[Effect of IL-17A on levels of antiheart autoantibodies in mice with viral myocarditis]

OBJECTIVE

To explore the effect of interleukin-17A (IL-17A) on the serum level of antiheart autoantibodies in mice with viral myocarditis.

METHODS

Male wild-type (WT) and IL-17A-deficient (IL-17A(-/-)) BALB/c mice were intraperitoneally injected with Coxsackie virus B3 (CVB3) for establishing VMC models (VMC-WT group and VMC-IL-17A(-/-) group). Meanwhile, a control group (WT group) of WT mice were established by i.p. administration of phosphate buffered saline (PBS). Paraffin sections of cardiac tissues were made 14 days after CVB3 injection. Myocardial histopathologic changes were evaluated by HE staining. The levels of anti-adenine nucleotide translocator (ANT) autoantibody, anti-β-myosin heavy chain (β-MHC) autoantibody and anti-cardiac L-type calcium channel (CACH2) autoantibody in sera were measured by ELISA.

RESULTS

Compared with WT group, the levels of anti-ANT-autoantibody and anti-β-MHC-autoantibody significantly increased in VMC-WT group (P<0.01, P<0.05), while the concentration of anti-CACH2-autoantibody showed no significant difference between WT and VMC-WT groups (P>0.05). Compared with VMC-WT group, the level of anti-ANT-autoantibody was reduced in VMC-IL-17A(-/-) group (P<0.05), while the levels of anti-β-MHC-autoantibody and anti-CACH2-autoantibody showed no significant difference between them (P>0.05).

CONCLUSION

IL-17A contributed to the secretion of anti-ANT-autoantibody of VMC mice, but had no effect on the secretion of anti-β-MHC-autoantibody and anti-CACH2-autoantibody in VMC mice.

Infectious tolerance to ADP/ATP carrier peptides induced by anti-L3T4 monoclonal antibody in dilated cardiomyopathy mice

CD4 T cells are suspected to play an important role in the pathogenesis of dilated cardiomyopathy (DCM). This study sought to evaluate whether anti-L3T4 monoclonal antibody (McAb) could induce the infectious tolerance to the adenosine diphosphate (ADP)/adenosine triphosphate (ATP) carrier peptides to protect mice from DCM. BALB/c mice (n = 16) were immunized with the peptides derived from human ADP/ATP carrier on the 1st, 14th, 28th, 49th, and 79th days, and some of them (n = 6) were also injected with anti-L3T4 McAb on the -1st, 0, and 1st days. On the 180th day, the splenocytes (SC) from the McAb-treated group were transferred into the syngeneic recipients (n = 6) who were also immunized with the peptides in the same manner. The sham-immunized mice were taken as the controls (n = 10). Results showed that the serum antibody against the ADP/ATP carrier examined with ELISA was positive in all mice only immunized with the peptides (DCM group), while negative in the McAb-treated, the SC-transferred, and the Control groups. The mRNA expression of IFN-gamma, IL-2, and IL-4, especially IL-4 in T cells investigated using real-time quantitative PCR and the percentages of T helper 1 (Th1) and Th2 subsets, especially Th2 subset detected with Flow Cytometry were all increased in DCM group, accompanied by the cardiac histopathological changes like those in DCM. Such findings were not seen in the other three groups. It concluded that anti-L3T4 McAb could inhibit the occurrence of DCM induced by the ADP/ATP carrier peptides in mice, and this immune tolerance could be transferred to the syngeneic recipients.

Analysis of IgG subclass antibodies and expression of T-Cell receptor signaling molecules in anti-CD4 monoclonal antibody treated mice with autoimmune cardiomyopathy

T-cell immune abnormality in patients of dilated cardiomyopathy has been intensively studied over the past 10 years. In this study, we aim to focus on the molecular mechanism of T-cells in autoimmune cardiomyopathy mouse model by detecting the expression of three T-cell signaling molecules. Balb/C mice (n = 12) were immunized with the peptides derived from human ADP/ATP carrier on the 1st, 14th, 28th, 49th and 79th days, and half of them were also injected with anti-L3T4 McAb on the - 1st, 0 and 1st days. The sham-immunized mice were taken as the controls (n = 6). The main result shows that the antibody response of IgG subclasses such as IgG1, IgG2b and IgG3 were definitely blocked except IgG2a in CD4+ cell-depleted Balb/C mice. In addition, the average mRNA expression of p56lck, p59fyn and zap-70 were all found to be dramatically higher in the mice immunized with only ADP/ATP carrier peptides than in the control-group. At meantime, reduced levels of the protein kinases p56lck, p59fyn and zap-70 were clearly observed in anti-CD4 McAb immunized group compared with DCM group. We propose that the proliferation of T-cells was significantly inhibited in anti-CD4 treated mice and CD4+ T-cells may play a critical role in ADP/ATP carrier caused mouse DCM.

Focused proteomics: towards a high throughput monoclonal antibody-based resolution of proteins for diagnosis of mitochondrial diseases

The availability of monoclonal antibodies (mAbs) against the proteins of the oxidative phosphorylation chain (OXPHOS) and other mitochondrial components facilitates the analysis and ultimately the diagnosis of mitochondrially related diseases. mAbs against each of the five complexes and pyruvate dehydrogenase (PDH) are the basis of a rapid and simple immunocytochemical approach [Hanson, B.J., Capaldi, R.A., Marusich, M.F. and Sherwood, S.W., J. Histochem. Cytochem. 50 (2002) 1281-1288]. This approach can be used to detect if complexes have altered assembly in mitochondrial disease due to mutations in nuclear encoded genes, such as in Leigh's disease, or in mitochondrially encoded genes, e.g., MELAS. Other mAbs have recently been obtained that can immunocapture each of the five OXPHOS complexes, PDH and the adenine nucleotide translocase (ANT) from very small amounts of tissue such as that obtained from cell culture or needle biopsies from patients. When adapted to a 96-well plate format, these mAbs allow measurement of the specific activity of each of the mitochondrial components individually and analysis of their subunit composition and state of posttranslational modification. The immunocapture protocol should be useful not only in the analysis of genetic mitochondrial diseases but also in evaluating and ultimately diagnosing late-onset mitochondrial disorders including Parkinson's disease, Alzheimer's disease, and late-onset diabetes, which are thought to result from accumulated oxidative damage to mitochondrial proteins such as the OXPHOS chain.

