Pierre Eftekhari

Autoantibodies against the angiotensin receptor (AT1) in patients with hypertension.

Sera from patients with malignant essential hypertension (n = 14), malignant secondary hypertension mainly attributable to renovascular diseases (n = 12) and renovascular diseases without malignant hypertension (n = 11) and from normotensive healthy blood donors (n = 35) were studied for the presence of autoantibodies against G-protein-coupled cardiovascular receptors. Autoantibodies against the angiotensin II receptor (AT1) were detected in 14, 33, 18 and 14% of patients with malignant essential hypertension, malignant secondary hypertension, renovascular diseases and control patients, respectively. Sensitivity of the enzyme immunoassay was assessed as 5 μg/ml IgG. Patients did not show antibodies against bradykinin (B2) or angiotensin II subtype 2 (AT2) receptors. Autoantibodies affinity-purified from positive patients localized AT receptors in Chinese hamster ovary transfected cells, and displayed a positive chronotropic effect on cultured neonatal rat cardiomyocytes. These results demonstrate the existence of autoantibodies against a functional extracellular domain of human AT1 receptors in patients with malignant hypertension, and suggest that these autoantibodies might be involved in the pathogenesis of malignant hypertension.

Anti-SSA/Ro52 autoantibodies blocking the cardiac 5-HT4 serotoninergic receptor could explain neonatal lupus congenital heart block

The 52‐kDa SSA/Ro (Ro52) ribonucleoprotein is an antigenic target strongly associated with the autoimmune response in mothers whose children develop neonatal lupus and congenital heart block. When sera from patients with systemic lupus erythematosus were used as autoimmune controls in an enzyme immunoassay to screen for antibodies against the human serotoninergic 5‐HT4‐receptor, a high correlation was found between the presence of anti‐Ro52 protein antibodies in such sera and antibodies reacting with a synthetic peptide, corresponding to the second extracellular loop of the human 5‐HT4 receptor (amino acid residues 165–185). Homology scanning between the 5‐HT4 peptide and the sequence of the Ro52 protein indicated two potential common epitopes located between residues 365 and 396 of the Ro52 protein. Cross‐reactivity was found between the peptide derived from the 5‐HT4 receptor, and a peptide corresponding to residues 365–382 of the Ro52 protein. Autoantibodies, affinity‐purified on the 5‐HT4 receptor peptide, specifically recognized both the Ro52 protein and the 5‐HT4 receptor protein in immunoblots. The affinity‐purified antibodies antagonized the serotonin‐induced L‐type Ca channel activation on human atrial cells. This effect could explain the electrophysiological abnormalities in neonatal lupus.

Isolation of the serotoninergic 5‐HT4(e) receptor from human heart and comparative analysis of its pharmacological profile in C6‐glial and CHO cell lines

RT–PCR technique was used to clone the human 5‐HT4(e) receptor (h5‐HT4(e)) from heart atrium. We showed that this h5‐HT4(e) receptor splice variant is restricted to brain and heart atrium. Recombinant h5‐HT4(e) receptor was stably expressed in CHO and C6‐glial cell lines at 347 and 88 fmol mg−1 protein, respectively. Expression of h5‐HT4(e) receptors at the cell membrane was confirmed by immunoblotting. The receptor binding profile, determined by competition with [3H]‐GR113808 of a number of 5‐HT4 ligands, was consistent with that previously reported for other 5‐HT4 receptor isoforms. Surprisingly, we found that the rank order of potencies (EC50) of 5‐HT4 agonists obtained from adenylyl cyclase functional assays was inversely correlated to their rank order of affinities (Ki) obtained from binding assays. Furthermore, EC50 values for 5‐HT, renzapride and cisapride were 2 fold lower in C6‐glial cells than in CHO cells. ML10302 and renzapride behaved like partial agonists on the h5‐HT4(e) receptor. These results are in agreement with the reported low efficacy of the these two compounds on L‐type Ca2+ currents and myocyte contractility in human atrium. A constitutive activity of the h5‐HT4(e) receptor was observed in CHO cells in the absence of any 5‐HT4 ligand and two 5‐HT4 antagonists, GR113808 and ML10375, behaved as inverse agonists. These data show that the h5‐HT4(e) receptor has a pharmacological profile which is close to the native h5‐HT4 receptor in human atrium with a functional potency which is dependent on the cellular context in which the receptor is expressed.

