Proposal of Lactobacillus kosoi Chiou et al. 2018 as a later heterotypic synonym of Lactobacillus micheneri McFrederick et al. 2018, elevation of Lactobacillus plantarum subsp. argentoratensis to the species level as Lactobacillus argentoratensis sp. nov., and Lactobacillus zhaodongensis sp. nov., isolated from traditional Chinese pickle and the intestinal tract of a honey bee (Apis mellifera)

Lactobacillus kosoi Chiou et al. 2018 and Lactobacillus micheneri McFrederick et al. 2018 are closely related, and they share 100 % 16S rRNA gene sequence similarity, 99.6 % pheS gene sequence similarity, 100 % rpoA gene sequence similarity, 97.3 % average nucleotide identity (ANI) value and 76.6 % in silico DNA-DNA hybridization (isDDH) value, indicating that they represent the same species. Fatty acid methyl esters (FAME) analysis and phenotypic characterization also indicated that L. kosoi and L. micheneri are very similar. We propose L. kosoi Chiou et al. 2018 as a later heterotypic synonym of L. micheneri McFrederick et al. 2018. The taxonomic position of Lactobacillus plantarum subsp. argentoratensis in the L. plantarum group was re-examined using a polyphasic approach, including sequence analyses of 16S rRNA, pheS, rpoA and recA genes, average nucleotide identity analysis, in silico DNA-DNA hybridization, fatty acid methyl ester analysis and phenotypic characterization. Results of 16S rRNA gene sequence analysis indicated that L. plantarum subsp. argentoratensis was closely related to L. plantarum subsp. plantarum, L. pentosus and L. paraplantarum in the L. plantarum group, sharing 99.6-99.7 % 16S rRNA gene sequence similarities. Results of pheS, rpoA and recA gene sequence analyses indicated that L. plantarum subsp. argentoratensis was most closely related to L. plantarum subsp. plantarum, having 91.8 % pheS gene sequence similarity, 98.9 % rpoA gene sequence similarity and 93.1 % recA gene sequence similarity. L. plantarum subsp. argentoratensis DSM 16365^T shared 95.6 % ANI value and 62.9 % isDDH value with L. plantarum subsp. plantarum ATCC 14917^T. The low isDDH value confirmed that L. plantarum subsp. argentoratensis and L. plantarum subsp. plantarum represent two different species, rather than two different subspecies in the L. plantarum group. On the basis of the data from polyphasic characterization obtained in the present study and in previous studies, L. plantarum subsp. argentoratensis is elevated to the species level and represents a novel species of the genus Lactobacillus, for which the name Lactobacillus argentoratensis sp. nov. is proposed and the type strain is DKO 22^T (=CIP 108320^T=DSM 16365^T=JCM 16169^T). Two novel Gram-stain-positive bacterial strains, designated 1206-1^T and F027-1-2, were isolated from traditional pickle in Heilongjiang Province, PR China, and from the intestinal tract of a honey bee (Apis mellifera) in Hubei Province, PR China, respectively. The two bacteria were characterized by a polyphasic approach, including 16S rRNA gene sequence analysis, pheS gene sequence analysis, rpoA gene sequence analysis, fatty acid methyl ester analysis, average nucleotide identity analysis, in silico DNA-DNA hybridization analysis and an analysis of phenotypic features. The results of 16S rRNA gene sequence analysis indicated that strains 1206-1^T and F027-1-2 were distantly related to Lactobacillus sharpeae, Lactobacillus hulanensis, Lactobacillus songhuajiangensis, Lactobacillus pantheris, Lactobacillus thailandensis, Lactobacillus camelliae, Lactobacillus jixianensis, Lactobacillus nasuensis, Lactobacillus baoqingensis, Lactobacillus manihotivorans and Lactobacillus porcinae. Strain 1206-1^T exhibited 94.2-96.4 % 16S rRNA gene sequence similarities, 69.5-83.3 % pheS gene sequence similarities and 73.1-90.3 % rpoA gene sequence similarities to type strains of phylogenetically related species. ANI and isDDH values between strain 1206-1^T and the type strains of phylogenetically related species were 52.7-73.7 % and 21.1-30.1 %, respectively. On the basis of the data obtained in the present study, a novel species, Lactobacillus zhaodongensis sp. nov. is proposed and the type strain is 1206-1^T (=CCM 8981^T=CCTCC AB 2019200^T=LMG 31620^T).

Biotransformation optimization of betulin into betulinic acid production catalysed by cultured Armillaria luteo-virens Sacc ZJUQH100-6 cells

AIMS

Betulinic acid has attracted attention in terms of its important biological and pharmacological characteristics. The main objective of this work was to optimize the variables of biotransformation process in order to enhance betulinic acid production from betulin catalysed by fungus Armillaria luteo-virens Sacc ZJUQH100-6.

METHODS AND RESULTS

Fractional factorial design and response surface methodology were applied to optimize the main parameters that affect betulinic acid production in the growing-cells system. Results indicated that the addition of Tween 80 and substrate concentration were identified as the significant factors on betulinic acid formation, and the central composite experimental design was then adopted to derive a statistical model for optimizing biotransformation conditions. The optimum conditions were observed at pH 6·0, 0·57% Tween 80, 15 mg l(-1) betulin and at 3 days of stage of inoculation.

CONCLUSIONS

Under the optimized conditions, the highest productivity of betulinic acid predicted was 9·32%, which increased by 74·53% in comparison with that of the nonoptimized. The verified experiment revealed that the model can well simulate betulin biotransformation. Moreover, the bioconversion of betulin and betulin-28-monooxygenase activities was compared between the optimized and the nonoptimized conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Current data imply that betulinic acid production from betulin can be effectively enhanced through biotransformation optimization strategy.