Assessment of membrane-bound mammal mitochondrial adenine nucleotide translocase topography by experimental antibodies

To gain insight into the immunogenicity of mitochondrial adenine nucleotide translocase (ANT), we raised antibodies against purified bovine heart ANT by induction of ascitic fluid in male Balb/c mice. We identified the antigenic determinants detected by these antibodies by (1) immunodetection of GST-ANT fusion proteins and selected partial constructs of ANT, (2) immunodetection of chemically synthesized overlapping peptides on solid support, and (3) back-titration ELISA. Results revealed a short epitope spreading of the antibodies, resulting in a small number of antigenic determinants. Thus, each antibody detects one or two major epitopes located in the putative hydrophilic loops M2 and M3. No evidence for the antigenicity of the first 133 amino acids of ANT was obtained. These well-characterized antibodies were used to study the topography of the membrane-bound ANT by back-titration ELISA with mitochondrial membranes. We demonstrated that amino acids 145-150 and 230-237 are fully accessible to the antibodies in native ANT, whereas regions 133-140 and 244-251 are not. Furthermore, we used mitochondria devoid of the outer membrane (mitoplasts) and inside-out submitochondrial particles (SMP) to establish the matrix or cytosolic orientation of loops M2 and M3. The results clearly show that these loops have a matrix orientation and thus support the six transmembrane segment model of ANT topography in the inner mitochondrial membrane.

Choline head groups stabilize the matrix loop regions of the ATP/ADP carrier ScAAC2

ATP/ADP carriers (AACs) are essential to the cell as they exchange ATP produced in mitochondria for cytosolic ADP. Monoclonal antibodies against the isoform 2 of Saccharomyces cerevisiae AAC (ScAAC2) were used to probe the accessibility of the matrix loops 1 and 3 depending on the environment of the carrier. In mitochondrial membranes ScAAC2 was not recognized, whereas in dodecylmaltoside the antibodies bound to the carrier, suggesting that the epitopes are hidden in the native environment. Exposure of the epitopes by detergents was reversed by reconstitution of the carrier in phospholipids or by exchanging with detergents having a choline or a trimethylammonium head group. Circular dichroism spectroscopy on peptides representing the C-terminal regions of all three matrix loops showed that only phosphocholine detergents induced a structural reorganization. Since in addition phosphatidylcholine was found to be tightly associated with the purified carrier, the matrix loop regions are likely to be associated to the membrane by phosphatidylcholine.

Epitope mapping of mitochondrial adenine nucleotide translocase-1 in idiopathic dilated cardiomyopathy

Mitochondrial adenine nucleotide translocase (ANT) is a specific target for the autoantibody response in idiopathic dilated cardiomyopathy (IDCM). We have undertaken an epitope analysis of ANT in IDCM by immunoblot with recombinant GST-ANT fusion proteins and with cellulose-bound decapeptides of human ANT1. Forty-five patients with IDCM, 17 patients with ischemic left ventricle dysfunction (LVD) and 20 controls were analyzed for circulating antibodies against ANT (AAb-ANT). Sixteen of the 45 (36%) IDCM patients showed AAb-ANT above controls. In immunoblots, AAb-ANT detected purified bovine heart ANT and GST-ANT1 and GST-ANT2 isoforms and, less frequently, the GST-ANT3 isoform. A construct lacking the last 146 amino acids did not react with AAb-ANT, indicating that the main epitopes are in the C-terminal 146 amino acids. Immunodetection of decapeptides covering this region shows that AAb-ANT detects at least three epitopes, demonstrating that ANT is the primary target of AAb-ANT. The most significant epitopes belong to the M2 and M3 hydrophilic loops of ANT suggesting that apart from being essential for its activity, these loops are highly immunogenic.

Possible association of HLA-DRB1 gene with the autoantibody against myocardial mitochondria ADP/ATP carrier in dilated cardiomyopathy

To probe the genetic background and immunopathogenesis of dilated cardiomyopathy (DCM) 77 patients with DCM, HLA-DRB1 gene polymorphism were analyzed by using the polymerase chain reaction/sequence specific primer (PCR/SSP) technique and autoantibody against myocardial mitochondria ADP/ATP carrier were examined by using the Immunoblot analysis. The frequency of HLA-DRB1*0901 allele was significantly higher in DCM patients in which autoantibody against ADP/ATP carrier of myocardial mitochondria is positive in contrast with those in which the autoantibody is negative (25.46% vs 3.45%, P < 0.05), the relative risk (RR) being 9.56. The other frequencies of HLA-DRB1 alleles have no significant difference in the antibody positive group and negative group. It is possible that a subset of DCM patients may exist in which autoimmunity is associated with genetic factors.

Adenine nucleotide translocator isoforms 1 and 2 are differently distributed in the mitochondrial inner membrane and have distinct affinities to cyclophilin D

Different isoforms of the adenine nucleotide translocase (ANT) are expressed in a tissue-specific manner. It was assumed that ANT-1 and ANT-2 co-exist in every single mitochondrion and might be differently distributed within the membrane structures that constitute the peripheral inner membrane or the crista membrane. To discriminate between ANT originating from peripheral or from cristal inner membranes we made use of the fact that complexes between porin, the outer-membrane pore protein, and the ANT can be generated. Such complexes between porin and the ANT in the peripheral inner membrane were induced in rat heart mitochondria and isolated from rat brain and kidney. Using ANT-isotype-specific antibodies and sequence analysis of the N-terminal end, it was discovered that the peripheral inner membrane contained ANT-1 and ANT-2, whereas the cristal membrane contained exclusively ANT-2. Cyclophilin was co-purified with the porin-ANT complexes, whereas it was absent in the crista-derived ANT. This suggested that ANT-1 might have a higher affinity for cyclophilin. This specific intra-mitochondrial distribution of the two ANT isotypes and cyclophilin D suggests specific functions of the peripheral and crista-forming parts of the inner membrane and the two ANT isotypes therein.

Disturbance of myocardial energy metabolism in experimental virus myocarditis by antibodies against the adenine nucleotide translocator

OBJECTIVE

The adenine nucleotide translocator (ANT) of the inner mitochondrial membrane is an autoantigen in myocarditis and in dilated cardiomyopathy. Clinical and experimental studies showed that specific autoantibodies inhibit the transmembrane nucleotide transport. In isolated hearts of guinea pigs immunized with the ANT, energy metabolism is disturbed. This metabolic disorder is related to functionally active specific antibodies and to a reduced heart function. This study tests whether similar immunological, metabolical and functional responses also occur in experimental virus myocarditis.