Induction of neonatal lupus in pups of mice immunized with synthetic peptides derived from amino acid sequences of the serotoninergic 5-HT4 receptor

We have previously suggested that the recognition of a cross‐reactive epitope on the 5‐HT4 receptor and the 52‐kDa SSA / Ro protein by serotonin‐antagonizing autoantibodies could explain the electrophysiological symptoms of congenital heart block in neonatal lupus. To confirm this hypothesis, we immunized female mice with four synthetic peptides corresponding to the recognized epitopes. All mice developed anti‐peptide antibodies, which cross‐reacted with the Ro52 and 5‐HT4 receptor peptides and recognized both cognate proteins. Peptide‐immune mice were mated. The pups from mice immunized with the Ro52 peptides had no symptoms of neonatal lupus apart from bradycardia. However, pups from mice immunized with the 5‐HT4 receptor peptides and bradycardia, atrioventricular block of type I or II, longer QT intervals, skin rashes and neuromotoric problems. The 5‐HT4 receptor was detectable in the different fetal tissues affected (heart, skin and brain) by immunohistochemistry. Hearts from diseased pups were less developed and showed disorganized myocardial hyperplasia, compared to the normal littermates. These results demonstrate that the serotoninergic 5‐HT4 receptor is the antigenic target of physiopathological autoantibodies in neonatal lupus.

Exploration of the ligand binding site of the human 5‐HT4 receptor by site‐directed mutagenesis and molecular modeling

Among the five human 5‐HT4 (h5‐HT4) receptor isoforms, the h5‐HT4(a) receptor was studied with a particular emphasis on the molecular interactions involved in ligand binding. For this purpose, we used site‐directed mutagenesis of the transmembrane domain. Twelve mutants were constructed with a special focus on the residue P4.53 of helix IV which substitutes in h5‐HT4 receptors the highly conserved S residue among the rhodopsin family receptors. The mutated receptors were transiently expressed in COS‐7 cells. Ligand binding or competition studies with two h5‐HT4 receptor agonists, serotonin and ML10302 and two h5‐HT4 receptor antagonists, [3H]‐GR113808 and ML10375 were performed on wild type and mutant receptors. Functional activity of the receptors was evaluated by measuring the ability of serotonin to stimulate adenylyl cyclase. Ligand binding experiments revealed that [3H]‐GR113808 did not bind to mutants P4.53A, S5.43A, F6.51A, Y7.43A and to double mutant F6.52V/N6.55L. On the other hand mutations D3.32N, S5.43A and Y7.43A appeared to promote a dramatic decrease of h5‐HT4(a) receptor functional activity. From these studies, S5.43 and Y7.43 clearly emerged as common anchoring sites to antagonist [3H]‐GR113808 and to serotonin. According to these results, we propose ligand‐receptor complex models with serotonin and [3H]‐GR113808. For serotonin, three interaction points were selected including ionic interaction with D3.32, a stabilizing interaction of this ion pair by Y7.43 and a hydrogen bond with S5.43. [3H]‐GR113808 was also docked, based on the same type of interactions with S5.43 and D3.32: the proposed model suggested a possible role of P4.53 in helix IV structure allowing the involvement of a close hydrophobic residue, W4.50, in a hydrophobic pocket for hydrophobic interactions with the indole ring of [3H]‐GR113808.

Immunomodulation by maternal autoantibodies of the fetal serotoninergic 5-HT4 receptor and its consequences in early BALB/c mouse embryonic development.

