Faculty Bibliography

OBJECTIVE: To assess in vivo the pathologic cascade leading to fibrosis in congenital heart block (CHB). In vitro studies suggest that CHB is initiated via apoptosis, resulting in translocation of SSA/Ro and SSB/La antigens and surface binding by maternal autoantibodies. These opsonized cardiocytes are phagocytosed by macrophages, which secrete factors inducing fibrosis. METHODS: Immunohistochemistry analysis was performed on formalin-fixed sections of 4 fetal hearts identified in utero as having CHB or isolated myocarditis; mothers had anti-SSA/Ro and anti-SSB/La antibodies. RESULTS: Apoptosis was most extensive in fetuses dying early and most pronounced in regions containing conduction tissue. Deposition of IgG was observed in hearts from fetuses with CHB/myocarditis, but not in 3 control hearts, and was colocalized with apoptotic cells. Giant cells and macrophages (frequently seen proximal to IgG and apoptotic cells) were present in septal and thickened fibrous subendocardial regions, most apparent in the youngest fetuses. Septal tissue also revealed extensive areas of fibrosis and microcalcification in which a predominant smooth muscle actin (SMA)-positive infiltrate (myofibroblast scarring phenotype) was observed. In contrast, there were no macrophages or SMA-positive cells (other than those lining blood vessels) in septal tissue from control hearts, although rare macrophages were seen in the working myocardium. CONCLUSION: In summary, findings in this unique autopsy material paralleled those in in vitro studies. These data support the notion of exaggerated apoptosis, probably due to ongoing inflammation caused by IgG binding and ingestion by macrophages. Transdifferentiation of cardiac fibroblasts to a scarring phenotype may be a pathologic process initiated by maternal antibodies, and persistence of this phenotype even after birth may relate to the progression of block seen in some infants postpartum

The neonatal lupus syndromes (NLS), while quite rare, carry significant mortality and morbidity in cases of cardiac manifestations. Although anti-SSA/Ro-SSB/La antibodies are detected in > 85% of mothers whose fetuses are identified with congenital heart block (CHB) in a structurally normal heart, when clinicians applied this testing to their pregnant patients, the risk for a woman with the candidate antibodies to have a child with CHB was at or below 1 in 50. While the precise pathogenic mechanism of antibody-mediated injury remains unknown, it is clear that the antibodies alone are insufficient to cause disease and fetal factors are likely contributory. In vivo and in vitro evidence supports a pathologic cascade involving apoptosis of cardiocytes, surface translocation of Ro and La antigens, binding of maternal autoantibodies, secretion of profibrosing factors (e.g., TGFbeta) from the scavenging macrophages and modulation of cardiac fibroblasts to a myofibroflast scarring phenotype. The spectrum of cardiac abnormalities continues to expand, with varying degrees of block identified in utero and reports of late onset cardiomyopathy (some of which display endocardial fibroelastosis). Moreover, there is now clear documentation that incomplete blocks (including those improving in utero with dexamethasone) can progress postnatally, despite the clearance of the maternal antibodies from the neonatal circulation. Better echocardiographic measurements which identify first degree block in utero may be the optimal means of approaching pregnant women at risk. Prophylactic therapies, including treatment with intravenous immunoglobulin, await larger trials. In order to achieve advances at both the bench and bedside, national research registries established in the US and Canada are critical

Transforming growth factor-beta (TGF-beta) has been considered an anti-inflammatory cytokine responsible for the bland removal of apoptotic cells. What is less established is the extent of secretion of this cytokine during the clearance of opsonized apoptotic cells via Fcgamma-mediated uptake. To date both decreased (favoring predominance of inflammation) and increased (favoring resolution of inflammation but potentially pro-fibrotic) responses have been demonstrated. IN an in vitro model of autoantibody-induced cardiac injury, we herein demonstrate that macrophages cocultured with apoptotic human fetal cardiocytes bound by anti-SSA/Ro antibodies secrete increased levels of TGF-beta. Prolonged secretion of this cytokine may contribute to the exuberant scarring seen in congenital heart block associated with maternal autoantibodies reactive with SSA/Rho and SSB/La antigens