METHODS AND RESULTS

Experimental virus myocarditis was induced in A.SW/SnJ-mice by Coxsackie B3 virus infection. Specific antibodies against the ANT were detected by Western Blot in 14 out of 19 infected animals. In the isolated perfused hearts of five of these 14 mice cytosolic and mitochondrial ATP/ADP-ratios, determined by nonaqueous fractionation, were significantly altered, signalling a reduced ANT function [cytosolic ATP/ADP: 59 +/- 18 vs. 136 +/- 20 (controls), mitochondrial ATP/ADP: 4.2 +/- 1.0 vs. 1.1 +/- 0.3], all P < 0.05. Also, left ventricular pressure [43 +/- 9 vs. 78 +/- 6 mmHg (noninfected controls)], rate-pressure product (15.8 +/- 3.2 vs. 30.5 +/- 3.0 mmHg/min/1000), dp/dt (2410 +/- 222 vs. 3250 +/- 118 mmHg/s), and oxygen consumption (4.7 +/- 0.9 vs. 7.3 +/- 0.7 mumol/g/min), all P < 0.05, were lowered.

CONCLUSION

The data support the hypothesis that a virus infection alters cardiac energy metabolism and function by an antibody-mediated modulation of the function of the ANT.

Impairment of myocardial calcium homeostasis by antibodies against the adenine nucleotide translocator

The adenine nucleotide translocator (ANT) is an autoantigen in myocarditis and dilated cardiomyopathy. Carrier-specific antibodies impair myocardial energy metabolism and heart function. They cross-react with a myolemmal calcium channel and alter calcium fluxes in isolated myocytes. To test whether antibodies against the ANT can alter calcium homeostasis in intact hearts, guinea pigs were immunized with the carrier protein and their isolated hearts loaded with the intracellular calcium indicator INDO-1. The diastolic and systolic ratios of fluorescence signals at 410 nm and 510 nm (emission wavelengths of the calcium-bound and calcium-free indicator), 'd-s410/510', were measured by excitation at 364 nm. This index of the transient calcium concentration associated with the contraction cycle correlated with the external heart work (EHW) in non-immunized controls. EHW of immunized animals was lower (76 +/- 62 vs 153 +/- 47 mJ/g/min in controls, p < 0.005) and the amplitude of d-s410/510 was elevated (27.6 +/- 4.1% of the average ratio of the whole heart cycle vs 21.7 +/- 1.2% in controls, p < 0.005) and essentially independent of EHW. Isoproterenol stimulation increased EHW in all hearts but d-s410/510 was hightened in control hearts, only. Thus, a disorder between cytosolic calcium transients and work was recorded in hearts from guinea pigs immunized with the ANT. It may contribute to an immunopathic mechanism of heart failure subsequent to myocarditis.

Direct demonstration of a specific interaction between cyclophilin-D and the adenine nucleotide translocase confirms their role in the mitochondrial permeability transition

A fusion protein between cyclophilin-D (CyP-D) and glutathione S-transferase (GST) was shown to bind to purified liver inner mitochondrial membranes (IMMs) in a cyclosporin A (CsA)-sensitive manner. Binding was enhanced by diamide treatment of the IMMs. Immobilized GST-CyP-D avidly bound a single 30 kDa protein present in Triton X-100-solubilized IMMs; immunoblotting showed this to be the adenine nucleotide translocase (ANT). Binding was prevented by pretreatment of the CyP-D with CsA, but not with cyclosporin H. Purified ANT also bound specifically to GST-CyP-D, but porin did not, even in the presence of ANT.

Interventional study of diltiazem in dilated cardiomyopathy: a report of multiple centre clinical trial in China. Chinese Cooperative Group of Diltiazem Intervention Trial in Dilated Cardiomyopathy

The aim of this study was to determine the interventional effects of diltiazem on autoantibody mediated myocardial damage in dilated cardiomyopathy (DCM). 221 patients with DCM in 16 hospitals were included in the multiple centre clinical trial from January 1995 to November 1996, using the diltiazem or placebo based on the background therapy for heart failure. Patients were randomly divided into groups for a single blind trial, followed by observation for an average of 7.4 months. After treatment, the heart function of 84% of patients in the diltiazem group recovered to grade I or II, but this occurred for 64% of patients in the placebo group. Heart-thorax ratio was decreased from 0.59+/-0.07 to 0.56+/-0.07 and the left ventricular end-diastolic dimension (LVEDd) from 65.40+/-8.60 mm to 61.12+/-9.86 mm, the left ventricular ejection fraction (EF) was increased from 35.75+/-10.78% to 42.52%+/-11.41% (P<0.01) in the diltiazem group (n=114). The above parameters were not significantly changed in the placebo group (n=107). Mortality was 3.5% in the diltiazem group and 11.2% in the placebo group (P<0.05). Further analysis also shows that LVEDd were reduced and EF were obviously elevated in patients with DCM of LVEDd <70 mm, but the above parameters weren't improved in patients of LVEDd >70 mm. The study suggests that diltiazem is safe and effective in the treatment of DCM, the action mechanism might be intervention in antibody-mediated myocardial damage and protection of myocardium. Diltiazem is suitable for the treatment of the early stage in DCM.

Cardiac cytotoxic mechanism mediated by antibodies against myocardial mitochondrial ADP/ATP carrier in patients with dilated cardiomyopathy

OBJECTIVE

To investigate mechanism of the antibody-mediated cardiac cytotoxicity and clinical significance in dilated cardiomyopathy (DCM), and study the effects of the antibodies against the myocardial mitochondrial ADP / ATP carrier from sera of patients with dilated cardiomyopathy on the guinea pig ventricular myocytes.

PATIENTS AND METHODS

This study included 18 patients with DCM (12 men and 6 women), with mean age of 43 years. Control group included 18 health donors, (9 men and 9 women), with mean age of 32 years. The antibodies against the ADP / ATP carrier and cell membrane 52 000 peptide were examined by immunoblotting. The antibody-mediated cardiac cytotoxicity was studied with the cytotoxic test and whole cell patch-clamp technique.

RESULTS

The antibodies against myocardial mitochondrial ADP / ATP carrier and cell membrane 52 000 peptide were positive in 18 patients with DCM, while negative in controls. The antibodies induced cytotoxic damage with time-dependent and enhanced Ca-current in cardiac myocytes. The increasing amplitude of peak Ca(2+)-current was 100 pA-840 pA (n = 8) in different dilution of the antibodies. The effect of the antibodies might be inhibited by verapamil, and were null in controls (n = 4).

CONCLUSIONS

The above findings suggest that an increase in the antibody-mediated Ca(2+)-current of cardiac myocytes is related to the cytotoxic damage in dilated cardiomyopathy.