BackgroundThe presence of functional 5-HT4 receptors in human and its involvement in neonatal lupus erythematosus (NLE) have prompted us to study the receptor expression and role during embryogenesis. Earlier we managed to demonstrate that female BALB/c mice immunized against the second extracellular loop (SEL) of the 5-HT4 receptor gave birth to pups with heart block. To explain this phenomenon we investigated the expression of 5-HT4 receptors during mouse embryogenesis. At the same time we looked whether the consequence of 5-HT4 receptor immunomodulation observed earlier is in relation to receptor expression.We studied the expression of 5-HT4 receptor at the mRNA level and its two isoforms 5-HT4(a) and 5-HT4(d) at the protein level in embryos from BALB/c mice, at 8th, 12th, 18th gestation days (GD) and 1 day post natal (DPN). Simultaneously the receptor activity was inhibited by rising antibodies, in female mice against SEL of the receptor. The mice were mated and embryos were collected at 8th, 12th, 18th GD and 1 DPN.Results5-HT4 receptor mRNA increased in brain from 12th GD to 1 DPN. Its expression gradually decreased in heart and disappeared at birth. This was consistent with expression of the receptor isoforms 5-HT4(a) and (d). Abnormalities like decreased number of embryos, growth delay, spina bifida and sinus arrhythmia from 12th GD were documented in pups of mice showing anti-5-HT4 receptor antibodies.Conclusionserotoninergic 5-HT4 receptor plays an important role in mouse foetal development. In BALB/c mice there is a direct relation between the expression of receptor and the deleterious effect of maternal anti-5-HT4 receptor autoantibodies in early embryogenesis.

Insulin interacts directly with Na⁺/K⁺ATPase and protects from digoxin toxicity.

Insulin has shown to have cardioprotective effect in diabetic patient after digoxin intoxication. The latter, prompted us to study whether insulin interacts directly with Na⁺/K⁺-ATPase. The interaction of insulin with Na⁺/K⁺-ATPase was explored using enzyme activity, Biacore and Western blot. We also used, flow cytometry, immunohistochemistry and chronotropy on both neonatal and adult rats cardiomyocytes. Insulin at concentration 1.7e⁻⁷ M blunted the effect of digoxin on Na⁺/K⁺-ATPase activity. In Western blot, the same insulin concentration decreased enzyme α subunit immunoreactivity. Insulin and digoxin decreased both enzyme α subunit immunoreactivity but insulin/digoxin co-treatment did not. Biacore confirmed a direct interaction between insulin and Na⁺/K⁺-ATPase. In neonatal rat cardiomyocytes, insulin plus digoxin induced cell apoptosis but not alone. In adult rat cardiomyocytes, insulin at optimal dose did not induce apoptosis but prevented the one induced by digoxin. In immunocytochemsitry both insulin and digoxin altered Na⁺/K⁺-ATPase α subunit immunoreactivity while their association did not. Finally, insulin increased the beating rate of neonatal rat cardiomyocytes (45±7 beats/min); so did digoxin (36±13 beats/min). The effect of insulin was prevented after pre-treated with digoxin. These results demonstrate that insulin interacts directly with Na⁺/K⁺-ATPase pump and alters the effect of digoxin. This would have important clinical relevance in cardiac complications related to type I and II diabetes.

Chronic bacterial infection activates autoreactive B cells and induces isotype switching and autoantigen‐driven mutations

