Chung-E Tseng

Arrhythmogenicity of IgG and anti-52-kD SSA/Ro affinity-purified antibodies from mothers of children with congenital heart block

An important advance in the description and understanding of congenital heart block (CHB) came in the 1970s with the observation that mothers of affected infants frequently had autoimmune diseases and, in particular, that many maternal sera contained antibodies to SSA/Ro and SSB/La ribonucleoproteins. Although the molecular biology of the candidate antigens has been extensively defined, the arrhythmogenic and electrophysiological effects of their cognate antibodies on the human fetal heart are unknown. In the present study, we provide evidence that IgG-enriched fractions and anti-52-kD SSA/Ro antibodies affinity-purified from sera of mothers whose children have CHB induce complete atrioventricular (AV) block in the human fetal heart perfused by the Langendorff technique and inhibit L-type Ca2+ currents at the whole-cell and single-channel level. Immunization of female BALB/c mice with recombinant 52-kD SSA/Ro protein generated high-titer antibodies that crossed the placenta during pregnancy and were associated with varying degrees of AV conduction abnormalities, including complete AV block, in the pups. These findings strongly suggest that anti-52-kD SSA/Ro antibodies are causally related to the development of CHB.

Serum and immunoglobulin G from the mother of a child with congenital heart block induce conduction abnormalities and inhibit L-type calcium channels in a rat heart model.

Although a strong clinical association exists between congenital heart block (CHB) and an immune response to SSA/Ro and SSB/La proteins, a causative role of these antibodies in the pathogenesis is just emerging. In a preliminary report, we have demonstrated that IgG fractions isolated from the sera of mothers whose children have CHB are arrhythmogenic in the human fetal heart. To more precisely define the arrhythmogenic effect of anti-SSA/Ro-SSB/La antibodies, we used the readily available rat heart model to record: 1) ECGs from Langendorff beating hearts;2) action potentials from atrioventricular (AV) nodal preparations;3) L-type Ca currents, ICa at the whole-cell and single channel levels; and 4) other currents such as the transient outward K+ current,Ito, the inward rectifier K+ current,IK1, and the Na+ current,INa. Perfusion of hearts with purified IgG (800 µg/mL), isolated from the serum of a mother with SSA/Ro and SSB/La antibodies whose child had CHB, resulted in bradycardia associated with 2:1 AV block. Simultaneous action potentials were recorded from dissected atrial and AV nodal areas of the rat heart. Superfusion of these preparations with the same mothers IgG fraction resulted in 2:1 AV block followed by complete inhibition of AV nodal action potential. Because AV nodal electrogenesis is largely dependent on ICa, the effect of these antibodies on ICa was subsequently determined. Superfusion of myocytes with whole serum or purified IgG (80 µg/mL) from the same mother consistently inhibited whole cell ICa, ensemble average Ba2+ currents (IBa) and open state probability, po, without affecting the channel conductance. IgG had no significant effect on Ito,IK1, or INa. Whole sera and IgG fractions from a healthy mother with no detectable anti-SSA/Ro or SSB/La antibodies did not inhibit ICa or IBa. These results demonstrate that IgG containing anti-SSA/Ro and -SSB/La antibodies induces complete AV block in beating hearts and in multicellular preparations, thus implicating a preferential interaction of these autoantibodies with Ca channels and/or associated regulatory proteins. This is consistent with the observed inhibition of Ca channels that may be a critical factor contributing to the pathogenesis of CHB.

Use of Pharmacogenetics, Enzymatic Phenotyping, and Metabolite Monitoring to Guide Treatment with Azathioprine in Patients with Systemic Lupus Erythematosus