The role of the ADP/ATP carrier in the pathogenesis of viral heart disease

The ADP/ATP carrier is an autoantigen in myocarditis and dilated cardiomyopathy, both of which are diseases related to virus infections. Sera of these patients bear carrier-specific autoantibodies inhibiting transmembrane nucleotide transport on isolated mitochondria. To further assess the role of the ADP/ATP carrier in viral heart disease, guinea pigs were immunized with the isolated ADP/ATP carrier protein and A-strain mice were infected with coxsackie B3 virus. Both species generated specific and carrier-inactivating antibodies after immunization/infection. The transport activity of the ADP/ATP carrier-estimated from the cytosolic-mitochondrial difference of the phosphorylation potential of ATP (delta G[cyt-mit])-markedly declined in guinea pig and mice hearts. A close relationship was observed between the magnitude of reduction of delta G(cyt-mit) and the decrease of cardiac function. Therefore, it seems plausible that carrier dysfunction induced by viral infection creates an imbalance in myocardial energy metabolism, and is responsible for the impairment of cardiac function. The underlying mechanism might be an autoimmune reaction triggered via molecular mimicry or a modulation of the expression of ADP/ATP carrier isoforms changing the overall transport capacity of the cardiac ADP/ATP carrier.

[Dynamic observation and significance of autoantibody against ADP/ATP carrier in dilated cardiomyopathy]

The presence and dynamic change of autoantibody against ADP/ATP carrier in patients with dilated cardiomyopathy (DCM) was studied by using indirect micro-solid-phase radioimmunoassay. A significant antibody titre was present in 16 of 48 DCM patients and most of them were in early stage of the disease. The titre of anti-ADP/ATP carrier antibody in DCM patients decreased gradually in a follow-up period of three months. The titre of this antibody in the serum from patients with coronary and rheumatic heart disease were within normal limits. Anti-ADP/ATP carrier antibody may play an important role in the pathogenesis, diagnosis and treatment of DCM.

Antibody-mediated imbalance of myocardial energy metabolism. A causal factor of cardiac failure?

The ADP-ATP carrier of the inner mitochondrial membrane is an autoantigen in myocarditis and dilated cardiomyopathy. Sera of patients with these diseases contain carrier-specific autoantibodies that inhibit the transmembrane nucleotide transport on isolated mitochondria. Guinea pigs immunized with the isolated ADP-ATP carrier protein also generate specific carrier-inactivating antibodies. In this study, we measured the cardiac function of guinea pigs immunized with the ADP-ATP carrier by determining the external heart work (EHW) of their isolated perfused spontaneously beating hearts stimulated by 4.0 mmol/L calcium and aortic ligature. Further, the electrogenic transport activity of the ADP-ATP carrier was estimated by calculating the cytosolic-mitochondrial difference of the phosphorylation potential of ATP [delta G(cyt-mit)] in the freeze-clamped isolated hearts by nonaqueous fractionation. The EHW of immunized guinea pigs was seen to be reduced by 54% (P < .005) compared with nonimmunized control guinea pigs, and delta G(cyt-mit) declined from 4.9 kJ/mol ATP in nonimmunized control hearts to 2.3 kJ/mol ATP in the hearts of the immunized guinea pigs (P < .005). The decisive result of this study, however, is the close relation observed between the magnitude of reduction of delta G(cyt-mit) and the size of the decrease in EHW (r = .87). Therefore, it seems plausible that antibody-mediated carrier dysfunction (creating the observed imbalance in myocardial energy metabolism) is responsible for the impairment of cardiac function. Our data support the hypothesis that immunopathic mechanisms in myocarditis and dilated cardiomyopathy can trigger subsequent heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)

Peroxidative damage to cardiac mitochondria. II. Immunological analysis of modified adenine nucleotide translocase

We have previously reported that treatment of isolated rat heart mitochondria with the free radical-generating system Cu2+/tert-butylhydroperoxide produces striking changes in the adenine nucleotide translocase (ANT) of the inner membrane. These changes include a small increase in apparent molecular weight as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by its disappearance from the polypeptide profile upon further oxidant treatment (Zwizinski and Schmid (1992) Arch. Biochem. Biophys. 294, 178-183). In order to characterize its peroxidative modification in more detail, we have purified rat heart ANT and prepared polyclonal antibody against it. Using this antibody, we have observed that increasing oxidant treatment results in a gradual increase in the ANT protein's apparent molecular weight by up to 1 kDa. The progressive nature of the molecular weight shift, which parallels the generation of thiobarbituric acid reactive substances, supports the hypothesis that this phenomenon may be the result of covalent addition of increasing amounts of lipid peroxidation products. Strong oxidative treatment of cardiac mitochondria also causes fragmentation and polymerization of the ANT protein. However, Western blot analysis showed that a major portion of the original ANT survives even extensive oxidation as a distinct, modified protein. Therefore, the almost complete disappearance of ANT from Coomassie-stained gels appears to be the result of cross-linking and fragmentation reactions, as well as a decreased efficiency of the Coomassie staining. Because a measurable molecular weight shift of ANT occurs at the mildest oxidative treatment tested (resulting in the production of only 1.1 nmol malondialdehyde/mg protein), it may be relevant as a parameter of myocardial ischemia-reperfusion injury.

Transfer of human myocarditis into severe combined immunodeficiency mice

Severe combined immunodeficiency (SCID) mice possess neither T nor B lymphocytes and are thus suitable recipients for lymphocytes of different species. Because autoimmune mechanisms are suspected in the pathogenesis of myocarditis (MC), we attempted to determine whether peripheral blood lymphocytes (PBLs) from patients with MC could be transferred into SCID mice and whether they had an autoimmunologic effect. Groups of three mice each were injected intraperitoneally with up to 50 million PBLs from five MC patients with autoantibodies against the adenine nucleotide translocator (ANT), a myocardial autoantigen. The PBLs from three healthy blood donors were used as controls. After 60 days, human PBLs could be demonstrated in the peripheral blood of the SCID mice transfused with the PBLs of MC patients, representing up to 9.9% of the peripheral blood mononuclear cells. The transfused SCID mice sera showed human immunoglobulin levels of up to 3 mg/mL, both IgG and IgM. Autoantibodies against ANT were present in the mice receiving PBLs from MC patients but not from the control subjects. In addition, infiltrating human lymphocytes were present in the hearts of the SCID mice transfused with PBLs from MC patients. The presence of an ongoing autoimmune process in the SCID mice transfused with PBLs from MC patients is suggested by increased levels of soluble interleukin-2 receptor in the serum in contrast to SCID mice transfused with PBLs from healthy blood donors. We conclude that the autoimmune reactions seen in human MC can be transferred to SCID mice by the transfer of PBLs from MC patients. These findings stress the significance of autoimmune mechanisms in the pathogenesis of human MC.

