Impairment of agonist-induced M2 muscarinic receptor activation by autoantibodies from chagasic patients with cardiovascular dysautonomia.

Previous studies showed that circulating autoantibodies against M2 muscarinic receptors (anti-M2R Ab) are associated with decreased cardiac parasympathetic modulation in patients with chronic Chagas disease (CD). Here we investigated whether the exposure of M2R to such antibodies could impair agonist-induced receptor activation, leading to the inhibition of associated signaling pathways. Preincubation of M2R-expressing HEK 293T cells with serum IgG fractions from chagasic patients with cardiovascular dysautonomia, followed by the addition of carbachol, resulted in the attenuation of agonist-induced Gi protein activation and arrestin-2 recruitment. These effects were not mimicked by the corresponding Fab fractions, suggesting that they occur through receptor crosslinking. IgG autoantibodies did not enhance M2R/arrestin interaction or promote M2R internalization, suggesting that their inhibitory effects are not likely a result of short-term receptor regulation. Rather, these immunoglobulins could function as negative allosteric modulators of acetylcholine-mediated responses, thereby contributing to the development of parasympathetic dysfunction in patients with CD.

The enteric nervous system in chagasic and idiopathic megacolon.

Chagas disease frequently causes megacolon. We investigated the enteric nervous systems in patients with chagasic megacolon compared to idiopathic megacolon and controls. Surgical specimens were obtained from 12 patients with chagasic megacolon (1 woman, 11 men, age range 41 to 72 y) and 9 patients with idiopathic megacolon (3 women, 6 men, age range 39 to 68 y), undergoing surgery for intractable constipation. A control group of 10 patients (9 women, 1 man, age range 43 to 75 y) undergoing left hemicolectomy for nonobstructing colorectal cancer was also studied. Colonic sections were investigated by conventional and immunohistochemical methods, also taking into consideration the presence of lymphocytes. Compared to controls, the 2 megacolon groups showed a decrease of enteric neurons (not due to increased apoptosis) and of enteric glial cells (all more important in chagasic patients). The interstitial cells of Cajal subtypes were decreased but not absent in megacolons, although an increase of the intramuscular subtype was found, suggesting a possible compensative mechanism. An increased amount of fibrosis was found in the smooth muscle and the myenteric plexus of chagasic patients compared to the idiopathic megacolon and the control group. A mild lymphocytic infiltration of the enteric plexuses (more evident in Chagas disease) was also found in megacolons but not in controls. Patients with chagasic megacolon display important abnormalities of several components of the enteric nervous system. Similar alterations, although of lesser severity, may be found in patients with idiopathic megacolon.