Prevention of experimental autoimmune cardiomyopathy in rabbits by receptor blockers

We investigated the effects of beta1-adrenoceptor blockade and M2-muscarinic receptor antagonist in rabbits which have developed dilated cardiomyopathy-like changes after immunization with the peptides from the second extracellular loop of human beta1-adrenoceptor (beta1-peptide) and M2-muscarinic receptor (M2-peptide). Ten rabbits, which were immunized with beta1-peptide once a month for one year, were treated with bisoprolol and 10 rabbits, which were immunized with M2-peptide, were treated with otenzepad. Although both groups treated with receptor blockade or antagonist showed an increased titer of anti-beta1-adrenoceptor or anti-M2-muscarinic receptor antibodies, myocardial damages were markedly less than those in beta1-peptide- or M2-peptide-immunized rabbits. This study indicates that anti-beta1-adrenoceptor and anti-M2-muscarinic receptor antibodies are of pathogenic importance in the development of human dilated cardiomyopathy, and that beta-adrenoceptor blockade, bisoprolol, and M2-muscarinic receptor antagonist, otenzepad, might be clinically useful for treatment of dilated cardiomyopathy.

Methimazole interferes with the progression of experimental autoimmune myocarditis in rats

In order to ascertain whether methimazole, a drug commonly used for the treatment of hyperthyroidism, interferes with the progression of autoimmune-mediated myocardial injury, we investigated the effect of methimazole on experimental autoimmune myocarditis (EAM) in rats. EAM was induced by immunization with porcine cardiac myosin. Methimazole administration markedly slowed the body weight growth in both normal and EAM rats, but did not induce morphologic change of cardiac tissue in normal rats. In EAM rats, macroscopic examination revealed discoloration of the cardiac surface, and histopathological examination by light microscopy showed extensive myocardial necrosis, infiltration by inflammatory cells and myocardial fibrosis. In the EAM rats treated with methimazole, the discolored areas on the cardiac surface were markedly diminished in size, and the myocardial necrosis, cellular infiltration and fibrosis were significantly less severe. To identify the mechanism responsible of this effect, we investigated the change of regulatory lymphocyte subsets in peripheral blood using an immunofluorescence technique with a flow cytometer. A decrease in the helper/suppressor T cell ratio as a result of the increased proportion of suppressor T cells and a decrease in the proportion of B cells were observed in normal rats after methimazole administration, and similar findings were made in the EAM rats treated with methimazole. These results indicate that methimazole interferes with the progression of EAM, and immunosuppression may, at least in part, be involved in the inhibitory effect of methimazole on EAM in rats.

Beneficial effect of muscarinic-2 antagonist on dilated cardiomyopathy induced by autoimmune mechanism against muscarinic-2 receptor

We have previously shown that a peptide corresponding to the sequence of the second extracellular loop of the human muscarinic-2 (M2) receptor (M2-peptide) was able to induce an autoimmune cardiomyopathy in rabbits. In this study, we investigated the effect of M2-antagonist (otenzepad) on M2-peptide-induced cardiomyopathy in rabbits. New Zealand White rabbits were divided into four groups: 1) control group, saline injection; 2) M2-peptide group, M2-peptide injection; 3) M2-antagonist group, otenzepad (30 mg/day) orally and saline injection; and (4) M2-antagonist + M2-peptide group, otenzepad (30 mg/day) orally and M2-peptide injection. The study duration was 1 year. Saline or peptide was injected once a month. All rabbits in both the M2-peptide group and the M2-antagonist + M2-peptide group had high titers of anti-M2-autoantibodies in their sera. Rabbits in the M2-peptide group showed an increase in heart weight, wall thinning and dilatation of the right ventricle. On the contrary, rabbits in the M2-antagonist + M2-peptide group had normal heart weight and shape. All rabbits in the M2-peptide group showed multifocal degeneration and necrosis of myocardial cells with moderate infiltration of inflammatory cells, while four rabbits in the M2-antagonist + M2-peptide group showed slight infiltration of inflammatory cells with normal myocardial cells and interstitium, and another three showed no histological changes in the hearts. In conclusion, M2-antagonist protects the myocardium from injury induced by autoimmune mechanism against M2-muscarinic receptor.

Growth hormone interferes with the progression of myocarditis in rats

In this study, we investigated whether recombinant human growth hormone (rhGH) influences the progression of myocarditis. We induced experimental autoimmune myocarditis in F344 rats by subcutaneous injection of cardiac myosin, and divided the rats into three groups: (1) control group, saline injection; (2) pre-treated group, subcutaneous injection of rhGH (100 mIU/rat/day for 10 days) before induction of experimental autoimmune myocarditis; and (3) post-treated group, subcutaneous injection of rhGH (100 mIU/rat/day for 10 days) after induction of experimental autoimmune myocarditis. On the 35th day after induction of experimental autoimmune myocarditis, all rats were sacrificed and the hearts were examined. The increase in body weight was smaller in the control group than the pre-treated group and the rate of heart weight/body weight was larger in the control group than in the two treated groups. Histopathologically, rats in the control group showed multifocal infiltration by inflammatory cells, mainly neutrophils, lymphocytes and macrophages, extensive fibrosis, and a higher proportion of mast cells in the inflamed region. In contrast, rats in the two treated groups showed only minor changes. We found that rhGH did not influence the distribution of lymphocytes in peripheral blood in the three groups, and that rhGH induced G1 checkpoint dysfunction, thereby arresting the cell cycle in G1 and inhibiting the proliferation of mast cells in vitro. These findings suggest a possible role for mast cells in the progression of myocarditis and the rhGH may be a candidate for use as a new tool to treat myocarditis.

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 microg/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.

Agonist-like activity of antibodies to angiotensin II receptor subtype 1 (AT1) from rats immunized with AT1 receptor peptide

In the present study, rats were immunized with angiotensin II receptor subtype 1 (AT1) receptor peptides for 3 months to see if the immunization produced specific anti-AT1 receptor antibodies and if continuous stimulation for 3 months affected blood pressure or induced morphological changes in the organs containing AT1 receptors. Our results showed that there were constant high levels of circulating antibodies throughout the study period in all rats of the immunized group, but not in the control rats, and that there were almost no significant cross-reactions of antisera with AT2 receptor peptide and alpha1 adrenoceptor peptide, except in four rats, which showed low cross-reactions with alpha1 adrenoceptor and AT2 receptor peptides. When an affinity-purified anti-AT1 receptor antibody was used, it specifically displayed the AT1-stimulatory positive chronotropic effect and also localized AT1 receptors. However, in the immunized group, saturation binding of AT1 in homogenates from kidneys showed no difference either in maximal binding sites (Bmax) or in antagonist affinity (Kd). No difference in mRNA of AT1a was found in either kidney or heart, and no morphological changes in the organs were observed, as compared with the control group. Furthermore, immunization did not cause hypertension. In conclusion, the synthetic peptide corresponding to the second extra-cellular loop of the human AT1 receptor was able to produce highly specific and functionally active anti-AT1 receptor antibodies, but unable to induce pathological structural changes or hypertension.