Induction of multiple heart autoantibodies in mice with coxsackievirus B3- and cardiac myosin-induced autoimmune myocarditis

When mice of certain strains are infected with the cardiotropic virus coxsackievirus B3 or are immunized with mouse cardiac myosin, myocarditis, accompanied by immune recognition of the myocardium, ensues. That both target organ injury and peripheral immunization lead to similar disease manifestations raise questions about the role of tissue damage in eliciting autoantibodies. A/J mice were infected with coxsackievirus B3 or immunized with mouse cardiac myosin and killed at weekly intervals for 4 wk. A portion of each heart was examined histologically for evidence of myocarditis and antibodies were eluted from the remaining heart tissue. Heart eluates and serum were tested for IgG antibodies to myosin and to adenine nucleotide translocator and branched chain ketoacid dehydrogenase molecules by ELISA. At each sampling time, coxsackievirus B3-infected mice exhibited high titers of circulating antibodies to myosin, adenine nucleotide translocator, and branched chain ketoacid dehydrogenase with successively increasing myocardial deposition of antibodies of each specificity. Among myosin-immunized mice, antibodies of all three specificities were eluted from the myocardium and were found in the serum, but only antibodies to myosin were present in appreciable amounts in the circulation. Antibodies to myosin, adenine nucleotide translocator, and branched chain ketoacid dehydrogenase were rarely observed in serum and heart eluates from control animals. This study indicates that myocardial injury may be a prerequisite for the induction of cardiac autoimmunity and suggests that as tissue damage accrues, recognition of additional cardiac Ag may occur.

Circulating heart autoantibodies in familial as compared with nonfamilial idiopathic dilated cardiomyopathy

BACKGROUND

Idiopathic dilated cardiomyopathy (DCM) is a serious heart disease characterized by enlargement of one or both ventricles and ventricular dysfunction. Although most patients have sporadic disease, 20% have been found to have familial DCM when relatives are investigated by echocardiography. No other factors have been identified to date that consistently distinguish familial from nonfamilial DCM. Although some patients have a family history of DCM, a "negative" family history does not exclude familial DCM because affected family members may be presymptomatic or undiagnosed. Because some patients have life-threatening complications at the time of initial assessment of DCM, identifying a serum marker predictive of familial disease would help determine which families would most likely benefit from echocardiographic investigation.

OBJECTIVE

In this study, our objective was to determine whether antiheart autoantibodies could be used to distinguish familial from nonfamilial idiopathic DCM.

METHODS

We analyzed serum specimens for antiheart antibodies from 19 patients categorized as having familial DCM and 15 classified as having nonfamilial DCM on the basis of echocardiographic investigation of first-degree relatives. The mean duration of disease in these 34 patients was 50 months at the time the serum specimens were obtained.

RESULTS

Titers of antibodies against the adenine nucleotide translocator, branched-chain keto acid dehydrogenase, and cardiac myosin did not distinguish between familial and nonfamilial cases of DCM.

Auto-antibody against adenine nucleotide translocator in dilated cardiomyopathy and myocarditis--incidence and relation to cardiac function and morphology

Using an enzyme-linked immunosorbent assay, we measured anti-adenine nucleotide translocater (ANT) antibody in control subjects and in patients with dilated cardiomyopathy (DCM), myocarditis, and other heart disease. Analysis with sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting, and immunoabsorption tests confirmed accurate purification of the ANT protein and correct measurement of anti-ANT auto-antibody. Anti-ANT antibody was detected in 6 of 37 cases (16%) of DCM and in 5 of 12 cases (42%) of myocarditis. This antibody was not positive in other heart diseases or in apparently healthy controls. There were no differences between anti-ANT autoantibody-positive and -negative DCM or myocarditis patients in any of the cardiac parameters examined (left ventricular ejection fraction, LVEF; left ventricular end-diastolic dimension, LVDd; and cardiothoracic ratio, CTR). Moreover, in patients who were positive for anti-ANT auto-antibody, no positive correlations were found between the parameters and anti-ANT antibody titers in either DCM or myocarditis. Although these results indicate that the detection of anti-ANT antibody was achieved at a high specificity and could have certain diagnostic value in DCM and myocarditis, there was no statistically significant relationship between the cardiac parameters (LVEF, LVDd, and CTR) and anti-ANT antibody titers in either DCM or myocarditis. Some compensatory mechanism of ventricular function may mask the effects of the anti-ANT auto-antibody or alternatively, this auto-antibody may have mimic effects on the pathogenesis and/or progression of DCM and myocarditis.

Chemical, immunological, enzymatic, and genetic approaches to studying the arrangement of the peptide chain of the ADP/ATP carrier in the mitochondrial membrane

In the process of oxidative phosphorylation, the exchange of cytosolic ADP3- against mitochondrial ATP4- across the inner mitochondrial membrane is mediated by a specific carrier protein. Two different conformations for this carrier have been demonstrated on the basis of interactions with specific inhibitors, namely carboxyatractyloside (CATR) and bongkrekic acid (BA). The two conformations, referred to as CATR and BA conformations, are interconvertible, provided that ADP or ATP are present. The functional ADP/ATP carrier is probably organized as a tetramer. In the presence of CATR or BA the tetramer is split into two dimers combined with either of the two inhibitors. The amino acid sequence of the beef heart carrier monomer (297 residues) contains three repeats of about 100 residues each. Experimental results obtained through different approaches, including photolabeling, immunochemistry, and limited proteolysis, can be interpreted on the basis of a model with five or six transmembrane alpha helices per carrier monomer. Two mobile regions involved in the binding of nucleotides and accessible to proteolytic enzymes have been identified. Each of them may be visualized as consisting of two pairs of short amphipathic alpha helices, which can be juxtaposed to form hydrophilic channels facilitating the nucleotide transport. Mutagenesis in yeast is currently being used to detect strategic amino acids in ADP/ATP transport.

The possible value of synthetic peptides in the diagnosis and therapy of myocarditis and dilated cardiomyopathy

The adenine nucleotide translocator (ANT) and myosin have been shown to be major autoantigens in myocarditis and dilated cardiomyopathy. We studied the use of synthetic peptides, with sequences derived from ANT and myosin, as antigens in screening tests for autoantibodies in myocarditis (MC) and dilated cardiomyopathy (DCM) and as absorbents for specific elimination of autoantibodies from the sera of patients. Using computer prediction of the secondary structure of the ANT and myosin we identified two sequences of the ANT and three sequences of myosin as possible main antigenic determinants. Using overlapping synthetic peptides and antibodies against them, the antigenicity of the selected determinants was shown. Of 72 sera from patients with MC or DCM 45 (62.5%) bound to the peptides derived from ANT, 32 (44.4%) reacted with the sequences from myosin, in contrast to healthy controls. Using the peptides from the ANT or myosin immobilized on thiopropyl-sepharose, more than 95% of the autoantibodies could be removed specifically from the positive sera. The results demonstrate the usefulness of synthetic peptides as antigens in antibody screening tests in MC and DCM and offers a new approach to the therapy of inflammatory heart disease by specific elimination of autoantibodies.