Objective. Individualized therapy based on genetic background and monitoring of metabolites can optimize drug safety and efficacy. Such an approach is available for azathioprine (AZA), the thiopurine antimetabolite. AZA exerts therapeutic effects when metabolized to the active thiopurine nucleotide, 6-thioguanine (6-TGN). In inflammatory bowel disease (IBD), 6-TGN levels in the target range of 235–400 pmol/8 ×108 red blood cells (RBC) are associated with a high likelihood of response. Our objective was to evaluate whether drug escalation based on metabolite levels improves efficacy and maintains safety in patients with systemic lupus erythematosus (SLE). Methods. We conducted a 6-month open-label dose-escalation clinical study of patients with active SLE treated with azathioprine dosed by body weight and metabolite levels. The primary endpoint was ≥50% improvement in any one parameter of disease activity, or 50% decrease in glucocorticoid dose. Results. Of 50 patients enrolled in the study, 21 achieved clinical responses, 13 of whom had 6-TGN < 235 pmol/8 ×108 RBC. Ten patients had no clinical response at 6 months, yet achieved either therapeutic IBD 6-TGN levels (> 235, n = 4) or received maximum AZA dose ≥3.5 mg/kg (n = 6). In 19 patients the drug was discontinued prematurely due to side effects or SLE activity. For those patients in whom either liver function test or white blood cell count abnormalities were encountered, metabolites guided attribution to drug or disease activity. Conclusion. Clinical responses in SLE can occur at levels of 6-TGN lower than the target range established for IBD. During followup, measurements of AZA metabolites may provide a rational approach to safety.

mRNA and protein expression of SSA/Ro and SSB/La in human fetal cardiac myocytes cultured using a novel application of the Langendorff procedure.

Irreversible congenital heart block (CHB) and the transient rash of neonatal lupus are strongly associated with maternal antibodies to SSA/Ro and SSB/La proteins; however, the precise mechanism by which these antibodies mediate organ-specific injury is not yet defined. Culturing of keratinocytes has provided critical insights. Accordingly, successful culturing of human fetal cardiac myocytes at high yield would constitute a powerful tool to directly examine conditions that promote expression of the target autoantigens. To accomplish this aim, fetal cardiac myocytes from 18- to 22-wk abortuses were established in culture using a novel technique in which cells were isolated after perfusion of the aorta with collagenase in a Langendorff apparatus. After preplating to decrease fibroblast contamination, cardiocytes were grown in flasks and slide chambers. Staining with monoclonal anti-sarcomeric α-actinin revealed the expected striations typical of cardiac myocytes in 70-90% of the cells after 4 d in culture. Furthermore, the cells were observed to beat at rates varying between 25-75 beats per minute (bpm) after the addition of 1.8 mM CaCl2. An average yield of 45-60 × 106 cells was obtained from a 3- to 5-g heart. Cellular localization of SSA/Ro and SSB/La by indirect immunofluorescence and demonstration of mRNA expression by reverse transcriptase polymerase chain reaction supports the feasibility of cultured cardiac myocytes for the study of congenital heart block. In contrast to the increased expression of SSA/Ro reported for keratinocytes, incubation of cultured human cardiac myocytes with either 17β-estradiol or progesterone did not alter mRNA expression or cellular localization of 48 kD SSB/La, 52 kD SSA/Ro, or 60 kD SSA/Ro. In summary, we describe a novel method to successfully culture human fetal cardiac myocytes that should provide a valuable resource for investigation of the molecular mechanism(s) contributing to the development of congenital heart block. Differential constitutive and estradiol-induced expression of 52 and 60 kD SSA/Ro in human cardiac myocytes compared with keratinocytes may be a factor contributing to the marked discordance of clinically detectable injury in these two target tissues.

Stability of immunoblot profile of anti-SSA/Ro-SSB/La antibodies over time in mothers whose children have neonatal lupus

Neonatal lupus is strongly associated with antibodies reactive with SSA/Ro-SSB/La pro teins, independent of maternal disease activity or classification. We sought to determine whether the fine specificity of antibody profiles remains stable or evolves over time and whether these findings relate to clinical status. Sera from 23 mothers whose children had neonatal lupus (22 heart block, one skin) were evaluated by SDS-immunoblot. For each mother two samples were available at least 13 months apart; the mean duration of time between testing was 45 months ± 27 S.D. (range 13-108 months). Twenty-two of the 23 initial profiles were identical to the results obtained in a later sample. The health status of seven (30%) of 23 mothers changed after the birth of the affected infant but the immunoblot specificity of the antibodies remained unchanged. SLE was the initial and final diagnosis in the only mother whose profiles differed, with development of weak reactivity to 48 kD SSB/La in addition to the 52 kD SSA/Ro after 14 months. In conclusion, the fine specificity of anti-SSA/Ro-SSB/La antibodies as assessed by immunoblot is highly stable for years. Progression of clinical status was not associated with a concomitant change in antibody profile.