Impairment of cardiac function and bioenergetics in adult transgenic mice overexpressing the bovine growth hormone gene

Cardiovascular abnormalities represent the major cause of death in patients with acromegaly. We evaluated cardiac structure, function, and energy status in adult transgenic mice overexpressing bovine GH (bGH) gene. Female transgenic mice expressing bGH gene (n = 11) 8 months old and aged matched controls (n = 11) were used. They were studied with two-dimensional guided M-mode and Doppler echocardiography. The animals (n = 6) for each group were examined with 31P magnetic resonance spectroscopy to determine the cardiac energy status. Transgenic mice had a significantly higher body weight (BW), 53.2+/-2.4 vs. 34.6+/-3.7 g (P < 0.0001) and hypertrophy of left ventricle (LV) compared with normal controls: LV mass/BW 5.6+/-1.6 vs. 2.7+/-0.2 mg/g, P < 0.01. Several indexes of systolic function were depressed in transgenic animals compared with controls mice such as shortening fraction 25+/-3.0% vs. 39.9+/-3.1%; ejection fraction, 57+/-9 vs. 77+/-5; mean velocity of circumferential shortening, 4.5+/-0.8 vs. 7.0+/-1.1 circ/sec, p < 0.01. Creatine phosphate-to-ATP ratio was significantly lower in bGH overexpressing mice (1.3+/-0.08 vs. 2.1+/-0.23 in controls, P < 0.05). Ultrastructural examination of the hearts from transgenic mice revealed substantial changes of mitochondria. This study provides new insight into possible mechanisms behind the deteriorating effects of long exposure to high level of GH on heart function.

Protective effect of bisoprolol on beta-1 adrenoceptor peptide-induced autoimmune myocardial damage in rabbits

Idiopathic dilated cardiomyopathy is a severe disease of unknown etiology. Accumulating evidence suggests that agonist-like autoantibodies against the beta 1 adrenoceptor in the circulation of dilated cardiomyopathy may play an important role. The aim of this study was to evaluate the effects of the selective beta 1-adrenoceptor blocker, bisoprolol, on beta 1-adrenoceptor peptide induced autoimmune myocardial damage. In the animal model of autoimmune cardiomyopathy induced by active immunization of rabbits with beta 1-adrenoceptor peptide, bisoprolol was given at a dose of 3 mg/day throughout the study period. Our results showed high titer of anti-beta 1-adrenoceptor antibody in the immunized group throughout the study but not in the group receiving only bisoprolol. Cross-reactivity to beta 2 adrenoceptors was observed in some of the immunized rabbits, but disappeared almost entirely after 6 months. As compared to the beta 1-adrenoceptor peptide immunized group without bisoprolol treatment, bisoprolol treated beta 1-receptor peptide immunized group showed increase in the wall thickness and decreases in cavity dimension in anatomical measurements and only mild alterations in macro- and microscopic examinations. Thus, our study clearly demonstrated a beneficial effect of bisoprolol in rabbits who have developed autoimmune myocardial damage.

Myocardial hypertrophy in transgenic mice overexpressing the bovine growth hormone (bGH) gene

OBJECTIVES

The main purpose of the present study was to characterize cardiac muscle hypertrophy using both qualitative and quantitative microscopy in mice overexpressing the bovine growth hormone.

RESULTS

Measurements of 30 fibres from each group revealed that fibre diameter in transgenic hearts was significantly larger than in control hearts. There was a significant decrease in interfibrillar space in transgenic hearts as compared with control hearts. The enlarged transgenic hearts displayed unchanged organelles such as normal myofibrils and mitochondria in a normal pattern, suggesting balanced growth. Myelin structures were occasionally observed between normal myofibrils. Moreover, myocardial beta-adrenergic receptors and muscarinic receptors in the hearts of transgenic mice overproducing GH were studied to see whether they are involved in the hypertrophic process. It was shown that the density of muscarinic receptors had decreased and the super-high affinity of muscarinic receptors was lost, without any significant changes in either the density or the affinity of beta-adrenergic receptors, as compared with controls.

CONCLUSIONS

These results demonstrate that a GH excess was able to induce significant myocardial hypertrophy and that there was a downregulation of muscarinic receptors.

Active immunization of combined beta1-adrenoceptor and M2-muscarinic receptor peptides induces cardiac hypertrophy in rabbits

BACKGROUND

The high prevalence of patients with dilated cardiomyopathy (DCM) with anti-beta1-adrenoceptor and/or anti-M2-muscarinic receptor autoantibodies in their sera has been observed. However, the pathophysiological role of these autoantibodies in the development of cardiomyopathy is unknown. We previously reported an experimental model of early-stage DCM-like cardiomyopathy induced by immunizing rabbits for 1 year with synthetic peptides corresponding to the sequence of the second extracellular loop of either beta1-adrenoceptor or M2-muscarinic receptor. Because approximately half the sera of patients with DCM that recognize one of the two receptor sequences also recognize the second sequence, a model was created in rabbits simultaneously immunized with the synthetic peptides corresponding to the second extracellular loop of the beta1-adrenoceptor and M2-muscarinic receptor.