The Ca-channel as cardiac autoantigen

We recently described autoantibodies to the ADP/ATP carrier of the inner mitochondrial membrane as an organ specific autoantigen found in high frequencies in sera of patients with myocarditis and dilated cardiomyopathy. These antibodies not only showed an intracellular binding at the mitochondrial membrane, but also crossreact with antigenic determinants at the cardiac myocyte plasma membrane. They therefore may account, at least in part, for the so-called sarcolemmal-bound IgG of heart-reactive autoantibodies found to be associated with these diseases. Heart muscle diseases are associated with electrocardiographic abnormalities such as complex ventricular arrhythmias and disturbed ventricular function. Our data indicate that abnormalities in current spread and impaired heart contractility might also be caused by an antibody mediated disturbance of calcium channel gating leading to prolongation of the action potential and potentiation of tension. The enhanced calcium permeability of the cell may moreover cause calcium overload and cell death. The calcium channel complex plays a central role in cardiac contractility. Disturbing calcium channel gating by antibodies might therefore contribute to the pathogenesis of these diseases.

Antibodies to ADP-ATP carrier--an autoantigen in myocarditis and dilated cardiomyopathy--impair cardiac function

The adenosine diphosphate (ADP)-adenosine triphosphate (ATP) carrier of the inner mitochondrial membrane is identified as an autoantigen in myocarditis and dilated cardiomyopathy. Sera of patients with these diseases contain autoantibodies to the ADP-ATP carrier capable of inhibiting nucleotide transport in vitro. Recently, an antibody-related infringement of energy metabolism was shown in intact perfused hearts isolated from guinea pigs immunized with the ADP-ATP carrier. A decreased cytosolic-mitochondrial difference of the phosphorylation potential of ATP was measured that originated from a reduction in mitochondrial-cytosolic nucleotide transport. Nonimmunized animals did not show these changes in energy metabolism, despite being in a comparable metabolic state and performing equal external heart work. To establish whether antibodies to the ADP-ATP carrier can also alter cardiac function, hemodynamic parameters of isolated hearts of guinea pigs that were preimmunized with the carrier protein were measured. Cardiac metabolism was stimulated by exposing the hearts to a high calcium concentration in conjunction with a maximum elevation of the afterload. Mean aortic pressure, stroke volume, stroke work, and external heart work were found to be lowered significantly (p less than 0.005). The external heart work of the immunized hearts reached only about 20% of the level performed by control hearts. Myocardial oxygen consumption was lowered 2.5-fold, whereas the extent of lactate production was found to be more than doubled. These results show a diminished cardiac performance of hearts from animals immunized with the ADP-ATP carrier. Our findings demonstrate that autoimmunity to the ADP-ATP carrier may contribute to the pathophysiology of dilated cardiomyopathy as a subsequent stage of myocarditis by causing an autoantibody-mediated reduction in cardiac function on the basis of an imbalance between energy delivery and demand.

Orientation of the N-terminal region of the membrane-bound ADP/ATP carrier protein explored by antipeptide antibodies and an arginine-specific endoprotease. Evidence that the accessibility of the N-terminal residues depends on the conformational state of the carrier

Two peptides corresponding to the amino acid sequences 1-11 (N-terminal peptide) and 288-297 (C-terminal peptide) of beef heart ADP/ATP carrier have been synthesized. After coupling to ovalbumin, they were injected into rabbits to raise polyclonal antibodies. The specificities of the generated antibodies were tested by enzyme-linked immunosorbent assay (ELISA) and (or) Western blot. Anti-N-terminal antibodies and anti-C-terminal antibodies reacted specifically with the corresponding peptide. However, only anti-N-terminal antibodies reacted with the isolated ADP/ATP carrier; they also reacted with the membrane-bound carrier in freeze-thawed mitochondria and mitoplasts, indicating that the first 10 amino acid residues of the membrane-bound carrier in mitochondria face the cytosol. On the basis that the ADP/ATP carrier can adopt two conformations, one trapped by carboxyatractyloside (CATR conformation) and the other by bongkrekic acid (BA conformation), the reactivity of the anti-N-terminal antibodies to the ADP/ATP carrier in mitoplasts or freeze-thawed mitochondria was tested for each conformation of the carrier. Only in the CATR conformation was the N-terminal region of the membrane-bound carrier reactive to the N-terminal antibodies; the contrasting weak reactivity of the carrier in the BA conformation suggested that the transition from the CATR conformation to the BA conformation results in a restricted conformation of the peptide chain corresponding to the first 10 amino acid residues or its partial burying in the lipid bilayer. These immunological data were complemented by enzymatic data pertaining to proteolysis of the membrane-bound ADP/ATP carrier by an arginine-specific endoprotease.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies to the ADP/ATP carrier, an autoantigen in myocarditis and dilated cardiomyopathy, penetrate into myocardial cells and disturb energy metabolism in vivo

We identified the ADP/ATP carrier, located within the inner mitochondrial membrane, to be an organ- and conformation-specific autoantigen in myocarditis and dilated cardiomyopathy. We also showed that autoantibodies to the ADP/ATP carrier inhibit the nucleotide transport in vitro. Specific binding of the autoantibodies to the carrier was demonstrated by radioimmunoassay and the immunoblot technique; the inhibition of the nucleotide transport was determined by the inhibitor stop method. To establish if these autoantibodies might also affect cardiac energy metabolism in vivo, we measured whether they are capable of penetrating into myocytes and whether subcellular ATP/ADP ratios and phosphorylation potentials of ATP change in hearts of guinea pigs that have been immunized with the isolated ADP/ATP carrier. An intracellular deposition of autoantibodies was observed by direct immunofluorescence and by immunoperoxidase staining on cryosections of the myocardial tissue of animals immunized with the ADP/ATP carrier. Furthermore, binding of autoantibodies to mitochondrial membrane structures was shown by immunoelectron-microscopic methods. The cytosolic and intramitochondrial distribution of adenine nucleotides in stimulated, isolated perfused hearts of guinea pigs immunized with the ADP/ATP carrier was measured by nonaqueous fractionation. Compared with controls performing equal external heart work, the cytosolic ATP decreased in the immunized animals, whereas the mitochondrial ATP increased strongly; ADP concentrations showed an opposite change. Thus, a resultant cytosolic decrease and a marked mitochondrial increase of the ATP/ADP ratio was established. As a consequence, the cytosolic-mitochondrial phosphorylation potential of ATP was diminished. These findings demonstrate that antibodies against intracellular antigens are able to penetrate into living cells, and that autoimmunity to the ADP/ATP carrier may contribute to the pathophysiology of myocarditis and dilated cardiomyopathy by causing an autoantibody-mediated imbalance between intracellular energy delivery and demand.

