Goin et al 1999;Sterin-Borda et al 2001). It also acted as a partial agonist, mimicking the effect of the muscarinic agonists carbachol and pilocarpine in a non-competitive manner Goin et al 1997).…”

“…Radioligand binding assays investigating the interaction of chagasic IgG with the muscarinic receptor indicated chagasic IgG acts as an allosteric antagonist of the muscarinic receptor. It decreased the number of receptors available for binding (B max ) without an associated effect on the affinity constant (K D ) of the radioligand Sterin-Borda et al 2001).…”

Endogenous Allosteric Modulators of G Protein–Coupled Receptors

“…Finally, in Chagas disease, digestive manifestations Endogenous GPCR Allosteric Modulators sometimes occur, leading to a syndrome called megaviscera (Haberland et al, 2013). Autoantibodies isolated from Chagasic patients with megacolon are able to bind and activate the M 2 mAChR, increasing the basal tone of the colon as well as inhibiting intracellular cAMP signaling (Sterin-Borda et al, 2001). …”