METHODS AND RESULTS

All rabbits (n = 8) immunized with both peptides had a high titer of both anti-beta1-adrenoceptor and anti-M2-muscarinic receptor autoantibodies in their sera, whereas none of the sera from control rabbits injected with saline (n = 9) was positive. No significant cross-reaction with peptides other than those used for immunization was found. The weight of the hearts of immunized rabbits increased significantly. The hearts of immunized rabbits showed marked concentric left ventricular hypertrophy with mild inflammatory cell infiltration. In these rabbits, mild or moderate interstitial fibrosis was also observed. In electron micrographs, immunized rabbits showed focal myofibrillar lysis, loss of myofilament, and a marked increase in the number of mitochondria and deposition of dense granules in both sarcoplasm and myofibrils. Conversely, one of the control rabbits showed scant mononuclear cell infiltration. However, in this control rabbit, no significant alteration was found by electron microscopy.

CONCLUSION

Our results showed the coexistence of both anti-beta1-adrenoceptor and anti-M2-muscarinic receptor autoantibodies in the sera has pathophysiological importance, shown by their ability to induce cardiac hypertrophy in rabbits.

The frequency of occurrence of anti-cardiac receptor autoantibodies and their correlation with clinical manifestation in patients with hypertrophic cardiomyopathy

The purpose of this study was to investigate the frequency of occurrence of autoantibodies against G-protein coupled cardiovascular receptors and their relation to the clinical manifestation of hypertrophic cardiomyopathy (HCM). Autoantibodies against beta1-receptors, Muscarin-2-receptors, Angiotensin-II-receptor subtype 1 and alpha1-receptors were determined with ELISA in 52 patients with HCM (37 male, 15 female, mean age 55 +/- 15 years) and 40 healthy, age and sex matched controls. The clinical characterization of the HCM-patients included ECG, 24-h Holter, and echocardiography. The results showed that there is no significant difference in the frequency of a single autoantibody between HCM-patients and controls. However, if the number of patients who have autoantibodies against beta1-receptors and/or Muscarin-2-receptors were counted together, there are significantly more autoantibodies in HCM compared to controls (11 vs. 2, p = 0.035). Analysis of clinical data from this pooled group of patients showed that in patients with autoantibodies, heart rate variability (HRV), ultra low frequency (ULF) and very low frequency (VLF) were decreased (HRV by 20%, ULF by 50%, and VLF by 46%, p < 0.008) whereas the QTc-interval was increased by 8% (p < 0.02 each). The ratio of septal to posterior wall thickness was increased by 23% (p = 0.05), and the preejection period was prolonged by 46% in patients with autoantibodies (p < 0.001). These results suggest that the existence of these autoantibodies could be associated with an advanced stage or a severe manifestation of HCM.

Autoantibodies against M2 muscarinic receptors in patients with cardiomyopathy display non-desensitized agonist-like effects

Circulating autoantibodies against the human M2 muscarinic receptors have been previously shown in 38% of patients with idiopathic dilated cardiomyopathy. The functional properties of these autoantibodies are reported herein. They were able to decrease the cell beating frequency of myocytes in cultured neonatal rat heart cells in a dose-dependent manner without desensitization over a period of more than 5 hours whereas the non-specific muscarinic receptor agonist carbachol also inhibited the heart cell beating frequency but was desensitized within 1 hour. In the same cell culture, anti-M2 muscarinic receptor autoantibodies were not able to induce internalization of muscarinic receptor whereas carbachol did. These results demonstrate for the first time that anti-M2 muscarinic receptor autoantibodies from patients with idiopathic dilated cardiomyopathy have stimulatory muscarinic activity in vitro, which differ from normal muscarinic agonists by non-desensitization.

Screening of serum autoantibodies to cardiac beta1-adrenoceptors and M2-muscarinic acetylcholine receptors in 408 healthy subjects of varying ages

Autoantibodies to cardiac beta1-adrenoceptors and M2-muscarinic receptors have mainly been found in the sera of patients with idiopathic dilated cardiomyopathy (DCM). In order to elucidate the pathological significance of these autoantibodies in DCM, it is necessary to understand their characteristic distribution in a healthy population of different genders and ages. The peptides corresponding to the sequences of the second extracellular loops of the human beta1-adrenoceptor and M2-muscarinic receptors were therefore used as antigens to screen the sera of 408 healthy subjects of different ages (ranging from 0.5 to 85 years). Of 408 sera, 41 (10.0%) and 46 (11.3%) recognized the beta1-adrenoceptor and M2-muscarinic receptor peptides respectively. Of the positive sera for beta1-adrenoceptors and M2-muscarinic receptors, up to 63.4% and 56.5% had both anti-beta1-adrenoceptor and anti-M2-muscarinic receptor autoantibodies respectively. The antibody titres of the positive sera of healthy subjects were all of a low level, with a geometric mean titre of 1:42+/-1.9 for anti-beta1-adrenoceptor antibodies and 1:51+/-1.7 for anti-M2-muscarinic receptor antibodies. The frequency of occurrence of autoantibodies to both receptors in the sera of healthy subjects increased significantly with age. In conclusion, the autoantibodies to beta1-adrenoceptors and M2-muscarinic receptors in the sera of healthy subjects are characterized by a low frequency of occurrence and low titre, with the frequency of occurrence increasing with age.

Immunohistochemical localization of angiotensin II receptors (AT1) in the heart with anti-peptide antibodies showing a positive chronotropic effect

Antibodies were produced against a synthetic peptide corresponding to amino acids (165-191) of the second extracellular loop of the human angiotensin II receptor subtype 1 (AT1) in rabbits. The purified antibodies had an apparent affinity of about 1 nM and were monospecific for the AT1-receptor peptide. Chemical modification of the carboxyl groups (glu at positions 173 and 185) and the sulfhydryl group (cys at position 180) of the AT1-receptor peptide did not alter the relative affinity of the coated AT1-receptor peptide to antibodies. The antibodies specifically stained CHO cells expressing the rat AT1a receptor. Immunoblots on rat kidney revealed that the antibody recognized a protein band of 59 +/- 3 kDa in a dose-dependent manner and this band was no longer detected after preincubating the antibodies with AT1-receptor peptide. Using electron microscopic and immunofluorescence immunocytochemistry techniques, angiotensin II receptors were detected in (1) the sarcolemma, T-tubules and nuclei of rat cardiomyocytes, (2) the transluminal side of endothelial cells and (3) fibroblast cells. These localizations are specific, as the immunostaining did not appear when preimmune rabbit serum was used and was blocked after preincubating antibodies with antigenic peptide. Functionally, these antibodies did not affect the ligand binding properties of the receptors but displayed agonist-like activity as shown by dose-dependent increases in beating frequency in cultured neonatal cardiomyocytes. These results suggest that the antibodies against the second extracellular loop of human AT1 receptors were able to specifically recognize AT1 receptors. In addition, they extend the observation that the second extracellular loop of the G-protein coupled membrane receptors is a specific target for antibodies with agonist-like activity.