[Viral myocarditis--new aspects of pathomechanisms, diagnosis and therapy]

The diagnosis of "viral myocarditis" remains uncertain in most cases, despite varied efforts to obtain diagnostic criteria and techniques. The combination of virological, histological and immunohistological data may offer an opportunity to improve diagnosis. The pathophysiological processes which are involved in the transition from myocarditis into dilated cardiomyopathy are still unclear. A variety of new data point out that viral infection induces a loss of self-tolerance and subsequent autoaggression towards myocardial structures. The management of viral myocarditis remains problematic and a specific form of therapy still does not exist. Studies on immune suppressive therapy are contradictory. Moreover, in these studies the diagnostic criteria were non-uniform and the number of patients was low. Nevertheless, immune suppressive therapy can be very effective in individual cases. But until now, a clear decision cannot be made on the selection of those patients who would respond favourably to immune suppressive therapy. Only controlled studies which consider the aetiology, the grade of clinical severity, the duration of clinical symptoms, the degree of cellular infiltration, and the histological alterations may answer the questions concerning the benefit of immune suppressive therapy for viral myocarditis and its sequelae. Until these studies are available, the general implementation of immune suppressive therapy in viral heart disease should not be recommended, especially in view of the incidence of side effects.

Antibody-mediated enhancement of calcium permeability in cardiac myocytes

Our study shows that antibodies, specific to the ADP/ATP carrier of the inner mitochondrial membrane, crossreact with the cell surface of cardiac myocytes, where the calcium channel seems to be the antigenic determinant. The antibodies enhanced the calcium current and suppressed its inactivation. Affinity-purified antibodies (IgG) exhibit an acute cytotoxic effect, which required extracellular calcium and was prevented by calcium channel blockers. Our findings suggest that antibody-mediated cytotoxicity results secondary to calcium overload caused by enhanced cellular calcium permeability, requiring no complement-dependent process.

Antibodies against ADP-ATP carrier enhance Ca2+ current in isolated cardiac myocytes

Antibodies previously described to inhibit specifically nucleotide transport (ADP-ATP carrier) of the inner mitochondrial membrane were found to bind specifically to the sarcolemma of the enzymatically isolated rat ventricular myocytes. In this communication, we report for the first time that a component of these antibodies enhanced the Ca2+ current in isolated cardiac myocytes and potentiated twitch tension in ventricular strips. Prolonged exposure of rat myocytes to large concentrations of antibodies caused spontaneous contractions, progressive cell deterioration, and death. Our results thus show that a component of antibodies against ADP-ATP carrier cross-reacts with cardiac sarcolemmal proteins enhancing the Ca2+ channel.

Mitochondrial protein import: differential recognition of various transport intermediates by antibodies

The precursors of the mitochondrial proteins ADP/ATP carrier (AAC) and F1-ATPase subunit beta (F1 beta) were accumulated at the stages of binding to receptor sites on the mitochondrial outer membrane, or in contact sites between outer and inner membranes. Specific antibodies raised against the mature proteins were added to the isolated mitochondria and efficiently bound to these translocation intermediates. Further movement of the precursors to consecutive steps along their import pathway was thereby inhibited. Controls showed that precursor proteins which were inserted into or translocated across the outer membrane were not recognized by the antibodies unless the mitochondrial membranes were disrupted. We conclude that the trapped translocation intermediates have antigenic sites exposed to the outside of the outer membrane.

Localization of immunoreactive regions in the beef heart adenine nucleotide carrier using rabbit antisera against the carboxyatractyloside-liganded and the sodium dodecyl sulfate denaturated carrier forms

The existence of different antigenic determinants in the beef heart adenine nucleotide (AdN) carrier was demonstrated by exploring the reactivity of fragments of the carrier protein with rabbit antisera directed against either the beef heart AdN carrier denatured with sodium dodecyl sulfate (NaDodSO4 carrier) or the beef AdN carrier liganded by the specific inhibitor carboxyatractyloside (CATR-carrier). The antigenic determinants reacting with antiserum to the CATR-carrier appeared to be close to the N- and C-terminal ends of the carrier protein, whereas those reacting with antiserum to the NaDodSO4 carrier were located preferentially in the central region of the protein. The same antisera were used to study the immunogenic specificity of the beef liver AdN carrier, the rat heart AdN carrier, and the rat liver AdN carrier. The beef liver and rat heart AdN carriers were found to react with both antisera whereas the rat liver AdN carrier reacted essentially with the CATR-carrier antiserum.

Primary biliary cirrhosis: assessment of the quantitative importance of the adenine nucleotide translocator protein as a major mitochondrial antigen

The adenine nucleotide translocator protein (ANT) is the first well-characterized mitochondrial polypeptide to be identified as an antigen for antimitochondrial autoantibodies (AMA) in PBC sera. Because of the potential use for a highly purified antigen as a tool in studying the aetiology of PBC, we have undertaken an assessment of the quantitative importance of ANT as a PBC-specific mitochondrial antigen. Immunoblotting and ELISA techniques were used. Both methods reveal PBC antibodies against isolated rat liver ANT. However, competitive ELISA experiments using purified rat liver ANT as the competing antigen show that anti-ANT antibodies in PBC serum comprise only a fraction of the total AMA. Furthermore, both ELISA and immunoblotting experiments show that rat liver ANT is not a specific antigen for PBC autoantibodies. Sera from patients with SLE, chronic active hepatitis, and sera from normal, control patients, have nearly the same, or higher, ANT antibody titres. Thus, ANT is not a good candidate as an antigen for the diagnosis of PBC.

Immunological analysis of auto-antibodies against the adenine nucleotide translocator in dilated cardiomyopathy

We have previously identified the adenine nucleotide translocator (ANT), an intrinsic protein of the inner mitochondrial membrane, as an auto-antigen in dilated cardiomyopathy (DCM). Further immunochemical characterization by crossed immunoelectrophoresis, indirect solid phase radioimmunoassay and immunoadsorption studies on the isolated translocator protein and mitochondria from heart, kidney and liver showed the existence of organ-specific antigenic determinants although partial crossreactivity between the three proteins was observed. Sera from 18 patients with histologically proven dilated cardiomyopathy were studied for their capacity to bind to the translocator protein. Seventeen of 18 patients showed significant binding, while in the sera of patients with coronary heart disease, suspected alcoholic heart disease or healthy blood donors, no anti-ANT antibodies were observed. Further studies showed organ-specific and functionally active autoantibodies, which decreased the ADP/ATP exchange rate from heart mitochondria. A close correlation was found between the antibody-titer and the hemodynamic function. These results give new evidence for autoimmunological events in dilated cardiomyopathy.