Despite its negative redox potential, nitroxyl (HNO) can trigger reactions of oxidation. Mechanistically, these reactions were suggested to occur with the intermediate formation of either hydroxyl radical (.OH) or peroxynitrite (ONOO-). In this work, we present further experimental evidence that HNO can generate.OH. Sodium trioxodinitrate (Na2N2O3), a commonly used donor of HNO, oxidized phenol and Me2SO to benzene diols and.CH3, respectively. The oxidation of Me2SO was O2-independent, suggesting that this process reflected neither the intermediate formation of ONOO- nor a redox cycling of transition metal ions that could initiate Fenton-like reactions. In solutions of phenol, Na2N2O3 yielded benzene-1,2-diol and benzene-1,4-diol at a ratio of 2:1, which is consistent with the generation of free.OH. Ethanol and Me2SO, which are efficient scavengers of.OH, impeded the hydroxylation of phenol. A mechanism for the hydrolysis of Na2N2O3 is proposed that includes dimerization of HNO to cis-hyponitrous acid (HO-N=N-OH) with a concomitant azo-type homolytic fission of the latter to N2 and.OH. The HNO-dependent production of.OH was with 1 order of magnitude higher at pH 6.0 than at pH 7.4. Hence, we hypothesized that HNO can exert selective toxicity to cells subjected to acidosis. In support of this thesis, Na2N2O3 was markedly more toxic to human fibroblasts and SK-N-SH neuroblastoma cells at pH 6.2 than at pH 7.4. Scavengers of.OH impeded the cytotoxicity of Na2N2O3. These results suggest that the formation of HNO may be viewed as a toxicological event in tissues subjected to acidosis

Although Abs to SSA/Ro-SSB/La are necessary for the development of congenital heart block (CHB), the low frequency suggests that fetal factors are contributory. Because CHB involves a cascade from inflammation to scarring, polymorphisms of the TNF-alpha promoter region and codons 10 and 25 of the TGF-beta gene were evaluated in 88 children (40 CHB, 17 rash, 31 unaffected siblings) and 74 mothers from the Research Registry for Neonatal Lupus (NL). Cytokine expression was assessed in autopsy material from two fetuses with CHB. Significantly increased frequency of the -308A (high-producer) allele of TNF-alpha was observed in all NL groups compared with controls. In contrast, the TGF-beta polymorphism Leu(10) (associated with increased fibrosis) was significantly higher in CHB children (genotypic frequency 60%, allelic frequency 78%) than unaffected offspring (genotypic frequency 29%, p = 0.016; allelic frequency 56%, p = 0.011) and controls, while there were no significant differences between controls and other NL groups. For the TGF-beta polymorphism, Arg(25), there were no significant differences between NL groups and controls. In fetal CHB hearts, protein expression of TGF-beta, but not TNF-alpha, was demonstrated in septal regions, extracellularly in the fibrous matrix, and intracellularly in macrophage infiltrates. Age-matched fetal hearts from voluntary terminations expressed neither cytokine. TNF-alpha may be one of several factors that amplify susceptibility; however, the genetic studies, backed by the histological data, more convincingly link TGF-beta to the pathogenesis of CHB. This profibrosing cytokine and its secretion/activation circuitry may provide a novel direction for evaluating fetal factors in the development of a robust animal model of CHB as well as therapeutic strategies in humans

The neonatal lupus syndromes, although quite rare, provide an excellent opportunity to examine disease from bench to bedside. During the past year numerous publications have reported basic and clinical research. Although anti-SSA/Ro-SSB/La antibodies are detected in more than 85% of mothers whose fetuses are identified with conduction abnormalities in a structurally normal heart, when clinicians applied this testing to their pregnant patients, the risk for a woman with the candidate antibodies to have a child with congenital heart block was at or below one in 50. Although the precise pathogenic mechanism of antibody-mediated injury remains unknown, it is clear that the antibodies alone are insufficient to cause disease, and fetal factors are likely contributory. In vivo and in vitro evidence supports a pathologic cascade involving apoptosis of cardiocytes, surface translocation of Ro and La antigens, binding of maternal autoantibodies, secretion of profibrosing factors from the scavenging macrophages, and transdifferentiation of cardiac fibroblasts to a myofibroblast scarring phenotype. Cross-reactivity of anti-52-kD SSA/Ro antibodies with a serotoninergic cardiac receptor, 5-hydroxytryptamine (HT)4, has been suggested but remains unconfirmed. The spectrum of cardiac abnormalities continues to grow, with varying degrees of block identified in utero and reports of late-onset cardiomyopathy (some of which display endocardial fibroelastosis). Moreover, there is now clear documentation that incomplete blocks (including those improving in utero with dexamethasone) can progress postnatally, despite the clearance of the maternal antibodies from the neonatal circulation. Better echocardiographic measurements that identify first-degree block in utero may be the optimal means of approaching pregnant women at risk. Prophylactic therapies, including treatment with intravenous immunoglobulin, await larger trials. Reassuringly, most children with neonatal lupus syndromes do not develop rheumatic diseases, although follow-up is limited to late adolescence. To further efforts both at the bench and bedside, national research registries established in the United States and Canada are critical