Myocardial injury due to G-protein coupled receptor-autoimmunity

One of the main mechanisms for dilated cardiomyopathy is likely to be autoimmune mediated myocardial damage. So far, a variety of autoantibodies have been detected against a number of putative autoantigens in the sera of patients with dilated cardiomyopathy. A growing body of studies have confirmed that autoantibodies against the second extracellular loop of beta 1-adrenoceptors and M2-muscarinic receptor are present in 30-40% of patients with dilated cardiomyopathy. These anti-beta 1-adrenoceptor and anti-M2-muscarinic receptor antibodies can not only decrease the binding sites of antagonist but also recognize the target receptors. Moreover, these two autoantibodies possess an 'agonist-like' stimulatory effect on the target receptors. In order to elucidate whether the autoantibodies against these autoimmune epitopes play an important role in the pathogenesis of dilated cardiomyopathy, we immunized rabbits over a period of one year with synthetic peptides corresponding to the second extracellular loop of the beta 1-adrenoceptor and the M2-muscarinic receptor. These peptides induced morphological changes in the heart similar to those found in dilated cardiomyopathy. These clinical and experimental findings suggest that these receptor autoantigens are of pathogenic importance in the development of dilated cardiomyopathy in vivo.

Anti-M2 muscarinic receptor antibodies inhibit beta-adrenoceptor-mediated inotropic response in rat myocardium

The modulation of the inotropic effect by affinity-purified antibodies against a synthetic peptide corresponding to the second extracellular loop of the human muscarinic M2 receptors was studied in adult rat ventricular myocardium. These anti-muscarinic M2 receptor antibodies shifted the dose-response relationship of the beta-adrenoceptor agonist isoproterenol to higher concentrations whereas preimmune rabbit immunoglobulin G (IgG) or antibodies against the N-terminus of the beta 1-adrenoceptor had no effect. This effect of anti-muscarinic M2 receptor antibodies was fully blocked after preincubation with the antigenic peptide. No significant change of maximal inotropic response to isoproterenol was observed in the presence of anti-muscarinic M2 receptor antibodies. The anti-muscarinic M2 receptor antibodies did apparently not hamper the access of the muscarinic receptor agonist carbachol. The muscarinic receptor antagonist atropine attenuated the effect of the anti-muscarinic M2 receptor antibodies. The present study demonstrates for the first time in intact adult ventricular myocardium a specific stimulatory muscarinic activity of antibodies raised against a part of the muscarinic M2 receptor protein.

Peptides derived from cardiovascular G-protein-coupled receptors induce morphological cardiomyopathic changes in immunized rabbits

An experimental model of early-stage cardiomyopathy was created by immunizing rabbits for 1 year with synthetic peptides corresponding to the sequence of the second extracellular loop of either beta-adrenoceptors or M2-muscarinic receptors. Thirty male rabbits were used and divided into three groups: a control group (n = 10), a group immunized with the peptide corresponding to the beta-adrenoceptor (beta 1 group) (n = 10) and a group immunized with the peptide corresponding to the M2-muscarinic receptor (M2 group) (n = 10). If the sera from both groups of immunized rabbits high-titres of anti-peptide antibodies were found throughout the study period but not in the sera from control rabbits or in the preimmune sera of immunized rabbits. No significant cross-reaction with peptides other than those used for immunization was found. The myocardial receptor density of both immunized groups displayed a strong trend toward receptor up-regulation. This was significant in the beta 1 group but not in the M2 group. Both groups of immunized rabbits displayed significantly enlarged ventricles and thinner walls, as compared with the control group. However, in contrast to the beta 1 group, which showed enlarged cavities in both left and right ventricles, the M2 group was mainly affected in the right ventricles. Moreover, morphological examinations of the hearts of rabbits from both immunized groups demonstrated focal myofibrillar lysis, loss of myofilament, mitochondrial swelling and condensation, sarcoplasmic vacuolation, deposition of dense granules in the sarcoplasm and the myofibrils. One of the sex control rabbit hearts which were examined showed mild degenerative changes in the myocardium and scant mononuclear cell infiltration. However, when all the control rabbit hearts were examined by electron microscopy, no significant alterations were found. These results suggest that immunization by peptides, corresponding to the target sequences for anti-receptor autoantibodies in idiopathic dilated cardiomyopathy, induces morphological changes in the heart similar to those found in the human disease.

Localization of alpha 1-adrenoceptors in rat and human hearts by immunocytochemistry

The localization of the alpha 1 adrenoceptors (alpha 1-AR) in the heart tissues from rat and human and in the cultured heart cells from neonatal rats was studied by indirect immunofluorescence and postembedding electronmicroscopical immuno-gold technique. With antipeptide antibodies directed against the second extracellular loop of the human alpha 1-AR (AS sequence 192-218), this receptor was found to be localized along the sarcolemma in both human and rat hearts. Similar localization sites were detected in cultivated rat neonatal cardiomyocytes. Beside the localization in cardiomyocytes, alpha 1-AR were identified in endothelial cells of capillaries and smooth muscle cells of coronary vessels, in neuronal endings, in mast cells of cultivated heart cells but not, or in less amount in fibroblasts. Interestingly, in the right atrium of rat heart the localization of alpha 1-AR was found to be near or on atrial natriuretic factor (ANF) granules, providing the basis for the alpha-adrenergic influence on ANF release. The immunocytochemical studies further confirm and complete the findings known by using autoradiographic binding studies with specific ligands.