Inhibition of the adenine nucleotide translocator by organ specific autoantibodies in primary biliary cirrhosis

Sera from 13 patients with proven primary biliary cirrhosis (PBC) were studied for the capacity to bind to the adenine nucleotide translocator (ANT) isolated from heart, kidney and liver mitochondria. Antibodies against the ANT from liver were detected in the serum of all PBC patients, while 10 of 13 sera were negative when tested with the ANT from heart. None of the sera showed a significant binding to the ANT from kidney. The specific binding and the organ specificity of the autoantibodies against the ANT from liver were also confirmed by immunoabsorption studies on the isolated proteins. To distinguish between antibody titre and antibody activity, we measured the ability of the antisera to inhibit the adenine nucleotide transport across inner mitochondrial membrane using isolated mitochondria from heart, kidney and liver. Six of 13 patient sera tested inhibited the adenine nucleotide transport from liver mitochondria, however, none of the sera inhibited the transport from heart or kidney mitochondria again indicating the organ specificity of the antigen and the autoantibodies.

Immunochemical characterization of the adenine nucleotide translocator. Organ specificity and conformation specificity

Antibodies have been prepared against purified preparations of the heart and kidney nucleotide translocator in the 'c'-conformation. The results show organ-specific antigenic determinants on the translocator proteins isolated from heart, kidney and liver although a partial cross-reactivity between these three proteins was demonstrable. The organ specificity was observed both with the solubilized and with the membrane-bound translocator protein indicating organ-specific determinants on exposed regions of the carrier. An organ-specific inhibition of the nucleotide transport in heart mitochondria by the heart carboxyatractylate-protein antiserum leads to the conclusion that the organ specificity is at least partially conditioned by the binding site for the substrate and/or the closely linked gate of the carrier protein. Apart from the organ specificity the results also demonstrate a specificity of the antibodies for the translocational conformations of the carrier: the 'c'-conformation stabilized in the carboxyatractylate-protein complex and the 'm'-conformation present in the bongkrekate-protein complex. However, after denaturation of the carboxytraktylate-protein and bongkrekate-protein complexes the binding of the anti-(carboxyatractylate-protein) antiserum to both inhibitor-protein complexes was nearly identical. The conformation specificity was also expressed by the inhibition of the conformation transition from the 'c'- to the 'm'- state. This side-specific inhibition of the nucleotide transport and the identical binding activity of the carboxyatractylate-protein antiserum against the denatured carboxyatractylate-protein and bongkrekate-protein complexes suggested that the conformation-specific antigenic determinants are topographic surface regions which are determined by the chain folding.

The mitochondrial adenine nucleotide translocator is an antigen in primary biliary cirrhosis

Circulating antibodies reacting specifically with the adenine nucleotide translocator from liver mitochondria were detected in sera from 12 patients with proven primary biliary cirrhosis (PBC) by a solid phase double antibody immunoradiometric assay (IRMA). Furthermore these antibodies were absorbed with the isolated adenine nucleotide translocator from liver mitochondria. None of the sera from 20 normal individuals, four patients with anti-mitochondrial positive pseudolupus syndrome (PLE) sera (M-3) and three patients with syphilis (anti-M-l) had antibodies directed against this protein from inner mitochondrial membrane. The adenine nucleotide translocator as antigen in PBC could clearly be distinguished from the ATPase associated PBC specific M-2 antigen. With the present study, for the first time, a well characterized protein from inner mitochondrial membrane has been clearly defined as an autoantigen in primary biliary cirrhosis.

An immunological study of the uncoupling protein of brown adipose tissue mitochondria

1. Ewes were injected with purified 32,000-Mr uncoupling protein from mitochondria of brown adipose tissue of cold-adapted rats in order to raise antibodies. 2. The existence of antibodies in the plasma of ewes and the cross-reactivity of plasmas were demonstrated and studied by 125I-labelled antigen-antibody reaction, double immunodiffusion, the inhibition of GDP binding to the 32,000 Mr protein and by immunohistochemistry. 3. The antibodies raised against the homogeneous protein yielded a single immunoprecipitation band with detergent-solubilized mitochondrial membranes of brown adipose tissue from rat, hamster, guinea-pig, rabbit and with the purified uncoupling protein of these animals. No immunoprecipitation was obtained with the protein purified from brown adipose tissue of term lamb foetus. 4. The GDP-binding activity of the uncoupling protein (isolated or in solubilized membranes) was largely inhibited by the antiserum. 5. The anti-(rat uncoupling protein) could not cross-react with solubilized membranes from liver or muscle, nor with the purified beef heart or rat liver ADP/ATP translocator.

Studies on the adenine nucleotide translocase from rat liver mitochondria. Isolation, partial characterization and immunochemical properties of carboxyatractylate-binding protein

1. Solubility of mitochondrial membranes in various solvent systems was determined quantitatively. The most effective agent was the anionic detergent, sodium dodecylsulphate, which solubilizes 90% of the protein at the concentration of 0.1% followed by Triton X-100 (70%), sodium deoxycholate (60%), Brij 56 (50%), and guanidine hydrochloride (40%) at a concentration of 2 M. 2. Affinity chromatography of a clear 0.1% sodium dodecylsulphate solution of digitonized mitochondria on Sepharose 4B containing carboxyatractylate always resulted in the separation of two fractions, one of which was not retained by the column and the other which could be obtained after elution with 2% sodium dodecylsulphate. 3. The retained protein showed a high binding specificity for ATP and [3H]atractylate when compared with the unretained fraction. The amount of bound [3H]atractylate or carboxyatractylate-sensitive binding of ATP was 10.5 +/- 4 nmol/mg protein, and 22 +/- 8 nmol/mg protein, respectively. 4. The major component within the retained fraction, comprising 85% of the total weight, was protein, followed by phospholipids (14%) and approximately 1% triglycerides. Sodium dodecylsulphate-polyacrylamide gel electrophoresis revealed a major (95%) and a minor (5%) component with an apparent molecular weight of 26000 +/- 1000 and 8300 +/- 400, respectively. The gels did not stain for carbohydrates. Ultracentrifugal analysis showed a single, symmetrical boundry. 5. Double immunodiffusion analysis gave a single precipitin line with the corresponding antiserum. [14C]ADP exchange of digitonin particles was completely inhibited by an antiserum to the carboxyatractylate binding protein fraction, whereas the adenine nucleotide transport of intact mitochondria remained unaffected. In the presence of specific immunoglobulins state-3 respiration rate of digitonin particles was prolonged and reduced by approximately 25%. State-4 respiration rate was unaffected.