The links between infections and the development of B‐cell‐mediated autoimmune diseases are still unclear. In particular, it has been suggested that infection‐induced stimulation of innate immune sensors can engage low affinity autoreactive B lymphocytes to mature and produce mutated IgG pathogenic autoantibodies. To test this hypothesis, we established a new knock‐in mouse model in which autoreactive B cells could be committed to an affinity maturation process. We show that a chronic bacterial infection allows the activation of such B cells and the production of nonmutated IgM autoantibodies. Moreover, in the constitutive presence of their soluble antigen, some autoreactive clones are able to acquire a germinal center phenotype, to induce Aicda gene expression and to introduce somatic mutations in the IgG heavy chain variable region on amino acids forming direct contacts with the autoantigen. Paradoxically, only lower affinity variants are detected, which strongly suggests that higher affinity autoantibodies secreting B cells are counterselected. For the first time, we demonstrate in vivo that a noncross‐reactive infectious agent can activate and induce autoreactive B cells to isotype switching and autoantigen‐driven mutations, but on a nonautoimmune background, tolerance mechanisms prevent the formation of consequently dangerous autoimmunity.

Autoantibodies Against Serotoninergic 5-HT4 Receptor in Patients with Heart Failure.

Serotoninergic 5-HT(4) receptors have been detected in several tissues including the heart. An autoimmune mechanism may underline the pathogenesis of heart failure. The aim of this work was to look for autoantibodies to the 5-HT(4) receptor in patients with heart failure. We looked for the presence of autoantibodies against 5-HT(4) receptor as well as angiotensin II type (AT1), β(1)-adrenoceptor, and muscarinic M2 receptors in the sera of 176 patients with heart failure (female: n=96, male: n=80) and in 108 controls (female: n=69; male: n=39). The prevalence of 5-HT(4) receptor autoantibodies was 18.8% (n=33) in the group of patients with heart failure and 4.6% (n=5) in the control group (p<0.002). The prevalence of autoantibodies against AT1 was 1.7 (n=3), β(1)-adrenoreceptor 0.6 (n=1), and muscarinic-receptor M2 4.2 (n=5). Female patients with diabetes and heart failure had a positive trend (p=0.07) to the presence of 5-HT(4) receptor autoantibodies. In the group of female heart failure patients we found a significant correlation with the presence of coronary heart disease (p=0.05). The clinical relevance of 5-HT(4) receptor autoantibodies has to be further studied. The prevalence of 5-HT(4) receptor autoantibodies was highly significant in patients with chronic heart failure. It was also a significant correlation between these autoantibodies and the female subgroup with coronary heart disease. It is conceivable that the increased prevalence of autoantibodies against the 5-HT(4) receptor in patients with heart failure is more than just an epiphenomenon.

Physiological intermolecular modification spectroscopy for the prediction of response to anti-tumor necrosis factor therapy in patients with inflammatory bowel diseases.

Background/Aims: Anti-tumor necrosis factor (TNF) antibodies have clinical efficiency only in a subgroup of patients with inflammatory bowel diseases (IBD). Prediction of clinical response is a critical clinical problem. Physiological intermolecular modification spectroscopy (PIMS) is a label-free technology performed in physiological conditions. PIMS enables real-time monitoring of dynamic molecular resonance of entire proteins and macromolecules of an individual. The aim of this study was to explore the capacity of PIMS to discriminate IBD patients regarding response to anti-TNF treatment. Methods: Protein extracts of peripheral blood mononuclear cells (PBMC) from 30 outpatients diagnosed with ulcerative colitis (UC) or Crohns disease (CD) and treated with infliximab were subjected to PIMS analysis in a blinded transversal study. Total protein from each patients PBMCs was challenged with infliximab. Dynamic changes in macromolecular interaction were registered while the temperature rose from -37 to 37°C. Individual macromolecular volume and molecular elasticity were determined for each patient. Results: Clinical data revealed that 67% of UC and 79% of CD patients responded to infliximab therapy during the 3-month study period based on their respective clinical activity score. These results confirm that PIMS data predicted response to anti-TNF therapy with an accuracy of 96%. Conclusion: PIMS stratified IBD patients into two groups, responders and nonresponders, which correlated with the clinical efficacy of anti-TNF therapy. PIMS seems to be a powerful technology to adapt IBD treatment to the individual patient. Further studies with PIMS might enable to predict clinical response to biological treatment in IBD patients before the therapy is initiated.