Effects of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic acetylcholine receptors on transmembrane potentials and currents in guinea pig ventricular myocytes

The effects of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic receptor on transmembrane potentials and currents in guinea pig single ventricular cells were analyzed using whole-cell patch clamp technique. These effects were compared with those of the muscarinic receptor agonists carbachol and acetylcholine. The antibodies shortened the action potential duration in a dose-dependent manner. By using a ramp or step rectangular pulse protocol, it was found that the antibodies increased the outward K+ current and decreased the inward basal ICa significantly. The reversal potential of both carbachol- and antibody-induced extra currents were close to -80 mV, being in proximity to the calculated Ek of -90 mV. A beta-adrenergic receptor agonist, isoprenaline, prolonged the action potential and increased the overshoot which could be inhibited by both antibody and carbachol. Isoprenaline increased inward ICa and outward Ik simultaneously. Both antibody and carbachol could significantly reduce the isoprenaline-stimulated ICa but not the isoprenaline-stimulated Ik. The antibody- or carbachol-induced outward K+ current and the depressant effects of antibody and carbachol on isoprenaline-stimulated ICa were partially antagonized by atropine. These results suggest that the anti-M2 muscarinic receptor antibodies display a stimulatory activity similar to muscarinic receptor agonist on the receptor-mediated electrophysiological events.

Characterization of anti-heart M2 muscarinic receptor antibodies--a combined clinical and experimental study

To elucidate the relationship between autoimmunity and idiopathic dilated cardiomyopathy has been one of today's heated topics in the field of heart research. So far it has been identified that there are a variety of autoantibodies including antireceptor autoantibodies. However, the role of these autoantibodies in the development of dilated cardiomyopathy has not been defined. An increasing number of in vitro studies showed that these autoantibodies had different functions, suggesting that they may play different roles in the pathogenesis of cardiomyopathy. The main purpose of this article is to briefly go through the results obtained from both clinical and experimental in vitro studies on anti-M2 muscarinic receptor antibodies to see where we stand in the understanding of the role of these autoantibodies in the pathogenesis of idiopathic dilated cardiomyopathy.

Anti-M2 muscarinic receptor autoantibodies and idiopathic dilated cardiomyopathy

Idiopathic dilated cardiomyopathy is an often fatal cause of heart failure and has been intensively studied over the last 50 years. One of the main mechanisms for this disease is likely to be autoimmunity-mediated myocardial damage. So far, a variety of autoantibodies have been detected against a number of putative cardiac autoantigens in the sera of patients with dilated cardiomyopathy and have thus received increased attention. This article will attempt to focus on clinical and experimental studies of autoimmunity induced by the M2 muscarinic receptor as a putative autoantigen and their implications in idiopathic dilated cardiomyopathy.

A synthetic peptide corresponding to the second extracellular loop of the human M2 acetylcholine receptor induces pharmacological and morphological changes in cardiomyocytes by active immunization after 6 months in rabbits

We have previously shown the presence of functional autoantibodies against the second extracellular loop of the human M2 acetylcholine receptor as an autoimmune epitope in 39% of patients with idiopathic dilated cardiomyopathy (DCM). To see if this autoimmune DCM can be experimentally reproduced, a synthetic peptide corresponding to the above autoimmune epitope was used as an autoantigen to immunize rabbits monthly for 6 months. Affinity-purified antibodies were able to display the negative chronotropic effects on neonatal rat cardiomyocytes in culture. The density of the M2 acetylcholine receptors was increased in the immunized rabbits compared to controls but the receptors showed only low-affinity binding sites for the agonist carbachol. Ultrastructural changes such as moderate sarcolemma alterations, mitochondrial swelling, disruption of cristae, and formation of myelin-like structures in the myocardial cells of rabbits immunized for 6 months suggest an immune-induced cardiotoxicity. With only a limited infiltration of inflammatory cells, these results point toward a pathophysiological role of anti-M2 acetylcholine receptor autoantibodies.

Effects of anti-peptide antibodies against human M2 muscarinic receptors on the cAMP generating system in guinea pig ventricles

The effects of anti-peptide antibodies (Ab) against the second extracellular loop of human muscarinic receptor-2 on the cAMP generating system in guinea pig ventricles were studied. These effects were compared with those of the muscarinic receptor agonist carbachol (Carb). It was shown that: (1) both Carb and Ab were able to inhibit the isoproterenol (Iso)-stimulated cAMP production of ventricles in a dose-dependent manner. Carb at 2 microM, 10 microM and 50 microM decreased Iso-stimulated cAMP production by 8.0 +/- 1.1, 15.8 +/- 1.2 and 28.4 +/- 1.7%, respectively; whereas Ab at 50 nM, 100 nM and 400 nM decreased it by 5.8 +/- 0.4, 16.8 +/- 1.4 and 30.6 +/- 2.5%, respectively. (2) Both Carb and Ab could also inhibit the basal cAMP content of ventricles significantly. Carb at 10 microM and Ab at 100 nM decreased it by 46.9 +/- 4.2% and 60.2 +/- 4.6%, respectively. (3) The inhibitory effects of both Ab and Carb on Iso-stimulated cAMP production were significantly prevented by atropine at 1.5 microM. (4) The inhibitory effect of Ab at 100 nM was almost completely abolished by the peptide (700 nM) used as immunogen. These findings suggest that the antibodies exhibit a stimulatory muscarinic activity similar to carbachol in the inhibitory modulation of cAMP production.

Abnormal immune system and hypertension: where are we?

In reviewing the available evidence, the involvement of an immunological mechanism behind hypertension has been proposed. However, whether altered immunological function is a primary factor in the pathogenesis of hypertension or secondary to tissue damage of vascular beds induced by hypertension is still poorly defined. A major difficulty has been the relative paucity of information about the nature of specific immune targets which initiate and perpetuate abnormal immune responses in hypertension. This article will discuss the status of understanding of the involvement of immunological factors in both clinical and experimental hypertension.

Anti-peptide antibodies against an autoimmune epitope on human muscarinic receptor mimic functional autoantibodies against the same epitope in patients with idiopathic dilated cardiomyopathy

A synthetic peptide corresponding to the sequence 169-193 of the second extracellular loop of the human muscarinic receptor-2 was used to raise antibodies in rabbits. Affinity-purified antibodies were able to interfere with muscarinic receptor radioligand binding and to recognize the muscarinic receptor protein in rats. The antibodies could also exert the physiological effects of muscarinic agonist stimulation as demonstrated by decreases in isoproterenol-stimulated cAMP accumulation in Guinea-pig ventricles, heart beating frequency in cultured meonatal cardiomyocytes, the maximal rate of rise of ventricular pressure and heart rate in rats in-vivo. These results demonstrate that the second extracellular loop of the muscarinic acetylcholine receptor-2 is an immunologically and functionally important domain and that rabbit antibodies have properties comparable to those found for autoantibodies against the same epitope in patients with idiopathic dilated cardiomyopathy.

Do immune system changes have a role in hypertension?

There is growing evidence to indicate that there is a strong association between changes in the immune system and the development of hypertension in both animal models and humans. Alterations in immune function in hypertension are generally accompanied by an increase in the level and secretion of immunoglobulin, a decrease in the number and function of T-lymphocytes, genetic predisposition, auto-antibodies against nuclear structure, smooth muscle cells, native thymus tissue and G-protein-coupled cardiovascular receptors. Although there is evidence from a variety of observations to suggest that an abnormal immune system is involved in the pathogenesis of hypertension, the immunological mechanism and the specific role of changes in the immune system in the development of hypertension have not been elucidated.

Localization of muscarinic receptors in human heart biopsies using rabbit anti-peptide antibodies

Immunocytochemistry of muscarinic receptors on human heart biopsies from patients with heart disease was studied using rabbit antibodies against a synthetic peptide corresponding to amino acids 168-192 of the second extracellular loop of the human M2 muscarinic receptor. By using both light and electron microscopic immunocytochemistry techniques, muscarinic receptors were visualized on sarcolemma of human myocytes from patients with different heart diseases such as coronary heart disease and dilated cardiomyopathy in adults and congenital heart disease in children. The patchy distribution of immunoreactivity suggests a muscarinergic activity in vivo. These reactivities were abolished by preincubation of antibodies with antigenic peptide and were not shown in the absence of antibodies. Moreover, these antibodies were able to interfere with muscarinic ligand binding in myocardium from human dilated cardiomyopathy as shown by decreases in binding sites and antagonist affinity. These results demonstrate that the antibodies against the second extracellular loop of the human M2 muscarinic receptor can specifically recognize muscarinic receptors in human tissue and display pharmacological activity in human diseased myocardium, confirming their usefulness for the study of localization and function of muscarinergic activity in the human heart.

Immunocytochemical studies of the Gi protein mediated muscarinic receptor-adenylyl cyclase system

The localization of three key signal transduction components was indicated in rat heart tissue by immunocytochemical and histochemical experiment. It was shown that: 1. The M2 muscarinic receptors are localized along outer cell membranes and T-tubule membranes of cardiomyocytes but additionally at membranes of endothelial cells and fibroblasts. 2. Gia was found along outer cell membranes of cardiomyocytes and other cells of the heart and also inside the cells of the perinuclear space in close contact to the nuclei envelope and the endoplasmic reticulum membranes. Goa were found to be associated mainly in atrial tissue, especially at the nerval (neuronal) endings located among the cardiac muscle cells. This was shown in parallel incubation with specific neuronal antibody as a marker for these structures. 3. Adenylyl cyclase was localized along the sarcolemma and the T-tubule membranes in normal cardiomyocytes of rat and guinea pig hearts. Under ischemic conditions, the adenylyl cyclase was also seen in junctional sarcoplasmic reticulum membranes. The reasons for this changed localization need further elucidation. Binding of the adenylyl cyclase within the molecular structure of the membrane or variation of the marker penetration remain to be clarified.

Dilated cardiomyopathy defines serum autoantibodies against G-protein-coupled cardiovascular receptors

In order further to identify the prevalence of anti-receptor autoantibodies in the sera of patients with dilated cardiomyopathy (DCM), we attempted to detect autoantibodies against a series of G-protein-coupled cardiovascular receptors in a well-defined population of DCM patients from Japan. Peptides corresponding to the sequences of the second extracellular loops of the human beta 1 and beta 2 adrenoceptors, alpha 1 adrenoceptors, M2 muscarinic acetylcholine receptors and angiotensin II-1 (AT1) receptors were used as antigens in an enzyme immunoassay to screen the sera from patients with DCM (n = 28). Nine sera from patients with DCM (32%) and 2 sera from healthy subjects (9%) recognized the beta 1 adrenoceptor peptide. Ten sera from patients (36%) and 3 sera from healthy subjects (13%) recognized the M2 receptor peptide. Thirty-six per cent of the patients with autoantibody against the beta 1 adrenoceptor peptide. Ten sera from patients (36%) and 3 sera from healthy subjects (13%) recognized the M2 receptor peptide. Thirty-six per cent of the patients with autoantibody against the beta 1 adrenoceptor had autoantibody against the M2 receptor. However, no significantly high frequencies of autoantibodies against the beta 2 adrenoceptor, alpha 1 adrenoceptor and AT1 receptor were found in DCM patients. Our results demonstrate that a subgroup of patients with DCM have a specific spectrum of autoantibodies which are specifically directed against the second extracellular loops of the beta 1 adrenoceptors and M2 muscarinic receptors rather than other cardiovascular receptors.

Functional epitope analysis of the second extracellular loop of the human heart muscarinic acetylcholine receptor

Two synthetic peptides corresponding to amino acids 172-181 and 169-193 of the second extracellular loop of the human M2 muscarinic receptor respectively were used to raise antibodies in rabbits. Affinity-purified antibodies were able not only to recognize a major band with a molecular weight of about 80 kDa on the electrotransferred membrane proteins of rat ventricular membranes but also to localize the muscarinic receptors on the sarcolemma and t-tubules of rat cardiomyocytes. Antibodies were also able to mimic muscarinic agonist stimulation as demonstrated by a negative chronotropic effect on cultured neonatal cardiomyocytes. In contrast with the antibodies raised against the peptide 169-193, the antibodies against the peptide 172-181 were unable to inhibit muscarinic ligand binding. These results suggest that the decapeptide 172-181 contains the B-cell epitope responsible for the functional effect of antibodies directed against the second extracellular loop of the receptor. Coupling this peptide by cystein 177 blocks the induction of antibodies with pharmacological effects but induces antibodies which are able to recognize the denatured receptor protein and to exert a negative chronotropic effect.

Functional autoimmune epitope on alpha 1-adrenergic receptors in patients with malignant hypertension

Because of the growing evidence that hypertensive disease is accompanied by immunological dysfunction, we have investigated autoimmunity in patients with malignant hypertension. Peptides corresponding to the sequence of the second extracellular loops of the human alpha 1-adrenergic receptor and the M2-muscarinic receptor were used as antigens in an ELISA. Serum from 4 (12%) of 33 healthy controls, 3 (20%) of 15 patients with malignant essential hypertension, and 7 (64%) of 11 with secondary hypertension showed positive responses in the ELISA for the alpha 1-adrenergic receptor peptide. Positive responses were significantly more common among the patients with secondary hypertension than in the other two groups (p < 0.01). By contrast, no autoantibodies against the M2-muscarinic receptor peptide were detected in either hypertensive group. Autoantibodies against the alpha 1-adrenergic receptor, affinity-purified from patients with positive responses, specifically recognised bands with molecular masses of 68, 40, and 37 kDa on immunoblotted membrane proteins of rat ventricles. The patients' autoantibodies caused a decrease in tritiated prazosin binding sites and an increase in heart beating frequency of neonatal cultured rat cardiomyocytes; antibodies purified from the controls had no effect. Circulating autoantibodies against the alpha 1-adrenergic receptor are present in a subgroup of patients with malignant hypertension. These autoantibodies have pharmacological activity in vitro, which suggests that they may be involved in the pathogenesis of malignant hypertension.

Gi-mediated muscarinic adenylyl cyclase inhibition in timolol-treated stunned porcine myocardium

The Gi-mediated muscarinic receptor-adenylyl cyclase system was examined in stunned myocardium induced by either three or five brief ischaemic periods after beta-adrenoceptor blockade by timolol (0.1 mg kg-1). The mid-left anterior descending coronary artery was occluded for 2, 10 and 2 min in four pigs, and for 2, 2, 5, 10 and 2 min in four other pigs. All the ischaemic periods were separated by 30 min of reperfusion and the biopsies were obtained 60 min after the last ischaemic period. Segment length function was measured in the ischaemic region and in the control region supplied by the left circumflex artery. In the two groups, the percentage systolic shortening was reduced equally, to 59 +/- 9 and 58 +/- 10% of control in the region subjected to ischaemia and only minimally in the control region. The biopsies from the stunned region from both groups showed: (1) no change in either the affinity for carbachol or the number of binding sites of the muscarinic receptors; (2) no alterations in messenger RNA encoding for the alpha subunit-2 of the inhibitory guanine nucleotide binding protein, as demonstrated by northern blot and solution hybridization; (3) no change in membrane-bound inhibitory guanine nucleotide binding protein, as shown by enzyme immunoassay utilizing a specific anti-peptide antibody, and (4) unchanged inhibition of stimulated adenylyl cyclase activity. These results suggest that there is an intact inhibitory guanine nucleotide binding protein-mediated muscarinic receptor adenylyl cyclase system in the stunned porcine myocardium.

Autoantibodies against cardiac G-protein-coupled receptors define different populations with cardiomyopathies but not with hypertension

It was previously shown that the second extracellular loop of cardiovascular G-protein-coupled receptors is an antigenic target for pharmacologically active autoantibodies in patients with idiopathic dilated cardiomyopathy. To extend these observations to cover patients with the same disease from different geographical origins or to patients with other cardiac diseases, peptides corresponding to the sequences of the second extracellular loops of the human M2 muscarinic receptors and beta adrenoceptors were used as antigens in an enzyme immunoassay. Sera from patients from Sweden and Japan with idiopathic dilated cardiomyopathy (DCM, n = 32), hypertrophic cardiomyopathy (HCM, n = 23), malignant essential hypertension (MEH, n = 11), malignant secondary hypertension (MSH, n = 10), and sera from healthy blood donors (HBD, n = 49) were tested. Sera from patients with DCM recognized the muscarinic receptor peptide in 38% of cases and the beta 1 adrenoceptor peptide in 31% of cases. In 50% of the positive patients, autoantibodies against both peptides coexisted as shown by competition experiments using both peptides as inhibitors. In HCM patients, there was a lower frequency of autoantibodies but with a higher but not significant predominance against the M2 peptide. No autoantibodies were detected in sera from patients with MEH or MSH. Autoantibodies against the M2 muscarinic receptors, affinity-purified from positive patients, displayed pharmacological activity as demonstrated by changes in the affinity and number of radioligand binding sites. In contrast, antibodies purified from positive HBD had no effect. These results confirm that autoantibodies displaying pharmacological activity against G-protein-coupled cardiovascular receptors are mainly restricted to patients with idiopathic dilated cardiomyopathy and that different autoantibody populations are responsible for the recognition of the different receptors.

Characterization of anti-peptide antibodies directed against an extracellular immunogenic epitope on the human alpha 1-adrenergic receptor

A synthetic peptide corresponding to amino acids 192-218 of the second extracellular loop of the human alpha 1A-adrenergic receptor was used to raise antibodies in rabbits. Affinity-purified antibodies specifically recognized main bands with a molecular weight of about 68, 40 and 37 kD on the electrotransferred membrane proteins of rat ventricle membranes. The incubation of these antibodies with rat myocardial membranes resulted in a decrease in the number of binding sites for the specific radiolabelled alpha 1-antagonist prazosin. These antibodies were also able to mimic the effects of agonist stimulation as demonstrated by a positive chronotropic effect on cultured cardiomyocytes. These results constitute the first immunochemical evidence of the presence of both the A and B subtypes of the alpha 1-adrenergic receptor in the heart. They also confirm that the second extracellular loop of the alpha 1-adrenergic receptors is an immunologically and functionally important domain.